Linear Wave Condition Research Articles

Response power of floating three-body wave energy converter with different shapes

A study on the hydrodynamic characteristics of buoys in a floating three-body WEC (wave energy converter) has been conducted in this paper using STAR-CCM+, based on the linear wave conditions, by numerically analyzing the impacts of buoy geometry (cuboid, cylindroid, boat-like, and capsule) on the floating motions and capture energy. Hinge constraints and hydraulic damping are considered in the numerical model, and the effects of wave parameters on the captured power of WECs are analyzed. Numerical results show that with the increase of wave period, the capture power of each WEC first increases and then decreases, and the capsule-shaped WEC has the largest power capture capability with a capture width of 0.469λ. While the boat-like also has a considerable capture width (0.459λ), with a lower wave resistance (6657.5 N) and 16% less mass, so this novel WEC has more potential for practical applications.

Hydrodynamic investigation on the submerged tunnel suspended from a fixed platform using SPH method

In this paper, the coupled dynamic motion characteristics of a tunnel element suspended from a platform have been studied at a 1:50 scaled model by using the weakly compressible Smoothed Particle Hydrodynamic (WCSPH) method. The corresponding numerical model was validated with the experimental published data of the motion characteristics of the tunnel suspended from a fixed platform, and the case of a floating structure with its mooring lines. Multiple linear wave conditions and different sinking depths of the submerged were involved in the numerical model for tunnel dynamic response and cable behavior investigation. Effects of the mooring system, the wave parameters, the tunnel sinking depth and its mooring configurations were studied. The numerical results were arranged to inform about the dynamic characteristics and mooring behavior for different case studies. The results indicate that the tunnel motions decrease with the increment of the tunnel sinking depth and decrease with the decreasing mooring angle. The natural periods of the tunnel-platform system play key roles in the wave condition impacts on the tunnel motions. It was found that the additional mooring system anchoring the tunnel to seabed played a specific role in reducing the tunnel motions in roll and sway, the motion amplitude of the tunnel in heave is mainly controlled by the suspension cables, particularly when subjected to lower sinking depth and longer period waves.

A wave damping model for flexible marsh plants with leaves considering linear to weakly nonlinear wave conditions

Marsh plants protect the coasts and coastal communities by dissipating wave energy. The dissipation of wave energy depends on the geometric (leaf and stem dimensions) and mechanical (material rigidity) properties of the plants. First, flexible plants bend in response to hydrodynamic drag (called reconfiguration), which diminishes wave decay relative to a rigid plant of the same morphology. Second, mutual sheltering between plant leaves and stem can reduce the drag, and thus wave damping. This study connects the prediction of drag on an individual plant and the measurement of wave decay over a meadow of plants to build a physically-based wave-damping model that includes leaves, the impact of reconfiguration, and the impact of sheltering between plant elements. Model plants were constructed to be both geometrically and dynamically similar to Spartina alterniflora . The wave damping model assumed linear wave conditions, but was validated using a wide range of weakly nonlinear wave conditions within model plants, over a patch of live Spartina anglica in the laboratory, and over a meadow of Spartina alterniflora in the field. After validation, the model was used to explore the variation in wave decay over a range of wave parameters and plant geometric and bio-mechanic parameters, including stem length, stem diameter, number of leaves per plant, leaf length, leaf width, the rigidity of the stem and the leaf. • A physics-based prediction for wave dissipation by flexible marsh plants with leaves was developed and validated with laboratory experiments. • The dependence of wave dissipation on water depth, wave amplitude, and wave period was explored in detail with model predictions. • The impact of leaf and stem geometry and mechanical properties on wave dissipation were revealed by systematic model predictions.

Research on Wave Attenuation Performance of Floating Breakwater

In this study, a new type of double-pontoon floating breakwater was designed to improve the wave attenuation performance through the addition of suspended Savonius propeller-blade. Its hydrodynamic characteristics were studied through numerical simulations and performance-testing experiment. The following investigations were performed in this study: Firstly, wave theory and hydrodynamic theory were combined to calculate the wave attenuation performance and motion response of double-pontoon floating breakwater under linear wave conditions. The numerical results showed that the wave attenuation performance was better under a specific wave period and height, the transmission coefficient reached a relatively small value, and the mooring line tension responded periodically and satisfied the condition of maximum breaking force. Secondly, three key geometric parameters of breakwater were researched, including the relative spacing of pontoons, the relative spacing between pontoons and blades, and the height–diameter ratio of Savonius blades. The calculation results showed that the pontoon spacing was closer to the wavelength and the breakwater wave attenuation performance was better. Lastly, experimental tests were also performed on the new double-pontoon floating breakwater and the results showed that the wave attenuation performance and numerical projections were basically the same, which verified the validity and effectiveness of the design method.

