Nick Lieven - Academia.edu (original) (raw)

Papers by Nick Lieven

Springer eBooks, Jul 6, 2022

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...

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

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

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

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...

For Aerospace, Civil and Mechanical Systems, 2005

15th International Conference on Adaptive Structures and Technologies (ICAST), 2007

2005 7th International Conference on Information Fusion, 2005

2007 IEEE International Fuzzy Systems Conference, 2007

The Autotaxi system is a safety critical sensor system developed to perform the sensing required ... more The Autotaxi system is a safety critical sensor system developed to perform the sensing required for an autonomous vehicle to drive safely along a dedicated paved guideway network. The host vehicle is equipped with a set of sensors used to detect and track any object of interest in the field of view. In this work a multiple-sensor obstacle identification and fusion approach for the Autotaxi system is proposed. Based on the knowledge about the vehicles, the obstacles to be detected, and the guideway network system, two obstacle classifier systems are designed using the principles of fuzzy logic. In Classifier 1 the classification process is carried out based on the obstacle's width and kind of road in which the host vehicle is navigating. In Classifier 2 the classification process is carried out based on the obstacle's width and height together with the kind of road in which the host vehicle is navigating. Furthermore, as different declarations of identity can be performed by using information from different sensors, a method to fuse these identity declarations is proposed. The viability of the proposed approach is demonstrated through a simulated example. Promising results are reported.