Mesh Generation Method Research Articles

Improving mesh generation in finite element analysis for functional morphology approaches

Finite Element Analysis (FEA) is a powerful tool for functional morphology purposes. The accuracy of the final results depends on the mesh generation and the quality of the mesh. This is especially important in vertebrates as they present a complex biological structure, implying a complex geometry and, consequently, mesh generation should be performed with a consistent criterion. The aim of this paper is to discuss different ways to create a mesh of a vertebrate structure with different mesh generation methods and give recommendations on how to generate an efficient mesh without exceeding computational limits. Topics such as quality of the mesh, suitability of the mesh and reliability of the mesh are introduced to help the generation of the mesh. In this case, the use of convergence procedures assures the results of a computational solution and can be a good solution for the vertebrate models. The skull of a Chinese giant salamander (Andrias davidiamus) is used as a case study

Traveltime computation and OBN seismic record simulation for rugged seafloor in VTI medium

ABSTRACT To improve the computational accuracy of seismic traveltime for complex structures in inhomogeneous media, a mesh generation method that is adaptive to a rugged seafloor or interface is presented. A hybrid mesh discrete velocity model consisting of conventional rectangular mesh and irregular quadrilateral mesh is also proposed. The local traveltime equations for the hybrid mesh are derived from the linear traveltime interpolation (LTI) method and are shown to be stable. The relationship between the group velocity and group angle is converted into that between group velocity and interpolated point coordinates, extending the LTI ray tracing algorithm to multiwave simulation in vertical transversely isotropic (VTI) medium by multi-stage partitioning. Computations of the first arrival, reflection, multiple reflection, multiple transmission conversion, and multiple reflection conversion seismic waves in the VTI medium with rugged seafloor and complex structural interfaces are realised. The results show that the proposed method can adapt to the rugged seafloor and velocity interfaces of complex structures, resulting in higher computational accuracy of the traveltime and ray paths for ocean bottom node (OBN) seismic wave simulation. The accuracy of the proposed method is verified by comparison with the finite-difference method. This method will be useful for modelling of seismic waves, wavefield identification, and study of seismic wave propagation in OBN seismic observations.

Automatic triangular and triangular-prism mesh generation for overland and subsurface water flow simulations

In this paper, an automatic mesh generator is developed to simulate density-dependent water flow and transport problems in watershed systems. The two-dimensional (2D) triangular mesh is generated by global Delaunay triangulation, and the three-dimensional (3D) triangular-prism mesh is generated by vertical stretch. The implementation procedures of mesh generation are adjusted according to the interaction options of one-dimensional (1D) river, 2D overland, and 3D subsurface flows. An improved boundary point generation algorithm is proposed to maintain appropriate correspondence of points and edges according to the discrete patterns of river reaches and dead ends. Overlapped nodes are generated on zero-width river reaches and zero-width junctions without storage to construct the numerical models for 2D overland simulations. An additional triangular mesh generation method is proposed to create additional triangles for filling the empty water zones of finite-width river reaches, junctions with storage, finite-width ponds, lakes, and dead ends. The boundary loops bounding each water area are identified correctly, and the additional grids are created compatibly, aiming at the finite-depth and zero-depth patterns of storage zones. The computation equations of relevant parameters used for 3D stretch from triangles to triangular-prisms are built, and the 1D/2D/3D correspondence on river reaches, junctions, ponds, lakes, dead ends, and control structures is established. Finally, practical examples for discretizing real-world water areas are provided to demonstrate the robustness and effectiveness of our developed mesh generator by using the skewness as the mesh quality metric.

Parallel and automatic isotropic tetrahedral mesh generation of misaligned assemblies

Mesh generation is a challenge for high-performance numerical simulation, one reason is the complex geometry representing solution domain makes pre-processing difficult, especially for those assembly model containing hundreds and thousands of components involving misaligned interfaces between neighboring parts, and no state-of-art meshing tools could provide automatic functions for processing such complex model, another reason is hundreds of millions or even billions meshes should be generated quickly, which also exceeds the capabilities of available tools. In this paper, a novel parallel and automatic mesh generation method is proposed. Firstly, a surface imprinting algorithm based on the hybrid representation of discrete and continuous surfaces is proposed to process misaligned assembly model automatically. Then, the repaired assembly model is used as an input for a carefully designed mesh generation pipeline which connects the procedures of mesh sizing control, and three-level parallel tetrahedral mesh generation in order. This proposed method could produce hundreds of millions consistent mesh qualified for high-performance numerical simulation based on thousands of geometry components. Numerical experiments on a giant dam model and an integrated circuit board model demonstrates the effectiveness of this method.

