Ice Forces Research Articles

DP in ice environments—development of a dynamic positioning in ice validation platform (DPIVP)

This paper presents the development of a dynamic positioning in ice validation platform (DPIVP) which is part of a larger research project aimed at developing dynamic positioning (DP) system technologies for ice-rich environments. One outcome is simulation software to aid research in this area. The DPIVP software was designed to realistically simulate the dynamics of ice-structure interactions for real-time applications and to validate components common to DP in ice simulations. The software consists of many components which the DPIVP ties together as a unified system. All components have well-defined interfaces. Many of them are also distributed, allowing execution on separate computers and/or CPUs which helps ensure real-time operation. These two characteristics also decreases coupling and encourages a more modular design with the benefit of easily substituting alternative component implementations without reprogramming the DPIVP. Alternate implementations are useful for conducting research in specific DP in ice areas without substantially changing the system, such as alternative ice force models, DP control algorithms, vessel models, 3D and 2D visualization, environment models, and data acquisition systems. The integrated system was tested and evaluated using unit testing, integration testing, and system testing. The completed system was also validated using test cases that match physical model tests; the results compared favorably. Although the software has some limitations, for example, validated ice-force models being limited to two vessels, and thus lacks the generality we wish, the end result is a working prototype that satisfies the research requirements and provides an architecture and framework for future development.

Mitigation of ice-induced vibrations for wind turbine foundation using damping vibration isolation

The single pile offshore wind turbine foundation is a typical flexible structure, and the dynamic interac-tion between ice and structure is complex. Ice-induced vibrations can affect the normal operation of the upper motor and the safety of the foundation structure. This paper takes the interaction between ice and offshore platform in the Bohai Sea as the research object and discusses the strategies to mitigate the ice- induced vibrations of offshore wind turbine foundation. Through a simplified mechanical model of a damping vibration isolation system, the relationship between the parameters of the damping isolation layer and the structural damping ratio was analyzed. Based on the numerical simulation results, it was found that the damping isolation layer with a damping ratio of 0.2 can play a better role in controlling structural displacement and acceleration response under the action of steady-state and random ice forces. It provides a reference for the design of ice-resistant and safe operation of the offshore wind turbine.

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

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

Experimental investigation on ice resistance of an arctic LNG carrier under multiple ice breaking conditions

In order to investigate the ice loads of an Arctic LNG carrier under different ice conditions, a series of model tests are carried out in an ice tank, the ship model is attached to the towing dynamometer and the resistance force is measured for the specified model speed in level ice, broken ice and brash ice. During the test observations, several phenomena, including the ice-hull interaction modes and the failure modes of ice are captured. Ice loads in level ice and brash ice condition present a characteristic of periodicity, while ice force fluctuated randomly in broken ice because of nonuniform distribution of ice foes. The results also show that ice resistance has a liner fitting relationship with the ship speed. The achievable speed in broken ice condition is almost 3.5 times of that in level ice with the same thickness. With the same thrust power and the same speed, in brash ice condition, the ship can transit the ice 2.7 times thickness of that in level ice condition. Besides, model test results are compared with the results derived from some empirical formulas and the empirical formulas appropriate for resistance estimation in different ice conditions are summarized according to the comparison result. Lindqvist formula is suitable for ice resistance in level ice condition, Zuve & Dobrodeev formula coincides well with the experimental result in broken ice condition, Dobrodeev formula is proper for ice resistance in brash ice condition.

Vehicle ride comfort analysis on sea-crossing bridges under drift ice load

To investigate the ride comfort when vehicles travelling over sea-crossing bridges subjected to ice load in cold sea regions, this study presented a dynamic analysis framework for a vehicle–bridge interaction system under ice-induced vibration. Based on the a real ice load spectrum in Bohai Sea, the ice force process during the interaction between ice and bridge is obtained, and is input into the vehicle-bridge coupling system as an external excitation. This framework was assessed with an interactive system consisting of 6 12-DOF trucks travelling over the pile-supported sea-crossing bridges. Ride comfort of vehicles is investigated under different conditions of vehicle velocity and ice strength and it is evaluated by utilizing newly recommended in the ISO 2631-1(1997). The results show that the vibration of the vehicle will not influence driving comfort of the driver when vehicles traveled over bridges without considering the actions of ice load. However, the evaluation indicator of driving comfort reached a little uncomfortable when vehicles traveled over bridges under ice strength exceeds 1.5 MPa. In addition, the ride comfort analysis based on ISO 2631/1(1985) was also investigated. But the criterion only evaluates the comfort in one direction, and it is disadvantageous for the quantitative evaluation of driving comfort and it may underestimate the overall vibration of vehicles and total evaluation results of vehicle ride comfort.

