Steady-State Control of Hybrid Foil-Magnetic Bearings

2012 ◽  
Author(s):  
Ye Tian ◽  
Yanhua Sun ◽  
Lie Yu
Keyword(s):  
Steady State ◽  
Load Capacity ◽  
Magnetic Bearing ◽  
Magnetic Bearings ◽  
State Control ◽  
Foil Bearings ◽  
Foil Bearing ◽  
State Controller ◽  
Steady State Control ◽  
And Control

A hybrid foil-magnetic bearing is combination of a foil bearing and a magnetic bearing, which takes advantages of both bearings while compensating each other the weaknesses. It is a solution of friction and wear of foil bearings at low speeds and limited load capacity of magnetic bearings. Furthermore, load sharing and control of dynamics can be achieved in a hybrid foil-magnetic bearing. However, in the hybrid foil-magnetic bearing, the journal should run at certain eccentricity and attitude angle in order to take part of the loads, but the magnetic bearing would attempt to force the journal to the reference position at all times while using a conventional PID controller. Therefore, it is necessary to design a new control algorithm to overcome the contradictions. In this paper, the steady-state characteristics of a hybrid foil-magnetic bearing were analyzed. Then a searching algorithm was presented and a steady-state controller was designed to determine the steady-state working position of the hybrid foil-magnetic bearings. Finally, simulations were done to verify performances of the searching algorithm and designed steady-state controller, and the results show its validity.

Operation and Control of a Supercritical CO2 Compressor

2021 ◽  
Author(s):  
Joshua D. Neveu ◽  
Stefan D. Cich ◽  
J. Jeffrey Moore ◽  
Jason Mortzheim
Keyword(s):  
Steady State ◽  
Critical Point ◽  
Operating Conditions ◽  
State Control ◽  
Power Cycle ◽  
Low Head ◽  
And Performance ◽  
Steady State Control ◽  
And Control ◽  
Thermal Sources

Abstract Among the list of advanced technologies required to support the energy industry’s novel Supercritical Carbon Dioxide (sCO2) power cycle is the need for a robust and responsive control system. Recent testing has been performed on a 2.5 MWe sCO2 compressor operating near the critical temperature (31C) and critical pressure (73.8 bar), developed with funding from the US DOE Apollo program and industry partners. While sCO2 compression has been performed before, operating near the critical point has many key benefits for power generation with its low head requirements and smaller physical footprint. However, with these benefits come unique challenges, namely controlling this system to steady-state operating conditions. Operating just above the critical point (35°C [95°F] and 8.5 MPa [1,233 psi]) there can be large and rapid swings in density produced by subtle changes in temperature, leading to increased difficulty in maintaining adequate control of the compressor system. This means that proper functionality of the entire compressor system, and its usefulness to a closed loop recompression Brayton power cycle, is largely dependent on variables such as thermal sources, precision and response time of the instrumentation, proper heat soaking, and strategic filling and venting sequences. While other papers have discussed the science behind and performance of sCO2 compressors, this paper will discuss the challenges associated with steady-state control of the compressor at or near operating conditions, how the fill process was executed for optimal startup, and changes that occurred while idling during trip events.

Modelling and Control of Processes by Computer

1970 ◽  
Vol 3 (9) ◽  
pp. T148-T154
Author(s):  
T. Robbins ◽  
N. W. Francis
Keyword(s):  
Steady State ◽  
Crude Oil ◽  
Normal Operator ◽  
State Control ◽  
Crude Oil Distillation ◽  
Operator Control ◽  
Steady State Control ◽  
And Control ◽  
Digital Computers

Two applications of digital computers to control of crude oil distillation units are outlined. Results from both applications are quoted and comparisons made with normal operator control of the units. Difficulties encountered with the applications are mentioned and comments are made on steady-state control. The purpose of this paper is to describe two aspects of the application of digital computers to the control of crude oil distillation units.

