• International Journal of Naval Architecture and Ocean Engineering
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• 제10권3호
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• pp.376-384
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• 2018

Selection of suitable ice class for ships operation is an important but not simple task. The increased exploitation of the Polar waters, both seasonal periods and geographical areas, as well as the introduction of new international design standards such as Polar Code, reduces the relevancy of using existing experience as basis for the selection, and new methods and knowledge have to be developed. This paper will analyse what can be the limiting ice thickness for ships navigating in the Russian Arctic and designed according to the Finnish-Swedish ice class rules. The permanent deformations of ice-strengthened shell structures for various ice classes is determined using MT Uikku as the typical size of a vessel navigating in ice. The ice load in various conditions is determined using the ARCDEV data from the winter 1998 as the basic database. By comparing the measured load in various ice conditions with the serviceability limit state of the structures, the limiting ice thickness for various ice classes is determined. The database for maximum loads includes 3-weeks ice load measurements during April 1998 on the Kara Sea mainly by icebreaker assistance. Gumbel 1 distribution is fitted on the measured 20 min maximum values and the data is divided into various classes using ship speed, ice thickness and ice concentration as the main parameters. Results encouragingly show that present designs are safer than assumed in the Polar Code suggesting that assisted operation in Arctic conditions is feasible in rougher conditions than indicated in the Polar Code.

• 한국태양에너지학회 논문집
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• 제32권1호
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• pp.15-24
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• 2012

IEC 61400-1 requires design lifetime of wind turbines at least 20 years, thus wind turbine should be assured for structural safety through load assessment. DLCs have been defined with respect to the load assessment in IEC 61400-1. In addition, if the extreme design values for DLC1.3 are equal or exceed the extreme design value for DLC1.1, DLC1.1 may be omitted. To omit DLC1.1, scale factor (c) will be increased in DLC1.3. However, this particular adjustment is not specified guidelines. Thus, this study was conducted. DLC1.1 was calculated for extrapolation of 50 years-extreme events using several probability distribution functions and fitting methods. And DLC1.3 was calculated for up to seven different values of scale factor (c) with $2{\leq}c{\leq}5$ in steps of 0.5. Finally, in this study, scale factor (c) that was the value of 4.51 was determined.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2010년도 학술발표회
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• pp.1691-1695
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• 2010

본 연구에서 AFDA(Approximate Full Distribution Approach)를 사용하여 하수관의 불능확률을 정량적으로 산정할 수 있는 신뢰성 모형이 개발되었다. 여러 도시의 연 최대강우강도(Yearly Maximum Rainfall Intensity)를 이용하여 그 확률분포함수를 분석하였고 우수관(Storm sewer)의 불능확률 산정을 위한 신뢰성 모형에 적용하였다. 연 최대강우강도 자료의 분석결과 우리나라 중부지방의 여러 중소도시에 대한 연 최대강우강도의 확률분포함수는 Gumbel분포와 일치하는 것으로 나타났다. 신뢰성 모형은 불능확률의 신뢰함수를 구하기 위해 하중(Load)을 규정하는 식은 합리식이 사용되었고 용량(Capacity)를 규정하는 식은 Darcy-Weisbach공식과 Manning의 공식이 사용되었다. 이렇게 개발된 신뢰성 모형을 실제 우수관에 적용하여 불능확률을 산정하는 신뢰성 해석을 수행하였다. Y자형 우수관망에서 2개의 관으로 유입하는 각각의 유량이 그 관의 허용유량을 초과할 경우를 불능확률로 가정하였고, 나머지 관의 경우는 두 개의 관으로부터 유입하는 유량과 그 세 번째 관의 매설지역의 우수유입량의 합이 그 관의 허용유량을 초과할 경우를 불능상태(state of system failure)로 간주하여 불능확률을 정량적으로 산정하였다. Darcy-Weisbach공식과 Manning의 공식을 사용한 신뢰성 해석결과를 비교하였으며 우수관 직경의 변화에 따른 불능확률을 산정하였다. 특정한 수치(설계직경)이하일 경우 불능확률이 급격히 증가하는 것으로 나타났다. 따라서 실제 우수관의 유효직경이 설계직경에 항상 가깝도록 불순물을 제거하는 것이 최선의 관리 방법이며 불능확률을 줄이는 최선의 방법일 것이다. 본 연구에서 개발된 신뢰성 모형은 우수관의 운용, 관리, 감독은 물론 설계에 활용이 가능 할 것이다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2011년도 학술발표회
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• pp.16-16
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• 2011

