Sandia Labs FY22 Laboratory Directed Research & Development Annual Report

CUTTING-EDGE METHODS AND TECHNIQUES ALLOW ACCURATE PREDICTION OF UHF WAVE PROPAGATION IN MISSION APPLICATIONS.

Predicting ultra-high frequency (UHF) wave propagation is important to many civilian and defense applications. Traditional finite element (FE) methods in the Sierra Mechanics code suite provide accurate prediction of structural response up to mid-frequencies. As frequency increases, pollution error limits prediction accuracy. This project developed and implemented cutting-edge numerical methods and techniques allowing accurate prediction at ultra-high frequencies. Pollution-mitigating higher-order elements were extended to elastodynamics in Sierra/Structural Dynamics. The pollution-limiting Discontinuous Petrov-Galerkin (DPG) method, developed

by Professor Leszek Demkowicz at Sandia Alliance partner University of Texas at Austin, was implemented as a stand-alone application within the Sierra framework. The Trilinos Project was leveraged for faster implementation, code portability, and graphics processing unit capability. A novel preconditioner was developed in conjunction with matrix-free methods to reduce computational cost. Some achievements, crucial to the success of the current Resilient & Agile Deterrence Mission Campaign projects were applied and will extend to Sierra Mechanics. Recent publications include an article in the SIAM Journal on Scientific Computing . (PI: Jerry Rouse)

A two-dimensional time-harmonic acoustics problem was used to verify the DPG implementation. The problem is shown on the right (forcing at midspan on left side, absorbing boundary on the right). Below, the exact solution (derived analytically) is shown on the left, and the DPG prediction is on the right. The length and width are normalized by the wavelength (X/lambda, Y/lambda). There is good agreement with the exact solution for the high-frequency acoustic waves in this problem, which confirms the implementation is working properly.

51

LABORATORY DIRECTED RESEARCH & DEVELOPMENT