• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.48-48
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• 2009

Conventionally in pulsed gas metal arc welding (GMAW-P), drop transfer is analyzed with simplest square pulse waveform. While the pulse current is described by four parameters (peak current magnitude and time plus base current magnitude and time), it deviates the real pulse shape. Real pulse can be better idealized by the trapezoidal pulse waveform described by two additional parameters, i.e., current rise and fall rate (dI/dt). Power source response rate is described by these parameters. In this work, the effect of these parameters on drop transfer is predicted by the force displacement model (FDM). While peak current has significant effects on drop detachment, drop transfer is also influenced by the current rise rate. Predictions indicate that the current rise rate can have considerable effects on the size of the detached drop if other pulse parameters are kept constant. FDM is applied to determine peak time for one drop one pulse condition (ODOP) when rests of the pulse parameters are given. The predicted range of ODOP shows good agreement with experimental data.

• 천문학회보
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• 제46권2호
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• pp.37.1-37.1
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• 2021

Observations suggest the star formation in nuclear rings of barred galaxies proceeds episodically in time and sometimes asymmetrically in space. Existing theories and numerical simulations suggest that the episodic star formation is perhaps due to either supernova feedback combined with fluid instabilities or time-varying mass inflow rate. However, it has been challenging to discern what dominates in shaping the star formation history because the effects of the inflow and feedback are blended in global simulations of nuclear rings. To understand their effects separately, we construct semi-global models of nuclear rings, which treat the mass inflow rate as a model parameter. By running simulations with the inflow rates kept constant or oscillating in time, we find that the star formation rate (SFR) of the rings varies coherently with the inflow rate, while the feedback is responsible only for stochastic fluctuations of the SFR within a factor of two. The feedback instead plays an important role in maintaining the vertical dynamical equilibrium and setting the depletion time. While the asymmetry in the inflow does not necessarily lead to the asymmetry in the star formation, we find that the rings undergo a transient period of lopsided star formation when the inflow rate of only one dust lane is suddenly increased.

• 한국자동차공학회논문집
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• 제10권1호
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• pp.244-254
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• 2002

To enhance the acceleration performance and fuel consumption rate of a vehicle, the torque converter is modified or newly-developed with reliable analysis model. Up to recently, the one dimensional performance model has been used for the analysis and design of torque converter. The model is described with constant parameters based on the concept of mean flow path. When it is used in practice, some experiential correction factors are needed to minimize tole estimated error. These factors have poor physical meaning and cannot be applied confidently to the other specification of torque converter. In this study, the detail dynamic model of torque converter is presented to establish the physical meaning of correction factors. To verify the validity of model, performance test was carried out with various input speed and oil temperature. The effect of oil temperature on the performance is analysed, and it is applied to the dynamic model. And, to obtain the internal flow pattern of torque converter, CFD(Computational Fluid Dyanmics) analysis is carried out on three-dimensional turbulent flow. Correction factors are determined from the internal flow pattern, and their variation is presented with the speed ratio of torque converter. Finally, the sensitivity of correction factors to the speed ratio is studied for the case of changing capacity factor with maintaining torque ratio.

• 한국농공학회지
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• 제40권1호
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• pp.68-77
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• 1998

The purpose of this paper is to establish a method estimating the daily urban water demand using statistical analysis that is used for developing the efficient management and operation of the water supply facilities, and accurary of the model is verified by error rate and F-value. The data used in this study were the daily urban water use, the weather conditions such as temperature, precipitation, relative humidity, etc, and the day of The week. The case study was taken placed for the city of Namwon in Korea. The raw data used in this study were rearranged either by month or by season for analysis purpose, and the statistical analysis was applied to the data to obtain the regression model As a result of this study, the linear regression model was developed to estimate the daily urban water use with weather condition. The regression constant and coefficients of the model were determined for each month of a year. The accuracy of the model was within 3% of average error and within 11% of maximum error. The resulting model was found to he useful to the practical operation and management of the water supply facilities.

