Local Ice Pressures Research Articles

Study on the Factors Influencing the Amplitude of Local Ice Pressure on Vertical Structures Based on Model Tests

Study on the Factors Influencing the Amplitude of Local Ice Pressure on Vertical Structures Based on Model Tests

A Framework for Structural Analysis of Icebreakers during Ramming of First-Year Ice Ridges

This paper presents a framework for structural analysis of icebreakers during ramming of first-year ice ridges. The framework links the ice-ridge load and the structural analysis based on the physical characteristics of ship–ice-ridge interactions. A ship–ice-ridge interaction study was conducted to demonstrate the feasibility of the proposed framework. A PC-2 icebreaker was chosen for the ship–ice interaction study, and the geometrical and physical properties of the ice ridge were determined based on empirical data. The ice ridge was modeled by solid elements equipped with the continuous surface cap model (CSCM). To validate the approach, the simulated ice resistance was computed using the Lindqvist solution and in situ tests of R/V Xuelong 2. First, the local ice-induced pressure on the hull shell was determined based on numerical simulations. Subsequently, the local ice pressure was applied to local deformable sub-structural models of the PC-2 icebreaker hull by means of triangular impulse loads. Finally, the structural response of sub-structural models with refined meshes was computed. This case study demonstrates that the proposed framework is suitable for structural analysis of ice-induced stresses in local hull components. The results show that the ice load and the structural response obtained based on the four first-year ice-ridge models show obvious differences. Furthermore, the ice load and corresponding structural response increases with the width of the ridge and with increasing ship speed.

Estimation of ice loads on offshore structures using simulations of level ice-structure collisions with an influence coefficient method

During their service, ice-class vessels are exposed to ice collision loads. Precise estimation of such ice loads is essential to the design of ice-class vessels. Due to difficulties encountered in real measurement of ice loads, a simple yet logically straightforward method, namely the influence coefficient method (ICM), has been widely employed to convert strain data to ice pressures. However, the method's accuracy and reliability depend on how strain gauges are arranged and load cells are divided accordingly. This study investigated those aspects in order to enhance the accuracy and reliability of the ICM in estimating ice loads incurred in collisions of ice with offshore structures. It began by developing a numerical model of level ice-structure interactions. For this, an ice-material model applying the Drucker-Prager (DP) plasticity model combined with an element erosion technique's simplified damage mechanics was developed. The developed numerical model was verified by comparing its results with the relevant model test data and corresponding numerical results available in the open literature, and good agreement was achieved. Next, the present study performed, based on the numerical simulation strategy thus validated, simulations of level ice collisions with actual offshore structures showing inflexible and deformable behaviors. Subsequently, a finite element (FE) model of the structures’ instrumented area, which is the same as the scantling used in the ice collision simulation, was developed to construct an influence coefficient matrix for the ICM. The structural responses, including stress/strain data and ice-contact pressure observed numerically, were then applied to an investigation of the ICM capability. The effects of the strain gage arrangements and corresponding load cells on the estimation of the local ice pressures acting on actual offshore structures were demonstrated. The proposed procedure is expected to provide insights into how the ICM can be improved in reliably and cost-effectively estimating ice loads on ice-class offshore structures.

Distribution Analysis of Local Ice Pressures in the Indentation Test at Various Velocities

When sea ice acts on vertical structures, there are much higher pressures in localized areas known as high-pressure zones (HPZs) than in other areas. The damage failure mode of sea ice varies with the sea ice velocity and affects the distribution of HPZs. In this study, an indentation test that drives ice sheet interaction with a vertical rigid plate (indentor) was designed, and a pressure sensor (consisting of 32 × 32 small pressure units of 100 mm2) was installed on the indentor face to measure the local ice pressure (LIP) at various velocities. The distribution of the LIPs along the ice thickness, the probability distribution of the LIPs and the distribution relationship of the LIPS in space and time were obtained from the measurement. The results show that the LIPs were mainly distributed in the middle of the sea ice, which is consistent with full-scale observations and previous research. Ductile failure of the sea ice results in a larger LIP distribution area than brittle failure at the same threshold kt (kt = σL/σcr). The probability distribution of the LIPs decreases exponentially with increasing pressure and follows a lognormal distribution. The maximum LIP appears at the peak moment of the global force when the sea ice failure mode is mainly ductile failure. However, the maximum LIP may not occur at the peak moment when the sea ice failure is mainly brittle failure and, instead can appear at any moment in the global force time history curve. The HPZ (which is larger than 7/8 times the maximum LIP) area is less than 2% of the nominal contact area at various velocities. The influence of the sea ice velocity on the spatial and temporal distribution of LIP is analyzed, and the results provide a reference for designing structures with local strength in ice regions.

