Abstract Horizontal welding is important for heavy or huge welding structures. Keyhole mode variable polarity plasma arc welding of aluminum alloy plates with medium thickness was carried out in horizontal position. T...Abstract Horizontal welding is important for heavy or huge welding structures. Keyhole mode variable polarity plasma arc welding of aluminum alloy plates with medium thickness was carried out in horizontal position. The characteristic of welding defects was introduced. Preliminary experiments indicated that the undercut defect could not be eliminated easily. The relationship between welding parameters and the undercut defect showed that this deject could be lessened by using higher heat input. The fluid flow of weld pool was observed by a high speed camera. The fluid flow in weld pool was not symmetric and much of molten metal gathered in the lower part. The fluid flow velocity in the lower part was bigger than that in the upper part. To this end, the formative mechanism of the undercut defect was proposed. The flowability of the molten metal was an influential factor for the undercut defect. A preheating method was designed to verify the formative mechanism.展开更多
Based on a dual-polarization high-frequency wave radar system, an adaptive system using horizontal antennas for the suppression of the Es layer interference （ELI） is deseribech The data received from the horizontal ...Based on a dual-polarization high-frequency wave radar system, an adaptive system using horizontal antennas for the suppression of the Es layer interference （ELI） is deseribech The data received from the horizontal antennas were correlated with the data received from the Vertically Polarized Antennas （VPAs） to estimate and cancel the interference adaptively in the VPAs. Suppressing the interference after each coherent integration time interval, about 25 dB signal-to-interference ratio is expected with the experimentally derived data.展开更多
近年来的工程实践表明,以速度频散特性为理论基础的传统瑞利面波法的实际应用存在场地限制的瓶颈问题.为克服该困难,本文从面波的基础理论着手,在前人建立的水平层状介质中瑞利面波速度频散方程的基础上,推导了水平层状介质中瑞利面波...近年来的工程实践表明,以速度频散特性为理论基础的传统瑞利面波法的实际应用存在场地限制的瓶颈问题.为克服该困难,本文从面波的基础理论着手,在前人建立的水平层状介质中瑞利面波速度频散方程的基础上,推导了水平层状介质中瑞利面波质点位移的解析解公式.以工程中常见的几种典型的水平层状地层模型为例,结合地脉动单点谱比法(HVSR,Horizontal to Vertical Spectral Ratio),对基阶瑞利面波的椭圆极化特征进行了数值模拟研究.研究结果表明:与瑞利面波的速度频散特性类似,其椭圆极化同样具有频散特性,且椭圆极化时的质点位移水平分量与垂直分量的频谱比与地层泊松比结构有关.瑞利面波的这种椭圆极化特性展示了利用单点瑞利面波的多分量评价地层泊松比结构的理论可行性.展开更多
基金This research is supported by the National Natural Science Foundation of China （Grant No. 51475105）.
文摘Abstract Horizontal welding is important for heavy or huge welding structures. Keyhole mode variable polarity plasma arc welding of aluminum alloy plates with medium thickness was carried out in horizontal position. The characteristic of welding defects was introduced. Preliminary experiments indicated that the undercut defect could not be eliminated easily. The relationship between welding parameters and the undercut defect showed that this deject could be lessened by using higher heat input. The fluid flow of weld pool was observed by a high speed camera. The fluid flow in weld pool was not symmetric and much of molten metal gathered in the lower part. The fluid flow velocity in the lower part was bigger than that in the upper part. To this end, the formative mechanism of the undercut defect was proposed. The flowability of the molten metal was an influential factor for the undercut defect. A preheating method was designed to verify the formative mechanism.
文摘Based on a dual-polarization high-frequency wave radar system, an adaptive system using horizontal antennas for the suppression of the Es layer interference （ELI） is deseribech The data received from the horizontal antennas were correlated with the data received from the Vertically Polarized Antennas （VPAs） to estimate and cancel the interference adaptively in the VPAs. Suppressing the interference after each coherent integration time interval, about 25 dB signal-to-interference ratio is expected with the experimentally derived data.
文摘近年来的工程实践表明,以速度频散特性为理论基础的传统瑞利面波法的实际应用存在场地限制的瓶颈问题.为克服该困难,本文从面波的基础理论着手,在前人建立的水平层状介质中瑞利面波速度频散方程的基础上,推导了水平层状介质中瑞利面波质点位移的解析解公式.以工程中常见的几种典型的水平层状地层模型为例,结合地脉动单点谱比法(HVSR,Horizontal to Vertical Spectral Ratio),对基阶瑞利面波的椭圆极化特征进行了数值模拟研究.研究结果表明:与瑞利面波的速度频散特性类似,其椭圆极化同样具有频散特性,且椭圆极化时的质点位移水平分量与垂直分量的频谱比与地层泊松比结构有关.瑞利面波的这种椭圆极化特性展示了利用单点瑞利面波的多分量评价地层泊松比结构的理论可行性.