Interdecadal variation in winter precipitation over non-monsoonal Eurasian regions

This study investigated the interdecadal variations in winter precipitation over the nonmonsoonal Eurasian regions (30°-70°N, 0°-80°E) (NER) and possible contributions of the Arctic sea ice for the period 1948‐2019. The dominant mode of the interdecadal variations in winter precipitation over NER (DM_NWPE) features opposite loading over the Mediterranean region and over the northern NER and Central Asia. The positive phase of DM_NWPE with enhanced precipitation over the Mediterranean region and suppressed precipitation over the northern NER and central Asia is associated with positive height anomalies over the high-latitude North Atlantic and Eurasia and negative height anomalies extending from the subtropical North Atlantic Ocean to western Eurasia. Increased sea ice in the Barents Sea may promote an atmospheric wave pattern extending to the downstream Eurasian regions, contributing to decreased precipitation over northern NER and Central Asia. Reduced sea ice in the Baffin Bay-Davis Strait-Labrador Sea (BDL) can promote a southeastward atmospheric wave pattern, contributing to enhanced precipitation over the Mediterranean region. The atmospheric response to the Arctic sea ice forcing is confirmed by experiments with a linear baroclinic model. A dipole pattern of sea surface temperature (SST) anomalies in the North Atlantic Ocean may contribute to the interdecadal variation in DM_NWPE. Further analysis showed that the Arctic sea ice-DM_NWPE relationship is primarily SST independent and the Arctic sea ice plays a more critical role in DM_NWPE variations than the North Atlantic SST anomalies.

Modelling of the Dynamically Positioned vessels and managed ice-field interaction dynamics using empirical-statistical techniques

Empirical models based on measurements are often preferred over high-fidelity numerical models when real-time predictions of broken ice-field actions on ships and floating offshore platforms are needed. This paper presents the methodologies and validations of a novel numerical model based on empirical-statistical techniques for predicting dynamically positioned (DP) vessels and ice-field interactions. The authors developed multiple regression models for predicting the time-averaged and average peaks of thruster forces and yawing moment of the DP vessel due to managed ice actions. Monte Carlo Simulations and other empirical techniques were then developed to predict the time series of the ice forces and moment on the DP vessel in managed ice scenarios. The authors then carried out model validations for several ice-field and vessel operating scenarios. The model showed reasonable accuracy in predicting the effects of several ice-field parameters on the forces and moments of two DP-controlled vessels. Subsequently, integration of the model into a DP-in-ice validation platform is offered, which can simulate and optimize the performance of a DP-controlled vessel in ice-infested water. Finally, the uniqueness and limitations of the models are discussed, and recommendations for future work are provided.

Andrew Clennel Palmer. 26 May 1938—21 December 2019

Andrew Clennel Palmer was internationally recognized for his major works on submarine pipeline design and engineering, although his work on the properties of ice and arctic engineering is equally noteworthy. His early research work at Cambridge, Brown and Liverpool Universities related to the mechanical properties of soils and sediments and the effect of temperature; this led to him aiding with the design of the trans-Alaska pipeline and work on major oil and gas pipelines in the UK sector of the North Sea. Andrew's successes drew him deeper into pipeline engineering and he worked with R. J. Brown & Associates in Houston, Texas, and in Holland, becoming vice-president and head of the London office in 1982. During a lull in the pipeline industry, Andrew returned to academe at the University of Manchester Institute of Science and Technology to develop a new course in offshore engineering. When the pipeline engineering industry recovered, Andrew started a company specializing in solving the many complex problems resulting from the installation of pipelines in ever-deeper waters. Andrew returned to Cambridge in 1996 as the first Research Professor of Petroleum Engineering in the Department of Engineering, a new post supported by the Jafar Foundation. He led a vigorous research group with strong connections to the pipeline industry, becoming president of the Pipeline Industries Guild in 1998; and he returned to the study of ice forces on offshore structures, also working with the university's Scott Polar Research Institute. On his retirement from Cambridge, Andrew moved to the National University of Singapore in 2006 as Keppel Chair Professor in the Department of Civil Engineering.

