Silvio Merazzi

Methods for the efficient calculation of the magnetohydrodynamic (MHD) stability properties of magnetically confined fusion

A magnetohydrodynamic (MHD) model is applied to the problem of the stability of magnetically confined ther monuclear plasmas of interest in the pursuit of fusion power. Previous studies limited to two-dimensional con figurations are here generalized to three-dimensional toroidal plasmas. Using finite Fourier representations in the angle coordinates and finite hybrid elements in the radial direction, we solve the discretized Euler-Lagrange equations to determine the linear stability properties of the plasma.

TERPSICHORE: A Three-Dimensional Ideal Magnetohydrodynamic Stability Program

The 3D ideal magnetohydrodynamic (MHD) stability code TERPSICHORE has been designed to take advantage of vector and microtasking capabilities of the latest generation CRAY computers. To keep the number of operations small most efficient algorithms have been applied in each computational step. The program investigates the stability properties of fusion reactor relevant plasma configurations confined by magnetic fields. For a typical 3D HELIAS configuration that has been considered we obtain an overall performance of 1.7 Gflops on an eight processor CRAY-YMP machine.

Virtual Engineering of Multi-Disciplinary Applications and the Significance of Seamless Accessibility of Geometry Data

The concept of virtual engineering (VEng) can be understood as a generalization of “multi-disciplinary problem solving”, an ever more used term in scientific computing. An abstract space consisting of the physical, the geometrical, and the cost function directions, called CGP, is introduced. The VEng problem can be seen as a complex manifold embedded in this space. Common standard data formats, unified data access, as well as open, non monolithic systems, are discussed. These contribute to smoothing the sharp edges and closing the gaps of the manifold. The significance of seamless accessibility of data is illustrated by means of the tightly coupled fluid-structure interaction in aero-elasticity.

3d Magnetohydrodynamic Equilibria with Anisotropic Pressure

An energy functional given by W = integral integral integral d3x[B2/(2mu0) + p(parallel-to)/(GAMMA - 1)] is proposed as a variational principle to determine three-dimensional (3D) magnetohydrodynamic (MHD) equilibria with anisotropic plasma pressure. It is demonstrated that the minimisation of W using an inverse coordinate spectral method reproduces the force balance relations that govern the MHD equilibrium properties of 3D plasmas with p(parallel-to) not-equal p(parpendicular-to) that have nested magnetic flux surfaces. Numerical procedures already developed for the scalar pressure model can be easily extended to the anisotropic pressure model. Specifically, a steepest descent procedure coupled with the application of a preconditioning algorithm to improve the convergence behaviour has been employed to minimise the energy of the system. The numerical generation of 3D torsatron equilibria with highly localised anisotropic pressure distributions attests to the robustness of the method of solution considered.

Software-Development Strategies for Parallel Computer Architectures

Abstract As pragmatic users of high performance supercomputers, we believe that nowadays parallel computer architectures with disturbed memories are not yet mature to be used by a wide range of application engineers. A big effort should be made to bring these very promising computers closer to the users. One major flaw of massively parallel machines is that the programmer has to take care himself of the data flow which is often different on different parallel computers. To overcome this problem, we propose that data structures be standardized. The data base then can become an integrated part of the system and the data flow for a given algorithm can be easily prescribed. Fixing data structures forces the computer manufacturer to rather adapt his machine to users demands and not, as it happens now, the user has to adapt to the innovative computer science approach of the computer manufacturer. In this paper, we present data standards chosen for our ASTRID programming platform for research scientist and engineers, as well as a plasma physics application which won the Cray Gigaflop Performance Awards 1989 and 1990 and which was succesfully ported on an INTEL iPSC/2 hypercube.

VISCOELASTIC STABILITY OF SHELLS NUMERICAL ASPECTS

This paper describes some results of a current work on viscoelastic behaviour of composite structures made in collaboration with the Aeronautical Research Institute of Sweden.

PROBLEM-SOLVING ENVIRONMENT FOR PARALLEL COMPUTERS

A program environment is presented that enables a co-operative design of high-technology products demanding interdisciplinary computer simulations for their optimisation. The system includes a multi-site, multi-machine, distributed data manager accessible by a data monitor. A client-server concept supports the user of massively parallel machines. The exchange of data between different executable scientific application modules is performed through the data base. Special modules to define the geometry, to decompose the domain in subdomains, to construct adaptive meshes in each subdomain, and to represent graphically the results run on workstations. Direct and iterative matrix solvers are embedded in the system. They optimally run on massively parallel machines. As a demonstration of the system, the high frequency wave generator (Gyrotron) application is presented.

Three-Dimensional Ideal Magnetohydrodynamic Stability on Parallel Machines

On the path towards a thermonuclear fusion reactor there are several technological and physical uncertainties to be understood and solved. One of the most fundamental problems is the appearance of many sorts of instabilities which can either enhance the energy outflow or even destroy the magnetic confinement of the fusion plasma. The knowledge of such instabilities is a prerequisite to a good understanding of the behaviour of actual experiments, and to the design of new devices. Most of the effort is devoted to the study of axisymmetric toroidal configurations such as tokamaks or spheromaks and to helically twisted toroidal devices such as stellarators.

Ideal magnetohydrodynamic stability computations for three-dimensional magnetic fusion devices

Reference CRPP-ARTICLE-1991-020doi:10.1016/0045-7825(91)90067-GView record in Web of Science Record created on 2008-04-16, modified on 2017-05-12

Viscoelastic Stability Analysis of Shells

Geometrically nonlinear viscoelastic deformations of shell structures are analyzed. On the basis of linear viscoelastic materials the stress-strain relations of orthotropic layers are developed. The inelastic effects of viscoelasticity are inserted into a computer code by means of the principle of virtual work, and the resulting integration technique leads to nonlinear equations which are solved by the modified Newton-Raphson method. Examples of the viscoelastic collapse of shell structures are given.