气液耦合系统中固有频率的实验研究

流体砰击现象广泛存在于海洋环境、航空航天等自然界与工程中.流体砰击大尺度结构过程中,自由液面破碎时会包裹气体进入流场,气液混合易导致局部砰击荷载增大,引起结构破坏的危险.砰击过程中,气室压力对自由液面固有模态的影响尚未有系统的研究报道.该文采用物理模型实验方法在二维储舱内设计并开展一系列实验,系统研究了两种不同的气室压力对耦合系统的固有频率和阻尼的影响.实验中采用高速摄影机记录了自由液面振荡过程,通过自主研制的图像处理软件提取自由液面波高.结果表明:在低气室压力下,晃荡能量主要集中于一阶固有频率;在高气室压力下,晃荡能量主要集中于二阶固有频率.随着气室压强的增大,影响液体晃荡的主要固有频率提高,而对应的阻尼比却随之降低.因此,气体可压缩性是研究流体晃荡的一个重要因素.     

微血管自律运动的流体力学及血液粘弹性质的影响

本文研究了微血管自律运动引起的血液流动,着重分析了血液的粘弹性质对压力升高及壁面摩阻的影响.结果表明,微血管自律运动具有人体“第二心脏”的作用,血液粘弹性质的影响与Weissenberg数及平均流量的大小有关.     

相关光谱式气体检测系统的光学仿真及优化

依据相关光谱式红外气体传感器检测原理,以系统中红外光与气体反应的气室为研究对象,利用光学设计专用软件Tracepro对理想红外朗伯光源在不同反射镜类型下光源的最佳位置进行了仿真分析;通过建立光路传输系统的数学模型,对气室不同结构尺寸下的光功率输出、以及气室内壁反射率对传感系统性能的影响进行了仿真与优化.在理论模型的基础上,根据仿真结果,确定了最佳气室模型的参数组合.实验结果表明,通过对气室中红外光源的位置、反射镜类型、气室长度等部分进行适当的优化修改后,可使探测器接收信号幅度得到明显提高,将有利于后级电路的信号放大、数模转换等处理过程,从而提高气体浓度检测的灵敏度和精度.     

可变动能打击武器系统外弹道解算

动能弹丸在空气中的运动过程十分复杂,近似属于刚体的一般运动,由于弹丸结构形状不是标准弹,枪膛内无膛线,弹丸飞行时不会产生绕其弹轴的转动运动,进行弹丸外弹道研究时,实际上只是对弹丸的平动运动进行分析计算和研究.利用以飞行距离x为自变量的自然坐标系质心运动方程组,通过引入假速度及西亚切替代对动能弹外弹道进行了解算,反向计算得出的恒量动能打击不同距离的有生目标对应的动能弹丸理想枪口初速.     

中心引力场中刚-弹耦合系统平面运动的相对平衡点的稳定性

研究了中心力场中的刚-弹耦合系统的平面运动动力学, 综合考虑了系统轨道运动与姿态运动, 利用变分原理给出了系统的运动方程. 并以广义Hamilton力学的视点, 利用能量-动量方法给出了一类相对平衡点的稳定性条件.     

带有初应力磁电弹覆盖层的介质中Love波的波速方程

研究了均匀半空间上含有有限厚度的初应力磁电弹覆盖层结构中Love波的波动方程问题.基于初应力下磁电弹材料的运动方程,应力自由的表面条件和连续的界面条件,得到了电磁学开路和短路时Love波的波速方程.结果对新型磁电弹表面波器件的理论研究具有重要的意义.     

初应力下功能梯度磁电弹材料的Love波传播

研究初应力下含磁电弹覆盖层的半无限大功能梯度磁电弹介质中Love波的传播问题.在电磁学开路和短路的边界条件下,基于初应力下功能梯度磁电弹材料的运动方程,应力自由的表面条件和连续的界面条件得到了Love波的波速方程,为功能梯度磁电弹材料表面波器件的发展提供了理论依据.     

用优选法推算柴油机配气凸轮运动方程

柴油机配气凸轮的设计是柴油机配气机构设计的核心.在实践中,我们经常遇到这样一种情况:即在具备了配气凸轮的实物时,如何求得凸轮的运动规律即凸轮的运动方程. 在鉴定一台柴油机的工作中,遇到了这类问题,为了评价它的设计,找出凸轮的运动规律,首先,我们对该柴油机的凸轮进行了测量.采用精度为0.001毫米的测长仪和精度     

梯度磁电弹材料界面的Stoneley波波速研究

研究均匀弹性半空间(y ≤ 0)和功能梯度磁电弹半空间(y≥0)界面的Stoneley波的波速.基于弹性介质和磁电弹介质的本构方程、运动方程和界面连续条件,得到了弹性半空间(y≤0)和磁电弹半空间(y≥0)界面处的Stoneley界面波波速方程,并讨论了梯度系数对波速的影响.研究结果对于界面波器件的研制提供理论依据.     

