scholarly journals Wave energy absorption by a submerged air bag connected to a rigid float

2017 ◽  
Vol 473 (2200) ◽  
pp. 20160861 ◽  
Author(s):  
A. Kurniawan ◽  
J. R. Chaplin ◽  
M. R. Hann ◽  
D. M. Greaves ◽  
F. J. M. Farley
Keyword(s):  
Wave Energy ◽  
New Wave ◽  
Middle Section ◽  
Energy Device ◽  
Numerical Predictions ◽  
Mean Pressure ◽  
Flow Through ◽  
The Mean ◽  
Air Bag ◽  
Good Agreement

A new wave energy device features a submerged ballasted air bag connected at the top to a rigid float. Under wave action, the bag expands and contracts, creating a reciprocating air flow through a turbine between the bag and another volume housed within the float. Laboratory measurements are generally in good agreement with numerical predictions. Both show that the trajectory of possible combinations of pressure and elevation at which the device is in static equilibrium takes the shape of an S. This means that statically the device can have three different draughts, and correspondingly three different bag shapes, for the same pressure. The behaviour in waves depends on where the mean pressure-elevation condition is on the static trajectory. The captured power is highest for a mean condition on the middle section.

The dispersion of matter in turbulent flow through a pipe

1954 ◽  
Vol 223 (1155) ◽  
pp. 446-468 ◽  
Keyword(s):  
Turbulent Flow ◽  
Capillary Tube ◽  
Resistance Coefficient ◽  
Mean Flow ◽  
Combined Action ◽  
Flow Through ◽  
The Mean ◽  
Coefficient Of Diffusion ◽  
Good Agreement ◽  
Made In

The dispersion of soluble matter introduced into a slow stream of solvent in a capillary tube can be described by means of a virtual coefficient of diffusion (Taylor 1953 a ) which represents the combined action of variation of velocity over the cross-section of the tube and molecluar diffusion in a radial direction. The analogous problem of dispersion in turbulent flow can be solved in the same way. In that case the virtual coefficient of diffusion K is found to be 10∙1 av * or K = 7∙14 aU √ γ . Here a is the radius of the pipe, U is the mean flow velocity, γ is the resistance coefficient and v * ‘friction velocity’. Experiments are described in which brine was injected into a straight 3/8 in. pipe and the conductivity recorded at a point downstream. The theoretical prediction was verified with both smooth and very rough pipes. A small amount of curvature was found to increase the dispersion greatly. When a fluid is forced into a pipe already full of another fluid with which it can mix, the interface spreads through a length S as it passes down the pipe. When the interface has moved through a distance X , theory leads to the formula S 2 = 437 aX ( v * / U ). Good agreement is found when this prediction is compared with experiments made in long pipe lines in America.

A theoretical study of viscous effects in peristaltic pumping

1994 ◽  
Vol 279 ◽  
pp. 177-195 ◽  
Author(s):  
Alden M. Provost ◽  
W. H. Schwarz
Keyword(s):  
Wave Propagation ◽  
Pressure Gradient ◽  
Flow Rate ◽  
Mean Flow ◽  
Viscous Effects ◽  
Transverse Waves ◽  
Peristaltic Pumping ◽  
Mean Pressure ◽  
Flow Through ◽  
The Mean

Intuition and previous results suggest that a peristaltic wave tends to drive the mean flow in the direction of wave propagation. New theoretical results indicate that, when the viscosity of the transported fluid is shear-dependent, the direction of mean flow can oppose the direction of wave propagation even in the presence of a zero or favourable mean pressure gradient. The theory is based on an analysis of lubrication-type flow through an infinitely long, axisymmetric tube subjected to a periodic train of transverse waves. Sample calculations for a shear-thinning fluid illustrate that, for a given waveform, the sense of the mean flow can depend on the rheology of the fluid, and that the mean flow rate need not increase monotonically with wave speed and occlusion. We also show that, in the absence of a mean pressure gradient, positive mean flow is assured only for Newtonian fluids; any deviation from Newtonian behaviour allows one to find at least one non-trivial waveform for which the mean flow rate is zero or negative. Introduction of a class of waves dominated by long, straight sections facilitates the proof of this result and provides a simple tool for understanding viscous effects in peristaltic pumping.

