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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

Design of diffractive optical elements through low-dimensional optimization

Peters, David W. 2001 August 1900 (has links)
The simulation of diffractive optical structures allows for the efficient testing of a large number of structures without having to actually fabricate these devices. Various forms of analysis of these structures have been done through computer programs in the past. However, programs that can actually design a structure to perform a given task are very limited in scope. Optimization of a structure can be a task that is very processor time intensive, particularly if the optimization space has many dimensions. This thesis describes the creation of a computer program that is able to find an optimal structure while maintaining a low-dimensional search space, thus greatly reducing the processor time required to find the solution. The program can design the optimal structure for a wide variety of planar optical devices that conform to the weakly-guiding approximation with an efficient code that incorporates the low-dimensional search space concept. This work is the first use of an electromagnetic field solver inside of an optimization loop for the design of an optimized diffractive-optic structure.
2

Encruamento e recristalização dos aços inoxidáveis EUROFER e ODS-EUROFER para aplicação em reatores de fusão nuclear. / Work hardening and recrystallization of EUROFER and ODS-EUROFER stainless steels to nuclear fusion reactors application.

Zimmermann, Angelo José de Oliveira 17 September 2009 (has links)
Este trabalho consiste em uma pesquisa sobre aços inoxidáveis ferríticomartensíticos de ativação reduzida (RAFM): EUROFER (9Cr-1W) e ODS-EUROFER (9Cr-1W-0,3Y2O3), envolvendo o encruamento e a recristalização destas duas ligas com o objetivo de estudar a influência de uma dispersão de partículas nanométricas na recristalização de aços inoxidáveis. O conceito de materiais de ativação reduzida é discutido e é apresentada a aplicação destes aços tanto na estrutura de diversor do ITER quanto na primeira parede no módulo de câmara fértil do reator DEMO. As placas, no estado revenido, foram laminadas a frio em um laminador de pequeno porte. As curvas de encruamento de ambos os materiais mostram um comportamento quase linear. Os tratamentos isócronos de uma hora, entre 300 e 750 °C, resultaram curvas de amolecimento que indicam uma forte resistência à recristalização da liga ODS-EUROFER, em concordância com os modelos teóricos. A liga EUROFER-97 apresentou recristalização muito similar a liga comercial 430, mas com maior dureza inicial, devido a maior quantidade de elementos intersticiais. / This work studies reduced activation ferritic-martensitic (RAFM) stainless steels: EUROFER (9Cr-1W) and ODS-EUROFER (9Cr-1W-0,3Y2O3), and their work hardening and recrystallization behaviour to better understand the influence of a dispersion of nanometric particles on the recrystallization process of stainless steels. The concept of reduced activation materials is discussed and the application of these steel alloys, such as in the divertor structure of ITER (International Thermonuclear Experimental Reactor) and as in the DEMO reactor breeding blanket first wall is shown. The plates, in the as-tempered condition, were cold rolled in a laboratory rolling mill. The work hardness curves of both materials presented an approximately linear behavior with strain increase. One hour isochronal treatments, in the temperature range from 300 to 750 °C, resulted in softening curves that indicated a strong resistance to recrystallization of the alloy ODS-EUROFER, supporting the theorical models. The EUROFER-97 recrystallization showed a similar behaviour to the commercial 430 alloy, however with higher initial hardness, due to the larger amount of interstitial elements.
3

Structural stability and mechanical strength of salt-affected soils

Barzegar, Abdolrahman. January 1995 (has links) (PDF)
Copies of author's previously published articles in pocket inside back cover. Bibliography: leaves 147-160. This thesis outlines the factors affecting soil strength and structural stability and their interrelationship in salt-affected soils. The objectives of this study are to investigate the influence of clay particles on soil densification and mellowing, the mellowing of compacted soils and soil aggregates as influenced by solution composition, the disaggregation of soils subjected to different sodicities and salinities and its relationship to soil strength and dispersible clay and the effect of organic matter and clay type on aggregation of salt-affected soils.
4

