The Shennongjia ski field lies at the edge of the Shennongjia nature reserves. The construction of the ski field will change the landscape pattern of the assessment district, and the production capacity and stability ...The Shennongjia ski field lies at the edge of the Shennongjia nature reserves. The construction of the ski field will change the landscape pattern of the assessment district, and the production capacity and stability of the regional ecosystem in a certain degree, and will exert an influence on the ecological integrality of animal and plant habitats. This paper assesses the structure and function of the landscape ecosystem in the Niuchangpin ski field at Shennongjia, by using the theory and method of landscape ecology and 3S techniques. Through the calculation and comparison of landscape diversity indices and landscape aggregation indices, the influence imposed by the ski field project on the regional ecological integrality and relevant sensitive ecological issues is predicted. The results indicated that biomass of the natural system would decrease by 430.26 t, and correspondingly the average Net Primary Productivity would drop to 881.55 g/m2·a. The construction of the ski field would not change the matrix status of woodland and, however, it has a strong ability to control the quality of ecosystem. Combining 3S techniques with landscape-ecological theory will help turn the qualitative assessment into the quantitive one on the eco-environment impact. In this study a significant exploration has been conducted in the aspect of ecological impact assessment of construction projects.展开更多
Autonomous aerial refueling(AAR)has demonstrated significant benefits to aviation by extending the aircraft range and endurance.It is of significance to assess system safety for autonomous aerial refueling.In this pap...Autonomous aerial refueling(AAR)has demonstrated significant benefits to aviation by extending the aircraft range and endurance.It is of significance to assess system safety for autonomous aerial refueling.In this paper,the reachability analysis method is adopted to assess system safety.Due to system uncertainties,the aerial refueling system can be considered as a stochastic system.Thus,probabilistic reachability is considered.Since there is a close relationship between reachability probability and collision probability,the collision probability of the AAR system is analyzed by using reachability analysis techniques.Then,the collision probability is accessed by using the Monte-Carlo experiment method.Finally,simulations demonstrate the effectiveness of the proposed safety assessment method.展开更多
In order to ensure the highest safety requirements, nuclear power plant structures (the containment structures, the fuel storages and transportation systems) should be assessed against all possible internal and extern...In order to ensure the highest safety requirements, nuclear power plant structures (the containment structures, the fuel storages and transportation systems) should be assessed against all possible internal and external impact threats. The internal impact threats include kinetic missiles generated by the failure of high pressure vessels and pipes, the failure of high speed rotating machineries and accidental drops. The external impact threats may come from airborne missiles, aircraft impact, explosion blast and fragments. The impact effects of these threats on concrete and steel structures in a nuclear power plant are discussed. Methods and procedures for the impact assessment of nuclear power plants are introduced. Recent studies on penetration and perforation mechanics as well as progresses on dynamic properties of concrete-like materials are presented to increase the understanding of the impact effects on concrete containment structures.展开更多
文摘避碰稳定性直接关乎无人艇航行安全,传感器对障碍速度观测的不确定性会导致避碰策略出现跳动,严重降低避碰稳定性.提出不确定性条件下的速度障碍(uncertain velocityobstacle, UVO)算法,在碰撞风险评估中采用自适应阈值的最近会遇点(closest point ofapproach, CPA)法,基于国际海事避碰规则(International Regulations for Preventing Collisions at Sea,COLREGS)建立边界缓冲区,从宏观上提升避碰过程的稳定性.为了减少无人艇避碰角度的变化次数,在无人艇的速度空间中对不确定性条件下的速度障碍(velocity obstacle,VO)区进行建模,并采用梯度下降法在代价空间进行局部寻优,从微观上提升避碰策略的稳定性.在仿真平台下进行UVO算法和VO算法的对比实验,结果表明UVO 算法的避碰策略跳动次数、避碰成功率和最近会遇距离3项指标均优于VO算法.在实艇海试中进行了对遇、交叉、追越等典型会遇场景的避碰实验,无人艇均能安全避过运动目标.实验结果证明了UVO算法具有较好稳定性和安全性.
基金The paper is funded by the Environment Impact Assessment ofShennongjia Ski Field Construction Project (No. 04046038).
文摘The Shennongjia ski field lies at the edge of the Shennongjia nature reserves. The construction of the ski field will change the landscape pattern of the assessment district, and the production capacity and stability of the regional ecosystem in a certain degree, and will exert an influence on the ecological integrality of animal and plant habitats. This paper assesses the structure and function of the landscape ecosystem in the Niuchangpin ski field at Shennongjia, by using the theory and method of landscape ecology and 3S techniques. Through the calculation and comparison of landscape diversity indices and landscape aggregation indices, the influence imposed by the ski field project on the regional ecological integrality and relevant sensitive ecological issues is predicted. The results indicated that biomass of the natural system would decrease by 430.26 t, and correspondingly the average Net Primary Productivity would drop to 881.55 g/m2·a. The construction of the ski field would not change the matrix status of woodland and, however, it has a strong ability to control the quality of ecosystem. Combining 3S techniques with landscape-ecological theory will help turn the qualitative assessment into the quantitive one on the eco-environment impact. In this study a significant exploration has been conducted in the aspect of ecological impact assessment of construction projects.
基金This work was supported by the National Natural Science Foundation of China(No.61933010).
文摘Autonomous aerial refueling(AAR)has demonstrated significant benefits to aviation by extending the aircraft range and endurance.It is of significance to assess system safety for autonomous aerial refueling.In this paper,the reachability analysis method is adopted to assess system safety.Due to system uncertainties,the aerial refueling system can be considered as a stochastic system.Thus,probabilistic reachability is considered.Since there is a close relationship between reachability probability and collision probability,the collision probability of the AAR system is analyzed by using reachability analysis techniques.Then,the collision probability is accessed by using the Monte-Carlo experiment method.Finally,simulations demonstrate the effectiveness of the proposed safety assessment method.
文摘In order to ensure the highest safety requirements, nuclear power plant structures (the containment structures, the fuel storages and transportation systems) should be assessed against all possible internal and external impact threats. The internal impact threats include kinetic missiles generated by the failure of high pressure vessels and pipes, the failure of high speed rotating machineries and accidental drops. The external impact threats may come from airborne missiles, aircraft impact, explosion blast and fragments. The impact effects of these threats on concrete and steel structures in a nuclear power plant are discussed. Methods and procedures for the impact assessment of nuclear power plants are introduced. Recent studies on penetration and perforation mechanics as well as progresses on dynamic properties of concrete-like materials are presented to increase the understanding of the impact effects on concrete containment structures.
