arXiv subjects

Olav Gundersen

Publications and source records attributed to Olav Gundersen.

8 recordsLinked to original sources

arXiv2026

Experimental investigation of a multi-buoy cooperative point-absorber wave energy converter

This study presents a proof-of-concept experimental investigation of a multi-buoy cooperative point-absorber wave energy converter (WEC). The proposed concept consists of an array of surface-penetrating buoys connected through a shared closed-loop hydraulic power take-off (PTO) system. Energy is extracted through the collective motion of the buoy array, where pressurised flow generated by individual buoys drives a turbine within the hydraulic circuit. A 1:40 scale model was tested in the wave tank facilities at the University of Oslo. Experiments with regular and irregular long-crested waves at two different incident angles were conducted to assess power absorption, wave period response, and interaction effects. Two array configurations were investigated: an eight-buoy array with an axis-to-axis spacing of 1.5 buoy diameters, and a four-buoy array with a 3.0 diameter spacing. Although piston head leakage affected the power measurements, our results demonstrate that the WEC absorbs incoming wave energy and produces measurable power. The eight-buoy configuration achieved the highest power output per buoy compared to the four-buoy configuration, but exhibited increased sensitivity to wave period and wave heading, due to buoy-buoy interactions, such as collisions. This study highlights buoy count and internal buoy spacing as key design parameters for cooperative point-absorber wave energy systems. The results indicate that higher buoy counts enhance hydraulic cooperation, and increased buoy spacing improves robustness to wave heading and reduces destructive interaction effects. We also suggest that a lower system inertia can improve responsiveness to shorter waves. These insights provide a foundation for further optimisation and future full-scale development.

physics.ao-ph↗

arXiv2024

An OpenMetBuoy dataset of Marginal Ice Zone dynamics collected around Svalbard in 2022 and 2023

Sea ice is a key element of the global Earth system, with a major impact on global climate and regional weather. Unfortunately, accurate sea ice modeling is challenging due to the diversity and complexity of underlying physics happening there, and a relative lack of ground truth observations. This is especially true for the Marginal Ice Zone (MIZ), which is the area where sea ice is affected by incoming ocean waves. Waves contribute to making the area dynamic, and due to the low survival time of the buoys deployed there, the MIZ is challenging to monitor. In 2022-2023, we released 79 OpenMetBuoys (OMBs) around Svalbard, both in the MIZ and the ocean immediately outside of it. OMBs are affordable enough to be deployed in large number, and gather information about drift (GPS position) and waves (1-dimensional elevation spectrum). This provides data focusing on the area around Svalbard with unprecedented spatial and temporal resolution. We expect that this will allow to perform validation and calibration of ice models and remote sensing algorithms.

physics.ao-ph↗

arXiv2022

A field investigation of the friction between cross-country skis and snow

Cross country skiing is an interplay between the active motion of the body of the skier and the physical interaction between the surface of the skis and the snow. Friction and glide between the ski base and the snow depend on the snow temperature, ski surface chemistry and roughness, dry friction with the snow crystals and liquid meltwater film flow properties. Although a great amount of resources are being spent on understanding glide and friction, a basic physical understanding of the phenomena at play is still at large and the methodology used for assessing the gliding quality of different full scale configurations is still coarse in real world applications, which limits novel development of robust methods to control and optimize glide. Such understanding and full scale testing is particularly important for designing new ski gliders. In the present work, we develop a novel experimental setup and use it to investigate through field experiments the basic mechanical phenomena that influence glide and friction of full scale skis on snow. The field setup features a mobile, novel linear tribometer allowing investigation with whole skis in realistic cross-country conditions (speed and load). The coefficient of friction between the skis and snow is obtained from a load cell, which reports the force necessary to pull a ski sled along a flat track. Simultaneously, thermistors measure the temperature at the ski-snow interface. In addition, a GPS measures displacement and velocity. The results obtained are in good agreement with several measurements reported from similar experiments, and provide a real-world validation of results obtained in the laboratory. In addition, we release the general tribometer setup as open source material in order to provide a foundation on which other research teams as well as cross-country teams can further iterate when designing later experiments.

physics.flu-dyn↗

arXiv2022

A dataset of direct observations of sea ice drift and waves in ice

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.

physics.geo-ph↗

arXiv2022

OpenMetBuoy-V2021: an easy-to-build, affordable, customizable, open source instrument for oceanographic measurements of drift and waves in sea ice and the open ocean

