• Ocean Systems Engineering
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• 제7권3호
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• pp.275-298
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• 2017

This paper provides a practical stochastic method by which the maximum equilibrium scour depth below a pipeline exposed to random waves plus a current on mild slopes can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes including the effect of breaking waves, and using the empirical formulas for the scour depth on the horizontal seabed by Sumer and Fredsøe (1996). The present approach is valid for wave-dominant flow conditions. Results for random waves alone and random wave plus currents have been presented and discussed by varying the seabed slope and water depth. An approximate method is also proposed, and comparisons are made with the present stochastic method. For random waves alone it appears that the approximate method can replace the stochastic method, whereas the stochastic method is required for random waves plus currents. Tentative approaches to related random wave-induced scour cases for random waves alone are also suggested.

• Journal of Korean Society of Rural Planning
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• 제3권1호
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• pp.23-32
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• 1997

The purpose of this study is to analyze structural and ecological characteristics of streams in rural village. The methods used in this study were measuring the section and surveying the vegetation of the stream at three points(upstream, inner village, downstream ) of 10 rural villages. The major findings of this study can be summarized as follows : 1) The average width of streams is 9 m, and the height of banks 3.1 m. the downstreams are the widest(average 10 m), and the inner-villages are the narrowest (average 8 m), and the slopes of basin are 7.33 %, 2.67 %, 1.39 % at upstream, inner-village, downstream respectively. 2) The downstreams are more contaminated than upstreams due to the sewage from the residents, especially livestock wastewater. 3) The dominant species in the streams are Persicaria thunbergii H. Gross (average Cover 17.76 %) and cumulus japonicas Sieb et. Zucc (average Cover 7.75 % ). 4) The average area covered by vegetation is 53.31 % the downstreams are covered 65.7 %, but inner-village area covered by vegetation is 46.6 %. 5) The problem found in this study are severe water contamination, poor accessibility to stream and poor vegetation of inner-village area, etc.

• Korean Journal of Soil Science and Fertilizer
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• 제42권3호
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• pp.160-166
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• 2009

We estimated site productivity for unstocked land based on the relationship between site index (i.e., average height of dominant trees at fixed age) and soil physico-chemical properties of Pinus densiflora stands. Site index relates to a direct method of determining a tree's response to a specific environment such as forest soil and climate conditions. We selected 78 sites in 22 P. densiflora stands of central temperate forest zone, and sampled soils for physicochemical analyzing. And 13 properties of soils were statistically treated by stepwise regression. In the degree of contribution of the variables to site index, the highly effective variables in A horizon were OM, clay content, sand content, available $P_2O_5$, and Exch. $Ca^{{+}{+}}$ inorder, and in B horizon T.N., O.M., Soil pH, cation exchange capacity(C.E.C.), and sand content in order. In both A and B horizon of the soil for P. densiflora stands, the variables commonly contributed to the site index were sand content and OM. These results may be useful to provide not only important criteria for establishment of Pinus densiflora stand sespecially in unstocked land but also aguidance for reforestation.

• Journal of Industrial Technology
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• 제22권B호
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• pp.219-230
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• 2002

The sliding stability of monolithic vertical caisson of composite breakwaters is quantitatively analyzed by using a reliability model, FMA of Level II, in order to study the variation of sliding failure of caisson due to the occurrence of extreme waves exceeded deepwater design wave. The reliability index and several parameters in the wave pressure formula are inter- related to find out the effects of extreme wave exceeded design wave on the sliding failure of vertical monolithic caisson. The sliding failure of caisson seems to be largely increased as the heights and periods of extreme waves exceeded design wave increase, also depends directly on the water depth in front of the composite breakwaters. From the numerical simulations carried out with several kinds of extreme waves exceeded design wave which are assumed to be occurred during the service periods of breakwater, it is found that the effects of the wave height on the sliding failure of caisson may be more dominant than those of wave periods and angles of wave incidence.

• Journal of ILASS-Korea
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• 제11권2호
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• pp.89-97
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• 2006

An inviscid axisymmetric model capable of predicting droplet bouncing and the detailed pre-impact motion, influenced by the ambient pressure, has been developed using boundary element method (BEM). Because most droplet impact simulations of previous studies assumed that a droplet was already in contact with the impacting substrate at the simulation start, the previous simulations could not accurately describe the effect of the gas compressed between a failing droplet and the impacting substrate. To properly account for the surrounding gas effect, an effect is made to release a droplet from a certain height. High gas pressures are computationally observed in the region between the droplet and the impact surface at instances just prior to impact. The current simulation shows that the droplet retains its spherical shape when the surface tension energy is dominant over the dissipative energy. When increasing the Weber number, the droplet surface structure is highly deformed due to the appearance of the capillary waves and, consequently, a pyramidal surface structure is formed; this phenomenon was verified with our experiment. Parametric studies using our model include the pre-impact behavior which varies as a function of the Weber number and the surrounding gas pressure.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2003년도 추계학술대회 논문집
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• pp.67-70
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• 2003

