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Results
Study On Optimal Design of Bulbous Bow For Deep Sea Trawlers Based On Viscous Flow Theory
Xie, Yonghe (Department of Naval Architecture and Civil Engineering / Zhejiang Key Libratory of Ship Engineering, Zhejiang Ocean University) | Li, Gangqiang (Department of Naval Architecture and Civil Engineering / Zhejiang Key Libratory of Ship Engineering, Zhejiang Ocean University)
ABSTRACT: The bulbous bow is often designed to reduce the resistance of the deep sea trawlers. Firstly, the viscous flow around ship hull is simulated based on Computational Fluid Dynamics (CFD) software FLUENT. The Volume of Fluid method (VOF) has been used with FLUENT for capture the free surface around the ship at design speed. Experiment has been established in order to verify and validate the numerical results, and it shows that the simulation results reach agreement well with experiment results. Secondly, the reference length, the reference breadth and the reference height of bulbous bow are selected as the key variables to be optimized. The bow wave-making resistance mechanism will be studied by changing these variables and comparing the corresponding results. In this paper, thirteen models are calibrated at the design speed under working condition: change only the length of bulbous bow in the first five models while keep the breadth and the height unchanged; only change the height in the next three models, and finally change only the breadth in the last five models. In the final part, the optimized model is obtained, and then the total resistance force at the complete speed will be calculated and compared with the origin model. The study shows that the total resistance based on the optimized model has been greatly reduced if compared with the origin model, especially at modern and high speed. INTRODUCTION In the preliminary design of ships, it is important to optimize and determine the ideal ship shape. When the ship heads in one direction, the wave making induced by the ship transmits and dissipates away from the hull. Meanwhile, the ship undergoes the opposite force. One of its components is known as the wave making resistance, which is the dominant among the total resistance force.
Steady And Unsteady Cavitating Performance Prediction of Ducted Propulsors
Kinnas, Spyros A. (Ocean Engineering Group, Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin) | Chang, Shu-Hao (Ocean Engineering Group, Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin) | Tian, Ye (Ocean Engineering Group, Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin) | Jeon, Chan-Hoo (Ocean Engineering Group, Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin)
ABSTRACT: A formerly developed vortex lattice method (VLM) is coupled with Renolds Averaged Navier Stokes based Computational Fluid Dynamics (CFD) tools, in order to predict the hydro-dynamic performance of ducted propulsion systems. The analysis of the performance for ducted propellers subject to steady and unsteady cavitating inflow is via applying a hybrid numerical method which couples a vortex lattice method (MPUF-3A) with RANS solvers for analyzing the viscous flow around the propulsor and the drag force on the hub and duct surfaces. The presence of the propeller is represented through distributed pressure gradients, or in other words, body forces. The body forces can be obtained from the potential flow method, and re-associated to the fluid domain revolved by the propeller blades. The propeller force distributions are considered as source terms (body forces) in the momentum equations of RANS solver. The effects of viscosity on the effective wake and on the performance of the propeller blade, as well as on the predicted hub and duct forces, can be assessed. INTRODUCTION The demand of high-speed marine vehicles for commercial has increased drastically in recent decades. Therefore, marine propulsors are designed with more complex geometries to satisfy various requirements, such as high efficiency, less noise and vibration, better course stability, lower vessel resistance and economic operation, etc. Following this trend, ducted propellers have become more and more popular in the contemporary design. The complexity of the geometric characteristics of the propulsion systems introduces complicated flow fields around the propulsors and thus creates a lot of challenges to the design and computational analysis. Using numerical methods to solve ducted propulsion systems is much more challenging than those of open propellers because of the complicate geometric configurations and the interactions among the components. The primary problems and challenges are caused by hydrodynamic cavitation and viscosity.
