Name: Dipankar Ghosh, Ph.D. Company: VR&D, Inc. Session # (SIM085) Performing Design Optimization Using SDRC/I-DEAS and GENESIS Structural Analysis and Optimization Software by Dipankar Ghosh Christophe Charpentier Iku Kosaka An interface to couple SDRC/I-DEAS with GENESIS structural analysis and optimization software is presented. It allows users to create the finite element model as well as shape, sizing and topology optimization data from within the SDRC/I-DEAS environment. A number of I-DEAS windows can be used to facilitate the creation of design information. Once GENESIS has performed the optimization, users can post-process results. SDRC/I-DEAS can display the analysis and design such as the shape changes for shape optimization, and response values (volume fraction) for topology optimization.

Outline Introduction Objective GENESIS Structural Analysis and Optimization Software SDRC/I-DEAS GENESIS-SDRC/I-DEAS Interface Design Example GENESIS/I-DEAS interface allows I-DEAS’s users to quickly create analysis and optimization data required by the GENESIS structural analysis and optimization software. We briefly describe the usage of the interface. A brief introduction of both I-DEAS and GENESIS software is provided. We also provide an example to show how this interface is typically used for the preliminary and detailed designs. Topology optimization can be used to come up with the material layout during preliminary design stage. Once the preliminary design is over, the detailed shape and sizing optimization is performed.

Introduction Optimization technology is widely acknowledged in engineering, but not widely used Reasons: Difficulty in creating design data Lack of time to educate engineers to perform optimization Lately, there has been some pressure to reduce the “time-to-market” This is an opportunity for software developers like us, and provide easy to use design tools Although the importance of design optimization has been widely acknowledged in the engineering community, it is not yet widely used as a standard design tool for various reasons. Non-technical reasons include difficulty in creating design data and lack of time to educate engineers to perform optimization. Many engineers spend most of their time modifying and analyzing their designs and making iterative changes, rather than modifying designs using optimization technique. However, since there is enormous pressure to shorten the time-to-market while enhancing the quality of product at the same time, those attitudes are gradually changing, and/or are under pressure to be changed. It is an opportunity for software developers like us to keep refining the state- of-the-art of optimization technologies, and to provide easy to use, user- friendly optimization tools, so that engineers can turn their attention and curiosity to this technology.

Introduction Recent Efforts: FEMB (ETA) & Msc.Patran can be used as pre- and post processors for GENESIS Structural analysis and optimization Msc.Patran can be used with Msc.Construct to perform topology optimization HyperMesh (Altair Engineering) can be used with OptiStruct to perform topology optimization In recent years, efforts to provide a pre- and post processing design optimization capability, either as an add-on interface or as a built-in for CAE tools, have been expended by several vendors. FEMB from Engineering Technology Associates (ETA), and MSC.Patran from MSC Software can be used for pre- and post processing GENESIS analysis and optimization. Altair Engineering has expanded HyperMesh to supply design optimization pre- and post-processing capabilities to their product, OptiStruct. MSC.Patran also has been integrated with MSC.Nastran and MSC.Construct, a topology optimization software from MSC Software.

Objective Develop a unified design tool, including drafting, pre-post processing, for both analysis and design optimization using SDRC/I-DEAS and GENESIS Allow not only CAE designers but also CAD designers to modify their designs in a systematic manner Demonstrate the design process using the tools developed here The main objective of this development is to provide unified design tool, including drafting, pre- and post processing, for both analysis and design optimization, using SDRC/I-DEAS and GENESIS. It will allow not only CAE designers but also CAD designers to modify their designs in a systematic manner. Here we also demonstrate the design process for realistic design application problems using the tool developed. We will first briefly introduce the GENESIS and SDRC/I-DEAS programs, and then discuss how the interface program is integrated into the SDRC/I- DEAS environment. Then the capabilities of the interface are described along with a design application.

