Atle Jensen

• Ayati, Anis Awal; Vollestad, Petter & Jensen, Atle (2018). Detailed measurements of interfacial dynamics in air-water pipe flow. Procedia IUTAM.  ISSN 2210-9838. Fulltekst i vitenarkiv.
• Dong, Tao; Shi, Zhongyuan & Jensen, Atle (2018). Bi-objective optimization of axial profile of pin fin with uniform base heat flux. Applied Thermal Engineering.  ISSN 1359-4311.  128, s 830- 836 . doi: 10.1016/j.applthermaleng.2017.09.037
• Kolaas, Jostein; Riise, Bjørn; Sveen, Kristian & Jensen, Atle (2018). Bichromatic synthetic schlieren applied to surface wave measurements. Experiments in Fluids.  ISSN 0723-4864.  59(8) . doi: 10.1007/s00348-018-2580-6
• Mossige, Endre Joachim; Jensen, Atle & Mielnik, Michal Marek (2018). Separation and Concentration without Clogging Using a High-Throughput Tunable Filter. Physical Review Applied.  ISSN 2331-7019.  9(5) . doi: 10.1103/PhysRevApplied.9.054007 Fulltekst i vitenarkiv. Vis sammendrag

  We present a detailed experimental study of a hydrodynamic filtration microchip and show how chip performance can be tuned and clogging avoided by adjusting the flow rates. We demonstrate concentration and separation of microspheres at throughputs as high as 29  ml/min and with 96% pureness. Results of streakline visualizations show that the thickness of a tunable filtration layer dictates the cutoff size and that two different concentration mechanisms exist. Particles larger than pores are concentrated by low-velocity rolling over the filtration pillars, while particles smaller than pores are concentrated by lateral drift across the filtration layer. Results of microscopic particle image velocimetry and particle-tracking velocimetry show that the degree of lateral migration can be quantified by the slip velocity between the particle and the surrounding fluid. Finally, by utilizing differences in inertia and separation mode, we demonstrate size-based separation of particles in a mixture

• Riise, Bjørn; Grue, John; Jensen, Atle & Johannessen, Thomas Berge (2018). A note on the secondary load cycle for a monopile in irregular deep water waves. Journal of Fluid Mechanics.  ISSN 0022-1120.  849, s R1- R12 . doi: 10.1017/jfm.2018.450
• Smith, Lisa; Kolaas, Jostein; Jensen, Atle & Sveen, Johan Kristian (2018). Investigation of surface structures in two phase wavy pipe flow by utilizing X-ray tomography. International Journal of Multiphase Flow.  ISSN 0301-9322. . doi: 10.1016/j.ijmultiphaseflow.2018.06.004
• Smith, Lisa; Kolaas, Jostein; Jensen, Atle & Sveen, Johan Kristian (2018). X-ray measurements of plunging breaking solitary waves. European journal of mechanics. B, Fluids.  ISSN 0997-7546. . doi: 10.1016/j.euromechflu.2018.03.007
• Ayati, Anis Awal; Kolaas, Jostein & Jensen, Atle (2017). A PIV investigation of stratified gas–liquid flow in a horizontal pipe. arXiv.org.  ISSN 2331-8422.
• Grafsrønningen, Stig & Jensen, Atle (2017). Large eddy simulations of a buoyant plume above a heated horizontal cylinder at intermediate Rayleigh numbers. International journal of thermal sciences.  ISSN 1290-0729.  112, s 104- 117 . doi: 10.1016/j.ijthermalsci.2016.09.032 Fulltekst i vitenarkiv.
• Hagemann, Ola; Jensen, Atle & Grafsrønningen, Stig (2017). Cooldown of Subsea Deadleg With a Cold Spot: Experimental and Numerical Heat-Transfer Analysis. Oil and Gas Facilities.  ISSN 1942-2431.  5(06) . doi: 10.2118/185170-PA
• Rabault, Jean; Kolaas, Jostein & Jensen, Atle (2017). Performing particle image velocimetry using artificial neural networks: a proof-of-concept. Measurement science and technology.  ISSN 0957-0233.  28(12) . doi: 10.1088/1361-6501/aa8b87 Fulltekst i vitenarkiv.
• Rabault, Jean; Sutherland, Graigory John; Gundersen, Olav & Jensen, Atle (2017). Measurements of wave damping by a grease ice slick in Svalbard using off-the-shelf sensors and open-source electronics. Journal of Glaciology.  ISSN 0022-1430.  63(238), s 372- 381 . doi: 10.1017/jog.2017.1 Fulltekst i vitenarkiv.
• Smith, Lisa; Jensen, Atle & Pedersen, Geir Kleivstul (2017). Investigation of breaking and non-breaking solitary waves and measurements of swash zone dynamics on a 5° beach. Coastal Engineering.  ISSN 0378-3839.  120, s 38- 46 . doi: 10.1016/j.coastaleng.2016.11.004 Fulltekst i vitenarkiv.
• Sutherland, Graigory John; Halsne, Trygve; Rabault, Jean & Jensen, Atle (2017). The attenuation of monochromatic surface waves due to the presence of an inextensible cover. Wave motion.  ISSN 0165-2125.  68, s 88- 96 . doi: 10.1016/j.wavemoti.2016.09.004 Fulltekst i vitenarkiv.
• Sutherland, Graigory John; Rabault, Jean & Jensen, Atle (2017). A method to estimate reflection and directional spread using rotary spectra from accelerometers on large ice floes. Journal of Atmospheric and Oceanic Technology.  ISSN 0739-0572.  34(5), s 1125- 1137 . doi: 10.1175/JTECH-D-16-0219.1 Fulltekst i vitenarkiv.
• Ayati, Anis Awal; Kolaas, Jostein; Jensen, Atle & Johnson, George William (2016). The effect of interfacial waves on the turbulence structure of stratified air/water pipe flow. International Journal of Multiphase Flow.  ISSN 0301-9322.  78, s 104- 116 . doi: 10.1016/j.ijmultiphaseflow.2015.09.007
• Kolaas, Jostein; Smith, Lisa; Jensen, Atle & Sveen, Johan Kristian (2016). Bichromatic Synthetic Schlieren for surface measurement, In  Proceedings of the 18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics.  Lisbon Simposia.  ISBN 978-989-98777-8-8.  Artikkel.  s 210 - 221 Fulltekst i vitenarkiv.
• Mossige, Endre Joachim; Jensen, Atle & Mielnik, Michal Marek (2016). An experimental characterization of a tunable separation device. Microfluidics and Nanofluidics.  ISSN 1613-4982.  20(12) . doi: 10.1007/s10404-016-1826-y Vis sammendrag

