APPLICATION OF SKELETON METHOD IN INTERCONNECTION OF CAE PROGRAMS USED IN VEHICLE DESIGN Jozef Bucha 1 Jana Gavačová 2 Tomáš Milesich 33 Keywords: CATIA V5, ADAMS/CAR, suspension, virtual vehicle, skeleton model Abstract This paper deals with the application of the skeleton method as the main element of interconnection of CAE programs involved in the process of vehicle design. This article focuses on the utilization of the skeleton method for mutual connection of CATIA V5 and ADAMS/CAR. Both programs can be used simultaneously during various stages of vehicle design. 1 INTRODUCTION Modern car design process is not just a simple step-by-step process. Nowadays there are interdisciplinary connections between various fields of mechanical engineering and the utilization of various types of programs [3] (CAD, FEM, MBD, ). This paper focuses on an interactive connection between CATIA V5 and ADAMS/CAR which is demonstrated on the skeleton model of a car and its components (suspension, steering, and chassis). The basic characteristics of a car are defined in the CATIA module CAVA as a determining part of the skeleton model. Other components of vehicle are connected to this main skeleton as subassemblies with their own skeletons. At the same time there are equal or compatible models made as templates of vehicle parts in ADAMS/CAR; for FEM analysis of vehicle suspension, components are modeled as flexible bodies by ADAMS/FLEX and used in ADAMS/CAR. 2 SKELETON MODEL IN CATIA The skeleton is a collection of specifications (a part in an or geometrical set in a part, or a design table), which involves the functional characteristics of the entire model (). The specification in CATIA can be surface geometry, wireframe geometry (points, line, and planes), parameters and formulas, axis systems (Fig.1). The main reason for skeleton modelling is to centralize key information in one place (usually the first part of the ). The main advantage of using skeleton modelling is that all information in the is stored in one place and is transferred through the product structure; every part or sub is constrained only to the skeleton part. Designers can work individually on different parts of the model, and all the necessary information is stored in the shared common skeleton part. All parts are positioned in the proper places during the entire design process [1]. The main skeleton part is defined in CATIA CAVA (special workbench for CATIA) and consists of four main model information areas (Overall vehicle data, Seats, Wheels, Loading 3 1,2,3 Faculty of Mechanical Engineering, Slovak University of Technology in Bratislava, Námestie Slobody 17, 812 31, Bratislava, 1 jozef.bucha@stuba.sk, 2 jana.gavacova@stuba.sk, 3 tomas.milesich@stuba.sk
planes). The main skeleton in CAVA also contains the positions of all subassemblies of the vehicle component. Fig. 2 shows the main skeleton of a virtual vehicle, with front and rear suspension added as subassemblies. CAVA base data Overall data, Seats,Wheels, Planes Skeleton,,... Front suspension Skeleton Rear suspension Skelton Steering Skelton Front suspension Rear suspension Steering Body Skelton Body Figure 1: Skeleton model of vehicle [1] Planes Front suspension references Wheels Figure.2: Skeleton model of vehicle Rear suspension references Seats+Manikin Figure.3: Double wishbone suspension skeleton The suspension skeleton (left part) of the double wishbone suspension used in the virtual vehicle is shown in Fig. 3. H1-H10 mark wireframe geometries (points) are the basic topological elements. The predefined variants of suspension layouts are stored as design tables in.excell files. CR1-CR7 mark the axis systems of the suspension components. Coloured lines are used just for visualization purposes. H4 H1 H8 H2 CR2 CR1 H10 H5 H9 CR7 CR3 CR6 H6 H3 H7 H3 H7 CR4,5,5H11 H11
Tab.1 shows the components of suspension used in the, the names of coordinate references, and important wireframe geometry which is delivered from the suspension skeleton to the individual parts. CR4 and CR 5 are references of the knuckle and wheel hub. Orientation of these axis systems is linked to the vehicle skeleton, and H11 point is the wheel centre. The position of this point is taken from the CAVA vehicle skeleton. The position of the H8 point (tierod inner point) is shared from the steering skeleton. Other points are defined directly by the coordinates in the suspension skeleton [2]. Table 1: Double wishbone suspension skeleton. Suspension component Coordinate reference Wireframe geometry Lower arm CR1 H1,H2,H3,H9 Upper arm CR2 H4,H5,H6 Tie-rod CR3 H7,H8 Knuckle CR4 H3,H6,H7,H11 Wheel hub CR5 H11 Lower strut CR6 H9,H10 Upper strut CR7 H9,H10 3 DESIGN OF SUSPENSION IN ADAMS/CAR The ADAMS/CAR program is part of the ADAMS software system and is specifically tailored for vehicle simulations. The process of virtual vehicle design consists of three phases: Creating templates. The template serves as the basic block of the vehicle; it defines the basic topology of the vehicle components, the physical properties of the parts, the geometry of the parts, and the types of joints and bushings used. One template can be used by multiple subsystems. Fig. 4 shows double wishbone suspension template. Creating subsystem. Every subsystem must be based on a template. In subsystems it is possible to alter some parametrical values and change the properties of springs and dampers. Creating assemblies. An is a collection of subsystems which together with test-rig compose valid suspension or full vehicle assemblies. Each type of has prescribed mandatory subsystems which have to be used.