A statistical downscaling prediction model for winter temperature over Xinjiang based on the CFSv2 and sea ice forcing

AbstractBased on a year‐to‐year increment approach, a statistical downscaling model is developed for winter temperature prediction over Xinjiang of northwest China by using the predicted 200‐hPa westerly wind in winter over the Ural Mountains from the Climate Forecast System version 2 (CFSv2) as well as the observed sea ice over the Barents Sea–Laptev Sea in the preceding September. The statistical downscaling hindcasts on the 1983–2018 winter temperature over Xinjiang show that the statistical downscaling method has significantly improved the prediction capability compared with the original CFSv2. Specifically, the temporal correlation coefficients increase from negative to positive in most of Xinjiang, with the values passing the significance test at 90% confidence level at 81% of the stations. The regional averaged root‐mean‐square error reduces by more than 20%. In addition, the anomaly correlation coefficient increases from 0.08 to 0.26, passing the significance test at 95% confidence level. For two typical cases of the extreme cold winter in 2011 and the extreme warm winter in 2016, the spatial distribution characteristics of temperature anomaly are well reproduced, which are generally consistent with the observations. Overall, the statistical downscaling model based on the year‐to‐year increment strategy is a relatively effective method for predicting the winter temperature in Xinjiang.

Interdecadal variation in atmospheric water vapour content over East Asia during winter and the relationship with autumn Arctic sea ice

AbstractThis study focused on the interdecadal variability in water vapour content (WVC) over East Asia during winter and its associated mechanisms. The interdecadal variation in the WVC over East Asia during winter was investigated using the empirical orthogonal function (EOF) method. The leading mode (EOF1, explained variance is 52.7%) of interdecadal variability in the WVC, which explains most of the interdecadal variation, exhibits a monopole pattern characterized by consistent WVC anomalies over East Asia. The mechanisms associated with the interdecadal variability in winter WVC over East Asia were further investigated, and it was found that the interdecadal variability in winter WVC over East Asia is modulated by three water vapour transport (WVT) branches from the eastern, western, and southern boundaries of East Asia that are associated with Eurasian winter circulation. Further analyses revealed that increased sea ice concentration over the Barents‐Kara Sea (SIC‐BKS) in October–November (ON) serves as the source of wave activity flux and stimulates a stationary wave train along the Eurasian continent to change the downstream atmospheric circulation. As a response, an abnormal cyclone, an abnormal anticyclone, and an abnormal cyclone are triggered over western Siberia, the northern area of East Asia, and the southern area of East Asia, which are together favourable for WVC sufficiency over East Asia. Sensitivity experiments by the Community Atmosphere Model, version 4 (CAM4) using sea ice forcing in the Barents Sea yield similar results to the observed data, further confirming our conclusion. Therefore, the SIC‐BKS in ON may be an important potential predictor for the interdecadal variability in winter WVC over East Asia.

Experimental study on ice-structure interaction phenomena of vertically sided structures

This study analyses the results from basin tests with a vertically sided cylindrical pile loaded by ice failing in crushing. Tests were performed with a ‘rigid’ structure and with structural models representing a series of single-degree-of-freedom (SDOF) oscillators covering a wide range of mass, frequency, and damping values. The structural models were represented by a real-time hybrid test setup, which combined physical and numerical components to measure real ice forces, apply the forces to a numerical structural model, and simulate the dynamics of the tested structural models in real-time. The test results are analysed and simple numerical simulations are performed to assess the relevance of several ice force characteristics observed from the ‘rigid’ structure tests to the ice-induced vibrations in the SDOF oscillators. The results from the rigid structure tests show that the median ice forcing frequency is linearly related to the ice drift speed. The mean and standard deviation of the ice forces on the rigid structure show a negative force-velocity gradient at low ice drift speeds and indications of a positive force-velocity gradient at higher ice drift speeds. The comparison of experimental results to the simulations of the single-degree-of-freedom oscillator tests shows that the positive force-velocity gradient at higher ice drift speeds allows to best capture the dynamics during continuous brittle crushing as observed in the experiments. Furthermore, the comparison shows that frequency lock-in initiation is primarily driven by the velocity-independent spatial frequency spectrum of the ice force signal. The added damping caused by the positive force-velocity gradient must be considered to capture the frequency lock-in initiation speeds measured in the constant deceleration experiments. The consideration of the negative force-velocity gradient at low relative velocities is not needed to capture these frequency lock-in initiation speeds as observed in the experiments. However, once frequency lock-in is initiated, the negative gradient is needed to correctly capture the dynamics during frequency lock-in. Analysis of the results shows that the peak forces during intermittent crushing at the end of the load build-up phase have a dependence on relative velocity equal to the load dependence on velocity of rigid structures at low speed. This indicates that intermittent crushing is not a purely brittle type of interaction.

