Ice Load Data Research Articles

Experimental research on propeller-ice contact process and prediction of extreme ice load

Due to the complex and diverse nature of the propeller-ice contact problem, understanding the contact mechanism and evaluating the ice loads remains challenging. This study investigates the propeller-ice contact problem and explores the internal factors influencing the ice loads through model experiments at different advanced velocities, rotational speeds, and milling depths. The recorded ice load data is then used to predict the extreme loads that the propeller may encounter throughout its life cycle using the probabilistic method. The experimental results reveal that the shadowing effect and angle of attack are the primary reasons advanced velocity affects ice load, with the latter factor also being the internal cause of the load change caused by the rotational speed change. Moreover, the nonlinear increase of the ice load with the cutting depth increase is due to the chord length's change. The probability method analysis shows that the maximum thrust and torque the blade may encounter during its life cycle are approximately 50% and 35% higher than the maximum data recorded in the test. Additionally, this manuscript introduces the ice-making process and proposes a more straightforward calculation method for the shadowing coefficient.

Study on the Dynamic Ice Load of Offshore Wind Turbines with Installed Ice-Breaking Cones in Cold Regions

The dynamic ice load of conical offshore wind turbines (OWTs) in cold regions is unclear. The ice force period is the key parameter used to establish an ice force model for conical structures. To obtain ice load data, a field monitoring system was installed on an OWT in a cold region in China. Based on the monitoring data, a new formula for calculating the ice force period of conical structures was established. By comparing the period calculated with this formula and the measured ice force period, it was found that the calculated data generally agreed with the measured data. Then, a random dynamic ice force model for conical OWTs can be established. Based on this ice force model, the ice-induced vibration of an OWT was analyzed with the ANSYS finite element software. The results are in good agreement with the measured data obtained from the OWT in the time and frequency domains. Therefore, the random dynamic ice force model established in this paper can be used to evaluate the ice resistance performance of conical OWTs in cold regions.

Model-scale tests on ice-structure interaction in shallow water: Global ice loads and the ice loading process

Laboratory-scale experiments on ice-structure interaction process in shallow water were performed by pushing a ten-meter-wide ice sheet against an inclined structure of the same width. Seven experiments were performed in three series: In one of the series, the compressive and flexural strengths were both about 50kPa, in the two other test series the ice strength was two and four times higher. The ice thickness was about 50 mm in all experiments. The loading process showed two phases: the ice load on the structure (1) first increased linearly with a rate that was constant for all experiments, after which (2) the loading process reached a steady-state phase with approximately constant load. The magnitude of ice loads was not proportional to ice strength, as the weakest ice yielded higher loads than the ice having twice its strength. The ice rubble grounded in all experiments, but the bottom carried only a small portion of the load. The load records could be normalized by a factor combining the weight and the characteristic length of the intact ice. Based on the normalization, a model explaining the loading process was derived; the weight of the incoming ice has a dominant role during phase (1), while buckling explains the change in the process to phase (2) when the ice is strong enough. The loading process for the weakest ice was different from that for the other two ice types used. For example, instead of forming a rubble pile consisting of distinct ice blocks, weakest ice formed a dense pile of slush. The normalized ice load data highlighted the differences in the loading process.

Scatter and error estimates in ice loads – Results from virtual experiments

This paper analyses peak ice loads on an inclined, rigid marine structure by using data from 2D combined finite-discrete element method simulations. The aim is look for answers to the questions: what type of distributions do peak ice loads follow, what type of data is needed for their analysis, and how should the data on peak ice loads be collected? In the simulations, an initially continuous ice sheet, modeled as a floating beam, breaks into smaller ice blocks as the sheet is pushed against the structure. Statistical tools were used to analyse the peak ice load distributions, error estimates, and peak ice load occurrences. Load distributions appeared to be right-skewed and thus non-normal. Gumbel distribution appeared to describe the data well. The results show that the large scatter in the ice load data is due to the ice-structure interaction process itself. Due to the scatter, a large number of observations are needed for studying peak ice load statistics: To reliably observe a 15% difference in peak loads due to a single parameter would require more than 80 observations in total. The results showed that high peak loads may occur even in the early stage of the ice-structure interaction process.

