Progress in Geometry Modeling and Mesh Generation Toward the CFD Vision 2030

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.

Future aerospace vehicles like hybrid wing/body, truss-braced wing, and “double bubble” would have pressurized noncircular fuselage structures and complex wing geometry. Traditional aircraft designs have led to the confidence and experience of designing such structures using the knowledge base built over the years and the resulting rules of thumb. However, there is a lack of experience of load calculations and design of complex, multifunctional, aircraft structural concepts for future aerospace vehicles. Designing such structures will require a physics-based optimization framework. Therefore, a new optimization framework, EBF3PanelOpt, is being developed. Commercial software MD-PATRAN (geometry modeling and mesh generation) and MD-NASTRAN (finite-element analysis) are integrated in EBF3PanelOpt framework using the Python programming environment to design stiffened panels with curvilinear stiffeners. Currently, EBF3PanelOpt optimizes the stiffened panel with curvilinear blade stiffeners, where the loads ar...

This paper presents a systematic literature review on advancements and applications of Finite Element Methods (FEM) and Laser Scanning Documentation (LSD) in Cultural Heritage Management. FEM is a numerical technique widely used in engineering and scientific disciplines for solving complex problems by dividing them into smaller, more manageable elements. LSD is a method for capturing and digitizing real-world objects and environments using laser scanning technology. The objective of this review is to explore recent advancements and diverse applications of FEM and LSD, as well as their combined utilization for enhanced analysis and documentation, and identify research gaps. Literature search was conducted systematically, covering research articles in the Scopus, Web of Science and ScienceDirect databases. The review further investigates the integration of LSD with FEM, focusing on the use of laser scanning technologies for accurate geometry acquisition, mesh generation, and model validation in the field of Cultural Heritage. A total of 60 articles were identified, on which data analysis was performed using thematic analysis. As a result, seven thematic areas were identified: Structural Assessment, Cloud2FEM Methods, Modeling, Deformation, Techniques, Diagnostics and Digital Twins (DTs). The findings of this review demonstrate a limited range of applications where FEM and LSD have been successfully employed. The review identifies emerging trends and future directions in the field and techniques to optimize FEM simulations and enhance LSD data processing. It provides a comprehensive overview of advancements and applications of FEM and LSD and identifies the need for further research, especially in integration of FEM and LSD in cultural heritage documentation.

We present a simple and robust Matlab code for polygonal mesh generation that relies on an implicit description of the domain geometry. The mesh generator can provide, among other things, the input needed for finite element and optimization codes that use linear convex polygons. In topology optimization, polygonal discretizations have been shown not to be susceptible to numerical instabilities such as checkerboard patterns in contrast to lower order triangular and quadrilaterial meshes. Also, the use of polygonal elements makes possible meshing of complicated geometries with a self-contained Matlab code. The main ingredients of the present mesh generator are the implicit description of the domain and the centroidal Voronoi diagrams used for its discretization. The signed distance function provides all the essential information about the domain geometry and offers great flexibility to construct a large class of domains via algebraic expressions. Examples are provided to illustrate the capabilities of the code, which is compact and has fewer than 135 lines.

In this paper we present our efforts to parallelize an unstructured quadrilateral mesh generator. Its serial version is based on the divider-and-conquer idea, and mainly includes two stages, i.e. geometry decomposition and mesh generation. Both stages are parallelized separately. A couple of parallel models are introduced and compared to parallelize the stage of geometry decomposition. A fine-grain level parallel algorithm proves preferable to that based on the task-dependency tree, with which the load imbalance brought by the improper utilization of the symmetry of the vertex pair matrix is removed nicely. Since the number of elements in sub-domains could be pre-computed before meshing, a simple static load balancing scheme is investigated, and the effect of granularity is also discussed briefly. Finally, experiments are designed to evaluate the performance of the parallel mesh generator in detail.

INTERACTIVE MESH GENERATION IN SOLID DYNAMICS HYDROCODES

This paper discusses current work on STRUCTURAL ASPECTS OF the design optimization of a Truss Braced Wing (TBW) configuration. These wings offer significat potential for performance improvements in terms of fuel efficiency, but also offer challenges for a structural designer. The details of the structural analysis and design methodology are presented. Two different design methodologies are discussed: structural sizing based on beam idealization considering only bending stiffness and static analysis, and a finite element based sizing optimization approach including aeroelastic effects. The paper reports all aspects of the two approaches: design parameterization, model geometry and mesh generation, analysis and optimization. The first approach has been used in the past at Virginia Tech for Multidisciplinary Design Optimization (MDO) studies of a Strut-Braced Wing (SBW), and extensions to sizing of a more general TBW configuration are discussed. The second approach is used to perform some parametric studies presented here. Comparative studies are performed for wings designed for rigid and flexible trim subject to static stress constraints. The aeroelastic performance of some TBW configurations is investigated. Only structural sizing parameters are treated as design variables. Conclusions are drawn from these results for guidance to the ongoing MDO studies of the TBW, to be reported in future papers.

