Experimental Study of Combined Wave and Ice Loads on a Fixed Offshore Structure

2021 ◽  
Author(s):  
Shafiul Mintu ◽  
David Molyneux
Keyword(s):  
Offshore Structures ◽  
Numerical Code ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Engineering Research ◽  
Combined Loads ◽  
Individual Wave ◽  
Ice Loads ◽  
Ice Floes ◽  
Memorial University Of Newfoundland

Abstract Ice floes in the marginal ice zone (MIZ) are exposed to wind, wave, and current forces which greatly influence the dynamics of the ice floes. ISO 19906 recommends considering combined wave and ice actions while designing offshore structures for arctic and cold regions. Few studies have focused on ice-structure interactions in waves. There are not many tools available to estimate these combined loads on structures. A numerical tool “SAMICE” has been developed to simulate the hydrodynamics of wave-ice interactions, but there exists a lack of data for a realistic MIZ under wave actions for validation studies of the numerical code. To address this gap and to investigate the hydrodynamics of ice floes under waves, a set of experiments was conducted at the wave tank of Ocean Engineering Research Center (OERC) of Memorial University of Newfoundland. A six-component dynamometer was used to measure the loads on a model scale aluminum cylindrical gravity-based offshore structure. Loads were measured for five regular waves of various steepness in combination with three current speeds. Two ice concentrations with various floe sizes of random shapes were prepared from polypropylene sheets to represent the MIZ. Most of the tests were repeated three times and a statistical approach was used to analyze the loads. The preliminary analysis shows that the average wave-ice loads may be determined by ISO guidelines, but the predictions of impulse loads from individual wave-driven ice floes are very uncertain.

Wave–current effects on large offshore structures

1989 ◽  
Vol 16 (4) ◽  
pp. 543-551 ◽  
Author(s):  
Michael Isaacson ◽  
John Baldwin
Keyword(s):  
Potential Flow ◽  
Offshore Structures ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Viscous Effects ◽  
Offshore Structure ◽  
Time Stepping ◽  
Waves And Currents ◽  
Flow Effects ◽  
Interaction Problem

The various effects that influence loads acting on a large offshore structure due to the combination of waves and currents are reviewed. These may be broadly associated with potential flow effects and viscous effects. The potential flow effects are nonlinear and may generally be investigated by perturbation or time-stepping methods. Viscous effects include the onset of flow separation, which affects the validity of the assumed potential flow, as well as steady and oscillatory forces. The fluid mechanics of the complete wave–current–structure interaction problem are not yet well understood and areas in need of additional research are identified. Key words: currents, drag, drift forces, hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

Experimental Investigation of Ice Mass Hydrodynamic Interaction With Offshore Structure in Close Proximity

2015 ◽  
Author(s):  
Tanvir Mehedi Sayeed ◽  
Bruce Colbourne ◽  
Heather Peng ◽  
Benjamin Colbourne ◽  
Don Spencer
Keyword(s):  
Hydrodynamic Interaction ◽  
Impact Load ◽  
Numerical Study ◽  
Numerical Models ◽  
Offshore Structures ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Area Of Interest ◽  
Close Proximity ◽  
The Impact

Iceberg/bergy bit impact load with fixed and floating offshore structures and supply ships is an important design consideration in ice-prone regions. Studies tend to divide the iceberg impact problem into phases from far field to contact. This results in a tendency to over simplify the final crucial stage where the structure is impacted. The authors have identified knowledge gaps and their influence on the analysis and prediction of iceberg impact velocities and loads (Sayeed et. al (2014)). The experimental and numerical study of viscous dominated very near field region is the main area of interest. This paper reports preliminary results of physical model tests conducted at Ocean Engineering Research Center (OERC) to investigate hydrodynamic interaction between ice masses and fixed offshore structure in close proximity. The objective was to perform a systematic study from simple to complex phenomena which will be a support base for the development of subsequent numerical models. The results demonstrated that hydrodynamic proximity and wave reflection effects do significantly influence the impact velocities at which ice masses approach to large structures. The effect is more pronounced for smaller ice masses.

Influence of added mass on ice impacts

1988 ◽  
Vol 15 (4) ◽  
pp. 698-708 ◽  
Author(s):  
Michael Isaacson ◽  
Kwok Fai Cheung
Keyword(s):  
Contact Point ◽  
Added Mass ◽  
Offshore Structures ◽  
Impact Model ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Proposed Model ◽  
Impact Problems ◽  
Ice Impacts ◽  
The Impact

The present paper applies potential theory to describe the variation of the added mass of an iceberg and its coupling effects on an offshore structure for various separation distances up to the point of contact. The strengths and weaknesses of the proposed model are discussed together with its practical application in ice mass impact problems. An impact model based on dynamic analysis is developed to calculate the impact force and response of a structure for head-on collisions. Both the contact-point added mass estimated in the present study and the traditionally assumed far-field added mass are used in the impact model separately. The results are compared and the crucial roles played by the ambient fluid during impact are discussed. Key words: added mass, hydrodynamics, ice impact, ocean engineering, offshore structures.

