We have investigated the sedimentation phenomena of colloidal dispersions composed of spherical ferromagnetic particles using Brownian dynamics simulations. We have attempted to clarify the conditions causing all particles to subside and high surface density thin films to form under strong magnetic field conditions by varying the applied magnetic field, magnetic force between particles, mass density, and solution temperature. The main results obtained are summarized as follows. As the mass density of the particles increases and magnetic force between particles decreases, cluster formation is difficult and, therefore, thin films are more likely to form. In addition, cluster formation is difficult because a strong magnetic field constrains the magnetic moment of a particle in the direction of the magnetic field, allowing a thin film to be formed. A limitation exists, however, where the thin film formation condition does not increase when the magnetic field exceeds a certain level. Furthermore, when the temperature of the liquid is low and the magnetic force between particles has an intermediate value, a unique cluster formed by two particles oriented in the magnetic field direction appears. However, as the temperature of the liquid increases, the cluster collapses because of the Brownian force, causing the desired thin film to be formed.

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  This study purpose is an improvement of convergence properties of an interface problem in the timeharmonic eddy current analysis based on the iterative domain decomposition method. A governing equation based on the A-φ method for the time-harmonic eddy current analysis is solved taking the magnetic vector potential A and the electric scalar potential φ as unknown functions. However, when a numerical model become huge, the convergence properties of the interface problem get worse. To overcome this difficulty, we introduce a pseudo-quadruple precision into iterative solvers in the interface problem and the subdomain problem. Convergence properties in the interface problem are improved by applying the pseudo-quadruple precision to both solvers for the interface problem and the subdomain problem.

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  Currently, in the design and evaluation of acoustic environments such as concert halls and live houses, the importance of acoustic analysis technology is increasing due to the dramatic performance improvement of computers in recent years. Due to the large-scale of the analysis area and expansion of the analysis frequency band, it is necessary to solve the large scale problem more than before in the wave acoustic analysis. Therefore, in this research, we are researching and developing a large-scale sound field analysis method based on the parallel finite element method. The iterative domain decomposition method is employed in the analysis method as parallel technique. In this research, pre-conditioners for the interface problem in the iterative domain decomposition method are considered. As a result, we have found that the balancing domain decomposition method is the most effective acoustical analysis. We also confirmed that the acoustic analysis code is very high accuracy with errors within the allowable range in a numerical analysis.

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