scholarly journals A level-set method for modeling the evolution of glacier geometry

2004 ◽  
Vol 50 (171) ◽  
pp. 485-491 ◽  
Author(s):  
Antoine Pralong ◽  
Martin Funk
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Level Set Method ◽  
Level Set ◽  
Numerical Solutions ◽  
Glacier Surface ◽  
Surface Evolution ◽  
Proposed Model ◽  
Steady State Solutions ◽  
Over Time

AbstractA level-set method is proposed for modeling the evolution of a glacier surface subject to a prescribed mass balance. This leads to a simple and versatile approach for computing the evolution of glaciers: the description of vertical fronts and overriding phenomena presents no difficulties, topological changes are handled naturally and steady-state solutions can be calculated without integration over time. A numerical algorithm is put forth as a means of solving the proposed model of glacier surface evolution. It is evaluated by comparing different numerical solutions of the model with analytical and published numerical solutions. The level-set method appears to be a reliable approach for dealing with different glaciological problems.

Medical Volumes Segmentation Approach Based on Level Set Method

2011 ◽  
Vol 65 ◽  
pp. 173-176
Author(s):  
Zhong Wei Li ◽  
Ming Jiu Ni ◽  
Zhen Kuan Pan
Keyword(s):  
Magnetic Resonance Angiography ◽  
Level Set Method ◽  
Level Set ◽  
Medical Application ◽  
Vascular Structure ◽  
Thin Structures ◽  
Proposed Model ◽  
Segmentation Approach ◽  
Computer Based ◽  
Segmentation Task

Volumes segmentation is an important part of computer based medical application for diagnosis and analysis of anatomical data. A segmentation approach based on the level set method is proposed for accurately extracting vasculature from magnetic resonance angiography (MRA) volumes in this paper. The proposed model has a boundary alignment term that is used for segmentation of thin structures. Finally the proposed model is applied to the segmentation of MRA volumes. The result shows that the proposed model by us can complete the segmentation task of vascular structure and cannot complete the same task by the model without boundary alignment term

Laminar flow past an abruptly accelerated elliptic cylinder at 45° incidence

1974 ◽  
Vol 65 (4) ◽  
pp. 711-734 ◽  
Author(s):  
H. J. Lugt ◽  
H. J. Haussling
Keyword(s):  
Steady State ◽  
Numerical Solutions ◽  
Fluid Flows ◽  
Elliptic Cylinder ◽  
Finite Difference Schemes ◽  
Quasi Steady State ◽  
Constant Vorticity ◽  
Transient Period ◽  
Incompressible Fluid Flows ◽  
Steady State Solutions

Numerical solutions for laminar incompressible fluid flows past an abruptly started elliptic cylinder at 45° incidence are presented. Various finite-difference schemes for the stream-function/vorticity formulation are used and their merits briefly discussed. Almost steady-state solutions are obtained forRe= 15 and 30, whereas forRe= 200 a Kármán vortex street develops. The transient period from the start to the steady or quasi-steady state is investigated in terms of patterns of streamlines and lines of constant vorticity and drag, lift and moment coefficients.

scholarly journals Existence and stability of steady-state solutions of the shallow-ice-sheet equation by an energy-minimization approach

2011 ◽  
Vol 57 (202) ◽  
pp. 345-354 ◽  
Author(s):  
Guillaume Jouvet ◽  
Jacques Rappaz ◽  
Ed Bueler ◽  
Heinz Blatter
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Mass Balance ◽  
Energy Minimization ◽  
Existence Of Solutions ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Existence And Stability ◽  
Steady State Solutions ◽  
Minimization Approach

AbstractThe existence of solutions of the non-sliding shallow-ice-sheet equation on a flat horizontal bed with a mass balance linearly depending on altitude is proven for fixed margins. Free-margin solutions for the same mass balance do not exist. Fixed-margin solutions show unbounded shear stress and nonzero mass flux at the margin. Steady-state solutions with realistic margins, vanishing ice flux and vanishing shear stress are found numerically for ice sheets with Weertman-type sliding.

