Thank you for coming to our gallery! Please enjoy some short movies obtained with our fluid-solid interactive (FSI) computation, called "MICS".
(To see the movies, please use the browsers supporting HTML video Tag.)
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Falling 3D rectangular object in vertical water duct (2008)

The first movie is a very simple example of FSI, in which a rectangular
solid object is falling in water within a vertical duct.
The interactive behaviors between the fluid and a solid object,
however, are not so easy to numerically predict.
We need sufficient resolution of fluid-cells with respect to
the solid object,
since the flows around the object are necessary to calculate adequately.
The meandering falling movements of the object closely related
to the eddies behind it,
where the pressure is relatively low and it causes the changes of the object
angles. In our FSI method, the pressure and viscous effects,
affected on the surface of the object, are estimated with a volume integral,
so that they can be easily treated in our method, MICS.

[ S. Ushijima, A. Fukutani and O. Makino,
"Prediction method for movements with collisions of arbitrarily-shaped objects in 3D free-surface flows",
Doboku Gakkai Ronbunshuu B,
Vol. 64, Issue 2, 128-138, 2008. (Japanese).
DOI
https://doi.org/10.2208/jscejb.64.128 ]

Free-surface flows over permeable weirs (2006)

The "permeable weirs" can be found in the actual rivers.
They are thought to be the environment-friendly water-management structures made of natural stones and materials.
The experiments were conducted to understand the failure process of the permeable weir, which is simply made using glass spheres (the bottom-layer spheres are fixed) in the flume due to the overflow. While one glass sphere is simply represented by a DEM particle, the flows around the sphere are calculated with the fluid-cells finer than a sphere. Thus, the fluid forces acting on each sphere are calculated from the pressure-gradient and viscous terms in our multiphase model (MICS). As a result of the comparisons with experiments, it has been confirmed that the predicted results reasonably agree with the experimentally observed results.

[ S. Ushijima, A. Fukutani and N. Yoshikawa,
"Numerical prediction for collapse of permeable dam
due to overflows with 3D multiphase-flow solver (3D MICS)",
Proc. Hydraulic Eng.,
Vol. 50, 841-846, 2006. (Japanese).
DOI
https://doi.org/10.2208/prohe.50.841 ]

Sloshing motions arise when horizontal accelerations are imposed on the tank including a liquid with a free-surface. In the present example, four elastic plates are set up inside the rectangular tank in such conditions. These plates are deformed due to the oscillating free-surface flows, while the sloshing motions are somewhat reduced by the plates. The following movie shows the computational results obtained with our FSI computational method (MICS). The deformations of the plates, which are represented with multiple tetrahedron elements, are calculated with a finite element method (FEM). The isolines of the vorticity vector lengths are also shown in the movie.

[ S. Ushijima, N. Kuroda and I. Nezu,
"3D numerical prediction for interaction between free-surface flows and elastic bodies with MICS and finite element method",
Proc. Hydraulic Eng.,
Vol.52, 1033-1038, 2008. (Japanese).
DOI
https://doi.org/10.2208/prohe.52.1033 ]

One million solid objects moving in free-surface flows (2014)

A parallel computation method has been developed to predict the motions of arbitrarily shaped solid objects transported in 3D free-surface flows, taking account of their collisions and fluid-solid mechanical interactions. The present parallelization is based on a domain decomposition method using flat MPI. In order to improve the load-balancing in case that nonuniform distributions of many objects arise in the whole computational area, the size of the sub-domains (shown by blue lines) can be changed according to the number of the objects included in the sub-domains.
Numerical experiments were conducted for the free-surface flow including 1,000,000 spheroids, each of which consists of 121 tetrahedron elements. The spheroids are transported by the free-surface flows caused by a dam-break condition. All spheroids are suspended in the liquid phase and they collide with each other in the movements. The movie shows a part of the computational domain so that we can see each spheroid.

[ K. Maruyama, K. Aoki and S. Ushijima,
"Dynamic load-balancing parallel computation method for multiple solid objects transported in fluids",
JSCE, A2, Applied Mechanics,
Vol.70, No.2, I_185-I_194, 2014. (Japanese).
DOI
https://doi.org/10.2208/jscejam.70.I_185 ]

In the events of tsunami, various tsunami-driven debris, such as vehicles parked near harbors, cause serious secondary damage in addition to the tsunami-induced flow itself. The numerical experiments were conducted with our FSI computational method (MICS) as shown in the following illustration:

On the ground, we have two artificial hills, higher than
the flat ground level, to show we can deal with the ground undulation.
The 240 vehicle models are placed
on the water-front side (left side of figure),
each of which is represented with about 400 tetrahedron elements.
Since the density of the vehicle models is smaller than that of water,
they are floated and transported in the tsunami-driven water flows.
Two cases of computations were conducted: "without" and "with" the Debris Control Structures (DCSs), which are cylindrical structures fixed on the ground to prevent the vehicles from being transported to the land area (right side of figure).
Using 400 cores of Cray-XE6, numerical procedures are parallelized with flat MPI.
Comparing the debris distributions in the following movie,
we can see the DCSs are expected to capture the tsunami-driven debris effectively.

