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KC-135: Particle Damping in Vibrating Cantilever Beams Midterm Report
Team Leader: Bill Tandy Rob Ross
John Hatlelid Tim Allison
Advisors: Marcus Kruger, Dr. Ronald Stearman
The University of Texas at Austin Department of Aerospace Engineering and Engineering Mechanics
March 5, 2004
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MEMORANDUM
TO: Dr. Ronald O. Stearman, Marcus Kruger, Jennifer Lehman FROM: William D. Tandy, Jr., Tim Allison, Rob Ross, John Hatlelid DATE: March 5, 2005 SUBJECT: KC-135 Particle Damping Project Midterm Report Dear Dr. Stearman: The following report contains detailed information about the KC-135 Particle Damping Project. After our proposal (submitted to NASA during the fall 2003 semester) was accepted by NASA, our objectives for this semester included building an experimental apparatus and conducting our experiment on the KC-135. This document gives the details regarding the various aspects of our project, including the project team, project background, supporting theory, structural and electrical design, budget, and schedule. You will find that our project is currently on schedule and within budget. We anticipate that we will accomplish all of our objectives this semester. Please do not hesitate to contact us if you have any questions. Sincerely, William D. Tandy, Jr. Project Leader Tim Allison Flight Crew Rob Ross Flight Crew John Hatlelid Flight Crew
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Abstract
Five students from the University of Texas at Austin are working with NASA’s student flight opportunity program to test the effectiveness of particle damping on cantilever beams in a reduced gravity environment. The concept of the experiment was derived from industry inquiry into the applicability of particle damping on space structures. However, due to a lack of data the idea has seen limited use on actual flight hardware. To investigate the effect of particle damping in a microgravity environment the team of students designed, built, and are currently testing a series of cantilever beams filled with particles of varying material properties. The accelerations at the end of the cantilever beam will be measured with an accelerometer and data recorded with National Instrument’s suite of software applications. It is expected that at the conclusion of testing that clear differences in the magnitude and frequency of accelerations will be evident when comparing nominal, ground gravity influences and the reduced gravity field environment available on NASA’s KC-135. The flight dates for the team are April 1-10.
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Acknowledgements
We would like to express our gratitude to the following individuals and companies:
Dr. Ronald O. Stearman: For providing advice regarding our equipment design and for supporting our team’s experiment with NASA.
Marcus Kruger: For his input during our weekly meetings. His
experience has been invaluable. NASA Reduced Gravity Office: For administrating the Reduced Gravity Student
Flight Opportunities Program and helping us with our experiment.
UT Department of ASE/EM: For the funds they provided to us and the equipment
they allowed us to borrow. We would have been unable to conduct the experiment without them.
Texas Space Grant Consortium: For providing funding to our project. They are
accomplishing their mission of making NASA’s goals achievable for every Texan.
Honeywell: For generously donating equipment for our project. National Instruments: For generously providing software licenses and
equipment.
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Table of Contents
1.0 Introduction................................................................................................................... 1 1.1 NASA Student Flight Opportunity ........................................................................... 1 1.2 Project Background................................................................................................... 1 1.3 Experiment Basis ...................................................................................................... 2 1.4 Experiment Setup...................................................................................................... 3
2.0 Project Description........................................................................................................ 4 2.1 Design the experiment .............................................................................................. 4 2.2 Write a successful TEDP .......................................................................................... 6 2.3 Fly the experiment .................................................................................................... 6 2.4 Draw conclusions from the data ............................................................................... 7
3.0 Team member’s roles.................................................................................................... 8 4.0 Theory ......................................................................................................................... 10
4.1 Particle Damping .................................................................................................... 10 4.2 Viscoelastic Damping ............................................................................................. 10 4.3 Frictional Damping ................................................................................................. 11 4.4 Beam Response to Harmonic Excitation ................................................................ 12 4.5 Analytical Goals...................................................................................................... 14
5.0 Test-bay Design .......................................................................................................... 16 6.0 Progress Made............................................................................................................. 21
6.1 Test Bay Structural Analysis .................................................................................. 21 6.2 Test Bay Construction............................................................................................. 21 6.3 Data Acquisition System Design ............................................................................ 21 6.4 DAQ System Hardware Acquisition....................................................................... 25 6.5 Experimental Hardware System Design ................................................................. 26 6.6 Experimental Hardware Acquisition....................................................................... 29
7.0 Project Budget............................................................................................................. 30 7.1 Project Costs ........................................................................................................... 30 7.2 Project Funding and Other Assistance.................................................................... 32 7.3 Financial Status of the Project ................................................................................ 34
8.0 Schedule...................................................................................................................... 35 9.0 References................................................................................................................... 37
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List of Figures and Tables
Table 1: Experiment Cost Details ...................................................................................32
Table 2: Sources of Funding and Other Assistance ........................................................34
Table 3: Project Tasks.....................................................................................................35
Figure 1: Setup for Vibrating Rod ....................................................................................3
Figure 2: Maxwell Model for Damping Particles ...........................................................11
Figure 3: Single Impact Particle Damper........................................................................12
Figure 4: Cantilever Beam with Harmonic Base Excitation...........................................12
Figure 5: Bottom test bay door with handle mount ........................................................18
Figure 6: Bottom test bay door with handle mount and hinges ......................................19
Figure 7: NI-6035 DAQ Card .........................................................................................23
Figure 8: NI-SC-2345 Shielded Carrier..........................................................................24
Figure 9: NI-SCC-ACC01 Accelerometer Module ........................................................25
Figure 10: Honeywell Sensotec PA Accelerometer........................................................28
Figure 11: Gant Chart .....................................................................................................36
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1.0 Introduction The following sections outline the background and introduction of the team’s project.