GENESIS Software GENESIS is a fully integrated structural analysis and design optimization software Created from the very beginning as a design software, as opposed to adding optimization to an analysis program Uses second generation approximation concepts and well established optimizers for faster convergence and efficient/robust performance GENESIS is a fully integrated structural analysis and optimization software. Unlike many other tools, GENESIS was designed from the very beginning as a design software. It uses second generation approximation concepts and well- established optimizers for faster convergence and efficient/robust performance in optimization process. GENESIS can simultaneously solve both member dimension (sizing) and coordinate location (shape) optimization problems and a wide range of options are available to define the design problem. For example, design variables may be individual member dimensions and/or grid locations, or may be linear or nonlinear combination of these. To create smooth variations in structural dimensions and shapes, a semi-automatic creation of basis vectors, DOMAIN, can be used. To simplify the task for designing frame or plate structures, a library of common elements is available. In addition to that, users can provide their own subroutine to calculate bar section properties as functions of the design variables or they can use “synthetic” functions to define the section properties at run time.

GENESIS Software Analysis: Design optimization: finite element method (FEM) static, normal modes, direct and modal frequency analysis, heat transfer, and system buckling Design optimization: Shape, sizing and topology optimization Structural analysis in GENESIS is based on finite element method. It supports static, normal modes, direct and modal frequency analysis, heat transfer, and system buckling calculations. GENESIS can simultaneously solve both member dimension (sizing) and coordinate location (shape) optimization problems and a wide range of options are available to define the design problem. GENESIS also could be used to perform topology optimization. Topology optimization is generally used in the preliminary design stage to come up with optimal material layout. Topology optimization in GENESIS is performed separately from shape/sizing optimization. The results obtained from topology optimization is generally refined using shape/sizing optimization.

GENESIS Software Typically requires < 10 detailed FEAs, even for large and complex design tasks No special knowledge of optimization technology is required! Input data deck is similar to NASTRAN data deck NASTRAN deck is easily converted to GENESIS deck, and then solve it using GENESIS Shape and sizing optimization in GENESIS normally requires less than 10 detailed finite element analyses even for large and complex designs. Users do not need to have any special knowledge of optimization to use optimization capabilities in GENESIS. The GENESIS data deck is very similar to NASTRAN data deck, and hence it could be created using many commercially available pre- and post processors. VR&D’s nas2gen software could also be used to convert NASTRAN deck automatically to GENESIS deck, and then solve the problem using GENESIS.

GENESIS Software Special Features: To create smooth variations of structural dimensions and shapes, semi-automatic DOMAIN elements are used Use topology optimization (material layout) for preliminary design, and refine it later using shape and sizing optimization BIGDOT Optimizer - allows 1000s of design variables GENESIS offers many unique features. To create smooth variations of structural dimensions and shapes, basic vectors can be created using DOMAIN elements. Topology optimization can be used for preliminary design to better utilize the material space. Topology optimization generally involves 10,000s of design variables, and this can be handled by using the V&RD BIGDOT optimizer. BIGDOT is a new optimizer that is now available within GENESIS.

SDRC/I-DEAS Computer-aided design tool Drafting, analysis and optimization Analysis options: linear statics, normal mode, constrained mode dynamics, buckling, heat transfer, potential flow, and nonlinear statics Only linear statics and normal mode analyses can be used in optimization. SDRC/I-DEAS is a very comprehensive computer aided design tool, including drafting, analysis (simulation), and optimization capabilities. Its drafting capabilities are especially powerful, allowing users to design complicated models in a flexible way. Available analysis options are linear statics, normal mode, constrained mode dynamics, buckling, heat transfer, potential flow, and nonlinear statics, and yet only linear statics and normal mode analyses can be used in optimization.

SDRC/I-DEAS Optimization can be performed using CAD parameters Still optimization is limited to entry level optimization Limited responses Only shape and sizing optimization No topology optimization The present development is intended to cover optimization, both entry level and high end capabilities Although several design optimization options are built into I-DEAS, applicable applications are limited to entry level optimization problems. One attractive optimization capability in I-DEAS is that users can directly optimize CAD parameters as design variables. However, since optimization problem size, usable analysis options and available responses are limited, a wide range of optimization problem cannot be performed. The present development is to provide an interface to link powerful CAD and robust optimization packages so that from entry to expert level design optimization problems can be solved in an unified fashion.

