Lars Willas Dreyer

• 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.

• 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.

• 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.

• Dreyer, Lars Willas; Eklund, Anders; Rognes, Marie Elisabeth; Malm, Jan; Qvarlander, Sara & Støverud, Karen-Helene [Vis alle 8 forfattere av denne artikkelen] (2024). Modeling CSF circulation and the glymphatic system during infusion using subject specific intracranial pressures and brain geometries. Fluids and Barriers of the CNS. 21(1). doi: 10.1186/s12987-024-00582-0. Fulltekst i vitenarkiv Vis sammendrag

  Background Infusion testing is an established method for assessing CSF resistance in patients with idiopathic normal pressure hydrocephalus (iNPH). To what extent the increased resistance is related to the glymphatic system is an open question. Here we introduce a computational model that includes the glymphatic system and enables us to determine the importance of (1) brain geometry, (2) intracranial pressure, and (3) physiological parameters on the outcome of and response to an infusion test. Methods We implemented a seven-compartment multiple network porous medium model with subject specific geometries from MR images using the finite element library FEniCS. The model consists of the arterial, capillary and venous blood vessels, their corresponding perivascular spaces, and the extracellular space (ECS). Both subject specific brain geometries and subject specific infusion tests were used in the modeling of both healthy adults and iNPH patients. Furthermore, we performed a systematic study of the effect of variations in model parameters. Results Both the iNPH group and the control group reached a similar steady state solution when subject specific geometries under identical boundary conditions was used in simulation. The difference in terms of average fluid pressure and velocity between the iNPH and control groups, was found to be less than 6% during all stages of infusion in all compartments. With subject specific boundary conditions, the largest computed difference was a 75% greater fluid speed in the arterial perivascular space (PVS) in the iNPH group compared to the control group. Changes to material parameters changed fluid speeds by several orders of magnitude in some scenarios. A considerable amount of the CSF pass through the glymphatic pathway in our models during infusion, i.e., 28% and 38% in the healthy and iNPH patients, respectively. Conclusions Using computational models, we have found the relative importance of subject specific geometries to be less important than individual differences in resistance as measured with infusion tests and model parameters such as permeability, in determining the computed pressure and flow during infusion. Model parameters are uncertain, but certain variations have large impact on the simulation results. The computations resulted in a considerable amount of the infused volume passing through the brain either through the perivascular spaces or the extracellular space.

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