- Europe (0.68)
- North America > Canada > Newfoundland and Labrador (0.46)
- North America > United States > Texas > Travis County > Austin (0.29)
- Energy > Oil & Gas > Upstream (1.00)
- Transportation > Marine (0.88)
Innovative Submerged Structures/Vegetation Effects On Coastal Erosion: Numerical Modeling of Hydro-Morphological Processes
Karambas, Th. A. (School of Civil Engineering, Aristotle University of Thessaloniki) | Koftis, Ch. (School of Civil Engineering, Aristotle University of Thessaloniki) | Koutandos, E. (School of Civil Engineering, Aristotle University of Thessaloniki) | Prinos, P. (School of Civil Engineering, Aristotle University of Thessaloniki)
ABSTRACT: In the present work the application of an advanced hydromorphological mathematical model for the design of innovative submerged structures for coastal protection, is presented. Non linear wave transformation in the surf and swash zone is computed by a non-linear breaking wave model based on the higher order Boussinesq equations for breaking and non breaking waves. The new Camenen and Larson (2007) transport rate formula involving unsteady aspects of the sand transport phenomenon is adopted for estimating the sheet flow sediment transport rates as well as the bed load and suspended load over ripples. Suspended sediment transport rate estimation is based on an exponential profile of sediment concentration for the steady equilibrium according to Camenen and Larson (2007, 2008). INTRODUCTION Over the past decades the problem of coastal erosion has expanded and there has been noted an important retreat of the shoreline. The solutions used to confront this problem until recently have been basically constituted of ‘hard’ conventional methods such as emerged breakwaters, seawalls, groynes. However, environmentally friendly coastal protection methods, such as submerged breakwaters and artificial reefs, have become nowadays increasingly popular. They can be considered as a ‘soft’ shore protection method, provided that it does not have optical harmful effect and mainly does not prevent significantly the circulation of waters, contrary to the conventional methods. A proper design of the above methods requires the use of advanced mathematical models, able to simulate the complicated hydromorphodynamic hydromorphodynamic processes of the nearshore region (including swash zone), such as nonlinear wave propagation, wave-induced current, sediment transport by waves and currents and bed morphology evolution. The Boussinesq models and their combination with a sediment transport model seem to be suitable for the above purpose (Karambas and Koutitas, 2002, Karambas, 2002 & 2004, Karambas and Karathanassi, 2004).
Simulation of Breaking Waves By Using an Improved SPH Method
Zheng, Xing (College of Shipbuilding Engineering, Harbin Engineering University, Schools of Engineering and Mathematical Science, City University) | Ma, Qing-Wei (College of Shipbuilding Engineering, Harbin Engineering University, Schools of Engineering and Mathematical Science, City University) | Duan, Wen-yang (Schools of Engineering and Mathematical Science, City University)
ABSTRACT: Recently we have developed an improved Smoothed Particle Hydrodynamic (SPH) method for modeling breaking waves. The main features of the method include solving higher order equations to find interpolation of unknown functions and their gradients, and with a new proposed scheme to identify free surface particles. In addition, the newly improved method is applied to sloshing breaking waves, and produces more reasonable pressure distribution and smoother pressure time history. INTRODUCTION Many meshless methods have been reported in the literatures, such as Smoothed Particle Hydrodynamics method(SPH)(Monaghan, 1988), Element Free Galerkin method(Belytschko, 1994), Reproducing Kernel Particle Method(RKPM) (Liu, 1995), Moving Particle Semi-implicit method(MPS) (Koshizuka, 1996), Meshless Local Petrov-Galerkin method(MLPG) (Atluri,1998; Ma, 2005), Finite Point Method(Onate, 1996; Fang, 2008), Finite Particle Method(Liu, 2005; Fang, 2009) and so on. Since their invention, they have been extended to solving various problems, such as the dynamic response of elastic-plastic materials(Benz, 1995; Libersky, 1993), breaking waves (Monaghan, 1994), solid friction(Cummins, 1999), incompressible fluids(Lo Edmond, 2002; Shao, 2003, 2006, 2009), multi-phase flows(Monaghan,1995; Colagrossi, 2003), viscoelastic flows(Ellero, 2002, 2005; Fang, 2006), underwater explosion(Liu, 2002, 2003a). For more information on the SPH method, we refer readers to the book by Liu and Liu(2003b) and the most recent review of the method by Liu (2010). Although much effort has been made to improve the SPH, it still requires further refinement, such as better methods for more stable pressure, better approaches to lower energy dissipation, and so on. Although there are a number of improved SPH methods to address these issues, such as incompressible SPH(ISPH) (Lo Edmond, 2002; Shao, 2003, 2006, 2009), Finite Particle Method(FPM) (Liu, 2005; Fang, 2009), and Modified SPH(MSPH) (Zhang, 2007, 2008), all of them need a good technique for identifying free surface particles. Inaccurate identification induces unrealistic pressure distribution, which causes instability.
