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Investigation of Iceberg Hydrodynamics
Talimi, Vandad (C-CORE, St. Johnโs) | Ni, Shaoyu (C-CORE, St. Johnโs) | Qiu, Wei (Memorial University of Newfoundland, St. Johnโs) | Fuglem, Mark (C-CORE, St. Johnโs) | MacNeill, Andrew (C-CORE, St. Johnโs) | Younan, Adel (ExxonMobil Production Company)
Abstract As offshore oil and gas developments increase in northern areas such as the Grand Banks and the Arctic region, the operators face challenging conditions. Icebergs are among one of the challenges for both surface and subsea structures if they drift toward those facilities. Prediction of the iceberg drift and dynamic response to any towing process requires a good understanding of hydrodynamic effects induced by currents, waves, tow lines, etc. A reasonable estimation of added mass and RAOs are other prominent parameters required when modeling iceberg dynamics is of interest. Having access to the high resolution full 3D iceberg profiles collected in 2012 (Younan et al. 2016), it is now possible to investigate iceberg hydrodynamics using numerical and experimental methods. This paper presents an overview of the numerical simulation results and lessons learned during various hydrodynamic simulations such as decay analysis, towing, and iceberg-structure interaction. The Diffraction Model and Computational Fluid Dynamics (CFD) are the tools utilized in these simulations. The conclusions provide key findings and suggestions for future analysis of iceberg hydrodynamics.
- North America > Canada > Quebec > Arctic Platform (0.89)
- North America > Canada > Nunavut > Arctic Platform (0.89)
- North America > Canada > Newfoundland and Labrador > Newfoundland > North Atlantic Ocean > Grand Banks Basin (0.89)
Abstract The flow around a circular cylinder at Reynolds numbers near the drag crisis was numerically simulated based on a dynamic Smagorinsky Large Eddy Simulation (LES) model at two Reynolds of Re = 1.0 ร 10 and 6.0 ร 10. The flow structures and the hydrodynamic force on the cylinder were analyzed. The numerical results show that the results at Re = 1.0 ร 10 follow the key feature of subcritical turbulent flow and the results with Re = 6.0 ร 105 capture the main features of the supercritical flow. This demonstrates that the Dynamic Smagorinsky LES model is a suitable numerical method for exploring high Reynolds flow around a circular cylinder. Introduction Slender structures are commonly used in civil, mechanical and offshore engineering, such as skyscrapers, chimneys, tubes in heat exchangers, bridge piers, subsea pipelines, risers and supporting frames of offshore platforms. Due to the strong engineering application background, hydro-/aerodynamics associated with slender structures have been widely researched. The flow around an isolated cylinder involves most of the generic flow features (flow separation, vortex shedding, recirculation, transition of turbulence within the wake and in the boundary layer), thus providing an excellent model for gaining insight into fluid mechanics around structures. As an important flow-structure interaction model, large amount of research about flow around circular cylinders has been published (Sumer and Fredsรธe 1997, Zdravkovich 2003).
- Research Report > New Finding (0.48)
- Research Report > Experimental Study (0.34)
LES investigations of flow over a sphere at Reynolds numbers between 104 and 105
Xiao, Zhijian (Huazhong University of Science and Technology) | Wang, Xianzhou (Huazhong University of Science and Technology) | Ding, Ziyou (Huazhong University of Science and Technology) | He, Ran (Huazhong University of Science and Technology) | Feng, Dakui (Huazhong University of Science and Technology)
Abstract Extensive studies have been conducted, both experimentally and numerically, in the last decades, however mostly on relatively low Reynolds numbers. The flow field around a sphere in an uniform flow is investigated by the numerical simulations using Large Eddy Simulation (LES) with a dynamic Smagorinsky type subgrid stress (SGS) model at the subcritical regimes (Re = 10 and 10) based on the freestream velocity and sphere diameter in the present paper. The CFD solver adopted in the simulations is Fluent and the fluid is water. Numerical results have verified the grid independence using three different grid quantities at Re=10 in the current paper. Compared with existing data, the LES can simulate accurately the flow field around a sphere at Re= 10 and 10. The hydrodynamic coefficients and Strouhal numbers are consistent with the experimental results. The structures of wake and the separation angle are also satisfied with experimental results. Introduction The study about the flows over a sphere that have a complex nature depending on the Reynolds number is of great interest to computational fluid dynamics (CFD). The vertical structure around it, depending on the Reynolds number, has been known to show diverse flow characteristics such as the axi-symmetric flow, and irregular rotation of separation points, unsteady flows, periodic vortex shedding, etc. A sphere is considered as an idealized model of three-dimensional axisymmetric bluff bodies. For engineering applications, typical bluff bodies whose shape resembles a sphere are balloons, wings at the high attack, thrusts of ship, bombs, oil-storage tanks, etc. In fact, the study about turbulent flows that exhibit massive separation over a sphere can be essential to investigate these complex flow structures as well as to provide useful information for validating CFD models (e.g. LES model). Because a sphere is a basic body, which has a large potential for various applications, many researchers have studied the flow over a sphere.
