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Evaluation of the efficiencies of helical anchor plates in sand by centrifuge model tests

Tsuha, Cristina de Hollanda Cavalcanti; Aoki, Nelson; Rault, G.; Thorel, L.; Garnier, J.
Fonte: CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS; OTTAWA Publicador: CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS; OTTAWA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.15%
The uplift capacity of helical anchors normally increases with the number of helical plates. The rate of capacity gain is variable, considering that the disturbance caused by the anchor installation is generally more pronounced in the soil mass above the upper plates than above the lower plates, because the upper soil layers are penetrated more times. The present investigation examines the effect of the number of helices on the performance of helical anchors in sand, based on the results of centrifuge model tests. Uplift loading tests were performed on 12 different types of piles installed in two containers of dry sand prepared with different densities. The measured fractions of the uplift capacity related to each individual helical plate of multi-helix anchors were compared with the fractions predicted by the individual bearing method. The results of this investigation indicate that in double- and triple-helix anchors, the contributions of the second and third plate to the total anchor uplift capacity decreased with the increase of sand relative density and plate diameter. In addition, these experiments demonstrated that the variation of the anchor load-displacement behavior with the number of helices also depends on these parameters.; Brazilian Agency CAPES (Ministry of Education); Brazilian Agency CAPES (Ministry of Education); French institute of science and technology for transport...

"Análise da laterotrusão condilar nos movimentos de lateralidade centrífuga e de Bennett em edentados completos" ; Condyle laterotrusion analysis on Bennett’s side shift and centrifuge lateral movements in edentate subjects

Hatushikano, Eder Jun
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 22/05/2006 PT
Relevância na Pesquisa
27.51%
Atualmente na odontologia ainda há muita dificuldade na compreensão do movimento de Bennett ou laterotrusão. Devido a questões de inviolabilidade inerentes à característica da articulação temporomandibular não é possível observar diretamente o seu interior, de maneira que a análise da sua dinâmica durante a função torna-se questionável. Assim, o autor trabalhou com imagens e inferências aplicadas numa metodologia utilizada para tal fim. A proposta dessa pesquisa foi a de analisar o comportamento condilar durante os movimentos de lateralidade Centrífuga e de Bennett em pacientes portadores de prótese total. Vinte e dois indivíduos receberam novas próteses totais. O registro maxilomandibular foi realizado com a técnica de Gysi com a plataforma e pua extraoral. Utilizando-se uma pua modificada de forma que esta realizasse dois registros (pua dupla) com o mesmo movimento e, ao invés da cera aplicada sobre a plataforma, o registro foi feito sobre um fino papel carbono aderido a esta com uma fita adesiva dupla face. Através de imagens digitalizadas do articulador e dos registros no carbono foi possível, com a utilização de um programa de tratamento de imagens, arbitrar e testar a posição do eixo vertical de rotação condilar durante a lateralidade centrífuga e de Bennett. Os resultados mostraram uma predominância nos eventos onde o eixo vertical do côndilo posicionou-se na região ântero-lateral e póstero-medial durante a lateralidade de Bennett...

Modelo teórico para controle da capacidade de carga à tração de estacas metálicas helicoidais em solo arenoso; Theoretical model to control on site the uplift capacity of helical screw piles embedded in sandy soil

Tsuha, Cristina de Hollanda Cavalcanti
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/11/2007 PT
Relevância na Pesquisa
27.32%
O monitoramento em campo de fundações em estacas metálicas helicoidais é baseado em correlações empíricas entre a capacidade de carga à tração e o torque medido durante a instalação. Nesta pesquisa é proposto um modelo teórico da relação entre o torque de instalação e a capacidade de carga à tração deste tipo de estaca em areias para ser utilizado como procedimento de controle durante a execução deste tipo de fundação. Para validar esta relação teórica e para avaliar o desempenho desta fundação em solos arenosos, foi realizado um programa experimental dividido em dois grupos: ensaios de campo e ensaios de laboratório. Em campo foram realizadas provas de carga à tração na Escola de Engenharia de São Carlos (EESC) e em Contagem (Minas Gerais). Os ensaios de laboratório foram divididos em três grupos. O primeiro corresponde aos ensaios de modelagem física em centrífuga realizados no Laboratoire Central des Ponts et Chaussées (LCPC) em Nantes, França. O segundo engloba ensaios de cisalhamento direto de interface entre o aço da hélice da estaca e diferentes areias, parte executada no LCPC e parte na EESC. O terceiro grupo refere-se a ensaios de torção de tubos de estacas metálicas helicoidais efetuados na EESC. A partir dos resultados dos ensaios...

