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Collaborating Authors
Reservoir Simulation
ABSTRACT The coupled level-set and volume-of-fluid (CLSVOF) method is widely accepted as one of the most advanced interface-capturing methods. It has been extended such that the implementation is possible on the overset grid systems, including embedding, overlapping and matching grids. However, as the VOF function depends on the cell size and cannot be interpolated between two grid blocks, the interpolation can only be done approximately. It is found that the CLSVOF application may produce apparent unphysical rough interface across block boundary. The present study addresses this issue and proposes new treatments to improve the quality of inter-grid VOF interpolation. The improved CLSVOF method is first tested on a free jet case with matching overset grids, and results are compared with those from the pure level-set method. The second test is on a simplified offshore platform in a hurricane wave environment. Again, both the pure level-set and CLSVOF calculations are made for comparison. Finally, the improved CLSVOF method is tested with the same 3D extreme wave condition but on a full platform with 32 pegs on the lower deck and 20 risers below it, thus involving complex overlapping grids. These tests demonstrate that the improved CLSVOF method is capable of capturing violent free surface flows involving complex overset grid configurations, with the interface quality across block boundary noticeably improved. INTRODUCTION Flows involving two different immiscible fluids with a well-defined interface are common phenomena in many industrial processes and have to be considered both in the design and operational stages. Free surface flows with air-water interactions are ever present in the ocean environment, and an offshore structure must be able to withstand considerable impulse wave loads (Chen, 2010, 2013; Zhao et al., 2015). Another crucial aspect is the sloshing phenomena inside LNG carrier tanks, especially under partially filled conditions. (Chen, 2011; Zhao and Chen, 2015) Model tests are reliable methods to predict the maximum impact loads, but uncertainty exists when scaling up the results to the prototype. Numerical simulations of the two-phase fluid flows are alternative methods in the analysis and prediction of these problems.
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Facilities Design, Construction and Operation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Multiphase flow (0.48)
ABSTRACT A local-analytic-based Navier-Stokes solver has been employed in conjunction with a compound ocean structure motion analysis program for time-domain simulation of passing ship effects induced by multiple post-Panamax class ships in the exact condition of a real waterway. The exact seabed bathymetry was reproduced to the utmost precision attainable using the NOAA geophysical database for Virginia Beach, NOAA nautical charts for Hampton Roads and Norfolk harbor, and echo sounding data for the navigation channel and waterfront facilities. A parametric study consists of 112 simulation cases with various combinations of ship lanes, ship speeds, ship heading (inbound or outbound), channel depths, drift angles, and passing ship coupling (in head-on or overtaking encounters) were carried out for two waterfront facilities at NAVSTA Norfolk and Craney Island Fuel Terminal. The present paper provides detailed parametric study results at the Craney Island facility to investigate the site-specific passing ship effects on the motion responses of two oiler ships moored at oblique angles relative to the navigation channel and passing ships. INTRODUCTION A federal navigation channel passes to the west of the Naval Station (NAVSTA) Norfolk waterfront and to the east of Craney Island as shown in Figure 1, with north to the right. The federal authority has launched a plan to reconfigure the channel to mitigate the passing ship effects resulted from the ever-increasing ship sizes after recent Panama Canal expansion. A detailed description of the facility layouts and passing ship scenarios is given in Huang, Chen and Chen (2018). Pressure pulses and wakes induced by passing ships are known hazards to moored vessels nearby. Excessive disturbances often interrupt ship operations at the pier or cause damages to ship hulls, pier structures, and interface outfits. Passing ships are normally regulated to cruise in designated lanes within allowable speed limits that do not hamper the efficiency of the waterway or compromise pier operations nearby. Key parameters dictating the passing ship effects include the lateral distance of ship lanes to piers, the size and speed of passing ships, the depth of navigation channel, the drift angles of the passing ships, the modes of passing ship coupling, and the shape and bathymetry of ship basins.
