×
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.

Elastic wave amplitude

Elastic wave amplitude

(OP)
As I have mentioned on other threads on this board: I have been reading several texts on the propagation of elastic waves in isotropic media lately. (And I appreciate the discussions we’ve had here on this topic.) If I could prevail upon someone again……..a question crossed my mind this weekend………….

In a lot of the afore mentioned texts……equations defining the motion of a variety of wave types are given. (I.e. Rayleigh, lamb, P-wave, etc, etc.) But one thing I am noticing in a lot of them is: the amplitude is typically a undefined variable/constant. The only case I have seen it defined for (outside of longitudinal waves from axial impact) is in the case of Rayleigh waves. In one text I have (on soil dynamics), the motion was a function of a initial amplitude…..and that amplitude was a localized displacement from a vertical load.

So I guess my question is: is this true for other wave types? Are these undefined constants typically all some sort of a function of a local displacement/deformation……possibly do to contact?

By the way, this is not considering vibration.....this is just considering the initial wave at the beginning of motion.

RE: Elastic wave amplitude

In books of waves in solids e.g., Graff, there are solutions to the wave equations (say plates or rods,..) with different force terms - say excited by different simple point loads (say harmonic or impulsive point loads).
https://www.amazon.co.uk/Motion-Elastic-Solids-Dov...

example:
Infinite rod (so standard long. wave equation describes it, no losses), with a point force in the centre exciting long. waves (F= Famp*exp(i*omega*t)*DiracDelta(x-xo))

The amplitude of the longitudinal wave is ~ Famp/(E_Youngs*Cross_Area*wave_number)

RE: Elastic wave amplitude

(OP)
Actually, that was one of the texts I am reading. And these thoughts occurred when I got to the section on lamb waves. It is somewhat vague on this point.

RE: Elastic wave amplitude

Not sure if there is a closed solution for point force excitation with Lamb waves - perhaps there is one, but could be a bit nasty :).

RE: Elastic wave amplitude

(OP)
Could I get some more opinions on this (my question [in bold] in the OP)? We've got some pretty sharp people here so I'd like to hear some more. Thanks.

EDIT: I guess what I am after is: forgetting about the dynamic amplification (and other things that happen with complex waves at certain frequencies), is the localized [Hertzian] displacement a maximum initial amplitude? (Sort of a ceiling if you will.) Thanks again.

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!