Design of a Vibration Absorber and Evaluation Using Teleoperation lab

Design of a Vibration Absorber and Evaluation Using Teleoperation Before coming to Lab: You will need to design a pendulum type vibration absorber length and mass using the following phy

Fig 1 Shake Table Lab Station

Design of a Vibration Absorber and Evaluation Using Teleoperation

Before coming to Lab: You will need to design a pendulum type vibration absorber (length and mass) using the following physical constraints The pendulum arm itself is

fixed to be a steel threaded rod with a length of 19.00cm and a diameter of 0.8cm The

mass (based on your design) can be placed on the rod with a permitted length between

5.00cm and 17.00cm measured from the top of the rod to the center of gravity of the

mass You can select any number of masses between 1 and 5 for your design, each having a mass of 46g and thickness of 0.50cm (3/16”) Refer to figure 2 Two nuts are

used to affix the masses to the threaded rod The

number of masses and the position of them on the

pendulum must be emailed to your lab TA by 9am on

the day of your lab so that he/she can set up the

proper design before your lab session begins Your

ability to communicate the design clearly to your TA

will factor in your grade for this lab

Objectives: To design and validate the performance

of a vibration absorber Observe the forced responses

and compare the responses with and without the

vibration absorber

Background: The multi-degree-of-freedom (MDOF)

system consists of a system including a two story

building model with a vibration absorber which is

driven by an instructional shake table The shake table provides an acceleration input to the structural system An integrated circuit DC accelerometer is placed on the moving surface of the shake table, and another accelerometer is attached to each of the building floors The acceleration of the third degree of freedom,

the vibration absorber, is not measured Signals are

acquired and transmitted to the client using a PC-based

data acquisition system Refer to figure 1

This experiment is to be conducted remotely using an

internet tool designed based on Network for Earthquake

Engineering Simulation (NEES) cyberinfrastructure

technology The student has the ability to use

teleoperation to run this experiment remotely using the

instructional shake table and to use the webcam to view

the experiment in real time A Graphical User Interface

(GUI) is used at the client side to select the frequency and

amplitude of the input motion to the shake table Data

from the three accelerometers (one on the table and the

other ones on the building floors) are streamed from the

server to the client at a remote computer (your computer)

using the Ring Buffered Network Bus (RBNB) Data and video are available for viewing

Fig 2 Vibration Absorber.

and storing at the client side (your computer) through the use of the real-time data viewer (RDV)

READING: Review notes and textbook sections on free and forced responses of MDOF

systems To perform this experiment, you will need to have an internet connection (not

wireless), java 1.6 installed, and use a computer that has Matlab available Note that the

computers in the CEC are recommended READ THE INSTRUCTIONS BELOW CAREFULLY BEFORE DOING THIS LAB

Procedure:

a) Follow the instructions provided in Appendix A of this experiment to open the RDV client from your PC

b) Using the video provided in the RDV client, sketch the experimental apparatus, test specimen and location of the sensors Plan on including a clean version of this

schematic diagram in your report

c) You will be provided with the measured responses of the test structure without the vibration absorber You will need to run the system with your vibration absorber design to validate the ability of your design to reduce the overall vibrations of the primary structural system STRUCTURAL DETAILS FOR THE BUILDING PLACED AT WASHU: The masses of the structure on each floor (including the

accelerometer and mounting plates) are 848g for the first floor and 1120g for the second floor The stiffness of each column is 68.5 N/m The stiffness on each floor

can be considered as two times the stiffness of each column Sensor readings are

given in gravities (1g=9.8 m/sec^2) The saturation level (maximum reading) for the

each accelerometer is +/-10g Note that in some cases there may be an offset in the accelerometer that you will need to remove in your data

d) Observe and record forced responses: Set the Ground Motion Parameters in the client

GUI to a sinusoid input with a frequency equal to that of the first mode of the primary structural system and an amplitude as indicated below:

 For all those students who run the experiment at Washington University in St.

