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An h-adaptive Discontinuous Galerkin Method for laminar Compressible Navier-Stokes Equations on Curved mesh

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Transactions of Nanjing University of Aeronautics and Astronautics 2016年第5期33卷 566-575页

作者： Sun Qiang l yu Hongqiang Wu Yizhao College of Aerospace Engineering Nanjing University of Aeronautics and Astronautics Nanjing 210016 P.R. China

An h-adaptive method is developed for high-order discontinuous Galerkin methods(DGM)to solve the laminar compressible Navier-Stokes(N-S)equations on unstructured *** vorticity is regarded as the indicator of *** elements where the vorticity is larger than a pre-defined upper limit are refined,and those where the vorticity is smaller than a pre-defined lower limit are coarsened if they have been refined.A high-order geometric approximation of curved boundaries is adopted to ensure the *** results indicate that highly accurate numerical results can be obtained with the adaptive method at relatively low expense.

关键词： h-adaptivity high-order discontinuous Galerkin methods(DGM) N-S equations high-order boundary approximation

Fast OBJ file importing and parsing in CUDA

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Computational Visual Media 2015年第3期1卷 229-238页

作者： Aidan l.Possemiers Ickjai lee James Cook University

Alias – Wavefront OBJ meshes are a common text file type for transferring 3D mesh data between applications made by different ***, as the mesh complexity gets higher and denser, the files become larger and slower to *** paper explores the use of GPUs to accelerate the importing and parsing of OBJ files by studying file read-time, runtime, and load resistance. We propose a new method of reading and parsing that circumvents GPU architecture limitations and improves performance, seeing the new GPU method outperforms CPU methods with a 6×– 8× speedup. When running on a heavily loaded system, the new method only received an 80% performance hit, compared to the160% that the CPU methods received. The loaded GPU speedup compared to unloaded CPU methods was3.5×, and, when compared to loaded CPU methods,8×. These results demonstrate that the time is right for further research into the use of data-parallel GPU acceleration beyond that of computer graphics and high performance computing.

关键词： parsing OBJ vertex buffer object(VBO) general-purpose programming on the graphics processing unit(GPGPU) compute unified device architecture(CUDA)

Strength of adhesive contacts: Influence of contact geometry and material gradients

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Friction 2017年第3期5卷 308-325页

作者： Valentin l.POPOV Roman POHRT Qiang lI Institute of Mechanics Technische Universit(a)t Berlin Berlin 10623 GermanyNational Research Tomsk Polytechnic University Tomsk 634050 Russia Institute of Mechanics Technische Universit(a)t Berlin Berlin 10623 Germany

The strength of an adhesive contact between two bodies can strongly depend on the macroscopic and microscopic shape of the surfaces. In the past, the influence of roughness has been investigated thoroughly. However, even in the presence of perfectly smooth surfaces, geometry can come into play in form of the macroscopic shape of the contacting region. Here we present numerical and experimental results for contacts of rigid punches with flat but oddly shaped face contacting a soft, adhesive counterpart. When it is carefully pulled off, we find that in contrast to circular shapes, detachment occurs not instantaneously but detachment fronts start at pointed corners and travel inwards, until the final configuration is reached which for macroscopically isotropic shapes is almost circular. For elongated indenters, the final shape resembles the original one with rounded corners. We describe the influence of the shape of the stamp both experimentally and numerically. Numerical simulations are performed using a new formulation of the boundary element method for simulation of adhesive contacts suggested by Pohrt and Popov. It is based on a local, mesh dependent detachment criterion which is derived from the Griffith principle of balance of released elastic energy and the work of adhesion. The validation of the suggested method is made both by comparison with known analytical solutions and with experiments. The method is applied for simulating the detachment of flat-ended indenters with square, triangle or rectangular shape of cross-section as well as shapes with various kinds of faults and to “brushes”. The method is extended for describing power-law gradient media.

关键词： adhesion boundary element method (BEM) flat-ended indenters gradient media

Modeling particle sedimentation in viscous fluids with a coupled immersed boundary method and discrete element method

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Particuology 2017年第2期15卷 191-199页

作者： Sayed M. Derakhshani Dingena l. Schott Gabriel lodewijks Faculty of Mechanical Maritime and Materials Engineering Delft University of Technology Delft Netherlands Department of Mechanical Engineering Faculty of Engineering University of Isfahan Isfahan Iran