Statistics of extreme rainfall play a vital role in engineering practice from the perspective of mitigation and protection of infrastructure and human life from flooding. While flood frequency assessments, based on river flood flow data are preferred, the analysis of rainfall data is often more convenient due to the finer spatial nature of rainfall recording networks, often with longer records, and potentially more easily transferable from site to site. The rainfall frequency analysis as a design tool has developed over the years in New Zealand from Seelye's daily rainfall frequency maps in 1947 to Thompson's web based tool in 2010. This paper will present a history of the development of New Zealand rainfall frequency analysis methods, and the details of the latest method, so that comparisons may in future be made with the development of Korean methods. One of the main findings in the development of methods was new knowledge on the distribution of New Zealand rainfall extremes. The High Intensity Rainfall Design System (HIRDS.V3) method (Thompson, 2011) is based upon a regional rainfall frequency analysis with the following assumptions: $\bullet$ An "index flood" rainfall regional frequency method, using the median annual maximum rainfall as the indexing variable. $\bullet$ A regional dimensionless growth curve based on the Generalised Extreme Value (GEV), and using goodness of fit test for the GEV, Gumbel (EV1), and Generalised Logistic (GLO) distributions. $\bullet$ Mapping of median annual maximum rainfall and parameters of the regional growth curves, using thin-plate smoothing splines, a $2km\times2km$ grid, L moments statistics, 10 durations from 10 minutes to 72 hours, and a maximum Average Recurrence Interval of 100 years.

• Asia-Pacific Journal of Atmospheric Sciences
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• 제54권4호
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• pp.599-610
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• 2018

The goal of this study was to statistically analyse the variability of global irradiance and ultraviolet erythemal (UVER) irradiance and their interrelationships with global and UVER irradiance, global clearness indices and ozone. A prediction of short-term UVER solar irradiance values was also obtained. Extreme values of UVER irradiance were included in the data set, as well as a time series of ultraviolet irradiance variability (UIV). The study period was from 2005 to 2014 and approximately 250,000 readings were taken at 5-min intervals. The effect of the clearness indices on global irradiance variability (GIV) and UIV was also recorded and bi-dimensional distributions were used to gather information on the two measured variables. With regard to daily GIV and UIV, it is also shown that for global clearness index ($k_t$) values lower than 0.6 both global and UVER irradiance had greater variability and that UIVon cloud-free days ($k_t$ higher than 0.65) exceeds GIV. To study the dependence between UIVand GIV the ${\chi}^2$ statistical method was used. It can be concluded that there is a 95% probability of a clear dependency between the variabilities. A connection between high $k_t$ (corresponding to cloudless days) and low variabilities was found in the analysis of bidimensional distributions. Extreme values of UVER irradiance were also analyzed and it was possible to calculate the probable future values of UVER irradiance by extrapolating the values of the adjustment curve obtained from the Gumbel distribution.

• Structural Engineering and Mechanics
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• 제77권2호
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• pp.197-215
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• 2021

