Emitting along Normals

[Mr. Green]

Hi,

I have a quick question for a problem I can't figure out in Houdini. It seems simple, but yet I can't wrap my head around it. How do you emit from an object and push/shoot out the fluid density of a pyro simulation along the emitter object's normals?

I know you can "add velocity" along a specific axis in the velocity tab of the Fluid Source node, but that shoots everything in one direction. What if I have a torus but want to shoot everything away from the torus in an even manner?

Is this possible in Houdini?

Thanks,

Aiden.

[Solitude]

Hi,

I have a quick question for a problem I can't figure out in Houdini. It seems simple, but yet I can't wrap my head around it. How do you emit from an object and push/shoot out the fluid density of a pyro simulation along the emitter object's normals?

I know you can "add velocity" along a specific axis in the velocity tab of the Fluid Source node, but that shoots everything in one direction. What if I have a torus but want to shoot everything away from the torus in an even manner?

Is this possible in Houdini?

Thanks,

Aiden.

The fluid source will pick up the v attribute from the geometry. The easiest way is probably to add a point sop, set it to add velocity, and make it $NX $NY $NZ which will take the normals and put it into v. You can then use the velocity scale parameters on the fluid source node or the dop source node to multiply the velocity to strengthen it.

[old school]

Even easier than using the Point SOP and typing $NX $NY and $NZ in to the Velocity parameters in the Particle tab is to:

just insert a VOP SOP and inside simply wire the Global Input's N tab to the Global Output's v tab and you are done. Super simple and it's threaded and waaayyyyy faster than the Point SOP. Plus it gets you in to VOPs which is always a good thing.

[ryew]

I can vouch for the ease-of-use with the method Old School suggests, I've used it with great success more than a few times now.

Adding a parameter node to multiply N by and promoting its value allows some quick and easy added control for scaling your velocity value as well

[Solitude]

Even easier than using the Point SOP and typing $NX $NY and $NZ in to the Velocity parameters in the Particle tab is to:

just insert a VOP SOP and inside simply wire the Global Input's N tab to the Global Output's v tab and you are done. Super simple and it's threaded and waaayyyyy faster than the Point SOP. Plus it gets you in to VOPs which is always a good thing.

That's actually how I always do it, I just know that for most people new to the software, vops are very scary at first and I don't usually suggest them anymore since I've seen quite a few people really hesitant on going to vops route when first starting out. I figure it comes with time. But it's definitely a good for people to get into and beats the crap out of most of the standard ops in terms of speed.

[mawi]

Or the easiest...

Change the source attribute in the velocity tab of the Fluid Source SOP from v to N.

However I do also prefer the VOP way since it adds so much control.

[Mr. Green]

I can vouch for the ease-of-use with the method Old School suggests, I've used it with great success more than a few times now.

Adding a parameter node to multiply N by and promoting its value allows some quick and easy added control for scaling your velocity value as well

Thanks everyone for getting back to me. I got busy and haven't touched Houdini in a while so that's why I didn't respond right away.

So I tried this method and it's still not giving me the results I am expecting. Based on the number I'm multiplying by the pyro should be shooting out "really far" from the sphere by now, however the density doesn't seem to be affected by the multiplication at all yet.

I attached a screenshot to show the VEX network, so maybe someone can point out which connection should go where.

Thank you very much.

[Ungoliant]

can you share the scene, maybe i can help