LiquidSrc Outgoing velocity

[s_gru]

i'm new and diving into things. for the outgoing velocity, is there a certain amount that would mimic a normal type of flow. normal, what do i mean about that, maybe i mean as if you poured water out of a pitcher at a dinner table?

do i have to change the outgoing velocity to try and match what it is i'm working with - water vs. honey or syrup?

also, do i have to change my scene units to cm or can i leave it at feet to work with PHX? vray 6 and whatever the latest version is of PHX for max.

thanks!

[Svetlin.Nikolov]

Hey,

Scene units are very important to the simulations. However, the important thing is the actual size of the object, and not the units you choose to view it - you can use cm, inches, meters, feet - all of these are good. What is important is that if you are simulating a volcano, it can't be a few inches tall - it has to be tens of thousands of inches, and vice versa - a candle flame can't be a hundred meters tall - it should be a fraction of a meter tall. Before you start simulating, check the Grid rollout of the Simulator and the sizes in units along the X, Y and Z directions. If the sizes are not the ones that the real world effect would have, and if you can't change the size of the simulator (for example, you are using some geometry that you can't rescale), then you can use the Scene Scale option to cheat the solver into thinking that the simulator box is larger or smaller scale than it actually is. Change it until you get the X/Y/Z sizes right.

Also note that often, in order to get a more cinematic view of the effect, you could use an artificially higher Scene Scale that would be accurate. This would make the effect slower and more epic. Often, when we watch videos of everyday fluids, like water pouring out of a faucet, it tends to look too fast to us, so by increasing the scale you can make it slower.

Once you get that right, you can move on to the Source and adjust the Outgoing Velocity - it's in [units] per second, so if you are viewing the units as Feet, start off with a believable value - e.g. for a faucet 10 feet per second would be super explosive, while 0.1 foot peer second would probably be too weak - try imagining how far should the liquid go if you were pouring it from a hose horizontally for example

In case you are just starting with Phoenix, make sure to check out these two parts of the Phoenix Basics series:
https://youtu.be/LZpv4QdkCJU
https://youtu.be/nG1o9e7XrqM

Cheers!

[s_gru]

thanks man! that's a great explanation of scene scale for me, i understand it bettter. thanks for the links, will watch over and over ha.

[s_gru]

follow up - would scene scale afftect outgoing velocity then? if i put in a value of 12inchs/sec made the scene scale larger or smaller that would affect it. i'll have fun playing around with that testing today. nice.

[Svetlin.Nikolov]

Yay, I hope it makes more sense now All the options that are in some units will keep working in the same units, otherwise it would be a hell to try and calculate everything in your head. The Scene Scale itself affects things like the gravity (larger scale makes smoke rise more slowly and epically and liquid fall down more slowly, it makes cooling take more time, etc.).

So outgoing velocity of 12 inches per sec should remain this fast always, trying to make the liquid travel 12 scene inches in the first 30 frames. If this liquid is shot horizontally, and the scene scale is higher, then the liquid would keep flying forward longer, as if it was shot by a dam break, and it would be harder to stop it. Vice versa - if the scale is lower, the liquid would start dropping much more quickly and would generally behave more chaotic.

[s_gru]

so i tried an emitter laying on the ground plane and it dispenses the liquid a lot slower than an emitter up a couple of feet in the air emitting towards the ground. maybe it's just an illusion, or maybe it's something to do with gravity interacting as well. like emitting honey out of the bottom of a small box about 1.5ft in the air. the same emitter on the ground plane however does match the outgoing velocity - it'll traverse 1ft in 30 frames. i even played with viscosity and stuff. so i'm just getting used to it.

[Svetlin.Nikolov]

Oh yes, if you have viscosity, it would be very hard to predict how far the liquid would go - it could stick to the emitter, etc.