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Alvis Ltd was formed in Coventry by Mr T G John in 1919 to manufacture motor cars. Alvis quickly became noted as a producer of innovative and high quality cars, which are now classic collectors' items, and went on to become one of the prestige names in the British automobile industry. Alvis started manufacturing armoured vehicles before World War 2 and afterwards became one of the leading names in the world supplying light armoured fighting vehicles. Starting with the Saladin and Saracen high mobility wheeled vehicles, and following this with the Scorpion, and later Stormer, tracked vehicles. Alvis has supplied a high proportion of the British Army's light armour and has exported to more than 40 countries.
Since 1993, Alvis has continued to enhance its focus on military vehicles. In a significant corporate development in 1997 the Group acquired Hägglunds Vehicle AB, the major Scandinavian manufacturer of light and medium armoured vehicles. Equally significantly, in 1998 the Group took over the armoured vehicle business of GKN plc in a transaction which saw GKN take a shareholding in the enlarged Group and the main UK manufacturing operation move from Coventry to Telford. Through these developments, Alvis has confirmed its position as Europe's leading manufacturer of light and medium armoured vehicles, and enhanced its strong strategic position in a rapidly consolidating sector.
The Multi-Role Armoured Vehicle (MRAV) is a new 8x8 European armoured utility vehicle for the new millennium. In its modular form, it provides maximum flexibility for multi-national operations. The MRAV accommodates 11 fully equipped soldiers. The MRAV programme, in which Alvis is teamed with other European defence manufacturers in the ARTEC consortium, is a central element of Alvis strategic planning for the early part of the new century.
Description of Work
CADFEM UK CAE Ltd. were contracted to assist Alvis Vickers Limited (AVL) in the analysis of the MRAV. The main body of this work commenced in April 2000. Since then a large volume of work has been carried out by AVL, CADFEM UK CAE Ltd. and Krauss Maffei Wegmann (KMW). The bulk of the analysis has been carried out on an analysis model created from Pro/ENGINEER by a joint AVL/CADFEM UK CAE Ltd./KMW working group during March-June 2000. This model has been subsequently modified by CADFEM UK CAE Ltd. using ANSYS. A further analysis model is currently under development at AVL, again using Pro/ENGINEER.
The analysis model used was created from mass, beam, shell and solid elements. Shell elements are used to model the main hull structure, with solid elements being used to model castings and fabrications. In some instances where castings and fabrications are attached to the hull platework, this attachment is made via shell elements that are used to simulate the weld connectivity. Beam elements are generally used to connect added mass elements or to connect castings/fabrications to a single point for load application.
The object of the analysis was to determine the suitability of the vehicle structure for some 75 load cases to simulate the operational loads that are applied to the vehicle. This was an iterative process that resulted in several modifications being made to the vehicle.
An instance of the models used for the analyses are shown in the figure on the previous page (without a mission module) and the figure below right (with a mission module). MRAV is designed such that a variety of mission modules (e.g. personnel carrier, command post, and ambulance) can be used on a common drive module.
The first model had a total of 262,601 elements, 156,457 nodes and solved each load case (using ANSYS) in 55 minutes on a Dell Precision 330 Pentium 4 1.4Ghz with 1GB of memory. The current model has a total of 617,971 elements, 281,718 nodes and solved each load case (using ANSYS) in 40 minutes on a Dell Precision 530 Dual Pentium 4 Xeon 1.7Ghz with 4GB of memory.
As Pro/ENGINEER (via Pro/MESH) creates only nodes, elements and loads within ANSYS, a procedure was developed using dummy loads to identify the locations used for load applications. This was achieved via using a series of ANSYS macros that selected nodes with particular dummy loads applied, and then added further geometry to the model.
An example of this is shown in the figure to the left, which shows the elements added to the model at one of the rear axle housings. The figure identifies locations on the model for which loads were supplied from a separate vehicle dynamic model. Beam elements had to be added to the model from Pro/ENGINEER to identify these locations correctly. The beam elements that meet at a point in the figure are to allow representation of the unsprung mass of the hub/wheel. The actual loading to be applied to the model was then applied via an ANSYS macro to numbered locations in the model, which were identified as nodal components in ANSYS (e.g. load location 201 in the model would be identified as a nodal component such as LN201).
Using this procedure, it is possible to have major geometric modifications made to the model geometry within Pro/ENGINEER, then to output a new instance of the model that is automatically set up with all required loading points, added masses, etc. It should be noted that some smaller analyses of particular regions of the vehicle were carried out at AVL within Pro/MECHANICA, but as most of the full vehicle load cases require analysis capabilities not available within Pro/MECHANICA (e.g. inertia relief) the model had to be run within ANSYS.
The results post processing focussed mainly on the welded joints within the vehicle. Any joints that looked problematic were evaluated further using FEWeld, a third party application that takes ANSYS results and evaluates the weld stress in further detail. A stress contour plot obtained from one of the load cases is shown in the figure to the right.
The analysis carried out has provided confidence in the structural design of MRAV. Further analyses are being carried out to investigate cost and weight saving measures on the design.
A methodology has been developed within AVL to integrate CAE within the engineering design process. CAD data is fed directly into ANSYS to create a "ready to run" FE model automatically. The analysis of the welded joints within the structure has also been streamlined to allow many joints to be checked over multiple load cases.