iMechanica - finite element analysis - Comments

How should I apply for this

Lin Ma — Thu, 25 Sep 2008 20:05:50 -0400

How should I apply for this position? Thanks.

Modularity is part of the FEAP design

Sanjay Govindjee — Tue, 23 Sep 2008 04:13:04 -0400

Modularity is part of the FEAP design; if you stick to modifying things through the many user interfaces for materials, elements, mesh commands, solution commands, plotting commands, etc. then you are pretty safe with respect to updates. If you muck around in the internal guts of the code then you need to be more careful. That said, if you do something invasive but it is useful to not just you, but also others, then Prof. Taylor will quite often include your developed features (maybe re-writing them) in the next release of the code.

Prof. Dr. Sanjay Govindjee
University of California, Berkeley

Say you have modified FEAP,

Achilleus — Mon, 22 Sep 2008 15:38:56 -0400

Say you have modified FEAP, and then next release of FEAP just comes
out. What do you do? Is FEAP modular enough so that you can insert
your modifications right in, from one release to another? As a user,
can you contribute to FEAP? How do you do that?

Thanks

Cris

Hey

oyunindir90 — Sun, 24 Aug 2008 16:46:32 -0400

one of the disadvantages of ELMER is it does not use PETSC and it's ability in solver paralization is limited.

oyun indir

thanks for the link

Rui Huang — Wed, 06 Aug 2008 11:02:14 -0400

Kodanda,

Thank you for the link to OpenDx. Will check it out later.

Re: program for mesh and results visualization

Kodanda Ram Mangipudi — Wed, 06 Aug 2008 05:06:48 -0400

Dear Prof. Rui Huang,

There is one free, actively developed, feature rich, easy to use program for visualizatio: OpenDx. This was initially developed by Intel and then given out for open development. www.opendx.org is the link. It can serve the purpose of any scientific resercher for visualization.

It has an easy interface for creating visualization macros which is just like drag, drop and connect the the modules with mouse.

Kodanda

meshfree code for non-linear lastoplastic equation

aswani006 — Wed, 06 Aug 2008 02:11:29 -0400

my name is aswin and i am doin my m.tech 2nd yr in IIT ROORKEE,INDIA

now i am doin project basedc on meshfree technique.

i am develop[ing code for elastoplastic problem

i have code for elastic pert.but i am not getting how to dvelop code for plastic part and how to solve that non-linear equation

please help me for my dessertation.

Re:NLGEOM in ANSYS

shrimad — Fri, 01 Aug 2008 17:08:00 -0400

Biswajit,

Thanks for the reply.

If I consider a small problem; a square as an axisymmetric model (giving rise to a cylinder in 3D). The material model is viscoelastic. If I have a line on the top surface and bottom surface and press the top surface to about half the height with the lower surface fixed (contact analysis, no friction) I get a deformed rectangle. I do the same with ANSYS and with my FEA code in FORTRAN. What happens is:

Without NLGEOM ON, I get an exact match with my code and ANSYS, but the volume is not conserved.

With NLGEON ON, I get a slightly larger rectangle and the volume is conserved in ANSYS in this case.

I want to conserve the volume in my FEA code also, and hence I am trying to understand what modification do I need to do in my FEA code? My FEA code follows Newton Raphson Method and the same algorithm as ANSYS for viscoelastic stress calculations. I am stuck in my research because of this. Please guide me with whatever you know.

Thanks,

Shriram

Research Assistant
Structural and Multidisciplinary Optimization Lab.

University of Florida

Re: NLGEOM in ANSYS

Biswajit Banerjee — Thu, 31 Jul 2008 23:24:37 -0400

The NLGEOM command activates corrections for large rigid body rotations and translations when a small strain constitutive relation is used. It is also activated for large strain material models. For details on the implementation you can go to Chapter 3. Structures with Geometric Nonlinearities of the ANSYS Theory Manual.

Using NLGEOM should have no impact on whether the incompressibility condition is satisfied. Incompressibility is usually satisfied using a Lagrange multiplier approach which can lead only to approximate satisfaction of incompressibility in a numerical code. However, there are are stress update algorithms that satisfy incompressibility exactly, often by using an exponential map - see Weber and Anand, 1988 (or so).

