Snag Option

The following example demonstrates some hypothetical inputs for a snag impulsive constraint. The snag impulsive constraint is often required when two vehicles collide head-on with a narrow overlap. With the original version of SMAC, simulations of narrow overlap head-on collision would produce results wherein the vehicles 'wedged' apart. In many instances for a narrow overlap head-on collision, the wheels or structure of the vehicles become momentarily interlocked during the collision which produces a CCW spinout subsequent to impact.

In our hypothetical example, ADVSAMP3, the interlock of the LF wheels is produced by the use of a snag impulsive constraint. The input cards are from Advanced sample project ADVSAMP3.prj, dataset ADVSAMP3.si5.

Care should be exercised in the use of the snag impulsive constraint and the preparation of inputs. The inputs for the snag impulsive constraint should be determined on an individual basis from an examination of the damage to the vehicles and extent of rotation. Also the specification of the location of the snag interlock position on vehicle one and the resulting location of the snag interlock position on vehicle 2 (produced by variation in the choice of initial time of the snag). In our hypothetical example, ADVSAMP3, the inputs were chosen based on the following criteria:

The initial contact overlap was determined by the extent of damage along the front of each vehicle

The LF wheel of vehicle 1 interlocked with the LF wheel of vehicle 2 which required  Snag option choice 2, and a location on vehicle 1  10" forward of the LF wheel centerline. (X1=60", Y1=-25")

The start time for the snag was determined by iterative adjustment until the start time produced a snag location in vehicle 2 coincided with a location 10" forward of the LF wheel of vehicle 2. (X2=60", Y2=-25")

The snag impulsive constraint was limited to 10 g's peak (vehicle weight * 10) / linear load-deflection rate of constraint

The onset of the snag was adjusted to limit the extent of damage along the vehicle length

 

The following is the inputs the snag impulsive constraint option is as follows:

 0.28    0.075   2.      60.     -25.    10000.  5.                            16

 

An echo of the inputs for the snag impulsive constraint option is as follows:

 

              TENSILE AND/OR IMPULSIVE FORCE                    

               TIME,BEGIN (T,I)FORCE   =    .280 SEC.                

               TIME (T,I)FORCE DURATION=    .075 SEC.                 

               (T,I)OPTION,REACTION LOC=     2.(=0 NONE,=1 SPACE FIXED,=2 VEH2)

               XSP1,X IN VEH 1,FORCE PT=  60.000 INCHES        

               YSP1,Y IN VEH 1,FORCE PT= -25.000 INCHES        

               AKSP,LINEAR LOAD-DEFLEC.= 10000.0 LB/IN         

               DELSPM,SATURATION DEFLEC=   5.000 INCHES

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SMACTHP Example with RICSAC2