Nick Lieven - Profile on Academia.edu (original) (raw)
Papers by Nick Lieven
The significant progress in sensing and data processing technology has made monitoring and damage... more The significant progress in sensing and data processing technology has made monitoring and damage detection of engineering structures increasingly attractive. This paper presents a reliable in-situ damage detection technique, which is based upon dynamic analysis of a composite structure using a bonded piezoceramic patches as an actuators and a Scanning Laser Doppler Vibrometer as a sensor. In addition Neural Networks have been considered to be a viable tool for handling the large number of data. A multilayer perceptron (MLP) neural networks, was trained and tested using the slope, the y-intercept of the linear fit of the root mean square of the Frequency Response Function (FRF rms ) and the Deviation of the FRF rms of a candidate composite structure.
The manifestation of mode veering in structural dynamic problems has been the subject of much deb... more The manifestation of mode veering in structural dynamic problems has been the subject of much debate in recent years. Initially regarded as an anomolly occurring predominantly as a result of numerical discretisation errors, it is now recognised as a phenomenon occurring in a wide range of exact analytical solutions. Myriad theoretical studies have explored the characteristics of the behaviour but despite this, supporting experimental data is scarce. A numerical and experimental investigation of mode veering is undertaken here. Structural loading is used to induce striss-stiffening effects in a redundant truss. Geometric nonlinearities are included in a static FE analysis to obtain a tangent stiffness, which is then used in a linear dynamic solution. The eigenvalues and eigenvectors are compared to the experimental data in the vicinity of a mode veering, where the behaviour of the real structure is found to correspond well with the theoretical observations. Practical implications of real-world mode veering are discussed.
Springer eBooks, Jul 6, 2022
Nonlinear Dynamics
Jin-Song Pei ( )
Nomenclature Symbols
Finite element model updating and system identification in symmetric structures is ham-pered by t... more Finite element model updating and system identification in symmetric structures is ham-pered by the inability of the eigenvalues to distinguish between symmetric parameter per-turbations. A typical approach is to employ eigenvectors, or even antiresonances, as updat-ing variables. These tend to be less accurate than the eigenvalue measurements however. In this paper, a method for updating symmetric parameters is presented based on quanti-tative information from the eigenvalues and qualitative information from the eigenvectors. It exploits the effect of eigenvalue curve veering, manifested through modal couplings. The curve veering is measured experimentally by variation of a control parameter. A com-putationally efficient updating scheme is applied, requiring only a single eigensolution at each iteration. Using experimental data the method is shown to be capable of produc-ing a unique solution to a doubly symmetric updating problem. The ideas presented are expected to prove valuable...
Power Grid Time Synchronization for Phase-Sensitive Vibration Measurements
Phase-sensitive vibration measurements, such as those used for modal analysis, require precise ti... more Phase-sensitive vibration measurements, such as those used for modal analysis, require precise time synchronization between sensors. However, current time synchronization approaches often require specialized hardware and may be impractical to use in certain environments. For example, global positioning system (GPS) synchronization requires GPS receivers and line of sight to GPS satellites, making it difficult to implement such systems underground or indoors.
Alarm configuration is one of the main challenges of power generation and associated industries. ... more Alarm configuration is one of the main challenges of power generation and associated industries. The configuration challenge is compounded by machines being operated under variable conditions as a change in operational condition i.e. speed or torque affects the vibration response. Thus, if the data used to determine the alarm and warning threshold levels characterises only limited range of operational conditions a false alarm may be triggered indicating onset of a fault while only the operational regimes have changed. Another possibility is the fault to be masked by change in the operational condition which leads to misdetection. Central to determining the alarm and warning threshold levels is establishing the type of the data distribution. The distributions are usually assumed to be Gaussian even though a number of possible distributions should be considered in the search of the best fit. Incorrect distribution fit may result in sub-optimal alarm configuration. In the present paper...
