APPLICATION OF LS-DYNA IN NUMERICAL ANALYSIS OF VEHICLE TRAJECTORIES

Errant vehicles may pose a serious threat to neighboring traffic of pedestrians, bicyclists, and even to their drivers in a densely populated urban environment. Accident reconstructions have indicated that street curbs do not offer any meaningful protection against errant vehicles, which can easily traverse street curbs even at small velocity and shallow angles. The paper presents research results of a study, in which computational mechanics was utilized to predict vehicle trajectories upon traversing standard Florida DOT street curbs. Computational analysis was performed using LS- DYNA computer code and two public domain, finite element models of motor vehicles: Ford Festiva and Ford Taurus. The suspension systems of the original vehicle models were evaluated and additional suspension components were identified and developed. The finite element models of the required suspension systems were developed using geometry from the actual suspension parts, captured using a digitizing arm. Due to complex geometry of these parts, the MSC-PATRAN preprocessor was used to create data for LS-DYNA code. Shock absorbers were modeled using discrete spring and damper elements. Connections for the modified suspension systems were carefully designed to assure proper range of motion for the suspension models. Inertia properties of the actual vehicles were collected using tilt-table tests and were used for LS-DYNA vehicle models. A standard FDOT street curb model was developed using rigid wall option in LS-DYNA. Initial, computational mechanics analyses suggest that vehicles tend to retain larger amount of their kinetic energy after traversing street curbs. It is therefore dangerous to anticipate that performance of street curbs would be comparable with that demonstrated by guardrails. In order to validate the assumed discrete numerical models and the results of LS-DYNA analyses, full-scale experimental tests have been performed at Texas Transportation Institute. Two types of vehicles have been tested: Ford Festiva and Ford Taurus, both for two values of approach angle: 15 and 90 degrees, with impact velocity of 45 mph. Experimental results including accelerations, displacements and overall vehicles behavior were registered by high-speed video cameras and have been compared with numerical results and computer animations. Verification results indicated a good correlation between computational analysis and full-scale test data. The study also indicated a strong importance of properly modeled suspension and tires on resulting vehicle trajectories. The major goal of the research was to study the behavior of various vehicles (from small Ford Festiva to pickup truck Chevrolet C2500), for different approach angles, velocities and curb profiles. Experiences gained in preliminary numerical analyses and experimental tests allow studying a matrix of critical cases without time- consuming and costly additional experimental testing.