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Shear and compression wave velocities are examined in assemblages of spherical glass beads in isotropic, triaxial and multiaxial stress states in the Cubical Cell Apparatus (CCA). The CCA enables application of non-rotational stress-states to a cube-shaped sample with independent control of the three principal stresses. Waves are transmitted using bender/extender elements (Lings & Greening 2001), the performance of which are assessed by laser vibrometry. Uncertainties in the analysis of wave velocities are examined in relation to the method of travel time assessment, extending to frequency and shape of the transmitted pulse waveform. Results suggest that uncertainties over wave travel time result largely from the mismatching of the transmitted waveform and the method by which its arrival is analysed. Methods based on cross-correlation are the most universally applicable and can be semi automated but still rely on the operator to correctly identify the wave arrival. Results for velocities in isotropic stress states are curve-fitted to a power law; the coefficients and exponents of these best fit curves appear to be related by an inverse power law, which is backed up by published data. How this may relate to material properties remains unclear. Additional laser vibrometry results from targets on the outside of a cubical sample enable examination of the propagation of the wavefront through the sample. The received traces for S-wave transmissions support the theory that the operation of the bender element produces sideways propagating P-wave 'lobes' (Lee and Santamarina 2005). The trend of their arrivals with distance between the bender and laser target supports the accepted use tip-to-tip travel distance for S-wave transmissions but suggests it may be too short for P-waves; this latter requires further experimental work.

A nonlinear stability analysis of a liquid sheet moving in an incompressible gas medium at rest subject to sinuous disturbances is presented. The first, second and third order governing equations have been derived along with appropriate initial and boundary conditions which describe the characteristics of the fundamental mode, and the first and second harmonics. It is found that the thinning of the sheet is caused by the growth of harmonic waves, and subsequent liquid sheet rupture occurs at every half wavelength interval. The amplitude growth rates of the disturbances are calculated at the dominant wavenumber for different initial amplitudes and are then compared with the predictions from the linear theory. The analysis also allows the determination of the breakup time and breakup length, and the effect of the flow parameters on the breakup time is also investigated. The present experimental study on the liquid sheet breakup explores the growth of liquid sheet instabilities and subsequent spray formation. Flow visualization reveals different flow regimes. Liquid sheet surface displacements, wavelengths and breakup lengths are measured using a photographic technique, and the drop sizes and velocities are measured simultaneously by the Phase Doppler Particle Analyzer (PDPA). The result of acoustic excitation for different regimes of liquid disintegration shows that for certain frequencies resonance and enhanced instability occur. However, in the spray regime where a fine spray is formed, although visually there are some effects of acoustic excitation on the wave development, the Phase Doppler Particle Analyzer (PDPA) measurements show no noticeable effect on the drop sizes and velocities. The theoretical predictions are compared with the experimental results for dominant wavelength and growth rate of the unstable waves on the liquid sheet surface. / Graduate

Oil-air separation is a key function in aero engines with closed-loop oil systems. Aero-engine separators are employed to separate oil from air before being released overboard. Typically, these devices make use of a porous medium such as an open-cell metal foam, in order to enhance oil separation. Although quite scarce, there has been some research aimed at developing a suitable modelling framework for aero-engine separators. However, numerical modelling of the air/oil flow through the open-cell metal foams employed in aero-engine separators has never been properly addressed. This thesis presents the development of a pore-scale numerical modelling approach to determine the transport properties of fluid flow through open-cell metal foams. Micro-computer tomography scans were used to generate 3D digital representations of several commercial open-cell metal foams. A code was developed in Matlab to render the CT images into 3D volumes and perform morphological measurements on the samples. Subsequently, conventional finite volume simulations are carried out in order to obtain the airflow and compute the pressure gradient across the investigated samples. Simulations were performed for a wide range of Reynolds numbers and the feasibility of using Reynolds-averaged Navier-Stokes (RANS) turbulence models is investigated. Validation was done by comparing the pore-scale pressure gradient results against experimental measurements. Further simulations were carried out to isolate and analyse particular effects in more detail, such as wall and entrance effects, fluid compressibility, time-dependent flow features, anisotropy of the foam structure and the impact of porosity and surface area on the pressure gradient. The oil phase within aero-engine separators has the form of disperse droplets. Thus, the oil phase in the pore-scale simulations was modelled using a Lagrangian particle tracking approach. Lagrangian simulations were run in steady state and one-way coupled, due to the low mass fraction of oil normally present within aero-engine separators Converged airflow pore-scale solutions were employed as the base flow for the Lagrangian tracking approach. A simplified oil capture criterion assumed the droplet trajectory to be terminated upon collision against the foam solid ligaments. The focus of the present work was on separation of small droplets with a diameter smaller than 10 microns. Hence, a series of calculations were performed using a representative droplet diameter range, and multiple flow velocities. The outcome of such approach was a qualitative evaluation of the oil separation effectiveness for several commercial open-cell metal foams under a representative range of flow regimes. Furthermore, rotational effects which are experienced by the metal foams within aero-engine separators were modelled using a moving frame of reference (MRF) approach. Finally, a methodology for upscaling the results obtained by the detailed pore-scale simulations into a simple macroscopic porous medium model is described, showing promising results. One of the aims of this work was to develop a numerical modelling framework able to provide an accurate representation of the airflow and a qualitative assessment of the oil capture within aero-engine separators. The feasibility of using the current state-of-the-art modelling framework is assessed. The separator design and geometry are based on the oil separation test rig located at the Karlsruhe Institute of Technology (KIT). Experimental measurements of the overall pressure drop and oil capture performed at KIT are used to validate the simulations. The methodology presented here overcomes some limitations and simplifications present in previous similar studies. The upscaled macroscopic porous medium model was applied to full aero-engine separator CFD simulations. Experiments and simulations were conducted for three different separator configurations, one without a metal foam, and two with metal foams of different pore sizes. For each configuration, a variation of air flow, shaft rotational speed and droplet size was conducted. The focus was on the separation of droplets with a diameter smaller than 10 \textmu m. Single-phase air flow simulation results showed that overall pressure drop increases with both increased shaft speed and air flow, largely in agreement with the experiments. Oil capture results proved to be more difficult to be captured by the numerical model and indicate that droplet re-atomization might play a significant role in the oil separation phenomena. Re-atomization, droplet-droplet collisions and droplet breakup were not considered at the present stage, but could be subject of future work. The modelling framework described here should not be seen as a definite answer but as an improvement upon the current state-of-the-art methodology, providing important lessons and recommendations for future work on aero-engine separators.