Fault Detection in Offshore Structures: Influence of Sensor Number, Placement and Quality

Within the Space@Sea project floating offshore islands, designed as an assembly of platforms, are used to create space in offshore environments. Offshore structures are exposed to harsh environment conditions. High wind speeds, heavy rainfall, ice and wave forces lead to highly stressed structures. The platforms at the Space@Sea project are connected by ropes and fenders. There exists the risk of a rope failing which is therefore investigated subsequently. To ensure the safety of the structure, the rope parameters are monitored by the Extended Kalman Filter (EKF). For platform arrangements, a large number of sensors is required for accurate fault diagnosis of these ropes, leading to high investment costs. This paper presents a strategy to optimize the number and placement of acceleration sensors attached to the floating platforms. There are also high demands on the sensors due to the harsh offshore conditions. Material deterioration and overloading may lead to decayed sensor performance or sensor defects. Maintenance of offshore sensors is difficult, expensive and often not feasible within a short time. Therefore, sensor measurement deviations must not affect reliable structure fault detection. The influence of defect sensors on the rope fault detection is examined in this study: Types, intensities, number, place of occurrence of defect sensors and the distance between defect sensors and rope faults are varied.

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.

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.

Dynamic Analysis of Monopile-Type Offshore Wind Turbine Under Sea Ice Coupling With Fluid-Structure Interaction

The interaction between vertical offshore wind turbine (OWT) and sea ice with fluid is a complex process including local and global crushing of ice fragments and vibration of OWT. It is crucial to study the ice resistance of OWT structures considering the fluid-structure interaction (FSI). This article investigates a complete process of dynamic sea ice-monopile OWT interaction considering soil-structure interaction (SSI) and FSI effects. A fully coupled dynamic collision model of sea ice and OWT incorporating with the explicit non-linear collision tool ANSYS/LS-DYNA is proposed. The simulated ice loads in this study is verified by different simulation methods and international static ice force standards closely related to ice dynamic characteristic parameters. Then, the dynamic response and damage of the OWT structure during ice-structure interaction are studied using the fully interaction model with FSI coupling. The simulated ice force can produce a significant vibration response in the structure coupling with FSI due to occurrence of ice-induced resonance in the ice velocity range of 2.5–3.5 cm/s. Finally, the effect of fluid on the sea ice-OWT interaction in the initial velocity collision of sea ice is analyzed. FSI coupling can cause a certain level of collision hysteresis, accelerate the failure of sea ice breaking and reasonably reduce the energy of the structure.

Effect of Ultrasonic Vibration on the Surface Adhesive Characteristic of Iced Aluminum Alloy Plate

Icings on moving machinery, such as wind turbines and aircraft wings, degrade their performance and safety. Ultrasonic vibration is considered one of the deicing methods. In this research, simulations and experiments are carried out to explore the effect of ultrasonic vibration on the adhesive characteristic of ice on aluminum alloy plates. Harmonic response analyses are conducted to analyze the changing and distributions of shear stresses at the adhesive interface under different frequencies and sizes of PZT patches. The results show that there is optimum side length and thickness of the PZT patch, as the size of the iced aluminum alloy plate is constant. In these conditions, the shear stresses at the adhesive interface are high. Then, experiments on adhesive torque of ice are carried out to calculate the adhesive shear stresses of ice. The results show that the adhesive force of ice decreases under the excitation of ultrasonic vibration. When the excited frequency is 79 kHz, the adhesive torsional shear stress is 0.014 MPa, which is only 7% of the one with no ultrasonic vibration.

