Two major areas were studied in this research to achieve more efficient and optimised method for the prediction of ship motion, and this research has two aims. The first aim was to improve an algorithm of the oscillatory problems for strip theory by means of reducing numerical integration using the desingularised method. A new way of distributing point sources was developed by the author in order to solve the boundary problem on the source distribution. Results showed that desingularsation can be utilised on rounded hull shapes. Although the desingularsation process reduces the computational time, the conventional method is more robust and stable due to the simple source panel distribution. The second aim was an investigation of viscous roll damping of ship motion with the influence of forward velocity, and several numerical simulations were developed in order to support wind-tunnel experimentation. The wind tunnel experimentation was conducted by using a 1.2 m NACA6521 modified cylindrical-bulb model to investigate the viscous effect on the rolling motion of the ship. Since viscous damping was very small under restrictions from the experimental condition, a normal method of collecting data of roll motion, in which a device is physically attached on the bulb model, was not suitable. As a solution, remote sensing was utilised to capture the motion picture by a digital video camera. A visual analysis was then conducted to obtain data of the roll motion of the bulb model inside the wind-tunnel test section. Two different numerical simulations were developed under the hypothesis that the forward velocity influences the boundary layer generation to cause viscous roll damping on the ship model hull. The first numerical simulation uses the energy method to produce damping coefficients, and the second numerical simulation requires solving the motion of equation numerically. It was discovered that the increase of forward velocity results in a linear increase of the viscous damping coefficient. The numerical simulation and experimental data agree closely. Therefore, the theory used to predict the viscous roll damping was shown to be reasonably accurate.

In the last few decades there has been a significant increase in the design strength and performance of different building materials. In particular, new methods, materials and admixtures for the production of concrete have allowed for strengths as high as 100 MPa to be readily available. In addition, the standard manufactured yield strength of reinforcing steel in Australia has increased from 400 MPa to 500 MPa. A perceived design advantage of higher-strength materials is that structural elements can have longer spans and be more slender than previously possible. An emerging problem with slender concrete members is that they can be more vulnerable to loading induced vibration. The damping capacity is an inherent fundamental quantity of all structural concrete members that affects their vibrational response. It is defined as the rate at which a structural member can dissipate the vibrational energy imparted to it. Generally damping capacity measurements, to indicate the integrity of structural members, are taken once the structure is in service. This type of non-destructive testing has been the subject of much research. The published non-destructive testing research on damping capacity is conflicting and a unified method to describe the effect of damage on damping capacity has not yet been proposed. Significantly, there is not one method in the published literature or national design codes, including the Australian Standard AS 3600-2001, available to predict the damping capacity of concrete beam members at the design stage. Further, little research has implemented full-scale testing with a view to developing damping capacity design equations, which is the primary focus of this thesis. To examine the full-range damping behaviour of concrete beams, two categories of testing were proposed. The categories are the 'untested' and 'tested' beam states. These beam states have not been separately investigated in previous work and are considered a major shortcoming of previous research on the damping behaviour of concrete beams. An extensive experimental programme was undertaken to obtain residual deflection and damping capacity data for thirty-one reinforced and ten prestressed concrete beams. The concrete beams had compressive strengths ranging between 23.1 MPa and 90.7 MPa, reinforcement with yield strengths of 400 MPa or 500 MPa, and tensile reinforcement ratios between 0.76% and 2.90%. The full- and half-scale beams tested had lengths of 6.0 m and 2.4 m, respectively. The testing regime consisted of a series of on-off load increments, increasing until failure, designed to induce residual deflections with increasing amounts of internal damage at which damping capacity (logarithmic decrement) was measured. The inconsistencies that were found between the experimental damping capacity of the beams and previous research prompted an initial investigation into the data obtained. It was found that the discrepancies were due to the various interpretations of the method used to extract damping capacity from the free-vibration decay curve. Therefore, a logarithmic decrement calculation method was proposed to ensure consistency and accuracy of the extracted damping capacity data to be used in the subsequent analytical research phase. The experimental test data confirmed that the 'untested' damping capacity of reinforced concrete beams is dependent upon the beam reinforcement ratio and distribution. This quantity was termed the total longitudinal reinforcement distribution. For the prestressed concrete beams, the 'untested' damping capacity was shown to be proportional to the product of the prestressing force and prestressing eccentricity. Separate 'untested' damping capacity equations for reinforced and prestressed concrete beams were developed to reflect these quantities. To account for the variation in damping capacity due to damage in 'tested' beams, a residual deflection mechanism was utilised. The proposed residual deflection mechanism estimates the magnitude of permanent deformation in the beam and attempts to overcome traditional difficulties in calculating the damping capacity during low loading levels. Residual deflection equations, based on the instantaneous deflection data for the current experimental programme, were proposed for both the reinforced and prestressed concrete beams, which in turn were utilised with the proposed 'untested' damping equation to calculate the total damping capacity. The proposed 'untested' damping, residual deflection and total damping capacity equations were compared to published test data and an additional series of test beams. These verification investigations have shown that the proposed equations are reliable and applicable for a range of beam designs, test setups, constituent materials and loading regimes.

