Damping Of Torsional Oscillations Research Articles

Self-Attenuation of Drillstring Torsional Vibrations Using Distributed Dampers

Summary During drilling operations, drillstring vibrations cause many downhole dysfunctions, resulting in underperformance, equipment failure, and possibly wellbore damage. Current drillstring vibration mitigation solutions are generally located at a single site, either at the topdrive or close to the bit. However, because the sources of vibration excitation are distributed along the whole drillstring, these single-point vibration damping solutions do not succeed in removing all vibration modes. A distributed vibration damping solution is investigated, wherein damping subs are placed at intervals along the drillstring. The drillpipe rotates on bearings inside the damping subs, thereby reducing mechanical torque. The damping sub has a slightly larger diameter than the neighboring tool joints, lifting the drillstring off the borehole wall and thus eliminating most of the mechanical friction between the damping subs. Viscous friction is introduced in the form of rotary eddy current brakes within the damping subs, which cause the damping of torsional oscillations. The damping sub moves axially on spur wheels supported by bearings, thereby reducing drag forces. The decoupling of rotary and axial movement is a key element for removing a source of excitation. Simulations made with a 4n degree-of-freedom (DOF) transient torque and drag model confirm the expected results. The results of simulations for a use case based on a complex 3D trajectory are presented. With damping subs every 30 m and a damping coefficient of 20 N·s/rd, the topdrive torque is reduced to 40% of that of a plain drillstring, and torsional stability is obtained across the topdrive speed range of 60 to 180 rev/min. By comparison, conventional nonrotating pipe protectors (NRPPs) would have reduced the topdrive torque to 30%, but torsional stability would have not been achieved because the expected damping coefficient was less than 0.02 N·s/rd. The design of the damping sub relies on readily available technological components that can sustain very high pressures and temperatures. The damping subs are therefore compatible with high-pressure/high-temperature applications, including geothermal drilling.

Stability and Dynamic Analysis of the PMSG-Based WECS With Torsional Oscillation and Power Oscillation Damping Capabilities

The direct-drive permanent-magnet synchronous generator (PMSG) based wind energy conversion system (WECS) with a soft drivetrain shaft is vulnerable to torsional oscillation when it participates in power oscillation damping (POD) services for the AC grid. This paper investigates three possible scenarios of incorporating both torsional oscillation damping (TOD) and POD controllers into PMSG-based WECS. A model of a PMSG-based offshore wind farm (OWF) connected to the IEEE 39-bus AC grid is developed and utilized to analyze the stability and dynamic performances of the WECS within these three scenarios. Comprehensive modal analysis is carried out to analyze the interaction between the torsional and power oscillations, and to tune the TOD and POD controllers to damp these oscillations simultaneously in each scenario. Furthermore, the dynamic performances of the PMSG-based WECS within these scenarios are evaluated through time-domain simulations. Then an optimal scenario for PMSG-based WECS to damp both oscillation types with close frequencies is identified, which is modulating the DC-link voltage for the TOD and the grid-side active power for the POD. This result can provide useful guidance for the future industrial application of the TOD and POD control in the PMSG-based WECS.

Torsional oscillation damping in wind turbines with virtual synchronous machine‐based frequency response

AbstractIn the quest of improving the frequency response capability of wind turbines, control solutions trying to emulate synchronous machines have been proposed. While their performance in terms of frequency support is relatively good, they may trigger torsional oscillations, cause fatigue and damage in the drivetrain, and reduce its lifetime. In this paper, the torsional oscillations caused by a virtual synchronous machine (VSM)‐based frequency controller are illustrated, and methods for damping them are introduced. Two torsional oscillation damping methods are compared and combined to derive an improved method. Dynamic simulation results show better damping performance from the combined damping method.

