1. Background & Motivation • ADCIRC Surge Guidance System (ASGS) provides forecast guidance for winds, waves and storm surge during a hurricane • For NC Coast, ADCIRC is run twice daily, and four times daily during severe storms • The NC-CERA website is shown on the right • The high-resolution mesh for North Carolina region is the NC9 mesh • Computationally expensive and hence used only during storm events • For daily forecasts, NC6b mesh is used • The comparison plots shows areas where there are difference in water levels between the NC9 Mesh and the NC9 X 4 mesh • These are regions where resolution of NC9 Mesh could be increased • Errors in mass conservation based on a simple mass balance (accumulation minus flux) will be calculated for each element of the NC6b mesh • Vertices will then be moved from regions with small mass residual errors to regions with large errors • Thus, the result will be an optimized mesh with improved accuracy in predictions • A mesh having four times the resolution of NC9 was created using SMS – NC9 X 4 • Water levels obtained from ADCIRC runs for Hurricane Irene on this mesh is taken as the “true” solution and was compared against water levels from ADCIRC runs on the NC9 mesh • This was done by mapping the global water levels file (fort.63) of NC9 mesh on to the NC9 X 4 mesh by linear interpolation • NC9 mesh was used in the generation of flood risk maps for FEMA • A hole representing the region to be is cut out from the original mesh • Morehead City (2011) and NC v2.6 (2008) are 10m resolution DEMs available for the NC region • Node strings are then drawn representing different features • The final hole-coverage is then converted to a mesh • Bathy-Topo values are then interpolated from the DEM onto the meshed hole using Half-element ADCIRC Cell Averaging and it is then merged on to the original mesh Optimizing the Design of Unstructured Meshes Describing North Carolina Coastal Regions to Improve Accuracy of Flood Predictions A. Thomas 1 , J.C. Dietrich 1 , J.G. Fleming 2 , B.O. Blanton 3 , R.A. Luettich Jr 4 Civil, Construction and Environmental Engineering, North Carolina State University 1 ; Seahorse Coastal Consulting 2 ; Renaissance Computing Institute, UNC Chapel Hill 3 ; Marine Sciences, UNC Chapel Hill 4 Mesh Elements NC6b 575,512 NC9 1,230,430 NC9 X 4 4,921,720 SL 16 9,945,623 • In other regions, meshes with much higher levels of resolution are used • Similar increase in resolution in targeted locations should improve the predictive accuracy of coastal flooding 2. How to Construct an Unstructured Mesh 3. Searching for Accuracy Errors 4. Results & Future Work Source: http ://nc-cera.renci.org/ Legend (m)

Describing North Carolina Coastal Regions to Improve ... · PDF fileSMS –NC9 X 4 • Water levels obtained from ADCIRC runs for Hurricane Irene on this mesh is taken as the “true”solution

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Page 1: Describing North Carolina Coastal Regions to Improve ... · PDF fileSMS –NC9 X 4 • Water levels obtained from ADCIRC runs for Hurricane Irene on this mesh is taken as the “true”solution

1. Background & Motivation

• ADCIRC Surge Guidance System (ASGS)provides forecast guidance for winds, wavesand storm surge during a hurricane

• For NC Coast, ADCIRC is run twice daily, andfour times daily during severe storms

• The NC-CERA website is shown on the right

• The high-resolution mesh for North Carolinaregion is the NC9 mesh

• Computationally expensive and hence usedonly during storm events

• For daily forecasts, NC6b mesh is used

• The comparison plots shows areas where there are difference inwater levels between the NC9 Mesh and the NC9 X 4 mesh

• These are regions where resolution of NC9 Mesh could beincreased

• Errors in mass conservation based on a simple mass balance(accumulation minus flux) will be calculated for each element ofthe NC6b mesh

• Vertices will then be moved from regions with small mass residualerrors to regions with large errors

• Thus, the result will be an optimized mesh with improvedaccuracy in predictions

• A mesh having four times the resolution of NC9 was created usingSMS – NC9 X 4

• Water levels obtained from ADCIRC runs for Hurricane Irene onthis mesh is taken as the “true” solution and was comparedagainst water levels from ADCIRC runs on the NC9 mesh

• This was done by mapping the global water levels file (fort.63) ofNC9 mesh on to the NC9 X 4 mesh by linear interpolation

• NC9 mesh was used in the generation of flood risk maps for FEMA

• A hole representing the region to be is cut out from the originalmesh

• Morehead City (2011) and NC v2.6 (2008) are 10m resolutionDEMs available for the NC region

• Node strings are then drawn representing different features

• The final hole-coverage is then converted to a mesh

• Bathy-Topo values are then interpolated from the DEM onto themeshed hole using Half-element ADCIRC Cell Averaging and it isthen merged on to the original mesh

Optimizing the Design of Unstructured MeshesDescribing North Carolina Coastal Regions to

Improve Accuracy of Flood PredictionsA. Thomas1, J.C. Dietrich1, J.G. Fleming2, B.O. Blanton3, R.A. Luettich Jr4

Civil, Construction and Environmental Engineering, North Carolina State University1; Seahorse Coastal Consulting2; Renaissance Computing Institute, UNC Chapel Hill3; Marine Sciences, UNC Chapel Hill4

Mesh Elements

NC6b 575,512

NC9 1,230,430

NC9 X 4 4,921,720

SL 16 9,945,623

• In other regions, meshes with muchhigher levels of resolution are used

• Similar increase in resolution intargeted locations should improve thepredictive accuracy of coastal flooding

2. How to Construct an Unstructured Mesh 3. Searching for Accuracy Errors

4. Results & Future Work

Source: http://nc-cera.renci.org/

Legend (m)

http://nc-cera.renci.org/