FAQ A04 - Powertrain: Why does speed of inertia have a different sign at left and right ports?

Category: Simcenter Amesim

Topic: Applicative solutions

Access Level: End User

Publish Date: November 2013

Question

Powertrain: Why does speed of inertia have a different sign at left and right ports?

Answer

A positive torque is applied to the left port so the velocity at this port is negative even if the inertia turns in the expected direction.

Due to this, the user could think that there is a mistake in his system but this is not the case because the velocity is actually seen as positive at the other port.

The sign convention can easily be explained when we look at the system on the left: the trigonometric direction of rotation defines the positive direction.

On the other side of this system, the rotary velocity is seen as negative.

Finally, if we look at the system on the right, a positive torque on the left tends to make the inertia turn in the anti-trigonometric direction (so clockwise).

This leads to a positive rotary velocity on port 1 (the right one) and a negative velocity on port 2 (the left one).

In the opposite case, a negative torque on port 1 would force the rotation in the clockwise direction so a positive rotary velocity for port 1 and a negative rotary velocity for port 2 would be induced.