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*Internal Fluid |
 
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*Internal Fluid
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*Internal Fluid |
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To define the properties of an internal fluid.
Refer to Internal Fluid for further information on this feature.
A block of two lines repeated as many times as necessary.
SET=Set Name
Level Above Mudline, Mass Density, [Internal Pressure],
[Velocity],
[CENTRIFUGAL=INCLUDE/EXCLUDE],
[AXIAL_INERTIA=INCLUDE/EXCLUDE],
[LATERAL_INERTIA=INCLUDE/EXCLUDE],
[DYNAMIC_PRESSURE=INCLUDE/EXCLUDE]
Internal Pressure and Velocity default to 0. The remaining terms – CORIOLIS, CENTRIFUGAL, AXIAL_INERTIA, LATERAL_INERTIA and DYNAMIC_PRESSURE – all default to INCLUDE.
Input: |
Description |
Set Name: |
The element set name. The default is all elements. |
Level Above Mudline: |
The level above the mudline to which the internal fluid extends. This affects element weights (in terms of whether an element is fluid filled or empty), and element internal pressures (via the internal fluid hydrostatic pressure contribution). See note (c). |
Mass Density: |
The mass density (mass per unit volume) of this internal fluid. |
Internal Pressure: |
The internal fluid constant pressure above hydrostatic. This defaults to a value of 0. See Note (e). |
Velocity: |
The internal fluid velocity. This defaults to a value of 0. See Notes (f) and (g). |
Coriolis Force: |
This is related to the internal fluid Velocity. Specifically, Coriolis Force is used to specify whether a Coriolis force term due to the velocity of the internal fluid is to be included or excluded from the equations of motion. The default is Include, indicating that the Coriolis force term is to be included. See Note (g). |
Centrifugal Force: |
This is related to the internal fluid Velocity. Specifically, Centrifugal Force is used to specify whether a centrifugal force term due to the velocity of the internal fluid is to be included or excluded from the equations of motion. The default is Include, indicating that the centrifugal force term is to be included. See Note (g). |
Axial Inertia: |
This option allows you to specify whether internal fluid contributes to the structure axial inertia in a dynamic analysis. The default is Include, indicating that the internal fluid contributes to axial inertia. See Note (h). |
Lateral Inertia: |
This option allows you to specify whether internal fluid contributes to the structure lateral inertia in a dynamic analysis. The default is Include, indicating that the internal fluid contributes to lateral inertia. See Note (i). |
Dynamic Pressure: |
This is related to the internal fluid Velocity. Specifically, Dynamic Pressure is used to specify whether a dynamic pressure term due to the velocity of the internal fluid is to be included or excluded from the equations of motion. The default is Include, indicating that the dynamic pressure term is to be included. See Notes (g). |
(a)The specification of internal fluid is optional. By default the structure is assumed empty, that is, filled with air.
(b)The element set name is associated with the elements comprising the set using the Element Sets table. Obviously different internal fluids can be defined for different element sets.
(c)The term Level Above Mudline is most meaningful for riser analysis. For example, a production riser is typically filled with oil, whereas a drilling riser contains mud. In such cases, the elevation input intuitively corresponds to the global X coordinate value at the uppermost end of the riser. Caution must be exercised in other situations however, such as pipeline analysis, where the structure is predominately flat. Theoretically, the elevation input should correspond exactly to the centreline of the pipeline, or marginally above it. In practice, it is strongly recommended that the elevation term is augmented to include a margin of safety. This is necessary to ensure that the pipeline remains flooded at all times throughout a simulation, irrespective of any local fluctuations in vertical displacement. Without an augmented elevation specification, certain portions of the pipeline could inadvertently be modelled as being empty, particularly in restart analyses (due to local deformations in the preceding analysis stage). If you have any concerns about pipeline flooding, you are advised to examine the input data echo section of the detailed output file.
(d)The internal diameter input with the geometric properties is used with the inputs here, to calculate the effect of the internal fluid.
(e)Refer to Hydrostatic Pressure for a discussion on how the hydrostatic pressure head due to the presence of internal fluid and slugs is modelled in Flexcom.
(f)The Flexcom internal fluid model caters for (i) uniform steady state internal flow, and (ii) multi-phase slug flow (the slug flow capability has a separate associated table Slugs). The uniform steady state internal fluid flow option is invoked by inputting a non-zero Velocity here.
(g)Steady state internal fluid flow induces both a centrifugal force (related to pipe curvature) and a Coriolis force (related to pipe rotation). Refer to Centrifugal Force and Coriolis Force for further details. An additional dynamic pressure term which affects pipe wall tension is also modelled. Refer to Dynamic Pressure for further details. Options are provided, as noted above, to suppress any of these terms in a particular analysis, allowing the relative significance of each term to be assessed.
(h)This modelling capability is specifically intended for the analysis of drilling risers in emergency disconnect mode (riser hangoff analysis). Refer to Inertial Effects for further details.
(i)The Lateral Inertia option operates in a similar manner to the Axial Inertia option, as it allows you to exclude internal fluid from the riser lateral inertia. Refer to Inertial Effects for further details.