Tsunamimodeling Lec 3 · Tsunamimodeling_Lec_3.pptx Author Lorena Barba Created Date 1/18/2013...

Tsunami modeling

Philip L-F. Liu Class of 1912 Professor

School of Civil and Environmental Engineering Cornell University

Ithaca, NY USA

PASI  2013:  Tsunamis  and  storm  surges  Valparaiso,  Chile    

January  2-­‐13,  2013    

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Analytical solutions of shallow water equations

for wave runup

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Analytical solutions   Two-dimensional shallow water equations

o Linear model o Nonlinear model

  Simply geometry o A uniform beach o A sloping beach connected to a constant depth

  Non-breaking waves o Theoretical criterion:

  Frictionless sea bottom

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Analytical solution by the transform technique

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Carrier & Greenspan (1958)

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Linear waves running up a simple beach

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  Shallow water equations   Non-breaking solitary waves   Basic idea: Keller & Keller + Carrier & Greenspan   Analytical solutions on the sloping beach   Run-up laws: 1/17/13   7  

Synolakis (1987): maximum runup height of solitary waves on a 1:19.85 beach

Theory  

Exp  (non-­‐breaking)  

Exp  (breaking)  

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Analytical solutions   Bathymetry

o The 1+1 beach (e.g. Synolakis) is more useful than the uniform sloping beach (Carrier & Greenspan)

  For the 1+1 beach o Linear wave model: no shoreline solutions o Nonlinear wave model: restricted to solitary waves

  Questions… o Is solitary wave a good model wave for tsunamis? o Extension of the analytical approach to a more

general (non-breaking) waveform? 1/17/13   9  

Solitary  waves  vs.  leading  tsunami  waves  

  Solitary  wave  o SoluJon  of  the  KdV  equaJon  o Permanent  form  

o Very  aQracJve  to  analyJcal  and  laboratory  studies    Solitary  waves  and  leading  tsunami  waves  are  generally  not  comparable  o Field  observaJons  o AnalyJcal  arguments  

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2011 Japan Tsunami: GPS wave gauge data

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Evolutions of solitary waves?

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Leading tsunami waves evolve into solitary waves?......NO!

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A better model wave for tsunamis?   Solitary wave paradigm

o Extensive studies have been based on the solitary wave theory o They are still important o They are still useful: use with care

o How good (or bad) of these past findings? o Improvement on the analytical approach? o Suggestion on the laboratory experiments?

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Effect of incident waveform on the runup height

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Effect of the incident waveform on the runup height

Runup  of  three  different  sech2(·∙)-­‐shape  waves  with  the  same  wave  height  but  different  wavelengths.  (a)  Incident  wave  forms;  (b)  EvoluJons  of  the  shoreline  Jps.  

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Same  acceleraJng  phase;    different  deceleraJng  phase  

(a)  Incident  wave  forms;  (b)  EvoluJons  of  the  shoreline.  1/17/13   17  

Analytical estimation of the runup height

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Extended analytical (asymptotic) solutions

  1+1 beach model (beach slope s)   Extend the approach by Synolakis (JFM 1987)   Shoreline solutions in the transformed domain

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New runup solutions for cnoidal waves (Chan & Liu 2012)

  Alternative expressions for the cnoidal waves

  Runup solutions

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Runup of cnoidal waves  

Symbols  are  the  experimental  data  of  Ohyama  (1987).  Solid  lines  plot  the  new  analyJcal  soluJons.  Water  depth  is  fixed  at  0.2  m.  Wave  frequencies  are  different  in  cases  (a)  to  (c).  

Maximum runup height on a 1:1 slope.

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Extension of the analytical approach

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Runup of leading tsunami waves

  Analytical solution o A quick estimation on the runup height

  Use the 2011 Japan Tsunami as an example o Record at a GPS-based station as the input

  Assuming a 1+1 beach with a 1-on-10 slope o Analytical approach works only for a simple beach o Estimation on the runup height: the final slope (the

closest to the shoreline) has the dominant effect on the runup (Kanoglu & Synolakis 1998)

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Estimation of the runup height

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