2017 25th European Signal Processing Conference (EUSIPCO), 2017
This paper proposes an adaptive vibration signal compression scheme composed of a lifting discret... more This paper proposes an adaptive vibration signal compression scheme composed of a lifting discrete wavelet transform (LDWT) with set-partitioning embedded blocks (SPECK) that efficiently sorts the wavelet coefficients by significance. The output of the SPECK module is input to an optimized context-based arithmetic coder that generates the compressed bitstream. The algorithm is deployed as part of a reliable and effective health monitoring technology for machines and civil constructions (e.g. power generation system). This application area relies on the collection of large quantities of high quality vibration sensor data that needs to be compressed before storing and transmission. Experimental results indicate that the proposed method outperforms state-of-the-art coders, while retaining the characteristics in the compressed vibration signals to ensure accurate event analysis. For the same quality level, up to 59.41% bitrate reduction is achieved by the proposed method compared to JPEG2000.
Dynamic Data Driven Modeling of Aero Engine Response
Model Validation and Uncertainty Quantification, Volume 3, 2020
Journal of Vibration and Acoustics, 2004
The significant progress in sensing and data processing technology has made monitoring and damage... more The significant progress in sensing and data processing technology has made monitoring and damage detection of engineering structures increasingly attractive. This paper presents a reliable in-situ damage detection technique, which is based upon dynamic analysis of a composite structure using bonded piezo-ceramic patches as actuators and a Scanning Laser Doppler Vibrometer as a sensor. In addition, Neural Networks have been considered to be a viable tool for handling the large number of data. A multilayer perceptron (MLP) neural networks, was trained and tested using the slope, the y-intercept of the linear fit of the root mean square of the Frequency Response Function FRFrms and the Deviation of the FRFrms of a candidate composite structure.
50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2009
48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2007
An Introduction to Damage Prognosis
Damage Prognosis, 2005
48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2007
The finite element model is the main tool used by helicopter manufacturers for the analysis of he... more The finite element model is the main tool used by helicopter manufacturers for the analysis of helicopter structures. The particular application addressed in this paper is for the prediction of vibration. High fidelity models that can accurately represent the structural dynamics are the key to producing effective low vibration designs. Helicopters with 'jet' smooth comfort are demanded by discriminating customers who also require ownership of vehicles with high reliability, low maintenance and reduced through life costs.
Rotor Vibration Reduction Using an Embedded Spanwise Absorber
Journal of the American Helicopter Society, 2012
This paper examines the effectiveness of an embedded spanwise Coriolis absorber in a rotor blade ... more This paper examines the effectiveness of an embedded spanwise Coriolis absorber in a rotor blade in reducing the in-plane vibratory hub loads. Simulations based on a light, four-bladed, hingeless rotor helicopter similar to the BO-105 showed that in high-speed flight (140 kt), over 85% reductions in both 4/rev longitudinal and lateral hub shears could nominally be achieved using an absorber mass 3% of the blade mass situated at 60% span, oscillating at 3/rev with an amplitude of about 0.03 ft. If the baseline in-plane vibration levels of the helicopter are increased to 0.1–0.12 g, the reduction achieved with the same absorber mass are in the range of 60%–70% while the absorber motion increases to 0.15 ft. The phase of the 3/rev absorber motion is critically important to realizing hub vibration reduction, and the absorber tuning frequency is set to a value close to, but not exactly at 3/rev, to achieve correct phasing. The absorber reduced the 4/rev in-plane hub forces by reducing th...
