Experimental Studies on Attenuation of Rotor-Stator Dynamics: Effects of High-Frequency Inclusion and Annular Fluid

2018 ◽  
Author(s):  
Meryem Kanzari ◽  
Mohammed AlQaradawi ◽  
Balakumar Balachandran
Keyword(s):  
High Frequency ◽  
Complex Dynamics ◽  
Experimental Studies ◽  
Flexible Rotor ◽  
Flexible Rotors ◽  
Speed Modulation ◽  
Model Predictions ◽  
Drive Speed ◽  
The Stability ◽  
Three Degree Of Freedom

Flexible, rotating structures can experience complex dynamics, when torsional and lateral motions are involved. Oilwell drill strings form one example of such structures. In the present study, the authors investigate the influence of sinusoidal drive speed modulation on whirling motions of flexible rotors with contact interactions. For two types of drilling-like operations, one with drill mud and another without drill mud, the stability of motions is studied. A laboratory-scale drill rig is used to study the dynamics of a flexible rotor, which is driven at one end and housed within a stator at the other end. Experimental results are presented and discussed for different drive speeds. The findings suggest that the addition of drill mud in the annular space between the rotor and stator along with high-frequency modulation in the drive input helps attenuate lateral motions. The torsional motions appear to be influenced more by the high-frequency drive speed modulation. A three-degree-of-freedom model has been constructed to study lateraltorsional dynamics of a rotor-stator system. The model predictions are compared with the experimental data. The findings of this work have relevance for constructing practical solutions to control whirl dynamics of flexible rotors such as drill strings.

Theoretical and Experimental Studies on Squeeze Film Stabilizers for Flexible Rotor-Bearing Systems Using Newtonian and Viscoelastic Lubricants

1990 ◽  
Vol 112 (4) ◽  
pp. 473-482 ◽  
Author(s):  
B. Halder ◽  
A. Mukherjee ◽  
R. Karmakar
Keyword(s):  
High Speed ◽  
Experimental Studies ◽  
Squeeze Film ◽  
Experimental Investigations ◽  
Flexible Rotor ◽  
Stability Range ◽  
High Speeds ◽  
Flexible Rotors ◽  
Rotor Bearing

A combination of a squeeze film damper and a plane journal bearing is studied as a stabilizing scheme. The damper is made to play the role of a stabilizer to postpone the instability threshold speeds of flexible rotors. Both Newtonian and viscoelastic fluids are used in the rotor-bearing system. Dynamics of the system is theoretically analyzed using bond graphs. Analysis reveals that the use of a Newtonian fluid in the stabilizer largely improves the high speed stability range. However, viscoelastic stabilizing fluid has a detrimental effect on highly flexible rotors. Experimental investigations, conducted on a flexible rotor (natural frequency, 30 Hz), confirm the theoretical findings. In addition, experiments indicate that though the use of viscoelastic stabilizing fluids leads to instability in flexible rotors, the growth of large amplitude whirl is postponed to very high speeds.

Stability of Flexible Rotors With a LeBlanc Balancer

2011 ◽  
Author(s):  
Leonardo Urbiola-Soto ◽  
Marcelo Lopez-Parra
Keyword(s):  
High Speed ◽  
Particle Image ◽  
Flexible Rotor ◽  
Rotating System ◽  
Stability Behavior ◽  
Piv Technique ◽  
Flexible Rotors ◽  
Image Velocimetry ◽  
The Stability ◽  
Stability Limits

Although the liquid balancer has nearly a century of having been introduced by LeBlanc, little information is available on the dynamic response and stability behavior of this kind of device. Earlier author’s research using a high-speed camera and a Particle Image Velocimetry (PIV) technique showed the existence of a fluid backward traveling wave inside the balancer cavity. This damping phenomenon helps enhance the unbalance response of the rotating system and also raises the stability limits. This paper shows that a flexible rotor employing a LeBlanc balancer has remarkable increase in the threshold speed of instability for aerodynamic cross-coupling and viscous internal friction damping.

scholarly journals NUMERICAL SIMULATION OF THE DYNAMICS OF A FLEXIBLE ROTOR WITH TWO BALL AUTO-BALANCERS

2020 ◽  
pp. 31-44
Author(s):  
Nikolay Zaytsev ◽  
◽  
Denis Zaytsev ◽  
Andrey Makarov ◽  
Dmitriy Mineev ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Mathematical Model ◽  
Cross Sections ◽  
Experimental Studies ◽  
Element Model ◽  
Rolling Friction ◽  
Published Data ◽  
Flexible Rotor ◽  
Flexible Rotors ◽  
The Mathematical Model