Estudo experimental em uma centrífuga de plasma iniciada por arco no vácuo; An experimental study in a centrifuge plasma arc starts in vacuo

Dallaqua, Renato Sergio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 05/10/1994 PT
Relevância na Pesquisa
27.43%
Na década de 80 houve um aumento na utilização de isótopos estáveis em física nuclear, medicina nuclear, ciências biomédicas; geociências etc e as previsões indicam para um crescimento no consumo destes isótopos nas próximas décadas. Dentro deste quadro, novos métodos de separação isotópica foram propostos e desenvolvidos, entre eles, a centrifuga de plasma iniciada por arco no vácuo. Este trabalho mostra os resultados experimentais obtidos na centrífuga de plasma iniciada por arco no vácuo desenvolvida no LAP/INPE desde 1981. Inicialmente é feita una descrição da descarga em arco no vácuo que é a fonte de plasma desta centrífuga e com as medidas realizadas, uma caracterização completa do plasma pode ser obtida. Os resultados teóricos obtidos de um modelo de fluido para a coluna de plasma em rotação são comparados com os obtidos experimentalmente e, algumas limitações deste separador isotópico sio mencionadas. Os efeitos de gases residuais nos parâmetros do plasma desta centrifuga foram estudados e1 os resultados mostraram que o melhor desempenho deste separador ocorre na ausência de gases na câmara de vácuo. Dos resultados experimentais obtidos foi feito um estudo comparativo entre os diferentes métodos de separação isotópica e...

Uso da Centrifuga para Determina????o da Reten????o de ??gua para Substratos ?? Base de Casca de Arroz; Use of Centrifuge for Determination of Water Retention for Substrates constituted of rice husks

DIAZ, B??rbara da Cunha
Fonte: Universidade Federal de Pelotas; Agricultura familiar; Programa de P??s-Gradua????o em Sistemas de Produ????o Agr??cola Familiar; UFPel; BR Publicador: Universidade Federal de Pelotas; Agricultura familiar; Programa de P??s-Gradua????o em Sistemas de Produ????o Agr??cola Familiar; UFPel; BR
Tipo: Tese de Doutorado Formato: application/pdf
POR
Relevância na Pesquisa
37.43%
The performance of a substrate is closely related to their physical and chemical properties, and the prior knowledge and study of these characteristics, permit evaluation of its quality and adjust to different use conditions. The agricultural problem in the production of plants in containers is to ensure optimal conditions for biomass production with a development of roots restricted to a small volume of substrate. Physical characterization aims to study the distribution volume of solid material, water and air, which is crucial for plant development. Currently the methodology applied in determining the physical properties of substrates is the same used for soil, presenting some limitations due to some peculiar attributes of the materials used as substrates. The objectives of this study were to develop a methodology for using the centrifuge for determining the water retention in substrates and compare two methods for determining the water retention curve applied to substrates, the tension table method combined with the Richards pressure chamber with the method of centrifuge. The study was conducted at Embrapa Temperate Climate in two steps. The first stage of the study was conducted to determine the centrifugation time necessary to extract all the water available to a given tension. In the second step the two methods were compared using the volume of water retained at different tensions. The study worked on five different substrates: 100% carbonized rice husks; 75% carbonized rice husks + 25% burnt rice husks...

Re-evaluation of the separation parameters based on the Berman-Olander long-bowl gas-centrifuge solution

DU TOIT C.g.; MERCURIO GIOVANNI
Fonte: SACAM Publicador: SACAM
Tipo: Contributions to Conferences Formato: CD-ROM
ENG
Relevância na Pesquisa
27.51%
The hydrodynamic equations for a long-bowl gas-centrifuge can be simplified to obtain a one-dimensional differential equation for the variation of the non-dimensional axial velocity in the radial direction. This equation can be solved subject to the relevant boundary conditions and conservation of mass to provide the required velocity distribution. Similarly the differential equation for the conservation of the light component in a uranium enrichment long-bowl gas-centrifuge may be simplified based on various assumptions. The simplified differential equation can then be solved in conjunction with the velocity distribution to provide the required separation performance of the gas-centrifuge. In this study the calculation of the separation performance of a long-bowl gas-centrifuge is re-evaluated. The re-evaluation is based on a finite element approach that was previously developed for the solution of the hydrodynamics. The results obtained in this study are compared with published data and it is concluded that the finite element approach provides a consistent basis for the calculation of the separative performance of a long-bowl gas-centrifuge.; JRC.E.8-Nuclear security

