• Design & Manufacturing
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• 제13권2호
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• pp.37-43
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• 2019

This study conducted a research as to condensation heat transfer friction loss headby using three types of flat micro multi-channel tubes with different processing of micro-fin and number of channels inside the pipes and different sizes of appearances. In addition, identical studies were conducted by using smoothing circular tubes with 5mm external diameter to study heat enhancement factor and pressure drop penalty factor. 1) The friction head loss showed an increase as the vapor quality and mass flux increased. In case of saturation temperature, it shows an increase as it gets lower. These factors are the reason occurring as the lower the saturation temperature is, the higher the density of refrigerant vapor gets. The influence of heat flux is similar as the dryness is low, but as it gets higher, it lowers in heat flux, and as the high temperature of high heat flux, it is a factor that occurs as the density gets lower. 2) RMS error of the in case of friction head loss, it showed to be predicted as 0.45~0.67 by Chisholm, Friedel, Lockhart and Martinelli. 3) As forfriction head loss penalty factor, the smaller the aspect ratio is, the larger the penalty factor gets, and as for the effect of micro-fin, the penalty factor increased because it decreases to the gas fluid the way groove for the refrigerant's flow.

• 소음진동
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• 제5권4호
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• pp.493-501
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• 1995

Optimum design of a viscoelastic damping layer which is unconstrainedly cohered on a steel plate is discussed from the viewpoint of the modal loss factor. Themodal loss factor is analyzed by using the energy method to the base steel plate and cohered damping layer. Optimum distributions of the viscoelastic damping layer for modes are obtained by sequentially changing the position of a piece of damping layer to another position which contributes to maximizing the modal loss factors. Analytical procedure performed by using this method simulated for 3 fundamental modes of an edge-fixed plate. Simulated results indicate that the modal loss factor ratios can be increase by as much as 210%, or more, by optimizing the thickness distribution of the damping layer to two times of the initial condition which is entirely covered. Optimum configurations for the modes are revealed by positions where added damping treatments become most effective. The calculated results by this method are validated by comparison with the experimental results and the calculated results obtained by the Ross-Ungar-Kerwin's model in the case of the layer is uniformly treated over the steel plate.

• 한국토양비료학회지
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• 제16권2호
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• pp.112-118
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• 1983

전국 51개(個) 측후소(測候所) 및 분실(分室)의 강우성적(降雨成績)을 이용(利用)하여 토양유실량을 여측(予測)하기 위한 강우인자(降雨因子)(R-factor)를 분석(分析) 검토(檢討)한 결과(結果) 조사지역(調査地域)의 연평균(年平均) R-치(値)는 438이었으며 일반적(一般的)으로 동부지역(東部地域)은 R-치(値)가 200~300으로 낮았고 서부(西部) 및 남부지역(南部地域)과 제주도에서는 300~700으로 높았다. R-치(値)와 강우량(降雨量)과의 관계)는 지수함수의 유의성(有意性)있는 상관이 있었으며 이 관계식을 이용(利用)해 R-치(値)를 추정(推定)할 수 있었다. 포장(圃場)에서 측정(測定)한 토양유실량과 토양유실여측공식에 의(依)해 계산(計算)된 토양유실량을 비교(比較)해 본 결과(結果) 강우인자(降雨因子)는 EI 30을 사용(使用)하는 것이 타당(妥當)하였다.

• Spatial Information Research
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• 제17권3호
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• pp.261-268
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• 2009

본 연구는 전국 토양유실분포도와 토양유실위험 등급도를 작성하는 것을 목적으로 하였다. 토양유실분포도는 RUSLE를 이용하였고, 강우-유출 침식성인자(R)는 기상청의 59개 기상관측소의 1977년부터 2006년까지 (30년간)의 강우량 자료를 이용하여 산정하였다. 빈도분석은 FARD를 이용하였고, 전국 R인자를 빈도별로 산정하였다. 전국 R인자 분석에서 낙동강 유역이 가장 작은 값을 한강유역이 큰 값을 갖는 것으로 분석되었다. 토양유실량 분석결과 토지피복별로 초지, 나지 밭의 크기 순서로 토양유실이 발생하고, 전체적으로 약17.2ton/ha 정도의 토양유실이 발생하는 것으로 분석되었다. 단위면적당 평균토양유실량은 나지와 초지에서 많은 토양유실이 발생하고 있다. 5년빈도 강우특성에서 전체 토양유실량은 15,000여 톤의 토양유실이 발생하는 것으로 나타났다. 토지피복별 면적비를 고려하면 논, 산림, 밭작물 재배지역에서 많은 토양유실이 발생하는 것으로 분석되었다. 토양유실 위험 등급도 작성은 토양유실위험 등급을 5개 등급으로 구분하여 수행하였다. 분석결과 토양유실위험 2등급인 보통지역이 전체 토양유실량 위험지역의 78.2%로 가장 많은 부분을 차지하고 있으며, 심각한 토양유실 위험지역은 분석지역 전체 중에서 약 1.1%인 $1,038km^2$정도인 것으로 분석되었다. 토지피복별로 심각한 토양유실 위험지역은 나지, 초지, 밭작물 재배지역의 순으로 각각 $93.5km^2$, $168.1km^2$, $327.4km^2$ 정도가 심각한 등급의 토양유실 위험지역으로 분석되었다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.1586-1590
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• 2006

In order to calculate the actual erosion according to the universal soil loss equation (USLE) and to estimate the impact of land use on soil erosion in Saemangeum, it is important to know the C-factor. Based on the USLE crop-growth stages, the cover-management C-factors were calculated for the main crop and crop rotation systems by National Institute of Agricultural Science and Technology. Combining this result with statistical data about crop cultivation area and crop rotation systems, C-factors of each administrative district in Saemangeum watershed were calculated. The range of C-factors were between 0.28 and 0.35. High C-factor value was obtained with Gimje (C = 0.35) and small C-factor values were found in Wanju (C = 0.28) and Jeongeup (C = 0.29). With this result, calculated annual soil loss was 2,804,483 ton per year. Because of the lack of sufficient statistical data about crop rotation systems, further studies are required on collecting field survey data.

