Arctic sea ice is retreating at a high rate, also due to the positive ice-albedo feedback loop: as ice melts and disappears, it reflects less sunlight, further accelerating ocean warming. One proposed way to slow the retreat is by thickening sea ice in winter, increasing its chances of surviving summer melt. This could be achieved by artificially flooding existing sea ice with seawater pumped from below, allowing it to freeze at the surface through exposure to cold air and thicken the ice layer. However, the effectiveness of this approach remains uncertain, as numerical models show contrasting results and few field experiments have been conducted. This study examines the growth and melt of ice through spring and summer after artificial flooding covering (Formula presented.), resulting in thickened (+26 cm) snow-covered first-year sea ice. Observations were carried out in Vallunden Lagoon (Van Mijenfjord), Svalbard, from 20 March to 24 June 2024, with flooding and intensive in situ measurements from 11–15 April. Artificial flooding significantly heated the upper two-thirds of the original 90 cm thick ice, increasing salinity. Surface albedo evolution was influenced by specific events such as slush formation, snow drift, and a major meltwater drainage event in spring. Artificial flooding resulted in thicker ice and delayed rotten ice formation by 6 days, but did not delay the disappearance of ice in summer compared to a non-flooded reference site. Experiments at other scales and locations could help reveal how local conditions and flooded area size influence results and the potential of this method.

The design of flexible vertical offshore structures exposed to ice, like offshore wind turbines, can become governed by ice loads and structural responses at low relative ice speeds. This study attempts to quantify the low-speed ice loads based on a hypothesized interaction mechanism linking the velocity dependence of global loads to specific states of the ice supported by model- and full-scale observations. The quantified velocity effect is applied to estimate potential global pressures at low speeds from high-speed crushing events from the full-scale measurement campaign at the Norströmsgrund lighthouse. It is estimated that the velocity effect may produce global pressures equivalent to applying an ice strength coefficient of 0.9 MPa to 1.6 MPa. These results substantiate an alternative physics-informed approach to account for the velocity effect for ice loads and provide an interpretation of the interaction scenario captured by the 1.8 MPa value in the ISO19906 design standard.

Several European and Canadian ice experts/scientists met in the summer of 2025 to address the critical need for publicly accessible ice-load data on offshore wind foundations. They proposed a "scientific" offshore wind turbine (OWT) foundation to be deployed in a location where OWTs are currently envisaged in ice-covered waters. The focus of this work is on two regions: the Gulf of Bothnia (Europe) and the Gulf of St. Lawrence (Canada). The paper presents preliminary analyses for the site selection of the proposed OWT foundation. The results of the analyses of the environmental conditions of the two regions are given, and several sites are proposed for each region. The study confirms that both regions meet the preset criteria. The final decision should balance the known environmental, geotechnical, and economic factors.

Offshore wind turbines in cold sea areas can be fitted with ice cones to reduce static and dynamic loads from drifting sea ice. The effectiveness of ice cones in reducing static loads has been tested in model-scale ice basin experiments. However, only a few experiments used compliant test setups to study ice-induced vibrations on conical structures. This study explores the dynamic interaction between level ice and a downward-bending cone with a 60° slope angle through ice basin tests with a hardware-in-the-loop system based on a hybrid technique, combining a physical indenter with a numerical structure model of an offshore wind turbine. Two types of periodic ice-induced vibrations were observed for the first time in an ice basin: bending failure-induced vibrations and unexpected vibrations caused by local failure at the ice-structure interface. The local failure had characteristics of both shear failure and crushing failure and occurred at low ice-structure interaction speeds during tests. Local failure-induced vibrations were significant in the dynamic test with an ice-drift speed of 5 mm s^-1, however they also contributed to the dynamic response of the structure at higher ice-drift speeds. Bending failure-induced vibrations occurred at critical ice-drift speeds (30 mm s^-1 to 40 mm s^-1 and 70 mm s^-1 to 100 mm s^-1) where the bending failure frequency matched the 1st or 2nd natural frequency of the structure model. The results show that ice-induced vibrations on conical structures occur at various ice-drift velocities for both previously known and unexpected ice failure modes. Furthermore, the results provide new insight into conducting ice basin tests on ice-structure interaction with compliant conical structures.

