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Pipeline Stability Modules

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CALCULATOR MODULE : DNVGL ST F101 Submarine Pipeline Flotation   ±

Calculate DNVGL-ST-F101 submarine pipeline flotation and vertical stability.

Select either the empty pipe or full pipe option. For vertical stability, the pipe specific gravity should be greater than or equal to 1.1.

The number of pipe internal and external layers, and the names of the layers can be changed on the setup page. The first internal layer is the line pipe. The line pipe wall thickness can either be selected from the pipe schedule, or the input value is used as the user defined value.

Reference : DNVGL-ST-F101 : Submarine Pipeline Systems (Download from the DNVGL website)

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CALCULATOR MODULE : Morison's Equation Subsea Pipeline Stability   ±

Calculate stability of on bottom structures using Morison's equation (Airy Stokes and Cnoidal waves).

For horizontal stability the horizontal wave and current loads must be less than the restraining friction force. For vertical stability the specific gravity should be greater than or equal to 1.1. Wave vertical velocity and acceleration are ignored. For some structures, depending on geometry, tipping should also be considered. Tipping does not generally occur on pipelines.

Refer also to : DNV-RP-F109 On-Bottom Stability Design Of Submarine Pipelines.

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CALCULATOR MODULE : DNVGL RP F109 Submarine Pipeline Stability   ±

Calculate DNVGL-RP-F109 pipeline lateral and vertical stability.

Static or absolute stability can be calculated for clay seabed, sandy seabed (D50 ≤ 50 mm), or rocky seabed (D50 > 50 mm). The single oscillation velocity corresponds to the maximum wave velocity in the return period. Maximum current velocity data should be used.

Dynamic stability can be calculated on clay and sandy seabeds for Lstable (pipe displacement ≤ 0.5 OOD), L10 (pipe displacement ≤ 0.5 OOD), or user defined pipe displacement. Significant current velocity data should be used.

Seabed wave velocity is calculated from the JONSWAP surface spectrum with an Airy wave transfer function. The calculation should only be used for elevations at or near the seabed. The Airy wave transform may not be valid in shallow water.

Reference : DNVGL-RP-F109 : On-Bottom Stability Design Of Submarine Pipelines (Download from the DNVGL website)

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CALCULATOR MODULE : DNVGL RP F109 Shields Number   ±

Calculate DNVGL RP-F109 Shields number and critical velocity.

Shields number is the ratio of shear force to weight force and is used to estimate the onset of seabed movement for non cohesive soils. The critical velocity corresponds to to the onset of seabed movement.

Reference : DNVGL-RP-F109 : On-Bottom Stability Design Of Submarine Pipelines (Download from the DNVGL website)

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CALCULATOR MODULE : DNVGL RP F109 Initial Seabed Penetration   ±

Calculate DNVGL RP-F109 initial pipeline penetration due to weight on sand and clay soils.

Penetration should be calculated for the maximum pipe weight, normally the water filled weight during pre commissioning. Pipe penetration or embedment is assumed to be zero on rocky seabeds.

Reference : DNVGL-RP-F109 : On-Bottom Stability Design Of Submarine Pipelines (Download from the DNVGL website)

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CALCULATOR MODULE : DNVGL RP F109 Piping And Self Burial   ±

Calculate DNVGL RP-F109 piping and pipeline self burial in non cohesive soils.

Piping occurs with mobile, non cohesive sandy seabeds due to the flow around and underneath the pipe. Self burial is self limiting as the flow reduces with burial depth. The equilibrium burial depth is calculated. The Shields number can be used to check the onset of seabed instability. Self burial is a gradual process which occurs over a period of time. Self burial should be calculated using a sea state significantly smaller than the maximum design sea state.

Reference : DNVGL-RP-F109 : On-Bottom Stability Design Of Submarine Pipelines (Download from the DNVGL website)

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CALCULATOR MODULE : DNVGL RP F109 Curved Pipeline Laying   ±

Calculate DNVGL RP-F109 curved pipeline laying on clay and sandy seabeds.

The lay tension force is calculated to balance the lateral tension force and the passive resistance due to pipe embedment and lateral friction. Pipe embedment is assumed to be zero on rocky seabeds. The pipeline will normally be empty during laying.

Reference : DNVGL-RP-F109 : On-Bottom Stability Design Of Submarine Pipelines (Download from the DNVGL website)

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CALCULATOR MODULE : DNVGL RP F109 Wave Spreading And Directionality   ±

Calculate DNVGL RP-F109 wave spreading and directionality from relative heading and spreading factor.

The wave spreading factor accounts for the "choppiness" or multi directional properties of wave groups. Locally generated waves are generally more multi directional and should have small spreading factors. Long range swells tend to be more uni directional, and can be used with large spreading factors.

Reference : DNVGL-RP-F109 : On-Bottom Stability Design Of Submarine Pipelines (Download from the DNVGL website)

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CALCULATOR MODULE : DNVGL RP F109 Wave Seabed Velocity   ±

Calculate DNVGL RP-F109 wave seabed velocity from the JONSWAP surface spectrum.

An Airy wave transform is used to calculate the significant seabed velocity, and zero upcrossing wave period. The calculation is not valid in shallow water, or at elevations greater than half the water depth.

Reference : DNVGL-RP-F109 : On-Bottom Stability Design Of Submarine Pipelines (Download from the DNVGL website)

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CALCULATOR MODULE : DNVGL RP F109 Wave Probability And Return Period   ±

Calculate DNVGL RP-F109 wave and current amplitude from return period data.

Current velocity, wave height, and wave period can be calculated from return period data using either the Weibull, Gumbel or Frechet probability distributions. Enter data as comma or tab separated sets (eg R, Vc), with each set on a new row. Data can also be copied and pasted from a spreadsheet, or from a text document.

Reference : DNVGL-RP-F109 : On-Bottom Stability Design Of Submarine Pipelines (Download from the DNVGL website)

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CALCULATOR MODULE : DNVGL RP F109 Check Value   ±
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