Particle damping vibration absorber is a dynamic vibration absorber that uses a mass block containing several particles as the mass element. It has the effect of broadening the effective frequency band of dynamic vibration absorbers and suppressing the secondary line spectrum of dynamic vibration absorbers. However, dynamic vibration absorber control techniques are sensitive to parameter selection, and the vibration equivalent mass of particle damping vibration absorbers changes with variations in excitation amplitude, affecting their vibration absorption performance and practical engineering applications. The method of building a 3D network into the mass block was proposed to improve the above defects. The influence of adding obstacle network into the mass block of particle damping vibration absorber was studied by experiment and simulation in this paper. The results show that when the vibration intensity of the particle damping vibration absorber is high, a part of the particles in the mass block enter a suspended flow state, leading to these particles not participating in the vibration process. As a result, equivalent mass of particle damping vibration absorber is changed, and the vibration absorption frequency has shifted. And the 3D network can keep the vibrational equivalent mass stable by breaking up the suspended flow state of the particles. And the vibration reduction effect is effectively improved on the specific vibration amplitude.

High-speed vessels face significant challenges in optimizing bow structures under slamming loads due to uncertainties in load magnitude and spatial distribution. This paper proposes a multi-stage topology optimization method integrating load uncertainty analysis and manufacturing constraints to balance lightweight design and engineering feasibility. Firstly, the uncertain loads are converted into multi-scenario worst-case loading problems. Through an iterative "critical load scenario-topology optimization" process, the critical load positions are dynamically updated. Then, a topology optimization strategy based on the Solid Isotropic Material with Penalization (SIMP) method is employed, incorporating geometric/manufacturing constraints to progressively derive an optimal stiffener layout that meets strength and stiffness requirements. Each iteration retains prior design outcomes and updates worst-case load scenarios to achieve progressive adaptation to uncertain loads. Finally, multiple iterations and geometric reconstruction convert high-density element clusters into manufacturable stiffener configurations. Finite element verification demonstrates that the optimized bow structure exhibits significantly reduced maximum displacement, more uniform multi-scenario responses, and compliance with lightweight and safety requirements. This method effectively addresses the computational burden of double-layer nested optimization, offering a novel approach for structural optimization of high-speed vessel bows under stochastic slamming loads.

An analytical model of pipe torsional stiffness in clockwise and counterclockwise directions is derived based on the helical winding structural characteristics of steel wires in the unbonded flexible pipe armour layers considering radial contraction and expansion phenomena. Taking a typical unbonded flexible pipe as an example, the bi-directional torsional stiffness analysis is conducted. The results show that the analytical model has a close match with the results of existing numerical model. It can be found that the error is 3.5% in clockwise torsion, and the error in counterclockwise torsion is 4.6%. This paper can provide a useful reference for the design and analysis of the torsional performance of flexible pipes.

The motion of ships and marine structures is a nonlinear motion with time series characteristics. The Long Short-Term Memory (LSTM) artificial neural network has the characteristics of memorizing time interval information and processing nonlinear data, which is very suitable for processing such nonlinear motion with time series characteristics. Therefore, LSTM has significant advantages in predicting the very short-term motion response of ships. In this paper, an improved LSTM method for the prediction of very short-term motion response of ships is proposed. This method converts the prediction of ship motion into the prediction of peak and valley values by means of extracting envelopes, which can reduce the data demand of the traditional LSTM model and simplify the complexity of the prediction curve, thereby significantly improving the forecast duration. In this paper, the improved LSTM was used to predict the regular wave curve, irregular wave curve and real ship motion curve. The results show that the improved LSTM prediction method can enlarge the maximum forecast duration of the traditional LSTM model from 6~8 s to about 20 s, and has ideal prediction results for special signals such as abrupt signals, which has high practical value.

The omnidirectional waterjet propeller, as a lateral thruster or dynamic positioning device, has attracted more and more attentions. Its hydrodynamic characteristics are a key factor in meeting the application requirements. However, there are limited related studies. The numerical simulation of hydrodynamic performance of the omnidirectional waterjet propeller was carried out in this paper. Based on the STAR-CCM+ software, the steady RANS method was applied to investigate the hydrodynamic performance of an omnidirectional waterjet propeller under two conditions, i. e. static water and flowing water. The results show that the hydrodynamic performance of both thrust magnitude and directionality is greatly affected by the magnitude and direction of incoming flow, and the influence is greater when the rotational speed is lower. The research in this paper reveals the thrust loss mechanism of the omnidirectional waterjet propeller. Its hydrodynamic performance should be evaluated according to its working conditions, and the low rotational speed operation should be avoided to ensure that hydrodynamic performance requirements are met.

