Learn About Vibrations!

Learn About Vibrations!

Welcome!

The ABRAVIBE blog is where you find all the resources for learning more about vibrations. Browse and download examples for the free MATLAB/Octave ABRAVIBE toolbox. Or browse the many theory examples, videos, and resources for the book "Noise and Vibration Analysis: Signal Analysis and Experimental Procedures," by Anders Brandt!

Video Channels on Youtube

VideosPosted by Anders Brandt Feb 10, 2015 18:39
The video I just posted (demonstrating convolution) is not the only video I have made. In the next few months I will be posting videos of lectures for a course on Experimental Vibration Analysis, that I currently run at SDU. You can find these videos, and more, on my Youtube channel, arranged into several playlists. I will post links here, whenever there is a new video directly related to ABRAVIBE, but not educational videos like the lectures. So make sure you check for new videos at Youtube!

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Demonstration of Convolution

VideosPosted by Anders Brandt Feb 10, 2015 18:16
Convolution is an extremely important mathematical concept if one wants to understand linear systems, or, for that matter, frequency analysis. Convolution is also, however, often a concept that many students have some difficulty grasping. Therefore, I have made this short demonstration video that I hope will clarify the concept for your. Please share this if you think it is good!



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Finite Element Verification and Calibration Example

ABRAVIBE ExamplesPosted by Anders Brandt Nov 12, 2013 19:18
This is a complete example of finite element model verification and calibration (sometimes known as correlation).

The example uses a finite element model built in the free CALFEM toolbox and experimental modal analysis results of the Plexiglas plate used throughout ABRAVIBE as an example structure. The idea of this example is to be simple and illustrative, so that the techniques are not hidden by practical difficulties. The example includes verification of mode shapes using the MAC matrix and frequency tables, and calibration by adjusting the Young's modulus to adjust the first bending mode of the FE model to fit the experimental data. In the Bibliography Section on this site there is a technical paper describing the example.


If you are signed in you can download the file by clicking here. Otherwise, please sign in and browse the resources at the main site.







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New Paper on Improved Impact Testing

DiscussionPosted by Anders Brandt Jun 23, 2013 20:42
If you do impact testing for frequency response measurements, you may want to read the paper that was just added to the bibliography section at http://www.abravibe.com/bibliography.html! In this paper, written by Anders Brandt and Rune Brincker, presented at IMAC 2010, the time domain processing method which is implemented into ABRAVIBE was presented in some detail. Make sure to read this if you make FRF measurements using impact testing!

If you like the ABRAVIBE toolbox, and this website - make sure you like our Facebook page http://www.facebook.com/TheAbravibe!

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Checklist for Experimental Modal Analysis

DiscussionPosted by Anders Brandt Jun 21, 2013 18:26
This is a one-page checklist in table format which can be used to ensure some important points are not forgotten during a modal analysis test.

If you are signed in you can download the file by clicking here. Otherwise, please sign in and browse the resources at the main site.

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Notes On Using the ABRAVIBE Toolbox for Experimental Modal Analysis

ABRAVIBE ToolboxPosted by Anders Brandt Jun 21, 2013 18:22
This 25-page technical note presents rather comprehensive information about how modal analysis is implemented in ABRAVIBE. The first part of the note discusses some very important practical aspects of how to perform a good experimental modal analysis (EMA) test. Among the things discussed are choice of measurement points, choice of support, how to check measurement data to ensure data are of good quality, etc. These points are very important. The note states that a good EMA test is at least 80 % measurements, and only maximum 20% parameter extraction. Without good data (frequency response functions) then your EMA test is doomed!

The second part of the note presents the theory for the three methods implemented for MDOF parameter extraction, that is Prony's method (for a single FRF), the least squares complex exponential (LSCE) method (for many FRFs but only one reference), and the polyreference time domain (PTD) method (for many FRFs and several references).

Finally, the previous example for ABRAVIBE, where the three methods are compared on real measured data, is presented with some key points.

The technical note includes a checklist which will also be published in another post at this site.

If you are signed in you can download the technical note by clicking here. Otherwise, please sign in and browse the resources at the main site.

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Modal Analysis Example and Bug Fix

ABRAVIBE ExamplesPosted by Anders Brandt Jun 09, 2013 18:28
A new modal analysis example is available! This example compares the three currently available options to the frf2ptime command; 'prony', 'lsce', and 'ptd'. It can serve as a reference for how to use these three options.
The example also includes a bug fix to the frf2ptime.m file, to make this command work for the Prony option.

The example uses the same synthetic data for the Plexiglass plate that the Plexi Modal Example uses, but comes with the data to make it independent of the previous example.

If you are signed in you can download the file by clicking here. Otherwise, please sign in and browse the resources at the main site.

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The bibliography is updated!

DiscussionPosted by Anders Brandt Mar 18, 2013 19:45
A recent paper from Proc. of the 31st IMAC conference is uploaded to the Bibliography section under About at www.abravibe.com. The paper describes the ABRAVIBE toolbox and its features. Go to the main site, or click here, to download it now!

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Problems registering? Other Problems? Let us know!

DiscussionPosted by Anders Brandt Mar 17, 2013 17:36
Today I'd like to mention a couple things of administrative nature.

First of all - thanks to all of you who use this site! In the first three weeks the ABRAVIBE toolbox alone has been downloaded almost 500 times! We are very grateful for your support!

We have noticed that some users register but never activate their account. This could be because the registration email end up in your spam folder. We do mention this in the text during the registration process, but if you have missed it - take a look for the registration email in your spam folder.

Another thing is feedback. If you have trouble registering, or downloading, we really want to hear about it! Use our contact form here, to notify of what is going wrong.

You can also use the social media to share your thoughts about us! Or why not suggest an idea for what you would like to see as a vibration example.

Be sure to share us with your friends on Facebook and LinkedIn if you like us!

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Modal Analysis Example and Important Upgrade for Modal Parameter Extraction

ABRAVIBE ExamplesPosted by Anders Brandt Mar 09, 2013 15:48
The ABRAVIBE example PlexiModal is an example of using the ABRAVIBE
toolbox to do experimental modal analysis of a Plexiglass plate using measured data.

The example uses data measured using impact testing, and the
polyreference time domain (PTD) method with two references, to be able to
estimate the first two modes which are strongly coupled on this plate.
The example shows all involved steps such as importing and sorting data,
curve-fitting for poles and mode shapes, and evaluating the results with
a MAC matrix and animation of the modes.

This example is good to use as a template for all modal analysis tasks
with the ABRAVIBE toolbox; just replace the data imported, and the
geometry created before animation, to use the script for your modal
analysis tasks!

In addition to this, the example includes an upgrade to the ABRAVIBE toolbox revision 1.2, with a new command enhancefrf which uses singular value decomposition to reduce the measured FRFs into a smaller number of principal responses to use for the modal parameter extraction. Also the command frf2ptime is updated to use FRF enhancement by default. These two functions will be included in the next release of the ABRAVIBE toolbox. The theory of FRF enhancement is covered in chapter 15 in the book "Noise and Vibration Analysis".

If you are signed in you can download the file by clicking here. Otherwise, please sign in and browse the resources at the main site.

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