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Sample records for model a-pleated sheets

  1. Simplified model for fouling of a pleated membrane filter

    NASA Astrophysics Data System (ADS)

    Sanaei, Pejman; Cummings, Linda

    2014-11-01

    Pleated filter cartridge are widely used to remove undesired impurities from a fluid. A filter membrane is sandwiched between porous support layers, then pleated and packed in to an annular cylindrical cartridge. Although this arrangement offers a high ratio of surface filtration area to volume, the filter performance (measured, e.g., by graph of total flux versus throughput for a given pressure drop), is not as good as a flat filter membrane. The reasons for this difference in performance are currently unclear, but likely factors include the additional resistance of the porous support layers upstream and downstream of the membrane, the pleat packing density (PPD) and possible damage to the membrane during the pleating process. To investigate this, we propose a simplified mathematical model of the filtration within a single pleat. We consider the fluid dynamics through the membrane and support layers, and propose a model by which the pores of the membrane become fouled (i) by particles smaller than the membrane pore size; and (ii) by particles larger than the pores.We present some simulations of our model, investigating how flow and fouling differ between not only flat and pleated membranes, but also for support layers of different permeability profiles. NSF DMS-1261596.

  2. Global ice sheet modeling

    SciTech Connect

    Hughes, T.J.; Fastook, J.L.

    1994-05-01

    The University of Maine conducted this study for Pacific Northwest Laboratory (PNL) as part of a global climate modeling task for site characterization of the potential nuclear waste respository site at Yucca Mountain, NV. The purpose of the study was to develop a global ice sheet dynamics model that will forecast the three-dimensional configuration of global ice sheets for specific climate change scenarios. The objective of the third (final) year of the work was to produce ice sheet data for glaciation scenarios covering the next 100,000 years. This was accomplished using both the map-plane and flowband solutions of our time-dependent, finite-element gridpoint model. The theory and equations used to develop the ice sheet models are presented. Three future scenarios were simulated by the model and results are discussed.

  3. FDTD modeling of thin impedance sheets

    NASA Technical Reports Server (NTRS)

    Luebbers, Raymond J.; Kunz, Karl S.

    1991-01-01

    Thin sheets of resistive or dielectric material are commonly encountered in radar cross section calculations. Analysis of such sheets is simplified by using sheet impedances. In this paper it is shown that sheet impedances can be modeled easily and accurately using Finite Difference Time Domain (FDTD) methods.

  4. FDTD modeling of thin impedance sheets

    NASA Technical Reports Server (NTRS)

    Luebbers, Raymond; Kunz, Karl

    1991-01-01

    Thin sheets of resistive or dielectric material are commonly encountered in radar cross section calculations. Analysis of such sheets is simplified by using sheet impedances. It is shown that sheet impedances can be modeled easily and accurately using Finite Difference Time Domain (FDTD) methods. These sheets are characterized by a discontinuity in the tangential magnetic field on either side of the sheet but no discontinuity in tangential electric field. This continuity, or single valued behavior of the electric field, allows the sheet current to be expressed in terms of an impedance multiplying this electric field.

  5. ISSM: Ice Sheet System Model

    NASA Technical Reports Server (NTRS)

    Larour, Eric; Schiermeier, John E.; Seroussi, Helene; Morlinghem, Mathieu

    2013-01-01

    In order to have the capability to use satellite data from its own missions to inform future sea-level rise projections, JPL needed a full-fledged ice-sheet/iceshelf flow model, capable of modeling the mass balance of Antarctica and Greenland into the near future. ISSM was developed with such a goal in mind, as a massively parallelized, multi-purpose finite-element framework dedicated to ice-sheet modeling. ISSM features unstructured meshes (Tria in 2D, and Penta in 3D) along with corresponding finite elements for both types of meshes. Each finite element can carry out diagnostic, prognostic, transient, thermal 3D, surface, and bed slope simulations. Anisotropic meshing enables adaptation of meshes to a certain metric, and the 2D Shelfy-Stream, 3D Blatter/Pattyn, and 3D Full-Stokes formulations capture the bulk of the ice-flow physics. These elements can be coupled together, based on the Arlequin method, so that on a large scale model such as Antarctica, each type of finite element is used in the most efficient manner. For each finite element referenced above, ISSM implements an adjoint. This adjoint can be used to carry out model inversions of unknown model parameters, typically ice rheology and basal drag at the ice/bedrock interface, using a metric such as the observed InSAR surface velocity. This data assimilation capability is crucial to allow spinning up of ice flow models using available satellite data. ISSM relies on the PETSc library for its vectors, matrices, and solvers. This allows ISSM to run efficiently on any parallel platform, whether shared or distrib- ISSM: Ice Sheet System Model NASA's Jet Propulsion Laboratory, Pasadena, California uted. It can run on the largest clusters, and is fully scalable. This allows ISSM to tackle models the size of continents. ISSM is embedded into MATLAB and Python, both open scientific platforms. This improves its outreach within the science community. It is entirely written in C/C++, which gives it flexibility in its

  6. Modeling Harris Current Sheets with Themis Observations

    NASA Technical Reports Server (NTRS)

    Kepko, L.; Angelopoulos, V.; McPherron, R. L.; Apatenkov, S.; Glassmeier, K.-H.

    2010-01-01

    Current sheets are ubiquitous in nature. occurring in such varied locations as the solar atmosphere. the heliosphere, and the Earth's magnetosphere. The simplest current sheet is the one-dimensional Harris neutral sheet, with the lobe field strength and scale-height the only free parameters. Despite its simplicity, confirmation of the Harris sheet as a reasonable description of the Earth's current sheet has remained elusive. In early 2009 the orbits of the 5 THEMIS probes fortuitously aligned such that profiles of the Earth's current sheet could be modeled in a time dependent manner. For the few hours of alignment we have calculated the time history of the current sheet parameters (scale height and current) in the near-Earth region. during both quiet and active times. For one particular substorm. we further demonstrate good quantitative agreement with the diversion of cross tail current inferred from the Harris modeling with the ionospheric current inferred from ground magnetometer data.

  7. The Elementary Marine Ice Sheet Model (EMISM)

    NASA Astrophysics Data System (ADS)

    Pattyn, Frank

    2015-04-01

    Ice sheet models become more and more components of global climate system modelling instead of stand-alone features to study cryospheric processes. Full coupling of ice sheet models to atmospheric and ocean models requires a standard for ice sheet models, and more precisely for marine ice sheet models, where complex feedbacks between ice and ocean, such as marine ice sheet instability, and the atmosphere, such as the elevation-mass balance feedback, operate at different time scales. Recent model intercomparisons (e.g., SeaRISE, MISMIP) have shown that basic requirements for marine ice sheet models are still lacking and that the complexity of many ice sheet models is focused on processes that are either not well captured numerically (spatial resolution issue) or are of secondary importance compared to the essential features of marine ice sheet dynamics. Here, we propose a new and fast computing ice sheet model, devoid of most complexity, but capturing the essential feedbacks when coupled to ocean or atmospheric models. Its computational efficiency guarantees to easily tests its advantages as well as limits through ensemble modelling. EMISM (Elementary Marine Ice Sheet Model) is a vertically integrated ice sheet model based on the Shallow-Ice Approximation extended a Weertman sliding law. Although vertically integrated, thermomechanical coupling is ensured through a simplified representation of ice sheet thermodynamics based on an analytical solution of the vertical temperature profile, enhanced with strain heating. The marine boundary is represented by a parameterized flux condition similar to Pollard & Deconto (2012), based on Schoof (2007). A simplified ice shelf is added to account for buttressing of ice shelves in this parameterization. The ice sheet model is solved on a finite difference grid and special care is taken to its numerical efficiency and stability. While such model has a series of (known) deficiencies with respect to short time effects, its overall

  8. Constitutive Modeling for Sheet Metal Forming

    SciTech Connect

    Barlat, Frederic

    2005-08-05

    This paper reviews aspects of the plastic behaviour common in sheet metals. Macroscopic and microscopic phenomena occurring during plastic deformation are described succinctly. Constitutive models of plasticity suitable for applications to forming, are discussed in a very broad manner. Approaches to plastic anisotropy are described in a somewhat more detailed manner.

  9. Models for polythermal ice sheets and glaciers

    NASA Astrophysics Data System (ADS)

    Hewitt, Ian J.; Schoof, Christian

    2017-02-01

    Polythermal ice sheets and glaciers contain both cold ice and temperate ice. We present two new models to describe the temperature and water content of such ice masses, accounting for the possibility of gravity- and pressure-driven water drainage according to Darcy's law. Both models are based on the principle of energy conservation; one additionally invokes the theory of viscous compaction to calculate pore water pressure, and the other involves a modification of existing enthalpy gradient methods to include gravity-driven drainage. The models self-consistently predict the evolution of temperature in cold ice and of water content in temperate ice. Numerical solutions are described, and a number of illustrative test problems are presented, allowing comparison with existing methods. The suggested models are simple enough to be incorporated in existing ice-sheet models with little modification.

  10. Model Program Evaluations. Fact Sheet

    ERIC Educational Resources Information Center

    Arkansas Safe Schools Initiative Division, 2002

    2002-01-01

    There are probably thousands of programs and courses intended to prevent or reduce violence in this nation's schools. Evaluating these many programs has become a problem or goal in itself. There are now many evaluation programs, with many levels of designations, such as model, promising, best practice, exemplary and noteworthy. "Model program" is…

  11. Modelling water isotopes in polar ice sheets

    NASA Astrophysics Data System (ADS)

    Lhomme, Nicolas

    2005-07-01

    Concentrations of water isotopes in marine sediments and ice cores are a key indicator for estimating global and regional fluctuations of past temperatures. Interpreting these concentrations requires an understanding of the storage capacity and exchanges among the ocean, atmosphere and cryosphere as well as an understanding of the dynamical behaviour of these reservoirs. The contribution of the latter remains poorly established because of the paucity of deep ice cores in Greenland and Antarctica and the difficulty of interpreting these cores. To obtain the water isotope composition of polar ice sheets and gain an understanding of their stratigraphy, I develop a tracer transport method first proposed by Clarke and Marshall (2002) and significantly improve it by introducing an interpolation technique that accounts for the particular age-depth relationship of ice sheets. I combine the tracers with numerical models of ice dynamics to predict the fine layering of polar ice masses such that it is locally validated at ice core sites, hence setting a new method to constrain reconstructions of ice sheets' climatic and dynamic histories. This framework is first applied and tested with the UBC Ice Sheet Model of Marshall and Clarke (1997). I predict the three-dimensional time-evolving stratigraphy of the Greenland Ice Sheet and use the ice core records predicted at GRIP, Dye 3 and Camp Century to better determine the minimal ice extent during the Eemian, 127 kyr ago, when the Earth's climate was somewhat similar to the present. I suggest that 3.5--4.5 m of sea level rise could be attributed to melting in Greenland. Tracers are also applied to Antarctica with the LGGE Ice Sheet Model of Ritz et al. (2001). The three-dimensional model is compared to simple flow models at the deep ice core sites of Dome C, Vostok and Dome Fuji to test the hypotheses on depositional and dynamical conditions used for interpreting ice cores. These studies lead to a well-constrained stratigraphic

  12. Ice Sheet System Model as Educational Entertainment

    NASA Astrophysics Data System (ADS)

    Perez, G.

    2013-12-01

    Understanding the importance of polar ice sheets and their role in the evolution of Sea Level Rise (SLR), as well as Climate Change, is of paramount importance for policy makers as well as the public and schools at large. For example, polar ice sheets and glaciers currently account for 1/3 of the SLR signal, a ratio that will increase in the near to long-term future, which has tremendous societal ramifications. Consequently, it is important to increase awareness about our changing planet. In our increasingly digital society, mobile and web applications are burgeoning venues for such outreach. The Ice Sheet System Model (ISSM) is a software that was developed at the Jet Propulsion Laboratory/CalTech/NASA, in collaboration with University of California Irvine (UCI), with the goal of better understanding the evolution of polar ice sheets. It is a state-of-the-art framework, which relies on higher-end cluster-computing to address some of the aforementioned challenges. In addition, it is a flexible framework that can be deployed on any hardware; in particular, on mobile platforms such as Android or iOS smart phones. Here, we look at how the ISSM development team managed to port their model to these platforms, what the implications are for improving how scientists disseminate their results, and how a broader audience may familiarize themselves with running complex climate models in simplified scenarios which are highly educational and entertaining in content. We also look at the future plans toward a web portal fully integrated with mobile technologies to deliver the best content to the public, and to provide educational plans/lessons that can be used in grades K-12 as well as collegiate under-graduate and graduate programs.

  13. Constitutive Modeling of Magnesium Alloy Sheets

    SciTech Connect

    Lee, M. G.; Piao, K.; Wagoner, R. H.; Lee, J. K.; Chung, K.; Kim, H. Y.

    2007-05-17

    Magnesium alloy sheets have unique mechanical properties: high in-plane anisotropy/asymmetry of yield stress and hardening response, which have not been thoroughly studied. The unusual mechanical behavior of magnesium alloys has been understood by the limited symmetry crystal structure of h.c.p metals and thus by deformation twinning. In this paper, the phenomenological continuum plasticity models considering the unusual plastic behavior of magnesium alloy sheet were developed for a finite element analysis. A new hardening law based on two-surface model was developed to consider the general stress-strain response of metal sheets such as Bauschinger effect, transient behavior and the unusual asymmetry. Three deformation modes observed during the continuous tension/compression tests were mathematically formulated with simplified relations between the state of deformation and their histories. In terms of the anisotropy and asymmetry of the initial yield stress, the Drucker-Prager's pressure dependent yield surface was modified to include the anisotropy of magnesium alloys. Also, characterization procedures of material parameters for the constitutive equations were presented and finally the correlation of simulation with measurements was performed to validate the proposed theory.

  14. Models for polythermal ice sheets and glaciers

    NASA Astrophysics Data System (ADS)

    Hewitt, Ian; Schoof, Christian

    2016-04-01

    The dynamics of ice-sheets and glaciers depend sensitively on their thermal structure. Many ice masses are polythermal, containing both cold ice, with temperature below the melting point, and temperate ice, with temperature at the melting point. The temperate ice is really an ice-water mixture, with water produced at grain boundaries by dissipative heating. Although the water content is typically small, it can have an important effect on ice dynamics; water content controls ice viscosity, and internal meltwater percolation affects hydrology. Locations where this may be important are in the enhanced shear layer at the base of fast-flowing outlet glaciers, and in the shear margins of ice streams. In this study, we present a simplified model to describe the temperature and water-content of polythermal ice masses, accounting for the possibility of gravity- and pressure-driven water drainage according to Darcy's law. The model is based on the principle of energy conservation and the theory of viscous compaction. Numerical solutions are described and a number of illustrative test problems presented. The model is compared with existing methods in the literature, including enthalpy gradient methods, to which it reduces under certain conditions. Based on the results of our analysis, we suggest a modified enthalpy method that allows for drainage under gravity but that can be relatively easily implemented in ice-sheet models.

  15. Nonlinear energy principle for model current sheets

    SciTech Connect

    Yoon, Peter H.; Lui, Anthony T.Y.

    2006-01-15

    It is demonstrated on the basis of exact invariants of nonlinear Vlasov equation and model current sheets that the change in magnetic topology (i.e., reconnection) in a finite closed system leads to the conversion of magnetic-field energy to particle energy. It is also shown that the volume-averaged conversion efficiency diminishes as the spatial average is taken over larger and larger system size, while it increases when the system size becomes smaller. This finding may have an important implication for numerical simulation of reconnection processes under finite geometry.

  16. Ice sheet model dependency of the simulated Greenland Ice Sheet in the mid-Pliocene

    NASA Astrophysics Data System (ADS)

    Koenig, S. J.; Dolan, A. M.; de Boer, B.; Stone, E. J.; Hill, D. J.; DeConto, R. M.; Abe-Ouchi, A.; Lunt, D. J.; Pollard, D.; Quiquet, A.; Saito, F.; Savage, J.; van de Wal, R.

    2015-03-01

    The understanding of the nature and behavior of ice sheets in past warm periods is important for constraining the potential impacts of future climate change. The Pliocene warm period (between 3.264 and 3.025 Ma) saw global temperatures similar to those projected for future climates; nevertheless, Pliocene ice locations and extents are still poorly constrained. We present results from the efforts to simulate mid-Pliocene Greenland Ice Sheets by means of the international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP). We compare the performance of existing numerical ice sheet models in simulating modern control and mid-Pliocene ice sheets with a suite of sensitivity experiments guided by available proxy records. We quantify equilibrated ice sheet volume on Greenland, identifying a potential range in sea level contributions from warm Pliocene scenarios. A series of statistical measures are performed to quantify the confidence of simulations with focus on inter-model and inter-scenario differences. We find that Pliocene Greenland Ice Sheets are less sensitive to differences in ice sheet model configurations and internal physical quantities than to changes in imposed climate forcing. We conclude that Pliocene ice was most likely to be limited to the highest elevations in eastern and southern Greenland as simulated with the highest confidence and by synthesizing available regional proxies; however, the extent of those ice caps needs to be further constrained by using a range of general circulation model (GCM) climate forcings.

  17. LGM ice sheets simulated with a complex fully coupled ice sheet - climate model

    NASA Astrophysics Data System (ADS)

    Ziemen, F.; Rodehacke, C.; Mikolajewicz, U.

    2012-04-01

    One major challenge in predicting future climate change is the validation of the numerical models. A particular good time period for testing ice sheet - climate interactions is the last glacial maximum (LGM). It combines large ice sheets with good proxy data cover. We use a coarse resolution complex climate model coupled with an ice sheet model to study the ice sheets and the climate of the last glacial maximum and validate our setup by comparing glacial as well as pre-industrial equilibrium experiments with reconstructions and the present state. Since the last glacial maximum climate is largely different from the pre-industrial climate, we can test our model under large perturbations that go beyond the linear range by running both setups. Our model comprises of the atmosphere-ocean-vegetation general circulation model ECHAM5/MPIOM/LPJ interactively coupled with the ice sheet model mPISM. mPISM is a modified version of the Parallel Ice Sheet Model from the University of Alaska, Fairbanks. We run ECHAM5 in T31 resolution (~ 3.75°), and mPISM on a 20 km grid covering most of the northern hemisphere. We do not use flux correction or anomaly maps in our models. For the surface mass balance, we use a positive degree day scheme with lapse rate correction and height desertification effect. We show results from steady state experiments under last glacial maximum as well as pre-industrial boundary conditions. In both cases, we are able to maintain reasonable ice sheet distributions. In the pre-industrial setup, the Greenland ice sheet looks realistic, and the only major deviation is an ice sheet forming in the Rocky Mountains due to a cold bias in ECHAM5 in this region. The last glacial maximum ice sheets largely agree with the reconstructions except for an ice sheet that forms in eastern Siberia and extends to the Alaskan end of the Laurentide ice sheet. The ice sheets never reach a perfectly steady state because parts show repeated surges resembling Heinrich events. Most

  18. Equilibrium ice sheet scaling in climate modeling

    SciTech Connect

    Verbitsky, M.Y.

    1992-03-01

    A set of simple scaling formulas related to ice sheet evolution is derived from the dynamic and thermodynamic equations for ice and is used to consider two common situations: (1) when we wish to estimate potential ice sheet characteristics given the prescribed net snow accumulation over an area; and (b) when we wish to reconstruct net snow accumulation and vertical temperature difference within the ice sheet area and volume. The scaling formulas are applied to the present day Antarctic and Greenland ice sheets, as well as to some ancient ice sheets, and are used to estimate the potential global sea level change due to greenhouse warming. 23 refs.

  19. Combined Radiation Belt - Plasma Sheet System Modeling

    NASA Astrophysics Data System (ADS)

    Aseev, Nikita; Shprits, Yuri; Kellerman, Adam; Drozdov, Alexander; Zhu, Hui

    2017-04-01

    Recent years have given rise to numerous mathematical models of the Earth's radiation belt dynamics. Driven by observations at geosynchronous orbit (GEO) where satellites (e.g. GOES and LANL) provide extensive in-situ measurements, radiation belt models usually take into account only diffusion processes in the energetic electron belts (100 keV and greater), leaving aside the dynamics of colder source population (tens of keV). Such models are able to reconstruct the radiation belt state, but they are not capable of predicting the electron dynamics at GEO, where many communication and navigation satellites currently operate. In this work we present combined four-dimensional electron radiation belt - plasma sheet model accounting for adiabatic advective transport, radial diffusion due to interaction with ULF waves, local acceleration of electrons, scattering into the atmosphere, magnetopause shadowing, and adiabatic effects due to contraction and expansion of the magnetic field. The developed model is applicable to energetic, relativistic and ultrarelativistic electrons as well as to source electron population. The model provides spatial particle distribution allowing us to compare and validate the model with multiple satellite measurements at different MLT sectors (e.g. Van Allen Probes, GOES, LANL, THEMIS). The model can be helpful for the prediction of crucial for satellite operators geosynchronous electron fluxes and electron radiation belt dynamics including the heart of the outer belt, slot region and inner belt.

  20. Modeling of Sandwich Sheets with Metallic Foam

    SciTech Connect

    Mata, H.; Jorge, R. Natal; Fernandes, A. A.; Parente, M. P. L.; Santos, A.; Valente, R. A. F.

    2011-08-22

    World-wide vehicles safety experts agree that significant further reductions in fatalities and injuries can be achieved as a result of the use of new lightweight and energy absorbing materials. On this work, the authors present the development and evaluation of an innovative system able to perform reliable panels of sandwich sheets with metallic foam cores for industrial applications. The mathematical model used to describe the behavior of sandwich shells with metal cores foam is presented and some numerical examples are presented. In order to validate those results mechanical experiments are carried out. Using the crushable foam constitutive model, available on ABAQUS, a set of different mechanical tests were simulated. There are two variants of this model available on ABAQUS: the volumetric hardening model and the isotropic hardening model. As a first approximation we chose the isotropic hardening variant. The isotropic hardening model available uses a yield surface that is an ellipse centered at the origin in the p-q stress plane. Based on this constitutive model for the foam, numerical simulations of the tensile and bulge test will be conducted. The numerical results will be validated using the data obtained from the experimental results.

  1. Isochronal ice sheet model: Simulate englacial tracer transport to reconstruct past climates and ice sheet volumes

    NASA Astrophysics Data System (ADS)

    Born, Andreas

    2015-04-01

    The full history of ice sheet and climate interactions is recorded in the vertical profiles of isotopic and other geochemical tracers in polar ice sheets. In addition, recent advances in radiostratigraphy uncover the englacial layering that contains information of past surface topographies and thus ice sheet volumes and sea level. Numerical simulations of these archives could afford great advances both in the interpretation of paleoclimatic tracers as well as to help improve ice sheet models themselves and future projections. However, fundamental mathematical shortcomings in existing ice sheet models subject tracers to spurious diffusion that renders such attempts unfeasible. Here, we propose a new vertical discretization for ice sheet models that eliminates numerical diffusion entirely. Vertical motion through the model mesh is avoided by mimicking the real-world ice flow as a thinning of underlying layers. Simulations of the last glacial cycle are presented that show good skill in reproducing the reconstructed profile of the oxygen isotopic ratio (δ18O) and the age scale (http://www.climate.unibe.ch/~born/ice_model.html).

  2. ISMIP6: Ice Sheet Model Intercomparison Project for CMIP6

    NASA Technical Reports Server (NTRS)

    Nowicki, S.

    2015-01-01

    ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6) targets the Cryosphere in a Changing Climate and the Future Sea Level Grand Challenges of the WCRP (World Climate Research Program). Primary goal is to provide future sea level contribution from the Greenland and Antarctic ice sheets, along with associated uncertainty. Secondary goal is to investigate feedback due to dynamic ice sheet models. Experiment design uses and augment the existing CMIP6 (Coupled Model Intercomparison Project Phase 6) DECK (Diagnosis, Evaluation, and Characterization of Klima) experiments. Additonal MIP (Model Intercomparison Project)- specific experiments will be designed for ISM (Ice Sheet Model). Effort builds on the Ice2sea, SeaRISE (Sea-level Response to Ice Sheet Evolution) and COMBINE (Comprehensive Modelling of the Earth System for Better Climate Prediction and Projection) efforts.

  3. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics

    PubMed Central

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-01-01

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas. PMID:25908601

  4. Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics.

    PubMed

    Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

    2015-04-24

    The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas.

  5. Saturn's Magnetodisc Current Sheet: Observations, Theory and Modelling

    NASA Astrophysics Data System (ADS)

    Arridge, C. S.; Russell, C. T.; Khurana, K. K.; Dougherty, M. K.

    Pioneer 11 Observations at Saturn identified a thin current sheet on the dawn flank which was interpreted as the cross-tail current sheet [Smith et al. 1981]. Observations by the Cassini spacecraft have rediscovered this thin current sheet but has been interpreted as a magnetodisc in Saturn's magnetosphere, not unlike the magnetodisc in the jovian magnetosphere [Arridge et al., Eos Trans. AGU 87(36)]. Studies of the MHD stress balance in this current sheet provide evidence that the centrifugal force causes the disc-like configuration [Arridge et al., submitted manuscript], in agreement with Voyager studies of the stress balance in the quasi-dipolar region of the magnetosphere [McNutt 1984]. In this talk we use magnetometer data to discuss the observational properties of this current sheet, discuss the ballooning of the field into the magnetodisc from a theoretical perspective, and efforts to develop global 3D empirical models of the current sheet.

  6. A Transient Initialization Routine of the Community Ice Sheet Model for the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    van der Laan, Larissa; van den Broeke, Michiel; Noël, Brice; van de Wal, Roderik

    2017-04-01

    The Community Ice Sheet Model (CISM) is to be applied in future simulations of the Greenland Ice Sheet under a range of climate change scenarios, determining the sensitivity of the ice sheet to individual climatic forcings. In order to achieve reliable results regarding ice sheet stability and assess the probability of future occurrence of tipping points, a realistic initial ice sheet geometry is essential. The current work describes and evaluates the development of a transient initialization routine, using NGRIP 18O isotope data to create a temperature anomaly field. Based on the latter, surface mass balance components runoff and precipitation are perturbed for the past 125k years. The precipitation and runoff fields originate from a downscaled 1 km resolution version of the regional climate model RACMO2.3 for the period 1961-1990. The result of the initialization routine is a present-day ice sheet with a transient memory of the last glacial-interglacial cycle, which will serve as the future runs' initial condition.

  7. An ice sheet model validation framework for the Greenland ice sheet

    DOE PAGES

    Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; ...

    2017-01-17

    We propose a new ice sheet model validation framework the Cryospheric Model Comparison Tool (CMCT) that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quanti- tative metricsmore » for use in evaluating the different model simulations against the observations. We find 10 that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, the model initial condition as well as output from idealized and dynamic models all provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CMCT, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past few

  8. An ice sheet model validation framework for the Greenland ice sheet

    NASA Astrophysics Data System (ADS)

    Price, Stephen F.; Hoffman, Matthew J.; Bonin, Jennifer A.; Howat, Ian M.; Neumann, Thomas; Saba, Jack; Tezaur, Irina; Guerber, Jeffrey; Chambers, Don P.; Evans, Katherine J.; Kennedy, Joseph H.; Lenaerts, Jan; Lipscomb, William H.; Perego, Mauro; Salinger, Andrew G.; Tuminaro, Raymond S.; van den Broeke, Michiel R.; Nowicki, Sophie M. J.

    2017-01-01

    We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013, using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin-scale and whole-ice-sheet-scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of < 1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate a predictive skill with respect to observed dynamic changes that have occurred on

  9. Modeling and Analysis of CSP Systems (Fact Sheet)

    SciTech Connect

    Not Available

    2010-08-01

    Fact sheet describing NREL CSP Program capabilities in the area of modeling and analysis of CSP systems: assessing the solar resource, predicting performance and cost, studying environmental impact, and developing modeling software packages.

  10. Present and future changes of ice sheets in a coupled ice sheet-climate model

    NASA Astrophysics Data System (ADS)

    Kapsch, Marie; Ziemen, Florian; Mikolajewicz, Uwe

    2017-04-01

    The future evolution of the ice sheets covering Greenland and Antarctica is of importance, as ice sheets hold more than 99% of the Earths' freshwater. If released into the oceans, this freshwater could significantly impact the global climate, most prominently the oceanic overturning circulation and the sea-level. To model past and future climate change it is therefore important to integrate ice sheet models (ISMs) into state-of-the-art Earth System Models (ESMs), in order to account for the full range of feedback processes between ice sheets and other climate components. However, the coupling of ISMs into ESMs remains challenging, especially due to the required downscaling of the surface mass balance (SMB) from the low resolution atmospheric grid of the ESM onto the high resolution ice sheet topography. Here we present results from model simulations with the Max Planck Institute ESM (MPI-ESM) coupled to the Parallel ISM (PISM; http://www.pism-docs.org). To bridge the gap between the different model resolutions of the atmospheric component of MPI-ESM and PISM a sophisticated energy balance model (EBM) is used to calculate and downscale the SMB. The modeled SMB for present-day climate conditions shows good agreement with SMB reconstructions from regional climate modeling (e.g. RACMO, MAR). To estimate the effect of different downscaling methods, simulations performed with the EBM are compared to simulations that use a commonly applied positive degree day approach. These comparisons are shown for simulations with present day as well as increasing greenhouse gas concentrations.

  11. Structural transitions in model beta-sheet tapes.

    PubMed

    Bellesia, Giovanni; Fedorov, Maxim V; Timoshenko, Edward G

    2008-05-21

    We present a molecular-scale simulation study of the structural transitions between helicoidal, helical, and tubular geometries in supramolecular beta-sheet tapes. Such geometries have been observed in different self-assembled amyloid systems (based on either natural or synthetic peptides) for which the beta-sheet tapes represent the simplest fibrillar aggregates. A coarse-grained model for the beta-sheet tapes is proposed, with chiral degrees of freedom and asymmetrical chemical properties, which provides a quantitative characterization of the structural transitions. A quantitative connection is established between the molecular properties and the elastic parameters of the supramolecular tapes.

  12. On the current sheet model with {kappa} distribution

    SciTech Connect

    Yoon, Peter H.; Lui, Anthony T. Y.; Sheldon, Robert B.

    2006-10-15

    The present paper (re)derives current sheet equilibrium solutions on the basis of the so-called {kappa} distribution functions for the particles. The present work builds upon a recent paper [W.-Z. Fu and L.-N. Hau, Phys. Plasmas 12, 070701 (2005)], where the authors formulated the equilibrium current sheet model with the {kappa} distribution. According to their work, however, the global temperature profile monotonically increases in the asymptotic regime. In the present paper it is shown that the presence of a finite stationary background population of the particles arrests the unlimited increase of the global temperature profile in the asymptotic limit. The present paper further extends the analysis by considering a current sheet model where the electron current is embedded within a thicker ion current layer, and where there exists a weak electrostatic potential drop across the current sheet.

  13. Active deformable sheets: prototype implementation, modeling, and control

    NASA Astrophysics Data System (ADS)

    Lind, Robert J.; Johnson, Norbert; Doumanidis, Charalabos C.

    2000-06-01

    Active deformable sheets are integrated smart planar sheet structures performing off-plane deformations under computer actuation and control, to take up a desired dynamic morphology specified in CAD software or obtained by 3-D scanning of a solid surface. The sheet prototypes are implemented in the laboratory by elastic neoprene foil layers with embedded asymmetric grids of SMA wires (Nitinol), which upon electrical contraction bend the sheet to the necessary local curvature distribution. An analytical model of such prototypes, consisting of an electrical, a thermal, a material and a mechanical module, as well as a more complex finite element thermomechanical simulation of the sheet structure have been developed and validated experimentally. Besides open-loop control of the sheet curvatures by modulation of the SMA wire actuation current, a closed-loop control system has been implemented, using feedback of the wire electrical resistance measurements in real time, correlating to the material transformation state. The active deformable sheets are intended for applications such as reconfigurable airfoils and aerospace structures, variable focal length optics and electromagnetic reflectors, flexible and rapid tooling and microrobotics.

  14. Modelling the Climate - Greenland Ice Sheet Interaction in the Coupled Ice-sheet/Climate Model EC-EARTH - PISM

    NASA Astrophysics Data System (ADS)

    Yang, S.; Madsen, M. S.; Rodehacke, C. B.; Svendsen, S. H.; Adalgeirsdottir, G.

    2014-12-01

    Recent observations show that the Greenland ice sheet (GrIS) has been losing mass with an increasing speed during the past decades. Predicting the GrIS changes and their climate consequences relies on the understanding of the interaction of the GrIS with the climate system on both global and local scales, and requires climate model systems with an explicit and physically consistent ice sheet module. A fully coupled global climate model with a dynamical ice sheet model for the GrIS has recently been developed. The model system, EC-EARTH - PISM, consists of the EC-EARTH, an atmosphere, ocean and sea ice model system, and the Parallel Ice Sheet Model (PISM). The coupling of PISM includes a modified surface physical parameterization in EC-EARTH adapted to the land ice surface over glaciated regions in Greenland. The PISM ice sheet model is forced with the surface mass balance (SMB) directly computed inside the EC-EARTH atmospheric module and accounting for the precipitation, the surface evaporation, and the melting of snow and ice over land ice. PISM returns the simulated basal melt, ice discharge and ice cover (extent and thickness) as boundary conditions to EC-EARTH. This coupled system is mass and energy conserving without being constrained by any anomaly correction or flux adjustment, and hence is suitable for investigation of ice sheet - climate feedbacks. Three multi-century experiments for warm climate scenarios under (1) the RCP85 climate forcing, (2) an abrupt 4xCO2 and (3) an idealized 1% per year CO2 increase are performed using the coupled model system. The experiments are compared with their counterparts of the standard CMIP5 simulations (without the interactive ice sheet) to evaluate the performance of the coupled system and to quantify the GrIS feedbacks. In particular, the evolution of the Greenland ice sheet under the warm climate and its impacts on the climate system are investigated. Freshwater fluxes from the Greenland ice sheet melt to the Arctic

  15. New Modelling of Localized Necking in Sheet Metal Stretching

    NASA Astrophysics Data System (ADS)

    Bressan, José Divo

    2011-01-01

    Present work examines a new mathematical model to predict the onset of localized necking in the industrial processes of sheet metal forming such as biaxial stretching. Sheet metal formability is usually assessed experimentally by testing such as the Nakajima test to obtain the Forming Limit Curve, FLC, which is an essential material parameter necessary to numerical simulations by FEM. The Forming Limit Diagram or "Forming Principal Strain Map" shows the experimental FLC which is the plot of principal true strains in the sheet metal surface, ɛ1 and ɛ2, occurring at critical points obtained in laboratory formability tests or in the fabrication process. Two types of undesirable rupture mechanisms can occur in sheet metal forming products: localized necking and shear induced fracture. Therefore, two kinds of limit strain curves can be plotted: the local necking limit curve FLC-N and the shear fracture limit curve FLC-S. Localized necking is theoretically anticipated to initiate at a thickness defect ƒin = hib/hia inside the grooved sheet thickness hia, but only at the instability point of maximum load. The inception of grooving on the sheet surface evolves from instability point to localized necking and final rupture, during further sheet metal straining. Work hardening law is defined for a strain and strain rate material by the effective stress σ¯ = σo(1+βɛ¯)n???ɛM. The average experimental hardening law curve for tensile tests at 0°, 45° and 90°, assuming isotropic plasticity, was used to analyze the plasticity behavior during the biaxial stretching of sheet metals. Theoretical predicted curves of local necking limits are plotted in the positive quadrant of FPSM for different defect values ƒin and plasticity parameters. Limit strains are obtained from a software developed by the author. Some experimental results of forming limit curve obtained from experiments for IF steel sheets are compared with the theoretical predicted curves: the correlation is

  16. MODELING DRIFT ALONG THE HELIOSPHERIC WAVY NEUTRAL SHEET

    SciTech Connect

    Burger, R. A.

    2012-11-20

    Drift along the wavy heliospheric neutral sheet is believed to play an important role in cosmic-ray modulation and can explain the peaked versus flat intensity profiles during consecutive solar magnetic epochs. Modulation models are becoming more and more realistic and in order to determine the role of the wavy neutral sheet more accurately, we revisit a previous calculation for drift along it. While mathematically correct, we argue that the previous expression for neutral sheet drift, which follows naturally from the standard expression for gradient and curvature drift, must be adapted in order for the drift speed to be less than particle speed. We compare the effect of both the previous and the current more accurate version of neutral sheet drift on cosmic-ray modulation with results obtained by other methods.

  17. Magneto-mechanical modeling of electrical steel sheets

    NASA Astrophysics Data System (ADS)

    Aydin, U.; Rasilo, P.; Martin, F.; Singh, D.; Daniel, L.; Belahcen, A.; Rekik, M.; Hubert, O.; Kouhia, R.; Arkkio, A.

    2017-10-01

    A simplified multiscale approach and a Helmholtz free energy based approach for modeling the magneto-mechanical behavior of electrical steel sheets are compared. The models are identified from uniaxial magneto-mechanical measurements of two different electrical steel sheets which show different magneto-elastic behavior. Comparison with the available measurement data of the materials shows that both models successfully model the magneto-mechanical behavior of one of the studied materials, whereas for the second material only the Helmholtz free energy based approach is successful.

  18. Impact of bedrock description on modeling ice sheet dynamics

    NASA Astrophysics Data System (ADS)

    Durand, G.; Gagliardini, O.; Favier, L.; Zwinger, T.; le Meur, E.

    2011-10-01

    Recent glaciological surveys have revealed a significant increase of ice discharge from polar ice caps into the ocean. In parallel, ice flow models have been greatly improved to better reproduce current changes and forecast the future behavior of ice sheets. For these models, surface topography and bedrock elevation are crucial input parameters that largely control the dynamics and the ensuing overall mass balance of the ice sheet. For obvious reasons of inaccessibility, only sparse and uneven bedrock elevation data is available. This raw data is processed to produce Digital Elevation Models (DEMs) on a regular 5 km grid. These DEMs are used to constrain the basal boundary conditions of all ice sheet models. Here, by using a full-Stokes finite element code, we examine the sensitivity of an ice flow model to the accuracy of the bedrock description. In the context of short-term ice sheet forecast, we show that in coastal regions, the bedrock elevation should be known at a resolution of the order of one kilometer. Conversely, a crude description of the bedrock in the interior of the continent does not affect modeling of the ice outflow into the ocean. These findings clearly indicate that coastal regions should be prioritized during future geophysical surveys. They also indicate that a paradigm shift is required to change the current design of DEMs describing the bedrock below the ice sheets: they must give users the opportunity to incorporate high-resolution bedrock elevation data in regions of interest.

  19. AFISMIP: Age Field in Ice Sheet Modeling Intercomparison Project

    NASA Astrophysics Data System (ADS)

    Parrenin, F.

    2009-04-01

    The last few years have seen a great deal of effort invested by various research groups in developing numerical ice sheet models. One interest of these models is to evaluate the age field of current or past ice sheets. Indeed, such a modeling exercise can be used to prospect for new drilling sites aiming at retrieving very old ice (e.g. >1 Myr). Reciprocally, observations on the age field provided by (1) already drilled ice cores or (2) internal layers measured by radio-echo sounding, can constrain the velocity field in ice sheet. The purpose of the proposed experiments is to address the accuracy of the numerical models of the age field. Numerical simulations will be inter-compared or confronted to analytical solutions.

  20. Phenomenological Model of Current Sheet Canting in Pulsed Electromagnetic Accelerators

    NASA Technical Reports Server (NTRS)

    Markusic, Thomas; Choueiri, E. Y.

    2003-01-01

    The phenomenon of current sheet canting in pulsed electromagnetic accelerators is the departure of the plasma sheet (that carries the current) from a plane that is perpendicular to the electrodes to one that is skewed, or tipped. Review of pulsed electromagnetic accelerator literature reveals that current sheet canting is a ubiquitous phenomenon - occurring in all of the standard accelerator geometries. Developing an understanding of current sheet canting is important because it can detract from the propellant sweeping capabilities of current sheets and, hence, negatively impact the overall efficiency of pulsed electromagnetic accelerators. In the present study, it is postulated that depletion of plasma near the anode, which results from axial density gradient induced diamagnetic drift, occurs during the early stages of the discharge, creating a density gradient normal to the anode, with a characteristic length on the order of the ion skin depth. Rapid penetration of the magnetic field through this region ensues, due to the Hall effect, leading to a canted current front ahead of the initial current conduction channel. In this model, once the current sheet reaches appreciable speeds, entrainment of stationary propellant replenishes plasma in the anode region, inhibiting further Hall-convective transport of the magnetic field; however, the previously established tilted current sheet remains at a fairly constant canting angle for the remainder of the discharge cycle, exerting a transverse J x B force which drives plasma toward the cathode and accumulates it there. This proposed sequence of events has been incorporated into a phenomenological model. The model predicts that canting can be reduced by using low atomic mass propellants with high propellant loading number density; the model results are shown to give qualitative agreement with experimentally measured canting angle mass dependence trends.

  1. Modeling the fracture of ice sheets on parallel computers.

    SciTech Connect

    Waisman, Haim; Bell, Robin; Keyes, David; Boman, Erik Gunnar; Tuminaro, Raymond Stephen

    2010-03-01

    The objective of this project is to investigate the complex fracture of ice and understand its role within larger ice sheet simulations and global climate change. At the present time, ice fracture is not explicitly considered within ice sheet models due in part to large computational costs associated with the accurate modeling of this complex phenomena. However, fracture not only plays an extremely important role in regional behavior but also influences ice dynamics over much larger zones in ways that are currently not well understood. Dramatic illustrations of fracture-induced phenomena most notably include the recent collapse of ice shelves in Antarctica (e.g. partial collapse of the Wilkins shelf in March of 2008 and the diminishing extent of the Larsen B shelf from 1998 to 2002). Other fracture examples include ice calving (fracture of icebergs) which is presently approximated in simplistic ways within ice sheet models, and the draining of supraglacial lakes through a complex network of cracks, a so called ice sheet plumbing system, that is believed to cause accelerated ice sheet flows due essentially to lubrication of the contact surface with the ground. These dramatic changes are emblematic of the ongoing change in the Earth's polar regions and highlight the important role of fracturing ice. To model ice fracture, a simulation capability will be designed centered around extended finite elements and solved by specialized multigrid methods on parallel computers. In addition, appropriate dynamic load balancing techniques will be employed to ensure an approximate equal amount of work for each processor.

  2. Two vortex-blob regularization models for vortex sheet motion

    NASA Astrophysics Data System (ADS)

    Sohn, Sung-Ik

    2014-04-01

    Evolving vortex sheets generally form singularities in finite time. The vortex blob model is an approach to regularize the vortex sheet motion and evolve past singularity formation. In this paper, we thoroughly compare two such regularizations: the Krasny-type model and the Beale-Majda model. It is found from a linear stability analysis that both models have exponentially decaying growth rates for high wavenumbers, but the Beale-Majda model has a faster decaying rate than the Krasny model. The Beale-Majda model thus gives a stronger regularization to the solution. We apply the blob models to the two example problems: a periodic vortex sheet and an elliptically loaded wing. The numerical results show that the solutions of the two models are similar in large and small scales, but are fairly different in intermediate scales. The sheet of the Beale-Majda model has more spiral turns than the Krasny-type model for the same value of the regularization parameter δ. We give numerical evidences that the solutions of the two models agree for an increasing amount of spiral turns and tend to converge to the same limit as δ is decreased. The inner spiral turns of the blob models behave differently with the outer turns and satisfy a self-similar form. We also examine irregular motions of the sheet at late times and find that the irregular motions shrink as δ is decreased. This fact suggests a convergence of the blob solution to the weak solution of infinite regular spiral turns.

  3. Constitutive modelling of aluminium alloy sheet at warm forming temperatures

    NASA Astrophysics Data System (ADS)

    Kurukuri, S.; Worswick, M. J.; Winkler, S.

    2016-08-01

    The formability of aluminium alloy sheet can be greatly improved by warm forming. However predicting constitutive behaviour under warm forming conditions is a challenge for aluminium alloys due to strong, coupled temperature- and rate-sensitivity. In this work, uniaxial tensile characterization of 0.5 mm thick fully annealed aluminium alloy brazing sheet, widely used in the fabrication of automotive heat exchanger components, is performed at various temperatures (25 to 250 °C) and strain rates (0.002 and 0.02 s-1). In order to capture the observed rate- and temperature-dependent work hardening behaviour, a phenomenological extended-Nadai model and the physically based (i) Bergstrom and (ii) Nes models are considered and compared. It is demonstrated that the Nes model is able to accurately describe the flow stress of AA3003 sheet at different temperatures, strain rates and instantaneous strain rate jumps.

  4. Uncertainty Quantification for Large-Scale Ice Sheet Modeling

    SciTech Connect

    Ghattas, Omar

    2016-02-05

    This report summarizes our work to develop advanced forward and inverse solvers and uncertainty quantification capabilities for a nonlinear 3D full Stokes continental-scale ice sheet flow model. The components include: (1) forward solver: a new state-of-the-art parallel adaptive scalable high-order-accurate mass-conservative Newton-based 3D nonlinear full Stokes ice sheet flow simulator; (2) inverse solver: a new adjoint-based inexact Newton method for solution of deterministic inverse problems governed by the above 3D nonlinear full Stokes ice flow model; and (3) uncertainty quantification: a novel Hessian-based Bayesian method for quantifying uncertainties in the inverse ice sheet flow solution and propagating them forward into predictions of quantities of interest such as ice mass flux to the ocean.

  5. On current sheet approximations in models of eruptive flares

    NASA Technical Reports Server (NTRS)

    Bungey, T. N.; Forbes, T. G.

    1994-01-01

    We consider an approximation sometimes used for current sheets in flux-rope models of eruptive flares. This approximation is based on a linear expansion of the background field in the vicinity of the current sheet, and it is valid when the length of the current sheet is small compared to the scale length of the coronal magnetic field. However, we find that flux-rope models which use this approximation predict the occurrence of an eruption due to a loss of ideal-MHD equilibrium even when the corresponding exact solution shows that no such eruption occurs. Determination of whether a loss of equilibrium exists can only be obtained by including higher order terms in the expansion of the field or by using the exact solution.

  6. Modeling the quiet time inner plasma sheet protons

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Ping; Lyons, Larry R.; Chen, Margaret W.; Wolf, Richard A.

    2001-04-01

    In order to understand the characteristics of the quiet time inner plasma sheet protons, we use a modified version of the Magnetospheric Specification Model to simulate the bounce averaged electric and magnetic drift of isotropic plasma sheet protons in an approximately self-consistent magnetic field. Proton differential fluxes are assigned to the model boundary to mimic a mixed tail source consisting of hot plasma from the distant tail and cooler plasma from the low latitude boundary layer (LLBL). The source is local time dependent and is based on Geotail observations and the results of the finite tail width convection model. For the purpose of self-consistently simulating plasma motion and a magnetic field, the Tsyganenko 96 magnetic field model is incorporated with additional adjustable ring-current shaped current loops. We obtain equatorial proton flow and midnight and equatorial profiles of proton pressure, number density, and temperature. We find that our results agree well with observations. This indicates that the drift motion dominates the plasma transport in the quiet time inner plasma sheet. Our simulations show that cold plasma from the LLBL enhances the number density and the proton pressure in the inner plasma sheet and decreases the dawn-dusk asymmetry of the equatorial proton pressure. From our approximately force-balanced simulations the magnetic field responds to the increase of pressure gradient force in the inner plasma sheet by changing its configuration to give a stronger magnetic force. At the same time, the plasma dynamics is affected by the changing field configuration and its associated pressure gradient force becomes smaller. Our model predicts a quiet time magnetic field configuration with a local depression in the equatorial magnetic field strength at the inner edge of the plasma sheet and a cross-tail current separated from the ring current, results that are supported by observations. A scale analysis of our results shows that in the

  7. Modeling the Fracture of Ice Sheets on Parallel Computers

    SciTech Connect

    Waisman, Haim; Tuminaro, Ray

    2013-10-10

    The objective of this project was to investigate the complex fracture of ice and understand its role within larger ice sheet simulations and global climate change. This objective was achieved by developing novel physics based models for ice, novel numerical tools to enable the modeling of the physics and by collaboration with the ice community experts. At the present time, ice fracture is not explicitly considered within ice sheet models due in part to large computational costs associated with the accurate modeling of this complex phenomena. However, fracture not only plays an extremely important role in regional behavior but also influences ice dynamics over much larger zones in ways that are currently not well understood. To this end, our research findings through this project offers significant advancement to the field and closes a large gap of knowledge in understanding and modeling the fracture of ice sheets in the polar regions. Thus, we believe that our objective has been achieved and our research accomplishments are significant. This is corroborated through a set of published papers, posters and presentations at technical conferences in the field. In particular significant progress has been made in the mechanics of ice, fracture of ice sheets and ice shelves in polar regions and sophisticated numerical methods that enable the solution of the physics in an efficient way.

  8. Modelling water flow under glaciers and ice sheets

    PubMed Central

    Flowers, Gwenn E.

    2015-01-01

    Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow ‘elements’ specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development. PMID:27547082

  9. Modelling water flow under glaciers and ice sheets.

    PubMed

    Flowers, Gwenn E

    2015-04-08

    Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow 'elements' specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development.

  10. Fully coupled ice sheet-earth system model: How does the Greenlandic ice sheet interact in a changing climate

    NASA Astrophysics Data System (ADS)

    Rodehacke, C.; Mikolajewicz, U.; Vizcaino, M.

    2012-04-01

    As ice sheets belong to the slowest climate components, they are usually not interactively coupled in current climate models. Therefore, long-term climate projections are incomplete and only the consideration of ice sheet interactions allows tackling fundamental questions, such as how do ice sheets modify the reaction of the climate systems under a strong CO2 forcing? The earth system model MPI-ESM, with the atmosphere model ECHAM6 and ocean model MPIOM, is coupled to the modified ice sheet model PISM. This ice sheet model, which is developed at the University of Fairbanks, represents the ice sheet of Greenland at a horizontal resolution of 10 km. The coupling is performed by calculating the surface mass balance based on 6-hourly atmospheric data to determine the boundary condition for the ice sheet model. The response of the ice sheet to this forcing, which includes orographic changes and fresh water fluxes, are passed back to the ESM. In contrast to commonly used strategies, we use a mass conserving scheme and do therefore neither apply flux corrections nor utilize anomaly coupling. Under a strong CO2 forcing a disintegrating Greenlandic ice sheet contributes to a rising sea level and has the potential to alter the formation of deep water masses in the adjacent formation sites Labrador Sea and Nordic Seas. We will present results for an idealized forcing with a growing atmospheric CO2 concentration that rises by 1% per year until four-times the pre-industrial level has been reached. We will discuss the reaction of the ice sheet and immediate responses of the ocean to ice loss.

  11. Multiscale modeling of thermal conductivity of polycrystalline graphene sheets.

    PubMed

    Mortazavi, Bohayra; Pötschke, Markus; Cuniberti, Gianaurelio

    2014-03-21

    We developed a multiscale approach to explore the effective thermal conductivity of polycrystalline graphene sheets. By performing equilibrium molecular dynamics (EMD) simulations, the grain size effect on the thermal conductivity of ultra-fine grained polycrystalline graphene sheets is investigated. Our results reveal that the ultra-fine grained graphene structures have thermal conductivity one order of magnitude smaller than that of pristine graphene. Based on the information provided by the EMD simulations, we constructed finite element models of polycrystalline graphene sheets to probe the thermal conductivity of samples with larger grain sizes. Using the developed multiscale approach, we also investigated the effects of grain size distribution and thermal conductivity of grains on the effective thermal conductivity of polycrystalline graphene. The proposed multiscale approach on the basis of molecular dynamics and finite element methods could be used to evaluate the effective thermal conductivity of polycrystalline graphene and other 2D structures.

  12. Quantitative rubber sheet models of gravitation wells using Spandex

    NASA Astrophysics Data System (ADS)

    White, Gary

    2008-04-01

    Long a staple of introductory treatments of general relativity, the rubber sheet model exhibits Wheeler's concise summary---``Matter tells space-time how to curve and space-time tells matter how to move''---very nicely. But what of the quantitative aspects of the rubber sheet model: how far can the analogy be pushed? We show^1 that when a mass M is suspended from the center of an otherwise unstretched elastic sheet affixed to a circular boundary it exhibits a distortion far from the center given by h = A*(M*r^2)^1/3 . Here, as might be expected, h and r are the vertical and axial distances from the center, but this result is not the expected logarithmic form of 2-D solutions to LaPlace's equation (the stretched drumhead). This surprise has a natural explanation and is confirmed experimentally with Spandex as the medium, and its consequences for general rubber sheet models are pursued. ^1``The shape of `the Spandex' and orbits upon its surface'', American Journal of Physics, 70, 48-52 (2002), G. D. White and M. Walker. See also the comment by Don S. Lemons and T. C. Lipscombe, also in AJP, 70, 1056-1058 (2002).

  13. VESL: The Virtual Earth Sheet Laboratory for Ice Sheet Modeling and Visualization

    NASA Astrophysics Data System (ADS)

    Cheng, D. L. C.; Larour, E. Y.; Quinn, J. D.; Halkides, D. J.

    2016-12-01

    We introduce the Virtual Earth System Laboratory (VESL), a scientific modeling and visualization tool delivered through an integrated web portal for dissemination of data, simulation of physical processes, and promotion of climate literacy. The current prototype leverages NASA's Ice Sheet System Model (ISSM), a state-of-the-art polar ice sheet dynamics model developed at the Jet Propulsion Lab and UC Irvine. We utilize the Emscripten source-to-source compiler to convert the C/C++ ISSM engine core to JavaScript, and bundled pre/post-processing JS scripts to be compatible with the existing ISSM Python/Matlab API. Researchers using VESL will be able to effectively present their work for public dissemination with little-to-no additional post-processing. This will allow for faster publication in peer-reviewed journals and adaption of results for educational applications. Through future application of this concept to multiple aspects of the Earth System, VESL has the potential to broaden data applications in the geosciences and beyond. At this stage, we seek feedback from the greater scientific and public outreach communities regarding the ease of use and feature set of VESL, as we plan its expansion, and aim to achieve more rapid communication and presentation of scientific results.

  14. Triple Value Simulation Model Fact Sheet

    EPA Pesticide Factsheets

    The Triple Value Simulation (3VS) is a high-level model that accounts for the complex relationships among economic, social and environmental systems in order to explore scenarios and solutions to improve the health of the Bay.

  15. Cryosphere Science Outreach using the Ice Sheet System Model and a Virtual Ice Sheet Laboratory

    NASA Astrophysics Data System (ADS)

    Cheng, D. L. C.; Halkides, D. J.; Larour, E. Y.

    2015-12-01

    Understanding the role of Cryosphere Science within the larger context of Sea Level Rise is both a technical and educational challenge that needs to be addressed if the public at large is to trulyunderstand the implications and consequences of Climate Change. Within this context, we propose a new approach in which scientific tools are used directly inside a mobile/website platform geared towards Education/Outreach. Here, we apply this approach by using the Ice Sheet System Model, a state of the art Cryosphere model developed at NASA, and integrated within a Virtual Ice Sheet Laboratory, with the goal is to outreach Cryospherescience to K-12 and College level students. The approach mixes laboratory experiments, interactive classes/lessons on a website, and a simplified interface to a full-fledged instance of ISSM to validate the classes/lessons. This novel approach leverages new insights from the Outreach/Educational community and the interest of new generations in web based technologies and simulation tools, all of it delivered in a seamlessly integrated web platform. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory undera contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

  16. Modelling the Antarctic Ice Sheet for the last 420kyr

    NASA Astrophysics Data System (ADS)

    Blasco, Javier; Álvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa

    2017-04-01

    Proxy data reveal that in the last glacial-interglacial cycles the Antarctic Ice Sheet (AIS) has experienced changes of its ice volume contributing to past sea-level variations. The AIS is nowadays the largest ice sheet in the world and potentially the largest contributor to a future long term sea-level rise. Because it suffers no significant ablation, it loses mass via basal melting and calving, driven by oceanic forcing. Therefore understanding ice-ocean interactions is crucial to study its past and future. In particular the West Antarctic Ice Sheet (WAIS) is specially sensitive to changes in oceanic temperatures since it rests in its major part below sea level. It also contains the two largest ice shelves of the world, the Ross Ice Shelf and the Filchner-Ronne Ice Shelf whose collapse is believed could accelerate inland ice flow, due to the loss of their buttressing effect, and enhance sea-level rise. The aim of this work is to simulate the AIS for the last 420kyr under varying orbital forcing using a hybrid ice sheet-ice shelf model. In particular, we will analyze the effect of past oceanic temperatures by including a parametrization for the basal melting of the ice shelves and grounding line dependent on observations and oceanic temperature anomalies. These experiments will shed light into the mechanisms involved in the interactions between ocean and cryosphere relevant for the assessment of the AIS stability in the future.

  17. Prototypical model for tensional wrinkling in thin sheets

    PubMed Central

    Davidovitch, Benny; Schroll, Robert D.; Vella, Dominic; Adda-Bedia, Mokhtar; Cerda, Enrique A.

    2011-01-01

    The buckling and wrinkling of thin films has recently seen a surge of interest among physicists, biologists, mathematicians, and engineers. This activity has been triggered by the growing interest in developing technologies at ever-decreasing scales and the resulting necessity to control the mechanics of tiny structures, as well as by the realization that morphogenetic processes, such as the tissue-shaping instabilities occurring in animal epithelia or plant leaves, often emerge from mechanical instabilities of cell sheets. Although the most basic buckling instability of uniaxially compressed plates was understood by Euler more than two centuries ago, recent experiments on nanometrically thin (ultrathin) films have shown significant deviations from predictions of standard buckling theory. Motivated by this puzzle, we introduce here a theoretical model that allows for a systematic analysis of wrinkling in sheets far from their instability threshold. We focus on the simplest extension of Euler buckling that exhibits wrinkles of finite length—a sheet under axisymmetric tensile loads. The first study of this geometry, which is attributed to Lamé, allows us to construct a phase diagram that demonstrates the dramatic variation of wrinkling patterns from near-threshold to far-from-threshold conditions. Theoretical arguments and comparison to experiments show that the thinner the sheet is, the smaller is the compressive load above which the far-from-threshold regime emerges. This observation emphasizes the relevance of our analysis for nanomechanics applications. PMID:22042841

  18. Propeller sheet cavitation noise source modeling and inversion

    NASA Astrophysics Data System (ADS)

    Lee, Keunhwa; Lee, Jaehyuk; Kim, Dongho; Kim, Kyungseop; Seong, Woojae

    2014-02-01

    Propeller sheet cavitation is the main contributor to high level of noise and vibration in the after body of a ship. Full measurement of the cavitation-induced hull pressure over the entire surface of the affected area is desired but not practical. Therefore, using a few measurements on the outer hull above the propeller in a cavitation tunnel, empirical or semi-empirical techniques based on physical model have been used to predict the hull-induced pressure (or hull-induced force). In this paper, with the analytic source model for sheet cavitation, a multi-parameter inversion scheme to find the positions of noise sources and their strengths is suggested. The inversion is posed as a nonlinear optimization problem, which is solved by the optimization algorithm based on the adaptive simplex simulated annealing algorithm. Then, the resulting hull pressure can be modeled with boundary element method from the inverted cavitation noise sources. The suggested approach is applied to the hull pressure data measured in a cavitation tunnel of the Samsung Heavy Industry. Two monopole sources are adequate to model the propeller sheet cavitation noise. The inverted source information is reasonable with the cavitation dynamics of the propeller and the modeled hull pressure shows good agreement with cavitation tunnel experimental data.

  19. Controls on interior West Antarctic Ice Sheet Elevations: inferences from geologic constraints and ice sheet modeling

    NASA Astrophysics Data System (ADS)

    Ackert, Robert P.; Putnam, Aaron E.; Mukhopadhyay, Sujoy; Pollard, David; DeConto, Robert M.; Kurz, Mark D.; Borns, Harold W.

    2013-04-01

    Knowledge of the West Antarctic Ice Sheet (WAIS) response to past sea level and climate forcing is necessary to predict its response to warmer temperatures in the future. The timing and extent of past interior WAIS elevation changes provides insight to WAIS behavior and constraints for ice sheet models. Constraints prior to the Last Glacial Maximum (LGM) however, are rare. Surface exposure ages of glacial erratics near the WAIS divide at Mt. Waesche in Marie Byrd Land, and at the Ohio Range in the Transantarctic Mountains, range from ∼10 ka to >500 ka without a dependence on elevation. The probability distribution functions (PDF) of the exposure ages at both locations, are remarkably similar. During the last glaciation, maximum interior ice elevations as recorded by moraines and erratics were reached between 10 ka and 12 ka. However, most exposure ages are older than the LGM and cluster around ∼40 ka and ∼80 ka. The peak in the exposure age distributions at ∼40 ka includes ages of alpine moraine boulders at Mercer Ridge in the Ohio Range. Comparison of the PDF of exposures ages from the Ohio Range and Mt. Waesche with the temperature record from the Fuji Dome ice core indicates that the youngest peak in the exposure age distributions corresponds to the abrupt warming during the Last Glacial termination. A prominent peak in the Ohio Range PDF corresponds to the penultimate termination (stage 5e). During the intervening glacial period, there is not a consistent relationship between the peaks in the PDF at each location and temperature. A combined ice sheet/ice shelf model with forcing scaled to marine δ18O predicts that interior WAIS elevations near the ice divide have varied ∼300 m over the Last Glacial cycle. Peaks in the PDF correspond to model highstands over the last 200 ka. In the simulated elevation history, maximum ice elevations at Ohio Range (+100 m) and Mt. Waesche (+60 m) occur at ∼10 ka, in agreement with observations from these sites

  20. Sensitivity of the Ice Sheet System Model to direct surface mass balance forcing over the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Schlegel, N. J.; Seroussi, H. L.; Morlighem, M.; Larour, E. Y.; Box, J. E.

    2011-12-01

    The Greenland Ice Sheet, which extends south of the Arctic Circle, is vulnerable to temperature perturbations in the Northern Hemisphere, and its complete retreat would raise global sea level by about 7 meters. Models of the ice sheet's past behavior suggest that Greenland's severe retreat was largely responsible for sea-level rise during the last interglacial period. A clear understanding of exactly how the ice sheet responded to past climate change requires a high-degree of spatial resolution, especially within the ice sheet's large drainage basins, as they contain outlets capable of high-velocity flow. The newly developed Ice Sheet System Model (ISSM) is a finite-element model capable of simulating transient ice flow on an anisotropic mesh. The adaptable mesh can be refined to higher resolutions in the areas of enhanced ice flow. These features offer a distinct advantage over previous models of the Greenland Ice Sheet, specifically in terms of modeling fast-flowing outlet glaciers. With use of established ISSM capabilities, we examined the sensitivity of Greenland's outlet glaciers to the new Arctic System Reanalysis (ASR) reconstruction of yearly surface mass balance forcing of the last 150 years. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Modeling, Analysis and Prediction (MAP) Program.

  1. A Catapult (Slingshot) Current Sheet Relaxation Model for Substorm Triggering

    NASA Astrophysics Data System (ADS)

    Machida, S.; Miyashita, Y.; Ieda, A.

    2010-12-01

    Based on the results of our superposed epoch analysis of Geotail data, we have proposed a catapult (slingshot) current sheet relaxation model in which earthward flows are produced in the central plasma sheet (CPS) due to the catapult (slingshot) current sheet relaxation, together with the rapid enhancement of Poynting flux toward the CPS in the lobe around X ~ -15 Re about 4 min before the substrom onset. These earthward flows are characterized by plasma pressure decrease and large amplitude magnetic field fluctuations. When these flows reach X ~ 12Re in the magnetotail, they give significant disturbances to the inner magnetosphere to initiate some instability such as a ballooning instability or other instabilities, and the substorm starts in the inner magnetosphere. The occurrence of the magnetic reconnection is a natural consequence of the initial convective earthward flows, because the relaxation of a highly stretched catapult current sheet produces a very thin current at its tailward edge being surrounded by intense magnetic fields which were formerly the off-equatorial lobe magnetic fields. Recently, Nishimura et al. [2010] reported that the substorm onset begins when faint poleward discrete arcs collide with equatorward quiet arcs. The region of earthward convective flows correlatively moves earthward prior to the onset. Thus, this region of the earthward convective flows seems to correspond to the faint poleward discrete arcs. Interestingly, our statistical analysis shows that the earthward convective flows are not produced by the magnetic reconnection, but they are attributed to the dominance of the earthward JxB force over the tailward pressure associated with the progress of the plasma sheet thinning.

  2. Formability models for warm sheet metal forming analysis

    NASA Astrophysics Data System (ADS)

    Jiang, Sen

    Several closed form models for the prediction of strain space sheet metal formability as a function of temperature and strain rate are proposed. The proposed models require only failure strain information from the uniaxial tension test at an elevated temperature setting and failure strain information from the traditionally defined strain space forming limit diagram at room temperature, thereby featuring the advantage of offering a full forming limit description without having to carry out expensive experimental studies for multiple modes of deformation under the elevated temperature. The Power law, Voce, and Johnson-Cook hardening models are considered along with the yield criterions of Hill's 48 and Logan-Hosford yield criteria. Acceptable correlations between the theory and experiment are reported for all the models under a plane strain condition. Among all the proposed models, the model featuring Johnson-Cook hardening model and Logan-Hosford yield behavior (LHJC model) was shown to best correlate with experiment. The sensitivity of the model with respect to various forming parameters is discussed. This work is significant to those aiming to incorporate closed-form formability models directly into numerical simulation programs for the purpose of design and analysis of products manufactured through the warm sheet metal forming process. An improvement based upon Swift's diffuse necking theory, is suggested in order to enhance the reliability of the model for biaxial stretch conditions. Theory relating to this improvement is provided in Appendix B.

  3. Sensitivity and initialisation of a moving mesh ice sheet model

    NASA Astrophysics Data System (ADS)

    Bonan, Bertrand; Baines, Michael J.; Nichols, Nancy K.; Partridge, Dale

    2014-05-01

    One of the most important issues in marine ice sheet modelling is tracking accurately the evolution of the snout and the grounding line. Here we present a moving mesh method that is well-suited to tracking moving phenomena accurately. We study the behaviour of the method for a flow line version using the Shallow Ice Approximation. The solution procedure uses the conservation of mass fractions to define a deformation velocity that generates movement of the support of the ice. The ice thickness is recovered using the conservation principle. In order to initialise the moving mesh model, we apply advanced inverse data assimilation techniques to the system. We develop particularly an Ensemble Kalman Filter (EnKF) approach in this context. EnKF is an efficient Monte-Carlo method based on Gaussian assumptions. Contrary to variational methods, it does not require the development of the adjoint of the model. The data assimilation procedure treats both the mesh point positions and the ice sheet thickness as unknown state variables and updates both of these at each assimilation step. The advantage of the ensemble approach is that it enables the sensitivity of the system to be understood and, more importantly, provides information on the correlations between the variables, in particular between the grid and the ice thickness. We demonstrate the success of the technique for noisy, infrequent, partial measurements of ice thickness, both with and without noisy measurements of the terminus position. The moving mesh and EnKF methods can be extended to coupled models of grounded ice sheets and floating ice shelves. The covariances between the states of the system at the grounding line derived by the method will provide valuable information on the coupled system. The techniques presented here can also be extended to include the estimation of parameters, such as the basal sliding coefficient and the bedrock topography, and to two dimensional ice sheets.

