In this paper both numerical and experimental investigations have been carried out to suppress the vortex-induced vibration （VIV） of a circular cylinder in an electrically low-conducting fluid. The electromagnetic f...In this paper both numerical and experimental investigations have been carried out to suppress the vortex-induced vibration （VIV） of a circular cylinder in an electrically low-conducting fluid. The electromagnetic forces （Lorentz forces） in the azimuthal direction were generated through the mounted electrodes and magnets locally on the surface of the cylinder, which have been proved having an accelerating effect to the fluid on the surface of the cylinder. Results of computations are presented for synchronous vibration phenomenon of a cylinder at Re = 200, which are in good agreement with previous computational results. With the Lorentz forces loaded, the VIV of the cylinder has been suppressed successfully. Experimental results have also shown the same tendency and are in reasonable agreement with the numerical results.展开更多
Instability of a wake controlled by a streamwise Lorentz force is investigated through a Floquet stability analysis. The streamwise Lorentz force, which is a two-dimensional control input created by an electromagnetic...Instability of a wake controlled by a streamwise Lorentz force is investigated through a Floquet stability analysis. The streamwise Lorentz force, which is a two-dimensional control input created by an electromagnetic actuator located on the cylinder surface,adjusts the base flow to affect the three-dimensional wake instability and achieve wake stabilization and transition delay. The instability mode at a Reynolds number Re = 300 can be transformed from B to A with N = 1.0, where N is an interaction number representing the strength of the Lorentz force relative to the inertial force in the fluid. The wake flow is Floquet stable when N increases to 1.3. The spanwise perturbation wavelengths are 3.926 D and 0.822 D in the modes A and B, respectively, where D is the cylinder diameter. In addition, the oscillating amplitudes of drag and lift are reduced with the increase in the interaction number. Particle tracing is used to explore the essential physical mechanism for mode transformation. The path lines show that suppression of flow separation hinders the fluid deformation and rotation, leading to the decrease in elliptic and hyperbolic instability regions, which is the material cause of mode transformation.All of the results indicate that wake stabilization and transition delay can be achieved under open-loop active control via the streamwise Lorentz force.展开更多
An open-plus-closed-loop （OPCL） control problem for the chaotic motion of a 3D rigid pendulum subjected to a constant gravitationM force is studied. The 3D rigid pendulum is assumed to be consist of a rigid body sup...An open-plus-closed-loop （OPCL） control problem for the chaotic motion of a 3D rigid pendulum subjected to a constant gravitationM force is studied. The 3D rigid pendulum is assumed to be consist of a rigid body supported by a fixed and frictionless pivot with three rotational degrees. In order to avoid the singular phenomenon of Euler＇s angular velocity equation, the quaternion kinematic equation is used to describe the motion of the 3D rigid pendulum. An OPCL controller for chaotic motion of a 3D rigid pendulum at equilibrium position is designed. This OPCL controller contains two parts： the open-loop part to construct an ideal trajectory and the closed-loop part to stabilize the 3D rigid pendulum. Simulation results show that the controller is effective and efficient.展开更多
为研究兆瓦级高效紧凑型核动力系统的运行特性,使用自主开发的热管堆瞬态分析程序TAPIRS(Transient Analysis code for heat Pipe and AMTEC power conversion space Reactor power System)和超临界二氧化碳布雷顿循环的瞬态分析程序SCT...为研究兆瓦级高效紧凑型核动力系统的运行特性,使用自主开发的热管堆瞬态分析程序TAPIRS(Transient Analysis code for heat Pipe and AMTEC power conversion space Reactor power System)和超临界二氧化碳布雷顿循环的瞬态分析程序SCTRAN/CO_(2)(Super Critical reactors Transient Analysis code/Carbon Dioxide)的耦合程序对其反应性、负荷、冷却水温度和流量等扰动进行了开环动态响应分析,并据此进行了控制系统设计。在此基础上,对线性变负荷、阶梯式变负荷以及甩负荷这三种变负荷运行工况进行了计算分析。结果表明:该核动力系统的转速对扰动的变化较为敏感,需要加以控制;低负荷下旁通会使压缩机流量上升,需对压缩机流量加以控制;系统在控制方案下能以6%FP(Full Power)·min^(−1)的速度实现0%~100%的负荷变动,且可以在任意负荷水平下运行;甩负荷下系统的波动时间变长,但是仍可达到新的稳态进行工作,且各参数处于安全范围内。本研究可为新型核动力系统的概念设计提供参考。展开更多