A consistent parallel isotropic unstructured mesh generation method based on multi-phase SPH

In this paper, we propose a consistent parallel unstructured mesh generator based on a multi-phase SPH method. A set of physics-motivated modeling equations are developed to achieve the targets of domain decomposition, communication volume optimization and high-quality unstructured mesh generation simultaneously. A unified density field is defined as the target function for both partitioning the geometry and distributing the mesh-vertexes. A multi-phase Smoothing Particle Hydrodynamics (SPH) method is employed to solve the governing equations. All the optimization targets are achieved implicitly and consistently by the particle relaxation procedure without constructing triangulation/tetrahedralization explicitly. The target of communication reduction is achieved by introducing a surface tension model between distinct partitioning sub-domains, which are characterized by colored SPH particles. The resulting partitioning diagram features physically localized sub-domains and optimized interface communication. The target of optimizing the mesh quality is achieved by introducing a tailored equation-of-state (EOS) and a smooth isotropic kernel function. The mesh quality near the interface of neighboring sub-domains is improved by gradually removing the surface-tension force once a steady state is achieved. The proposed method is developed basing on a new parallel environment for multi-resolution SPH to exploit both coarse- and fine-grained parallelism. A set of benchmarks are conducted to verify that all the optimization targets are achieved consistently within the current framework.

Rapid Aerodynamic Calculation Method for Hypersonic Gliding Vehicle

The accuracy and efficiency are always conflict in the process of aerodynamic shape design, especially for hypersonic gliding vehicle (HGV). In this work, a rapid aerodynamic calculation method for hypersonic gliding vehicle is conducted, including shape parametric modelling, automatic mesh generation and rapid computational fluid dynamics (CFD) method. In details, the aerodynamic shapes of HGV are modelled by multi-section solids, which parameterized by class function/shape function transformation (CST) method and exponential function. Then, the computational meshes are generated automatically in two steps: one is generating surface mesh by Delaunay method, and another is generating volume mesh by adaptive Cartesian method. In order to minor the computational cost, the hypersonic aerodynamic are analysed by combining the Euler equation and the viscosity force. We have tested the accuracy and efficiency of this rapid aerodynamic calculation method in two flight states for a typical HGV. Compared with Navier Stokes (NS) equations, the results shown the errors of axial aerodynamic force are all less than 6%, but time costs are reduced in hundreds of times.

Bare-Hand Depth Perception Used in Augmented Reality Assembly Supporting

Augmented Reality (AR) had been used in mechanical assembly supporting. The current reported researches of AR assembly supporting system (ARASS) less concerned about the interaction between the operators' hands and virtual objects, especially on the occlusion between hands and virtual objects. The correct occlusion results would make ARASS more immersive and then the operators' interaction experiences were increased. To address this issue, this paper presented a bared-hand depth perception method that was designed for improving interaction experience in ARASS. The method was based on an interaction scene that was designed for AR mechanical assembly supporting. The method consisted of two components: hand segmentation and hand mesh generation. Hand segmentation method segmented operator's hand areas from depth image of scene and divided hand area into several sub areas that provided hand information. Hand surface mesh generation method generated hand surface meshes in 3D space based on the results of hand segmentation. The meshes were used to solve the occlusion problem of hand area in AR scene. The results verified that the bared-hand depth perception method could handle the occlusion between operator's hands and virtual objects correctly in real-time and recognize hand information in a limited space. The method could increase operators' depth perception of bared hand and make ARASS more immersive.

Numerical Study of Customised Mesh for Twin Screw Vacuum Pumps

The market for dry vacuum pumps is expected to increase in the coming years. Improving the efficiency of these machines requires comprehensive understanding of the flow dynamics within the working chambers. For this purpose, Computational Fluid Dynamics (CFD) is used as it offers better insight of the working process of a screw machine. In this study, a twin-screw vacuum pump with a large helix angle was analysed. This is a challenging case for CFD due to the limitations of grid generation in the transverse plane on the mesh quality. Two types of transverse meshes were generated using the software SCORGTM: casing to rotor non-conformal mesh and casing to rotor conformal mesh. The quality of the mesh in terms of aspect ratio and orthogonality were compared. The casing to rotor conformal mesh was used with ANSYS Fluent in order to obtain performance characteristics of the vacuum pump with the moderate helix angle of 62° such as the mass flow rate, rotor torque, and indicated power. The performance prediction results were satisfactory but the grid quality was relatively low with orthogonality reaching 40° and aspect ratio over 250 in some cases. As the helix angle increases the quality of mesh decreases. This paper presents the new development of a grid generation algorithm which uses the normal rack to map the fluid domain in the normal plane instead of the transverse plane. This new mesh generation method is expected to better align the computational grid with the main and leakage flows in order to significantly improve grid quality and reduce the numerical diffusion in case of screw machines with large helix angles.

