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As the second task of this thesis, we shall propose some mathematical model to simulate the movement of a floating bridge under some moving loadings. The floating bridge system consists of three parts, i.e. river (fluid), floating bridge (multibody system) and vehicles (load) which pass the bridge. Our objective is to find the motion and dynamical responses of the floating bridge with a truck or tracklayer passing on it. The floating bridge is a system of steel rectangular boxes which can be seen as rigid bodies connected by some kinematic joints. In fact, such system is a fluid-structure coupled system and one must treat the governing equations for the floating bridge and fluid, i.e. Euler-Lagrange equations and Navier-Stokes equations, simultaneously. In our work, we apply the one-leg method and operator splitting arbitrary Lagrangian-Eulerian method to solve the coupled system. / When performing dynamical analysis of a constrained mechanical system, a set of index-3 differential algebraic equations, i.e. Euler-Lagrange equations, are often needed to describe the time evolution of the mechanical system. In this thesis, we apply one-leg multi-step methods to integrate the DAEs directly. To overcome some difficulties leading to certain numerical instabilities, a velocity elimination technique is applied to generate a framework that the position and velocity profiles can be obtained in two separate stages: only the position variables and Lagrange multipliers take part in the convergent nonlinear iterations at each time step while the velocity is calculated by the multi-step formula directly without any iteration. The framework is constructed in a manner such that it satisfies all the constraints at the position level and involves variables as few as possible during the iteration. Some convergence analysis are presented and good stability and high efficiency can be seen through the experiments of some benchmark problems. / Zhao Yubo. / "July 2005." / Adviser: Zou Jun. / Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0310. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 244-276). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

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The convenience of Operational Modal Analysis (OMA), over conventional Experimental Modal Analysis (EMA), has seen to its increasing popularity over the last decade for the purpose of evaluating dynamic properties of structures. OMA features an advantage of requiring only output information, which is in tandem with its main drawback of lacking scaled modeshape information. While correctly scaled modeshapes can be assumed under a restrictive assumption of spectrally white inputs, in reality, input spectra are at best broadband in nature. In this thesis, an OMA method for Multiple-Input Multiple-Output (MIMO) applications in mechanical structures is developed. The aim is to separate MIMO responses into a collection of Single-Input Single-Output (SISO) processes (matrix FRF) using cepstral-based methods, under less restrictive and hence more realistic coloured broadband excitation. Existing cepstral curve-fitting techniques can be subsequently applied to give regenerated FRFs with correct relative scaling. This cepstral-based method is based on the matrix Mean Differential Cepstrum (MDC) and operates in the frequency domain. Application of the matrix MDC onto MIMO responses leads to a matrix differential equation which together with the use of finite differences, directly solves or identifies the matrix FRF in a propagative manner. An alternative approach based on whitened MIMO responses can be similarly formulated for the indirect solution of the matrix FRF. Both the direct and indirect approaches can be modified with a Taylor series approximation to give a total of four propagative solution sequences. The method is developed using relatively simple simulated and experimental systems, involving both impulsive and burst random excitations. Detailed analysis of the results is performed using more complicated Single-Input Multiple-Output (SIMO) and MIMO systems, involving both driving and non-driving point measurements. The use of the matrix MDC method together with existing cepstral curve-fitting technique to give correct relative scaling is demonstrated on a simulated MIMO system with coloured inputs. Accurate representation of the actual FRFs is achieved by the matrix MDC technique for SIMO set-ups. In MIMO scenarios, excellent identification was obtained for the case of simulated impulsive input while the experimental and burst random input cases were less favourable. The results show that the matrix MDC technique works in MIMO scenarios, but possible noise-related issues need to be addressed in both experimental and burst random input cases for a more satisfactory identification outcome.

Jets in crossflow are used in a wide range of engineering applications and have been studied for more than 60 years. The transversal penetration and structure of a jet placed in a crossflow is known to be strongly three-dimensional. It is believed that, by using a pulsed jet inclined in the crossflow direction, the momentum transport can be controlled in two very efficient ways: the pulse can increase the jet penetration and the mixing downstream, while the inclination avoids the creation of a reverse flow at the jet exit and may extend the mixing area further downstream. Although some results are available in the literature focusing on components of this problem, none addresses the combination of these two factors. Moreover, most of these studies use elaborate flow visualizations and 2-D velocity measurement methods that may not be adequate to elucidate the complexity of such a flow. This study addresses these issues by using stereoscopic PIV measurements for a steady and fully modulated jet at a constant mean velocity ratio, V[subscript r], of 3.4. For the steady jet case, the effect of the jet Reynolds number, Re[subscript j], is investigated. For the pulsed case, the effect of a low pulsing frequency is considered as well as the pulse duty cycle. For each case, the mean three-component velocity field is examined. Proper Orthogonal Analysis (POD) of vorticity and turbulent kinetic energy are used to further evaluate the vortical and turbulent characteristics of the jet. In addition, a vortex detection algorithm, and 3D rendering of the flow streamlines are used to study the near field vortical flow structure of the jet flow. / Graduation date: 2006