电力电子变压器(solid state transformer,SST)是实现配电网分布式能源、新型负荷/储能灵活接入的关键装备,针对应用于SST中高频隔离环节的CLLC型直流变压器开展了电路参数的鲁棒性分析与优化设计研究。CLLC型直流变压器可利用开环控制...电力电子变压器(solid state transformer,SST)是实现配电网分布式能源、新型负荷/储能灵活接入的关键装备,针对应用于SST中高频隔离环节的CLLC型直流变压器开展了电路参数的鲁棒性分析与优化设计研究。CLLC型直流变压器可利用开环控制简化控制复杂度,实现宽范围下接近恒定的双向电压增益,并采用高频变压器的漏感作为谐振电感,降低电路设计难度。提出了一种用于CLLC直流变压器的参数设计方法,利用该方法,即使电感电容值出现设计偏差时,所设计的CLLC直流变压器也具有良好的电压调节能力与软开关特性。分析了高频隔离变压器与器件寄生参数对直流变压器轻载下电压增益的影响,最后开展了典型直流变压器设计,并在PSIM软件中进行了仿真验证。展开更多
To improve the energy efficiency of a direct expansion air conditioning(DX A/C) system while guaranteeing occupancy comfort, a hierarchical controller for a DX A/C system with uncertain parameters is proposed. The con...To improve the energy efficiency of a direct expansion air conditioning(DX A/C) system while guaranteeing occupancy comfort, a hierarchical controller for a DX A/C system with uncertain parameters is proposed. The control strategy consists of an open loop optimization controller and a closed-loop guaranteed cost periodically intermittent-switch controller(GCPISC). The error dynamics system of the closed-loop control is modelled based on the GCPISC principle. The difference,compared to the previous DX A/C system control methods, is that the controller designed in this paper performs control at discrete times. For the ease of designing the controller, a series of matrix inequalities are derived to be the sufficient conditions of the lower-layer closed-loop GCPISC controller. In this way, the DX A/C system output is derived to follow the optimal references obtained through the upper-layer open loop controller in exponential time, and the energy efficiency of the system is improved. Moreover, a static optimization problem is addressed for obtaining an optimal GCPISC law to ensure a minimum upper bound on the DX A/C system performance considering energy efficiency and output tracking error. The advantages of the designed hierarchical controller for a DX A/C system with uncertain parameters are demonstrated through some simulation results.展开更多
文摘In this paper both numerical and experimental investigations have been carried out to suppress the vortex-induced vibration （VIV） of a circular cylinder in an electrically low-conducting fluid. The electromagnetic forces （Lorentz forces） in the azimuthal direction were generated through the mounted electrodes and magnets locally on the surface of the cylinder, which have been proved having an accelerating effect to the fluid on the surface of the cylinder. Results of computations are presented for synchronous vibration phenomenon of a cylinder at Re = 200, which are in good agreement with previous computational results. With the Lorentz forces loaded, the VIV of the cylinder has been suppressed successfully. Experimental results have also shown the same tendency and are in reasonable agreement with the numerical results.
基金Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education(No.20133219110039)
文摘Instability of a wake controlled by a streamwise Lorentz force is investigated through a Floquet stability analysis. The streamwise Lorentz force, which is a two-dimensional control input created by an electromagnetic actuator located on the cylinder surface,adjusts the base flow to affect the three-dimensional wake instability and achieve wake stabilization and transition delay. The instability mode at a Reynolds number Re = 300 can be transformed from B to A with N = 1.0, where N is an interaction number representing the strength of the Lorentz force relative to the inertial force in the fluid. The wake flow is Floquet stable when N increases to 1.3. The spanwise perturbation wavelengths are 3.926 D and 0.822 D in the modes A and B, respectively, where D is the cylinder diameter. In addition, the oscillating amplitudes of drag and lift are reduced with the increase in the interaction number. Particle tracing is used to explore the essential physical mechanism for mode transformation. The path lines show that suppression of flow separation hinders the fluid deformation and rotation, leading to the decrease in elliptic and hyperbolic instability regions, which is the material cause of mode transformation.All of the results indicate that wake stabilization and transition delay can be achieved under open-loop active control via the streamwise Lorentz force.