  By the use of an experimental setup for microfluidic flows, we have characterized the separation and concentration characteristics of the so-called Trilobite™ separation unit. Our separation unit consists of microfluidic channels and an elliptical separation geometry with a solid and a permeable wall region. We show that it is possible to adjust the thickness of different flow layers by changing the flow rates and pressure drop over the permeable wall. For high pressure drops, the separator shows promising concentration characteristics. For low pressure drops, an increase in flow rate results in a thinning of the flow layers. For sufficiently high flow rates, it should therefore be possible to create flow layers sufficiently thin that the particle separation is entirely dominated by hydrodynamic forces. This, in turn, will enable clog-free particle separation.

• Rabault, Jean; Sutherland, Graigory John; Ward, Brian; Christensen, Kai Håkon; Halsne, Trygve & Jensen, Atle (2016). Measurements of Waves in Landfast Ice Using Inertial Motion Units. IEEE Transactions on Geoscience and Remote Sensing.  ISSN 0196-2892.  54(11), s 6399- 6408 . doi: 10.1109/TGRS.2016.2584182
• Smith, Lisa; Hu, Bin; Kolaas, Jostein; Jensen, Atle & Sveen, Johan Kristian (2016). X-ray PTV Measurements of Solitary Waves, In  Proceedings of the 18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics.  Lisbon Simposia.  ISBN 978-989-98777-8-8.  Artikkel.  s 2604 - 2612 Fulltekst i vitenarkiv.
• Yang, Zhaochu; Dong, Tao; Jensen, Atle & Halvorsen, Einar (2016). Integratable Capacitive Sensor for Identification of Microfluidic Two-Phase Flow Patterns in Lab-on-Chip Devices. Journal of microelectromechanical systems.  ISSN 1057-7157.  25(1), s 197- 206 . doi: 10.1109/JMEMS.2015.2502281 Vis sammendrag

  This paper presents a feasible solution for a real-time sensing of microfluidic two-phase flow in lab-on-chip devices. A capacitive flow pattern sensor has been realized by employing an interdigital electrode configuration and a thin dielectric film. Three main flow patterns were observed in the microchannel, namely, droplet, short slug, and long slug flows. The output signal from the sensor was a real-time capacitance variation induced by the different flow patterns passing the sensing area. Experimental results give an indication of the flow patterns, due to the profile of capacitance variation. Furthermore, the identification of the flow patterns was achieved by autocorrelation of the capacitance variation and evaluation of a constant, specific for a given flow pattern in terms of linear velocity relation. This two-phase flow pattern sensor has potential to be used with other fluids, as long as they are immiscible and have very distinct dielectric properties.

