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• conduct a parametric theoretical and numerical investigation of vibro-convective buoyancy-driven flow in differentially heated cylindrical containers
• investigate buoyant vibro-convective transport regimes in Bridgman-type systems with a focus on the use of vibration to suppress, or control, convection in order to achieve transport control during crystal growth.
• assess the feasibility of vibro-convective control as a means of offsetting "g-jitter" effects under microgravity conditions
• exchange information with the experimental group of Prof. R. Feigelson (Stanford University) and the group of Prof. E. Zharikov at the General Physics Institute (GPI) of the Russian Academy of Science who are undertaking a complementary experimental program.  

• The character of natural buoyant convection in rigidly contained inhomogeneous fluids can be drastically altered by vibration of the container boundaries or through the introduction of vibration sources into the interior of the fluid.
• Control of convective transport continues to be an important aspect of crystal growth research. Control of convection through static and rotating magnetic fields is being actively pursued by several groups. However, there are many instances, whether due to materials properties or other practical considerations, use of magnetic fields to induce stirring or suppress flow may not be an option. In such cases, vibrational control could become an attractive alternative.
• Vibrations are expected to play a crucial influence on heat and mass transfer onboard of the ISS (especially demonstrated during the recent Workshop held in ESTEC, Sept. 1998). Substantial vibrations will exist on ISS in a wide frequency spectrum.s
• While active vibration isolation can be a partial solution, it will not solve the problems that might arise due to the quasi-steady and very low-frequency acceleration components related to the gravity gradient and other orbital factors. Thus as an alternative to vibration isolation, one might envisage using vibration to either suppress flow or to provide flow regimes tailored to particular crystal growth experiments. These flows would not be accessible under terrestrial conditions due to strong natural convection effects.

• Buoyant vibro-convective motion can occur when oscillatory displacement of a container causes the acceleration of a container wall relative to the fluid inside.  
• The vibration may be viewed as a time-dependent modulation of steady gravity.
• In a closed container filled with a homogeneous fluid, the fluid will eventually move as a rigid body with the container. If, however, the density of the fluid is not homogeneous, fluid motion may ensue. This will depend on the orientation of the vibration directions with respect to the local density gradients and, in some cases, a critical threshold must also be exceeded.
• For density gradients caused by temperature, such motion is called thermo-vibrational.
• If the density of the fluid is homogeneous, but body forces are not homogeneous, fluid motion will take place (angular vibrations)

SUMMARY

• Efficient numerical method for 3D thermal vibrational convection is developed and implemented in the software; carefully tested; good agreement with experimental data is obtained
• A parametric study of the general buoyant-vibrational flow in a Bridgman growth system is being performed for both semiconductor and oxide melts
• The influence of angle between a direction of vibration and ampoule axis (temperature gradient) has been studied for high-frequency translational vibrations. Zero angle - no influence of the vibration on a flow. The maximum effect corresponds to an angle of 90 degrees. Here transport is significantly enhanced
• Influence of g-jitter and forced vibrations is been analyzed
• All kinds of vibration can cause average melt flow for a parameter range for practical semiconductor/oxide growth. Rotational (angular) and polarized vibrations result in more intensive melt flow than translational ones. Typical flow patterns for different flow regimes have been identified
• The vibrational influence is stronger for oxides than for semiconductors
• Simultaneous action of vibrations and magnetic field is currently being studied for semiconductor melts