Universal Mechanism Simulation of Tracked Vehicle Dynamics with www.umlab.ru um@umlab.ru This presentation is devoted to the problems of simulation of tracked vehicle dynamics with UM. The program has been developed at Laboratory of Computations Mechanics, Bryansk State Technical University, Russia

Examples of tracked vehicle (TV) models Main components of TV models Contents Examples of tracked vehicle (TV) models Main components of TV models Development of a model of TV Models of force elements Simulation of TV dynamics

Examples of TV models TV of different types Tank Crawler transporter 371 bodies, 1916 d.o.f. Crawler transporter 263 bodies, 1332 d.o.f. D.o.f. means ‘degrees of freedom’ Excavator 138 bodies, 128 d.o.f.

Examples of TV models Jump by speed 15 m/s

Examples of TV models Model developed in 2003 The model has been developed in2003 with the help of the first version of the UM Caterpillar module for simulation of TV dynamics Model developed in 2003

Examples of TV models

Examples of tracked vehicle (TV) models Main components of TV models Development of a model of TV Models of force elements Simulation of TV dynamics

Main components of TV model Sprocket Idler with tension device Rollers Track links Suspension and road wheels UM generates a track model automatically with help of a database of main elements in figure. A rear drive TV is shown. Components of a track model Main system of coordinates for TV model

Main components of TV model Torsion bar suspension Suspension bogie For types of standard suspensions from UM database are shown on slide. Suspension torsion bogie Fixed suspension Standard suspensions as subsystems

Main components of TV model Simplified model of idler on a crank Advanced model of idler on a crank Idler on a slider Three types if idler with tensioner from UM database. The tension device is used for setting a desired tension of the track, as well as for absorption of impacts. The tensioner spring has a definite preload, which exceeding leads to the compression of the spring. Standard models of idler with tension device

Main components of TV model A pin toothing is implemented in UM Sprocket radius is computed according to the number of teeth and distance between the track link joints Sprocket

Main components of TV model Ro r Rs h μ/2  Ro μ/2 h Rs LJ RT RP r The most frequently used tooth profiles are generated automatically according to specified geometric parameters Generator of sprocket tooth profile

Main components of TV model Main menu command for call the tooth generator Generator of tooth profiles

Main components of TV model Track link with rigid joint Track link with flexible joint (bushing) Track link with two parallel bushings (double pin) In case of track link with one pin, the link is modeled be one rigid body. Two rigid bodies are . Bushings can be both linear and nonlinear Standard track link models

Main components of TV model A support roller is a rigid body with one rotationsl degree of freedom Support roller

Main components of TV model The user can develop his own components of TV such suspension subsystem, idler or track link, and add it to the UM database. The new component should be registered on the local computer User defined components Registration of a new component of TV

Examples of tracked vehicle (TV) models Main components of TV models Development of a model of TV Models of force elements Simulation of TV dynamics

Development of TV model Track is generated automatically with the help of components from the database The track structure includes - position of the track Left/Right - number of suspension units - number of rollers (can be zero) - number of track links Step.1 Setting track structure

Development of TV model Step.2 Suspension The user set geometric parameters such as coordinates of torsions, length of torsion arm etc.

Development of TV model Step.3 Adding sprocket The user sets the tooth profile, the number of teeth, sprocket/track step ratio as well as geometric parameters.

Development of TV model Step.4 Adding idler The user selects a type of the tension mechanism from the drop-down box and sets geometrical parameters of the idler.

Development of TV model Step.5 Creation the track chain. Enveloping curve The user selects the type of track link, assigns the pin profile, length of track link and othe parameters. According to the geometrical data for positions of all the wheels and their radii, UM computes the enveloping curve and generates track links with joints in their exact positions along the track.

Development of TV model Step.6 Completion of track model. Adding dampers Dampers Characteristics of shock absorber Some elements must be added to the model to complete its development. In particular, shock absorbers must be added.

Development of TV model Set.7 Adding a hull A hull image is often imported from a CAD software such as SolidWorks, Autodesk Inventor, Pro/E, UG atc.

Development of TV model Set.8 Adding the second track The second track can be added by a single copying the first one. Sometimes, the tracks have different geometric parameters; in this case the parameters of the second track can be modified.

Examples of tracked vehicle (TV) models Main components of TV models Development of a model of TV Models of force elements Simulation of TV dynamics

Models of force elements Pin-sprocket interactions Contact interactions of track pins with sprocket teeth transfers traction and brake torque to the track. Positions of contact points are computed according to positions of the bodies taking into account exact profiles of pin and tooth.

Models of force elements Pin-sprocket interaction A compliant contact model is used. Contact forces depend on penetration of pin and tooth profiles and produce two components: the normal force N and the friction force F. The normal component is the linear function of the penetration and its derivative. Compliant contact model

Models of force elements Wheel-link interaction S R  δ Normal contact force is proportional to the area S of penetration

Models of force elements Wheel-link interaction Force versus penetration model Here δ0 is the deflection under the load P; c(δ) is the stiffness versus penetration law

Models of force elements Wheel-link interaction The obtained relations are generalized for a contact of a wheel with a polyline corresponding to the track chain.

