Takamasa MORI
Development of a numerical algorithm for objects moving under the tsunami wave forces
Tokuzou HOSOYAMADA
Tsunami wave forces acting on a lot of objects such as building, houses, cars and ships are tremendously huge. On 2011.Mar.11th, Higashi-Nihon big earthquake disasters occurred in Pacific Ocean of Tohoku districts and tsunami hit many coastal areas in Tohoku. It was possible to see the wave motion and record the disasters by handy camcorder, which is very common these days. The motion pictures are uploaded to video web site and are open to public.
It is very clear to see tsunami running up to the ground includes objectives mentioned before. To understand interaction of tsunami wave and the objects by numerical simulation, a new algorithm should be developed and implemented to finitedifference method(FDM) of numerical wave simulation.
In this study, a new algorithm is developed and added to numerical code for tsunami wave run-up scheme by FDM. In two-dimensional space, wave forces have two directions(Fx, Fy) and rotation torque (T) and motion has 3 degree of freedom (X, Y, ¦È). Wave forces are mainly normal direction of body surface. That is to to say, wave pressure. In this algorithm, tangential directional force, namely shear stress is evaluated. Rotational torque is calculated by summing up of external products of force vectors on the surface and position vector of the working point relative to center of gravity of the objects. Kinematic boundary condition between objects and wave is also implemented by imposing the velocity of the objects to surface boundary of the object.
Numerical results are confirmed by making motion picture of the calculation. Objects moves by wave action of tsunami and stop when tsunami wave goes down. Temporal history of wave forces shows rapid change when wave reaches the objects, which is characteristics of interaction of moving body and ambient fluid.
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