One of the major accomplishments in the latest release of Rocky is the new fully integrated motion kernel, which offers support for combined geometry motions. Combined motions were previously only possible by using third-party multi-body dynamics (MBD) simulation tools. But now in Rocky 4, you can apply all the combined, complex motions you want to your geometries right within the DEM software–no need for utilizing any 3rd party motion tools.
So what’s the big deal with supporting combined motions? Well, let’s take a closer look at some of the more complex movements you can create in Rocky 4.
Combined Motion Example: Conical Dryer
https://www.youtube.com/watch?v=1BJKGOi6Uo8 Video A: ConicalDryer Simulation
Video A shows a Double Screw Cone Dryer, which is commonly used to mix and dry various powdered and wet bulk materials. In this simulation, two screws—one longer (Figure 1, 5) and one short (Figure 1, 6)—rotate independently upon their own axes of motion, while the central shaft holding the two screws (Figure 1, 4) rotates the whole assembly upon yet a third axis of motion.
Figure 1: Conical dryer components
This kind of combined motion is now possible within Rocky 4 due to the newly introduced concept of Motion Frames. Each frame that you create has its own axis of motion. Upon this axis, you define what kind of prescribed and/or free-body motions you want, and then you assign that Motion Frame to a geometry. Creating a child or nested frame beneath another (parent) frame links the motion of the child to the parent. And using the new Motion Preview window allows you to view all your motions before ever processing the simulation. Pretty great, right?
This cone dryer example therefore requires three separate Motion Frames. The first parent frame is assigned to the central shaft geometry and defines the rotation of the whole system. Two child frames of this parent frame are created, one each for the two screws that will rotate around their own respective axes of motion. Figure 2 shows how these three separate frames appear in the Data panel of the Rocky UI; note that the parent frame has the two child frames nested beneath it to indicate the linked relationship between the three frames.
Figure 2: Rocky 4 Data panel showing three Conical Dryer Motion Frames
Nested Motions Example: Excavator
https://www.youtube.com/watch?v=2NXJHNmNswY Video B: Excavator Simulation
Now, let’s look at a more complex example. Video B shows a standard excavator machine. Unlike the previous example, which had only three separate axes of motion, this one has five: one to rotate the shovel, two to rotate each portion of the arm, one to rotate the main body of the machine, and one to translate the whole system along its tracks.
Because each component is an extension of the others, each axis of motion must therefore be linked to the motion of the other components in the system. Sounds complicated to set up, right? Not with Rocky Motion Frames.
As with the first example, nested Motion Frames are used to create a parent-child relationship between the five separate axes of motion. Here, the first parent frame defines the translation of the track. A child of the track frame then defines the rotation of the main body of the machine. A child of that frame then defines the motion of the first arm portion, and so on. Figure 3 shows how these five separate but nested frames appear in the Data panel of the Rocky UI.
Figure 3:Rocky 4 Data panel showing five nested Excavator Motion Frames
Free Body Rotation Example: Dump Truck
Video C: Dump Truck Simulation
But what if you want free body motions in your simulation? Not a problem! Rocky 4 can predict six degrees of freedom (6dof) motions along with your prescribed motions, and will also allow you to apply additional forces to your free body translations or additional moments to your free body rotations.
Video C shows a common dump truck. Here, three different Motion Frames define the various movements seen. One parent frame is created to translate the whole truck system. To that parent frame, a child frame is created to rotate the bed and tailgate of the truck as it is raised. To that frame, a final child frame is created that represents the free body rotation of the tailgate itself.
During the video, you can see how the free body motion enables the rock particles to affect the tailgate’s movements; the tailgate bounces up and down in response to the material coming into contact with it, just as it would in the field.
Many Different Motions; Combine them All!
Besides the prescribed and free body translation and rotation motion examples shown above, Rocky 4 can handle many other kinds of prescribed motions, including vibrations, pendulum or swinging motions. Rocky even has a special Motion Frame specifically for cone crushers, which combines various types of prescribed and free body motions into a user-friendly setup.
Try it Out
If you already have Rocky 4, you can set up and preview complex motions yourself by following our self-guided workshops. For example, existing Rocky customers can view Workshop 07 on the Customer Portal for the Conical Drier example shown in Video A. (Note that portal registration is required for entry.)
If you don’t yet have Rocky 4 and are curious to see how it will handle your equipment’s complex motions, contact us to set up a test case.