• 대한조선학회논문집
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• 제32권1호
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• pp.25-36
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• 1995

확률적인 접근법으로서의 신뢰성 해석법의 소개와 이의 선체 구조 강도 평가 방법에의 적용에 관해 고찰하였다. 당사에서 건조한 유조선 및 살물선 34척을 대상으로 인장 항복강도, 보강판의 압축 최종강도, 그리고 선각 거어더의 최종강도 등 몇몇 대표적인 종강도 파괴양식에 대해 신뢰성 해석을 수행하였다. 해석결과로서 각 선박에 대한 신뢰도 지수를 보이고 종강도에 대한 신뢰성 해석시의 목표 신뢰도 지수를 제시하였다. 배길이와 건조연도에 따른 신뢰도 지수의 변화를 검토하였으며 결과로서 각 선박의 안전도가 큰 차이를 보임을 알 수 있었다. 각 선박에 대해 균일한 수준의 신뢰도를 제공하기 위하여 부분 안전계수를 이용한 새로운 강도 평가 기준을 마련하였다. AFOSM 방법 및 신뢰성 조건(RC) 방법에 따라 부분 안전계수를 계산하고 이를 비교하였으며 원하는 신뢰도를 줄 수 있는 설계식을 RC 방법으로 구하였다. 부분 안전계수로부터 구한 새로운 설계식을 사용하여 신뢰성 해석을 수행한 선박에 대해 재해석을 실시하였다. 그 결과 처음보다 많이 개선된 균일한 수준의 신뢰도를 얻을 수 있었고 이로부터 신뢰성 해석의 적용가능성과 유용성을 확인하였다.

• Earthquakes and Structures
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• 제11권3호
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• pp.517-538
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• 2016

This paper presents a probabilistic fragility analysis for two groups of bridges: simply supported and integral bridges. Comparisons are based on the seismic fragility of the bridges subjected to accelerograms of two seismic sources. Three-dimensional finite-element models of the bridges were created for each set of bridge samples, considering the nonlinear behaviour of critical bridge components. When the seismic hazard in the site is controlled by a few seismic sources, it is important to quantify separately the contribution of each fault to the structure vulnerability. In this study, seismic records come from earthquakes that originated in strike-slip and reverse faulting mechanisms. The influence of the earthquake mechanism on the seismic vulnerability of the bridges was analysed by considering the displacement ductility of the piers. An in-depth parametric study was conducted to evaluate the sensitivity of the bridges' seismic responses to variations of structural parameters. The analysis showed that uncertainties related to the presence of lap splices in columns and superstructure type in terms of integral or simply supported spans should be considered in the fragility analysis of the bridge system. Finally, the fragility curves determine the conditional probabilities that a specific structural demand will reach or exceed the structural capacity by considering peak ground acceleration (PGA) and acceleration spectrum intensity (ASI). The results also show that the simply supported bridges perform consistently better from a seismic perspective than integral bridges and focal mechanism of the earthquakes plays an important role in the seismic fragility analysis of highway bridges.

• 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.

• 대한조선학회논문집
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• 제38권1호
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• pp.116-122
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• 2001

본 논문에서는 화재안전공학에서 사용되는 모델링 기법과 통계자료들을 검토하고 구조 신뢰성 분야의 확률론적 안전도 평가방법을 도입하여 선박에 대한 방화설계나 선급 규정을 정량적으로 평가하는 방법을 마련하였다. 본 논문에서 개발된 FSEM(Fire Safety Evaluation Module)은 화재안전도의 척도로서 마지막으로 대피하는 사람의 사망확률을 산정하는 프로그램이며, 이를 이용해서 규정에 의한 방화설비를 갖춘 소규모의 화재실에서 대피자에 대한 사망확률을 추정해 보았고, 민감도 해석을 통해 선박에 대한 정량적인 화재안전 평가에의 적용가능성을 검토해 보았다. 계산결과와 검토로부터 선박화재에 대한 새로운 설계지표와 대피상황에서의 인간행동에 대한 폭넓은 연구의 필요성 및 선박의 특수 상황을 고려할 수 있는 새로운 화재진척 모델에 대한 개발이 수행되어야 함을 제시하였다.

