Torsional Transient Response - Speed Dependent Excitation

Torsional Transient Response – Speed Dependent Excitations

For torsional transient analysis, DyRoBeS allows two types of excitations. One is the time dependent excitation, such as short circuit torque, and the other is the speed dependent excitation, such as synchronous motor startup. For time dependent excitation, the excitation input can be either in the equation format or from a data file. For more information on the time dependent inputs, click Torsional Excitations in Equations and Torsional Excitations in Data Files. For speed dependent excitation, the driving and load torques are entered in Torsional Driving Torque and Load Torque.

Results for a compressor driven by a 4200 kW, 50 Hz, 4 Poles synchronous motor during startup transient are presented below. Note that the results can be displayed vs. time or speed.

Torsional Startup Driving and Load Torques

This option displays the torsional startup driving and load torques vs. time or speed. This option is used to check the input torques. The following figure shows a plot of the synchronous motor starting average torque and oscillating torque and the compressor load torque The time required to accelerate the system up to the synchronous speed is determined by the numerical integration of the torsional equation of motion.

Torsional Startup Speed vs. Time

This option displays the torsional transient startup driver speed vs. time. You can change the graph title, labels, number of divisions and many others by changing the default settings in the Setting dialog under Options menu.

Torsional Startup Transient Element Deflection

This option displays the torsional startup transient element deflection vs. time or speed. The following figure shows that the first resonance occurs at about 5 seconds (800 rpm) after the startup and the second resonance occurs at about 11 seconds (1330 rpm) after the startup.

There are two frequencies below 2X line frequency. They are:

70.89 rad/sec = 11.28 Hz = 677 rpm
290.52 rad/sec = 46.24 Hz = 2774 rpm

Therefore, the two resonant speeds are: 806 rpm and 1331 rpm.

Torsional Startup Transient Element Vibratory Torque

This option displays the torsional startup transient element vibratory torque vs. time or speed.

Torsional Startup Transient Element Vibratory Stress