This article discusses the growing trend among providers of computer-aided engineering analysis tools to market different types of analysis software packages, many of them integrated with computer-aided design packages and all of them accessible to engineers without special training. Common computer software tools offer speed and ease of use to designers who must make repetitive calculations. Engineers who use analysis programs nowadays use those programs to complement their CAD software. In other words, without design there is generally no need for analysis. The reasons engineers use CAD software are usually the same much like the reasons they turn to analysis software. Analysis reduces the number of prototypes necessary and further not only reduces development costs and but also shortens the design cycle. Additionally, such an analysis can decrease the time and cost of testing both virtual and actual prototypes. By decreasing testing and prototype time, the product gets to market quicker.
The growing trend among providers of computer-aided engineering analysis tools is to market different types of analysis software packages, many of them integrated with computer-aided design packages and all of them accessible to engineers without special training, according to Bruce Jenkins, executive vice president of Daratech, a Cambridge, Mass., CAE market research firm.
“The initiative in the analysis software provider community is to package modeling and analysis packages and make them easier to use by ordinary rank-and-file engineers,” he said. Traditionally, engineers specifically trained in finite element analysis ran studies on prototypes of the parts or products, Jenkins said. But with the relatively recent advent of easy-to-use software packages, mechanical engineers who perhaps haven’t been specifically trained in FEA handbook techniques can still perform fluid-flow, finite element, and thermal analysis, or many other kinds of calculations with the software’s help. And they carry out these analyses on virtual—that is, computer-generated—prototypes of the part or product before it’s produced.
Virtual prototyping and analysis software packages can shave an engineering firm’s production costs because companies don’t have to make as many prototypes or hire highly trained specialists. But they do have to determine the type of analysis software most needed and train engineers to use it. And the type of software that suits the engineering firm’s needs can change quickly, depending on the specific project, possibly requiring more than one software package.
The majority of analysis takes place among everyday design engineers struggling to validate or choose among different systems or components, according to Integrated Technologies Engineering, a Milford, Ohio, advanced materials testing firm that does research on new materials and develops software that analyzes process and test data. ITE has published a white paper on practical approaches to engineering analysis.
Common computer software tools offer speed and ease of use to designers who must make repetitive calculations. Some of the tools include MathCAD software from MathSoft in Cambridge, Mass.; DesignView software from Mentor Graphics in Boulder, Colo., and spreadsheet programs, such as Excel. These software programs feature documents into which users plug relevant numbers to get final results, according to ITE.
A Step Up
FEA, which solves simultaneous, algebraic equations, is one step up from this number-plugging approach. FEA lets engineers simulate a wide variety of physical phenomena, including laminar flow, turbulent flow, impact, and nonlinear geometric or material simulations. The variety of easy-to-use FEA tools now available to rank-and-file designers is the growing trend to which Jenkins referred.
The problem, Jenkins said, is that even with the new software, the accuracy of the analysis—an analysis of the stress across a part, for example—is dependent on how accurately the engineer has modeled the part and has applied the stress conditions during analysis. In other words, analysis results—even for simple spreadsheet analyses—are only as good as the decisions of the engineer who designed the part and who ran the analysis.
“That’s why expert knowledge, at some point in the process, is still usually required,” Jenkins said. “You have to know how to define the loads and the boundary conditions so the results are correct. You could arrive at convergence, but it could be that the numbers converge to the wrong conclusion.
“This has been the devil in the details with these analysis programs,” Jenkins added. “It’s easy to describe the model inaccurately, and that, of course, won’t yield accurate results, though they will look like accurate results.”
In answer to the problem—inaccurate results that seem to the user to be the correct answer— software vendors are now releasing simplified analysis programs that step the nonexpert user through a tightly defined series of actions, which help the user avoid inaccurate or faulty definitions of a problem. These software programs then step users through the analysis results to make sure they’re well understood, Jenkins said.
“Sure, there may be a stress point that shows up, but what should a designer do to remove the high stress? How should they move the design to ensure that it doesn’t go from too much stress to not enough stress?” he said. These basic analysis programs are intended to help with these questions.
What Analysis Does
According to ITE, engineers who use analysis programs nowadays use them to complement their CAD software. In other words, without design there is generally no need for analysis. The reasons engineers use CAD software are usually the same as the reasons they turn to analysis software.
One is to reduce costs in design and production. Analysis reduces the number of prototypes necessary and so reduces development costs and shortens the design cycle. Additionally, analysis can decrease the time and expense of testing both virtual and actual prototypes. By decreasing testing and prototype time, the product gets to market quicker.
Analysis can save on other costs associated with a product. According to ITE, analysis can reduce the number of components in a system because the computer can handle more iterations than are possible using physical prototypes, to assess combined parts and find ways to link parts effectively.
Analysis also can help produce a better product because it can improve a product’s performance by reducing weight, for example, or increasing durability. Fewer product failures can reduce warranty claims and lower warranty costs.
It Hits the Spot
Sandvik Mining and Construction in Turku, Finland, for example, makes hydraulic attachments for rock excavation, demolition, and recycling. It uses CAE software to analyze hammer parts, hammer housings, and pulverizer parts for its Rammer range of products. Engineers sought to reduce maintenance costs through machine design.