Oscillatory forcing of flow through porous media. Part 2. Unsteady flow

2002 ◽  
Vol 465 ◽  
pp. 237-260 ◽  
Author(s):  
D. R. GRAHAM ◽  
J. J. L. HIGDON
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Pressure Gradient ◽  
Flow Rate ◽  
Flow Through Porous Media ◽  
Mean Flow ◽  
Two Fluids ◽  
Mean Pressure ◽  
Flow Through ◽  
The Mean

Numerical computations are employed to study the phenomenon of oscillatory forcing of flow through porous media. The Galerkin finite element method is used to solve the time-dependent Navier–Stokes equations to determine the unsteady velocity field and the mean flow rate subject to the combined action of a mean pressure gradient and an oscillatory body force. With strong forcing in the form of sinusoidal oscillations, the mean flow rate may be reduced to 40% of its unforced steady-state value. The effectiveness of the oscillatory forcing is a strong function of the dimensionless forcing level, which is inversely proportional to the square of the fluid viscosity. For a porous medium occupied by two fluids with disparate viscosities, oscillatory forcing may be used to reduce the flow rate of the less viscous fluid, with negligible effect on the more viscous fluid. The temporal waveform of the oscillatory forcing function has a significant impact on the effectiveness of this technique. A spike/plateau waveform is found to be much more efficient than a simple sinusoidal profile. With strong forcing, the spike waveform can induce a mean axial flow in the absence of a mean pressure gradient. In the presence of a mean pressure gradient, the spike waveform may be employed to reverse the direction of flow and drive a fluid against the direction of the mean pressure gradient. Owing to the viscosity dependence of the dimensionless forcing level, this mechanism may be employed as an oscillatory filter to separate two fluids of different viscosities, driving them in opposite directions in the porous medium. Possible applications of these mechanisms in enhanced oil recovery processes are discussed.

Analysis of Heat Transfer and Fluid Flow Through a Spirally Fluted Tube Using a Porous Substrate Approach

1994 ◽  
Vol 116 (3) ◽  
pp. 543-551 ◽  
Author(s):  
Vijayaragham Srinivasan ◽  
Kambiz Vafai ◽  
Richard N. Christensen
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Porous Substrate ◽  
The Finite Element Method ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Friction Factors ◽  
Flow Through ◽  
Good Agreement

An innovative approach was opted for modeling the flow and heat transfer through spirally fluted tubes. The model divided the flow domain into two regions. The flutes were modeled as a porous substrate with direction-dependent permeabilities. This enabled modeling the swirl component in the fluted tube. The properties of the porous substrate such as its thickness, porosity, and ratio of the direction-dependent permeabilities were obtained from the geometry of the fluted tube. Experimental data on laminar Nusselt numbers and friction factors for different types of fluted tubes representing a broad range of flute geometry were available. Experimental data from a few of the tubes tested were used to propose a relationship between the permeability of the porous substrate and the flute parameters, particularly the flute spacing. The governing equations were discretized using the Finite Element Method. The model was verified and applied to the other tubes in the test matrix. Very good agreement was found between the numerical predictions and the experimental data.

scholarly journals Clogging Impacts on Distribution Pipe Delivery of Street Runoff to an Infiltration Bed

Water ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 1045 ◽  
Author(s):  
Min-Cheng Tu ◽  
Robert Traver
Keyword(s):  
Pressure Head ◽  
Analysis Of Covariance ◽  
Lower Section ◽  
Pipe Length ◽  
Maintenance Schedule ◽  
Satisfactory Performance ◽  
Mean Pressure ◽  
Flow Through ◽  
The Mean ◽  
Bed Clogging

The performance of flow through orifices on a perforated distribution pipe between periods with and without partial clogging (submersion of part of the distribution pipe) was compared. The distribution pipe receives runoff and delivers it to an underground infiltration bed. Clogging appeared in winter but was reduced in summer. Performance of flow delivery was found to be defined by the effective pipe length and the pressure head. ANCOVA (ANalysis of COVAriance) was used to examine the clogging effect with flow rate plotted against the effective pipe length times the square root of the mean pressure head, and found that it was significant during low or no rainfall. During larger storms, clogging had little effect on pipe performance. Clogging might be caused by leaves and other trash accumulating in the lower section of the pipe in winter and its effect was insignificant when the water level rose in the pipe, utilizing significantly more orifices on the distribution pipe. Larger storms might also move the debris, thus exposing the orifices. The current maintenance schedule was sufficient to keep the distribution pipe at a satisfactory performance even though partial clogging can exist.

