Hello and welcome to the next edition in our introductory series to rotor dynamics analysis. In this installment, we’ll be looking at the specific purposes and objectives of performing rotor dynamics analyses; as well as the differences between lateral and torsional analysis. If you haven’t read the other entries in this series, you can find them here:
- Series Preface
- What is Rotor Dynamics? And Where is it Found?
- Why is Rotor Dynamics so Important?
- What API Standards Govern Rotor Dynamics Analysis?
- Basic Definitions and Fundamental Concepts of Rotating Equipment Vibrations
In earlier posts, we’ve established what the basic definitions and concepts are; shown the consequences of improperly performing rotor dynamics analyses; as well as what standards are in place to ensure these breakdowns and catastrophes are avoided. That raises the question, what exactly are we trying to do by performing rotor dynamics analyses?
We know based on our previous articles we are trying to determine the critical speed and in turn determine if further damping and other measures need to be taken to ensure that there is a proper separation margin between the operating speed of the machine and its critical speeds. But what will this accomplish? The answer is actually 3 answers!
- We want to minimize and/or eliminate unplanned failures as much as possible, especially when these machines are counted on to keep planes in the air, the lights on, and in some cases, people alive! Have a look at this article from Halloween if you want an idea of what would happen if all our turbomachinery just stopped working.
- Secondly, we want a low vibration level. In addition to providing comfort in the case of an aero engine or a car’s turbocharger, lower vibration levels ensures less undue wear and tear on expensive rotor train components.
- Lastly, and this correlates with the others, ensure low maintenance requirements. Naturally the machine that can do its job the longest will be the one people desire, and rotor dynamics analyses play a large role when it comes to maximizing the service intervals for turbomachinery.
Overall, the purpose of rotor dynamics analyses, is to ensure maximize machine reliability in the interest of time, money, and most importantly, safety. Now let’s get into the differences between lateral and torsional rotor dynamics.
Rotor dynamics is typically split into two distinct kinds of analyses which are constantly brought up; lateral and torsional rotor dynamics. So, what is the difference between the two?