PIAS Manual  2023
Program for the Integral Approach of Shipdesign
Hulltran: hullform transformation
With this module a transformation is applied on a hullform which is already available in PIAS format. This original hull is called the parent hull, and the transformed one the daughter. With this transformation the following shape parameters can be changed:

  • Length, breadth and draft. This is simply a matter of multiplication by linear scale factors.
  • The length of the parallel body.
  • Block coefficient.
  • Longitudinal centre of buoyancy.
  • Midship coefficient.
The parent only serves as source and remains unchanged. The daughter form lives under its own filename and is after transformation not connected to the parent in any way. Apart from this main task, this module offers the option to combine distinct aft ship and fore ship hulls. However, this is a bit of a side issue.

Main menu

Transform hullform

This option is used for the full blown transformation, where the hull as such is distorded. The applied transformation method is the same as `inflate/deflate' in Fairway, see Inflate/deflate frames for an introduction. With this option a sub menu appears with just two choices:

Enter main dimensions and coefficients of the transformed vessel

Here the following parameters can be given:

  • The filename of the transformed form. Here the filename of the daughter form should be given (which must, obviously, differ from that of the parent. Also here the `&'-character can be applied, which makes the daughter to be written in the same directory as the parent (identical to the `&'-facility of composed hullforms, as discussed in Hullforms).
  • Name. This is simply a textual description attached to the daughter form.
  • Length.
  • Breadth.
  • Draft.
  • Block coefficient, with a maximum modification of ±0.05.
  • Longitudinal centre of buoyancy in % van LPP, with a maximum modification of ±4%.
  • Midship coefficient, with a maximum modification of ±0.02.

Perform the transformation

Which make the transformation to be applied. In order to memorize the applied parameters a single page with the existing and the new hull form parameters is printed.

Change length of parallel midbody

Enter parallel midbody particulars

The change of the parallel body will be executed forward of the last frame in the aftship (For the division between aftship and foreship reference is made to [Aftship] in Frames (frame positions and frame shapes). In thi smenu should be given:

  • For `filename' and `name' we refer to the discussion in Enter main dimensions and coefficients of the transformed vessel.
  • The length to add. There are no principal limitations on increasing the length of the parallel body. A decrease of the length of the parallel body is defined by entering a negative length. This decrease is limited to half the length of the parallel body.
  • Whether the vessel has a sloped keelline. In that case on APP and FPP the heights above base of the (moulded) keelline should be given. The program will then shift the ordinates vertically, in order to to match the slope of the keelline.
  • Shift baseline to intersection keelline - half length. If `yes' is given then the baseline is shifted in a fashion that, if the baseline intesects the keel line at LPP/2, with the parent, then this will also be the case with the daughter. Whith `no' the baseline will keep its position with respect to the aftship.

Perform midbody modification

With this option the daughter form is actually generated (a page with parameters changes will be printed here too).

Combine two ship hulls (aft ship and fore ship)

With this option two hull forms can be combined, in the sense that the aft ship of one hull form, and the fore ship of another will be glued together in a single new file which contains the combined hull. However, this a bit of a fringe, a single time this function may prove to be convenient, however, those are the exceptions. For normal use PIAS also offers facilities to use multiple hull forms. Those are not aggregated into a single file, instead they are treated in stability calculations (and the like) as a rigid combination. This mechanism, which offers more flexibility than explicitly combininghull forms, is discussed in Hullforms.

The operation of this option is assumed to be evident.