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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.

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.