A new appendage resistance prediction method, which mitigates the technical issues with the existing test procedure, has been developed and presented in this paper. The primary aspects of the new method are 1) the Froude's equivalent flat plate friction drag concept extensively used in the marine industry will not be used in the present method, instead, an aerodynamic profile drag concept for resistance prediction is presented, 2) the turbulent stimulators extensively used in existing model appendage resistance tests will not be used in the proposed test procedure, which eliminates the need for high-speed tests and the problematic issue of estimating the parasitic drag associated with turbulence stimulators, 3) the important juncture vortex drag associated with appendages is considered, 4) the effective velocity entering the stern appendages on resistance is considered, 5) the new scaling formula to relate model profile drag and juncture vortex drag to full-scale appendage drag is developed and presented in this paper.
- Energy > Oil & Gas > Upstream (1.00)
- Transportation (0.89)
Global Performance of a Square-Type Semi-Submersible KRISO Multi-Unit Floating Wind Turbine; Numerical Simulation vs Model Test
Kim, H. C. (Texas A&M University) | Kim, M. H. (Texas A&M University) | Kim, K. H. (Korea Research Institute of Ships and Ocean Engineering) | Hong, K. (Korea Research Institute of Ships and Ocean Engineering) | Bae, Y. H. (Jeju National University)
Abstract The global performance of the Korea research institute of ships and ocean engineering (KRISO) square-type semi-submersible multi-unit floating offshore wind turbine (MUFOWT) in irregular waves is numerically simulated by using the multi-turbine-floater-mooring coupled dynamic analysis program. The developed time-domain numerical-simulation tool is extended from the FAST/CHARM3D coupled dynamics program for the single turbine on single floater. FAST has been developed by the National Renewable Energy Laboratory (NREL) for years for the single unit. Recently, KRISO has designed and studied the square-type MUFOWT, in which four 3MW wind turbines are installed at each corner of a single floater. Additionally, twenty four point-absorber-type linear-generator-based wave energy converters are set up - six wave energy converters at each side of the platform. For verification, KRISO performed a series of model tests for this MUFOWT with 1:50 Froude scale. In this paper, the MUFOWT simulation program is used to reproduce the KRISO model test results. In the fully coupled multi-turbine/hull/mooring dynamic simulations, the complete second-order difference-frequency wave forces are also included. The analysis results are systematically compared with the model test results, which shows reasonable correlation between them. Introduction The importance of clean renewable energy has been underscored to secure new energy sources and protect environments. Especially, wind energy is appealing since it is economically competitive, technologically proven, infinitely renewable, and does not make any waste or carbon emission. Although they are considered to be more difficult to design than fixed offshore wind turbines, floating wind turbines have many advantages compared to onshore or bottom fixed offshore wind turbines. In general, they are less restricted by governmental regulation and residents' opposition, with higher-quality wind, and less sensitive to space/size/noise/visual/foundation restrictions. In this regard, if the technology is completely developed, floating offshore wind turbines are expected to be more popular to generate considerable amounts of clean renewable energy at competitive prices compared to other energy sources (Henderson et al., 2002; Henderson et al., 2004; Musial et al., 2004; Tong, 1998; Wayman et al., 2006).
Abstract Cavitation erosion can often be related to the strong unsteady characteristics of cloud cavitation. The current study focuses on the capability of LES to predict the unsteady behavior of the cavitating flow around a NACA0015 hydrofoil. The Large Eddy Simulation (LES) results can reproduce more unsteady phenomena than the unsteady Reynolds-Averaged Navier-Stokes (URANS) results, and can predict closer location of cavitation closure, resulting in more accurate shedding frequency and oscillation frequency of the lift and drag. It is indicated that the LES method can provide a sound numerical basis for further quantitative forecast of cavitation erosion. Introduction Cavitation is a complex multiphase flow that often occurs in fluid flow systems where the local fluid pressure drops to a certain critical pressure (often taken as the vapor pressure of the fluid)(Frederick and Hammitt, 1980). It was first recognized in marine engineering by its negative effect on a newly built destroyer, Great Britain's HMS Daring, resulting in unexpected poor power performance. The cavitation phenomenon often involves complex hydrodynamic and mechanical mechanisms, and even thermal and illuminative effects. It generally occurs in fluid engineering systems such as marine propulsion systems, rudder system and hydraulic turbines. According to the typical shapes, cavitation phenomenon can be divided into the following types: bubble cavitation, sheet cavitation, cloud cavitation and supercavitation(Wang et al., 2001). The observed cavitation phenomena in the marine propulsion system and other hydraulic machinery often bring negative effects. Cavitation induced noise and vibration have significant influences on the safety of engines and vessels, and will bring huge threaten to the stealth of navy vessels. In particular, cavitation erosion is one of the most harmful consequence, and can often be related to the strong unsteady characteristics of cloud cavitation. Therefore, the evolution and the unsteady dynamics of the cloud cavitation over the hydrofoil have been a hot topic in the cavitating flow research field.
- Transportation > Marine (1.00)
- Transportation > Passenger (0.81)
- Leisure & Entertainment > Sports > Sailing (0.81)
- (2 more...)
