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Published Articles

The Volume 8, No 2, June 2003

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A New Approach to Diagnostics of the Combustion Process in Diesel Engines using Vibration Measurements Part I: Reconstruction of cylinder pressure from vibration measurements

Grover Zurita Villarroel and Anders Agren


There is a steadily growing demand for reliable, non-invasive measurement methods which can be used to monitor combustion in diesel engines. An effective, non-invasive method would make it possible for those using diesel engines to economically detect malfunctions during combustion. The main objective of this paper is to show how, through reconstruction, it is possible to generate data on combustion parameters, which can then be used for engine diagnostics. The combustion parameters are the maximum cylinder pressure (pmax, ) and the derivative of the pressure rise (dp/da). The idea is based on reconstruction by using the transfer function, TF, from the combustion chamber to the engine surface and the measured vibration response signal of the engine surface. The analysis is based on a non-linear method called complex cepstrum and signal processing techniques. The TFs were modified to fit slightly different situations such as other cylinders of the same engine; where use can be made of symmetry. A new approach based on a new tailor-made window for reconstruction of the cylinder pressure is also presented. A matrix with engine TFs for varying speed and load was obtained. The matrix can be used as a data bank of TFs for reconstruction of the cylinder pressure at different operating conditions. An extensive analysis of the cycle-to-cycle variations was carried out, both for the measured and reconstructed cylinder pressure. The main parameters of the cylinder pressure; the maximum cylinder pressure (pmax, ) and the derivative of the pressure rise (dp/da), are thoroughly examined in order to validate the procedure.

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A New Approach to Diagnostics of the Combustion Process in Diesel Engines using Vibration Measurements Part II: Detection of the start of combustion using reconstructed pressure signals

Grover Zurita Villarroel and Dan Haupt


Part I of this investigation describes the technique of using reconstructed vibration signals to calculate the cylin- der pressure in a diesel engine. This approach uses cepstrum techniques and a newly developed windowing tech- nique (that combines Hanning and exponential windows) to reconstruct the pressure signal from vibration meas- urements. Here, in Part II, this approach is investigated and developed further. The aim in this part is to deter- mine if reconstructed cylinder pressure can be used for detection of the start of the combustion process (SOC) in reciprocating engines. The method customarily used for this type of data capture involves recording of cylinder pressure using pressure transducers mounted on the top of a cylinder head. This method has some obvious disad- vantages; it is intrusive, is inappropriate for the more demanding on-board-conditions, and limited lifetime trans- ducers are expensive when used in a harsh environment A simpler and easier method is the one proposed in Part I of this paper i.e., a non-invasive method based on reconstructed pressure signals. The research conducted in connection with Part I demonstrated that reconstructed pressure signals can be used for heat release rate cal- culations as well as for calculations of the first derivative of cylinder pressure. Furthermore, by using the results obtained, the start of the combustion can be estimated with a reasonable degree of accuracy.

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Vibration Analysis of Skew Plates of Generally Varying Thickness Subjected to Uniaxial In-Plane Forces

Ahmed S. Ashour


The finite strip transition matrix technique is developed for the analysis of flexural vibration of a skew plate of varying thickness subjected to in-plane force. First, convergence studies and comparisons with results available from the literature are reviewed. Second, a parametric study is presented which investigates the influence of the aspect ratio, the skew angle and the tapered ratio on the natural frequencies of skew plates without in-plane forces for different plate configurations. Finally, the influence of the in-plane force on the natural frequencies of such plates is considered. The results presented in this paper confirm the accuracy, generality, and reliability of the above technique.

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Elastic Properties of and Dependence on Microstructure of Phosphate Based Bioactive Glasses

