Ice Model Tests for Ice Loads and Encroachment of Fixed Offshore Structures

2018 ◽  
Author(s):  
Christian Schroeder
Author(s):  
Subodh Chander ◽  
Ayhan Akinturk ◽  
Bruce Colbourne

Most of the research done on ice-structure interaction deals with the ice at the sea surface. Whereas majority of ice-strengthened regions of ships and offshore structures are well below the waterline. The aim of this research is to examine the mechanics of ice loads caused by submerged ice blocks colliding with the structure. The kinematics is an essential determinant of the energy that is available to drive the ice crushing process during the collision. The present research aims to develop a model to represent the mechanics of such collisions and set a direction for future work. This study includes experimental and numerical components. Various physical experiments have been conducted using a submerged ice model moving solely due to its buoyancy. Using high speed camera the experiments are recorded and analysed to determine the kinematics of collision. These include location, velocity and acceleration of the model ice as a function of time. In parallel, numerical simulations have being conducted using FLOW 3DTM software. The results of the experiments are used to validate the numerical model of the underwater collision. The results shows that added mass plays an important role during the underwater impact collisions. The paper presents some preliminary results obtained during this research.


Author(s):  
Peter Jochmann ◽  
Karl-Ulrich Evers ◽  
Walter L. Kuehnlein

The drilling rig Sunkar, owned and operated by Parker Drilling under contract to Agip KCO, was the first drilling rig in the North Caspian Sea. In this area sea ice may occur between November and April. The original ice protection concept of the drilling rig was based on the fact that ice loads were partly taken and/or reduced by two rows of heavy piles. As an alternative concept ice model tests for Sunkar with installed ice barriers (Ice Rubble Generators) around the rig were carried out in the Large Ice Model Basin of HSVA in order to establish the design ice loads and to prove that the design forces can be reduced significantly by using these ice barriers. The test series were carried out in 1.3 m thick level ice with a bending strength of 770 kPa. Ice drift angle, ice drift speed, spacing between the ice barriers, as well as the angle of the ice barriers were varied. The design water level simulated in the model tests was about 4 m. As maximum measured ice load values are a result of coincidental ice failure occurrences these values are much more scattered than the mean values of ice model tests. Even if an individual model test could be repeated exactly, i.e. exactly within measurable limits, the maximum load would be different. Therefore the design load needs to be obtained by using a sophisticated statistical approach. To establish the design load an extreme value distribution, a Gumbel-Probability-Distribution (GPD) for each individual model run has been applied. The ice model tests have shown that a significant ice force reduction can be achieved if the drilling rig Sunkar is protected with ice barriers. The reduction of the maximum horizontal global ice load amounts to approx. 63% when Sunkar is protected by ice barriers. The ice barriers initiate ice rubble and areas of rafted ice as well as ice accumulation between the barriers, which lead to ice bridging with a spacing of 60 to 80 m between the ice barriers. As a final result it was found that the stability of Sunkar will be sufficient under any angle of drifting ice if ice barriers are installed.


Author(s):  
Torbjørn Hals ◽  
Nils Albert Jenssen

The paper presents the results from a series of ice model tests performed as part of the DYPIC (Dynamic Positioning in Ice Conditions) research program. DYPIC is a research and development project within the EU’s ERA NET MARTEC project. The major purpose of the DYPIC project is development of equipment and methods for DP Ice Model testing which allows the prediction of station keeping capability of different vessel types and offshore structures under various ice conditions. The first DYPIC model tests performed in 2011 was conducted with two significantly different vessel sizes, a 68.0000 m3 volume displacement arctic drillship and an 8.600 m3 polar research vessel. The model scale was 1/30 for the arctic drillship and 1/18.6 for the Polar Research Vessel. The model tests were performed in the ice model basin at HSVA using vessel models equipped with thruster capacity similar to full scale operation according to DP class 2 / 3 operations. The DP control system was also modified from normal open water DP operations in order to cope with the highly varying ice drift loads acting on the vessel. The test program gave data supporting the development of numerical models of ice loads from managed ice, see reference [6]. The main focus in this paper is on the station keeping performance and associated thrust utilization as a function of varying ice drift loads. The results and data collected in the first year of the DYPIC program demonstrates that DP ice model tests will be a valuable tool for evaluation of vessel performance prior to moving on to full scale arctic DP operations.


Author(s):  
Gesa Ziemer ◽  
Karl-Ulrich Evers ◽  
Christian Voosen

Model tests in ice have been conducted at the Large Ice Basin of HSVA with cylindrical and conical, compliant structures exposed to drifting level ice to investigate the influence of slope and compliance on the ice load and its breaking frequency. Main goal of the test campaign was to study the importance of structural feedback during ice-cone interaction. This is a major issue e.g. for numerical simulation of offshore structures during design phase. Four shapes were tested: 50°, 60°, 80° and 90° slope angle. The cylinder was tested in order to define the worst case scenario regarding magnitude of ice load and severity of ice-induced vibrations. Stiffness and natural frequency of the structure were chosen similar to typical values for offshore wind turbine support structures. All shapes were tested both in a compliant and fixed configuration. The breaking frequency was found to be more pronounced for the lower slope angles where the ice failed in flexural failure only, while a transition to crushing failure as observed on a cylindrical structure takes place at 80° cone angle already. This results in significantly higher ice loads on the 80° cone than on those with lower angles, but a reduced risk of severe ice-structure interaction due to the unsteady nature of the mixed mode breaking process. Although the breaking frequency is rather constant e.g. during ice impact on the 60° cone, it was not possible during the model tests to match the ice drift speed and the dynamics of the structure in a way that causes resonance. However, model test results prove that there is a risk of conical structures with low natural frequencies and low stiffness in ice plane being excited by periodic ice failure in their natural frequency, thus response amplification may take place and pose a risk to the structural integrity of conical offshore structures exposed to sea ice. This paper presents the model test setup, analysis of the results, and general findings.