A Comparison of the Steady-State and Dynamic Performance of First- and Second-Generation Foil Bearings

2010 ◽  
Author(s):  
M. J. Conlon ◽  
A. Dadouche ◽  
W. M. Dmochowski ◽  
R. Payette ◽  
J.-P. Be´dard
Keyword(s):  
Steady State ◽  
Experimental Evaluation ◽  
First Generation ◽  
Second Generation ◽  
Load Capacity ◽  
Dynamic Stiffness ◽  
Dynamic Performance ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Stiffness And Damping

Oil-free foil bearing technology has advanced intermittently over the years, driven by research efforts to improve both steady-state and dynamic performance characteristics, namely: load capacity, stiffness, and damping. Bearing designs are thus classified according to “generation”, with first-generation bearings being the most primitive. This paper presents an experimental evaluation of a first- and a second-generation foil bearing, and aims to provide the high-fidelity data necessary for proper validation of theoretical predictive models of foil bearing performance. The aforementioned test bearings were fabricated in-house, and are both 70mm in diameter with an aspect ratio of 1; bearing manufacturing details are provided. The work makes use of a facility dedicated to measuring both the steady-state and dynamic properties of foil bearings under a variety of controlled operating conditions. The bearing under test is placed at the midspan of a horizontal, simply-supported, stepped shaft which rotates at up to 60krpm. Static and dynamic loads of up to 3500N and 450N (respectively) can be applied by means of a pneumatic cylinder and two electrodynamic shakers. The bearings’ structural (static) stiffnesses are highly nonlinear, and this affects the accuracy of the dynamic coefficient determination. Both dynamic stiffness and damping are found to vary nonlinearly with excitation frequency, and are over-predicted by a structural experimental evaluation — the film plays an important role in bearing dynamics. The second-generation bearing is found to have a higher load capacity, dynamic stiffness, and damping than the first-generation bearing.

scholarly journals On Linear Coding Schemes for Stabilizing LTI Control with Multiple Sensors

2010 ◽  
Vol 6 (1) ◽  
pp. 514521
Author(s):  
Anna N. Kim
Keyword(s):  
Steady State ◽  
Time Instant ◽  
Wireless Channel ◽  
State Control ◽  
Control Cost ◽  
Transmit Power ◽  
Multiple Sensors ◽  
Coding Schemes ◽  
Steady State Control ◽  
And Control

We examine the problem of designing the encoding and control policies of a linear stochastic control system, where the communication channel between the plant state observer (sensor) and the controller is a lossy wireless channel that is constrained in terms of transmit power and bandwidth. For a first-order ARMA modeled plant with Gaussian statistics, when there are two sensors observing the plant, nonlinear encoding is shown to result in smaller cost at time instant [Formula: see text] compared to the linear schemes, if transmissions are carried out over parallel Gaussian independent channels. In this paper, optimal linear coding schemes for the case of multiple sensors are examined. They are shown to minimize the control cost at the infinite time horizon, when the wireless channel is accessed using time division multiplexing. Our analysis is carried out for when separation between the state estimation and control is possible, and the optimal steady state control law is certainty equivalent. The distortion lower bound for estimating the plant state is derived, along with the necessary conditions on the transmit power that minimize the steady state control cost. We also propose a linear scheme that reaches the distortion bound asymptotically under relaxed conditions.

Acute endurance exercise induces changes in vasorelaxation responses that are vessel-specific

2013 ◽  
Vol 304 (7) ◽  
pp. R574-R580 ◽  
Author(s):  
Juan M. Murias ◽  
Kenneth N. Grise ◽  
Mao Jiang ◽  
Hana Kowalchuk ◽  
C. W. James Melling ◽  
...  
Keyword(s):  
Steady State ◽  
Endurance Exercise ◽  
State Control ◽  
Average Response ◽  
Dynamic Adjustment ◽  
Acute Bout ◽  
Vascular Responsiveness ◽  
Femoral Vessels ◽  
Steady State Control ◽  
And Control

