Torsional Vibration Monitoring Research Articles

The risk matrix application to assess the installation of torsional vibration monitoring systems on ships

According to statistics, the number of accidents related to the failures of ship engine and propulsion systems remains in second place among the total number of accidents. One of the reasons for the destruction of diesel crankshafts, intermediate and propeller shafts, elastic couplings and other elements of shaft lines are torsional vibrations in combination with other types of fluctuations and vibrations. The main method for monitoring the level of torsional vibrations in ship’s shaft lines remains periodic torsiography or strain measurement. The widespread introduction of diagnostic and control systems on ships leads to the technical possibility of constant monitoring of the level of torsional vibrations, which will allow you to reduce the risks of accidents in the periods between torsiography. Like any new technical solution, the introduction of torsional vibration monitoring systems requires a scientific justification of the need for their application, which can be carried out with using risk theory. The results of applying the risk matrix to justify the installation of torsional vibration monitoring systems in marine propulsion systems are presented in the paper. As a result, a risk matrix with quantitative parameters is obtained to justify the installation of torsional vibration monitoring systems and reduce the risks of ship’s shaft line breakdowns. As an example, the application of the risk matrix for “OT” type tugs, which are widely used for various operations on the Russian waterways, is considered. It is established that for these types of vessels, the use of a monitoring system will be justified to reduce the risks of accidents, serious accidents and catastrophes that may arise from the development of dangerous torsional vibrations. A method for applying the assessment of the damage degree from an accident occurrence to determine the reduction of economic costs when using torsional vibration monitoring systems is proposed in the paper. It is found that for the “OT” type tugs, the installation of torsional vibration monitoring systems will be justified, both from the point of view of economics and reducing the accidents risks of ship engine and propulsion systems.

Экономическая эффективность применения систем мониторинга крутильных колебаний на судах

A torsional vibration monitoring system is being investigated, and an assessment of the economic efficiency of its implementation on ships is made. A schematic diagram of the torsional vibration monitoring system is illustrated and a photograph of an experimental sample of the monitoring system is provided. An assessment of the economic efficiency of the implementation of torsional vibration monitoring systems on ships is being carried out to prevent the occurrence of emergency situations with marine propulsion systems. The rules of classification societies, scientific and technical literature in the field of torsional oscillations and industrial economics, and the authors' own research were used as materials. The methods used are analysis and computational experiment. Data on the economic costs of the shipowner in the event of emergency situations in case of fatigue failures of elements of ship's engine and propulsion systems were obtained. An assessment of the costs for the development, installation and maintenance of a torsional vibration monitoring system on ships was made; as well as an approximate assessment of the volume of the Russian domestic market for installation and maintenance of torsional vibration monitoring systems on ships. It is noted that the cost of the consequences of propeller shaft failures ranges from several million to tens of millions of rubles. It is concluded that the development and implementation of torsional vibration monitoring systems will reduce the cost of the shipowner for a routine assessment of the technical condition of torsional vibration dampers and reduce the risks of costly accidents with shipboard engine complexes.

EXPERIMENTAL EVALUATION OF THE ANTIVIBRATOR TECHNICAL CONDITION

One of the key problems that have developed today in the fleet during the operation of ships is the termination of supplying products from leading foreign manufacturers of dampers and antivibrators of torsional vibrations, which ensure the safe operation of critical elements of the engine complex. Also, the next confirmation of relevance is the fact that there are no maintenance service centers on the territory of the Russian Federation, nor specialists who carry out the defection and repair of such devices. The results of experimental studies to assess changes in the technical condition of the antivibrator, which is the driven part of the clutch disc of a well-known foreign manufacturer for a KAMAZ truck, at the laboratory stand of the Marine Technology Service testing center of the Astrakhan State Technical University, are presented in the paper. The purpose of the tests is to evaluate the changes in vibration and torsional vibrations occurring in the elements of the laboratory stand at different states of the damping springs of the antivibrator. It should be noted that this device is used on YAMZ-236 engines, which is convertible on the ship. The change in the technical condition of the antivibrator is ensured by a complete limitation of the stroke (jamming) of the damping springs. Mechanical jamming is performed sequentially for each spring package and by measuring tangential stresses in the shaft of the laboratory stand and vibration acceleration on the bearing assembly rack. To conduct the experiments, the measuring base of the test center, including a torsional vibration monitoring system, a 1st class vibrometer, an Ecophysics-110 spectrum analyzer, etc., is used. It has been experimentally established that when the free travel of the damping springs of the anti-vibrator is completely limited, tangential stresses in the shaft and vibrations on the bearing assembly of the laboratory stand increase. It is also determined that the average tangential stresses in the shaft are more effective in terms of the criterion for diagnosing the antivibrator technical condition than the maximum stresses. The most informative for antivibration diagnostics are the octave frequencies of 4, 63 and 125 Hz, at which there is a significant change in vibration acceleration along all three axes X, Y, Z, depending on the number of jammed springs. The accumulation of theoretical and practical research in this area, in the future, may lead to the development of a methodology for the non-selective assessment of the technical condition of ship mechanical dampers and antivibrators of torsional vibrations.