• 한국임상약학회지
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• 제26권1호
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• pp.59-69
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• 2016

Background: The subcutaneous formulation of biologic disease-modifying antirheumatic drugs (DMARDs) was preferred due to favored self-administration and would be an economical treatment option for patients with rheumatoid arthritis. This study was to compare the economic impact of biologic DMARDs administered by subcutaneous injection in patients with rheumatoid arthritis who had inadequate response to conventional DMARDs. Methods: The cost-minimization analysis was conducted to estimate the lifetime health care costs of treatment sequences with subcutaneous biologic DMARDs as first-line therapy from a health care system perspective. The Markov model was developed to represent the transitions through treatment sequences based on American College of Rheumatology response rate and discontinuation rate. The health care costs comprised the cost of medications, administration, dispensing, outpatient visits, test/diagnostic examination, palliative therapy and treatment of serious infection. All costs were expressed in 2016 Korean Won (KRW) and discounted at 5%. Results: The mean lifetime health care cost per patient was lowest in the etanercept sequence, which was estimated at KRW 63,441,679. The incremental costs of the treatment sequence started with adalimumab, golimumab, abatacept, and tocilizumab were KRW 7,985,730, KRW 4,064,669, KRW 2,869,947, and KRW 4,282,833, respectively, relative to etanercept sequence. These differences in costs mainly were attributable to medication costs. One-way and probabilistic sensitivity analyses confirmed that etanercept represented the option with the lowest cost compared with comparators. Conclusion: This study found that etanercept is likely a cost-saving treatment option among subcutaneous biologic DMARDs in patients with rheumatoid arthritis.

• Computers and Concrete
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• 제15권2호
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• pp.259-277
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• 2015

The lack of experimental studies on the mechanical behavior of reinforced concrete (RC) haunched beams leads to difficulties in statistical and reliability analyses. This study performs stochastic and reliability analyses of the ultimate shear capacity of RC haunched beams based on nonlinear finite element analysis. The main aim of this study is to investigate the influence of uncertainty in material properties and geometry parameters on the mechanical performance and shear capacity of RC haunched beams. Firstly, 65 experimentally tested RC haunched beams and prismatic beams are analyzed via deterministic nonlinear finite element method by a special program (ATENA) to verify the efficiency of utilized numerical models, the shear capacity and the crack pattern. The accuracy of nonlinear finite element analyses is verified by comparing the results of nonlinear finite element and experiments and both results are found to be in a good agreement. Afterwards, stochastic analyses are performed for each beam where the RC material properties and geometry parameters are assigned to take probabilistic values using an advanced simulating procedure. As a result of stochastic analysis, statistical parameters are determined. The statistical parameters are obtained for resistance bias factor and the coefficient of variation which were found to be equal to 1.053 and 0.137 respectively. Finally, reliability analyses are accomplished using the limit state functions of ACI-318 and ASCE-7 depending on the calculated statistical parameters. The results show that the RC haunched beams have higher sensitivity and riskiness than the RC prismatic beams.

• The Journal of Advanced Prosthodontics
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• 제8권1호
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• pp.53-61
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• 2016

PURPOSE. This study conducted an analysis of cost-effectiveness of the implant and conventional fixed dental prosthesis (CFDP) from a single treatment perspective. MATERIALS AND METHODS. The Markov model for cost-effectiveness analysis of the implant and CFDP was carried out over maximum 50 years. The probabilistic sensitivity analysis was performed by the 10,000 Monte-Carlo simulations, and cost-effectiveness acceptability curves (CEAC) were also presented. The results from meta-analysis studies were used to determine the survival rates and complication rates of the implant and CFDP. Data regarding the cost of each treatment method were collected from University Dental Hospital and Statistics Korea for 2013. Using the results of the patient satisfaction survey study, quality-adjusted prosthesis year (QAPY) of the implant and CFDP strategy was evaluated with annual discount rate. RESULTS. When only the direct cost was considered, implants were more cost-effective when the willingness to pay (WTP) was more than 10,000 won at $10^{th}$ year after the treatment, and more cost-effective regardless of the WTP from $20^{th}$ year after the prosthodontic treatment. When the indirect cost was added to the direct cost, implants were more cost-effective only when the WTP was more than 75,000 won at the $10^{th}$ year after the prosthodontic treatment, more than 35,000 won at the $20^{th}$ year after prosthodontic treatment. CONCLUSION. The CFDP was more cost-effective unless the WTP was more than 75,000 won at the $10^{th}$ year after prosthodontic treatment. But the cost-effectivenss tendency changed from CFDP to implant as time passed.

