Automation of CAE Tasks to Improve Work Efficiency

Transcription

1 Automation of CAE Tasks to Improve Work Efficiency Bhanu Pratap Sharma Asst. Manager, CAE Powertrain Maruti Suzuki India Limited, Gurgaon , India in Mandar M Kulkarni Manager, CAE Powertrain Maruti Suzuki India Limited, Gurgaon , India mandarm.kulkarni@maruti.co. in Santhosh Kr Sundararajan Team-Lead, QA, SimLab Altair Engineering India Pvt. Ltd. Bengaluru , India santhoshkumar.sundararajan@altair.co m Keywords: Automation, Meshing, Modelling, SimLab, Altair, Script, Efficiency Abstract It was the industrial revolution that sparked the ideas like productivity, efficiency, effectiveness and many more; ideas which changed the course of history, ideas which changed the way man used to work. One only needs to take a glance at the contemporary world and can easily spot their presence and the huge effect they have on the businesses and ultimately on the life of a common man. These are among the basic ingredients whose presence in any business is of utmost priority to make it a successful one in this continually growing competitive market. The product development cycle in an automotive organization would probably be a near perfect example to understand the above mentioned effect. Computers equipped with the right hardware and smart software can help in squeezing the development cycle time significantly. The following paper essentially echoes the intent described above. It explains a project done by us with Altair India support team to automate the modelling process using Altair SimLab This automation can perform nearly all the pre-processing tasks of a typical structural CAE analysis i.e. meshing, applying rigid connections, making bolts/pre-loading sections, contact creation and load application within a duration of 2 to 3 hours. To put things into perspective, the same set of tasks took nearly 30 hours when done manually using the conventional software. Although we have taken the example of an engine mounting bracket assembly to describe the overall process, the scope of application of this modelling approach for other design components has also been discussed in this paper. Introduction The competition in the market has always been growing at an ever increasing pace and the manufacturing sector has shown interest in this growth by adopting latest technologies available at hand. The concept stage of any product development cycle nowadays has an extensive use of Computer Aided Engineering. Although the use of CAE itself (instead of Testing) in the concept stage has proven to be a huge time and money savior, nevertheless there always remains a scope of improvement. While evaluating multiple design iterations of a given part/assembly in a limited amount of time, the modelling task always becomes the bottleneck of the whole analysis process. Although the meshing process is the very foundation of the Finite Element Analysis, and requires relevant knowledge of element sizes, types, densities and their impact on the results, nevertheless, in some cases it becomes repetitive and consumes a lot of time. In order to tackle this problem, a major part of the modelling process can be automated using the Process Automation utility provided by Altair in their modelling tool SimLab. Process Automation by definition can simply mean that a standard process is first finalized by mutual understanding of its users and is then run by a computerized machinery subject to some pre-defined controls and internal feedback mechanisms to obtain the same output that one would have achieved had the process been performed manually. 1

2 The Process Automation utility in SimLab works similarly apart from the fact that there are no internal feedback mechanisms in the process. It enables the user to set controls for meshing, creating rigid connections, creating contacts and applying loads and boundary conditions. The user has to first manually perform all these steps and record these in the form of a file called the script file which is later executed on the CAD of iteration model using the SimLab Process Automation utility. SimLab supports three recording formats i.e., JavaScript, Python and XML. The process described in this paper uses the JavaScript format. Once the modelling is completed, the user can stop the recording process and save the file as a.js (JavaScript) file. Apart from this main script file, the user has to export the files containing mesh controls and contact definitions for later use. This file is then edited in a text editor to make it generic which is explained in later sections. The next section shall describe the script recording process and the modelling methodology followed. The difficulties and the limitations of the current approach that one faces make the foundation of one s inclination towards a more organized, simplistic and wherever and whenever possible an automated approach. The set of tasks which are now automated previously took nearly five to six times more time to complete. Apart from the difference in time, another difference lies in the quality of mesh and thus the quality of results, the latter one gets highlighted prominently when there are assembly elements in our model. The variation in mesh quality can be attributed to the absence of a quick access file containing all the mesh controls which when imported in the model applies the controls to every component and result in almost same mesh quality be it from iteration to iteration or from model to model. Table 1.1 highlights the level of efficiency of the Process Automation utility. Table I: Comparison of time between Manual and Automated approaches Process Methodology The complete process broadly consists of two stages, first stage is the script recording stage which means storing all the actions that the user performs on the very first CAD in the form of a text file (otherwise called as the script file); and the second stage is simply the script execution which is the execution of the same action sequence on a different CAD of same model (presumably an iteration/countermeasure design). The process seems very basic and simplistic and yet is very effective. There are some pre and post requisites for the first stage mentioned above; before recording the process the user must have the following 2

