Numerical Modelling of the Interaction of Moving Fish Nets and Fluid

2021 ◽  
pp. 1-10
Author(s):  
Tobias Martin ◽  
Gang Wang ◽  
Hans Bihs
Keyword(s):  
Stokes Equations ◽  
Navier Stokes ◽  
Force Model ◽  
Lumped Mass ◽  
Navier Stokes Equations ◽  
Linear System Of Equations ◽  
Lumped Mass Method ◽  
Proposed Model ◽  
Significant Difference ◽  
Dynamic Equilibria

Abstract The significant difference in length scales between the flow around a moving fish net and the flow around each twine of the net prevents the resolution of the complete structure within a discrete fluid domain. In this paper, this issue is overcome by calculating the net and fluid dynamics separately and incorporate their interaction implicitly. The forces on the net are approximated using a screen force model, and the motion of the net is computed with a lumped mass method. Here, a linear system of equations is derived from the dynamic equilibria and kinematic relations. The net model is coupled to the CFD solver REEF3D which solves the incompressible Navier-Stokes equations using high-order finite differences in space and time. Several numerical calculations are provided, and the comparison of loads and velocity reduction with available measurements indicates the good performance of the proposed model.

scholarly journals Numerical Modelling of the Interaction of Moving Fish Nets and Fluid

2020 ◽  
Author(s):  
Tobias Martin ◽  
Gang Wang ◽  
Hans Bihs
Keyword(s):  
Stokes Equations ◽  
Navier Stokes ◽  
Force Model ◽  
Lumped Mass ◽  
Navier Stokes Equations ◽  
Linear System Of Equations ◽  
Lumped Mass Method ◽  
Proposed Model ◽  
Significant Difference ◽  
Dynamic Equilibria

Abstract The significant difference in length scales between the flow around a moving fish net and the flow around each twine of the net prevents the resolution of the complete structure within a discrete fluid domain. In this paper, this issue is overcome by calculating the net and fluid dynamics separately and incorporate their interaction implicitly. The forces on the net are approximated using a screen force model, and the motion of the net is computed with a lumped mass method. Here, a linear system of equations is derived from the dynamic equilibria and kinematic relations. The net model is coupled to the CFD solver REEF3D which solves the incompressible Navier-Stokes equations using high-order finite differences in space and time. Several numerical calculations are provided, and the comparison of loads and velocity reduction with available measurements indicates the good performance of the proposed model.

scholarly journals On Linear and Non-Linear Approximation In the Theory of Convective Heat Transfer

2021 ◽  
pp. 44-51
Author(s):  
M. Y. Davidzon
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Stokes Equations ◽  
Linear Equations ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Linear System Of Equations ◽  
Non Linear ◽  
Non Linear System

A system of linear equations that is currently widely used to describe convective heat transfer does not seem to be able to explain some experimental facts. One of the reasons for this may lie in using Newton’s and Fourier’s linear laws when deriving energy and Navier-Stokes equations. Replacing linear equations with nonlinear ones, as well as using an expression for surface heat flux density that is based on laws of physics instead of expressions called ‘cooling laws,’ would allow to solve a wider range of problems, and also would better agree with the experimental data. The use of proposed non-linear system of equations would also permit engineers in chemical, textile, defense, power, and other industries to design more economical and smaller-sized heat exchange devices.

scholarly journals Simulating of the admixture spreading in a steady 2D lengthy stream of the viscous fluid

2013 ◽  
Vol 2 (1) ◽  
pp. 91-97
Keyword(s):  
Viscous Fluid ◽  
Small Parameter ◽  
Stokes Equations ◽  
Numerical Study ◽  
Computer Experiments ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Convection Diffusion ◽  
Proposed Model ◽  
And Diffusion

The problem of the passive contaminant spreading in a steady viscous fluid stream is discussed while the admixture's dissipation and diffusion are taken into account. The channel is assumed to be a horizontal plane, curvilinear and quite lengthy, so that the ratio of the stream width to its length can be regarded as a small parameter. A mathematical model of the process derived by the small parameter technique from the 2D steady Navier-Stokes equations for incompressible viscous fluid and non-steady convection-diffusion equation of a substance in the moving medium is introduced. A finite element method is applied for numerical study of the proposed model and results of computer experiments are presented.