V. Rajendran, A. Nishara Begum, Amany A. El-Kheshen, Fatma H. El-Batal


In recent years, bioactive glasses have gained considerable interest among scientists due to their potential appli- cations, such as in the medical field for the replacement of damaged/diseased body parts. One has to optimise the composition of bioactive glasses for effective bonding with bone/dental applications. The preparation of these glasses with different compositions and the characterisation of their physical, chemical and mechanical properties are essential to improve the bioactivity. Ultrasonic non-destructive characterisation of materials is a unique tool used not only for defect characterisation in industry, but also for materials characterisation over a wide range of temperatures. For the present investigation, bioactive glasses in or near the bioactive region, such as Si-Al-K-Na-B-Ce-Ca-Ba-Ti (P2O5 free), Si-Al-K-Li-Na-Zr-P and Si-Al-Na-Ca-Mg-P systems, have been pre- pared with different compositions by normal melting and annealing techniques. Measurements of ultrasonic ve- locities, both longitudinal and shear, and of attenuation have been made at room temperature with such bioactive glasses for different thermal treatments operated at a fundamental frequency of 5 MHz. Further, frequency- dependent ultrasonic velocity and attenuation measurements were made for different frequencies of longitudinal waves. The frequency-dependent attenuation was fitted into a linear relation . The a=beta*f^N bserved increases in density, velocities and elastic constants of bioactive glasses as a function of thermal treatment temperature in the above bioactive glasses are due to an increase in network bonds per unit volume and not due to structural rearrangement/cross-link changes. The observed results have been found to be useful in optimising the composi- tion of bioactive glasses for suitable biomedical applications.

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Structural Dynamics of Large Space Structures Having Random Parametric Uncertainties

Robert M. Koch


Deployable periodic large space structures have been shown to exhibit high dynamic sensitivity to period- breaking imperfections and uncertainties. These can be brought on by manufacturing or assembly errors, struc- tural imperfections, as well as nonlinear and/or nonconservative joint behaviour. In addition, the necessity of precise pointing and position capability can require the consideration of these usually negligible and unknown parametric uncertainties and their effect on the overall dynamic response of large space structures. This work de- scribes the use of a new design approach for the global dynamic solution of beam-like periodic space structures possessing parametric uncertainties. Specifically, the effect of random flexible joints on the free vibrations of simply supported periodic large space trusses is considered. The formulation is a hybrid approach in terms of an extended Timoshenko beam continuum model, Monte Carlo simulation scheme, and first-order perturbation methods. The mean and mean-square response statistics for a variety of free random vibration problems are de- rived for various input, random joint stiffness probability distributions. The results of this effort show that, al- though joint flexibility has a substantial effect on the modal dynamic response of periodic large space trusses, the effect of any reasonable uncertainty or randomness associated with these joint flexibilities is insignificant.

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A Cancellation Method for Background Noise in Sound and Electromagnetic Environments by Using a Digital Filter for Power State Variables

Akira Ikuta, Mitsuo Ohta


The observed phenomena in real wave motion type environments (sound, vibration, and electromagnetic) are in- evitably contaminated by the background noise of arbitrary distribution and type. Therefore, in order to evaluate a wave motion type environment, it is necessary to establish some estimation methods to remove the undesirable effects of the background noise. In this paper, we propose a digital filter for estimating the power state variable of a specific signal with the existence of background noise of non-Gaussian distribution form. By applying the well-known least-mean-square method for the moment statistics with several orders, a practical method for esti- mating the specific signal is derived. The effectiveness of the proposed theoretical method is experimentally confirmed by applying it to estimation problems in real sound and magnetic field environments.

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Finite Element Modelling and Active Vibration Control of Piezolaminated Plates/Shells

Sudhakar A. Kulkarni and Kamal M. Bajoria


In this paper, a finite element formulation for shell structures containing integrated distributed piezoelectric sen- sors and actuators is presented. Higher-order shear deformation theory is used in the formulation, which incor- porates the warping of the cross section due to transverse shear stresses, and assumes a parabolic shear strain variation over the thickness. The distributed piezoelectric sensor layer monitors the shape deformation due to the direct effect and the distributed actuator layer suppresses the deflection via the converse piezoelectric effect. The static deflection of the bimorph beam is compared with the literature. The active vibration control performance of the piezolaminated curved beam with distributed sensors and actuators and the variation of the damping effect with different gains and actuator coverage are investigated.

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Sound Propagation over Flat Ground with an Impedance Discontinuity

D. Ouis


The problem of sound propagation over a flat plane with a line of impedance discontinuity is considered. The sound excitation source is assumed to be linear and set parallel to the line of impedance discontinuity. The solu- tion to this problem is formulated by considering the plane wave spectrum decomposition of a cylindrical source, this is incorporated in the solution to the problem of plane wave diffraction by a wedge with different face impedances. The propagation over a plane surface is then taken as the special case of a wedge whose angle is equal to 180o. The present solution is, however, a high frequency asymptotic formulation, and comparisons are therefore made with two other available models, approximate also, but using instead a point-like sound source. A practical application of the present study would include the evaluation of the insertion loss of a noise barrier on a ground with different acoustical properties on either side of the barrier. The properties of the sound field above the ground may be studied prior to erecting the noise barrier at the line of impedance discontinuity.

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