Numerical techniques have increasingly been used to model fluid–particle two-phase flows. Coupling the immersed boundary method （IBM） and discrete element method （DEM） is one promising approach for modeling particulate flows. In this study, IBM was coupled with DEM to improve the reliability and accuracy of IBM for determining the positions of particles during the sedimentation process within viscous fluids. The required ratio of the particle diameter to the grid size （D/dx） was determined by comparing the simulation results with the analytical solution and experimental data. A dynamic mesh refinement model was utilised in the IBM model to refine the computational fluid dynamics grid near the particles. In addition, an optimum coupling interval between the IBM and DEM models was determined based on the experimental results of a single particle sedimentation within silicon oil at a Reynolds number of 1.5. The experimental results and the analytical solution were then utilised to validate the IBM–DEM model at Reynolds numbers of 4.1, 11.6, and 31.9. Finally, the validated model was utilised to investigate the sedimentation process for more than one particle by modeling the drafting-kissing-tumbling process and the Boycott phenomenon. Benchmark tests showed that the IBM–DEM technique preserves the advantages of DEM for tracking a group of particles, while the IBM provides a reliable and accurate approach for modeling the particle–fluid interaction.

关键词： Immersed boundary method Discrete element method Particle sedimentation Boycott phenomenon

Changes in free amino acids and polyamine levels in Satsuma leaves in response to Asian citrus psyllid infestation and water stress

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Insect Science 2014年第6期21卷 707-716页

作者： Nasir S. A. Malik Jose l. Perez Madhurababu Kunta Joseph M. Patt Robert l. Mangan USDA-ARS ERRC 600 E Mermaid lane Wyndmoor PA 19038-8598 USDA-ARS SPARC 2881 F&B Road College Station TX 77845 Texas A&M University-Kingsville Citrus Center 312 North International Blvd Weslaeo TX 78596 U. S. Horticultural Research laboratory 2001 South Rock Road Fort Pierce FL 34945 Subtropical Horticultural Research Station 13601 Old Coulter Road Miami FL 33158 USDA-ARS 2413 E. Hwy 83 Weslaco TX 78596 USA

The effects of biotic and abiotic stresses on changes in amino acids and polyamine levels in Satsuma orange （Citrus unshiu; cultivar Owari） leaves were inves- tigated. Asian citrus psyllids Diaphorina citri （Kuwayama）（ACP） infestation was used to induce biotic stress while a water deficit was imposed to induce abiotic stress. Potted trees were infested by placing 50 psyllids on 3 citrus leaves enclosed in nylon mesh bags for 5 d. A parallel set of plants were kept water stressed by maintaining the soil at 20% water holding capacity for 5 d. levels of total free amino acids were higher in water stressed and ACP infested leaves. Polyamine putrescine increased in infested leaves but not in water stressed leaves. Proline was the most abundant amino acid and its levels significantly increased by both biotic and abiotic stresses. Proline levels in infested leaves were significantly higher than the water stressed leaves. Histidine, methionine, asparagine, arginine, serine, and leucine levels also increased significantly in infested leaves, but in water stressed leaves only leucine, methionine, and threonine increased. levels of amino acids, such as tyrosine, isoleucine, phenylalanine, glutamic acid, and alanine, declined in infested leaves. Under water stress asparagine, phenylalanine, serine, and histidine also declined compared to controls. This indicates that while proteolysis occurred under both stresses, metabolic conversion of amino acids was different under the two stresses. In ACP infested leaves some amino acids may be used as feeding material and/or converted into secondary metabolites for defense.

关键词： amino acids citrus Diaphorina citri polyamines

lattice Boltzmann Flux Solver:An Efficient Approach for Numerical Simulation of Fluid Flows

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Transactions of Nanjing University of Aeronautics and Astronautics 2014年第1期31卷 1-15页

作者： Shu Chang Wang Y Yang l M Wu J Department of Mechanical Engineering National University of Singapore College of Aerospace Engineering Nanjing University of Aeronautics and Astronautics

A lattice Boltzmann flux solver(lBFS)is presented for simulation of fluid *** the conventional computational fluid dynamics(CFD)solvers,the new solver also applies the finite volume method to discretize the governing differential equations,but the numerical flux at the cell interface is not evaluated by the smooth function approximation or Riemann ***,it is evaluated from local solution of lattice Boltzmann equation(lBE)at cell *** versions of lBFS are presented in this *** is to locally apply one-dimensional compressible lattice Boltzmann(lB)model along the normal direction to the cell interface for simulation of compressible inviscid flows with shock *** other is to locally apply multi-dimensional lB model at cell interface for simulation of incompressible viscous and inviscid *** present solver removes the drawbacks of conventional lattice Boltzmann method(lBM)such as limitation to uniform mesh,tie-up of mesh spacing and time interval,limitation to viscous *** examples show that the present solver can be well applied to simulate fluid flows with non-uniform mesh and curved boundary.

