关于带弹性支座结构体系的计算

对带弹性支座结构体系的计算可采用弹性刚度系数法、力矩分配法以及能量法等进行求解，且其它不带弹性支座的结构体系也可转化为弹性支座结构体系进行计算。     

基于Abaqus平面刚架的数值模拟

以工程力学理论和有限元理论为基础,研究平面刚架结构在受特定载荷下的位移问题。通过理论分析计算和Abaqus有限元数值模拟,计算出位移结果,同时研究了刚架结构中载荷与位移的关系。     

Reduction in ground reaction force variables with instructed barefoot running

BackgoundBarefoot (BF) running has recently increased in popularity with claims that it is more natural and may result in fewer injuries due to a reduction in impact loading. However, novice BF runners do not necessarily immediately switch to a forefoot strike pattern. This may increase mechanical parameters such as loading rate, which has been associated with certain running-related injuries, specifically, tibial stress fractures, patellofemoral pain, and plantar fasciitis. The purpose of this study was to examine changes in loading parameters between typical shod running and instructed BF running with real-time force feedback.MethodsForty-nine patients seeking treatment for a lower extremity injury ran on a force-sensing treadmill in their typical shod condition and then BF at the same speed. While BF they received verbal instruction and real-time feedback of vertical ground reaction forces.ResultsWhile 92% of subjects (n = 45) demonstrated a rearfoot strike pattern when shod, only 2% (n = 1) did during the instructed BF run. Additionally, while BF 47% (n = 23) eliminated the vertical impact transient in all eight steps analyzed. All loading variables of interest were significantly reduced from the shod to instructed BF condition. These included maximum instantaneous and average vertical loading rates of the ground reaction force (p < 0.0001), stiffness during initial loading (p < 0.0001), and peak medial (p = 0.001) and lateral (p < 0.0001) ground reaction forces and impulses in the vertical (p < 0.0001), medial (p = 0.047), and lateral (p < 0.0001) directions.ConclusionAs impact loading has been associated with certain running-related injuries, instruction and feedback on the proper forefoot strike pattern may help reduce the injury risk associated with transitioning to BF running.     

Determining the minimum number of passive stretches necessary to alter musculotendinous stiffness

Abstract

In this study, we examined the minimum number of constant-torque passive stretches necessary to reduce musculotendinous stiffness. Thirteen healthy individuals (mean age 22 years, s = 3; stature 1.67 m, s = 0.1; mass 66 kg, s = 13 kg) volunteered to participate in the investigation and underwent four 30-s constant-torque passive stretches of the plantar flexor muscles. Musculotendinous stiffness was examined from the angle–torque curves generated prior to the passive stretches, at the beginning of each 30-s stretch, and immediately following the four 30-s passive stretches. The results indicated that musculotendinous stiffness of the plantar flexors was reduced following two 30-s constant-torque passive stretches (P < 0.05) compared with the pre- musculotendinous stiffness assessment. Musculotendinous stiffness remained depressed following the third and fourth stretches, but did not decrease further. These findings suggest that two 30-s bouts of constant-torque passive stretching may be necessary to cause a significant decrease in musculotendinous stiffness of the plantar flexor muscles.     

Influence of ingesting a carbohydrate-electrolyte solution before and during a 1-hour run in fed endurance-trained runners

Abstract

The aim of this study was to determine whether the ingestion of a carbohydrate-electrolyte solution would improve 1-h running performance in runners who had consumed a meal 3 h before exercise. Ten endurance-trained male runners completed two trials that required them to run as far as possible in 1 h on an automated treadmill that allowed changes in running speed without manual input. Following the consumption of the pre-exercise meal, which provided 2.5 g carbohydrate per kilogram body mass (BM), runners ingested either a 6.4% carbohydrate-electrolyte solution or placebo solution (i.e. 8 ml · kg BM^?1) 30 min before and 2 ml · kg BM^?1 at 15-min intervals throughout the 1-h run. There were no differences in total distance covered (placebo: 13,680 m, s = 1525; carbohydrate: 13,589 m, s = 1635) (P > 0.05). Blood glucose and lactate concentration, respiratory exchange ratio, and carbohydrate oxidation during exercise were not different between trials (P > 0.05). There were also no differences in ratings of perceived exertion, felt arousal or pleasure–displeasure between trials (P > 0.05). In conclusion, the ingestion of a 6.4% carbohydrate-electrolyte solution did not improve 1-h running performance when a high carbohydrate meal was consumed 3 h before exercise.     

裕昌楼斜而不危的力学分析

从力学角度分析了位于漳州市南靖县书洋镇下版村的裕昌楼,看起来摇摇欲坠,却经受七百年风雨侵蚀和无数次地震的考验,至今依然如故的原因.根据土楼建造程序、“龙骨”架在外墙小槽内与内圈竖直木柱上横梁的事实,提出了土楼的建筑等效结构模型;根据动力学扰动理论确定的扰动区厚度、三合土弹性模量和埋入土墙深度,计算出柔性固定端的等效转动刚度系数;从几何静力学、分析静力学和材料力学的压杆稳定3个方面,分析得出外墙斑驳、楼内“东歪西斜”的福建现存最古老土楼裕昌楼的极限承载能力比一般土楼极限承载能力高25．9%,其原因除墙体中埋入杉木或竹片,甚至放进大石块为墙骨以增强抗力外,力学静定结构是斜而不危另一重要因素.     

框架结构考虑塑性区长度的静力全过程分析

本文采用三维杆系力学分析模型对钢结构框架进行分析,避免了传统的有限元方法要对构件大量划分网格进行计算而导致的计算自由度巨大,计算耗时的缺点。对于杆件单元,本文采用了一种变刚度的杆单元模型,建立了考虑塑性铰分布长度影响的构件单元刚度矩阵。在此基础上对经典的算例模型进行了静力全过程分析。     

VDS-A01客车前空气悬架参数计算

以VDS-A01客车前空气悬架为研究对象,充分考虑了其他系统和外界条件对悬架计算结果精度的影响,计算了前空气悬架的刚度、固有频率和侧倾刚度,计算结果与实验结果相对偏差在3％以内,计算结果满足设计要求.该参数计算方法对客车空气悬架开发与设计具有良好的借鉴意义.     

拟合曲线槽干气密封气膜刚度的计算及测试

推导了两光滑平板间干气密封微尺度流动场的非线性雷诺方程,应用PH线性化方法、迭代法对非线性雷诺方程近似求解,得到气膜压力的近似解析式;利用极坐标下的流线方程,通过Maple程序求解压力方程和流线方程得到流线,此流线就是符合条件的拟合曲线。对拟合曲线槽干气密封气膜刚度进行计算与测试,并与螺旋槽进行比较。研究结果表明：在相同工况下,拟合曲线槽干气密封气膜刚度比螺旋槽大,且气膜刚度比螺旋槽稳定,这在工程实践中具有重要意义和应用价值。     

IC芯片粘片机并联焊头机构的动刚度分析

针对所设计的IC芯片粘片机的并联焊头机构,建立了机构的振动方程和动刚度模型,使用Matlab软件得出了机构在整个工作空间的动刚度特性曲线,并对其分布进行了分析.根据这些曲线,说明所设计的并联焊头机构的动刚度能满足IC芯片粘片机的工作要求.