Ice Model Tests Research Articles

A CFD-DEM-FEM coupling method for the ice-induced fatigue damage assessment of ships in brash ice channels

Polar transport ships frequently traverse in the brash ice channel opened by icebreakers. Although the substantial ice resistance caused by direct collisions with the level ice is avoided, the hull still encounters collisions with the brash ice, leading to periodic damage and exacerbating the fatigue issues of the hull structure. To address the fatigue challenges faced by ships sailing in the brash ice channels, this paper proposes an ice-induced fatigue damage assessment method based on the CFD-DEM-FEM. Referring to the brash ice model test conducted at the Hamburg Ship Model Basin (HSVA), a discrete element ice model and a numerical brash ice tank are established using the CFD-DEM coupling method. The simulated ship-ice interaction is compared with HSVA’s experimental results to validate the reliability of the numerical brash ice tank and ice load. The ice load time history resulting from the ship-brash ice collision is applied to the hull, and the hot spot stress time history under each fatigue sub-condition is calculated using the FEM. The improved rain-flow counting method is employed to determine the stress level of the hot spot stress time history, and the S-N curve method based on the linear cumulative damage criterion is used to calculate the total fatigue damage of hot spots. Finally, the results of the proposed method are compared with those of the LR method. This study can serve as a valuable reference for the ice-induced fatigue assessment of ships navigating in brash ice channels.

Scaling principles for model testing in old brash ice channel

Climate warming sets higher requirements for sustainability in ship industry, which fuels the introduction of stricter power restrictions and new types of ship hull design. The new designs invite us to reconsider the principles in model scale testing in ice, which is the state-of-the-art method to predict vessel's ice performance prior to its construction. Ice model testing principles were originally developed for the evaluation of performance in level ice at slow speed, but currently those principles are widely applied for ice model testing in other ice conditions as well.The forces forming the vessel resistance in a brash ice channel are different compared to forces forming the vessel resistance in level ice. In consequence, the current model scale testing principles are suboptimal when predicting vessel's performance in an old, frequently operated brash ice channel, as our earlier research indicates that the prediction is conservative especially for modern merchant ship bow shapes with high stem angles. An old brash ice channel is especially interesting, as it is the determining ice condition in Finnish-Swedish Ice Class Rules ice class granting process.This paper addresses the problem by introducing a new similitude number – a Channel number – to be applied alongside the currently applied Froude and Cauchy similitudes. The Channel number aims to realistically scale the dominating forces that form the resistance of the vessel in an old brash ice channel by developing further the modelling of the resistance component induced by displacing the ice fragments. This necessitates considering the brash ice fragment interaction and inertia forces. The new scaling principle, which supplements the currently applied Froude-Cauchy scaling principle by the Channel number, is considered more accurate for brash ice conditions. It is designed to predict fairly and uniformly the ship resistance for all bow shapes avoiding potential overpowering of the modern bow types with a high stem angle. This would contribute to providing a good harmonization of ships' expected ice performance with ice classes, and, further, improve the fleet schedule predictability that the logistic chains demand from the transportation.

The choice of ice conditions for ice model tests to support the industrial development of the Оb’ Вay

The Ob’ Bay has long been the main center for the development of the Russian oil industry in the Arctic region. The rapid growth of shipping and the active creation of port infrastructure in this area are an integral part of the strategy for the development of the Russian Arctic. The main feature of the hydrometeorological regime of the Ob’ Bay is the annual presence of ice for a long time. Determining the ice performance of icebreakers, tugboats and heavy-tonnage vessels designed for the region, as well as ice loads on marine platforms and hydraulic structures, is a most important task in the creation thereof.The paper describes research carried out in the ice model tank of the Krylov State Research Centre over the past twenty years. The research supports the design and operation of new technical facilities intended for the industrial development of the Ob’ Bay. In the completed study, two main areas of research can be distinguished, namely the interaction of ships and engineering structures with ice formations in the Ob’ Bay. The paper emphasizes a significant dependence of the possibility of conducting ice tests and proper analysis of findings on the quality of the initial data, primarily hydrology and ice parameters.The results of ice model tests analysis, especially the ice impact on offshore and hydraulic structures for the Ob’ Bay, show the need to change approaches to determining theoretical ice loads and, as a result, to expand ice model testing programs. The simulation of the worst-case scenario, when all ice parameters are determined for a given probability and are not consistent with each other, leads to a significant overestimation of ice loads and the physical modeling of unrealistic combinations of ice conditions.Each ice impact scenario should contain the maximum value of only one main ice parameter corresponding to the probability. The main ice parameters include the thickness, the flexural strength or compression strength and the speed of ice drift. In this case, ice parameters should be selected in accordance with the chosen main one in the modeling scenario. It should not be the result of the same maximum value calculation for the given observation period as for the main ice parameter.

