Modeling the flow around and the hydrodynamic drag on net meshes using REEF3D

2021 ◽  
pp. 1-21
Author(s):  
Gang Wang ◽  
Tobias Martin ◽  
Liuyi Huang ◽  
Hans Bihs
Keyword(s):  
Open Source ◽  
Empirical Formula ◽  
Hydrodynamic Forces ◽  
Hydrodynamic Drag ◽  
Hydrodynamic Coefficients ◽  
Flume Experiments ◽  
Simulation Accuracy ◽  
Flow Interactions ◽  
Fluid Properties ◽  
Good Agreement

Abstract The hydrodynamics and flow around net meshes has recently drawn more and more attention because it is closely related to the expected forces on aquaculture. In terms of modelling the hydrodynamic forces on nets, Morison or screen force models are ordinarily. However, they mainly rely on empirical, experimental or cylindrical hydrodynamic coefficients, neglecting the flow interactions between adjacent net twines. In this study, the open-source hydrodynamic toolbox REEF3D is adopted to analyze the flow around net meshes and investigate the hydrodynamic drag on the structure. The simulation accuracy is in good agreement with flume experiments and previous research. The results demonstrate that 2 × 2 or 3 × 3 mesh cases are more reliable for studying the flow around net meshes including the flow interactions around adjacent twines. It is further shown that controlling the solidity of the net through changing net bar diameters has different effects on the flow around meshes than controlling it by the twine length. This paper presents a first step in the aim to derive a new empirical formula for the drag coefficients depending on the solidity and fluid properties which is more appropriate for to the physics involved in offshore conditions.

scholarly journals Numerical Simulation of Hydrodynamics Around Net Meshes Using REEF3D

2020 ◽  
Author(s):  
Gang Wang ◽  
Tobias Martin ◽  
Liuyi Huang ◽  
Hans Bihs
Keyword(s):  
Numerical Simulation ◽  
The Other ◽  
Force Model ◽  
Hydrodynamic Coefficients ◽  
Fish Farms ◽  
Flume Experiments ◽  
Simulation Accuracy ◽  
Safety Issues ◽  
Flow Interactions ◽  
Good Agreement

Abstract Hydrodynamics and turbulence around net meshes have drawn more and more attention because it is closely related to forces on the structures and safety issues of offshore fish farms. In terms of numerical modeling of forces on nets, Morison or screen force model is ordinarily adopted to account for its hydrodynamics. However, these methodologies mainly rely on empirical experimental or cylindrical hydrodynamic coefficients, neglecting flow interactions between adjacent cruciforms or net bars. In this study, REEF3D open-source hydrodynamic toolbox is adopted to analyze flow around net meshes explicitly and investigate the hydrodynamics related to forces on the structure. The simulation accuracy is in good agreement with flume experiments and previous research. Flow velocity and vorticity around net bars and knots are investigated. The results demonstrate that 2 × 2 or 3 × 3 mesh cases are more reliable when studying turbulence around net meshes, flow interactions around adjacent net bars, knots should be taken into consideration. Two patterns to control Sn, one is to change the diameter of net bars and the other is to control length, have different effects on the flow around meshes. This paper presents a first step in the aim to derive a new empirical formula for Cd depending on Sn, and Re, which are more related to the physics in offshore conditions.

scholarly journals Critical shear rate and torque stability condition for a particle resting on a surface in a fluid flow

2016 ◽  
Vol 808 ◽  
pp. 397-409 ◽  
Author(s):  
Arshad Kudrolli ◽  
David Scheff ◽  
Benjamin Allen
Keyword(s):  
Shear Rate ◽  
Quantitative Description ◽  
Fluid Flows ◽  
Hydrodynamic Coefficients ◽  
Critical Shear Rate ◽  
Wide Range ◽  
Experimental Apparatus ◽  
Fluid Properties ◽  
Drag And Lift ◽  
Good Agreement

