Liang Sun

Integrating wave energy converters (WECs) onto floating offshore wind turbine platforms has emerged as a recent focal point of research aiming to achieve synergistic marine energy utilization and enhance the spatial efficiency of renewable energy. The power performance of WECs relies on hydrodynamic interactions with the floating platform. However, the coupled dynamic response and power generation mechanism remain unclear. This study establishes a multi-body model for the constrained motion of floating-platform and point-absorber WECs in the frequency domain. The power performance of WECs under different arrangements is compared and optimized. The performance of different hydrodynamic models in the South China Sea is analyzed further. The results indicate that exceptional peak performance is achieved when a single point absorber is placed on the floating platform. However, its performance under the full spectrum of wave frequencies in real sea conditions is suboptimal. Conversely, as the number of point absorbers on the floating platform increases, the performance of the hybrid system becomes more stable in real sea conditions. Furthermore, the array arrangement of point absorbers on the floating platform leads to multiple peaks in their power performance, and in selected array arrangements, the average power generation at specific frequencies is significantly superior to that of a single point absorber on the floating platform.

To investigate the overtopping and slamming phenomena that occur in the interactions between waves and oscillating surge wave energy converters (OSWECs), a two-dimensional numerical wave flume was established using computational fluid dynamics (CFD) software Fluent by adding the momentum source terms into the original Navier–Stokes equation. Numerical convergence studies of the mesh sizes and time steps were firstly performed to ensure the sufficient accuracy of the numerical model. The variations in the wave heights along the wave propagation direction in the wave-generating area, working area, and wave-absorbing area were analyzed. The dynamics of the flap-type OSWEC were simulated using the overset mesh function embedded in Fluent. In addition, the numerical results were compared with the experimental data, and good agreements were achieved. External torque was applied to the hinge joint of the OSWEC to simulate the forces due to the power take-off (PTO) system, and the identified optimal PTO damping was compared with the numerical results based on the potential flow theory, which verified the correctness of the numerical PTO system. On this basis, nonlinear wave slamming by the sharp-eagle OSWEC was analyzed. The results show that under certain incident wave conditions, the sharp-eagle OSWEC can effectively reduce the maximum rotation angle and angular velocity compared with those of the flap-type OSWEC, and there is no overtopping that occurring for the sharp-eagle OSWEC. Furthermore, the sharp-eagle OSWEC performs better than the flap-type OSWEC.

Tube trailers with large capacity glass fiber wrapped composite cylinders with steel liners have entered the Chinese market to deliver compressed gases since 2011. The tube trailers with the composite cylinders can carry more gases than those with full steel cylinders, and are welcomed by the market. However, the outer surfaces of the composite layers of the cylinders are susceptible to abrasion damages as resin-based glass fiber composites have low surface hardness. Effect of outer surface defects on the large capacity composite cylinders for tube trailers was investigated in this paper using finite element analysis. First, a mesh model of the large capacity composite cylinder without any defects was built according to its actual geometrical dimensions, in which each layer of the composite overwrap was modeled using a layer of solid elements. Second, the meshes corresponding to surface defects with different surface sizes and different depths were killed using element birth and death method to generate surface defects. Then, the models under internal pressure were solved to obtain stress distribution and predict burst pressure. Numerical results show that the surface defects decrease the burst pressure of the cylinders, and the defect depth has a more important effect on the burst pressure than the surface sizes of the defects. Based on the numerical results, three suggestions to deal with the surface defects were proposed: 1) the cylinders having surface defects with depths less than 1 mm can be acceptable, 2) those having surface defects with depths greater than 3 mm should be condemned, and 3) those having surface defects with depths between 1 mm and 3 mm may be repaired but the inspection interval of the cylinders must be shortened.