INTERACTIVE MESH GENERATION IN SOLID DYNAMICS HYDROCODES

We present computational flow analysis of a vertical-axis wind turbine (VAWT) that has been proposed to also serve as a tsunami shelter. In addition to the three-blade rotor, the turbine has four support columns at the periphery. The columns support the turbine rotor and the shelter. Computational challenges encountered in flow analysis of wind turbines in general include accurate representation of the turbine geometry, multiscale unsteady flow, and moving-boundary flow associated with the rotor motion. The tsunami-shelter VAWT, because of its rather high geometric complexity, poses the additional challenge of reaching high accuracy in turbine-geometry representation and flow solution when the geometry is so complex. We address the challenges with a space–time (ST) computational method that integrates three special ST methods around the core, ST Variational Multiscale (ST-VMS) method, and mesh generation and improvement methods. The three special methods are the ST Slip Interface (ST-SI) method, ST Isogeometric Analysis (ST-IGA), and the ST/NURBS Mesh Update Method (STNMUM). The ST-discretization feature of the integrated method provides higher-order accuracy compared to standard discretization methods. The VMS feature 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 blades. 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 blade and other turbine geometries and increased accuracy in the flow solution. The STNMUM enables exact representation of the mesh rotation. A general-purpose NURBS mesh generation method makes it easier to deal with the complex turbine geometry. The quality of the mesh generated with this method is improved with a mesh relaxation method based on fiber-reinforced hyperelasticity and optimized zero-stress state. We present computations for the 2D and 3D cases. The computations show the effectiveness of our ST and mesh generation and relaxation methods in flow analysis of the tsunami-shelter VAWT.

MeshONet: A generalizable and efficient operator learning method for structured mesh generation.

An ANN-based element extraction method for automatic mesh generation

Three-dimensional finite element method (FEM) is widely used as an effective numerical simulation technique to solve the complex engineering problem. Usually, the more complex engineering problem has more complex structure and shape; the FEM simulation technique is that needs to discrete the structure and shape of the problem by mesh. In addition, the correct generation of mesh is one of the most significant issues that directly affect to the accuracy of the FEM simulation. The hexahedral mesh is better than tetrahedral mesh in solving the complex engineering problem. The common methods of hexahedral automatic mesh generation have been used in some commercial soft already, but its adaptation is not enough to solve for practical applications of the complex engineering problems. A new method of mesh generation technique was proposed by improved waveform mesh generating method, and realized by C++ developing program in Linux OS. The method could generate some effective and smoothly mesh models by quadrilateral element or hexahedron element, and not only generated revolution curve surface meshes, but also generated random meshes according to free functions too. The results shown that the hexahedral mesh models of the complex shapes were generated as the shape function apply to regular mesh side as a waveform constraint.

Computational Fluid Dynamics (CFD) methods have been developed into effective fluid simulation means to be used on the hydraulic design in the field of nuclear reactor. However, it is difficult to generate suitable mesh and select turbulence model for simulation because of the complex geometry structure and flow behavior in the pressure vessel. Based on CFX software, a hydraulic computation model of typical pressurized water reactor is established and the flow distribution at core inlet is analyzed. The simplified geometry model consists cold legs, downcomer, lower plenum, secondary support component, core support plate, and lower core plate. The computation model is divided into three parts for mesh generation, including the part of inlet and downcomer, the part of lower plenum and core inlet section, and the part of core. In order to reach the independence of grid several methods of mesh generation which contains different mesh density at local key parties are investigated to screen out the suitable mesh scheme. The k-ε, k-ω, and SST k-ω turbulence model are respectively used for simulation and the sensitivity of turbulence model at different locations of flow field is analyzed. The results show that the mass flow rate of the near wall flow field, computed by using k-ω turbulence model, is consistent with SST k-ω model, while the mass flow rate of central flow field computed by using k-ε turbulence agrees with SST k-ω model. The result computed by using k-ε turbulence model shows relatively uniform flow distribution at core inlet, which is more consistent with the measured data with the average difference of 3.1%. By using the k-ε model, the probability distribution of the difference between the calculated results and the experimental values follows the law of Normal distribution. The final coolant flow distribution at each orifice is evaluated, and the maximum normalized flow flux is found at center orifice while the flow rate at the edge of core is relatively lower.