EXPERIMENTAL STUDY OF DAMPED OSCILLATIONS OF A TORSIONAL PENDULUM

A laboratory work methodic on the experimental study of damping torsion oscillations under educational laboratory conditions was developed in this article. A torsion pendulum, which is usually used for bullet flight speed experimental determination based on angular momentum, mechanical energy conservation laws, and the laws of natural oscillations patterns, was used for this purpose. A torsion pendulum is a rod suspended on a vertically stretched steel wire and capable of performing oscillatory motion in the horizontal plane. Two rectangle shaped bodies are attached at the rod's ends, also two identical cylindrical weights that can be moved, changing the inertia moment of the pendulum, and locked in a chosen position, are arranged on the steel rod. Damping parameter dependencies are studied: the damping coefficient, damping logarithmic decrement, relaxation time, amount of oscillations during relaxation and the mechanical system quality factor against pendulum inertia moment. The least squares method was used in the processing of the experimental results. The results from this experimental study prove theoretical dependencies fidelity. The method used in this study may be recommended for physical practicum at universities when there is not a finished installation for the damping of torsional oscillations.

Measurement of the Kinematic Viscosity of Melted Mixtures of Sodium, Lithium, and Beryllium Fluorides and the Effect of the Eutectic Additive Cerium Trifluoride on the Viscosity

Experimental data on the kinematic viscosity and liquidus temperature of certain fused mixtures of sodium, lithium, and beryllium fluorides were obtained, by the method of damping of torsional oscillations of a cylinder with the experimental melt, in validation of the concept of molten-salt incinerator reactors for incinerating transuranium elements from spent nuclear fuel from light-water reactors. The measurements were conducted from the liquidus temperature to 800°C. The effect of the addition of cerium trifluoride on the viscosity of the eutectic melt 58NaF–15LiF–27BeF2 was studied. It was shown that the additive appreciably reduces the viscosity at low temperature and also lowers the liquidus temperature. The parameters characterizing the temperature dependence of viscosity were determined for the experimental melts.

Conventional and fuzzy PODCs for DFIG‐based wind farms and their impact on inter‐area and torsional oscillation damping

Contribution to the damping of inter-area and torsional oscillation modes, in doubly fed induction generators (DFIG) based wind farms, by power oscillation damping controllers (PODCs) based on two conventional structures and a fuzzy control strategy is investigated in this study. In this regard, a PODC with no lead/lag compensation is designed first and then a PODC with one lead/lag block is developed using eigenvalue techniques and the application of an iterative process based on the bat optimisation algorithm (BOA). Moreover, a fuzzy PODC, based on a simple fuzzy controller and tuned with the BOA according to the system transient response under a critical perturbation, is also designed. Comparative performance of the three PODCs is evaluated on a multi-machine power system. It is observed that all three PODCs can contribute to improving the damping of inter-area oscillations. However, eigenvalue analysis and non-linear time domain simulations reveal that each of them may also impact to a lesser or greater extent the shaft torsional oscillation mode damping. Their relative impact in this regard is also investigated.

Effect of PODCs for DFIG Based Wind Farms in the Inter-area and Torsional Oscillation Damping

The damping contribution to inter-area and torsional oscillation modes of two power oscillation damping controllers (PODCs) in doubly-fed induction generators based wind farms is investigated in this paper. On one side, a no lead/lag compensation PODC is designed through eigenvalue analysis. On the other side, a PODC with lead/lag compensation is developed with the inclusion of an iterative process based on the bat optimization algorithm. Despite that both PODCs can effectively improve the damping of inter-area oscillations in this work, results from eigenvalue analysis and nonlinear time domain simulations of a sample multimachine power system reveal the relative negative impact that both of them may have on the shaft torsional oscillation mode damping.

Fuzzy logic control of SVS for damping SSR in series compensated power system

SUMMARY In this paper, a fuzzy logic-based supplementary controller has been developed for the Static VAR System (SVS) to damp torsional oscillations due to subsynchronous resonance (SSR) in a series compensated power system. The performance of the proposed controller has been tested on the IEEE second bench mark model for SSR studies. Time domain simulation has been carried out in a Matlab/Simulink environment. The results show that the conventional proportional integral voltage controller of SVS is not sufficient to damp SSR torsional oscillations, and significant damping of torsional oscillations has been achieved with the proposed fuzzy logic supplementary controller. Copyright © 2014 John Wiley & Sons, Ltd.

