Large vessel-shaped fish cages are promising large aquaculture structures developed in recent years, with maximum structure length of nearly 400 meters. The effects of the hydrodynamics on the nets and the frames will be significant for the cage deformation response in waves, which will increase the complexity of the cage design. In this paper, a coupled dynamic model of a large vessel-shaped fish cage is used to calculate the motion and structural response in the time domain. Firstly, the floating body of the cage is discretized into multi-module units, connected by equivalent elastic beams. The nonlinear effects of the net and steel frames are considered. A floating cage model considering the deformation of the floating body is then established in time domain for dynamic analysis. The radiation force of the floating body is solved by applying the added mass and damping directly or the state space method, and the hydrodynamic loads on the net and steel frames considering the disturbing effect of floating body are calculated by Morison formula. The results show that the hydrodynamics of the net and frames have an obvious influence on the response of the fish cage and the cross-sectional elasticity produces a certain degree influence on the net twine tension, which provides reference for structural analysis and cross-sectional design of the large vessel-shaped fish cages.

The soft yoke mooring system is one of the main mooring methods of FPSO. The motion state of the mooring system under the combined action of wind and wave and other environmental loads shows the dynamic characteristics of high aggregation of multiple degrees of freedom and modal mixing. In this paper, in view of the traditional clustering algorithm that cannot obtain the characteristics of small clusters characterizing extreme operating conditions, a BCALoD clustering algorithm based monitoring data extraction method for soft yoke mooring systems was proposed for compression and dynamical analysis of the massive data. The clustering results show that the cluster centers of multiple data clusters correspond to the mooring attitude under normal operating conditions, but the cluster centers of relatively few data clusters contain not only the mooring attitude under extreme operating conditions but also the mooring attitude under normal operating conditions. The horizontal and vertical mooring forces were calculated for each clustering condition by extracting the time course data of each clustering center based on the original data and combining with the multibody dynamic modelling of soft yoke mooring system. The results of the force analysis based on the clustering show that the mooring forces of the clustered normal and extreme conditions are as expected, and that the extreme force states under the normal behavior of the mooring attitude are found in particular, which characterize the inadequacy of the design consideration of the soft yoke mooring system. It is shown that the clustering method in this paper has the ability to effectively extract the dangerous conditions of the soft yoke mooring system, and that it is important to pay attention not only to the forces in extreme attitudes, but also to the extreme forces generated by the coupling of attitude motion.

A design method for wake-adapted contra-rotating propellers (CRPs) with optimal circulation distribution was presented based on the vortex lattice model in lifting surface theory. The implicit relations of propeller thrust and torque with the radial circulation distributions of CRPs were modelled via neural network, where the input data for training of the neural network were yielded from an in-house vortex-lattice code. Subject to the requirements for total thrust and torque-balance, a genetic algorithm was employed to optimize the radial circulation distributions of the forward and aft propellers to maximize the total efficiency. Taking the optimal radial circulation distributions and a prescribed chordwise distribution of circulation as the objective, the camber surface geometries and pitch distributions of the forward and aft propellers were designed. Numerical example was presented with the CRPs for a high-speed underwater vehicle, and the design results were then validated in self-propulsion simulation by solving the unsteady RANS equations. While the efficiency and torque-balance of the designed CRPs are slightly improved against the prototype, the minimum pressure values on blade surfaces are significantly increased, which is favorable for retarding the inception of cavitation.

In this paper, a NURBS-based geometric parametric level set topology optimization method is proposed to address the challenges faced by the traditional topology optimization method in seamlessly integrating CAD and CAE and dealing with the fragmentation between geometric modeling, structural analysis, and optimization design for complex ship structures. Firstly, the ship structure is immersed in a three-variable NURBS 3D solid structure. Then, a ray-tracing-algorithm is employed to quickly determine the relevant geometric information of the design domain, boundary, and load application area, such as units and control points, in order to establish the NURBS-based geometric parametric level set topology optimization method. By this method, the limitations of traditional NURBS-based topology optimization, which is restricted by regular NURBS topology, are overcome. The method can handle any complex CAD model. It is demonstrated through numerical examples that the computational efficiency of the algorithm can be improved by more than 30% compared to the traditional geometric SIMP method.

