Modal Based Optimization of TAPS Using OptiStruct Yogesh Jaju Sr. Manager CAE Dana India Technical Centre Pvt. Ltd 501 Pride Silicon Plaza Pune 411016 India Ulhas Patil Sr. Project Engineer - CAE Dana India Technical Centre Pvt. Ltd 501 Pride Silicon Plaza Pune 411016 India Abbreviations: NVH, TAPS, FEA, CAE Keywords: Stress, Frequency, Optimization, Modal analysis, Harmonic analysis Abstract In this paper, we present a methodology to reduce the design cycle time for optimization of thermal acoustical protective shields (TAPS). In the current design process, the amount of turnaround time is either developing a new design or a proposal design to fix the failure of existing TAPS design due to high stresses, was the major concern due to the manual iterative process that was followed. To reduce the turnaround time, topography optimization feature in OptiStruct has been successfully used to minimize the stresses in the TAPS and at the same time, maximize its natural frequency within given constraints. Introduction TAPS (thermal acoustical protective shields) is a highly functional engine component composed of various layers, each with a specific function to perform. These shields protect surrounding components like wiring harnesses, sensors, fuel pipes, etc., from extreme temperatures; suppress noise and lower overall mass with the use of thinner materials, leading to improved fuel economy. TAPS is an important aspect of the overall vehicle development process. It involves optimizing the exhaust system routing and designing to protect various components that are in near proximity. Features and Benefits 1. Three-layer construction 2. Insulating/damping center layer (Exceptional thermal performance, NVH improvements reduce surface noise) 3. Fully hemmed edges (Eliminate sharp edges, increasing worker safety, Eliminate vibrations associated with un-hemmed edges) 4. Low-mass designs (High damping factor allows thinner metal selection) The main objective of this study was to develop a methodology using the modal based frequency/stress optimization available in OptiStruct to reduce the design and development cycle time of TAPS. Simulation Driven Innovation 1
Current Process The current CAE process of either a new TAPS design or fixing an issue with an existing design involved 2 different analyses, which were carried out repeatedly with each geometry change (iteration) until the design targets were met. Geometry changes made in a standard CAD software were evaluated for each new iterations on the TAPS through the two sets of analyses mentioned below, which was fully manual and hence, extremely time consuming. As such, the turnaround time for either new TAPS development or fixing a test/field issue was very high and therefore, it was imperative to explore the optimization features available in OptiStruct to improve the CAE process efficiency. Modal Analysis - to extract the Eigen frequencies and mode shapes. Harmonic Analysis - to find out stresses induced by applying acceleration at extracted resonant frequencies The whole cycle could sometimes take as high as 20 days to provide the CAE driven TAPS design solution! New optimization process (using OptiStruct) As a part of the optimization process, following steps were followed to get an optimized shape of TAPS: 1. Create two collectors to separate the TAPS geometry in two different parts such as Design Space (area available for optimization) and Non-Design space (area which is not available for optimization considering manufacturability, space, packaging constraints, etc.). 2. Define properties and materials. 3. Define boundary conditions. 4. Set up the Modal frequency analysis to evaluate resulting stresses. 5. Apply the Parameters to perform topography optimization such as design variable, response, design constraints, and objective. 6. Run the modal based optimization analysis by selecting OptiStruct as the solver After running the optimization analysis with all above mentioned parameters, we extracted the output of optimization analysis in the form of an interim design, which was subsequently analyzed separately in Abaqus to get interim modal and harmonic FEA results for validation/comparison purpose. Once the interim design model CAE results were available and found to be within the desired range, then the next step was to fine tune the interim design of TAPS (using any standard CAD package) considering all practical constraints such as formability, packaging, assembly, mounting, etc., These steps are shown below in figure 1. Modal and harmonic analysis of the fine tuned model were re-performed to ensure that the necessary frequencies and stress levels of optimized TAPS design are still within the desired range. Simulation Driven Innovation 2
Figure 1: Typical input and output of Topography Optimization using OptiStruct Results & Discussions One of the actual TAPS design is shown below to illustrate the usage of the developed optimization method. The main objective of this analysis was to reduce the von-mises stress on TAPS below 150 MPa induced by applying acceleration in Z direction on extracted first eigen frequency. Optimization method developed in OptiStruct was successfully used to achieve the desired results. Results of the fine tuned design were validated with independent Abaqus results. The comparison of results obtained using manual and optimized methods is shown in figures 2 & 3 below. Simulation Driven Innovation 3
Figure 2: Results of manual method (iterative) to achieve TAPS targets Simulation Driven Innovation 4
Figure 3: Results using optimization method to achieve TAPS targets The total CAE driven TAPS development time in this method is about 5-7 days, which is a significant improvement compared to the manual method! Simulation Driven Innovation 5
The flow chart shown in figure 4 below provides a detailed comparison between the two methods. Figure 4: Comparison of manual and developed optimization methods Benefits Some of the key benefits of the developed process are: 1. Significant reduction in the turnaround time for development of new or failed TAPS designs. 2. The process of making manual changes in current method to iteratively achieve desired targets is mostly eliminated in the developed optimized method. 3. Manual intervention is necessary only during fine tuning of the interim design 4. Chances of manual subjectivity are minimized once the set process is followed Simulation Driven Innovation 6
Challenges Some of the key challenges that are involved in such projects are as under: Future Plans 1. Accurate definition of design and non-design areas. 2. Correct interpretation of the interim design shape that is the outcome of the optimization analysis. 3. Experience and knowledge of the designer in incorporating optimized shape in the actual design taking into account all practical constraints as described earlier. We would like to continue to deploy the developed method for TAPS for all future work and further enhance the method as we gain more and more experience using it. Conclusions Developed method in OptiStruct is quite successful in significantly reducing the turnaround time for TAPS development. The interim design provides considerable insight into the necessary design changes that are required to achieve design targets. These coupled with engineering judgment and knowledge of the product itself will help use the method optimally in all future work on TAPS. ACKNOWLEDGEMENTS The authors would like to thank Mr. Prashant Bhat, Technical Manager, Altair India (Pune) for his patient coaching to us throughout this study and for offering valuable tips on the usage of OptiStruct. REFERENCES [1] Shielding Systems from Power Technologies Group," www.dana.com Simulation Driven Innovation 7