基于DQM的空间轴对称流体饱和多孔热弹性柱体动力学特性研究

在热局部平衡条件下研究了空间轴对称不可压流体饱和多孔热弹性柱体在表面温度载荷作用下的动力学特性。基于de Boer多孔介质混合物理论,给出了问题的数学模型;其次综合采用微分求积方法-二阶向后差分法-Newton-Raphson迭代法求解了数学模型,得到柱体各离散点处未知物理量的数值结果,进而可分析柱体的动力学特性。为了验证该方法的正确性,计算了不可压流体饱和多孔弹性柱体的动力固结问题,并与de Boer等的解析结果进行了比较,两者吻合良好,也证明DQM有较小的计算量和较高的精度。最后分别研究和比较了柱体只受到表面外载荷作用下的动力学特性和受到两种表面温度载荷与外载荷联合作用下的动力学特性,考察了材料的某些参数对柱体动力学特性的影响。     

沿水平向运动的水中截断圆柱体辐射波浪问题的解析解答

根据线性势波理论,分析了水中截断圆柱体作水平简谐运动时结构周围的辐射波浪。利用分离变量法,分别得到了含有未知常数的三个流体子域速度势的简谐表达形式,并采用一个较为简单的匹配方法使其在流体子域的共同边界上满足压力和法向速度的连续条件。于是求解得到了速度势,进而可得到由等效附加质量和附加阻尼表示的柱体侧面上的动水力。不仅能考虑自由表面波对动水压力的影响,也适用于位于任意水深处的截断圆柱体。实例分析表明,该方法具有较高的计算精度;同时对于截断圆柱体,采用Morison方程中的动水附加惯性力项会高估柱体侧面上的动水力。     

钻井液及井壁对石油钻柱振动的影响分析

本文对钻井液及井壁对石油钻柱振动的影响问题进行了研究。文中把在狭长井眼里充满钻井液液流中的钻柱运动简化为一圆柱体在充满流体的环形空间中的振动问题，对钻井液连同井壁对钻柱振动所带来的共同影响作用和钻柱的受力状况进行了分析，进而求解了处井眼里环空钻井液流体中的钻柱振动问题，并利用油田现场数据进行了例算和讨论。     

微间距平板Poiseuille流动的稳定性

在忽略了其他微尺度效应的前提下，讨论了黏性修正和壁面滑移对微间距平板Poiseuille流动稳定性的影响．利用固壁对流体分子的作用力修正流体表观黏性，从而使流体表观黏性成为离壁面距离的函数．边界滑移修正使用纳维滑移边界模拟．利用线性小扰动法分析流动的稳定性，并用切比雪夫配置点法求解模型方程．计算结果显示，表观黏性修正在一定条件下可使平均流出现拐点，流动更易失稳；而边界滑移则增大了平均流的丰满程度，使流动更加稳定．当黏性修正模型参数ξ和n较大时，滑移长度的影响会被极大地减弱．     

二维声子晶体的对称性对声学带隙的影响

用平面波展开方法计算了正三、四、六、八棱柱体及圆柱体按正方点阵排列的二维水-水银声子晶体的声学带隙结构．首先研究了非圆柱体的旋转对带隙的影响，发现在给定的柱体和（较低的）填充率下带隙宽度的最大值和最小值均出现在晶体结构对称性最高时．通过调节柱体的方位，找出各填充率下的最宽带隙，结果表明：在水／水银系统中，带隙宽度随柱体对称性的提高而增大；在水银／水系统中，除正四棱柱晶体带隙最宽以外，情况正好相反．     

地震作用下水-轴对称柱体相互作用的子结构分析方法

针对水-轴对称柱体动力相互作用问题,提出了一种地震作用下水-结构相互作用的时域子结构分析方法。基于三维不可压缩水体的波动方程和边界条件,利用分离变量法将其转换为环向解析、竖向和径向数值的二维模型;基于比例边界有限元推导了截断边界处无限域水体的动力刚度方程,并将水体内域有限元方程和人工边界处的动水压力进行耦合,从而得到结构表面的动水压力方程;将轴对称柱体结构的有限元方程与动水压力方程耦合,从而得到水-轴对称柱体结构系统的时域有限元方程;数值算例验证该文提出的水-轴对称动力相互作用的子结构方法,结果表明:该文方法具有很高的精度和计算效率。通过对水中轴对称结构地震响应和自振频率的分析表明:地震动水压力对结构自振频率和动力响应的影响随水深的增加而增大。     