We advance a quantitative description of the critical shear rate $\dot{\unicode[STIX]{x1D6FE}_{c}}$ needed to dislodge a spherical particle resting on a surface with a model asperity in laminar and turbulent fluid flows. We have built a cone-plane experimental apparatus which enables measurement of $\dot{\unicode[STIX]{x1D6FE}_{c}}$ over a wide range of particle Reynolds number $Re_{p}$ from $10^{-3}$ to $1.5\times 10^{3}$. The condition to dislodge the particle is found to be consistent with the torque balance condition after including the torque component due to drag about the particle centre. The data for $Re_{p}<0.5$ are in good agreement with analytical calculations of the drag and lift coefficients in the $Re_{p}\rightarrow 0$ limit. For higher $Re_{p}$, where analytical results are unavailable, the hydrodynamic coefficients are found to approach a constant for $Re_{p}>1000$. We show that a linear combination of the hydrodynamic coefficients found in the viscous and inertial limits can describe the observed $\dot{\unicode[STIX]{x1D6FE}_{c}}$ as a function of the particle and fluid properties.

Dynamic Stability Response of Piggyback Pipelines

2010 ◽  
Author(s):  
Hammam Zeitoun ◽  
Masˇa Brankovic´ ◽  
Knut To̸rnes ◽  
Simon Wong ◽  
Eve Hollingsworth ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Dynamic Response ◽  
Dynamic Stability ◽  
Large Diameter ◽  
Hydrodynamic Forces ◽  
Model Testing ◽  
Equivalent Diameter ◽  
Pipeline System ◽  
Hydrodynamic Coefficients ◽  
Hydrodynamic Loads

One of the main aspects of subsea pipeline design is ensuring pipeline stability on the seabed under the action of hydrodynamic loads. Hydrodynamic loads acting on Piggyback Pipeline Systems have traditionally been determined by pipeline engineers using an ‘equivalent pipeline diameter’ approach. The approach is simple and assumes that hydrodynamic loads on the Piggyback Pipeline System are equal to the loads on a single pipeline with diameter equal to the projected height of the piggyback bundle (the sum of the large diameter pipeline, small diameter pipeline and gap between the pipelines) [1]. Hydrodynamic coefficients for single pipelines are used in combination with the ‘equivalent diameter pipe’ to determine the hydrodynamic loads on the Piggyback Pipeline System. In order to assess more accurately the dynamic response of a Piggyback Pipeline System, an extensive set of physical model tests has been performed to measure hydrodynamic forces on a Piggyback Pipeline System in combined waves and currents conditions, and to determine in-line and lift force coefficients which can be used in a dynamic stability analysis to generate the hydrodynamic forces on the pipeline [2]. This paper describes the implementation of the model testing results in finite elements dynamic stability analysis and presents a case study where the dynamic response of a Piggyback Pipeline System was assessed using both the conventional ‘equivalent diameter approach’ and the hydrodynamic coefficients determined using model testing. The responses predicted using both approaches were compared and key findings presented in the paper, in terms of adequacy of the equivalent diameter approach, and effect of piggyback gap (separation between the main line and the secondary line) on the response.

Coupling of Heave and Roll for High-Speed Planing Hulls

2014 ◽  
Author(s):  
Carolyn Q. Judge
Keyword(s):  
High Speed ◽  
Hydrodynamic Forces ◽  
Hydrodynamic Coefficients ◽  
Lift Forces ◽  
Surface Changes

For planing hulls, dynamic lift reduces the submergence of the hull, allowing small motions to result in large changes in hydrodynamic forces and moments. The dynamic lift forces acting on the bottom of a planing hull dominate the hydrodynamics and these lift forces are known to depend on speed and wetted surface. As a planing boat rolls the wetted surface changes, which affects the dynamic lift. A series of tests using a wooden prismatic planing hull model with a constant deadrise of 20 degrees were done at static heel and heave positions as well as oscillating heave conditions. This paper presents the results from these experiments, primarily looking at the hydrodynamic coefficients in heave as a function of heel angle and exploring the coupling between these motions for a prismatic high-speed planing hull.