Figure 4: Template of double wishbone suspension. The template depicted in Fig. 4 is used for both front and rear suspensions of a vehicle (Fig. 5). Figure 5: Front and rear suspension subsystems. Front and rear subsystems (Fig. 5), together with other subsystems (steering, brakes, powertrain, wheels ) are used for full vehicle (Fig. 6). Figure 6: Full vehicle of vehicle
4 INTEGRATION OF FLEXIBILITY A very important option of ADAMS is the possibility of replacing rigid parts with flexible parts using the ADAMS/FLEX module. The properties of the flexible bodies are defined in a mnf file (modal neutral file). This file contains important information about the inertial and flexibility properties of a deformable body. The mnf file also contains information about incorporation of a flexible body into ADAMS. To determine the minimum number of mode shapes, modified Craig-Bampton method (Component mode synthesis, CMS) is used. Flexible bodies can be created with ANSYS, NASTRAN or directly in ADAMS using ADAMS/AUTOFLEX. An example of the flexible body of the left lower control arm from the rear suspension is depicted in fig. 7. Figure 7: Generated flexible body of lower control arm Fig. 8 shows results of the static analysis of a rear suspension with flexible bodies.
5 CONCLUSIONS Figure 8: Static load of rear suspension with flexible bodies The use of the CAD skeleton method, with the proposed interconnection of CATIA and ADAMS software in the process of vehicle design, brings many advantages. Designers or teams of designers using the CAD program CATIA and the MBD program ADAMS/CAR, together with the described skeleton models, can benefit from the advantages of both programs (modelling capability of CATIA, automated testing of fulfilment of vehicle standards during the design process in CATIA CAVA and virtual vehicle testing in ADAMS/CAR). The application of ADAMS/FLEX and ADAMS/DURABILITY plugins in ADAMS/CAR also makes it possible to use flexible bodies, compute stresses and generate input files for durability analysis, incorporate the control modules in MATLAB into the vehicle [6], or to make optimization using ADAMS/INSIGHT. Another benefit of the described interconnection is a decrease in design time. One team can design the vehicle components in CATIA, another team can make simulations, and a third can generate flexible bodies independently. Some processes can be automated with macros in CATIA or ADAMS. The main disadvantage of the skeleton method is that it should be used from the beginning of the design process. Flexible models generated with the Craig Bampton method can be used only in linear analysis. The skeleton method is mostly suitable for mechanical models with different variations of dimensions but with the same kinematics or function (suspensions, engines, boom arms, etc.)
Acknowledgments This contribution has been elaborated partially as a result of a research project supported by European Structural Funds No. 26240220076 - "Industrial research into the methods and procedures in generative design and knowledge engineering in car development". REFERENCES [1] Bucha, J., Gavačová, J.: Application of CAD Skeleton Method in Process of Design of Virtual Vehicle, Transport Means 2014, Kaunas University of Technology, Lithuania, 2014, ISSN 2351-4604 [2] Bucha, J., Gavačová, J.: Application of CAD Skeleton Method in Generative Design of Virtual Vehicle, KOD 2014, University of Novi Sad, Novi Sad, 2014, ISBN 978-86- 7892-615-0 [3] Gavačová, J., Vereš, M.: Procedure for Developing Shaped Models Using the Generative Design Method, In: Modern Methods of Construction Design, 2014, p. 435-441 [4] Blundell, M., Harty, D.: The Multibody System Approach to Vehicle Dynamics, Elsevier Butterworth-Heinemann, ISBN 0-7506-5112-1, 2004 [5] Macey, S., Wardle, G.:. H-point: The Fundamentals of Car Design & Packaging, Design Studio Press, ISBN 978-933492-37-7, Passadena, 2008 [6] Danko, J., Magdolen, Ľ., Masaryk, M., Bugár, M., Madarás, J.: Energy Management System Algorithms for the Electric Vehicle Applications. In: Mechatronics 2013: 10th International conference, Brno, Czech Republic, Springer International Publishing, 2014. - ISBN 978-3-319-02293-2. - S. 25-31