Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Experimental study on wave reflection and transmission on a slit-type permeable breakwaterin wave and current field reproduced in a basin
Katsuya Hirayama, Sotaku Yamada, and Yuki Hamano
Coastal Hydraulic Engineering Department, Port and Airport Research InstituteYokosuka, Kanagawa, Japan

ABSTRACT

vertical porous wall with different porous shapes and porosities areobtained by a theoretical analysis and a physical model experiment(Jarlan, 1961; Kondo, 1979; Li et al., 2006).

The results of 3D model experiment conducted by using Environmental
Intelligent Basin (EIB) for investigating both the reflection andtransmission rates on a new slit-type permeable breakwater areintroduced. In EIB, a random wind wave is generated by a serpent-typewave maker and tidal currents are produced by a horizontal current
generator. These specifications are also introduced in this paper. It isrealized that the tidal current which penetrates the permeable
breakwater through slits enhances the wave transmission when it flows
in the same direction to the incident wave propagation, although such
effect must be counteracted when the tidal current flows in the opposite
direction.

In our previous study (Hirayama et al., 2021), 3D model experiment of
which scale was 1/16 was conducted to investigate wave reflection andtransmission on the vertical slit-type permeable breakwater, while arandom wind wave was generated by a serpent-type wave maker withand without tidal currents which are produced by a horizontal current
generator in a basin. In this study, the experimental results areintroduced with the specifications for the experimental basin, in order
to introduce the hydraulic performance in wave and current field of a
new type vertical permeable breakwater. In addition, while the resultsof 2D model experiment are introduced, it is discussed that the wave
transmission through rubble mounds, of which occurrence is also
supposed with referring the water particle oscillations measured behindthe permeable and impermeable breakwaters, is negligible.

KEY WORDS:Wave; current; basin; permeable breakwater;reflection; transmission; slit.

INTRODUCTIONMETHOD OF 3D MODEL EXPERIMENTIn these days, various vertical permeable breakwaters are sometimes
installed to shield a harbor basin from wind waves, not only reducing
reflected waves but also less obstructing sea water exchange. In general,
although the smaller vertical permeable breakwaters are built withupright wave dissipating blocks, larger ones are constructed with slitcaissons in which permeable plate are equipped (OCDI, 2020).
However, because such special caissons have complex structure, theirconstruction costs may be higher than ones of normally structured
caissons. Therefore, in Mikawa port which is located at the end of
Mikawa bay in the middle part of Japanese main island, a permeable
breakwater is being built by using normal caissons of which placementis spaced in 1m among them while each space is regarded as a slit.

Brief introduction of wave and current basin
Both a serpent-type wave maker and a horizontal current generator are
installed in a basin of which length is 40m and width is 29m. The
maximum water depth is 0.8m. The basin named as the Environmental
Intelligent Basin (EIB) has been administrated by the wave group in thePort and Airport Research Institute since 2001.
Serpent-type wave maker
The serpent-type wave maker has three faces for generating a mutidirectional irregular wave in a whole area of basin (See Fig. 1). The
first face which consists of 53 wave paddles and the third face which
consists of 35 wave paddles are set along the length and the width of
the basin, respectively. The second face which consists of 3 wave
paddles is set at the corner between the first and the third faces. Here,the width of each wave paddle is 0.6m. In each face, they are connected

Actually, because the thickness of these caissons except their footing isonly 2.3m while the height of them including their upper part works is
9.4m and the width is 9m (See Fig. 2), the completed breakwater ofwhich length is 360m will be totally looked like a thin vertical platewith many slits. The reflection and transmission rates of such a thin

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