Model reduction in integrated controls-structures design

It is the objective of this paper to present a model reduction technique developed for the integrated controls-structures design of flexible structures. Integrated controls-structures design problems are typically posed as nonlinear mathematical programming problems, where the design variables consist of both structural and control parameters. In the solution process, both structural and control design variables are constantly changing; therefore, the dynamic characteristics of the structure are also changing. This presents a problem in obtaining a reduced-order model for active control design and analysis which will be valid for all design points within the design space. In other words, the frequency and number of the significant modes of the structure (modes that should be included) may vary considerably throughout the design process. This is also true as the locations and/or masses of the sensors and actuators change. Moreover, since the number of design evaluations in the integrated design process could easily run into thousands, any feasible order-reduction method should not require model reduction analysis at every design iteration. In this paper a novel and efficient technique for model reduction in the integrated controls-structures design process, which addresses these issues, is presented

Robust eigensystem assignment for second-order estimators

An approach for the robust eigensystem assignment of flexible structures using full state or output feedback is developed. Using the second-order dynamic equations, the approach can assign the eigenvalues of the system via velocity and displacement feedbacks, or acceleration and velocity feedbacks. The eigenvalues and eigenvectors of the system are assigned, via the second-order eigenvalue problem for the structural system, in two steps. First, an orthonormal basis spanning the attainable closed-loop eigenvector space corresponding to each desired closed-loop eigenvalue is generated using the Singular Value or QR decompositions. Second, a sequential procedure is used to choose a set of closed-loop eigenvectors that are as close as possible to the column space of a well-conditioned target matrix. Among the possible choices of the target matrix, the closest unitary matrix to the open-loop eigenvector matrix appears to be a suitable choice. A numerical example is given to illustrate the proposed algorithm

Modelling thermo-mechanical response of metal canister disposed in engineered barrier systems