The first objective is to introduce the NASA project, followed by the impetus driving the
experiment. A brief description of the theoretical basis of the experiment is the next step,
and finally, a rough sketch of the experiment setup is outlined.
1.1 NASA Student Flight Opportunity NASA sponsors students annually in their Reduced Gravity Student Flight Opportunity
Program. The purpose of the program is to enable students to perform experiments and
collect data in a near zero gravity environment. The reduction in gravity is achieved by
using a KC-135 aircraft that flies a parabolic trajectory above the Gulf of Mexico.
According to NASA the aircraft will fly approximately four sets of ten parabolas, for a
total of forty periods of reduced gravity. Each period of reduced gravity lasts
approximately thirty seconds.
While the flights are the focus of the student program, NASA will first work with
students in a week long orientation process. Some of the highlights are medical exams,
orientation sessions, hyperbaric chamber testing and working one-on-one with a NASA
engineer on the experiment setup.
1.2 Project Background The concept of the experiment was derived from Bill Tandy’s internship experience with
Ball Corporation in Boulder, Colorado. The company was investigating unique solutions
for the problem of reducing the magnitude of vibrations on a space structure. Among the
competing designs was the use of numerous particles enclosed within hollow structural
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beams. Although the preliminary analysis showed promise, it was decided that the lack
of data for a system in reduced gravity posed too great a risk compared to more
traditional methods. Upon learning that NASA’s reduced gravity office was once again
offering students the opportunity to fly on their KC-135, a team was formed with the goal
of gathering vibration data in a reduced gravitational environment for a structural
component damped with particles.
1.3 Experiment Basis Particle damping works by dissipating kinetic energy through other forms of energy such
as sound and heat. Additionally, the mostly random motion of the particles effectively
increases the natural frequency of the structural member. However, it is seen from
previous research that the effectiveness of particle damping depends strongly on the
material properties of the particles and the volume available for particle motion [1]. In
general, it is seen that particles with higher density perform better than lower density
particles, but at the cost of increased weight.
A particle’s energy loss will be most effective when it converts all of its kinetic energy to
thermal energy or in the creation of sound waves. A particle that travels faster before an
impact will convert more energy than a slower version of identical material properties.
Therefore, an ideal fill volume will allow a particle to travel to near a constant velocity
before impacting with another particle or the structural wall. From another point of view,
the smaller the distance between particles the more the combined particles approach a
homogenous mass. Although the additional mass will inherently reduce vibration due to
inertial properties, the mass will counteract the goal of minimal mass structures.
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Therefore, there is an optimal fill ratio of particles given a volume and material properties
for each situation.
1.4 Experiment Setup To investigate the described phenomena the team decided to test cantilever beams with
an accelerometer attached to one end and a vibrator at the other end (See Figure 1). The
strategy involves varying the particle material and fill ratio in twelve otherwise identical
rods. A thirteenth control rod, which will contain no particles, will be used to compare
collected data. To further compare data the experiment will be run on the ground at
nominal values of gravity, and then in the KC-135 aircraft where relative acceleration of
gravity approaches zero. The data collected will be used to create average acceleration
magnitude vs. time plots. Specifically, the plots will be used to investigate three areas:
the transient, steady-state, and decay periods.
Figure 1. Setup for Vibrating Rod
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2.0 Project Description The project was broken up into three key areas. The first step was to design the
experiment. To do so involved considering numerous variables such as the requirements
set by NASA and ensuring that the project goals did not exceed the team’s time
constraints. The next step was to perform the tests on the ground and in the air. Finally,
the third step will be to reduce the data to comprehensible and comparable data trends.
2.1 Design the experiment The experiment design was based on meeting several different goals. The first and most
important objective was to meet budget constraints. Regardless of the importance of the
work, if it couldn’t be done within the available funds we would not be able to proceed.
From this constraint it was decided that the structure would be reduced from an original
design of a cylinder with inward pointed radial beams to a simple cantilever beam. It was
also decided that it would be necessary to procure as much equipment as possible through
donations.
Next, it was necessary to decide exactly what sort of samples to test. There are a number
of different criteria which are important in the design of a structure which undergoes
frequent vibration. These include the displacement magnitude seen under vibration and
the natural frequency of the structural supports. However, from Bill’s experience in
industry, the values which are used most often are the power spectral density of the
acceleration of the beam when compared with a range of frequencies at different time
intervals. Unfortunately, the time constraints of the experiment prevented the team from
testing under a range of frequencies. Therefore it was decided to test a control specimen
at a specified frequency and then test the remaining beams at the same frequency and
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measure the accelerations of the tip of the beam over a time interval. The control
specimen is identical to the other beams except that it does not contain any particles. By
comparing the magnitudes of the accelerations for each beam with the control specimen,
correlations and comparative plots could be made. Conclusions can then be drawn from
the formatted data.
The third objective was to test as many different types of particles as possible within the
time constraint, which is set by the number of parabolas flown by NASA. The KC-135
will fly approximately 30 parabolas. Each parabola provides nearly zero gravitational
influence on the experiment for approximately twenty seconds. The time between
experiment windows is about one minute. The original plan called for thirty different
pre-filled beams which would be attached to a vibrator in between the aforementioned
experiment windows. However, from first hand accounts of previous flyers it was
determined that due to the nearly two and a half gravitational field effect at the bottom of
the parabola that swapping beams between parabola peaks would not be practical. The
solution was to swap beams during parabola peaks and reduce the number of beams by
half. It was then decided to allow a factor of safety in case an experiment needed to be
redone or there was insufficient preparation time so that the final number of beams was
set to twelve.
With a rough idea of the layout of the experiment it was necessary to determine the
particle properties. The goal of the experiment was to compare different particles and
their effect on structural damping, both on the ground and at reduced gravitational levels.
