B to the depth H is large, the sliding wedge failure will occur at the external corner, and the active earth pressure of the external corner in the range of wedge-shaped slider will not change with the change of size B. When the ratio of the side length B to the depth H is small, the displaced soil is composed of two parts, and the earth pressure varies with the change of size B. In this paper, the magnitude and distribution law of the active earth pressure obtained by the horizontal micro-layered limit equilibrium analysis method is similar to the three-dimensional simulation value of the Midas/GTS software, which can prove the feasibility and rationality of the theoretical calculation.Taking the external corner with equal lengths as the research object, two failure modes of the equilateral external corner are established, and the active earth pressure calculation formula of the equilateral external corner in the limit state is further deduced when the external angle is 90°. The comparison between the theoretical calculation results and Midas/GTS simulation results shows that when the ratio of the side length  And the plane shape of the foundation pit becomes more irregular, leading to a large number of excavations with external corners. Due to the free surface on both sides of the external corner in the foundation pit, the stress distribution at the external corner is complex, and it is more sensitive to the surface stress level, the change in groundwater level and the stiffness of the support system. Therefore, special attention needs to be paid to the external corner, and it is necessary to do more research on the three-dimensional failure form of the external corner and the calculation of earth pressure in excavation engineering. The picture of the external corner in the excavation is shown in Fig. The construction site of excavation engineering is easily affected by surrounding buildings and all kinds of pipe networks, subways and comprehensive pipe corridors5 present the concept of plane strain ratio PSR  to describe the influence degree of the pit corner effect; and carried out a large number of studies on the pit corner effect. Based on the concept of PSR, through the numerical simulation of a large number of regular deep foundation pits, an empirical formula of PSR has been summarized and put forward by Finno6. Many scholars have also conducted monitoring tests and three-dimensional numerical simulations of the regular foundation pit13. Li et al.14 believe that the three-dimensional failure mechanism is related to the soil arching effect and then deduce the three-dimensional earth pressure calculation equation for internal corners. Based on this theory, Lin et al.15 simplified the curve of the soil arching and then obtained the equations to calculate the three-dimensional active earth pressure of the retaining wall using the horizontal micro-layered limit equilibrium analysis method16. In addition, many scholars20 have studied the three-dimensional earth pressure calculation of internal corners according to different conditions. These research results show that the foundation pit has obvious three-dimensional characteristics, and it is essential to use a three-dimensional model to calculate the earth pressure in the foundation pit. However, all the above studies take the internal corner as the research object, and previous studies24 have shown that the external corner is not conducive to the safety and stability of the foundation pit, so it is necessary to pay more attention to the external corner. Zhang22 study found that when the external corner displacement occurs, the soil around the positive angle will produce deformation similar to the wedge-shaped slider. Pan et al.25 pointed out that when the side length of the external corner is identical to the excavation depth, the slip surface of the external corner is approximately spherical. Wang et al.26 classified the external corner according to the proportional relationship between the length of both sides for the external corner and the plane size of the foundation pit, and the research shows that the side length of the external corner is an essential factor affecting the deformation. Moradi23 studied the effect of the external corner on the deformation of the soil-nailed wall through experiments and evaluated the influence of the nail arrangement on the performance of the soil-nailed wall. Wu et al.27 studied the spatial effect of the soil-nailed wall by using the three-dimensional elastic–plastic model, and the results show that the internal corner is beneficial to the stability of the foundation pit, while the external corner is very disadvantageous to the stability of the foundation pit. Research at this stage shows that the external corners protruding from the foundation pit are more prone to excessive deformation, and are more likely to be unstable or damaged. And the earth pressure is closely related to the deformation, so it is necessary to study the earth pressure of the external corner.The research on the three-dimensional failure mode of the foundation pit is mostly aimed at the foundation pit with the regular plane shape , but the research on the three-dimensional failure mode of the external corner is less. In the three-dimensional study of the regular foundation pit, OuIn the past, most of the studies on the pit corner effect of the foundation pit are based on three-dimensional numerical simulation. Compared with the internal corner of the foundation pit, research on the external corner is very rare, and there is still a lack of theoretical research on the external corner of the foundation pit. Therefore, this paper studies the three-dimensional failure mode of the external corner in the foundation pit and puts forward two different failure models related to the side length of the external corner. The horizontal stratification analysis method is used to theoretically analyze the external corner with a turning angle of 90°, and the corresponding earth pressure calculation formula is obtained. The three-dimensional finite element numerical calculation is carried out using Midas/GTS software, and the simulation results are compared with the theoretical method. It is verified that the two failure models proposed in this paper are aimed at the external corner with the same length on both sides, and the theoretical calculation results of earth pressure are consistent with the simulation results of the software.Two different failure modes are proposed for the external corner with equal length on both sides. One of them is shown in Fig. As shown in Fig. 30. The limited soil on both sides of the external corner will restrict the development of the external corner slip surface so that the slip surface cannot completely intersect with the ground surface. And the displaced soil behind the retaining wall can be composed of the upper area I and the lower area II. In addition, it is worth noting that the failure mode in Fig. As shown in Fig. Assuming that the depth of the foundation pit does not change, only the lengths of the sides on both sides of the external corner change, and the failure mechanisms of the two above-mentioned external corners with equal side lengths are analyzed in conjunction with Figs. B is the length of the two sides of the external corner with equal length, H is the depth of the foundation pit, θ is the angle between the slip surface of the wedge-shaped slider and the vertical line, and the angle of the external corner is 90°. In the same way, when the length of both sides of the equal external corner is relatively short  is the angle between the sliding direction of the slider and the vertical line AO, φ is the angle of internal friction of the soil, and dW is the weight of the element.When The static equilibrium differential equation in the vertical direction of the element:A1, A2, A3, A4 and A5 are the areas of plane IEFJ, plane HIJG, plane HEFG, plane HEJ and plane GJF respectively.In this equation,Since the sides of the external corner are equal, the slider of the external corner should be a symmetrical structure. If its symmetry is considered, there is entclass1pt{minimaOB and OC directions is equivalent, and only the static equilibrium equation in one direction is considered, then the static equilibrium differential equation in the OB direction is:Because the wedge-shaped slider is symmetrical, the equilibrium of the differential slider in both σx = σy, A1 = A2, σx = λσz , and Eq. 19\documeIn this equation,Therefore, when the side length of the external corner satisfies B of the external corner. The earth pressure strength around the wedge-shaped slider will not change with the side length of the external corner. When the side length of the external corner satisfies the B for the external corner. It is worth noting that Eqs. \documenthat Eqs.  and (22)When When the side length of the external corner satisfies AOC or AOB.The formula for calculating the resultant force of active earth pressure can be obtained by integrating Eq.  in planeThe following formula for calculating the resultant force of active earth pressure can be obtained from Eq. .24\documThe resultant action position of active earth pressure in the horizontal x direction is as follows.In this equation,Substituting Eq.  into Eq.The resultant action position of active earth pressure in the horizontal z direction is as follows.In this equation,Substituting Eq.  into Eq.Calculation of resultant force for the active earth pressure in zone IIntegrating Eq.  can get Since the slider in zone I is a prismatic slider, the action position of the resultant earth pressure in zone I in the x direction is at the midpoint of the side length of the external corner, and the coordinates in the x direction is as follows,The height z of the active earth pressure resultant action point in zone I is as follows,In this equation,Calculation of resultant force for the active earth pressure in zone IIIntegrating Eq.  can get The action position of the resultant active earth pressure in the horizontal x direction of zone II is as follows,In this equation,The height z of the resultant action point of active earth pressure in zone II is as follows,In this equation,The calculation formula of the total active earth pressure resultant force of zone I and zone II is as follows,The formula for calculating the action point of the total active earth pressure resultant force in Zone I and Zone II is as follows,When the side length of the external corner satisfies To further verify the feasibility of the calculation theory and better reflect the magnitude and distribution of active earth pressure at the external corner of the foundation pit. The three-dimensional finite element analysis is carried out in the deep foundation pit by using Midas/GTS software, and there is an external corner with equal lengths on both sides in this foundation pit.2. To facilitate the calculation, the soil layer adopts a single sand layer and the cohesion is not considered. The excavation depth of the foundation pit is 9 m, divided into three layers, and each layer is excavated by 3 m. The supporting structure is equivalent to a plate element with a thickness of 0.8 m, embedded depth of 11 m and elastic modulus of 30GPa. The interface element simulates the wall and soil interaction, and the angle of the external corner is 90°. Because the friction between the retaining wall and soil is not considered in the theoretical hypothesis, the roughness factor of the wall-soil interface in the model is 0. The side lengths of the external corner are 3 m × 3 m, 4 m × 4 m, 8 m × 8 m, 10 m × 10 m, and 12 m × 12 m respectively to calculate the model. As shown in Fig. The modified Mohr–Coulomb constitutive model is selected for the soil model. The width affected is 3 to 4 times the depth of excavation and the depth affected is 2 to 4 of the excavation depthThe cloud diagram of the displacement isoline calculated by finite element software is shown in Fig. entclass1pt{minimaentclass1pt{minimav is introduced, as shown in Fig. v is the average value of the active earth pressure strength of all monitoring points at the same horizontal height, σi is the active earth pressure strength of each monitoring point in the same horizontal plane, and i is the number of monitoring points.To further prove the feasibility of this method, the simulation value of active earth pressure calculated by finite element software is compared with the calculated value according to this method to verify the rationality of the theory. In the theoretical method of this paper, when deducing the active earth pressure theory of the external corner, the normal stress caused by the interaction between the supporting structure and soil at the same horizontal height is simplified to the uniform distribution. However, in the Midas/GTS finite element software calculation, the active earth pressure obtained by the interface element is not uniformly distributed at the same horizontal height. Therefore, to verify the rationality of the calculation model and theory more reasonably, the variable σv and the theoretical calculation results in this paper when the side length of the external corner is equal to 3 m and 4 m respectively. It can be seen that the earth pressure strength obtained by software simulation and the earth pressure calculated by the theoretical method in this paper are both linearly distributed. The active earth pressure strength calculated by the theoretical method in this paper is slightly smaller than that of the finite element software, but