Please Help ! URGENT - Tetrahedral Fluid Elements --- How to assign ??

[cdeepakroy]

Hello,

I want to model a hemisphere filled with saline/water, and see how it responds to gravitational load.

BOUNDARY CONDITION - The base plane of the hemisphere is totally fixed.

Load -- Gravity is applied to the whole body in the negative y-direction.

I am using a mesh consisting wholly of four-node tetrahedral elements ( Element Type = C3D4 ).

How and What kind of material properties should i assign to the tetrahedral elements ???

Do i have to use Hydrostatic material properties ???

Is the element type --> C3D4 correct or should i be using something like F3D4 for hydrostatic fluid elements ???

Eagerly waiting for any help ....

Thanks in advance ....

Regards,

Deepak

 

[corus]

Surely this is just a hydrostatic pressure loading with gravity? Don't use 4 noded tets but use C3D10M elements if you can't use hexahedral elements.

corus

 

[cdeepakroy]

Hello corus,

Thanx a lot for the reply ....

Now im a lil confused ....

Im actually new to both Finite Element Analysis and ABAQUS ......

I am actually using an open-source automatic tetrahedral mesh generator called TETGEN ( url:

http://tetgen.berlios.de/

). The library takes a hemispherical surface as input and generates a tetrahedral mesh with 4-node tet elements. Do you know of any open source Hexahedral mesh generators ???

And Can you please tell me in a bit detail what material properties i should be assigning and what loading coniditions should i be assigning .....

Right now i am applying gravity loading using the python script as follows:

*********************

import load

mymodel.Gravity( name = 'Gravitational Load' , createStepName = 'GravityLoadStep' , comp2 = -1.0 )

This shows up as follows in the input file:

** LOADS
**
** Name: Gravitational Load Type: Gravity
*Dload
, GRAV, 1., 0., -1., 0.

********************

Is this correct ?? How do i define the hydristatic pressure loading ....

Say i want to fill the hemisphere with water .....

I would give the density == 1000 kg/m3

what additional properties should i be defining .....

Eagerly waiting for your help ......

Regards,

Deepak

 

[corus]

In the past for developing my own code I've used geompack as a mesh generator

http://members.allstream.net/~bjoe/

See if that is of any use.
I'm not sure why you're using a python script when it's just as easy to manually edit the .inp file in any Notepad type program.
You should look at the notes that come with Abaqus or any 'getting started' type notes as the question you ask about material properties seems too basic to answer really. The hydrostatic pressure load is applied as a function of height using *dsload where the pressure P=pgh

corus

 

[brep]

>> Do you know of any open source Hexahedral mesh generators ???

If you are using Python scripts, this must mean you are using ABAQUS/CAE to run it... Therefore you already have a very powerful hex mesher.

 

[cdeepakroy]

Hello Corus and Brep,

Thanx a lot for your prompt inputs.

The application i am trying to solve is ---- i want to see how a breast implant responds to gravitational load.

Using the simplest approximation possible, A breast implant is like a balloon which is filled with saline solution. There are round breast implants which is a hemispherical baloon filled with saline solution. There are also anatomic breast implants which resemble the anatomic shape of the breast more closely.

**************

>>>> Corus asked ----- I'm not sure why you're using a python script when it's just as easy to manually edit the .inp file in any Notepad type program.

The reason i am doing this is because i have developed a seperate application using C++ and opengl which allows the design of the shape of an implant interactively.

Then this closed surface mesh, is fed as input to a mesh generator which outputs a tetrahedral mesh.

Then i write out the nodes (*Node) and tetrahedral elements (*Element, type=C3D4) of the tetrahedral mesh to an ABAQUS input file (*.inp).

Irrespective of the geometry i write to this input file, I have a python script which imports this Input model and sets up the material properties, loading/bounding conditions and submits the job for analysis, since these are independent of the implant shape/geometry i use.

Once the analysis is done, it writes out the deformed shape which is inturn read and visualized by my C++ application.

****************

>>>>> Brep suggested ---- If you are using Python scripts, this must mean you are using ABAQUS/CAE to run it... Therefore you already have a very powerful hex mesher.

Well if i export the closed surface mesh out from my C++ application, then is there any facility in abaqus to convert it into a soid mesh with tetrahedral/hexahedral elements ????

If so i would be very happy, and there wont exist a need for a mesh generator.

*************************

More questions:

1. Is the modeling method/material properties/loading conditions descirbed in my previous post correct for this problem.

2. I want to know how to define the material properties for the saline solution.

3. I want to know how to define the gravitational load on the implant.

Your help would be greatly appreciated ......

Thanks in advance .....

Regards,

Deepak