Mesh Generation Methods and Moving Mesh Generation Using Developed Program

Mesh Generation Methods and Moving Mesh Generation Using Developed Program

Modal analysis of an airborne four-claw spherical stabilized platform based on ANSYS

In order to make the design of an airborne four-claw spherical stabilized platform better and determine whether the dynamic characteristics of the stabilized platform with new materials meet the design requirements, the three-dimensional model of the stabilized platform is established by using SolidWorks software. After reasonable simplification, the finite element model is established by importing ANSYS software. The first six natural frequencies and modes of an airborne four-claw spherical stabilized platform with new materials are obtained by modal analysis using ANSYS software. In the process of establishing the finite element model, different mesh generation methods are compared, and the mesh distortion is reduced from 0.74 to 0.38 by changing the mesh correlation and refinement. The comparison results show that the comprehensive mesh generation method can improve the quality of the mesh. The modal analysis results show that the designed four-claw spherical stabilized platform has no resonance in the frequency range of 80MPa ∼ 160MPa, which meets the design requirements.

Design and characteristic analysis of a four-claw spherical photoelectric stabilization platform

Airborne photoelectric stabilization platform is an important tracking and scanning equipment. In order to make the photoelectric stabilization platform smaller and lighter, a four-claw spherical photoelectric stabilization platform is proposed. The four-claw spherical photoelectric stabilization platform is driven by piezoelectric motors with parallel structure. SolidWorks software is used to build the three-dimensional model of the stabilized platform. After reasonable simplification, the finite element model is built in ANSYS software. Comparing different mesh generation methods in the process of establishing finite element model, the mesh distortion is reduced from 0.74 to 0.38 by changing the mesh correlation and refinement. Different materials are used to design the platform, and the mass of the platform under different materials is compared. The platform mass of the new material is 30.3% and 66.4% less than that of the other two materials. The static characteristics of the platform with new materials are analyzed, and the maximum deformation and stress of the platform are analyzed. The results show that the designed airborne spherical photoelectric stabilized platform with new materials meets the requirements of stiffness and strength, which provides a reference for the design of such platform.

Control of element shape and alignment for 3D solution adaptive mesh generation

A new 3D metric-aligned and metric-orthogonal method for anisotropic tetrahedral mesh generation is presented. The approach uses an advancing-point type point placement that aligns the elements with the underlying metric field and creates quasi-structured local topology. It is based on well-proven methodology and adds novel point-placement strategies that produce solution-adapted anisotropic meshes that are both sized and aligned with the solution gradients upon which the metric field is based. The overall methodology is extended to 3D from a previously developed 2D process. Results for analytical examples and a CFD simulation case are presented that demonstrate that aligned high-quality anisotropic tetrahedral meshes can be reliably generated.

Modeling and simulation of bullet-barrel interaction process for the damaged gun barrel

In this paper, the influences of bore damage on the bullet-barrel interaction process and the mechanism of how bore damage results in the end of a machine gun barrel's service life were studied, which had seldom been paid attention to in the past several decades. A novel finite element mesh generation method for the damaged barrel and a new transient coupled thermo-mechanical finite element (FE) model, which were based on the damage data obtained through barrel life tests, were developed to simulate the interior ballistics process of a coupled bullet-barrel system. Additionally, user subroutine VUAMP was developed in the FE model in order to take the bullet base pressure brought by propellant gas into account. Good consistency between the simulation results and the experimental results verified the preciseness of the proposed mesh generation method and the FE model. The simulation results show that the increase of bullet's initial disturbance at the muzzle and the variation of its surface morphology caused by bore damage are primarily responsible for the life end of this 12.7 mm machine gun barrel.

