Barry A. Coutermarsh

All-Season Virtual Test Site for a Real-Time Vehicle Simulator

Abstract : A virtual, all-season test site for use in real-time vehicle simulators and mobility models was constructed of an Army firing range in Northern Vermont. The virtual terrain will mimic the terrain of our Virtual Data Acquisition and Test Site (VDATS) at Ethan Allen Firing Range (EAFR). The objective is to realistically simulate on- and off-road vehicle performance in all weather conditions for training and vehicle design for the US Army. To this end, several spatial datasets were needed to accurately map the terrain and estimate the state-of-the- ground and terrain strength at different times of the year. The terrain strength is characterized by terramechanics properties used in algorithms to calculate the forces at the vehicle-terrain interface. The performance of the real vehicles will be compared to the simulated vehicle performance of operator-in-the-loop and unmanned vehicles for validation of the simulations. Real vehicles are instrumented and perform maneuvers at the test site to develop and validate mathematic models describing vehicle behavior in all-season conditions, including snow, ice, frozen and thawing ground.

Static analysis of floating ice block stability

A laboratory study was performed to measure the pressures caused by fluid acceleration beneath a floating parallel-piped block. Dynamic fluid pressure was measured at discrete points beneath the block for various fluid velocities, block angles of attack and block thickness-to-depth ratios. Some of these pressures tended to stabilize the block while others tended to underturn it. The measured pressures were used to calculate block underturning moments and a hydrostatic analysis was used to calculate a block righting moment. From this, a densimetric Froude underturning criteria is presented.

Modeling Heavy Wheel Loading on Frozen and Unfrozen Ground

Two ABAQUS 3-D Finite Element Models (FEM) were constructed with hyper-elastic rubber tires loaded on unfrozen and frozen ground conditions (0, 7.62, 15.24, 22.86, and 30.48 cm frost depths), one contained a statically loaded tire, and the other contained a tire rolling at 8.05 km/h. The ground was constructed of multiple layers, allowing each of the respective frost depths to be adequately modeled. This was accomplished by changing the material properties in the layers to match the given frost condition. The material models used in the FEM simulations are representative of a frost-susceptible soil, which was used in full scale unpaved road tests at CRREL. The interest in this modeling is to see how the stress and displacement change as a function of frost depth as a heavy tire rolls over the surface. Stress and displacement data collected from the ABAQUS FEM simulations are compared to experimental data. The results show similar trends between the ABAQUS and experimental data for vertical displacement and vertical stress below the contact patch.

Using Soil Stress State Transducers in Freezing Ground

Three instrumented test sections of sand, silt and clay, were constructed to monitor the impact of frost layers on vehicle induced stresses and to assess the performance of the sensors used to measure such stresses. One of the instruments used to measure in-situ stress is the soil Stress State Transducer (SST), which was installed at 12.7cm depth within each of the test soils. The SST was designed by the USDA Agricultural Research Service, National Soil Dynamics Laboratory and the Auburn University Department of Agricultural Engineering, and has been used in many studies on vehicle induced stresses in agricultural soils, but not previously in freezing soil. Each SST consists of six semiconductor pressure transducers installed in a small sphere. Soil displacements, temperature and moisture and strength profiles were also monitored. Trafficking of the test sections was performed at frost depths ranging from zero to over 50 cm. The SSTs functioned very well in frozen ground. The signals clearly showed the passage and sometimes the bow wave in front of each tire, and then the large vertical pressure spike as each tire passes over the sensor. The stress magnitudes diminish as the ground freezes above the sensors and then decrease further as the frost envelops the entire sensor.

One-Dimensional Computer Models to Estimate Frost Depth

The impacts and detrimental effects of frost in regions that experience seasonal variation are well documented. The effects of successive freezing and thawing cycles on soil and other substrates, as well as vehicle mobility through the surface-vehicle interface, play a prominent role in transportation. Freezing and thawing are not limited to only geographic locations that experience severe and prolonged cold; even brief periods of low temperatures or freeze-thaw cycling can disrupt transportation operations. At selected locations in North Korea, the depth of frost penetration was estimated using a one-dimensional heat flow model based on the Modified Berggren solution. At one of the locations, the progression and duration of frost penetration over five successive freezing seasons was estimated using a separate one-dimensional heat and moisture flux model. With uncertainties regarding climate change under consideration in design and operations, this type of analysis is even more crucial. A spreadsheet and graphical user interface (GUI) are proposed for ease-of-use by persons unfamiliar with thermal analysis and heat transfer in soils. A tool of this type would lead users through the necessary calculations and assumptions.