- Transportation > Marine (1.00)
- Energy > Oil & Gas > Upstream (0.68)
- Government > Regional Government > North America Government > United States Government (0.56)
- Transportation > Freight & Logistics Services > Shipping (0.48)
- Data Science & Engineering Analytics > Information Management and Systems (0.68)
- Reservoir Description and Dynamics > Reservoir Simulation (0.47)
Abstract The vortex-induced motion (VIM) of semi-submersible platforms becomes an important issue with the recent development of deep draft semi-submersible platforms. As a result of the increased draft, the semi-submersibles are susceptible to coherent vortex shedding, and the platform VIM increases significantly. The VIM of semi-submersibles is more complex than those of spars and mono-column hulls due to the wake interaction of vortices shed from multiple columns. In general, the vortex-induced motion of deep draft semi-submersible platform is characterized mainly by three degree-of-freedom motions with surge (in-line), sway (transverse), and yaw motions. In the present study, numerical simulations are performed for a semi-submersible with four square columns subjected to a current at a 45 degree incidence angle. Calculations were performed using the Finite-Analytic Navier-Stokes (FANS) code in conjunction with a moving overset grid approach to accommodate the relative motions between the semi-submersible hull, wake, and background grid blocks. Simulations are performed both for the full scale and the 1:70 model platforms to check the validity of the Froude scaling law. Various current speeds corresponding to different reduced velocities are simulated. Motion responses and the flow fields for both the model and full scale platforms are studied. Comparisons are made with experimental data to demonstrate the capability of the present CFD approach.
- North America > United States > Texas (0.16)
- North America > United States > Hawaii (0.16)
- Reservoir Description and Dynamics > Reservoir Simulation (0.87)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.71)
ABSTRACT A coupled level-set (LS) and volume-of-fluid (VOF) method has been developed for time-domain simulation of violent free surface flows around two- and three-dimensional structures. The advection of the VOF function is performed using a mixed second-order Eulerian and Lagrangian scheme with a piecewise linear interface calculation (PLIC). A mass correction scheme is implemented to compensate for the mass change and maintain a divergence-free velocity field. The level-set function is solved using a fifth-order Weighted Essentially Non-Oscillatory (WENO) scheme. The coupled level-set and volume of fluid (CLSVOF) interface-capturing method is employed in conjunction with the Finite-Analytic Navier-Stokes (FANS) method for time-domain simulation of violent free surface flow problems. Moreover, a chimera domain decomposition approach is implemented using an overset grid system including embedding and overlapping grids for accurate resolution of flow around structures. The simulations results demonstrated the capability of the CLSVOF method in maintaining mass conservation for violent free surface flow problems.
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.50)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics (0.46)
- Reservoir Description and Dynamics > Reservoir Simulation (0.36)
Greenwater damage to offshore structures results from high pressures and dynamic loads that occur when wave crests inundate the structure far above the waterline in areas not designed to withstand such pressures. In the present study, a Navier-Stokes method has been employed in conjunction with a level-set interface-capturing method for the prediction of slamming forces and green water on offshore platforms. The governing equations are formulated in curvilinear coordinate system and discretized using the finite-analytic method on a non-staggered grid. For the additional level set equations of evolution and re-initialization, we use the 3rd-order TVD (total variation diminishing) Runge-Kutta scheme for time derivative, and the 3rd-order ENO (essentially non-oscillatory) scheme for spatial derivatives. The present method was validated first for the impact pressure prediction in a sloshing LNG tank. Simulations were then performed for the slamming of a 2D half-cylinder and a 3D hemisphere to illustrate the capability of the present method to deal with complex free surface flows involving relative motions between different computational blocks. The level-set RANS method was then employed for time-domain simulations of 2D and 3D offshore platforms in a numerical wave tank. Both The wave runup and greenwater on the platform decks were successfully predicted. INTRODUCTION Greenwater loads on offshore platform occur when an incoming wave significantly exceeds the free board and water runs on the deck. The primary difficulty in the simulation of the greenwater phenomena lies in the tracking of the air-water interface. Many methods have been proposed to predict the interface between two different fluids. They could be classified into two different approaches: the interface-tracking methods and the interface-capturing methods. The interface-tracking methods follow the free surface motions and use boundary-fitted grids which are re-adjusted in each time step whenever the free surface moves. In contrast, the interface-capturing methods do not define a sharp free surface boundary.
