Future railway vehicles are going to be designed lighter in order to achieve higher speed. Suppressing the flexible modes becomes a crucial issue for improving the ride quality of the light-weight high speed railway vehicles. The concept of smart structure brings structural damping to flexible structures by integrating smart actuators and sensors onto the structure. Smart structure eliminates the need for extensive heavy mechanical actuation systems and achieves higher performance levels through their functionality for suppressing the flexible modes. Active secondary suspension is the effective conventional approach for vibration control of the railway vehicle to improve the ride quality. But its ability in suppressing the flexible modes is limited. So it is motivated to combine active structural damping for suppressing the flexible modes and the vibration control through active secondary suspension which has an effect on both rigid and flexible modes. The side-view model of the flexible-bodied railway vehicle integrated with piezoelectric actuators and sensors is derived. The procedure for selection of placement configurations of the piezoelectric actuators and sensors using structural norms is presented. Initial control studies show that the flexibility of the vehicle body will cause a considerable degradation in ride quality if it is neglected in the design model. Centralized and decentralized control strategies with various control approaches (e.g. modal control with skyhook damping, LQG/H2 control, H_infinity control and model predictive control (MPC))are applied for the combined control of active structural damping and active suspension control. The active structural damping effectively suppresses the flexible modes as a complement to the work of the active suspension control.

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No description available.

Variable speed drives employing induction motors have been widely used in industry for decades. Today there is a continually increasing demand for more precise and flexible speed control usually with close attention to energy efficiency. The inverter is used because of its reliability, flexibility and relatively low cost. However its output a.c. voltage is not sinusoidal so the core losses in the induction motors consequently increase. This research is centred on the design and testing of the stator winding configuration of three phase induction motors with various coil pitches and measure the dynamic performance under sinusoidal and PWM supplies. Measurements were carried out to determine the behavior of harmonic losses and the efficiency of four identical three-phase 746 W induction motors with stator coil pitches of 180 , 160 , 140 and 120 . The motors were fed from either a three-phase inverter or a three-phase sinusoidal voltage supply. The switching frequency was varied from 4 kHz to 16 kHz and the modulation frequency was varied between 30 Hz to 60 Hz. Simulations were carried out using OPERA 2D software under sinusoidal voltage supply. The phenomenon of chording by l/n* of pole pitch to suppress the n* harmonic was particularly followed by motors with 120 and 160 coil pitches under sinusoidal voltage supply. This phenomenon was also followed by 120 , 140 and 160 coil pitch motors under PWM voltage supply at all the switching frequencies and modulation * frequencies. The motor with 120 coil pitch showed a drastical increase in the lower order voltage harmonic components with simulation under sinusoidal supply when compared to full pitch motor. The total voltage harmonic distortion due to the third, fifth and ninth harmonics was less for the motor with 120 coil pitch under PWM voltage at higher switching frequencies and under over modulation condition. The efficiency of the same motor was higher at full load and over loads under all the switching frequencies and modulation frequencies. The measurement results and discussion enable motor manufacturers to consider 120 coil pitch motor under PWM voltage supply and 160 coil pitch motor under sinusoidal voltage supply for the 746 W induction motors as the increase in the efficiencies were 12% and 5% respectively when compared to full pitch motor.