2011 Annual Meeting of the North American Fuzzy Information Processing Society, 2011
In this work a novel wavelet-fuzzy logic approach to structural health monitoring is proposed bas... more In this work a novel wavelet-fuzzy logic approach to structural health monitoring is proposed based on wavelet transform theory and fuzzy logic technology. The proposed method combines the effectiveness of the Wavelet Packet Transform (WPT) as a tool for feature extraction and the capabilities of fuzzy sets to model vagueness and uncertainty. Two stages of operation are considered: pattern training and health monitoring. Pattern training is concerned with the determination of fuzzy sets based baseline patterns representing health condition states for which training data are available. Health monitoring is concerned with the classification of new data into the different structural health states. This classification problem is solved based on determining degrees of membership values to each one of the previously defined fuzzy patterns. In order to demonstrate the effectiveness and viability of the proposed approach, the method was applied to data collected from an experiment involving repeatedly impact excitations of an aluminum cantilever beam. Different damage cases in the beam where emulated by adding a lumped mass at different locations. The measured vibration response data provided by six accelerometers were analyzed. Results show that the method is effective in classifying the different damage cases.
2011 Annual Meeting of the North American Fuzzy Information Processing Society, 2011
In this paper, a structural damage identification approach is proposed combining adaptive network... more In this paper, a structural damage identification approach is proposed combining adaptive network-based fuzzy inference system (ANFIS) and 2D wavelet transform (2D WT) technologies. The approach is referred to as ANFIS-2D-WT. First, measured structure vibration response signals from multiple sensors are arranged as a 2D image signal. Then, 2D WT is applied with a twofold objective, perform sensor data fusion and work as a feature extractor. After 2D WT is applied, the energy distribution in different frequency bands of the resultant sub-2D signals is calculated. Based on its energy percentage contribution, selected elements of the obtained feature vector are taken as inputs for the ANFIS. The output of the ANFIS is a condition index, which can be a Boolean value (0 or 1) for level 1 damage assessment use (damage detection), or a number of values for level 2 damage assessment use (damage localisation). Provided an ANFIS model is well trained by the available data, it can be used for health monitoring and damage localisation. The proposed approach was applied to the data obtained from an experiment involving a cantilever beam for damage detection and localisation. The testing results show that the method is successful in detecting and classifying structural damage even in the presence of noise.
Noncontacting Excitation and Measurement of Light Structures
Journal of Vibration and Acoustics, 2003
This paper demonstrates a new method of conducting a noncontacting vibration measurement on light... more This paper demonstrates a new method of conducting a noncontacting vibration measurement on light structures. Although laser vibrometry provides a routine method of acquiring response data, the method of achieving noncontacting point excitation of structures remains problematic. This is the primary concern of the paper. There is understandable motivation to develop a viable noncontacting excitation method as exciting methods involve contact thereby altering the structure’s in-situ properties. The method demonstrated in the paper explores the use of focused acoustic excitation. An ellipsoid cavity has been constructed which is designed to emit focused plane wave excitation over an area of 1 in. diameter, thus approximating to point excitation. The paper outlines the design and construction of the ellipsoid shell and discusses the design parameters in relation to the frequency response and footprint of the excitation. The results presented compare measurements acquired via this new me...
Sensing and Data Acquisition Issues for Damage Prognosis
For Aerospace, Civil and Mechanical Systems, 2005
15th International Conference on Adaptive Structures and Technologies (ICAST), 2007
Magnetic fiber reinforced composite material is being developed which utilizes hollow glass fiber... more Magnetic fiber reinforced composite material is being developed which utilizes hollow glass fibers filled with active ferromagnetic material. The resulting material maintains structural integrity as is, providing a possible means of electrical power generation from a dynamically loaded structure. The hollow glass fibers are manufactured in-house using a bespoke fiber drawing facility. Hard magnetic powder materials are introduced into the hollow fiber cores to provide an active ferromagnetic function. The first part of this article discusses the ongoing work to manufacture, characterize, and optimize active magnetic fiber reinforced composite materials. Recent advances in smart material actuators have led to the development of piezoceramic 'patches' that utilize the piezoelectric effect of individual fibers encased in a protective environment. Previously, these patches have been either positioned on the surface or embedded within the structure, disrupting the composite lay-up. The second part of the article outlines a study of the feasibility of embedding piezoelectric fibers directly into a composite lay-up, thereby allowing a composite laminate to deform due to internal actuation. Potential improvements to the work have been identified and future work has been proposed to further understand and maximize the performance of integrated piezoelectric fiber composites.
