Mode Shapes calculated in Matlab Toolbox MACEC 3.3

[E2015]

Dear all,

I am using Matlab Toolbox MACEC 3.3 for EMA of a railway sleeper (both concrete and timber).

The resulting mode shapes I obtain are unity scaled modal mass mode shapes and they appear as complex numbers. For each mode calculated I also have information about Modal phase collinearities and Mean phases and mean phase deviations.

My question is following: How can I plot the mode shapes if they appear as complex numbers?

Many thanks,

Emina

Emina B.

 

[GregLocock]

You can animate them, but it is hard to plot them. You could try overplotting the deformed shape every 45 degrees, but there's no definitive method. I suppose the other option is to plot the real and imaginary deformed shapes separately. A genius might be able to decipher them.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[E2015]

Thank you for your reply.

Actually I can plot the mode shapes within the toolbox. The animation of the mode that I get within the toolbox looks like this:

However, I have to save the mode shape vector and plot it outside the toolbox environment. But in that case I don't know how to deal with modes that come as complex numbers.

I have followed your instruction: "I suppose the other option is to plot the real and imaginary deformed shapes separately"
and for the plotted mode in Macec I have calculated the real and imaginary part.

This is the plot of the imaginary part of the mode shape vector:

And this is the plot of the real part of the mode shapes vector:

Does it mean from the above plots that I can actually use the plot of the imaginary part of the mode shape to represent the actual deformed shape?
And why the plot of the real part looks like this?
Is it common to get the deformed shape that is close to the actual deformed shape for that mode with the imaginary part instead of real part?

Many thanks,

Emina







Emina B.

 

[GregLocock]

Yes, in a normal modes analysis the resonance occurs at a 90 degree phase shift, so the imaginary part is the mode shape. In real life this occurs with simple systems such as a steel beam or plate. As you add complexities like point damping, clearances and so on then the phase plot vs frequency becomes much more complex, and the imaginary part of the response is not necessarily the important bit.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?