Blar i NTNU Open på forfatter "Hansen, Alex"
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A bridge between statistical learning and agent based modelling in stock market predictions
Hellenes, Arne Herman (Master thesis, 2016)The research related to agent based modelling and statistical learning has increased in the recent years, as alternatives to main stream econometrics. This project combines the three for constructing and evaluating a ... -
A Model for the Mixing of Black Carbon Aerosols and Mineral Dust Particles in the Atmosphere
Berntsen, Simen (Master thesis, 2016)The process when freshly emitted black carbon particles are forming clusters and the mixing of these black carbon clusters and mineral dust particles has been simulated for a two-dimensional system. This has been done by ... -
A Monte Carlo Algorithm for Immiscible Two-Phase Flow in Porous Media
Savani, Isha; Sinha, Santanu; Hansen, Alex; Bedeaux, Dick; Kjelstrup, Signe; Vassvik, Morten (Journal article; Peer reviewed, 2017)We present a Markov Chain Monte Carlo algorithm based on the Metropolis algorithm for simulation of the flow of two immiscible fluids in a porous medium under macroscopic steady-state conditions using a dynamical pore ... -
A Numerical Study of Transient Friction and Transient Friction Modelling in Ramp-up and Ramp-down Flow Conditions Similar to Pump Ramp-up and Valve Closure in Gas Transport Pipelines
Birkeland, Sigmund Andreas (Master thesis, 2014)When gas is transported in long pipelines, computational models are used as tools to plan and to optimize hydraulic capacities. Because of the length of the pipelines the models are mostly one-dimensional (1D) which in ... -
A Renormalization Group Procedure for Fiber Bundle Models
Pradhan, Srutarshi; Hansen, Alex; Ray, Purusattam (Journal article; Peer reviewed, 2018)We introduce two versions of a renormalization group scheme for the equal load sharing fiber bundle model. The renormalization group is based on formulating the fiber bundle model in the language of damage mechanics. A ... -
A Simulated Annealing Approach to Electrical Resistivity Tomography
Wiken, Håvard Eidal (Master thesis, 2018)In this study, a new approach to Electrical Resistivity Tomography (ERT) data inversion was investigated. ERT is a geophysical method for imaging the subsurface. An electrical current is injected into the surface, and the ... -
Accumulated Plastic Strain Program
Valnes, Lars Magnus (Master thesis, 2014)In this thesis we will look at the implementation and results of the APS program. The program computes the accumulated plastic strain in a umbilical tube for the deformations axial tension, bending and internal pressure. ... -
Aging and Failure of a Polymer Chain under Tension
Charan, Harish; Hansen, Alex; Hentschel, H. George E.; Procaccia, Itamar (Peer reviewed; Journal article, 2021)The rupture of a polymer chain maintained at temperature T under fixed tension is prototypical to a wide array of systems failing under constant external stress and random perturbations. Past research focused on analytic ... -
Anomalous diffusion in systems with concentration-dependent diffusivity: exact solutions and particle simulations
Hansen, Alex; Flekkøy, Eirik Grude; Baldelli, Beatrice (Journal article; Peer reviewed, 2020)We explore the anomalous diffusion that may arise as a result of a concentration dependent diffusivity. The diffusivity is taken to be a power law in the concentration, and from exact analytical solutions we show that the ... -
Burst Dynamics, Upscaling and Dissipation of Slow Drainage in Porous Media
Måløy, Knut Jørgen; Moura, Marcel; Hansen, Alex; Flekkøy, Eirik Grude; Toussaint, Renaud (Peer reviewed; Journal article, 2021)We present a theoretical and experimental investigation of drainage in porous media. The study is limited to stabilized fluid fronts at moderate injection rates, but it takes into account capillary, viscous, and gravitational ... -
Can Local Stress Enhancement Induce Stability in Fracture Processes? Part I: Apparent Stability
Kjellstadli, Jonas Tøgersen; Bering, Eivind; Hendrick, Martin; Pradhan, Srutarshi; Hansen, Alex (Journal article; Peer reviewed, 2019)By comparing the evolution of the local and equal load sharing fiber bundle models, we point out the paradoxical result that stresses seem to make the local load sharing model stable when the equal load sharing model is ... -
Can Local Stress Enhancement Induce Stability in Fracture Processes? Part II: The Shielding Effect
Kjellstadli, Jonas Tøgersen; Bering, Eivind; Pradhan, Srutarshi; Hansen, Alex (Journal article; Peer reviewed, 2019)We use the local load sharing fiber bundle model to demonstrate a shielding effect where strong fibers protect weaker ones. This effect exists due to the local stress enhancement around broken fibers in the local load ... -
Crack localization and the interplay between stress enhancement and thermal noise
Sinha, Santanu; Roy, Subhadeep; Hansen, Alex (Peer reviewed; Journal article, 2021)We study the competition between thermal fluctuations and stress enhancement in the failure process of a disordered system by using a local load sharing fiber bundle model. The thermal noise is introduced by defining a ... -
Criterion for Imminent Failure During Loading—Discrete Element Method Analysis
Debski, Wojciech; Pradhan, Srutarshi; Hansen, Alex (Peer reviewed; Journal article, 2021)It has recently been reported that the equal load sharing fiber bundle model predicts the rate of change of the elastic energy stored in the bundle reaches its maximum before catastrophic failure occurs, making it a possible ... -
Critical Behaviour of the Local Load Sharing Fiber Bundle Model
Dahle, Magnus Holter-S (Master thesis, 2016)A generalised, history independent, Local Load Sharing Fiber Bundle Model, describing damage propagation in materials as failing fibers under under external load is studied. If the fibers' thresholds $t$ are drawn from an ... -
Detection and Localization of High-Frequency Interception Signals using Compressive Sensing
Breisjøberg, Torjus (Master thesis, 2013)We investigate detection and localization of high-frequency interception signals underwater using a fairly new framework known as Compressive Sensing. Within this framework we can sample at sub-Nyquist rate and still be ... -
Dynamic Wettability Alteration in Immiscible Two-phase Flow in Porous Media: Effect on Transport Properties and Critical Slowing Down
Flovik, Vegard; Sinha, Santanu; Hansen, Alex (Journal article; Peer reviewed, 2015)The change in contact angles due to the injection of low salinity water or any other wettability altering agent in an oil-rich porous medium is modeled by a network of disordered pores transporting two immiscible fluids. ... -
Effective Rheology of Bi-viscous Non-newtonian Fluids in Porous Media
Talon, Laurent; Hansen, Alex (Peer reviewed; Journal article, 2020)We model the flow of bi-viscous non-Newtonian fluids in porous media by a square lattice where the links obey a piece-wise linear constitutive equation. We find numerically that the flow regime, where the network transitions ... -
Effective rheology of two-phase flow in a capillary fiber bundle model
Roy, Subhadeep; Hansen, Alex; Sinha, Santanu (Journal article; Peer reviewed, 2019)We investigate the effective rheology of two-phase flow in a bundle of parallel capillary tubes carrying two immiscible fluids under an external pressure drop. The diameter of the tubes vary along the length which introduce ... -
Ensemble distribution for immiscible two-phase flow in porous media
Savani, Isha; Bedeaux, Dick; Kjelstrup, Signe; Vassvik, Morten; Sinha, Santanu; Hansen, Alex (Journal article, 2017)We construct an ensemble distribution to describe steady immiscible two-phase flow of two incompressible fluids in a porous medium. The system is found to be ergodic. The distribution is used to compute macroscopic flow ...