Numerical Simulation for Evolutionary History of Three-Dimensional Basin

ＮＵＭＥＲＩＣＡＬＳＩＭＵＬＡＴＩＯＮＦＯＲＥＶＯＬＵＴＩＯＮＡＲＹＨＩＳＴＯＲＹＯＦＴＨＲＥＥ－ＤＩＭＥＮＳＩＯＮＡＬＢＡＳＩＮＹｕａｎＹｉ－ｒａｎｇ（袁益让）；ＷａｎｇＷｅｎ－ｑｉａ（王文洽）；ＹａｎｇＤａｎ－ｐｉｎｇ（羊丹平）（Ｄｅｐａｒｔｍｅ...     

Numerical simulation of three-dimensional free surface flow in isopycnal co-ordinates

In this paper a semi-implicit method for three-dimensional circulation in isopycnal co-ordinates is derived and discussed. It is assumed that the flow is hydrostatic and characterized by isopycnal surfaces which can be represented by explicit, single-valued functions. The hydrostatic pressure is determined by using the conjugate gradient method to solve a block pentadiagonal linear system. The horizontal velocities are determined by solving a large set of tridiagonal systems. The stability of the resulting algorithm is shown to be independent of the surface and internal gravity wave speeds. © 1997 John Wiley & Sons, Ltd.     

Numerical models for vehicle exhaust dispersion in complex urban areas

Two numerical models are presented for predicting vehicle exhaust dispersion in complex urban areas with or without the wind field. The models not only reflect the effect of building and street canyon configuration on the pollutant propagation, but also are able to predict the turbulent energy produced by moving vehicles on the road. In particular, in the discrete model, turbulent energy and pollutant concentration produced by each vehicle are dynamically described in the Lagrangian method. The pollutant propagation is calculated with the advection–diffusion equation. The Reynolds averaged Navier–Stokes equations are numerically solved for the wind flows. The movement and heat release rate of the vehicles are treated as sources of the turbulent energy equation for the computation of turbulent energy produced by the moving vehicles. This paper reports the detailed implementation of the models. Four typical numerical tests were carried out to represent the performance of the proposed numerical models. Copyright © 2010 John Wiley & Sons, Ltd.     

三维复杂流动的间断有限元方法模拟

本文基于三维可压缩Euler方程,采用基于Runge-Kutta时间离散的间断有限元方法(RKDG方法),对三维前台阶、三维Riemann问题和球Riemann等问题进行了模拟。结果表明,本文的RKDG方法能够在很少的网格内清晰地捕捉到三维复杂流场中的激波和接触间断;同时,将球Riemann问题中z=0.4平面压强沿到对称轴距离的分布与文献中的近似精确解相比,吻合较好,这也验证了本文的RKDG方法不仅能够进行三维复杂流场的定性描述,也能够应用于三维复杂流场的定量计算。     

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 of three-dimensional saturated flow in randomly heterogeneous porous media

This paper presents a numerical method for simulating flow fields in a stochastic porous medium that satisfies locally the Darcy equation, and has each of its hydraulic parameters represented as one realization of a three-dimensional random field. These are generated by using the Turning Bands method. Our ultimate objective is to obtain statistically meaningful solutions in order to check and extend a series of approximate analytical results previously obtained by a spectral perturbation method (L. W. Gelhar and co-workers). We investigate the computational aspects of the problem in relation with stochastic concepts. The difficulty of the numerical problem arises from the random nature of the hydraulic conductivities, which implies that a very large discretized algebraic system must be solved. Indeed, a preliminary evaluation with the aid of scale analysis suggests that, in order to solve meaningful flow problems, the total number of nodes must be of the order of 10⁶. This is due to the requirement that x _i gl _i L _i , where x _i is the mesh size, _i is a typical correlation scale of the inputs, and L _i is the size of the flow domain (i = 1, 2, 3). The optimum strategy for the solution of such a problem is discussed in relation with supercomputer capabilities. Briefly, the proposed discretization method is the seven-point finite differences scheme, and the proposed solution method is iterative, based on prior approximate factorization of the large coefficient matrix. Preliminary results obtained with grids on the order of one hundred thousand nodes are discussed for the case of steady saturated flow with highly variable, random conductivities.     

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.     

Numerical solution of the transport equation for passive contaminants in three-dimensional complex terrains

This paper presents a numerical solution of the transport equation for heat and species in complex three-dimensional spaces. The solution domain of the equation is transformed into a cube, as also is the governing equation; the resultant equation is solved in the transformed space via a finite difference technique. The validity of the developed computer code is tested by predicting test cases for which either analytical or reliable experimental results exist. Results are also presented for the rate of convergence of the method and the computer storage requirements, from which the validity, the flexibility and the economy of the developed method are proved for flows in real three-dimensional complex terrains.     

Numerical simulation of three-dimensional instability of flow past a short cylinder

The plane-parallel flow past an infinitely long circular cylinder becomes three-dimensional starting with Reynolds numbers Re ≈ 190. The corresponding instability mode is called mode A. When Re ≈ 260, vortex structures with a smaller cross scale are formed in the wake as a result of a secondary three-dimensional instability (mode B). The transition to three-dimensionality for a short cylinder bounded by planes is considered. The length of the cylinder is chosen to eliminate the unstable perturbations of mode A. Two instability modes similar to modes A and B modified under the effect of the bounding lateral planes are found. The problems of three-dimensional flow are numerically solved using the Navier-Stokes equations.     

