自由度对鱼类自主游动数值模拟结果的影响

采用自适应浸没边界方法,数值模拟了仿生鱼在不同自由度个数情况下的游动,对比分析了自由度个数对仿生鱼受力、能耗、推进效率以及尾涡结构的影响。研究结果表明,推进效率随着自由度个数的增加而略有降低;当仿生鱼在自主游动过程中没有侧向运动速度时,侧向受力幅值会大幅度提高。另外,当采用"六自由度模型"进行模拟时,仿生鱼很难沿直线运动,从而导致定量分析的困难。     

A cellular scale numerical study of the effect of mechanical properties of erythrocytes on the near-wall motion of platelets

The effect of mechanical properties of erythrocytes on the near-wall motion of platelets was numerically studied with the immersed boundary method. Cells were modeled as viscous-fluid-filled capsules surrounded by hyper-elastic membranes with negligible thickness. The numerical results show that with the increase of hematocrit, the near-wall approaching of platelets is enhanced, with which platelets exhibit larger deformation and orientation angle of its near-wall tank-treading motion, and the lateral force pushing platelets to the wall is increased with larger fluctuation amplitude. Meanwhile the near-wall approaching is reduced by increasing the stiffness of erythrocytes.     

钢筋混凝土结构在主余震作用下的概率累积损伤分析

本文利用我们在文献［１］中建立的主震与余震地面运动随机过程模型，以及在文献［２］中给出的带有负刚度段的三线性模型解析表达式，提出了钢筋砼结构在主震作用后，余震１作用下以及余震１作用后、余震２作用下的恢复力模型及其解析表达式；通过弹塑性随机地震反应分析，提出了结构在主震、余震１和余震２作用下的累积损伤模型及期望波损度与可靠性分析方法，最后给出了一两层钢筋砼框的算例。     

Explicit criteria of absolute stability for the real second canonical form of control system

In this paper,some explicit criteria of absolute stability for the trivial solution of the real second canonical form of nonlinear control system are given,which include and improve the criteria in paper[1].By applying these criteria to the well-known equation of the longitudinal motion of aircraft,some results are obtained,which include and improve the corresponding results in papers[1,2,3,4].     

Bifurcations of periodic solutions for plane mappings

In this paper,using some techniques,we prove that there exists the regular homoclinic point for Taylor mapping with 4相似文献   

Comparison of organized motions in a constant and an adverse pressure gradient turbulent flow

The distribution of the statistical properties of coherent motions across a fully developed feed pipe is observed to change drastically as adverse pressure gradient is applied in a conical diffuser. These changes are associated with distortion of the turbulence structure and becomes more pronounced as the flow approaches detachment. A conceptual model based on present measurements effectively accounts for major turbulence characteristics in the diffuser.     

TP-5型半自动胶片判读仪及其在爆轰测试中的应用

TP-4型半自动胶片判读仪主要用于判读高速电影摄影仪和高速转镜相机的测试结果和数据处理。文中阐述了这种仪器对后者判读的原理、软件功能及判读程序,并列出数据处理的典型结果。根据对多个爆炸事件同时性、爆炸波波形差、炸药爆速以及分幅图形判读和数据处理的实例表明,结果是可靠的,判读程序是合理和适用的。     

Numerical study on the effect of nozzle pressure and yarn delivery speed on the fiber motion in the nozzle of Murata vortex spinning

Murata vortex spinning (MVS) is a recently developed spinning technology which utilizes high speed swirling airflow to insert twist into the yarn. The motional characteristics of the flexible fibers in the airflow inside the MVS nozzle are of vital importance to the yarn formation mechanism and properties. The fiber motion in the MVS nozzle involves fluid-structure interaction (FSI) and contact problems. In this paper, a two-dimensional FSI model combined with the fiber-wall contact is introduced to simulate a single fiber moving in the airflow inside the MVS nozzle. The model is solved using a finite element code ADINA. Based on the model, the motional characteristics of the fiber are analyzed and the effect of two process parameters - the nozzle pressure and yarn delivery speed - on the fiber motion and, in turn, the yarn tenacity is discussed. The results indicate that the fiber firstly undergoes a false-twisting process. Subsequently, its trailing end splays out and whirls within the nozzle chamber for several turns to helically wrap and make the spun yarn. The results also show that the effect of the nozzle pressure on the tenacity of the produced MVS yarn is not obvious. The increased yarn delivery speed leads to the decreased MVS yarn tenacity. The numerical results show good agreement with the experimental results provided by other researchers.     

The theory of relativistic analytical mechanics of the rotational systems

I'IntroductionThespinningmotionisintrinsicattributeofmicroscopicparticle.In1979,R.BengtssonandS.Frauendorfaccuratlymeasuredthemaximumvolumesofthespinningrotativevelocityof14kindsofnucleons,andtheresultsshowedthatthemaximumvolumesofthespinningrotativevelocityofeachnucleonaredifferent[ll.Withthede\'elopingofmodernscienceandtechnology,moreandmoreexperimentalfactsrelatedtothehighspeedrotationquestions,theEinstein'srelativitytheoryandtherotationaltheoryofclassicalmechanicsarenotsuitabletothesepro…     

Resonances of a Harmonically Forced Duffing Oscillator with Time Delay State Feedback

The paper presents analytical and numerical studies of the primary resonance and the 1/3 subharmonic resonance of a harmonically forced Duffing oscillator under state feedback control with a time delay. By using the method of multiple scales, the first order approximations of the resonances are derived and the effect of time delay on the resonances is analyzed. The concept of an equivalent damping related to the delay feedback is proposed and the appropriate choice of the feedback gains and the time delay is discussed from the viewpoint of vibration control. In order to numerically solve the problem of history dependence prior to the start of excitation, the concepts of the Poincaré section and fixed points are generalized. Then, a modified shooting scheme associated with the path following technique is proposed to locate the periodic motion of the delayed system. The numerical results show the efficacy of the first order approximations of the resonances.