The main ballast tank is an important component of a submarine submerging and surfacing system. To correctly simulate the working process of a submerging and surfacing system, modeling and simulation analysis of the main ballast tank based on MWorks were carried out. Firstly, the models of water injection system, conventional blowdown system and emergency blowdown system were built using MWorks. Then, the model’s reliability was verified by comparison with CFD simulation results. Finally, the impact of factors such as back pressure and sea opening area on the injection and drainage process of the main ballast tank was analyzed. The results show that the relative error of main ballast tank blowing time between the MWorks simulation results and the CFD simulation results is within 10%; increasing back pressure will increase the blowing time and reduce the structural strength requirements for the main ballast tank; increasing the sea opening area will reduce the filling time, blowing time and the structural strength requirements for the main ballast tank. The main ballast tank system models built with MWorks have fast calculation speed and accurate regularity characteristics, which facilitates the rapid adjustment of engineering design parameters to determine design input.

A rapid design method for a marine propeller with an arbitrary radial circulation distribution was proposed in this paper. Based on the lifting surface model, a genetic algorithm was employed to design the pitch and maximum camber distributions, using given camber line shapes, aiming to achieve a chordwise distribution of circulation that is as close as possible to the specified one. Subsequently, the design problem related to specified chordwise circulation distribution was solved, the redesign process of which starts with the above designed propeller. The camber line shape of each blade section was corrected according to the difference between current chordwise circulation distribution and the specified one, so that the circulation distribution of the designed propeller converges iteratively to the expected one. By applying these methods, a five-bladed highly skewed propeller was redesigned under open water conditions, and the design results were numerically validated with RANS simulation results. The hydrodynamic performances and pressure distributions of the designed propeller are in good agreement with the design objectives, thus indicating that the proposed design methods are simple, fast, and reasonably accurate.

Steel/GFRP L-shaped joint and similar components are common in ship manufacture. In this paper, a steel/GFRP L-joint with ±45° groove structure was designed, and the effect of parameters such as glueing length on the performance of the L-joint was investigated through the compression experiments of steel/GFRP L-joints. In the numerical analysis of the steel/GFRP L-joint, the complexity of the ±45° groove structure glueing interface structure and the multi-interface and multi-scale were considered, and the stiffness equivalence method was used to equate the groove structure to a cohesive unit layer of 0 thickness. The failure modes of the L-joint were analyzed in detail concerning the compressive load and displacement by comparing the compression experimental results with the simulation, and the steel/GFRP L-joint exhibits better compressive performance when the bonding length is 100 mm.

A fuzzy adaptive sliding mode based method was designed to control the precise pitching motion of a bionic robotic fish in response to the problem of numerous gait control parameters and imprecise dynamics modelling for the co-propulsion of 3-degree-of-freedom pectoral fins, flexible body and caudal fin. Firstly, based on the given 3-degree-of-freedom pectoral fin and flexible body co-propulsion motion law, the relationship between the fish body thrust/moment and the pectoral fin phase difference and body fluctuation frequency was established by the least-squares method using CFD numerical simulation. Secondly, the designed fuzzy adaptive sliding mode controller was used to achieve the free-diving motion of the robotic fish, taking the smooth curve with the current and the desired depth levels as asymptotes, as the desired motion trajectory. The fuzzy adaptive sliding mode controller was designed to achieve the free diving motion of the machine fish. The fuzzy controller was used to analyse and calculate the adaptive law of fuzzy control rule to compensate the uncertainty term of the dynamics model and the disturbance term of the water current during the movement of the robot fish in real time, and combined with the sliding mode controller to reduce the system jitter to achieve the accurate tracking of the trajectory. Finally, the results of the simulation and the pool experiments show that the robot fish is able to swim between different depths in a fast and smooth manner, and the movement trajectories are smooth with the maximal depth deviation of only 0.08 m, and the steady state error remains at 0.04 m, verifying the effectiveness of the proposed method.

The volume fraction equation is an important control equation for multiphase flow such as cavitation, which is derived from the mass conservation equation in incompressible cases. However, there is currently no universally recognized descriptive form for compressible fluids. The paper uses the body-fixed coordinate system as a reference frame to describe the problem, focusing on local fluid units. Starting from the volume changes of multiphase fluids, the relationship between the body derivative of volume fraction and the local average velocity divergence of each phase fluid is derived. The article also discusses the relationship between the volume fraction equation and the mass conservation equation, as well as the influence of phase transition and compressibility on the evolution of volume fraction. The forms of the volume fraction equations under two-phase pressure equilibrium are provided.