Study on the Influence of Mesh Grouping on Numerical Simulation Results of Fish Cages

2019 ◽  
Author(s):  
Liuyi Huang ◽  
Yuyan Li ◽  
Yi Ni ◽  
Hui Cheng ◽  
Xinxin Wang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Hydrodynamic Equation ◽  
Single Point ◽  
Computational Time ◽  
Area Method ◽  
Solidity Ratio ◽  
Equivalent Area ◽  
Fish Cages ◽  
Accuracy Of Results ◽  
Volume Method

Abstract The Morison Model is widely applied in the numerical simulation for the hydrodynamics assessment of fish cage. In the Morison model, hydrodynamic forces are calculated based on twines. To reduce the computational time, mesh grouping methods (replacement of multiple meshes with less number of equivalent meshes) have been implemented widely in the calculation. However, as the hydrodynamic equation for a mesh is quite different under wave and current, it is not appropriate to use the classical mesh grouping. On the basis of basic hydrodynamic equations of the meshes with current and wave, this paper carried out the study about theoretical analysis of two methods (the equivalent area method and the equivalent volume method) of the mesh grouping, using main parameters of nets such as the diameter, solidity ratio and elastic modulus related to mesh grouping. A single-point mooring cage, of which tension and displacement could be calculated with finite element method, was selected as a case to carry out the verification of two mesh grouping methods. Flume model experiment was used to validate the accuracy of mesh grouping methods. The results indicated that, the equivalent area method has a higher accuracy in the pure current condition, while the equivalent volume method was more accurate in combined waves and current. The accuracy of results using mesh grouping to analyze hydrodynamics of nets within a certain range of grouping times could be insured with an improved calculation speed. This paper can provide practical advice on the mesh grouping process in the numerical simulation of fish cages and fishing gear.

Non-stationary process characteristics of the gas outflow into a liquid

2019 ◽  
Vol 14 (2) ◽  
pp. 82-88
Author(s):  
M.V. Alekseev ◽  
I.S. Vozhakov ◽  
S.I. Lezhnin
Keyword(s):  
Numerical Simulation ◽  
Liquid Column ◽  
Gas Content ◽  
Liquid Lead ◽  
Gas Flows ◽  
Asymptotic Model ◽  
Process Characteristics ◽  
Significant Difference ◽  
Order Of Magnitude ◽  
Volume Method

A numerical simulation of the process of the outflow of gas under pressure into a closed container partially filled with liquid was carried out. For comparative theoretical analysis, an asymptotic model was used with assumptions about the adiabaticity of the gas outflow process and the ideality of the liquid during the oscillatory one-dimensional motion of the liquid column. In this case, the motion of the liquid column and the evolution of pressure in the gas are determined by the equation of dynamics and the balance of enthalpy. Numerical simulation was performed in the OpenFOAM package using the fluid volume method (VOF method) and the standard k-e turbulence model. The evolution of the fields of volumetric gas content, velocity, and pressure during the flow of gas from the high-pressure chamber into a closed channel filled with liquid in the presence of a ”gas blanket“ at the upper end of the channel is obtained. It was shown that the dynamics of pulsations in the gas cavity that occurs when the gas flows into the closed region substantially depends on the physical properties of the liquid in the volume, especially the density. Numerical modeling showed that the injection of gas into water occurs in the form of a jet outflow of gas, and for the outflow into liquid lead, a gas slug is formed at the bottom of the channel. Satisfactory agreement was obtained between the numerical calculation and the calculation according to the asymptotic model for pressure pulsations in a gas projectile in liquid lead. For water, the results of calculations using the asymptotic model give a significant difference from the results of numerical calculations. In all cases, the velocity of the medium obtained by numerical simulation and when using the asymptotic model differ by an order of magnitude or more.

scholarly journals Numerical Simulation of Intrachamber Processes in the Power Plant

2021 ◽  
Vol 11 (11) ◽  
pp. 4990
Author(s):  
Boris Benderskiy ◽  
Peter Frankovský ◽  
Alena Chernova
Keyword(s):  
Numerical Simulation ◽  
Power Plant ◽  
Flow Structure ◽  
Power Plants ◽  
Control Volume ◽  
Conjugate Problem ◽  
Topological Features ◽  
Gas Dynamic ◽  
Calculation Results ◽  
Volume Method