Numerical Simulation of 3D Dam-break Flow By FEM-Level Set Method
Wang, Jifei (State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Zou, Ruizhi (State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Wan, Decheng (State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University)
ABSTRACT: An interface capturing approach based on a level set function for simulating transient two-phase viscous incompressible flows is applied in this paper. A narrow-band signed distance function is adopted to indicate the phase fields and the interface. The multiphase flow is numerically solved by three stages with finite element method (FEM):solving a two-fluid Navier-Stokes equation over the whole domain; transporting the level set function with the obtained velocity field; the level set function correction through a renormalization with continuous penalization which preserves the thickness of the interface. In this paper, the classical 3D Dam-break benchmark cases are tested for verification, which yielded good agreement with the experimental data. INTRODUCTION Free surface flows have showed the importance in naval technology and offshore engineering, such as sloshing in the tank, wave generated by ship's motion, wave-structure interaction, and so on. Performing accurate, robust and efficient simulations of the free surface flows has been the object of numerous research projects for several decades. The dam-break problem is a critical part in the design and management of hydraulic engineering, which has been studied both experimentally and numerically. Martin and Moyce conducted an experimental study on this problem in the early 1950s. Then, numerous researchers simulated dambreak flow by kinds of numerical methods, which make it a classical benchmark. Interface tracking methods can be purely Lagrangian, as particle methods, or they are developed as Arbitrary Lagrangian-Eulerian (ALE) approaches. The most widely used particle methods are Smoothed Particle Hydrodynamics (SPH) and Moving Particle Semi-Implicit (MPS). Zhang et al. (2010) have done the comparative study of SPH and MPS methods for numerical simulations of 2D dam-break problems. Later, Zhang et al. (2011) have applied a modified MPS method in 3D dam-break problem, showing good agreement with experimental data.
- Research Report > Experimental Study (0.67)
- Research Report > New Finding (0.48)
A Pseudo-Compressibility Finite Difference Method For Single-Phase Surface Flow Computations
Huang, J. (Ocean Engineering Research Centre, Memorial University of Newfoundland) | Qiu, Wei (Ocean Engineering Research Centre, Memorial University of Newfoundland) | Hally, David (Defence R&D Canada – Atlantic)
ABSTRACT: A numerical method has been developed to compute the viscous ship flow on non-orthogonal curvilinear grids. The single-phase level set method is adopted to capture the free surface, and an eigenvaluebased pseudo-compressibility finite difference method is used to solve the fully-coupled pressure and velocity equations. In this method, the pressure-velocity system is only solved in the water region. The pressure and velocity are extended from the free surface into the air region along the direction of the level set gradients by enforcing the free surface interfacial jump conditions. The turbulence equations are decoupled from the pressure-velocity system but are solved in a similar way by extending the values of the values at the free surface into the air. The level set function is calculated using a simple transport equation followed by a non-conservative reinitialization step. Both steps are decoupled from the pressure-velocity and turbulence equations. The deferred-correction approach is used for all the equations to achieve high-order precision for the convection terms and to minimize the computational cost. Validations have been carried out for the free surface flows around a Wigley hull and a surface combatant model, DTMB 5512. The numerical results are in good agreement with the experimental data. INTRODUCTION Computational fluid dynamics (CFD) has been widely used to predict ship resistance. The methods used for simulating viscous free surface flow can be grouped in two main classes: surface tracking and surface capturing. In a surface tracking method, the grid is moved to determine the configuration of the free surface at next time step. Surface capturing methods solve the flow on a fixed Eulerian grid and use an auxiliary equation to determine the profile of the free surface. Surface tracking methods are limited by their ability to deal with distorted or breaking waves.
