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*Slugs |
 
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*Slugs
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*Slugs |
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To specify parameters relating to slug flow.
Refer to Slug Flow for further information on this feature.
Block of lines defining the slug data. The format used depends on whether the slugs have constant properties over the course of the analysis, or whether the slug properties vary as a function of time.
An optional line may be included at the beginning of the keyword to indicate if the visual display of slug elements in the structural animation is required or not.
[DISPLAY=Display] [, ELEMENTS=No.of Display Elements]
For slugs with constant properties, the following block of three lines is used:
PROPERTIES=CONSTANT
SET=Set Name
Length, Density, [Velocity], Start Time, [No. of Slugs], [Time Lag]
[, COLOUR=Colour]
For slugs with time-varying properties, the following block of four lines is used:
PROPERTIES=TIME VARIANT
FILE=File Name
SET=Set Name
Length, Start Time, [No. of Slugs], [Time Lag], Column Number,
[VELOCITY=Velocity Profile] [, COLOUR=Colour]
The last line of the block may be repeated if more than one slug is present in a particular element set. The last two lines of the block may be repeated to define slugs in different element sets. When specifying time-varying slugs, several slugs may share the same ASCII file – otherwise a new file name should precede the element set specification. The entire block of lines may be repeated to combine both constant and time-varying slugs in the same analysis.
Display may be either YES (the default) or NO. The No. of Slugs defaults to 1. A value for Time Lag is only valid, and must be greater than 0, if No. of Slugs is greater than 1. Velocity defaults to the internal fluid velocity for the element set. If the File Name input contains spaces then it should be enclosed in double quotation marks. For time variant slugs, Velocity Profile may be either INTERPOLATED (the default) or CONSTANT.
The format of the ASCII file which characterises time-varying slugs is as follows:
Time t0, Slug A head velocity at t0, Slug A tail velocity at t0, Slug A head density at t0, Slug A tail density at t0 [, Slug B head velocity at t0, Slug B tail velocity at t0, Slug B head density at t0, Slug B tail density at t0, …]
Time t1, Slug A head velocity at t1, Slug A tail velocity at t1, Slug A head density at t1, Slug A tail density at t1 [, Slug B head velocity at t1, Slug B tail velocity at t1, Slug B head density at t1, Slug B tail density at t1, …]
Time t2, Slug A head velocity at t2, Slug A tail velocity at t2, Slug A head density at t2, Slug A tail density at t2 [, Slug B head velocity at t2, Slug B tail velocity at t2, Slug B head density at t2, Slug B tail density at t2, …]
…
…
Time tn, Slug A head velocity at tn, Slug A tail velocity at tn, Slug A head density at tn, Slug A tail density at tn [, Slug B head velocity at tn, Slug B tail velocity at tn, Slug B head density at tn, Slug B tail density at tn, …]
Note that all times specified in the data file are relative to the time when the slug enters the model. In other words, they are elapsed times post slug entry, rather than absolute simulation times. So Time t0 (which should be equal to zero in the data file) corresponds to the simulation time when the slug first enters the model. This means that different slugs with different start times can all share the same input file.
Further rows are added to define slug properties at additional times, from time t3 up to time tn.
Further columns may be added to define properties for additional slugs. Alternatively you may prefer to create a new ASCII file for each slug definition. If you have only one type of slug in the simulation, then you will only define properties for Slug A (i.e. there is no Slug B, or Slug C).
Refer to the Notes section for further information.
