Ice Tank Tests Research Articles

Image analysis methods for the flow of ice pieces on a hull surface in ice tank tests

Image analysis methods for the flow of ice pieces on a hull surface in ice tank tests

Experimental Study on IRV Ramming Artificial Model Ice

When the icebreaker sails in the polar region, it adopts continuous and ramming icebreaking operations. When the ice condition exceeds the design working condition, it uses the ramming icebreaking method to advance. The nonlinear icebreaking process and complex ice conditions make it difficult to accurately predict the ice-strengthened ships’ ramming performance. This paper develops a scale-ratio brittle model of ice to simulate thick, level ice and predicts the ice penetration distance and bow load of an icebreaking research vessel (IRV) model at different speeds. The test results show that the penetration distance of the scoop-shaped bow IRV increases with the ramming speed and the average and extreme values of the contact load increase with the increase in the speed. The experimental results are a valid complement to the ice tank tests and do not cover all aspects of ship design. The main purpose is to develop a test program and performance prediction scheme for studying penetration distance and ice load during ram icebreaking.

A comparison of regression models for the ice loads measured during the ice tank test

To evaluate the time-domain positioning performance of arctic marine structures, it is necessary to generate an ice load appropriate for the current position and heading of the structure. The position and orientation angle of a floating body continuously change with time. Therefore, an ice load is required for any attitude in the time-domain simulation. In this study, we present a fundamental technique for analyzing ice loads in the frequency domain based on data measured at various angles in the ice-water tank experiment. We perform spectral analysis instead of general FFT to analyze the ice load, which has the characteristics of a random signal. To generate the necessary ice load in the time domain, we must first interpolate the measured data in the frequency domain. Using the Blackman-Tukey method, we estimate the spectrum for the measured data, then process the data to generate the training set required for machine learning. Based on the results, we perform regression analysis by applying four representative techniques, including linear regression, random forest, or neural network, and compare the results with MSE. The deep neural network method performed best, but we provide further discussion for each model.

Research on self-propulsion simulation of a polar ship in a brash ice channel based on body force model

Main engine power prediction is important for polar ships operating in brash ice channels, which is one of the most important concerns of shipowners. Self-propulsion simulation is an efficient method to predict the developed power. At present, such models as the discretized propeller model (DPM) and the body force model (BFM) are used for self-propulsion simulation. However, these models are often limited to open water. There is little research on self-propulsion calculations in ice-infested water. This paper presents the BFM to carry out self-propulsion simulations in a brash ice channel. Research on simulation strategy for open water performance based on the BFM is carried out. Ship–ice–water interactions are simulated using computational fluid dynamics-discrete element method (CFD-DEM) coupling method. Both loaded and ballast conditions are considered in the model-scale self-propulsion simulations. Numerical results based on the BFM are compared with the simulation results based on the DPM, as well as model test results. Ship–propeller–ice interactions and propeller suction effects are also compared with photographs taken at an ice tank test. The results show that the differences of the developed power based on the BFM for both loaded and ballast conditions are 8.94% and 15.25%, respectively. The prediction accuracies of the developed power based on the BFM for both loaded and ballast conditions are 1.56% and 7.01%, respectively; lower than those based on the DPM. However, the computation efficiency based on the BFM is 12 times higher than that based on the DPM. To conclude, the proposed BFM could be used as an effective means to calculate the developed power and to evaluate the trend of hull-line optimization at the development stage.

Influence of seasonal and regional variation of ice properties on ship performance in the Arctic

The ongoing growth and digitalization of Arctic shipping strengthen the relevance of the models for ship performance prediction. Most of existing models consider ice thickness, total concentration, and other geometrical parameters of ice, while the change of ice flexural strength is usually neglected. This article aims at answering the question of how the flexural strength of level ice depends on the season and region of the Arctic, and on how this variation influences the ice performance of a ship. For this purpose, we developed a method to estimate the properties of ice of a given thickness based on the data on natural conditions in a certain region. Sensitivity analysis of this method showed that seasonal and regional changes in the flexural strength of ice could be predicted using the data on air temperature and seawater salinity. The available climatic data allowed us to analyze a spatiotemporal variability of these two parameters in the Russian Arctic. To predict the performance of constructed ships in ice, we developed a resistance scaling approach. Its accuracy was examined using full-scale data, ice tank tests, and numerical model results for 21900M-type icebreakers. This study concludes that variation of ice properties significantly affects ice performance of a ship and should be considered when simulating year-round navigation in the Arctic.