Ball auto-balancing devices can to compensate changes of unbalance "on the move" only for rotors operating at supercritical speeds. For automatic balancing of such rotors, classified as flexible rotors, several auto-balancers located in different cross sections of the shaft are necessary. This makes it necessary to account bending fluctuations on studies of dynamics of the rotor with auto-balancers, that is especially important in the design of the real rotors. In view of the complexity of experimental studies of such rotors in the article the method of direct numerical simulation of the dynamics of the flexible rotor system – supports – auto-balances is considered. The methodological basis of this method is the use of a discrete multi-mass rotor model, which is equivalent in dynamic characteristics to a real rotor, and also the equations of dynamics of the system discrete rotor – supports – auto-balancers, obtained in the direct form of recording. For definition of discrete masses and a matrix of coefficients of influence of stiffness of rotor cross-sections it is supposed to use calculations for finite-element model of a real rotor by existing software complexes of the engineering analysis. The mathematical model of the system dynamics obtained by the Lagrange method takes into account the non-stationarity of the rotor rotation speed, the influence of gravity and the rolling friction of the balls in the auto-balancer cages. Verification of the mathematical model was performed by reproducing the published data using a computational model for a two-support single-disk three-mass rotor with a two-ball auto-balancer. For a four-mass rotor with two two-ball auto-balancers, the results of numerical simulation of dynamics for the modes of acceleration, steady-state rotation and deceleration are presented. It is shown that for the system under consideration, only partial auto-balancing takes place in the steady rotation mode, including after a stepwise increase of the imbalance.

The Excitability of Flexible Rotors in Short Sleeve Bearings

1975 ◽  
Vol 97 (1) ◽  
pp. 105-115 ◽  
Author(s):  
E. J. Hahn
Keyword(s):  
Flexible Rotor ◽  
External Disturbances ◽  
Stability Threshold ◽  
Flexible Rotors ◽  
Rotor Bearing ◽  
Operating Regions ◽  
The Stability ◽  
Linearized Model ◽  
Lubricant Viscosity ◽  
Bearing System

Assuming the short bearing approximation and constant lubricant properties, the root loci of the pertinent characteristic function were obtained for the linearized model of a simple symmetric flexible rotor bearing system. Using these loci, design maps consisting of lines of constant damping and vibration frequency pertaining to the dominant roots are presented as a function of the equilibrium eccentricity ratio and a frequency parameter for relevant degrees of flexibility. These maps display undesirable operating regions where external disturbances such as shock or unbalance loading are likely to excite undesirable vibrations, as well as regions of instability. The maps may conveniently be used to determine the effect of changing journal speed, lubricant viscosity and/or bearing clearance. Increased flexibility is seen to reduce the stability threshold in a predictable manner and to reduce damping at the pin-pin critical speed. The approach is applicable to more complex rotor bearing systems. It is felt that the use of such maps will enhance the understanding of rotor bearing system behavior, particularly at operating regions close to the stability threshold.

Effects of high frequency drive speed modulation on rotor with continuous stator contact

2017 ◽  
Vol 131-132 ◽  
pp. 559-571 ◽  
Author(s):  
Abdullah AlZibdeh ◽  
Mohammed AlQaradawi ◽  
Balakumar Balachandran
Keyword(s):  
High Frequency ◽  
Speed Modulation ◽  
Drive Speed

Calculation-and-experimental estimation of the role of the frequency ratio in changing the endurance at two-frequency deformation modes

2019 ◽  
Vol 85 (1(I)) ◽  
pp. 64-71 ◽  
Author(s):  
M. M. Gadenin
Keyword(s):  
High Frequency ◽  
Experimental Studies ◽  
Low Frequency ◽  
Reduction Factor ◽  
Single Frequency ◽  
Cyclic Loads ◽  
Small Ratio ◽  
Harmonic Components ◽  
Deformation Modes

The cycle configuration at two-frequency loading regimes depends on the number of parameters including the absolute values of the frequencies and amplitudes of the low-frequency and high-frequency loads added during this mode, the ratio of their frequencies and amplitudes, as well as the phase shift between these harmonic components, the latter having a significant effect only with a small ratio of frequencies. Presence of such two-frequency regimes or service loading conditions for parts of machines and structures schematized by them can significantly reduce their endurance. Using the results of experimental studies of changes in the endurance of a two-frequency loading of specimens of cyclically stable, cyclically softened and cyclically hardened steels under rigid conditions we have shown that decrease in the endurance under the aforementioned conditions depends on the ratio of frequencies and amplitudes of operation low-frequency low-cycle and high-frequency vibration stresses, and, moreover, the higher the level of the ratios of amplitudes and frequencies of those stacked harmonic processes of loading the greater the effect. It is shown that estimation of such a decrease in the endurance compared to a single frequency loading equal in the total stress (strains) amplitudes can be carried out using an exponential expression coupling those endurances through a parameter (reduction factor) containing the ratio of frequencies and amplitudes of operation cyclic loads and characteristic of the material. The reduction is illustrated by a set of calculation-experimental curves on the corresponding diagrams for each of the considered types of materials and compared with the experimental data.

scholarly journals Delay compensation based controller for rotary electrohydraulic servo system

2021 ◽  
Author(s):  
Zakarya Omar ◽  
Xingsong Wang ◽  
Khalid Hussain ◽  
Mingxing Yang
Keyword(s):  
High Frequency ◽  
Dead Time ◽  
Sliding Mode ◽  
Servo System ◽  
Smith Predictor ◽  
Delay Compensation ◽  
Mechanical Parts ◽  
System Output ◽  
Electrohydraulic Servo System ◽  
The Stability

