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#39123 - 11/22/10 04:28 AM Blast Drag Coefficient factor
kaaliappan Offline
Member

Registered: 08/18/10
Posts: 24
Loc: singapore
Hi
in one of my offshore platform project the client is asking to do blast analysis with cd=1.5 (shape factor)
blast drag coefficient as 1.5 is it ok because if i use this i am getting heavy loads on supports and it needs more guides

for wind also they ask to put cd=1
but for the pipe mostly it will be 0.6-0.7

give me some suggestions

regards
kaaliappan

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#39124 - 11/22/10 04:36 AM Re: Blast Drag Coefficient factor [Re: kaaliappan]
MoverZ Offline
Member

Registered: 11/22/06
Posts: 1195
Loc: Hants, UK
Read a fluid mechanics text. Drag factor on a cylinder can be as high as 3.0 for blast loads.

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#39126 - 11/22/10 06:08 AM Re: Blast Drag Coefficient factor [Re: kaaliappan]
tsvprao Offline
Member

Registered: 06/03/09
Posts: 13
Loc: Norway

Hi

Blast drag coefficient can as high as 10. This is possible when low reynold number acheived. But blast loads generally significant, where reynolds number of fluid is quite high. Again depend on reynolds number/Mach no. to could go upto 3. Not to add more ambiquity, i have been working in offshore for last 3 years and practice followed by companies is drag coefficient factor of 0.67 and DLF of 1.5 to 1.67. The product of drag coefficient and DLF is 0.67 * 1.5 = 1 or 1.1 are given as input in CAESAR.

You may read DNV-RP-D101, there is a good guidance. It is available on internet for free. Just use google to find location of DNV report.

best regards

Rao

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#39219 - 11/26/10 08:03 AM Re: Blast Drag Coefficient factor [Re: tsvprao]
danb Offline
Member

Registered: 04/22/05
Posts: 1326
Loc: ...
I was working too on this and DNV asked for a CD=1.1 and DLF=1.5, therefore product was 1.65. At that time DNV-RP-D101 was not yet issued and I had hard time.

Regards,
_________________________
Dan

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#39220 - 11/26/10 08:15 AM Re: Blast Drag Coefficient factor [Re: danb]
tsvprao Offline
Member

Registered: 06/03/09
Posts: 13
Loc: Norway

Hi

It is issued in Oct2008, you may refer to 3.11.2.5 of DNV RP regarding drag coefficient.
http://exchange.dnv.com/Publishing/Codes/ToC_edition.asp#Recommended Practices

There is also some notes available in HSE (UK), executive report 285.

regards

Rao

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#39221 - 11/26/10 08:22 AM Re: Blast Drag Coefficient factor [Re: tsvprao]
danb Offline
Member

Registered: 04/22/05
Posts: 1326
Loc: ...
Not to forget about the Fabig Technical Note 8. See the abstract at:

http://www.fabig.com/NR/rdonlyres/839B01...hnicalNote8.pdf

Regards,
_________________________
Dan

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#39766 - 12/27/10 06:04 AM Re: Blast Drag Coefficient factor [Re: danb]
Shabeer Offline
Member

Registered: 12/26/07
Posts: 265
Loc: india
hai kaaliappan,

I am also doing a blast load analysis for off-shore piping, can you give your load case for reference....

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#39785 - 12/28/10 02:11 PM Re: Blast Drag Coefficient factor [Re: Shabeer]
Richard Ay Offline
Member

Registered: 12/13/99
Posts: 6049
Loc: Houston, Texas, USA
It is one of the other fields on the Allowable Stress dialog. Check tje "help".
_________________________
Regards,
Richard Ay

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#39787 - 12/28/10 11:21 PM Re: Blast Drag Coefficient factor [Re: Richard Ay]
Shabeer Offline
Member

Registered: 12/26/07
Posts: 265
Loc: india
Hai richard AY,

Whether we have to check nozzle load for blast load cases or not? i am doing analysis for static, transit and blast condition. All the load cases are different combination.Some of the support type are provided in static condition, nozzle load are with in the limit and same support are to be provided in blast condition, nozzle load are not with in allowable. can you give a conclusion for above one.

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#39798 - 12/29/10 08:39 AM Re: Blast Drag Coefficient factor [Re: Shabeer]
Richard Ay Offline
Member

Registered: 12/13/99
Posts: 6049
Loc: Houston, Texas, USA
I haven't seen consideration for "blast loads" in any of the Equipment Codes. However, this does not mean that this condition shouldn't be checked. This is something you'll have to discuss with the owner.
_________________________
Regards,
Richard Ay

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#40000 - 01/08/11 11:59 AM Re: Blast Drag Coefficient factor [Re: Richard Ay]
Shabeer Offline
Member

Registered: 12/26/07
Posts: 265
Loc: india
Dear Richard Ay,

Thank lot, now i have to discuss with Client.

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