To accomplish this goal a variety of particles would need to be selected. The variables
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the team chose to modify were the particle density, size and the amount of particles
within the beam. Specifically, the first material will have the least density and will be
available in two different sizes. Each of these sizes will be used to fill one beam 50%
and another beam 75%. The same will be done with a higher density material. Finally, a
third material of the highest density will be used, following the same logical process. By
varying the properties through twelve iterations and testing each sample multiple times
through two days of flights it is expected that consistent data will be collected from
which reasonable conclusions will be able to be made.
2.2 Write a successful TEDP As part of the process of flying with NASA, numerous reports with in depth discussion of
relevant topics needed to be created. In particular, NASA requires a Test Equipment
Data Package (TEDP) which discusses the experiment and required safety in detail. The
report was successfully completed and sent to NASA for approval on February 20, 2004.
2.3 Fly the experiment The experiment will fly April seventh and eighth, barring inclement weather. In case of
unsafe flying conditions there are two alternate days, the ninth and tenth of April. The
team will be in Houston from April first to the tenth as part of the NASA requirements
for further medical exams and training. During this time the team will also be able to
spend time with NASA engineers to discuss in person the objectives of the experiment, as
well as its implementation. Any modifications will be made according to their
suggestions both before and after the first flight. As a team we will also be able to
analyze the first flight’s data and make any changes before the second flight the next day.
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2.4 Draw conclusions from the data The accelerometer data collected during both ground experiments and in-flight
experiments will be used to draw conclusions about the effectiveness of particle damping
in microgravity. The peak acceleration amplitude will be plotted against time, allowing
us to see the length and magnitude of vibration in each sample during the transient,
steady-state, and decay periods of vibration. Dr. Stearman has also recommended that we
record the transfer function of the signal and obtain damping information from that. We
are currently examining that option to see how to implement it in our experiment.
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3.0 Team member’s roles It was determined at the beginning of the project that in order to successfully complete
the experiment within the allowed time frame that responsibilities would need to be
delegated to each team member. Each item of importance was discussed as a team before
being assigned to a member for the remainder of the project. The team had weekly team
meetings and near daily discussions which allowed for a constant stream of
communication between the team members.
Because the experiment concept originated from Bill Tandy’s experiences and also
because he was the most familiar with the technical nature of the project goals it was
decided that he should be the team leader. As the team leader his primary responsibilities
were to manage the team paperwork and correspondence with NASA, attend the
aerospace department’s faculty update meetings, arrange and attend community outreach
activities through the department, and to otherwise assume responsibility for the project
as a whole.
Tim Allison’s strengths include exceptional dedication and organizational skills. Based
on these skills he was initially assigned the responsibility of finding and applying for
additional funds. Shortly thereafter he was assigned the task of collecting and sending
the medical evaluation forms for NASA, as well as managing the travel arrangements for
the team while in Houston. Tim also works with Dr. Benninghof, professor of the
university’s structural dynamics department. With this background Tim was assigned the
theoretical sections of all the papers due during the course of the project.
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Robert Ross has an aptitude for construction and design. He was therefore assigned the
task of designing and constructing the experiment’s cabinet, used for both running the
experiment and for transporting it on the ground and in the aircraft. His approach was
based off initial specifications laid out by NASA and also by preliminary designs drawn
in the experiment design stage. It was also Rob’s responsibility to locate and purchase
the necessary materials for the cabinet. In addition to the cabinet, Rob volunteered to
complete weekly memos for the team and for Dr. Stearman, the project’s faculty advisor.
John Hatlelid is thorough and diligent when completing assignments. Based on these
assets he was asked to research the equipment necessary to complete the experiment.
After determining the required information his goal was to apply to the appropriate
companies for donations and/or student discounts. John was also responsible for
collecting and sending paperwork to NASA.
In addition to individual roles, all team members were expected to contribute to the
required reports and to participate in any miscellaneous tasks that needed to be
completed. Also, although individuals were assigned large tasks, the help of all team
members were required to complete each area of importance. In general, all team
members worked on all aspects of the project with each individual being the primary
person responsible for specific tasks.
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4.0 Theory This section describes the physical principles behind particle damping, explains the
response problem for our system, and explains the theory-oriented goals we have
developed for our project.
4.1 Particle Damping Particle damping is a creative technique used to reduce vibrations in a structure. Particles
are placed in a cavity attached to or inside a structure and dissipate energy when the
structure vibrates. This energy dissipation is accomplished by two mechanisms:
viscoelastic damping and frictional (coulomb) damping.
4.2 Viscoelastic Damping This type of damping is due to inelastic collisions among damping particles and between
the particles and cavity walls. A collision between two bodies results in a transfer and
loss of energy, and is governed by the following two equations [1]:
aabb vmvmvmvm 22112211 +=+ (1)
bb
aa
vvvv
e12
21
−−
= (2)
In equations (1) and (2), m stands for the particle mass, v for velocity, and the subscripts
“a” and “b” denotes quantities after and before the collision, respectively. The quantity e
is called the coefficient of restitution between the two bodies. For a perfectly elastic
collision (where kinetic energy is conserved), e equals one. All real collisions have a
coefficient of restitution that is less than one; they are inelastic to some degree and some
energy is lost. The particles can be represented by Maxwell models (see Figure 2), and
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their stress-strain behavior is described by the following equation [2]:
ησσε
+=dtd
Edtd 1 (3)
In equation (3), ε represents the particle strain, E is the Young’s Modulus of the material,
σ is the stress within the material, and η represents the strength of the dashpot in the
model. This dashpot represents the viscoelastic damping within each particle.
