短跑运动员跟腱生物力学特性的实验研究

通过对短跑运动员和非运动员跟腱弹性模量和刚度的比较研究。探讨短跑运动对人体跟腱生物力学特性的影响。研究结果表明,短跑训练后跟腱的弹性模量和刚度明显增加,提示训练能够改善跟腱的力学性能,表明训练后既能增加跟腱的体能储备,又能使其承受更大的载荷,并在一定程度上可减少跟腱疲劳损伤的发生．     

跑步疲劳进程中下肢生物力学模式的非线性变化研究

目的:确定跑步疲劳进程中下肢生物力学模式的变化,包括垂直和前后地面反作用力(ground reaction force,GRF)、垂直地面反作用力(vertical ground reaction force,vGRF)负载率、关节力学和刚度。方法:14名男性受试,采用Vicon红外摄像头和Bertec三维测力跑台,每隔2 min采集受试疲劳干预中的15 s GRF数据以及标记点轨迹。受试需穿着统一的跑鞋在测力跑台以恒速3.33 m/s跑至疲劳。满足以下标准时,干预结束:1)最大心率大于当下年龄的90%;2)受试不能继续跑步。对比受试跑至疲劳进程中4个时刻(疲劳前、33%、67%和100%)的着地冲击和下肢三关节触地角度、最大角度、关节活动度、角度变化量、关节蹬伸力矩和刚度等特征,采集并分析受试安静状态、疲劳后即刻、疲劳后4 min、疲劳后9 min的血乳酸浓度。结果:与疲劳前相比,1)血乳酸浓度在疲劳后即刻、疲劳后4 min和疲劳后9 min均显著增加;2)垂直/前后矢状轴GRF和vGRF负载率等参数在疲劳干预过程中均未观察到显著性变化;3)髋关节活动度在疲劳过程的33%、67%和100%时刻显著增加,膝关节活动度在67%时刻显著增加;4)踝关节运动学及踝、膝和髋关节的蹬伸力矩峰值均无变化;5)垂直刚度在67%和100%时刻显著降低。结论:疲劳干预过程中,GRF特征参数均没有明显变化,但是观察到下肢运动学和动力学模式的非线性改变。特别是从疲劳干预中期开始,人体下肢通过增加髋、膝关节活动度并减小垂直刚度实现“软着陆”策略,维持相似的冲击力特征,以减小长时间跑步可能带来损伤的风险。     

H型钢梁柱顶底角钢、腹板双角钢连接的试验研究

通过三个H型铜梁柱顶底角铜、腹板双角铜连接节点原型试件在往复荷载作用下的试验研究，分析带双腹板角铜的顶底角铜的连接刚度、承载能力和延性特征，得出腹板角铜对连接的承载力有明显改善的结论，并建议在计算连接抗弯承载力时应考虑腹板连接的影响．     

汽车悬置系统隔振性能分析与优化设计

针对传统汽车悬置系统能量解耦率低,振动传递率高的问题,建立了悬置系统动力学分析模型。将汽车动力总成悬置系统的振动性能分析和参数测试与系统模态耦合和振动能量解耦匹配理论相结合,采用MATLAB软件编制的程序来计算系统能量分布,并在满足悬置系统设计约束的前提下对系统悬置刚度值与布置参数进行了优化。某型号汽车悬置系统优化设计与振动性能测试结果验证了优化方案的有效性和可行性。     

深基坑开挖预留土堤理论研究及工程应用

相邻或盆式开挖深基坑施工时，基坑内侧或外侧的预留土堤应作为深基坑设计因素而予以考虑。基坑预留土堤土压力与它的形状及围护结构等因素相关。场地条件许可时，应采用原状土预留土堤，可用库仑土压力理论分析。当采用加固土预留土堤时，可采用抗侧刚度分配法分析。预留土堤规模及土压力可以通过计算机分析实现，也可采用图解法分析。     

Translational torsional coupled model based nonlinear dynamic analysis of an NGW planetary gear train

This paper aims to investigate the nonlinear dynamic behaviors of an NGW planetary gear train with multi-clearances and manufacturing/assembling errors. For this purpose, an analytical translational ? torsional coupled dynamic model is developed considering the effects of time-varying stiffness, gear backlashes and component errors. Based on the proposed model, the nonlinear differential equations of motion are derived and solved iteratively by the Runge-Kutta method. An NGW planetary gear reducer with three planets is taken as an example to analyze the effects of nonlinear factors. The results indicate that the backlashes induce complicated nonlinear dynamic behaviors in the gear train. With the increment of the backlashes, the gear system has experienced periodic responses, quasi-periodic response and chaos responses in sequence. When the planetary gear system is in a chaotic motion state, the vibration amplitude increases sharply, causing severe vibration and noise. The present study provides a fundamental basis for design and parameter optimization of NGW planetary gear trains.     

