• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.3
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• pp.221-230
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• 1996

The Suh and Park's analytical model. originally developed to calculate wave reflection from a conventional fully perforated caisson breakwater, is applied to a partially perforated caisson breakwater by approximating the vertical wall of the lower part of the front face of the caisson as a very steep sloping wall. Also, in the model, the inertial resistance term at the perforated wall is modified by using the blockage coefficient proposed by Kakuno and Liu. The model is compared against the hydraulic experimental data reported by Park et al. in 1993. Both the experimental data and the analytical model results show that the influence of inertial resistance is important so that wave reflection becomes minimum when B/L. is approximately 0.2 (in which R : wave chamber width, and 1, : wave length inside the wave chamber), which is somewhat smaller than the theoretical value B/L, : 0.25 obtained by assuming that the influence of inertial resistance is negligible. It is also shown that the analytical model based on a linear wave theory tends to overpredict the reflection coefficient as the wave nonlinearity increases, thus the model is preferably to be used for ordinary waves of small steepness.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.1
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• pp.11-20
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• 2003

In this paper we examine several methods tor calculating the reflection of irregular waves from a perforated-wall caisson breakwater using a regular wave model. The first method is to approximate the irregular waves as a regular wave whose height and period are the same as the root-mean-squared wave height and significant wave period, respectively, of the irregular waves. The second is to use the regular wave model, repeatedly, for each frequency component of the irregular wave spectrum. The wave period is determined according to the frequency of the component wave, and the root-mean-squared wave height is used for all the frequencies. The third method is the same as the second one except that the wave height corresponding to the energy of each component wave is used. Comparison with experimental data from previous authors shows the second method is the most adequate, giving reasonable agreement in both frequency-averaged reflection coefficients and reflected wave spectra.

• KIEAE Journal
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• v.11 no.1
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• pp.3-8
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• 2011

Sound absorbing materials used for lightweight panels and interior material are mainly made of fibroid material such as glass wool or rock wool. However these fiber type sound absorbing materials have some problems such that sound absorption could be decreased as time goes by because of durability. In addition, dust scattering from fiber type material can cause another problem in health. In this point of view, this study aims to develop environment friendly sound absorbing material using Hwangto(so called loess or yellow soil), a traditional housing material. Hwangto is natural housing material in Korea and generally known for improving indoor air quality. Hwangto panel is made to construct on the floor, wall and ceiling, and expected that there is not enough absorption. Present study tried to develop environment friendly sound absorbing material that has high sound absorption performance with good environment performance in terms of air quality. Pore rate was designed to maximize the absorption in the specific frequency bands, and two kinds of backing space were applied in order to see the effect of backing space. As a result peak frequency that has maximum absorption is going high as the pore rate is increased. The backing space provides more absorption and makes the peak frequency down to low.

• Journal of Korean Society of Water and Wastewater
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• v.19 no.3
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• pp.318-322
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• 2005

We applied a commercially available computational fluid dynamics model, FLOW-3D, to design a settling basin inlet structure for the intended O sewage plant. In addition, we analyzed the extent to which the inlet sewage water was distributed as a result, firstly, of the location and width of a submerged baffle wall and, secondly, of the opening ratio of a baffle wall with opening holes. The application results show that the flow is unstable due to the generation of eddies in both sides of the submerged baffle wall when the submerged baffle wall is located close to the inlet. The eddies and subsequent instability also occur when the submerged baffle wall is located close to the baffle wall with opening holes. Moreover, the discharge that passes through the midsection of the settling basin increases as the width of the submerged baffle wall increases. At the O sewage plant, when the submerged baffle wall with a width of 2.4 m was located 2 m from the inlet structure and the opening ratio of the baffle wall was 7 percent, the most satisfactory distribution of the inlet sewage water occurred at the entrance of the settling basin.

• Water for future
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• v.19 no.2
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• pp.131-138
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• 1986

Both hydraulic and dynamic characteristics of a single perforated wall are studied theoretically and experimentally. Theoretically, the effect of evanescent modes on wave force acting on a single perated wall is studied by use of the Horiguchi theory. The wave force on the perforated wall is presented to be insensitive to evanescent modes. According to experimental study, The larger perforation ratio(${\gamma}$) grows, the weaker the wave force on the wall becomes sensitively. And in the small value of l/D (ratio of wall thickness(l) to hole diameter(D)) where the holes on the wall are regarded as orifice, the wave force on the wall is insensitive to the variation of l/D. Energy loss coefficient f is estimated at 1.0 in this small value of l/D by use of Horiguchi theory. But in the large value of l/D where the holes are regarded as pipe, the wave force on the wall is relatively sensitive to the variation of l/D and f is estimated at 1.5 by use of Horiguchi theory.

