Structural Analysis of Aquaculture Nets: Comparison and Validation of Different Numerical Modelling Approaches

2014 ◽  
Author(s):  
Heidi Moe-Føre ◽  
Per Christian Endresen ◽  
Karl Gunnar Aarsæther ◽  
Jørgen Jensen ◽  
Martin Føre ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Current Flow ◽  
Cross Flow ◽  
Structural Response ◽  
Parameter Study ◽  
High Current ◽  
Hydrodynamic Load ◽  
Physical Model Tests ◽  
Wake Effects ◽  
Drag Term

The performance of three different numerical methods were compared and evaluated against data from physical model tests. A parameter study of a simplified net cage model subjected to a steady flow was performed by all methods, varying the net solidity and the flow velocity. The three numerical methods applied models based on springs, trusses or triangular finite elements. Hydrodynamic load calculations were based on the drag term in Morison’s equation and the cross-flow principle. Different approaches to account for wake effects were applied. In general, the presented numerical methods should be able to calculate loads and deformations within acceptable tolerance limits for low to intermediate current flow velocities and net solidities, while numerical analyses of high solidity nets subjected to high current velocities tend to overpredict the drag loads acting on the structure. To accurately estimate hydrodynamic loads and structural response of net structures with high projected solidity, new knowledge and methods are needed.

Structural Analysis of Aquaculture Nets: Comparison and Validation of Different Numerical Modeling Approaches

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Heidi Moe-Føre ◽  
Per Christian Endresen ◽  
Karl Gunnar Aarsæther ◽  
Jørgen Jensen ◽  
Martin Føre ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Current Flow ◽  
Cross Flow ◽  
Structural Response ◽  
Parameter Study ◽  
Hydrodynamic Load ◽  
Water Currents ◽  
Physical Model Tests ◽  
Wake Effects ◽  
Drag Term

The performance of three different numerical methods were compared and evaluated against data from physical model tests of nets subjected to a static load due to water currents. A parameter study of a simplified net cage model subjected to a steady flow was performed by all methods, varying the net solidity and the flow velocity. The three numerical methods applied models based on springs, trusses, or triangular finite elements. Hydrodynamic load calculations were based on the drag term in Morison's equation and the cross-flow principle. Different approaches to account for wake effects were applied. In general, the presented numerical methods should be able to calculate loads and deformations within acceptable tolerance limits for low to intermediate current flow velocities and net solidities, while numerical analyses of high solidity nets subjected to high current velocities tend to overpredict the drag loads acting on the structure. To accurately estimate hydrodynamic loads and structural response of net structures with high projected solidity, new knowledge and methods are needed.

Vortex and Wake Effects on Closely Spaced Marine Risers

2006 ◽  
Author(s):  
G. Germain ◽  
B. Gaurier ◽  
M. Le Boulluec ◽  
E. Fontaine ◽  
J. Capul
Keyword(s):  
Water Channel ◽  
Cross Flow ◽  
Structural Response ◽  
Reynolds Numbers ◽  
Ongoing Research ◽  
Marine Risers ◽  
Steady Current ◽  
Close Proximity ◽  
Wake Effects ◽  
Fluid Interaction

The present paper describes some ongoing research performed for a better understanding of the hydrodynamic loads acting on a riser placed in the wake of an upstream one. Experiments on model tests scaled with real configurations for dual riser interaction in uniform and steady current are presented. A particular attention is paid on how fluid interaction between two cylinders of equal diameter in tandem configuration can significantly modify their structural response in term of amplitude and frequency, compared to that of a single cylinder. The circulation water channel allows to reach Reynolds numbers from 5.5 103 to 5 104. Both in-line and cross-flow responses have been studied and are presented as functions of the reduced velocity. Observations demonstrate that wake effects can be relatively strong. If the dynamic of the upstream cylinder becomes to be well understood, the dynamic of the downstream one is hence much more complex and difficult to predict. When risers become in close proximity due to wake induced oscillations, collisions between cylinders can be observed. Comparisons between experimental and numerical results of the dynamics of a single riser in a flow are also presented.

