The experiments and numerical simulation were conducted for ZL205A aluminum alloy cylindrical shell casting. The formation mechanism of the linear segregation produced by the low pressure die casting (LPDC) process wa...The experiments and numerical simulation were conducted for ZL205A aluminum alloy cylindrical shell casting. The formation mechanism of the linear segregation produced by the low pressure die casting (LPDC) process was investigated. And the heat transfer of the casting during solidification process was analyzed by simulation technique, resulting from the information of linear segregation obtained by plenty of experiments. The new linear segregation criterion was proposed through the simulation and experimental results. It was found that the melting metal with high Cu contents was feeding the crack shrinkage formed by the tearing under the effect of feeding pressure during the later solidification, which led to the formation of linear segregation. The control methods for the linear segregation were suggested based on the proposed mechanism. Finally, the criterion of linear segregation was confirmed by the production of the actual castings.展开更多
通过逐步多元线性回归(MLR)模型研究了2018~2023年新疆天山北坡主要城市(乌鲁木齐市、昌吉市、石河子市、五家渠市)人为排放与气象因素对臭氧(O_(3))变化的相对贡献,并基于OMI卫星数据(HCHO和NO_(2)对流层柱浓度)与地面观测数据(O_(3)和...通过逐步多元线性回归(MLR)模型研究了2018~2023年新疆天山北坡主要城市(乌鲁木齐市、昌吉市、石河子市、五家渠市)人为排放与气象因素对臭氧(O_(3))变化的相对贡献,并基于OMI卫星数据(HCHO和NO_(2)对流层柱浓度)与地面观测数据(O_(3)和NO_(2))确定了天山北坡地区的FNR(ratio of the tropospheric columns of formaldehyde to nitrogen dioxide)阈值,揭示了区域性差异、季节性特征和前体物敏感性变化规律.结果表明,天山北坡地区O_(3)整体呈波动上升趋势,年均值为86.97μg/m^(3),其中暖季(107.63μg/m^(3))高于冷季(66.31μg/m^(3)),2020年因疫情导致排放减少,O_(3)浓度降至最低(86.72μg/m^(3)).各城市年增长速率差异明显,昌吉市为3.87μg/(m^(3)·a),石河子市为1.51μg/(m^(3)·a).气象因素对O_(3)浓度变化具有显著影响,其中温度和湿度为关键因素.乌鲁木齐市和五家渠市的气象因素贡献较高(分别为50%和60%),而昌吉市和石河子市的贡献较低(分别为29%和44%).NO_(2)柱浓度呈现下降趋势(年下降速率为0.22×10^(15)molec/(cm^(2)·a)),而HCHO柱浓度保持相对稳定,表明VOCs排放可能有所增加.FNR值分析结果表明,O_(3)生成敏感性(OFS)阈值为:FNR<1.75时,臭氧生成受VOCs控制;FNR>3.67时,O_(3)生成受NO_(x)控制;1.75<FNR<3.67为过渡状态.暖季(4~9月),O_(3)光化学产生的敏感性主要受NO_(x)控制.本研究揭示了天山北坡地区O_(3)生成的时空变化特征和前体物敏感性规律,为制定更加精准的O_(3)污染控制策略提供了科学依据.展开更多
The new method which uses the consensus algorithm to solve the coordinate control problems of multiple unmanned underwater vehicles （multi-UUVs） formation in the case of leader-following is adapted. As the communica...The new method which uses the consensus algorithm to solve the coordinate control problems of multiple unmanned underwater vehicles （multi-UUVs） formation in the case of leader-following is adapted. As the communication between the UUVs is difficult and it is easy to be interfered under the water, time delay is assumed to be time-varying during the members communicate with each other. Meanwhile, the state feedback linearization method is used to transfer the nonlinear and coupling model of UUV into double-integrator dynamic. With this simplified double-integrator math model, the UUV formation coordinate control is regarded as consensus problem with time-varying communication delays. In addition, the position and velocity topologies are adapted to reduce the data volume in each data packet which is sent between members in formation. With two independent topologies designed, two cases of communication delay which are same and different are considered and the sufficient conditions are proposed and analyzed. The stability of the multi-UUVs formation is proven by using Lyapunov-Razumilkhin theorem. Finally, the simulation results are presented to confirm and illustrate the theoretical results.展开更多
To carry out the deep space exploration tasks near Sun-Earth Libration point L2, the CRTBP dynamic model was built up and the numerical conditional quasi-periodic orbit （Lissajons orbit） was computed near L2. Then, ...To carry out the deep space exploration tasks near Sun-Earth Libration point L2, the CRTBP dynamic model was built up and the numerical conditional quasi-periodic orbit （Lissajons orbit） was computed near L2. Then, a formation controller was designed with linear matrix inequality to overcome the difficuhy of parameter tuning. To meet the demands of formation accuracy and present thruster＇s capability, a threshold scheme was adopted for formation control. Finally, some numerical simulations and analysis were completed to demonstrate the feasibility of the proposed control strategy.展开更多
