Subglacial water plays an important role in the regulation of an ice sheet's mass balance. It may be the dominant control on the velocities of ice streams and outlet glaciers on scales of months to millennia. Recent satellite observations of ice surface elevation changes have given researchers new insights into how subglacial water is stored and transported. Localized uplift and settling of the ice surface implies that lakes exist beneath the ice sheet that are being filled and drained on relatively short time scales. %At the base of an ice sheet water can be transported through a variety of drainage networks or stored in subglacial lakes. Here, a numerical investigation of the mechanisms of transport and storage of subglacial water and the associated time scales is presented. Experiments are carried out using a finite element model of coupled ice and water flow. The first experiment seeks to understand the relationship between the depth of a basal depression and the area over which the feature affects basal water flow. It is found that as the perturbation to a topographic depression's depth is increased, water is rerouted in response to the perturbation. Additionally it is found that the relationship between perturbation depth and the extent upstream to which its effects reach is nonlinear. The second experiment examines how the aspect ratio of bed features (prolate, oblate, or equidimensional) influences basal water flow. It is found that the systems that develop and their interactions are mediated by both the topography and the feedbacks taken into account by the coupling of the systems in the model. Features oriented parallel to ice and water flow are associated with distributed fan systems that develop branches which migrate laterally across the domain and interact with one another on monthly and yearly timescales. Laterally oriented features develop laterally extensive ponds. As the ratio of longitudinal to lateral dimension of the topography is increased, a combination of these two water distributions is seen.

Graduation date: 1994

A new Earth system model of intermediate complexity, LOVECLIM, has been developed in order to study long-term future climate changes. In particular, LOVECLIM includes an interactive Greenland and Antarctic ice sheet model (AGISM) as well as an oceanic carbon cycle model (LOCH). Those climatic components can have a great impact on future climate. However, most studies investigating future climate changes do not take them into account. The few studies in recent literature assessing the impact of polar ice sheets on future climate draw very different conclusions, which shows the need for developing such a model. The aim of this study is to analyse the possible perturbations of climate induced by human activities over the next millennia. A particular attention is given to the evolution of the oceanic thermohaline circulation. A series of numerical simulations have been performed with LOVECLIM over the next millennia using various forcing scenarios. The global equilibrium warming computed by the model ranges from 0.55°C to 3.75°C with respect to preindustrial times. The model does not simulate a complete shut down of the oceanic thermohaline circulation but a transient weakening followed by a quasi-recovering at equilibrium. In most of the projections, the Greenland ice sheet undergoes a continuous reduction in volume, leading to an almost total disappearance in the most pessimistic scenarios. The impact of the Greenland deglaciation on climate has been assessed through sensitivity experiments. The removal of the Greenland ice sheet is responsible for a regional amplification of the global warming inducing a total melt of Arctic sea ice in summer. The freshwater flux from Greenland generates large salinity anomalies in the North Atlantic Ocean that reduce the rate of North Atlantic Deep Water formation, slowing down the oceanic thermohaline circulation.

A new Earth system model of intermediate complexity, LOVECLIM, has been developed in order to study long-term future climate changes. In particular, LOVECLIM includes an interactive Greenland and Antarctic ice sheet model (AGISM) as well as an oceanic carbon cycle model (LOCH). Those climatic components can have a great impact on future climate. However, most studies investigating future climate changes do not take them into account. The few studies in recent literature assessing the impact of polar ice sheets on future climate draw very different conclusions, which shows the need for developing such a model. The aim of this study is to analyse the possible perturbations of climate induced by human activities over the next millennia. A particular attention is given to the evolution of the oceanic thermohaline circulation. A series of numerical simulations have been performed with LOVECLIM over the next millennia using various forcing scenarios. The global equilibrium warming computed by the model ranges from 0.55°C to 3.75°C with respect to preindustrial times. The model does not simulate a complete shut down of the oceanic thermohaline circulation but a transient weakening followed by a quasi-recovering at equilibrium. In most of the projections, the Greenland ice sheet undergoes a continuous reduction in volume, leading to an almost total disappearance in the most pessimistic scenarios. The impact of the Greenland deglaciation on climate has been assessed through sensitivity experiments. The removal of the Greenland ice sheet is responsible for a regional amplification of the global warming inducing a total melt of Arctic sea ice in summer. The freshwater flux from Greenland generates large salinity anomalies in the North Atlantic Ocean that reduce the rate of North Atlantic Deep Water formation, slowing down the oceanic thermohaline circulation.