• Preventive Nutrition and Food Science
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• 제13권2호
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• pp.104-111
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• 2008

As a way to account for the variability of the primary model parameters in the secondary modeling of microbial growth, three different regression approaches were compared in determining the confidence interval of the temperature-dependent primary model parameters and the estimated microbial growth during storage: bootstrapped regression with all the individual primary model parameter values; bootstrapped regression with average values at each temperature; and simple regression with regression lines of 2.5% and 97.5% percentile values. Temperature dependences of converted parameters (log $q_o$, ${\mu}_{max}^{1/2}$, log $N_{max}$) of hypothetical initial physiological state, maximum specific growth rate, and maximum cell density in Baranyi's model were subjected to the regression by quadratic, linear, and linear function, respectively. With an advantage of extracting the primary model parameters instantaneously at any temperature by using mathematical functions, regression lines of 2.5% and 97.5% percentile values were capable of accounting for variation in experimental data of microbial growth under constant and fluctuating temperature conditions.

• 한국추진공학회지
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• 제11권2호
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• pp.71-78
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• 2007

Polyethylene-GOX 조합 추진제를 이용하여 소형 하이브리드 로켓 모터의 연소 특성에 관한 실험적 연구를 수행하였다. 단일 포트 형상으로 가공된 연료 그레인을 사용하였으며, 연소 전후 연료 그레인의 질량 변화를 통해 평균 후퇴율을 결정하였다. 평균 후퇴율식은 Marxman[3,4]과 Altman[14]의 이론식을 기반으로 도출되었으며, 이를 실험 측정치와 비교한 결과, Marxman의 후퇴율 모델이 Altman의 모델 보다 다소 정확함을 확인하였다. 또한, PE-GOX 추진제의 평균 후퇴율에 대한 고찰로부터 하이브리드로켓 모터 작동 시 일정 산화제 유량 하에서 유입 연료 유량 변화가 상당히 적어 O/F 변화가 미미함 을 알 수 있었다.

• 방사성폐기물학회지
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• 제5권1호
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• pp.29-37
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• 2007

특정 구획으로 유입된 오염물질이 해당 구획 내부에 순간적으로 균일하게 분포한다는 구획모델에 대한 기본가정의 한계로 인해, 전통적인 단일구획모델로는 불포화대에서 오염물질의 이동현상을 적절하게 예측할 수 없다. 한편 물리적으로 동일한 불포화대를 여러 개의 구획으로 구분한 다중구획모델링 기법은 실제 불포화대에서의 오염물질 이동 지연효과를 적절하게 설명할 수 있으나, 지금까지 일반적인 해석해가 보고된 바 없으며 고려하는 구획의 개수가 증가할수록 모델링에 많은 시간이 소요되는 등의 한계가 있다. 이러한 문제점을 해결하기 위하여, 이류가 지배적인 조건 하에서 불포화대의 오염물질 이동현상에 대한 다중구획모델을 수립하고 이를 해석적인 방법으로 계산할 수 있는 일반해를 유도한 후, 다중구획모델을 단일구획모델로 근사할 수 있는 수학적 제약조건을 도출하였다. 단순화된 근사방법론의 유효성은 가상적인 조건 하에서 간단한 수치해석적 방법을 통해 검증하였다. 물리적으로 동일한 특성을 갖는 불포화대를 단일 구획으로 가정할 경우, 불포화대로부터 포화대로 유입되는 오염물질의 전이율은 상수가 아닌 시간 종속적인 명목전이율로 표현할 수 있음을 증명하였다. 또한 명목전이율은 불포화대 구획간 전이율에 민감하며 오염층으로부터의 전이율에 대한 민감도는 미미한 것으로 나타났다. 이 연구에서 개발된 단순화된 근사방법론은 많은 시간이 요구되는 다중구획 모델링을 통하지 않고 불포화대 오염물질 이동현상을 신속하고 합리적으로 예측하기 위한 목적으로 활용될 수 있을 것으로 기대된다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제14권2호
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• pp.129-136
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• 2014

