Many large composite structures are manufactured using sandwich laminates to achieve high specific bending strength and stiffness. Examples include wind turbine blades, where self-weight becomes increasingly important as blade size increases. Resin infusion of three-dimensional sandwich laminates can result in complex resin flow paths, and subsequent defect formation, which are difficult to predict. The core material used for sandwich construction and its interaction with liquid resins may also influence the formation of defects, and in the case of balsa this effect can be used to reduce defect severity. In order to evaluate the effect of cored sandwich laminate construction on the formation of defects, this thesis concentrates on the characterisation of commonly used core materials and their interaction with liquid resin under high vacuum conditions. It also considers two numerical flow-modelling packages which are shown to be effective at the prediction of flow front convergence for monolithic laminate, but over-estimate defect severity when modelling air- permeable cored laminates. For balsa core, experiments indicate that the available pore space can act as sink for trapped air, which can aid the reduction of defects where multiple flow fronts converge due to the complexity of flow in sandwich laminates. Empirical data for air absorption and desorption rates in balsa core were obtained using a custom-designed experiment. Using these data a theoretical model was developed that can indicate available pore space, which can inform optimum processing conditions, such as time under vacuum. The diffusion coefficients obtained for air absorption and desorption in balsa are very similar, and lie in the middle of published ranges for hard woods at around 2 x 10 -7 m2/s. The methodology developed for this research project represents actual behaviour of air absorption/desorption during resin infusion, whilst other techniques do not, merely measuring diffusion of air through a sample not allowing for finite pore space. In consequence, infusion strategies can be planned more precisely because core/resin interaction is better understood. Knit line defect formation could be predicted with greater accuracy with suitably modified flow-modelling programs.

Construction projects involving the installation or repair of subsurface structures or utilities often require dewatering to induce a temporary lowering of the local groundwater elevation to facilitate construction. In the event that a known contaminant plume is present in an adjacent area, this dewatering may inadvertently draw the contaminant into the previously uncontaminated work area. Uretek Holdings, Inc. has developed its Injectable BarrierSM to be installed prior to dewatering exercises to provide a groundwater cut-off by reducing the potential movement of groundwater due to the hydraulic gradient induced by dewatering. A benefit of Injectable BarrierSM as compared to conventional methods of hydraulic control is that excavation is not required prior to its installation and no excess soils are generated through its installation. Injectable BarrierSM is a proprietary process registered with the United States Patent and Trademark Office by Uretek Holdings, Inc. Since methodical in-situ testing of the effectiveness of the Injectable BarrierSM has not been performed to date, it was the focus of this research to test the performance of the barrier under in-situ conditions utilizing a subsurface environment indicative of a West-Central Florida location. A testing plot to perform this research was selected on Hillsborough County property in Tampa, Florida which provided both a relatively shallow groundwater elevation in addition to a clay confining layer at a relatively shallow depth, making this an ideal location for testing the performance of the Injectable BarrierSM. After establishing the native conditions through baseline pump testing and repeating the testing procedure following the installation of the Injectable BarrierSM, a quantification of the reduction in hydraulic conductivity was achieved. Pumping tests were performed on the Injectable BarrierSM at its standard spacing as well as modified versions of the barrier with variation in the lateral spacing to include 6 foot, 4 foot, 3 foot, and 2 foot injection patterns to determine if a modified injection process could improve its performance. The 3 foot lateral spacing corresponding to the standard Injectable BarrierSM process indicated a 20% reduction in the hydraulic conductivity following its installation. By performing a small scale excavation following the completion of all pumping tests, it was discovered that the dispersion of the material in the subsurface appeared insufficient to provide the coverage needed to establish a barrier capable of further reducing the local hydraulic conductivity, especially at the shallowest injection depth of 3 feet below land surface (ft bls). It is concluded that modified amounts of injected material, closer lateral injection spacing, and potentially modified injection temperatures and component ratios could increase the effectiveness of the Injectable BarrierSM.

