Evaluation of Q-Values of a Rotor-Bearing System Using a Modal Open Loop Transfer Function

2009 ◽  
Author(s):  
Hiroyuki Fujiwara ◽  
Yasuo Fukushima ◽  
Naohiko Takahashi ◽  
Hiroto Oyama ◽  
Osami Matsushita
Keyword(s):  
Transfer Function ◽  
Damping Ratio ◽  
Magnetic Bearing ◽  
Open Loop ◽  
Active Magnetic Bearing ◽  
Q Value ◽  
Oil Whip ◽  
Displacement Sensors ◽  
Loop Transfer Function ◽  
Value Estimation

As indicated by ISO standard 10816, Q-value estimation is very important for rotating machinery commission and/or machine safety operation. Impulse tests and resonance curve measurements are commonly contributed to Q-value estimation. Instead of two methods, we are developing a new method using open-loop transfer function (Go) at real operational condition. In this paper, we present a theoretical background on how to measure the open loop transfer function. Our key technique is the measurement of the modal coordinates with a combination of several displacement sensors. Concerning the experimental measurement of Go, we use multiple sensors and only one active magnetic bearing (AMB) in a rotor system supported by oil-film/ball bearing. This Go is converted to damping ratio. In fact, a smaller damping ratio is recognized just before oil-whip instability by our open loop measurement. In addition, we set a dynamic damper which has been developed for suppression of oil whip instability, and an increasing damping ratio is also recognized by our method.

Evaluation of Q-Values of a Rotor-Bearing System Using a Modal Open Loop Transfer Function

2008 ◽  
Author(s):  
Hiroyuki Fujiwara ◽  
Hirot Oyama ◽  
Norihisa Anegawa ◽  
Osami Matsushita
Keyword(s):  
Transfer Function ◽  
Model Simulation ◽  
Damping Ratio ◽  
Open Loop ◽  
New Method ◽  
Q Value ◽  
Response Measurement ◽  
Loop Transfer Function ◽  
Rotor Bearing ◽  
Bearing System

One of the key features of vibration characteristics (e.g., critical speed, damping ratio, Q-value, instability margin, etc.) of a rotor-bearing system can be described by their eigenvalues. The eigenvalues are conventionally evaluated by feed forward excitations, e.g., hammering test, harmonic sweep excitation, and unbalance response measurement. However it has been difficult to identify their damping ratios under various conditions. In this paper, we introduce a new method using a modal open loop transfer function. This method provides a more accurate Q-value and can help to identify the damping ratio by considering only the mode which we want to measure. We applied this method to a few models and some test rigs: 1) 3DOF model (simulation), 2) A flexible rotor equipped with active magnetic bearings (experiment). As a result, we concluded: 1) As the number of sensors is increased, the accuracy of the measurement also increases. 2) Our new method is more effective in terms of the accuracy of modal damping ratio than the conventional method is.

Robust Feedback Control of a Baffled Plate via Open-Loop Optimization

2001 ◽  
Vol 124 (1) ◽  
pp. 154-157 ◽  
Author(s):  
P. De Man ◽  
A. Franc¸ois ◽  
A. Preumont
Keyword(s):  
Genetic Algorithm ◽  
Control System ◽  
Transfer Function ◽  
Open Loop ◽  
Displacement Sensor ◽  
Search Procedure ◽  
Loop Optimization ◽  
Loop Transfer Function ◽  
Poles And Zeros ◽  
Siso System

A SISO control system is built by using a volume displacement sensor and a set of actuators driven in parallel with a single amplifier. The actuators location is optimized to achieve an open-loop transfer function which exhibits alternating poles and zeros, as for systems with collocated actuators and sensors; the search procedure uses a genetic algorithm. The ability of a simple lead compensator to control this SISO system is numerically demonstrated.

Model-Based Control of Combustion Instabilities

2005 ◽  
Author(s):  
Aimee S. Morgans ◽  
Ann P. Dowling
Keyword(s):  
Transfer Function ◽  
Controller Design ◽  
Open Loop ◽  
Operating Conditions ◽  
Combustion Instabilities ◽  
Lean Premixed Combustion ◽  
Model Based Control ◽  
Model Based ◽  
Loop Transfer Function ◽  
Mathematical Approximation

