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Item type:Publication, Access status: without files , Model scale investigation of aspects influencing the ice resistance of ships sailing ahead in level ice(2020-01-02); For a reliable prediction of the total resistance in ice in an early ship design stage, it is of great importance to have knowledge on the different influencing aspects. Three of the quite poorly investigated aspects of ship resistance in ice are evaluated for a contemporary common ice-breaking ship type with model tests in ice: The different components of the total resistance in ice are investigated by tests in pre-sawn ice. The additional resistance of a skeg in the bow area is analysed with model tests in ice with an instrumented skeg. The ship bottom ice coverage is determined by means of an underwater image analysis methodology. The results of these investigations are given and discussed.Publicationtype: Journal Article101 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigation on semi-empirical coefficients and exponents of a resistance prediction method for ships sailing ahead in level ice(2019-10-03); In this paper, the semi-empirical coefficients and exponents of an ice resistance prediction method, i.e. refined Lindqvist formula, are investigated. Thereby, the coefficients and exponents which are not fully based on analytical considerations or geometrical properties are substituted by variables. By means of a computer algorithm these variables are optimised within specific boundary limits with regard to the total resistance in ice. Furthermore, the state of the art ranges for the ice resistance portions induced at the water line and below the water line are considered. The optimisation is based on a set of scaled model tests with several ice breaking ship models under different conditions, i.e. ship speed and level ice thickness.Publicationtype: Journal Article36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigations on the level ice resistance of ships with conventional bow shapesA literature study of existing methods for estimating the resistance of ships in ice is presented and a review of the influence of several ship particulars on the level ice resistance is made. The applicability of the Lindqvist method to vessels with conventional bow shapes is assessed, pointing out the strengths and weaknesses of the formulation. The concept of an improved method based on weighting factors is presented. Finally, recommendations for a model test campaign with an instrumented model are given in order to acquire sufficient knowledge to develop a revised method.Publicationtype: Conference Paper42 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , An experimental method for model propeller-ice interaction in air: concept and first resultsOne of the aims of the German national funded research project ProEis is to develop a methodology for determination of ice loads on model propellers which will then aid in improving and developing software tools for their prediction. For this purpose, a prototype device has been designed at HSVA within this project which is used to guide defined ice floes with one degree of freedom into a model propeller where they are milled and the resulting forces and moments are measured. This paper focuses on the description of the ice feeding device and presents some first results with respect to the physical process as well as measured load characteristics. For now, experiments are conducted in absence of water in order to exclude all hydrodynamic effects. A podded propeller is used which allows measuring of shaft torque and shaft thrust. A high speed video camera is also employed to record the propeller-ice interaction process at 5000 frames per second, allowing to observe the milling process in detail. Two basic impact patterns are observed with respect to their relative load levels. When the greater part of the leading edge of the propeller strikes the ice from the top, i.e. it crushes the granular layer and cuts off a relatively large chunk of ice, the maximum shaft thrust is approximately 1.5 times as high as when the leading edge of the propeller makes contact at the front face of a floe, scraping off a thin layer of ice. Shaft torque is mostly unaffected by the type of impact. The performance of the ice feeding device and the findings of the first tests presented here are reviewed and discussed critically. Recommendations for the planning of such tests and possible improvements of the device are given.Publicationtype: Conference Paper79 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Methodology to assess the floe size and distribution along a ship hull during model scale ice tests for self-propelled ships sailing ahead in level iceThe influence of ice parameters and ship hull form characteristics on the ice floe behaviour along a ship hull is of great importance when assessing the ice breaking performance of a ship advancing in level ice. Good ice breaking performance includes both low ice breaking resistance and high propulsion efficiency. The latter is reduced when ice interacts with the propeller. Despite the importance of understanding the ice floe behaviour along a ship hull, only little information is available on the issue. Thus, a method is developed to assess the floe size and distribution along a ship hull during model scale ice tests based on a detailed image analysis of underwater video recordings. As a result, the influence of ice and ship parameters on the ice floe size and distribution along the ship hull in level ice can be analysed.Publicationtype: Journal Article89 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of bow design on ice breaking resistance(2016-06-01); One of the main contributions to the resistance in level ice is the breaking force which is mainly influenced by the bow shape, beside ice properties and the ship's speed. Understanding the influence of the bow shape on the ice breaking resistance is essential for the assessment of the hull form in an early design stage. However, at a first glance the bow shapes of modern ice breaking vessels seem to be quite similar. Thus, a need exists to evaluate the contribution of the ice breaking force to the resistance in ice methodically for different bow shapes. Since model tests are still the most reliable resistance prediction method, they form the basis for the analysis of the ice breaking process at the bow. Specifically, breaking patterns and geometric bow parameters are investigated. The findings are compared with the selected semi-empirical method of Lindqvist. On this basis the Lindqvist approach is evaluated with further model test results and theoretical considerations. Finally, refinements of the Lindqvist formula are suggested where appropriate based on the analysis.Publicationtype: Journal Article73 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Methodology for investigation of ice breaking performance(International Society of Offshore and Polar Engineers (ISOPE), 2016-06); Understanding the influence of the ship hull design on the ship-ice interaction is essential for its assessment in an early design stage. Within the research project ProEis an investigation is carried out which is based on a holistic consideration of the ice breaking process. This paper aims to present an improved testing procedure to enable the development of a numerical simulation procedure that predicts the twoway coupled hydrodynamic interaction of the vessel with the turbulent nonlinear flow as well as the collision of the pre-broken ice and the ship hull and a companion tool which determines the bow ice-breaking pattern. Analysis results of the influence of different bow shape (parameters) on the breaking pattern are given followed by a first evaluation of the ice flow along the ship hull.Publicationtype: Conference Paper35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A framework for a design and optimization platform for ships in arctic conditions(Curran Associates, Inc., 2015-06); ; ; ; Climate changes and recent discoveries of hydrocarbon resources in the High North have strongly influenced research and development activities in arctic marine and offshore industries, resulting in new design approaches, methods and tools. These are, however, usually not readily available and rarely appear as a full ship design package, which lead to the objective of this study: The development of a design and optimization platform for ships in arctic conditions. This software framework will incorporate most of the significant aspects relevant to the design of arctic ships. These aspects are the topics of a series of research projects by the Sustainable Arctic Sea Transport (SAST) research group at NTNU's Marine Technology Department. The design process within the framework commences with a module for the mission definition and the ship's operational profile. Based on these requirements the corresponding route-specific ice conditions are obtained from an integrated database. The mission specifications and expected ice condition scenarios provide the constraints for the optimization procedure. The analysis of the ice-ship interaction takes place in the framework modules being currently developed within the SAST group. These methods cover the area of ice-breaking pattern and local ice loads, ice resistance prediction, estimation of sliding resistance, machinery response and propulsion evaluation, structural response to service and accidental ice loads, followed by an assessment of the accidental consequences. The final step in the optimization routine is a compliance module that assesses whether the design goals are met or if further optimization iterations are required. The modules listed above, their interdependencies and the design and optimization process will be systematically described in the paper. The main feature of the software framework will be the optimization of a ship under the specified constraints and operational conditions. In addition, the platform will offer numerous further applications, e.g. detailed performance assessment of new or existing designs, simulation-based design selection, selection of ice class, hull form, machinery elements, etc. Furthermore, the framework will allow the use of each module individually and is intended to provide a knowledge base of the SAST research results. In its full development stage, the platform will allow the visualization of the ship-ice interaction modules and, once completed, will be publicly available.Publicationtype: Conference Paper55