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首页> 外文学位 >The modeling, simulation, and control of transport phenomena in a thermally destabilizing Bridgman crystal growth system.
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The modeling, simulation, and control of transport phenomena in a thermally destabilizing Bridgman crystal growth system.

机译：热不稳定的Bridgman晶体生长系统中的传输现象的建模，仿真和控制。

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This thesis presents a comprehensive examination of the modeling, simulation, and control of axisymmetric flows occurring in a vertical Bridgman crystal growth system with the melt underlying the crystal. The significant complexity and duration of the manufacturing process make experimental optimization a prohibitive task. Numerical simulation has emerged as a powerful tool in understanding the processing issues still prevalent in industry.; A first-principles model is developed to better understand the transport phenomena within a representative vertical Bridgman system. The set of conservation equations for momentum, energy, and species concentration are discretized using the Galerkin finite element method and simulated using accurate time-marching schemes. Simulation results detail the occurrence of fascinating nonlinear dynamics, in the form of stable, time-varying behavior for sufficiently large melt regimes and multiple steady flow states. This discovery of time-periodic flows for high intensity flows is qualitatively consistent with experimental observations. Transient simulations demonstrate that process operating conditions have a marked effect on the hydrodynamic behavior within the melt, which consequently affects the dopant concentration profile within the crystal.; The existence of nonlinear dynamical behavior within this system motivates the need for feedback control algorithms which can provide superior crystal quality. This work studies the feasibility of using crucible rotation to control flows in the vertical Bridgman system. Simulations show that crucible rotation acts to suppress the axisymmetric flows. However, for the case when the melt lies below the crystal, crucible rotation also acts to accelerate the onset of time-periodic behavior. This result is attributed to coupling between the centrifugal force and the intense, buoyancy-driven flows.; Proportional, proportional-integral, and input-output linearizing controllers are applied to vertical Bridgman systems in stabilizing (crystal below the melt) and destabilizing (melt below the crystal) configurations. The spatially-averaged, axisymmetric kinetic energy is the controlled output. The flows are controlled via rotation of the crucible containing the molten material. Simulation results show that feedback controllers using crucible rotation effectively attenuate flow oscillations in a stabilizing configuration with time-varying disturbance. Crucible rotation is not an optimal choice for suppressing inherent flow oscillations in the destabilizing configuration.
机译：本文提出了对垂直布里奇曼晶体生长系统中轴心对称流动的建模，仿真和控制的全面研究。制造过程的巨大复杂性和持续时间使实验优化成为一项艰巨的任务。数值模拟已成为了解行业中仍普遍存在的加工问题的有力工具。建立了第一性原理模型，以更好地理解具有代表性的垂直Bridgman系统中的传输现象。动量，能量和物种浓度的守恒方程组使用Galerkin有限元方法离散化，并使用精确的时间步长方案进行模拟。仿真结果以稳定的时变行为形式（对于足够大的熔体状态和多个稳态流动状态）详细描述了令人着迷的非线性动力学的发生。对于高强度流的时间周期流的发现在质量上与实验观察一致。瞬态仿真表明，工艺操作条件对熔体中的流体力学行为有显着影响，因此会影响晶体中的掺杂剂浓度分布。该系统中非线性动力学行为的存在激发了对可提供卓越晶体质量的反馈控制算法的需求。这项工作研究了使用坩埚旋转来控制垂直Bridgman系统中的流动的可行性。仿真表明，坩埚旋转可抑制轴对称流动。但是，对于熔体位于晶体下方的情况，坩埚旋转也可以加速时间周期行为的开始。该结果归因于离心力与强烈的浮力驱动流之间的耦合。比例，比例积分和输入-输出线性化控制器应用于稳定化（晶体在熔体下方）和不稳定化（晶体在熔体下方）配置的垂直Bridgman系统。空间平均轴对称动能是受控输出。通过包含熔融材料的坩埚的旋转来控制流量。仿真结果表明，使用坩埚旋转的反馈控制器在具有时变扰动的稳定配置中有效地衰减了流量振荡。坩埚旋转不是抑制不稳定结构中固有的流量振荡的最佳选择。

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