How to simulate the effects of water 2

[bisav]

Hi everybody,

I have a doubt in PATRAN.
How to simulate the effects of water weight effectively.

My model is simple cylindrical tank, in fact a huge tank. Tank is completely filled with water. Now I want to run it for the modal analysis(Normal Modes). How do I give the weight of the water effectively to the container. If I create a mass element at the centre and attach it with all the nodes of the tank using RBE2 connection, the system becomes very stiff. And if I give non structural mass (value is calculated by total mass divided by the total surface area) in the element property of the tank wall, I think that either is not the correct way to simulate water. Because each wall will be carrying huge loads which I feel is not the correct way to do it.

Can anybody help me.?

Thanks
Bibin

 

[Onda]

I think the best way to keep in account the mass of the water is to use the MFLUID card. this card allow the iteration between structural and fluid 'virtual' elements.

From Basic Dynamic Analysis User’s Guide:

Virtual Fluid Mass
Small motions of incompressible fluids may be coupled directly to the structure with this option.
Fluids may be coupled to the interior and exterior surfaces (with infinite fluid boundaries).
There is no explicit fluid model; only the wetted structural elements (ELIST) have to be defined.
Although free surfaces are allowed, no gravity effects are included directly. Since the fluid is
represented by a coupled mass matrix attached directly to the structural points, this capability is
allowed in all dynamic solution sequences. This capability may be used to model a wide variety
of fluid-structure interaction problems. Some examples are fuel tanks, nuclear fluid containers,
drilling platforms, and underwater devices.

 

[bisav]

thank you for the suggestions guyzzz.........

 

[mufazzal123]

Hello,

I doing a Modal analysis on a Fuel tank.
I have tried the FEM-BEM method with ACMODL card and have got some results. Also I have matched the Mass of the fuel with the fluid elements.
Now I want to compare these results with the MFLUID card.
I am able to run the analysis correctly but I have problems determining the Virtual Mass Added by this card.
This is the ouput that I am getting in the F06 file:
[highlight #FCE94F] ^^^===================================================
^^^ACTUAL VIRTUAL MASS: COLUMN 1 (X,Y,Z)
^^^AMLS VIRTUAL MASS: COLUMN 2 (X,Y,Z)
^^^===================================================
0 MATRIX VMASS (GINO NAME 101 ) IS A REAL 2 COLUMN X 3 ROW RECTANG MATRIX.
0COLUMN 1 ROWS 1 THRU 3 --------------------------------------------------
ROW
1) 3.9874E-03 2.0983E-03 1.2682E-02
0COLUMN 2 ROWS 1 THRU 3 --------------------------------------------------
ROW
1) 3.3834E-03 1.7239E-03 9.0933E-03[/highlight]

I need to have 17e-3 of fuel, the data here should be in Tons.

Can anybody help me to interpret this data or how the Mfluid card writes the Virtual Mass

 

[nvhuser]

Hello everyone,

anyone knows if it is correct to include Solid elements in the Fluid-Structure interaction?
I am doing some simulations using ACMODL card, and the SSET that I have in the baseline model has solid elements (CHEXA from the structure), and one-dimension elements (CBUSH, CROD, RBE2, etc) included. What should be the effect of including this type of elements (1D and 3D) in the interaction?

Thank you in advance!

 

[bisav]

you cannot connect fluid elements and solid elements via node merging in patran. it will show error while analysing. i.e, both solid and fluid element should not share the same node.

Stress Engineer