• Ayati, Anis Awal; Kolaas, Jostein; Jensen, Atle & Johnson, George William (2015). Combined simultaneous two-phase PIV and interface elevation measurements in stratified gas/liquid pipe flow. International Journal of Multiphase Flow.  ISSN 0301-9322.  74, s 45- 58 . doi: 10.1016/j.ijmultiphaseflow.2015.03.024
• Grafsrønningen, Stig & Jensen, Atle (2015). Unsteady Reynolds averaged Navier–Stokes simulations of a buoyant plume above a cylinder. Proceedings of the Institution of Civil Engineers: Engineering and Computational Mechanics.  ISSN 1755-0777.  168(1), s 35- 42 . doi: 10.1680/eacm.12.00014
• Kolaas, Jostein; Drazen, David Adam & Jensen, Atle (2015). Lagrangian measurements of two-phase pipe flow using combined PIV/PTV. Journal of Dispersion Science and Technology.  ISSN 0193-2691.  36(10), s 1473- 1482 . doi: 10.1080/01932691.2014.996888
• Taklo, Tore Magnus Arnesen; Trulsen, Karsten; Gramstad, Odin; Krogstad, Harald E & Jensen, Atle (2015). Measurement of the dispersion relation for random surface gravity waves. Journal of Fluid Mechanics.  ISSN 0022-1120.  766, s 326- 336 . doi: 10.1017/jfm.2015.25 Fulltekst i vitenarkiv.
• Ayati, Anis Awal; Kolaas, Jostein; Jensen, Atle & Johnson, George William (2014). A PIV investigation of stratified gas-liquid flow in a horizontal pipe. International Journal of Multiphase Flow.  ISSN 0301-9322.  61, s 129- 143 . doi: 10.1016/j.ijmultiphaseflow.2014.01.008
• Ayati, Anis Awal; Tutkun, Murat & Jensen, Atle (2014). PIV measurement of two-phase pipe flows: from idealized air/water conditions to more realistic oil/SF6 flows at high pressure.. arXiv.org.  ISSN 2331-8422.
• Grue, John; Kolaas, Jostein & Jensen, Atle (2014). Velocity fields in breaking-limited waves of finite depth. European journal of mechanics. B, Fluids.  ISSN 0997-7546.  47, s 97- 107 . doi: 10.1016/j.euromechflu.2014.03.014 Fulltekst i vitenarkiv.
• Harbitz, Carl Bonnevie; Glimsdal, Sylfest; Løvholt, Finn; Kveldsvik, Vidar; Pedersen, Geir Kleivstul & Jensen, Atle (2014). Rockslide tsunamis in complex fjords: From an unstable rock slope at Åkerneset to tsunami risk in western Norway. Coastal Engineering.  ISSN 0378-3839.  88, s 101- 122 . doi: 10.1016/j.coastaleng.2014.02.003 Vis sammendrag

