Leo Lazauskas

[Leo Lazauskas]

No, DelftShip cannot calculate the drag using those empirical methods.

[Leo Lazauskas]

What about window 32-bit version?

That will require me to spend a few hours changing some parts of the code.
I’ll have a look at it after I finish and release versions for catamarans, Surface
Effect Ships and hovercraft.

[Leo Lazauskas]

To me it seems that the problem must be in DelftShip (maybe because I use the free version?), since Michlet works fine.

Thanks a lot by the way for Michlet, Leo, since I am studying naval architecture you can be sure that I appreciate it. I read the manual and documentation – is there maybe some description how Michlet calculates the resistance? I’m just asking out of curiosity and to be able to judge the results.

There is a description of similar numerical methods to what I use in
the 1st SWPE Report at:
http://www.cyberiad.net/library/pdf/tls99.pdf
I actually use higher order Filon transforms, but the above report
should give you the flavour of the methods.
Other algorithms are described in reports on my web page:
http://www.cyberiad.net/leo.htm

Good luck with your studies!
Leo.

[Leo Lazauskas]

Ok figured out how to take the measurements but my offset file is not importing like it should. Although, I found exporting and then importing an offset table from one of the sample file yields plots that look nothing like the originals.

Can anyone help?

Did you find out how to do this?
I am having the same problem.
If anyone wants to try to reproduce the error, I used the NPL 100A example file.
Delftship creates an offsets file, but I can’t get it to import the offsets correctly.

I really hope somebody can help us here, because it would very much enlarge the number of high-accuracy (e.g. benchmark) hulls we could supply to the Defltship database. I have many hulls that I could supply if I was confident that Delftship could import them. (I am also trying to get Michlet and some other codes to export offset files in formats that can be read by Delftship.)

I hate to be critical of a very fine product, and I know the staff are very busy improving the program, but it is not a good look for Delftship to leave such a fundamental question like this unanswered for so long.

[Leo Lazauskas]

But when I open the mlt-file in some text-editor to check the values, all values are zero (e.g. Gravity, density but also length or draught of the model and many more) – the offset-table on the other hand looks fine.

The problem does not only occur with my model – I checked a few models from the download-section and the problem occured with every one.

I have never seen that problem. (I wrote Michlet, btw)
On rare occasions I get a messed up offset table, but that can be fixed by choosing a different number of waterlines or stations.

I hope somebody can help you because I am currently working on using Delfship/Michlet exported files as input to some other computer programs that calculate dynamic sinkage and trim, near-field wave patterns and fluid velocities.
Good luck,
Leo.

[Leo Lazauskas]

Icare,
I think that it would be irresponsible and completely unprofessional to do that.
You should advise your members that they are misapplying the formula.

[Leo Lazauskas]

Any place I can get a manual??, ususally i learn to use a software by just click on the icons and see what happenes, but here no icon at all, so I´m asuming that works by writen commands, so I´m kind of lost

That method definitely will not work, so the program is probably not for you.
Michlet is a complicated program that requires some experience with naval architectural terms and hydrodynamics concepts.

The manuals can be found in in the docs sub-directory after you unzip the program. You should also go through each example.

Remember, too, that Michlet is NOT a boat design program. It is a “hydrodynamics workbench”.

[Leo Lazauskas]

Where can i get a demo of godzilla?, sounds interesting…

Michlet and Godzilla are not separate programs.
The Michlet home page is:
http://www.cyberiad.net/michlet.htm

[Leo Lazauskas]

It’s a very good start, but “design” is so much more than minimising calm-water resistance.
For your particular circumstance, sea-keeping seems like a much stronger driver of the
final design.

All the best with your venture!
Leo.

[Leo Lazauskas]

Hi Leo,

WOW!!

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!
Leo.

[Leo Lazauskas]

Hi Leo & Guille1963,
My problem isn’t with Michlet, it works perfectly with the output from Delftship, with no changes to the export file. Does this mean that since I haven’t made any changes to the export file the Pressure, Resistance and Wave Analysis output I get, is rubbish!

My problem has been with Godzilla. I’ve worked through the examples and the manual and I still get the momentary flashing screen, although it stays longer than before. My out.mlt shows “error: Nothing to optimise. Check limits on parameters”. And the godzout.mlt shows “0.0,0.000000”.

Does this mean that the design I have is already optimised to the limit or does it mean that my input data needs a lot of scrutiny?

It means that there are no variables to optimise.
This can happen when all the allowable minimum and maximum values are identical for each variable.
For example, if the minimum allowable length is the same as the maximum allowable length, then length will not be varied during the optisation process.
Try allowing a range of values for the hull length AND the length overall.

[Leo Lazauskas]

Error messages are written to the out.mlt file.

There were some changes made in Michlet which means that a couple of lines have to be changed in the file created by Delftship. These were described in the manual.

[Leo Lazauskas]

Thanks Leo.

I’m working through the examples and reading the manual and it’s becoming self explanatory.

What I would like to know is, once I’ve optimised my hull design in Godzilla, can I then use this output data as input back into Delftship?

Not directly.
However, if you calculate the drag after running Godzilla or Michlet, the program produces files names fsoff1.txt,… fsoff5.txt which contain offsets that can be read by Delftship.
You will then have to input various values required by Delftship.

Good luck!
Leo.

[Leo Lazauskas]

Godzilla requires quite a few extra lines that are not generated by Delftship.
You must read the Michlet and Godzilla manuals and work through the examples.

[Leo Lazauskas]

Michlet can calculate SWATH resistance. Delftship outputs a file that can be used my Michlet. Some minor editing of the file might be necessary, depending on the version you are using.

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