Thermoacoustic and buoyancy-driven transport in a square side-heated cavity filled with a near-critical fluid

1996 ◽  
Vol 316 ◽  
pp. 53-72 ◽  
Author(s):  
Bernard Zappoli ◽  
Sakir Amiroudine ◽  
Pierre Carles ◽  
Jalil Ouazzani
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Square Cavity ◽  
Piston Effect ◽  
Navier Stokes Equations ◽  
Significant Difference ◽  
Buoyancy Driven Convection ◽  
Volume Method ◽  
Very High

The mechanisms of heat and mass transport in a side-heated square cavity filled with a near-critical fluid are explored, with special emphasis on the interplay between buoyancy-driven convection and the Piston Effect. The Navier–Stokes equations for a near-critical van der Waals gas are solved numerically by means of an acoustically filtered, finite-volume method. The results have revealed some striking behaviour compared with that obtained for normally compressible gases: (i) heat equilibration is still achieved rapidly, as under zero-g conditions, by the Piston Effect before convection has time to enhance heat transport; (ii) mass equilibration is achieved on a much longer time scale by quasi-isothermal buoyant convection; (iii) due to the very high compressibility, a stagnation-point effect similar to that encountered in high-speed flows provokes an overheating of the upper wall; and (iv) a significant difference to the convective single-roll pattern generated under the same conditions in normal CO2 is found, in the form of a double-roll convective structure.

Stokes Roughness Effects on Hydrodynamic Lubrication. Part I—Comparison Between Incompressible and Compressible Lubricating Films

1986 ◽  
Vol 108 (2) ◽  
pp. 151-158 ◽  
Author(s):  
Y. Mitsuya ◽  
S. Fukui
Keyword(s):  
Carrying Capacity ◽  
Stokes Equations ◽  
Hydrodynamic Lubrication ◽  
Navier Stokes ◽  
Load Carrying Capacity ◽  
Roughness Effects ◽  
Navier Stokes Equations ◽  
Large N ◽  
Significant Difference ◽  
Load Carrying

A perturbation method for the Navier-Stokes equations is presented for analyzing Stokes roughness effects on hydrodynamic lubrication in both incompressible and compressible films. The solution is obtained from direct numerical calculation by using an actual rough spacing, without applying the currently accepted assumption that the roughness height should be small. The roughness wavelength and height influences on flow rate, load carrying capacity and frictional force are clarified. Secondary quantities induced by Stokes effects are found to be proportional to wavenumber n squared for sufficiently large n values, so that the amount of the Stokes effect can be determined by the spacing to wavelength squared ratio. A significant difference between incompressible and compressible films is that Stokes roughness increases the flow resistance of and then enhances the load carrying capacity of incompressible films, while it inversely affects compressible films. The compressibility with respect to secondary pressure induced by the Stokes effects can be neglected for any compressibility number, no matter how large, as long as the local compressibility number, defined by the wavelength, is small.

scholarly journals Development of a Semi-analytical Dynamic Thrust Force Model

2021 ◽  
Author(s):  
Marin Akter ◽  
Mohammad Abdul Alim ◽  
Md Manjurul Hussain ◽  
Kazi Shamsunnahar Mita ◽  
Anisul Haque ◽  
...  
Keyword(s):  
Water Mass ◽  
Stokes Equations ◽  
Thrust Force ◽  
Variational Iteration Method ◽  
Navier Stokes ◽  
Force Model ◽  
Dynamic Force ◽  
Navier Stokes Equations ◽  
Cyclone Sidr ◽  
Saint Venant Equations

Abstract A moving water mass generates force which is exerted on its moving path. Cyclone generated storm surge or earthquake generated tsunami are specific examples of moving water mass the generates force along the coasts. In addition to human lives, these moving water masses cause severe damages to the coastal infrastructure due to tremendous force exerted on these structures. To assess the damage on these infrastructures, an essential parameter is the resultant force exerted on these structures. To evaluate the damages, there is hardly any quantitative method available to compute this force. In this paper we have developed a semi-analytical model, named as Dynamic Force Model (DFM), by using Variational Iteration Method to compute this force. As governing equations, we have used the Saint Venant equations which are basically 1D shallow water equations derived from the Navier-Stokes equations. The verified, calibrated and validated DFM is applied in Bangladesh coastal zone to compute dynamic thrust force due to tropical cyclone SIDR.

scholarly journals PARALLEL COMPUTATION OF ROTATING FLOWS

1999 ◽  
Vol 4 (1) ◽  
pp. 124-134
Author(s):  
L. K. Lundin ◽  
V. A. Barker ◽  
J. N. Sørensen
Keyword(s):  
Stokes Equations ◽  
Rotating Flows ◽  
Navier Stokes ◽  
Second Step ◽  
Governing Equations ◽  
Time Level ◽  
Navier Stokes Equations ◽  
Linear System Of Equations ◽  
Wide Range ◽  
New Time

This paper deals with the simulation of 3‐D rotating flows based on the velocity‐vorticity formulation of the Navier‐Stokes equations in cylindrical coordinates. The governing equations are discretized by a finite difference method. The solution is advanced to a new time level by a two‐step process. In the first step, the vorticity at the new time level is computed using the velocity at the previous time level. In the second step, the velocity at the new time level is computed using the new vorticity. We discuss here the second part which is by far the most time‐consuming. The numerical problem is that of solving a singular, large, sparse, over‐determined linear system of equations, and the iterative method CGLS is applied for this purpose. We discuss some of the mathematical and numerical aspects of this procedure and report on the performance of our software on a wide range of parallel computers.