Rammer is a line of hydraulic hammers that break rocks and stone. The one-meter-long cylindrical piston of a large hammer is made of steel and weighs more than 200 kilograms (about 440 pounds). It strikes the work tool that bores into the ground at a velocity of 10 meters, or about 32 feet, per second.
Engineers had to perform software analysis in order to understand what happens to the piston and tool as a result of the high impact, said Eero Ojala, the Sandvik engineer who oversaw the analysis project.
Engineers wanted to find the degree of bending caused when the tool was driven at an inclined angle to the ground by the hammer. For analysis, Ojala and his team used Lusas software from Lusas Engineering Software Products of Surrey, England.
Engineers needed to model only half the piston, because it was symmetrical, Ojala said. They also ascribed material properties to the area that represented the ground the tool strikes to see how ground itself affected tool bend.
The software then automatically modeled the contact between the piston and the striking tool, which is one of the features of new software programs that Jenkins described as helping engineers find correct answers. In this case, the engineers didn’t have to model every aspect of the striking tool and the piston and then represent the contact made between these two tools. The software was able to find and simulate that contact based on numbers already provided.
Analysis results showed engineers that when the tool is thrust asymmetrically against the ground, the tool bends highly, in Ojala’s words. The bending is deflected back into the piston, causing that to bend as well. Engineers hadn’t expected the piston to bend as much as it did, Ojala said. Thanks to the analysis, they discovered it might be necessary to reduce operation of the hydraulic hammer on inclines. The analysis also showed the importance of supporting the piston with good bearings to avoid bending effects.
FEA for Everyone
Matthew Stein, owner of Stein Design in Truckee, Calif., said he has had considerable experience with traditional thermal and stress analysis, but discovered the benefits of using FEA after analyzing the complex parts of a flow meter at his firm.
“Since we’re a small consulting firm and don’t have a full-time analyst on staff we can’t afford to spend a lot of time and money on training to run a complicated FEA program,” he said. He chose to install a program called DesignSpace from ANSYS of Canonsburg, Pa. The software runs in tandem with his SolidWorks CAD software from SolidWorks of Concord, Mass.
Stein used the software when designing plastic modular flow meters for Renau Electronic Laboratories in Chatsworth, Calif. The meters are installed in commercial coffee makers, vending machines, and water filtration devices, and must be designed to withstand long-term pressures at near-boiling temperatures. If the plastic housing on the flow meter failed, it could cause a flood in an office or restaurant where the meters are used.
The project involved working with complex plastic injection-molded parts. Using handbook calculations would have been difficult, Stein said, and would have required the need for a lot of safety factors built into the design to compensate for potential inaccuracies in the calculations. In this case, the simulation analysis package was a necessary tool for analyzing the plastic parts, Stein said.
For acceptable high-temperature performance at a reasonable price, Stein chose to work with a 20 percent glass-filled polypropylene. His first analysis of the part as it was originally designed showed a maximum equivalent stress of 3,152 pounds per square inch at the housing’s bottom center. To meet Renau’s needs, however, he needed a stress factor of 1,800 psi.
To strengthen the part without adding greatly to its cost, Stein turned back to his CAD program. Thanks to the analysis simulation, he had an idea of what to do. He added ribs around the bottom of the housing and increased the radius of the inside cap. He ran the analysis again: His design changes had decreased maximum equivalent stress to 1,403 psi, he said.
Stein Design turned to its analysis software again when designing a prefiltration device for a water filter. Water filters sieve sediment and other impurities from drinking water. A prefilter is a 3-inch disc used in carbon-block drinking water filters.
Some customers, however, had experienced continued problems with cracked or burst prefilter housings made by The Water Safety Corp. of America in Sparks, Nev., which subsequently pulled from the market all of the models containing these prefilters.
Water Safety asked Stein Design to find a way to design prefilters so they didn’t crack or burst, Stein said. He made a number of design changes to a CAD model and then immediately ran an analysis of the changes to see if they were feasible. This is called “running a what-if scenario.”
The prefilters had been designed a decade ago on a drawing board by an engineer who used handbook stress-analysis techniques, Stein said. Because of welding compatibility with the main filter housing, Stein had only a limited choice of material. He chose to mold and test polycarbonate because of its strength and toughness, he said.
He thought the cracks that showed up previously in the prefilter might be reduced by use of polycarbonate, but while the cracks decreased during field tests, they were still present.
By running a series of analyses on designs and then changing the designs according to results, Stein was able to distribute stress more evenly across the cover. He added shallow ribs to the cover, for example, to improve the strength of what he found to be a high-stress zone. After a series of revisions, he was able to reduce the maximum stress in the inner slot edges where the cover meets the base from 12,948 psi on the first model to between 7,950 psi and 9,250 psi on his revised model.
“The software allowed me to come up with an acceptable solution to catastrophic failure problems, which we couldn’t solve with traditional analysis methods,” Stein said.
As the owner of a small engineering consulting firm, Stein was able to carry out this series of analyses using software he purchased himself and with minimal training costs, he said.
According to Jenkins, many small and midsize engineering firms can run analyses that weren’t possible even a decade ago, using new engineering software.