Journal of Korean Society of Coastal and Ocean Engineers (한국해안·해양공학회논문집)

Korean Society of Coastal and Ocean Engineers (한국해안·해양공학회)
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Numerical Analysis of Synchronous Edge Wave Known as the Driving Mechanism of Beach Cusp

Beach Cusp 생성기작으로 기능하는 Synchronous Edge Wave 수치해석

  • Lee, Hyung Jae (Department of Civil Engineering, University of Seoul) ;
  • Cho, Yong Jun (Department of Civil Engineering, University of Seoul)
  • 이형재 (서울시립대학교 토목공학과) ;
  • 조용준 (서울시립대학교 토목공학과)
  • Received : 2019.11.04
  • Accepted : 2019.12.20
  • Published : 2019.12.31
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Abstract

In this study, we carried out the 3D numerical simulation to investigate the hydraulic characteristics of Synchronous Edge wave known as the driving mechanism of beach cusp using the Tool Box called the ihFoam that has its roots on the OpenFoam. As a wave driver, RANS (Reynolds Averaged Navier-Stokes equation) and mass conservation equation are used. In doing so, we materialized short-crested waves known as the prerequisite for the formation of Synchronous Edge waves by generating two obliquely colliding Cnoidal waves. Numerical results show that as can be expected, flow velocity along the cross section where waves are focused are simulated to be much faster than the one along the cross section where waves are diverged. It is also shown that along the cross section where waves are focused, up-rush is moving much faster than its associated back-wash, but a duration period of up-rush is shortened, which complies the typical characteristics of nonlinear waves. On the other hand, due to the water-merging effect triggered by the redirected flow toward wave-diverging area at the pinacle of run-up, along the cross section where waves are diverged, offshore-ward velocity is larger than shore-ward velocity at the vicinity of shore-line, while at the very middle of shoaling process, the asymmetry of flow velocity leaned toward the shore is noticeably weakened. Considering that these flow characteristics can be found without exception in Synchronous Edge waves, the numerical simulation can be regarded to be successfully implemented. In doing so, new insight about how the boundary layer streaming occur are also developed.

Beach cusp의 생성기작으로 기능하는 Synchronous Edge wave의 수리특성을 살펴보기 위한 3D 수치모의를 OpenFOAM 기반 tool box인 IHFOAM을 활용하여 수행하였다. 파랑모형은 RANS[Reynolds Averaged Navier-Stokes equation]와 연속방정식으로 구성하였으며, Synchronous Edge wave 형성에 필요한 연안방향으로 파고가 변조되는 short-crested waves는 동일한 주기와 파고를 지니는 두 개의 Cnoidal wave가 전면 해역에서 비스듬히 조우되도록 조파하여 재현하였다. 모의결과 파랑 집중단면에서의 유속이 파랑 분산단면보다 전체적으로 크게 모의되었다. 또한 파랑 집중단면의 경우 해안방향 흐름[up-rush]이 먼 바다방향 흐름[back-wash]보다 세기는 우월하나 지속기간은 짧은 비선형 파동계의 일반적인 성정을 지니는 것으로 모의되었다. 이와 더불어 처오름 정점에서 양쪽의 분산단면으로 흐름이 나뉘며 약해지는 b ack-wash로 인해 up-rush 최대유속은 back-wash 최대유속의 두 배 가까이 증가하는 것으로 관측되었다. 이에 비해 파랑 분산단면의 경우 집수효과로 해안 인근 수역에서는 먼 바다방향 흐름이 해안방향흐름보다 우월하게 모의되었다. 또한 천수 중간 수역에서는 해안방향 흐름이 여전히 우세하나 비대칭 정도는 현저하게 감소하였다. 이러한 수리특성은 Synchronous Edge wave의 전형적인 성정으로 수치모의가 성공적으로 이루어진 것으로 판단된다. 이 과정에서 너울이 우월한 해양환경에서 해빈이 느리지만 점진적으로 복원되는 과정에서 주 기작으로 기능하는 경계층 streaming에 대한 새로운 해석도 제시되었다.

