Computational Science and E-Systems Research

11-4 Technology to Speed up Fluid Structure Interaction Simulation－ Simulation Technologies for Flow-Induced Vibration in a Nuclear Power Plant －Vertex Judgment by MC (Front view)Set boundary

Flow

Fluid mesh

Flow

Flow

T=12.44 s

T=12.47 s

Vertices outside ofa structure

Boundary
Vertices ina structure

Structure meshFig.11-8 Setting of boundaries using MC
Using the results of a judgment regarding whether vertices areincluded in the structure mesh, the boundaries in a calculation
domain are set. The processing cost is significantly reduced
because the shape is calculated approximately.

T=12.39 s

Fig.11-10 Time variations in cylinder deformation
Red shows high-stress region; blue shows low-stress region.
The figure indicates that the cylinder deforms because of
the pressure difference around it. The deformation amount isenlarged 100 times.

（a）（b）
Drag coefficient (Cd)

Cylinder

Flow

1.4
1.2
1.0

Experiment Cd = 1.0

0.8
0.6
56

78

910Time (s)Flow-induced vibration is a very important phenomenon in anuclear power plant because it causes breaks in the instrumentsor pipes. To analyze this phenomenon, fluid structureinteraction simulation technologies have received considerable
attention in recent years. In a fluid structure interaction
simulation, a mesh consisting of small polyhedra is generally
used to describe the fluid and structure regions. To date, amethod that describes accurately the shape of the boundary
between the fluid mesh and the structure mesh has been used.
In this method, when the structure shape is highly deformed,
the mesh shape also becomes awkward. Consequently, thesimulation accuracy and speed are reduced. One of the methodsof overcoming this problem is the immersed boundary method.
However, setting the boundary conditions in the calculation
domain requires considerable time.
In this study, a new algorithm that uses Marching Cube (MC)to set the boundaries approximately was invented (Fig.11-8).
The processing speed is more than 20 times faster than that ofFig.11-9 Pressure and time variations in drag coefficient(a) Pressure distributions. High pressure (red) occurs at theupstream side, and low pressure (blue) occurs at the downstreamside. (b) Drag coefficient versus time. The simulation result
exhibits good agreement with the experimental data.

traditional methods. This makes it possible to finish a simulationthat requires half a year by traditional methods within 10 days.
Consequently, the method enables us to perform more practicalsimulations.
For verification, the method was applied to a simulation of theflow-induced vibration around a circular cylinder. Figs.11-9(a)and 11-10 show that the simulation can compute the deformationof a cylinder due to a pressure difference around it. The dragcoefficient (Fig.11-9(b)) and amount of deformation of thecylinder are in good agreement with the experimental data. Thisstudy confirmed that the proposed method maintains adequate
accuracy for application to practical problems.
This method enables us to perform large-scale complex
simulations of flow-induced vibration with adequate accuracy
within a practical timeframe. It is hoped that the method willcontribute to the development of technologies to increase thesafety of nuclear power plants.

Reference
Kino, C. et al., Flow Analysis around an In-Line Forced Oscillating Circular Cylinder using IB-Method, Nippon Kikai Gakkai Ronbunshu, B Hen, vol.78,no.796, 2012, p.2113-2126 (in Japanese).

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JAEA R&D Review 2013