Analytical studies of a large-scale laminar soil-box for experiments in soil-structure-interaction

Nuclear facilities frequently have deep massive foundations, which are large enough to affect the response of neighboring soil and the nature of ground shaking these facilities have to withstand. Despite this well-recognized phenomenon, the ramifications of soil-structure interaction (SSI) are not completely understood due to the complexity of the mechanics involved. As a consequence, only simplified elastic models are currently used to study SSI for these and other facilities. To address this situation, the U.S. Department of Energy (DOE) has funded a multi-institutional project to investigate SSI effects in nuclear facilities. To this end, the research team at University of Nevada Reno (UNR) is fabricating a 400-ton, laminar, biaxial soil box and corresponding shake table, which will be used to (a) explore SSI phenomena at a scale not currently possible in the U.S., and (b) validate the ESSI nonlinear computational framework, developed by UC Davis. This thesis presents some of the numerical analyses that have been conducted in order to inform the design of the soil-box and shake-table, and to understand the (a) dynamic behavior of the soil-box, (b) the role of soil nonlinearity, (c) the fundamental interaction of the soil with the walls of the box, and (d) the effect of friction and gapping at the soil-wall interface. The preliminary design phase included the modelling of a 1D soil-column in DEEPSOIL and compared results from linear, equivalent linear and nonlinear analyses, for a suite of eight recorded ground motions obtained from the PEER database, and different scale factors, with scaled PGAs between 0.25g and 1.0g. Simulation of the nonlinear hysteretic soil-behavior was achieved via the use of the Pressure-Dependent Modified Kodner Zelesko model and the new General Quadratic Hyperbolic model. The effect of several parameters, such as the hysteretic soil material, the reference curve, the time-step and the time-scaling of the input motion, on the results of the nonlinear dynamic analyses was also evaluated. Furthermore, finite element modeling and nonlinear dynamic analyses of a 1D soil column and a more realistic 2D slice of the soil including the box walls were conducted in LS-DYNA using a nested surface plasticity model. Different mesh sizes, wall configurations, and contact conditions at the soil-wall interface, ranging from frictionless contact to perfect contact, were examined in order to decipher the role of sliding, friction and gapping on the behavior of the box. Wall configurations with and without vertical constraints, with linear axial springs, and with compression-only springs were investigated. The boundary effect close to the walls was also examined and the area of uniform soil stresses was identified for different design alternatives. The nonlinear dynamic analyses were used to quantify the base shear, overturning moment, pressures below the box, response spectra at different locations of the soil, forces in the walls, and the accelerations, displacements, strains and stresses of the soil and the box. The advanced numerical analyses presented in this thesis give an insight into the seismic behavior of the soil-box and are expected to be useful to other research teams designing their own soil-box. The numerical work demonstrated that:• Equivalent linear site response analyses give similar results with nonlinear analyses for small to moderate levels of shaking (PGA=0.5g), but they over-predict the base shear forces and under-predict the shear strains for higher levels of shaking.• The soil nonlinearity limits the increase of the base shear, offsets the fundamental period of the soil (from 0.13sec to about 0.5-0.6sec for input motions with PGA=1.04g), increases significantly the soil-strains (1-7% for aforementioned motions), and results in de-amplification of the input motion towards the surface.• It is important to use soil materials models (GQ/H) that can properly simulate the soil behavior at large-strains by reaching the correct shear strength especially at high levels of shaking, because such models can give a significantly different response of the soil column and reduce the base shear by 15% and increase the maximum shear strains by a factor of 2.• Laminar walls that are flexible in every direction (lateral and vertical) are witnessing vertical soil displacements in regions close to the walls, indicating that the soil is not in pure shear. For this case the stresses are not uniform along the whole length of a layer, with soil regions closer to the walls witnessing different stresses than the ones close to the center of the box, demonstrating the existence of a significant boundary effect caused by the walls.• Large overturning moment is generated at the bottom of the soil-box during strong lateral shaking, and this moment can introduce significant uplift in the walls, meaning that they should be designed not only for shear but also for tension.• To ensure that the soil-box will behave as realistically as possible, it is necessary to have walls with small lateral shear stiffness but very high axial and bending stiffness, together with a high-coefficient of friction at the soil-wall interface, which will transfer the complementary shear of the soils to the walls and ensure a minimal/negligible boundary effect

