Influence of the Perforated Rate on the Wave Attenuation Performance of Perforated Caisson Set on a Rubble Bed

A Jarlan-type perforated caisson (JTPC) was an important form of structure in offshore and coastal engineering and its wave attenuation performance was greatly affected by μ (the perforated rate). In the present research, a numerical model based on VARANS equations was tested by comparing the simulation results with physical experiments and then adopted to study the effect of a larger range of μ on wave attenuation performance which included both the horizontal wave forces and the reflection coefficients. Conclusions were drawn that the total horizontal wave force and the reflection coefficient both tended to decrease and then increase with increasing μ; when the reflection coefficient reached its minimum value as about μ=0.2, the wave force at the seaward side of the perforated front wall tended to be equal to that at the solid rear wall; the total horizontal wave force reached its minimum value as about μ=0.3.

Influence of Wave-Absorbing Chamber Width on the Wave Attenuation Performance of Perforated Caisson Sitting on Rubble-Mound Foundation

A Jarlan-type perforated caisson consisted of a perforated front wall, a solid rear wall, and a wave-absorbing chamber between them. The wave-absorbing chamber was the main feature of the perforated caisson, and its width had a great effect on wave attenuation performance. In this study, a larger range of the wave-absorbing chamber width was observed in model experiments to investigate the effect on wave attenuation performance including the reflection coefficients and the horizontal wave forces of a perforated caisson sitting on a rubble-mound foundation. A resistance-type porosity numerical model based on the volume-averaged Reynolds-averaged Navier–Stokes (VARANS) equations was validated by comparing the present results with those of previously reported and present experiments. The validated numerical model was then used for extended research. It was found that the reflection coefficients, the total horizontal wave force, and its components all tended to oscillate in a decrease ⟶ increase ⟶ decrease manner with increasing the wave-absorbing chamber width. The reflection coefficients and wave forces acting on both sides of the perforated front wall were found to be synchronized regardless of perforation ratio or the rubble-mound foundation height.

A Field Experiment on Wave Forces on an Energy-Absorbing Breakwater

The U-OWC is a caisson breakwater embodying a device for wave energy absorption. Under the wave action, the pressure acting on the upper opening of the vertical duct fluctuates, producing a water discharge alternatively entering/exiting the plant through the U-duct, formed by the duct and the chamber. The interaction between incoming waves and the water discharge alters the wave pressure distribution along the wave-beaten wall of this breakwater compared with the pressure distributions on a vertical pure reflecting wall. As a consequence, the horizontal wave forces produced on the breakwater are also different. A small scale U-OWC breakwater was put off the eastern coast of the Strait of Messina (Southern Italy) to measure the horizontal wave force. Experimental results were compared with Boccotti’s and Goda’s wave pressure formulas, carried out for conventional upright breakwaters, to check their applicability on the U-OWC breakwaters. Both models are suitable for design of U-OWC breakwaters even if they tend to overestimate by up to 25% the actual horizontal loads on the breakwater. Indeed, the greater the absorption of the energy is, the lower the wave pressure on the breakwater wall is.

Oscillating Wave Surge Converter-Type Attachment for Extracting Wave Energy While Reducing Hydroelastic Responses of Very Large Floating Structures

This paper presents an oscillating wave surge converter (OWSC)-type attachment, comprising a submerged vertical flap connected to the fore edge of a very large floating structure (VLFS) with hinges and linear power take-off (PTO) systems, for extracting wave energy while reducing hydroelastic responses of VLFS. In terms of reductions in hydroelastic responses of VLFS, the OWSC-type attachment is better than the recently proposed raft wave energy converter (WEC)-type attachment for relatively short waves (T < 7 s) and better than the conventional anti-motion device comprising a submerged vertical flap rigidly connected to the fore edge of VLFS for all wave periods. Importantly, the horizontal wave force acting on the submerged flap for the OWSC-type attachment is smaller than that for the conventional anti-motion device, leading to a more economical mooring system. In terms of wave energy extraction, the OWSC-type attachment is better than the raft WEC-type attachment for intermediate and long waves (T ≥ 7 s). In addition, for maximizing power production, the required flap length for the OWSC-type attachment is much smaller than the required pontoon length for the raft WEC-type attachment (about λ/10 as compared to about λ/3, where λ is the incident wavelength).

