The high sound pressure levels (SPL's) radiated inside the payload fairing by its vibrating frame causes 40% of the satellite damage in the initial phases of the launch. Numerous experiments conducted on the advanced vibration absorbers such as the distributed vibration absorbers (DVA's) and the heterogeneous blankets (HG blankets) have shown great potential in reducing the vibration levels and the SPL's inside the payload fairings. Despite their good performance, little is known about the detailed mechanisms by which it is achieved. In addition, these vibration absorbers are currently empirically and experimentally designed which is a very cumbersome and time consuming process. To overcome the aforementioned limitations, there is a need for development of numerical techniques to understand the physics behind their functionality and to study the influence of the geometric layout or the choice of materials on their performance. This work presents the development and validation of the finite element (FE) models to understand the physics behind the functionality of these vibration absorbers. The development of these FE models can be broadly classified in to three stages. In the first stage, the FE models of the individual components was developed and validated. In second stage, the fully coupled 3D-FE models of the advanced vibrations absorbers such as the DVA's and the HG blankets were validated. Finally, fully coupled 3D-FE models of these vibration absorbers coupled to the structural and acoustics domains were validated . Parametric studies were performed on these fully coupled 3D-FE models in order to understand the effect of the variation in the material properties and geometrical configuration of these vibration absorbers on their response and also on their vibro-acoustic attenuation capabilities. The knowledge base built from the parametric studies was later used for the development of the optimized designs of these vibration absorbers. / Master of Science

No description available.

No description available.

In this thesis we examine some of the interesting aspects of stability for some convection problems. Specifically, the first part of the thesis deals with the Bénard problem for various Non-Newtonian fluids, whereas the second part develops a stability analysis for convection in a porous medium. The work on stability for viscoelastic fluids includes nonlinear stability analyses for the second grade fluid, the generalised second grade fluid, the fluid of dipolar type and the fluid of third grade. It is worth remarking that throughout the work the viscosity is supposed to be any given function of temperature, with the first derivative bounded above by a positive constant. The connection between the two parts of the thesis is made through the method used to approach the nonlinear stability analysis, namely the energy method. It is shown in the introductory chapter how this method works and what are its advantages over the linear analysis. Nonlinear stability results established in both Part I and Part II are the best one can get for the considered physical situations. Different choices of energy have been considered in order to achieve conditional or unconditional nonlinear stability results.

We prove the existence of a one-parameter family of solutions of the porous medium equation, a nonlinear heat equation. In our work, with space dimension 3, the interface is a half line whose end point advances at constant speed. We prove, by using maximum principle, that the solutions are stable under a suitable class of perturbations. We discuss the relevance of our solutions, when restricted to two dimensions, to gravity driven flows of thin films. Here we extend the results of J. Iaia and S. Betelu in the paper "Solutions of the porous medium equation with degenerate interfaces" to a higher dimension.

The unique properties of engineered nanoparticles have many potential applications in oil reservoirs, e.g., as emulsion stabilizers for enhanced oil recovery, or as nano-sensors for reservoir characterization. Long-distance propagation (>100 m) is a prerequisite for many of these applications. With diameters between 10 to 100 nanometers, nanoparticles can easily pass through typical pore throats in reservoirs, but physicochemical interaction between nanoparticles and pore walls may still lead to significant retention. A model that accounts for the key mechanisms of nanoparticle transport and retention is essential for design purposes. In this dissertation, interactions are analyzed between nanoparticles and solid surface for their effects on nanoparticle deposition during transport with single-phase flow. The analysis suggests that the DLVO theory cannot explain the low retention concentration of nanoparticles during transport in saturated porous media. Moreover, the hydrodynamic forces are not strong enough for nanoparticle removal from rough surface. Based on different filtration mechanisms, various continuum transport models are formulated and used to simulate our nanoparticle transport experiments through water-saturated sandpacks and consolidated cores. Every model is tested on an extensive set of experimental data collected by Yu (2012) and Murphy (2012). The data enable a rigorous validation of a model. For a set of experiments injecting the same kind of nanoparticle, the deposition rate coefficients in the model are obtained by history matching of one effluent concentration history. With simple assumptions, the same coefficients are used by the model to predict the effluent histories of other experiments when experimental conditions are varied. Compared to experimental results, colloid filtration model fails to predict normalized effluent concentrations that approach unity, and the kinetic Langmuir model is inconsistent with non-zero nanoparticle retention after postflush. The two-step model, two-rate model and two-site model all have both reversible and irreversible adsorptions and can generate effluent histories similar to experimental data. However, the two-step model built based on interaction energy curve fails to fit the experimental effluent histories with delay in the leading edge but no delay in the trailing edge. The two-rate model with constant retardation factor shows a big failure in capturing the dependence of nanoparticle breakthrough delay on flow velocity and injection concentration. With independent reversible and irreversible adsorption sites the two-site model has capability to capture most features of nanoparticle transport in water-saturated porous media. For a given kind of nanoparticles, it can fit one experimental effluent history and predict others successfully with varied experimental conditions. Some deviations exist between model prediction and experimental data with pump stop and very low injection concentration (0.1 wt%). More detailed analysis of nanoparticle adsorption capacity in water-saturated sandpacks reveals that the measured irreversible adsorption capacity is always less than 35% of monolayer packing density. Generally, its value increases with higher injection concentration and lower flow velocities. Reinjection experiments suggest that the irreversible adsorption capacity has fixed value with constant injection rate and dispersion concentration, but it becomes larger if reinjection occurs with larger concentration or smaller flow rate. / text

No description available.

