Tornado Effects

8/8/2019 Tornado Effects

1/14

Tornado EffectsDynamics

One thing that has been asked fairly often was how to make a tornado effect. To tell the truth, I

didn't really know, so I've been experimenting with things off and on through the last few months.

All of a sudden, it hit me! I was creating a spiral shape using a well-known method, when I noticed

that the effect made a very tornado-like shape. The rest developed from that. So, let's go through itstep-by-step!

First, create a curve going straight up from the origin,

with a CV placed about every 2 grid lines or so (using

a default grid arrangement) as in Fig 1.

Create a Nurbs Circle. Make the following changes:

Translate X : -.5

Rotate X : 90

Radius : .04

Sweep : 90Sections : 3

You should see something similar to Fig 2.

While the Circle is selected, press Insert (above the

Delete key on the keyboard) and Grid Snap (X) thepivot of the circle to the origin. (Fig 3)

Now, select the Nurbs Circle and then the Curve inthat order. Go to the Modeling Menu Set and Surfaces

> Extrude. In the Channel Box, under Inputs, make

these changes:

Fixed Path : ON

Use Component Pivot : ONUse Profile Normal : OFF

Rotation : 5000

Scale : 6

You will hopefully see something similar to Fig 4.

You can adjust your Rotation and Scale numbers and

the orientation of the circle to get the kind of overall

8/8/2019 Tornado Effects

2/14

shape you'd like to model your tornado after.

You can delete the history of the new "tornado" shape

(Edit > Delete by Type > History) and delete the

curves. Rename the object Tornado.

Now, select the new tornado shape. In the channelbox, select Rotate Y. Right click and select

Expressions from the menu. The Expression Editor

will open. In the Expression area, type the following:

Tornado.rotateY = frame * #

Put a number in the "#" spot. The higher the number,

the faster the tornado will spin. You can always edit

this later. Now, if you play your animation, the

tornado should spin like a top. (Fig 5)

Ok, now we're gonna add Dynamics. Select the

Tornado and go to the Dynamics Menu Set and

Particles > Emit from Object > Options. In the

options, choose Surface for emitter type and create it.When you press play, particles should be emitting

from the surface of the object. It's possible that the

particles may be emitting from the interior surface,rather than the exterior. If so, Reverse your tornado

surface direction (Modeling Menu Set - Edit NURBS

> Reverse Surface Direction). (Fig 6)

Open the emitter's Attributes and make the followingchanges:

Rate : 1000

Speed : 0

Now, we have more particles and instead of them

emitting away from the tornado, they'll stay on thesurface. Select the particles and make the following

changes in their attributes:

Lifespan Mode : Random RangeLifespan : 2

Lifespan Random : .25

Particle Render Type : Cloud (s/w) (click Current

Render Type button)Radius: .661

8/8/2019 Tornado Effects

3/14

Threshold: .661

Now, if you hide the tornado surface object, you'll just

have a spinning cone of cloud particles. You may

need to adjust the emitter rate, particle radius, etc. toget the look you want. (Fig 7)

Now that we have it spinning though, you also want itto move around, not just stay rigid. To do this, you

could probably use a number of methods, like bones

and soft-body simulations or whatnot, but a lattice

seems to work fine. Unhide the tornado object, select

it, and create a Lattice (Animation Menu Set - Deform> Create Lattice). (Fig 8 and 9)

Before adjusting the Lattice, open the Outliner and

select both the lattice and the base that was created

with it. Scale them up a bit to ensure that the tornadowill always remain inside it and never pop out

accidently. Now, it's just a matter of animating the

lattice to get the tornado to move and deform as you'dlike! The expression will keep the torado objectspinning while the Lattice changes its shape. It's up to

you to get the Cloud particles to look like you want

them, but I hope this tutorial has helped you get thetornado started and looking like you'd want. Don't

forget about using different Fields on the particles like

turbulence and so forth to get different effects.

Realistic LiquidDynamics

For this tutorial, I'm going to go over creating a certain type of water effect. No two effects are thesame, so you may need to modify your own scenes to show how you want the water to look. For my

scene, I'm going to simulate a large gush of water emitting from some sort of tube like you'd see in a

sewer or something. The water will then hit the ground and accumulate in a corner.

8/8/2019 Tornado Effects

4/14

Now, before we get started, I should point out how taxing on a compuer particle effects can be. I'm

running a 2 Ghz processor with half a gig of RAM, and my system still renders this stuff out really

slowly, so bear with me.