Resistance Performance of a Ship in Model-Scaled Brash Ice Fields Using CFD and DEM Coupling Model

The brash ice channel formed with icebreaker navigation is a normal working scenario for ice-going vessels. Therefore, it is necessary to study brash ice resistance in this condition. In this study, CFD and DEM coupling methods were adopted to investigate the resistance performance of a ship sailing in model-scaled brash ice fields, considering the collision force and friction resistance, among the brash ice, and the water resistance and hydrodynamic force of brash ice, which make up physical scenarios of navigation in the brash ice channel. To study the effect of aforementioned parameters on the average total resistance, the time step, iteration, and brash ice stiffness were analyzed; we found that a time step of 0.02 s, iteration of 10, and brash ice stiffness of 1000 N/m that showed better repeatability of the physical phenomenon, and it was used to reproduce working conditions created in the HSVA ice tank test. The error between the numerical simulation results and the test results is less than 5%, which shows the robustness of the present coupling strategy. Finally, the effects of ship–ice friction coefficient, ice thickness, ice shape, brash ice channel width, and ice concentration on the resistance of the ship were investigated and verified with the published results.

CFD-DEM based full-scale ship-ice interaction research under FSICR ice condition in restricted brash ice channel

The CFD-DEM simulations are performed to investigate the suitable ship-ice contact model and research the full-scale ship-ice interaction characteristics in the restricted brash ice channel. The discrete element method has been coupled in the viscous flow CFD solver to establish the brash ice model, combining with the VOF model of Euler Multiphase flow to simulate the interaction between the ship and brash ice. The AFRAMAX oil tanker ice test in Hamburg Ship Model Basin (HSVA) has been taken as the research reference. Firstly, the computed mean total ice resistance of different density grids show the monotonic convergence and meet the experimental results well. Secondly, three ship-ice contact models are applied to simulate the ship-ice collision, and the maximum relative error of total ice resistance is within −5.5%. Thirdly, the parametric study of ice shape and restitution coefficient is researched, which shows the ice shape could be the vital factor affecting the simulated total ice resistance. Finally, The full-scale total ice resistance under Finnish-Swedish Ice Class Rules (FSICR) IA and IB ice conditions are compared and discussed among the experiment, FSICR method, Dobrovin's empirical method, and CFD-DEM simulations. Moreover, the characteristics of collision, accumulation, extrusion, rolling, and sliding in the ship-ice interaction process are well consistent with the observations in the ice tank test, which indicates the proposed full-scale CFD-DEM approach of direct evaluating the ship-brash ice interaction shows reasonable results and practical value.

Repeatability of ice-tank tests with broken ice

This study investigates the repeatability of ice-tank tests with broken ice. Ice-tank test campaigns normally do not perform multiple repetitions of tests with the same initial conditions. Therefore, the repeatability of ice-tank tests with broken ice is not well understood. Data from two test campaigns are analysed. The first test campaign studied the interaction between a 4-legged structure with a vertical waterline and several broken and intact level ice conditions. In the second test campaign, a ship hull geometry was tested. We analyse selected test cases from each test campaign. The ice-tank tests are reproduced using a 3-D discrete element method (DEM) model. Each analysed test case is simulated 20 times. The only difference between each simulation is the initial position of the ice floes. The numerical simulation results show that changes in the initial floe positions can cause large changes in the statistical properties of the ice load. Often, a single random interaction event can be identified that is responsible for the change in the results. Such interaction events can cause additional floe accumulation ahead of the structure, thereby influencing the load statistics for a large portion of the interaction length. The observed events occur both in the numerical simulations and in the physical ice-tank tests. This result indicates that ice-tank tests with broken ice have a poor repeatability; a change in an uncontrolled condition, such as the exact initial floe positions, can lead to a large variation in the experimental results.

