Model tests of dynamic ice loading on the Chinese JZ-20-2 jacket platform

1992 ◽  
Vol 19 (5) ◽  
pp. 819-832 ◽  
Author(s):  
G. W. Timco ◽  
M. B. Irani ◽  
J. Tseng ◽  
L. K. Liu ◽  
C. B. Zheng
Keyword(s):  
Ice Sheets ◽  
Ice Thickness ◽  
Bohai Bay ◽  
Test Program ◽  
Jacket Platform ◽  
Prototype Structure ◽  
Ice Conditions ◽  
Ice Loads ◽  
Structure Orientation ◽  
Good Agreement

A model test program has been performed to study the dynamic ice loads on a jacket platform used in Bohai Bay, China. The tests were performed at a geometric scale factor of 1:26. The prototype structure/foundation compliance was modelled and the structure was subjected to scaled ice sheets corresponding to the ice conditions in the Bohai Bay. The loads, moments, displacements, and accelerations of the structure were measured. The test variables include the ice thickness, ice speed, elevation of ice cover, and structure orientation with respect to the ice motion. An analysis of the data shows good agreement with measured full-scale information. Key words: ice, loads, dynamic, vibration, jacket structure, foundation, China.

Methodology to Evaluate Sea Ice Loads for Seasonal Operations

2015 ◽  
Author(s):  
Jan Thijssen ◽  
Mark Fuglem
Keyword(s):  
Sea Ice ◽  
Offshore Structures ◽  
Ice Thickness ◽  
Safety Level ◽  
Site Specific ◽  
Design Load ◽  
Ice Load ◽  
Ice Conditions ◽  
Design Loads ◽  
Ice Loads

Offshore structures designed for operation in regions where sea ice is present will include a sea ice load component in their environmental loading assessment. Typically ice loads of interest are for 10−2, 10−3 or 10−4 annual probability of exceedance (APE) levels, with appropriate factoring to the required safety level. The ISO 19906 standard recommends methods to determine global sea ice loads on vertical structures, where crushing is the predominant failure mode. Fitted coefficients are proposed for both Arctic and Sub-Arctic (e.g. Baltic) conditions. With the extreme ice thickness expected at the site of interest, an annual global sea ice load can be derived deterministically. Although the simplicity of the proposed relation provides quick design load estimates, it lacks accuracy because the only dependencies are structure width, ice thickness and provided coefficients; no consideration is given to site-specific sea ice conditions and the corresponding exposure. Additionally, no term is provided for including ice management in the design load basis. This paper presents a probabilistic methodology to modify the deterministic ISO 19906 relations for determining global and local first-year sea ice loads on vertical structures. The presented methodology is based on the same ice pressure data as presented in ISO 19906, but accounts better for the influence of ice exposure, ice management and site-specific sea ice data. This is especially beneficial for ice load analyses of seasonal operations where exposure to sea ice is limited, and only thinner ice is encountered. Sea ice chart data can provide site-specific model inputs such as ice thickness estimates and partial concentrations, from which corresponding global load exceedance curves are generated. Example scenarios show dependencies of design loads on season length, structural geometry and sea ice conditions. Example results are also provided, showing dependency of design loads on the number of operation days after freeze-up, providing useful information for extending the drilling season of MODUs after freeze-up occurs.

scholarly journals Airborne River-Ice Thickness Profiling with Helicopter-Borne UHF Short-Pulse Radar

1987 ◽  
Vol 33 (115) ◽  
pp. 330-340 ◽  
Author(s):  
Steven A Arcone ◽  
Allan J Delaney
Keyword(s):  
Short Pulse ◽  
Hanging Wall ◽  
Open Water ◽  
High Water ◽  
High Water Content ◽  
Ice Thickness ◽  
Frazil Ice ◽  
Pulse Radar ◽  
Detailed Surface ◽  
Ice Conditions

