MECHENG 722: Engineering Vibrations – Lab Project

Introduction
In this project you are required to process the vibration (accelerance) measurements that
you took in Lab 2 (cantilever beam) to estimate natural frequencies, mode shapes and loss
factors using the SDOF circle fit method and the M-files available on Canvas. The use of the
M-files was described in the last lecture on Vibration Measurement and Testing – see the
lecture recording for details.

Note: if your data is no good let me know and I will provide input data for you.

Procedure
Load your data for input accelerance (i.e. when you hit near the tip). Using the circle fit
method estimate natural frequencies and loss factors for the first 3 modes. Calculate the
natural frequencies (you can use your software from project A).

Estimate these modal properties for one or more other impact points and compare.

For other impact points estimate only the diameter of the modal circles for only two of the
modes (you choose which), from which you can estimate the mode shapes of these 2 modes.

Report
Present your results in a report. A formal report (abstract, introduction, conclusions etc.) is
not required. Hand-written material is perfectly satisfactory. However, your submission
should be well presented, neatly laid out and easy to follow and should focus on the results
and your discussion of them. Your discussion should reveal a good understanding of factors
that influence the predictions and the experimentally-derived estimates. Graphs should be
properly labeled. Marks will be deducted for poor presentation. There are no formal length
requirements.

The report should contain:
1. A table showing the theoretically predicted and experimentally estimated natural
frequencies (in Hz) for the first 3 modes together with your estimates of the loss
factors of those modes.
2. A graph that overlays the theoretical and experimentally estimated mode shapes
(scaled appropriately) for each of the two modes being analysed (i.e. one graph for
each mode).
3. A written section with your observations and comments on the results. You can
include extra graphs, etc as evidence of your observations if required. Comment on
the similarities and differences between the predictions and the values derived from
measured data, and suggest possible reasons for these.

2
Submission: Due date: 12.00 pm Friday 21 May.
This project counts as 10% of the total assessment for the paper.

Note that this is an individual project. Evidence of copying will be treated in accordance with
the University regulations on cheating.

VSS 24/3/2021



















































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