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General HydroStatics
Ship Stability Software |
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Command of the Week
(New or interesting aspects of GHS that you may not know about) |
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APPEND.WIZGF
(Requires GHS with LEw, CG, LS, MB) |
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When you simulate the loading of a massive cargo by its rolling onto the deck,
you can put the Multi-Body (MB) capability of GHS to good use.
Unless the cargo is partly immersed as it is being loaded, the problem
can be simplified by combining the load geometry with the ship geometry
instead of approaching it as a true two-body problem.
The screen shot below is of a simple example. |
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At each increment of the roll-on we want to find the ballast arrangement
that achieves the desired trim (such as zero) and the draft that levels
the deck with the pier from which the cargo is being delivered.
A convenient way to position the load along with its weight and the ground support on the pier is to use the APPEND.WIZGF wizard, which is available as a GLM button and also as a wizard you can run from within GHS. Below is a look at the wizard dialog where you specify the ground points. |
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The wizard also handles the positioning of the load
and the defining of its weight distribution.
A ballast arrangement that achieves the desired draft and trim should also keep the shear and bending moment close to zero across the transition from the dock to the ship's deck. A quick look at the LS curves will confirm that. |
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Slightly less ballast at the same draft and trim makes the load hold
the stern down more than it should and creates a bending moment
at the transition as can be seen in the following LS graph.
(These shear and bending moments are actually quite small throughout the length of the ship as can be seen by the numbers. The scaling of the graph makes them appear large at first glance.) |
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The APPEND wizard is the most convenient way to set this up, but it is not
the only way. It is not really necessary to combine geometry files; the
same graphical effect could be obtained by relocating sail parts. But it
is more convenient to combine parts from separate files using APPEND.
You can also generate the ground points by more direct means, but
APPEND makes it more convenient as it adjusts the points according
to the position of the load. And the weight distribution can be set
directly with ADD commands, but since APPEND takes care
of this too, it is more convenient.
In fact you can work out the ballast without using the MB module. But MB and APPEND.WIZGF make it more convenient, which is what computers are all about. |
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Questions, comments, or requests?
Contact Creative Systems, Inc. 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 Click here for an index to this and previous COWs |