Oscillating-water-column (OWC) wave energy converters (WECs) have attracted worldwide attention because of their simple structures and easy maintenance. However, they still face the issues of low energy conversion efficiency and narrow effective frequency bandwidth. A numerical simulation of the hydrodynamic performance of an offshore stationary dual-OWC array was conducted. Based on the potential flow theory, a nonlinear aerodynamic model considering air-liquid coupling was constructed by introducing aerodynamic and artificial damping on the first and second-order free surface boundaries of the OWC chamber. A set of physical experiments were carried out to validate the numerical model, and a good agreement between the experimental and numerical results was achieved. The results show that the chamber resonant frequency shifts due to the multiple diffraction waves between component devices. Appropriate array arrangement helps to improve the relative capture width and effective frequency bandwidth of the OWC wave energy devices, with a maximum increase of 61.7% and 24.5%, respectively.

With the rapid development of the transportation industry, ship-bridge collision accidents occur from time to time and bring about loss of life and property. Ship-bridge anticollision facilities can reduce the damage of ships while protecting the bridge structure. In view of the shortcomings of traditional steel box, such as high stiffness and unchangeable protection position, a new self-floating ship-bridge anti-collision device is designed based on gradient foam aluminum composite sandwich structure. A ship-anticollision device-bridge pier collision model considering pile-water-soil coupling effect was established by finite element software LS-DYNA. The damage characteristics of ship-anticollision device-pier under typical collision loads were studied, and the crashworthiness of anticollision device under cases with different ship speed and ship collision angle were evaluated. The results show that the anticollision device has excellent buffering and energy absorption characteristics, which can effectively reduce the peak value of collision force, prolong the collision time, reduce the damage of pier and effectively reduce the damage of bow structure.

The hub effects are usually ignored in the propeller lifting-surface design based on potential flow theory, the circulation of root is constrained to zero, and the hub is neglected when dealing with boundary value problems. Herein, the theoretical design method of propeller considering hub effects was established by coupling image method of two-dimensional flow problem with lifting-surface design method. Two propellers were designed for a ship by the methods with and without consideration of hub effects respectively, the geometrical shapes, hydrodynamic coefficients and pressure distributions of two propellers were compared. It is shown that hub effects in lifting-surface design has no obviously influences on hydrodynamic coefficients, but the pressure distributions of the propeller designed by the method considering hub effects is in better agreement with design goals. At the same time, considering hub effects could help to reduce loading of leading edge in external radius, that would be beneticial to postponing cavitation inception.

This paper aims to propose an improved theory of homogenization for acoustic coatings, the acoustic coating with periodic cavities can be considered equivalent to a uniform layer, thus improving the computational efficiency of sound absorption. Based on the traditional homogenization theory, parameters of equivalent density, modulus, and thickness for the acoustic coating by are derived incorporating the potential flow theory and the Minnaert resonance scattering theory. The sound absorption coefficient of the coating is then obtained through analytical calculation. This paper specifically addresses the effectiveness, efficiency, and adaptability of the proposed algorithm, thus offering technical support for accurately predicting the sound absorption coefficient of acoustic coatings within the middle and low-frequency range.

With the development of high flow turbopumps, the size and speed of impellers have increased rapidly, resulting in the coupling vibration phenomenon of the turbopump. In order to keep the turbopump running smoothly and reduce its vibration and noise, the coupling dynamics characteristics of the turbopump rotor system were studied in this paper. Firstly, based on the simplified finite element model of the turbopump, it was found that when the rotor frequencies of different orders approach each other in the Campbell chart, two coupling characteristics phenomena of curve turning and merging would occur. Further analysis of the rotor modes conducted for the coupling characteristic phenomenon showed the different orders of the coupling characteristic modes would affect each other. Secondly, a two-degree-of-freedom system was used to simulate the coupling characteristics of the rotor, and then the effects of coupling degree, damping and gyroscopic torque on the characteristics were analyzed. Finally, investigation on the coupling dynamic characteristics of the two-degree-of-freedom system revealed that the dynamic response would change abruptly when the curve turning and merging occurred, leading to the increase of the coupling vibration amplitude and even the instability of the system. The research results could provide theoretical guidance for the safe and stable operation of rotor systems.

Based on the SPH numerical simulation method, this paper presents an analysis of the wave variation of regular and irregular waves propagating along an inshore island reef with a floating structure, and the dynamic response of a tethered floating structure under the island reef topography, respectively. The results show that the floating structure attenuates irregular waves better than regular waves when a tethered floating structure is installed in front of the shore reef, and changes in wave height have little effect on the attenuation of floating structure wave height. However, changes in wave period have a greater impact on the attenuation effect of the floating structure, and the floating structure is less effective in attenuating the wave height of long-period waves. The maximum vertical displacement, maximum longitudinal rocking angle and maximum transverse oscillation values of the floating structure all show an increasing trend with wave height increasing under different regular wave height conditions, with the maximum longitudinal rocking angle being the most sensitive to changes in wave height and the maximum vertical displacement being the least sensitive.