  An unstable rock volumeof more than 50 millionm3 has been detected in the Åkerneset rock slope in the narrow fjord, Storfjorden, Møre & Romsdal County, Western Norway. If large portions of the volume are released as a whole, the rockslide will generate a tsunami that may be devastating to several settlements and numerous visiting tourists along the fjord. The threat is analysed by amultidisciplinary approach spanning fromrock-slope stability via rockslide and wave mechanics to hazard zoning and risk assessment. The rockslide tsunami hazard and the tsunami early-warning system related to the two unstable rock slopes at Åkerneset and Hegguraksla in the complex fjord systemare managed by Åknes/Tafjord Beredskap IKS (previously the Åknes/Tafjord project). The present paper focuses on the tsunami analyses performed for this company to better understand the effects of rockslide-generated tsunamis fromÅkerneset and Hegguraksla. Two- and threedimensional site-specific laboratory experiments are conducted to study the generation, propagation, and run-up of thewave for several potential rockslide scenarios fromÅkerneset. Furthermore, the two models GloBouss and DpWaves are applied for numerical simulations of the generation/propagation phase and a third model MOST is applied for numerical simulations of the near-shore propagation and inundation of the wave in selected locations. Strong emphasis is put on verification, validation, and sensitivity of the numerical models. The best match between the numerical simulations and the laboratory experiments is found for the larger scenarios with the linear dispersive solution for the propagation phase; the corresponding calculated run-up values are remarkably similar to the ones observed during the laboratory experiments. During the risk assessment it was found that the rockslide tsunami hazard (probability of impact) is higher than accepted by the Norwegian Planning and Building Act. This should at that time prevent any further development in all the exposed areas of the entire fjord system. The Act is today altered to open for specified further development in the various hazard zones. The results of the tsunami analyses are applied in risk management in terms of hazard map production and land-use planning. Two failure scenarios for each of the two unstable rock slopes are designed for the hazard zoning. The larger and less probable scenarios (1 in 5000 years) are applied for evacuation zones and routes, while the smaller and more probable scenarios (larger than 1 in 1000 years) are applied for location and design of less critical facilities accepted in the inundation zone.

• Lindstrøm, Erika Kristina; Pedersen, Geir Kleivstul; Jensen, Atle & Glimsdal, Sylfest (2014). Experiments on slide generated waves in a 1:500 scale fjord model. Coastal Engineering.  ISSN 0378-3839.  92, s 12- 23 . doi: 10.1016/j.coastaleng.2014.06.010 Vis sammendrag

  An unstable rock-slope is detected in Åkerneset, located in Storfjorden, Western Norway. In the future this rockslope will produce a slide and a subsequent tsunami. In accordance to this future event, experiments in a 1:500 scale model of the inner part of Storfjorden are performed,where themodel geometry is made after the real fjord bathymetry, while the slide is an idealized slide of block-type. The slide motion is monitored and the generated waves are measured at a number of wave gauges in the model. At selected locations local details of the flow, velocities and inundation are measured by digital image techniques and acoustic probes. Features of the wave system and the inundation are elaborately discussed with a view to the future event as well as to the application of models.

• Grafsrønningen, Stig & Jensen, Atle (2013). Natural convection heat transfer from three vertically arranged horizontal cylinders with dissimilar separation distance at moderately high Rayleigh numbers. International Journal of Heat and Mass Transfer.  ISSN 0017-9310.  57(2), s 519- 527 . doi: 10.1016/j.ijheatmasstransfer.2012.10.076
• Kolaas, Jostein; Jensen, Atle & Mielnik, Michal Marek (2013). Visualization and measurements of flows in micro silicon Y-channels. The European Physical Journal E : Soft matter.  ISSN 1292-8941.  36(2) . doi: 10.1140/epje/i2013-13019-x Vis sammendrag

  Velocities and accelerations are measured and visualized in silicon microchannels using particle tracking velocimetry (PTV). Both pulsatile and stationary flows are generated in channels with different geometry. Distinct differences between flow regimes and geometries are shown. Flow separation occurred at Re = 84 for the channel with an expanded bifurcation shown by streamlines from long exposed images. Moving least squares are used to find the ensemble-averaged positions of the measured velocities from tracking. This is needed to find the local and convective accelerations.

