• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.3
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• pp.198-203
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• 1993

Hydraulic experiments were carried out to investigate the reflection characteristics of perforated breakwaters in regular wave conditions varying the width of wave chamber and the shape of perforated wall. It was found that the reflection coefficient of the perforated breakwater was very sensitive to the change of wave chamber width. giving its minimal value when the width of the wave chamber is approximately 0.2 times the wave length in the wave chamber. This phenomenon may be resulted from the wave resonance inside the wave chamber. The reflection coefficients slightly varied for all shapes of perforated wall. i.e., vortical slit, horizontal slit or circular hole. However, the reflection trend of the structure was not significantly affected by the shape of the perforated wall.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.4
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• pp.321-328
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• 2006

In the present study extensisve numerical experiments are conducted using the CFD code, FLUENT, to investigate the energy dissipation due to perforated walls for various wall-thickness and flow conditions. A new empirical formula for energy loss coefficient considering the effect of the thickness of perforated wall is obtained based on the results of computational experiments. It is found that the energy loss coefficient decreases as the wall-thickness increases and the maximum coefficient reduction reaches upto 40% of the value calculated using the conventional formulas for the sharp-crested orifice. To check the validity of the new formula the reflection coefficient of waves due to perforated wall is evaluated and compared with the results of existing theories and hydraulic experiments. The result shows that the new formula is superior to the conventional ones.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1455-1462
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• 2013

This study examines the reflection of a partially perforated wall with single chamber by 2D and 3D hydraulic experiments. The effects of slit shape on the front wall, relative chamber width and wave steepness were discussed. For the normal incident wave condition, the reflections of horizontal slit case were lower than that of the vertical slit with the similar porosity, but the differences are not significant. When the wave steepness is relatively small, the reflection coefficients are large. In the oblique incidence, the normalized wave heights along a perforated wall with similar porosity are almost same for the vertical and horizontal slit walls and therefore the difference by slit shape can be ignored.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.205-208
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• 2002

Numerous studies have been performed to develop an analytical model that can predict the reflection of regular or irregular waves from a perforated-wall caisson breakwater. Though such irregular wave models as Suh et at. (2001) become available, regular wave models are still in extensive use because of their simplicity. In the present study, using the regular wave model of Fuggazza and Natale(1992), the reflection of irregular waves from a perforated-wall caisson breakwater was calculated in several different methods. First, the regular wave model was re-validated by the hydraulic model tests. Though the model somewhat over-predicted the reflection coefficients at larger values and under-predicted them at smaller values, overall agreement was pretty good between calculation and measurement. Then, the regular wave model was applied to calculate the irregular wave reflection in the experiments of Suh et at.(2001) and Bennett et al. (1992). In applying the regular wave model to irregular wave reflection, several different methods were used. The results showed that it is the most reasonable to use the regular wave model repeatedly for each frequency component of the irregular wave specuum with the root-mean-squared wave height for all the frequencies .

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.4
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• pp.243-249
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• 1992

Hydraulic experiments were carried out to investigate the hydraulic characteristics of solid and perforated-wall caissons of a mixed type breakwater for regular waves of various heights and periods. It was found that a perforated-wall caisson is more advantageous than a solid caisson for such hydraulic characteristics as reflection. transmission, and runup at the front face of the caissons and that the experimental results agree reasonably well with existing theoretical or empirical relationships. Especially the reflection coefficient of a perforated-wall caisson. mainly governed by the resonance in the wave chamber, was found to be minimum when the width of the wave chamber is approximately a quarter of the wave length in the wave chamber.

• Earthquakes and Structures
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• v.6 no.2
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• pp.181-199
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• 2014

The infill walls, whose contribution to the earthquake resistance of a structure is generally ignored due to their limited lateral rigidities, constitute a part of the lateral load bearing system of an RC frame structure. A common method for improving the earthquake behavior of RC frame structures is increasing the contribution of the infill walls to the overall lateral rigidity by strengthening them through different techniques. The present study investigates the influence of externally bonded perforated steel plates on the load capacities, rigidities, and ductilities of hollow brick infill walls. For this purpose, a reference (unstrengthened) and twelve strengthened specimens were subjected to monotonic diagonal compression. The experiments indicated that the spacing of the bolts, connecting the plates to the wall, have a more profound effect on the behavior of a brick wall compared to the thickness of the strengthening plates. Furthermore, an increase in the plate thickness was shown to result in a considerable improvement in the behavior of the wall only if the plates are connected to the wall with closely-spaced bolts. This strengthening technique was found to increase the energy absorption capacities of the walls between 4 and 14 times the capacity of the reference wall. The strengthened walls reached ultimate loads 30-160% greater than the reference wall and all strengthened walls remained intact till the end of the test.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2317-2328
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• 2013