- North America > United States > Texas (0.29)
- North America > United States > California (0.28)
- Reservoir Description and Dynamics > Reservoir Simulation (0.94)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.75)
- Data Science & Engineering Analytics (0.69)
Vortex-induced vibrations (VIV) is an important design consideration for marine risers in offshore drilling and production. In an effort to better understand the VIV phenomena, we present numerical simulation results for two-dimensional incompressible flow past freely vibrating multi-cylinder configurations found in offshore engineering. Of interest is the response of the structure for low mass ratio, low damping, and high Reynolds number flow conditions. The governing incompressible Navier-Stokes equations are numerically solved and time-integrated using a local-analytic-based discretization procedure, implemented in conjunction with overset (Chimera) grid capabilities for zonal-based resolution of the flow field.
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Risers (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
ABSTRACT Cavitation tests have shown that propeller induced cavitating pressure is sensitive to the inflow in front of the propeller. It is well-known that this inflow is different from the nominal wake in bare hull condition. Due to the interactions among the nominal wake, propeller, and hull, the real flow to the propeller behaves differently and affects the propeller performance, blade cavity pattern, and fluctuating pressure generated. In this study, comparisons between Euler and RANS (Reynolds-Averaged Navier-Stokes) equation simulations are performed to find out their differences on the predictions of propeller blade cavitation and its induced hull pressure. INTRODUCTION In propeller design, the real inflow, which is critical to the propeller performance and blade cavitation, is usually considered including three components, namely, nominal velocity, propeller induced velocity and interaction velocity. Early studies shown, for an axisymmetric body fully submerged in water, the interaction velocity is mainly due to the nominal wake and propeller interaction (Huang and Groves, 1980). Based on that, a simplified approach using inviscid rotational flow model (Euler equation simulation) can be adopted in propeller/nominal wake interaction calculation by ignoring the effect due to the presence of body (Choi, 2000). As known, with the presence of a propeller near hull structure, the flow through the propeller plane is contracted and accelerated through the interaction of the propeller induced velocities and nominal wake under the effect of hull boundary. Not only superposition of the nominal wake and the induced velocity doesn't accurately model the real flow in front of propeller but even including the propeller/nominal wake interaction is inadequate since the hull boundary effect still has influence to the real flow passing through the propeller. This propeller/hull interaction would become more and more critical especially when the propeller tip clearance to hull becomes smaller and smaller.
- Energy > Oil & Gas > Upstream (0.93)
- Transportation > Marine (0.90)
- Reservoir Description and Dynamics > Reservoir Simulation (0.48)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics (0.48)
- Data Science & Engineering Analytics > Information Management and Systems (0.47)
- Reservoir Description and Dynamics > Fluid Characterization > Fluid modeling, equations of state (0.34)
ABSTRACT A three-dimensional potential flow numerical method was developed for the study of harbor resonance and the wave reflections and diffractions around a modular hybrid pier with two moored ships. The method solves the Laplace equation for unsteady body-wave problems using a chimera domain decomposition approach. In order to facilitate time-domain simulations of harbor oscillation problems, a separate wavemaker grid was used for concurrent computation of the incident wave field in the absence of the structures. An absorbing beach was placed in front of the wavemaker with appropriate damping functions to eliminate the wave reflections and diffractions from the structures and/or the irregular harbor shorelines. This enables us to maintain the same incident wave field for long-duration simulations over many wave periods. The method was employed first for time-domain simulation of the wave diffractions around a combined breakwater and floating platform configuration with two different wave headings. Calculations were then performed for the diffraction wave patterns around an integrated pier system with two ships moored alongside a modular hybrid pier. Finally, the method was extended for time-domain simulation of harbor resonance in the San Diego Bay. The numerical results clearly illustrated the effectiveness of the absorbing beach approach for harbor resonance problems involving complex structures and realistic harbor configurations. INTRODUCTION The U.S. Navy is developing a floating pier as a potential replacement for the aging berthing facilities in use. This innovative pier features a double deck layout on modular construction with pontoon floats. It gains remarkable economical incentives from its operational versatility and relocatability. Their performance is influenced by the ambient water and nearby vessels. As hydrodynamic data and design experiences pertinent to floating piers are scarce, an extensive analysis was launched to explore factors that may be critical to conceptual design, structural integrity and operational efficiency.
