Numerical simulation based on three-dimensional model of inner stereocilia

A three-dimensional inner stereocilium model is established by PATRAN.According to the relevant data, the corresponding pressure is applied to one side of the inner stereocilia. The top displacement of the inner stereocilia along the cross section of the basilar membrane(the x-displacement) is similar to the available data in the literature, which verifies the correctness of the model. Based on Castigliano's theorem,the displacement of a single stereocilium is achieved under the inverted triangle force.The results are in good agreement with the data obtained from the finite element(FE)model, which confirms the validity of the formula. With the FE model, the effects of the movement of the hair cells and fluid in the cochlear duct on the x-displacements of the inner stereocilia are studied. The results show that the movement of the hair cells affects the x-displacements of the inner stereocilia, especially for the shortest stereocilium, and the fluid in the cochlear duct affects the x-displacements of the inner stereocilia, especially for the middle stereocilium. Moreover, compared with the effects of the hair cells on the stereocilia, the effect of the cochlear duct fluid is greater.     

Numerical simulation based on two-directional freeze and thaw algorithm for thermal diffusion model

Freeze-thaw processes significantly modulate hydraulic and thermal characteristics of soil. The changes in the frost and thaw fronts (FTFs) affect the water and energy cycles between the land surface and the atmosphere. Thus, the frozen soil comprising permafrost and seasonally frozen soil has important effects on the land surface hydrology in cold regions. In this study, a two-directional freeze and thaw algorithm is incorporated into a thermal diffusion equation for simulating FTFs. A local adaptive variable-grid method is used to discretize the model. Sensitivity tests demonstrate that the method is stable and FTFs can be tracked continuously. The FTFs and soil temperature at the Qinghai-Tibet Plateau D66 site are simulated hourly from September 1, 1997 to September 22, 1998. The results show that the incorporated model performs much better in the soil temperature simulation than the original thermal diffusion equation, showing potential applications of the method in land-surface process modeling.     

Discrete maximum principle based on repair technique for diamond type scheme of diffusion problems

In this paper, two repair techniques are proposed for diamond schemes of anisotropic diffusion problems to ensure that the repaired solutions satisfy the discrete maximum principle. One of them is an extension of that in [Liska R, Shashkov M. Enforcing the discrete maximum principle for linear finite element solutions of second‐order elliptic problems. Communications in Computational Physics 2008; 3(4):852–877.] for linear finite element solutions, which is a local repair technique, and another is a new global repair technique. Both of them keep total energy conservation and are easy to be implemented in existing codes. Numerical examples show that these two repair techniques do not destroy the accuracy of solution for the diamond schemes on distorted meshes. Copyright © 2012 John Wiley & Sons, Ltd.     

Numerical simulation of complex ratcheting tests with a multi-mechanism model type

The paper is devoted to the study of the capabilities of the so called 2M1C model, which was proposed some years ago by one of the authors. The main originality of the model lies in its loading function that composes 2 mechanisms (2M) to build one yield criterion (1C). The predictions of the model are evaluated by considering 1D and 2D ratcheting test results of the literature. Such evaluation reveals the difficulty for the 2M1C model to describe simultaneously 1D and 2D ratcheting using the same set of material parameters. This weakness is generally observed for most of the existing phenomenological models. In order to correct the problem, a modification of the kinematic hardening rules is proposed. A comparison between the predictions of the new model with the same set of 1D and 2D ratcheting test results, considered above, leads to encouraging conclusions about the capabilities of the new formulation.     

A maximum principle for the analysis of elastic-plastic systems

Summary We consider an elastic-plastic body subjected to a specific programme of static loading. In the analysis of the behaviour of the body in the course of the individual steps of the loading programme some difficulties arise if the variational principles of the theory of plasticity are applied. We then propose a maximum principle which appears suitable for the formulation of simple and direct computing procedures. For an elastic-perfectly plastic material the function to be maximized represents the differential energy dissipated in the single infinitesimal step starting from the elastic solution. In that function the variables are the plastic distortions. Since the energy dispersed by the effect of these latter must at every point be positive or zero, the maximum in question is a field maximum and therefore the property is not variational.The principle is demonstrated both for elastic-perfectly plastic materials and for elastic—work-hardening materials. Materials with regular yield surfaces are at first considered; the demonstration is then extended to the case of singular yield surfaces.First published in Rendiconti dell'Istituto Lombardo, Classe di Scienze, A 99, 125–140, 1965.     