Author(s):  
Andrew Cornett

Many deck-on-pile structures are located in shallow water depths at elevations low enough to be inundated by large waves during intense storms or tsunami. Many researchers have studied wave-in-deck loads over the past decade using a variety of theoretical, experimental, and numerical methods. Wave-in-deck loads on various pile supported coastal structures such as jetties, piers, wharves and bridges have been studied by Tirindelli et al. (2003), Cuomo et al. (2007, 2009), Murali et al. (2009), and Meng et al. (2010). All these authors analyzed data from scale model tests to investigate the pressures and loads on beam and deck elements subject to wave impact under various conditions. Wavein- deck loads on fixed offshore structures have been studied by Murray et al. (1997), Finnigan et al. (1997), Bea et al. (1999, 2001), Baarholm et al. (2004, 2009), and Raaij et al. (2007). These authors have studied both simplified and realistic deck structures using a mixture of theoretical analysis and model tests. Other researchers, including Kendon et al. (2010), Schellin et al. (2009), Lande et al. (2011) and Wemmenhove et al. (2011) have demonstrated that various CFD methods can be used to simulate the interaction of extreme waves with both simple and more realistic deck structures, and predict wave-in-deck pressures and loads.


Author(s):  
William Hidding ◽  
Guillaume Bonnaffoux ◽  
Mamoun Naciri

The reported presence of one third of remaining fossil reserves in the Arctic has sparked a lot of interest from energy companies. This has raised the necessity of developing specific engineering tools to design safely and accurately arctic-compliant offshore structures. The mooring system design of a turret-moored vessel in ice-infested waters is a clear example of such a key engineering tool. In the arctic region, a turret-moored vessel shall be designed to face many ice features: level ice, ice ridges or even icebergs. Regarding specifically level ice, a turret-moored vessel will tend to align her heading (to weather vane) with the ice sheet drift direction in order to decrease the mooring loads applied by this ice sheet. For a vessel already embedded in an ice sheet, a rapid change in the ice drift direction will suddenly increase the ice loads before the weathervaning occurs. This sudden increase in mooring loads may be a governing event for the turret-mooring system and should therefore be understood and simulated properly to ensure a safe design. The paper presents ADWICE (Advanced Weathervaning in ICE), an engineering tool dedicated to the calculation of the weathervaning of ship-shaped vessels in level ice. In ADWICE, the ice load formulation relies on the Croasdale model. Ice loads are calculated and applied to the vessel quasi-statically at each time step. The software also updates the hull waterline contour at each time step in order to calculate precisely the locations of contact between the hull and the ice sheet. Model tests of a turret-moored vessel have been performed in an ice basin. Validation of the simulated response is performed by comparison with model tests results in terms of weathervaning time, maximum mooring loads, and vessel motions.


1998 ◽  
Vol 14 (04) ◽  
pp. 265-276
Author(s):  
Ivo Senjanovic

This review paper covers extensive investigations which were undertaken in order to verify the idea of launching of ships and other floating structures from a horizontal berth by a set of turning pads. This includes structural dynamics during launching, model tests and strength analysis of the structure and the launching system. The most important results, which were used for the design of the launching system, are presented. The preparation of a barge for side launching is described, and the full-scale measurement results are compared with the test results. The advantages of building ships and offshore structures on a horizontal berth are pointed out in the conclusion.


2021 ◽  
Author(s):  
Daniel de Oliveira Costa ◽  
Julia Araújo Perim ◽  
Bruno Guedes Camargo ◽  
Joel Sena Sales Junior ◽  
Antonio Carlos Fernandes ◽  
...  

Abstract Slamming events due to wave impact on the underside of decks might lead to severe and potentially harmful local and/or global loads in offshore structures. The strong nonlinearities during the impact require a robust method for accessing the loads and hinder the use of analytical models. The use of computation fluid dynamics (CFD) is an interesting alternative to estimate the impact loads, but validation through experimental data is still essential. The present work focuses on a flat-bottomed model fixed over the mean free surface level submitted to regular incoming waves. The proposal is to reproduce previous studies through CFD and model tests in a different reduced scale to provide extra validation and to identify possible non-potential scale effects such as air compressibility. Numerical simulations are performed in both experiments’ scales. The numerical analysis is performed with a marine dedicated flow solver, FINE™/Marine from NUMECA, which features an unsteady Reynolds-averaged Navier-Stokes (URANS) solver and a finite volume method to build spatial discretization. The multiphase flow is represented through the Volume of Fluid (VOF) method for incompressible and nonmiscible fluids. The new model tests were performed at the wave channel of the Laboratory of Waves and Currents (LOC/COPPE – UFRJ), at the Federal University of Rio de Janeiro.


Author(s):  
Dianshi Feng ◽  
Sze Dai Pang ◽  
Jin Zhang

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.


Sign in / Sign up

Export Citation Format

Share Document