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In prior studies researchers have been interested in automating the process by which the Simulation Model of Automobile Collisions (SMAC) is used to reconstruct an accident. The SMAC program requires an initial approximation of the impact speeds and the positions and orientations at impact. And with a SMAC reconstruction you can sometimes get a reasonably close match and then spend many hours on iterative runs trying to match as best as possible the overall body of physical evidence. The prior research on automation of SMAC (during the time period 1975-1980) was constrained by computer time and resources. Those research projects were performed on mainframe computers where all applications included charges for CPU time and memory resources. Today with gigahertz Pentium computers and unlimited memory, aside from the initial cost of the computer, the cost per SMAC run is virtually free and the time for a run is measured in seconds rather than minutes.

The Simulation Model of Automobile Collisions (SMAC) computer program, developed in the early 1970's, includes a complex collision algorithm for monitoring, detecting and modeling the collision interactions of motor vehicles. A detailed review of some aspects of the logic, rationale and, in particular, limitations of the original SMAC collision algorithm is presented. This paper presents refinements in the definition of the collision interface, the definition of collision type, the vehicle proximity and collision detection logic, and the form of supplementary impulsive constraints on relative motions. The effects of the modifications of the SMAC algorithm on reconstruction results are presented in the form of direct comparisons of results obtained with the original and modified algorithms.

The trajectory solution procedures of the original CRASH program included both the SPIN routine and an exploratory trajectory simulation option to approximate and refine the linear and angular velocities at separation. The resulting separation speeds were then used to determine the impact speeds by means of application of the principle of conservation of linear momentum. This paper presents a detailed review of the logic, rationale and limitations of the trajectory solution procedures of the original CRASH program and discusses a number of refinements including: incorporation of the principle of conservation of angular momentum, approximations of the effects of changes during collision in the positions and orientations of the two vehicles and of the effects of external forces and moments that act on the two-body system during the collision, and adaptations of optimization techniques for error reduction and convergence in iterative solutions.

Research performed in the 1970's revealed significant limitations in the available documentation of vehicle crush information and trajectory spinout information. As a result a series of full-scale crash tests were performed which became known as the Research Input for Computer Simulation of Automobile Collisions (RICSAC) crash tests. Previous research using the RICSAC test results, particularly in relation to the validation of accident reconstruction computer programs, has varied widely in acceptance, interpretation and presentation of the RICSAC test results. This paper presents a detailed review and decipherment in useable form of the original 12 crash tests that were performed within the RICSAC program. A new method of analyzing accelerometer data from arbitrary sensor positions, on the basis of discrete measures of the vehicle responses rather than complete time-histories, is defined.

Effects of restitution on damage interpretations are compounded by the fact that restitution acts to reduce the amount of residual deformation, for a given maximum dynamic crush, while also acting to increase the total impact speed change. This paper presents a revised analytical procedure to include restitution effects for the CRASH program and refinements to the restitution modeling within the SMAC program. The conversion of vehicle impact test results into inputs for the two revised programs is also included. The effects of the refinements to the damage analysis procedures on reconstruction results are illustrated by direct comparisons with corresponding results produced by the original SMAC and CRASH programs and with measured data from full scale vehicle impact tests.

A brief description and history of the Highway Vehicle Obstacle Simulation Model (HVOSM) computer program is presented. A number of references are cited that include applications of HVOSM and which present detailed descriptions of related extensions and refinements. This paper focuses attention on simulation developments of HVOSM and validation efforts specifically related to the simulation of collisions with concrete median barriers (CMB).

A brief description and history of the SMAC computer program, including its relationship to CRASH, is presented. The rationale for a continued interest in the SMAC approach to reconstruction is discussed. Modifications and refinements that have contributed to the current capabilities of SMAC-87 are briefly described, representative results of applications are presented and planned future developments are defined.

A revised damage analysis procedure for CRASH, which includes restitution effects, is described. The proposed calculation procedure has the potential capability of (1) improving the delta-V accuracy in low-speed collisions and (2) segregating stiffness and restitution properties. The analytical approach can provide a basis for refinement of the categorization of vehicles through its use of additional crush property descriptors. Sample results from applications of a prototype computer routine are presented and compared with corresponding results from the original damage routine of CRASH. The reported research has been supported by McHenry Consultants, Inc.