• Smart Structures and Systems
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• 제10권4_5호
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• pp.485-499
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• 2012

Mode shape expansion is useful in structural dynamic studies such as vibration based structural health monitoring; however most existing expansion methods can not consider the modelling errors in the finite element model and the measurement uncertainty in the modal properties identified from vibration data. This paper presents a reliable approach for expanding mode shapes with consideration of both the errors in analytical model and noise in measured modal data. The proposed approach takes the perturbed force as an unknown vector that contains the discrepancies in structural parameters between the analytical model and tested structure. A regularisation algorithm based on the Tikhonov solution incorporating the L-curve criterion is adopted to reduce the influence of measurement uncertainties and to produce smooth and optimised expansion estimates in the least squares sense. The Canton Tower benchmark problem established by the Hong Kong Polytechnic University is then utilised to demonstrate the applicability of the proposed expansion approach to the actual structure. The results from the benchmark problem studies show that the proposed approach can provide reliable predictions of mode shape expansion using only limited information on the operational modal data identified from the recorded ambient vibration measurements.

• Nuclear Engineering and Technology
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• 제39권2호
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• pp.133-142
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• 2007

The Electric Power Research Institute (EPRI) demonstrated a method for monitoring the performance of instrument channels in Topical Report (TR) 104965, 'On-Line Monitoring of Instrument Channel Performance.' This paper presents the results of several models originally developed by EPRI to monitor three nuclear plant sensor sets: Pressurizer Level, Reactor Protection System (RPS) Loop A, and Reactor Coolant System (RCS) Loop A Steam Generator (SG) Level. The sensor sets investigated include one redundant sensor model and two non-redundant sensor models. Each model employs an Auto-Associative Kernel Regression (AAKR) model architecture to predict correct sensor behavior. Performance of each of the developed models is evaluated using four metrics: accuracy, auto-sensitivity, cross-sensitivity, and newly developed Error Uncertainty Limit Monitoring (EULM) detectability. The uncertainty estimate for each model is also calculated through two methods: analytic formulas and Monte Carlo estimation. The uncertainty estimates are verified by calculating confidence interval coverages to assure that 95% of the measured data fall within the confidence intervals. The model performance evaluation identified the Pressurizer Level model as acceptable for on-line monitoring (OLM) implementation. The other two models, RPS Loop A and RCS Loop A SG Level, highlight two common problems that occur in model development and evaluation, namely faulty data and poor signal selection

• Journal of Positioning, Navigation, and Timing
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• 제12권1호
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• pp.51-58
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• 2023

Geofencing supports unmanned aerial vehicle (UAV) operation by defining stay-in and stay-out regions. National Aeronautics and Space Administration (NASA) has developed a prototype of the geofencing function, SAFEGUARD, which prevents stayout region violation by utilizing position estimates. Thus, SAFEGUARD depends on navigation system performance, and the safety risk associated with the navigation system uncertainty should be considered. This study presents a methodology to compute the safety risk assessment-based along-track position error bound under nominal and Global Navigation Satellite Systems (GNSS) failure conditions. A Kalman filter system using pseudorange measurements as well as pseudorange rate measurements is considered for determining the position uncertainty induced by velocity uncertainty. The worst case pseudorange and pseudorange rate fault-based position error bound under the GNSS failure condition are derived by applying a Receiver Autonomous Integrity Monitor (RAIM). Position error bound simulations are also conducted for different GNSS fault hypotheses and constellation conditions with a GNSS/INS integrated navigation system. The results show that the proposed along-track position error bounds depend on satellite geometries caused by UAV attitude change and are reduced to about 40% of those of the single constellation case when using the dual constellation.

• Wind and Structures
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• 제11권1호
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• pp.51-70
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• 2008

CFD is applied to evaluate pedestrian wind comfort at outdoor platforms in a high-rise apartment building. Model validation is focused on generic building sub-configurations that are obtained by decomposition of the actual complex building geometry. The comfort study is performed during the design stage, which allows structural design changes to be made for wind comfort improvement. Preliminary simulations are performed to determine the effect of different design modifications. A full wind comfort assessment study is conducted for the final design. Structural remedial measures for this building, aimed at reducing pressure short-circuiting, appear to be successful in bringing the discomfort probability estimates down to acceptable levels. Finally, the importance of one of the main sources of uncertainty in this type of wind comfort studies is illustrated. It is shown that the uncertainty about the terrain roughness classification can strongly influence the outcome of wind comfort studies and can lead to wrong decisions. This problem is present to the same extent in both wind tunnel and CFD wind comfort studies when applying the same particular procedure for terrain relation contributions as used in this paper.

• 한국연안방재학회지
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• 제6권3호
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• pp.111-120
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• 2019

In coastal morphological modelling, there are a number of input factors: wave height, water depth, sand particle size, bed friction coefficients, coastal structures and so forth. Measurements or estimates of these input data may include uncertainties due to errors by the measurement or hind-casting methods. Therefore, it is necessary to consider the uncertainty of each input data and the range of the uncertainty during the evaluation of numerical results. In this study, three uncertainty factors are considered with regard to the prediction of coastal erosion in Ilsan beach located in Ilsan-dong, Ulsan metropolitan city. Those are wave diffraction effect of XBeach model, wave input scenario and the specification of the coastal structure. For this purpose, the values of mean wave direction, significant wave height and the height of the submerged breakwater were adjusted respectively and the followed numerical results of morphological changes are analyzed. There were erosion dominant patterns as the wave direction is perpendicular to Ilsan beach, the higher significant wave height, and the lower height of the submerged breakwater. Furthermore, the rate of uncertainty impacts among mean wave direction, significant wave height and the height of the submerged breakwater are compared. In the study area, the uncertainty influence by the wave input scenario was the largest, followed by the height of the submerged breakwater and the mean wave direction.

