Underwater target azimuth estimation is a critical technology in array signal processing, with wide applications in military operations, marine resource development, and environmental monitoring. A comprehensive review of the current development status of underwater target azimuth estimation methods is provided in this paper. Firstly, an introduction to the acoustic mathematical model based on an uniformly distributed sound pressure line array was given. Next, azimuth estimation methods are classified into four categories: classical beamforming, statistical, subspace, and AI-based Direction of Arrival (DOA) estimation methods. Key factors affecting azimuth estimation accuracy, such as array calibration errors, array geometry, signal processing techniques, and underwater acoustic channel characteristics, were also analyzed. Finally, the paper discussed the limitations of current azimuth estimation technologies and proposed future research directions, including multimodal data fusion, integration of deep learning with physical models, and the development of new array structures etc, to enhance the accuracy and robustness of underwater azimuth estimation.

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.

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.

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.

Combining the resonance method and the direct wave extracting method, the dynamic mechanical parameters of viscoelastic materials in a continuous and wide frequency range under controllable water pressure were measured. A pressure chamber test system capable of realizing underwater pressurization was built, a short time broadband impulse generated by an electromagnetic shaker was employed to excite a bar-like sample attached inside the pressure vessel. On one hand, the resonance method was used to calculate the mechanical parameters at resonance frequencies while on the other hand, the direct wave signal was extracted, and the mechanical parameters in a wide frequency range were calculated by the wave velocity method. The broadband mechanical parameters (including the storage modulus and loss factor) under variable water pressure conditions (0.1-6 MPa) for two types of viscoelastic materials were obtained. The experimental results agree well with each other, proving the test method in this paper could directly determine the Young’s modulus at frequencies ranging from 500 Hz to 5000 Hz under variable water pressure. This method provides simplified processing for underwater dynamic mechanical parameter measurements.

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.

The welding displacement of marine medium plate caused by welding seriously affects the structural integrity. Butt-welded joint of AH36 steel with the thickness of 14 mm was fabricated using CO₂ welding process and the out-of-plane displacement was straightened using self-developed electromagnetic induction back-heating equipment. A series of experiments were conducted to measure the microstructure, mechanical performance, transverse residual stress and out-of-plane displacement. A welding-back-heating numerical simulation method was proposed, and applied to predict the heating conduction, stress, strain and out-of-plane displacement during the processes of butt welding and back heating. Based on the deformation theory, the transverse bending moment after butt welding and back heating was computed. Results show that the microstructure is mainly cementite and back heating almost has no influence on either the microstructure or mechanical performance. The peak value of transverse residual stress is mainly at the weld seam and becomes larger due to back heating. The back heating generates a larger transverse compressive plastic strain near the surface of AH36 plate, thereby obviously straightening the out-of-plane deformation through the transverse bending moment.

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.

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.

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.