Maximum Load Rate Research Articles

Comparative study of toughness and energy evaluation of laminated bamboo composites and toughening mechanism

As toughness becomes an important mechanical property of construction materials, scientific toughness assessment is vital to the development of new materials and helpful for material innovation. For laminated bamboo composites in which the failure modes are relatively uncertain, different methods were applied to evaluate the toughness of bamboo laminate. A comparative study of various toughness evaluation methods was conducted for laminated bamboo. The meaning and error of the toughness expressed by the energy release rate or J-integral determined by different methods were interpreted and analyzed. Based on the calculated toughness, the toughening mechanism of bidirectional laminated bamboo was explored. The results show that the ratio of transverse bamboo strip volume Vf vertical to the initial notch direction has a positive impact on the initial stiffness, maximum load, and energy release rate. Besides that, the layup or arrangement of bamboo strips would also affect the mechanical properties and fracture toughness of laminated bamboo, of which the effect is investigated by dividing the fracture parameters by Vf. It is concluded that the major mechanism for increasing the ductility and the toughness before the maximum load (expressed by D2/D1 and GIcun/Vf or GIc0.8d/Vf) is the crack deflection caused by the hierarchical structure composed of vascular bundles (fiber) and parenchyma tissue (matrix) in a single layer of bamboo laminae. However, the ductility and the toughness after the maximum load (expressed by D3/D2 and GIc0.8d/GIcun) are mainly enhanced by the alternatively arranged bamboo laminae of different fiber directions.

Medium-voltage feeder blocks division method considering source-load uncertainty and characteristics complementary clustering

Existing feeder block division methods fail to consider the complementary characteristics and uncertainty between power sources and loads, which result in excessive feeder blocks, low inter-block balance, and significant disparity in net load peak-valley difference. To address these issues, a medium-voltage feeder block division method that considers the uncertainty and complementary characteristics of sources and loads is proposed. Firstly, based on the probability density characteristics of sources and loads, an uncertainty model of DG output and load demand is established. Secondly, considering the constraints of block maximum load rate and feeder non-crossing, a feeder block division model is established. Additionally, a set of center circles is defined, and based on this, an improved K-means clustering algorithm is proposed. The initial clustering centers based on the center circles is set, and the clustering centers based on the arcs of the center circles corrected. And the weighted distances between power sources and clustering centers are calculated. An algorithm flow for improved K-means clustering feeder block division is designed accordingly. Finally, the case studies show that the result of block division is improved.

An auxiliary optimization method for electric heating renovation based on using a clustering algorithm

The large amount of pollutants emitted by coal heating in winter is one of the main causes of haze, which brings great trouble to people’s lives. To reduce air pollution caused by coal burning and improve air quality, the state advocates the transformation of traditional electric heating methods to accelerate the transformation of China’s energy system to a clean and low-carbon model and improve the utilization rate of renewable energy in China. Therefore, this article through the calculation of the residual capacity of the retrofit and the calculation of the air conditioning load to assist the electric heating transformation. Firstly, the average power of the transformer during a high power period is calculated instead of taking the maximum power directly, which solves the problem of small residual capacity caused by a large maximum load rate and maximizes the transformable capacity. Secondly, the cluster analysis of air conditioning heating as one of the typical electric heating methods is carried out by the K-means clustering method, and the air conditioning load is obtained as the data reference during the electric heating transformation to assist the optimization transformation of electric heating. The two methods are further studied and verified by two examples, and the theory guides the practice to assist the electric heating transformation and achieve the goal of energy saving and emission reduction.

Do Between-limb Strength Differences in the Elbow Flexors Affect Their Neuromuscular and Strength Adaptations to Short-term Strength Training?