The Comparison of The Effectiveness of Local Ice and Manual Pressure Application in Decreasing Pain Related to Intramuscular Injection

Objective: Because of the pain they cause, injection applications can constitute a negative experience for both the patients and the nurses performing the application. This study was planned to compare the effectiveness of local ice and manual pressure applications in decreasing the injection pain experienced by patients. Methods:This study performed a university hospital in Turkey. Onehundred and five patients,45 in the lokal ıce group, 45 in the manuel pressure group and 45 in the control group, met the inclusion criteria and completed the study. The local ice group received cold ice application to the injection area before injection. The manual pressure group was received 10 seconds of pressure applied by the researcher to the injection area before injection. The control group received routine injection. Study data was collected using The Wong‐Baker FACES Pain Rating Scale and The Visual Analog Pain Scale. Results: A statistically significant difference among the groups with regard to mean WBS and VAS scores was found as a result of the study. The control group received a higher score compared to the groups which underwent manuel pressure and local ice applications. Conclusions: It was concluded that local ice and manuel pressure applications before IM injections were effective in decreasing the injection pains of patients.

Discrete Element Analysis of High-Pressure Zones of Sea Ice on Vertical Structures

In cold regions, ice pressure poses a serious threat to the safe operation of ship hulls and fixed offshore platforms. In this study, a discrete element method (DEM) with bonded particles was adapted to simulate the generation and distribution of local ice pressures during the interaction between level ice and vertical structures. The strength and failure mode of simulated sea ice under uniaxial compression were consistent with the experimental results, which verifies the accuracy of the discrete element parameters. The crushing process of sea ice acting on the vertical structure simulated by the DEM was compared with the field test. The distribution of ice pressure on the contact surface was calculated, and it was found that the local ice pressure was much greater than the global ice pressure. The high-pressure zones in sea ice are mainly caused by its simultaneous destruction, and these zones are primarily distributed near the midline of the contact area of sea ice and the structure. The contact area and loading rate are the two main factors affecting the high-pressure zones. The maximum local and global ice pressures decrease with an increase in the contact area. The influence of the loading rate on the local ice pressure is caused by the change in the sea ice failure mode. When the loading rate is low, ductile failure of sea ice occurs, and the ice pressure increases with the increase in the loading rate. When the loading rate is high, brittle failure of sea ice occurs, and the ice pressure decreases with an increase in the loading rate. This DEM study of sea ice can reasonably predict the distribution of high-pressure zones on marine structures and provide a reference for the anti-ice performance design of marine structures.

Local pressures for ships in ice: Probabilistic analysis of full-scale line-load data

