3. Modeling A

3.1. Characteristics of modeling

The geometry of the structures and the characteristics of the material constituting the shells have been presented previously.

Concerning the absolute wall roughness of the structures, a value of \({10}^{–5}m\) is taken.

The surrounding fluid is water. The values taken for density and kinematic viscosity are respectively

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: label: EQ-None

{rho} _ {f} =1000mathrm {kg}/{m} ^ {3}

We consider the unconfined flow up and down stream of structures.

The resolution model used is the analytical model MOCCA_COQUE absorbed in the Code_Aster (operator CALC_FLUI_STRU). The fifth air mode of the structure is selected and then the coupling problem is solved for this mode. Average flow velocities vary from \(0\) to \(40m/s\) in steps of \(5m/s\). For this mode, the changes in the natural frequency and in the reduced damping are thus obtained as a function of the flow speed.

3.2. Characteristics of the mesh

The two shells are meshed in the same way. In order to make them integral to each other, a group of elements connecting the nodes is added at the embedment level.

We have:	17 knots on a vertical generator
	60 knots on a crown
	960 QUAD4 stitches on each shell
	60 QUAD4 meshes to secure the two shells (embedded base)

3.3. Features tested

Operator DEFI_FLUI_STRU: definition of the characteristics of a hardware configuration consisting of two coaxial cylindrical shells for a fluid-structure coupling calculation; keyword factor COQUE_COAX.

Operator CALC_FLUI_STRU: resolution of fluid-structure coupling for a configuration of the « coaxial shells » type; calculation of changes in modal parameters (reduced frequencies and damping) as a function of the fluid flow speed.