This thesis documents a PhD level research program, undertaken at the Industrial Institute Swinburne, Swinburne University of Technology between the years of 1997 and 2000. The research program investigated electromagnetic energy regenerative vibration damping; the process of recovering energy from damped, vibrating systems. More specifically, the main research objective was to determine the performance of regenerative damping for the application of vehicle suspension systems. This question emerged due to the need for continuous improvement of vehicle efficiency and the potential benefits possible from the development of regenerative vehicle suspension. It was noted, at the outset of this research, that previous authors had undertaken research on particular aspects of regenerative damping systems. However in this research, the objective was to undertake a broader investigation which would serve to provide a deeper understanding of the key factors. The evaluation of regenerative vibration damping performance was achieved by developing a structured research methodology that began with analysing the overall requirements of regenerative damping and, based on these requirements, investigated several important design aspects of the system. The specific design aspects included an investigation of electromagnetic machines for use as regenerative damping devices. This analysis concentrated on determining the most promising electromagnetic device construction based on its damping and regeneration properties. The investigation then proceeded to develop an 'impedance-matching' regenerative interface, in order to control the energy flows in the system. This form of device had not been previously developed for electromagnetic vibration damping, and provided a significant advantage in maximising energy regeneration while maintaining damping control. The results from this analysis, when combined with the issues of integrating such a system in vehicle suspension, were then used to estimate the overall performance of regenerative damping for vehicle suspension systems. The methodology and findings in this research program provided a number of contributing elements to the field, and provided an insight into the development of regenerative vehicle systems. The findings revealed that electromagnetic regenerative vibration damping may be feasible for applications such as electric vehicles in which energy efficiency is a primary concern, and may have other applications in similar vibrating systems.

<p>The purpose of this thesis is to implement and test a semi-active damping system based on a concept from an earlier thesis. The project includes implementation of mechanical, hydraulic and electronic hardware, aswell as controller software. The idea is to measure the movements of the vehicle chassis and based on these measurements set the damping torque using hydraulics. To be able to develop, test and evaluate the system, realistic input data must be available. To acquire such data, driving trials have been conducted on a variety of tracks.</p><p>The first part of the system is the sensors that measure chassis movements. Both accelerometers and a gyro has been used. To remove drift and high frequency vibrations, the signals are filtered. The suggested controller from the earlier thesis requests damping torque based on the dampers vertical velocity. When accelerometer signals are integrated, measurement and rounding errors causes drift in the velocity. To compensate for this, a floating average is calculated and used.</p><p>The main hydraulic component is a pressure reduction valve that controls the pressure inside the damper. Higher pressure will give higher damping torque. The reaction speed of the system is mostly depending on the hydraulic components. It is important to know the time delay from a change in the valve control signal, to when the actual pressure in the damper has been reached. Tests have shown that a large step, going from 10 Bar to 60 Bar takes approximately 46ms, and that a small step from 1 Bar to 20 Bar takes 63ms. The valve is faster when higher pressure levels are requested. In addition to the hydraulic response time the delay through the signal filters, measured to about 14ms, must be added.</p><p>The sensors are affected by vibrations. If these can be reduced, the digital filters can be made less sharp with a lower filter delay as result. It is also important to have a good control computer so that large rounding errors in the filter calculations can be avoided. This would greatly decrease drift in the integrated velocity.</p>

<p>This thesis focuses on the electromechanical processes of generation and damping of transient waves in bars with attached piezoelectric members. In particular, the influence of amplifier and electrical circuitry on the mechanical waves is of interest.</p><p>A straight bar element containing piezoelectric members is viewed as a linear system with one electrical and two mechanical ports where it interacts with external electrical and mechanical devices through voltage, current, forces and velocities. For the modelling of the piezoelectric bar element (PBE) and its environment, coupled piezoelectric theory is used with allowance for the dynamics of the PBE and attached electrical and mechanical devices.</p><p>Two applications are considered for a PBE that constitutes a part of a long bar, viz. generation and damping of extensional waves. In the first, simulations and experiments were performed when the PBE was driven by a power amplifier. In the second, simulations and experiments were performed when the PBE supplied an output voltage to an external load.</p><p>In the case of wave generation, the influence of amplifier characteristics in terms of DC voltage gain, 3 dB cut-off frequency, output impedance and current constraints on the output voltage and current of the amplifier and the waves generated are studied. Further, generation of waves of prescribed shapes are studied for a specific amplifier. In general, good agreement between simulated and experimental results was obtained.</p><p>In the case of wave damping, the influence of external electrical loads and incident waveforms on reflected and transmitted waves, and on gener-ated voltage, current, electrical power and dissipated energy, are studied. In general, fair agreement between simulated and experimental results was obtained. The fractions of a few percent of wave energy dissipated in the exter-nal load were well below the 50 percent achievable for a harmonic wave under condition of electrical impedance matching.</p>

Thesis (M.S.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1982. / Includes bibliographical references (leaves 151-153).

