Storage Format |
 
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Storage Format |
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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. 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 Excel.
Text based files allow the data to be readily examined and interpreted, but have the disadvantage that for a long simulation with many outputs requested, the file size can be quite 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 you are interested in creating your own customised timetrace files, for example to perform cycle counting on some arbitrary time series, the Import format is the preferred option. The GRD file (this is the file extension used by Flexcom to denote timetrace output files) is comprised of a header block containing some general settings and the names of the stored variables, with the main body of the file containing the actual time histories. The layout of a text based file (i.e. either Import or ASCII format) is now described.
•Line 1: Storage format (e.g. Import)
•Line 2: Program version (e.g. Flexcom 8.2.1)
•Line 3: Analysis title
•Line 4: Integer value indicating if a random sea is present in the analysis (a value of 1 denotes Yes, a value of 0 denotes No)
•Line 5: Integer value indicating if a fixed time step is used in the analysis (a value of 1 denotes Fixed, a value of 0 denotes Variable)
•Line 6: Number of data series stored in the main body of the file (including Wave Elevation, which is stored by default by Flexcom)
•Line 7: Number of outputs per line in the main body of the file (relates specifically to the ASCII format only, and is typically assigned a value of 4)
•Line 8: Maximum cut-off frequency of all random seastates in the analysis (this variable is assigned a value of 0.0 if the analysis does not contain any random seas)
•Line 9: Dominant direction of random sea in the analysis (this variable is assigned a value of 0.0 if the analysis does not contain a random sea, or if more than one random sea is present)
•Line 10: Acceleration due to gravity, Base units (see note (a)), Unit system flag (see note (b))
•Line 11: Analysis fixed time step (this variable is assigned a value of 0.0 if the analysis uses a variable time step)
•Line 12: Name of the first time series stored in the main body of the file (typically the first time series corresponds to Wave Elevation, which is stored by default by Flexcom)
•Line 13: Scale factor for the first time series stored in the main body of the file
The remainder of the header block is comprised of pairs of lines similar to Lines 12 and 13, listing the names and scale factors of any subsequent time series stored in the main body of the file. The total number of time series is defined in Line 6, and the number of lines in this section must be consistent with this definition.
In relation to unit systems, the following points are noteworthy.
(a). Base units depend on the extension of the keyword files, and has the value = 1 (if .keyxm), = 2 (if .keyxi) = 3 (if value of "Acceleration due to gravity" is not recognized as metric or imperial), and = 4 (if .keyx, and "Acceleration due to gravity" is recognized as metric or imperial).
(b). Unit system flag refers to the unit system actually used in the analysis, and = 1 (if metric), = 2 (if imperial) = 3 (user defined but value of "Acceleration due to gravity" is not recognized as metric or imperial, and = 4 (if user defined and "Acceleration due to gravity" is recognized as metric or imperial).
In the case of an Import format file, the remaining lines contain N values, where N is the total number of time series as defined in Line 6, plus one for the actual time values themselves. The first value represents time, and the remaining values represent the various parameters (as listed in Lines 12, 14 etc.) corresponding to that particular time.
In the case of an ASCII format file, the layout is a little more cumbersome. The main body of the file is organised into blocks of lines. The first line of the block contains the time value on its own. The next line contains a maximum of N values, where N is the number of outputs per line as defined in Line 7. These values represent the various parameters (as listed in Lines 12, 14 etc.) corresponding to the time value. If the total number of time series (as defined in Line 6) is less than or equal to the number of outputs per line (as defined in Line 7), this line concludes the block of data for this time step. Otherwise subsequent lines (containing a maximum of N values) are used to present values for the remaining data series at the relevant time value. Once the block of data is complete, the next block begins with the time value for the next time, and so on.
•*TIMETRACE is used to request the storage of results for timetrace postprocessing (this is mainly used in the area of time domain fatigue analysis).