×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Logarithmic sine sweep: how to compute cycles?

## Logarithmic sine sweep: how to compute cycles?

(OP)
Hi,

I am running a transient simulation in Nastran. The structure undergoes a sine-sweep base acceleration and I need to compute the number of cycles the structure will se during the whole simulation.
How do I do that knowing the sweep rate (R [oct/min]), the total duraton (T [s]) and the frequency range (Df [Hz])?

Thank you
Regards

### RE: Logarithmic sine sweep: how to compute cycles?

And what have you found so far? I'll assume you mean that num_cycles=(zero_crossings/2)-1

In my opinion the first thing to do is use Df and the number of octaves (T/60*R) to find a start frequency. The simplest approach from then is to model the waveform and count zero crossings, but a calculus based approach is more elegant.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

### RE: Logarithmic sine sweep: how to compute cycles?

(OP)
This equation
num_cycles=(zero_crossings/2)-1
is what I was missing. Since I generated the sweep using Matlab, I could just make it count the number of zero-crossing points and use it in the previous equation.
Until now I was trying to follow the procedure explained in the book written by Wijker, but I was not sure about the result I got (nearly 1500 cycles). I will cross check the result.

Thank you!

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!