毛细管内气泡变形及脉动运动模拟

运用VOF模型结合CSF模型对毛细管内气泡的运动变形进行研究分析。首先对毛细管内不同气泡直径的运动变形进行数值计算,考虑气泡受粘性力、惯性力和表面张力的作用,计算得到气泡经历圆形、弹状、箭头状,直至破裂成气泡流;然后对管内气泡运动时气泡破裂进行数值模拟,结果表明不同直径的气泡均存在破裂临界毛细值;最后对毛细管两边施加脉动载荷,分析脉动载荷下气泡运动情况,得出随着脉动压力波的增加,气泡在管内的脉动运动更加剧烈,气泡外形也是随压力的脉动变化发生周期性变化。     

集中药包土中爆炸成腔的三维数值模拟

运用数值模拟的方法对土中封闭爆炸成腔进行了仿真研究。介绍了用LS -DYNA3D求解运算的基本过程 ,并运用该程序对集中装药条件下土中爆炸成腔进行了三维模拟。结果表明 :该程序可以用来模拟土中爆炸成腔 ,得到的空腔与药包半径之比与实验基本吻合。     

水下爆炸冲击波数据记录仪的设计与实现

本文从水下爆炸冲击波的概念出发,介绍了水下爆炸冲击波的特征,应用爆炸气泡运动理论确定了波形参数。然后根据水下冲击波的特征,分析了水下爆炸冲击波数据记录仪的测试原理,介绍了两种模拟实际水下爆炸冲击波信号的测试方法。再通过简易的水下爆炸试验,得到了冲击波的压力-时间历史曲线及其参数并与理论值作了比较。最后通过直线拟合和误差分析进一步证明了文中提出的水下爆炸冲击波测试方法是一套科学的、有效的冲击波压力测试方法。     

水介质中换能器的声场分布建模及仿真

在水声目标探测的优化中,为精确仿真水声换能器在水中的声场传播分布规律,首先利用多元高斯声束叠加模型,建立水声换能器的表面声压分布模型,然后通过频域有限差分法求解KZK传播方程,得到发射声场在水下分布规律和谐波特性,最后通过MATLAB进行数值仿真,得到各阶次谐波在声轴方向上的径向和轴向的分布情况,结果表明谐波阶次越高,波束越窄,声场能量较集中;各阶次谐波在轴向一定位置附近声压达到最大值,之后由于水介质的吸收效应逐渐衰减.上述研究对开展水下探测、非线性声场成像等具有重要的参考价值.     

水下缆索环流阻力分析

研究水下缆索系统优化问题,非对称缆在流体中存在的环流,不仅产生侧向阻力,同时导致切向力和法向力之间呈现非线性关系,使速度投影法失效.为解决上述问题,提出一种根据坐标变换的算法,可将原始阻力直接获得三个阻力分量,适用于各种缆型的阻力计算;同时能避免缆流夹角的求解和符号处理问题,使算法得到了简化.在速度和缆体两种坐标系下,依据算法分别建立了相应的阻力计算模型.基于水下缆索有限段动力学模型,对典型非对称缆索水下运动过程进行了仿真,结果表明能正确反映缆索的水下运动规律,并证明了模型的正确性,解决了水下缆索存在的问题.     

水下滑翔机海洋环境深平均流估计方法

提出了水下滑翔机海洋环境深平均流估计方法．首先,基于水下滑翔机稳态运动模型,研究海水密度差异和耐压舱体压缩变形对水下滑翔机运动速度的影响,建立水下滑翔机运动速度快速计算模型,并证明了该模型的正确性及有效性．然后,利用得到的水下滑翔机运动速度和船位推算方法结合,给出了海洋环境深平均流估算方法．利用该深平均流估算方法对3台水下滑翔机海上试验过程中的深平均流进行估算,并分析了估算结果的有效性．实验结果证明利用本文得到的深平均流可以提高水下滑翔机船位推算中的定位精度．     

某型强光爆震弹冲击波超压致伤半径仿真研究

研究某型强光爆震弹的冲击波超压致伤特性.为得到某型强光爆震弹对于人员致伤的安全半径,依据LS-DYNA结构非线性分析工具,结合爆炸冲击波超压的致伤效应理论,建立了相应的仿真模型并进行实验分析.先基于理论公式进行计算,对比理论计算数据和仿真数据,通过数值拟合,得出了仿真结果与理论计算结果的对比曲线,并结合实际分析了仿真数据的可靠性.结果表明,利用仿真数据可以计算出冲击波超压对人员致伤的安全半径,并具有一定的实践指导意义.     

