The following are our responses to questions we have received on SAE paper 97-0949 "CRASH-97 - Refinement of the Trajectory Solution Procedure"
Answer #1: During a collision, impulses act at each of the four wheel locations. The magnitudes of the impulses are dependent on a number of factors:
To approximate the effects of the external impulsive forces on the momentum equations, a new routine was created and tested as a part of SAE 97-0949. The routine was used together with the procedure which calculates the approximate separation locations and orientations. The ranges of the impulsive factors tested were:
An iterative procedure was required for refinement of the separation positions and orientations, from which the impulsive factors could be approximated. The impulse terms calculated were then included in the linear and angular momentum equations.
Answer #2: The primary evidence that one vehicle was stopped
in the case of a longitudinal and/or co-linear case is the extent of damage.
If the Delta-V from damage is approximately equal to the speed of separation,
a stopped vehicle may be indicated. Another discriminator or clue that
a vehicle may be stopped which exists in the momentum solution procedure
is a comparison of the calculated common and separation velocities.
For the results reported in SAE 97-0949, two simple tests for each vehicle were incorporated:
In the reported results of SAE 97-0949 to maintain focus on the trajectory solution procedure, the damage solution was not used, so the program defaulted to use the input VDI to approximate a ballpark damage-based Delta-V. A preliminary 5 MPH threshold was established for the comparison tests. The implementation of the low speed and/or stationary vehicle test in m-crash is as follows:
The next phase of the testing of the m-crash program will be to include the damage measurements. The refined values from the damage based solution procedure (outlined in SAE 97-0960) used in combination with the refinements to the trajectory solution procedure (from this paper, SAE 97-0949) should further improve the ability of the m-crash program to detect stationary and/or low speed vehicles.