Advanced turbine generator torsional vibration evaluation method using Kalman filtering

Turbine generator torsional vibration is becoming a major concern in modern power grids with a high level of changeability due to the operation of renewable energy sources. The traditional absence of standard torsional vibration monitoring and a lack of experience with the operation of torsional vibration monitoring systems opens up a wide range of opportunities for the design of torsional vibration monitoring systems and the possibility of their installation in power plants. As the measured signals are adversely affected by noise, proper filtering is essential for capturing the torsional vibration information. The benefits of the designed Kalman filtering method are the computational efficiency and the possibility of tackling two different types of noise: the state noise and the measurement noise. The feasibility of the proposed method is demonstrated by case studies based on practical signals measured on steam turbine generators.

A relative torsional vibration monitoring method for intelligent ships and associated error analysis

In this era of rapidly developing transport technology, shipping accounts for two thirds of the total international trade and transport industry. Nowadays, 'ship intelligence' is an important avenue to pursue in the development of the shipping industry and it requires ships and their working machinery to undergo real-time and high-precision inspection and diagnoses of their operational state. This paper develops a simple method for monitoring relative torsional vibration using multiple measuring points, which is suitable for the monitoring of intelligent ship rotating machinery. A proof-ofprinciple prototype is also designed to verify whether this calculational method can achieve clearer and more accurate physical significance and engineering practicability compared with the traditional single-point measuring method. According to the test results, under the condition of 100 pulses per revolution and at a speed of less than 3000 r/min, the relative error of speed measurement of the proof-of-principle prototype is within ±0.011%, which is close to the theoretical maximum accuracy of a 54 MHz sampling rate. The measurement result for the relative torsional angle shows that the maximum error is less than 0.17 mrad, the relative error is less than 1.75% and the maximum error in the amplitudes of the first and third harmonics is 9 mdeg. These accuracies are higher than those of the traditional method, which are 2.62% and 12 mdeg, respectively, in this study. Under the condition of speed fluctuations and rolling vibration, distortion occurs in the time-domain and frequency-domain torsional angle curves when the single-point measuring method is adopted. With the multi-point measuring method, much more accurate measurement values of the torsional angle are acquired compared with the single-point measuring method and accurate time-domain and frequency-domain curves are also obtained. Finally, the health status of the torsional angle is evaluated using an intelligent dynamic alarm system with a torsional vibration threshold, which has a better evaluation effect in line with the engineering practice and specification requirements. Therefore, this simple multi-point relative torsional vibration inspection method has universal applicability and wide application value.

Research on torsional vibration monitoring system of ship power shafting

In this paper, the real-time monitoring technology of ship power system torsional vibration is studied. The photoelectric non-contact measurement method is used to measure the torsional vibration intensity of shafting, and the analysis service network management platform is established to realize the functions of real-time monitoring of shafting torsional vibration and upload and collect alarm data, through the front-end system, the torsional vibration strength and other parameters of the shafting are collected and transmitted to the background. The data of the background system is used to calculate and analyze, and the status of the shafting is alarmed. The system realizes continuous monitoring and data recording of torsional vibration index of ship power system, and ensures the operation performance and safe operation of ship power system. It provides theoretical and technical support for the future development of new technologies and related research, such as durability simulation and durability virtual test of ship power critical parts.