Interface Details GENESIS and I-DEAS are stand alone programs Make use of Open I-DEAS Interface can access FEM data and pre- and post processing capabilities of I-DEAS GENESIS specific data is stored in I-DEAS’s database Since both GENESIS and I-DEAS are stand alone programs, and are not developed in the same environment, a well organized program architecture should be made in advance. One of the key issues is how the interface program can access the FEM data and pre-processing capabilities of I-DEAS. Fortunately, these essential functions can be provided by I-DEAS’s open architecture, also known as Open I-DEAS, which allows a third party program to access its database, and to use its graphical tools. Through Open I-DEAS, the program collects information from graphics, puts information into graphics, accesses the database, and creates GENESIS design data as if these functions are just like other I-DEAS’s functions.

Interface Details The interface’s main dialog box is launched from the User Application Launcher, which allows a third party program to run, and each interface function is executed from the icon in the dialog box that is independent of the I-DEAS’s icon panel. The main dialog box for the interface is shown here. The common functionality such as creating design variables, tables, and equations are accessed from relevant functions on the main dialog.

Overall Methodology Steps: Start with a design space, perform topology optimization to come up with optimal design space Interpret the topology results, create the FEA model for shape/sizing optimization perform shape/sizing optimization with detailed design specifications The overall design strategy generally involves (1) starting with a material design space, perform topology optimization to come up with an optimal distribution of the material, (2) Interpret the topology optimization results, and create the finite element model for shape and sizing optimization, and (3) perform shape/sizing optimization with detailed design specifications.

Design Example Topology Optimization A bracket used to attach a strut to a rail Minimize global strain energy subject to material constraint Mass fraction Retain 30%, 50%, 70% mass A bracket used to attach a strut to a rail is designed using the tools described above. To solve this problem, two independent design optimization problems were defined and solved in sequence. First, we specified the potentially designable space and used topology optimization with a specified amount of material. Then the obtained results were interpreted and CAD (lines and surfaces) data as well as an initial FE model for shape design were created. Finally, shape optimization problem was used with detailed design specifications.

Design Example Create topology data During the topology optimization, a certain amount of material will be removed from the material design space. In this first phase, we focused on obtaining an efficient structure to carry the primary load . The above figure shows all of the topology optimization dialogs to specify the GENESIS topology data. The main topology dialog (titled Topology) appears after pressing the “Topology…” button on the main dialog. This has a snapshot of currently defined topology design data, and allows access dialogs for data creation or modification. As one can see, the design goal was placed on minimizing global strain energy subjected to material constraint. This problem was solved for three different values for the material constraint, namely 30%, 50%, and 70%. Like any other GENESIS data, topology optimization data can also be created manually. Topology optimization requires about 10 lines of additional data.

Design Example Topology results 70% material 30% material 50% material Topology optimization results can be difficult to interpret since they often contain zigzag borders and/or some degree of gray zone. To overcome these problems, and to help designer interpret the solution easier, GENESIS version 6.0 provides the iso-density surface, which will visualize the 3-D structures as smooth FE surfaces. The above figures show the topology design solutions using iso-density surface for each material constraint case. Although the first two solutions (30% and 50%) and the third solution (70%) are topologically different, tendencies are very similar. The main difference is the size of the cut out hole, thus the first two cases developed an open hole and the third case developed a closed hole. Therefore, the conservative design (the third case) was chosen as an initial candidate design for shape optimization, and CAD (lines and surfaces) data was created based on this solution. Since we can incorporate the potentially removable material location from the topology solutions, relatively simple initial design is created and meshed.

Design Example Topology results Isometric View Front View Side View Candidate design for shape and sizing optimization Generate CAD (lines and surfaces) Create FEA model for shape/sizing optimization Isometric View Front View Side View

Design Example Topology results Took out about 30% of the material Structural performance was not degraded much All three topology runs (30%, 50% and 70%) converged in 20-25 design cycles, and showed very interesting trends. The structural responses of the full solid (100% material) model and of the optimized (with 70% material constraint) model are summarized to compare performance. Although the topology optimization took out 30% of the material, the structural performance was not degraded very much. Therefore, we can conclude that most of the unnecessary material was removed from designable space.