Numerical simulation of an ice-strengthened bulk carrier in brash ice channel

In this paper, the CFD-DEM coupling numerical method was applied to study the ship resistance of a certain type of ice-strengthened Panama bulk carrier in the brash ice channel. The ship-water interaction is established under Euler framework, and the ship-ice interaction is realized by means of the DEM method under Lagrange framework. The DEM ice particles modelling and the establishment of numerical brash ice channel were firstly carried out with reference to the HSVA ice tank test image and test parameters. Next, the influence of DEM ice particle shape on contact force and ship-ice interaction was studied. After that, the influence of the one-way coupling and two-way coupling computational scheme between fluid and particles on the calculation accuracy and the interaction phenomenon was studied and analyzed. Finally, the ship-ice interaction process and mechanical behavior of ship and particle interaction in the brash ice channel was simulated, and the numerical results were compared with the experiment of HSVA ice tank. The results show that the CFD-DEM coupling numerical method which takes full account of the effect of ship-water and the interaction between fluid and particles, can well simulate the phenomenon and process of ship-ice interaction, and compared with the experimental results, the average error of the numerical prediction is about 5.03–5.23% for ICE-1 case with one-way and two-way coupling. The CFD-DEM coupling numerical method includes water resistance, which improves the prediction accuracy of the alone DEM calculation method. The research work in this paper can provide a reference for the numerical prediction of navigation process of ships in the brash ice channel.

The effect of ice floe shape on the load experienced by vertical-sided structures interacting with a broken ice field

In this study, numerical experiments are conducted to investigate the effect of ice floe shape on the load experienced by vertical-sided structures interacting with a broken ice field. We create numerical ice fields with different floe shapes and otherwise identical properties. These fields are used to simulate ice-structure interaction with vertical-sided structures. First, we investigate the effect of floe shape in ice-tank tests by comparing the numerical results to the ice tank test results. Then, we conduct a sensitivity study to investigate the correlation between the floe shape effect and other parameters. The primary finding is that the ice floe shape has a large influence on the mean and standard deviation of the ice load in interaction scenarios dominated by ice accumulation and clearance around the structure. In particular, square floes, which are often used in ice tank tests, result in higher mean loads and standard deviations than other floe shapes. The simulation results show that the greater length and higher stability of force chains is the primary mechanism causing the floe shape effect. The floe shape effect is exacerbated in confined conditions, where the force chains may cause bridging between the structure and a rigid boundary. The presence and length of ‘parallel opposite edges’ is an important factor influencing the floe shape effect. This result is novel compared to earlier studies, which only consider body ‘roundness’ or ‘angularity’ in assessing shape effects. We demonstrate the importance of using accurate floe shapes in ice tank tests and in discrete element method (DEM) modelling of broken ice-structure interaction scenarios.

An implicit time-stepping scheme and an improved contact model for ice-structure interaction simulations

This paper presents a novel time-stepping scheme for the modelling of discrete ice-structure interaction. The scheme extends the non-smooth discrete element modelling (NDEM) technique to enable compliant continuous and discontinuous contacts. This increases the accuracy and expands the applicability range of the NDEM technique related to ice-structure interaction problems. We derive the parameters representing the compliant behaviour of contacts. The accuracy of the presented scheme for discontinuous contacts is compared to an existing, simpler scheme that limits the contact force based on a maximum force assumption. The comparison shows that the derived scheme results in more accurate contact forces, for the same time step size, as previously applied NDEM schemes in ice-structure interaction. An example simulation is compared against ice tank tests of a 4-legged, vertical-walled structure moving through a broken ice field.

Numerical modeling of ice loads on an icebreaking tanker: Comparing simulations with model tests

A numerical model is presented to simulate the dynamic ice loads acting on an icebreaking tanker in level ice, considering the action of ice in the vicinity of the waterline caused by breaking of intact ice and the effect of submersion of broken ice floes. The numerical simulations are also compared with ice tank tests. For these tests, ice rubble accumulation contributes to a high ice load and thus was taken into consideration in the simulations in addition to the ice-breaking forces. In the simulations, an icebreaking tanker fixed by artificial high stiffness mooring lines was towed through an intact ice sheet. The setup of the numerical simulation was as similar to the ice tank setup as possible. The ice loads were compared between model tests and simulations by varying the ice drift speed, the relative ice drift angles and ice properties. The results show that the simulated ice loads are in good agreement with the experimental results in terms of the mean values, standard deviations, and maximum and extreme force distributions, although there are some deviations between the predicted and measured results for certain cases. Some of the possible reasons that may explain the differences have been presented. The numerical model can be applied to predict the ice loads on moored or dynamic structures with station-keeping operations in level ice with a constant drift direction, and it can be extended to variable relative ice drift directions.

Manoeuvring performance of podded propulsors behind a ship

This study investigates the performance of podded propulsors in various operating conditions: open water and different ice conditions. The model used in this study is an icebreaker driven by twin-podded propulsors. Preliminary results from ice tank tests are presented. These include steering moment generated by the propulsors, thrust and torque of the propellers and the forces exerted on the hull at the location of the connection of the propulsors for different levels of ice and pack ice conditions, as well as in open water.

