Visualization of ABAQUS Finite Element Analysis Results using 3D-Rendering Software

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1 Visualization of ABAQUS Finite Element Analysis Results using 3D-Rendering Software Sandro Gämperle and Robert Eberlein Sulzer Innotec, Sulzer Markets and Technology AG P.O.Box, CH-8401 Winterthur, Switzerland Abstract: Numerical simulation (esp. FE-Analysis) becomes more and more common in research and development. Over just a few decades it evolved from a highly specialized application with lots of cpu power consummation to a widely used engineer s standard tool. The evaluation of simulation results is normally done with internal post processors which are capable to represent data with fundamental visualization techniques only. These post processors are mostly limited in their functionality to represent data. What s more, up to now FE-Analyses are a mere tool for research and development engineers-often there is no further use of the data created. Due to its extensive animation and visualization functionality, 3D-rendering software allows a higher quality in representing the data created by FE-Analyses. This in turn simplifies the access to the data for engineers as well as for laymen. The output of such rendering software is a rendered image or animation which can be integrated into almost any kind of document which makes the procedure very customer-friendly. Thus, these images resp. animations can be used for marketing purposes as well (exhibitions, leaflets, customer contact, etc.). An implementation of such a proceeding is exemplarily shown by a representative example of Sulzer Innotec. Data created by an FE-Analysis in ABAQUS is converted and then imported into rendering software. Once loaded into this software, the extended visualization functionality is being used to visualize the data. It is intended to show the differences between a representation in a common post-processor (like ABAQUS/Viewer) and a visualization realized with the help of 3Drendering software ABAQUS Users Conference 1

2 1. Introduction The interpretation of FE-Analyses is normally done with interactive postprocessors that are able to produce three-dimensional representations of the results in form of contour plots, deformed geometry plots, XY plots, etc. Although there are several possibilities to represent data with these postprocessors, the visualization functionality and therefore the quality of the three-dimensional representations is often limited and lacks the high quality level which can be achieved with 3D-rendering software. These software packages are normally used in broadcast, video and product design and offer extensive animation and visualization functionality. In many cases, the capabilities of FE-postprocessors well meet the requirements of a standard FEanalysis task. In other cases, an improved image quality is an advantage in terms of accessibility and insight into the data. Such cases could be customer contact, illustrations in leaflets and technical reports or exhibitions. A general concept to represent analysis data using 3D-rendering software is therefore consecutively presented. Additionally, the concept is verified at an example that was implemented at Sulzer Innotec in cooperation with Centerpulse AG and was part of a project to build a numerical simulation model of the human lumbar spine ABAQUS Users Conference

3 2. Concept Generally, an FE-Analysis is divided into several steps. The first step is normally to read the input data (CAD model, material data, etc.) into a preprocessor where the modeling and FE-meshing is done. The FE-model is then read into a solver where the actual FE-Analysis takes place. As a next step, the analysis results are imported into a postprocessor, to provide a better accessibility to the numerical data. Figure 1. Flowchart of typical FE-Analysis The output of such a postprocessor is a 3D-representation of the FE-model which can interactively be rotated, panned and zoomed by the user. The representation possibilities vary from deformed plots over contour plots to XY-plots. This form of data representation is valuable and necessary for evaluating and discussing the numerical results obtained by the FE-Analysis among engineers in a project team. Still, the data provided by postprocessors is not always easy to understand for external people who are not directly involved in a particular project. Additionally, it would be very cost effective to make further use of the data provided by the FE-Analysis, since only the post-processing step must be altered. The idea is to process the data not only with a FE-postprocessor but also with 3D-rendering software. The extended animation and rendering functionality of such software allows producing high quality (rendered) still images and animations which can be used externally for marketing purposes like customer contact, leaflets and exhibitions ABAQUS Users Conference 3

4 Within the scope of this paper, a possible solution strategy from step 1 import data to step 4 visualize results is given. Since the data interfaces between the steps strongly depend on the utilized software, the solution presented is not a general but rather a particular solution based on the software infrastructure of Sulzer Innotec. But since the general concept remains the same, it should be simple to adapt all the various steps to different software infrastructures. Figure 2 shows an extended flow chart and the software infrastructure that was available to realize the following example. Figure 2. Flowchart of updated FE-Analysis ABAQUS Users Conference

5 3. Comparison Postprocessor vs. 3D-Renderer There are several 3D-rendering packages available on the market. The functionality of most of them is sufficient for the purpose of post processing FE-data. They only differ from each other in terms of highly specialized features and accordingly pricing. To verify the concept described above, the 3D-rendering software 3dsmax from discreet has been chosen. There are several reasons for this decision. First of all, the first author had been able to gather profound experience with this software before and secondly, it is a good choice regarding the ratio functionality versus price. The software offers a huge number of features to render and animate whole virtual worlds in which one can embed any desired three dimensional objects or FE-Models. It would take too long to discuss all its features here and therefore, the following comparison chart gives a brief overview over the main differences between a FE-postprocessor and a 3D-rendering software in general and ABAQUS/Viewer and 3dsmax in particular. Table 1. Comparison Chart ABAQUS/Viewer 3dsmax. Postprocessor: ABAQUS/Viewer 3D-Rendering Software: dicreet 3dsmax Realtime/Interactive! # Import of ABAQUS/Solver Data! # High Quality Rendering #! Keyframe Animation #! Advanced Lighting #! Polygonal Modeling Tools* #! Special Effects** #! Embed FE-Model in "Virtual World" #! Generate Still Images!! Generate Movies limited! * to create and modify polygonal objects/fe-models ** effects like: depth of field, motion blur, camera blur, glow and flare 2003 ABAQUS Users Conference 5

