Dissertations / Theses on the topic 'Soil structure – Mathematical models'
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1
Romanel, Celso. "A global-local approach for dynamic soil-structure interaction analysis of deeply embedded structures in a layered medium." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184762.
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The most popular method for dynamic soil-structure interaction analysis is the finite element method. The versatility in problems involving different materials and complex geometries is its main advantage, yet the FEM can not simulate unbounded domains completely. Several schemes have been proposed to overcome this shortcoming, such as the use of either imperfect or perfect transmitting boundaries, infinite elements and hybrid techniques. However, most of them were derived on the assumption that the soil mass can be represented as a homogeneous material despite the fact that stratified soil deposits are a common occurrence in nature. A hybrid method is proposed in this research for soil-structure interaction analysis in the frequency domain involving a multilayered linear elastic half-space. The near field region (structure and a portion of soil surrounding it) is modeled by finite elements while the far field formulation is obtained through the classical wave propagation theory based on the assumption that the actual scattered wave fields can be represented by a set of line sources. Traction reciprocity between the two regions is satisfied exactly, while the displacement continuity across the common interface is enforced in a least-squares sense. The two-dimensional system is excited by harmonic body waves (P and SV) propagating with oblique incidence. The structure can be considered either on the surface or deeply embedded in the multilayered half-space. Analytic solutions for the far field domain is obtained through the combined response of four simple problems that take into account the overall effects of the incident, reflected and scattered wave fields. The delta matrix technique is employed in order to eliminate the loss of precision problem associated with the Thomson-Haskell matrix method in its original form. Special numerical schemes are used to transform the solution from the κ- into the ω-plane due to the presence of poles on the path of integration. The few numerical examples studied in this research validate the proposed hybrid technique, but the relatively high computational cost required for evaluation of the Green's functions is still a serious drawback. Some suggestions are made to minimize the problem as well as to extend this technique to cases involving material attenuation and forced vibrations.
2
Romanel, Celso 1952. "DYNAMIC SOIL-STRUCTURE INTERACTION IN A LAYERED MEDIUM." Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/276511.
Full textAbstract:
The most popular method in dynamic soil-structure interaction analysis is the finite element method. The versatility in problems involving different materials and complex geometries is its main advantage, yet FEM can not simulate unbounded domains completely. A hybrid method is proposed in this research, which models the near field (structure and surrounding soil) by finite elements and the far field by a continuum approach. The system is excited by monochromatic body waves (P and SV) propagating with oblique incidence and harmonic time dependence. The far field problem is solved using Thomson-Haskell formulation associated with the delta matrix technique. The soil profile does not contain any soft layer and the layers are assumed to be linearly elastic, isotropic, homogeneous and perfectly bonded at the interfaces. Two-dimensional (in-plane) formulation is considered and the analysis is performed on both k- and o-planes through time and spatial Fourier transforms of the field equations and boundary conditions. (Abstract shortened with permission of author.)
3
Uchaipichat, Anuchit Civil & Environmental Engineering Faculty of Engineering UNSW. "Experimental investigation and constitutive modelling of thermo-hydro-mechanical coupling in unsaturated soils." Awarded by:University of New South Wales. School of Civil and Environmental Engineering, 2005. http://handle.unsw.edu.au/1959.4/22068.
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A thermo-elastic-plastic model for unsaturated soils has been presented based on the effective stress principle considering the thermo-mechanical and suction coupling effects. The thermo-elastic-plastic constitutive equations for stress-strain relations of the solid skeleton and changes in fluid content and entropy for unsaturated soils have been established. A plasticity model is derived from energy considerations. The model derived covers both associative and non-associative flow behaviours and the modified Cam-Clay is considered as a special case. All model coefficients are identified in terms of measurable parameters. To verify the proposed model, an experimental program has been developed. A series of controlled laboratory tests were carried out on a compacted silt sample using a triaxial equipment modified for testing unsaturated soils at elevated temperatures. Imageprocessing technique was used for measuring the volume change of the samples subjected to mechanical, thermal and hydric loading. It is shown that the effective critical state parameters M, ???? and ???? are independent of temperature and matric suction. Nevertheless, the shape of loading collapse (LC) curve was affected by temperature and suction. Furthermore, the temperature change affected the soil water characteristic curve and an increase in temperature caused a decrease in the air entry suction. The simulations from the proposed model are compared with the experimental results. The model calibration was performed to extract the model parameters from the experimental results. Good agreement between the results predicted using the proposed model and the experimental results was obtained in all cases.
4
Yamamoto, Nobutaka. "Numerical analysis of shallow circular foundations on sands." University of Western Australia. School of Civil and Resource Engineering, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0038.
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This thesis describes a numerical investigation of shallow circular foundations resting on various types of soil, mainly siliceous and calcareous sands. An elasto-plastic constitutive model, namely the MIT-S1 model (Pestana, 1994), which can predict the rate independent behaviour of different types of soils ranging through uncemented sands, silts and clays, is used to simulating the compression, drained triaxial shear and shallow circular foundation responses. It is found that this model provides a reasonable fit to measured behaviour, particularly for highly compressible calcareous sands, because of the superior modelling of the volumetric compression. The features of the MIT-S1 model have been used to investigate the effects of density, stress level (or foundation size), inherent anisotropy and material type on the response of shallow foundations. It was found that the MIT-S1 model is able to distinguish responses on dilatant siliceous and compressible calcareous sands by relatively minor adjustment of the model parameters. Kinematic mechanisms extracted from finite element calculations show different deformation patterns typical for these sands, with a bulb of compressed material and punching shear for calcareous sand, and a classical rupture failure pattern accompanied by surface heave for siliceous sand. Moreover, it was observed that the classical failure pattern transforms gradually to a punching shear failure pattern as the foundation size increases. From this evidence, a dimensional transition between these failure mechanisms can be defined, referred to as the critical size. The critical size is also the limiting foundation size to apply conventional bearing capacity analyses. Alternative approaches are needed, focusing mainly on the soil compressibility, for shallow foundations greater than the critical size. Two approaches, 1-D compression and bearing modulus analyses, have been proposed for those foundation conditions. From the validations, the former is applicable for extremely large foundations, very loose soil conditions and highly compressible calcareous materials, while the latter is suitable for moderate levels of compressibility or foundation size. It is suggested that appropriate assessment of compression features is of great importance for shallow foundation analysis on sand.
5
Chin, Victor B. L. "The dynamic response of pile-soil interfaces during pile driving and dynamic testing events." Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/9421.
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Bienen, Britta. "Three-dimensional physical and numerical modelling of jack-up structures on sand." University of Western Australia. School of Civil and Resource Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0208.
Full textAbstract:
Mobile offshore jack-up drilling rigs are not custom-designed for a particular location but rated for typical operating characteristics, like water depths. They may be deployed at a number of different sites during their design life. Under the current guidelines, the jack-up is required to be assessed for its suitability for each new proposed location, assuming environmental loading conditions due to wind, waves and current corresponding to a 50-year return period storm applicable to the site. Traditionally, these assessments have been performed in two dimensions, simplifying the jack-up to a plane frame and the loading conditions to be in-plane with the rig's 'axis of symmetry'. This thesis introduces a computer program, named SOS_3D, for the fluid-structure-soil interaction analysis of jack-up response in three dimensions. Extensive experimental series have been performed to provide evidence for the generalisation of the foundationsoil interaction model to general six degree-of-freedom loading conditions and its applicability to load paths and stress levels relevant to jack-up spudcans. These experiments included (1) 1g single footing tests, (2) centrifuge single footing tests and (3) centrifuge model jack-up tests. The latter tests highlighted differences in response and mode of failure depending on the loading direction of the jack-up and re-iterated the importance of three-dimensional modelling. The numerical program SOS_3D introduced early in this thesis was shown to represent a useful tool for the prediction of jack-up behaviour under general combined loading in three dimensions. It provided reasonably good, conservative predictions of the experimentally measured jack-up behaviour.
