Supercomputing of Tsunami Damage Mitigation Using Offshore Mega-Floating Structures

Transcription

1 International Innovation Workshop on Tsunami, Snow Avalanche and Flash Flood Energy Dissipation January 21-22, 2016, Maison Villemanzy in Lyon, France Supercomputing of Tsunami Damage Mitigation Using Offshore Mega-Floating Structures Jun Ishimoto Innovative Energy Research Center, Multiphase Flow Energy Laboratory Institute of Fluid Science, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai , Japan

2 Outline 1. Overview of tsunami mitigation by mega-float motion 2. 3D FSI simulation of mega-float motion and water traveling wave using ALE 3. Scale modeling of tsunami-structure interaction 4. 2D numerical procedure using SPH 5. Numerical results (Effect of the installing on the mega float) 6. Damage evaluation and tsunami behavior when the sand particle is mixed

3 Background The magnitude 9.0 earthquake (The Great East Coast Earthquake) hit off the Sendai coast area in Japan, March 11, 2011 and created a huge tsunami which claimed more than 20,000 lives. As a defense against tsunami damage, construction of large-sturdy breakwater and seawall in the vicinity of the coast are merely symptomatic treatment, such a conventional fundamental solutions. Coast Offshore Therefore, we propose the new fundamental mitigation technique to reduce the seawater level and hydrodynamic damage of offshore tsunami (Proposed by Prof. T. Shoji) by using fluid-structure interaction (FSI) of mega-floating structures.

4 FSI simulation of mega-float motion and water traveling wave

5 1. Model A Number of elements for fluid part: 300,000 elements Number of elements for mega-float part: 4,174 elements Boundary conditions: Pool bottom wall, side wall, top wall All non-slip conditions Fluid phase ALE Euler elements (Water and Air) Initial conditions: Wave length: 42 m, Water level: 1.0 m, Traveling velocity of the waves: 6.0 m/s Water depth: 8.0 m, Length: 200 m, Width: 60 m Mega float Lagrange rigid shell elements Mass: 1030 ton Total length: 37 m, Width: 26 m, Height: 4.6m FSI computation Physical time: 60 s CPU time: 8 hours 45 min (6CPU)

6 2. Model B Number of elements for fluid part: 300,000 elements Number of elements for mega-float part: 8,188 elements Boundary conditions: Pool bottom wall, side wall, top wall All non-slip conditions Fluid phase ALE Euler elements (Water and Air) Initial conditions: Wave length: 42 m, Water level: 1.0 m, Traveling velocity of the waves: 6.0 m/s Water depth: 8.0 m, Length: 200 m, Width: 60 m Mega float Lagrange rigid shell elements Mass: 2,027 ton Total length: 73 m, Width: 26 m, Height: 4.6 m FSI computation Physical time: 60 s CPU time: 9 hours 20 min (6CPU)

7 Numerical results (a) Model A (b) Model B (b) Without float The effect of water level and wave breaking behavior is reduced, and hydrodynamic force mitigation can be achieved by momentum exchange between sea water and mega-float.

8 Numerical results (Enlarged view ) (a) Model A (b) Model B Translational motion and vibration of mega-float are converted to dissipate the hydrodynamic force, and that contribute to reduce the sea water level. The water level is effectively reduced in the large float case than that in small float case.

9 1. Overview of tsunami mitigation by mega-float motion 2. Scale modeling of tsunami-structure interaction 3. Numerical procedure 4. Numerical results 5. Snow modeling and DEM (for Avalanche problem)

10 Objectives To evaluate the mitigation effect of mega-float structure on tsunami s momentum, we have developed a scale modeling method for huge geometry such as offshore mega-float region. Furthermore developed FSI supercomputing method for the tsunami behavior of its interface causing deformation when in collision with structures which has the inertial motion. Makes it possible to target a huge area with a small computer memory Same Froude Number Fr = U Lg Floating structure model by scale modeling Huge region Fr = (Inertia) (Gravitational force) Scale modeling

11 Tsunami height (m) Scale modeling of Fukushima offshore tsunami historical survey data (Contribution from Prof. F. Imamura) Extracted the large amplitude profile as enveloped wave Time series of the tsunami at the 120 m depth off shore the Fukushima power plant Time after 40 earthquake 60 (minutes) Bathymetry (m) Coss-section of the bathymetry offshore the Fukushima daiichi power plant Distance 10 from the 15 coastline 20 (km) 25 30

