Stator Whirl With Rotors in Bearing Clearance

1967 ◽  
Vol 89 (3) ◽  
pp. 381-389 ◽  
Author(s):  
F. F. Ehrich ◽  
J. J. O’Connor
Keyword(s):  
Physical Model ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Contact Point ◽  
Analog Computer ◽  
Vibration Response ◽  
Stable Operation ◽  
Bearing Clearance ◽  
Bearing Contact ◽  
Acceleration And Deceleration

In order to identify and assess the effects of stator dynamics on vibration of high speed rotating machinery, a physical model with two degrees of freedom (one for the rotor and one for the stator) has been defined. Assuming that vibratory motion, as excited by rotor unbalance, is synchronous and axisymmetric, the analysis is linear and straightforward. The calculated vibration response reveals and quantifies some new and important phenomena which are a function of the level of bearing clearance (as related to unbalance level) and of the relative values of the rotor and stator natural frequencies. In particular, the following phenomena are noted: 1. As in simpler models, bearing clearance results in a reduction in system critical speed and can result in a “rightward leaning” critical peak causing hysteresis in response on acceleration and deceleration. 2. In certain ranges of parameters, two vibration modes are possible at high supercritical rotational speeds. One, termed stator whirl, results in stator amplitudes proportional to bearing clearance which are much larger than would be expected with very tight or very loose bearings. 3. Amplitude jump phenomena are very often experienced at a rotational speed equal to stator natural frequency. 4. Hysteresis phenomena, opposite in direction to that associated with a right-leaning critical peak, can be experienced on the subcritical side of the critical peak. 5. Disconnected from the main vibration response curve, branches of stable operation are evident and are hypothesized to be realizable if the system is subjected to momentary disturbances. The results have been verified by an analog computer simulation of the same system, and the effects of component damping and friction at the bearing contact point have been evaluated. Some regimes of asynchronous nonaxisymmetric motion in the analog computer model have been sensed, even though the physical model is axisymmetric.

Dynamic and Compliant Characteristics of a Cartesian-Guided Tripod Machine

2004 ◽  
Vol 128 (2) ◽  
pp. 494-502 ◽  
Author(s):  
Jeng-Shyong Chen ◽  
Wei-Yao Hsu
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Mechanical Vibration ◽  
Maximum Amplitude ◽  
High Gain ◽  
Velocity Change ◽  
Flexible Mode ◽  
Look Ahead ◽  
High Acceleration ◽  
Acceleration And Deceleration

This paper is focused on the dynamic and compliant characteristics of a three-axis parallel kinematic machine called a Cartesian-guided tripod (CGT), which has a passive leg locking the platform three rotational degrees of freedom. Because no constraint mechanism is perfect with infinite rigidity, a compliance model has been developed to determine the maximum amplitude of the passive-leg parasitic motions using given loads. System compliance, dynamic characteristics, vibration modes, and servo-contouring errors of the CGT driving system have also been evaluated under high-speed machining conditions. The nonlinear dynamic effects, such as inertia and gravity, can be controlled within acceptable accuracy using the high-gain servo-feedback control techniques. The CGT dominant flexible mode occurs on the horizontal platform-leg vibration. The platform-leg flexible mode can produce significant jerk-induced mechanical vibration on the platform when a sudden velocity change is commanded. Look-ahead Cartesian-based path acceleration and deceleration control was found to be an efficient tool to reduce the jerk-induced mechanical vibration, although the CGT was drive controlled at the joint level. It was found that at high acceleration application, such as high-speed mold and die machining, the elastic elongation of the driving leg caused by the high acceleration force became the dominant contouring error sources.

A Solid-State On-Load Tap Changer for the Power Transformers of 10—0.4 kV Distribution Networks

Vestnik MEI ◽  
2020 ◽  
Vol 6 (6) ◽  
pp. 82-90
Author(s):  
Dmitriy I. Panfilov ◽  
◽  
Mikhail G. Astashev ◽  
Aleksandr V. Gorchakov ◽  
◽  
...  
Keyword(s):  
Solid State ◽  
Physical Model ◽  
High Speed ◽  
Power Transformer ◽  
Voltage Control ◽  
Power Transformers ◽  
Control Algorithms ◽  
Load Voltage ◽  
Tap Changer ◽  
Load Tap Changer

The specific features relating to voltage control of power transformers at distribution network transformer substations are considered. An approach to implementing high-speed on-load voltage control of serially produced 10/0.4 kV power transformers by using a solid-state on-load tap changer (SOLTC) is presented. An example of the SOLTC circuit solution on the basis of thyristor switches is given. On-load voltage control algorithms for power transformers equipped with SOLTC that ensure high reliability and high-speed operation are proposed. The SOLTC performance and the operability of the suggested voltage control algorithms were studied by simulation in the Matlab/Simulink environment and by experiments on the SOLTC physical model. The structure and peculiarities of the used simulation Matlab model are described. The SOLTC physical model design and its parameters are presented. The results obtained from the simulating the SOLTC operation on the Matlab model and from the experiments on the SOLTS physical model jointly with a power transformer under different loads and with using different control algorithms are given. An analysis of the experimental study results has shown the soundness of the adopted technical solutions. It has been demonstrated that the use of an SOLTC ensures high-speed voltage control, high efficiency and reliability of its operation, and arcless switching of the power transformer regulating taps without load voltage and current interruption. By using the SOLTC operation algorithms it is possible to perform individual phase voltage regulation in a three-phase 0.4 kV distribution network. The possibility of integrating SOLTC control and diagnostic facilities into the structure of modern digital substations based on the digital interface according to the IEC 61850 standard is noted.

