| 1. |
- Baissa, Wirtu, et al.
(författare)
-
Vibration-based structural damage identification using wavelet transform
- 2008
-
Ingår i: Mechanical Systems and Signal Processing. - : Elsevier BV. - 1096-1216 .- 0888-3270. ; 22:5, s. 1194-1215
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new damage identification technique based on the statistical moments of the energy density function of the vibration responses in the time-scale (or time-frequency) domain. The continuous wavelet transform is first conducted to decompose the vibration responses into discrete energy distributions as a joint function of time and scale. The principal structural response features are then extracted from the energy density functions using moments. Consequently, the zeroth-order moment (ZOM) known as the total energy of the joint density function is computed at each measurement grid point for the pre-damage and post-damage states and is then implemented for detection and localization of damage in a concrete plate model and in a steel plate girder of a bridge structure. The significant contribution is that the wavelet coefficients are transformed into a new damage identification parameter in the space domain which is considered to be a novel application of the wavelet analysis coefficients. The major advantage is that the time-frequency analysis conducted using the wavelet transform provides a powerful tool to characterize deterministic as well as random (stationary and non-stationary) responses and can be used to detect slight changes in the response characteristics and local variations. Finally, comparison of the results obtained from the proposed method and those obtained from existing non-model-based damage identification techniques shows that the proposed method is more sensitive to damage than these other methods.
|
|
| 2. |
- Ericsson, Stefan, et al.
(författare)
-
Towards automatic detection of local bearing defects in rotating machines
- 2005
-
Ingår i: Mechanical systems and signal processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 19:3, s. 509-535
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we derive and compare several different vibration analysis techniques for automatic detection of local defects in bearings. Based on a signal model and a discussion on to what extent a good bearing monitoring method should trust it, we present several analysis tools for bearing condition monitoring and conclude that wavelets are especially well suited for this task. Then we describe a large-scale evaluation of several different automatic bearing monitoring methods using 103 laboratory and industrial environment test signals for which the true condition of the bearing is known from visual inspection. We describe the four best performing methods in detail (two wavelet-based, and two based on envelope and periodisation techniques). In our basic implementation, without using historical data or adapting the methods to (roughly) known machine or signal parameters, the four best methods had 9-13% error rate and are all good candidates for further fine-tuning and optimisation. Especially for the wavelet-based methods, there are several potentially performance improving additions, which we finally summarise into a guiding list of suggestion.
|
|
| 3. |
- Johnsson, Roger
(författare)
-
Cylinder pressure reconstruction based on complex radial basis function networks from vibration and speed signals
- 2006
-
Ingår i: Mechanical systems and signal processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 20:8, s. 1923-1940
-
Tidskriftsartikel (refereegranskat)abstract
- Methods to measure and monitor the cylinder pressure in internal combustion engines can contribute to reduced fuel consumption, noise and exhaust emissions. As direct measurements of the cylinder pressure are expensive and not suitable for measurements in vehicles on the road indirect methods which measure cylinder pressure have great potential value. In this paper, a non-linear model based on complex radial basis function (RBF) networks is proposed for the reconstruction of in-cylinder pressure pulse waveforms. Input to the network is the Fourier transforms of both engine structure vibration and crankshaft speed fluctuation. The primary reason for the use of Fourier transforms is that different frequency regions of the signals are used for the reconstruction process. This approach also makes it easier to reduce the amount of information that is used as input to the RBF network. The complex RBF network was applied to measurements from a 6-cylinder ethanol powered diesel engine over a wide range of running conditions. Prediction accuracy was validated by comparing a number of parameters between the measured and predicted cylinder pressure waveform such as maximum pressure, maximum rate of pressure rise and indicated mean effective pressure. The performance of the network was also evaluated for a number of untrained running conditions that differ both in speed and load from the trained ones. The results for the validation set were comparable to the trained conditions.
|
|
| 4. |
- Linderholt, Andreas, 1968-, et al.
(författare)
-
Optimizing the informativeness of test data used for computational model updating
- 2005
-
Ingår i: Mechanical systems and signal processing. - : Elsevier. - 0888-3270 .- 1096-1216. ; 19:4, s. 736-750
-
Tidskriftsartikel (refereegranskat)abstract
- In advance of a computational model updating or an error localisation, it can be advantageous to make a preparatory error localisation using data from a nominal analytical model. The purpose is then to select parameters for quantifying model errors and also to design effective tests for determining the best parameter setting. For successful subsequent error localisation, the test data must be informative with respect to the model parameters chosen when such data become available after test. The demand for test data informativeness puts requirements on the experiment with regard to spatial resolution of sensors, bandwidth of excitation, signal-to-noise ratios, etc.Optimising a test design is a huge task, sometimes impossible in practice, due to its combinatorial nature. The number of possible sensor/actuator placement combinations grows rapidly as the number of sensor and actuator candidates increases. For industrial sized problems, finding a sub-optimal solution may be a more realistic target. Such solutions are sought in this work.The aim of this study is to quantify data informativeness, shown to relate to the Fisher information matrix, with respect to physical parameters that are used in error localisation and model updating. Deterministic finite-element models in combination with stochastic noise models are used for assessing data informativeness, and a procedure for test design optimisation with respect to this is devised.
|
|
| 5. |
- Mahata, Kaushik, et al.
