×
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.

# Generating random envelope

## Generating random envelope

(OP)
See attachment picture

I want to place orange structure in the blue structure.

1) The orange structure was analyzed, isolated, with a specific random input. Accelerations on the structure were extracted.
2) The blue was analyzed, together with the orange, and with a similar random input of the orange alone. Then the acceleration at the orange location was extracted.

Now I want to re-analyze the orange structure with the a PSD function that envelopes the accelerations in 2)
The problem is that the accelerations in the orange structure in 2) more than 10x higher than the input in 1) and 2).

Meaning I will have to analyze and test the orange structure with 10x max acceleration than it was initially designed. Is this overconservative?

### RE: Generating random envelope

Not sure I get the question. Are you saying that the accelerations experienced (by the orange structure when mounted in the blue) are 1/10th of the orange structure spec limits ? Do you know the PSD applied to the blue structure ?

should've looked at the pic, and thought a little more. So the accelerations of orange structure are higher than the input when it is supported by the blue structure.

So you drive the blue+orange structure with higher loads than orange alone (since it has more mass) ?

It sounds to me like the blue structure doesn't adequately support the orange, and has set up some sort of harmonic resonance.

### RE: Generating random envelope

#### Quote:

Meaning I will have to analyze and test the orange structure with 10x max acceleration than it was initially designed. Is this overconservative?

Yes, probably overconservative. The bigger question is how you can get 10x the acceleration from a passive structure? That would seem to violate conservation of energy. Are you referring to peak, or rms, acceleration? It's possible you have a resonance, in the range of interest, which is bad, in of itself, or you have some sort of error in your simulation.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

### RE: Generating random envelope

I'll warn you right now... taking an attitude with people who are trying to help is a fast way to get the thread deleted and you booted. Take a deep breath and help us help you...

Dan - Owner
http://www.Hi-TecDesigns.com

#### 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.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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!