Large Eddy Simulation (LES) method was employed to simulate the pressure fluctuations on the wall of NACA 0015 hydrofoil. The spatio-temporal correlation characteristics were studied using wavenumber-frequency spectrum (WFS), and six empirical models were used to predict the WFS on the hydrofoil. The results show that at zero angle of attack, as the position of sensors moves towards the trailing edge, the dimensionless convection velocity gradually approaches the theoretical predicted value of 0.7. At the same incoming velocity, the spectral level of the WFS at the ridge increases with the increase of the angle of attack. The predictions of the six empirical models show differences from the simulation results, with the Efimtsov model having the minimum values and the Ffowcs-Williams model having the maximum values. The simulation results fall between the predicted values of the Efimtsov model and those of the Corcos model.

With the rapid development of offshore wind power industry, the protection of wind turbine foundations has become increasingly important in engineering practice. Based on wave diffraction theory in stratified waters, this paper employs the eigenfunction expansion method to derive analytical solutions for wave interaction with concentric arc-shaped structures. The dimensionless wave loads induced by surface wave and internal wave as well as the corresponding maximum wave elevation distributions are obtained. The results show that the double-layer arc structure exhibits superior wave attenuation performance compared to the single-layer configuration. In stratified fluids, the wave loads induced by surface wave and internal wave are of comparable magnitude, indicating that the influence of internal waves cannot be neglected. Parameters such as wave incident angle, water depth, porosity, arc angle, and radius ratio significantly affect wave loading characteristics. Proper selection of porosity and arc angle can further enhance wave attenuation performance and optimize construction costs.

When an underwater vehicle navigates near a wall, the flow field around the underwater vehicle will be changed, which greatly affects its stability and maneuverability. Based on the CFD method, the hydrodynamic performance, including straight-ahead performance, oblique navigation performance, was analyzed under the conditions of near upper wall, bottom wall and vertical narrow channel. Finally, the following conclusions are drawn: when the underwater vehicle sails at a constant speed near the upper or bottom wall, it generates increased resistance, body suction and tail suction. When the vehicle approaching the upper wall at different distances, the directions of vertical force and pitching moment will be changed, and the ratio of direction transition interval is between 5-6 and 3-4, respectively. When the underwater vehicle sails at a constant speed near the vertical narrow channel, the influence of the wall effect on its vertical force and pitching moment has a relatively obvious competition relationship, and the competitive percentage accounts for about 50%. All hydrodynamic coefficients can be fitted by quadratic polynomials based on the reciprocal of the spacing ratio. The hydrodynamic coefficient of wall effect can be obtained from a graph by monitoring the combinations of different upper and lower spacing ratios when simulating the maneuverability of underwater vehicles.

Cavity flows are common phenomena for underwater vehicles. For example the drain holes of the submarine are one of the typical cavity flows. There are some complex turbulent phenomena in the cavity, such as shear layer K-H instability, coupling between shear layer and cavity recirculation. So far, many difficulties remain for CFD numerical simulation. Firstly, the setup of an accurate inflow condition is crucial for analyzing turbulent coherent structures inside the cavity with the high fidelity due to the fact that the flow upstream of the cavity is usually in an utterly turbulent state. Secondly, there are frequency components with second-order oscillation modes besides the ones with first-order oscillation modes in the cavity flow. However, the CFD numerical simulation still faces challenges for such second-order oscillation flows. In this paper, a DFSEM-WMHRL method is developed to perform high fidelity CFD simulation for such complex cavity flows, where the WMHRL is a hybrid RANS/LES method with the wall-modelled capability, and the DFSEM is a divergence free synthetic eddy method with the turbulent inlet generation capability. Through a series of numerical simulations on the channel flow with $ {Re}_{\tau }=395 $, the turbulence kinetic energy resolution index r_k and the combined conditions for the RANS/LES hybrid boundary positions are firstly confirmed, indicating the capability of the proposed method for analyzing the second-order statistics of the channel flow with high fidelity. Moreover, numerical simulations were carried out for the cavity flow with $ {Re}_{{\mathrm{D}}}=3360 $ and $ L/D=2 $ based on the proposed method. The results show that the DFSEM-WMHRL method can accurately analyze both second-order statistical characteristics and the fine spectral structures caused by self-sustaining oscillations in the cavity flow.