A rapidly melting ice sheet produces a distinctive geometry of sea level (SL) change. Thus, a network of SL observations may, in principle, be used to infer sources of meltwater flux. We outline a new method, based on a Kalman smoother, for using tide gauge observations to estimate the individual sources of global SL change. The Kalman smoother technique iteratively calculates the maximum likelihood estimate of Greenland and West Antarctic ice sheet melt rates at each time step, and it allows for data gaps while also permitting the estimation of non-linear trends. We have also implemented a fixed multi-model Kalman filter that allows us to rigorously account for additional contributions to SL changes, such as glacial isostatic adjustment and thermal expansion. We report on a series of detection experiments based on synthetic SL data that explore the feasibility of extracting source information from SL records before applying the new methodology to historical tide gauge records. In the historical tide gauge study we infer a global mean SL rise of ~1.5 ± 0.5 mm/yr up to 1970, followed by an acceleration to a rate of ~2.0 ± 0.5 mm/yr in 2008. In addition to its connection to SL, Greenland and its large ice sheet act as a barrier to storm systems traversing the North Atlantic. As a result of the interaction with Greenland, low-pressure systems located in the Irminger Sea, between Iceland and Greenland, often produce strong low-level winds. Through a combination of modeling and the analysis of rare in-situ observations, we explore the evolution of a lee cyclone that resulted in three high-speed-wind events in November 2004. Understanding Greenland’s role in these events is critical in our understanding of local weather in this region.

This thesis is one part of a lean project initiated by Luvata Sweden AB in Finspang casting department. The primary goal of that project is to increase the production efficiency, reduce costs and improve the quality of the copper coil. The aim of this thesis is to develop standardized work in casting department at Luvata Sweden AB Finspang. The research is based on lean thinking and organized in three steps. FIRST STEP: This step implies value stream mapping (VSM) of the current manufacturing process. VSM technique is applied in order to create an overview of the entirety production flow in a casting department, to visualize non-value added activities and to identify process wastes. SECOND STEP: By using lean tools as: Waste Management, SMED and Visual Management, thesis work intends to clean the production process. 7 Wastes or seven forms of Muda were studied at Luvata Finspang. The source of 5 wastes were identified and reduced/eliminated. SMED (single minute exchange of dies) analysis was carried out for a changeover during a casting montage in order to reduce the changeover time and streamline the montage process. Spaghetti diagram was applied particularly to inspect the best location for all montage materials, equipments and tools in a casting floor. Ensuring the efficient implementation of Waste Management and SMED practices Visual Management technique was used. This mean expresses the information about production process, its real-time status and results in a way that could be understood by operators in a shop floor. It is important to clean a production process before the standardized work can be developed, since the purpose of standardized work is to represent the best practice: method and sequence for each process. THIRD STEP: The last thesis step focuses on developing standardized work sheets as a steering tool for operators to follow the best practice while executing their tasks in each work center (melting, casting, rolling) and during the casting montage. The standardized work sheets are designed to show the approved way to perform the specific procedures and are expected to motivate operators to perform theirs job in the common way. That would consequently reduce high variation in operators performance. It would probably take several years before any reasonable improvements could be observed. However the developed standardized work sheets are already placed in the shop floor and successfully used by operators this is my small contribution to a big improvement project!

