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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.

The Simulation Model of Automobile Collisions (SMAC) computer program has been developed for the purpose of achieving uniformity in the use of analytical techniques for interpretation of physical evidence in investigations of highway accidents. The comprehensive output information of the SMAC program (kinematics, tire tracks, and vehicle damage) permits extensive, detailed comparisons with physical evidence in the iterative runs used to achieve a “best fit,” and the predicted vehicle responses provide a basis for relatively refined categorization of occupant exposures. The generality included in the inputs of the SMAC program permits approximation of the effects of driver control inputs, damage to vehicle running gear, and traversal of terrain zones with different friction properties. The analytical approach is outlined, and specific assumptions are defined. Comparisons are presented between analytical predictions and results of staged collisions.

A digital computer simulation of complex, three-dimensional dynamics of automobiles on irregular terrain is described which is suitable for studies related to vehicle braking systems and to the driving task, including the upper limits of control as well as the linear ranges of operation. The reported simulation is an extended version of an earlier, validated mathematical model. A number of refinements and extensions of the analytical treatments of tire forces, suspension properties, and terrain definitions, have been incorporated. Also, analytical representations of the braking system and driveline, and approximations of rolling resistance and aerodynamic drag, have been introduced. Sample outputs of the modified computer program are presented and discussed.

For several staged collisions, results obtained with closed form reconstruction calculations and with a computerized step-by-step procedure are compared with measured responses. A refined, closed-form reconstruction procedure is defined, derivations of the analytical relationships are outlined and detailed results of sample applications are presented. Closed form calculation procedures for estimating impact conditions became a topic of interest in relation to the development of an automatic starting routine for iterative applications of the Simulation Model of Automobile Collisions (SMAC) computer program. The accuracy of initial estimates of speeds determines the total number of iterative adjustments of SMAC that are required to achieve an acceptable overall match of the evidence. Since a high degree of success was achieved in the refinement of such calculation procedures, the end product, by itself, is considered to be a valuable aid to accident investigations.

A program of research was conducted to examine the validity of a digital computer simulation of an automobile occupant during a frontal, head-on collision. The simulation is designed to permit a detailed study of the effects of several types of restraint systems on occupant responses in a confined compartment, where injury-producing contact forces occur. The effects on occupant responses produced by the positions, orientations, and load-deflection properties of contacted interior surfaces are also simulated. This progress report covers one phase of a CAL long-range program of development of simulation techniques for study of occupant/vehicle and vehicle/obstacle collision responses. Detailed comparisons are presented of responses from instrumented sled tests and corresponding computed responses from the simulation. The comparisons include forces in restraint belts and on contacted surfaces, accelerations of the dummy, and the detailed kinematics of the dummy itself.

An unusual application of a computer simulation of automobile dynamics to the design of a thrill show stunt is described. The rationale for development of the simulation for highway safety applications is discussed and the general analytical approach is described. Computer graphics displays of simulation outputs, consisting of detailed perspective drawings of the vehicle and terrain features or obstacles at selected intervals of time during a simulated maneuver, are presented. For the presentation of the paper, computer graphics displays of simulation outputs will be animated through the use of motion picture film. Also, motion picture coverage of both developmental tests and public performances of the Astro Spiral Jump will be shown.

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.

AN ELEVEN-DEGREE-of-freedom nonlinear mathematical model of an automobile traversing a variety of irregular terrain features and encountering a variety of roadside obstacles has been formulated and programmed for a digital computer. The primary objective of the described research has been to develop analytical means of evaluating existing and proposed roadside energy conversion systems. However, the developed computer simulation also has potential applications in the reconstruction of single vehicle accidents and in studies of the driving task at the upper limits of vehicle control. A unique feature is the simulation of combined cornering and ride motions. In its present form, the computer program includes open-loop evasive maneuvers. The results of a review of single vehicle accident statistics and measurements of structural load-deformation properties of automobiles, performed within this research program, are both presented.

Correlation of injury with the nature and severity of the acceleration exposure in actual highway accidents is complicated by problems with uniformity in the interpretation of accident evidence. The SMAC and CRASH computer programs have been developed with the objective of providing aids for interpretation of physical evidence. Through the use of such aids in accident studies, it is possible to establish injury thresholds and mechanisms for living humans in relatively detailed exposures and under different conditions of restraint and protection. In addition to providing refined measures of the performance of protective devices, such studies can provide an improved basis for evaluation of test devices (i.e., anthropomorphic dummies and other surrogate crash victims). The existing forms and the evidence requirements of the SMAC and CRASH programs are described and results of pilot application studies are presented and discussed.