Ice Flexural Strength Research Articles

Investigations on Flexural Strength of a Columnar Saline Model Ice under Circular Plate Central Loading

The properties of ice strength have a significant impact on the design and safety of structures in ice-infested waters. To analyze the flexural strength of columnar saline model ice, we conducted circular plate center loading tests at the Small Ice Model Basin of the China Ship Scientific Research Center (CSSRC SIMB) in China. The tests involved varying the loading rate and ice temperature, and a numerical model was developed using FEM and LS-DYNA for validation and comparison. The results of the tests revealed the crack propagation process, stress distribution, load response, and failure mode of the model ice. The model ice displayed typical brittle failure, and the flexural strength was linearly related to ice temperature but not significantly correlated with loading rate. The porosity of the model ice affected the load response and time of failure but not the failure mode. The model ice with 7% porosity had a 7.8% reduction in load response compared to the nonporous model ice. This study provides a reliable method for measuring and analyzing the flexural strength of model ice. It also serves as a foundation for further research on the interaction between structures and ice sheets.

Analysis and realization of the influence of sea ice flexural strength on ice resistance in numerical simulation of icebreaking by icebreaker

Ice resistance of icebreaker navigating in ice area is the main reference index for the ship design and the selection of the main engine. Researchers gradually use the numerical simulation method to study ice resistance and its influencing factors because of the development of computer technology. But there are few studies on the effect of sea ice flexural strength on ice resistance in the numerical simulation. In this study, a method was proposed to simulate the change of sea ice flexural strength numerically by changing the parameters of the sea ice material model, so as to realize the influence analysis on ice resistance. Firstly, the material model that can realize the simulation of the icebreaker running ahead in level ice was determined. Then, the parameters of the material model affecting the flexural strength numerically were determined. Taking the material model adopted in this paper as an example, the parameters were plastic failure strain, Young's modulus, and compressive yield strength. Finally, the value criterion of influence parameters was put forward in the given design space and applied to the numerical simulation of the icebreaker running ahead in level ice. It was demonstrated that the method could realize the influence of sea ice flexural strength on ice resistance in the numerical simulation. This study is a new attempt in the numerical simulation of the icebreaker running ahead in level ice and it can help ship designers to analyze the navigation performance of icebreakers in different ice areas.

A Universal Formula for Evaluating the Compressive and Flexural Strength of Sea Ice at Thermodynamic Calculations

A Universal Formula for Evaluating the Compressive and Flexural Strength of Sea Ice at Thermodynamic Calculations

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.

Flexural and compressive strength of the landfast sea ice in the Prydz Bay, East Antarctic

Abstract. A total of 25 flexural and 55 uniaxial compressive strength tests were conducted in laboratory using landfast sea ice samples collected in the Prydz Bay. Three-point bending tests were performed at ice temperatures of −12 to −3 ∘C with force applied vertically to original ice surface, and compressive strength tests were performed at −3 ∘C with a strain-rate level of 10−6–10−2 s−1 in the directions vertical and horizontal to ice surface. Judging from crystal structure, the ice samples were divided into congelation ice, snow ice, and a mixture of the two. The results of congelation ice showed that the flexural strength had a decreasing trend depending on porosity rather than brine volume, based on which a mathematical equation was established to estimate flexural strength. Both flexural strength and effective modulus of elasticity increased with increasing platelet spacing. The uniaxial compressive strength increased and decreased with strain rate below and above the critical regime, respectively, which is 8.0 × 10−4–1.5 × 10−3 s−1 for vertically loaded samples and 2.0 × 10−3–3.0 × 10−3 s−1 for horizontally loaded samples. A drop-off in compressive strength was shown with increasing sea ice porosity. Consequently, a model was developed to depict the combined effects of porosity and strain rate on compressive strength in both ductile and brittle regimes. The mechanical strength of mixed ice was lower than congelation ice, and that of snow ice was much weaker. To provide a safe guide for the transportation of goods on landfast sea ice in the Prydz Bay, the bearing capacity of the ice cover is estimated with the lower and upper envelopes of flexural strength and effective elastic modulus, respectively, which turned out to be a function of sea ice porosity.

