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Numerical Simulation of Landslide-Generated Tsunami Waves and the Slide Deformability

Yavari-Ramshe, Saeedeh | 2016

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 48095 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ataie-Ashtiani, Behzad
  7. Abstract:
  8. Potential landslides located in the borders of each water body may generate massive and destructive impulsive waves called landslide-generated waves (LGWs) which can be a major threat to human life and his possessions, offshore and coastal installations, dam bodies and hydraulic structures. This research is devoted to numerical modeling of LGW hazards with focus on the impulse wave generation stage including landslide movement, landslide/water surface interactions and consequent tsunami generation. The main purpose of this work is to study the effects of landslide deformability on the impulsive wave characteristics numerically in an introduced state-of-the-art numerical structure. The majority of available numerical studies consider landslide as a rigid body moving with prescribed kinematic properties. On the other hand, there are a few numerical models which are able to simulate the simultaneous interactions between landslide deformations and water surface fluctuations as a coupled system. However, for a massive sliding mass, landslide deformations have significant effects on more accurate estimation of the generated wave properties, seabed erosion/sedimentation and its final topographic changes. At first, a granular type flow model is developed which solves the incompressible Euler equations under Savage–Hutter assumptions. The model is derived in a local coordinate system along a nonerodible bed to take its curvature into account. Moreover, simultaneous appearance of flowing/ static regions is simulated by considering a basal friction resistance which keeps the granular flow from moving when the angle of granular flow is less than the angle of repose. A well-balanced second-order finite volume scheme, based on the Q-scheme of Roe, is introduced to discretize the system of model equations. The proposed scheme preserves stationary solutions up to second order and deals with different situations of wet/dry transitions by a modified nonlinear wet/dry treatment. Numerical results indicate the improved properties and robustness of the proposed finite volume structure. In addition, the granular flow properties are estimated with a computational error of less than 5%. These errors are consistently less than those obtained by using similar existing finite volume schemes without the proposed modifications, which can result in up to 30% overestimation.Then, the model is generalized for a two-layer flow including a layer of granular type flow moving beneath a layer of an incompressible inviscid fluid (e.g. water).The model solves the 731 incompressible Euler equations for both layers as a fully coupled system. Landslide is treated as a two-phase (solid/fluid) coulomb mixture; considering Mohr-Coulomb material where the normal and longitudinal stresses are related with a factor K, the earth pressure coefficient. Moreover, the slide/bottom interaction is defined using a Coulomb friction type relation. The model is validated using two sets of experimental data on subaerial and submarine LGWs. Impulsive wave properties are estimated with a computational error less than 5% as well as landslide deformations. Then, the calibrated model is applied to investigate the effects of landslide deformations on water surface fluctuations in comparison with a simpler model considering a rigid landslide. The model results confirm the importance of both rheological behavior and two-phase nature of landslide in proper estimation of generated wave properties and formation patterns. Rigid slide modeling often overestimate the characteristics of induced waves. With a proper rheological model for landslide, the numerical prediction of LGWs gets more than 30% closer to experimental measurements. Single-phase landslide results in relative errors up to about 30% for maximum positive and about 70% for maximum negative wave amplitudes. Besides, two-phase constitutive structure of landslide has strong effects on landslide deformations, velocities, elongations and traveling distances
  9. Keywords:
  10. Finite Volume Method ; Shock Wave ; Tsunami ; Subaerial Landslide ; Landslide Generated Waves (LGW) ; Coulomb Mixture ; Savaye-Hutter (SH)Assumptian ; Submarine Landslide

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