Skimming impacts and rebounds on shallow liquid layers

2010 ◽  
Vol 467 (2127) ◽  
pp. 653-674 ◽  
Author(s):  
Peter D. Hicks ◽  
Frank T. Smith
Keyword(s):  
Fluid Dynamics ◽  
Liquid Layer ◽  
Liquid Water ◽  
Close Agreement ◽  
Fluid Motion ◽  
Small Time ◽  
The Body ◽  
Time Behaviour ◽  
Time Analysis ◽  
Water Exit

The evolution of the combined solid–fluid motion when a solid body undergoes a skimming impact with (and rebounds from) a shallow liquid layer is investigated. A model is derived coupling the motion of the body to the fluid dynamics of the liquid layer. This predicts that the lift on the body induced by the pressure in the liquid layer is sufficient to entirely retard its incident downward motion before causing the body to rise out of the liquid. Water exit is predicted at a finite scaled time. Analysis for the small-time behaviour immediately after touchdown, and also as water exit is approached, shows close agreement with numerical prediction.

scholarly journals Skimming impacts and rebounds of smoothly shaped bodies on shallow liquid layers

2020 ◽  
Vol 124 (1) ◽  
pp. 41-73
Author(s):  
Ryan A. Palmer ◽  
Frank T. Smith
Keyword(s):  
Shallow Water ◽  
Liquid Layer ◽  
Contact Point ◽  
Water Layer ◽  
Small Time ◽  
The Body ◽  
Body Motion ◽  
Water Model ◽  
Initial Contact ◽  
Trailing Edge

Abstract Investigated in this paper is the coupled fluid–body motion of a thin solid body undergoing a skimming impact on a shallow-water layer. The underbody shape (the region that makes contact with the liquid layer) is described by a smooth polynomic curve for which the magnitude of underbody thickness is represented by the scale parameter C. The body undergoes an oblique impact (where the horizontal speed of the body is much greater than its vertical speed) onto a liquid layer with the underbody’s trailing edge making the initial contact. This downstream contact point of the wetted region is modelled as fixed (relative to the body) throughout the skimming motion with the liquid layer assumed to detach smoothly from this sharp trailing edge. There are two geometrical scenarios of interest: the concave case ($$C<0$$ C < 0 producing a hooked underbody) and the convex case ($$C > 0$$ C > 0 producing a rounded underbody). As C is varied the rebound dynamics of the motion are predicted. Analyses of small-time water entry and of water exit are presented and are shown to be broadly in agreement with the computational results of the shallow-water model. Reduced analysis and physical insights are also presented in each case alongside numerical investigations and comparisons as C is varied, indicating qualitative analytical/numerical agreement. Increased body thickness substantially changes the interaction structure and accentuates inertial forces in the fluid flow.

scholarly journals Fluid flow lifting a body from a solid surface

2018 ◽  
Vol 474 (2219) ◽  
pp. 20180286 ◽  
Author(s):  
Samire Balta ◽  
Frank T. Smith
Keyword(s):  
Numerical Study ◽  
Ground Effect ◽  
Flow Speed ◽  
Small Time ◽  
The Body ◽  
Thin Body ◽  
Time Analysis ◽  
Air Vehicle ◽  
Lift Off ◽  
Nonlinear Fluid

If a body is at rest on horizontal ground and a sudden horizontal flow of fluid is applied, the body either remains on the ground (rocking, rolling, sliding or spinning) or is lifted off impulsively. This lift-off is followed by a return to the ground or by a fly-away in the sense of continued departure from the ground. Related phenomena arise in the lift-off of an air vehicle from, effectively, moving ground. The present investigation seeks fairly precise mechanistic conditions under which lift-off and subsequent return or fly-away occur for a thin body or more generally for any thin gap of fluid between a body and the ground. Nonlinear fluid–solid interaction takes place in which the motion of the body and the surrounding fluid affect each other. Small-time analysis on lift-off and a numerical study are presented, followed by large-time analysis showing a critical flow speed for fly-away for any shape of the body. The changes in ground effect, from being dominant during lift-off to diminishing in fly-away, are explored together with relevant applications.

scholarly journals CONTRIBUTION TO THE STUDY OF SEDIMENT TRANSPORT ON A HORIZONTAL BED DUE TO WAVE ACTION

2011 ◽  
Vol 1 (6) ◽  
pp. 20 ◽  
Author(s):  
G. E. Vincent
Keyword(s):  
Boundary Layer ◽  
Wave Propagation ◽  
Sediment Transport ◽  
Liquid Velocity ◽  
Fluid Motion ◽  
Wave Action ◽  
The Body ◽  
Density Currents ◽  
Open Sea ◽  
Land Surfaces

