• 대한기계학회논문집A
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• 제34권11호
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• pp.1705-1713
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• 2010

피로시험의 결과가 큰 편차를 보이는 하이브리드 복합재 조인트부에 대해서 통계적 피로수명 평가법을 이용하여 신뢰도 높은 피로수명을 추정하고자 한다. 저상버스 차체에 사용되는 하이브리드 복합재 조인트부를 절취하여 시험대상으로 하였으며, 이 조인트 시편으로 외팔보형 피로굽힘시험을 수행하였다. 피로시험 데이터를 정규분포, 대수정규분포, 와이블 분포를 이용하여 근접시킨 피로수명 곡선들과 각각 비교함으로써 하이브리드 복합재 조인트부의 내구수명 추정에 가장 적합한 확률분포를 선정하였다. 선정된 와이블 확률분포를 이용해 확률-응력-수명(P-S-N) 곡선을 구함으로써 하이브리드 복합재 조인트부에 대한 통계적 수명예측 평가절차와 신뢰성설계의 기초자료를 제시하였다.

• 대한영양사협회학술지
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• 제14권4호
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• pp.337-350
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• 2008

The principal objective of this study was to assess the nutritional status and dietary quality in low-income elderly individuals residing at home (LH) or in health care facilities (LHCF) with dietitian. This study was conducted via anthropometric measurements, questionnaire interviews, and dietary surveys using a 24 hr recall method with 120 low-income elderly individuals (LHCF=46, LH=74). The average ages of the LH and LHCF group were 76.3 years and 78.6 years, respectively. The LH group evidenced a significantly higher frequency of skipping meals than the LHCF group. The average energy intakes of the LHCF and LH group were 1921.0 kcal and 1443.9 kcal, with a significant difference (p<0.001). Most of the nutrient intake and intake rates for recommended intake were significantly higher among the LHCF group as compared with the LH group. The LHCF group showed significantly higher values for the nutrient adequacy ratio (NAR), the mean adequacy ratio (MAR), nutrient density (ND), and the index of nutritional quality (INQ) by dietary qualitative estimation than in the LH group. The Korean diet diversity scores (KDDS) were 3.66 for LH group and 4.93 for the LHCF group, thus were significantly higher in the LHCF group than in the LH group. The results of the present study demonstrate that the LH group appeared to experience more dietary problems than the LHCF group. It was suggested that nutritional education is needed for low-income elderly individuals living at home, in order for them to learn proper dietary management. This can be achieved via educational programs in social welfare institutions, incentives toward employment as a dietitian, and implementation of community-based support.

• International Journal of Fluid Machinery and Systems
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• 제9권1호
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• pp.66-74
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• 2016

Concerning the numerical simulation of high-speed water jet with intensive cavitation this paper presents a practical compressible mixture flow method by coupling a simplified estimation of bubble cavitation and a compressible mixture flow computation. The mean flow of two-phase mixture is calculated by URANS for compressible fluid. The intensity of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the mean flow, and the effect of cavitation on the flow turbulence is considered by applying a density correction to the evaluation of eddy viscosity. High-speed submerged water jets issuing from a sheathed sharp-edge orifice nozzle are treated when the cavitation number, ${\sigma}=0.1$, and the computation result is compared with experimental data The result reveals that cavitation occurs initially at the entrance of orifice and bubble cloud develops gradually while flowing downstream along the shear layer. Developed bubble cloud breaks up and then sheds downstream periodically near the sheath exit. The pattern of cavitation cloud shedding evaluated by simulation agrees experimental one, and the possibility to capture the unsteadily shedding of cavitation clouds is demonstrated. The decay of core velocity in cavitating jet is delayed greatly compared to that in no-activation jet, and the effect of the nozzle sheath is demonstrated.

• Smart Structures and Systems
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• 제20권6호
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• pp.769-780
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• 2017

Cable force monitoring is an essential and critical part of the safety evaluation of cable-supported bridges. A reasonable cable force monitoring scheme, particularly, sensor placement related to accurate safety assessment and budget cost-saving becomes a major concern of bridge administrative authorities. This paper presents optimal sensor placement for cable force monitoring by selecting representative sensor positions, which consider the spatial correlativeness existing in the cable group. The limited sensors would be utilized for maximizing useful information from the monitored bridges. The maximum information coefficient (MIC), mutual information (MI) based kernel density estimation, as well as Pearson coefficients, were all employed to detect potential spatial correlation in the cable group. Compared with the Pearson coefficient and MIC, the mutual information is more suitable for identifying the association existing in cable group and thus, is selected to describe the spatial relevance in this study. Then, the bond energy algorithm, which collects clusters based on the relationship of surrounding elements, is used for the optimal placement of cable sensors. Several optimal placement strategies are discussed with different correlation thresholds for the cable group of Nanjing No.3 Yangtze River Bridge, verifying the effectiveness of the proposed method.