4.3 Frictional Damping Friction occurs in the beam as particles rub against each other and against the cavity
walls. The friction converts the kinetic energy to thermal energy, damping out the
vibrations in the beam. The shear force acting on each particle due to oblique impacts
between particles is [1]
( ) NtS FvF µsgn−= (4)
In equation (4), vt is the relative tangential velocity, µ is the coefficient of friction, and FN
is the normal force acting on the particles. In the past, the friction between the particles
and the cavity walls has been fairly accurately modeled by treating all of the particles as a
single large particle [1]. The particle damper may then be treated as a single particle
impact damper (see Figure 3), and the equations of motion for the system become [1]
( )yxgmFkxxcxm aux &&&&& −−=++ sgnµ (5)
( )yxgmym auxpart &&&& −= sgnµ (6)
Figure 2. Maxwell Model for Damping Particles [2]
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In equations (5) and (6), maux is the combined mass of the particles, x and y are the axial
locations of the cavity and the particle, respectively, and F is the excitation force. The
usefulness of these equations in a microgravity environment is much more limited,
however, because the value of g is approximately zero.
4.4 Beam Response to Harmonic Excitation The initial goal for the project was to obtain an analytical solution for each test sample.
With the assistance of structural dynamics expert Dr. Bennighof at the University of
Texas at Austin, the team was able to obtain an analytical expression for the response of a
cantilever beam with a harmonic base excitation (see Figure 4).
First, the expressions for the potential energy (V) and kinetic energy (T) of the system
were expressed analytically:
( ) ( )( ) ( ) ( )( )2
0
2 ,21,
21 tLutymdxtxutyAT end
L
&&&& +++= ∫ ρ (7)
( ) ( )( ) ( )( )∫∫ ′′=′′+′′=LL
dxtxuEIdxtxutyEIV0
2
0
2 ,21,
21 (8)
u(x,t)y(t)=Y0sin(ωt)
Figure 3. Single Particle Impact Damper [1]
Figure 4. Cantilever Beam with Harmonic Base Excitation
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In equations (7) and (8), ρ is the density of the rod material, A is the cross-sectional area,
EI is the flexural rigidity of the rod, and mend is the mass mounted on the end of the rod.
The y-coordinate describes the vertical motion of the rod mount relative to the aircraft
and u is the coordinate describing the vertical motion of the rod centerline relative to the
rod mount. Next, the variation in each of the energies was calculated:
( ) ( )( ) ( ) ( )( ) ( ) ( )( ) ( ) ( )( )tLutytLutymdxtxutytxutyAT end
L
,,,,0
&&&&&&&& δδδδρδ +++++= ∫ (9)
( ) ( )dxtxutxuEIVL
∫ ′′′′=0
,, δδ (10)
It was necessary to calculate these expressions for variations in energy in order to use the
extended Hamilton’s Principle to find an equation of motion. Extended Hamilton’s
Principle can be derived from the principle of virtual work, but the derivation is lengthy
and only the result is given below [3]:
02
1
=+−∫ dtWVTt
tncδδδ , if ( ) ( ) 0, 2,12,1 =+ txuty δδ (11)
Inserting equations (9) and (10) into equation (11), with δWnc equal to zero (there are no
forces other than the base excitation acting on the system, and the base excitation has
already been accounted for in the energy expressions), and after using integration by parts
several times, we obtain
( )( ) ( ) ( )∫ ∫ =+″′′−++−2
1 0
0......t
t
L
dtudxuEIuyuyA δδδρ &&&& (12)
Noting that δu is an arbitrary virtual displacement and can be set to any nonzero value,
we can conclude that the terms multiplying δu must be equal to zero. Rearranging those
terms gives the partial differential equation (PDE) describing the motion of the system:
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( ) yAuEIuA &&&& ρρ −=″′′+ (13)
The modes of vibration can be found by solving the free response problem, i.e. setting the
right-hand side of equation (13) equal to zero. We can then employ the separation of
variables technique so ( ) ( ) ( )tFxUtxu =, . This method splits the PDE into two ordinary
differential equations (ODEs). The solution of the x-ODE is an algebraic eigenvalue
problem, which has an infinite number of solutions. Each solution represents a mode of
vibration and allows us to calculate the natural frequencies and deformation shape
associate with that mode.
Eventually, the orthogonality property of the modes can be used to calculate an ODE for
each mode and we can solve for the time-dependent portion of the response. Although
we have not yet calculated the mode shapes and solved the modal ODEs, we do know
that the final solution will be of the form [3]
( ) ( ) ( )txUtxu rr
r η∑∞
=
=1
, (14)
In equation (14), the Ur’s are the solutions to the algebraic eigenvalue problem and the
ηr’s are solutions to the modal ODEs. This infinite sum may be truncated after many
terms, leading to an analytical solution for the motion of the beam.
4.5 Analytical Goals As shown in the previous sections, relationships have been derived to describe
viscoelastic damping, frictional damping, and the response of a cantilever beam.
Initially, our goal had been to combine these relationships to predict the motion of each
sample. However, after speaking with Dr. Bennighof, it became apparent that finding
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analytical solutions for our samples is a much more complex task than for a simple
hollow rod. This fact compelled us to modify our goals; we have determined that finding
analytical solutions for every sample is beyond the scope of our project. Instead, we will
examine the effects of particle damping by analyzing the data acquired during our
experiments on the KC-135 and on the ground. The methods for data reduction have
been explained previously in section 2.4, “Draw Conclusions From the Data”.
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5.0 Test-bay Design In considering the design of our test bay we first had to answer the question, “How is the
experiment going to be designed?” We all agreed that the best way to implement an
experiment in a microgravity environment, which promotes clumsiness and involves
many hazards, would be to fully automate the process. Everyone would agree that
experimental procedures that consist of pressing a single button to run the experiment,
retrieve all of the data, and terminate the experiment automatically would be ideal. We
will be designing our experiment to do just that. In order to design an automated
experiment, we needed to design a test bay that would complement our desire to enjoy
the free floating portion of the microgravity flight. However, it was important that our
desire to enjoy the time spent in flight not be the only determining factor in our design.
