Peculiarities of Multi-Legged Platform Operation in Ice Condition

2014 ◽  
Author(s):  
Evgeny Karulin ◽  
Marina Karulina
Keyword(s):  
Mutual Influence ◽  
Experimental Studies ◽  
Vertical Axis ◽  
Research Centre ◽  
Interaction Processes ◽  
Ice Drift ◽  
Ice Concentration ◽  
Broken Ice ◽  
Ice Conditions ◽  
Ice Floes

A usage of multi-legged structures in ice conditions involves some peculiarities that should be taken into account both while designing the platform and while planning technological operations nearby it. In 2010–2013 a range of theoretical and experimental studies were performed at the Krylov State Research Centre, St. Petersburg, Russia. The work aimed to investigate main peculiarities of multi-legged structure interaction with ice, such as 1). mutual influence on ice action on each leg, 2) jamming of the inner space between legs and blocking the space between the front legs with ice floes, and 3) arisen yaw moments about the platform vertical axis due to unsymmetrical ice action on the legs. Three series of model tests with various multi-legged structures models were carried out in the Ice Basin. The presented in the paper main results show effect of key parameters on the interaction processes and on the ice action. During the tests the following parameters were varying: distance between the legs, ice drift speed and direction, broken ice concentration and the ice pieces size. Also, the paper contains results of numerical simulations of some tested scenarios in broken ice conditions. The numerical model is based on discrete element method, and it enables to extend a range of the investigations.

Image Processing for the Analysis of an Evolving Broken-Ice Field in Model Testing

2012 ◽  
Author(s):  
Qin Zhang ◽  
Solange van der Werff ◽  
Ivan Metrikin ◽  
Sveinung Løset ◽  
Roger Skjetne
Keyword(s):  
Image Processing ◽  
Water Area ◽  
Test Results ◽  
Detection Algorithms ◽  
Ice Concentration ◽  
Broken Ice ◽  
Ice Field ◽  
Ice Floes ◽  
Processing Techniques ◽  
Ice Forces

Dynamic positioning (DP) experiments in model ice were carried out in the ice tank at the Hamburg Ship Model Basin (HSVA) in the summer of 2011. In these experiments the behavior of two different ships in a broken-ice field were studied. One of the main parameters characterizing a broken-ice field is the ice concentration, defined as the fraction of the total water area covered by ice. In this paper, image processing techniques are applied to derive the ice concentration in the model basin. Several points in time are analyzed in order to describe the evolution of the ice field. The applied techniques include methods for identifying individual ice floes and calculating the ice concentration in the vicinity of the model ship. Ice floe boundaries are then obtained, and the ice floe size distribution and shape factor may further be extracted from the images. The image processing methods applied in this work are object extraction and edge detection algorithms, which are further customized to ice identification. The obtained results can be used for relating the ice field characteristics to the model test results, such as the vessel’s displacements and the corresponding ice forces.

Discrete Element Modelling of Pack Ice Interaction With Floating Structures

2015 ◽  
Author(s):  
Jie Dai ◽  
Heather Peng
Keyword(s):  
Discrete Element ◽  
Wave Force ◽  
Interaction Force ◽  
Discrete Element Modelling ◽  
Empirical Formulas ◽  
Pack Ice ◽  
Broken Ice ◽  
Ice Conditions ◽  
Ice Field ◽  
Ice Floes

This paper presents a two-dimensional numerical model for ship-ice interaction simulatiion using the discrete element method (DEM). The simulation was conducted for a broken ice field with hundreds of circular ice floes and various combinations of ice conditions. A viscous-elastic ice rheology was adopted to model the dynamic behavior of each individual ice floe. Both ship-ice and ice-ice contacts were considered in the interaction force. Environment forces, including wind force and wave force, were calculated by empirical formulas. An algorithm was developed to log each contact and solve motions of individual ice floe and the ship. The resistance of ship advancing in ice was predicted and compared with model test results.

scholarly journals Characterizing sudden changes in Arctic sea ice drift and deformation on synoptic timescales

2016 ◽  
Author(s):  
Jennifer V. Lukovich ◽  
Cathleen A. Geiger ◽  
David G. Barber
Keyword(s):  
Sea Ice ◽  
Oil And Gas ◽  
Beaufort Sea ◽  
Arctic Sea Ice ◽  
Ice Drift ◽  
Shock Response ◽  
Near Shore ◽  
Sea Ice Drift ◽  
Ice Conditions ◽  
Ice Floes