Fatigue From Vortex-Induced Vibrations of Free Span Pipelines Using Statistics of Current Speed and Direction

2003 ◽  
Author(s):  
Rune Yttervik ◽  
Carl M. Larsen ◽  
Gunnar K. Furnes
Keyword(s):  
Fatigue Damage ◽  
Current Velocity ◽  
Current Flow ◽  
Flow Direction ◽  
Cross Flow ◽  
Longitudinal Axis ◽  
Current Speed ◽  
Parameter Study ◽  
Span Length ◽  
Vortex Induced Vibrations

A section of a sub sea pipeline that is suspended between two points on an uneven seafloor is often referred to as ‘a free span pipeline’. Pipelines, installed on a seabed with a highly irregular topography, may have to be designed with several free spans. If a free span is exposed to a current flow, vortex-induced vibrations (VIV) of the suspended part of the pipeline may occur. These vibrations may cause unacceptable fatigue damage in the structure. Statistical distributions of current speed and direction close to a small mountain on the seabed (approximately 20 m high and 40 m wide) are established based on full-scale measurements of the current velocity in the area. Some results from recent model tests of VIV in free span pipelines, including some tests in which the flow direction was not perpendicular to the longitudinal axis of the pipe, are shown. These results indicate that it is sufficient to use the component of the current velocity vector that is normal to the pipe when using empirical models for estimating the response due to vortex shedding. An existing empirical model for analysis of VIV [1] is extended such as to include oscillations in the same plane as the current flow (in-line VIV). The effect of including the directional variability of the current when estimating the VIV fatigue damage, using the extended VIV model on a typical free span pipeline, is demonstrated, and found to be of great importance. A parameter study, in which the length of the free span is varied, is also carried out. The conclusion from this study is that a reduction of free span length affects the parameters that govern the accumulation of fatigue damage differently. Stresses are increased, but the number of current conditions capable of inducing VIV is reduced when the length of the span is reduced. It is therefore difficult to predict whether the accumulated damage will increase or decrease when the span length is reduced, and detailed analyses are required for each particular free span and current distribution. The damage from in-line VIV is generally lower than the damage from the cross flow VIV for all but the shortest span lengths.

Careful Parameter Study to Enhance the Effect of Injecting Heavy Fuel Oil Into a Crossflow Using Numerical Approaches

2018 ◽  
Author(s):  
Masoud Darbandi ◽  
Ali Fatin ◽  
Gerry E. Schneider
Keyword(s):  
Flow Velocity ◽  
Cross Flow ◽  
Droplet Breakup ◽  
Computational Method ◽  
Fuel Oil ◽  
Injection Velocity ◽  
Parameter Study ◽  
Spray Parameters ◽  
Heavy Fuel Oil ◽  
Spray Characteristics

The flow and spray parameters can have noticeable roles in heavy fuel oil (HFO) spray finesse. As known, the interaction between droplets and cross flow should be considered carefully in many different industrial applications such as the process burners and gas turbine combustors. So, it would be so important to investigate the effect of injecting HFO into a crossflow more subtly. In this work, the effects of various flow and spray parameters on the droplet breakup and dispersion parameters are investigated numerically using the finite-volume-element method. The numerical method consists of a number of different models to predict the droplets breakup and their dispersion into a cross flow including the spray-turbulence interaction one. An Eulerian–Lagrangian approach, which suitably models the interaction between the droplets and turbulence, and also models the droplets secondary breakup is used to investigate the interactions between the flow and the droplet behaviors. After validating the computational method via comparing them with the data provided by the past researches, four test cases with varying swirl number, air axial velocity, droplet size, and fuel injection velocity are examined to find out the effects of preceding parameters on some spray characteristics including the droplets path, sauter mean diameter (SMD), and dispersed phase mass concentration. The results show that the droplets inertia and the flow velocity magnitude have significant effects on spray characteristics. As the droplets become more massive, the deflection of spray in flow direction becomes less. Also, increasing of flow velocity causes more deflection for sprays with the same droplet sizes.