No description available.

No description available.

RBCCPS / Evaporation is one of the inherent processes of the earth’s ecosystem. Water bodies, earth’s surface and vegetation all contribute significantly towards the total evaporation which eventually leads to the formation of clouds. The factors which affect the total evaporation (evaporation & transpiration) are the surface temperature, ambient temperature, relative humidity, external wind speed, pressure, surface area and geometry. This thesis deals with the contributors of total evaporation individually viz. open water bodies; soil-like surfaces; and leaf-like surfaces. A ceramic infrared heater has been used to mimic the heating due to sun’s radiation in all the experiments which were conducted in the quiescent atmosphere. This thesis has been broadly categorized into two parts: - (a) evaporation from bare water surface; and (b) evaporation from a porous media. In part (a), we present experimental results on the evaporation from a bare water surface heated either from above using the infrared radiations or from below using immersed heaters. Heating from below leads to unstable stratification and convection while infrared heating from above leads to stable stratification. The effect of water-side convection on the evaporation from a bare water surface has been investigated and all the experimental results have been combined to obtain a power law relation between Sherwood number (Sh) and Rayleigh number (Ra). Part (b) of the thesis has been further split into three major categories: - (1) evaporation from spheres based conventional porous media; (2) evaporation from unconventional porous media containing rods, capillaries, and plates; and (3) evaporation from leaf-like surfaces. In all the experiments, a precision weighing balance was used to measure the evaporation rate. A thermal camera was used to get the surface temperature fields, and fluorescein dye mixed with water gave insightful results on the evaporation process. In particular the red deposits of fluorescein particles revealed the evaporation sites. In most of the experiments, the infrared heating was of the order of 1000W/m2. Different sized glass and acrylic containers were used in this thesis. Mono-disperse glass beads (closest to mimic the natural soils), stainless steel balls, sieved natural sand and hydrophobic Ball Grid Array balls have been used to create the spheres-based conventional porous media. Evaporation was found to undergo three stages which depended on the spheres size and the heat flux supplied. In the 1st stage of evaporation capillary film(s) pulls water from beneath the porous media to the top surface and the evaporation rate remained high, close to that obtained from a water surface. Capillary break-up occurs in the transition regime which is followed by the 2nd stage of evaporation where a new vaporization plane is formed within the porous media. In the 2nd stage, heat is conducted through the top dried layer to the water below where evaporation takes place and the evaporation rate drops drastically. Transition to 2nd stage happened earlier for coarser spheres at constant heat flux. Along with the wetting properties, the spheres size has been found to effect capillary break-up length (a measure of capillary film strength) and hence the duration of the stages of evaporation drastically. Surface images captured using the thermal camera clearly showed the presence of water till the capillary break-up. The capillary break-up length was also found to be affected significantly by the heat flux. Apart from the experimental findings of mono-disperse spheres, two layers of different sized glass spheres have also been investigated. The presence of complicated network of textural layering in the earth’s surface is a well-known fact. Preferential evaporation was clearly seen in the experiments with texturally layered porous media independent of the orientation viz. vertical or horizontal layering. The stacking positions are found to be critical in determining the overall evaporation characteristics. The geometry of a pore between three spheres in mutual contact is very complicated. Simpler pore geometry would be between two rods/plates in contact or three rods in mutual contact or stacks of either of these two. We call these types of the porous media as “Unconventional porous media” as they possess many unique features not shown by a conventional porous media. The evaporation characteristics of vertically stacked rods was found to be dominated by the corner films present in the near-zero radii contacts. Unlike the conventional porous media, the capillary break-up length was found not to depend on the rod diameter. The capillary break-up length for vertically stacked rods was larger than for the spheres case and was also found to be independent of the heat flux, for the range investigated in this thesis. A mathematical model has been developed for understanding the evaporation from the vertically stacked rods. Experiments with horizontally stacked pencil leads showed early capillary break-up while with horizontally stacked glass rods, capillary break-up was not observed. Experimental investigations of porous media containing vertically stacked plates have also been studied. Water trapped between two consecutive plates are treated as 2D source of evaporation. Plants regulate their O2-CO2 content via tiny holes present on the leaves called “Stomata”. The average size of a stoma is nearly 20μm and the total area covered by stomata is close to 5% of the leaf area. However the higher transpiration rates (60-70 % compared to a bare water source) sustained by a plant has remained a mystery for the phytologists. In view of this we mimic the leaf-type using regularly spaced holes on the silicon wafers from which water evaporates. The leaf-mimics had different hole-diameter but open area ratio was kept constant. In all the cases the evaporation ratio (ratio of the evaporation rate from the leaf mimic to that of the evaporation rate of a bare water surface at the same surface temperature) was found to increase at lower heat fluxes. With increasing the hole-size evaporation rate was found to decrease. The leaf-mimic with the smallest hole-size had the highest evaporation rate and the evaporation ratio increased from 0.46 at 800W/m2 to 0.64 at 400W/m2. The 3D nature of diffusion near these tiny holes enhances the evaporative flux which explains the high evaporation rates even for low open area ratios.