Space\u2013time VMS flow analysis of a turbocharger turbine with isogeometric discretization: computations with time-dependent and steady-inflow representations of the intake/exhaust cycle

Many of the computational challenges encountered in turbocharger-turbine flow analysis have been addressed by an integrated set of space–time (ST) computational methods. The core computational method is the ST variational multiscale (ST-VMS) method. The ST framework provides higher-order accuracy in general, and the VMS feature of the ST-VMS addresses the computational challenges associated with the multiscale nature of the unsteady flow. The moving-mesh feature of the ST framework enables high-resolution computation near the rotor surface. The ST slip interface (ST-SI) method enables moving-mesh computation of the spinning rotor. The mesh covering the rotor spins with it, and the SI between the spinning mesh and the rest of the mesh accurately connects the two sides of the solution. The ST Isogeometric Analysis enables more accurate representation of the turbine geometry and increased accuracy in the flow solution. The ST/NURBS Mesh Update Method enables exact representation of the mesh rotation. A general-purpose NURBS mesh generation method makes it easier to deal with the complex geometries involved. An SI also provides mesh generation flexibility in a general context by accurately connecting the two sides of the solution computed over nonmatching meshes, and that is enabling the use of nonmatching NURBS meshes in the computations. The computational analysis needs to cover a full intake/exhaust cycle, which is much longer than the turbine rotation cycle because of high rotation speeds, and the long duration required is an additional computational challenge. As one way of addressing that challenge, we propose here to calculate the turbine efficiency for the intake/exhaust cycle by interpolation from the efficiencies associated with a set of steady-inflow computations at different flow rates. The efficiencies obtained from the computations with time-dependent and steady-inflow representations of the intake/exhaust cycle compare well. This demonstrates that predicting the turbine performance from a set of steady-inflow computations is a good way of addressing the challenge associated with the multiple time scales.

Entropy generation analysis of wet-steam flow with variation of expansion rate using NURBS-based meshing technique

In this paper, the entropy generation is introduced as a criterion to analyze the impact of variation of expansion rate in a two-dimensional viscous wet-steam flow through stationary cascades of a steam turbine. In addition, for the first time the NURBS-based mesh generation method is introduced and assessed in the field of wet-steam flow. In the mentioned method, the computational grid with “curved” boundaries is generated by non-uniform rational B-spline (NURBS) surface that describes the geometry of the cascade. The results, which are validated against well-established experiments, reveal that compared to the typical H-type grid, employing the generated NURBS-based mesh significantly reduce the computational error of numerical simulation. According to the obtained results, the prediction errors of static pressure distribution and droplet average radius are reduced by 31% and 78.44%, respectively. Furthermore, it is observed that decreasing the expansion results in moving the nucleation zone toward downstream of the blade and increasing the rate of droplets nucleation. Additionally, the liquid mass fraction as well as the amount of entropy and total entropy generation in the fluid flow increases.

Methods for computation of flow-driven string dynamics in a pump and residence time

We present methods for computation of flow-driven string dynamics in a pump and related residence time. The string dynamics computations help us understand how the strings carried by a fluid interact with the pump surfaces, including the blades, and get stuck on or around those surfaces. The residence time computations help us to have a simplified but quick understanding of the string behavior. The core computational method is the Space–Time Variational Multiscale (ST-VMS) method, and the other key methods are the ST Isogeometric Analysis (ST-IGA), ST Slip Interface (ST-SI) method, ST/NURBS Mesh Update Method (STNMUM), a general-purpose NURBS mesh generation method for complex geometries, and a one-way-dependence model for the string dynamics. The ST-IGA with NURBS basis functions in space is used in both fluid mechanics and string structural dynamics. The ST framework provides higher-order accuracy. The VMS feature of the ST-VMS addresses the computational challenges associated with the turbulent nature of the unsteady flow, and the moving-mesh feature of the ST framework enables high-resolution computation near the rotor surface. The ST-SI enables moving-mesh computation of the spinning rotor. The mesh covering the rotor spins with it, and the SI between the spinning mesh and the rest of the mesh accurately connects the two sides of the solution. The ST-IGA enables more accurate representation of the pump geometry and increased accuracy in the flow solution. The IGA discretization also enables increased accuracy in the structural dynamics solution, as well as smoothness in the string shape and fluid dynamics forces computed on the string. The STNMUM enables exact representation of the mesh rotation. The general-purpose NURBS mesh generation method makes it easier to deal with the complex geometry we have here. With the one-way-dependence model, we compute the influence of the flow on the string dynamics, while avoiding the formidable task of computing the influence of the string on the flow, which we expect to be small.

