scholarly journals A mathematical analysis of an extended model describing sea ice-induced frequency lock-in for vertically sided offshore structures

2021 ◽  
Author(s):  
Andrei K. Abramian ◽  
Sergei A. Vakulenko ◽  
Wim T. van Horssen
Keyword(s):  
Sea Ice ◽  
Mathematical Analysis ◽  
Offshore Structures ◽  
Extended Model ◽  
Lock In

Scale Effect in Ice Flexural Strength

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Mohamed Aly ◽  
Rocky Taylor ◽  
Eleanor Bailey Dudley ◽  
Ian Turnbull
Keyword(s):  
Flexural Strength ◽  
Sea Ice ◽  
Probabilistic Models ◽  
Scale Effects ◽  
Offshore Structures ◽  
Bridge Piers ◽  
Freshwater Ice ◽  
Flexural Failure ◽  
Ice Loads ◽  
Ice Strength

Ice flexural strength is an important parameter in the assessment of ice loads on the hulls of ice-class ships, sloped offshore structures, and sloped bridge piers. While scale effects in compressive ice strength are well known, there has been debate as to the extent of scale effects in ice flexural strength. To investigate scale effects during flexural failure of both freshwater and saline ice, a comprehensive up-to-date database of beam flexural strength measurements has been compiled. The database includes 2073 freshwater ice beam tests with beam volumes between 0.00016 and 2.197 m3, and 2843 sea ice beam tests with volumes between 0.00048 and 59.87 m3. The data show a considerable decrease in flexural strength as the specimen size increases, when examined over a large range of scales. Empirical models of freshwater ice flexural strength as a function of beam volume, and of saline ice as function of beam and brine volumes have been developed using regression analysis. For freshwater ice, the scale-dependent flexural strength is given as: σf=839(V/V1)−0.13 For sea ice, the dependence of flexural strength has been modeled as: σ=1324(V/V1)−0.054e−4.969vb. Probabilistic models based on the empirical data were developed based on an analysis of the residuals, and can be used to enhance probabilistic analysis of ice loads where ice flexural strength is an input.

Fracture of Multi-Year Sea Ice Under Triaxial Stresses: Apparatus Description and Preliminary Results

1989 ◽  
Vol 111 (3) ◽  
pp. 258-263 ◽  
Author(s):  
P. R. Sammonds ◽  
S. A. F. Murrell ◽  
M. A. Rist
Keyword(s):  
Sea Ice ◽  
Triaxial Compression ◽  
Offshore Structures ◽  
Arctic Sea Ice ◽  
Strain Rates ◽  
Preliminary Results ◽  
Brittle Behavior ◽  
Triaxial Stresses ◽  
Arctic Sea ◽  
Constant Displacement

The forces that arctic sea ice can exert on offshore structures are strongly influenced by ice fracture. Fracture of multi-year sea ice has been studied in the laboratory under triaxial compression using a new triaxial mechanical testing cell for ice. A description of this apparatus is given, which enables the confined brittle behavior of ice to be investigated at temperatures down to −90°C and at strain rates up to 10−2/s under closed-loop constant displacement rate control. Preliminary results for the fracture of multi-year sea ice under confined conditions at −10°C are presented.

scholarly journals Analysis of Offshore Structures Based on Response Spectrum of Ice Force

2019 ◽  
Vol 7 (11) ◽  
pp. 417 ◽  
Author(s):  
Liu ◽  
Li ◽  
Zhang
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Response Spectrum ◽  
Time History ◽  
Offshore Structures ◽  
Potential Threat ◽  
Influence Coefficients ◽  
Design Response Spectrum ◽  
Ice Force ◽  
Bending Failure

With the development of large-scale offshore projects, sea ice is a potential threat to the safety of offshore structures. The main forms of damage to bottom-fixed offshore structures under sea ice are crushing failure and bending failure. Referred to as the concept of seismic response spectrums, the design response spectrum of offshore structures induced by the crushing and bending ice failure is presented. Selecting the Bohai Sea in China as an example, the sea areas were divided into different ice zones due to the different sea ice parameters. Based on the crushing and bending failure power spectral densities of ice force, a large amount of ice force time-history samples are firstly generated for each ice zone. The time-history of the maximum responses of a series of single degree of freedom systems with different natural frequencies under the ice force are calculated and subsequently, a response spectrum curve is obtained. Finally, by fitting all the response spectrum curves from different samples, the design response spectrum is generated for each ice zone. The ice force influence coefficients for crushing and bending failure are obtained, which can be used to estimate the stochastic sea ice force acting on a structure conveniently in a static way. A comparison of the proposed response spectrum method with the Monte Carlo method by a numerical example shows good agreement.