水-椭圆柱体相互作用分析的精确和简化模型

针对柔性椭圆柱体在水中的振动问题,提出一种代替水-结构动力相互作用的附加质量模型。基于椭圆柱体动水压力的计算公式建立了水中椭圆柱体的自由振动方程,进一步推导了水中椭圆柱体自振频率和振型的解析公式;基于振型叠加法推导了水中椭圆柱体地震动力反应的计算公式;通过附加质量代替水-结构相互作用,提出了水中椭圆柱体自振频率的计算公式;通过曲线拟合给出了附加质量的简化计算公式,该简化公式数学表达简单,适用于工程应用。     

利用FEM/IBEM计算流体介质中的壳体的结构声耦合问题

利用有限元和间接边界元的声振耦合方程同时计算结构表面的振动和相应的辐射声场，将结构的物理坐标转化成模态基本量来表示，对完全耦合的结构动力学方程及声场方程进行解耦，对浸汉于两种流体介质中的椭圆球壳体的数值计算结果表明，流体介质改变了结构的共振特性及声辐射特性。本文的数值方法可用于任意复杂结构在流体介质中的振动和声分析。     

含曲线裂纹柱体扭转问题的新边界元法

研究了带曲线裂纹柱体的扭转断裂问题,推导出了可以直接应用于任意形状截面含有任意形状曲线裂纹的柱体扭转问题的新的边界积分方程,并建立了带裂纹柱体扭转问题的边界元数值计算方法,提出了裂纹尖端的奇异元和线性元插值模型,给出了抗扭刚度和应力强度因子的边界元计算公式。该文对含有圆弧裂纹、曲线裂纹及直线裂纹的不同截面形状柱体的典型问题进行了数值计算,所得结果证明了边界元方法的正确性和有效性。     

潜艇感应磁场的三维积分方程法数值计算研究

论述了应用积分方程法计算潜艇感应磁场的数值方法，采用底面为部分圆环的柱体剖分单元，推导了耦合系数的计算公式，编制了数值计算程序，对潜艇船模进行了计算，取得了较好的计算效果。     

On the explicit analytic solutions of an Oldroyd 6-constant fluid

This paper deals with some steady unidirectional flows of an Oldroyd 6-constant fluid. The modelled differential equation is non-linear and proposes some new mathematical difficulties. The governing non-linear equation for the steady flow of an Oldroyd 6-constant fluid is different than from the Newtonian fluid and involves the non-Newtonian features. Moreover, the exact analytic solutions are obtained for Couette, Poiseuille and generalized Couette flows for all values of non-Newtonian parameters. The homotopy analysis method (HAM) is used to construct the solutions.     

Some simple flows of a Burgers’ fluid

The problems dealing with some unidirectional flows of a Burgers’ fluid are investigated. By using the constitutive equation for a Burgers’ fluid in the literature, the governing time-dependent equation is modeled. Based on the flow conditions described, three flow situations are solved and the exact analytic solutions are given using the Fourier transform technique. Finally, the previous solutions, corresponding to second grade fluid, Oldroyd-B fluid, Maxwell fluid and Newtonian fluid, appear as the special cases of the present analysis.     

Prediction of Thermodynamic Properties of Liquid Air

In this work, a simple equation of state (EoS) has been used to predict some thermodynamic properties of air as a pseudo-pure fluid; as a ternary mixture of nitrogen, oxygen, and argon; and as a binary mixture of nitrogen and oxygen at different temperatures and pressures. A comparison with literature tabulated values has been made. The agreement of calculated densities with corresponding tabulated values is good for which the average absolute deviations are better than 0.06% if we assume air as a pseudo-pure fluid, and 0.9% and 1.2% if we consider air as a ternary mixture and as a binary mixture, respectively. To show the ability of this equation of state to predict density, the calculated densities of air have been compared with those computed by other methods.     

Non-orthogonal stagnation-point flow of a micropolar fluid

This paper considers the problem of steady two-dimensional flow of a micropolar fluid impinging obliquely on a flat plate. The flow under consideration is a generalization of the classical modified Hiemenz flow for a micropolar fluid which occurs in the boundary layer near an orthogonal stagnation point. A coordinate decomposition transforms the full governing equations into a primary equation describing the modified Hiemenz flow for a micropolar fluid and an equation for the tangential flow coupled to the primary solution. The solution to the boundary-value problem is governed by two non-dimensional parameters: the material parameter K and the ratio of the microrotation to skin friction parameter n. The obtained ordinary differential equations are solved numerically for some values of the governing parameters. The primary consequence of the free stream obliqueness is the shift of the stagnation point toward the incoming flow.     