AbstractThe ice-thickness profiling performance of a helicopter-mounted short-pulse radar operating at approximate center frequencies of 600 and 900 MHz was assessed. The antenna packages were mounted 1.2 m off the skid of a small helicopter whose speed and altitude were varied from about 1.8 to 9 m/s and 3 to 12 m. Clutter from the helicopter offered minimal interference with the ice data. Data were acquired in Alaska over lakes (as a proving exercise) and two rivers, whose conditions varied from open water to over 1.5 m of solid ice with numerous frazil-ice formations. The most readily interpretable data were acquired when the ice or snow surface was smooth. Detailed surface investigations on the Tanana River revealed good correlations of echo delay with solid ice depth, but an insensitivity to frazil-ice depth due to its high water content. On the Yukon River, coinciding temporally coherent surface and bottom reflections were associated with solid ice and smooth surfaces. All cases of incoherent surface returns (scatter) occurred over ice rubble. Rough-surface scattering was always followed by the appearance of bottom scattering but, in many cases, including a hanging-wall formation of solid frazil ice, bottom scattering occurred beneath coherent, smooth-surface reflections. Areas of incoherent bottom scattering investigated by drilling revealed highly variable ice conditions, including frazil ice. The minimum ice thickness that could be resolved from the raw data was about 0.2 m with the 600 MHz antenna and less than 0.15 m with the 900 MHz antenna.

scholarly journals Elastic properties of floating sea ice from air-coupled flexural waves

2021 ◽  
Author(s):  
Rowan Romeyn ◽  
Alfred Hanssen ◽  
Bent Ole Ruud ◽  
Tor Arne Johansen
Keyword(s):  
Sea Ice ◽  
Elastic Properties ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Flexural Wave ◽  
Ice Thickness ◽  
Linear Filter ◽  
Flexural Stiffness ◽  
Flexural Waves ◽  
Impulsive Source

Abstract. Air-coupled flexural waves appear as wave trains of constant frequency that arrive in advance of the direct air-wave from an impulsive source travelling over a floating ice sheet. The frequency of these waves varies with the flexural stiffness of the ice sheet, which is controlled by a combination of thickness and elastic properties. We develop a theoretical framework to understand these waves, utilizing modern numerical and Fourier methods to give a simpler and more accessible description than the pioneering, yet unwieldly analytical efforts of the 1950's. Our favoured dynamical model can be understood in terms of linear filter theory and is closely related to models used to describe the flexural waves produced by moving vehicles on floating plates. We find that air-coupled flexural waves are a robust feature of floating ice-sheets excited by impulsive sources over a large range of thicknesses, and we present a simple closed-form estimator for the ice thickness. Our study is focussed on first-year sea ice of ~20–80 cm thickness in Van Mijenfjorden, Svalbard, that was investigated through active source seismic experiments over four field campaigns in 2013, 2016, 2017 and 2018. The air-coupled flexural frequencies for sea-ice in this thickness range are ~60–240 Hz. While air-coupled flexural waves for thick sea-ice have received little attention, the higher frequencies associated with thin ice on fresh water lakes and rivers are well known to the ice-skating community and have been reported in popular media. Estimation of ice physical properties, following the approach we present, may allow improved surface wave modelling and wavefield subtraction in reflection seismic studies where flexural wave noise is undesirable. On the other hand, air-coupled flexural waves may also permit non-destructive continuous monitoring of ice thickness and flexural stiffness using simple, relatively inexpensive microphones located in the vicinity of the desired measurement location, either above the ice-sheet or along the shoreline. In this case, naturally forming cracks in the ice may be an appropriate impulsive source capable of exciting flexural waves in floating ice sheets in a passive monitoring context.

