Model scaling

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This topic contains 7 replies, has 3 voices, and was last updated by  vincecate 6 years, 9 months ago.

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• #582

vincecate
Participant

Two good pages on the scaling issues are http://en.wikipedia.org/wiki/Similitude_%28model%29 and http://en.wikipedia.org/wiki/Similitude_of_ship_models .

Basically if you scale dimensions down by 25 and speed down by 5 things will happen at the same relative fraction of hull speed. If wave heights and wave lengths are scaled by 25 then wave speeds are also down by 5. So things work out well. However, in the model everything is happening 5 times faster. So if you see something tip back and forth every 2 seconds in the model it would be every 10 seconds in the full sized version. A 10 knott wind in the model is like a 50 knott wind in full scale.

#3101

Participant

Great find ! So the wave testing videos just have to be linearly slowed down and the result should be good enough ? I guess the only remaining discrepancies will be due to the different ratio of viscous and dynamic drags.

#3111

vincecate
Participant

If we imagine a full scale one being 16 times bigger, or 144 foot diameter, then slowing down by 4 is correct. So that is what I have done. Really if I could have figured out how to do 3.5 I would have for my 1/4 acre 112 foot diameter size. I wish my camera could shoot at 4 times the framerate so it looked better when slowed down. Video below and I have also updated my “Tension circle house” proposal to include the new video.

I really don’t think surface tension and surface friction etc are a problem for the models we will be doing.

#3115

Anonymous

I tried to put some comments in the discussion page for the tension circle house, but bloody Drupal would not let me. Sigh.

In large waves, the people in the house are really going to get shaken around a lot. We want to minimize interaction with big waves.

#3124

vincecate
Participant

>I tried to put some comments in the discussion page for the tension circle house, but bloody Drupal would not let me. Sigh.

Let me start a new thread for the “tension circle house” and take your other comment there.

#3126

vincecate
Participant

Wayne, I would really like to see the video of your spar buoy test in the wave tank. Could you slow it down by the square-root of the scaling factor and post it?

#3129

vincecate
Participant

I figured out how to publish the movie at a better quality. So I have a video slowed for scaling that I like better:

#3132

vincecate
Participant

Have started a wiki page on scale models. Found a few more links.

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