Ships navigating in ice-covered regions will inevitably collide with ice ridges. Compared to other ice bodies, ice ridges exhibit more complicated mechanical behaviors due to the scale and structure characteristics. In this paper, nonlinear finite element method is used to investigate the interaction between a polar ship and an ice ridge. The ice ridge is modelled as elastic-plastic material based on Drucker-Prager yield function, with the consideration of the influence of cohesion, friction angle and material hardening. The material model is developed in LS-DYNA and solved using semi-implicit mapping algorithm.The stress distribution of ice ridge and ship, and the ice load history are evaluated through the simulation of multiple collisions. In addition, parametric analysis is performed to investigate the influence of ridge thickness and impact velocity on the ice load and energy absorption.

A tunneled planing hull has unique hybrid hydrodynamic and aerodynamic characteristics due to the presence of a tunnel. In this paper, experimental and numerical investigations on hydrodynamic analysis of a tunneled planing hull are carried out. The resistance tests of models with three different masses (127.4 kg, 159.5 kg, 202.9 kg) are conducted for the Froude number in the range of 0.761≤Fn≤1.925. The results of resistance measured by towing tank imply that the tunneled planing hull with a larger displacement has a superior resistance performance. The numerical simulation of Reynolds Average Navier Stokes (RANS) equations based on the finite volume method is performed to analyze the hull characteristics in calm water (M=159.5 kg) with two degrees of freedom (sinkage and trim). The numerical results are compared with the experimental data, which shows good agreement. Pressure distribution, wave profiles and lift forces obtained by SST k-ω and Realizable k-ε turbulence models are compared and discussed. Finally, the local fluid flow of streamline around the hull can be divided into four regions due to the presence of a tunnel, which is different from the behaviors of the conventional planing monohull with prismatic form.

Due to the difficulty of attenuation of middle and low frequency band sound waves in the process of propagation, the control of middle and low frequency broadband sound waves has become a challenging topic, so it is necessary to develop new materials and structures with low frequency sound absorption and noise reduction functions. The special properties of acoustic metamaterials provide new ideas for the development of sound absorption and insulation. In order to effectively control the noise in the middle and low frequency bands, a new spatial spiral acoustic metamaterial was designed and optimized by using the finite element software COMSOL Multiphysics, and the sound absorption and sound insulation performance in the 100~2500 Hz frequency band were calculated and analyzed. With the help of 3D printing for completing the preparation of metamaterial, the sound absorption and insulation performance of spiral acoustic metamaterial were compared in an experimental study to verify the accuracy of the calculation method.

As a magnetic spring to provide restoring force for the rigid oscillator, the magnetic levitation support system is of great significance in the flow-induced vibration ocean current energy capture. To investigate the influence of different magnetic spring stiffness on the flow-induced vibration of cylindrical oscillators, the coupling model of the flow-induced vibration of a rigid cylindrical oscillator and its magnetic suspension support was constructed by using the RANS and the Maxwell-Ampere law without free current. The amplitude ratio, vibration frequency and wake vortex shedding pattern of the rigid cylindrical oscillator were analyzed under the action of magnetic spring stiffness of different magnetic suspension support forces. The results show that (1) the amplitude ratio of the oscillator increases first and then decreases with the increase of the flow velocity, and the maximum amplitude ratio decreases gradually with the increase of the spacing; (2) the oscillator reaches the maximum amplitude ratio of 0.844 at a flow velocity of 0.8 m/s and a spacing of 3.8D; (3) the vibration frequency of the oscillator increases with the increase of the spacing, and the growth trend tends to be gentle; (4) the oscillator reaches the maximum vibration frequency of 1.62 Hz at a flow velocity of 0.9 m/s and a spacing of 3.4D; (5) the wake vortex mode becomes more complex with the increase of spacing and velocity, and four wake vortex modes have appeared in the whole velocity range.

Ship structures operate continuously in the marine environment, where they are prone to fatigue crack growth (FCG) under complex alternating loading, therefore it is of great significance to accurately predict the FCG and ensure the safety of structures. In this paper, the load spectrum constructed by the spectral method was combined with an improved unique curve crack growth model, and a method was proposed to more accurately predict the FCG in the near-threshold regime for ship structures under spectral loading. A balcony opening corner in a cruise ship was taken as an example; the method for determining the shape exponents in the improved model was given, the FCG of this structure under spectral loading was predicted, and the effects of the initial crack length and crack growth model on the FCG were discussed. The results show that the prediction method can more accurately predict the FCG in the near-threshold regime, and the prediction result is more conservative than that predicted by the unique curve model recommended in the regulations of CCS. The method presented in this paper can also provide a reference for the fatigue life assessment of other marine structures.