the overall trend of the data is in good agreement with each other. The main reason for the analysis is that when calculating by the finite element software, the soil displacement often can not reach the displacement value required by the active earth pressure in the limit state. Therefore, the active earth pressure strength calculated by the finite element software is slightly larger than that calculated by the theoretical method in this paper. In addition, the theoretical method and software simulation results show that when the lengths of the sides of the external corner are 3 m and 4 m respectively, there is little difference in the active earth pressure strength between them in the range of 2 m from the top of the foundation pit. However, when the depth z is greater than 2 m, the two curves appear obvious "bifurcation", which indicates that the earth pressure strength distribution law calculated by the theoretical method in this paper is consistent with the results of the finite element simulation.When the side length of the external corner is 3 m and 4 m respectively ( the Eq. . Figure v and the theoretical calculation results with the side length of 8 m, 10 m and 12 m respectively (B. As shown in Fig. v is almost coincident with the simulation of Midas/GTS software. And it is not much different from the value of earth pressure strength calculated by the theoretical method in this paper. It can be shown that the earth pressure strength calculated by the software does not change with the change of edge length B, which is consistent with the theory of this paper. In addition, the earth pressure strength calculated in this paper and the σv obtained by software simulation still have linear distribution.When the side length of the external corner is 8 m, 10 m and 12 m respectively, the earth pressure strength is calculated according to the Eq. . Figure from Eq.  that whev at the bottom of foundation pit shows the irregular distribution.Figures B is greater than According to the difference in the side length, the external corner can be divided into two categories. The first type is that the length of the side length When the turning angle of the external corner is 90°, the active earth pressure around the two kinds of the external corner is deduced theoretically by using the horizontal micro-layered limit equilibrium analysis method. The formulas for calculating the strength of active earth pressure and the resultant force and acting point of earth pressure are obtained respectively. For the first kind of the external corner, the active earth pressure in the range of the external corner wedge-shaped slider will not change with the side length of the external corner, while for the second kind of the external corner, the earth pressure in the range of the external corner slider will change with the change of the side length for the external corner.In this paper, the theoretical calculation results are compared with the simulation results of Midas/GTS software. The comparison results show that there is little difference between the earth pressure values calculated by the theoretical method and the simulation values of Midas/GTS software, and the magnitude and distribution of the main earth pressure values are the same, which proves that the method in this paper is feasible and reasonable.In this paper, the failure model of the external corner with equal side length on both sides is established in excavation engineering . The calculation formula of active earth pressure for this type of external corner under different side length is derived according to the established failure model. The main conclusions are as follows:


The number of older adults in need of care and living at home is increasing in Europe. At the same time, the number of professional caregivers is decreasing. This development reinforces the need for assistive technology to support care recipients in their own homes and promote their independence. One of the main challenges of independent living is the preparation of food. Interactive robots could assist older adults with difficulties performing physically demanding tasks. Within the project AuRorA , an interactive voice-controlled robot arm was developed as an assistance system in the kitchen.The aim of the study was to assess how older adults evaluate the AuRorA system and to collect data on actual willingness to use the technology. Older adults were asked to evaluate the system in terms of usefulness, usability, accessibility and intention to use.Due to the ongoing coronavirus disease 2019 (COVID-19) pandemic, the older adults evaluated the system via an online survey. The validated questionnaire Technology Usage Inventory (short: TUI) was used in conjunction with self-developed questionnaires to collect data on study population characteristics.A total of 106 participants were included in the analysis. The acceptance, usability and usefulness of the system were rated as medium, while the intention to use was rated as low. A significant strong correlation was found between the TUI subscales intention to use and usefulness.It can be assumed that the actual need of the individual participant for such a robotic assistive system had an influence on the evaluation of the system. The perceived usefulness may have been a crucial influence on the intention to use and the overall assessment of the system.The online version of this article (10.1007/s00391-022-02105-8) contains supplementary material, which is available to authorized users. The majority of older adults in need of care are cared for in their own homes by professional or informal caregivers. The preparation of meals in particular is difficult for people with physical disabilities. Assistive robotic technologies could relieve the burden on caregivers and increase the independence of users; however, there is little research on how older adults evaluate such technologies for home use and on their actual willingness to use them.The continuing growth of the proportion of older adults in European has been accompanied by an increase in the number of people in need of long-term care. At the same time, most older adults wish to remain in their own living situation for as long as possible and without the support of others. Even in the event of them needing care, they often prefer to be cared for at home by outpatient care services . RemainiThese changes in society and the concomitant increased need for home care strengthen the demand for technological assistance systems to enhance the quality of life, health and independence of those in need of care and to relieve the burden on caregivers. The positive effects on health and quality of life resulting from integrating modern technologies into the daily lives of older adults are well documented .Klein refers to eating and drinking as “basic activities” that play a central role in every life . HoweverAgainst the background of this problem, the AuRorA project was initiated , which aims to support older adults in preparing food in their own homes by developing an innovative interactive robotic solution.At the core of the assistance system AuRorA is the lightweight robotic arm Universal-Robot UR5  Fig. . The robDe Graaf et al. stated that in the evaluation of a robotic technology for personal and domestic use, specific emphasis should be placed on exploring the target group’s acceptance and intention to use the technology. Acceptance of robotic technologies by older adults has been found to be closely related to the perceived usefulness of these systems ; howeverWhat are the basic attitudes of older adults towards the technology presented in this study?How do older adults evaluate the AuRorA system in terms of accessibility, perceived usability and usefulness?How do older adults evaluate the intention to use the robotic assistance system?We sought to answer the following research questions:Due to the ongoing coronavirus disease 2019 (COVID-19) pandemic, we conducted an online survey so that the study could be carried out without direct face-to-face contact. We created a detailed video of a prototypical cooking process with the AuRorA system to be used in the survey  was used for the evaluation of the AuRorA system . The ansFor the development of the digital assessment underlying this study, we used the tool REDCap  .We sent the survey to the members of the internal database of the Geriatrics Research Group of Charité — Universitätsmedizin Berlin via email. We also contacted various senior citizen facilities that agreed to forward the link. Healthy individuals with a minimum age of 65 years and internet access were included in the study.We analyzed the data using IBM SPSS Statistics 27 . For all the variables, we calculated mean values and standard deviations. Since ordinal data were present, we calculated the Spearman’s rank correlation coefficient to measure the correlation between the key variables of the TUI. We specified a significance level of 0.05 for the analysis. To interpret the calculated Spearman’s rank correlation coefficients, we considered the approach and cut-off values by Schober et al. .Table The results of the TUI questionnaire are presented in Table The average score for accessibility of the AuRorA system was 7.29 (SD = 3.46). A look at the individual items shows that financial accessibility in particular  was rated critically . Similarly, evaluation of the acquisition effort involved (“I think that acquiring this technology does not require much effort.”) achieved a low score of 2.29 (SD = 1.65).The perceived usability of the assistance system achieved a mean score of 14.93 (SD = 3.95), placing it just in the upper third of the scale. Likewise, the scores for individual items showed that application and comprehensibility of the system’s operation were rated rather positively , which corresponds to a value in the lower third of the scale. Here, a look at the underlying values of individual questions is particularly informative Fig. . The firThe total score given by the older adults surveyed in this study in relation to their intention to use the system was 80.19 SD = 76.51). This is in the lower third of the overall scale. The intention to use scale consists of three questions, concerning respondents’ actual intention to use, intention to purchase and desire to have access to the technology. The mean scores for all three questions reached the lower third of the scale  with greater perceived usefulness being related to higher intention to use [p < 0.001) as well as the intention to use and skepticism  are in the range of a moderate correlation [For a better understanding of factors which may have an influence the intention to use by the older adults, we calculated correlation coefficients between the intention to use and other factors Table . The intn to use . Other srelation . It can The medium to low evaluation of the AuRorA system in this study is reflected by the results of other studies that have researched the acceptance of older adults regarding robotic assistance systems. Many studies reported a low level of willingness to use and implement robotic solutions for the target group , 20. BroThe number of people with an officially recognized degree of disability was relatively small in this study. The medium to low ratings for acceptability and usefulness of the AuRorA system could be due to the lack of the individual need for assistance among the study participants. Heerink et al. described the perceived usefulness as a crucial factor influencing the intention to use an assistance system . This goThe eighth Ageing Report of the German Government emphasized the importance of taking ethical considerations into account when exploring the development, distribution and usage of digital technologies for older adults .In this context, ethical aspects that are important regarding presented technology should be discussed. First, the aspect of distributive justice needs to be addressed. The AuRorA kitchen system is a functional demonstrator that is not yet ready for introduction into the market. However, it is foreseeable that both acquisition and installation will be very costly. Within this study, the participants critically assessed the affordability of the system. The medium rating for accessibility of the system in this study  is in line with the results of other studies. Becker et al. have also emphasized the concern of older adults that due to the unclear financing possibilities of robotics for home use, they are uncertain about the financial feasibility of such a system . EspeciaThe low ratings for the perceived usefulness of the AuRorA system may be influenced by the general attitude of older adults towards robotic systems . This asIn this study, only an officially recognized degree of disability was queried, which, however, does not necessarily have to imply a limitation in the preparation of food. Thus, as a further evaluation step studies should enroll more participants with support needs in relation to food preparation. Furthermore, the specific needs and technical competencies of especially vulnerable groups, such as people with dementia, should be addressed in the future development of the AuRorA system.Less tech-savvy individuals may not have been reached by the online survey. Survey methods like face-to-face interviews are preferable for reaching the target group.Mostly healthy older adults were included in this study. The results cannot be generalized to older adults in the need of support for preparing meals.There are still barriers to introduction of assistive robotics for older adults, especially financial barriers were considered critically.The perceived usefulness may have a crucial influence on the intention to use and the overall evaluation of the system.The AuRorA robotic systemTechnology commitment of the study participants


