Modulation of short waves by long waves

1978 ◽  
Vol 13 (1-4) ◽  
pp. 203-214 ◽  
Author(s):  
Allan M. Reece
Keyword(s):  
Long Waves ◽  
Short Waves

scholarly journals EROSION AROUND A PILE DUE TO CURRENT AND BREAKING WAVES

1988 ◽  
Vol 1 (21) ◽  
pp. 102 ◽  
Author(s):  
E.W. Bijker ◽  
C.A. De Bruyn
Keyword(s):  
Shear Stress ◽  
Breaking Waves ◽  
Velocity Profiles ◽  
Long Waves ◽  
Orbital Velocity ◽  
Bottom Shear Stress ◽  
Normal Waves ◽  
Short Waves ◽  
A Current

Tests have been performed on a vertical pile subject to current only and to a combination of current with normal waves and current with breaking waves. The scour around the pile produced by current only is decreased by normal short waves superimposed upon that current and increased when breaking waves are superimposed upon the current. After analysis of the velocity profiles in the undisturbed area upstream of the pile and next to the pile, the following explanation is found for this phenomenon. When normal short waves are superimposed upon a current, the bottom shear stress of the combination of current with waves is increased more in the undisturbed area than next to the pile in the scour area. This results in a decrease of the scour around the pile. Due to the large values of the orbital velocity under breaking waves this effect is reversed for the combination of a current with breaking and relatively long waves. This results in an increase of the scour around the pile.

The Propagation of Compressional Waves in a Dispersive Elastic Rod: Part II—Experimental Results and Comparison With Theory

1957 ◽  
Vol 24 (2) ◽  
pp. 240-244
Author(s):  
Julius Miklowitz ◽  
C. R. Nisewanger
Keyword(s):  
Shock Tube ◽  
Longitudinal Mode ◽  
Long Waves ◽  
Experimental Results ◽  
Radial Mode ◽  
Approximate Representation ◽  
Elastic Rod ◽  
Compressional Waves ◽  
Short Waves

Abstract Experimental results, obtained by employing an aerodynamic shock tube for rod excitation, are presented. Comparison of these results with the theoretical information presented in Part I is made. It is shown that the Mindlin-Herrmann theory, through its upper mode (radial), offers a good approximate representation of the moderately short waves that predominate at the later times at a random station of the rod. The very short waves of this same radial mode, however, govern the early disturbance, thus precluding the possibility of representing this portion of the disturbance, which the experiment shows to be composed of relatively long waves, by the longitudinal mode of the theory.

Long waves induced by short-wave groups over an uneven bottom

1984 ◽  
Vol 139 ◽  
pp. 219-235 ◽  
Author(s):  
Chiang C. Mei ◽  
Chakib Benmoussa
Keyword(s):  
Group Velocity ◽  
Short Wave ◽  
Long Waves ◽  
Finite Region ◽  
Variable Depth ◽  
Wave Groups ◽  
One Dimensional ◽  
Uneven Bottom ◽  
Short Waves ◽  
Horizontal Bottom

Unidirectional and periodically modulated short waves on a horizontal or very nearly horizontal bottom are known to be accompanied by long waves which propagate together with the envelope of the short waves at their group velocity. However, for variable depth with a horizontal lengthscale which is not too great compared with the group length, long waves of another kind are further induced. If the variation of depth is only one-dimensional and localized in a finite region, then the additional long waves can radiate away from this region, in directions which differ from those of the short waves and their envelopes. There are also critical depths which define caustics for these new long waves but not for the short waves. Thus, while obliquely incident short waves can pass over a topography, these second-order long waves may be trapped on a ridge or away from a canyon.

Surface Oscillations of Water in a Rotating Cylindrical Vessel

1930 ◽  
Vol 26 (4) ◽  
pp. 446-452 ◽  
Author(s):  
R. O. Street
Keyword(s):  
Circular Cylinder ◽  
Surface Waves ◽  
Cross Section ◽  
Circular Cross Section ◽  
Cylindrical Vessel ◽  
Long Waves ◽  
Horizontal Velocity ◽  
Uniform Rotation ◽  
Tidal Waves ◽  
Short Waves