The construction of common treadmills significantly affects biomechanical and metabolic variables

ABSTRACT

Surface compliance has been shown to affect leg stiffness and energetics. It is unknown if compliance differences between common treadmills would elicit such changes. Therefore, the purpose of this study was to determine if compliance design differences of common treadmills would affect the mechanics and energetics of running. Eleven runners ran at moderate, self-selected, matched belt speeds for three minutes on two treadmills: compliant (CT) and rigid (RT) decks. During the last minute of each trial, oxygen consumption and six markers describing the torso, thigh, shank and foot, and one marker to determine treadmill deflection were recorded. Leg stiffness, continuous relative phase (CRP) and CRP variability were calculated. Compared to RT, running on CT resulted in a significantly more compliant leg (8.591 kN?m^?1 > 9.063 kN?m^?1), lower oxygen consumption (34.69 ml?kg^?1?min^?1 < 36.86 ml?kg^?1?min^?1), different coordination patterns and greater variability, particularly during the push-off phase. These results are inconsistent with the literature because the deck of CT rebounds back at the runner during the absorption phase and away from the runner during the push-off phase. Therefore, care should be taken when using treadmills for research and comparing mechanical and energetic measures between studies.     

Stability performance of buckling-restrained brace with brace joints

The stability and ductility of four buckling-restrained braces （BRBs） with brace joints were studied. The load-carrying element of BRB was fabricated with steel （Chinese Q235）, and a layer of colloidal silica sheet （0.5 mm in thickness） or four layers of plastic film （0.2 mm in thickness） were used as unbonding materials to provide space to prevent the buckling of inner core in higher modes and facilitate its lateral expansion in case of compression. Based on the equation of BRBs with brace joints of different restrained stiffnesses, the buckling load is calculated considering the initial geometric imperfections and residual stress, and the theoretical values agree well with the experiment re- sults. It is concluded that the buckling load and ductility of BRBs are influenced greatly by the restrained stiffness of brace joints. If the restrained stiffness is deficient, the unstrained segment of BRBs with less stiffness will buckle firstly. As a result, the ultimate load of BRBs decreases, and the maximum compression load is reduced to about 65% of the maximum tension load; the stiffness also degenerates, and there is a long decreasing stage on the back-bone curve in compression phase; the ductility decreases, i.e., the ultimate tension ductility and ultimate compression ductil- ity are approximately 15 and 1.3 respectively, and the cumulative plastic ductility is only approximately 200. If the restrained stiffness of joint is large enough, the stability will be improved as follows： the yielding strength and ultimate strength of BRBs are nearly the same, and there is an obvious strain intensification in both tension and compression phases; the ductility of brace also increases obviously, i.e., the ultimate tension ductility and ultimate compression ductility are both approximately 14, and the cumulative plastic ductility reaches 782.     

机床工艺系统静刚度计算机测试系统的研究

介绍了机床工艺系统静刚度的概念。提出了静刚度测试系统的总体设计方案，并对该系统主要软件和硬件部分进行了说明与开发。     

Examination of the neuromechanical factors contributing to golf swing performance

This study investigated the relationship between a range of neuromechanical variables in the lower- and upper-body, and golf performance. Participants were assessed for individual muscle stiffness, vertical stiffness (Kvert), flexibility, power and maximal isometric strength. Furthermore, golf performance was determined by handicap and club head speed. Pearson’s correlations quantified the relationships between neuromechanical variables and performance measures. Participants were also separated into relatively high club head speed (HC) and low club head speed (LC) groups and compared for physical characteristics. Club head speed showed positive relationships with Kvert and power and a negative relationship with hip mobility. The HC group exhibited superior Kvert and power, while strength and flexibility measures were not related to performance. Higher levels of lower-body stiffness, rate of force development and power output appear to be beneficial for generating superior club head speed. A stiffer system may reduce the time needed to remove the “slack” from the series elastic component therefore, reducing electromechanical delay and enhancing rate of force development. The large positive association with rate of force development suggests that increasing this component, along with power production may be superior focal components for training in golfers due to the short duration of the downswing.