7
Manivannan, Ganeshalingam Aerospace Civil & Mechanical Engineering Australian Defence Force Academy UNSW. "Viscoplastic modelling of embankments on soft soils." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Aerospace, Civil and Mechanical Engineering, 2005. http://handle.unsw.edu.au/1959.4/38743.
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A major instrumented geosynthetic reinforced approach embankment was constructed to 5.5 m elevation above ground, with prefabricated vertical drains, over a soft compressible clay deposit at Leneghan, Newcastle, Australia in May 1995. The field monitoring of settlements for over six years shows that the embankment manifests significant creep. The instrumentation, field performance and the finite element analyses for predicting the long-term performance of this embankment are described in this thesis. The maximum settlement of 1.1 m was observed one year after the completion of construction. However, the embankment continued to settle at a rate of 0.4 mm/day for the next 5 years. The horizontal displacements of 0.09-0.14 m at various locations and the maximum reinforcement strains of 0.67% were recorded. A numerical model was developed to perform a fully coupled large deformation elasto-viscoplastic finite element analysis for this performance prediction based on creep model proposed by Kutter and Sathialingam (1992). The foundation soil was modelled with creep material behaviour using six noded linear strain triangular elements. A well-documented case history ??? Sackville embankment, New Brunswick, Canada was analysed using this model as a benchmark problem and the model was found to predict all the behaviour characteristics reasonably well. The results obtained from finite element analysis using this model are shown to be in reasonable agreement with the observed performance of Leneghans embankment in terms of settlements, horizontal displacements, excess pore pressures and geosynthetic strains. But, the prediction of settlements was less than satisfactory beyond April 1999. Finite element analyses were performed to study the sensitivity of this embankment behaviour on the variation of hydraulic conductivity values and geosynthetic reinforcement properties. This sensitivity study indicated that the kv variation, the kh/kv ratio and the nominal values of geosynthetic properties adopted in the benchmark analysis are reasonable enough for the long-term behaviour prediction.
8
Abdelhedi, Anouar. "Modélisation de l'effet de groupe dans le clouage des pentes." Paris 6, 1986. http://www.theses.fr/1986PA066042.
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De récentes expérimentations réalisées sur des sites réels, ont permis de mettre en évidence la complexité du comportement de groupe de pieux dans une pente instable. On fait le point sur les méthodes existantes et on approfondit l'étude du mécanisme du comportement du sol au voisinage d'une rangée de pieux en se limitant au phénomène d'interaction sol-pieu. Apres étude bibliographique du phénomène donnant lieu à la programmation de deux des méthodes les plus significatives, on réalise deux approches en déformation: modélisation en continuum élastique permettant de prendre en compte une géométrie de maillage des pieux quelconques et d'appliquer au groupe une sollicitation en déplacement très générale, modélisation s'appuyant sur la méthode des éléments finis et sur un modèle bidimensionnel horizontal simulant l'écoulement du sol entre une rangée de pieux. Comparaison de diverses méthodes.
9
Barrett, Gary Edward. "Infiltration in water repellent soil." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28618.
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Observations made at Goat Meadows - a small sub-alpine basin located near Pemberton, British Columbia -demonstrated that a layer which is either water repellent or has only a limited affinity for water is present at most vegetated sites. The layer is typically a few centimetres in thickness, and is usually located at or near the top of the profile: it was present only in the zone of accumulation of organic matter. The spatial distribution of the layer did not appear to be related to the distribution of any particular species of plant. Sampling of sub-alpine sites in the Cascade, Selkirk, and Purcell Mountains indicated that such layers are common in the alpine - sub-alpine ecotone of southern British Columbia.
The relationship between ponding depth and infiltration rate was explored through experiments conducted on samples collected near Ash Lake, in Goat Meadows. These samples were chosen for analysis because the repellent layer was in excess of thirty centimetres thick at this site. Infiltration rates remained below 2x10⁻⁹ m/s for all samples, even given ponding depths of up to forty centimetres. Breakthrough of liquid water was not observed, even after one month, which implies that most of the infiltration occurred as vapour transfer.
In order to observe the movement of liquid water through water repellent media, a plexiglas cell was constructed. A synthetic water repellent sand with uniform surface properties was used as the medium. It was found that up to some critical depth, there was no entry of water into the medium. As the ponding depth was increased in steps, the front would advance in steps: it remained stationary between these step-increases in ponding depth. As the front advanced, protuberances or "fingers" began to develop. At some critical ponding depth, a finger would grow without bound. These observations pose a challenge to existing models of infiltration, since it appears that heterogeneity at the scale of individual pores must be invoked to explain them, but it is usually assumed that the properties of a porous medium are continuous at this scale.
The thermodynamics of filling and emptying of pores is considered with emphasis on the effects of pore shape and of variations in the physicochemical properties at the scale of the pore. This thermodynamic analysis provides the conceptual basis for development of a model of infiltration in which pore-scale heterogeneity is preserved. Although it was not developed as such, the model follows the approach of cellular automata, in which local relations between pores or "cells" govern the behaviour of the system. The model replicated the observations of infiltration into synthetic water repellent porous media well: both the halting advance of the front as the ponding depth was increased and the development of fingers were simulated. The fact that such complex behaviour was predicted using only a simple set of physically based rules confirms the power of the approach.Arts, Faculty of
Geography, Department of
Graduate
10
Sorooshian, Soroosh, and Vijai Kumar Gupta. "Improving the Reliability of Compartmental Models: Case of Conceptual Hydrologic Rainfall-Runoff Models." Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1986. http://hdl.handle.net/10150/614011.
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11
Dang, Hoang Kien 1981. "The application of a multilaminate model to simulate tunnelling in structured clays : a dissertation." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99755.
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Due to the complex characteristics of tunneling problems, tunneling engineering is perhaps one of the areas in which numerical methods are more frequently adopted in practice. One important application is to examine the influence of an excavation and construction procedures on the stress distribution and deformation in the ground surrounding the opening and on the tunnel lining. Another important aspect of tunneling problems that can be accounted for in a numerical analysis is the complex geometry associated with typical applications. This is not only related to the shape of the opening, but also to the presence of non-homogenous or non-isotropic soil strata.A constitutive model that is suitable for the analysis of structured clays has been developed in this study based on the multilaminate framework. The model takes into account the elastic unloading-reloading, inherent and induced anisotropy, destructuration and bonding effects. The model is implemented into Plaxis finite element program, successfully calibrated and used to investigate the response of structured sensitive clay to the construction of the Gatineau tunnel in Gatineau, Quebec and the Ottawa sewer tunnel in Ottawa, Ontario. Numerical results were compared to the field measurements taken during the tunnel construction. To improve the performance of the numerical model, an implicit integration algorithm is implemented and proven to be very effective as compared to the conventional explicit integration methods. The effect of different soil parameters including bonding and anisotropy on the tunneling induced displacements and lining stresses is also examined using a comprehensive parametric study. The results indicated that soil bonding and anisotropy have significant effects on the shape of the settlement trough as well as the magnitudes of surface displacements and lining stresses induced by tunneling.
12
Pitsillis, Zachry Steven. "Estimating dynamic affine term structure models." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15731.
