Download - Wave Modeling
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Wave Modeling
Local Wave Transformations
Billy L. Edge & Margery Overton
CVEN 695-02
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Bathymetric Data
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Why do we need wave models?• Wave climate assessment at the project site is important to
most coastal & ocean engineering projects, including- navigation and channel studies- on/offloading of ships- optimization of harbor layouts- design of structures (breakwaters, etc.)- shoreline erosion projects, etc.
• Nearshore wave conditions are normally determined from deepwater conditions- long-term nearshore wave data are usually unavailable- transform offshore wave data to nearshore (wind-generation, shoaling, refraction, breaking, dissipation, bottom friction) – regional scale models- investigate local scale phenomena (refraction, wave reflection, diffraction,
nonlinear wave-wave and wave-current interaction) –local scale models
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Regional Scale Wave Modeling
• Scale O(100 km~5000 km)– Spectral wind-wave models (WAM)
• Scale O(10 km ~100 km)– Spectral wind-wave models (STWAVE and SWAN)– Dominant process: wind input, shoaling and refraction– Wave action: conservation equation– Assume phase-averaged wave properties vary slowly
over distances of the order of a wavelength– Cannot accurately resolve rapid variations that occur at
sub-wavelength scale due to wave reflection/diffraction
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Local Scale Wave Modeling
• Scale O(1 km ~ 10 km)– Elliptic mild-slope model (CGWAVE)– Parabolic mild-slope model (REFDIF)– Boussinesq wave model (BOUSS-2D)– Dominant processes: shoaling, refraction, breaking,
reflection, diffraction, wave nonlinearities due to interactions of different frequencies and ambient currents and structures
– All models use vertically integrated eqns for wave propagation in 2D horizontal plane
– CGWAVE assumes hyperbolic cosine variation of the velocity potential over depth, and BOUSS-2D assumes a quadratic variation
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Summary of Model Features
Phase resolvingPhase averagingPhase averaging
Diffraction/Reflection
Nonlinear Interactions
Wave-Current Interaction
Wave Breaking
Shoaling/Refraction
BOUSSCGWAVE/REFDIFSTWAVE
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Spectral Wind-Wave Models
• Advantages– wind-wave generation– shoaling, refraction, breaking– wave-current interaction– applicable to large domains (deep to shallow water)
• Disadvantages– reflection, diffraction– steady-state
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Elliptic Mild-Slope Models
• Advantages– well suited for long-period oscillations– shoaling, refraction, breaking, bottom friction– reflection, diffraction– wave-current interaction (in future version)– flexibility of finite elements
• Disadvantages– nonlinear interactions in shallow water (in future
version)
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Parabolic Mild-Slope Models
• Advantages– shoaling, refraction, breaking, bottom friction– Refraction, reflection, diffraction– wave-current interaction
• Disadvantages– Grid limitations in size and regular gridding
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Boussinesq Wave Models
• Advantages– shoaling, refraction, breaking, bottom friction– reflection, diffraction, nonlinear interactions– wave-induced currents, wave-current interaction
• Disadvantages– computationally intensive– 2-D very computationally intensive
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Applicability
• STWAVE:– ideal for wave propagation in open water
• SWAN:– time dependent, larger domain
• Mild-Slope:– ideal for long-period oscillations in harbors (CGWAVE)– suited for strong diffraction & reflection– more flexibility with finite element method(CGWAVE)– rapid solutions(REFDIF)
• BOUSS-2D:– ideal for wave transformation near entrance channels
and harbors – nonlinear interactions in shallow water– wave-induced currents near structures and surfzone
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Engineering Practice - 1
• CORPS wave models have good physics to provide reliable estimates to projects
• Integrated with tools (SMS,etc.)• Used in support of a variety of research and engineering studies• Have strengths & weaknesses – no one model can do it all!• Validated with field/lab data & checked against analytical
solutions
• MIKE21 wave models …
• DELFT3D wave models …
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• Wind forcing• Current forcing• Wave-current• Regional modeling• Deepwater wave
transformation up to pre-breaking depths
• Finite difference• Spectral, steady
state• Quick to run• Good front end
STWAVE computed wave Heights
STWAVE
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CGWAVE
• Diffraction • Reflection• Refraction• Breaking• Bottom friction• Entrance losses• Finite element mesh• Spectral sea state• Wave-current
Interaction (in testing)
• Wave-wave Interaction (in testing)
• No wind Input CGWAVE Sea state for Morro Bay, CA
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BOUSS-2D
• Time-dependent• Open coast, harbor
and surf zone waves• Shoaling, refraction,
reflection, diffraction,dissipation and run-up
• Finite difference• Random spectral sea
state modeling• Wave-induced
currents• Nonlinear waves,
sub- and super-harmonics BOUSS-2D Simulation for Everglades project
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Engineering Practice -3
• Have to use models if no nearshore field data available• Using models that are in common practice and have acceptance in
the engineering community is preferred to one of a kind models • Project-specific problems must determine the type of model for a
study• Detailed model documentation is necessary
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Grays Harbor, Washington
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Grays Harbor, Washington
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Entrained Sand
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Regions of Application of Wave Models
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Solitary/Cnoidal Waves
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Wave Prediction (Deep Water)
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Combined Refraction and Shoaling(Dean and Dalrymple)
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Random Waves
• Analysis Methods– Eye– ZUC– ZDC– Spectral
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Random Wave Spectra
JONSWAP
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Wave Spectra2
2 2( )4 exp22 4 5
JONSWAPmax
Pierson Moskowitzmax
5( ) (2 ) exp4
where
0.07 , 0.09,
and peak frequency
0 0081, Phillips Constant
EE
m
m
f ff
m
m
m
m
fE f g ff
f ff f
fα .
TMAPierson MoskowitzOther
JONSWAP
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Mild Slope Equation
http://www.coastal.udel.edu/refdif/img20.htm
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CONCLUSIONS
• BOUSS-2D is a powerful nonlinear model for estimating waves in shallow and intermediate water depths where wave diffraction and nonlinearities are important
• Model is ready for project applications• SMS interface of BOUSS-2D • MAKE THINGS AS SIMPLE AS POSSIBLE BUT NO
SIMPLER!!! – “Albert Einstein”
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REFDIF