A semi-submersible platform of V-shaped base with NREL 5 MW wind turbine is designed. Hydrodynamic load, aerodynamic load and mooring system were coupled for calculation and analysis. Hydrodynamic load was based on potential flow theory, aerodynamic load was based on leaf element momentum theory, and mooring system was based on quasi-static method. By coupling program F2A, AQWA software and FAST software are linked to complete the time-domain fully coupled simulation of the platform under the combined action of wind, wave and current, and the dynamic response of the floating wind turbine under different current loads are calculated and analyzed. The results show that velocity and incidence angle of current load have great influence on motion response and mooring force of floating wind turbine.
The effect of different obstacle arrangements on the explosion flame dynamics of inhomogeneous hydrogen-air mixture is investigated by numerical simulation,and the explosion characteristic parameters predicted by the simulation are all in good agreement with the experimental results.The simulation results show that the premixed flame undergoes four stages of evolution in the tube:spherical flame,finger flame,conical flame,and flocculent flame.When the flame passes through the obstacle,the flow field is seriously unstable,resulting in serious distortion of the flame.When the obstacle is ar-ranged on both sides,the flame reaches the pipe outlet first,and the pressure reaches the peak the fastest.The obstacle at the tube top can significantly increase the explosion pressure,and compared with the bottom arrangement,the explosion peak overpressure increases by 23％and 74％when the obstacle is arranged on both sides and at the top of the tube,respectively.This study can provide theoretical guidance for hydrogen safety planning and explosion protection.
The simulation of radiated noise from underwater vehicles and the signal propagation characteristics in un-derwater acoustic channels are two hot topics in the field of underwater acoustics.Simulate the radiated noise power spec-trum of underwater vehicles through empirical formulas and the design of FIR filters.On this basis,combined with the Bell-hop acoustic toolbox,simulate radiated noise signals transmitted through ocean channels.A study was conducted on the ocean channel under the ice water interface using the Burke-Twersky(B-T)ice water model.The results show that the power spectrum amplitude undergoes varying degrees of attenuation based on horizontal propagation distance and sound source depth.Moreover,the presence of boundaries on ice water causes additional reflection and loss of sound lines,resulting in an additional attenuation of the power spectrum at the receiving point of 20～30 dB.
Addressing the ongoing challenge of enhancing propulsion efficiency in rim-driven thrusters (RDTs), a novel energy-saving appendage was designed to mitigate energy dissipation and improve efficiency. Computational fluid dynamics was utilized to examine the disparities in open-water performance between RDTs with and without this appendage. The Reynolds-Averaged Navier–Stokes equations were solved using the Moving Reference Frame approach within the established STAR-CCM+ software. The accuracy of these methodologies was confirmed through a comparison of numerical simulations with experimental data. A meticulous analysis evaluated the alterations in propulsion efficiency of RDTs pre- and post-appendage integration across various advance coefficients. Additionally, a comprehensive assessment of thrust and torque coefficient distributions facilitated a comprehensive understanding of the appendage’s energy-saving potential. Results demonstrated that the new appendage diminishes the diffusive wake behind the rotor disk, fostering a more uniform flow distribution. A notable reduction in the low-pressure zone on the rotor blade’s thrust side was observed, accompanied by an elevation in the high-pressure area. This generated a distinct pressure disparity between the blade’s thrust and suction sides, mitigating the low-pressure region at the blade tip and reducing the likelihood of cavitation. The manuscript further elucidates the rationale behind these alterations, providing detailed insights into flow field dynamics.
Considering the background of ship emission control area, multi-objective ship speed optimization is carried out with fuel cost and charter cost as optimization objectives to reduce ship operating costs and improve ship energy efficiency. A multi-objective optimization method based on the combination of butterfly optimization algorithm and linear weighting is selected to obtain the Pareto optimal solution set. Finally, the ideal point distance method is used as the decision-making approach to determine the best compromise solution from the Pareto optimal solution set. The results show that when optimizing the sailing speed, fuel costs decrease by 1.98%, sailing costs decrease by 17.32%, and overall operating costs for ships can be effectively reduced by 5.62%, greatly improving the economic efficiency of shipowners and shipping companies while meeting environmental requirements.