A friction stir welding equipment with high rotation speed and constant load is successfully developed in this study to weld the multi-laminated silicon steel sheets widely used on regular transformers. This equipment consists of a spinning unit, a loading unit, and a feeding unit. A WC round rod with 3 mm diameter is used as welding tool. Under different operating conditions, such as the normal load(140~480 N), the spindle speed (12000~24000rpm), the feeding rate (0~1.58 mm/s), the welding characteristics and the welding mechanism of multi-laminated silicon steel sheets, and the welding feasibility of the transformer are investigated. Firstly, the contour map of welding depth in terms of spindle speed,normal load, and depth of point welding is established for dwell welding time 15 seconds. Secondly, based on this contour map, two experimental conditions of the long-pass welding tests are selected to investigate the effect of normal load (Fd), the spindle speed (Ns), and the feeding rate (f) on the failure load of weld under the shear. According to the experimental results, the empirical formula is obtained as Ff =40.6(Fd¡DNs)1.123(f)-0.791. In this formula,(Fd¡DNs)1.123(f)-0.791 is proportional to the frictional work per unit moving distance. With the larger frictional work, this represents the heat generation of the workpiece material is higher with more uniform friction stir, so that the bonding strength of the material increases and the failure load of weld is larger. According to the micrograph observations, the thermo-mechanically affected zone is significantly influenced by high heat action generated from the friction between the tool and the weld surface region, so that the plastic flow of the workpiece material occurs to cause the multi-laminated silicon steel sheets bonding together. Finally, the transformer is successfully welded under the experimental conditions of the long-pass welding tests with the smaller welding depth and the better failure load.

The cold, lightless, and high pressure aquatic environment at the base of the East Antarctic Ice Sheet is of interest to a wide range of disciplines. Stable subglacial lakes and their connecting channels remain perennially liquid three kilometers below some of the coldest places on Earth. The presence of subglacial water impacts flow of the overlying ice and provides clues to the geologic properties of the bedrock below, and may harbor unique life forms which have evolved out of contact with the atmosphere for millions of years. Periodic release of water from this system may impact ocean circulation at the margins of the ice sheet. This research uses airborne radar sounding, with its unique ability to infer properties within and at the base of the ice sheet over large spatial scales, to locate and characterize this unique environment. Subglacial lakes, the primary storage mechanism for subglacial water, have been located and classified into four categories on the basis of the radar reflection properties from the sub-ice interface: Definite lakes are brighter than their surroundings by at least two decibels (relatively bright), and are both consistently reflective (specular) and have a reflection coefficient greater than --10 decibels (absolutely bright). Dim lakes are relatively bright and specular but not absolutely bright, possibly indicating non-steady dynamics in the overlying ice. Fuzzy lakes are both relatively and absolutely bright, but not specular, and may indicate saturated sediments or high frequency spatially heterogeneous distributions of sediment and liquid water (i.e. a braided steam). Indistinct lakes are absolutely bright and specular but no brighter than their surroundings. Lakes themselves and the different classes of lakes are not arranged randomly throughout Antarctica but are clustered around ice divides, ice stream onsets and prominent bedrock troughs, with each cluster demonstrating a different characteristic lake classification distribution. In the bedrock trough of Adventure Subglacial Trench, analysis of satellite altimetry is combined with radar sounding data to calculate a mass budget and infer a flow mechanism for a two cubic kilometer discharge reported to have traveled between two lakes in the region from 1996 -1998. The volume released from the source lake exceeded the volume received by the destination lakes by one and a tenth cubic kilometers, indicating that some water must have escaped downstream from the lowest destination lake over the course of the event. Release of water from the source lake preceded arrival of the water at the destination lakes, 260 kilometers away, by about three months. Water continued draining from the destination lakes for several years after surface subsidence at the source lake had ceased. By 2003, a total of one and a half cubic km or nearly 75% of the water released by the source lake had traveled downstream from the destination lakes. Hydraulic modeling work indicates that the initial release of water from the source lake could have been accommodated by a self-enlarging semicircular channel. Subsequent evolution of the discharge and the three-month delay between release of water from the source lake and arrival of that water at the destination lakes indicates that a shallower and broader distributed water system is responsible for the transport of subglacial water in this region. Such a system would be more stable for the given icebedrock geometry and may explain the observations of intermittent flat bright bedrock reflections in radar data acquired upstream from the destination lake in 2000. For the purpose of better understanding the long-term water budget of the Dome C region, an area upstream of Adventure Trench, eleven dated isochronal internal layers within the ice penetrating radar data were tracked. An age-depth relationship, derived from the European ice core through Dome C is used to calculate strain, estimate melt, model ice temperature, and determine absolute basal reflectivity for the entire region which covers over 28,000 square kilometers. The two largest subglacial lakes within the survey, Concordia and Vincennes, are both associated with enhanced basal melting on their upstream shores at rates locally greater than two millimeters per year. Widely distributed melt rates in the major topographic valleys upstream of these lakes are generally less than one millimeter per year throughout the region with slightly higher melts in the basin draining into Vincennes Subglacial Lake. Although published estimates for geothermal flux are capable of explaining the behavior of ice and water in most of the area, an additional source of basal heat is required to explain melt anomalies and subglacial lakes along the Concordia Ridge. Lake Concordia is expected to discharge water on a similar scale and duration as that observed in Adventure Trench, with a repeat cycle of a few hundred years. / text