Modeling of the Two-Phase Closed Thermosyphon

1987 ◽  
Vol 109 (3) ◽  
pp. 722-730 ◽  
Author(s):  
J. G. Reed ◽  
C. L. Tien
Keyword(s):  
Steady State ◽  
Analysis Tool ◽  
Governing Equations ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Proposed Model ◽  
The Times ◽  
Steady State Solutions ◽  
Liquid And Vapor Phases

A comprehensive model is developed to predict the steady-state and transient performance of the two-phase closed thermosyphon. One-dimensional governing equations for the liquid and vapor phases are developed using available correlations to specify the shear stress and heat transfer coefficients. Steady-state solutions agree well with thermosyphon flooding data from several sources and with film thickness data obtained in the present investigation. While no data are available with which to compare the transient analysis, the results indicate that, for most systems, the governing time scale for system transients is the film residence time, which is typically much longer than the times required for viscous and thermal diffusion through the film. The proposed model offers a versatile and comprehensive analysis tool which is relatively simple.

A CFD-Radial Motion Coupled Model for the Evaluation of the Features of Journal Bearings in External Gear Machines

2015 ◽  
Author(s):  
Matteo Pellegri ◽  
Andrea Vacca
Keyword(s):  
Steady State ◽  
Film Flow ◽  
Coupled Model ◽  
Journal Bearings ◽  
Instantaneous Axis Of Rotation ◽  
Proposed Model ◽  
Rigid Model ◽  
Hydrodynamic Effects ◽  
The Impact ◽  
Steady State Solutions

This paper presents an approach for the evaluation of the effects related to the behavior of the journal bearings on the operation of external gear machines (EGMs). In EGMs journal bearings usually support shafts of both gears. The prediction of their instantaneous axis of rotation is a key feature of EGMs, affecting the displacing action of the inter-teeth volumes and the leakages at the tip of each tooth. Past approaches presented in the literature for the evaluation of the radial micro-motions of the gears are based on classic simplified models for the hydrodynamic journal bearings based on steady-state solutions of the fluid film neglecting important hydrodynamic effects due to film squeeze — which can be relevant in case of significant radial loads variations — or they concentrate the focus of the study on the journal bearing itself regardless of the impact on the global machine operation. This work presents a CFD model coupled with a rigid model for the evaluation of the radial motions of the journal that permits to overcome the above-mentioned limitations of the existing approaches of study. The paper details the proposed model, in particular as concerns the CFD approach to solve the film flow and its coupling with a previously developed model (HYGESim) developed by the authors’ team for the evaluation of the overall operation of the EGM, used also to find the instantaneous loads on the gears. The potentials of the proposed approach are shown for the case of a pump for high pressure applications. For this case the results show how it is necessary to have a detailed approach for the evaluation of the journal bearings for a correct evaluation of the overall EGM behavior. In particular, the importance of hydrodynamic squeeze effects are shown, by comparing the model prediction with those given by the commonly used simplified steady-state approach. The comparison of simulation results with experimental data is also shown as pertain to pump case wear associated to the break in process.

scholarly journals A description of crevasse formation using continuum damage mechanics

2003 ◽  
Vol 37 ◽  
pp. 77-82 ◽  
Author(s):  
Antoine Pralong ◽  
Martin Funk ◽  
Martin P. Lüthi
Keyword(s):  
Level Set Method ◽  
Level Set ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Interface Motion ◽  
Glacier Surface ◽  
Polycrystalline Ice ◽  
Isotropic Damage ◽  
Good Agreement

AbstractContinuum damage mechanics describes the progressive deterioration of material subjected to loading. Jointly used with a level-set method, it proves to be a promising approach to computing the interface motion of a damaged material. For polycrystalline ice, a local isotropic damage evolution law (generalized Kachanow’s law) applied to Glen’s flow law allows the description of tertiary creep and facilitates the modeling of crevasse opening using a failure criterion based on damage accumulation. The use of a level-set method permits the description, in a continuum approach, of the motion of a fractured glacier surface. Using these methods, a model is developed. The ability of this model to describe phenomena connected to crevasse opening is presented. The rupture of a large ice block from a hanging glacier is computed and analyzed. The regular acceleration of such an unstable ice block prior to its collapse is calculated and compared to the acceleration function obtained from observations. A good agreement between the two acceleration functions was found.