Purpose. The present study quantified between-limb responses to strength training in the stronger (STR) versus weaker (WEA) elbow flexors in participants with symmetric (SYM) or asymmetric (ASY) 1-RM strength. Methods. Neural, hypertrophic and strength adaptations to 4 weeks (3∙wk-1) of unilateral elbow flexion training of both arms were examined in 24 participants (6 men and 6 women in each group) who had not undertaken strength training in the past 12 months. Changes in one-repetition maximum load (1-RM strength), isokinetic (20°·s-1 and 210°·s-1) and isometric (MVIC) strength and rate of force development (RFD) as well as muscle activation (EMG; normalised to maximum M-wave amplitude) and size (CSAFlexor) were measured. Transcranial magnetic stimulation was used to assess motor evoked potential amplitude (MEP) and cortical silent period duration (cSP). Results. Following training, significant increases in 1-RM strength (SYM, STR: ∆ = 2.4±1.1 kg, WEA: ∆ = 1.9±1.1 kg; ASY, STR: ∆ = 1.8±0.7 kg, WEA: ∆ = 1.7±0.7 kg) and CSAFlexor (SYM, STR: ∆ = 107±98 mm2, WEA: ∆ = 121±64 mm2; ASY, STR: ∆ = 108±73 mm2, WEA: ∆ = 105±65 mm2) were observed, although they were not different between arms in either group. Increases in isokinetic strength were also detected, but only in STR (SYM: 20°·s-1, 210°·s-1; ASY: 20°·s-1). No statistical changes were detected in MVIC, RFD, EMG, MEP or cSP. Correlation analyses demonstrated both similarities and differences in the between-limb responses when comparing the groups. Conclusion. Between-limb responses to strength training in participants with and without strength symmetry were similar, although isokinetic strength increases were only observed in the stronger arms. However, the correlation results suggest that individual differences exist between the groups, signalling that between-limb responses can differ in individuals with and without strength asymmetry.

Research on Differential Steering Dynamics Control of Four-Wheel Independent Drive Electric Tractor

Traditional tractors can only achieve steering through mechanical structures such as steering knuckles and steering trapezoids. Among them, the mechanical structure is more complex, and various parts are easily damaged, making the tractor malfunction. The four-wheel independent drive differential steering mode differs from the traditional Ackermann steering mode, which realizes steering by controlling the inner and outer wheel torque, which can accurately steer the working state of high-end agricultural machinery equipment and improve the operating efficiency of agricultural machinery equipment. Aiming at the dynamic control problem in the steering of electric tractor four-wheel independent drive, a layered control strategy based on the sliding mode control of yaw torque at the upper level and the optimal torque distribution level based on the mean load rate of vehicle tires at the lower was proposed. By analyzing the differential steering mechanism of a four-wheel independent drive, a dynamic model of differential steering of the electric tractor is established, and a dynamic controller of a four-wheel independent drive is designed according to the layered control strategy. The upper controller tracks and controls the expected yaw speed on the basis of the sliding mode control to track the driver’s intention, and the lower controller realizes the optimal torque distribution based on the principle of the optimal average load rate of the vehicle tire to ensure the steering stability of the electric tractor. The effect of the controller was simulated and analyzed under typical conditions of double line shift, serpentine, and step. The results showed that the sliding mode controller is better than the PID controller in driver intention tracking. Compared with the average allocation strategy, the average maximum load rate of the vehicle tire under the three working conditions is reduced by 16.9%, 13.8%, and 17.3%, respectively, which proves the effectiveness of the layered control strategy. In the real car test, the sliding mode controller is better than the PID controller in the driver intention tracking. This study has important guiding significance for improving the maneuverability and stability of electric tractors.

Application of multiple regression models in the analysis of kinematic parameters in competitive gymnastics

Abstract Nowadays, the progress of competitive gymnasts needs more and more help from sports science, and it is from the mechanics perspective that human movement science analyzes this complex system of the human body. In this paper, the back handsprings in gymnastics were tested and recorded with a motion capture system to evaluate the back handsprings’ technical movements quantitatively. A multiple regression model was used to model the dynamics of the human body and carry out simulation calculations to analyze and study the movement patterns and lower limb stresses. The results showed that the maximum load rate through the back handspring experimental stage was (379.91±101.23) BW/s, and the time of appearance of the maximum load rate was (0.025±0.003) s. The maximum load decay rate was (-321.61±107.21) BW/s, and the time of appearance of the maximum load decay rate was (0.043±0.005) s. The difference between the results and the actual test value difference between the results and the actual test values was less than 0.005, indicating the feasibility of applying the multiple regression model to the kinematic parameters analysis of competitive gymnastics. The multiple regression-based kinematic parameter analysis models can effectively solve the problem of force on the bones and joints of difficult gymnastic movements, which can better assist trainers in learning gymnastic items and provide theoretical support and reference basis for the development and training of difficult skills in competitive gymnastics.

