柔性腿无缘轮黏滞-滑动过程的被动动态行走运动特性分析

为了分析存在摩擦力情况下柔性腿无缘轮的运动步态,分析了柔性腿无缘轮黏滞与滑动两种运动状态相互转换的条件,通过拉格朗日第一类方程建立了系统的动力学模型,在建模时解除了单支撑阶段的切向约束条件,增加了摩擦力项以实现当摩擦力不足时的滑动状态建模.分析了不同摩擦因数下柔性腿无缘轮的运动步态情况,发现了最多可能产生4种运动行为.研究了不同步态对于系统能量的影响,并发现滑动的产生增加了系统在单支撑阶段的动能.利用Newton-Raphson迭代法和庞加莱映射发现了4种运动行为均存在不动点并且轨迹稳定,同时发现柔性腿无缘轮具有滑动的步态有着良好的鲁棒性.通过研究不同初始动能对系统滑动步态的影响,发现了系统动能或者角速度在一定的范围内存在一个极小的停滞区间,使得系统单支撑阶段在通过直立平衡面附近时会产生长时间的滑动,导致系统的不稳定     

石英谐振器的电路设计与力-频特性的研究

根据共模抑制原理,基于一种单基多电极石英晶体谐振器的结构,设计了一种新型的信号处理电路,这种电路将同一晶体基片上不同位置的谐振器对应的谐振频率作混频处理,然后采用差频、求和,最后倍频输出的方式输出,描述了各部分电路的设计.在分析石英谐振器的能限理论及力一频特性的基础上,用此方案设计的电路进行AT切同基三电极石英谐振器的力一频特性实验,记录了不同加力方式下的力一频特性,结果显示这种电路优化了力一频系数,线性度良好.在一定的加力方式下,经求和电路处理后的力一频系数可达139.72 Hz/N.     

机器学习在预测人体运动地面反作用力中的应用综述

三维地面反作用力（Ground reaction force, GRF）是人体运动分析的重要测量参数,但其测量受到一定限制。本文系统归纳了机器学习在预测GRF中的应用现状。以“ground reaction force”与“machine learning”“neural network”组合为关键词检索,筛选利用机器学习模型预测GRF的研究。共纳入14篇研究,研究的动作包括步行、跑步及个别专项动作,利用不同的学习算法来预测GRF,输入参数包括足底压力参数、运动捕捉获取的人体运动学参数等,均采用相关系数及均一化均方根误差作为评价指标。结果显示,利用机器学习预测GRF可获得极好的预测精度。利用机器学习模型预测GRF在人体运动中的应用还有待更多的研究,如增加用于机器学习的数据集大小可进一步提高学习模型的预测性能等。     

基于关联分析的中老年体检数据的挖掘

根据中老年体检报告,运用Apriori算法挖掘各个指标之间的联系,为医生、患者提供诊断参考与建议。通过安徽省某三甲医院的体检数据,筛选出40岁及以上的中老年人群为研究对象,应用数据挖掘中关联规则的Apriori算法对超重、心电图、脂肪肝、血脂、血压、血糖、尿常规、吸烟、饮酒、总胆固醇等体检指标之间的关联关系进行分析研究。研究表明,体检者的个人不良习惯、超重、高龄、高血糖和脂肪肝等都密切相关,互相影响,提出中老年人群应加强对慢性疾病的预防,保持良好的作息习惯等相关建议。     

Biomechanical characteristics of slipping during unconstrained walking,turning, gait initiation and termination

Slipping biomechanics was investigated on both non-contaminated and oil-contaminated surfaces during unconstrained straight-line walking (‘walking’), turning, gait initiation and termination. In walking, backward slipping was more frequent, whereas forward slipping was more frequent when turning. Stopping and gait initiation engendered only forward and backward slipping, respectively. Based on slip distance and sliding velocity, severity of forward slipping was least in walking than for the other gait tasks, whereas the tasks had similar effects on backward slipping. Relative to the dry surface, heel and foot contact angles reduced and heel contact (HC) velocity increased for all gait tasks on the contaminated surface. Ground reaction forces were generally lower on the contaminated surface, suggesting kinetic adaptation immediately following HC. Required coefficient of friction (RCoF) did not correlate with slip distance suggesting that RCoF may not be a useful kinetic parameter for assessing slipping risk on contaminated surfaces.

Practitioner Summary: Slipping is hazardous in everyday locomotion and occupational settings. This study investigated foot control kinematics and kinetics across various gait tasks on both a non-contaminated and an oil-contaminated walking surface. Turning, gait termination and gait initiation were associated with a greater risk of slip-related falls than unconstrained walking.     

Ordering Method and Empirical Study on Multiple Factor Sensitivity of Group Social Attitudes Based on Entropy Theory

When studying the various factors affecting a group’s social attitudes, minor changes in a factor will easily cause changes to other factors due to theirassociation and relevance to each other; therefore, such a factor is more sensitive, although there is a difference between sensitivity and importance.In order to comprehensively learn about the influence of multiple factors, explorations based on entropy theory have been conducted to determine thesensitivity of each factor, to specify the difference between the frequency and sensitivity priority of entropy theory, and to provide a method, a way ofthinking, and a detailed basis for the resolution of actual problems.     

典型钢混Π型主梁断面的涡振特性及其响应预测研究

In order to study the vortex-induced vibration characteristics of the H-shaped girder section and predict its response? taking a long-span steel-concrete n-shaped girder cable-stayed bridge as the background, the vortex-induced vibration characteristics of the girder with different mass and damping ratios were tested in the wind tunnel. The dynamic parameters of the girder were identified by free vibration test, and the amplitude-varying clamping ratio and amplitude-varying frequency of the girder under different wind speeds were extracted. Furthermore the vortex-induced force model of the main beam is established based on the amplitude-varying aerodynamic derivative. At the same time, the vortex-induced force model is used to predict the vortex-induced vibration amplitude and vortex-induced vibration interval of the main beam under different damping ratios. The results show that the vertical modal parameters of the steel-concrete H-shaped girder show different development rules in different wind speed ranges, which can be divided into five wind speed ranges. Based on the Scanlan self-excited force model, a vortex-induced force model containing only two aerodynamic derivatives of Hi and HI is established. By comparing with the results of vortex-induced vibration amplitude and vortex-induced vibration interval of wind tunnel test, the correctness of the vortex-induced force model and its vortex-induced aerodynamic derivative method is verified. At the same time, compared with the wind tunnel test results under different damping ratios, it is verified that the vortex-induced force model is universal. The research conclusions can provide reference for the establishment of vortex vibration mechanism and vortex excitation force model of II-shaped main girder section. © 2023 Journal of Dynamics and Control. All rights reserved.