JPH0365857B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for investigating load-dependent vibrations of rotating machines such as steam turbines, gas turbines, generators, compressors, blowers, and pumps.

Load-dependent low-frequency vibrations that occur in rotating machines such as steam turbines and compressors are extremely complex phenomena that have not yet been fully understood.
This phenomenon is caused by the generation of low-order natural frequency components in the rotating shaft system depending on the load, and is thought to be caused by the flow inside the steam turbine or compressor. However, since the characteristics of this type of vibration do not become apparent unless it is under load, the only way to investigate the phenomenon was to measure and analyze the vibration that occurred. Therefore, data can only be obtained when this type of vibration occurs, and how much margin is there for machines that do not generate vibration?
There was no way to know if the situation was severe.

In order to know the stability margin against this type of vibration, it is necessary and sufficient to know what the damping ratio of the lower-order mode of the rotating shaft system is. To do this, it is necessary to collect data during operation, and to do so, it is necessary to apply some external disturbance and find the damping ratio from the response. However, until now there has been no safe and effective method for this.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for investigating load-dependent vibrations of rotating machines that can elucidate the characteristics of load-dependent low-frequency vibrations of rotating machines and determine the stability margin for this type of vibration during operation.

The present invention will be explained below with reference to the drawings, but first the apparatus used to carry out the method of the present invention will be explained.

This device includes a vibrator that can apply an excitation force from a bearing part of a rotating machine toward the center of a rotating shaft, a controller that controls the output of this vibrator, and a controller that is installed on the rotating shaft. a vibration detector that detects a vibration response signal from the vibrator; a load controller that can control load conditions step by step while keeping the rotational speed of the rotating machine constant; and a reference signal and excitation signal from the controller. It consists of a function that inputs a force signal and a vibration response signal from the vibration detector and extracts a component that responds to the excitation force, and a vibration analysis device that calculates a damping ratio or allowable excitation coefficient from these data.

Figure 1 shows a specific example of this, where 1 is a test rotor that is directly connected to a load (not shown) and is the subject of the test, 2 is a bearing that supports the test rotor, and 3 is an inertial vibrator 4, for example. The jig 4 for fixing the bearing 2 to the bearing 2 is a directly mounted type vibrator that does not require a reaction force support device, and is an inertial type vibrator that applies an excitation force of an arbitrary frequency to the bearing stand. 5 is an excitation force detector for measuring the magnitude and frequency of excitation force applied to the bearing 2 by the vibrator 4; 6 is a vibration detector for measuring the vibration of the test rotor 1; Various types of sensors are used, including non-contact displacement meters, contact vibration velocity meters, and accelerometers. Reference numeral 7 denotes an oscillator that generates vibration waves necessary for testing, and usually generates a sine wave of an arbitrary frequency. Reference numeral 8 denotes an energy source for supplying excitation energy, which is a hydraulic source when the exciter 4 is hydraulic, and a power amplifier when the exciter is electromagnetic. 9 is a device for controlling the magnitude of the force generated by the vibrator, and 10 is a signal for accurately giving the frequency of vibration, such as a sine wave, a rectangular wave, or a pulse wave. Reference numeral 11 denotes a signal indicating the excitation force, which is either the output of the excitation force detector 5 as it is or a signal whose amplitude has been adjusted. 1
2 is a signal from the vibration detector 6 indicating vibrations of the test rotor 1, bearing 2, etc. 13 is the reference signal 10;
A function that inputs the excitation force signal 11 and vibration response signal 12 and extracts the component corresponding to the excitation force, and extracts the transfer function, modal characteristics (natural frequency, natural frequency, etc.) from these data.
damping ratio, etc.), such as a mechanical impedance measuring device.

The vibrator 4 may be of any type as long as it is capable of applying an excitation force toward the center of the rotating shaft from the bearing portion of the rotating machine and can be vibrated with a sine wave or a pulse wave.

The excitation conditions of the vibrator 4 may be any of the following: sweeping excitation in the frequency range of interest at a resonant frequency, intermittent excitation in a pulsed manner, and interruption after excitation, or random excitation.

Next, the mechanical impedance measuring device described above will be explained with reference to FIG. In Fig. 2, 21 is a test object (corresponding to the test rotor 1 in Fig. 1), 22 is an exciter (corresponding to 4 in Fig. 1), 23 is a power amplifier, 24 is an oscillator, and 25 is a test object. A force gauge 21 is attached to measure the excitation force F, 26 is a plurality of accelerometers that measure the response acceleration of each part of the object 21, 27 is a multi-channel amplifier, and 28 is an excitation frequency component from the force signal and acceleration signal. 29 is a multi-channel vector filter that extracts analog/
A digital converter, 30 is a pulse counter for counting the excitation frequency, 31 is a digital calculator for calculating mechanical impedance from the acquired data, and is composed of a data acquisition program 32, a calibration calculation program 33, and an impedance calculation program 34. ing. 35 is a plotter that outputs the calculated mechanical impedance as a graph, 36 is a printer, 37 is an external storage device for data storage, 38
is the range signal.

