A wave load computation approach in direct strength analysis of semi-submersible platform structures was presented in this paper. Considering the differences in shape of pontoon, column and beam, the combination of ac...A wave load computation approach in direct strength analysis of semi-submersible platform structures was presented in this paper. Considering the differences in shape of pontoon, column and beam, the combination of accumulative chord length cubic parameter spline theory and analytic method was adopted for generating the wet surface mesh of platform. The hydrodynamic coefficients of platform were calculated by the three-dimensional potential flow theory of the linear hydrodynamic problem for platform with low forward speed. The equation of platform motions was established and solved in frequency domain, and the responses of wave-induced loads on the platform can be obtained. With the interpolation method being utilized, the pressure loads on shell elements for finite element analysis (FEA) were converted from those on the hydrodynamic computation mesh, which pave the basis for FEA with commercial software.A computer program based on this method has been developed, and a calculation example of semi-submersible platform was illustrated.Analysis results show that this method is a satisfying approach of wave loads computation for this kind of platform.展开更多
Upward lightning flashes initiated simultane- ously from two towers separated by a distance of 3420 m were analyzed in detail based on high-speed camera images and S-band Doppler radar echo intensity. Both discharges ...Upward lightning flashes initiated simultane- ously from two towers separated by a distance of 3420 m were analyzed in detail based on high-speed camera images and S-band Doppler radar echo intensity. Both discharges lasted more than 250 ms and were self-initiated from the towers in the form of upward positive leaders with a time difference of less than 4 ms. Abundant recoil leaders oc- curred transiently in the remnant channel sections during the development of the upward lightning. The number of recoil leaders over the lower tower was greater than over the higher tower. When the concurrent upward flashes occurred, the radar echo intensity in the area of the towers was no more than 45 dBZ and the towers were separately located beneath two echo centers with low altitudes of 2-3 kin.展开更多
文摘A wave load computation approach in direct strength analysis of semi-submersible platform structures was presented in this paper. Considering the differences in shape of pontoon, column and beam, the combination of accumulative chord length cubic parameter spline theory and analytic method was adopted for generating the wet surface mesh of platform. The hydrodynamic coefficients of platform were calculated by the three-dimensional potential flow theory of the linear hydrodynamic problem for platform with low forward speed. The equation of platform motions was established and solved in frequency domain, and the responses of wave-induced loads on the platform can be obtained. With the interpolation method being utilized, the pressure loads on shell elements for finite element analysis (FEA) were converted from those on the hydrodynamic computation mesh, which pave the basis for FEA with commercial software.A computer program based on this method has been developed, and a calculation example of semi-submersible platform was illustrated.Analysis results show that this method is a satisfying approach of wave loads computation for this kind of platform.
基金supported by the National Basic Research Program of China (Grant No.2014CB441405)the National Natural Science Foundation of China (Grant No.41375012)
文摘Upward lightning flashes initiated simultane- ously from two towers separated by a distance of 3420 m were analyzed in detail based on high-speed camera images and S-band Doppler radar echo intensity. Both discharges lasted more than 250 ms and were self-initiated from the towers in the form of upward positive leaders with a time difference of less than 4 ms. Abundant recoil leaders oc- curred transiently in the remnant channel sections during the development of the upward lightning. The number of recoil leaders over the lower tower was greater than over the higher tower. When the concurrent upward flashes occurred, the radar echo intensity in the area of the towers was no more than 45 dBZ and the towers were separately located beneath two echo centers with low altitudes of 2-3 kin.