Models of force elements Restrictive force and moment C ht T y x y αx The force and moment prevent the lateral shift and rotation of a link

Models of force elements Track-ground interaction Two main model of the ground: Spring-damper model without sinkage Soil with sinkage Contact point One contact point is automatically assigned to each of the links. It is planned to implement a user-defined set of contact points for each of the links

Models of force elements Bekker ground model Here p is the normal link-ground pressure b is the minimal size on the contact patch b (length of a track link) n, kc , k are the model parameters z is the sinkage depth

Models of force elements Examples of terrain models Normal force versus sinkage depth for different soils

Models of force elements Loading Unloading/ Reloading Example of track load force versus sinkage by loading and unloading/reloading processes

Модели силовых взаимодействий Tangential strength (Janosi, Hanamoto) Here j is the shear displacement of the link since the first contact with soil p is the normal pressure c is the cohesion  is the angle of internal friction K is an empirical constant The tangential stress model is used for computation of friction forces in interaction of a link with the soil.

Модели силовых взаимодействий Database of terrain parameters The user can add terrain models to the database

Examples of tracked vehicle (TV) models Main components of TV models Development of a model of TV Models of force elements Simulation of TV dynamics

Simulation of TV dynamics Dynamic analysis of TV as a set of tests List of auxiliary tests: Equilibrium Track tension Computation of initial velocities List of main tests: Vertical harmonic loading Straight motion Open loop steering Test with driver: 2D curve 3D testing area

Simulation of TV dynamics Test: equilibrium This is an auxiliary test intended for finding coordinates of bodies in the TV equilibrium state. The test is necessary because positions of bodies in the TV model after its development in the UMInput are specified approximately. The user stops the test when the kinetic energy value becomes small enough.

Simulation of TV dynamics Test: track tension This is an auxiliary test, which is used for setting a desired track tension. The main result of the test is the plot of tension force vs. elongation of the tension rod or a preload in the bushings.

Simulation of TV dynamics Test: Computation of initial velocities The test is necessary for automatic computation of initial velocities of TV bodies by the given value of the TV speed, when one of the main dynamic tests is executed. As a rule, it is enough to create a file of initial conditions corresponding to one speed, e.g. 5 m/s. With this file, the program computes start velocities for any speed of TV using a scale factor.

Simulation of TV dynamics Test: Vertical harmonic loading The test allows the user to get nonlinear vertical characteristics of the suspension by a slow harmonic excitation

Simulation of TV dynamics Test: straight motion Harmonic irregularities in opposite phase

Simulation of TV dynamics Test: straight motion Тест: движение по прямой In-phase harmonic irregularities

Simulation of TV dynamics Test: straight motion Jump

Simulation of TV dynamics Test: straight motion Trench

Simulation of TV dynamics Test: straight motion Barrier

Simulation of TV dynamics A simplified modeling a gunshot is made by application of a definite impulse. Click the picture by the mouse to get an animation Gunshot

Simulation of TV dynamics Click the picture by the mouse to get an animation

Simulation of TV dynamics Click the picture by the mouse to get an animation

Simulation of TV dynamics Click the picture by the mouse to get an animation

Simulation of TV dynamics. Open steering test Longitudinal speed 8 m/s Difference in sprocket speeds 0.7 m/s If a driveline is not included in the model of TV, the open lop control of TV is set as the difference in circular speeds of the left and right sprockets

Simulation of TV dynamics. Open steering test Longitudinal speed 0 m/s Difference in sprocket speeds 0.7 m/s

Simulation of TV dynamics Driver model: closed loop control for TV turning Desired path TV Lp x y Driver model: the track speed difference is proportional to the deviation y of a point with preview Lp from the desired path with a reaction delay dt. Closed loop control

Simulation of TV dynamics: test with driver Test: motion on a 2D curve

Simulation of TV dynamics: testing area Testing area is created in one of the CAD programs (SolidWorks, Inventor, PRO/E…) A set of routes is specified by the user Speed along the route can be variable A testing area (TA) is a surface with a set of testing obstacles. The TV model overcames the obstacles according to a route defined by the user. The image of TA is created in one of the CAD programs and imported to UM format in the standard manner.

Simulation of TV dynamics: test with driver Testing area Speed history along the route

Simulation of TV dynamics: test with driver Motion of an excavator along the route

Simulation of TV dynamics Excavator manipulations

Simulation results Any kinematic variables (trajectories, velocities, accelerations of any point, angles of rotation, angular velocities and accelerations of bodies) Plots of applied forces Plots of reaction forces Plots of special variables related to TV dynamics Animation files Special tools for multivariant calculations and processing of their results Factorial experiments

Special variables in the wizard of variables Animation of hystograms

Processor requirements UM implements parallel computation of TV dynamics with the help of multithreading It is strongly recommended to use multi-core processors The highest performance is achieved on eight-core processors (four physical + four logical cores)

Universal Mechanism Simulation of Tracked Vehicle Dynamics with www.umlab.ru um@umlab.ru