On the Flexural Failure of Thick Ice Against Sloping Structures

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Fwu Chyi Teo ◽  
Leong Hien Poh ◽  
Sze Dai Pang
Keyword(s):  
Reference Model ◽  
Ice Sheets ◽  
Axial Loading ◽  
Breaking Load ◽  
Ice Thickness ◽  
Design Code ◽  
Modified Model ◽  
Flexural Failure ◽  
Bending Effect ◽  
Loading Eccentricity

This paper investigates the breaking load of ice sheets up to 6 m thick, against a sloping structure. The reference model by Croasdale, which the design code is based on, neglects the edge moment arising from the loading eccentricity, as well as a second-order bending effect induced by the axial loading in its formulation. In this paper, the model is reformulated to incorporate these effects into the governing equation, as well as to account for the occurrence of local crushing at the point of contact between the ice sheet and sloping structure. For thin ice, predictions from the modified model resemble closely those by Croasdale's model. As the ice thickness increases, however, significant deviations from the reference model can be observed. For thick ice, the terms omitted for brevity in the reference model have a significant influence, without which the breaking load is under-estimated. It is furthermore demonstrated that against sloping structures, the dominant failure mode is that of flexural, except in very limiting cases where it switches to crushing.

Research on the Influences of Broken Ice Parameters on Maneuverable Forces of Ice-Going Ship Oblique Sailing

2021 ◽  
Author(s):  
Shenyu Xuan ◽  
Chengsheng Zhan ◽  
Zuyuan Liu ◽  
Binfeng He ◽  
Qiaosheng Zhao ◽  
...  
Keyword(s):  
Time History ◽  
Test Results ◽  
Ship Maneuvering ◽  
Average Value ◽  
Ocean Science ◽  
Broken Ice ◽  
Ice Conditions ◽  
Ice Field ◽  
Ice Resistance ◽  
Good Agreement

Abstract The broken ice is one of the most common ice conditions for ice-going ships, and the research of ship maneuvering movement in broken ice field can improve sailing safety. In this paper, the discrete element method (DEM) was adopted to study the maneuverable forces, including resistance and transverse force, of ice-going ship oblique sailing in broken ice fields. First, the Araon model tests data of Korea Institute of Ocean Science & Technology (KIOST) was used to verify the ice resistance of direct sailing under different ice sizes and model speeds, and the numerical results are in good agreement with the test results. Second, the influences of broken ice parameters (including concentration, thickness, and shape) on ship-ice interaction and maneuverable forces distribution were researched. The maneuverable forces on the ice-going ships are mainly from the ship-ice interaction. The time history curves of maneuverable forces were analyzed from the average value of maneuverable forces, the average value of peak maneuverable forces, and the number of peaks. Besides, the parameters of broken ice have a heavy influence on the movement of broken ice around the hull, such as accumulating and sliding. The analysis of the broken ice movement contributes to understanding the influences of broken ice parameters on ice-going ships.

Sea Ice Thickness Detection Using Coastal BeiDou Reflection Setup in Bohai Bay

2020 ◽  
pp. 1-5
Author(s):  
Yun Zhang ◽  
Sijia Hang ◽  
Yanling Han ◽  
Shuhu Yang ◽  
Zhonghua Hong ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ice Thickness ◽  
Bohai Bay ◽  
Sea Ice Thickness

scholarly journals Ice Thickness and Sea Depth Derived from Reflection-Seismic Measurements on the Central Part of Filchner-Ronne Ice Shelf, Antarctica

1988 ◽  
Vol 11 ◽  
pp. 14-18 ◽  
Author(s):  
J. Determann ◽  
F. Thyssen ◽  
H. Engelhardt
Keyword(s):  
Drill Hole ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Reflection Seismic ◽  
Seismic Records ◽  
3D Processing ◽  
Seismic Measurements ◽  
Good Agreement ◽  
Made In

In January 1986, reflection-seismic measurements were made in the central part of Filchner-Ronne Ice Shelf, north of Henry and Korff ice rises, by a German oversnow traverse. With the help of a newly developed “ice streamer”, two people were able to obtain seismic records nearly every 5km over a distance of 150km within 3d. Processing of digitally recorded seismograms yielded profiles of ice thickness and sea depth. The ice thickness varies from 400 to 500 m and is in good agreement with the thickness of 465 m at a drill hole. The reflection-seismic results are comparable with those obtained from aerogeophysical measurements.