  4. Refreezing on the Greenland ice sheet: a model comparison

    NASA Astrophysics Data System (ADS)

    Steger, Christian; Reijmer, Carleen; van den Broeke, Michiel; Ligtenberg, Stefan; Kuipers Munneke, Peter; Noël, Brice

    2016-04-01

    Mass loss of the Greenland ice sheet (GrIS) is an important contributor to global sea level rise. Besides calving, surface melt is the dominant source of mass loss. However, only part of the surface melt leaves the ice sheet as runoff whereas the other part percolates into the snow cover and refreezes. Due to this process, part of the meltwater is (intermediately) stored. Refreezing thus impacts the surface mass balance of the ice sheet but it also affects the vertical structure of the snow cover due to transport of mass and energy. Due to the sparse availability of in situ data and the demand of future projections, it is inevitable to use numerical models to simulate refreezing and related processes. Currently, the magnitude of refrozen mass is neither well constrained nor well validated. In this study, we model the snow and firn layer, and compare refreezing on the GrIS as modelled with two different numerical models. Both models are forced with meteorological data from the regional climate model RACMO 2 that has been shown to simulate realistic conditions for Greenland. One model is the UU/IMAU firn densification model (FDM) that can be used both in an on- and offline mode with RACMO 2. The other model is SNOWPACK; a model originally designed to simulate seasonal snow cover in alpine conditions. In contrast to FDM, SNOWPACK accounts for snow metamorphism and microstructure and contains a more physically based snow densification scheme. A first comparison of the models indicates that both seem to be able to capture the general spatial and temporal pattern of refreezing. Spatially, refreezing occurs mostly in the ablation zone and decreases in the accumulation zone towards the interior of the ice sheet. Below the equilibrium line altitude (ELA) where refreezing occurs in seasonal snow cover on bare ice, the storage effect is only intermediate. Temporal patterns on a seasonal range indicate two peaks in refreezing; one at the beginning of the melt season where

  5. On the impact of buttressing on numerical ice sheet models.

    NASA Astrophysics Data System (ADS)

    Cornford, Stephen; Martin, Daniel; Lee, Victoria; Payne, Antony; Ng, Esmond

    2016-04-01

    Idealized problems with little or no lateral variation are frequently used to study numerical ice sheet models that are then applied to realistic problems that have substantial lateral stresses. Given that the strong lateral variation can, for example, result in a stable grounding line on retrograde slope - an impossible result otherwise - it seems unwise to assume that any conclusion drawn from an unbuttressed flow-line geometry can be extrapolated to the general case. We will present results from two problems which do involve significant lateral stresses, the idealized MISMIP+ tests and 1000-year simulations of the entire Antarctic ice sheet, both resolved to sub-kilometre spatial resolution with the BISICLES ice sheet model. We will consider some numerical issues - for example, whether sub-grid friction schemes are as useful as they appear to be in flow-line problems. We will also consider the impact of the Coulomb limited basal traction law proposed by Tsai (2015), which results in flow-line marine ice streams that are more sensitive to climate perturbations than with the usual Weertman law: to what extent does that hold true in buttressed ice streams?

  6. Hindcasting to measure ice sheet model sensitivity to initial states

    NASA Astrophysics Data System (ADS)

    Aschwanden, A.; Aðalgeirsdóttir, G.; Khroulev, C.

    2013-07-01

    Validation is a critical component of model development, yet notoriously challenging in ice sheet modeling. Here we evaluate how an ice sheet system model responds to a given forcing. We show that hindcasting, i.e. forcing a model with known or closely estimated inputs for past events to see how well the output matches observations, is a viable method of assessing model performance. By simulating the recent past of Greenland, and comparing to observations of ice thickness, ice discharge, surface speeds, mass loss and surface elevation changes for validation, we find that the short term model response is strongly influenced by the initial state. We show that the thermal and dynamical states (i.e. the distribution of internal energy and momentum) can be misrepresented despite a good agreement with some observations, stressing the importance of using multiple observations. In particular we identify rates of change of spatially dense observations as preferred validation metrics. Hindcasting enables a qualitative assessment of model performance relative to observed rates of change. It thereby reduces the number of admissible initial states more rigorously than validation efforts that do not take advantage of observed rates of change.

  7. An ice sheet model of reduced complexity for paleoclimate studies

    NASA Astrophysics Data System (ADS)

    Neff, Basil; Born, Andreas; Stocker, Thomas F.

    2016-04-01

    IceBern2D is a vertically integrated ice sheet model to investigate the ice distribution on long timescales under different climatic conditions. It is forced by simulated fields of surface temperature and precipitation of the Last Glacial Maximum and present-day climate from a comprehensive climate model. This constant forcing is adjusted to changes in ice elevation. Due to its reduced complexity and computational efficiency, the model is well suited for extensive sensitivity studies and ensemble simulations on extensive temporal and spatial scales. It shows good quantitative agreement with standardized benchmarks on an artificial domain (EISMINT). Present-day and Last Glacial Maximum ice distributions in the Northern Hemisphere are also simulated with good agreement. Glacial ice volume in Eurasia is underestimated due to the lack of ice shelves in our model. The efficiency of the model is utilized by running an ensemble of 400 simulations with perturbed model parameters and two different estimates of the climate at the Last Glacial Maximum. The sensitivity to the imposed climate boundary conditions and the positive degree-day factor β, i.e., the surface mass balance, outweighs the influence of parameters that disturb the flow of ice. This justifies the use of simplified dynamics as a means to achieve computational efficiency for simulations that cover several glacial cycles. Hysteresis simulations over 5 million years illustrate the stability of the simulated ice sheets to variations in surface air temperature.

  8. Damage Mechanics in the Community Ice Sheet Model

    NASA Astrophysics Data System (ADS)

    Whitcomb, R.; Cathles, L. M. M., IV; Bassis, J. N.; Lipscomb, W. H.; Price, S. F.

    2016-12-01

    Half of the mass that floating ice shelves lose to the ocean comes from iceberg calving, which is a difficult process to simulate accurately. This is especially true in the large-scale ice dynamics models that couple changes in the cryosphere to climate projections. Damage mechanics provide a powerful technique with the potential to overcome this obstacle by describing how fractures in ice evolve over time. Here, we demonstrate the application of a damage model to ice shelves that predicts realistic geometries. We incorporated this solver into the Community Ice Sheet Model, a three dimensional ice sheet model developed at Los Alamos National Laboratory. The damage mechanics formulation that we use comes from a first principles-based evolution law for the depth of basal and surface crevasses and depends on the large scale strain rate, stress state, and basal melt. We show that under idealized conditions it produces ice tongue lengths that match well with observations for a selection of natural ice tongues, including Erebus, Drygalski, and Pine Island in Antarctica, as well as Petermann in Greenland. We also apply the model to more generalized ideal ice shelf geometries and show that it produces realistic calving front positions. Although our results are preliminary, the damage mechanics model that we developed provides a promising first principles method for predicting ice shelf extent and how the calving margins of ice shelves respond to climate change.

  9. The climate - Greenland ice sheet Feedback as simulated by the coupled ice sheet/climate model EC-EARTH - PISM

    NASA Astrophysics Data System (ADS)

    Yang, Shuting; Madsen, Marianne S.; Rodehacke, Christian; Svendsen, Synne H.

    2014-05-01

    Recent observations show that mass loss from the Greenland ice sheet has increased during the past decades, in line with the warming trend in the Arctic. Studies have suggested that the ice sheet mass discharge through fast moving outlet glaciers and ice streams may be triggered by intrusions of warm seawater into fjords, implying the possibility for fjord-terminating glaciers to respond to ocean and atmospheric changes on annual to decadal time scales. Meanwhile, the rapid changes in ice sheet topography and surface runoff could alter the atmospheric and ocean circulation. To understand the interactions of ice sheet and atmosphere and ocean, process based, climate - ice sheet coupled models are needed. Recently a fully coupled global climate model with a dynamical ice sheet model for the Greenland ice sheet, EC-EARTH - PISM, has been developed. The model system consists of the atmosphere, ocean and sea ice model system, EC-EARTH, and the Parallel Ice Sheet Model, PISM. The coupling of the PISM includes a modified surface physical parameterization in EC-EARTH adapted to the land ice surface over glaciated regions in Greenland. The PISM ice sheet model is forced with the surface mass balance (SMB) directly computed inside the EC-EARTH atmospheric module and accounting for the precipitation, the surface evaporation, and the melting of snow and ice over land ice. PISM returns the simulated basal melt, ice discharge and ice cover (extent and thickness) as boundary conditions to EC-EARTH. This coupled system is mass and energy conserving without being constrained by any anomaly correction or flux adjustment, and hence is suitable for investigation of ice sheet - climate feedbacks. PISM is initialized with the standard paleo-climatological spin-up followed by forcing with the EC-EARTH preindustrial climate to reach an equilibrium state with the model preindustrial climate. The EC-EARTH - PISM system is then integrated under preindustrial conditions until it has reached a

  10. Material Models for Simulation of Superplastic Mg Alloy Sheet Forming

    NASA Astrophysics Data System (ADS)

    Taleff, Eric M.; Hector, Louis G.; Verma, Ravi; Krajewski, Paul E.; Chang, Jung-Kuei

    2010-06-01

    Accurate prediction of strain fields and cycle times for fine-grained Mg alloy sheet forming at high temperatures (400-500 °C) is severely limited by a lack of accurate material constitutive models. This paper details an important first step toward addressing this issue by evaluating material constitutive models, developed from tensile data, for high-temperature plasticity of a fine-grained Mg AZ31 sheet material. The finite element method was used to simulate gas pressure bulge forming experiments at 450 °C using four constant gas pressures. The applicability of the material constitutive models to a balanced-biaxial stress state was evaluated through comparison of simulation results with bulge forming data. Simulations based upon a phenomenological material constitutive model developed using data from both tensile elongation and strain-rate-change experiments were found to be in favorable accord with experiments. These results provide new insights specific to the construction and use of material constitutive models for hot deformation of wrought, fine-grained Mg alloys.

  11. Modeling the sensitivity of the Greenland Ice Sheet to Holocene climate variability using the Ice Sheet System Model (ISSM).

    NASA Astrophysics Data System (ADS)

    Cuzzone, J. K.; Larour, E. Y.; Schlegel, N.; Briner, J. P.

    2016-12-01

    Although confidence regarding the trajectory of future ice loss for the Greenland Ice Sheet (GIS) is high, the rate and magnitude of these changes remain uncertain. Efforts to model the sensitivity of the GIS to future climate change therefore remain a high priority. One method showing promising results in helping to constrain unknown parameters, which are important for modeling the GIS more precisely, involves data assimilation of existing products (i.e. CrySat, ICEsat, IceBridge, etc.). These have been used to invert for unknown parameters such as basal friction and surface mass balance. Using the near past and present data sources, however, does not provide enough information temporally to determine the sensitivity of the GIS to climate change over centennial to millennial scales. Here, we use data assimilation capabilities within the Ice Sheet System Model (ISSM) framework, which now make it possible to use existing and developing paleoclimate records to test new simulations of the GIS during the Holocene. By allowing the model to capture the required forcings needed to reproduce the reconstructed history of the ice sheet, paleoclimate records serve as a metric to improve accuracy in model spinups towards present day. In particular, we focus on the southwestern GIS, an area where past modeling efforts have shown significant middle Holocene retreat inland of the present day margin. Preliminary results of ISSM simulations including critical glaciological diagnostics (e.g. velocity, surface height, margin position, and mass-flux at the margin) during the Holocene will be presented, with particular attention being given to the paleoclimate archives used as data assimilation targets.

  12. Optimization of Cultured Human Corneal Endothelial Cell Sheet Transplantation and Post-Operative Sheet Evaluation in a Rabbit Model.

    PubMed

    Yamaguchi, Masahiro; Shima, Nobuyuki; Kimoto, Miwa; Ebihara, Nobuyuki; Murakami, Akira; Yamagami, Satoru

    2016-09-01

    To optimize cultured human corneal endothelial cell (cHCEC) sheet transplantation technique for maintenance of cHCEC viability. cHCEC sheets cultured on a collagen scaffold were covered with or without Viscoat® and exposed to humidified air in the incubator. cHCEC sheets with or without Viscoat® were transplanted into cadaveric porcine eyes by the DSAEK technique with full air tamponade and incubated for various time periods. Then cell viability was determined by using the live/dead assay kit. cHCEC sheets with Viscoat® were transplanted into rabbit eyes and the sheets were histologically evaluated before and 14 days after transplantation. A collagen scaffold and Viscoat® were effective for protecting cHCEC from damage due to air exposure in vitro. All cells died after 18 hours of air exposure in porcine eyes in Viscoat® untreated control. In contrast, Viscoat® treatment sustained full cell viability following 2 hours and could maintain approximately 80% viability after 18 hours. In a rabbit model, transplanted cHCEC sheet with Viscoat® maintained cell density at 2803 ± 229 mm(2) (18% cell loss) and expression of N-cadherin, zonula occludens-1, and actin-filament localized to cell boundary as similar as donor HCEC. Viscoat® can contribute to cHCEC protection from damage caused by exposure to air.

  13. Simulations of the Greenland ice sheet with the ice sheet model SICOPOLIS including a fully coupled model of basal hydrology

    NASA Astrophysics Data System (ADS)

    Calov, Reinhard; Beyer, Sebastian; Greve, Ralf; Kleiner, Thomas; Rückamp, Martin; Humbert, Angelika; Ganopolski, Andrey

    2017-04-01

    We present simulations with the dynamic/thermodynamic ice sheet model SICOPOLIS (version 3) coupled to HYDRO, a model of basal hydrology. SICOPOLIS describes the evolution of ice thickness, temperature and water content of ice sheets. Recently, the treatment of longitudinal and lateral stresses ("shelfy stream approximation") for the dynamics and the enthalpy method as an alternative method for solving the energy equation were included into the model. HYDRO describes the basal water transport using the hydrological potential. In a bi-directional coupling, HYDRO receives the basal water fluxes from SICOPOLIS, while the basal water from HYDRO affects the basal sliding in SICOPOLIS. Here, we present offline simulations with HYDRO as well as simulations with SICOPOLIS-only and the coupled model SICOPOLIS-HYDRO. Several sensitivity studies highlight the importance of basal processes. In particular, we inspect the role of horizontal resolution. It shows that not only horizontal resolution plays an important role for resolving outlet glaciers, but also the coupled model better reproduces outlet glaciers compared to the uncoupled one; even the North-East-Greenland Ice Stream is modelled quite well without the need for special regional tuning.

  14. Assessing the predictability of a coupled climate-ice sheet model system for the response of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Adalgeirsdottir, G.; Stendel, M.; Bueler, E.; Christensen, J. H.; Drews, M.; Mottram, R.

    2009-04-01

    The wild card for reliable sea level rise prediction is the contribution of the Greenland Ice Sheet. There is an urgent need to determine the predictability of models that simulate the response of Greenland Ice Sheet to rising temperatures and the amount of freshwater flux that can be expected into the ocean. Modelling efforts have been limited by poorly known boundary and initial conditions, low resolution and lack of presentation of fast flowing ice streams. We address these limitations by building a model system consisting of a high resolution regional climate model (HIRHAM4), that has been run for the period 1950-2080 at 25 km, and Parallel Ice Sheet Model (PISM), which simulates spatially and temporally varying ice streams by combining the solutions of the Shallow Shelf and Shallow Ice Approximations. The surface mass balance is simulated with a positive-degree-day method. The important and poorly constrained model component is the past climate forcing, which serves the purpose of initializing the model by simulating the present ice sheet and observed rate of mass changes. Simulated gradients of mass loss due to warming trends of past decade and prediction for the future are presented as well as estimated sensitivities due to the various model component uncertainties.

  15. Material Characterization and Modeling for Industrial Sheet Forming Simulations

    NASA Astrophysics Data System (ADS)

    Mattiasson, Kjell; Sigvant, Mats

    2004-06-01

    In the present paper a project carried out at Volvo Cars Corp. and Chalmers University of Technology, with the purpose of improving material characterization and modeling for sheet forming simulation, is described. One of the primary targets has been to identify a material testing procedure, which is capable of providing effective stress-strain data at considerably larger strains than what can be achieved in a standard uniaxial tensile test. Another objective has been to advance from the common Hill '48 material model to a more flexible one, and, furthermore, to identify suitable test procedures for determining the parameters of such a model. A third objective has been to find practical examples, in which the importance of a careful material modeling can be clearly demonstrated.

  16. Ice-sheet modelling accelerated by graphics cards

    NASA Astrophysics Data System (ADS)

    Brædstrup, Christian Fredborg; Damsgaard, Anders; Egholm, David Lundbek

    2014-11-01

    Studies of glaciers and ice sheets have increased the demand for high performance numerical ice flow models over the past decades. When exploring the highly non-linear dynamics of fast flowing glaciers and ice streams, or when coupling multiple flow processes for ice, water, and sediment, researchers are often forced to use super-computing clusters. As an alternative to conventional high-performance computing hardware, the Graphical Processing Unit (GPU) is capable of massively parallel computing while retaining a compact design and low cost. In this study, we present a strategy for accelerating a higher-order ice flow model using a GPU. By applying the newest GPU hardware, we achieve up to 180× speedup compared to a similar but serial CPU implementation. Our results suggest that GPU acceleration is a competitive option for ice-flow modelling when compared to CPU-optimised algorithms parallelised by the OpenMP or Message Passing Interface (MPI) protocols.

  17. Temperature Dependent Constitutive Modeling for Magnesium Alloy Sheet

    SciTech Connect

    Lee, Jong K.; Lee, June K.; Kim, Hyung S.; Kim, Heon Y.

    2010-06-15

    Magnesium alloys have been increasingly used in automotive and electronic industries because of their excellent strength to weight ratio and EMI shielding properties. However, magnesium alloys have low formability at room temperature due to their unique mechanical behavior (twinning and untwining), prompting for forming at an elevated temperature. In this study, a temperature dependent constitutive model for magnesium alloy (AZ31B) sheet is developed. A hardening law based on non linear kinematic hardening model is used to consider Bauschinger effect properly. Material parameters are determined from a series of uni-axial cyclic experiments (T-C-T or C-T-C) with the temperature ranging 150-250 deg. C. The influence of temperature on the constitutive equation is introduced by the material parameters assumed to be functions of temperature. Fitting process of the assumed model to measured data is presented and the results are compared.

  18. A parallel high-order accurate finite element nonlinear Stokes ice sheet model and benchmark experiments: A PARALLEL FEM STOKES ICE SHEET MODEL

    SciTech Connect

    Leng, Wei; Ju, Lili; Gunzburger, Max; Price, Stephen; Ringler, Todd

    2012-01-04

    The numerical modeling of glacier and ice sheet evolution is a subject of growing interest, in part because of the potential for models to inform estimates of global sea level change. This paper focuses on the development of a numerical model that determines the velocity and pressure fields within an ice sheet. Our numerical model features a high-fidelity mathematical model involving the nonlinear Stokes system and combinations of no-sliding and sliding basal boundary conditions, high-order accurate finite element discretizations based on variable resolution grids, and highly scalable parallel solution strategies, all of which contribute to a numerical model that can achieve accurate velocity and pressure approximations in a highly efficient manner. We demonstrate the accuracy and efficiency of our model by analytical solution tests, established ice sheet benchmark experiments, and comparisons with other well-established ice sheet models.

  19. Simulating the Antarctic ice sheet in the late-Pliocene warm period: PLISMIP-ANT, an ice-sheet model intercomparison project

    NASA Astrophysics Data System (ADS)

    de Boer, B.; Dolan, A. M.; Bernales, J.; Gasson, E.; Goelzer, H.; Golledge, N. R.; Sutter, J.; Huybrechts, P.; Lohmann, G.; Rogozhina, I.; Abe-Ouchi, A.; Saito, F.; van de Wal, R. S. W.

    2015-05-01

    In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals in Earth history is of fundamental importance. The late Pliocene warm period (also known as the PRISM interval: 3.264 to 3.025 million years before present) can serve as a potential analogue for projected future climates. Although Pliocene ice locations and extents are still poorly constrained, a significant contribution to sea-level rise should be expected from both the Greenland ice sheet and the West and East Antarctic ice sheets based on palaeo sea-level reconstructions. Here, we present results from simulations of the Antarctic ice sheet by means of an international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP-ANT). For the experiments, ice-sheet models including the shallow ice and shelf approximations have been used to simulate the complete Antarctic domain (including grounded and floating ice). We compare the performance of six existing numerical ice-sheet models in simulating modern control and Pliocene ice sheets by a suite of five sensitivity experiments. We include an overview of the different ice-sheet models used and how specific model configurations influence the resulting Pliocene Antarctic ice sheet. The six ice-sheet models simulate a comparable present-day ice sheet, considering the models are set up with their own parameter settings. For the Pliocene, the results demonstrate the difficulty of all six models used here to simulate a significant retreat or re-advance of the East Antarctic ice grounding line, which is thought to have happened during the Pliocene for the Wilkes and Aurora basins. The specific sea-level contribution of the Antarctic ice sheet at this point cannot be conclusively determined, whereas improved grounding line physics could be essential for a correct representation of the migration of the grounding-line of the Antarctic ice sheet during the Pliocene.

  20. Modelling the marine advance of the last Cordilleran ice sheet

    NASA Astrophysics Data System (ADS)

    Seguinot, Julien; Rogozhina, Irina

    2014-05-01

    Marine advance of the last Cordilleran ice sheet onto the north-eastern Pacific continental shelf may have caused rapid fluctuations of sea level and potentially impacted upon human migration into North America. However the position of the former ice front was critically controlled by a process that remains poorly understood: glacier calving. Geomorphological reconstructions show that part of the presently oceanic areas were ice-covered, allowing for downstream formation of the well-studied Puget and Juan de Fuca lobes. Here we use a numerical glacier model (PISM) to reconstruct the former marine front of the Cordilleran ice sheet and its impact on upstream ice dynamics. Our simulations show that the use of a thickness-based calving law leads to a strong deficit of marine ice cover in the areas where existing reconstructions suggest its advance. In contrast, a physically-based parametrization of glacier calving using the main components of the strain rate tensor (eigencalving; A. Levermann, T. Albrecht, R. Winkelmann, M. A. Martin, M. Haseloff, and I. Joughin, The Cryosphere, 6, 273-286, 2012) reproduces the geomorphologically inferred ice extent.

  1. Catapult current sheet relaxation model confirmed by THEMIS observations

    NASA Astrophysics Data System (ADS)

    Machida, S.; Miyashita, Y.; Ieda, A.; Nose, M.; Angelopoulos, V.; McFadden, J. P.

    2014-12-01

    In this study, we show the result of superposed epoch analysis on the THEMIS probe data during the period from November, 2007 to April, 2009 by setting the origin of time axis to the substorm onset determined by Nishimura with THEMIS all sky imager (THEMS/ASI) data (http://www.atmos.ucla.edu/~toshi/files/paper/Toshi_THEMIS_GBO_list_distribution.xls). We confirmed the presence of earthward flows which can be associated with north-south auroral streamers during the substorm growth phase. At around X = -12 Earth radii (Re), the northward magnetic field and its elevation angle decreased markedly approximately 4 min before substorm onset. A northward magnetic-field increase associated with pre-onset earthward flows was found at around X = -17Re. This variation indicates the occurrence of the local depolarization. Interestingly, in the region earthwards of X = -18Re, earthward flows in the central plasma sheet (CPS) reduced significantly about 3min before substorm onset. However, the earthward flows enhanced again at t = -60 sec in the region around X = -14 Re, and they moved toward the Earth. At t = 0, the dipolarization of the magnetic field started at X ~ -10 Re, and simultaneously the magnetic reconnection started at X ~ -20 Re. Synthesizing these results, we can confirm the validity of our catapult current sheet relaxation model.

  2. A generalized hinged-magnetodisc model of Jupiter's nightside current sheet

    NASA Technical Reports Server (NTRS)

    Khurana, Krishan K.

    1992-01-01

    A nonaxial hinged magnetodisk model of Jupiter's nightside current sheet is presented. The model organizes the current sheet crossings equally successfully for all three of the spacecraft that have visited the nightside of Jupiter. The model assumes that the hinging is caused by the action of the solar wind forcing on the magnetotail of Jupiter. It is found necessary to include both the hinging of the current sheet and the propagation delay to obtain good fits to the observations.

  3. A generalized hinged-magnetodisc model of Jupiter's nightside current sheet

    NASA Technical Reports Server (NTRS)

    Khurana, Krishan K.

    1992-01-01

    A nonaxial hinged magnetodisk model of Jupiter's nightside current sheet is presented. The model organizes the current sheet crossings equally successfully for all three of the spacecraft that have visited the nightside of Jupiter. The model assumes that the hinging is caused by the action of the solar wind forcing on the magnetotail of Jupiter. It is found necessary to include both the hinging of the current sheet and the propagation delay to obtain good fits to the observations.

  4. Response of the Antarctic ice sheet to ocean forcing using the POPSICLES coupled ice sheet-ocean model

    NASA Astrophysics Data System (ADS)

    Martin, D. F.; Asay-Davis, X.; Price, S. F.; Cornford, S. L.; Maltrud, M. E.; Ng, E. G.; Collins, W.

    2014-12-01

    We present the response of the continental Antarctic ice sheet to sub-shelf-melt forcing derived from POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010. Simulations are performed at 0.1 degree (~5 km) ocean resolution and ice sheet resolution as fine as 500 m using adaptive mesh refinement. A comparison of fully-coupled and comparable standalone ice-sheet model results demonstrates the importance of two-way coupling between the ice sheet and the ocean. The POPSICLES model couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). BISICLES makes use of adaptive mesh refinement to fully resolve dynamically-important regions like grounding lines and employs a momentum balance similar to the vertically-integrated formulation of Schoof and Hindmarsh (2009). Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests like MISMIP3D (Pattyn et al., 2013) and realistic configurations (Favier et al. 2014). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). A companion presentation, "Present-day circum-Antarctic simulations using the POPSICLES coupled land ice-ocean model" in session C027 describes the ocean-model perspective of this work, while we focus on the response of the ice sheet and on details of the model. The figure shows the BISICLES-computed vertically-integrated ice velocity field about 1 month into a 20-year coupled Antarctic run. Groundling lines are shown in green.

  5. Modelling heterogeneous meltwater percolation on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Ligtenberg, S.

    2015-12-01

    The Greenland Ice Sheet (GrIS) has experienced an increase of surface meltwater production over the last decades, with the latest record set in the summer of 2012. For current and future ice sheet mass balance assessments, it is important to quantify what part of this meltwater reaches the ocean and contributes to sea level change. Meltwater produced at the surface has several options: it can infiltrate the local firn pack, where it is either stored temporarily or refrozen, or it can run off along the surface or via en-glacial drainage systems. In this study, we focus on the first; more specifically, in which manner meltwater percolates the firn column. Over the past years, GrIS research has shown that meltwater does not infiltrate the firn pack homogeneously (i.e. matrix flow), but that inhomogeneities in horizontal firn layers causes preferential flow paths for meltwater (i.e. piping). Although this process has been observed and studied on a few isolated sites, it has never been examined on the entire GrIS. To do so, we use the firn model IMAU-FDM with new parameterizations for preferential flow, impermeable ice lenses and sub-surface runoff. At the surface, IMAU-FDM is forced with realistic climate data from the regional climate model RACMO2.3. The model results are evaluated with temperatures and density measurements from firn cores across the GrIS. By allowing for heterogeneous meltwater percolation, the model is able to store heat and mass much deeper in the firn column. This is, however, in part counteracted by the inclusion of impermeability of ice lenses, which causes part of the meltwater to run off horizontally.

  6. Climate Model Dependency in Understanding the Antarctic Ice Sheet during the Warm Late Pliocene

    NASA Astrophysics Data System (ADS)

    Dolan, A. M.; de Boer, B.; Bernales, J.; Hunter, S. J.; Haywood, A.

    2015-12-01

    In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals of Earth history is fundamentally important. A warm period in the Late Pliocene (3.264 to 3.025 million years before present) can serve as a potential analogue for projected future climates. Although Pliocene ice locations and extents are still poorly constrained, a significant contribution to sea-level rise should be expected from both the Greenland ice sheet and the West and East Antarctic ice sheets based on palaeo sea-level reconstructions and geological evidence Following a five year international project PLISMIP (Pliocene Ice Sheet Modeling Intercomparison Project) we present the final set of results which quantify uncertainty in climate model-based predictions of the Antarctic ice sheet. In this study we use an ensemble of climate model forcings within a multi-ice sheet model framework to assess the climate (model) dependency of large scale features of the Antarctic ice sheet. Seven coupled atmosphere-ocean climate models are used to derive surface temperature, precipitation and oceanic forcing that drive three ice sheet models (over the grounded and floating domain). Similar to results presented over Greenland, we show that the reconstruction of the Antarctic ice sheet is sensitive to which climate model is used to provide the forcing field. Key areas of uncertainty include West Antarctica, the large subglacial basins of East Antarctica and the overall thickness of the continental interior of East Antarctica. We relate the results back to geological proxy data, such as those relating to exposure rates which provide information on potential ice sheet thickness. Finally we discuss as to whether the choice of modelling framework (i.e. climate model and ice sheet model used) or the choice of boundary conditions causes the greatest uncertainty in ice sheet reconstructions of the warm Pliocene.

  7. Climate Model Dependency and Understanding the Antarctic Ice Sheet during the Warm Late Pliocene

    NASA Astrophysics Data System (ADS)

    Dolan, Aisling; de Boer, Bas; Bernales, Jorge; Hunter, Stephen; Haywood, Alan

    2016-04-01

    In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals of Earth history is fundamentally important. A warm period in the Late Pliocene (3.264 to 3.025 million years before present) can serve as a potential analogue for projected future climates. Although Pliocene ice locations and extents are still poorly constrained, a significant contribution to sea-level rise should be expected from both the Greenland ice sheet and the West and East Antarctic ice sheets based on palaeo sea-level reconstructions and geological evidence. Following a five year international project PLISMIP (Pliocene Ice Sheet Modeling Intercomparison Project) we present the final set of results which quantify uncertainty in climate model-based predictions of the Antarctic ice sheet. In this study we use an ensemble of climate model forcings within a multi-ice sheet model framework to assess the climate (model) dependency of large scale features of the Antarctic ice sheet. Seven coupled atmosphere-ocean climate models are used to derive surface temperature, precipitation and oceanic forcing that drive three ice sheet models (over the grounded and floating domain). Similar to results presented over Greenland, we show that the reconstruction of the Antarctic ice sheet is sensitive to which climate model is used to provide the forcing field. Key areas of uncertainty include West Antarctica, the large subglacial basins of East Antarctica and the overall thickness of the continental interior of East Antarctica. We relate the results back to geological proxy data, such as those relating to exposure rates which provide information on potential ice sheet thickness. Finally we discuss as to whether the choice of modelling framework (i.e. climate model and ice sheet model used) or the choice of boundary conditions causes the greatest uncertainty in ice sheet reconstructions of the warm Pliocene.

  8. Ice Sheet Model Intercomparison Project (ISMIP6) contribution to CMIP6

    NASA Astrophysics Data System (ADS)

    Nowicki, Sophie M. J.; Payne, Anthony; Larour, Eric; Seroussi, Helene; Goelzer, Heiko; Lipscomb, William; Gregory, Jonathan; Abe-Ouchi, Ayako; Shepherd, Andrew

    2016-12-01

    Reducing the uncertainty in the past, present, and future contribution of ice sheets to sea-level change requires a coordinated effort between the climate and glaciology communities. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) is the primary activity within the Coupled Model Intercomparison Project - phase 6 (CMIP6) focusing on the Greenland and Antarctic ice sheets. In this paper, we describe the framework for ISMIP6 and its relationship with other activities within CMIP6. The ISMIP6 experimental design relies on CMIP6 climate models and includes, for the first time within CMIP, coupled ice-sheet-climate models as well as standalone ice-sheet models. To facilitate analysis of the multi-model ensemble and to generate a set of standard climate inputs for standalone ice-sheet models, ISMIP6 defines a protocol for all variables related to ice sheets. ISMIP6 will provide a basis for investigating the feedbacks, impacts, and sea-level changes associated with dynamic ice sheets and for quantifying the uncertainty in ice-sheet-sourced global sea-level change.

  9. Preliminary empirical model of inner boundary of ion plasma sheet

    NASA Astrophysics Data System (ADS)

    Cao, J. B.; Zhang, D.; Reme, H.; Dandouras, I.; Sauvaud, J. A.; Fu, H. S.; Wei, X. H.

    2015-09-01

    The penetration of the plasma sheet into the inner magnetosphere is important to both ring current formation and spacecraft charging at geosynchronous orbit. This paper, using hot ion data recorded by HIA of TC-1/DSP, establishes an empirical model of the inner boundary of ion plasma sheet (IBIPS) on the near equatorial plane. All IBIPS are located inside geocentric radial distance of 9 RE. We divided local times (LT) into eight local time bins and found that during quiet times (Kp ⩽ 2-), the IBIPS is closest to the Earth on the pre-midnight side (LT = 1930-2130) and farthest on the dawn side (LT = 0430-0730), which differs from previous spiral models. The geocentric radius of IBIPS in each local time bin can be described by a linear fitting function: Rps = A + Bkp · Kp. The changing rate Bkp of the radius of IBIPS relative to Kp index on the midnight side (LT = 2230-0130) and post-night side (LT = 0130-0430) are the two largest (0.66 and 0.67), indicating that the IBIPS on the night side (LT = 2230-0430) moves fastest when Kp changes. Since the IBIPSs in different local times bins have different changing rates, both the size and shape of IBIPS change when Kp varies. The correlation coefficients between the radius of IBIPS and the instantaneous Kp increase with the increase of ΔT (the time difference between IBIPS crossing time and preceding Kp interval), which suggests that with the increase of ΔT, the radius of IBIPS is more and more controlled by instantaneous Kp, and the influence of preceding Kp becomes weaker. The response time of IBIPS to Kp is between 80 and 95 min. When ΔT > 95 min, the correlation coefficient basically keeps unchanged and only has a weak increase, suggesting that the IBIPS is mainly determined by the convection electric field represented by instantaneous Kp.

  10. Sheet Hydroforming Pre-bulging Numerical Model Improvement

    NASA Astrophysics Data System (ADS)

    Gabriele, Papadia; Antonio, Del Prete; Alfredo, Anglani

    2010-06-01

    Sheet hydroforming has gained increasing interest during the last years, especially as application in the manufacturing of some components for automotive, aerospace, and electrical appliances[1,2]. Many parameters influence the process of sheet hydroforming, one of them is the pre-bulging[3]. Different studies have been also done to determine the optimal forming parameters through FEA[4,5]. In the case of sheet hydromechanical forming process the blank is first placed on the lower die (a fluid chamber combined with draw ring) and then, after sealing the blank between blank holder and draw ring, punch progresses to deform the blank[6]. Pressure of the fluid chamber is also increased simultaneously with the punch progression[7]. In this paper, the pre-bulging effect on active hydromechanical deep drawing process has been investigated experimentally and numerically. Pre-bulging includes two parameters: pre-bulging height and pre-bulging pressure, which influence the forming process significantly[3]. Numerical simulations and experimental tests were carried out for a given shape to investigate the pre-bulging effect on the maximum hydroforming depth. During this activity, the authors have verified that the low numerical—experimental accuracy detected it was caused also by the simulation of the pre-bulging phase. The authors have analyzed the problem to define a correct procedure to simulate the pre-bulging phase. From this point of view, nine different levels of pre-bulging (taking into account the level equal to zero also) have been tested to experimentally calculate the Thickness Percentage Reduction (TPR) at the maximum pre-bulging height. For each level, the experiment has been conducted two times for a total number of eighteen experiments. The experimental TPR values have been compared with the numerical ones reaching a good accuracy only in the case of pre-bulging height greater than forty millimeters. The experimental activity has given a valid contribution to

  11. Experimental design for three interrelated Marine Ice-Sheet and Ocean Model Intercomparison Projects

    NASA Astrophysics Data System (ADS)

    Asay-Davis, X. S.; Cornford, S. L.; Durand, G.; Galton-Fenzi, B. K.; Gladstone, R. M.; Gudmundsson, G. H.; Hattermann, T.; Holland, D. M.; Holland, D.; Holland, P. R.; Martin, D. F.; Mathiot, P.; Pattyn, F.; Seroussi, H.

    2015-11-01

    Coupled ice sheet-ocean models capable of simulating moving grounding lines are just becoming available. Such models have a broad range of potential applications in studying the dynamics of marine ice sheets and tidewater glaciers, from process studies to future projections of ice mass loss and sea level rise. The Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP) is a community effort aimed at designing and coordinating a series of model intercomparison projects (MIPs) for model evaluation in idealized setups, model verification based on observations, and future projections for key regions in the West Antarctic Ice Sheet (WAIS). Here we describe computational experiments constituting three interrelated MIPs for marine ice sheet models and regional ocean circulation models incorporating ice shelf cavities. These consist of ice sheet experiments under the Marine Ice Sheet MIP third phase (MISMIP+), ocean experiments under the ice shelf-ocean MIP second phase (ISOMIP+) and coupled ice sheet-ocean experiments under the MISOMIP first phase (MISOMIP1). All three MIPs use a shared domain with idealized bedrock topography and forcing, allowing the coupled simulations (MISOMIP1) to be compared directly to the individual component simulations (MISMIP+ and ISOMIP+). The experiments, which have qualitative similarities to Pine Island Glacier Ice Shelf and the adjacent region of the Amundsen Sea, are designed to explore the effects of changes in ocean conditions, specifically the temperature at depth, on basal melting and ice dynamics. In future work, differences between model results will form the basis for evaluation of the participating models.

  12. Towards Industrial Application of Damage Models for Sheet Metal Forming

    NASA Astrophysics Data System (ADS)

    Doig, M.; Roll, K.

    2011-05-01

    Due to global warming and financial situation the demand to reduce the CO2-emission and the production costs leads to the permanent development of new materials. In the automotive industry the occupant safety is an additional condition. Bringing these arguments together the preferable approach for lightweight design of car components, especially for body-in-white, is the use of modern steels. Such steel grades, also called advanced high strength steels (AHSS), exhibit a high strength as well as a high formability. Not only their material behavior but also the damage behavior of AHSS is different compared to the performances of standard steels. Conventional methods for the damage prediction in the industry like the forming limit curve (FLC) are not reliable for AHSS. Physically based damage models are often used in crash and bulk forming simulations. The still open question is the industrial application of these models for sheet metal forming. This paper evaluates the Gurson-Tvergaard-Needleman (GTN) model and the model of Lemaitre within commercial codes with a goal of industrial application.

  13. Enthalpy benchmark experiments for numerical ice sheet models

    NASA Astrophysics Data System (ADS)

    Kleiner, T.; Rückamp, M.; Bondzio, J. H.; Humbert, A.

    2015-02-01

    We present benchmark experiments to test the implementation of enthalpy and the corresponding boundary conditions in numerical ice sheet models. Since we impose several assumptions on the experiment design, analytical solutions can be formulated for the proposed numerical experiments. The first experiment tests the functionality of the boundary condition scheme and the basal melt rate calculation during transient simulations. The second experiment addresses the steady-state enthalpy profile and the resulting position of the cold-temperate transition surface (CTS). For both experiments we assume ice flow in a parallel-sided slab decoupled from the thermal regime. We compare simulation results achieved by three different ice flow-models with these analytical solutions. The models agree well to the analytical solutions, if the change in conductivity between cold and temperate ice is properly considered in the model. In particular, the enthalpy gradient on the cold side of the CTS goes to zero in the limit of vanishing temperate-ice conductivity, as required from the physical jump conditions at the CTS.

  14. Simulating the Antarctic ice sheet in the Late-Pliocene warm period: PLISMIP-ANT, an ice-sheet model intercomparison project

    NASA Astrophysics Data System (ADS)

    de Boer, Bas; Dolan, Aisling; Bernales, Jorge; Gasson, Edward; Goelzer, Heiko; Golledge, Nick; Sutter, Johannes; Huybrechts, Phillipe; Lohmann, Gerrit; Rogozhina, Irina; Abe-Ouchi, Ayako; Saito, Fuyuki; van de Wal, Roderik

    2015-04-01

    In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals in Earth history is of fundamental importance. The Late-Pliocene warm period (also known as the PRISM interval: 3.264 to 3.025 million years before present) can serve as a potential analogue for projected future climates. Although Pliocene ice locations and extents are still poorly constrained, a significant contribution to sea-level rise should be expected from both the Greenland ice sheet and the West and East Antarctic ice sheets based on palaeo sea-level reconstructions. Here, we present results from simulations of the Antarctic ice sheet by means of an international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP-ANT). For the experiments, ice-sheet models including the shallow ice and shelf approximations have been used to simulate the complete Antarctic domain (including grounded and floating ice). We compare the performance of six existing numerical ice-sheet models in simulating modern control and Pliocene ice sheets by a suite of four sensitivity experiments. Ice-sheet model forcing fields are taken from the HadCM3 atmosphere-ocean climate model runs for the pre-industrial and the Pliocene. We include an overview of the different ice-sheet models used and how specific model configurations influence the resulting Pliocene Antarctic ice sheet. The six ice-sheet models simulate a comparable present-day ice sheet, although the models are setup with their own parameter settings. For the Pliocene simulations using the Bedmap1 bedrock topography, some models show a small retreat of the East Antarctic ice sheet, which is thought to have happened during the Pliocene for the Wilkes and Aurora basins. This can be ascribed to either the surface mass balance, as the HadCM3 Pliocene climate shows a significant increase over the Wilkes and Aurora basin, or the initial bedrock topography. For the latter, our simulations with the recently

  15. Sheet metal forming optimization by using surrogate modeling techniques

    NASA Astrophysics Data System (ADS)

    Wang, Hu; Ye, Fan; Chen, Lei; Li, Enying

    2017-01-01

    Surrogate assisted optimization has been widely applied in sheet metal forming design due to its efficiency. Therefore, to improve the efficiency of design and reduce the product development cycle, it is important for scholars and engineers to have some insight into the performance of each surrogate assisted optimization method and make them more flexible practically. For this purpose, the state-of-the-art surrogate assisted optimizations are investigated. Furthermore, in view of the bottleneck and development of the surrogate assisted optimization and sheet metal forming design, some important issues on the surrogate assisted optimization in support of the sheet metal forming design are analyzed and discussed, involving the description of the sheet metal forming design, off-line and online sampling strategies, space mapping algorithm, high dimensional problems, robust design, some challenges and potential feasible methods. Generally, this paper provides insightful observations into the performance and potential development of these methods in sheet metal forming design.

  16. Modeling of thin heterogeneous sheets in the discontinuous Galerkin method for 3D transient scattering problems

    NASA Astrophysics Data System (ADS)

    Boubekeur, Mohamed; Kameni Ntichi, Abelin; Pichon, Lionel

    2016-02-01

    This paper presents a modeling of heterogeneous sheets in the time domain discontinuous Galerkin method. An homogenization model combined to a sheet interface condition is used to avoid the mesh of these sheets in order to study the transient response of heterogeneous enclosures. The validation of this approach is based on a comparison with the case when the sheet is meshed. To illustrate the efficiency of the interface condition, the simulation of a 3D cavity is performed. Contribution to the topical issue "Numelec 2015 - Elected submissions", edited by Adel Razek

  17. Theoretical modeling of the plasma-assisted catalytic growth and field emission properties of graphene sheet

    SciTech Connect

    Sharma, Suresh C.; Gupta, Neha

    2015-12-15

    A theoretical modeling for the catalyst-assisted growth of graphene sheet in the presence of plasma has been investigated. It is observed that the plasma parameters can strongly affect the growth and field emission properties of graphene sheet. The model developed accounts for the charging rate of the graphene sheet; number density of electrons, ions, and neutral atoms; various elementary processes on the surface of the catalyst nanoparticle; surface diffusion and accretion of ions; and formation of carbon-clusters and large graphene islands. In our investigation, it is found that the thickness of the graphene sheet decreases with the plasma parameters, number density of hydrogen ions and RF power, and consequently, the field emission of electrons from the graphene sheet surface increases. The time evolution of the height of graphene sheet with ion density and sticking coefficient of carbon species has also been examined. Some of our theoretical results are in compliance with the experimental observations.

  18. Modeling the heliospheric current sheet: Solar cycle variations

    NASA Astrophysics Data System (ADS)

    Riley, Pete; Linker, J. A.; Mikić, Z.

    2002-07-01

    In this report we employ an empirically driven, three-dimensional MHD model to explore the evolution of the heliospheric current sheet (HCS) during the course of the solar cycle. We compare our results with a simpler ``constant-speed'' approach for mapping the HCS outward into the solar wind to demonstrate that dynamic effects can substantially deform the HCS in the inner heliosphere (<~5 AU). We find that these deformations are most pronounced at solar minimum and become less significant at solar maximum, when interaction regions are less effective. Although solar maximum is typically associated with transient, rather than corotating, processes, we show that even under such conditions, the HCS can maintain its structure over the course of several solar rotations. While the HCS may almost always be topologically equivalent to a ``ballerina skirt,'' we discuss an interval approaching the maximum of solar cycle 23 (Carrington rotations 1960 and 1961) when the shape would be better described as ``conch shell''-like. We use Ulysses magnetic field measurements to support the model results.

  19. Comparing Galileo Electron Density Measurements to the Khurana and Kivelson Jovian Current Sheet Model

    NASA Astrophysics Data System (ADS)

    Ansher, J. A.; Khurana, K. K.; Gurnett, D. A.; Holland, D. L.; Kivelson, M. G.; Martin, R. F.; Persoon, A. M.

    2002-05-01

    Electron density has been determined throughout much of Galileo's primary mission at Jupiter (December 7, 1995 to November 6, 1997) by observing plasma waves measured by the plasma wave instrument on board the spacecraft. At radial distances less than about 20 RJ from Jupiter, upper hybrid emissions can be used to determine the density, while the low frequency cutoff of continuum radiation can be used to do so at radial distances greater than 20 RJ. The density data set is used to identify spacecraft encounters with Jupiter's magnetotail current sheet during the primary mission by assuming that electron density is highest at the center of the current sheet. These encounters are compared to predictions of the current sheet location made by Khurana and Kivelson's 1998 current sheet model, and data from the Galileo magnetometer instrument. As Jupiter rotates, the spacecraft encounters one pair of plasma sheet crossings during each ten-hour rotation period. During these encounters, Galileo passes through the central current sheet once moving from north to south, and once from south to north. Electron density is usually seen to increase, reach a maximum value when Galileo is near the center of the current sheet, and then decrease as the spacecraft leaves the plasma sheet. Average densities measured at the center of the current sheet range between 1 cm-3 at 20 RJ, and 0.01 cm-3 at 120 RJ. Comparison with the Khurana and Kivelson model indicates good correlation between electron density maxima and predicted current sheet location for radial distances less than about 50 RJ. At larger radial distances, the co-incidence is significantly less. This same radial relationship also exists between the density maxima, and the measured current sheet locations identified by the reversal of the magnetic field's radial component. This may indicate physical differences in current sheet structure at larger radial distances, and potentially suggests adjustments to the Khurana and Kivelson

  20. Current state and future perspectives on coupled ice-sheet - sea-level modelling

    NASA Astrophysics Data System (ADS)

    de Boer, Bas; Stocchi, Paolo; Whitehouse, Pippa L.; van de Wal, Roderik S. W.

    2017-08-01

    The interaction between ice-sheet growth and retreat and sea-level change has been an established field of research for many years. However, recent advances in numerical modelling have shed new light on the precise interaction of marine ice sheets with the change in near-field sea level, and the related stability of the grounding line position. Studies using fully coupled ice-sheet - sea-level models have shown that accounting for gravitationally self-consistent sea-level change will act to slow down the retreat and advance of marine ice-sheet grounding lines. Moreover, by simultaneously solving the 'sea-level equation' and modelling ice-sheet flow, coupled models provide a global field of relative sea-level change that is consistent with dynamic changes in ice-sheet extent. In this paper we present an overview of recent advances, possible caveats, methodologies and challenges involved in coupled ice-sheet - sea-level modelling. We conclude by presenting a first-order comparison between a suite of relative sea-level data and output from a coupled ice-sheet - sea-level model.

  1. Simulating the Antarctic ice sheet in the Late-Pliocene warm period: PLISMIP-ANT, an ice-sheet model intercomparison project

    NASA Astrophysics Data System (ADS)

    de Boer, B.; Dolan, A. M.; Bernales, J.; Gasson, E.; Goelzer, H.; Golledge, N. R.; Sutter, J.; Huybrechts, P.; Lohmann, G.; Rogozhina, I.; Abe-Ouchi, A.; Saito, F.; van de Wal, R. S. W.

    2014-11-01

    In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals in Earth history is of fundamental importance. The Late-Pliocene warm period (also known as the PRISM interval: 3.264 to 3.025 million years before present) can serve as a potential analogue for projected future climates. Although Pliocene ice locations and extents are still poorly constrained, a significant contribution to sea-level rise should be expected from both the Greenland ice sheet and the West and East Antarctic ice sheets based on palaeo sea-level reconstructions. Here, we present results from simulations of the Antarctic ice sheet by means of an international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP-ANT). For the experiments, ice-sheet models including the shallow ice and shelf approximations have been used to simulate the complete Antarctic domain (including grounded and floating ice). We compare the performance of six existing numerical ice-sheet models in simulating modern control and Pliocene ice sheets by a suite of four sensitivity experiments. Ice-sheet model forcing fields are taken from the HadCM3 atmosphere-ocean climate model runs for the pre-industrial and the Pliocene. We include an overview of the different ice-sheet models used and how specific model configurations influence the resulting Pliocene Antarctic ice sheet. The six ice-sheet models simulate a comparable present-day ice sheet, although the models are setup with their own parameter settings. For the Pliocene simulations using the Bedmap1 bedrock topography, some models show a small retreat of the East Antarctic ice sheet, which is thought to have happened during the Pliocene for the Wilkes and Aurora basins. This can be ascribed to either the surface mass balance, as the HadCM3 Pliocene climate shows a significant increase over the Wilkes and Aurora basin, or the initial bedrock topography. For the latter, our simulations with the recently

  2. High-resolution coupled ice sheet-ocean modeling using the POPSICLES model

    NASA Astrophysics Data System (ADS)

    Ng, E. G.; Martin, D. F.; Asay-Davis, X.; Price, S. F.; Collins, W.

    2014-12-01

    It is expected that a primary driver of future change of the Antarctic ice sheet will be changes in submarine melting driven by incursions of warm ocean water into sub-ice shelf cavities. Correctly modeling this response on a continental scale will require high-resolution modeling of the coupled ice-ocean system. We describe the computational and modeling challenges in our simulations of the full Southern Ocean coupled to a continental-scale Antarctic ice sheet model at unprecedented spatial resolutions (0.1 degree for the ocean model and adaptive mesh refinement down to 500m in the ice sheet model). The POPSICLES model couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), with the BISICLES ice-sheet model (Cornford et al., 2012) using a synchronous offline-coupling scheme. Part of the PISCEES SciDAC project and built on the Chombo framework, BISICLES makes use of adaptive mesh refinement to fully resolve dynamically-important regions like grounding lines and employs a momentum balance similar to the vertically-integrated formulation of Schoof and Hindmarsh (2009). Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests like MISMIP3D (Pattyn et al., 2013) and realistic configurations (Favier et al. 2014). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). For the POPSICLES Antarctic-Southern Ocean simulations, ice sheet and ocean models communicate at one-month coupling intervals.

  3. The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 1: Model description

    NASA Astrophysics Data System (ADS)

    Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

    2011-09-01

    We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011) and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP). A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011).

  4. The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 1: Model description

    NASA Astrophysics Data System (ADS)

    Winkelmann, R.; Martin, M. A.; Haseloff, M.; Albrecht, T.; Bueler, E.; Khroulev, C.; Levermann, A.

    2010-08-01

    We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams naturally emerge through this approach and can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid scale representation of calving front motion (Albrecht et al., 2010) and a physically motivated dynamic calving law based on horizontal spreading rates. The model is validated within the Marine Ice Sheet Model Intercomparison Project (MISMIP) and is used for a dynamic equilibrium simulation of Antarctica under present-day conditions in the second part of this paper (Martin et al., 2010).

  5. Results of the Greenland Ice Sheet Model Initialisation Experiments ISMIP6 - initMIP-Greenland

    NASA Astrophysics Data System (ADS)

    Goelzer, H.; Nowicki, S.; Edwards, T.; Beckley, M.; Abe-Ouchi, A.; Aschwanden, A.; Calov, R.; Gagliardini, O.; Gillet-chaulet, F.; Golledge, N. R.; Gregory, J. M.; Greve, R.; Humbert, A.; Huybrechts, P.; Larour, E. Y.; Lipscomb, W. H.; Le cl´h, S.; Lee, V.; Kennedy, J. H.; Pattyn, F.; Payne, A. J.; Rodehacke, C. B.; Rückamp, M.; Saito, F.; Schlegel, N.; Seroussi, H. L.; Shepherd, A.; Sun, S.; Vandewal, R.; Ziemen, F. A.

    2016-12-01

    Earlier large-scale Greenland ice sheet sea-level projections e.g. those run during ice2sea and SeaRISE initiatives have shown that ice sheet initialisation can have a large effect on the projections and gives rise to important uncertainties. The goal of this intercomparison exercise (initMIP-Greenland) is to compare, evaluate and improve the initialization techniques used in the ice sheet modeling community and to estimate the associated uncertainties. It is the first in a series of ice sheet model intercomparison activities within ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6). Two experiments for the large-scale Greenland ice sheet have been designed to allow intercomparison between participating models of 1) the initial present-day state of the ice sheet and 2) the response in two schematic forward experiments. The forward experiments serve to evaluate the initialisation in terms of model drift (forward run without any forcing) and response to a large perturbation (prescribed surface mass balance anomaly). We present and discuss final results of the intercomparison and highlight important uncertainties with respect to projections of the Greenland ice sheet sea-level contribution.

  6. ISMIP6 - initMIP: Greenland ice sheet model initialisation experiments

    NASA Astrophysics Data System (ADS)

    Goelzer, Heiko; Nowicki, Sophie; Payne, Tony; Larour, Eric; Abe Ouchi, Ayako; Gregory, Jonathan; Lipscomb, William; Seroussi, Helene; Shepherd, Andrew; Edwards, Tamsin

    2016-04-01

    Earlier large-scale Greenland ice sheet sea-level projections e.g. those run during ice2sea and SeaRISE initiatives have shown that ice sheet initialisation can have a large effect on the projections and gives rise to important uncertainties. This intercomparison exercise (initMIP) aims at comparing, evaluating and improving the initialization techniques used in the ice sheet modeling community and to estimate the associated uncertainties. It is the first in a series of ice sheet model intercomparison activities within ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6). The experiments are conceived for the large-scale Greenland ice sheet and are designed to allow intercomparison between participating models of 1) the initial present-day state of the ice sheet and 2) the response in two schematic forward experiments. The latter experiments serve to evaluate the initialisation in terms of model drift (forward run without any forcing) and response to a large perturbation (prescribed surface mass balance anomaly). We present and discuss first results of the intercomparison and highlight important uncertainties with respect to projections of the Greenland ice sheet sea-level contribution.

  7. LIVVkit: An extensible, python-based, land ice verification and validation toolkit for ice sheet models

    DOE PAGES

    Kennedy, Joseph H.; Bennett, Andrew R.; Evans, Katherine J.; ...

    2017-03-23

    To address the pressing need to better understand the behavior and complex interaction of ice sheets within the global Earth system, significant development of continental-scale, dynamical ice sheet models is underway. Concurrent to the development of the Community Ice Sheet Model (CISM), the corresponding verification and validation (V&V) process is being coordinated through a new, robust, Python-based extensible software package, the Land Ice Verification and Validation toolkit (LIVVkit). Incorporated into the typical ice sheet model development cycle, it provides robust and automated numerical verification, software verification, performance validation, and physical validation analyses on a variety of platforms, from personal laptopsmore » to the largest supercomputers. LIVVkit operates on sets of regression test and reference data sets, and provides comparisons for a suite of community prioritized tests, including configuration and parameter variations, bit-for-bit evaluation, and plots of model variables to indicate where differences occur. LIVVkit also provides an easily extensible framework to incorporate and analyze results of new intercomparison projects, new observation data, and new computing platforms. LIVVkit is designed for quick adaptation to additional ice sheet models via abstraction of model specific code, functions, and configurations into an ice sheet model description bundle outside the main LIVVkit structure. Furthermore, through shareable and accessible analysis output, LIVVkit is intended to help developers build confidence in their models and enhance the credibility of ice sheet models overall.« less

  8. LIVVkit: An extensible, python-based, land ice verification and validation toolkit for ice sheet models

    NASA Astrophysics Data System (ADS)

    Kennedy, Joseph H.; Bennett, Andrew R.; Evans, Katherine J.; Price, Stephen; Hoffman, Matthew; Lipscomb, William H.; Fyke, Jeremy; Vargo, Lauren; Boghozian, Adrianna; Norman, Matthew; Worley, Patrick H.

    2017-06-01

    To address the pressing need to better understand the behavior and complex interaction of ice sheets within the global Earth system, significant development of continental-scale, dynamical ice sheet models is underway. Concurrent to the development of the Community Ice Sheet Model (CISM), the corresponding verification and validation (V&V) process is being coordinated through a new, robust, Python-based extensible software package, the Land Ice Verification and Validation toolkit (LIVVkit). Incorporated into the typical ice sheet model development cycle, it provides robust and automated numerical verification, software verification, performance validation, and physical validation analyses on a variety of platforms, from personal laptops to the largest supercomputers. LIVVkit operates on sets of regression test and reference data sets, and provides comparisons for a suite of community prioritized tests, including configuration and parameter variations, bit-for-bit evaluation, and plots of model variables to indicate where differences occur. LIVVkit also provides an easily extensible framework to incorporate and analyze results of new intercomparison projects, new observation data, and new computing platforms. LIVVkit is designed for quick adaptation to additional ice sheet models via abstraction of model specific code, functions, and configurations into an ice sheet model description bundle outside the main LIVVkit structure. Ultimately, through shareable and accessible analysis output, LIVVkit is intended to help developers build confidence in their models and enhance the credibility of ice sheet models overall.

  9. Fact Sheet: Documenting Ground-Water Models Selection at Site Contaminated with Radioactive Substance

    EPA Pesticide Factsheets

    This fact sheet summarizes the report by a joint Interagency Environmental Pathway Modeling Working Group. It was designed to be used by technical staff responsible for identifying and implementing flow and transport models to support cleanup decisions.

  10. Free Wake Techniques for Rotor Aerodynamic Analylis. Volume 2: Vortex Sheet Models

    NASA Technical Reports Server (NTRS)

    Tanuwidjaja, A.

    1982-01-01

    Results of computations are presented using vortex sheets to model the wake and test the sensitivity of the solutions to various assumptions used in the development of the models. The complete codings are included.

  11. Calculations of axisymmetric vortex sheet roll-up using a panel and a filament model

    NASA Technical Reports Server (NTRS)

    Kantelis, J. P.; Widnall, S. E.

    1986-01-01

    A method for calculating the self-induced motion of a vortex sheet using discrete vortex elements is presented. Vortex panels and vortex filaments are used to simulate two-dimensional and axisymmetric vortex sheet roll-up. A straight forward application using vortex elements to simulate the motion of a disk of vorticity with an elliptic circulation distribution yields unsatisfactroy results where the vortex elements move in a chaotic manner. The difficulty is assumed to be due to the inability of a finite number of discrete vortex elements to model the singularity at the sheet edge and due to large velocity calculation errors which result from uneven sheet stretching. A model of the inner portion of the spiral is introduced to eliminate the difficulty with the sheet edge singularity. The model replaces the outermost portion of the sheet with a single vortex of equivalent circulation and a number of higher order terms which account for the asymmetry of the spiral. The resulting discrete vortex model is applied to both two-dimensional and axisymmetric sheets. The two-dimensional roll-up is compared to the solution for a semi-infinite sheet with good results.

  12. Simulating the Antarctic ice sheet in the Late-Pliocene warm period: PLISMIP-ANT, an ice-sheet model intercomparison project

    NASA Astrophysics Data System (ADS)

    de Boer, Bas; Dolan, Aisling M.; Hill, Daniel J.; van de Wal, Roderik S. W.

    2014-05-01

    In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals in Earth history is of fundamental importance. The Late-Pliocene Warm Period (also known as the PRISM interval: 3.29 to 2.97 million years before present) can serve as a potential analogue for projected future climates, with a global annual mean surface-air temperature warming of 1.76 °C. Although Pliocene ice locations and surface extents are still poorly constrained, a significant contribution to sea-level rise should be expected from Greenland and West and, possibly, East Antarctica based on palaeo sea-level reconstructions. Here, we present results from simulations of the Antarctic ice sheet by means of an international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP-ANT). We include an overview of the different ice-sheet models used and how specific model configurations influence the resulting Pliocene Antarctic ice sheet. For the experiments, ice-sheet models including the shallow ice and shelf approximations have been used to simulate the complete Antarctic domain (including grounded and floating ice). We compare the performance of the ice-sheet models in simulating modern control and Pliocene ice sheets by a suite of sensitivity experiments. Ice-sheet model forcing fields are taken from the PlioMIP results incorporating multiple coupled atmosphere-ocean general circulation models (GCM). We show that ice-sheet models simulate a present-day ice sheet which is comparable to the observations, and find no systematic biases introduced when using different GCM forcing relative to observational climate forcing. This project includes multiple ice-sheet models forced with multiple climate model output, from which a comprehensive assessment can be made as to the uncertainties of ice-sheet extent on Antarctica. These results may eventually serve as a new constraint on the extent of the Antarctic ice sheet during the Late-Pliocene Warm Period

  13. Surface Energy and Mass Balance Model for Greenland Ice Sheet and Future Projections

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojian

    The Greenland Ice Sheet contains nearly 3 million cubic kilometers of glacial ice. If the entire ice sheet completely melted, sea level would raise by nearly 7 meters. There is thus considerable interest in monitoring the mass balance of the Greenland Ice Sheet. Each year, the ice sheet gains ice from snowfall and loses ice through iceberg calving and surface melting. In this thesis, we develop, validate and apply a physics based numerical model to estimate current and future surface mass balance of the Greenland Ice Sheet. The numerical model consists of a coupled surface energy balance and englacial model that is simple enough that it can be used for long time scale model runs, but unlike previous empirical parameterizations, has a physical basis. The surface energy balance model predicts ice sheet surface temperature and melt production. The englacial model predicts the evolution of temperature and meltwater within the ice sheet. These two models can be combined with estimates of precipitation (snowfall) to estimate the mass balance over the Greenland Ice Sheet. We first compare model performance with in-situ observations to demonstrate that the model works well. We next evaluate how predictions are degraded when we statistically downscale global climate data. We find that a simple, nearest neighbor interpolation scheme with a lapse rate correction is able to adequately reproduce melt patterns on the Greenland Ice Sheet. These results are comparable to those obtained using empirical Positive Degree Day (PDD) methods. Having validated the model, we next drove the ice sheet model using the suite of atmospheric model runs available through the CMIP5 atmospheric model inter-comparison, which in turn built upon the RCP 8.5 (business as usual) scenarios. From this exercise we predict how much surface melt production will increase in the coming century. This results in 4-10 cm sea level equivalent, depending on the CMIP5 models. Finally, we try to bound melt water

  14. Influence of ocean model treatment on late Paleozoic ice sheet growth

    NASA Astrophysics Data System (ADS)

    Tilevitz, C.; Poulsen, C. J.

    2016-12-01

    The late Paleozoic ice age was a period of time 340-250 Ma during which ice sheets grew and shrank across the Gondwanan supercontinent. Atmospheric general circulation models (GCMs) have previously been used to generate late Paleozoic climates suitable for the growth of large ice sheets on the Gondwanan supercontinent to investigate the climate conditions necessary for ice sheet growth. These simulations included a slab ocean with diffusive heat transport that lacks the ability to accurately capture the ocean dynamics of the Paleozoic. In this work, a series of experiments are conducted to investigate the sensitivity of ice sheets to the ocean treatment. Four experiments are conducted: (i) The NCAR Community Earth System Model (CESM)'s fully dynamic ocean is used to explore Permian ice sheet growth under more realistic conditions. (ii)The GENESIS GCM, which uses a slab ocean, is run to directly compare the two ocean models. (iii) The CESM slab ocean model is run using heat fluxes from the CESM simulation. (iv)GENESIS in fixed-SST mode is run using surface temperatures from the CESM simulation. All experiments are conducted for two atmospheric pCO2 concentrations (280 and 560 ppm). Climatologies from this set of experiments are then used to drive the Penn State University three-dimensional ice sheet model (ISM). Our results show that late Paleozoic ice sheets are sensitive to ocean dynamics. The ice sheets that result from both the GENESIS slab and SST cases have volumes of 108 km3 for both CO2 concentrations, and the CESM slab ocean case produced volumes of .5-108 km3 for both cases. The fully dynamic CESM simulation, however, produced ice sheets of 108 km3 for the 280 ppm CO2 case, but only 106 km3 for the 560 ppm CO2 case. This dramatic difference suggests that modeled ice sheets possess a critical sensitivity to pCO2 concentrations in a fully dynamic climate system.

  15. Modelling the long-term impact of surface warming on Greenland ice sheet mass loss

    NASA Astrophysics Data System (ADS)

    Yang, Shuting; Anker Pedersen, Rasmus; Madsen, Marianne S.; Svendsen, Synne H.; Langen, Peter L.

    2017-04-01

    Projections of future sea level changes require understanding of the response of the Greenland ice sheet to future climate change. Numerous feedbacks between the ice sheet and the climate system mean that comprehensive model setups are required to simulate the concurrent ice sheet and climate changes. Here, the ice sheet response to a warming climate has been studied using a model setup consisting of an earth system model (EC-Earth) interactively coupled to an ice sheet model (PISM). The coupled system has been employed for a 1400-year simulation forced by historical radiative forcing from 1850 onward continued along an extended RCP8.5 scenario to beyond year 3200. The simulation reveals that the rate of mass loss from the Greenland ice sheet increases substantially after 2100. The mass loss hereafter continues at a steady rate, even as the warming rate gradually levels off. As the coupled setup does not include the direct impact of oceanic forcing, the mass loss is due to the combination of a negative surface mass balance and a dynamic response to the surface warming. Increased melt exceeds regional precipitation increases in the surface mass balance, while the surface warming increases the enthalpy (per unit volume) of the ice sheet potentially impacting the rheology and thereby the ice flow. The relative roles of the surface mass balance changes and the dynamic response of the ice flow are further investigated using additional ice sheet model sensitivity experiments, where the ice sheet is forced by the time-varying surface mass balance from the coupled model. We aim to quantify the impact of the simulated surface warming on the ice flow by means of a hybrid simulation where the ice sheet is forced by the surface mass balance from the coupled setup while keeping the ice surface temperature constant. This allows for assessment of the impact of the surface mass balance change, isolated from the dynamical response to the warming surface.

  16. Cell sheet transplantation of cultured mesenchymal stem cells enhances bone formation in a rat nonunion model.

    PubMed

    Nakamura, Akifumi; Akahane, Manabu; Shigematsu, Hideki; Tadokoro, Mika; Morita, Yusuke; Ohgushi, Hajime; Dohi, Yoshiko; Imamura, Tomoaki; Tanaka, Yasuhito

    2010-02-01

    Orthopedic surgeons have long been troubled by cases involving nonunion of fractured bones. This study aimed to enhance bone union by cell sheet transplantation of mesenchymal stem cells. A nonunion model was made in rat femur, and rat bone marrow cells were cultured in medium containing dexamethasone and ascorbic acid phosphate to create a cell sheet that could be scraped off as a single sheet. Cell sheets were transplanted onto fractured femurs without a scaffold in the model. X-ray and histological analysis were performed at 2, 4 and 8 weeks. Ultrasonography and biomechanical analysis were performed at 8 weeks. X-ray photographs and histological sections showed callus formation around the fracture site in the cell sheet-transplanted group (sheet group). Bone union was obtained in the sheet group at 8 weeks. By contrast, the control group (without sheet transplantation) showed nonunion of the femur. The results of pullout evaluation in the vertical direction of the femur in the sheet group were significantly better than that of the control group. Analysis of the origin of de novo formed bone using the Sry gene, which was used as a marker for donor cells, showed that transplanted cells without scaffolds could survive and differentiate into osteogenic lineage cells in vivo. These results showed that the femoral fracture in our model was completely cured by the transplantation of a cell sheet created by tissue engineering techniques. Thus, we think that cell sheet transplantation can contribute to hard tissue reconstruction in cases involving nonunion, bone defects and osteonecrosis. (c) 2009 Elsevier Inc. All rights reserved.

  17. A Novel Method of Modeling the Deformation Resistance for Clad Sheet

    SciTech Connect

    Hu Jianliang; Yi Youping; Xie Mantang

    2011-08-22

    Because of the excellent thermal conductivity, the clad sheet (3003/4004/3003) of aluminum alloy is extensively used in various heat exchangers, such as radiator, motorcar air conditioning, evaporator, and so on. The deformation resistance model plays an important role in designing the process parameters of hot continuous rolling. However, the complex behaviors of the plastic deformation of the clad sheet make the modeling very difficult. In this work, a novel method for modeling the deformation resistance of clad sheet was proposed by combining the finite element analysis with experiments. The deformation resistance model of aluminum 3003 and 4004 was proposed through hot compression test on the Gleeble-1500 thermo-simulation machine. And the deformation resistance model of clad sheet was proposed through finite element analysis using DEFORM-2D software. The relationship between cladding ratio and the deformation resistance was discussed in detail. The results of hot compression simulation demonstrate that the cladding ratio has great effects on the resistance of the clad sheet. Taking the cladding ratio into consideration, the mathematical model of the deformation resistance for clad sheet has been proved to have perfect forecasting precision of different cladding ratio. Therefore, the presented model can be used to predict the rolling force of clad sheet during the hot continuous rolling process.

