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Optimization of a Test Rig Platform

Mechanical Solutions Incorporated designed a platform for testing axial fans at different speeds. The platform was designed to avoid any natural frequencies within the test speed range of the fans. A number of design iterations were required until a design was proposed that could satisfy the frequency criteria (safety margin from major excitation sources) without creating an excessively large and heavy structure.

Figure 1: Example of an Optimized Linkage Part Using GTAM Software

Mechanical Solutions approached CAE Associates to ask if we could develop a methodology that would allow them to come up with a lighter-weight design with less time and effort.  CAE Associates proposed a method that uses the Genesis Topological Optimization for ANSYS Mechanical (GTAM) software developed by Vanderplaats, Inc.  This is an ACT extension within Mechanical that provides an easy-to-use interface and connection to the Genesis topological optimization software. The user sets up a finite element model starting with material properties, loads, boundary conditions, and simplified geometry. The optimization routine carves away material to obtain objectives while satisfying a set of user-specified constraint conditions. The GTAM interface provides menus for defining design regions, constraints, and objectives, for running the optimization software, and for post-process the optimized solution. Optimized geometry can then be exported in STL format for further geometry development, or even 3D printing.  An example of a linkage part optimized to minimize weight is shown in Figure 1. The starting geometry is a simple domain of material with the features needed for applying loads and constraints.  The optimized shape is the optimized topology that minimizes weight while satisfying stress limits. The final geometry is based on the optimized shape but recreated in a form that can be dimensioned and machined.

Figure 2: Optimized Test Rig Platform

CAE Associates started with a solid block of material representing the geometric boundaries of the test rig platform (top left image in Figure 2). All external rigid bodies, point masses, and constraints were assigned. The topological optimization was set up to minimize the mass fraction while limiting the natural frequencies of the lowest modes to values greater than the lowest frequencies of the current design. The optimized solution is shown in the center of the Figure 2 (Optimized Shape). From this solution, the geometry was reconstructed using beams and shells (Final Geometry, Figure 2). The total weight of this design was 22% lighter than their original design and required considerably less design effort. This methodology was presented to Mechanical Solutions as an effective way to reduce weight, cost, and design time for their test platforms and for other parts they design.

"In order to meet the weight and structural natural frequency constraints, CAE Associates provided an efficient tool which streamlined the design of a specialized testing platform, saving the company time and money over manually iterating the design and analysis process." - Vlad Skidelsky, Mechanical Solutions, Inc.