Stack design_STS-1

[israr1]

Hello everyone,

For stack, designed as per STS-1, i am in a situation that critical velocity is lower than design velocity.
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.

Izzy

 

[israr1]

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.


Izzy

 

[DSB123]

isar1,
You have asked the same question twice - this is not the done thing.
As regards you question. Introducing strakes does not negate the nedd to check for resonance. How do you know how many - their width- the spacing of these strakes? I think you should employ a qualified stack design engineer.

 

[JStephen]

In some cases, it may be practical to adjust some of the thicknesses to adjust the frequency.

 

[israr1]

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 the attachment.

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

I request you to explain the same if possible.

Thanks.

 

[israr1]

DSB123,

Exactly, i do agree with you.

But i am not able to understand the reason for statement in Dennis Moss (See the attachment- Extract from Dennis Moss).

 

[MJCronin]

israr1:

Have you contacted the people who developed the computer program (COADE) that you are using ?

What did they have to say ?

MJCronin
Sr. Process Engineer