Michlet 9.32 Released

[Leo Lazauskas]

Michlet can now run in the background. The screenshot shows 4 copies
of Godzilla running (each with a different random seed) while using a
text editor on another project.

If you find Michlet useful, please consider making a small (e.g.
$10 to $100) donation through PayPal on the Michlet page at:
http://www.cyberiad.net/michlet.htm

INSTALLATION AND REMOVAL
------------------------
After downloading the file, unzip it into a convenient sub-directory.
To remove the program, just delete the directory. Michlet does not
change any system files.

Manuals are in the docs directory. Start with michman.pdf, the Michlet
manual.

< 3/25/2015: See http://www.boatdesign.net/forums/design-software/michlet-9-33-released-52865.html >

 

[lukskywalker]

Export from Delftship fails

For some reason the delftship output misses some variables. I can adjusts the input file afterwhich Michlet accepts the input correctly.
Strange thing is now that the estimate of the wave resistance is way too high.
What can I do?
Thanks,
L

 

[Leo Lazauskas]

For some reason the delftship output misses some variables. I can adjusts the input file afterwhich Michlet accepts the input correctly.
Strange thing is now that the estimate of the wave resistance is way too high.
What can I do?
Thanks,
L

It is impossible to advise you without seeing your input file.

Which version of DelftShip are you using? I know that there were versions
that produced good Michlet files, but there have been some recent revisions,
or they reverted to previous versions. (I tried to get answers from Delftship
but they have not answered by emails for several months now.)

 

[lukskywalker]

Input file

Thanks,

Herewith my input file.
Resistance (wave) is much too high.
Many thanks,

Michiel

 

[Leo Lazauskas]

Herewith my input file.
Resistance (wave) is much too high.
Many thanks,

Michiel

That was easy
Michlet is a thin-ship code and your L/B=4.6 vessel is certainly not a thin ship.
I would try OpenFoam or some other CFD code that can handle tankers and
other bluff ships.

Good luck!

 

[daiquiri]

Leo, I know this is a stupid question, but... How stringent is the following requirement, in your opinion (from the Michlet manual):

"The shapes of the hulls can be dierent from each other, however, they are assumed to be symmetric with respect to their own centreplanes. The overall vessel need not be laterally symmetric."​

I guess that it comes from the placement of point sources along the centreline of the hull. So, how big would be the error if one tried to analyse a hull with this waterline shape, for example: http://ikarus342000.com/P95page.htm ?
And how big mathematical and programming effort would be required to introduce point vortices or to place sources along a curved line, in order to simulate the "cambered" centreline of the demihulls - if it's possible at all?
Cheers!

 

[Leo Lazauskas]

Leo, I know this is a stupid question, but... How stringent is the following requirement, in your opinion (from the Michlet manual):

"The shapes of the hulls can be dierent from each other, however, they are assumed to be symmetric with respect to their own centreplanes. The overall vessel need not be laterally symmetric."​

I guess that it comes from the placement of point sources along the centreline of the hull. So, how big would be the error if one tried to analyse a hull with this waterline shape, for example: http://ikarus342000.com/P95page.htm ?
And how big mathematical and programming effort would be required to introduce point vortices or to place sources along a curved line, in order to simulate the "cambered" centreline of the demihulls - if it's possible at all?
Cheers!

Slavi:
I have sometimes used a simple approximation for asymmetric hulls by
making a symmetric demihull with the same thickness distribution as
the asymmetric hull. For very thin hulls the difference is negligible.
I really wouldn't want to guess for the Icarus catamaran because the
L/B is quite large. For thin-ship theory, the thinner the better, of
course.

I have code that I have used, but it doesn't solve the (very difficult!)
equivalent of the lifting-surface equation with a free-surface.
My code assumes a given vortex distribution and then calculates the wave
resistance using Havelock sources, just like Michlet and Flotilla, plus
Havelock horseshoe vortices. (Havelock sources and vortices are just
like the usual ones found in aerodynamics, except that they satisfy a
linearised free-surface boundary condition).

I did the calculations for the attached paper by E.O. Tuck. In short,
the gain from using asymmetric hulls is very small. At some Froude
numbers, the asymmetric hulls are superior, at others they are worse
than the symmetric demihulls. Interestingly, the wave resistance can be
reduced to a similar degree by using symmetric demihulls with a
slightly different hull spacing.

