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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Comparison of Experimental and Theoretical Forces on a Model Dredge Cutterhead

Permenter, Rusty 2010 December 1900 (has links)
Dredging is a critical part of maintaining the nation’s ports and harbors that play a major role in international trade. The design of dredge equipment requires knowledge of the forces expected on an average dredge. For a cutter suction dredge one of the largest forces is applied on the cutter head. To determine the design criteria for a given cutter suction dredge the forces on the cutter head must be known. Forces on a 33 cm (13 inch) model cutter head have been measured using a model cutter suction dredge 10.2 cm ( (4 inch)) suction and 3 inch (7.6 cm) discharge) in the Haynes Coastal Engineering Laboratory. The experimental results are compared to the results of a previously developed theory for estimating cutterhead forces. A MATLAB program is written and used to solve the theoretical equations. The sediment used in the study had a d50 of 0.27 mm and an angle of internal friction of 21.6°. The sediment is contained in the deep sediment pit 7.6 m (25 ft long), 3.7 m wide(12 ft ) and 1.5 m deep(5 ft) in the dredge/tow tank that is 45.7 m long(150 ft), 3.7 m wide(12 ft), and 3.0 m deep(10 ft). The objectives of the study are to calculate the forces using existing theory and MATLAB program and compare the theoretical results to those measured in the laboratory. The effects of the depth of cut, direction of swing, and cutter rpm on the forces acting on the cutter head are evaluated. The forces on the cutterhead are determined through the use of a set of six load cells rated at 13.3 kN (3000 lb). The load cell measurements allow direct calculation of the forces on the cutter head through the use of static equilibrium equations with the assumption of a constant swing speed. Once the forces are determined the results can be scaled to fit an actual dredge and then be applied in the determination of dredge design characteristics. The study shows the ability of the theory to determine the forces within an order or magnitude. The theoretical forces allow design of a cutter using a factor of safety. The variability of the forces in the laboratory study shows the assumption that the cutting forces are generally steady is not always valid.
2

Numerical modelling of reinforced concrete structure under monotonic and earthquake-like dynamic loading

Chuang, Tsai-Fu January 2001 (has links)
No description available.
3

Three dimensional formulation for the stress-strain-dilatancy elasto-plastic constitutive model for sand under cyclic behaviour.

Das, Saumyasuchi January 2014 (has links)
Recent experiences from the Darfield and Canterbury, New Zealand earthquakes have shown that the soft soil condition of saturated liquefiable sand has a profound effect on seismic response of buildings, bridges and other lifeline infrastructure. For detailed evaluation of seismic response three dimensional integrated analysis comprising structure, foundation and soil is required; such an integrated analysis is referred to as Soil Foundation Structure Interaction (SFSI) in literatures. SFSI is a three-dimensional problem because of three primary reasons: first, foundation systems are three-dimensional in form and geometry; second, ground motions are three-dimensional, producing complex multiaxial stresses in soils, foundations and structure; and third, soils in particular are sensitive to complex stress because of heterogeneity of soils leading to a highly anisotropic constitutive behaviour. In literatures the majority of seismic response analyses are limited to plane strain configuration because of lack of adequate constitutive models both for soils and structures, and computational limitation. Such two-dimensional analyses do not represent a complete view of the problem for the three reasons noted above. In this context, the present research aims to develop a three-dimensional mathematical formulation of an existing plane-strain elasto-plastic constitutive model of sand developed by Cubrinovski and Ishihara (1998b). This model has been specially formulated to simulate liquefaction behaviour of sand under ground motion induced earthquake loading, and has been well-validated and widely implemented in verifcation of shake table and centrifuge tests, as well as conventional ground response analysis and evaluation of case histories. The approach adopted herein is based entirely on the mathematical theory of plasticity and utilises some unique features of the bounding surface plasticity formalised by Dafalias (1986). The principal constitutive parameters, equations, assumptions and empiricism of the existing plane-strain model are adopted in their exact form in the three-dimensional version. Therefore, the original two-dimensional model can be considered as a true subset of the three-dimensional form; the original model can be retrieved when the tensorial quantities of the three dimensional version are reduced to that of the plane-strain configuration. Anisotropic Drucker-Prager type failure surface has been adopted for the three-dimensional version to accommodate triaxial stress path. Accordingly, a new mixed hardening rule based on Mroz’s approach of homogeneous surfaces (Mroz, 1967) has been introduced for the virgin loading surface. The three-dimensional version is validated against experimental data for cyclic torsional and triaxial stress paths.
4