Probabilistic estimation of level ice resistance on ships based on sea ice properties measured along summer Arctic cruise paths

The decline of Arctic sea ice makes trans-Arctic transport possible in the summer, which increases the requirement of ice-strengthened vessels. Accurate estimation of ice resistance is necessary for ice-strengthened ship design and this process requires data on various ice properties. The objective of this study was to investigate the probabilistic characteristics of Arctic sea ice properties associated with estimations of ice resistance on ships. To achieve this aim, measurements of ice properties were collected from Arctic voyages conducted in the summers of 2008−2016. Ice thickness and ice concentration were observed along ship routes, and ice flexural strength and effective modulus were determined based on the physical properties of ice. The ice–hull kinetic friction coefficient was estimated according to ship velocity. Statistical analyses were conducted on these ice properties. The results showed that most ice properties can be described using existing statistical models (Burr XII, Beta, Gamma, and generalized extreme value distributions), with the exceptions of ice concentration, ice salinity and temperature, as well as friction coefficient. Furthermore, a Monte Carlo simulation was employed to estimate the ice resistance of a ship moving forward in a level ice zone based on a well-established empirical equation. The results showed that the distribution of ice resistance conformed to a Gamma distribution. The correlation coefficients between ice density and flexural strength as well as effective modulus had negligible effects on the simulation results. This study provides a helpful guide for the design of ice-strengthened ships and related numerical simulations required for summer trans-Arctic navigation.

Prediction of ice resistance for ice-going ships in level ice using artificial neural network technique

Ice resistance is affected by many parameters, i.e., ship geometries, ice properties and interaction properties. Over the years, various methods ranging from empirical, semi-empirical, numerical methods and various of their combinations were developed to calculate the ice resistance with certain degree of success. In this study, from a brand-new perspective, a data-driven approach for estimating ice resistance based on the artificial neural network was proposed. The artificial neural network (ANN) is one of the main tools for machine learning. It can accurately and efficiently correlate directly the inputs and outputs of complex and nonlinear systems, such as the ice resistance calculation system. This physical system involves several interaction phases and at least three groups of input parameters (i.e., ship, ice and interaction characteristics). Following the basic idea of ANN, we trained and built six ANN models based on datasets that were collected over past decades involving both model tests and full-scale measurements. The six different ANN models differ in the amount of input parameters. Based on comparative studies, among all the input parameters (i.e., 7 variables in total: ship length, ship breadth, ship draft, stem angle, ship speed, ice flexural strength and ice thickness), we found that the ship breadth, ice thickness and ship speed have the largest influence on the calculation of ice resistance. Afterwards, the 7-variable ANN model's prediction was compared with existing semi-empirical methods and measurements; and favorable agreement was achieved with fairly simple matrix form formulas (i.e., Eq. (19)). The formula offers another simple, yet reliable approach to calculate ice resistance. However, since the method is data driven, high quality data are always needed in improving the predicting capability of the relevant ANN model following the methodology outlined in this paper.

Statistics of thickness and strength of first-year ice along the Northern Sea Route

In this paper, statistics of ice thickness and ice strength of first-year sea ice along the Northern Sea Route (NSR) is studied to provide useful information for the design and operation of Arctic ships. Specifically, ice thickness, ice strength and other physical parameters of the sea ice are estimated. Four representative sites are selected to study the ice environment and ice strength in different sea areas along the NSR during the ice growth season. Besides that, a good knowledge of the co-variation relationships between these ice parameters in a particular region would promote the estimation of ice loads acting on structures located in this region. In this work, a novel probabilistic model is introduced to describe the probability distribution of the ice flexural strength. The co-variation relationships between ice thickness and ice strength are quantified in terms of correlation coefficients. The influence of air temperature on ice properties is also investigated and discussed.

