ALE有限元法解二维自由面流体大晃动问题

从Navier Stokes方程和连续性方程出发 ,在ALE描述下 ,用四边形单元对所求区域加以划分 ;并借助于Galerkin加权余量法导出相应的有限元方程组 ,在有限元计算中速度和压力均采用四节点线性插值函数 ;通过二维自由面流体大晃动问题实例的计算 ,给出相应的计算结果 ,阐明了该方法的优越性和局限性 .

用拉格朗日法求二维带自由面流体数值解

直接从 N-S方程和连续性方程出发 ,采用四边形元对所求区域加以划分 ;介绍了用拉格朗日有限元法求二维带自由面流体非线性数值解 ,通过实例计算 ,给出了相应结果 .在证明该方法有效性的基础上 ,讨论了粘性系数的大小对流体运动的影响 。

Simulation of Wave Impact on a Horizontal Deck Based on SPH Method

A numerical model was established for simulating wave impact on a horizontal deck by an improved incompressible smoothed particle hydrodynamics (ISPH). As a grid-less particle method, the ISPH method has been widely used in the free-surface hydrodynamic flows with good accuracy. The improvement includes the employment of a corrective function for enhancement of angular momentum conservation in a particle-based calculation and a new estimation method to predict the pressure on the horizontal deck. The simulation results show a good agreement with the experiment. The present numerical model can be used to study wave impact load on the horizontal deck.

A New Arrangement with Nonlinear Sidewalls for Tanker Ship Storage Panels

Sloshing phenomenon in a moving container is a complicated free surface flow problem. It has a wide range of engineering applications, especially in tanker ships and Liquefied Natural Gas (LNG) carriers. When the tank in these vehicles is partially filled, it is essential to be able to evaluate the fluid dynamic loads on tank perimeter. Different geometric shapes such as rectangular, cylindrical, elliptical, spherical and circular conical have been suggested for ship storage tanks by previous researchers. In this paper a numerical model is developed based on incompressible and inviscid fluid motion for the liquid sloshing phenomenon. The coupled BEM-FEM is used to solve the governing equations and nonlinear free surface boundary conditions. The results are validated for rectangular container using data obtained for a horizontal periodic sway motion. Using the results of this model a new arrangement of trapezoidal shapes with quadratic sidewalls is suggested for tanker ship storage panels. The suggested geometric shape not only has a maximum surrounded tank volume to the constant available volume, but also reduces the sloshing effects more efficiently than the existing geometric shapes.

Construction of Wave-free Potentials and Multipoles in a Two-layer Fluid Having Free-surface Boundary Condition with Higher-order Derivatives

There is a large class of problems in the field of fluid structure interaction where higher-order boundary conditions arise for a second-order partial differential equation. Various methods are being used to tackle these kind of mixed boundary-value problems associated with the Laplace’s equation （or Helmholtz equation） arising in the study of waves propagating through solids or fluids. One of the widely used methods in wave structure interaction is the multipole expansion method. This expansion involves a general combination of a regular wave, a wave source, a wave dipole and a regular wave-free part. The wave-free part can be further expanded in terms of wave-free multipoles which are termed as wave-free potentials. These are singular solutions of Laplace’s equation or two-dimensional Helmholz equation. Construction of these wave-free potentials and multipoles are presented here in a systematic manner for a number of situations such as two-dimensional non-oblique and oblique waves, three dimensional waves in two-layer fluid with free surface condition with higher order partial derivative are considered. In particular, these are obtained taking into account of the effect of the presence of surface tension at the free surface and also in the presence of an ice-cover modelled as a thin elastic plate. Also for limiting case, it can be shown that the multipoles and wave-free potential functions go over to the single layer multipoles and wave-free potential.

New Liquid Metal Experimental Loop

In this paper we report the rebuilding of liquid metal experimental loop （LMEL） to avoid loop danger in running. In the new loop, We have eliminated the hidden trouble of the inherent safety in the former loop, obtained more stable magnetic field region, upgraded the reliability of the data acquisition and processing. New LMEL can provide the more extensive experiments on MHD effects and their thermal-hydraulics on the liquid metal divertor and the liquid metal blanket.