In this study, particle impact damping is measured for a cantilever beam with a particle-filled enclosure attached to its free end. Many particle materials are tested: lead spheres, steel spheres, glass spheres, tungsten carbide pellets, lead dust, steel dust, and sand. The effects of particle size are also investigated. Particle diameters are varied from about 0.2 mm to 3 mm. The experimental data collected is offered as a resourceful database for future development of an analytical model of particle impact damping.

Internal friction has been known to be a cause of whirl instability in built-up rotors since the early 1900's. This internal damping tends to make the rotor whirl at shaft speeds greater than a critical speed, the whirl speed usually being equal to the critical speed. Over the years of research, though models have been developed to explain instabilities due to internal friction, its complex and unpredictable nature has made it extremely difficult to come up with a set of equations or rules that can be used to predict instabilities accurate enough for design. This thesis deals with suggesting improved methods for predicting the effects of shrink fits on threshold speeds of instability. A supporting objective is to quantify the internal friction in the system by measurements. Experimental methods of determining the internal damping with non-rotating tests are investigated, and the results are correlated with appropriate mathematical models for the system. Rotating experiments were carried out and suggest that subsynchronous vibration in rotating machinery can have numerous sources or causes. Also, subsynchronous whirl due to internal friction is not a highly repeatable phenomenon.

Abstract Micro-electromechanical systems (MEMS) are subject to inevitable and inherent uncertainties in their dimensional and material parameters. Those lead to variability in their performance and reliability. Manufacturing processes leave substantial variability in the shape and geometry of the device due to its small dimensions and high feature complexity, while the material properties of a component are inherently subject to scattering. The effects of these variations have to be considered and a modeling methodology is needed in order to ensure required MEMS performance under uncertainties. Furthermore, in the design of high-Q micro-resonators, dissipation mechanisms may have detrimental effects on the quality factor (Q). One of the major dissipation phenomena to consider is thermoelastic damping, so that performances are directly related to the thermoelastic quality factor, which has to be predicted accurately. The purpose of this research is to develop a numerical method to analyze the effects of geometric and material property random variations on the thermoelastic quality factor of micro-resonators. The extension of the Perturbation Stochastic Finite Element Method (PSFEM) to the analysis of strongly coupled multiphysic phenomena allows the quantification of the influence of uncertainties, making available a new efficient numerical tool to MEMS designers. Résumé Dans le domaine des microsystèmes électromécaniques (MEMS), les micro-résonateurs jouent un rôle important pour le développement de micro-capteurs de plus en plus précis (ex : micro-accéléromètres). Dans cette optique daugmentation de la précision, les pertes dénergie qui limitent les performances des micro-résonateurs doivent être identifiées et quantifiées. Le facteur limitant des micro-résonateurs actuels est leur facteur de qualité thermo-élastique, qui doit donc être prédit de manière précise. De plus, suite à la tendance actuelle de miniaturisation et complexification accrues des MEMS, les sources de dispersions sont très nombreuses, à la fois sur les constantes physiques des matériaux utilisés et sur les paramètres géométriques. La mise au point doutils numériques permettant de prendre en compte les incertitudes de manière efficace est donc primordiale afin daméliorer les prestations densemble du microsystème et dassurer un certain niveau de robustesse et de fiabilité. Le but de cette recherche est de développer une méthode numérique pour analyser les effets des variations aléatoires des propriétés matérielles et géométriques sur le facteur de qualité thermo-élastique de micro-résonateurs. Pour ce faire, lapproche dite perturbative de la méthode des éléments finis stochastiques (PSFEM) est étendue à lanalyse de phénomènes multiphysiques fortement couplés, fournissant ainsi aux acteurs de lindustrie des MEMS un nouvel outil de conception efficace.

This thesis focuses on the electromechanical processes of generation and damping of transient waves in bars with attached piezoelectric members. In particular, the influence of amplifier and electrical circuitry on the mechanical waves is of interest. A straight bar element containing piezoelectric members is viewed as a linear system with one electrical and two mechanical ports where it interacts with external electrical and mechanical devices through voltage, current, forces and velocities. For the modelling of the piezoelectric bar element (PBE) and its environment, coupled piezoelectric theory is used with allowance for the dynamics of the PBE and attached electrical and mechanical devices. Two applications are considered for a PBE that constitutes a part of a long bar, viz. generation and damping of extensional waves. In the first, simulations and experiments were performed when the PBE was driven by a power amplifier. In the second, simulations and experiments were performed when the PBE supplied an output voltage to an external load. In the case of wave generation, the influence of amplifier characteristics in terms of DC voltage gain, 3 dB cut-off frequency, output impedance and current constraints on the output voltage and current of the amplifier and the waves generated are studied. Further, generation of waves of prescribed shapes are studied for a specific amplifier. In general, good agreement between simulated and experimental results was obtained. In the case of wave damping, the influence of external electrical loads and incident waveforms on reflected and transmitted waves, and on gener-ated voltage, current, electrical power and dissipated energy, are studied. In general, fair agreement between simulated and experimental results was obtained. The fractions of a few percent of wave energy dissipated in the exter-nal load were well below the 50 percent achievable for a harmonic wave under condition of electrical impedance matching.