  18. Modeling of Firn Compaction for Estimating Ice-Sheet Mass Change from Observed Ice-Sheet Elevation Change

    NASA Technical Reports Server (NTRS)

    Li, Jun; Zwally, H. Jay

    2011-01-01

    Changes in ice-sheet surface elevation are caused by a combination of ice-dynamic imbalance, ablation, temporal variations in accumulation rate, firn compaction and underlying bedrock motion. Thus, deriving the rate of ice-sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion, which do not involve changes in mass, and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability. We use a 25 year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model. We apply this formulation to ICESat measurements of surface elevation change at three locations on the Greenland ice sheet in order to separate the accumulation-driven changes from the ice-dynamic/ablation-driven changes, and thus to derive the corresponding mass change. Our calculated densities for the accumulation-driven changes range from 410 to 610 kg/cu m, which along with 900 kg/cu m for the dynamic/ablation-driven changes gives average densities ranging from 680 to 790 kg/cu m. We show that using an average (or "effective") density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign.

  19. Regions of negative Bz in the Tsyganenko 1989 model neutral sheet

    NASA Technical Reports Server (NTRS)

    Donovan, E. F.; Rostoker, G.; Huang, C. Y.

    1992-01-01

    A disturbing feature of the Tsyganenko (1989) model magnetic field, namely the occurrence of negative Bz in the model neutral sheet is pointed out. On the basis of observations of Bz in the neutral sheet it is concluded that this is an artifact of the model and not a real effect. This feature of the model should be considered when the model is used either to infer mappings from the ionosphere to the vicinity of the neutral sheet or as a tool in theoretical studies. It is proposed that in the development of future models, it would be useful for the distribution of Bz in the neutral sheet to be imposed as a constraint on the model.

  20. Progress and Challenges in Coupled Ice-Sheet/Climate Modeling with CESM

    NASA Astrophysics Data System (ADS)

    Fyke, J. G.; Sacks, W.; Vizcaino, M.; Lipscomb, W. H.; Price, S. F.

    2014-12-01

    Bidirectional coupling of ice sheet models and climate models opens the door to research of ice-sheet/climate interaction at a global scale. However, difficulties encountered in achieving this coupling have proven non-trivial and include both: 1) Technical challenges. Ocean and atmosphere model components cannot easily handle dynamic boundaries; land surface model components cannot easily simulate exposed glacial ice, firn evolution, or evolving land surfaces; coupling infrastructure cannot easily accept new earth system components; and ice sheet models typically operate at an order of magnitude higher spatial resolution than climate models and on regional domains, and require very long integrations to reach an equilibrium state. 2) Scientific challenges. The glaciological modeling and climate modeling communities often work on topics that cover very different spatiotemporal scales; carry out research using very different models and with very different modeling paradigms; and do not consider coupled ice-sheet/climate behavior across the various ice-sheet/climate physical interfaces. These technical and scientific challenges are being tackled within the Community Earth System Model. The resulting coupled architecture ("CESM-CISM") is now capable of simulating the Greenland ice sheet (GrIS) in the climate system. The model includes a relatively sophisticated representation of surface mass balance (SMB), explicit resolution of important ice-sheet climate communication pathways, and prognostic ice dynamics. First results, underpinned by modelled SMB validation, have explored changes in GrIS mean SMB and its variability, partially-coupled GrIS evolution, and emergence of an anthropogenic signal in SMB under RCP8.5 climate forcing. Ongoing work with the evolving CESM-CISM will set the stage for fully-coupled simulations of Greenland in past and future climates, and also for potential integration of the Antarctic ice sheet into a true coupled modeling framework.

  1. Results of the Greenland ice sheet model initialisation experiments: ISMIP6 - initMIP-Greenland

    NASA Astrophysics Data System (ADS)

    Goelzer, Heiko; Nowicki, Sophie; Edwards, Tamsin; Beckley, Matthew

    2017-04-01

    Ice sheet model initialisation has a large effect on projected future sea-level contributions and gives rise to important uncertainties. The goal of this intercomparison exercise for the continental-scale Greenland ice sheet is therefore to compare, evaluate and improve the initialisation techniques used in the ice sheet modelling community. The initMIP-Greenland project is the first in a series of ice sheet model intercomparison activities within ISMIP6 (Ice Sheet Model Intercomparison Project for CMIP6). The experimental set-up has been designed to allow comparison of the initial present-day state of the Greenland ice sheet between participating models and against observations. Furthermore, the initial states are tested with two schematic forward experiments to evaluate the initialisation in terms of model drift (forward run without any forcing) and response to a large perturbation (prescribed surface mass balance anomaly). We present and discuss results that highlight the wide diversity of data sets, boundary conditions and initialisation techniques used in the community to generate initial states of the Greenland ice sheet.

  2. Greenland Ice Sheet sensitivity and sea level contribution in the mid-Pliocene warm period - Pliocene Ice Sheet Model Intercomparison Project PLISMIP

    NASA Astrophysics Data System (ADS)

    Koenig, S. J.; Dolan, A. M.; de Boer, B.; Stone, E. J.; Hill, D. J.; DeConto, R. M.; Abe-Ouchi, A.; Lunt, D. J.; Pollard, D.; Quiquet, A.; Saito, F.; Savage, J.; van de Wal, R.

    2014-07-01

    The understanding of the nature and behavior of ice sheets in past warm periods is important to constrain the potential impacts of future climate change. The mid-Pliocene Warm Period (2.97 to 3.29 Ma) has global temperatures similar to those projected for future climates, nevertheless Pliocene ice locations and extents are still poorly constrained. We present results from the efforts to simulate mid-Pliocene Greenland ice sheets by means of the international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP). We compare the performance of existing numerical ice sheet models in simulating modern control and mid-Pliocene ice sheets by a suite of sensitivity experiments guided by available proxy records. We quantify equilibrated ice sheet volume on Greenland, identifying a potential range in sea level contributions from warm Pliocene scenarios. A series of statistical measures are performed to quantify the confidence of simulations with focus on inter-model and inter-scenario differences. We find that Pliocene Greenland ice sheets are less sensitive to differences in ice sheet model configurations and internal physical quantities, than to changes in imposed climate forcing. We conclude that Pliocene ice was most likely to be limited to highest elevations in East and South as simulated with the highest confidence and by synthesizing available regional proxies, although extents of those ice caps need to be further constrained by using a range of GCM climate forcings.

  3. Regional localisation of left ventricular sheet structure: integration with current models of cardiac fibre, sheet and band structure.

    PubMed

    Gilbert, Stephen H; Benson, Alan P; Li, Pan; Holden, Arun V

    2007-08-01

    The architecture of the heart remains controversial despite extensive effort and recent advances in imaging techniques. Several opposing and non-mutually compatible models have been proposed to explain cardiac structure, and these models, although limited, have advanced the study and understanding of heart structure, function and development. We describe key areas of similarity and difference, highlight areas of contention and point to the important limitations of these models. Recent research in animal models on the nature, geometry and interaction of cardiac sheet structure allows unification of some seemingly conflicting features of the structural models. Intriguingly, evidence points to significant inter-individual structural variability (within constrained limits) in the canine, leading to the concept of a continuum (or distribution) of cardiac structures. This variability in heart structure partly explains the ongoing debate on myocardial architecture. These developments are used to construct an integrated description of cardiac structure unifying features of fibre, sheet and band architecture that provides a basis for (i) explaining cardiac electromechanics, (ii) computational simulations of cardiac physiology and (iii) designing interventions.

  4. Modelling Greenland ice sheet inception and sustainability during the Late Pliocene

    NASA Astrophysics Data System (ADS)

    Contoux, C.; Dumas, C.; Ramstein, G.; Jost, A.; Dolan, A. M.

    2015-08-01

    Understanding the evolution and dynamics of ice sheet growth during past warm periods is a very important topic considering the potential total removal of the Greenland ice sheet. In this regard, one key event is the full glaciation of Greenland that occurred at the end of the Pliocene warm period, which remains partially unexplained. Previous modelling studies succeeded in reproducing this full glaciation either by imposing an unrealistically low CO2 value or by imposing a partial ice sheet over the surface of Greenland. Although they highlight some fundamental mechanisms, none of these studies are fully satisfactory because they do not reflect realistic conditions occurring during the Late Pliocene. Through a series of simulations with the IPSL-CM5A coupled climate model used to force the GRISLI ice sheet model, we show that a drop in CO2 levels does not lead to an abrupt inception of the Greenland ice sheet. High ablation rates in central and northern Greenland combined with low accumulation prevent such an abrupt inception. Ice sheet inception occurs when low summer insolation and CO2 levels below modern values are combined, the Greenland ice sheet being restricted to the southeast region, where high topography favours this build-up. This ice sheet experiences only partial melting during summer insolation maxima combined with high CO2 levels. Further growth of the ice sheet with recoupling experiments is important at 360 and 280 ppm during insolation minima. Thus, the full glaciation at 2.6 Ma could be the result of a cumulative build-up of the Greenland ice sheet over several orbital cycles, leading to progressively more intense glaciations during low summer insolation periods. Although this result could be a shortcoming of the modelling framework itself, the gradual glacial inception interpreted from the oxygen isotope record could support our scenario.

  5. Tail plasma sheet models derived from Geotail particle data

    NASA Astrophysics Data System (ADS)

    Tsyganenko, N. A.; Mukai, T.

    2003-03-01

    Simple analytical models have been derived for the first time, describing the 2-D distribution (along and across the Earth's magnetotail) of the central plasma sheet (CPS) ion temperature, density, and pressure, as functions of the incoming solar wind and interplanetary magnetic field (IMF) parameters, at distances between 10 and 50 RE. The models are based on a large set of data of the Low-Energy Particle (LEP) and Magnetic Field (MGF) instruments, taken by Geotail spacecraft between 1994 and 1998, comprising 7234 1-min average values of the CPS temperature and density. Concurrent solar wind and IMF data were provided by the Wind and IMP 8 spacecraft. The accuracy of the models was gauged by the correlation coefficient (c.c.) R between the observed and predicted values of a parameter. The CPS ion density N is controlled mostly by the solar wind proton density and by the northward component of the IMF. Being the least stable characteristic of the CPS, it yielded the lowest c.c. RN = 0.57. The CPS temperature T, controlled mainly by the solar wind speed V and the IMF Bz, gave a higher c.c. RT = 0.71. The CPS ion pressure P was best controlled by the solar wind ram pressure Psw and by an IMF-related parameter F = B⟂?, where B⟂ is the perpendicular component of the IMF and θ is its clock angle. In a striking contrast with N and T, the model pressure P revealed a very high c.c. with the data, RP = 0.95, an apparent consequence of the force balance between the CPS and the tail lobe magnetic field. No significant dawn-dusk asymmetry of the CPS was found beyond the distance 10 RE, in line with the observed symmetry of the tail lobe magnetic field. The plasma density N is lowest at midnight and increases toward the tail's flanks. Larger (smaller) solar wind ion densities and northward (southward) IMF Bz result in larger (smaller) N in the CPS. In contrast to the density N, the temperature T peaks at the midnight meridian and falls off toward the dawn/dusk flanks

  6. A new REBO potential based atomistic structural model for graphene sheets.

    PubMed

    Shakouri, A; Ng, T Y; Lin, R M

    2011-07-22

    A new atomistic structural model is developed here for graphene sheets based on the stiffnesses from the REBO potential. Using this model, the flexural vibration natural frequencies and buckling loads of rectangular single-layer graphene sheets of different sizes, chiralities and boundary conditions are calculated. The newly developed atomistic structural model is verified by comparing the calculated fundamental natural frequencies for small-sized graphene sheets with those obtained from ab initio density functional theory (DFT) frequency analysis. The vibration and buckling analysis results are also compared with those of an earlier atomistic structural model based on the AMBER potential as well as the equivalent continuum model for graphene sheets. Through this study, it is observed that graphene sheets display very slight anisotropic characteristics in flexural vibration and buckling. Also, it is shown that the atomistic structural model cannot be replaced by a classical equivalent continuum model such as a plate model. Most significantly, we verify that the new atomistic structural model based on the REBO potential predicts more accurate natural frequencies and buckling loads for graphene sheets, which are considerably lower than those predicted by the earlier atomistic structural model based on the AMBER potential.

  7. Using cosmogenic exposure dates to evaluate modeled Greenland Ice Sheet behavior

    NASA Astrophysics Data System (ADS)

    Applegate, P. J.; Kirchner, N.

    2012-04-01

    Cosmogenic exposure dates represent an untapped data set for evaluation and calibration of ice sheet models on Greenland. Ice sheet models contain simplified numerical descriptions of many processes affecting real ice sheets, including ice flow, surface mass balance, isostasy, and basal sliding. These models provide a crucial means of filling spatial and temporal gaps between paleo-data, and projecting the future behavior of ice sheets in a warming world. Such models must be tuned to data before their results can be considered reliable. Cosmogenic exposure dating of bedrock, erratic boulders, and trimlines on nunataks in Antarctica is often used to tune ice sheet models, but this approach has not been applied in Greenland due to the lack of appropriate topographic "dipsticks." Here, we demonstrate how cosmogenic exposure dates can be used to evaluate ice sheet model results in Greenland. Our starting point is a recently-published, 125 ka-long run with the ice sheet model SICOPOLIS (sicopolis.greveweb.net; Greve et al. 2011, Annals of Glaciology 52, 23-30). For each 10 km square ice sheet model grid cell that contains exposure dates, we project the elevations of the sample sites onto a hypsometric curve constructed using a finer-resolution digital elevation model. The hypsometric curve and the modeled history of ice thickness within each grid box determines when each sampled point became exposed. We then compare the model-predicted exposure times to the cosmogenic-derived apparent exposure times. Model-data agreement is relatively good where and when the margin is terrestrial (near Kangerlussuaq in western Greenland), but poorer where the ice margin interacts with the water (near Jakobshavn, on Store Koldewey Island, and in Scoresby Sund). We comment on the partitioning of residuals between model problems and geomorphic issues in the data. This work is novel because it 1) provides a new methodology for comparing ice sheet model results to chronologic data, and 2

  8. A coronal magnetic field model with horizontal volume and sheet currents

    NASA Technical Reports Server (NTRS)

    Zhao, Xuepu; Hoeksema, J. Todd

    1994-01-01

    When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside the source surface or by limiting the interaction to thin current sheets between oppositely directed field regions. Yet observations and numerical Magnetohydrodynamic (MHD) calculations suggest the presence of non-force-free volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the magnetostatic equilibria developed by Bogdan and Low and the current-sheet modeling technique developed by Schatten. The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coro nal helmet structures better than the current-sheet model.

  9. Application of a Reduced Texture Methodology to Model the Plasticity of Anisotropic Extruded Aluminum Sheets

    NASA Astrophysics Data System (ADS)

    Luo, Meng; Rousselier, Gilles; Mohr, Dirk

    2011-08-01

    A recently developed Reduced Texture Methodology (RTM) featuring (i) a significantly reduced number of crystallographic orientations, (ii) a special experiment-based parameter calibration procedure, and (iii) reasonable computational time for industrial applications is adopted to model the anisotropic plastic behavior of a 2 mm-thick extruded aluminum 6260-T6 sheet. Firstly, the full-thickness sheet is modeled with twelve crystallographic orientations, and the model parameters are identified through an optimization procedure based on uniaxial tensile tests with seven different material orientations. The calibrated model describes well the stress-strain curves and Lankford ratios for all directions, while the optimized grain orientations are in good agreement with EBSD measurements. However, the EBSD results also reveal that the present sheet exhibits a strong heterogeneity through the thickness as far as crystallographic orientations and grain sizes are concerned. To account for this heterogeneity, eight grain orientations are selected out of the total twelve for the full-thickness sheet to model the 0.7 mm-thick central layer of the sheet based on the EBSD measurements. It is found that the reduced eight-grain model provides good predictions of the macroscopic responses in uniaxial tensile tests on reduced-thickness specimens, even without further calibration. A combined calibration is also performed to determine the final set of parameters which provide excellent modeling for both the full-thickness sheet (twelve-grain model) and its central layer (eight-grain model).

  10. A Model for the Electrically Charged Current Sheet of a Pulsar

    NASA Astrophysics Data System (ADS)

    DeVore, C. Richard; Antiochos, Spiro K.; Black, Carrie; Harding, Alice Kust; Kalapotharakos, Constantinos; Kazanas, Demosthenes; Timokhin, Andrey

    2014-06-01

    Global-scale electromagnetohydrodynamic solutions for the magnetosphere of a pulsar consist of a region of low-lying, closed magnetic field near the star bounded by opposite-polarity regions of open magnetic field along which the pulsar wind flows into space. Separating these open-field regions is a magnetic discontinuity - an electric current sheet - consisting of nonneutral plasma. We have developed a self-consistent model for the internal structure of this sheet by generalizing the charge-neutral Vlasov/Maxwell equilibria of Harris (1962) and Hoh (1966) to allow a net electric charge. The resulting equations for the electromagnetic field are identical for Maxwell (nonrelativistic) and Jüttner/Synge (relativistic) distribution functions of the particles. The solutions have a single sign of net charge everywhere, with the minority population concentrated near the current sheet and the majority population completely dominant far from the sheet. As the fractional charge imbalance at the sheet increases, for fixed relative drift speed and total thermal pressure of the particles, both the electric- and magnetic-field strengths far from the sheet increase. The electrostatic force acts to disperse the charged particles from the sheet, so the magnetic force must increase proportionately, relative to the charge-neutral case, to pinch the sheet together and maintain the equilibrium. The charge imbalance in the sheet that can be accommodated has an upper bound, which increases monotonically with the relative drift speed. Implications of the model for the steady-state structure of pulsar magnetospheres will be discussed. The model also provides a rigorous starting point for investigating electromagnetohydrodynamic and kinetic instabilities that could lead to magnetic reconnection and current-sheet disruption in pulsars. Exploratory particle-in-cell simulations of representative equilibria are presented in a companion paper at this conference (C. E. Black et al. 2014).This

  11. Rotator cuff repair using cell sheets derived from human rotator cuff in a rat model.

    PubMed

    Harada, Yoshifumi; Mifune, Yutaka; Inui, Atsuyuki; Sakata, Ryosuke; Muto, Tomoyuki; Takase, Fumiaki; Ueda, Yasuhiro; Kataoka, Takeshi; Kokubu, Takeshi; Kuroda, Ryosuke; Kurosaka, Masahiro

    2017-02-01

    To achieve biological regeneration of tendon-bone junctions, cell sheets of human rotator-cuff derived cells were used in a rat rotator cuff injury model. Human rotator-cuff derived cells were isolated, and cell sheets were made using temperature-responsive culture plates. Infraspinatus tendons in immunodeficient rats were resected bilaterally at the enthesis. In right shoulders, infraspinatus tendons were repaired by the transosseous method and covered with the cell sheet (sheet group), whereas the left infraspinatus tendons were repaired in the same way without the cell sheet (control group). Histological examinations (safranin-O and fast green staining, isolectin B4, type II collagen, and human-specific CD31) and mRNA expression (vascular endothelial growth factor; VEGF, type II collagen; Col2, and tenomodulin; TeM) were analyzed 4 weeks after surgery. Biomechanical tests were performed at 8 weeks. In the sheet group, proteoglycan at the enthesis with more type II collagen and isolectin B4 positive cells were seen compared with in the control group. Human specific CD31-positive cells were detected only in the sheet group. VEGF and Col2 gene expressions were higher and TeM gene expression was lower in the sheet group than in the control group. In mechanical testing, the sheet group showed a significantly higher ultimate failure load than the control group at 8 weeks. Our results indicated that the rotator-cuff derived cell sheet could promote cartilage regeneration and angiogenesis at the enthesis, with superior mechanical strength compared with the control. Treatment for rotator cuff injury using cell sheets could be a promising strategy for enthesis of tendon tissue engineering. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:289-296, 2017. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

  12. Comparison of ice-sheets impact on atmospheric circulation in PMIP3 models

    NASA Astrophysics Data System (ADS)

    Beghin, Pauline; Charbit, Sylvie; Dumas, Christophe; Peterschmitt, Jean-Yves

    2013-04-01

    The presence of continental-scale ice sheets during past ice ages affected the climatic system. With an altitude of several thousand meters and a cold reflective surface, ice sheets influenced the atmospheric circulation through induced changes in planetary waves. Subsequently, temperatures and precipitations were modified all over the Northern Hemisphere. These changes had an important impact on the evolution of ice sheets themselves. Previous studies using General Circulation Models (GCM) forced by Last Glacial Maximum (LGM) conditions have shown that the topography of ice sheets exerted a key role on the pattern of planetary waves (Kageyama and Valdes 2001, Pausata et al., 2011). The aim of this study is to compare the response of eight climatic models to the presence of ice sheets in different contexts, such as the LGM, the pre-industrial period and the Pliocene. To do this, we used the climatic outputs from numerical experiments carried out within the framework of the PMIP3 project. The analysis is made in terms of geopotential height, surface air temperature and snowfall. This approach allows a better understanding of the relationship between ice sheets and planetary waves. Moreover, such an inter-comparison study is a mean to quantify the dispersion between climatic fields simulated by different models and to investigate to which extent the simulated interactions between ice sheets and atmospheric circulation are dependent upon models.

  13. A Model for Shaping Membrane Sheets by Protein Scaffolds

    PubMed Central

    Schweitzer, Yonatan; Shemesh, Tom; Kozlov, Michael M.

    2015-01-01

    Membranes of peripheral endoplasmic reticulum form intricate morphologies consisting of tubules and sheets as basic elements. The physical mechanism of endoplasmic-reticulum shaping has been suggested to originate from the elastic behavior of the sheet edges formed by linear arrays of oligomeric protein scaffolds. The heart of this mechanism, lying in the relationships between the structure of the protein scaffolds and the effective intrinsic shapes and elastic properties of the sheets’ edges, has remained hypothetical. Here we provide a detailed computational analysis of these issues. By minimizing the elastic energy of membrane bending, we determine the effects of a rowlike array of semicircular arclike membrane scaffolds on generation of a membrane fold, which shapes the entire membrane surface into a flat double-membrane sheet. We show, quantitatively, that the sheet’s edge line tends to adopt a positive or negative curvature depending on the scaffold’s geometrical parameters. We compute the effective elastic properties of the sheet edge and analyze the dependence of the equilibrium distance between the scaffolds along the edge line on the scaffold geometry. PMID:26244738

  14. Comparing thin-sheet models with 3-D multilayer models for continental collision

    NASA Astrophysics Data System (ADS)

    Lechmann, S. M.; May, D. A.; Kaus, B. J. P.; Schmalholz, S. M.

    2011-10-01

    Various models have been proposed to explain tectonic deformations during continent collision. A frequently applied model is the thin viscous sheet model which is however not fully 3-D and assumes a priori diffuse thickening as the dominant deformation style. We compare a fully 3-D multilayer numerical model with a corresponding thin viscous sheet numerical model for the scenario of continent indentation. In our comparison we focus on the three basic viscous deformation styles thickening, buckling (folding) and lateral crustal flow. Both numerical models are based on the finite element method (FEM) and employ either a linear or power-law viscous rheology. The 3-D model consists of four layers representing a simplified continental lithosphere: strong upper crust, weak lower crust, strong upper mantle and weak lower mantle. The effective viscosity depth-profile in the 3-D model is used to calculate the depth-averaged effective viscosity used in the thin-sheet model allowing a direct comparison of both models. We quantify the differences in the strain rate and velocity fields, and investigate the evolution of crustal thickening, buckling and crustal flow resulting from the two models for two different phases of deformation: (1) indentation with a constant velocity and (2) gravitational collapse after a decrease of the indenting velocity by a factor of 5. The results indicate that thin-sheet models approximate well the overall large-scale lithospheric deformation, especially during indentation and for a linear viscous rheology. However, in the 3-D model, additional processes such as multilayer buckling and lower crustal flow emerge, which are ignored in the thin-sheet model but dominate the deformation style in the 3-D model within a range of a few hundreds of kilometres around the collision zone and indenter corner. Differences between the 3-D and thin-sheet model are considerably larger for a power-law viscous than for a linear viscous rheology. Buckling and lower

  15. A New Modelling of Blanking for Thin Sheet in Copper Alloys with Dynamic Recrystallization

    SciTech Connect

    Touache, A.; Thibaud, S.; Chambert, J.; Picart, P.

    2007-05-17

    Precision blanking process is widely used by electronic and micromechanical industries to produce small and thin components in large quantities. To take account of the influence of strain rate and temperature on precision blanking of thin sheet in copper alloys, we have proposed a thermo-elasto-visco-plastic modelling. In addition, dynamic recrystallization takes place in Cual copper alloy during the blanking process of thin sheet. A new modelling of dynamic recrystallization based on the thermodynamics of irreversible processes is presented. Blanking simulations of Cual copper sheet are carried out in order to analyze the softening effect induced by dynamic recrystallization.

  16. A Test of Source-Surfae Model Predictions of Heliospheric Current Sheet Inclination

    NASA Technical Reports Server (NTRS)

    Burton, M. E.; Smith, E. J.; Crooker, N. U.; Siscoe, G. L.

    1993-01-01

    The orientation of the heliospheric current sheet predicted from a source surfae model is compared with the orientation determined from minimum variance analysis of ISEE-3 magnetic field data at 1 AU near solar maximum.

  17. Glaciological constraints on current ice mass changes from modelling the ice sheets over the glacial cycles

    NASA Astrophysics Data System (ADS)

    Huybrechts, P.

    2003-04-01

    The evolution of continental ice sheets introduces a long time scale in the climate system. Large ice sheets have a memory of millenia, hence the present-day ice sheets of Greenland and Antarctica are still adjusting to climatic variations extending back to the last glacial period. This trend is separate from the direct response to mass-balance changes on decadal time scales and needs to be correctly accounted for when assessing current and future contributions to sea level. One way to obtain estimates of current ice mass changes is to model the past history of the ice sheets and their underlying beds over the glacial cycles. Such calculations assist to distinguish between the longer-term ice-dynamic evolution and short-term mass-balance changes when interpreting altimetry data, and are helpful to isolate the effects of postglacial rebound from gravity and altimetry trends. The presentation will discuss results obtained from 3-D thermomechanical ice-sheet/lithosphere/bedrock models applied to the Antarctic and Greenland ice sheets. The simulations are forced by time-dependent boundary conditions derived from sediment and ice core records and are constrained by geomorphological and glacial-geological data of past ice sheet and sea-level stands. Current simulations suggest that the Greenland ice sheet is close to balance, while the Antarctic ice sheet is still losing mass, mainly due to incomplete grounding-line retreat of the West Antarctic ice sheet since the LGM. The results indicate that altimetry trends are likely dominated by ice thickness changes but that the gravitational signal mainly reflects postglacial rebound.

  18. Exploring β-Sheet Structure and Interactions with Chemical Model Systems

    PubMed Central

    Nowick, James S.

    2009-01-01

    Conspectus “What I cannot create, I do not understand. ” —Richard P. Feynman β-Sheets consist of extended polypeptide strands (β-strands) connected by a network of hydrogen bonds and occur widely in proteins. Although the importance of β-sheets in the folded structures of proteins has long been recognized, there is a growing recognition of the importance of intermolecular interactions among β-sheets. Intermolecular interactions between the hydrogen-bonding edges of β-sheets constitute a fundamental form of biomolecular recognition (like DNA base pairing) and are involved protein quaternary structure, protein-protein interactions, and peptide and protein aggregation. The importance of β-sheet interactions in biological processes makes them potential targets for intervention in diseases such as AIDS, cancer, and Alzheimer’s. This Account describes my research group’s use of chemical model systems to study the structure and interactions of β-sheets. Chemical model systems provide an excellent vehicle with which to explore β-sheets, because they are smaller, simpler, and easier to manipulate than proteins. Synthetic chemical models also provide the opportunity to control or modulate natural systems or to develop other useful applications and may eventually lead to new drugs with which to treat diseases. In our “artificial β-sheets”, molecular template and turn units are combined with peptides to mimic the structures of parallel and antiparallel β-sheets. The templates and turn units form folded, hydrogen-bonded structures with the peptide groups and help prevent the formation of complex, ill-defined aggregates. Templates that duplicate the hydrogen-bonding pattern of one edge of a peptide β-strand while blocking the other edge have proven particularly valuable in preventing aggregate formation and in promoting the formation of simple monomeric and dimeric structures. Artificial β-sheets that present exposed hydrogen-bonding edges can form well

  19. What is important to get right when modelling the Greenland ice sheet?

    NASA Astrophysics Data System (ADS)

    Mottram, Ruth; Langen, Peter; Boberg, Fredrik; Fausto, Robert; Vandecrux, Baptiste; Box, Jason; Hesselbjerg Christensen, Jens

    2017-04-01

    Ice sheet and glacier models need accurate surface mass balance inputs to accurately reproduce ice sheet extent and likely evolution. In recent years a number of different regional climate models (RCMs) have produced subtly different estimates of ice sheet surface mass balance (SMB) for the Greenland ice sheet. While the total ice sheet SMB number is often similar from these, there can be substantial differences spatially and in terms of the components of surface mass balance: precipitation, melt, runoff, retention and sublimation. The substantial increase in the amount of observational data available from Greenland allows us to compare not only models and data but also to optimize models to get the best SMB estimates. Using carefully designed sensitivity experiments we explore the importance of albedo, retention and refreezing parameters choices, precipitation, model resolution and topography in HIRHAM5, a typical RCM run at 5km resolution over Greenland, to create the best possible representations of surface mass balance of the Greenland ice sheet. Our analysis shows that the 5km resolution of HIRHAM more accurately captures precipitation over the ice sheet, compared with the old 25km resolution. Compared with 68 ice cores from the accumulation area the simulated mean annual net accumulation bias is -5% (correlation coefficient of 0.90). The retention scheme of the model is able to reproduce the subsurface temperature structure and occurrence of perennial firn aquifers and perched ice layers. However, small differences in parameter choices, while important locally, are not significant over the whole ice sheet. Modelled SMB compares favourably with 1041 PROMICE observations. Varying parameter choices means that a regression slope of 0.95-0.97 can be obtained (depending on model configuration) with a correlation coefficient of 0.75-0.86 and mean bias -3%. Our experiments clearly show that albedo choices are more important to modelled SMB than retention parameters

  20. Observational support for the current sheet catastrophe model of substorm current disruption

    NASA Technical Reports Server (NTRS)

    Burkhart, G. R.; Lopez, R. E.; Dusenbery, P. B.; Speiser, T. W.

    1992-01-01

    The principles of the current sheet catastrophe models are briefly reviewed, and observations of some of the signatures predicted by the theory are presented. The data considered here include AMPTE/CCE observations of fifteen current sheet disruption events. According to the model proposed here, the root cause of the current disruption is some process, as yet unknown, that leads to an increase in the k sub A parameter. Possible causes for the increase in k sub A are discussed.

  1. Assessing the formability of metallic sheets by means of localized and diffuse necking models

    NASA Astrophysics Data System (ADS)

    Comşa, Dan-Sorin; Lǎzǎrescu, Lucian; Banabic, Dorel

    2016-10-01

    The main objective of the paper consists in elaborating a unified framework that allows the theoretical assessment of sheet metal formability. Hill's localized necking model and the Extended Maximum Force Criterion proposed by Mattiasson, Sigvant, and Larsson have been selected for this purpose. Both models are thoroughly described together with their solution procedures. A comparison of the theoretical predictions with experimental data referring to the formability of a DP600 steel sheet is also presented by the authors.

  2. Coupled Ice Sheet and Basal Hydrology Regional Model for Dome A, East Antarctica

    NASA Astrophysics Data System (ADS)

    Wolovick, M.; Bell, R. E.; Buck, W. R.; Creyts, T. T.; Abdi, A.

    2011-12-01

    Interactions between an ice sheet and water at its base play an important role in ice sheet dynamics. In addition to causing slip, water accretes to the base of ice sheets, changing rheology and thus flow rate. Recent work (Bell et al, 2011) has shown that frozen-on basal ice can comprise as much as 50% of the ice sheet thickness. The addition of this volume of frozen-on ice affects the thermal budget by releasing latent heat, and requiring that an equal mass of ice melted upstream of the accretion site. Melt and accretion represent source and sink terms in the mass and energy conservation equations of the ice sheet coupled through a subglacial water layer. To investigate these interactions we have developed a coupled, time-dependent numerical model of ice sheet and basal hydrologic dynamics for the Dome A region of East Antarctica. The model uses the Shallow Ice Approximation (SIA) for ice flow with the temperature dependence of rheology and incorporates a full three-dimensional treatment of temperature advection and diffusion. Beneath the ice we incorporate three-dimensional temperature diffusion within the bedrock. The ice model is coupled to a dynamic basal hydrology model that includes both melt and freeze-on. Because water velocities can be much higher than ice velocities, the model uses asynchronous timestepping between the basal hydrology system and the ice system. We investigate whether basal accretion is a steady state or an episodic process and to constrain the rates of accretion. Preliminary results indicate that most of the major accretion sites can be reproduced in a steady state model, and that accretion rates are on the order of millimeters per year. In addition, we use the model to learn about mass and energy fluxes in ice sheet-bed interactions more generally. Future goals include using this model to invert for the accumulation rate and geothermal flux boundary conditions of the ice sheet.

  3. Modeling North American Ice Sheet Response to Changes in Precession and Obliquity

    NASA Astrophysics Data System (ADS)

    Tabor, C.; Poulsen, C. J.; Pollard, D.

    2012-12-01

    Milankovitch theory proposes that changes in insolation due to orbital perturbations dictate the waxing and waning of the ice sheets (Hays et al., 1976). However, variations in solar forcing alone are insufficient to produce the glacial oscillations observed in the climate record. Non-linear feedbacks in the Earth system likely work in concert with the orbital cycles to produce a modified signal (e.g. Berger and Loutre, 1996), but the nature of these feedbacks remain poorly understood. To gain a better understand of the ice dynamics and climate feedbacks associated with changes in orbital configuration, we use a complex Earth system model consisting of the GENESIS GCM and land surface model (Pollard and Thompson, 1997), the Pennsylvania State University ice sheet model (Pollard and DeConto, 2009), and the BIOME vegetation model (Kaplan et al., 2001). We began this study by investigating ice sheet sensitivity to a range of commonly used ice sheet model parameters, including mass balance and albedo, to optimize simulations for Pleistocene orbital cycles. Our tests indicate that choice of mass balance and albedo parameterizations can lead to significant differences in ice sheet behavior and volume. For instance, use of an insolation-temperature mass balance scheme (van den Berg, 2008) allows for a larger ice sheet response to orbital changes than the commonly employed positive degree-day method. Inclusion of a large temperature dependent ice albedo, representing phenomena such as melt ponds and dirty ice, also enhances ice sheet sensitivity. Careful tuning of mass balance and albedo parameterizations can help alleviate the problem of insufficient ice sheet retreat during periods of high summer insolation (Horton and Poulsen, 2007) while still accurately replicating the modern climate. Using our optimized configuration, we conducted a series of experiments with idealized transient orbits in an asynchronous coupling scheme to investigate the influence of obliquity and

  4. Estimating the impact of internal climate variability on ice sheet model simulations

    NASA Astrophysics Data System (ADS)

    Tsai, C. Y.; Forest, C. E.; Pollard, D.

    2016-12-01

    Rising sea level threatens human societies and coastal habitats and melting ice sheets are a major contributor to sea level rise (SLR). Thus, understanding uncertainty of both forcing and variability within the climate system is essential for assessing long-term risk of SLR given their impact on ice sheet evolution. The predictability of polar climate is limited by uncertainties from the given forcing, the climate model response to this forcing, and the internal variability from feedbacks within the fully coupled climate system. Among those sources of uncertainty, the impact of internal climate variability on ice sheet changes has not yet been robustly assessed. Here we investigate how internal variability affects ice sheet projections using climate fields from two Community Earth System Model (CESM) large-ensemble (LE) experiments to force a three-dimensional ice sheet model. Each ensemble member in an LE experiment undergoes the same external forcings but with unique initial conditions. We find that for both LEs, 2m air temperature variability over Greenland ice sheet (GrIS) can lead to significantly different ice sheet responses. Our results show that the internal variability from two fully coupled CESM LEs can cause about 25 35 mm differences of GrIS's contribution to SLR in 2100 compared to present day (about 20% of the total change), and 100m differences of SLR in 2300. Moreover, only using ensemble-mean climate fields as the forcing in ice sheet model can significantly underestimate the melt of GrIS. As the Arctic region becomes warmer, the role of internal variability is critical given the complex nonlinear interactions between surface temperature and ice sheet. Our results demonstrate that internal variability from coupled atmosphere-ocean general circulation model can affect ice sheet simulations and the resulting sea-level projections. This study highlights an urgent need to reassess associated uncertainties of projecting ice sheet loss over the next few

  5. NON-EQUILIBRIUM IONIZATION MODELING OF THE CURRENT SHEET IN A SIMULATED SOLAR ERUPTION

    SciTech Connect

    Shen Chengcai; Reeves, Katharine K.; Raymond, John C.; Murphy, Nicholas A.; Ko, Yuan-Kuen; Lin Jun; Mikic, Zoran; Linker, Jon A.

    2013-08-20

    The current sheet that extends from the top of flare loops and connects to an associated flux rope is a common structure in models of coronal mass ejections (CMEs). To understand the observational properties of CME current sheets, we generated predictions from a flare/CME model to be compared with observations. We use a simulation of a large-scale CME current sheet previously reported by Reeves et al. This simulation includes ohmic and coronal heating, thermal conduction, and radiative cooling in the energy equation. Using the results of this simulation, we perform time-dependent ionization calculations of the flow in a CME current sheet and construct two-dimensional spatial distributions of ionic charge states for multiple chemical elements. We use the filter responses from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory and the predicted intensities of emission lines to compute the count rates for each of the AIA bands. The results show differences in the emission line intensities between equilibrium and non-equilibrium ionization. The current sheet plasma is underionized at low heights and overionized at large heights. At low heights in the current sheet, the intensities of the AIA 94 A and 131 A channels are lower for non-equilibrium ionization than for equilibrium ionization. At large heights, these intensities are higher for non-equilibrium ionization than for equilibrium ionization inside the current sheet. The assumption of ionization equilibrium would lead to a significant underestimate of the temperature low in the current sheet and overestimate at larger heights. We also calculate the intensities of ultraviolet lines and predict emission features to be compared with events from the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory, including a low-intensity region around the current sheet corresponding to this model.

  6. Evaluating ice sheet model performance over the last glacial cycle using paleo data

    NASA Astrophysics Data System (ADS)

    Robinson, Alexander; Alvarez-Solas, Jorge; Montoya, Marisa

    2015-04-01

    Estimating the past evolution of ice sheets is important for improving our understanding of their role in the Earth system and for quantifying their contribution to sea-level changes. Limited but significant paleo data and proxies are available to give insights into past changes that are valid, at least, on a local scale. Meanwhile, models can be used to provide a mechanistic picture of ice sheet changes. Combined data-model comparisons are therefore useful exercises that allow models to be confronted with real-world information and lead to better understanding of the mechanisms driving changes. In turn, models can potentially be used to validate the data by providing a physical explanation for observed phenomena. Here we focus on the evolution of the Greenland ice sheet through the last glacial cycle to highlight common problems and potential opportunities for data-model comparisons. We will present several examples of how present generation model results are inconsistent with estimates from paleo data, either in terms of the boundary forcing given to the model or the resulting characteristics of the ice sheet. We also propose a set of data-model comparisons as the starting point for developing a more standardized paleo model performance check. Incorporating such a test into modeling efforts could generate new insights in coupled climate - ice sheet modeling.

  7. Coupled Models and Parallel Simulations for Three-Dimensional Full-Stokes Ice Sheet Modeling

    SciTech Connect

    Zhang, Huai; Ju, Lili

    2011-01-01

    A three-dimensional full-Stokes computational model is considered for determining the dynamics, temperature, and thickness of ice sheets. The governing thermomechanical equations consist of the three-dimensional full-Stokes system with nonlinear rheology for the momentum, an advective-diffusion energy equation for temperature evolution, and a mass conservation equation for icethickness changes. Here, we discuss the variable resolution meshes, the finite element discretizations, and the parallel algorithms employed by the model components. The solvers are integrated through a well-designed coupler for the exchange of parametric data between components. The discretization utilizes high-quality, variable-resolution centroidal Voronoi Delaunay triangulation meshing and existing parallel solvers. We demonstrate the gridding technology, discretization schemes, and the efficiency and scalability of the parallel solvers through computational experiments using both simplified geometries arising from benchmark test problems and a realistic Greenland ice sheet geometry.

  8. Modelled Growth and Decay of the Cordilleran Ice Sheet Through the Last Glacial Cycle

    NASA Astrophysics Data System (ADS)

    Marshall, S. J.; Banwell, A.

    2015-12-01

    The Cordilleran Ice Sheet in western North America had an enigmatic evolution during the last glacial cycle, developing out of sync with the larger Laurentide and global glaciation. The geological record suggests that the ice sheet emerged late, ca. 45 ka, growing to be a fully-established ice sheet in isotope stages 3 and 2 and deglaciating late in the glacial cycle. This has been a challenge to model, and is a paleoclimatic curiosity, because the western Cordillera of North America is heavily glacierized today, and one would intuitively expect it to act as an inception centre for the Pleistocene ice sheets. The region receives heavy precipitation, and modest cooling should induce large-scale glacier expansion. Indeed, a Cordilleran Ice Sheet quickly nucleates in isotope substage 5d in most ice sheet modeling studies to date, and is a resilient feature throughout the glaciation. The fact that a full-scale Cordilleran Ice Sheet did not develop until relatively late argues for either: (a) ice sheet models that have been inadequate in resolving the process of alpine-style glaciation, i.e., the coalescence of alpine icefields, or (b) a climatic history in western North America that deviated strongly from the hemispheric-scale cooling which drove the growth of the Laurentide and Scandinavian Ice Sheets, as recorded in Greenland. We argue that reasonable reconstructions of Cordilleran Ice Sheet growth and decay implicate a combination of these two considerations. Sufficient model resolution is required to capture the valley-bottom melt that suppresses icefield coalescence, while early-glacial cooling must have been modest in the Pacific sector of North America. We argue for a persistent warm, dry climate relative to that in eastern North America and the Atlantic sector, likely associated with positive feedbacks between atmospheric circulation and the nascent Laurentide Ice Sheet (i.e., peristent circulation patterns similar to those of 2014-2015). This must have been

  9. The model of a collisionless current sheet in a homogeneous gravity field

    NASA Astrophysics Data System (ADS)

    Veselovsky, Igor S.; Kislov, Roman A.; Malova, Helmi V.; Khabarova, Olga V.

    2016-10-01

    The self-consistent 1D kinetic Harris-like model of a collisionless current sheet is developed for the case of the current sheet experiencing the impact of an external uniform gravity field. The ambipolar Pannekoek-Rosseland electric field appears in the system as a result of the additional drift motion of ions and electrons. This produces separation of charges, which is responsible for corresponding changes of the current sheet form. The presence of gravitation leads to formation of asymmetric distributions of the magnetic field as well as the plasma and the current density changes. Our estimations show that gravity-forced disruptions of the current sheet profile may occur in the Mercurial magnetosphere and, most probable, in the Io plasma torus near the Jupiter. Also, the model can be applied to magnetospheres of exoplanets.

  10. Vortex sheet modeling with higher order curved panels. Ph.D Thesis Final Technical Report

    NASA Technical Reports Server (NTRS)

    Nagati, M. G.

    1985-01-01

    A numerical technique is presented for modeling the vortex sheet with a deformable surface definition, along which a continuous vortex strength distribution in the spanwise direction is applied, so that by repeatedly modifying its shape, its true configuration is approached, in the proximity of its generating wing. Design problems requiring the inclusion of a realistic configuration of the vortex sheet are numerous. Examples discussed include: control effectiveness and stability derivatives, longitudinal stability, lateral stability, canards, propellers and helicopter rotors, and trailing vortex hazards.

  11. Intermittent Turbulence and SOC Dynamics in a 2-D Driven Current-Sheet Model

    NASA Technical Reports Server (NTRS)

    Klimas, A. J.; Uritsky, V.; Vinas, A. F.; Vassiliasdis, D.; Baker, D. N.

    2005-01-01

    Borovsky et al. have shown that Earth's magnetotail plasma sheet is strongly turbulent. More recently, Borovsky and Funsten have shown that eddy turbulence dominates and have suggested that the eddy turbulence is driven by fast flows that act as jets in the plasma. Through basic considerations of energy and magnetic flux conservation, these fast flows are thought to be localized to small portions of the total plasma sheet and to be generated by magnetic flux reconnection that is similarly localized. Angelopoulos et al., using single spacecraft Geotail data, have shown that the plasma sheet turbulence exhibits signs of intermittence and Weygand et al., using four spacecraft Cluster data, have confirmed and expanded on this conclusion. Uritsky et al., using Polar UVI image data, have shown that the evolution of bright, nightside, UV auroral emission regions is consistent with many of the properties of systems in self-organized criticality (SOC). Klimas et al. have suggested that the auroral dynamics is a reflection of the dynamics of the fast flows in the plasma. sheet. Their hypothesis is that the transport of magnetic fludenergy through the magnetotail is enabled by scale-free avalanches of localized reconnection whose SOC dynamics are reflected in the auroral UV emission dynamics. A corollary of this hypothesis is that the strong, intermittent, eddy turbulence of the plasma sheet is closely related to its critical dynamics. The question then arises: Can in situ evidence for the SOC dynamics be found in the properties of the plasma sheet turbulence? A 2-dimensional numerical driven current-sheet model of the central plasma sheet has been developed that incorporates an idealized current-driven instability with a resistive MHD system. It has been shown that the model can evolve into SOC in a physically relevant parameter regime. Initial results from a study of intermittent turbulence in this model and the relationship of this turbulence to the model's known SOC

  12. Application of GRACE to the Evaluation of an Ice Flow Model of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Schlegel, N.; Wiese, D. N.; Watkins, M. M.; Larour, E. Y.; Box, J. E.; Fettweis, X.; van den Broeke, M. R.; Morlighem, M.; Boening, C.; Seroussi, H. L.

    2014-12-01

    Quantifying Greenland's future contribution to sea level rise is a challenging task and requires accurate estimates of ice flow sensitivity to climate change. Transient ice flow models are promising tools for estimating future ice sheet behavior. However, confidence in these types of future projections is low, especially because evaluation of model historical runs is so challenging due to the scarcity of continental-wide data for validation. For more than a decade, NASA's GRACE has continuously acquired time-variable measurements of the Earth's gravity field and has provided unprecedented surveillance of mass balance of the ice sheets, offering an opportunity for ice sheet model evaluation. Here, we take advantage of a new high-resolution (~300 km) monthly mascon solution for the purpose of mass balance comparison with an independent, historical ice flow model simulation using the Ice Sheet System Model (ISSM). The comparison highlights which regions of the ice sheet differ most from GRACE. Investigation of regional differences in trends and seasonal amplitudes between simulations forced with three different Regional Climate Model (RCM)-based estimates of surface mass balance (SMB) allows us to make conclusions about the relative contributions of various error sources in the model hindcast. This study constitutes the first regional comparison of GRACE data and an ice sheet model. Conclusions will aid in the improvement of RCM SMB estimates as well as ice sheet simulation estimates of present and future rates of sea level rise. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Program and President's and Director's Fund Program.

  13. Theoretical study of the structural stability of molecular chain sheet models of cellulose crystal allomorphs.

    PubMed

    Uto, Takuya; Mawatari, Sho; Yui, Toshifumi

    2014-08-07

    The structural stabilities of the molecular chain sheets constituting the crystal structures of the cellulose allomorphs Iα, Iβ, II, and IIII were investigated by density functional theory (DFT) optimization of the isolated chain sheet models with finite dimensions. The DFT-optimized chain sheet models of the two native cellulose crystals developed a right-handed twist with a similar amount of twisting. The DFT-optimized cellulose II (010) and (020) models twisted in opposite directions with right- and left-handed chirality, respectively. The cellulose IIII (1-10) model retained the initial flat structure after the DFT-optimization. The structural features of the DFT-optimized chain sheet models were reflected in the structures of the parent crystal models observed in solvated molecular dynamics (MD) simulations. The minor conformations of the hydroxymethyl groups proposed in the real crystal structures were detected in the MD crystal models and the DFT-optimized (010) model of cellulose II. The crystal chain packing and crystal conversions are interpreted in terms of principal chain sheet stacking.

  14. A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)

    NASA Astrophysics Data System (ADS)

    Zhang, Tong; Price, Stephen; Ju, Lili; Leng, Wei; Brondex, Julien; Durand, Gaël; Gagliardini, Olivier

    2017-01-01

    We present a comparison of the numerics and simulation results for two "full" Stokes ice sheet models, FELIX-S (Leng et al. 2012) and Elmer/Ice (Gagliardini et al. 2013). The models are applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d). For the diagnostic experiment (P75D) the two models give similar results ( < 2 % difference with respect to along-flow velocities) when using identical geometries and computational meshes, which we interpret as an indication of inherent consistencies and similarities between the two models. For the standard (Stnd), P75S, and P75R prognostic experiments, we find that FELIX-S (Elmer/Ice) grounding lines are relatively more retreated (advanced), results that are consistent with minor differences observed in the diagnostic experiment results and that we show to be due to different choices in the implementation of basal boundary conditions in the two models. While we are not able to argue for the relative favorability of either implementation, we do show that these differences decrease with increasing horizontal (i.e., both along- and across-flow) grid resolution and that grounding-line positions for FELIX-S and Elmer/Ice converge to within the estimated truncation error for Elmer/Ice. Stokes model solutions are often treated as an accuracy metric in model intercomparison experiments, but computational cost may not always allow for the use of model resolution within the regime of asymptotic convergence. In this case, we propose that an alternative estimate for the uncertainty in the grounding-line position is the span of grounding-line positions predicted by multiple Stokes models.

  15. Adipose-derived stem cell sheet transplantation therapy in a porcine model of chronic heart failure.

    PubMed

    Ishida, Osamu; Hagino, Ikuo; Nagaya, Noritoshi; Shimizu, Tatsuya; Okano, Teruo; Sawa, Yoshiki; Mori, Hidezo; Yagihara, Toshikatsu

    2015-05-01

    Adipose-derived stem cells (ASCs) are a promising resource for cell transplantation therapy for damaged heart tissue. Cell death in the graft early after transplantation represents the main cause of unsatisfactory therapeutic efficacy, but tissue-engineered cell sheets grown in temperature-responsive cell culture dishes may enable improved engraftment of transplanted cells. We investigated the therapeutic potential of this method in chronic myocardial ischemia in swine. We created a porcine model of chronic heart failure by implanting an ameroid constrictor around the main trunk of the left anterior descending artery, just distal to the circumflex branch. Simultaneously, ASCs were obtained from a piece of subcutaneous adipose tissue and expanded to form ASC sheets using temperature-responsive dishes. Four weeks after ameroid constrictor placement, triple-layered ASC sheets were transplanted onto the area of the ischemic myocardium (sheet group, n = 7). Controls (n = 7) received no sheet. Just before and 4 weeks after transplantation, left ventriculography (LVG) and coronary angiography (CAG) were performed. LVG revealed a significant improvement in the left ventricular ejection fraction of the sheet group compared with controls (47.6 ± 2.9% vs 41.4 ± 2.8%, P < 0.05). Furthermore, development of collateral vessels was only detected in the sheet group with right CAG. Histologic analysis demonstrated that engrafted ASC sheets grew to form a thickened layer that included newly formed vessels. ASC sheet transplantation therapy is an intriguing therapeutic method for ischemic heart failure. Copyright © 2015 Elsevier Inc. All rights reserved.

  16. Modelling large-scale ice-sheet-climate interactions following glacial inception

    NASA Astrophysics Data System (ADS)

    Gregory, J. M.; Browne, O. J. H.; Payne, A. J.; Ridley, J. K.; Rutt, I. C.

    2012-10-01

    We have coupled the FAMOUS global AOGCM (atmosphere-ocean general circulation model) to the Glimmer thermomechanical ice-sheet model in order to study the development of ice-sheets in north-east America (Laurentia) and north-west Europe (Fennoscandia) following glacial inception. This first use of a coupled AOGCM-ice-sheet model for a study of change on long palæoclimate timescales is made possible by the low computational cost of FAMOUS, despite its inclusion of physical parameterisations similar in complexity to higher-resolution AOGCMs. With the orbital forcing of 115 ka BP, FAMOUS-Glimmer produces ice caps on the Canadian Arctic islands, on the north-west coast of Hudson Bay and in southern Scandinavia, which grow to occupy the Keewatin region of the Canadian mainland and all of Fennoscandia over 50 ka. Their growth is eventually halted by increasing coastal ice discharge. The expansion of the ice-sheets influences the regional climate, which becomes cooler, reducing the ablation, and ice accumulates in places that initially do not have positive surface mass balance. The results suggest the possibility that the glaciation of north-east America could have begun on the Canadian Arctic islands, producing a regional climate change that caused or enhanced the growth of ice on the mainland. The increase in albedo (due to snow and ice cover) is the dominant feedback on the area of the ice-sheets and acts rapidly, whereas the feedback of topography on SMB does not become significant for several centuries, but eventually has a large effect on the thickening of the ice-sheets. These two positive feedbacks are mutually reinforcing. In addition, the change in topography perturbs the tropospheric circulation, producing some reduction of cloud, and mitigating the local cooling along the margin of the Laurentide ice-sheet. Our experiments demonstrate the importance and complexity of the interactions between ice-sheets and local climate.

  17. Using paleoclimate data to improve models of the Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    King, M. A.; Phipps, S. J.; Roberts, J. L.; White, D.

    2016-12-01

    Ice sheet models are the most descriptive tools available to simulate the future evolution of the Antarctic Ice Sheet (AIS), including its contribution towards changes in global sea level. However, our knowledge of the dynamics of the coupled ice-ocean-lithosphere system is inevitably limited, in part due to a lack of observations. Furthemore, to build computationally efficient models that can be run for multiple millennia, it is necessary to use simplified descriptions of ice dynamics. Ice sheet modeling is therefore an inherently uncertain exercise. The past evolution of the AIS provides an opportunity to constrain the description of physical processes within ice sheet models and, therefore, to constrain our understanding of the role of the AIS in driving changes in global sea level. We use the Parallel Ice Sheet Model (PISM) to demonstrate how paleoclimate data can improve our ability to predict the future evolution of the AIS. A large, perturbed-physics ensemble is generated, spanning uncertainty in the parameterizations of four key physical processes within ice sheet models: ice rheology, ice shelf calving, and the stress balances within ice sheets and ice shelves. A Latin hypercube approach is used to optimally sample the range of uncertainty in parameter values. This perturbed-physics ensemble is used to simulate the evolution of the AIS from the Last Glacial Maximum ( 21,000 years ago) to present. Paleoclimate records are then used to determine which ensemble members are the most realistic. This allows us to use data on past climates to directly constrain our understanding of the past contribution of the AIS towards changes in global sea level. Critically, it also allows us to determine which ensemble members are likely to generate the most realistic projections of the future evolution of the AIS.

  18. Accurate and stable time stepping in ice sheet modeling

    NASA Astrophysics Data System (ADS)

    Cheng, Gong; Lötstedt, Per; von Sydow, Lina

    2017-01-01

    In this paper we introduce adaptive time step control for simulation of the evolution of ice sheets. The discretization error in the approximations is estimated using "Milne's device" by comparing the result from two different methods in a predictor-corrector pair. Using a predictor-corrector pair the expensive part of the procedure, the solution of the velocity and pressure equations, is performed only once per time step and an estimate of the local error is easily obtained. The stability of the numerical solution is maintained and the accuracy is controlled by keeping the local error below a given threshold using PI-control. Depending on the threshold, the time step Δt is bound by stability requirements or accuracy requirements. Our method takes a shorter Δt than an implicit method but with less work in each time step and the solver is simpler. The method is analyzed theoretically with respect to stability and applied to the simulation of a 2D ice slab and a 3D circular ice sheet. The stability bounds in the experiments are explained by and agree well with the theoretical results.

  19. A digital elevation model of the Greenland ice sheet and validation with airborne laser altimeter data

    NASA Technical Reports Server (NTRS)

    Bamber, Jonathan L.; Ekholm, Simon; Krabill, William B.

    1997-01-01

    A 2.5 km resolution digital elevation model (DEM) of the Greenland ice sheet was produced from the 336 days of the geodetic phase of ERS-1. During this period the altimeter was operating in ice-mode over land surfaces providing improved tracking around the margins of the ice sheet. Combined with the high density of tracks during the geodetic phase, a unique data set was available for deriving a DEM of the whole ice sheet. The errors present in the altimeter data were investigated via a comparison with airborne laser altimeter data obtained for the southern half of Greenland. Comparison with coincident satellite data showed a correlation with surface slope. An explanation for the behavior of the bias as a function of surface slope is given in terms of the pattern of surface roughness on the ice sheet.

  20. Buckling analysis of multi-layered graphene sheets based on a continuum mechanics model

    NASA Astrophysics Data System (ADS)

    Jandaghian, A. A.; Rahmani, O.

    2017-05-01

    In this paper, buckling analysis of biaxially compressed multi-layered graphene sheets with a continuum plate model is reported. The equations of motion are analytically solved to obtain closed-form solution for buckling loads of all edges simply supported multi-layered graphene sheets. The interaction of van der Waals (vdWs) pressure between the layers is incorporated in the formulation to determine the buckling behavior of simply supported MLGSs. Explicit formulae are derived for predicting the critical buckling loads of double- and triple-layered graphene sheets, and they clearly indicate the effect of vdW interaction on the critical buckling loads. The critical buckling loads are calculated for various numbers of layered graphene sheets, and the obtained results show that the vdW force has no effect on the first critical buckling load of an MLGS, but plays a significant role in all higher first critical buckling loads for all combinations of m and n.

  1. Light manipulation with flat and conformal inhomogeneous dispersive impedance sheets: an efficient FDTD modeling.

    PubMed

    Jafar-Zanjani, Samad; Cheng, Jierong; Mosallaei, Hossein

    2016-04-10

    An efficient auxiliary differential equation method for incorporating 2D inhomogeneous dispersive impedance sheets in the finite-difference time-domain solver is presented. This unique proposed method can successfully solve optical problems of current interest involving 2D sheets. It eliminates the need for ultrafine meshing in the thickness direction, resulting in a significant reduction of computation time and memory requirements. We apply the method to characterize a novel broad-beam leaky-wave antenna created by cascading three sinusoidally modulated reactance surfaces and also to study the effect of curvature on the radiation characteristic of a conformal impedance sheet holographic antenna. Considerable improvement in the simulation time based on our technique in comparison with the traditional volumetric model is reported. Both applications are of great interest in the field of antennas and 2D sheets.

  2. Finite Element Prediction of Sheet Forming Defects Using Elastic-Plastic, Damage and Localization Models

    NASA Astrophysics Data System (ADS)

    Haddag, Badis; Abed-Meraim, Farid; Balan, Tudor

    2007-05-01

    In this work, an advanced anisotropic elastic-plasticity model is combined with a damage model and a strain localization criterion in the aim to describe accurately the mechanical behavior of sheet metals. Large strain, fully three-dimensional, implicit time integration algorithms are developed for this model and implemented in the finite element code Abaqus. The resulting code is used to predict the strain localization limits as well as the springback after forming of sheet steels. The impact of strain-path dependent hardening models on the limit strains and on the amount of springback is addressed.

  3. Numerical simulations of circular vortex sheets by using two regularization models

    NASA Astrophysics Data System (ADS)

    Sohn, Sung-Ik

    2013-10-01

    We perform numerical simulations for circular vortex sheets by using two regularization models and present the late-time evolution of unstable interfaces. We also give a linear stability analysis for the circular vortex sheet and find that the sheet is always susceptible to the Kelvin-Helmholtz instability. The numerical results show that the motion of the circular sheet is similar to that of the periodic vortex sheet at an early time, but the secondary instability at a late time depends on the wavenumber of the initial perturbation. The interface of the initial two-modes evolves two primary and two secondary roll-ups while the interface of the initial four-modes has four symmetric roll-ups until late times and does not form a secondary instability. The non-symmetric interface of the single-mode develops to a structure more complex than that of the symmetric interfaces, having continuously evolved roll-ups and a strong interaction of spirals. We also give quantitative comparisons of the Krasny model and the Beale-Majda model. The solutions of the two models are similar on a large scale, but are different on a small scale. The solution of the Beale-Majda model exhibits somewhat irregular features for a small regularization parameter while the Krasny model gives well-regularized solutions with fine resolution.

  4. A Hybrid Vortex Sheet / Point Vortex Model for Unsteady Separated Flows

    NASA Astrophysics Data System (ADS)

    Darakananda, Darwin; Eldredge, Jeff D.; Colonius, Tim; Williams, David R.

    2015-11-01

    The control of separated flow over an airfoil is essential for obtaining lift enhancement, drag reduction, and the overall ability to perform high agility maneuvers. In order to develop reliable flight control systems capable of realizing agile maneuvers, we need a low-order aerodynamics model that can accurately predict the force response of an airfoil to arbitrary disturbances and/or actuation. In the present work, we integrate vortex sheets and variable strength point vortices into a method that is able to capture the formation of coherent vortex structures while remaining computationally tractable for control purposes. The role of the vortex sheet is limited to tracking the dynamics of the shear layer immediately behind the airfoil. When parts of the sheet develop into large scale structures, those sections are replaced by variable strength point vortices. We prevent the vortex sheets from growing indefinitely by truncating the tips of the sheets and transfering their circulation into nearby point vortices whenever the length of sheet exceeds a threshold. We demonstrate the model on a variety of canonical problems, including pitch-up and impulse translation of an airfoil at various angles of attack. Support by the U.S. Air Force Office of Scientific Research (FA9550-14-1-0328) with program manager Dr. Douglas Smith is gratefully acknowledged.

  5. The sea level response to ice sheet freshwater forcing in the Community Earth System Model

    NASA Astrophysics Data System (ADS)

    Slangen, Aimée B. A.; Lenaerts, Jan T. M.

    2016-10-01

    We study the effect of a realistic ice sheet freshwater forcing on sea-level change in the fully coupled Community Earth System Model (CESM) showing not only the effect on the ocean density and dynamics, but also the gravitational response to mass redistribution between ice sheets and the ocean. We compare the ‘standard’ model simulation (NO-FW) to a simulation with a more realistic ice sheet freshwater forcing (FW) for two different forcing scenario’s (RCP2.6 and RCP8.5) for 1850-2100. The effect on the global mean thermosteric sea-level change is small compared to the total thermosteric change, but on a regional scale the ocean steric/dynamic change shows larger differences in the Southern Ocean, the North Atlantic and the Arctic Ocean (locally over 0.1 m). The gravitational fingerprints of the net sea-level contributions of the ice sheets are computed separately, showing a regional pattern with a magnitude that is similar to the difference between the NO-FW and FW simulations of the ocean steric/dynamic pattern. Our results demonstrate the importance of ice sheet mass loss for regional sea-level projections in light of the projected increasing contribution of ice sheets to future sea-level rise.

  6. The sea level response to ice sheet freshwater forcing in the Community Earth System Model

    NASA Astrophysics Data System (ADS)

    Slangen, Aimée; Lenaerts, Jan

    2017-04-01

    We show the effect of a realistic ice sheet freshwater forcing on sea-level change in the fully coupled Community Earth System Model (CESM). This not only includes the effect on the ocean density and dynamics, but also the gravitational response to mass redistribution between ice sheets and the ocean. We compare a 'standard' model simulation (NO-FW) to a simulation with a more realistic ice sheet freshwater forcing (FW) for two different climate scenario's (RCP2.6 and RCP8.5) for 1850-2100. We find that the effect on the global mean thermosteric sea-level change is small compared to the total thermosteric change, but on a regional scale the ocean steric/dynamic change shows larger differences in the Southern Ocean, the North Atlantic and the Arctic Ocean (locally over 0.1 m). The gravitational fingerprints of the net sea-level contributions of the ice sheets are computed separately, showing a regional pattern with a magnitude that is similar to the difference between the NO-FW and FW simulations of the ocean steric/dynamic pattern. Our results demonstrate the importance of ice sheet mass loss for regional sea-level projections in light of the projected increasing contribution of ice sheets to future sea-level rise.

  7. Fuels planning: science synthesis and integration; environmental consequences fact sheet 10: The Understory Response Model

    Treesearch

    Steve Sutherland; Melanie Miller

    2005-01-01

    The Understory Response Model is a species-specific computer model that qualitatively predicts change in total species biomass for grasses, forbs, and shrubs after thinning, prescribed fire, or wildfire. The model examines the effect of fuels management on plant survivorship and reproduction. This fact sheet identifies the intended users and uses, required inputs, what...

  8. Fuels planning: science synthesis and integration; environmental consequences fact sheet 11: Smoke Impact Spreadsheet (SIS) model

    Treesearch

    Trent Wickman; Ann Acheson

    2005-01-01

    The Smoke Impact Spreadsheet (SIS) is a simple-to-use planning model for calculating particulate matter (PM) emissions and concentrations downwind of wildland fires. This fact sheet identifies the intended users and uses, required inputs, what the model does and does not do, and tells the user how to obtain the model.

  9. Modelling the Eurasian Ice Sheet through a full (Weichselian) glacial cycle

    NASA Astrophysics Data System (ADS)

    Siegert, Martin J.; Dowdeswell, Julian A.; Hald, Morten; Svendsen, John-Inge

    2001-11-01

    Recently acquired glacial geological and oceanographic datasets provide information on the Weichselian glaciations of Scandinavia and the Eurasian Arctic. A numerical ice-sheet model, forced by global sea level and solar insolation changes, was run to reconstruct ice sheets compatible with these data. A 'maximum' reconstruction assumes that the modern-type temperature distribution across the Eurasian Arctic is reduced by 10 °C at three stages during the Weichselian, which are related to minimum levels of solar insolation. Conversely, a 'minimum' model incorporates a reduction in temperature of only 5 °C in Early and Middle Weichselian time. The 'maximum' reconstruction employs the relatively larger sea-level fall suggested by the δ18O deep-sea record, while the 'minimum' run uses the more conservative sea-level estimate from New Guinea coral reef terraces. The maximum model predicts three major glacial advances in the Weichselian. These compare well to geological evidence for ice-sheet growth during the Early, Middle and Late Weichselian. Geological evidence for the Late Weichselian ice sheet is compatible with either reconstruction if ice growth across the Taymyr Peninsula is curtailed. The models show that ice-sheet advance caused by the interaction of sea level and solar insolation changes yields a time-dependent ice volume function similar to that established from the geological record. Periods of seasonally open water within the seas bordering the Eurasian Arctic generally occur prior to glaciation, and may provide a source of precipitation for ice-sheet growth. In contrast, periods of ice-rafted debris deposition and depletion in surface-ocean δ18O in sea-floor sediments compare well with the model's determination of ice-sheet decay and melting.

  10. Outreach/education interface for Cryosphere models using the Virtual Ice Sheet Laboratory

    NASA Astrophysics Data System (ADS)

    Larour, E. Y.; Halkides, D. J.; Romero, V.; Cheng, D. L.; Perez, G.

    2014-12-01

    In the past decade, great strides have been made in the development of models capable of projecting the future evolution of glaciers and the polar ice sheets in a changing climate. These models are now capable of replicating some of the trends apparent in satellite observations. However, because this field is just now maturing, very few efforts have been dedicated to adapting these capabilities to education. Technologies that have been used in outreach efforts in Atmospheric and Oceanic sciences still have not been extended to Cryospheric Science. We present a cutting-edge, technologically driven virtual laboratory, geared towards outreach and k-12 education, dedicated to the polar ice sheets on Antarctica and Greenland, and their role as major contributors to sea level rise in coming decades. VISL (Virtual Ice Sheet Laboratory) relies on state-of-the art Web GL rendering of polar ice sheets, Android/iPhone and web portability using Javascript, as well as C++ simulations (back-end) based on the Ice Sheet System Model, the NASA model for simulating the evolution of polar ice sheets. Using VISL, educators and students can have an immersive experience into the world of polar ice sheets, while at the same exercising the capabilities of a state-of-the-art climate model, all of it embedded into an education experience that follows the new STEM standards for education.This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Science Program.

  11. A Model for the Electrically Charged Current Sheet of a Pulsar

    NASA Astrophysics Data System (ADS)

    DeVore, C. R.; Antiochos, S. K.; Black, C. E.; Harding, A. K.; Kalapotharakos, C.; Kazanas, D.; Timokhin, A.

