A finite element modelling technique is being developed as a management tool that can be used to predict and avoid excessive soil compaction. Values of normal stress between a rigid wheel and the soil were obtained using an instrumented bar across the width of the wheel. These values were used to apply loads to the finite element model. A non-linear stress-strain relationship was used that shows that soil compaction is a function of both normal and shearing stress. The linear-elastic parameters, Young's Modulus and Poisson's ratio, are updated at small increments of load to follow the non-linear stress-strain relationship closely. Values of octahedraI normal (mean normal) and major principal stress are predicted accurately in some situations but not at the high load condition in an initially uniformly loose soil profile.

Soil stress states were measured beneath the path of a rigid wheel (137 cm diameter). A multivariate analysis of variance was conducted on the data to determine the effect on stress state caused by dynamic and tractive wheel loads, in different soil types and with or without the presence of a hardpan. Results should aid in decisions concerning soil compaction due to wheel loads.

Soil stresses under a rigid wheel loading were predicted with a finite element model using each of three different soil compaction models as the constitutive relationship. An energy analysis compared the energy lost in traction to energy absorbed in compaction as predicted by the finite element model. One constitutive relationship resulted in underprediction of energy absorbed in compaction while the other two resulted in overprediction. The method of energy analysis is shown to be a useful tool for evaluating accuracy of soil stress and strain predictions by a finite element model.

ABSTRACT Three-dimensional, color, real-time, interactive computer graphic simulation of mechanized tree felling is described. Buttons and dials serve as accelerator, steering wheel, brakes, and other control devices of a feller-buncher. Animation employs real vehicle parameters and actual forest stand data. The view through the feller-buncher windshield is displayed on a graphics terminal screen. Trees are cut and stacked by simulation operator. Data indicating initial and final state of forest are produced. Application to design is discussed.

ABSTRACT Dynamic properties of a wooden post (viscous damping, mass, and stiffness) were measured and used along with corresponding characteristics of a shaker (unbalanced mass, total mass, eccentricity, and frequency of rotation) in the development of a mathematical model to predict applied shaker force and motion. Three lengths of a wooden post were cantilever supported in a concrete base structure and shaken with an inertia-type linear trunk shaker. Motion and force at the point of attachment were measured and analyzed. Predominate components of the system were generated force, total shaker mass, and post stiffness. Measured force and motion data were used to calculate an effective post stiffness. Force and displacement amplitudes and post stiffness predicted by the model agreed reasonably well with measured values.