The design of flexible vertical offshore structures exposed to crushing ice, such as offshore wind turbines, can become governed by ice loads and the structural response associated with low relative speeds between ice and structure. Low ice speeds can cause significant loads due to pressure synchronization and/or increase in contact, potentially larger than those observed at high ice speeds, which is often referred to as the velocity effect. In this study, the dataset from the full-scale measurement campaign at the Norströmsgrund lighthouse is reanalyzed. Several instances of ice load amplification are identified and presented, to confirm that synchronization and the velocity effect developed. The increase in ice load is quantified and discussed in the context of a theoretical framework, and model- and full-scale observations of the velocity effect on other structures. Then several events of high-speed crushing are investigated and the potential global pressures at low speeds for those events are estimated based on the theoretical framework. These estimates are compared to typical high-speed global crushing pressures used to define the ice strength coefficient CR for the Baltic Sea. It is found that the velocity effect may produce global pressures equivalent to a CR factor above 0.9 MPa. The results provide a theoretical substantiation for inclusion of the velocity effect and a possible physical interpretation of the recommended value of 1.8 MPa in the ISO 19906 design standard.

In this paper, we focus on investigating ship activities in the United States’ Arctic waters and developing new viscoelastic materials that can mimic specific ice behavior. This is a significant challenge, and we discuss potential positive outcomes and how the acquired knowledge can contribute to understanding ice behavior in Arctic and Sub-Arctic regions. We first define ice and ship statistics, providing a foundational understanding of potential ice–ship interactions. We then describe the development of thought experiments for wave–ice interactions and the creation of a numerical environment for modeling purposes. This step is crucial for simulating various scenarios related to ice and wave dynamics, ultimately contributing to the design of ships capable of navigating safely in diverse Arctic conditions. Finally, stakeholder and community engagement is addressed, recognizing the importance of involving local perspectives and insights to ensure practical, socially responsible, and effective solutions.

A field campaign in the Vallunden lagoon in the Van Mijenfjorden on Spitsbergen was conducted to gather data on sea ice restoration by artificial flooding. Sea ice thickening was initiated by pumping sea water from below the first-year sea ice onto the surface without removing the covering snow layer. Part of the data was collected by four thermistor strings, two radiation sensors, and one anemometer. All measurement systems were left in the field until recovery of the floating systems in summer. Data provided by the measurement devices were received remotely to gather data before, during, and after the flooding phase (including the melting for as long as the sensors were sending data). Furthermore, coring systems were used to extract 88 ice cores for analysis of temperature, density and bulk salinity profiles along the full length of the ice cores before, during and within four days after flooding. The data set can be used to investigate physical processes involved in the ice growth before, during and after flooding. The data can be used to understand the development, growth and melting of snow ice. The radiation data can be used to analyze the (reflected) radiation of the initial, flooded and melting ice. Data gathered during the melting can be used to investigate the melting of thickened sea ice with different initial conditions prior to the onset of melting. Data on bulk salinity can be used to investigate short-term salt migration. Combing the different insights, growth- and melting models of sea ice including snow and snow ice can be validated. The understanding of melt-water drainage events could be improved and flow models for simulation of artificial flooding of snow-covered first-year sea ice could be further developed using the data.

The study investigated the use of a Hardware-in-the-Loop (HiL) technique applied in model ice experiments to enable the analysis of offshore structures with low natural frequencies under dynamic ice loading. Traditional approaches were limited by facility capacities and ineffective downscaling of the geometry of the offshore structures. The goal of the present study was to overcome these challenges and to enhance the understanding and explore the applicability of a hybrid testing technique in model ice experiments. To achieve the objective, 204 Hardware-in-the-Loop simulations in model Ice (HiLI) were analyzed. Results showed robust behavior and good performance of the HiLI due to minimal variation in measured delay, normalized root mean square error, and peak tracking error and low magnitudes of such parameters despite alterations in factors such as the choice of the numerical structural model, physical prototype, measurement system, and ice type. Notably, the performance of the HiLI was affected when testing with warm model ice or scaling for harsh ice conditions, attributed to a reduced signal-to-noise ratio and instability of the system, respectively. Experimental identification of the critical delay, along with the application of an analytical stability criterion, revealed that the instability observed, was likely induced by reducing the structural stiffness of the numerical structural model to fulfil the scaling requirements when testing for harsh ice conditions. Additionally, the study showed improved HiLI performance when the physical prototype was in contact with the model ice. This observation was further analyzed and is assumed to be caused by the coupling between the ice and physical prototype, causing a coupled and thus increased eigenfrequency of the physical prototype-ice system.