Ships operating in ice might be exposed to significant ice loading. Using a probabilistic semi-empirical method known as the event-maximum method, the long-term maximum level of ice loading on a ship can be estimated based on parent distributions of short-term full-scale ice load measurements. The event-maximum method is used to model the relationship between extreme local ice pressures and impact area by estimating parameters corresponding to the inverse slope (α) and intercept (x0) for the line of best fit for the tail of ranked peak pressure data versus the natural logarithm of the Weibull plotting position. These best-fit lines are assumed to follow an exponential distribution and associated α and x0 values are produced for different local design areas. This allows for the determination of α-area curves, which reflects the relationship between ice pressure and the local design area. Previous studies have determined α-area curves for different geographical areas such as the Beaufort Sea and South Bering Sea, representing different ice types including both first-year and multi-year ice. In this study, two separate sets of full-scale ice load measurements having been considered, namely measurements from the Kara Sea and the Barents Sea, as well as measurements from the Antarctic Ocean. Using these two datasets, two new α-area curves have been generated that represent among other operating areas (the Kara Sea and the Barents Sea), operating modes (icebreaker assisted operation) and impact areas (aft shoulder) not covered by other curves. Earlier formulations of the event-maximum method are based on local design areas in which the width and height of areas are defined by the size of instrumented rectangular panel areas (or combinations of those areas) on the bow of the vessel from which the data were collected. In that approach, ice thickness is not directly considered since the height of individual panels is based on the dimensions of instrumented areas and moreover, detailed ice thickness records were not available for those data sets. In the present study, an alternative approach has been developed to extend the event maximum method for use with ship line-load data. In this approach ice pressures are calculated by dividing the ice force measured on frames by the corresponding line-load area (ALL), which is the product of the width (W) that is based on frame spacing and an assumed line-load height (H) corresponding to 30% of the maximum prevailing ice thickness, as per best design practice, along the lines of the Finnish-Swedish ice class rules. Data already presented as line-loads (in units of force per unit width), are converted to pressures by dividing line-loads by height H. The event definition used in the present approach is defined as the maximum pressure corresponding to 10- or 20-min intervals, as opposed to the impact event definition used in earlier works. In applying this extended method to develop new α-area curves, valuable insights into the relationship between local peak ice pressure and prevailing ice thickness have been gained for the above-mentioned full-scale measurements. The determined curves indicate a negative correlation between prevailing ice thickness and maximum local nominal ice pressure. Finally, it has been demonstrated that it is feasible to apply such curves in combination with the principle of the event-maximum method to estimate the maximum nominal ice pressure expected for a ship given a specified transit distance in sea ice with different prevailing thicknesses.

Investigations on the ship-ice impact: Part 1. Experimental methodologies

In the structural design of the Polar Class ships, glancing impact with ice has been considered as the governing load scenario for dimensioning the bow structure. At present, non-linear transient dynamic analysis has been reckoned as a fundamental requirement in the assessment of the structural strength of ships with higher ice classes. Under such requirement, understanding of the dynamic characteristics of the ship-ice impact load appears significant importance. The present study aims to investigate the spatial and temporal variations of the impact loads by simulating the glancing impact events between a polar research vessel and giant ice floes in ice tank. The ship-ice impact loads were recorded by a grid-based tactile sensor attached on the bow area of the model ship. To achieve a reasonable simulation on the design scenario described by the IACS Unified Requirements for Polar Class Ships (UR I), a series of methodological calibration tests were preliminarily carried out to determine the key parameters that should be carefully monitored and controlled, accompanying with thorough discussions on the ship-ice impact process. This paper provides detailed information on the preliminary methodological calibrations and the tactile data processing techniques, including the identification of the ship-ice contact area, the depiction of the ice loading trail and the outline of the spatial distributions of local ice pressures. A companion paper provides detailed analyses and discussions regarding the spatial and temporal variation of the ice impact loads from the formal tests based on the proposed testing procedures obtained by the methodological calibrations.

The ice extrusion test: a novel test setup for the investigation of ice-structure interaction – results and validation

ABSTRACT Understanding ice-structure interaction is critical for an efficient and safe design of offshore structures and ships in ice-covered waters. During the last decades a variety of field experiments, full-scale measurements on ships and laboratory tests have been conducted. Within this paper, a novel experimental setup of the ice extrusion test for the investigation crushing loads is proposed. Due to the flexible design of the experiment brittle and ductile ice loads can be investigated in the laboratory at different load levels. A comprehensive test series with more than 350 tests has been carried out to investigate the system behaviour. The failure mode of the ice is mostly determined by the test speed. The ratio of gap height and sample diameter is the most important parameter for the load level. A validation against full-scale data showed that with this experimental setup it is possible to generate relevant nominal local ice pressures.