Full-scale flexural strength of sea ice and freshwater ice in Spitsbergen Fjords and North-West Barents Sea

The present paper describes the results of a rather long series of full–scale, flexural–strength tests on ice beams (over 70 tests) performed in–situ in seawater and freshwater ice at and near Svalbard archipelago during the period 2010–2018. Ice thickness varied in the range of 0.2–0.8 m. Based on a comprehensive analysis of the test data, characteristic plots of ice flexural strength and effective elastic modulus versus the liquid–brine–volume fraction, which varied over a large range of 0–0.2 and were obtained specifically for the geographic region under consideration. The observed range in flexural strength for seawater ice was 0.109–0.415 MPa, and the same for freshwater ice was 0.275–0.807 MPa. The test results with cantilever beams did not show a dependence of the ice flexural strength on the direction of bending force applied to the free end of a beam. Experiments complemented with numerical analysis have demonstrated that stress concentrations in root sections of cantilever ice beams have significant impact on the accuracy of measurement of flexural strength of freshwater ice. It is noted that modifications have to be introduced in the methodology that is used to measure the effective elastic modulus of ice based on the free–end deflection of cantilever ice beams.

빙해역 시운전 해석을 위한 환경조건 보정 방법 및 검증

Vessel’s ice speed performances will be verified in ice sea trial but environmental conditions of ice fields are changeable according to the weather condition of ice trial area. Speed performance has to correct in the no wind, wave and current etc. after sea trial. Especially finding ice fields which is exact the same as owner’s ice thickness and strength requirements is not easy. Therefore speed correction according to environment condition has to be done after sea trial measurements. Correction methods for ice thickness, ice strength, wave, wind and ship draft, trim, ice drift etc. are checked in ice sea trial based on literature review such as ISO standard, ITTC recommendation, journal papers and proceedings of conferences. Possibility of application for current and ice drift correction in ice field are discussed and measuring schemes and procedures of correction methods are described in this paper. All of correction schemes are calculated for ‘Araon’ which is ice breaking research vessel with Arctic and Antarctic ice field test results. Analyzed results shows that Araon is satisfied with her official ice speed performance of 3 knots with 10MW power at 1m ice thickness, 570kPa ice flexural strength.

Scale Effect in Ice Flexural Strength

Ice flexural strength is an important parameter in the assessment of ice loads on the hulls of ice-class ships, sloped offshore structures, and sloped bridge piers. While scale effects in compressive ice strength are well known, there has been debate as to the extent of scale effects in ice flexural strength. To investigate scale effects during flexural failure of both freshwater and saline ice, a comprehensive up-to-date database of beam flexural strength measurements has been compiled. The database includes 2073 freshwater ice beam tests with beam volumes between 0.00016 and 2.197 m3, and 2843 sea ice beam tests with volumes between 0.00048 and 59.87 m3. The data show a considerable decrease in flexural strength as the specimen size increases, when examined over a large range of scales. Empirical models of freshwater ice flexural strength as a function of beam volume, and of saline ice as function of beam and brine volumes have been developed using regression analysis. For freshwater ice, the scale-dependent flexural strength is given as: σf=839(V/V1)−0.13 For sea ice, the dependence of flexural strength has been modeled as: σ=1324(V/V1)−0.054e−4.969vb. Probabilistic models based on the empirical data were developed based on an analysis of the residuals, and can be used to enhance probabilistic analysis of ice loads where ice flexural strength is an input.

DEM Simulation of Uniaxial Compressive and Flexural Strength of Sea Ice: Parametric Study

AbstractMicroscale parameters have significant influence on the macromechanical behaviors of brittle materials in the discrete-element method (DEM). The rational determination of microparameters is still an open problem to model the failure characteristics of brittle materials. In this study, a three-dimensional DEM with bonded-particles is adopted to simulate the failure process of brittle materials. Interparticle friction and softening failure criteria are applied in the DEM simulations. The physical experimental data of sea ice are adopted to calibrate the DEM results. The influences of the interparticle friction coefficient and the bonding strength of bonded particles on the failure processes of sea ice are analyzed with the DEM simulations of the uniaxial compressive and flexural strengths of sea ice. The ratio of uniaxial compressive to flexural strength is used to calibrate the interparticle strengths and friction coefficient of bonded particles in comparison with experimental data. The relationshi...

