Page 96 - Practical Design Ships and Floating Structures

71

3.3 Rules of Creation

Instead of expecting a comprehensive specification of each element utilized to model the desired shape,
an inverse procedure is applied to most features within the FRIENDSIIIP-Modeler. A midship section
for instance could be specified and set up with just a single information, namely the beam at the design
waterline. Without any additional information, all necessary parameters would be derived from the
principle dimensions, see Figure 3. The parameters draft, beam and freeboard have been included in
the MIDSEC block in order to simplify the picture. Any additional information given by the user
specializes the shape of this design feature and possibly induces changes in topology. Figure 4 shows
the extract of the midship section's block complemented by a parameter called deadrise. Its default
value is zero but here it has been modified to 4'. Figure 5 extends the specification by a straight part at
its bottom. The corresponding shapes of the initial section and the modified ones are depicted in Figure
7
I.

draft
beamtnec
freeboard
beamltDul mIN.bean
deadrise deg
flatOfBotton 0.6 W1N.bean
Figure 5: Midship section specification (Part 3)

As stated above, the generation process follows a methodology which depends on the existence of
specific parameters. According to the naval architects' language, a set of parameters has been
introduced and chosen as the basis for a generation hierarchy. Figure 3 to Figure 5 depict the
parameterisation of the midship section applying parameters located at a similar priority level. Other
parameters exist at higher and lower levels, respectively. The parameter for the design waterline beam
for example is located one level below since a combination of drafi, a large deadrise angle combined
with a straight part from the flat of bottom may cause a dependency. (For conventional merchant ships
this case is not relevant.)

draft
beamtDec
freeboard 1.0 MOIN.freeboard /I
bean& t D wl MIN.bean
deadrise deg
flatOfBattoa 0.6 MOIN.bean
bilgeRadius 3.2
Figure 6: Midship section specification (Part 4)
In contrast to the set of coexisting parameters in the previous figures, an example of a higher level
parameter is the bilge radius, see Figure 6. Stating a bilge radius dominates the generation process and
causes the parameters for the flat of bottom and the beam at the design waterline to be overruled and,
thus, ignored. In addition, a straight part for the flat of side is created which makes the section become
a typical midship section.