published_or_final_version / Applied Geosciences / Master / Master of Science

A fracture and permeability analysis was performed on the Santana Tuff because of its similarity to the Topopah Springs unit at the Yucca Mountain site. The Topopah Springs unit is the proposed horizon for the spent nuclear fuel repository. Because of the impossibility of completely characterizing the flow properties of the unit without destroying the characteristics that make it desirable as a repository, other ash flow tuffs must be studied. The Santana Tuff and the Topopah Springs tuff both are rhyolitic in composition, nonwelded to densely welded and fractured. Fractures were examined at six outcrop locations spanning a five mile area. Stereonets and rose diagrams were constructed from over 312 fracture orientations. Although the composite data showed two major orientations of nearly vertical fractures, fracture trends at individual outcrops showed a variety of preferred orientations. Over 900 surface permeability measurements were taken using a mini-permeameter. The samples were categorized by three observed types of surface weathering: fresh, weathered, or varnished. Fracture surfaces were generally classified as weathered. The average permeabilities for the samples are 55.33 millidarcies, 5.03 millidarcies, and 3.31 millidarcies, respectively. The one-way statistical analysis performed on the data indicated that the permeability of fresh tuff surfaces is significantly different than both the permeabilities of the weathered and varnished tuffs, using both a least significant difference and greatest significant difference test. However, no difference was shown to exist between the weathered and varnished tuff permeabilities. Samples of fresh, weathered, and varnished tuffs were examined by X-Ray Defraction, the Scanning Electron Microscope, and in thin section. The SEM analysis showed surface differences between the three weathering classifications. The weathered and varnished samples were similar, exhibiting a platy, lamellate texture. The fresh surfaces were irregular and jagged. In thin section, a thin rind of dark minerals (FE-oxides) is observed on the edges of the varnished samples and in microcracks. This fills surface pores and causes the reduction in permeability. Two other zones of weathering have been identified in some of the samples, which may also cause changes in permeability. Tuff permeabilities were also analyzed for directional dependence. After an ash flow tuff is deposited and cooled, it may undergo flattening of pumice fragments and glass shards. These flattened fragments can be identified in handsamples, and are indicative of the direction of flow emplacement. The analysis showed that permeability is enhanced parallel to the emplacement direction, which is generally horizontal. Cut surfaces showed a 30% decrease in permeability perpendicular to flow direction. On varnished surfaces, this trend is still evident, although decreased in magnitude. This is expected because of the clay particles which make up the desert varnish. This study indicates that the formation of low permeability weathering rinds in association with vertical fractures may inhibit infiltration at the surface. It may accelerate infiltration at depth and allow more fluid to penetrate vertically into the tuff. In the event that fluid is absorbed into the matrix, it will travel horizontally, along the enhanced permeability parallel to the emplacement direction. / text

Uniaxial consolidation tests of resedimented mudrocks from the offshore Gulf of Mexico reveal compression and permeability behavior that is in many ways similar to those of intact core specimens and field measurements. Porosity (n) of the resedimented mudrock also falls between field porosity estimates obtained from sonic and bulk density well logs at comparable effective stresses. Laboratory-prepared mudrocks are used as testing analogs because accurate in-situ measurements and intact cores are difficult to obtain. However, few direct comparisons between laboratory-prepared mudrocks, field behavior, and intact core behavior have been made. In this thesis, I compare permeability and compressibility of laboratory-prepared specimens from Gulf of Mexico material to intact core and field analysis of this material. I resediment high plasticity silty claystone obtained from Plio-Pleistocene-aged mudrocks in the Eugene Island Block 330 oilfield, offshore Louisiana, and characterize its compression and permeability behavior through constant rate of strain consolidation tests. The resedimented mudrocks decrease in void ratio (e) from 1.4 (61% porosity) at 100 kPa of effective stress to 0.34 (26% porosity) at 20.4 MPa. I model the compression behavior using a power function between specific volume (v=1+e) and effective stress ([sigma]'v): v=1.85[sigma]'v-⁰̇¹⁰⁸. Vertical permeability (k) decreases from 2.5·10-¹⁶ m² to 4.5·10-²⁰ m² over this range, and I model the permeability as a log-linear function of porosity (n): log₁₀ k=10.83n - 23.21. Field porosity estimates are calculated from well logs using two approaches; an empirical correlation based on sonic velocities, and a calculation using the bulk density. Porosity of the resedimented mudrock falls above the sonic-derived porosity and below the density porosity at all effective stresses. Measurements on intact core specimens display similar compression and permeability behavior to the resedimented specimens. Similar compression behavior is also observed in Ursa Basin mudrocks. Based on these similarities, resedimented Gulf of Mexico mudrock is a reasonable analog for field behavior. / text

Equipment and procedures for the rapid measurement of the water vapor permeability of polymer films and food coatings has been evaluated. The method uses an electronic sensor to measure the concentration increase in water vapor diffusing through a film into a chamber of known volume. Air of known humidity is passed over each side of the film to establish a desired equilibrium relative humidity differential prior to each test. Experimental results showed that moisture vapor transmission rates of polymer packaging films and edible coatings could be determined in a range from 0.25 to 12 hours instead of the usual 24 hour period required by existing tests. Permeance values for Teflon, high density polyethylene (HDPE), polyethylene terephtalate (PET) and three coating materials were measured at relative humidity differentials between 0 - 100% and temperatures between 5 and 30°C. Results were found to be similar to values reported in the literature using standard measurement methods. This method allows the measurement of film and coating permeance values at temperature and relative humidity values close to actual food storage conditions. / Graduation date: 1994