Qualitative Description of a Shoulder Ice Barrier-Ice Interaction During Model Tests

This paper describes, qualitatively and through visual observations, the ice-sheet interaction with a shoulder ice barrier (SIB) during model tests. The model tests were performed in the Hamburg Ship Model Basin (HSVA) during July 2007. Since the SIB represents a new concept in ice barrier structures, model tests were intended to evaluate the general performance of the SIB. The paper describes seven different experiments where the ice thickness, the ice flexural strength, and the shoulder angle of the SIB are the parameters which are varied among them. The results are presented in two sections. The first part refers to observations common to all the experiments, where the ice failure mode and shoulder performance are given special attention. The second part describes the phenomena observed in each particular experiment in more detail. The former analysis allows for the visual identification of three phases (as mentioned in previous publications) and gives a deeper insight into the characteristics of each phase. The latter analysis on the contrary, allows us to achieve interesting conclusions about the SIB performance under different ice conditions and with different shoulder inclinations. A comparison between the failure mode observed during the model tests and observations presented in the literature of full scale vertical and sloped structures, ice interaction with rubble accumulation, is performed. The similarities found in the study between the model and full scale observations lead us to assume that the observed model test behavior may be expected during ice-SIB interaction in full scale conditions. However, some events that could be associated with the problems of the model, such as ice scaling, are highlighted. As a conclusion regarding the SIB performance, it is shown that the shoulder section, which is the principal innovation of the concept, satisfactorily accomplishes its task and represents a key modification to traditional ice barriers in generating smaller ice pieces and avoiding ice overriding.

Experimental Studies on Elastic Modulus and Flexural Strength of Sea Ice in the Bohai Sea

This paper deals with measurements of the elastic modulus and the flexural strength of sea ice collected at nine sites in the Bohai Sea in the two consecutive winters of 2008–2010. Experimental results show that both elastic modulus and flexural strength increase with a decrease of brine volume and have an exponential relationship with brine volume. The elastic modulus is independent of stress rate, but the flexural strength increases linearly with the increase of stress rate. This paper presents a single-parameter (i.e., brine volume) exponential equation for the elastic modulus and a two-parameter (i.e., brine volume and stress rate) exponential equation for the flexural strength, respectively. Finally, the relationship between the elastic modulus and the flexural strength is discussed.

On the flexural strength of DUT-1 synthetic model ice

Based on the statistical values of Bohai ice physical and mechanical parameters—such as density, compressive strength, flexural strength, shear strength, elastic modulus and friction coefficient—an ideal synthetic model ice was designed following the scale of 1:10–1:30. A model ice prescription and making art were found and called DUT-1 Ice. In order to know the flexural strength of DUT-1 Ice in detail, two stages of experiment were arranged. During the first stage, over 500 samples for a series of systematic tests were done. It is found that ductile bending occurs below 350–400 kPa/s in three-point bend test and 60–65 kPa/s in cantilever bend test. Their corresponding failure time are in the range of 0.03–0.38 s and 0.5–0.76 s, respectively, which is in the range of flexural failure time of simulated natural ice. Comparison of flexural strength of downward and upward loading cantilever tests gives the affirmation of isotropy of the model ice because of its granular structure. After 1 h wetting, the peak flexural strength of three-point specimens becomes steady and maintains this state for more than 4 h. This period gives us enough time to conduct model tests of ice behaviors or ice interactions with structures. In the second stage, another 500 specimens was tested. The effects of cement content and curing period were obtained, and the selection method of suitable peak flexural strength for different ices and test scale can be done based on the effects. Similar with natural ice, DUT-1 Ice flexural strength increases with increased wetted density. The ratio of elastic modulus and flexural strength over 2000 indicated that DUT-1 Ice is capable of physical simulations of ice bending failures with inclined structures, with waves, ice pile-up and ice jam processes.