• Mo, Weihua; Jensen, Atle & Liu, Philip L.F. (2013). Plunging solitary wave and its interaction with a slender cylinder on a sloping beach. Ocean Engineering.  ISSN 0029-8018.  74(1), s 48- 60 . doi: 10.1016/j.oceaneng.2013.09.011
• Pedersen, Geir Kleivstul; Lindstrøm, Erika Kristina; Bertelsen, Arnold F; Jensen, Atle; Laskovski, Daniela & Sælevik, Gunnstein (2013). Runup and boundary layers on sloping beaches. Physics of fluids.  ISSN 1070-6631.  25(1) . doi: 10.1063/1.4773327
• Sælevik, Gunnstein; Jensen, Atle & Pedersen, Geir Kleivstul (2013). Runup of solitary waves on a straight and a composite beach. Coastal Engineering.  ISSN 0378-3839.  77, s 40- 48 . doi: 10.1016/j.coastaleng.2013.02.007
• Grafsrønningen, Stig & Jensen, Atle (2012). Natural convection heat transfer from two horizontal cylinders at high Rayleigh numbers. International Journal of Heat and Mass Transfer.  ISSN 0017-9310.  55(21-22), s 5552- 5564 . doi: 10.1016/j.ijheatmasstransfer.2012.05.033
• Grafsrønningen, Stig & Jensen, Atle (2012). Simultaneous PIV/LIF measurements of a transitional buoyant plume above a horizontal cylinder. International Journal of Heat and Mass Transfer.  ISSN 0017-9310.  55(15-16), s 4195- 4206 . doi: 10.1016/j.ijheatmasstransfer.2012.03.060
• Grue, John & Jensen, Atle (2012). Orbital velocity and breaking in steep random gravity waves. Journal of Geophysical Research - Oceans.  ISSN 2169-9275.  117 . doi: 10.1029/2012JC008024
• Drazen, David Adam; Lichtsteiner, Patrick; Häfliger, Philipp; Delbrück, Tobi & Jensen, Atle (2011). Toward real-time particle tracking using an event-based dynamic vision sensor. Experiments in Fluids.  ISSN 0723-4864.  51(5), s 1465- 1469 . doi: 10.1007/s00348-011-1207-y
• Grafsrønningen, Stig; Jensen, Atle & Reif, Bjørn Anders Pettersson (2011). PIV investigation of buoyant plume from natural convection heat transfer above a horizontal heated cylinder. International Journal of Heat and Mass Transfer.  ISSN 0017-9310.  54(23-24), s 4975- 4987 . doi: 10.1016/j.ijheatmasstransfer.2011.07.011
• Gyles, Brian; Grafsrønningen, Stig; Dahl, Tine Bauck; Hægland, Bjarte; Schüller, Reidar Barfod; Jensen, Atle & Sanchis, Arnaud Clovis Marcel (2011). Natural Convention - Subsea Cooling; Theory, Simultations, Experiments and Design, In  Volume 1: Offshore Technology; Polar and Arctic Sciences and Technology.  ASME Press.  ISBN 978-0-7918-4433-5.  OMAE2011-49030.  s 11 - 20
• Sanchis, Arnaud Clovis Marcel & Jensen, Atle (2011). Dynamic masking of PIV images using the Radon transform in free surface flows. Experiments in Fluids.  ISSN 0723-4864.  51(4), s 871- 880 . doi: 10.1007/s00348-011-1101-7
• Sanchis, Arnaud Clovis Marcel; Johnson, George William & Jensen, Atle (2011). The formation of hydrodynamic slugs by the interaction of waves in gas–liquid two-phase pipe flow. International Journal of Multiphase Flow.  ISSN 0301-9322.  37(4), s 358- 368 . doi: 10.1016/j.ijmultiphaseflow.2010.11.005
• Fructus, Dorian; Carr, M; Grue, John; Jensen, Atle & Davies, PA (2009). Shear-induced breaking of large internal solitary waves. Journal of Fluid Mechanics.  ISSN 0022-1120.  620, s 1- 29 . doi: 10.1017/S0022112008004898
• Skartlien, R.; Drazen, David Adam; Swailes, DC & Jensen, Atle (2009). Suspensions in turbulent liquid pipe flow: Kinetic modelling and added mass effects. International Journal of Multiphase Flow.  ISSN 0301-9322.  35(11), s 1017- 1035 . doi: 10.1016/j.ijmultiphaseflow.2009.07.001
• Sælevik, Gunnstein; Jensen, Atle & Pedersen, Geir Kleivstul (2009). Experimental investigation of impact generated tsunami; related to a potential rock slide, Western Norway. Coastal Engineering.  ISSN 0378-3839.  56(9), s 897- 906 . doi: 10.1016/j.coastaleng.2009.04.007
• Carr, Magda; Fructus, Dorian; Grue, John; Jensen, Atle & Davies, Peter A. (2008). Convectively induced shear instability in large amplitude internal solitary waves. Physics of fluids.  ISSN 1070-6631.  20(126601)
• Lader, PF; Olsen, A; Jensen, Atle; Sveen, JK; Fredheim, A & Enerhaug, B (2007). Experimental investigation of the interaction between waves and net structures - Damping mechanism. Aquacultural Engineering.  ISSN 0144-8609.  37, s 100- 114 . doi: 10.1016/j.aquaeng.2007.03.001
• Jensen, Atle; Clamond, Didier; Huseby, Morten & Grue, John (2007). On local and convective accelerations in steep wave events. Ocean Engineering.  ISSN 0029-8018.  34 . doi: 10.1016/j.oceaneng.2006.03.013
• Lader, Pål; Jensen, Atle; Sveen, Johan Kristian; Fredheim, Arne; Enerhaug, Birger & Fredriksson, D (2007). Experimental investigation of wave forces on net structures. Applied Ocean Research.  ISSN 0141-1187.  29(3), s 112- 127 . doi: 10.1016/j.apor.2007.10.003
• Grue, John & Jensen, Atle (2006). Experimental velocities and accelerations in very steep wave events in deep water. European journal of mechanics. B, Fluids.  ISSN 0997-7546.  25, s 554- 564
• Jensen, Atle; Mayer, Stefan & Pedersen, Geir Kleivstul (2005). Experiments and computation of onshore breaking solitary waves. Measurement science and technology.  ISSN 0957-0233.  16, s 1913- 1920
• Clamond, Didier; Grue, John; Jensen, Atle & Huseby, Morten (2004). PIV measurements of the velocity field in steep wave events, In  PIV and Water Waves.  World Scientific.  ISBN 981-238-914-8.  7.2.  s 282 - 284
• Jensen, Atle; Huseby, Morten; Clamond, Didier; Pedersen, Geir Kleivstul & Grue, John (2004). PIV measurements of accelerations in water waves, In  PIV and Water Waves.  World Scientific.  ISBN 981-238-914-8.  7.1.  s 279 - 281
• Jensen, Atle & Pedersen, Geir Kleivstul (2004). Optimization of acceleration measurements using PIV. Measurement science and technology.  ISSN 0957-0233.  15, s 2275- 2283
• Jensen, Atle; Pedersen, Geir Kleivstul & Wood, Deborah (2003). An experimental study of wave run-up at a steep beach. Journal of Fluid Mechanics.  ISSN 0022-1120.  486, s 161- 181
• Wood, Deborah; Pedersen, Geir Kleivstul & Jensen, Atle (2003). Modelling of run up of steep non-breaking waves. Ocean Engineering.  ISSN 0029-8018.  30, s 625- 644
• Grue, John; Clamond, Didier; Huseby, Morten & Jensen, Atle (2003). Kinematics of extreme waves in deep water. Applied Ocean Research.  ISSN 0141-1187.  25, s 355- 366
• Jensen, Atle & Grue, John (2002). On the difference in the speed of gravity waves in a physical and numerical wave tank. Wave motion.  ISSN 0165-2125.  36
• Jensen, Atle; Sveen, Johan Kristian; Grue, John; Richon, J. B. & Gray, C. (2001). Accelerations in water waves by extended Particle Image Velocimetry. Experiments in Fluids.  ISSN 0723-4864.  30
• Grue, John; Jensen, Atle; Rusås, Per-Olav & Sveen, J. Kristian (2000). Breaking and broadening of internal solitary waves. Journal of Fluid Mechanics.  ISSN 0022-1120.  413, s 181- 217
• Grue, John; Jensen, Atle; Rusås, Per-Olav & Sveen, Johan Kristian (2000). Breaking and broadening of internal solitary waves. Journal of Fluid Mechanics.  ISSN 0022-1120.  413
• Grue, John; Jensen, Atle; Rusås, Per-Olav & Sveen, Johan Kristian (1999). Properties of large amplitude internal waves. Journal of Fluid Mechanics.  ISSN 0022-1120.  380, s 257- 278 Vis sammendrag

