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.

Aiming at the problem of predicting the sound radiation characteristics of cylindrical shells with internal substructures, this paper carried out theoretical and experimental research on the sound radiation characteristics of cylindrical shells with internal substructures. In theory, a hybrid calculation method based on the combination of condensed transfer function method, direct stiffness method and precise transfer matrix method was proposed, which can calculate the sound radiation characteristics of cylindrical shells with internal substructures. In the experiment, the linear excitation method was used to obtain the vibration response at each measuring point and the sound pressure at the underwater reference point, which were compared with the analytical calculation results. The analytical calculation results are in good agreement with the experimental test results.

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.

To investigate the impact of extreme waves, based on the physical model test in a wave tank, this paper aims to study the characteristics of wave impact pressure and impulse generated by focused waves with different breaking stages on a plate-square column structure. Wavelet denoising, empirical mode decomposition, and local weighted linear regression methods were used to process the experimental data. The wave pressure at different parts of square columns was obtained, and the temporal and spatial distribution features of wave pressure were explored. Based on the time integral of wave impact pressure, the time-varying characteristics of the pressure impulse at the typical part of the structure were analyzed. Additionally, the effects of wave breaking stage, initial air gap, and trim angle on the spatial variation of pressure impulse were discussed in detail. The results show that the maximum impact pressure impulse generated by the focused waves is significantly affected by the breaking stage, the initial air gap, and the trim angle. Waves with crest curling or even premature breaking usually produce larger impact pressure impulses. Meanwhile, the plate-square column structure with small initial air gap and positive trim angle is subjected to a larger impact pressure impulse. This study provides a valuable reference for further investigation of the impact of extreme waves on semi-submersible platforms.

Springing and whipping have a non-negligible effect on the structural strength and fatigue life of containerships, and they have also been the focus and attention of researchers, of which linear springing is a more unique fluid-structure interaction phenomenon. In this paper, the ship motion and structural response in the linear springing state in waves of a 20,000 TEU containership model with a scaling ratio of 1∶49 were investigated by using both model tests and numerical calculations. The motion and sectional bending moment of the model were measured in the wave tank, and the numerical calculation was realized by two-way coupling of computational structural dynamics and CFD taking into account the fluid viscosity, and the effectiveness of the coupling method was verified by comparing the calculation results with the experimental data. The results of the ship motion and structural response under linear springing are analyzed, and it is found that the linear springing does not have much effect on the ship motion, but it will significantly enhance the structural sectional loads, the elastic resonance makes the structural response to be concentrated in the two-node vibration. The structural response obtained based on the rigid body is much smaller than that of the experimental and flexible body results, so the dynamic elastic coupling phenomenon between the hull and the surrounding flow field needs to be taken into account in the assessment of the ship's strength and fatigue performance.

There is a strong coherence between random wind and wave environment elements, which not only affects the synchronization and intensities of fluctuating wind and random wave in combined wind-wave propagation process, and but also affects the accurate calculations of combined wind-wave action on offshore structures. Therefore, based on the CFD numerical simulation methods of random wave and fluctuating wind fields, a numerical flume for simulations of combined wind-wave propagation was established, then a series of numerical simulations of combined propagation of fluctuating wind and random wave were carried out. Based on the analysis of numerical results, the influences of wind speed position height, significant wave height, wave peak frequency and basic wind speed on the coherence between wind and wave were explored. According to the influence characteristics of these factors, a calculation function model of wind-wave coherence value of combined wind-wave propagation was proposed. Then, the parameters of the coherence function model were determined by a series of numerical fits according to the numerical results under various influencing factors. Based on this, a concrete calculation expression describing the coherence value of combined wind-wave propagation was established.

Numerical simulations of a ship in cavitation flow before and after the installation of a stern flap were conducted for the DTMB5415 benchmark ship model, considering factors such as ship speed, propeller speed, and ship wake. The results show that owing to the dual effects of change of propeller inflow and decrease in propeller speed, the cavitation area and cavitation start-stop angle of the propeller increase after the installation of a stern flap. The blade frequency amplitude of the propeller excitation force/torque decreased by an average of 9% at Fr=0.28 with the stern flap installed. Owing to the negative impact of the propeller cavitation, the corresponding reduction was only 2.5% at Fr=0.413. The hull surface fluctuating pressure was mainly affected by a decrease in the propeller speed after the installation of a stern flap. The average reductions in the blade frequency amplitude at low and high speeds were 17% and 12%, respectively.

The trajectory planning of unmanned ships is an important part of unmanned ships autonomous navigation. A trajectory planning method for unmanned ship dynamic collision avoidance was proposed based on improved PRM algorithm and event triggering mechanism. Firstly, PRM and A* were combined to obtain the PRM-A* algorithm, and a trajectory planning model for unmanned ships was established based on the PRM-A* algorithm. A grid map was established based on the current environmental situation, the PRM-A* algorithm was used to plan the collision avoidance path of unmanned ships, and an S-T grid map of the collision avoidance path was established. The PRM-A* algorithm was used to plan the speed of unmanned ships on the S-T grid map, thus obtaining the collision avoidance trajectory of unmanned ships at the current time. Secondly, a dynamic collision avoidance model was established for unmanned ships based on the event triggering mechanism. An unmanned ship collision risk assessment model was established based on the TCPA and DCPA of unmanned ships, based on which event triggering condition was set. When the event was triggered, the unmanned ship collision avoidance trajectory was planned based on the current time window environmental situation. Finally, simulation experiments were conducted on the trajectory planning of unmanned ships in open and restricted waters. The results show that the algorithm can effectively make an unmanned ship avoid static and moving obstacles in waters, save computational resources, and improve computational performance.

The study of probability characteristics of ice loads can offer more precise input loads for the assessment of ship structural safety, taking into account the uncertainties involved in the interaction between polar ships and sea ice. By integrating the ice load estimation formula with a statistical characteristic analysis method, a Monte Carlo-based approach was proposed to investigate the probabilistic characteristics of ice loads on polar ships. According to the typical sea area and route, the scenarios of interaction between the midship and bow of the vessel with sea ice were considered separately. Based on the study of the probability distribution types and statistical parameters of the relevant variables, the ice loads at different positions was calculated by the method presented in this paper, and the corresponding probability density function was obtained. It can be found that the probability characteristics of ice force in the midship can be accurately modeled by a normal distribution, and the Weibull distribution can be used to describe the probability characteristics of both horizontal and vertical ice forces at the bow. Moreover, the horizontal force exerted on the ship due to ice crushing is significantly greater than that resulting from its bending failure.

The storm model is a simplified model to describe the random wave loads borne by the ship structures in complex marine environments. This paper proposed an improved Newman model, namely the NPhi model, to consider the load order and interaction effects of storm models, which is based on the Newman model, considering the load interaction effects in Huang’s model and the improved McEvily model. An overload coefficient was introduced into the effective stress intensity factor range to characterize the hysteresis and acceleration phenomena caused by overload. Using the crack propagation program established in this paper, the correctness of the test results using the propagation from multi-level block loading and storm model was verified, and the influence of overload coefficient was studied. Based on the study by the Fatigue and Fracture Technical Committee of the International Ship and Offshore Structures Congress (ISSC), it is shown that the NPhi model has better prediction ability compared to other typical crack propagation models. Additionally, a reasonable overload coefficient value is crucial for the prediction results.