Mohammadafzali, S. (Centre for Arctic Resource Development) | Sarracino, R. (Centre for Arctic Resource Development) | Taylor, R. (Memorial University of Newfoundland) | Stanbridge, C. W. (Memorial University of Newfoundland) | Marchenko, A. (The University Centre in Svalbard)
Flexural failure of sea ice is of interest in many different applications, ranging from understanding rubble formation processes to modeling bending failure of ice sheets against sloped structures and ship hulls. In this paper we present a brief summary of recent in-situ experiments carried out on side-loaded sea ice beam specimens on the ice fields near Storfjorden, Svalbard. Results from these tests have been used to parameterize a discrete element model of ice fracture under flexural loading. Simulations of these experiments in 3D have been carried out using a new material model within the open-source Discrete Element Method (DEM) code WooDEM which features cohesive bonds in tension, shear, flexure and torsion based on a contact model with normal, shear, torsional and flexural springs. A comparison of simulated and field test results, along with recommendations for future work is provided.
Hamilton, Matthew (Avalon Holographies Inc.) | Maynard, Aaron (GRI Simulations Inc.) | Jujuly, Muhammad (Memorial Univeristy) | Adeoti, Ibraheem (Memorial Univeristy) | Rahman, Aziz (Memorial Univeristy) | Adey, Matthew (GRI Simulations Inc.)
We present an integration of new capabilities of simulation and visualization for subsea analysis and design into an existing virtual arctic simulation environment (VASE). The existing system (previously presented) provides interactive, high-fidelity simulation capabilities for remotely-operated vehicles (ROV) in arctic environments for subsea trenching along with support for visualization of integrated data from sub-bottom and multibeam sonar imaging devices. This paper describes integration of the existing VASE with computation fluid dynamics (CFD) simulation capability for simulation of flow assurance and fluid-structure interaction design issues relevant to arctic subsea oil and gas field design.
The presented integrated simulation system allows for rapid, streamlined evaluation of pipeline designs in an integrated data, whole-field context. In particular, detailed analysis of pipeline fatigue risk factors due to slugging and effects of hydrate formation can be performed through integrated CFD analysis capabilities. The system's intuitive pipeline design allows for rapid alteration of pipe and flow lines in response to feedback from bathymetry and soil data, ROV accessibility requirements and structural analysis through flow induced vibration and fluid structure-interaction simulations.
It is demonstrated how various pipeline and jumper designs can be rapidly created in the VASE with design strategies motivated by the integrated whole field data visualization environment. Once pipe and jumper designs are specified, they can be exported for external analysis. We demonstrate this analysis through two fluid-structure interaction models (slugging and hydrate formation model). This allows for effective design in arctic environments, including design of pipeline routes in context of trenching and general management of cold water conditions. Overall, the system can also serve to function as a planning and data management system for subsequent training of pilots for inspection as part of asset integrity management.
In northern regions, ice forces, or actions, must be considered in the design of structures such as light piers, bridge piers, and offshore platforms. Estimates of ice forces in Canadian waters are usually obtained by consulting design standards such as those developed by the International Organization for Standardization (ISO) and the Canadian Standards Association (CSA). These design standards draw on available analytical formulae. Field measurements are available from several sources that suggest reasonable agreement with analytical results for simple cases involving wide structures.
One of the remaining uncertainties in estimating design loads, however, is the contribution of force imposed below the waterline due to unconsolidated keels of ice ridges. Only cursory guidance is provided by the standards associations and their analytical design equations. Close inspection of those formulae show that force estimates can become excessive in situations where the expected keel depth is great compared to the designed structure width. Such scenarios would be expected in offshore oil and gas operations where drilling risers, jack-up legs, and even jacket structures may be exposed to ice ridges.
