Development of disaster damage prediction system for flotsam mixed tsunami and tsunami damage
mitigation using offshore Mega-floating Structures
Jun Ishimoto** Institute of Fluid Science, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan. E-mail: ishimotojun@ieee.org

Abstract
The behavior of flotsam mixed tsunami is investigated by a new type of integrated super computation using ALE method (Arbitrary Lagrangian-Eulerian Method) andSPH method (Smoothed Particle Hydrodynamics Method). The fully hydrodynamic governing equations without shallow-water theory were used to calculate tsunami
characteristics of water flow with flotsam and debris. Our ALE model predicted the effect of fluid-solid coupled interaction in a limited region, and the model
predictions were favorably compared with the scale modeling analysis. This study, our first attempt to simulate the degree of damage caused by the flotsam
mixed tsunami, can help optimize the strength of seashore buildings and structures against future tsunami threats. This study also can help estimate
structural damage that can be caused by large-scale natural disasters like hurricanes, storms and tornados, and help to develop effective mitigation
tools and systems.
Objectives

BackgroundA recent numerical study of tsunami simulation conducted by oceanic
scientists predicted damage in a relatively large, approximately several
100km square area [1-3]. Their model used some assumptions including
the shallow-water theory [4-7].
Although conventional simulation techniques success for predicting
tsunami height and inundation area, because of the use of a shallowwater approximation (vertical velocity profile is assumed uniform),with respect to the impact force exerted on the object structure cannot
be accurately predicted.
Especially for predicting damage of land and buildings in relatively
small area, such as an industrial plant, it is not possible to apply forconventional situation procedure.

We are focusing on a relatively limited region to be analyzed, such as power plants andindustrial plants, taking into account the interaction of the structure and the tsunami, fracture
behavior and structural deformation.
We are also developing a simultaneous simulation method for the flotsam mixed tsunami
behavior of its interface causing deformation when in collision with structures.
In addition, the scale modeling analysis for flotsam mixed tsunami is conducted and comparedwith numerical results.

Wide region

Conducted by JWA (JapanWeather Association)

Narrow region (Precise approach)

2. Computational result of the flotsam mixed tsunami behavior

The hydrodynamic impact behavior of the tsunami on the vehicles is reasonable simulated by
the drifting behavior of the vehicles. It was found that the vehicles were covered by tsunami
and were washed by the tsunami’s inertia.
The vehicle is covered with tsunami and is washed with tsunami’s inertia
The lumber mixed tsunami’s hydrodynamic impact behavior to the water gate.

The lumber mixed tsunami’s hydrodynamic impact behavior to thewater gate.

160
140

Specifications
Tsunami: Euler element（260288 elements）•

Water gate： Lagrange element （22728elements）（Concrete section：Rigid body,
Water gate： Elastic-plastic body）•

Computational geometry for tsunami struck
to water gate•

Flow velocity of tsunami: 3.0 m/s•

Size of water gate: width: 5.0m, height: 2.5m

Computational result of the flotsam mixed tsunami behavior by SPH method (SmoothedParticle Hydrodynamics Method). Two small tanks are rolled up and are impacting to the large tank.
Simulation result

Impact force of lumber mixed
with a tsunami was two times
greater than that of single
phase tsunami (withoutflotsam case)80
60

Without lumber(Single-phase)40

Flotsam: Lagrange elements（Rigid body,Specific weight: 0.9, Total mass 1.1 ton）
（1260 el elments）

With lumber(Mixed tsunami)

The impact forces
increased to as twice

100Force (kN)•120

20-0.15

Fig. 4. Lumber mixed tsunami’s hydrodynamic impact behavior on the water gate.

Computational result of the flotsam mixed tsunami behavior by SPH method (Smoothed
Particle Hydrodynamics Method). Two small tanks are rolled up and are impacting to the large tank.
Impact stress profile of the land structure with flotsam mixed tsunami impingement; an elastic-plastic
body assumption was applied for the land structure

00.05

0.25

0.45

0.65
0.85
Time(sec)

1.05

1.25

1.45

1.65

Effect of flotsam (lumber) in the tsunami on the impact force to the water gate

Computational result of the flotsam mixed tsunami behavior by SPH method (SmoothedParticle Hydrodynamics Method). Two small tanks are rolled up and are impacting to the large tank.
Impact force of tank to landstructure

Flotsam mixed tsunami(Secondary wave)

Single phase tsunami (without flotsam,leading wave):
Maximum 3.5 MN
Flotsam mixed tsunami (Secondary wave)
Maximum: 42 MN

20 m/sSingle phase tsunami (withoutflotsam, leading wave)
Velocity scholar
magnitude(a) Small tank mixed tsunami flow characteristics and its impact behavior on a land structure
The flow characteristics and behavior of its interface deformation and collision with the land
structures were clearly simulated.

When the flotsam impinges:
Maximum impact stress: 100 MPa
Corresponding maximum plastic strain: 0.0015
is numerically obtained.

Flotsam mixed tsunami (Secondary wave, PovRAY rendering)

When the two small tanks impinge the larger tank land structure the maximum impact stress was 100MPa,
and a corresponding maximum plastic strain of 0.0015 was numerically obtained.

The impact force magnitude offlotsam (small tank) mixedtsunami was over 10 times
than that of single phase(without flotsam case) tsunami.

Effect of flotsam mixing with tsunami on the impact force with a land structure

Conclusion
1.Two different supercomputing approaches, including the ALE method (Arbitrary Lagrangian-Eulerian Method) and SPH method (Smoothed
Particle Hydrodynamics Method), were used to investigate flow characteristics of a flotsam mixed tsunami.
2.The flotsam mixed tsunami behavior associated with interface deformation and collision with land structures was reasonably reproduced by thesupercomputing methods.
3.The impact stress profile of land structures with flotsam mixed tsunami impingement was computationally predicted. As a result, it was shown thatthe impact force of a flotsam mixed tsunami would be over 10 times greater than that of single phase tsunami (without flotsam case). It was also
found that the scale effects of mixture density and density differences between flotsam and seawater is the dominant factor for tsunami impact force
and damage prediction.
Transdisciplinary Fluid Integration Research Center Institute of Fluid Science, Tohoku University