Numerical simulation of the flow around a simplified vehicle model with active flow control

Large-eddy simulation (LES) was used to study the influence and the resulting flow mechanisms of active flow control applied to a two-dimensional vehicle geometry. The LES results were validated against existing Particle Image Velocimetry (PIV) and force measurement data. This was followed by an exploration of the influence of flow actuation on the near-wake flow and resulting aerodynamic forces. Not only was good agreement found with the previous experimental study, but new knowledge was gained in the form of a complex interaction of the actuation with the coherent flow structures. The resulting time-averaged flow shows a strong influence of the extension of the actuation slots and the lateral solid walls on the near-wake flow structures and thereby on the resulting drag.     

Numerical simulation of polyhedral crystal growth based on a mathematical model arising from non–local thermomechanics

In this work we present some results of the numerical simulation of the growth of a crystal from its melt, taking into account faceting. The simulation is based on a numerical solution of a three–dimensional generalized Stefan problem. That problem arises from a non–local thermomechanical theory applied to a continuous system with an interface and embodies ideas from the dislocation theory of crystal growth. In the model, the crystal surface is an isotherm and the growth velocity of a crystal face depends on the velocities of the other faces and on the whole crystal configuration as well as on the temperature gradient. A front fixing formulation of the model is considered. This is a conservative form of the Isotherm Migration Method [6, 7, 8, 9, 10, 11] in spherical coordinates. The numerical solution is based on an explicit finite difference discretization of the resulting non–linear equations. We develop a theoretical analysis of the interface equations that drive the crystal face motion. Numerical results, showing evolution of complex crystals with configuration changing during the growth, are in accord with experimental results. Furthermore, numerical experiments offer useful information on the influence of certain parameters in the model on the growth process. Received: March 21, 1996     

On the principle of minimal entropy production for Navier-Stokes-Fourier fluids

In this paper we discuss the principle of minimal entropy production, proposed by Prigogine [1], which affirms that the global entropy production approaches a minimum as a process becomes stationary. We point out in two particular cases that this principle produces field equations that do not agree with the equations of balance of mass, momentum and energy. The processes considered are: • heat conduction in a fluid at rest • shear flow and heat conduction in an incompressible fluid. Now is the appropriate time to review Prigogine's principle, since in recent years a new, and different principle of minimal entropy production has been proposed. This is the “minimax principle” postulated by Struchtrup & Weiss [2]. Within the context of extended thermodynamics this new principle shows great promise. Received April 1, 1999     

基于Vreman亚格子模型的有限开口空间内热驱动流数值模拟

利用基于Vreman亚格子模型的大涡模拟技术对有开口的单室和双室房间内热驱动流进行了数值模拟,利用函数分析法定量分析了模拟结果的准确性,并与Smagorinsky亚格子模型的模拟结果进行了比较.结果表明,Vreman和Smagorinsky亚格子模型的计算结果均能够满足工程的需求,但Vreman亚格子模型在开口附近区域的温度和U速度计算结果在整体上比Smagorinsky亚格子模型更接近实验值;Vreman亚格子模型未像Sma-gorinsky亚格子模型那样过高地估算壁面附近高温区域的粘性耗散;对于单室房间内热烟气层高度的预测,采用Vreman模型得到的计算结果准确性比Smagorinsky亚格子模型提高近50％.     

基于分离式共结点模型的钢筋混凝土结构爆破拆除数值模拟

通过大型有限元分析软件ANSYS/LS-DYNA,充分考虑钢筋和混凝土在结构倒塌时各自的受力状态和强度差异,运用分离式共节点模型模拟钢筋混凝土结构建筑物的爆破拆除倒塌过程.通过对倒塌过程中钢筋混凝土支撑立柱内侧和外侧的钢筋单元、混凝土单元的承载失效过程分析研究,对数值模拟效果与实际爆破效果对比分析得出:分离式共结点模型...     