压电谐振驱动三足机器人的平面运动

设计并实现了一类利用压电陶瓷片作动,由三条曲梁足支撑的振动驱动机器人.建立了在一条足共振驱动下机器人水平运动的动力学方程,数值计算解释了摩擦作用下的运动机理,寻找到异性摩擦对运动方向、速度的影响和压电激励频率与运动速度间的关系.通过建立圆弧曲梁控制方程求解圆弧型足面内振动的固有频率及振型,设计了三组不同频率的圆弧曲梁足参数,实验制作了机器人模型,利用压电控制三足间振动的共振切换,实现了预想的三个方向的运动以达到平面运动的效果,实验测量了机器人的运动速度与理论计算吻合得较好.     

考虑液滴尺寸分布气液两相爆轰流场数值仿真

研究脉冲爆轰发动机喷射装置模型问题,针对两相爆轰流场中燃料液滴半径实际上分布的不均匀性,为了建立更符合实际的模型,提出了多尺寸分布的两相爆轰方程.应用二维守恒元和求解元方法(CE/SE方法)对其进行数值仿真,得到了液滴初始半径分布对管内流场的影响.液滴初始半径分组时爆轰波速度介于不分组时最小液滴半径和最大液滴半径的计算值之间;分析了液滴初始半径不同分组时,液滴平均半径越小,爆轰波最大压力和爆轰波出口速度越大.仿真结果证明用CE/SE方法可有效捕获两相爆轰波间断能力.研究成果为脉冲爆轰发动机喷射雾化装置设计提供设计依据.     

解扩散方程的指数时间差分方法

指数时间差分方法是近年来提出求解刚性常微分方程的一种新的数值计算方法.指数时间差分方法是一种积分方法,而不是经典的差分方法.利用指数时间差分方法求解扩散方程,如一维拟线性对流扩散方程和Allen-Cahn扩散方程.扩散方程在空间方向离散后转化成刚性常微分方程.用显式指数时间差分方法和相应阶的显式Runge-Kutta方法求解刚性常微分方程.数值结果表明显式指数时间差分方法具有相同阶的显式Runge-Kutta方法相应的精度,稳定性显著提高,而且能很好地模拟扩散方程的演化行为.指数时间差分方法可用于刚性常微分方程的数值计算.     

A multiphase compressible model for the simulation of multiphase flows

A compressible model able to manage incompressible two-phase flows as well as compressible motions is proposed. After a presentation of the multiphase compressible concept, the new model and related numerical methods are detailed on fixed structured grids. The presented model is a 1-fluid model with a reformulated mass conservation equation which takes into account the effects of compressibility. The coupling between pressure and flow velocity is ensured by introducing mass conservation terms in the momentum and energy equations. The numerical model is then validated with four test cases involving the compression of an air bubble by water, the liquid injection in a closed cavity filled with air, a bubble subjected to an ultrasound field and finally the oscillations of a deformed air bubble in melted steel. The numerical results are compared with analytical results and convergence orders in space are provided.     

Behavior of a micron-sized air bubble in operating FDBs using the discrete phase modeling method

This paper investigates the motion of a micron-sized air bubble in the operating fluid dynamic bearings (FDBs) of a spindle motor in a computer hard disk drive. The flow field of FDBs is calculated by solving the Navier–Stokes equation and the continuity equation. The two-phase flow in the air-oil interface is simultaneously solved by using the finite volume method and the volume of fluid (VOF) method. We then analyze the motion of a micron-sized air bubble by applying the discrete phase modeling (DPM) method to the calculated flow field of FDBs. The motion of a micron-sized air bubble determined using the DPM method is verified by comparison with the trajectory of the micron-sized air bubble determined using the VOF method. The trajectories of a micron-sized air bubble with different initial positions in the FDBs are discussed.     

Bubble Stabilization of Spectral Methods: The Multidimensional Case

A spectral Legendre method for the advection-diffusion equation is stabilized with the addition of locally supported bubble functions. It is shown that the spectral accuracy of the scheme is preserved and its stability is increased. Several strategies for choosing the stabilization parameter are proposed and compared with the aid of numerical tests.     

多体系统动力学数值解法

多体系统动力学研究的主要内容动力学建模与数值解法是多体系统动力学研究的主要内容之一。对多体系统动力学方程及其动力学数值解法的研究成果进行了较为全面的阐述。多体系统动力学及动力学方程进行了简单的归纳和总结,多体系统动力学数值求解,特别是刚柔耦合多体系统微分／代数方程的数值解法等研究热点进行了详细的阐述,并简要展望了多体系统动力学数值解法今后的发展趋势,为多体系统动力学计算机仿真奠定了基础。     

热泡式喷墨的建模与分析

喷墨过程的数值建模是建立在一维热传导公式,温度—压强关系式和能量、物质转换关系的平衡的基础上的。一维热传导公式用来考虑气泡和它周围液体之间的能量交换以及气—液交界层的温度分布。温度—压强关系式和能量转换关系用来考虑气泡的增长和破裂过程。气泡产生的初始温度、初始压强以及控制电压等参数都在本模型中进行分析,分析的结果为设计喷墨打印机提供了最基础的资料。     