Ice loads on inclined marine structures - Virtual experiments on ice failure process evolution

Failure of level ice against an inclined marine structure has been simulated using a two-dimensional finite-discrete element method. The simulation model is deterministic, but very sensitive to initial conditions. This allowed us to create ice load data and to study the evolution of the ice failure process. The mean load, the standard deviation, and the maximum load increased during the ice failure process. Ice thickness had a strong effect on the ice load and also the plastic limit of ice had an effect, especially when the ice was thick. The coefficient of variation of the ice load was initially high and then continuously decreased during the ice failure process. This suggests that the ice failure process did not reach a stationary stage, showed high probability of extreme peak loads, and that distributions with a constant coefficient of variation should not be used for this kind of ice loading processes. Extreme value analysis, with the assumption that the ice load follow a log-normal distribution on each time step, fitted the data well and suggested that the maximum ice load increases with sample size. Further, it appears that the peak ice loads are bounded by the crushing capacity of the ice even in the case of an inclined structure. The statistical analysis of simulated ice load data further suggests that observations from short interaction processes, or with small sample sizes, may lead to very inaccurate ice load estimates.

The statistical analysis of peak ice loads in a simulated ice-structure interaction process

This paper analyses peak ice load data from 2D combined finite-discrete element method simulations. In these simulations, an initially continuous ice sheet, modeled as a floating beam, breaks into smaller ice blocks as the sheet is pushed against an inclined structure. Multivariate linear regression modeling and the variable elimination method were used in the analysis of the data. The analysis gave valuable insight into the peak ice load data in a simulated ice-structure interaction process. It was found that the peak ice load data can be estimated with good accuracy using only five parameters: the ice thickness, the inclination angle of the structure, the shear strength of ice, the ice-structure, and ice–ice friction coefficients. The ice thickness and the structure's inclination angle had the strongest relative effects, with their importance changing during the process. The results also showed that the stage of the ice-structure interaction process should be taken into account in ice load models. The results of this paper underline the importance of the statistical analysis of ice load data and give valuable suggestions for future work.

쇄빙연구선 ARAON호의 남극해 쇄빙운항 중 계측된 스트레인게이지 데이터 분석

Estimation of correct ice load under various operating conditions is important during the design and the operation stages of an icebreaker. Normal operating conditions are expected from the official field ice trials and also from general ice transit action. In this paper ice load for the Korean icebreaking research vessel, ARAON, under normal operating condition, is discussed. Published ice load data from full-scale sea trials of six icebreakers were analysed to derive an empirical ice load prediction formula. The IBRV ARAON had sea ice trials during 2010 and 2012 summer season. Strain gauge signal were recorded during her icebreaking voyage and the measured strain data were converted to the equivalent hull stress values. The effect of ARAON's speed in ice and the hull stresses are investigated. By comparing the empirical formula and ice load calculation based von measured data, it is recommended to use the empirical ice load estimation formula for the initial design stage.

정상운항 상태에서 쇄빙선박에 작용하는 설계 빙하중 추정

AbstractIce load is one of the important design parameters for the construction of icebreaking vessels. In this paper, the design ice load prediction for the icebreaking vessels under normal operating condition in ice-covered sea is discussed. The ice loads under normal operating condition are expected from sea trials in moderate ice conditions. In this sense the extreme ice loads during heavy ramming or accidental collision are not considered. Current study describes the global ice load on the hull of the icebreaking vessels. Available ice load data from full-scale sea trials are collected and analyzed according to various ship-ice interaction parameters including displacement, stem angle, speed of a ship and flexural strength and thickness of sea ice. The ice load prediction formula is compared with the collected full-scale sea trials data and it shows a good agreement. ※Keywords: Icebreaking vessels(쇄빙선박), Design ice load(설계 빙하중), Global ice load(전체 빙하중), Normal operating conditions(정상운항 상태)

쇄빙상선의 빙하중 추정식 고찰

One of the concerns that arise during navigation in ice-covered waters is the magnitude of ice loads encountered by ships. However, the accurate estimation of ice loads still remains as a rather difficult task in the design of icebreaking vessels. This paper focuses on the development of simple ice load prediction formulas for the icebreaking cargo vessels. The maximum ice loads are expected from unbroken ice sheet and these loads are most likely to be concentrated at the bow area. Published ice load data for icebreaking vessels, from the model tests and also from full-scale sea trials, are collected and then several ice load prediction formulas are compared with these data. Finally, based on collected data, a semi-empirical ice load prediction formula is recommended for the icebreaking cargo vessels.