A Numerical Investigation of Gap and Shape Effects on a 2D Plunger-Type Wave Maker

The installation of plunger-type wave makers in experimental tanks will generally include a gap between the back of the wedge and the wall of the tank. In this study, we analyze the influence of this gap on the wave making performance of the plunger using two-dimensional (2D) CFD calculations for a range of nearly linear wave conditions and compare the results with both experimental measurements and linear potential flow theory. Three wedge-shaped profiles, all with the same submerged volume, are considered. Moreover, the generated waves are compared with the predictions of linear potential flow theory. The calculations are made using the commercial ANSYS FLUENT finite-volume code with dynamic meshes to solve the Navier–Stokes equations and the volume of fluid scheme to capture the air–water interface. Furthermore, the linear potential flow solution of Wu (J Hydraul Res 26:481–493, 1988) is extended to consider an arbitrary profile and serve as a reference solution. The amplitude ratios of the generated waves predicted by the CFD calculations compare well with the predictions of linear potential flow theory for a simple wedge, indicating that viscous effects do not influence this ratio for small-amplitude motions in 2D. By contrast, significant higher harmonic components are produced by larger amplitude motions. Also, the simple wedge is found to produce the smallest spurious higher harmonic content in the far-field wave.

Loading and Blade Deflection of a Tidal Turbine in Waves

A coupled numerical model has been developed and validated to study the fluid–structural interaction responses of a three-bladed tidal turbine in aligned waves and current. The unsteady blade element momentum (BEM) theory was combined with modal analysis for hydro-elastic calculation. Both the loading and deflection of the blade were studied. The dynamic loading on the blade due to structural deformation was much smaller than the wave-induced loading under linear wave conditions for the given condition. The linear response amplitude operators (RAOs) of the loads and the blade tip deflections were obtained and used to predict the linear responses. Although both sum- and difference-frequency responses can be identified from time domain simulations, the wave-induced load and the deflection of the blade are dominated by the first-order contributions. The maximum deflection of the blade tip could reach 1.3 m (203% of the means) in the flapwise direction and 0.35 m (210% of the mean) in the edgewise direction with a wave peak period of 11.3 s and a significant wave height of 5.5 m.

Simulating Investigation on the Motion and Power Response of Double Raft Wave Energy Capturer with Different Shapes

Wave energy is considered as one of the most promising renewable energy sources. Compared with the point type, the line absorbing wave power generation device has a greater advantage in the large scale power generation because of its higher wave energy capture efficiency and greater stand-alone power. Study on the hydrodynamic characteristics of floating bodies in a double raft type wave power generation device is conducted in this paper, focusing on the linear wave conditions, through numerically analyzing the impacts of floating body geometry (cuboid, cylinder, elliptic cylinder or capsule) on the floating body wave motion and energy. The results show that there is little difference between the wave forces in the vertical direction of different floating bodies while capsule has the largest relative pitch angle and maximum wave energy capture power. The conclusions will contribute to the further theoretical study and application design in raft type wave energy device.

Hydrodynamic response of a submerged tunnel element suspended from a twin-barge under random waves

It is possible that the excessive dynamic responses of tunnel elements could jeopardize the safety and accuracy of installation procedures used during subsea tunnel construction. To investigate the motion characteristics of the tunnel element, experimental measurements of a moored tunnel element suspended from a twin-barge were conducted in a wave flume at a geometric scale of 1:50. A corresponding numerical model was developed to simulate the dynamic response of the tunnel-barge system in realistic sea conditions, using hydrodynamic parameters from a radiation/diffraction potential model. Multiple linear wave conditions and three immersion depths were tested. The results indicate that the motion response of the tunnel element increases with decreasing immersion depth, and the natural periods of the tunnel, barge and combined tunnel-barge system play key roles in the influence of wave conditions on the motions of the tunnel. It was found that the low-frequency motion of the tunnel element is large in small wave periods. The mooring system under such conditions needs to be considered carefully during system design in order to safely control the motions of the tunnel-barge system in energetic ocean environments.

Freak waves under typhoon conditions

Benjamin‐Feir Index (BFI) and directional spread are measures of nonlinear four‐wave interactions and resultant indices of possible conditions for freak waves. Temporal‐spatial distributions of BFI and directional spread are examined with numerical simulations of a spectral wave model using typhoon conditions. The spatial distributions of wave characteristics such as significant wave height, wave period, BFI and directional spread are different from each other around the eye of the typhoon. BFI is significantly large in the fourth quadrant of the typhoon, while waves are steep and have narrow frequencies and directional spectra. Freak waves resulting from nonlinear four‐wave‐wave interactions have a greater potential of occurring in the fourth quadrant of the typhoon than in the other quadrants. Furthermore, crossing sea states from two‐wind‐wave systems can be observed behind the eye of the typhoon. The crossing, two‐wind systems are also dangerous sea states, although as observed, they are closer to linear wave conditions. Finally, the characteristics of possible freak wave conditions during typhoons are verified with field data.