Cavitation is a special physical phenomenon that exists in fluids, and the cavitation model is a key technology in cavitation flow calculation, which describes the cavitation phase transition process. The rate of cavitation phase transition is directly related to the nucleus density. In this paper, the R-P equation and nucleus transport equation are used to improve the bubble dynamics-based cavitation model, so that the new model includes the influence of nucleus density evolution with the cavitation process. The improved cavitation model can effectively simulate the collapse process of two-dimensional vapor bubbles. In the final stage of vapor bubble collapse, the evolution of gas phase volume occupancy can reach 0 in a limited time while maintaining the stability of the calculation process. The simulation results are in better agreement with the theoretical results.

The interaction between waves and marine structures involves complex geometric boundaries, wave impacting, overtopping. To accurately simulate this complex phenomenon, DualSPHysics is employed to build a numerical wave flume based on Smoothed Particle Hydrodynamics (SPH), which is a grid-free particle method. In order to validate the accuracy of the model, regular waves are generated by a piston-type wavemaker. By analyzing the wave height with different particle spacing, the model was demonstrated that it can generate stable regular waves. Furthermore, the impact of regular waves on a vertical wall is simulated with the model. Under the action of wave impact and inertial force of the water, the pressure at different positions on the vertical wall shows the following characteristics: it quickly reaches the peak in a short time, then decreases, increases again, and finally decreases. The time series of pressure have a saddle shape. By comparing the wave shape and velocity field at the same time, it is found that the angle between the wave and the vertical wall, as well as the water head rise, are the main factors leading to this saddle-shaped pressure curve.

The collection of seabed ore particles is a critical phase in the development of deep-sea mineral resources. The wall-jet nodule-collection device has significant engineering value due to its high collection efficiency and minimal disturbance to the surface sediment of the seabed. In this study, high-speed imaging and computer-based image processing techniques were employed to investigate the influence of the jet Reynolds number (Re) on the dynamic behavior of ore particles. Based on Particle Image Velocimetry (PIV), the impact of Re, height-to-particle-diameter ratio (h/d), and jet thickness-to-particle-diameter ratio (b/d) on the distribution characteristics of the mining flow field were analyzed. The experimental results reveal that ore particles demonstrate distinct movement characteristics in different regions of the collection flow field. These regions are categorized into a translation zone, a startup zone, and a continuation zone. Under the same Re, in the range of 1.5 ≤ h/d ≤ 2.25, decreasing h/d had a limited impact on the flow characteristics near the lowest point of the convex curved wall (y/d = 0), and facilitated ore particle entry into high-velocity gradient flow regions near the wall, thereby effectively promoting particle elevation. Under the same Re, for the range of 0.1 ≤ b/d ≤ 0.4, reducing b/d increased the velocity gradient of the high-speed flow region near the wall, and enhanced the vertical lifting force on particles, improving collection efficiency. This study offers valuable insights for the design and engineering application of new, efficient, and low-disturbance collection devices.

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.

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.

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.

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.

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 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.

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.