  Properties of solitary waves propagating in a two-layer fluid are investigated comparing experiments and theory. In the experiments the velocity field induced by the waves, the propagation speed and the wave shape are quite accurately measured using particle tracking velocimetry (PTV) and image analysis. The experiments are calibrated with a layer of fresh water above a layer of brine. The depth of the brine is 4.13 times the depth of the fresh water. Theoretical results are given for this depth ratio, and, in addition, in a few examples for larger ratios, up to 100[ratio]1. The wave amplitudes in the experiments range from a small value up to almost maximal amplitude. The thickness of the pycnocline is in the range of approximately 0.13-0.26 times the depth of the thinner layer. Solitary waves are generated by releasing a volume of fresh water trapped behind a gate. By careful adjustment of the length and depth of the initial volume we always generate a single solitary wave, even for very large volumes. The experiments are very repeatable and the recording technique is very accurate. The error in the measured velocities non-dimensionalized by the linear long wave speed is less than about 7-8% in all cases. The experiments are compared with a fully nonlinear interface model and weakly nonlinear Korteweg-de Vries (KdV) theory. The fully nonlinear model compares excellently with the experiments for all quantities measured. This is true for the whole amplitude range, even for a pycnocline which is not very sharp. The KdV theory is relevant for small wave amplitude but exhibit a systematic deviation from the experiments and the fully nonlinear theory for wave amplitudes exceeding about 0.4 times the depth of the thinner layer. In the experiments with the largest waves, rolls develop behind the maximal displacement of the wave due to the Kelvin-Helmholtz instability. The recordings enable evaluation of the local Richardson number due to the flow in the pycnocline. We find that stability or instability of the flow occurs in approximate agreement with the theorem of Miles and Howard.

