Simulation of parametric-tracked-vehicle-models with SAMCEF Mecano Christian Freier Rheinmetall Landsysteme GmbH Abstract: To analyse the behaviour of high mobile tracked-vehicles, Rheinmetall Landsysteme GmbH uses multi-body-simulation with SAMCEF Mecano (MOTION module). In parameter-studies it is only necessary to change a few model-parameters on existing models and calculate it several times. Examples are the determination of running-gear-performance of tracked-vehicles, tilt-moment of recovery-vehicles (crane).for this, it was efficient to create a possibility to make automatic parameter-variations including automatic post-processing. A full parametric tracked-vehiclemodel was developed, where parameters define geometry, physical properties and form of ground and obstacles. The input of parameters is now easy and oriented to practice. With that feature it is possible to execute parameter-analyses without any interaction. Extrait:Pour analyser le comportement de véhicule à chenilles très mobile, Rheinmetall Landsysteme utilise le logiciel de simulation Multi-Corps SAMCEF Mecano (module MOTION). En analyse paramétrique, il est nécessaire de changer plusieurs paramètres du modèle et de relancer les calculs à de nombreuses reprises. C est le cas, par exemple pour la détermination du niveau de performance du mécanisme de transmission du véhicule à chenilles ou du calcul du moment de bascule de la grue d un char de dépannage. Pour cette raison, il était important de disposer d un processus automatisé permettant de récupérer et d analyser les variations de paramètres et incluant le post-processing automatique. Un modèle paramétrique complet de véhicule à chenilles a été développé, dans lequel les paramètres définissent la géométrie, les propriétés physiques, le contour de terrain et les obstacles. L introduction des paramètres est facilitée et permet de nombreux essais. Grâce à cette caractéristique, il est maintenant possible de lancer des analyses paramétriques sans interaction Introduction Rheinmetall Landsysteme GmbH is a leading supplier of wheeled and tracked armoured vehicles. Modern tracked vehicles are equipped with high performance suspension systems. Requirements for light high mobile systems e.g. for air transportable vehicles make it necessary to optimise geometry and component characteristics. Essential for dimensioning and construction of system components is the knowledge of acting loads and its dynamic interactions. Complex mechanisms, like track suspension systems could be investigated by Multi-body simulation only. This article explains how a parametric multi-body-system for tracked vehicles is developed with SAMCEF Bacon and MECANO Motion to simulate different vehicles with costeffective handling. 9 th SAMTECH Users Conference 2005 1/11
High mobile track-suspension-system The following figures show two examples of different running-gear configurations of Rheinmetall tracked vehicles: Armoured Recovery Vehicle (ARV) Buffalo, 56 t idler wheel with tracktension-system support wheel bump stop driving gear track driving direction road arm road wheel Airtransportable weapon carrier Wiesel 2, 4 t driving gear idler wheel with track-tensiondamper driving direction Figure 1: Heavy and light running gears 9 th SAMTECH Users Conference 2005 2/11
The principle of modern running gear is similar. High mobile running gears consist of roadarms, wheels, support-wheels, idler wheel, driving gear, spring and damper elements and bump stops. But each vehicle type has different characteristics that have to take into consideration: all wheels are rubber-coated and have different spring and damping characteristics. orientation of road-arms can be pushed or pulled direction. driving gears can be placed in front or at rear. track-elements are connected by rubber-coated-bolts that allow tension and bending characteristics (spring and damping). to guarantee track-tension (to prevent loose the track), each vehicle type has a different track-tensioning-system. damping can be realized by hydraulic velocity-dependent elements or friction elements with linear or non-linear characteristics. limiter like rigid or hydraulic bump stops are implemented to absorb high energies and protect spring and damper elements. suspension-systems for the road wheels can be realized e.g. by torsion-bars or hydrop-units. Because of torsion-bar length, heavy vehicles have non-symmetric running-gears. a) Torsion-bar with friction damper b) Hydrop-element with hydraulic-damping Figure 2: Suspension systems 9 th SAMTECH Users Conference 2005 3/11
Parameters The parameters could be divided in different groups: vehicle parameters (geometry, dimension of parts) which define the vehicle configuration, and simulation-parameters (ground, velocity, total vehicle-mass) which should be investigated. Vehicle Parameters Vehicle parameters are e.g. sub-origin points of vehicle fixed points (hinge points of roadarms, connection points of system components), geometry-sizes or single masses. The data of characteristics are stored, so far as possible, as parameters (ABRE /name text ). Static angles of road-arms and wheel positions are constructed by BACON geometry elements. They depend on required ground-clearance and are calculated automatically. Only the position of track nodes must be calculated in advanced by use of multi-body-simulation and stored in a separate bank-file. Figure 3: Generation of initial track-positions With help of the #inquire command it is possible to determine road arm and track angles of an existing vehicle model while reading in the vehicle data. It is necessary to calculate the initial static pre-moments. static track-angle static road-arm-angle ground clearence Figure 4: Static road arm angles and track angles 9 th SAMTECH Users Conference 2005 4/11
