michlet

[mermont]

Good morning all

I've read your posts about Michlet .It seems very interresting but how it works?
Mermont

[Guest625101138]

Paragraph 1.2 on this site explains the maths Michlet incorporates to calculate wave resistance.
http://www.cyberiad.net/library/kayaks/skmag/skmag.htm
The software also includes algorithms for determining viscous drag and form drag.

You need a bit of boat knowledge to apply Michlet and some experimentation with the input and output files but once you master this it gives very good results.

Calculating wave resistance using analytical methods is not a trivial exercise so, despite its compact form, Michlet is very powerful.

If you have any interest in boat design and do not have other CFD software then you should take a few hours to study Michlet. Even if you have other software you should look at the Godzilla optimisation module of Michlet. It can save years of trial and error to evolve an optimum hull. I have tested it on more than 10 operating hulls and it yields results within 10 % of measured power throughout the range at displacement speeds. (I consider it more accurate than this but it is not easy to eliminate all drag components on a real boat.)

Rick W.

[mermont]

Thank's Rick
But is Dos or Windows program?

[Guest625101138]

Originally Posted by mermont

Thank's Rick
But is Dos or Windows program?

Does it matter? It runs with windows. Here is a a quote from the developer, Leo Lazauskas, regarding the interface.

>The Michlet interface was designed for left-hand operation by slouching pirates. It is not meant for people who sit up straight because that's what they were told to do by the nuns at their gurly school.<

As I inferred before don't be fooled by your initial impression of the software it has a very powerful engine. Lots of go and very efficient. Take a bit of time to get full value from the output.

The fundamantal of using the software is to open the .mlt input and output files with a text editor like Notepad. Try the sample files before you start with your own hull design.

Rick W.

[mermont]

Ok Rick
i'm going to try it now.
Do you built your boats with Freeship designs and Mitchlet calculations?

[Guest625101138]

Originally Posted by mermont

Ok Rick
i'm going to try it now.
Do you built your boats with Freeship designs and Mitchlet calculations?

I determine the constraints for my boat such as displacement and design speed then use Godzilla to produce an optimum hull. I then import the offset file into FreeShip and design the above surface portion of the hull using Freeship.

Sometimes I simplify the lines to make it easy to develop the hull in aluminium. The attached photo set shows a hull designed for a displacement of 100kg and design speed of 12kph.

The boat I am currently building is designed for 95kg and 12kph. I am building it with a solid foam core and carbon fibre reinforcement. It is almost identical to the lines Godzilla produced. I usually do a bit of smoothing in FreeShip and then rerun the hull in Michlet to confirm I have not increased the drag.

Rick W.

[yipster]

i second Rick, fine program it is, not mentioned here it may help to say you have to change teh source file in the program to get own design in and calculated.
rtfm (readthefuckingmanual)

[TLB]

Impossible for me to use godzilla with my own table of offset from freeship.
Michlet run correctly, but when i try to run godzilla (after have copying the godzilla part in the .MLT file), there is nothing.
Could someone help me.
Tanguy

[Martijn_vE]

You have to make sure that the parameters in the godzilla part of the file actually comply with the model. Godzilla is very sensitive when it comes to setting the optimization parameters. Also make sure to check the file out.mlt because it contains the error messages.

[Guest625101138]

Originally Posted by TLB

Impossible for me to use godzilla with my own table of offset from freeship.
Michlet run correctly, but when i try to run godzilla (after have copying the godzilla part in the .MLT file), there is nothing.
Could someone help me.
Tanguy

I cannot understand why you would want to use Godzilla on an existing hull design. It will make radical modifications depending on the constraints you set. I use the generalised hull form to start with in Godzilla. It is generated using four parameters in a single line such as:
>......
# Offsets
1,1,0,0
# Displacements
......<

If you want to determine the drag of a hull designed in Freeship then you simply export the hull from FreeShip as a Michlet .mlt file. You can edit the .mlt file directly if you want to change parameters such as wave patch or speed range. You then put this file in the same folder as the Michlet executable and rename it to in.mlt so Michlet will find it. (You need to delete the previous in.mlt)

There is also a file generated called out.mlt that contains the cause of Michlet/Godzilla not starting up. It will usually have the incompatible data. This can take some time to think through but it means you have asked it to do something that is logically impossible like have a starting hull length that is outside the range of the target hull length.

Rick W.

[TLB]

Thank you, i will test the out.mlt to see the problems.
We have no budget to test those models on navier stokes CFD, but we want to test an innovative hull and i want to constrain those ideas.
Brgds
tanguy

[Guest625101138]

If you already have a hull design and want to determine the drag then you only need to run Michlet.

To do this from FreeShip use menu <File> <Export> <Michlet>. This opens a window that allows you to select various parameters. I only ever change the number of stations and waterlines here. All the other parameters can be more easily edited in the .mlt file you produce.

Obviously you did not generate the hull in Godzilla so to see how good your design is you should create an alternate design using Godzilla with the constraints like length and stability set to the same as your design. It will indicate the merit or otherwise of what you have produced.

I got very frustrated using trial and error to determine wave drag until I found Michlet/Godzilla. My 11th design was straight from Godzilla and it is by far the best.

Rick W.

[TLB]

Thank you Rick

[TLB]

The problem is OK, i have resolved it with out.mlt
Many thanks for you threads.
Tanguy