Under a severe environment of multiple hazards such as earthquakes and winds, the life-cycle performance of engineering structures may inevitably be deteriorated due to the fatigue effect caused by long-term exposure to wind loads, which would further increase the structural vulnerability to earthquakes. This paper presents a framework for evaluating the lifetime structural seismic performance under the effect of wind-induced fatigue considering different sources of uncertainties. The seismic behavior of a high-rise steel-concrete composite frame with buckling-restrained braces (FBRB) during its service life is systematically investigated using the proposed approach. Recorded field data for the wind hazard of Fuzhou, Fujian Province of China from Jan. 1, 1980 to Mar. 31, 2019 is collected, based on which the distribution of wind velocity is constructed by the Gumbel model after comparisons. The OpenSees platform is employed to establish the numerical model of the FBRB and conduct subsequent numerical computations. Allowed for the uncertainties caused by the wind generation and structural modeling, the final annual fatigue damage takes the average of 50 groups of simulations. The lifetime structural performance assessments, including static pushover analyses, nonlinear dynamic time history analyses and fragility analyses, are conducted on the time-dependent finite element (FE) models which are modified in lines with the material deterioration models. The results indicate that the structural performance tends to degrade over time under the effect of fatigue, while the influencing degree of fatigue varies with the duration time of fatigue process and seismic intensity. The impact of wind-induced fatigue on structural responses and fragilities are explicitly quantified and discussed in details.

• 신재생에너지
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• 제17권4호
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• pp.1-8
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• 2021

To determine the wind turbine class in the offshore of the Korean Peninsula, the reference wind speed for a 50-y return period at the hub height of a wind turbine was estimated using the reanalysis data sets. The most recent reanalysis data, ERA5, showed the highest correlation coefficient (R) of 0.82 with the wind speed measured by the Southwest offshore meteorological tower. However, most of the reanaysis data sets except CFSR underestimated the annual maximum wind speed. The gust factor of converting the 1 h-average into the 10 min-average wind speed was 1.03, which is the same as the WMO reference, using several meteorological towers and lidar measurements. Because the period, frequency, and path of typhoons invading the Korean Peninsula has been changing owing to the climate effect, significant differences occurred in the estimation of the extreme wind speed. Depending on the past data period and length, the extreme wind speed differed by more than 30% and the extreme wind speed decreased as the data period became longer. Finally, a reference wind speed map around the Korean Peninsula was drawn using the data of the last 10 years at the general hub-height of 100 m above the sea level.

• 한국습지학회지
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• 제19권1호
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• pp.30-36
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• 2017

평상시 및 홍수시 하천에 유출되는 토사로 인한 SS(Suspended Solid)농도는 실측을 원칙으로 하여야 하나, 환경영향평가, 하천기본계획 등에서와 같이 각종 개발사업에 따른 SS농도의 변화를 제시하기 위해서는 실측이 아닌 추정이 필요하지만 추정 방법이 규정된 바 없는 실정이다. 따라서, 본 연구에서 RUSLE법에 의한 토사유출량과 특정 빈도 홍수량 산정결과를 이용하여 하천내의 SS농도를 추정하는 수문학적 방법에 대한 제안을 하고자 한다. SS는 실트 점토질 토사 및 콜로이드 입자 등이 해당된다. 그러나, 본 연구에서는 토사유출량 중에서 일반적으로 부유토사에 해당하지 않는 모래를 제외하고, 실트 또는 점토질의 토사에 한해 부유사 기준으로 설정하였다. 농도 추정을 위한 유량은 평상시 유량은 1~2년, 홍수시 유량은 30~100년을 기준으로 하였다. 한편, 확률강우량 분석 소프트웨어는 Fard2006을 사용하였는 바, 2년빈도 미만에 대해서는 강우데이터와 Gumbel분포형 빈도계수를 이용하여 산정하였다. 위와 같은 방법에 의해 실트 및 점토의 토사유출량과 홍수량에 의한 유출용적을 이용하여 SS농도를 추정한 결과, 개발전 자연상태 및 개발중 나대지 상태에서의 SS농도는 유의한 수준을 보이는 것으로 판단된다. 특히, 유로경사에 따라 토사유출량의 차이가 큰 점에 착안하여 SS농도를 유로경사로 나눈 값은 지형인자가 다르더라도 비교적 일정한 범위로 나타남을 확인할 수 있었다. 따라서, 향후 보다 많은 유역에 대하여 연구가 진행된다면 SS농도 추정방법에 대한 지침으로 발전시킬 수 있을 것으로 판단된다.