Experimental Investigation on Hydrodynamic Coefficients of a Column-Stabilized Fish Cage in Waves

This study on hydrodynamic coefficients of a column-stabilized fish cage under wave action plays an important role in the anti-wave design of cages. The regular wave test was used to study the horizontal wave force of the jacket and column-stabilized fish cage under different wave heights, periods, and incident angles; the finite element model of the jacket and the column-stabilized fish cage was established according to the test model. On the basis of the calculation of the finite element model, combined with the wave force obtained from the experiment, the hydrodynamic coefficients of the structure was fitted by the least squares method, and then the drag force, inertial force, and total force of the structure under different conditions were calculated. The results show that the hydrodynamic coefficients of the jacket and netting under the wave condition were more obvious with the change of the KC number and wave incident angles. And as the wave height increased, the drag force, the inertial force, and the proportion of the drag force to the horizontal wave force both increased. When the wavelength was large, the same trend occured as the wave period increased. When the wave incident angles were different, the forces of the jacket and the column-stabilized fish cage were always small in lateral low-frequency waves, which is consistent with the change law of hydrodynamic coefficients of the jacket and netting.

Study on Hydrodynamics of a New Comb-type Floating Breakwater Fixed on the Water Surface

Through the physical model cross-section experiment, the effects of the relative width and groove depth on the transmission coefficient, horizontal wave force and vertical wave force of the new comb-type floating breakwater (FBW) model under fixed condition are observed. The results show that the hydrodynamic parameters of the new comb-type FBW are mainly influenced by its relative width under the action of regular wave, and the transmission coefficient decreases with the increase of its relative width. Especially when the relative width is 0.139 to 0.188, the transmission coefficient of the new comb-type FBW decreases rapidly with the increase of the relative width, and the horizontal wave force and the vertical wave force change slowly. This indicates that the new comb-type FBW has obvious effect on wave dissipation about short and medium waves. In addition, numerical investigations of selected experiment cases are conducted using RANS based commercial CFD code Flow3D. The numerical results show a good ability to capture the hydrodynamic interaction effect of the fixed FBW.

Numerical calculation of total horizontal wave force on a perforated caisson with a top cover based on smoothed particle hydrodynamics method

The revised smoothed particle hydrodynamics method based on Riemann solution has been used to calculate the total horizontal wave force acting on a perforated caisson with a top cover. The interaction process between the wave and perforated caisson is simulated in a two-dimensional numerical wave flume which is verified by linear regular wave theory, water particles flowing in or out of the dissipation chamber are also described in this article, including the distribution of velocity vector. The effect of main non-linear influence factor on total horizontal force is examined here; wave pressure distribution along the height of the perforated caisson in front, inner side or the rear wall of the dissipation chamber is also presented in order to exhibit the more practical performance of perforated caisson with a top cover. The relationship between the total horizontal force and top cover height is anglicized, and the influence of top cover height on components of the total horizontal force is discussed here. A comparison between the numerical total horizontal force results and values tested from the test data is finished; it can be seen that the numerical results agree well with the test data. It is concluded that the smoothed particle hydrodynamics method described in this article can be utilized to calculate the total horizontal force on a perforated caisson with a top cover.

Wave Effect on Slotted Breakwaters Considering Evanescent Modes

The present paper outlines the numerical calculation of wave runup, maximum horizontal wave force on the breakwater and maximum overturning moment on the slotted breakwater. For regular waves, using eigenfunction expansion method, a numerical model is developed that can compute wave transmission coefficient, wave reflection coefficient, and runup and wave force and its related momentum acting on the breakwater. To examine validity of the developed models, experimental measurements of Isaacson (1998) are compared with numerical results. Comparisons between measured and predicted values show that the mathematical model is able to adequately reproduce most of the important features of the experimental results. Wave runup and maximum horizontal wave force decreases by increasing porosity. As the relative water depth increases, wave runup and wave force decreases with respect to an impermeable breakwater. On the other hand, decreasing of relative draft, leads to much more reduction of relative wave force and runup with respect to impermeable one.