Däck-mark Interaktion hos skogsmaskiner
The most predominant method for forest harvesting in Sweden is the cut-to-length method based on two-machines, a harvester that fells trees and cut them in a predefined length, and a forwarder which transports logs to a landing area for further transport to a processing facility. New machine solutions have to be much gentler to the ground than today?s machines. To be able to develop a forestry machine that preserves the terrain requires a proper understanding of the interaction between tire and soil.The goal of the project is to contribute to the existing knowledge of forest machine tire-soil interaction and to develop a tire-soil model that enables dynamic simulations of forest machines operating in rough terrain. The modeling has especially been focused on the interaction between tires and soft ground.A comparison of theoretical data of different WES-based terrain interaction models and a comparison test data from a full scale field test is presented. Field test data included soil penetration and wheel rut depth (both first and multi-pass) data measured for two different forwarders with and without load for different tire pressures. Ground pressure at different depths below the wheel-soil interface and the soil moisture, were also measured. MATLAB was the primary modeling and analysis tool.Contribution from roots layers to bearing capacity has been analyzed through an extensive literature study and some analytical models were formulated using existing theories. Increase in bearing capacity has been estimated using available experimental data. Suitability of each model was also discussed. Because experimental data are not available in plenty, attention was paid to use as less parameters as possible, thus to increase use of the models. A program to estimate bearing capacity using different WES-based methods was created. The program is written in MATLAB and consists of a graphical user interface.The existing Valmet 860.3 Adams MBS model, developed through a series of degree project work, was modified to simulate effects from soft soil. Adams soft-soil model was used to develop the model. Tire properties were according to Trelleborg Twin 428 710/45-26.5. The stability of the model on a steep terrain with obstacles was examined and was found satisfactory. Since Adams soft soil road model is based on Bekker?s sink model, the results were compared with WES-based methods. The possibility of developing a user-written tire/road model based on WES-method was also presented.