Subsynchronous resonance mitigation using variable‐speed wind energy conversion systems

This work proposes a strategy to mitigate subsynchronous resonance (SSR) in synchronous generators using variable-speed wind energy conversion systems (WECSs) based on full converter wind turbines. A supplementary active and reactive power to be delivered by WECSs located near synchronous generators is designed to reduce the SSR phenomenon. These supplementary signals are calculated using an observer-based controller tuned through an optimal quadratic technique which allows to minimise the WECS control effort, whereas a good torsional oscillation damping is accomplished. The power ratio between the WECS and the synchronous generator, impact on the power quality and communication time-delay requirements are also discussed. The authors compare two control approaches: the first one uses mechanical measurements of the synchronous generator (measures which have high observability of torsional modes), whereas the second one uses voltage measurements at the wind farm connection point. In this way, two control schemes using remote and local measurements are proposed, and advantages and disadvantages of both schemes are presented. The proposed scheme can provide satisfactory torsional damping under a wide range of operating points, avoiding to include dedicated SSR damping equipment, and using the new wind farms installed in the network. Eigenvalue analysis and non-linear time-domain simulations confirm the good performance of the WECS-based SSR damping controller.

Torsional Oscillations of the Anelastic Earth

Summary Tables are calculated which make it possible to determine the periods of torsional oscillations of the Earth for real models, close to the Gutenberg model. Numerical experiments on the influence of not great variations of density, shear modulus and the transverse waves velocities on the periods in the different zones of the Earth are carried out (the zones A, B, C, D), and numerical experiments on the influence of the different distributions of absorption function on the damping of torsional oscillations of the Earth are carried out. A comparison of experimental and theoretical data is made (including damping). Finally, the problems, connected with improvement of initial real models of the Earth, are considered.

On the problem of dynamic damping of torsional oscillations of a machine drive

The efficiency of a Pringle dynamic damper used for suppressing forced and parametric torsional oscillations of a main drive taking into account the variable reduced moment of inertia of the machine and dynamic performance of the electric motor is investigated.

The exploration of the lunar interior using torsional oscillations

The diagnostic capabilities of the torsional oscillations for probing the structure of the interiors of the Moon are investigated. Models with no core, a liquid core, and a solid core are considered. The profiles of compressional and shear wave velocities, V P and V S, for the lunar interior estimated by Bills and Ferrari (J. Geophys. Res. 82 (1977) 1306), Goins et al. (J. Geophys. Res. 86 (1981b) 5061) and Nakamura (J. Geophys. Res. 8 (1983) 677) from the Apollo lunar seismic network are used. For all these models the periods of torsional oscillations for fundamental modes ℓ=2–100 and four overtones have been calculated. The derivatives of the dimensionless eigenfrequency with respect to the dimensionless shear modulus and density are calculated and tabulated for use. These data can be used for the determination of corrections to the model density and shear modulus distributions due to their small change. The damping of torsional oscillations is also studied. Several trial distributions of the dissipative function Q as a function of radius are considered. It is shown, that the torsional modes with ℓ⩾7, n=0 can be recorded. These modes provide information on the external layers down to about 500 km depth.

Hydrodynamic stability of He II periodic boundary layer flows

He II periodic boundary layer experiments on the damping of torsional oscillations of a sphere have been re-analyzed based on recent classical stability theory. We have verified this theory using a torsionally oscillating sphere and an electrochemical visualization scheme in water. We show that macroscopic He II periodic boundary layer flows exhibit instabilities that are described by classical stability criteria if the kinematic viscosity is regarded as the dynamic viscosity over the total fluid density.

The Spectrum of Torsional Oscillations of the Moon

The diagnostic potentialities of the torsional oscillations for probing the structure of the interiors of the Moon are investigated. Models with no core, a liquid core, and a solid core are considered. The profiles of compressional and shear wave velocities VP and VS for the lunar interior estimated by Bills and Ferrari (1977), Goins et al. (1981), and Nakamura (1983) from the Apollo lunar seismic network are used. For all these models, the periods of torsional oscillations for n = 2–100 and four overtones have been calculated. The derivatives of the dimensionless eigenfrequency with respect to the dimensionless shear modulus and density are calculated and tabulated for use. These data can be used to determine corrections to the model density and shear modulus distributions due to their small change. The damping of torsional oscillations is studied. Several trial radial distributions of the dissipative function Q are considered.