• 한국토양비료학회지
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• 제45권1호
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• pp.112-117
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• 2012

The Revised Universal Soil Loss Equation (RUSLE) is a revision of the Universal Soil Loss Equation (USLE). However, changes for each factor of the USLE have been made in RUSLE which can be used to compute soil loss on areas only where significant overland flow occurs. RUSLE which requires standardized methods to satisfy new data requirements estimates soil movement at a particular site by utilizing the same factorial approach employed by the USLE. The rainfall erosivity in the RUSLE expressed through the R-factor to quantify the effect of raindrop impact and to reflect the amount and rate of runoff likely is associated with the rain. Calculating the R-factor value in the RUSLE equation to predict the related soil loss may be possible to analyse the variability of rainfall erosivity with long time-series of concerned rainfall data. However, daily time step models cannot return proper estimates when run on other specific rainfall patters such as storm and daily cumulative precipitation. Therefore, it is desirable that cross-checking is carried out amongst different time-aggregations typical rainfall event may cause error in estimating the potential soil loss in definite conditions.

• 한국재료학회지
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• 제2권3호
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• pp.220-227
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• 1992

전기유변유체(electrorheological fluid : ERF)는 크기가 $10^{-6}m$정도를 가진 분극성이 강한 입자 분말을 유전유체속에 혼합하여 만든 콜로이드용액으로서 외부전기 장에 의하여 액체상태로부터 겔(gel)상태로 상태변환을 한다. 상태변환과정은 가역과정이며 $10^{-3}$초 정도의 빠른 시간내에 이루어진다. 본 논문에서는 주기적응력이나 주기적 변형이 가해지는 강제진동실험을 통하여 ERF의 점탄성 특성을 조사하였다. 점탄성은 복소수로서 실수부인 동적전단탄성율(storage shear modulus, G')과 허수부인 동적손실율(loss modulus, G")의 합으로 표현된다. 동적전단탄성율은 강제진동의 진폭과 주파수의 함수로 외부전기장에 의하여 크게 변화되었으나 손실계수(loss factor, ${\eta}=G"/G'$)는 진동의 진폭, 진동수 및 외부전기 장에 거의 독립적이었다. 실험(1)은 강제진동의 진폭을 고정하고 진동수를 변화하는 방법(frequency sweep)과 실험(2)는 진동 진폭을 변화시키는 방법(amplitude sweep)으로 실행했다. 본 실험에서는 cornstarch입자를 corn oil에 혼합한 것과 zeolite입자를 silicone oil에 흔합한 콜로이드 용액이 ERF로서 사용되었으며 인가된 전기장은 약$(1~3){\times}10^6V/m$의 직류전기장이 가하여졌다.기장이 가하여졌다.

• 한국농공학회논문집
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• 제65권3호
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• pp.29-42
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• 2023

Universal Soil Loss Equation (USLE) is suggested and employed in the policy to conserve soil resources and to manage the impact of development, since soil loss is very essential to nonpoint source pollution management. The equation requires only five factors to estimate average annual potential soil loss, USLE is simplicity provides benefits in use of the equation. However, it is also limitation of the model, since the estimated results are very sensitive to the five factors. There is a need to examine the application procedures. Three approaches to estimate potential soil loss were examined, In the first approach, all factors were prepared with raster data, soil loss were computed for each cell, and sum of all cell values was determined as soil loss for the watersheds. In the second approach, the mean values for each factor were defined as representing USLE factors, and then the five factors were multiplied to determine soil loss for the watersheds. The third approach was same as the second approach, except that the Vegetative and Mechanical measure was used instead of the Cover and management factor and Support practice factor. The approaches were applied in 38 watersheds, they displayed significant difference, moreover no trends were detected for the soil loss at watersheds with the approaches. Therefore, it was concluded that there is a need to be developed and provided a typical guideline or public systems so that soil loss estimations have consistency with the users.

• The Journal of the Acoustical Society of Korea
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• 제21권4E호
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• pp.164-169
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• 2002

This paper proposes a hybrid method for vibration analysis in the medium to high frequency ranges using Power Flow Analysis (PFA) algorithm and Statistical Energy Analysis (SEA) coupling concepts. The main part of the developed method is the application of coupling loss factor (CLF) suggested in SEA to the power transmission, reflection coefficients in PI' A boundary conditions. The developed hybrid method shows very promising results with regard to the applications for the various damping loss factors in wide frequency ranges. And also this paper presents the applied results of Power Flow Finite Element Method (PFFEM) by forming the new joint element matrix with CLF to analyze the various plate structures in shape. The analytical results of automobile, complex plate structures show good agreement with those of PFFEM using the PFA coefficients.

• Journal of Power Electronics
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• 제7권1호
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• pp.55-63
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• 2007

This paper proposes a simple unity power factor zero-voltage-transition (ZVT) pulse-width-modulated (PWM) single-phase rectifier, which features reduced switching and conduction losses. The switching loss reduction is achieved by a simple auxiliary commutation circuit, and the conduction loss reduction is achieved by employing a single-stage converter, rather than a typical double-stage converter comprising of a front-end rectifier and a boost rectifier. Furthermore, thanks to good features such as a simple PWM control at constant frequency, low switch stress, low Var rating of commutation circuits, and simple power circuit structure, it is suitable for high power applications. The principles of operation are explained in detail, and a major characteristics analysis and the experimental results of the new converter are also included in this paper.