p- elements
p- elements
(OP)
what is the major difference between p-elements and h-elements. where are they to be used?
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
|
RE: p- elements
Oops, forgot, the methodes are normally applied to complicated models, where analitical solutions does not exist, so the analyst is not sure about the regions with highly stress gradients.
cheers
RE: p- elements
Besides, even if p-elements were more computationally intensive, the efficiencies gained by using p-elements would more than make this supposed 'loss' up, even if there was one. I would guess that more than 90-95% of my time to get good FE results from analyzing any particular problem are due to problem setup and postprocessing analysis. By using p-elements, my job is much easier in the postprocessing analysis task--I know how to thoroughly (and quickly!) check for numerical error, something h-element people cannot do as quickly, efficiently or thoroughly. I know my results are good, for the model I have made. I still have to use my brain, though--reality and my model could be completely different if I don't do 'sanity checks'.
RE: p- elements
RE: p- elements
Just my $0.02 worth.
Best regards,
Matthew Ian Loew
m.loew@ssss.com
RE: p- elements
Computationally, I think some of what was said was in error. One of the major benefits for that the iterative p-code solver has it it can selectively refine a mesh. In general, for a properly converged model the p-code will solve faster than the h-code. Scott mentioned a good point about setting up a mesh and the time it takes.
On the other hand you if you use the p-code to converge a solution, you need to solve it muliple times. If the analyst is familiar with similar problems he can come up with a satisfactory mesh and it may solve one pass faster than several by adjusting the order and checking convergence.
While I have seen lack of convergence botch up problems, if the analyst doesnt know how to achieve convergence and needs a p-code to do it, your probably screwed anyway.
RE: p- elements
http://www.comco.com/phlex/hp-adapt.html
cheers
RE: p- elements
p-version ;polynomial order is increased, Element forumation changes
h-version: elemnet size is altered
Both these depend on error levels. It is found that A h-refinement produces many a transition elements which may have to be formulated as degenerate elemnts this more so tends to a p-version analysis. There has always been an effect realized in terms of polynomial. but then its not specifically termed as p-version. We can say h version also has effects that a p- version causes and vice versa.
as such better go in for h-p. Zuardy is right.
raj
RE: p- elements
Title: Discussion Comparing P and H Method of Stress Continuity at Nodes (www.ptc.com/cs/tpi/111558.htm)
Best regards,
Matthew Ian Loew
RE: p- elements
In general some of the reasons I prefer FEA codes like Nastran over the Mechanica type codes are:
(a.) Mechanica is not as comprehensive as all the other FEA codes.
(b.) Mechanica isn't very flexible in what one can do with regard to auto-meshing and element formulation; for example one has more control over Rigid Links I don't believe even the current Mechanica code could handle the Rigid Links as eloquently as say Nastran.
(c.) Nastran is the defacto standard for FEA analysis results {can be a factor when working with large aerospace companies (Boeing & Lockheed) or auto manufactures (Ford & GM) }. Now I'm not suggesting Mechanica isn't accurate, but in my consulting business I typically end up having to supply solutions to these companies in the Nastran code as well as in Mechanica or any other code my clients might be using.
(d.) The solution times for a fine grid meshed H-Method (like Nastran) is probably an order of magnitude faster than an equivalent Mechanica P-Method coded model.
(e.) I can recall several Pro-E CAD models that even experienced users were not able to get Mechanica to develop an auto-mesh. With more comprehensive software tools like the ones found in Nastran we are able idealized these CAD models in a relatively short period of time. I had to due some tune-up of the idealizations but I got them.
Some of the More Obvious Downsides of Mechanica:
(a.) Pretty much stuck with Linear analysis only.
(b.) I don't think the current release of Mechanica can do either Large Deflections, Non-Linear Stress/Strain, or Resonant Vibrations with Load Stiffening. Maybe they can do that now, I would have to check.
(b.) Base Excitation for Dynamic Response [ Random & Sinusoidal ] - Not a big deal for most problems but there are many cases where one would like to subject models to variable input excitation at different points instead of *shaking* the entire model on it's supports {or Boundary Conditions}.
(c.) Mechanica's claim to fame when it was called Rasna was that one didn't need to develop detailed meshes. One only had to crudely mesh regions and Mechanica by virtue it's P-method internally updates the order of polynomials until convergence of the solution is achieved One Downside here is that one still needs to define proper patches [2-D] and hyper-patches [3-D] for the models to converge. Another downside is the length of processing time. Today's automeshing tools make the meshing aspects a moot point. With Nastran one can still do a lot more when it come to manipulating the idealization.
(d.) One aspect of the Mechanica code that I've witnessed is that some users take the idea of not needing to develop proper meshes too far and end up with solutions that aren't as good as they should be. The solution to this problem is to do lots of sample problems and spend a lot of time using the software. [Same with any other code.]
(e.) On the more practical ends, the Mechanica code has a limited element library - Nastran has a lot of flexibility in this area.
(f.) One interesting note is that when Mechanica P-Method [and the other FEA codes as well] list comparisons of their solution accuracy they compare to Nastran H-Method. Typically though every FEA code today gives good results if used properly.
The types of analysis most companies perform are typically -Linear Static's, Resonant Vibrations, and Dynamic Response to Sinusoidal Excitation. Every FEA code can do this. Mechanica included. I suppose the most attractive aspect of Nastran over Mechanica is the Comprehensive Modeling capability [ I know that word *comprehensive* covers a lot of ground], more Flexible modeling tools and Defacto industry standard.
That's about all I can come up with on the spur of the moment. Give me a call if you have any specific questions. I think this might be a good topic for one of my articles for Machine Design's FEA Update Column.
David R. Dearth, P.E.
Applied Analysis & Technology
E-mail "AppliedAT@aol.com"
RE: p- elements
raj
Raj
RE: p- elements
David R. Dearth, P.E.
Applied Analysis & Technology
E-mail "AppliedAT@aol.com"