Keywords

References

  1. Cho, Y.J. (2019a). Numerical analysis of the beach stabilization effect of an asymmetric ripple mat. Journal of Korean Society of Coastal and Ocean Engineers, 31(4), 209-220. https://doi.org/10.9765/KSCOE.2019.31.4.209
  2. Cho, Y.J. (2019b). Grand circulation process of beach cusp and its seasonal variation at the Mang-Bang Beach from the perspective of trapped mode Edge Waves as the driving mechanism of beach cusp formation. Journal of Korean Society of Coastal and Ocean Engineers, 31(5), 265-277. https://doi.org/10.9765/KSCOE.2019.31.5.265
  3. Cho, Y.J. and Bae, J.H. (2019). On the feasibility of freak waves formation within the harbor due to the presence of Infra-gravity waves of bound mode underlying the ever-present swells. Journal of Korean Society of Coastal and Ocean Engineers, 31(1), 17-27. https://doi.org/10.9765/KSCOE.2019.31.1.17
  4. Cho, Y.J. and Kim, I.H. (2019). Preliminary study on the development of platform for the selection of an optimal beach stabilization measures against the beach erosion-centering on the yearly sediment budget of the Mang-Bang beach. Journal of Korean Society of Coastal and Ocean Engineers, 31(1), 28-39. https://doi.org/10.9765/KSCOE.2019.31.1.28
  5. Cho, Y.J., Kim, I.H. and Cho, Y.J. (2019). Numerical analysis of the grand circulation process of Mang-Bang beach- centered on the shoreline change from 2017. 4. 26 to 2018. 4. 20. Journal of Korean Society of Coastal and Ocean Engineers, 31(3), 101-114. https://doi.org/10.9765/KSCOE.2019.31.3.101
  6. Dodd, N., Stoker, A.M., Calvete, D. and Sriariyawat, A. (2008). On beach cusp formation. J. Fluid Mech., 597, 145-169. https://doi.org/10.1017/S002211200700972X
  7. Eckart. C. (1951). Surface waves on water of variable depth. Wave Report 100, University of California, Scripps Institution of Oceanography, Ref No 51-12, 99 pp.
  8. Guza, R.T. (1974). Excitation of edge waves and their role in the formation of beach cusps. University of California, San diego, Ph.D., 1974 Oceanography.
  9. Lara, J.L., Garcia, N. and Losada, I.J. (2006). RANS modelling applied to random wave interaction with submerged permeable structures. Coastal Engineering, 53, 395-417. https://doi.org/10.1016/j.coastaleng.2005.11.003
  10. Longuet-Higgins, M.S. (1953). Mass transport in water waves. Phil Trans R Soc Lond A, 245, 535-581. https://doi.org/10.1098/rsta.1953.0006
  11. Losada, I.J., Gonzalez-Ondina, J.M., Diaz, G. and Gonzalez, E.M. (2008). Numerical simulation of transient nonlinear response of semi-enclosed water bodies: model description and experimental validation. Coastal Engineering, 55(1), 21-34. https://doi.org/10.1016/j.coastaleng.2007.06.002
  12. Pengzhi, L. and Philip, L. (1999). Internal wave-maker for Navier-Stokes equations model. Journal of Waterway, Port, Coastal and Ocean Engineering, 125. 207-214. https://doi.org/10.1061/(ASCE)0733-950X(1999)125:4(207)
  13. Schaffer, H.A. and Klopman, G. (2000). Review of multidirectional active wave absorption methods. Journal of Waterway, Port, Coastal, and Ocean Engineering, 126(2), 88-97.
  14. Wei, G. and Kirby, J. (1995). Time-dependent numerical code for extended Boussinesq equations. Journal of Waterway Port Coastal and Ocean Engineering, 121(5), 251-261. https://doi.org/10.1061/(ASCE)0733-950X(1995)121:5(251)