Direct measurements and CFD simulations on ice-induced hull pressure of a ship in floe ice fields

Floe ice fields are expected to replace level ice to be the most common environment for future polar sea transportation under the long-term trend of global warming. In this study, the authors aim to develop a viable analysis procedure to predict the ice-induced hull pressure characteristics for ships navigating in floe ice fields. A novel ice model test procedure is established, which is characterized by making use of non-refrigerated synthetic model ice and tactile pressure sensors to measure the hull pressure. The numerical tool is based on a state-of-the-art CFD-DEM numerical framework; a novel method to monitor the hull pressure during the interaction between the hull and ice floes during the CFD-DEM simulations. Statistical analysis indicates the probability distributions of the ice pressure from the experiment and the numerical results are comparable. Besides, the impacts of ship speed and ice floe concentration on the hull pressure distribution are also examined. Increasing speed and ice concentration will make the probability distribution of ice pressure shift towards the high-pressure going interval, resulting in an increased mean of ice pressure. It is also found that increased speed leads to a smaller variance, while increased ice concentration results in a larger variance.

EXPERIMENTAL STUDYING A POSSIBILITY OF CLOSE-COUPLED TOWING OF LARGE-SIZED VESSELS BY ICEBREAKER

The experimental studies in the ice model tank of the Krylov State Research Centre are described in the paper. This study aimed at researching a possibility of close-coupled towing of large-sized vessels by icebreaker. The displacement of considered commercial vessels is several times greater than the icebreaker displacement. Due to the fact that an amount of cargo transported along the Northern Sea Route is growing every year and new terminals are being constructed for the export of raw materials extracted in the Arctic, it has been shown in the paper that new transport vessels with high cargo capacity should be designed and built for the efficient operation of terminal. It has also been shown that the organization of independent year-round operation of such vessels in the Arctic region is extremely difficult, therefore, even at the stage of their design it’s important to consider the possibility of their escorting by existing icebreakers. The feasibility of close-coupled towing in the escorting of large-sized vessels with low ice class by icebreakers in the Arctic waters has been studied in the paper. The models of the greatest existing nuclear-powered icebreaker and conditional bulk carrier are used as an object of the ice model tests. The study of the close-coupled towing features in the continuous flat ice conditions is carried out at straightforward movement and gyration, as well as for the case of an emergency stop of the icebreaker. During ice model tests the ice forces acting on the hull of the model are measured, as well as the load on a towing notch with rubber fenders in the stern of icebreaker and the tension in the wire rope. The comparison of the wire rope tension with its breaking force is taken as a criterion to assess the possibility of the close-coupled towing operation. The results can be used as the basis for choosing the hull concept of the future large-sized vessels, its ice class and main dimensions and in strategic simulations of Arctic marine transport systems.

Full-Scale/Model-Scale Comparison of Podded Icebreaker’s Performance in Ice with Flexural Strength Measurement Study

_ This paper provides the results of model tests in ice to evaluate the performance of the USCG Mackinaw Icebreaker that was equipped with two podded propulsors and compares with the data obtained from the full-scale ice trials. The objective of this collaborative model test program between the NRC and USCG was to understand the capability and limitation of the model tests with podded vessels in ice. As a result, the model tests showed a good agreement with attainable speeds at selected power levels but an overestimation of the ice resistance by an average of 7% (from 10% to 25%). Further discussion of podded icebreaker performance including turning circle tests in ice is provided and future work is proposed. This paper also provides a discussion of two different flexural strength test methods, which are simple beam and cantilever beam tests. Introduction The number of icebreakers with podded propulsors has been increasing in recent years and many new icebreakers are planning to use the pods because of high maneuverability and additional benefits such as low noise and vibration, and various usages of the propeller wake. The first pod unit (1.3 MW) was installed in a utility vessel Seili in 1990. Since then, several ice-going tankers/ icebreakers have used single or multiple pod units, which had up to 16 MW power (Wilkman et al. 2018).

