一维活塞问题激波解的整体存在性

本文用改进的Glimm格式的方法,研究一维活塞问题当活塞的运动速度是一个常数的扰动时含有激波的弱解的存在性.对波的相互作用以及扰动波在主激波和活塞上的反射作出了精确的估计,在对主激波的强度不加限制的情况下证明了激波解的整体存在性.     

一维活塞问题激波解的整体存在性

本文用改进的Glimm格式的方法,研究一维活塞问题当活塞的运动速度是一个常数的扰动时含有激波的弱解的存在性.对波的相互作用以及扰动波在主激波和活塞上的反射作出了精确的估计,在对主激波的强度不加限制的情况下证明了激波解的整体存在性.     

一维不定常流方程的Harten解

为了利用一个二阶五点差分格式,对一维不定常流方程,计算强平面爆炸波遇不动固壁正反射的解,本文采用一定的技巧构造了边界和次边界的差分格式,并推算了初值的自模拟解析解.同时对初值的奇性提出了处理方法,从而满意地得到了这个较为困难问题的计算结果.本文提出和所利用的差分格式在处理激波间断问题方面具有实用意义.     

双缸单作用活塞泵中活塞匀速运动的探讨

通常双缸单作用活塞泵的恒转速运行会导致管路流量波动,使之在恒流量场合较少应用.对双缸单作用活塞泵的运动建立微分方程,给出了MATLAB7的仿真结果,提出了活塞近似匀速运动的条件,并对电动机转轴的角速度的计算方法作了讨论,得出了在中、低速运行时采用变角速度控制能近似实现恒流量的结论.     

基于映射函数的三阶WENO改进格式及其应用

低耗散、高分辨率激波捕捉格式对含激波流场的数值模拟具有重要意义.在传统三阶WENO格式（WENO-JS3）和三阶WENO Z格式（WENO-Z3）基础上,基于映射函数,给出WENO-M3、WENO MZ3格式.选用Sod激波管、激波与熵波相互作用、双爆轰波碰撞及双Mach(马赫)反射等经典算例,考察上述格式的计算性能.数值结果表明,WENO-MZ3格式相较其他格式具有耗散低、对流场结构分辨率高的特性.为了进一步扩展WENO-MZ3格式的应用范围,采用该格式数值研究封闭方形舱室内柱形高压、高密度气体爆炸波传播过程,波系演化规律以及壁面典型测点压力载荷.数值计算结果表明WENO-MZ3格式能够较好地模拟包含高压比、高密度比的爆炸波且给出数值耗散较小的壁面压力载荷.     

相对论Euler方程组二维活塞问题激波解的局部存在性

考虑二维轴对称相对论Euler方程组的活塞问题.利用轴对称的特点,使用适当的变量先将原问题转化为一维问题,然后通过Taylor展开的方法构造原问题的一个N阶近似解,再利用对相应线性问题所作的能量估计,用Newton迭代法,最终证明其活塞问题激波解的局部存在性.     

基准、标准组合比对的理论与计算

对两同类量的差值或比值进行独立测量,我们称之为比对.例如:测量两个公斤砝码的质量差;测量两个活塞压力计活塞有效面积之比,等等.这种相对测量的方法,通常能获得很高的测量精度,而它对测量的要求比绝对测量又容易实现.所以,在我院各计量领域中,在按国际决议的基准量值定义,用绝对测量的方法复现了绝对的量值后,各     

强引力场中的一维活塞过程

本文在直角坐标系、柱坐标及球坐标系中研究一维匀速活塞在强引力场中的动力学过程.用特征线法数值求解流体力学方程组,得出符合活塞速度条件及联结条件的解.分析讨论了不同坐标系对压缩区,常流区,稀疏区流场、激波传播速度及活塞面上声速的影响.     

油压缓冲器油孔的设计与计算

油压缓冲器的简单示意图如图1所示.当缓冲器受运动着的物体碰撞后,由于缓冲器中油的抵抗力的作用使物体逐渐停住.活塞上有油孔,油孔大油抗力就小,油孔小油抗力就大.缓冲器中配有复原弹簧,它是当工作载荷离去时起到使活塞恢复工作前的位置的作用.油压缓冲器在整个工作过程中要求总抗力函数(包括油抗力函数与弹簧抗力函数之和)的最大值愈小愈好,而且要求当活塞行至终点时对缸底不发生刚性冲击.在设计缓冲器吋,油孔规格是关键.     

摆动活塞发动机的运动学计算

延安柴油机厂的工人师付和技术人员遵照伟大领袖毛主席关于“中国人民有志气,有能力,一定要在不远的将来,赶上和超过世界先进水平”的教导,在学习了三角活塞旋转发动机、差速型旋转活塞发动机及其他类型发动机经验的基础上,提出了一个比其他发动机有着结构简单、紧凑等特点的新型发动机——摆动活塞发动机.     

Flow of fluids with microstructure between parallel plates—I

The basic equations for fluids with microstructure are applied to the steady flow between two parallel plates under the action of a constant pressure gradient. The flow is governed by a microstructure parameter α*. The classical flow is recovered when α* → ∞, while maximum effects of microstructure correspond to α* → 0. For a Poiseuille flow, the microstructure fluid exhibits resistance to motion greater than or equal to that of the classical flow. For a Couette flow it is shown that for a given applied velocity to the moving plate, the shearing stress at the plate is greater than or equal to that corresponding to the classical flow situation. For a Generalised Couette flow, it is shown that for a given pressure gradient in the direction of flow, the flow is retarded; while for an adverse pressure gradient the back flow is controlled.     

