TMD to Improve Isolation at Mount?
TMD to Improve Isolation at Mount?
(OP)
Greetings:
I have a situation where an isolated vehicle cab structure has poor dynamic stiffness in one direction, at approximately 300 Hz, and therefore has poor isolation. This results in noise at the operator's ear at 300 Hz. Since in this case redesigning the structure is not an option, would inserting a tuned-mass damper at this location be likely to give an improvement in isolation and thus a reduction in noise?
This is an idea I've been toying with for a while, but I thought I'd seek some outside opinions before I started making a prototype and running a test.
Any thoughts would be appreciated.
Best regards,
Robert
I have a situation where an isolated vehicle cab structure has poor dynamic stiffness in one direction, at approximately 300 Hz, and therefore has poor isolation. This results in noise at the operator's ear at 300 Hz. Since in this case redesigning the structure is not an option, would inserting a tuned-mass damper at this location be likely to give an improvement in isolation and thus a reduction in noise?
This is an idea I've been toying with for a while, but I thought I'd seek some outside opinions before I started making a prototype and running a test.
Any thoughts would be appreciated.
Best regards,
Robert





RE: TMD to Improve Isolation at Mount?
The way i'd approach it is to use an accelerometer and a mic to find the actual noise path (ie check that the noise is coherent with the vibration), find where the vibration is strongest, measure the mounting point's inertance at that frequency with a bonk test, get a mass at least 10% of that, and then tune the spring.
What's the noise source?
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: TMD to Improve Isolation at Mount?
This is a diesel-powered commercial truck, and the noise levels are "higher than desired."
Thanks!
- Robert
RE: TMD to Improve Isolation at Mount?
Walt
RE: TMD to Improve Isolation at Mount?
RE: TMD to Improve Isolation at Mount?
A bodyside damper would be larger, but at higher frequency it could be smaller. So I'd expect you to need a couple of kg, at least at the development stage.
You should be able to pull 6 dB out of it, if there is only one path.
Have you thought about curing the problem at the source?
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: TMD to Improve Isolation at Mount?
If that 300Hz changes in the future, the TMD may not be such an elegant mechanism anymore.
You could design an 'optimal' TMD. That is, design the absorber mass, stiffness, and damping for optimal performance over a larger frequency band. That way if the 300Hz changes in the future, it won't be as detrimental.
Fe
RE: TMD to Improve Isolation at Mount?
I know NVH is usually a horrible bodge, but it seems to me the correct engineering solutions are twofold
(a) redesign the isolators so they isolate and are durable
(b) cure noise problems at source.
Back in the real world...
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: TMD to Improve Isolation at Mount?
Although, I like your (b).
Fe
RE: TMD to Improve Isolation at Mount?
The source in this case btw is a 15L 6-cyl turbocharged Diesel engine making 450 HP and 1550 lb-ft of torque.
But the reason for wanting a "band-aid" approach is to avoid the glacial pace of a redesign program, and management's unwillingness to devote any resources to such a project: the 300 Hz problem is due to a weakness in the cab structure, and not due to any particularly bad vibration from the engine.
I'm expected to just wave my magic NVH wand over the truck and "make it better."
Greg, thanks for the helpful hints as to how to actually go about this.
Best regards,
Rob