In this study, an integrated simulation method of floating wind turbines based on wind-wave joint probability model and Modelica coupling simulation framework is constructed for the development of renewable energy in the South China Sea islands and reefs. Taking the island and reef sea area of Sansha City as the research object, the joint probability distribution model of wind and wave is reconstructed by historical meteorological data, and the data of island and reef sea area of Sansha City are established by combining with ocean current data. Based on the Modelica platform, a fully coupled numerical model of aerodynamics-hydrodynamics-control-structure-mooring is developed to study the coupled dynamic response characteristics of Spar-type floating wind turbine in the island reef area of Sansha City. The results show that the peak pitch angle of the platform is 4.74° (<5 ° design threshold) under working conditions. The maximum tension safety factor of mooring system meets the requirements of China Classification Society. Under rated conditions, the turbine speed is stable at 11.98 rpm (rated value 12.1 rpm), and the power output reaches 4.60 MW (rated power 5 MW). The research verifies the engineering applicability of the proposed method system, and provides an innovative technical evaluation framework and scientific decision-making basis for the deployment of floating wind power projects in the South China Sea islands.

The phenomenon of vibration interference among multiple risers is one of the hot topics in ocean engineering. As a basic model of multi-pipe systems, the dual staggered flexible pipe system is widely used to analyze vortex-induced vibration (VIV) behavior. In this paper, the VIV characteristics associated with a dual staggered flexible pipe system is investigated by a two-way fluid-structure interaction method. The results show that the influence of staggered angles on the in-line and cross-flow vibration responses of upstream and downstream pipes is distinctly different. Owing to the short-range interference between dual pipes, the amplitude of downstream pipe is generally larger than that of upstream pipe, more likely to demonstrate "multi-mode competition" phenomenon. Due to the effect of staggered arrangement and small spacing ratio, the interation between fluid and dual pipes is relatively strong, leading to the failure of forming regular shedding vortex in the wake of the dual pipe system. Through the analysis of vibration response and phase difference at the peaks and valleys of RMS amplitude envelopes, related to the dual staggered flexible-pipe, it is found that when the staggered angle of dual flexible-pipes increases from 15° to 60°, the votex shedding mode changes from "2P" to "2S", the fluid excitation frequency and intensity of the upstream pipe become weakened, and the vibration displacement phase difference and lift force coefficient phase difference of the upstream and downstream pipes are reduced.

In this paper, an underwater explosion acoustic-structure interaction numerical model of air-backed glass fiber reinforced composite foam sandwich panel is established using a nonlinear finite element software ABAQUS. The damage characteristics of composite foam sandwich panel under underwater explosion are investigated. Full-scale air-backed composite foam sandwich panel underwater explosion experiments were conducted in a large-scale explosion pool, which validated the accuracy of the acoustic-structure interaction numerical model. The results indicate that under underwater explosion loading, the air-backed composite foam sandwich panel primarily experiences delamination damage. The damage is concentrated at the center of the panel and along the surrounding boundaries. As the shock factor increases, the damage of the cohesive layer gradually extends inward from the surrounding boundaries. As the foam core density increases, the impact resistance of the composite foam sandwich panel progressively improves.

Considering the directional differences in the distribution of environmental conditions, the directional design criteria can be adopted as long as no jeopardizing to the structure reliability is introduced. Compared with the omnidirectional design condition, the directional criteria can optimize the structural design by redistributing the exceedance probability on all directional sectors. The directional design conditions that meet the requirements of the target reliabilities can be determined by the iterative method proposed in this paper, and the optimal structural design and the corresponding directional design condition can be determined by design analysis and comparison for specific structures. The statistical uncertainty impact caused by distribution fitting and large extrapolation needs to be carefully considered, and using the proposed "combination method" to derive the environmental condition distribution is an effective solution to reduce this impact.

The accurate prediction of bending stiffness and damage mode is important for understanding the bending mechanical behavior of reinforced thermoplastic pipe (RTP). Presently, adopting two-dimensional theoretical models, or simplifing three-dimensional stress state based on Lekhnitskii stress function, are the two main common approaches to analyse the bending performance of composite flexible pipes. The methods above, however are, difficult to accurately predict the stress distribution of each layer and the initial damage critical point of RTP under bending conditions. This paper firstly conducted geometric analysis of the section shape of RTP under bending conditions, and established a parametric representation method based on geometric analysis for the section deformation of each layer. Considering the nonlinear stiffness degradation of the material, a three-dimensional constitutive relationship of RTP was established. Then, combined with the virtual work principle, an analysis model for the bending mechanical properties of RTP was established. Further, the four-point bending test was carried out to verify the rationality of the theoretical model, and the influence of initial ovality and winding angle on the bending stiffness of RTP was analyzed. The results show good agreement between experimental data and theoretical model calculations. The bending stiffness of RTP is mainly affected by the winding angle and slightly affected by the initial ovality.

