This section discusses the following topics:
Modal analyses of the 2D axisymmetric model with and without gyroscopic effects included are discussed in this section.
The modal analysis without gyroscopic effects is performed using the Block Lanczos (LANB) solver, extracting twelve modes.
The following input fragment shows the steps to extract these modes:
/solu antype, modal ! Perform Modal analysis modopt, lanb, 12 ! Use Block Lanczos solver to extract 12 modes mxpand, 12 ! Expands all the modes solve finish
The rotational velocity is specified with the OMEGA or CMOMEGA command. The gyroscopic effects of the rotating structure are included using the CORIOLIS command.
The modal analysis with gyroscopic effects is performed on the model using the complex QRDAMP eigensolver.
The following input fragment shows the steps to perform the modal analysis with gyroscopic effects:
/SOLU /com, Select all the rotating elements supporting Coriolis command esel,,ename,,272 esel,a,ename,,21 cm,rot_part, elem esel, all /com, Specify rotational velocity to the structure/rotating elements. pival = acos(-1) spinRpm = 50000 ! Rotational velocity in rpm spinRds = spinRpm*pival/30 cmomega, rot_part, spinRds ! Apply rotational velocity along rotating velocity (X) /com, Activate Coriolis command and choose QRDAMP eigensolver antype, modal ! Perform Modal analysis modopt, qrdamp, 12,,, on ! Use QRDAMP solver to extract 12 complex modes mxpand, 12 ! Expand all the modes coriolis, on,,, on ! Last field specifies stationary reference frame solve finish
Before performing a Campbell diagram analysis, a modal analysis must be performed with multiple load steps corresponding to different angular velocities. A Campbell diagram plot (PLCAMP command) shows the evolution of the natural frequencies with respect to the rotational speed. The PRCAMP command prints out the critical speeds based on the Campbell diagram plot for a synchronous (unbalanced) or asynchronous force.
The following input fragment shows the steps to perform the Campbell Diagram Analysis:
/SOLU /com, Select all rotating elements supporting Coriolis command esel,,ename,,272 esel,a,ename,,21 cm, rot_part, elem esel, all /com, Activate Coriolis command and pick the QRDAMP eigensolver antype, modal ! Perform Modal analysis modopt, qrdamp, 12,,,on ! Use QRDAMP solver to extract 12 complex modes mxpand, 12 ! Expand all the modes coriolis, on,,, on ! Last field specifies stationary reference frame /com, Solve modal analysis for different angular velocities pival = acos(-1) spinRpm = 0 ! Rotational velocity in rpm spinRds = spinRpm*pival/30 cmomega, rot_part, spinRds solve spinRpm = 50000 ! Rotational velocity in rpm spinRds = spinRpm*pival/30 cmomega, rot_part, spinRds solve spinRpm = 100000 ! Rotational velocity in rpm spinRds = spinRpm*pival/30 cmomega, rot_part, spinRds solve finish /com, Post process the Campbell diagram plot /POST1 prcamp,, 1.0, rpm,, rot_part ! Prints Campbell diagram data /show, png /rgb, index, 100, 100, 100, 0 ! Set white background /rgb, index, 0, 0, 0, 15 plcamp,, 1.0, rpm,, rot_part ! Plots Campbell diagram data finish
A harmonic analysis of the 2D axisymmetric model is performed within a speed range of 0 to 100,000 rpm (a frequency range of 0 to 1666.67 Hz) using 200 substeps. The first seven modes in this frequency range are excited.
In this analysis, the unbalance is considered as loading. (see Boundary Conditions and Loading for more details).
A structural damping coefficient of 1 percent is considered (DMPSTR).
The frequency of excitation is specified as synchronous with the rotational velocity (SYNCHRO). The rotational velocity (CMOMEGA) determines only the rotational velocity direction vector of the rotating component. The spin of the rotor is automatically calculated (HARFRQ).
The following input fragment shows the steps to perform the unbalance response analysis:
/SOLU spinRds = 1 ! Rotating velocity of the shaft to specify the spin axis spinRpm1 = 0 ! Begin speed in rpm spinRpm2 = 100000 ! End speed in rpm begin_freq = spinRpm1/60 ! Equivalent begin frequency in Hz end_freq = spinRpm2/60 ! Equivalent end frequency in Hz antype, harmic ! Perform Harmonic analysis hropt, full ! Select Full Harmonic analysis option nsubst, 200 harfrq, begin_freq, end_freq ! Defines the frequency range kbc, 1 dmpstr, 0.01 ! Specify damping ratio of 1% synchro,,rot_part ! Specify synchronous analysis cmomega,rot_part,spinRds ! Define the rotational velocity direction vector coriolis,on,,, on ! Includes gyroscopic effect solve finish