From micro-scale to technical dimension—Challenges in the simulation ofdense gas-particle flows

正Supported by the Sino-German Center for Research Promotion,an organization jointly founded by the National Natural Science Foundation of China (NSFC) and the German Research Foundation     

Numerical solution of three-dimensional thermoplasticity problems for bodies of complex shape

Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Prikladnaya Mekhanika, Vol. 24, No. 8, pp. 24–30, August, 1988.     

Numerical simulation of high pressure release and dispersion of hydrogen into air with real gas model

Hydrogen is a renewable and clean source of energy, and it is a good replacement for the current fossil fuels. Nevertheless, hydrogen should be stored in high-pressure reservoirs to have sufficient energy. An in-house code is developed to numerically simulate the release of hydrogen from a high-pressure tank into ambient air with more accuracy. Real gas models are used to simulate the flow since high-pressure hydrogen deviates from ideal gas law. Beattie–Bridgeman and Abel Noble equations are applied as real gas equation of state. A transport equation is added to the code to calculate the concentration of the hydrogen–air mixture after release. The uniqueness of the code is to simulate hydrogen in air release with the real gas model. Initial tank pressures of up to 70 MPa are simulated.     

Numerical simulation of three-dimensional duct flows of incompressible fluids by using the stream-tube method

Numerical simulation of three-dimensional flows generally involves solving large-scale problems. In this paper we consider the stream-tube method in three-dimensional duct flows. The analysis uses the concept of stream tubes in a mapped computational domain of the physical domain where the streamlines are parallel and straight. The incompressibility equation is automatically verified and the primary unknowns of the problem are, in addition to the pressure, the transformation functions between the two domains. It is also shown that the flow may be computed by considering successive subdomains (the stream tubes). This results in a reduction of computing time and storage area. Incompressible viscous and elastic liquids involving memory-integral equations may be considered in the flow simulations. This part of the paper examines three-dimensional flows of Newtonian fluids. The method is applied to the flow in a duct involving a threefold rotational symmetry, where the discretized relevant equations are solved by using the Levenberg-Marquardt algorithm.     

Numerical simulation of three-dimensional flow-induced microstructure in a simplified prosthetic hip joint with nematic liquid crystal lubricant

The nature of liquid crystalline materials leads to a preferred direction of molecules in the vicinity of solid surfaces that gives them outstanding tribological properties. Intrinsic molecular order of liquid crystalline materials close to the solid boundaries protects the rubbing surfaces against wear. Due to the bio-compatible nature of most lyotropic liquid crystalline materials, they have been considered as viable candidates to be used as bio-lubricants. In order to understand the complex flow patterns and microstructure of liquid crystals, in this paper, start-up flow-induced microstructure of a nematic liquid crystal in a simplified capsular space of prosthetic hip joint was studied using the Landau-de Gennes nematodynamic theory. Flow streamlines, dimensionless pressure distribution, and rheological properties for a liquid crystal and for synovial fluid affected by rheumatoid arthritis (RA) were presented and compared. The liquid crystals exhibited higher degrees of net pressure lifting force across the capsular gap while forming an ordered molecular layer close to the solid surfaces that protects the surface against wearing mechanism while decreasing the coefficient of friction (COF). Formation of molecular microstructure in vicinity of solid surfaces with perpendicular orientation to the normal surface vector was observed.     

Numerical solutions of the shallow water equations with discontinuous bed topography

A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with z_b^‐ for the left and z_b⁺ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd.     

复杂应力状态下木材力学性能的数值模拟

针对木材复杂的各向异性材料特点,建立了能反映木材正交各向异性弹性、抗拉和抗压强度不等、抗拉或抗剪时发生脆性破坏而受压时发生塑性变形等特性的本构模型。将木材弹性应力—应变关系简化为正交各向异性;选用Yamada-Sun强度准则来判断木材抗压时是否屈服,抗拉或抗剪时是否发生应变软化;通过引入损伤因子和弹性应变能,建立了木材...     

Numerical simulation of quasi-static compression on a complex rubber foam

A complex rubber foam under quasi-static compression is simulated using the finite element method(FEM). The present work sets up the phenomenological constitutive model for the silicon rubber. The computerized tomography(CT) technique is utilized to reconstruct the real complex foam geometries. The quasi-static uniaxial compression on the foam is simulated in ABAQUS. The present work obtains the stress response as the nominal strain nearly reaches 80% and the foam exhibits hyper-elastic behavior. The FEM results achieve good agreements with the data obtained from the multi-scale simulation and the tests as the nominal strain is less than 60%.     

NUMERICAL SIMULATION OF FLOW OF HIGHLY VISCOELASTIC FLOW IN THREE－DIMENSIONAL VARYING THICK SLIT CHANNEL

（杨伯源）（李勇）ＮＵＭＥＲＩＣＡＬＳＩＭＵＬＡＴＩＯＮＯＦＦＬＯＷＯＦＨＩＧＨＬＹＶＩＳＣＯＥＬＡＳＴＩＣＦＬＯＷＩＮＴＨＲＥＥ－ＤＩＭＥＮＳＩＯＮＡＬＶＡＲＹＩＮＧＴＨＩＣＫＳＬＩＴＣＨＡＮＮＥＬ￥ＹａｎｇＢｏｙｕａｎ；ＬｉＹｏｎｇ（Ｄｅｐａｒｔ...