热泡式喷墨的建模与分析

喷墨过程的数值建模是建立在一维热传导公式，温度-压强关系式和能量、物质转换关系的平衡的基础上的。一维热传导公式用来考虑气泡和它周围液体之间的能量交换以及气-液交界层的温度分布。温度-压强关系式和能量转换关系用来考虑气泡的增长和破裂过程。气泡产生的初始温度、初始压强以及控制电压等参数都在本模型中进行分析，分析的结果为设计喷墨打印机提供了最基础的资料。     

Numerical Simulation of the Evolution of a Gas Bubble in a Liquid Near a Wall

A numerical technique based on the application of the boundary element method is proposed for studying the axially symmetric dynamics of a bubble in a liquid near a solid wall. It is assumed that the liquid is ideally incompressible and its flow is potential. The process of expansion and contraction of a spheroidal bubble is considered, including the toroidal phase of its movement. The velocity and pressure fields in the liquid surrounding the bubble are evaluated along with the shape of the bubble surface and the velocity of its displacement. The numerical convergence of the algorithm with an increase in the number of boundary elements and a refinement of the time step is shown, and comparison with the experimental and numerical results of other authors is performed. The capabilities of the technique are illustrated by solving a problem of collapse of a spheroidal bubble in water. The bublle is located a short distance from the wall.     

计入空气阻尼的MEMS微谐振器非线性动力学研究

针对横向振动MEMS微谐振器,计入非线性空气阻尼力,对微谐振器非线性动力学特性进行研究.建立微谐振器非线性动力学模型,计入滑移边界条件和稀薄气体效应,利用FLUENT和MATLAB对Navier-Stokes方程和动力学方程进行求解.经过与国外实验对比,可得出考虑非线性阻尼力的平板振幅值非常接近实验值,振幅峰-峰值误差仅为6%,且优于线性动力学的分析结果.为MEMS器件非线性动力学特性分析提供理论依据.     

基于泡沫大小动态分布的浮选生产过程加药量健康状态分析

针对矿物浮选过程泡沫大小分布随着药剂量的改变而动态变化的特点,提出一种基于泡沫大小动态分布特征的具有自学习功能的浮选生产过程加药量健康状态统计模式识别方法.首先,通过泡沫图像分割、气泡尺寸分布核密度估计获得浮选气泡大小的概率密度分布函数,采用无监督的最远邻聚类方法获得典型药剂量添加状态下的气泡尺寸统计分布特征集;然后,采用简单的贝叶斯推理方法获得测试时间段对应的药剂添加健康状态分析识别结果,并根据浮选生产工况状态的动态变化对各典型药剂状态下的气泡大小统计分布特征集进行在线学习修正.实验结果表明,所提出方法能实时获取泡沫尺寸分布的动态变化,实现浮选药剂操作健康状态的自动识别与评价,为进一步实现浮选生产过程的加药量优化控制奠定了基础.     

Unsteady development of a deformable bubble rising in a quiescent liquid

An accurate finite-volume based numerical method for the simulation of an isothermal two-phase flow, consisting of a rising deformable bubble translating in a quiescent, unbounded liquid, is presented. This direct simulation method is built on a sharp interface concept and developed on an Eulerian, Cartesian fixed-grid with a cut-cell scheme and marker points to track the moving interface. The unsteady Navier–Stokes equations in both liquid and gas phases are solved separately. The mass continuity and momentum flux conditions are explicitly matched at the true surface phase boundary to determine the evolving interface shape and movement of the bubble. The highlights of this method are that it utilizes a combined Eulerian–Lagrangian approach, and is capable of treating the interface as a sharp discontinuity. A fixed underlying grid is used to represent the control volume. The interface, however, is denoted by a separate set of marker particles which move along with the interface. A quadratic curve fitting algorithm with marker points is used to yield smooth and accurate information of the interface curvatures. This numerical scheme can handle a wide range of density and viscosity ratios. The bubble is assumed to be spherical and at rest initially, but deforms as it rises through the liquid pool due to buoyancy. Additionally, the flow is assumed to be axisymmetric and incompressible. The bubble deformation and dynamic motion are characterized by the Reynolds number, the Weber number, the density ratio and the viscosity ratio. The effects of these parameters on the translational bubble dynamics and shape are given and the physical mechanisms are explained and discussed. Results for the shape, velocity profile and various forces acting on the bubble are presented here as a function of time until the bubble reaches terminal velocity. The range of Reynolds numbers investigated is 1 < Re < 100, and that of Weber number is 1 < We < 10.