• Nuclear Engineering and Technology
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• 제30권4호
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• pp.364-376
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• 1998

The statistical analysis method was applied to the evaluation of fracture toughness in the ductile-brittle transition temperature region. Because cleavage fracture in steel is of a statistical nature, fracture toughness data or values show a similar statistical trend. Using the three-parameter Weibull distribution, a fracture toughness vs. temperature curve (K-curve) was directly generated from a set of fracture toughness data at a selected temperature. Charpy V-notch impact energy was also used to obtain the K-curve by a $K_{IC}$ -CVN (Charpy V-notch energy) correlation. Furthermore, this method was applied to evaluate the neutron irradiation embrittlement of reactor pressure vessel (RPV) steel. Most of the fracture toughness data were within the 95% confidence limits. The prediction of a transition temperature shift by statistical analysis was compared with that from the experimental data.

• Structural Engineering and Mechanics
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• 제63권6호
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• pp.809-824
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• 2017

The accurate evaluation of wind characteristics and wind-induced structural responses during a typhoon is of significant importance for bridge design and safety assessment. This paper presents an expectation maximization (EM) algorithm-based angular-linear approach for probabilistic modeling of field-measured wind characteristics. The proposed method has been applied to model the wind speed and direction data during typhoons recorded by the structural health monitoring (SHM) system instrumented on the arch Jiubao Bridge located in Hangzhou, China. In the summer of 2015, three typhoons, i.e., Typhoon Chan-hom, Typhoon Soudelor and Typhoon Goni, made landfall in the east of China and then struck the Jiubao Bridge. By analyzing the wind monitoring data such as the wind speed and direction measured by three anemometers during typhoons, the wind characteristics during typhoons are derived, including the average wind speed and direction, turbulence intensity, gust factor, turbulence integral scale, and power spectral density (PSD). An EM algorithm-based angular-linear modeling approach is proposed for modeling the joint distribution of the wind speed and direction. For the marginal distribution of the wind speed, the finite mixture of two-parameter Weibull distribution is employed, and the finite mixture of von Mises distribution is used to represent the wind direction. The parameters of each distribution model are estimated by use of the EM algorithm, and the optimal model is determined by the values of $R^2$ statistic and the Akaike's information criterion (AIC). The results indicate that the stochastic properties of the wind field around the bridge site during typhoons are effectively characterized by the proposed EM algorithm-based angular-linear modeling approach. The formulated joint distribution of the wind speed and direction can serve as a solid foundation for the purpose of accurately evaluating the typhoon-induced fatigue damage of long-span bridges.

• 한국해안·해양공학회논문집
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• 제36권2호
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• pp.50-60
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• 2024

우리나라 해안공학계에서 신뢰성 기반설계가 빠르게 체화되는 계기를 제공하기 위해 다 수의 한계상태를 지닌 직립방파제 신뢰성 해석과 신뢰성 기반 최적 설계를 우리나라를 대표하는 항이 운영 중인 부산, 군산 전면해역을 대상으로 수행하였다. 이 과정에서 상당한 정도의 신뢰성 해석을 수행하기 위해, 특정 재현 빈도의 설계 파 사용은 지양하였으며, 직립방파제의 파괴 여부를 결정하는 확률변수인 파력, 양력, 전도 모멘트에 내재한 불확실성은 장기 파랑 관측자료를 빈도 해석하여 얻은 확률모형을 사용하여 기술하였다. 직립식 방파제의 한계상태는 활동, 전도, 지지력을 고려하여 세 개로 구성하였으며, 파력과 양력, 모멘트 사이의 밀접한 상관성은 Nataf 결합확률분포를 사용하여 기술하였다. 모의 결과, 쉽게 예상해볼 수 있듯 활동만을 고려하는 경우 파괴확률이 과소하게 산출되는것을 확인하였으며, 특정 재현 빈도에 근거한 설계 파랑으로는 방파제 파괴확률을 일정하게 담보할 수 없다는 것을 확인하였다. 이에 비해 신뢰 지수가 𝛽 = 3.5~4를 충족하도록 최적 설계된 방파제는 두 해역에서 모두 균질한 파괴확률을 확보하는 것으로 모의 되었다.