First, I'll make my scene which you can download

HERE. It is simply a "L" shaped wall along with acylindrical pipe object. I've also put in simple 3-point

lighting. A camera object is placed were I'll berendering my example pics if you want the same

view.

PART 1: SETUP

First, we'll head to the Dynamics menu displays (F4)and choose Particles > Create Emitter. (Fig 1)

In the emitter's attributes (CTRL + A), make these

changes:

Emitter Type: Volume

Volume Shape: Cylinder

Away From Axis: 0

Along Axis: 1

What this does is change the point of emission to an

area of emission. The particles will emit from an area,rather than just a single point in space. Since the

"water" will be exiting a pipe, I've made the area of

emission into the shape of a cylinder. I've changedhow the particles are emitted from the default of

emitting from the axis of the area to emitting along

the axis of the area. If you press play, you should seesomething similar to what is found in Figure 2, with

the particles emitting along the axis of the cylindrical

shape. Rotate and resize the emitter to fit into the

pipe.

If your water effect is different, such as a shower head

or something, your particular settings may vary to

achieve what you are looking for.

Now, we'll mess with the particles themselves. Pressplay and allow the particles to emitt for a second or

two. Press stop. The particles should be frozen in their

current place. Select them. Go into the attributes and

make these changes (Fig 3):

8/8/2019 Tornado Effects

5/14

Particle Render Type: Blobby Surface (s/w)

Click the Current Render Type button and make these

changes:

Radius: .130

This makes the particles react to each other as BlobbySurfaces, which is more liquid-like. We're not done

by a long shot, but before we continue, let's put a

water shader on the particles. I like using a certainUtility combination that makes transparancy of the

particles fade toward the center of each. I'll show you

how to do this next.

PART TWO: THE WATER SHADER

Alrighty, this is really quite simple.

1. Open the Hypershade. Create a blinn material node.Create a Sampler Info and Color Blend utility node.

(Fig 4)

2. Middle click and drag the Sampler Info utility onto

the Color Blend. The Connection Editor will pop up.ChooseFacing Ratio on the Sampler Info side and

Blenderon the Blend Color side. Close the

Connection Editor.

3. Middle click and drag the Color Blend utility ontothe Blinn material and choose Transparancy as the

attribute to map. You should get an effect like in Fig.

5.

4. Next, Dbl click the Color Blend node to open itsattributes. Change color one to white and color 2 to

black. You'll notice that the outer edge of the blinn

material is opaque, while the inner area fades totransparant. I'm going to adjust mine a little to be light

grey in color 1, and dark grey in color 2. That way,

the outer edge won't be totally opaque, and the innerarea won't fade to totally transparant. (Fig 6)

5. Open the Blinn material's attributes and give it your

desired color. You can also mess with it a bit more.

For example, I'm going to give my ambient color a

bluish charge as well as map the specular color with a

8/8/2019 Tornado Effects

6/14

Brownian texture to give it a little more interesting

look as well as choose the material preference of your

choice, such as anisotropic. (Fig 7)

Name and apply the shader to the particles.

PART THREE: TWEAKING LIKE MAD!

Now, we're going to finish up the tweaking on the

particles and the emitter to get the look of a huge

torrent of water gushing out of a sewer pipe. First ofall, let's see a render of what we've got so far: Fig 8.

Obviously, not quite there. I'm going to increase the

rate of emission waaay up.... like 10,000! Now when

you hit play, you'll see this big, blue... thing startpushing its way out of the pipe... not exactly fluid, eh?

Let's also increase the speed of these things. Nowbecause we're using a Volume Emitter, the normal

Speed attribute no longer controls the speed. Instead,we're going to increase the Along Axis to... say, 10.

Now let's see what we've got: Fig 9.

It's shooting out of there pretty quick now, but when it

gets across the hallway, there, it just goes straightthrough the wall! Let's setup collisions. First, select

the particles, then shift select the floor/wall object. Go

to Particles > Make Collide. Now, when the particlesreach the wall, they'll collide with it rather than pass

through it. But, this water shouldn't be reaching all the

way over there, though, right?

