• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.88-94
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• 1999

Recently, PTFE-polyimide composites are being used self-lubricating parts for industrial field. Thus, this study is mainly concerned with friction and wear properties for the piston ring of non-lubricating air compressor which made of PTFE-polyimide composites. The friction and wear test was carried out for the different composition ratio under the atmosphere room temperature and constant load of 7.69N and their friction and wear properties were compared with each other at various sliding speed. Notable results are summarized as follows. PTFE 100% showed that friction coefficient was almost same values at 0.94 and 1.88m/s but the value was decreased at 2.83m/s because the friction temperature is higher than low speed. PTFE 80%-PI 20% showed the lowest mean friction coefficient at 2.83m/s. PTFE 20%-PI 80% showed the highest friction coefficient at 0.94m/s and the value was decreased at high speed but the value is higher than other materials except PTFE 100 %. PI 100% showed the highest friction coefficient at 0.94 and 1.88m/s because adhesive wear mainly occurred that speed. PTFE 100% showed highest specific wear rate on the whole. Specific wear rate of PTFE 80%-PI 20% was almost the same value with PTFE 20%-PI 80%. PI 100% showed the lowest value at high sliding speed because the friction surface was thicken and carbonated by high friction temperature.

• Structural Engineering and Mechanics
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• 제22권6호
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• pp.665-683
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• 2006

The strength behaviors of Fiber Reinforced Plastics (FRP) Composites can be greatly influenced by the properties of constitutive materials, the laminate structures, and load conditions etc, accompanied by many uncertainty factors. So the reliability study on FRP is an important subject of research. Many achievements have been made in reliability studies based on the probability theory, but little has been done on the roles played by fuzzy variables. In this paper, a fuzzy reliability model for FRP laminates is established first, in which the loads are considered as random variables and the strengths as fuzzy variables. Then a numerical model is developed to assess the fuzzy reliability. The Monte Carlo simulation method is utilized to compute the reliability of laminas under the maximum stress criterion. In the second part of this paper, a generalized fuzzy reliability model (GFRM) is proposed. By virtue of the fact that there may exist a series of states between the failure state and the function state, a fuzzy assumption for the structure state together with the probabilistic assumption for strength parameters is adopted to construct the GFRM of composite materials. By defining a generalized limit state function, the problem is converted to the conventional reliability formula that enables the first-order reliability method (FORM) applicable in calculating the reliability index. Several examples are worked out to show the validity of the models and the efficiency of the methods proposed in this paper. The parameter sensitivity analysis shows that some of the mean values of the strength parameters have great influence on the laminated composites' reliability. The differences resulting from the application of different failure criteria and different fuzzy assumptions are also discussed. It is concluded that the GFRM is feasible to use, and can provide an effective and synthetic method to evaluate the reliability of a system with different types of uncertainty factors.

• 산업경영시스템학회지
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• 제39권1호
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• pp.25-30
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• 2016

It is critical to forecast the maximum daily and monthly demand for power with as little error as possible for our industry and national economy. In general, long-term forecasting of power demand has been studied from both the consumer's perspective and an econometrics model in the form of a generalized linear model with predictors. Time series techniques are used for short-term forecasting with no predictors as predictors must be predicted prior to forecasting response variables and containing estimation errors during this process is inevitable. In previous researches, seasonal exponential smoothing method, SARMA (Seasonal Auto Regressive Moving Average) with consideration to weekly pattern Neuron-Fuzzy model, SVR (Support Vector Regression) model with predictors explored through machine learning, and K-means clustering technique in the various approaches have been applied to short-term power supply forecasting. In this paper, SARMA and intervention model are fitted to forecast the maximum power load daily, weekly, and monthly by using the empirical data from 2011 through 2013. $ARMA(2,\;1,\;2)(1,\;1,\;1)_7$ and $ARMA(0,\;1,\;1)(1,\;1,\;0)_{12}$ are fitted respectively to the daily and monthly power demand, but the weekly power demand is not fitted by AREA because of unit root series. In our fitted intervention model, the factors of long holidays, summer and winter are significant in the form of indicator function. The SARMA with MAPE (Mean Absolute Percentage Error) of 2.45% and intervention model with MAPE of 2.44% are more efficient than the present seasonal exponential smoothing with MAPE of about 4%. Although the dynamic repression model with the predictors of humidity, temperature, and seasonal dummies was applied to foretaste the daily power demand, it lead to a high MAPE of 3.5% even though it has estimation error of predictors.