A new method of unstructured mesh generation is presented. The advancing front method and Delauney triangulation have been commonly applied to it. In the former method, interior mesh nodes are generated based on the nodes on boundaries and parameters defined by the user. Unsuitable setting of parameters, however, may lead to failure in mesh generation. On the other hand, the latter method can accomplish mesh generation without failure, though the user has to set all the nodes. The present method, based on Delauney triangulation, requires the user to set only a few nodes on boundaries, and the other mesh nodes are generated automatically according to the curvature or proximity of boundaries. The perfomance of the presented method is illustrated in a region with multiple bodies.

A novel appro ach for generating unstructured meshes using elliptic smoothing is presented. Like structured mesh generation methods, the approach begins with the construction of a computational mesh. The computational mesh is used to solve elliptic partial differential equations that control grid point distributions and improve mesh quality. Two types of elliptic partial differential equations are employed; modified linear -elastic theory and Winslow equation s, with or without forcing functions . Results are included to il lustrate the use of these methods for unstructured mesh generation, mesh boundary shape modification, mesh untangling and mesh movement.

Quadrilateral Mesh Generation with Deferred Constraint Insertion

Delaunay method is a representative method in FEM. The quality of mesh generation by this method, however, depends on the allocation of nodes. Crossed Circle Method (CCM) was developed for solving this problem. CCM is the method of two-dimensional mesh generation that allocates nodes in advance only on a domain boundary and adds nodes automatically in the inside of domain. In this research, we developed the program that generates mesh automatically with three-dimensional tetrahedron elements using CCM. In addition, we checked our program with some mesh generation. CCM is based on Delaunay method. In Delaunay method, the circumscribed circle of the triangle does not contain any other nodes. When nodes except vertexes are contained in the circumscribed circle, the diagonal line of the quadrangle made from two adjoining triangles is swapped. In this research, we developed three-dimensional CCM, for tetrahedron elements and we proposed the following algorithm. First, when nodes except vertexes are contained inside the circumscribed sphere of a tetrahedron in the three-dimensional Delaunay method, the nodes are swapped, as shown in Figure 1. Tetrahedron elements will increase in number from two to three. Second, circumscribed sphere is calculated for three tetrahedrons after the swap, respectively. Only when the center of the circumscribed sphere is included in both of remaining two circumscribed spheres, it is investigated whether the existing node is in the near. When there is no existing node, the center-of-gravity point of the triangle of which is the center of three circumscribed spheres is added. Figure 2 is the example of mesh created by three-dimensional CCM. Some numerical examples showed the validity of this method using developed program.

Important problems in Computational Medicine exist that can benefit from the implementation of adaptive mesh refinement techniques. Biological systems are so inherently complex that only efficient models running on state of the art hardware can begin to simulate reality. To tackle the complex geometries associated with medical applications we present a general purpose mesh generation scheme based upon the Delaunay tessellation algorithm and an iterative point generator. In addition, automatic, two- and three-dimensional adaptive mesh refinement methods are presented that are derived from local and global estimates of the finite element error. Mesh generation and adaptive refinement techniques are utilized to obtain accurate approximations of bioelectric fields within anatomically correct models of the heart and human thorax. Specifically, we explore the simulation of cardiac defibrillation and the general forward and inverse problems in electrocardiography (ECG). Comparisons between uniform and adaptive refinement techniques are made to highlight the computational efficiency and accuracy of adaptive methods in the solution of field problems in computational medicine.