• 대한원격탐사학회지
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• 제21권6호
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• pp.493-503
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• 2005

본 연구에서는 경기도 포천군 일대의 지하수 부존특성 가능지역을 공간적으로 예측하기 위하여 GIS 기반으로 Weight of Evidence(WofE) 기법을 적용하였다. 기본 자료로는 지하수 산출 특성분석과 관련된 수문지질학적 인자인 지표피복, 지형, 지질 등의 자료를 GIS 정보로 입력하였다. 그리고, 베이지안 확률 분석기법(Bayesian Method)에 기반하여 기본자료와 함께 선구조, 암상, 수계밀도, 식생, 토양, 토지이용현황등과 같이 산출성에 영향을 주는 인자들에 대하여 지하수 부존가능 지수와 사전/사후확률을 구하였다. 이들 자료에 대해 다시 WofE 기법을 적용하여, 각 인자들의 W+, W- 가중 값들을 계산하였다. 또한 이러한 결과의 차이 값으로 공간적인 상관관계를 구하여 지하수 산출특성의 예측가능도를 작성하고자 하였다. 본 연구에 적용한 방법은 잠재된 지하수 부존 지역과 주변 지역의 공간적 분포를 파악하는 데 유용한 것으로 생각된다.

• 농업생명과학연구
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• 제52권6호
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• pp.37-47
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• 2018

본 연구의 목적은 전국에 분포하는 일본잎갈나무 임분에 대해 산림시업 수행이 직경분포변화에 미치는 영향에 대해 분석하였다. 본 연구에 사용한 자료는 국가산림자원조사 중 시업지 232plots, 비시업지 47plots의 고정표본점 자료를 활용하였다. 직경분포모델은 Weibull 누적분포함수를 사용하였으며, 분석 방법에는 백분위(Percentile)에 근거한 직경모형추정, 백분위(Percentile)에 대한 모수복구 방법을 사용하였다. 개발한 모델을 이용하여 산림시업의 수행여부에 따른 시나리오(임령, 지위지수, 임분밀도) 별임분생장량을 예측한 결과, 시업지 임분의 최대임목본수를 차지하는 평균 흉고직경의 이동이 비시업지 임분에 비해 이동량과 생장량이 더 높게 나타났으며, 대경목이 차지하는 비율 또한 시업지 임분이 높게 예측되었다. 본 연구의 결과는 직경급에 따른 목재생산량의 장기적인 예측과 동적인 임분구조 해석에 기초적인 정보를 제공할 수 있을 것으로 사료되어진다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2023년도 학술발표회
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• pp.174-174
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• 2023

The impact of global warming on the south Asian summer monsoon is of critical importance for the large population of this region. This study aims to investigate the future changes of the precipitation extremes during pre-monsoon and monsoon, across this region in a more organized regional structure. The study area is divided into six major divisions based on the Köppen-Geiger's climate structure and 10 sub-divisions considering the geographical locations. The future changes of extreme precipitation indices are analyzed for each zone separately using five indices from ETCCDI (Expert Team on Climate Change Detection and Indices); R10mm, Rx1day, Rx5day, R95pTOT and PRCPTOT. 10 global climate model (GCM) outputs from the latest CMIP6 under four combinations of SSP-RCP scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) are used. The GCMs are bias corrected using nonparametric quantile transformation based on the smoothing spline method. The future period is divided into near future (2031-2065) and far future (2066-2100) and then the changes are compared based on the historical period (1980-2014). The analysis is carried out separately for pre-monsoon (March, April, May) and monsoon (June, July, August, September). The methodology used to compare the changes is probability distribution functions (PDF). Kernel density estimation is used to plot the PDFs. For this study we did not use a multi-model ensemble output and the changes in each extreme precipitation index are analyzed GCM wise. From the results it can be observed that the performance of the GCMs vary depending on the sub-zone as well as on the precipitation index. Final conclusions are made by removing the poor performing GCMs and by analyzing the overall changes in the PDFs of the remaining GCMs.

