Abstract
The motion stability of the Unmanned Surface Vessel (USV) is threatened by the action of waves under a rough sea state. In the present paper, the motion of a large-scale USV is numerically simulated under high sea state of level 5 and 7. The overset grid method and Reynolds Averaged Navier–Stokes (RANS) approach are employed to solve Navier–Stokes (N-S) equations. For the case of wave incident angle 0° and 30°, the heave, pitch and roll motion response of a large scale USV are investigated by using the six Degrees of Freedom (6-DOF) numerical model. The effects of different sea states, as well as different wave directions, on the motion of USV are compared. The comparative results indicate that the response of this USV in waves is the periodic free-motion according to the corresponding amplitude, which does not exceed the stable range, and there are no overturning and other situations that may affect the safety, in the case of level 5 and 7 sea states. The corresponding pressure at the bottom of this USV meets the range of material strength, and no structural damage or injury to the hull occurs, although the pressure varies at different wave periods. For the case of different wave directions, the analysis of the boundary layer thickness shows that the wave direction is of great importance to the boundary layer thickness distribution, both in the level 5 and level 7 sea states.
Highlights
In recent years, a variety of unmanned surface vehicles (USV) have emerged around the world for different operation requirements
The results show that the peak value of the additional resistance and motion response of the trimaran is mainly affected by the wavelength [14]
The dynamic fluid body interaction (DFBI) module [18] combined with overset mesh method simulates the heave, pitch, and roll motion of the USV in response to forces exerted by the wave
Summary
A variety of unmanned surface vehicles (USV) have emerged around the world for different operation requirements. The motion response and resistance performance in a real sea state are very important for the safe and efficient completion of the task for USV. The numerical methods for predicting ship motion response in waves include classical potential flow theory and unsteady Reynold’s time-averaged equations (RANS). Tahsin found that in the case of high-speed navigation, the additional resistance and motion response obtained by the RANS equation are most different from those based on potential flow theory [13]. Deng Rui et al studied the additional resistance and motion response of the trimaran under different wave amplitude conditions by using the method of viscosity based on RANS. The RANS method and SST k-ω are applied as the turbulent model to solve the N-S equation and simulates the motion of the USV in the high sea states of 5 and 7 levels. The differences of the motion response under different wave directions are compared, and the hull pressure and boundary layer distribution under different working conditions are studied
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