| Author | Usman Riaz |
|---|---|
| Title | An Automated Modeling, Meshing, and Adaptive Framework for Tokamak Plasma Simulations |
| Year | 2024 |
| Journal | Ph.D. dissertation |
| Pages | 136 |
| School | Department of Mechanical, Aerospace, and Nuclear Engineering |
| Institution | Rensselaer Polytechnic Institute |
| Abstract | The accurate representation of a problem domain in terms of a geometric model and its effective discretization into a mesh plays an important role in achieving higher-quality simulation results and better computational efficiency. In this work, an automated modeling and meshing infrastructure with adaptive mesh control is developed to support large-scale fusion plasma simulations. The goal of the presented work is to develop a framework that accurately constructs the tokamak geometric models and discretize these model such that they meet the simulation needs of specific simulation codes. The modeling and meshing procedures for two fusion plasma codes, XGC and M3D-C1, are presented. An automated modeling and meshing framework, TOMMS, was developed to support the magnetic field-aligned and one-element deep meshing requirements of XGC. Recent developments to extend this infrastructure to better support the near flux field following meshing requirements of the XGC are presented. The first extension is a procedure to effectively represent a general set of O-point and X-points configurations. The second extension is a procedure to decompose the geometric model that includes the tokamak wall, selected flux curves and the separatrix curves in a manner such that an appropriate set of mesh generation procedures can be applied to each sub-region. The third extension is the application of appropriate mesh generation procedures in each sub-region to create the desired final mesh. Also, the procedures to provide the mesh information needed for the efficient execution of XGC computational operations are presented. The M3D-C1 code requires unstructured high-order triangular elements on the 2D poloidal plane for 2D simulations and 3D wedge elements which are constructed from the extrusion of 2D elements in the toroidal direction for 3D simulations. As part of work to extend M3D-C1 to a wide range of tokamak geometries, a generalized modeling and meshing infrastructure was developed to support the modeling of tokamaks with any configuration of physical features. The goal of this development is to support construction of model geometries with an arbitrary number of model loops and better control on mesh property settings on individual model entities. Moreover, a set of procedures to support a-priori mesh modifications to generate the initial M3D-C1 meshes with desired resolution are presented. In M3D-C1 simulations, the plasma equilibrium evolves over time. To effectively simulate those changes in plasma during a simulation, the mesh needs to be adapted dynamically. A mesh adaptation approach driven by an SPR error estimator is developed. 2.5D mesh adaptation procedure to extend 2D error-based mesh adaptation approach to 3D is also presented. |
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