Simulation Parameters Following the geometry parameters also parameters of ground form, vehicle velocity, driving situations (acceleration, breaking, initial velocity) must be defined. Other parameters that also could be changed can defined as simulation-parameters, e.g. special geometric dimensions, spring-damper characteristics, static ground-clearance, static pre-moments of road arms, total-mass. total-mass initial velocity end velocity Figure 5: Simulation parameters ground The ground structure and geometry including its parameters, as shown in following figure, are defined by functions. Contact between track and ground is defined by.mcc SURF NFCY Opt 2. Half-round obstacle trapeze obstacle ditch high angle high width lenght ramp stair plane angle high sinus belgian block terrain amplitude 100 mm 100 mm lenght 7m Figure 6: Ground-examples 9 th SAMTECH Users Conference 2005 5/11
Multi-body-Model Armoured Recovery Vehicle (ARV) Figure 7: CAD-model rest-mass point Multi-body model All track-system components and modules are connected with rigid-elements (.MCE RIGI) to rest-mass-point. This mass point represents the mass and inertias which are not separately taken into consideration and is located at the resulting coordinate of the rest-mass. All necessary mathematic calculations are made inside bank-files with mathematic operations that are possible with BACON-command language. It is now possible to define total coordinates, total mass and total inertias of the basic vehicle as parameters. All other vehicle components as track-system elements, vehicle main parts (dozer, crane, turret, engine) as well as their characteristics are defined in separate files. Now it is possible to use them for similar but different vehicle systems or to replace them for easily if required. 9 th SAMTECH Users Conference 2005 6/11
Contacts The MECANO-model contains contact-elements between wheel and track, track and ground, road-arms and bump stop-elements. For the example Armoured Recovery Vehicle there are 2x(13x82+82+7) = 2310 contacts. Figure 8: Separated parts of the track system To reduce calculation time a set of minimum contacts for static position is defined (red). Depending on calculation time and driving-velocity, only necessary contact-nodes are automatically taken into consideration. (to reach the obstacle, only red and blue track elements have contact with wheel 1). end-time Figure 9: Minimum contact definition for wheel 1 start-time 9 th SAMTECH Users Conference 2005 7/11
Post-Processing For Post-Processing, diagrams and views for pictures and animations are predefined with SAMCEF-command langue with the benefit to reduce the effort by defining only once e.g. titles, adapting units and overlaying different curves. Most diagrams e.g. acceleration at drivers seat, pitch angle, wheel forces, etc. can be used for most vehicle analysis and provides an easy and fast way to verify and document simulation results. Nowadays wireframe-animations with BACON are replaced by CAD-animations made with SAMCEF Field. Figure 10: Predefined diagrams and views 9 th SAMTECH Users Conference 2005 8/11
Multi-Calculations For many investigations it is only necessary to vary a few simulations parameters without modifying the basic vehicle model. For multi calculation a system was developed to execute many jobs by the following loop: simulation parameter Set 1 Set 2 Set n ramp ramp ramp property 30% property 30% property 30% init velocity 20 km/h init velocity 25 km/h init velocity 30 km/h vehicle parameter Create external bank-fíles with a set of simulation and vehicle parameters Set1.dat + vehicle.dat calculation1.dat Create main file bacon.exe Read in model bank-file goto next calculation calculation1.sdb calculation1.sam mecano.exe Export for computation Calculate MECANO Motion calculation1_me.des calculation1_me.fac Create results bacon.exe Figure 11: Multi-calculation diagram1.jpg diagram2.jpg Post-Processing with predefined diagrams calculation1.doc 9 th SAMTECH Users Conference 2005 9/11
The automatic calculation cycle starts by creating an external bank-fíle (set.dat) with a set of simulation parameters (SAMCEF-abbreviations e.g. ground, vehicle velocity). With SAMCEF-Bacon the model bank-file including simulation parameters is read in and exported for computation. After calculation with MECANO Motion, SAMCEF Bacon executes automatically the Post-Processing with predefined diagrams that are exported as pictures and implemented in WinWord-documents. With that feature it is possible to execute parameter analyses without any interaction! It can also be used for other SAMCEF calculations as ASEF, MECANO-Structure, DYNAM, e.t.c. In following example to evaluate the performance of the ARV running gear, the vehicle should drive on different ramps (30%, 40%, 50% uphill) with increasing velocities. For this twenty simulation runs must be executed. Figure 12: Example Armoured Recovery Vehicle driving onto a ramp onto ramp 30% 40% 50% 6 km/h 8 km/h 10 km/h 12 km/h 14 km/h 14 km/h 16 km/h 16 km/h 18 km/h 20 km/h 20 km/h 22 km/h 22 km/h 24 km/h 24 km/h 26 km/h 28 km/h 30 km/h 32 km/h 34 km/h 9 th SAMTECH Users Conference 2005 10/11
Additional Examples Leopard 2 and PUMA: Comparison of running gear performance on sinus-wave Excavator of the Armoured Engineer vehicle Armoured Recovery Vehicle: Craning Wiesel 2: backward driving 60%-ramp Figure 13: Additional examples Future simulation-model It would be fine to convert the developed track simulation system to SAMCEF Field by integration of a command language like used in BACON. The advantage should be the new possibility to use contact with parts and the direct method to create CAD-animations. 9 th SAMTECH Users Conference 2005 11/11