Sign convention for rotary speeds and torques

sign convention

An arrow is displayed on the rotary load icon. As with linear loads, when you have a chain of these, the arrows should all point in the same direction. If you break this rule, Simcenter Amesim will compensate and the results will still be correct but much more difficult to understand. Basically the well known right-hand corkscrew rule is used.

Figure 117: External variables of the rotary load

If you look at the system in the figure Figure 116 and also in the figure above, you can see the external variables of the rotary load submodel MECRL0. Only the port 2 velocity is displayed in the variable list.

Procedure

1. Look at port 2 in the External Variables dialog box, imagine looking in the direction of rev/min and operating a right-hand corkscrew.

This gives the direction of rotation.

2. Now look at the port 2 torque denoted by .

The right-hand corkscrew rule indicates this torque opposes the velocity. Initially the rotary speed is zero.

In the A part of the system, the 600 Nm torque opposes the velocity and will make the velocity negative.

In the B part of the system, the 600 Nm is applied at port 1 and assists the velocity and will make the velocity positive. Note For more information about sign conventions, please consult the Mechanical library manual.

In our example, see the figure Figure 116: the modulo blocks between the angle sensor and the general stopper will convert the angle produced by the sensor to the range 0 to 360 degrees.

3. Run a simulation and plot the output from the sensor of system A.

You see how it decreases steadily.

4. Look at the output from the modulo block of system A.

5. You will see an angle in degrees always in the range 0 to 360° as it should be. However, the graph is not very satisfactory as in the following figure.

Figure 118: Output of the modulo block of system A

Many readers will immediately recognize this phenomenon as aliasing.