Abstract:
为避免复杂贴体网格的生成和动、静界面滑移网格技术插值带来的误差，提出采用浸入边界法模拟流体刚体的耦合运动.借助求解不可压缩N-S方程组的分步投影方法的思想，来求解基于浸入边界法的耦合系统方程.其中刚体边界离散点的作用力密度通过强制满足刚体边界的滑移条件（位移和速度一致）导出，结合刚体定轴旋转的动量矩定理，采用Newmark时间积分方法，实现对刚体运动特性的预测.同时，通过δ光滑函数，将刚体边界离散点的作用力密度转换到流体的欧拉网格点上，实现对流场速度的修正.在空间离散上，对流项采用Quick迎风格式，扩散项采用中心差分格式，采用2阶显式Adams-Bashforth法离散时间项.以雷诺数为300的圆柱绕流为基准数值算例，验证数值计算结果的可靠性. To avoid the deviation produced in the traditional body-fitted numerical methods and the complex interpolation for sliding mesh on the interface between stator and rotor, a new numerical simulation method was presented for studying on free rotation of rigid body about a fixed axis under fluid force. A mathematical model was established to describe the interaction between immersed rigid body and fluid based on the projection step method. In this paper, the moment source was not pre-calculated, but determined implicitly in such a way that velocity at the immersed boundary interpolated from the corrected velocity field accurately satisfied the no slip boundary conditions, also, the displacement and velocity of rigid body was updated according to the theorem of moment of momentum. The Quick upwind scheme and the second central scheme were applied to solve convection and diffusion terms respectively. The second explicit Adams-Bashforth method was used to the time discretization. Taking the flow over one circular cylinder with Reynolds number 300 as the basic numerical example, the present immersed boundary method(IBM) was validated.

Abstract:
传统CFD方法在振动钝体绕流计算中常借助动网格技术，网格再生任务繁重。针对于此，本文利用可在静止网格中计算动边界绕流问题的浸入边界算法（IBM），编写数值模拟程序，分别对竖向强迫正弦振动方柱（Re=UD/v=103、振幅恒定、振动频率变化）以及桥梁断面（Re=UB/v=7.5×103、振幅、振动频率均变化）展开气动特性和流场特征结构分析。初步研究结果表明，振幅恒定为方柱高度的14%时，其涡脱锁定区长度为0.06~0.2，锁定区后端（Stc>0.2）振动方柱涡脱频率回归静止涡脱频率；不同振幅下的桥梁断面阻力系数均在静止涡脱频率处产生峰值，桥梁断面升力系数则在此处均出现归零效应，且振幅越大，归零效应愈明显。 In conventional CFD method,dynamic mesh technique is always used in numerical simulation of flow past vibrating bodies,which would inevitably create a huge task of grid regeneration.To deal with this situation,Immersed Boundary Method (IBM),which can compute the moving boundary on the stable gird,is adopted in this paper to promote the calculation efficiency.The computation of flows around a harmonically oscillating square cylinder (Re=UD/v=103,constant oscillating amplitude,varying oscillation frequency) and a bridge section (Re=UB/v=7.5×103,varying oscillating frequency and amplitude) in transverse mode is carried out respectively to analyze theiraerodynamic characteristics.Preliminary research results indicate that the length of lock-in region is 0.06~0.2 when oscillating amplitude is fixed to 14% of the square cylinder's height.The vortex shedding of oscillating square cylinder moves back to stable condition beyond Stc=0.2.Mean drag coefficients of the oscillating bridge section under different oscillating amplitudes all reach maxmum values near the stable vortex shedding frequencies whereas mean lift coefficients of the oscillating bridge section all come back to zero at this point.

Abstract:
In this paper we present a numerical scheme to simulate a moving rigid body with arbitrary shape suspended in a rarefied gas. The rarefied gas is simulated by solving the Boltzmann equation using a DSMC particle method. The motion of the rigid body is governed by the Newton-Euler equations, where the force and the torque on the rigid body is computed from the momentum transfer of the gas molecules colliding with the body. On the other hand, the motion of the rigid body influences the gas flow in its surroundings. We validate the numerical results by testing the Einstein relation for Brownian motion of the suspended particle. The translational as well as the rotational degrees of freedom are taken into account. It is shown that the numerically computed translational and rotational diffusion coefficients converge to the theoretical values.

