This study investigates the roll decay of a fishing vessel by experiments and computational fluid dynamics(CFD)simulations.A fishing vessel roll decay is tested experimentally for different initial roll angles.The rol...This study investigates the roll decay of a fishing vessel by experiments and computational fluid dynamics(CFD)simulations.A fishing vessel roll decay is tested experimentally for different initial roll angles.The roll decay is also simulated numerically by CFD simulations and is validated against the experimental results.It shows that the roll damping could be obtained by CFD with high level of accuracy.The linear and nonlinear damping terms are extracted from the CFD roll decay results and are used in a potential-based solver.In this way we are using a hybrid solver that benefits the accuracy of the CFD results in terms of roll damping estimation and the fast computations of the potential-based solver at the same time.This hybrid method is used for reproducing the free roll decays at Fn=0 and also in analyzing some cases in waves.The experiments,CFD and the hybrid parts are described in detail.It is shown that the suggested method is capable of doing the simulations in a very short time with high level of accuracy.This strategy could be used for many seakeeping analyses.展开更多
High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong c...High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong coupling between rigid body motions and hydrodynamic analysis. In addition, free surface should be predicted with good accuracy for each time step. In this paper, velocity and pressure fields are coupled by use of the fractional step method. On the basis of in- tegration of the two-phase viscous flow induced stresses over the hull, acting loads （forces and moments） are calculated. With the strategy of boundary-fitted body-attached mesh and calculation of 6-DoF motions in each time step, time history of ship motions including displacements, speeds and accelerations are evaluated. For the demonstration of the software capabilities, circular cylinder slamming is simulated as a simple type of water slamming. Then, a high-speed planing catamaran is investigated in the case of steady forward motion. All of the results are in good concordance with experimental data. The present method can be widely implemented in design as well as in the performance prediction of high-speed vessels.展开更多
Challenges associated with path-following control for commercial displacement vessels under varying loading and draught conditions are addressed in this study.Adaptive control with the adaptation law technique is used...Challenges associated with path-following control for commercial displacement vessels under varying loading and draught conditions are addressed in this study.Adaptive control with the adaptation law technique is used to mitigate the adverse effects of uncertainty and unmodeled parameters on path-following,particularly in the presence of ocean disturbances.The proposed adaptive path-following control estimates the effect of unmodeled parameters and dynamic behavior by the state estimator.Then,the proposed structure adjusts the gains of the L1 controller.The indirect L1 control is used in the main controller,and stability proof is provided based on Lyapunov theory.The adaptive path-following control is proposed for the underactuated-very large crude carrier 2(VLCC2)as a benchmark vessel.Hydrodynamic coefficients for full load and ballast conditions are determined using empirical formulas.Simulations are conducted in these loading conditions,accounting for a twoknot ocean current,two-knot wind,and waves up to sea state 5.Results highlight that the fixed structure,such as the PID controller,fails to deliver satisfactory performance due to significant variations in the vessel’s mass,inertia,and draught.By contrast,the adaptive path-following control demonstrates robustness under varying conditions by effectively estimating the vessel’s unmodeled parameters.展开更多
文摘This study investigates the roll decay of a fishing vessel by experiments and computational fluid dynamics(CFD)simulations.A fishing vessel roll decay is tested experimentally for different initial roll angles.The roll decay is also simulated numerically by CFD simulations and is validated against the experimental results.It shows that the roll damping could be obtained by CFD with high level of accuracy.The linear and nonlinear damping terms are extracted from the CFD roll decay results and are used in a potential-based solver.In this way we are using a hybrid solver that benefits the accuracy of the CFD results in terms of roll damping estimation and the fast computations of the potential-based solver at the same time.This hybrid method is used for reproducing the free roll decays at Fn=0 and also in analyzing some cases in waves.The experiments,CFD and the hybrid parts are described in detail.It is shown that the suggested method is capable of doing the simulations in a very short time with high level of accuracy.This strategy could be used for many seakeeping analyses.
文摘High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong coupling between rigid body motions and hydrodynamic analysis. In addition, free surface should be predicted with good accuracy for each time step. In this paper, velocity and pressure fields are coupled by use of the fractional step method. On the basis of in- tegration of the two-phase viscous flow induced stresses over the hull, acting loads （forces and moments） are calculated. With the strategy of boundary-fitted body-attached mesh and calculation of 6-DoF motions in each time step, time history of ship motions including displacements, speeds and accelerations are evaluated. For the demonstration of the software capabilities, circular cylinder slamming is simulated as a simple type of water slamming. Then, a high-speed planing catamaran is investigated in the case of steady forward motion. All of the results are in good concordance with experimental data. The present method can be widely implemented in design as well as in the performance prediction of high-speed vessels.
文摘Challenges associated with path-following control for commercial displacement vessels under varying loading and draught conditions are addressed in this study.Adaptive control with the adaptation law technique is used to mitigate the adverse effects of uncertainty and unmodeled parameters on path-following,particularly in the presence of ocean disturbances.The proposed adaptive path-following control estimates the effect of unmodeled parameters and dynamic behavior by the state estimator.Then,the proposed structure adjusts the gains of the L1 controller.The indirect L1 control is used in the main controller,and stability proof is provided based on Lyapunov theory.The adaptive path-following control is proposed for the underactuated-very large crude carrier 2(VLCC2)as a benchmark vessel.Hydrodynamic coefficients for full load and ballast conditions are determined using empirical formulas.Simulations are conducted in these loading conditions,accounting for a twoknot ocean current,two-knot wind,and waves up to sea state 5.Results highlight that the fixed structure,such as the PID controller,fails to deliver satisfactory performance due to significant variations in the vessel’s mass,inertia,and draught.By contrast,the adaptive path-following control demonstrates robustness under varying conditions by effectively estimating the vessel’s unmodeled parameters.
