DD(X) UNDEX
DD(X) Machinery and Electronics Shock Mitigation Rafting: Equipment
Testing and Modeling
Joel Myers, Northrop Grumman Ship Systems
Mr. Jeff O'Brien, Anteon
Brendan Woolrich, Anteon
Vince Godino,
Dr.
Abstract: The DD(X) approach for reducing the shock
environment for machinery and electronics equipment is to employ shock
mitigated rafting systems. The reduced shock environment allows for the
use of commercial-off-the-shelf (COTS) or modified COTS (MOTS) equipment
instead of heavier and more expensive shock hardened equipment. The
testing methods developed for screening and qualification of the equipment are
presented. The static and dynamic equipment responses from the tests are
also used to build the finite element representations of the equipment in the
overall raft finite element model.
Several tests are performed on unique components (e.g. cabinets). First,
a static “pull test” is conducted to simulate maximum anticipated deflections
under shock and to determine whether any modifications are required prior to
qualification testing. This test also provides fundamental stiffness
properties used in modeling the component. Second, a “twang” test is
performed to derive damping properties of the component. Third, a “chirp”
test is conducted using base motion excitation. The test procedure is
described along with criteria that may be used to show that the test machine
meets the required input level. Alternative testing approaches are also
discussed.
An approach to selecting appropriate SRS criteria for shock qualification and
design is presented. Lessons learned during the test series are presented
that contribute to the SRS criteria development process.
Finally, equipment model development using the test data from the test series
is presented. A novel method for generating simplified shock finite
element models based on test data is shown.
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