This paper considers the issues of numerical modeling of nonstationary spatial gas dynamics in the pre-nozzle volume of the combustion chamber of a power plant with a cylindrical slot channel at the power plant of the mass supply surface. The numerical simulation for spatial objects is based on the solution conjugate problem of heat exchange by the control volume method in the open integrated platform for numerical simulation of continuum mechanics problems (openFoam). The calculation results for gas-dynamic and thermal processes in the power plant with a four-nozzle cover are presented. The analysis of gas-dynamic parameters and thermal flows near the nozzle cover, depending on the canal geometry, is given. The topological features of the flow structure and thermophysical parameters near the nozzle cap were studied. For the first time, the transformation of topological features of the flow structure in the pre-nozzle volume at changes in the mass channel’s geometry is revealed, described, and analyzed. The dependence of the Nusselt number in the central point of stagnation on the time of the power plants operation is revealed.

On the Friction Coefficient in the Numerical Simulation of Tidal Wave Propagation

2010 ◽  
Author(s):  
Z. Y. Song ◽  
C. Cheng ◽  
F. M. Xu ◽  
J. Kong
Keyword(s):  
Numerical Simulation ◽  
Wave Propagation ◽  
Friction Factor ◽  
Tidal Wave ◽  
Computational Time ◽  
Numerical Dissipation ◽  
Courant Number ◽  
Time Step ◽  
Large Time Step ◽  
The Relationship

Based on the analytical solution of one-dimensional simplified equation of damping tidal wave and Heuristic stability analysis, the precision of numerical solution, computational time and the relationship between the numerical dissipation and the friction dissipation are discussed with different numerical schemes in this paper. The results show that (1) when Courant number is less than unity, the explicit solution of tidal wave propagation has higher precision and requires less computational time than the implicit one; (2) large time step is allowed in the implicit scheme in order to reduce the computational time, but the precision of the solution also reduce and the calculation precision should be guaranteed by reducing the friction factor: (3) the friction factor in the implicit solution is related to Courant number, presented as the determined friction factor is smaller than the natural value when Courant number is larger than unity, and their relationship formula is given from the theoretical analysis and the numerical experiments. These results have important application value for the numerical simulation of the tidal wave.

scholarly journals Predicting the Heading Misalignment of a Vessel-Shaped Offshore Fish Farm Under Waves and Currents

2018 ◽  
Author(s):  
Lin Li ◽  
Zhiyu Jiang ◽  
Jungao Wang ◽  
Muk Chen Ong
Keyword(s):  
Reference Site ◽  
Single Point ◽  
Fish Farm ◽  
Misalignment Angle ◽  
Integrated Method ◽  
Open Sea ◽  
Waves And Currents ◽  
Spread Area ◽  
Fish Cages ◽  
Current Reduction

A vessel-shaped fish farm concept for open sea applications has been proposed recently. The whole system consists of a vessel-shaped floater, fish cages positioned longitudinally along the floater, and a single-point mooring system. The whole system weathervanes; this feature increases the spread area for the fish waste. However, the downstream cages may experience reduced water exchange when the vessel is parallel to the currents. This situation may jeopardize the fish health. A dynamic positioning (DP) system may be necessary to improve the flow conditions. This paper investigates the misalignment angle between the heading of the vessel-shaped fish farm and the currents under combined wave and current conditions. The misalignment angle is critical for the estimation of the DP system consumption. A numerical model of the fish farm system with flexible nets is developed. Current reduction factors are included to account for the flow velocity reductions between the net panels. The heading of the system is obtained by finding the equilibrium condition of the whole system under each combined wave and current condition. An integrated method using metamodels is proposed and applied for the prediction of the misalignment angle for a reference site. The probability distribution of the misalignment angle between the vessel heading and the currents is calculated using the Kriging metamodel for the reference site. Based on the prediction, the requirement for the DP system to improve the flow condition in the fish cages is discussed.