Louis (WASHU), the first mode frequency should be considered as 1.12 Hz (Use 1.10 to avoid resolution limitations) and the amplitude of 0.0013m

 For all those students who run the experiment at University of Connecticut

(UCONN), the first mode frequency should be considered as 0.89 Hz and the amplitude of 0.02in

e) Run the excitation Observe the responses and EXPORT data for the entire

response (To export data refer to Appendix – step 9 to step 12)

f) Repeat step (d) at the frequency corresponding to the second mode of the primary

structural system and the same amplitude as indicated below:

 For all those students who run the experiment at Washington University in St.

Louis (WASHU), the second mode frequency should be considered as 3.12Hz (Use 3.10 to avoid resolution limitations) and the same amplitude of 0.0013m

 For all those students who run the experiment at University of Connecticut

(UCONN), the second mode frequency should be considered as 2.8 Hz and the same amplitude of 0.02in

2

After the lab: Describe qualitatively the response for this type of excitation in your

report Note: you should begin each test with the structure at rest therefore you should

wait until you stop seeing motion at the camera

NOTE: The mode frequency values can be corroborated by solving the “eigenproblem”

using the corresponding values for stiffness and masses of the system

Disconnect the connection so that the next user will be able to connect

Theory: After the lab, using the data provided to you for the responses of the primary

structural system without the vibration absorber at the two natural frequencies of the system, and the data that you obtained during the experiment, evaluate your design Comment on the ability of your design to reduce the vibrations of the primary system

Report:

The lab report has not set format

Appendix: Teleoperation of the Shake Table

1.) Contact your TA by IM to be sure that the experiment is set up and ready

to go

2.) Open the Teleoperation Control Panel available at the link:

http://mase.wustl.edu/wusceel/UCIST/MASE431/lab5_page.htm

3.) Right click on “CLICK HERE TO LAUNCH EXPERIMENT” and

choose “save target as” to save on a desired location as “RDV.jnlp” A

window containing Figure 3 (shown below) will open, indicating everything is working properly

4.) Adjust frequency and amplitude sliders to the desired value

(REMEMBER THE VALUES THAT MUST BE USED FOR THE AMPLITUDE AND THE FREQUENCY DEFINED AT STEPS “d” AND “f” UNDER PROCEDURE).

5.) Press the “START” button View the experiment as the table starts up.

6.) If you can not view the video and vibration data simultaneously, try

manually change the ‘Time Scale’ from the drop down menu to a larger number

7.) The “red data” corresponds to accelerometer placed on the shake table.

The “blue data” corresponds to the accelerometer placed at the first floor

of the building

8.) The “green data” corresponds to the accelerometer placed at the second

floor of the building

9.) To export the data as a file, follow the following path through the menus:

File - Export - Export data Channels

10.) A window “Export data to Disk” will appear Choose the desired time

and select the desired channels as indicated below:

 For the WASHU-RDV: Select JUST the boxes with extension

“NEES a_tbl(g)/1 (Shake table), “NEES f1(g)/0 (First floor) and “NEES f2(g)/0 (Second Floor)

 For the UCONN-RDV: Select JUST the boxes with extension

“xdda1/0” (First floor), “xdda2/0”(Second floor) and “xddg/0” (Shake table).

11.) Select the location to send the obtained data by using the “Browse”

button and click on “Export”

12.) A “data.dat” file will be created by default at the location that you

choose containing the data for the experiment You are encouraged to use different names for your “data.dat” file so you do not overwrite your old data when new data is exported Ex: “data_1.dat” and

“data_2.dat” .“data.dat” file should be opened with a “txt” extension 13.) After a short time the “START” button will be re-enabled automatically

and no new data will be collected from the experiment At this time adjust your frequency and amplitude values and hit “START” again to run the next sinusoidal excitation

14.) Repeat from step 5 to step 13 to obtain the data associated to the second

mode frequency ( Read step “f” under procedure)

NOTE: If any problems occur during the experiment, please contact your TA by IM

or phone (314) 935-4436 Class IM: MASE431@hotmail.com

Please do not exceed your time window so that the next group will have their full time allotment

Figure 3 View of the RDV window in operation

4