Abstract. In this study, we develop a framework for the assessment of sudden changes in sea ice drift and associated deformation processes in response to atmospheric forcing and ice–coastal interactions, based on analysis of ice buoy triplet centroids and areas. Examined in particular is the spatiotemporal evolution in sea ice floes that are tracked with GPS beacons deployed in triplets in the southern Beaufort Sea at varying distances from the coastline in fall, 2009 – triplets A to D, with A (D) located closest to (furthest from) the coastline. This study illustrates the use of shock-response diagnostics to evaluate eight identified sudden changes or shock events on daily timescales. Results from this analysis show that shock events in the southern Beaufort Sea occur in at least one of two forms: (1) during a reversal in winds, or (2) sustained north/easterly winds, with response mechanisms governed by ice conditions and interactions with the coastline. Demonstrated also is the emergence of a shear-shock event (SSE) that results in reduced ice concentrations for triplets B, C, and D, one, three and five days following the SSE, respectively and loss of synchronicity in ice-atmosphere interactions. The tools developed in this study provide a unique characterization of sea ice dynamical processes in the southern Beaufort Sea, with implications for quantifying "shock-response" systems relevant for ice hazard assessments and forecasting applications required by oil and gas, marine transportation, and indigenous use of near shore Arctic areas.

Ice Loading Decrease at Life Cycle Main Stages for Fixed Offshore Structures

2015 ◽  
Author(s):  
Valery M. Shaposhnikov ◽  
Anatolii V. Aleksandrov ◽  
Oleg E. Litonov ◽  
Viktor V. Platonov
Keyword(s):  
Experimental Studies ◽  
Offshore Structures ◽  
Research Centre ◽  
Ice Load ◽  
Ice Drift ◽  
Load Monitoring ◽  
Design Values ◽  
Ice Loads ◽  
Ice Resistance ◽  
Positive Effect

At the present time design values of ice loads on fixed offshore structures are rather conservative. Conservatism of design ice loads consists in assuming the most unfavorable ice action direction and the worst ice drift speed; the most unfavorable combination of the consolidated layer thickness, ridge keel depth and ice strength; as well as supposing the ice ultimate strength value constant along the whole ice–structure contact area perimeter. With accumulation of the knowledge on ice formation failure under interaction with ice-resistant fixed platforms, the requirements contained in Rules of classification societies are reduced. For example, for the last forty years the lowering of requirements to design ice load values was equal to about four times [1]. For the last time specialists of Krylov State Research Centre have performed design and experimental studies where further tendency to decreasing design values of ice loads is traced. Ice monitoring is one of the main elements for justification of design ice load values’ decrease. Modern monitoring systems permit to warn about occurrence of a state close to a limit one, as well as to record actual ice loads. Ice load monitoring is a necessary part of accident prevention during ice-resistant structures operation. Monitoring of ice loads is a necessary part for providing safe operation of ice-resistance structures, and systematic accumulation of monitoring data for several years gives a positive effect in the form of justified decrease of static and dynamic design ice loads.

The Arctic Ship Shape Platform for Well Maintenance, Survey and Workover

2014 ◽  
Author(s):  
Sergey V. Verbitsky ◽  
Alexey A. Agafonov ◽  
Eduard N. Fomitchyov ◽  
Maksim V. Kovalev ◽  
Irina G. Chesnokova ◽  
...  
Keyword(s):  
Production Systems ◽  
Cost Effective ◽  
The Arctic ◽  
Research Centre ◽  
First Year ◽  
Arctic Conditions ◽  
Broken Ice ◽  
Ice Conditions ◽  
Drilling Rigs ◽  
The Cost

The conceptual design of floating ship shape platform for well maintenance, survey and workover in prospective fields of Russian Arctic and Sakhalin Island shelf (further The platform) was developed by Krylov State Research Centre specialists with the assistance of CDB “Korall”. The platform under design intended for operation in the Arctic conditions and designed to resist the ice formations such as continuous thin first-year ice and broken ice being the first one in the world practice. The form and chosen hull ice strengthening class allow ensuring safe operation in the mentioned ice conditions. The main purpose for development of the platform was to minimize the offshore wells downtime providing the cost effective way for maintenance of subsea production systems comparing with floating drilling rigs and drilling vessels that takes a significant investment. The economic assessments have shown that operation of such platform will cost two to three times less than renting of a rig or drillship. Having the working deck space of about 1,000 m2 and the ability to download a variety of equipment the platform can perform a variety of testing and wells repairing procedures both for underwater wellhead and for wells operated on fixed platforms.

Wave propagation through fields of pack ice

1963 ◽  
Vol 255 (1057) ◽  
pp. 313-339 ◽  
Keyword(s):  
Wave Spectrum ◽  
Experimental Studies ◽  
Normal Wave ◽  
Weddell Sea ◽  
Sea Waves ◽  
Pack Ice ◽  
Order Of Magnitude ◽  
Ice Conditions ◽  
Ice Field ◽  
Ice Floes

