• Journal of Navigation and Port Research
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• v.44 no.4
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• pp.305-311
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• 2020

Rising sea levels along the coast from global warming causes the increase of wave energy along the coast. This rise in sea levels results in relatively deep water levels, which would incur the loss of sand that had not occurred in the past from erosion in coastal areas. Generally, it has been challenging to protect against coastal erosion, and the slope, cross-sectional shape, and materials are selected for the site conditions depending on the change in external forces. However, the application of counter measures based on insufficient understanding of the phenomenon is causing various damage, indicating the need for technological development and converging technologies to improve credibility. In this study, we developed eco-friendly permeable biopolymer concrete blocks to control the coastal erosion by using the Bio-Coast, an effective porous structure that mitigates the destructive erosion caused by the rising sea levels. The hexagonal design of Bio-Coast was derived from the honeycomb, columnar joints, and clover, which are durable and stable structures in nature, and the design was changed to apply bumps on the Bio-Coast filling in the form of a clover to reduce wave overtopping and run-up. Applying the field condition of beaches on the east coast of Korea, the block weight and size were decided and the prototype blocks were manufactured and are ready for field placement. In particular, it is intended to protect coastal areas from destructive erosion by natural and artificial external forces, and to extend the design to river,s lakes, and natural walking trails, to improve the efficiency of quality control and process control through the use of blocks.

• Journal of Digital Contents Society
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• v.19 no.8
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• pp.1585-1592
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• 2018

Due to un-balancing weight allocation on the wheelchair the existing wheelchair system are faced with the risk of flipping or falling when a wheelchair goes up to a hill. In to order to be safer during riding the wheelchair, in this paper, we proposed a real-time new solution using the integrated Gyro Sensor and Tilt Sensor for controlling the balance. Because the typical property of wheelchair is for the special user who meets the difficulty in moving on foot the maintain the balance of wheel-chair systems have become important and helpful. In our method, we calculate the seat angle using information from Tilt Sensor. However, due to the law of inertia when a wheelchair is moving there is a deviation in the output value of Tilt Sensor. Therefore, we have to optimize the value of the angle by utilizing the acceleration that is the output of the Gyro Sensor. We took the advantages by using the combination of Gyro and Tilt sensors. Moreover, we also solved the consumption issue of the whole system. Through various experimentations with usage of ZigBee sensor module, the power consumption for the balancing system is reduced significantly.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.6
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• pp.644-653
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• 2013

In this paper, a formulation for obliquely incident electromagnetic wave has been presented for an analysis of highpower electromagnetic pulse penetration into multilayered dispersive media. Based on generalized models of measured dielectric constants and propagation channels reflecting the Earth's general features, the propagation phenomenon of the obliquely incident early-time(E1) high altitude electromagnetic pulse(HEMP) is analyzed. In addition, the polarization and critical angle are also considered. It is found that the total reflection occurs at an incident angle of about 38 degrees at the soil-rock interface, and that the parallel-polarized E1 HEMP penetrates better than the perpendicular-polarized one. The peak level of the penetrating electric field is found to be 5.6 kV/m at normal incidence, regardless of the type of polarization, and E1 HEMP is greatly reduced near the critical angle. Moreover, the penetrating E1 HEMP is analyzed as a variation of moisture content and depth of materials, resulting E1 HEMP could be useful in determining the levels of shielding required for buried facilities.

• Journal of Radiation Protection and Research
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• v.24 no.4
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• pp.215-223
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• 1999

Characteristics of radiation field in the steam generator(S/G) water chamber of a PWR were investigated and the anticipated effective dose rates to the worker in the S/G chamber were evaluated by Monte Carlo simulation. The results of crud analysis in the S/G of the Kori nuclear power plant unit 1 were adopted for the source term. The MCNP4A code was used with the MIRD type anthropomorphic sex-specific mathematical phantoms for the calculation of effective doses. The radiation field intensity is dominated by downward rays, from the U-tube region, having approximate cosine distribution with respect to the polar angle. The effective dose rates to adults of nominal body size and of small body size(The phantom for a 15 year-old person was applied for this purpose) appeared to be 36.22 and 37.06 $mSvh^{-1}$) respectively, which implies that the body size effect is negligible. Meanwhile, the equivalent dose rates at three representative positions corresponding to head, chest and lower abdomen of the phantom, calculated using the estimated exposure rates, the energy spectrum and the conversion coefficients given in ICRU47, were 118, 71 and 57 $mSvh^{-1}$, respectively. This implies that the deep dose equivalent or the effective dose obtained from the personal dosimeter reading would be the over-estimate the effective dose by about two times. This justifies, with possible under- or over- response of the dosimeters to radiation of slant incidence, necessity of very careful planning and interpretation for the dosimetry of workers exposed to a non-regular radiation field of high intensity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.3
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• pp.87-98
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• 1990

The present Study dealt with the earthquake-resistant design of cantilever retaining walls supporting cohesionless soils. With design examples of three different types of cantilever retaining walls, the factors of safety against sliding were computed at various values of horizontal acceleration coefficient and compared with each other. The horizontal inertia effect due to the weights of concrete wall itself and a portion of backfill was taken into account in the analyses, and also Mononobe-Okabe pseudo-static solution method was modified to deal with various states different from limiting equilibrium state. From the analyses of safety against sliding, it was found that a cantilever retaining wall with sloped base was the most efficient type in earthquake resistant design. It was also found that by sloping the base, the width of the base slab could be reduced, resulting in the least volume of concrete, excavation and backfill as compared to the other types of walls. In the case of a cantilever retaining wall with sloped feel, the efficiency similar to that of a wall with sloped base could be expected under static loading as well as at relatively low level of earthquake loading. However, this efficiency became vanished with the increase of horizontal acceleration coefficient, since the rate of reduction in developed earth pressures on the heel became smaller. In addition, the design charts with different soil friction angles as well as with different earthquake resistant design criteria of safety factor against sliding were presented for the design of cantilever retaining walls sith sloped base.

