Optimize Designs Efficiently

By Memo Romero

Today, the vast majority of design engineers appreciates the value of FEA (finiteelement analysis). Few use such tools regularly, and still fewer have integratedFEA into the their daily design methodology. With so many products available,many of which are fully integrated with state-of-the-art MCAD packages, it seemsunlikely that any real design would escape stress, thermal, or dynamic simulationsomewhere between conceptualization and production. Indeed, FEA tools have becomeso powerful, fast, and user friendly that they are being used much more than theywere even a few years ago.

Yet it is also true that in bowing to design cycle time pressures, many engineersforego the use of FEA and rely on hand calculations and experience for criticaldesign decisions. For many companies, particularly small to mid-sized, there isstill the question of what the tool buys an engineer versus the cost, time, andeffort to use it. Justifying that the tools are in fact necessary or valuableremains an ongoing challenge. Enter PlassoTech’s 3G.author. This relatively newproduct takes significant steps in addressing these and other FEA usage concerns.A streamlined and intelligent MCAD importation process ensures that all geometryis captured and used properly, making even complex assemblies truly painless.Its robust mesher and fast solver use both adaptive h- and p- methods, easilyhandling disparate geometries in the same model. Efficient design optimization,arguably the holy grail of using numerical methods, is 3G.author’s most salientcapability.

It has a quick learning curve, allowing just about any design engineer to seefor herself the power of FEA. MCAD Interface Integration with preeminent MCADsoftware has become a must for FEA tools. Fading are the days of exporting 3Dgeometry in formats such as IGES, STEP, and STL, and re-importing them into asimulation tool, losing all associativity in the process. Similarly, model simplification,such as eliminating fillets and small features, is becoming less and less necessary.3G.author’s capability of seamlessly importing MCAD assemblies from Autodesk Inventor,Pro/Engineer, Solid Edge, and SolidWorks, while not unique, is remarkably simpleand efficient. It is as simple as locating the assembly file and creating a projectname. Appropriate folders, subfolders, and files are instantly created to managemultiple simulations with the same core geometry. Additionally, intelligence isbuilt into the importation process so as to maintain the ability to parameterizegeometric dimensions, and lay the foundation for optimization. If the MCAD geometryhas changed, 3G.author has the ability to easily clone the model, maintainingall material property assignments and simulation setups, known as “function studies.“An example of a SolidWorks imported assembly is shown in Figure 1 (below).

Figure 1: 3G.author’s MCAD interface

Any of the sketch or feature dimensions shown can be set aside for parameteroptimization. Robust Meshing and Fast Solving 3G.author has its meshing so wellintegrated in the tool that by default a user need not perform meshing as a separatestep. Materials are assigned, boundary conditions are placed, and the problemis then simulated. Behind the scenes, a tetrahedral mesh is automatically createdusing default settings, which works well for the vast majority of problems. Theartwork at the top of the opening page (28) illustrates a meshed example of asmall semiconductor package with complex wirebonds. Should the geometry proveproblematic (usually the result of the 3D modeling tool), 3G.author has sophisticateddiagnostics, such as local mesh control and advanced mesh settings to remedy anygeometry or mesh problems. In terms of speed, 3G.author has ample horsepower.To illustrate, a static linear thermal model containing 44,789 elements and 71,835nodes was solved on a 2.4GHz Pentium IV machine with 1GB of RAM. After the problemwas defined, the total mesh and solve time was 58 seconds. With this kind of speedan engineer can analyze dozens of combinations during lunch. Design OptimizationOptimization is perhaps 3G.author’s strongest capability. In contrast to othertools, these features are an inherent part of the software, clearly in the mindsof the developers from the beginning.

Figure 2: This basic assembly depicts two devices to illustrate parameter optimization.

These features are available even in the basic package; there is no need to purchasethis as an added capability. For engineers looking to design real products andsystems, an efficient method of optimizing either materials or geometric parametersis a necessity. Cumbersome methods and approaches are quickly relegated to occasionalusage or forgotten altogether. 3G.author provides a straightforward means of selectingparameters of interest, assigning a range of values, and intelligently simulatingthe resulting permutations to arrive at an optimal design. How this process workscan be illustrated with a simple example. In the semiconductor industry a constantproblem is reducing operating temperatures of devices, whether a CPU chip or apower transistor. The designer must intelligently place these devices on a circuitsubstrate (often with heat spreading metal layers) to minimize thermal resistance,while optimizing the design for cost, size, reliability, etc. Figure 2 (above)depicts a simple assembly containing two devices where the designer has flexibilityin the distance between devices and the heat spreader thickness. Variations inboth of these parameters will affect the maximum device temperature, as well asthe cost and size of the product.

Figure 3: Geometric parameter optimization is simple using the available table.

Thus, a useful simulation strategy is one that allows for efficient simulationof the various dimensional configurations. It is simple to select the two parametersand place them (with a right mouse click) in a design optimization table (seeFigure 3, above). Specifying a range of acceptable values for each parameter isstraightforward, and the resulting simulation sets are automatically created.Either an exhaustive full factorial set or a “smart set” of runs can be solved.A smart set captures extreme conditions and helps conserve disk space and reducesimulation time. In our test, the right combination of device spacing and heatspreader thickness was quickly determined. Learning Curve It is often the casethat the most powerful tools also have the steepest learning curves, taking manyhours of dedicated effort to achieve a return on investment. 3G.author bucks thistrend by focusing on the core elements of finite element analysis; i.e., geometry,materials, and boundary conditions. Things are laid out simply and menus are keptshort. Only seven toolbars are needed to capture the full array of features. Whilethe tool may not be difficult to master, there is plenty of advanced capabilitybuilt in, and designers can rest assured that 3G.author will analyze even themost complex problems effectively.

Memo Romero is a design and analysis consultant in Phoenix, AZ. Send your comments to Memoc/o Desktop Engineering Feedback.

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