Many other factors have gone into the design such as the requirements set forth by
NASA, the size restriction on the KC-135, and the materials available. These are factors
that seem to have been prescribed for us to a certain extent. The test bay must be able to
withstand 9 G’s, all of the components must stay attached to the test bay, and it all has to
fit in the test cabin within the KC-135. This space requirement is also closely related to a
more important design factor: human interaction (i.e. procedures); we wanted to provide
ample room for ourselves to move around the test bay during the flight. Overall, these
factors played a major role in the aesthetics of the test bay, but not so much in how we
intended to interact with it.
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Our interactions with the test bay are the major factor in the test bay and overall
experiment design. Human interaction should be the major factor in the design of just
about everything. It’s one thing to be able to make some calculations and lower the
weight of an aircraft; it’s a totally different thing to make sure the pilot of that aircraft
intuitively knows where the cockpit is located.
Donald Norman suggests in his book, “The Design of Everyday Things”, that things
should be obvious. He tells a story in which his friend got stuck in the breezeway of a
building [4]. This man walked through the first door of the breezeway, he inadvertently
got distracted between the first and second door, and when he went to walk through the
second door he had shifted to the hinge side of the door. The door wouldn’t open, as if it
were locked, so he attempted to go back outside, on the hinge side again. Something can
be taken from this situation aside from the obvious humor of a man being locked in a
breezeway between two unlocked doors. It is clear that the proper use of the doors was
not obvious.
That story is interesting because it actually has a lot to do with the design of the doors on
our test bay. Keep in mind that these doors are going to be the beginning and end of our
interactions with the test bay, and we will be interacting with them in a 1.8 G
environment, not a 1 G environment. Anybody who has ever been hit in the head by a
luggage compartment door underneath a bus can appreciate and anticipate the differences
a 1.8 G environment would have on the ensuing head injury. For this reason, our test
section (bottom) door opens down so that it lays flat on the floor when open. But this
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raises a problem that the breezeway door designers didn’t think about. How do you
design a flat handle that pulls a door open and make its use obvious to the user? A door
meant to be pushed open is one that could incorporate a flat plate, similar to the door you
see in the entrance of a kitchen. But, this door must be pulled open (it would consume all
the area on the inside of the test section if it were pushed open) and it must have a flat
handle on the outer side. Any handle that extrudes out of the surface of the door would
prevent it from laying flat on the floor, which is a problem because our magnified weight
could overstress the door as we stand on it during the 1.8 G phase. The team’s solution to
this problem was a handle that extends vertically from the end off the door. In the spirit
of making things obvious to the user (reader) as suggested by Donald Norman, we
decided to include Figure 5 as a probable description:
Figure 5: Bottom test bay door with handle mount.
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This design is not perfected yet. Norman suggests that the problem with doors is that
people “don’t know what to do” [4] when they approach a door. It is obvious that the
door should not be pushed open, but the design still lends itself susceptible to someone
trying to pull it straight up. There need to be more visual clues that indicate that the door
opens flat. Properly placed hinges do the trick, as shown in Figure 6:
Figure 6: Bottom test bay door with handle mount and hinges.
As you can see, this door can open flat as required, and with the assistance of hinges that
are placed in plain sight at the bottom, the door now has an obvious proper function.
This design also has an unanticipated benefit. The handle can act as a restraint for the
upper test bay doors that open like traditional cabinet doors. Norman calls this a
“physical constraint”. Notice how this physical constraint is made “more effective by its
ease to see and interpret. The set of actions is restricted before anything has been done,
while other designs may restrict a proper function only after it has been attempted” [4].
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Our procedures specifically call for the bottom test bay doors to open first and for the
upper test bay doors to be closed first, so this design also hints at some of the correct
specimen-swap procedures. This is in agreement with Norman’s design theory.
Finally, we would like to address the audience of our design. When you are writing a
book entitled “The Design of Everyday Things”, it becomes apparent that your audience
is everyone, or at least a very large portion of the world’s population. This is not the case
for our test bay. Specifically it is designed for an audience of four, who incidentally
happen to be the designers. For us, the proper operation of the bottom door will not be an
issue, but the smooth and coordinated swap of test specimens during the 40 second 1.8 G
phase will be. This highlights an added plus to the handle design on our bottom door.
The physical constraints provided by the handle on the upper test bay doors enables us to
eliminate an upper test bay door latch, which in turn saves time. Furthermore, while an
uninformed bystander may look at the layout of our test specimens, which are behind
those upper doors, with confusion, we will know that they are laid out in a specific
configuration aimed at minimizing the timing of the specimen swap procedures. This test
bay is definitely not designed with emphasis on how the general population would
interact with it; rather, it is designed with an emphasis of how we will interact with it.
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6.0 Progress Made
The initial progress of the experiment was primarily concerned with the design of the test
bay, data acquisition system, and experimental hardware.
6.1 Test Bay Structural Analysis A structural analysis was preformed on the 7-ply that will make up the walls and shelves
of the test bay. This structural analysis assumed that all the test equipment detached and
collided with the same wall at the same time. Taking into consideration the number of
bolts and the diameter of the washers used, it was found that such a collision would result
in a load of approximately 30 psi on the walls. The ultimate tensile strength of 7-ply is
on the order of 5000 psi [5] and therefore would be more than adequate to completely
contain all of our test equipment under a 9 G load.
6.2 Test Bay Construction The supplies for the test bay have all been purchased, with the exception of the 7-ply for
the walls and the shelves. Test bay construction is well underway. The frame is
completely finished. All that remains to complete the test bay construction is adding the
walls, shelves, and doors, as well as some miscellaneous items such as restraint handles
and pipe insulation that will act as padding on the corners.
