Utilization
of Vehicle Test Course Speed Distributions to Refine Methods of Vehicle
Scenario Derivation for Laboratory Vibration Test Schedule (LVTS) Development.
Mr. Jesse Porter,
Mr. Michael
Abstract: The Aberdeen
Technical Test Center (ATC) and the Redstone Technical Test Center (RTTC)
studied speed distributions of ground vehicles tested on ATC road courses with
the intent to validate and refine distributions utilized during Laboratory
Vibration Test Schedule (LVTS) development. ATC and RTTC develop LVTS for
qualification of military hardware transported on various military
platforms. LVTS’s are intended to impart an
equivalent lifetime of fatigue into a system in a matter of hours utilizing
shaker tables, and consist of a spectral representation of the field vibration
with an associated test duration. LVTS development requires comprehensive
characterization of a systems vibration exposure, including duration for each
exposure condition. For ground vehicle transportation, vibration exposure
levels are measured via road testing on surfaces designed to replicate the
actual field environment. Individual data samples are acquired at
numerous speed steps (called data ru!
ns) over the expected speed range for a given surface. The required
exposure times for the individual data runs can be directly calculated from a
distribution of the total transportation miles into the individual speed
steps. Unfortunately, scenario information to this fidelity is typically
not available, and the mileage distribution must be derived. Given the
absence of other methods, RTTC developed a means to derive this association as
accurately and consistently as possible with the information available.
The method produces a shaped statistical distribution utilizing the Beta
function. The Beta function inputs include data run speeds, the average
speed, the maximum speed, and the analyst selected shaping parameters of Alpha
and Beta. Tables have been established at RTTC to allow consistency in
the selection of Alpha and Beta based on the ratio of the average and maximum
speeds. As no speed distribution data were available to RTTC at the time
the parameter selectio!
n tables were established, the tables are
subjective. ATC no!
w mainta
ins a database of test vehicle parameters, including histograms of speed
recorded during road testing. The database contains numerous vehicles
tested during the past few years, many of which include thousands of miles of
testing. The histograms of selected vehicles were compared to speed
distributions derived using the RTTC method to validate the use of the Beta
function. Additionally, the comparisons allowed refinement of the Alpha
and Beta selection tables. Affects of the test course limiting factors (length,
shape, speed limits, etc.) were also considered.
To return to the
Program, use the back button above