• Journal of Ship and Ocean Technology
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• v.10 no.1
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• pp.1-9
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• 2006

The resistance reduction by an air lubrication effect of a large air cavity covering the hull bottom surface and the similarity relations involved have been investigated with a series of towing tank tests of three geometrically similar models. The test results of geometrically similar models have indicated that a large air cavity was formed beneath the bottom having a backward-facing step by artificially supplying air is effective for resistance reduction. The areas of air cavity and the required flow rates of air are directly related to the effective wetted surface area. The traditional extrapolation methods seem to be applicable to the estimation of the resistance in the tested range if corrections are made to account the changes in the frictional resistance caused by the changes in the effective wetted surface area. To investigate the effectiveness of air lubrication in improving the resistance performance of a practical ship, a small test boat having a backward-facing step under its bottom has been manufactured and speed trials in a river have been performed. Air has been supplied artificially into the downstream region of the bottom step to form a large air cavity covering the bottom surface. The results have confirmed the practical applicability of air lubrication for the resistance reduction of a small high-speed boat.

• Journal of computational fluids engineering
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• v.14 no.4
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• pp.56-61
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• 2009

This study deals with the numerical investigation on two-dimensional lubrication characteristics of micro-dimple shapes fabricated on solid surfaces by using the commercial CFD code (Fluent V.6.3) to examine the influence of micro dimple depth and width on the reduction in friction under the sliding plate condition. In addition, single and multiple dimple arrays are simulated, all for a fixed area fraction of dimple on the surface. As a result, it is found that the existence of micro-dimpled surface makes it possible to substantially reduce the friction forces exerted on the surfaces, and such an optimum dimple depth would be present because the dimple depth larger than the optimum value did no longer affect the reduction in shear stresses, indicating that the reduction of friction is likely to be associated with inner flows of lubricant inside dimples. Moreover, it is observed that at the fixed area fraction, the friction reduction increases with the increase of dimple diameter.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.3
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• pp.407-415
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• 2018

This study analyzed the role of dams for the flood control by the observed and simulated hourly flood discharge data. The study area was the Nakdong river basin with Andong and Imha dams. For the analysis 31 flood events from 1997 to 2010 were selected. In the analysis of the flood reduction rate (FRR) of dam itself, the FRR was not decreased with higher size of floods which is not as we expected. In order to see the trend of flood reduction rate depending on the flood size, flood discharge volume presents it better than peak flood discharge. In the comparison of the flood reduction effects of the two dams, Andong dam has 7% larger flood reduction influence at the Sungju gauging station (SGS) located farthest from the selected watershed. Comparing the ratio of the watershed area based on the covered size of the SGS, the FRR of dam is smaller than the area rate. The impact of FRR of dam showed that the FRR fell below 10% when reaching the size of watershed area corresponding to 8.5 times of the size of watershed area of the dam which is larger than Namhan river basin (7 times).

• Journal of People, Plants, and Environment
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• v.23 no.6
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• pp.637-646
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• 2020

Background and objective: The main objective of this study is to measure the amount of particulate matter (PM) reduction under different characteristics of leaves in 18 different species of indoor plants. Methods: First, a particular amount of PM was added to the glass chambers (0.9×0.86×1.3 m) containing the indoor plant (height = 40 ± 20 cm), and the PM concentration were measured at 2-hour intervals. The experiment with the same conditions was conducted in the empty chamber as the control plot. Results: The range of PM reduction per unit leaf area of 18 species of experimental plants was 3.3-286.2 ㎍·m^-2 leaf, total leaf area was 1,123-4,270 cm², and leaf thickness was 0.14-0.80 mm and leaf size 2.27-234.47 cm². As time passed, the concentration of PM decreased more in the chamber with plants than in the empty chamber. Among the 18 indoor plants, the ones with the greatest reduction in PM2.5 in 2 hours and 4 hours of exposure to PM2.5 were Pachira aquatica and Dieffenbachia amoena. As the exposure time of PM increased, the efficiency of reducing PM2.5 was higher in plants with medium-sized leaves than plants with large or small leaves. The effect of reducing PM2.5 was higher in linear leaves than round or lobed leaves. Plants with high total leaf area did not have advantage in reducing PM because the leaves were relatively small and there were many overlapping parts between leaves. In the correlation between leaf characteristics and PM 2.5 reductions, all leaf area and leaf thickness showed a negative and leaf size showed a positive correlation with PM reduction. Conclusion: The PM reduction effect of plants with medium-sized leaves and long linear leaves was relatively high. Moreover, plants with a large total leaf area without overlapping leaves will have advantaged in reducing PM. Plants are effective in reducing PM, and leaf characteristics are an important factor that affects PM reduction.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.628-631
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• 2007

One of the structural measures for the peak flow reduction is infiltration facilities. There are many types in infiltration facilities - infiltration basin, trench, bed, porous pavement, percolated subdrain, dry well. In this study runoff reduction effect of infiltration trench is analyzed by WinSLAMM. Runoff reduction effect is investigated by each design rainfall and temporal pattern of rainfall particularly. The biggest reduction is shown in Yen and Chow's temporal pattern of design rainfall and the smallest reduction is shown in Huff's first quartile pattern. Runoff reduction rate is presented about 6 to 14 percentage, and the larger return period, the smaller runoff reduction rate.