Stability analysis of a single three dimensional rock block: effect of dilatancy and high-velocity water jet impact

Asadollahi, Pooyan 27 May 2010 (has links)
In simulation of closely- or separately-joined rock masses, stability of rock blocks is of primary concern. However, there seems to be no approach that can handle general modes of simultaneous sliding and truly large rotation under general forces, including non-conservative forces such as water forces. General causes of failure for rock blocks, such as limit points, bifurcation points, and dynamic instability (divergence and flutter), have never been addressed. This research implements a formulation, called BS3D(an incremental-iterative algorithm introduced by Tonon), for analyzing general failure modes of rock blocks under conservative and non-conservative forces. Among the constitutive models for rock fractures developed over the years, Barton's empirical model has been widely used because it is easy to apply and includes several important factors associated with fracture characteristics. Although Barton's failure criterion predicts peak shear strength of rock fractures with acceptable precision, it has some weaknesses in estimating the peak shear displacement, post-peak shear strength, dilation, and surface degradation in unloading and reloading. In this dissertation, modifications are made to Barton's original model in order to address these weaknesses. The modified Barton’s model is validated by a series of direct shear tests on rock fractures and implemented in BS3D to consider the dilatant behavior of fractures. The mechanical behavior of a rock block formed in the roof of a tunnel is governed by its geometry, the mechanical characteristics and the deformability of the fractures forming the block, the deformability of the block and that of the surrounding rock mass, and the stresses within the rock. BS3D, after verification and validation, is used to investigate the effect of dilatancy on stability of rock blocks formed in the roof of a circular tunnel. High-velocity plunging jets, issuing from hydraulic artificial or natural structures, can result in scouring of the rock riverbed or the dam toe foundation. Assessment of the extent of scour is necessary to ensure the safety of the dam and to guarantee the stability of its abutments. BS3D is used to investigate effect of high-velocity jet impact on stability of rock blocks in plunge pools. / text
5

The Influence of Grain Shape on Dilatancy

Cox, Melissa Reiko Brooke January 2008 (has links)
Grain shape is a key factor affecting the mechanical properties of granular materials. However, grain shape quantification techniques to distinguish one granular material from another have not reached a stage of development for inclusion in modeling the behavior of granular materials. Part of the problem is the equipment of choice for grain shape measurement is the scanning electron microscope. This is a relatively expensive and complex device. In this research, a practical approach using light microscopy to quantify grain shape and to identify the key shape parameters that can distinguish grains was investigated. A light microscope was found to produce grain images with sufficient quality for the purpose of observing the grain shape profile. Several grain shape parameters were determined for eight different sands - four sands chosen for this study and four sands from an outside source. Six of these - Circularity, Roundness, Sphericity, Aspect Ratio, Compactness and ModRatio - are shown to be the key shape parameters that differentiate these sand grains.Relationships between the six key grain shape parameters and dilatancy were developed to enable a better understanding of the mechanics of granular materials and for potential use in practice. Data to build the relationships were obtained using a light microscope, digital image processing software (ImageJ), and direct shear tests on four uniform sands composed of grains with varying, somewhat-homogeneous, shape profiles - ranging from very rounded grains in one granular conglomerate to very angular shaped grains in another.A Weighted Single Sand Shape Factor (WSSSF) was derived from all of the six key shape parameters was developed using Weighted Factor Analysis. A good correlation was found to exist between dilatancy and WSSSF. The correlation also incorporates normal effective stress, relative density and the critical state friction angle. Verification was conducted through the introduction of a subangular to subrounded sand that was not used in building the correlation. The correlation proved to provide a good estimate of the dilatancy of sands based on the physical properties of grains and the applied loading.
6

Two-layer flow behaviour and the effects of granular dilatancy in dam-break induced sheet-flow

Spinewine, Benoit 02 December 2005 (has links)
In case of exceptional floods induced by the failure of a dam, huge amounts of sediments may be eroded. This results in large-scale modifications of the valley morphology and may drastically increase the resulting damages. The objective of the research is to advance the understanding of sediment transport under dam-break flows. For such highly erosive and transient floods, it is crucial to account explicitly for sediment inertia, and therefore traditional “clear-water” modelling approaches are largely inappropriate. The present approach relies on a two-layer idealisation of the flow behaviour. Separating a clear-water flow region from the underlying sediment bed, the transported sediments are confined in a flow layer of finite thickness, endowed with its proper inertia, density and velocity. The thesis also pinpoints granular dilatancy as an essential mechanism of interaction between the layers. When passing from a solid-like to a fluid-like behaviour as they are entrained by the flow, the eroded sediment grains dilate along the vertical, and this generates vertical exchanges of mass and momentum that should be accounted for. The thesis proceeds first with experimental investigations. Laboratory dam-break waves are reproduced in a dedicated flume, exploring different bed configurations and sediment densities. Imaging observations are used to support the proposed phenomenological description of the flow. Within a shallow-water framework, theoretical and numerical endeavours are then developed to investigate the implications on the flow dynamics of the two essential contributions of the proposed description, i.e. the two-layer flow behaviour, and the effects of granular dilatancy.
7

