Adam Koenig, Wichita State University Mentors: Dr. Ron Riggs, University of Hawai’i, Manoa Dr. Sungsu Lee, Chungbuk National University Krystian Paczkowski, University of Hawai’i, Manoa HARP REU Program, August 3, 2011

Overview Background and Motivation Benefits of CFD Approach Description of Utilized CFD Tools Simulation Description Results Conclusions and Recommendations

Background and Motivation Experiments have collected data on tsunami bore formation 1,2 Tsunami blockage and funneling is less studied Such data would be useful for establishing design parameters for structures in and around streets that would be affected by this channeled flow, especially if flow is accelerated

Goals Numerically simulate tsunami bore channeled through a city street Identify effects and phenomena caused by buildings obstructing bore flow Quantify relationships between tsunami bore parameters and flow properties in the street

Benefits of CFD approach Much more inexpensive than experimental tests No scaling problems Greater flexibility in test parameters

Software/Models This study uses OpenFOAM v 1.7.1, a free, open-source CFD software package for a wide range of fluid problems Solver: InterFoam, a solver for two incompressible, immiscible fluids that uses a VOF method to generate a volume where the sharp interface between phases would exist Turbulence: k-ε model, a RANS based turbulence model with transport equations for turbulent kinetic energy and turbulent dissipation

Hardware JAWS system at Hawaii Open Supercomputing Center 320 Dell PowerEdge 1955 blades with four 3.0 GHz processors per blade Cisco SDR infiniband (10Gbit/sec) interconnect

Domain Description The domain of this test consists of a 120×290×30 ft rectangular prism with two half-buildings obstructing the end The half-buildings are each 45 feet wide and 90 feet long

Domain Description The inlet consists of a 3.6 ft high patch spanning the back wall of the domain The inlet speed was controlled by setting a constant velocity condition across the surface of the inlet. Tests showed that there was no difference in the channel flow of a total pressure inlet was used. The inlet speed was adjust to give the desired Froude number of the bore. The study focused on bore Froude numbers between 2 and 3 from experimental data 1,2.

The Mesh The mesh consists of two groups of hexahedral cells stacked in the domain Mesh density is 1.25 ft/cell in horizontal directions Vertical density is 0.9 ft/cell up to the height of the inlet, and 1.65 ft/cell from top of the inlet to the top of the domain This meshing allows for acceptable resolution throughout the domain with improved resolution in majority of flow area

The Mesh

Limitations/Difficulties Zero velocity boundary condition in wall above inlet Data is only valid until reflected bore strikes back wall Reason for long domain Open boundary resulted in flow anomalies and crashed simulations Gap Aspect Ratio Dimensions chosen to fit regular two-way street and building size based on Empire State Building Actual aspect ratios would vary considerably

Simulation Example

Observations Water pools in front of obstructing buildings at height significantly greater than bore height Original bore reflected back out to sea as a hydraulic jump Remaining water cascades between buildings into the street

Results

Conclusions Pooling height, outlet height, and outlet velocity all positively correlated to bore Froude number. Height ratio independent of bore Froude number Outlet velocity never exceeds bore velocity, but numbers are very close at low Froude numbers Possibly a consequence of inlet height and sheet flow in bore Reflected bore relatively constant for tested range, but possible negative correlation

Recommendations for Future Work Study effect of gap aspect ratio on flow property relationships Determine whether inlet height affects funneling behavior and whether inlet height affects bore shape

Acknowledgements Krystian Paczkowski, for his insight into the inner workings of OpenFOAM software Dr. Susan Brown, for continuous assistance with data storage issues Dr. Ron Riggs and Dr. Sungsu Lee, for their guidance and insight into fluid behavior problems This material is based upon work supported by the National Science Foundation under Grant No Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Works Cited 1 Robertson, I. N., H. R. Riggs, and A. Mohamed. "Experimental Results of Tsunami Bore Forces on Structures." Proceedings of the 27th International Conference on Offshore Mechanics and Arctic Engineering. Estoril, Portugal. Print. 2 Robertson, I. N., H. R. Riggs, K. Paczkowski, and A. Mohamed. "Tsunami Bore Forces On Walls." Proceedings of the ASME th International Conference on Ocean, Offshore, and Arctic Engineering. Rotterdam, The Netherlands. Print.

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