In JET, during some vertical displacement events (VDEs), the plasma current and position are toroidally asymmetric. These events are referred to as asymmetric VDEs (AVDEs). Analysis of the interactions among the current carrying systems reveals that the repelling force between the plasma and the vessel is of little significance in asymmetric events, even if it is the main symmetric repelling force. The sideways force acting on the vessel is shown to be due mainly to the interaction with the toroidal field of the asymmetric circulation of currents in the wall. The asymmetric current path in the vessel is then calculated analytically for a simplified geometry and used together with experimental data to estimate the sideways force on the vessel.

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A time-domain boundary integral equation (BIE) solution of the magnetic field integral equation (MFIE) for large electromagnetic scattering problems is presented. It employs isoparametric curvilinear quadratic elements to model fields, geometry, and time dependence, eliminating staircasing problems. The approach is implicit, which seems to provide both stability and permits arbitrary local mesh refinement to model geometrically difficult regions without the significant cost penalty explicit methods suffer. Error dependence on discretization is investigated; accurate results are obtained with as few as five nodes per wavelength. The performance both on large scatterers and on low-radar cross section (RCS) scatterers is demonstrated, including the six wavelength "NASA almond," two spheres, a thirteen wavelength missile, and a "high-Q" cavity.

SUMMARYThe GMRES (Generalized Minimal RESidual) iterative method is receiving increased attention as a solver for the large dense and unstructured matrices generated by boundary element elastostatic analyses. Existing published results are predominantly for two-dimensional problems, of only medium size. When these methods are applied to large three-dimensional problems, which actually do require efficient iterative methods for practical solution, they fail. This failure is exacerbated by the use of the pre-conditioning otherwise desirable in such problems. The cause of the failure is identified as being in the orthogonalization process, and is demonstrated by the divergence of the 'true' residual, and the residual calculated during the GMRES algorithm. It is shown that double precision arithmetic is required for only the small fraction of the work comprising the orthogonalization process, and exploitation of this largely removes the penalties associated with the use of double precision. Additionally, it is shown that full re-orthogonalization can be employed to overcome the lack of convergence, extending the applicability of the GMRES to significantly larger problems. The approach is demonstrated by solving three-dimensional problems comprising &4000 and &5000 equations.1997 by John Wiley & Sons, Ltd.

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