Human disorientation as a factor in spacecraft centrifuge design

Howse, Christopher E.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado Formato: xvi, 128 p. : col. ill. ;
Relevância na Pesquisa
37.43%
Approved for public release, distribution is unlimited; Weightlessness is the major contributing factor behind the degradation of bone mass, muscle tone, and aerobic capacity during long-term space missions. With the loss of bone mass progressing at up to two percent per month, long duration and interplanetary missions shall remain the sole duty of robotic explorers until sufficient countermeasures are developed. Several countermeasures are either in use, or under development to alleviate this problem. Exercise is currently used to reduce the severity of bone loss and muscle atrophy. Exercise has proven ineffective despite the fact two hours of daily exercise together with elaborate apparatus have been devoted to simulating the load of Earth's gravity. Drug therapy and other, more exotic, countermeasures are also under consideration, but the side-effects of these other treatments and the fact that they do not directly address the root cause of the negative effects of weightlessness means that they may only reduce, not cure, those problems. Only artificial gravity addresses the root cause, weightlessness itself. This thesis addresses the need to balance the effects of Coriolis on human disorientation with the engineering costs of constructing a centrifuge for human occupation in space.; Lieutenant...

CENTRIFUGE MODELLING STUDY OF CONTRASTING STRUCTURAL STYLES IN THE SALT RANGE AND THE POTWAR PLATEAU, PAKISTAN

FAISAL, SHAH
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
37.32%
The ENE-trending Himalayan fold-thrust belt in Pakistan exhibits contrasting deformation styles both along and across the strike. The centrifuge modelling technique has been used to investigate these variations in structural style. For the purpose of modelling, the Salt Range and Potwar Plateau (SR/PP) stratigraphy has been grouped into four mechanical units. From bottom to top these are the Salt Range Formation, carapace unit (Cambrian-Eocene platform sequences), Rawalpindi Group, and Siwalik Group. These stratigraphic units of alternating competence, composed of thin layers of plasticine modelling clay and silicone putty, rest on a rigid base plate that represents the crystalline basement of the Indian plate. The models are built at a linear scale ratio of ~10-6 (1mm=1km) and deformed in a centrifuge at 4000g. The models are subjected to horizontal shortening by collapse and lateral spreading of a “hinterland wedge” which simulates overriding by the Himalayan orogen (above the Main Boundary Thrust). The models of the central SR/PP show that the accretionary wedge develops a prominent culmination structure with fault-bend fold geometry over the frontal ramp, while the eastern SR/PP is more internally deformed by detachment folds...

Investigation of Softening Instability Phenomena Under Simulated Infinite Slope Conditions in Centrifuge Tilting Table Tests

Wolinsky, Eric
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
37.43%
Element test results reported in the literature under both triaxial and plane strain conditions indicate that loose saturated granular specimens can experience softening instability at stress ratios lower than what might otherwise be expected given the critical state friction angle of the soil. The region of potential softening instability in stress-space is often explained using the framework of the instability line. This phenomenon is particularly relevant to shallow slopes of 1 to 2 m depth. However, the practical realities of sample preparation for triaxial testing make performing tests below 20 to 30 kPa of confining stress exceptionally difficult. In this thesis, the development of a centrifuge tilt-table test device is described which aims to test the behaviour of loose granular slopes under stress paths of increasing slope inclination or increasing pore water pressure. A system of instrumentation including pore pressure transducers, inclinometers, displacement transducers, and high-resolution cameras was designed to monitor the behaviour of the slope model. The development of a system to provide a controlled groundwater level within the slope model proved to be particularly challenging. The results of two competing design concepts are presented for the water boundary condition and discussed. The centrifuge tilt-table is used to compare the physical response of a slope to the behaviour predicted by the infinite slope and softening instability models using scale model centrifuge testing. If softening instability is a rigorous concept...

