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This paper concentrates on some important aspects, restrictions and problems that should be considered when modelling off-highway vehicles. The main modelling interest is focused on log forwarder machines, see Figure 1 but indicated principles are easily generalize to the other kind of vehicles and machines. The mechanics, hydraulics, hydrostatic propelling system with control system, tire-road-interaction and system interaction were modelled by using ADAMS® (Automatic Dynamic Analysis of Mechanical Systems, ADAMS is a registered trademark of Mechanical Dynamics, Inc.) dynamic simulation software. Also the modelling of flexible parts with lumped-mass approach and assumed modes methods are discussed. The matters are examined mainly from the point of view of modelling techniques with the ADAMS dynamic simulation software.

This paper describes the development of a virtual prototype of a log forwarder using ADAMS dynamic system simulation software. The mechanics, hydraulics, hydrostatic propelling system with control system, tire-road-interaction and system interaction was modeled by using ADAMS. Also the flexibility of the boom mechanism was modeled. The virtual model was then verified with several different tests on actual hardware. This investigation concentrated on the simulation of forwarder dynamics, particularly in situations when the forwarder was moving. Firstly the virtual model performed a maneuver, in which the forwarder drove over small bump on the road at different speeds and loads. The same test was then performed with an actual forwarder, instrumented with acceleration sensors, placed on the bogie axles and a tachometer mounted on the propeller shaft to measure shaft rotational speed. Relatively good correspondence between measured and simulated results was achieved.

The present paper introduces a method based on dynamic simulation for determining the cyclic stresses in a hydraulically driven log crane. A detailed simulation model that defines a log crane was constructed. The simulation model incorporates a flexible spatial mechanism and a complicated hydraulic circuit. The complete simulation model was built up in the ADAMS mechanical analysis software environment in which the flexible mechanism model and the equations describing the hydraulic system were combined. The complete simulation model was verified by comparing actual measurements to numerical results. This comparison shows that there is a clear correspondence between the simulated and measured results. It was thus shown that it is possible to create a simulation model which can be used realistically for determining stresses in fatigue analysis. The obtained model was employed in the study of the fatigue stresses which are formed when the crane is being loaded.

The main purpose of this investigation was to develop the virtual prototype of the whole log forwarder by using ADAMS dynamic system simulation software. The virtual prototype contains hydraulic systems of the loader (except the grapple), mechanisms (steering, bogie axles), tire-terrain interaction, the log loader with structural flexibility and the control systems of the loader. Then the virtual prototype was validated with a simple procedure describing loading dynamics.