An Extended Equation of State Modeling Method II. Mixtures

This work is the extension of previous work dedicated to pure fluids. The same method is extended to the representation of thermodynamic properties of a mixture through a fundamental equation of state in terms of the Helmholtz energy. The proposed technique exploits the extended corresponding-states concept of distorting the independent variables of a dedicated equation of state for a reference fluid using suitable scale factor functions to adapt the equation to experimental data of a target system. An existing equation of state for the target mixture is used instead of an equation for the reference fluid, completely avoiding the need for a reference fluid. In particular, a Soave–Redlich–Kwong cubic equation with van der Waals mixing rules is chosen. The scale factors, which are functions of temperature, density, and mole fraction of the target mixture, are expressed in the form of a multilayer feedforward neural network, whose coefficients are regressed by minimizing a suitable objective function involving different kinds of mixture thermodynamic data. As a preliminary test, the model is applied to five binary and two ternary haloalkane mixtures, using data generated from existing dedicated equations of state for the selected mixtures. The results show that the method is robust and straightforward for the effective development of a mixture- specific equation of state directly from experimental data.     

二元混合工质HFC32/125绝热指数计算模型分析

绝热指数与定压比热在制冷系统数值分析和计算中极为重要。本文以纯物质的PR状态方程为基础，利用适当的混合法则对绝热指数和定压比热进行理论推导，得出适用于二元混合工质的绝热指数与定压比热方程；对HFC32／125的定压比热分区进行数值拟合，得出定压比热的拟合方程，本文对理论推导和数值拟合的结果进行比较，从而为系统分析和计算提供精确热物理性质方程。     

声固耦合系统数值计算方法的研究与应用

机械设备的振动噪声控制至关重要,声固耦合问题是机械振动噪声分析领域常见的多物理场耦合问题.对声固耦合分析方法进行研究,为声固耦合分析提供一定的理论依据.声固耦合问题可分为强耦合与弱耦合两类,声固耦合方法可根据耦合程度计算公式或工程经验选择;基于结构有限元法与声学边界元法研究了2种耦合方法的耦合方程与耦合流程,采用主流的振动噪声分析软件对具体声固耦合实例进行分析,得到模型在2种不同耦合方法下计算的模型和场点的频率响应结果.2种耦合方式的计算结果在整个曲线走势与出现峰值的频率方面基本一致.在高频区域,弱耦合方法由于忽略了空气对结构振动的阻尼作用,计算结果的数值较大.对于薄壁结构,空气对结构的影响较大,应采用强耦合;对于质量或厚度较大的物体,可采用弱耦合.结果论证了声固耦合方法的选择依据,总结了声固耦合方法的应用范围.     

A numerical model for determining the motion of a bubble close to a fixed rigid structure in a fluid

This paper is concerned with the problem of modelling the motion of a bubble close to a rigid structure in an infinite fluid. It is well known that the boundary integral method is a powerful technique for modelling the motion of a single bubble in a fluid. In this paper we shall present a modified boundary integral method for modelling the motion of a bubble close to a fixed finite rigid structure, and discuss a numerical scheme for solving the resulting integral equation for three-dimensional problems. Finally, we illustrate our method with some typical numerical results.     

弹性支承输流管道固有频率计算

本文建立了两端弹性支承输流管模型,导出该模型管道随内流体流速变化的固有振动特性方程,并对上游铰支加扭簧支承,下游铰支的模型进行了计算和实验,计算结果和实验数据吻合较好.结果表明,输流管各阶固有频率随内定常流的流速增加而降低。     

An Extended Equation of State Modeling Method I. Pure Fluids

A new technique is proposed here to represent the thermodynamic surface of a pure fluid in the fundamental Helmholtz energy form. The peculiarity of the present method is the extension of a generic equation of state for the target fluid, which is assumed as the basic equation, through the distortion of its independent variables by individual shape functions, which are represented by a neural network used as function approximator. The basic equation of state for the target fluid can have the simple functional form of a cubic equation, as, for instance, the Soave–Redlich–Kwong equation assumed in the present study. A set of nine fluids including hydrocarbons, haloalkane refrigerants, and strongly polar substances has been considered. For each of them the model has been regressed and then validated against volumetric and caloric properties generated in the vapor, liquid, and supercritical regions from highly accurate dedicated equations of state. In comparison with the underlying cubic equation of state, the prediction accuracy is improved by a factor between 10 and 100, depending on the property and on the region. It has been verified that about 100 density experimental points, together with from 10 to 20 coexistence data, are sufficient to guarantee high prediction accuracy for different thermodynamic properties. The method is a promising modeling technique for the heuristic development of multiparameter dedicated equations of state from experimental data.