Design Example Realization of topology optimization Isometric View Using the topology optimization results, the finite element model for shape optimization is created. Isometric View Front View Side View

Design Example Shape and Sizing Optimization More detailed and complete design Multiple load cases Point load Natural frequency Objective function: mass (minimize) Constraints: Von Mises stress < 200 MPa Fundamental frequency > 850 Hz During topology optimization, we considered preliminary design solutions using simplified criteria. Here, we will focus on more a detailed and complete design problem. Two important loading conditions are considered to design this bracket. In the first load case, 15000N of the point load (same as the topology design problem) was applied to simulate force through an object attached to the bracket. The second load case calculates natural frequencies to control vibration or vibration noise. For topology we considered only the point load case and intentionally left out the frequency load case. We could have considered both load cases, if we wanted to. To improve the initial design, the following optimization problem is formulated: Minimize Mass Subject to Von Mises Stress < 200MPa Fundamental frequency > 850Hz

Design Example Shape Optimization DOMAINs QUAD4 and TRIA3 Domains with Shape changes considered here are for two locations suggested by the topology design results, and are shown in the above figures. The first figure shows the HEXA DOMAIN, and perturbation vectors that are governed by four independent design variables and the second figure shows five QUAD4 DOMAINs and four TRIA3 DOMAINs, and the perturbation vectors which are also governed by four independent design variables. QUAD4 and TRIA3 Domains with DVGRIDCs HEXA Domain with DVGRIDCs

Design Example Perturbation (DVGRIDC) vectors are governed by 8 design variables Here we show the eight independent design variables and their bounds. The perturbation vectors (DVGRIDCs data) are governed by these design variables.

Design Example Create DOMAINs All the shape optimization data can also be created using the interface, like the way we did it for topology optimization. The dialogs to create the DOMAIN are shown here. First you create a DOMAIN of a specific type (HEXA, QUAD4, TRIA3 etc.), and then include a number of nodes in it. Corner nodes can be specific either manually, and/or could be picked directly from the model using your mouse. Once the corner nodes have been specified/picked, the internal nodes can be selected again automatically. Typically you will allow the interface to include all the internal nodes automatically, and then deselect any node(s), that you do not want to include in your domain.

Design Example Create DVGRIDCs Once the DOMAIN(s) have been created, you will need to specify the perturbation vectors or basis vectors (DVGRIDC data). Perturbation vectors can be specified on any grid location that belongs to a DOMAIN element. The DVGRIDC data are used internally to automatically create the DVGRID data for all the DOMAIN grids. The automation generation is based on isoparametric interpolation functions.

Design Example Shape optimization results design variables reached the side constraint values Further weight reduction is possible While expanding bounds, make sure mesh is not distorted Topology results were used to create the initial finite element model for the shape design. As one can see, the response values between the final solution of topology model and the initial shape design model are remarkably similar. The results for the shape optimization are shown here. We see that the objective function (mass) was further reduced by 7.8% (from 15.89 Kg to 14.65 Kg). None of the constraints were violated. The fact that all the design variables reached to the side constraint bounds indicates that further weight reduction may be possible by choosing the larger side constraint bounds. In this shape optimization problem, side constraint bounds are determined by the DOMAIN size to avoid the mesh distortion, thus, the larger DOMAIN and more transitional DOMAINs will be required to be able to expand them.

Design Example Shape optimization results Initial design for shape Final design for shape optimization

Conclusions A tool to interface GENESIS with I-DEAS has been presented I-DEAS users now have access to GENESIS analysis and optimization capabilities Users can perform a wide range of structural optimizations using these tools A tool to interface GENESIS with SDRC/I-DEAS is presented, and is explained with a design example. This interface provides the capability to create design optimization data for GENESIS with SDRC/I-DEAS, and allows the users to perform a wide range of structural optimizations using these tools. The results show the advantages that can be obtained using these tools developed here.