基于扰动状态概念与E-B模型的粗粒料力学行为模拟

考虑到基于复杂弹塑性模型与扰动状态概念的本构模型在数值积分时的困难,以Duncan-Chang(E-B)模型描述材料在相对完整状态(RI)下的响应,用临界状态模型描述材料在完全调整状态(FA)下的力学行为。依据常规三轴试验曲线判断材料状态的转变并建议了相应的扰动因子计算方法。利用Abaqus软件实现了相应的程序代码,数值算例模拟了堆石料的三轴试验,结果表明邓肯-张模型与扰动状态概念的结合在模拟应变软化、剪缩与剪胀方面具有良好能力。在此基础上进一步模拟了某混凝土面板堆石坝的施工、蓄水、退水的过程,数值结果表明变形分布符合一般规律,且在定量上与原型观测吻合较好。     

Numerical simulation of gas-solid flow with two fluid model in a spouted-fluid bed

The flow characteristics in a spouted-fluid bed differ from those in spouted or fluidized beds because of the injection of the spouting gas and the introduction of a fluidizing gas. The flow behavior of gas-solid phases was predicted using the Eulerian-Eulerian two-fluid model （TFM） approach with kinetic theory for granular flow to obtain the flow patterns in spouted-fluid beds. The gas flux and gas incident angle have a significant influence on the porosity and particle concentration in gas-solid spouted-fluid beds. The fluidizing gas flux affects the flow behavior of particles in the fountain. In the spouted-fluid bed, the solids volume fraction is low in the spout and high in the annulus. However, the solids volume fraction is reduced near the wall.     

Uniqueness and the maximum principle for quasilinear elliptic equations with quadratic growth conditions

In this paper, we show that the maximum principle holds for quasilinear elliptic equations with quadratic growth under general structure conditions.Two typical particular cases of our results are the following. On one hand, we prove that the equation (1) {ie77-01} where {ie77-02} and {ie77-03} satisfies the maximum principle for solutions in H ¹()L(), i.e., that two solutions u ₁, u ₂H¹() L() of (1) such that u ₁u₂ on , satisfy u ₁u₂ in . This implies in particular the uniqueness of the solution of (1) in H ₀ ¹ ()L().On the other hand, we prove that the equation (2) {ie77-04} where fH^–1() and g(u)>0, g(0)=0, satisfies the maximum principle for solutions uH¹() such that g(u)¦Du|{²L¹(). Again this implies the uniqueness of the solution of (2) in the class uH ₀ ¹ () with g(u)¦Du|{²L¹().In both cases, the method of proof consists in making a certain change of function u=(v) in equation (1) or (2), and in proving that the transformed equation, which is of the form (3) {ie77-05}satisfies a certain structure condition, which using ((v₁ -v ₂)⁺)ⁿ for some n>0 as a test function, allows us to prove the maximum principle.     

Numerical simulation of droplet coalescence based on the SPH method

In this paper, the smoothed particle hydrodynamics (SPH) method is employed in modeling and numerical simulation of droplet coalescence. Considering the effect of tangential force on boundary material, besides normal force, tangential force is also introduced in the continuum surface force (CSF) model. The formation of droplet, the coalescence processes of two droplets and three droplets are simulated by the modified CSF model. The validity of the modified model is verified from the aspects of the morphological change of the droplet, the smoothness of free surface and the conservation of the centroid of the system. Compared with finite element method, the results of the modified CSF model show that tangential force plays a crucial role in the CSF model when dealing with model boundary with curves and sharp angles.     

基于三维细观模型的全级配混凝土静态力学性能的数值模拟

根据混凝土材料的细观组成和力学特性,研究了骨料几何形状和空间分布规律,建立全级配混凝土三维凸多面体随机细观模型,引入了混凝土细观组份材料的本构模型,分别模拟了单轴、双轴和三轴状态下混凝土的静态力学性能,并建立混凝土梁的三维宏细观分析模型,研究了三点弯曲梁的变形及裂缝扩展情况。结果表明,本文建立的细观力学模型的计算结果与实验数据吻合较好,可以较好地模拟各种复杂应力条件下混凝土的静态力学性能和损伤破坏机理。     

Numerical simulation for the air entrainment of aerated flow with an improved multiphase SPH model

Aerated flow is a complex hydraulic phenomenon that exists widely in the field of environmental hydraulics. It is generally characterised by large deformation and violent fragmentation of the free surface. Compared to Euler methods (volume of fluid (VOF) method or rigid-lid hypothesis method), the existing single-phase Smooth Particle Hydrodynamics (SPH) method has performed well for solving particle motion. A lack of research on interphase interaction and air concentration, however, has affected the application of SPH model. In our study, an improved multiphase SPH model is presented to simulate aeration flows. A drag force was included in the momentum equation to ensure accuracy of the air particle slip velocity. Furthermore, a calculation method for air concentration is developed to analyse the air entrainment characteristics. Two studies were used to simulate the hydraulic and air entrainment characteristics. And, compared with the experimental results, the simulation results agree with the experimental results well.