This paper investigates the problem of controlling a chasing spacecraft(chaser)to track and rendezvous with an uncontrolled target.Based on the actual situation,the torque-free motion of an axisymmetric prolate rigid ...This paper investigates the problem of controlling a chasing spacecraft(chaser)to track and rendezvous with an uncontrolled target.Based on the actual situation,the torque-free motion of an axisymmetric prolate rigid body is employed to represent the short-term attitude motion of the tumbling target.By taking advantage of the dual quaternion’s compact and efficient description of the general rigid motion,the coupled and integrated model of the 6-degree-of-freedom(6-DOF)relative motion between the chaser and the tumbling target is derived in the chaser’s body fixed frame after taking full consideration of coordinate transformation.Based on the logarithm of dual quaternion,a sliding mode control(SMC)law based on the exponential reaching law and the continuous relay function is brought forward to address the problem of synchronization control of the 6-DOF relative motion.Simulation results illustrate the effectiveness of the proposed method.展开更多
We investigate the close-range relative motion and control of a spacecraft approaching a tumbling target. Unlike the traditional rigid-body dynamics with translation and rotation about the center of mass（CM）, the ki...We investigate the close-range relative motion and control of a spacecraft approaching a tumbling target. Unlike the traditional rigid-body dynamics with translation and rotation about the center of mass（CM）, the kinematic coupling between translation and rotation is taken into consideration to directly describe the motion of the spacecraft＇s sensors or devices which are not coincident with the CM. Thus, a kinematically coupled 6 degrees-of-freedom（DOF） relative motion model for the instrument（feature point） is set up. To make the chaser spacecraft＇s feature point track the target＇s, an optimal tracking problem is defined and a control law with a feedback-feedforward structure is designed. With quasi-linearization of the nonlinear dynamical system, the feedforward term is computed from a specified constraint about the dynamical system and the reference model, and the feedback action is derived starting from the state-dependent Ricca equation（SDRE）. The proposed controller is compared with an existing suboptimal tracking controller, and numerical simulations are presented to illustrate the effectiveness and superiority of the proposed method.展开更多
One of the objectives of car manufacturers is to improve engine performance, reduce consumption reduce emissions. To achieve this objective, it is important to understand the phenomena involved in the combustion chamb...One of the objectives of car manufacturers is to improve engine performance, reduce consumption reduce emissions. To achieve this objective, it is important to understand the phenomena involved in the combustion chambers of engines. These phenomena are numerous and complex in nature such: the aerodynamics, fuel-air mixture, turbulence, combustion and the cycle to cycle instabilities that cause more problems. One of the factors responsible for the phenomenon of cycle to cycle variations is the instability of the characteristics of the vortex flow Tumble. This instability may be due to changes in initial conditions. This study is achieved in order to contribute in a better understanding of engine flow by using a Detached Eddy Simulation Shear-Stress Transport (DES SST) model, which is a hybrid RANS/LES model. These simulations have been performed with the commercial CFD (computational fluid dynamic) code (FLUENT) coupled with our own development based on UDF facilities given by FLUENT. To explore the suitability of the 3D DES STT to simulate the internal flow, the calculation is performed for a model tumbling flow at constant volume. This flow has been measured in an experimental set up and measurements are used to initiate and to validate simulations. For this case study, we consider simplified engine geometry. To generate tumbling motion, we use non-reacting DES with a single cycle (SC) strategy. Also, with this strategy we study the effect of initial conditions on the instabilities that accompany a vortex type tumble.展开更多
目的 探讨父子打闹游戏质量与学龄前期儿童社会能力的关系,以及儿童性别的调节效应。方法 采用父母游戏与照顾问卷(parental play and care questionnaire,PPCQ)、幼儿社会能力与行为评定量表(social competence and behavior evaluatio...目的 探讨父子打闹游戏质量与学龄前期儿童社会能力的关系,以及儿童性别的调节效应。方法 采用父母游戏与照顾问卷(parental play and care questionnaire,PPCQ)、幼儿社会能力与行为评定量表(social competence and behavior evaluation,SCBE-30)、自编人口学问卷对3~6岁学龄前期儿童的801对父母,共1 602人进行调查。结果 相关分析表明,父子打闹游戏质量与儿童社会能力呈显著正相关(r=0.15,P<0.01)。儿童性别在父子打闹游戏质量与儿童社会能力之间的调节作用显著。父子打闹游戏质量对女孩社会能力的预测作用显著(β=0.26,P<0.001);父子打闹游戏质量并不能显著预测男孩的社会能力(β=0.06,P=0.16)。结论 儿童性别调节了父子打闹游戏质量对学龄前期儿童社会能力的影响。展开更多
3 degrees of freedom(DOF)exterior ballistic computer models are used in fragment studies to calculate individual trajectories of each fragment based on drag coefficient and the projected(presented)area in the directio...3 degrees of freedom(DOF)exterior ballistic computer models are used in fragment studies to calculate individual trajectories of each fragment based on drag coefficient and the projected(presented)area in the direction of velocity of center of mass.The expectation of a randomly distributed projected area is commonly used for fragments that tumble(random rotation)during flight.We forecast a model where the expected drag coefficient is dependent of shape and Mach number.Rotation or tumbling only affects the expected projected area.Models of projected areas during tumbling and rotation are presented.An examination of the data by Mc Cleskey(1988)indicates that the volume of the fragment to the power of2/3 is a better parameter to characterize the drag coefficient of the fragments than the maximum projected area.Hydrocode simulations are used to verify results and to study projected area and drag coefficient of fragments.展开更多
Back to 1994, a transient price hike of cocoon silk eventually led to a predicament for Chinese silk industry in the following years. A decade later, is that slump going to happen again?
