Dynamic analysis of the ball-racket impact in the game of tennis

A new approach to the study of the impact phase in tennis is presented. It allows, in particular, an analysis of the forces transmitted to the arm joints from the racket and calculation of the speed variation of ball and racket subsequent to their impact.

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Sommario In questo lavoro viene proposto un nuovo approccio allo studio della fase d'urto racchetta-pallina nel gioco del tennis. Esso consente, in particolare, di analizzare le sollecitazioni trasmesse dalla racchetta alle articolazioni del braccio, e calcolare la variazione delle velocita' della pallina e della racchetta provocate dal loro impatto.

     

跖骨疲劳性骨折模型设计及生物力学分析

建立了疲劳性骨折实验模型，通过生物力学分析方法研究了跖骨疲劳性骨折机理，为有效预防、治疗该创伤的发生提供生物力学理论依据。l例健康成人新鲜足标本，剔除软组织，保留韧带、关节囊，去除足第一跖骨干及相连拇指，钢丝足底固定，替代足底腱膜，包埋标本并固定于MTS试验机上，对标本进行疲劳载荷实验，载荷为350N，循环加载频率为lHz，观察实验变化，记录循环次数。结果表明，当载荷循环次数为29285次时，第二跖骨干骺端发生肉眼可见的斜形骨折。可见在扁平足或足过度内旋等造成第二跖骨承受过大体重、过度应力下容易导致疲劳性骨折。生物力学因素包括解剖的变异在疲劳性骨折产生方面具有重要的作用。     

新月形尾鳍推进的流体力学分析

本文运用三维波动柔板位流模型与最佳游动方式理论,继续分析了新月形鱼尾的推进性能,从而实现了对鱼类三种主要推进模式的较为系统的研究。理论分析表明,高速海洋动物所具有的大展弦比、尖叶梢、中等后掠的新月形尾能获得接近于最佳的推进性能。对海豚游动特性的理论估算也给出了令人满意的结果。     

股骨形态及应力应变的三维有限元分析

建立了一个针对高危女性人群股骨结构的三维有限元模型,分析了运动荷载作用下此类股骨的应力和应变分布以及股骨破坏的可能部位.结果表明:运动荷载使股骨产生较大的横向位移和弯曲变形;股骨颈处的应力和应变最大,容易在股骨颈处以及大转子与股骨干的连接部位附近发生破坏.模拟结果为研制适用于此类人群的高性能人工股骨提供了参考.     

从生物力学到力学生物学的进展

本文介绍了现代生物力学的发展历程和冯元帧先生的贡献、力学生物学的概念与发展以及我国生物力学的发展历程和力学生物学的研究新进展;思考了从生物力学到力学生物学的进展与现状;展望了我国生物力学学科发展的愿景.     

Micro air vehicle-motivated computational biomechanics in bio-flights: aerodynamics, flight dynamics and maneuvering stability

Aiming at developing an effective tool to unveil key mechanisms in bio-flight as well as to provide guidelines for bio-inspired micro air vehicles（MAVs） design,we propose a comprehensive computational framework,which integrates aerodynamics,flight dynamics,vehicle stability and maneuverability.This framework consists of（1） a Navier-Stokes unsteady aerodynamic model;（2） a linear finite element model for structural dynamics;（3） a fluidstructure interaction（FSI） model for coupled flexible wing aerodynamics aeroelasticity;（4） a free-flying rigid body dynamic（RBD） model utilizing the Newtonian-Euler equations of 6DoF motion;and（5） flight simulator accounting for realistic wing-body morphology,flapping-wing and body kinematics,and a coupling model accounting for the nonlinear 6DoF flight dynamics and stability of insect flapping flight.Results are presented based on hovering aerodynamics with rigid and flexible wings of hawkmoth and fruitfly.The present approach can support systematic analyses of bio- and bio-inspired flight.     

触摸法评价物体柔软性的感知觉力学原理分析

物体柔软性的触觉认知机理是当前感官工程研究的重点. 基于触摸法评价物 体柔软性时物体与指尖软组织的力学作用过程,及指尖皮下机械刺激感受体接受机械刺激的 模式,建立了与这一机械作用过程等效的生物力学模型; 基于该模型,提出 并证明了表征触觉系统感应、辨别物体柔软性的能力指标------机械敏感性和感觉 敏感性; 以提出的两个指标,参数化讨论了人的触觉系统在判断和辨别物体柔软性的一般 力学原理. 理论研究证明,以触摸方式评价物体柔软性时,皮下触觉感受体及相应高级认知 系统的感知能力取决于物体与皮肤软组织的抗压力阻,且与触摸力的动态变化有关. 也正是 传递机械信号的介质------软组织的可变形性致使触觉感测系统有别于实验室压缩仪的工作 模式.     

Internal Tension: A Novel Hypothesis Concerning the Mechanical Properties of the Vitreous Humor

The vitreous humor is a soft viscoelastic gel composed of a complex network of biomolecules (primarily collagen and polyhyaluronic acid, “hyaluronan”). While extensive progress has been made in identifying the components of the vitreous, lack of sufficient experimental methods has hampered previous efforts to quantitatively define its mechanical properties. To address this issue, we have developed a novel “cleat” tool geometry for dynamic shear rheometry. Using this geometry we find that the shear moduli of vitreous decline by roughly a factor of five to steady-state values within an hour after removal from the eye. Steady-state values (Porcine: G′ = 2.6 ± 0.9 Pa, and G″ = 0.65 ± 0.41 Pa, n = 9; Bovine: G′ = 6.5 ± 2.0 Pa, and G″ = 2.0 ± 0.6 Pa, n = 17) are significantly larger than previously reported. The decrease in modulus also correlates with a decrease in mass (65 ± 11 %, n = 8) that occurs spontaneously after the vitreous is extracted. Rheological findings, taken in combination with biochemical analyses suggest that hyaluronan, a ubiquitous polyelectrolyte in connective tissue, contributes to vitreous stiffness by inducing tension in the network in vivo.     

生物力学与骨组织工程

组织工程是生物工程中的一个重要部分,是多学科交叉而形成的新兴工程技术学科．从生物力学角度研究组织工程有特殊意义,因为生物力学在生长、重建和成形方面发挥着极其重要的作用,而组织工程需要这些知识来研究和制造组织．文章介绍了组织工程的概念和生物力学的作用,主要讨论骨的生长、重建、成形和骨的组织工程中的一些重要问题      

Some problems associated with the disturbed matrix Lyapunov equation for linear time-invariant discrete systems

Both the Lyapunov stability and popov’s hyperstability ofdiscrete linear time-invariant system in case of system para-meter disturbance are discussed in this paper.The allowabledisturbance ranges are given so that the maintenance of theLyapunov stability and the popov’s hyperstability of a dis-crete linear system is guaranteed.The results find theirsignificance in the MRAC.