Status and needs for ice tank testing in a changing climate

150 years ago, the first modern icebreaker in the world was designed by the naval architect Carl Ferdinand Steinhaus and built for purpose of removing ice barriers on the river Elbe in Hamburg, Germany. No model tests were performed at that time. Later, in the first half of the 20th century, “model tests” for ships were carried out in natural ice on lakes. In the 1950th the first-generation ice model basins were put in operation and ice model testing became a standard method in the icebreaker design process. This paper discusses the influence of the economic and environmental development in arctic regions, driven by shipping and offshore activities in environmental changing Arctic Waters, on the ice model basin design, equipment and testing methods. The developments will be presented with examples from The Hamburg Ship Model Basin (HSVA). To complete the overview, an outlook to future trends is attempted.

빙마찰계수에 따른 쇄빙탱커의 빙저항 변화

This study describes the model tests in ice according to the frictional coefficient of an ice-breaking ship and the change in ice resistance by the analysis method for each component of ice resistances. The target vessel is a 90K DWT ice-breaking tanker capable of operating in ARC7 ice conditions in the Arctic Ocean, and twin POD propellers are fitted. The hull was specially painted with four different frictional coefficients on the same ship model. The total ice resistance can be separated by ice breaking, ice buoyancy, ice clearing resistances through the tests in level ice, pre-sawn ice and creep test in pre-sawn ice under sea ice thickness of 1.2 m and 1.7 m. Ice resistance was analyzed by correcting the thickness and bending strength of model ice by the ITTC correction method. As the frictional coefficient between the hull and ice increases, ice buoyancy and clearing resistances increase significantly. When the surface of the hull is rough, it is considered that the broken ice pieces do not slip easily to the side, resulting in an increase in ice buoyancy resistance. Also, the frictional coefficient was found to have a great influence on the ice clearing resistance as the ice thickness became thicker.

Research on total resistance of ice-going ship for different floe ice distributions based on virtual mass method

This paper presents the virtual mass method to implement the prediction of total resistance for ice-going ship in floe ice region based on the combined method of CFD and DEM. Two ways of floe ice distribution are adopted for the analysis and comparison. The synthetic ice model test has been conducted to determine the optimal virtual mass coefficients for the two different floe ice distributions. Moreover, the further verification and prediction are developed in different ice conditions. The results show that, the fixed and random distributions in numerical method can simulate the interaction of ship and ice vividly, the trend of total resistance varying with the speed and ice concentration obtained by the numerical simulation is consistent with the model test. The random distribution of floe ice has higher similarity and better accuracy than fixed distribution.

Ice interaction processes during ice encroachment

Ice encroachment is the accumulation of ice atop a platform and results when ice drifts against a platform. Most often this occurs in shallow water but in principle can occur in deep water if the ice drift length is long enough. As the ice drifts against the platform it is broken and generates rubble and ice piles in front of the platform, and with sufficient drift duration blocks of ice can be pushed up and onto the platform. This must be taken into account when designing structures in the Caspian Sea and other shallow water areas where there is significant ice drift. Ice can encroach on the structure by ice ride-up and pile-up. Consequently, the height and extent of the ice piling up on top of the structures must be taken into account in designing the layout, and often a protective ice encroachment zone is made all around the structure. The aim of this paper is to provide an outline of various approaches and parameters to consider where ice encroachment may occur. The study is supported by analysis of dedicated ice model test data, numerical simulations using Discrete Element Models, and full scale data of ice encroachment events. The intent is to give an understanding of the physics of ice encroachment and support in the design of shallow water offshore structures. In particular, the results indicate the importance of ice strength in the process and especially the maximum pile height. If the ice is weaker, the pile grows horizontally in a seaward direction in front of the structure, and conversely, stronger ice forms ice encroachment with greater vertical and also horizontal extent on the platform. The results also show that once the maximum pile height is established subsequent drift enlarges the seaward extent of the rubble pile in front of the structure.

Model scale investigation of aspects influencing the ice resistance of ships sailing ahead in level ice

ABSTRACTFor 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.

