An industrial honking silo was extensively instrumented to examine its wall vibration and acoustic response. Spectral analyses acceleration and acoustic pressure measurements show that honking comprises of a fundamental acoustic frequency and a harmonic series of peaks at integer multiples of the fundamental frequency. The results indicate that the sound is generated by the silo walls acting as large speakers and is not due to resonance inside the silo, as in a flute or organ pipe. The above measurements indicate that during honking the silo vibrates in some of its specific natural modes. Finite element (FE) models are used to examine the free vibration characteristics of the instrumented silo and other silos that are known to honk. Both 3D and axisymmetric models are considered. Considerable attention is focused on the latter as excitations that cause honking are expected to by axisymmetric. In addition closed form solutions on vibration characteristics of thin cylindrical shells are discussed. The latter are used to develop an understanding of free vibration characteristics and to validate the FE models. The FE models of the simple cylindrical shell are transformed to a real silo structure by additions such as roof, hopper and thickness variations and the influence of these implementations is examined. It is found that introduction of hopper and the roof introduces additional modes and thickness variation makes a small change to the natural frequencies. Additionally, the influence of the bulk solid stored in the silo is also considered. The analyses indicate that during honking the stored solid is uncoupled from the shell.

The solid iron rotor body and the metal slot wedges on the rotor form the damper system of a turbogenerator. The damper winding and eddy current effects in the rotor of a synchronous machine are allowed for by the axis impedance functions. The most part of the investigation is devoted to experimental and theoretical study of the nature of the axis impedance functions. For each axis an equivalent circuit is derived, which includes a variable complex impedance Zkd or Zkci to allow for the effect of the eddy currents in the solid iron rotor body. A method of calculating the axis operational impedances of a turbogenerator from the equivalent circuits has been described. Some of the improved methods of determining the axis impedances by the method of frequency response, developed in the college laboratory are used. Some tests have been made on site on a 60-MW and a 30-MW turbogenerator. Extensive experimental work was carried out on a small model machine or "micro-machine", which was fitted with a four-pole solid iron rotor. In a small machine the large pole-pitch to axial length ratio and the slot opening to air-gap length ratio affect the purely theoretical results, which have to be modified by some empirical factors. Tests have demonstrated that the operational impedances of a turbogenerator, with a solid iron rotor, unlike those of an idealised synchronous machine, are inherently non-linear. Due to the non-linearities two distinct classes of non-synchronous operations appear: (a) transient conditions for which the flux reverses, (b) transient conditions for which the flux does not reverse. Suitable approximations are made in deriving equations for the rotor impedances, to suit the particular type of transient conditions. Theoretical results have been compared with test results and a close agreement has been obtained. By applying a suitable approximation the part which relates to the damping effect can be separated from the functions, which relate to the steady state and transient effects. By separating the impedance functions into components, an accurate formula for determining the subtransient component of the three-phase short-circuit current of an unloaded solid iron rotor generator has been derived. The existing methods of calculating the damping torque following transient disturbances

No description available.

No description available.

A study of the expression for the response power spectral density of linear systems to random pressures shows that the response problem essentially reduces to evaluating the joint acceptance of the system with the pressure field. A novel method using a coordinate transformation is presented. This method enables one to determine very simply the joint acceptance of a beam that has arbitrary end constraints with a pressure field that has a spatial-pressure correlation function that is easily described mathematically. The joint acceptance of a simply supported beam with a reverberant acoustic field as a function of mode number and nondimensionalized frequency parameter (beam length/acoustic wavelength) has been computed for the first 16 modes. An engineering approximation for the joint acceptance of a simply supported flat plate with a reverberant acoustic field is obtained from the beam results. The method is also used to determine very simply beam and flat-plate joint acceptance with a turbulent-boundary-layer pressure field and with an acoustic plane wave.

This research describes the application of vibration and structural measurement techniques to ensure rubber to metal bonded spring quality. The use of VibroAcoustic Emission in the manufacturing process in a robust and reliable method is described and together with the use of structural measurement techniques, offers rubber-to-metal spring manufacturers an adaptable and robust set of tools which to assure product conformance and quality. The first technique is capable of detecting cracks, lamination, porosity and inclusions on single-layer, double or single-bonded components. This is made by measurement of the structural response of the product to a knO\Vl1 energy input, and normalising the resulting modal response by a factor proportional to the spring pseudo-static stiffness. The second technique, using Vibro-Acoustic Emission, detects the formation of cracks and disbond during a conventional tensile or shear bond test. The natural micro-void cracking detected can be discriminated from a bond-failure event by using a lower frequency range that uses the dynamic response of the supporting metals as a filter (thus 'vibro-acoustic emission'). This new technique can be used to differentiate between bond ruptures and dynamic Mullins effect noise by the use of data processing filters and optimised test timing. The implementation of a production line test system is described, allowing the analysis of potential enhancements and future improvements to the manufacturing process and the test process.

No description available.

No description available.

No description available.

Future space mission proposals include many large optical structures which must be capable of maintaining high shape accuracy. Typically, dimensional stability of the order of microns must be maintained over distances of tens of meters. In the past, this stability has been achieved by the use of organic composite materials, such as carbon fibre reinforced plastic (CFRP), which are thermally unresponsive, lightweight and stiff. These materials, however, are both expensive and subject to unknown changes in their properties during their space exposure lifetime. Hence, active control allows the use of more conventional engineering materials and the construction of larger and more ambitious structures. In a typical application the two main effects to be controlled are vibrations, due mainly to on-board disturbances, such as torque wheels, and quasi-static disturbances, caused by effects such as temperature gradients or initial lack-of-fit of structural members. This dissertation describes a system which provides 6DOF alignment correction of a payload mounted at the tip of a flexible structure, subject to dynamic and quasi-static disturbances, using a Stewart platform arrangement. The six legs of the platform are formed by a new type of actuator. The actuator uses a stick-slip motion, driven by an inertial mass. The dynamics of the actuator are described and its ability to control both dynamic and quasi-static disturbances is examined, experimentally. The inherently non-linear input-output response of the actuator is quantified and modelled. The flexible structure, used for experimental tests, consists of a pantographic mast. The modal parameters are identified through the use of a numerical model verified by modal tests that have been carried out on the actual structure. Important joint effects are examined and modelled. The modal model is combined with a rigid body model of the Stewart platform to produce a non-linear analytical model of the interaction between the structure and the actuators. This is used to estimate the performance and examine the stability of the closed-loop controlled system.