Se alle arbeider i Cristin

• Rabault, Jean; Jensen, Atle; Sutherland, Graig & Christensen, Kai Håkon (2018). An investigation into the interaction between waves and ice.
• Rabault, Jean; Kolaas, Jostein & Jensen, Atle (2018). Using modern Artificial Neural Networks for performing end-to-end Particle Image Velocimetry.
• Rabault, Jean; Sutherland, Graig & Jensen, Atle (2018). Novel Field and Laboratory Observations of Wave-ice Interactions in Various Sea Ice Types.
• Mossige, Endre Joachim; Jensen, Atle & Mielnik, Michal Marek (2017). Erratum to: An experimental characterization of a tunable separation device. Microfluidics and Nanofluidics.  ISSN 1613-4982.  21(1) . doi: 10.1007/s10404-016-1833-z
• Rabault, Jean; Sutherland, Graigory John & Jensen, Atle (2017). Investigation of wave damping by grease ice through field measurements and laboratory experiments..
• Sutherland, Graigory John; Rabault, Jean & Jensen, Atle (2017). A Look at the Directional Spread in Sea Ice: Observations from the Barents Sea..
• Ayati, Anis Awal & Jensen, Atle (2016). Wave induced fluctuations in the gas phase of stratified gas-liquid pipe flow.
• Rabault, Jean; Halsne, Trygve; Sutherland, Graigory John & Jensen, Atle (2016). PTV investigation of the mean drift currents under water waves.
• Rabault, Jean; Sutherland, Graigory John & Jensen, Atle (2016). Measurements of waves in Landfast Ice in Svalbard: Effect of flexural stress on waves properties.
• Ayati, Anis Awal & Jensen, Atle (2015). Wind-Wave Interaction in Stratified Gas/Liquid Pipe Flow. 17th International Conference on Multiphase Production Technology.
• Mossige, Endre Joachim; Jensen, Atle & Mielnik, Michal Marek (2015). Characterization of the Trilobite Hydrodynamic Particle Separation Microchip with μPIV. Vis sammendrag

  A hydrodynamic micro particle separator has been tested by means of streakline visualizations and Particle Image Velocimetry (PIV) for different flow configurations. By adjusting the pressure drop and the Reynolds number, it is possible to determine the thickness of a flow layer that ends up as permeate. The results of the streakline visualizations show that the permeate flow thickness decreases with decreasing pressure drop between the inlet and the permeate outlet. Increasing the Reynolds number has the same effect. A phase averaged PIV method was used to extract the velocity fields from the image data. By visual inspection of the velocity vector plots, it was found that the location of the stagnation points on the separator pillars depend on the Reynolds number.