The dynamic adjustment and amplitude of the endothelium-dependent vasorelaxation of the carotid, aorta, iliac, and femoral vessels were measured in response to acute low- (LI) or high-intensity (HI) endurance exercise. Vasorelaxation to 10−4 M ACh was evaluated in 10 control, 10 LI, and 10 HI rats. Two-millimeter sections of carotid, aorta, iliac, and femoral arteries were mounted onto a myography system. Vasorelaxation responses were modeled as a monoexponential function. The overall τ (control, 10.5 ± 6.0 s; LI, 10.4 ± 5.7 s; HI, 11.0 ± 6.9 s) and time-to-steady-state (control, 47.6 ± 24.0 s; LI, 46.2 ± 22.8 s; HI, 49.1 ± 28.3 s) was similar in LI, HI, and control ( P > 0.05). The overall (average of four vessel-type) % vasorelaxation was larger in LI (73 ± 16%) and HI (73 ± 16%) than in control (66 ± 19%) ( P < 0.05). The overall rate of vasorelaxation was greater in LI (1.9 ± 0.9%·s−1) and HI (1.9 ± 1.1%·s−1) compared with control (1.6 ± 0.7%·s−1) ( P < 0.05). The vessel-specific responses (average response for the three conditions) showed that carotid displayed a slower adjustment (τ, 18.9 ± 4.4 s; time-to-steady-state, 80.4 ± 18.4 s) compared with the aorta (τ, 10.3 ± 3.8 s; time-to-steady-state, 46.3 ± 15.2 s), the iliac (τ, 6.3 ± 2.1 s; time-to-steady-state, 30.3 ± 9.0 s), and the femoral (τ, 6.0 ± 1.9 s; time-to-steady-state, 29.3 ± 8.4 s). The % vasorelaxation was larger in the carotid (82 ± 14%) than in the aorta (67 ± 16%), iliac (61 ± 13%), and femoral (71 ± 19%) ( P > 0.05). The rate of vasorelaxation was carotid (1.1 ± 0.2%·s−1), aorta (1.5 ± 0.4%·s−1), iliac (2.2 ± 0.8%·s−1), and femoral (2.6 ± 1.0%·s−1). In conclusion, an acute bout of endurance exercise increased vascular responsiveness. The dynamic and percent adjustments were vessel-specific with vessel function likely determining the response.

Oil-Free Foil Bearings as a Reliable, High Performance Backup Bearing for Active Magnetic Bearings

2002 ◽  
Author(s):  
E. E. Swanson ◽  
H. Heshmat
Keyword(s):  
High Speed ◽  
High Performance ◽  
Dynamic Performance ◽  
Magnetic Bearing ◽  
Magnetic Bearings ◽  
Stable Operation ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Limited Life ◽  
Rolling Element

Gas turbine engines and other high speed rotating machinery supported by magnetic bearings require some form of backup bearing to ensure reliable and safe operation. To date, this backup capability has been provided by either rolling element bearings or solid lubricated bushings. Both of these solutions have drawbacks — must notably limited life and uncertain dynamic performance. In many cases, the backup bearing system requires substantial maintenance following an activation event. An alternative approach investigated in this work is the use of a compliant foil bearing as a backup bearing. This work discusses tests of this concept on a test rig with a 63 kg rotor. In this application, the foil bearing demonstrated smooth, stable operation during a variety of simulated magnetic bearing failure events, and allowed for continued operation of the rotor following the simulated failures.

Foil Gas Bearing With Compression Springs: Analyses and Experiments

2007 ◽  
Vol 129 (3) ◽  
pp. 628-639 ◽  
Author(s):  
Ju-ho Song ◽  
Daejong Kim
Keyword(s):  
Loss Factor ◽  
Load Capacity ◽  
Underlying Structure ◽  
Equivalent Viscous Damping ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Different Types ◽  
Structural Loss ◽  
Compression Springs ◽  
Gas Bearing

A new foil gas bearing with spring bumps was constructed, analyzed, and tested. The new foil gas bearing uses a series of compression springs as compliant underlying structures instead of corrugated bump foils. Experiments on the stiffness of the spring bumps show an excellent agreement with an analytical model developed for the spring bumps. Load capacity, structural stiffness, and equivalent viscous damping (and structural loss factor) were measured to demonstrate the feasibility of the new foil bearing. Orbit and coast-down simulations using the calculated stiffness and measured structural loss factor indicate that the damping of underlying structure can suppress the maximum peak at the critical speed very effectively but not the onset of hydrodynamic rotor-bearing instability. However, the damping plays an important role in suppressing the subsynchronous vibrations under limit cycles. The observation is believed to be true with any air foil bearings with different types of elastic foundations.

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