Application of STATCOM for damping torsional oscillations in series compensated AC systems

This paper presents the results of a study on the application of the recently developed FACTS device, the static compensator (STATCOM), for the damping of torsional oscillations that occur in a series compensated AC system. The IEEE first benchmark system is considered for this study. In order to suppress unstable torsional mode oscillations, a STATCOM with a PI controller to regulate the bus voltage, and with an auxiliary signal derived from the generator speed deviations is employed at the generator terminal. The eigenvalue analysis technique is used for small signal analysis and optimization of the control system parameters is done through step response studies. In addition, dynamic performance of the nonlinear system with optimized STATCOM controller is evaluated under a three-phase fault. Results from the analytical and digital simulation studies reveal the technical feasibility of using STATCOM for damping of turbine-generator torsional oscillations in series compensated AC systems.

Effect of mode inertia on the analysis of torsional dynamics in series capacitor compensated power systems

The accuracy of mode inertia, determined from manufacturer supplied turbogenerator mechanical data is not well established, but some studies suggest that in certain cases appreciable error may exist. This paper considers the effect of errors in mode inertia values on the prediction of torsional oscillation damping in series capacitor compensated power systems. Both series resonance and parallel resonance are considered using two different test networks from the IEEE Benchmark Models for Subsynchronous Resonance. The results show that, for parallel resonance, mode inertia error does not have a large affect on torsional damping predictions. However, for series resonance, mode inertia error can cause significant error in the prediction of damping for some modes, thus affecting conclusions about the maximum safe amount of series compensation in a network.

Sensor Placement for Driveline Control

Vehicular drivelines can be instrumented with sensors in different locations. Control and damping of torsional oscillations will therefore lead to, depending on sensor location, control problems where the control objective signal is not the same as the measured output signal. It turns out that it is convenient to work with a modified complementary sensitivity function, being modified with a dynamic output ratio. The specific characteristics of a driveline model is analyzed using these concepts, and the consequences for design of feedback controllers are discussed.

DAMPING OF TORSIONAL OSCILLATIONS–A COORDINATED APPROACH

ABSTRACT Damping of torsional oscillations using coordinated control through power system stabilizer (PSS) and thyristor controlled reactor(TCR) is presented in this paper. The PSS has modal speed deviations as its feedback signal. The reactive power control is achieved through thyristor controlled reactor (TCR) at the machine terminals. Generator speed deviation is used as auxiliary signal and terminal voltage feedback signal as main control signal for TCR. The following control strategies have been analysed : a PSS with modal speed control b PSS with modal speeds plus TCR with terminal voltage control c PSS with modal speeds plus TCR with complete controls (voltage feed back signal and generator speed deviation signal) The main objective of this paper is to discuss the modelling aspects and analyse different control strategies for damping torsional oscillations in series compensated ac transmission system. The control parameters like gains and time constants have been obtained by performing repeated eig...

Performance of a shunt reactor controller with non-identical parallel turbogenerators

The damping of torsional oscillations in two parallel generating units using a single common controlled shunt reactor is investigated. The shunt reactance is regulated using either a speed signal from one of the generating units or a combined speed signal from both units. The effect of load differences and torsional mode frequency differences between the units on the performance of a controller designed assuming truly identical units is investigated. Results indicate that for the controller using only a single generator speed signal as input, it is better for the damping of a particular mode to take the input signal from the generator with the higher mode frequency for that mode. When the generator speed signals are combined to form the controller input, then mode frequency differences do not detract from the controller's performance but load differences do.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Damping of torsional oscillations using excitation control of synchronous generator: the IEEE Second Benchmark Model investigation

A simple lead-lag excitation controller using generator shaft speed deviation ( Delta omega ) as a feedback signal to damp all of the IEEE Second Benchmark Model, system-1 torsional oscillations is presented. In order to stabilize all the torsional modes, modal control theory is used to determine the parameters of the dynamic output feedback controller. Various degrees of series compensation, different loading conditions, and torsional mode shapes for a torsional oscillations study are also investigated. In addition, time-domain simulation using a nonlinear system model are examined to demonstrate the effectiveness of the proposed countermeasure under torque disturbance conditions. >