202 research outputs found
Radial deformation of the earth by oceanic tidal loading
A high-degree spherical harmonic series is used to compute the radial deformation of the Earth by oceanic tidal loading. By exploiting fast numerical transforms, this approach is found to be much more efficient, but no less accurate, than the traditional Green's function approach. The method is used to derive an atlas of load tide maps for 10 constitutents of the NSWC ocean tide model
An Efficient Spectral Dynamical Core for Distributed Memory Computers
The practical question of whether the classical spectral transform method, widely used in atmospheric modeling, can be efficiently implemented on inexpensive commodity clusters is addressed. Typically, such clusters have limited cache and memory sizes. To demonstrate that these limitations can be overcome, the authors have built a spherical general circulation model dynamical core, called BOB (“Built on Beowulf”), which can solve either the shallow water equations or the atmospheric primitive equations in pressure coordinates.
That BOB is targeted for computing at high resolution on modestly sized and priced commodity clusters is reflected in four areas of its design. First, the associated Legendre polynomials (ALPs) are computed “on the fly” using a stable and accurate recursion relation. Second, an identity is employed that eliminates the storage of the derivatives of the ALPs. Both of these algorithmic choices reduce the memory footprint and memory bandwidth requirements of the spectral transform. Third, a cache-blocked and unrolled Legendre transform achieves a high performance level that resists deterioration as resolution is increased. Finally, the parallel implementation of BOB is transposition-based, employing load-balanced, one-dimensional decompositions in both latitude and wavenumber.
A number of standard tests is used to compare BOB's performance to two well-known codes—the Parallel Spectral Transform Shallow Water Model (PSTSWM) and the dynamical core of NCAR's Community Climate Model CCM3. Compared to PSTSWM, BOB shows better timing results, particularly at the higher resolutions where cache effects become important. BOB also shows better performance in its comparison with CCM3's dynamical core. With 16 processors, at a triangular spectral truncation of T85, it is roughly five times faster when computing the solution to the standard Held–Suarez test case, which involves 18 levels in the vertical. BOB also shows a significantly smaller memory footprint in these comparison tests
HSMA: An O(N) electrostatics package implemented in LAMMPS
We implement two recently developed fast Coulomb solvers, HSMA3D [J. Chem.
Phys. 149 (8) (2018) 084111] and HSMA2D [J. Chem. Phys. 152 (13) (2020)
134109], into a new user package HSMA for molecular dynamics simulation engine
LAMMPS. The HSMA package is designed for efficient and accurate modeling of
electrostatic interactions in 3D and 2D periodic systems with dielectric
effects at the O(N) cost. The implementation is hybrid MPI and OpenMP
parallelized and compatible with existing LAMMPS functionalities. The
vectorization technique following AVX512 instructions is adopted for
acceleration. To establish the validity of our implementation, we have
presented extensive comparisons to the widely used particle-particle
particle-mesh (PPPM) algorithm in LAMMPS and other dielectric solvers. With the
proper choice of algorithm parameters and parallelization setup, the package
enables calculations of electrostatic interactions that outperform the standard
PPPM in speed for a wide range of particle numbers
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