Hao Wu

An air-lubricated planing hull with integrated air channels presents a transformative approach for enhancing marine vessel performance by significantly reducing hydrodynamic resistance. Within the framework of air-layer drag reduction research, the precise definition and optimization of geometric design parameters are critical, as they directly influence the formation and stability of the air layer and the hydrodynamic characteristics of the hull. Applying a fully parameterized modeling approach to the air-lubricated planing hull is highly relevant and pivotal for advancing systematic, performance-driven hull design and optimization in modern naval architecture. This study proposes a fully parameterized modeling method specifically designed for such crafts. The method utilizes B-spline curves to represent the planar projections of the primary hull contours and the sectional lines of key hull surfaces. The hull surfaces are fitted using non-uniform rational B-Spline (NURBS) surfaces, and the design parameters are smoothed according to the principle of minimum strain energy, leading to fair and smooth hull surfaces. A dedicated program is developed based on this method. It facilitates the rapid generation of smooth hull forms for an air-lubricated planing hull solely from design parameters without depending on parent hull forms. This approach provides geometric hull samples for optimizing the hydrodynamic performance of the air-lubricated planing hull.

The maximum diving depth of modern submarines has always been increasing. Although this has been useful and in some cases necessary, it usually comes with some risks. For instance, when a submarine encounters an emergency situation that requires immediate ascent from great depths, the situation becomes more dangerous, especially due to its rolling characteristics. To investigate the effect of unsteady forces during free ascent motion of submarines at great depths on submarine rolling, in this study, the SST-DDES model combined with the overset grid technique was used for the numerical simulation of a submarine free ascent. Water tank experiments for free ascent were conducted to validate the numerical approach, which confirmed the reliability of the numerical method. Following this, the CFD method was employed to conduct an initial exploratory investigation into the free ascent motion of deep-submergence submarines. The free ascent motion of submarines at great depths under five different degrees of freedom combinations was studied. The computational results indicated that submarines are more prone to roll over during free ascent at great depths. At a depth six times the length of the submarine, the maximum roll angle underwater reaches 22.8°. In addition, unsteady rolling moments, lateral forces, and yawing moments have a significant effect on submarine rolling, intensifying the tendency to roll. Furthermore, it was observed that the vertical hydrodynamic attack angle β is related to the rolling stability of the submarine, such that a moderate decrease in β is beneficial for the rolling stability. The numerical calculation method and preliminary research findings can provide theoretical support for controlling the ascent motion of real submarines.

When a submarine encounters an emergency situation, it should take emergency-surfacing actions by moving upward with a large angle of attack in the vertical plane. Previous research has often neglected the effect of vertical plane motion on the lateral force (F_y), rolling moment (M_x), and yawing moment (M_z). To examine the flow characteristics of submarines at high angles of attack on the vertical plane, the SST-DDES method is adopted in conjunction with adaptive mesh refinement (AMR) technology, and the new Omega vortex detection method is employed as the AMR criterion for numerical calculations. The obtained results are then appropriately verified by conducting water tank experiments, and the effects of different angles of attack and heel angles on F_y, M_x, and M_z are methodically examined. The results reveal that, in the flow around the vertical plane of a submarine, the influence of F_y and M_z cannot be ignored. In addition, when the vertical velocity of the hull is greater than 0.6 m/s, the influence of M_x cannot be overlooked either. When the angle of attack on the vertical plane of the submarine is greater than 25°, the effects of F_y, M_x, and M_z cannot be neglected, and the effect of M_z is particularly prominent, with its amplitude close to or greater than the average value of the pitch moment (M_y). The obtained results reveal that the presence of the heel angle (θ) intensifies the forces on the hull for F_y, M_x, and M_z, and the forces caused by the vertical velocity at F_y, M_x, and M_z cannot be neglected. These findings can provide a mechanical analysis basis for the analysis of nonlinear motion phenomena during submarine surfacing.

Maneuverability is one of the submarine’s most important features, and is closely related to hydrodynamic coefficients. The submarine standard motion equation is the most commonly used hydrodynamic mathematical model, estimating more than 100 hydrodynamic coefficients. This paper applies the Bayesian ridge regression model to identify a submarine’s hydrodynamic coefficients. Specifically, the proposed approach combines the URANS equation with a six-degree-of-freedom motion model and a body force propeller model, and uses overset grid technology to simulate the underwater six-degree-of-freedom navigation motion of the SUBOFF submarine. The submarine’s required hydrodynamic coefficients are obtained by collecting relevant velocity and angular velocity data and applying the Bayesian ridge regression model for data identification. Meanwhile, CFD simulation of the restraint model test for the SUBOFF submarine is conducted to obtain the related hydrodynamic coefficients. Through comparative experiments, we validate that the proposed Bayesian ridge regression model identification method is effective and reliable; most of the errors in the hydrodynamic coefficients were within 10%, with a maximum error of −43.26%, providing more comprehensive and timely hydrodynamic coefficients than traditional CFD restraint model tests. Furthermore, the hydrodynamic coefficient identification results were used to invert the submarine’s spatial motion, and we demonstrated that the resulting trajectory, velocity, and angular velocity curves all fit well.