Centrifuge Modelling of Instability in Granular Soils under Infinite Slope Conditions

Jacobs, EMILY
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
37.15%
Rainfall induced granular flow slides pose a significant risk in many areas of the world. These failures, characterized by the sudden release of material in a fluid-like manner, are the result of static liquefaction occurring in these slopes. The static liquefaction phenomenon has been linked to instability. Instability behaviour is primarily studied under undrained triaxial conditions, and although many instability theories have therefore been defined in this stress space, these have been shown to also extend into plane strain conditions. In order to further investigate this behaviour under these stress conditions, Wolinsky et al. (2013) developed a tilt-table soil box for use in a geotechnical centrifuge to analyze instability in infinite slope soil models. This testing apparatus has been used to simulate instability in plane strain under both dry and saturated soil conditions. Stress-controlled experiments were performed on dry infinite slope soil models to investigate the effects of both void ratio and effective stress on instability behaviour. By performing these tests dry, this test apparatus provides the ability to decouple the triggers of instability from the corresponding response in pore pressure and the consequences. The results of this testing confirmed that the instability line angle is a function of both void ratio and effective stress. As the void ratio decreases and effective stress in the soil model increases...

Scales modified for use on board the human centrifuge in the MIT Man Vehicle Lab

Samuelson, Heather Marie
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 54 p.
ENG
Relevância na Pesquisa
27.57%
The MIT Man Vehicle Lab (MVL) is currently performing research on the effects of rotational artificial gravity on humans through the use of a short-radius centrifuge. The MVL centrifuge allows subjects to spin in the supine position with their heads at the center of rotation and their feet facing outwards. To collect information regarding actual forces experienced by a subject while on the centrifuge, a set of scales was designed specifically to measure the equivalent of the human body's weight in artificial gravity. These were mounted on board a stair stepper exercise device to measure the forces exerted at the feet of subjects while exercising. Exercise is particularly important in preventing microgravity-induced deconditioning of the body and without exercise a deconditioned subject might not be able to withstand the stress of experiencing artificial gravity. The primary focus of the research is to gain a better understanding of the overall effects resulting from artificial gravity on humans and eventually to alleviate undesirable ones. The Contek WCS-20® bathroom scale was redesigned to fit on board the stair stepper device on the centrifuge and to safely and securely measure the forces exerted by each foot of a subject while exercising.; (cont.) It was also modified to give continuous force readouts; measurements were made while a subject was performing simple exercises on a stair stepper device in artificial gravity. The subject was spun at 0...

A Hand-Powered, Portable, Low-Cost Centrifuge for Diagnosing Anemia in Low-Resource Settings

Brown, Jocelyn; Theis, Lauren; Kerr, Lila; Zakhidova, Nazima; O'Connor, Kelly; Uthman, Margaret; Oden, Z. Maria; Richards-Kortum, Rebecca
Fonte: The American Society of Tropical Medicine and Hygiene Publicador: The American Society of Tropical Medicine and Hygiene
Tipo: Artigo de Revista Científica
Publicado em 01/08/2011 EN
Relevância na Pesquisa
27.62%
This report describes the development of a hand-powered centrifuge to determine hematocrit values in low-resource settings. A hand-powered centrifuge was constructed by using a salad spinner. Hematocrit values were measured by using the hand-powered device, and results were compared with those of a benchtop centrifuge. The packed cell volume (PCV) measured with the hand-powered device correlated linearly with results obtained with a benchtop centrifuge (r = 0.986, P < 0.001). The PCVs measured with the hand-powered centrifuge were consistently 1.14 times higher than those measured with the benchtop system. The 14% increase in PCV measured with the hand-powered centrifuge is caused by increased plasma trapped in the cell column. The reader card was adjusted to compensate for trapped plasma. A hand-powered centrifuge and calibrated reader card can be constructed for U.S. $35 and can accurately determine hematocrit values. It is suitable for use in low-resource settings because it is mechanically-powered, inexpensive, and accurate.

Interaction between surface structures and tunnelling in sand: centrifuge and computational modelling

Giardina, Giorgia; DeJong, Matthew J.; Mair, Robert J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; published version
EN
Relevância na Pesquisa
37.15%
This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.tust.2015.07.016; The dataset supporting this article can be found on the Cambridge University Repository at https://www.repository.cam.ac.uk/handle/1810/249085.; Tunnelling in urban areas requires a careful estimation of the consequence of soil settlements on existing buildings. In this paper the interaction between the excavation of a tunnel in sand and surface structures is investigated. A two dimensional finite element model is presented and validated through comparison with centrifuge test results, both with and without structures. The model is then used to perform a sensitivity study on the effect of building weight on soil movements and structural deformations. The results of the validation indicate that assuming a no-tension interface between the soil and the structure is essential to capture the soil-structure interaction that was experimentally observed. The parametric analyses show that the relation between the building stiffness and the tunnelling-induced deformations depends on the building weight.; Financial support was provided by the Engineering and Physical Sciences Research Council of the United Kingdom, under grant reference number EP/K018221/1.

