Space-based optical(SBO)space surveillance has attracted widespread interest in the last two decades due to its considerable value in space situation awareness(SSA).SBO observation strategy,which is related to the per...Space-based optical(SBO)space surveillance has attracted widespread interest in the last two decades due to its considerable value in space situation awareness(SSA).SBO observation strategy,which is related to the performance of space surveillance,is the top-level design in SSA missions reviewed.The recognized real programs about SBO SAA proposed by the institutions in the U.S.,Canada,Europe,etc.,are summarized firstly,from which an insight of the development trend of SBO SAA can be obtained.According to the aim of the SBO SSA,the missions can be divided into general surveillance and space object tracking.Thus,there are two major categories for SBO SSA strategies.Existing general surveillance strategies for observing low earth orbit(LEO)objects and beyond-LEO objects are summarized and compared in terms of coverage rate,revisit time,visibility period,and image processing.Then,the SBO space object tracking strategies,which has experienced from tracking an object with a single satellite to tracking an object with multiple satellites cooperatively,are also summarized.Finally,this paper looks into the development trend in the future and points out several problems that challenges the SBO SSA.展开更多
In order to control the growth of space debris,a novel tethered space robot(TSR) was put forward.After capture,the platform,tether,and target constituted a tethered combination system.General nonlinear dynamics of the...In order to control the growth of space debris,a novel tethered space robot(TSR) was put forward.After capture,the platform,tether,and target constituted a tethered combination system.General nonlinear dynamics of the tethered combination system in the post-capture phase was established with the consideration of the attitudes of two spacecrafts and the quadratic nonlinear elasticity of the tether.The motion law of the tethered combination in the deorbiting process with different disturbances was simulated and discussed on the premise that the platform was only controlled by a constant thrust force.It is known that the four motion freedoms of the tethered combination are coupled with each other in the deorbiting process from the simulation results.A noticeable phenomenon is that the tether longitudinal vibration does not decay to vanish even under the large tether damping with initial attitude disturbances due to the coupling effect.The approximate analytical solutions of the dynamics for a simplified model are obtained through the perturbation method.The condition of the inter resonance phenomenon is the frequency ratio λ_1=2.The case study shows good accordance between the analytical solutions and numerical results,indicating the effectiveness and correctness of approximate analytical solutions.展开更多
Performances and efficiencies of displacement ventilation(DV) and partial ventilation(PV) for industrial halls of different configurations as well as the heat and mass transports within the industrial halls were numer...Performances and efficiencies of displacement ventilation(DV) and partial ventilation(PV) for industrial halls of different configurations as well as the heat and mass transports within the industrial halls were numerically investigated. Three levels of Rayleigh number(5.8×1010, 1.0×1012 and 2.1×1012) and two values of source contaminant flux(5 mg/s and 50 mg/s) were considered. The inlet Reynolds numbers were 2×104, 5×104, 1.5×105 and 4.5×105 for DV and 5×105, 1×106, 2×106 and 4×106 for PV, respectively. From the results, it is concluded that the above parameters have very complex impacts on the conjugated heat and mass transports. From points of view of acceptable indoor air quality and ventilation efficiency, PV at Re=1×106 with side-located sources and 65% of the supply air extracted through floor level outlets is the best choice when Ra=5.8×1010. However, DVs at Re=5×104 and Re=1.5×105with center-located sources and floor-mounted air suppliers are the best choices for Ra=1.0×1012 and Ra=2.1×1012, respectively. When source contaminant flux reaches 50 mg/s, local extraction as a supplement of general ventilation is recommended. The results can be a first approximation to 3D numerical investigation and preliminary ventilation system design guidelines for high-rise industrial halls.展开更多
基金This work was supported by the National Natural Science Foundation of China(61690210,61690213).
文摘Space-based optical(SBO)space surveillance has attracted widespread interest in the last two decades due to its considerable value in space situation awareness(SSA).SBO observation strategy,which is related to the performance of space surveillance,is the top-level design in SSA missions reviewed.The recognized real programs about SBO SAA proposed by the institutions in the U.S.,Canada,Europe,etc.,are summarized firstly,from which an insight of the development trend of SBO SAA can be obtained.According to the aim of the SBO SSA,the missions can be divided into general surveillance and space object tracking.Thus,there are two major categories for SBO SSA strategies.Existing general surveillance strategies for observing low earth orbit(LEO)objects and beyond-LEO objects are summarized and compared in terms of coverage rate,revisit time,visibility period,and image processing.Then,the SBO space object tracking strategies,which has experienced from tracking an object with a single satellite to tracking an object with multiple satellites cooperatively,are also summarized.Finally,this paper looks into the development trend in the future and points out several problems that challenges the SBO SSA.
基金Project (51475411) supported by the National Natural Science Foundation of ChinaProject (LY15E070002) supported by Zhejiang Provincial Natural Science Foundation of China
文摘In order to control the growth of space debris,a novel tethered space robot(TSR) was put forward.After capture,the platform,tether,and target constituted a tethered combination system.General nonlinear dynamics of the tethered combination system in the post-capture phase was established with the consideration of the attitudes of two spacecrafts and the quadratic nonlinear elasticity of the tether.The motion law of the tethered combination in the deorbiting process with different disturbances was simulated and discussed on the premise that the platform was only controlled by a constant thrust force.It is known that the four motion freedoms of the tethered combination are coupled with each other in the deorbiting process from the simulation results.A noticeable phenomenon is that the tether longitudinal vibration does not decay to vanish even under the large tether damping with initial attitude disturbances due to the coupling effect.The approximate analytical solutions of the dynamics for a simplified model are obtained through the perturbation method.The condition of the inter resonance phenomenon is the frequency ratio λ_1=2.The case study shows good accordance between the analytical solutions and numerical results,indicating the effectiveness and correctness of approximate analytical solutions.
基金Project(2011BAJ03B07)supported by National Twelve Five-year Science and Technology Support Program of ChinaProject supported by the China Scholarship Council+1 种基金Project(51276057,51376198)supported by the National Natural Science Foundation of ChinaProject(CX2014B064)supported by Hunan Provincial Innovation Foundation for Postgraduate,China
文摘Performances and efficiencies of displacement ventilation(DV) and partial ventilation(PV) for industrial halls of different configurations as well as the heat and mass transports within the industrial halls were numerically investigated. Three levels of Rayleigh number(5.8×1010, 1.0×1012 and 2.1×1012) and two values of source contaminant flux(5 mg/s and 50 mg/s) were considered. The inlet Reynolds numbers were 2×104, 5×104, 1.5×105 and 4.5×105 for DV and 5×105, 1×106, 2×106 and 4×106 for PV, respectively. From the results, it is concluded that the above parameters have very complex impacts on the conjugated heat and mass transports. From points of view of acceptable indoor air quality and ventilation efficiency, PV at Re=1×106 with side-located sources and 65% of the supply air extracted through floor level outlets is the best choice when Ra=5.8×1010. However, DVs at Re=5×104 and Re=1.5×105with center-located sources and floor-mounted air suppliers are the best choices for Ra=1.0×1012 and Ra=2.1×1012, respectively. When source contaminant flux reaches 50 mg/s, local extraction as a supplement of general ventilation is recommended. The results can be a first approximation to 3D numerical investigation and preliminary ventilation system design guidelines for high-rise industrial halls.