Extensive research has been carried out over the years to reduce the acoustic noise resulting from vibration of electromagnetic cores mainly caused by magnetostriction. This project presents the results of a basic experimental study of magnetostriction in strips of magnetic materials commonly used in electromagnetic cores which gives an important new understanding of the phenomenon. The presence of mechanical resonance in the laminations is highlighted here for the first time. A standard magnetising system was built and a new method of measuring magnetostriction was used. A single point laser vibrometer was used to measure magnetostrictive vibration of the samples. The magnetostriction of grain-oriented materials cut at various angles to the rolling direction, non-oriented samples with different silicon content and nickel iron strips was measured over a wide range of magnetising frequencies and at peak flux densities up to 1.O Tesla. Magnetostriction measurement results were used to identify magnetisation induced mechanical resonance of the samples. The magnetising frequency at resonance was derived from the relationship of velocity, frequency and wavelength of an electromagnetically excited strip. Theoretical value of the fundamental resonant frequency and its harmonics were calculated and compared with measured values. The variation of the acoustic noise in a three- phase transformer core under no-load condition with various switching frequencies and different modulation indices was measured under pulse-width modulation and sinusoidal voltage excitation. All measurements were repeated at least five times to assess experimental accuracy and uncertainties. Results suggest that under resonance, transformer cores can produce excessive noise and potentially long term deterioration of lamination coating and possible core failure. Extrapolation of the results to larger cores infer that the phenomenon can possibly occur in cores with different length laminations leading to variability of noise output according to how close the magnetising frequency or predominant harmonics are to the resonant frequency. These findings demonstrate the importance of the interaction between basic magnetostriction and geometrical factors that are contributing towards the total noise output and care that must be taken when characterising the basic magnetostriction of samples of different sizes magnetised at different frequencies.

Transcendental stiffness matrices for vibration (or buckling) analysis have long been available for a range of structural members. Such stiffness matrices are exact in the sense that they are obtained from an analytical solution of the governing differential equations of the member. Hence, assembly of the member stiffnesses to obtain the overall stiffness matrix of the structure results in a transcendental eigenproblem that yields exact solutions and which can be solved with certainty using the Wittrick-Williams algorithm. Convergence is commonly achieved by bisection, despite the fact that the method is known to be relatively slow. Quicker methods are available, but their implementation is hampered by the highly volatile nature of the determinant of the structure's transcendental stiffness matrix, particularly in the vicinity of the poles, which may or may not correspond to eigenvalues. However, when the exact solution exists, the member has a recently discovered property that can also be expressed analytically and is called its member stiffness determinant. The member stiffness determinant is a property of the member when fully clamped boundary conditions are imposed upon it. It is then defined as the determinant of the member stiffness matrix when the member is sub-divided into an infinite number of identical sub-members. Each sub-member is therefore of infinitely small length so that its clamped-ended natural frequencies are infinitely large. Hence the contribution from the member stiffness matrix to the Jq count of the W-W algorithm will be zero. In general, the member stiffness determinant is normalised by dividing by its value when the eigenparameter (i.e. the frequency or buckling load factor) is zero, as otherwise it would become infinite. Part A of this thesis develops the first two applications of member stiffness determinants to the calculation of natural frequencies or elastic buckling loads of prismatic assemblies of isotropic and orthotopic plates subject to in-plane axial and transverse loads. A major advantage of the member stiffness determinant is that, when its values for all members of a structure are multiplied together and are also multiplied by the determinant of the transcendental overall stiffness matrix of the structure, the result is a determinant which has no poles and is substantially less volatile when plotted against the eigenparameter. Such plots provide a significantly better platform for the development of efficient, computer-based routines for convergence on eigenvalues by curve prediction techniques. On the other hand, Part B presents the development of exact dynamic stiffness matrices for three models of sandwich beams. The simplest one is only able to model the flexural vibration of asymmetric sandwich beams. Extending the first model to include axial and rotary inertia makes it possible to predict the axial and shear thickness modes of vibration in addition to those corresponding to flexure. This process culminates in a unique model for a three layer Timoshenko beam. The crucial difference of including axial inertia in the second model, enables the resulting member dynamic stiffness matrix (exact finite element) to be included in a general model of two dimensional structures for the first time. Although the developed element is straight, it can also be used to model curved structures by using an appropriate number of straight elements to model the geometry of the curve. Finally, it has been shown that considering a homogeneous deep beam as an equivalent three-layer beam allows the beam to have additional shear modes, besides the flexural, axial and fundamental shear thickness modes. Also for every combination of layer thickness, the frequencies of the three-layer beam are less than the corresponding frequencies calculated for the equivalent beam model with only one layer, since it is equivalent to providing additional flexibility to the system. However, a suitable combination of layer thicknesses for any mode may be found that yields the minimum frequency. It is anticipated that these frequencies would probably be generated by a single layer model of the homogeneous beam if at least a third order shear deformation theory was incorporated. Numerous examples have been given to validate the theories and to indicate their range of application. The results presented in these examples are identical to those that are available from alternative exact theories and otherwise show good correlation with a selection of comparable approximate results that are available in the literature. In the latter case, the differences in the results are attributable to many factors that vary widely from different solution techniques to differences in basic assumptions.