The complex relationship between irregular corrosion defects and pipeline failure presents substantial challenges for pipeline safety assessments. To investigate the interaction between irregular corrosion defect parameters and pipeline failure bending moments, a theoretical calculation model for the ultimate bending moment of pipelines with irregular corrosion defects was first established under the individual or combined effects of internal pressure, axial force, and bending moment, based on the Net Section Collapse criterion. Then, the accuracy and reliability of the proposed model were verified through experimental data from the literature and finite element analyses. Finally, taking API 5L X80 pipeline steel as an example, the impacts of defect shape, depth ratio, length ratio, and relative position of shallow and deep defects on the ultimate bending moment of pipelines with irregular corrosion defects were analyzed under three different working conditions. The research results indicate that the ultimate bending moment of the pipeline is related to the shape of the corrosion defect. Considering the shape of the corrosion defect in the calculation of the ultimate bending moment can avoid the underestimation of residual strength. The increase in the depth length ratio of irregular corrosion defects reduces the ultimate bending moment of the pipeline. When the depth length ratio remains constant, the larger the depth/length of the corrosion defect, the faster the rate of decrease of the ultimate bending moment. Additionally, adding internal pressure and axial force loads also reduces the ultimate bending moment. When a deep corrosion defect is located in the center of a shallow corrosion defect, the ultimate bending moment reaches its minimum. As the deep corrosion defect moves from the center towards the edge of the shallow corrosion defect, the ultimate bending moment of the pipeline gradually increases but the change is not significant. This paper presents a failure assessment method with the merits of clear physical concept and convenient calculation for pipelines with irregular corrosion defects, which enriches and develops the relevant theories of pipeline safety assessment.

With the continuous development of underwater detection technology towards low frequency domain, the sound absorption ability of conventional underwater acoustic coating needs to be significantly enhanced. In order to obtain better low-frequency sound absorption effect, a Topology-Shape-Topology (TST) optimization method is investigated in this paper. A new underwater acoustic coating is designed using the method which optimizes the distribution of materials in the anechoic layer. Compared with the traditional cavity-type acoustic coating, the acoustic structure designed by TST optimization method can achieve excellent sound absorption performance in the range of 200–1000 Hz. The peak value of sound absorption coefficient can come up to 0.9 at 321 Hz, and the average of sound absorption coefficient within the studied frequency range is above 0.8, resulting in an effective improvement of the low frequency sound absorption effect of the traditional underwater acoustic coating. Moreover, the underlying mechanism behind the sound absorption performance is revealed to obtain a further understanding of distribution regularities of materials. The study provides a new idea for the design of underwater acoustic coatings.

The wall pressure fluctuation of the turbulent boundary layer (TBL) is a primary source of flow-induced vibration noise. Due to their broadband and highly chaotic features, it is difficult to accurately capture the complex spatio-temporal variations of the phenomenon. To analyze these intricate characteristics, the wavenumber-frequency spectrum is needed. And both experimental and theoretical modeling in this field have become critical research topics. This paper investigated the convection velocity characteristics of the TBL wall pressure fluctuations wavenumber-frequency spectrum. In the low-speed wind tunnel experiments a linear array of pressure sensors was used to measure TBL wall pressure fluctuations. The cross-spectral matrix (CSM) method was adopted to derive the wavenumber-frequency spectrum, obtaining the convection velocity at various wind speeds. Concurrently, hot-wire anemometer measurements were made for boundary layer parameters, which were normalized to analyze convection velocity characteristics. The new convection velocity prediction model was developed and applied to the classical Chase I wavenumber-frequency spectrum model. Comparisons with experimental data showed strong agreement between the convection ridge in Chase I model and measurements, validating the new model’s broad applicability across wind speeds and frequencies. This study provides new theoretical insights and technical pathways for TBL wall-pressure wavenumber-frequency spectrum modeling and ship noise control technology.

Ship maneuverability is one of the most critical navigation performance of ships. The SIMMAN workshop is a systematic and authoritative international academic event focusing on the verification and validation of ship maneuvering prediction methods, which has garnered widespread attention worldwide. Based on a review of the SIMMAN workshop programs, latest developments, and related literature, this paper systematically summarizes the main research content, progress, and significant achievements of the three workshops. Furthermore, it analyzes the development trends and research directions in international ship maneuvering prediction methods and model test technologies as reflected by these workshops, and elucidates the insights they provide for the advancement of ship maneuverability testing and prediction methodologies.