An immersed body boundary method is adopted to track the motions of a towing cylinder, and a homogenous multiphase Eulerian-Eulerian fluid approach is used to capture the free surface. The Reynolds average Navier-Stoc...An immersed body boundary method is adopted to track the motions of a towing cylinder, and a homogenous multiphase Eulerian-Eulerian fluid approach is used to capture the free surface. The Reynolds average Navier-Stockes(RANS) solver is applied to all gird nodes to deal with different velocities of the nodes that are in the body boundary, near the boundary and out of the boundary and their effect on the fluid. The towing cylinder resistance at different submerged depths in the tank is presented. The simulation results are compared with the experimental data, and the method is verified and validated. Finally, the hydrodynamic characters of the cylinder are discussed further. The numerical and experimental results show that at high speeds, the deeper the cylinder submerges, the lower resistance it suffers. The resistance coefficient trough is obtained at Froude number in the range of 0.3 < F r < 0.4. These phenomena can provide some suggestions on the small waterplane area twin hull(SWATH) design.展开更多
The horizontal vibration of towed seismic streamers is a main reason for effciency reduction of the seismic survey and tail tangling.A vibration suppression scheme of towed seismic streamers is investigated in this pa...The horizontal vibration of towed seismic streamers is a main reason for effciency reduction of the seismic survey and tail tangling.A vibration suppression scheme of towed seismic streamers is investigated in this paper.The towed seismic streamer is divided into two spans,a controlled span,i.e.,the low tension span, and an uncontrolled span,i.e.,the high tension span,by a bird.The system model includes a hyperbolic partial differential equation with variable coeffcient describing the towed seismic streamers,and an ordinary differential equation describing the dynamic of bird.Robust based-model knowledge and adaptive controllers,based on the Lyapunov method,are designed to isolate the vibration of towed seismic streamers caused by the course deviations of towing vessel,the variations of towing vessel velocity and the variations of towed seismic streamer density.The robust based-model knowledge and adaptive controllers exponentially and asymptotically drive the span-towed seismic streamer displacement to zero,respectively.A finite difference scheme is used to validate the effciency of the control law.The proposed controller can isolate effectively the disturbance originated from the towed vessel, and can provide the improved damping but not sacrifice the isolation performance.The adaptive scheme can tolerate the lack of knowledge of some uncertain parameters and can directly execute the online adjustment of the parameters.Meanwhile,the proposed control law is robust and can resist the model uncertainty due to parameter incertitude,model error and unknown disturbance and so on.The control law only includes velocity and slope,while it does not need the displacement which is diffcult to measure in the practical operations.Thus it is easy to implement.展开更多
基金Fund of State Key Laboratory of Ocean Engineering of Shanghai Jiao Tong University(No.GKZD010059-22)
文摘An immersed body boundary method is adopted to track the motions of a towing cylinder, and a homogenous multiphase Eulerian-Eulerian fluid approach is used to capture the free surface. The Reynolds average Navier-Stockes(RANS) solver is applied to all gird nodes to deal with different velocities of the nodes that are in the body boundary, near the boundary and out of the boundary and their effect on the fluid. The towing cylinder resistance at different submerged depths in the tank is presented. The simulation results are compared with the experimental data, and the method is verified and validated. Finally, the hydrodynamic characters of the cylinder are discussed further. The numerical and experimental results show that at high speeds, the deeper the cylinder submerges, the lower resistance it suffers. The resistance coefficient trough is obtained at Froude number in the range of 0.3 < F r < 0.4. These phenomena can provide some suggestions on the small waterplane area twin hull(SWATH) design.
基金the National Natural Science Foundation of China(No.51079083)
文摘The horizontal vibration of towed seismic streamers is a main reason for effciency reduction of the seismic survey and tail tangling.A vibration suppression scheme of towed seismic streamers is investigated in this paper.The towed seismic streamer is divided into two spans,a controlled span,i.e.,the low tension span, and an uncontrolled span,i.e.,the high tension span,by a bird.The system model includes a hyperbolic partial differential equation with variable coeffcient describing the towed seismic streamers,and an ordinary differential equation describing the dynamic of bird.Robust based-model knowledge and adaptive controllers,based on the Lyapunov method,are designed to isolate the vibration of towed seismic streamers caused by the course deviations of towing vessel,the variations of towing vessel velocity and the variations of towed seismic streamer density.The robust based-model knowledge and adaptive controllers exponentially and asymptotically drive the span-towed seismic streamer displacement to zero,respectively.A finite difference scheme is used to validate the effciency of the control law.The proposed controller can isolate effectively the disturbance originated from the towed vessel, and can provide the improved damping but not sacrifice the isolation performance.The adaptive scheme can tolerate the lack of knowledge of some uncertain parameters and can directly execute the online adjustment of the parameters.Meanwhile,the proposed control law is robust and can resist the model uncertainty due to parameter incertitude,model error and unknown disturbance and so on.The control law only includes velocity and slope,while it does not need the displacement which is diffcult to measure in the practical operations.Thus it is easy to implement.
