Vibration Monitoring Techniques Research Articles

Fault Detection of Reciprocating Compressors using a Model from Principles Component Analysis of Vibrations

Traditional vibration monitoring techniques have found it difficult to determine a set of effective diagnostic features due to the high complexity of the vibration signals originating from the many different impact sources and wide ranges of practical operating conditions. In this paper Principal Component Analysis (PCA) is used for selecting vibration feature and detecting different faults in a reciprocating compressor. Vibration datasets were collected from the compressor under baseline condition and five common faults: valve leakage, inter-cooler leakage, suction valve leakage, loose drive belt combined with intercooler leakage and belt loose drive belt combined with suction valve leakage. A model using five PCs has been developed using the baseline data sets and the presence of faults can be detected by comparing the T2 and Q values from the features of fault vibration signals with corresponding thresholds developed from baseline data. However, the Q -statistic procedure produces a better detection as it can separate the five faults completely.

Guest Editorial

The eight papers in this special section focus on fractional horsepower electric drives. The section covers a wide range of subjects, namely, machine designs, thermal exchange problems, vibration monitoring, and control techniques.

Vibration time series analysis of bubbling and turbulent fluidization

A non-intrusive vibration monitoring technique was used to study the hydrodynamics of a gas–solid fluidized bed. Experiments were carried out in a 15cm diameter fluidized bed using 226, 470 and 700μm sand particles at various gas velocities, covering both bubbling and turbulent regimes. Auto correlation function, mutual information function, Hurst exponent analysis and power spectral density function were used to analyze the fluidized bed hydrodynamics near the transition point from bubbling to turbulent fluidization regimes. The first pass of the autocorrelation function from one half and the time delay at which it becomes zero, and also the first minimum of the mutual information, occur at a higher time delay in comparison to stochastic systems, and the values of time delays were maximum at the bubbling to turbulent transition gas velocity. The maximum value of Hurst exponent of macro structure occurred at the onset of regime transition from bubbling to turbulent. Further increase in gas velocity after that regime transition velocity causes a decrease in the Hurst exponent of macro structure because of breakage of large bubbles to small ones. The results showed these methods are capable of detecting the regime transition from bubbling to turbulent fluidization conditions using vibration signals.

Novel Dynamic Rotor and Blade Deformation and Vibration Monitoring Technique

Monitoring rotor deformations and vibrations dynamically is an important task for improving both the safety and the lifetime as well as the energy efficiency of motors and turbo machines. However, due to the high rotor speed encountered in particular at turbo machines, this requires concurrently high measurement rate and high accuracy, which is hardly possible to achieve with currently available measurement techniques. To solve this problem, in this paper, we present a novel nonincremental interferometric optical sensor that measures simultaneously the in-plane velocity and the out-of-plane position of laterally moving objects with micrometer precision and concurrently with microsecond temporal resolution. It will be shown that this sensor exhibits the outstanding feature that its measurement uncertainty is generally independent of the object velocity, which enables precise deformation and vibration measurements also at high rotor speed. Moreover, this sensor does not require an in situ calibration and it allows a direct measurement of blade velocity variations in contrast to blade tip timing systems. For application under harsh environmental conditions such as high temperatures, a robust and miniaturized fiber-optic sensor setup was developed. To demonstrate the capability of this sensor, measurements of tip clearance changes and rotor blade vibrations at varying operating conditions of a transonic centrifugal compressor test rig at blade tip velocities up to 600 m/s are presented among others.

Feature Selection and Fault Classification of Reciprocating Compressors using a Genetic Algorithm and a Probabilistic Neural Network

Reciprocating compressors are widely used in industry for various purposes and faults occurring in them can degrade their performance, consume additional energy and even cause severe damage to the machine. Vibration monitoring techniques are often used for early fault detection and diagnosis, but it is difficult to prescribe a given set of effective diagnostic features because of the wide variety of operating conditions and the complexity of the vibration signals which originate from the many different vibrating and impact sources. This paper studies the use of genetic algorithms (GAs) and neural networks (NNs) to select effective diagnostic features for the fault diagnosis of a reciprocating compressor. A large number of common features are calculated from the time and frequency domains and envelope analysis. Applying GAs and NNs to these features found that envelope analysis has the most potential for differentiating three common faults: valve leakage, inter-cooler leakage and a loose drive belt. Simultaneously, the spread parameter of the probabilistic NN was also optimised. The selected subsets of features were examined based on vibration source characteristics. The approach developed and the trained NN are confirmed as possessing general characteristics for fault detection and diagnosis.

