Atle Jensen

• Lande, Øystein; Meyer, Herman Martens; Dreyer, Lars Willas; Rabault, Jean; Krzywkowski, Théo & Jensen, Atle (2026). Feasibility Study of an Ultra-Low-Cost 3D-Printed Wave Buoy for Water Wave Measurement. Water Waves. ISSN 2523-367X. doi: 10.1007/s42286-026-00153-w. Fulltekst i vitenarkiv Vis sammendrag

  This paper presents a feasibility study of an ultra-low-cost wave buoy for measuring water waves, built from a 3D-printed hull and an off-the-shelf data logger with an integrated MEMS inertial measurement unit. The buoy records continuously and carries no telemetry, which reduces the average power consumption to 4.7 mA, so that two D-cell batteries sustain more than 6 months of sampling at 100 Hz. A custom firmware stores the raw sensor data in binary form with a GPS-disciplined UTC time base, and the surface elevation is reconstructed in postprocessing through orientation estimation, removal of the gravity component, adaptive band selection, and double integration. The validation is organized so that each stage isolates a single source of error. Under pure translation, where the orientation of the sensor is constant, the measured acceleration amplitude equals the target on average and three sensors agree with one another to within 1–2%. Under pure rotation about an axis through the sensor, where the true vertical displacement is zero, the reconstructed angle agrees with an exact reference to within 1.6%. The stationary noise of the sensor is propagated through the processing chain to give the smallest resolvable excursion as a function of period, and the response of the hull is computed by a radiation–diffraction analysis and confirmed by free-decay tests. The complete system is then tested in nine irregular sea states in a wave basin, with peak periods from 1 to 3 s and steepness from 0.011 to 0.033. The reconstructed motion reproduces the optically tracked motion of the buoy closely in every sea state. Compared with a fixed wave probe, the buoy records lower crests and deeper troughs, and the difference grows with steepness, which reflects the response of a freely floating body to the wave field rather than an error of the instrument. The total materials cost is below $200, and we conclude that 3D printing combined with low-cost MEMS sensors provides a viable route to affordable wave measurement, in particular for sheltered and nearshore waters where the wave periods are short.

• Lande, Øystein; Jensen, Atle & Johannessen, Thomas Berge (2026). A laboratory experiment and procedure for deterministic validation of numerical wave models. Journal of Fluid Mechanics. ISSN 0022-1120. 1037. doi: 10.1017/jfm.2026.11658. Fulltekst i vitenarkiv Vis sammendrag

  We present an experimental dataset of focused dispersive wave groups, specifically designed to validate wave models and assess their capacity to propagate dispersive waves across significant distances in both deep- and shallow-water environments. The steepness of the wave groups varies from low to highly steep configurations, exhibiting pronounced nonlinear behaviours, including wave-breaking phenomena. The experiments were conducted in two distinct basin configurations: a constant-depth (deep water) set-up and a trapezoidal shoal, introducing inhomogeneity from deep- to shallow-water conditions. For selected tests, particle image velocimetry was used to capture kinematic measurements necessary for kinematics and energy assessment. Each test was performed with multiple repetitions to ensure data consistency and reliability. Furthermore, we utilised a Navier–Stokes two-phase flow model to demonstrate the reproducibility of wave groups in the numerical domain with a high degree of accuracy, employing the recorded wave paddle motion from the experiments as the boundary condition. The results were compared against linear wave theory where applicable, and we propose a benchmarking procedure for the systematic assessment and comparison of results across different wave models and varying levels of refinement.

• Su, Pin-Tzu; Didenkulova, Irina & Jensen, Atle (2025). Transport of tsunami-driven debris over a slope. Ocean Engineering. ISSN 0029-8018. 348. doi: 10.1016/j.oceaneng.2025.124028. Fulltekst i vitenarkiv Vis sammendrag

  We study tsunami-induced transport of heavy and floating debris over a slope. The work is performed experimentally in a small wave flume, which is 3 m long and 0.1 m wide with the water depth of 0.05 m. Tsunami is modeled by breaking solitary waves with amplitude (a), normalized by the water depth (hw) equal to a/hw = 0.5. Three succeeding waves propagate towards a sedimentary beach breaking on the slope, and impact debris which are initially placed at different locations along the slope with respect to the wave breaking point. We use spherical debris with two different densities. The heavy ones are lying on the slope, while the light ones are floating at the surface. The sea bed slope is covered with 0.02 m layer of sand. We use sediments of two different sizes to study the interaction of debris with sedimentary environment. The main measured parameter is displacement of the debris along the slope, which is analyzed with respect to the characteristics (densities) of the debris, their initial positions, number of consecutive waves and the size of the sediments

• Marchenko, Aleksey & Jensen, Atle (2025). Methods of laboratory investigations of wave drift of model icebergs. Proceedings - International Conference on Port and Ocean Engineering under Arctic Conditions. ISSN 0376-6756. doi: https:/www.poac.com/Papers/2025/pdf/POAC25_paper_40.pdf. Fulltekst i vitenarkiv Vis sammendrag