CostCounter: A Better Method for Collision Mitigation in Cuckoo Hashing

Hardware is often required to support fast search and high-throughput applications. Consequently, the performance of search algorithms is limited by storage bandwidth. Hence, the search algorithm must be optimized accordingly. We propose a CostCounter (CC) algorithm based on cuckoo hashing and an Improved CostCounter (ICC) algorithm. A better path can be selected when collisions occur using a cost counter to record the kick-out situation. Our simulation results indicate that the CC and ICC algorithms can achieve more significant performance improvements than Random Walk (RW), Breadth First Search (BFS), and MinCounter (MC). With two buckets and two slots per bucket, under the 95% memory load rate of the maximum load rate, CC and ICC are optimized on read-write times over 20% and 80% compared to MC and BFS, respectively. Furthermore, the CC and ICC algorithms achieve a slight improvement in storage efficiency compared with MC. In addition, we implement RW, MC, and the proposed algorithms using fine-grained locking to support a high throughput rate. From the test on field programmable gate arrays, we verify the simulation results and our algorithms optimize the maximum throughput over 23% compared to RW and 9% compared to MC under 95% of the memory capacity. The test results indicate that our CC and ICC algorithms can achieve better performance in terms of hardware bandwidth and memory load efficiency without incurring a significant resource cost.

Collaborative Determination Method of Metro Train Plan Adjustment and Passenger Flow Control under the Impact of COVID-19

Aiming at the problem of metro operation and passenger transport organization under the impact of the novel coronavirus (COVID-19), a collaborative determination method of train planning and passenger flow control is proposed to reduce the train load rate in each section and decrease the risk of spreading COVID-19. The Fisher optimal division method is used to determine reasonable passenger flow control periods, and based on this, different flow control rates are adopted for each control period to reduce the difficulty of implementing flow control at stations. According to the actual operation and passenger flow changes, a mathematical optimization model is established. Epidemic prevention risk values (EPRVs) are defined based on the standing density criteria for trains to measure travel safety. The optimization objectives of the model are to minimize the EPRV of trains in each interval, the passenger waiting time and the operating cost of the corporation. The decision variables are the number of running trains during the study period and the flow control rate at each station. The original model is transformed into a single-objective model by the linear weighting of the target, and the model is solved by designing a particle swarm optimization and genetic algorithm (PSO-GA). The validity of the method and the model is verified by actual metro line data. The results of the case study show that when a line is in the moderate-risk area of COVID-19, two more trains should be added to the full-length and short-turn routes after optimization. Combined with the flow control measures for large passenger flow stations, the maximum train load rate is reduced by 35.18%, and the load rate of each section of trains is less than 70%, which meets the requirements of COVID-19 prevention and control. The method can provide a theoretical basis for related research on ensuring the safety of metro operation during COVID-19.

A new algorithm of the scheduling of a flexible manufacturing system based on genetic algorithm

In the flexible manufacturing system, a reasonable production scheduling is crucial in shortening the processing completion time and improving the equipment utilization. Traditional manual scheduling cannot effectively solve the complex workshop scheduling problems and cannot provide a scheduling solution that meets the requirements in a short period of time, which can lead to a decrease in processing efficiency. Aiming at the complex job shop scheduling problem, the genetic algorithm is used to find the optimal scheduling solution in this study, taking the number of overdue jobs, the total overdue time, the job completion time, the comprehensive load rate and the maximum load rate of the machine tool as the performance indicators of the scheduling algorithm. The chromosomes are designed as process gene chain and equipment gene chain to improve the diversity and the robustness to scheduling problems of chromosome through crossover, variation, selection and other processes. The impact of different parameter settings on the performance indicators of each scheduling algorithm is researched by adjusting the four algorithm-related parameters, and there has been a certain improvement in the results of the scheduling problems. This study provides a reference for the design and optimization of production scheduling algorithm based on genetic algorithm.