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics (0.89)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.64)
ABSTRACT: The operating experiences for more than 10 years of hydrate and wax management of pipelines by direct electrical heating have proved high reliability, robustness and operating simplicity. The system is in use for pipelines ranging up to 40 km length and water depths down to approx. 500 m. As the oil and gas industry is moving towards deeper water and longer transport distances, electrical heating becomes even more attractive. In deeper waters plug removal by depressurization may be impossible. Cost and weight are important issues when DEH are being adapted for deep water installations. In general increasing the system power frequency reduces the size and weight of electrical equipment and higher frequencies are now being addressed in the new development programme of DEH for deep water fields. INTRODUCTION The DEH (direct electrical heating) system is at present qualified for power frequencies of 50/60 Hz fed from the local network commonly used in the North Sea. However, utilizing higher power frequencies will be beneficial due to reduced weight and volume of power supply equipment as well as reducing cross section area for the cables used in DEH, and hence reduced CAPEX for DEH installations. It is generally considered beneficial for development of deep water fields that the cross section area is reduced. Also the potential thermal constraints for the riser cables will be reduced when increasing the frequency. Furthermore increasing frequency reduces the amount of current being transferred to seawater and length of the CTZs (current transfer zones) at the heated pipeline ends. It is therefore expected that increased frequency reduces the amount of anodes needed for ac current transfer and ac corrosion protection. A first approach to the use of higher frequency is to look at 100 Hz, and consider 200 Hz as well.
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (0.34)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.34)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Offshore pipelines (0.34)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.32)
Concrete Destructure Due to Ice-Indentation Pore Pressure
Jacobsen, Stefan (Department of structural engineering, Norwegian University of Science and Technology & Department of hydroengineering, theory of buildings and structures, Far Eastern Federal University) | Kim, Lev V. (Department of structural engineering, Norwegian University of Science and Technology & Department of hydroengineering, theory of buildings and structures, Far Eastern Federal University) | Pomnikov, Egor E. (Department of structural engineering, Norwegian University of Science and Technology & Department of hydroengineering, theory of buildings and structures, Far Eastern Federal University)
ABSTRACT Ice in contact with marine structures cause abrasion of surfaces. The widely differing concrete surface roughness may cause high short-time contact pressure. Water between ice and concrete can then be pressed into the subsurface pores. The indentation contact area determined as function of pressure, concrete surface roughness and mechanical properties of concrete and ice can be used to determine water penetration depth. This paper shows the proposed model and that it can predict observed abrasion for properties of permeability, tensile strength, ice movement, pressure and number of contacts. INTRODUCTION A quarter of the world undiscovered petroleum resources can be located in the Arctic and Far-Eastern seas. The plans of exploration of these areas make actual the problems of ice forces effect on structures on more severe conditions as were met earlier. There are three limiting states which govern GBS behavior under ice actions:- strength and stability of GBS and its elements under ice forces - deformations of GBS and its elements influencing on the workability - fatigue strength of GBS elements. Ice mechanics and numerical simulation of ice-structure interaction are major research interests today. One of the research topic is ice abrasion relating to third limiting state. Ice movement can cause severe abrasion of coastal and offshore concrete structures such as gravity base structures (GBS), marine bridges, piers, sea wind mill foundations or concrete dams in rivers. The operation experience of platforms in the Sea of Okhotsk show that the ice abrasion is dangerous phenomena and can cause the material destruction in water level. Ice can also act in the pores of concrete as hydraulic pressure (Powers, 1945), as a propagating ice front in a concrete frost test or due to different thermal expansion coefficients concrete-ice. This abrasion can affect the service life and precautions are therefore necessary when designing and producing concrete structures for the arctic.
