(The following is excerpted from a paper by Dr. K. K. Bhatia, Rowan University, Glassboro, NJ, that was presented at a recent COMSOL conference. To learn more read the research paper: www.COMSOL.com/academic/papers/1529)
Although personal computers have brought major changes to higher education, a debate continues as to when the appropriate time is to introduce certain topics that seriously rely on computational power. For instance, is simulating partial differential equations (PDEs) using finite-element analysis (FEA) suitable for an undergraduate class? My recent experiences with COMSOL Multiphysics® show that it can be done. Such an approach not only gives the students an introduction to a new tool and new knowledge but also motivates them to master these concepts when they later study them in detail.<
It started with thermodynamics
Last year, along with a colleague, Dr. Eric Constans, I introduced the concept of “design-build-test” to my 1st-semester junior-level thermodynamics course and his mechanical design course. Student teams built steam engines and air compressors from scratch using raw metal stock. They discovered — through pistons seizing, for instance — that a major part of the task is keeping the cylinders and components cool. They tried various methods; one team even used a block of ice.
Keeping an engine running taught thermodynamics concepts, but students didn’t yet understand heat transfer effects. I decided to have the students design an air-cooled motorcycle engine block and then study it using modeling software. The cooling requirements of such an engine are not trivial and thus made for a challenging project.
The students worked with the following parameters of a Harley-Davidson engine.
Although finite element modeling is usually absent from undergraduate courses, I saw this as an opportunity to introduce them to a new skill, and even more as a way to help them understand the fundamental physics and practical applications of the PDEs they saw in their textbooks but never really embraced or even understood.
Students in this modeling project learned about temperature distribution in the engine block of a motorcycle.
For this project, the only choice of software for me was COMSOL Multiphysics. This software supplies an intuitive menu structure and graphics-driven user interface where the equations are clearly visible. In addition, it provides direct access to the underlying equations. This initial project would give them some experience working with PDEs. Then, when they later take a course in FEA, they will have a stronger motivation for paying attention to aspects such as boundary conditions or solvers that otherwise might seem somewhat arcane.
Here’s the way the project ran: The students first heard a 1-hour introduction to finite element analysis, after which they got a 1-hour introduction to COMSOL Multiphysics focusing on CAD import, manipulating PDEs, boundary and subdomain conditions, getting a mesh and a solution, and generating post-processing plots.
Next came a half-hour discussion of the project details: to design the engine block for a V-twin air-cooled motorcycle engine. The rough specifications for bore, stroke, vee angle, and block material came from a Harley-Davidson engine. The students were to design a block that would stay at a temperature lower than 350º C while cruising at 60 mph.
The students’ real work started with an analysis on paper of a simplified block design, making a first guess at the number of cooling fins, their geometries, and sizes. Then, using assumptions and hand calculations, they arrived at a rough answer for the heat generation and dissipation from the running engine.
Then they moved to actual design. They drew the engine block and its cooling fins in SolidWorks. After they created the 3D geometry, it was brought into COMSOL using the CAD Import Module.
The results at this stage were already interesting. Roughly half of the teams came up with conventional designs, while the other half let their imaginations run wild and put cooling fins in odd locations. For instance, one team placed huge fins across the cylinders. At times like this I would inject some manufacturing concerns, which sometimes meant they had to do a redesign.
“No risks, no gain”
With the CAD geometry imported into COMSOL, they could then set up the model and generate a plot of the block’s temperature. Some students used the Heat Transfer Module while others simply modeled the steady-state heat conduction equation (Laplace equation) using the Coefficient Form. Whether a conventional or unconventional design, in about half the cases the modeling results were within 10º C of the hand calculations. In fact, comparing the hand calculations to the model results not only made them comfortable with the model results but also drove home the important lesson of not putting blind trust in them.
In that regard, I believe that students can learn a great deal through their mistakes, or as I like to say, “no risks, no gain.” I wanted my students to have a chance to fail because with SolidWorks and the COMSOL Multiphysics live connection they can quickly reiterate a modified design.
One of my main goals was to make the students comfortable with PDEs so the next time they ran into one they wouldn’t be afraid to deal with it. With any other simulation tool except COMSOL Multiphysics this wouldn’t have been possible. They’d likely be working with the PDEs “blind” as if the tool were a black box, and they wouldn’t have direct access to the equations. It was also great that the students kept within the time plan—the teams spent roughly 15 hours on the project including the CAD design and model analysis. Almost universally, the feeling among the students is that “modeling is really cool!”
Comsol
www.comsol.com
Dr. Bhatia joined the faculty in Mechanical Engineering at Rowan University (Glassboro, NJ) as an assistant professor after completing his Ph.D. at the Pennsylvania State University (PSU). While working on clean energy at PSU, Dr. Bhatia also designed and developed alternative fuel vehicles. While at Rowan University, he has focused his efforts on direct methanol fuel cells and advanced powertrain vehicles.
Filed Under: Software • FEA, ENGINEERING SOFTWARE