Model-based control has been successfully implemented on an atmospheric pressure lean premixed combustion rig. The rig incorporated a pressure transducer in the combustor to provide a sensor measurement, with actuation provided by a fuel valve. Controller design was based on experimental measurement of the open loop transfer function. This was achieved using a valve input signal which was the sum of an identification signal and a control signal from an empirical controller to eliminate the non-linear limit cycle. The transfer function was measured for the main instability occurring at a variety of operating conditions, and was found to be fairly similar in all cases. Using Nyquist and H∞-loop shaping techniques, several robust controllers were designed, based on a mathematical approximation to the measured transfer function. These were implemented experimentally on the rig, and were found to stabilise it under a variety of operating conditions, with a greater reduction in the pressure spectrum than had been achieved by the empirical controller.

scholarly journals Analytical Multiloop Control for Multivariable Systems with Time Delays

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Zhiguo Wang ◽  
Peng Wei
Keyword(s):  
Transfer Function ◽  
Process Model ◽  
Controller Design ◽  
Design Method ◽  
Open Loop ◽  
Multivariable Systems ◽  
Performance Improvements ◽  
Loop Transfer Function ◽  
Multiloop Control ◽  
Multiloop Control System

In this paper, a new design method with performance improvements of multiloop controllers for multivariable systems is proposed. Precise expression is developed to show the relationship between the dynamic- and steady-state characteristics of the multiloop control system and its parameters. First, an equivalent transfer function (ETF) is introduced to decompose the multivariable system, based on which the multiloop controller parameters are calculated. According to the ETF matrix property, an analytical expression for the PI controller for multivariable systems is derived in terms of substituting the ETF matrix for the inverse open-loop transfer function. In the proposed controller design method, no approximation of the inverse of the process model is needed, implying that this method can be applied to some multivariable systems with high dimensions. The simulation results obtained from several examples demonstrate the effectiveness of the proposed method.

Controlling Journal Bearing Instability Using Active Magnetic Bearings

2007 ◽  
Author(s):  
A. El-Shafei ◽  
A. S. Dimitri
Keyword(s):  
Journal Bearing ◽  
Magnetic Bearing ◽  
Journal Bearings ◽  
Active Magnetic Bearing ◽  
Rotating Speed ◽  
Damping Characteristics ◽  
Oil Whip ◽  
Novel Approach ◽  
Oil Whirl ◽  
Load Carrying

Journal Bearings are excellent bearings due to their large load carrying capacity and favorable damping characteristics. However, Journal bearings are known to be prone to instabilities. The oil whirl and oil whip instabilities limit the rotor maximum rotating speed. In this paper, a novel approach is used to control the Journal bearing (JB) instability. An Active Magnetic Bearing (AMB) is used to overcome the JB instability and to increase its range of operation. The concept is quite simple: rather than using the AMB as a load carrying element, the AMB is used as a controller only, resulting in a much smaller and more efficient AMB. The load carrying is done by the Journal bearings, exploiting their excellent load carrying capabilities, and the JB instability is overcome with the AMB. This results in a combined AMB/JB that exploits the advantages of each device, and eliminates the deficiencies of each bearing. Different controllers for the AMB to control the JB instability are examined and compared theoretically and numerically. The possibility of collocating the JB and the AMB is also examined. The results illustrate the effectiveness of the concept.

Destabilization of Forward Rub in Rotor Magnetic Bearing Systems Using Actively Controlled Auxiliary Bearings

2010 ◽  
Author(s):  
Iain S. Cade ◽  
M. Necip Sahinkaya ◽  
Clifford R. Burrows ◽  
Patrick S. Keogh
Keyword(s):  
Design Feature ◽  
Magnetic Bearing ◽  
Open Loop ◽  
Active Magnetic Bearing ◽  
Loop Control ◽  
Bending Mode ◽  
Operating Limits ◽  
Auxiliary Bearing ◽  
Contact Free ◽  
Bearing System

During fault conditions, rotor displacements in magnetic bearing systems may potentially exceed safety/operating limits. Hence it is a common design feature to incorporate auxiliary bearings adjacent to the magnetic bearings for the prevention of rotor/stator contact. During fault conditions the rotor may come into contact with the auxiliary bearings, which may lead to continuous rub type orbit responses. In particular, forward rub responses may become persistent. This paper advances the methodology by considering an actively controlled auxiliary bearing system. An open-loop control strategy is adopted to provide auxiliary bearing displacements that destabilize established forward rub orbit responses. A theoretical approach is undertaken to identify auxiliary bearing motion limits at which forward rub responses become unstable. Experimental validation is then undertaken using a rotor/active magnetic bearing system with an actively controlled auxiliary bearing system under piezoelectric actuation. Two different operating speeds below the first bending mode of the rotor are considered and the applied harmonic displacements of the auxiliary bearing are shown to be effective in restoring contact free levitation.

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