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Item type:Publication, Access status: without files , Challenges with sea ice action on structuresfor Offshore windEU 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.Publicationtype: Conference Paper42 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Estimation of model ice properties in ice tank operations with numerical models(POAC, 2023-06); ; ; Conducting model ice tests is still the state of the art in predicting the performance of ships and structures in ice. This is also valid for other occurrences such as waves in ice or ice feature formation processes. In an ice tank ice properties such as the flexural strengths and the thickness usually formulate the target properties towards which the ice production process is adjusted. This also means that prior to testing the properties are measured and in case target properties are not yet met additional tempering or cooling is done until target conditions are met. Conducting cantilever beam tests for the flexural strength and plate deflection tests for the elastic modulus is time consuming in the time critical ice production process. The plate deflection tests itself can take up to an hour including all preparation This paper presents a method that reduces the time needed to conduct property tests in the ice tank, while providing deeper insight into the ice properties. The first method uses a parametric finite element model, which reproduces the cantilever beam tests. With an iterative routine, the elastic or strain modulus of the ice is determined as well as the nominal stress at failure (flexural stress), the elastic stress at the root corners and the buoyancy force. Especially, the latter is in some cases of particular interest and it has been for decades under debate whether this can be read from the force recordings of the cantilever beam tests. The method increases the amount of information of the ice sheet properties significantly and reduces the time spent on ice property testing. The methods are applied and tested for different ice sheets and measurements from the Hamburg Ship Model Basin (HSVA). It is shown that the elastic modulus can be determined with a good agreement (better than 4% for regular model ice of around 30 mm thickness) to the plate deflection tests. Furthermore, the effective strain modulus and the buoyancy force is delivered as result.Publicationtype: Conference Paper58 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , High-speed Impact Drop Tower Tests of Cylindrical Granular Ice Specimens(POAC, 2023-06); ; ; Global warming might increase the marginal ice zone, and it increases the accessibility of the Northern Sea Route and the Northwest Passage for the shipping industry, which reduces the shipping time and fuel consumption in comparison to the Suez Canal Route on single voyages. Thus it is presumed that global warming will enlarge the area of possible propeller-ice and wave-ice structure interactions with ships and structures of lower ice classes or less ice strengthening. The interaction velocities between ice and marine structures are often relatively slow, but some scenarios have high relative interaction velocities, such as in propeller-ice interactions. However, experimental data and knowledge on the mechanical behavior in the high-velocity range of ice are scarce. This paper describes high-speed impact drop tower tests of cylindrical granular ice specimens, where adjusting the initial drop height can regulate the impact energy level. Depending on the prevailing conditions, sea ice growth can result in several different grain structures. This study utilizes granular fresh water ice, which allows consistency and repeatability of the mechanical behavior and results in conservatively (high) measured compressive strength values compared to saline sea ice. Two test cases are shown and analyzed. In the first case, the hammer impacts the ice specimen positioned on the measuring platform. In the second case, the specimen is also positioned on the measuring platform, but rubber plates are placed between the hammer, the ice specimen, and the measuring platform. All test cases are conducted at three different impact velocities. Force-displacement curves are shown besides high-speed recordings to distinguish between failure modes, and the influence of the end-cap conditions by using rubber plates is discussed. In addition, the paper compares the data from drop tower tests to conventional ice compression tests. This study highlights the impact of boundary conditions and seeks to contribute to developing numerical ice material models for a more economical and safer design of structures in ice, expecting high-speed interactions with ice.Publicationtype: Conference Paper86 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A growth model for aqueous model iceExperimental testing in model ice is still the state-of-the-art method for the performance prediction of ships and structures in ice. For frequently produced ice thicknesses large experience is available to estimate the growth rate and the final thickness. However, the prediction of growth rate for model ice thicknesses outside this range come with major uncertainties. An accurate growth prediction of the ice requires a physical growth model that can account for the complex boundary conditions. Such a model is also useful when boundary conditions change, for example the renewing of the cooling system. In this work, we propose a growth prediction model for model ice in The Hamburg Ship Model Basin (HSVA). In the HSVA, the ice is artificially seeded during the beginning of ice growth to modify the mechanical properties of the ice. We used a traditional thermodynamic ice growth model and modified it so that it takes the seeding procedure into account. We used measurements of air temperature and ice thickness to tune the tank specific model parameter. For the best fitting parameters, the mean squared difference between our model and measurements is 2.17 mm. We speculate that most of this difference is due to a strong post-growth that is not correctly represented in the model. Nevertheless, the model provides a significant improvement and help for the modelling of thin ice. By modelling the post-growth process individually, the model could be further improved. This, however, requires more measurements of the ice thickness during post-growth.Publicationtype: Conference Paper71