Research on Testing and Calculation Analysis of Cargo Bay Fire-Extinguishing Agent Concentration Based on Different Loading in Civil Aircraft

In the history of international aviation, there have been many fire accidents of the cargo compartment. To ensure that the fire is extinguished in time when the cargo compartment is on fire, and to ensure the safety of aircraft and personnel, the design of the cargo compartment fire extinguishing system needs to be verified according to CCAR 25. According to the AC851-1 guidance, the verification of the cargo compartment's fire extinguishing system design aims to test and calculate the concentration of fire extinguishing agents used for the C-class cargo compartment based on different loading conditions of civil aircraft. Through the flight test of the cargo compartment under a no-load condition, it can be seen that the concentration of fire extinguishing agents in the cargo compartment is higher than 5% in the initial phase, higher than 3% in the 39,000ft and 10,000ft level flight phase, and the entire flight test phase is maintained above the suppression concentration required by the test, which meets the system design requirements. The concentration of fire extinguishing agents in the cargo compartment under a no-load condition is calculated and analyzed according to the maximum load rate (full load), and the result is higher than the required 3% suppression concentration.

Silver nanoparticles on UiO-66 (Zr) metal-organic frameworks for water disinfection application

Drinking water disinfection is an essential process to assure public health all over the world. In this study, silver nanoparticles (AgNPs) on UiO-66 (Zr) Metal-Organic Frameworks (Ag@UiO-66) is proposed as a potential water disinfection strategy. AgNPs are synthesized using polyvinyl pyrrolidone (PVP) as stabilizing agent, and sodium borohydride as reducing agent are subsequently embedded on UiO-66, a high-stability organometallic framework. The effect of premixing time, reaction time and reactant concentration on the loading rate of AgNPs on UiO-66 was investigated. The maximum load rate of AgNPs on UiO-66 could reach 13% when the premixing time is 3h, the reaction time is 45min and the concentration of AgNO3 is 10μg/mL. The formation of AgNPs loaded on UiO-66 was observed and confirmed with ultraviolet and visible spectrophotometry (UV-Vis), scanning electron microscopy (SEM), infrared emission spectroscopy (IES) and X-ray diffraction (XRD) analysis. Ag@UiO-66 exhibited strong antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, with minimum inhibitory concentrations (MIC) of 64 and 128μg/mL, respectively. The germicidal efficacy of Ag@UiO-66 enhanced significantly as the temperature rose from 4°C to 37°C. The results indicate that Ag@UiO-66 is potential candidate as a feasible water disinfection material.

Evaluating the feasibility of combined use of the Northern Sea Route and the Suez Canal Route considering ice parameters

Even though the Arctic ice is melting and Polar routes are being extensively studied, the amount of cargo shipped through the Northern Sea Route (NSR) remains low. Employing current data on the NSR operation provided by China Ocean Shipping Company, this paper investigates annual profitability of the NSR-SCR combined use, when a vessel sails through the NSR in summer and the SCR in winter. A Handysize general cargo ship is used as a model vessel since it allows reaching nearly maximum load rate and can sail through shallow areas of the NSR. This article proposes including ice thickness and ice conditions in the traditional cost comparison. The first parameter directly affects sailing speed, and hence other cost variables, while the second one is included in the official NSR navigation rules and connected with icebreaker escort fee. This paper also contributes to the existing literature by considering total shipping cost as a function of a vessel's ice class with corresponding building premiums and fuel consumption increments. The proposed approach is easily replicable, so shipping companies might use it to rethink their positions on shipping through the NSR. The overall conservative comparison reveals that the NSR-SCR combined shipping scheme can only be more competitive than sailing through the SCR if a shipping company provides a sufficient load rate on the NSR leg and uses a ship of a reliable ice class to navigate throughout the summer navigation. The NSR-SCR combined shipping scheme becomes attractive if the NSR leg is short, and the crude oil price is high.

Research on energy storage depth planning of AC / DC distribution network based on toughness enhancement technology

At present, due to the abnormal objective function setting result of AC / DC distribution network energy storage depth planning method, the operation cost of power supply network has been increased frequently. Therefore, the energy storage depth planning method of AC / DC distribution network based on toughness enhancement technology is designed. The minimum peak valley difference, maximum load rate and minimum load change are taken as the energy storage depth planning objectives of AC / DC distribution network. The economic mathematical model of distribution network planning is constructed by using toughness enhancement technology and objective function to complete the in-depth planning of distribution network. So far, the energy storage depth planning method of AC / DC distribution network based on toughness enhancement technology has been completed. Simulation experiment has been constructed. Through the comparison, it can be seen that this method has better effect than the original method, possessing stronger control ability for operation components.