    2014-01-01

    Global-scale electromagnetohydrodynamic solutions for the magnetosphere of a pulsar consist of a region of low-lying, closed magnetic field near the star bounded by opposite-polarity regions of open magnetic field along which the pulsar wind flows into space. Separating these open-field regions is a magnetic discontinuity - an electric current sheet - consisting of nonneutral plasma. We have developed a self-consistent model for the internal structure of this sheet by generalizing the charge-neutral Vlasov/Maxwell equilibria of Harris (1962) and Hoh (1966) to allow a net electric charge. The resulting equations for the electromagnetic field are identical for Maxwell (nonrelativistic) and Jüttner/Synge (relativistic) distribution functions of the particles. The solutions have a single sign of net charge everywhere, with the minority population concentrated near the current sheet and the majority population completely dominant far from the sheet. As the fractional charge imbalance at the sheet increases, for fixed relative drift speed and total thermal pressure of the particles, both the electric- and magnetic-field strengths far from the sheet increase. The electrostatic force acts to disperse the charged particles from the sheet, so the magnetic force must increase proportionately, relative to the charge-neutral case, to pinch the sheet together and maintain the equilibrium. The charge imbalance in the sheet that can be accommodated has an upper bound, which increases monotonically with the relative drift speed. In the limit of maximum charge imbalance and field strength, the density of majority particles asymptotically approaches a uniform value far from the sheet, rather than falling exponentially to zero as in the charge-neutral case. This model provides a rigorous starting point for investigating electromagnetohydrodynamic and kinetic instabilities that could lead to magnetic reconnection and current-sheet disruption in pulsar magnetospheres. Exploratory

  12. Modeling Abrupt Change in Global Sea Level Arising from Ocean - Ice-Sheet Interaction

    SciTech Connect

    Holland, David M

    2011-09-24

    It is proposed to develop, validate, and apply a coupled ocean ice-sheet model to simulate possible, abrupt future change in global sea level. This research is to be carried out collaboratively between an academic institute and a Department of Energy Laboratory (DOE), namely, the PI and a graduate student at New York University (NYU) and climate model researchers at the Los Alamos National Laboratory (LANL). The NYU contribution is mainly in the area of incorporating new physical processes into the model, while the LANL efforts are focused on improved numerics and overall model development. NYU and LANL will work together on applying the model to a variety of modeling scenarios of recent past and possible near-future abrupt change to the configuration of the periphery of the major ice sheets. The project's ultimate goal is to provide a robust, accurate prediction of future global sea level change, a feat that no fully-coupled climate model is currently capable of producing. This proposal seeks to advance that ultimate goal by developing, validating, and applying a regional model that can simulate the detailed processes involved in sea-level change due to ocean ice-sheet interaction. Directly modeling ocean ice-sheet processes in a fully-coupled global climate model is not a feasible activity at present given the near-complete absence of development of any such causal mechanism in these models to date.

  13. Can Milankovitch orbital variations initiate the growth of ice sheets in a general circulation model?

    NASA Technical Reports Server (NTRS)

    Rind, D.; Peteet, D.; Kukla, G.

    1989-01-01

    The possibility of initiating the growth of ice sheets by solar insolation variations is examined. The study is conducted using a climate model with three different orbital configurations corresponding to 116,000 and 106,000 yr before the present and a modified insolation field with greater reductions in summer insolation at high northern latitudes. Despite the reduced summer and fall insolation, the model fails to maintain snow cover through the summer at locations of suspected ice sheet initiation. The results suggest that there is a discrepancy between the model's response to Milankovitch perturbations and the geophysical evidence of ice sheet initiation. If the model results are correct, the growth of ice shown by geophysical evidence would have occurred in an extremely ablative environment, demanding a complicated strategy.

  14. Can Milankovitch orbital variations initiate the growth of ice sheets in a general circulation model?

    NASA Technical Reports Server (NTRS)

    Rind, D.; Peteet, D.; Kukla, G.

    1989-01-01

    The possibility of initiating the growth of ice sheets by solar insolation variations is examined. The study is conducted using a climate model with three different orbital configurations corresponding to 116,000 and 106,000 yr before the present and a modified insolation field with greater reductions in summer insolation at high northern latitudes. Despite the reduced summer and fall insolation, the model fails to maintain snow cover through the summer at locations of suspected ice sheet initiation. The results suggest that there is a discrepancy between the model's response to Milankovitch perturbations and the geophysical evidence of ice sheet initiation. If the model results are correct, the growth of ice shown by geophysical evidence would have occurred in an extremely ablative environment, demanding a complicated strategy.

  15. New Anisotropic Constitutive Models For HCP Sheet Forming Simulations

    NASA Astrophysics Data System (ADS)

    Cazacu, Oana; Barlat, Frédéric; Nixon, Michael E.

    2004-06-01

    In this paper, we present a new macroscopic isotropic yield criterion expressed in terms of the principal values of the stress deviator that captures the asymmetry in yielding between tension and compression. Comparisons with the results of polycrystalline simulations performed by Hosford and Allen show that this isotropic criterion describes very well the asymmetry in yielding due to activation of twinning. Furthermore, extensions of this criterion to orthotropy are presented. To introduce anisotropy we use two approaches: (a) the generalized invariants approach of Cazacu and Barlat, and (b) the linear transformation approach (Barlat et al.). The ability of the proposed formulations to describe both the asymmetry and anisotropy in yielding of hcp (Mg-Li) sheet is demonstrated.

  16. SEMIC: an efficient surface energy and mass balance model applied to the Greenland ice sheet

    NASA Astrophysics Data System (ADS)

    Krapp, Mario; Robinson, Alexander; Ganopolski, Andrey

    2017-07-01

    We present SEMIC, a Surface Energy and Mass balance model of Intermediate Complexity for snow- and ice-covered surfaces such as the Greenland ice sheet. SEMIC is fast enough for glacial cycle applications, making it a suitable replacement for simpler methods such as the positive degree day (PDD) method often used in ice sheet modelling. Our model explicitly calculates the main processes involved in the surface energy and mass balance, while maintaining a simple interface and requiring minimal data input to drive it. In this novel approach, we parameterise diurnal temperature variations in order to more realistically capture the daily thaw-freeze cycles that characterise the ice sheet mass balance. We show how to derive optimal model parameters for SEMIC specifically to reproduce surface characteristics and day-to-day variations similar to the regional climate model MAR (Modèle Atmosphérique Régional, version 2) and its incorporated multilayer snowpack model SISVAT (Soil Ice Snow Vegetation Atmosphere Transfer). A validation test shows that SEMIC simulates future changes in surface temperature and surface mass balance in good agreement with the more sophisticated multilayer snowpack model SISVAT included in MAR. With this paper, we present a physically based surface model to the ice sheet modelling community that is general enough to be used with in situ observations, climate model, or reanalysis data, and that is at the same time computationally fast enough for long-term integrations, such as glacial cycles or future climate change scenarios.

  17. Application of a texture parameter model to study planar anisotropy of rolled steel sheets

    NASA Astrophysics Data System (ADS)

    Delannay, L.; Van Houtte, P.; Van Bael, A.; Vanderschueren, D.

    2000-07-01

    A new model for texture characterization in steel sheets has recently been developed. The model makes use of 25 parameters defined in the orientation distribution function (ODF). Experimental textures consisting of the alpha and gamma fibres and/or the Goss and cube components can be reproduced. The model is briefly described. Then, it is shown how industrial steel sheet texture can be optimized with regard to planar anisotropy and formability. The latter study relies on the generation of a series of ODFs which have characteristic differences compared to the given experimental ODF. The r-value profiles are predicted for each of the generated textures using the Taylor theory.

  18. A Model Based Approach to Increase the Part Accuracy in Robot Based Incremental Sheet Metal Forming

    SciTech Connect

    Meier, Horst; Laurischkat, Roman; Zhu Junhong

    2011-01-17

    One main influence on the dimensional accuracy in robot based incremental sheet metal forming results from the compliance of the involved robot structures. Compared to conventional machine tools the low stiffness of the robot's kinematic results in a significant deviation of the planned tool path and therefore in a shape of insufficient quality. To predict and compensate these deviations offline, a model based approach, consisting of a finite element approach, to simulate the sheet forming, and a multi body system, modeling the compliant robot structure, has been developed. This paper describes the implementation and experimental verification of the multi body system model and its included compensation method.

  19. An Excursion Set Model of the Cosmic Web: the Abundance of Sheets, Filaments And Halos

    SciTech Connect

    Shen, Jiajian; Abel, Tom; Mo, Houjun; Sheth, Ravi; /Pennsylvania U.

    2006-01-11

    We discuss an analytic approach for modeling structure formation in sheets, filaments and knots. This is accomplished by combining models of triaxial collapse with the excursion set approach: sheets are defined as objects which have collapsed along only one axis, filaments have collapsed along two axes, and halos are objects in which triaxial collapse is complete. In the simplest version of this approach, which we develop here, large scale structure shows a clear hierarchy of morphologies: the mass in large-scale sheets is partitioned up among lower mass filaments, which themselves are made-up of still lower mass halos. Our approach provides analytic estimates of the mass fraction in sheets, filaments and halos, and its evolution, for any background cosmological model and any initial fluctuation spectrum. In the currently popular {Lambda}CDM model, our analysis suggests that more than 99% of the mass in sheets, and 72% of the mass in filaments, is stored in objects more massive than 10{sup 10}M{sub {circle_dot}} at the present time. For halos, this number is only 46%. Our approach also provides analytic estimates of how halo abundances at any given time correlate with the morphology of the surrounding large-scale structure, and how halo evolution correlates with the morphology of large scale structure.

  20. Modelling the plastic anisotropy of aluminum alloy 3103 sheets by polycrystal plasticity

    NASA Astrophysics Data System (ADS)

    Zhang, K.; Holmedal, B.; Hopperstad, O. S.; Dumoulin, S.

    2014-10-01

    The plastic anisotropy of AA3103 sheets in the cold-rolled condition (H18 temper) and in the fully annealed condition (O temper) was studied experimentally and numerically in this work. The microstructure and texture of the two materials were characterized and the anisotropic plastic behaviour was measured by in-plane uniaxial tension tests along every 15° from the rolling direction to the transverse direction of the sheet. Five polycrystal plasticity models, namely the full-constraint Taylor model, the Alamel model, the Alamel type III model, the visco-plastic self-consistent crystal plasticity model and the crystal plasticity finite element method (CPFEM), were employed to predict the plastic anisotropy in the plane of the sheet. Experimentally observed grain shapes were taken into consideration. In addition, a hybrid modelling method was employed where the advanced yield function Yld2004-18p was calibrated to stress points provided by CPFEM simulations along 89 in-plane strain-paths. This provided a close approximation to in-plane CPFEM predictions and is one convenient way to include the influence of realistic grain morphology on the plastic anisotropy. Based on comparisons between the experimental and the predicted results, the hybrid modelling method is considered as the most accurate way of describing the plastic anisotropy. The Alamel type III and Alamel models are also recommended as accurate and time-efficient models for predicting the plastic anisotropy of the AA3103 sheets in H18 and O tempers.

  1. Improving Climate Literacy Using The Ice Sheet System Model (ISSM): A Prototype Virtual Ice Sheet Laboratory For Use In K-12 Classrooms

    NASA Astrophysics Data System (ADS)

    Halkides, D. J.; Larour, E. Y.; Perez, G.; Petrie, K.; Nguyen, L.

    2013-12-01

    Statistics indicate that most Americans learn what they will know about science within the confines of our public K-12 education system and the media. Next Generation Science Standards (NGSS) aim to remedy science illiteracy and provide guidelines to exceed the Common Core State Standards that most U.S. state governments have adopted, by integrating disciplinary cores with crosscutting ideas and real life practices. In this vein, we present a prototype ';Virtual Ice Sheet Laboratory' (I-Lab), geared to K-12 students, educators and interested members of the general public. I-Lab will allow users to perform experiments using a state-of-the-art dynamical ice sheet model and provide detailed downloadable lesson plans, which incorporate this model and are consistent with NGSS Physical Science criteria for different grade bands (K-2, 3-5, 6-8, and 9-12). The ultimate goal of this website is to improve public climate science literacy, especially in regards to the crucial role of the polar ice sheets in Earth's climate and sea level. The model used will be the Ice Sheet System Model (ISSM), an ice flow model developed at NASA's Jet Propulsion Laboratory and UC Irvine, that simulates the near-term evolution of polar ice sheets (Greenland and Antarctica) and includes high spatial resolution capabilities and data assimilation to produce realistic simulations of ice sheet dynamics at the continental scale. Open sourced since 2011, ISSM is used in cutting edge cryosphere research around the globe. Thru I-Lab, students will be able to access ISSM using a simple, online graphical interface that can be launched from a web browser on a computer, tablet or smart phone. The interface will allow users to select different climate conditions and watch how the polar ice sheets evolve in time under those conditions. Lesson contents will include links to background material and activities that teach observation recording, concept articulation, hypothesis formulation and testing, and

  2. Examining the Reliability and Validity of Clinician Ratings on the Five-Factor Model Score Sheet

    ERIC Educational Resources Information Center

    Few, Lauren R.; Miller, Joshua D.; Morse, Jennifer Q.; Yaggi, Kirsten E.; Reynolds, Sarah K.; Pilkonis, Paul A.

    2010-01-01

    Despite substantial research use, measures of the five-factor model (FFM) are infrequently used in clinical settings due, in part, to issues related to administration time and a reluctance to use self-report instruments. The current study examines the reliability and validity of the Five-Factor Model Score Sheet (FFMSS), which is a 30-item…

  3. Examining the Reliability and Validity of Clinician Ratings on the Five-Factor Model Score Sheet

    ERIC Educational Resources Information Center

    Few, Lauren R.; Miller, Joshua D.; Morse, Jennifer Q.; Yaggi, Kirsten E.; Reynolds, Sarah K.; Pilkonis, Paul A.

    2010-01-01

    Despite substantial research use, measures of the five-factor model (FFM) are infrequently used in clinical settings due, in part, to issues related to administration time and a reluctance to use self-report instruments. The current study examines the reliability and validity of the Five-Factor Model Score Sheet (FFMSS), which is a 30-item…

  4. Atomistic finite element model for axial buckling and vibration analysis of single-layered graphene sheets

    NASA Astrophysics Data System (ADS)

    Rouhi, S.; Ansari, R.

    2012-01-01

    In this article, an atomistic model is developed to study the buckling and vibration characteristics of single-layered graphene sheets (SLGSs). By treating SLGSs as space-frame structures, in which the discrete nature of graphene sheets is preserved, they are modeled using three-dimensional elastic beam elements for the bonds. The elastic moduli of the beam elements are determined via a linkage between molecular mechanics and structural mechanics. Based on this model, the critical compressive forces and fundamental natural frequencies of single-layered graphene sheets with different boundary conditions and geometries are obtained and then compared. It is indicated that the compressive buckling force decreases when the graphene sheet aspect ratio increases. At low aspect ratios, the increase of aspect ratios will result in a significant decrease in the critical buckling load. It is also indicated that increasing aspect ratio at a given side length results in the convergence of buckling envelops associated with armchair and zigzag graphene sheets. The influence of boundary conditions will be studied for different geometries. It will be shown that the influence of boundary conditions is not significant for sufficiently large SLGSs.

  5. Using palaeoclimate data to improve models of the Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Phipps, Steven; King, Matt; Roberts, Jason; White, Duanne

    2017-04-01

    Ice sheet models are the most descriptive tools available to simulate the future evolution of the Antarctic Ice Sheet (AIS), including its contribution towards changes in global sea level. However, our knowledge of the dynamics of the coupled ice-ocean-lithosphere system is inevitably limited, in part due to a lack of observations. Furthemore, to build computationally efficient models that can be run for multiple millennia, it is necessary to use simplified descriptions of ice dynamics. Ice sheet modelling is therefore an inherently uncertain exercise. The past evolution of the AIS provides an opportunity to constrain the description of physical processes within ice sheet models and, therefore, to constrain our understanding of the role of the AIS in driving changes in global sea level. We use the Parallel Ice Sheet Model (PISM) to demonstrate how palaeoclimate data can improve our ability to predict the future evolution of the AIS. A 50-member perturbed-physics ensemble is generated, spanning uncertainty in the parameterisations of three key physical processes within the model: (i) the stress balance within the ice sheet, (ii) basal sliding and (iii) calving of ice shelves. A Latin hypercube approach is used to optimally sample the range of uncertainty in parameter values. This perturbed-physics ensemble is used to simulate the evolution of the AIS from the Last Glacial Maximum ( 21,000 years ago) to present. Palaeoclimate records are then used to determine which ensemble members are the most realistic. This allows us to use data on past climates to directly constrain our understanding of the past contribution of the AIS towards changes in global sea level. Critically, it also allows us to determine which ensemble members are likely to generate the most realistic projections of the future evolution of the AIS.

  6. A new glacial isostatic adjustment model of the Innuitian Ice Sheet, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Simon, K. M.; James, T. S.; Dyke, A. S.

    2015-07-01

    A reconstruction of the Innuitian Ice Sheet (IIS) is developed that incorporates first-order constraints on its spatial extent and history as suggested by regional glacial geology studies. Glacial isostatic adjustment modelling of this ice sheet provides relative sea-level predictions that are in good agreement with measurements of post-glacial sea-level change at 18 locations. The results indicate peak thicknesses of the Innuitian Ice Sheet of approximately 1600 m, up to 400 m thicker than the minimum peak thicknesses estimated from glacial geology studies, but between approximately 1000 to 1500 m thinner than the peak thicknesses present in previous GIA models. The thickness history of the best-fit Innuitian Ice Sheet model developed here, termed SJD15, differs from the ICE-5G reconstruction and provides an improved fit to sea-level measurements from the lowland sector of the ice sheet. Both models provide a similar fit to relative sea-level measurements from the alpine sector. The vertical crustal motion predictions of the best-fit IIS model are in general agreement with limited GPS observations, after correction for a significant elastic crustal response to present-day ice mass change. The new model provides approximately 2.7 m equivalent contribution to global sea-level rise, an increase of +0.6 m compared to the Innuitian portion of ICE-5G. SJD15 is qualitatively more similar to the recent ICE-6G ice sheet reconstruction, which appears to also include more spatially extensive ice cover in the Innuitian region than ICE-5G.

  7. Modeling the transition of the inner plasma sheet from weak to enhanced convection

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Ping; Lyons, Larry R.; Chen, Margaret W.; Toffoletto, Frank R.

    2004-12-01

    We seek to determine whether the adiabatic plasma transport and energization resulting from electric and magnetic drift can quantitatively account for the plasma sheet under weak and enhanced convection observed by Geotail presented in the companion paper [, 2004]. We use a modified Magnetospheric Specification Model to simulate the dynamics and distributions of protons originating from the deep tail and low-latitude boundary layer (LLBL) under an assigned, slowly increasing convection electric field. The magnetic field is Tsyganenko 96 model, modified so that force balance is maintained along the midnight meridian. Our simulation results reproduce well the observed radial profiles and magnitudes of pressure and magnetic field. The changes of these parameters with convection strength are also well reproduced, indicating that the electric and magnetic drift control the large-scale structure of the plasma sheet. The plasma flows near midnight are diverted toward dusk by diamagnetic drift. We obtain a steady state plasma sheet under strong and steady convection, showing that magnetic drift and field line stretching bring the plasma sheet away from possible convection disruption. The protons from the LLBL strongly affect the plasma sheet density and temperature during quiet times but not during enhanced convection. For the same cross-polar cap potential, stronger shielding of the convection electric field results in smaller energization. The penetration electric field is important in moving the plasma sheet to smaller geocentric radial distance. Our results suggest that the frozen-in condition E = -v × B is not valid in the inner plasma sheet because of strong diamagnetic drift.

  8. [Training and development of the nursing staff: a model of spread sheet cost].

    PubMed

    Jerico, Marli de Carvalho; Castilho, Valéria

    2004-09-01

    This paper presents a model of spread sheet cost for training and development programs to the nursing staff in a hospital organization. Significant items of the total cost have been considered in relation to its elaboration and proper functioning. This model is divided into four parts: Item 1--data related to the training programs; Item 2--direct costs of these programs; Item 3--indirect costs (Continuum Educational Center structure), and Item 4--cost amount. The use of spread sheet cost may provide knowledge and managementfor the nurses and nurse managers. However, the related costs should be reviewed according to each service.

  9. FELIX: advances in modeling forward and inverse ice-sheet problems

    NASA Astrophysics Data System (ADS)

    Gunzburger, Max; Hoffman, Mattew; Leng, Wei; Perego, Mauro; Price, Stephen; Salinger, Andrew; Stadler, Georg; Ju, Lili

    2013-04-01

    Several models of different complexity and accuracy have been proposed for describing ice-sheet dynamics. We introduce a parallel, finite element framework for implementing these models, which range from the "shallow ice approximation" up through nonlinear Stokes flow. These models make up the land ice dynamical core of FELIX, which is being developed under the Community Ice Sheet Model. We present results from large-scale simulations of the Greenland ice-sheet, compare models of differing complexity and accuracy, and explore different solution methods for the resulting linear and nonlinear systems. We also address the problem of finding an optimal initial state for Greenland ice-sheet via estimating the spatially varying linear-friction coefficient at the ice-bedrock interface. The problem, which consists of minimizing the mismatch between a specified and computed surface mass balance and/or the mismatch between observed and modeled surface velocities, is solved as an optimal control problem constrained by the governing model equations.

  10. Bayesian calibration of a post-LGM model of Laurentide ice-sheet evolution

    NASA Astrophysics Data System (ADS)

    Tarasov, L.; Peltier, W. R.

    2003-04-01

    Though numerous inferences have been made with regard to the deglaciation history of the Wisconsin North American ice sheet complex, no attempt has been made to place objective confidence ranges on these inferences. Furthermore, past efforts to reconstruct the Wisconsin deglaciation history have relied on restricted discipline-specific constraints. Approaches based on dynamical glacial models have ignored geophysical constraints such as Relative Sea Level histories. Geophysical based reconstructions, on the other hand, have ignored glaciological self-consistency and Marine Limit data. To remedy this situation, we present a Bayesian calibration of a 3D thermo-mechanically coupled ice-sheet systems model using: 1) a large set of Relative Sea Level observations (from 415 sites), 2) Marine Limit observations, 3) a North-South transect of gravity measurements, 4) direct observations of the present day rate of basal uplift at Yellowknife, 5) and a new high-resolution ice margin chronology derived from geological and geomorphological observations. Given the large parameter space (O(20) parameters), Bayesian neural networks, trained from a thousand runs of the ice-sheet systems model, are employed to simulate the glacial model within the statistical analyses. The end result is a posterior distribution for model parameters (and thereby modelled glacial histories) given the observational data sets that thereby also takes into account data uncertainty. Strong support is provided for a multi-domed Laurentide ice-sheet. We also identify key dynamical processes (ie most relevant model parameters) along with critical geographic regions in need of further data.

  11. Geophysical constraints on the dynamics and retreat of the Barents Sea ice sheet as a paleobenchmark for models of marine ice sheet deglaciation

    NASA Astrophysics Data System (ADS)

    Patton, Henry; Andreassen, Karin; Bjarnadóttir, Lilja R.; Dowdeswell, Julian A.; Winsborrow, Monica C. M.; Noormets, Riko; Polyak, Leonid; Auriac, Amandine; Hubbard, Alun

    2015-12-01

    Our understanding of processes relating to the retreat of marine-based ice sheets, such as the West Antarctic Ice Sheet and tidewater-terminating glaciers in Greenland today, is still limited. In particular, the role of ice stream instabilities and oceanographic dynamics in driving their collapse are poorly constrained beyond observational timescales. Over numerous glaciations during the Quaternary, a marine-based ice sheet has waxed and waned over the Barents Sea continental shelf, characterized by a number of ice streams that extended to the shelf edge and subsequently collapsed during periods of climate and ocean warming. Increasing availability of offshore and onshore geophysical data over the last decade has significantly enhanced our knowledge of the pattern and timing of retreat of this Barents Sea ice sheet (BSIS), particularly so from its Late Weichselian maximum extent. We present a review of existing geophysical constraints that detail the dynamic evolution of the BSIS through the last glacial cycle, providing numerical modelers and geophysical workers with a benchmark data set with which to tune ice sheet reconstructions and explore ice sheet sensitivities and drivers of dynamic behavior. Although constraining data are generally spatially sporadic across the Barents and Kara Seas, behaviors such as ice sheet thinning, major ice divide migration, asynchronous and rapid flow switching, and ice stream collapses are all evident. Further investigation into the drivers and mechanisms of such dynamics within this unique paleo-analogue is seen as a key priority for advancing our understanding of marine-based ice sheet deglaciations, both in the deep past and in the short-term future.

  12. Modelling the Laurentide Ice Sheet using improved ice margin chronologies and glacio-isostatic observations

    NASA Astrophysics Data System (ADS)

    Gowan, Evan; Tregoning, Paul; Purcell, Anthony; Lambeck, Kurt

    2013-04-01

    Creating models of the Laurentide ice sheet is challenging, due to the deficiency of chronological constraints and the uneven spatial resolution of data to determine the evolution of the glacio-isostatic response after deglaciation. Previous models relied on uncalibrated radiocarbon constrained margins that proved to have deficiencies in recent studies. Additionally, many recent Laurentide ice sheet models have been developed by incorporating climatic parameters that are poorly resolved for the late glacial period. We present a new ice sheet model by an iterative process of changing basal shear stress values and ice sheet margin location. A particular focus of this study is to determine the thickness and extent of the western Laurentide ice sheet, where there were few well dated observations of glacio-isostatic motion until recently. The volume of an ice sheet during long periods depends mostly on basal shear stress and margin position, which are the main parameters that we vary to fit our model to glacio-isostatic observations. We build our ice model using the assumption of perfectly plastic, steady-state conditions, with variable basal shear stress. Basal shear stress values depend on the surficial geology underlying the ice, and are at a minimum in offshore regions that have soft, deformable sediments, and at a maximum in areas with exposed crystalline bedrock. This approach may not capture dynamic and short lived features of the ice sheet, such as ice streams and stagnant ice, but gives an approximation of average conditions to produce ice volumes that fit geophysical observations. We adjust the margin location when the shear stress conditions alone cannot account for the observed glacio-isostatic response. The constraints on the response include relative sea level benchmarks, sea level highstand positions and proglacial lakes. We repeat the analysis using different rheological profiles to determine the dependence the Earth model has on the estimation of ice

  13. Data assimilation for moving mesh methods with an application to ice sheet modelling

    NASA Astrophysics Data System (ADS)

    Bonan, Bertrand; Nichols, Nancy K.; Baines, Michael J.; Partridge, Dale

    2017-09-01

    We develop data assimilation techniques for non-linear dynamical systems modelled by moving mesh methods. Such techniques are valuable for explicitly tracking interfaces and boundaries in evolving systems. The unique aspect of these assimilation techniques is that both the states of the system and the positions of the mesh points are updated simultaneously using physical observations. Covariances between states and mesh points are generated either by a correlation structure function in a variational context or by ensemble methods. The application of the techniques is demonstrated on a one-dimensional model of a grounded shallow ice sheet. It is shown, using observations of surface elevation and/or surface ice velocities, that the techniques predict the evolution of the ice sheet margin and the ice thickness accurately and efficiently. This approach also allows the straightforward assimilation of observations of the position of the ice sheet margin.

  14. Evaluation of a multi-layer adipose-derived stem cell sheet in a full-thickness wound healing model.

    PubMed

    Lin, Yen-Chih; Grahovac, Tara; Oh, Sun Jung; Ieraci, Matthew; Rubin, J Peter; Marra, Kacey G

    2013-02-01

    Cell sheet technology has been studied for applications such as bone, ligament and skin regeneration. There has been limited examination of adipose-derived stem cells (ASCs) for cell sheet applications. The specific aim of this study was to evaluate ASC sheet technology for wound healing. ASCs were isolated from discarded human abdominal subcutaneous adipose tissue, and ASC cell sheets were created on the surface of fibrin-grafted culture dishes. In vitro examination consisted of the histochemical characterization of the ASC sheets. In vivo experiments consisted of implanting single-layer cell sheets, triple-layer cell sheets or non-treated control onto a full-thickness wound defect (including epidermis, dermis, and subcutaneous fat) in nude mice for 3 weeks. Cell sheets were easily peeled off from the culture dishes using forceps. The single- and triple-layer ASC sheets showed complete extracellular structure via hematoxylin & eosin staining. In vivo, the injury area was measured 7, 10, 14 and 21 days post-treatment to assess wound recovery. The ASC sheet-treated groups' injury area was significantly smaller than that of the non-treated control group at all time points except day 21. The triple-layer ASC sheet treatment significantly enhanced wound healing compared to the single-layer ASC sheet at 7, 10 and 14 days. The density of blood vessels showed that ASC cell sheet treatment slightly enhanced total vessel proliferation compared to the empty wound injury treatment. Our studies indicate that ASC sheets present a potentially viable matrix for full-thickness defect wound healing in a mouse model. Consequently, our ASC sheet technology represents a substantial advance in developing various types of three-dimensional tissues.

  15. A sensitivity analysis for a thermomechanical model of the Antarctic ice sheet and ice shelves

    NASA Astrophysics Data System (ADS)

    Baratelli, F.; Castellani, G.; Vassena, C.; Giudici, M.

    2012-04-01

    The outcomes of an ice sheet model depend on a number of parameters and physical quantities which are often estimated with large uncertainty, because of lack of sufficient experimental measurements in such remote environments. Therefore, the efforts to improve the accuracy of the predictions of ice sheet models by including more physical processes and interactions with atmosphere, hydrosphere and lithosphere can be affected by the inaccuracy of the fundamental input data. A sensitivity analysis can help to understand which are the input data that most affect the different predictions of the model. In this context, a finite difference thermomechanical ice sheet model based on the Shallow-Ice Approximation (SIA) and on the Shallow-Shelf Approximation (SSA) has been developed and applied for the simulation of the evolution of the Antarctic ice sheet and ice shelves for the last 200 000 years. The sensitivity analysis of the model outcomes (e.g., the volume of the ice sheet and of the ice shelves, the basal melt rate of the ice sheet, the mean velocity of the Ross and Ronne-Filchner ice shelves, the wet area at the base of the ice sheet) with respect to the model parameters (e.g., the basal sliding coefficient, the geothermal heat flux, the present-day surface accumulation and temperature, the mean ice shelves viscosity, the melt rate at the base of the ice shelves) has been performed by computing three synthetic numerical indices: two local sensitivity indices and a global sensitivity index. Local sensitivity indices imply a linearization of the model and neglect both non-linear and joint effects of the parameters. The global variance-based sensitivity index, instead, takes into account the complete variability of the input parameters but is usually conducted with a Monte Carlo approach which is computationally very demanding for non-linear complex models. Therefore, the global sensitivity index has been computed using a development of the model outputs in a

  16. The Influence of Earth structure on a coupled Antarctic ice sheet - sea level model

    NASA Astrophysics Data System (ADS)

    Gomez, N. A.; Pollard, D.; Holland, D. M.; Latychev, K.

    2014-12-01

    Earth structure beneath the Antarctic Ice Sheet is characterized by significant lateral variability. A stable, thick craton exists in the east, while the west is underlain by a large continental rift system and a relatively thin lithosphere. Moreover, high resolution seismic tomography indicates slow wave speeds in the shallow mantle below WAIS, suggesting a hot, low viscosity asthenosphere. Variations in viscoelastic Earth structure can impact predictions of relative sea-level change and present-day crustal deformation rates by: 1) altering the timing and geometry of load-induced Earth deformation; and 2) perturbing, via a sea-level feedback (Gomez et al., EPSL, 2013), the timing and extent of the ice-sheet retreat. In this talk we use a coupled ice sheet - sea level model to explore the sensitivity of predictions of glacial isostatic adjustment and ice-sheet evolution in the Antarctic region to variations in Earth model parameters. We begin with a large suite of simulations in which 1-D (depth dependent) viscosity structure is varied over ranges that capture depth profiles inferred beneath the West and East Antarctic. We also present a simulation that incorporate 3-D variations in lithospheric thickness and mantle viscosity. The calculations will focus both on the evolution of the region since the Last Glacial Maximum and on projections of future, climate change driven ice-sheet retreat.

  17. Modeling Primary Breakup: A Three-Dimensional Eulerian Level Set/Vortex Sheet Method for Two-Phase Interface Dynamics

    NASA Technical Reports Server (NTRS)

    Herrmann, M.

    2003-01-01

    This paper is divided into four parts. First, the level set/vortex sheet method for three-dimensional two-phase interface dynamics is presented. Second, the LSS model for the primary breakup of turbulent liquid jets and sheets is outlined and all terms requiring subgrid modeling are identified. Then, preliminary three-dimensional results of the level set/vortex sheet method are presented and discussed. Finally, conclusions are drawn and an outlook to future work is given.

  18. SPH non-Newtonian Model for Ice Sheet and Ice Shelf Dynamics

    SciTech Connect

    Tartakovsky, Alexandre M.; Pan, Wenxiao; Monaghan, Joseph J.

    2012-07-07

    We propose a new three-dimensional smoothed particle hydrodynamics (SPH) non-Newtonian model to study coupled ice sheet and ice shelf dynamics. Most existing ice sheet numerical models use a grid-based Eulerian approach, and are usually restricted to shallow ice sheet and ice shelf approximations of the momentum conservation equation. SPH, a fully Lagrangian particle method, solves the full momentum conservation equation. SPH method also allows modeling of free-surface flows, large material deformation, and material fragmentation without employing complex front-tracking schemes, and does not require re-meshing. As a result, SPH codes are highly scalable. Numerical accuracy of the proposed SPH model is first verified by simulating a plane shear flow with a free surface and the propagation of a blob of ice along a horizontal surface. Next, the SPH model is used to investigate the grounding line dynamics of ice sheet/shelf. The steady position of the grounding line, obtained from our SPH simulations, is in good agreement with laboratory observations for a wide range of bedrock slopes, ice-to-fluid density ratios, and flux. We examine the effect of non-Newtonian behavior of ice on the grounding line dynamics. The non-Newtonian constitutive model is based on Glen's law for a creeping flow of a polycrystalline ice. Finally, we investigate the effect of a bedrock geometry on a steady-state position of the grounding line.

  19. Miocene to recent ice elevation variations from the interior of the West Antarctic ice sheet: Constraints from geologic observations, cosmogenic nuclides and ice sheet modeling

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Sujoy; Ackert, Robert P.; Pope, Allen E.; Pollard, David; DeConto, Robert M.

    2012-07-01

    Observations of long-term West Antarctic Ice Sheet (WAIS) behavior can be used to test and constrain dynamic ice sheet models. Long-term observational constraints are however, rare. Here we present the first constraints on long-term (Miocene-Holocene) WAIS elevation from the interior of the ice sheet near the WAIS divide. We use geologic observations and measurements of cosmogenic 21Ne and 10Be in bedrock surfaces to constrain WAIS elevation variations to <160 m above the present-day ice levels since 7 Ma, and <110 m above present-day ice levels since 5.4 Ma. The cosmogenic nuclide data indicate that bedrock surfaces 35 m above the present-day ice levels had near continuous exposure over the past 3.5 Ma, requiring average interior WAIS elevations to have been similar to, or lower than present, since the beginning of the Pliocene warm period. We use a continental ice sheet model to simulate the history of ice cover at our sampling sites and thereby compute the expected concentration of the cosmogenic nuclides. The ice sheet model indicates that during the past 5 Ma interior WAIS elevations of >65 m above present-day ice levels at the Ohio Range occur only rarely during brief ice sheet highstands, consistent with the observed cosmogenic nuclide data. Furthermore, the model's prediction that highstand elevations have increased on average since the Pliocene is in good agreement with the cosmogenic nuclide data that indicate the highest ice elevation over the past 5 Ma was reached during the highstand at 11 ka. Since the simulated cosmogenic nuclide concentrations derived from the model's ice elevation history are in good agreement with our measurements, we suggest that the model's prediction of more frequent collapsed-WAIS states and smaller WAIS volumes during the Pliocene are also correct.

  20. Plasma Sheet Thickness at Jupiter From Galileo Measurements of Electron Density and a New Model of Jupiter's Magnetic Field

    NASA Astrophysics Data System (ADS)

    Ansher, J. A.; Khurana, K. K.; Kivelson, M. G.; Gurnett, D. A.; Holland, D. L.; Martin, R. F.

    2005-05-01

    Electron density has been determined throughout much of Galileo's primary mission at Jupiter (December 7, 1995 to November 6, 1997) by observing plasma waves measured by the plasma wave instrument on board the spacecraft. The density data set is used here to identify spacecraft encounters with Jupiter's magnetotail plasma sheet during the primary mission by assuming that electron density is highest at the center of the plasma sheet. As Jupiter rotates, the spacecraft encounters one pair of plasma sheet crossings during each ten-hour rotation period. Electron density is usually seen to increase as Galileo enters the plasma sheet, reach a maximum value near the center of the plasma sheet, and then decrease as the spacecraft exits the plasma sheet. This signature is clearest in the data at radial distances between 20 RJ, and 50 RJ from Jupiter. Plasma sheet thickness is determined by identifying the z-coordinate of the spacecraft as it enters and exits the plasma sheet. The z-position is measured with respect to a newer magnetic field model by Khurana and Kivelson. This work seeks to determine the plasma sheet thickness in Jupiter's magnetotail, where other instruments observe a thicker plasma sheet in the midnight and dusk sectors and a thinner, more distinct sheet in Jupiter's dawn sector.

  1. The added value of high-resolution climate modeling of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    van de Berg, Willem Jan; van Meijgaard, Erik; van Ulft, Bert; Machguth, Horst; Noël, Brice; van den Broeke, Michiel

    2016-04-01

    The local surface mass balance (SMB) of glaciers and ice sheets is to a very high extent related to topography. Subsequently, spatial variability in the SMB is also related to the spatial scales in the topography. The typical topographic length scales on the Greenland Ice Sheet are from several to over hundred kilometers. Therefore, regional climate models with resolutions between 5 and 25 kilometers normally capture the SMB of the Greenland Ice Sheet well. In this study, we analyze the added value of high-resolution regional climate simulations compared to statistical downscaling. For this aim, the regional climate model RACMO2 has been run for South Greenland for the period 2007-2014 using resolutions of 60, 20, 6.6 and 2.2 kilometer. Modeled and downscaled SMB from these four simulations are analyzed and evaluated against ablation observations. Our results show that the strong correlation of runoff to elevation makes statistical downscaling a robust tool to refine modeled spatial SMB patterns. However, only high-resolution climate modeling can improve the physical representation of the SMB in lower ablation zone, because the summertime interaction between the warm air over the tundra and the colder air over the ice sheet starts to be resolved. As a result, the runoff in the lower ablation zone is more enhanced compared to lower resolution simulations and statistical downscaled SMB.

  2. Large-scale Ice Discharge Events in a Pure Ice Sheet Model

    NASA Astrophysics Data System (ADS)

    Alverson, K.; Legrand, P.; Papa, B. D.; Mysak, L. A.; Wang, Z.

    2004-05-01

    Sediment cores in the North Atlantic show evidence of periodic large-scale ice discharge events between 60 ka and 10 ka BP. These events occurred with a typical period between 5 kyr and 10 kyr. During each event, a significant amount of ice was discharged from the Hudson Bay region through the Hudson Strait and into the North Atlantic. This input of freshwater through the melting of icebergs is thought to have strongly affected the Atlantic thermohaline circulation. One theory is that these periodic ice discharge events represent an internal oscillation of the ice sheet under constant forcing. A second theory requires some variable external forcing on an unstable ice sheet to produce a discharge event. Using the ice sheet model of Marshall, an attempt is made to simulate periodic large-scale ice discharge events within the framework of the first theory. In this case, ice sheet surges and large-scale discharge events occur as a free oscillation of the ice sheet. An analysis of the activation of ice surge events and the thermodynamic controls on these events is also made.

  3. Greenland ice sheet variability and sensitivity to forcing during the warm Pliocene A numerical modeling study

    NASA Astrophysics Data System (ADS)

    Koenig, Sebastian Jan

    The cryosphere and its interactions with other components of the climate system are considered to be major influences on global climate change through the Cenozoic and into the future. However, fundamental dynamics and secondary feedbacks that drive long-term ice sheet variability on Greenland remain poorly understood. Here, a numerical climate-ice sheet modeling study is conducted with the aim of reconstructing most likely locations, timing and variability of continental ice in the mid to late Pliocene and the transition into the Pleistocene. Simulations using the GENESIS v3 General Circulation Model coupled to the Penn State Ice Sheet-Shelf Model are compared with a range of independent numerical ice sheet model simulations under Pliocene boundary conditions and validated against available proxy reconstructions. This study aims at investigating the sensitivity of an ice-free and glaciated Greenland to changes in climate forcings, and the modulation of those forcings through internal feedbacks with focus on the dynamical thresholds involved in the growth and retreat of continental ice on Greenland. Orbital changes of latitudinal and seasonal solar radiation, in combination with prevalent atmospheric pCO2 levels, are found to pace the timing of the cryospheric response. Internal feedbacks invoked though local surface characteristics on Greenland in concert with far field changes in Arctic sea surface temperature and sea ice conditions control the energy and moisture budget on Greenland with consequences for its mass balance. In the Pliocene, inception of Greenland ice is inhibited during interglacials and ice volume is limited even when orbits are favorable for ice sheet growth. During Pliocene warmth, a present-day Greenland Ice Sheet cannot be maintained and ice was most likely restricted to the highest elevations in the East and South, contributing ˜6m of equivalent sea level rise. This assessment of the sensitivity and survivability of Greenland Ice Sheet in a

  4. Exact energy principle in magnetic reconnection for current-sheet models.

    PubMed

    Yoon, Peter H; Lui, Anthony T Y

    2005-05-06

    On the basis of an exact nonlinear energy principle, it is shown that the change in magnetic topology (i.e., reconnection) in a finite-domain system leads to the conversion of magnetic field energy to particle energy. However, it is also shown that the conversion efficiency gradually disappears as the system size increases. This principle is demonstrated with model current-sheet equilibria including Harris and Fadeev solutions, as well as a current-sheet equilibrium which contains a singular current layer. The finding that energy conversion in reconnection is highly dependent on the system size may have an important implication for numerical simulations performed under finite geometry.

  5. Exact Energy Principle in Magnetic Reconnection for Current-Sheet Models

    SciTech Connect

    Yoon, Peter H.; Lui, Anthony T.Y.

    2005-05-06

    On the basis of an exact nonlinear energy principle, it is shown that the change in magnetic topology (i.e., reconnection) in a finite-domain system leads to the conversion of magnetic field energy to particle energy. However, it is also shown that the conversion efficiency gradually disappears as the system size increases. This principle is demonstrated with model current-sheet equilibria including Harris and Fadeev solutions, as well as a current-sheet equilibrium which contains a singular current layer. The finding that energy conversion in reconnection is highly dependent on the system size may have an important implication for numerical simulations performed under finite geometry.

  6. BRITICE-CHRONO: Constraining rates and style of marine-influenced ice sheet decay to provide a data-rich playground for ice sheet modellers

    NASA Astrophysics Data System (ADS)

    Clark, Chris

    2014-05-01

    Uncertainty exists regarding the fate of the Antarctic and Greenland ice sheets and how they will respond to forcings from sea level and atmospheric and ocean temperatures. If we want to know more about the mechanisms and rate of change of shrinking ice sheets, then why not examine an ice sheet that has fully disappeared and track its retreat through time? If achieved in enough detail such information could become a data-rich playground for improving the next breed of numerical ice sheet models to be used in ice and sea level forecasting. We regard that the last British-Irish Ice Sheet is a good target for this work, on account of its small size, density of information and with its numerous researchers already investigating it. BRITICE-CHRONO is a large (>45 researchers) NERC-funded consortium project comprising Quaternary scientists and glaciologists who will search the seafloor around Britain and Ireland and parts of the landmass in order to find and extract samples of sand, rock and organic matter that can be dated (OSL; Cosmogenic; 14C) to reveal the timing and rate of change of the collapsing British-Irish Ice Sheet. The purpose is to produce a high resolution dataset on the demise on an ice sheet - from the continental shelf edge and across the marine to terrestrial transition. Some 800 new date assessments will be added to those that already exist. This poster reports on the hypotheses that underpin the work. Data on retreat will be collected by focusing on 8 transects running from the continental shelf edge to a short distance (10s km) onshore and acquiring marine and terrestrial samples for geochronometric dating. The project includes funding for 587 radiocarbon, 140 OSL and 158 TCN samples for surface exposure dating; with sampling accomplished by two research cruises and 16 fieldwork campaigns. Results will reveal the timing and rate of change of ice margin recession for each transect, and combined with existing landform and dating databases, will be

  7. A synchronous strobed laser light sheet for helicopter model rotor flow visualization

    NASA Technical Reports Server (NTRS)

    Leighty, Bradley D.; Rhodes, David B.; Jones, Stephen B.; Franke, John M.

    1990-01-01

    A synchronous, strobed laser light sheet has been developed for use in flow visualization of a helicopter rotor model. The light sheet strobe circuit included selectable blade position, strobe duration, and multiple pulses per revolution for rotors having 2 to 9 blades. The flow was seeded with propylene glycol. Between runs, a calibration grid board was placed in the plane of the laser sheet and recorded with the video camera at the position used to record the flow field. A slip-sync mode permitted slow motion visualization of the flow field over complete rotations of the rotor. The system was used to make two-dimensional flow field cuts of a four-bladed rotor operating at advance ratio of 0.37 at wind tunnel speeds up to 79.25 meters per second (260 feet per second).

  8. PISM, a Parallel Ice Sheet Model (stable0.3 release)

    NASA Astrophysics Data System (ADS)

    Bueler, Ed; Aschwanden, Andy; Della Guistina, Daniella; Hock, Regine; Khroulev, Constantine; Maxwell, David; Truffer, Martin

    2010-05-01

    The PISM project provides an open source, well-documented, completely-parallel, high-resolution ice sheet model. It has these features: (1) a hierarchy of available stress balances, including shallow ice and shelf approximations, a hybrid of these, and a (planned) higher-order scheme, (2) verification and validation tools, (3) a polythermal, enthalpy-based conservation of energy scheme, (4) inversion of surface velocities (planned), and (5) extensible coupling to atmospheric and ocean circulation and climate models. This year's stable release demonstrates the ability of PISM to model the whole Greenland ice sheet at uniform 2 km resolution, running on more than 200 processors using PETSc/MPI. The result is close approximation to present-day surface velocity measurements. Our poster shows preliminary results from the SeaRISE assessment of sea level rise, the application of PISM to the polythermal glacier Storglaciaren, and the application to the whole Antarctic ice sheet at high resolution. It also gives a quick reference "cheat sheet" for users of PISM. PISM is funded by NASA's Modeling, Analysis, and Prediction program.

  9. Analysis of the heliospheric current sheet at Earth's orbit and model comparisons

    NASA Technical Reports Server (NTRS)

    Lepping, R. P.; Szabo, A.; Peredo, M.; Hoeksema, T.

    1995-01-01

    IMP 8 magnetic field data for the first half of the year 1994, i.e., for about 6 solar rotations, are analyzed around regions of sector boundary crossings with the purpose of obtaining both gross- and fine-scale characteristics of the related heliospheric current sheets separating the observed sectors. For purposes of estimating the attitudes of the normals to the sector boundaries. analysis intervals (sometimes 30 min or more in length) allowing the field to fully complete an excursion of about 180 deg were used in the study, which consisted of variance analyses of the field within those intervals. The resulting boundary normals were analyzed and compared to known (generic) models of projected heliospheric current sheets and to a coronal field model for the same time period. One of the most outstanding features of the resulting ensemble of estimated boundary normals for this period is that they strongly prefer low inclinations, indicating that the observations do not support a 1 AU model that predicts a current sheet whose surface is approximately parallel with the sun's equator, such as the 'sombrero' model. They instead support a model that predicts a relatively high inclination current sheet at 1 AU. Also the normals assume a surprisingly large range of longitudes, somewhat favoring those consistent with a Parker model (45 deg and 225 deg) and/or radial alignment (0 deg and 180 deg). These boundary structures, as defined, are shown typically to be as broad as several hundred proton gyroradii, but having embedded within them very thin structures associated with stronger currents. Such thin structures have normals usually differing markedly from the gross boundary. For some crossings there are indications of a wave-like structure in the current sheet as it passed the spacecraft.

  10. The sea-level fingerprint of the Antarctic ice sheet: an ensemble GIA modelling approach

    NASA Astrophysics Data System (ADS)

    Spada, Giorgio; Galassi, Gaia; Melini, Daniele

    2017-04-01

    During the last decade, Glacial Isostatic Adjustment (GIA) modelling has seen a considerable development, stimulated by the increasing number and quality of sea-level observations and of various geodetic constraints. The fundamental equation of GIA (the Sea Level Equation) accounts for a number of physical ingredients that make GIA modelling quite realistic, such as rotational effects on sea-level change, the migration of the shorelines, and the time-evolving topography in the presence of marine based ice. However, concerning the spatiotemporal distribution of the late-Pleistocene ice sheets, the GIA models published in the literature by different groups are characterised by significantly different features. These are the volumes of the ice sheets at the Last Glacial Maximum, the presence and the duration of abrupt melting episodes (meltwater pulses) and the timing of the end of deglaciation. These differences can be mainly attributed to the different sets of proxies employed to constrain the melting chronology and, sometimes, to different assumptions about the Earth's viscosity profile. One of most important sources of uncertainty is the melting chronology of the Antarctic ice sheet, which is poorly constrained by the limited amount of relative sea-level data available in the near field of the ice sheet. To test whether the GIA models developed so far for the deglaciation of Antarctic ice sheet are converging or not towards a unique solution, here we collectively consider the models of the melting history of Antarctica published in the literature so far and for each of them we solve the Sea Level Equation. Following a multi-model ensemble approach, we estimate the ensemble mean and its uncertainty, in terms of the geometry and of the time history of the sea-level fingerprints.

  11. A Smoothed Particle Hydrodynamics Model for Ice Sheet and Ice Shelf Dynamics

    SciTech Connect

    Pan, Wenxiao; Tartakovsky, Alexandre M.; Monaghan, Joseph J.

    2012-02-08

    Mathematical modeling of ice sheets is complicated by the non-linearity of the governing equations and boundary conditions. Standard grid-based methods require complex front tracking techniques and have limited capability to handle large material deformations and abrupt changes in bottom topography. As a consequence, numerical methods are usually restricted to shallow ice sheet and ice shelf approximations. We propose a new smoothed particle hydrodynamics (SPH) model for coupled ice sheet and ice shelf dynamics. SPH is a fully Lagrangian particle method. It is highly scalable and its Lagrangian nature and meshless discretization are well suited to the simulation of free surface flows, large material deformation, and material fragmentation. In this paper SPH is used to study ice sheet/ice shelf behavior, and the dynamics of the grounding line. The steady state position of the grounding line obtained from the SPH simulations is in good agreement with laboratory observations for a wide range of simulated bedrock slopes, and density ratios similar to those of ice and sea water. The numerical accuracy of the SPH algorithm is further verified by simulating the plane shear flow of two immiscible fluids and the propagation of a highly viscous blob of fluid along a horizontal surface. In the experiment, the ice was represented with a viscous newtonian fluid. For consistency, in the described SPH model the ice is also modeled as a viscous newtonian fluid. Typically, ice sheets are modeled as a non-Newtonian fluid, accounting for the changes in the mechanical properties of ice. Implementation of a non-Newtonian rheology in the SPH model is the subject of our ongoing research.

  12. Modelling sheet erosion on steep slopes in the loess region of China

    NASA Astrophysics Data System (ADS)

    Wu, Bing; Wang, Zhanli; Zhang, Qingwei; Shen, Nan; Liu, June

    2017-10-01

    The relationship of sheet erosion rate (SE), slope gradient (S) and rainfall intensity (I), and hydraulic parameters, such as flow velocity (V), shear stress (τ), stream power (Ω) and unit stream power (P), was investigated to derive an accurate experimental model. The experiment was conducted at slopes of 12.23%, 17.63%, 26.8%, 36.4%, 40.4% and 46.63% under I of 48, 60, 90, 120, 138 and 150 mm h-1, respectively, using simulated rainfall. Results showed that sheet erosion rate increased as a power function with rainfall intensity and slope gradient with R2 = 0.95 and Nash-Sutcliffe model efficiency (NSE) = 0.87. Sheet erosion rate was more sensitive to rainfall intensity than to slope gradient. It increased as a power function with flow velocity, which was satisfactory for predicting sheet erosion rate with R2 = 0.95 and NSE = 0.81. Shear stress and stream power could be used to predict sheet erosion rate accurately with a linear function equation. Stream power (R2 = 0.97, NSE = 0.97) was a better predictor of sheet erosion rather than shear stress (R2 = 0.90, NSE = 0.89). However, a prediction based on unit stream power was poor. The new equation (i.e. SE = 7.5 ×1012S1.43I3.04 and SE = 0.06 Ω - 0.0003 and SE = 0.011 τ - 0.01) would improve water erosion estimation on loess hillslopes of China.

  13. Last Interglacial climate and sea-level evolution from a coupled ice sheet-climate model

    NASA Astrophysics Data System (ADS)

    Goelzer, Heiko; Huybrechts, Philippe; Loutre, Marie-France; Fichefet, Thierry

    2016-12-01

    As the most recent warm period in Earth's history with a sea-level stand higher than present, the Last Interglacial (LIG, ˜ 130 to 115 kyr BP) is often considered a prime example to study the impact of a warmer climate on the two polar ice sheets remaining today. Here we simulate the Last Interglacial climate, ice sheet, and sea-level evolution with the Earth system model of intermediate complexity LOVECLIM v.1.3, which includes dynamic and fully coupled components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. In this setup, sea-level evolution and climate-ice sheet interactions are modelled in a consistent framework.Surface mass balance change governed by changes in surface meltwater runoff is the dominant forcing for the Greenland ice sheet, which shows a peak sea-level contribution of 1.4 m at 123 kyr BP in the reference experiment. Our results indicate that ice sheet-climate feedbacks play an important role to amplify climate and sea-level changes in the Northern Hemisphere. The sensitivity of the Greenland ice sheet to surface temperature changes considerably increases when interactive albedo changes are considered. Southern Hemisphere polar and sub-polar ocean warming is limited throughout the Last Interglacial, and surface and sub-shelf melting exerts only a minor control on the Antarctic sea-level contribution with a peak of 4.4 m at 125 kyr BP. Retreat of the Antarctic ice sheet at the onset of the LIG is mainly forced by rising sea level and to a lesser extent by reduced ice shelf viscosity as the surface temperature increases. Global sea level shows a peak of 5.3 m at 124.5 kyr BP, which includes a minor contribution of 0.35 m from oceanic thermal expansion. Neither the individual contributions nor the total modelled sea-level stand show fast multi-millennial timescale variations as indicated by some reconstructions.

  14. Greenland Ice Sheet seasonal and spatial mass variability from model simulations and GRACE (2003-2012)

    NASA Astrophysics Data System (ADS)

    Alexander, Patrick M.; Tedesco, Marco; Schlegel, Nicole-Jeanne; Luthcke, Scott B.; Fettweis, Xavier; Larour, Eric

    2016-06-01

    Improving the ability of regional climate models (RCMs) and ice sheet models (ISMs) to simulate spatiotemporal variations in the mass of the Greenland Ice Sheet (GrIS) is crucial for prediction of future sea level rise. While several studies have examined recent trends in GrIS mass loss, studies focusing on mass variations at sub-annual and sub-basin-wide scales are still lacking. At these scales, processes responsible for mass change are less well understood and modeled, and could potentially play an important role in future GrIS mass change. Here, we examine spatiotemporal variations in mass over the GrIS derived from the Gravity Recovery and Climate Experiment (GRACE) satellites for the January 2003-December 2012 period using a "mascon" approach, with a nominal spatial resolution of 100 km, and a temporal resolution of 10 days. We compare GRACE-estimated mass variations against those simulated by the Modèle Atmosphérique Régionale (MAR) RCM and the Ice Sheet System Model (ISSM). In order to properly compare spatial and temporal variations in GrIS mass from GRACE with model outputs, we find it necessary to spatially and temporally filter model results to reproduce leakage of mass inherent in the GRACE solution. Both modeled and satellite-derived results point to a decline (of -178.9 ± 4.4 and -239.4 ± 7.7 Gt yr-1 respectively) in GrIS mass over the period examined, but the models appear to underestimate the rate of mass loss, especially in areas below 2000 m in elevation, where the majority of recent GrIS mass loss is occurring. On an ice-sheet-wide scale, the timing of the modeled seasonal cycle of cumulative mass (driven by summer mass loss) agrees with the GRACE-derived seasonal cycle, within limits of uncertainty from the GRACE solution. However, on sub-ice-sheet-wide scales, some areas exhibit significant differences in the timing of peaks in the annual cycle of mass change. At these scales, model biases, or processes not accounted for by models related

  15. An Imminent Revolution in Modeling Interactions of Ice Sheets With Climate

    NASA Astrophysics Data System (ADS)

    Hughes, T.

    2008-12-01

    Modeling continental ice sheets was inaugurated by meteorologists William Budd and Uwe Radok, with mathematician Richard Jenssen, in 1971. Their model calculated the thermal and mechanical regime using measured surface accumulation rates, temperatures, and elevations, and bed topography. This top-down approach delivered a basal thermal regime of temperatures or melting rates for an assumed basal geothermal heat flux. When Philippe Huybrechts and others incorporated time, largely unknownpast surface conditions had a major effect on present basal thermal conditions. This approach produced ice-sheet models with only a slow response to external forcing, whereas the glacial geological record and climate records from ice and ocean cores show that ice sheets can have rapid changes in size and shape independent of external forcing. These top-down models were wholly inadequate for reconstructing former ice sheets at the LGM for CLIMAP in 1981. Ice-sheet areas,elevations, and volumes provided the albedo, surface topography, and sea-surface area as input to climate models. A bottom-up model based on dated glacial geology was developed to provide the areal extent and basal thermal regime of ice sheets at the LGM. Basal thermal conditions determined ice-bed coupling and therefore the elevation of ice sheets. High convex ice surfaces for slow sheet flow lower about 20 percent when a frozen bed becomes thawed. As further basal melting drowns bedrock bumps that "pin" basal ice, the ice surface becomes concave in fast stream flow that ends as low floating ice shelves at marine ice margins. A revolution in modeling interactions between glaciation, climate, and sea level is driven by new Greenland and Antarctic data from Earth-orbiting satellites, airborne and surface traverses, and deep drilling. We anticipate continuous data acquisition of surface albedo, accumulation/ablation rates, elevations, velocities, and temperatures over a whole ice sheet, mapping basal thermal conditions

  16. Reconstruction of the Greenland ice sheet dynamics in a fully coupled Earth System Model

    NASA Astrophysics Data System (ADS)

    Rybak, Oleg; Volodin, Evgeny; Huybrechts, Philippe

    2016-04-01

    Earth system models (ESMs) are undoubtedly effective tools for studying climate dynamics. Incorporation of evolving ice sheets to ESMs is a challenging task because response times of the climate system and of ice sheets differ by several orders of magnitude. Besides, AO GCMs operate on spatial and temporal resolutions substantially differing from those of ice sheet models (ICMs). Therefore elaboration of an effective coupling methodology of an AO GCM and an ICM is the key problem of an ESM construction and utilization. Several downscaling strategies of varying complexity exist now of data exchange between modeled climate system and ice sheets. Application of a particular strategy depends on the research objectives. In our view, the optimum approach for model studying of significant environmental changes (e.g. glacial/interglacial transitions) when ice sheets undergo substantial evolution of geometry and volume would be an asynchronous coupling. The latter allows simulation in the interactive way of growth and decay of ice sheets in the changing climatic conditions. In the focus of the presentation, is the overview of coupling aspects of an AO GCM INMCM32 elaborated in the Institute of Numerical Mathematics (Moscow, Russia) to the Greenland ice sheet model (GrISM, Vrije Uninersiteit Brussel, Belgium). To provide interactive coupling of INMCM32 (spatial resolution 5°×4°, 21 vertical layers and temporal resolution 6 min. in the atmospheric block) and GrISM (spatial resolution 20×20 km, 51 vertical layers and 1 yr temporal resolution), we employ a special energy- and water balance model (EWBM-G), which serves as a buffer providing effective data exchange between INMCM32 and GrISM. EWBM-G operates in a rectangle domain including Greenland. Transfer of daily meanings of simulated climatic variables (air surface temperature and specific humidity) is provided on the lateral boundarias of the domain and inside the domain (sea level air pressure, wind speed and total

  17. Failure analysis of AZ31 magnesium alloy sheets based on the extended GTN damage model

    NASA Astrophysics Data System (ADS)

    Wang, Rui-ze; Chen, Zhang-hua; Li, Yu-jie; Dong, Chao-fang

    2013-12-01

    Based on the Gurson-Tvergaard-Needleman (GTN) model and Hill's quadratic anisotropic yield criterion, a combined experimental-numerical study on fracture initiation in the process of thermal stamping of Mg alloy AZ31 sheets was carried out. The aim is to predict the formability of thermal stamping of the Mg alloy sheets at different temperatures. The presented theoretical framework was implemented into a VUMAT subroutine for ABAQUS/EXPLICIT. Internal damage evolution due to void growth and coalescence developed at different temperatures in the Mg alloy sheets was observed by scanning electron microscopy (SEM). Moreover, the thermal effects on the void growth, coalescence, and fracture behavior of the Mg alloy sheets were analyzed by the extended GTN model and forming limit diagrams (FLD). Parameters employed in the GTN model were determined from tensile tests and numerical iterative computation. The distribution of major and minor principal strains in the specimens was determined from the numerical results. Therefore, the corresponding forming limit diagrams at different stress levels and temperatures were drawn. The comparison between the predicted forming limits and the experimental data shows a good agreement.

  18. Development and Applications of the Community Ice Sheet Model

    SciTech Connect

    Hoffman, Matthew J.; Lipscomb, William H.; Price, Stephen F.; Johnson, Jesse; Sacks, William

    2012-07-23

    The initial goals of the project are: (1) create a model for land ice that includes relevant and necessary dynamics, physical processes, and couplings; and (2) apply that model to say something more substantial about SLR in Lme for IPCC AR5 (AR6?).

  19. Implementation of virtual models from sheet metal forming simulation into physical 3D colour models using 3D printing

    NASA Astrophysics Data System (ADS)

    Junk, S.

    2016-08-01

    Today the methods of numerical simulation of sheet metal forming offer a great diversity of possibilities for optimization in product development and in process design. However, the results from simulation are only available as virtual models. Because there are any forming tools available during the early stages of product development, physical models that could serve to represent the virtual results are therefore lacking. Physical 3D-models can be created using 3D-printing and serve as an illustration and present a better understanding of the simulation results. In this way, the results from the simulation can be made more “comprehensible” within a development team. This paper presents the possibilities of 3D-colour printing with particular consideration of the requirements regarding the implementation of sheet metal forming simulation. Using concrete examples of sheet metal forming, the manufacturing of 3D colour models will be expounded upon on the basis of simulation results.

  20. Modeling Antarctic Ice Sheet retreat in warm climates: a historical perspective.

    NASA Astrophysics Data System (ADS)

    Pollard, D.; Deconto, R. M.; Gasson, E.

    2016-12-01

    Early modeling of Antarctic Ice Sheet size vs. climate focused on asymmetry between retreat and growth, with much greater warming needed to cause retreat from full ice cover, due to Height Mass Balance Feedback and albedo feedback. This led to a long-standing model-data conflict, with models needing 1000 to2000 ppmv atmospheric CO2 to produce retreat from full size, vs. proxy data of large ice fluctuations despite much lower CO2 since the Miocene.Subsequent modeling with marine ice physics found that the West Antarctic Ice Sheet could undergo repeated warm-period collapses with realistic past forcing. However, that yields only 3 to 7 m equivalent sea-level rise above modern, compared to 10 to 20 m or more suggested by some geologic data. Large subglacial basins in East Antarctica could be vulnerable to the same processes,but did not retreat in most models due to narrower and shallower sills.After recent modifications, some ice sheet models were able to produce warm-period collapse of major East Antarctic basins, with sea-level rise of up to 15 m. The modifications are (i) hydrofracturing by surface melt, and structural failure of ice cliffs, or (ii) numerical treatment at the grounding line. In these models, large retreat occurs both for past warmintervals, and also for future business-as-usual scenarios.Some interpretations of data in the late Oligocene and Miocene suggest yet larger fluctuations, between 50 to 100% of modern Antarctic size. That would require surface-melt driven retreat of some terrestrial East Antarctic ice, despite the hysteresis issue raised above. A recent study using a coupled climate-ice sheet model found that with a finer climate gridand more frequent coupling exchange, substantial retreat of terrestrial Antarctica can occur with 500 to 840 ppmv CO2, much lower than in earlier models. This will allow meaningful interactions between modeling and deeper-time geologic interpretations since the late Oligocene.

  1. The potential of cell sheet technique on the development of hepatocellular carcinoma in rat models.

    PubMed

    Alshareeda, Alaa T; Sakaguchi, Katsuhisa; Abumaree, Mohammed; Mohd Zin, Nur Khatijah; Shimizu, Tatsuya

    2017-01-01

    Hepatocellular carcinoma (HCC) is considered the 3rd leading cause of death by cancer worldwide with the majority of patients were diagnosed in the late stages. Currently, there is no effective therapy. The selection of an animal model that mimics human cancer is essential for the identification of prognostic/predictive markers, candidate genes underlying cancer induction and the examination of factors that may influence the response of cancers to therapeutic agents and regimens. In this study, we developed a HCC nude rat models using cell sheet and examined the effect of human stromal cells (SCs) on the development of the HCC model and on different liver parameters such as albumin and urea. Transplanted cell sheet for HCC rat models was fabricated using thermo-responsive culture dishes. The effect of human umbilical cord mesenchymal stromal cells (UC-MSCs) and human bone marrow mesenchymal stromal cells (BM-MSCs) on the developed tumour was tested. Furthermore, development of tumour and detection of the liver parameter was studied. Additionally, angiogenesis assay was performed using Matrigel. HepG2 cells requires five days to form a complete cell sheet while HepG2 co-cultured with UC-MSCs or BM-MSCs took only three days. The tumour developed within 4 weeks after transplantation of the HCC sheet on the liver of nude rats. Both UC-MSCs and BM-MSCs improved the secretion of liver parameters by increasing the secretion of albumin and urea. Comparatively, the UC-MSCs were more effective than BM-MSCs, but unlike BM-MSCs, UC-MSCs prevented liver tumour formation and the tube formation of HCC. Since this is a novel study to induce liver tumour in rats using hepatocellular carcinoma sheet and stromal cells, the data obtained suggest that cell sheet is a fast and easy technique to develop HCC models as well as UC-MSCs have therapeutic potential for liver diseases. Additionally, the data procured indicates that stromal cells enhanced the fabrication of HepG2 cell sheets

  2. Sea-level and solid-Earth deformation feedbacks in ice sheet modelling

    NASA Astrophysics Data System (ADS)

    Konrad, Hannes; Sasgen, Ingo; Klemann, Volker; Thoma, Malte; Grosfeld, Klaus; Martinec, Zdeněk

    2014-05-01

    The interactions of ice sheets with the sea level and the solid Earth are important factors for the stability of the ice shelves and the tributary inland ice (e.g. Thomas and Bentley, 1978; Gomez et al, 2012). First, changes in ice extent and ice thickness induce viscoelastic deformation of the Earth surface and Earth's gravity field. In turn, global and local changes in sea level and bathymetry affect the grounding line and, subsequently, alter the ice dynamic behaviour. Here, we investigate these feedbacks for a synthetic ice sheet configuration as well as for the Antarctic ice sheet using a three-dimensional thermomechanical ice sheet and shelf model, coupled to a viscoelastic solid-Earth and gravitationally self-consistent sea-level model. The respective ice sheet undergoes a forcing from rising sea level, warming ocean, and/or changing surface mass balance. The coupling is realized by exchanging ice thickness, Earth surface deformation and sea level periodically. We apply several sets of viscoelastic Earth parameters to our coupled model, e.g. simulating a low-viscous upper mantle present at the Antarctic Peninsula (Ivins et al., 2011). Special focus of our study lies on the evolution of Earth surface deformation and local sea level changes, as well as on the accompanying grounding line evolution. N. Gomez, D. Pollard, J. X. Mitrovica, P. Huybers, and P. U. Clark 2012. Evolution of a coupled marine ice sheet-sea level model, J. Geophys. Res., 117, F01013, doi:10.1029/2011JF002128. E. R. Ivins, M. M. Watkins, D.-N. Yuan, R. Dietrich, G. Casassa, and A. Rülke 2011. On-land ice loss and glacial isostatic adjustment at the Drake Passage: 2003-2009, J. Geophys. Res. 116, B02403, doi: 10.1029/2010JB007607 R. H. Thomas and C. R. Bentley 1978. A model for Holocene retreat of the West Antarctic Ice Sheet, Quaternary Research, 10 (2), pages 150-170, doi: 10.1016/0033-5894(78)90098-4.