In such a device, a sinusoidal voltage from an oscillator 24 enters an exciter 22 via a power amplifier 23, and the exciter 22 excites the object 21, but the oscillator 24 is an automatic sweep whose frequency changes over time. Since it is a sine wave oscillator, it can be swept in any frequency range.

The force gauge 25 measures the force applied to the subject 21 by the vibrator 22, and the accelerometer 26 measures the force applied to the subject 21 by the vibrator 22.
The force gauge 25 and the accelerometer 26 generate voltages proportional to the measured force and acceleration, respectively, and this voltage signal is amplified by the multichannel amplifier 27.

The signals measured by the force gauge 25 and the accelerometer 26 also include components other than the excitation frequency due to the nonlinear characteristics of the subject 21 and noise.
In this device, the multi-channel vector filter 28
The excitation frequency component is extracted from the voltage signal measured by the method.

The excitation frequency components of the force signal and acceleration signal output from the multi-channel vector filter 28 are digitized by the analog/digital converter 29 and input to the digital computer 31.

At that time, the output of the oscillator 24 is transmitted to the pulse counter 3.
0 is input, the excitation frequency is measured, and the measured value of this excitation frequency is input to the digital computer 31.

In the digital computer 31, first, the analog/digital converter 2 is
The force and acceleration digital signals from 9 and the measurement values of the excitation frequency from the pulse counter 30 are collected,
Next, the calibration calculation program 33 converts the voltage value into a physical quantity, the impedance calculation program 34 integrates the acceleration A and converts it into a velocity V, and divides the force F by the velocity V to calculate the mechanical impedance Z. It is made to be sought after. Here, the mechanical impedance Z is data that is being processed when determining the damping ratio using the half power method. In other words, V=A/jω (integration) Z=F/V (division) However, A: Acceleration (complex number) V: Velocity (complex number) ω: Excitation frequency (real number) Z: Mechanical impedance (complex number) The mechanical impedance is obtained by performing the following.

Next, the method of the present invention will be explained. The method of the present invention is applicable to a rotating machine in which an excitation force can be applied toward the center of the rotating shaft from the bearing part of the rotating machine.
The present invention is characterized in that the rotational speed of the rotary machine is kept constant, the load conditions are changed stepwise, and the damping ratio or allowable excitation coefficient of the rotary machine is determined from the vibration response data for each load condition.

The method of the present invention will be explained below. The rotating machine is operated at a steady rotation speed (constant) as shown in Figure 3,
The no-load state is maintained for a predetermined period of time, and a no-load vibration test is performed in this state. In this vibration test, the vibration frequency is gradually changed in the range of interest and the vibration response is measured. This data is collected and analyzed, and the damping ratio ξ or allowable excitation coefficient K is determined as described below.
Calculate.

Next, the rotation speed of the rotating machine is kept constant, and the load is increased to, for example, 1/4, 2/4, 3/4, 4/4, and steady operation is performed for a predetermined time for each load state, Gradually change the frequency in the range of interest and measure the vibration response. This data is acquired and analyzed to calculate the damping ratio ξ or the allowable excitation coefficient K as described later.

The above-mentioned method of determining the damping ratio includes, for example, a method of determining it from a frequency response curve (Bode diagram or Nyquist diagram) (half-power method) or a free damping method which will be described later. The former method focuses on the resonance part of the vibration response curve and reads the natural frequency ω indicating the maximum amplitude of the mode component and the frequencies ω ₁ and ω ₂ indicating about 70% of the maximum amplitude. This is determined from the Bode diagram in FIG. 4 and the Nyquist diagram in FIG. Then, find the damping ratio ξ from the following equation.

ξ=ω ₂ −ω ₁ /ω ₂ +ω ₁ The following relationship exists between the damping ratio ξ and the permissible excitation coefficient K.

K=2mω ² ξ where m: modal mass.

The allowable excitation coefficient K was determined for each load state from the above formula, and is plotted in FIG. 6. For example, the following can be said from FIG.