The advancement of complex Internet of Things (IoT) devices in recent years has deepened their dependency on network connectivity, demanding low latency and high throughput. At the same time, expanding operating conditions for these devices have brought challenges that limit the design constraints and accessibility for future hardware or software upgrades. These limitations can result in data loss because of out-of-order packets if the design specification cannot keep up with network demands. In addition, existing network reordering solutions become less applicable due to the drastic changes in the type of network endpoints, as IoT devices typically have less memory and are likely to be power-constrained. One approach to address this problem is reordering packets using reconfigurable hardware to ease computation in other functions. Field Programmable Gate Array (FPGA) devices are ideal candidates for hardware implementations at the network endpoints due to their high performance and flexibility. Moreover, previous research on packet reordering using FPGAs has serious design flaws that can lead to unnecessary packet dropping due to blocking in memory. This research proposes a scalable hardware-focused method for packet reordering that can overcome the flaws from previous work while maintaining minimal resource usage and low time complexity. The design utilizes a pipelined approach to perform sorting in parallel and completes the operation within two clock cycles. FPGA resources are optimized using a two-layer memory management system that consumes minimal on-chip memory and registers. Furthermore, the design is scalable to support multi-flow applications with shared memories in a single FPGA chip. The advancement in Internet of Things (IoT) devices has increased demands for new network technologies. Due to the broader usage of IoT devices, endpoints have to meet different bandwidths and latency requirements, depending on their applications . At the IoT devices are collections of various sensors connected with actuators and processing systems to provide real-time data collection and data transfer . They arCloud and edge computing are some of the many approaches to handle these constraints and reduce the network dependency of IoT devices. Edge computing devices, similar to IoT devices, are placed near the data-collecting hardware, with the addition of storage and real-time data processing capabilities before forwarding to the network layer . The cloAs a reconfigurable and custom design approach in the hardware domain, Field Programmable Gate Arrays (FPGAs) can be a suitable solution as the hardware network processing layer in edge and IoT devices. FPGAs have many uses in industrial applications because of custom digital logic design, which is popular in telecommunications, robotics, and automotive sectors, with practical applications from data centers to embedded devices . They arAs mentioned earlier, IoT and edge devices have covered a broader range of applications than ever. Therefore, it is crucial to ensure that real-time traffic is delivered with minimal loss or interruptions. One issue causing data loss for uncontrolled packet delivery, especially in low-latency applications such as data streaming, is out-of-order packet arrivals at network endpoints. Without proper processing, packets can be dropped, leading to unwanted delays and loss of critical data collection . Packet FPGAs have the potential to be applied to edge devices for packet reordering. Previous research has used FPGAs to reorder out-of-order packets for audiovisual streaming applications . HoweverThe motivation for this work is to address the packet reordering challenge for modern IoT development with unique design constraints. We propose a hardware method that can address the design flaws of previous solutions. At the same time, this method can be applied to different traffic characteristics of various devices, and it is flexible for future upgrades without the need to redesign.Providing a reconfigurable solution to packet reordering in hardware, which can be tailored for unique IoT applications.Allowing simultaneous insertion and release of packets, eliminating the design flaws in existing solutions.Inserting a packet in the correct order in two clock cycles with a runtime of O(1).Providing scalable support to multiple flows.The contributions of this paper are as follows:The rest of this paper is organized in the following order. This section summarizes the networking background for IoT devices, related works in FPGAs to improve connectivity, and some challenges arising from previous packet reordering research. Different factors, including network congestion, multiple flows, hardware or software bugs, insufficient bandwidth, or security issues, cause data loss. This can lead to severe consequences for real-time IoT applications such as autonomous driving, virtual reality, and health monitoring sensors. Mostacero-Agama analyzed the impact of latency on IoT devices and found that increasing the distance between the network providers and the receivers increased latency . At the In recent years, the uses for FPGAs have been transitioning from prototypes or small productions into final product integration. With the need for device updates over time, FPGAs offer a reconfigurable advantage compared with Application-Specific Integrated Circuits (ASICs). ASICs have higher performance, consume less power, and their design can be more optimized for a specific application. However, if a device needs modification, the hardware must go through manufacturing and reassembly, costing more time for deployment ,20. ReceThe research by Yang took on the challenge of handling low-latency IoT applications using FPGAs . They adTo improve the flexibility of IoT hardware, Lee’s group developed a metamorphic IoT platform consisting of a cluster of connected edge computing devices that could be reconfigured on demand through a cloud network . The edgOutside the scope of IoT, researchers have considered using FPGAs as replacements for CPUs in networking hardware. For example, Nakanishi used FPGAs to build a network-embedded system for TCP/IP without the need for a CPU . They teNetwork connectivity for IoT devices can be provided through different interfaces, for example, WiFi, 5G cellular, Bluetooth, or Ethernet. Even though more IoT-specified protocols have been developed, traditional network protocols such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are still applicable for many IoT applications. TCP is the preferred reliable protocol when slower network speed is not an issue. However, TCP can delay communication for applications that require low latency due to its three-way handshaking, which slows down the packet transmission and results in more power consumption . FurtherOne work focused on reordering was carried out by Zhou . They prAnother related work in solving the out-of-order problem is Beneš’s work on packet reordering . Their rExisting solutions to packet reordering from the previous section offered innovative techniques in the hardware domain. However, there are some drawbacks to these works. Although Zhou’s method scales well with multiple TCP connections, its dependency on the ACK information to determine the in-order status makes it inflexible to other protocols. In addition, Zhou compared the sequence value in series within a set of predefined registers and comparators; this can increase the computing time required to place them in the correct location.N packets, and Packets 2 to N are occupied. When Packet 1 finally arrives, it is written into memory slot 1. Now, we have all N packets that are in order. At this point, the system should be capable of accepting Packets in the range of Beneš’s approach stores the metadata of the packets in the memory addresses indicated by the lower bits of the sequence numbers and releases packets when the memory slot of the expected sequence is filled. However, the scheme has a major flaw as it does not consider the time needed to retrieve packets that are in order. As a result, it can potentially discard packets as the memory slots might be occupied by packets already in order. For example, suppose the system supports the sorting of Our method improves upon the foundations of the relevant reordering research and avoids loopholes in existing approaches. The goal is to minimize resource usage, allowing the flexibility to scale the flow to fit different network demands and applications. Furthermore, the design parameters are independent of specific protocols. Finally, we aim to achieve the time complexity of O(1) by taking advantage of the parallel processing capability in FPGAs. Our packet reordering approach is simple to implement and can be targeted to a wide range of FPGA devices.This section describes the reordering method with our hardware design approach. As mentioned earlier, the goal is to design a high-performance, cost-effective scheme to perform packet reordering. Our approach takes advantage of the hardware parallel shift registers to store data and reorder the sequence simultaneously with O(1) time complexity. We link these registers to create a pipeline where out-of-sequence packet references are stored and sorted in place. When a new packet arrives from the network, its sequence number is arranged in the pipeline in the correct ascending order within a fixed number of clock cycles. In our design, it is possible to achieve sorting and insertion in two clock cycles with the reordering module. The basic idea is explained as follows. Packets arrive from the network receiver and are fed into the reordering module. At the interface, we have an input manager that extracts the sequence from the packet while the packet is stored in the external memory. Only the sequence number and the reference pointer of the packet are passed to the sorting pipeline, which contains a series of shift registers. Each stage of the pipeline includes two fields: the sequence number and the packet pointer. The sorting pipeline has a property that the sequence numbers are always kept in ascending order. We use this property to identify the insertion position of the new packet in one cycle. After the packet is inserted into the correct place, the pipeline will remain in ascending order. Finally, the in-sequence packets are allowed to be retrieved by the output manager and forwarded to the network. During the sorting process, a dynamic packet pointer manager keeps track of the connections between the external memory addresses and the sequence numbers in the pipeline. This module translates the addresses into smaller-size reference pointers using an additional on-chip memory layer, indirectly linking the sequences to their contents in the external memory.We only use the sequence number from the packet for the sorting pipeline without the original payload. The entire content is stored in the external memory, while the sequence number is extracted along with the memory address. However, using the full memory address as a pointer for the sequence can be costly. Therefore, we propose a scalable approach using a second memory layer in the FPGA, which is handled by the dynamic packet pointer manager. We use the addresses to this local memory as the reference pointer in our reordering module. Since the total number of out-of-order packets is limited, this drastically reduces the overall resource usage. The memory pointer arrangement is described in more detail in This proposed method can offer a scalable solution to the high-bandwidth network by using the reprogrammable capacity of the FPGA to adjust the size of the sorting pipeline. The pipeline size defines the maximum number of sequence numbers to be sorted; in other words, it is also the total number of available shift registers. Increasing the size allows more out-of-order sequences to be sorted while waiting for the in-sequence packet to arrive. The reordering module uses minimal resources to achieve a large pipeline size for applications requiring high network throughput.It should be noted that the proposed method in this example shows a single flow. However, it can be scaled to multiple flows using multiple sorting pipelines connecting to a shared memory resource, as discussed in U be the sequence of packets with arriving time U. The method requires sorting the set of arriving out-of-ordered packets in ascending order within the pipeline.This section describes the problem definition and our formal method to address it. The problem definition is as follows: Let P containing M stages of shift registers is defined as M is determined by the span, which is the maximum out-of-order packet distance. Since there are no duplicate sequence numbers, the values of The formal parameters and symbols used to describe the method can be found in k, which separates the pipeline stages into two sets: M, there are at most We first find a critical point k, the next step is to create an empty spot in the pipeline to insert the tuple k and the command to the sorting pipeline, we can shift the set either to the left or to the right.After determining the position Algorithm 1 Procedure to insert a new packet k such that    Find    for        There are three cases to operate the sorting pipeline: inserting a new packet, releasing a packet from the pipeline, or both. We describe the insertion, release, and concurrent insertion and release methods as Algorithms 1–3, respectively.Algorithm 2 Procedure to release a packet.   