Study on the procedure to obtain an attainable speed in pack ice

The cost evaluation for voyage route planning in an ice-covered sea is one of the major topics among ship owners. Information of the ice properties, such as ice type, concentration of ice, ice thickness, strength of ice, and speed-power relation under ice conditions are important for determining the optimal route in ice and low operational cost perspective. To determine achievable speed at any designated pack ice condition, a model test of resistance, self-propulsion, and overload test in ice and ice-free water were carried out in a KRISO ice tank and towing tank. The available net thrust for ice and an estimation of the ice resistance under any pack ice condition were also performed by I-RES. The in-house code called ‘I-RES’, which is an ice resistance estimation tool that applies an empirical formula, was modified for the pack ice module in this study.Careful observations of underwater videos of the ice model test made it possible to understand the physical phenomena of underneath of the hull bottom surface and determine the coverage of buoyancy. The clearing resistance of ice can be calculated by subtracting the buoyance and open water resistance form the pre-sawn ice resistance. The model test results in pack ice were compared with the calculation results to obtain a correlation factor among the pack ice resistance, ice concentration, and ship speed. The resulting correlation factors were applied to the calculation results to determine the pack ice resistance under any pack ice condition. The pack ice resistance under the arbitrary pack ice condition could be estimated because software I-RES could control all the ice properties.The available net thrust in ice, which is the over thrust that overcomes the pack ice resistance, will change the speed of a ship according to the bollard pull test results and thruster characteristics (engine & propulsion combination). The attainable speed at a certain ice concentration of pack ice was determined using the interpolation method. This paper reports a procedure to determine the attainable speed in pack ice and the sample calculation using the Araon vessel was performed to confirm the entire process. A more detailed description of the determination of the attainable speed is described. The attainable speed in 1.0 m, 90% pack ice and 540 kPa strength was 13.3 knots.

Model Tests With a Compliant Cylindrical Structure to Investigate Ice-Induced Vibrations

A compliant cylindrical structure has been built and tested in a series of model tests in ice in the Large Ice Model Basin at HSVA. The structure's stiffness in ice plane is higher in ice drift direction than crosswise, enabling the model to vibrate in different geometrical oscillation patterns. In total, four ice sheets have been used to perform tests in different ice thickness, covering a wide range of ice drift velocities between 0.005 and 0.15 m/s in model scale. Several events of ice-induced vibrations were observed throughout the test campaign. Oscillations are found to reach different types of beginning steady states, depending on ice drift velocity and ice thickness. Dynamic amplification of structural response in ice plane as well as ratio of static and dynamic forces is highly dependent on the type of vibration. While the dynamic amplification is highest when the ice load's frequency equals the first natural frequency of the structure, the highest dynamic forces occur when the crushing frequency is an integer fraction of the natural frequency. The paper describes the design of the test setup, instrumentation and calibration, performance and analysis of conducted tests, and general findings.

On the Scalability of Model-Scale Ice Experiments

Ice model tests are a frequently used mean to assess and predict the performance of ships and structures in ice. The model ice composition is adjusted to comply with Froude and Cauchy similitude. Recent research indicates that the internal mechanics of Aalto model-scale ice and sea ice differ significantly. This consequently limits the scalability and challenges state-of-the-art scaling procedures. This paper presents a qualitative assessment on selected topics to assess the differences between model-scale ice and sea ice and the influence of related experiments on determined mechanical properties. Furthermore, existing scaling approaches are discussed in context of recent research findings.

Calculation of ice clearing resistance using normal vector of hull form and direct calculation of buoyancy force under the hull

The ice-resistance estimation technique for icebreaking ships had been studied intensively over recent years to meet the needs of designing Arctic vessels. Before testing in the ice model basin, the estimation of a ship’s ice resistance with high reliability is very important to decide the delivered power necessary for level ice operation. The main idea of previous studies came from several empirical formulas, such as Poznyak and Ionov (1981), Enkvist (1972) and Shimansky (1938) methods, in which ice resistance components such as icebreaking, buoyancy and clearing resistances were represented by the integral equations along the Design Load Water Line (DLWL). The current study proposes a few modified methods not only considering the DLWL shape, but also the hull shape under the DLWL. In the proposed methodology, the DLWL shape for icebreaking resistance and the hull shape under the DLWL for buoyancy and clearing resistances can be directly considered in the calculation. Especially, when calculating clearing resistance, the flow pattern of ice particles under the DLWL of ship is assumed to be in accordance with the ice flow observed during ice model testing. This paper also deals with application examples for a few ship designs and its ice model testing programs at the AARC ice model basin. From the comparison of results of the model test and the estimation, the reliability of this estimation technique has been discussed.

