Perfect fluid forces in fish propulsion: the solution of the problem in an elliptic cylinder co-ordinate system

1961 ◽  
Vol 261 (1306) ◽  
pp. 316-328 ◽  
Keyword(s):  
Perfect Fluid ◽  
Elliptic Cylinder ◽  
Travelling Wave ◽  
Finite Width ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Fluid Forces ◽  
Low Aspect Ratio ◽  
Fish Propulsion ◽  
General Force

This paper is a discussion of perfect fluid forces involved in fish propulsion. First, the two-dimensional problem is solved in elliptic cylinder co-ordinates in which the surface, or strip μ = 0 is used to approximate a ‘fish’. A travelling wave with linearly increasing ampli­tude is imposed on the strip to represent the motion of the fish. The problem then is in­vestigated for a rigid strip of finite width oscillating about the forward end. Results of this calculation are used to correct the general force expression to the case of low aspect ratio. Experimental results are then discussed which verify the validity of the calculations.

On Elastodynamic Diffraction of Waves From a Line-Load by a Crack

1984 ◽  
Vol 51 (2) ◽  
pp. 335-338 ◽  
Author(s):  
A. K. Gautesen
Keyword(s):  
Plane Wave ◽  
Simple Relation ◽  
Finite Width ◽  
Far Field ◽  
Angle Of Incidence ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Line Load ◽  
Fixed Angle ◽  
Plane Wave Incident

For the two-dimensional problem of elastodynamic diffraction of waves by a crack of finite width, we assume that the solution corresponding to incidence of a plane wave of either longitudinal or transverse motions under a fixed angle of incidence is known. We first show how to construct the solution corresponding to an in-plane line-load (the Green’s function) from this known solution. We then give a simple relation between the far field scattering patterns corresponding to a plane wave incident under any angle and the far field scattering patterns corresponding to the known solution. This relation is a generalization of the principle of reciprocity.

Modifications of the Godunov method for computing disturbance propagation in an elastic body

2016 ◽  
Vol 11 (1) ◽  
pp. 119-126 ◽  
Author(s):  
A.A. Aganin ◽  
N.A. Khismatullina
Keyword(s):  
Elastic Body ◽  
Godunov Method ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Order Accuracy ◽  
One Dimensional ◽  
Disturbance Propagation ◽  
Linear Waves ◽  
Longitudinal And Shear Waves ◽  
Contact Discontinuities

Numerical investigation of efficiency of UNO- and TVD-modifications of the Godunov method of the second order accuracy for computation of linear waves in an elastic body in comparison with the classical Godunov method is carried out. To this end, one-dimensional cylindrical Riemann problems are considered. It is shown that the both modifications are considerably more accurate in describing radially converging as well as diverging longitudinal and shear waves and contact discontinuities both in one- and two-dimensional problem statements. At that the UNO-modification is more preferable than the TVD-modification because exact implementation of the TVD property in the TVD-modification is reached at the expense of “cutting” solution extrema.

The Two-dimensional Problem with Free Boundary in Problems of Medicine

2021 ◽  
Author(s):  
Fatimat Kh. Kudayeva ◽  
Aslan Kh. Zhemukhov ◽  
Aslan L. Nagorov ◽  
Arslan A. Kaygermazov ◽  
Diana A. Khashkhozheva ◽  
...  
Keyword(s):  
Free Boundary ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Problem With Free Boundary

Two-dimensional buoyant plumes in a uniform co-flow

2021 ◽  
Vol 932 ◽  
Author(s):  
Gary R. Hunt ◽  
Jamie P. Webb
Keyword(s):  
Theoretical Investigation ◽  
Analytical Solutions ◽  
Richardson Number ◽  
Relative Magnitude ◽  
Dynamical Behaviour ◽  
Finite Width ◽  
Two Dimensional ◽  
Buoyant Plumes ◽  
The Subject ◽  
Flow Case

The behaviour of turbulent, buoyant, planar plumes is fundamentally coupled to the environment within which they develop. The effect of a background stratification directly influences a plumes buoyancy and has been the subject of numerous studies. Conversely, the effect of an ambient co-flow, which directly influences the vertical momentum of a plume, has not previously been the subject of theoretical investigation. The governing conservation equations for the case of a uniform co-flow are derived and the local dynamical behaviour of the plume is shown to be characterised by the scaled source Richardson number and the relative magnitude of the co-flow and plume source velocities. For forced, pure and lazy plume release conditions the co-flow acts to narrow the plume and reduce both the dilution and the asymptotic Richardson number relative to the classic zero co-flow case. Analytical solutions are developed for pure plumes from line sources, and for highly forced and highly lazy releases from sources of finite width in a weak co-flow. Contrary to releases in quiescent surroundings, our solutions show that all classes of release can exhibit plume contraction and the associated necking. For entraining plumes, a dynamical invariance spatially only occurs for pure and forced releases and we derive the co-flow strengths that lead to this invariance.

scholarly journals The influence of vortices upon the resitance experienced by solids moving through a liquid

1928 ◽  
Vol 119 (781) ◽  
pp. 146-156 ◽  
Keyword(s):  
Perfect Fluid ◽  
Relative Motion ◽  
Constant Velocity ◽  
Fluid Motion ◽  
Resultant Force ◽  
The Other ◽  
Two Dimensional ◽  
Perfect Fluids ◽  
Potential Problems ◽  
The Moment

(1) It is not so long ago that it was generally believed that the "classical" hydrodynamics, as dealing with perfect fluids, was, by reason of the very limitations implied in the term "perfect," incapable of explaining many of the observed facts of fluid motion. The paradox of d'Alembert, that a solid moving through a liquid with constant velocity experienced no resultant force, was in direct contradiction with the observed facts, and, among other things, made the lift on an aeroplane wing as difficult to explain as the drag. The work of Lanchester and Prandtl, however, showed that lift could be explained if there was "circulation" round the aerofoil. Of course, in a truly perfect fluid, this circulation could not be produced—it does need viscosity to originate it—but once produced, the lift follows from the theory appropriate to perfect fluids. It has thus been found possible to explain and calculate lift by means of the classical theory, viscosity only playing a significant part in the close neighbourhood ("grenzchicht") of the solid. It is proposed to show, in the present paper, how the presence of vortices in the fluid may cause a force to act on the solid, with a component in the line of motion, and so, at least partially, explain drag. It has long been realised that a body moving through a fluid sets up a train of eddies. The formation of these needs a supply of energy, ultimately dissipated by viscosity, which qualitatively explains the resistance experienced by the solid. It will be shown that the effect of these eddies is not confined to the moment of their birth, but that, so long as they exist, the resultant of the pressure on the solid does not vanish. This idea is not absolutely new; it appears in a recent paper by W. Müller. Müller uses some results due to M. Lagally, who calculates the resultant force on an immersed solid for a general fluid motion. The result, as far as it concerns vortices, contains their velocities relative to the solid. Despite this, the term — ½ ρq 2 only was used in the pressure equation, although the other term, ρ ∂Φ / ∂t , must exist on account of the motion. (There is, by Lagally's formulæ, no force without relative motion.) The analysis in the present paper was undertaken partly to supply this omission and partly to check the result of some work upon two-dimensional potential problems in general that it is hoped to publish shortly.

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