Ablation excited by current pulses is a very critical physical process in pulse plasma thrusters(PPT).Its effects on wall-plasma interaction directly determine the PPT performances.In order to reveal the process of th...Ablation excited by current pulses is a very critical physical process in pulse plasma thrusters(PPT).Its effects on wall-plasma interaction directly determine the PPT performances.In order to reveal the process of the ablated wall interaction with the discharge plasma in PPT,ablation models formulated by three different boundary conditions at the wall-plasma interface are studied.These are the two widely used high-speed evaporation models(Model-L and Model-M),and the recently developed Keida-Zaghloul model(Model-K)of the Knudsen layer that takes into account the internal degrees of freedom on the energy flux conservation.First,fundamental mechanisms of the three ablation models are clarified by comparative analysis in order to gain a comprehensive understanding of the wall-plasma interaction.Then,the applicability of different ablation models with the numerical solutions of LES-6 PPT is investigated in detail using magnetohydrodynamic(MHD)modeling.Results show that Model-L and Model-M are actually special cases of Model-K when a simplified jump conditions limited by high velocity at the vapor/plasma interface is used;A ratio of ablation rate in Model-L to that in Model-M is about 0.8at the same wall surface temperature,while it rises to 1 at different surface temperature determined by Model-L and Model-M in PPT.Even though Model-K solution requires significant computational time,it shows more accurate ablation feature for the wall-plasma interaction and possesses better computing precision of impulse bit during post-pulse which is useful for future studies of the late time ablation.展开更多
针对脉冲等离子体推进器作为执行机构的微纳卫星姿态控制系统(attitude control system,ACS)仿真的需要,采用脉冲信号控制双旋翼实验平台对微纳卫星姿态控制系统进行半实物仿真。使用Elman神经网络PID的控制策略,在线调整PID参数,适应...针对脉冲等离子体推进器作为执行机构的微纳卫星姿态控制系统(attitude control system,ACS)仿真的需要,采用脉冲信号控制双旋翼实验平台对微纳卫星姿态控制系统进行半实物仿真。使用Elman神经网络PID的控制策略,在线调整PID参数,适应动态系统。通过半实物仿真平台的对比试验,验证了Elman神经网络PID控制系统自适应能力强、超调量小等优点,同时也验证了双旋翼实验平台对于脉冲等离子推进器半实物仿真的有效性。展开更多
基金Project supported by Ph.D.Programs Foundation of Ministry of Education of China(20121101120004)Basic Research Foundation of Beijing Institute of Technology(20120142015)
文摘Ablation excited by current pulses is a very critical physical process in pulse plasma thrusters(PPT).Its effects on wall-plasma interaction directly determine the PPT performances.In order to reveal the process of the ablated wall interaction with the discharge plasma in PPT,ablation models formulated by three different boundary conditions at the wall-plasma interface are studied.These are the two widely used high-speed evaporation models(Model-L and Model-M),and the recently developed Keida-Zaghloul model(Model-K)of the Knudsen layer that takes into account the internal degrees of freedom on the energy flux conservation.First,fundamental mechanisms of the three ablation models are clarified by comparative analysis in order to gain a comprehensive understanding of the wall-plasma interaction.Then,the applicability of different ablation models with the numerical solutions of LES-6 PPT is investigated in detail using magnetohydrodynamic(MHD)modeling.Results show that Model-L and Model-M are actually special cases of Model-K when a simplified jump conditions limited by high velocity at the vapor/plasma interface is used;A ratio of ablation rate in Model-L to that in Model-M is about 0.8at the same wall surface temperature,while it rises to 1 at different surface temperature determined by Model-L and Model-M in PPT.Even though Model-K solution requires significant computational time,it shows more accurate ablation feature for the wall-plasma interaction and possesses better computing precision of impulse bit during post-pulse which is useful for future studies of the late time ablation.
文摘针对脉冲等离子体推进器作为执行机构的微纳卫星姿态控制系统(attitude control system,ACS)仿真的需要,采用脉冲信号控制双旋翼实验平台对微纳卫星姿态控制系统进行半实物仿真。使用Elman神经网络PID的控制策略,在线调整PID参数,适应动态系统。通过半实物仿真平台的对比试验,验证了Elman神经网络PID控制系统自适应能力强、超调量小等优点,同时也验证了双旋翼实验平台对于脉冲等离子推进器半实物仿真的有效性。
