Launch vehicles produce high levels of acoustic energy and vibration loads that can severely damage satellites during
launch. Because of these high loads, the satellite structure is much more robust than it needs to be for on-orbit
operations. Traditionally, acoustic foam is used for acoustic mitigation; however, it is ineffective at frequencies below
500 Hz. For this reason we investigated three different modified acoustic foam concepts consisting of a thin metal foil, a
semi-rigid spacer, and a melamine foam substrate to improve the low frequency acoustic performance of the melamine
foam. The goal of the Hybrid Acoustically Layered Foil (HALF) Foam concept was to excite bending waves within the
plane of the foil to cause inter-particle interactions thus increasing the transmission loss of the foam. To determine the
performance of the system, a transmission loss tube was constructed, and the normal incidence transmission loss for each
sample was measured. The tests confirm the excitation of bending waves at the target frequency of 500 Hz and a
significant increase, on the order of 8 dB, in the transmission loss.
Extreme noise and vibration levels at lift-off and during ascent can damage sensitive payload components. Recently, the Air Force Research Laboratory, Space Vehicles Directorate has investigated a composite structure fabrication approach, called chamber-core, for building payload fairings. Chamber-core offers a strong, lightweight structure with inherent noise attenuation characteristics. It uses one-inch square axial tubes that are sandwiched between inner and outer face-sheets to form a cylindrical fairing structure. These hollow tubes can be used as acoustic dampers to attenuate the amplitude response of low frequency acoustic resonances within the fairing’s volume. A cylindrical, graphite-epoxy chamber-core structure was built to study noise transmission characteristics and to quantify the achievable performance improvement. The cylinder was tested in a semi-reverberant acoustics laboratory using bandlimited random noise at sound pressure levels up to 110 dB. The performance was measured using external and internal microphones. The noise reduction was computed as the ratio of the spatially averaged external response to the spatially averaged interior response. The noise reduction provided by the chamber-core cylinder was measured over three bandwidths, 20 Hz to 500 Hz, 20 Hz to 2000 Hz, and 20 Hz to 5000 Hz. For the bare cylinder with no acoustic resonators, the structure provided approximately 13 dB of attenuation over the 20 Hz to 500 Hz bandwidth. With the axial tubes acting as acoustic resonators at various frequencies over the bandwidth, the noise reduction provided by the cylinder increased to 18.2 dB, an overall increase of 4.8 dB over the bandwidth. Narrow-band reductions greater than 10 dB were observed at specific low frequency acoustic resonances. This was accomplished with virtually no added mass to the composite cylinder.
The cost of performing any mission on orbit is a strong function of the cost of getting the mass into orbit and the mass of a spacecraft is driven by the launch loads that the components must be deigned to survive. Additionally, these design loads vary between launch vehicles so if circumstances arise that require a change in launch vehicle significant time and money can be spent in modifying and testing to meet different requirements. Technologies that reduce both the vibration and acoustic environments during launch have the potential to both reduce the design load levels, and eventually equalize them between boosters. To this end the Air Force Research Laboratory, Space Vehicles Directorate in cooperation with the Space Test Program, Boeing SVS, CSA Engineering, and Delta Velocity have been investigating methods to decrease the acoustic and vibration loads induced on payloads by the launch environment and demonstrating them on a sounding rocket launch. The Vibro-Acoustic Launch Protection Experiment (VALPE) mission included an acoustically designed Chamber-Core skin, two passive/active vibration isolation experiments, a passive/active acoustic damping experiment, and an energy recovery experiment integrated onto a Terrier-Improved Orion sounding rocket and launched from NASA Wallops Island. A description of the overall mission, experiments, and general results from the flight test are discussed.
Aeroelastic control of flutter by means of trailing edge surfaces can be a very effective method, providing that
the actuation system is capable of generating suffcient force and displacement over the bandwidth of interest.
This effort describes the mechanical design aspects of a flap actuation system using V-stack piezoelectric
actuator and Q-parameterization technique for identifying the plant at supercritical speeds. A flap actuation
mechanism that takes advantage of the shape of the actuator (V) was designed. In order to validate the
actuation concept the actuator was integrated into a NACA 0015 typical section that was tested in the wind
tunnel at Duke University. An initial nominal controller was designed to stabilize the typical section for a
limited range of speeds above the open-loop flutter boundary. The technique of Q-parameterization was then
used to parameterize the unstable system as a function of stable systems, each derived from the nominal
controller. Operating in closed loop, flutter was suppressed at the speed it occurred in open loop, and the
flutter boundary was extended by more than 50%.
Aeroelastic control of wings by means of a distributed, trailing-edge control surface is of interest with regards to maneuvers, gust alleviation, and flutter suppression. The use of high energy density, piezoelectric materials as motors provides an appealing solution to this problem. A comparative analysis of the state of the art actuators is currently being conducted. A new piezoelectric actuator design is presented. This actuator meets the requirements for trailing edge flap actuation in both stroke and force. It is compact, simple, sturdy, and leverages stroke geometrically with minimum force penalties while displaying linearity over a wide range of stroke. The V-Stack Piezoelectric Actuator, consists of a base, a lever, two piezoelectric stacks, and a pre-tensioning element. The work is performed alternately by the two stacks, placed on both sides of the lever. Pre-tensioning can be readily applied using a torque wrench, obviating the need for elastic elements and this is for the benefit of the stiffness of the actuator. The characteristics of the actuator are easily modified by changing the base or the stacks. A prototype was constructed and tested experimentally to validate the theoretical model.
Conference Committee Involvement (9)
Industrial and Commercial Applications of Smart Structures Technologies IX
9 March 2015 | San Diego, California, United States
Industrial and Commercial Applications of Smart Structures Technologies VIII
11 March 2014 | San Diego, California, United States
Industrial and Commercial Applications of Smart Structures Technologies VII
10 March 2013 | San Diego, California, United States
Industrial and Commercial Applications of Smart Structures Technologies VI
12 March 2012 | San Diego, California, United States
Industrial and Commercial Applications of Smart Structures Technologies V
7 March 2011 | San Diego, California, United States
Industrial and Commercial Applications of Smart Structures Technologies IV
8 March 2010 | San Diego, California, United States
Industrial and Commercial Applications of Smart Structures Technologies III
9 March 2009 | San Diego, California, United States
Industrial and Commercial Applications of Smart Structures Technologies II
10 March 2008 | San Diego, California, United States
Industrial and Commercial Applications of Smart Structures Technologies
19 March 2007 | San Diego, California, United States