Numerical Investigation of Cavitation Interacting with Pressure Wave

A computational fluid dynamics solver based on homogeneous cavitation model is employed to compute the two-phase cavitating flow. The model treats the two-phase regime as the homogeneous mixture of liquid and vapour which are locally assumed to be under both kinetic and thermodynamic equilibrium. As our focus is on pressure wave formation, propagation and its impact on cavitation bubble, the compressibility effects of liquid water have to be accounted for and hence the flow is considered to be compressible. The cavitating flow disturbed by the introduced pressure wave is simulated to investigate the unsteady features of cavitation due to the external perturbations. It is observed that the cavity becomes unstable, locally experiencing deformation or collapse, which depends on the shock wave intensity and freestream flow speed.     

Nearly parallel Blasius flow with slip

The steady boundary layer flow past a moving horizontal flat plate with a slip effect at the plate in a free stream with constant speed, slightly different from the plate speed is studied. An analytic perturbation solution of order two is obtained for the velocity. With respect to the parallel flow both the boundary layer and the inverted boundary layer characters of the flow are plotted and discussed. It is observed that under high slip, the flow becomes a nearly parallel flow with an increased speed.     

Solutions to a class of transport problems with radially dominant convection

For fluid systems dealing with drops and bubbles, there are many situations in which the flow is dominated by a radial field. An analysis is carried out for a general class of problems, in which the primary flow is a purely radial type in a spherical geometry and the secondary flow is a perturbation on it. In particular, the flow solutions are obtained for a particle in extensional flow, rotating particle, and a particle in a linear shear flow. In addition, the steady state heat/mass flow equations with radial convection are solved in a fairly general form for spherical boundaries. The solutions lead to a new class of polynomials for the radial functions of the separated solutions. Some of the fundamental properties of these polynomials have also been derived.     

Receptivity of the boundary layer with separation bubble to external sound waves

The receptivity problem of laminar separated two-dimensional boundary-layer under influence of external acoustic waves is considered. Basic features of this theory were formulated by Ruban (1984) and then Goldstein (1985), but these investigations were limited by small perturbations of steady parallel flow only. The current paper takes into account essentially nonparallel regimes of base flow, including attached flows, flow with separated bubbles and the base flow at marginal value of parameter. The steady flow near a corner point of profile is of considerable interest and a question naturally arises about the sensitivity of separation bubble inside the boundary layer to external disturbances such as sound waves. Another question arises about the sensitivity of near critical base flow, namely if corner is concave there is a marginal angle which limits existence of such base flow. This fact usually is linked with sudden reconstruction of full flow pattern past a profile. Development of perturbations inside the interaction region may give some answers about the appearance of turbulence. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Coverage Maximization with Autonomous Agents in Fast Flow Environments

This work examines the cooperative motion of a group of autonomous vehicles in a fast flow environment. The magnitude of the flow velocity is assumed to be greater than the available actuation to each agent. Collectively, the agents wish to maximize total coverage area defined as the set of points reachable by any agent within T time. The reachable set of an agent in a fast flow is characterized using optimal control techniques. Specifically, this work addresses the complementary cases where the static flow field is smooth, and where the flow field is piecewise constant. The latter case arises as a proposed approximation of a smooth flow that remains analytically tractable. Furthermore, the techniques used in the piecewise constant flow case enable treatment for obstacles in the environment. In both cases, a gradient ascent method is derived to maximize the total coverage area in a distributed fashion. Simulations show that such a network is able to maximize the coverage area in a fast flow.     

Finite-volume modelling of system with compressible flow propelled and actuated body motion

A finite-volume model for the gas flow in a compressible flow driven system with two moving components is developed and applied. In this system, high pressure and temperature compressible flow propels one body along a main flow channel. When this body passes an opening in the main flow channel, some of the high pressure gas bleeds off, entering a secondary, telescoping, flow channel that empties into a plenum. The bleed-off flow causes the pressure in the plenum to increase, actuating the motion of a secondary (actuated) body that forms a bounding surface of the plenum, causing the plenum to expand and the secondary channel to lengthen.     

Structural bifurcation of divergence-free vector fields near non-simple degenerate points with symmetry

In this study, topological features of an incompressible two-dimensional flow far from any boundaries is considered. A rigorous theory has been developed for degenerate streamline patterns and their bifurcation. The homotopy invariance of the index is used to simplify the differential equations of fluid flows which are parameter families of divergence-free vector fields. When the degenerate flow pattern is perturbed slightly, a structural bifurcation for flows with symmetry is obtained. We give possible flow structures near a bifurcation point. A flow pattern is found where a degenerate cusp point appears on the x-axis. Moreover, we also show that bifurcation of the flow structure near a non-simple degenerate critical point with double symmetry is generic away from boundaries. Finally, we give an application of the degenerate flow patterns emerging when index 0 and -2 in a double lid driven cavity and in two dimensional peristaltic flow.     

Analysis of blood flow through a modelled artery with an aneurysm

The intention of the present work is to carry out a systematic analysis of flow features in a tube, modelled as artery, having a local aneurysm in presence of haematocrit. The arterial model is treated to be axi-symmetric and rigid. The blood, flowing through the modelled artery, is treated to be Newtonian and non-homogeneous. For a thorough quantitative analysis of the flow characteristics such as wall pressure, flow velocity, wall shear stress, the unsteady incompressible Navier-Stokes equations in cylindrical polar co-ordinates under the laminar flow conditions are solved by using the finite-difference method. Finally, the numerical illustrations presented in this paper provide an effective measure to estimate the combined influence of haematocrit and aneurysm on flow characteristics. It is found that the magnitude of wall shear stress and also the length of separation increase with increasing values of the haematocrit parameter. The length of flow separation increases but the peak value of wall shear stress decreases with the increasing length of aneurysm. The peak value of wall shear stress as well as the length of separation increases with the increasing height of the aneurysm.