14 results
Now showing1 - 10 of 14
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Simulated ice loads on a ship propeller and comparison with full-scale measurements(Elsevier, 2025-10-15); ; ; ; A methodology to better estimate the loads of ice acting on the propeller of a ship is developed. Based on measurements conducted in the North Pole region, an existing failure model for ice based on the Mohr–Coulomb nodal split approach is modified to better represent the lower strength of polar ice compared to laboratory ice. The modified material model for the sea ice is used to compute the propeller torque and a load spectrum for the propeller-ice interaction of the research ship S.A. Agulhas II. To this end, a floe-ice breaking simulation is used to estimate the size and shape of the ice cusps hitting the propeller of this ship. In the next step, a set of finite element simulations of the propeller-ice interaction utilizing the modified Mohr–Coulomb nodal split model is conducted. Based on this, the load spectrum is computed and compared with the measured torque on the propeller shaft of the S.A. Agulhas II. The successful reproduction shows the applicability of the approach to better estimate the loads exerted by the ice on the propeller.Publicationtype: Journal Article55 31 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Propeller-ice interaction experiments on a scaled S.A. Agulhas II propellerBetween 2011 and 2020, over 16% more incidents of machinery damage and failure were reported in the waters within the Arctic Circle compared to the rest. In addition, Allianz (AGCS) also reported that machinery damages and failures account for more than 45% of all incidents in Arctic waters, which are caused by the exposure of the propulsion system to ice contact. A better understanding of the propeller-ice interaction process would allow a more efficient propeller design and a safer operation in ice-covered waters. However, full-scale measurements of propeller-ice loads are unique. In addition, propeller-ice loads determined in model tanks are hard to transfer to full scale due to the model ice properties and the large scaling of the propeller. Moreover, holistic propeller-ice simulations have yet to be created, capturing the complex ice failure and representing realistic loads. This paper presents propeller-ice interaction experiments on the propeller of S.A. Agulhas II on a scale of 1:3. The experiments focus on contact milling and impact loads. The test matrix consists of different interaction velocities up to 4 m/s using a drop-tower, cylindrical ice specimen with diameters up to 200 mm, and three different contact conditions from milling loads to impact loads. The specimens consist of granular freshwater ice with high uniaxial strength, and the reports of the measured interaction force and the strains measured on the propeller should provide valuable information for future simulations of the propeller-ice interaction process.Publicationtype: Conference Paper35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On methodology for a digital twin of ship propulsion under harsh environmental conditions(American Society of Mechanical Engineers (ASME), 2024-06); ; ; ; The propulsion system of a ship is a critical element for its safety and integrity. Therefore, it must be maintained properly to ensure that a vessel is able to fulfill its primary purpose. The need for maintenance is even more pronounced in ships where extreme environmental conditions, such as ice-covered waters, are expected. This is due to an increase in the magnitude and uncertainty of loads and therewith the increase in possible damages if the propulsion system fails. The use of digital twins is becoming increasingly popular in shipping and can also be used for intelligent maintenance and operation prediction of the propulsion system. This paper proposes the methodology of creating such a digital twin with a specific focus on the required measurement infrastructure, modeling of components, loads, and damage as well as how all of these aspects are combined. The digital twin was created using a polar supply and research vessel, S.A. Agulhas II. Bearings are discussed from the view of high-fidelity simulations and wear modeling. The propeller is modeled as a point mass with the propeller laws for predicting the hydrodynamic torque and thrust. Shaft dynamics are modeled using either a lumped-mass torsional model, a modal model, or a finite element model. Damage of the shaft and the propeller is based on SN-curve fatigue calculations. The motor torque is modeled using an equivalent circuit model while motor damage is modeled by estimating the hottest temperature within the motor windings. Ice-breaking simulations are used as inputs to propeller-ice interaction models to obtain insight into the loads caused by these interactions. The material properties of ice used during simulations are validated using experiments. The need for further validation for low-fidelity models and the need for reduced order modeling or surrogate models for high-fidelity models are discussed. Finally, the implementation of this digital twin is discussed based on the developed model and the found problems that still need to be overcome to increase the technology readiness level.Publicationtype: Conference Paper41 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Influence of the ice shape on ice-structure impact loads(Elsevier, 2024-05); ; ; ; Ships that are navigating in ice covered waters are at risk of colliding with icebergs or ice floes, which can lead to severe damage to the ship‘s hull in certain conditions. Predicting these loads is of great importance for the design and safety of ships. Ice loads are