• 자원환경지질
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• 제4권4호
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• pp.225-234
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• 1971

With the advance of civilization and steadily increasing population rivalry and competition for the use of the sewage, culverts, farm irrigation and control of various types of flood discharge have developed and will be come more and more keen in the future. The author has tried to calculated a formula that could adjust these conflicts and bring about proper solutions for many problems arising in connection with these conditions. The purpose of this study is to find out effective sewage, culvert, drainage, farm irrigation, flood discharge and other engineering needs in the Taegu area. If demands expand further a new formula will have to be calculated. For the above the author estimated methods of control for the probable expected rainfall using a formula based on data collected over a long period of time. The formula is determined on the basis of the maximum daily rainfall data from 1921 to 1971 in the Taegu area. 1. Iwai methods shows a highly significant correlation among the variations of Hazen, Thomas, Gumbel methods and logarithmic normal distribution. 2. This study obtained the following major formula: ${\log}(x-2.6)=0.241{\xi}+1.92049{\cdots}{\cdots}$(I.M) by using the relation $F(x)=\frac{1}{\sqrt{\pi}}{\int}_{-{\infty}}^{\xi}e^{-{\xi}^2}d{\xi}$. ${\xi}=a{\log}_{10}\(\frac{x+b}{x_0+b}\)$ ($-b<x<{\infty}$) ${\log}(x_0+b)=2.0448$ $\frac{1}{a}=\sqrt{\frac{2N}{N-1}}S_x=0.1954$. $b=\frac{1}{m}\sum\limits_{i=1}^{m}b_s=-2.6$ $S_x=\sqrt{\frac{1}{N}\sum\limits^N_{i=1}\{{\log}(x_i+b)\}^2-\{{\log}(x_0+b)\}^2}=0.169$ This formule may be advantageously applicable to the estimation of flood discharge, sewage, culverts and drainage in the Taegu area. Notation for general terms has been denoted by the following. Other notations for general terms was used as needed. $W_{(x)}$ : probability of occurranec, $W_{(x)}=\int_{x}^{\infty}f_{(n)}dx$ $S_{(x)}$ : probability of noneoccurrance. $S_{(x)}=\int_{-\infty}^{x}f_(x)dx=1-W_{(x)}$ T : Return period $T=\frac{1}{nW_{(x)}}$ or $T=\frac{1}{nS_{(x)}}$ $W_n$ : Hazen plot $W_n=\frac{2n-1}{2N}$ $F_n=1-W_x=1-\(\frac{2n-1}{2N}\)$ n : Number of observation (annual maximum series) P : Probability $P=\frac{N!}{{t!}(N-t)}F{_i}^{N-t}(1-F_i)^t$ $F_n$ : Thomas plot $F_n=\(1-\frac{n}{N+1}\)$ N : Total number of sample size $X_l$ : $X_s$ : maximum, minumum value of total number of sample size.

• 한국수자원학회논문집
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• 제48권6호
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• pp.451-461
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• 2015

본 연구에서는 태풍의 경로 및 규모를 이용한 호우분리기법을 통해 한반도에 유발된 강우를 집중호우와 태풍강우로 분류하고, 지역별 강우특성 및 경향성 분석을 수행하였다. 또한 호우분리를 통한 비정상성 빈도해석을 수행하여 미래확률강우량을 산정하였으며, 이에 대한 정량적인 비교 및 평가를 수행하였다. 분석결과, 전기간 자료, 태풍강우 및 집중호우의 증가 및 감소율이 각각 상이하며, 증가 및 감소경향이 서로 상반되는 지점도 나타났다. 또한 호우분리를 통한 비정상성 빈도해석을 수행한 결과, 비교적 합리적인 미래확률강우량이 산정됨을 확인할 수 있었으며, 전기간 자료를 이용한 미래확률강우량과 비교한 결과 한반도 남부 및 동부지역에서 상대적으로 큰 차이가 나타났다. 호우분리기법을 적용한 비정상성 빈도해석 결과는 태풍 및 집중호우의 지역적인 변화특성을 잘 반영하는 것으로 나타나 수공구조물 설계 및 미래 기후변화와 관련된 치수대책 및 정책수립에 활용도가 높을 것으로 판단된다.