(författare)
-
On the estimation of complex modulus and Poisson's ratio using longitudinal wave experiments
- 2006
-
Ingår i: Mechanical systems and signal processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 20:8, s. 2080-2094
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider different least-squares-based approaches for estimating the complex Young's modulus and the complex Poisson's ratio of a viscoelastic material using a longitudinal wave propagation experiment. We present a statistical analysis of different estimation approaches and compare their performances. The analytical covariance expressions are validated using experimental data.
|
|
| 6. |
|
|
| 7. |
- Sjövall, Per, 1977, et al.
(författare)
-
Component system identification and state-space model synthesis
- 2007
-
Ingår i: Mechanical Systems and Signal Processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 21:7, s. 2697-2714
-
Tidskriftsartikel (refereegranskat)abstract
- A scheme for synthesis of subsystem state-space models to be used for analysis of dynamic behaviour of built-upstructures is presented. Using measurements on each component, subsystem models are identified adopting contemporary system identification methods. The subsystem state-space models are transformed into a coupling form, at which kinematic constraints and equilibrium conditions for the interfaces are introduced. The procedure is applied to a plane frame structure, which is built up of two components. It is found that the non-trivial model order determination constitutes a crucial step in the process. If the model order is incorrect at subsystem level, the synthesized model may radically fail to describe the properties of the built-up structure. It is also found that the identified subsystem models need to satisfy certain physically motivated constraints, e.g. reciprocity and passivity. Different approaches and methods to aid the model order determination and the estimation of physically consistent state-space models at subsystem level are discussed.
|
|
| 8. |
- Sjövall, Per, 1977, et al.
(författare)
-
Substructure System Identification from Coupled System Test Data
- 2007
-
Ingår i: Mechanical Systems and Signal Processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 22:1, s. 15-33
-
Tidskriftsartikel (refereegranskat)abstract
- System identification in the context of linear structural dynamics and mechanical vibrations is addressed. Morespecifically, the focus is on large systems built up by components and the identification of its subsystems using test data of the complete system. A method based on reconstruction of the interface forces acting between the unknown subsystem and its neighbour is presented. Theoretical aspects regarding frequency domain load identification are illuminated. The causes and consequences of an ill-conditioned matrix inversion are emphasized. It is shown that the load identification and thus also the subsystem identification is sensitive to the existence of general anti-resonances in the frequency domain of interest. Different methods for validation of an identified subsystem are discussed. Two numerical examples with artificial test data are given to illustrate the procedure: a simple lumped parameter system and a slightly more complex distributed parameter system. The technique is also successfully applied to a physical test setup consisting of a plane frame structure built up from two components.
|
|
| 9. |
- Tatar, Kourosh, et al.
(författare)
-
Laser vibrometry measurements of an optically smooth rotating spindle
- 2007
-
Ingår i: Mechanical systems and signal processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 21:4, s. 1739-1745
-
Tidskriftsartikel (refereegranskat)abstract
- Laser doppler vibrometry (LDV) is a well-established non-contact method, commonly used for vibration measurements on static objects. However, the method has limitations when applied to rotating objects. The LDV signal will contain periodically repeated speckle noise and a mix of vibration velocity components. In this paper, the crosstalk between vibration velocity components in laser vibrometry measurements of a rotating dummy tool in a milling machine spindle is studied. The spindle is excited by an active magnetic bearing (AMB) and the response is measured by LDV in one direction and inductive displacement sensors in two orthogonal directions simultaneously. The work shows how the LDV crosstalk problem can be avoided if the measurement surface is optically smooth, hence the LDV technique can be used when measuring spindle dynamics.
|
|
| 10. |
- Åkesson, Henrik, et al.
(författare)
-
Analysis of dynamic properties of boring bars concerning different clamping conditions
- 2009
-
Ingår i: Mechanical systems and signal processing. - : Elsevier Ltd. - 0888-3270 .- 1096-1216. ; 23:8, s. 2629-2647
-
Tidskriftsartikel (refereegranskat)abstract
- Boring bars are frequently used in the manufacturing industry to turn deep cavities in workpieces and are usually associated with vibration problems. This paper focuses on the clamping properties’ influence on the dynamic properties of clamped boring bars. A standard clamping housing of the variety commonly used in industry today has been used. Both a standard boring bar and a modified boring bar have been considered. Two methods have been used: Euler–Bernoulli beam modeling and experimental modal analysis. It is demonstrated that the number of clamping screws, the clamping screw diameter sizes, the screw tightening torques, the order the screws are tightened has a significant influence on a clamped boring bars eigenfrequencies and its mode shapes orientation in the cutting speed—cutting depth plane. Also, the damping of the modes is influenced. The results indicate that multi-span Euler–Bernoulli beam models with pinned boundary condition or elastic boundary condition modeling the clamping are preferable as compared to a fixed-free Euler–Bernoulli beam for modeling dynamic properties of a clamped boring bar. It is also demonstrated that a standard clamping housing clamping a boring bar with clamping screws imposes non-linear dynamic boring bar behavior.
|
|
