Effects of flexible motion on tsunami wall durability or whatever

Effects of flexible motion on tsunami wall efficacyHARP REU 2011Nicholas McClendon, Rice UniversityMentors: H.R. Riggs, Sungsu Lee, Krystian Paczkowski

Contents(1) Flexible wall studyBackgroundModels and MethodsAdaptive Mesh RefinementResults(2) Adaptive mesh studyDecomposed domainWhole domain(3) Domain decomposition studySetupResultsFlexible wall studyBackground: Tsunami WallsTsunami walls are designed to reduce the damage done by tsunami waves on coastal structuresTypical design parameters:MaterialTypically reinforced concrete, can be steelPhysical dimensions1 12 meters high100s of meters longLocationDistance from sea affects forces sustainedDistance from the coastal structures its protecting affects damage done

Flexible Wall StudyMotivationRigid walls are subject to quick and unpredictable failureFlexible walls absorb the force of incoming waves, increasing durability, reducing impact force, and allowing failure to be predicted more readily

GoalTo develop an understanding of the effects of flexible motion on tsunami wall efficacy for possible real-world applicationHow? Compare forces sustained by a flexible wall to the forces sustained by a rigid one

Models and MethodsMathematical models:K-Epsilon turbulence modelNewtonian transport modelLinear viscous fluid modelNumerical solversinterFoam solverMultiphase solver for two incompressible fluidsNumerical technique is the Volume of Fluid MethodinterDyMFoam solverinterFoam + mesh modification capabilitiesFlexible wall is modeled using a rigid block with a torsional spring applied at the baseNaturally, as with any simulation, we must make simplifications to the true analytical solution in order to make the simulation reasonable to solve. Here we use a uniform discretization of the domain into 90,000 square cells, and we use numerical techniques to approximate the behavior of the fluids according to our mathematical models.6Adaptive Mesh RefinementAMR refers to refinement of mesh during computationStatic AMRSuperimposes finer sub-grids on areas of interestDynamic AMRAlters size, shape, orientation, and/or number of cellsLayering, remeshing, and smoothing

Uniformly fine meshes are computationally costly, so static AMR only refines areas of interest. In some simulations (such as mine), boundaries move, so adapting the mesh to boundary movement is necessary.

Remeshing vs smoothing deflection of the wall was not great enough to warrant remeshing (and it would have been more computationally expensive)7Domain SetupSetup:20m x 1.8m x 0.1m domain2-dimensional simulation2 phasesLiquid (dambreak scenario)GasBoundary conditions:Rigid wall on sides/bottomAtmosphere on top (permits inflow/outflow)90,000-cell meshSimulations dimensions are reasonable to test experimentallyTest the simulation many times, varying the spring constant each time to determine how the spring constant and angle of deflection relate to the forces sustained by the wallDomain Setup

Flexible Wall Simulations

Results (spring constant variance)

Results (spring constant variance)

Results (spring constant variance)

Results (spring constant variance)Conclusion: Allowing for deflection of the wall to absorb impact force of the wave does reduce the forces sustained by approximately 1 percent per degree of deflection.Flexible walls could provide effective impact force reduction of tsunami boresFurther study:Walls which use the impact and uplift forces of the tsunami bore to raise into placeResults (mesh convergence)

Results (mesh convergence)

Adaptive mesh studyAdaptive Mesh StudyGoal: Observe the effects of adaptive meshing on the consistency of results of a control caseinterFoamWall is simply part of boundaryinterDyMFoamWall is a separate (fixed) objectAdaptive meshing used

Adaptive Mesh StudyinterFoam, 8 processorsinterDyMFoam, 8 processors

Adaptive Mesh StudyinterFoam, 8 processors

Velocity magnitude (m/s) snapshot at 1.05 seconds

interDyMFoam, 8 processors

Velocity magnitude (m/s) snapshot at 1.05 seconds

Adaptive Mesh StudyinterFoam vs. interDyMFoam, 1 processor

Adaptive Mesh StudyConclusions:Subdomain coupling for dynamic meshing (dynamicMotionSolverFvMesh) needs to be fixed if it is to be used in the future (otherwise cannot trust results from runs done in parallel)On a single processor, results obtained from the control case using static and dynamic meshing align very closely, so the use of dynamic meshing tools is validated for the 1-processor caseDomain decomposition studyDomain Decomposition StudySetup a dambreak scenarioDomain is 40m x 3.2m x 1mDam is 1m x 20mDecomposed the domain into 1, 2, 4, 8, 16, 32, 64, and 128 subdomainsSolved on HOSC using interFoam for multiphaseMeasured several key values (eg. splash height, computation time) from each trialCredit also goes to Adam Koenig and Trent Thurston for gathering and analyzing data for this study.

ResultsNumber of processors1248163264128Time to reach wall4.40 s4.40 s4.40 s4.35 s-4.40 s4.40 s4.35 sPeak force on wall22397 N (5.2s)

16696 N (5.1s)

14451 N (5.1s)

22259 N(5.15s)-13748 N(5.15s)--Max splash height2.04 m (5.2s)1.74 m(5.1s)1.60 m (5.1s)2.09 m(5.15s)-1.64 m(5.15s)1.89 m(5.15s)1.87 m(5.15s)Computation time (ClockTime)182 h131 h93 h31 h-8 h7.6 h5.6 hProcessor time182 h262 h373 h245 h-237 h786 h718 h* Red text denotes measurements extrapolated from partially-completed simulations.Results# processors vs. clock time# processors vs. processor time

ResultsConclusions:Alternating domain decomposition can result in unpredictable variations in resultsComputation clocktime reduces with increasing numbers of processors (up to 32 processors), then levels outProcessor time remains low until # of processors exceeds 32Too few processors doesnt experience the benefits of parallel computingToo many processors loses time in communication between nodesIt seems like 16 or 32 processors would be ideal, at least for this simulation, as computations can be executed most quickly without wasting resourcesReferenceshttp://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2007/PiroozMoradnia/OpenFOAM-rapport.pdfhttp://perso.crans.org/kassiotis/openfoam/movingmesh.pdfhttp://openfoamwiki.net/index.php/Main_FAQhttp://www.openfoam.com/docs/user/http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2008/ErikEkedahl/6dofbeamer.pdfhttp://web.student.chalmers.se/groups/ofw5/Advanced_Training/DynamicMesh.pdf

Acknowledgment and DisclaimerId like to thank the following people and organizations for their help and support: Dr. Brown, Dr. H.R. Riggs, Prof. Sungsu Lee, Krystian Paczkowski, The University of Hawaii at Manoa, UHM College of Engineering, National Science Foundation, the OpenFOAM community.

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.