The Design and Calculation of the Mooring System in Floating Body with Rope Wheel Device

2013 ◽  
Vol 361-363 ◽  
pp. 378-381
Author(s):  
Yan Gang Wang ◽  
Xing Hua Tong ◽  
Lin Sen Zhu ◽  
Yong Liu
Keyword(s):  
Potential Energy ◽  
Wave Energy ◽  
Low Cost ◽  
Floating Body ◽  
Mooring System ◽  
New Wave ◽  
Floating Structure ◽  
Energy Device ◽  
Key Technology ◽  
Energy Theory

Floating body with rope wheel structure is a new wave energy device, which is simple and low cost. Mooring system is the key technology of this device, which is use to limit the horizontal motion of the floating structure in the designated area. In this paper, potential energy theory has been used in the process of design and calculation of mooring system. Using the result of calculation, the motion of the floating body has been simulated numerically.

Numerical Predictions for the Flow Induced by an Enclosed Rotating Disc

1988 ◽  
Author(s):  
John W. Chew ◽  
Craig M. Vaughan
Keyword(s):  
Experimental Data ◽  
Reasonable Agreement ◽  
Mixing Length ◽  
Mean Flow ◽  
Rotating Disc ◽  
Numerical Predictions ◽  
Stationary Disc ◽  
The Mean ◽  
Radial Outflow ◽  
Good Agreement

Finite difference solutions are presented for turbulent flow in the cavity formed between a rotating and a stationary disc, with and without a net radial outflow of fluid. The mean flow is assumed steady and axisymmetric and a mixing length model of turbulence is used. Grid dependency of the solutions is shown to be acceptably small and results are compared with other workers’ experimental data. Theoretical and measured disc moment coefficients are in good agreement, while theoretical and measured velocities are in reasonable agreement. It is concluded that the mixing-length model is sufficiently accurate for many engineering calculations of boundary layer dominated flows in rotating disc systems.

An Approximate Analysis of the Unsteady Lift on Airfoils in Cascade

1972 ◽  
Vol 94 (4) ◽  
pp. 233-240 ◽  
Author(s):  
R. E. Henderson ◽  
J. H. Horlock
Keyword(s):  
Equations Of Motion ◽  
Lift Coefficient ◽  
Axial Flow ◽  
Frequency Parameter ◽  
Steady Flows ◽  
Approximate Analysis ◽  
Mean Pressure ◽  
Flow Through ◽  
The Mean ◽  
Unsteady Lift

An approximate analysis is presented for determining the unsteady lift on airfoils in moving cascades, subject to disturbances in the inlet axial flow. The equations of motion are averaged across the pitch, and the mean pressure in each channel and the pressure difference across it are obtained. The lift on a reference blade dividing two blade channels is then estimated. The analysis is limited to flows in which the frequency parameter based on blade pitch is small, and to blading of low lift coefficient. Comparisons are given with earlier analyses, for flow past isolated airfoils (Sears), for quasi-steady flows through cascades (Gearhart, et al.), and for flow through an actuator disk of small blade chord and flow through cascades of flat blades (Whitehead).

The plane Symmetric sudden-expansion flow at low Reynolds numbers

1993 ◽  
Vol 248 ◽  
pp. 567-581 ◽  
Author(s):  
F. Durst ◽  
J. C. F. Pereira ◽  
C. Tropea
Keyword(s):  
Maximum Flow ◽  
Reynolds Numbers ◽  
Sudden Expansion ◽  
Channel Height ◽  
Low Reynolds Numbers ◽  
Plane Symmetric ◽  
Numerical Predictions ◽  
Flow Through ◽  
Volume Method ◽  
Good Agreement

Detailed velocity measurements and numerical predictions are presented for the flow through a plane nominally two-dimensional duct with a Symmetric sudden expansion of area ratio 1:2. Both the experiments and the predictions confirm a symmetry-breaking bifurcation of the flow leading to one long and one short Separation zone for channel Reynolds numbers above 125, based on the upstream channel height and the maximum flow velocity upstream. With increasing Reynolds numbers above this value, the short separated region remains approximately constant in length whereas the long region increases in length.The experimental data were obtained using a one-component laser-Doppler anemometer at many Reynolds number values, with more extensive measurements being performed for the three Reynolds numbers 70, 300 and 610. Predictions were made using a finite volume method and an explicit quadratic Leith type of temporal discretization. In general, good agreement was found between measured and predicted velocity profiles for all Reynolds numbers investigated.

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