AbstractThe typical power-assisted hip exoskeleton utilizes rotary electrohydraulic actuator to carry out strength augmentation required by many tasks such as running, lifting loads and climbing up. Nevertheless, it is difficult to precisely control it due to the inherent nonlinearity and the large dead time occurring in the output. The presence of large dead time fires undesired fluctuation in the system output. Furthermore, the risk of damaging the mechanical parts of the actuator increases as these high-frequency underdamped oscillations surpass the natural frequency of the system. In addition, system closed-loop performance is degraded and the stability of the system is unenviably affected. In this work, a Sliding Mode Controller enhanced by a Smith predictor (SMC-SP) scheme that counts for the output delay and the inherent parameter nonlinearities is presented. SMC is utilized for its robustness against the uncertainty and nonlinearity of the servo system parameters whereas the Smith predictor alleviates the dead time of the system’s states. Experimental results show smoother response of the proposed scheme regardless of the amount of the existing dead time. The response trajectories of the proposed SMC-SP versus other control methods were compared for a different predefined dead time.

scholarly journals Performance Evaluation of Heading-and-Winning Machines in the Conditions of Potash Mines

2021 ◽  
Vol 11 (8) ◽  
pp. 3444
Author(s):  
Sergey A. Lavrenko ◽  
Dmitriy I. Shishlyannikov
Keyword(s):  
Energy Efficiency ◽  
Experimental Studies ◽  
Efficiency Coefficient ◽  
Mechanized Method ◽  
Methodological Approaches ◽  
The Stability ◽  
Technical Solutions ◽  
Potash Mine ◽  
Complex Indicators ◽  
Potassium Magnesium

The authors focus on the process of potash ore production by a mechanized method. They show that currently there are no approved procedures for assessing the performance of heading-and-winning machines operating in the conditions of potash mines. This causes difficulties in determining the field of application of heading-and-winning machines, complicates the search for implicit technical solutions for the modernisation of existing models of mining units, prohibits real-time monitoring of the stability of stope-based technological processes and makes it difficult to assess the performance of the services concerning mining enterprises. The work represents an aggregate assessment of the performance of heading-and-winning machines for potash mines by determining complex indicators describing the technological and technical levels of organising the work in stopes. Such indicators are the coefficients of productivity and energy efficiency, respectively. Experimental studies have been carried out in the conditions of the potash mine of the Verkhnekamskoye potassium-magnesium salt deposit to assess the performance of the latest and most productive Ural-20R heading-and-winning machines manufactured in Russia. Using the above methodological approaches, this paper shows that the unsatisfactory technological performance of the studied machine is due to the low productivity of the mine district transport. The average productivity coefficient was 0.29. At the same time, high values of the energy efficiency coefficient show that the productivity of the machine is on par with design conditions.

scholarly journals Extended-State-Observer-Based Super Twisting Control for Pneumatic Muscle Actuators

Actuators ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 35
Author(s):  
Yu Cao ◽  
Zhongzheng Fu ◽  
Mengshi Zhang ◽  
Jian Huang
Keyword(s):  
Control Method ◽  
Experimental Studies ◽  
State Observer ◽  
Extended State Observer ◽  
Extended State ◽  
Pneumatic Muscle ◽  
System States ◽  
The Stability ◽  
Twisting Control ◽  
Muscle Actuators

This paper presents a tracking control method for pneumatic muscle actuators (PMAs). Considering that the PMA platform only feedbacks position, and the velocity and disturbances cannot be observed directly, we use the extended-state-observer (ESO) for simultaneously estimating the system states and disturbances by using measurable variables. Integrated with the ESO, a super twisting controller (STC) is design based on estimated states to realize the high-precision tracking. According to the Lyapunov theorem, the stability of the closed-loop system is ensured. Simulation and experimental studies are conducted, and the results show the convergence of the ESO and the effectiveness of the proposed method.

An Efficient Galerkin BEM to Compute High Acoustic Eigenfrequencies

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Mario Durán ◽  
Jean-Claude Nédélec ◽  
Sebastián Ossandón
Keyword(s):  
Numerical Method ◽  
Integral Equations ◽  
High Frequency ◽  
High Accuracy ◽  
Integral Representations ◽  
Stability And Convergence ◽  
Symmetric Matrices ◽  
Frequency Interval ◽  
Numerical Treatment ◽  
The Stability

An efficient numerical method, using integral equations, is developed to calculate precisely the acoustic eigenfrequencies and their associated eigenvectors, located in a given high frequency interval. It is currently known that the real symmetric matrices are well adapted to numerical treatment. However, we show that this is not the case when using integral representations to determine with high accuracy the spectrum of elliptic, and other related operators. Functions are evaluated only in the boundary of the domain, so very fine discretizations may be chosen to obtain high eigenfrequencies. We discuss the stability and convergence of the proposed method. Finally we show some examples.

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