Reliability of Adjustable Speed Drives

The reliability of ASDs has improved very much. The resulting MTBF from realistic estimation (which is 44 years) shows an MTBF for standard LV drives that will be acceptable for most applications in the chemical industry where programs such as Improve Reliability, Equipment Justification and Minimization, and Risk-Based Engineering are common. The highest effect in improving the MTBF lays in optimizing the engineering and failure response with respect to thermal overload trips. There is still one more remark to make on reliability. The problem with frequency converters, in situations where production losses and repair costs are very high, such as fans for a furnace, is the inability to monitor the electronics and smoothly shut down the plant before trip occurs. Mechanical equipment, such as a gearbox with all available vibration monitoring techniques, should still have an advantage in these cases.

Adaptive state detection of gearboxes under varying load conditions based on parametric modelling

Conventional vibration monitoring techniques are unable to provide accurate state analysis of a gearbox under varying load condition. This paper proposes a novel technique for state detection of gearbox, which fits a time-varying autoregressive model to the gear motion residual signals applying a noise-adaptive Kalman filter, in the healthy state of the target gear. The optimum autoregressive model order, which provides a compromised model fitting for the healthy gear motion residual signals collected under various load conditions, is determined with the aid of a specific model order selection method proposed in this study. Consequently, a robust statistical measure, which takes the percentage of outliers exceeding the three standard deviation limits is applied to evaluate the state of the target gear, where the standard deviation of autoregressive model residuals takes its maximum in all tested gear motion residual signals for model order selection. The proposed technique is validated using full lifetime vibration data of gearboxes operating from new to failure under four distinct load conditions. The investigated load conditions include: (1) constant load, (2) one jump from 100 to 200% nominal torque level, (3) one jump from 100 to 300% nominal torque level, and (4) constant changed to sinusoidal. In each application, the specific model order selection and comparison of the proposed gear state indicator with three counterparts proposed in recent studies are addressed in detail. The Kolmogorov–Smirnov test is also performed as a complementary statistical analysis. The results show that the proposed technique possesses a highly effective and robust property in the state detection of gearbox, which is independent of varying load condition as well as remarkable stability, early alarm for incipient fault and significant presence of fault effects. The proposed gear state indicator can be directly employed by an on-line maintenance program as a reliable quantitative covariate to schedule optimal maintenance decision for rotating machinery.

Validity of bolt‐removal and gap‐insertion techniques to experimentally simulate the vibration of a cracked rotor

ABSTRACTExperimental studies of the vibration of a cracked rotor are essential in the development of vibration monitoring techniques. The greatest difficulty in conducting experimental parameter studies is the extensive amount of work required when placing a fatigue crack (FC) of known size and location in the structure. Two alternative techniques, the bolt‐removal method (BRM) and the gap‐insertion method (GIM), have been suggested to provide an easy mechanism to experimentally simulate the behaviour of a breathing crack. This study aims to qualitatively and quantitatively evaluate these methods and compare them with the results from a grown FC in a slow rotating drum specimen. Deflection results show good agreement, particularly in the vertical direction. For the horizontal direction the two simulation techniques overestimate the deflection from the FC for large crack sizes. However, overall GIM and BRM provide close enough results to support the usage in experimental parameter studies at significantly lower cost.

Non-contact vibration measurement based on an extrinsic Fabry–Perot interferometer implemented using arrays of single-mode fibres

This paper presents a novel non-contact vibration-monitoring technique based on transient measurements from a Fabry–Perot interferometric displacement sensor implemented using single-mode fibre. Two different extrinsic sensor configurations are demonstrated using one-fibre and two-fibre arrays of 4/125 µm single-mode fibre butted with a gradient-index lens. The design concept, mathematical modelling and results are demonstrated. The sensor configurations exploit fringe discrimination over multiple orders. A working range up to 14 µm is demonstrated for the measurement of vibration amplitude at 1 kHz excitation using the one-fibre configuration. Similar tests using the two-fibre configuration indicated a displacement measurement up to 65 µm and vibration measurement up to 7 µm at 2.5 kHz. The two-fibre configuration is also assessed in conjunction with an absolute scheme for the measurement of vibration using dual-wavelength signal processing. In this scheme, two wavelength signals are captured from the sensing interferometer to provide unambiguous measurement of vibration direction.