Top views (Upper = Without DCSs, Lower = With DCSs)

[ K. Aoki, S. Ushijima, H. Itada and D. Toriu,
"Parallel computations for many floating objects transported by tsunami flows",
PANACM 2015, pp.611-622, Buenos Aires, Argentina, 2015. ]

Gravel particles transported by waterfall (2017)

It is easily expected that the gravel particles on a waterfall basin are transported by the momentum of the falling water.
This simple process was numerically simulated taking account of the elementary process in mechanics as detailed as possible, using a supercomputer (Cray CS400 2820XT) with 552 parallel computations (elapsed time was about 289 hours for actual 5 sec. in experiment!).
Since the air, water and solid phases are included in the 3D computational area,
our multiphase model (MICS) was employed to simulate the local scour and deposition
on a gravel bed, consisting of about 16,700 gravel particles with a diameter of around 7 mm, caused by falling water from a rectangular-notch weir as shown in the following movie.
The fluid forces acting on
a gravel particle were estimated from the volume integral of the pressure and viscosity terms included in the momentum equations for the multiphase field.
The particle-particle collision forces are estimated with multiple contact-detection spheres (CDSs) included in each gravel-particle model.

(1) Whole view of computations
(Colorful particles are not "candies" but "gravel particles".)

In our computations, representative 26 shapes of gravel
particles were selected and each shape was represented with about 100 tetrahedron elements. Multiple contact-detection spheres are set up inside of each gravel model. The 26 shapes are shown by different colors, so there should be 26 colors for 16,700 gravel models in the movie.

(2) Close view (Left=Computation, Right=Experiment)

Note:
(a) Calculated particles are shown only on near side (0 < x2 < 40mm). (b) Some air bubbles can be shown if using another visualization method.

[ S. Ushijima, D. Toriu, H. Yanagi and D. Yagyu,
"Computations on transportations of gravel particles due to overflows taking account of particle-particle and particle-fluid mechanical interactions",
JSCE, A2, Applied Mechanics,
Vol.73, No.2, I_377-I_386, 2017. (Japanese).
DOI
https://doi.org/10.2208/jscejam.73.I_377 ]

In a hydraulics field, an event, in which the sediment on the bottom of water is locally removed due to water flows, is sometimes called "scour". Regarding the local "scour" caused by a vertically downward water jet,
we tried to make a numerical simulation to understand its mechanism using our particle-scale FSI prediction method using a supercomputer
(1,088-process parallelization using Cray XC40 in Kyoto Univ.).
To calculate the flows around one gravel particle,
about 374 fluid cells are set up in the computations.
We also conducted an experiment using a vertically downward water jet (about 1.2 m/s) impinging during about 3 sec. on a gravel bed consisting of about 16,700 gravel particles with a diameter of around 7 mm (the same particles used in the above waterfall problem).
The unsteady process of the local scour
is categorized into three stages,
(A) unsteady-scouring stage,
(B) saltation-collapse equilibrium, and
(C) stationary state with the angle of repose.
It was confirmed that the calculated gravel-bed shapes in all three stages
are in good agreement with the experimental results.
In particular,
during the (B) stage,
it was shown that the numbers
of rising saltation particles and falling collapsed ones
are approximately equivalent
and that
almost uniform scoured surfaces
are consequently maintained.
Please do not be surprised
that some particles appear and disappear in the movie,
since we visualized the only particles included in the front layer
(0 < x2 < 32mm in the depth of 160 mm) to make clear the scoured shape.

Note: (a) Calculated particles are shown only on near front side.
(b) Isolines indicate the magnitude of vorticity vectors.

[ S. Ushijima, D. Toriu, H. Yanagi and H. Tanaka,
"Numerical prediction for transportation of gravel particles and saltation-collapse equilibrium due to vertical jet",
JSCE, A2, Applied Mechanics,
Vol.75, No.2, I_289-I_300, 2019. (Japanese). JSCE Applied Mechanics Outstanding Paper Award
DOI https://doi.org/10.2208/jscejam.75.2_I_289 ]

Deformation of soft materials under free-surface motions (2020)

Next, let us consider a "soft" material deformed in flows.
In this movie, the visco-hyperelastic materials are numerically simulated in a free-surface Newtonian flow with a full-Eulerian method. In the full-Eulerian method, since we need not to trace the solid objects in a Lagrangian way, the parallelization of the computational method is easier than
Eulerian-Lagrangian methods.
In the following movies, the parameter "G" is non-dimensional shear modulus, which can be thought as "rigidity" or "hardness" of the solid object. So, under the effects of free-surface movements, we can see the deformations of the suspended "soft" spheres with "G=0.1" are larger than those of the "hard" spheres with "G=10". On the other hand, as you might guess, the wave motions are also affected by the deformations of the spheres. It was confirmed that the wave heights are reduced in case of the "hard" spheres with "G=10".

[ S. Ushijima, N. Guinea and D. Toriu,
"Numerical Prediction for Damping Effects of Suspended Deformable Bodies on Wave Motions of Free-Surface Flows",
Trans. Japan Soc. for Simulation Technology,
Vol.12, No.1, pp.2-7, 2020.
DOI https://doi.org/10.11308/tjsst.12.2 ]