The acoustic analogy theory is currently the most significant theoretical framework in the field of flow acoustics, with widespread engineering applications. Thus, this paper focuses on the development history and engineering applications of the acoustic analogy theory, concentrating on the three core issues: sound sources, acoustic variables, and wave operators. It then analyzes and prospects the future research of the acoustic analogy theory, considering the major needs in China and adapting to the era of artificial intelligence. The purpose is to provide some useful references for scholars through the analysis and summary of the acoustic analogy theory, and also to offer possible solutions for some engineering problems.

Some ship equipment with weak anti-shock properties has the flowing characteristics such as small space proportion, variable and large shock loads, dynamic load changes, rigid-flexible state transitions and passive operation. Howerver, these needs cannot be met by traditional vibration isolation devices. Therefore, this paper proposed a novel integrated bi-directional vibration isolation device and conducted the corresponding structural design. Then, the dynamic model of the vibration isolation device was established to predict the dynamic response under complex loading and to explore the effects of frequency and damping ratio on the anti-shock properties of the device. Finally, the test bench for the vibration isolation device was built to verify the validity of the structural design and theoretical analysis. The results show that the direction of the impact load and dynamic sway load affects the anti-shock properties of the vibration isolation device, When the loads act in the same direction, the anti-shock performance will be improved, whereas when the performance will be decreased if the loads act in opposite directions. As the frequency or damping ratio increases, the anti-shock properties of the vibration isolation device gradually decrease, thus requires optimization based on key performance indicators. The test results of the vibration isolation device have smooth curves without distortion, and the overall trend is basically the same as that of the theoretical calculation results, which can verify the validity of the structural design and theoretical analysis. The results of the study can provide useful guidance for the design of vibration isolation and anti-shock for weak ship equipment.

As offshore floating structures continue to grow larger, the rain load of large offshore floating structures under extreme conditions has become one of the focal points of concern for designers. Based on the discrete particle model and the rain load calculation formula, this paper completed the rain load calculation for different wind field and raindrop spectrum combination states of the offshore platform, and the study shows that the rain load caused by fluctuating wind is much more discrete than the raindrop spectrum; the rain load of the offshore platform under the action of fluctuating wind follows Gamma distribution; and the rain load variation caused by time-varying rain field follows normal distribution; when the rainfall intensity R is 800 mm/h, the exceedance probability is 95%, the rain load accounts for 4.65%, and the maximum rain load accounts for 8.07%. The research results help to reveal the influencing factors of rain load on offshore platforms and can provide data support for designers to select rain load reasonably.

In recent years, shipowners have become increasingly concerned about the actual performance in the real marine environment. At present, ship design optimization is mainly conducted based on performance in still water which has a certain difference from real-sea performance. The factors influencing the powering performance of ships in wind and waves were investigated taking series oil tankers, bulk carriers, and container ships as the research subjects. The theory of two-dimensional strip was used to calculate the added resistance under typical sea states BF6 and BF8. The propeller was redesigned using graph method to research the influence of light running margin in the wind and waves. The results show that the principal dimensions have a significant impact on the added resistance of oil tankers and bulk carriers, and have a relatively small impact on container ships. Therefore, it is necessary to consider the ship type separately when optimizing the powering performance in wind and waves. In addition, with the increase of the light running margin, the reserved space for power becomes increasingly sufficient.

The traditional low-order finite element model is usually used to obtain the acoustic scattering field of a submarine structure, and then to evaluate the acoustic stealth performance. However, the traditional finite element method is affected by the numerical pollution effect, and requires very dense mesh to obtain reliable numerical solutions for problems with relatively medium and high frequencies, leading to prohibitive cost in mesh division. In this paper, the overlapping finite element method (OFEM) and Dirichlet-to-Neumann (DtN) mapping technique are combined to construct a coupled numerical model for the acoustic scattering of underwater elastic targets. When constructing local approximations in the OFEM, the virtual nodes are used to generate partition of unity functions, while no degrees of freedom are assigned to these virtual nodes. The novel OFEM can be directly applied to low-order finite element models and achieve higher-order approximations of the unknown variables. Numerical examples show that the OFEM can reduce the numerical error significantly and has broad application prospects in the prediction of underwater acoustic scattering by elastic targets.

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 main design calculation methods applicable to the reinforcement of spherical shell openings were systematically summarized focusing on the simulation of pressure bearing structures in a large-scale deep-sea cold seep environment. Then, as an example, the reinforcement effect was studied based on equal area method, pressure area method, and limit analysis method respectively under the conditions of opening ratio of 0.1-0.6 and pressure of 21 MPa for a ϕ5000 mm spherical shell. Quantitative analysis was conducted on the influence of the reinforcement length of the spherical shell and the reinforcement length of the connecting pipe on the stress distribution of the local structure in the joint zone between the ball and column, and a scaled model was used for verification. The results indicate that the dense reinforcement method needs less reinforced area and is more economical for high-pressure large-opening reinforcement design, and that the increase in the reinforced lengths of the spherical shell and the connecting pipe will effectively reduce the stress concentration factor at the junction and improve the ultimate strength of the local structure. However, the increase in the length of the connecting pipe has a certain marginal effect. On the premise of manufacturing feasibility, the reinforcement length of the spherical shell should be increased as much as possible. The structural stress calculation results based on finite element method are in good agreement with the measured results.

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 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 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.