The South sea of China is affected by tropical cyclones and typhoons in the western Pacific Ocean, which are prone to double-peak or even multi-peak waves in the form of mixed waves, which are potentially hazardous to the operational safety of marine floating structures. Therefore, based on the potential flow theory and considering the influence of different loading states, a comparative study was conducted on the motion response of FPSO and shuttle tanker side-by-side system under double-peak spectral wave and single-peak spectral wave states. The motion responses of the two hulls in the double-peak spectral wave states of mainly wind waves, wind waves and surge are equal, and mainly surge and the single-peak spectral wind waves state are calculated respectively. The calculation results show that (1) the amplitude of the motion of the two hulls in vertical, horizontal and longitudinal directions increases with the increase of the ratio of the low-frequency energy to the total energy; (2) it is the largest when the surge is dominant, the second largest when the wind waves and surge are equal, and the smallest when the wind waves are dominant; (3) the motion amplitude of both hulls in the double-peak spectral waves is greater than that of the single-peak spectral wind waves under the premise that the total energy is the same, and (4) the motion amplitude of both hulls in the double-peak spectral waves is greater than that of the single-peak spectral wind waves. The study shows that the influence of double-peak spectral waves should be considered in the mooring design and safety planning of FPSO operation system.

The phenomenon of icing on the surface of superstructure of ships and marine structures is the result of a large number of water droplets impacting on the cold wall surface to form a water film and then accumulating ice. And surely, at a high wind speed more water droplets often collide with vertical structures. The movement and freezing behaviors of water droplets can have a significant effect on the icing process and final icing shape on the surface of the structures. Based on the VOSET gas-liquid interface tracking method coupling with VOF and Level-Set, and Enthalpy-Porosity phase change method, a unidirectional coupling model between water droplets and isolated cold plate was established using the large coefficient method. Simulation of the freezing process of a single water droplet impacting an isolated cold plate was achieved, and the phenomenon of the air entrainment was reproduced. The effects of factors such as water droplet velocity, component surface wettability on the freezing process were analyzed. The process of multiple water droplets impacting a vertical structure surface to form a liquid film and freeze was further simulated. The relevant results can provide technical support for the prediction of the typical component surface icing of superstructure and the study of anti-icing and de-icing methods.

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.

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.

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.

The use of acoustic holography technology for identifying moving sound sources and predicting their sound field in limited water areas is of great significance for studying the sound source and radiation characteristics of underwater vehicles. However, the acquisition of sound pressure radiated by moving sound sources and the influence of interface effects in limited water areas have brought difficulties to the application of acoustic holography technology in limited water areas. In view of this, the motion of the sound source was considered and the linear array measurement and moving frame technology were used to obtain holographic pressure radiated by moving sound sources. Considering the influence of interface effects in limited water areas, three holographic inversion models were constructed based on the equivalent source method in three different interface situations. Numerical simulations were conducted on cylindrical shells in limited water areas, and the results showed that the three inversion methods can achieve better sound source identification and sound field prediction results compared to the free field inversion method without considering interface reflection. A moving standard sound source experiment was conducted in a lake, and the experimental results showed that the proposed method can effectively locate the sound source and accurately predict the sound field.

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.

The flexible boundary constraints have a significant effect on the vibration characteristics of rectangular stiffened plates excited by turbulent boundary layer. In this paper, springs were used to simulate flexible boundary constraints. The response function of an underwater rectangular plate was derived based on the energy principle, combined with the power spectra density expression caused by turbulent boundary layer, and the power spectral density of the plate velocity was obtained. It is shown that the boundary spring stiffness has an effect on the response of the plate. As the spring stiffness of the boundary displacement increases, the vibration response of the plate at low frequencies decreases. The effect of the boundary spring stiffness on the vibration response of plate excited by TBL converges when the boundary displacement spring stiffness k_d is larger than 10¹⁰ N/m². The effect of stiffened rib direction and the number of stiffened ribs on the vibration response of stiffened plate was also studied in this paper. Compared with an unreinforced plate, the vibration response of a stiffened plate at low frequency was effectively reduced. The results can serve as a theoretical reference for the analysis of the vibration characteristics of rectangular stiffened plates excited by turbulent boundary layer under flexible boundary constraints.

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.

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.