• Geomechanics and Engineering
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• 제32권6호
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• pp.583-600
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• 2023

The resilient modulus (M_R) of various pavement materials plays a significant role in the pavement design by a mechanistic-empirical method. The M_R determination is done by experimental tests that need time and money, along with special experimental tools. The present paper suggested a novel hybridized extreme gradient boosting (XGB) structure for forecasting the M_R of modified base materials subject to wet-dry cycles. The models were created by various combinations of input variables called deep learning. Input variables consist of the number of W-D cycles (WDC), the ratio of free lime to SAF (CSAFR), the ratio of maximum dry density to the optimum moisture content (DMR), confining pressure (σ₃), and deviatoric stress (σ_d). Two XGB structures were produced for the estimation aims, where determinative variables were optimized by particle swarm optimization (PSO) and black widow optimization algorithm (BWOA). According to the results' description and outputs of Taylor diagram, M1 model with the combination of WDC, CSAFR, DMR, σ₃, and σ_d is recognized as the most suitable model, with R² and RMSE values of BWOA-XGB for model M1 equal to 0.9991 and 55.19 MPa, respectively. Interestingly, the lowest value of RMSE for literature was at 116.94 MPa, while this study could gain the extremely lower RMSE owned by BWOA-XGB model at 55.198 MPa. At last, the explanations indicate the BWO algorithm's capability in determining the optimal value of XGB determinative parameters in M_R prediction procedure.

• 에너지공학
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• 제21권1호
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• pp.55-67
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• 2012

미래의 청정 에너지자원인 가스하이드레이트 개발을 위해 국내 부존이 유망한 울릉분지 5개의 지역에 대하여 2007년 시추작업을 수행하여 모든 시추공으로부터 물리검층 자료를 취득하였으며 이중 UBGH1-04, UBGH1-09, UBGH1-10 시추공에서 코어 자료를 취득하였다. 이 연구에서는 기확립한 가스하이드레이트 퇴적층 물성 추정 기법 및 UBGH1-04, UBGH1-09, UBGH1-10 시추공에서의 물성 추정 결과를 바탕으로 사용자 친화적 소프트웨어인 "KMU GH Logs 2010"을 개발하였다. 또한 코어 미회수 시추공인 UBGH1-01 및 UBGH1-14 시추공의 물리검층 자료를 이용하여 가스하이드레이트 퇴적층의 물성을 추정하였다. 밀도 검층 자료를 사용하여 공극률을 추정하였으며, 전기비저항 검층 및 음파 검층을 이용하여 가스하이드레이트포화율을 추정하였다. 물리검층 자료와 코어의 퇴적상 분석 자료를 이용하여 선형 판별 분석 기법을 통해 퇴적상을 추정함으로써 가스하이드레이트 해리의 징후가 나타나는 DITM 및 MSS 퇴적상에 대한 판별이 가능함을 확인하였다.

• 수산해양기술연구
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• 제48권2호
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• pp.128-136
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• 2012

Hybrid surveys using hydroacoustic and fish sampling gears such as trammel net, trap were conducted to investigate total biomass, distribution and dominant fish species of the demersal fishes in the marine ranching area (MRA) of Jeju. Four surveys were carried out in June, August, October and November using 38kHz quantitative echo sounder. Catch data using trammel net and trap were used to calculate biomass and to examine dominant fish species. Fish schools were mainly detected in the waters of 20 meters below and around Chagwido waters. By the result of fishing experiments, fish species living in MRA of Jeju were about 40 species, dominant fish species of a detectable fish such as Family Sparidae and Family Monacanthidae etc. were identified 59.4~68.8% of total biomass. Based on the hydroacoustic data, fish length-weight function and target strength information, mean density of the demersal fish estimated were as follows; 0.88g/$m^2$ on June, 1.12g/$m^2$ on August, 1.35g/$m^2$ on October and 1.18g/$m^2$ on November. An estimated average biomass in MRA of Jeju was founded 20.5 tons in 2007, 20.6 tons in 2008, 23.0 tons in 2009, 25.9 tons in 2010. The results showed that biomass of MRA is getting increased slowly. Therefore the hybrid survey method using hydroacoustic and fish sampling gears is assured an effective biomass survey in the waters of mixed species.