Function and Methods

VeCor is a tool for automated assessment and correction of non-oblique VTB and VTV vehicle crash test data. The impact direction accelerations and the total barrier force (if VTB test) are input with any available supplementary information and the set of calibration, bias, and time shift errors which best explain deviations from physical, kinematic, and measured relationships are computed and reported. The corrected UDS files can also be generated if desired.

Default relationships provided by VeCor consider bias in the pulse tails, differences in the velocities within each vehicle at the end of the test, deviations from momentum/impulse balance over the duration of contact, and the time of initial response for each pulse. The default relationships can be altered or suppressed by the user.

Optional relationships include specifying velocities, displacements, or relative displacements of pulses at specific instant. The weight applied to each relationship by VeCor to determine a best solution is controlled by confidence ranges for each relationship, which can be user-specified or allowed to default to preset values. Relative timing constraints can also be specified to assure that the sequence of initial responses agrees with knowledge of the vehicle construction.

Typical inputs required for an accurate solution would be the velocity and displacement of a target pulse in each vehicle at a time near the end of the pulses, relative crush between the accelerometers of each vehicle, and the approximate time of separation between the vehicles or vehicle and barrier.

VeCor uses a weighted quadratic minimization approach to determine the best solution for the errors in each pulse. The time shifts appear nonlinearly, requiring a grid/gradient search of the time shift domain. The user can control the thoroughness of this search, although searching from many points is time consuming and has been unnecessary in trials. For any time shift solution, the calibration and bias solutions are found by solving a linear system of equations for the unique zero of the gradient of the total deviation error.

Features and Options

VeCor allows a wide range of supplementary information to be used in determining the pulse errors. Although more information assures a better result, a reasonable solution may be possible with very little information. By assigning small contributions to the total error for the pulse errors themselves, VeCor generates determinate (i.e., nonsingular) minimization problems and allocates reasonable amounts to each pulse error when the supplementary information alone is insufficient to uniquely determine all of the pulse errors.

The user can control the solution by supplying reasonable 95% confidence ranges for the supplementary information and the pulse errors. This determines the weighting applied to deviation errors for each relationship.

Setup and Run Instructions

The command line syntax is: VeCor [input_file]

VeCor will prompt for a VeCor input file if none is specified on the command line.

Usage Recommendations

Barrier force signals with positive-valued impact loads must be given a "+" sign flag in the VeCor input file. Negative-valued barrier forces can be given a "-" sign flag or no sign flag.

Relative displacement (DR) targets can be added for signals from the same or symmetric locations, such as multiple occupant compartment signals or the left and right front wheels in a full frontal impact. The DR confidence bands should usually be fairly loose (50-200 mm), especially for less consistent motions such as wheel or engine top and bottom signals.

Set film displacement constant (DC) targets with a 1 ms time span and bands of 25-50 mm for high confidence targets and 50-200 mm for low confidence targets.

Use a velocity scatter (VS) target override specifying the full time-span for final velocities to be brought together and adjust the confidence band as needed to obtain sufficiently consistent final velocities.

Set momentum balance (MO) target time span to 10- 20 ms around the time when the barrier force, if available, and the accelerations drop to near zero.

Apply top-of- engine film displacement targets to the Engine - Top signal only.

Use wide/standard target confidence intervals first and then reduce/adjust as necessary.

Check/correct any signals yielding negative calibration values for sign-inversion.

Check/correct any signals yielding large calibration values for units mis-scaling. If signals with large but unknown mis-scaling will be used an estimated scaling (1/Calibration) value should be specified for the signal in the S column and refined over a few VeCor runs to allow the full scaling correction to be made without distorting the rest of the solution. A similar approach can be applied for large biases.

Known Problems and Constraints

VeCor is currently limited to impact direction pulses from non-oblique VTB and VTV crash tests.

VeCor solutions may be degraded by the presence of significant nonsystematic errors (instrument rotations, signal clips, channel failure, etc.), or if insufficient or inaccurate supplementary information is provided. In such cases the VeCor solution will still indicate the presence of large errors, and the corrected data may still be useful for some quantitative applications. It is best remove obvious large non-systematic errors before running VeCor.

VeCor is limited to one force pulse and up to 20 accelerometer pulses. Search of the time shift domain from more than a single point may be impractically time-consuming for interactive runs with more than five pulses.

Additional Documentation

See The VeCor Program for complete VeCor documentation.

A template for the input file can be found in the VeCor Input Template.

A history of program changes can be found in the VeCor Change Log.