This report compares surface elevation change and volume change esti- mates from three methods: repeat track (RT), crossover (CX), and overlapping footprints (OFP). These three methods use different approaches to group- ing elevation point measurements taken at different measurement epochs and estimating elevation change. Volume changes are calculated from elevation changes in the same manner for all three methods but differences in sampling resolution between the methods affect volume change estimates in different ways. The recently reprocessed Release 633 version of elevation measurements from the Geoscience Laser Altimeter System (GLAS), flown on the Ice, Cloud and land Elevation Satellite (ICESat), are used in this analysis. Both elevation changes and volume changes are compared for both the Greenland Ice Sheet (GrIS) and the Antarctic Ice Sheet (AIS). Additionally, uncertainties in the estimates for each method are quantified and compared. Results are separated by drainage systems and by above/below 2000 m surface elevation for the GrIS. For the AIS, results are aggregated to the East, West, and Penin- vi sula regions. Volume change estimates agree well for the three methods for the GrIS, with estimates of -227.75 ± 2.12 km³/yr, -249.30 ± 3.42 km³/yr, and -218.24 ± 7.39 km³/yr for the RT, CX, and OFP methods, respectively. These estimates are similar to those published from previous studies. For the AIS, however, larger discrepancies are found in the estimates. This stems primarily from a large discrepancy in the volume change estimate of the East AIS, where the RT, CX, and OFP methods estimate volume changes of 33.39 ± 1.42 km³/yr, 46.42 ± 5.46 km³/yr, and -2.72 ± 2.12 km³/yr, respectively. It's not entirely clear why this large discrepancy exists in this particular region, and elevation change estimates for a few particular drainage systems in this region are examined. Previously published volume changes for the AIS also show a large scatter and more work must be done to reconcile the various estimates. Finally, the volume change uncertainties reported do not completely account for the discrepancies in most regions. Additional analysis must be done to completely quantify all error sources. / text

Pattern formation in buckled membranes was studied along with the morphology of flowers formed at the tip of silicon nanowires and ripples formed in suspended graphene sheets. Nash's perturbation method was tested for a simple case where initial and final metrics embed smoothly and there is a smooth path from one surface to another and was found to work successfully. The method was tested in more realistic conditions where a smooth path was not known and the method failed. Cylindrical flower-like membranes with a metric of negative Gaussian curvature were simulated in three and four dimensions. These four dimensional flowers had 2 orders of magnitude less energy than their three dimensional counterparts. Simulations were used to show that the addition of a fourth spatial dimension did not relieve all bending energy from the cylindrical membranes. Patterns formed at the tip of silicon nanowires were studied and found to be of the Dense Branching Morphology type. The rate of branching is dependent on the curvature of the gold bubble on which they are grown. Graphene was simulated using the modified embedded atom method potential and buckles were found to form if the carbon bonds were stretched. An energy functional was found for the energy of a sheet with a metric different from that of flat space. / text