• 한국환경과학회지
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• 제11권12호
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• pp.1205-1215
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• 2002

To evaluate the change for water quality after the water gate operation in Shiwha lake, in situ survey were conducted on september in 2000 and January, march, jane in 2001. Chemical characteristics and eutrophication level was estimated from the survey data. The water quality of the Shihwa lake was greatly affected by pollutant load from rainfall, and formation of stratification in summer and winter was increased to effect on nutrient release from sediment. Especially, high concentration of chlorophyll-a was occurred in autumn, due to increased nutrient, high water temperature and low salinity after rainfall runoff. The mean concentration of DIN, DIP were 0.346mg/L, 0.0217mg/L in surface water and 0.826mg/L, 0.0415mg/L in bottom water, respectively, which were over III grade of seawater standard. Also high percentage of ammonia nitrogen to DIN in bottom water for autumn and winter was affected by released nutrient from sediment. Correlation analysis of chlorophyll-a versus TSS was shown that organic matter was affected by autochthonous organic matter stem from the algae, these factor showed reverse correlation about salinity. Closely correlations among to the water quality constituent in continuity survey was appeared. The results of eutrophication index estimation showed the high potentiality of red tide occurrence in Shiwha lake, particularity in summer or fall. Overall water quality was greatly improve to compared with measuring data during 1997~1998 at the beginning water gate operation, which reported by KORDI. Therefore, to improve of water quality in Shiwha lake, we need to establish of management plan about nutrient release from sediment, rainfall runoff, maximum of seawater exchange.

• The Journal of Advanced Prosthodontics
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• 제6권4호
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• pp.266-271
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• 2014

PURPOSE. The purpose of this study was to compare the fracture strength of the metal and the bond strength in metal-ceramic restorations produced by selective laser sintering (SLS) and by conventional casting (CAST). MATERIALS AND METHODS. Non-precious alloy (StarLoy C, DeguDent, Hanau, Germany) was used in CAST group and metal powder (SP2, EOS GmbH, Munich, Germany) in SLS group. Metal specimens in the form of sheets ($25.0{\times}3.0{\times}0.5mm$) were produced in accordance with ISO 9693:1999 standards (n=30). To measure the bond strength, ceramic was fired on a metal specimen and then three-point bending test was performed. In addition, the metal fracture strength was measured by continuing the application of the load. The values were statistically analyzed by performing independent t-tests (${\alpha}=.05$). RESULTS. The mean bond strength of the SLS group (50.60 MPa) was higher than that of the CAST group (46.29 MPa), but there was no statistically significant difference. The metal fracture strength of the SLS group (1087.2 MPa) was lower than that of the CAST group (2399.1 MPa), and this difference was statistically significant. CONCLUSION. In conclusion the balling phenomenon and the gap formation of the SLS process may increase the metal-ceramic bond strength.

• Wind and Structures
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• 제27권2호
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• pp.71-88
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• 2018

At the University of Western Ontario (UWO), numerical tools represented in semi-closed form solution for the conductors and finite element modeling of the lattice tower were developed and utilized significantly to assess the behavior of transmission lines under downburst wind fields. Although these tools were validated against other finite element analyses, it is essential to validate the findings of those tools using experimental data. This paper reports the first aeroelastic test for a multi-span transmission line under simulated downburst. The test has been conducted at the three-dimensional wind testing facility, the WindEEE dome, located at the UWO. The experiment considers various downburst locations with respect to the transmission line system. Responses obtained from the experiment are analyzed in the current study to identify the critical downburst locations causing maximum internal forces in the structure (i.e., potential failure modes), which are compared with the failure modes obtained from the numerical tools. In addition, a quantitative comparison between the measured critical responses obtained from the experiment with critical responses obtained from the numerical tools is also conducted. The study shows a very good agreement between the critical configurations of the downburst obtained from the experiment compared to those predicted previously by different numerical studies. In addition, the structural responses obtained from the experiment and those obtained from the numerical tools are in a good agreement where a maximum difference of 16% is found for the mean responses and 25% for the peak responses.