Hybrid reconstruction method for indirect monitoring of an ice load of a steel gate in a cold region

The steel gate of a hydraulic complex may be subjected to ice loads during freezing periods in cold regions, threatening the gate safety. The ice load on the gate is usually affected by several factors, including the ice thickness, snow cover, and changes in water level and temperature. The ice pressure distribution on the gate cannot be readily estimated by theoretical analysis or empirical formulae. Therefore, structural strain and local ice pressure data were collected over 140 days during the winter of 2016–2017 to investigate the structural deformation and local ice pressure distribution. A hybrid reconstruction method (HCM) was developed for establishing the ice pressure distribution using the monitoring data, and the effectiveness of the HCM was analysed based on several uniform load patterns and the Chebyshev polynomial functions. The ice pressure distributions on the gate were reconstructed during the entire monitoring period, considering the collected data for the lowest temperature of each day. The reconstructed ice pressure distribution, i.e., the equivalent and uniform ice pressure within every individual cell, was lower than 0.1 MPa in most parts of the gate.

Field measurement of the reduction in local pressure from ice management

Local ice pressures are an important design consideration for vessels performing offshore stationkeeping operations, particularly in the late spring and early fall shoulder seasons when they tend to govern over global loading in the development of operating limits. This paper presents analysis of full-scale data that demonstrates the reduction in local pressures provided by ice management. The data was collected during the Oden Arctic Technology Research Cruise in 2015. The distinguishing aspect of this program was the use of two icebreakers, Oden and Frej, which provided the unique opportunity to conduct a full-scale stationkeeping trial in realistic managed ice conditions. Previous local ice pressure data collection programs have occurred during transit in unmanaged ice, ramming of multi-year ice and bergy bit impacts. These have been used to establish recommendations for local design pressures, however they are not completely representative of conditions while stationkeeping in managed ice. In this study the up-crossing rate method was used to analyze local pressure data collected from strain gaged load panels on the Frej's hull. The results indicate that local pressures from stationkeeping in managed ice are two to four times lower than the transiting cases most analogous to previous data. This provides a sound basis for advocating local design pressures that are lower than current recommendations, and also more representative of actual operating conditions. This can potentially extend the operating envelope of offshore vessels leading to significant savings, while still maintaining limits consistent with accepted risk profiles.

Probabilistic Analysis of Local Ice Loads on a Lifeboat Measured in Full-Scale Field Trials

This paper presents an analysis of local ice loads measured during full-scale field trials conducted in 2014 with a totally enclosed motor propelled survival craft (TEMPSC) in controlled pack ice conditions. These data were collected as part of an ongoing research program that aims to identify the limitations of conventional TEMPSC operating in sea ice environments and to provide insight as to how these limitations might be extended. During the 2014 trials, local ice loads were measured at two locations on the TEMPSC's bow area. These loads were the most severe measured to date and corresponded to an average ice floe mass that was approximately 1.25 times the mass of the fully loaded TEMPSC. The event-maximum method of local ice pressure analysis was used to analyze these field data to improve understanding of the nature of ice loads for such interactions and to evaluate the suitability of this approach for design load estimation for TEMPSCs (i.e., lifeboats) in ice. The event-maximum method was adapted for the present application, so as to link exceedance probabilities with design load levels for a given scenario. Comparison of the 2014 results with a previous analysis of 2013 field trials data supports earlier conclusions that these interactions are highly influenced by kinetic energy, since more massive ice floes are observed to impart significantly higher loads on the lifeboats. Illustrative examples examining the influence of ice concentration and sail-away distance have also been provided. The work establishes links between extreme loads and the exposure of the lifeboat to ice for different operating conditions. Based on this work it is concluded that the event-maximum method provides a promising approach for establishing risk-based design criteria for lifeboats if field data are available which adequately represent ice conditions encountered during the design life of the lifeboat.

A study on measurements of local ice pressure for ice breaking research vessel “ARAON” at the Amundsen Sea

In this study, a local ice pressure prediction has been conducted by using measured data from two ice breaking tests that was conducted for a relatively big ice floe at Amundsen Sea in the Antarctica from January 31 to March 30 2012. The symmetry of load was considered by attaching strain gauges on the same sites inside the shell plating of ship at the port and the starboard sides in the bow thrust room. Using measured strain data, after the ice pressure was converted by the influence coefficient method and the direct method, the two values were found to be similar.

