FEA, Finite Element Anaylsis

[brian eiland]

I did a little search on this subject prior to making this new posting and discovered a number of threads addressing the subject. But they all seemed to geared toward a particular analysis of say mast, or sails, or hulls etc.
The one thread that spoke to design software in general, a polling;
Best Marine Design Software for Hull Design? (2001-2005)
had been closed for further submissions, so I decided to start this new thread dealing with FEA in particular, and in general.

New Software Approach Hints at FEA Breakthrough;

Promises More Efficient Overall Design Process

by Emil Venere

Mechanical engineers at Purdue University have developed software that promises to increase the efficiency of creating parts for everything from cars to computer hardware by making it possible to quickly evaluate and optimize complex designs.

The new approach integrates the design and analysis processes, which are now carried out separately. Currently, the geometry of a part is first created using computer-aided design (CAD) software. This geometry is then converted into a mesh of simple shapes, such as triangles or rectangles, which, when analyzed using a computer, indicates the part's strength and other characteristics. The painstaking procedure, called finite element analysis, is extensively used in industry.

"It's like taking a continuous curve and breaking it into pieces," says Ganesh Subbarayan, a professor of mechanical engineering at Purdue. "Otherwise, the form is too complex to analyze."

After the finite element model of the part is created, the part is analyzed to see how well it will perform. If a portion of the shape is found to need redesigning, the part's entire mesh must be recreated to reflect the change.

"After the designer designs the object, it is thrown over to the analyst, and the analyst says, 'OK, I think, based on my analysis, that your design has to be modified this way,' and then throws it back to the designer, who makes the modification," Subbarayan says. "That is not very integrated and not very efficient, and that's the reason these problems take so much time and computational power to solve.

"We are trying to speed up this process to make it more efficient by rethinking the way analysis is carried out. Instead of waiting until the end of the CAD process to do the analysis, we are trying to unify both the CAD design and analysis so that they are carried out concurrently."

Information about the software tool is detailed in a research paper recently published online and will appear in the May issue of the journal Advances in Engineering Software. The paper was written by doctoral student Xuefeng Zhang and Subbarayan. The software tool is based on theoretical work by another doctoral student, Devendra Natekar. Natekar graduated in 2002 and now works for Intel Corp., and Zhang graduated in 2004 and now works at General Electric's Global Research Center.

The method could be especially important when dealing with the corporate sensitivities of global competition.

"The overall philosophy behind the design approach can be extended to enable one to understand the impact of changes in suppliers' components on the performance of a complex system without revealing details of the components or the system," Subbarayan says. "This will enable suppliers to retain their proprietary design knowledge without revealing each other's intellectual property. Such strategies are critical as products are increasingly designed and produced in a globally distributed manner."

The software application, which was written by Zhang as part of his thesis, contains about 35,000 lines of Java code.

"That is a big and complex code," Subbarayan says. "If you take problems like finding the optimal shape for common automotive and aircraft structures, you have to somehow find the shape that has the least weight but at the same time won't break. We call that process shape optimization or topology optimization. These shapes have holes in them for bolting them in place or to reduce their weight. You have to decide whether to have one hole or two holes or 10 holes in a part, exactly where to put those holes and how to shape the holes."

Finite element modeling is the de facto analysis tool for numerous industries, Subbarayan says.

"When you use finite elements, you convert the complex differential equations that describe the physics of the part's behavior into simpler algebraic equations that the computer can solve," he says. "It's a powerful method because it enables you to take any complex problem and solve it.

"To describe the geometry, you take this complex object and break it into primitive objects like cubes, spheres, or cones. With our approach, if I only modify some portion of the part, I only modify the primitives directly associated with that portion I am changing and not all of the primitives. If I only change the shape of a specific hole in the part, for example, the rest of the primitive objects are the same shape, so why should I need to reconstruct the whole geometry and remesh the whole geometry?"

Subbarayan calls the approach a "hierarchical, constructive, meshless procedure" because it enables engineers to analyze the changing design of a part without recreating the complex mesh of elements.

"The way it is now, the same CAD software used to make the shape of the part can't be used to analyze the mesh," Subbarayan says. "But now, the same CAD software or some similar CAD-friendly software will be able to do the analysis, and in a much more efficient manner because there is no remeshing."

Subbarayan began working on the project in 1998.

Purdue researchers are using the software tool to design new materials at the microscopic level, and the method also promises to help engineers create optimized shapes of droplets of solder to ensure longer-lasting circuit boards. A similar application is creating optimized arrangement of particles in "thermal interface materials" as they are inserted into microprocessors for heat dissipation. The material is sandwiched between silicon chips and metal heat sinks to serve as a buffer between the two surfaces so that the expanding and contracting metal does not cause the brittle silicon to crack.

"These are all problems in which a shape needs to be modified," Subbarayan says. "In the case of solder, you are talking about what shape a droplet should take — the boundaries of the droplet are constantly modified until the optimal shape is found."

Source: Ganesh Subbarayan, Purdue News Service
Purdue University
_______________________________________
ABSTRACT

JNURBS: An Object-Oriented, Symbolic Framework for Integrated, Meshless Analysis and Optimal Design

Xuefeng Zhang and Ganesh Subbarayan

In this paper, we propose a design-analysis integrated CAD framework termed jNURBS. jNURBS, developed using the Java language, is an extensible, object-oriented framework that enables meshless analysis of physical behavior and optimal design. The geometry as well as the analysis fields (displacement, temperature etc.) are described mathematically using a common representation, namely the non-uniform rational B-spline (NURBS). Thus, NURBS serves to design the geometry as well as carry out meshless analysis, thereby, integrating the design and analysis in an efficient manner. The program kernel provides tools to symbolically describe complex multiphysics problems, methods to manipulate the NURBS entities, a set of primitive NURBS entities, and an iterative optimization solver. The problems are symbolically defined using a newly developed high-level, natural language description through an interface termed JNS (jNURBS Script). A number of example problems, selected from meshless structural analysis, material microstructure simulation, shape optimal design, and equilibrium shape of droplets, are presented to demonstrate the effectiveness and versatility of the framework

[nero]

Great post! maybe it will be inexpensive and easy to use software.