Torsional Vibration Extraction of Dual-Period Instantaneous Angular Speed Measurement of the Generalized Incremental Encoder

Abstract Torsional vibration is key information in monitoring the condition of the shaft system. Using the vector superposition principle, the relationship between the rotation motion and the torsional vibration of the shaft is analyzed. This paper proposes a generalized incremental encoder model and constructs a piecewise function to describe the principle of the pulse output type speed measuring device. The incremental encoder uses a fixed angular increment to stamp the time component of the angular motion of the shaft, thereby establishing a discrete relationship between the angular motion of the shaft and the time component. The relationship between the angular resolution of the encoder and the torsional vibration signal sampling theorem is deduced. The asymmetric under-sampling of the torsional vibration signals is explained from the perspective of signal sampling. According to the index period invariance of the reconstruction of the encoder disk angle sequence, a dual-period instantaneous angular speed (IAS) calculation method is proposed, which uses all the time stamps, avoiding the sampling bandwidth idle caused by the single-period method, causing the torsional vibration signal to obtain more detailed information, and its analysis bandwidth is twice that of the single-period method. Simulation and experiment verified the correctness and superiority of the research content. Finally, the calculation method was packaged as a functional module and embedded in an online torsional vibration monitoring device applied to two 1000 Mw nuclear power turbine generator sets.

Torsional vibration characteristics and experimental study of cracked rotor system with torsional oscillation

Root causes of numerous crack failures are attributed to the torsional oscillation between the turbine generator and the grid. To prevent such kind of failures, torsional vibration monitoring system has been intensively installed in reality and the torsional vibration is more and more observed in the operation. However, the mechanism of the characteristics of torsional vibration of the rotor system with and without cracks has not been well explored. Therefore this work presents the dynamic analysis and experimental study on the rotor system with transverse and slant cracks. For simulating the torsional oscillation in reality, excitation device is designed in the experiments and torsional vibration is measured. Based on this, the characteristics of lateral and torsional vibration of the rotor system are compared. The results show that, (i) although the slant crack presents more significant later-torsional vibration (especially for the breathing crack), the transverse cracked rotor system show higher amplitudes in the fundamental frequency and harmonic components (especially for the open crack) and (ii) the torsional excitation introduces more obvious vibration fluctuation in the rotor system with cracks (observed from the orbits and the torsional vibration).

Lateral and Torsional Vibration Monitoring of Multistack Rotor Induction Motors

In this article, both the lateral and torsional vibrations in multistack rotor induction motors (IM) are modeled in the same framework, and the corresponding precursors in the current waveform are analyzed in detail. Due to the very large rotor length-to-diameter ratio, rotor vibrations can become a major issue in these types of high-torque motors. In order to monitor the vibration components, the lumped mass-spring model for the rotors and couplings is developed to calculate the natural frequencies and torsional-mode shapes of the mechanical system. To model the electrical part, stator windings are split up into several identical windings that are connected in series and correspond to each rotor stack. Since the torsional vibration does not remarkably affect the winding symmetry, the dq model for each section is sufficient to describe the motor behavior during torsional oscillation. Similarly, for the lateral vibration, the mechanical system is modeled in all lateral directions and all modes. Due to the loss of symmetry, the abc model is used for each rotor and stator. In this modeling approach, all inductances (self and mutual of stator and rotor and the mutual inductances between the stator and rotor) are needed. To mimic the effect of lateral vibrations on the motor inductances, a new approach is developed using winding function theory. In this model, all inductances are formulated as a function of eccentricity severity and angle, and a new analytical IM model is developed to show the effects of lateral vibration. Finally, the experimental results are presented and compared with the analytical results.

Torsional Vibration Analysis of Shaft in an Induced Draft Fan Due to Variable Frequency Drive

The torsional vibration problem of shaft in an induced draft fan (IDF) caused by frequency conversion driving technology is a result of dynamic electro-mechanical coupling behavior during the energy conversion. Therefore, it is difficult to understand the mechanism of torsional vibration by only analyzing the mechanical structure or the electrical structure. In this paper, eigenvalue structural analysis (ESA) and time-domain transient analysis, which are typically used to examine sub-synchronous resonance (SSR), are employed to resolve this issue. It is difficult to develop a linear model for complex controllers with ESA as ESA can cause certain errors during the linearization and estimation of initial values of equilibrium points. On the contrary, time-domain analysis not only offers a small-step integration technique to simulate a realistic condition but also facilitates transient analysis of complex controllers. Transient analysis has been used to study the influence of elastic parameters of shaft, self-damping coefficients, resistance of the stator side, smooth reactance of the stator side, and voltage-frequency ratio on the control of target frequency converters and cascade multilevel high-voltage frequency converters. In this paper,It is also advised to avoid torsional resonance region with torsional-vibration monitoring during the operation of the system, and stator resistance can be added and the voltage-frequency rate can be adjusted to obtain an integrated control of an active torsional-vibration system.