This paper studies the problem of the formation control for the multiple nonholonomic agents on a plane. A dynamic feedback linearization method is used to transform the dynamical model of each agent into two third-or...This paper studies the problem of the formation control for the multiple nonholonomic agents on a plane. A dynamic feedback linearization method is used to transform the dynamical model of each agent into two third-order integrator chains. A decentralized formation control law with the inter-agent damping .injection is derived. The asymptotical stability of the overall system is proven using the Lyapunov method. The simulation of the formation maneuver of a planar vehicle shows the effectiveness of the proposed method.展开更多
Spacecraft formation flying is an attractive new concept in international aeronautic fields because of its powerful functions and low cost. In this paper, the formation design and PD closed-loop control of spacecraft ...Spacecraft formation flying is an attractive new concept in international aeronautic fields because of its powerful functions and low cost. In this paper, the formation design and PD closed-loop control of spacecraft formation flying in elliptical orbits are discussed. Based on two-body relative dynamics, the true anomaly is applied as independent variable instead of the variable of time. Since the apogee is considered as the starting point, the six integrating constants are calculated. Therefore, the algebraic solution is obtained for the relative motion in elliptical orbits. Moreover, the formation design is presented and both circular formation and line formation are provided in terms of an algebraic solution. This paper also discusses the PD-closed loop control for precise formation control in elliptical orbits. In this part, the error-type state equation is put forward and the linear quadratic regulator （LQR） method is used to calculate PD parameters. Though the gain matrix calculated from LQR is time-variable because the error-type state equation is time variable, the PD parameters are also considered as constants because of their small changes in simulation. Finally, taking circular formation as an example, the initial orbital elements are achieved for three secondary spacecraft. And the numerical simulation is analyzed under PD formation control with initial errors and J2 perturbation. The simulation results demonstrate the validity of PD closed-loop control scheme.展开更多
Formation control is essential for an underwater mobile sensing network(UMSN) ,and an ad hoc network which wirelessly connects underwater vehicles of sensing and/or observing types via acoustic communications,to fulfi...Formation control is essential for an underwater mobile sensing network(UMSN) ,and an ad hoc network which wirelessly connects underwater vehicles of sensing and/or observing types via acoustic communications,to fulfill mobile sensing tasks.The problem of formation control for a UMSN with varying topology is studied in this paper.The methodology of synthesizing distributed formation controller which stabilizes a UMSN with varying topology is proposed on the basis of the stability analysis of linear time-varying systems.展开更多
文摘The experiments and numerical simulation were conducted for ZL205A aluminum alloy cylindrical shell casting. The formation mechanism of the linear segregation produced by the low pressure die casting (LPDC) process was investigated. And the heat transfer of the casting during solidification process was analyzed by simulation technique, resulting from the information of linear segregation obtained by plenty of experiments. The new linear segregation criterion was proposed through the simulation and experimental results. It was found that the melting metal with high Cu contents was feeding the crack shrinkage formed by the tearing under the effect of feeding pressure during the later solidification, which led to the formation of linear segregation. The control methods for the linear segregation were suggested based on the proposed mechanism. Finally, the criterion of linear segregation was confirmed by the production of the actual castings.
文摘通过逐步多元线性回归(MLR)模型研究了2018~2023年新疆天山北坡主要城市(乌鲁木齐市、昌吉市、石河子市、五家渠市)人为排放与气象因素对臭氧(O_(3))变化的相对贡献,并基于OMI卫星数据(HCHO和NO_(2)对流层柱浓度)与地面观测数据(O_(3)和NO_(2))确定了天山北坡地区的FNR(ratio of the tropospheric columns of formaldehyde to nitrogen dioxide)阈值,揭示了区域性差异、季节性特征和前体物敏感性变化规律.结果表明,天山北坡地区O_(3)整体呈波动上升趋势,年均值为86.97μg/m^(3),其中暖季(107.63μg/m^(3))高于冷季(66.31μg/m^(3)),2020年因疫情导致排放减少,O_(3)浓度降至最低(86.72μg/m^(3)).各城市年增长速率差异明显,昌吉市为3.87μg/(m^(3)·a),石河子市为1.51μg/(m^(3)·a).气象因素对O_(3)浓度变化具有显著影响,其中温度和湿度为关键因素.乌鲁木齐市和五家渠市的气象因素贡献较高(分别为50%和60%),而昌吉市和石河子市的贡献较低(分别为29%和44%).NO_(2)柱浓度呈现下降趋势(年下降速率为0.22×10^(15)molec/(cm^(2)·a)),而HCHO柱浓度保持相对稳定,表明VOCs排放可能有所增加.FNR值分析结果表明,O_(3)生成敏感性(OFS)阈值为:FNR<1.75时,臭氧生成受VOCs控制;FNR>3.67时,O_(3)生成受NO_(x)控制;1.75<FNR<3.67为过渡状态.暖季(4~9月),O_(3)光化学产生的敏感性主要受NO_(x)控制.本研究揭示了天山北坡地区O_(3)生成的时空变化特征和前体物敏感性规律,为制定更加精准的O_(3)污染控制策略提供了科学依据.
