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*Timetrace

Purpose

To request the storage of results for timetrace postprocessing (this is mainly used in the area of time domain fatigue analysis).

Theory

Refer to Timetrace Postprocessing for further information on this feature.

Keyword Format

The data begins with up to three lines, most of which are optional, which define general parameters relating to subsequent postprocessing of timetrace output. The individual timetrace requests then follow, in blocks of lines according to output type.

The first line, which is optional, defines miscellaneous variables relating to the duration and format of output:

[START=Output Start Time] [, END=Output End Time] [, INTERVAL=Interval] [, STORAGE=Format]

The second line specifies data relating to the calculation of statistics and spectra by the Timetrace Postprocessor. It is required in the case of a random sea analysis, but optional otherwise.

STATISTICS=No. of Ensembles [, Calculation Start Time] [, Time Step]

The third line, which is again optional, specifies the procedure to be used in the computation of extreme values by the Timetrace Postprocessor.

[EXTREME=Calculation Procedure]

The fourth line is required if the line with EXTREME= is present. The format of the fourth line depends on the Calculation Procedure specified – the options are RAYLEIGH (the default) and WEIBULL. For RAYLEIGH extrema postprocessing, the fourth line takes the following format:

DATA=[Storm Duration] [, Probability]

For WEIBULL extrema postprocessing, it takes the following format:

DATA=[Storm Duration] [, Probability] [, Threshold]

Block of lines requesting motion timetrace output. The second line can be repeated as often as necessary.

TYPE=MOTION

Node (Number or Label), DOF

Block of lines requesting force timetrace output. The requests can be made on the basis of element sets or individual elements. The requests may be mixed and/or repeated as often as necessary.

Force timetrace output request for an element set:

TYPE=FORCE

SET=Set Name

Local Node, Variable [, LOCATION=Location]

 

Refer to Force Variable Input for further information on acceptable Variable values. Refer to Location Parameter Input for further information on the significance of the Location input. The significance of the Local Node Input used during postprocessing depends on whether element based outputs are stored on a node or integration point basis.

Force timetrace output request for an individual element:

TYPE=FORCE

ELEMENT=Element (Number or Label)

Local Node, Variable [, LOCATION=Location]

Block of lines requesting reaction timetrace output. The second line can be repeated as often as necessary.

TYPE=REACTION

Node (Number or Label), DOF

A Time Step value is required in a random sea dynamic analysis with a variable time-step; it is ignored in the case of an analysis with a fixed step. The DATA= line is required if EXTREME= is invoked. This keyword is not relevant for frequency domain dynamic analysis.

Output Start Time and Calculation Start Time both default to the analysis start time. End Time defaults to the analysis end time. If no Interval value is specified, data is output at all solution times. Format can be ASCII, BINARY (the default) or IMPORT. Calculation Procedure can be RAYLEIGH or WEIBULL. Storm Duration defaults to 3 hours and Probability to 0.01 (1%). Threshold defaults to 1. If you specify a node/element label rather than a number, it must be enclosed in {} brackets. Scale defaults to 1 (see Note a).

timetrace - Storage

Purpose

To specify data relating to the frequency and format of timetrace output.

Table Input

Notes

(a)In earlier versions of Flexcom, timetrace output was stored in ASCII format by default. In this case, values at each solution time are output on a series of lines – the actual solution time (only) is on the first line of the series, and the requested outputs are then on subsequent lines, typically four values to a line. This means the data can be readily examined and interpreted, but has the disadvantage that for a long simulation with many outputs requested, the file size can be large. The recommended storage method is now Binary – the main advantages being that storage/retrieval of data tends to be quicker, and file sizes are smaller, but means that you cannot edit the file manually. If the Import format is requested, the file format is similar to ASCII, but all values at a particular solution time, including the actual solution time itself, are output on a single line. This allows the data to be readily imported into, say, Excel.

timetrace - Statistics

Purpose

To specify the start time for the calculation of response statistics in any subsequent Timetrace Postprocessing run.

Table Input

Notes

(a)The use of this table is optional. By default, the start time for the calculation of statistics is the first timetrace output time.

(b)The entry you specify here is also used as the start time for the calculation of response spectra in a random sea analysis.

timetrace - Spectra

Purpose

To define parameters relating to the calculation of response spectra in any subsequent Timetrace Postprocessing run.

Table Input

Notes

(a)The procedure used by Flexcom in calculating spectra is as follows. Firstly, the output timetrace is divided equally into a number of smaller timetraces or ensembles. A spectrum for each ensemble is then calculated using the Fast Fourier Transform (FFT) algorithm. Finally, the actual spectrum to be output is found as an average of the spectra calculated for each ensemble. This standard procedure minimises the statistical error associated with the FFT process. You specify the number of ensembles to be used in this process using the No. of Ensembles entry above. This value should always be greater than 1.

(b)The FFT algorithm requires a record with a fixed time step. When you perform a variable step analysis, obviously such a record is not available, and so Flexcom must synthesise one by interpolating from the variable step record. The Time Step entry tells Flexcom what time step to use in the synthesised record.

Extreme Values - Rayleigh

Purpose

To specify parameter values to be used in calculating extreme values with the Rayleigh distribution in any subsequent Timetrace Postprocessing run.

Table Input

Notes

(a)Refer to Extreme Values for a detailed discussion of all aspects of specifying data relating to extreme value postprocessing.

(b)Note that the Extreme Values – Rayleigh and Extreme Values – Weibull tables are mutually exclusive. Specification of data in either table indicates the extreme value postprocessing approach which you wish to use.

Extreme Values - Weibull

Purpose

To specify parameter values to be used in calculating extreme values with the Weibull distribution in any subsequent Timetrace Postprocessing run.

Table Input

Notes

(a)Refer to Extreme Values for a detailed discussion of all aspects of specifying data relating to extreme value postprocessing.

(b)A threshold equal to 1 denotes all the maxima/minima in the timetrace will be used to calculate the extreme values.  A threshold equal to 1/n (e.g. 1/3) uses the upper 1/n of largest maxima and lowest 1/n of smallest minima to calculate the extreme value.

(c)Note that the Extreme Values – Rayleigh and Extreme Values – Weibull tables are mutually exclusive. Specification of data in either table indicates the extreme value postprocessing approach which you wish to use.

timetrace - Motion

Purpose

To request timetraces of the motions of selected nodes.

Table Input

Notes

(a)If any timetrace is requested, then by default a timetrace of wave elevation at Y = Z = 0 (that is, at the vertical axis) is included in the output.

timetrace - Force (By Set)

Purpose

To request timetraces of restoring forces in specified element sets.

Table Input

Notes

(a)Refer to Force Variable Input for further information on acceptable Variable values.

(b)If any timetrace is requested, then by default a timetrace of wave elevation at Y = Z = 0 (that is, at the vertical axis) is included in the output.

(c)Refer to Location Parameter Input for further information on the significance of the Location input.

timetrace - Force (By Element)

Purpose

To request timetraces of restoring forces in specified elements.

Table Input

Notes

(a)Refer to Force Variable Input for further information on acceptable Variable values.

(b)If any timetrace is requested, then by default a timetrace of wave elevation at Y = Z = 0 (that is, at the vertical axis) is included in the output.

(c)Refer to Location Parameter Input for further information on the significance of the Location input.

timetrace - Reaction

Purpose

To request timetraces of reactions at restrained nodes.

Table Input

Notes

(a)If any timetrace is requested, then by default a timetrace of wave elevation at Y = Z = 0 (that is, at the vertical axis) is included in the output.