In this study, the effect of wave chamber slab on wave pressure along the first and second wall of the perforated caisson breakwater was investigated by performing physical experiment. The experiment was performed without and with the wave chamber slab of the perforated caisson by varying the front wall porosity. The discrepancy in magnitudes of the measured wave pressure along the both walls of the perforated caisson was apparent according to the existence of the wave chamber slab as significantly greater pressures were acquired for all the test cases when the wave chamber was closed upward by the slab. As a result, the magnitudes of the total wave force calculated by integration of the measured wave pressure also were much larger for the caisson breakwater having the wave chamber slab, exceeding the value based on the well known Takahashi's formula (Takahashi and Shimosako, 1994). With respect to the porosity of the front wall, meanwhile, higher pressures were obtained with a larger porosity, at both the first and second wall of the breakwater.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.6
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• pp.343-351
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• 2014

The reflection and transmission coefficients of waves due to perforated wall are mainly determined by both the porosity and wall thickness of the perforated wall and the period and nonlinearity of incident waves. Among them the wall thickness is very important because it affects the head loss coefficient and the inertia length of the wall. However, by employing the head loss coefficient derived for sharp crested orifice, the previous researches have neglected, or incorrectly considered the effect of wall thickness on the head loss coefficient. Even though it is considered, the effect of the inertia length is neglected in some empirical formulae. Thus, the effect of wall thickness on the reflection and transmission coefficients of waves is not properly considered. In this study comprehensive experiments are conducted for the perforated walls with various thicknesses, and the results are compared with those predicted by the empirical formulae. As a result it is found that the existing formulae can not properly consider the effect of wall thickness, and it is confirmed that a new formula which can correctly consider the effect of wall thickness on the head loss coefficient is necessary.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2013.10a
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• pp.149-150
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• 2013

Recently, various types of perforated breakwaters are being constructed for protecting offshore storm waves. In general, perforated breakwaters have wave chambers with perforated walls at seaside. Purposes of the wave chambers are to reduce wave reflections and maximum wave forces acting on the breakwater. Impact wave forces due to wave breaking can attack to the perforated wall directly, so the effects have to be considered in the design of the perforated wall carefully. Using resonance channels for wave energy dissipation, a new concept perforated breakwater is proposed, which is free from impact loads. Numerical simulation was made for wave reflection characteristics of the breakwater with respect to major design parameters. Numerical analysis was carried out using the Galerkin's FE model based on the linear potential theory considering energy dissipation on the perforated plate. Variations of wave reflection was investigated according to perforated ratios of perforated plate.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.1
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• pp.25-33
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• 2010

The matching condition at a perforated wall with vertical slits involves the permeability parameter, which can be calculated by two different methods. One expresses the permeability parameter in terms of energy dissipation coefficient and jet length at the perforated wall, being advantageous in that all the related variables are known, but it gives wrong result in the limit of long waves. The other expresses the permeability parameter in terms of friction coefficient and inertia coefficient, giving correct result from short to long waves, but the friction coefficient should be determined on the basis of a best fit between measured and predicted values of such hydrodynamic coefficients as reflection and transmission coefficients. In the present study, an empirical formula for the friction coefficient is proposed in terms of known variables, i.e., the porosity and thickness of the perforated wall and the water depth. This enables direct estimation of the friction coefficient without invoking a best fit procedure. To obtain the empirical formula, hydraulic experiments are carried out, the results of which are used along with other researchers' results. The proposed formula is used to predict the reflection and transmission coefficients of a curtain-wall-pile breakwater, the upper part of which is a curtain wall and the lower part consisting of a perforated wall with vertical slits. The concurrence between the experimental data and calculated results is good, verifying the appropriateness of the proposed formula.