1,721,358 research outputs found
An Application of Instantaneous Spectral Entropy for the Condition Monitoring of Wind Turbines
Full text linkFor economic and environmental reasons, the use of renewable energy sources is a key aspect of the ongoing transition to a sustainable industrialised society. Wind energy represents a major player among these natural, carbon-neutral sources. Nevertheless, wind turbines are often subject to mechanical faults, especially due to ageing. To alleviate Operation and Maintenance costs, Vibration-Based Inspection and Condition Monitoring have been proposed in recent times. This research proposes Instantaneous Spectral Entropy and Continuous Wavelet Transform for anomaly detection and fault diagnosis, departing from gearbox vibration time histories. The approach is validated on experimental data recorded from a turbine suffering bearing failure and total gearbox replacement. From a computational point of view, the proposed algorithm was found to be efficient and therefore even potentially applicable for real-time monitoring
The use of frequency ratios to diagnose structural damage in varying environmental conditions
No full textOne of the main problems of damage vibration diagnostics based on the change of natural frequencies of structures is the influence of ambient and operational factors (temperature, humidity, wind, heavy traffic etc.) on natural frequencies. In some cases, this effect is comparable or even more significant than the effect of damage itself and reliable diagnostics of damage becomes problematic. In this paper, the use of the ratios between natural frequencies of different mode shapes is proposed as a characteristic of damage rather than the change of natural frequencies. The study has demonstrated that these ratios are fundamentally unaffected by the environmental and operational factors. Application of the proposed method is illustrated using the examples of the Z24 prestressed concrete bridge and the Sanctuary of Vicoforte. Firstly, an analytical study was performed to calculate the mode shapes and natural frequencies of damaged multi-span beam-like structure taking into account the model of crack-like damage in a hollow concrete beam. The results reveal that, in order to identify local damage of subcritical size, natural frequency data of at least four modes of vibration are necessary. Secondly, the natural frequencies acquired experimentally on the Z24 bridge and Sanctuary of Vicoforte have been used to prove that the ratios between natural frequencies can be a useful diagnostic tool in the field of structural health monitoring
Non-Destructive Techniques for the Condition and Structural Health Monitoring of Wind Turbines: A Literature Review of the Last 20 Years
Full text linkA complete surveillance strategy for wind turbines requires both the condition monitoring (CM) of their mechanical components and the structural health monitoring (SHM) of their load-bearing structural elements (foundations, tower, and blades). Therefore, it spans both the civil and mechanical engineering fields. Several traditional and advanced non-destructive techniques (NDTs) have been proposed for both areas of application throughout the last years. These include visual inspection (VI), acoustic emissions (AEs), ultrasonic testing (UT), infrared thermography (IRT), radiographic testing (RT), electromagnetic testing (ET), oil monitoring, and many other methods. These NDTs can be performed by human personnel, robots, or unmanned aerial vehicles (UAVs); they can also be applied both for isolated wind turbines or systematically for whole onshore or offshore wind farms. These non-destructive approaches have been extensively reviewed here; more than 300 scientific articles, technical reports, and other documents are included in this review, encompassing all the main aspects of these survey strategies. Particular attention was dedicated to the latest developments in the last two decades (2000–2021). Highly influential research works, which received major attention from the scientific community, are highlighted and commented upon. Furthermore, for each strategy, a selection of relevant applications is reported by way of example, including newer and less developed strategies as well
Structural damage detection based on features insensitive to ambient factors
No full textVibration based damage detection usually faces two fundamental problems, namely the low sensitivity to the relatively small but potentially dangerous damage, and the dependence of vibration characteristics of structures on ambient factors (primarily temperature). Indeed, the effect of ambient factors on the vibration characteristics may be more significant than the influence of damage. In such situations, the reliable detection of damage is practically impossible. To solve this problem, the ratios of the natural frequencies for various mode shapes have been used. As the presented investigation reveals, these ratios are independent of the ambient factors and hence can improve substantially the sensitivity and reliability of damage detection. To illustrate the higher efficiency of the proposed ratios applied to damage detection, the analytical model of the reinforced Z24 concrete bridge with the damage of crack type was developed. The natural frequencies of bending vibrations in vertical and horizontal planes at different crack depths and locations were calculated and compared with those measured on the Z24 bridge, demonstrating that the sensitivity of the natural frequencies change and ratios of frequencies for various mode shapes with respect to the size of damage is of the same order. At the same time, as opposed to the change of natural frequencies, the frequency ratios are dependent only on the parameters of damage, which makes them a much more efficient tool for health monitoring of structures operating in variable ambient conditions