Diagnostics of Shaft Trains of Large Turbine Sets for Integrity Using Torsional Vibration Measurements

A promising solution to the problem of early detection for the growth of fatigue cracks in shaft trains of large turbine units at nuclear and thermal power stations based on the results of torsional vibration monitoring by the method of time intervals is considered. It has been demonstrated in the laboratory that this method enables us to detect the growth of fatigue cracks in the shafts of rotor systems from a decrease in the value on natural frequencies of torsional oscillations. However, attempts to use it in the industry were not so successful due to a slight influence of fatigue cracks on the values of the natural frequencies of torsional oscillations as compared with the effect of other factors. Nevertheless, the data obtained in the study of torsional oscillations of the shaft train in a turbine installation of an operating 300-MW power unit using a high-precision optoelectronic monitoring system enabled the establishment and consideration of the effect that the turbine operating conditions has on the natural frequencies of torsional oscillations for the first time. A modal finite-element analysis of the turbine installation shaft train’s most dangerous annular fatigue crack, which cannot be detected at an early stage of development using standard or special vibration-monitoring systems during steady state operation of the turbine installation, has been performed. The analysis yielded the dependence of the torsional natural frequencies on the cross-sectional area and location of the fatigue crack. Monitoring of fatigue crack development has been demonstrated to be performed by measuring the natural frequencies of torsional oscillations (or vibrations) during steady state operation of the turbine set considering the effect of its operating conditions.

Instantaneous Rotation Speed Measurement System Based on Variable Reluctance Sensors for Torsional Vibration Monitoring

In this paper, a system for the measurement of the instantaneous speed of rotating parts in turbines is proposed and modeled. The system is based on traditional and widely used variable reluctance sensors often mounted on-board for other purposes. By coupling this sensors with ad hoc rotating target (novel design) and front-end circuit, it is possible to extend the application of this sensor to accurate instantaneous angular speed monitoring, and to exploit it for torsional vibration monitoring or, in general, for the measurement of any other meaningful quantity related to the variation of the angular speed, useful for machine health monitoring and incipient fault diagnosis. The proposed rotating target produces a signal close to the pure sine wave, with the specific purpose of improving accuracy in torsional vibration monitoring. The complete system was modeled, also taking into account the effect of nonidealities in order to evaluate its performance. Experimental results confirm the satisfactory results obtained from simulations, and show the reduction of the magnitude of the higher order harmonics in the output signal spectrum ensuring improved performance for any torsional vibration monitoring assembly employing the proposed system.

Research on Torsional Vibration Monitoring System of Steam Turbine Generator Unit

In order to effectively analyze the torsional vibration characteristics of turbo-generators, this paper designs and implements a torsional vibration monitoring systen via virtual instrumentation technology. The system hardware adopts PXI system. The system software is developed by LabVIEW language. The monitoring system records speed signals from the turbo-generators and extracts directly the total torsional vibration from the speed signals utilizing zero-phase digital filter. It seperates torsional vibration modes from the total torsional vibration and analyzes the corresponding characteristics of each mode. Field tests were conducted in a real power system to verify the performance of the monitoring systemThe results show that the torsional vibration measurement system detects the torsional vibration of turbo-generators accurately and the system fulfills the practical application demands.

Gearbox Damage Diagnosis usingWavelet Transform Technique

Vibration-based schemes are founded on the assumption that vibration signals from gearboxes measured using accelerometers reflect their condition accurately. A large number of vibration based techniques are used to make this reflection. They include various spectral analyses such as traditional Fourier transform, short-time Fourier transform, amplitude phase modulation and time synchronous averaging and non-parametric special estimation. Recently, Wavelet Transform (WT) has been proven to be more suitable for analysis of vibration signals, since most of the time-vibration signals have instantaneous impulse trains and exhibit a transient (non-stationary) nature. This paper uses an adaptive wavelet filter, based on the Morlet wavelet, applied on the torsional vibration data measured from a single-stage gearbox with artificially induced cracks in the gear. This is done to extract some parameters and check their diagnostic behavior in an effort to search for those with the most potential and appropriateness for future health monitoring schemes. The results demonstrate that the adaptive wavelet filter is found to be very effective in detection of symptoms from vibration signals of a gearbox with early tooth cracks. Moreover the influence of crack depth, speed, and load on the wavelet entropy are interduced. Multi-hour tests were conducted and recordings were acquired using torsional vibration monitoring. The transitions in the wavelet entropy values with the recording time were highlighted suggesting critical changes in the operation of the gearbox.