Cyclic nanoindentation studies of HgCdTe epitaxial films

Hg1−xCdxTe (x∼0.29) epitaxial films have been subjected to cyclic nanoindentation using spherical indenter from tribological aspects related to the development of polishing process for preparing defect free surface. Different loading/unloading rates of 0.5, 1 and the 4 mNs−1 with a peak load of 10 mN were used for 10 nanoindentation cycles. An open jaw shape was observed in the load-displacement curve for loading/unloading rate of 0.5 mNs−1, while hysteresis loops were observed for 1 and 4 mNs−1 loading/unloading rates. This phenomenon is explained in light of the regimes of elastic/anelastic deformation and smooth plastic flow. Pop-in during first loading cycle was observed at loading/unloading rates of 1 and 4 mNs−1, which was attributed to elasto-plastic transition. Multiple pop-in events of low extent were also found in the form of serrations in load-displacement curves for loading/unloading rates of 0.5 and 1 mNs−1. Based on these observations, the maximum load and minimum loading rate during polishing process for this material has been suggested. The mechanical properties of these films, such as contact stiffness and hardness have been extracted for different loading/unloading rates. The effect of indenter geometry on deformation behaviour using Berkovich indenter is also reported.

The difference of creep compliance for wood cell wall CML and secondary S2 layer by nanoindentation

Wood is generally considered a linear orthotropic viscoelastic. The creep of cell wall under long-term load is important for the deformation and destruction of wood. The aim of this study was to investigate the difference of creep compliance between compound middle lamella (CML) and secondary S2 layers by nanoindentation creep testing. The results indicated that the creep compliance of cell wall under compression along grain increased with the maximum load and loading rate increasing. Furthermore, the creep compliances and creep compliance percentages of the CML layer were more than that of the secondary S2 layer, and the viscoelastic behavior of the CML layer also was more sensitive to MC compared with the S2 layer. Finally, the Burgers’ model was appropriate for predicting the viscoelastic behavior of wood cell walls. The parameters of Burgers’ model dropped markedly with increased MC. These parameters in the CML layer also were lower than those of S2 layer. The differences of creep properties between the CML and S2 layers can prove that the slippage failure of cell wall under compression along grain occurs in the S2 layer.

Influence factors of pop-in in the nanoindentation micromechanical property measurement of gas-bearing shale

Abstract Studying the micromechanical properties of gas-bearing shale is very important for understanding it. In the nanoindentation measurement of gas-bearing shale, the load-displacement curve often shows pop-in at the loading stage, namely the change of load is small but the change of penetration depth is large. Pop-in can introduce a large error in the calculation of the mechanical parameter. To investigate the influence factors of pop-in, the maximum load, load rate and sample characteristics have been addressed. The results show that pop-in is related to cracks and pores in the shale. Due to the heterogeneity of shale, pop-in cannot be avoided, but can be reduced by choosing reliable load modes and test parameters. Pop-in can increase the maximum indentation depth and decrease the elastic modulus and hardness. The influence of pop-in on hardness is larger than on the elastic modulus. At a high load rate it is easy to induce pop-in. The influence of the load rate on pop-in is larger than that of the maximum load.

Nanoindentation of cubic silicon carbide on silicon film

In this work, mechanical properties of an epitaxial silicon carbide-on-silicon (3C-SiC-on-Si) sample were extracted using a Micro Materials Nanotest® indentation system. Maximum load, penetration depth and loading rate were set at 25 mN, 550 nm and 5 mN s−1, respectively. We first plot the load-depth curve of 3C-SiC film and Si substrate. Then, we find the maximum values of hardness, tensile modulus, shear strength, shear modulus and tensile stress of 3C-SiC film. The obtained data provide evidence of the suitability of this film to be applied as an electroacoustic transducer.

