<p> Soil moisture is at the centre of the water balance and is of great concern with regards to crop growth and yield, irrigation planning, fertilization, climate change and non-point source pollution control. Information on soil moisture is not widely available, resulting in researchers relying on mathematical models to gain insight into soil moisture conditions. This thesis primarily focuses on long-term soil moisture characteristics, under given climate, soil and vegetation conditions. Long-term soil moisture characteristics are best described by statistics such as average soil moisture, and its standard deviation and frequency/probability distribution. After an extensive review of existing explicit or implicit soil moisture models, a deterministic water balance model was developed to simulate soil moisture at a point within the root-zone. The hydrological processes involved in the water balance are modelled using well-established methods. The continuous simulation model is unique from other leading deterministic models as it introduces the ecohydrological perspective by modelling actual evapotranspiration as a function of plant access to soil moisture. The validation of the model demonstrates that simplified soil moisture modelling is rational and practical.</p> <p> Soil moisture modelling is dependent on various input parameters related to the climate, soil and vegetation. Both local and global sensitivity analyses were carried out to investigate which input parameters influence the soil moisture regime the most. The analyses concluded that parameters representing soil texture are most important and thereby indicated that evapotranspiration is the most dominant process as it is significantly controlled by these parameters. Due to concerns of the impact of climate change and urban stormwater management, a better understanding of urban area soil moisture dynamics is required. The applicability of the continuous simulation model was demonstrated by investigating the influence of global warming on long-term soil moisture and evapotranspiration. Statistical analyses carried out on the post-simulated long-term soil moisture values clearly showed that even though temperatures are increasing, soil moisture and evapotranspiration have also increased because of the overall increase in precipitation. This phenomenon gives insight into the precipitation characteristics being strong enough to overpower the soil moisture loss process of evapotranspiration. As a part of the overall research, an analysis on antecedent soil moisture values for the purpose of urban stormwater management was performed. Empirical equations were derived to obtain antecedent soil moisture values from soil characteristics. Antecedent soil moisture information is essential in the application of the design storm approach while designing urban stormwater management infrastructure.</p> <p> The main purpose for the development and use of the deterministic model was to better understand the statistics and sensitivity of soil moisture and not as a predictive tool.</p> / Thesis / Doctor of Philosophy (PhD)

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Carbon/epoxy laminates are receiving greater attention by the infrastructure, marine, and offshore oil industries due to the need for superior performance capabilities. Such applications generally involve subjecting materials to harsh temperature and moisture conditions. The objective of this study was to provide a greater understanding of how temperature and moisture affect the strength and fatigue behavior of carbon/epoxy composites and the issues involved in modeling these effects. Results from thermal analysis and quasi-static testing on neat resin and unidirectional laminates as a function of temperature and moisture are presented which provide insight into how material properties vary with temperature and moisture and form the inputs necessary to evaluate composite strength and damage models. Fatigue life and damage accumulation testing results provide further insight into the effects of temperature and moisture and also provide a means for model validation. Generally, composite strength was found to be compromised by temperature but enhanced with moisture, while fatigue life was reduced by both temperature and moisture. Crack density with fatigue cycles was found to decrease with temperature but increase for immersed fatigue. Testing also revealed discrepancies between the edge replication and radiography methods for determining crack density. The analytical phase of the work considered a composite strength model and a damage evolution model to predict crack density. The composite strength model was found to provide an accurate dry, room temperature prediction which could be extended to an accurate prediction of wet specimen strength, but the results at elevated temperature fell conservative. The validation of the damage model proved inconclusive as it was found that the results are very sensitive to quantities such as thermal residual stresses and first ply failure. Currently, no reliable methods are available in the literature to determine these values accurately. However, the model was able to predict the decrease in crack density at elevated temperatures. The increase in crack density for immersed fatigue was not predicted. Overall, the study revealed that a more basic understanding of "in-situ" ply properties are needed before one can consider the use of predictive models in practical applications, especially in varying environments. / Ph. D.

The primary purpose of this study was to measure experimentally the uniaxial (tangential direction) equilibrium moisture profiles in moisture-sealed wood samples subjected to constant but different temperatures T on opposite faces, and to compare these profiles with those predicted by each of several theoretical models. Each test assembly consisted of eight end matched wood laminae, each 0.2 cm thick, for a total thickness of 1.6 cm in the tangential direction. Opposite faces of each moisture-sealed assembly were exposed continuously for approximately five weeks to different but constant temperatures until the original uniform moisture content M redistributed itself to a new constant but non-uniform moisture profile. At moisture equilibrium, the individual wood laminae were removed from the assembly and their moisture contents measured gravimetrically. Both temperature, T vs x, and moisture profiles, M vs x, where x is the distance from the cold face were plotted for each test. The experimental variables considered were wood species (yellow poplar and hard maple), initial moisture content (9%, 12%, and 15%), and temperature range (15°C to 35°C, and 25°C to 45°C). Each condition was replicated 3 or 4 times, giving a total number of 44 different tests. At the steady state, a moisture content profile opposite to the temperature gradient was established. The temperature gradient dT/dx was constant in all cases, with the moisture content profile increasing almost exponentially with decreasing temperature. The absolute magnitude of the calculated ratio dM/dT was found to vary with initial moisture content, temperature range, and species. The Soret coefficient, defined as - ( 1/M )( dM/dT ), was also calculated and was found to vary with the above variables as the dM/dT ratio. These two quantities always increased with wood moisture content. They were also slightly higher at the higher temperature range. There was only a small difference between species, with yellow poplar giving somewhat higher mean values. The Soret coefficient was generally in the range of 0.03 to 0.05 per degree Kelvin, except for the extremely high moisture contents near and above fiber saturation, where the calculated values approached 0.5 per degree Kelvin. The ratio dM/dT was analyzed in terms of five different theoretical models, two of which are based on nonequilibrium thermodynamics (NET) and three on classical thermodynamics. All models require sorption isotherm and heat of sorption data; and in some cases, the activation energy for moisture transport through wood. Adsorption and desorption isotherm data were obtained at 30°C for both species. Heat of sorption and moisture transport activation energy data used in testing the models were taken from the literature. The two NET models provided the best agreement with the experimental values of dM/dT. The Siau model gave the next best prediction, followed by the Stanish model, with the Skaar- Siau model giving the poorest agreement with the experimental results. The heat of transfer was also computed using the two NET models as well as those of Stanish and Siau. Values ranged from 5500 to 17000 cal/mol and from 8100 to 9900 cal/mol based on the Nelson model. The corresponding values for the Stanish for the general NET model and from model range from 15200 to 16500; while those of the Siau model varied between 11700 to 13600 cal/mol. Calculations of other quantities from the information generated in these experiments revealed that at the steady state, vapor pressure and spreading pressure were not constant across the thickness of the material; the chemical potential of water vapor and sorbed water were equal at all points indicating local equilibrium; and that the sorbed water and water vapor entropies were more or less constant across the thickness of the sample. / Ph. D.