In this paper, we outline and validate a computational fluid dynamics (CFD) method for determining the hydrodynamic forces of an escort tug in indirect towing mode. We consider a range of yaw angles from 0ยฐ to 90ยฐ and a travel speed of 8 knots. We discuss the effects of scaling on prediction of flow separation and hydrodynamic forces acting on the vessel by carrying out CFD studies on both model and full-scale escort tugs performing indirect escort maneuvers. As the escort performance in terms of maximum steering forces is strongly dependent on the onset of flow separation from the hull and skeg of the tug, the model-scale simulations under-predict the maximum steering force by 12% relative to the full-scale simulations. In addition, we provide a method for converting the hydrodynamic forces of the CFD escort study into towline and thrust forces.
- North America > United States (0.93)
- Europe (0.93)
- North America > Canada > British Columbia (0.28)
- Transportation > Marine (1.00)
- Shipbuilding (0.69)
- Energy > Oil & Gas > Upstream (0.68)
Abstract The authors performed a computational fluid dynamics (CFD) analysis of a self-elevating mobile offshore drilling unit (SE MODU) as a replacement for wind tunnel testing. The authors utilized an unsteady RANS method to model wind forces on an SE MODU for a variety of wind headings. The simulation produced force and moment data for individual structural components of the SE MODU. The final data set presented sufficient information to calculate overturning moments of the SE MODU in a range of wind conditions. This paper discusses several techniques developed for the SE MODU analysis: meshing of disparate structural scales, accurate simulation of large intricate structures, and accurate description of dynamic effects. The paper presents methodology for calculation of a center of effort that correctly relates vector force to vector moment in all three dimensions. The authors demonstrate that center of effort was not appropriate to dynamic flow situations; direct moment coefficients were more suitable. As part of the validation process, CFD analysis was performed on a similar SE MODU design and compared to existing wind tunnel results. This paper compared forces and moments in all three axes for multiple wind headings. The CFD analysis compared very well with wind tunnel results, showing only a 10% difference from the experiment. The project revealed several advantages of CFD over traditional wind tunnels in this application. The insights from CFD showed the contribution of each structural component to overturning moment, and results revealed significant elements of overturning moment not considered by the current industry standards. CFD analysis required a similar level of effort as a wind tunnel test but produced far more detailed knowledge.
Abstract Strong ocean currents flowing past bluff offshore structures such as semisubmersibles and tension-leg platforms (TLP) can instigate large amplitude vortex-induced motion (VIM). This can lead to significant fatigue loads on the mooring system and its attachments. Simulating this problem numerically is of particular interest to the offshore industry in order to determine design loads and to avoid or suppress motion and vibration of the structure. But despite this being a classical flow problem, it remains a major numerical challenge, particularly at high Reynolds numbers where most offshore platforms operate. The difficulty arises from the strong nonlinear nature of the governing Navier-Stokes equations and the unsteady turbulent nature of the physical flow itself. This study was therefore conducted to identify best practices for using Computational Fluid Dynamics (CFD) to estimate the loads imposed by uniform currents past a stationary bluff body (representing a semisubmersible column). Several Reynolds numbers were chosen to cover the subcritical, transcritical, and supercritical flow regimes. Two Reynolds-Averaged Navier-Stokes (RANS) software packages were used, the open source code OpenFOAM and the commercial code STAR-CCM+. Verification of the numerical model and validation of results against published experimental test data is presented and the implications discussed. The paper provides several key elements that should be considered when modeling a uniform current past bluff body at high Reynolds number.
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.36)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.34)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (0.34)
A Separate-Phase Drag Model and a Surrogate Approximation for Simulation of the Steam-Assisted-Gravity-Drainage Process
Padrino, Juan C. (Los Alamos National Laboratory) | Ma, Xia (Los Alamos National Laboratory) | VanderHeyden, W. Brian (BP America) | Zhang, Duan Z. (Los Alamos National Laboratory)
Summary General, ensemble phase-averaged equations for multiphase flows were specialized for the simulation of the steam-assisted-gravity-drainage (SAGD) process. In the average momentum equation, fluid/solid and fluid/fluid viscous interactions are represented by separate force terms. This equation has a form similar to that of Darcy's law for multiphase flow but augmented by the fluid/fluid viscous forces. Models for these fluid/fluid interactions are suggested and implemented into the numerical code CartaBlanca. Numerical results indicate that the model captures the main features of the multiphase flow in the SAGD process, but the detailed features, such as plumes, are missed. We find that viscous coupling among the fluid phases is important. Advection time scales for the different fluids differ by several orders of magnitude because of vast viscosity differences. Numerically resolving all these time scales is time consuming. To address this problem, we introduce a steam-surrogate approximation to increase the steam-advection time scale, while keeping the mass and energy fluxes well-approximated. This approximation leads to approximately a 40-fold speedup in execution speed of the numerical calculations at the cost of a few percentage errors in the relevant quantities.
- North America > United States (1.00)
- North America > Canada > Alberta (0.28)