The significant progress in sensing and data processing technology has made monitoring and damage... more The significant progress in sensing and data processing technology has made monitoring and damage detection of engineering structures increasingly attractive. This paper presents a reliable in-situ damage detection technique, which is based upon dynamic analysis of a composite structure using a bonded piezoceramic patches as an actuators and a Scanning Laser Doppler Vibrometer as a sensor. In addition Neural Networks have been considered to be a viable tool for handling the large number of data. A multilayer perceptron (MLP) neural networks, was trained and tested using the slope, the y-intercept of the linear fit of the root mean square of the Frequency Response Function (FRF rms ) and the Deviation of the FRF rms of a candidate composite structure.
The manifestation of mode veering in structural dynamic problems has been the subject of much deb... more The manifestation of mode veering in structural dynamic problems has been the subject of much debate in recent years. Initially regarded as an anomolly occurring predominantly as a result of numerical discretisation errors, it is now recognised as a phenomenon occurring in a wide range of exact analytical solutions. Myriad theoretical studies have explored the characteristics of the behaviour but despite this, supporting experimental data is scarce. A numerical and experimental investigation of mode veering is undertaken here. Structural loading is used to induce striss-stiffening effects in a redundant truss. Geometric nonlinearities are included in a static FE analysis to obtain a tangent stiffness, which is then used in a linear dynamic solution. The eigenvalues and eigenvectors are compared to the experimental data in the vicinity of a mode veering, where the behaviour of the real structure is found to correspond well with the theoretical observations. Practical implications of real-world mode veering are discussed.
Springer eBooks, Jul 6, 2022
Nonlinear Dynamics
Jin-Song Pei ( )
Nomenclature Symbols
Finite element model updating and system identification in symmetric structures is ham-pered by t... more Finite element model updating and system identification in symmetric structures is ham-pered by the inability of the eigenvalues to distinguish between symmetric parameter per-turbations. A typical approach is to employ eigenvectors, or even antiresonances, as updat-ing variables. These tend to be less accurate than the eigenvalue measurements however. In this paper, a method for updating symmetric parameters is presented based on quanti-tative information from the eigenvalues and qualitative information from the eigenvectors. It exploits the effect of eigenvalue curve veering, manifested through modal couplings. The curve veering is measured experimentally by variation of a control parameter. A com-putationally efficient updating scheme is applied, requiring only a single eigensolution at each iteration. Using experimental data the method is shown to be capable of produc-ing a unique solution to a doubly symmetric updating problem. The ideas presented are expected to prove valuable...
Power Grid Time Synchronization for Phase-Sensitive Vibration Measurements
Phase-sensitive vibration measurements, such as those used for modal analysis, require precise ti... more Phase-sensitive vibration measurements, such as those used for modal analysis, require precise time synchronization between sensors. However, current time synchronization approaches often require specialized hardware and may be impractical to use in certain environments. For example, global positioning system (GPS) synchronization requires GPS receivers and line of sight to GPS satellites, making it difficult to implement such systems underground or indoors.
Alarm configuration is one of the main challenges of power generation and associated industries. ... more Alarm configuration is one of the main challenges of power generation and associated industries. The configuration challenge is compounded by machines being operated under variable conditions as a change in operational condition i.e. speed or torque affects the vibration response. Thus, if the data used to determine the alarm and warning threshold levels characterises only limited range of operational conditions a false alarm may be triggered indicating onset of a fault while only the operational regimes have changed. Another possibility is the fault to be masked by change in the operational condition which leads to misdetection. Central to determining the alarm and warning threshold levels is establishing the type of the data distribution. The distributions are usually assumed to be Gaussian even though a number of possible distributions should be considered in the search of the best fit. Incorrect distribution fit may result in sub-optimal alarm configuration. In the present paper...