scholarly journals Two methods for firn-area and mass-balance monitoring of Svalbard glaciers with SAR satellite images

2004 ◽  
Vol 50 (168) ◽  
pp. 116-128 ◽  
Author(s):  
Max König ◽  
Jan-Gunnar Winther ◽  
Jack Kohler ◽  
Florian König
Keyword(s):  
Mass Balance ◽  
Satellite Images ◽  
Synthetic Aperture ◽  
Sar Image ◽  
Negative Mass ◽  
Sar Images ◽  
Glacier Surface ◽  
Absolute Mass ◽  
Measured Mass ◽  
Over Time

AbstractThis paper presents two methods for glacier monitoring on Svalbard using synthetic aperture radar (SAR) satellite images. Both methods were developed on glaciers in the Kongsfjorden area. The first method monitors the firn area extent and the firn line over time by thresholding and filtering the SAR image. Manual detection of the threshold is preferable, but using a constant threshold for all images also gives adequate results. A retreat of the firn-line position is visible, especially on Kongsvegen, corresponding to consecutive years of negative mass balance. The second method applies a k-means classification to three clusters on the glacier surface. The areal extent of the resulting class on the upper part of the glacier correlates remarkably well with the independently measured mass balance of Kongsvegen, having a correlation coefficient of around 0.89 for the various glaciers. This is because the snow from the accumulation area influences the k-means classification. Thus, on glaciers where mass-balance values are available, new mass-balance values can be predicted solely from SAR images. For glaciers where no mass balance is available, the area change cannot be calibrated to absolute mass-balance values, but relative changes can be predicted.

scholarly journals A mathematical framework for modelling cambial surface evolution using a level set method

2011 ◽  
Vol 108 (6) ◽  
pp. 1001-1011 ◽  
Author(s):  
Damien Sellier ◽  
Michael J. Plank ◽  
Jonathan J. Harrington
Keyword(s):  
Level Set Method ◽  
Level Set ◽  
Mathematical Framework ◽  
Surface Evolution

Upwelling of a stratified fluid in a rotating annulus: steady state. Part 2. Numerical solutions

1973 ◽  
Vol 59 (2) ◽  
pp. 337-368 ◽  
Author(s):  
J. S. Allen
Keyword(s):  
Steady State ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Rotational Frequency ◽  
Navier Stokes ◽  
Rossby Number ◽  
Navier Stokes Equations ◽  
Finite Difference Approximations ◽  
Side Walls ◽  
Steady State Solutions

Numerical solutions of finite-difference approximations to the Navier–Stokes equations have been obtained for the axisymmetric motion of a Boussinesq liquid in a rigidly bounded rotating annulus. For most of the cases studied, a temperature difference is maintained between the top and bottom surfaces such that essentially a basic stable density stratification is imposed on the fluid. The side walls are thermally insulated and the motion is driven by a differential rotation of the top surface. Approximate steady-state solutions are obtained for various values of the Rossby number ε and the stratification parameter S = N2/Ω2, where N is the Brunt–Väisälä frequency and Ω is the rotational frequency. The changes in the flow field with the variation of these parameters is studied. Particular attention is given to an investigation of the meridional, or up welling, circulation and its dependence on the stratification parameter. The effects on the flow of different boundary conditions, such as an applied stress driving, specified temperature at the side walls and an applied heat flux at the top and bottom surfaces, are also investigated.

Numerical Investigation of Oil Slug Trapped in Capillary Tube With a Level Set Method

2013 ◽  
Author(s):  
Liming Dai ◽  
Xiaojie Wang
Keyword(s):  
Level Set Method ◽  
Level Set ◽  
Annular Flow ◽  
High Efficiency ◽  
Numerical Solutions ◽  
Capillary Tube ◽  
Water Film ◽  
Governing Equations ◽  
Two Phase

An investigation of the motion of oil drops trapped in an axisymmetric capillary tube saturated with water is carried out. The governing equations for core-annular flow are derived in detail. Numerical solutions for capturing the evolution of interface are developed by making use of a level set method. A second-order projection method is applied to obtain the velocity field of the incompressible two-phase flow. The results show the high efficiency of the method and the key role of water film in improving the mobilization of oil slugs.

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