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VDB Analysis (Laplacian, Divergence)

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I'm trying to use VDB instead of volume to Analise the Curvature and the Gradient but the Gradient seems to give me way different results. Am I missing something ? 
I used a  SOP Solver, took the Surface from the Geo node, used Convert VDB to VDB, then VDB Analysis to Gradient, and a bit of VDB Smooth.

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On 29.04.2020 at 6:00 PM, Pazuzu said:

When I worked on that solver (from the vimeo video) I used the standard pyroclastic noise displacement, but I used also the curvature (or you can use laplacian as well) as the main factor for the pyroclastic displacement and decimation. So yes that was my restriction/mask, mainly to have a more nicer evolving material, and I think it works, of course, the video just shows the backbone of the system, but you can have way better details developing it a bit more.


Hello!  I want to ask you if you can find out a little more about your model of implicit buoyancy, what principle does the temperature affect the pressure, if the pressure field cannot be changed, I tried to follow your steps, but the pressure field is always unstable in its values.  How do you get the direction of buoyancy?  is it a tricky gradient or just an upward vector multiplied by some values.  I tried to repeat the result, but I feel that I lack knowledge and somewhere there is a gap

 

gyazo.com/b7e8f63499982ce9b25baf5b3704bf8d
 

gyazo.com/2a4e7e5de03e4333d02ead96505a58d7
 

Here are my feeble attempts to do it.  Thanks for the answer!

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Posted (edited)
20 hours ago, kuvaka said:


Hello!  I want to ask you if you can find out a little more about your model of implicit buoyancy, what principle does the temperature affect the pressure, if the pressure field cannot be changed, I tried to follow your steps, but the pressure field is always unstable in its values.  How do you get the direction of buoyancy?  is it a tricky gradient or just an upward vector multiplied by some values.  I tried to repeat the result, but I feel that I lack knowledge and somewhere there is a gap

 

gyazo.com/b7e8f63499982ce9b25baf5b3704bf8d
 

gyazo.com/2a4e7e5de03e4333d02ead96505a58d7
 

Here are my feeble attempts to do it.  Thanks for the answer!

Hi Kuvaka,

Really nice results you have! Regards the buoyancy direction, you can use an explicit one as the basis, typically as inverted gravity direction. The main idea of the implicit buoyancy model that I worked on was to derive a buoyancy direction using the pressure differences but also to not be 100% implicit because its always nice to have control over something. So the idea is that you can initialize this buoyancy direction to then be mixed with the implicit one that the system will produce. For the implicit direction is all about to use the inverse of pressure differences as a factor for the initialized buoyancy direction, this will give you a direction that will go aligned with gravity (if you use gravity as the the buoyancy direction) for the positive pressure (inverted), and a direction that goes in reverse in relation with gravity for the negative pressure. Because both vectors will converge, you can use this convergence at your advantage to generate a general swirl that will be aligned with the buoyancy vector that you took to initialize the system. You have many options to compute a flow out of two convergent vectors in Houdini. Then  you use the temperature as a factor to drive the magnitude of this new implicit flow or swirl to now apply it to the system velocity and to control the general swirl movement of the simulation. I hope all of this is clear!

Alejandro

Edited by Pazuzu
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Posted (edited)
1 hour ago, Pazuzu said:

Hi Kuvaka,

Really nice results you have! Regards the buoyancy direction, you can use an explicit one as the basis, typically as inverted gravity direction. The main idea of the implicit buoyancy model that I worked on was to derive a buoyancy direction using the pressure differences but also to not be 100% implicit because its always nice to have control over something. So the idea is that you can initialize this buoyancy direction to then be mixed with the implicit one that the system will produce. For the implicit direction is all about to use the inverse of pressure differences as a factor for the initialized buoyancy direction, this will give you a direction that will go aligned with gravity (if you use gravity as the the buoyancy direction) for the positive pressure (inverted), and a direction that goes in reverse in relation with gravity for the negative pressure. Because both vectors will converge, you can use this convergence at your advantage to generate a general swirl that will be aligned with the buoyancy vector that you took to initialize the system. You have many options to compute a flow out of two convergent vectors in Houdini. Then  you use the temperature as a factor to drive the magnitude of this new implicit flow or swirl to now apply it to the system velocity and to control the general swirl movement of the simulation. I hope all of this is clear!

Alejandro

Thanks for the answer, it's cool! I managed to figure out some things myself, but still the use of pressure is not completely clear). thanks for the answer

My little test)

pyroclastic_016.[0001-0158].mp4

Edited by kuvaka
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