- North America > United States (0.68)
- Europe (0.68)
- Asia > Russia > Far Eastern Federal District (0.29)
Three-Dimensional Model For Wave-Induced Dynamic Soil Response Around Breakwaters
Zhang, Y. (Center for Marine Geotechnical Engineering, State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University) | Zhang, J-S. (State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University) | Zhang, H. (Division of Civil Engineering, University of Dundee) | Zhao, H. (Division of Civil Engineering, University of Dundee) | Jeng, D-S. (Division of Civil Engineering, University of Dundee)
ABSTRACT: In this paper, a three-dimensional porous model for wave-seabedstructure interactions (PORO-WSSI-3D) will be developed by integrating 3D wave and seabed models. Unlike previous research, the Navier-Stokes equation is solved with internal wave generation for the flow model, while Biot's dynamic seabed behavior is considered in the seabed model. With the newly developed 3D model, the wave-seabed interactions around breakwater heads are used as numerical example. Numerical results demonstrate the capacity of the proposed numerical model. The parametric study illustrates the significant influence of wave and soil characteristics on the pore pressure in a porous seabed. INTRODUCTION Breakwaters have been widely used as one of coastal defense structures in the world. The design of breakwaters has attracted great attentions from coastal engineers. Recently, it has been reported that numerous marine structures have been vulnerable to liquefaction of the foundation seabed, which further leads to the degradation of their structure and function in as little as a few years, and often results in collapse of marine structures (Lundgren et al., 1989; Franco, 1994; Chung et al., 2006). It has been well known that when ocean waves propagated over the ocean surface, they exert dynamic force fluctuations on the sea floor. These fluctuations further generate excess pore pressure within the soil skeleton, which is a major factor in the seabed instability. Recently, numerous investigations for the wave-induced oscillatory soil response have been carried out since the 1970s. Among these, Yamamoto et al. (1978) proposed an analytical solution of the wave-induced oscillatory soil response in an infinite seabed. Regarding the mechanism of pore pressure build-up, Sumer and Cheng (1999) developed an analytical solution with the periodic shear stress obtained from Hsu and Jeng (1994), which has been first published in the book written by Sumer and Fredsøe (2002).
- Europe (0.46)
- Asia > China (0.29)
- North America > United States (0.28)
- Research Report > New Finding (0.49)
- Research Report > Experimental Study (0.34)
ABSTRACT: Experiments and numerical simulations are carried out to investigate the flow-induced vibration of an elastically-supported, circular cylinder placed near a plane boundary. The flow field is visualized using the hydrogen bubble technique. Two modes of flow-induced oscillations are recognized, namely fore-backward oscillation at lower flow speeds, and transverse oscillation at higher flow speeds. In numerical simulations, the Navier-Stokes equations for unsteady incompressible viscous flow combined with a k-ω turbulence model are solved via finite element method. Arbitrary Lagrangian-Eulerian (ALE) method using an overlapping grid system is used to capture the motion of the cylinder. INTRODUCTION The vortex induced vibration (VIV) of pipelines is a major topic in coastal and offshore engineering since it may lead to fatigue destruction of pipelines, causing tremendous economic losses and environmental disaster. So far, many experimental and numerical investigations on VIV problems have been conducted, most of them concerning isolated pipelines, usually represented by circular cylinders in research, such as Mendes and Branco (1999), Zhou and So et al. (1999), etc. On the other hand, for the VIV problem of pipelines near the seabed, there is far less literature available than there is for the isolated pipeline case. With the presence of seabed, the flow is constrained by the bottom boundary. Previous surveys of flow around a fixed cylinder reveals that when the gapto- diameter ratio decreases to less than 0.3, the regular vortex shedding is suppressed. Chen and Su (2011) investigate the whole procedure from ignition to the steady stage of the flow around a circular cylinder above planar boundary; found that vortex shedding does happen at the starting flow stage even though the gap ratio is less than 0.3. A few cycles of vortex shedding may happen before the final steady flow state is reached for small gap ratios.
- Reservoir Description and Dynamics > Reservoir Simulation (0.87)
- Data Science & Engineering Analytics > Information Management and Systems (0.87)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring (0.55)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.49)