The calculation of ship wave drift load is of great significance to the prediction of ship maneuvering motion. Current studies on the wave drift load of ships mainly focus on the case of zero drift angle (Seo et al., 2021; Chen et al., 2021), however, in the real sea states, the ships move with a certain drift angle. In this paper, TEBEM method (Taylor expansion boundary element method) is used to calculate surge and sway wave drift forces and yaw drift moment of a ship with drift angle in oblique waves, and the comparison is made with the wave drift load of a ship without drift angle. Finally, the influence of drift angle on second-order wave drift load of ship is analyzed in detail. When the wave length-to-ship length ratio is small, the surge drift force decreases and the sway drift force increases with the increase of drift angle, and the drift angle have minor effect on yaw drift moment.
In addition to the first-order wave force, the ship with speed in the wave will also be subjected to the second-order wave drift load. In recent years, with the attention paid to the energy consumption of ships and the maneuverability of ships in waves, the surge drift forces (added resistance) have been extensively studied. However, there are few studies on the sway wave drift forces and yaw drift moment of a ship in oblique waves, and even less on the second-order wave drift load of ships with drift Angle in oblique waves. However, under severe sea conditions or rolling resonance, the sway drift force and the yaw drift moment may become very large and have a great influence on the ship's maneuvering. Moreover, the ship usually has a certain drift angle when moving under real sea conditions, and the existence of drift angle will affect the calculation of second-order wave drift load. Therefore, in order to improve the prediction accuracy of ship maneuverability in waves, it is very important to study the second-order drift load of ships with drift angle in oblique waves.
At present, the research on second-order wave drift load of ships mainly focuses on the following three aspects, which are experimental method, the computational fluid dynamics (CFD) method and the potential flow method. The experimental method is still the most reliable method to measure the second-order wave drift load of ships. Guo and Steen (2011) conducted model tests for the surge wave drift force on KVLCC2. Park et al. (2018) completed experiments under the oblique waves to measure the added resistance on a tanker, and wave direction was changed from 180° to 0°. Seo et al. (2021) measured surge and sway wave drift forces and yaw drift moment of the KVLCC2 model ship under different wave direction by a direct method using force sensors, and an indirect method using tensiometers. The measurement results of these two methods differ obviously when the wave length-to-ship length ratio is small. With the development of computer technology, CFD (the Computational Fluid Dynamics) method is widely used in solving nonlinear response of ship and added resistance. However, there are few scholars use CFD method to solve sway wave drift forces and yaw drift moment of a ship in oblique waves, the main reason is that CFD method is seriously time-consuming, and unsuitable for routine ship design applications (Sadat-Hosseini et al. 2013; Tezdogan et al. 2015; Sigmund et al. 2018). In comparison, the potential flow method based on the Rankine panel method with forward speed is more robust and efficient. Using a Rankine panel method, Lyu et al. (2017) obtained surge wave drift force (added resistance), sway wave drift force and yaw wave drift moment coefficients for a containership and a cruise ship at ship heading angles from 0 to 180deg. Yasukawa et al. (2019) calculated the wave drift load using a zero-speed, three-dimensional panel method and a strip theory based Kochin function method and the calculated results are in good agreement with the experimental results. Zhang et al. (2020) calculated the second-order drift load of model ships at zero speed and with speed based on a time Romain Rankine panel method. Seo et al. (2021) used the frequency domain Rankine panel method to calculate the second-order wave drift load of KVLCC2 model ship under different waves, and compared it with the experimental value. The results show that the numerical results are in good agreement when the wave length-to-ship length ratio is large. These only calculated the second-order wave drift load of ships under different waves, ignoring the existence of ship drift angle.