Experimental studies of penetration of sea waves and swell into fields of loose pack ice were carried out by means of a ship-borne wave recorder, during a voyage into the Weddell Sea in R.R.S. John Biscoe in 1959—60. This reconnaissance study has provided the first systematic data within an ice field of the variation of wave amplitudes and period over the normal wave spectrum of 4 to 24 s. Although observations were confined to a single ship, a reasonably constant background of swell, together with varied ice conditions, has made it possible to draw certain conclusions for waves and swell of relatively small amplitudes. The penetration of long ocean swell, of periods from 11 to 23 s, into ice fields consisting of large floes of more than half a wavelength across takes place by bending of the floes. The results suggest that the fraction of the wave energy penetrating such an ice field is proportional to A 4/A3, where h is the thickness of the ice floes and A the wavelength of the swell. For periods of less than 10 s, floes of around 1.5 m thick and 40 m or less in diameter approximate to rigid floating plates. For these periods, the main energy cut-off took place when floe diameters were about one-third of the wavelength; little loss of energy occurred when floes were less than one-sixth of the wavelength across, while no detectable penetration took place when the floes were half a wavelength or more in diameter. Consideration of the results, together with limited evidence available from tide and gravimeter observations, shows that most long waves penetrate polar ice fields with little loss of energy. Discussion of the energy required to bend large ice floes indicates that long-period swell is propagated through regions covered by pack ice with little loss of energy only when the energy required to bend the floes is at least an order of magnitude smaller than the total energy of the waves.

scholarly journals Countermeasures for Ice Covered Waters

1999 ◽  
Vol 71 (1) ◽  
pp. 173-191 ◽  
Author(s):  
David Dickins ◽  
Ian Buist
Keyword(s):  
Oil Recovery ◽  
Cold Temperatures ◽  
Response Options ◽  
Pack Ice ◽  
Ice Concentration ◽  
Site Access ◽  
Broken Ice ◽  
Ice Conditions ◽  
Fast Ice ◽  
Safe Working

This chapter describes the state of knowledge regarding the most applicable countermeasures to deal with oil on, in or among ice. Countermeasures are discussed in the context of seasonal variations in ice conditions and observations of oil fate and behaviour in a variety of different situations. The behaviour of oil spilled in ice covered waters is governed largely by the ice concentration in the case of broken ice, and the processes of encapsulation and subsequent migration in the case of solid (fast) ice). Each season presents different drawbacks and advantages for spill response. During freezeup and breakup, drifting ice and limited site access tend to restrict the possible response options and significantly reduce recovery effectiveness. Mid-winter, although associated with long periods of darkness and cold temperatures, provides a stable ice cover that not only naturally contains the oil nearshore within a relatively small area but also provides a safe working platform for oil recovery and transport. For the case of spills under or on fast ice, there are a range of effective countermeasures options which can result in very high recovery effectiveness. Countermeasures to deal with spills in moving pack ice are much more limited and likely to result in highly variable recovery values depending on a variety of natural conditions and logistics constraints.

scholarly journals Improving Multiyear Sea Ice Concentration Estimates with Sea Ice Drift

2016 ◽  
Vol 8 (5) ◽  
pp. 397 ◽  
Author(s):  
Yufang Ye ◽  
Mohammed Shokr ◽  
Georg Heygster ◽  
Gunnar Spreen
Keyword(s):  
Sea Ice ◽  
Sea Ice Concentration ◽  
Ice Drift ◽  
Ice Concentration ◽  
Sea Ice Drift

scholarly journals Studies on laser-driven shocks using a Nd:glass laser

1997 ◽  
Vol 15 (2) ◽  
pp. 297-316 ◽  
Author(s):  
L.J. Dhareshwar ◽  
N. Gopi ◽  
C.G. Murali ◽  
B.S. Narayan ◽  
U.K. Chatterjee
Keyword(s):  
Experimental Studies ◽  
Research Centre ◽  
High Peak Power ◽  
Laser Shock ◽  
X Ray ◽  
Pressure Profiles ◽  
Ablation Pressure ◽  
Laser Velocity ◽  
Work Done ◽  
Nd:Glass Laser

A review of work done on laser generated shocks in solids using a high-peak-power Nd:glass laser in the Laser and Plasma Technology Division of the Bhabha Atomic Research Centre is presented in this paper. The 20-J/5-ns Nd:glass laser used in the experiments is able to produce focused laser intensities in the range of 5 × 1011-1013 W/cm2 and a shock pressure in the range of 0.1–5 Mbar. A l-J/100-ps Nd:glass laser is also being developed for laser shock studies, details of which are presented. Several diagnostics have been developed for laser shock studies of which the main diagnostics are optical shadowgraphy, optical interferometry, and laser velocity interferometry for particle velocity measurement. The measurement of ablation pressure in various types of targets, the scaling of ablation pressure with laser intensity, the effect of laser beam nonuniformity on shockfront or ablation pressure uniformity, the smoothing of shockfront and pressure profiles in high-Z coated and high-Z doped targets, and so on, are the various experimental studies conducted. We have tried to study X-ray driven ablation in aluminum and plastic targets using gold and copper as X-ray producing targets. Uniform pressure of about 0.1 Mbar has been generated over an area of 4 mm2

Sign in / Sign up

Export Citation Format

Share Document