2017 25th European Signal Processing Conference (EUSIPCO), 2017
This paper proposes an adaptive vibration signal compression scheme composed of a lifting discret... more This paper proposes an adaptive vibration signal compression scheme composed of a lifting discrete wavelet transform (LDWT) with set-partitioning embedded blocks (SPECK) that efficiently sorts the wavelet coefficients by significance. The output of the SPECK module is input to an optimized context-based arithmetic coder that generates the compressed bitstream. The algorithm is deployed as part of a reliable and effective health monitoring technology for machines and civil constructions (e.g. power generation system). This application area relies on the collection of large quantities of high quality vibration sensor data that needs to be compressed before storing and transmission. Experimental results indicate that the proposed method outperforms state-of-the-art coders, while retaining the characteristics in the compressed vibration signals to ensure accurate event analysis. For the same quality level, up to 59.41% bitrate reduction is achieved by the proposed method compared to JPEG2000.
Dynamic Data Driven Modeling of Aero Engine Response
Model Validation and Uncertainty Quantification, Volume 3, 2020
Journal of Vibration and Acoustics, 2004
The significant progress in sensing and data processing technology has made monitoring and damage... more The significant progress in sensing and data processing technology has made monitoring and damage detection of engineering structures increasingly attractive. This paper presents a reliable in-situ damage detection technique, which is based upon dynamic analysis of a composite structure using bonded piezo-ceramic patches as actuators and a Scanning Laser Doppler Vibrometer as a sensor. In addition, Neural Networks have been considered to be a viable tool for handling the large number of data. A multilayer perceptron (MLP) neural networks, was trained and tested using the slope, the y-intercept of the linear fit of the root mean square of the Frequency Response Function FRFrms and the Deviation of the FRFrms of a candidate composite structure.
50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2009
48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2007
An Introduction to Damage Prognosis
Damage Prognosis, 2005
48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2007
The finite element model is the main tool used by helicopter manufacturers for the analysis of he... more The finite element model is the main tool used by helicopter manufacturers for the analysis of helicopter structures. The particular application addressed in this paper is for the prediction of vibration. High fidelity models that can accurately represent the structural dynamics are the key to producing effective low vibration designs. Helicopters with 'jet' smooth comfort are demanded by discriminating customers who also require ownership of vehicles with high reliability, low maintenance and reduced through life costs.
Rotor Vibration Reduction Using an Embedded Spanwise Absorber
Journal of the American Helicopter Society, 2012
This paper examines the effectiveness of an embedded spanwise Coriolis absorber in a rotor blade ... more This paper examines the effectiveness of an embedded spanwise Coriolis absorber in a rotor blade in reducing the in-plane vibratory hub loads. Simulations based on a light, four-bladed, hingeless rotor helicopter similar to the BO-105 showed that in high-speed flight (140 kt), over 85% reductions in both 4/rev longitudinal and lateral hub shears could nominally be achieved using an absorber mass 3% of the blade mass situated at 60% span, oscillating at 3/rev with an amplitude of about 0.03 ft. If the baseline in-plane vibration levels of the helicopter are increased to 0.1–0.12 g, the reduction achieved with the same absorber mass are in the range of 60%–70% while the absorber motion increases to 0.15 ft. The phase of the 3/rev absorber motion is critically important to realizing hub vibration reduction, and the absorber tuning frequency is set to a value close to, but not exactly at 3/rev, to achieve correct phasing. The absorber reduced the 4/rev in-plane hub forces by reducing th...
2011 Annual Meeting of the North American Fuzzy Information Processing Society, 2011
In this work a novel wavelet-fuzzy logic approach to structural health monitoring is proposed bas... more In this work a novel wavelet-fuzzy logic approach to structural health monitoring is proposed based on wavelet transform theory and fuzzy logic technology. The proposed method combines the effectiveness of the Wavelet Packet Transform (WPT) as a tool for feature extraction and the capabilities of fuzzy sets to model vagueness and uncertainty. Two stages of operation are considered: pattern training and health monitoring. Pattern training is concerned with the determination of fuzzy sets based baseline patterns representing health condition states for which training data are available. Health monitoring is concerned with the classification of new data into the different structural health states. This classification problem is solved based on determining degrees of membership values to each one of the previously defined fuzzy patterns. In order to demonstrate the effectiveness and viability of the proposed approach, the method was applied to data collected from an experiment involving repeatedly impact excitations of an aluminum cantilever beam. Different damage cases in the beam where emulated by adding a lumped mass at different locations. The measured vibration response data provided by six accelerometers were analyzed. Results show that the method is effective in classifying the different damage cases.
