Dave Lindeman | 3 Jan 21:07 2011

Re: Linear Vs NonLinear elements

As you've mentioned, quadratic elements can more accurately represent 
curved surfaces.  In addition, they are better at capturing concentrated 
gradients.  In general, you never want to use linear tetrahedral or 
triangular elements (except perhaps for heat transfer problems).  A 
linear tetrahedral element will, for example, will be a constant strain 
element -- i.e., it will not be capable of capturing the strain gradient 
across the element.  In the Benchmarks Manual you'll find a cantilever 
beam problem where they've compared the performance of various elements 
and mesh refinements.

Regards,
Dave

Dave Lindeman
Lead Research Specialist
3M Company
3M Center 235-3F-08
St. Paul, MN 55144
641-733-6383

On 1/3/2011 11:55 AM, Ali Khajehgani wrote:
> Thanks Dave & Sridharan for answering my question,
>
> Can I ask what the practical differences are between linear and quadratic
> elements. For instance in a stress analysis where I want to use tet-elements
> what should I chose and how will this affect my results? I have seen that in
> metal forming simulations the quadratic elements represent the geometry
> better but it also take longer time to run.
>
> What do you suggest for a structural stress analysis and why?
>
> Many thanks!!
>
> Br
>
> Ali
>
> From: Abaqus <at> yahoogroups.com <mailto:Abaqus%40yahoogroups.com>
> [mailto:Abaqus <at> yahoogroups.com <mailto:Abaqus%40yahoogroups.com>] On
> Behalf Of
> sridharan.venkataramanan <at> wipro.com
> <mailto:sridharan.venkataramanan%40wipro.com>
> Sent: 3. januar 2011 17:05
> To: Abaqus <at> yahoogroups.com <mailto:Abaqus%40yahoogroups.com>
> Subject: RE: [Abaqus] Linear Vs NonLinear elements
>
> Ali,
>
> Linear element meaning 1st order elements. Does not mean they are
> limited to linear FEA! In fact for most of the non-linear cases linear
> brick element (reduced integration/hybrid/incompatible) are widely used.
> The case is different with solid tetrahedron elements though. Since the
> 4 noded tet is very stiff, we recommend using parabolic tetrahedron
> elements. Do not get confused with element order (linear or parabolic)
> with analysis type (linear or non linear).
>
> Regards,
>
> V.Sridharan
>
> CAE Competency Head | Engineering Design Services | Wipro Technologies
> |Bangalore
>
> From: Abaqus <at> yahoogroups.com <mailto:Abaqus%40yahoogroups.com>
> <mailto:Abaqus%40yahoogroups.com>
> [mailto:Abaqus <at> yahoogroups.com <mailto:Abaqus%40yahoogroups.com>
> <mailto:Abaqus%40yahoogroups.com> ] On Behalf
> Of denzel_washington25
> Sent: 03 January 2011 02:21
> To: Abaqus <at> yahoogroups.com <mailto:Abaqus%40yahoogroups.com>
> <mailto:Abaqus%40yahoogroups.com>
> Subject: [Abaqus] Linear Vs NonLinear elements
>
> Dear All,
>
> In the mesh module in abaqus we can chose between linear or quadratic
> elements for 3D stress elements. Its also possible to use linear
> elements in non linear analysis. How can this be explained? I thought
> that linear elements can only be used in linear analysis? does these
> linear elements have non linear capabilities?
> Can anyone explain this to me? any paper that describe this in detail.
> I want to know the formulation for linear and nonLinear elements.
>
> Many Thanks.
>
> Ali
>
> [Non-text portions of this message have been removed]
>
> [Non-text portions of this message have been removed]
>
> 

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Gmane