Journal of the Korean Society for Marine Environment & Energy (한국해양환경ㆍ에너지학회지)

The Korean Society for Marine Environment and Energy (한국해양환경•에너지학회)
권호 표지
DOI QR코드

DOI QR Code

The Effect of Sampling Rate on Statistical Properties of Extreme Wave

파랑자료의 sampling rate가 극한파의 통계에 미치는 영향

  • Kim, Do Young (Department Naval Architecture and Ocean Engineering, Hongik University)
  • Received : 2013.01.08
  • Accepted : 2013.02.06
  • Published : 2013.02.25
Download PDF
⟨ Previous Next ⟩

Abstract

In this paper time series wave data are simulated using wave spectrum with random phases of the wave signal. The simulated wave signals are used to study the effect of the sampling rate on the ocean wave characteristics. Effect of sampling rate on wave data which include extreme wave such as freak waves are examined and various wave characteristics including abnormality index (AI), kurtosis of wave profile and maximum wave height are examined. Various wave heights are decreased as the sampling rate decreases. The zero-th moment of the wave spectrum does not affect much on the sampling rate but the second moment are greately affected on the sampling rate. The error due to the sampling rate is decreases as the wave period increases. The error in significant wave height based on the wave spectrum $H_s$ is smaller than that on the time domain method $H_{1/3}$. AI index and kurtosis of wave profile do not deviate much from the exact date as long as the sampling rate is greater than 1 Hz. Ocean wave measurement with the sampling frequency higher than 1 Hz will result the error less than 5% in estimating the height of extreme waves.

이 논문에서는 시계열의 파랑자료를 시뮬레이션 하여 파랑계측에서 sampling rate가 파랑자료의 각종 통계적 특성에 미치는 영향을 살펴보았다. 파랑자료의 Sampling rate가 freak wave와 같은 극한파의 통계특성에 미치는 영향을 파악하기 위하여, 이상(AI)지수, 파형의 첨도(kurtosis) 그리고 최대파고 등의 변화를 살펴보았다. Sampling rate가 커지면 각종 파고의 크기가 줄어드는 경향을 보인다. Sampling rate가 커지면 파랑스펙트럼의 0차 모멘트는 큰 변화가 없지만 2차 모멘트는 큰 영향을 받아서, Tz는 과대평가되고 대역폭은 과소평가된다. 따라서 sampling rate변화에 따른 유의파고 크기의 오차는 스펙트럼법에 의한 유의파고 $H_s$가 개별파법에 의한 유의파고 $H_{1/3}$ 보다 작게 나타난다. Sampling rate에 의해서 발생한 오차의 크기는 파랑의 주기가 커지면 줄어드는 경향을 보인다. 파형의 첨도와 AI지수는 sampling rate가 1 Hz 이상인 경우는 큰 오차를 주지 않는다. 일반적으로 freak wave와 같은 극한파가 포함된 파랑을 계측할 때, 1 Hz의 이상의 samping rate로 계측한 해양파의 자료를 사용한다면 sampling rate가 최대파고의 크기의 미치는 오차가 5% 이하가 될 것으로 예상된다.

Keywords

References

  1. Guedes, S.C., Cherneva, Z. and Antao, E.M., 2004, Abnormal waves during Hurricane Camille. J Geophys Res 109.
  2. Kalif, C., Pleinovsky, E. and Slunyaev, A., 2009, Rogue Waves in the Ocean., Springer.
  3. Kim, D.Y., 2010, "On the Characteristics of Freak Wave Occurrence", J. Korean Soc. for Marine Environmental Eng., Vol.14, No.2, pp. 138-145. https://doi.org/10.7846/JKOSMEE.2011.14.2.138
  4. Longuet-Higgins, M.S., 1980, "On the distribution of the heights of sea waves: some effects of non-linearity and finite bandwidth", J. Geophy. Res. Vol.85, C3, pp. 1519-1523. https://doi.org/10.1029/JC085iC03p01519
  5. Mori, N., Paul, C.L. and Yasuda, T., 2002, Analysis of freak wave measurements in the Sea of Japan, Ocean Engineering 29, pp. 1399-1414. https://doi.org/10.1016/S0029-8018(01)00073-7
  6. Mori, N., 2004, Occurrence probability of a freak wave in a nonlinear wave field, Ocean Engineering 31, pp. 165-175. https://doi.org/10.1016/S0029-8018(03)00119-7
  7. Mori, N., 1997, Occurrence properties of giant freak waves in Sea Area aroud Japan, J. waterway, port, coastal Engineering, July/Aug. pp. 209-213.
  8. Shin, S., Hong, K.-Y. and Moon, J.-S., 2007, "Wave Data Analysis for Investigation of Freak Wave Characteristics", J. Lorean Navigation and Port Research, Vol.31, No.6, pp. 471-478. https://doi.org/10.5394/KINPR.2007.31.6.471
  9. Stansell, P, Wolfram, J. and Linfoot, B., 2002, Effect of sampling rate on wave heght statistics, Ocean Eng. 29, 1023-1047. https://doi.org/10.1016/S0029-8018(01)00066-X
  10. Stansell, P., 2004, Distributions of extreme wave, crest and trough heights measured in the North Sea, Ocean Engineering, 32 pp.
  11. Tucker, M.J., 1991, Waves in Ocean Engineering, Ellis Horwood.
  12. Yasuda, T. and Mori, N., 1997, Occurrence of giant freak waves in sea area around Japan, J. Waterway, Port, Coastal, and Ocean Engineering, 123(4), pp. 209-213. https://doi.org/10.1061/(ASCE)0733-950X(1997)123:4(209)