Atle Jensen

• Ramirez de La Torre, Reyna Guadalupe & 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.
• Løken, Trygve Kvåle; Lande-Sudall, David Roger; Jensen, Atle & Rabault, Jean (2024). Grid Turbulence Measurements with an Acoustic Doppler Current Profiler. Fluids. ISSN 2311-5521. 9(3), s. 1–14. doi: 10.3390/fluids9030060. Fulltekst i vitenarkiv Vis sammendrag

  The motivation for this study is to investigate the abilities and limitations of a Nortek Signature1000 acoustic Doppler current profiler (ADCP) regarding fine-scale turbulence measurements. Current profilers offer the advantage of gaining more coherent measurement data than available with point acoustic measurements, and it is desirable to exploit this property in laboratory and field applications. The ADCP was tested in a towing tank, where turbulence was generated from a grid towed under controlled conditions. Grid-induced turbulence is a well-studied phenomenon and a good approximation for isotropic turbulence. Several previous experiments are available for comparison and there are developed theories within the topic. In the present experiments, a Nortek Vectrino acoustic Doppler velocimeter (ADV), which is an established instrument for turbulence measurements, was applied to validate the ADCP. It was found that the mean flow measured with the ADCP was accurate within 4% of the ADV. The turbulent variance was reasonably well resolved by the ADCP when large grid bars were towed at a high speed, but largely overestimated for lower towing speed and smaller grid bars. The effective cutoff frequency and turbulent eddy size were characterized experimentally, which provides detailed guidelines for when the ADCP data can be trusted and will allow future experimentalists to decide a priori if the Nortek Signature can be used in their setup. We conclude that the ADCP is not suitable for resolving turbulent spectra in a small-scale grid-induced flow due to the intrinsic Doppler noise and the low spatial and temporal sample resolution relative to the turbulent scales.

• 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.
• Weber, Jan Erik H.; Whitchelo, Yiyi; Pirolt, Jon Alexander; Christensen, Kai Håkon; Rabault, Jean & Jensen, Atle (2023). Observations of transient wave-induced mean drift profiles caused by virtual wave stresses in a two-layer system. Journal of Fluid Mechanics. ISSN 0022-1120. 975( A12). doi: 10.1017/jfm.2023.864. Fulltekst i vitenarkiv
• Iida, Takahito; Jensen, Atle & Zen, Maria (2023). Simplified estimation of wave attenuation in marginal ice zone using homogenized scattering model. Applied Ocean Research. ISSN 0141-1187. 138. doi: 10.1016/j.apor.2023.103663. Fulltekst i vitenarkiv
• Feneuil, Blandine Fleur Prudence; Iqbal, Kasi Tassawar; Jensen, Atle; Brandt, Luca; Tammisola, Outi & Carlson, Andreas (2023). Experimental and numerical investigation of bubble migration in shear flow: Deformability-driven chaining and repulsion. Physical Review Fluids. ISSN 2469-990X. 8(6). doi: 10.1103/PhysRevFluids.8.063602. Fulltekst i vitenarkiv Vis sammendrag

  We study the interaction-induced migration of bubbles in shear flow and observe that bubbles suspended in elastoviscoplastic emulsions organize into chains aligned in the flow direction, similarly to particles in viscoelastic fluids. To investigate the driving mechanism, we perform experiments and simulations on bubble pairs, using suspending fluids with different rheological properties. First, we notice that, for all fluids, the interaction type depends on the relative position of the bubbles. If they are aligned in the vorticity direction, then they repel, if not, then they attract each other. The simulations show a similar behavior in Newtonian fluids as in viscoelastic and elastoviscoplastic fluids, as long as the capillary number is sufficiently large. This shows that the interaction-related migration of the bubbles is strongly affected by the bubble deformation. We suggest that the cause of migration is the interaction between the heterogeneous pressure fields around the deformed bubbles, due to capillary pressure.

• Ramirez de La Torre, Reyna Guadalupe & Jensen, Atle (2023). Sizing of particles and droplets using 3D-PTV, an OpenPTV post-processing tool. Measurement Science and Technology. ISSN 0957-0233. 34(6). doi: 10.1088/1361-6501/acc11d. Fulltekst i vitenarkiv
• Rabault, Jean; Müller, Malte; Voermans, Joey; Brazhnikov, Dmitry; Turnbull, Ian & Marchenko, Aleksey [Vis alle 28 forfattere av denne artikkelen] (2023). A dataset of direct observations of sea ice drift and waves in ice. Scientific Data. ISSN 2052-4463. 10. doi: 10.1038/s41597-023-02160-9. Fulltekst i vitenarkiv Vis sammendrag

  Variability in sea ice conditions, combined with strong couplings to the atmosphere and the ocean, lead to a broad range of complex sea ice dynamics. More in-situ measurements are needed to better identify the phenomena and mechanisms that govern sea ice growth, drift, and breakup. To this end, we have gathered a dataset of in-situ observations of sea ice drift and waves in ice. A total of 15 deployments were performed over a period of 5 years in both the Arctic and Antarctic, involving 72 instruments. These provide both GPS drift tracks, and measurements of waves in ice. The data can, in turn, be used for tuning sea ice drift models, investigating waves damping by sea ice, and helping calibrate other sea ice measurement techniques, such as satellite based observations.

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• Rabault, Jean; Müller, Malte; Hope, Gaute; Breivik, Øyvind; Nose, Takehiko & Voermans, Joey [Vis alle 16 forfattere av denne artikkelen] (2023). Collecting Marginal Ice Zone ground truth observations: recent deployments, data use, and outstanding questions.
• Feneuil, Blandine Fleur Prudence; Carlson, Andreas; Jensen, Atle; Iqbal, Kazi Tassawar; Tammisola, Outi & Brandt, Luca (2022). Bubble migration in complex fluids: experiments and simulations.

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