PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

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Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.- Current velocity (v)- Pipe's diameter (D)- Density of streaming water (ρ)- Pipe's distance above seabed (f)The forces can mathematically be expressed as follows :F D =1 2CD⋅ ⋅ ρ ⋅ v ⋅ D2A.4-10)F L =1 2CL⋅ ⋅ ρ ⋅ v ⋅ D2A.4-11)C D = drag coefficientC L = lift coefficientρ = density of streaming water (kg/m 3 )v = current velocity (m/s)D = external diameter of pipe (m)F D = drag force (N/m)F L = lift force (N/m)The coefficients F D and F L are in principle dependent of Reynolds number and roughness of thebottom.Reynolds number (ref. A.2-1) can be expressed :v ⋅ DR e =A.4-12)νν = viscosity of water ≈ 1.3 ⋅10 -6 (m 2 /s)The coefficients will normally vary within the range 0.5-1.2. Values for a pipeline laying on theseabed can be taken from fig. A.4.5.2 and A.4.5.3 .C DR eFig. A.4.5.2 Drag coefficient, C DSide 56 av 84
Pipelife Norge ASPE CATALOGUE-SUBMARINE APPLICATIONS, PIPELIFE NORGE AS, December 2002.C LR eFig. A.4.5.3 Lift coefficient, C LThe lifting force will be reduced as the distance (f) between pipe and seabed increases.If f = 0.5 ⋅D the lifting force will be approximately 10% of the lifting force for a pipeline laying directlyon the seabed. This is a vital detail in design of concrete weights.Example 4A current is attacking a pipeline at an angle 45ºfrom the centreline as shown beside.V= 1 m/sThe pipe's diameter is 500 mm.Density of water is 1000 kg/m 3 .Assume that C L = 0.20 and C D = 1.0.Calculate the drag force and the lift force.Solution :The velocity component perpendicular to the pipelinecan be written :α = 45 oD= 500mmv N = v ⋅ sin αA.4-13)Inserting this expression into A.4-10) and A.4-11) we get :F D =1 2 2C D ⋅ ⋅ ρ ⋅ v ⋅ sin α ⋅ D2A.4-14)F L =1 2 2C L ⋅ ⋅ ρ ⋅ v ⋅ sin α ⋅ D2A.4-15)Putting in values from example 4 gives :F D =12 21.0 ⋅ ⋅1000⋅1⋅ sin 45 ⋅ 0.5 N/m = 125 N2F L =12 20.2 ⋅ ⋅1000⋅1⋅ sin 45 ⋅ 0.5 N/m = 25 N2Side 57 av 84
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PE Pipe Technical Catalogue (PDF) - Pipelife Norge AS

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