海氷の一軸圧縮強度と荷重ピーク値の確率分布について

The strength of natural sea ice has a lot of scatter due to variations in its growing process. For engineering purposes, it is necessary to understand this strength randomness. The uniaxial compressive strength of natural sea ice at Lake Saroma was analyzed statistically to find an appropriate probability density function that would fit the strength data. Furthermore, peaks occurring in subsequent ice load data obtained in medium scale field indentation tests carried out by the JOIA project were analyzed statistically, since it had been found that each peak load was due to flaking failure of ice in an independent ice failure zone. From a Chi square test for goodness of fit, it was found that both uniaxial compressive strength and peak load fit a log-normal density function with 3 parameters. From this, a method for generating strength and peaks of ice load based on ice failure in the brittle condition can be developed.

Ice force spectrum on narrow conical structures

This paper presents an ice force spectrum model for narrow conical offshore structures deployed in ice infested areas. The force spectrum is developed from a spectral analysis of ice load data that was obtained in full-scale tests on the JZ20-2 platform in Bohai Bay. The results show that the power spectral density (PSD) function of the ice force has characteristics of both a narrow band and a wide band random process when the ice sheets fail by bending and the broken ice pieces are totally cleared up. The PSD function of the ice force can be approximated by the Neumann spectrum. This spectrum is the basis for the ice force model that is presented in this paper. This model can be used in a dynamic analysis of narrow, conical offshore structures that are exposed to the action of drifting ice floes.

Ice loads on the Molikpaq in the Canadian Beaufort Sea

The Molikpaq is a steel caisson structure that was used in the 1980s in the Canadian Beaufort Sea for exploration drilling of oil and gas. It was very extensively instrumented. Part of the instrumentation was designed to measure the ice loads. This paper presents an overview discussion of the characteristics and instrumentation of the Molikpaq. It presents detailed information on 188 ice loading events from both first-year and multi-year ice for different ice macrostructures including level ice, ridges, hummock ice and isolated floes. Investigation of the ice loads has shown that the Line Load (global load per unit length of the structure) increases with increasing ice thickness. The analysis of the ice loads in terms of the failure mode of the ice provides additional insight and explains some of the scatter in the ice load data.

ICE LOAD OF MULTI ICE FAILURE ZONES

The paper introduces the method which calculates ice load of multi-ice- failure zones from that of single failure zone. The method is based on correlation coefficient of a pair of ice loads on a single failure zone, in addition to auto-cor elation coefficient of ice load on a single failure zone. Non-uniform contact ofan ice sheet with a structure and statistical distribution of strength of natural ice are considered using ice load data obtained in the JOIA project.

Theoretical aspects of iceload measurements on fixed rods and overhead line conductors: A transfer function for dry rime-ice accretion

This paper is concerned with theoretical aspects of the methodology of iceload measurements on an overhead line conductor (OHLC) of finite span and finite torsional stiffness. The purpose is to establish the relationships between the iceload on a fixed rod or sampler and the spatial average iceload on an OHLC. A theoretical database, generated using dynamical models for rime-ice accretion on conductors, is carefully analysed to express iceload data as a function of meteorological conditions and the mechanical properties of the OHLC. These results provide the required ratios of the iceload on a sampler to that on OHLCs as a function of time during an icing incident. A transfer function, relating theoretically predicted iceloads on an OHLC to that for a sampler, is then constructed and should prove useful in the development of the corresponding methodology for relating sets of field measurements in this way. For design purposes progress in the latter is desirable.

Ice edge contact and failure

A model of ice loads and failure during ice-structure contact is proposed. The model is shown to be in good agreement with measured ice load data. The causes of variability and randomness in ice loads are addressed. Chaos theory is employed to analyze the behavior of the iterative sequence of cracks in the model. A simple set of analytical equations is used to model the ice contact process. The chaotic behavior of the equations is due to asymmetrical ice flaking. The resulting ice forces can be described with probability distributions derived from mechanical parameters. Comparison is made with measured ice forces from one set of tests and measured pressure-area values from another. Limitations and future directions are discussed.

Thirteenth Canadian Geotechnical Colloquium: Ice design criteria for wide arctic structures

The derivation of design global ice loads for wide vertical caisson-type arctic exploration structures is presented. Correction factors are applied to global ice-load data measured during ice–structure interactions to create a set of design criteria for two typical exploration structures: circular (100 m diameter) and rectangular (160 × 50 m). Return periods for the proposed deterministic design ice loads for these two structures are then determined for typical ice conditions encountered in the Harrison Bay shear zone area in 20–30 m of water. Key words: exploration structures, global design ice loads, risk, probability of exceedence, return periods.