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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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Hopper Spilling and Flooding (review)
(Requires GHS with Advanced Features) |
| If you tip a ship with an open hopper past a certain point, either the cargo starts spilling out or seawater starts flooding in, and if you rotate it far enough you get both spilling and flooding together. The SPILLING tank type is good for spilling the cargo, as shown below, and one might hope it would give a first approximation of the stability. |
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(Since the displacement of the vessel becomes less as the cargo spills, we get righting moments
plotted instead of arms. GHS does this to make a truer picture, because the moment is the reality.)
Now for a realistic stability calculation we need to account for the seawater that floods over the cargo. There is a strategy for handling this that involves making the geometry with two coincident hoppers, but a more direct way is to make use of the fact that EXTEND HOPPER can add flooding on top of cargo in the same tank. It can also account for the fact that the repose angle of denser cargos is likely to lag the heel angle. EXTEND HOPPER can be accessed conveniently either through the wizard HOPPER.WIZCO or more suitably for run files through the macro library HOPPER.LIB. Here is the library usage information: |
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| And here is a sample of what you can get in a report: |
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Well, the first cut ignoring the incoming seawater wasn't worthy of being called an approximation
unless we don't care what happens beyond 15 degrees.
Let's see what happens with the hull being rotated open and the hopper empty. Having opened the hull with SplitHull.wizgf, it becomes a simple flooded stability problem. |
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And there is more. As you can see from the usage information shown above, HOPPER.LIB offers a mode for solid,
non-shifting cargo of any permeability as well as two formulas for mud lag.
The EXTEND command taps into certain Advanced Features that make use of GHSX. Wizards or macro library files are provided to make the extensions easy to use. If a GHS report is being generated, Advanced-Feature report pages are seamlessly integrated into the body of the GHS report. |
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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 |