A modeling approach to simulate ice-induced vibrations of vertically sided offshore structures in ice tank experiments is presented. The technique combines replica modeling with the preservation of kinematics during ice-structure interaction. The technique was chosen based on the theoretical understanding that ice-induced vibrations are caused by an energy exchange between the structure and the ice. The mechanism is controlled by primarily four aspects: the kinematics during ice-structure interaction, the degree to which the ice can resist higher loading at low velocities prior to failure (velocity effect), the existence of a transition speed from ductile-to-brittle failure, and the mean ice load level. A model ice type which resulted in a velocity effect and provided a transition speed comparable to that of sea ice was developed and used during ice tank experiments. A scaling factor, derived from the comparison between the mean brittle crushing ice load of the full-scale event and the in-situ measured mean brittle crushing model ice load, was applied to scale structure properties of a numerical model. This model was implemented during real-time hybrid simulations in model ice to preserve kinematics during the ice-structure interaction. To verify the proposed scaling approach, rigid indenter experiments covering velocities from 0.1 mm s⁻¹ to 500 mm s⁻¹ and dynamic ice-induced vibration experiments of structures with varying aspect ratios (8 and 12) and shapes (cylindrical and rectangular) were conducted. Neither the aspect ratio nor shape appeared to influence the development of ice-induced vibrations significantly. The approach was qualitatively validated by reproducing full-scale ice-induced vibrations as experienced by the Molikpaq platform and Norströmsgrund lighthouse.

The effect of misalignment between wind- and ice loading direction on the development of ice-induced vibrations of offshore wind turbines has been investigated experimentally. In the experiments a hybrid test setup was used to study the structural response to combined loading from physical model ice and numerically applied wind. The motivation for this study was the high uncertainty in the design of offshore wind turbine support structures in cold regions, caused by scarcity of full-scale and model-scale data on ice-structure interaction. Test results revealed that misaligned scenarios result in the development of sustained ice-induced vibrations in the ice load direction. The test results also showed that ice-induced vibrations can develop up to higher ice drift speeds for misaligned scenarios than for aligned scenarios. Both observations are considered to be related to low total damping in the ice drift direction for a misaligned scenario. Further comparison between a 90°-misaligned operational and an aligned idling scenario revealed that wind-induced structural displacements perpendicular to the ice drift direction do not cause the ice to fail. On the contrary, it was shown that the ice constrains the wind-induced motion for low relative velocities between ice and structure. For high relative velocities, wind-induced displacements approach those in open water as the ice fails in rapid succession at the sides of the structure during crushing. The analysis of a misaligned scenario with a smaller misalignment angle revealed that vibrations occur perpendicular to the ice drift direction and are characterized by relatively low amplitude and high frequency. The ice, being in contact with the structure, neither prevented those vibrations nor failed.

EU urgently needs to increase the development of secure and green energy, and this includes renewables such as Offshore wind energy. An expansion of Offshore wind will include the Baltic where sea ice is one of the major uncertainties. To ensure that the wind turbines are safe for people and the environment, while keeping them economically competitive betterguidelines and regulations should be developedcollaboratively by European industry and academia. There are unsolved challenges with respect to ice action on structures for offshore wind. However, in the current draft for Horizon Europe WorkProgramme 2023-2024 on Climate, Energy and Mobility1, the challenges related to sea ice with regards toOffshore wind energy are not mentioned. In order to meet the crucial green energy goals, it is our statement that it is imperative to include sea ice in the final version.

Cyclic crushing experiments with a haversine velocity waveform were performed on passively confined, freshwater columnar ice specimens for a variety of velocities and frequencies. The aim of the experiments was to study the ice deformation and failure behavior in crushing when loaded at a predefined displacement pattern closely resembling the frequency lock-in regime of ice-induced vibrations. The focus of the experiments was on the development of load and ice deformation behavior at the grain and ice specimen scales during each cycle. To this end, the deformation and failure of the ice were observed with crossed-polarized light to highlight the microstructure in-situ during cyclic crushing. It was shown that there are dichotomous mechanical behaviors of the damaged and confined ice during a single crushing cycle: brittle at high velocity and non-brittle at low velocity. At low velocity, ice fracture was interrupted and stress relaxation occurred until the predefined velocity began increasing in the cycle. The stress relaxation in the load was accompanied by stress-optic effects in the ice. It was found that a load peak-velocity hysteresis developed in each crushing cycle: peak loads following the non-brittle behavior were temporarily higher than the peak loads of the brittle behavior. The temporary load peak enhancement tended to increase with increasing duration of stress relaxation, i.e. the peak enhancement tended to increase with decreasing velocity and frequency. Negligible peak enhancement and stress relaxation duration were observed for the highest frequency and mean velocity tested of 2 Hz and 10 mm s⁻¹, respectively. For tests with a minimum velocity of 1 mm s⁻¹, no stress relaxation was observed in the load measurement. Preliminary results from deviating from the haversine velocity waveform by increasing the minimum velocity showed that the stress relaxation duration decreases, but the non-brittle peak load does not decrease. It is speculated that ice anelastic ice behavior could account for the rapid stress relaxation at low velocity. It is unclear what causes the hysteresis, although it is speculated that dynamic strain aging might play a role. The change in ice behavior during the experiments demonstrates a mechanism which develops rapidly and might therefore incite the development of the frequency lock-in regime of ice-induced vibrations of vertically-sided structures.