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Nearshore circulation system

Nearshore circulation system. Chang Hsien Kuo. 國立交通大學土木工程學系 中華民國 102 年 4 月 18 日. Surf zone (type of breakers). Movement of sand on the beach. Movement parallel ( ↔ ) to shoreline Caused by wave refraction (bending) Each wave transports sand either upcoast or downcoast

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Nearshore circulation system

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  1. Nearshore circulation system Chang HsienKuo 國立交通大學土木工程學系 中華民國102年4月18日

  2. Surf zone (type of breakers)

  3. Movement of sand on the beach • Movement parallel (↔) to shoreline • Caused by wave refraction (bending) • Each wave transports sand either upcoast or downcoast • Huge volumes of sand are moved within the surf zone • The beach resembles a “river of sand”

  4. Wave set-up Cross-shore balance of momentum

  5. Wave run-up Regular wave (Miche, 1951) Irregular wave (Mase, 1989) Surf Parameter =:

  6. Longshore current and longshore drift • Longshore current = zigzag movement of water in the surf zone • Longshore drift = movement of sediment caused by longshore current

  7. Nearshore circulation system Longshore current and Rip current Depth-averaged momentum equations and continuity Eq.

  8. Wave induced longshore current Longuet-Higgins (1970) Assumption: 1. Longshore homogeneity ( 2.No wind forcing (Rs=0) 3. Uniform sloping bottom (d=x*tanβ)

  9. Wave induced longshore current Wave forcing Bottom friction 紊流渦動滯度模式 (eddy viscosity model), Reynolds stress P: lateral mixing coefficient

  10. longshore current Wave forcing Slope-type

  11. longshore current Normalized variables and equations Special case: p=1 (linear ratio of eddy viscosity to offshore difference) ; q=1 (uniform slope)

  12. Solution of Euler equations Particular solution Eigen value

  13. Boundary conditions Four conditions Solution

  14. Boundary conditions Chang, H.K. and H.W. Hsu (1996), Longshore current on an equilibrium beach,” China Ocean Engineering, 10(2), 181-192.

  15. Mean longshore current longshore current at mid-surf zone is regarded as mean longshore current Komarand Inman, 1970 um: orbital velocity Komar, 1979 Hbr : root-mean-square wave breaker height Hbs : significant wave breaker height Shore protection manual, 1984 tanβ: beach slope

  16. Observed longshore current Wave height and current at surf zone

  17. Observed cross-shore current Four conditions

  18. Recent study-1 Hasaki coast of Japan

  19. Recent study-1 Marine climate: height and direction of wave and wind Longshore current

  20. Recent study-1 Longshore current in northward or southward directions

  21. Recent study-1 shear stress at the bottom Wind induced shear stress at the surface

  22. Recent study-1 Radiation stress And shear stress at the bottom

  23. Recent study-1 Longshore current of different season

  24. Recent study-2

  25. Recent study-2 Wave height variations by seven models

  26. Recent study-2 Longshore current by seven models

  27. Recent study-2 Comparison with measured longshore current

  28. Recent study-2 Comparison with measured longshore current for spilling breaker

  29. Recent study-2 Comparison with measured longshore current for plunging breaker

  30. Recent study-2 Comparison with measured longshore current for some cases of Leadbetter

  31. Recent study-2 Comparison with measured longshore current for some cases of DELII

  32. Recent study-2 Comparison with measured longshore current for some cases of HORS

  33. Recent study-2 Suggested parameters

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