In this paper, the application of the diffusion equation to the problem of moisture movement below the fiber saturation point is investigated. The general diffusion equation was solved by numerical methods for the case of a concentration-dependent coefficient and a boundary condition of a specified concentration variation. Experimental concentration-distance curves were generated from the drying of yellow poplar. Solutions to the diffusion equation using coefficients from the literature were then compared with the experimental data. The diffusion coefficient of yellow poplar was determined directly from the concentration-distance curves by the method of Matano. On the basis of the above information, a diffusion coefficient was determined which accurately describes the drying of yellow poplar between 61 and 181 moisture content. / Master of Science

Climatic variables have been used to calculate evapotranspiration loss by many researchers. Evapotranspiration formulas have been developed for local use in predicting soil moisture in many parts of the United States. The objective of this study was to develop a method to estimate soil moisture in Virginia using data collected by the Agricultural Engineering Department, Virginia Polytechnic Institute, Blacksburg, Virginia. The first step in the study was to determine the relationship between soil moisture and loss pan evaporation. This relationship was found on a seasonal cumulated basis. For shorter periods, the results were poor. No workable relation could be found that would satisfactorily estimate soil moisture from any of these procedures. A soil moisture accounting system based on the soil moisture balance principle was then devised in which daily evapotranspiration loss was calculated by Van Bavel’s nomogram method. Daily soil moisture and measure soil moisture were compared by the student t-test for paired observations. The results of the statistical analysis indicated it could be used to estimate soil moisture in local conditions. Finally, the correlation between daily evapotranspiration and pan evaporation was determined. A high correlation was found. The problem encountered in analyzing the data available for this study indicated the need for a detailed statistically controlled experiment. Hence an experimental design has been formulated that, hopefully, will allow an systematic investigation and evaluation of the problem. / Master of Science

Although the drying process can improve the overall quality and usefulness of forest products, if drying is not carefully controlled, drying loss can be substantial. As most drying defects occur when the lumber moisture content is above fiber saturation point (FSP), measurement of moisture content (MC) above FSP is critically important. In this study, a technique was developed which permits use of an electrical resistance moisture meter RDX-1 (Delmhorst Instrument Company) to measure MCs of red oak and yellow-poplar during drying when MC is above FSP. The Lignomat in-kiln probe electrode was used throughout experiments. Two experiments were conducted. The first dealt with developing a two-point technique to measure MC above FSP. The other evaluated the effect of the moisture gradient on the MC reading from the meter. During the drying, pin electrode also was used when oven-dry MC was about 40% in order to compare the MC readings by the pin electrode and the probe electrode. The experimental results show the correlation between the MC readings and oven-dry MC of the sample is quite high during drying; the correlation of each sample is higher than 0.9. Based on this relationship, two-point technique of measuring MC above FSP was developed. This technique can predict MC above FSP of red oak within 5%, and the MC of yellow-poplar within 10%. From the experiment, it was found, when MC is above FSP, MC readings measured by probe electrodes are significantly different from those measured by pin electrodes. It was also found that the moisture gradient affects the MC readings dramatically. The depths of probes inserted into the boards are an important parameter for measuring MC. Different depths yield different MC readings. / Master of Science

An experimental apparatus was built and operated for the measurement of moisture permeability of building materials. The data are for use in resolution of problems associated with moisture buildup in porous building materials. The apparatus is capable of maintaining simultaneous humidity and temperature differences across a test specimen. In contrast with existing experimental methods, the relative humidity on either side of the specimen is controlled without the use of quiescent saturated salt solutions. Forced-air convection at the surface of the specimen is used, resulting in uniform spatial conditions and faster results. Data are obtained for fiberboard sheathing at various temperature and humidity setpoints. The apparatus consists of two environmental chambers between which a wood-based test specimen is sealed. An external forced-air conditioning system using distilled water and molecular sieve desiccant humidifies or dries the chamber air as needed. The moisture transfer rate across the specimen is determined gravimetrically: the desiccant column is weighed to measure its change in mass as a result of moisture diffusion across the specimen. The apparatus is capable of maintaining relative humidities over a range of 5 to 65 percent RH, with a temperature difference across the specimen of up to 20°C. Furthermore, the apparatus is capable of automated relative humidity and temperature control to within ±0.5 percent RH and ±0.5°C of the setpoints, respectively. Test results for fiberboard sheathing subjected to a range of humidity and temperature conditions are presented. Results are compared with the limited data from the literature. Recommendations for improvement of the data measurement methods are included. / Master of Science