Underwater stability is one of the important overall performances of deep-sea human occupied vehicles (HOVs). The stability of HOVs is measured by metacentric height (GB), which is closely related to the operation and safety of HOVs. The metacentric height of HOV changes due to the change of ocean parameters and its own ballast during movement. Based on the basic formula of metacentric height and the buoyancy loss calculation method for HOV pressure structure, buoyancy material and hydraulic oil, a mathematical model of metacentric height for HOVs was established in this paper, and a method of underwater stability analysis for HOVs was proposed. Taking “SHEN HAI YONG SHI” HOV as the research object, the underwater stability of HOVs was calculated and analyzed, and the variation law of the metacentric height of HOVs was obtained, which can provide a reference for the design of HOVs.

Based on the discrete module methodology, this paper proposes a numerical method to estimate the mean drift forces on flexible floating bodies. The continuous structure was first discretized into rigid modules connected by elastic beams. The first-order hydroelastic responses were solved by coupling the hydrodynamics on modules and the structural stiffness of elastic beams in the frequency domain. Based on the first-order motions of the modules, the second-order mean drift forces on each rigid module were calculated by second-order multi-body hydrodynamic theory. The motions and mean drift forces of a freely floating flexible barge using the proposed method were verified against the results obtained by the 3D hydroelastic theory based on modal superposition. Moreover, due to the discrete property of the present method for hydrodynamics, the method can be directly extended to inhomogeneous wave conditions.

The cooling system can be carried out by the flow pressure difference through the outside protrusion of an underwater vehicle. This system can prevent the low line frequency pipe noise from the pump’s excitation. However, the protrusion is external, generating the hydrodynamic noise and destroying the acoustic stealth of underwater vehicles. Two protrusion models with a rectangular inlet and a circular inlet were created. The flow field and sound field were numerically calculated. The generation property of the hydrodynamic noise from the two protrusions on the condition of different flow velocities was analyzed. It is indicated that the total radiated sound power of the protrusion with the rectangular inlet is slightly lower than that with the circular inlet. To further reduce the hydrodynamic noise, the protrusion with the rectangular inlet was carried out by the flow control through the serrations. The noise reduction effect of the protrusion with the rectangular inlet by the leading-edge serrations is better than that by the tail-edge serrations. The optimized parameters of the serrations were summarized. To validate the numerical calculation results, four protrusion models were designed and fabricated, and the experimental tests were done in the gravity low-noise water tunnel. The results show that the protrusion with the rectangular inlet by the serrations optimization has a better noise reduction effect in the frequency range from 10 Hz to 2000 Hz. The results in this paper can provide some references for the low-noise design of protrusions of underwater vehicles.

Springback compensation is the main difficulty in the forming of double-curved hull plates by reconfigurable mold. In this paper, springback ratio matrix and springback ratio feature value were proposed by referring to the expression of springback ratio of single-curved plate. Springback ratio matrix describes the springback value of local point of plate while springback ratio feature value describes the whole plate. The conclusion of springback of single-curved plate using springback ratio matrix and springback ratio feature value was consistent with that of the literatures. The forming experiments were conducted and the springback results were described by springback ratio matrix and springback ratio feature value. The results show that springback of saddle-type plates is less than that of sail-type plates when the radii of curvature in both directions are equal, and the springback ratio results based on elastic-plastic theory agree with those of the experiments. A new springback compensation algorithm based on springback ratio matrix was proposed. It is concluded that the springback compensation algorithm based on springback ratio matrix has a better compensation effect.

A marine umbilical is usually bundled by different functional components, the mechanical properties of which are very different. Under the action of external load, unreasonable cross-sectional layouts may lead to large cross-sectional deformation and contact pressure between components, thus affecting the umbilical service life. Firstly, a method to realize the compactness of cross-section layout was given by minimizing the cross-section radius. The symmetry of cross-sectional layout was described by introducing virtual gravity index based on the tensile stiffness of components while a quantifiable index was proposed to describe the fatigue wear problem between vulnerable components like steel pipes. Then, the multi-objective optimization model of cross-section layout was established considering the above three objectives. The genetic algorithm was introduced to solve the optimization model and three representative cross-section layouts were automatically obtained. Finally, the numerical simulation was used to verify and evaluate the different cross-sectional layouts, and then the optimal cross-section layout design was obtained. The results show that the optimization method proposed in this paper can improve the ability of global optimization, which has certain guiding significance for the cross-sectional layout design of umbilicals.

