Three Dimensional Numerical Modelling of Pier Scour Under Current and Waves Using Level Set Method

2014 ◽  
Author(s):  
Mohammad Saud Afzal ◽  
Hans Bihs ◽  
Arun Kamath ◽  
Øivind A. Arntsen
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Free Surface ◽  
Level Set Method ◽  
Level Set ◽  
Three Dimensional ◽  
Critical Shear Stress ◽  
Offshore Structures ◽  
Time Step ◽  
Pier Scour

Stability of offshore structures can be threatened by local scouring which could ultimately lead to their failure. As a consequence, knowledge of the scouring mechanism and the accurate prediction of the characteristic scour geometry is very important for the design of such structures. A three-dimensional computational fluid dynamics model is used to calculate the scour and the deposition pattern around a pier for two different boundary conditions: constant discharge and regular waves. The computational fluid dynamics (CFD) model solves Reynolds-Averaged Navier-Stokes (RANS) equations in all three dimensions. The location of the free surface is represented using the level set method, which calculates the complex motion of the free surface in a very realistic manner. For the implementation of waves, the CFD code is used as a numerical wave tank. For the geometric representation of the moveable sediment bed, the level set method is used. The numerical results for the local scour prediction are compared with physical experiments. The performance of the turbulence models, the formulations of the critical shear stress for the sloping bed and the effect of the variation of the sediment time stepping are investigated. The decoupling of the hydrodynamic and the morphodynamic time step is tested and found to be a reasonable assumption. For the two situations of local pier scour under current and wave conditions, the numerical model predicts the general evolution (geometry, location and maximum scour depth) and time development of the scour hole accurately.

Three-Dimensional Numerical Modeling of Pier Scour Under Current and Waves Using Level-Set Method

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Mohammad Saud Afzal ◽  
Hans Bihs ◽  
Arun Kamath ◽  
Øivind A. Arntsen
Keyword(s):  
Free Surface ◽  
Level Set Method ◽  
Level Set ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Reasonable Assumption ◽  
Cfd Model ◽  
Time Step ◽  
Pier Scour

A three-dimensional (3D) computational fluid dynamics (CFD) model is used to calculate the scour and the deposition pattern around a pier for two different boundary conditions: constant discharge and regular waves. The CFD model solves Reynolds-Averaged Navier–Stokes (RANS) equations in all three dimensions. The location of the free-surface is represented using the level-set method (LSM), which calculates the complex motion of the free-surface in a very realistic manner. For the implementation of waves, the CFD code is used as a numerical wave tank. For the geometric representation of the moveable sediment bed, the LSM is used. The numerical results for the local scour prediction are compared with physical experiments. The decoupling of the hydrodynamic and the morphodynamic time step is tested and found to be a reasonable assumption. For the two situations of local pier scour under current and wave conditions, the numerical model predicts the general evolution (geometry, location, and maximum scour depth) and time development of the scour hole accurately.

Three-dimensional computational fluid dynamics simulation of valve-induced water hammer

2016 ◽  
Vol 231 (12) ◽  
pp. 2263-2274 ◽  
Author(s):  
Shuai Yang ◽  
Dazhuan Wu ◽  
Zhounian Lai ◽  
Tao Du
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Method Of Characteristics ◽  
Three Dimensional ◽  
Water Hammer ◽  
Dynamics Simulation ◽  
Computational Fluid Dynamics Simulation ◽  
Time Step ◽  
Obvious Effect ◽  
Simulation Results

In this study, three-dimensional computational fluid dynamics simulation was adopted to evaluate the valve-induced water hammer phenomena in a typical tank-pipeline-valve-tank system. Meanwhile, one-dimensional analysis based on method of characteristics was also used for comparison and reference. As for the computational fluid dynamics model, the water hammer event was successfully simulated by using the sliding mesh technology and considering water compressibility. The key factors affecting simulation results were investigated in detail. It is found that the size of time step has an obvious effect on the attenuation of the wave and there exists a best time step. The obtained simulation results have a good agreement with the experimental data, which shows an unquestionable advantage over the method of characteristics calculation in predicting valve-induced water hammer. In addition, the computational fluid dynamics simulation can also provide a visualization of the pressure and flow evolutions during the transient process.

Application of Computational Fluid Dynamics/Computational Structural Dynamics Coupling for Analysis of Rotorcraft Airloads and Blade Loads in Maneuvering Flight

2012 ◽  
Vol 57 (3) ◽  
pp. 1-21 ◽  
Author(s):  
Mahendra J. Bhagwat ◽  
Robert A. Ormiston ◽  
Hossein A. Saberi ◽  
Hong Xin
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Three Dimensional ◽  
Good Control ◽  
Substantial Improvement ◽  
Comprehensive Analysis ◽  
Time Step ◽  
Loosely Coupled ◽  
Maneuvering Flight ◽  
Tightly Coupled

This paper presents coupled calculations of both the airloads and structural loads for the UH-60A main rotor during the UTTAS pull-up maneuver performed under the NASA/Army UH-60A Airloads Program. These calculations were performed using OVERFLOW-2, a computational fluid dynamics (CFD) solver, coupled to the Rotorcraft Comprehensive Analysis System (RCAS), a rotorcraft comprehensive analysis. For time-varying maneuvers, the two codes were tightly coupled and exchanged airloads and structural deflections at every time step. The coupled solution methodology gives improved airload prediction because of the ability to model three-dimensional transonic effects on the advancing blade, stall events on the retreating blade, as well as the aeroelastic deformations. Correlation with data for both the airloads and structural loads is reasonably good. Control load predictions also show good correlation with data, which is a substantial improvement over conventional analyses. A quasisteady loosely coupled approximate solution was also examined and was found to give good airload and structural load predictions, for this relatively slow maneuver.

Simulation of the Motion of Two Bubbles in Aluminum Foams Produced Process by Using Level Set Method

2015 ◽  
Vol 757 ◽  
pp. 13-17 ◽  
Author(s):  
Zhi Xin Zhao ◽  
Jian Hua Niu ◽  
Lan Huang ◽  
Huan Ran Wang
Keyword(s):  
Fluid Dynamics ◽  
Velocity Field ◽  
Level Set Method ◽  
Level Set ◽  
Three Dimensional ◽  
Wake Flow ◽  
Aluminum Foams ◽  
Projected Area ◽  
Wake Zone ◽  
Two Bubbles

In this paper, the three-dimensional motion of two bubbles in melt Aluminum was simulated by using level set method. Through changing the positions and sizes of two bubbles, the influence of bubbles wake flow and their interaction are considered. Our numerical simulations demonstrate the bubbles characteristic behavior such as distortion, attraction, and repulsion. The velocity field around the bubbles reveals the interaction between the wakes of two bubbles in fluid dynamics. For the two bubbles placed horizontally or vertically, it is found that the coalescence of bubbles may happen when 50% of the below bubble’s projected area enters the wake zone of the upper bubble.

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