Electrode conduction processes in air plasmas

1962 ◽  
Vol 13 (3) ◽  
pp. 465-477 ◽  
Author(s):  
D. W. George ◽  
H. K. Messerle
Keyword(s):  
Magnetic Field ◽  
Shock Tube ◽  
Current Flow ◽  
Electronic Conductivity ◽  
The Other ◽  
High Current ◽  
Air Plasma ◽  
Air Plasmas ◽  
Current Densities

Using an electrically driven shock tube with initial pressures of 0.1 to 1.0 mm Hg and shock speeds of about Mach 12 to 15, the resistance of an air plasma between two parallel probes has been measured by two different techniques and the results compared. In one, external voltages of from 0 to 100 V were applied to the probes and in the other, electromagnetically induced voltages of from 0 to 25 V were produced by the plasma's motion in a magnetic field of up to 3500 G. In either case the resistance was found to decrease as the current flow increased and was consistent with the equilibrium electronic conductivity of the air plasma at high current densities.

Factors controlling the tentacle and polyp expansion behaviour of selected temperate Anthozoa

2006 ◽  
Vol 86 (5) ◽  
pp. 977-992 ◽  
Author(s):  
James J. Bell ◽  
Claire Shaw ◽  
John R. Turner
Keyword(s):  
Predator Avoidance ◽  
Current Flow ◽  
Time Of Day ◽  
High Current ◽  
Light Levels ◽  
Turbulent Flow Regime ◽  
Flow Turbulence ◽  
Predator Abundance ◽  
Expansion Behaviour ◽  
Anemonia Viridis

Although the factors influencing patterns of expansion and contraction of polyps and tentacles for tropical anthozoans has been well described there is still little information for temperate species. This study investigated the patterns of tentacle and polyp expansion behaviour of nine species of temperate Anthozoa in response to current flow, turbulence, food availability and time of day (light) at Lough Hyne Marine Nature Reserve (Ireland). In the absence of current flow, Metridium senile, Caryophyllia smithii, Alcyonium hibernicum and Corynactis viridis exhibited nocturnal expansion of polyps or tentacles with contraction occurring in the daytime, while Alcyonium digitatum, Actinia equina and Cerianthus lloydii showed no differences between light and dark periods. The symbiont containing species Anthopleura ballii and Anemonia viridis expanded or raised their tentacles during daylight hours (tentacle contraction is not possible for A. viridis), although in shallow waters (3 m) Anthopleura ballii tentacles were contracted at midday (highest light levels) presumably to prevent damage from ultraviolet radiation. The contraction of tentacles during light periods was considered a predator avoidance response since zooplankton availability did not vary between light and dark periods, while predator abundance (particularly fish) is greater during daylight. Even though M. senile, Alcyonium hibernicum and Corynactis viridis showed little expansion during daylight periods in the absence of current flow, tentacles and polyps were expanded at midday during periods of high current flow. A greater number of expanded polyps and tentacles were also recorded for A. digitatum, Anemonia viridis and Cerianthus lloydii during high flow conditions compared with periods of low/no flow (Caryophyllia smithii not examined). Actinia equina only exhibited tentacle expansion in response to the creation of a turbulent flow regime, which was determined from laboratory observations. Since species demonstrating contraction during daylight in the absence of current flow expanded their tentacles and polyps when subjected to high current flow, the need for feeding appears to be more important than predator avoidance in controlling expansion behaviour.