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.

Results From Model Testing of Ice Protection Piles in Shallow Water

2006 ◽  
Author(s):  
Arne Gu¨rtner ◽  
Joachim Berger
Keyword(s):  
Model Test ◽  
Oil And Gas ◽  
Offshore Structures ◽  
Full Scale ◽  
Offshore Structure ◽  
Oil And Gas Fields ◽  
Ice Loads ◽  
Drifting Ice ◽  
Ice Model Test ◽  
Gas Fields

The development of oil and gas fields in shallow icy waters, for instance in the Northern Caspian Sea, have increased the awareness of protecting offshore structures by means of ice barriers from the impacts of drifting ice. Protection could be provided by Ice Protection Piles (IPPs), installed in close vicinity to the offshore structure to be protected. Piles then take the main loads from the drifting ice by pre-fracturing the advancing ice sheet. Hence, the partly shielded offshore structure could be designed according to significant lower global design ice loads. In this regard, various configurations of pile arrangements have been model tested during the MATRA-OSE research project in the Ice Model Test Basin of the Hamburg Sip Model Basin (HSVA). The main objective was to analyse the behaviour of ice interactions with the protection piles together with the establishment of design ice loads on an individual pile within the pile arrangement. The pile to pile distances within each arrangement were varied from 2 to 8 times the pile diameter for both, vertical and inclined (30° to the horizontal) pile arrangements. Two test runs with 0.1 m and 0.5 m thick ice (full scale values) were conducted respectively. The full scale water depth was 4 m. Based on the model test observations, it was found that the rubble generation increases with decreasing pile to pile distances. Inclined piles were capable to produce more rubble than vertical piles and considerable lower ice loads were measured on inclined arrangements compared to vertical arrangements. As initial rubble has formed in front of the arrangements, the rubble effect accelerated considerable. Subsequent to the build-up of rubble accumulations, no effect of the pile inclination on the exerted ice loads could be observed. If piles are used as ice barriers, the distance between the piles should be less than 4D for inclined piles and 6D for vertical piles to allow sufficient rubble generation. Larger distances only generated significant ice rubble after initial grounding of the ice had occurred.

Analysis and Probabilistic Modeling of the Unstationary Ice Loads Stochastic Process, Based on Experiments With Models of Offshore Structures

2015 ◽  
Author(s):  
Petr Zvyagin ◽  
Kirill Sazonov
Keyword(s):  
Stochastic Process ◽  
Time Series ◽  
Statistical Analysis ◽  
Probabilistic Modeling ◽  
Offshore Structures ◽  
Offshore Structure ◽  
Sample Mean ◽  
Ice Loads ◽  
Time Series Simulation ◽  
Fuzzy C Means Algorithm

Experiments with models of platforms and offshore structures with vertical and inclined panels, which were conducted at Krylov Research Center (St. Petersburg), demonstrated that sometimes ice loads time series registered in these experiments cannot be considered as stationary. At the same time until nowadays methods and algorithms of probabilistic modeling were mainly based on the assumption of ice loads time series stationarity. That is because the analysis and modeling for stationary stochastic process is easier than for those unstationary. In the paper the method for determining the presence of unstationarity in ice loads time series, based on statistical analysis, is described. This method employs sample mean normality. Fuzzy C-means algorithm is used to cluster autocorrelation vectors, which are built for different fragments of time series. In the paper ice loads time series, got in experiments in ice tank with offshore structure columns and basement models, are investigated on their unstationarity. The algorithm of unstationary ice loads time series simulation is offered.

Wave and current forces on fixed offshore structures

1988 ◽  
Vol 15 (6) ◽  
pp. 937-947 ◽  
Author(s):  
Michael Isaacson
Keyword(s):  
Key Words ◽  
Recent Literature ◽  
Offshore Structures ◽  
Design Criteria ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Detailed Survey ◽  
Ice Loads ◽  
Hydrodynamic Data ◽  
Design Construction

The Canadian Standards Association standard S471 "General requirements, design criteria, environment, and loads, Part 1 of the CSA code for the design, construction and installation of fixed offshore structures" contains an appendix "Wave and current loads." To compliment this appendix, the present paper provides a more detailed survey of this topic with a review of the recent literature and recommendations of hydrodynamic data needed in offshore design. In addition, hydrodynamic considerations in the calculation of earthquake and ice loads are mentioned. Key words: currents, current forces, hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