6.3 Data Acquisition System Design Based on the recommendations from professors, TAs, and other design teams, National
Instruments hardware was decided upon for the data acquisition system. Initially a call
was placed to the National Instruments office in Austin Texas. The office requested a
few details about the experiment and offered to have a National Instruments
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representative visit campus to discuss possible data acquisition options. The National
Instruments representative, Travis Fergusson, visited the University of Texas at Austin on
February 8, 2004. He recommended a set of equipment for data acquisition based on our
projects needs. The data acquisition system consists of accelerometer data which is fed
into a laptop for data reduction. This process requires a series of hardware to properly
transform and condition the signal into one that can be read by the computer. The first
major component in this system is the data acquisition card that interfaces with the
laptop.
NI – 6036 DAQ Card
The data acquisition card recommended by Travis Fergusson was the NI-6036 DAQ card
(see Figure 7). This card is a good solution for this experiment because it is lightweight
and can be interfaced with a laptop, which is a key requirement for the experiment
because the team did not want to use a cumbersome desktop computer onboard the KC-
135. This data acquisition card is also useful because of its high sampling rate. If the
sampling rate of the data acquisition card is not high enough, the signal will not be
properly reproduced in the data. The NI-6036 data acquisition card has a maximum
sampling rate of 200 kS/s [6]. This will be more than sufficient for the purposes of this
experiment. The data acquisition card has a maximum of sixteen inputs. Since the
experiment only requires data from two accelerometers, the experiment requirements are
satisfied. The data acquisition card is also low cost, which is another key motivator in
equipment selection for this experiment. Finally, the data acquisition card requires that
the signal from the accelerometers be properly conditioned. This is accomplished
through a signal line conditioner, which is discussed in the next section.
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SCC Line Conditioner
The signal line conditioner recommended by both Travis Fergusson and the National
Instruments Online Data Acquisition Advisor was SCC line conditioning. SCC line
conditioning offers a low cost solution to signal conditioning. This system is also
lightweight and modular. Many of the alternative signal conditioning systems are bulky
and would not fit into the test cabinet. SCC line conditioning also offers the advantage of
being an entirely modular system [7]. There are a variety of modules available that plug
into the signal conditioner to allow the use of a variety of sensor types. The backbone of
the SCC signal conditioning system is the NI-SC-2345 shielded carrier.
NI-SC-2345 Shielded Carrier
The carrier system is the “heart” of the signal conditioning system. The carrier interfaces
with the data acquisition card and has modules attached to it for interfacing with the
accelerometers (see Figure 8). Additionally, this model is ideal because it is designed to
operate with the E-Series data acquisition cards manufactured by National Instruments
[7]. The NI-6036 data acquisition card being used in this experiment is one of the E-
Series data acquisition cards [6]. Also, the chosen carrier is very lightweight and
designed to be portable. Given the limited amount of space and weight constraints of the
experiment, the carrier’s portability is a key advantage. As an added benefit, the carrier
Figure 7: NI-6036 DAQ Card
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can support up to twenty modules for data input and output. Since there are only two
accelerometers being used in this experiment, this parameter is more than sufficient.
Power is input to the carrier from a variety of options, depending on the exact model
ordered from National Instruments. One of the available options is 120 VAC power
which is available on the KC-135 [7]. The SC-2345 interfaces with National Instruments
LabVIEW software [7]. The experiment will be easier to automate since the carrier
interfaces with LabVIEW. The SC-2345 is compatible with all recent versions of the
Windows operating system, which is all that is available for the experiment [7]. In order
for the SC-2345 to receive signals from the accelerometers, the appropriate SCC modules
must be connected to the SC-2345.
NI-SCC-ACC01 Accelerometer Modules
The SCC modules for interfacing with accelerometers are the NI-SCC-ACC01 (Figure 9).
These modules provide power to an accelerometer and send the accelerometer’s output to
the SC-2345. The SCC-ACC01 inputs the analog output of the accelerometer. The
SCC-ACC01 provides a 4 milliamp current excitation to the accelerometer [8]. This is
Figure 8. NI-SC-2345 Shielded Carrier
25
what provides the power for the accelerometer. The module then filters out any signals
coming from the accelerometer above a frequency of 19 kHz [8]. Filtering is convenient
because it will prevent an overwhelming amount of erroneous data from being fed into
the data acquisition system. The module applies a gain of 2 to the accelerometer signal
[8]. The voltage range of the signal is between plus and minus five volts [8]. Each of
these modules can only interface with one accelerometer. Since two accelerometers will
be used, two of these modules are required. This is well within the limits of the SC-2345.
6.4 DAQ System Hardware Acquisition Once all of the desired hardware was selected, John Hatlelid began the process of
obtaining all of the needed hardware. Because of the limited budget of the program, the
research team needed as much of the hardware donated as possible. Travis Fergusson
recommended that the team contact Jason Clifton for hardware donations. An e-mail was
sent to Mr. Clifton on February 9, 2004 informing him of our project. After waiting
some time for a response from Mr. Clifton, Dr. Bishop informed us that Mr. Clifton was
the head of National Instruments academic division. Because of this, there was a concern
that Mr. Clifton was extremely busy and might not have a chance to read the request.
Dr. Bishop recommended that we contact Jim Cahow, another National Instruments
Figure 9: NI-SCC-ACC01 Accelerometer Modules
26
employee. After an initial contact with Mr. Cahow, he requested a formal proposal with
a detailed technical abstract. A modified and updated version of the NASA proposal was
sent to Mr. Cahow. This proposal detailed the scientific merit of the experiment and
informed Mr. Cahow of the exact National Instruments hardware needed. On
March 4, 2004 a response was received from Mr. Cahow stating the he was interested in
our project and thought the proposal looked sufficient. Mr. Cahow requested that the
team complete the National Instruments Student Partnership form. This form is to
formalize the process of obtaining National Instruments hardware and is currently being
completed. It will be sent to Mr. Cahow on March 5, 2004.