A cut/paste job from the ANSYS manual follows.

-- Biswajit

3.3. Large Rotation

If the rotations are large but the mechanical strains (those that cause stresses) are small, then a large rotation procedure can be used. A large rotation analysis is performed in a static (ANTYPE,STATIC) or transient (ANTYPE,TRANS) analysis while flagging large deformations (NLGEOM,ON) when the appropriate element type is used. Note that all large strain elements also support this capability, since both options account for the large rotations and for small strains, the logarithmic strain measure and the engineering strain measure coincide.

3.3.1. Theory

Large Strain presented the theory for general motion of a material point. Large rotation theory follows a similar development, except that the logarithmic strain measure ((Equation 3–6)) is replaced by the Biot, or small (engineering) strain measure: (3–37)where: [U] = stretch matrix [I] = 3 x 3 identity matrix 3.3.2.

Implementation

A corotational (or convected coordinate) approach is used in solving large rotation/small strain problems (Rankin and Brogan(66)). "Corotational" may be thought of as "rotated with". The nonlinearities are contained in the strain-displacement relationship which for this algorithm takes on the special form:(3–38)where: [Bv] = usual small strain-displacement relationship in the original (virgin) element coordinate system [Tn] = orthogonal transformation relating the original element coordinates to the convected (or rotated) element coordinates

The convected element coordinate frame differs from the original element coordinate frame by the amount of rigid body rotation. Hence [Tn] is computed by separating the rigid body rotation from the total deformation {un} using the polar decomposition theorem, (Equation 3–5). From (Equation 3–38), the element tangent stiffness matrix has the form: (3–39)and the element restoring force is: (3–40)where the elastic strain is computed from: (3–41) is the element deformation which causes straining as described in a subsequent subsection.

The large rotation process can be summarized as a three step process for each element:

Determine the updated transformation matrix [Tn] for the element.

Extract the deformational displacement from the total element displacement {un} for computing the stresses as well as the restoring force .

After the rotational increments in {Δu} are computed, update the node rotations appropriately.

All three steps require the concept of a rotational pseudovector in order to be efficiently implemented (Rankin and Brogan(66), Argyris(67)).

Chandra, Thanks for the

shrimad — Thu, 31 Jul 2008 11:25:47 -0400

Chandra,

Thanks for the reply.

I couldn't find the technical details in the ANSYS help menu. By theory manual do you mean the 'help' section or it is something different? Please let me know.

Thanks once again.

Shriram

It uses a Hencky or

Chandra Veer Singh — Wed, 30 Jul 2008 22:22:52 -0400

It uses a Hencky or logarithmic strain measure, which is ln(U), where U is the right stretch matrix obtained by polar decomposition of the deformation gradient. For calculating Hencky strain, it uses the eigen values and eigen vectors of U. You can read more in ANSYS theory manual, there is a chapter on structural nonlinearity.

Chandra Veer Singh

I doubt that the emergence

Christopher — Wed, 04 Jun 2008 04:32:15 -0400

I doubt that the emergence of an open-source trading platform is going to encroach upon the success of Portware and FlexTrade anytime soon, but it could offer firms more freedom to do things on their own at a lower price point.

As a self-introduction,

yoshiaki yamada — Mon, 31 Mar 2008 06:05:34 -0400

As a self-introduction, please visit: Journal of Material Processing Technology, Articles in vol.140(1903), 1-5 Y.Yamada, Mechanics of Materials, I saw and participated: a reminiscence.

As a self-introduction,

yoshiaki yamada — Mon, 24 Mar 2008 05:37:43 -0400

As a self-introduction, please visit: Journal of Material Processing Technology, Articles in vol.140(1903), 1-5, Y.Yamada, Mechanics of Materials, I saw and participated: a reminiscence.

please help me if you can

prabukarthi — Sat, 09 Feb 2008 08:18:37 -0500

iam doing my project in warm deep drawing i want to know how to do simulation of WDD using abaqus software