12 Numerical procedure of tsunami wave motion with scale modeling In the computation with scale modeling, Froude (Fr) number becomes the same value to adjust the parameters with reference to data of the actual tsunami behavior. To create the tsunami wave motion with scale modeling, we employed a piston-type wavemaking method which is one of the experimental technique used in tsunami test tank. As a compromise between computer memory and accuracy, two-dimensional model analysis was assumed to the computational geometry. Tsunami height (m) Extracted the large amplitude profile as enveloped wave 0 Time 20 after 40 earthquake (minutes) Fr Mega-floating structure model by scale model

13 Numerical procedure of tsunami wave creation with scale modeling Actual surveyed Scale model data 1/100 1/1000 Measurement position 28km offshore Water depth, h (m) Wave height, (m) max Measurement time 40 min Period, T (s) Propagation velocity, C (m / s) Froude number, Fr (-) 4.47 Wavelength, λ (m) 82, Piston amplitude, Sa (m) Tsunami height (m) Extracted the large amplitude profile as enveloped wave 0 Time 20 after 40 earthquake (minutes) Fr Mega-floating structure model by scale model

14 1. Overview of tsunami mitigation by mega-float motion 2. Scale modeling of tsunami-structure interaction 3. Numerical procedure 4. Numerical results 5. Snow modeling and DEM (for Avalanche problem)

15 Computational geometry created by scale modeling Smoothed-particle hydrodynamics(sph) has been used 28 km 28 km Thickness: 10m Water depth: 100 m Offshore distance: 10km Assumed original mega float geometry Scale modeled geometry Total length (m) 72.0 Hight (m) 3.0 Water depth (m) 1.2 SPH particle number Length of floating structure (m) 9.54 Specific gravity of float 0.5 Total element of structure m Piston Floating structure (Rigid body) Length: 9.54 m Thickness: 0.05 m History of piston velocity Time (s) Piston velocity (s) Piston horizontal gravity level is accelerated to 9.8G within 4.0 s. Small scaled computational geometry created by scale modeling

16 Piston-type wave-making method Wave propagation velocity: ω g 2 tanh( ) gt π C kh tanh h = = = k k 2π λ Wave length: 2 gt 2π h λ = tanh 2π λ h: water depth ω : circular frequency 2π k = : wave number λ 2 ( kh) ( ) cosh ( ) ζ 2sinh a = S kh+ sinh kh kh a S a : Piston stroke amplitude ζ a : Tsunami wave amplitude Piston Scale model (1/100) Case 1 Case 2 Water depth, h (m) 1.2 Wave height, (m) ζ a Propagation velocity, C (m / s) Froude number, Fr (-) 4.47 Piston amplitude, S a (m) Actual piston flow velocity profile Case 1 Case 2 Maximum velocity (m/ s) 1.25 m/s 2.5 m/s Duration (triangular wave) 0.2 s 0.2 s t s 16 sec computation requires total 13 to 17 hrs. operation.

17 1. Overview of tsunami mitigation by mega-float motion 2. Scale modeling of tsunami-structure interaction 3. Numerical procedure 4. Numerical results (Effect of the installing on the mega float) 5. Snow modeling and DEM (for Avalanche problem)

18 Effect of the installing on the mega float R are installed on the mega float surface to enhance turbulent eddy generation for dissipation of tsunami hydrodynamic energy. Downward Downward Tsunami breaker is slipping on the upper smooth surface of downward. Tsunami impact energy was effectively dissipated by turbulent eddy generation around the uneven portion in the sea water. Upward Upward Tsunami breaker is captured by upward, momentum exchange between tsunami and float is performed, the float will perform a translational motion with breaking tsunami riding on.

19 Water level detection just downstream portion of the float with groove-like protrusions Large amplitude of water level for 1st wave. 2 Downward Upward 2

20 Conclusions! Maximum water level just downstream portion of the float was decreased compared in the single phase tsunami case.! Inertial motion of mega-floating structures can contribute to reduce the tsunami s seawater-level and to dissipate a hydrodynamic energy of offshore tsunami.! of for.