MagIC v5.10: a two-dimensional message-passing interface (MPI) distribution for pseudo-spectral magnetohydrodynamics simulations in spherical geometry

We discuss two parallelization schemes for MagIC, an open-source, high-performance, pseudo-spectral code for the numerical solution of the magnetohydrodynamics equations in a rotating spherical shell. MagIC calculates the non-linear terms on a numerical grid in spherical coordinates, while the time step updates are performed on radial grid points with a spherical harmonic representation of the lateral directions. Several transforms are required to switch between the different representations. The established hybrid parallelization of MagIC uses message-passing interface (MPI) distribution in radius and relies on existing fast spherical transforms using OpenMP. Our new two-dimensional MPI decomposition implementation also distributes the latitudes or the azimuthal wavenumbers across the available MPI tasks and compute cores. We discuss several non-trivial algorithmic optimizations and the different data distribution layouts employed by our scheme. In particular, the two-dimensional distribution data layout yields a code that strongly scales well beyond the limit of the current one-dimensional distribution. We also show that the two-dimensional distribution implementation, although not yet fully optimized, can already be faster than the existing finely optimized hybrid parallelization when using many thousands of CPU cores. Our analysis indicates that the two-dimensional distribution variant can be further optimized to also surpass the performance of the one-dimensional distribution for a few thousand cores.

Penilaian Potensi Bencana Gempabumi dan Tsunami untuk Pelindungan Infrastruktur Migas dan PLTU di Cilacap, Jawa Tengah

Kilang minyak Pertamina dan PLTU Indonesia Power milik pemerintah di Kota Cilacap berada di wilayah dengan percepatan tanah puncak (PGA) = 0,4-0,5 g, percepatan pseudo spectral (PSA Ss) = 0,9-1 g dan (PSA S1) = 0,4-0,5g pada situs batuan SB, 2% probabilitas dalam 50 tahun (SNI 1726:2019). Penilaian potensi bencana gempabumi di kota ini pada kelas situs SC memiliki nilai SDS= 0,67g dan SD1= 0,43 g, sedangkan SDS = 0,73g dan SD1= 0,50 g pada kelas situs SD. Sesuai dengan ketentuan SNI 1726:2019, struktur gedung dan non gedung katagori risiko I, II, III dan IV pada kelas situs SC dan SD tersebut di atas berkatagori desain seismik D. Gaya geser desain seismik pada dasar silos tangki minyak adalah Qd = (0,24~ 0,34)*10496,4 x 103 =(2.309,21~2.519,14) x 103 (N). Potensi landaan tsunami dengan runup high berkisar antara 2,5-6 m. Bangunan gedung dan non gedung yang tidak sesuai dengan katagori desain seismik, dapat dilakukan penguatan atau retrofitting sesuai ketentuan. Untuk memperkecil gaya geser desain seismik pada dasar silos, dapat dilakukan dengan rekayasa keteknikan pada fondasi. Untuk meminimalisir bahaya tsunami dapat dibuat tembok penahan atau ditanam pemecah gelombang tsunami (sea wave tsunami breaker) di sekitar kilang minyak dan PLTU yang berhadapan langsung dengan laut. Jalur evakuasi tsunami berupa jalan lebar dengan arah selatan-utara dan bangunan bertingkat penyelamatan tsunami di sepanjang jalan di kota ini sebaiknya dibuat, khususnya di wilayah sekitar kilang minyak dan PLTU.Katakunci: Katagori risiko, katagori desain seismik, runup high, tsunami.

A pseudo-spectral Strang splitting method for linear dispersive problems with transparent boundary conditions

The present work proposes a second-order time splitting scheme for a linear dispersive equation with a variable advection coefficient subject to transparent boundary conditions. For its spatial discretization, a dual Petrov–Galerkin method is considered which gives spectral accuracy. The main difficulty in constructing a second-order splitting scheme in such a situation lies in the compatibility condition at the boundaries of the sub-problems. In particular, the presence of an inflow boundary condition in the advection part results in order reduction. To overcome this issue a modified Strang splitting scheme is introduced that retains second-order accuracy. For this numerical scheme a stability analysis is conducted. In addition, numerical results are shown to support the theoretical derivations.

Relational database used for ground-motion model development in the NGA-sub project

The Next-Generation Attenuation for subduction zone regions project (NGA-Sub) has developed data resources and ground motion models for global subduction zone regions. Here we describe the NGA-Sub database. To optimize the efficiency of data storage, access, and updating, data resources for the NGA-Sub project are organized into a relational database consisting of 20 tables containing data, metadata, and computed quantities (e.g. intensity measures, distances). A database schema relates fields in tables to each other through a series of primary and foreign keys. Model developers and other users mostly interact with the data through a flatfile generated as a time-stamped output of the database. We describe the structure of the relational database, the ground motions compiled for the project, and the means by which the data can be accessed. The database contains 71,340 three-component records from 1880 earthquakes from seven global subduction zone regions: Alaska, Central America and Mexico, Cascadia, Japan, New Zealand, South America, and Taiwan. These data were processed on a component-specific basis to minimize noise effects in the data and remove baseline drifts. Provided ground motion intensity measures include peak acceleration, peak velocity, and 5%-damped pseudo-spectral accelerations for a range of oscillator periods.

Mathematical Modeling of Soliton-Like Modes at Optical Rectification

We discuss the results of numerical modeling of forming optical-terahertz bullets at the process of optical rectification. Our calculations are based on a generalization of the well-known Yajima - Oikawa system, which describes the nonlinear interaction of short (optical) and long (terahertz) waves. The generalization relates to situations when the optical component is close to a few-cycle pulse. We study the influence of the number of optical pulse oscillations on the formation of an optical-terahertz bullet. We develop original nonlinear conservative pseudo-spectral difference scheme approximating the generalization of the Yajima-Oikawa system. It is realized with the help of FFT algorithm. Mathematical modeling demonstrates scheme efficiency.

Numerical simulation of a stabilizing Poiseuille-type polymer fluid flow in the channel with elliptical cross-section

This work is devoted to the numerical analysis of stabilization of the incompressible viscoelastic polymer fluid flow in the channel with elliptical cross-section. To describe the flow, mesoscopic rheological relations are used, and resolving non-stationary equations are derived. For solving them a special pseudo-spectral method is developed and implemented. As time increases, under certain conditions on the parameters of flow the solution to the non-stationary problem stabilizes and converges to the one of three branches of the solution to the corresponding stationary problem. It is shown that the variation of the parameters describing polymer microstructure leads to the switch of stabilized solution between these branches. The work provides the results of simulation of the flow stabilization and the analysis of the threshold values of parameters at which the switching occurs.