Texture mapping is a common operation to increase the realism of three-dimensional meshes at low cost. We propose a new texture optimization algorithm based on the reduction of the physical space allotted to the texture image. Our algorithm optimizes the use of texture space by computing a warping function for the image and new texture coordinates. Neither the mesh geometry nor its connectivity are modified by the optimization. Our method uniformly distributes frequency content of the image in the spatial domain. In other words, the image is stretched in high frequency areas, whereas low frequency regions are shrunk. We also take into account distortions introduced by the mapping onto the model geometry in this process. The resulting image can be resampled at lower rate while preserving its original details. The unwarping is performed by the texture mapping function. Hence, the space-optimized texture is stored as-is in texture memory and is fully supported by current graphics hardware. We present several examples showing that our method significantly decreases texture memory usage without noticeable loss in visual quality.

Electromagnetic (EM) methods are important geophysical tools for mineral exploration. Forward and inverse computer modeling are commonly used to interpret EM data. Real-life geology can be complex, and our computer modeling tools need to faithfully represent subsurface features to achieve accurate data interpretation. Traditional rectilinear meshes are less flexible and have difficulty conforming to the complex geometries of realistic geologic models, resulting in large numbers of mesh cells. In contrast, unstructured grids can represent complex geologic structures efficiently and accurately. However, building realistic geologic models and discretizing these models with unstructured grids suitable for EM modeling can be difficult and requires significant effort and specialized computer software tools. Therefore, it is important to develop workflows that can be used to facilitate model building and mesh generation. We have developed a procedure that can be used to build arbitrarily complex geologic models with topography using unstructured grids and a finite-volume time-domain code to calculate EM responses. We present an example of a trial-and-error modeling approach applied to a real data set collected at a uranium exploration project in the Athabasca Basin in Canada. The uranium mineralization is closely related to graphitic fault conductors in the basement. The deep burial depth and small thickness of the graphitic fault conductors demand accurate data interpretation results to guide subsequent drill testing. Our trial-and-error modeling approach builds initial realistic geologic models based on known geology and downhole data and creates initial geoelectrical models based on physical property measurements. Then, the initial model is iteratively refined based on the match between modeled and real data. We show that the modeling method can obtain 3D geoelectrical models that conform to known geology while achieving a good match between modeled and real data. The method can also provide guidance of where future drill holes should be directed.

Today automatic meshing of CAD geometry is the most common method of FEM mesh generation. However, to get results of acceptable accuracy with universal meshing algorithms it is necessary to use rather small-sized elements which leads to high memory and CPU time consumption. Furthermore, the irregularity of automatically generatated meshes makes it difficult to create well-defined local areas with different material properties. A solution for this problem is the application of predefined building blocks (FEM-Features) which contain algorithms for a problem-adapted mesh generation. These building blocks may be realised as in an object-oriented modelling system. By employing interface objects, it is easy to combine design objects to form complex geometries. The technique is explained by an example.

This paper summarizes the High-Order Technical Focus Group (HO-TFG) submissions for the joint 4th AIAA High Lift Prediction (HLPW-4) and 3rd Geometry and Mesh Generation Workshop (GMGW-3). The goal of the workshop was to assess the state-of-the-art in mesh generation and computational fluid dynamics software. The Common Research Model High-Lift (CRM-HL) variant served as the primary focus of the workshop, and a two-dimensional airfoil section from the CRM-HL was used as a verification test case. The HO-TFG was tasked with generating high-order curved meshes for both geometries, and computing high-order solutions using both Reynolds-averaged Navier–Stokes and scale-resolving formulations. While limited by computational resources, the final results demonstrate the potential of higher-order methods to increase solution accuracy with a lower degree-of-freedom count relative to second-order discretizations.