With a view to explaining the phenomena of sediment transport in the open sea, outside the wave breaking area, the author carried out a laboratory investigation of wave action on a horizontal bed. He puts forward a number of new results regarding : 1 - The state of turbulence near the bed and the stability of the oscillatory laminar boundary layer. 2 - The setting in notion of materials under the influence of wave alone. 3 - The entrapment current caused by wave action close to the bed. 4 - The transport of material under wave action only. 5 - The indirect action of wave on the bed. The main conclusions reached are as follows : 1/ - The results given by Kuon Li regarding the onset of turbulence within the oscillatory boundary layer overestimate the range of laminar conditions. Vo (maximum orbital velocity) and e (roughness) are the principle factors governing the transition. Test waves are either generally laminar, or are only slightly turbulent within the body of liquid, but they are, however, more often turbulent in the immediate neighbourhood of the bed. 2/ - The Investigation of conditions for the onset of grain movement of the bed material shows that the action of wave can be appreciable, even at depths of several tens of metres. A wave of 6 metres amplitude, with a total length of 120 metres, would be capable of putting a 0.3 mm sand grain into motion at a depth of 60 metres. 3/ - The experimental investigation, as well as the viscous fluid theory, shows the existence, close to the bed, of an entrainment current of liquid particles which always works In the direction of wave propagation. 4/ - In test flumes, this entrainment current forms part of a mass transport within the liquid, the vertical distribution of which varies with the characteristics of the fluid motion. On a horizontal bed, It generally gives rise to an effective sediment transport, in the direction of wave propagation, as the preponderant part of the liquid velocity component, near the bed. is in this direction. 5/ - Owing to the existence of the pass transport current and the onset of suspension of material above the bed, some sediment transport can exist out to sea. These results give an explanation of why, under the action of long and regular wave . material tends to be carried in the direction of the waves and build up on the beach whereas, under storm conditions, a strong resultant turbulence produces suspension and favours erosion of the beach. 6/ - On a sloping bed, transport towards the shore is counterbalanced by the effect of gravity, currents caused by winds from seaward and density currents set up in the wave break area so that finally material eroded from land surfaces are, In part, gradually carried away towards the open sea.

Fluid dynamics of flapping aquatic flight in the bird wrasse:three-dimensional unsteady computations with fin deformation

2002 ◽  
Vol 205 (19) ◽  
pp. 2997-3008 ◽  
Author(s):  
Ravi Ramamurti ◽  
William C. Sandberg ◽  
Rainald Löhner ◽  
Jeffrey A. Walker ◽  
Mark W. Westneat
Keyword(s):  
Fluid Dynamics ◽  
Steady State ◽  
Three Dimensional ◽  
Force Production ◽  
Time History ◽  
The Body ◽  
Vertical Acceleration ◽  
Field Variation ◽  
Pectoral Fin ◽  
Pectoral Fins

SUMMARY Many fishes that swim with the paired pectoral fins use fin-stroke parameters that produce thrust force from lift in a mechanism of underwater flight. These locomotor mechanisms are of interest to behavioral biologists,biomechanics researchers and engineers. In the present study, we performed the first three-dimensional unsteady computations of fish swimming with oscillating and deforming fins. The objective of these computations was to investigate the fluid dynamics of force production associated with the flapping aquatic flight of the bird wrasse Gomphosus varius. For this computational work, we used the geometry of the wrasse and its pectoral fin,and previously measured fin kinematics, as the starting points for computational investigation of three-dimensional (3-D) unsteady fluid dynamics. We performed a 3-D steady computation and a complete set of 3-D quasisteady computations for a range of pectoral fin positions and surface velocities. An unstructured, grid-based, unsteady Navier—Stokes solver with automatic adaptive remeshing was then used to compute the unsteady flow about the wrasse through several complete cycles of pectoral fin oscillation. The shape deformation of the pectoral fin throughout the oscillation was taken from the experimental kinematics. The pressure distribution on the body of the bird wrasse and its pectoral fins was computed and integrated to give body and fin forces which were decomposed into lift and thrust. The velocity field variation on the surface of the wrasse body, on the pectoral fins and in the near-wake was computed throughout the swimming cycle. We compared our computational results for the steady, quasi-steady and unsteady cases with the experimental data on axial and vertical acceleration obtained from the pectoral fin kinematics experiments. These comparisons show that steady state computations are incapable of describing the fluid dynamics of flapping fins. Quasi-steady state computations, with correct incorporation of the experimental kinematics, are useful when determining trends in force production, but do not provide accurate estimates of the magnitudes of the forces produced. By contrast, unsteady computations about the deforming pectoral fins using experimentally measured fin kinematics were found to give excellent agreement, both in the time history of force production throughout the flapping strokes and in the magnitudes of the generated forces.