  3. The potential of cell sheet technique on the development of hepatocellular carcinoma in rat models

    PubMed Central

    Sakaguchi, Katsuhisa; Abumaree, Mohammed; Mohd Zin, Nur Khatijah; Shimizu, Tatsuya

    2017-01-01

    Background Hepatocellular carcinoma (HCC) is considered the 3rd leading cause of death by cancer worldwide with the majority of patients were diagnosed in the late stages. Currently, there is no effective therapy. The selection of an animal model that mimics human cancer is essential for the identification of prognostic/predictive markers, candidate genes underlying cancer induction and the examination of factors that may influence the response of cancers to therapeutic agents and regimens. In this study, we developed a HCC nude rat models using cell sheet and examined the effect of human stromal cells (SCs) on the development of the HCC model and on different liver parameters such as albumin and urea. Methods Transplanted cell sheet for HCC rat models was fabricated using thermo-responsive culture dishes. The effect of human umbilical cord mesenchymal stromal cells (UC-MSCs) and human bone marrow mesenchymal stromal cells (BM-MSCs) on the developed tumour was tested. Furthermore, development of tumour and detection of the liver parameter was studied. Additionally, angiogenesis assay was performed using Matrigel. Results HepG2 cells requires five days to form a complete cell sheet while HepG2 co-cultured with UC-MSCs or BM-MSCs took only three days. The tumour developed within 4 weeks after transplantation of the HCC sheet on the liver of nude rats. Both UC-MSCs and BM-MSCs improved the secretion of liver parameters by increasing the secretion of albumin and urea. Comparatively, the UC-MSCs were more effective than BM-MSCs, but unlike BM-MSCs, UC-MSCs prevented liver tumour formation and the tube formation of HCC. Conclusions Since this is a novel study to induce liver tumour in rats using hepatocellular carcinoma sheet and stromal cells, the data obtained suggest that cell sheet is a fast and easy technique to develop HCC models as well as UC-MSCs have therapeutic potential for liver diseases. Additionally, the data procured indicates that stromal cells enhanced

  4. Variations of the Antarctic Ice Sheet in a coupled ice sheet-Earth-sea level model: sensitivity to viscoelastic Earth properties.

    NASA Astrophysics Data System (ADS)

    Pollard, David; Gomez, Natalya; DeConto, Robert

    2017-04-01

    A coupled ice sheet-Earth-sea level model is applied to long-term variations of the Antarctic ice sheet. Five different viscoelastic profiles in the global Earth model are used to explore feedbacks on ice sheet variability, including one with a thin lithosphere and weak upper mantle (LVZ) representative of properties under West Antarctica. These profiles are globally homogeneous, with no lateral variations. Simulations are performed for (1) the deglacial retreat of the last 20,000 years, (2) the future 5000 years with greenhouse-gas scenario RCP8.5, and (3) the warm Pliocene 3 Ma. For the deglacial period a large ensemble of 625 runs is analyzed, with overall scores computed vs. geologic and modern data. For each of the 5 Earth profiles, the top-scoring sets of the other model parameters in the ensemble are used to perform future and Pliocene simulations. There is little difference in the last deglacial retreat between LVZ and the other Earth profiles. In contrast, the LVZ profile produces significantly more negative feedback and less ice retreat in the future and Pliocene runs. This is due to faster timescales of retreat and larger temporal lags of bedrock rebound in the latter runs, allowing the different Earth profiles to have greater influence on ice-sheet retreat. However, the reduced retreat with LVZ occurs primarily in East Antarctic basins, where the LVZ profile may not be realistic, emphasizing the need for lateral heterogeneity in the Earth model.

  5. Quantifying `missing melt' in regional climate model predictions of Greenland ice sheet change

    NASA Astrophysics Data System (ADS)

    Leeson, A.; Eastoe, E.; Fettweis, X.

    2016-12-01

    Since 2010, the rate of mass loss from Greenland has increased and the ice sheet has experienced more episodes of rare and extreme surface melt. In addition to directly removing more of the ice sheet into the sea, extreme melt events reduce the reflectivity of the ice sheet and can warm the perennial snow pack through latent heat release when the melt water refreezes, both of which act as a positive feedback to further enhance melt. As such, an understanding of the frequency, duration and magnitude of extreme melt events is necessary to constrain predictions of future ice sheet state. Melting on Greenland is typically predicted using Regional Climate Models (RCM), however, although RCMs are excellent at reproducing 'normal' conditions (low amplitude/frequency signals) and long term trends, they may not resolve unusually high/low magnitude features, particularly of either small spatial scale or short temporal duration. Extreme melt events for example, typically only last for a day or so and thus their effects are likely omitted from RCM estimates of future ice sheet change. Here, we present a new climatology of historic extreme melt events on Greenland, diagnosed using tools from Extreme Value Theory Statistics. We use these data to evaluate the ability of the MAR (Modele Atmospherique Regional) RCM to reproduce the frequency, magnitude and duration of extreme melt events in the past, with forcing by both re-analysis (ERA-Interim) and GCM (CMIP5) predictions at the model boundaries. By modelling the relationship between MAR predicted values, and observations, we are able to estimate the degree to which MAR over/under estimates melting due to the omission of extreme events for a given boundary forcing. We use this relationship together with MAR predictions of future change to quantify the likely amount of `missing melt' in MAR-based projections of global sea level rise due to these short term, high magnitude perturbations.

  6. Using an Earth System Model to Better Understand Ice Sheet Variability Through the Pleistocene

    NASA Astrophysics Data System (ADS)

    Tabor, C. R.; Poulsen, C. J.; Pollard, D.

    2015-12-01

    We use an Earth System model with a dynamic land-ice component to explore several inconsistencies between traditional Milankovitch theory and δ18O sediment records of the Pleistocene. Our model results show that a combination of albedo feedbacks, seasonal offset of precession forcing, and orbital cycle duration differences can explain much of the 41-kyr glacial cycles that characterize the early Pleistocene. The obliquity-controlled changes in annual average high-latitude insolation produce large variations in arctic vegetation-type and sea-ice cover, which amplify the land-ice response. In contrast, the seasonal nature of the precession insolation signal dampens net ice-melt. For instance, when precession enhances ice melt in the spring, it reduces ice melt in the fall, and vice versa. The lower frequency of obliquity cycles in combination with amplified climate sensitivity due to albedo feedbacks help produce a larger ice-volume response to cycles of obliquity compared to precession, despite precession contributing more to variations in high-latitude summer insolation. In addition, we can simulate the appearance of a 100-kyr ice-volume signal by reducing basal sliding in the ice sheet model. Model experiments with enhanced basal drag have greater ice sheet elevation because the ice sheets are not able to flow as quickly, leading to increased ice thickness at the expense of ice extent. These thicker ice sheets have colder surface temperatures, receive more snowfall, and do not readily advance past the ice equilibrium line. Greater high-latitude summer insolation from the combination of high obliquity and precession/eccentricity is then necessary to cause complete ice sheet retreat. This research lends support to the regolith hypothesis, which proposes gradual erosion of high-latitude northern hemisphere regolith by multiple cycles of glaciation helped cause the mid-Pleistocene transition.

  7. Polar ice sheets during the Cretaceous? Insights from coupled numerical modelling.

    NASA Astrophysics Data System (ADS)

    Ladant, Jean-Baptiste; Donnadieu, Yannick

    2017-04-01

    Most proxy estimates of Cretaceous climates reveal oceanic and terrestrial temperatures substantially warmer than modern's. Fossils of crocodilian species and remains of what is now low-latitude flora have been unearthed in polar locations. On top of that, direct evidence of polar ice sheets have yet to be found. The Cretaceous has thus historically been considered as a long and stable period of supergreenhouse with elevated CO2 levels. Since a couple of decades however, studies have suggested that dynamical climatic variations affect the Cretaceous greenhouse, in particular with the episodic growth of ephemeral polar ice sheets, for which indirect evidence have been argued for. In addition, new estimates of CO2 levels suggest more modest values (400 - 1500 ppm), potentially in the range of those in place during Cenozoic glaciations. Here, we use a suite of models of climate and ice sheets to investigate the impact of the changing palaeogeography during the Middle-Late Cretaceous (120 - 70 Ma) on the development of ice sheets on polar latitudes. We show that palaeogeography alone, through a series of complex feedbacks, has the potential to significantly alter the CO2 threshold for the onset of ice sheets, nucleating in particular at higher CO2 concentrations in the Aptian ( 800 ppm) and the Maastrichtian ( 700 ppm) than in the Cenomanian-Turonian ( 400 ppm). Our simulations demonstrate notably that part of the Cenomanian-Turonian climatic optimum can be explained by its specific palaeogeography and support the vision of an ice-free Earth during this stage. In addition, our numerical work derives Aptian and Maastrichtian glacial CO2 threshold that are in the range of latest data compilations, thus adding to the growing body of evidence suggesting that ice sheets were once present during these stages.

  8. JEDI: Jobs and Economic Development Impacts Model Fact Sheet

    SciTech Connect

    S. Hendrickson; S.Tegen

    2009-12-01

    The Jobs and Economic Development Impact (JEDI) models are user-friendly tools that estimate the economic impacts of constructing and operating power generation and biofuel plants at the local(usually state) level. First developed by NREL's Wind Powering America program to model wind energy jobs and impacts, JEDI has been expanded to biofuels,concentrating solar power, coal, and natural gas power plants.

  9. Results from ISOMIP+ and MISOMIP1, two interrelated marine ice sheet and ocean model intercomparison projects

    NASA Astrophysics Data System (ADS)

    Asay-Davis, X.; Galton-Fenzi, B.; Gwyther, D.; Jourdain, N.; Martin, D. F.; Nakayama, Y.; Seroussi, H. L.

    2016-12-01

    MISMIP+ (the third Marine Ice Sheet MIP), ISOMIP+ (the second Ice Shelf-Ocean MIP) and MISOMIP1 (the first Marine Ice Sheet-Ocean MIP) prescribe a set of idealized experiments for marine ice-sheet models, ocean models with ice-shelf cavities, and coupled ice sheet-ocean models, respectively. Here, we present results from ISOMIP+ and MISOMIP1 experiments using several ocean-only and coupled ice sheet-ocean models. Among the ocean models, we show that differences in model behavior are significant enough that similar results can only be achieved by tuning model parameters (the heat- and salt-transfer coefficients across the sub-ice-shelf boundary layer) for each model. This tuning is constrained by a desired mean melt rate in quasi-steady state under specified forcing conditions, akin to tuning the models to match observed melt rates. We compare the evolution of ocean temperature transects, melt rate, friction velocity and thermal driving between ocean models for the five ISOMIP+ experiments (Ocean0-4), which have prescribed ice-shelf topography. We find that melt patterns differ between models based on the relative importance of overturning strength and vertical mixing of temperature even when the models have been tuned to achieve similar melt rates near the grounding line. For the two MISOMIP1 experiments (IceOcean1 without dynamic calving and IceOcean2 with a simple calving parameterization), we compare temperature transects, melt rate, ice-shelf topography and grounded area across models and for several model configurations. Consistent with preliminary results from MISMIP+, we find that for a given coupled model, the use of a Coulomb-limited basal friction parameterization below grounded ice and the application of dynamic calving both significantly increase the rate of grounding-line retreat, whereas the rate of retreat appears to be less sensitive to the ice stress approximation (shallow-shelf approximation, higher-order, etc.). We show that models with similar

  10. A new model for cone sheet emplacement: data from the Isle of Skye (UK) and numerical modeling

    NASA Astrophysics Data System (ADS)

    Tibaldi, A.; Bistacchi, A.; Pasquare, F.; Rust, D.

    2009-12-01

    The mechanics of intrusive sheet propagation from a shallow magma chamber is of paramount importance in understanding eruptive processes and the internal growth and stability of volcanoes. In order to contribute to these topics, we went back to the classical Cuillins cone sheet complex on the Isle of Skye, where the roots of a Tertiary basaltic volcano are exposed (Anderson, 1936, Proceedings of the Royal Society of Edinburgh, 56, 128-157), and performed a new field and numerical modeling study. Our structural data show that, in the Cuillins complex, inward dipping cone sheets have a constant average dip angle (ca. 45°) and show either pure dilational or hybrid shear kinematics. These might be general features of cone sheet complexes, since they are in agreement with results from Gran Canaria (Schirnick, van den Bogaard, Schmincke, 1999, Geology, 27, 207-210). In order to explain these data, we developed a set of finite element models, which for the first time include an elasto-plastic rheology and consider the total stress field deriving from gravity, tectonics and magma chamber overpressure. Numerical modeling shows that only in the case of a shallow oblate magma chamber may cone sheets be predicted for realistic magma overpressure values (ca. 10-20 MPa). In contrast, cone sheets should not develop, for realistic overpressures (< 40 MPa), with sub-spherical or prolate magma chambers. In any case, cone sheets appear to be confined within a distance from the central axis of about 1-1.2 diameters of the magma chamber and in the volume immediately above it, whilst radial dikes dominate beyond the 1-1.2 diameter limit. When a realistic regional stress field is considered, the radial dikes progressively merge into a regional swarm of parallel dikes, oriented perpendicular to the least compressive stress axis. Of significance for active volcanoes, the following points can be highlighted: (i) the association of cone sheets and radial dikes is likely to be linked to a

  11. Process modelling and die design concepts for forming aircraft sheet parts

    NASA Astrophysics Data System (ADS)

    Hatipoğlu, H. A.; Alkaş, C. O.

    2016-08-01

    This study is about typical sheet metal forming processes applied in aerospace industry including flexform, stretch form and stretch draw. Each process is modelled by using finite element method for optimization. Tensile, bulge, forming limit and friction tests of commonly used materials are conducted for defining the hardening curves, yield loci, anisotropic constants, forming limit curves and friction coefficients between die and sheet. Process specific loadings and boundary conditions are applied to each model. The models are then validated by smartly designed experiments that characterize the related forming processes. Lastly, several examples are given in which those models are used to predict the forming defects before physical forming and necessary die design and process parameter changes are applied accordingly for successful forming operations.

  12. Advances in modelling subglacial lakes and their interaction with the Antarctic ice sheet.

    PubMed

    Pattyn, Frank; Carter, Sasha P; Thoma, Malte

    2016-01-28

    Subglacial lakes have long been considered hydraulically isolated water bodies underneath ice sheets. This view changed radically with the advent of repeat-pass satellite altimetry and the discovery of multiple lake discharges and water infill, associated with water transfer over distances of more than 200 km. The presence of subglacial lakes also influences ice dynamics, leading to glacier acceleration. Furthermore, subglacial melting under the Antarctic ice sheet is more widespread than previously thought, and subglacial melt rates may explain the availability for water storage in subglacial lakes and water transport. Modelling of subglacial water discharge in subglacial lakes essentially follows hydraulics of subglacial channels on a hard bed, where ice sheet surface slope is a major control on triggering subglacial lake discharge. Recent evidence also points to the development of channels in deformable sediment in West Antarctica, with significant water exchanges between till and ice. Most active lakes drain over short time scales and respond rapidly to upstream variations. Several Antarctic subglacial lakes exhibit complex interactions with the ice sheet due to water circulation. Subglacial lakes can therefore-from a modelling point of view-be seen as confined small oceans underneath an imbedded ice shelf.

  13. A continuum mixture model of ice stream thermomechanics in the Laurentide Ice Sheet 1. Theory

    NASA Astrophysics Data System (ADS)

    Marshall, Shawn J.; Clarke, Garry K. C.

    1997-01-01

    We employ a continuum mixture framework to incorporate ice streams in a three-dimensional thermomechanical model of the Laurentide Ice Sheet. The ice mass is composed of a binary mixture of sheet ice, which deforms by viscous creep, and stream ice, which flows by sliding and/or sediment deformation at the bed. Dynamic and thermal evolutions are solved for each component in the mixture, with coupling rules to govern transfer between flow regimes. We describe two different transfer mechanisms: (1) creep exchange, the nourishment of ice streams by viscous creep inflow from the surrounding ice sheet, and (2) bed exchange, the activation, growth, and deactivation of ice streams, perpetrated by transfers of bed area between flow constituents. This paper develops the underlying mixture theory. We express the governing equations for mass, momentum, and energy balance in a form suitable for direct incorporation in existing numerical models of ice thermomechanics. A companion paper in this issue explores mixture and ice stream behavior in applications with the Laurentide Ice Sheet.

  14. A test of source-surface model predictions of heliospheric current sheet inclination

    NASA Technical Reports Server (NTRS)

    Burton, M. E.; Crooker, N. U.; Siscoe, G. L.; Smith, E. J.

    1994-01-01

    The orientation of the heliospheric current sheet predicted from a source surface model is compared with the orientation determined from minimum-variance analysis of International Sun-Earth Explorer (ISEE) 3 magnetic field data at 1 AU near solar maximum. Of the 37 cases analyzed, 28 have minimum variance normals that lie orthogonal to the predicted Parker spiral direction. For these cases, the correlation coefficient between the predicted and measured inclinations is 0.6. However, for the subset of 14 cases for which transient signatures (either interplanetary shocks or bidirectional electrons) are absent, the agreement in inclinations improves dramatically, with a correlation coefficient of 0.96. These results validate not only the use of the source surface model as a predictor but also the previously questioned usefulness of minimum variance analysis across complex sector boundaries. In addition, the results imply that interplanetary dynamics have little effect on current sheet inclination at 1 AU. The dependence of the correlation on transient occurrence suggests that the leading edge of a coronal mass ejection (CME), where transient signatures are detected, disrupts the heliospheric current sheet but that the sheet re-forms between the trailing legs of the CME. In this way the global structure of the heliosphere, reflected both in the source surface maps and in the interplanetary sector structure, can be maintained even when the CME occurrence rate is high.

  15. Translating hydrologically-relevant variables from the ice sheet model SICOPOLIS to the Greenland Analog Project hydrologic modeling domain

    NASA Astrophysics Data System (ADS)

    Vallot, Dorothée; Applegate, Patrick; Pettersson, Rickard

    2013-04-01

    Projecting future climate and ice sheet development requires sophisticated models and extensive field observations. Given the present state of our knowledge, it is very difficult to say what will happen with certainty. Despite the ongoing increase in atmospheric greenhouse gas concentrations, the possibility that a new ice sheet might form over Scandinavia in the far distant future cannot be excluded. The growth of a new Scandinavian Ice Sheet would have important consequences for buried nuclear waste repositories. The Greenland Analogue Project, initiated by the Swedish Nuclear Fuel and Waste Management Company (SKB), is working to assess the effects of a possible future ice sheet on groundwater flow by studying a constrained domain in Western Greenland by field measurements (including deep bedrock drilling in front of the ice sheet) combined with numerical modeling. To address the needs of the GAP project, we interpolated results from an ensemble of ice sheet model runs to the smaller and more finely resolved modeling domain used in the GAP project's hydrologic modeling. Three runs have been chosen with three fairly different positive degree-day factors among those that reproduced the modern ice margin at the borehole position. The interpolated results describe changes in hydrologically-relevant variables over two time periods, 115 ka to 80 ka, and 20 ka to 1 ka. In the first of these time periods, the ice margin advances over the model domain; in the second time period, the ice margin retreats over the model domain. The spatially-and temporally dependent variables that we treated include the ice thickness, basal melting rate, surface mass balance, basal temperature, basal thermal regime (frozen or thawed), surface temperature, and basal water pressure. The melt flux is also calculated.

  16. Modelling the Antarctic Ice Sheet during the Mid-Pliocene using the Adaptive Mesh Resolution Model, BISICLES

    NASA Astrophysics Data System (ADS)

    Kennedy, A. T.; Cornford, S. L.; Lunt, D. J.; Payne, A. J.

    2016-12-01

    Paleo ice sheet models provide valuable tools to test our understanding of the cryosphere-ocean-climate system and how it might respond under warm conditions. However, the long time scales and uncertainty in boundary conditions required for paleo simulations usually necessitates the use of highly parameterised and simplified model techniques, and not the use of state-of-the-art models. One such state-of-the-art model which has been used for the present day is BISICLES which, due to its adaptive mesh refinement capabilities, can explicitly model highly localised and dynamic features such as grounding line migration and ice streams. We will show results testing the suitability of using such a model for a paleo application, including the model's sensitivity to uncertainty in the ice volume, bedrock properties and climatic/oceanic forcing. We will also show preliminary results of modelling the Antarctic Ice Sheet state at the Mid-Pliocene, a period when the ice sheet is expected to have contributed many metres worth of global mean sea level increase. We will highlight the range of ice mass loss under different parameterisation and forcing schemes and the level of agreement with previous data and modelling studies, e.g. Miller et al (2012) and DeConto & Pollard (2016). It remains too computationally expensive to run BISICLES for a full glacial-interglacial cycle for example, but this model could still prove valuable for assessing the role of highly dynamic features in past ice sheets. This work will help bridge a gap in understanding of the strengths and weaknesses of the simpler models used in paleo ice sheet modelling compared to the state-of-the-art models used for present day and future prediction.

  17. Modeling of resistive sheets in finite element solutions

    NASA Astrophysics Data System (ADS)

    Jin, J. M.; Volakis, John L.; Yu, C. L.; Woo, Alex C.

    1992-01-01

    A formulation is presented for modeling a resistive card in the context of the finite element method. The appropriate variational function is derived and for variational purposes results are presented for the scattering by a metal-backed cavity loaded with a resistive card.

  18. Modeling of resistive sheets in finite element solutions

    NASA Astrophysics Data System (ADS)

    Jin, J. M.; Volakis, J. L.; Yu, C. L.; Woo, A. C.

    1992-06-01

    A formulation is presented for modeling a resistive card in the context of the finite element method. The appropriate variational function is derived and for variational purposes results are presented for the scattering by metal-backed cavity loaded with a resistive card.

  19. Computer Modeling of Carbon Metabolism Enables Biofuel Engineering (Fact Sheet)

    SciTech Connect

    Not Available

    2011-09-01

    In an effort to reduce the cost of biofuels, the National Renewable Energy Laboratory (NREL) has merged biochemistry with modern computing and mathematics. The result is a model of carbon metabolism that will help researchers understand and engineer the process of photosynthesis for optimal biofuel production.

  20. Sheet Hydroforming Process Numerical Model Improvement Through Experimental Results Analysis

    NASA Astrophysics Data System (ADS)

    Gabriele, Papadia; Antonio, Del Prete; Alfredo, Anglani

    2010-06-01

    The increasing application of numerical simulation in metal forming field has helped engineers to solve problems one after another to manufacture a qualified formed product reducing the required time [1]. Accurate simulation results are fundamental for the tooling and the product designs. The wide application of numerical simulation is encouraging the development of highly accurate simulation procedures to meet industrial requirements. Many factors can influence the final simulation results and many studies have been carried out about materials [2], yield criteria [3] and plastic deformation [4,5], process parameters [6] and their optimization. In order to develop a reliable hydromechanical deep drawing (HDD) numerical model the authors have been worked out specific activities based on the evaluation of the effective stiffness of the blankholder structure [7]. In this paper after an appropriate tuning phase of the blankholder force distribution, the experimental activity has been taken into account to improve the accuracy of the numerical model. In the first phase, the effective capability of the blankholder structure to transfer the applied load given by hydraulic actuators to the blank has been explored. This phase ended with the definition of an appropriate subdivision of the blankholder active surface in order to take into account the effective pressure map obtained for the given loads configuration. In the second phase the numerical results obtained with the developed subdivision have been compared with the experimental data of the studied model. The numerical model has been then improved, finding the best solution for the blankholder force distribution.

  1. Shallow ice approximation, second order shallow ice approximation, and full Stokes models: A discussion of their roles in palaeo-ice sheet modelling and development

    NASA Astrophysics Data System (ADS)

    Kirchner, N.; Ahlkrona, J.; Gowan, E. J.; Lötstedt, P.; Lea, J. M.; Noormets, R.; von Sydow, L.; Dowdeswell, J. A.; Benham, T.

    2016-09-01

    Full Stokes ice sheet models provide the most accurate description of ice sheet flow, and can therefore be used to reduce existing uncertainties in predicting the contribution of ice sheets to future sea level rise on centennial time-scales. The level of accuracy at which millennial time-scale palaeo-ice sheet simulations resolve ice sheet flow lags the standards set by Full Stokes models, especially, when Shallow Ice Approximation (SIA) models are used. Most models used in paleo-ice sheet modeling were developed at a time when computer power was very limited, and rely on several assumptions. At the time there was no means of verifying the assumptions by other than mathematical arguments. However, with the computer power and refined Full Stokes models available today, it is possible to test these assumptions numerically. In this paper, we review (Ahlkrona et al., 2013a) where such tests were performed and inaccuracies in commonly used arguments were found. We also summarize (Ahlkrona et al., 2013b) where the implications of the inaccurate assumptions are analyzed for two paleo-models - the SIA and the SOSIA. We review these works without resorting to mathematical detail, in order to make them accessible to a wider audience with a general interest in palaeo-ice sheet modelling. Specifically, we discuss two implications of relevance for palaeo-ice sheet modelling. First, classical SIA models are less accurate than assumed in their original derivation. Secondly, and contrary to previous recommendations, the SOSIA model is ruled out as a practicable tool for palaeo-ice sheet simulations. We conclude with an outlook concerning the new Ice Sheet Coupled Approximation Level (ISCAL) method presented in Ahlkrona et al. (2016), that has the potential to match the accuracy standards of full Stokes model on palaeo-timescales of tens of thousands of years, and to become an alternative to hybrid models currently used in palaeo-ice sheet modelling. The method is applied to an ice

  2. Models of strain variation in nappes and thrust sheets: A review

    NASA Astrophysics Data System (ADS)

    Sanderson, David J.

    1982-10-01

    Strain within nappes and thrust sheets can be modelled using simple boundary conditions. An original rectangular prism of material resting on a thrust plane is considered to be subject to various pure and simple shear components operating parallel to the thrust. Deformation gradient tensors are determined for the models and solutions found for the principal strains. A two-dimensional model considers heterogeneous simple shear combined with a stretch (α) in the direction of shear. Simple shear zones arise as a special case where α = 1. Recumbent fold nappes, characteristic of gravitational collapse, can be modelled with α > 1, and thrust sheets with layer parallel shortening and folding with α < 1. Differential transport of nappes gives rise to additional wrench-type shears. Solutions for the principal strains in this type of model are found and used to interpret side-wall ramps and steep zones parallel to nappe movements. By including a stretch in the transport direction these differential transport models produce prolate strains ( α > 1) and oblate strains ( α < 1). Finally a brief consideration of bending strains produced in a sheet passing over a ramp indicates reversals in the shear direction during the strain history. These predict possible crenulation of early thrust fabrics at ramps.

  3. Simulating Heinrich events in a coupled atmosphere-ocean-ice sheet model

    NASA Astrophysics Data System (ADS)

    Mikolajewicz, Uwe; Ziemen, Florian

    2016-04-01

    Heinrich events are among the most prominent events of long-term climate variability recorded in proxies across the northern hemisphere. They are the archetype of ice sheet - climate interactions on millennial time scales. Nevertheless, the exact mechanisms that cause Heinrich events are still under discussion, and their climatic consequences are far from being fully understood. We contribute to answering the open questions by studying Heinrich events in a coupled ice sheet model (ISM) atmosphere-ocean-vegetation general circulation model (AOVGCM) framework, where this variability occurs as part of the model generated internal variability without the need to prescribe external perturbations, as was the standard approach in almost all model studies so far. The setup consists of a northern hemisphere setup of the modified Parallel Ice Sheet Model (mPISM) coupled to the global coarse resolution AOVGCM ECHAM5/MPIOM/LPJ. The simulations used for this analysis were an ensemble covering substantial parts of the late Glacial forced with transient insolation and prescribed atmospheric greenhouse gas concentrations. The modeled Heinrich events show a marked influence of the ice discharge on the Atlantic circulation and heat transport, but none of the Heinrich events during the Glacial did show a complete collapse of the North Atlantic meridional overturning circulation. The simulated main consequences of the Heinrich events are a freshening and cooling over the North Atlantic and a drying over northern Europe.

  4. NREL's System Advisor Model Simplifies Complex Energy Analysis (Fact Sheet)

    SciTech Connect

    Not Available

    2015-01-01

    NREL has developed a tool -- the System Advisor Model (SAM) -- that can help decision makers analyze cost, performance, and financing of any size grid-connected solar, wind, or geothermal power project. Manufacturers, engineering and consulting firms, research and development firms, utilities, developers, venture capital firms, and international organizations use SAM for end-to-end analysis that helps determine whether and how to make investments in renewable energy projects.

  5. Modeling of different scenarios of thin current sheet equilibria in the Earth’s magnetotail

    SciTech Connect

    Ul’kin, A. A.; Malova, H. V. Popov, V. Yu.; Zelenyi, L. M.

    2015-02-15

    The Earth’s magnetosphere is an open dynamic system permanently interacting with the solar wind, i.e., the plasma flow from the Sun. Some plasma processes in the magnetosphere are of spontaneous explosive character, while others develop rather slowly as compared to the characteristic times of plasma particle motion in it. The large-scale current sheet in the magnetotail can be in an almost equilibrium state both in quiet periods and during geomagnetic perturbations, and its variations can be considered quasistatic. Thus, under some conditions, the magnetotail current sheet can be described as an equilibrium plasma system. Its state depends on various parameters, in particular, on those determining the dynamics of charged particles. Knowing the main governing parameters, one can study the structure and properties of the current sheet equilibrium. This work is devoted to the self-consistent modeling of the equilibrium thin current sheet (TCS) of the Earth’s magnetotail, the thickness of which is comparable with the ion gyroradius. The main objective of this work is to examine how the TCS structure depends on the parameters characterizing the particle dynamics and magnetic field geometry. A numerical hybrid self-consistent TCS model in which the tension of magnetic field lines is counterbalanced by the inertia of ions moving through the sheet is constructed. The ion dynamics is considered in the quasi-adiabatic approximation, while the electron motion, in the conductive fluid approximation. Depending on the values of the adiabaticity parameter κ (which determines the character of plasma particle motion) and the dimensionless normal component of the magnetic field b{sub z}, the following two scenarios are considered: (A) the adiabaticity parameter is proportional to the particle energy and b{sub z} = const and (B) the particle energy is fixed and the adiabaticity parameter is proportional to b{sub z}. The structure of the current sheet and particle dynamics in it

  6. Modeling of different scenarios of thin current sheet equilibria in the Earth's magnetotail

    NASA Astrophysics Data System (ADS)

    Ul'kin, A. A.; Malova, H. V.; Popov, V. Yu.; Zelenyi, L. M.

    2015-02-01

    The Earth's magnetosphere is an open dynamic system permanently interacting with the solar wind, i.e., the plasma flow from the Sun. Some plasma processes in the magnetosphere are of spontaneous explosive character, while others develop rather slowly as compared to the characteristic times of plasma particle motion in it. The large-scale current sheet in the magnetotail can be in an almost equilibrium state both in quiet periods and during geomagnetic perturbations, and its variations can be considered quasistatic. Thus, under some conditions, the magnetotail current sheet can be described as an equilibrium plasma system. Its state depends on various parameters, in particular, on those determining the dynamics of charged particles. Knowing the main governing parameters, one can study the structure and properties of the current sheet equilibrium. This work is devoted to the self-consistent modeling of the equilibrium thin current sheet (TCS) of the Earth's magnetotail, the thickness of which is comparable with the ion gyroradius. The main objective of this work is to examine how the TCS structure depends on the parameters characterizing the particle dynamics and magnetic field geometry. A numerical hybrid self-consistent TCS model in which the tension of magnetic field lines is counterbalanced by the inertia of ions moving through the sheet is constructed. The ion dynamics is considered in the quasi-adiabatic approximation, while the electron motion, in the conductive fluid approximation. Depending on the values of the adiabaticity parameter κ (which determines the character of plasma particle motion) and the dimensionless normal component of the magnetic field b z , the following two scenarios are considered: (A) the adiabaticity parameter is proportional to the particle energy and b z = const and (B) the particle energy is fixed and the adiabaticity parameter is proportional to b z . The structure of the current sheet and particle dynamics in it are studied as

  7. Present-day Circum-Antarctic Simulations using the POPSICLES Coupled Ice Sheet-Ocean Model

    NASA Astrophysics Data System (ADS)

    Asay-Davis, X.; Martin, D. F.; Price, S. F.; Maltrud, M. E.; Collins, W.

    2014-12-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period 1990 to 2010. Simulations are performed at 0.1o (~5 km) ocean resolution and with adaptive ice-sheet model resolution as fine as 500 m. We compare time-averaged melt rates below a number of major ice shelves with those reported by Rignot et al. (2013) as well as other recent studies. We also present seasonal variability and decadal trends in submarine melting from several Antarctic regions. Finally, we explore the influence on basal melting and system dynamics resulting from two different choices of climate forcing: a "normal-year" climatology and the CORE v. 2 forcing data (Large and Yeager 2008).POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program (Smith and Gent, 2002), and the BISICLES ice-sheet model (Cornford et al., 2012). POP2x includes sub-ice-shelf circulation using partial top cells (Losch, 2008) and boundary layer physics following Holland and Jenkins (1999), Jenkins (2001), and Jenkins et al. (2010). Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP; Losch, 2008) and other continental-scale simulations and melt-rate observations (Kimura et al., 2013; Rignot et al., 2013). BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh (2009) to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3D; Pattyn et al., 2013) and realistic configurations (Favier et al. 2014).A companion presentation, "Response of the Antarctic Ice Sheet to ocean forcing using the POPSICLES coupled ice sheet-ocean model" in session C024 covers the ice-sheet response to these melt rates in the coupled simulation

  8. Quantitative analogue modelling of the surface deformation associated with cone-sheet and dyke emplacement

    NASA Astrophysics Data System (ADS)

    Guldstrand, Frank; Bjugger, Fanny; Galland, Olivier; Burchardt, Steffi; Hallot, Erwan

    2014-05-01

    Inclined cone-sheets and sub-vertical dykes constitute the two principal types of magmatic sheet intrusions produced by volcanic systems. In active volcanic systems, the emplacement of sheet intrusions causes measurable surface deformation, which is analyzed through geodetic models. Geodetic model output is classically the shape of underlying intrusions causing the surface deformation, however, the results of these models are not testable as the subsurface intrusion is not accessible. Such test would only be doable with a physical system in which both (1) the surface deformation pattern and (2) the 3D shape of the underlying intrusion are known. In addition, established geodetic models only consider static magma intrusions, and do not account for emplacement and propagation processes. This would require combined good time- and space-resolution, which is not achievable with classical geodetic monitoring systems. We present a series of analogue models that may be a way of accurately linking surface deformation to the underlying intrusions and associated emplacement processes. We systematically varied depth of intrusion, the cohesive properties of the silica powder representing the country rock and the velocity of injected magma. The pressure of the intruding vegetable oil was measured through time, and the model surface topography was monitored. The low viscosity magma was simulated by molten vegetable oil, which solidified after intrusion; the solidified intrusion was then excavated and its shape was measured. By linking the development of the surface uplift in height, area, and volume with the pressure data from the onset of intrusion until the time of eruption, we identify characteristic laws of surface deformation. First results indicate that the pattern of uplift over time varies, depending on whether deformation is caused by a dyke- or a cone-sheet-shaped intrusion. The results from all experiments may enable us to distinguish the two intrusion types using

  9. Fact Sheet: A Technical Guide to Ground-Water Model Selection at Sites Contaminated with Radioactive Substances

    EPA Pesticide Factsheets

    This fact sheet summarizes the findings of a report drafted by a joint Interagency Environmental Pathway Modeling Working Group. It is to be used by technical staff responsible for implementing flow and transport models to support cleanup decisions.

  10. Advances in Constitutive and Failure Models for Sheet Forming Simulation

    NASA Astrophysics Data System (ADS)

    Yoon, Jeong Whan; Stoughton, Thomas B.

    2016-08-01

    Non-Associated Flow Rule (Non-AFR) can be used as a convenient way to account for anisotropic material response in metal deformation processes, making it possible for example, to eliminate the problem of the anomalous yielding in equibiaxial tension that is mistakenly attributed to limitations of the quadratic yield function, but may instead be attributed to the Associated Flow Rule (AFR). Seeing as in Non-AFR based models two separate functions can be adopted for yield and plastic potential, there is no constraint to which models are used to describe each of them. In this work, the flexible combination of two different yield criteria as yield function and plastic potential under Non-AFR is proposed and evaluated. FE simulations were carried so as to verify the accuracy of the material directionalities predicted using these constitutive material models. The stability conditions for non-associated flow connected with the prediction of yield point elongation are also reviewed. Anisotropic distortion hardening is further incorporated under non-associated flow. It has been found that anisotropic hardening makes the noticeable improvements for both earing and spring-back predictions. This presentation is followed by a discussion of the topic of the forming limit & necking, the evidence in favor of stress analysis, and the motivation for the development of a new type of forming limit diagram based on the polar effective plastic strain (PEPS) diagram. In order to connect necking to fracture in metals, the stress-based necking limit is combined with a stress- based fracture criterion in the principal stress, which provides an efficient method for the analysis of necking and fracture limits. The concept for the PEPS diagram is further developed to cover the path-independent PEPS fracture which is compatible with the stress-based fracture approach. Thus this fracture criterion can be utilized to describe the post-necking behavior and to cover nonlinear strain-path. Fracture

  11. Integrated Modelling of Damage and Fracture in Sheet Metal Forming

    NASA Astrophysics Data System (ADS)

    Peerlings, R. H. J.; Mediavilla, J.; Geers, M. G. D.

    2007-05-01

    A framework for finite element simulations of ductile damage development and ductile fracture during metal forming is presented. The damage evolution is described by a phenomenological continuum damage model. Crack growth and fracture are treated as the ultimate consequences of the damage process. Computationally, the initiation and growth of cracks is traced by an adaptive remeshing strategy, thereby allowing for opening crack faces. The application of the method to the fabrication of food-can lids demonstrates its capabilities, but also some of its limitations.

  12. Failure Analysis of Warm Stamping of Magnesium Alloy Sheet Based on an Anisotropic Damage Model

    NASA Astrophysics Data System (ADS)

    Zhao, P. J.; Chen, Z. H.; Dong, C. F.

    2014-11-01

    Based on the frame work of continuum damage mechanics, a research work of anisotropic damage evolution in warm stamping process of magnesium alloy sheets has been carried out by means of a combined experimental-numerical method. The aim was to predict formability of warm stamping of AZ31 Mg alloy sheets by taking the thermal and damage effects into account. In the presented work, a temperature-dependent anisotropic yield function suitable for cold rolling sheet metals together with an anisotropic damage model was implemented into the a VUMAT subroutine for ABAQUS/EXPLICIT. The evolution of internal damage in the form of void growth and coalescence in AZ31 Mg alloy sheet was observed by means of scanning electron microscopy (SEM). Moreover, a coupled thermo-mechanical simulation of the stamping process was performed using the implemented code at different temperatures. The parameters employed in the simulation were determined by the standard tensile tests and algebraic manipulation. The overall anisotropic damage process from crack initiation to final propagation in local area of blank was simulated. Numerical results show that the prediction of the site of crack initiation and the orientation of crack propagation are consistent with the data observed in warm stamping experiments.

  13. Kinetic model of force-free current sheets with non-uniform temperature

    NASA Astrophysics Data System (ADS)

    Kolotkov, D. Y.; Vasko, I. Y.; Nakariakov, V. M.

    2015-11-01

    The kinetic model of a one-dimensional force-free current sheet (CS) developed recently by Harrison and Neukirch [Phys. Rev. Lett. 102(13), 135003 (2009)] predicts uniform distributions of the plasma temperature and density across the CS. However, in realistic physical systems, inhomogeneities of these plasma parameters may arise quite naturally due to the boundary conditions or local plasma heating. Moreover, as the CS spatial scale becomes larger than the characteristic kinetic scales (the regime often referred to as the MHD limit), it should be possible to set arbitrary density and temperature profiles. Thus, an advanced model has to allow for inhomogeneities of the macroscopic plasma parameters across the CS, to be consistent with the MHD limit. In this paper, we generalise the kinetic model of a force-free current sheet, taking into account the inhomogeneity of the density and temperature across the CS. In the developed model, the density may either be enhanced or depleted in the CS central region. The temperature profile is prescribed by the density profile, keeping the plasma pressure uniform across the CS. All macroscopic parameters, as well as the distribution functions for the protons and electrons, are determined analytically. Applications of the developed model to current sheets observed in space plasmas are discussed.

  14. Kinetic model of force-free current sheets with non-uniform temperature

    SciTech Connect

    Kolotkov, D. Y.; Nakariakov, V. M.; Vasko, I. Y.

    2015-11-15

    The kinetic model of a one-dimensional force-free current sheet (CS) developed recently by Harrison and Neukirch [Phys. Rev. Lett. 102(13), 135003 (2009)] predicts uniform distributions of the plasma temperature and density across the CS. However, in realistic physical systems, inhomogeneities of these plasma parameters may arise quite naturally due to the boundary conditions or local plasma heating. Moreover, as the CS spatial scale becomes larger than the characteristic kinetic scales (the regime often referred to as the MHD limit), it should be possible to set arbitrary density and temperature profiles. Thus, an advanced model has to allow for inhomogeneities of the macroscopic plasma parameters across the CS, to be consistent with the MHD limit. In this paper, we generalise the kinetic model of a force-free current sheet, taking into account the inhomogeneity of the density and temperature across the CS. In the developed model, the density may either be enhanced or depleted in the CS central region. The temperature profile is prescribed by the density profile, keeping the plasma pressure uniform across the CS. All macroscopic parameters, as well as the distribution functions for the protons and electrons, are determined analytically. Applications of the developed model to current sheets observed in space plasmas are discussed.

  15. Modelling subglacial erosion and englacial sediment transport of the North American ice sheets

    NASA Astrophysics Data System (ADS)

    Hildes, Dave Henry Degast

    The glacial geology of North America is a rich resource upon which reconstructions of ice sheets are made. Numerical modelling of ice sheets based on ice physics is an alternate avenue for cryospheric reconstruction. However, such algorithms are unable to draw from the full wealth of geomorphic data because a large-scale forward model of basal processes, necessary to link the ice and the bed, is not available. I develop a process-based model of sediment production, entrainment, deposition and transport to fill this conspicuous gap. Subglacial abrasion is modelled following Hallet [1979, 1981] and a quarrying model, dependent on subcritical crack growth, is constructed. Entrainment proceeds predominantly by intrusion into the sediment [Iverson and Semmens, 1995] and when basal melt exceeds the rate of entrainment, englacial sediment is deposited. Both vertical redistribution of englacial sediment within an ice column and lateral transport of debris is considered. Ice entrains loose debris from the bed, transports it downstream and deposits an allochthonous debris train, observable on the modern landscape. This can be modelled when an accurate geologic representation of the bed is used, allowing the exploitation of distinct lithologies as natural tracers of ice motion. Also, incorporation of the differences in physical properties between various lithologies is possible with such a lithologically realistic description of the bed. Several processes are functions of bed topography and a description of small-scale topography within a large-scale grid is required; a downscaling method is therefore developed. Basal-ice processes must be coupled to both ice sheet conditions and subglacial hydrology. The Marshall-Clarke thermo-mechanical ice sheet model [Marshall, 1996; Marshall and Clarke, 1997a,b; Marshall et al., 2000] gives the necessary ice sheet fields and provides the forcing for the hydrology model of Flowers [2000] which in turn delivers subglacial water pressure

  16. Full Stokes finite-element modeling of ice sheets using a graphics processing unit

    NASA Astrophysics Data System (ADS)

    Seddik, H.; Greve, R.

    2016-12-01

    Thermo-mechanical simulation of ice sheets is an important approach to understand and predict their evolution in a changing climate. For that purpose, higher order (e.g., ISSM, BISICLES) and full Stokes (e.g., Elmer/Ice, http://elmerice.elmerfem.org) models are increasingly used to more accurately model the flow of entire ice sheets. In parallel to this development, the rapidly improving performance and capabilities of Graphics Processing Units (GPUs) allows to efficiently offload more calculations of complex and computationally demanding problems on those devices. Thus, in order to continue the trend of using full Stokes models with greater resolutions, using GPUs should be considered for the implementation of ice sheet models. We developed the GPU-accelerated ice-sheet model Sainō. Sainō is an Elmer (http://www.csc.fi/english/pages/elmer) derivative implemented in Objective-C which solves the full Stokes equations with the finite element method. It uses the standard OpenCL language (http://www.khronos.org/opencl/) to offload the assembly of the finite element matrix on the GPU. A mesh-coloring scheme is used so that elements with the same color (non-sharing nodes) are assembled in parallel on the GPU without the need for synchronization primitives. The current implementation shows that, for the ISMIP-HOM experiment A, during the matrix assembly in double precision with 8000, 87,500 and 252,000 brick elements, Sainō is respectively 2x, 10x and 14x faster than Elmer/Ice (when both models are run on a single processing unit). In single precision, Sainō is even 3x, 20x and 25x faster than Elmer/Ice. A detailed description of the comparative results between Sainō and Elmer/Ice will be presented, and further perspectives in optimization and the limitations of the current implementation.

  17. Discrete Element Modeling of Oscillatory Sheet Flow Using Medium and Coarse Spherical Sand Grains.

    NASA Astrophysics Data System (ADS)

    Cobb, M. M.; Calantoni, J.; Holland, T.; Odonoghue, T.

    2006-12-01

    Oscillatory wave-driven sheet flow transports large quantities of surf and swash zone sediment and is fundamental to understanding the redistribution of sediments during the morphodynamic evolution of wave dominated sandy beaches. In order to better understand sheet flow processes and their sensitivity to grain size distributions sediment transport simulations that explicitly describe the small-scale grain-fluid interactions are performed. In this study asymmetric second order stokes wave oscillatory sheet flow is investigated using a discrete element model (DEM). We examine the time averaged total transport, time-dependent transport with depth, and time-dependent concentration with depth for second order stokes waves with periods of 5 and 7.5 seconds and amplitudes of 1 and 1.5 meters, respectively, over beds with medium (D50 = 0.28 mm) and coarse (D50 = 0.51 mm) grains. Direct comparisons are made between model results and data taken at the Aberdeen Oscillatory Flow Tunnel. For coarse grain cases the model predictions are 15-25% greater than the measured total transport in the experiments. Model-data comparisons of the time dependent concentration as a function of depth reveal good agreement within the bedload layer, suggesting that the DEM is successfully describing the same physical processes involved in the sheet flow transport. In addition, correlations between the time-dependent concentrations at different depths indicate that the model has the same spatio-temporal structure exhibited by the laboratory measurements. However, the DEM, which is coupled to a simple one-dimensional mixing length fluid model, underpredicts total transport for medium grains since it cannot account for the substantial amount of suspended sediment that most likely contributes to the measured total transport.

  18. Contribution of Greenland ice sheet melting to sea level rise during the last interglacial period: an approach combining ice sheet modelling and proxy data

    NASA Astrophysics Data System (ADS)

    Quiquet, A.; Ritz, C.; Punge, H. J.; Salas y Mélia, D.

    2012-08-01

    In the context of global warming, the contribution of the two major ice sheets, Antarctica and Greenland, to global sea level rise is a subject of key importance for the scientific community (4th assessment report of the Intergovernmental Panel on climate change, IPCC-AR4, Meehl et al., 2007). By the end of the next century, a 3-5 °C warm up is expected in Greenland. Similar temperatures in this region were reached during the last interglacial (LIG) period due to a change in orbital configuration rather than to anthropogenic forcing. Ice core evidence suggests that the Greenland Ice Sheet (GIS) has survived this warm period but great uncertainties remain about the total Greenland ice reduction during the LIG and its sea level rise contribution. In order to improve our confidence in future state projections, we first intend to reconstruct the past states of the GIS using ice sheet modelling, and confront the simulations with paleo data. The chosen methodoly of paleoclimate reconstruction is strongly based on proxy data. Proxy data are also used to constrain the ice sheet model during the calibration phase. Our estimates of Greenland melting contribution to sea level rise during the LIG period range from 0.65 to 1.5 m of sea level equivalent.

  19. A current sheet model for the Earth's magnetic field

    NASA Astrophysics Data System (ADS)

    Stump, Daniel R.; Pollack, Gerald L.

    1998-09-01

    As an example in magnetostatics we consider the main magnetic field of the Earth and its current sources. The measured field on the surface is accurately given, in tables of the International Geological Reference Field, in terms of Gaussian coefficients. By applying Maxwell's equations to these data we calculate the extended field, inside the Earth, and give graphical representations of it. We also construct a simple theoretical model of the source of the field, in which the field is the result of currents flowing on the surface of a sphere inside the Earth. The current sources which give the observed field are calculated in terms of vector spherical harmonics. The stream function and currents are displayed on a Mercator projection for a sphere whose radius is half the Earth's radius. Interesting properties of vector operations on the Mercator plane are analytically and graphically described.

  20. Borehole temperature response for competing models of Laurentide ice sheet dynamics

    NASA Astrophysics Data System (ADS)

    Rath, Volker; Alvarez-Solas, Jorge; Robinson, Alex; Montoya-Redondo, Marisa

    2013-04-01

    Borehole temperature profiles (BTP) are not only the source for estimates of the background geothermal heat flow, but also allow the reconstruction of past surface temperature changes. Though shallow boreholes (e. g. less than 500 m) are abundant in most continental areas, their use is inhibited by the necessity of extracting the paleoclimatic signal present in the borehole temperature at any depth. However, assuming a long-term ground surface temperature history (GSTH), a generalized reduced temperature may be used for the interpretation of the shallow observations. To derive or test the required assumptions, very deep boreholes (say, > 2000 m) are highly important also for the investigation of shallow measurements. In areas which were influenced by the Last Glacial Period (LGP), the existence of the large scale ice sheets (e.g. the Laurentide or Weichselian), the spatial distribution of basal conditions, and the timing of their retreat have a major influence on the subsurface temperature regime. Though for parts of its history no longer directly related to atmospheric temperature, deep BTPs carry information on basal conditions, oceanic transgressions, and retreat histories, and can thus contribute to the confirmation/rejection, or even calibration of ice sheet models. From this it follows that a meaningful interpretation of the paleoclimatic signal can only proceed with a reasonable understanding of the regional ice sheet behavior, and, in order to quantify the effects, a calibrated numerical ice sheet model. From such a model, synthetic long term GSTHs may be generated, which can subsequently be used to derive the generalized reduced temperatures for the shallow BTPs. This approach is challenging in several aspects: (1) high-resolution, high-order/hybrid ice sheet models are only now emerging, and the physics at the base (e.g. ice streams) needs improvement; (2) a calibration in the sense of a Bayesian inverse problem are rare, and (3) appropriate sets of

  1. An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model

    NASA Technical Reports Server (NTRS)

    Pollard, D.

    1978-01-01

    The astronomical theory of the Quaternary ice ages is incorporated into a simple climate model for global weather; important features of the model include the albedo feedback, topography and dynamics of the ice sheets. For various parameterizations of the orbital elements, the model yields realistic assessments of the northern ice sheet. Lack of a land-sea heat capacity contrast represents one of the chief difficulties of the model.

  2. An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model

    NASA Technical Reports Server (NTRS)

    Pollard, D.

    1978-01-01

    The astronomical theory of the Quaternary ice ages is incorporated into a simple climate model for global weather; important features of the model include the albedo feedback, topography and dynamics of the ice sheets. For various parameterizations of the orbital elements, the model yields realistic assessments of the northern ice sheet. Lack of a land-sea heat capacity contrast represents one of the chief difficulties of the model.

  3. Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models

    NASA Astrophysics Data System (ADS)

    Levermann, A.; Winkelmann, R.; Nowicki, S.; Fastook, J. L.; Frieler, K.; Greve, R.; Hellmer, H. H.; Martin, M. A.; Meinshausen, M.; Mengel, M.; Payne, A. J.; Pollard, D.; Sato, T.; Timmermann, R.; Wang, W. L.; Bindschadler, R. A.

    2014-08-01

    The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02-0.14 m; 90% range: 0.0-0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04-0.21 m; 90% range: 0.01-0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these

  4. Assessing the links between Greenland Ice Sheet Surface Mass Balance and Arctic climate using Climate Models and Observations

    NASA Astrophysics Data System (ADS)

    Mottram, Ruth; Rodehacke, Christian; Boberg, Fredrik; Langen, Peter; Sloth Madsen, Marianne; Høyer Svendsen, Synne; Yang, Shuting; Hesselbjerg Christensen, Jens; Olesen, Martin

    2016-04-01

    Changes in different parts of the Arctic cryosphere may have knock-on effects on other parts of the system. The fully coupled climate model EC-Earth, which includes the ice sheet model PISM, is a useful tool to examine interactions between sea ice, ice sheet, ocean and atmosphere. Here we present results from EC-Earth experimental simulations that show including an interactive ice sheet model changes ocean circulation, sea ice extent and regional climate with, for example, a dampening of the expected increase in Arctic temperatures under the RCP scenarios when compared with uncoupled experiments. However, the relatively coarse resolution of the climate model likely influences the calculated surface mass balance forcing applied to the ice sheet model and it is important therefore to evaluate the model performance over the ice sheet. Here, we assess the quality of the climate forcing from the GCM to the ice sheet model by comparing the energy balance and surface mass balance (SMB) output from EC-Earth with that from a regional climate model (RCM) run at very high resolution (0.05 degrees) over Greenland. The RCM, HIRHAM5, has been evaluated over a wide range of climate parameters for Greenland which allows us to be confident it gives a representative climate forcing for the Greenland ice sheet. To evaluate the internal variability in the climate forcing, we compare simulations from HIRHAM5 forced with both the EC-Earth historical emissions and the ERA-Interim reanalysis on the boundaries. The EC-Earth-PISM RCP8.5 scenario is also compared with an EC-Earth run without an ice sheet to assess the impact of an interactive ice sheet on likely future changes. To account for the resolution difference between the models we downscale both EC-Earth and HIRHAM5 simulations with a simple offline energy balance model (EBM).

  5. Shape change in mouthguard sheets during thermoforming - part 2: effect of the anteroposterior position of the model on mouthguard thickness.

    PubMed

    Takahashi, Mutsumi; Araie, Yoshiaki; Satoh, Yoshihide; Iwasaki, Shin-Ichi

    2017-04-01

    Mouthguards can reduce the risk of sports-related injuries, but the sheet material and thickness have a large effect on their efficacy and safety. The aim of this study was to investigate the effect of model position in the molding machine on the reduction in mouthguard thickness. Ethylene vinyl acetate sheets and olefin copolymer sheets were used for thermoforming by a pressure- or a vacuum-forming machine. The working model was trimmed to the height of 25 mm at the maxillary central incisor and 20 mm at maxillary first molar. For both pressure forming and vacuum forming, the model was placed with the anterior rim of the model positioned 40, 30, 25, 20, or 10 mm from the front of the sheet frame. An additional test was carried out at 50 mm for vacuum forming. The sheet thickness after fabrication was determined for the incisal edge, labial surface, and buccal surface using a specialized caliper. The difference of the model position on the reduction in thickness in each forming device and sheet material was analyzed by one-way analysis of variance and Bonferroni's multiple comparison tests. The reductions in thickness at the incisal edge and labial surface were about -60% and -50%, respectively, for the distance of 25 mm from the front of forming table. That position was the same as the height of the anterior part of the model for each molding machine and sheet material. The anterior thickness after molding became greater as the distance between the model and the sheet frame became smaller. The results showed that the thickness reduction was large when the distance from the model to the frame was small. This demonstrates the importance of centering the sheet and the model to achieve the most stable molding when positioning the model in the forming unit. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  6. Autologous preconditioned mesenchymal stem cell sheets improve left ventricular function in a rabbit old myocardial infarction model

    PubMed Central

    Tanaka, Yuya; Shirasawa, Bungo; Takeuchi, Yuriko; Kawamura, Daichi; Nakamura, Tamami; Samura, Makoto; Nishimoto, Arata; Ueno, Koji; Morikage, Noriyasu; Hosoyama, Tohru; Hamano, Kimikazu

    2016-01-01

    Mesenchymal stem cells (MSCs) constitute one of the most powerful tools for therapeutic angiogenesis in infarcted hearts. However, conventional MSC transplantation approaches result in insufficient therapeutic effects due to poor retention of graft cells in severe ischemic diseases. Cell sheet technology has been developed as a new method to prolong graft cell retention even in ischemic tissue. Recently, we demonstrated that hypoxic pretreatment enhances the therapeutic efficacy of cell sheet implantation in infarcted mouse hearts. In this study, we investigated whether hypoxic pretreatment activates the therapeutic functions of bone marrow-derived MSC (BM-MSC) sheets and improves cardiac function in rabbit infarcted hearts following autologous transplantation. Production of vascular endothelial growth factor (VEGF) was increased in BM-MSC monolayer sheets and it peaked at 48 h under hypoxic culture conditions (2% O2). To examine in vivo effects, preconditioned autologous BM-MSC sheets were implanted into a rabbit old myocardial infarction model. Implantation of preconditioned BM-MSC sheets accelerated angiogenesis in the peri-infarcted area and decreased the infarcted area, leading to improvement of the left ventricular function of the infarcted heart. Importantly, the therapeutic efficacy of the preconditioned BM-MSC sheets was higher than that of standardly cultured sheets. Thus, implantation of autologous preconditioned BM-MSC sheets is a feasible approach for enhancing therapeutic angiogenesis in chronically infarcted hearts. PMID:27347329

  7. The Effect of Solar Forcing on the Greenland Ice Sheet during the Holocene - A Model Study

    NASA Astrophysics Data System (ADS)

    Bügelmayer, Marianne; Roche, Didier; Renssen, Hans

    2014-05-01

    Abrupt climate changes did not only happen during glacials but also during interglacials such as the Holocene. Marine sediments provide evidence for the periodic occurrence of centennial-scale events with enhanced iceberg discharge during the past 11.000 years (Bond et al., 2001). These events were chronologically linked to reduced solar activity as reconstructed using cosmogenic isotopes (Bond et al., 2001), indicating that even an external forcing that is considered to be small, has a potential impact on climate due to several feedback mechanisms (Renssen et al., 2006). The interactions between climate and solar irradiance have been investigated using numerical models (e.g. Haigh, 1996; Renssen et al, 2006), but so far without dynamically computing the Greenland ice sheet and iceberg calving. Thus, the impact of solar variations on iceberg discharge and the underlying mechanisms have not been analysed so far. To analyse the effect of variations in solar activity on the Greenland ice sheet (GIS) and the iceberg calving, as well as possible feedback mechanisms that enhance the impact of the total solar irradiance, we use the earth system model of intermediate complexity (iLOVECLIM, Roche et al., 2013), coupled to the ice sheet/ice shelf model GRISLI (Ritz et al., 2001) and to a dynamic-thermodynamic iceberg module (Jongma et al., 2009, Bügelmayer et al., 2014) to perform transient experiments of the last 6000 years. The experiments are conducted applying reconstructed atmospheric greenhouse gas concentrations, volcanic aerosol loads, orbital parameters and variations in the total solar irradiance. We present the response of the coupled model to different solar irradiance scenarios to evaluate modeled GIS sensitivity to relatively modest variations in radiative forcing. Moreover, we investigate the dependence of the model results on the chosen model sensitivity. References: Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M. N., Showers, W., … Bonani, G

  8. A balanced water layer concept for subglacial hydrology in large scale ice sheet models

    NASA Astrophysics Data System (ADS)

    Goeller, S.; Thoma, M.; Grosfeld, K.; Miller, H.

    2012-12-01

    There is currently no doubt about the existence of a wide-spread hydrological network under the Antarctic ice sheet, which lubricates the ice base and thus leads to increased ice velocities. Consequently, ice models should incorporate basal hydrology to obtain meaningful results for future ice dynamics and their contribution to global sea level rise. Here, we introduce the balanced water layer concept, covering two prominent subglacial hydrological features for ice sheet modeling on a continental scale: the evolution of subglacial lakes and balance water fluxes. We couple it to the thermomechanical ice-flow model RIMBAY and apply it to a synthetic model domain inspired by the Gamburtsev Mountains, Antarctica. In our experiments we demonstrate the dynamic generation of subglacial lakes and their impact on the velocity field of the overlaying ice sheet, resulting in a negative ice mass balance. Furthermore, we introduce an elementary parametrization of the water flux-basal sliding coupling and reveal the predominance of the ice loss through the resulting ice streams against the stabilizing influence of less hydrologically active areas. We point out, that established balance flux schemes quantify these effects only partially as their ability to store subglacial water is lacking.

  9. Modelling the Isotopic Response to Antarctic Ice Sheet Change During the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Holloway, Max; Sime, Louise; Singarayer, Joy; Tindall, Julia; Valdes, Paul

    2015-04-01

    Ice sheet changes can exert major control over spatial water isotope variations in Antarctic surface snow. Consequently a significant mass loss or gain of the West Antarctic Ice Sheet (WAIS) would be expected to cause changes in the water isotope record across Antarctic ice core sites. Analysis of sea level indicators for the last interglacial (LIG), around 125 to 128 ka, suggest a global sea level peak 6 to 9 m higher than present. Recent NEEM Greenland ice core results imply that Greenland likely provided a modest ~2m contribution towards this global sea level rise. This implies that a WAIS contribution is necessary to explain the LIG sea level maxima. In addition, Antarctic ice core records suggest that Antarctic air temperatures during the LIG were up to 6°C warmer than present. Climate models have been unable to recreate such warmth when only orbital and greenhouse gas forcing are considered. Thus changes to the Antarctic ice sheet and ocean circulation may be required to reconcile model simulations with ice core data. Here we model the isotopic response to differing WAIS deglaciation scenarios, freshwater hosing, and sea ice configurations using a fully coupled General Circulation Model (GCM) to help interpret Antarctic ice core records over the LIG. This approach can help isolate the contribution of individual processes and feedbacks to final isotopic signals recorded in Antarctic ice cores.

  10. Force-free collisionless current sheet models with non-uniform temperature and density profiles

    NASA Astrophysics Data System (ADS)

    Wilson, F.; Neukirch, T.; Allanson, O.

    2017-09-01

    We present a class of one-dimensional, strictly neutral, Vlasov-Maxwell equilibrium distribution functions for force-free current sheets, with magnetic fields defined in terms of Jacobian elliptic functions, extending the results of Abraham-Shrauner [Phys. Plasmas 20, 102117 (2013)] to allow for non-uniform density and temperature profiles. To achieve this, we use an approach previously applied to the force-free Harris sheet by Kolotkov et al. [Phys. Plasmas 22, 112902 (2015)]. In one limit of the parameters, we recover the model of Kolotkov et al. [Phys. Plasmas 22, 112902 (2015)], while another limit gives a linear force-free field. We discuss conditions on the parameters such that the distribution functions are always positive and give expressions for the pressure, density, temperature, and bulk-flow velocities of the equilibrium, discussing the differences from previous models. We also present some illustrative plots of the distribution function in velocity space.

  11. Heat and mass transfer in nanofluid thin film over an unsteady stretching sheet using Buongiorno's model

    NASA Astrophysics Data System (ADS)

    Qasim, M.; Khan, Z. H.; Lopez, R. J.; Khan, W. A.

    2016-01-01

    The heat and mass transport of a nanofluid thin film over an unsteady stretching sheet has been investigated. This is the first paper on nanofluid thin film flow caused by unsteady stretching sheet using Buongiorno's model. The model used for the nanofluid film incorporates the effects of Brownian motion and thermophoresis. The self-similar non-linear ordinary differential equations are solved using Maple's built-in BVP solver. The results for pure fluid are found to be in good agreement with the literature. Present analysis shows that free surface temperature and nanoparticle volume fraction increase with both unsteadiness and magnetic parameters. The results reveal that effect of both nanofluid parameters and viscous dissipation is to reduce the heat transfer rate.

  12. Trimming Simulation of Forming Metal Sheets Isogeometric Models by Using NURBS Surfaces

    NASA Astrophysics Data System (ADS)

    Herrero-Adan, D.; Cardoso, Rui P. R.; Adetoro, O. B.

    2016-08-01

    Some metal sheets forming processes need trimming in a final stage for achieving the net- shape specification and for removing micro-cracks and irregularities. In numerical simulation, since the exact final edge location is a priori unknown in the original metal blanket, the trimming needs to be done once the forming is finished. During the forming internal stresses are generated inside the sheet. When trimming those stresses configuration is changed to achieve equilibrium as a consequence of the material removal. In this paper a novel method for simulating the trimming is presented. The part to trim is modelled using isogeometric analysis (IGA). The new surface generated is modelled with non-uniform rational B-splines (NURBS). Due to the IGA characteristics a total geometrical accuracy and an efficient residual stresses recalculation are accomplished.

  13. A customized light sheet microscope to measure spatio-temporal protein dynamics in small model organisms.

    PubMed

    Rieckher, Matthias; Kyparissidis-Kokkinidis, Ilias; Zacharopoulos, Athanasios; Kourmoulakis, Georgios; Tavernarakis, Nektarios; Ripoll, Jorge; Zacharakis, Giannis

    2015-01-01

    We describe a customizable and cost-effective light sheet microscopy (LSM) platform for rapid three-dimensional imaging of protein dynamics in small model organisms. The system is designed for high acquisition speeds and enables extended time-lapse in vivo experiments when using fluorescently labeled specimens. We demonstrate the capability of the setup to monitor gene expression and protein localization during ageing and upon starvation stress in longitudinal studies in individual or small groups of adult Caenorhabditis elegans nematodes. The system is equipped to readily perform fluorescence recovery after photobleaching (FRAP), which allows monitoring protein recovery and distribution under low photobleaching conditions. Our imaging platform is designed to easily switch between light sheet microscopy and optical projection tomography (OPT) modalities. The setup permits monitoring of spatio-temporal expression and localization of ageing biomarkers of subcellular size and can be conveniently adapted to image a wide range of small model organisms and tissue samples.

  14. A Customized Light Sheet Microscope to Measure Spatio-Temporal Protein Dynamics in Small Model Organisms

    PubMed Central

    Rieckher, Matthias; Kourmoulakis, Georgios; Tavernarakis, Nektarios; Ripoll, Jorge; Zacharakis, Giannis

    2015-01-01

    We describe a customizable and cost-effective light sheet microscopy (LSM) platform for rapid three-dimensional imaging of protein dynamics in small model organisms. The system is designed for high acquisition speeds and enables extended time-lapse in vivo experiments when using fluorescently labeled specimens. We demonstrate the capability of the setup to monitor gene expression and protein localization during ageing and upon starvation stress in longitudinal studies in individual or small groups of adult Caenorhabditis elegans nematodes. The system is equipped to readily perform fluorescence recovery after photobleaching (FRAP), which allows monitoring protein recovery and distribution under low photobleaching conditions. Our imaging platform is designed to easily switch between light sheet microscopy and optical projection tomography (OPT) modalities. The setup permits monitoring of spatio-temporal expression and localization of ageing biomarkers of subcellular size and can be conveniently adapted to image a wide range of small model organisms and tissue samples. PMID:26000610

  15. Neoproterozoic 'snowball Earth' simulations with a coupled climate/ice-sheet model.

    PubMed

    Hyde, W T; Crowley, T J; Baum, S K; Peltier, W R

    2000-05-25

    Ice sheets may have reached the Equator in the late Proterozoic era (600-800 Myr ago), according to geological and palaeomagnetic studies, possibly resulting in a 'snowball Earth'. But this period was a critical time in the evolution of multicellular animals, posing the question of how early life survived under such environmental stress. Here we present computer simulations of this unusual climate stage with a coupled climate/ice-sheet model. To simulate a snowball Earth, we use only a reduction in the solar constant compared to present-day conditions and we keep atmospheric CO2 concentrations near present levels. We find rapid transitions into and out of full glaciation that are consistent with the geological evidence. When we combine these results with a general circulation model, some of the simulations result in an equatorial belt of open water that may have provided a refugium for multicellular animals.

  16. Validity of the thin viscous sheet approximation in models of continental collision

    NASA Astrophysics Data System (ADS)

    Garthwaite, Matthew C.; Houseman, Gregory A.