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Duffee and Stanton (2012) demonstrated some pointed problems in estimating affine term structure models when the price of risk is dynamic, that is, risk factor dependent. The risk neutral parameters are estimated with precision, while the price of risk parameters are not. For the Gaussian models they investigated, these problems are replicated and are shown to stem from a lack of curvature in the log-likelihood function. This geometric issue for identifying the maximum of an essentially horizontal log-likelihood has statistical meaning. The Fisher information for the price of risk parameters is multiple orders of magnitude smaller than that of the risk neutral parameters. Prompted by the recent results of Christoffersen et al. (2014) a remedy to the lack of curvature is attempted. An unscented Kalman filter is used to estimate models where the observations are portfolios of FRAs, Swaps and Zero Coupon Bond Options. While the unscented Kalman filter performs admirably in identifying the unobserved risk factor processes, there is little improvement in the Fisher information.
13
Park, Soojin. "Modelling soil-landform continuum on a three-dimensional hillslope." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670238.
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Mtundu, Nangantani Davies Godfrey. "The Stochastic Behavior of Soil Moisture and Its Role in Catchment Response Models." PDXScholar, 1987. https://pdxscholar.library.pdx.edu/open_access_etds/527.
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The object of current efforts at investigating catchment response is to derive a physically based stochastic model of the watershed. Recent studies have, however, indicated that a limiting factor in deriving such models is the dependence of hydrologic response on initial soil moisture. The dependence affects the distributions and moments of the hydrological processes being investigated. A stochastic model of soil moisture dynamics is developed in the form of a pair of stochastic differential equations (SDE's) of the Ito type. The sources of stochasticity are linked to the random inputs of rainfall and evapotranspiration (ET). One of the SDE's describes the "surplus" case, in which sufficient infiltration always occurs to allow for moisture depletion by the processes of drainage through and ET out of the root zone. The other SDE represents the "deficit" case, in which lack of adequate moisture leads only to an ET-controlled depletion process. Sample functions and moments of moisture evolution are obtained from the SDE's. From the general model of soil moisture, a specific model of initial soil moisture (the moisture at the beginning of a rainstorm event) is developed and its moments are derived. Furthermore, the probability distribution of initial moisture is postulated to permit the assessment of how initial moisture affects the estimation of hydrologic response. The moisture dynamics model reveals that the stochastic properties of moisture ae sensitive to initial conditions in the watershed only for less permeable soils under the "surplus" state but are practically insensitive to such conditions for more permeable soils. The stochastic properties are also less sensitive to initial conditions for all soil types whenever under the "deficit" state. These results suggest that hydrologic processes, such as precipitation excess and infiltration, depend on initial moisture only in regions where the soils are generally less permeable and where the climate tends to sustain a "wet" environment, whereas in arid or semi-arid regions, such processes would not depend on initial moisture. These conclusions imply that, in arid regions, an effective value of initial moisture such as the mean can be used to estimate the properties of the hydrologic processes, whereas in "wet" environments, more accurate values of the properties must be "weighted" based on the probability distribution of initial soil moisture.
15
Musa, Zulkarnain 1964. "An accelerated conjugate direction procedure for slope stability analysis." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276912.
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CSLIP2 (De Natale, 1987) is the only slope stability program that utilizes a "direction set" optimization routine in its search for the minimum safety factor. However, CSLIP2 which employs Powell's Conjugate Direction Method permits only the horizontal and vertical directions (x and y) to be used as the initial direction set. The efficiency of the existing search routine is improved by replacing the x-y coordinate directions with initial directions that are parallel to and perpendicular to the principal axis of the safety factor contours.
16
Sande, Leif Andrew. "Experimental Studies on Infiltration/Soil-Water Movement Processes and Green-AMPT Modeling." Thesis, North Dakota State University, 2011. https://hdl.handle.net/10365/29329.
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Experimental studies on infiltration/soil-water movement processes are vital to
better understanding movement of soil-water in the vadose zone. The objective of this
experimental research was to investigate infiltration/soil-water movement processes
utilizing laboratory experiments and computer modeling. Small scale laboratory soil box
infiltration experiments were conducted and utilized for the improved parameterization of
the Green-Ampt (GA) saturated moisture content parameter to produce an effective
moisture content parameter (Be) for utilization in a modified GA model. By incorporating ?e
values into GA modeling, modeling results showed greatly improved wetting front
prediction across different soil conditions. A new soil packing method was proposed for
replicating complex microtopographical surfaces with uniform bulk densities in laboratory
soil box experiments which proved efficient and effective at accomplishing both objectives.
A rainfall simulator and an instantaneous-profile laser scanner were used to simulate
rainfall and quantify surface microtopography for experiments. The results clearly show the
effect of microtopography on infiltration and soil-water movement characteristics. This
offers valuable insight into infiltration/soil-water movement processes as affected by
different soil and surface microtopographic conditions.National Science Foundation (Grant No. EAR-0907588)
17
Aldaikh, Hesham S. H. "Discrete models for the study of dynamic structure-soil-structure interaction." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633205.
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The problem of Dynamic Structure-Soil-Structure Interaction (SSSI) refers to the mutual interaction of adjacent buildings in built-up high density areas through the underlying soil under earthquake excitation. Due to the complexity of the problem, past studies have mainly considered the use of intricate mathematical formulations or the computationally demanding numerical Finite Element and Boundary Element methods. In the present study, linear elastic two-dimensional formulations are proposed using simple discrete lumped parameter models for structures and soil for groups of two and three adjacent buildings systems. The formulation includes a rotational spring as a key buildings interaction mechanism. Inverse power laws are proposed for this rotational interaction and for soil/foundation springs stiffnesses which turn out to be functions of spacing between adjacent buildings. These relationships are obtained by equating energies from the low order discrete and high order Finite Element models.
18
Hendrickson, Jene Diane, and Soroosh Sorooshian. "CALIBRATION OF RAINFALL-RUNOFF MODELS USING GRADIENT-BASED ALGORITHMS AND ANALYTIC DERIVATIVES." Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ), 1987. http://hdl.handle.net/10150/614186.
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In the past, derivative-based optimization algorithms have not
frequently been used to calibrate conceptual rainfall -riff (CRR)
models, partially due to difficulties associated with obtaining the
required derivatives. This research applies a recently- developed
technique of analytically computing derivatives of a CRR model to a
complex, widely -used CRR model. The resulting least squares response
surface was found to contain numerous discontinuities in the surface
and derivatives. However, the surface and its derivatives were found
to be everywhere finite, permitting the use of derivative -based
optimization algorithms. Finite difference numeric derivatives were
computed and found to be virtually identical to analytic derivatives.
A comparison was made between gradient (Newton- Raphsoz) and
direct (pattern search) optimization algorithms. The pattern search
algorithm was found to be more robust. The lower robustness of the
Newton-Raphsoi algorithm was thought to be due to discontinuities and a
rough texture of the response surface.
19
Huang, Xin, and 黃昕. "Exploring critical-state behaviour using DEM." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206742.
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The critical state soil mechanics (CSSM) framework originally proposed by Schofield & Wroth (1968) has been shown to capture the mechanical behaviour of soils effectively. The particulate implementation of the discrete element method (DEM) can replicate many of the complex mechanical characteristics associated with sand. This research firstly shows that the CSSM framework is useful to assess whether a DEM simulation gives a response that is representative of a real soil. The research then explores the capacity of DEM to extend understanding of soil behaviour within the CSSM framework.
The influence of sample size on the critical-state response observed in DEM simulations that use rigid-wall boundaries was examined. The observed sensitivity was shown to be caused by higher void ratios and lower contact densities adjacent to the boundaries. When the void ratio (e) and mean stress (p’) of the homogeneous interior regions were considered, the influence of sample size on the position of the critical state line (CSL) in e-log(p’) space diminished.
A parametric study on the influence of the interparticle friction (μ) on the load-deformation response was carried out. The macro-scale stress-deformation characteristics were nonlinearly related to μ and the particle-scale measures (fabric, contact force distribution, etc.) varied systematically with μ. The limited effect of increases in μ on the overall strength at high μ values (μ>0.5) is attributable to transition from sliding-dominant to rolling-dominant contact behaviour. A μ value higher than 0.5 leads to a CSL in e-log(p’) space that does not capture real soil response.