if               for                     Algorithm 3 Procedure to insert a new packet    Release    if k such that        Find               for                     Algorithm 1 describes the inserting procedure for the new packet arrival. When the new sequence is not the expected in-sequence value, the procedure is executed to insert the tuple Algorithm 2 describes the packet-releasing procedure, assuming no packet arrives. The algorithm keeps an expected in-sequence counter U into the pipeline simultaneously, we only need to shift the pipeline stages to the left up to the critical point Algorithms 1 and 2 describe the procedures for inserting an out-of-order packet and releasing an in-sequence packet separately. However, we want to achieve the highest throughput possible in high-speed networks. Algorithm 3 describes the procedure of handling the two cases concurrently. The intuition is described as follows. When a packet is released from the pipeline stage The key feature of the sorting pipeline is that it maintains the ascending order after the placement of k be the critical point, where Let Theorem 1.Inserting the value .Proof. S is empty. When the first element is inserted, it will be placed in the first location S is also in ascending order.Base step: It is trivial to show that the condition is satisfied when k breaks the sequence S into two sub-sequences: k. We analyze the following three cases.S are greater than Case 1 , which can be synthesized into any FPGA device. The system architecture in The input manager is the front-end module of the FPGA that interacts with new packets coming from the network. As mentioned in The sorting pipeline module handles the sorting operations. Two values stored in the pipeline are the sequence number and the reference pointer; both values move together during the sorting process. Before sending packets to the network layer, the output manager retrieves in-order sequences from the sorting pipeline. At this stage, the output manager communicates with the dynamic packet pointer manager to translate the reference pointer to its address in the external memory. Using this address, the output manager reads the packet content from the memory. However, accessing data from the memory can experience a delay of several clock cycles during the read operation. To compensate for this, we introduce a FIFO at the output manager to send in-order sequences into a queue to be released one by one as soon as the read operation is completed.The main feature of the sorting pipeline module is the ability to process all registers in parallel, different from iterations through each element in sequential programming. This feature helps achieve minimal sorting time; the new packet can be inserted and sorted in two clock cycles. To accomplish this, we connect a series of comparator blocks to each pipeline stage and compare the new sequence value k, is the first location where k. Depending on the designer’s choice, they can invert output signals from the comparators. In addition, the comparator results are also used to identify which set is to be shifted. When a shift-right command is enabled from the controller, registers receiving an output of 1 from the comparator are shifted to the right toward the end of the pipeline by one position.The insertion position, k. Then, all registers receiving 1 from the comparator outputs are shifted to the right simultaneously, resulting in an empty slot available for Packet 4. At the same time, Packet 4 is inserted into position k, taking advantage of the properties of hardware registers. The new pipeline contains 3, 4, 5, 6, and 8 after the operation.The purpose of the controller within the sorting pipeline module is to send commands to perform the shifting and insertion operations in the pipeline. The commands enable shifting according to one of the three algorithms proposed in We use a counter to store the expected in-sequence packet to check if a sequence is in-order. The counter starts from the first sequence and only increments when it equals the sequence value of the first stage register. Recall from When an packet experiences a long delay, it may arrive much later in the flow or is not received at all in the case of a lost packet. To address this issue, there is a maximum waiting timer to trigger the counter increment to ensure the flow’s continuation.In addition, the controller verifies the in-sequence status of the incoming packet from the input manager. This verification step lets the incoming packet bypass the sorting pipeline in two cases. The first case occurs when the incoming packet is already in order and the packet is sent to the output manager directly. The second case happens if the arrived sequence number is smaller than the expected in-sequence counter when the packet has a long delay. The delayed packet is stored in a separate memory location and sent to output afterwards. The decision of handling late packets is left to the end application.Following Beneš’s approach, we store the packet in the external memory and process the flow using only its metadata . The benM is 64, we only need to store 9 bits instead of 64 bits. This pointer scheme significantly reduces the size of each register in the FPGA compared with mapping the external address directly. The proposed approach avoids the flaw in Beneš’s approach. Storing long addresses in registers takes up resources. Hence, a proposed improvement capable of reducing data width for the pipeline’s address pointer is to use a second layer of FPGA’s internal memory pointing to the external address. The width of the internal memory is equal to the maximum number of bits in the external memory address, and its depth is To manage the internal address more efficiently, we create a FIFO to keep track of the free memory addresses dynamically. This method does not use linked lists; we can utilize any empty address as soon as one is freed up. Furthermore, since the dynamic packet pointer manager interfaces with the input manager, it can quickly provide the input manager with an available memory slot in the queue.The method described so far focuses mainly on a single flow between the sender and the receiver. However, the IoT consists of multiple devices constantly communicating. The multi-flow approach distributes the data from multiple sources, achieving higher throughput . As a reThis section provides the results from prototyping the reordering scheme on the FPGA hardware. First, This section describes how each module is implemented using the proposed method on the FPGA. The modules were written using Verilog HDL, utilizing Quartus Prime software to perform synthesis, transforming Verilog register-transfer level design to bit streams to be programmed onto the FPGA. FPGA devices contain dedicated blocks of on-chip memories, or block random access memories (BRAMs), with various sizes based on the FPGAs. We use the BRAMs as the internal memory resource storing the addresses of the external memory. BRAM of up to 32 Kbits each is becoming the standard, offering 32 bits of memory width and 1 Kbits of depth . Beneš rWe do not show the input manager module and the external memory connections in order to simplify the explanation. The sequence number extracted from the input is fed into the pipeline controller for sorting. The counter is the internal register within the controller to keep track of the current in-order value. The controller compares the counter with the arriving sequence and the first register of the pipeline, as described in M total number of registers, we generate M comparator instances to send comparison results to the registers.The shift registers in the pipeline are wired to its left and right neighbors to enable shifting. It is a standard digital design method to shift all data bits at once in one clock cycle. As mentioned earlier, we use comparator blocks as indicators for the pipeline. If the pipeline has The output manager uses a multiplexer to select the sequence released from the pipeline, or a by-passed value directly from the input manager, depending on the operation. The output from the multiplexer is fed into the FIFO queue. Only the BRAM address from the pipeline’s reference pointer matters at this level. The queue identifies the BRAM memory location, matches it with the external memory address, and retrieves the entire packet.We implemented the proposed packet reordering scheme in the FPGA hardware using Verilog HDL and tested the design using the DE0-CV FPGA development board from Terasic.We performed circuit verification with the ModelSim software to probe the digital signals to ensure that the outputs were as expected from a randomized set of inputs. We captured different states of the design and viewed the internal values at specific clock cycles in ModelSim.The signals shown in We implemented the prototype on the Intel Cyclone V FPGA within the DE0-CV board for hardware testing and verification. The HDL modules were synthesized into the FPGA hardware using Quartus software. Timing analysis was performed to ensure that the design logic satisfied the hold and setup times with a 100 MHz clock. It should be noted that the hardware test was specifically set up to verify the packet reordering method. The packet sequence numbers were randomly generated and fed into the reordering module. Since packets were sorted every two clock cycles (50 million packets per second under the 100 MHz clock), we had two verification modes: automatic and manual modes. In the automatic mode, the output sequences were put into a FIFO, and a verification module was used to check the sequence for in-order delivery. In the manual mode, using the seven-segment displays on the FPGA kit, we could view the current input sequence and the values in the first stage of the pipeline. To verify the outputs, we used an enable switch button on the board to display the values stored in the output FIFO. The advantage of using the proposed method in FPGAs is its configurable features. We can reprogram the device to expand the pipeline size or the data width of the registers to fit different operational conditions. For instance, we can use a smaller pipeline size in a more stable network to save energy and resources. The opposite is also applicable if we expect many out-of-order packets with long delays. The modern FPGA architecture consists of adjustable logic modules (ALMs) as its main building block for reprogrammable complex logic functions. Increasing the data width, the number of BRAM blocks, the FIFO size, or the number of shift registers will take up more ALMs and on-chip memory bits. Choosing a suitable FPGA chip is crucial to strike a balance between cost and resources to meet the demand.We compare the memory and ALMs utilization in FPGAs to analyze resource usage by altering various design parameters. The data are from synthesis results using the Quartus Prime Lite edition on the Cyclone V FPGA. For the baseline design, we use 16-bit sequence numbers with 32 shift registers to make up the sorting pipeline. The reference pointer will need 6 bits to map its BRAM address.Furthermore, we look into the resource utilization of the baseline design on a range of low-end to high-end FPGA devices, as shown in As discussed in In this paper, we propose a scalable hardware-based approach to reorder packets for IoT devices using FPGAs. The proposed method can be implemented on reconfigurable hardware close to the endpoint for out-of-order packet processing, meeting the new design constraints of modern IoT and edge devices. It also overcomes the design flaws of the previous work on packet reordering. The reordering algorithm has a minimal time complexity of O(1), is scalable to multi-flow applications, and is simple to implement on FPGAs. Shifting and insertion operations in the sorting pipeline are completed in two clock cycles using the proposed method. When synthesized on a high-end FPGA, the design for a single flow uses less than 1% of both the ALMs and the block memory bits. In addition, we scale the design to fit multiple pipelines into one FPGA, and it takes less than 13% of ALMs when running 16 pipelines in parallel on an Intel Arria 10 FPGA. Furthermore, the design parameters, including the data width and the pipeline size, are adjustable to fit various operations and network demands. In the future, the reordering scheme can be synthesized to the endpoint of a network receiver. The fully integrated system can go through further field tests to gather more data on network traffic, monitor dropped packets, and accurately measure latency. Digital logic can be optimized further to ensure that the reordering scheme works with a higher frequency, meeting the demands of high-speed network applications.In practical applications, this reordering method can benefit the vendors and customers in the industry. With the vast application of IoT in recent years, the network edges have also diverged from their traditional networking characteristics. It is costly to design hardware to cover all specifications or individual custom circuits for each device. Therefore, it is beneficial to move toward a reconfigurable hardware approach by taking advantage of the capability of future modifications for long-term usage. There is great potential to reduce overall costs in the device life cycle by using FPGAs as networking hardware.


