scholarly journals Numerical Study on Wave-induced Motion of Offshore Structures Using Cartesian-grid based Flow Simulation Method

2012 ◽  
Vol 26 (6) ◽  
pp. 7-13 ◽  
Author(s):  
Bo Woo Nam ◽  
Yonghwan Kim ◽  
Kyung Kyu Yang ◽  
Sa Young Hong ◽  
Hong Gun Sung
Keyword(s):  
Numerical Study ◽  
Flow Simulation ◽  
Simulation Method ◽  
Offshore Structures ◽  
Cartesian Grid ◽  
Induced Motion ◽  
Wave Induced ◽  
Grid Based

Numerical Study on Vortex-Induced Motions of Semisubmersibles With Three Columns With Different Sections Types

2019 ◽  
Author(s):  
Chenling Tian ◽  
Longfei Xiao ◽  
Mingyue Liu ◽  
Lijun Yang ◽  
Jing Liu
Keyword(s):  
Wind Turbine ◽  
Lift Force ◽  
Transverse Direction ◽  
Numerical Study ◽  
Offshore Structures ◽  
Detached Eddy Simulation ◽  
Fluid Forces ◽  
Eddy Simulation ◽  
Resonance Behavior ◽  
Induced Motion

Abstract Vortex-induced motion (VIM) phenomenon is a great challenge for design and operation of offshore structures subjected to ocean flow. Semi-submersibles with three columns are often applied to the field of wind turbine, suffering VIM motions probably. In recent years, it is showed that many factors have more or less influence on VIM of platforms. A comparison of circular columns with square columns on VIM characteristics of three-column semisubmersibles is carried out using the detached eddy simulation (DES) method via Star-ccm+ software. This paper analyzes motions in the transverse direction and yaw, as well as fluid forces including drag force and fluctuating lift force. The results show that transverse amplitudes of semisubmersible with three square columns are much lower than those of semisubmersible with three circular columns at all incidences. Besides, the authors conclude that the semisubmersible with three square columns do not experience obvious resonance behavior, which is different from the semisubmersible with three circular columns. Besides, galloping phenomenon occurred at large reduced velocities at 0°-incidence for the semisubmersible with three square columns, which is likely not induced by lift force directly. Meanwhile, in these cases, yaw amplitudes are also larger than the others. This may be due to the galloping behavior, which is just a conjecture.

A Method to Upgrade Iceberg Velocity Statistics to Include Wave-Induced Motion

1987 ◽  
Vol 109 (3) ◽  
pp. 278-286 ◽  
Author(s):  
J. H. Lever ◽  
D. Sen
Keyword(s):  
Three Dimensional ◽  
Interaction Model ◽  
Environmental Parameters ◽  
Offshore Structures ◽  
Grand Banks ◽  
Drilling Rig ◽  
Velocity Statistics ◽  
Impact Risk ◽  
Induced Motion ◽  
Wave Induced

Iceberg impact design loads for offshore structures can be estimated by incorporating an ice/structure interaction model in a probabilistic framework, or risk analysis. The relevant iceberg and environmental parameters are input in statistical form. Iceberg velocity statistics are usually compiled from drilling rig radar reports, and hence represent estimates of average hourly drift speeds. Yet it is the instantaneous ice velocity which is the relevant input to the simulation of the iceberg/structure collision process. Thus, risk analyses based on mean drift speed distributions will only yield valid results for the subset of conditions where wave-induced iceberg motion is negligible. This paper describes a method which, for the first time, systematically accounts for wave-induced motion in iceberg impact risk analyses. A linear three-dimensional potential flow model is utilized to upgrade iceberg velocity statistics to include the influence of Grand Banks sea-state conditions on instantaneous ice motion. The results clearly demonstrate the importance of including wave-induced motion in iceberg impact risk analyses.

scholarly journals Numerical Study on Wave-Induced Motion Response of Tension Leg Platform in Waves