True-triaxial simulations with different intermediate stress ratios (b) were performed. The dependency of strength on b agreed with empirical failure criteria for sands and was related to a change of buckling modes of the strong force chains as b increased. DEM simulations showed that the position of the CSL in e-log(p’) space depends on the intermediate stress ratio b. This sensitivity seems to be related to the dependency of the directional fabric anisotropy on b. The link between the state parameter and both soil strength and dilatancy proposed by Jefferies & Been (2006) was reproduced in DEM simulations.
A new rotational resistance model was proposed and it was shown that the new model can qualitatively capture the influence of particle shape on the mechanical behaviour of sand. However, it was shown that the effect of rotational resistance is limited and to quantitatively compare the DEM simulation results with laboratory testing data, e.g., the critical-state loci, it is necessary to use non-spherical particles.published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy
20
Galadima, A., and J. C. Silvertooth. "Mathematical Models of Potassium Release Kinetics for Sonoran Desert Soils of Arizona." College of Agriculture, University of Arizona (Tucson, AZ), 1998. http://hdl.handle.net/10150/210381.
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The objective of this study was to determine the potassium (K) release kinetics of clay samples from 10 agricultural representative soils of Arizona by successive extraction using Ca-saturated cation resin. A 1993 physical and chemical characterization of the soils revealed that all soils contain smectite-mica K bearing minerals. Four mathematical models (power function, Elovich, parabolic diffusion and first-order) were used to describe the nonexchangeable K release reaction involving 700-hr cumulative reaction time. Comparison of the models using the coefficient of determination (r²) and the standard error of the estimate (SE) indicated that the Elovich and the power function equations overall displayed the best fit. The first-order rate and for the most part, the parabolic diffusion equation did not describe the K release very well. The constants a and b for the Elovich and the power function equations, which represent the intercept and the release rate of the nonexchangeable K respectively, are at least in the order of magnitude as those found by others in several previous studies.
21
Sylvester, Matthew. "Calibrating Term Structure Models to an Initial Yield Curve." Master's thesis, Faculty of Commerce, 2021. http://hdl.handle.net/11427/33027.
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The modelling of the short rate offers many advantages, with the models explored in this dissertation all offering closed-form, analytic formulae for bond prices and for options on bonds. Often, a vital primary condition is for a model to be calibrated to the initial term structure and to recover the bond prices observed in the market – that is, to be calibrated to the initial yield curve. Under the two exogenous models explored in this dissertation, the Hull-White and the CIR++, the effect of increasing the volatility parameter of the SDE increases the mean of the short rate. Increasing volatility of an SDE is a common approach to stress testing a model, as such, the consequences of bumping volatility in a calibrated model is a vital concern. The Hull-White model and CIR++ model were calibrated to market data, with the former being able to match the observed cap prices, while the latter failed, displaying an upper bound on cap prices. Investigating this, under CIR++ model, bond option prices are shown to not be straightforward increasing functions of the volatility parameter. In fact, for high volatility, bond option prices display an upper limit before decreasing, thus providing a limit to the level of cap prices too. This dissertation points to the reason residing in the underlying CIR model from which the CIR++ is based on, and the manner in which the model is extended
22
趙學安 and Xuean Zhao. "Electrochemical capacitance in a mesoscopic structure." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31239778.
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Yu, Albert Chun-ming. "The dynamics of capital structure choice." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/24408.
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This thesis employs two-period state-contingent model based upon the "tax shield plus bankruptcy costs" approach to examine the dynamic capital structure decision. By allowing recapitalization at the end of period one, we can analyse the dynamics of the firm's capital structure choice. Also, the effect of a call provision on bonds can be examined.
Simulated results show that the firm will recapitalize at the end of period one only if the gain in firm value, with- or ex-dividend, resulting from recapitalization exceeds the after-tax flotation costs. There exists a tolerable recapitalization boundary within which the firm will not recapitalize. This implies that the empirically observed capital structure is not necessarily at the acme of the firm value function, as most empirical studies assume.
Another important result is that a call provision on bonds may be wealth reducing; the call provision may reduce the wealth of shareholders by inducing recapitalization in states which is suboptimal if there is no call provision, and incurs flotation costs which could have been avoided. The gain in firm value resulting from recapitalization may be too small to justify the extra flotation costs and thus reduces the overall firm value.Business, Sauder School of
Graduate
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Zhao, Qian, and 赵倩. "A thermomechanical approach to constitutive modeling of geomaterials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47166836.
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Modeling of the mechanical behavior of geomaterials is a fundamental yet very
difficult problem in geotechnical engineering. The difficulty lies in that the
engineering behavior of geomaterials is strongly nonlinear and anisotropic,
depending on confining pressure, void ratio, stress history, and drainage conditions.
A traditional approach to the modeling of geomaterials is to formulate empirical
equations to fit experimental data. Generally, this approach is not able to provide
physical insights into the diverse responses observed in the soil mechanics
laboratories. Another conventional approach is to make use of the classical
plasticity theory, established mainly for metals, to develop constitutive models for
geomaterials. While this approach is capable of shedding light on the mechanisms
involved, it has been recognized that such models may violate the basic laws of
physics.
The objective of this thesis is to apply a new approach to constructing constitutive
models for geomaterials, by making use of thermomechanical principles. The
essence of the new approach is that the constitutive behavior of geomaterials can be
completely determined once two thermomechanical potentials, i.e. the free energy
and dissipation rate functions, are specified. The yield function and flow rule in the
classical plasticity theory can be established from the two potentials, and the
models so derived satisfy the basic laws of physics automatically. In this thesis, the
theoretical framework for constructing thermomechanical models is introduced.
Several concepts in relation to plastic work, dissipated and stored energy are
discussed. Both the isotropic and anisotropic models are formulated and realized in
this framework and the generated predictions are compared with the test data of a
series of triaxial compression tests on sand. To address the important density- and
pressure-dependent behaviors of sand in the framework, a state-dependent
thermomechanical model is developed, by introducing the state parameter into the
dissipation rate function such that a unique set of model parameters is able to
predict the behaviors of sand for a wide variation of densities and pressures. Finally,
a thermomechanical model for predicting the complex unloading and reloading
behaviors of sand is developed by modifying the hardening laws, and the
performance of this model is investigated.published_or_final_version
Civil Engineering
Master
Master of Philosophy
25
He, Shu Yu. "Field study on influence of atmospheric parameters and vegetation on variation of soil suction around tree vicinity." Thesis, University of Macau, 2018. http://umaclib3.umac.mo/record=b3868734.
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Schwellnus, Adrian. "Linear-Rational Term Structure Models With Flexible Level-Dependent Volatility." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29215.
Full textAbstract:
The Linear-Rational Framework for the modelling of interest rates is a framework which allows for the addition of spanned and unspanned factors, while maintaining a lower bound on rates and tractable valuation of interest rate derivatives, particularly swaptions. The advantages of having all these properties are significant. This dissertation presents the Linear-Rational Framework, and specializes the factor process to a class of diffusion models which allows for the degree of state dependence of volatility to be estimated. This dissertation then finds that the estimated state dependent volatility structure is significantly different to that of typical models, where it is set it a priori. The effect the added degree of freedom has on the model implied swaption skew is then analysed.
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Ramnarayan, Kalind. "Level Dependence in Volatility in Linear-Rational Term Structure Models." Master's thesis, Faculty of Commerce, 2019. http://hdl.handle.net/11427/31207.