Torsional vibration monitoring platform for turbine generator based on virtual instrument technology

Torsional vibration monitoring platform for turbine generator based on virtual instrument technology

Torsional Vibration Effects on Induction Machine Current and Torque Signatures in Gearbox-Based Electromechanical System

The monitoring of heavy-duty electromechanical systems is crucial for their preventive maintenance planning. In these systems, the mechanical anomalies such as load troubles, great torque dynamic variations, and torsional oscillations lead to shaft fatigue and aging of other mechanical parts such as bearings and gearboxes. In this paper, a gearbox-based electromechanical system is investigated. Initially, a simple gearbox dynamic model is used to show the effects of rotating input, output, and mesh frequency components on the electromagnetic torque and consequently on the stator current signature. By this model, the influence of transmission error, eccentricities of pinion/wheel, and teeth contact stiffness variation is demonstrated for a healthy gearbox. Then, it is shown that the electrical machine can be considered as a torque sensor through electromagnetic torque estimation for torsional vibration monitoring without any extra mechanical sensor. A test-rig based on a 5.5-kW three-phase squirrel-cage induction motor connected to a wound-rotor 4-kW induction generator via a one-stage gearbox has been used to validate the proposed method.

선박용 엔진 진동 분석 및 모니터링 시스템(EVAMOS) 개발에 관하여

Engine builders have separately developed and applied torsional, axial and structural vibration monitoring system on most marine engines. These systems displayed their results for engine or ship operation engineers and were not regularly stored at the hardware of computer. So, the history and trend of various engine and hull vibrations were not supported for preventive maintenance and to protect the failure of these activity or function. The integrated vibration or stress monitoring system(EVAMOS : engine vibration analysis and monitoring system) in marine diesel engine, its accessories and hull structure have been developed by the dynamics laboratory of Mokpo Maritime University during last 3 years. This paper introduces the design conception and ability of commercial software EVAMOS with field data on several actual tests.

A spectral simulation approach to evaluate probabilistic measurement precision of a reactor coolant pump torsional vibration shaft crack monitoring system

A prototype torsional vibration monitoring system has been installed on two reactor coolant pumps at Tennessee Valley Authority Sequoyah Power Plant Unit 1 nuclear reactor for shaft crack monitoring. The system uses a change in torsional natural frequencies as a diagnostic feature since as a crack grows the shaft line torsional dynamics change commensurately. For effective diagnostic monitoring, it is critical to know the inherent feature variation resulting from the instrumentation and data processing. The integrated nature of the prototype hardware/software system and the inaccessibility of the equipment inside the reactor containment building make it impossible to evaluate the measurement capability in a traditional instrumentation chain approach. Hence, a simulation-based evaluation was performed to determine the cumulative effect of the measurement system on the uncertainty in the torsional natural frequency estimation. The identification algorithm operates on the measured torsional spectrum to estimate a natural frequency. All of the inherent measurement and data processing uncertainties ultimately affect the spectrum in some manner. Therefore, if the characteristics of the reactor coolant pump torsional spectrum can be replicated via a model; it can be used to assess the overall prototype system measurement uncertainty. The underlying premise is that the line shaft dynamics remain constant, in the absence of a fault, and hence any natural frequency variation is due strictly to the measurement system uncertainty. To this end, a single degree of freedom simulation model was first developed which matched the natural frequency and damping of a crack sensitive torsional mode in the reactor coolant pump. The model input was carefully selected such that the averaged spectral amplitude and variance from the ensembles matched the measured reactor coolant pump torsional vibration. The model was then used to create one hundred sample responses that replicated pump spectral response in a statistical sense. The same data processing routines used in the prototype system were applied to the simulation data thus creating sample populations of the natural frequency and damping. Statistical tolerance limits containing 99.9% of the sample population with a 99.9% probability were used to quantify the system's measurement uncertainty. The limits for the crack sensitive mode 3 of the reactor coolant pump were (1) natural frequency: ±0.04740 Hz and (2) damping ratio: ±0.00036.

Torsional vibration monitoring apparatus for rotating shaft system

Torsional vibration monitoring apparatus for rotating shaft system

Torsional vibration monitoring method and an apparatus for performing the same

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