Re: Delftship and Godzilla/Michlet

DELFTship forum Hull modeling Delftship and Godzilla/Michlet Re: Delftship and Godzilla/Michlet

Leo Lazauskas

Hi Leo,


I did as you suggested and widened the length variables from the design 6.4 to a min 5.0 and max 10.0. I also changed a single speed to 5 design speeds. And the program sprung into action.

I stopped it after 2 million evaluations. Will it eventually stop by itself?

The changes made during the evaluation were to: length, beam, wetted surface area, LCB and LCF. These were all reduced. It gave me a best fitness of 10.5498, is this good?
So is this the optimised hull design?

I ran the Pressure, Resistance and Wave options after the evaluation and I will endeavour to compare the before and after traces – still to do!

At this moment in time I’m one happy bunny………!

Many thanks.

It should stop after 9 million evaluations, I think. That is the limit in version 9.30 which I haven’t released yet.

I can’t comment on whether the fitness is good or bad. It depends on the objective function, the number of design speeds, and the vessel.

It’s now time for a little humility 🙂
I don’t mean this to sound harsh, but you have very little idea of what you are doing at his stage.
You should go through the examples and read the manual a few times.

On the bright side, you have made a great start by using one variable and seeing how that changed.

Remember that in this sort of optimisation, you should re-run Godzilla a few times, using a different random seed each time. If the program gives you the similar lengths each time, then you can have some confidence about the result.

If you find the optimal length is sometimes short, other times long, then that is interesting in its own right. The shorter hull will have less skin friction, but probably higher wave resistance. The longer hull will have higher skin-friction and lower wave resistance. Now it is up to you to decide which hull is suitable for your particular application.

If the length of your vessel hit one of the constraints (e.g. 5.0 or 10.0) increase the maximum or decrease the minimum. What you want is for the “optimal” length to be between the two constraints, and not equal to one of them, if you can help it. Sometimes a vessel wants to be as short, or long, as it can get. Then, other constraints should examined carefully.

Have fun!