Stable operation of multiple-lateral-mode ridge-waveguide lasers for high-speed printing

1997 ◽  
Vol 33 (3) ◽  
pp. 214
Author(s):  
R. LaComb ◽  
D.K. Wagner ◽  
L. DiMarco ◽  
J. Connolly
Keyword(s):  
High Speed ◽  
Ridge Waveguide ◽  
Stable Operation ◽  
Waveguide Lasers ◽  
Lateral Mode ◽  
Ridge Waveguide Lasers

scholarly journals Aerodynamics of inclined cylindrical bodies free-flying in a hypersonic flowfield

2021 ◽  
Vol 62 (9) ◽  
Author(s):  
Patrick M. Seltner ◽  
Sebastian Willems ◽  
Ali Gülhan ◽  
Eric C. Stern ◽  
Joseph M. Brock ◽  
...  
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Numerical Data ◽  
Static Stability ◽  
Free Flight ◽  
Aerodynamic Coefficients ◽  
Flow Topology ◽  
Motion Data ◽  
Continuous Rotation ◽  
German Aerospace

Abstract The influence of the flight attitude on aerodynamic coefficients and static stability of cylindrical bodies in hypersonic flows is of interest in understanding the re/entry of space debris, meteoroid fragments, launch-vehicle stages and other rotating objects. Experiments were therefore carried out in the hypersonic wind tunnel H2K at the German Aerospace Center (DLR) in Cologne. A free-flight technique was employed in H2K, which enables a continuous rotation of the cylinder without any sting interferences in a broad angular range from 0$$^{\circ }$$ ∘ to 90$$^{\circ }$$ ∘ . A high-speed stereo-tracking technique measured the model motion during free-flight and high-speed schlieren provided documentation of the flow topology. Aerodynamic coefficients were determined in careful post-processing, based on the measured 6-degrees-of-freedom (6DoF) motion data. Numerical simulations by NASA’s flow solvers Cart3D and US3D were performed for comparison purposes. As a result, the experimental and numerical data show a good agreement. The inclination of the cylinder strongly effects both the flowfield and aerodynamic loads. Experiments and simulations with concave cylinders showed marked difference in aerodynamic behavior due to the presence of a shock–shock interaction (SSI) near the middle of the model. Graphic abstract

scholarly journals Cavitation between cylinder-liner and piston-ring in a new designed optical IC engine

2021 ◽  
pp. 146808742110080
Author(s):  
Jamshid Malekmohammadi Nouri ◽  
Ioannis Vasilakos ◽  
Youyou Yan
Keyword(s):  
High Speed ◽  
Contact Point ◽  
Cylinder Liner ◽  
Optical Methods ◽  
Engine Management System ◽  
Great Success ◽  
Ic Engine ◽  
Contact Points ◽  
Lubricant Flow ◽  
Cavitation Intensity

A new engine block with optical access has been designed and manufactured capable of running up to 3000 r/min with the same specification as the unmodified engine. The optical window allowed access to the full length of the liner over a width of 25 mm to investigate the lubricant flow and cavitation at contact point between the rings and cylinder-liner. In addition, it allowed good access into the combustion chamber to allow charged flow, spray and combustion visualisation and measurements using different optical methods. New custom engine management system with build in LabView allowed for the precise full control of the engine. The design of the new optical engine was a great success in producing high quality images of lubricant flow, cavitation formation and development at contact point at different engine speeds ranging from 208 to 3000 r/min and lubricant temperatures (30°C–70°C) using a high-speed camera. The results under motorised operation confirmed that there was no cavitation at contact points during the intake/exhaust strokes due to low in-cylinder presure, while during compression/expansion strokes, with high in-cylinder pressure, considerable cavities were observed, in particular, during the compression stroke. Lubricant temperatures had the effect of promoting cavities both in their intensity and covered ring area up to 50°C as expected. Beyond that, although the cavitation intensity increases further with temperature, its area reduces due to possible collapse of the cavitating bubbles at higher temperature. The change of engine speed from 208 to 800 r/min increased cavitating area considerably by 52% of the ring area and was further increased by 19% at 1000 r/min. After that, the results showed very small increase in cavitation area (1.3% at 2000 r/min) with similar intensity and distribution across the ring.