一类对称性破缺的刚-弹耦合系统的运动稳定性

研究了一类对称性破缺的刚-弹耦合系统的Poisson结构和Casimir函数,它们在定常运动的稳定性研究中起重要作用。作为具体实例,给出了重力作用下定点转动的刚-弹耦合系统的Casimir函数的具体形式,最后还给出了圆周轨道上的刚-弹耦合系统的一类定常运动的稳定性充分条件。     

Premature in-bore separation of sabot-jacketed projectiles

The premature separation of saboted projectiles undergoing high-mach-number in-bore acceleration is investigated. Results from a simplified numerical model for the problem are presented. Measured short-term velocity history for a typical projectile is used to describe the motion of a nonuniformly accelerating piston. Two numerical algorithms for calculating the shocked flow in tront of the accelerating piston are presented. Mach number and pressure time histories for the flow afford corrective input to the sabot design process. © 1993 John Wiley & Sons, Inc.     

Effect of superficial velocity on pressure fluctuations in a gas–solid fluidized bed: A stochastic analysis

The characteristics of a gas–solid fluidized bed are influenced by complicated and stochastic phenomena, e.g. jetting and the bubbling of the fluidizing medium and the motion of the fluidized particles. In this study pressure fluctuations due to the bubble movement were measured by means of a pressure probe over a range of time. The resultant time series have been analysed by determining their autocorrelation function and power spectrum with emphasis on the examination of the effect of the superficial velocity of the fluidizing gas. A stochastic model of bubble motion in a fluidized bed has been developed. This model visualizes the bubble motion in a fluidized bed to consist of the random movement, generating irregular signals, and the linear movement, generating wave-like signals. A theoretical autocorrelation function and a power spectral density function have been derived based on the model.     

Computing a flattest, undercut-free parting line for a convex polyhedron, with application to mold design

A parting line for a polyhedron is a closed curve on its surface, which identifies the two halves of the polyhedron for which mold-boxes must be made. A parting line is undercut-free if the two halves that it generates do not contain facets that obstruct the de-molding of the polyhedron. Computing an undercut-free parting line that is as “flat” as possible is an important problem in mold design. In this paper, algorithms are presented to compute such a parting line for a convex polyhedron, based on different flatness criteria.     

Magnetohydrodynamic flow of a rarefied gas near an accelerated porous plate

An investigation is made of the flow of an electrically conducting rarefied gas due to the time-varying motion of an infinite porous plate, the gas being permeated by a transverse magnetic field. The suction is taken to be a constant and the magnetic lines of force are taken to be fixed relative to the fluid. The effects of magnetic field, rarefaction parameter, suction parameter are shown by means of some tables. The expressions of the skin friction for the two particular cases have also been obtained.     

The problem of wave momentum,radiation pressure and other quantities in the case of plane motions of an ideal gas

Small vibrations and waves of an ideal fluid gas (a liquid or gas) are considered in the quadratic approximation. Actual values of the momentum density and the pressure and also their averaged values are obtained in a number of specific characteristic problems. It is shown that the momentum of an isolated wave with a mean density equal to the density of the unperturbed medium, and the radiation pressure are due to non-linearity of the system of equations, and that this wave has no momentum if its profile remains unchanged during its motion. The latter assertion is also true for finite-amplitude waves.     

Integration of the equations of gas dynamics for 2.5-dimensional solutions

We integrate the equations of gas dynamics in finite form for the solutions in which the thermodynamic parameters depend only on one spatial variable. The corresponding motion of gas represents the nonlinear superposition of the one-dimensional gas motion corresponding to the invariant system and the two-dimensional motion determined by noninvariant functions. These motions are called 2.5-dimensional. We reduce the invariant system to a first-order implicit ordinary differential equation. We study various solutions of the latter. We construct some continuous and discontinuous solutions to the equations of gas dynamics and give their physical interpretation.     

A 2D-Planar Dielectrophoretic Model with Electro-Thermally Induced Fluid Motion and the Stability of Trapping Zones

Dielectrophoresis (DEP) is an electrokinetics-based phenomenon that involves the motion of a particle due to the interaction between an applied nonuniform electric field and an induced dipole moment. This technique is very effective in particle manipulation and separation. Earlier studies on control-amenable models to describe the motion of a neutrally buoyant, neutrally charged particle in a chamber with a parallel electrode array have restricted the motion of the particle to one dimension. Here, incorporating the electro-thermal fluid motion as well, we present a 2D-planar DEP model and study the effect of electro-thermal fluid motion on particle trapping.