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Estimation of Berthing Velocity Using Probability Distribution Characteristics in Tanker Terminal

확률분포 특성을 이용한 탱커부두에서의 선박접안속도 예측값 추정

  • Lee, Sang-Won (Graduate School, Korea Maritime and Ocean University) ;
  • Cho, Jang-Won (Korea Institute of Maritime and Fisheries Technology) ;
  • Cho, Ik-Soon (Department of Ship Operation, Korea Maritime and Ocean University)
  • Received : 2019.03.12
  • Accepted : 2019.04.16
  • Published : 2019.06.30

Abstract

Berthing energy is majorly influenced by the berthing velocity. It is necessary to design an appropriate berthing velocity for each pier, since excessive berthing velocity can cause berthing accident causing damage to the ship and pier. In this study, as a statistical approach for berthing velocity, the probability distributions suitable for the berthing velocities were confirmed using the K-S test, the A-D test and the Q-Q plot. As a result, the frequency distribution of the berthing velocity was found to be suitable using the Weibull distribution as well as the lognormal distribution. Additionally, the predicted values obtained through estimation of the berthing velocity using the concept of probability of exceedance in this study is proposed as a reference of design berthing velocity. It can be observed that the design berthing velocity is set to be somewhat low so that it does not practically match with the reality. This study and its results can be expected to contribute to the development of a proper design velocity calculation method.

선박의 접안과정 중 발생하는 접안에너지는 접안속도와 밀접한 관계가 있다. 접안속도가 과다할 경우 선박 및 부두에 손상이 발생하는 접안사고로 이어질 수 있으므로 적절한 접안속도를 설계하는 것이 중요하다. 선박접안속도의 경우, 일반적으로 대수정규분포를 따른다고 가정하고 있으나 국내에서는 이에 대한 검증이나 연구가 없어 해외의 사례를 바탕으로 설계접안속도를 설정하고 있는 상황이다. 이에 본 연구에서는 부두의 선박접안속도 분석을 통계학적으로 접근하여 실측데이터와 확률분포를 비교하여 가장 적합한 확률분포를 찾고자 하였다. 적합도 검정으로는 K-S(Kolmogorov-Smirnov) 검정, A-D(Anderson-Darling) 검정, Q-Q(Quantile-Quantile) 플롯 등을 이용하여 접안속도 실측치 분포에 적합한 확률분포를 확인하였다. 분석 결과, 접안속도의 빈도분포는 선박의 재화상태에 따라 만재 시, 대수정규분포, 경하 시에는 와이블분포와 적합함을 확인하였다. 또한 적합도 검정 결과를 이용하여 초과확률에 해당하는 접안속도 예측치를 산출하였다. 이 예측값과 해당 부두의 설계접안속도와 비교 해본 결과, 예측값이 설계값을 크게 초과함을 확인하였다. 이를 통해 설계 시의 접안속도가 현실과 맞지 않게 다소 낮게 설정되어 있음을 알 수 있으며, 이 결과를 바탕으로 적정 설계접안속도 산정법 개선에 기여할 수 있을 것으로 기대된다.

Keywords

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Fig. 1 Relationship between DWT and berthing velocity

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Fig. 2 Brolsma’s curve

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Fig. 3 Scatter plot of berthing velocity

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Fig. 4 Fender performance curve

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Fig. 5 Average freight rate assessment(AFRA) scale

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Fig. 6 Frequency distribution of berthing velocity

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Fig. 7 Result of K-S test

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Fig. 8 Result of A-D test

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Fig. 9 Q-Q probability plot

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Fig. 10 Comparison of R square in Q-Q plot

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Fig. 11 Probability of exceedance(laden, under 100 K DWT)

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Fig. 12 Probability of exceedance(laden, over 100 K DWT)

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Fig. 13 Probability of exceedance(ballast, under 100 K DWT)

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Fig. 14 Probability of exceedance(ballast, over 100 K DWT)

Table 1 Berth particular and operation regulations

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Table 2 Number of data collected by DWT

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Table 3 Frequency count of berthing velocity

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Table 4 Test results in K-S test

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Table 5 Test results in A-D test

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Table 6 Result for goodness of fit test

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Table 7 Extreme value estimates of the berthing velocity(Laden)

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Table 8 Extreme value estimates of the berthing velocity(Ballast)

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