scholarly journals Numerical simulation of pulsatile blood flow: a study with normal artery, and arteries with single and multiple stenosis

2021 ◽  
Vol 68 (1) ◽  
Author(s):  
Md. Alamgir Kabir ◽  
Md. Ferdous Alam ◽  
Md. Ashraf Uddin
Keyword(s):  
Blood Flow ◽  
Numerical Simulations ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Area Reduction ◽  
Significant Difference ◽  
Stenosed Artery ◽  
Fluid Properties ◽  
Flow Through

AbstractNumerical simulations of pulsatile transitional blood flow through symmetric stenosed arteries with different area reductions were performed to investigate the behavior of the blood. Simulations were carried out through Reynolds averaged Navier-Stokes equations and well-known k-ω model was used to evaluate the numerical simulations to assess the changes in velocity distribution, pressure drop, and wall shear stress in the stenosed artery, artery with single and double stenosis at different area reduction. This study found a significant difference in stated fluid properties among the three types of arteries. The fluid properties showed a peak in an occurrence at the stenosis for both in the artery with single and double stenosis. The magnitudes of stated fluid properties increase with the increase of the area reduction. Findings may enable risk assessment of patients with cardiovascular diseases and can play a significant role to find a solution to such types of diseases.

A viscous blade body force model for computational fluid dynamics–based throughflow analysis of axial compressors

2021 ◽  
pp. 095441002199955
Author(s):  
Jian Li ◽  
Jinfang Teng ◽  
Mingmin Zhu ◽  
Xiaoqing Qiang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Stokes Equations ◽  
Skin Friction Coefficient ◽  
Navier Stokes ◽  
Force Model ◽  
Navier Stokes Equations ◽  
Design Speed ◽  
Airfoil Cascade ◽  
Throughflow Model

In recent years, the computational fluid dynamics (CFD) techniques have attracted enormous interest in the throughflow calculations, and one of the major concerns in the CFD-based throughflow method is the modeling of blade forces. In this article, a viscous blade force model in the CFD-based throughflow program was proposed to account for the loss generation. The throughflow code is based on the axisymmetric Navier–Stokes equations. The inviscid blade force is determined by calculating a pressure difference between the pressure and suction surfaces, and the viscous blade force is related to the local kinetic energy through a skin friction coefficient. The viscous blade force model was validated by a linear controlled diffusion airfoil cascade, and the results showed that it can correctly introduce the loss into the CFD-based throughflow model. Then, the code was applied to calculate the transonic NASA rotor 67, and the calculated results were in good agreement with the measured results, which showed that the calculated shock losses reduce the dependence of the throughflow calculation on the empirical correlation. Last, the 3.5-stage compressor P&W3S1 at 85%, 100%, and 105% of the design speed was performed to demonstrate the reliability of the viscous blade force model in a multistage environment. The results showed that the CFD-based throughflow method can easily predict the spanwise mixing due to the inclusion of the turbulence model, and predicted results were in acceptable agreement with the experimental results. In a word, the proposed viscous blade force model and CFD-based throughflow model can achieve the throughflow analysis with an acceptable level of accuracy and a little time-consuming.

scholarly journals A 2D vertical model for simulating surface and subsurface flows using finite element–finite volume methods

2019 ◽  
Vol 21 (5) ◽  
pp. 761-780
Author(s):  
Leila Farrokhpour ◽  
Masoud Montazeri Namin ◽  
Morteza Eskandari-Ghadi
Keyword(s):  
Stokes Equations ◽  
Time Discretization ◽  
Finite Volume Methods ◽  
Navier Stokes ◽  
Step Method ◽  
Fractional Step Method ◽  
Navier Stokes Equations ◽  
Proposed Model ◽  
Wide Range ◽  
Subsurface Flows

Abstract A numerical model is presented for simulation of hydrodynamics of a 2D vertical free surface domain consisting of an arbitrary partitioned porous and non-porous area. To this end, modified Navier–Stokes equations are considered which could be applied in surface water and in subsurface flows, simultaneously. A wide range of Reynolds number has been considered, from which non-Darcy effects have also been taken into account. A fractional step method has been used in the time discretization procedure, where the convection and diffusion terms are separated from the pressure term while solving the momentum equations. To include the variation of surface elevation in computation, the domain has been divided into two parts, namely, ‘interior subdomain’, which never gets dry during the simulation period, covered by fixed unstructured triangular grids and ‘top layer’ with only a one layer structured grid, the position of which varies with the water surface. The validation of the proposed model has been achieved by comparison of its results with both theoretical and experimental data reported in the literature.

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