基金supported by the National Natural Science Foundation of China(No.11072038)the Municipal Key Programs of Natural Science Foundation of Beijing(No.KZ201110772039)
文摘An open-plus-closed-loop （OPCL） control problem for the chaotic motion of a 3D rigid pendulum subjected to a constant gravitationM force is studied. The 3D rigid pendulum is assumed to be consist of a rigid body supported by a fixed and frictionless pivot with three rotational degrees. In order to avoid the singular phenomenon of Euler＇s angular velocity equation, the quaternion kinematic equation is used to describe the motion of the 3D rigid pendulum. An OPCL controller for chaotic motion of a 3D rigid pendulum at equilibrium position is designed. This OPCL controller contains two parts： the open-loop part to construct an ideal trajectory and the closed-loop part to stabilize the 3D rigid pendulum. Simulation results show that the controller is effective and efficient.
文摘为研究兆瓦级高效紧凑型核动力系统的运行特性,使用自主开发的热管堆瞬态分析程序TAPIRS(Transient Analysis code for heat Pipe and AMTEC power conversion space Reactor power System)和超临界二氧化碳布雷顿循环的瞬态分析程序SCTRAN/CO_(2)(Super Critical reactors Transient Analysis code/Carbon Dioxide)的耦合程序对其反应性、负荷、冷却水温度和流量等扰动进行了开环动态响应分析,并据此进行了控制系统设计。在此基础上,对线性变负荷、阶梯式变负荷以及甩负荷这三种变负荷运行工况进行了计算分析。结果表明:该核动力系统的转速对扰动的变化较为敏感,需要加以控制;低负荷下旁通会使压缩机流量上升,需对压缩机流量加以控制;系统在控制方案下能以6%FP(Full Power)·min^(−1)的速度实现0%~100%的负荷变动,且可以在任意负荷水平下运行;甩负荷下系统的波动时间变长,但是仍可达到新的稳态进行工作,且各参数处于安全范围内。本研究可为新型核动力系统的概念设计提供参考。
文摘电力电子变压器(solid state transformer,SST)是实现配电网分布式能源、新型负荷/储能灵活接入的关键装备,针对应用于SST中高频隔离环节的CLLC型直流变压器开展了电路参数的鲁棒性分析与优化设计研究。CLLC型直流变压器可利用开环控制简化控制复杂度,实现宽范围下接近恒定的双向电压增益,并采用高频变压器的漏感作为谐振电感,降低电路设计难度。提出了一种用于CLLC直流变压器的参数设计方法,利用该方法,即使电感电容值出现设计偏差时,所设计的CLLC直流变压器也具有良好的电压调节能力与软开关特性。分析了高频隔离变压器与器件寄生参数对直流变压器轻载下电压增益的影响,最后开展了典型直流变压器设计,并在PSIM软件中进行了仿真验证。
基金supported by the National Natural Science Foundation of China(61773220,61876192,61907021)the National Natural Science Foundation of Hubei(ZRMS2019000752)+2 种基金the Fundamental Research Funds for the Central Universities(2662018QD057,CZT20022,CZT20020)Academic Team in Universities(KTZ20051)School Talent Funds(YZZ19004)。
文摘To improve the energy efficiency of a direct expansion air conditioning(DX A/C) system while guaranteeing occupancy comfort, a hierarchical controller for a DX A/C system with uncertain parameters is proposed. The control strategy consists of an open loop optimization controller and a closed-loop guaranteed cost periodically intermittent-switch controller(GCPISC). The error dynamics system of the closed-loop control is modelled based on the GCPISC principle. The difference,compared to the previous DX A/C system control methods, is that the controller designed in this paper performs control at discrete times. For the ease of designing the controller, a series of matrix inequalities are derived to be the sufficient conditions of the lower-layer closed-loop GCPISC controller. In this way, the DX A/C system output is derived to follow the optimal references obtained through the upper-layer open loop controller in exponential time, and the energy efficiency of the system is improved. Moreover, a static optimization problem is addressed for obtaining an optimal GCPISC law to ensure a minimum upper bound on the DX A/C system performance considering energy efficiency and output tracking error. The advantages of the designed hierarchical controller for a DX A/C system with uncertain parameters are demonstrated through some simulation results.
