粘着行为中预压紧力和分离速度及相对湿度对分离力影响的实验研究

在改变粘着试验中接触副预压紧力、接触副分离速度以及环境相对湿度的条件下，利用表面力仪实时测量了新鲜解理云母接触副分离过程的分离力，并观察了接触后解理云母接触区的状态．结果表明：在保持弹性接触时，预压紧力对分离力影响不大，接触材料的表面能决定分离力的强度；当预压紧力超过临界值时，接触表面发生塑性变形，在一定范围内分离力随预压紧力的增加而增大；在干接触时分离速度与分离力无直接联系，但在存在大粘度中间层液体时，分离速度的增加可使分离力显著增大；分离力随相对湿度的增加而增大．     

张力等参有限单元的构造及其在分离流动计算中的应用

本文利用张力样条函数，构造了一种十二节点张力等参有限单元。它不仅具有等参元的一切特点，而且具有张力可调的独特性质，从而在一定程度上可调整插值函数以达到较好的收敛收和计算精度。在分离流动计算中，尤其可以显示出它独特的优越性。本文的两个分离流动算例说明了这一点。     

膨胀管分离装置分离时间测试研究

本文采用裂纹扩展计和超动态应变测试相结合的方法,对炸药索的传爆速度及分离结构响应断裂时间进行了实验研究。同时,还分析了内外分离板分离的同步性、两端起爆的同步性。结果表明:对于本文测试的分离结构,其内外分离板分离的同步性较好,滞后时间仅1μs;扁平管接收到爆轰信号到分离板断裂的时间差约为6μs;尽管采用两端起爆,但是实际中由于火工品的差异,并不能够实现两端完全同步起爆,滞后时间长达50μs。     

加载速度对两种缓冲包装材料静态压缩特性的影响

聚苯乙烯和聚乙烯缓冲包装材料是粘弹性材料．本文的实验研究表明，当应变速度在一定范围内变化时此类材料与时间有关的应力可分离为一个时间函数与一个应变函数的乘积．分析结果还表明，测定此类材料的静态压缩特性时，加载速度在一定范围内的变化对试验结果的影响可以略去不计．     

钝体高超声速三维分离流场特性数值研究

以双子星座简化外形为模型，通过有限差分法求解全Ｎ－Ｓ方程，数值研究了高超声速绕流中的三维分离流动特性。来流Ｍ＿∞＝７．０，Ｒｅ＿∞＝４．５×１０￣５，攻角范围为１０°－４０°。首先通过与实验油流照片的比较，证明了本文计算分离结构定性上的正确性。然后研究了不同攻角下背风面三维分离结构的变化，给出了柱段背风区常点型开式分离随攻角变化转变为整体闭式分离的过程，并从物理上分析了这种转变过程的合理性，认为不同分离形态在分离线起始点附近都有共同的压力条件，即垂直于分离线的逆压梯度，因此横向分离可以从常点型开式分离直接转化为闭式分离。     

基于传递函数法的带多个外挂机翼颤振分析

基于带外挂机翼结构和气动特点，使用带有半解析半数值特性的传递函数方法进行处理．首先，通过机翼的运动微分方程、二元机翼非定常气动力Therdorson 模型、结合外挂挂载处的内力平衡与位移状态条件，得到了三维的带多个外挂大展弦比机翼的颤振微分方程．进而，使用传递函数方法，先将颤振计算方程整理成为状态空间方程形式，结合求解复特征值的方法，完成了带多个外挂大展弦比机翼的动气动弹性稳定性分析．对比已有文献的计算结果以及通过有限元方法进行的仿真结果，证实了文章所提计算方法的准确性和高效性，结合传递函数方法的优势，进一步将文章方法拓展到机翼的固有频率和发散速度求解．文章结尾，分析了外挂数量、外挂质量、转动惯量及位置分布等变量对带多个外挂大展弦比机翼的动气动弹性稳定性的影响．     