Droplet formation from a rigid and a vibration nozzle driven by a pulsing pressure is simulated. Droplet formation is simulated by using one-dimensional model. For the case of droplet formation from a vibration nozzle, the nozzle vibration is simulated by large deflection plate vibration equation. Droplet formation from a rigid nozzle is studied simply by setting the nozzle deflection always to be zero. The one-dimensional model is solved by MacCormack method. The large deflection plate vibration equation is solved by mode shape approximation and Runga--Kuta time integration method. Three different effect factors, the driving pressure thrust input effects, the fluid viscosity effects, and the nozzle vibration effects, on droplet formation are studied. The driving pressure thrust input effects and the fluid viscosity effects are studied based on a rigid nozzle. The nozzle vibration effects are studied by comparing the results from a vibration nozzle with the results from a rigid nozzle. Results show: 1) the primary droplet break-off time is constant if the driving pressure magnitude is high, but the primary droplet volume and primary droplet velocity increase slightly as the driving pressure thrust input increase; 2) higher thrust input can possibly result in the occurrence of overturn phenomenon; 3) increasing the fluid viscosity cause the primary droplet break-off later, but the primary droplet volume and the primary droplet velocity does not change significantly by fluid viscosity; 4) the nozzle vibration effect on the primary droplet break-off time and the primary droplet size is small, but the nozzle vibration cause the primary droplet velocity to increase by an amount of the nozzle vibration velocity magnitude; 5) nozzle vibration cause longer liquid thread to form and the total satellite droplet volume to increase significantly which eventually break into multiple satellite droplet. / Graduation date: 2004

Understanding the processes involved in the transport of dissolved gas plumes in groundwater aquifers is essential for comprehending the effect that these transport processes can have on site characterization and remedial design applications. Previous laboratory and field studies have indicated that dissolved gas transport in groundwater can be greatly affected by the presence of even small amounts of trapped gas in the pore space of an aquifer. Recently, Fry et al. (1995) reported an increase in retardation factors R (where R=pore water velocity/dissolved gas velocity) for dissolved oxygen with increasing amounts of trapped gas. Fry showed that the retardation factor for a dissolved gas can be predicted using a relationship between the dimensionless Henry's Law constant for the dissolved gas, the volumetric gas content (i.e., the fraction of the total volume occupied by trapped gas), and the volumetric water content (i.e., the fraction of total volume occupied by water). In their experiments, Fry et al. (1995) found this relationship in an equilibrium model accurately predicted observed retardation factors for dissolved oxygen when the volumetric gas content was small, but underpredicted retardation factors for larger volumetric gas contents. Also, predicted breakthrough curves for dissolved oxygen obtained by incorporating this relationship into the advection-dispersion equation did not match the shape of experimentally observed breakthrough curves. The experimental curves were asymmetrical with long tails indicating that the local equilibrium assumption is inaccurate and suggesting that mass transfer of oxygen between the aqueous and trapped gas phases is diffusion limited. In an effort to gain further understanding of this process, a kinetic model was developed for dissolved gas transport that includes a diffusion type expression for the rate of gas transfer between the mobile aqueous and trapped gas phases. The model was tested in a series of transport experiments conducted in sand packed columns with varying amounts and composition of trapped gas. The kinetic model was found to better fit the shape of dissolved oxygen breakthrough and elution curves than the equilibrium model of Fry et al. (1995). This model was then extended to the case of two-dimensions to simulate dissolved gas transport in the presence of trapped gas under conditions that approximate injection and extraction wells used to distribute dissolved gases in an aquifer (e.g. to promote in situ bioremediation processes or to perform a dissolved gas tracer test). We then compared these predicted concentrations with measured concentrations obtained in a series of dissolved gas transport experiments in a large-scale physical aquifer model using two dissolved gases (oxygen and hydrogen) with very different physical properties. The model could accurately fit the development and movement of these plumes providing that key parameters, the amount of trapped gas and the effective mass transfer coefficient, were adjusted between the injection and drift stages. / Graduation date: 1997

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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