The present work examines available approaches for evaluating ridge keel forces, including passive pressure calculations. The processes of ice rubble failure and the corresponding stress distributions are considered in the context of classical soil mechanics applied in geotechnical engineering. Design standards are also used to calculate ice forces for a range of ridge keel properties, keel geometries, and structure design widths. Field measurements from the Norströmsgrund lighthouse and the offshore Molikpag caisson are then examined and compared to the forces obtained using these approaches.
The authors conclude that the shape factor adopted in ISO 19906 plays an important role in calculations considering narrow structures and deep keels. It is also shown that the sensitivity of ridge keel load calculation to geometric factors varies considerably with structure width. Furthermore, an absence of real world data from ridge keel interactions with very narrow structures precludes validation of present models in these situations and should be the focus of data collection and model refinement.
Ice infested shallow waters of the North Caspian Sea imposes challenging tasks like ice pile up, fatigue due to ice-induced vibrations and ice impact loads, which strongly affect the structural integrity of offshore installations. This paper explores the potential application of a Minimal Facilities Platform or is also known as a Conductor Supported Wellhead Platform (CSWP) in the North Caspian Sea region and specifically focuses on the design optimization of the substructure due to ice loads. The CSWP has not been used in the cold climate regions before. The intention of this research is to prove feasibility of CSWP to withstand loads in the ice infested shallow waters. The substructure design was optimized by application of an ice resistant conical structure with specific inclination angle at the ice-structure interface. Usually conical structures reduce ice loads and ice induced vibrations. However, a fatigue capacity may be reduced due to geometrical discontinuity with the increase of inclination angle. This was shown in the design analysis.
Jujuly, Muhammad (C-RISE, Memorial university of Newfoundland) | Thodi, Premkumar (C-RISE, Memorial university of Newfoundland) | Rahman, Aziz (C-RISE, Memorial university of Newfoundland) | Khan, Faisal (C-RISE, Memorial university of Newfoundland)
The purpose of this study is to investigate subsea pipeline leaks and their impact on the surroundings. A numerical approach using a computational fluid dynamics (CFD) package is used. The subsea condition is extremely harsh due to the remoteness and inaccessibility. Marine pipeline can be damaged directly by contact with drifting sea ice. Trenched pipeline is at risk as well, as it may be damaged by corrosion, or the pipeline could be plastically deformed by the resulting seabed shake down event. Furthermore, due to the remoteness and harsh climate of the under the ocean, it is difficult to conduct normal maintenance procedures. Leakage of pipelines in arctic subsea environment can have severe consequences. Leak detection and location identification in a timely manner is crucial because of the economic impact of a hydrocarbon spill to its stakeholders can be huge. Pipeline leakage could have an adverse impact on life, the environment, the economy and corporate reputation. It is imperative to take additional precautions while operating in the subsea regions, so rapid leak detection and location identification is crucially important. In this paper, a numerical modeling of a subsea pipeline leakage is performed using a 3-D turbulent flow model in computational fluid dynamics (CFD). Four different types of fluids are tested in this study, with specified operating conditions.
It is difficult to conduct small-scale experiments on subsea pipeline with leakage, mainly because; the pipeline may need to release hydrocarbons to the environment. Further, since the industrial full-scale pipeline is large in diameter, fluid thermodynamics cannot be captured accurately in a small-scale, laboratory environment. Thus, a numerical simulation can provide a better understanding of pipeline internal flow and the consequences of pipeline leaks in different scales, reducing the cost and number of experiments. Commercially available ANSYS (FLUENT) computational fluid dynamics software is used to serve this purpose. ANSYS workbench provides integrated design, meshing technology, and large degree of freedom for pre- and post-processing for the fluid flow simulation in pipeline.
