Extensions and refinements

Several extensions and refinements of the original SMAC program have been implemented into the m-smac program.  A brief summary or areas of extension and refinement follows:


Collision Modeling Extensions

      The radial vector scan routine has been modified to permit a 1 degree increment between radial vectors.   (The original version permitted a minimum of 2 degree increments.) (Input on Field 1, Card 13.)

      An optional adjustment capability of the longitudinal and lateral location of the coordinate center for the collision radius vectors has been added. (The original SMAC limited the location of the center of the collision interface to the center of gravity ) (Input card 96)

Impulsive constraints

      A simulation capability has been incorporated for optional impulsive constraints on the relative motions of the two vehicles during a portion of the collision contact. In many impacts, two colliding vehicles may momentarily interlock, with relative motion constraints that are independent of the magnitudes of the collision forces and therefore not adequately modeled with simple inter-vehicle friction. This option has been added to permit the modeling of such impulsive constraints (Input cards 16,18).

Steer degree of freedom

      The effects on vehicle motion that are produced by the responses of undamaged steering systems to external forces can be significant during spinout motions. This option has been added to permit the inclusion of those effects on the vehicle trajectory   (Input cards 25, 26.)

Polygon friction zones

      In addition to the existing linear boundary between terrain friction zones,  an option has been added to permit the additional definition of up to two polygon bounded terrain areas.  (Input cards 30,31,32.)

ReRead option

      In many collisions, tires may become deflated during the crash phase and/or during the subsequent spinout. SMAC has the provision to model time-history changes in the wheel Torque and Steering. However the modeling of changes in properties of the vehicle (such as tire side-force characteristics) were limited to a constant value. Refinements to m-smac permit the alteration of vehicle and/or tire properties at a selected time during the course of a simulation run. (Fields 2,3,4, Card 9999.)

Rear wheel steer time history

      The original SMAC has the provision to include a rear steer angle  (field 5, cards  4, 5). This value will remain constant during the simulation run. A refinement to the Steer tables has been added to permit the optional specification of changes in the rear steer angles during the simulation run, in the same manner as the front wheel steer tables. (Input Cards 10,11)

Articulated vehicles

      The reconstruction of highway accidents sometimes involves analysis of the collision responses of articulated vehicles  (e.g., tractor trailers and automobiles with trailers).  The m-smac program has added the optional capability to include the simulation of the additional degrees of freedom and tires associated with trailers on one or both of the vehicles.  (Input cards 2, 3, 20, 21, 22, 23.)

Optional Tire Friction Specification

      In some reconstructions, individual tires may exhibit different frictional properties due to inflation loss, rim gouging, and/or different tread materials (trucks vs. automobile tires).   This option permits modeling the changes that may occur.  (Fields 6-9, cards 6,7.)

Barrier option

      m-smac includes the provision for including the interaction between Vehicle 1 and a User defined barrier. The inputs for the barrier option are entered on cards 27, 28 and 29.

Please refer to the References 9, 10 & 11 for further information on the extensions and refinements.