Co-Occurrence Probability Analysis of Sea Ice at Yingkou and Huludao Observation Stations of China

2017 ◽  
Author(s):  
Shanshan Tao ◽  
Zhifeng Wang ◽  
Ri Zhang ◽  
Sheng Dong
Keyword(s):  
Sea Ice ◽  
Probability Distributions ◽  
Joint Probability ◽  
Offshore Structures ◽  
Early Spring ◽  
Probability Analysis ◽  
Ice Thickness ◽  
Occurrence Probability ◽  
Sea Ice Thickness ◽  
Ice Conditions

Co-occurrence probability analysis of sea ice between adjacent areas is very helpful for the hazard prevention and protection strategy making of coastal and offshore engineering. Yingkou and Huludao with similar latitudes are located on the opposite sides of Liaodong Bay of China. Their sea ice conditions are both apparent in winter and early spring, so it is useful to study on the co-occurrence situations of sea ice conditions between these two areas. Based on the annual maximum sea ice thickness of Yingkou and Huludao observation stations, the co-occurrence probability analysis of sea ice thickness is conducted. The joint probability distributions of sea ice thickness between these adjacent areas are constructed by using univariate maximum entropy distributions and four bivariate copulas. Both marginal curve fittings are very well, and the model determined by Gumbel-Hougaard copula describes the bivariate sea ice thickness data best. Then different cases of co-occurrence probabilities of sea ice thickness between Yingkou and Huludao are presented, and they can provide references to the hazard protection of the coastal and offshore structures between these two areas.

Ice Forces due to Changes in Water Level and Adfreeze Bond Strength Between Sea Ice and Various Materials

1988 ◽  
Vol 110 (1) ◽  
pp. 74-80 ◽  
Author(s):  
N. Nakazawa ◽  
H. Saeki ◽  
T. Ono ◽  
T. Takeuchi ◽  
S. Kanie
Keyword(s):  
Bond Strength ◽  
Sea Ice ◽  
Water Level ◽  
Bending Strength ◽  
Construction Materials ◽  
Ice Cover ◽  
Offshore Structures ◽  
Method Of Calculation ◽  
Bending Failure ◽  
Ice Forces

In cold regions, changes in water level can induce vertical forces on offshore structures (such as caisson and tower types) when sea ice cover to structure adfreeze bonding is present. This paper summarized the theoretical analyses of vertical ice forces as well as the results of experiments which identified the parameters required when estimating sea ice adfreeze bond strength. 1) Vertical Ice Forces. The authors have proposed a method of calculation that estimates the vertical ice forces taking the following into account: bending failure of the ice cover and adfreeze bond failure (shear induced). Calculation of vertical ice forces by this method requires the following information: bending strength of ice. Young’s modulus of ice, Poisson’s ratio of ice, and adfreeze bond strength to various materials. 2) Adfreeze Bond Strength of Sea Ice. The authors have been conducting, for 6 yr, adfreeze bond strength experiments between sea ice and various common construction materials for offshore structures such as concrete and steel. The following conclusions have been drawn from this study: (i) under certain conditions, the adfreeze bond strength of sea ice greatly depends on the surface roughness of construction materials; (ii) adfreeze bond strength increases with decreasing sea ice temperature; (iii) adfreeze bond strength decreases, approaching a constant, with increasing structure diameter; (iv) adfreeze bond strength increases, approaching a constant, with increasing ice thickness; (v) adfreeze bond strength is not greatly affected by push out velocity and stress rate.

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.

Experimental Study of Sea Ice Forces on a Structure and its Stability

2011 ◽  
Vol 243-249 ◽  
pp. 4750-4753 ◽  
Author(s):  
Ji Wu Dong ◽  
Zhi Jun Li ◽  
Li Min Zhang ◽  
Guang Wei Li ◽  
Hong Wei Han
Keyword(s):  
Experimental Study ◽  
Sea Ice ◽  
Offshore Structures ◽  
Sea Bed ◽  
Ice Loads ◽  
Level Ice ◽  
Ice Floes ◽  
The Stability ◽  
Ice Forces ◽  
Concrete Model

A structure was designed to reduce the large forces exerted by level ice on offshore structures in shallow icy waters, by breaking the large ice floes into small pieces from flexing-induced failure. A series of model tests was conducted to simulate ice loads on the structure. A concrete model of it was adopted to verify the stability of the structure under the action of ice floes, which had five different thicknesses. The results show that ice forces on the structure are low and that the stability of the structure under different sea bed is good.

Measurements of Sea-Ice Stresses Near Grounded Obstacles

1980 ◽  
Vol 102 (3) ◽  
pp. 144-147
Author(s):  
W. M. Sackinger ◽  
R. D. Nelson
Keyword(s):  
Tensile Stress ◽  
Sea Ice ◽  
Crack Formation ◽  
Offshore Structures ◽  
Impulsive Loading ◽  
Compressive Stresses ◽  
Pressure Ridge ◽  
Multiyear Ice

Stresses were measured in multiyear sea ice near a grounded floe island. Compressive stresses as high as 250 psi (1.72 MPa) were observed, in the form of impulses. A second installation in annual sea ice near a grounded pressure ridge showed tensile stress of 100 psi (0.69 MPa), followed by crack formation. These stresses were localized to a range of the order of 100 m. Localized compressive stresses in multiyear ice near grounded offshore structures may exceed 250 psi (1.72 MPa), and impulsive loading should be expected.

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