Examination of the Flow Separation Characteristics Around a Streamlined Axisymmetric Shape

2005 ◽  
Author(s):  
C. R. Baker ◽  
T. L. Jeans ◽  
A. G. Gerber ◽  
A. G. L. Holloway ◽  
G. D. Watt
Keyword(s):  
Axisymmetric Body ◽  
Hydrodynamic Forces ◽  
The Body ◽  
Estimation Methods ◽  
Body Region ◽  
Force Estimation ◽  
Uncertainty Range ◽  
Flow Features ◽  
Yaw Angle ◽  
Good Agreement

Using computational fluid dynamics (CFD), a study was conducted to predict the hydrodynamic forces and moments on an axisymmetric body over a range of yaw angles and Reynolds numbers. Computational results for hydrodynamic forces and moments show good agreement with experimental data, being within the experimental uncertainty range at most yaw angles. Deviations outside of the uncertainty range occurred for the lateral (Y) force values at yaw angles greater than 15 degrees. The development of the after-body vortex shows good agreement with experimental observation. Primary and secondary separation points and shear stress streamline behaviour are also compared with experiment data at a yaw angle of 24 degrees. Results are discussed with a view to identifying flow features critical to the development of new force estimation methods. The after-body vortex, at increasing yaw angles, influences the overall force and moment predictions through a complex interaction between the transport of after-body vorticity and the detachment/reattachment locations of the boundary layer. Adequate modeling of this after-body region is increasingly important at high yaw angles. One of the most important features that influences the overall forces and moments is the circumferential position of shear layer detachment and reattachment, which have a direct impact on the pressure distribution along the body.

Study of Flow Behavior in a Vibrating Pipe on Offshore Platform

2003 ◽  
Author(s):  
Dezhong Li ◽  
Ning Mei ◽  
Jian Su
Keyword(s):  
Flow Behavior ◽  
Offshore Platform ◽  
Polynomial Method ◽  
Flow Parameters ◽  
Pressure Distributions ◽  
Incompressible Viscous Flow ◽  
Fluid Properties ◽  
Oscillating Fluid Mechanics ◽  
The Mathematical Model ◽  
Good Agreement

The purpose of this paper is to study flow behavior in a vibrating pipe on offshore platform. The mathematical model of unsteady, incompressible, viscous flow in a vibrating pipe is established according to the basic theory of oscillating fluid mechanics. The governing equations of flow are decomposed into a system for steady flow and another for flow oscillation, with the equations of the differential coefficients of flow parameters solved by using the parametric polynomial method. Velocity and pressure distributions are obtained for different flow conditions. Numerical results indicate that the flow behavior in the vibrating pipe on offshore platform is strongly affected by fluid properties and the pipe structure. A good agreement is obtained when comparing the results with the variational solution in constant cross-section, which shows that the method proposed in this work is effective for studying flow behavior in a vibrating pipe on offshore platform.

Unsteady Hydrodynamic Forces due to Rotor-Stator Interaction on a Diffuser Pump With Identical Number of Vanes on the Impeller and Diffuser

2005 ◽  
Vol 127 (4) ◽  
pp. 743-751 ◽  
Author(s):  
M. Zhang ◽  
H. Tsukamoto
Keyword(s):  
Computational Study ◽  
Pressure Fluctuations ◽  
Vortex Method ◽  
Hydrodynamic Forces ◽  
Pump Impeller ◽  
Vaned Diffuser ◽  
Fluid Forces ◽  
Rotor Stator Interaction ◽  
Identical Number ◽  
Good Agreement

Experimental and computational study was developed for unsteady hydrodynamic forces on a diffuser pump impeller excited by the interaction between the impeller and the vaned diffuser with the same number of vanes as impeller. Unsteady flow calculations are made using commercially available CFD software, CFX-TASCflow, as well as the two-dimensional vortex method. Calculated pressure and fluid forces on the impeller show good agreement with measured ones. It has been demonstrated that the fluid forces on the impeller with the same number of vanes as the vaned diffuser are smaller compared with other combinations of vane numbers. However, the pressure fluctuations are found to be greater than other cases.