A Magnetic Drive Actuator for Micro Electrical Discharge Machining

2012 ◽  
Vol 591-593 ◽  
pp. 303-306
Author(s):  
Xiao You Zhang ◽  
Akio Kifuji ◽  
Dong Jue He
Keyword(s):  
Electrical Discharge ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Electrical Discharge Machining ◽  
Magnetic Coupling ◽  
Magnetic Bearings ◽  
Coupling Mechanism ◽  
Micro Electrical Discharge Machining ◽  
Long Stroke ◽  
Magnetic Drive

Electrical discharge machining has the capability of machining all conductive materials regardless of hardness, and has the ability to deal with complex shapes. However, the speed and accuracy of conventional EDM are limited by probability and efficiency of the electrical discharges. This paper describes a three degrees of freedom (3-DOF) controlled, wide-bandwidth, high-precision, long-stroke magnetic drive actuator. The actuator can be attached to conventional electrical discharge machines to realize a high-speed and high-accuracy EDM. The actuator primarily consists of thrust and radial magnetic bearings, thrust and radial air bearings and a magnetic coupling mechanism. By using the thrust and radial magnetic bearings, the translational motions of the spindle can be controlled. The magnetic drive actuator possesses a positioning resolution of the order of micrometer, a bandwidth greater than 100Hz and a positioning stroke of 2mm.

Design, Construction and Control of a Remotely Operated Vehicle (ROV)

2011 ◽  
Author(s):  
Alireza Marzbanrad ◽  
Jalil Sharafi ◽  
Mohammad Eghtesad ◽  
Reza Kamali
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Remotely Operated Vehicle ◽  
Six Degrees Of Freedom ◽  
Depth Sensors ◽  
Control Schemes ◽  
On Line ◽  
Operation Unit ◽  
And Control ◽  
Design Construction

This is report of design, construction and control of “Ariana-I”, an Underwater Remotely Operated Vehicle (ROV), built in Shiraz University Robotic Lab. This ROV is equipped with roll, pitch, heading, and depth sensors which provide sufficient feedback signals to give the system six degrees-of-freedom actuation. Although its center of gravity and center of buoyancy are positioned in such a way that Ariana-I ROV is self-stabilized, but the combinations of sensors and speed controlled drivers provide more stability of the system without the operator involvement. Video vision is provided for the system with Ethernet link to the operation unit. Control commands and sensor feedbacks are transferred on RS485 bus; video signal, water leakage alarm, and battery charging wires are provided on the same multi-core cable. While simple PI controllers would improve the pitch and roll stability of the system, various control schemes can be applied for heading to track different paths. The net weight of ROV out of water is about 130kg with frame dimensions of 130×100×65cm. Ariana-I ROV is designed such that it is possible to be equipped with different tools such as mechanical arms, thanks to microprocessor based control system provided with two directional high speed communication cables for on line vision and operation unit.

Beam-Vibration Analysis With the Electric-Analog Computer

1950 ◽  
Vol 17 (1) ◽  
pp. 13-26
Author(s):  
G. D. McCann ◽  
R. H. MacNeal
Keyword(s):  
Steady State ◽  
Vibration Analysis ◽  
Degrees Of Freedom ◽  
Analog Computer ◽  
Accurate Solution ◽  
Rotary Inertia ◽  
Beam Vibration ◽  
Lumped Constant ◽  
Electric Analog

Abstract The authors have developed a true dynamic analogy which has been used with the Cal Tech electric-analog computer for the rapid and accurate solution of both steady-state and transient beam problems. This analogy has been found well suited to the study of beams having several coupled degrees of freedom, including torsion, simple bending, and bending in a plane. Damping and effects such as rotary inertia may be handled readily. The analogy may also be used in the study of systems involving combined beams and “lumped-constant” elements.

Numerical study on the mechanism of drag reduction for interceptors on planning boats

2021 ◽  
Author(s):  
Lianzheng Cui ◽  
Zuogang Chen ◽  
Yukun Feng
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Numerical Study ◽  
Dynamic Pressure ◽  
Motion Model ◽  
Gauge Pressure ◽  
Reduction Effect ◽  
Pressure Resistance ◽  
Viscous Pressure

The drag reduction effect of interceptors on planning boats has been widely proven, but the mechanism of the effect has been rarely studied in terms of drag components, especially for spray resistance. The resistance was caused by the high gauge pressure under the boats transformed from the dynamic pressure, and it is the largest drag component in the high-speed planning mode. In this study, numerical simulations of viscous flow fields around a planning boat with and without interceptors were conducted. A two degrees of freedom motion model was employed to simulate the trim and sinkage. The numerical results were validated against the experimental data. The flow details with and without the interceptor were visualized and compared to reveal the underlying physics. A thinner and longer waterline could be achieved by the interceptor, which made the boat push the water away more gradually, and hence, the wave-making resistance could be decreased. The improved waterline also reduced the component of the freestream normal to the hull surface and led to the less transformed dynamic pressure, resulting in the lowAer spray resistance. Furthermore, the suppression of the flow separation could also be benefited from the interceptor; the viscous pressure resistance was therefore decreased.

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