Non-Linear Modeling of Ocean Current Turbine Blades Under Large Deflection

2016 ◽  
Author(s):  
Takuya Suzuki ◽  
Hassan Mahfuz
Keyword(s):  
Large Scale ◽  
Large Deflection ◽  
Turbine Blades ◽  
Structural Response ◽  
Ocean Current ◽  
Hydrodynamic Load ◽  
Linear Modeling ◽  
Non Linear ◽  
The Difference ◽  
Current Turbine

This paper presents a non-linear modeling approach for large-scale ocean current turbine (OCT) blades. During the operation, OCT blades are subjected to a hydrodynamic load that has fluid density 800 times higher than that of air. The fluid load on OCT blades are sufficient to cause large deflection; therefore, a method that couples the blade’s deflection and the hydrodynamic load is required. For this purpose, we developed a non-linear model for turbine blades based on blade element momentum (BEM) theory. The newly developed method considers interplay between blade’s deflection and the hydrodynamic load. In addition, geometric non-linearity is also considered in the analysis, which provides a more accurate prediction of the structural response. For validation purposes, the developed method and a set of existing National Renewable Energy Laboratory (NREL) codes were used to calculate the deflection of the OCT blade. A comparison of flap-wise and edge-wise deflections given by both methods were determined and the results showed a good correlation between the two methods. This comparison was made only for small deflection since NREL codes cannot account for large deflection. In the next step, to investigate the effect of non-linearity, both linear and non-linear analyses were performed for a large-scale OCT blade where deflection was indeed large. In this study, we analyzed a flexible blade made of E-glass/epoxy composite. The difference in deflection was about 11% for the flexible blade since the fluid-structure interaction was significant as the blade deflection was large.

Local Current Flow in Mixed-Phase Silicon Solar Cells and Correlation to Light-Induced Open-Circuit Voltage Enhancement

2006 ◽  
Vol 910 ◽  
Author(s):  
Baojie Yan ◽  
C.-S. Jiang ◽  
H. R. Moutinho ◽  
M. M. Al-Jassim ◽  
Jeffrey Yang ◽  
...  
Keyword(s):  
Solar Cells ◽  
Current Flow ◽  
Volume Fraction ◽  
Cell Structure ◽  
Open Circuit ◽  
Phase Region ◽  
Mixed Phase ◽  
High Current ◽  
Conductive Atomic Force Microscopy ◽  
Local Current

AbstractWe use conductive atomic force microscopy (C-AFM) to measure the local current flow in the mixed-phase hydrogenated silicon n-i-p solar cell structure without the top ITO contact. The forward biased C-AFM images reveal that for the fully amorphous region the current is very low on the entire surface. However, high current spikes appear in the mixed-phase region, where the current spikes are correlated to the formation of nanocrystallite aggregations with a diameter of ~500 nm. Furthermore, the density of the current spikes increases from the mixed-phase to the substantially nanocrystalline regions. The nanocrystallite aggregation supports our previously proposed parallel-connected two-diode model for Voc drops with crystalline volume fraction and light-induced Voc increase in the mixed-phase solar cells. Adding a 50-nm thick a-Si:H buffer layer between the p and i layers significantly reduces the magnitude of the high current spikes, even the top morphology appears unaffected. This result is also consistent with the previously proposed two-diode model for explaining the carrier transport in the mixed-phase solar cells.

Investigation of Hot Film Calibration for Entropy Generation Rate Calculations

2002 ◽  
Author(s):  
R. Mahon ◽  
P. Frawley ◽  
M. R. D. Davies
Keyword(s):  
Boundary Layer ◽  
Numerical Methods ◽  
Circular Cylinder ◽  
Constant Temperature ◽  
Entropy Generation ◽  
Cross Flow ◽  
Entropy Generation Rate ◽  
Hot Wire ◽  
Hot Film ◽  
The Relationship

The objective of this paper is to investigate in detail the relationship between results obtained from flow over a circular cylinder in cross flow using Hot Film and Hot Wire Constant Temperature Anemometry (C.T.A.). The experimental results are compared with those obtained using numerical methods. The results obtained from Hot Wire Anemometry are used to attempt to calibrate the Hot Film Sensors for the purpose of evaluating entropy generation rates in the boundary layer of the cylinder.

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