Numerical analysis of the bending strength of model-scale ice

Performance simulation tools are of high significance for the design and especially the optimization of ships and offshore structures. However, for ice covered waters such tools are hardly available and are either costly as ice model tests or have a limited range of validity, such as semi-empirical formulas. This arises from the complexity of ice as material and insufficient knowledge on its mechanics. This paper presents a numerical analysis for model-scale ice in which material parameters are developed that can represent: tension, compression and in-situ downward bending. Those parameters are incorporated into a material model following the Lemaitre damage law. The developed material characteristics for model-scale ice are intended to support the design process of ships and offshore structures. The key phenomenon joining the deformation processes in bending together with those in compression and tension, proved to be the through thickness dependency of properties. This analysis and development is a continuation of previously presented parameters for compression and tension and is developed in agreement with experimental evidence.

입자형 EG/AD 모형빙 준비기법 연구

This study proposed a new method of preparing granular ethylene glycol/aliphatic detergent (EG/AD) model ice that has both strength and uniform thickness. Various sheets of granular model ice prepared in ice tanks are surveyed and their preparation procedures are analyzed. We not only made a new granular model ice using the EG/AD solution but also measured its thickness, strength, and density. In addition, we found that the strength of the model ice could be controlled by varying the time and air temperature in the consolidation phase. Based on the results of this study, we verified that granular EG/AD model ice can be prepared more uniformly and effectively than columnar EG/AD model ice. This study is intended to contribute to reducing the time required for the ice model test and the operation of the ice model basin.

Experimental and Numerical Investigation of Dynamic Positioning in Level Ice

Offshore operations in ice-covered waters are drawing considerable interest from both the public and private sectors. Such operations may require vessels to keep position during various activities, such as lifting, installation, crew change, evacuation, and possibly drilling. In deep waters, mooring solutions become uneconomical and, therefore, dynamic positioning (DP) systems are attractive. However, global loads from drifting sea ice can be challenging for stationkeeping operations of DP vessels. To address this challenge, the current paper investigates DP in level ice conditions using experimental and numerical approaches. The experimental part describes a set of ice model tests which were performed at the large ice tank of the Hamburg Ship Model Basin (HSVA) in the summer and autumn of 2012. Experimental design, instrumentation, methods, and results are presented and discussed. The numerical part presents a novel model for simulating DP operations in level ice, which treats both the vessel and the ice floes as separate independent bodies with six degrees-of-freedom. The fracture of level ice is calculated on-the-fly based on numerical solution of the ice material failure equations, i.e., the breaking patterns of the ice are not precalculated. The numerical model is connected to a DP controller and the two systems interchange data dynamically and work in a closed-loop. The structures of the models, as well as the physical and mathematical assumptions, are discussed in the paper. Finally, several ice basin experiments are reproduced in the numerical simulator, and the results of the physical and numerical tests are compared and discussed.

Numerical assessment of a double-acting offshore vessel's performance in level ice with experimental comparison

In this paper a numerical model is used to investigate the level ice performance of a double-acting intervention vessel, and the results are compared with a limited set of experimental data. The icebreaking capability and maneuverability in level ice are analyzed by evaluating the behavior of the vessel when it is running both ahead and astern. The simulated icebreaking patterns, h–v curves, and turning circles in different modes of operation are discussed and compared partly with the corresponding ice model tests. The simulation results can supplement the experimental data by providing more information about the vessel's maneuverability in level ice and identifying the physical foundation for the exhibited performance of the vessel. The paper also presents the implementation of a random crack size model for more realistic icebreaking behavior, giving more consistent evaluation of the ship's performance in various ice conditions.

Ice Resistance Model Test Technology for 110K Tanker Adopting FSICR Ice Class IA

Ship model test in ice towing tank is one of the key technologies for the design of ice-strengthened ship, and is the primary measure of determining the ship required minimum engine output power in ice navigation and checking whether satisfies the requirements of ice class rules. Researched the relevant requirements of 1A ice-strengthened ship based on the Finnish-Swedish ice class rules (FSICR), which is minimum engine output power according to the forward form of hull line and according to standard formulas. Studied the technical requirements of ice model test. Determined the minimum engine output power for 110k oil tanker with ice class 1A based on ice model test.