An integral-equation method for determining the fluid motion due to a cylinder heaving on water of finite depth

1980 ◽  
Vol 372 (1748) ◽  
pp. 93-110 ◽  
Keyword(s):  
Integral Equation ◽  
Fundamental Solution ◽  
Integral Equations ◽  
Fluid Motion ◽  
Integral Equation Method ◽  
Finite Depth ◽  
The Body ◽  
Wave Source ◽  
Method Of Integral Equations ◽  
Infinite Set

The method of integral equations is used here to calculate the virtual mass of a half-immersed cylinder heaving periodically on water of finite constant depth. For general sections this method is more appropriate than the method of multipoles; particular sections that are considered are the circle and the ellipse. Green’s theorem is applied to the potential and to a fundamental solution (wave source) satisfying the conditions at the free surface, at the bottom and at infinity, but not necessarily on the body. An integral equation for the potential on the body only is thus obtained. For the simplest choice of fundamental solution the method breaks down at a discrete infinite set of frequencies, as is well known. When the fundamental solution was modified, however, a different integral equation could be obtained for the same unknown function and this was found not to break down for the circle and ellipse. The present numerical results are in good agreement with those obtained by the method of multipoles which for the circle is more efficient than the method of integral equations but which is not readily applicable to other sections. Much effort now goes into such calculations.

scholarly journals Unsteady low Reynolds number flow in a heated tube of slowly varying section

1988 ◽  
Vol 30 (2) ◽  
pp. 179-202 ◽  
Author(s):  
A. R. Bestman
Keyword(s):  
Fluid Motion ◽  
The Body ◽  
Axial Component ◽  
Axial Distance ◽  
Mean Flow ◽  
Steady Streaming ◽  
Reynolds Number Flow ◽  
Number Flow ◽  
The Mean ◽  
Oscillatory Pressure

AbstractFluid motion established by an oscillatory pressure gradient superimposed on a mean, in a tube of slowly varying section, is studied when the temperature of the tube wall varies with axial distance. Particular attention is focussed on the mean flow and steady streaming components of the oscillatory flow of higher approximation. For the velocity components, the axial component takes the pride of place, since this component is responsible for convection of nutrients to various parts of the body of a mammal in systematic circulation. A salient point in the paper concerns consequences of free convection currents at a constriction (stenosis).

Ingestion Rates and Aspects of Water, Sodium and Energy Metabolism in Caged Swamp Buffalo, Bubalus Bubalis, From Isotope Dilution and Materials Balances.

1982 ◽  
Vol 30 (5) ◽  
pp. 779 ◽  
Author(s):  
CK Williams ◽  
B Green
Keyword(s):  
Body Mass ◽  
Close Agreement ◽  
Bubalus Bubalis ◽  
The Body ◽  
High Rate ◽  
Evaporative Heat Loss ◽  
Northern Australia ◽  
Water Turnover ◽  
Daily Rate ◽  
Swamp Buffalo

Exchanges of DM, sodium, water and energy were estimated on caged swamp buffalo of body mass (W) 297 plus or minus 13 kg. Estimates of feed ingestion estimated from rates of 22Na and 3H turnover were in close agreement with estimates from weighing. Tritium equilibrated in 6 h and 22Na in 12 h. Tritium space was 78.9 plus or minus 1.6% of body mass at 6 h and 83.9 plus or minus 1.1% at 24 h. The body pool of exchangable Na was 40.56 plus or minus 1.79 mmol/kg W at 12 h, and 44.62 plus or minus 2.12 mmol/kg W at 24 h. The daily rate of water turnover was 34.72 plus or minus 2.33 litres or 326.1 plus or minus 17.2 ml/kg W0.82, about three times that expected on the basis of body size, reflecting adaptation to a tropical swamp habitat. It was due mainly to the high rate of imbibition, 30.78 plus or minus 2.15 litres daily or 289.1 plus or minus 16.3 ml/kg W0.82 daily. Daily rates of water loss were partitioned as: faecal, 9.99 plus or minus 0.761 (94.1 plus or minus 7.0 ml/kg W0.82); urinary, 10.39 plus or minus 0.76 litres (98.2 plus or minus 7.6 ml/kg W0.82); pulmocutaneous, 14.34 plus or minus 1.37 litres (133.8 plus or minus 8.9 ml/kg W0.82). Swamp buffalo are unlikely to be able to satisfy their water requirements from food alone during the dry season in northern Australia. The daily rate of Na turnover was 6.29 plus or minus 0.41 mmol/kg W0.75. Na in the faeces was low, 8.3 plus or minus 0.9 mmol/kg dry faeces, indicating very effective alimentary absorption of Na. Apparent digestible energy intake (DE) per day for maintenance was about 651 plus or minus 41 kJ/kg W0.75. Daily rates of evaporative heat loss were high, 481 plus or minus 33 kJ/kg W0.75, exceeding the non-evaporative component of the DE, 321 plus or minus 35 kJ/kg W0.75; evaporative processes may have contributed to the high maintenance DE.

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