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

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−−

= (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

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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

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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

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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

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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.

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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

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Figure 1 – Gant Chart

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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).