Full textAbstract:
The degree of level dependence in interest rate volatility is analysed in the linearrational term structure model. The linear-rational square-root (LRSQ) model, where level dependence is set a priori, is compared to a specification where the factor process follows CEV-type dynamics which allows a more flexible degree of level dependence. Parameters are estimated using an unscented Kalman filter in conjunction with quasi-maximum likelihood. An extended specification for the state price density process is required to ensure reliable parameter estimates. The empirical analysis indicates that the LRSQ model generally overestimates level dependence. Although the CEV specification captures the degree of level dependence in volatility more accurately, it has a trade-off with analytical tractability. The optimal specification, therefore, depends on the type of model implementation and general economic conditions.
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Richard, Paul François. "A computer analysis of the flow of water and nutrients in agricultural soils as affected by subsurface drainage." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/29171.
Full textAbstract:
A computer model was developed in order to determine the effects of drainage practices on nutrient losses from level agricultural soils.
The model performs a daily simulation of the vertical flow of water, nitrogen, phosphorus, and heat, and of the growth of crops. A water flow submodel calculates the depth of the water table based on daily predictions of evaporation, transpiration, flow to drains and ditches, and deep percolation. An original saturated-unsaturated flow algorithm is used to determine moisture infiltration, redistribution, and upward flow in the soil matrix, as well as bypassing flow in the soil macropores and horizontal flux between the soil matrix and the macropores, and surface runoff. Nutrient movement occurs by mass flow. Heat flow, nutrient biochemical transformations, and crop growth are determined by using well established relations.
Field tests were carried out for a period of two years on an experimental site in the Lower Fraser Valley of British Columbia. The water table depth was measured on a continuous basis. Grab samples of drainwater and observation wells were obtained periodically and analyzed for nitrogen (N0₃-N, NH₄-N, and TKN) and phosphorus (P0₄-P and TP). The field results show a decrease in the concentration of all nutrients over the sampling period, and provide evidence that denitrification and bypassing flow are important mechanisms affecting the nutrient balance of this soil.
These results were used to calibrate the model. An excellent fit of the observed water table profile and an adequate fit of the observed drain concentration of nitrate were obtained. The simulation revealed that bypassing flow is a very important transfer mechanism in this soil and must be included in order to obtain a satisfactory fit of the experimental data.
A sensitivity analysis of the model showed that the patterns of moisture flow have a predominant influence on the rate of nutrient leaching. In particular, it was found that the nutrient concentration in drain water is a strong function of the hydraulic conductivity of the soil matrix and of the horizontal distance between the soil macropores, which control the ratio of moisture flow in the soil matrix to the macropore flow and the lateral diffusion of nutrients between the soil matrix and the macropores.
The effects of four different drainage designs on nutrient losses were simulated over a period of two years for three different soils and two different nutrient distributions in the soil. It was found that there is a large difference between the amount of nutrients leached from drainage systems using different drainage coefficients. There was also a large difference in the response of two drainage designs based on the same drainage coefficient but using different depth and spacing of drains. Transient effects, as determined by the initial vertical distribution of the nutrients, were seen to remain dominant over the two year duration of the simulation.
The model was found to be useful in explaining the apparent contradictions found in the literature assessing the effects of subsurface drainage on nutrient losses. The results from the model show these effects to be strongly site and condition specific. Furthermore, the model shows that soils and drainage designs that produce similar volumes of drain flow may exhibit very different leaching responses, and that drainage designs equivalent from a hydraulic standpoint can be very dissimilar in their potential for leaching nutrients. The model provides a tool which can be used to determine the appropriateness of different drainage designs in soils where minimizing nutrient losses is critical.Science, Faculty of
Resources, Environment and Sustainability (IRES), Institute for
Graduate
29
Pawlowska, Bogna Julia. "Mathematical models of microbial evolution : cooperative systems." Thesis, University of Exeter, 2016. http://hdl.handle.net/10871/26819.
Full textAbstract:
Microbes usually live in large communities, where they interact with other organisms and species. These interactions include cooperation, when individuals facilitate each others growth and reproduction. Such cooperation has been for instance observed within pathogens in the process of infection. Therefore, given the number and the frequency of infectious diseases, understanding the nature and the dynamics of microbial cooperation may be a crucial step in modern medicine. Microbes often secrete costly enzymes which extracellularly metabolise resources available in the environment. This external metabolism is a form of ’public good cooperation’, in which individuals invest their energy in producing ’public goods’, available to other organisms. To study this phenomenon we deploy mathematical models which are based on biologically relevant assumptions. Our models not only aim to capture the dynamics of studied microbial communities, but also to remove the natural complexity arising in the empirical studies and thus to provide a mechanistic understanding of their results. We first recover and explain the recent empirical finding, about mixed strain infections, showing that an addition of a low virulent strain which does not produce public goods (termed ’cheat’) may counter-intuitively enhance the total population virulence. What drives this result turns out to be an interaction of two different cooperative traits and the presence of spatial structure. Next we study the competition between the strains that do and do not produce public goods. Our results depend on environmental conditions, such as resource concentration and population density, but they are also determined by the degree of spatial structure - the ecological trait which so far has been treated only as a binary variable. Finally, we identify some environmental threats for the external metabolism feeding strategy, and we examine its competitiveness in comparison to ’internal metabolism’, in which the costly enzymes are private.
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Anderson, James William Justin. "Probabilistic models of RNA secondary structure." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:3e58e9d9-c58d-4616-8e88-4082d1ca0e2a.
Full textAbstract:
This thesis develops probabilistic models of RNA secondary structure. The first chapter introduces RNA secondary structure prediction, in particular stochastic context-free grammars (SCFGs), and considers a novel method for automated design of SCFGs. Many SCFGs are found with a similar predictive quality as those commonly used for RNA secondary structure prediction. The second chapter discusses the effect alignment quality, evolutionary distance between sequences, and number of sequences in an alignment have on RNA secondary structure prediction. By combining statistical alignment and SCFG models we can, in a statistically sound setting, average structure predictions over the space of alignments to decrease loss created by poor alignments. The third chapter incorporates additional biological information about RNA secondary structure formation into the decoding of the SCFG posterior distribution. Combining iterative helix formation, phylogenetic modelling, and a distance function between alignment columns leads to the an improvement in the accuracy of comparative RNA secondary structure prediction. Finally, appendices briefly discuss further work concerning probabilistic models of RNA secondary structure which may be of interest to the reader.
31
Karlsson, Anton. "Population Models with Age and Space Structure." Thesis, Linköpings universitet, Matematik och tillämpad matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-134926.
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In this thesis, basic concepts of populational models are studied from a theoretical point of view, especially the long term behaviours. All models are at least time dependent with additional age structure, spatial structure. The last model which is an extension of the von Foerster equation, is dependent on all o f these structures and have a long-term solution for large values of time. Modeling population is a frequent subject in modern biology. It is hard to create a model that appears as realistic as possible. First one might consider that a population size is governed by the current size of the population, along with rates of how each individual contributes (give birth), so that the population increases. and how frequent an individual dies, causing the population to decrease in size. However these sort of models can only describe the size of population in a shorter span of time.
32
Ahmad, Faheem. "Numerical modelling of transport of pollutant through soils." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08182009-040239/.
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Wall, Steven E. "Structure and evolution of thermohaline staircases in tropical North Atlantic." Thesis, Monterey, Calif. : Naval Postgraduate School, 2007. http://bosun.nps.edu/uhtbin/hyperion-image.exe/07Dec%5FWall.pdf.
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Thesis (M.S. in Physical Oceanography)--Naval Postgraduate School, December 2007.Thesis Advisor(s): Radko, Timour. "December 2007." Description based on title screen as viewed on January 24, 2008. Includes bibliographical references (p. 83-86). Also available in print.
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Liu, Ying, and 劉影. "Limit equilibrium methods for slope stability analysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B42576684.
