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Lines

Lines represent the primary object of interest in most models created in DeepLines, such as risers, cables, pipelines, mooring lines, etc. The built-in options are designed to facilitate the modelling of common offshore systems for drilling and production, both rigid and flexible. But the powerful capabilities of DeepLines permits a multitude of different real-word objects to be represented by lines. The ability to modify the hydrodynamic response in all 6 degrees of freedom makes the line element in DeepLines able to represent literally any slender object, even ones which do not have a symmetrical cross- section.

In the upper part of the line edit window, you can edit the line name. The OK button will validate all changes performed while the Cancel option will leave the line unchanged.

Lines must be modeled by creating a particular arrangement of segment properties, previously defined by the user, as detailed in the Line segment types help page. Both line ends can be connected to any structure (floater, arch, line) and/or apply constraint applied: boundary condition, displacement, force

The internal fluid is defined in a second panel via the density and a reference pressure; although a line composed of Cable/Chain elements cannot have internal fluid. The differential pressure effect as well as the internal fluid mass contribution will be calculated automatically.

Several different type of line are available within DeepLines :

  • Flexible lines / Generic lines: This type of line allows you to model a large variety of risers and is composed of a succession of sections and segments. These lines can be rigid or flexible, representing respectively a homogeneous section such as steel, and a composite carcass construction where the mechanical properties such as bending stiffness are defined outside Deeplines and entered directly as data. A flexible line is created with a default flexible type a property while a generic line is created with a default generic type property.

  • Drilling riser: This type of line was specially created to deal with drilling operations from a floating vessel and is composed of different drill joint types. The major difference to Generic Lines is that drill joints have a particular length and so the actual number of joints will be entered instead of a global length; auxiliary lines are also modeled, as noted in the Segment Type help page for Drill Joints.

  • Trelline: The Trelline is an export line system owned by Trelleborg composed of bonded flexible hoses for which no simple relationship exists to derive the stress in the different layers from the tension, bending moment, internal and external pressure. A new hose type has been included in the line segment types for which the stress in several components can be interpolated from pre-existing proprietary Excel databases provided by Trelleborg, based on the tension, bending moment and pressure differential. This particular hose type allows for example to calculate the fatigue damage of Trelline export lines directly within the GUI.

  • Winch lines: Winch lines are cable elements which allow you to perform dynamic installation analyses of risers and pipelines. They may also be used to simulate lay-down of heavy equipment. Winch lines allow you to define real-world winch behaviour including the cable elements. Cable elements initially connected to a reference node are progressively released over the time-domain simulation to simulate the effect of the cable being reeled-in or paid-out. This functionality is enhanced via the availability of a pulley element.

  • Bent Lines: Bent Line components are used to model spools or equivalent pipe featuring multiple bends. Compared to the Generic Line component, a Bent Line is built as a succession of straight and bent pipe segments. The total length and shape of Bent Lines is derived from the properties of the straight and bent segments. These properties must be input in the Shape Definition tab.

Lines components may be created by:

  • Clicking the toolbar button to create a generic line. Clicking the arrow on the right hand of the button yields a drop down menu from which you may further select the type of line to be created, as shown below:

  • From the menu item Model/New line

Each line can be modified by:

  • Double clicking on the line in the 3D window

  • Double clicking on the line component name in the model browser

The line is a continuous slender structure composed of sections, which are divided at primary points: sections are divided into several segments. Finally, these lengths are divided ('partitioned') into beam elements. Each section or segment can be assigned a Segment Type (which defines the mechanical properties).. Several actions can be conducted to mesh the lines :

  • If the line is composed of a single segment type, you can immediately set the number of required elements in the Partition box.

  • If the line is composed of different segment types, it must be split into segments according to the start and end of each type required. For each segment, the segment type and its element partitioning can be modified independently of the other segments, so different segments are often used to set higher element resolution (reduced spacing) to achieve finer results at areas of interest, while having larger element spacing in other areas to ensure the model remains efficient at run-time.

  • The line can also be split into Sections which can be useful to create and position intermediate nodes to better represent the riser shape; the intermediate nodes between Sections can also be selected to connect lines, arches, forces, displacements, or to impose particular boundary conditions.

The beam-element length set by the partition number for each Segment or Section should be short enough to prevent convergence or tolerance errors at run-time, while not wasting computing resources. For short lines, a length of 1.0m is typical with 0.2m near ends or areas of interest, areas of high bending, rapid or large displacement etc. For longer lines, e.g. deepwater risers, a much longer element length (e.g. 10m or more) can be used for parts of the model which are not subject to significant motion in order to save processor resources without altering results accuracy.

Warning

Two adjacent Segments or Sections must have an element length ratio which must not exceed around 1.5 ~ 2 to ensure accurate calculations. It may be necessary for you to create intermediate transition segments so that the maximum aspect ratio does not exceed this acceptable limit.

In the line data entry tables, copy/paste to or from an Excel spreadsheet is possible, making the creation of models faster and more reliable.