    2011-02-01

    The two-dimensional thin viscous sheet approximation is widely used to describe large-scale continental deformation. It treats the lithosphere as a fluid layer in which deformation results from a balance between buoyancy forces and tectonic boundary conditions. Comparisons between two-dimensional thin sheet and full three-dimensional solutions of a simple indenter model show that appreciable differences exist, especially when the indenter half width, D, is of the same order as the thickness of the deforming layer, L (i.e., D/L ≈ 1). These differences are amplified by increasing the power law exponent of the viscous constitutive law (n) but decrease as the Argand number (Ar) is increased. The greatest differences between two-dimensional and three-dimensional solutions are found at the indenter corner, where the thin sheet consistently overestimates vertical strain rates. Differences between strain rates at the corner may be 50% or greater for small Argand numbers. Other differences arise because a lithospheric root zone is formed in the three-dimensional solutions and vertically averaged strain rate is decreased in regions close to the indenter. This effect is absent from thin sheet calculations since the thickness of the load-bearing layer is assumed constant. In general, the thin viscous sheet approximation provides a reasonably accurate estimate of long wavelength deformation for D/L as low as 1 if n is less than ˜3. However, even at large D/L the solutions may be inaccurate close to strain rate concentrations at the indenter corners where horizontal gradients of deformation are large.

  17. Analysis of the RPE sheet in the rd10 retinal degeneration model

    SciTech Connect

    Jiang, Yi

    2011-01-04

    The normal RPE sheet in the C57Bl/6J mouse is subclassified into two major tiling patterns: A regular generally hexagonal array covering most of the surface and a 'soft network' near the ciliary body made of irregularly shaped cells. Physics models predict these two patterns based on contractility and elasticity of the RPE cell, and strength of cellular adhesion between cells. We hypothesized and identified major changes in RPE regular hexagonal tiling pattern in rdl0 compared to C57BL/6J mice. RPE sheet damage was extensive but occurred in rd10 later than expected, after most retinal degeneration. RPE sheet changes occur in zones with a bullseye pattern. In the posterior zone around the optic nerve RPE cells take on larger irregular and varied shapes to form an intact monolayer. In mid periphery, there is a higher than normal density of cells that progress into involuted layers of RPE under the retina. The periphery remains mostly normal until late stages of degeneration. The number of neighboring cells varies widely depending on zone and progression. RPE morphology continues to deteriorate long after the photoreceptors have degenerated. The RPE cells are bystanders to the rd10 degeneration within photo receptors, and the collateral damage to the RPE sheet resembles stimulation of migration or chemotaxis. Quantitative measures of the tiling patterns and histopathology detected here, scripted in a pipeline written in Perl and Cell Profiler (an open source Matlab plugin), are directly applicable to RPE sheet images from noninvasive fundus autofluorescence (FAF), adaptive optics confocal scanning laser ophthalmoscope (AO-cSLO), and spectral domain optical coherence tomography (SD-OCT) of patients with early stage AMD or RP.

  18. Absorption of calcium ions on oxidized graphene sheets and study its dynamic behavior by kinetic and isothermal models

    NASA Astrophysics Data System (ADS)

    Fathy, Mahmoud; Abdel Moghny, Th.; Mousa, Mahmoud Ahmed; El-Bellihi, Abdel-Hameed A.-A.; Awadallah, Ahmed E.

    2016-11-01

    Sorption of calcium ion from the hard underground water using novel oxidized graphene (GO) sheets was studied in this paper. Physicochemical properties and microstructure of graphene sheets were investigated using Raman spectrometer, thermogravimetry analyzer, transmission electron microscope, scanning electron microscope. The kinetics adsorption of calcium on graphene oxide sheets was examined using Lagergren first and second orders. The results show that the Lagergren second-order was the best-fit model that suggests the conception process of calcium ion adsorption on the Go sheets. For isothermal studies, the Langmuir and Freundlich isotherm models were used at temperatures ranging between 283 and 313 K. Thermodynamic parameters resolved at 283, 298 and 313 K indicating that the GO adsorption was exothermic spontaneous process. Finally, the graphene sheets show high partiality toward calcium particles and it will be useful in softening and treatment of hard water.

  19. The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet-climate model

    NASA Astrophysics Data System (ADS)

    Stap, Lennert B.; van de Wal, Roderik S. W.; de Boer, Bas; Bintanja, Richard; Lourens, Lucas J.

    2017-09-01

    Since the inception of the Antarctic ice sheet at the Eocene-Oligocene transition (˜ 34 Myr ago), land ice has played a crucial role in Earth's climate. Through feedbacks in the climate system, land ice variability modifies atmospheric temperature changes induced by orbital, topographical, and greenhouse gas variations. Quantification of these feedbacks on long timescales has hitherto scarcely been undertaken. In this study, we use a zonally averaged energy balance climate model bidirectionally coupled to a one-dimensional ice sheet model, capturing the ice-albedo and surface-height-temperature feedbacks. Potentially important transient changes in topographic boundary conditions by tectonics and erosion are not taken into account but are briefly discussed. The relative simplicity of the coupled model allows us to perform integrations over the past 38 Myr in a fully transient fashion using a benthic oxygen isotope record as forcing to inversely simulate CO2. Firstly, we find that the results of the simulations over the past 5 Myr are dependent on whether the model run is started at 5 or 38 Myr ago. This is because the relation between CO2 and temperature is subject to hysteresis. When the climate cools from very high CO2 levels, as in the longer transient 38 Myr run, temperatures in the lower CO2 range of the past 5 Myr are higher than when the climate is initialised at low temperatures. Consequently, the modelled CO2 concentrations depend on the initial state. Taking the realistic warm initialisation into account, we come to a best estimate of CO2, temperature, ice-volume-equivalent sea level, and benthic δ18O over the past 38 Myr. Secondly, we study the influence of ice sheets on the evolution of global temperature and polar amplification by comparing runs with ice sheet-climate interaction switched on and off. By passing only albedo or surface height changes to the climate model, we can distinguish the separate effects of the ice-albedo and surface

  20. Modelling the liquid-water vein system within polar ice sheets as a potential microbial habitat

    NASA Astrophysics Data System (ADS)

    Dani, K. G. Srikanta; Mader, Heidy M.; Wolff, Eric W.; Wadham, Jemma L.

    2012-06-01

    Based on the fundamental and distinctive physical properties of polycrystalline ice Ih, the chemical and temperature profiles within the polar ice sheets, and the observed selective partitioning of bacteria into liquid water filled veins in the ice, we consider the possibility that microbial life could survive and be sustained within glacial systems. Here, we present a set of modelled vertical profiles of vein diameter, vein chemical concentration, and vein water volume variability across a range of polar ice sheets using their ice core chemical profiles. A sensitivity analysis of VeinsInIce1.0, the numerical model used in this study shows that the ice grain size and the local borehole temperature are the most significant factors that influence the intergranular liquid vein size and the amount of freeze-concentrated impurities partitioned into the veins respectively. Model results estimate the concentration and characteristics of the chemical broth in the veins to be a potential extremophilic microbial medium. The vein sizes are estimated to vary between 0.3 μm to 8 μm across the vertical length of many polar ice sheets and they may contain up to 2 μL of liquid water per litre of solid ice. The results suggest that these veins in polar ice sheets could accommodate populations of psychrophilic and hyperacidophilic ultra-small bacteria and in some regions even support the habitation of unicellular eukaryotes. This highlights the importance of understanding the potential impact of englacial microbial metabolism on polar ice core chemical profiles and provides a model for similar extreme habitats elsewhere in the universe.

  1. Modelling the Climate Response to the Antarctic Ice Sheet at 35MY Ago

    NASA Astrophysics Data System (ADS)

    Justino, Flavio; Stordal, Frode

    2014-05-01

    This presentation will discuss the main features of the Earth climate related to changes in Antarctic topography. The results are based on a coupled modelling experiment (Speedy-Nemo) forced with the ice sheet topography as proposed by DeConto and Pollard (Nature 2003). Changes in the MOC, atmospheric and oceanic heat fluxes and modification in the atmospheric and oceanic circulations will be shown.

  2. Smoothed particle hydrodynamics non-Newtonian model for ice-sheet and ice-shelf dynamics

    SciTech Connect

    Pan, W.; Tartakovsky, A. M.; Monaghan, J. J.

    2013-06-01

    Mathematical modeling of ice sheets is complicated by the non-linearity of the governing equations and boundary conditions. Standard grid-based methods require complex front tracking techniques and have limited capability to handle large material deformations and abrupt changes in bottom topography. As a consequence, numerical methods are usually restricted to shallow ice sheet and ice shelf approximations. We propose a new smoothed particle hydrodynamics (SPH) non-Newtonian model for coupled ice sheet and ice shelf dynamics. SPH, a fully Lagrangian particle method, is highly scalable and its Lagrangian nature and meshless discretization are well suited to the simulation of free surface flows, large material deformation, and material fragmentation. In this paper, SPH is used to study 3D ice sheet/ice shelf behavior, and the dynamics of the grounding line. The steady state position of the grounding line obtained from SPH simulations is in good agreement with laboratory observations for a wide range of simulated bedrock slopes, and density ratios, similar to those of ice and sea water. The numerical accuracy of the SPH algorithm is verif;ed by simulating Poiseuille flow, plane shear flow with free surface and the propagation of a blob of ice along a horizontal surface. In the laboratory experiment, the ice was represented with a viscous Newtonian fluid. In the present work, however, the ice is modeled as both viscous Newtonian fluid and non-Newtonian fluid, such that the effect of non-Newtonian rheology on the dynamics of grounding line was examined. The non-Newtonian constitutive relation is prescribed to be Glen’s law for the creep of polycrystalline ice. A V-shaped bedrock ramp is further introduced to model the real geometry of bedrock slope.

  3. Magnetotail Current Sheet Thinning and Magnetic Reconnection Dynamics in Global Modeling of Substorms

    NASA Technical Reports Server (NTRS)

    Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.; DeZeeuw, D. L.; Gombosi, T. I.

    2008-01-01

    Magnetotail current sheet thinning and magnetic reconnection are key elements of magnetospheric substorms. We utilized the global MHD model BATS-R-US with Adaptive Mesh Refinement developed at the University of Michigan to investigate the formation and dynamic evolution of the magnetotail thin current sheet. The BATSRUS adaptive grid structure allows resolving magnetotail regions with increased current density up to ion kinetic scales. We investigated dynamics of magnetotail current sheet thinning in response to southwards IMF turning. Gradual slow current sheet thinning during the early growth phase become exponentially fast during the last few minutes prior to nightside reconnection onset. The later stage of current sheet thinning is accompanied by earthward flows and rapid suppression of normal magnetic field component $B-z$. Current sheet thinning set the stage for near-earth magnetic reconnection. In collisionless magnetospheric plasma, the primary mechanism controlling the dissipation in the vicinity of the reconnection site is non-gyrotropic effects with spatial scales comparable with the particle Larmor radius. One of the major challenges in global MHD modeling of the magnetotail magnetic reconnection is to reproduce fast reconnection rates typically observed in smallscale kinetic simulations. Bursts of fast reconnection cause fast magnetic field reconfiguration typical for magnetospheric substorms. To incorporate nongyritropic effects in diffusion regions we developed an algorithm to search for magnetotail reconnection sites, specifically where the magnetic field components perpendicular to the local current direction approaches zero and form an X-type configuration. Spatial scales of the diffusion region and magnitude of the reconnection electric field are calculated self-consistently using MHD plasma and field parameters in the vicinity of the reconnection site. The location of the reconnection sites and spatial scales of the diffusion region are updated

  4. Calibration of Gurson-type models for porous sheet metals with anisotropic non-quadratic plasticity

    NASA Astrophysics Data System (ADS)

    Gologanu, M.; Kami, A.; Comsa, D. S.; Banabic, D.

    2016-08-01

    The growth and coalescence of voids in sheet metals are not only the main active mechanisms in the final stages of fracture in a necking band, but they also contribute to the forming limits via changes in the normal directions to the yield surface. A widely accepted method to include void effects is the development of a Gurson-type model for the appropriate yield criterion, based on an approximate limit analysis of a unit cell containing a single spherical, spheroidal or ellipsoidal void. We have recently [2] obtained dissipation functions and Gurson-type models for porous sheet metals with ellipsoidal voids and anisotropic non-quadratic plasticity, including yield criteria based on linear transformations (Yld91 and Yld2004-18p) and a pure plane stress yield criteria (BBC2005). These Gurson-type models contain several parameters that depend on the void and cell geometries and on the selected yield criterion. Best results are obtained when these key parameters are calibrated via numerical simulations using the same unit cell and a few representative loading conditions. The single most important such loading condition corresponds to a pure hydrostatic macroscopic stress (pure pressure) and the corresponding velocity field found during the solution of the limit analysis problem describes the expansion of the cavity. However, for the case of sheet metals, the condition of plane stress precludes macroscopic stresses with large triaxiality or ratio of mean stress to equivalent stress, including the pure hydrostatic case. Also, pure plane stress yield criteria like BBC2005 must first be extended to 3D stresses before attempting to develop a Gurson-type model and such extensions are purely phenomenological with no due account for the out- of-plane anisotropic properties of the sheet. Therefore, we propose a new calibration method for Gurson- type models that uses only boundary conditions compatible with the plane stress requirement. For each such boundary condition we use

  5. Decadal-Scale Response of the Antarctic Ice sheet to a Warming Ocean using the POPSICLES Coupled Ice Sheet-Ocean model

    NASA Astrophysics Data System (ADS)

    Martin, Daniel; Asay-Davis, Xylar; Cornford, Stephen; Price, Stephen; Ng, Esmond; Collins, William

    2016-04-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period from 1990 to 2010. We use the CORE v. 2 interannual forcing data to force the ocean model. Simulations are performed at 0.1 degree (~5 km) ocean resolution with adaptive ice sheet resolution as fine as 500 m to adequately resolve the grounding line dynamics. We discuss the effect of improved ocean mixing and subshelf bathymetry (vs. the standard Bedmap2 bathymetry) on the behavior of the coupled system, comparing time-averaged melt rates below a number of major ice shelves with those reported in the literature. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and the consequent dynamic response of the grounded ice sheet. POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program, and the BISICLES ice-sheet model. POP2x includes sub-ice-shelf circulation using partial top cells and the commonly used three-equation boundary layer physics. Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP) and other continental-scale simulations and melt-rate observations. BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d) and realistic configurations.

  6. Decadal-Scale Response of the Antarctic Ice sheet to a Warming Ocean using the POPSICLES Coupled Ice Sheet-Ocean model

    NASA Astrophysics Data System (ADS)

    Martin, D. F.; Asay-Davis, X.; Cornford, S. L.; Price, S. F.; Ng, E. G.; Collins, W.

    2015-12-01

    We present POPSICLES simulation results covering the full Antarctic Ice Sheet and the Southern Ocean spanning the period from 1990 to 2010. We use the CORE v. 2 interannual forcing data to force the ocean model. Simulations are performed at 0.1o(~5 km) ocean resolution with adaptive ice sheet resolution as fine as 500 m to adequately resolve the grounding line dynamics. We discuss the effect of improved ocean mixing and subshelf bathymetry (vs. the standard Bedmap2 bathymetry) on the behavior of the coupled system, comparing time-averaged melt rates below a number of major ice shelves with those reported in the literature. We also present seasonal variability and decadal melting trends from several Antarctic regions, along with the response of the ice shelves and the consequent dynamic response of the grounded ice sheet.POPSICLES couples the POP2x ocean model, a modified version of the Parallel Ocean Program, and the BISICLES ice-sheet model. POP2x includes sub-ice-shelf circulation using partial top cells and the commonly used three-equation boundary layer physics. Standalone POP2x output compares well with standard ice-ocean test cases (e.g., ISOMIP) and other continental-scale simulations and melt-rate observations. BISICLES makes use of adaptive mesh refinement and a 1st-order accurate momentum balance similar to the L1L2 model of Schoof and Hindmarsh to accurately model regions of dynamic complexity, such as ice streams, outlet glaciers, and grounding lines. Results of BISICLES simulations have compared favorably to comparable simulations with a Stokes momentum balance in both idealized tests (MISMIP-3d) and realistic configurations.The figure shows the BISICLES-computed vertically-integrated grounded ice velocity field 5 years into a 20-year coupled full-continent Antarctic-Southern-Ocean simulation. Submarine melt rates are painted onto the surface of the floating ice shelves. Grounding lines are shown in green.

  7. Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting

    NASA Astrophysics Data System (ADS)

    Gladstone, Rupert Michael; Warner, Roland Charles; Galton-Fenzi, Benjamin Keith; Gagliardini, Olivier; Zwinger, Thomas; Greve, Ralf

    2017-01-01

    Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flow-line model accounting for all stress components and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting.Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction in resolution dependence.A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line.Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), impact on capability to simulate marine ice sheets. If there exists an abrupt change across the grounding line in either basal drag or basal melting, then high resolution will be required to solve the problem. However, the plausible combination of a physical dependency of basal drag on effective pressure, and the possibility of low ice shelf basal melt rates next to the grounding line, may mean that some marine ice sheet systems can be reliably simulated at

  8. Leveraging Cloud Technology to Provide a Responsive, Reliable and Scalable Backend for the Virtual Ice Sheet Laboratory Using the Ice Sheet System Model and Amazon's Elastic Compute Cloud

    NASA Astrophysics Data System (ADS)

    Perez, G. L.; Larour, E. Y.; Halkides, D. J.; Cheng, D. L. C.

    2015-12-01

    The Virtual Ice Sheet Laboratory(VISL) is a Cryosphere outreach effort byscientists at the Jet Propulsion Laboratory(JPL) in Pasadena, CA, Earth and SpaceResearch(ESR) in Seattle, WA, and the University of California at Irvine (UCI), with the goal of providing interactive lessons for K-12 and college level students,while conforming to STEM guidelines. At the core of VISL is the Ice Sheet System Model(ISSM), an open-source project developed jointlyat JPL and UCI whose main purpose is to model the evolution of the polar ice caps in Greenland and Antarctica. By using ISSM, VISL students have access tostate-of-the-art modeling software that is being used to conduct scientificresearch by users all over the world. However, providing this functionality isby no means simple. The modeling of ice sheets in response to sea and atmospheric temperatures, among many other possible parameters, requiressignificant computational resources. Furthermore, this service needs to beresponsive and capable of handling burst requests produced by classrooms ofstudents. Cloud computing providers represent a burgeoning industry. With majorinvestments by tech giants like Amazon, Google and Microsoft, it has never beeneasier or more affordable to deploy computational elements on-demand. This isexactly what VISL needs and ISSM is capable of. Moreover, this is a promisingalternative to investing in expensive and rapidly devaluing hardware.

  9. Intercomparison of granular stress and turbulence models for unidirectional sheet flow applications

    NASA Astrophysics Data System (ADS)

    Chauchat, J.; Cheng, Z.; Hsu, T. J.

    2016-12-01

    The intergranular stresses are one of the key elements in two-phase sediment transport models. There are two main existing approaches, the kinetic theory of granular flows (Jenkins and Hanes, 1998; Hsu et al., 2004) and the phenomenological rheology such as the one proposed by Bagnold (Hanes and Bowen, 1985) or the μ(I) dense granular flow rheology (Revil-Baudard and Chauchat, 2013). Concerning the turbulent Reynolds stress, mixing length and k-ɛ turbulence models have been validated by previous studies (Revil-Baudard and Chauchat, 2013; Hsu et al., 2004). Recently, sedFoam was developed based on kinetic theory of granular flows and k-ɛ turbulence models (Cheng and Hsu, 2014). In this study, we further extended sedFoam by implementing the mixing length and the dense granular flow rheology by following Revil-Baudard and Chauchat (2013). This allows us to objectively compare the different combinations of intergranular stresses (kinetic theory or the dense granular flow rheology) and turbulence models (mixing length or k-ɛ) under unidirectional sheet flow conditions. We found that the calibrated mixing length and k-ɛ models predicts similar velocity and concentration profiles. The differences observed between the kinetic theory and the dense granular flow rheology requires further investigation. In particular, we hypothesize that the extended kinetic theory proposed by Berzi (2011) would probably improve the existing combination of the kinetic theory with a simple Coulomb frictional model in sedFoam. A semi-analytical solution proposed by Berzi and Fraccarollo(2013) for sediment transport rate and sheet layer thickness versus the Shields number is compared with the results obtained by using the dense granular flow rheology and the mixing length model. The results are similar which demonstrate that both the extended kinetic theory and the dense granular flow rheology can be used to model intergranular stresses under sheet flow conditions.

  10. From Discrete to Continuum Models of Three-Dimensional Deformations in Epithelial Sheets

    PubMed Central

    Murisic, Nebojsa; Hakim, Vincent; Kevrekidis, Ioannis G.; Shvartsman, Stanislav Y.; Audoly, Basile

    2015-01-01

    Epithelial tissue, in which cells adhere tightly to each other and to the underlying substrate, is one of the four major tissue types in adult organisms. In embryos, epithelial sheets serve as versatile substrates during the formation of developing organs. Some aspects of epithelial morphogenesis can be adequately described using vertex models, in which the two-dimensional arrangement of epithelial cells is approximated by a polygonal lattice with an energy that has contributions reflecting the properties of individual cells and their interactions. Previous studies with such models have largely focused on dynamics confined to two spatial dimensions and analyzed them numerically. We show how these models can be extended to account for three-dimensional deformations and studied analytically. Starting from the extended model, we derive a continuum plate description of cell sheets, in which the effective tissue properties, such as bending rigidity, are related explicitly to the parameters of the vertex model. To derive the continuum plate model, we duly take into account a microscopic shift between the two sublattices of the hexagonal network, which has been ignored in previous work. As an application of the continuum model, we analyze tissue buckling by a line tension applied along a circular contour, a simplified set-up relevant to several situations in the developmental contexts. The buckling thresholds predicted by the continuum description are in good agreement with the results of stability calculations based on the vertex model. Our results establish a direct connection between discrete and continuum descriptions of cell sheets and can be used to probe a wide range of morphogenetic processes in epithelial tissues. PMID:26153712

  11. Modeling the inner plasma sheet pressure and magnetic field under enhanced convection

    NASA Astrophysics Data System (ADS)

    Wang, C.; Lyons, L.; Chen, M.; Wolf, R.

    In order to understand the evolution of the proton pressure and magnetic field in the inner plasma sheet from quiet to disturbed times, we incorporate a modified version of the Magnetospheric Specification Model with a modified version of the Tsyganenko 96 magnetic field model to self-consistently simulate protons and magnetic field under an increasing convection electric field with two-dimensional force balance maintained along the midnight meridian. The local-time dependent proton differential fluxes assigned to the model boundary are mixture of hot plasma from the distant tail and cooler plasma from the low latitude boundary layer and are constructed based on Geotail observations and the results of the finite-tail-width- convection model. We previously used this model to simulate the inner plasma sheet under weak convection corresponding to a cross polar-cap potential drop ( PC) equal to 26 kV and obtained two-dimensional quiet time equilibrium for proton and magnetic field that agrees well with observations both qualitatively and quantitatively. We start our simulation for enhanced convection with this quiet time equilibrium and time independent boundary particle sources and increase thePC steadily from 26 kV to 146 kV in 5 hours. The simulations are also run to steady states separately by keepingP C constant after it is increased to 98 and to 146 kV. The magnitude of the simulated proton pressure and its increase from quiet to moderate activity ( P C = 98 kV) are consistent with most observations. Our results at high activity (P C = 146 kV) underestimate the observed pressure, a disagreement that indicates possible dependence of the boundary particle sources on activity. The pressure equatorial profiles show a dawn dusk asymmetry as a result of stronger enhancement on the dusk side than on the dawn side as convection is increased. The equatorial m gnetic field strength decreases more in the near-Eartha plasma sheet than at larger radial distances as theP C

  12. Friction and lubrication modeling in sheet metal forming simulations of a Volvo XC90 inner door

    NASA Astrophysics Data System (ADS)

    Sigvant, M.; Pilthammar, J.; Hol, J.; Wiebenga, J. H.; Chezan, T.; Carleer, B.; van den Boogaard, A. H.

    2016-11-01

    The quality of sheet metal formed parts is strongly dependent on the tribology, friction and lubrication conditions that are acting in the actual production process. Although friction is of key importance, it is currently not considered in detail in stamping simulations. This paper presents a selection of results considering friction and lubrication modeling in sheet metal forming simulations of the Volvo XC90 right rear door inner. For this purpose, the TriboForm software is used in combination with the AutoForm software. Validation of the simulation results is performed using door inner parts taken from the press line in a full-scale production run. The results demonstrate the improved prediction accuracy of stamping simulations by accounting for accurate friction and lubrication conditions, and the strong influence of friction conditions on both the part quality and the overall production stability.

  13. Prediction Of Formability In Sheet Metal Forming Processes Using A Local Damage Model

    NASA Astrophysics Data System (ADS)

    Teixeira, P.; Santos, Abel; César Sá, J.; Andrade Pires, F.; Barata da Rocha, A.

    2007-05-01

    The formability in sheet metal forming processes is mainly conditioned by ductile fracture resulting from geometric instabilities due to necking and strain localization. The macroscopic collapse associated with ductile failure is a result of internal degradation described throughout metallographic observations by the nucleation, growth and coalescence of voids and micro-cracks. Damage influences and is influenced by plastic deformation and therefore these two dissipative phenomena should be coupled at the constitutive level. In this contribution, Lemaitre's ductile damage model is coupled with Hill's orthotropic plasticity criterion. The coupling between damaging and material behavior is accounted for within the framework of Continuum Damage Mechanics (CDM). The resulting constitutive equations are implemented in the Abaqus/Explicit code, for the prediction of fracture onset in sheet metal forming processes. The damage evolution law takes into account the important effect of micro-crack closure, which dramatically decreases the rate of damage growth under compressive paths.

  14. Century/millennium internal climate oscillations in an ocean-atmosphere-continental ice sheet model

    NASA Technical Reports Server (NTRS)

    Birchfield, Edward G.; Wang, Huaxiao; Rich, Jonathan J.

    1994-01-01

    We demonstrate in a simple climate model that there exist nonlinear feedbacks between the atmosphere, ocean, and ice sheets capable of producing century/millennium timescale internal oscillations resembling those seen in the paleoclimate record. Feedbacks involve meridional heat and salt transports in the North Atlantic, surface ocean freshwater fluxes associated with melting and growing continental ice sheets in the northen hemisphere and with Atlantic to Pacific water vapor transport. The positive feedback between the production of North Atlantic Deep Water (NADW) and the meridional salt transport by the Atlantic thermohaline circulation tends to destabilize the climate system, while the negative feedback between the freshwater flux, either to or from the continental ice sheets, and meridional heat flux to the high-latitude North Atlantic, accomplished by the thermohaline circulation, stabilizes the system. The thermohaline circulation plays a central role in both positive and negative feedbacks because of its transport of both heat and salt. Because of asymmetries between the growth and melt phases the oscillations are, in general, accompanied by a growing or decreasing ice volume over each cycle, which in the model is reflected by increasing or decreasing mean salinity.

  15. Numerical Modeling of Magnesium Alloy Sheet Metal Forming at Elevated Temperature

    SciTech Connect

    Lee, Myeong-Han; Oh, Soo-Ik; Kim, Heon-Young; Kim, Hyung-Jong; Choi, Yi-Chun

    2007-05-17

    The development of light-weight vehicle is in great demand for enhancement of fuel efficiency and dynamic performance. The vehicle weight can be reduced effectively by using lightweight materials such as magnesium alloys. However, the use of magnesium alloys in sheet forming processes is still limited because of their low formability at room temperature and the lack of understanding of the forming process of magnesium alloys at elevated temperatures. In this study, uniaxial tensile tests of the magnesium alloy AZ31B-O at various temperatures were performed to evaluate the mechanical properties of this alloy relevant for forming of magnesium sheets. To construct a FLD (forming limit diagram), a forming limit test were conducted at temperature of 100 and 200 deg. C. For the evaluation of the effects of the punch temperature on the formability of a rectangular cup drawing with AZ31B-O, numerical modelling was conducted. The experiment results indicate that the stresses and possible strains of AZ31B-O sheets largely depend on the temperature. The stress decreases with temperature increase. Also, the strain increase with temperature increase. The numerical modelling results indicate that formability increases with the decrease in the punch temperature at the constant temperature of the die and holder.

  16. Century/millennium internal climate oscillations in an ocean-atmosphere-continental ice sheet model

    NASA Technical Reports Server (NTRS)

    Birchfield, Edward G.; Wang, Huaxiao; Rich, Jonathan J.

    1994-01-01

    We demonstrate in a simple climate model that there exist nonlinear feedbacks between the atmosphere, ocean, and ice sheets capable of producing century/millennium timescale internal oscillations resembling those seen in the paleoclimate record. Feedbacks involve meridional heat and salt transports in the North Atlantic, surface ocean freshwater fluxes associated with melting and growing continental ice sheets in the northen hemisphere and with Atlantic to Pacific water vapor transport. The positive feedback between the production of North Atlantic Deep Water (NADW) and the meridional salt transport by the Atlantic thermohaline circulation tends to destabilize the climate system, while the negative feedback between the freshwater flux, either to or from the continental ice sheets, and meridional heat flux to the high-latitude North Atlantic, accomplished by the thermohaline circulation, stabilizes the system. The thermohaline circulation plays a central role in both positive and negative feedbacks because of its transport of both heat and salt. Because of asymmetries between the growth and melt phases the oscillations are, in general, accompanied by a growing or decreasing ice volume over each cycle, which in the model is reflected by increasing or decreasing mean salinity.

  17. A calving law for ice sheet models; Investigating the role of surface melt on dynamics of Greenland outlet glaciers

    NASA Astrophysics Data System (ADS)

    Nick, F. M.; van der Veen, C. J.; Vieli, A.

    2008-12-01

    alving of icebergs accounts for perhaps as much as half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. We have formulated a calving model that can be readily incorporated into time-evolving numerical ice-flow models. Our model is based on downward penetration of water-filled surface crevasses and upward propagation of basal crevasses. A calving event occurs when the depth of the surface crevasse (which increases as melting progresses through the summer) reaches the height of the basal crevasse. Our numerical ice sheet model is able to reproduce observed seasonal changes of Greenland outlet glaciers, such as fluctuations in flow speed and terminus positions. We have applied the model to Helheim Glacier on the east coast, and Petermann Glacier in the northwest. Our model suggests that rapid retreat of the claving front is highly affected by the amplified calving rate due to increasing water level in surface crevasses during warmer summers. Our results show little response to seasonally enhanced basal lubrication from surface melt. This modeling study provides insights into the role of surface and basal hydrology to ice sheet dynamics and on how to incorporate calving in ice sheet models and therefore advances our ability to predict future ice sheet change.

  18. Modelling West Antarctic ice sheet growth and collapse through the past five million years.

    PubMed

    Pollard, David; DeConto, Robert M

    2009-03-19

    The West Antarctic ice sheet (WAIS), with ice volume equivalent to approximately 5 m of sea level, has long been considered capable of past and future catastrophic collapse. Today, the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams. Grounding lines are several hundred metres below sea level and the bed deepens upstream, raising the prospect of runaway retreat. Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms. Its variation since the Last Glacial Maximum is best known, with grounding lines advancing to the continental-shelf edges around approximately 15 kyr ago before retreating to near-modern locations by approximately 3 kyr ago. Prior collapses during the warmth of the early Pliocene epoch and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes, and by the discovery of open-ocean diatoms in subglacial sediments. Until now, however, little direct evidence of such behaviour has been available. Here we use a combined ice sheet/ice shelf model capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing to simulate Antarctic ice sheet variations over the past five million years. Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands. Transitions between glacial, intermediate and collapsed states are relatively rapid, taking one to several thousand years. Our simulation is in good agreement with a new sediment record (ANDRILL AND-1B) recovered from the western Ross Sea, indicating a long-term trend from more frequently collapsed to more glaciated states, dominant 40-kyr cyclicity in the Pliocene, and major retreats at

  19. Surface Mass Balance Distributions: Downscaling of Coarse Climates to drive Ice Sheet Models realistically

    NASA Astrophysics Data System (ADS)

    Rodehacke, Christian; Mottram, Ruth; Langen, Peter; Madsen, Marianne; Yang, Shuting; Boberg, Fredrik; Christensen, Jens

    2017-04-01

    The surface mass balance (SMB) is the most import boundary conditions for the state of glaciers and ice sheets. Hence its representation in numerical model simulations is of highest interest for glacier, ice cap and ice sheet modeling efforts. While descent SMB distributions of the current climate could be interfered with the help of various observation techniques and platforms, its construction for older past and future climates relies on input from spatially coarse resolved global climate models or reconstructions. These coarse SMB estimates with a footprint in the order of 100 km could hardly resolve the marginal ablations zones where the Greenland ice sheets, for instance, loses snow and ice. We present a downscaling method that is based on the physical calculation of the surface mass and energy balance. By the consequent application of universal and computationally cheap parameterizations we get an astonishing good representation of the SMB distribution including its marginal ablation zone. However the method has its limitations; for example wrong accumulation rates due to an insufficient precipitation field leaves its imprint on the SMB distribution. Also the still not satisfactory description of the bare ice albedo, in particular, in parts of Greenland is a challenge. We inspect our Greenland SMB fields' for various forcings and compare them with some widely used reference fields in the community to highlight the weakness and strength of our approach. We use the ERA-Interim reanalyzes period starting in 1979 directly as well as dynamically downscaled by our regional climate model HIRHAM (5 km resolution). Also SMB distributions obtained from the climate model EC-Earth with a resolution of T159 (approx. 125 km resolution in Greenland) are used either directly or downscaled with our regional climate model HIRHAM. Model-based End-of-the-century SMB estimates give an outlook of the future.

  20. Firn meltwater retention on the Greenland Ice Sheet: a model comparison

    NASA Astrophysics Data System (ADS)

    Steger, Christian R.; Reijmer, Carleen H.; van den Broeke, Michiel R.; Wever, Nander; Forster, Richard R.; Koenig, Lora S.; Kuipers Munneke, Peter; Lehning, Michael; Lhermitte, Stef; Ligtenberg, Stefan R. M.; Miège, Clément; Noël, Brice P. Y.

    2017-01-01

    Runoff has recently become the main source of mass loss from the Greenland Ice Sheet and is an important contributor to global sea level rise. Linking runoff to surface meltwater production is complex, as meltwater can be retained within the firn by refreezing or perennial liquid water storage. To constrain these uncertainties, the outputs of two offline snow/firn models of different complexity (IMAU-FDM and SNOWPACK) are compared to assess the sensitivity of meltwater retention to the model formulation (e.g., densification, irreducible water content, vertical resolution). Results indicate that model differences are largest in areas where firn aquifers form, i.e., particularly along the south-eastern margin of the ice sheet. The IMAU-FDM simulates higher densification rates for such climatic conditions and prescribes a lower irreducible water content than SNOWPACK. As a result, the model predicts substantially lower amounts of refreezing and liquid water storage. SNOWPACK performs better for this area, confirmed both by density profiles from firn cores and radar-inferred observations. Refreezing integrated over the entire ice sheet and averaged for the period 1960 - 2014 amounts to 216 Gt a-1 (IMAU-FDM) and 242 Gt a-1 (SNOWPACK), which is 41% and 46% of the total liquid water input (snowmelt and rainfall). The mean areal extents of perennial firn aquifers for 2010 - 2014 simulated by the models are 55,700 km2 (IMAU-FDM) and 90,200 km2 (SNOWPACK). Discrepancies between modeled firn profiles and observations emphasize the importance of processes currently not accounted for in most snow/firn models, such as vertical heterogeneous percolation, ponding of water on impermeable layers, lateral (sub-)surface water flow, and the issue of ill-constrained refreezing conditions at the base of firn aquifers.

  1. Gelatin sealing sheet for arterial hemostasis and anti-adhesion in vascular surgery: a dog model study.

    PubMed

    Hu, Yinghao; Yamashita, Keigo; Tabayashi, Nobuoki; Abe, Takehisa; Hayata, Yoshihiro; Hirose, Tomoaki; Hiraga, Shun; Tojo, Takashi; Suzuki, Shuko; Ikada, Yoshito; Taniguchi, Shigeki

    2015-01-01

    The bilayer gelatin sealing sheet was developed as a safe, effective, easy-to-handle and low-cost hemostatic agent. To examine the feasibility of gelatin sealing sheets using a canine arterial hemorrhage model. In vivo degradation of gelatin sealing sheets was examined by implanting subcutaneously in rats. For the hemostatic and anti-adhesion efficacy investigations, femoral arteries of dogs were pricked with syringe needle to make a small hole and a gelatin (i.e. experimental group) or fibrin glue sealing sheet (i.e. control group) was applied on the hole to stop bleeding (n=8). After discontinuation of the bleeding, the skin incisions were closed and re-examined 4 weeks postoperatively. From the degradation study, 4 h thermally treated gelatin sheet which degraded within 3 weeks in vivo was chosen for the further hemostatic study. In all cases of gelatin and fibrin glue sealing sheets, bleeding from the needle hole on canine femoral arteries was effectively stopped. Postoperative adhesions and inflammation at the site in the experimental group were significantly less than those in the control group (P<0.01 for adhesion scores). The gelatin sealing sheet was found to be as effective as the fibrin glue sealing sheet as a surgical hemostatic agent, and more effective in preventing postoperative adhesions.

  2. On the position of the near-earth neutral sheet - A comparison of magnetic model predictions with empirical formulas

    NASA Technical Reports Server (NTRS)

    Peredo, Mauricio; Stern, David P.

    1991-01-01

    A detailed comparison of the near-earth neutral sheet position according to several approximations has been made. In particular, two empirical formulas for the neutral sheet location, recently derived from AMPTE/CCE data, have been compared with the corresponding positions derived from Tsyganenko's magnetic field models. Cylindrical coordinates referenced to the geodipole have been used, and the position of the neutral sheet has been identified by the reversal of the radial component of the magnetic field. The analysis reveals that, in the region X(GSM) = -9 to -5 earth radii, abs. value of Y(GSM) not greater than 5 earth radii, close agreement exists between the empirical formulas and the Tsyganenko models. Furthermore, the Tsyganenko models provide a representation for the neutral sheet position in the transition region between near-earth and distant tail models.

  3. Free oscillations in a climate model with ice-sheet dynamics

    NASA Technical Reports Server (NTRS)

    Kallen, E.; Crafoord, C.; Ghil, M.

    1979-01-01

    A study of stable periodic solutions to a simple nonlinear model of the ocean-atmosphere-ice system is presented. The model has two dependent variables: ocean-atmosphere temperature and latitudinal extent of the ice cover. No explicit dependence on latitude is considered in the model. Hence all variables depend only on time and the model consists of a coupled set of nonlinear ordinary differential equations. The globally averaged ocean-atmosphere temperature in the model is governed by the radiation balance. The reflectivity to incoming solar radiation, i.e., the planetary albedo, includes separate contributions from sea ice and from continental ice sheets. The major physical mechanisms active in the model are (1) albedo-temperature feedback, (2) continental ice-sheet dynamics and (3) precipitation-rate variations. The model has three-equilibrium solutions, two of which are linearly unstable, while one is linearly stable. For some choices of parameters, the stability picture changes and sustained, finite-amplitude oscillations obtain around the previously stable equilibrium solution. The physical interpretation of these oscillations points to the possibility of internal mechanisms playing a role in glaciation cycles.

  4. Finite element modelling of high air pressure forming processes for polymer sheets

    NASA Astrophysics Data System (ADS)

    Jiang, W.-G.; Warby, M. K.; Whiteman, J. R.; Abbott, S.; Shorter, W.; Warwick, P.; Wright, T.; Munro, A.; Munro, B.

    In this paper we describe the mathematical modelling and computational simulation of the high air pressure (HAP) thermoforming process which is used in the creation of thin walled polymeric structures. This involves, using data from material tests, an elastic-plastic constitutive equation valid for large deformations and a constrained deformation in which there is frictional contact between the polymeric sheet and a constraining surface (the mould surface). Despite a number of simplifying assumptions and some uncertainities in the mathematical model the finite element computations presented predict quite well the actual shape and thickness distribution which are found on sample products.

  5. Numerical models for the prediction of failure for multilayer fusion Al-alloy sheets

    SciTech Connect

    Gorji, Maysam; Berisha, Bekim; Hora, Pavel; Timm, Jürgen

    2013-12-16

    Initiation and propagation of cracks in monolithic and multi-layer aluminum alloys, called “Fusion”, is investigated. 2D plane strain finite element simulations are performed to model deformation due to bending and to predict failure. For this purpose, fracture strains are measured based on microscopic pictures of Nakajima specimens. In addition to, micro-structure of materials is taken into account by introducing a random grain distribution over the sheet thickness as well as a random distribution of the measured yield curve. It is shown that the performed experiments and the introduced FE-Model are appropriate methods to highlight the advantages of the Fusion material, especially for bending processes.

  6. Planetary period modulations of Saturn's magnetotail current sheet: A simple illustrative mathematical model

    NASA Astrophysics Data System (ADS)

    Cowley, S. W. H.; Provan, G.; Hunt, G. J.; Jackman, C. M.

    2017-01-01

    We mathematically model the modulation effects on Saturn's equatorial magnetotail and magnetodisk current sheet produced by the combined magnetic field perturbations of the northern and southern planetary period oscillation (PPO) systems, specifically north-south displacements associated with the radial perturbation field and thickness modulations associated with the colatitudinal perturbation field. Since the phasing of the two PPO systems is taken to be related to the radial field perturbations, while the relative phasing of the colatitudinal perturbations is opposite for the two systems, the north-south oscillations reinforce when the two PPO systems are in phase, while the thickening-thinning effects reinforce when they are in antiphase. For intermediate relative phases we show that when the northern PPO system leads the southern the sheet is thicker when moving south to north than when moving north to south, while when the northern PPO system lags the southern the sheet is thicker when moving north to south than when moving south to north, thus leading to sawtooth profiles in the radial field for near-equatorial observers, of opposite senses in the two cases. Given empirically determined modulation amplitudes, the maximum sawtooth effect is found to be small when one system dominates the other, but becomes clear when the amplitude of one system lies within a factor of 2 of the other.

  7. Reconstructing the Last Glacial Maximum ice sheet in the Weddell Sea embayment, Antarctica, using numerical modelling constrained by field evidence

    NASA Astrophysics Data System (ADS)

    Le Brocq, A. M.; Bentley, M. J.; Hubbard, A.; Fogwill, C. J.; Sugden, D. E.; Whitehouse, P. L.

    2011-09-01

    The Weddell Sea Embayment (WSE) sector of the Antarctic ice sheet has been suggested as a potential source for a period of rapid sea-level rise - Meltwater Pulse 1a, a 20 m rise in ˜500 years. Previous modelling attempts have predicted an extensive grounding line advance in the WSE, to the continental shelf break, leading to a large equivalent sea-level contribution for the sector. A range of recent field evidence suggests that the ice sheet elevation change in the WSE at the Last Glacial Maximum (LGM) is less than previously thought. This paper describes and discusses an ice flow modelling derived reconstruction of the LGM ice sheet in the WSE, constrained by the recent field evidence. The ice flow model reconstructions suggest that an ice sheet consistent with the field evidence does not support grounding line advance to the continental shelf break. A range of modelled ice sheet surfaces are instead produced, with different grounding line locations derived from a novel grounding line advance scheme. The ice sheet reconstructions which best fit the field constraints lead to a range of equivalent eustatic sea-level estimates between approximately 1.4 and 3 m for this sector. This paper describes the modelling procedure in detail, considers the assumptions and limitations associated with the modelling approach, and how the uncertainty may impact on the eustatic sea-level equivalent results for the WSE.

  8. Towards a GIS assessment of numerical ice-sheet model performance using geomorphological data

    NASA Astrophysics Data System (ADS)

    Napieralski, Jacob; Hubbard, Alun; Li, Yingkui; Harbor, Jon; Stroeven, Arjen P.; Kleman, Johan; Alm, Göran; Jansson, Krister N.

    A major difficulty in assimilating geomorphological information with ice-sheet models is the lack of a consistent methodology to systematically compare model output and field data. As an initial step in establishing a quantitative comparison methodology, automated proximity and conformity analysis (APCA) and automated flow direction analysis (AFDA) have been developed to assess the level of correspondence between modelled ice extent and ice-marginal features such as end moraines, as well as between modelled basal flow directions and palaeo-flow direction indicators, such as glacial lineations. To illustrate the potential of such an approach, an ensemble suite of 40 numerical simulations of the Fennoscandian ice sheet were compared to end moraines of the Last Glacial Maximum and the Younger Dryas and to glacial lineations in northern Sweden using APCA and AFDA. Model experiments evaluated in this manner were ranked according to level of correspondence. Such an approach holds considerable promise for optimizing the parameter space and coherence of ice-flow models by automated, quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence.

  9. Elasto-Plasticity Behavior of Type 5000 and 6000 Aluminum Alloy Sheets and Its Constitutive Modeling

    SciTech Connect

    Tamura, Shohei; Sumikawa, Satoshi; Hamasaki, Hiroshi; Yoshida, Fusahito; Uemori, Takeshi

    2010-06-15

    To examine the deformation characteristic of type 5000 and 6000 aluminum alloy sheets, uniaxial tension, biaxial stretching and in-plane cyclic tension-compression experiments were performed, and from these, r-values (r{sub 0}, r{sub 45} and r{sub 90}), yield loci and cyclic stress-strain responses were obtained. For the accurate description of anisotropies of the materials, high-ordered anisotropic yield functions, such as Gotoh's biquadratic yield function and Barlat's Yld2000-2d, are necessary. Furthermore, for the simulation of cyclic behavior, an advanced kinematic hardening model, such as Yoshida-Uemori model (Y-U model), should be employed. The effect of the selection of material models on the accuracy of the springback prediction was discussed by performing hat bending FE simulation using several yield functions and two types of hardening laws (the isotropic hardening model and Y-U model).

  10. Physically-based in silico light sheet microscopy for visualizing fluorescent brain models

    PubMed Central

    2015-01-01

    Background We present a physically-based computational model of the light sheet fluorescence microscope (LSFM). Based on Monte Carlo ray tracing and geometric optics, our method simulates the operational aspects and image formation process of the LSFM. This simulated, in silico LSFM creates synthetic images of digital fluorescent specimens that can resemble those generated by a real LSFM, as opposed to established visualization methods producing visually-plausible images. We also propose an accurate fluorescence rendering model which takes into account the intrinsic characteristics of fluorescent dyes to simulate the light interaction with fluorescent biological specimen. Results We demonstrate first results of our visualization pipeline to a simplified brain tissue model reconstructed from the somatosensory cortex of a young rat. The modeling aspects of the LSFM units are qualitatively analysed, and the results of the fluorescence model were quantitatively validated against the fluorescence brightness equation and characteristic emission spectra of different fluorescent dyes. AMS subject classification Modelling and simulation PMID:26329404

  11. Physically-based in silico light sheet microscopy for visualizing fluorescent brain models.

    PubMed

    Abdellah, Marwan; Bilgili, Ahmet; Eilemann, Stefan; Markram, Henry; Schürmann, Felix

    2015-01-01

    We present a physically-based computational model of the light sheet fluorescence microscope (LSFM). Based on Monte Carlo ray tracing and geometric optics, our method simulates the operational aspects and image formation process of the LSFM. This simulated, in silico LSFM creates synthetic images of digital fluorescent specimens that can resemble those generated by a real LSFM, as opposed to established visualization methods producing visually-plausible images. We also propose an accurate fluorescence rendering model which takes into account the intrinsic characteristics of fluorescent dyes to simulate the light interaction with fluorescent biological specimen. We demonstrate first results of our visualization pipeline to a simplified brain tissue model reconstructed from the somatosensory cortex of a young rat. The modeling aspects of the LSFM units are qualitatively analysed, and the results of the fluorescence model were quantitatively validated against the fluorescence brightness equation and characteristic emission spectra of different fluorescent dyes. Modelling and simulation.

  12. Numerical investigation of dynamics of unsteady sheet/cloud cavitating flow using a compressible fluid model

    NASA Astrophysics Data System (ADS)

    Chen, Guang-Hao; Wang, Guo-Yu; Huang, Biao; Hu, Chang-Li; Wang, Zhi-Ying; Wang, Jian

    2015-02-01

    In this paper, a compressible fluid model is proposed to investigate dynamics of the turbulent cavitating flow over a Clark-Y hydrofoil. The numerical simulation is based on the homogeneous mixture approach coupled with filter-based density correction model (FBDCM) turbulence model and Zwart cavitation model. Considering the compressibility effect, the equation of state of each phase is introduced into the numerical model. The results show that the predicted results agree well with experimental data concerning the time-averaged lift/drag coefficient and shedding frequency. The quasi-periodic evolution of sheet/cloud cavitation and the resulting lift and drag are discussed in detail. Especially, the present compressible-mixture numerical model is capable of simulating the shock waves in the final stage of cavity collapse. It is found that the shock waves may cause the transient significant increase and decrease in lift and drag if the cavity collapses near the foil surface.

  13. Characterizing West Greenland ice sheet runoff losses from modeled and measured data

    NASA Astrophysics Data System (ADS)

    Moustafa, S.; Rennermalm, A. K.; Tedesco, M.; Mote, T. L.; Koenig, L.; Smith, L. C.; Hagedorn, B.; Overeem, I.; Sletten, R. S.; Mikkelsen, A. B.; Hasholt, B.; van As, D.; Hall, D. K.

    2016-12-01

    Increased surface meltwater runoff from the Greenland ice sheet (GrIS) accounts for half or more of total mass loss. Despite its importance, modeled meltwater runoff fluxes are poorly constrained, primarily due to a lack of direct in situ observations. Here, we present an inter-comparison of modeled and observed discharge for three drainage basins -Naujat Kuat (Nuuk), Watson, and North River (Thule) - moving from south to north along West Greenland. Modeled runoff outputs are obtained from the surface mass balance Modèle Atmosphérique Régional (MAR), and integrated for several catchment realizations. Our analyses reveal that (1) MAR is overestimating runoff losses for all three catchments and (2) drainage basin delineation can cause great uncertainty in model runoff estimates. This study's findings offers a unique opportunity to examine runoff estimates of surface mass balance models and will inform future development and parameterization of these models.

  14. Sensitivity of the Greenland ice sheet evolution and flow on basal conditions - a parameter study with the PISM model

    NASA Astrophysics Data System (ADS)

    Nielsen, L. T.; Hvidberg, C. S.

    2014-12-01

    The basal boundary conditions of the Greenland ice sheet have an important control on the ice flow pattern and dynamical evolution of the ice sheet. Basal melting and sliding conditions cannot be observed directly, but observables such as ice thickness, surface velocity and the internal radar layer structure contain indirect information of the basal conditions. The northeast ice stream extend to the interior parts indicating that basal conditions are also important in the interior parts. The purpose of this study is to investigate the sensitivity of the large-scale evolution of the Greenland Ice Sheet on millennial to glacial/interglacial time scales to parameters controlling basal sliding and ice flow. In the study, we use the Parallel Ice Sheet Model (PISM) to examine the response of the ice sheet evolution to the choices of dynamic parameters. The investigated parameters relates to the parameterization of the basal processes and ice viscosity, these includes the enhancement factor, the exponent in the basal sliding relation employed in the model and the parameterization of the basal material. We run the PISM model through the last glacial/interglacial cycle for an ensemble of model parameters sets to obtain the evolution of the ice sheet using the same climate reconstruction as surface boundary conditions in all experiments in order to estimate the sensitivity of the ice sheet evolution to the choices of dynamic parameters alone. The paleo-climatic spinup of the seaRISE experiment is used as surface boundary conditions. The results of the ensemble experiments are compared using time series of global variables and by comparing snapshots of the ice sheet at predefined times. We discuss the regional differences and sensitivity to the model parameters, and further discuss the evaluation of the parameter combinations by comparing the modelled ice flow pattern to observed present day velocities.

  15. Modeled Northern Hemisphere ice-sheet-climate interactions and contributions to sea-level change since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Heinemann, M.; Timmermann, A.; Elison Timm, O.; Saito, F.; Abe-Ouchi, A.

    2013-12-01

    One of the most recent massive climate change events in earth's history was the last glacial termination 19-9 thousand years before present (ka BP). Northern Hemisphere ice-sheets receded quickly, causing global sea level to rise by more than 100 m, meltwater was injected into the North Atlantic halting its deepwater formation, atmospheric CO2 concentrations rose by almost 100 ppmv, and the global surface warmed by about 4°C. It is still unresolved what exactly caused this deglacial climate change and ice sheet melting. To address this question, we set out to conduct a series of transient modeling experiments with a coupled 3-dimensional ice-sheet-climate model (iLove). The model includes atmosphere-ocean-sea ice-vegetation components of the intermediate complexity model LOVECLIM and uses bi-directional coupling to the ice-sheet model IcIES. Supporting Milankovitch theory, our results indicate that the deglaciation was initiated by orbital parameter changes. However, according to our model, rising CO2 concentrations after 17 ka BP accelerated the deglaciation. Without this deglacial CO2 increase, large parts of North America and Scandinavia would be covered by ice sheets today. Present sea level would be as much as 100 m lower, and still dropping by about 2.5 m per thousand years due to growing ice sheets. Despite the deglacial CO2-rise and global warming of 4°C, the simulated Greenland ice-sheet only looses about 25% of its volume during the deglaciation, and grows again in the Holocene after 8 ka BP at a rate of about 0.1 m sea level equivalent per thousand years. Our results indicate that the stability of the Greenland ice sheet during the deglaciation and Holocene is supported by changes of the atmospheric stationary wave pattern, and by the deglacial sea ice retreat.

  16. Theory and simulations of a multi-scale magnetotail current sheet model

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Swisdak, M. M.; Guzdar, P. N.

    2010-12-01

    One of the key problems in modeling of the solar wind-magnetosphere interaction is the description of the magnetotail reconnection onset. It is widely accepted, that the explosive release of energy accumulated in the magnetotail, which occurs during substorms and bursty bulk flows, must involve some form of unsteady magnetic reconnection. However, the specific features of the magnetotail reconnection and its proper description at the kinetic level, not to speak about its reduced form suitable for global MHD modeling, remain poorly understood. Moreover, until recently the onset of spontaneous reconnection was thought to be fully prohibited, because the sufficient stability criterion of the corresponding plasma wave, the ion tearing mode, was fulfilled within the WKB approximation for all types of the considered magnetotail equilibria. Recently it was found (Sitnov and Schindler, 2010), that the ion tearing stability criterion might be relaxed in the tail current sheet models, which have more than two characteristic spatial scales. In particular, the substantial tearing destabilization takes place for equilibria with accumulation of the magnetic flux at the tailward end of an extended thin current sheet. We consider generalizations of the Sitnov-Schindler model including seed X-lines, and analyze their linear and nonlinear stability properties, as well as implications of the new stability criterion for global MHD models. The nonlinear stability issues are investigated with the help of an open-boundary modification of the full-particle code P3D (Zeiler et al., 2002).

  17. Higher-order ice-sheet modelling accelerated by multigrid on graphics cards

    NASA Astrophysics Data System (ADS)

    Brædstrup, Christian; Egholm, David

    2013-04-01

    Higher-order ice flow modelling is a very computer intensive process owing primarily to the nonlinear influence of the horizontal stress coupling. When applied for simulating long-term glacial landscape evolution, the ice-sheet models must consider very long time series, while both high temporal and spatial resolution is needed to resolve small effects. The use of higher-order and full stokes models have therefore seen very limited usage in this field. However, recent advances in graphics card (GPU) technology for high performance computing have proven extremely efficient in accelerating many large-scale scientific computations. The general purpose GPU (GPGPU) technology is cheap, has a low power consumption and fits into a normal desktop computer. It could therefore provide a powerful tool for many glaciologists working on ice flow models. Our current research focuses on utilising the GPU as a tool in ice-sheet and glacier modelling. To this extent we have implemented the Integrated Second-Order Shallow Ice Approximation (iSOSIA) equations on the device using the finite difference method. To accelerate the computations, the GPU solver uses a non-linear Red-Black Gauss-Seidel iterator coupled with a Full Approximation Scheme (FAS) multigrid setup to further aid convergence. The GPU finite difference implementation provides the inherent parallelization that scales from hundreds to several thousands of cores on newer cards. We demonstrate the efficiency of the GPU multigrid solver using benchmark experiments.

  18. Electromagnetic Scattering Model Performance Assessment of the Global Ice Sheet Mapping Orbiter Concept

    NASA Astrophysics Data System (ADS)

    Niamsuwan, N.; Johnson, J. T.; Gogineni, P.; Jezek, K. C.

    2006-12-01

    Conditions beneath polar ice are important factors in ice dynamics. Obtaining information on subsurface structures that may be under several km of ice requires use of low frequency electromagnetic sensors. Such measurements have been demonstrated from both ground and airborne platforms in recent experimental campaigns. For larger scale measurements, the Global Ice Sheet Mapping Orbiter (GISMO) mission has been proposed. This NASA Instrument Incubator Program project is a collaboration between Ohio State University, the University of Kansas, Vexcel Corporation and NASA. The GISMO design utilizes an INSAR strategy in which ice sheet reflected signals received by a dual-antenna system are used to produce an interference pattern. The resulting interferogram can be used to filter out surface clutter so as to reveal the signals scattered from the base of the ice sheet. Current simulations of GISMO performance and interpretability are limited by a lack of knowledge of possible electromagnetic scattering interactions at the ice base, including the influence of the base topographical structure and the presence or absence of any water layers. An improved electromagnetic wave scattering model is therefore needed in order to describe the possible range of scattering effects at the basal layered rough surface, and to include these effects in GISMO simulations. This presentation will discuss three distinct electromagnetic models for scattering from a layered rough surface: the Small Perturbation Method (SPM), the Kirchhoff approximation (also know as physical optics (PO)) and the associated geometrical optics method, and numerical methods based on exact simulations of the electromagnetic boundary value problem. The formulation of each of these approaches will be reviewed, as well as the associated advantages and limitations of each. Sample scattering results from the three models for a one-dimensional surface profile will be illustrated for varying assumed base-layers in order

  19. Modeling Greenland ice sheet present-day and near-future runoff contribution.

    NASA Astrophysics Data System (ADS)

    Peano, Daniele; Colleoni, Florence; Masina, Simona

    2014-05-01

    The last IPCC report [AR5, IPCC] has shown an increasing contribution from Greenland melting to global sea-level over the last decade, increasing from 0.09 mm/year (period 1992-2001) to 0.59 mm/year (period 2002-2011). Given its strategic location, i.e. close to the main North Atlantic ocean convection sites, it is therefore of importance to better assess ice sheet melting and its impact on regional ocean processes. So far, runoff estimate from ice sheet has been poorly constrained (e.g. [Hanna et al., 2005], [Hanna et al., 2008]) and most of the time the few estimates comes from regional atmospheric models or general circulation models (e.g. [Edwards et al., 2013], [Fettweis et al., 2013]). Here, we present the results from the implementation of a routing scheme into the thermo-mechanical ice sheet-ice shelves model GRISLI [Ritz et al, 2001], applied to the Greenland ice sheet mass evolution over the 20th and 21st centuries. The routing scheme is based on the "multiple flow direction" developed by [Quinn et al., 1991]. We further improved this scheme by considering topographic depressions as possible "lakes" to be filled by meltwater. In this way, when a depression is filled, only the extra water is routed towards the Greenland coasts. This allow us to obtain an estimate of the total amount of freshwater reaching the ocean at each time step of the model integration, as well as a time-varying spatial distribution of the runoff along the coasts of Greenland. This routing scheme is applied in routing both surface and basal meltwater. Surface meltwater is computed by means of a PDD method [Fausto et al., 2007] on which only a fraction is considered for routing while the basal melting rate is part of the heat balance at the ice-bed interface. Runoff is simulated on a 5km x 5km horizontal grid and validation is performed over the 20th century using mean annual total precipitation and air temperature at 2 meters from Era-Interim reanalysis [Dee et al., 2011]. Near future

  20. Dynamical ice sheet model coupling with the GEOS-5 AGCM: A preliminary assessment

    NASA Astrophysics Data System (ADS)

    Cullather, R. I.; Zhao, B.; Nowicki, S.; Suarez, M. J.

    2013-12-01

    Dynamical ice sheet models (ISMs) have been developed to address well-known limitations in eustatic change prediction capabilities. Coupling ISMs to an atmospheric general circulation model (AGCM) is not straightforward, due in part to the extreme difference in spatial scales between the ISM mesh and AGCM grid. In given locations, ISM element edge lengths may be a few km or less, while the AGCM typically has grid spacings on the order of 10s to 100s of km. The Goddard Earth Observing System Model, version 5 (GEOS-5) is a finite-volume AGCM and employs a cube-sphere atmospheric grid (nominally 1° resolution) and a catchment-based land surface scheme that operates on sub-grid scale areas, or tiles, that describe surface characteristics. The land surface component communicates with the atmosphere on a semi-implicit time step via the exchange grid. In this study, coupling between the AGCM and the ISM is facilitated through sub-grid scale land surface tiles that are defined for each element of the ISM. The ISM used here is the Ice Sheet System Model (ISSM) from NASA Jet Propulsion Laboratory and Univ. California at Irvine, which has been adapted for the Greenland Ice Sheet using the 72,320-element Schlagel mesh and using a shallow ice approximation. In the AGCM, land surface tiles are uniquely characterized through a simple downscaling parameterization of surface temperature within each AGCM grid box using a defined lapse rate. On each land surface tile, GEOS-5 employs an advanced snow hydrology model for improved representation of the ice sheet surface mass balance. This preliminary assessment focuses on the differences in the AGCM surface mass balance and surface temperature fields resulting from the downscaling measures employed in the context of an exchange grid, semi-implicit coupling with the atmosphere, and the response of the ISM. Differences in AGCM computational performance with the addition of Greenland tiles is examined, and comparative advantages of

  1. A Viscoplastic Material Model Based on Overstress for the Simulation of Incremental Sheet Forming of Thermoplastics

    NASA Astrophysics Data System (ADS)

    Yonan, S. Alkas; Haupt, P.; Kwiatkowski, L.; Franzen, V.; Brosius, A.; Tekkaya, A. E.

    2011-05-01

    This article introduces a phenomenological material model developed for simulation of viscoplastic behavior of thermoplastics during cold forming. The model presented has no yield surface and is based on the existence of an equilibrium stress and a non-linear strain-rate dependent overstress. Within the first approach the hardening and softening are neglected. The results of specific material characterization tests on three thermoplastics (HDPE, PVC and PC) and the model response in comparison to the experiments are presented. A good accordance between model predictions and experimental results for HDPE and sufficient match for PVC and PC are observed. It is intended to apply the constitutive model to the simulation of incremental sheet forming processes (ISF).

  2. Calculation of Forming Limits for Sheet Metal using an Enhanced Continuous Damage Fracture Model

    NASA Astrophysics Data System (ADS)

    Nguyen, Ngoc-Trung; Kim, Dae-Young; Kim, Heon Young

    2011-08-01

    An enhanced continuous damage fracture model was introduced in this paper to calculate forming limits of sheet metal. The fracture model is a combination of a fracture criterion and a continuum damage constitutive law. A modified McClintock void growth fracture criterion was incorporated with a coupled damage-plasticity Gurson-type constitutive law. Also, by introducing a Lode angle dependent parameter to define the loading asymmetry condition, the shear effect was phenomenologically taken into account. The proposed fracture model was implemented using user-subroutines in commercial finite element software. The model was calibrated and correlated by the uniaxial tension, shear and notched specimens tests. Application of the fracture model for the LDH tests was discussed and the simulation results were compared with the experimental data.

  3. Development of a Prediction Model Based on RBF Neural Network for Sheet Metal Fixture Locating Layout Design and Optimization.

    PubMed

    Wang, Zhongqi; Yang, Bo; Kang, Yonggang; Yang, Yuan

    2016-01-01

    Fixture plays an important part in constraining excessive sheet metal part deformation at machining, assembly, and measuring stages during the whole manufacturing process. However, it is still a difficult and nontrivial task to design and optimize sheet metal fixture locating layout at present because there is always no direct and explicit expression describing sheet metal fixture locating layout and responding deformation. To that end, an RBF neural network prediction model is proposed in this paper to assist design and optimization of sheet metal fixture locating layout. The RBF neural network model is constructed by training data set selected by uniform sampling and finite element simulation analysis. Finally, a case study is conducted to verify the proposed method.

  4. Glacial isostatic adjustment associated with the Barents Sea ice sheet: A modelling inter-comparison

    NASA Astrophysics Data System (ADS)

    Auriac, A.; Whitehouse, P. L.; Bentley, M. J.; Patton, H.; Lloyd, J. M.; Hubbard, A.

    2016-09-01

    The 3D geometrical evolution of the Barents Sea Ice Sheet (BSIS), particularly during its late-glacial retreat phase, remains largely ambiguous due to the paucity of direct marine- and terrestrial-based evidence constraining its horizontal and vertical extent and chronology. One way of validating the numerous BSIS reconstructions previously proposed is to collate and apply them under a wide range of Earth models and to compare prognostic (isostatic) output through time with known relative sea-level (RSL) data. Here we compare six contrasting BSIS load scenarios via a spherical Earth system model and derive a best-fit, χ2 parameter using RSL data from the four main terrestrial regions within the domain: Svalbard, Franz Josef Land, Novaya Zemlya and northern Norway. Poor χ2 values allow two load scenarios to be dismissed, leaving four that agree well with RSL observations. The remaining four scenarios optimally fit the RSL data when combined with Earth models that have an upper mantle viscosity of 0.2-2 × 1021 Pa s, while there is less sensitivity to the lithosphere thickness (ranging from 71 to 120 km) and lower mantle viscosity (spanning 1-50 × 1021 Pa s). GPS observations are also compared with predictions of present-day uplift across the Barents Sea. Key locations where relative sea-level and GPS data would prove critical in constraining future ice-sheet modelling efforts are also identified.

  5. An ice-sheet scale comparison of eskers with modelled subglacial drainage routes

    NASA Astrophysics Data System (ADS)

    Livingstone, Stephen J.; Storrar, Robert D.; Hillier, John K.; Stokes, Chris R.; Clark, Chris D.; Tarasov, Lev

    2015-10-01

    Eskers record the signature of channelised meltwater drainage during deglaciation providing vital information on the nature and evolution of subglacial drainage. In this paper, we compare the spatial pattern of eskers beneath the former Laurentide Ice Sheet with subglacial drainage routes diagnosed at discrete time intervals from the results of a numerical ice-sheet model. Perhaps surprisingly, we show that eskers predominantly occur in regions where modelled subglacial water flow is low. Eskers and modelled subglacial drainage routes were found to typically match over distances of < 10 km, and most eskers show a better agreement with the routes close to the ice margin just prior to deglaciation. This supports a time-transgressive esker pattern, with formation in short (< 10 km) segments of conduit close behind a retreating ice margin, and probably associated with thin, stagnant or sluggish ice. Esker-forming conduits were probably dominated by supraglacially fed meltwater inputs. We also show that modelled subglacial drainage routes containing the largest concentrations of meltwater show a close correlation with palaeo-ice stream locations. The paucity of eskers along the terrestrial portion of these palaeo-ice streams and meltwater routes is probably because of the prevalence of distributed drainage and the high erosion potential of fast-flowing ice.

  6. An object-oriented, coprocessor-accelerated model for ice sheet simulations

    NASA Astrophysics Data System (ADS)

    Seddik, H.; Greve, R.

    2013-12-01

    Recently, numerous models capable of modeling the thermo-dynamics of ice sheets have been developed within the ice sheet modeling community. Their capabilities have been characterized by a wide range of features with different numerical methods (finite difference or finite element), different implementations of the ice flow mechanics (shallow-ice, higher-order, full Stokes) and different treatments for the basal and coastal areas (basal hydrology, basal sliding, ice shelves). Shallow-ice models (SICOPOLIS, IcIES, PISM, etc) have been widely used for modeling whole ice sheets (Greenland and Antarctica) due to the relatively low computational cost of the shallow-ice approximation but higher order (ISSM, AIF) and full Stokes (Elmer/Ice) models have been recently used to model the Greenland ice sheet. The advance in processor speed and the decrease in cost for accessing large amount of memory and storage have undoubtedly been the driving force in the commoditization of models with higher capabilities, and the popularity of Elmer/Ice (http://elmerice.elmerfem.com) with an active user base is a notable representation of this trend. Elmer/Ice is a full Stokes model built on top of the multi-physics package Elmer (http://www.csc.fi/english/pages/elmer) which provides the full machinery for the complex finite element procedure and is fully parallel (mesh partitioning with OpenMPI communication). Elmer is mainly written in Fortran 90 and targets essentially traditional processors as the code base was not initially written to run on modern coprocessors (yet adding support for the recently introduced x86 based coprocessors is possible). Furthermore, a truly modular and object-oriented implementation is required for quick adaptation to fast evolving capabilities in hardware (Fortran 2003 provides an object-oriented programming model while not being clean and requiring a tricky refactoring of Elmer code). In this work, the object-oriented, coprocessor-accelerated finite element

  7. Numerical simulation of thick sheet slitting processes: Modelling using continuum damage mechanics

    NASA Astrophysics Data System (ADS)

    Ghozzi, Y.; Labergere, C.; Saanouni, K.