• 산업경영시스템학회지
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• 제38권4호
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• pp.117-131
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• 2015

Conventional data envelopment analysis (DEA) models require that inputs and outputs are given as crisp values. Very often, however, some of inputs and outputs are given as imprecise data where they are only known to lie within bounded intervals. While a typical approach to addressing this situation for optimization models such as DEA is to conduct sensitivity analysis, it provides only a limited ex-post measure against the data imprecision. Robust optimization provides a more effective ex-ante measure where the data imprecision is directly incorporated into the model. This study aims to apply robust optimization approach to DEA models with imprecise data. Based upon a recently developed robust optimization framework which allows a flexible adjustment of the level of conservatism, we propose two robust optimization DEA model formulations with imprecise data; multiplier and envelopment models. We demonstrate that the two models consider different risks regarding imprecise efficiency scores, and that the existing DEA models with imprecise data are special cases of the proposed models. We show that the robust optimization for the multiplier DEA model considers the risk that estimated efficiency scores exceed true values, while the one for the envelopment DEA model deals with the risk that estimated efficiency scores fall short of true values. We also show that efficiency scores stratified in terms of probabilistic bounds of constraint violations can be obtained from the proposed models. We finally illustrate the proposed approach using a sample data set and show how the results can be used for ranking DMUs.

• 한국물환경학회지
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• 제37권5호
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• pp.369-380
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• 2021

In this work, we analyzed the effects of drought on the water temperature (WT) of Nakdong river basin major river sections using Standardized Precipitation Index (SPI) and WT data. The analysis was carried out on a seasonal basis. After calculating the optimal time scale of the SPI through the correlation between the SPI and WT data, we used the copula theory to model the joint probability distribution between the WT and SPI on the optimal time scale. During spring and fall, the possibility of environmental drought caused by high WT increased in most of the river sections. Notably, in summer, the possibility of environmental drought caused by high WT increased in all river sections. On the other hand, in winter, the possibility of environmental drought caused by low WT increased in most river sections. From the risk map, which quantified the sensitivity of WT to the risk of environmental drought, the river sections Nakbon C, Namgang E, and Nakbon K showed increased stress in the water ecosystem due to high WT when drought occurred in summer. When drought occurred in winter, an increased water ecosystem stress caused by falling WT was observed in the river sections Gilan A, Yongjeon A, Nakbon F, Hwanggang B, Nakbon I, Nakbon J, Nakbon K, Nakbon L, and Nakbon M. The methodology developed in this study will be used in the future to quantify the effects of drought on water quality as well as WT.

• 한국수자원학회논문집
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• 제54권9호
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• pp.705-718
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• 2021

본 연구에서는 위성 원격 감지 자료를 사용하여 생태학적 가뭄의 가능성을 조사하였다. 먼저 MODIS에서 제공하는 정규식생지수와 지표면온도로 부터 식생건강성지수를 추정하였다. 그런 다음 우리나라 전 지역에 분포하고 있는 기상청 ASOS 주요 60개 지점 주변의 산림지역에서 다양한 강수/증발산 시나리오에 따른 식생 관련 가뭄의 가능성을 추정하기 위한 결합 확률모델을 구성하였다. 본 연구의 결과는 대기의 수분공급이 열악하거나 대기의 수분 요구량이 과도한 조건에서 산림 식생과 관련된 가뭄의 위험 패턴을 보여준다. 또한 다양한 기상학적 가뭄 조건에서 산림 식생과 관련된 가뭄 위험의 민감도를 나타낸다. 이러한 연구 결과는 의사 결정권자가 가뭄 위험을 평가하고 온난화 시대에 산림 식생과 관련된 가뭄 완화 전략을 개발할 수 있는 통찰력을 제공할 것으로 기대된다.