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Cottereau, Régis. "Probalilistic models of impedance matrices : application to dynamic soil-structure interaction." Châtenay-Malabry, Ecole centrale de Paris, 2006. http://www.theses.fr/2006ECAP1034.
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Dans de nombreux domaines d’application, comme en génie civil ou en aéronautique, les ingénieurs sont confrontés a des problèmes de dimensionnement de structures en contact avec un domaine non-borné. Pour ces problèmes, seule la structure intéresse réellement les ingénieurs, et le domaine extérieur n’a d’importance que par sa raideur équivalente, en statique, ou sa matrice d’impédance, en dynamique. Par ailleurs, les domaines infinis considérés dans ces applications sont souvent mal connus ou complexes à modéliser. Cela entraîne des erreurs et incertitudes pour les estimations faites sur la structure, qui peuvent être en partie prises en compte par des approches probabilistes. On propose donc dans cette thèse un modèle probabiliste des matrices d'impédance, qui généralise l'approche non-paramétrique proposée récemment par Soize pour les prédictions des vibrations de structures aléatoires. La construction de ce modèle probabiliste nécessité tout d'abord la construction d'un modèle déterministe approché, dit à variables cachées, des matrices d'impédance suivant leurs propriétés de base, dont, notamment, la causalité. Ce modèle doit être identifié à partir de calculs numériques ou de mesures, et la procédure d'identification est également developpée dans le cadre de la thèse. Deux applications sont proposées. Le modèle non-paramétrique de matrice d'impédance est d'abord comparé, sur un cas simple d'interaction dynamique sol-structure, à un modèle paramétrique pour illustrer les principales différences entre les approches. Ensuite, un cas plus industriel de dimensionnement sismique permet d'envisager l'utilisation pratique du modèle probabiliste non-paramétriqueIn many application fields, as in civil engineering or aeronautics, engineers have to deal with design problems where the structure is coupled to an unbounded domain. For these problems, only the structure is of interest, and the behavior of the exterior domain is taken into account through its equivalent stiffness, in statics, or its impedance matrix, in dynamics. The models for the unbounded domains considered in these applications are usually coarse and the information available on their properties scarse and polluted. This leads to errors in the estimation of the behavior of the structure, which may partially be taken into account by using probabilistic approaches. We present, in this Ph. D. Thesis a probabilistic model of impedance matrices, which generalizes the nonparametric approaches introduced recently by Soize for the predictions of vibrations in random structures. The construction of this probabilistic model first requires the construction of a deterministic model, so-called hidden variables model, that verifies the basic properties of impedance matrices, among which the causality. The hidden variables model has to be identified from numerical results or experimental measures, and the identification procedure is also developed in this thesis. Two applications are presented. Our nonparametric model of the impedance matrix is first compared to a parametric model, on a classical problem in dynamic soil-structure interaction, to illustrate the main differences between the two approaches. Then, it is used in a more industrial seismic design problem, to show the practical application of the nonparamatric probabilistic model of impedance matrices
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Tokwe, Thabo. "Kalman Filtering and the Estimation of Multi-factor Affine Term Structure Models." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29465.
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When optimising the likelihood function one often encounters various stationary points and sometimes discontinuities in the parameter space (Gupta and Mehra, 1974). This is certainly true for a majority of multi-factor affine term structure models. Practitioners often recover different parameter optimisations depending on the initial parameters. If these parameters result in different option prices, the implications would be severe. This paper examines these implications through numerical experiments on the three-factor Vasicek and Arbitrage-free Nelson-Siegel (AFNS) models. The numerical experiments involve Kalman filtering as well as likelihood optimisation for parameter estimation. It was found that the parameter sets lead to the same short rate process and thus the same model. Moreover, likelihood optimisation in the AFNS does not result in different parameter sets irrespective of the starting point.
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Sun, Tek-kei, and 孫廸麒. "Numerical modeling of skin friction and penetration problems in geotechnical engineering." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/195991.
Full textAbstract:
Numerical modeling using finite element method (FEM) is well-recognized as a powerful method for both engineers and researchers to solve boundary value problems. In the modeling of geotechnical problems, the analyses are often limited to simple static problems with either steady-state effective or total stress approach while the transient response (development and dissipation of excess pore water pressure, uex) is seldom considered. Besides, infinitesimal small soil deformation is usually assumed. The simulation is further complicated when the soil-structure interaction problems involve significant soil displacements; like a pile subject to negative skin friction (NSF) and a cone/pile penetration. However, conventional FEM analysis prematurely terminates due primarily to excessive mesh distortion. One could see that simulating a transient problem with large deformation and distortion remains a great challenge. In this study, advanced FE simulations are performed to give new insights into the problems of (1) a pile subject to NSF; and (2) a cone penetration. The transient response of the NSF problem is modeled with the fluid-coupled consolidation technique and geometric nonlinearity. The fluid-coupled cone penetration problem is modeled with a newly developed adaptive approach.
The NSF and cone penetration simulations involve complex soil-structure interface modeling. Two types of modified interface responses are developed and verified which consider fluid coupling. The developed algorithm is applied to back analyze a case history of a pile subject to NSF induced by surcharge loading. Promising results were shown. Development of dragload and neutral plane (NP) with time is studied. NP locates at 75% of the pile embedded length (D) in long-term. Next, a parametric study is performed to investigate the influences of pile geometries, ground compressibility and loading conditions towards the pile responses. The long-term NP locates at around 0.55D to 0.65D in the studied engineering scenarios. The maximum downdrag can be up to 10% of the pile diameter. NP shifts upward when the head load increases. A simple design chart is proposed which helps engineers to estimate the long-term axial load distribution. An illustrative example is given to demonstrate the application and performance of the chart.
The study is extended to investigate the cone penetration problem. An advanced adaptive method is developed and implemented into the FE package ABAQUS to resolve the problems of numerical instability, excessive mesh distortion and premature termination. The proposed method is verified by modeling a ground consolidation problem. Next, total stress back analysis of cone penetration is conducted with the proposed method. The development of cone factor predicted by the proposed method gives a better match with the laboratory result when comparing with the built-in ALE method. Next, the development and dissipation of uex during cone advancing with the proposed method and fluid-coupled technique is investigated. uex develops dramatically around the cone tip. The soil permeability is back calculated from the dissipation test and agrees well with the input value. It is believed that the construction effects of a press-in pile and the subsequence NSF on that pile can be modeled by utilizing the finding of this study.published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy
38
SOMASUNDARAM, SUJITHAN. "CONSTITUTIVE MODELLING FOR ANISOTROPIC HARDENING BEHAVIOR WITH APPLICATIONS TO COHESIONLESS SOILS (INDUCED, KINEMATIC, NON-ASSOCIATIVENESS)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/188165.
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A constitutive model based on rate-independent elastoplasticity concepts is developed to simulate the behavior of geologic materials under arbitrary three-dimensional stress paths, stress reversals and cyclic loading. The model accounts for the various factors such as friction, stress path, stress history, induced anisotropy and initial anisotropy that influence the behavior of geologic materials. A hierarchical approach is adapted whereby models of progressively increasing sophistication are developed from a basic isotropic-hardening associative model. The influence of the above factors is captured by modifying the basic model for anisotropic (kinematic) hardening and deviation from normality (nonassociativeness). Both anisotropic hardening and deviation from normality are incorporated by introducing into the formulation a second order tensor whose evolution is governed by the level of induced anisotropy in the material. In the stress-space this formulation may be interpreted as a translating potential surface Q that moves in a fixed field of isotropic yield surfaces. The location of the translating surface in the stress-space, at any stage of the deformation, is given by the 'induced anisotropy' tensor. A measure to represent the level of induced anisotropy in the material is defined. The validity of this representation is investigated based on a series of special stress path tests in the cubical triaxial device on samples of Leighton Buzzard sand. The significant parameters of the models are defined and determined for three sands based on results of conventional laboratory test results. The model is verified with respect to laboratory multiaxial test data under various paths of loading, unloading, reloading and cyclic loading.