driven by a range of parameters, including ice properties such as the compressive strength, the geometry of the ship's hull and values related to the interaction (e.g. impact velocity). Classification rules and requirements for polar vessels account for these parameters to a certain extent. However, sea ice exhibits not only variability of its properties but also the geometry of the ice shows a high degree of diversity: icebergs and ice floes exist in multiple different shapes. Therefore, this paper addresses the ice-structure interaction process, focusing on the influence of the initial ice contact shape and its impact on the local load. Additionally, the paper explores the feasibility of pinpointing geometric parameters of the ice responsible for influencing these loads. Ultimately, understanding which ice shape in contact poses the greatest risk would be valuable for improving numerical simulations for the worst case scenario and, consequently, enhancing the safety of ships in ice-prone environments. To achieve this, a comprehensive drop tower test campaign on a small-scale has been conducted at the test facilities of the Hamburg University of Technology. In these experiments, single impacts of differently shaped ice specimens against a rigid 50 mm steel plate in normal direction were investigated. In the experiments, a drop hammer was released from a predefined drop height to realize a brittle failure of the ice at an interaction velocity of about 2000 mm/s. This falls within the lower range of ship-ice interaction speeds. The drop hammer fell onto the ice specimen which was positioned centered underneath the drop hammer. The investigated specimen geometries were cylindrical shapes of 200 mm diameter with varying caps of cone, dome, wedge, ellipse and other shapes. Overall, 27 different shaped ice specimens were tested. The analysis includes the failure behavior of the ice specimens and the load introduced by the specific contact shapes. Two main failure modes were observed depending on the ice geometry, which showed significant differences in the load magnitude. Further relations between the initial contact area, the cone angle, and the specimen length to the peak force, maximum pressure, and energy were identified.Publicationtype: Journal Article64 141 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Derivation of a numerical propeller-ice interaction model(Norwegian University of Science and Technology, Department of Marine Technology, 2024-04-04); ; Ice is a strain rate-dependent material showing ductile and brittle behavior and can play a critical role in maritime operations. Particularly in propeller-ice interactions, with high strain rates, ice fails brittle. Such interactions not only induce potential damage to the propeller, but also have a significant impact on the entire drive train of vessels in ice. The determination of ice-induced loads on propellers is a significant challenge, as direct measurements are usually not possible and indirect measurements are contaminated and superimposed with various other signals. Therefore, this paper delves into the domain of dynamic finite element simulations focusing on the interaction between ice and ship propellers in connection with dedicated small scale experiments. Experiments emulating propeller-ice milling-type interactions have been employed to enhance the knowledge of propeller-ice interaction and ice as a material. These experiments serve as input to refine the numerical model, which is a state-of-the-art Mohr-Coulomb Nodal Split (MCNS) ice material model. The aim is to determine the ice loading on the propeller numerically and to compare the experimental results with the simulation. These simulations in combination with the experiments provide insight into complex propeller-ice dynamics and enable investigating the applicability of the MCNS model for propeller-ice simulations. The discussion includes the observed phenomena, emphasizing the propagation of brittle fractures and their effects on the propeller. In summary, this study comprehensively explores propeller-ice interactions through finite element simulations. This research contributes to the understanding of ice-induced mechanical challenges in the maritime realm by considering the brittle behavior of ice.Publicationtype: Conference Paper54 178 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Experimental and numerical analysis of ice crushing tests with different shaped ice specimens(American Society of Mechanical Engineers (ASME), 2023-06); ; ; ; Ships operating in ice covered waters are exposed to the risk of colliding with an iceberg or ice floe. Predicting the loads in ice-structure interaction is crucial for the safety of existing ships and the optimization of the ship structures in the future. The ice geometry and the interaction velocity are two parameters, among others, that have a high influence on the acting forces and pressures. There has not been much research on the influence of the ice geometry in ice-structure interaction tests in the past. This paper analyzes the failure mode, peak forces, and energy of different ice specimen geometries at different interaction velocities in small-scale crushing tests and identifies shapedependent effects. Furthermore, a first attempt is made to numerically simulate these experiments with the Mohr-Coulomb Nodal Split (MCNS) ice model in order to extend the applicability of the model to more general ice-structure interaction problems. Overall 21 different ice shapes were tested in crushing experiments with a hydraulic piston and drop tower experiments and were simulated with the MCNS model. In addition, the influence of the interaction velocity was analyzed for 13 shapes at