There still remain many challenging topics for CFD to numerically simulate flow around a bluff body at subcritical Reynolds numbers, such as the high-fidelity resolving and capturing for instability structures in the shear layer, as well as the periodic shrinkage and enlargement of the recirculation region. This paper presents the development of a RANS-based wall-modeled large eddy simulation method (RANS-WMLES) to provide a high-fidelity CFD tool for numerically simulating such complex flow phenomena around a bluff body. Such a new method is different from traditional hybrid RANS/LES models. In particular, for the new method the transition from RANS to LES can be achieved through a filtering parameter which is only related to local grid parameters. Moreover, the transition can be pre-controlled through two customizable parameters and for not only the transition boundary positions between RANS and LES, but also the ability of resolving turbulent kinetic energy. A series of numerical simulations for flow past a sphere at subcritical Reynolds number Re=3700 show that the new method is capable of resolving and capturing with high-fidelity temporally/spatially developed coherent structures for such complex three-dimensional flows around a sphere.

Computational bottlenecks and geographical restrictions can be effectively overcomed by cloud-enabled CFD software, while collaborative resource sharing is promoted through integrated cloud ecosystems. This paper investigated the cloud-based application of CFD software for predicting added resistance and motion response of surface ships, utilizing a Browser/Server (B/S) architecture. The study presented an overall architecture for the cloudification of large-scale CAE software, along with component-based flow construction, web-based lightweight CFD data techniques. Key challenges in the cloudification of ship CFD software, including efficient allocation of computing resources, complex human-computer interactions, and effective cloud-based CFD data visualization, etc., had been addressed. In this research, ship CFD software was transitioned from local installations to cloud-based solutions, enabling user interaction through browser interfaces and computations are performed on server nodes. This work provides valuable insights and a reference framework for the cloud-based deployment of other CAE softwares.

In the process of oil and gas development, semi-submersible platforms operate relocation between wells by retracting and releasing mooring chains. In this paper, a fast well relocating optimization method of semi-submersible platform based on greedy algorithm was proposed in view of the traditional method that cannot obtain relocation strategy quickly. Three sets of relocation operations were selected in this study, an optimization analysis of relocation strategy was carried out for windlasses normal operation and windlasses failure operation. The results show that under normal operation, the optimized strategy has a significant improvement in terms of optimization effect and calculation cost compared with the original strategy and the best strategy. Under windlasses failure operation, it shows that the feasibility of relocation is closely related to the distance and direction of the relocation operation. A comparison of relocation strategy was made between the normal operation and the windlasses failure operation, it was found that the retracted length of the mooring chains and the number of operating steps increased under windlasses failure operation, and the stability keeps changing with different working conditions.

In order to investigate the hydrodynamic characteristics of submarines moving in ice regions, a mathematical model and corresponding numerical method, considering the coupling interaction of submarine, water and ice, were established based on RANS equations for level ice and brash ice conditions. The ice sheet was regarded as a no-slip wall boundary with a tangential velocity equal to the incoming flow speed, while the discrete element method incorporated with a linear elastic model was employed to simulate the motion and collision of brash ice. The SUBOFF submarine model was selected as the research object. The influence of sea ice on the resistance was numerically investigated first after mesh convergence analysis. Then further calculations were conducted on resistance components for different submerged depths and speeds under various ice conditions. And wave patterns of the SUBOFF were analyzed for free surface and brash ice condition. Numerical results show that the sea ice predominantly affects the pressure resistance, especially the wave-making component, while there are little differences in frictional resistances for different submerged depths and ice conditions. As the submarine moves under level ice, a significant decrease in pressure resistance and total resistance is observed owing to the lack of wave disturbance. In contrast, when navigating in water covered by brash ice, waves are generated. However, the random and uncertain collisions of floating ice lead to strong fluctuations in the pressure resistance and total resistance curves. And the corresponding average resistance values are slightly smaller than those in open sea due to the wave attenuation induced by brash ice. Furthermore, the submerged depth and forward speed are found to have a significant impact on the hydrodynamic characteristics of the submarine sailing in ice regions. With the increase of submerged depth, both pressure and total resistances will gradually decrease and tend to be consistent. Generally, the increase of forward speed will lead to larger resistance. However, when the submarine navigates beneath the open sea or brash ice, the pressure resistance increases at first and then decreases slightly, which makes the total resistance to grow at a slower rate.

Based on the slicing theory, a time domain model of flow-induced vibration of 3D rotating slender structure is established by combining computational Fluid dynamics (CFD) and finite element method, and the flow vibration characteristics under the action of water flow and rotation are studied. Under the action of water flow, the trajectory of non-rotating elongated structure is mainly "8" shaped. Under the combined effects of flow and rotation, the motion direction of rotating slender body is opposite to its rotation direction, resulting in backward whirling. When the flow velocity is 0.46 m/s, vibration is jointly influenced by the flow and rotation. As the rotational frequency increases, the trajectory of the rotating elongated body transitioned gradually from a "8" shape to a circle. When the flow velocity is 1.02 m/s, the frequency is close to the theoretical intrinsic frequency, and the main cause of vibration is Vortex-Induced Vibration (VIV). The vortex motion is completely suppressed. There is a frequency-locking interval near the intrinsic frequency of the cylinder. The relative amplitude of the transverse vibration of the rotating cylinder increases with the flow velocity in the locking interval, while the frequency ratio remains unchanged.