Matlab weird help

Jun 2014
8
0
Zuzaru
Hey,

Thank you for your help, I really appreciate it!

Isro
 
Jun 2014
27
6
Britain
Hi isro1

I have had a look at your data and have tried to fit an exponential decay to the envelope.

You can see on the attachment a plot of the data where I have corrected the zero position on the y axis using the average of the values rather than the median.

median = 1.5822 average = 1.7613

The difference is insignificant compared to the asymmetry of the oscillations which is highlighted

by the plot of y = 28e^(-1.9x)sin(31x-0.1) (in green).

(a) the decay does not follow a simple exponential decay law and

(b) the frequency of the oscillations is not constant.

For these reasons I feel that it will not be possible to find a single exponential to model the peaks and the troughs simultaneously.

Regards

Plot of data and model.PNG
 
Jun 2014
8
0
Zuzaru
Thank you for looking over the data! It is really great to get a second opinion on it!

Do you think it would still be so asymmetric if we consider just the movement starting at peak 4 and ending at peak 8? The start point of the graph is so high in amplitude as the system was initially displaced manually, so maybe the first part should be ignored anyway...? What do you think?
 
Jun 2014
27
6
Britain
Hi isro1

I am glad that you found my comments useful.

I agree that the early oscillations should be ignored.

Having skimmed through an old Physics text book on simple harmonic motion I read a comment on the simple pendulum ( a bob on a string ).

'Mathematically the motion is only close to simple harmonic for small oscillations ie < 10 degrees.'

I have fitted another damped sine wave on the attachement which seems to follow the data quite well for peaks 7,8,9 and 10.

I think that your system might be settling down - the question then is can you measure the displacements with sufficient accuracy ?

Regards
 

Attachments

Jun 2014
8
0
Zuzaru
Hey,

Thank you again for your input! That's the problem, that I am not sure what is sufficient accuracy for this experiment. it seems the damping is changing as the system slows down, hence the different curves that fit the experimental data at different times (different peaks)...

I guess that for the centring I will just stick to using the average or the median in excel...

Thanks again! Really appreciate it! It was really good to get another opinion on this. :)
 
Jun 2014
27
6
Britain
Hi

I enjoyed the challenge of looking at your data - best of luck with the experiment.

Regards
 
Jan 2016
3
0
romania
I need help with this project in MATLAB

1. Represent while marking on the axis the significant values for the signals x1(t), x2(t) and x3(t) for 10 periods, 20 periods and 40 periods. (you should use the vectorial method).
x1(t)=10t^2-8t+14 for t included in the domain [o;30] [ms]
x2(t)=x1(t)*dirac_T1(t); *=convolution; T1=30
x3(t)=x1(t)*dirac_T2(t); *=convolution; T2=60

2. Recover Half-wave and double alternating the signals x4(t) si x5(t). (plot them)

x4(t)=x1(t)*SUM_from_k=0_to_20{(-1)^k x dirac(t-k x T1)}; x=product; * convolution

x5(t)=x1(t)*SUM_from_k=0_to_20{(-1)^(k+1) x dirac(t-k x T2)}; x=product; * convolution

3.calculate the continue components of the signals x2(t) and x3(t) considering on an infinite period. (must have an accuracy of 6 decimal places)

4. Represent the signal: x1(t) without continue component; x2(t) without continue component; x3(t) without continue component, considering the signals at the point 3..
 

skeeter

MHF Helper
Jun 2008
16,217
6,765
North Texas
I need help with this project in MATLAB

1. Represent while marking on the axis the significant values for the signals x1(t), x2(t) and x3(t) for 10 periods, 20 periods and 40 periods. (you should use the vectorial method).
x1(t)=10t^2-8t+14 for t included in the domain [o;30] [ms]
x2(t)=x1(t)*dirac_T1(t); *=convolution; T1=30
x3(t)=x1(t)*dirac_T2(t); *=convolution; T2=60

2. Recover Half-wave and double alternating the signals x4(t) si x5(t). (plot them)

x4(t)=x1(t)*SUM_from_k=0_to_20{(-1)^k x dirac(t-k x T1)}; x=product; * convolution

x5(t)=x1(t)*SUM_from_k=0_to_20{(-1)^(k+1) x dirac(t-k x T2)}; x=product; * convolution

3.calculate the continue components of the signals x2(t) and x3(t) considering on an infinite period. (must have an accuracy of 6 decimal places)

4. Represent the signal: x1(t) without continue component; x2(t) without continue component; x3(t) without continue component, considering the signals at the point 3..
you may be better served by starting a new post rather than piggy-backing on an older post.