Aerospace & Defense Technology - October 2022 - 34

Tech Briefs
the three. Assuming there is no future
atmospheric intelligence, the PV array
will likely be underutilized and as a
result, excess fuel and energy storage
requirements will likely be incurred.
This work was performed by Gail
Vaucher, Morris Berman, Gordon
Parker, Michael Lee, Sean D'Arcy, Robert
Jane, and Thomas Price for the
Army Research Laboratory. For more
information, download the Technical
Support Package (free white
paper) at mobilityengineeringtech.
com/tsp under the Data Acquisition
category. ARL-0248
Laboratory Test Requirements for Marine Shock
Isolation Seats
Establishing practical testing procedures, instrumentation system guidance, data processing requirements,
and test criteria to demonstrate the effectiveness of a passive seat in reducing simulated wave impact loads
in a laboratory before installation in a high-speed planing craft.
Naval Surface Warfare Center, West Bethesda, Maryland
T
his research provides preliminary guidance
for laboratory testing of marine
shock isolation seats. The purpose of the
test is to demonstrate the effectiveness of
a passive seat in reducing simulated wave
impact loads in a laboratory before installation
in a high-speed planing craft.
Small craft that operate at high speeds
in rough seas subject the crew and passengers
to wave impacts that may cause
extreme discomfort. Craft designers therefore
often include shock isolation seats to
mitigate these negative effects. Current
design practice is to install seats that
employ springs and dampers (i.e., shock
absorber) or leaf-spring assemblies as protection
mechanisms. They are referred to
as passive seats because the spring-damper
assembly responds to individual wave
impacts with no active elements that
change in real time to adapt to the environment.
Spring-damper
assemblies are also
employed as protection mechanisms
on land vehicles (e.g., tractors, trucks,
automobiles, buses) and on-board larger
ships for mine blast protection.
Experience has demonstrated that
dynamic environments are different,
and that seats designed for land vehicle
or mine blast applications may not
protect against the unique characteristics
of wave impacts on small highspeed
craft. Seats have been installed in
craft only to find out during subsequent
seakeeping trials that they provide
little to no protection or amplify
base input motions. There is, therefore,
a need to provide guidance on how to
simulate these unique wave impacts in
a laboratory test that will demonstrate
the mitigation performance of passive
shock isolation seats prior to installation
in a high-speed craft.
Anthropomorphic test device (ATD) and steel plate payload weights (Photo courtesy of Defense Research
and Development Canada Atlantic)
34
mobilityengineeringtech.com
High-speed craft motions include all
six degrees of freedom: three translational
(i.e., heave, surge, sway) and three
rotational (i.e., pitch, roll, and yaw).
During severe wave impacts in head seas
the largest accelerations are in the vertical
(i.e., heave) direction, but the other
response degrees of freedom are just as
important for people. Feedback from
personal experiences indicates that any
force out of plane with the vertical axis
of standing or sitting that induces body
torque or bending can be just as punishing
as the vertical shock input. Simulation
of fore-aft accelerations during a
laboratory test is recommended herein
as a test option achieved by an angle
insert below the seat. Specific guidance
for required off-axis testing (i.e., not just
vertical testing) will be included in future
revisions as data becomes available.
This guide is applicable to shock isolation
seats used in high-speed planing
craft. The test criteria presented herein
are intended for planing craft ranging
from 7-meters to 30-meters in length.
The test procedures are intended only
for passive seats with no active sensors
or mechanisms for real-time adaptaAerospace
& Defense Technology, October 2022

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Aerospace & Defense Technology - October 2022

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