We present the development of a three-dimensional Vehicle/Tire/Terrain Interaction Model (VTTIM) consisting of a general 3D tire-terrain traction model which operates on a novel deformable terrain representation that utilizes a soil compaction model. Rather than utilizing popular empirical terramechanics models that only consider the pressure/sinkage directly under the tire, the governing equations of the terrain are based on i) the propagation of subsoil stresses due to vehicular loads, and ii) the resulting stress/strain which is based on a visco-elastic-plastic soil model developed by Ayers and Bozdech. The implementation of the terrain model is modularized in the form of an API, as the vehicle and tire are assumed to be contained in commercial simulation software as to focus on the implementation of the deformable terrain model. A number of test simulations are run using a rigid tire with and without grousers to show the capability of the VTTIM to predict tire forces for use in vehicle mobility and traction performance simulations. Power and energy required to deform the terrain will also be presented with the simulation results, which allows the prediction of the extra power required by a vehicle traveling on off-road, deformable soil.

A time-accurate finite element model for predicting the dynamic response of tracked vehicles is presented. The model supports flexible continuous belt-type tracks and segmented-tracks consisting of rigid and/or flexible links connected using revolute joints. The flexible multibody system representing the tracked vehicle is modeled using rigid bodies, flexible bodies, joints and actuators. Flexible bodies are modeled using total-Lagrangian brick, membrane, beam, truss and linear/rotational spring elements. The penalty method is used to impose the joint/contact constraints. An asperity-based friction model is used to model joint/contact friction. A recursive bounding box contact search algorithm is used to allow fast contact detection between finite elements and other elements as well as general triangular/quadrilateral surfaces. The governing equations of motion are solved along with joint/constraint equations using a time-accurate explicit solution procedure. The model can help improve the design of tracked vehicles including increasing the vehicle's stability and durability.

A time-accurate finite element model for predicting the coupled dynamic response of tanker trucks and their liquid payloads is presented along with an experimental validation of the model. The tanker truck components are modeled using rigid bodies, flexible bodies, joints and actuators. The model is validated using a full-scale army heavy class tactical trailer carrying a water tank. The trailer is placed on an n-post motion base simulator which was used to perform harmonic/ramp pitch, roll and stir excitations of the trailer in order to simulate typical road maneuvers. Experiments were carried out with an empty tank and a 65%-filled tank. The time-histories of the tires and suspension system deflections are measured for the various input motion excitations. The experiment's measurements are compared with the results predicted using the computational model. The comparison shows that the model can predict with reasonably good accuracy the test tanker-trailer's dynamic response.

As part of the evaluation of vehicle simulation models, a vehicle dynamics engineer typically desires to compare simulation results to test data from actual vehicles and/or results from known, or higher fidelity simulations. Depending on the type of model, several types of tests and/or maneuvers may need to be compared. For military vehicles, there is the additional requirement to run specific types of maneuvers for vehicle model evaluations to ensure that the vehicle complies with procurement requirements. A thorough evaluation will run two different categories of tests/maneuvers. The first category consists of laboratory type tests that include weight distribution, kinematics and compliance, steering ratio, and other static measures. The second category consists of dynamic maneuvers that include handling, drive train, braking, ride, and obstacle types. In this paper, a process for proper evaluation of vehicle simulation models is presented. A method for evaluating simulation results from different simulation programs is also presented.

: A study for validating a time-accurate explicit finite element code for modeling fully-coupled flexible multibody systems carrying liquid-filled tanks is presented. The multibody system includes rigid bodies, flexible bodies, joints, and actuators. Rigid bodies rotational equations of motion are written in a body-fixed frame with the total rigid body rotation matrix updated each time step using incremental rotations. Flexible bodies are modeled using total-Lagrangian spring, truss, beam and hexahedral solid elements. A penalty model is used to impose the joint/contact constraints. An asperity based friction model is used to model joint/contact friction. The fluid governing equations of motion are the incompressible Arbitrary Lagrangian-Eulerian Navier- Stokes equations along with a large-eddy simulation (LES) turbulence model. The fluid's free-surface is modeled using an acceptor-donor volume-of-fluid based algorithm. Coupling between the fluid and solid is achieved by solving Newton's equations of motions at the fluid-solid interface nodes. The validation study is conducted using a multibody system consisting of a rigid baffled tank mounted on suspension springs. The springs are connected to a rigid frame mounted on two linear hydraulic-actuators. Experiments with various input ramp and harmonic excitation from the actuators are performed and the results of the experiments are compared to the results obtained using the model. The system response is measured using linear-displacement transducers at the springs and two cameras showing side and front views of the tank. The results show that the model can predict with reasonably good accuracy the test system's dynamic response.