• 한국지반공학회논문집
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• 제28권1호
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• pp.17-27
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• 2012

압밀층 두께와 같은 지층 변수들은 공간적인 분포 추정 자체도 중요하지만 추정에 수반되는 불확실성을 정량적으로 평가하는 것도 중요하다. 본 연구에서는 송도신도시 압밀층 두께 추정결과의 국부적 불확실성을 지시자 방법을 이용하여 평가하였다. 지시자 방법을 이용하여 작성한 각 위치에서의 조건부 누적분포함수의 평균을 이용하여 송도신도시 압밀층 두께의 공간적 분포를 추정하였으며, 추정결과의 불확실성은 조건부 분산을 이용하여 평가할 수 있었다. 이러한 분석결과는 송도신도시 이차압축침하량의 공간적 분포추정과 추정결과의 불확실성 평가에 활용할 수 있었다.

• 한국대기환경학회지
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• 제29권3호
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• pp.275-286
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• 2013

It is well known that exposure to high level of PM (particulate matter) can adversely affect human health. However, little is known about health burden of PM considering the relationship, exposed level of PM, and health level in local communities. And, there is scarcely methodical assessment of uncertainty for application to policies of these assessment results. The scope of this study is divided into two parts: firstly to estimate the death burden of PM10 (particulate matter less then $10{\mu}m$ in diameter) in Seoul metropolitan region, and secondly to evaluate potential uncertainties in these estimates. To estimate the death burden of PM10 in Seoul metropolitan region from 2005~2010, we firstly assessed the relationship between daily mean PM10 and daily death counts in Seoul from 2000~2010, and calculated the death burden of PM10 using BenMAP (Environmental Benefits Mapping and Analysis Program). After that, we identified and characterized uncertainties to substantially influence the results of death burden. The daily mortality risk was increased 1.000227 times (p-value/0.001) associated with $1{\mu}g/m^3$ increase of daily mean PM10 for all ages population, Seoul. And, death burdens of PM10 in Seoul metropolitan region were estimated from 5.51 in 2005 to 5.12 in 2010 per 100,000 people. Finally, we categorized context, model, and input uncertainty and characterized these uncertainties in three dimensions (i.e. location, level, and nature) using uncertainty typology. In our study, we argue that uncertainties need to be identified, assessed, reported and interpreted in order for assessment results to adequately support decision making, such as the establishment of air quality standards based on health burden of air quality.

• 대한교통학회지
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• 제32권6호
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• pp.694-702
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• 2014

국가 온실가스를 산정, 보고, 검정을 관장하는 온실가스종합정보센터가 2010년에 출범된 후, 주요 업무의 집합체인 국가 온실가스 인벤토리 보고서가 2012년부터 해마다 발간되었다. 보고서에는 부문별 온실가스 배출량 및 불확도가 보고되고 있지만, 대부분의 부문에서 불확도의 기입은 단순히 IPCC 가이드라인의 기본값으로 대체되고 있는 실정이다. IPCC 가이드라인은 부문별 온실가스 배출량을 산정함에 있어 Tier 수준에 따른 구체적인 산정식을 제시하고 있지만, 불확도의 경우 확률밀도함수 추정 또는 몬테카를로 방법 등을 적용한 국가고유 방법론의 개발을 권고하고 있다. 도로교통부문도 배출량이 Tier 1수준으로 산정되고 있지만 불확도는 보고되지 못하고 있는 실정이다. 본 연구는 도로교통부문에서 일반자가용자동차대형을 대상으로 활동자료인 연간 주행거리, 연비 그리고 배출계수를 이용하여 연간 배출량을 산정하는데 국한하지 않고 불확도 산정에 적용되는 여러 통계적 기법 중에 한 가지인 붓스트랩 및 몬테카를로 방법을 소개하는데 있다.

• 환경정책연구
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• 제8권3호
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• pp.163-180
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• 2009

이 논문에서는 전체 표본을 2개의 표본으로 분리하여 지불의사금액의 유도방식에 따라 WTP가 얼마나 차이가 있는가를 분석하였다. 즉 온실가스 감축의 편익 가치를 추정하기 위해 양분선택형 방식과 다중범위 이산선택형 방식을 비교 분석하였다. 주요 분석결과를 정리하면 다음과 같다. 첫째, 지불의사 유도방식에 따른 지불의사금액의 차이는 일반적 기대치와 일치하는 것으로 나타났다. 양분선택형 방식의 평균 WTP는 다중범위 이산선택형의 MBYES와 PRYES의 사이에 존재하는 것으로 분석되었다. 즉 양분선택형의 경우 월 평균 WTP가 7,470원인 반면 MBYES의 WTP는 11,999원이며 PRYES의 WTP는 6,704원으로 나타났다. 둘째, 선호 불확실성을 반영한 다중범위 이산선택형의 평균 WTP는 정책의사 결정에 있어 다양한 판단기준을 제시할 수 있다. 즉 사업평가의 기준이 되는 편익/비용분석에 있어 선호불확실성의 정도를 반영한 다양한 사업평가가 가능하다는 것이다.

• 기술혁신학회지
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• 제5권1호
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• pp.59-71
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• 2002

Risk, or exposure to uncertainty, is an inherent of risk-adjusted discount rate. It is therefore important part factor in the determination of risk-adjusted discount rate. This paper suggests the method to quantify risk and explains the process how to transfer quantified risk into incremental discount rate. The estimates of underlying risks will help determine the size of appropriate risk-adjusted discount rate with logical and scientific way when the technology valuation is made.