Hard disk drives (HDD) in computer are used extensively as data storage capacity. The trend in the computer industry to produce smaller disk drives rotating at higher speeds requires an improved understanding of fluid motion in the space between disks. Laser sheet and digital camera was used for 2-dimensional visualization of the unsteady flow between the center pair of two co-rotating disks in air with a cylindrical enclosure (or shroud). Geometric parameters are gap height (H) between disks, and gap distance (G) between disk tip and shroud. The lobe-structured boundary between inner region and outer region was detected by inserted particles, and the number of dominant vortices was determined clearly It is found from flow visualization that the number of vortex cells can be correlated with Reynolds number based on H which is defined as $Re_H={\Omega}RH/v$ ranging from $3.18\times10^3\;to\;1.43\times10^4$, and decreases as the disk speed increases. The lobe pattern by vortex cells is changed to a circular pattern for the wide gap than narrow one.

• Proceedings of the Korean Society of Crop Science Conference
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.48-48
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• 2017

The objectives of this study were to determine the dominance frequency of plant species between spring and summer, to provide useful information toward the conservation to increasing production cattle feed in grazing area in Hiroshima, Japan. The frequency of dominant plant species can adapt in the spring and summer, that consist of Paspalum dilatatum (spring 69.32% and summer 78.98%), Paspalum notatum (spring 47.73% and summer 98.30%), Trifolium repens (spring 73.86% and summer 81.25%). The observed plant species also influenced some productivity, which consists of plant height (spring 16.64 cm and summer 21.55 cm), vegetation cover rates (spring 77.18% and summer 81.36%, chlorophyll content (spring 41.72 mg/g Fw and summer 36.28 mg/g Fw), diversity index (spring 0.94 and summer 0.80), evenness index (spring 0.93 and summer 0.67), and species numbers (spring 32.0 and summer 21.0). It is proposed that Paspalum dilatatum, Paspalum notatum, and Trifolium repens, can be used to increase productivity of plant species as cattle feeds.

• Journal of the Korean Society of Industry Convergence
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• 제6권4호
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• pp.299-305
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• 2003

This research is for the relationship with heat treatment cooling temprature and the characteristic of Mechanical properties of Boron-Addition-Steel, the main material and SM25C steel, the sub material, structure viewing fractography, hardness test, tensite test and are carried out after the manufacturing small-specimen treated with heat of $750^{\circ}C$, $850^{\circ}C$, $1050^{\circ}C$. The influence to the Mechanical properties accompanied by AISI51B20, Boron-Addition-steel shows the following result. 1. The influenc of heat treatment by the content of cabon-steel is dominant. Addition of boron result is Strengthening structure effectively by segregation and improving over all mechanical characters such as good. it results from the increase of temacity by the stability of inter granular with improvement of harden-ability. 2. Boron-Addition-Steel exist in the from of martensite structure accompanied by the ferrite precipitition centering around grain boundary, and is improved to Hv 200. 3. The height of harden-ability and fatigue stress the influence of heat results from crystal structure of martensite by difference of strength level in the structure of ferrite and doesn't have am effect on sensibility of temperature, and turns out to defend on production and growth of Matrix-structure-factor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.742-747
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• 2004

Hard disk drives (HDD) in computer are used extensively as data storage capacity. PIV measurement system was used fur 2-dimensional visualization of the unsteady flow between co-rotating disks in air both with a shroud and both with a actual-like case. Geometric parameters are gap height (H) between disks in the case of shroud. The lobe- structured boundary between inner region and outer region was visualized, and the number of dominant vertices was determined clearly. It is found from flow visualization that the number of vortex cells can be correlated with Reynolds number based on H which is defined as R $e_{H}$ =ΩRH/v ranging from 7.96$\times$10$^2$ to 1.43$\times$10$^4$, and decreases as the disk speed increases. In the case of a actual-like case, the boundary between inner region and outer region appears cleary when head position located at outer diameter with no damper. It is detected with a case of head position middle diameter that the tip wake is generated behind HGA using PIV measurement and calculation.n.

• Journal of the Korean Society of Safety
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• 제24권2호
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• pp.76-82
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• 2009

The NIOSH lifting equation has been used as a dominant tool in evaluating the hazard levels of lifting tasks. Although it provides two different ways for each simple and complex lifting task, the NIOSH simple lifting equation is almost used for not only simple tasks but also complex tasks. However, most of lifting tasks in industries are in the form of complex lifting. Therefore some errors occur inevitably in the evaluation of complex lifting tasks. Among complex lifting tasks, a multi-stacking task is the most popular in lifting tasks. To compensate the error in the evaluation of multi-stacking tasks by using the NIOSH simple lifting equation, a set of calculations for finding LIs(Lifting Indices) was performed for the systematically varying multi-stacking tasks. Then a regression model which finds the equivalent height in simple lifting task for multi-stacking task was established. By using this model, multi-stacking tasks can be evaluated with less error. To validate this model, some real multi-stacking tasks were evaluated as examples.