Based on the theory of fluid-structure coupling dynamics, a smoothed particle hydrodynamic model of a two-dimensional rectangular tank was established. Dummy particles were utilized for the treatment of wall boundary in the simulation. Firstly, the effectiveness of the model was verified by comparing simulation results with experimental results. Then, the effects of rolling excitations and various liquid filling levels on impact pressure were discussed. On this basis, different baffle structures were designed, including single and combined baffles. After that, the characteristics of free liquid surface morphology and impact pressure were investigated at the resonance frequency and 30% filling rate. The results show that (1) the roll amplitude has the greatest effect on the pressure peak at the resonance frequency; (2) with the increase of filling level, the double peak characteristics of impact pressure disappear gradually; (3) the T-baffle is beneficial to reduce the level of impact load as the baffle scale is small; (4) and the double T-shaped baffle is effective in reducing impact force at the bottom of the tank.

In order to investigate the analytical calculation method of stress for circular holed infinite plate reinforced with rim bar, the average stress of rim bar region was regarded in the generalized plane stress state approximately and stress function was expressed as two undetermined holomorphic complex functions by complex analysis method in elasticity. The stress function as well as stress was solved through rim bar boundary condition, stress and displacement connection condition between rim bar and panel. Reinforcement coefficient of rim bar was proposed to describe the effect of the rim bar on alleviating stress concentration. Calculation examples demonstrate that the evaluation results of this proposed method have a good agreement with those of FEM, and that the reinforcement effect of the rim bar is obvious since the stress of circular holed infinite plate with rim bar is less than that of infinite plate absent of rim bar generally. Rim bar reinforcement effect is superior to annular additional thick plate in the case of maintaining the same volume of reinforcement components.

To effectively suppress cylindrical vortex induced vibration (VIV), the suppression of cylindrical VIV based on the combined control rod-forced rotation structure was discussed in this paper. Numerical simulations of the cylindrical VIV at low Reynolds number were carried out for comparison and analysis of the flow characteristics, vibration response and hydrodynamic response under different numbers of control rods and rotation rates of the cylinder. The results show that compared with the bare cylinder, the control rods have a positive effect on VIV suppression. For three and five control rods, up to 98% of the cylindrical amplitude suppression can be achieved by adjusting the rotation rate (three control rods, rotation rate 0.4-0.6; five control rods, rotation rate 0-0.2). The amplitude suppression range of the cylinder is identical to the drag reduction range of the cylinder. For the four and six control rods, the effect of rotation on amplitude suppression is small. Vortex shedding on the main cylindrical surface and vortex merging will cause high amplitude fluctuations in the fluid force coefficients, resulting in a high cylindrical amplitude response. For the cylindrical surface with no vortex merging and insignificant vortex shedding, there are no significant fluctuations in the fluid force coefficients and the cylindrical amplitude is significantly reduced.

Conventional bistable wave energy devices have been demonstrated in regular waves by adding adaptive properties to solve the problem of low energy absorption caused by the intrawell oscillation.The power capture performance of an adaptive bistable float wave energy converter (WEC) in irregular waves was studied.The motion equations were established and solved numerically by the fourth-order Runge-Kutta method. The power capture performance of adaptive bistable WEC, conventional bistable WEC and linear WEC was investigated under different device parameters. The results show that with proper device parameters, the adaptive bistable WEC can significantly improve the energy capture performance, and is more suitable for wave energy capture in actual sea conditions than linear and conventional bistable devices.

In order to consider the attenuation effect of the pore medium on the wave propagation deformation, linear resistance, nonlinear resistance and inertial force are introduced in the governing equations of the permeable medium fluid. The exact kinematic and kinetic boundary conditions are used on free surface, and the exact kinetic boundary conditions are adopted on the underwater boundary conditions, and the vertical velocity satisfies the continuity and the horizontal velocity satisfies the momentum equality condition between the free water and the water in permeable medium. Firstly, the three-dimensional Boussinesq-type water-wave equations expressed in two sets of computational velocities with the highest spatial derivative of 3 were derived to suit the wave motion of single-layer permeable seabed. Secondly, Fourier analysis was performed on the newly-presented equations, and the phase velocities and decay rates of the equations were compared with the analytical solutions of Stokes linear waves. The analytical solutions of the equation are in good agreement with the analytical solutions of Stokes linear waves in the range of a dimensionless water depth of h₁/L< 1.0 (deep water wavelength L=gT²/(2π)) at 1% error with a relative water depth of h₂/h₁=0.1-10, which exceeds the range of applicability with any Boussinesq-type model in history. Further, a numerical model of the two-dimensional flume was developed and the numerical model was solved using a prediction-correction-iterative finite-difference method, and a composite fourth-order Adams-Bashforth-Moulton scheme was chosen for time iteration. Finally, the wave evolution over the permeable terrain was simulated and numerical simulations were carried out. Comparison with the relevant experimental results shows a good agreement.