Aerodynamic drag reduction is required with new stringent constraints on pollutant emissions and fuel efficiency of ground vehicles. In this context, active flow control is a promising approach to achieve this target. This study focuses on applying different flow control strategies on the square-back Ahmed model to reduce aerodynamic drag. A steady blowing jet, a synthetic jet and an unsteady jet are located at the back edges of the model as flow control devices. A numerical study based on the 3D WMLES simulation was performed to evaluate the drag reduction capabilities of these devices at different operating conditions. The results showed that a maximum aerodynamic drag reduction of 26.51% was achieved when using a steady blowing jet, and 17.27% with an unsteady jet. In contrast, the effect of the synthetic jet on the aerodynamic drag of the model is solely at high control frequencies.

With the continuous increase in ship size combined with the generally slower increase in the sizes of waterways, the need for the prediction of ship maneuvering in shallow waterways continues to attract attention from the international scientific community. Ship behavior in shallow water is relevant in seabed effects that result in changing the hydrodynamic forces acting on a ship. In this study, the maneuvering characteristics of a container ship with four degrees of freedom in shallow water are analyzed. The Reynolds-Averaged Navier Stokes approach in Ansys Fluent code is used to produce the maneuvering coefficients through the simulations of forward running, static drift, static heel, circular motion, the combined motions, and the pure roll motion of the KRISO container ship. The maneuvering characteristics of the ship are estimated for evaluating the ship behaviors in shallow-water conditions. The obtained results show that the roll has a significant decrease and the ship’s turning diameter has a significant increase when the ship operates in a shallow waterway. The predicted maneuvering characteristics of the ship are in good agreement with those of free-running model tests, indicating that the numerical simulation based on the Computational Fluid Dynamics method has good capability to predict the maneuvering derivatives and the four-DOF ship maneuvering motion in shallow water as well.

Comparative Study of Drag Reduction of Square-back Vehicle Geometry using Steady blowing and Fluidic Oscillators Method

This study presents the predicted hydrodynamic characteristics of different rudder plane configurations on the stern of a full-scale submarine in deep water, which are obtained using the Reynolds-Averaged Navier–Stokes method in Ansys Fluent Solver. First, the results obtained for the X-rudder plane configuration are verified according to previous numerical and experimental results in order to assess the accuracy of the simulation procedure. The X-rudder plane, Y-rudder plane, and Cross-rudder plane configurations in deep water with deflection angles ranging from −21 degrees to +21 degrees are then simulated. Next, the hydrodynamic forces and moments of the Cross-plane, X-plane, and Y-plane rudder configurations obtained through simulation are analyzed using Taylor’s expansion to estimate the hydrodynamic coefficients. The obtained results demonstrate that the X-force of the X-plane rudder configuration is larger than the corresponding forces acting on the Cross-plane rudder and Y-plane rudder configurations. Meanwhile, the Y-force and Z-force of the X-plane rudder configuration are significantly greater than the corresponding forces of the left configurations. The same tendency can be seen in the moment of the X-plane rudder about the y- and z-axes. However, the roll moment induced by the Y-plane and Cross-plane rudder configurations is significantly larger than that under the X-plane rudder configuration.

Modern ship designs are being developed for various purposes in uncrewed operation. In particular, low-speed uncrewed surface vehicle (USV) catamarans have been applied as rescued boats in recent years. Therefore, predicting the performance of this ship type in calm water and waves is necessary. This study investigates the response, shear force, and bending moment of a low-speed USV catamaran operating in regular and irregular waves. Numerical simulations are conducted using the Ansys AQWA solver, which employs the boundary element method to model inviscid flow. The catamaran’s responses in regular waves, with the ratio of wavelength to ship length ranging from 0.4 to 2.0, are compared with the experimental data. The catamaran’s behavior in irregular waves is then determined from integrating its responses in regular waves over the encounter wave spectrum. Additionally, the catamaran’s responses and the wave-induced vertical shear force and the bending moment at the x- and y-axes within a frequency range of 0.2 to 3.0 rad/s are analyzed. We demonstrated that the heave, roll, and pitch of the catamaran align well with the corresponding experimental data. Significant vertical shear forces are observed at a wavelength-to-ship-length ratio of 1.0, particularly at one-fourth of the ship's length from either end. The transverse bending moment is significant in a wide range of wave frequencies for the ship in beam seas. The findings show that the maximum midship vertical bending moment in the frequency range of 1.5 to 3.0 when the ship moves in head waves should be considered. The vertical shear force and transverse midship bending moment in the whole frequency domain should be assessed when the catamaran operates in beam waves.

Motion characteristics of unmanned surface vehicle are mainly affected by sea wave during its operation. This paper shows the numerical results of the unmanned surface ship at various scales in irregular waves based on the boundary element method. The effects of different sea states on each scaled model in a head sea, bow quartering sea, and beam sea are analyzed to predict the safety region of the ship motion. The significant amplitudes of ship motion are obtained from the ship motion responses in regular waves. Steady wave drift forces in the cases of bow oblique sea are calculated to find the impact of second-order waves on the models. It is proved that the motion of model C is remarkable in the narrow frequency domain from 0.2 to 1.4 rad/s but the ship responses of model A are considerable in the range of frequency of 0.2 to 2.5 rad/s. The significant amplitude of surge and pitch motion reaches the peak values in head sea conditions while the peak values of yaw motion are in the oblique sea of 120 degrees. The left motion is maximum in head sea condition.