6 It can easily be seen that 3dsmax offers more extensive features for creating high quality render images and animations. The software allows creating sceneries by combining any desired objects into a virtual world. FE-models can then be imported into these sceneries. Although it is possible to create high quality images/movies with 3dsmax, they can t be generated in real-time. They have to be calculated rendered by the software in advance. At first sight, this seems like a drawback in comparison to ABAQUS/Viewer which gives the user an interactive, real-time data view. But the purpose of post processing FE-data with 3D-rendering software is the generation of images and animations to incorporate them for example into customer presentations, leaflets, exhibitions, etc. Therefore they do not need to be generated in real-time but they more importantly do have to have the highest image quality that is possible. Another point is the import of data created by ABAQUS into 3dsmax. 3dsmax is as every other 3D-rendering software available on the market - not able to interpret.odb and.fil file formats created by ABAQUS solver. Therefore, a file format exchange has to be done. Beside the native formats.max and.3ds, 3dsmax is able to import several file formats such as AutoCAD (.dxf), IGES (.igs), StereoLitho (.stl) and VRML (.wrl). Among these, the VRML file format is chosen because it is not a proprietary but rather an open 3D interchange format and which is widely known and used. To convert.fil files to.wrl files, sight3ds from immersivesim is used which is a customized version of aba2vrml that is available from immersivesim as well. By setting parameters in this command line software, several options can be set such as step and increment number, fringe plot output and fringe plot range. 4. Example The example used to verify the concept discussed above is a FE-model of an individual human lumbar spine. It consists of the segments L2-S1 including intervertebral discs and ligaments. For a detailed account on soft tissue modeling in the human lumbar spine, refer to (Eberlein, 2000). MSC Patran is used to create the FE-model. Subsequently, ABAQUS is employed to solve the FEproblem. Post processing is done with ABAQUS/Viewer on one hand and on the other hand with the 3D-rendering software 3dsmax from discreet. The FE-model of the human lumbar spine is loaded by flexion and extension within the physiological limits at the top of the L2 vertebra, whereas the lower end of the sacrum is fixed. This setup corresponds to experimental tests carried out on the same individual at Centerpulse AG. The numerical results are validated with respect to the experimental findings which are of minor interest here ABAQUS Users Conference

7 5. Visualization 5.1 Visualization with ABAQUS/Viewer The following pictures illustrate post processing with ABAQUS/Viewer. Fig. 3 and Fig 4 show an extension resp. a flexion of the lower spine. The contour plot shown visualizes the displacement magnitude and the deformation scale factor is 1. Figure 3. Extension of lumbar spine Figure 4. Flexion of lumbar spine 2003 ABAQUS Users Conference 7

8 5.2 Visualization with 3dsmax To better visualize the location of the FE-model of the lower spine in the human body, an animation is done with 3dsmax that starts with a view of a human chest and then zooms in to show the FE-model within the context of the human body. The camera rotates around the chest and moves downwards at the same time. Arriving at the hip, the camera downward movement stops and the viewer can see the blue colored FE-model. During an additional 360 turn around the model, everything except the FE-model is gradually faded out. Following that, the camera movement stops and the deformation of the FE-model is shown. The lower spine structure performs a flexion and an extension movement subject to the loading conditions acting on the model. A contour plot visualizes the displacement magnitude. Figure 5. Visualization of a human chest and lumbar spine (blue) ABAQUS Users Conference

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10 Figure 6. Animation of lumbar spine done with 3dsmax This animation is just an example and illustrates how the post processing of FE-data can be further enhanced by using 3D-rendering software. Virtually every kind of scenario can be realized with these software packages. 6. Conclusion 3D-software packages normally used in film, broadcast and internet media can further extend and complement post processing capabilities of FE-post processors like ABAQUS/Viewer. By post processing FE results with 3D rendering software, these results can be used for marketing purposes as well. The lumbar spine shown here is just an example of what is possible to achieve with 3D rendering software and serves as a verification example for the several steps that are necessary from numerical FE data to a visualization of that data. In the future, more examples will be created and the steps will be further improved. In general, Sulzer Innotec is capable to provide enhanced FE post-processing based on 3D rendering technology according to customer demand ABAQUS Users Conference

11 7. References 1. Eberlein, R., Holzapfel, G.A. and Schulze-Bauer, C.A.J. An Anisotropic Model for Annulus Tissue and Enhanced Finite Element Analyses of Intact Lumbar Disc Bodies Computer Methods in Biomechanics and Biomedical Engineering, Vol. 4, pp , ABAQUS Users Conference 11