2014 ◽  
Vol 28 (6) ◽  
pp. 508-516
Author(s):  
Yoon Sang Cho ◽  
Bo Woo Nam ◽  
Sa Young Hong ◽  
Jin Ha Kim ◽  
Hyun Jo Kim
Keyword(s):  
Numerical Study ◽  
Tension Leg Platform ◽  
Motion Response ◽  
Induced Motion ◽  
Wave Induced

Development of Rapid Simulation Method for Automotive Aerodynamics

2010 ◽  
Author(s):  
Kei Akasaka ◽  
Kenji Ono
Keyword(s):  
Flow Simulation ◽  
Simulation Method ◽  
Turnaround Time ◽  
Cartesian Grid ◽  
Scale Model ◽  
Repair Work ◽  
Eddy Simulation ◽  
High Reynolds ◽  
Time Required ◽  
Automotive Aerodynamics

Computational fluid dynamics (CFD) is now widely used as an essential tool in the development of automotive aerodynamics. However, the time required for repairing non-watertight geometries has recently become a serious problem in current CFD processes. Therefore, we developed an efficient simulation method that allows the flow around a non-watertight geometry to be computed on a Cartesian grid. This method can substantially reduce the turnaround time and effort required for CFD processes, because the repair work can be eliminated. The proposed method adopts an embedded boundary condition technique to capture arbitrary shapes more accurately on the background Cartesian grid. In addition, a local mesh refinement technique enables higher computational efficiency to be realized, and large-eddy simulation (LES) is used to reproduce high-Reynolds-number turbulent flow. Preliminary tests were performed on an engine bay configuration that had non-watertight geometries and a 1/5-scale model of an automobile configuration. As a result, the proposed method was confirmed to enable rapid grid generation and flow simulation around non-watertight geometries. Moreover, the computed results showed good agreement with experimental data.

A Model Study of the Wave-Induced Motion of Small Icebergs and Bergy Bits

1988 ◽  
Vol 110 (1) ◽  
pp. 101-107 ◽  
Author(s):  
J. H. Lever ◽  
E. Reimer ◽  
D. Diemand
Keyword(s):  
Wave Diffraction ◽  
Open Water ◽  
Offshore Structures ◽  
Full Scale ◽  
Grand Banks ◽  
Model Study ◽  
Induced Motion ◽  
Region 10 ◽  
Diffraction Effects ◽  
Wave Induced

Wave tank studies were conducted to determine the kinematics of “small” ice masses in storm waves typical of the Grand Banks region (10–14-s periods, 12–15-m heights). The models tested spanned the range of full-scale masses from growlers and bergy bits (10–103 tonnes), to small icebergs (104–105 tonnes). In open water, models smaller than 1/13 wavelength behaved essentially as particles of fluid. The corresponding full-scale kinetic energies associated with such motions could exceed 107 J. Models approximately 1/2 wavelength in size could attain energies in the surge direction in excess of 109 J, largely through wave diffraction effects. Significant heave resonance motions were also seen. Tank studies additionally revealed that wave-driven ice-structure impacts of substantial energy could occur, although wave diffraction from the structure could also have a considerable influence on nearby ice motion. The conclusion is reached that wave-induced motion of small ice masses represents a significant environmental hazard to the operation of offshore structures in ice-infested waters.

Forced Convection Analysis in a Vertical Square Cavity With a Vortex Promoter

2010 ◽  
Author(s):  
Enrique A. Damian-Ascencio ◽  
Abel Hernandez-Guerrero ◽  
Cuauhtemoc Rubio-Arana ◽  
Gregory Kowalski
Keyword(s):  
Numerical Study ◽  
Flow Simulation ◽  
Simulation Method ◽  
Governing Equations ◽  
Square Cavity ◽  
Eddy Simulation ◽  
Thermal Boundary Conditions ◽  
Aspect Ratios ◽  
Large Eddy ◽  
Forced Convection Analysis