Right! We need gravity! Select the particles and go toFields > Gravity. With the particles selected, the

gravity is applied to them. Now, we can see our

"bubble-beam" is arcing downward and actuallybounces off the ground! (Fig 10)

First, let's get rid of all these bubbles, and actually get

some water in there. The Threshold attribute of the

Blobbies is what controls the way the particles"merge" with each other. The higher the threshold, the

further a particle can be from another to merge. Let's

start off with a small number. A Threshold of .3 gives

us Fig 11, while a larger number of .8 gives us theeffect in Fig 12. You may also need to adjust the

radius of the particles to get the effect you want. If

you're doing a scene with water coming from a

8/8/2019 Tornado Effects

7/14

kitchen sink, your particle radius would probably be

higher than on a large scene such as this because of

the volume of water involved. For example, in Fig 13,I've increased the radius while keeping a high

threshold. In this image, we have a larger radius of .63

with a threshold of .8. This makes the water lookmuch thicker, almost gooey like sludge. So you'll find

yourself experimenting with the balance of Threshold

and Particle Radius to get the water effect you want.

Now, let's see about fixing the "bouncing" water.Water will bounce slightly when it hits a surface, but

it shouldn't bounce like a rubber ball. If you select

your floor object, you'll find a new attribute in the

Channel Box called the GeoConnector. In this section,you'll find Tessellation Factor, Resilience, and

Friction. Resilience is how "bouncy" the surface is,

while Friction is how "slippery' the surface is. A lowresilience and low friction will have a rigid, but slick

surface, like a non-stick frying pan. I'm going to set

resilience and friction to .25. Also, I'm going to add aTurbulence Field by selecting the particles, and

choosing Fields > Turbulence. Adjust the magnitude

of the gravity and turbulence to your liking. I'm using

Gravity magnitude of 9, with a turbulence of 30. I getthis result: Fig 14.

Obviously, we're getting closer, yet if I'm wanting a

huge gush of water to be coming out of that pipe, I'mgoing to need larger particles, yet have them becomesmaller when they hit the ground. There is a way to

do this, however you'll need to know exactly how

long the animation is going to last. For mine, let's sayit'll be a 5 second animation: 150 frames. Open the

particle's attributes and change the Lifespan to

Constant of 5 seconds.

Then, scroll down to the Per Particle (Array)Attributes. We're going to add an effect to the radius

controls of each particle. Click the General buttonbelow the PP (Array) section. In the box that opens,click the Particle tab. This opens up a HUGE list of

different attributes of particles that you can change.

Look in there until you find radiusPP. Select it andclick OK. (Fig 15)

8/8/2019 Tornado Effects

8/14

In the array section, you'll see that radiusPP has been

added to the list. Right click and select Create Ramp.

You'll see the particles grow HUGE. That's ok. Now,right click on it again and choose Edit Ramp from the

new menu. You'll see a black to white gradient. The

gradient colors determine the radius of the particlesfrom their "birth" to their "death". The default of

black to white makes the particles start off huge and

dwindle until they die 5 seconds into the animation.We're going to change it so they start off small, but

then dwindle to even smaller when they die. Black is

small, white is large, while the top of the gradient is

death, bottom is birth. With this in mind, make thefollowing change: Fig 16.

As a result, we get the following: Fig 17.

I hope this tutorial gets you on your way to creating

realistic liquid effects! Email me any comments,

questions, or concerns you may have with this lesson.

There's still a ton of different things you can do to addto the realism of the liquid, such as using multiple

water emmitters to show a varied water flow, particle

emission upon particle collision to show little "splash"when the water hits the floor, lots of stuff! Here's

what I came up with after a few different effects.

What I did in this scene was have the liquid particles

emit more liquid upon hitting the surface (the purpleparticles) and also emit steam as if it were corrosive

acid or something. The reason I emitted additional

liquid, was because the huge torrent of liquid comingout of the pipe didn't seem to create a large enough

amount of liquid on the floor, so emitting MORE

liquid upon contact makes it seem that much more

large. It'll take a bit of experiementing to get it allworking like you want. Good luck, and thanks!

8/8/2019 Tornado Effects

9/14

R i d e T h e F l o w !This tutorial shows how to create a Camera Ride on a Particle Flow system.A Script Operator assigns the transformation of a particle to a scene camera which then

travels with the particles in the middle of the stream.

Final Result

Download the Sample Scene

Watch the Ride Preview AVI (2.9MB, DivX 5.2)

Particle View Setup

8/8/2019 Tornado Effects

10/14

8/8/2019 Tornado Effects

11/14

The Particle View contains 3 Events All events feature Find Target Test which redirect the particles to different scene

objects. When the particles come close to the object, they change to the next Event. All Events feature an instanced Rotation Operator which is set to orient the particles

along the motion direction using Speed Space Follow and X:90, Z:-90 rotationsabout the axes. All Events feature an instanced Script Operator which is described below. It moves a

scene camera to one of the particles.

