Numerical Simulation of Tsunami Bore Flow through a Constricted ChannelAdam Koenig, Wichita State University
Mentors: Dr. Ron Riggs, University of Hawai’i, ManoaDr. Sungsu Lee, Chungbuk National UniversityKrystian Paczkowski, University of Hawai’i, Manoa
HARP REU Program, August 3, 2011
OverviewBackground and Motivation
Benefits of CFD Approach
Description of Utilized CFD Tools
Simulation Description
Results
Conclusions and Recommendations
Background and MotivationExperiments have collected data on tsunami
bore formation1,2
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
GoalsNumerically 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/ModelsThis 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 Center320 Dell PowerEdge 1955 blades with four 3.0
GHz processors per bladeCisco SDR infiniband (10Gbit/sec) interconnect
Domain DescriptionThe 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 DescriptionThe inlet consists of a 3.6 ft high patch
spanning the back wall of the domainThe 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 data1,2.
The MeshThe mesh consists of two groups of
hexahedral cells stacked in the domainMesh density is 1.25 ft/cell in horizontal
directionsVertical 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/DifficultiesZero velocity boundary condition in wall above
inletData is only valid until reflected bore strikes back
wall Reason for long domain
Open boundary resulted in flow anomalies and crashed simulations
Gap Aspect RatioDimensions chosen to fit regular two-way street and
building size based on Empire State BuildingActual aspect ratios would vary considerably
Simulation Example
ObservationsWater 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
1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.80
0.5
1
1.5
2
2.5
3
3.5
4
Pool Height vs. Bore Froude Number
Bore Froude Number
Pool
Heig
ht
(m)
Results
1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.80
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Outlet Height vs. Bore Froude Number
Bore Froude Number
Outl
et
Heig
ht
(m)
Results
1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.80
0.5
1
1.5
2
2.5
3
Pool to Outlet Height Ratio vs. Bore Froude Number
Bore Froude Number
Pool
to O
utl
et
Heig
ht
Rati
o
Results
1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.80
1
2
3
4
5
6
7
8
9
Outlet Velocity vs. Bore Froude Number
Outlet Velocity Bore Velocity
Bore Froude Number
Outl
et
Velo
cit
y (
m/s
)
Results
1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.80
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Reflected Froude Number vs. Bore Froude Number
Bore Froude Number
Reflecte
d F
roude N
um
ber
ConclusionsPooling 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 numbersPossibly a consequence of inlet height and
sheet flow in boreReflected 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
AcknowledgementsKrystian Paczkowski, for his insight into the inner
workings of OpenFOAM softwareDr. Susan Brown, for continuous assistance with data
storage issuesDr. 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. 0852082. 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 Cited1Robertson, 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.
2Robertson, I. N., H. R. Riggs, K. Paczkowski, and A. Mohamed. "Tsunami Bore Forces On Walls." Proceedings of the ASME 2011 30th International Conference on Ocean, Offshore, and Arctic Engineering. Rotterdam, The Netherlands. Print.
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