Purpose -The quality of crystals grown in space can be diversely affected by the melt flows induced by g-jitter associated with a space vehicle. This paper presents a full three-dimensional (3D) transient finite element analysis of the complex fluid flow and heat and mass transfer phenomena in a simplified Bridgman crystal growth configuration under the influence of g-jitter perturbations and magnetic fields. Design/methodology/approach -The model development is based on the Galerkin finite element solution of the magnetohydrodynamic governing equations describing the thermal convection and heat and mass transfer in the melt. A physics-based re-numbering algorithm is used to make the formidable 3D simulations computationally feasible. Simulations are made using steady microgravity, synthetic and real g-jitter data taken during a space flight. Findings -Numerical results show that g-jitter drives a complex, 3D, time dependent thermal convection and that velocity spikes in response to real g-jitter disturbances in space flights, resulting in irregular solute concentration distributions. An applied magnetic field provides an effective means to suppress the deleterious convection effects caused by g-jitter. Based on the simulations with applied magnetic fields of various strengths and orientations, the magnetic field aligned with the thermal gradient provides an optimal damping effect, and the stronger magnetic field is more effective in suppressing the g-jitter induced convection. While the convective flows and solute transport are complex and truly 3D, those in the symmetry plane parallel to the direction of g-jitter are essentially two-dimensional (2D), which may be approximated well by the widely used 2D models. Originality/value -The physics-based re-numbering algorithm has made possible the large scale finite element computations for 3D g-jitter flows in a magnetic field. The results indicate that an applied magnetic field can be effective in suppressing the g-jitter driven flows and thus enhance the quality of crystals grown in space. Paper type Research paper

A 3-D transient finite element model is developed to represent the oscillating thermal convection induced in a simplified Bridgman configuration filled with a Ga-doped germanium melt in microgravity under the influence of an external magnetic field. The model development is based on the penalty-finite element solution of the equations describing the transport of momentum, heat and solution and also the electromagnetic field distribution in the melt pool. Automatic time step control is applied to help speed up the calculations. Numerical performance of finite element simulations for this class of problems is discussed. In particular, various types of finite element formulations were studied to minimize the global matrix size and to investigate the computational efficiency. Numerical simulations are conducted to study the convection and magnetic damping effects as a function of frequency, directions and amplitudes of g-jitter and also the direction and magnitudes of the applied magnetic fields. The results show that the g-jitter driven flow is time dependent and complex convection pattern can develop in a 3-D configuration even when the thermal conditions are symmetric and that the convection can be suppressed with an applied magnetic field.