Exergy, exergoeconomic and environmental analysis of diesel engine operating with EGR rate

This research presents the effects of exhaust gas recirculation (EGR) and load on a diesel engine. The operational conditions of diesel engine were different loads (5-30 kW) with increment of 5 kW and EGR rate (0-10%) with increment of 2.5%. The engine was supplied with blend of diesel and 7% of biodiesel. The exergetic, exergoeconomic and environmental analysis were investigated in order to evaluate the cost and pollutant emissions of electricity. The results reveal that the load increases the exergetic efficiency, exergy destruction, fuel cost rate and reduces the specific power cost and relative cost difference. In addition, the EGR rate decreases the exergetic efficiency and increases exergy destruction, fuel cost rate, relative cost difference and specific power cost. At low load, the specific total pollution damage is predominant, then the higher EGR rate is desired. At high load, reduction of performance is significant with EGR rate, and total pollution damage loses significance, then the lower EGR rate is desired. Therefore, the maximum load and EGR rate of 2.5% are the best condition under the exergoeconomic and environmental point of view.

Study on the method of fault set for AC/DC system operation considering wind power

With the rapid development of power system, wind power becomes an important generating way in AC/DC hybrid power grid. Due to the interference between the wind power and the AC network, the risk of DC system continuous commutation failure will be affected. In order to evaluate this effect reasonably, a method for running out of the fault set is presented in this study. Firstly, a distribution factor is proposed to determine the power line transfer after wind power or power line fault, the line with maximum load rate is chosen as the candidate failure lines; Secondly, the η short-circuit ratio and η effective short-circuit ratio indexes of the DC system is evaluated after every fault; they are used to judge whether the cascading fault of AC system induces the transient overvoltage of the converter bus to lead to wind turbines to take off the power grid net. Thus, a cascading fault sequence of the AC system is formed, and a cascading fault set that causes the transient overvoltage of the converter bus is completed. Finally, the simulation results calculated by power system department-bonneville power administration show that when the commutation failure occurs in the DC system, the system runs out immediately, and the validity of the method is verified.

Distal Forelimb Kinematics During the Extended Trot of Dressage Horses Ridden on Two Different Arena Surfaces

IntroductionSuspensory apparatus injuries are common in dressage horses. Studies demonstrate that surface type affects hoof forces and distal limb kinematics of equine athletes. Because synthetic race surfaces have lower stiffness and limb loads than dirt surfaces, it was hypothesized that dressage horses have less fetlock hyperextension on a synthetic surface than a dirt surface.MethodsTwo‐dimensional, high‐speed videos (250 Hz, 2 ppcm) of 6 dressage horses (ages 8–13; 5 males, 1 female) during extended trot on dirt and synthetic surfaces (6 trials (strides) per horse per surface) were digitized (low‐pass Butterworth filter, 15 Hz). Fetlock and solar hoof angles determined from skin and hoof markers were compared between surfaces using a mixed model ANCOVA that accounted for horse velocity (saddle billet marker) and repeated horse measures. Surface mechanical behaviors were characterized using a track testing device. Maximum force, time to maximum force, maximum displacement, resting rebound, maximum vertical rebound, average stiffness, and maximum load rate were compared between surfaces and time of day (morning, afternoon) using a general linear model ANOVA.ResultsMaximum and toe off fetlock angles were greater on the synthetic surface compared to dirt (Δ = 2°, P = 0.070). Mean maximum fetlock angle on the synthetic surface was 260°. The maximum load rate of the synthetic surface was 5 times greater than the dirt surface (P = 0.0086).ConclusionsSynthetic surfaces were designed to reduce injuries in equine athletes. Because suspensory apparatus elongation is largely dependent on fetlock extension, it is possible that suspensory apparatus strain is greater on synthetic surfaces. Thus, surface design may require more refinement to promote injury prevention based on horse discipline and gait.Ethical Animal ResearchThe University of California, Davis Institutional Animal Care and Use Committee reviewed and approved the protocols used in the study. Owner informed consent was obtained for all study horses. Sources of funding: Merial (A Sanofi Company) in association with the Student Training in Advanced Research (STAR) program, School of Veterinary Medicine, University of California, Davis and the Endowed Research Funds of School of Veterinary Medicine, University of California, Davis. Competing interests: none.