• Journal of the Korean earth science society
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• v.24 no.7
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• pp.635-649
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• 2003

Heavy metal concentrations and benthic foraminiferal distributions were investigated in three short sediment cores in order to understand the pollution history in Masan Bay. Sedimentation rates were 0.33 cm/yr, 0.20 cm/yr and 0.33 cm/yr in the inner bay, the out fall of Dugdong sewage disposal plant, and bay mouth, respectively. The rapid increases of copper, zinc and lead concentrations at the core depth of 10 cm the upper part indicated that Masan Bay has been polluted with industrial wastes since the 1940s. Benthic foraminifera in core sediments show that the variations in their distribution were followed by industrial pollution in the bay. The number of individuals and species diversity decreased, whereas agglutinated tests increased upward in the cores with increased heavy metal pollution. These shifts effectd the abundance of few tolerant forms and consequently decreased the species diversity. The opportunistic species Eggerella advena and Trochammina pacifica increased in polluted sediments. These species can be used as an indicator for assessments of environmental quality in Masan Bay.

• Transactions of The Korea Fluid Power Systems Society
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• v.7 no.2
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• pp.13-18
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• 2010

To improve the performance of the bent-axis type axial piston pump driven by the tapered piston, it is necessary to know the driving characteristics and mechanism of the tapered piston and the cylinder block. Since each piston not only rotates on its axis and reciprocates in the cylinder bore, but also revolves around the axis of the driving shaft, it is difficult to analyze the driving mechanism theoretically. The theoretical mechanism for the bent-axis type axial piston pump is studied by using the geometrical method. The driving range of the tapered piston is determined by theoretical equations. The experimental results show that the cylinder block is driven by one tapered piston in a limited range and the core parameters such as driving factor of the piston and the ahead delay angle influenced performance of the bent-axis type axial piston pump.

• 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 .

• Transactions of The Korea Fluid Power Systems Society
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• v.1 no.3
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• pp.7-13
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• 2004

The hydraulic pump for a Electro-hydrostatic Actuator for aircrafts should be able to quickly feed large volume of oil into hydraulic cylinder in order to reduce the response time. On the other hand, it should be also able to precisely dispense small amount of oil by low-speed operation so that the steady state position control error of the EHA can be accurately compensated. This paper is focused on the investigation how the plasma coating surface treatment of cylinder barrel with CrSiN can contribute to the reduction of low-speed friction torque of a bent-axis type piston pump. The results showed that the reduction of the friction torque was not remarkable, but that the anti-wear characteristics of the CrSiN-coated cylinder barrel were much better that those of the original one.

• Food Science and Preservation
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• v.13 no.1
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• pp.8-12
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• 2006

The effects of packaging treatments with either low density polyethylene (LDPE) or polypropylene (PP) films on the quality of leaf lettuce were evaluated. It was also stored within a plastic bag (LDPE and PP films) with 4 pelf orated holes (6mm diameter). Changes in weight loss, color difference, anthocyanin, chlorophyll, water content, and general appearance (shape of lettuce) ware investigated Total weight of leaf lettuce packaged within non-pelf orated films decreased slowly over the storage periods at 5 and $20^{\circ}C$. The weight loss of leaf lettuce showed no significant difference between non-pelf orated and perforated films at $20^{\circ}C$. General appearance in leaf lettuce stored at $20^{\circ}C$ was not significantly affected by packaging treatments with LDPE and PP films. The shelf life of non-packaged leaf lettuce at $5^{\circ}C$ was 8 days, whereas packaging treatments with LDPE and PP films showed freshness in leaf lettuce for 30 days of storage. Total chlorophyll and water contents of leaf lettuce packaged within pelf orated and non-pelf orated films decreased gradually during storage. However, no remarkable changes in color difference, levels of chlorophyll and anthocyanin, and water contents were observed in leaf lettuce packaged within perforated and non-pelf orated films. In this experiment, leaf lettuce packaged within LDPE or PP films without any punching holes at $5^{\circ}C$ was the most desirable for extending the quality. These results suggest that non-pelf orated packaging treatment in combination with low storage temperature could be effective in prolonging the shelf life of leaf lettuce