Abstract:
The numerical simulation of granular systems of even moderate size is a challenging computational problem. In most investigations, either Molecular Dynamics or Event-driven Molecular Dynamics is applied. Here we show that in certain cases, mainly (but not exclusively) for static granular packings, the Bottom-to-top Reconstruction method allows for the efficient simulation of very large systems. We apply the method to heap formation, granular flow in a rotating cylinder and to structure formation in nano-powders. We also present an efficient implementation of the algorithm in C++, including a benchmark.

Abstract:
We describe a fast direct numerical simulation (DNS) method that promises to directly characterise the hydraulic roughness of any given rough surface, from the hydraulically smooth to the fully rough regime. The method circumvents the unfavourable computational cost associated with simulating high-Reynolds-number flows by employing minimal-span channels (Jimenez & Moin 1991). Proof-of-concept simulations demonstrate that flows in minimal-span channels are sufficient for capturing the downward velocity shift, that is, the Hama roughness function, predicted by flows in full-span channels. We consider two sets of simulations, first with modelled roughness imposed by body forces, and second with explicit roughness described by roughness-conforming grids. Owing to the minimal cost, we are able to conduct DNSs with increasing roughness Reynolds numbers while maintaining a fixed blockage ratio, as is typical in full-scale applications. The present method promises a practical, fast and accurate tool for characterising hydraulic resistance directly from profilometry data of rough surfaces.

Abstract:
This paper studies the numerical solution of traveling singular sources problems. In such problems, a big challenge is the sources move with different speeds, which are described by some ordinary differential equations. A predictor-corrector algorithm is presented to simulate the position of singular sources. Then a moving mesh method in conjunction with domain decomposition is derived for the underlying PDE. According to the positions of the sources, the whole domain is splitted into several subdomains, where moving mesh equations are solved respectively. On the resulting mesh, the computation of jump $[\dot{u}]$ is avoided and the discretization of the underlying PDE is reduced into only two cases. In addition, the new method has a desired second-order of the spatial convergence. Numerical examples are presented to illustrate the convergence rates and the efficiency of the method. Blow-up phenomenon is also investigated for various motions of the sources.

Abstract:
Generally all Magnetic Resonance Imaging (MRI) techniques are affected by magnetic and electric properties of measured materials, resulting in errors in MR image. Using numerical simulation we can solve the effect of changes in homogeneity of static and RF magnetic fields caused by specimen made from conductive and/or magnetic material in MR tomograph. This paper deals with numerical simulation of material susceptibility influence to magnetic field.

Abstract:
Scalar Tensor Vector Gravity(STVG) is one of a modified gravity theory developed by John Moffat(2005). MOG is abbreviated name for this theory.This theory is added a massive vector field to Brans-Dicke theory. It can explain a galactic rotary curve and the structure formation without dark matter. Without dark energy,acceleration universe too. However,these are claims by the developer and collaboraters.This theory was only inspected by simple approximate calculation. Therefore it needs more objective verifications.We will carried out verification from the viewpoint of N-body simulation. Such study is already accomplished by Brandao(2010).However, they did not precisely formulate N-body simulation on MOG. This paper shows formulation of the N-body simulation on MOG more precisely.

Abstract:
We adopt cylindrical-coordinate FDTD algorithm to simulate and analyse a 0.4-m-long column configuration plasma antenna. FDTD method is useful for solving electromagnetic problems, especially when wave characteristics and plasma properties are self-consistently related to each other. Focus on the frequency from 75MHz to 400MHz, the input impedance and radiation efficiency of plasma antennas are computed. Numerical results show that, different from copper antenna, the characteristics of plasma antenna vary simultaneously with plasma frequency and collision frequency. The property can be used to construct dynamically reconfigurable antenna. The investigation is meaningful and instructional for the optimization of plasma antenna design.

Abstract:
Grid direction selection and grid size design are two important elements that need to be considered in the grid direction design in reservoir numerical simulation. Reservoir engineers normally utilize geological data (such as the distribution of fractures, low permeability zones,
faults and major stress) and simulation experiences to design the grid direction of simulation model qualitatively. The research of the paper indicates that the key to determine the grid direction is to determine the principal permeability direction. Under the circumstances of few static materials, a new grid direction determination method has been developed by using field data (well location map and inter-well permeability) on the bases of Darcy’s law and tensor analysis theory. The grid direction of WZ11-7 Oilfield simulation model has been determined using four production wells and two production zones (L_{1} and L_{3}) in WZ11-7-2 well group, the results are in conformity with the geological
studied major stress. Therefore, this method can give insights into the numerical simulation study.