A series of measurements taken with two instrumented track bicycles in a velodrome are presented. The bicycle wheel speed, cadence, roll angle, steering angle, power, and airspeed are recorded. The experimentally-measured values are compared to existing theoretical models of roll and steering angles. The accuracy of the roll angle calculations is dependent on the fidelity of the modelled cyclist path and decreases for higher riding speeds. Experimental measurements of the steering angle show a reasonable agreement to theoretical calculations, albeit with reduced steering angles on the bends at higher speeds. There is also seen an increasing steering angle oscillation within each pedal cycle with increasing bicycle velocity which may influence a cyclist’s rolling resistance and the aerodynamic flow around the bicycle’s front end. Observations are made of changes in the flow field ahead of the bicycle due to the presence of other riders on the track, showing an effective tailwind of up to 0.7 m/s. The measured power shows a decrease at the bend entry due to the changing roll angle. Data presented in this paper provides new insights and can help to provide a validation of values used in existing track cycling analytic models. These models usually measure the wheel speed and power output and then, depending on the model’s complexity, calculate various other parameters to estimate either lap time or aerodynamic drag. A common feature of cycling mathematical models, primarily for track cycling, is the difference in velocity between the wheels  and compared it to a model of a point mass undergoing uniform circular motion. However, both of these studies were designed for general cycling, rather than track cycling where the roll angles are much greater, the track is banked, there is a non-zero roll rate during bend transitions , and the bicycle often follows a standard, well-defined curve. Work has also been completed for motorcycle roll angles8, however there can be large differences between the steering and roll angles for a motorcycle compared to a track cyclist due to the greater vehicle mass, wider tyres, and higher likelihood of the motorcycle rider displacing their centre of gravity away from the centreline of the motorcycle compared to a track cyclist.Studies comparing an experimentally-measured roll angle and a calculated roll angle have been completed by others but, to the best of the authors’ knowledge, not in a velodrome. Sanjurjo et al9 measured the steering angle around a 250 m velodrome track, showing a mean of approximately 1° on the straights, 4° on the bends and ± 2.5° with every pedal stroke. However, Kyle9 only provides 8.5 s of data where the exact position of the velodrome bend/straights is unclear and the experimental method is not detailed. Typical track cycling models currently ignore steering angles10, an exception being a forward-integration model by Fitton and Symons5 which uses calculations involving the track bank angle and bicycle geometry to calculate a quasi-steady-state steering angle. The steering input over a lap is not presented by Fitton and Symons5, with only the bend apex steering input provided over a range of speeds.There have been minimal efforts to measure the steering input for track cycling, which could differ from the requirements for road cycling. Restricting ourselves to pursuit events that largely follow the velodrome datum (black) line, a track cyclist will only provide minor adjustments to the steering angle as turning is generally achieved by rolling through the bends. A study by Kyle12. The longitudinal distance and lateral offset behind a cyclist at which the wake becomes negligible due to natural mixing, spreading, and dissipation is largely unknown. Research has been conducted at up to 6.9 m downstream of a single cyclist for the four cardinal crank angle positions, demonstrating a lateral shifting of the wake due to asymmetry of the cyclist12. Union Cycliste Internationale (UCI) road time trial regulations specify a region 2 m wide and 25 m long that must be avoided to prevent drafting effects13. However, work by Blocken et al.14 has shown that there can be a 7% drag reduction when a cyclist is 50 m behind a motorcycle, demonstrating that the wake remains for a long distance. A cyclist would provide a smaller, but somewhat similar wake to a motorcycle. The presence of increased turbulence behind other riders in a velodrome has been previously measured in a team pursuit event, with a turbulence intensity of 16.1% measured when drafting directly behind another cyclist compared to 1.5% for a solo rider15. It has also been recently proposed that research should be conducted into the measurement and influence of turbulence on cycling aerodynamics16.When cycling outdoors, an individual or group of cyclists create a low speed, turbulent wake behind themselves that dissipates naturally into the atmosphere17. In this scenario, the wake of each individual cyclist would merge to create a swirling flow along the track, reducing the effective head-wind and hence aerodynamic drag. The cyclists on a velodrome are not usually packed as close as in a road peloton, but this swirling flow could be compared to the inside of a peloton where the aerodynamic drag of a sheltered cyclist has been shown to be 5–10% of their isolated drag18. Work on speed skating has shown that skaters in an indoor skating oval can create a wind flow of 5–6 km/h along with increased mechanical turbulence19. This swirling tailwind flow has been mentioned before in the cycling literature20, but there has been no work completed in quantifying it as far as the authors are aware.When competing inside a velodrome, the average effective distance between two opposing pursuit teams/individuals is half the lap length, generally 125 m; much further than the previously-described longest measured drafting distance of 50 m. As there is no external wind and the cyclists travel around the same path, the wake may not have enough time to dissipate before the next riders arrive, and so there can be a build-up of slow-moving, turbulent airflow that is entrained by the movement of the cyclists. The size of this wake is likely to be dependent on the number of cyclists, their speed, position on the track, and the length of the race. The smallest wake would occur in a qualification time trial where there is only a single rider on the track for a maximum of three laps. In contrast, the largest wake would occur during a bunch race where there can be up to 24 riders for up to 200 laps of a 250 m trackThis work aims to simultaneously measure the roll angle, steering angle, power, airspeed and wheelspeed of a bicycle to provide insight into the movement of a track cyclist in a velodrome. This can be used to provide guidance in competitive track cycling or further research on aerodynamics and bicycle dynamics on banked tracks.21. A second bicycle measured wheel speed, cadence, power, and roll angle. The bicycle-fixed coordinate system has the x-axis directed to the bicycle’s rear, the y-axis to the bicycle’s right, and the z-axis upwards. This orientation has a positive roll angle  cadence, power, crank angle and steering angle Fig. a21. A se−1 in the circular bends by following a half sine wave trough-to-peak path22. All theoretical calculations assume that the cyclist follows the datum line exactly and all laps start at the pursuit line in the middle of the home straight and are left-turning.The measured results were compared to standard theoretical calculations of roll and steering used in previous track cycling models. To do so, a custom geometric model of the 250 m velodrome datum line was defined with reference to theodolite measurements of the physical line. This track model consists of two straight segments, two circular arcs in the middle of the bends, and four transition curves connecting the straights and the bends. The transition curves were designed with the curvature increasing from zero in the straights to 0.0465 m22:5 with wheel cornering and camber stiffness coefficients obtained from Doria and Roa23.By assuming the cyclist/bicycle system is a point mass and equating moments about the tyre/track contact point, the roll angle can be calculated from the wheel speed and track geometry with24.The roll angle results from the standard bicycle are shown in Fig. A test was conducted by riding the standard bicycle behind a derny (motorised pacing bicycle) for two laps at a constant speed and then accelerating to a higher speed for further laps. The use of a derny facilitated steady speed pacing and allowed higher velocities than was achievable by a solo rider. The results for the roll angle across various speeds are shown in Fig. .15) that is present due to the averaging over just seven laps, but on a larger scale some clear patterns emerge. There is a distinctive increase in 18.The measured wheel speed , the relative speed increase achieved with a velocity ratio of In addition to the change in airspeed, there is also an increase in the turbulence when riding in the wake of a series of riders. When riding half a lap behind the other cyclists, the turbulence intensity of the streamwise flow component approximately doubles, whereas the spanwise and vertical components triple relative to their empty track values which indicates further mixing of the flow in all directions. The ratios 28 but little work has been done verifying this intermediate result. The accuracy of the roll angle calculations is highly dependent on the accuracy of the modelled bicycle turn curvature and it decreases with higher speeds as the cyclist will tend to deviate further from the velodrome datum line and ride wider in the straights, reducing the roll rate. Using an adjustable track geometry model22, it would be possible to replicate this deviation by creating an artificial cyclist path with a wider track span, an increased lap length, and an identical circular arc bend. This keeps the bend apex in the same position but shortens the straights and extends the bend transition length to simulate a cyclist riding wide along the straights.There is a good agreement between the measured and calculated roll angle for an isolated cyclist. This is desirable as it demonstrates that with just a measure of wheel speed and an accurate model of the velodrome track geometry, the roll angle can be determined for an individual pursuit with a lap-averaged RMS error range of 1.9° to 4.9°. Several models used to predict lap times or calculate aerodynamic drag require this calculation29 who specify a minimum power output at the point of highest velocity in the bends for a 4000 m individual pursuit. The reason for this power decrease in a bend is unclear from a simple overview of the typical track cycling power demand model10. The aerodynamic drag should remain relatively constant through a bend as 15. In contrast, the power demand from rolling resistance is likely to increase due to the increased wheel speed and