The program was divided into segments: (Week 1) geometric modeling and mesh generation (Weeks 2 and 3) error estimation and adaptive strategies. Participants in the program came from a wide variety of disciplines dealing with remarkably analogous problems in this area. Ideas were exchanged and interdisciplinary collaboration was initiated in informal contexts as well as in the talks and question periods. In the talks, a number of algorithms were described along with specific applications to problems of great current interest in various scientific and engineering disciplines. In this emerging field, participants developed criteria for evaluation of algorithms and established guidelines for selection of algorithms appropriate to any specific problem. Special features of a problem may include curved surfaces, complicated boundaries, evolving interfaces (such as occur in coating flows), and/or criticality of error estimation.

Purpose Automatic mesh generation is still a challenge problem for combustion fluid dynamics simulations because of the high-quality requirement and complexity of geometries. This paper aims to find an efficient automatic analysis model creation and mesh generation method to save the time for pre-processing in numerical simulations. Design/methodology/approach Based on the previous work, we explore effective model processing and mesh generation methods from practical engineering applications. Considering the automation and high quality requirement, we construct an automatic mesh generation procedure for combustion fluid dynamics problems. Findings The numerical results show that the procedure we proposed in this paper can automatically generate high quality mesh for combustion fluid dynamics simulations. The strategy of fluid model construction is time-saving and with high-precision. The mesh generation method in our procedure is automatic and efficient. Practical implications The procedure proposed in this paper is applicable to the practical engineering application model, such as aircraft simulation, aeroengine simulation and so on. The procedure has been integrated into an numerical simulation software. Originality/value The method proposed in this paper has very practical application value. It can be used in the practical application and saves a lot of manual processing time for numerical stimulation specialists.

The 1st AIAA Geometry and Mesh Generation Workshop (GMGW-1) was held in conjunction with the AIAA Aviation Forum and Exposition 2017 and in collaboration with the 3rd AIAA Computational Fluid Dynamics (CFD) High Lift Prediction Workshop (HiLiftPW-3). As the first AIAA workshop on these topics, GMGW-1's broad objectives were to assess the current state-of-the art in geometry preprocessing and mesh generation technology as well as software as applied to aircraft and spacecraft systems. The workshop was intended to identify and develop understanding of areas of needed improvement in terms of performance, accuracy, and applicability. It was also to provide a foundation for documenting best practices for geometry preprocessing and mesh generation. The genesis of GMGW-1 is found in the indictments levied against geometry preprocessing and mesh generation - not undeservedly - by the NASA CFD Vision 2030 Study. In order to create a reference against which future progress in geometry preprocessing and mesh generation can be measured, the organizers of GMGW-1, with the assistance of the organizers of HiLiftPW- 3, focused GMGW-1 on generation of meshes of the NASA High Lift Common Research Model (HL-CRM). Some of the generated meshes were provided for use by the participants in HiLiftPW-3. All meshes and the processes by which they were generated were analyzed by GMGW-1 as a first assessment of state of the art practices. The results of GMGW-1 added quantitative detail to known problem areas including geometry modeling, data interoperability, and amount of human intervention. They do provide a clear path toward a vision of geometry preprocessing and mesh generation in the year 2030. The next milepost along this path will be a second workshop.

An improved method for finite element mesh generation of geometrically complex structures with application to the skullbase

A new method for calculating the flow about or through complex bodies is presented. This method is designed to reduce the total analysis time by combining the best, or time saving, features of the structured and unstructured approaches. Automated grid generation procedures are used to produce single structured block grids. Automation is achieved by transforming all geometries to the same topology, such as a sphere in 3D and a circle in 2D. This procedure is called topology conversion. A second procedure, called structure conversion, is used to make a single structured surface grid on the homotopic body. A conventional grid generation method is then applied to discretize the flow volume. The resulting grid is a single structured block and is body conformed. A fast structured flow solver was used to obtain solutions. Bi-plane configurations are used for 2D examples. A duct with N AC AGO 12 cross-section is used for a 3D example. It is hoped that the present technology can be applied directly to Navier-Stokes simulations about complex bodies, such as a complete aircraft configuration with ducts or multiple bodies, and that the total analysis time required will be significantly less than that for the present structured or unstructured approaches.