[MikeJohns]

Not sure how this differs that much from existing methods. Nearly all of us have some in house FEA and we adopt a system where we can move smoothly between the CAD application and the FEA package. All the better FEA packages have model creation ability embedded anyway, however CAD packages are better at the CAD side so everyone tends to draws in the CAD package and import the file into the FEA package.
The drawings are needed for other reasons and the automeshing of the imported drawing in the FEA package is pretty quick.

There are some relatively cheap and very capable FEA packages out now but hopefully this in-house software will be an open scource project .

[Rick Loheed]

Thought I would jump in and put in my 2 cents worth. I worked as a technician in the Purdue University ME school at the Thermal Sciences and Propulsion Center, now known as Zucrow Laboratories, doing gas turbine and rocket research while I attended classes at Purdue, although I am not familiar with these researchers, the meshless part sounds appealing.

But as for FEA in CAD, SolidWorks comes with a built in version of COSMOS which I use sometimes, although it is not terribly flexible for constraints and loads. It does a credible job of meshing with an internal 'Wizard' you don't have control over, but with pretty impressive results for an integrated design tool.

My current 'mainstream heavy hitter package' is Algor's FEMPRO, which will open Rhino files and also does a good job with SolidWorks. Most all of the appendages I've designed, since I work in the motion control end of boats, are done with FEMPRO at some stage.

My 'cheap low end' package is Cadre Pro- exporting meshes created in Rhino along with lines for beam elements works pretty well, surprisingly enough. After requesting the capability for Von Mises stress Jim Haynes, the author, implemented Von Mises Stresses for the plate elements. It also does a very credible job at dynamics- very impressive for the low price he charges.

The propeller bearing strut I designed a few years back, shown in active response in the enclosed GIF files, a direct screen capture from Cadre Pro. The meshes were created using Rhino, beleive it or not.

[MikeJohns]

If you liked Cadre Pro which is an excellent package for the price then you would love Strand (Straus in Europe) we finalised on that after trialing various packages , still Cadre Pro has some very nice features. No bricks though.

[Rick Loheed]

Yes, no bricks and no bending shells for awhile in Cadre, but the price is very low, so it is in my mind an easy choice if you don't have any FEA capability. Originally I bought it for $60 just to learn more about FEA, and was pleasantly surprised although as with all complex scientific endeavors, it has a learning curve and some degree of difficulty. I first bought it during the Compuserve DOS days, it's been so long ago! Mostly I used it to double check the first critical speed for lift fans for SES, including the UT-928 built at OceanFast/ISY in Henderson, WA. At that time, I was the only field service project engineer with on the road FEA capability in our company.

Since it has come up previously, I looked at the Strand website and will investigate further. We bought Algor, and so far it is allright but no dynamic response without more $$. That's where I still use Cadre Pro.

[Raggi_Thor]

I checked out the Cadre Lite program, it's 142USD + shipping.
Do you think this will be useful for typical small boat designs, keels, centerboards etc?

[MikeJohns]

Raggi

Just note that the FEA packages really are an engineers tool or you can be caught out easily. If you are conversant then Cadre is definately suitable, but we played with Cadre Pro so you may need to check the limitations in the Lite version.

Funny thing is we found many of the Demo versions to be so crippled as to be useless for assesment, another engineer leant us a handful of cracked packages that he bought from Thailand to trial and we settled on Strand. We actually bought the program after trialing it as cracked software and finding that it could do some of the really complex problems we needed FEA for.

[jamac]

I would like to add that we too have used Strand for a number of years and have tackled some tricky problems with it. See our website (www.malinmarine.com - newsletter 03) for some details of work we have done with Strand7.

Developer response has also been excellent.

HTH

JA

[Rick Loheed]

Can you give me an idea of the price range?

[Raggi_Thor]

While I have your attention :-) !
Anyone using ALGOR?
I have tried it on simple parts and it seems to be easy to use.

[Rick Loheed]

Yes, I mentioned it previously. I don't have the dynamics module, but I do use FEMPRO and Algor's FEM solver with both Rhino and SolidWorks models.

Algor does a very credible job, but I can only compare driving it with Cadre Pro and SDRC Ideas, which I used previously on a Unix machine. Like any other FEA and simulation software, it can and will bite back if you are not careful. However it does a very good job once you master the meshing procedures, and has brick elements of course. You have to merge beam element models or else create the beams in FEMPRO, which I have done many times. IT also has very nice automated pin joints.

WARNING* Models from Rhino must not contain internal voids, or they get treated as separate parts not hollow solids. You must 'drill' holes in them so the internal voids are recognized properly. This is a known limitation of Rhino.

Cadre Pro is not in the same league as Algor or Strand, but gives a lot of bang for a small amount of $$ if you can figure it out.

[Raggi_Thor]

Thank you for lightning quick response :-)
I will try to work more on Algor with Alibre Design (almost a "Solid Works / Inventor Light")

[Rick Loheed]

Your Welcome. Working late in Trondheim, I see. It is already quitting time in Maryland!

My colleague is, at this moment, jetting over to Norway (Mandal) for some meetings at Umoe.

[Raggi_Thor]

Yes, it's time to quit now, just past midnight :-)
Umoe is a large company here, and the boss Mr Ullstein Moe is building boats in China I believe.