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Davary, Kamran. "Soil moisture redistribution modeling with artificial neural networks." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36905.
Full textAbstract:
This study sought to investigate the application of artificial neural networks (ANN) and fuzzy inference systems (FIS) to variably saturated soil moisture (VSSM) redistribution modelling. An enhanced approach to such modelling, that lessens computation costs, facilitates input preparation, handles data uncertainty, and realistically simulates soil moisture redistribution, was our main objective.An initial review of existing soil hydrology models provided greater insight into current modelling challenges and a general classification of the models. The application of AI techniques as alternative tools for soil hydrology modelling was explored.
A one-dimensional (1D) model based on ANN and FIS was developed. To estimate fluxes more accurately, multiple ANNs were trained and combined by way of an FIS. The main body of the model employed the ANN-FIS module to model soil moisture redistribution throughout the profile. When tested against the SWAP93 model, the ANN-FIS model gave a good match and maximum error of <8%; however, it did not show a notable computation cost shift.
The investigation proceeded with development of another ANN-based 1D modelling approach. This time, the soil profile or flow region, regardless of its depth, was divided into ten equal parts (compartments). The ANN was trained to estimate moisture patterns for a whole soil profile, from the previous day's soil moisture pattern and boundary conditions, and the current day's boundary conditions. The model was tested against SWAP93 where an average SCORE of 90.4 indicated a good match. The computation cost of the ANN-based model was about one-third that of SWAP93.
At this point the study sought to develop a 3D modelling approach. The ANN was trained to estimate the nodal soil moisture changes through time under the influence of six neighbouring nodes (in a 3D space, two on each axis). The model's accuracy was tested against the SWMS-3D model. An average SCORE of 91 and a 15-fold decrease in computation costs showed a quite acceptable performance. Results suggest that this approach is potentially capable of realistically modelling 3D VSSM redistribution with less computation time.
Finally, pros and cons of these ANN-based modelling approaches are compared and contrasted, and some recommendations on future work are given.
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Christian, James Robert. "Modelling studies on a marine plankton community : biological, temporal and spatial structure." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/27859.
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The SELECT model (Frost, 1982) is analyzed, criticized, and extended to embrace new information about the feeding behaviour of copepods and the structure of the planktonic food web in a series of alternative models. Diel variations in photosynthesis, grazing, and predation on copepods (temporal structure) and patchiness of zooplankton and their predators (spatial structure) are modelled in other variants. It is observed that the vertical, temporal, and (horizontal) spatial structure of the planktonic ecosystem are important components of ecosystem models that can not safely be ignored. It is further observed that a convincing mechanism for the termination of diatom blooms is lacking and should be a subject of intensive research, and that the status of chlorophyll-containing microflagellates as phototrophs is questionable and should be reconsidered.Science, Faculty of
Zoology, Department of
Graduate
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Obando, Vallejos Benjamin. "Mathematical models for the study of granular fluids." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0274/document.
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Cette thèse vise à obtenir et à développer des modèles mathématiques pour comprendre certains aspects de la dynamique des fluides granulaires hétérogènes. Plus précisément, le résultat attendu consiste à développer trois modèles. Nous supposons dans un premier temps que la dynamique du matériau granulaire est modélisée à l’aide d’une approche fondée sur la théorie du mélange. D’autre part, pour les deux modèles restant, nous considérons que le fluide granulaire est modélisé à l’aide d’une approche multiphase associant des structures et des fluides rigides. Plus exactement : • Dans le premier modèle, nous avons obtenu un ensemble d’équations basées sur la théorie du mélange en utilisant des outils d’homogénéisation et une procédure thermodynamique. Ces équations reflètent deux propriétés essentielles des fluides granulaires : la nature visqueuse du fluide interstitiel et un comportement de type Coulomb de la composante granulaire. Avec nos équations, nous étudions le problème de Couette entre deux cylindres infinis d’un écoulement hétérogène granulaire dense, composé d’un fluide newtonien et d’une composante solide. • Dans le deuxième modèle, nous considérons le mouvement d’un corps rigide dans un matériau viscoplastique. Les équations 3D de Bingham modélisent ce matériau et les lois de Newton régissent le déplacement du corps rigide. Notre résultat principal est d’établir l’existence d’une solution faible pour le système correspondant. • Dans le troisième modèle, nous considérons le mouvement d’un corps rigide conducteur thermique parfait dans un fluide newtonien conducteur de la chaleur. Les équations 3D de Fourier-Navier-Stokes modélisent le fluide, tandis que les lois de Newton et l’équilibre de l’énergie interne modélisent le déplacement du corps rigide. Notre principal objectif dans cette partie est de prouver l’existence d’une solution faible pour le système correspondant. La formulation faible est composée de l’équilibre entre la quantité du mouvement et l’équation de l’énergie totale, qui inclut la pression du fluide, et implique une limite libre due au mouvement du corps rigide. Pour obtenir une pression intégrable, nous considérons une condition au limite de glissement de Navier pour la limite extérieure et l’interface mutuelleThis Ph.D. thesis aims to obtain and to develop some mathematical models to understand some aspects of the dynamics of heterogeneous granular fluids. More precisely, the expected result is to develop three models, one where the dynamics of the granular material is modeled using a mixture theory approach, and the other two, where we consider the granular fluid is modeled using a multiphase approach involving rigid structures and fluids. More precisely : • In the first model, we obtained a set of equations based on the mixture theory using homogenization tools and a thermodynamic procedure. These equations reflect two essential properties of granular fluids : the viscous nature of the interstitial fluid and a Coulomb-type of behavior of the granular component. With our equations, we study the problem of a dense granular heterogeneous flow, composed by a Newtonian fluid and a solid component in the setting of the Couette flow between two infinite cylinders. • In the second model, we consider the motion of a rigid body in a viscoplastic material. The 3D Bingham equations model this material, and the Newton laws govern the displacement of the rigid body. Our main result is the existence of a weak solution for the corresponding system. • In the third model, we consider the motion of a perfect heat conductor rigid body in a heat conducting Newtonian fluid. The 3D Fourier-Navier-Stokes equations model the fluid, and the Newton laws and the balance of internal energy model the rigid body. Our main result is the existence of a weak solution for the corresponding system. The weak formulation is composed by the balance of momentum and the balance of total energy equation which includes the pressure of the fluid, and it involves a free boundary (due to the motion of the rigid body). To obtain an integrable pressure, we consider a Navier slip boundary condition for the outer boundary and the mutual interface
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Teng, Jack 1979. "Structure and energetics in theoretical food webs." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80884.
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This thesis studies how structure and energetics influence complex food web dynamics. In Chapter 1, I approach the question by studying a simple food web model that can be modified to include different structural and energetic features. In Chapter 2, I study stability and food web properties in assembled webs that are structured by body-size restrictions and a generalist-specialist tradeoff. The results of both chapters suggest that structure and energetics must be considered to understand food web dynamics. In Chapter 1, I find that food web structure can be modified by weak and strong energetic flows and stabilize dynamics through asynchrony. In Chapter 2, I find that food web assembly with different assemblages of generalists or specialists leads to structures that have corresponding differences in the stability and properties of food webs. Hence, my thesis reexamines the relationship of complexity and dynamics from a topological and energetic framework.
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Kowalczyk, Piotr Jozef. "Validation and application of advanced soil constitutive models in numerical modelling of soil and soil-structure interaction under seismic loading." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/275675.
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This thesis presents validation and application of advanced soil constitutive models in cases of seismic loading conditions.
