Improved Storm Surge Model Prediction Using a High Resolution Unstructured Grid

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Improved Storm Surge Model Prediction Using a
High Resolution Unstructured Grid
Jian Shen Virginia Institute of Marine
Sciences College of William and Mary
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Unstructured 3D Model (UnTRIM)

• UnTRIM incorporates an Unstructured grid into
  TRIM model (Tidal, Residual, Intertidal Mudflat),
  originally developed by Vincenzo Casulli
• It simulates three-dimensional hydrodynamic and
  transport processes
• It uses an orthogonal unstructured grid
• It conserves mass locally as well as globally
• It uses Eulerian-Langangian transport scheme
• It employs semi-implicit finite difference and
  finite volume method- very efficient
  computationally
• It is capable of simulating wet-dry processes

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Orthogonal Grid Structure

• Use polygons to represent a prototype estuary
  (3-, 4-, 5-sides)
• Better fitting complicated geometry in estuarine
  and coastal environment
• Using orthogonal grid simplifies the numerical
  algorithm

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Grid Structure
Water depth
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Isabel Simulation Studies

• Study the accuracy of model prediction of Isabel
  forced by a stationary, circular wind model
• Compare model prediction with and without
  simulating inundation
• Study influence of open boundary condition
  specification on surge simulation
• still boundary condition vs. inverse pressure
  adjust boundary condition

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Model Grids
Surface element 121338
Surface element 239541
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Grid layout at York and James Rivers
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Model Calibration

• Calibrate model for tide
• forced by 9 tidal constituents M2, S2, K1,
  O1, Q1, K2, N2, M4, and M6
• Model was run for 3 months and the results of the
  last 29 days were used for computing tidal
  harmonics
• Timestep 5 min.

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Tidal Simulation (M2 tide)
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Tidal Simulation (K1)
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Observation Stations
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Tidal Constituents Comparison (Amplitude)
Amplitude is in m Observations are based on 1992
data
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Tidal Constituents Comparison (phase)
Phase is in degree
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Isabel Simulation Results
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Comparison of Model Results(with and without
inundation)
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Comparison of Model Results(with and without
inundation)
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Influence of Open Boundary Condition
Inverse Pressure Adjustment
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Comparison with ADCIRC

• UnTrim
• With inverse pressure adjustment
• Timestep 5 minutes
• ADCIRC
• Without inverse pressure adjustment
• Timestep 5 sec

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Comparison with ADCIRC
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Conclusions

• Grid resolution is crucial for accurately
  simulating surge and inundation
• Wind filed is critical in accurately simulation
  storm surge
• Unstructured model is a robust tool for
  simulating tide and storm surge