General HydroStatics
Ship Stability Software
Command of the Week
(New or interesting aspects of GHS that you may not know about)

ROTATE statement
(Requires GHS PM 16.20 or later)

Within the Part Maker CREATE command is the optional ROTATE statement, which rotates the present component according to the given angles.

An application for this would be structures such as the one shown here where the same shape appears at different orientations.



Thanks to the ROTATE statement, the shape of the arms need be defined only once.

Here we create the shape for the arms:


 CREATE HULL\ARM0.C
  TOP 9
  BOT 0
  OUT 9 @ 0, 4 @ 49
  SPACING 1
 /


Now the pattern shape, which we have attached to HULL as ARM0.C, can be borrowed to make the other two arms at their particular angles.

 CREATE HULL\ARM1.S
 SHAPE ARM0.C
 ROTATE 0,0,120
 /
 
 CREATE HULL\ARM2.S
 SHAPE ARM0.C
 ROTATE 0,0,-120
 /


Note that we have used only "starboard" components to make these arms. Centerline components, where the points are defined for only half of the effective shape, are not suitable subjects for rotation. But there is a slight advantage to having the original unrotated arm be a centerline component—as will be explained later.

It only remains to create the core cylinder and fit the arms to it:


 CREATE HULL\CORE.C
  CYL (48) 0,0,-1,  0,0,19, 29
 /
 
 MODIFY ARM0.C
  FIT CORE.C
 /
 
 MODIFY ARM1.S
  FIT CORE.C
 /
 
 MODIFY ARM2.S
  FIT CORE.C
 /


The sections of ARM0.C are split in way of the core. If it had been created as ARM0.S, it would have worked just as well, and it would have had the same volume; but when displaying the plan view of the geometry, a line would show between the disjoint halves of those stations, which you can see is absent now.


The whole-ship rotation featured in a recent COW made use of the ROTATE statement. It took each component in the model, borrowed its shape as we have done here, applied the rotation, then deleted the original component.

Special treatment is required for any closed centerline component when its shape is borrowed to make a non-centerline component because when rotated in azimuth, the centerline gap shows up as a gap between sections. This is not a problem if you are creating the geometry with rotation in mind because you will make separate P & S components. But when rotating a given geometry that contains such things you will need the RotateShip.wizgf wizard. However, the secret of how to treat those CL components is not well guarded, and it will be leaked if you ask for it.


Questions, comments, or requests?
Contact Creative Systems, Inc.

support@ghsport.com

USA phone: 360-385-6212 Fax: 360-385-6213
Office hours: 7:00 am - 4:00 pm Pacific Time, Monday - Friday

Mailing address:
PO Box 1910
Port Townsend, WA 98368 USA

www.ghsport.com

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