复合材料网球拍的力学分析

本文用材料力学方法分析了复合材料网球拍的力学问题,设计监进行了相应的网球拍试验。分析了三种网球拍——传统的木拍、仿造的玻璃钢拍和进口的碳纤维增强塑料拍,在弯曲、侧压、扭转和冲击荷载作用下的内力和变形,与试验结果的一致性说明简化方法是足够精确的。从三种网球拍的主要参数——抗弯刚度和抗扭刚度来看,碳纤维增强塑料拍的刚度最佳,木拍次之,玻璃钢拍比木拍略差,其原因在于玻璃钢拍未经力学设计。按本文分析作为设计的依据,定能制造出力学性能更佳的复合材料网球拍。     

动脉局部狭窄时脉动流的有限元分析

本文利用有限元方法研究动脉局部狭窄下的脉动流流场,重点考查在50％与80％面积狭窄下的速度分布、压力分布、壁面剪应力分布及流动分离情况。几何形状及边界条件均模拟相应的脉动流实验模型。采用测得的随时间变化的速度分布作为入口端条件,并利用罚函数和逆风格式等计算技巧得出了光滑的与实验基本相符的速度、压力波形。本文讨论了不同狭窄下速度、压力、壁面剪应力的分布形态,给出了脉动流中狭窄处局部流动分离的间歇性变化规律,并结合实验与临床应用进行了讨论。     

变角度纤维复合材料层合斜板的颤振分析

假设纤维方向角沿层合板的长度方向线性变化，研究了变角度纤维复合材料层合斜板的颤振．通过坐标变换将斜板变换为正方形板，采用层合板表面连续变化的速度环量来模拟空气对其的作用，速度环量分布利用Cauchy积分公式计算．建立了系统的Lagrange方程并采用Ritz法得到了层合板的自振频率和颤振/不稳定性分离临界速度．通过数值算例验证了本文模型和方法的正确性和收敛性，分析了各个铺层内纤维方向角的变化对自振频率和颤振/不稳定性分离临界速度的影响．研究结果表明，通过纤维的变角度铺设，可有效地提高层合板的基频和颤振/不稳定性分离临界速度．经合理设计的变角度复合材料层合板具有抑制颤振的作用．     

明渠中跌坎后突扩分离流数值研究

利用大涡模拟技术，对明渠中跌坎后的二维突扩分离流结构进行了数值模拟，探讨了这类典型分离流各特征区的流动性质，分析了再附区壁面上不同测点处脉动压力的统计特征，并与试验结果进行了比较．在数值模拟中，采用了弱压缩流的控制方程和非均匀网格系统．     

Ball spin generation for oblique impacts with a tennis racket

In this paper, we describe an experimental investigation of the oblique impact between a tennis ball and head clamped tennis racket. It was found that the magnitude of the ball rebound spin was not a function of the material, gage or tension of the string used in the tennis racket. Furthermore, it was concluded that all strings exhibit a sufficiently large friction coefficient that the ball begins to roll during impact. There is anecdotal evidence from tennis players that suggests that a high string tension or a rough string surface enable them to impart more spin to the ball. For example, players have been quoted as saying that a high string tension makes the strings “bite” into the ball, giving more spin. The data reported in this study do not support these observations. Analysis of the experimental data has shown that the balls are rebounding from the surface with more spin than would typically be associated with rolling. A second experiment showed that the balls commenced rolling at the mid-point of the impact. This information was used in a theoretical model to show that the spin that acts on the ball during the impact can be higher than the value of the rolling spin at the end of the impact.     

??????????????????????

本文用概率函数分析方法研究了乒乓球拍形状和尺寸对乒乓球迎击概率的影响．基于将球拍的外轮廓线视为一条等概率曲线，导出了满足最高迎击球概率的球拍外轮廓线的数学表达式，给出了相应的计算结果．计算结果表明，现有球拍平面形状和尺寸有待进一步改进和完善，减小打漏球的失误，使其具有最大的迎击球概率．     

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.

---

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.

     

乒乓球运动中弧圈球的定量探究及其应用

运用流体力学和理论力学, 对乒乓球运动中的弧圈球弧线进行定量分析, 并 用Matlab软件求解及模拟其弧线. 结果发现, 乒乓球的旋转对于其空中运行轨迹有明显的影 响. 其结论对于``假动作'的判断有积极的指导意义.     