• 대한금속재료학회지
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• 제47권5호
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• pp.283-289
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• 2009

This paper dealt with a statistical analysis for evaluating the creep crack growth rate (CCGR) for Modified 9Cr-1Mo (ASTM Grade 91) steel. The CCGR data was obtained by the creep crack growth (CCG) tests conducted under various applied loads at $600^{\circ}C$. To obtain logically the B and q values used in the CCGR equation, three methods such as the least square fitting method (LSFM), the mean value method (MVM) and the probabilistic distribution method (PDM) were adopted and their CCGR lines were compared, respectively. In addition, a number of random variables were generated by using the Monte Carlo simulation (MCS), and the CCGR lines were predicted probabilistically. It was found that both the B and q coefficients followed a 2-parameter Weibull distribution well. In the case of the ranges of 10-90% for the probability variables, P(B, q), the CCGR lines were predicted. Fractographic study was conducted from the specimen after the CCG tests.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2005년도 춘계학술대회 논문집
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• pp.245-251
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• 2005

연안 및 항만시설물의 설계에서 심해 설계파 및 풍속은 매우 중요한 설계 파라메타이다. 특히, 최근 부각되고 있는 방재공학 측면에서 이러한 정보에 대한 분석단계는 필수적이라 할 수 있다. 본 연구에서는 완도관측소의 기상연보에서 제시한 1978년부터 2003년까지의 풍속자료와 한국해양연구원 파랑정보시스템에서 제공하는 16방향별 최대 유의파 산출자료를 이용하여 극치분석을 수행하였다. 특성분석에 사용된 극치분포함수는 Weibull, Gumbel, Log-Pearson Type-III, Normal, Lognormal, Gamma 분포이며, 각 분포함수의 매개변수는 모멘트법, 최우도법 그리고 확률 가중 모멘트법으로 추정하였다. 또한, 극치분포함수의 적함성은 5${\%}$의 유의수준 즉, 95${\%}$신뢰도 수준으로 $x^{2}$및 K-S 검정을 실시하였다. 그 결과, 한국 남서연안의 심해 설계파고는 Gumbel 분포형이 가장 적합한 모형으로 파악되었으나, 본 연구의 대상영역에 적합한 모형은 각각의 극치자료에 따라 선정된 확률분포에 의해 다르게 나타났다.

• Wind and Structures
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• 제38권3호
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• pp.215-229
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• 2024

Guyed mast structures exhibit characteristics such as high flexibility, low mass, small damping ratio, and large aspect ratio, leading to a complex wind-induced vibration response mechanism. This study analyzed the time- and frequency-domain characteristics of the wind-induced response of a guyed mast structure using measured acceleration response data obtained from the Shenzhen Meteorological Gradient Tower (SZMGT). Firstly, 734 sets of 1-hour acceleration samples measured from 0:00 October 1, 2021, to 0:00 November 1, 2021, were selected to study the vibration shapes of the mast and the characteristics of the generalized extreme value (GEV) distribution. Secondly, six sets of typical samples with different vibration intensities were further selected to explore the Gaussian property and modal parameter characteristics of the mast. Finally, the modal parameters of the SZMGT are identified and the identification results are verified by finite element analysis. The findings revealed that the guyed mast vibration shape exhibits remarkable diversity, which increases nonlinearly along the height in most cases and reaches a maximum at the top of the tower. Moreover, the GEV distribution characteristics of the 734 sets of samples are closer to the Weibull distribution. The probability distribution of the structural wind vibration response under strong wind is in good agreement with the Gaussian distribution. The structural response of the mast under wind loading exhibits multiple modes. As the structural response escalates, the first three orders of modal energy in the tower display a gradual increase in proportion.

• 대한기계학회논문집A
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• 제24권2호
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• pp.303-310
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• 2000

Fracture toughness of five different reactor pressure vessel steels was characterized in the transition temperature region by the ASTM E1921-97 standard method using Charpy-sized small specimens. T he predominant fracture mode of the tested steels was transgranular cleavage in the test conditions. A statistical analysis based on the Weibull distribution was applied to the interpretation of the scattered fracture toughness data. The size-dependence of the measured fracture toughness values was also well predicted by means of the Weibull probabilistic analysis. The measured fracture toughness transition curves followed the temperature-dependence of the ASTM master curve within the expected scatter bands. Therefore, the fracture toughness characteristics in the transition region could be described by a single parameter, so-called the reference temperature (T。), for a given steel. The determined reference temperatures of the tested materials could not be correlated with the conventional index temperatures from Charpy impact tests.

