Numerical Study on the Hydrodynamic Characteristics of a Double-Row Floating Breakwater Composed of a Pontoon and an Airbag

Abstract

By adding a cylindrical airbag on the leeward side of a cuboid pontoon, a new-type double-row floating breakwater is designed to improve the wave attenuation performance, and its hydrodynamic characteristics are studied through numerical simulations. First, based on the smoothed particle hydrodynamics (SPH) method, a numerical model used to simulate the interaction between waves and moored floating bodies is built. The fluid motion is governed by the Navier–Stokes equations. The motion of the floating body is computed according to Newton’s second law. The modified dynamic boundary condition is employed to treat the solid boundary. The lumped-mass method is adopted to implement the mooring system. Then, two physical model experiments on waves interaction with cuboid and dual cylindrical floating pontoons are reproduced. By comparing the experimental and numerical wave transmission coefficients, wave reflection coefficients, response amplitude operators and mooring force, the reliability of the numerical model is validated. Finally, the validated numerical model is applied to study the influence of separation distance and wave parameters on the hydrodynamic characteristics of the double-row floating breakwater. The results indicate that the optimal separation distance between pontoon and airbag is 0.75 times the wavelength. At such separation distance and within the concerned 1–4 m wave heights and 4–7 s wave periods, the pontoon-airbag system presents better wave attenuation performance than a single pontoon. This improvement weakens as wave height increases while it strengthens as the wave period increases. In addition, the double-row floating breakwater is more effective in a high-wave regime than in a low-wave regime. In the case of short waves, attention should be paid to the stability and mooring reliability of the seaward pontoon, while in the case of long waves, care needs to be taken of the leeward airbag.

Analysis of fluid force and flow fields during gliding in swimming using smoothed particle hydrodynamics method

“…All DBPs participate in Eqs 6, 8 as fluid particles. The calculated density is further smoothed by the mean density of fluid particles within the kernel support (Cheng et al, 2021) as Eq. 17:…”

Experimental Study on Hydrodynamic Characteristics of Barge-Type Breakwaters under Different Mooring Methods

“…Chen Cheng et al [10] found that the addition of wing plates on both sides of the traditional floating square box could provide better wave dissipation in long-period waves, and Chun-Yan Ji et al [11] proposed a new barrel-shaped breakwater and carried out two-dimensional flume tests, which showed that this cylindrical floating breakwater had better wave dissipation performance than the traditional double-floating box breakwater. Xiaofei Cheng et al [12] found through numerical simulations that adding an airbag after 0.75 times the wavelength of the floating breakwater could increase the wave dissipation performance of the breakwater, and that the wave dissipation performance would be enhanced as the wave period increased. Xiang-qian Mao et al [13] carried out wave load analysis on a floating breakwater with an arc-shaped layout based on three-dimensional potential flow theory.…”

Comparison of Hydrodynamic Performances Between Single Pontoon and Double Pontoon Floating Breakwaters Through the SPH Method

“…Breakwaters are used to protect harbors and beaches against wave action. Many types of breakwaters have been developed, such as bottom-mounted breakwater (Gao et al, 2020(Gao et al, , 2021Wang et al, 2019;Li et al, 2020;Liu et al, 2021) and floating breakwater (FB) (Ren et al, 2017;Dai et al, 2018). Although the traditional bottom-mounted breakwater has a good wave reflecting/dissipating ability, it suffers from high cost and negative impact on the shore ecology.…”

“…However, the reflection coefficients were almost identical between two types. To improve the wave-attenuation ability of the SPFB, Cheng et al (2021) proposed a new-type DPFB by adding an airbag on the leeward side of the SPFB. They studied the influences of the spacing between two pontoons on the hydrodynamic characteristics, and concluded that the proposed DPFB was superior to SPFB in reducing the wave transmission and the optimal pontoon spacing was 75% of the wavelength.…”

“…However, compared with ISPH, WCSPH can be easily programmed and is particularly suitable for parallel computation. Recently, SPH has been extensively adopted in ocean engineering and coastal engineering such as slamming phenomenon (Gómez-Gesteira and Dalrymple, 2004;Lind et al, 2015;Altomare et al, 2015;Cheng et al, 2017;Ren et al, 2021), wave generation (Ni et al, 2018;Altomare et al, 2018;Wen and Ren, 2018;He et al, 2021) and waves interactions with breakwaters (Meringolo et al, 2015;Khayyer et al, 2018;He et al, 2018He et al, , 2019Tripepi et al, 2020;Quartier et al, 2021). Reviews of the applications of SPH and other particle methods in engineering fields have been presented by Gotoh andKhayyer (2018) andLuo et al (2021).…”