Prediction of Ice-Resistance Distribution for R/V Xuelong Using Measured Sea-Ice Parameters

Increasing human activity in polar areas is making ice-going ships more indispensable in multiple operation scenarios. An improvement in ice-resistance prediction, which cannot be performed without accurate ice parameters, will promote the development of hull design and operational safety in ice-infested waters. The Nataf transformation is applied to generate correlated pseudo-random numbers which represent ice parameters; then, as a numerical method, the circumferential crack method is introduced to calculate the ice resistance of R/V Xuelong in level ice. The main factors which may have a large influence on simulated ice load are studied. The simulation results show that the Burr distribution is the most suitable model to describe the distribution of ice resistance calculated and ice-force amplitude concentrated at a lower level. The statistical results are also discussed and compared with similar research through empirical formulas and Monte Carlo methods. The present simulation can obtain more detailed information during the icebreaking process compared to similar research: the ice force at each time step is achieved; the key ice-force amplitude can be collected, which can benefit studies on hull structure; and potential stress generated by sea ice can be predicted. The present numerical tools and simulation results can provide a reference for ice-going ships sailing in level ice in most scenarios with regard to ice resistance and operational safety.

Fatigue life prediction of pile-supported sea-crossing bridges subject to random ice forces

As a natural disaster in cold sea regions, ice forces can cause strong vibration of offshore structures, and even threaten the safety of structures. The elevated steel pile caps are the most commonly used substructure foundation type of sea-crossing bridges and the large-scale caps are generally used to resist ice forces. The fatigue damage of sea-crossing bridges with steel piles under ice forces is directly related to the fluctuating stresses. Therefore, this paper carried out the fatigue damage analysis and fatigue life prediction of sea-crossing bridges subjected to random ice forces in Bohai Sea. In order to considering long-range condition of sea ice, the statistical characters of sea ice properties such as, ice velocity, ice thickness and ice strength are carried out. The ice forces processes are simulated utilizing the random ice force spectrum model for vertical and conical structures. Fatigue damage of sea-crossing bridges with vertical and conical caps is analyzed using the rainflow cycle counting technique and Palmgren-Miner's rule. The fatigue life is estimated based on the cumulative fatigue damage and the real period of drift ice in Bohai Sea. Results show that the fatigue damage increases obviously as a result of increases in the stress caused by increased sea ice parameters. The sea-crossing bridges with conical caps can prolong the fatigue life by more than 45% in comparison with sea-crossing bridges with vertical caps. The cone ice-resistant cap has a good effect on mitigating fatigue damage of sea-crossing bridges in drift ice covered water regions.

Ice sintering: Dependence of sintering force on temperature, load, duration, and particle size

We present experiments along with an approximate, semi-analytic, close-form solution to predict ice sintering force as a function of temperature, contact load, contact duration, and particle size during the primary stage of sintering. The ice sintering force increases nearly linear with increasing contact load but nonlinear with both contact duration and particle size in the form of a power law. The exponent of the power law for size dependence is around the value predicted by general sintering theory. The temperature dependence of the sintering force is also nonlinear and follows the Arrhenius equation. At temperatures closer to the melting point, a liquid bridge is observed upon the separation of the contacted ice particles. We also find that the ratio of ultimate tensile strength of ice to the axial stress concentration factor in tension is an important factor in determining the sintering force, and a value of nearly 1.1 MPa can best catch the sintering force of ice in different conditions. We find that the activation energy is around 41.4KJ/mol, which is close to the previously reported data. Also, our results suggest that smaller particles are “stickier” than larger particles. Moreover, during the formation of the ice particles, cavitation and surface cracking is observed which can be one of the sources for the variations observed in the measured ice sintering force.

A nested high-resolution unstructured grid 3-D ocean-sea ice-ice shelf setup for numerical investigations of the Petermann ice shelf and fjord

Three-dimensional numerical simulation of circulation in fjords hosting marine-terminating ice shelves is challenging because of the complexity of processes involved in such environments. This often requires a comprehensive model setup. The following elements are needed: bathymetry (usually unknown beneath the glacier tongue), ice shelf draft (impacting water column thickness), oceanographic state (including tidal elevation, salinity, temperature and velocity of the water masses), sea ice and atmospheric forcing. Moreover, a high spatial resolution is needed, at least locally, which may be augmented with a coarser and computationally cheaper (nested) model that provides sufficiently realistic conditions at the boundaries. Here, we describe procedures to systematically create such a setup that uses the Finite Volume Community Ocean Model (FVCOM) for the Petermann Fjord, Northwest Greenland. The first simulations are validated against temperature and salinity observations from the Petermann Fjord in September 2019. We provide•Complete bathymetry, ice-draft and water column thickness datasets of the Petermann Fjord, with an improved representation of the topography underneath the glacier tongue.•Boundary conditions for ocean, atmosphere and sea ice derived from a suite of high-resolution regional models that can be used to initialize and run the regional ocean model with realistic geophysical settings.