• The Plant Pathology Journal
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• 제33권2호
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• pp.206-211
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• 2017

The effect of temperature on the rate of systemic infection of potatoes (Solanum tuberosum L. cv. Chu-Baek) by Potato virus Y (PVY) was studied in growth chambers. Systemic infection of PVY was observed only within the temperature range of $16^{\circ}C$ to $32^{\circ}C$. Within this temperature range, the time required for a plant to become infected systemically decreased from 14 days at $20^{\circ}C$ to 5.7 days at $28^{\circ}C$. The estimated lower thermal threshold was $15.6^{\circ}C$ and the thermal constant was 65.6 degree days. A systemic infection model was constructed based on experimental data, using the infection rate (Lactin-2 model) and the infection distribution (three-parameter Weibull function) models, which accurately described the completion rate curves to systemic infection and the cumulative distributions obtained in the PVY-potato system, respectively. Therefore, this model was useful to predict the progress of systemic infections by PVY in potato plants, and to construct the epidemic models.

• 한국응용곤충학회지
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• 제52권2호
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• pp.133-140
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• 2013

흰등멸구, Sogatella furcifera (Horvath), 의 온도에 따른 알 및 약충 발육 기간을 $12.5{\sim}5{\pm}1^{\circ}C$범위에서 $2.5^{\circ}C$ 간격으로 10개 항온, 14:10(L:D) h 광, 상대습도 20~30% 조건에서 조사하였다. 알은 $12.5^{\circ}C$를 제외한 모든 온도 조건에서 1령으로 성공적으로 발육하였으며, $1.5^{\circ}C$에서 22.5일로 가장 길었고, $32.5^{\circ}C$에서 5.5일로 가장 짧았다. 약충은 $15{\sim}32.5^{\circ}C$ 온도범위에서 성충까지 발육 가능하였으며, 약충 전체 발육기간은 $15^{\circ}C$에서 51.9일로 가장 길었으며 온도가 증가함에 따라 짧아져 $32.5^{\circ}C$에서 9.0일로 가장 짧았다. 온도와 발육률과의 관계를 설명하기 위해 선형 및 7개의 비선형(Analytis, Briere 1, 2, Lactin 2, Logan 6, Performance, Modified Sharpe and DeMichele) 모델을 사용하여 분석하였다. 선형 모델을 이용하여 추정한 알과 약충 전기간 발육을 위한 발육영점온도는 각각 $10.2^{\circ}C$와 $12.3^{\circ}C$였으며 발육에 필요한 유효적산온도는 각각 122.0, 156.3 DD였다. 7가지 비선형 모델 중 Briere 1 모델이 모든 발육단계에서 온도와 발육률과의 관계를 가장 잘 설명하였다($r^2$= 0.88~0.99). 알 및 유충의 발육단계별 발육완료 분포는 사용된 3가지 비선형(2-parameter, 3-parameter Weibull, Logistic) 모델 모두 2령과 5령을 제외한 발육단계에서는 비교적 높은 $r^2$(0.91~0.96) 값을 보여 양호한 모형 적합성을 보였다.

• 한국응용곤충학회지
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• 제49권4호
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• pp.305-312
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• 2010

흑다리긴노린재 [Paromius exiguus (Distant)]의 온도에 따른 발육 시험을 15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5, $35{\pm}1^{\circ}C$의 9개 항온, 광주기 14L:10D, 상대습도 20-30% 조건에서 수행하였다. 알은 $15^{\circ}C$에서 발육하지 못하였으며 $17.5^{\circ}C$에서 발육기간이 28.2일로 가장 길었고 온도가 증가함에 따라 짧아져 $35^{\circ}C$에서 5.9일이 소요되었다. 약층은 $17.5^{\circ}C$와 $35^{\circ}C$에서 1령 약층을 넘기지 못하고 모두 사망하였으나, $20-32.5^{\circ}C$ 범위에서는 온도가 증가할수록 발육기간이 짧아지는 경향을 보였고, 4령을 제외한 모든 영기에서 $32.5^{\circ}C$에서의 발육기간이 $30^{\circ}C$와 같거나 더 길어져 발육속도가 둔화되는 경향을 보였다. 온도와 발육율과의 관계를 설명하기 위해 선형 및 3개의 비선형(Briere 1, Lactin 2, Logan 6) 모형을 사용하여 분석하였다. 선형모형을 이용하여 추정한 알과 전체 약층발육의 발육영점온도는 $13.8^{\circ}C$와 $15.3^{\circ}C$였으며 발육 유효적산온도는 각각 109.9, 312.5DD였다. 3가지 비선형 모형 종 Logan-6 모형이 모든 발육단계에서 온도와 발육율과의 관계를 가장 잘 설명하였다 ($r^2$=0.94-0.99). 알 및 유충의 발육단계별 발육완료 분포는 3-parameter Weibull 함수를 사용하였으며 모든 발육단계에서 높은 $r^2$ (0.91-0.99) 값을 보여 양호한 모형 적합성을 보였다.