Numerical and experimental investigation of free vibration of multilayer delaminated composite beams and plates

The use of vibration-monitoring techniques as non-destructive methods for detection of delaminations in layered composite beam and plate structures is a current field of interest for many researchers. However, an extensive search of published literature shows that information on numerical and especially experimental investigations into the dynamic behaviour of delaminated layered composite beams and plates is limited. For this reason the present authors have developed theoretical models and carried out an extensive experimental investigation to establish changes in the first three bending natural frequencies due to delaminations. The subsequent results of these numerical calculations are consistent with the results of the corresponding experimental investigations.

Overview of Wear Modes and Vibration Monitoring Techniques in Gearbox Systems

The paper presents a review of gear wear modes with the associated vibration monitoring techniques. It highlights the potential and limitations of these techniques and indicates aspects of diagnosis and prognosis that need further attention.

Flexibility monitoring of offshore platforms

Flexibility monitoring has been proposed as an ambient vibration monitoring technique for detecting the occurrence and location of damage on steel jacket offshore platforms. The technique is based on the heuristic observation that the fundamental mode shapes of platforms closely resemble the deflections of a shear beam caused by a concentrated load at its free end in the associated direction. This paper presents a theoretical framework for evaluating the flexibility monitoring concept. Detailed studies are performed with the following three objectives: 1. 1. To investigate the nature of the relationship between the flexibility ratios used in damage detection that are obtained from mode shape measurements and the true flexibility ratios for a structure derived from its stiffness properties. 2. 2. To assess the effects of both random and bias errors arising from inaccuracies in the data measurement systems and parameter estimation algorithms on the reliability of damage detection. 3. 3. To assess through a modal sensitivity analysis: (i) the influence of the structural framing system on the damage detection ability, (ii) the damage detection capability under multiple member failures, and (iii) the ability to discriminate between structural damage and changes in foundation stiffness and structural mass. The paper also includes a brief introductory review of the history of vibration monitoring research in order to provide the necessary perspective within which to view the present development.

Vibration Monitor for Rotating Machines Using Average Frequency Technique

A vibration monitoring technique has been developed which can be applied to continuous monitoring and to patrol checking of many kinds of rotating machines in nuclear power plants. In this method, the vibrating condition in such equipment are represented in terms of two parameters, i.e. a vibration amplitude (RMS value) and an average frequency. The average frequency is defined as the root value of the second moment of the vibration frequency weighted by the power spectrum. The average frequency can be calculated by simple analogue circuits and does not need the spectrum analysis. Using these two parameter, not only the occurrence of abnormal vibration but also the type of vibration can be detected.

Vibration Monitor for Rotating Machines Using Average Frequency Technique

A vibration monitoring technique has been developed which can be applied to continuous monitoring and to patrol checking of many kinds of rotating machines in nuclear power plants. In this method, the vibrating condition in such equipment are represented in terms of two parameters, i.e. a vibration amplitude (RMS value) and an average frequency. The average frequency is defined as the root value of the second moment of the vibration frequency weighted by the power spectrum. The average frequency can be calculated by simple analogue circuits and does not need the spectrum analysis. Using these two parameter, not only the occurrence of abnormal vibration but also the type of vibration can be detected.

Paper 22: Development of Vibration Monitoring Techniques to Aid in Evaluating the Mechanical Performance of Rotating Machinery

Considerable effort has been expended towards improving the thermodynamic performance of rotary air compressors and full advantage has been taken of these advances by modifying the design, installation, or application of the machines in full-scale plant. In large industrial units the economics of operation are demonstrated by the availability of the plant, i.e. time available for production. This reflects directly on the mechanical reliability and, in particular, the means for monitoring the mechanical performance in order to give forward warning of maintenance or adjustment requirements. For this purpose various techniques are in the course of development and this paper deals with the amplification of vibration monitoring equipment of the accelerometer and proximity probe types.