- North America > United States > Texas (0.28)
- North America > United States > California > San Diego County > San Diego (0.25)
- Reservoir Description and Dynamics > Reservoir Simulation (0.49)
- Data Science & Engineering Analytics > Information Management and Systems (0.35)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.34)
This paper describes an ongoing effort to integrate Computational Fluid Dynamic methods into a system for predicting the performances of multi-component propulsors in a turbulent ship flow environment. These methods include a Reynolds-Averaged Navier-Stokes (RANS) code for ship turbulent flow calculations and a Vortex-Lattice Method (VLM) based program MPUF3A for sheet cavitating propeller flow analyses. The combination of these methods provides a new level of realism for modeling the flow field around a ship with thick turbulent boundary layers and multi-component propulsor/hull interaction. The bottlenecks caused by inadequate grid generation methods and a lack of code integration, which have prevented the use of these numerical methods for practical configurations in design time frame, have been substantially alleviated by the incorporation of zonal calculation techniques, advanced gridding tools, and a chimera gridding method that allows arbitrary grid block overlap. Validations of the calculation method were performed for a contra-rotating propeller, CR404 system, and a series 60, CB = 0.6, ship hull with a MAU propeller. Comparisons of the computational results to the measurement data are documented in this paper. Also, to demonstrate the predictive capability of the method, simulations were carried out for the series 60 ship hull with a single propeller and a contrarotating propeller under model and full scale conditions.
- Transportation > Marine (1.00)
- Energy > Oil & Gas > Upstream (0.48)
- Data Science & Engineering Analytics > Information Management and Systems (0.69)
- Reservoir Description and Dynamics > Reservoir Simulation (0.54)
ABSTRACT A Reynolds-Averaged Navier-Stokes (RANS) method has been employed in conjunction with a chimera domain decomposition technique for time-domain simulation of transient flow induced by a berthing DDG-51 ship undergoing translational and/or rotational motions. The method solves the mean flow and turbulence quantities using an arbitrary combination of embedded, overlapped or matched grids. The unsteady RANS equations were formulated in an earth-fixed reference frame and transformed into general curvilinear, moving coordinate systems. A chimera domain decomposition technique was employed to accommodate the relative motions between different grid blocks. Calculations have been performed for a DDG-51 guided missile destroyer in translational and rotational motions to demonstrate the capability of the chimera RANS approach for time-domain simulation of the ship and berthing structure interactions. The numerical solutions successfully captured many important features of the transient flow around berthing ships including the underkeel flow acceleration, separation around the bow and stern area, flow recirculation behind the ship, water cushion between the ship and harbor quaywall, and the complex interaction among bow, shoulder and stern wave systems. INTRODUCTION Berthing damage can result in substantial economic and operational penalties. Even in a well-executed berthing, a large ship possesses enormous kinetic energy that can seriously damage the berthing structure as well as the ship itself. Fender systems are provided at a berth to absorb the kinetic energy of the berthing ship and to mitigate impact forces. The amount of the energy to be absorbed and the maximum impact force are the prevailing criteria for fender system design. Currently, the most commonly used fender-system design methodology accounts for the influence of the ambient water with a simple constant coefficient (Lee et al., 1975; Plotkin, 1977; Keuning and Beukelman, 1979; Fontijn, 1980, 1988). In order to improve the fender-system design.
- Government (1.00)
- Energy > Oil & Gas > Upstream (1.00)