2011 Annual Meeting of the North American Fuzzy Information Processing Society, 2011
In this paper, a structural damage identification approach is proposed combining adaptive network... more In this paper, a structural damage identification approach is proposed combining adaptive network-based fuzzy inference system (ANFIS) and 2D wavelet transform (2D WT) technologies. The approach is referred to as ANFIS-2D-WT. First, measured structure vibration response signals from multiple sensors are arranged as a 2D image signal. Then, 2D WT is applied with a twofold objective, perform sensor data fusion and work as a feature extractor. After 2D WT is applied, the energy distribution in different frequency bands of the resultant sub-2D signals is calculated. Based on its energy percentage contribution, selected elements of the obtained feature vector are taken as inputs for the ANFIS. The output of the ANFIS is a condition index, which can be a Boolean value (0 or 1) for level 1 damage assessment use (damage detection), or a number of values for level 2 damage assessment use (damage localisation). Provided an ANFIS model is well trained by the available data, it can be used for health monitoring and damage localisation. The proposed approach was applied to the data obtained from an experiment involving a cantilever beam for damage detection and localisation. The testing results show that the method is successful in detecting and classifying structural damage even in the presence of noise.
Noncontacting Excitation and Measurement of Light Structures
Journal of Vibration and Acoustics, 2003
This paper demonstrates a new method of conducting a noncontacting vibration measurement on light... more This paper demonstrates a new method of conducting a noncontacting vibration measurement on light structures. Although laser vibrometry provides a routine method of acquiring response data, the method of achieving noncontacting point excitation of structures remains problematic. This is the primary concern of the paper. There is understandable motivation to develop a viable noncontacting excitation method as exciting methods involve contact thereby altering the structure’s in-situ properties. The method demonstrated in the paper explores the use of focused acoustic excitation. An ellipsoid cavity has been constructed which is designed to emit focused plane wave excitation over an area of 1 in. diameter, thus approximating to point excitation. The paper outlines the design and construction of the ellipsoid shell and discusses the design parameters in relation to the frequency response and footprint of the excitation. The results presented compare measurements acquired via this new me...
Sensing and Data Acquisition Issues for Damage Prognosis
For Aerospace, Civil and Mechanical Systems, 2005
15th International Conference on Adaptive Structures and Technologies (ICAST), 2007
Magnetic fiber reinforced composite material is being developed which utilizes hollow glass fiber... more Magnetic fiber reinforced composite material is being developed which utilizes hollow glass fibers filled with active ferromagnetic material. The resulting material maintains structural integrity as is, providing a possible means of electrical power generation from a dynamically loaded structure. The hollow glass fibers are manufactured in-house using a bespoke fiber drawing facility. Hard magnetic powder materials are introduced into the hollow fiber cores to provide an active ferromagnetic function. The first part of this article discusses the ongoing work to manufacture, characterize, and optimize active magnetic fiber reinforced composite materials. Recent advances in smart material actuators have led to the development of piezoceramic 'patches' that utilize the piezoelectric effect of individual fibers encased in a protective environment. Previously, these patches have been either positioned on the surface or embedded within the structure, disrupting the composite lay-up. The second part of the article outlines a study of the feasibility of embedding piezoelectric fibers directly into a composite lay-up, thereby allowing a composite laminate to deform due to internal actuation. Potential improvements to the work have been identified and future work has been proposed to further understand and maximize the performance of integrated piezoelectric fiber composites.