• Rabault, Jean; Sutherland, Graigory John; Christensen, Kai H.; Halsne, Trygve & Jensen, Atle (2015). Measurements of waves in ice using IMUs: instruments assessment and wave detection in landfast ice in Svalbard.
• Lindstrøm, Erika Kristina; Jensen, Atle; Pedersen, Geir Kleivstul & Glimsdal, Sylfest (2013). Scale effects and stability of viscous boundary layers in wave tank experiments.
• Lindstrøm, Erika Kristina; Jensen, Atle; Pedersen, Geir Kleivstul; Glimsdal, Sylfest & Sælevik, Gunnstein (2013). Impact and wave generation by sub-aerial slides in a fjord geometry.
• Taklo, Tore Magnus Arnesen; Trulsen, Karsten; Gramstad, Odin; Krogstad, Harald E & Jensen, Atle (2013). Direct measurement of dispersion relation for random surface gravity waves on deep water.
• Taklo, Tore Magnus Arnesen; Trulsen, Karsten; Krogstad, Harald E; Gramstad, Odin; Nieto Borge, Jose Carlos & Jensen, Atle (2013). Direct measurement of nonlinear dispersion relation for water surface waves.
• Grafsrønningen, Stig; Jensen, Atle & Reif, Bjørn Anders Pettersson (2012). PIV investigation of a buoyant plume above heated horizontal cylinder.
• Lindstrøm, Erika Kristina; Jensen, Atle; Pedersen, Geir Kleivstul; Sælevik, Gunstein & Glimsdal, Sylfest (2012). Impact and wave generation by sub-aerial slides in a fjord geometry.
• Lindstrøm, Erika Kristina; Pedersen, Geir Kleivstul; Jensen, Atle & Bertelsen, Arnold F (2012). Evolution of boundary layers on beaches.
• Lindstrøm, Erika Kristina; Pedersen, Geir Kleivstul; Jensen, Atle & Bertelsen, Arnold F (2012). Evolution of boundary layers on beaches.
• Gyles, Brian; Hægland, Bjarte; Dahl, Tine Bauck; Sanchis, Arnaud Clovis Marcel; Grafsrønningen, Stig; Schüller, Reidar Barfod & Jensen, Atle (2011). Natural convection - Subsea cooling; Theory, simulations, experiments and design.
• Jensen, Atle (2011). Flows in pipes and channels.
• Jensen, Atle (2010). Runup of solitary waves and wave impact on a vertical wall; experiments and computations.
• Kolaas, Jostein & Jensen, Atle (2010). Lagrangian measurements, using highspeed PTV in turbulent pipe flow.
• Jensen, Atle; Mayer, Stefan & Pedersen, Geir Kleivstul (2005). A breaking wave; experiments and computations.
• Jensen, Atle; Pedersen, Geir Kleivstul & Mayer, Stefan (2005). Dynamics of a collapsing breaking wave.
• Trulsen, Karsten; Jensen, Atle & Grue, John (2005). Water wave kinematics of steep irregular waves - systematic perturbation approach, empirical law, PIV measurements and engineering practice.
• Clamond, Didier; Grue, John; Huseby, Morten & Jensen, Atle (2003). Theoretical and experimental analysis of the velocity profile under crest of extreme water waves.
• Jensen, Atle & Sveen, Johan Kristian (2002). High-speed digital camera and image processing system enables reliable PIV measurements in water waves. InVision.  2(1)
• Sveen, Johan Kristian & Jensen, Atle (2002, 01. oktober). Image-processing system speeds water-wave analysis. [Internett].  Vision System design.
• Clamond, Didier; Grue, John; Huseby, Morten & Jensen, Atle (2002). PIV measurements of the velocity field in steep waver wave events.
• Jensen, Atle; Huseby, Morten; Clamond, Didier; Pedersen, Geir Kleivstul & Grue, John (2002). PIV measurements of accelerations in water waves.
• Grue, John; Jensen, Atle; Rusås, Per-Olav & Sveen, Johan Kristian (2000). On the dynamics of highly nonlinear solitary waves in a stratified fluid.
• Grue, John; Jensen, Atle; Rusås, Per-Olav & Sveen, Johan Kristian (2000). Solitary waves in stratified fluid: modelling and experiment.
• Huseby, Morten; Jensen, Atle & Grue, John (2000). An experimental investigation of ringing loads on a vertical cylinder in transient waves. Vis sammendrag

  Over the last years we have worked with experiments on higher harmonic wave loads on a vertical cylinder in a wave tank. This was motivated by ringing events observed in model tests of large off shore structures. The ringing problem also partly motivated development of numerical models which predict higher harmonic forces. Since the frequency of the ringing oscillation typically is about 3-5 times the fundamental frequency of incoming waves, the third harmonic component of the force was hoped to possibly give an explanation of the ringing problem. Testing the accuracy and the region of validity of these models was also a motivation for us in our previous work.

• Jensen, Atle; Sveen, Johan Kristian; Huseby, Morten & Grue, John (2000). Measurements of velocities and accelerations in steep irregular water waves.
• Grue, John; Huseby, Morten; Jensen, Atle & Sveen, Johan Kristian (1999). Modelltankdemonstrasjon av bolger til havs.

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