scholarly journals Liquid Brine in Ice Shelves

1975 ◽  
Vol 14 (70) ◽  
pp. 125-136 ◽  
Author(s):  
R. H. Thomas
Keyword(s):  
Steady State ◽  
Heat Transport ◽  
Thermal Equilibrium ◽  
Transport Model ◽  
Percolation Model ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Brine Layer ◽  
Good Agreement

Holes drilled into thin areas of the Brunt Ice Shelf encounter a layer of liquid brine less than 1 m thick approximately at sea-level. Assuming the brine to be moving horizontally, analysis of its effects on thermal equilibrium gives an estimate of steady-state annual brine flow that is in good agreement with the value deduced from a percolation model. The effect of firn density on percolation rates is such that the slope of an active brine layer increases rapidly as ice thickness increases. However, the heat transport model predicts that brine layers are unlikely to be active in both very thick and very thin ice shelves.

Model Tests on a Spar in Level Ice and Ice Ridge Conditions

2009 ◽  
Author(s):  
John Murray ◽  
Stephane LeGuennec ◽  
Don Spencer ◽  
Chang K. Yang ◽  
Wooseuk Yang
Keyword(s):  
Full Scale ◽  
Scale Model ◽  
Test Facility ◽  
Mooring System ◽  
Scaling Effects ◽  
Line System ◽  
Restoring Forces ◽  
Ice Conditions ◽  
Ice Loads ◽  
Level Ice

1:30 and 1:50 model-scale ice tests of an ice-resistant Spar design were carried out to determine the loads on the Spar in level ice and ice ridges. Due to limitations in the depth of the ice test facility, the hull draft and mooring system were truncated. The 1:30 scale model was towed through the ice on a fixed and compliant dynamometer. The stiffness characteristics of the compliant dynamometer matched the horizontal stiffness of the full-scale mooring system. The purpose of these tests was to compare the mooring and ice loads measured in fixed and compliant conditions. The 1:50 scale model was truncated by 70 m. Its mooring system was modeled using a four-line system designed to give the same global restoring forces as the full-scale mooring system. The model was fitted with vertical plates on the exterior of the hull to compensate for loss of added mass and added moment of inertia. A limited number of tests were carried out at the two model scales in the same ice conditions to investigate scaling effects. The mooring and ice loads measured in the fixed and compliant conditions were found to be similar, indicating that loads estimated, assuming the structure is fixed, provide good estimates. Good agreement between the two models was also found for the tests carried out in the same ice conditions, suggesting that the scaling effects may be negligible.

scholarly journals Upper and lower limits on the stability of calving glaciers from the yield strength envelope of ice

2011 ◽  
Vol 468 (2140) ◽  
pp. 913-931 ◽  
Author(s):  
J. N. Bassis ◽  
C. C. Walker
Keyword(s):  
Yield Strength ◽  
Water Depth ◽  
Shear Failure ◽  
Ice Sheets ◽  
Direct Consequence ◽  
Ice Thickness ◽  
Tightly Coupled ◽  
The Stability ◽  
Induced Changes ◽  
Lower Limits

Observations indicate that substantial changes in the dynamics of marine-terminating ice sheets and glaciers are tightly coupled to calving-induced changes in the terminus position. However, the calving process itself remains poorly understood and is not well parametrized in current numerical ice sheet models. In this study, we address this uncertainty by deriving plausible upper and lower limits for the maximum stable ice thickness at the calving face of marine-terminating glaciers, using two complementary models. The first model assumes that a combination of tensile and shear failure can render the ice cliff near the terminus unstable and/or enable pre-existing crevasses to intersect. A direct consequence of this model is that thick glaciers must terminate in deep water to stabilize the calving front, yielding a predicted maximum ice cliff height that increases with increasing water depth, consistent with observations culled from glaciers in West Greenland, Antarctica, Svalbard and Alaska. The second model considers an analogous lower limit derived by assuming that the ice is already fractured and fractures are lubricated by pore pressure. In this model, a floating ice tongue can only form when the ice entering the terminus region is relatively intact with few pre-existing, deeply penetrating crevasses.

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