6.5 Experimental Hardware System Design The experimental hardware consists of the accelerometers, shaker, and equipment used to
drive the shaker. Hardware must be carefully selected for the experiment to operate
properly. For instance, the accelerometers must be properly selected to ensure that the
data obtained in the experiment is useful.
Accelerometer Selection
Two accelerometers are used in this experiment. One is mounted on the point mass at the
tip of the cantilever beam to measure the response at the end of the beam. The other
accelerometer is mounted outside of the test bay to determine the overall acceleration of
the aircraft.
The selected accelerometers needed to meet a variety of requirements. Primarily, the
accelerometers needed to be light. If the accelerometers were heavy, they would have a
significant impact on the response of the beam. Along with being lightweight, the
27
accelerometers must also be small in size. This is a matter of convenience. If the
accelerometers were large, they would be difficult to attach to the experiment.
Additionally, the accelerometers must have a high natural frequency. This is because if
the response of the beam is around the accelerometer’s natural frequency, the data output
by the accelerometer will be inaccurate.
John Hatlelid is a former Honeywell employee. Since Honeywell is an accelerometer
manufacturer, the team decided to see if any Honeywell accelerometers matched the
requirements. Initially the team wanted to use the Honeywell Sensotec MA35
accelerometer. However it was determined that this accelerometer would be difficult to
obtain. Lorenzo Rankins, a Honeywell employee, suggested the Honeywell Sensotec PA
accelerometer for this experiment (see Figure 10).
The PA is a suitable accelerometer for the experiment. The PA has a frequency range
from 3-5,000 Hz [9], while the response of the experiment system is not expected to
exceed 5,000 Hz. It was thus determined that the PA is a good compromise because it is
designed to measure both high and low frequencies. However, since the accelerometer is
not attempting to measure high frequencies, the resolution in the expected response range
will not be compromised. From further investigation it was found that the natural
frequency of the PA accelerometer is 30 kHz [9], which is well above any expected
output of the beam. Finally, the PA accelerometer weighs 3 ounces, which is small
enough for the experiment [9] and the accelerometer “is well suited to a rough
28
environment” [9]. Having a rugged accelerometer is important, because the team cannot
obtain a large number of accelerometers.
Shaker and Shaker Input Hardware Selection
A shaker is needed to provide an excitation to the cantilever beam. The shaker is driven
using a power supply and function generator. The power supply provides the power to
drive the shaker and the function generator provides the waveform to determine the
frequency and peak to peak displacement of the shaker.
There is a wide range of shakers available. The size and weight limitations of the
experiment are the driving factor in shaker selection. The shaker only needs to provide
an output of 100 Hz; with approximately 0.75 inches of displacement. Fortunately, the
majority of shakers on the market are able to provide this output. However, the
experiment’s limiting factor in obtaining a shaker is cost. Several companies were
contacted regarding shakers and it was determined that the team could not purchase a
Figure 10. Honeywell Sensotec PA Accelerometer
29
shaker given the team’s budget. The team then consulted Dr. Stearman about using one
of his shakers and is awaiting final approval.
Unfortunately, the shaker input hardware cannot be determined until the shaker has been
determined because the shaker input is dependent upon the shaker used. There are a wide
variety of power options available on the KC-135 so the exact shaker input device is only
limited by the output frequency. Virtually all function generators can output a signal of
100 Hz; for this reason the shaker input device will be determined by the shaker used in
the experiment.
6.6 Experimental Hardware Acquisition To obtain the accelerometers the team contacted Honeywell. The initial contact was with
John Hatlelid’s former supervisor, Harry Zulch. Mr. Zulch was able to direct the team
towards the sensors division inside of Honeywell. Next, the team contacted Lorenzo
Rankins, a representative of the sensors division in Honeywell. The team initially
requested the Sensotec MA35 accelerometer, but Mr. Rankin responded that Honeywell
would be able to supply the Sensotec PA accelerometer, which he felt matched the design
criteria of the experiment. Honeywell has agreed to donate at least one PA
accelerometer.
The team has talked with Dr. Stearman about using one of his shakers and input devices.
Dr. Stearman is also willing to provide an accelerometer if the team cannot obtain
another one from Honeywell or another source.
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7.0 Project Budget Although NASA provides a microgravity environment via the KC-135 for free, all
research teams are required to solicit any other needed funds from other sources. This
section explains the project costs and sources of funding.
7.1 Project Costs The team estimated that $5000 was needed for equipment, travel, lodging, and medical
costs. This amount is broken down in this section and summarized in Table 1.
Rods
This budget item covers the hollow copper rods that will be filled with damping particles
and excited by the shaker. A large number of rods are required because each rod must be
pre-filled with various configurations of damping particles in order to test a variety of
configurations quickly.
Cabinet Materials
This category covers all of the costs associated with cabinet construction, i.e. steel angle
irons, steel support struts, steel L-clamps, MDF base and shelves, 7-ply walls, bolts, and
door latches.
Damping Particles
We plan to purchase three types of damping particles (sand, metal BBs, and plastic BBs)
to place inside the various rods at different fill ratios.
Rod Mount
The rod mount is the component that will connect the rods to the shaker.
Miscellaneous Construction
31
This category provides a safety margin for any incidental expenses incurred for
equipment.
Casters
These heavy-duty casters will be used for loading and unloading of equipment on the
KC-135.
Wiring
This category includes the cost of surge protectors and electrical wiring used to connect
electrical components of the experiment.
End Masses
A large mass will be placed at the end of each rod in order to increase vibration
amplitude.
Meals
A cost of $7 per person per meal was assumed for the 5 team members over a 10-day stay
in Houston.
