Importing hydrodynamic data: Generic text files

You can use generic text files to import data from, for example, a ship response calculation program other than AQWA or WAMIT, or from model test results, so long as the data in the file are in suitable tabular form and you add the appropriate markers to the file to indicate the data to OrcaFlex.

The file must contain data for one or more named draughts. If any of these draughts does not already exist for the selected vessel type, it will be created at the time of import with the default OrcaFlex vessel type data. If any named draught does already exist, then any data it contains of the same type as that given in the text file will be deleted. Data of other types for those draughts will not be affected. So, for example, if your text file contains only displacement RAO data, then importing these data will not have any effect on load RAOs, QTFs, or any other data for that draught. If the draught already exists, then the data other than displacement RAOs will remain unchanged; if it does not exist, then the data other than displacement RAOs will take the values of the default OrcaFlex vessel type.

This means that for each draught you import, all the displacement RAOs (for example) for that draught must be in a single file, but you can choose to put the displacement RAOs for all draughts in a single file or have separate files for separate draughts.

The types of data which can be imported in this way are

Specifying conventions and units

You can add markup to the file to define the conventions and units of the data contained in the file. If any of these conventions do not match those for the selected vessel type, or the units do not match those prevailing in the OrcaFlex model, then OrcaFlex will convert the imported data from the declared source conventions/units to the model conventions/units as part of the import process. A typical markup block for conventions is

***OrcaFlex Conventions Start***
***OrcaFlex Conventions End***

The block begins with a line containing the string OrcaFlex Conventions Start and ends with a line containing OrcaFlex Conventions End. The lines in between specify the conventions using the standard OrcaFlex data names and values.

This list contains all possible conventions settings that can be included in the block. Note that the waves are referred to by convention is not allowed because the WP, WFH or WFR header string identifies the period/frequency convention. In addition the symmetry convention should not be specified in this block: instead you should simply set it to the appropriate value in the OrcaFlex model.

If some conventions are omitted then OrcaFlex uses the prevailing value from the selected vessel type conventions. If the block is omitted altogether then a warning is issued and no conventions conversion is performed at all. Not all of these conventions are relevant to all of the imported data: Newman QTFs and added mass and damping require only the direction conventions.

The units of the data contained in the file are specified in a similar way:

***OrcaFlex Units Start***
***OrcaFlex Units End***

This list contains all possible units settings that can be included in the block. For displacement RAOs the length unit is the only one which is used and consequently the force units may be omitted if the file contains only displacement RAOs. For load RAOs and QTFs both length and force units are required.

Warning: This units setting does not apply to added mass and damping matrices. These are not converted automatically to OrcaFlex model units, since their scaling is rather more complicated. You must ensure that either their units are consistent with the OrcaFlex model, or scale the data yourself.

If some units settings are omitted then OrcaFlex uses the prevailing value from the OrcaFlex model. If the block is omitted altogether then a warning is issued and no units scaling is performed.

Note: The reference origins are not read in from the file. They should be set on the import vessel data form.

Importing RAOs

A text RAO file must contain the RAO data in the following form. It is usually easy to create a suitable file by adding a few lines to your original response data file – see the examples below for specific program output.

Importing QTFs

Full QTFs are at present only imported from AQWA and WAMIT results files. Newman QTFs are imported from both of these, and may also be imported from generic text files in much the same way as RAOs.

Since QTFs contain no phase information, the conventions relating to phase have no relevance and all QTFs are assumed to be given relative to waves of unit amplitude, so the RAOWaveUnit convention is implicitly amplitude. Hence, of the convention settings, only the direction conventions (SurgePositive, etc.) apply to QTFs. Both the length and force unit settings apply, if given.

The format of the markup for QTFs follows that of RAOs, with these exceptions:

Importing added mass and damping

Similarly to RAOs and QTF data, frequency-dependent added mass and damping may be imported from generic text files with the addition of suitable markup, so long as they are presented in the usual $6{\times}6$ matrix form. This only applies to independent vessel data: multibody data cannot be imported in this way.

Only the direction conventions (SurgePositive, etc.) of the convention settings apply to these data. The unit settings, which may be in use for RAO or QTF import, do not apply to the added mass and damping data import. Instead, in view of the wide variety of ways in which these data are presented by diffraction analysis packages, you are required to define a scaling factor or factors with which to reinstate the data to their full dimensional form. The scaling factor(s) may take one of a number of forms:

Note that the scaling factors may be entered multiple times and will be updated each time they are encountered. This may be useful if, say, they depend on frequency.

Each $6{\times}6$ matrix is delineated by the identifiers OrcaFlex Added Mass Matrix Start and OrcaFlex Added Mass Matrix End, or OrcaFlex Damping Matrix Start and OrcaFlex Damping Matrix End as appropriate. Immediately following the Start line should be a line nominating the draught into which to import the data, Draught DraughtName, as for RAO import, followed by a line defining the period (WP x for x seconds) or frequency (WFR x or WFH x for x rad/sec or Hz respectively). There is no corresponding Direction, since added mass and damping are not directional data. Some packages output the digits 1,2,..,6 as row and column headers to each matrix: if these are present, OrcaFlex will ignore them and will not treat them as actual data values.


Examples are given of the markup required for the output from three commonly-encountered analysis packages:

OrcaFlex can import data produced by other programs (or any other means) so long as they are in the format described above. By following these examples, you should be able to import any such data.