A Study on Effect of Bow Shape on Icebreaking Resistance

In the 1st report, it was shown that the icebreaking resistance at low ship speed is proportional to the total crack length independently of the bow shape, and is determined by the tangent of hull stem angle at the hull/ice contact point. The effect of bow shape on the icebreaking resistance is investigated in detail by analyzing the results of extensive model experiment with three different bow forms. The icebreaking resistance is obtained by subtracting the resitance in pre-sawn ice from that in level ice.This paper studies the speed dependency of icebreaking resistance, i.e. the increase of icebreaking resistance with ship speed, comparing it with the vertical motion of ship bow. The major results are as follows : (1) As the ship speed increases, icebreaking resistance increases as a linear function of bow vertical motion. A spoon bow shows the lowest speed dependency, a wedge-shaped bow is the second, and a concave bow is the highest. The icebreaking resistance nondimensionalized by ice flexural strength, ice thickness and tangent of stem angle at the hull/ice contact point increases linearly with the heave amplitude at bow nondimensionalized by ice thickness, independently of the bow shape.(2) Frequency analyses of resistance and bow heave have shown three origins of icebreaking resistance. They are (a) resistance due to hull motion, (b) resistance due to icebreaking at the shoulder, and (c) resistance due to icebreaking at the bow center. The former two components are large in case of the wedge-shaped and concave bows. The third component is large in case of the spoon bow.(3) The rotation of broken ice piece is closely related to ship motion and broken ice piece size and shape. Such ice/ship motion coupled resistance can not be well removed by a pre-sawn ice test.(4) The resistance increase due to broken ice piece rotation is determined by the rotation speed and broken ice piece shape. The rotation speed depends on the hull inclination angle at hull/ice contact point. The broken ice piece shape depends on the bow waterline angle and curvature.(5) Because of the above-mentioned relationship between bow shape and broken ice piece, the wedge-shaped and concave bows produce very large and long ice pieces at the shoulder and the ice piece rotation speed is high, while the spoon bow gives wider but shorter (less slender shaped) ice pieces whose rotation speed is low. This is the reason why the spoon bow shows the lowest speed dependency of ice resistance.

A Study on Effect of Bow Shape on Icebreaking Resistance

A ship, advancing in a level ice field with continuous icebreaking mode, is subject to several components of ice resistance such as resistance due to breaking of ice, ice buoyancy, removing ice and ship motion. Although the third and forth components increase with ship speed, the first component, i. e. icebreaking resistance, is the most significant. This paper studies the icebreaking resistance at low ship speed.The results of model experiments on icebreaking resistance were analyzed in detail for three different bows. They were a conventional wedge-shaped bow, spoon bow and concave bow. The following results were obtained.(1) Independently of the bow shape, icebreaking resistance is in proportion to the total crack length, ice flexural strength and ice thickness squared.(2) Decreasing hull stem angle at ice contact point raises the width of broken ice piece, resultingin shorter crack length. The icebreaking resistance nondimensionalized by the ice flexural strength and ice thickness is determined by the tangent of hull stem angle at the contact point.(3) Since the spoon bow has smaller stem angle and larger waterline angle, the total crack length becomes shorter compared to the other bows. This is the reason why the spoon bow gives the lowest ice resistance.

Changes in the Flexural Strength of Ice under Radiation Decay

The strength of an ice cover significantly affects the timing and severity of breakup on northern rivers. During the pre-breakup period, thermal and radiative warming is known to significantly decrease such strength. Although reductions in strength with temperature are reasonably well known, there is a dearth of data concerning strength changes due to internal radiative melt. In the spring of 1989, near Floral, Saskatchewan, Canada, a detailed series of experiments were conducted to determine changes in flexural strength, porosity and optical properties of the ice cover. The test data strongly support existing theoretical models of strength reduction due to porosity development in columnar grained ice. Experimental methods and results with respect to flexural testing, porosity determinations and radiation energy balance are discussed.

Flexural Strength of Ice on Temperate Lakes

AbstractLarge, simply supported beams of temperate lake ice generally yield significantly higher f1exural strengths than the same beams tested in the cantilever mode. Data support the view that a significant stress concentration may exist at the fixed corners of the cantilever beams. Maximum effects are experienced with beams of cold, brittle ice substantially free of structural imperfections; the stress concentration factor may exceed 2.0 in this kind of ice. In ice that has undergone extensive thermal degradation the stress concentration effect may be eliminated entirely. Simply supported beams generally test stronger when the top surface is placed in tension. This behavior is attributed to differences in ice type; the fine-grained, crack-free top layer of snow-ice usually reacting more strongly in tension than the coarse-grained bottom lake ice which is prone to cracking.