• Asian-Australasian Journal of Animal Sciences
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• 제18권8호
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• pp.1135-1140
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• 2005

Dogs are a very good indicator of the pollution load on the environment. They share people's environment and are exposed to the action of the same pollutants. This study was to estimate the heavy metal contents in dog hairs in domestic districts, and to assess effects of age, sex, feed habits, living area, breeding environment and smoking habit of owner. The mean concentrations of heavy metals in 204 samples were 0.09${\pm}$0.10 ${\mu}g$/g, 0.21${\pm}$0.09 ${\mu}g$/g, 0.82${\pm}$0.09 ${\mu}g$/g and 0.48${\pm}$0.07 ${\mu}g$/g (Cadmium (Cd), Mercury (Hg), Lead (Pb) and Chromium (Cr)) in dog hairs, respectively. Concentrations of Pb, Cd, Hg and Cr in dog hairs in Yeongnam including Ulsan and Seoul, were higher than in Chungchong and Honam, and concentrations of Pb were significantly different (p<0.01). Concentrations of Cd, Hg, Pb and Cr in dog hairs increased with age (p<0.05). Only dogs fed commercial pet foods had significantly higher Cd and Cr concentrations in hairs than dogs fed dog feed and human diet (p<0.01 in Cd and p<0.05 in Cr). Cr concentrations of dog hairsfrom dogs kept on cement floors were the highest of the other environments (p<0.01). Heavy metal concentrations of dogs owned by smokers, were higher than dogs of non-smokers, but there were no significant differences.

• 대한기계학회논문집
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• 제17권6호
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• pp.1321-1329
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• 1993

본 연구에서는 이들보다 매우 간단한 IS법, 즉 초기 변형률법(ISM: initial strain method)에 의한 크리프 수명예측식을 고안하여, 현재 화력발전용 고압 로터강 에 사용되고 있는 1%Cr-Mo-V강과 발전소 효율향상을 위해 최근 국내최초로 개발된 12% Cr강에 대하여 도출하였고, 이 도출식이 앞에서 언급한 여러 파라메트에 의한 결과와 비교 평가하여 장시간 강도 및 수명예측식으로 사용될 수 있음을 입증하였다.

• 대한기계학회논문집A
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• 제25권10호
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• pp.1528-1534
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• 2001

In order to improve Leak-Be(ore-Break methodology, more precisely the crack growth evaluation, a round robin analysis was proposed by the CEA Saclay. The aim of this analysis was to evaluate the crack initiation life, penetration life and shape of through wall crack under cyclic bending loads. The proposed round robin analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but the crack initiation cycle was higher than the experimental result.

• 한국정보처리학회논문지
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• 제6권8호
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• pp.2271-2280
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• 1999

본고에서는 움직임 추정 성능을 개선하고 과도한 연산량과 전송 부담을 경감시키기 위해 HBMA에 기반한 가변 움직임 추정 기법을 제안한다. 제안된 알고리즘은 크게 다음과 같이 네 단계로 구성된다. 우선, 연속된 두 프레임 간의 차영상 윤곡 정보에서 정의한 블록 활동도를 평균하여 현재 영상의 평균 블록 활동도를 산출한다. 두 번째로, 이렇게 산출한 평균 블록 활동도를 통해 카메라 패닝의 유무를 검출한 후, 웨이블렛 변환에 의해 구성한 피라미드 계층 구조상에서 카메라 패닝 벡터를 추정하여 보상한다. 다음으로, 카메라 패닝 보상 후에 정의한 블록 활동도를 토대로 각 블록을 움직임 블록, 준 움직임 블록, 비 움직임 블록 중 어느 하나로 분류한 검색 테이블을 작성한다. 마지막으로, 제안된 가변 HBMA는 검색 테이블을 참조하여 블록 크기를 가변시키고 초기 탐색 계층 및 탐색 영역을 적응적으로 선정함으로써 피라미드 계층 구조상에서 효율적인 고속 움직임 추정을 수행할 수 있다. 이상에서 설명한 각 단계에서 요구되는 비용함수는 차영상 윤곽정보를 통해 획득한 블록 활동도를 공통적으로 이용한다.