The CFD simulation results in this study showed that the flow rate of the fluid escaping from the leak increases with pipeline operating pressure. The static pressure and pressure gradient along the axial length of the pipeline have observed a sharp signature variation near the leak orifice. This signature has been captured using pressure gradient curves. The temperature profiles near leak orifice indicate that the temperature is observed to increase slightly in the case of incompressible fluids; however, temperature drops rapidly for the compressible fluids. Transient simulation is performed to obtain the acoustic signature of the pipe near leak orifice. The power spectral density (PSD) signal is strong near the leak orifice and it dissipates as the distance and orientation from the leak orifice increase. The high-pressure fluid flow generates more noise than the low-pressure fluid flow. In order to model the turbulence large eddy simulation (LES) used and Ffowcs-Williams and Hawking (FW-H) model in FLUENT was activated to generate acoustic data. Time step of the simulation was selected At = 0.0005 s and the number of simulation 20000 to get higher frequency noise signal.
Liu, Jiancheng Jessie (American Bureau of Shipping) | Liu, Xiang (American Bureau of Shipping) | Chen, Yingying (American Bureau of Shipping) | Long, Xue (Dalian University of Technology) | Ji, Shunying (Dalian University of Technology)
Existing standards and codes do not comprehensively address and provide all necessary guidance and requirements for the design of Arctic offshore structures. Reliably assessing ice loads on offshore structures remains a challenge for industry, especially as "new" Arctic platform concepts are proposed for deployment in lighter ice operations, e.g. Arctic SEDU (Self- Elevating Drilling Units) and Arctic CSDU (Column-Stabilized Drilling Units). As a pragmatic solution, a comprehensive approach including relevant field measurements, physical model tests and numerical simulations is usually adopted in assessing the ice loads for a particular design. Field measurement results are limited in number and there is often uncertainty concerning actual ice conditions and load measurement techniques. Furthermore several data sets are constrained with proprietary restrictions. In particular no direct field data is available for the example "new" structures (SEDUs and CSDUs). Physical model tests always present challenges due to scale issues, ice property calibration, measurement uncertainties and high costs. Therefore, numerical simulations using the validated DEM tool based on the related field/model test data are anticipated to provide supplementary information for standards/rule-based designs.
ABS has expended efforts to develop practical and advanced tools to assess the ice loads on offshore structures for several years. One promising numerical approach, a graphic processing unit (GPU) based Discrete Element Method (DEM) model, processes the computations in parallel and solves the DEM model with millions of particles for complicated ice-structure interaction problems, e.g. ice simultaneously loading on multiple legs and ice loading on a large CSDU. The paper presents details of the developing ABS GPU-DEM tool, status of the verification program, plans for the current and the future developments and applications. Included are brief descriptions of background technologies, an approach to derive the DEM model bonding strength inputs, and validation studies of ice breakage simulations based on the Bohai Bay Jacket ice data. The ice load simulations for fixed and floating structures, i.e. jack-up legs and the Kulluk floating drilling platform, are also shown to demonstrate the tool's capability and feasibility for Arctic offshore structure design. The interactions of ice and fixed/floating structures were analyzed, which provides useful references for future ice load modelling and offshore structure design.
The current practice for protecting wellheads and associated subsea facilities from icebergs on the Grand Banks is an Excavated Drill Centre (EDC), which is simply an excavation in the seabed in which wellheads and associated facilities are placed. Free-floating icebergs simply drift over an EDC, with the exception of those that roll as they pass over an EDC and increase draft sufficiently to enter. The risk from gouging icebergs entering an EDC is a function of the clearance between the surrounding undisturbed seabed and the top of the facilities in the EDC, and the distribution of gouging iceberg keel penetration depths. A field program conducted in Bonavista Bay in 2015 was used to estimate iceberg rolling rates, and an analysis of high resolution iceberg profile data collected in 2012 was used to determine the associated distribution of iceberg draft changes that occur due to rolling, and thus the rate at which iceberg keels penetrate an EDC due to rolling events. Modeled iceberg grounding rates and iceberg scour data from the Jeanne d'Arc were used to estimate the rate at which gouging icebergs enter EDCs. Iceberg gouge data from the Jeanne d'Arc and a dynamic time-step iceberg simulation using the 2012 iceberg profile data were used to determine the impact rate for facilities in the EDC as a function of the distance between the midline and the top of the facilities (clearance). The analysis addresses some of the conservatisms in the current approach, allowing for reduced EDC excavation depths.
