Cable On-Bottom Stability

[pipeline058]

Guys,

I was involved in a on-bottom stability evaluation of a subsea cable using common recommended approach of DNV-RP-E305.

While I found the cable unstable based on this RP, I realized that some people evaluate Cable stability with a very simple method, ignoring Wave action. this approach results in less required stability and so on

1- Is thereany difference between stability evaluation of Pipes and cables?

2- Is DNV-RP-E305 (or new F109) applicable for cables?

 

[BigInch]

Its for pipelines only. But not to say that the things arn't similar. If there is no shoaling, the orbital wave motion reduces to zero at the mudline. I think there is no shoaling if the depth is greater than 1/2 the wavelength, but I don't remember too well, so check into that.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[pipeline058]

BigInch,
I think 1/2 wavelength is correct. but it will be applied to both pipeline and cable or any other structure.
I mean no matter the case is pipe or cable, the method seems to be the same.
in addition, my case is in shallow water (less than 50m). Interesting is that there are some other cables in the region which has been installed before and they would be evaluated unstable using E305 approach.

 

[BigInch]

"Shallow" water usually means that it is shallow in relation to the max wave and there will be shoaling effects, so you will have a horizontal velocity component of the wave orbital motion at the bottom and probably some shoaling currents too.

I can't imagine much difference between the analysis of each, except for the increased flexibiity of the cable, so certainly many concepts from F109 could be applicable.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/