3 set of files since these are imported during the script recording stage: Names.dat, Parameter.xml, Group_Template.xml, Mesh_Specification.xml, Contact_Definition_File.dat; and after the script recording stage the user needs to make some changes in the script file in any text editor to make it a generic one, the reason of which is explained later in the section. The files described above respectively contain the names of all the components available in the model; parameters such as maximum bolt dia., global mesh size and many others; the standard group names which later get called by the mesh controls and bolt pretension commands; mesh specifications/controls; contact generation commands. To thoroughly understand the Process Automation Utility the assembly model of an engine mounting was used. Majority of the steps discussed in Table I were recorded in the script. The sequence of steps essentially remains same in both the stages i.e., script recording and script execution ; the only difference is that when one is recording the script, one needs to perform all the steps manually whereas while execution one has to perform only those steps which are non-recordable which in this case are the first two steps as described below. Let us look at the flow of the overall process: 1. Defining a project folder and importing Parameter.xml a. The project folder is the one where our script file gets saved. b. The Parameter.xml file may contain the numerical values which we wish to vary from model to model e.g. global mesh size; number of elements along a cylinder s circular edge; washer offset distance; name of the CAD file etc. Figure.1 shows a snapshot of a typical parameter file. These parameters can be later called either in the mesh controls or while saving the model in between. Figure.1 Sample parameter file in.xml format 2. Importing CAD and mapping Body and Group Names a. The CAD/geometry file is imported in the SimLab GUI. SimLab has an excellent capability of imprinting the CAD bodies while importing. This helps in achieving matching mesh at mating areas and thereby reducing the chances of errors which usually come in analyses involving contacts. b. SimLab identifies the Names.dat file in the project folder and the user maps the body names one by one as shown in Figure.2. Special groups (groups of faces, edges etc.) are the ones that are later used to either define specific mesh controls, or for defining loads and boundary conditions for contact definition in some cases. Once the user has mapped the body and the group names, the user can start the recording process by selecting the preferred choice of language (JavaScript/Python/XML). SimLab will create a Project.txt file in the project directory where all the actions done by the user henceforth will get recorded. 3. Selecting features to create more groups a. All those features which can be selected by giving ranges of radii i.e., filets, circles, cylinders etc. are selected using the feature based selection command and kept in separate 3

4 groups which the user later calls via the mesh specifications to apply respective mesh controls. Figure.2 Mapping body names and group names 4. Importing Mesh_Specification.xml a. When the user imports the Mesh_Specification.xml, the controls that it contains get automatically applied to all the groups made in Step 3 above provided the names of the groups made by user are consistent with the ones written in the mesh spec file. The mesh controls provided in SimLab cover almost all the critical features where the flow of mesh can get distorted; for example fillets, cylinders, mating areas in between two components etc. 5. Surface meshing and Volume meshing a. Once the mesh controls are applied successfully, the user can give the command for surface mesh and subsequently the volume meshing. As the quality of mesh is directly dependent upon the mesh controls we define, the mesh quality that we obtained in SimLab was of superior quality in comparison to the conventional tools that we use. One can note that there is no quality checking after surface meshing here which can be incorporated to make the automated modelling process more robust and reliable. Also, the steps hereafter are specific to the type of analysis to be performed later on, i.e., if the analysis has no contacts and bolt pretension steps, then the user can straightaway jump to the last step i.e., exporting the meshed model. 6. Transferring groups a. Since the face groups made initially contain CAD faces and not mesh faces, and thus cannot be used for creating RBE2 and loads, so they need to be transferred to the Mesh body first. 7. Separating bodies and creating surface interaction a. Since the mesh controls defined for the contact areas caused the bodies to have matching and equivalence nodes, thus the bodies need to be separated before proceeding to define the contacts. b. Surface interaction property is defined with friction coefficient and other relevant variables. 4

5 8. Importing Contact_Definition_File.dat a. On importing this file, SimLab automatically applies all the contacts that are defined in this file provided the body names mapped in the 2 nd step are consistent with the ones present in the contact definition file. b. Defining contacts in SimLab is very effective and user-friendly. The user only needs to define the tolerance limit, choose the relevant surface interaction property, and finally select the bodies; SimLab automatically finds contact areas based upon input tolerance value and generates contact surfaces. 9. Create assembly elements (RBE2/3, CBAR etc.) a. This is when the special groups mapped in Step 2 are called and RBE2 spiders are created at the bolt locations using the Bolt-Head option under the Bolt-Modelling tab of SimLab. Figure.3 shows a representative image from the model to show the result. Face group defined in Step 2 RBE2 spider created using Bolt-Head command Figure.3 Bearing cap after creating RBE2 Figure.4 Bolt pre-tension creation 10. Create bolt pretension surface a. To create pre-tension surface the user needs to define the cross-section plane. This was done by making a group of the top face of the bolt head from CAD, transferring it to respective mesh, and finally defining another plane offset from it. This process is done by using the utility functions which are inserted in between the script after completing the recording process; Figure.4 shows an illustration of the process. 11. Exporting solver deck a. The model is exported as an.inp file. Figure.5. below shows a comparison of final mesh output obtained manually and from the automation process. Manually modelled Modelled using script Figure.5 Comparison of final mesh output 5

