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Stack Design_STS-1

08/22/2017 6:30 AM

Hello everyone,
For stack, designed as per STS-1, i am in a situation that mean critical velocity is lower than Critical speed for vortex shedding.
So far i know by introducing helical strakes or other attachments, critical velocity can be increased.
But my question is how to evaluate critical velocity after introducing strakes.
Please provide your opinion/ guidance on same.

Further to above:
In Dennis Moss, Chapter 6: special designs, it says that Vortex shedding can be eliminated by introducing helical strakes upto top 1/3 portion of stack.
As per above, does it mean that by introducing strakes there is no need to check for vortex shedding.
If so than how to validate it on paper

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#1

Re: Stack design_STS-1

08/22/2017 6:33 AM

Googling <...STS-1...> brings up loads of stuff on NASA's Space Shuttle, and on antibodies.

Remember that any equation is merely a mathematical abstract of observed fact...

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#2
In reply to #1

Re: Stack design_STS-1

08/22/2017 6:43 AM

Thank you very much for immediate response.

Can you provide any references for calculating critical velocity after introducing helical strakes so that same can be proved (for transparency with client).

Or else how to handle client on same.

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#3
In reply to #2

Re: Stack design_STS-1

08/22/2017 6:53 AM

There are four references here.

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#4
In reply to #3

Re: Stack design_STS-1

08/22/2017 9:07 AM

After increasing thickness of components when I checked output for STS in pvelite, it is observed that still critical velocity for vortex shedding is less than the mean critical velocity.

To investigate further for the cause of failure, I checked ovalling frequency.

But I found that ovalling frequency is more than natural frequency of vessel even with less thickness of shell components. See below image for reference.

Still, I am not able to conclude the reason for failure.

I request you to explain the same if possible.

Thanks.

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#6
In reply to #4

Re: Stack design_STS-1

08/22/2017 10:41 AM

It seems there are other forces at work here; you need to identify these forces. What is the surrounding terrain and structures that might play a role?

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#7
In reply to #6

Re: Stack design_STS-1

08/22/2017 11:17 AM
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#5

Re: Stack design_STS-1

08/22/2017 10:16 AM

I found this:

ASME-STS-1-2006

Is this the standard you are referring to?

I did not see anything about vortex shedding, and the document search option is not working (for me at least).

Now this one from MIT, is probably applicable for your use:

Vortex-induced vibrations of a long flexible cylinder in shear flow

Good luck going forward. Let us know what you come up with.

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#8
In reply to #5

Re: Stack design_STS-1

08/23/2017 10:50 AM

Section 5 Dynamic Wind Loads started at the end of the ASME excerpt you found...

The second reference seems to be focused on structures maybe more flexible than a stack, but good stuff, nevertheless.

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#9
In reply to #8

Re: Stack design_STS-1

08/23/2017 11:38 AM

Thanks. That being out of my specialty, I can merely point, click, and pass along, and say stuff that makes me seem smart.

Most of us can tell when I am full of it.

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