Comportamento mecânico de um solo cimentado curado sob tensão em ensaios triaxiais / Mechanical behaviour of a cemented soil cured under stress in triaxial tests

Dalla Rosa, Francisco January 2006 (has links)
O comportamento de solos estruturados por cimentação é fortemente influenciado pelo estado de tensões existente durante a deposição do agente cimentante. Procedimentos rotineiros de extração e preparação de amostras em laboratório geralmente causam danos à estrutura natural do material, impedindo, muitas vezes a observação do comportamento real do ponto de vista de rigidez e de deformabilidade. A simulação, em laboratório, das condições de confinamento durante a formação da estrutura cimentante, torna-se uma condição necessária para o estudo do comportamento desses materiais. Seguindo essa linha, o trabalho busca avaliar a influência da tensão de confinamento (tensão de cura) existente durante a formação da cimentação no comportamento deste material, a partir de ensaios triaxiais drenados consolidados isotropicamente. Assim, neste estudo propõe-se a utilização de um solo artificialmente curado sob tensão, observando em conjunto a essa variável a influência do nível de cimentação bem como os efeitos oriundos da tensão confinantes utilizada na fase de cisalhamento. Procurou-se avaliar características de deformabilidade e resistência, através de uma análise do comportamento dos materiais. A avaliação das superfícies de plastificação foi realizada a partir da análise de pequenas deformações do solo cimentado. A análise tensãodilatância se desenvolveu com base no exame do comportamento do material a deformações relativamente grandes. Os resultados mostraram, no geral, que o comportamento do material cimentado foi fortemente influenciado pela variação da tensão de cura, tanto a pequenas bem como a deformações relativamente grandes. / The behavior of cemented structured soils is strongly influenced by the existing stress state during the addition of the cementation agent. The common procedures for laboratory sampling usually cause damage to the natural structure of the materials, hindering, many times, the identification of the real behavior in regard to deformability and stiffness properties. The simulation, in laboratory environment, of confining conditions during the cement structure formation turns to be a mandatory circumstance for the study of the material’s behavior. Inside this context, this work aims to evaluate the influence of the existing confining stress (stress cure) during the cement formation in the behavior of the material, through isotropic drained triaxial tests. Thus, it suggested in this study the usage of artificially cemented soil cured under stress, with parallel observation of the influence of the cement degree, as well the effects from the confining stress used during the shearing stage. It was also evaluated deformability and strength characteristics through behavior analyses of the materials. An assessment of the yield surfaces was carried on from soil cemented small deformation analysis. The evaluation of stress-dilatancy was developed based on the exam of relatively large deformation behavior. The results showed that the general behavior of this material was strongly influenced by the variation of the stress curing both at small strains and at relatively large strains.
8

Comportamento mecânico de um solo cimentado curado sob tensão em ensaios triaxiais / Mechanical behaviour of a cemented soil cured under stress in triaxial tests