Firstly, results of three advanced soil constitutive models are compared with examples of shear stack experimental data for free field response in dry sand for shear and compression wave propagation. Higher harmonic generation in acceleration records, observed in experimental works, is shown to be possibly the result of soil nonlinearity and fast elastic unloading waves. This finding is shown to have high importance on structural response, real earthquake records and reliability of conventionally employed numerical tools. Finally, short study of free field response in saturated soil reveals similar findings on higher harmonic generation.
Secondly, two advanced soil constitutive models are used, and their performance is assessed based on examples of experimental data on piles in dry sand in order to validate the ability of the constitutive models to simulate seismic soil-structure interaction. The validation includes various experimental configurations and input motions. The discussion on the results focuses on constitutive and numerical modelling aspects. Some improvements in the formulations of the models are suggested based on the detailed investigation.
Finally, the application of one of the advanced soil constitutive models is shown in regard to temporary natural frequency wandering observed in structures subjected to earthquakes. Results show that pore pressure generated during seismic events causes changes in soil stiffness, thus affecting the natural frequency of the structure during and just after the seismic event. Parametric studies present how soil permeability, soil density, input motion or a type of structure may affect the structural natural frequency and time for its return to the initial value. In addition, a time history with an aftershock is analysed to investigate the difference in structural response during the earthquake and the aftershock.
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Stutz, Hans Henning [Verfasser]. "Hypoplastic Models for Soil-Structure Interfaces - Modelling and Implementation / Hans Henning Stutz." Kiel : Universitätsbibliothek Kiel, 2016. http://d-nb.info/1122110855/34.
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Miller, Kendall Mar 1958. "INTERPRETIVE SCHEME FOR MODELING THE SPATIAL VARIATION OF SOIL PROPERTIES IN 3-D (AUTOCORRELATION, STOCHASTIC, PROBABILITY)." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/276981.
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Odeh, Inakwu Ominyi Akots. "Soil pattern recognition in a South Australian subcatchment /." Title page, contents and abstract only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09pho23.pdf.
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O???Brien, Peter Banking & Finance Australian School of Business UNSW. "Term structure modelling and the dynamics of Australian interest rates." Awarded by:University of New South Wales. School of Banking and Finance, 2006. http://handle.unsw.edu.au/1959.4/28283.
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This thesis consists of two related parts. In the first part we conduct an empirical examination of the dynamics of Australian interest rates of six different maturities, covering the whole yield curve. This direct study of the long rates is quite novel. We use maximum likelihood estimation on a variety of models and find some results that are in stark contrast to previous studies. We estimate Poisson-jump diffusion (PJD) models and find very strong evidence for the existence of jumps in all daily interest rate series. We find that the PJD model fits short-rate data significantly better than a Bernoulli-jump diffusion model. We also estimate the CKLS model for our data and find that the only model not rejected for all six maturities is the CEV model in stark contrast to previous findings. Also, we find that the elasticity of variance estimate in the CKLS model is much higher for the short-rates than for the longer rates where the estimate is only about 0.25, indicating that different dynamics seem to be at work for different maturities. We also found that adding jumps to the simple diffusion model gives a larger improvement than comes from going from the simple diffusion to the CKLS model. In the second part of the thesis we examine the Flesaker and Hughston (FH) term structure model. We derive the dynamics of the short rate under both the original measure and the risk-neutral measure, and show that some criticisms of the bounds for the short rate may not be significant in actual applications. We also derive the dynamics of bond prices in the FH model and compare them to the HJM model. We also extend the FH model by allowing the martingale to follow a jump-diffusion process, rather than just a diffusion process. We derive the unique change of measure that guarantees the family of bond prices is arbitrage-free. We derive prices for caps and swaptions, and extend the results to include Bermudan swaptions and show how to price options with the jump-diffusion version of the FH model.
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Deknatel, William Brockway. "USE OF THE SOLUTION MODELS TO CALCULATE THE ACTIVITY COMPOSITION RELATIONS OF MAGNESIAN CALCITES (SOLID, CARBONATES)." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/291512.
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Abou, Nahra Joumana. "Modeling phosphorus transport in soil and water." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102946.
Full textAbstract:
The main objective of this project was to investigate and model phosphorus (P) transport in soil column studies. A model named HYDRUS-NICA was developed, by coupling a hydrological and transport model (HYDRUS-1D model) with an aqueous chemical model (non-ideal competitive adsorption - NICA), to improve the predictions of P transport in soil and water. The HYDRUS-NICA model was developed by replacing the non-linear empirical (Freundlich and Langmuir) equations of the HYDRUS-1D model with the NICA model equations. The numerical accuracy of the HYDRUS-NICA model was then evaluated by comparing the relative errors produced by the HYDRUS-NICA and HYDRUS-1D models. The results showed that the numerical schemes of the HYDRUS-NICA code are stable.The ability of the NICA model to describe phosphate (PO4) adsorption to soil particles was tested using soils collected from agricultural fields in southern Quebec. The surface charge and PO4 adsorption capacity of these soils were measured. Results were used to estimate the NICA model parameters using a non-linear fitting function. The NICA model accurately described the surface charge of these soils and the PO4 adsorption processes.
The HYDRUS-1D model was applied to simulate water flow and PO4 transport in re-constructed soil column experiments. The HYDRUS-1D model was calibrated based on physical and chemical parameters that were estimated from different experiments. Overall, the HYDRUS-1D model successfully simulated the water flow in the columns; however, it overestimated the final adsorbed PO4 concentrations in the soil. The discrepancies in the results suggested that the HYDRUS-1D model could not account for the differences in the soil structure found in the columns, or that the Freundlich isotherm could not adequately describe PO4 adsorption.
The HYDRUS-NICA model was calibrated and validated with results from re-packed column experiments. The simulated results were then compared with results obtained by the HYDRUS-1D model. The overall goodness-of-fit for the HYDRUS-1D model simulations was classified as poor. The HYDRUS-NICA model improved significantly the prediction of PO4 transport, with the coefficient of modeling efficiency values being close to unity, and the coefficient of residual mass values being close to zero. The HYDRUS-NICA model can be used as a tool to improve the prediction of PO4 transport at the field scale.
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Faria, Rogério Teixeira de. "Simulation of irrigation requirements for Parana State, Brazil." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41290.
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A risk analysis of drought and an assessment of irrigation requirements were ascertained for a wheat (Triticum aestivum L.) crop in Parana, Brazil, using 28 years of historical weather data. Two soil moisture models, The Versatile Soil Moisture Budget (VB4) and SWACROP models, were compared using data from six wheat cropping periods. The models showed good performance in predicting soil moisture contents, but SWACROP underpredicted soil evaporation and runoff, and VB4 did not separate evapotranspiration into its components. Therefore, a new soil moisture model was proposed. In the new model, a Darcy type equation was used to calculate fluxes in the soil profile, and inputs of daily rainfall and potential evapotranspiration were partitioned during the day using simple disaggregation methods. Crop growth input parameters, interacting with weather and soil inputs, were used to calculate a detailed output of the water balance components. The validation of the model showed predictions of soil water contents and evapotranspiration in close agreement with field data.A crop yield model based on the stress day index approach was selected from an evaluation of seven crop-water production functions using wheat field data. This model was combined with the soil moisture model to assess risks of drought during the establishment and development of non-irrigated wheat crops with different planting dates. Irrigation management strategies were simulated to identify net system delivery capacities and application frequencies that promote maximum yield with minimum requirements of water. Yield reductions in non-irrigated wheat due to water stress varied between 16%, for early plantings, to 50%, for late plantings. Maximum yields with minimum applied water was obtained by the use of low intensity (5 to 10 mm) and frequent (3 to 5 days) irrigations. System delivery capacity requirements varied from 1.5 to 3.0 mm/day, according to planting dates.