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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