Creating useful visualizations of your fluid simulation results can be sometimes be a challenge. Images of contour plots, isosurfaces, or streamlines may not be sufficient to communicate your point. Sometimes you need to combine results together and use visual effects to transition between them. Cue up keyframe animation. In case you are not familiar with the term, “keyframe” means that multiple visualization techniques (zooming, flying around, fading, time-animation, contours, isosurfaces, etc.) are combined together in one animation file. Keyframe animations generally require some planning and testing before creating the final result, especially as you get more skilled and start adding more results/effects. However, if you are willing to put in a bit of extra effort, you may find that you have not only communicated your point well, but have also visually engaged your target audience, whether the audience is your managers, your customers, or that hostile crowd at a technical conference.
CFD-Post, the post-processing tool of choice for the ANSYS CFD solvers, presents a straightforward interface for creating keyframe animations. If you click on the “film” icon along the top row of GUI, the Animation Dialog appears.
Figure 1 – Animation Dialog in CFD-Post
The basic idea of a keyframe animation is that you create multiple keyframes, which are connected by transition frames. Each keyframe is essentially a snapshot of whatever is in the GUI window, and when you animate them together CFD-Post interpolates in three-dimensional space to create transitions between your keyframes.
Let’s walk through an example. I want to do a zoom effect on my race car model. I’ll start from a “global” view of the entire model (Figure 2a).
Figure 2a – Global view of car model
Next, I’ll insert my first keyframe by clicking the blank page icon in the keyframe animation dialog menu. This keyframe will have 80 distinct frames (interpolation points) between itself and the next specified keyframe.
Figure 2b – Create first keyframe: 80 intermediate frames
Now, since I want to animate the “zoom” portion, I’ll zoom in closer (Figure 3a).
Figure 3a – Zoom view of car model
Next, create the second keyframe at this position.
Figure 3b – Create second keyframe: 80 intermediate frames
Click “Save Movie” box, and then select the “Play” button to record it. Here is the result:
Figure 4 – 80-frame animation from Keyframe 1 to Keyframe 2
For the next part of my keyframe animation example, I’ll add in a CFD result: pressure contours on the surface of the car. First, the solid color on the surface of the car will need to be faded out, and then we can fade in the pressure contour.
I can create Keyframe 3 to account for the fading out of the sold blue on the surface. First, I need to specify that the transparency = 1 (“0” denotes no transparency, “1” denotes 100% transparent) for the surface group that comprises the surface of the car (Surface Group 1). This will allow the algorithm to start with transparency = 0 at Keyframe 2 (the default), and end with transparency = 1 at Keyframe 3. Next, I need to account for the fading in of the pressure contour. Thus, I create a contour of the static pressure on the surface of the car (Contour 1) and set its transparency = 1. Then, select the new keyframe icon to create Keyframe 3.
Figure 5 – Create Keyframe 3 to represent fade-out of blue surface
Finally, I can create Keyframe 4 to account for the fading in of the pressure contours on the surface. Now, all that is required to set the transparency of the pressure contour (Contour 1) to “Transparency = 0”. Then, select the new keyframe icon for Keyframe 4 (reference Figure 6).
Figure 6 – Create Keyframe 4 to represent fade-in of pressure contour
Now,to record/save the keyframe animation, select “Save Movie” in the Animation dialog menu shown in Figure 6. I typically select “Loop”, and “Repeat” = 1. The “Bounce” option reverses the animation when it reaches the end. The finished product is shown in Figure 7.
Figure 7– 160-frame animation from Keyframe 1 through Keyframe 4
Now that I have demonstrated how the keyframe functionality works in CFD-Post, it becomes apparent how to create keyframes. The first step is plan out the keyframes in the animation; essentially, visualize an image that represents each keyframe. Then, experiment with the transitions between them; fading, zooming, flying around, etc. Finally, put the entire keyframe animation (keyframes plus transitions) together and let your customer, manager, or colleagues watch in awe.