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*Load

Purpose

To define arbitrary loading.

Theory

Refer to Point and Distributed Loads and User-Subroutine Loads for further information on this feature.

Keyword Format

Load data is specified in blocks, with each block beginning with a TYPE= line defining the load type. This is then followed by as many lines as necessary to specify the loads of that type, and this in turn is then followed as necessary by data for other types.

Block defining point loads. The format of the second and subsequent lines depends on whether the loading is based on a single numerical value or a file containing a range of time-dependent values.

TYPE=CONSTANT

Node (Number or Label), DOF, Load Value

or

Node (Number or Label), DOF, FILE=File Name, Column Number

 

Block defining distributed loads. The format of the second and subsequent lines depends on whether the loading is based on a single numerical value or a file containing a range of time-dependent values.

TYPE=DISTRIBUTED

Start Element (Number or Label), End Element (Number or Label), Co-ordinate Direction, Load Value

or

Start Element (Number or Label), End Element (Number or Label),

Co-ordinate Direction, FILE=File Name, Column Number

 

Line defining a user subroutine:

USER=File Name

Block defining point loads specified in a user subroutine:

TYPE=SUBROUTINE, LOAD=POINT

Node (Number or Label), DOF

 

Block defining distributed loads specified in a user subroutine:

TYPE=SUBROUTINE, LOAD=DISTRIBUTED

Start Element (Number or Label), End Element (Number or Label), Co-ordinate Direction

 

Block defining vessel RAO loads:

TYPE=VESSEL

Node (Number or Label), DOF

 

Block defining harmonic loads:

TYPE=HARMONIC

Node (Number or Label), DOF, Amplitude [, Phase]

 

If any user subroutine loads are defined, then the USER=option is mandatory. File Name should include the entire path of the file including its extension. If a file name or any part of its path contains spaces then it should be enclosed in double quotation marks. If you specify a node/element label rather than a number, it must be enclosed in {} brackets. The user subroutine option is not relevant for frequency domain dynamic analysis. Vessel and harmonic loads are only relevant for frequency domain dynamic analysis.

Constant Loads

Purpose

To define the location, direction and magnitude of constant (time invariant) loads.

Table Input (Point Loads – Constant)

Table Input (Distributed Loads – Constant)

Notes

(a)Loads are input as components in the global coordinate directions. A load oblique to the coordinate axes is specified as three load components.

(b)Uniformly distributed loads are specified as acting on an element or group of consecutive elements, defined in terms of a start element and an end element (start and end elements are the same for a load acting on a single element).

Time Varying Loads

Purpose

To define the location, direction and magnitude of time-dependent loads.

Table Input (Point Loads – Time Varying)

Table Input (Distributed Loads – Time Varying)

Notes

(a)Loads are input as components in the global coordinate directions. A load oblique to the coordinate axes is specified as three load components.

(b)Uniformly distributed loads are specified as acting on an element or group of consecutive elements, defined in terms of a start element and an end element (start and end elements are the same for a load acting on a single element).

(c)The data file is ASCII based, and its format depends on the number of loads which are specified in this manner. In general the file contains one column of data for the time and an additional column for each load definition. The layout of data within the text file must be consistent with the definition of loads in the keyword file, the latter being governed by the Column Number parameter. Force columns are labelled upwards from one (i.e. the time column is considered ‘column zero’).

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 loads in a single data file.

(d)When a time varying load is specified, Flexcom reads the relevant force data from the specified data file at the relevant time. The program uses linear interpolation to obtain force values at solution times intermediate to those specified in the data file. For solution times before the earliest time specified in the load file, Flexcom uses the earliest force values available. Similarly, for solution times after the latest time in the load file, Flexcom continues to use the values corresponding to the latest available time.

Subroutine Loads

Purpose

To define the point/area of application and direction of loads, the magnitude of which is defined, typically as a function of time, in a user-subroutine.

Table Input (Point Loads)

Table Input (Distributed Loads)

Table Input (Subroutine File)

Notes

(a)Refer to User-Subroutine Loads for a detailed discussion of the load user-subroutine facility.

(b)Loads are input as components in the global coordinate directions. This means that a force oblique to the coordinate axes is specified as three load components.

(c)The name of the DLL file containing the subroutine that defines the magnitude of the load specified in the Subroutine Loads – Point or Subroutine Loads – Distributed table must be specified using the Subroutine File table.

(d)Uniformly distributed loads are specified as acting on an element or group of consecutive elements, defined in terms of a start element and an end element (start and end elements are the same for a load acting on a single element).

(e)Subroutine loads are not relevant for frequency domain dynamic analysis.

Vessel Loads

Purpose

To specify the point of application and direction of point loads computed from vessel RAOs.

Table Input

Notes

(a)Vessel loads are used to specify frequency-dependent time-varying loads, for example, the variation in top tension of a riser connected to a TLP.

(b)The analysis type must be frequency domain dynamic if vessel loads are to be specified. The name of the file containing the load RAO must be specified in the Loads - RAO File table.

(c)Vessel loads can be used with constant point loads. In this case, the constant load (applied at all frequencies) is added to the vessel load at each particular frequency.

Harmonic Loads

Purpose

To specify the parameters relating to harmonically varying point loads in a frequency domain regular wave analysis.

Table Input

Notes

(a)Harmonic point loads are input as components in the global coordinate directions. This means that a force oblique to the coordinate axes is specified as three load components.

(b)The analysis type must be frequency domain dynamic if harmonic loads are to be specified. If you specify such loads, then the analysis must have one or many regular waves invoked. The harmonic load has the same period as the analysis regular wave(s).