Many offshore operations are today located in the so called marginal ice zone (MIZ) in which ice is broken up and moved by waves. The impact of ice and waves will cause high loads on offshore structures. Typical operations as vessel approach and launching of rescue and evacuation crafts can also be affected negatively. The correlation of wave parameters and resulting ice field properties is one key factor for the prediction and simulation of such processes. First results of the laboratory test campaigns have shown that they can fill gaps left in the description and quantification of wave ice interaction processes by theoretic models, satellite observation and field measurement campaigns.
A model testing campaign with wave propagation into a solid ice field has been carried out in a 70m by 10m ice model basin. The wave parameters (length and height) were increased stepwise and the interaction process with the ice sheet was monitored and documented. Relevant parameters like the crack length and orientation and resulting floes size distribution after different runs of wave application were measured and analysed by image processing. The relation between controlled wave parameters and ice field properties in the basin are compared to theoretic approaches which are based on linear wave- and elasticity theory.
The interaction processes of waves and model ice result in a typical pattern with areas of smaller floes at the ice edge and increasing floe size with distance from the first contact zone. The floe size decreases with duration of wave application until reaching a minimum which can be related to the wave length and height (wave steepness). The first breakup of the ice sheet is observed at certain wave amplitude depending on the ice thickness.
The main purpose of the test campaign was to assess the feasibility of combined wave ice tests in a model basin. Thereby the focus was to compare observations and results of the model tests to observations in nature and theoretic descriptions of wave ice interaction. This analysis provides valuable information on scaling problems, limitations of testing range and model ice behavior in cyclic loading. The information can be used to evaluate the significance of such model tests for ice scenarios and load investigations for offshore installations.
Ice may form in pipelines where ambient temperature is below freezing point of water. It was reported that ice delayed the restart of the Poplar pipeline system which gathers crude from Montanan and North Dakota (
This paper investigates the mechanisms of ice formation, its behaviors and impacts on oil transportation systems. A 2-inch inner diameter carbon steel flow loop was instrumented to measure pressure, temperature, and differential pressure. The effects of pipeline components, fluid properties, and water fractions were analyzed using the experimental setup. The experimental results show that ice formation can restrict flow at the low sport in front of the flow meter, the inserted thermocouples, and the perforated plate. Annular ice deposition was found at the pipe wall. The morphology of the deposition on the pipe wall was rime ice, indicating the deposition was due to small ice crystals sticking to the pipe surface. In addition, the formation of annular deposition requires a negative temperature gradient. The mechanisms for ice deposition along the pipe are discussed.
C-CORE is engaged in understanding the iceberg and sea ice design loads needs of the energy sector. As the energy industry ventures into oceans with greater ice cover and more icebergs, there is a significant need for efficient engineering tools to plan and manage operations in exploration, production, and safety. Industry requires a range of scenarios for their risk assessments, where existing simulations can be computationally and time intensive.
C-CORE has recently started using the benefit of the General Purpose Computing on Graphical Processing Units (GPGPU) approach. This approach has shown significant speed up of several numerical ice engineering applications related to icebergs and sea ice. The investigated model types are Monte-Carlo type approaches for probabilistic design method, and quadratic discriminant. GPU computing with Compute Unified Device Architecture (CUDA) is a new approach to solve complex problems and transform the GPU into a massively parallel processor.
The present study applies the GPGPU technology to a Monte-Carlo simulation, used for a sea ice load application. The objective of this study is to measure the performance of the GPU using CUDA, and compare against the serial Central Processing Unit (CPU) using C++ and MATLAB implementations. Results show a speedup of up to 2,600 times of the GPGPU implementation compared to the MATLAB implementation, reducing the elapsed time from about 1.5 hour to about 2 seconds. This strongly indicates that the GPGPU approach can help the industry to significantly reduce the time required for the simulations.