Submarine landslide flows simulation through centrifuge modelling

Gue, Chang Shin
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
37.74%
Landslides occur both onshore and offshore. However, little attention has been given to offshore landslides (submarine landslides). Submarine landslides have significant impacts and consequences on offshore and coastal facilities. The unique characteristics of submarine landslides include large mass movements and long travel distances at very gentle slopes. This thesis is concerned with developing centrifuge scaling laws for submarine landslide flows through the study of modelling submarine landslide flows in a mini-drum centrifuge. A series of tests are conducted at different gravity fields in order to understand the scaling laws involved in the simulation of submarine landslide flows. The model slope is instrumented with miniature sensors for measurements of pore pressures at different locations beneath the landslide flow. A series of digital cameras are used to capture the landslide flow in flight. Numerical studies are also carried out in order to compare the results obtained with the data from the centrifuge tests. The Depth Averaged Material Point Method (DAMPM) is used in the numerical simulations to deal with large deformation (such as the long runout of submarine landslide flows). Parametric studies are performed to investigate the validity of the developed centrifuge scaling laws under the initial and boundary conditions given in the centrifuge tests. Both the results from the centrifuge tests and numerical simulations appear to follow the proposed centrifuge scaling laws...

Centrifuge Modeling of Deep Excavations and Their Interaction With Adjacent Buildings

Elshafie, M. Z. E. B.; Choy, C. K. C.; Mair, R. J.
Fonte: ASTM International Publicador: ASTM International
Tipo: Article; accepted version
EN
Relevância na Pesquisa
37.32%
This is a preprint of an article published in Geotechnical Testing Journal. The final version is available from http://www.astm.org/DIGITAL_LIBRARY/JOURNALS/GEOTECH/PAGES/GTJ20120209.htm.; Major cities in the world are experiencing a rapid growth in population while becoming increasingly overcrowded and congested. In recent years, this has created a huge demand for underground infrastructure, which often involves the design of major mass transit tunnel systems; these tunnel systems (underground tunnels and metro stations) are becoming increasingly necessary to construct in very close proximity to existing buildings. The prediction of excavation-induced deformations therefore becomes a key issue in the planning and design process for these schemes. However, current design approaches are conservative and often lead to unnecessary concern and expenditure in the design and provision of protective measures. A better understanding of the mechanisms involved in the excavation-soil-structure interaction could reduce costs and help avoid potential problems. A series of small-scale model tests was carried out in the geotechnical centrifuge at Cambridge University to investigate the interaction between excavations and model buildings. Excavations (simulated by adopting a novel two-fluid technique) in a ?free-field? were also undertaken to assess the difference between free-field ground movements and those affected by a stiff model building. A detailed description of the centrifuge models and test procedures is presented in this paper...

Tuned mass damper effects on the response of multi-storied structures observed in geotechnical centrifuge tests

Jabary, Raz Najat; Madabhushi, Gopal Santana Phani
Fonte: Universidade de Cambridge Publicador: Universidade de Cambridge
Tipo: Relatório Formato: .xlsx
Relevância na Pesquisa
37.51%
This dataset provides the raw responses in Excel (in Volts) of microelectromechnical and piezo-electric accelerometers positioned on the structural model or equivalent shear beam (ESB) container used to conduct the centrifuge tests considered in ?Tuned mass damper effects on the response of multi-storied structures observed in geotechnical centrifuge tests? (accepted on 23rd June 2015 for publication in Soil Dynamics and Earthquake Engineering). Fig. 2 in the accompanying research paper shows a layout of all instrument positions in the model. The calibration factors (g/V) of all accelerometers are provided below. Multiplication of the raw response (V) by the calibration factor (g/V) results in acceleration response (g). Loose sand Instrument (-) / Calibration Factor (g/V) M1/51.88 (first floor response) M2/53.05 (second floor response) P1/8.80 (ESB input) Dense-loose-dense sand Instrument (-) / Calibration Factor (g/V) M1/56.82 (first floor response) M2/43.43 (second floor response) P1/6.61 (ESB input) The raw data was recorded in centrifuge tests conducted with the Turner beam centrifuge facilities available at the Schofield Centre (High Cross, Madingley Road, Cambridge, CB3 0EL) between 10/06/2013 and 27/09/2013. Below is a list of the file names of the instrument response recordings...

