How to simulate the effects of water
How to simulate the effects of water
(OP)
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
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





RE: How to simulate the effects of water
Hydrostatic pressure (P)?
P = Rho * g * h
Rho = fluid density , g = acceleration, h = fluid depth
Indeed the use of RBE2 is wrong and it will make the structure very stiff and cause numerical issues...
Here the variable is the water depth. With Femap it is easy to create such a pressure function of depth (so the element centroid, or node position) using data surface...Also I know that with Patran it is feasible too by creating spatial PCL function or tabular input. look at the attached pdf which explains how to create spatial and temporal variation of loads.
Hope this helps
Seif Eddine Naffoussi, Stress Engineer
www.Innovamech.com
33650 Martillac û France
RE: How to simulate the effects of water
Greetings for the day.
Thank you for the reply.
I have already applied this variable pressure by using spatial fields PCL function. That is for the stress analysis. Now that I want to do the MODAL analysis. This pressures won't be taken into account for modal analysis. But for modal analysis, I want to simulate the mass of the water effectively. I want to give the mass to the model in a correct manner. For this reason only in the modal analysis I removed the pressure function and created a mass element with the mass of the water at the center and attached it with tank using RBE2, but that is not the correct way, it makes the structure very stiff.
Bibin
RE: How to simulate the effects of water
Then you have to deal with MAT10 and PFLUID (field n° 8 in the PSOLID nastran card) to represents the water properties and assign this properties to the solid elements.
You will need to define some information like the mass density, speed of sound to calculate the bulk modulus...
Regards,
Seif Eddine Naffoussi, Stress Engineer
www.Innovamech.com
33650 Martillac û France
RE: How to simulate the effects of water
But how can we give the connection between fluid element(hex elements and the side wall) ?
Node connection or any other connection. Node connection seems to be difficult since it is a big structure, so there will be so many nodes. And if I didn't connect it with the side walls will it be the correct way to approach to the problem???
Regards
Bibin.
RE: How to simulate the effects of water
Seif Eddine Naffoussi, Stress Engineer
www.Innovamech.com
33650 Martillac û France
RE: How to simulate the effects of water
RE: How to simulate the effects of water
Thanks Composite curves.
RE: How to simulate the effects of water
Seif Eddine Naffoussi, Stress Engineer
www.Innovamech.com
33650 Martillac û France
RE: How to simulate the effects of water
Hello
Good Morning
Node merging was not a problem. But while running it shows error. It seems like fluid elements can't be attached to structural elements.
The following is the error showing in F06,
USER FATAL MESSAGE 5419 (MODGM2)
STRUCTURAL ELEMENT QUAD4, ID = 1, REFERENCES FLUID GRID POINT ID = 1
And below is the error definition I found out,
*** USER FATAL MESSAGE 5419 (MODGM2) STRUCTURAL ELEMENT %1 ID =%2 IS ATTACHED TO A FLUID GRID POINT ID =%3
So is it not possible to attach a fluid elements with structural elements? If it is so how will we give the connection??
Regards
Bisav
RE: How to simulate the effects of water
Seif Eddine Naffoussi, Stress Engineer
www.Innovamech.com
33650 Martillac û France
RE: How to simulate the effects of water
RE: How to simulate the effects of water
Seif Eddine Naffoussi, Stress Engineer
www.Innovamech.com
33650 Martillac û France
RE: How to simulate the effects of water
RE: How to simulate the effects of water
Seif Eddine Naffoussi, Stress Engineer
www.Innovamech.com
33650 Martillac û France
RE: How to simulate the effects of water
RE: How to simulate the effects of water
Seif Eddine Naffoussi, Stress Engineer
www.Innovamech.com
33650 Martillac û France
RE: How to simulate the effects of water
RE: How to simulate the effects of water
RE: How to simulate the effects of water
It is at this point that you need to pick up the patran users guide and read to find out how ACMODL is supported thro' patran.
RE: How to simulate the effects of water
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.
RE: How to simulate the effects of water
RE: How to simulate the effects of water
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:
^^^===================================================
^^^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
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
RE: How to simulate the effects of water
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!
RE: How to simulate the effects of water
Stress Engineer