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*Wake UpstReam |
 
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*Wake UpstReam
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*Wake UpstReam |
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To specify the composition of the upstream structure in terms of element sets, for use in wake interference calculations. The keyword also selects the wake interference model to be used, and defines associated data to characterise the wake field.
Refer to Wake Interference for further information on this feature.
The keyword begins with a mandatory line selecting the wake interference model which can be HUSE, BLEVINS or USER and optional additional OUTPUT= which can be Yes or No. This is followed by an optional line to define the path to the Flexcom analysis file containing the upstream structure. This is followed by a mandatory line defining the set(s) of elements which comprise the upstream structure. In the case of a User-Defined wake interference model, the relevant set names and corresponding Drag and Lift coefficients are input through an external data file. As with the Huse and Blevin’s models, the data entry in terms of set name, drag & lift coefficients may be repeated as many times as necessary to represent the upstream structure
Mandatory line selecting the wake interference model:
MODEL=Wake Effect Model [, OUTPUT=YES]
Optional line defining upstream structure analysis file:
[UPSTREAM_FILE=Full Path of Upstream Structure Analysis File]
Mandatory line defining upstream structure element set(s):
SET=Element Set Name
The element set name is followed by a single line with three coefficient values:
[k1, k2, k3]
The element set name is followed by a single line with three coefficient values:
[a1, a2, a3]
The entire block of data (i.e. element set name and associated wake field data) may be repeated as many times as necessary to completely define the upstream structure.
The USER defined Drag & Lift coefficients are input through a separate data file by a mandatory line; WAKE_USER_FILE= Full path of USER Drag & Lift data. If the file name or any part of its path contains spaces then it should be enclosed in double quotation marks. The format of the data file will be a line containing the element set name which is followed by blocks of lines which define the wake field in terms of drag and lift coefficient data. A first line with either TYPE=DRAG or TYPE=LIFT indicates which data is being input (they can be specified in either order). Note that the coefficient data represents coefficient factors rather than absolute coefficient values. The first line following TYPE= lists the transverse separation values at which the coefficient factors are defined, normalised with respect to the drag diameter of the upstream structure. Each line after that starts with a longitudinal separation value, again normalised with respect to the drag diameter of the upstream structure, followed by coefficient factors corresponding to the separation values. If L represents the centre-to-centre distance between upstream and downstream structures in the longitudinal direction (direction of undisturbed flow), and T is the centre-to-centre spacing in the transverse direction (normal to undisturbed flow); then the ith normalised separations are denoted li=Li/Dd and ti =Ti/Dd . The following then summarises the above:
TYPE=DRAG
t1, t2, t3, ...... tn
l1, Cdf(l1,t1), Cdf(l1,t2), Cdf(l1,t3) ....... Cdf(l1,tn)
l2, Cdf(l2,t1), Cdf(l2,t2), Cdf(l2,t3) ....... Cdf(l2,tn)
...
...
lm, Cdf(lm,t1), Cdf(lm,t2), Cdf(lm,t3) ....... Cdf(lm,tn)
TYPE=LIFT
t1, t2, t3, ....... tn
l1, Clf(l1,t1), Clf(l1,t2), Clf(l1,t3) ....... Clf(l1,tn)
l2, Clf(l2,t1), Clf(l2,t2), Clf(l2,t3) ....... Clf(l2,tn)
...
...
lm, Clf(lm,t1), Clf(lm,t2), Clf(lm,t3) ....... Clf(lm,tn)
A sample USER-Defined data file is as follows:
SET=Riser-UP-set1
TYPE=DRAG
-12.0, -8.0, -4.0, -2.0, 0.0, 2.0, 4.0, 8.0, 12.0
0.2, 1.0, 1.0, 1.0, 0.1, 0.1, 0.1, 1.0, 1.0, 1.0
1.0, 1.0, 0.6, 0.4, 0.2, 0.1, 0.2, 0.4, 0.6, 1.0
2.0, 1.0, 0.6, 0.6, 0.4, 0.2, 0.4, 0.6, 0.6, 1.0
4.0, 1.0, 0.8, 0.6, 0.6, 0.2, 0.6, 0.6, 0.8, 1.0
8.0, 1.0, 1.0, 0.8, 0.8, 0.4, 0.8, 0.8, 1.0, 1.0
12.0, 1.0, 1.0, 1.0, 0.8, 0.6, 0.8, 1.0, 1.0, 1.0
TYPE=LIFT
-12.0, -8.0, -4.0, 0.0, 4.0, 8.0, 12.0
1.0, 0.0, 1.6, 0.8, 0.0, 0.8, 1.6, 0.0
4.0, 0.0, 1.2, 0.6, 0.0, 0.6, 1.2, 0.0
12.0, 0.0, 1.0, 0.5, 0.0, 0.5, 1.0, 0.0
SET=Riser-UP-set2
TYPE=DRAG
-12.0, -8.0, -4.0, -2.0, 0.0, 2.0, 4.0, 8.0, 12.0
0.2, 1.0, 1.0, 1.0, 0.1, 0.1, 0.1, 1.0, 1.0, 1.0
1.0, 1.0, 0.6, 0.4, 0.2, 0.1, 0.2, 0.4, 0.6, 1.0
2.0, 1.0, 0.6, 0.6, 0.4, 0.2, 0.4, 0.6, 0.6, 1.0
4.0, 1.0, 0.8, 0.6, 0.6, 0.2, 0.6, 0.6, 0.8, 1.0