Dalla Rosa, Francisco January 2006 (has links)
O comportamento de solos estruturados por cimentação é fortemente influenciado pelo estado de tensões existente durante a deposição do agente cimentante. Procedimentos rotineiros de extração e preparação de amostras em laboratório geralmente causam danos à estrutura natural do material, impedindo, muitas vezes a observação do comportamento real do ponto de vista de rigidez e de deformabilidade. A simulação, em laboratório, das condições de confinamento durante a formação da estrutura cimentante, torna-se uma condição necessária para o estudo do comportamento desses materiais. Seguindo essa linha, o trabalho busca avaliar a influência da tensão de confinamento (tensão de cura) existente durante a formação da cimentação no comportamento deste material, a partir de ensaios triaxiais drenados consolidados isotropicamente. Assim, neste estudo propõe-se a utilização de um solo artificialmente curado sob tensão, observando em conjunto a essa variável a influência do nível de cimentação bem como os efeitos oriundos da tensão confinantes utilizada na fase de cisalhamento. Procurou-se avaliar características de deformabilidade e resistência, através de uma análise do comportamento dos materiais. A avaliação das superfícies de plastificação foi realizada a partir da análise de pequenas deformações do solo cimentado. A análise tensãodilatância se desenvolveu com base no exame do comportamento do material a deformações relativamente grandes. Os resultados mostraram, no geral, que o comportamento do material cimentado foi fortemente influenciado pela variação da tensão de cura, tanto a pequenas bem como a deformações relativamente grandes. / The behavior of cemented structured soils is strongly influenced by the existing stress state during the addition of the cementation agent. The common procedures for laboratory sampling usually cause damage to the natural structure of the materials, hindering, many times, the identification of the real behavior in regard to deformability and stiffness properties. The simulation, in laboratory environment, of confining conditions during the cement structure formation turns to be a mandatory circumstance for the study of the material’s behavior. Inside this context, this work aims to evaluate the influence of the existing confining stress (stress cure) during the cement formation in the behavior of the material, through isotropic drained triaxial tests. Thus, it suggested in this study the usage of artificially cemented soil cured under stress, with parallel observation of the influence of the cement degree, as well the effects from the confining stress used during the shearing stage. It was also evaluated deformability and strength characteristics through behavior analyses of the materials. An assessment of the yield surfaces was carried on from soil cemented small deformation analysis. The evaluation of stress-dilatancy was developed based on the exam of relatively large deformation behavior. The results showed that the general behavior of this material was strongly influenced by the variation of the stress curing both at small strains and at relatively large strains.
9

Comportamento mecânico de um solo cimentado curado sob tensão em ensaios triaxiais / Mechanical behaviour of a cemented soil cured under stress in triaxial tests

Dalla Rosa, Francisco January 2006 (has links)
O comportamento de solos estruturados por cimentação é fortemente influenciado pelo estado de tensões existente durante a deposição do agente cimentante. Procedimentos rotineiros de extração e preparação de amostras em laboratório geralmente causam danos à estrutura natural do material, impedindo, muitas vezes a observação do comportamento real do ponto de vista de rigidez e de deformabilidade. A simulação, em laboratório, das condições de confinamento durante a formação da estrutura cimentante, torna-se uma condição necessária para o estudo do comportamento desses materiais. Seguindo essa linha, o trabalho busca avaliar a influência da tensão de confinamento (tensão de cura) existente durante a formação da cimentação no comportamento deste material, a partir de ensaios triaxiais drenados consolidados isotropicamente. Assim, neste estudo propõe-se a utilização de um solo artificialmente curado sob tensão, observando em conjunto a essa variável a influência do nível de cimentação bem como os efeitos oriundos da tensão confinantes utilizada na fase de cisalhamento. Procurou-se avaliar características de deformabilidade e resistência, através de uma análise do comportamento dos materiais. A avaliação das superfícies de plastificação foi realizada a partir da análise de pequenas deformações do solo cimentado. A análise tensãodilatância se desenvolveu com base no exame do comportamento do material a deformações relativamente grandes. Os resultados mostraram, no geral, que o comportamento do material cimentado foi fortemente influenciado pela variação da tensão de cura, tanto a pequenas bem como a deformações relativamente grandes. / The behavior of cemented structured soils is strongly influenced by the existing stress state during the addition of the cementation agent. The common procedures for laboratory sampling usually cause damage to the natural structure of the materials, hindering, many times, the identification of the real behavior in regard to deformability and stiffness properties. The simulation, in laboratory environment, of confining conditions during the cement structure formation turns to be a mandatory circumstance for the study of the material’s behavior. Inside this context, this work aims to evaluate the influence of the existing confining stress (stress cure) during the cement formation in the behavior of the material, through isotropic drained triaxial tests. Thus, it suggested in this study the usage of artificially cemented soil cured under stress, with parallel observation of the influence of the cement degree, as well the effects from the confining stress used during the shearing stage. It was also evaluated deformability and strength characteristics through behavior analyses of the materials. An assessment of the yield surfaces was carried on from soil cemented small deformation analysis. The evaluation of stress-dilatancy was developed based on the exam of relatively large deformation behavior. The results showed that the general behavior of this material was strongly influenced by the variation of the stress curing both at small strains and at relatively large strains.
10

砂の力学モデルとしての多重せん断モデルの大変形解析の定式化およびその適用性に関する研究

上田, 恭平 23 March 2010 (has links)
Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15312号 / 工博第3191号 / 新制||工||1480(附属図書館) / 27790 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 井合 進, 教授 田村 武, 教授 岡 二三生 / 学位規則第4条第1項該当

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