The purpose of this study is to present the development and application of residual flow procedure for analysis of three-dimensional (3-D) steady-state and transient seepage. The finite element equations are derived using a pseudo-variational principle which leads to a transient residual flow (load) vector that, in turn, is used to correct the position of the free surface iteratively. The procedure involves a fixed mesh which requires no mesh regeneration during transient analysis and during iterations. The procedure is also capable of handling material nonhomogeneities and anisotropy with relative ease. Several applications are made including verification with respect to closed-form solutions, and with results from a laboratory glass bead model simulating three-dimensional situations. For these glass beads, the coefficients of permeability and specific storage are also evaluated experimentally.

Subsurface fluids may travel along paths having a minimum permeabilility greater than the effective permeability of the rock. This may have an important impact on contaminant migration. A stochastic approach related to percolation theory is advanced to address the question of what is the probability that a high permeability path extends across a given volume of the subsurface. The answer is sought numerically through subdividing the volume of interest into a three-dimensional grid of elements and assigning a random permeability to each element. Four permeability processes are considered: 1) Stationary with independence between grid elements; 2) Stationary and autocorrelated; 3) Nonstationary due to conditioning on measured values; and 4) Random rock volume included in grid. The results utilizing data from fractured granites suggest that in large grids, at least one path having a minimum permeability in excess of the "effective" rock permeability will cross the grid. Inclusion of autocorrelation causes an increase in the expected value of the minimum permeability of such a path. It also results in a significantly increased variance of this permeability. Conditioning on field permeabilities reduces the variance of this value over that obtained by unconditional, correlated simulation, but still produces a variance greater than that obtained when independence was assumed. When conditioning is performed, the mean of the minimum permeabilities along these paths is dependent on the principal axis of the path. Finally, including a random rock volume by allowing the length of the grid to be random increases the variance of the minimum permeability.

Thermodiffusion is one of the mechanisms in transport phenomena in which molecules are transported in a multicomponent mixture driven by temperature gradients. Thermodiffusion in associating mixtures presents a larger degree of complexity than non-associating mixtures, since the direction of flow in associating mixtures may change with variations in composition and temperature. In this study a new activation energy model is proposed for predicting the ratio of evaporation energy to activation energy. The new model has been implemented for prediction of thermodiffusion for acetone-water, ethanol-water and isopropanol-water mixtures. In particular, a sign change in the thermodiffusion factor for associating mixtures has been predicted, which is a major step forward in modeling of thermodiffusion for associating mixtures. In addition, a new model for the prediction of thermodiffusion coefficients for linear chain hydrocarbon binary mixtures is proposed using the theory of irreversible thermodynamics and a kinetics approach. The model predicts the net amount of heat transported based on an available volume for each molecule. This model has been found to be the most reliable and represents a significant improvement over the earlier models. Also a new approach to predicting the Soret coefficient in binary mixtures of linear chain and aromatic hydrocarbons using the thermodynamics of irreversible processes is presented. This approach is based on a free volume theory which explains the diffusivity in diffusion-limited systems. The proposed model combined with the Shukla and Firoozabadi model has been applied to predict the Soret coefficient for binary mixtures of toluene and n-hexane, and benzene and n-heptane. Comparisons of theoretical results with experimental data show a good agreement. The proposed model has also been applied to estimate thermodiffusion coefficients of binary mixtures of n-butane & carbon dioxide and n-dodecane & carbon dioxide at different temperature. The results have also been incorporated into CFD software FLUENT for 3-dimensional simulations of thermodiffusion and convection in porous media. The predictions show the thermodiffuison phenomenon is dominant at low permeabilities (0.0001 to 0.01), but as the permeability increases convection plays an important role in establishing a concentration distribution. Finally, the activation energy in Eyring’s viscosity theory is examined for associating mixtures. Several methods are used to estimate the activation energy of pure components and then extended to mixtures of linear hydrocarbon chains. The activation energy model based on alternative forms of Eyring’s viscosity theory is implemented to estimate the thermodiffusion coefficient for hydrocarbon binary mixtures. Comparisons of theoretical results with the available thermodiffusion coefficient data have shown a good performance of the activation energy model.

<p>This study described porosity and permeability distribution in the deep marine play of the central Bredasdorp Basin, Block 9, offshore South Africa using methods that include thin section petrography, X-ray diffraction, and scanning electron microscopy, in order to characterize their porosity and permeability distributions, cementation and clay types that affect the porosity and permeability distribution. The study included core samples from nine wells taken from selected depths within the Basin.</p>