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Note the water wheel (selected) failing to spin

Apologies if this doesn't light correctly, I omitted the HDRI I was using to save space for upload and download of the .blend. Plug in your HDRI of choice and the scene should look fine (or turn off HDRI and light as you desire!).

I'm trying to turn a physics object through contact with the Mantaray liquid simulation and it's not working.

The simulation particle system is set to render as a simple object with a sphere rigidbody with sphere collision.

The domain also has a passive rigidbody and collision system - added this out of desperation, and it doesn't seem to be doing much.

The water wheel is a Fluid effector set to collision.

The water wheel also has an active rigidbody and collision system set to mesh - which doesn't seem to be doing much.

The wheel attached to the pole behind it with an empty set to Generic physics constraint (having some problems getting that to rotate reliably on the Y axis, but that's not the main problem).

Can anybody tell me how to get this waterwheel spinning with Mantaflow?

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  • $\begingroup$ I'm trying to turn a physics object through contact with Mantaray liquid. Do you have any resources, which say that this would work? $\endgroup$
    – Leander
    Commented May 6, 2020 at 12:49
  • $\begingroup$ Uh, I encountered a couple of videos that seemed to demonstrate this happening. I'll try to track them down for you. Have I been barking up the wrong tree with this? I'd admit, after working with the Effectors set to Collision for a bit, I figured this action would be available. If you can definitively correct me on this, I'd really appreciate it! $\endgroup$
    – Reverend Speed
    Commented May 6, 2020 at 12:57
  • $\begingroup$ It would be knew to me, that doesn't mean no one has figured out a way to do it. $\endgroup$
    – Leander
    Commented May 6, 2020 at 12:59
  • $\begingroup$ Belatedly, I note that on of my references is faked, as mentioned in the comments: youtube.com/watch?v=RVlXncgtQus Leander, I don't suppose I could ask you a related question? blenderartists.org/t/… $\endgroup$
    – Reverend Speed
    Commented May 6, 2020 at 13:00
  • $\begingroup$ I don't have a blenderartists account right now, sorry. $\endgroup$
    – Leander
    Commented May 6, 2020 at 13:06

3 Answers 3

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Bi-directional fluid-structure interaction is quite an advanced topic. (Bi-directional meaning that the fluid reacts to forces applied by the structural domain and vice versa)

There is of course specialized software which can perform these simulations. However, most current simulation packages focus on simulating either the fluid or the rigid (or deformable) bodies accurately and model the other as simply as possible.

That's why in almost all those nice 3D visualisations of fluid-structure-interaction (at least outside the scientific or engineering world) the motion of the rigid (or soft) bodies will most certainly be faked with non-simulated animation.

Further reading e.g: research.manchester.ac.uk/portal/files/70404430/FULL_TEXT.PDF

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Here is another example of an "active" water wheel that is affected by the water particles. As noted by others, much tuning would be required to make the weight and velocity of the water affect the wheel, include the friction and weight of the wheel itself. But this is proof of concept that this can be done in blender.

enter image description here

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Here is a modification to your blend file where I:

  • most important: modify the effector to overcome a problem in fluid collision requiring > 0.5 Surface Thickness (reported)
  • enable "Use Effector" for effector, WWheel
  • I moved the effector and Flow closer to the WWheel to shorten my simulation time
  • Per some comments above, I cheated to simulation the rotation of the WWheel, yet used it as a collision obj on the Flow
  • changed the cache location to be relative so as to work for me.
  • disable Mesh for my convienence

enter image description here

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