Numerical modelling of real-time sub-structure testing

Williams, David Michael January 2000 (has links)
Current dynamic testing methods can prove unrealistic due to the scale at which test components are modelled, the rate at which they are loaded or the boundary conditions to which they are subjected. A new test method, termed "Real-Time Sub-Structure Testing" seeks to provide a more realistic testing environment for energy dissipative components. The method tests structural components at full or large scale and in real-time. The physical test interacts with a computer model of the structure surrounding the test component. In this way, the in-situ behaviour of the test component is evaluated in relation to the overall structural response. The testing method requires fast and realistic modelling of the surrounding structure and a rapid interaction with the physical test specimen. For these reasons, a new non-linear finite element method has been proposed in order to model the surrounding structure behaviour efficiently. The method uses the Central Difference Method time stepping integration scheme together with a newly devised basis. The proposed basis consists of the structure’s elastic modes and additional Ritz vectors, which are calculated from the inelastic static displacement shapes of the structure. The displacement shapes correspond to the same static spatial distribution of loading as the intended dynamic excitation, and are intended to characterise the inelastic behaviour of the structure. The method has been validated against a Newmark event to event algorithm as well as Drain2DX. The non-linear dynamic response of a propped cantilever beam and portal frame structure was investigated. The response evaluated by the algorithm agrees closely with both validation analyses. The new algorithm was also shown to be faster than the Newmark procedure in simple benchmark tests. In addition, a numerical model of the testing apparatus has been developed in order to simulate complete tests for the purposes of testing procedure development and validation. The model is developed using Matlab Simulink. Parameters for the model are deduced from published data, experimental component tests and open loop step response calibrations. The model behaviour was found to be very sensitive to the parameters used. However, after calibration against open loop tests the model reproduces the observed laboratory behaviour to a good degree of accuracy. In an attempt to predict the behaviour of an actual test, the laboratory model has been coupled with the new structural solution algorithm to simulate a virtual test. The simulated results compare well with experimentally observed data demonstrating the usefulness of the overall simulation as a test modelling tool.
5

Structural stability and mechanical strength of salt-affected soils / by Abdolrahman Barzegar.

Barzegar, Abdolrahman January 1995 (has links)
Copies of author's previously published articles in pocket inside back cover. / Bibliography: leaves 147-160. / xvi, 160 leaves, [6] leaves of plates : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis outlines the factors affecting soil strength and structural stability and their interrelationship in salt-affected soils. The objectives of this study are to investigate the influence of clay particles on soil densification and mellowing, the mellowing of compacted soils and soil aggregates as influenced by solution composition, the disaggregation of soils subjected to different sodicities and salinities and its relationship to soil strength and dispersible clay and the effect of organic matter and clay type on aggregation of salt-affected soils. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1996
6

Encruamento e recristalização dos aços inoxidáveis EUROFER e ODS-EUROFER para aplicação em reatores de fusão nuclear. / Work hardening and recrystallization of EUROFER and ODS-EUROFER stainless steels to nuclear fusion reactors application.

Angelo José de Oliveira Zimmermann 17 September 2009 (has links)
Este trabalho consiste em uma pesquisa sobre aços inoxidáveis ferríticomartensíticos de ativação reduzida (RAFM): EUROFER (9Cr-1W) e ODS-EUROFER (9Cr-1W-0,3Y2O3), envolvendo o encruamento e a recristalização destas duas ligas com o objetivo de estudar a influência de uma dispersão de partículas nanométricas na recristalização de aços inoxidáveis. O conceito de materiais de ativação reduzida é discutido e é apresentada a aplicação destes aços tanto na estrutura de diversor do ITER quanto na primeira parede no módulo de câmara fértil do reator DEMO. As placas, no estado revenido, foram laminadas a frio em um laminador de pequeno porte. As curvas de encruamento de ambos os materiais mostram um comportamento quase linear. Os tratamentos isócronos de uma hora, entre 300 e 750 °C, resultaram curvas de amolecimento que indicam uma forte resistência à recristalização da liga ODS-EUROFER, em concordância com os modelos teóricos. A liga EUROFER-97 apresentou recristalização muito similar a liga comercial 430, mas com maior dureza inicial, devido a maior quantidade de elementos intersticiais. / This work studies reduced activation ferritic-martensitic (RAFM) stainless steels: EUROFER (9Cr-1W) and ODS-EUROFER (9Cr-1W-0,3Y2O3), and their work hardening and recrystallization behaviour to better understand the influence of a dispersion of nanometric particles on the recrystallization process of stainless steels. The concept of reduced activation materials is discussed and the application of these steel alloys, such as in the divertor structure of ITER (International Thermonuclear Experimental Reactor) and as in the DEMO reactor breeding blanket first wall is shown. The plates, in the as-tempered condition, were cold rolled in a laboratory rolling mill. The work hardness curves of both materials presented an approximately linear behavior with strain increase. One hour isochronal treatments, in the temperature range from 300 to 750 °C, resulted in softening curves that indicated a strong resistance to recrystallization of the alloy ODS-EUROFER, supporting the theorical models. The EUROFER-97 recrystallization showed a similar behaviour to the commercial 430 alloy, however with higher initial hardness, due to the larger amount of interstitial elements.

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