Reliability test is focusing to detect the unexpected reliability failure and solve them for the high quality of products. The test data should be used to assess and project the current level of interesting product reliability and so it is very important to have the accurately assessing methodology with test data. There are two type of trend for test data as constant and changing one during testing and this paper shows the difference in the assessing results of these two cases. There is less information how to define the existence of reliability growth rate changing and calculate the parameters of the reliability growth models to make an accurate assessment with such condition, so i established the process and mathematical model to calculate the parameters at such condition to make reliability growth curve with high Goodness of Fit. I validated the new method with the data made from Monte Carlo Simulation and case from Demko (1993). Even the assessed result with the new methodology may be different with the case by case because of very diversity in test condition and testing product quality, but the process and method founded in this research can be applied to any case using Duane and AMSAA model for their test data assessment. I also present the evaluation method to see the effectiveness with new one which is a conventional knowledge and not popular to use, so it is possible to compare the results with the newly presented and conventional method for better business decision.

• 한국응용곤충학회지
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• 제55권2호
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• pp.119-128
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• 2016

본 연구는 양배추에서 무테두리진딧물의 온도발육실험, 성충수명, 산자실험을 통해 매개변수를 추정하여, 약충의 온도발육모형, 무시성충의 산자모형 작성에 필요한 기본모형들을 제공하기 위해 실시하였다. 6개의 온도(10, 15, 20, 25, 30, $35{\pm}1^{\circ}C$, 16L:8D)에서 실험한 결과로 저온인 $10^{\circ}C$에서는 성공적으로 발육하지 못했다. 약충 발육기간은 온도가 증가할수록 $30^{\circ}C$까지는 감소하였고 $35^{\circ}C$에서는 다시 증가하였는데, $15^{\circ}C$에서 18.5일, $30^{\circ}C$에서 5.9일 이었다. 약충전체 직선회귀식에서 발육영점온도(DT)는 $7.9^{\circ}C$로 나타났으며, 유효적산온도(DD)는 126.3일이었다. 전기약충(1+2령), 후기약충(3+4령), 전체약충 발육률에 대한 비선형모형(Lactin 2 model)과 발육기간 분포 모형(Weibull model)을 작성하였다. 성충수명은 $15^{\circ}C$에서 비정상적으로 18.2일을 보였고, $20^{\circ}C$에서 24.4일, $30.0^{\circ}C$에서 16.4일의 범위에 있었으며, 성충 생리적 연령계산을 위한 노화율 모형작성에 이용되었다. 총 산자수는 $20^{\circ}C$에서 91.6마리로 최대값을 보였다. 본 연구를 통하여 무테두리진딧물 무시성충 산란모형 작성에 필요한 온도별 총산자수, 연령별 누적산자율, 연령별 생존율 모형 등 3개의 기본모형을 추정하였다.

• 대한안전경영과학회지
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• 제16권2호
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• pp.217-230
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• 2014

The purpose of this study is to develop the Generalized Depreciation Function (GDF) and Winfrey Depreciation Function (WDF) by reviewing methods for the depreciation accountings. The Depreciation Accounting Models (DAM), including straight-line model, declining-balance model, sum-of-the-year-digit model and sinking fund model presented in this paper, are reclassified into the charging pattern of increasing type, decreasing type and constant type. This paper also discusses the development of the GDFs based on convex type, concave type and constant type according to the demand pattern of product, frequency of plant usage, deterioration of time, relative inadequacy, Capital Expenditure (CAPEX) and Operating Expenditure (OPEX) of the Total Productive Maintenance (TPM). The WDFs presented in this paper depict a sudden degradation of plant performance by measuring the change of TPM activity at the midpoint of useful life of asset. The WDFs are classified into left-modal type, symmetrical type and right-modal type by varying the value of skewness and kurtosis. Moreover, three increasing patterns, such as convex, concave and linear types, are used in this paper to present the distinct identification of WFDs by using Instantaneous Depreciation Rate (IDR) in terms of Performance Depreciation Function (PDF) and Depreciation Density Function (DDF). In order to have better understanding of depreciation models, the numerical examples are used for evaluating the Net Operating Less Adjusted Tax (NOPLAT) and Economic Value Added (EVA). It is concluded that the depreciation models showing a large dispersion of EVA require the adjustment of NOPLAT and Invested Capital (IC) based on the objective cash basis and net operating activity for reducing the variation of EVA.