• Journal of Advanced Navigation Technology
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• v.13 no.5
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• pp.677-683
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• 2009

In this study, we designed and implemented testbed for localization algorithm by using a area reduction method in outdoor environment. The proposed algorithm used 3 steps of area reduction method, which estimated blind nodes position. Also, we have experimented with using a Zigbee module for 5 fixed reference nodes and 4 blind nodes in sensor field of $60m{\times}23m$. The results show that our algorithm is improved the localization accuracy even at the number of ref. node is fixed and the number of blind node is increased. In future research, we will be adding the function of seamless localization in indoor and NLOS(non-line of sight) environment.

• Journal of the Korean Society of Hazard Mitigation
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• v.2 no.3 s.6
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• pp.109-117
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• 2002

An analysis to allocate storage space for sediment accumulation during the economic life of the reservoir is required in the planning or design of a reservoir. This analysis has been the most difficult and tedious aspect to deal with reservoir sedimentation because of the interaction between the various parameters related to the hydraulics of flow, reservoir operating policy, inflowing sediment load. The approach to analyzing spatial distribution of deposits has relied on empirical methods, all of which required a great deal of simplification from the actual physical phenomena. For the purpose of this study, reservoir sedimentation rate computed by Empirical Area Reduction Method is compared with measuring rate along the Soyang-gang Dam. As a conclusion, reservoir sedimentation rate can be estimated exactly by Empirical Area Reduction Method.

• Environmental and Resource Economics Review
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• v.16 no.3
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• pp.451-483
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• 2007

Recently, the problem of noise has received much attention in the urban environment. This paper attempts to measure the economic benefits of urban noise reduction in the metropolitan area. To this end, the dichotomous choice contingent valuation method is applied. In particular, recently proposed one and one-half bound model that reduces the potential for response bias in the double bound model while maintaining much of its efficiency. We surveyed a randomly selected sample of 800 households in the metropolitan area and asked respondents questions in person-to-person interviews about how they would willing to pay for the noise reduction. Respondents overall accepted the contingent market and were willing to contribute a significant amount (997 to 1,778 won), on average, per household per month. This willingness varies according to individual characteristics such as concerns about noise, dwelling area, and income. The aggregate value of the noise reduction in the sampled metropolitan area amounts to approximately 79.26 to 141.35 billion won per year.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.6
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• pp.843-849
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• 2010

This paper presents definition of symmetry of a ship section where three symmetries are proposed: material, geometric, and load symmetries. Precise terminologies of centroid, moment plane, and neutral axis plane are also defined. It is suggested that force vector equilibrium as well as force equilibrium are necessary condition to determine new position of neutral axis due to translational and rotational mobility. It is also stated that new reference datum of ENMP(elastic neutral moment plane), PNMP(fully plastic moment plane), ENAP(elastic neutral axis plane), and INAP(inelastic neutral moment plane) are required to define asymmetric section properties such as second moment of area, elastic section modulus, yield moment, fully plastic moment, and ultimate moment. Since collision-induced damage and flooding-induced biaxial bending moment produce typical asymmetry of section, the section properties are calculated for a typical VLCC. Geometry asymmetry is determined from ABS and DNV rules and two moment planes of 0/30 degs are assumed for load asymmetry. It is proved that the property reduction ratios directly calculated from second moment of area are usually larger than area reduction ratio. Reduction ratio of ultimate moment capacity shows almost linearly proportional to area reduction ratio. Mobility of elastic and inelastic neutral axis planes is visually provided.

• Journal of The Korean Society of Grassland and Forage Science
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• v.35 no.3
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• pp.251-256
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• 2015

The study was conducted to determine greenhouse gas (GHG) inventories in grasslands. After 'Low Carbon Green Growth' was declared a national vision on 2008, Medium-term greenhouse gas reduction was anticipated for 30% reduction compared to Business As Usual (BAU) by 2020. To achieve the reduction targets and prepare to enforce emissions trading (2015), national GHG inventories were measured based on the 1996 Intergovernmental Panel on Climate Change Guidelines (IPCC GL). The national Inventory Report (NIR) of Korea is published every year. Grassland sector measurement was officially added in 2014. GHG removal of grassland soil was measured from 1990 to 2012. Grassland area data of Korea was used for farmland area data in the "Cadastral Statistical Annual Report (1976~2012)". Annual grassland area corresponding to the soil classification was used "Soil classification and commentary in Korea (2011)". Grassland area was divided into 'Grassland remaining Grassland' and 'Land converted to Grassland'. The accumulated variation coefficient was assumed to be the same without time series changes in grassland remaining grassland. Therefore, GHG removal of soil carbon was calculated as zero (0) in grassland remaining grassland. Since the grassland area increases constantly, the grassland soil sinks constantly . However, the land converted to grassland area continued to decrease and GHG removal of soil carbon was reduced. In 2012 (127.35Gg $CO_2$), this removal decreased by 76% compared to 1990 (535.71 Gg $CO_2$). GHG sinks are only grasslands and woodlands. The GHG removaled in grasslands was very small, accounting for 0.2% of the total. However, the study provides value by identifying grasslands as GHG sinks along with forests.