    2013-05-01

    This work consists on the modelling and numerical simulation of specific cutting processes of thick sheets using advanced constitutive equations accounting for elastoplasticity with mixed hardening and ductile damage. Strong coupling between all the mechanical fields and the ductile damage is accounted for. First the complex kinematics of the slitting process is described. Then, the fully and strongly coupled constitutive equations are presented. Finally the influence of the main technological parameters of the slitting process is studied focusing in the minimization of the cutting forces.

  8. Conical Current Sheets in a Source-Surface Model of the Heliosphere

    NASA Astrophysics Data System (ADS)

    Schulz, M.

    2007-12-01

    Different methods of modeling the coronal and heliospheric magnetic field are conveniently visualized and intercompared by applying them to ideally axisymmetric field models. Thus, for example, a dipolar B field with its moment parallel to the Sun's rotation axis leads to a flat heliospheric current sheet. More general solar B fields (still axisymmetric about the solar rotation axis for simplicity) typically lead to cone-shaped current sheets beyond the source surface (and presumably also in MHD models). As in the dipolar case [Schulz et al., Solar Phys., 60, 83-104, 1978], such conical current sheets can be made realistically thin by taking the source surface to be non-spherical in a way that reflects the underlying structure of the Sun's main B field. A source surface that seems to work well in this respect [Schulz, Ann. Geophysicae, 15, 1379-1387, 1997] is a surface of constant F = (1/r)kB, where B is the scalar strength of the Sun's main magnetic field and k (~ 1.4) is a shape parameter. This construction tends to flatten the source surface in regions where B is relatively weak. Thus, for example, the source surface for a dipolar B field is shaped somewhat like a Rugby football, whereas the source surface for an axisymmetric quadrupolar B field is similarly elongated but somewhat flattened (as if stuffed into a cone) at mid-latitudes. A linear combination of co-axial dipolar and quadrupolar B fields generates a somewhat pear-shaped (but still convex) source surface. If the region surrounded by the source surface is regarded as current-free, then the source surface itself should be (as nearly as possible) an equipotential surface for the corresponding magnetic scalar potential (expanded, for example, in spherical harmonics). The solar wind should then flow not quite radially, but rather in a straight line along the outward normal to the source surface, and the heliospheric B field should follow a corresponding generalization of Parker's spiral [Levine et al

  9. Interdisciplinary Determination of Ice Sheet Accumulation Patterns: Combined Atmospheric Modeling and Field and Remote Sensing Studies

    NASA Technical Reports Server (NTRS)

    Shuman, C. A.; Bindschadler, R. A.

    1999-01-01

    This research is focusing on two related areas that are fundamental to the NASA PARCA (Program for Arctic Regional Climate Assessment) program. The primary research area is the determination of the amount, rate, and timing of accumulation at distributed sites in the dry snow zone of Greenland and evaluation of these results in light of accumulation modeling results. The secondary research area is the calibration of the isotope "thermometer" at these ice sheet sites as well as the determination of long-term temperature trends in Greenland.

  10. Analysis of induction-type coilgun performance based on cylindrical current sheet model

    SciTech Connect

    He, J.L.; Levi, E.; Zabar, Z.; Birenbaum, L.; Naot, Y. )

    1991-01-01

    This paper presents a method based on a cylindrical current sheet model for the analysis and design of induction-type coilguns. The paper starts with a derivation of closed-form formulas which relate the dimensions of the gun to the performance expressed in terms of propulsive and local maximum forces on the projectile, power factor and efficiency of the system, thermal stress of the projectile armature, distributions of the flux density around the launcher, and the system parameters in a multisection coilgun. The paper ends with a numerical example.

  11. Interdisciplinary Determination of Ice Sheet Accumulation Patterns: Combined Atmospheric Modeling and Field and Remote Sensing Studies

    NASA Technical Reports Server (NTRS)

    Shuman, C. A.; Bindschadler, R. A.

    1999-01-01

    This research is focusing on two related areas that are fundamental to the NASA PARCA (Program for Arctic Regional Climate Assessment) program. The primary research area is the determination of the amount, rate, and timing of accumulation at distributed sites in the dry snow zone of Greenland and evaluation of these results in light of accumulation modeling results. The secondary research area is the calibration of the isotope "thermometer" at these ice sheet sites as well as the determination of long-term temperature trends in Greenland.

  12. Particle orbits in model current sheet with a nonzero B(y) component

    NASA Technical Reports Server (NTRS)

    Zhu, Zhongwei; Parks, George

    1993-01-01

    The problem of charged particle motions in magnetotaillike model current sheets is revisited with the inclusion of a nonzero dawn-dusk magnetic field component. Three cases are examined considering both trapped and escaped orbits. The results show that a nonzero B(y) component disturbs the particle orbits by destroying orbit symmetry in the phase space about the z = 0 plane. It also changes the bounce frequency of particle orbits. The presence of B(y) thus modifies the Speiser orbits, particularly near the ejection phase. The process of ejected particle such as ejection direction, ejection velocity, and pitch angles are shown to depend on the sign of the charge.

  13. The relation of bifurations in a biaxially loaded rubber sheet and the constitutive modeling of rubber

    SciTech Connect

    Haslach, H.W. Jr.

    1995-12-31

    Treloar`s experiments on a thin rubber sheet under in-plane biaxial tensile loads produced asymmetric as well as equal in-plane stretches. At two loads, the two stretches differed by 7.5% and 12.4% respectively. At an intermediate load, there was a stable equal stretches state. Treloar later said that relaxation was negligible since the results were reproducible and independent of the order of force application. Specimen anisotropy and lack of strain uniformity were also eliminated as a cause. Kearsely first pointed out the significance of these experiments to studies of elastic stability of rubber models. The predictability of this result is a test for the validity of the various constitutive models for rubber. First, Ogden`s plane stress stability and bifurcation criteria are reviewed. A coordinate transformation of a generalized energy function for the biaxially loaded sheet makes it possible to describe the Mooney-Rivlin bifurcation as a cusp catastrophe and to verify that the neo-Hookean and other classical models have no bifurcations. The Mooney-Rivlin model predicts unstable equal stretch states above the bifurcation value, but Treloar`s experiments contradict this. These models cannot, then, be the correct constitutive models for rubber. Preliminary ideas on the conditions that an isothermal constitutive model must satisfy to reproduce Treloar`s experiments are proposed. A thermoelastic generalization of the Mooney-Rivlin model, developed with N. N. Zeng, predicts that raising the temperature slightly lowers the value of the bifurcation load. Nonequilibrium processes such as relaxation or sinusoidal loading are modeled using a generalized energy function in place of classical viscoelastic constitutive relations.

  14. Equivalent Young's modulus and thickness of graphene sheets for the continuum mechanical models

    NASA Astrophysics Data System (ADS)

    Shi, Jin-Xing; Natsuki, Toshiaki; Lei, Xiao-Wen; Ni, Qing-Qing

    2014-06-01

    The Young's modulus and the thickness of graphene sheets (GSs) are the two major material constants when continuum mechanical models are used to analyze the mechanical behaviors of GSs. It should be pointed out that the equivalent Young's modulus and the thickness of GSs should correspond to both stretching and bending loading conditions. In this Letter, the same as "Yakobson paradox," we predicted the equivalent Young's modulus and the thickness of GSs using an analytical method linked with an atomic interaction based continuum model and a continuum elastic model. Based on the proposed method, by unifying the Young's modulus of GSs in the cases of both stretching and bending, and by determining the matching thickness in the same time, the equivalent Young's modulus and the thickness of GSs utilized in continuum mechanical models are calculated and proposed to be 2.81 TPa and 1.27 Å, respectively.

  15. Cell Sheet Transplantation for Esophageal Stricture Prevention after Endoscopic Submucosal Dissection in a Porcine Model

    PubMed Central

    Pidial, Laetitia; Camilleri, Sophie; Bellucci, Alexandre; Casanova, Amaury; Viel, Thomas; Tavitian, Bertrand; Cellier, Christophe; Clement, Olivier

    2016-01-01

    Background & Aims Extended esophageal endoscopic submucosal dissection (ESD) is highly responsible for esophageal stricture. We conducted a comparative study in a porcine model to evaluate the effectiveness of adipose tissue-derived stromal cell (ADSC) double cell sheet transplantation. Methods Twelve female pigs were treated with 5 cm long hemi-circumferential ESD and randomized in two groups. ADSC group (n = 6) received 4 double cell sheets of allogenic ADSC on a paper support membrane and control group (n = 6) received 4 paper support membranes. ADSC were labelled with PKH-67 fluorophore to allow probe-based confocal laser endomicroscopie (pCLE) monitoring. After 28 days follow-up, animals were sacrificed. At days 3, 14 and 28, endoscopic evaluation with pCLE and esophagography were performed. Results One animal from the control group was excluded (anesthetic complication). Animals from ADSC group showed less frequent alimentary trouble (17% vs 80%; P = 0.08) and higher gain weight on day 28. pCLE demonstrated a compatible cell signal in 4 animals of the ADSC group at day 3. In ADSC group, endoscopy showed that 1 out of 6(17%) animals developed a severe esophageal stricture comparatively to 100% (5/5) in the control group; P = 0.015. Esophagography demonstrated a decreased degree of stricture in the ADSC group on day 14 (44% vs 81%; P = 0.017) and day 28 (46% vs 90%; P = 0.035). Histological analysis showed a decreased fibrosis development in the ADSC group, in terms of surface (9.7 vs 26.1 mm²; P = 0.017) and maximal depth (1.6 vs 3.2 mm; P = 0.052). Conclusion In this model, transplantation of allogenic ADSC organized in double cell sheets after extended esophegeal ESD is strongly associated with a lower esophageal stricture’s rate. PMID:26930409

  16. Cell Sheet Transplantation for Esophageal Stricture Prevention after Endoscopic Submucosal Dissection in a Porcine Model.

    PubMed

    Perrod, Guillaume; Rahmi, Gabriel; Pidial, Laetitia; Camilleri, Sophie; Bellucci, Alexandre; Casanova, Amaury; Viel, Thomas; Tavitian, Bertrand; Cellier, Christophe; Clement, Olivier

    2016-01-01

    Extended esophageal endoscopic submucosal dissection (ESD) is highly responsible for esophageal stricture. We conducted a comparative study in a porcine model to evaluate the effectiveness of adipose tissue-derived stromal cell (ADSC) double cell sheet transplantation. Twelve female pigs were treated with 5 cm long hemi-circumferential ESD and randomized in two groups. ADSC group (n = 6) received 4 double cell sheets of allogenic ADSC on a paper support membrane and control group (n = 6) received 4 paper support membranes. ADSC were labelled with PKH-67 fluorophore to allow probe-based confocal laser endomicroscopie (pCLE) monitoring. After 28 days follow-up, animals were sacrificed. At days 3, 14 and 28, endoscopic evaluation with pCLE and esophagography were performed. One animal from the control group was excluded (anesthetic complication). Animals from ADSC group showed less frequent alimentary trouble (17% vs 80%; P = 0.08) and higher gain weight on day 28. pCLE demonstrated a compatible cell signal in 4 animals of the ADSC group at day 3. In ADSC group, endoscopy showed that 1 out of 6 (17%) animals developed a severe esophageal stricture comparatively to 100% (5/5) in the control group; P = 0.015. Esophagography demonstrated a decreased degree of stricture in the ADSC group on day 14 (44% vs 81%; P = 0.017) and day 28 (46% vs 90%; P = 0.035). Histological analysis showed a decreased fibrosis development in the ADSC group, in terms of surface (9.7 vs 26.1 mm²; P = 0.017) and maximal depth (1.6 vs 3.2 mm; P = 0.052). In this model, transplantation of allogenic ADSC organized in double cell sheets after extended esophegeal ESD is strongly associated with a lower esophageal stricture's rate.

  17. Efficient traversal of beta-sheet protein folding pathways using ensemble models.

    PubMed

    Shenker, Solomon; O'Donnell, Charles W; Devadas, Srinivas; Berger, Bonnie; Waldispühl, Jérôme

    2011-11-01

    Molecular dynamics (MD) simulations can now predict ms-timescale folding processes of small proteins; however, this presently requires hundreds of thousands of CPU hours and is primarily applicable to short peptides with few long-range interactions. Larger and slower-folding proteins, such as many with extended β-sheet structure, would require orders of magnitude more time and computing resources. Furthermore, when the objective is to determine only which folding events are necessary and limiting, atomistic detail MD simulations can prove unnecessary. Here, we introduce the program tFolder as an efficient method for modelling the folding process of large β-sheet proteins using sequence data alone. To do so, we extend existing ensemble β-sheet prediction techniques, which permitted only a fixed anti-parallel β-barrel shape, with a method that predicts arbitrary β-strand/β-strand orientations and strand-order permutations. By accounting for all partial and final structural states, we can then model the transition from random coil to native state as a Markov process, using a master equation to simulate population dynamics of folding over time. Thus, all putative folding pathways can be energetically scored, including which transitions present the greatest barriers. Since correct folding pathway prediction is likely determined by the accuracy of contact prediction, we demonstrate the accuracy of tFolder to be comparable with state-of-the-art methods designed specifically for the contact prediction problem alone. We validate our method for dynamics prediction by applying it to the folding pathway of the well-studied Protein G. With relatively very little computation time, tFolder is able to reveal critical features of the folding pathways which were only previously observed through time-consuming MD simulations and experimental studies. Such a result greatly expands the number of proteins whose folding pathways can be studied, while the algorithmic integration of

  18. Ring dykes as partially captured inclined sheets: insights from field observations and numerical modelling

    NASA Astrophysics Data System (ADS)

    Browning, John; Gudmundsson, Agust

    2014-05-01

    The subsurface structure of caldera-bounding ring faults remains a contentious issue. Analogue models provide useful insights into an underlying fault structure; however, results are commonly benchmarked only by near-surface observations and geophysical interpretations. Here we present field observations of a deeply eroded and uniquely well exposed section of caldera ring fault in a Tertiary central volcano in south-western Iceland. The Hafnarfjall ring fault represents the outermost fault complex of an elliptical caldera with an original diameter of approximately 5 km. Vertical displacement is estimated to be > 300 m on the steeply inward-dipping ring fault. Field observations (presented here) of the exposed section of the ring fault, however, show that the fault does not exhibit a constant dip. Hafnarfjall is a predominantly basaltic edifice made of many hundreds of lava flows, although thin layers of tuff and intrusions of more evolved magmas are also observed. These layers have contrasting mechanical properties; therefore local heterogeneities within the original edifice may have altered the stress field enough to influence the propagation of ring faults during collapse. The lava pile on the outer margins of the caldera dips shallowly to the southeast. Within the caldera, dips increase dramatically toward the centre of subsidence and, furthermore, increase with depth. Several thin (< 1 m) dykes occupy an approximately 5 m section within the ring fault; this region is interpreted to have once acted mechanically as the fault core with a lower stiffness or Young's modulus than the surrounding host rock. Many faults which have been active over an extended period develop a damage zone around the fault core; this is a zone of high fracture frequency which is generally stiffer than the core but softer or more compliant than the surrounding host rock. We observe a number of inclined sheets, presumably originating from the shallow magma chamber within the caldera margin

  19. Equilibrium sensitivities of the Greenland ice sheet inferred from the adjoint of the three- dimensional thermo-mechanical model SICOPOLIS

    NASA Astrophysics Data System (ADS)

    Heimbach, P.; Bugnion, V.

    2008-12-01

    We present a new and original approach to understanding the sensitivity of the Greenland ice sheet to key model parameters and environmental conditions. At the heart of this approach is the use of an adjoint ice sheet model. MacAyeal (1992) introduced adjoints in the context of applying control theory to estimate basal sliding parameters (basal shear stress, basal friction) of an ice stream model which minimize a least-squares model vs. observation misfit. Since then, this method has become widespread to fit ice stream models to the increasing number and diversity of satellite observations, and to estimate uncertain model parameters. However, no attempt has been made to extend this method to comprehensive ice sheet models. Here, we present a first step toward moving beyond limiting the use of control theory to ice stream models. We have generated an adjoint of the three-dimensional thermo-mechanical ice sheet model SICOPOLIS of Greve (1997). The adjoint was generated using the automatic differentiation (AD) tool TAF. TAF generates exact source code representing the tangent linear and adjoint model of the parent model provided. Model sensitivities are given by the partial derivatives of a scalar-valued model diagnostic or "cost function" with respect to the controls, and can be efficiently calculated via the adjoint. An effort to generate an efficient adjoint with the newly developed open-source AD tool OpenAD is also under way. To gain insight into the adjoint solutions, we explore various cost functions, such as local and domain-integrated ice temperature, total ice volume or the velocity of ice at the margins of the ice sheet. Elements of our control space include initial cold ice temperatures, surface mass balance, as well as parameters such as appear in Glen's flow law, or in the surface degree-day or basal sliding parameterizations. Sensitivity maps provide a comprehensive view, and allow a quantification of where and to which variables the ice sheet model is

  20. Evaluation of the Surface Representation of the Greenland Ice Sheet in a General Circulation Model

    NASA Technical Reports Server (NTRS)

    Cullather, Richard I.; Nowicki, Sophie M. J.; Zhao, Bin; Suarez, Max J.

    2014-01-01

    Simulated surface conditions of the Goddard Earth Observing System model, version 5 (GEOS 5) atmospheric general circulation model (AGCM) are examined for the contemporary Greenland Ice Sheet (GrIS). A surface parameterization that explicitly models surface processes including snow compaction, meltwater percolation and refreezing, and surface albedo is found to remedy an erroneous deficit in the annual net surface energy flux and provide an adequate representation of surface mass balance (SMB) in an evaluation using simulations at two spatial resolutions. The simulated 1980-2008 GrIS SMB average is 24.7+/-4.5 cm yr(- 1) water-equivalent (w.e.) at.5 degree model grid spacing, and 18.2+/-3.3 cm yr(- 1) w.e. for 2 degree grid spacing. The spatial variability and seasonal cycle of the simulation compare favorably to recent studies using regional climate models, while results from 2 degree integrations reproduce the primary features of the SMB field. In comparison to historical glaciological observations, the coarser resolution model overestimates accumulation in the southern areas of the GrIS, while the overall SMB is underestimated. These changes relate to the sensitivity of accumulation and melt to the resolution of topography. The GEOS-5 SMB fields contrast with available corresponding atmospheric models simulations from the Coupled Model Intercomparison Project (CMIP5). It is found that only a few of the CMIP5 AGCMs examined provide significant summertime runoff, a dominant feature of the GrIS seasonal cycle. This is a condition that will need to be remedied if potential contributions to future eustatic change from polar ice sheets are to be examined with GCMs.

  1. Concentrated englacial shear over rigid basal ice, West Antarctica: implications for modelling and ice sheet flow

    NASA Astrophysics Data System (ADS)

    Ross, Neil; Siegert, Martin

    2014-05-01

    Basal freeze-on, deformation and ice crystal fabric re-organisation have been invoked to explain thick, massive englacial units observed in the lower ice column of both the Antarctic and Greenland ice sheets. Whilst recognised as having very different rheological properties to overlying meteoric ice, studies assessing the impact of these basal units on the large-scale flow of an ice sheet have so far been limited. We report the discovery of a previously unknown, extensive (100 km long, more than 25 km wide, and up to 1 km thick) englacial unit of near-basal ice beneath the onset zone of the Institute Ice Stream, West Antarctica. Using radio-echo sounding observations, we describe the form and physical characteristics of this englacial unit, and its impact on the stratigraphy and internal deformation of the overlying ice. The lower englacial unit, characterised by a highly-deformed to massive structure, is inferred to be rheologically distinct from the overlying ice column. The overlying ice contains a series of englacial 'whirlwind' features, which are traceable and exhibit longitudinal continuity between flow-orthogonal radar lines. In our data, these whirlwinds are the representation of englacial layer buckling, and therefore provide robust evidence for enhanced ice flow. The interface between the primary ice units is sharp and abrupt, and at a macro-scale is characterised by a series of high-amplitude long-wavelength undulations. Immediately above this interface, whirlwind features are deformed and display evidence for flow-orthogonal horizontal shear, consistent with the deformation of the overlying ice across the basal ice unit. This phenomenon is not a local process, it is observed above the entirety of the currently mapped extent of the basal ice, nor is it dependent on flight orientation, the direction of shear is consistent regardless of flight orientation. These findings have clear significance for our understanding and ability to realistically model ice

  2. Differential measurement and model calculations of cosmic ray latitudinal gradient with respect to the heliospheric current sheet

    NASA Technical Reports Server (NTRS)

    Christon, S. P.; Cummings, A. C.; Stone, E. C.; Behannon, K. W.; Burlaga, L. F.

    1986-01-01

    Simultaneous magnetic field and charged particle measurements from the Voyager spacecraft with heliographic latitude separations of more than 10 deg are used to investigate the distribution of about 1-GeV galactic cosmic ray protons with respect to the heliospheric current sheet in the outer solar system. By comparing the ratio of cosmic ray flux at Voyager 1 to that at Voyager 2 during periods of relatively quiet interplanetary conditions when the spacecraft are either both north or both south of the heliospheric current sheet, an average latitude component of the gradient of the cosmic ray flux on opposite sides of the current sheet is derived under restricted interplanetary conditions of -0.22 + or - 0.03 pct/deg, equivalent to a decrease of about 1 percent/AU away from the current sheet at about 12 AU. The results for these limited periods are in qualitative agreement with propagation models incorporating particle drifts.

  3. The palaeoglaciology of the central sector of the British and Irish Ice Sheet: reconciling glacial geomorphology and preliminary ice sheet modelling

    NASA Astrophysics Data System (ADS)

    Evans, David J. A.; Livingstone, Stephen J.; Vieli, Andreas; Cofaigh, Colm Ó.

    2009-04-01

    Digital elevation models of the area around the Solway Lowlands reveal complex subglacial bedform imprints relating the central sector of the LGM British and Irish Ice Sheet. Drumlin and lineation mapping in four case studies show that glacier flow directions switched significantly through time. These are summarised in four major flow phases in the region: Phase I flow was from a dominant Scottish dispersal centre, which transported Criffel granite erratics to the Eden Valley and forced Lake District ice eastwards over the Pennines at Stainmore; Phase II involved easterly flow of Lake District and Scottish ice through the Tyne Gap and Stainmore Gap with an ice divide located over the Solway Firth; Phase III was a dominant westerly flow from upland dispersal centres into the Solway lowlands and along the Solway Firth due to draw down of ice into the Irish Sea basin; Phase IV was characterised by unconstrained advance of Scottish ice across the Solway Firth. Forcing of a numerical model of ice sheet inception and decay by the Greenland ice core record facilitates an assessment of the potential for rapid ice flow directional switching during one glacial cycle. The model indicates that, after fluctuations of smaller radially flowing ice caps prior to 30 ka BP, the ice sheet grows to produce an elongate, triangular-shaped dome over NW England and SW Scotland at the LGM at 19.5 ka BP. Recession after 18.5 ka BP displays a complex pattern of significant ice flow directional switches over relatively short timescales, complementing the geomorphologically-based assessments of palaeo-ice dynamics. The palaeoglaciological implications of this combined geomorphic and modelling approach are that: (a) the central sector of the BIIS was as a major dispersal centre for only ca 2.5 ka after the LGM; (b) the ice sheet had no real steady state and comprised constantly migrating dispersal centres and ice divides; (c) subglacial streamlining of flow sets was completed over short phases

  4. Validation of formability of laminated sheet metal for deep drawing process using GTN damage model

    NASA Astrophysics Data System (ADS)

    Lim, Yongbin; Cha, Wan-gi; Ko, Sangjin; Kim, Naksoo

    2013-12-01

    In this study, we studied formability of PET/PVC laminated sheet metal which named VCM (Vinyl Coated Metal). VCM offers various patterns and good-looking metal steel used for appliances such as refrigerator and washing machine. But, this sheet has problems which are crack and peeling of film when the material is formed by deep drawing process. To predict the problems, we used finite element method and GTN (Gurson-Tvergaard-Needleman) damage model to represent damage of material. We divided the VCM into 3 layers (PET film, adhesive and steel added PVC) in finite element analysis model to express the crack and peeling phenomenon. The material properties of each layer are determined by reverse engineering based on tensile test result. Furthermore, we performed the simple rectangular deep drawing and simulated it. The simulation result shows good agreement with drawing experiment result in position, punch stroke of crack occurrence. Also, we studied the fracture mechanism of PET film on VCM by comparing the width direction strain of metal and PET film.

  5. Nonrigid Medical Image Registration by Finite-Element Deformable Sheet-Curve Models

    PubMed Central

    Wang, Yue; Freedman, Matthew T.; Adali, Tulay; Shields, Peter

    2006-01-01

    Image-based change quantitation has been recognized as a promising tool for accurate assessment of tumor's early response to chemoprevention in cancer research. For example, various changes on breast density and vascularity in glandular tissue are the indicators of early response to treatment. Accurate extraction of glandular tissue from pre- and postcontrast magnetic resonance (MR) images requires a nonrigid registration of sequential MR images embedded with local deformations. This paper reports a newly developed registration method that aligns MR breast images using finite-element deformable sheet-curve models. Specifically, deformable curves are constructed to match the boundaries dynamically, while a deformable sheet of thin-plate splines is designed to model complex local deformations. The experimental results on both digital phantoms and real MR breast images using the new method have been compared to point-based thin-plate-spline (TPS) approach, and have demonstrated a significant and robust improvement in both boundary alignment and local deformation recovery. PMID:23165046

  6. Constitutive model based on dislocation density and ductile fracture of Monel 400 thin sheet under tension

    NASA Astrophysics Data System (ADS)

    Wang, Chuanjie; Xue, Shaoxi; Chen, Gang; Zhang, Peng

    2017-03-01

    In micro-scaled plastic deformation, material strength and ductile fracture behaviors of thin sheet in tension are quite different from those in macro-scale. In this study, uniaxial tensile tests of Monel 400 thin sheets with different microstructures were carried out to investigate the plastic deformation size effect in micro-scale. The experimental results indicate that the flow stress and fracture strain departure from the traditional empirical formula when there are only fewer grains across the thickness. And the number of dimples on the fracture surface is getting smaller with the decreasing ratio of specimen thickness to grain size. Then, a constitutive model based on dislocation density considering the free surface effect in micro-scale is proposed to reveal the mechanism of the flow stress size effect. In addition, a model is proposed considering the surface roughening inducing the thickness nonuniform and the decrease of micro-voids resulting from the reduction of grain boundary density with the decreasing ratio of specimen thickness to grain size. The interactive effects of the surface roughening and the decrease of micro-voids result in the earlier fracture in micro tension of the specimen with fewer grains across the thickness.

  7. Validation of formability of laminated sheet metal for deep drawing process using GTN damage model

    SciTech Connect

    Lim, Yongbin; Cha, Wan-gi; Kim, Naksoo; Ko, Sangjin

    2013-12-16

    In this study, we studied formability of PET/PVC laminated sheet metal which named VCM (Vinyl Coated Metal). VCM offers various patterns and good-looking metal steel used for appliances such as refrigerator and washing machine. But, this sheet has problems which are crack and peeling of film when the material is formed by deep drawing process. To predict the problems, we used finite element method and GTN (Gurson-Tvergaard-Needleman) damage model to represent damage of material. We divided the VCM into 3 layers (PET film, adhesive and steel added PVC) in finite element analysis model to express the crack and peeling phenomenon. The material properties of each layer are determined by reverse engineering based on tensile test result. Furthermore, we performed the simple rectangular deep drawing and simulated it. The simulation result shows good agreement with drawing experiment result in position, punch stroke of crack occurrence. Also, we studied the fracture mechanism of PET film on VCM by comparing the width direction strain of metal and PET film.

  8. Constitutive model based on dislocation density and ductile fracture of monel 400 thin sheet under tension

    NASA Astrophysics Data System (ADS)

    Wang, Chuanjie; Xue, Shaoxi; Chen, Gang; Zhang, Peng

    2017-02-01

    In micro-scaled plastic deformation, material strength and ductile fracture behaviors of thin sheet in tension are quite different from those in macro-scale. In this study, uniaxial tensile tests of Monel 400 thin sheets with different microstructures were carried out to investigate the plastic deformation size effect in micro-scale. The experimental results indicate that the flow stress and fracture strain departure from the traditional empirical formula when there are only fewer grains across the thickness. And the number of dimples on the fracture surface is getting smaller with the decreasing ratio of specimen thickness to grain size. Then, a constitutive model based on dislocation density considering the free surface effect in micro-scale is proposed to reveal the mechanism of the flow stress size effect. In addition, a model is proposed considering the surface roughening inducing the thickness nonuniform and the decrease of micro-voids resulting from the reduction of grain boundary density with the decreasing ratio of specimen thickness to grain size. The interactive effects of the surface roughening and the decrease of micro-voids result in the earlier fracture in micro tension of the specimen with fewer grains across the thickness.

  9. A MODEL FOR THE ELECTRICALLY CHARGED CURRENT SHEET OF A PULSAR

    SciTech Connect

    DeVore, C. R.; Antiochos, S. K.; Black, C. E.; Harding, A. K.; Kalapotharakos, C.; Kazanas, D.; Timokhin, A. N.

    2015-03-10

    Global-scale solutions for the magnetosphere of a pulsar consist of a region of low-lying, closed magnetic field near the star, bounded by opposite-polarity regions of open magnetic field along which the pulsar wind flows into space. Separating these open-field regions is a magnetic discontinuity—an electric current sheet—consisting of generally nonneutral plasma. We have developed a self-consistent model for the internal equilibrium structure of the sheet by generalizing the charge-neutral Vlasov/Maxwell equilibria of Harris and Hoh to allow for net electric charge. The resulting equations for the electromagnetic field are solved analytically and numerically. Our results show that the internal thermal pressure needed to establish equilibrium force balance, and the associated effective current-sheet thickness and magnetization, can differ by orders of magnitude from the Harris/Hoh charge-neutral limit. The new model provides a starting point for kinetic or fluid investigations of instabilities that can cause magnetic reconnection and flaring in pulsar magnetospheres.

  10. JEDI: Jobs and Economic Development Impacts Model, National Renewable Energy Laboratory (NREL) (Fact Sheet)

    SciTech Connect

    Not Available

    2009-12-01

    The Jobs and Economic Development Impact (JEDI) models are user-friendly tools that estimate the economic impacts of constructing and operating power generation and biofuel plants at the local (usually state) level. First developed by NREL's Wind Powering America program to model wind energy jobs and impacts, JEDI has been expanded to biofuels, concentrating solar power, coal, and natural gas power plants. Based on project-specific and default inputs (derived from industry norms), JEDI estimates the number of jobs and economic impacts to a local area (usually a state) that could reasonably be supported by a power generation project. For example, JEDI estimates the number of in-state construction jobs from a new wind farm. This fact sheet provides an overview of the JEDI model as it pertains to wind energy projects.

  11. Application of a shear-modified GTN model to incremental sheet forming

    NASA Astrophysics Data System (ADS)

    Smith, Jacob; Malhotra, Rajiv; Liu, W. K.; Cao, Jian

    2013-12-01

    This paper investigates the effects of using a shear-modified Gurson-Tvergaard-Needleman model, which is based on the mechanics of voids, for simulating material behavior in the incremental forming process. The problem chosen for analysis is a simplified version of the NUMISHEET 2014 incremental forming benchmark test. The implications of the shear-modification of the model specifically for incremental sheet forming processes are confirmed using finite element analysis. It is shown that including the shear term has a significant effect on fracture timing in incremental forming, which is not well reflected in the observed tensile test simulations for calibration. The numerical implementation and the need for comprehensive calibration of the model are briefly discussed.

  12. Data-Model Comparisons of Plasma Sheet Ion Temperatures during Moderate Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    Keesee, A. M.; Ilie, R.; Liemohn, M. W.; Trigo, B.; Robison, G.; Carr, J., Jr.

    2014-12-01

    Ion heating occurs during geomagnetic storms as a result of many physical processes, including magnetic reconnection and adiabatic heating. Ion temperatures calculated from TWINS energetic neutral atom (ENA) data provide a global view of regions of heated ions in the plasma sheet. Two storms of similar, moderate magnitude are analyzed, a coronal mass ejection (CME)-driven storm that occurred on 26 September 2011 and a high speed stream (HSS)-driven storm on 13 October 2012. We present a comparison of the ion temperatures during the storms to patterns observed in a superposed epoch analysis of ion temperatures [Keesee et al., 2013] and compare the October storm to a previously analyzed HSS-driven storm [Keesee et al., 2012]. We also present a comparison of observed ion temperatures to those calculated from a simulation of each storm using the Space Weather Modeling Framework, including the BATS-R-US MHD model coupled with the HEIDI inner magnetosphere model.

  13. Parameterization of grounding-line cliff failure in an Antarctic ice sheet model

    NASA Astrophysics Data System (ADS)

    Pollard, David; DeConto, Robert

    2014-05-01

    Two mechanisms have recently been added to a 3-D ice-sheet model that can produce drastic retreat into East Antarctic sub-glacial basins during past warm periods, as implied by (albeit uncertain) geologic evidence. The two mechanisms, (1) structural failure of large tidewater cliffs, and (2) enhanced ice-shelf calving due to meltwater draining into crevasses, present challenges in their parameterization within coarse-grid models. Here we describe details and choices in the parameterization of structural failure at deep grounding lines, its incorporation into the large-scale dynamical equations, and the sensitivity of model results to these choices. In addition, a parameterization of melt-enhanced calving is described, along with a simple representation of the clogging effects of ice melange in narrow seaways, and their effects on Antarctic simulations.

  14. Modeling Greenland Ice Sheet Snow and Firn Densities: Role of Dry Snow Density, Liquid Water, and Model Setup

    NASA Astrophysics Data System (ADS)

    Alexander, P. M.; Koenig, L.; Tedesco, M.; Kuipers Munneke, P.; Fettweis, X.; Ligtenberg, S.; Noel, B.; van den Broeke, M. R.; Miège, C.

    2016-12-01

    Snow and firn densities on the Greenland Ice Sheet (GrIS) play an important role in the surface mass balance (SMB), a key component of the ice sheet's contribution to sea level change. Snow and firn densities influence the storage of liquid water, the exchange of heat between the atmosphere and the ice sheet, and the transport of snow by wind. Density is also necessary for converting altimetry and radar-derived thickness changes into mass changes. We compare density profiles from the Modèle Atmosphérique Régionale (MAR) and the Firn Densification Model of the Institute for Marine and Atmospheric Research, Utrecht (IMAU FDM) with in situ profiles from the Surface Mass Balance Working Group (SUMup) community dataset. The IMAU FDM is forced with atmospheric output from the RACMO2 regional climate model. In dry snow areas the parameterization for initial snow density is responsible for the largest MAR biases. In areas of melt and refreezing, parameterization for liquid water and errors in accumulation play an important role in differences between models and model biases. In ablation areas with a shallow snowpack, accumulation errors affect the thickness of snow above ice, and influence the density profile as a result. Model initialization and spinup time also influence simulated profiles. In addition to comparison with observations, we investigate the source of inter-model differences, local errors and biases by applying the same atmospheric forcing to the two models, using model outputs and weather station data from the Greenland Climate Network (GC-Net).

  15. Rainfall and sheet power model for interrill erosion in steep slope

    NASA Astrophysics Data System (ADS)

    Shin, Seung Sook; Deog Park, Sand; Nam, Myeong Jun

    2015-04-01

    The two-phase process of interrill erosion consist of the splash and detachment of individual particles from soil mass by impact of raindrops and the transport by erosive running water. Most experimental results showed that the effect of interaction between rainfall impact and surface runoff increases soil erosion in low or gentle slope. Especially, the combination of rain splash and sheet flow is the dominant runoff and erosion mechanism occurring on most steep hillslopes. In this study, a rainfall simulation was conducted to evaluate interrill erosion in steep slope with cover or non-cover. The kinetic energy of raindrops of rainfall simulator was measured by disdrometer used to measure the drop size distribution and velocity of falling raindrops and showed about 0.563 rate of that calculated from empirical equation between rainfall kinetic energy and rainfall intensity. Surface and subsurface runoff and sediment yield depended on rainfall intensity, gradient of slope, and existence of cover. Sediment from steep plots under rainfall simulator is greatly reduced by existence of the strip cover that the kinetic energy of raindrop approximates to zero. Soil erosion in steep slope with non-cover was nearly 4.93 times of that measured in plots with strip cover although runoff was only 1.82 times. The equation of a rainfall and sheet power was used to evaluate sediment yields in steep slope with cover or non-cover. The power model successfully explained physical processes for interrill erosion that combination of raindrop impact and sheet flow increases greatly soil erosion in steep slope. This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology(No. 2013R1A1A3011962).

  16. Assessing the Impact of Retreat Mechanisms in a Simple Antarctic Ice Sheet Model Using Bayesian Calibration

    PubMed Central

    Shaffer, Gary; Pollard, David; Guan, Yawen; Wong, Tony E.; Forest, Chris E.; Keller, Klaus

    2017-01-01

    The response of the Antarctic ice sheet (AIS) to changing climate forcings is an important driver of sea-level changes. Anthropogenic climate change may drive a sizeable AIS tipping point response with subsequent increases in coastal flooding risks. Many studies analyzing flood risks use simple models to project the future responses of AIS and its sea-level contributions. These analyses have provided important new insights, but they are often silent on the effects of potentially important processes such as Marine Ice Sheet Instability (MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well justified and result in more parsimonious and transparent model structures. This raises the question of how this approximation impacts hindcasts and projections. Here, we calibrate a previously published and relatively simple AIS model, which neglects the effects of MICI and regional characteristics, using a combination of observational constraints and a Bayesian inversion method. Specifically, we approximate the effects of missing MICI by comparing our results to those from expert assessments with more realistic models and quantify the bias during the last interglacial when MICI may have been triggered. Our results suggest that the model can approximate the process of MISI and reproduce the projected median melt from some previous expert assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the observed data during the last interglacial period and our mean projection is roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year 2100. These results suggest that missing MICI and/or regional characteristics can lead to a low-bias during warming period AIS melting and hence a potential low-bias in projected sea levels and flood risks. PMID:28081273

  17. Assessing the Impact of Retreat Mechanisms in a Simple Antarctic Ice Sheet Model Using Bayesian Calibration.

    PubMed

    Ruckert, Kelsey L; Shaffer, Gary; Pollard, David; Guan, Yawen; Wong, Tony E; Forest, Chris E; Keller, Klaus

    2017-01-01

    The response of the Antarctic ice sheet (AIS) to changing climate forcings is an important driver of sea-level changes. Anthropogenic climate change may drive a sizeable AIS tipping point response with subsequent increases in coastal flooding risks. Many studies analyzing flood risks use simple models to project the future responses of AIS and its sea-level contributions. These analyses have provided important new insights, but they are often silent on the effects of potentially important processes such as Marine Ice Sheet Instability (MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well justified and result in more parsimonious and transparent model structures. This raises the question of how this approximation impacts hindcasts and projections. Here, we calibrate a previously published and relatively simple AIS model, which neglects the effects of MICI and regional characteristics, using a combination of observational constraints and a Bayesian inversion method. Specifically, we approximate the effects of missing MICI by comparing our results to those from expert assessments with more realistic models and quantify the bias during the last interglacial when MICI may have been triggered. Our results suggest that the model can approximate the process of MISI and reproduce the projected median melt from some previous expert assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the observed data during the last interglacial period and our mean projection is roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year 2100. These results suggest that missing MICI and/or regional characteristics can lead to a low-bias during warming period AIS melting and hence a potential low-bias in projected sea levels and flood risks.

  18. Comparative Study of Three Data Assimilation Methods for Ice Sheet Model Initialisation

    NASA Astrophysics Data System (ADS)

    Mosbeux, Cyrille; Gillet-Chaulet, Fabien; Gagliardini, Olivier

    2015-04-01

    The current global warming has direct consequences on ice-sheet mass loss contributing to sea level rise. This loss is generally driven by an acceleration of some coastal outlet glaciers and reproducing these mechanisms is one of the major issues in ice-sheet and ice flow modelling. The construction of an initial state, as close as possible to current observations, is required as a prerequisite before producing any reliable projection of the evolution of ice-sheets. For this step, inverse methods are often used to infer badly known or unknown parameters. For instance, the adjoint inverse method has been implemented and applied with success by different authors in different ice flow models in order to infer the basal drag [ Schafer et al., 2012; Gillet-chauletet al., 2012; Morlighem et al., 2010]. Others data fields, such as ice surface and bedrock topography, are easily measurable with more or less uncertainty but only locally along tracks and interpolated on finer model grid. All these approximations lead to errors on the data elevation model and give rise to an ill-posed problem inducing non-physical anomalies in flux divergence [Seroussi et al, 2011]. A solution to dissipate these divergences of flux is to conduct a surface relaxation step at the expense of the accuracy of the modelled surface [Gillet-Chaulet et al., 2012]. Other solutions, based on the inversion of ice thickness and basal drag were proposed [Perego et al., 2014; Pralong & Gudmundsson, 2011]. In this study, we create a twin experiment to compare three different assimilation algorithms based on inverse methods and nudging to constrain the bedrock friction and the bedrock elevation: (i) cyclic inversion of friction parameter and bedrock topography using adjoint method, (ii) cycles coupling inversion of friction parameter using adjoint method and nudging of bedrock topography, (iii) one step inversion of both parameters with adjoint method. The three methods show a clear improvement in parameters

  19. What can adjoint modelling tell about the response of the Greenland Ice Sheet to changes in basal sliding?

    NASA Astrophysics Data System (ADS)

    McGovern, Jonathan; Rutt, Ian; Murray, Tavi; Utke, Jean

    2013-04-01

    Studying the future behaviour of the Greenland Ice Sheet is important considering the ice sheet has a sea-level equivalent of 7 metres and the rate of mass loss from it is increasing (Velicogna, 2009). Examining the modelled response of the Greenland Ice Sheet to changes in forcing parameters can give insight into how it will behave in the future. The response of the ice sheet to specific changes in forcing parameters is referred to as the sensitivity. Being able to obtain model sensitivities in as little computation time as possible would be useful for examining the future response of the Greenland Ice Sheet. Adjoint models allow sensitivities to be obtained more efficiently than the conventional way, when considering spatially varying parameters. Conventionally, such sensitivities are obtained by perturbing a parameter at every grid point in turn and calculating the sensitivity at every grid point. Adjoint sensitivities, though, are calculated in a single step. This reduces the computational cost when obtaining sensitivities over large model domains. The adjoint method also has the advantage that it gives the exact value of the model sensitivity, rather than a finite difference approximation to it. We present the adjoint of a finite difference, shallow ice, thermomechanical ice sheet model with basal sliding, applied to the Greenland Ice Sheet. This adjoint model is obtained using the OpenAD automatic differentiation tool (Utke, 2006), which is open source. The adjoint model is validated by comparing adjoint and forward model sensitivities over 100 years. This work builds on the work of Heimbach (2009). We use the adjoint model to examine the sensitivity of the model to changes in basal sliding. About half the mass loss from the Greenland Ice Sheet occurs from surface runoff and half from dynamic mass loss (Broeke, 2009). Melt-water from Greenland Ice Sheet supra-glacial lakes can percolate to the bed through moulins. The melt-water that reaches the bed can then

  20. Modeling the inner plasma sheet protons and magnetic field under enhanced convection

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Ping; Lyons, Larry R.; Chen, Margaret W.; Wolf, Richard A.; Toffoletto, Frank R.

    2003-02-01

    In order to understand the evolution of the protons and magnetic field in the inner plasma sheet from quiet to disturbed conditions, we incorporate a modified version of the Magnetospheric Specification Model (MSM) with a modified version of the Tsyganenko 96 (T96) magnetic field model to simulate the protons and magnetic field under an increasing convection electric field with two-dimensional (2-D) force balance maintained along the midnight meridian. The local time dependent proton differential fluxes assigned to the model boundary are a mixture of hot plasma from the mantle and cooler plasma from the low latitude boundary layer (LLBL). We previously used this model to simulate the inner plasma sheet under weak convection corresponding to a cross polar cap potential drop (ΔΦPC) equal to 26 kV and obtained 2-D quiet time equilibrium for proton and magnetic field that agrees well with observations. We start our simulation for enhanced convection with this quiet time equilibrium and time-independent boundary particle sources and increase ΔΦPC steadily from 26 to 146 kV in 5 hours. Simulations are also run separately to steady states by keeping ΔΦPC constant after it is increased to 98 and 146 kV. The magnitudes of proton pressure, number density, and temperature and their increase from quiet to moderate activity (ΔΦPC = 98 kV) are consistent with most observations. Our simulation at high activity (ΔΦPC = 146 kV) underestimates the observed pressure and temperature. This disagreement indicates possible dependence of the boundary particle sources on activity and possible effects of solar wind dynamic pressure enhancements that have not yet been included in our simulation. The simulated equatorial pressures and temperatures show stronger enhancement on the dusk side than on the dawn side as convection is increased, while density profiles show an increase on the dawn side and a decrease on the dusk side. The simulated proton flow speed at the equatorial plane

  1. Modeling the West Antarctic and Greenland ice sheets: New dynamic, thermodynamic, and isostatic insights

    NASA Astrophysics Data System (ADS)

    Parizek, Byron R.

    Numerical simulations indicate that the apparent long-term persistence and short-term variability of the Ross ice streams in West Antarctica are tied to regional thermal conditions and local basal lubrication. Modelling results suggest that the flux of latent heat in a throughgoing hydrologic system fed by melt beneath thick inland ice maintains the lubrication of the ice streams despite their tendency to freeze to the bed, and would allow additional thinning and grounding-line retreat. However, the efficiency of basal water distribution may be a constraint on the system. Because local thermal deficits promote basal freeze-on (especially on topographic highs), observed short-term variability is likely to persist. Furthermore, simulations indicate that the ice streams have experienced only small deglacial thickness changes and are thinning more rapidly than their beds are rising isostatically. Thickness changes of O (100)m are modelled at the modern grounding line through the last glacial cycle. Coupled ice and bedrock models indicate isostatic rebound is raising the ice sheet at the modern grounding line faster than the rising sea level is submerging it. While, in and of itself, this could potentially lead to a grounding-line re-advance, ice flow is modelled to respond to recent changes in temperature, accumulation rate, and basal processes more rapidly than it does to bedrock-elevation and/or sea-level fluctuations. Future projections of the Greenland ice sheet indicate a faster contribution to sea-level rise in a warming world than previously believed, based on numerical modelling using a parameterization of recent results showing surface-meltwater lubrication of Greenland ice flow (Zwally et al., 2002). Numerous simulations were conducted to test a wide range of parameter space linking surface melt with a new sliding law based on Zwally et al. data under different global warming scenarios. Comparisons to reconstructions generated with a traditional sliding

  2. Did Variations in the Total Solar Irradiance affect the Greenland Ice Sheet during the Holocene? - A Model Study

    NASA Astrophysics Data System (ADS)

    Bügelmayer, M.; Roche, D. M.; Renssen, H.

    2014-12-01

    Marine sediments provide evidence for the periodic occurrence of centennial-scale events with enhanced iceberg discharge during the past 11.000 years. It has been suggested that these events were caused by reductions in solar activity, indicating that an external forcing that is considered small, could have a potential impact on climate due to feedback mechanisms. These proposed interactions between climate and solar irradiance have been investigated using numerical models, but so far without dynamically computing the Greenland ice sheet and iceberg calving. We therefore use the earth system model iLOVECLIM coupled to the ice sheet/ice shelf model GRISLI and to a dynamic-thermodynamic iceberg module to investigate the effect of variations in total solar irradiance (TSI) on the Greenland ice sheet, as well as on iceberg calving and transport. We have performed fifteen different transient ensemble experiments of the last 6000 years, applying reconstructed atmospheric greenhouse gas concentrations, volcanic aerosol loads and orbital parameters as forcing. In ten of these fifteen experiments, we additionally apply reconstructed variations of the TSI that differ in amplitude (weak or strong). The resulting transient evolution of the Greenland ice sheet fits well to observations and we do find strong fluctuations in the calving flux as computed by GRISLI. But these fluctuations occur in all the experiments performed, independent of the use of TSI forcing, indicating that internal ice sheet variability causes the simulated variations. Thus, we cannot confirm the impact of the total solar irradiance on the ice rafted debris in our coupled climate - ice-sheet - iceberg model, but our experiments do suggest that internal ice sheet variability may be a possible alternative explanation for the Holocene ice rafting events that have been observed in Atlantic sediment cores.

  3. Numerical modeling of subglacial erosion and sediment transport beneath the Laurentide Ice Sheet

    NASA Astrophysics Data System (ADS)

    Melanson, A.; Bell, T.; Tarasov, L.

    2012-04-01

    Present-day sediment distribution offers a potentially strong constraint on past ice sheet evolution. However, glacial system models (GSMs) cannot address this while lacking physically-based representations of subglacial sediment generation and transport. Incorporation of these elements in GSMs is also required in order to understand the impact of changing sediment cover on glacial cycle dynamics. Towards this goal, we present a subglacial process model that incorporates mechanisms for sediment production, entrainment, transport, and deposition. An abrasion law based on Hallet's model and a quarrying law dependent on basal water pressure and bed roughness are used to calculate bedrock erosion. The incorporation of loose debris in the basal ice is modeled by regelation intrusion and basal freeze-on, depending on the thermal condition and the availability of water at the base. The entrained debris is subsequently transported along the ice sheet's internal velocity field and vertically mixed through a diffusion equation that accounts for folding and thrust faulting. The inclusion of vertical mixing lowers the basal debris concentration and allows more regelation entrainment. Soft bed deformation is included as an advective component within the subglacial sediment, the rheology of which is assumed to be weakly non-linear. Deposition occurs whenever the basal ice is debris-laden and the melting rate exceeds the entrainment rate. The model is coupled to the MUN 3D GSM, which includes a newly developed subglacial hydrology module. The GSM itself has been subject to Bayesian calibration for North American and Eurasian deglaciation and thus a probabilistic ensemble of deglacial chronologies is available. With this calibrated ensemble, we compare the range of calculated sediment thickness fields and cumulative erosion over the last glacial cycle against the present-day pattern of glacigenic sediment and the geological estimates of glacial erosion over North America

  4. Large-Ensemble modeling of last deglacial and future variations of the Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Pollard, David; DeConto, Robert; Chang, Won; Applegate, Patrick; Haran, Murali

    2015-04-01

    Recent observations of thinning and retreat of the Pine Island and Thwaites Glaciers identify the Amundsen Sea Embayment (ASE) sector of West Antarctica as particularly vulnerable to future climate change. To date, most future modeling of these glaciers has been calibrated using recent and modern observations. As an alternate approach, we apply a hybrid 3-D ice sheet-shelf model to the last deglacial retreat of Antarctica, making use of geologic data from ~20,000 years BP to present, focusing on the ASE but including other sectors of Antarctica. Following several recent ice-sheet studies, we use Large-Ensemble statistical techniques, performing sets of ~500 to 1000 runs with varying model parameters. The model is run for the last 40 kyrs on 10 to 20-km grids, both on continental domains and also on nested domains over West Antarctica. Various types of objective scores for each run are calculated using reconstructed past grounding lines, relative sea level records, measured uplift rates, and cosmogenic elevation-age data. Runs are extended into the future few millennia using RCP scenarios. The goal is to produce calibrated probabilistic ranges of model parameter values and quantified envelopes of future ice retreat. Preliminary results are presented for Large Ensembles with (i) Latin HyperCube sampling in high-dimensional parameter space, using statistical emulators and Markov Chain Monte Carlo techniques, and (ii) dense "factorial" sampling with a smaller number of parameters. Different ways of combining the types of scores listed above are explored. One robust conclusion is that for the warmer future RCP scenarios, most reasonable parameter combinations produce retreat deep into the West Antarctic interior. Recently proposed mechanisms of hydrofracturing and ice-cliff failure accelerate future West Antarctic retreat, and later produce retreat into East Antarctic basins.

  5. Ductile Fracture of AHSS Sheets under Multi-axial Loading: Experiments and Modeling

    NASA Astrophysics Data System (ADS)

    Dunand, M.; Mohr, D.

    2011-08-01

    Fracture experiments on TRIP-assisted steel sheets covering a wide range of stress states (from shear to equibiaxial tension) are performed to create a comprehensive experimental database to calibrate and evaluate the shear-modified Gurson model (Nielsen and Tvergaard, 2010) and the Modified Mohr-Coulomb (MMC) fracture model (Bai and Wierzbicki, 2010). The experimental program includes notched tensile tests as well as fracture experiments on butterfly-shaped specimens under combined tension and shear loading. Both phenomenological fracture models are physics-inspired and take the effect of the first and third stress tensor invariants into account in predicting the onset of ductile fracture. The MMC model is based on the assumption that the initiation of fracture is determined by a critical stress state, while the shear-modified Gurson model assumes void growth as the governing mechanism. The model accuracy is quantified based on the predictions of the displacements to fracture for experiments which have not been used for calibration. It is found that the MMC model predictions agree well with all experiments (less than 4% error), while less accurate predictions are observed for the shear-modified Gurson model. A comparison of plots of the strain to fracture as a function of the stress triaxiality and the normalized third invariant reveals significant differences between the two models except within the vicinity of stress states that have been used for calibration.

  6. Flow past a permeable stretching/shrinking sheet in a nanofluid using two-phase model.

    PubMed

    Zaimi, Khairy; Ishak, Anuar; Pop, Ioan

    2014-01-01

    The steady two-dimensional flow and heat transfer over a stretching/shrinking sheet in a nanofluid is investigated using Buongiorno's nanofluid model. Different from the previously published papers, in the present study we consider the case when the nanofluid particle fraction on the boundary is passively rather than actively controlled, which make the model more physically realistic. The governing partial differential equations are transformed into nonlinear ordinary differential equations by a similarity transformation, before being solved numerically by a shooting method. The effects of some governing parameters on the fluid flow and heat transfer characteristics are graphically presented and discussed. Dual solutions are found to exist in a certain range of the suction and stretching/shrinking parameters. Results also indicate that both the skin friction coefficient and the local Nusselt number increase with increasing values of the suction parameter.

  7. Flow Past a Permeable Stretching/Shrinking Sheet in a Nanofluid Using Two-Phase Model

    PubMed Central

    Zaimi, Khairy; Ishak, Anuar; Pop, Ioan

    2014-01-01

    The steady two-dimensional flow and heat transfer over a stretching/shrinking sheet in a nanofluid is investigated using Buongiorno’s nanofluid model. Different from the previously published papers, in the present study we consider the case when the nanofluid particle fraction on the boundary is passively rather than actively controlled, which make the model more physically realistic. The governing partial differential equations are transformed into nonlinear ordinary differential equations by a similarity transformation, before being solved numerically by a shooting method. The effects of some governing parameters on the fluid flow and heat transfer characteristics are graphically presented and discussed. Dual solutions are found to exist in a certain range of the suction and stretching/shrinking parameters. Results also indicate that both the skin friction coefficient and the local Nusselt number increase with increasing values of the suction parameter. PMID:25365118

  8. An Interconnect Sheet Resistance Model Considering CMP Pattern Effects in 45 nm Process

    NASA Astrophysics Data System (ADS)

    Ma, Tianyu; Chen, Lan; Ruan, Wenbiao

    Side effects in Cu interconnect chemical mechanical polishing (CMP) process - dishing and erosion - will both influence chip surface topography and deteriorate interconnect electrical characteristics such as interconnect resistance. In this paper, test chip was designed for measurement of both surface topography and electrical characteristics of Cu interconnect after CMP process. An interconnect sheet resistance model considering dishing and erosion effects is proposed and verified by experimental results. For most test structures, difference between prediction results and measurement results are less than 4%. This model is applicable to other CMP processes in which dishing and erosion are positive or negative, and it can also be easily integrated into state-of-art CMP simulators for accurate interconnect resistance prediction.

  9. Weighted current sheets supported in normal and inverse configurations - A model for prominence observations

    NASA Technical Reports Server (NTRS)

    Demoulin, P.; Forbes, T. G.

    1992-01-01

    A technique which incorporates both photospheric and prominence magnetic field observations is used to analyze the magnetic support of solar prominences in two dimensions. The prominence is modeled by a mass-loaded current sheet which is supported against gravity by magnetic fields from a bipolar source in the photosphere and a massless line current in the corona. It is found that prominence support can be achieved in three different kinds of configurations: an arcade topology with a normal polarity; a helical topology with a normal polarity; and a helical topology with an inverse polarity. In all cases the important parameter is the variation of the horizontal component of the prominence field with height. Adding a line current external to the prominence eliminates the nonsupport problem which plagues virtually all previous prominence models with inverse polarity.

  10. Validation of Finite Element Model used to Analyze Sheet Metal Punching Process in Automotive Part Manufacturing

    NASA Astrophysics Data System (ADS)

    Chantarapanich, N.; Siripanya, A.; Sucharitpwatskul, S.; Wanchat, S.

    2017-05-01

    Punching process is an operation that a scrap is separated from a metal sheet by a punch. Improper setting of punching conditions may lead to excessive of material deformation around edge region (burr), which may weakening the strength of produced part. Analysis of punching mechanics would be beneficial reducing defective part. One of effective analysing tool for this application is Finite Element (FE) method. The aim of this study is to develop reliable FE model for analysis of punching process. The FE model was developed based on 2D. FE result was validated with experimental testing result by comparing burr height. It was found that FE result is -1.79% difference compared to experimental result. Good agreement between FE and experimental result was obtained.

  11. Weighted current sheets supported in normal and inverse configurations - A model for prominence observations

    NASA Technical Reports Server (NTRS)

    Demoulin, P.; Forbes, T. G.

    1992-01-01

    A technique which incorporates both photospheric and prominence magnetic field observations is used to analyze the magnetic support of solar prominences in two dimensions. The prominence is modeled by a mass-loaded current sheet which is supported against gravity by magnetic fields from a bipolar source in the photosphere and a massless line current in the corona. It is found that prominence support can be achieved in three different kinds of configurations: an arcade topology with a normal polarity; a helical topology with a normal polarity; and a helical topology with an inverse polarity. In all cases the important parameter is the variation of the horizontal component of the prominence field with height. Adding a line current external to the prominence eliminates the nonsupport problem which plagues virtually all previous prominence models with inverse polarity.

  12. Contact Modelling in Isogeometric Analysis: Application to Sheet Metal Forming Processes

    NASA Astrophysics Data System (ADS)

    Cardoso, Rui P. R.; Adetoro, O. B.; Adan, D.

    2016-08-01

    Isogeometric Analysis (IGA) has been growing in popularity in the past few years essentially due to the extra flexibility it introduces with the use of higher degrees in the basis functions leading to higher convergence rates. IGA also offers the capability of easily reproducing discontinuous displacement and/or strain fields by just manipulating the multiplicity of the knot parametric coordinates. Another advantage of IGA is that it uses the Non-Uniform Rational B-Splines (NURBS) basis functions, that are very common in CAD solid modelling, and consequently it makes easier the transition from CAD models to numerical analysis. In this work it is explored the contact analysis in IGA for both implicit and explicit time integration schemes. Special focus will be given on contact search and contact detection techniques under NURBS patches for both the rigid tools and the deformed sheet blank.

  13. Phase field modeling of grain structure evolution during directional solidification of multi-crystalline silicon sheet

    NASA Astrophysics Data System (ADS)

    Lin, H. K.; Lan, C. W.

    2017-10-01

    Evolution of grain structures and grain boundaries (GBs), especially the coincident site lattice GBs, during directional solidification of multi-crystalline silicon sheet are simulated by using a phase field model for the first time. Since the coincident site lattice GBs having lower mobility, tend to follow their own crystallographic directions despite thermal gradients, the anisotropic energy and mobility of GBs are considered in the model. Three basic interactions of GBs during solidification are examined and they are consistent with experiments. The twinning process for new grain formation is further added in the simulation by considering twin nucleation. The effect of initial distribution of GB types and grain orientations is also investigated for the twinning frequency and the evolution of grain size and GB types.

  14. Comparison of adjoint and nudging methods to initialise ice sheet model basal conditions

    NASA Astrophysics Data System (ADS)

    Mosbeux, Cyrille; Gillet-Chaulet, Fabien; Gagliardini, Olivier

    2016-07-01

    Ice flow models are now routinely used to forecast the ice sheets' contribution to 21st century sea-level rise. For such short term simulations, the model response is greatly affected by the initial conditions. Data assimilation algorithms have been developed to invert for the friction of the ice on its bedrock using observed surface velocities. A drawback of these methods is that remaining uncertainties, especially in the bedrock elevation, lead to non-physical ice flux divergence anomalies resulting in undesirable transient effects. In this study, we compare two different assimilation algorithms based on adjoints and nudging to constrain both bedrock friction and elevation. Using synthetic twin experiments with realistic observation errors, we show that the two algorithms lead to similar performances in reconstructing both variables and allow the flux divergence anomalies to be significantly reduced.

  15. Siple Coast Ice Streams in a General Antarctic Ice Sheet Model.

    NASA Astrophysics Data System (ADS)

    Verbitsky, Mikhail

    2005-07-01

    In an earlier paper by Verbitsky and Saltzman, a vertically integrated, high-resolution, nonlinearly viscous, nonisothermal ice sheet model was presented to calculate the “present-day” equilibrium regime of the Antarctic ice sheet. Steady-state solutions for the ice topography and thermodynamics, represented by the extent of the areas of basal melting, were shown to be in good agreement with both observations and results obtained from other three-dimensional thermodynamical equations. The solution for the basal temperature field of the West Antarctic Siple Coast produced areas at the pressure melting point separated by strips of frozen-to-bed ice, the structure of which looks very similar to ice streams A-E. Since the possible response of the Siple Coast basal temperature pattern to global warming and to associated changes in the snowfall rate is not obvious, a special sensitivity study was conducted. Results of such a study suggest that increased precipitation rate and associated intensification of ice advection can effectively “shut down” West Antarctic ice streams.

  16. Modeling the Strength of β-sheet Structures in Silk Crystals and Protein Molecules

    NASA Astrophysics Data System (ADS)

    Grubb, David

    2012-02-01

    The mechanical response of β-sheet structures to a tensile force directed along the axis of one chain can be modeled as an array of elastic springs. The 3-D potential of H-bonds in β-sheets gives a shear stiffness of 4.5Nm-1 and the chain repeat stiffness is 60Nm-1. Nanocrystals >3.5nm long with >=20 H-bonds/chain are the strong component of spider silk. They behave much like macro-scale objects, and two conditions must be met for pull-out failure: (1) the load on the most stressed H-bond exceeds the bond strength. (2) the energy of the system is lower after failure. (1) is the critical condition, and the predicted pull-out load is 3-4 times the H-bond strength. An energetically favorable `stick-slip' process is kinetically forbidden. Arrays within a single molecule such as titin have fewer bonds and can fail at low loads by the `stick-slip' process. The logarithmic rate dependence of failure load observed in AFM is 50pN/decade and the stick-slip prediction is 30pN/decade. Simulations at short times and high loads give slopes >10x higher, matching the prediction for failure at a single bond.

  17. Modeling the effect of doping on the catalyst-assisted growth and field emission properties of plasma-grown graphene sheet

    NASA Astrophysics Data System (ADS)

    Gupta, Neha; Sharma, Suresh C.; Sharma, Rinku

    2016-08-01

    A theoretical model describing the effect of doping on the plasma-assisted catalytic growth of graphene sheet has been developed. The model accounts the charging rate of the graphene sheet, kinetics of all the plasma species, including the doping species, and the growth rate of graphene nuclei and graphene sheet due to surface diffusion, and accretion of ions on the catalyst nanoparticle. Using the model, it is observed that nitrogen and boron doping can strongly influence the growth and field emission properties of the graphene sheet. The results of the present investigation indicate that nitrogen doping results in reduced thickness and shortened height of the graphene sheet; however, boron doping increases the thickness and height of the graphene sheet. The time evolutions of the charge on the graphene sheet and hydrocarbon number density for nitrogen and boron doped graphene sheet have also been examined. The field emission properties of the graphene sheet have been proposed on the basis of the results obtained. It is concluded that nitrogen doped graphene sheet exhibits better field emission characteristics as compared to undoped and boron doped graphene sheet. The results of the present investigation are consistent with the existing experimental observations.

  18. Modeling the effect of doping on the catalyst-assisted growth and field emission properties of plasma-grown graphene sheet

    SciTech Connect

    Gupta, Neha; Sharma, Suresh C.; Sharma, Rinku

    2016-08-15

    A theoretical model describing the effect of doping on the plasma-assisted catalytic growth of graphene sheet has been developed. The model accounts the charging rate of the graphene sheet, kinetics of all the plasma species, including the doping species, and the growth rate of graphene nuclei and graphene sheet due to surface diffusion, and accretion of ions on the catalyst nanoparticle. Using the model, it is observed that nitrogen and boron doping can strongly influence the growth and field emission properties of the graphene sheet. The results of the present investigation indicate that nitrogen doping results in reduced thickness and shortened height of the graphene sheet; however, boron doping increases the thickness and height of the graphene sheet. The time evolutions of the charge on the graphene sheet and hydrocarbon number density for nitrogen and boron doped graphene sheet have also been examined. The field emission properties of the graphene sheet have been proposed on the basis of the results obtained. It is concluded that nitrogen doped graphene sheet exhibits better field emission characteristics as compared to undoped and boron doped graphene sheet. The results of the present investigation are consistent with the existing experimental observations.

  19. 2D subglacial drainage system model applied to a catchment of the Greenland ice sheet

    NASA Astrophysics Data System (ADS)

    Werder, M. A.; Joughin, I. R.; Hewitt, I.; Bamber, J. L.; van den Broeke, M. R.; Flowers, G. E.; Schoof, C.; Shean, D. E.

    2012-12-01

    We present results from a 2D glacial drainage system model (GlaDS, see last paragraph for model details) applied to a 3000 km2 catchment of the Greenland ice sheet in the vicinity of the lake studied by Das et al. (2008). We run the model for the 2009 and 2010 melt seasons using new bed and surface DEMs and force it with input from a distributed surface mass balance model driven with RACMO data (van den Broeke et al., 2009). The water is routed to the subglacial system either through crevasses, moulins or lakes as determined from satellite imagery. The model calculates subglacial water pressure which is fed into a sliding law and used as a proxy for ice flow speed. We compare these modelled ice flow speeds to measurements of speed derived from TerraSAR-X at 11-day intervals. The model produces a switch from a inefficient distributed system in winter to an efficient and arborescent channelized system as surface water input increases. Channels form predominately where water input to the bed is large and localized, i.e. at moulins and lakes. High subglacial water pressures accompany this winter-summer switch causing a speedup of ice flow. Diurnal variations in water input lead to variations of water pressure in the vicinity of channels, the size of the area affected being dependent on storage and conductivity of the distributed system. We compare the model results to the measured data and discuss their agreements and discrepancies. The GlaDS model is a new two dimensional numerical model of glacier hydrology which combines distributed and channelized drainage at the ice-bed interface coupled to an englacial water routing and storage component (Hewitt et al., 2012). Notably the model determines the location of the channels as part of the solution by allowing R-channels to form on any of the edges of the used, unstructured triangular grid. The distributed system is represented by a water sheet which is a continuum description of a linked-cavity system and exchanges

  20. Effect of rapid grounding line migration investigated with 3D ice sheet-ice shelf models (MISMIP3d)

    NASA Astrophysics Data System (ADS)

    Pattyn, F.; Docquier, D.; Durand, G.; Favier, L.; Gagliardini, O.; Hindmarsh, R.; Zwinger, T.; Mismip3d Participants

    2012-04-01

    Understanding and attributing future sea-level changes demands serious efforts on the development of efficient ice sheet-ice shelf models that capture the essential physics and mechanics of grounding line behavior. While semi-analytical solutions for grounding line behavior are available for the flowline case, such solution fails to exist for more complex three-dimensional geometries. A way of evaluating the quality of ice sheet models is to verify them against more complex model solutions under controlled conditions (Marine Ice Sheet Model Intercomparison - MISMIP). Given the computational demands of such models, it is extremely attractive from a computational point of view to use flux/thickness parameterizations in 3d models. Here we investigated the transition between ice sheet and ice shelf with series of different numerical models, ranging from full Stokes (Elmer/Ice) models, pseudo-spectral methods to a 2d vertically integrated finite-difference 'shelfy-stream' model, taking into account grounding line dynamics, and using parameterizations by Schoof (2007) and Pollard and DeConto (2009). Rapid grounding line migration was provoked by changing sliding at the grounding line, resulting in curved grounding lines influenced by lateral effects. We tested whether flux parameterizations are still valid under such conditions, especially when buttressing effects are taken into account. Results of other participants in the intercomparison exercise are presented alongside the initial benchmark results.