Field measurement of local ice pressures on the ARAON in the Beaufort Sea

This study conducted four field measurements of local ice pressure during the icebreaking voyage of the icebreaking research vessel “ARAON” in the Chukchi and Beaufort seas from July to August of 2010. For measurements, 14 strain gauges, including 8 strain gauge rosettes, were set on the bow of the port side. Influence coefficients were determined using a finite element model of the instrumented area and they were used to convert the measured strains on the hull structure to local ice pressures. The converted maximum pressure was calculated as 2.12 MPa on an area of 0.28 m2. Pressure-area curves were developed from the surveyed pressure data and the results were compared with previously measured data. The study results are expected to provide an understanding of local ice pressures and thus be useful in the structural design of ice class ships.

해빙과의 접촉 면적을 고려한 국부 빙압력 추정 연구

Ice loads may be conveniently categorized as local ice loads and global ice loads. Local ice loads are often defined as ice pressures acting on local areas of shell plates and stiffeners. Therefore, local ice loads are defined in all ice class rules. However, directly measuring the local ice pressure using the actual ice class vessel is a very difficult task because appropriate instruments for direct measurement must be installed on the outer hull, and they are easily damaged by direct ice contacts/impacts. This paper focuses on the estimation of the local ice pressure using the data obtained from icebreaking tests in the Arctic sea in 2010 using the Korean icebreaking research vessel (IBRV) ARAON. When she contacted the sea ice, the local deformation of the side shell was measured by the strain gauges attached to the inside of the shell. Simultaneously, the contact area between the side shell and sea ice is investigated by analyzing the distribution of the measured strain data. Finally, the ice pressures for different contact areas are estimated by performing a structural analysis.

북극해 계측자료에 기초한 아라온호의 국부 빙압력 계산 연구

The icebreaking research vessel (IBRV) ARAON had her second ice trial in the Arctic Ocean in the summer season of 2010. During the voyage, the local ice loads acting on the bow of the port side were measured using 14 strain gauges. These measurements were carried out in three icebreaking performance tests. To convert the measured strains into the local ice pressures, a finite element model of the instrumented area was developed. The influence coefficient method (ICM), which uses the influence coefficient from the finite element model, and the direct method, which uses the measured strain, were selected as the conversion methods. As a result, the maximum measured pressure was 1.236MPa, and the average difference between ICM and the direct method was about 5% for an area of <TEX>$0.2m^2$</TEX>. The pressure-area relationship of the measurement falls below the range of the existing pressure-area curve, which is due to the low ice strength of melted ice in the summer.

Local Design Pressures for Structures in Ice: Analysis of Full-Scale Data

The design of structures for ice conditions requires knowledge of local ice pressures to allow for appropriate levels of structural strengthening. Full-scale field data are keys to enhancing our understanding and modeling of ice behavior. Data collected during icebreaker ramming events represent an important source of information for use in design load estimation, and the evaluation of design methodologies. This paper examines several ship-ice interaction data sets using the ‘event-maximum’ method of local pressure analysis developed by Jordaan and et al. (1993, “Probabilistic Analysis of Local Ice Pressures,” ASME J. Offshore Mech. Arct. Eng., 115, pp. 83–89). In this method, the local pressure is obtained from a normalized curve, which contains two parameters α and x0. The parameter α is a function of the area, well represented by the curve α=CaD, where a is the local area of interest, and C and D are constants. The parameter x0 is assumed a constant for a given design scenario. An alternative approach, the up-crossing rate method, is presented in a companion paper (2009, “Estimation of Local Ice Pressure Using Up-Crossing Rate,” Proceedings of the OMAE 2009, Honolulu, HI). Local pressure analysis results for data from the USCGS Polar Sea, CCGS Terry Fox, CCGS Louis St. Laurent, and Swedish Icebreaker Oden are presented. A discussion of panel exposure, event duration, and the effects of these factors on x0 is given. New design curves are included. For all data considered, the calculated values of α fall below the design curve. For the design, it is recommended that α is calculated using a C value based on the impact data collected under ice conditions similar to those for the design scenario; D may be treated as a constant having a value of −0.7. A design value of x0 may be determined based on the analysis of appropriate data sets. The treatment of exposure is described for data analysis and design. The effects of exposure must be removed during data analysis to provide a design curve based on single panel exposure. For the design, estimates from the design curves must be adjusted to properly reflect the design exposure.

