Reducing greenhouse gases, saving energy resources and mass optimization require technological changes towards increasingly electric vehicles. At the same time, performance improvement of semiconductor and dielectric ...Reducing greenhouse gases, saving energy resources and mass optimization require technological changes towards increasingly electric vehicles. At the same time, performance improvement of semiconductor and dielectric materials further promotes electronic components confinement, resulting in a significant increase of embedded power densities. In the particular case of future hybrid propulsion aircrafts, electrical power that intended to supply reactors would be converted through power electronics components mounted on power busbars and insulated by solid dielectrics materials. These dielectrics materials have to respond to various electrical constraints of use (HVDC), in spite of environment change of aircraft parameters such as low pressure, temperature and thermal cycles, humidity... Unfortunately, partial discharges phenomenon is the most problem within electrical insulation system (EIS). Based on a topological model of power busbars designed for power converters dedicated to hybrid aircraft, partial discharge studies were conducted by simulation in various charging conditions of a PTFE insulator. Simulation results, which focus on electric field thresholds criteria of partial discharge inception voltage in air, reveal a net sensitivity of a space charge accumulation and distribution on dielectrics behaviour even for low space charge density, depending on their location in dielectrics. Compared to the behaviour observed with implanted homocharges, when by increasing homocharges density from 0.5 C/m3 to 2 C/m3 we observe a decrease of electric field by 450%, simulation results show a highest risk of partial discharge inception when heterocharges are accumulated inside dielectrics. Their accumulation increases the electric field in triple points beyond electric field thresholds of partial discharge inception in air. The simulated electric field reaching 22 kV/mm with only 2 C/m3 of heterocharges density accumulated in dielectric/busbars interfaces.展开更多
虚拟管道宽度直接影响了管道内无人机的流速,但目前虚拟管道规划的方法并不能保证管道宽度,容易造成堵塞,严重影响无人机通行效率。对此,提出一种虚拟管道空间满足规划方法,可以在包含障碍物的环境中得到一条满足虚拟管道空间要求的管...虚拟管道宽度直接影响了管道内无人机的流速,但目前虚拟管道规划的方法并不能保证管道宽度,容易造成堵塞,严重影响无人机通行效率。对此,提出一种虚拟管道空间满足规划方法,可以在包含障碍物的环境中得到一条满足虚拟管道空间要求的管道生成线。主要包括路径搜索和轨迹优化,基于快速探索随机树*(rapidly exploring random tree*,RRT*)搜索,通过空间检测判断每段路径周围是否有足够空间,若无足够空间则重新拓展搜索,替换掉空间不足的路径段。在轨迹优化过程中,使用均匀B样条参数化轨迹,并设计碰撞代价函数和光滑代价函数,使轨迹远离障碍物,为虚拟管道规划提供足够空间。仿真测试验证了所提方法在大规模集群中的优越性和鲁棒性。在仿真测试中,15架无人机集群通行时间平均降低20%。展开更多
随着空中交通流量的增长,尾流间隔精细化、动态化缩减成为民航发展的一种趋势,研究尾流演化过程也成为民航领域关注的前沿科学问题。基于此,采用雷诺平均N-S方程方法研究了B737-800飞机有无融合式翼梢小翼对飞机尾涡的演化过程影响。利...随着空中交通流量的增长,尾流间隔精细化、动态化缩减成为民航发展的一种趋势,研究尾流演化过程也成为民航领域关注的前沿科学问题。基于此,采用雷诺平均N-S方程方法研究了B737-800飞机有无融合式翼梢小翼对飞机尾涡的演化过程影响。利用美国国家航空航天局(National Aeronautics and Space Administration,NASA)动态尾流系统中尾涡消散模型(aircraft vortex spacing system prediction algorithm,APA)计算了不同气象环境参数下有无小翼的尾涡环量变化。结果表明:融合式翼梢小翼可以分割翼尖涡,有效改变翼尖气流的流动特性,增大速度梯度,减小尾涡速度、尾涡能量集中程度和尾涡强度;不同大气湍流耗散率和大气层结稳定度下,小翼对尾涡强度的减小量不同。展开更多
文摘Reducing greenhouse gases, saving energy resources and mass optimization require technological changes towards increasingly electric vehicles. At the same time, performance improvement of semiconductor and dielectric materials further promotes electronic components confinement, resulting in a significant increase of embedded power densities. In the particular case of future hybrid propulsion aircrafts, electrical power that intended to supply reactors would be converted through power electronics components mounted on power busbars and insulated by solid dielectrics materials. These dielectrics materials have to respond to various electrical constraints of use (HVDC), in spite of environment change of aircraft parameters such as low pressure, temperature and thermal cycles, humidity... Unfortunately, partial discharges phenomenon is the most problem within electrical insulation system (EIS). Based on a topological model of power busbars designed for power converters dedicated to hybrid aircraft, partial discharge studies were conducted by simulation in various charging conditions of a PTFE insulator. Simulation results, which focus on electric field thresholds criteria of partial discharge inception voltage in air, reveal a net sensitivity of a space charge accumulation and distribution on dielectrics behaviour even for low space charge density, depending on their location in dielectrics. Compared to the behaviour observed with implanted homocharges, when by increasing homocharges density from 0.5 C/m3 to 2 C/m3 we observe a decrease of electric field by 450%, simulation results show a highest risk of partial discharge inception when heterocharges are accumulated inside dielectrics. Their accumulation increases the electric field in triple points beyond electric field thresholds of partial discharge inception in air. The simulated electric field reaching 22 kV/mm with only 2 C/m3 of heterocharges density accumulated in dielectric/busbars interfaces.
文摘虚拟管道宽度直接影响了管道内无人机的流速,但目前虚拟管道规划的方法并不能保证管道宽度,容易造成堵塞,严重影响无人机通行效率。对此,提出一种虚拟管道空间满足规划方法,可以在包含障碍物的环境中得到一条满足虚拟管道空间要求的管道生成线。主要包括路径搜索和轨迹优化,基于快速探索随机树*(rapidly exploring random tree*,RRT*)搜索,通过空间检测判断每段路径周围是否有足够空间,若无足够空间则重新拓展搜索,替换掉空间不足的路径段。在轨迹优化过程中,使用均匀B样条参数化轨迹,并设计碰撞代价函数和光滑代价函数,使轨迹远离障碍物,为虚拟管道规划提供足够空间。仿真测试验证了所提方法在大规模集群中的优越性和鲁棒性。在仿真测试中,15架无人机集群通行时间平均降低20%。
文摘随着空中交通流量的增长,尾流间隔精细化、动态化缩减成为民航发展的一种趋势,研究尾流演化过程也成为民航领域关注的前沿科学问题。基于此,采用雷诺平均N-S方程方法研究了B737-800飞机有无融合式翼梢小翼对飞机尾涡的演化过程影响。利用美国国家航空航天局(National Aeronautics and Space Administration,NASA)动态尾流系统中尾涡消散模型(aircraft vortex spacing system prediction algorithm,APA)计算了不同气象环境参数下有无小翼的尾涡环量变化。结果表明:融合式翼梢小翼可以分割翼尖涡,有效改变翼尖气流的流动特性,增大速度梯度,减小尾涡速度、尾涡能量集中程度和尾涡强度;不同大气湍流耗散率和大气层结稳定度下,小翼对尾涡强度的减小量不同。