Tuned mass damper effects on the response of multi-storied structures observed in geotechnical centrifuge tests

Jabary, R. N.; Madabhushi, S. P. G.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; published version
EN
Relevância na Pesquisa
37.15%
This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.soildyn.2015.06.013; Tuned mass dampers (TMDs) are widely used to reduce vibrations in structures. However, very little research is available on the experimental investigation of TMDs and their performance in soilstructure systems. In this paper, a series of geotechnical centrifuge tests was conducted to investigate the effects of TMDs on the response of a multiple-storey sway frame structure undergoing dynamic soil-structure interaction (SSI). Structural responses were recorded for a wide range of input motion characteristics, damper configurations and soil profiles. The practicality associated with the use of TMDs in the damping of resonant structures in light of unexpected earthquake characteristics different from design earthquakes was experimentally demonstrated. Tuning a TMD to soil-structure system properties rather than fixed-base structural properties was found to double the improvement in damping and reduce the original peak response by nearly half. The potential effectiveness of a detuned mass damper in light of significant SSI was also demonstrated.; The financial help during the course of the study was extended by the Engineering and Physical Sciences Research Council (EPSRC).

Two-phase soil study: A. Finite strain consolidation, B. Centrifuge scaling considerations

Tan, Thiam-Soon
Fonte: California Institute of Technology Publicador: California Institute of Technology
Tipo: Report or Paper; PeerReviewed Formato: application/pdf
Publicado em 01/01/1985
Relevância na Pesquisa
27.62%
Two different aspects of the behavior of soil as a two-phase medium are studied, namely, the consolidation of soil and scaling relations for soils in centrifuge testing. PART A -- First a consistent approach is presented that unifies all current theories of consolidation of soil. For one-dimensional finite strain consolidation, a Lagrangian finite element scheme is then given and tested against three different experiments and found to give consistent results. For a quick solution to a particular problem, the regular perturbation method applied to the formulation in which the dependent variable is the natural strain is shown to give the most consistent results. For the Eulerian formulation, the material derivative contains a convective term. This convective effect is then analytically studied and found not to be negligible for a final natural strain greater than 10%. A method is then introduced that can account for both the moving boundary and the convective effect. This method is tested in a finite difference scheme and found to give identical results with the Lagrangian finite element scheme for the one-dimensional case. Finally the method is used for the axisymmetric problem of consolidation by vertical drain. The solution to this case suggests that arching and subsequent load redistribution should be considered. PART B -- Conceptually...

The impact of uncertain centrifuge capillary pressure on reservoir simulation

Subbey, Sam; Christie, Michael; Sambridge, Malcolm
Fonte: SIAM Publications Publicador: SIAM Publications
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.32%
The capillary pressure in a reservoir determines the saturation distribution, and hence the total in situ volumes of fluids (oil/water/gas). The accurate knowledge of the capillary pressure distribution is one of the primary factors that may be decisive in the reliable estimation of hydrocarbon reserves. The centrifuge procedure provides laboratory data, which can be inverted to derive capillary pressure curves in laboratory conditions. The derived laboratory capillary pressure curves are then scaled up for full-field simulation of petroleum reservoirs. The inversion procedure is uncertain and gives nonunique capillary pressure curves. The standard industrial practice, however, has been to derive a single capillary pressure curve, and ignoring the uncertainty. Since the capillary pressure is uncertain, estimates of important reservoir parameters dependent on capillary pressure distribution are uncertain. This paper shows how the uncertainty in centrifuge capillary pressure can be quantified. It also shows how this uncertainty propagates through the scale-up process and impacts on the estimate of the oil recovery potential. We illustrate using a simple, two-phase (oil/water) synthetic reservoir model.

Centrifuge modelling of a soil nail retaining wall

Jacobsz,S W
Fonte: Journal of the South African Institution of Civil Engineering Publicador: Journal of the South African Institution of Civil Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2013 EN
Relevância na Pesquisa
37.57%
This paper describes a physical model of a soil nail retained excavation face which was tested in the new geotechnical centrifuge at the University of Pretoria. As centrifuge modelling is new in South Africa, a short introduction to this technique is presented. The mobilisation of soil nail forces and their maximum values in response to excavation in the model were compared to measurements recently made in an instrumented 10 m high soil nail retaining structure for the Gautrain system in Pretoria. Results were also compared to predictions made using a simple failure wedge analysis and a database of eleven full-scale instrumented soil nail walls from the literature. The centrifuge model data compared well with both full-scale situations and theoretical analyses. The results suggest that soil nail forces measured in the centrifuge are conservative due to the mobilisation of a portion of the shear strength of the model soil during the acceleration of the centrifuge, leaving less un-mobilised shear strength available to resist loads resulting from the excavation.