There are some recent papers online that investigate the performance of
asymmetric catamarans similar to the Icarus that might also give you
some insights. See:

George Zaraphonitis, Dimitris Spanos, and ,postolos Papanikolaou
"Numerical and Experimental Study on the Wave Resistance of Fast
Displacement Asymmetric Catamarans",
HIPER'01, 2001.
http://www.naval.ntua.gr/sdl/Publications/Proceedings/HIPER01paper.pdf

Corrado Damiano, Giuseppe Lupo, Antonio Mancuso, and Gabriele Virzì Mariotti,
"CFD Study of an Innovative Catamaran with Asymmetrical Hulls",
Advances in Water Resource and Protection (AWRP) Volume 1 Issue 1, January 2013.
http://www.seipub.org/awrp/Download.aspx?ID=2755

 

[daiquiri]

Very interesting papers Leo, especially the Greek one. It gives a very interesting insight to the trends for different Froude numbers and demihull separations. Thanks.

Somehow, I am not surprised by the results you and Tuck have obtained in comparing the gains of adding camber vs. increasing demihull separation. The wave train (and the associated resistance) is essentially created by the volume of the hull moving through the water, and is hence related to the local time-rate of change of submerged volume as the hull passes with a speed V through a given point (please correct me if I'm wrong on this point).
The introduction of waterline camber (say, towards outside) displaces the submerged demihull volume towards outside, which can also be simulated by symmetrical demihulls being displaced a bit outwards, in order to obtain the similar rate of change of the submerged volume, at the same speed. So, for small changes in camber and hull spacing, it should imo always be possible to find equivalent pairs between the two hull sets.

Explained in layman's terms, but hopefully gives the idea of what I mean.

Cheers!

 

[lukskywalker]

That was easy
Michlet is a thin-ship code and your L/B=4.6 vessel is certainly not a thin ship.
I would try OpenFoam or some other CFD code that can handle tankers and
other bluff ships.

Good luck!

Yes I know that it is better suited for thin ships, but it says in the manual that it should be able to handle L/B of 5. I agree that 4.6 is not thin at all, but would not expect the results to be so far off.

Many thanks,

L

 

[Leo Lazauskas]

Yes I know that it is better suited for thin ships, but it says in the manual that it should be able to handle L/B of 5. I agree that 4.6 is not thin at all, but would not expect the results to be so far off.

It was worth a try, given that the alternatives can be very slow.

It really depends on the hull, and the speed. It will give better results for high Froude numbers.
Michlet and Flotilla can give reasonable results for some fine transom stern hulls
with L/B = 5 at high Fr. At low Fr, as you have seen, the wave resistance is
unreasonably high.

 

[lukskywalker]

thanks

 

[malith]

Hi all!!

I downloaded the Michlet from the given link.
But when i'm running it on win 7 64x, software is very slow. It takes couple of seconds to respond.
Sometimes it even stop responding.

then i tried it in win 7 32x. it worked perfectly!! but i want to run it on 64x.

Please help!!!

Thank you

 

[Leo Lazauskas]

Hi all!!

I downloaded the Michlet from the given link.
But when i'm running it on win 7 64x, software is very slow. It takes couple of seconds to respond.
Sometimes it even stop responding.

then i tried it in win 7 32x. it worked perfectly!! but i want to run it on 64x.

Please help!!!

Thank you

Sorry, it sounds like a problem with your machine.
It works well on all the 64 bit machines I have tried under Win 7 and even (the demonically-possessed) Win 8.1.

 

[TANSL]

In Windows 7 and 8 typically have problems with self-protections the system adopts by default. If that were the case, you must enter as Administrator to remove these protections.
The self-protections are a bit absurd because they never prevents a good virus to appropriate system. But this is the opinion of a "non-expert" in computer science which have to fight with the computer.

 

[malith]

thanks for all the help!!!!

i was manged to run the program in my computer. it was a compatibility issue.

currently i'm trying analyse total resistance of catamaran hull. i molded a demi-hull on delft ship and was able to analyse single hull.

but when i'm trying to input it as a catamaran it gives an error "Hull 2 ERROR: Bad number of trim speeds"

please help me

a zip containing all files including the model is attached

thank you very much!!!