8.0, 1.0, 1.0, 0.8, 0.8, 0.4, 0.8, 0.8, 1.0, 1.0
12.0, 1.0, 1.0, 1.0, 0.8, 0.6, 0.8, 1.0, 1.0, 1.0
TYPE=LIFT
-12.0, -8.0, -4.0, 0.0, 4.0, 8.0, 12.0
1.0, 0.0, 1.6, 0.8, 0.0, 0.8, 1.6, 0.0
4.0, 0.0, 1.2, 0.6, 0.0, 0.6, 1.2, 0.0
12.0, 0.0, 1.0, 0.5, 0.0, 0.5, 1.0, 0.0
The use of *WAKE UPSTREAM is compulsory if wake interference effects are to be included in an analysis and may only be invoked in a static or quasi-static analysis. If the Upstream Structure Analysis File is included, it should be specified without extension. If it contains spaces, then it should be enclosed in double quotation marks. Element Set Name must be an existing element set, defined in the initial static analysis of the upstream structure. The specification of drag and lift data is required if Wake Effect Model is set to USER. The l and t values must be specified in ascending order.
The Upstream Structure Analysis File is the name of the file for the static or quasi-static analysis with current of the upstream structure. It is required if the two structures under consideration are being analysed in separate models. It is omitted where the upstream and downstream structures are included in the same model. The specification of the k1, k2 and k3 values for Huse’s formulation is optional – these default to 0.25, 1 and 0.693 respectively. Likewise, the specification of the a1, a2 and a3 values for Blevins’ formulation is optional – these default to 1, 4.5 and -10.6 respectively.
To specify the formulation to be used in calculating wake interference effects and request additional output from wake modelling calculations.
Input: |
Description |
Formulation: |
The options are Huse's (the default), Blevins' and User-Defined. |
Output: |
The options are No (the default) and Yes. See Note (b). |
To specify the path to the analysis file containing the upstream structure file if the two structures are modelled separately.
Input: |
Description |
Upstream File: |
Path of Upstream Structure Analysis File. See Note (c). |
To specify parameters relating to Huse’s wake interference formulation.
Input: |
Set Name: |
k1: |
k2: |
k3: |
Description |
The name of the set that contains the elements on the upstream structure that you want to include in the wake interference analysis with the corresponding coefficients. The default is All. Can be specified as many times as required. |
The k1 coefficient of Huse’s formulation equation. The default is 0.25. |
The k2 coefficient of Huse’s formulation equation. The default is 1. |
The k3 coefficient of Huse’s formulation equation. The default is 0.693.
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To specify parameters relating to Blevins’ wake interference formulation.
Input: |
Set Name: |
a1: |
a2: |
a3: |
Description |
The name of the set that contains the elements on the upstream structure that you want to include in the wake interference analysis with the corresponding coefficients. The default is All. Can be specified as many times as required. |
The a1 coefficient of Blevins’ formulation equation. The default is 1. |
The a2 coefficient of Blevins’ formulation equation. The default is 4.5 |
The a3 coefficient of Blevins’ formulation equation. The default is -10.6.
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To specify the USER defined Drag & Lift data file to be used with the User-Defined Wake Model.
Input: |
Description |
User Wake File: |
The file path of the USER defined data file containing Drag & Lift coefficients for upstream structure sets. See Note (d). |
(a)Refer to Wake Interference for a detailed discussion of the wake interference modelling capabilities in Flexcom and the significance of all associated inputs.
(b)If you invoke this option, Flexcom presents detailed information regarding the wake modelling calculations. Specifically, for every integration point on every element of the downstream structure, the following is provided:
•Longitudinal (L) and transverse (T) centre-to-centre distance to upstream structure
•Reduced current velocity
•Drag and lift coefficients
•Lift Force
This information may be useful in some circumstances in understanding wake interference analysis results, but in general it is not required, so this option would be rarely invoked.
(c)This entry is optional, and is only relevant if the upstream and downstream structures are analysed in separate models.
(d)In the case of a User-Defined wake interference model, the relevant set names and corresponding Drag and Lift coefficients are input through an external data file. As with the Huse and Blevin’s models, the data entry in terms of set name, drag & lift coefficients may be repeated as many times as necessary to represent the upstream structure.