Gravitational wave astronomy

The first decade of the new millenium should see the first direct detections of gravitational waves. This will be a milestone for fundamental physics and it will open the new observational science of gravitational wave astronomy. But gravitational waves already play an important role in the modeling of astrophysical systems. I review here the present state of gravitational radiation theory in relativity and astrophysics, and I then look at the development of detector sensitivity over the next decade, both on the ground (such as LIGO) and in space (LISA). I review the sources of gravitational waves that are likely to play an important role in observations by first- and second-generation interferometers, including the astrophysical information that will come from these observations. The review covers some 10 decades of gravitational wave frequency, from the high-frequency normal modes of neutron stars down to the lowest frequencies observable from space. The discussion of sources includes recent developments regarding binary black holes, spinning neutron stars, and the stochastic background.Comment: 29 pages, 2 figures, as submitted for special millenium issue of Classical and Quantum Gravit

Eigensystem realization algorithm modal identification experiences with mini-mast

This paper summarizes work performed under a collaborative research effort between the National Aeronautics and Space Administration (NASA) and the German Aerospace Research Establishment (DLR, Deutsche Forschungsanstalt fur Luft- und Raumfahrt). The objective is to develop and demonstrate system identification technology for future large space structures. Recent experiences using the Eigensystem Realization Algorithm (ERA), for modal identification of Mini-Mast, are reported. Mini-Mast is a 20 m long deployable space truss used for structural dynamics and active vibration-control research at the Langley Research Center. A comprehensive analysis of 306 frequency response functions (3 excitation forces and 102 displacement responses) was performed. Emphasis is placed on two topics of current research: (1) gaining an improved understanding of ERA performance characteristics (theory vs. practice); and (2) developing reliable techniques to improve identification results for complex experimental data. Because of nonlinearities and numerous local modes, modal identification of Mini-Mast proved to be surprisingly difficult. Methods were available, ERA, for obtaining detailed, high-confidence results

Software-based gradient nonlinearity distortion correction

The primary purpose of the thesis is to discuss the use of Magnetic Resonance Imaging (MRI) in functional proton radiosurgery. The methods presented in this thesis were specifically designed to correct gradient nonlinearity distortion, the single greatest hurdle that limits the deployment of MRI-based functional proton radiosurgery systems. The new system central in the thesis fully utilized MRI to provide localization of anatomical targets with submillimeter accuracy. The thesis provides analysis and solutions to the problems related to gradient nonlinearity distortion. The characteristics of proton radiosurgery are introduced, in addition to a discussion of its advantages over other current methods of radiation oncology. A historical background for proton radiosurgery is also presented, along with a description of its implementation at Loma Linda University Medical Center (LLUMC), where a new system for functional proton radiosurgery has been proposed and is currently under development

Channel Management and differentiation strategies: A case study from the market for fresh produce

The paper analyses the current differentiation strategies in the market for fresh produce. First a short review of the literature on channel structure and product differentiation is presented, in order to identify, on a theoretical grounding the incentives for differentiation strategies. Second, a case study is drawn of a UK channel intermediary organisation carrying out differentiation policies in the fresh produce category (on behalf of UK multiple retailer customers) supplied by a dedicated Italian grower. Results show that in the fresh produce industry there is room for product differentiation, but with contradictory welfare effects.fresh produce, product differentiation, channel structure and management, Agribusiness, Marketing,

Part 3: Systemic risk in ecology and engineering

The Federal Reserve Bank of New York released a report -- New Directions for Understanding Systemic Risk -- that presents key findings from a cross-disciplinary conference that it cosponsored in May 2006 with the National Academy of Sciences' Board on Mathematical Sciences and Their Applications. ; The pace of financial innovation over the past decade has increased the complexity and interconnectedness of the financial system. This development is important to central banks, such as the Federal Reserve, because of their traditional role in addressing systemic risks to the financial system. ; To encourage innovative thinking about systemic issues, the New York Fed partnered with the National Academy of Sciences to bring together more than 100 experts on systemic risk from 22 countries to compare cross-disciplinary perspectives on monitoring, addressing and preventing this type of risk. ; This report, released as part of the Bank's Economic Policy Review series, outlines some of the key points concerning systemic risk made by the various disciplines represented - including economic research, ecology, physics and engineering - as well as presentations on market-oriented models of financial crises, and systemic risk in the payments system and the interbank funds market. The report concludes with observations gathered from the sessions and a discussion of potential applications to policy. ; The three papers presented in this conference session highlighted the positive feedback effects that produce herdlike behavior in markets, and the subsequent discussion focused in part on means of encouraging heterogeneous investment strategies to counter such behavior. Participants in the session also discussed the types of models used to study systemic risk and commented on the challenges and trade-offs researchers face in developing their models.Financial risk management ; Financial markets ; Financial stability ; Financial crises