﻿ Model Options

# Model Options

Initiate pipeline design

The various options to influence the way calculations are done can be selected here.

 Model Options: Bend Angle

This option lays down the influence of the stiffness of the straight pipe on the adjacent bend.

 Infinite: No stiffness influence of straight pipe on adjacent bend. The bend is considered to have a 'infinite' bend angle from a stiffness point of view as in the case of a pure ring-shaped pipeline structure. This is the standard built-in situation. Limited: Stiffness influence of straight pipe on adjacent bend considered. The bend is considered to become stiffer due to the adjacent straight pipe section dependent on the magnitude of the bend angle. The smaller the bend angle, the greater the influence. This option gives a better approach of the bend behaviour. This option is only available if the Non-Linear Limited Bend Angle (Q) module and the Ovalisation Redistribution (R) module (required for module Q) are present. This option is only selectable when analysis type General is selected

This options is not available in the free Educational version.

 Model Options: Geometry Model

This option allows switching between geometrically linear or non-linear analysis.

 Model Options: Section Model

This option allows switching between 1st (Non-Ovalising) and 2nd order (Ovalising) ovalisation effect.

Non-Ovalising:

This is the common standard bend stiffness and stress intensification procedure: the bend stiffness is independent of the bending curvature of the bend section. This method is a first order approach.

Ovalising:

In reality the bend stiffness is non-linear with the curvature due to the ovalisation of the cross-section. This second order effect is taken into account if this option is selected. It also implies the geometrically non-linear and limited bend angle options.

As a result of the ovalisation in the bend the adjacent straight pipe sections will become ovalised as well, resulting in an ovalisation redistribution over the bend and adjacent pipe sections. This redistribution of the ovalisation and inherent stressing is taken into account, as well as the interaction between soil loads at bends and the resulting cross-sectional ovalisation and related longitudinal pipe bending.

The influence of the 'Ovalising'-option increases when the bend radius decreases.

This option is available only if the following modules are present:

 • Geometric Non-Linear (N) module
 • Non-Linear Limited Bend Angle (Q) module
 • Ovalisation Redistribution (R) module (required for module Q)

This options is not available in the free Educational version.

 Model Options: Material Model

This option allows switching between material elastic (Linear) or elasto-plastic (Non-Linear) behaviour.

This option is only available in the Non-Linear / Elasto-Plastic Material (M) module. However the following modules are also required (for module M):

 • Geometric Non-Linear (N) module
 • Non-Linear Limited Bend Angle (Q) module
 • Ovalisation Redistribution (R) module (required for module Q)

This options is not available in the free Educational version.

 Model Options: Soil Ring-Stiffening

This option allows taking into account the cross-sectional lateral soil support (Apply) or disregard it (Ignore).

If Soil Ring-Stiffening is applied, horizontal soil support springs are applied at the points of the cross-section which move outward. To the soil springs the value of KLH or (KLT+KLS)/2 is assigned whichever has the lowest value. The soil resistance is maximised at 50 % of the lowest bearing capacity (horizontal RH or vertical (RVS+RVT)/2). Average values of the soil parameters involved are applied, so without uncertainty factors.

This option is only available if the Soil Ring-Stiffening (U) module is present. However the following modules are also required:

 • Geometric Non-Linear (N) module
 • Non-Linear Limited Bend Angle (Q) module
 • Ovalisation Redistribution (R) module (required for module Q)

This options is not available in the free Educational version.

 Model Options: Soil Model

This option allows switching between "Standard", "Upheaval Buckling" or "Pipe on Seabed".

 Standard: The standard soil behaviour is applicable for completely buried pipelines as described sub DF3.2. The parameter values from Design Function 3.2 are kept constant during the iteration process. Upheaval Buckling: The soil parameters are adapted after each iteration to meet the values valid at the newly calculated depth location. This option is useful for so-called upheaval buckling calculations where the pipeline may even move to (above) the ground level, which has to be specified in table G-LEVEL. This functionality is only applicable on pipeline parts where the RVT > 0. This option is only available if the Upheaval Buckling (Z) module and the Geometric Non-Linear (N) module are present. Pipe on Seabed: The soil parameters have to be specified for a pipe with the axis at ground level, so half the diameter is below the ground surface, which has to be specified in table G-LEVEL. The soil parameters are interpolated dependent on the calculated imprint in the ground surface. This option is used in offshore pipe-lay calculations to improve iteration stability. This functionality is only applicable on pipeline parts where the RVT = 0. This option is only available if the Back tension offshore pipe-laying (B) module and the Geometric Non-Linear (N) module are present.

This options is not available in the free Educational version.

 Model Options: Ovalisation Redistribution
 In case the Ovalisation Redistribution (R) module is available, redistribution of cross-sectional deformations can be enabled. If disabled (None), the successive cross-sections deform independently. If enabled (Allowed), the redistribution of deformations due to the shell behaviour of coupled adjoining cross-sections is taken into account. This module requires the Stress (S) module. This options is not available in the free Educational version.
 If this option is enabled (Apply), when settlements are specified and the pipeline does not follow due to its stiffness or when - without settlements - the pipeline moves upwards, so that a gap results beneath the pipeline, and the existing top (soil) load exceeds the downward soil reaction from output table SOILREA, additional loadings, bending moments, soil reactions and displacements resulting from the loading difference are collected in output table ADDCROS. If this option is disabled (Ignore), output table ADDCROS remains empty.
 Model Options  for Analysis Types

Not every model option is available for all analysis types. Only for the General analysis type all options are available. For the other analysis types some options are not available because they are not supported by the associated codes.

 Model options Analysis types General NEN 3650 Belgian Law ASME B31.4 ASME B31.8 Bend Angle 1 Geometry Model Section Model 1 Material Model Soil Ring-Stiffening Soil Model Ovalisation Redistribution Loading Redistribution

1 The NEN 3650 does not support the Bend Angle and Section Model options. However, when Soil Ring-Stiffening is applied the Bend Angle option is set to Limited and the Section Model Option is set to Ovalising.

H1003, last changed: 14/09/2016