This paper is devoted chiefly to the consideration of the surface oscillations of water contained in a vessel in the shape of a circular cylinder with its axis vertical, when the motion is slightly disturbed from a uniform rotation about the axis of the vessel. The work was undertaken with the hope of finding some indication of the effect of the depth of the water in the vessel on the period of the surface waves, and for the purpose a vessel of circular cross-section was naturally chosen. It is shown that a slight change of shape does not affect the periods of the oscillations. The solution of the corresponding problem when the surface oscillations take the form of “long waves” or “tidal waves” is well known, and the present paper deals only with “short waves,” for which the horizontal velocity is not the same at all depths.

scholarly journals On the action of tuned rectangular frame aerials when receiving short waves

1932 ◽  
Vol 136 (829) ◽  
pp. 193-209 ◽  
Keyword(s):  
Wave Length ◽  
Long Waves ◽  
Direct Component ◽  
Short Waves ◽  
Rectangular Frame ◽  
Critical Areas ◽  
Two Component ◽  
Maximum Current ◽  
Mutual Action

Some preliminary experiments in 1927 showed that the maximum current produced by the incidence of short wireless waves on a tuned rectangular frame aerial was very critically dependent on the dimensions of the frame. An increase or decrease in the width or height of the frame by only a few centimetres might change the current many hundred fold, such current variations being quite independent of the tuning. Furthermore the reduction of current caused by, say, a decrease in the frame width could be compensated by an increase in the frame height and vice versa , but the changes in dimensions were not equal in magnitude, neither was their product a constant. In fact, the maximum current depended on the shape of the frame and also varied irregularly with the area. For a given wave-length there were certain critical areas for maximum current, and doubling the area of a frame did not quadruple the current (as when receiving long waves) but the current was reduced to one of negligible magnitude, although the frame was kept properly tuned. It was found that these anomalous effects could be explained by taking into consideration, not only the action of the passing wave, but also the mutual action between the currents flowing in adjacent parts of the frame. In order to do this, it is convenient to consider the current in any limb as the resultant of two component currents ; namely a “direct” component due to the incidence of the wave on the particular limb, and an “indirect” component due to the effects of the currents in adjacent limbs. These two components will, in general, differ in phase and amplitude, and the problem reduces to the determination of those conditions which tend to produce the maximum resultant current.

A nonlinear mechanism for the generation of sea waves

1969 ◽  
Vol 311 (1506) ◽  
pp. 371-389 ◽  
Keyword(s):  
Wave Propagation ◽  
Surface Waves ◽  
Orbital Motion ◽  
Long Waves ◽  
Shear Instability ◽  
Sea Waves ◽  
Short Waves ◽  
Long Wave ◽  
Nonlinear Mechanism ◽  
Surrounding Fluid

Recent observations of the growth of sea waves under the action of wind have established that the rate of growth is several times greater than has yet been accounted for. In this paper a new mechanism of wave generation is proposed, based on the idea of a maser-like action of the short waves on the longer waves. It is shown that when surface waves decay they impart their momentum to the surrounding fluid. Short waves are readily regenerated by shear instability. But a longer wave passing through shorter waves causes the short waves to steepen on the long-wave crests. Hence the short waves impart more of their momentum to the crests of the long waves, where the orbital motion of the long waves is in the direction of wave propagation. If the short waves are decaying only weakly (under the action of viscosity), the effect on the long waves is slight. But when the short waves are forced to decay strongly by breaking on the forward slopes of the long waves the gain of energy by the latter is greatly increased. Calculations suggest that the mechanism is capable of imparting energy to sea waves at the rate observed.

The dependency of inshore long waves on the characteristics of offshore short waves

1988 ◽  
Vol 12 (3) ◽  
pp. 213-231 ◽  
Author(s):  
R.C. Nelson ◽  
P.D. Treloar ◽  
N.V. Lawson
Keyword(s):  
Long Waves ◽  
Short Waves

Long Waves—Short Waves; A Solvable Model

1978 ◽  
Vol 35 (4) ◽  
pp. 650-664 ◽  
Author(s):  
Alan C. Newell
Keyword(s):  
Solvable Model ◽  
Long Waves ◽  
Short Waves

Observations on long waves sweeping through short waves

Tellus ◽  
1971 ◽  
Vol 23 (4-5) ◽  
pp. 364-370 ◽  
Author(s):  
JIN WU
Keyword(s):  
Long Waves ◽  
Short Waves
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