The twisting tennis racket

This paper describes, analyzes, and explains a novel twisting phenomenon which occurs in a triaxial rigid body (such as a tennis racket) when it is rotating about an axis initially near its unstable intermediate principal axis.     

竹质框架模型受侧向冲击测试及分析简

针对第六届全国大学生结构设计竞赛命题要求设计一个四层缩尺竹质吊脚楼框架,测试其在侧向冲击载荷作用下的加速度响应. 采用有限元软件LS-DYNA,对模型进行模拟分析. 结果表明,有限元计算与加载测试所得的加速度时程曲线吻合较好. 以该模型为基础进行参数分析,结果表明随拉带初始松弛量增大、撞击板质量减小,结构加速度响应增大;相较入射球质量,入射球速度对结构峰值加速度的影响更敏感,随入射球速度增大,结构峰值加速度增大.     

Transient analysis of a tennis racket using PC-based finite elements and experimental techniques

A method has been developed to facilitate the fully stressed design optimization of a tennis racket. The method consists of a PC-based finite-element model with experimental verification, and transient analysis using experimentally determined dynamic loading data. Results are obtained and discussed. Paper was presented at the 1988 SEM Spring Conference held in Portland, OR on June 5–10.     

Understanding the Dynamic Behaviour of a Tennis Racket under Play Conditions

The ‘feel’ of tennis rackets is of increasing importance to manufacturers seeking product differentiation in a context where further performance enhancements are prevented by a combination of mechanical limits and regulations imposed to protect the integrity of the sport. Vibrations excited during a shot contribute greatly to the perception of ‘feel’. Previous studies have been reported but none has covered the full set of mode families or the frequency range in this study. In-plane vibrations associated with the routine use of topspin shots in modern tennis have not been documented so far in the literature. To consider modal behaviour, multiple measurements during play conditions are required but this is practically impossible. This paper proposes an alternative approach and successfully relates a comprehensive modal analysis on a freely suspended racket to vibration measurements under play conditions. This is achieved through an intermediate stage comprising a necessarily more limited modal analysis on a hand-gripped racket and use of the mass modification modal analysis tool. This stage confirmed the prevailing view that hand-gripping can be considered as a mass modification distributed along the handle of the freely suspended racket but the associated mass was much lower than that of an actual hand and the hand also increased the damping ratio of frame modes significantly. Furthermore, in frame vibration measurements during forehand groundstrokes, a greater reduction in bending mode frequencies was observed, consistent with a mass-loading of around 25 % of the actual hand as a consequence of the tighter grip. In these play tests, the first two bending modes, the first torsional mode, the first eight stringbed modes, the first three hoop modes and the third in-plane bending mode were identified, with the stringbed modes being particularly prominent.     

PROPAGATION OF IMPACT PULSE IN A CHAIN OF ELASTIC BALLS

采用Hertz 接触理论处理牛顿摆中球与球之间的相互接触,建立球链碰撞模型,观察到碰撞过程中类似孤立波的传播现象。为了便于处理“n 对m”碰撞的计算,编写了带有GUI (graphic user interface) 界面的计算程序,可以研究不同撞击球个数对撞击过程的影响,包括球心位置、球心速度以及相邻小球间的变形量与相互作用力随时间的变化规律。进一步比较了一维球链模型和三维有限元模型的结果,并实验观察了碰撞过程的细节,得到一致性结论。     

Dynamic Contact Behavior of a Golf Ball during Oblique Impact: Effect of Friction between the Ball and Target

The oblique impact between a golf ball and a polymethyl methacrylate (PMMA) target with smooth transparent surfaces was studied using a high-speed video camera. Video images of the impact were recorded from the backside of the target and were used to determine the contact time, contact area, and the displacement and rotation of the ball along the target. The average tangential and angular velocities were determined as functions of the inbound ball velocity. As the inbound ball velocity increased, the contact area and average tangential and angular velocities also increased while the contact time decreased. An oiled PMMA target was used to study the effect of reduced friction between the ball and target. The results were compared with earlier data for a steel target with relatively rough surfaces. The contact area and time were unaffected by friction, but the average tangential velocity increased while the average angular velocity decreased as the friction decreased.