A Nonlinear Reduced Order Method with Overset Adaptive Cartesian/Unstructured Grid for Moving Body Simulations

An innovative hybrid nonlinear reduced order method (ROM) for deforming unstructured mesh and overset Cartesian grid for moving body problems is proposed. Utilizing the properties of a maximum 6 degrees of freedom (DOF) of a moving body, the proposed method computes the grid deformation using nonlinear large deformation theory to preserve the original grid quality under each DOF, so that no extra computations are required during the unsteady motion, just matrix-vector multiplications. The introduction of the overset Cartesian method will provide the flexibility when dealing with extremely large deformations and deterioration of grid quality. The present method has the merits of reduced grid distortion, minimum modification to an existing code, efficient moving grid methodology with simple matrix multiplication, and minimized needs of hole-cutting and donor cell searching of overset grid. The Phase I effort is on the testing of each individual components of the method, including nonlinear ROM for unstructured deformation; overset Cartesian grid for coupling with an unstructured grid; a controlling strategy and criteria to switch between the two methods; and the successful demonstration. In Phase II, an API will be developed so that the proposed methodology is generic enough to be utilized by a variety of solvers and flow functions. The technology will be demonstrated on USM3D solver.