Browsing NTNU Open by Author "Ellingsen, Simen Andreas Ådnøy"
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A Framework for Modeling Linear Surface Waves on Shear Currents in Slowly Varying Waters
Li, Yan; Ellingsen, Simen Andreas Ådnøy (Journal article; Peer reviewed, 2019)We present a theoretical and numerical framework—which we dub the direct integration method (DIM)—for simple, efficient, and accurate evaluation of surface wave models allowing presence of a current of arbitrary depth ... 
An Improved Method for Determining Near‐Surface Currents From Wave Dispersion Measurements
Smeltzer, Benjamin Keeler; Æsøy, Eirik; Ådnøy, Anna; Ellingsen, Simen Andreas Ådnøy (Journal article; Peer reviewed, 2019)A new inversion method for determining near‐surface shear currents from a measured wave spectrum is introduced. The method is straightforward to implement and starts from the existing state‐of‐the‐art technique of assigning ... 
Design and control of precision dropondemand herbicide application in agricultural robotics
Urdal, Frode; Utstumo, Trygve; Vatne, Jan Kåre; Ellingsen, Simen Andreas Ådnøy; Gravdahl, Jan Tommy (Chapter, 2014)Dropondemand weed control is a field of research within Precision Agriculture, where the herbicide application is controlled down to individual droplets. This paper focuses on the fluid dynamics and electronics design ... 
Dispersion forces in Micromechanics: Casimir and CasimirPolder forces affected by geometry and nonzero temperature
Ellingsen, Simen Andreas Ådnøy (Doktoravhandlinger ved NTNU, 15038181; 2011:29, Doctoral thesis, 2011)The present thesis focuses on several topics within three separate but related branches of the overall field of dispersion forces. The three branches are: temperature corrections to the Casimir force between real materials ... 
Effect on Doppler Resonance From a NearSurface Shear Layer
Smeltzer, Benjamin Keeler; Li, Yan; Ellingsen, Simen Andreas Ådnøy (Chapter, 2017)For waves generated by a wave source which is simultaneously moving and oscillating at a constant frequency ω, a resonance is well known to occur at a particular value τres of the nondimensional frequency τ = ωV/g (V: ... 
Experimental study of surface waves on strongly sheared currents  Laboratory, design, building, testing, and measurements
Æsøy, Eirik (Master thesis, 2017)In this thesis experimental methods to measure sheardependent wave dispersion is implemented and used to study waves propagating on currents. To achieve such measurements one needs to establish the following measurement ... 
Initial Value Problems for Water Waves in the Presence of a Shear Current
Li, Yan; Ellingsen, Simen Andreas Ådnøy (Proceedings of the twentyfifth International Ocean and Polar Engineering Conference;ISOPE 2015, Chapter; Conference object; Peer reviewed, 2015)We obtain a general solution for the initial value problems of water waves with a shear current of uniform vorticity beneath the surface in three dimensions. Linearized governing equations and boundary conditions ... 
Langmuirtype vortices in wallbounded flows driven by a crisscross wavy wall topography
Akselsen, Andreas Holm; Ellingsen, Simen Andreas Ådnøy (Peer reviewed; Journal article, 2020)We investigate a mechanism to manipulate wallbounded flows whereby wavelike undulations of the wall topography drives the creation of bespoke longitudinal vortices. A resonant interaction between the ambient vorticity ... 
Multiple resonances of a moving oscillating surface disturbance on a shear current
Ellingsen, Simen Andreas Ådnøy; Li, Yan (Journal article; Peer reviewed, 2016) 
Numerical analysis of nonlinear oscillations of micrometre size fluid droplets
Frøynes, Olav Are (Master thesis, 2014)Nonlinear oscillations of free viscous drops are investigated by solving the full NavierStokes equation using the finite element software COMSOL Multiphysics. Oscillations are investigated for droplets released form static ... 
Numerical study of curvedmesh tailoring of freesurface shear profile
Ludvigsen, Stian Isefjær (Master thesis, 2019)Krummede nettinger blir ofte brukt til å endre hastighetsprofilet i testområdet i eksperimentelle anlegg. De eksisterende uttrykkene som kan brukes til å bestemme formen på nettingen, gitt strømningsforholdene opp og ... 
Numerical study of surface waves on a shear current  Waves behind a surface obstacle
Kvamme, Ørjan (Master thesis, 2018)This master's thesis has made investigation into waves and currents interaction numerically by the use of an oscillating cylinder as a wavemaker. Three cases were investigated: still water, uniform flow and linear shear ... 
Oblique waves on a vertically sheared current are rotational
Ellingsen, Simen Andreas Ådnøy (Journal article; Peer reviewed, 2016)In the study of surface waves in the presence of a shear current, a useful and much studied model is that in which the shear flow has constant vorticity. Recently it was shown by Constantin (2011) that a flow of constant ... 
Observation of surface wave patterns modified by subsurface shear currents
Smeltzer, Benjamin Keeler; Æsøy, Eirik; Ellingsen, Simen Andreas Ådnøy (Journal article; Peer reviewed, 2019)We report experimental observations of two canonical surface wave patterns – ship waves and ring waves – skewed by subsurface shear, thus confirming effects predicted by recent theory. Observed ring waves on a still surface ... 
PathFollowing Methods for Calculating Linear Surface Wave Dispersion Relations on Vertical Shear Flows
Maxwell, Peter; Ellingsen, Simen Andreas Ådnøy (Journal article; Peer reviewed, 2020)The pathfollowing scheme in Loisel and Maxwell (SIAM J Matrix Anal Appl 39(4):1726–1749, 2018) is adapted to efficiently calculate the dispersion relation curve for linear surface waves on an arbitrary vertical shear ... 
Sheared freesurface flow over threedimensional obstructions of finite amplitude
Akselsen, Andreas Holm; Ellingsen, Simen Andreas Ådnøy (Journal article; Peer reviewed, 2019)When shallow water flows over uneven bathymetry, the water surface is modulated. This type of problem has been revisited numerous times since it was first studied by Lord Kelvin in 1886. Our study analytically examines ... 
Surface water waves on depth dependent flows
Li, Yan (Doctoral theses at NTNU;2017:194, Doctoral thesis, 2017)The present thesis provides essential insights into surface water waves propagating atop a horizontal current whose magnitude and direction may vary arbitrarily with water depth. A comprehensive theory in this regard is ... 
Surface Waves Generated by a Translating and Oscillating Source Atop Realistic Shear Flows
Li, Yan; Ellingsen, Simen Andreas Ådnøy (Chapter, 2018)We analyze surface waves generated by a translating, oscillating surface disturbance atop a horizontal background flow of arbitrary depth dependence, with a focus on determining the Doppler resonance. For a critical value ... 
The Error in Predicted Phase Velocity of Surface Waves atop a Shear Current with Uncertainty
Maxwell, Peter; Smeltzer, Benjamin Keeler; Ellingsen, Simen Andreas Ådnøy (Journal article; Peer reviewed, 2019)The effect of a depthdependent shear current U(z) on surface wave dispersion is conventionally calculated by assuming U(z) to be an exactly known function, from which the resulting phase velocity c(k) is determined. This, ... 
Transient wave resistance upon a real shear current
Li, Yan; Smeltzer, Benjamin Keeler; Ellingsen, Simen Andreas Ådnøy (Journal article; Peer reviewed, 2018)We study the waves and wavemaking forces acting on ships travelling on currents which vary as a function of depth. Our concern is realism; we consider a real current profile from the Columbia River, and model ships with ...