基金Projects(51309067,51679057,51609048)supported by the National Natural Science Foundation of ChinaProject(JC2016007)supported by the Outstanding Youth Science Foundation of Heilongjiang Province,ChinaProject(HEUCFX041401)supported by the Fundamental Research Funds for the Central Universities,China
文摘The new method which uses the consensus algorithm to solve the coordinate control problems of multiple unmanned underwater vehicles （multi-UUVs） formation in the case of leader-following is adapted. As the communication between the UUVs is difficult and it is easy to be interfered under the water, time delay is assumed to be time-varying during the members communicate with each other. Meanwhile, the state feedback linearization method is used to transfer the nonlinear and coupling model of UUV into double-integrator dynamic. With this simplified double-integrator math model, the UUV formation coordinate control is regarded as consensus problem with time-varying communication delays. In addition, the position and velocity topologies are adapted to reduce the data volume in each data packet which is sent between members in formation. With two independent topologies designed, two cases of communication delay which are same and different are considered and the sufficient conditions are proposed and analyzed. The stability of the multi-UUVs formation is proven by using Lyapunov-Razumilkhin theorem. Finally, the simulation results are presented to confirm and illustrate the theoretical results.
文摘To carry out the deep space exploration tasks near Sun-Earth Libration point L2, the CRTBP dynamic model was built up and the numerical conditional quasi-periodic orbit （Lissajons orbit） was computed near L2. Then, a formation controller was designed with linear matrix inequality to overcome the difficuhy of parameter tuning. To meet the demands of formation accuracy and present thruster＇s capability, a threshold scheme was adopted for formation control. Finally, some numerical simulations and analysis were completed to demonstrate the feasibility of the proposed control strategy.
基金supported by the National Natural Science Foundation of China (No. 10832006)
文摘This paper studies the problem of the formation control for the multiple nonholonomic agents on a plane. A dynamic feedback linearization method is used to transform the dynamical model of each agent into two third-order integrator chains. A decentralized formation control law with the inter-agent damping .injection is derived. The asymptotical stability of the overall system is proven using the Lyapunov method. The simulation of the formation maneuver of a planar vehicle shows the effectiveness of the proposed method.
文摘Spacecraft formation flying is an attractive new concept in international aeronautic fields because of its powerful functions and low cost. In this paper, the formation design and PD closed-loop control of spacecraft formation flying in elliptical orbits are discussed. Based on two-body relative dynamics, the true anomaly is applied as independent variable instead of the variable of time. Since the apogee is considered as the starting point, the six integrating constants are calculated. Therefore, the algebraic solution is obtained for the relative motion in elliptical orbits. Moreover, the formation design is presented and both circular formation and line formation are provided in terms of an algebraic solution. This paper also discusses the PD-closed loop control for precise formation control in elliptical orbits. In this part, the error-type state equation is put forward and the linear quadratic regulator （LQR） method is used to calculate PD parameters. Though the gain matrix calculated from LQR is time-variable because the error-type state equation is time variable, the PD parameters are also considered as constants because of their small changes in simulation. Finally, taking circular formation as an example, the initial orbital elements are achieved for three secondary spacecraft. And the numerical simulation is analyzed under PD formation control with initial errors and J2 perturbation. The simulation results demonstrate the validity of PD closed-loop control scheme.
基金the National High Technology Research and Development Program (863) of China (No.2006AA09Z233)
文摘Formation control is essential for an underwater mobile sensing network(UMSN) ,and an ad hoc network which wirelessly connects underwater vehicles of sensing and/or observing types via acoustic communications,to fulfill mobile sensing tasks.The problem of formation control for a UMSN with varying topology is studied in this paper.The methodology of synthesizing distributed formation controller which stabilizes a UMSN with varying topology is proposed on the basis of the stability analysis of linear time-varying systems.