Hotel Fees
The ASE/EM department has arranged for the team to stay at the Hilton Hotel in Houston
for 9 nights at approximately $100/night.
Travel
The ASE/EM department has arranged the rental of two minivans for a period of 11 days.
This category covers the rental cost as well as the cost for gasoline.
Student Physicals
32
Four of the students were required to receive a special physical from an FAA-certified
medical examiner. The fifth team member already had a valid FAA medical certificate
and was exempted from this requirement.
Item
Quantity Cost per Item Total Cost
Supplies and Materials - - - Rods 24 $15 $360 Cabinet Materials 1 $410 $410 Damping Particles 1 $100 $100 Rod Mount 1 $60 $60 Miscellaneous Construction 1 $50 $50 Casters 4 $10 $40 Wiring 1 $25 $25 End Masses 1 $5 $5 Travel, Lodging and Medical - - - Meals 150 $7 $1050 Hotel Fees 9 $100 $900 Travel 2 $850 $1700 Student Physicals 4 $75 $300
TOTAL COST $5000
7.2 Project Funding and Other Assistance The team was able to obtain funding and other financial assistance from several sources.
The sources and assistance received from each source are explained below and
summarized in Table 2.
NASA Reduced Gravity Office (RGO)
In addition to allowing us to fly our experiment free of charge on the KC-135, the NASA
RGO is providing engineering and medical support for us.
Table 1. Experiment Cost Details
33
UT Dept. of Aerospace Engineering & Engineering Mechanics
The chairman of the department, Dr. Robert H. Bishop, generously agreed to provide
$3000 for our experiment. Dr. Bishop’s motivation for providing funding was that he
wished to support a research project conducted by students from within the department.
Dr. Ronald O. Stearman, also from the department, has indicated that he is willing to lend
a shaker to the team if they are unable to obtain one from another source. Efforts to
obtain a shaker through this point have been unsuccessful and we will likely borrow Dr.
Stearman’s shaker.
Finally, the team has requested permission to use the digital video camera and a laptop
computer owned by the department’s learning resource center (LRC). The team leader,
Bill Tandy, currently works there and is following up with the lab director.
Texas Space Grant Consortium
The Texas Space Grant Consortium (TSGC) is a group of 35 institutions that are joined
to ensure that the benefits of space research and technology are available to all Texans.
After reviewing our application and budget, TSGC has offered to provide $2000 towards
any lodging, travel, and medical expenses incurred by our team.
National Instruments
National Instruments (NI) has an education software licensing agreement with the
University of Texas that allows us to use their LabView software at no charge. They are
also in the process of considering our requests for donations or price cuts on data
acquisition cards and function generators.
34
Honeywell
Honeywell has agreed to provide the team with the accelerometers required for our
experiment. One of our team members, John Hatlelid, was previously employed by them
and was able to obtain donations by speaking with his former supervisor.
Institution Type and Amount of Assitance UT Dept. of ASE/EM $3000, Shaker, Digital Video Camera,
Laptop Computer Texas Space Grant Consortium $2000 National Instruments LabView Software, DAQ Card, Function
Generator Honeywell Accelerometers
7.3 Financial Status of the Project The project is currently within budget, although the test assembly construction has not
been completed. Some materials were less expensive than anticipated, leaving extra
funds to handle any unforeseen expenses. It is expected that the project will easily be
completed within the budget detailed above.
Table 2. Sources of Funding and Other Assistance
35
8.0 Schedule The schedule of this project is driven by the assigned flight period of April 1st through
April 10th at which point all aspects of the project must be completed by this date.
Naturally, the tasks must be completed during the project in a nearly sequential order.
Ground experiments must be completed prior to the experiments on-board the aircraft
because there needs to be a way of verifying if the experimental data is valid. Prior to
conducting the ground tests the entire test setup needs to be built and tested. NASA
requires that the teams conduct outreach programs to educated people about the research
project and the aerospace industry in general. These projects will carried out during the
duration of the project. In order to visualize the project schedule a GANT chart was
created with all of the project milestones. This is a convenient way of visualizing the
task hierarchy. Table 3 shows the tasks that need to be completed. Figure 11 is the
GANT chart generated for the project.
Table 3 – Project Tasks
36
Figure 1 – Gant Chart
37
9.0 References 1. Olson, Stephen E. “Development of Analytical Methods for Particle Damping.” CSA Engineering Technical Papers.1999. http://www.csaengineering.com/techpapers/
techpapers.shtml (5 Mar. 2004). 2. Liechti, K.M. “Aerospace Materials Laboratory (ASE 324L) Manual.” 2002, p. 78. 3. Meirovitch, Leonard. “Distributed-Parameter Systems: Exact Solutions.” Fundamentals of Vibrations, 1st ed., McGraw-Hill, New York, 2001, pp. 374-458. 4. Norman, Donald A. The Design of Everyday Things, Basic Books, New York, 1988,
pp. 3-85. 5. Clouston, P., and Lam, F., “Computational modeling of Strand-Based Wood
Composites in Compression.” 2000. http://timber.ce.wsu.edu/Resources/ papers/1-3-3.pdf (3 March 2004).
6. “NI-6036 Data Sheet.” http://www.ni.com/pdf/products/us/4daqsc205-207_229_238-
243.pdf (3 Mar 2004). 7. “NI-SC-2345 Data Sheet.” http://www.ni.com/pdf/products/us/4daqsc251-52_266-
69_194-96.pdf (3 Mar 2004). 8. “NI-SCC Configuration Guide” http://www.ni.com/pdf/products/us/4daqsc253-
265_194-196.pdf (3 Mar 2004). 9. “Honeywell Sensotec PA Accelerometer Product Data Sheet.”
http://www.sensotec.com/pdf/pa.pdf (3 Mar 2004).