Spectral Element Methods for Compressible Fluid Flow
Spectral Element Library in Fortran for Fluids (SELF-Fluids) originally started as a project to put together tools for implementing spectral element methods in 3-D. The focus has been primarily developing tools for Nodal Discontinuous Galerkin Methods in 3-D. The refinement of these tools is spurred through the development of a high-end Compressible Navier Stokes fluids solver ( sfluid ) that helps guide improvements in the underlying SELF API. Additionally, this development paradigm provides the open source community with a high order fluids solver that runs on multicore and Nvidia GPU platforms.
The sfluid binary, which drives mesh generation, initial condition setup, and forward integration can be built for serial execution or with CUDA, OpenMP, MPI, MPI+CUDA, or MPI+OpenMP.
In July of 2018. SELF-Fluids was selected to participate in the SPEC project as a candidate benchmark application for HPC platforms.
Fast Equilibration of Ocean Tracers Software (FEOTS)
This project began during my PostDoc at Los Alamos National Laboratory. General Circulation Models (GCMs) are used to simulate the world's oceans and are expensive to run at eddy-resolving resolutions. Modeling the distribution of biogeochemical tracers in the oceans can help illuminate the impacts climate change has on ocean acidification, phytoplankton population distribution, and chemical ratios in ocean sediments. However, studying these impacts requires tracer distributions have reached a quasi-steady state; currently, estimates for the equilibration time scale is O( 1000 years ). Forward integration of a full GCM is far too costly to equilibrate ocean tracers.
FEOTS is a tool that assists in diagnosing GCM velocity and diffusion fields (transport operators) through the use of impulse fields and their response to advection and diffusion operators. These fields can be used to reconstruct transport operators that can be used to drive lightweight passive tracer simulations in an "offline mode". In addition to the lighter weight of this post-processing tool, posing the equilibration problem as a nonlinear minimization problem can reduce the number of iterations to reach an equilibrated tracer field
Gulf Stream Separation in General Circulation Models
Climate models currently struggle with the more traditional, coarse ( O(100 km) ) representation of the ocean. In these coarse ocean simulations, western boundary currents are notoriously difficult to model accurately. The modeled Gulf Stream is typically seen exhibiting a mean pathway that is north of observations, and is linked to a warm sea-surface temperature bias in the Mid-Atlantic Bight. Although increased resolution ( O(10 km) ) improves the modeled Gulf Stream position, there is no clean recipe for obtaining the proper pathway.
The 70 year history of literature on the Gulf Stream separation suggests that we have not reached a resolution on the dynamics that control the current’s pathway just south of the Mid-Atlantic Bight. Without a concrete knowledge on the separation dynamics, we cannot provide a clean recipe for accurately modeling the Gulf Stream at increased resolutions. Further, any reliable parameterization that yields a realistic Gulf Stream path must express the proper physics of separation.
The goal of this project was to determine what controls the Gulf Stream separation. To do so, I examined the results of a model intercomparison study and a set of numerical regional terraforming experiments. It is argued that the separation is governed by local dynamics that are most sensitive to the steepening of the continental shelf, consistent with the topographic wave arrest hypothesis of Stern (1998). A linear extension of Stern’s theory is provided, which illustrates that wave arrest is possible for a continuously stratified fluid.