This paper presents a 2-D numerical study of the effect on the heat transfer from a promoter of turbulence in a vertical square cavity. The transient, turbulent flow simulation is for a fluid with a Prandtl number of 0.7 and constant properties. The thermal boundary conditions considered are isothermal cavity walls. In the analysis various aspect ratios and blockage fractions (10%, 25% and 50%) were examined at a constant Reynolds number (Re = 5000). The governing equations are solved using the LES (Large Eddy Simulation) method. The results demonstrate that increasing the channel blockage makes it more difficult to generate turbulence but increases the channel residence time of the fluid.

Stochastic simulation for determining the design flood of cascade reservoir systems

2012 ◽  
Vol 43 (1-2) ◽  
pp. 54-63 ◽  
Author(s):  
Baohong Lu ◽  
Huanghe Gu ◽  
Ziyin Xie ◽  
Jiufu Liu ◽  
Lejun Ma ◽  
...  
Keyword(s):  
Simulation Model ◽  
Stochastic Simulation ◽  
Southern China ◽  
Flow Simulation ◽  
Simulation Method ◽  
Simulation Approach ◽  
Design Flood ◽  
Design Values ◽  
Stochastic Simulation Model ◽  
The Impact

Stochastic simulation is widely applied for estimating the design flood of various hydrosystems. The design flood at a reservoir site should consider the impact of upstream reservoirs, along with any development of hydropower. This paper investigates and applies a stochastic simulation approach for determining the design flood of a complex cascade of reservoirs in the Longtan watershed, southern China. The magnitude of the design flood when the impact of the upstream reservoirs is considered is less than that without considering them. In particular, the stochastic simulation model takes into account both systematic and historical flood records. As the reliability of the frequency analysis increases with more representative samples, it is desirable to incorporate historical flood records, if available, into the stochastic simulation model. This study shows that the design values from the stochastic simulation method with historical flood records are higher than those without historical flood records. The paper demonstrates the advantages of adopting a stochastic flow simulation approach to address design-flood-related issues for a complex cascade reservoir system.

A NUMERICAL STUDY ON THE HEMODYNAMIC AND SHEAR STRESS OF DOUBLE ANEURYSM THROUGH S-SHAPED VESSEL

2015 ◽  
Vol 27 (04) ◽  
pp. 1550033 ◽  
Author(s):  
Mahdi Halabian ◽  
Alireza Karimi ◽  
Borhan Beigzadeh ◽  
Mahdi Navidbakhsh
Keyword(s):  
Blood Flow ◽  
Mechanical Behavior ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Flow Simulation ◽  
The Body ◽  
Sweep Angle ◽  
Abdominal Aortic ◽  
Hemodynamic Characteristics ◽  
Refined Meshes

Abdominal aortic aneurysm (AAA) is a degenerative disease defined as the abnormal ballooning of the abdominal aorta (AA) wall which is usually caused by atherosclerosis. The aneurysm grows larger and eventually ruptures if it is not diagnosed and treated. Aneurysms occur mostly in the aorta, the main artery of the chest and abdomen. The aorta carries blood flow from the heart to all parts of the body, including the vital organs, the legs, and feet. The objective of the present study is to investigate the combined effects of aneurysm and curvature on flow characteristics in S-shaped bends with sweep angle of 90° at Reynolds number of 900. The fluid mechanics of blood flow in a curved artery with abnormal aortic is studied through a mathematical analysis and employing Cosmos flow simulation. Blood is modeled as an incompressible non-Newtonian fluid and the flow is assumed to be steady and laminar. Hemodynamic characteristics are analyzed. Grid independence is tested on three successively refined meshes. It is observed that the abrupt expansion induced by AAA results in an immensely disturbed regime. The results may have implications not only for understanding the mechanical behavior of the blood flow inside an aneurysm artery but also for investigating the mechanical behavior of the blood flow in different arterial diseases, such as atherosclerosis.

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