How to maintain the same volume in Galapagos

Hi all,

I am new at this so here it goes. I am working with a sample file (04Box2pointcontrolladybugradiation) from Dr Yun Kyu Yi in order to understand how galapagos works. I found the file in this link ;

http://www.grasshopper3d.com/group/ladybug/forum/topics/knowledge-s...

My question if it is possible to change the shape of the box maintaining the same volume during the optimisation with galapagos? I also check this discussion http://www.grasshopper3d.com/forum/topics/change-shape-but-maintain..., but in this case does not work...

Any advice is welcome!

Thanks

Attachments:

04Box2pointcontrolladybugradiation.gh, 380 KB

Replies to This Discussion

Permalink Reply by David Rutten on July 23, 2015 at 9:05am

If you wish to retain a volume you have to relinquish at least some control over the shape itself. In the case of a box you have two options:

Choose the width and height freely, but the depth must have a certain value in order for the volume to be correct.
Choose all dimensions freely, but then scale the entire box in order to achieve volume constancy.

Which of these do you want?

Permalink Reply by josefina on July 23, 2015 at 9:18am

Thank you for your answer! I want to choose all dimensions freely and then scale the entire box.

Permalink Reply by David Rutten on July 23, 2015 at 9:34am

Attachments:

volume.gh, 6 KB

Permalink Reply by josefina on July 23, 2015 at 10:41am

Thank you David! It works perfectly!

Permalink Reply by Nik Willmore on July 24, 2015 at 2:00pm

More of a math lesson than a Galapagos one, and (T/V)^(1/3) wasn't obvious to me for anything but a uniform cube, since the cube root only spits out one number for the whole non-uniform box, a value not corresponding to any edge of it, but I'm a benchtop chemist by training.

Permalink Reply by David Rutten on July 24, 2015 at 2:50pm

Volume increases with the third power of the linear size, regardless of the shape. So to increase a certain volume by a factor of 8, you have to double the size, because 2^3=8. Conversely, to make a volume a factor of x bigger, the scaling factor needs to be x^(1/3) which is the same as the cube-root of x.

In this case we don't just want to make the volume x bigger, we need to get a specific volume, so the first step is to compute x, which is the Target volume divided by the Current volume.

Permalink Reply by David Rutten on July 24, 2015 at 2:52pm

In order to get a specific area, just replace all cubes and cube-roots with squares and square-roots.

Permalink Reply by Nik Willmore on July 24, 2015 at 2:59pm

That's why giant spiders in black and white movies would fall down and why straps get so big on bras, but the cube root of volume of an arbitrary box is still an "object length" that requires a head for math rather than tactile geometry.

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