Approved for public release, distribution is unlimited / Damping of welded structures is a subject of great interest and application for the navy as relates to ship shock survivability and acoustic transmission of ship noise. The purpose of this research is to study the effects of welding on damping. A generic model of a warship's hull structure was used to study damping effects. The model's natural frequencies and mode shapes were calculated using a finite element model prior to model testing. The frequency response and natural frequencies of the model were determined experimentally by exciting the model and measuring the response throughout the structure using Frequency Response Functions (FRF's). The results were compared with the finite element modeling. The damping ratio of the model in relation to position from excitation was calculated using the half-power point method and then a more detailed analysis of frequency dependent damping versus position was made using modal parameter extraction using the Complex Exponential Method. / Lieutenant, United States Navy

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When planning for a tunnel, the ground conditions in which the tunnel is going to be excavated through will be investigated to different extent. Lack of relevant pre-investigation data or misinterpretations of the available data can cause both economical and/or unexpected stability problems. Weakness zones that are expected to cross the tunnel could be investigated thoroughly with a variety of methods. Refraction seismicity survey and 2D resistivity survey are two geophysical methods that are common in Norway for obtaining information about the rock quality in weakness zones. In this work, a twin tunnel under construction in Bodø (northern Norway) called the Bodøtunnel is studied. The predictions based on the pre-investigation for crossing of some expected weakness zones are compared to the actual conditions encountered during tunneling. Tunneling observations (Geological mapping and photos), rock samples and measurement while drilling (MWD) were used to describe the weakness zones that were encountered during tunneling. Rock samples were collected from two weakness zones and the general rock mass. These samples were tested in a point bearing machine for determination of their uniaxial compressive strength (UCS). These results indicated that the rock samples gathered from the weakness zones had significantly lower UCS than the samples from the rock mass. This was exceedingly clear for the samples of fault rock gathered in connection with a shear zone. The results from this work demonstrate that refraction seismicity had a high success rate for locating weakness zones, with the exception for the crossed narrow zones that were interpreted lacking a shear component. Empirical formulas relating Q-value and UCS with the seismic wave speed were used for calculating these factors for some interesting locations. The empirically calculated UCS was similar to the obtained UCS from the point bearing tests, while the empirically calculated Q-value showed large deviations from the mapped Q-value. The resistivity measurements had a low success rate so far in this project; the reason for this could be disturbances in the ground and the location of the resistivity profiles, which had to adapted to the nearby railroad. It should be noted that only one full resistivity profile has been crossed and the rest of the profiles are expected to be more accurate. Based on the results from the crossed profile(s), the suitability of resistivity survey 2D in urban areas can be brought to question. This work also stumbled upon problems regarding the definition of weakness zones. Shear/fault zones are one of the more common type of weakness zones encountered in tunneling. These kind of zones often consists of different parts. Depending on which parts are regarded as a weakness zone by the responsible engineers, the Q-value might differ due to the SRF. Different scenarios were also evaluated with numerical modeling for the expected remaining major weakness zones. This analysis highlights the importance of differentiation between more fractured zones and zones containing fault rock, such as breccia. The width of the zone had a major impact on the stability while the dip for wide zones had a minor impact on the stability, as long the zones dip is not so small that both tunnels are intersected at the same time. The rock mechanical parameter of the weakness zones that had the most impact on the overall stability was the cohesion.

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