基金supported by the National Science Foundation of China(61427809)
文摘This paper investigates the problem of controlling a chasing spacecraft(chaser)to track and rendezvous with an uncontrolled target.Based on the actual situation,the torque-free motion of an axisymmetric prolate rigid body is employed to represent the short-term attitude motion of the tumbling target.By taking advantage of the dual quaternion’s compact and efficient description of the general rigid motion,the coupled and integrated model of the 6-degree-of-freedom(6-DOF)relative motion between the chaser and the tumbling target is derived in the chaser’s body fixed frame after taking full consideration of coordinate transformation.Based on the logarithm of dual quaternion,a sliding mode control(SMC)law based on the exponential reaching law and the continuous relay function is brought forward to address the problem of synchronization control of the 6-DOF relative motion.Simulation results illustrate the effectiveness of the proposed method.
基金Project supported by the Major Program of the National Natural Science Foundation of China(Grant Nos.61690210 and 61690213)
文摘We investigate the close-range relative motion and control of a spacecraft approaching a tumbling target. Unlike the traditional rigid-body dynamics with translation and rotation about the center of mass（CM）, the kinematic coupling between translation and rotation is taken into consideration to directly describe the motion of the spacecraft＇s sensors or devices which are not coincident with the CM. Thus, a kinematically coupled 6 degrees-of-freedom（DOF） relative motion model for the instrument（feature point） is set up. To make the chaser spacecraft＇s feature point track the target＇s, an optimal tracking problem is defined and a control law with a feedback-feedforward structure is designed. With quasi-linearization of the nonlinear dynamical system, the feedforward term is computed from a specified constraint about the dynamical system and the reference model, and the feedback action is derived starting from the state-dependent Ricca equation（SDRE）. The proposed controller is compared with an existing suboptimal tracking controller, and numerical simulations are presented to illustrate the effectiveness and superiority of the proposed method.
文摘One of the objectives of car manufacturers is to improve engine performance, reduce consumption reduce emissions. To achieve this objective, it is important to understand the phenomena involved in the combustion chambers of engines. These phenomena are numerous and complex in nature such: the aerodynamics, fuel-air mixture, turbulence, combustion and the cycle to cycle instabilities that cause more problems. One of the factors responsible for the phenomenon of cycle to cycle variations is the instability of the characteristics of the vortex flow Tumble. This instability may be due to changes in initial conditions. This study is achieved in order to contribute in a better understanding of engine flow by using a Detached Eddy Simulation Shear-Stress Transport (DES SST) model, which is a hybrid RANS/LES model. These simulations have been performed with the commercial CFD (computational fluid dynamic) code (FLUENT) coupled with our own development based on UDF facilities given by FLUENT. To explore the suitability of the 3D DES STT to simulate the internal flow, the calculation is performed for a model tumbling flow at constant volume. This flow has been measured in an experimental set up and measurements are used to initiate and to validate simulations. For this case study, we consider simplified engine geometry. To generate tumbling motion, we use non-reacting DES with a single cycle (SC) strategy. Also, with this strategy we study the effect of initial conditions on the instabilities that accompany a vortex type tumble.
文摘目的 探讨父子打闹游戏质量与学龄前期儿童社会能力的关系,以及儿童性别的调节效应。方法 采用父母游戏与照顾问卷(parental play and care questionnaire,PPCQ)、幼儿社会能力与行为评定量表(social competence and behavior evaluation,SCBE-30)、自编人口学问卷对3~6岁学龄前期儿童的801对父母,共1 602人进行调查。结果 相关分析表明,父子打闹游戏质量与儿童社会能力呈显著正相关(r=0.15,P<0.01)。儿童性别在父子打闹游戏质量与儿童社会能力之间的调节作用显著。父子打闹游戏质量对女孩社会能力的预测作用显著(β=0.26,P<0.001);父子打闹游戏质量并不能显著预测男孩的社会能力(β=0.06,P=0.16)。结论 儿童性别调节了父子打闹游戏质量对学龄前期儿童社会能力的影响。
文摘3 degrees of freedom(DOF)exterior ballistic computer models are used in fragment studies to calculate individual trajectories of each fragment based on drag coefficient and the projected(presented)area in the direction of velocity of center of mass.The expectation of a randomly distributed projected area is commonly used for fragments that tumble(random rotation)during flight.We forecast a model where the expected drag coefficient is dependent of shape and Mach number.Rotation or tumbling only affects the expected projected area.Models of projected areas during tumbling and rotation are presented.An examination of the data by Mc Cleskey(1988)indicates that the volume of the fragment to the power of2/3 is a better parameter to characterize the drag coefficient of the fragments than the maximum projected area.Hydrocode simulations are used to verify results and to study projected area and drag coefficient of fragments.
文摘Back to 1994, a transient price hike of cocoon silk eventually led to a predicament for Chinese silk industry in the following years. A decade later, is that slump going to happen again?