centrifugal force. The decrease in power is thus likely to be due to changes in kinetic and potential energy from the motion of the centre of gravity through the transitions. When leaning into a bend, there is a decrease in potential energy due to the lower centre of gravity, which is transformed into an increase in kinetic energy. The cyclist will accordingly reduce their power output at the bend entry and then increase it through the bend exit. Fitton and Symons5 include this change in potential energy in their mathematical model as both a positive and negative influence on power. This change in power between the bends and the straights is also likely to be dependent on the rider, with different athletes riding with different styles. The causes of the change in power between the straights and the bends should be an area for further research.The calculated velocity of the centre of gravity was shown to be relatively constant throughout the lap when the cyclist was instructed to maintain a constant lap time. This is in contrast to the wheel speed which showed a substantial increase in the bends, and the power which decreased at the start of the bends before steadily increasing as the cyclist exited the bends. This variation in power has been previously observed by Craig and Norton5 and is likely due to an increasing deviation from the datum line and the cyclist taking a more circular trajectory. It could also be due to the simplified, linear theoretical steering calculations not fully encompassing the complete non-linear bicycle dynamics. These observations are important as a track cyclist experiences increased scrubbing resistance when the front wheel is turned away from the direction of travel9. The change in steering angle can also influence the airflow around the front of the bicycle, inducing a further airflow yaw angle and changing the aerodynamic profile of the bicycle front21.This work presents measured and calculated steering angles around a velodrome track, showing a steering angle of approximately 2° in the bends and up to a ± 1.5° oscillation within each pedal cycle. The results show a decreasing bend steering angle and increasing steering oscillation with increasing wheel speed. The decreasing bend steering angle with increasing speed differs to previous theoretical calcuations.30 measured an un-specified speed of airflow tangential to the direction of motion of a team pursuit squad. Spoelstra et al.31 describe a “systematic tailwind” from the motion of a single cyclist in a closed hall. D'Auteuil et al.19 describe this flow entrainment on speed skating ovals where airspeeds up to 1.6 m/s were postulated. This artificial tailwind can reduce the aerodynamic drag experienced by a cyclist; as an example, the earlier suggested speed increase of 3.5% results in an 8.4 s time advantage over a 4 min race. However, if they remain half a lap apart, this tailwind is likely to impact all competitors on the track equally.The increased tailwind observed with other riders on the track is a feature that has been commented on in prior work, but to date only anecdotal evidence has been supplied. Fitton et al20. Turbulence properties can change the characteristics of the flow around a rider, particularly the initiation of laminar-to-turbulent transition in the boundary layer, which dictates the occurrence of the drag crisis34. It has been previously shown for speed skating, which operates in a very similar Reynolds number range to track cycling, that replicating on-track turbulence in a wind tunnel can induce the drag crisis at a lower wind speed compared to low-turbulence results19. Further work on large commercial vehicles has also shown the importance of replicating the real-world turbulence for aerodynamic research36. This has an implication for cycling research as the primary method for drag reduction of the rider is through the use of artificial roughness to induce the drag crisis37. If there is an increased level of atmospheric turbulence, then the drag crisis could be naturally induced on bluff body components and the addition of artificial roughness will increase the skin friction without any corresponding reduction in the pressure drag, increasing the total drag rather than reducing it. Detailed investigations into the effects of freestream turbulence on cycling should be an area for future research.The increasing turbulence observed when behind a group of riders, even when they are 125 m ahead of a cyclist, is an important result as the majority of cycling aerodynamic research is conducted using low-turbulence wind tunnels or computational fluid dynamics modelsThis paper outlines a series of experimental measurements from an instrumented track bicycle in a velodrome. The roll angle is measured and compared to existing theoretical calculations, showing good agreement when the cyclist follows the track datum line, confirming the applicability of quasi-steady dynamical models to pursuit cycling. Measurements of the steering angle show reasonable agreement with calculated values and show an approximately 2° turn in the bends. When riding at higher speeds, the cyclist is seen to take a more circular trajectory to extend the bend transition and reduce the roll rate, and the steering angle oscillation over each pedal cycle is found to increase. The measured power shows a higher value in the straights and a decrease at the bend entry where there is a conversion between potential and kinetic energy due to the change in roll angle. There is also a change in the airflow when other riders are present, creating a swirling flow around the track, reducing the apparent headwind and increasing the freestream turbulence experienced by an isolated cyclist. This swirling and turbulent flow could have an impact on potential drag reduction techniques for track cycling..21. Magnetic reed switches on the rear wheel and the cranks provide wheel speed and pedalling cadence, respectively. An optical switch measures the crank angle with a measurement tolerance of 360°/53 = 6.8° using the method detailed in Fitzgerald et al.21. A push-button placed on the handlebars is used for the rider to signal particular events and for time synchronisation between different Data Acquisition Systems (DAQ). A non-contact rotating analogue rotary position sensor is mounted to the top of the steering axis and records the steering angle with a 0.4° resolution at a 500 Hz sampling frequency. Two beacon transmitters placed at either pursuit line in the middle of the straights were detected by a receiver mounted on the bicycle, providing accurate times of every half-lap. A crank-based power meter recorded the rider’s input power and cadence (Schoberer Rad Meßtechnik (SRM), Germany). The aerodynamic data, wheel speed, cadence, crank angle, and push button signals were recorded by one DAQ, , whilst the steering angle, beacon receiver, cadence, and push button signals were recorded by a second DAQ , and the power and cadence by a third (SRM PowerControl V). The same signals from the cadence sensor and push button were recorded by all DAQs for common-time synchronisation.Testing was completed with the primary bicycle  shown in Fig. A second track bicycle , known as the standard bicycle, had a 9-axis Inertial Measurement Unit (IMU), including a 3D accelerometer, 3D gyroscope and 3D magnetometer, firmly mounted posterior to the seat tube. The IMU sensor outputs were fused with a commercial Kalman filtering system  to calculate 3D orientation measurements. This bicycle had a crank-based SRM power meter, cadence sensor and a five-magnet wheel speed sensor for improved speed resolution. Lap timing was recorded with a beacon receiver which detected the transmitters placed at both pursuit lines. All data was simultaneously logged with a single custom-built DAQ system. The standard bicycle does not have the bulky pannier rack or probe holders and so doesn’t have the capacity to record the aerodynamic data, crank angle, or steering angle. However, this DAQ system is small and lightweight and so has a negligible influence on the aerodynamics or mass distribution of the bicycle, permitting it to be ridden in a ‘race ready’ state. This enabled testing of the roll angle at higher speeds.The pressure probe has a manufacturer-specified accuracy of ± 0.3 m/s and ± 1° in yaw and pitch for speeds of 2–30 m/s in a ± 45° cone, with a frequency response of 600 Hz and 16 bit digital resolution. The probe was aligned to the bicycle frame at the velodrome track with a custom-built alignment fan with an estimated alignment error of ± 0.5° in yaw and pitch angles. The IMU has an angular resolution of 0.05°, dynamic accuracy of 2°, and a 100 Hz sampling rate. The power meter has 8 strain gauges with an accuracy of ± 0.5%.The bicycles were ridden by two elite male cyclists who provided informed consent before participating. All experimental methods were performed according to relevant guidelines and regulations, and the procedures were approved by the University of Adelaide Human Research Ethics Committee (H-2019-018). The rider’s lap times were paced by their coach with instructions to maintain a speed that provided as consistent a lap time as possible. The cyclist maintained a time-trial position on the bicycles and no instructions on how to ride were provided. Testing behind the derny involved two laps at a consistent speed interspaced with an accelerating lap to achieve the next consistent speed..22. This model has G3 geometric continuity across the lap, providing continuous acceleration and roll rate. There is no change in elevation of the modelled datum line. Measurements of the bank angle were taken from the theodolite data and checked with an inclinometer.Testing was conducted at the Adelaide SuperDrome with a 250 m lap length as defined by the black datum line marked on the track surface. The track geometry was measured by a theodolite survey, providing detailed 3D coordinates of the velodrome surface. A custom mathematical model with an apex turn radius of 21.5 m and track span of 45 m was fitted to the measured geometric data, with the method fully detailed in Fitzgerald et alOne of the errors in this testing is that the rider does not always exactly follow the datum line; rather they will generally ride high in the straights and then come in close around the bends. There is also a certain level of variability in the bicycle path which can serve to increase the ridden distance compared to the official lap distance. The extent of this discrepancy can be estimated by calculating the ridden distance around the track from the wheel speed sensor, and it was found that the rider rode an extra 2.8 ± 0.67 m (mean ± standard deviation) each lap. This will impact the true turn radius at each position around the velodrome, influencing theoretical calculations of 5. In addition, lateral aerodynamic forces due to curved aerodynamic flow and turning of the front wheel are not considered, which could have an impact on both roll and steering angles. The results presented are for a steady-state lap where large accelerations, such as occur in sprinting, do not have an influence.The cyclist and bicycle are modelled as a combined point mass at the centre of gravity in the symmetry plane, ignoring the influence of any features such as bicycle geometry, gyroscopic effects, movement of the cyclist/bicycle due to pedalling, or general movement of the cyclist. The calculations assume that the steering input is small and thus does not influence calculations of roll22. With an accurate model of the track geometry for a particular velodrome, the overall results presented here could be replicated at any velodrome.Considering a variety of distinct cyclists instead of only one would enrich the analysis on roll and steering angle. Different cyclists may have different styles of riding and follow different paths around the velodrome, which could influence roll angles, power output, and steering angles. This was a pilot study to observe the major effects, and future work could involve the testing of a variety of cyclists to achieve a more representative observation of the general professional cycling population. Additionally, this experiment has been conducted at only one velodrome, and different velodromes have different geometries, so these results may not be representative of all velodromes. However, the overall geometries of most 250 m velodromes are very similar, having small differences between straight lengths and bend radii, with the largest differences being with banking styles