The article presents the results of a theoretical study on determining the suitability of using electrical contact gaskets (ECG) in industrial conditions (Castner direct graphitization furnaces), made of coke-pitch composite using additive technologies based on the Fused Deposition Modeling (FDM) method.
 Numerical analysis of the physical state of ECG under the conditions of industrial application was performed on the basis of the mathematical statement of the thermo-elastic-plasticity problem and the algorithm of implicit inverse mapping of its solution based on the finite element method in the Mathcad programming environment. To construct the geometry and tetraid mesh of the ECG model, a freely open program code was used - the Gmsh CAD system for grid generation, and for the visualization of the results of physical field calculations, the free open program code ParaView was used.
 The study of the thermo-elastic-plastic state of ECG under the conditions of the graphitization process in Castner furnaces was carried out in the temperature range up to 900 °С, at which the thermoplastic properties of the material are manifested. At the same time, such physical fields of ECG were analyzed as temperature distribution, resulting displacements, equivalent elastic stresses according to Mises, equivalent total, elastic and plastic deformations according to Mises, and the volume fraction of ECG material in a plastic state, depending on the temperature level and radial gradient temperatures (radial temperature difference) of electrical contact gaskets.
 Numerical simulation of the thermo-elastic-plastic state of the ECG was carried out under the conditions of force loading by external pressure on the lateral surface of the gasket of 2.5 MPa and different values ​​of the radial temperature difference in the range of 15–90 °C in the temperature range up to 900 °C. It was established that: at the stages of formation of semi-coke and coke in the material of the coke-pitch composite ECG under the thermomechanical conditions of operation of the Kastner furnace, a margin of strength of not less than unity was obtained; with the subsequent increase in the temperature level in the Castner furnace to 3000 °C and above, the raw material of ECG, as a result of thermal destruction, has already turned into coke and, therefore, its mechanical properties have become close to the mechanical properties of electrode blanks in columns that are subjected to graphitization. This gives reason to assert that the ECGs will not be mechanically destroyed during the entire graphitization campaign of the Castner furnace.
 On the basis of the analysis of the results of numerical simulation, the possibility of using ECGs made from dispersion-reinforced composite materials (coke-pitch mixtures) by the FDM method in the technology of graphitizing electrode products according to the Сastner method is substantiated.

NanoFEM platform is a new research environment based on the finite element method (FEM) for Technology CAD (TCAD) simulation and visualization of nanoscale devices, such as MOSFET transistors. The simulation in NanoFEM platform is based on solving partial differential equations corresponding to physical processes in modelled devices. A user or developer can provide these equations in a variational form format, and can define solver modules based on a FEM library with ability of automatic generation of finite elements and finite element forms. Solver modules can define fields for simulation and visualization and boundary conditions. Simple boundary conditions and material properties can also be specified directly in the graphical user interface. Geometry for the solved case can be defined either in graphical user interface or using Python scripting. Quality tetrahedral meshes necessary for FEM simulations are generated automatically. Visualization and post-processing is available in graphical user interface. We present some of related major existing solutions, namely open source geometry editors, mesh generators, computation libraries and visualization tools for FEM. We discuss major software components of the NanoFEM platform, i.e. Salome Platform and DOLFIN/FEniCS. We present an example simulation and visualization in NanoFEM platform. This is a simulation of the Poisson's equation on a 3D structure consisting of several geometry groups and materials forming a FinFET transistor with a mesh consisting of hundreds of thousands tetrahedrons. Because NanoFEM platform consists almost entirely of open source software components, others could eventually build similar solutions including, but not limited to TCAD device simulations after reading and reviewing the NanoFEM platform design and components.

Engineering optimization relies routinely on deterministic computer based design evaluations, typically comprising geometry creation, mesh generation and numerical simulation. Simple optimization routines tend to stall and require user intervention if a failure occurs at any of these stages. This motivated us to develop an optimization strategy based on surrogate modelling, which penalizes the likely failure regions of the design space without prior knowledge of their locations. A Gaussian process based design improvement expectation measure guides the search towards the feasible global optimum.

The high head Pelton turbines operate with extreme conditions. In case to need a sudden stop of operation, one of the important parts is jet deflector, which can be in push-out, or cut-of options. The paper presents the optimisation procedure of Pelton Turbine push-out jet deflector shape using numerical simulation of three-dimensional turbulent flow in order to minimize the forces, stresses, deformations and torque of jet deflector servomotor. The calculations are performed using the CFD package Ansys CFX. The steps for flow modelling, 3-D geometry definition, mesh generation, pre-processing and post-processing, as well as the optimised results obtained from the numerical simulation of the flow in the jet-deflector are presented. The work corresponds with the actual approach of methods development for flow simulation and calculations of Pelton Turbines. The kinematic and dynamic flow parameters are calculated based on CFD simulations. The results of the calculations represents reliable tool in the procedure of development and construction of Pelton Turbines parts.