Anisotropic mesh adaptation for steady convection-dominated problems based on bubble-type local mesh generation

ABSTRACTFor convection–diffusion equations, it is difficult to obtain accurate solutions due to the presence of layers when convection dominates the diffusion. In this work, a new anisotropic adaptive meshing algorithm for convection-dominated problems is designed to optimize the mesh alignment, size and aspect ratio. Three main techniques are used. First, the streamline upwind Petrov–Galerkin (SUPG) method is used to stabilize the numerical scheme. Second, the a posteriori error estimator is computed and a new metric tensor is deduced. Third, optimal anisotropic meshes are generated by the anisotropic bubble-type local mesh generation (ABLMG) method. Compared with other mesh generation strategies, high-quality mesh can be obtained efficiently. Our algorithm is tested on several examples and the numerical results show that the algorithm is robust.

A computational study of the effect of particle migration on the low-flow limit in slot coating of particle suspensions

Slot coating of particle suspensions is commonly used in the manufacturing of a wide variety of products. An important limit in this process is known as low-flow limit, which refers to the minimum wet film thickness that can be coated at a given substrate velocity. Recent studies have shown that shear-induced particle migration leads to a highly non-uniform particle distribution in the coating bead, playing an important role in the flow dynamics in slot coating of particulate systems. In this work, we extend the previous analyses to investigate the effects of particle migration on the low-flow limit in slot coating of particle suspensions at both dilute and concentrated conditions. As a first approximation, the suspension is modeled as a Newtonian liquid with a concentration-dependent viscosity, and shear-induced particle migration is described according to the diffusive flux model. The resulting set of governing equations is solved with a stabilized finite element method coupled with the elliptic mesh generation method for the free-boundary problem. The results show that particle migration changes the liquid viscosity near the downstream meniscus and strongly affects the force balance that sets the critical operating conditions at the low-flow limit. Remarkably, it was found that particle migration enlarges the operating window of the process when the suspensions are compared to a Newtonian liquid with the same bulk properties, especially at high concentrations.

An isotropic unstructured mesh generation method based on a fluid relaxation analogy

In this paper, we propose an unstructured mesh generation method based on Lagrangian-particle fluid relaxation, imposing a global optimization strategy. With the presumption that the geometry can be described as a zero level set, an adaptive isotropic mesh is generated by three steps. First, three characteristic fields based on three modeling equations are computed to define the target mesh-vertex distribution, i.e. target feature-size function and density function. The modeling solutions are computed on a multi-resolution Cartesian background mesh. Second, with a target particle density and a local smoothing-length interpolated from the target field on the background mesh, a set of physically-motivated model equations is developed and solved by an adaptive-smoothing-length Smoothed Particle Hydrodynamics (SPH) method. The relaxed particle distribution conforms well with the target functions while maintaining isotropy and smoothness inherently. Third, a parallel fast Delaunay triangulation method is developed based on the observation that a set of neighboring particles generates a locally valid Voronoi diagram at the interior of the domain. The incompleteness of near domain boundaries is handled by enforcing a symmetry boundary condition. A set of two-dimensional test cases shows the feasibility of the method. Numerical results demonstrate that the proposed method produces high-quality globally optimized adaptive isotropic meshes even for high geometric complexity.

Triangular mesh generation on free-form surfaces based on bubble dynamics simulation

Purpose Modern CAD systems facilitate the creation of any surface geometry imaginable, and complex surfaces for free-form grid shells are often represented by a set of Non-Uniform Rational B-Splines surface patches. But it remains an intractable issue how to generate high-quality grids on complex surfaces efficiently. To solve this issue, an automatic triangular mesh generation method is presented, based on bubble dynamics simulation and a modified Delaunay method. Design/methodology/approach A moderate amount of points are first distributed on a given surface. Next, by regarding the points as elastic bubbles with the same size and introducing the forces acting on bubbles, the motion control equations of bubbles are established. The equilibrium state of the bubble system is found by Verlet algorithm. Then, the Voronoi diagram on the surface is obtained by calculating the intersection between the surface and the three-dimensional (3D) Voronoi diagram of the centers of bubbles. Finally, a triangular mesh, Delaunay triangulation on the surface, is determined based on the dual change of the Voronoi diagram. Findings This method generates meshes on the surface directly, unlike mapping-based methods, avoiding the mapping distortion. Examples are given to demonstrate the successful execution of this method. The result also illustrates that this method is applicable to various surfaces in high automation level and resultant meshes are highly uniform and well-shaped. Originality/value Thus, this method provides the convenience for the geometry design of complex free-form grid structure.