There is a wide consensus within the polar science, meteorology, and oceanography communities that more in-situ observations of the ocean, atmosphere, and sea ice, are required to further improve operational forecasting model skills. Traditionally, the volume of such measurements has been limited by the high cost of commercially available instruments. An increasingly attractive solution to this cost issue is to use instruments produced in-house from open source hardware, firmware, and post processing building blocks. In the present work, we release the next iteration of the open source drifter and waves monitoring instruments. The new design is both significantly less expensive, much easier to build and assemble for people without specific microelectronics and programming competence, more easily extendable and customizable, and two orders of magnitude more power efficient. Improving performance and reducing noise levels and costs compared with our previous generation of instruments is possible in large part thanks to progress from the electronics component industry. As a result, we believe that this will allow scientists in geosciences to increase by an order of magnitude the amount of in-situ data they can collect under a constant instrumentation budget. In the following, we offer 1) detailed overview of our hardware and software solution, 2) in-situ validation and benchmarking of our instrument, 3) full open source release of both hardware and software blueprints. We hope that this work, and the associated open source release, may be a milestone that will allow our scientific fields to transition towards open source, community driven instrumentation. We believe that this could have a considerable impact on many fields, by making in-situ instrumentation at least an order of magnitude less expensive and more customizable than it has been for the last 50 years.

physics.ins-det↗

arXiv2021

Iceberg stability during towing in a wave field

Due to their large mass and small aspect ratio, icebergs pose a threat to boats and offshore structures. Small icebergs and bergy bits can cause harm to platform hulls and are more difficult to discover remotely. As icebergs are dynamic mediums, the study of icebergs in relation to safe human operations requires the rigorous analysis of the ice-ocean interaction, in particular with waves and currents. In this paper, we present iceberg towing experiments and analyze iceberg stability from GPS tracks and inertial motion unit data. The towline tension as well as the boat motion relative to the iceberg was measured. Different scenarios were investigated by changing the towing strategy with regards to towing speed, direction (straight or curved trajectory) and acceleration. Large amplitude roll oscillations with period of approximately 30 s were observed immediately after the load dropped and the iceberg returned to a stable static position. In two of the cases, the iceberg flipped over partly or entirely after some towing time. From the load cell, we observed oscillations in the system with periods of approximately 6 s, which were attributed to the rope elastic properties and the iceberg response. The load oscillations increased when the towing direction was against the waves as opposed to perpendicular to the waves.

physics.ao-ph↗

arXiv2019

An Open Source, Versatile, Affordable Waves in Ice Instrument for Scientific Measurements in the Polar Regions

Sea ice is a major feature of the polar environments. Recent changes in the climate and extent of the sea ice, together with increased economic activity and research interest in these regions, are driving factors for new measurements of sea ice dynamics. Waves in ice are important as they participate in the coupling between the open ocean and the ice-covered regions. Measurements are challenging to perform due to remoteness and harsh environmental conditions. While progress has been made in observing wave propagtion in sea ice using remote methods, these are still relatively new measurements and would benefit from more in situ data for validation. In this article, we present an open source instrument that was developed for performing such measurements. The versatile design includes an ultra-low power unit, a microcontroller-based logger, a small microcomputer for on-board data processing, and an Iridium modem for satellite communications. Virtually any sensor can be used with this design. In the present case, we use an Inertial Motion Unit to record wave motion. High quality results were obtained, which opens new possibilities for in situ measurements in the polar regions. Our instrument can be easily customized to fit many in situ measurement tasks, and we hope that our work will provide a framework for future developments of a variety of such open source instruments.

physics.ao-ph↗

arXiv2008

Thermal imaging on simulated faults during frictional sliding

Heating during frictional sliding is a major component of the energy budget of earthquakes and represents a potential weakening mechanism. It is therefore important to investigate how heat dissipates during sliding on simulated faults. We present results from laboratory friction experiments where a halite (NaCl) slider held under constant load is dragged across a coarse substrate. Surface evolution and frictional resistance are recorded. Heat emission at the sliding surface is monitored using an infra-red camera. We demonstrate a link between plastic deformations of halite and enhanced heating characterized by transient localized heat spots. When sand 'gouge' is added to the interface, heating is more diffuse. Importantly, when strong asperities concentrate deformation, significantly more heat is produced locally. In natural faults such regions could be nucleation patches for melt production and hence potentially initiate weakening during earthquakes at much smaller sliding velocities or shear stress than previously thought.

physics.geo-ph↗