Damping ratio ξ<0 - Completely unstable 0<ξ<0.01 - Almost unstable 0.01<ξ<0.02 - Stable but with a small margin 0.02<ξ<0.04 - Moderately stable ξ>0.04 - Sufficiently stable Like this The system uses an externally controllable excitation force to generate vibrations at the minimum necessary level, thereby providing valuable data on the stability of the actual machine. Note that the above excitation force does not cause any harm to actual operation.

According to the embodiments described above, the characteristics of load-dependent low-frequency vibrations can be clarified, and the stability margin against this type of vibration during operation can be known.

Next, a second embodiment of the present invention will be described. Similar to FIG. 3, a rotating machine is operated at a steady rotation speed for each load, and an excitation test is performed under each load state. The same equipment as in Figure 1 is used for this test, but the vibration investigation method is different. That is, the excitation frequency is set to resonate at a constant excitation frequency as shown in FIG. 8 in accordance with the point of interest, and the excitation force is abruptly cut off. Record the vibration response data in this state, measure the free attenuation by filtering the data with the frequency of interest, and calculate the amplitudes A ₁ , A ₂ , A ₃ , ... A _o from the response waveform in Figure 8. The logarithmic attenuation rate δ is determined by sequential reading and the following equation.

δ=lnA ₂ /A ₁ or δ=1/nlnA _o /A ₁ where ln is the natural logarithm and n is the number of peaks.

FIG. 9 shows the relationship between the logarithmic attenuation rate δ and the number of peaks obtained in this manner. FIG. 10 shows the relationship between the damping ratio and the load, and the following equation holds between the damping ratio ξ and the logarithmic damping ratio δ.

ξ=δ/2π This embodiment also provides the same effects as the previous embodiment.

Although an inertial type vibrator was used as the vibrator in the above embodiment, the vibrator is not limited to this, and it is possible to apply a vibrating force from the bearing part of the rotating machine toward the center of the rotating shaft. If the device can be excited by pulse waves, etc., it can be of the reaction type (a vibrator is attached directly to the specimen and supported on a reaction support device via a force meter on the opposite side of the vibrator), Any of the non-contact electromagnetic exciters shown in FIGS. 11a and 11b may be used. This electromagnetic vibrator is designed so that a rotating shaft 41 can be directly vibrated by an electromagnet 40. Therefore, it is possible to effectively transmit the excitation force to the test object, such as the rotor,
This excitation force can be measured by an excitation force detector 42 attached to the base of the electromagnet 40. Also the 11th
As shown in Figure b, by installing two electromagnets 40 at right angles and adjusting the phase angle of the excitation force acting on both electromagnets to ±90°, this type of vibration can be easily generated in the forward direction (direction of rotation). It is possible to vibrate in the same direction (swinging in the same direction) or in the opposite direction, making it possible to obtain more accurate test results.

According to the present invention described above, it is possible to provide a load-dependent vibration investigation method for a rotating machine that can determine the natural frequency and damping ratio stability margin of the rotating machine when the load condition is changed.

[Brief explanation of drawings]

1A and 1B are a partial front view and a schematic configuration diagram showing an example of implementing the method of the present invention, FIG. 2 is a schematic configuration diagram showing an example of the vibration analysis apparatus of FIG. 1,
FIG. 3 is a flowchart for explaining one embodiment of the present invention, FIGS. 4 and 5 are Bode diagrams and Nyquist diagrams for determining the damping ratio, and FIG.
The figure is a diagram showing the relationship between load, damping ratio, and allowable excitation coefficient for explaining the same embodiment, and FIG. 7 is a flowchart for explaining another embodiment of the method of the present invention.
Figures 8 to 10 are diagrams showing the relationship between time and vibration waveform, diagrams showing the relationship between the number of peaks and logarithmic damping ratio, and diagrams showing the relationship between load and damping ratio, respectively, for explaining the method of the same embodiment. The figures shown in FIGS. 11a and 11b are a sectional view and a schematic configuration diagram showing an example of a non-contact electromagnetic vibrator. 1... Test rotor, 2... Bearing, 4... Vibrator, 5...
Excitation force detector, 6... Vibration detector, 7... Oscillator, 9
...Control device, 13...Vibration analysis device.

Claims (1)

[Claims] 1. In a rotating machine that is capable of applying an excitation force toward the center of the rotating shaft from the bearing part, the rotating machine is installed in a box of the bearing while keeping the rotational speed of the rotating machine constant and changing the load conditions in stages. The damping ratio or allowable excitation coefficient of the rotating machine is determined from the vibration response data for each load condition obtained by the inertial vibrator and the vibration detector that detects the vibration of the shaft or bearing. Load-dependent vibration investigation method.