The vehicle dynamics module (VEHDYN 4.0) includes many enhancements to the previously documented and released VEHDYN II model and the internally developed, but not released, VEHDYN 3.0 model. The VEHDYN 3.0 model accepted the vehicle in a settled, or equilibrium, configuration instead of the "zero-force" configuration (the force acting on each suspension spring is assumed to be zero) required by VEHDYN II. VEHDYN 3.0 also included a special suspension and a band track model that were required to model the Caterpillar 30/30 engineering vehicle. VEHDYN 3.0 was further enhanced to add several other effects including: (1) a vehicle underside interference model that computes the normal and drag forces that occur when the underside of a vehicle's sprung mass comes in contact with the terrain profile, (2) a wheel damping model which computes an additional normal force component to represent the wheel's resistance to change, (3) a vehicle-terrain interface model to allow the terrain to deform, (4) accelerating and decelerating the vehicle using tractive force-speed relations and the soil-slope resistance, (5) rotational springs for enhanced suspension beam modeling, (6) a water-vehicle buoyancy and drag model to be used when a vehicle crosses a water-filled terrain obstacle, (7) numerous new run-type options including multi-run ride and shock performance sequences, slope climbing, obstacle crossing, etc., and (8) new postprocessors for animation. This report documents the VEHDYN 4.0 program, including the new enhancements, the input and output files and 12 example problems. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.
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