In this study, a certain percentage of lignin in original bamboo kraft black liquor (BKBL) was separated, and the residual BKBL with low lignin content was expected to be fed into the alkali recovery boiler to reduce the heat transfer load of the alkali recovery boiler. With the decrease in lignin content, the rheological properties/volumetric isothermal expansivity (VIE) of BKBL change. When the lignin content was 70% remaining in the original BKBL, the viscosity of BKBL with low lignin content is close to that of the passivated BKBL at the same solids content, the dynamic viscoelasticity is superior, and the VIE decreases by 57.2%. When the amount of desilication agent is 1.5%, the viscosity of BKBL with low lignin content did not change much, and the VIE increased sharply and was 62.7% higher than that of the passivated BKBL. Therefore, the combination of partial lignin separation process and sodium aluminate desilication process can effectively improve the ability of alkali recovery boiler to deal with BKBL and reduce the influence of “silicon interference”. Hence, it is imperative to realize the “integration of forest and pulp”. However, the “Silicon Interference” of non-wood pulping and the contradiction between the increase in pulp demand and the insufficient capacity of the existing alkali recovery system restrict the development of pulp paper integration. Improving pulp production capacity is the key to expand the treatment capacity of alkali recovery system and reduce the impact of “Silicon Interference”8. Building a new alkali recovery system is the most direct and effective method, but is bound to increase the production cost of the pulp mill. If the black liquor from a new pulp production line shares the original alkali recovery system with the black liquor from the existing production lines, the expansion of pulp production capacity may become a reality. There is about 25% of the lignin in bamboo material, which enters the bamboo kraft black liquor (BKBL) during cooking. Especially, lignin (0.5 tons) will enter the BKBL with the production of 1 ton of bamboo pulp. Lignin is a high-quality renewable raw material that can be used as a substitute for many petroleum-based products. Therefore, it is useful to separate a certain percentage of lignin from BKBL as a byproduct14. The revenue from the sales of lignin brings additional economic benefits to the pulp mill, which can be used to cover the upfront investment in building a lignin separation unit. At the meantime, the residual black liquor could be still pumped to the alkali recovery system. This can reduce the heat exchange load of alkali recovery boiler and improve the treatment capacity of black liquor18. In addition, it has a certain desilication effect when separating lignin due to the adsorption of silicon by lignin, which is helpful for overcoming the “Silicon Interference”20.The current situation in the Chinese pulp and paper industry is challenging as carbon emissions exceed the target, creating difficulty in realizing the goal of carbon peak and carbon net-zero24. Therefore, the proportion of extracted lignin is very important and needs to achieve a balance between the rheological and isothermal expansion properties. Specific experimental data must be provided to support whether it can replace the high-temperature passivation section or reduce the passivation treatment time based on the declining degree of viscosity, and whether the adverse impact on the expansion performance can be tolerated in actual production process.The problem of “Silicon Interference” in non-wood pulping is very serious, and the extraction of some lignin cannot completely solve it. In view of this situation, our research group proposed the process of “desilication from green liquor by BKBL combustion”. Desilication agent is added before the BKBL enters the recovery boiler, and the green-liquor-silicon-insoluble (GLSI) substance is formed in the combustion stage. The desilication purpose from green liquor can be achieved by filtering the GLSI substance, and the white mud with low silicon content can be recycled. The alkali recovery circulation system can form a closed loop. Therefore, the influence of desilication agent on the rheological and isothermal expansion properties of BKBL also needs to be considered. The extracted lignin is beneficial to the flow and may hinder the isothermal expansion characteristics (VIE) of black liquora, storage modulus G′, dissipation modulus G″, and the dynamic viscosity η′ of high solids content BKBL. The VIE value of BKBL was measured and its variation pattern was analyzed. The promoting or inhibiting effect of extracted lignin on rheological parameters was investigated, and the improving or hindering effect of adding desilication agent on isothermal expansion properties was also discussed.The rheology and VIE of BKBL with low lignin content and high solids content were systematically studied. We analyzed the rheological parameters, the changes in apparent viscosity η3, the total solid content was 475.00 g/L, the organic content was 270.88 g/L, and the inorganic content was 204.12 g/L. The organic components of BKBL mainly include lignin and hemicellulose, while the inorganic components include Na2SO4, Na2SiO3, SiO2, and Si (OH)4. Sulfuric acid  was purchased from Sinopharm Chemical Reagent Co., Ltd. Aluminum sulfate (Al2(SO4)3, AR, 99.8%) provided by Damao Chemical Reagent Factory Co., Ltd. Partial sodium aluminate  was obtained from Sinopharm Chemical Reagent Co., Ltd.The BKBL from Kraft pulping in G2 tower continuous digester was provided by Guizhou Chitianhua Co., Ltd, China. The relative density was 1.21 g/cm2SO4 was added into the beaker, adjusting continuously until the pH reaches to 2. The acidified BKBL was left and precipitated for 1 h at 80 °C, and all the precipitated lignin was filtrated out. The filtered lignin was washed with distilled water and dried to a constant weight in an oven at 105 °C, and the lignin content of original BKBL was calculated. According to the above method, the pH of original BKBL was adjusted slightly with sulfuric acid in order to separate 10%, 20% and 30% lignin  from the BKBL, respectively. Therefore, the residual BKBL has low lignin content with 70%, 80% and 90% lignin compared to the original BKBL, respectively. Then all the BKBL samples were concentrated to 80 wt% at 80 °C in a vacuum drying oven, which named BKBLx . In addition, the effect of adding desilication agent on the rheological properties was studied. BKBL70 was divided into three sections, with 0%, 0.5% and 1.5% of the desilication agent NaAlO2 added into the three sections, respectively.The preparation process of BKBL with low lignin and high solids content was shown in Fig. −1 in the apparent viscosity test, and the vibration frequency was set at 0–105 rad/s in the dynamic viscoelasticity test.The rheological parameters of BKBL were tested by using a dynamic rheometer . The test was carried out using a 25 mm diameter copper parallel plate fixture with a spacing of 700 µm between the upper and lower parts of the fixture. The range of shear rate was varied from 0 to 100 sThe VIE of BKBL was tested in a muffle furnace . 2.5 g of BKBL were weighted with corundum crucible and put into muffle furnace, and the muffle furnace was then heated from room temperature to 300 °C and kept for 1 h in order that the black liquor is carbonized and expands fully. The volume of carbonized black liquor in corundum crucible with dry particles was measured. The ratio of volume to mass was obtained as the VIE of BKBL.27. Sinquefield found that the viscosity of wood pulp black liquor with solid content of 10–30% increased with the increase of solid content28. Jawaid et al. found that the viscosity of medium-concentration wood pulp black liquor (note: solids content 37–47%) increased with the increase of solid content29. Wallmo found that when the extraction amount of lignin was 60%, the viscosity of black liquor decreased by 75% (note: solids content 50%)30. Moosavifar et al. found that after the removal of lignin, the viscosity can be reduced by one order of magnitude at most, and the boiling point of black liquor will also decrease correspondingly31. In the above studies, the object base is wood pulp black liquor. Therefore, it is necessary to study the black liquor of non-wood pulp. Zhang and Sun studied the dynamic viscoelastic characteristics of BKBL with medium concentration and the effect of desilication agent33. In order to improve the treatment capacity of black liquor, they concluded that future trend is to separate some lignin from black liquor before being sent it to alkali recovery boiler for combustion. However, attention should be paid to the dynamic viscoelasticity of BKBLX with low lignin content and high solid content.Zamanet al. found black liquor with high solids content is non-newtonian fluid. Its viscosity and viscoelasticity increase with the increase of solid content. In addition, he used “Power-law” to fit the viscosity changes within the test range, estimated the viscosity value and viscoelastic modulus value of black liquor at higher solid content and temperature through these modelsx were shown in Fig. x decreases significantly with the increase in shear rate when 98 °C. The curve of BKBL90 and BKBL80 are similar to that of original BKBL, but the viscosity and thickening rate decreased with the decrease in lignin content. The apparent