关键词： finite volume method flux solver compressible flow incompressible flow Navier-Stokes equation lattice Boltzmann equation

A Novel Staggered Semi-implicit Space-Time Discontinuous Galerkin Method for the Incompressible Navier-Stokes Equations

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Communications on Applied Mathematics and Computation 2021年第4期3卷 607-647页

作者： F.l.Romeo M.Dumbser M.Tavelli Department of Civil Environmental and Mechanical EngineeringUniversity of TrentoVia Mesiano 7738123 TrentoItaly

A new high-order accurate staggered semi-implicit space-time discontinuous Galerkin(DG)method is presented for the simulation of viscous incompressible flows on unstructured triangular grids in two space *** staggered DG scheme defines the discrete pressure on the primal triangular mesh,while the discrete velocity is defined on a staggered edge-based dual quadrilateral *** this paper,a new pair of equal-order-interpolation velocity-pressure finite elements is *** the primary triangular mesh(the pressure elements),the basis functions are piecewise polynomials of degree N and are allowed to jump on the boundaries of each *** the dual mesh instead(the velocity elements),the basis functions consist in the union of piecewise polynomials of degree N on the two subtriangles that compose each quadrilateral and are allowed to jump only on the dual element boundaries,while they are continuous *** other words,the basis functions on the dual mesh arc built by continuous finite elements on the *** choice allows the construction of an efficient,quadrature-free and memory saving *** our coupled space-time pressure correction formulation for the incompressible Navier-Stokes equations,the arbitrary high order of accuracy in time is achieved through tire use of time-dependent test and basis functions,in combination with simple and efficient Picard *** numerical tests on classical benchmarks confirm that the proposed method outperforms existing staggered semi-implicit space-time DG schemes,not only from a computer memory point of view,but also concerning the computational time.

关键词： Incompressible Navier-Stokes equations Semi-implicit space-time discontinuous Galerkin schemes Staggered unstructured meshes Space-time pressure correction method High-order accuracy in space and time

AN ADAPTIVE EFG-FE COUPlING METHOD FOR THE NUMERICAl SIMUlATION OF EXTRUSION PROCESSES

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Acta Metallurgica Sinica(English letters) 2008年第5期21卷 380-388页

作者： l.C. liu X.H. Doug C.X. li National Die ＆ Mold CAD Engineering Research Center Shanghai Jiaotong University Shanghai 200030 China

An adaptive EFG-FE coupling method is proposed and developed for the numerical simulation of lateral extrusion and forward-backward extrusion. Initially, the simulation has been implemented by using a conventional FE model. During the deforming process, mesh quality is checked at every incremental step. Distorted elements are automatically converted to EFG nodes, whereas, the less distorted elements are reserved. A new algorithm to generate EFG nodes and interface elements is presented. This method is capable of dealing with large deformation and has higher computational efficiency than using an EFG method wholly. Numerical results demonstrate that the adaptive EFG-FE coupling method has reasonable accuracy and is effective for local bulk metal forming such as extrusion processes.

关键词： meshless method Coupling method Numerical simulation Extrusion process

A node-based smoothed point interpolation method for dynamic analysis of rotating flexible beams

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Acta Mechanica Sinica 2018年第2期34卷 409-420页

作者： C.F.Du D.G.Zhang l.li G.R.liu College of Civil Science and Engineering Yangzhou University School of Sciences Nanjing University of Science and Technology School of Aerospace Systems University of Cincinnati

We proposed a mesh-free method, the called node-based smoothed point interpolation method(NS-PIM),for dynamic analysis of rotating beams. A gradient smoothing technique is used, and the requirements on the consistence of the displacement functions are further weakened. In static problems, the beams with three types of boundary conditions are analyzed, and the results are compared with the exact solution, which shows the effectiveness of this method and can provide an upper bound solution for the *** means that the NS-PIM makes the system soften. The NS-PIM is then further extended for solving a rigid-flexible coupled system dynamics problem, considering a rotating flexible cantilever beam. In this case, the rotating flexible cantilever beam considers not only the transverse deformations,but also the longitudinal deformations. The rigid-flexible coupled dynamic equations of the system are derived via employing lagrange’s equations of the second type. Simulation results of the NS-PIM are compared with those obtained using finite element method(FEM) and assumed mode method. It is found that compared with FEM, the NS-PIM has anti-ill solving ability under the same calculation conditions.

关键词： meshfree method NS-PIM Rigid-flexible coupled system dynamics Rotating beams Dynamic response