The main objective of this thesis is to describe and implement a rate-dependent (viscoplastic) constitutive equations for copper based canister using a single internal state variable and use it for modelling disposal schemes subjected to shear conditions. The model of Bodner and Partom (BP) is considered for this purpose (Bodner & Partom, 1975). To evaluate the copper's response to variations in strain rate throughout a temperature range, this model uses viscoplastic constitutive equations based on a single internal state variable that is a function of plastic work. The BP constitutive model has been implemented in CODE_BRIGHT computer code (DIT-UPC, 2021; Olivella et al., 1994; Olivella et al., 1996). The constitutive equation is verified against existing results and its validation is carried out by assessing the capability to reproduce experiments. For verification, the stress-strain response of a bar under uniaxial tensile conditions at a constant velocity was simulated with CODE_BRIGHT and the results compared with the solution obtained from Stealth Finite Difference Code and the semi-analytical solutions. In addition, it is analyzed the reaction of a canister installed inside an engineered barrier which undergoes hydration and swelling until it reaches full saturation prior to shearing. The implemented elasto-viscoplastic model actually represents the behavior of the canister in yielding conditions. Although the canister is very stiff and strong compared to the clay components where it will be emplaced in a clay volume shear deformations occurring on the engineered barrier system (EBS) will have an impact on the canister (Börgesson, 1986). Finally, a repository of nuclear spent fuel is analyzed under extreme conditions as it is a long-life system and has to resist all types of environmental conditions, for instance earthquakes and glaciations. After model implementation and verification in CODE BRIGHT this program has been used to model the canister-clay shear tests in 2D and 3D. In the Mock-up scale and Full-scale in 2D and 3D models, a comparison between the total stress method (mechanical analysis only) and the effective stress method (hydro-mechanical analysis) has been investigated. Experimental results from a canister-clay shear test (Börgesson, 1986) have been compared to the findings of the numerical model using CODE BRIGHT. Sensitivity analysis on viscosity for total stress calculations and permeability for effective stress calculations have been performed in the Mock-up scale and Full-scale. In the canister-clay shear test, a mesh sensitivity analysis and also a comparison between the updated mesh (Lagrangian method) and the fixed mesh method have been carried out. Finally, in two and three dimensions, the simulation of canister-clay shear tests based on impact of discontinuity (the discontinuity is in the rock and due to it, there is shearing in canister-rock system), as well as sensitivity analysis of parameters and mesh in mechanical and a coupled hydro-mechanical analysis, have been investigated.El principal objetivo de esta tesis es describir e implementar una ecuación constitutiva dependiente de la velocidad (viscoplástica) para un contenedor a base de cobre usando una única variable de estado interna y usarlo para modelar esquemas de almacenamiento sujetos a condiciones de cizallamiento. Para ello se considera el modelo de Bodner y Partom (BP) (Bodner & Partom, 1975). Para evaluar la respuesta del cobre a las variaciones en la velocidad de deformación a lo largo de un rango de temperatura, este modelo utiliza ecuaciones constitutivas viscoplásticas basadas en una única variable de estado interno que es una función del trabajo plástico. El modelo constitutivo de BP se ha implementado en programa de ordenador CODE_BRIGHT (DIT-UPC, 2021; Olivella et al., 1994; Olivella et al., 1996). La ecuación constitutiva se verifica con los resultados existentes y su validación se lleva a cabo evaluando la capacidad para reproducir experimentos. Para la verificación, se simuló la respuesta tensión-deformación de una barra en condiciones de tracción uniaxial a velocidad constante con CODE_BRIGHT y se compararon los resultados con la solución obtenida de Stealth Finite Difference Code y las soluciones semi-analíticas. Además, se analiza la reacción de un contenedor instalado dentro de una barrera de ingeniería, que sufre hidratación e hinchazón hasta que alcanza la saturación completa antes del cizallamiento. El modelo elasto-viscoplástico implementado realmente representa el comportamiento del contenedor en condiciones de plastidad. Aunque el contenedor es muy rígido y resistente en comparación con los componentes de arcilla donde se colocará, las deformaciones por cizallamiento que ocurren en el sistema de barrera de ingeniería (EBS) tendrán un impacto en el contenedor (Börgesson, 1986). Por último, el contenedor de combustible nuclear gastado se podrá analizar en condiciones extremas, ya que es un sistema de larga duración y debe resistir todo tipo de condiciones ambientales, por ejemplo, terremotos y glaciaciones. Después de la implementación y verificación del modelo en CODE BRIGHT, este programa se ha utilizado para modelar las pruebas de cizallamiento en 2D y 3D. En la escala Mock-up y Full-scale en modelos 2D y 3D, se ha llevado a cabo una comparación entre el método de tensiones totales (solo análisis mecánico) y el método de tensiones efectivas (análisis hidromecánico). Los resultados experimentales de una prueba de cizallamiento canister en arcilla (Börgesson, 1986) se han comparado con los resultados del modelo numérico utilizando CODE BRIGHT. El análisis de sensibilidad sobre la viscosidad para los cálculos de tensión total y la permeabilidad para los cálculos de tensión efectiva se han realizado en la escala Mock-up y Full-scale. En la prueba de cizalla de contenedor-arcilla, se ha realizado un análisis de sensibilidad de la malla y también una comparación entre el método que actualiza la malla con los desplazamientos (método Lagrangiano) y el método de malla fija. Finalmente, en dos y tres dimensiones, se ha realizado la simulación de ensayos de cizallamiento contenedor-arcilla basados en el impacto de la presencia de una discontinuidad (la discontinuidad está en la roca y por ello hay cizallamiento en el sistema), así como análisis de sensibilidad de parámetros. y malla en análisis mecánico e hidromecánico acopladoPostprint (published version

A study on the sensitivity and simultaneous adjustment of a hoop-column antenna surface

The results of a recent surface adjustment of the 15-meter diameter hoop-column antenna are presented. A least-squares differential algorithm is used to adjust the surface shape as close as possible to a perfect parabola. Since the desired perfect parabola is not uniquely known a priori, parameters of the perfect parabola are included in the design vector along with the cable length changes. As an extension to an earlier study, lateral sensitivity is included in the least-squares adjustment procedure. In addition, the effect of cable length uncertainties on the surface RMS error is considered and an error bound is derived. The results in this study indicate an improvement over earlier studies. The sensitivity analysis provided a quantitative measure of the needed accuracy of the cable adjustments in the laboratory. Recommendations are included to further enhance shape adjustment

