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

(Requires GHS with LEw, CG, LS, MB)

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.

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.

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.

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.)

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.

Questions, comments, or requests?
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