Instantaneous Spectral Entropy: An Application for the Online Monitoring of Multi-Storey Frame Structures
Full text linkDamage assessment techniques based on entropy measurements have been recently proposed for the structural health monitoring of civil structures and infrastructures. A quasi-real-time approach, based on the use of instantaneous spectral entropy (ISE) over an uninterrupted stream of data, is discussed here. The methodology is proposed for the detection of sudden damage-related structural changes (more specifically, linear stiffness reductions and nonlinear breathing cracks). The method operates by framing the continuous stream of vibration signals and comparing the single frames to a known baseline. The approach is also suitable for nonstationary signals originating from nonlinearly behaving structures. The procedure is validated on an experimental benchmark: a laboratory-scaled model of a three-storey single-span frame metallic structure. Three different definitions of entropy and six candidate time–frequency/time-scale transforms have been tested to find the optimal settings
A shape sensing methodology for beams with generic cross-sections: Application to airfoil beams
Full text linkThis work presents a shape sensing method capable of handling some geometrical complexities commonly observed in aerospace structures. The method presented is based on the one-dimensional inverse Finite Element Method (1D-iFEM), which is capable of accurately reconstructing structural displacements of beam structures using surface strain measurements. The effects of cross-sectional variation in shear strains due to transverse or torsional loads for any general beam profile is accounted for in this 1D-iFEM formulation. The introduction of these effects allows the use of iFEM for the shape sensing of solid or thin-walled prismatic beams with any general beam profile. The performance of the new method is demonstrated through some example problems of prismatic beams under various static loading scenarios
Explicit formula to estimate natural frequencies of a double-beam system with crack
No full textn the present study, an analytical formula to estimate natural frequencies of a simply supported double-beam system in the presence of open crack is derived. Euler-Bernoulli hypothesis was applied to beams, and Winkler model was used for inner layer. Material properties and cross section geometry of beams could be arbitrary and different from each other. To obtain natural frequencies, Eigenvalue problem solving finally yields an algebraic equation which must be solved numerically and does not show effects of different damage parameters in the explicit form. In this regard, Rayleigh method was applied to derive explicit formulation for natural frequencies. In the case of crack occurrence, the mode shapes of intact beam were modified by adding cubic polynomial functions to represent crack effect. The unknown coefficients of polynomial functions were calculated by using boundary conditions of the system and compatibility conditions at the crack section. Using the obtained admissible functions and Rayleigh method, an explicit formulation was achieved for natural frequencies. The problem one more time was solved using the differential transform method to approve the accuracy of the analytical formulation for the cracked double-beam system. Comparison of analytical and numerical results indicates good accuracy of derived formulation for natural frequencies of the cracked double-beam system
Shape sensing of beams with complex cross-sections using the inverse Finite Element Method
No full textThis paper presents the iFEM formulation for beams with complex cross-sectional profiles having at most one plane of symmetry. As the iFEM has already been successfully used for the shape sensing of beams with circular or rectangular cross sections, this work paves the way for formulating a generalized one-dimensional beam element, applicable for any kind of cross-section. Challenges arising due to the asymmetry of the profile, in regard to sensor placement on the surface of the beam and accurate prediction of transverse shear strain measures from experimental strain measurements are addressed. The new formulation is illustrated with the specific case of a beam with a symmetric airfoil profile (NACA 0016), subjected to symmetrically and asymmetricallyapplied static load conditions
Structural damage detection based on proper orthogonal decomposition: Experimental verification
No full textThe present paper describes a new structural damage detection method based on the monitoring of vibrational properties of the structure. Sensors record the accelerations of several points of the structure. The recorded data are then used to compute the proper orthogonal modes. The comparison between the proper orthogonal modes of the undamaged structure and those of the damaged structure provides information on damage location. Experimental results are presented
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