Estimation of Local Ice Pressure Using Up-Crossing Rate

Ice load estimation is required in the design of ships and offshore structures for arctic and subarctic conditions. This paper focuses on the estimation of local ice pressures. The “event-maximum” method for local ice pressure analysis is a probabilistic method based on the maximum pressure of a given event; other local peaks in the data are not included. To study how this may affect local ice pressure estimates, a new probabilistic method based on the up-crossing rate was developed. Field data from 1982 Polar Sea arctic trials in the Beaufort Sea are processed as a time series. Up-crossing rates at different local pressure levels are obtained for local areas of interest. A relationship between up-crossing rate and local pressure-area results is established. Results from the analysis of full-scale data using the event-maximum method are presented for the selected data set; a more comprehensive set of results for the analysis of available ship-ice interaction data is presented in a companion paper. For a sample case, local ice pressure estimates obtained using the up-crossing rate method are compared with results obtained using the event-maximum method. The local pressure-area relationship is found to be similar for both the up-crossing rate method and the event-maximum method. For design curves based on the data set considered, estimates using the event-maximum method were more conservative than those obtained using the up-crossing rate method. The up-crossing rate approach is promising; analysis of additional data sets is recommended to allow broader comparison of the methods.

Local ice pressures for multiyear ice accounting for exposure

Abstract Local pressures are generally determined based on extreme pressures obtained in measurements. The exposure of structural components is an issue that needs attention. Exposure can be considered in everyday terms as “the longer you fish, the bigger the fish you catch.” In the case of design of offshore structures for ice environments, the more numerous the number of ice–structure interaction events, the greater the likelihood of a particular load being exceeded. The number of interactions with multiyear ice is different for say the Beaufort and Chukchi Seas, and varies with location within these areas. These differences are expressed in terms of the exposure of the structure to multiyear ice. Exposure may also vary depending on location within the structure. Structure above or below the ice belt may receive few interactions resulting in small local pressures. The paper presents a generalization of a method for accounting for exposure, originally developed for ship rams. The particular application is multiyear ice interacting with a structure. The panel data from the Beaufort Sea experience of the Molikpaq structure is used as an example. Exposure is an important parameter that can be taken into account with the method. The previous relationship α = 1.25 a − 0.7 obtained for ship rams can be reasonably applied to multiyear ice, where 10 min of multiyear ice interaction is approximately equivalent to 1 Kigoriak ship ramming event. The method is promising for use in codes, for example with the new ISO Code 19906.

Local ice pressures measured on a strain gauge panel during the CCGS Terry Fox bergy bit impact study

Abstract A field test program was carried out with the CCGS Terry Fox off the northeast coast of Newfoundland in June 2001. During these trials, a total of 178 impacts occurred between the vessel and bergy bits whose sizes ranged from 20 t to 22,000 t, at ship speeds from 0.2 to 6.5 m/s. An area on the port bow was instrumented using 120 strain gauges. An in situ calibration of the instrumented area was performed to measure the response of the various gauges to a known load. A finite element model of the instrumented area was developed. The in situ measurements were used to validate and adjust the finite model. Using the calibrated finite element model, strains measured on the hull structure were converted into pressures on the hull. Of the 178 ship–bergy bit impacts, 60% caused loads on the area of the hull instrumented with strain gauges. The maximum pressure measured was 11.3 MPa on an area of 0.12 m 2 and maximum force of 5 MN was measured on the instrumented area during a direct impact. From the pressures measured, pressure–area curves were developed, total forces were calculated and the correlation between various parameters such as velocity and bergy bit mass was analyzed.