  An experiment was conducted at the University Centre in Svalbard to study the drift of model icebergs in an acrylic wave flume. A model scale of 1:400 was applied on both icebergs and waves. Iceberg models of cylindrical shape (floaters) were made from paraffin. The diameters and heights of the floaters were smaller 7 cm and 6 cm, respectively. All models had stable buoyancy with vertical axis in calm water. A plunger-type wave maker generated periodic waves with a frequencies less than 4 Hz in the tank. The video recordings were used to reconstruct the movements of the floater’s centers of gravity. The video recordings were processed in Wolfram Mathematica software and subjected to pixel analysis. A fiber optic strain sensor (FBG sensor) was used to measure the force applied to the floaters by waves. It was found that the mean drift speed of floaters is several times higher than the Stokes drift speed at the water surface. The amplitude of floaters movement in the vertical direction was similar the wave amplitude. The pitch oscillations of the floaters occurred around some constant non-zero pitch, which was absent in calm water. The mean value of the force applied to the floater turned out to be close was found close to the wave drift force acting on a fixed floater with a vertical axis of the same diameter as in the experiment.

• Rabault, Jean; Halsne, Trygve; Carrasco, Ana; Korosov, Anton; Voermans, Joey & Bohlinger, Patrik [Vis alle 28 forfattere av denne artikkelen] (2025). Buoy measurements of strong waves in ice amplitude modulation: a signature of the impact of sea ice closedness on waves in ice attenuation. The Cryosphere. ISSN 1994-0416. 19(11), s. 6229–6260. doi: 10.5194/tc-19-6229-2025. Fulltekst i vitenarkiv Vis sammendrag

  The Marginal Ice Zone (MIZ) forms a critical transition region between the ocean and sea ice cover, as it protects the close ice further in from the effect of the steepest and most energetic open ocean waves. As waves propagate through the MIZ, they become exponentially attenuated. Unfortunately, the associated attenuation coefficient is difficult to accurately estimate and model, and there are still large uncertainties around which attenuation mechanisms dominate depending on the conditions. This makes it difficult to predict waves in ice attenuation, as well as sea ice breakup and dynamics. Here, we report in situ observations of strongly modulated waves in ice amplitude, with a modulation period of around 12 h. We show that simple explanations, such as changes in the incoming open water waves or the direct effect of tides and currents and bathymetry on the propagating waves, cannot explain the observed modulation. Therefore, the wave height modulation observed in the ice comes from a modulation of the waves in ice attenuation coefficient. We gather evidence that sea ice convergence and divergence is likely the factor driving this modulation in the attenuation coefficient, through its influence on the ice “closedness”. This implies that the level of sea ice “closedness” needs to be taken into account by future dissipation parameterizations.

• Marchenko, Aleksey; Jensen, Atle; Rabault, Jean; Sutherland, Graig & Zenkin, Alex (2025). Experimental study of the drift of floating disks in regular waves. Applied Ocean Research. ISSN 0141-1187. 165. doi: 10.1016/j.apor.2025.104800. Fulltekst i vitenarkiv Vis sammendrag

  Small icebergs, bergy bits and fragments of consolidated ice ridges can gain significant kinetic energy and pose a significant impact threat for ships and offshore installations in the Barents Sea. An experimental study of the response of floating disks simulating bergy bits to regular waves was conducted in the wave flume of the University of Oslo. The geometric scale factor, which determines the ratios of the disk sizes and wavelengths at full and laboratory scales, was equal to 400. The study focused on the mean drift and surge motion of the disks. Based on the results of 50 tests, the dependencies of normalized mean drift velocities and surge amplitudes on three dimensionless parameters expressed via the diameters and heights of the disks, the wave amplitudes and wavelengths were approximated. Based on the experimental data, it has been found that regular swell with an amplitude of 1 m may influence the drift of bergy bits with an average velocity of about 40 cm/s. The amplitudes of surge and heave oscillations of bergy bits turned out to be similar to the amplitudes of the swell. The latter was confirmed by data obtained from a buoy equipped with an inertial measurement unit (IMU) installed on a bergy bit in the Barents Sea in 2019. A model of bergy bit drift under regular waves was formulated, based on the balance of wave drift forces, wave damping force, and form drag force. The form drag coefficient has been calculated depending on the product of the disk diameter and the wave number according to the model with using the experimental data.

• Dreyer, Lars Willas; Rabault, Jean; Jensen, Atle; Dæhlen, Ingrid; Kristoffersen, Yngve & Breivik, Øyvind [Vis alle 7 forfattere av denne artikkelen] (2025). Direct in-situ observations of wave-induced floe collisions in the deeper Marginal Ice Zone. Cold Regions Science and Technology. ISSN 0165-232X. 240. doi: 10.1016/j.coldregions.2025.104642. Fulltekst i vitenarkiv Vis sammendrag

  Ocean waves propagating through the Marginal Ice Zone (MIZ) and the pack ice are strongly attenuated. This attenuation is critical for protecting sea ice from energetic wave events that could otherwise lead to sea ice break-up and dislocation over large areas. Despite the importance of waves-in-ice attenuation, the exact physical mechanisms involved, and their relative importance, are still uncertain. Here we present direct in-situ measurements of floe-floe interactions under the influence of waves, including collisions between adjacent floes. The collision events we report are aligned with the incoming wave direction, and phase-locked to the wave signal, which indicates that the individual collisions we detect are wave-induced. The observations indicate a possible correlation between sudden increases in wave activity and the frequency of floe-floe collisions.