  1. A Dynamic Antarctic Ice Sheet in the Miocene and Pliocene: Resolving a Classic Model-Data Paradox

    NASA Astrophysics Data System (ADS)

    Deconto, R. M.; Gasson, E.; Pollard, D.

    2015-12-01

    Proxy ice volume and sea-level indicators imply a highly dynamic Antarctic Ice Sheet in the Miocene and early-mid Pliocene, especially if the Northern Hemisphere is assumed to be ice-free. Until now, the presumed insensitivity of a fully developed Antarctic Ice Sheet to orbital forcing and a wide range of greenhouse gas concentrations has made Miocene and Pliocene ice volume variability difficult to reconcile. Here, we show how the inclusion of new ice-model physics, more highly resolved atmospheric models, and new ice-climate coupling techniques are reducing the strength of Antarctic Ice Sheet hysteresis, bringing data-model comparisons into better agreement. This is especially true in light of new atmospheric CO2 reconstructions hinting at concentrations higher than previous estimates. The global implications of a more dynamic Antarctic cryosphere in the Neogene will be discussed in light of its potential impact on the atmosphere and global ocean circulation.

  2. Characterization of the Greenland Ice Sheet evolution in a changing climate using a multi-model approach

    NASA Astrophysics Data System (ADS)

    Seroussi, H. L.; Morlighem, M.; Larour, E. Y.; Rignot, E. J.; Aubry, D.; Ben Dhia, H.

    2011-12-01

    Hybrid models that combine several ice flow approximations of varying order of complexity have the potential to improve continental-scale projections of ice sheet dynamics in a changing climate. Indeed, this approach allows the use of higher-order or full-Stokes models in critical areas, such as the vicinity of the grounding line, while being compatible with available computational resources as simpler models are employed in non-critical areas. Here, we use this approach to model the Greenland Ice Sheet and project its evolution for the next 500 years under different climate scenarios set up by the SeaRISE assessment. The model is initialized using data assimilation to constrain basal friction under the ice sheet and therefore starts from a configuration close to the present-day conditions. A set of experiments is then performed to assess the influence of changes in: 1) atmospheric conditions (air temperature and precipitation), 2) basal conditions (increase in basal lubrication due to enhanced melting) and 3) oceanic conditions (melting under ice shelves and at marine-terminated fronts). We employ the Ice Sheet System Model (ISSM, http://issm.jpl.nasa.gov), a thermo-dynamic finite element model developed at JPL/UCI to perform these simulations. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory, University of California Irvine and Ecole Centrale Paris under a contract with the National Aeronautics and Space Administration's Modeling, Analysis and Prediction (MAP) Program.

  3. Fact Sheet: Environmental Pathway Models-Ground-Water Modeling in Support of Remedial Decision Making at Sites Contaminated with Radioactive Material

    EPA Pesticide Factsheets

    This fact sheet was designed to be used by technical staff responsible for identifying and implementing flow and transport models to support cleanup decisions at hazardous and radioactive waste sites.

  4. Modeling of past and future variations of the Antarctic Ice Sheet with Large Ensembles.

    NASA Astrophysics Data System (ADS)

    Pollard, D.; Deconto, R. M.; Chang, W.; Applegate, P. J.; Haran, M.

    2015-12-01

    Recent observations of thinning and retreat of the Pine Island and Thwaites Glaciers identify the Amundsen Sea Embayment (ASE) sector of West Antarctica as particularly vulnerable to future climate change. To date, most future modelingof these glaciers has been calibrated using recent and modern observations. As an alternate approach, we apply a hybrid 3-D ice sheet-shelf model to the last deglacial retreat of Antarctica, making use of geologic data from ~20,000 years BP to present, focusing on the ASE but including other sectors of Antarctica. Following several recent ice-sheet studies, we use Large Ensemble statistical methods, performing sets of ~600 runs over the last 30,000 years with systematically varying model parameters. Objective scores for each run are calculated using modern data and past reconstructed grounding lines, relative sea level records, cosmogenic elevation-age data and uplift rates.Two types of statistical methods are used to analyze the Large-Ensembleresults: simple averaging weighted by the aggregate score, and more advancedBayesian emulation and calibration methods that rigorously account for some of the uncertainties in the model and observations. Results for best-fit parameter ranges and envelopes of equivalent sea-level rise with the simple averaging method agree quite well with the more advanced techniques, but only for a Large Ensemble with dense (Full Factorial) parameter sampling. Runs are extended into the future using RCP scenarios, with drastic retreat mechanisms of hydrofracturing and structural ice-cliff failure. In most runs this produces grounding-line retreat into the West Antarctic interior, and into East Antarctic basins for RCP8.5, and the Large Ensemble analysis provides sea-level-rise envelopes with well defined parametric uncertainty bounds.

  5. Advances in Antarctic Mantle and Crustal Physics and Implications for Ice Sheet Models and Isostatic Adjustment Measurements

    NASA Astrophysics Data System (ADS)

    Ivins, Erik; Adhikari, Surendra; Seroussi, Helene; Larour, Eric; Wiens, Douglas; Scheinert, Mirko; Csatho, Beata; James, Thomas; Nyblade, Andrew

    2015-04-01

    The problem of improving both solid Earth structure models and assembling an appropriate tectonic framework for Antarctica is challenging for many reasons. The vast ice sheet cover is just one item in a long list of difficult observational challenges faced by solid Earth scientists. The ice sheet has a unique potential for causing relatively rapid global sea-level rise over the next couple of hundred years. This potential provides great impetus for employing extraordinary efforts to improve our knowledge of the thermo-mechanical properties and of the mass and energy transport systems operating in the underlying solid Earth. In this presentation we discuss the role of seismic mapping of the mantle and crust, heat flux inferences, models and measurements as they affect the state of the ice sheet and the predictions of present-day and future solid Earth glacial isostatic adjustment, global and regional sea-level variability. To illustrate the sensitivity to solid Earth parameters for deriving a model temperature at the base of the ice sheet, Tb, we have computed the differences between two models to produce maps of δTb, the differential temperature to the melting point at the base of the ice sheet using the ISSM 3-D Stokes flow model. A 'cold' case (with surface crustal heat flux qGHF = 40 mW/m^2) is compared to a 'hot' geothermal flux case (qGHF = 60 mW/m^2). Differences of δ Tb = 6 - 10 °C are predicted between the two heat flux assumptions, and these have associated differences in predicted ice velocities of a factor of 1.8-3.6. We also explore the hypothesis of a mantle plume, and its potential compatibility or incompatibility with basal ice sheet conditions in West Antarctica.

  6. Modeling of Directional Hardening Based on Non-Associated Flow for Sheet Forming

    NASA Astrophysics Data System (ADS)

    Yoon, Jeong Whan; Stoughton, Thomas B.

    2010-06-01

    This work describes a material model for sheet metal forming that takes into account anisotropic hardening under conditions of proportional loading. Conventional isotropic and kinematic hardening models constrain the shape of the yield function to remain fixed throughout plastic deformation, which is not consistent with most test data from aluminum alloys obtained under proportional loading. Conventional hardening models are shown to introduce systemic errors in stresses in different loading conditions at low and high levels of strain that tend to amplify the effect of stress miscalculation on the prediction of springback. A new model is described in which four stress-strain functions are explicitly integrated into the yield criterion in closed form solution. The model is based on non-associated flow so that this integration does not affect the accuracy of the plastic strain components. The model is expected to lead to a significant improvement in stress prediction under conditions dominated by proportional loading, and this is expected to directly improve the accuracy of springback prediction for these processes.

  7. Friction and lubrication modelling in sheet metal forming simulations of the Volvo XC90 inner door

    NASA Astrophysics Data System (ADS)

    Sigvant, M.; Pilthammar, J.; Hol, J.; Wiebenga, J. H.; Chezan, T.; Carleer, B.; van den Boogaard, A. H.

    2016-08-01

    The quality of sheet metal formed parts is strongly dependent on the friction and lubrication conditions that are acting in the actual production process. Although friction is of key importance, it is currently not considered in detail in stamping simulations. This paper presents project results considering friction and lubrication modelling in stamping simulations of the Volvo XC90 inner door. For this purpose, the TriboForm software is used in combination with the AutoForm software. Validation of the simulation results is performed based on door-inner parts taken from the press line in a full-scale production run. The project results demonstrate the improved prediction accuracy of stamping simulations.

  8. Rotating flow over a stretching sheet in nanofluid using Buongiorno model and thermophysical properties of nanoliquids

    NASA Astrophysics Data System (ADS)

    Bakar, Nor Ashikin Abu; Bachok, Norfifah; Arifin, Norihan Md.

    2017-08-01

    The boundary layer flow and heat transfer in rotating nanofluid over a stretching sheet using Buongiorno model and thermophysical properties of nanoliquids is studied. Four types of nanoparticles, namely silver (Ag), copper (Cu), alumina (Al2O3) and titania (TiO2) are used in our analysis with water as the base fluid (Prandtl number, Pr = 6.2). The nonlinear partial differential equations are transformed into ordinary differential equations by using the similarity transformation. The numerical solutions of these equation is obtained using shooting method in Maple software. The numerical results is concentrated on the effects of nanoparticle volume fraction φ, Brownian motion Nb, thermophoresis Nt, rotation Ω and suction S parameters on the skin friction coefficient and heat transfer rate. Dual solutions are observed in a certain range of the rotating parameter.

  9. Breaking of relativistically intense longitudinal space charge waves: A description using Dawson sheet model

    NASA Astrophysics Data System (ADS)

    Sengupta, Sudip

    2014-02-01

    Spatio-temporal evolution of relativistically intense longitudinal space charge waves in a cold homogeneous plasma is studied analytically as well as numerically, as an initial value problem, using Dawson sheet model. It is found that, except for very special initial conditions which generates the well known longitudinal Akhiezer-Polovin mode, for all other initial conditions, the waves break through a novel mechanism called phase mixing at an amplitude well below the Akhiezer-Polovin limit. An immediate consequence of this is, that Akhiezer-Polovin waves break when subjected to arbitrarily small longitudinal perturbations. We demonstrate this by performing extensive numerical simulations. This result may be of direct relevance to ultrashort, ultraintense laser/beam pulse-plasma interaction experiments where relativistically intense waves are routinely excited.

  10. Non-proportional/Non-monotonous Deformation Modeling of an Ultra High Strength Automotive Steel Sheet

    NASA Astrophysics Data System (ADS)

    Verma, Rahul K.; Ogihara, Yuki; Kuwabara, Toshihiko; Chung, Kwansoo

    2011-08-01

    In this work, as non-proportional/non-monotonous deformation experiments, two-stage and tension-compression-tension uniaxial tests were performed, respectively, for a cold rolled ultra high strength dual phase steel sheet: DP780. Deformation behaviors under such deformation paths were found different than those of the ultra low carbon single phase steels observed by Verma et al. (Int. J. Plast. 2011, 82-101). To model the newly observed deformation behaviors, the combined type constitutive law previously proposed by Verma et al. (Int. J. Plast. 2011, 82-101) was successfully applied here. Permanent softening observed during reverse loading was properly characterized into the isotropic and kinematic hardening parts of the hardening law using tension-compression-tension test data. The cross effect observed in two-stage tests was also effectively incorporated into the constitutive law.

  11. Energy and pitch angle distributions for auroral ions using the current sheet acceleration model

    NASA Technical Reports Server (NTRS)

    Jaeger, E. F.; Speiser, T. W.

    1974-01-01

    Using a dipole-plus-tail magnetic field model, H(+), He(+2), and O(+6) ions are followed numerically, backward in time, from an output plane perpendicular to the axis of the geomagnetic tail, to their point of entrance to the magnetosphere as solar wind particles in the magnetosheath. An adiabatic or guiding center approximation is used in regions where the particles do not interact directly with the current sheet. A Maxwellian distribution with bulk flow is assumed for solar wind particles in the magnetosheath. Bulk velocity, density, and temperature along the magnetopause are taken from the fluid calculations of Spreiter. Using Liouville's theorem, and varying initial conditions at the output plane, the distribution function is found as a function of energy and pitch angle at the output plane. These results are then mapped to the auroral ionosphere using guiding center theory.

  12. Breaking of relativistically intense longitudinal space charge waves: A description using Dawson sheet model

    SciTech Connect

    Sengupta, Sudip

    2014-02-11

    Spatio-temporal evolution of relativistically intense longitudinal space charge waves in a cold homogeneous plasma is studied analytically as well as numerically, as an initial value problem, using Dawson sheet model. It is found that, except for very special initial conditions which generates the well known longitudinal Akhiezer-Polovin mode, for all other initial conditions, the waves break through a novel mechanism called phase mixing at an amplitude well below the Akhiezer-Polovin limit. An immediate consequence of this is, that Akhiezer-Polovin waves break when subjected to arbitrarily small longitudinal perturbations. We demonstrate this by performing extensive numerical simulations. This result may be of direct relevance to ultrashort, ultraintense laser/beam pulse-plasma interaction experiments where relativistically intense waves are routinely excited.

  13. Sheet conductor model of brain slices for stimulation and recording with planar electronic contacts.

    PubMed

    Fromherz, Peter

    2002-06-01

    Current and voltage in a brain slice are considered, taking into account the boundary conditions at the surface to an electrolyte bath and at the substrate of an electron conductor. A sheet conductor model is introduced with ohmic leak conductance to the bath and capacitive coupling to the substrate. It assigns a current-source density of neuronal activity to extracellular field potentials recorded by planar contacts, and it relates the current of planar capacitive contacts to the field potential that elicits neuronal activity. Two examples are analytically solved: the recording across a layered brain slice and the stimulation by a circular electrode. The study forms the basis for neurophysical experiments with brain slices or retinae on microelectronic chips.

  14. Model of β-Sheet of Muscle Fatty Acid Binding Protein of Locusta migratoria Displays Characteristic Topology.

    PubMed

    Kizilbash, Nadeem A; Hai, Abdul; Alruwaili, Jamal

    2013-01-01

    The β-sheet of muscle fatty acid binding protein of Locusta migratoria (Lm-FABP) was modeled by employing 2-D NMR data and the Rigid Body Assembly method. The model shows the β-sheet to comprise ten β-strands arranged anti-parallel to each other. There is a β-bulge between Ser 13 and Gln 14 which is a difference from the published structure of β-sheet of bovine heart Fatty Acid Binding Protein. Also, a hydrophobic patch consisting of Ile 45, Phe 51, Phe 64 and Phe 66 is present on the surface which is characteristic of most Fatty Acid Binding Proteins. A "gap" is present between βD and βE that provides evidence for the presence of a portal or opening between the polypeptide chains which allows ligand fatty acids to enter the protein cavity and bind to the protein.

  15. Large-scale modeling of the Antarctic ice sheet using a massively-parallelized finite element model (CIELO).

    NASA Astrophysics Data System (ADS)

    Larour, E.; Rignot, E.; Morlighem, M.; Seroussi, H.

    2008-12-01

    We implemented a fully-three-dimensional, thermo-mechanical, finite element model of the Antarctic Ice Sheet with a spatial resolution varying from 10 km inland to 2 km along the coast on a massively-parallelized architecture named CIELO and developed at JPL. The model is based on a "Pattyn" type formulation for ice sheets, and a "MacAyeal shelf-stream" formulation for ice shelves. Both types of formulations are coupled using penalty methods, which enables a considerable reduction of the computational load. Using a simple law of basal friction (based on locally computed balanced velocities), the model is able to replicate the location and order-magnitude speed of major ice streams and ice shelves. We then coupled the model with observations of ice motion from SAR interferometry to refine the pattern of basal friction using an inverse control method (MacAyeal 1993). The result provides an excellent agreement with observations and a first complete mapping of the pattern of basal friction along the coast of Antarctica at a resolution compatible with the size of its glaciers and ice streams.

  16. Hybrid modeling of the formation and structure of thin current sheets in the magnetotail

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Winske, Dan; Birn, Joachim

    1996-01-01

    Hybrid simulations are used to investigate the formation of a thin current sheet inside the plasma sheet of a magnetotail-like configuration. The initial equilibrium is subjected to a driving electric field which is qualitatively similar to what would be expected from solar wind driving. As a result, a new current sheet with the thickness of approximately the ion inertial length is formed. The current density inside the current sheet region is supplied largely by the electrons. Ion acceleration in the cross-tail direction is absent as the driving electric field fails to penetrate into the equatorial region.

  17. A New Design for Digital Elevation Models of Bedrock Underlying Ice Sheets

    NASA Astrophysics Data System (ADS)

    Drouet, A.; Durand, G.; Gillet-chaulet, F.; Le Meur, E.; Braun, J.; Sacchettini, M.; Young, D. A.; Blankenship, D. D.; Greenbaum, J.; Wright, A.; Rignot, E. J.; Gim, Y.; Mouginot, J.; Kirchner, D.

    2011-12-01

    Proper knowledge of bedrock topography is an important prerequisite in order to model ice sheet behavior and estimate their future contribution to sea level rise. Today, 5-km resolution Digital Elevation Models are commonly used by modelers to obtain bedrock elevation on their grid nodes. This chosen resolution is questionable since most of the ice outflow goes through outlet glaciers whose size is of a similar order of magnitude, leading modelers to refine their grid with maximum mesh resolution of the order of 100 m. In this study, we show that for modeling purposes, using current 5-km regular DEMs requires an 'undermeshing' interpolation that can locally lead to up to 100% relative error on the ice thickness value as well as opposite directions of the bedrock slope. We here propose to modify the way DEMs are usually processed. This paradigm shift consists of moving from static DEMs with interpolated data on a regular mesh to more flexible ones that return a direct interpolation at the precise locations required by the user mesh. An illustration with the Astrolabe drainage basin (East Antarctica) is described, based on intensive ice thickness radar measurements that have been performed over the last 3 years. Eventually, an application under the form of a web interface is proposed to demonstrate the feasibility of such a procedure.

  18. Modeling the Self-organized Critical Behavior of Earth's Plasma Sheet Reconnection Dynamics

    NASA Technical Reports Server (NTRS)

    Klimas, Alexander J.

    2006-01-01

    Analyses of Polar UVI auroral image data show that bright night-side high-latitude W emissions exhibit so many of the key properties of systems in self-organized criticality that an alternate interpretation has become virtually impossible. These analyses will be reviewed. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the magnetotail plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques (and more) that have been applied to the auroral image data have also been applied to this Poynting flux. New results will be presented showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. A strong correlation between these key properties of the model and those of the auroral UV emissions will be demonstrated. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.

  19. Modeling the Self-organized Critical Behavior of the Plasma Sheet Reconnection Dynamics

    NASA Technical Reports Server (NTRS)

    Klimas, Alex; Uritsky, Vadim; Baker, Daniel

    2006-01-01

    Analyses of Polar UVI auroral image data reviewed in our other presentation at this meeting (V. Uritsky, A. Klimas) show that bright night-side high-latitude UV emissions exhibit so many of the key properties of systems in self-organized criticality (SOC) that an alternate interpretation has become virtually impossible. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques, and more, that have been applied to the auroral image data have also been applied to this Poynting flux. Here, we report new results showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. Further, we find a strong correlation between these key properties of the model and those of the auroral UV emissions. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.

  20. Modeling the Self-organized Critical Behavior of Earth's Plasma Sheet Reconnection Dynamics

    NASA Technical Reports Server (NTRS)

    Klimas, Alexander J.

    2006-01-01

    Analyses of Polar UVI auroral image data show that bright night-side high-latitude W emissions exhibit so many of the key properties of systems in self-organized criticality that an alternate interpretation has become virtually impossible. These analyses will be reviewed. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the magnetotail plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques (and more) that have been applied to the auroral image data have also been applied to this Poynting flux. New results will be presented showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. A strong correlation between these key properties of the model and those of the auroral UV emissions will be demonstrated. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.

  1. Modeling the Self-organized Critical Behavior of the Plasma Sheet Reconnection Dynamics

    NASA Technical Reports Server (NTRS)

    Klimas, Alex; Uritsky, Vadim; Baker, Daniel

    2006-01-01

    Analyses of Polar UVI auroral image data reviewed in our other presentation at this meeting (V. Uritsky, A. Klimas) show that bright night-side high-latitude UV emissions exhibit so many of the key properties of systems in self-organized criticality (SOC) that an alternate interpretation has become virtually impossible. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques, and more, that have been applied to the auroral image data have also been applied to this Poynting flux. Here, we report new results showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. Further, we find a strong correlation between these key properties of the model and those of the auroral UV emissions. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.

  2. Effectiveness of Bone Marrow Stromal Cell Sheets in Maintaining Random-Pattern Skin Flaps in an Experimental Animal Model.

    PubMed

    Kira, Tsutomu; Omokawa, Shohei; Akahane, Manabu; Shimizu, Takamasa; Nakano, Kenichi; Nakanishi, Yasuaki; Onishi, Tadanobu; Kido, Akira; Inagaki, Yusuke; Tanaka, Yasuhito

    2015-11-01

    Bone marrow stromal cells can be applied therapeutically to enhance angiogenesis; however, the use of bone marrow stromal cell suspensions reduces efficiency because of low-level attachment. The authors hypothesized that bone marrow stromal cell sheets would facilitate cell fixation, thus enhancing angiogenesis. The authors investigated flap survival area and enhancement of angiogenic factors in a rat random-pattern skin flap model after application of bone marrow stromal cell sheets. Bone marrow stromal cell sheets (prepared from 7-week-old rat femurs) were cultured under four different hypoxic conditions. Sheets with the highest angiogenic potential, determined by an in vitro pilot study, were injected into subcutaneous layers of the rat dorsum (bone marrow stromal cell sheet group). A control group (phosphate-buffered saline only) was included. On day 2 after injection, caudally based random-pattern skin flaps (12 × 3 cm) were elevated. On day 7 after elevation, surviving skin flap areas were measured. Skin samples were harvested from each flap and gene expression levels of vascular endothelial growth factor and basic fibroblast growth factor were measured by quantitative real-time polymerase chain reaction. Skin flap survival area (71.6 ± 2.3 percent versus 51.5 ± 3.3 percent) and levels of vascular endothelial growth factor and basic fibroblast growth factor were significantly higher in the bone marrow stromal cell sheet group than in the control group (p < 0.05). Implantation of bone marrow stromal cell sheets increased the survival area of random-pattern skin flaps. Expression of angiogenic factors may have contributed to the increased flap survival.

  3. Cartilage repair using mesenchymal stem cell (MSC) sheet and MSCs-loaded bilayer PLGA scaffold in a rabbit model.

    PubMed

    Qi, Yiying; Du, Yi; Li, Weixu; Dai, Xuesong; Zhao, Tengfei; Yan, Weiqi

    2014-06-01

    The integration of regenerated cartilage with surrounding native cartilage is a major challenge for the success of cartilage tissue-engineering strategies. The purpose of this study is to investigate whether incorporation of the power of mesenchymal stem cell (MSC) sheet to MSCs-loaded bilayer poly-(lactic-co-glycolic acid) (PLGA) scaffolds can improve the integration and repair of cartilage defects in a rabbit model. Rabbit bone marrow-derived MSCs were cultured and formed cell sheet. Full-thickness cylindrical osteochondral defects (4 mm in diameter, 3 mm in depth) were created in the patellar groove of 18 New Zealand white rabbits and the osteochondral defects were treated with PLGA scaffold (n = 6), PLGA/MSCs (n = 6) or MSC sheet-encapsulated PLGA/MSCs (n = 6). After 6 and 12 weeks, the integration and tissue response were evaluated histologically. The MSC sheet-encapsulated PLGA/MCSs group showed significantly more amounts of hyaline cartilage and higher histological scores than PLGA/MSCs group and PLGA group (P < 0.05). In addition, the MSC sheet-encapsulated PLGA/MCSs group showed the best integration between the repaired cartilage and surrounding normal cartilage and subchondral bone compared to other two groups. The novel method of incorporation of MSC sheet to PLGA/MCSs could enhance the ability of cartilage regeneration and integration between repair cartilage and the surrounding cartilage. Transplantation of autologous MSC sheet combined with traditional strategies or cartilage debris might provide therapeutic opportunities for improving cartilage regeneration and integration in humans.

  4. Modelling mass loss and spatial uncertainty of the West Antarctic Ice Sheet: a data assimilation approach

    NASA Astrophysics Data System (ADS)

    Bamber, Jonathan L.; Schoen, Nana; Zammit-Mangion, Andrew; Rougier, Jonty; Luthcke, Scott; King, Matt

    2013-04-01

    Quantifying ice mass loss from the Antarctic Ice Sheet remains an important, yet still challenging problem. Although some agreement has been reached as to the order of magnitude of ice loss over the last two decades, in general methods lack statistical rigour in deriving uncertainties and for East Antarctica and the Peninsula significant inconsistencies remain. Here, we present rigorously-derived, error-bounded mass balance trends for part of the Antarctic ice sheet from a combination of satellite, in situ and regional climate model data sets for 2003-2009. Estimates for glacial isostatic adjustment (GIA), surface mass balance (SMB) anomaly, and ice mass change are derived from satellite gravimetry (the Gravity Recovery and Climate Experiment, GRACE), laser altimetry (ICESat, the Ice, Cloud and land Elevation Satellite) and GPS bedrock elevation rates. We use a deterministic Bayes approach to simultaneously solve for the unknown parameters and the covariance matrix which provides the uncertainties. The data were distributed onto a finite element grid the resolution of which reflects the gradients in the underlying process: here ice dynamics and surface mass balance. In this proof of concept study we solve for the time averaged, spatial distribution of mass trends over the 7 year time interval. The results illustrate the potential of the approach, especially for the Antarctic Peninsula (AP), where, due to its narrow width and steep orography, data coverage is sparse and error-prone for satellite altimetry. Results for the ice mass balance estimates are consistent with previous estimates and demonstrate the strength of the approach. Well-known patterns of ice mass change over the WAIS, like the stalled Kamb Ice Stream and the rapid thinning in the Amundsen Sea Embayment, are reproduced in terms of mass trend. Also, without relying on information on ice dynamics, the method correctly places ice loss maxima at the outlets of major glaciers on the AP. Combined ice mass

  5. Towards a morphogenetic classification of eskers: Implications for modelling ice sheet hydrology

    NASA Astrophysics Data System (ADS)

    Perkins, Andrew J.; Brennand, Tracy A.; Burke, Matthew J.

    2016-02-01

    Validations of paleo-ice sheet hydrological models have used esker spacing as a proxy for ice tunnel density. Changes in crest type (cross-sectional shape) along esker ridges have typically been attributed to the effect of changing subglacial topography on hydro- and ice-dynamics and hence subglacial ice-tunnel shape. These claims assume that all eskers formed in subglacial ice tunnels and that all major subglacial ice tunnels produced a remnant esker. We identify differences in geomorphic context, sinuosity, cross-sectional shape, and sedimentary architecture by analysing eskers formed at or near the margins of the last Cordilleran Ice Sheet on British Columbia's southern Fraser Plateau, and propose a morphogenetic esker classification. Three morphogenetic types and 2 subtypes of eskers are classified based on differences in geomorphic context, ridge length, sinuosity, cross-sectional shape and sedimentary architecture using geophysical techniques and sedimentary exposures; they largely record seasonal meltwater flows and glacial lake outburst floods (GLOFs) through sub-, en- and supraglacial meltwater channels and ice-walled canyons. General principles extracted from these interpretations are: 1) esker ridge crest type and sinuosity strongly reflect meltwater channel type. Eskers formed in subglacial conduits are likely to be round-crested with low sinuosity (except where controlled by ice structure or modified by surging) and contain faults associated with flank collapse. Eskers formed near or at the ice surface are more likely to be sharp-crested, highly sinuous, and contain numerous faults both under ridge crest-lines and in areas of flank collapse. 2) Esker ridges containing numerous flat-crested reaches formed directly on the land-surface in ice-walled canyons (unroofed ice tunnels) or in ice tunnels at atmospheric pressure, and therefore likely record thin or dead ice. 3) Eskers containing macroforms exhibiting headward and downflow growth likely record

  6. Joint Model and Parameter Dimension Reduction for Bayesian Inversion Applied to an Ice Sheet Flow Problem

    NASA Astrophysics Data System (ADS)

    Ghattas, O.; Petra, N.; Cui, T.; Marzouk, Y.; Benjamin, P.; Willcox, K.

    2016-12-01

    Model-based projections of the dynamics of the polar ice sheets play a central role in anticipating future sea level rise. However, a number of mathematical and computational challenges place significant barriers on improving predictability of these models. One such challenge is caused by the unknown model parameters (e.g., in the basal boundary conditions) that must be inferred from heterogeneous observational data, leading to an ill-posed inverse problem and the need to quantify uncertainties in its solution. In this talk we discuss the problem of estimating the uncertainty in the solution of (large-scale) ice sheet inverse problems within the framework of Bayesian inference. Computing the general solution of the inverse problem--i.e., the posterior probability density--is intractable with current methods on today's computers, due to the expense of solving the forward model (3D full Stokes flow with nonlinear rheology) and the high dimensionality of the uncertain parameters (which are discretizations of the basal sliding coefficient field). To overcome these twin computational challenges, it is essential to exploit problem structure (e.g., sensitivity of the data to parameters, the smoothing property of the forward model, and correlations in the prior). To this end, we present a data-informed approach that identifies low-dimensional structure in both parameter space and the forward model state space. This approach exploits the fact that the observations inform only a low-dimensional parameter space and allows us to construct a parameter-reduced posterior. Sampling this parameter-reduced posterior still requires multiple evaluations of the forward problem, therefore we also aim to identify a low dimensional state space to reduce the computational cost. To this end, we apply a proper orthogonal decomposition (POD) approach to approximate the state using a low-dimensional manifold constructed using ``snapshots'' from the parameter reduced posterior, and the discrete

  7. Experimental design for three interrelated marine ice sheet and ocean model intercomparison projects: MISMIP v. 3 (MISMIP +), ISOMIP v. 2 (ISOMIP +) and MISOMIP v. 1 (MISOMIP1)

    NASA Astrophysics Data System (ADS)

    Asay-Davis, Xylar S.; Cornford, Stephen L.; Durand, Gaël; Galton-Fenzi, Benjamin K.; Gladstone, Rupert M.; Hilmar Gudmundsson, G.; Hattermann, Tore; Holland, David M.; Holland, Denise; Holland, Paul R.; Martin, Daniel F.; Mathiot, Pierre; Pattyn, Frank; Seroussi, Hélène

    2016-07-01

    Coupled ice sheet-ocean models capable of simulating moving grounding lines are just becoming available. Such models have a broad range of potential applications in studying the dynamics of marine ice sheets and tidewater glaciers, from process studies to future projections of ice mass loss and sea level rise. The Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP) is a community effort aimed at designing and coordinating a series of model intercomparison projects (MIPs) for model evaluation in idealized setups, model verification based on observations, and future projections for key regions of the West Antarctic Ice Sheet (WAIS). Here we describe computational experiments constituting three interrelated MIPs for marine ice sheet models and regional ocean circulation models incorporating ice shelf cavities. These consist of ice sheet experiments under the Marine Ice Sheet MIP third phase (MISMIP+), ocean experiments under the Ice Shelf-Ocean MIP second phase (ISOMIP+) and coupled ice sheet-ocean experiments under the MISOMIP first phase (MISOMIP1). All three MIPs use a shared domain with idealized bedrock topography and forcing, allowing the coupled simulations (MISOMIP1) to be compared directly to the individual component simulations (MISMIP+ and ISOMIP+). The experiments, which have qualitative similarities to Pine Island Glacier Ice Shelf and the adjacent region of the Amundsen Sea, are designed to explore the effects of changes in ocean conditions, specifically the temperature at depth, on basal melting and ice dynamics. In future work, differences between model results will form the basis for the evaluation of the participating models.

  8. Ice-age simulations with a caving ice-sheet model

    SciTech Connect

    Pollard, D.

    1982-01-01

    Further extensions and results of a simple northern hemispheric ice-sheet model are described for the Quaternary ice ages. The basic model predicts ice thickness and bedrock deformation in a north-south cross section, with a prescribed snow-budget distribution shifted uniformly in space to represent the orbital perturbations. An ice calving parameterization crudely representing proglacial lakes or marine incursions can attack the ice whenever the tip drops below sea level. As in Pollard (1982a) the basic model produces a large approx. 100,000-yr response and agrees fairly well with the delta/sup 18/O deep-sea core records. Three extensions of the model are described: an alternative treatment of bedrock deformation, a more realistic ice-shelf model of ice calving, and a generalized parameterization for such features as the North Atlantic deglacial meltwater layer. Much the same ice-age simulations and agreement with the delta/sup 18/O records as with the original model are still obtained. The observed phase-correlation between the 100,000-yr cycles and eccentricity is examined. First, the model is shown to give a approx. 100,000-yr response to nearly any kind of higher-frequency forcing. Although over the last two million years the model phase is mainly controlled by the precessional modulation due to eccentricity, over just the last 600,000-yr the observed phase can also be simulated with eccentricity held constant. A definitive conclusion on the phase-control of the Quaternary ice ages is prevented by uncertainty in the deep-sea core time scales before approx. 600,000-yr B.P. In an appendix the model is applied to West Antarctica where unforced internal oscillations occur with periods of about 50,000-yr.

  9. Dynamic materials testing and constitutive modeling of structural sheet steel for automotive applications. Final progress report

    SciTech Connect

    Cady, C.M.; Chen, S.R.; Gray, G.T. III

    1996-08-23

    The objective of this study was to characterize the dynamic mechanical properties of four different structural sheet steels used in automobile manufacture. The analysis of a drawing quality, special killed (DQSK) mild steel; high strength, low alloy (HSLA) steel; interstitial free (IF); and a high strength steel (M-190) have been completed. In addition to the true stress-true strain data, coefficients for the Johnson-Cook, Zerilli-Armstrong, and Mechanical Threshold Stress constitutive models have been determined from the mechanical test results at various strain rates and temperatures and are summarized. Compression, tensile, and biaxial bulge tests and low (below 0.1/s) strain rate tests were completed for all four steels. From these test results it was determined to proceed with the material modeling optimization using the through thickness compression results. Compression tests at higher strain rates and temperatures were also conducted and analyzed for all the steels. Constitutive model fits were generated from the experimental data. This report provides a compilation of information generated from mechanical tests, the fitting parameters for each of the constitutive models, and an index and description of data files.

  10. Modelling geomagnetically induced currents in midlatitude Central Europe using a thin-sheet approach

    NASA Astrophysics Data System (ADS)

    Bailey, Rachel L.; Halbedl, Thomas S.; Schattauer, Ingrid; Römer, Alexander; Achleitner, Georg; Beggan, Ciaran D.; Wesztergom, Viktor; Egli, Ramon; Leonhardt, Roman

    2017-06-01

    Geomagnetically induced currents (GICs) in power systems, which can lead to transformer damage over the short and the long term, are a result of space weather events and geomagnetic variations. For a long time, only high-latitude areas were considered to be at risk from these currents, but recent studies show that considerable GICs also appear in midlatitude and equatorial countries. In this paper, we present initial results from a GIC model using a thin-sheet approach with detailed surface and subsurface conductivity models to compute the induced geoelectric field. The results are compared to measurements of direct currents in a transformer neutral and show very good agreement for short-period variations such as geomagnetic storms. Long-period signals such as quiet-day diurnal variations are not represented accurately, and we examine the cause of this misfit. The modelling of GICs from regionally varying geoelectric fields is discussed and shown to be an important factor contributing to overall model accuracy. We demonstrate that the Austrian power grid is susceptible to large GICs in the range of tens of amperes, particularly from strong geomagnetic variations in the east-west direction.

  11. Insights from Thermo-Mechanically Coupled Modeling of High-Elevation Regions of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Sommers, A. N.; Rajaram, H.; Colgan, W. T.

    2014-12-01

    As observations become more plentiful through remote sensing and numerical models become increasingly sophisticated, a clear priority of the ice sheet modeling community is to compare model simulations with observations. Temperature and velocity conditions within the Greenland ice sheet and at the bed remain largely unknown with the exception of sparse borehole measurements, but much can be inferred from rigorous thermo-mechanically coupled modeling. Surface velocities on the Greenland ice sheet are well constrained, both from satellite imagery and field observations. We take advantage of the observed surface velocities at the PARCA stakes around the 2,000m elevation contour of the ice sheet as modeling targets that represent a broad range of flow characteristics in different regions. Prescribing ice geometry, we use a two-dimensional thermo-mechanically coupled model to calculate 'steady-state' velocity and temperature profiles throughout the depth of the ice along flowlines from the main divide to the 2,000m elevation contour. Vertical velocity calculations are based on first principles of mass conservation, accounting for convergence and divergence of the streamtube width, and the enthalpy-based temperature calculations also incorporate the effects of liquid water content in temperate ice through the flow law parameter. Numerous insights from our simulations are presented for different regions, such as the influence of variable geothermal heat flux, the treatment of basal boundary conditions, and appropriate enhancement factors based on the age of ice. Results indicate that areas of temperate bed do exist in the high-elevation interior in certain sections of Greenland. Also highlighted is the importance of including temperature calculations in ice sheet modeling, particularly in regions with a temperate bed. For example, on the west coast, computations assuming a constant temperature of -5°C result in a 41% underestimation of the surface velocity at the 2,000m

  12. East-Antarctic outlet-glacier susceptibility from a data-driven ice-sheet/ice-shelf modelling approach

    NASA Astrophysics Data System (ADS)

    Pattyn, F.; Favier, L.; Drews, R.; Berger, S.; Sun, S.; Van Liefferinge, B.

    2016-12-01

    Understanding the future behaviour of marine sections of the Antarctic ice sheet requires high-resolution data coverage, extended with measurements enabling the validation and initialization of ice-sheet models. Short-term (decades, centuries) projections of ice mass change are generally based on data assimilation methods, requiring accurate knowledge of surface and bed topography, surface velocities and englacial temperatures. Steady-state thermodynamical modelling enables to retrieve englacial temperatures, which are in turn highly dependent on the knowledge of the geothermal heat flow, ice geometry, ice velocity and surface accumulation rates. We present different modelling strategies that enable evaluating the impact of uncertainties in datasets on model performance and ice-sheet susceptibility to change. We established a comprehensive geophysical dataset of the Roi Baudouin ice shelf (East Antarctica) based on, amongst others, radar (high and low frequency, phase-sensitive) and GNSS measurements. Comparison of our measurements with global satellite-derived datasets of surface elevation, ice-flow speed, grounding-line position and ice thickness clearly depict pitfalls as small-scale features, such as pinning points, ice-shelf channels and errors in bathymetry. Our model analysis demonstrates that uncertainties in ice thickness leads to large differences in calculated basal temperatures and basal melt rates. In peripheral areas of the Antarctic ice sheet, uncertainties in surface elevation (precise dome positions) hamper model initializations driven by surface velolocity data. Finally, errors in the initialization of ice-shelf viscosity due to inaccurate mapping of pinning points significantly delays grounding-line retreat in response to ocean perturbation, hence making outlet glaciers seemingly more stable than expected. The analysis led to the identification of crucial data needs (temporal, spatial) for initialization of ice-sheet models.

  13. Non-alignment stagnation-point flow of a nanofluid past a permeable stretching/shrinking sheet: Buongiorno's model.

    PubMed

    Hamid, Rohana Abdul; Nazar, Roslinda; Pop, Ioan

    2015-10-06

    The paper deals with a stagnation-point boundary layer flow towards a permeable stretching/shrinking sheet in a nanofluid where the flow and the sheet are not aligned. We used the Buongiorno model that is based on the Brownian diffusion and thermophoresis to describe the nanofluid in this problem. The main purpose of the present paper is to examine whether the non-alignment function has the effect on the problem considered when the fluid suction and injection are imposed. It is interesting to note that the non-alignment function can ruin the symmetry of the flows and prominent in the shrinking sheet. The fluid suction will reduce the impact of the non-alignment function of the stagnation flow and the stretching/shrinking sheet but at the same time increasing the velocity profiles and the shear stress at the surface. Furthermore, the effects of the pertinent parameters such as the Brownian motion, thermophoresis, Lewis number and the suction/injection on the flow and heat transfer characteristics are also taken into consideration. The numerical results are shown in the tables and the figures. It is worth mentioning that dual solutions are found to exist for the shrinking sheet.

  14. Modelling the impact of variations in ice sheet runoff on fjord and coastal biological productivity over annual to decadal timescales

    NASA Astrophysics Data System (ADS)

    Sole, A. J.; Cowton, T. R.

    2015-12-01

    Each summer, vast quantities of surface-derived ice sheet meltwater runs off from the Greenland Ice Sheet. Much of this runoff is injected into glaciated fjords at depth beneath marine-terminating glaciers. Due to its low relative density, the runoff rises as a buoyant plume up the glaciers' calving fronts, entraining deep fjord water as it does so. This deep, ambient water tends to be relatively rich in nutrients and so the runoff plumes act to fertilise the surface layers of the fjord, leading to an observed late season spike in biological productivity in the fjord's surface layers. Although surface melting and runoff from the Greenland Ice Sheet are predicted to increase significantly in the coming years and decades, the potential effect of this on fjord and coastal biological productivity is yet to be quantified. Here we present simulations of fjord circulation and biological productivity using the Massachusetts Institute of Technology general circulation model (MITgcm), and a new coupled representation of buoyant runoff plumes which enables decadal time period experiments of large three dimensional fjords. We investigate the effect on biological productivity of varying ice sheet runoff, ocean properties, near-surface winds and fjord geometry and bathymetry. We find that variations in ice sheet runoff are particularly important for biological productivity because the rate of discharge controls the depth at which the plumes reach neutral buoyancy and therefore whether the nutrient-rich deep water is delivered to the photic zone.

  15. Middle ear mucosal regeneration with three-dimensionally tissue-engineered autologous middle ear cell sheets in rabbit model.

    PubMed

    Yaguchi, Yuichiro; Murakami, Daisuke; Yamato, Masayuki; Hama, Takanori; Yamamoto, Kazuhisa; Kojima, Hiromi; Moriyama, Hiroshi; Okano, Teruo

    2016-03-01

    The likelihood of recurrent retraction and adhesion of newly formed tympanic membrane is high when middle ear mucosa is extensively lost during cholesteatoma and adhesive otitis media surgery. If rapid postoperative regeneration of the mucosa on the exposed bone surface can be achieved, prevention of recurrent eardrum adhesion and cholesteatoma formation, for which there has been no definitive treatment, can be expected. Suture-less transplantation of tissue-engineered mucosal cell sheets was examined immediately after the operation of otitis media surgery in order to quickly regenerate middle ear mucosa lost during surgery in a rabbit model. Transplantable middle ear mucosal cell sheets with a three-dimensional tissue architecture very similar to native middle ear mucosa were fabricated from middle ear mucosal tissue fragments obtained in an autologous manner from middle ear bulla on temperature-responsive culture surfaces. Immediately after the mucosa was resected from middle ear bone bulla inner cavity, mucosal cell sheets were grafted at the resected site. Both bone hyperplasia and granulation tissue formation were inhibited and early mucosal regeneration was observed in the cell sheet-grafted group, compared with the control group in which only mucosal removal was carried out and the bone surface exposed. This result indicates that tissue engineered mucosal cell sheets would be useful to minimize complications after the surgical operation on otitis media and future clinical application is expected.

  16. Model for flow of Casson nanofluid past a non-linearly stretching sheet considering magnetic field effects

    NASA Astrophysics Data System (ADS)

    Mustafa, M.; Khan, Junaid Ahmad

    2015-07-01

    Present work deals with the magneto-hydro-dynamic flow and heat transfer of Casson nanofluid over a non-linearly stretching sheet. Non-linear temperature distribution across the sheet is considered. More physically acceptable model of passively controlled wall nanoparticle volume fraction is accounted. The arising mathematical problem is governed by interesting parameters which include Casson fluid parameter, magnetic field parameter, power-law index, Brownian motion parameter, thermophoresis parameter, Prandtl number and Schmidt number. Numerical solutions are computed through fourth-fifth-order-Runge-Kutta integration approach combined with the shooting technique. Both temperature and nanoparticle volume fraction are increasing functions of Casson fluid parameter.

  17. Model Experiments and Elasto-Plastic Finite Element Analysis about Seepage Failure of Sand Behind Fixed Sheet Pile

    NASA Astrophysics Data System (ADS)

    Okajima, Kenji; Tanaka, Tadatsugu; Zhang, Shanji; Komatsu, Takahiro

    Constructing civil engineering structures, temporaly or permanent water proofing sheet piles often are used. The stability of seepage failure are carefully applied to those sheet piles, although many troubles of seepage failure were reported. On this problem the predictive method of the deformation and critical water head is required. In this study we carried out the model experiments which were designed for studying the seepage failure of soil behind fixed sheet piles and our elasto-plastic finite element method was applied to verify the effectiveness. Terzaghi method is very famous method for this problem and Terzaghi method was investigated by experiments data. As a result, it was confirmed that elasto-plastic finite element method was effectiveness and Terzaghi method was useful for this problem.

  18. Initializing the Greenland ice sheet to investigate its sensitivity to climate changes: a study with the GRISLI model.

    NASA Astrophysics Data System (ADS)

    Le clec'h, Sébastien; Dumas, Christophe; Kageyama, Masa; Charbit, Sylvie; Ritz, Catherine; Gallée, Hubert; Fettweis, Xavier

    2016-04-01

    The Greenland Ice Sheet (GrIS) is bound to play a crucial role in sea level rise over the next century. In this context, initializing Greenland ice sheet models properly is of prime importance. In this work, we will use the GRenoble Ice Shelf and Land Ice (GRISLI) model at 5km resolution (Ritz et al., 2001) to evaluate the evolution of the Greenland ice sheet under different climate forcings. The first step is to choose the most appropriate parameters to obtain a realistic Greenland ice sheet for present day. To perform this initialization, we use an inverse method and determine the basal stress given the observed geometry and mean climate between 1979 and 2014. We use the mean climate computed by the MAR regional atmospheric model (Fettweis et al.,2013) forced by reanalyses. At the end of this first step, we run a first simulation using the mean climate to check if the model is not drifting. In a second step, we apply three other climatologies built from MAR. We use: 1/ the warmest years of the period, 2/ the coolest years, 3/ the 2012 extreme melt event year (Nilsson et al, 2015). For each experiment we analyse the impact of these different climates on mass balance in 7 different regions (corresponding to drainage basins) of Greenland.

  19. Coupling Planet Simulator Mars, a general circulation model of the Martian atmosphere, to the ice sheet model SICOPOLIS

    NASA Astrophysics Data System (ADS)

    Stenzel, O. J.; Grieger, B.; Keller, H. U.; Greve, R.; Fraedrich, K.; Kirk, E.; Lunkeit, F.

    2007-11-01

    A general circulation model of the Martian Atmosphere is coupled with a 3-dimensional polythermal ice-sheet model of the polar ice caps. With this combination a series of experiments is carried out to investigate the impact of long-term obliquity change on the Martian north polar ice cap (NPC). The behaviour of the NPC is tested under obliquities of θ=15∘, 25∘ and 35∘. With increasing obliquity the area covered by the NPC gets smaller but does not vanish. However, when started from an ice-free condition the models develop an ice cap only for low obliquities. The 'critical' obliquity at which a build-up of a new polar cap is possible is θ=22∘.

  20. A 3 Ga old polythermal ice sheet in Isidis Planitia, Mars: Dynamics and thermal regime inferred from numerical modeling

    NASA Astrophysics Data System (ADS)

    Souček, Ondřej; Bourgeois, Olivier; Pochat, Stéphane; Guidat, Thomas

    2015-09-01

    Isidis Planitia is a 1350 km wide impact crater located close to the martian equator. To test the hypothesis that the 2.8 to 3.4 Ga old Thumbprint Terrain preserved on the floor of this basin is a glacial landform assemblage, we perform a numerical simulation of glaciation with a thermo-mechanically coupled model of ice sheet dynamics. As model inputs, we use surface temperatures and ice accumulation patterns predicted by a General Circulation Model based on the present-day atmospheric characteristics, and values of the geothermal heat flux provided by a global model of planetary thermal evolution. We find that, under favorable orbital conditions, an ice sheet covering the entire basin can develop in 2 to 5 Ma, with a maximum thickness of 4.9 km. The modeled ice sheet is polythermal: it is permanently cold-based in the periphery and, due to a negative heat-flux anomaly, also in the center, while the pressure melting point is reached in an intermediate ring. Our simulation is consistent with the interpretation that the Thumbprint Terrain is a martian equivalent of terrestrial ribbed moraines and has formed below a wet-based ice sheet. It supports also the interpretation that sinuous ridges and linear valleys observed at the periphery of the basin are parts of a subglacial network of eskers and tunnel valleys that drained the glacial meltwater outwards, across the cold-based periphery of the ice sheet. This work strengthens the hypothesis that glaciers thick as much as several km may have existed on Mars several Ga ago and that glacial basal melting may have contributed to the production and flow of surface liquid water at that time, under an atmosphere no thicker than the present-day one.

  1. Model calibration for ice sheets and glaciers dynamics: a general theory of inverse problems in glaciology

    NASA Astrophysics Data System (ADS)

    Giudici, Mauro; Baratelli, Fulvia; Vassena, Chiara; Cattaneo, Laura

    2014-05-01

    Numerical modelling of the dynamic evolution of ice sheets and glaciers requires the solution of discrete equations which are based on physical principles (e.g. conservation of mass, linear momentum and energy) and phenomenological constitutive laws (e.g. Glen's and Fourier's laws). These equations must be accompanied by information on the forcing term and by initial and boundary conditions (IBC) on ice velocity, stress and temperature; on the other hand the constitutive laws involves many physical parameters, which possibly depend on the ice thermodynamical state. The proper forecast of the dynamics of ice sheets and glaciers (forward problem, FP) requires a precise knowledge of several quantities which appear in the IBCs, in the forcing terms and in the phenomenological laws and which cannot be easily measured at the study scale in the field. Therefore these quantities can be obtained through model calibration, i.e. by the solution of an inverse problem (IP). Roughly speaking, the IP aims at finding the optimal values of the model parameters that yield the best agreement of the model output with the field observations and data. The practical application of IPs is usually formulated as a generalised least squares approach, which can be cast in the framework of Bayesian inference. IPs are well developed in several areas of science and geophysics and several applications were proposed also in glaciology. The objective of this paper is to provide a further step towards a thorough and rigorous theoretical framework in cryospheric studies. Although the IP is often claimed to be ill-posed, this is rigorously true for continuous domain models, whereas for numerical models, which require the solution of algebraic equations, the properties of the IP must be analysed with more care. First of all, it is necessary to clarify the role of experimental and monitoring data to determine the calibration targets and the values of the parameters that can be considered to be fixed

  2. Effects of rapid grounding line retreat investigated with three-dimensional ice sheet-ice shelf models

    NASA Astrophysics Data System (ADS)

    Pattyn, F.; Docquier, D.; Durand, G.; Favier, L.; Gagliardini, O.; Hindmarsh, R. C.; Zwinger, T.

    2011-12-01

    Understanding and attributing future sea-level changes demands serious efforts on the development of efficient ice sheet - ice shelf models that capture the essential physics and mechanics of grounding line behavior. While semi-analytical solutions for grounding line behavior are available for the flowline case, such solution fails to exist for more complex three-dimensional geometries. A way of evaluating the quality of ice sheet models is to verify them against more complex model solutions under controlled conditions. Given the computational demands of such models, it is extremely attractive from a computational point of view to use flux/thickness parameterizations in 3d models. Here we investigated the transition between ice sheet and ice shelf with series of different numerical models, ranging from full Stokes (Elmer/Ice) models, pseudo-spectral methods to a 2d vertically integrated finite-difference 'shelfy-stream' model, taking into account grounding line dynamics, and using parameterizations by Schoof (2007) and Pollard and DeConto (2009). Rapid grounding line migration was provoked by changing sliding at the grounding line, resulting in curved grounding lines influenced by lateral effects. We tested whether flux parameterizations are still valid under such conditions, especially when buttressing effects are taken into account.

  3. A matrix dependent/algebraic multigrid approach for extruded meshes with applications to ice sheet modeling

    SciTech Connect

    Tuminaro, Raymond S.; Perego, Mauro; Tezaur, Irina Kalashnikova; Salinger, Andrew G.; Price, Stephen

    2016-10-06

    A multigrid method is proposed that combines ideas from matrix dependent multigrid for structured grids and algebraic multigrid for unstructured grids. It targets problems where a three-dimensional mesh can be viewed as an extrusion of a two-dimensional, unstructured mesh in a third dimension. Our motivation comes from the modeling of thin structures via finite elements and, more specifically, the modeling of ice sheets. Extruded meshes are relatively common for thin structures and often give rise to anisotropic problems when the thin direction mesh spacing is much smaller than the broad direction mesh spacing. Within our approach, the first few multigrid hierarchy levels are obtained by applying matrix dependent multigrid to semicoarsen in a structured thin direction fashion. After sufficient structured coarsening, the resulting mesh contains only a single layer corresponding to a two-dimensional, unstructured mesh. Algebraic multigrid can then be employed in a standard manner to create further coarse levels, as the anisotropic phenomena is no longer present in the single layer problem. The overall approach remains fully algebraic, with the minor exception that some additional information is needed to determine the extruded direction. Furthermore, this facilitates integration of the solver with a variety of different extruded mesh applications.

  4. A matrix dependent/algebraic multigrid approach for extruded meshes with applications to ice sheet modeling

    DOE PAGES

    Tuminaro, Raymond S.; Perego, Mauro; Tezaur, Irina Kalashnikova; ...

    2016-10-06

    A multigrid method is proposed that combines ideas from matrix dependent multigrid for structured grids and algebraic multigrid for unstructured grids. It targets problems where a three-dimensional mesh can be viewed as an extrusion of a two-dimensional, unstructured mesh in a third dimension. Our motivation comes from the modeling of thin structures via finite elements and, more specifically, the modeling of ice sheets. Extruded meshes are relatively common for thin structures and often give rise to anisotropic problems when the thin direction mesh spacing is much smaller than the broad direction mesh spacing. Within our approach, the first few multigridmore » hierarchy levels are obtained by applying matrix dependent multigrid to semicoarsen in a structured thin direction fashion. After sufficient structured coarsening, the resulting mesh contains only a single layer corresponding to a two-dimensional, unstructured mesh. Algebraic multigrid can then be employed in a standard manner to create further coarse levels, as the anisotropic phenomena is no longer present in the single layer problem. The overall approach remains fully algebraic, with the minor exception that some additional information is needed to determine the extruded direction. Furthermore, this facilitates integration of the solver with a variety of different extruded mesh applications.« less

  5. Benchmarking the thermodynamic analysis of water molecules around a model beta sheet.

    PubMed

    Huggins, David J

    2012-06-05

    Water molecules play a vital role in biological and engineered systems by controlling intermolecular interactions in the aqueous phase. Inhomogeneous fluid solvation theory provides a method to quantify solvent thermodynamics from molecular dynamics or Monte Carlo simulations and provides an insight into intermolecular interactions. In this study, simulations of TIP4P-2005 and TIP5P-Ewald water molecules around a model beta sheet are used to investigate the orientational correlations and predicted thermodynamic properties of water molecules at a protein surface. This allows the method to be benchmarked and provides information about the effect of a protein on the thermodynamics of nearby water molecules. The results show that the enthalpy converges with relatively little sampling, but the entropy and thus the free energy require considerably more sampling to converge. The two water models yield a very similar pattern of hydration sites, and these hydration sites have very similar thermodynamic properties, despite notable differences in their orientational preferences. The results also predict that a protein surface affects the free energy of water molecules to a distance of approximately 4.0 Å, which is in line with previous work. In addition, all hydration sites have a favorable free energy with respect to bulk water, but only when the water-water entropy term is included. A new technique for calculating this term is presented and its use is expected to be very important in accurately calculating solvent thermodynamics for quantitative application.

  6. A matrix dependent/algebraic multigrid approach for extruded meshes with applications to ice sheet modeling

    SciTech Connect

    Tuminaro, Raymond S.; Perego, Mauro; Tezaur, Irina Kalashnikova; Salinger, Andrew G.; Price, Stephen

    2016-10-06

    A multigrid method is proposed that combines ideas from matrix dependent multigrid for structured grids and algebraic multigrid for unstructured grids. It targets problems where a three-dimensional mesh can be viewed as an extrusion of a two-dimensional, unstructured mesh in a third dimension. Our motivation comes from the modeling of thin structures via finite elements and, more specifically, the modeling of ice sheets. Extruded meshes are relatively common for thin structures and often give rise to anisotropic problems when the thin direction mesh spacing is much smaller than the broad direction mesh spacing. Within our approach, the first few multigrid hierarchy levels are obtained by applying matrix dependent multigrid to semicoarsen in a structured thin direction fashion. After sufficient structured coarsening, the resulting mesh contains only a single layer corresponding to a two-dimensional, unstructured mesh. Algebraic multigrid can then be employed in a standard manner to create further coarse levels, as the anisotropic phenomena is no longer present in the single layer problem. The overall approach remains fully algebraic, with the minor exception that some additional information is needed to determine the extruded direction. Furthermore, this facilitates integration of the solver with a variety of different extruded mesh applications.

  7. Benchmarking the Thermodynamic Analysis of Water Molecules Around a Model Beta Sheet

    PubMed Central

    Huggins, David J.

    2016-01-01

    Water molecules play a vital role in biological and engineered systems by controlling intermolecular interactions in the aqueous phase. Inhomogeneous fluid solvation theory provides a method to quantify solvent thermodynamics from molecular dynamics or Monte Carlo simulations and provides an insight into intermolecular interactions. In this study, simulations of TIP4P-2005 and TIP5P-Ewald water molecules around a model beta sheet are used to investigate the orientational correlations and predicted thermodynamic properties of water molecules at a protein surface. This allows the method to be benchmarked and provides information about the effect of a protein on the thermodynamics of nearby water molecules. The results show that the enthalpy converges with relatively little sampling, but the entropy and thus the free energy require considerably more sampling to converge. The two water models yield a very similar pattern of hydration sites and these hydration sites have very similar thermodynamic properties, despite notable differences in their orientational preferences. The results also show that a protein surface affects the free energy of water molecules to a distance of approximately 4.0 Å, which is in line with previous work. In addition, all hydration sites have a favourable free energy with respect to bulk water, but only when the water-water entropy term is included. A new technique for calculating this term is presented and its use is expected to be very important in accurately calculating solvent thermodynamics for quantitative application. PMID:22457119

  8. Modelling the influence of Lake Agassiz on Glacial Isostatic Adjustment and deglaciation of the Laurentide ice sheet

    NASA Astrophysics Data System (ADS)

    Berends, Tijn; van de Wal, Roderik; de Boer, Bas; Bradley, Sarah

    2016-04-01

    ANICE is a 3-D ice-sheet-shelf model, which simulates ice dynamics on the continental scale. It uses a combination of the SIA and SSA approximations and here it is forced with benthic δ18O records using an inverse routine. It is coupled to SELEN, a model, which solves the gravitationally self-consistent sea-level equation and the solid earth deformation of a spherically symmetrical rotating Maxwell visco-elastic earth, accounting for all major GIA effects. The coupled ANICE-SELEN model thus captures ice-sea-level feedbacks and can be used to accurately simulate variations in local relative sea-level over geological time scales. In this study it is used to investigate the mass loss of the Laurentide ice-sheet during the last deglaciation, accounting in particular for the presence of the proglacial Lake Agassiz by way of its GIA effects and its effect on the ice sheet itself. We show that the mass of the water can have a significant effect on local relative sea-level through the same mechanisms as the ice-sheet - by perturbing the geoid and by deforming the solid earth. In addition we show that calving of the ice-shelf onto the lake could have had a strong influence on the behaviour of the deglaciation. In particular, when allowing lake calving, the ice-sheet retreats rapidly over the deepening bed of Hudson Bay during the deglaciation, resulting in a narrow ice dam over Hudson Strait. This dam collapses around 8.2 Kyr causing a global sea level rise of approximately 1 meter - an observation that agrees well with field data (for example, LaJeunesse and St. Onge, 2008). Without lake calving the model predicts a drainage towards the Arctic ocean in the North.

  9. Modeling the transition between upper plane bed regime and sheet flow without an active layer formulation. Preliminary results.

    NASA Astrophysics Data System (ADS)

    Viparelli, E.; Hernandez Moreira, R. R.; Blom, A.

    2015-12-01

    A perusal of the literature on bedload transport revealed that, notwithstanding the large number of studies on bedform morphology performed in the past decades, the upper plane bed regime has not been thoroughly investigated and the distinction between the upper plane bed and sheet flow transport regimes is still poorly defined. Previous experimental work demonstrated that the upper plane bed regime is characterized by long wavelength and small amplitude bedforms that migrate downstream. These bedforms, however, were not observed in experiments on sheet flow transport suggesting that the upper plane bed and the sheet flow are two different regimes. We thus designed and performed experiments in a sediment feed flume in the hydraulic laboratory of the Department of Civil and Environmental Engineering at the University of South Carolina at Columbia to study the transition from upper plane bed to sheet flow regime. Periodic measurements of water surface and bed elevation, bedform geometry and thicknesses of the bedload layer were performed by eyes, and with cameras, movies and a system of six ultrasonic probes that record the variations of bed elevation at a point over time. We used the time series of bed elevations to determine the probability functions of bed elevation. These probability functions are implemented in a continuous model of river morphodynamics, i.e. a model that does not use the active layer approximation to describe the sediment fluxes between the bedload and the deposit and that should thus be able to capture the details of the vertical and streamwise variation of the deposit grain size distribution. This model is validated against the experimental results for the case of uniform material. We then use the validated model in the attempt to study if and how the spatial distribution of grain sizes in the deposit changes from upper plane bed regime to sheet flow and if these results are influenced by the imposed rates of base level rise.

  10. Hesperian polythermal glaciation in Isidis Planitia, Mars - Ice sheet dynamics and thermal regime inferred from numerical modeling

    NASA Astrophysics Data System (ADS)

    Souček, Ondřej; Bourgeois, Olivier; Pochat, Stéphane; Guidat, Thomas

    2015-04-01

    We test the hypothesis that the Thumbprint Terrain observed on the floor of Isidis Planitia, a giant impact crater located close to the martian equator, is a landform assemblage inherited from a glaciation during the Hesperian. For this purpose, we perform numerical simulations with a coupled thermo-mechanical model of ice sheet dynamics. We use surface temperatures and ice accumulation/ablation patterns predicted by a climatic Global Circulation Model, and values of the geothermal heat flux provided by a global model of planetary thermal evolution. We find that, with atmospheric physical properties similar to the current ones and under favorable orbital conditions, net ice accumulation in the northwestern part of Isidis Planitia leads within a few Ma to the development of a massive ice sheet, as much as 4.9 km in thickness, over the entire basin. The modeled ice sheet is polythermal: its center and its periphery are permanently frozen to the base, while the pressure melting point is reached episodically in an intermediate ring. Our simulations suggest that the propagation of thermo-mechanical melting waves in this ring is responsible for the formation of the Thumbprint Terrain, a probable martian equivalent of terrestrial ribbed moraines. They support the interpretation that sinuous ridges and linear valleys observed at the periphery of the basin are parts of a subglacial network of eskers and tunnel valleys that drained glacial meltwater outwards, across the cold-based outer part of the ice sheet. This work strengthens the hypothesis that massive glaciers covered large portions of the martian surface before the Amazonian and that basal melting below the wet-based portions of these ice sheets contributed significantly to the production and flow of liquid water in the ancient martian history.

  11. A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)

    DOE PAGES

    Zhang, Tong; Price, Stephen F.; Ju, Lili; ...

    2017-01-25

    Here, we present a comparison of the numerics and simulation results for two "full" Stokes ice sheet models, FELIX-S (Leng et al. 2012) and Elmer/Ice. The models are applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d). For the diagnostic experiment (P75D) the two models give similar results (< 2 % difference with respect to along-flow velocities) when using identical geometries and computational meshes, which we interpret as an indication of inherent consistencies and similarities between the two models. For the standard (Stnd), P75S, and P75R prognostic experiments, we find that FELIX-S (Elmer/Ice) grounding linesmore » are relatively more retreated (advanced), results that are consistent with minor differences observed in the diagnostic experiment results and that we show to be due to different choices in the implementation of basal boundary conditions in the two models. While we are not able to argue for the relative favorability of either implementation, we do show that these differences decrease with increasing horizontal (i.e., both along- and across-flow) grid resolution and that grounding-line positions for FELIX-S and Elmer/Ice converge to within the estimated truncation error for Elmer/Ice. Stokes model solutions are often treated as an accuracy metric in model intercomparison experiments, but computational cost may not always allow for the use of model resolution within the regime of asymptotic convergence. In this case, we propose that an alternative estimate for the uncertainty in the grounding-line position is the span of grounding-line positions predicted by multiple Stokes models.« less

  12. High-resolution, Antarctic Ice Sheet simulations forced by submarine melting simulated by the Accelerated Climate Model for Energy (ACME)

    NASA Astrophysics Data System (ADS)

    Price, S. F.; Asay-Davis, X.; Fyke, J. G.; Hoffman, M. J.; Jacobson, D.; Petersen, M. R.; Tezaur, I.; Perego, M.; Salinger, A.; Turner, A. K.; Wolfe, J.

    2016-12-01

    The capability for simulating sub-ice shelf circulation and submarine melting and freezing has recently been added to the U.S. Department of Energy's Accelerated Climate Model for Energy (ACME). With this new capability, we use an eddy permitting ocean model to conduct two sets of simulations in the spirit of Spence et al. (GRL, 41, 2014), who demonstrate increased warm water upwelling along the Antarctic coast in response to poleward shifting and strengthening of Southern Ocean westerly winds. These characteristics, symptomatic of a positive Southern Annual Model (SAM), are projected to continue into the 21st century under anthropogenic climate change (Fyfe et al., J. Clim., 20, 2007). In our first simulation, we force our climate model using repeat cycles of the standard CORE interannual forcing dataset (Large and Yeager; Clim. Dyn., 33, 2009). These melt rates are used to force our high-resolution (30-to-1 km) ice sheet model, MPAS-Land Ice, offline and to derive a quasi-steady state ice sheet model initial condition. In our second simulation, we force our climate model using an altered version of CORE interannual forcing, based on the latter half of the full time series, which we take as a proxy for a future climate state biased towards a positive SAM. Melt rate anomalies from this second simulation are then used to force our ice sheet model offline out to year 2100. We compare ocean model states and sub-ice shelf melt rates with observations and present estimates for Antarctic Ice Sheet mass loss from our simulations.

  13. Longitudinal Inter-Comparison of Modeled and Measured West Greenland Ice Sheet Meltwater Runoff Losses (2004-2014)

    NASA Astrophysics Data System (ADS)

    Moustafa, S.; Rennermalm, A. K.; Tedesco, M.; Mote, T. L.; Koenig, L.; Smith, L. C.; Hagedorn, B.; Overeem, I.; Sletten, R. S.; Mikkelsen, A. B.; Hasholt, B.; Hall, D. K.

    2015-12-01

    Increased surface meltwater runoff, that exits the Greenland ice sheet (GrIS) margin via supra-, en-, and sub-glacial drainage networks into fjords, pro-glacial lakes and rivers, accounts for half or more of total mass loss. Despite its importance, modeled meltwater runoff fluxes are poorly constrained, primarily due to a lack of direct in situ observations. Here, we present the first ever longitudinal (north-south) inter-comparison of a multi-year dataset (2004-2014) of discharge for four drainage basins - Watson, Akuliarusiarsuup Kuua, Naujat Kuat, and North Rivers - along West Greenland. These in situ hydrologic measurements are compared with modeled runoff output from Modèle Atmosphérique Régional (MAR) regional climate model, and the performance of the model is examined. An analysis of the relationship between modeled and actual ice sheet runoff patterns is assessed, and provides insight into the model's ability to capture inter-annual and intra-annual variability, spatiotemporal patterns, and extreme melt events. This study's findings will inform future development and parameterization of ice sheet surface mass balance models.

  14. Polar predictability: exploring the influence of GCM and regional model uncertai