Input: |
Description |
Display: |
The options are Yes (the default) and No. See Note (f). |
Number of Display Elements: |
The maximum number of elements to be used for slug display purposes. This entry is optional and a default value is used if unspecified. See Note (f). |
Use this input format to define slugs whose properties remain constant over time (i.e. their length, density and velocity do not change during a simulation)
Input: |
Description |
Set Name: |
The element set name. The default is all elements. |
Slug Length: |
The length of the slug(s) being defined. |
Slug Density: |
The density of the slug(s) being defined. |
Slug Velocity: |
The velocity of the slug(s) being defined. |
Start Time: |
The time at which the slug (or the first of a series of similar slugs) enters the first element in the set. |
No. of Slugs: |
The number of slugs in a series with the present slug properties. This entry defaults to 1, indicating that a single slug rather than a series of slugs is being defined. |
Time Lag: |
This is an optional entry, only used when a series of slugs is being defined. Time Lag is the delay between the times that each slug in the series enters the first element of the set. |
Colour: |
This is an optional entry to specify the colour of the slug in the structural animation. The entry must be the name of a standard colour or a user defined colour. A list of the standard colours can be found in the *COLOUR DEFINE keyword. |
Input: |
Description |
File Name: |
The name of the ASCII file containing the time-varying data. See Note (e). |
Set Name: |
The element set name. The default is all elements. |
Slug Length: |
The initial length of the slug(s) being defined. |
Start Time: |
The time at which the slug (or the first of a series of similar slugs) enters the first element in the set. |
No. of Slugs: |
The number of slugs in a series with the present slug properties. This entry defaults to 1, indicating that a single slug rather than a series of slugs is being defined. |
Time Lag: |
This is an optional entry, only used when a series of slugs is being defined. Time Lag is the delay between the times that each slug in the series enters the first element of the set. |
Column Number: |
The column of data in the external file which contains the slug head velocity as a function of time. Data columns are labelled upwards from one (i.e. the time column is considered ‘column zero’). The remaining data for a particular slug is assumed to directly follow the velocity column within the file. The order of inputs is (i) velocity at slug head, (ii) velocity at slug tail, (iii) density at slug head, and (iv) density at slug tail, respectively. |
Velocity Profile: |
The options are Interpolated (default) and Constant. The Interpolated option means that the velocity at a given point on the slug is computed by linear interpolation along the slug using head and tail velocities. Constant means that the distance travelled by head and tail are calculated using head and tail velocities, but the velocity of the slug at all points is equal to the head velocity. This approach means that a slug can have varying lengths but a constant velocity. |
Colour: |
This is an optional entry to specify the colour of the slug in the structural animation. The entry must be the name of a standard colour or a user defined colour. A list of the standard colours can be found in the keyword *COLOUR DEFINE. |
(a)The element set name is associated with the elements comprising the set using the Element Sets table. Obviously, different slug flow specifications can be defined for different element sets.
(b)Use as many lines as you need to completely define the slug data for a particular set. Simply leave the Set Name column blank for second and subsequent lines if specifying further slugs or series of slugs. For subsequent sets, put the set name in the Set Name column and specify the slug data in the same way.
(c)For slugs of constant properties, Slug Velocity is an optional input. By default, the velocity of a slug within a set is equal to the internal fluid velocity for that set, which is specified using the Internal Fluid table.
(d)When specifying time-varying slugs, several slugs may share the same ASCII file. Simply leave the File Name column blank for second and subsequent lines if specifying further slugs which pertain to the same input file. If you wish to use a different file name, insert the file name in the File Name column and specify the slug data in the same way.
(e)The data file is ASCII based, and its format depends on the number of time-varying slugs which are associated with the data file. In general the file contains one column of data for the time and four additional columns for each slug definition – relating to instantaneous (i) velocity at slug head, (ii) velocity at slug tail, (iii) density at slug head, and (iv) density at slug tail, respectively. The layout of data within the text file must be consistent with the definition of time-varying slugs in the keyword file – this is governed by the Column Number parameter. Data columns are labelled upwards from one (i.e. the time column is considered ‘column zero’). So for example, the head velocity for the first slug would typically be located in Column No.1, the head velocity for the second slug in Column No. 5, and so forth. See Slug ASCII File Format for an illustration.
•All times specified in the data file are relative to the time when the slug enters the model. In other words, they are elapsed times post slug entry, rather than absolute simulation times. So Time t0 (which should be equal to zero in the data file) corresponds to the simulation time when the slug first enters the model. This means that different slugs with different start times can all share the same input file.
•Columns of data in the ASCII data file should be separated by blank spaces or tabs. Comment lines, denoted by a capital ’C’ in the first column, are permitted, while lines that are completely blank are ignored. You can specify several time-varying slugs in a single data file.
(f)Slugs are displayed in Flexcom using a series of auxiliary elements, which provide a very helpful means of visualising the slug flow post-simulation. Although visualisation is an integral part of understanding slug induced loads, the use of auxiliary elements does result in increased database file sizes, which take up more disk space, and may also have some impact on simulation and post-processing times. For maximum efficiency, some users prefer to set the Slug Display option to No, and switch it on occasionally, for example to visually inspect slug paths during critical load cases only. The maximum number of display elements is set equal to the number of elements times the number of slugs, but this amount of elements is conservative and highly unlikely to be ever required in practice. Hence you may manually choose the required number of display elements if you wish. Refer to Slug Flow Visualisation for further details.