Evaluation of the Ice Load Acting on an Arctic Offshore Structure With Different Ice Drifting Angle

2020 ◽  
Author(s):  
Young-Shik Kim ◽  
Yun-Ho Kim ◽  
Hyung-Do Song ◽  
Jin-Ho Jang ◽  
Solyoung Han ◽  
...  
Keyword(s):  
Evaluation Method ◽  
Offshore Structures ◽  
Mean Value ◽  
Experimental Methodology ◽  
The Arctic ◽  
Design Stage ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Ice Load ◽  
National University

Abstract In this study, an evaluation method and results for ice load acting on an Arctic offshore structure with various ice drifting angles are discussed. Korea Research Institute of Ships and Ocean Engineering (KRISO) has conducted a research project to develop a hull form design for year-round floating type offshore structures in the Arctic condition with dynamic positioning and mooring system. Six cooperating organizations participated in the project: Samsung Heavy Industry, Korean Register, Pusan National University, Korea Maritime & Ocean University, Dong-Eui University, and Inha Technical College. In the design stage of an Arctic offshore structure, ice load consideration is the key component for the safety and reliability analysis. However, there is no generally used tool for evaluation of ice load acting on an Arctic offshore structures. In this study, ice loads acting on an Arctic FPSO in managed ice conditions with various ice drifting angles are examined by experimental methodology. Dramatic mean value changes in ice load with different ice drifting angles are observed in the model test. This experimental ice load evaluation method can be applied to the other types of offshore structure which might operate in sea ice condition.

Downtime Analysis Techniques for Complex Offshore and Dredging Operations

2004 ◽  
Author(s):  
Remmelt J. van der Wal ◽  
Gerrit de Boer
Keyword(s):  
Wind Waves ◽  
Weather Forecast ◽  
Offshore Structures ◽  
Operational Mode ◽  
Offshore Structure ◽  
Hydrodynamic Models ◽  
Time Step ◽  
Made In

Offshore operations in open seas may be seriously affected by the weather. This can lead to a downtime during these operations. The question whether an offshore structure or dredger is able to operate in wind, waves and current is defined as “workability”. In recent decades improvements have been made in the hydrodynamic modelling of offshore structures and dredgers. However, the coupling of these hydrodynamic models with methods to analyse the actual workability for a given offshore operation is less developed. The present paper focuses on techniques to determine the workability (or downtime) in an accurate manner. Two different methods of determining the downtime are described in the paper. The first method is widely used in the industry: prediction of downtime on basis of wave scatter diagrams. The second method is less common but results in a much more reliable downtime estimate: determination of the ‘job duration’ on basis of scenario simulations. The analysis using wave scatter diagrams is simple: the downtime is expressed as a percentage of the time (occurrences) that a certain operation can not be carried out. This method can also be used for a combination of operations however using this approach does not take into account critical events. This can lead to a significant underprediction of the downtime. For the determination of the downtime on basis of scenario simulations long term seastate time records are used. By checking for each subsequent time step which operational mode is applicable and if this mode can be carried out the workability is determined. Past events and weather forecast are taken into account. The two different methods are compared and discussed for a simplified offloading operation from a Catenary Anchor Leg Mooring (CALM) buoy. The differences between the methods will be presented and recommendations for further applications are given.

Parameter Sensitivity in Numerical Modelling of Ice-Structure Interaction With Cohesive Element Method

2016 ◽  
Author(s):  
Dianshi Feng ◽  
Sze Dai Pang ◽  
Jin Zhang
Keyword(s):  
Element Model ◽  
Offshore Structures ◽  
Parameter Sensitivity ◽  
The Arctic ◽  
Cohesive Element ◽  
Structure Interaction ◽  
Marine Structure ◽  
Ice Loads ◽  
The Stability ◽  
Element Method

The increasing marine activities in the Arctic has resulted in a growing demand for reliable structural designs in this region. Ice loads are a major concern to the designer of a marine structure in the arctic, and are often the principal factor that governs the structural design [Palmer and Croasdale, 2013]. With the rapid advancement in computational power, numerical method is becoming a useful tool for design of offshore structures subjected to ice actions. Cohesive element method (CEM), a method which has been widely utilized to simulate fracture in various materials ranging from metals to ceramics and composites as well as bi-material systems, has been recently applied to predict ice-structure interactions. Although it shows promising future for further applications, there are also some challenging issues like high mesh dependency, large variation in cohesive properties etc., yet to be resolved. In this study, a 3D finite element model with the use of CEM was developed in LS-DYNA for simulating ice-structure interaction. The stability of the model was investigated and a parameter sensitivity analysis was carried out for a better understanding of how each material parameter affects the simulation results.

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