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No description available.

Excessive human-induced vibrations of assembly structures have been reported more frequently over the past two decades. In the automotive industry, the evaluation of the response of the human body to vibration is an important and active research area due to its significance in design safety. For example, the results of on-going research has led to the establishment of a number of models for predicting the effects of sitting posture, vibration magnitude and direction on the response of the human body when it is exposed to different types of vibration motion. However, research focusing on structural engineering applications remains scarce, leading to inadequate design standards. For example, current structural design guidelines focus on human-induced vertical forces and assume linear structural behaviour, however, the most widely publicized problems have involved horizontal vibrations and many real-life structures are characterized by nonlinear behaviour. Following a brief investigation of vibration perception and comfort for subjects occupying a vibrating rig-structure, this dissertation focuses on human- induced horizontal forces and examines the effect of nonlinear structural behaviour. Dynamic horizontal loads of individuals performing predefined manoeuvres such as swaying and vertical jumping were measured in a laboratory setting. The fundamental force due to swaying occurred at the activity frequency. By contrast, the fundamental horizontal force due to vertical jumping did not always occur at the activity frequency. Furthermore, tests conducted for swaying were used to establish the relationship between the side-to-side force and the velocity of the subject's centre of mass. A customized footswitch system was also developed to monitor synchronization among individuals performing as a group in order to form a crowd loading model. Models of analytic forces were derived based on measured data and used to evaluate structural response by focusing on a finite element model of a demountable grandstand characterized by nonlinear structural behaviour. The frequency spectra of displacement and acceleration responses showed clear peaks at the fundamental and the third harmonic of the swaying force, demonstrating the capability of the horizontal force to excite resonance. The resonant frequency decreased at higher levels of excitation, indicating a reduction in the stiffness due to the onset of nonlinear behaviour. Finally, load cases assuming synchronized and perfectly periodic group forces produced a significantly higher response compared to unsynchronized and imperfect group loads. 11.

The thesis is divided into two parts. Part I describes a new electro-optical method of recording accurately the whirling vibrations of a vertical, centrally loaded shaft under laboratory conditions. The design and analysis of a novel type of regulator is given: this maintains a high degree of calibration accuracy despite short-term and long-term changes of illumination and photocell characteristics. The automatic measurement of shaft speed and frequency by electronic counter and master clock is described; and an electromagnetic method of exciting transverse vibration under small applied loads. In Part II, following a short historical review of the literature, so-called ideal conditions are criticised, particularly as applied.to the assumption of constant shaft speed independent of the characteristics of the prime-mover, and to the practical uncertainty of the exact nature of the end-fixings. Experiments on the natural frequency of transverse vibration under various conditions are described, and the bearings used shown to be a close approximation to free-free fixings. The simple equations of the system are derived and theoretical curves given of amplitude and phase, including a case of non-linear damping. Experimental measurements are compared. Experiments disclose the existence of sub-critical and hyper-critical instability when the torque-speed characteristic of the driving motor is poor. The hypercritical instability or runaway, is simply explained: the sub-critical instability is analysed by deriving the differential equations of the system in full and inserting the initial conditions and the characteristic of the driving motor. These equations are non-linear and their solution is carried out on an analogue computer, although the nature of the equations militates against an accurate result. Experiments are carried out to show that partial suppression of the dangerous vibration in the region of the critical speed may be obtained by means of bearings possessing a non-linear profile and giving rise to a restoring force of the form (ax + bx3), x being the deflection. The form of the response is in accordance with the solution of Duffing's equation and exhibits the 'jump' phenomenon. Several points of detail and a qualitative analogue of a variable stiffness system are discussed in appendices.