• Journal of Korea Water Resources Association
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• v.41 no.8
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• pp.761-772
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• 2008

The object of this study is to develop the model that solves the numerically difficult problems in hydraulic engineering and to demonstrate the applicability of this model by means of various test examples, such as, verification in the gradually varied unsteady condition, three steady flow problems with the change of bottom slope with exact solution, and frictional bed with analytical solution. The governing equation of this model is the integral form of the Saint-Venant equation satisfying the conservation laws, and finite volume method with the Riemann solver is used. The evaluation of the mass and momentum flux with the HLL Riemann approximate solver is executed. MUSCL-Hancock scheme is used to achieve the second order accuracy in space and time. This study introduce the new and simple technique to discretize the source terms of gravity and hydrostatic pressure force due to longitudinal width variation for the balance of quantity between nonlinear flux and source terms. The results show that the developed model's implementation is accurate, robust and highly stable in various flow conditions with source terms, and this model is reliable for one-dimensional applications in hydraulic engineering.

• Journal of Korea Water Resources Association
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• v.30 no.1
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• pp.83-93
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• 1997

The purpose of the study is to analyze the sensitivity of the parameters that affect the runoff and water quality in the studied drainage basins. SWMM model is applied to the four drainage basins located at Namgazwa and Sanbon in Seoul and Gray Haven and Kings Creek in the USA. first of all, the optimum values of the parameters which have least simulation error to the observed data, are detected by iteration procedure. These are used as the standard values which are compared against the procedure. These are used as the standard values which are compared against the varied parameter values. In order to catch the effectiveness of the parameters to the computing result, the parameters are changed step by setp, and the results are compared to the standard results in flowerate and quality of the sewer. The study indicates that the discharge is greatly affected by the types of runoff surface, i.e., impervious area remarkably affects the peak flow and runoff volume while the surface storage affects the runoff volume at mild sloped basins. In addition, the major parameters affecting the pollution concentrations and loadings are the contaminant accumulation coefficient per unit area per time and the continuous dry weather days. Furthermore, the factors that affect the water quality during the initial rainfall period are the rainfall intensity, transport capacity coefficient and its power coefficient. Consequently, in order to simulate the runoff-water quality, it is needed to evaluate previous data in the research performed for the studied basins. To accurately estimated from the tributary areas and the rational computation methods of the pollutants calculation should be introduced.

• Journal of Korea Water Resources Association
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• v.37 no.11
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• pp.969-978
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• 2004

According to the report of hydrologic modeling study, from a quantitative point of view, a lumped model is more efficient than a distributed model. A distributed model has to simplify geospatial characteristics for the shake of restricted application on computer calculation and field observation. In this reason, a distributed model can not help having some errors of water quantity modelling. However, considering a distribution of rainfall-runoff reflected spatial characteristics, a distributed model is more efficient to simulate a flow of surface water, The purpose of this study is modeling of spatial rainfall-runoff of surface water using grid based distributed model, which is consisted of storage function model and essential basin-channel parameters( slope, flow direction & accumulation), and that procedure is able to be executed at a personal computer. The prototype of this model is developed in Heongseong Multipunose Dam basin and adapted in Hapchon Multipurpose Dam basin, which is larger than the former about five times. The efficiency coefficients in result of two dam basin simulations are more than about 0.9, but ones at the upstream water level gauge station meet with bad result owing to overestimated rating curves in high water level. As a result of this study, it is easily implemented that spatially distributed rainfall-runoff model using GIS, and geophysical characteristics of the catchment, hereafter it is anticipated that this model is easily able to apply rainfall data by real time.

• Journal of Wetlands Research
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• v.6 no.3
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• pp.119-126
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• 2004

In recent, the critical rainfall duration concept is widely used but we do not have understandable criteria yet. However, the critical rainfall duration is usually calculated considering concentration time, runoff model using effective rainfall, and unit hydrograph for the estimation of design flood. This study is to derive the regression equations between the critical rainfall duration and hydrologic components such as the basin area, slope, length, CN, and so on. We use a GIS tool which is called the ArcView for the estimation of hydrologic components and the HEC-1 module which is provided in WMS model is used for the runoff computation. As the results, the basin area, basin slope, and basin length had a great influence on the estimations of peak runoff and critical rainfall duration. We also investigated the sensitivities for the peak runoff and critical duration of rainfall from the correlation analysis for the involved components in the runoff estimation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.135-139
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• 2017

The main reason for heat accidents occurring at the after stern tube bearing (STB) is excessive local pressure caused by the deflection of the propulsion shaft due to propeller loads. The probability of a heat accident is increased by the low flexibility of the shaft system in very large crude oil carriers (VLCCs) as the engine power and shaft diameter increase and the distance decreases between the forward and after STBs. This study proposed shaft system with only an after STB and no forward STB for a flexibility acquisition method for a VLCC shaft system under hull deformation. A Hertzian contact condition was applied, which assumes a half-elliptical pressure distribution along the contact width for the calculation of the local squeeze pressure. The propeller loads, heat effect, and hull deflection under engine operating conditions are also considered. The results show that the required design criteria were satisfied by building a partial slope at the white metal, which is the material at the axial contact side in the after STB. This system could reduce building cost by simplification of the shaft system.