One of the main reasons that Clear Motion ODS was developed was to produce better animation quality. Other systems are available which will animate structural motion. However, these systems commonly introduce distortion of the animated motion due to rotation.

Why is Rotation a Problem?

When you model of a structure, you will typically create a model with more nodes than will be actually measured. This produces a realistic looking model, without requiring the measurement of hundreds or thousands of points on the structure.

This causes a problem for most ODS programs. They use linear interpolation to estimate the motion of the non-measured points. When the measured structure is undergoing rotation, this can lead to significant distortion of the animation.

Clear Motion ODS uses solid body rotation to solve this problem. The rotation of the measured points is used to produce better estimates the motion of the non-measured points.

Pendulum Example

The example below will illustrate this problem more clearly. The left and right animations both show the motion of a simple pendulum. There are two measured points on the pendulum. One is at the top pivot, and the other is at the center of the bottom weight.

pendulum with rotation
Solid Body Rotation
pendulum, no rotation
Linear Interpolation

Although the motion is very simple, the linear interpolation method distorts the shape of the rod and the circular weight. With rotation, the rod and weight keep their proper shape, with much less distortion. In more typical systems, the motion is likely to be much more complex. Clear Motion ODS compensates for rotation for you automatically.

Real Example - Compressor Vibration

The pendulum above is a basic example. Below is an example of the measured motion of an actual compressor that illustrates similar motion. The motion of the compressor cylinder causes the discharge bottle to rotate about its axis. Using solid body rotation, this is shown clearly (left). On the right, however, linear interpolation is used and the cylindrical bottle appears to distort badly.

compressor with rotation
Solid Body Rotation
compressor, no rotation
Linear Interpolation

This apparent distortion can lead to erroneous conclusions about the system motion. In fact, it appears as if the cylindrical bottle shell may have high stresses in the bottle shell. However, as the image in the left shows, most of the actual bending occurs in the nozzle between the cylinder and discharge bottle, not in the bottle shell.

As these cases show, linear interpolation does not work well when the measured structure is rotating. This is a very common problem, since a structure is just as likely to have rotational motion as linear motion. With Clear Motion ODS, the effects of rotation on the animation are handled for you, producing much better, more accurate, and easier to understand animation.