viscosity of BKBL70 maintains a downward trend within the testing range, and there is no shear thickening observed. The main reason is the decrease in the strength of network structure formed in BKBL70 because of the significant reduction of lignin content in BKBL70, which could be destroyed without high shear. Compared with the previous work in our group, it is found that the apparent viscosity of BKBL70 is approximately the same as that of the passivated BKBL at the shear rate of 100 s−1 when they have the same solid content. Therefore, the purpose of viscosity reduction may be achieved by extracting some lignin in commercial production process, and the passivation section may be eliminated in the alkali recovery system or the passivation time may be shortened, so as to effectively reduce the energy consumption in alkali recovery system.The viscosity of BKBL affects the pump transportation and evaporation efficiency. The results of the apparent viscosity of BKBLThe reason why the reduction of lignin content helps to reduce the viscosity of black liquor is that in the process of acid precipitation, lignin is separated step by step. The lignin with the largest molecular weight was first separated. The strength of the network structure formed by lignin decreases, when the content of lignin decreases, which is manifested by the decrease of the viscosity of black liquor.The shear thinning of BKBL apparent viscosity can be explained by “polymer conformational change theory”. BKBL with high solids content only contains a small amount water, and there exist organic macromolecules including lignin in the form of long linear chains. As long as the length of some molecular chains is greater than a certain value, the molecular chains will entangle with each other and form entangled floccules somewhere in the black liquor. The number of entangled floccules is in a dynamic equilibrium, and a network structure may be formed with the polymers in the black liquor when the equilibrium is broken. Some energy is stored in the internal network during the BKBL flow, and the external performance is that BKBL has high viscosity and is difficult to flow. As BKBL is subjected to continuous shearing, the direction of its internal disordered molecular chains is gradually consistent with the shear force  deformation of the materials during deformation, reflecting the elastic-solid property of the materials. Loss modulus, G″, i.e., viscosity modulus, refers to the energy lost due to viscous deformation (irreversible) of materials during deformation, reflecting the viscous flow of the materials.x first decrease slightly and then increase with the increase in oscillation frequency. Moreover, the G″ is always higher than the G″, indicating that the reversible deformation is greater than the irreversible deformation for BKBLx. The decrease in lignin content is responsible for the decrease in the G′ and G″, indicating that the viscoelasticity decreases. Even when BKBLx encounters elbows, valves, nozzles and other structures in the pumping process, the movement obstacles encountered by BKBLx are far less than those encountered by the original BKBL in the normal straight pipe transportation.As can be seen from Fig. x and original BKBL show the trend of shear thinning, which is similar to the trend of apparent viscosity ηa. This further proved that the separation of some lignin is benificial to the pumping and transportation of BKBLx.Dynamic viscosity η′ refers to the change rate of loss modulus G″ with angular frequency ω. The dynamic viscosity can eliminate the measurement error of apparent viscosity caused by elastic deformation during the flow of some BKBL samples, so we measured the dynamic viscosity to evaluate the fluidity of the black liquor. Figure 70 increased when NaAlO2 was added at zero oscillation frequency. With the increase in oscillation frequency, G′ and G″ decreased rapidly at first, and then started to increase when the oscillation frequency was greater than 10 rad/s. The viscoelastic modulus of BKBL70 with adding desilication agent was less than that of the original BKBL70. That is to say desilication agent has little adverse effect on viscoelasticity of black liquor at high oscillation frequency.It can be seen from Fig. 70 dynamic viscosity η′ with angular frequency is similar to that of the apparent viscosity ηa, and they all show a trend of shear thinning. At low oscillation frequency, desilication agent leads ηa to increase, indicating that the viscous kinetic energy loss of BKBL increases at this time. The apparent viscosity of BKBL samples decreases when adding NaAlO2 desilication agent, which is consistent with to the previous results.It can be seen from Fig. 70, the reason why the dynamic viscosity with 0.5% NaAlO2 is greater than that with 1.5% NaAlO2 is that the viscosity of the former is greater than that of the latter, and the kinetic energy loss caused by high viscosity is also greater. When the angular frequency is close to 100 rad/s, the dynamic viscosity of BKBL70 with 1.5% desilication agent is lower, because the dynamic viscosity is closer to the actual viscosity than the apparent viscosity at high oscillation frequency. This shows that the viscosity of BKBL70 decreases with the increase in the amount of desilication agent.As for BKBL70 at 80 °C is much lower than that at 98 °C, indicating that BKBL70 is mainly elastic-solid at 80 °C. Dynamic viscosity tends to be the real viscosity with the increase in angular frequency, and the reason is that the main role of stress is to make BKBL70 undergo elastic deformation. The dynamic viscosity of BKBL70 decreases rapidly at 98 °C and is slightly lower than that at 80 °C when the oscillation frequency is close to 100 rad/s. This further shows the importance of high temperature for BKBL transport.Figure 2 desilication agent will cause little adverse effect on viscosity but a certain viscosity reduction effect when BKBL70 are pumped into the alkali recovery boiler.The shearing effect and stress on BKBL in pipeline transportation and nozzle atomization are much higher than those in the lab testing process. Therefore, it is reasonable to speculate that adding NaAlOPapermakers can judge the difficulty of concentration and dryness of black liquor in the boiler and predict the swollen degree of the bottom cushion layer according to the VIE of black liquor. The larger the VIE value, the more swollen the bottom bed, and the easier the air goes through the bed, the better the actual combustion effect. The VIE of straw pulp black liquor is the smallest among the various raw materials black liquor because of its high silicon content and high viscosity. Therefore, it is essential to ensure that the VIE of BKBLx is greater than that of straw pulp black liquor, so that a good bed can be formed at the bottom of alkali recovery boiler.2 VIE of BKBL were measured by VIE of BKBLx in Fig. x decreases with the decrease in lignin content, and the VIE of original BKBL is almost twice that of BKBL70, indicating that the lignin content has a great influence on the VIE of BKBLx, which is due to the release of gas during the thermal decomposition of lignin. It is concluded that the reason for the decrease of VIE is the decrease in gas emissions due to the decrease in lignin content in BKBLx34. Although the decrease in lignin content directly leads to the decrease in the VIE of BKBLx, the increase in VIE will be more obvious in the presence of promoting factors. Impact on NaAlO2 desilication agent on VIE may be caused by the viscosity reduction effect of NaAlO2. It can be seen from the previous research that the addition of NaAlO2 can effectively reduce the apparent viscosity of BKBL at zero shear rate and improve the elastic modulus of BKBL at zero oscillation frequency. Therefore, adding a small amount of desilication agent can significantly promote the VIE of BKBL.It was indicated that the effect of lignin content and NaAlO70 with different desilication agent are shown in Fig. 2 has clear improving influence on VIE due to its viscosity reduction, and acidic desilication agent Al2(SO4)3 has no significant effect. The reason is that Al2(SO4)3 leads to the increase in the viscosity and elastic solid properties of BKBL, and the improvement for elastic solid properties and hindering effect for the increase in the viscosity can offset each other. Therefore, the VIE of BKBL will not change significantly. The VIE of BKBL70 with alkaline NaAlO2 desilication agent added was 62.72% higher than that of passivated BKBL. Furthermore, a small amount of desilication agent can reduce the adverse effect of extracted lignin on the expansion performance of BKBL. In this work, the desilication rate is the highest and meanwhile the VIE value reaches the maximum, when the amount of desilication agent is 1.5%.The changes of the VIE of passivated BKBL and BKBLIn brief, the separation of some lignin can not only greatly decrease the viscosity of BKBL, but also reduce its adverse effect on the expansion performance by adding desilication agent. What’s more, the combined use of “Partial Lignin Separation Process” and “Desilication from Green Liquor through Black Liquor Combustion Process” can improve the processing capacity of BKBL and ultimately helping to improve the production capacity of pulp.X decrease. When 30% lignin was separated from the original BKBL, the apparent viscosity of the remaining black liquor-BKBL70 was close to that of the passivated BKBL with the same solids content, and the storage modulus and dissipation modulus were lower than those of the original BKBL. The VIE of BKBL70 is smaller than that of the passivated BKBL with the same solids content by 57.2% BKBL70 has a trend of transition from non-Newtonian fluid to Newtonian fluid, but the VIE declines too much, which induce that BKBL70 cannot form a cushion with a good intumescent performance at the bottom of the alkali recovery boiler. The adverse influence on decreasing lignin content of VIE can be compensated by adding NaAlO2 desilication agent, and the VIE of BKBL70 is significantly increased with adding 1.5% NaAlO2 desilication agent by 62.7% higher than that of passivation black liquor. In addition, the apparent viscosity of BKBL decreases with adding a small amount of NaAlO2 desilication agent, and the rheological properties of BKBL70 are not be clearly affected, which is beneficial to the pumping and transportation of BKBL.In order to improve the ability of alkali recovery boiler to treat BKBL and reduce the impact of “Silicon Interference”, a certain percentage of lignin was separated from BKBL, and we intend to send the remaining BKBL with low lignin content to the existing alkali recovery boiler. Therefore, we studied the rheological and VIE of BKBL with high solid and low lignin content, and the effect of desilication agent on them. The viscosity and VIE of BKBL are closely related to lignin content. With the decrease in lignin content, the apparent viscosity and VIE of BKBL