AN EMPIRICAL FORMULA FOR Q STATE POTTS MODEL IN D DIMENSIONS

1994 ◽  
Vol 08 (17) ◽  
pp. 1059-1064
Author(s):  
C. Y. PAN
Keyword(s):  
Renormalization Group ◽  
Critical Points ◽  
Potts Model ◽  
Critical Exponents ◽  
Empirical Formula ◽  
Group Method ◽  
Critical Properties ◽  
Renormalization Group Method ◽  
Primary Reference ◽  
Good Agreement

Based upon the known results of the critical properties of the q state Potts ferromagnets obtained by different methods, we proposed an empirical formula of the model. It gives the critical points and the critical exponents for general Potts spin value q in any d dimensions which are in good agreement with all the available results. It improves the results given by Migdal–Kadanoff renormalization group method. It gives more accurate results than Hajdukovic conjecture to the problem of interest. This empirical formula may serve as the primary reference to the problem of interest.

Quantification of Hydrodynamic Forces due to Torsional and Axial Vibrations in Ship Propellers

2013 ◽  
Author(s):  
B. P. M. van Esch ◽  
J. J. A. van Hooijdonk ◽  
N. W. H. Bulten
Keyword(s):  
Experimental Data ◽  
Open Water ◽  
Hydrodynamic Forces ◽  
Hydrodynamic Coefficients ◽  
Water Condition ◽  
Reduced Frequency ◽  
Vibratory Motion ◽  
Trailing Vortices ◽  
Axial Vibrations ◽  
Oscillating Plate

CFD is used to compute the hydrodynamic coefficients for torsional and axial vibrations, for one type of the Wageningen B-series of ship propellers in open-water condition. It is shown that the wakes shed from the blades have an influence on the magnitude and the phase of the damping forces. The dependency on reduced frequency of the vibratory motion is explained. This phenomenon can be related to the lift deficiency of trailing vortices in the wake of an oscillating plate, as derived by Theodorsen and Von Kármán and Sears, and is frequently overlooked by more recent investigations. Results of the calculations are compared with theoretical and experimental data from literature.

scholarly journals Computation of the Diffraction Transfer Matrix and the Radiation Characteristics in the Open-Source BEM Code NEMOH

2016 ◽  
Author(s):  
Francesc Fàbregas Flavià ◽  
Cameron McNatt ◽  
François Rongère ◽  
Aurélien Babarit ◽  
Alain H. Clément
Keyword(s):  
Open Source ◽  
Transfer Matrix ◽  
Body Wave ◽  
Finite Depth ◽  
Interaction Theory ◽  
Floating Bodies ◽  
Radiation Characteristics ◽  
Speed Up ◽  
Multi Body ◽  
Good Agreement

Until now, widely available boundary element method (BEM) codes did not allow the calculation of two non-conventional hydrodynamic operators, which characterize the way a body diffracts and radiates waves, known as Diffraction Transfer Matrix and Radiation Characteristics respectively. When embedded into the finite-depth interaction theory developed by [1], they drastically speed up the computation of the added mass, damping and excitation force coefficients of a group (“farm”) of floating bodies. This paper presents the implementation of their computation in the open source BEM solver NEMOH using the methodology proposed by [2]. Results for two different geometries, a cylinder and a square box, are presented and compared to an alternative computational approach developed by [3]. A very good agreement between them is found. In addition, the hydrodynamic operators of the cylinder are compared to a semi-analytical solution available in the literature showing a good match. Results obtained using the finite-depth interaction theory are shown for a generic multi-body wave energy converter (WEC) demonstrating how the capabilities added to the BEM software NEMOH can facilitate the numerical modeling of the hydrodynamic interactions in large arrays of bodies.

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