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.

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.

With the continuous development and consumption of traditional land resources, the development and utilization of new water energy has become a new trend, and a large number of various floating structures have appeared. As the key to ensure the safe and stable operation of floating structures, mooring systems have always been the focus of the industry. In this paper, a large number of literature review and research were carried out on the existing floating structure mooring systems, the types of floating structures were summarized, the mooring system structures were analyzed from the aspects of the classification of the mooring systems, the way of chain distributions, the bottom anchorage foundation types and the new mooring systems, and the characteristics and advantages and disadvantages of various mooring cable materials were discussed. The static characteristics and dynamic response of the mooring systems were analyzed according to a large number of existing literatures, and the applicability evaluation and recommendation of various mooring methods were given through a comprehensive analysis of the water depth, seabed topography, geology, platform function, wind and wave conditions, economy and other aspects of the mooring engineering, and the shortcomings of the existing research were pointed out, and the current research direction still needs to be further developed.

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.

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.

With an 80 000 DWT bulk carrier taken as the optimization object, two new hull lines design technologies based on the hull fusion method and regional feature analysis were applied by combining ship CFD resistance and self-propulsion assessment for the research on hull lines design and performance analysis, aiming at the hydrodynamic performance under design draft. With the whole design process starting with the reference ship, the hull line automatic deformation designs of the bow and stern part were made respectively in order to reduce the resistance and improve the wave making and stern wake distribution. By analyzing the CFD numerical simulation evaluation results under the same model scale, a series of design hulls with good performance were successfully obtained. Finally, the simulation results were verified by model test under the design draft in still water. Compared with the design prototype, the received power trial prediction of the final design scheme at the speed of 14.0 kn was reduced by about 5.6%.

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.

In order to evaluate the 3D effects of wave glider spring hydrofoil mechanism in waves on its dynamic performance, a numerical computational model of the wave glider spring hydrofoil mechanism was developed. Based on the overset mesh technology, the dynamic performance between 2D and 3D hydrofoils was analyzed and studied by using CFD FLUENT software. The results show that due to the limited span of the 3D hydrofoil, the tip vortex phenomenon is generated at the wing tip, resulting in reduced hydrofoil dynamic performance, and that the forward propulsion efficiency of the 3D hydrofoil is reduced by 22.1% compared with that of the 2D hydrofoil. Then, the bionic principle was used to design the wave glider bionic hydrofoil. It is found that the bionic hydrofoil reduces the loss of hydrofoil power performance by the tip vortex, while the forward thrust of the bionic hydrofoil is increased by 17.6% and the efficiency by 10.4% compared with the 3D hydrofoil of the same spreading chord ratio. Finally, the experimental comparison shows that the CFD simulation data and the experimental data have the same trend, and the reliability of the CFD simulation model is verified.

Aiming at the actual demand of improving the numerical simulation of unsteady submarine motion in maneuvering condition, the overset mesh was used to directly model six degree of freedom coupling motion of a submarine and the independent motion of each control surface, and the sliding mesh was used to directly simulate the propeller rotation at the stern of a submarine, so as to carry out the research on the numerical simulation of a generic submarine in self-propulsion and free running maneuvering conditions. Through the procedure of numerical simulation in typical working conditions, such as submerged self-propulsion, turning maneuver, zigzag maneuver, crashback, etc., the issues of submarine/propeller/rudder hydrodynamic coupling modeling and PD (proportional-derivative) numerical control realization of autopilot in maneuvering condition were emphatically solved, and the technology of free running submarine model numerical simulation based on overset mesh was established. At the same time, the surrounding flow phenomenon and the time-history change process of kinematics and dynamics parameters of the submarine in maneuvering condition were analyzed. By comparing the numerical simulation results of typical dynamics parameters with the model test results, the practicability of the approach for engineering prediction was verified. The research can provide a guidance for the prediction and evaluation of submarine maneuverability and seaworthiness. It is beneficial for the improvement of free running submarine model tests.