Numerical Simulation of Powder Dispersion Performance by Different Mesh Types

2016 ◽  
Vol 680 ◽  
pp. 82-85
Author(s):  
Jian Cai ◽  
Lan Chen ◽  
Umezuruike Linus Opara
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Fine Particle ◽  
Particle Deposition ◽  
Tetrahedral Mesh ◽  
Computational Time ◽  
Kinetic Characteristics ◽  
Powder Dispersion ◽  
Simulation Results ◽  
Time Accuracy

OBJECTIVE To investigate the influence of mesh type on numerical simulating the dispersion performance of micro-powders through a home-made tube. METHODS With the computational fluid dynamics (CFD) method, a powder dispersion tube was meshed in three different types, namely, tetrahedral, unstructured hexahedral and prismatic-tetrahedral hybrid meshes. The inner flow field and the kinetic characteristics of the particles were investigated. Results of the numerical simulation were compared with literature evidences. RESULTS The results showed that using tetrahedral mesh had the highest computational efficiency, while employing the unstructured hexahedral mesh obtained more accurate outlet velocity. The simulation results of the inner flow field and the kinetic characteristics of the particles were slightly different among the three mesh types. The calculated particle velocity using the tetrahedral mesh had the best correlation with the changing trend of the fine particle mass in the first 4 stages of the new generation impactor (NGI) (R2 = 0.91 and 0.89 for powder A and B, respectively). Conclusions Mesh type affected computational time, accuracy of simulation results and the prediction abilities of fine particle deposition.

scholarly journals Numerical Study on the Heading Misalignment and Current Velocity Reduction of a Vessel-Shaped Offshore Fish Farm

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Lin Li ◽  
Zhiyu Jiang ◽  
Jungao Wang ◽  
Muk Chen Ong
Keyword(s):  
Numerical Study ◽  
Single Point ◽  
Fish Farm ◽  
Misalignment Angle ◽  
Fish Welfare ◽  
Integrated Method ◽  
Waves And Currents ◽  
Spread Area ◽  
Fish Cages ◽  
Current Reduction

Recently, the concept of a vessel-shaped fish farm was proposed for open sea applications. The fish farm comprises a vessel-shaped floater, five fish cages, and a single-point mooring system. Such a system weathervanes, and this feature increases the spread area of fish waste. Still, the downstream cages may experience decreased exchange of water flow when the vessel heading is aligned with the current direction, and fish welfare may be jeopardized. To ameliorate the flow conditions, a dynamic positioning (DP) system may be required, and its power consumption should relate to the heading misalignment. This paper proposes an integrated method for predicting the heading misalignment between the vessel-shaped fish farm and the currents under combined waves and currents. A numerical model is first established for the fish farm system with flexible nets. Current reduction factors are included to address the reduction in flow velocity between net panels. The vessel heading is obtained by finding the equilibrium condition of the whole system under each combined wave and current condition. Then, the Kriging metamodel is applied to capture the relation between the misalignment angle and environmental variables, and the probability distribution of this misalignment angle is estimated for a reference site. Finally, the requirement for the DP system to improve the flow condition in the fish cages is discussed.

Analysis and Numerical Simulation of no Reacting Swirling Flow by Using URANS Approach

2021 ◽  
Vol 57 ◽  
pp. 67-79
Author(s):  
Merouane Habib ◽  
Senouci Mohammed
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Swirling Flow ◽  
Navier Stokes ◽  
Governing Equations ◽  
Simulation Based ◽  
Classical Models ◽  
Recirculation Zones ◽  
Computational Fluid Dynamics Cfd ◽  
Volume Method

In this paper, we investigate the no-reacting swirling flow by using the numerical simulation based to the unsteady Reynolds-averaged Navier-Stokes approach. The numerical simulation was realized by using a computational fluid dynamics CFD code. The governing equations are solved by using the finite volume method with two classical models of turbulence K-epsilon and Shear Stress K-ω. The objective of this paper is therefore to evaluate the performance of the two models in predicting the recirculation zones in a swirled turbulent flow. The current models are validated by comparing the numerical results of the axial, radial and tangential velocities to the experimental data from literature.

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