Ice Tank Tests on Ice Rubble Loads Against a Cable-Moored Conical Platform

Presented herein are ice-tank data concerning ice-rubble loads against a moored conical platform. Of prime interest is how rubble-ice loads are influenced by horizontal stiffness of the platform’s mooring system. An important, and heretofore undocumented, feature of rubble loading and clearing around the platform is the accumulation of ice rubble as a false bow, or prow, at the platform’s leading perimeter. The ice-tank data show that, under certain conditions of ice-rubble loading, the lowest stiffness of mooring tested resulted in prow instability and sloughing, which in turn lead to a cyclic pattern of loading, and to rubble congestion around the platform. An outcome of such rubble congestion was a marked increase in the overall rubble-ice load exerted against the platform.

Baltic Ice Class IA를 적용한 115K Ice Tanker 개발

There are very few numbers of 115K FPP (Fixed Pitch Propulsion) Tankers for the Baltic ice class IA because the minimum power requirement of FMA (Finish- Swedish Maritime Association) needs quite large engine power and the 40 m Beam is out of calculation range of FMA minimum power requirements. The shipyard has no choice except to increase the engine power to satisfy FMA minimum power requirement Rule. And the operation cost, efficiency of hullform and its building cost are not good from the ship owners' point of view To solve this problem, the experience of ice breaking tanker development and the ice tank test results were adopted. The main idea to reduce the ice resistance is by reducing waterline angle at design load waterline. The reason behind the main idea is to reduce the ice-clearing force. Two hull forms were developed to satisfy Baltic Ice class IA. Two ice tank tests and one towing tank test was performed at MARC (Kvaener-Masa Arctic Research Center) and SSMB (Samsung Ship Model Basin) facilities, respectively. The purpose of these tests was to verify the performance in ice and open water respectively The hull form 2 shows less speed loss compared to Hull form 1 in open water operation but hull form 2 shows very good ice clearing ability. finally the Hull Form 2 satisfying Baltic ice class IA. The merit of this hull form is to use the same engine capacity and no major design changes in hull form and other related designs But the hull structure has to be changed according to the ice class grade. The difference in two hull form development methods, ice model test methods and analysis methods of ice model test will be described in this paper.

Modelling floating offshore units moored in broken ice: comparing simulations with ice tank tests

A numerical simulation model that simulates the behaviour of a vessel moored in broken ice has been used to compare results from numerical simulations with ice tank tests. In the simulations a tanker moored on an eight legged catenary mooring of the Submerged Turret Loading (STL) concept was towed through a broken ice field. The setup of this situation was as similar to the ice tank setup as possible. The results predicted by the model are in qualitative agreement with the experimental results, but the amplitudes tend to be overpredicted. The predicted frequency of oscillation in surge is slightly lower than what was measured. The deviations between predicted and measured results may in part be explained by the differences in model and ice tank setup, and in part by poor representation of various load limiting mechanisms. However, with the qualitative agreement achieved, and the differences between model and experimental setup in mind, it is reasonable to believe that the numerical model may yield realistic results in further full-scale simulations.

FIRST YEAR RIDGE LOAD ESTIMATION ON A VERTICAL SIDED STRUCTURE

This paper describes the experimental study on the first year ridge load. The authors attempted to estimate ridge load by the ice tank tests despite the lack of the field data setting rough assumptions. Ridges were built in the ice tank using molds. The consolidation depth was controlled with the insulation sheet and room temperature. 800mm wide rectangular indentor with segmented ice pressure panels in water line and ridge keel direction was used to measure the local pressure characteristics. The tests were performed varying the indentation velocity, compliance of the indentor. An estimation of the fist year ridge load exerted on a vertical sided structure is attempted using the test results.

ICE LOADS AS A FUNCTION OF STRUCTURE STIFFNESS

Vertical sided structures may have advantages over inclined structures in terms of construction costs and past experiences. Although, it is well recognized that even a massive structure may vibrate if a load exceeds certain level after the lesson of Molikpaq experienced in 1986. Designers shall know the parameters that cause vibrations while structures indent against various ice features. The vibration may inversely affect design loads and foundation stability. A five-year ice load research program was executed from 1993 to 1997 to clarify the characteristics and develop the computer code capable of simulating vibrations and associated loads. Extensive ice tank tests were performed to observe crushing phenomena and obtain the verification data for the computer code. In this paper, highlights of test results are summarized to feature the non-simultaneous and simultaneous failure modes.