interaction velocities of 10, 100 and 2000 mm/s. The specimen shapes included among others a cylinder, cones, truncated cones, elliptical, dome-shaped and wedge-shaped. In the experiments, the load, the displacement, and the failure behavior were recorded. Especially the peak force, energy, and failure mode were used for the analysis and comparison with the simulation results. The results show a high dependency of the failure mode and peak forces on the specimen shape, initial contact area, and interaction velocity. The MCNS model is capable to predict trends of the peak load depending on the initial contact area and generated different failure behaviors depending on the ice geometry to some extent. However, there is potentially room for improvement, especially considering the triaxiality and the influence of the interaction velocity.Publicationtype: Conference Paper25 - 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 , Lessons learned: the influence of testing properties on uniaxial compression tests of ice(American Society of Mechanical Engineers (ASME), 2022-06); ; This paper describes the influence of testing properties (test rig stiffness and PID controller settings) on the uniaxial com-pression test of granular laboratory-made ice in a single-factor design experiment. Global warming causes the decline of sea ice in the Arctic regions. Enabling the Northern Sea Route and the Northwest Passage to be more accessible for the shipping in-dustry and therefore reduces the energy consumption compared to the Suez Canal Route. Nevertheless, ice will remain an inter-acting element with ships and structures in Polar and Sub-Arctic regions. A good assessment of forces exerted by the ice on the off-shore structure or the ship is essential for designing these arctic structures. Ice-structure interactions depend on the mechanical properties of the ice, which are still not fully explored but can be determined by experimental testing. Over the years, many exper-iments have been conducted with similar test setups but different testing properties. Therefore the influence of the test properties on the compressive strength of ice is analyzed and discussed by comparing the results of different test settings in this paper. The tests are conducted in a single-factor design experiment. The applied velocities range from 0.01 mm/s to 500 mm/s, causing the ice to behave ductile at lower velocities and brittle at higher velocities.Publicationtype: Conference Paper32 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Splitting-tests of laboratory-made granular ice with a propeller-like indenter(American Society of Mechanical Engineers (ASME), 2022-06); ; Global warming will decline the sea ice in the upcoming decades. However, sea ice will prevail long enough in the sub-arctic and polar regions to remain a challenge for the shipping industry and arctic engineers. The decline in sea ice makes some economically interesting routes through ice-covered water more accessible. Still, at the same time, climatic changes can cause more dynamics of ice sheets and ice features. Therefore a bet-ter understanding of ice-propeller interaction is required with experimentally validated simulations. Propeller contact loads can be classified into milling loads and impact loads. The in-put ice property for existing numerical models of propeller ice interaction is usually the compressive strength at relatively low strain rates representing the impact scenario. Independent from the applied interaction velocity, a compressive test does not de-scribe the milling type interaction well, which is characterized by fracture and splitting of the ice. This paper describes the splitting-Test of laboratory-made granular ice with a propeller-like indenter. Splitting-Tests of granular ice specimens show no dependence on the L/D ratio. The force measurement during the splitting-Tests shows a dependency on the thickness of the inden-ter and, in addition, for the 6 mm wide indenter, a rate depen-dency. The force measurement of the splitting-Test with the 3 mm wide indenter shows no rate dependency. The higher specific strain energies in splitting-Tests of ice could lead to the lower measured forces.Publicationtype: Conference Paper37 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Data from uniaxial compressive testing of laboratory-made granular ice(Elsevier, 2022-05-06); ; Uniaxial compressive tests of laboratory-made granular fresh-water ice were conducted in a cold room in the ductile and brittle strain rate range at -10.83°C ±0.74°C. Ice specimens with a length to diameter ratio of 2.5 showing brittle behavior failed by axial splitting. With the Instron Labtronic 8800, the operator controlled the tests at a frequency of 4,000 Hz. The data acquisition rate was 25,000 Hz, and for faster experiments, 100,000 Hz. The operator controlled on a random basis the hydraulic cylinder by either the cylinder displacement or the specimen displacement. Increasing as well as constant and decreasing compression strength trends with increasing strain rates could be shown in the past. The data presented here show a lower compressive strength at strain rates higher than 4*10−3 s−1. The data consist of the time history of the specimen and cylinder displacement measurement (in mm), and the force measurement (in kN). The data is available as a separate .xlsx file for each test performed. In total, 123 tests were performed. If the test was performed with a 10 mm gap, the label ends with a ‘g’. The abbreviations are separated with an underscore. The data provided here can be used to validate ice-material models or for ice-testing databases for machine learning purposes.Publicationtype: Data PaperScopus© Citations 4 70 169