6 Once all the above steps were over, the script recording was stopped and a.js file was saved which was further edited in a text editor. Utility functions for bolt pre-tension plane offset ( var PlanePoint1=[]; var PlanePoint2=[]; var PlanePoint3=[]; SimLabUtility.OffsetPlane(PlanePoint1, PlanePoint2, PlanePoint3, offsetdistance); ), functions for defining standard model name during final model export and in between file saving ( var Result = SimLabUtility.GetStringParameter("SimLab Parameters"); ) were inserted in the script file. Apart from utility functions, the numerical values like maximum diameter for bolthole selection, max radii for fillet selection etc. were parameterized. The parameterization can simply be done by replacing the numerical value in the script by the corresponding name of the parameter prefixed with a $ sign. The material and property assignment was separately written in the master run file since this step could not be recorded in the script. To avoid any inconsistency between the master file and the one exported above, the names of all the components were kept same in both the files. Benefits Summary Like every other automation, our basic purpose was to reduce the overall time taken to do the modelling which was successfully achieved. The benefit of automation was not only seen in terms of the time that we saved but this also helped in standardizing the mesh controls and thus the quality of mesh and the final analysis results. Quantitatively speaking, the amount of time taken was surprisingly reduced from nearly 30 hours to about 2 hours i.e., the automation process is nearly 7 times more efficient. The time taken to do the modelling manually is only indicative (considering the current project as an example) and will surely depend upon the complexity of the assembly at hand but given the reduced number of manual operations in the automation process and majority of the tasks being done by the script; it can be said that the automation will always be able to reduce the overall time by a factor of at least 4-5 times. Moreover, the scripting process of SimLab is easy to understand and very user-friendly, i.e., the user need not be an expert in JavaScript/Python/XML (languages used by SimLab for Process recording) to use it and that is because the user has to only start and stop the recording and do only minor editing in the final script file, the major part is done by SimLab itself. Challenges Our reliability on the automation process basically depended upon the quality of the output that we received form it which was the meshed model of a given CAD. To obtain a good quality mesh output, the controls defined in the Mesh_Specificatio.xml were very important and it was a challenging task for us to adjust them. Arriving at the right set of mesh controls was not an easy task and we had to try a few iterations for it. Once the mesh controls were set and a good quality mesh had been obtained, the next challenge was to carefully pick the relevant utility functions and insert them in the script to make it a generic one. One important thing that we came to know about the process automation was that we had to make different scripts for different assemblies for example; one cannot use the script of a RH engine mount assembly for modelling the assembly of LH engine mount because of a very simple reason i.e., both these assemblies will have different set of components (e.g., transmission casing in LH mount, maybe crankcase in RH mount). Since the scripts work on the basis of component/body names, every script is model specific. Apart from these on-job challenges, one more challenge was there which was to familiarize ourselves with the GUI of a tool (SimLab) that we had not been using on a regular basis nevertheless as we got along with the project we succeeded in overcoming it. 6

7 Future Plans In the short run, we are planning to apply this process to engine mounting assemblies of other variants. In the long run, we plan to implement the process to prepare full engine model for Powertrain-MBD Analysis. This goal shall be obtained by preparing scripts for every component separately (e.g, one file for modelling cylinder head, one file for modelling transmission casing LH and so on) and then combining all the models in the final script. This will significantly reduce the overall human effort and time taken for modelling/pre-processing. Conclusion It has always been the endeavor of the engineering community to devise new mechanisms and invent new machines to make the life of modern man more and more ergonomic. To achieve this goal in this modernized and rapidly growing world where time is the most important asset, the community strives to work towards assigning the less creative and more mundane tasks to the machines, presumably because machines are good at it; and investing the time saved in obtaining new solutions. Working towards the same goal we took up the project of automation of the modelling/meshing process which consumes most of the pre-processing time in any simulation activity. The project was done on an engine mounting assembly of a passenger vehicle. The automation enabled us to prepare the model of three different iterations of the base design in a single day which otherwise would have taken nearly 2 weeks, which was a huge time saving. We plan to use this process automation for building the model of major engine components for Powertrain- MBD analysis in future. ACKNOWLEDGEMENTS We would like to thank the Management from MSIL Engineering and Altair India s Technical Support Team for their guidance and continuous support to help us explore, understand and effectively apply the Process Automation Utility using SimLab (v17.2). REFERENCES [1] SimLab Help 17.2, SimLab Altair Engineering [2] Java Script Definitions, 7