A finite volume algorithm based on overlapping meshes for simulation of hydrodynamic problems

A finite volume algorithm was established in order to investigate two-dimensional hydrodynamic problems. These include viscous free surface flow interaction with free rigid bodies in the case of large and/or relative motions. Two-phase flow with complex deformations at the interface was simulated using a fractional step-volume of fluid algorithm. In addition, body motions were captured by an overlapping mesh system. Here, flow variables are transferred using a simple fully implicit non-conservative interpolation scheme which maintains the second-order accuracy of implemented spatial discretisation. Code was developed and an appropriate set of problems investigated. Results show good potential for development of a virtual hydrodynamics laboratory.

Numerical Simulation of MHD Jet Flows

Liquid metal free surface flows （films, jets and droplets） are considered as diverter/ limiter system and first wall in fusion reactor, but the knowledge Of liquid metal free surface under a non-uniform magnetic field is very limited. In this article, the stability of a jet flow under a gradient magnetic field is investigated, and its MHD effects are the top concern. Based on numerical simulation and experimental results, a simplified model is developed to analyze the MHD effects of the jet flow and to explain the reason why it can keep stable under a strong non-uniform magnetic field.

Implementation of the moving particle semi-implicit method on GPU

The Moving Particle Semi-implicit (MPS) method performs well in simulating violent free surface flow and hence becomes popular in the area of fluid flow simulation. However, the implementations of searching neighbouring particles and solving the large sparse matrix equations (Poisson-type equation) are very time-consuming. In order to utilize the tremendous power of parallel computation of Graphics Processing Units (GPU), this study has developed a GPU-based MPS model employing the Compute Unified Device Architecture (CUDA) on NVIDIA GTX 280. The efficient neighbourhood particle searching is done through an indirect method and the Poisson-type pressure equation is solved by the Bi-Conjugate Gradient (BiCG) method. Four different optimization levels for the present general parallel GPU-based MPS model are demonstrated. In addition, the elaborate optimization of GPU code is also discussed. A benchmark problem of dam-breaking flow is simulated using both codes of the present GPU-based MPS and the original CPU-based MPS. The comparisons between them show that the GPU-based MPS model outperforms 26 times the traditional CPU model.

Improved Implicit SPH Method for simulating free surface flows of power law fluids

Implicit smoothed particle hydrodynamics method has been proposed to overcome the problem that only very small time steps can be used for high viscosity fluids(such as power law fluids)in order to obtain a stable simulation.However,the pressure field is difficult to simulate correctly with this method because the numerical high-frequency noise on the pressure field cannot be removed.In this study,several improvements,which are the diffusive term in the continuity equation,the artificial viscosity and a simplified physical viscosity term in the momentum equation,are introduced,and a new boundary treatment is also proposed.The linear equations derived from the momentum equation are large-scale,sparse and positive definite but unsymmetrical,therefore,Conjugate Gradient Squared(CGS)is used to solve them.For the purpose of verifying the validity of the proposed method,Poiseuille flows with Newtonian and power law fluids are solved and compared with exact solution and traditional SPH.Drops of different fluid properties impacting a rigid wall are also simulated and compared with VOF solution.All the numerical results obtained by the proposed method agree well with available data.The proposed method shows the higher efficiency than traditional SPH and the less numerical noise on the pressure field and better stability than implicit SPH.

A Free Surface Sharpening Strategy Using Optimization Method

VOF method which consists in transporting a discontinuous marker variable is widely used to capture the free surface in computational fluid dynamics.There is numerical dissipation in simulations involving the transport of the marker.Numerical dissipation makes the free surface lose its physical nature.A free surface sharpening strategy based on optimization method is presented in the paper.The strategy can keep the location of the free surface and local mass conservation at both time,and can also keep free surface in a constant width.It is independent on the types of solvers and meshes.Two famous cases were chosen for verifying the free surface sharpening strategy performance.Results show that the strategy has a very good performance on keeping local mass conservation.The efficiency of prediction of the free surface is improved by applying the strategy.Accurate modeling of flow details such as drops can also be captured by this method.