• Ølberg, Judith Thu; Bohlinger, Patrik; Breivik, Øyvind; Christensen, Kai Håkon; Furevik, Birgitte Rugaard & Hole, Lars Robert [Vis alle 11 forfattere av denne artikkelen] (2024). Wave measurements using open source ship mounted ultrasonic altimeter and motion correction system during the one ocean circumnavigation. Ocean Engineering. ISSN 0029-8018. 292. doi: 10.1016/j.oceaneng.2023.116586. Fulltekst i vitenarkiv Vis sammendrag

  This study reviews the design and signal processing of ship borne ultrasonic altimeter wave measurements. The system combines a downward facing ultrasonic altimeter to capture the sea surface elevation as a time series, and an inertial measurement unit to compensate for the ship’s motion. The methodology is cost-effective, open source, and adaptable to various ships and platforms. The system was installed on the barque Statsraad Lehmkuhl and recorded data continuously during the 20-month One Ocean Expedition. Results from 1-month crossing of the Tropical Atlantic are presented here. The one-dimensional wave spectrum and associated wave parameters are obtained from the sea surface elevation time series. The observed significant wave height agrees well with satellite altimetry and a spectral wave model. The agreement between observations and the spectral wave model is better for the mean wave period than the peak period. We perform Doppler shift corrections to improve wave period estimates by accounting for the speed of the ship relative to the waves. This correction enhances the accuracy of the mean period, but not the peak period. We suggest that the Doppler correction could be improved by complementing the data sources with directional wave measurements from a marine X-band radar.

• Torre, Reyna Guadalupe Ramirez de La & Jensen, Atle (2024). Experiments on droplet production from solitary waves impacting on a vertical wall. Ocean Engineering. ISSN 0029-8018. 301. doi: 10.1016/j.oceaneng.2024.117517. Fulltekst i vitenarkiv Vis sammendrag

  This work presents the results of an experimental investigation of solitary waves impacting on a vertical flat wall. The aim of the study was to correlate the wave characteristics and breaking stage before impact to the droplet production after the impact. The main characteristic of these experiments is that the wall height is lower than the wave height. The droplet sizes were obtained by combining 3D particle tracking velocimetry with an in-house code. Droplet diameters between 0.3–22 mm were measured at a distance of 35 cm and 68 cm from the wall. It was found that the breaking stage before the impact has a large influence on the mean size of the droplets produced, especially when there is air trapped between the wall and the wave at the impact moment. It was found that the mean droplet size decreases with the ratio of water jet velocity after impact and the wave speed. The resulting distributions of droplet sizes were compared to three different theoretical models used in other droplet production studies. Results were also compared to previous experimental studies of droplet formation from breaking waves to determine the best fit to the experimentally obtained distribution.

• Su, Pin-Tzu; Didenkulova, Ira & Jensen, Atle (2024). Solitary wave-induced boulder transport on a beach. Ocean Engineering. ISSN 0029-8018. 313. doi: 10.1016/j.oceaneng.2024.119318. Fulltekst i vitenarkiv Vis sammendrag

  The influence of sediment on a slope on boulder transport is studied experimentally at the Hydrodynamics Laboratory of the University of Oslo. Experiments are conducted in a small 3 m long and 10 cm wide wave tank, filled with 5 cm of water. The transport of boulders is induced by breaking solitary waves with an amplitude normalized by water depth a/ℎ𝑤 = 0.5. Generated solitary waves propagate towards a 1:10 beach. The experiments are conducted in two set-ups: (i) empty Polymethyl methacrylate (PMMA) bottom of the flume, (ii) the slope covered by a thin layer of 65 μm sand. The boulders are represented by concrete blocks of different shape and size. They are placed alternately (one at a time) at different locations on the beach slope with respect to wave breaking point. Transport of boulders and their dynamics is studied with respect to boulder characteristics (size, orientation), their initial position and inclusion of sediment. It is shown that presence of sediment enhances boulder transport. In particular, in this set-up, the presence of sediment increased the boulder transport in 2–5 times. The maximum displacement increase was observed for boulders with the smallest length and height and the largest width initially located at the breaking position. Another interesting result regards the type of boulder motion. The boulders experienced either sliding or turning over. Boulders whose height was at least twice as large as their length exhibited turning-over. This held for boulders placed both on an empty PMMA slope and on a sedimentary slope. However, the largest boulder displacement on an empty PMMA slope occurred due to turning over, while on a sedimentary slope it occurred due to sliding.

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