Natural Language - Script Enable the Transformation Matrix channel In the Init handler, get the Camera from the scene by its unique name If the Camera does not exist, create a new one, assign a unique name In the Proceed handler, define a local variable to store the particle index. Define a second variable to define the ID of the particle to ride on.

If the particle already exists, get its index in the current Event Set the current particle to the index of the particle in the current Event Copy the transformation of the current particle to the transformation of the Camera

Complete Script

on ChannelsUsed pCont do(

pCont.useTM = true)

on Init pCont do( global pflow_travel_camera_170268 = $pflow_travel_camera_170268 ifpflow_travel_camera_170268 == undefuned then

pflow_travel_camera_170268 = FreeCamera name:"pflow_travel_camera_170268")

on Proceed pCont do(

index = 0rideParticleId = 400

ifpCont.hasParticleId rideParticleId &index then(pCont.particleIndex = indexpflow_travel_camera_170268.transform = pCont.particleTM

))

8/8/2019 Tornado Effects

12/14

on Release pCont do(

)

Step-By-Step Comments

on ChannelsUsed pCont do(

The ChannelsUsedhandler defines the channels to be used by the Script Operator - youcannot get or set particle related values from the particle container without specifying whichproperties you need access to. This way, Particle Flow does not have to provide the ScriptOperator with all possible channels (and there can be an arbitrary number of channels inParticle Flow) but only with those that are actually needed. This conserves memory!The parameterpContcontains the Particle Container.

pCont.useTM = true

Since we want to read the Transformation Matrix of the particles in order to orient theCamera, we will need access to the TM channel.

)

on Init pCont do(

The Init handler is executed when the Operator is being initialized.We will use it to get an existing scene Camera, check its validity and create a new one if noCamera existed.

global pflow_travel_camera_170268 = $pflow_travel_camera_170268

Create a global variable with a unique name and get the scene camera by its unique name.The Camera must have a unique name to make sure the correct object is referenced by thescript.

if pflow_travel_camera_170268 == undefuned thenpflow_travel_camera_170268 = FreeCamera name:"pflow_travel_camera_170268"

In the variable is undefined, there was no Camera with this name in the scene.In this case, we create a new Free Camera with the unique name and assign it to thevariable.

)

8/8/2019 Tornado Effects

13/14

on Proceed pCont do(

The Proceed handler contains the main code of the script.It will be evaluated every time the Operator is proceeded.

The pCont parameter references the Particle Container of the Event the Operator is locatedin.

index = 0

We will need a user-defined local variable to store the index of the particle to ride on.We initialize to 0.

rideParticleId = 400

This variable contains the Particle ID we want to ride on.

if pCont.hasParticleId rideParticleId &index then(

Now we call the .hasParticleId method in the Particle Container.We pass the Particle ID as parameter, and the indexvariable by reference.The method returns true when a particle with the specified ID exists in the container.

What is the difference between ParticleID and ParticleIndex?

The ParticleID is a sequential number given to every new born particle in a ParticleSystem.This ID identifies the particle throughout its whole life and stays the same when a particlechanges from Event to Event.

Every Particle Container of every Event contains a pool of particles.These particles are always numbered from 1 to the number of particles in the pool withoutgaps.When particles change between Events, the ParticleIndex will change, and the pools will berenumbered to avoid gaps.

Since we want to stick to the same particle no matter which Event it is in, we want toaccess it by the Particle ID.But we also want to access the corresponding ParticleIndex in every Event the script isevaluated in.Using the .hasParticleId method, we get true orfalse depending on whether the particle isin the current Event or not.

8/8/2019 Tornado Effects

14/14

If it is in the Event, we also get the actual ParticleIndex of this particle inside the variableindex.

pCont.particleIndex = index

Now we can set the current particle in the current Event to access its TransformationMatrix.

pflow_travel_camera_170268.transform = pCont.particleTM

Finally, we get the Transformation Matrix of the current particle and assign it to thetransformation of the Camera.

)

The If context ends here. If the particle ID does not exist in the current Event, the script will

do nothing.Since the particle with ID 400 can be only in one Event at a time, but the script is instancedin 3 different Events, the Camera will be affected by just one Script Operator a time.

)

on Release pCont do(

)