FRICTION MEASUREMENT IN PRECISION GLASS MOLDING

Extensive growth of state-of-the-art technologies has created a demand for high quality lenses and has driven the industry toward an inexpensive process for manufacturing of aspheric glass lenses called Precision Glass Molding (PGM). Finite Element Analysis (FEA) has been used to predict the right mold geometry. Having a realistic simulation to predict mold geometry depends on the correct model of material behavior and friction coefficient at elevated temperature. Finding the static and dynamic coefficient of friction experimentally between two flat surfaces at elevated temperature is the subject of this research. The equipment used in this study was originally designed for the Precision Glass Molding (PGM) process and was modified for friction measurement by using molds designed specifically for the friction test. The performance of this apparatus was validated using a steel-steel friction pair at room temperature and a steel-BK7 pair at elevated temperature. The frictional behavior of two different types of oxide glasses; BK7 and Soda-Lime-Silica glass have been studied. During trials at which the temperature is above the glass transition temperature, the results show the effect of glass viscoelasticity in the friction data. This effect is in the form of exponential increase in friction force data prior to the onset of sliding. Moreover, the effect of stick-slip phenomenon can be seen as a jump in the position data (in the order of microns in tangential direction). Coulomb\u27s Law has been used to calculate the friction coefficient. An average friction coefficient has been defined and calculated for some trials, providing a quantitative value for dynamic friction coefficient at different process parameters. The final part of the investigation involved using the Design of Experiment approach to include a broader range of processing parameters and do a sensitivity analysis to find the effect of temperature, normal force, feed rate, and surface finish on dynamic friction coefficient. The finding from the current investigation demonstrates reasonable changes in dynamic friction of glass due to its viscoelastic properties close to its transition temperature. These friction data can be used to improve the accuracy of simulations of the PGM process

Spectral spatiality in the acousmatic listening context

Sounds are often experienced as being spatially higher or lower in congruence with their frequency ‘height’ (i.e. pitch register). The term ‘spectral spatiality’ refers to this impression of spatial height and vertical depth as evoked by the perceived occupancy of evolving sound-shapes (spectromorphologies) within the continuum of audible frequencies. Chapters One and Two draw upon a diverse body of literature to explore the cognitive and physiological processes involved in human spatial hearing in general, and spectral spatiality in particular. Thereafter the potential pertinence of a spectral space consciousness in the acousmatic listening experience is highlighted, particularly with regard to more abstract acousmatic contexts where sounds do not directly invoke familiar source identities. Chapters Three and Four further elaborate aspects of spectral space consciousness and propose a terminological framework for discussing musical contexts in terms of their spectral space design. Consequently, it is argued that in acousmatic music, spectral spatiality must be considered as an inseparable aspect of spatiality in general, although its pertinence only becomes directly highlighted in particular musical contexts. The recurring theme in this thesis is that, in acousmatic music, 'space' is not a parameter but a multifaceted quality that is inherent to all sounds. As well as providing an analytical framework for discussing spatiality in acousmatic music, this thesis highlights the compositional potentials offered by spectral spatiality, particularly in relation to the creation of perspectival image in multichannel works. For instance, the possibility of (re)distributing the spectral components of a sound around the listener (circumspectral image) is discussed in context, and a software tool is presented that enables an intuitive and experimental approach to the composition of circumspectral sounds for 6 and 8 channel loudspeaker configurations. This thesis is useful for both composers and analysts interested in aspects of spatiality in acousmatic music. It also offers some insight into spectral space consciousness in non-acousmatic music, and may therefore contribute towards a more general understanding of the nature of our spatial experience in music

An Integrated FAHP-PROMETHEE Approach For Selecting The Best Flexible Manufacturing System

This paper proposes an integrated approach to the decision-making problem that combines the Fuzzy Analytical Hierarchy Process (FAHP) and the Preference Ranking Organization Method for Enrichment Evaluations (PROMETHEE) with the purpose of Evaluation of Flexible Manufacturing Systems with a Group Decision Support System (GDSS). The FAHP is used to determine the weights for each criterion and PROMETHEE is applied to get the final ranking and GAIA plane is used to highlight the conflicts, the similarities and independences among the criteria and the DMs. Finally, a numerical example proposed in this paper determines the most appropriate FMS alternative