scholarly journals MODEL STUDIES OF IMPULSIVELY-GENERATED WATER WAVES

1966 ◽  
Vol 1 (10) ◽  
pp. 26 ◽  
Author(s):  
Jan M. Jordaan

The wave action due to a sudden impulse in a body of water was studied in a wave basin with beach in the laboratory. Waves were impulsively generated in the 90 ft. tank of water, 3 ft. deep, by the impact or sudden withdrawal of a paraboloidal plunger 14 ft. in diameter. The waves had a dominant height of 2 inches and period of 3 seconds, respectively, at a distance of 50 ft. from the plunger. Such waves are scale representations of those generated by sudden impulses in the ocean, such as an underwater nuclear explosion, a sudden change in the ocean bed due to earthquakes, or the impact of a land slide. The waves produced by a downward impulse, or by an underwater explosion, form a dispersive system: whose properties are not constant as in a uniform progressive wave train. Wave periodicities, celerities and wave lengths increase with time of travel and wave heights decrease with travel distance. Theory has already been developed to predict the wave properties at a given travel time and distance for given source energy, displacement and travel path depth profile (Jordaan 1965). Measurements agree fairly well with predictions.

1976 ◽  
Vol 1 (15) ◽  
pp. 45 ◽  
Author(s):  
Udo Berger ◽  
Soren Kohlhase

As under oblique wave approach water waves are reflected by a vertical wall, a wave branching effect (stem) develops normal to the reflecting wall. The waves progressing along the wall will steep up. The wave heights increase up to more than twice the incident wave height. The £jtudy has pointed out that this effect, which is usually called MACH-REFLECTION, is not to be taken as an analogy to gas dynamics, but should be interpreted as a diffraction problem.


According to linear theory the wave intensity of a slowly varying wave train becomes particularly large near caustics. In this paper it is shown how the waves are modified when the wave intensity is sufficient for nonlinear effects to begin to be important. Two types of near-linear caustics can arise in which nonlinearity either tends to advance or to retard the reflexion of waves from the caustic. General examples are given in terms of one-dimensional wave propagation, and of propagation in a uniform medium. Detailed consideration is given to a particular example: small-amplitude water waves on deep currents. This helps to provide an interpretative framework for the large-amplitude results presented in the companion paper (Peregrine & Thomas 1979). For the more exceptional case of triple roots, or cusped caustics, the increase in wave intensity is even more dramatic. In three appendices the analysis for caustics is extended to some higher-order cases.


1988 ◽  
Vol 197 ◽  
pp. 415-427 ◽  
Author(s):  
Bernard Le Méhauté

A theory for water waves created by the impact of small objects such as raindrops on an initially quiescent body of water is established. Capillary and dissipative viscous effects are taken into account in addition to gravity. It is shown that the prevailing waves are in a mixed capillary–gravity regime around a wavenumber km which corresponds to the minimum value of the group velocity. The waves are described as function of time and distance by the linear superposition of two transient wave components, a ‘sub-km’ (k < km) component and a ‘super-km’ (k > km) component. The super-km components prevail at a short distance from the drop, whereas only the sub-km ones remain at a larger distance. The relative time history of the wavetrain is independent of the size of the drop, and its amplitude is proportional to the drop momentum when it hits the free surface. The wave pattern is composed of a multiplicity of rings of amplitude increasing towards the drop location and is terminated by a trailing wave with an exponential decay. The number of rings increases with time and distance.


2000 ◽  
Vol 1 (2) ◽  
pp. 2
Author(s):  
J. W. Johnson

Wave diffraction is the phenomenon in which water waves are propagated into a sheltered region formed by a breakwater or similar barrier which interrupts a portion of a regular wave train (Fig. 1). The principles of diffraction have considerable practical application in connection with the design of breakwaters as discussed by Dunham (1951) at the Long Beach Conference. The phenomenon is analogous to the diffraction of light, sound, and electromagnetic waves. Two general types of diffraction problems usually are encountered: one, the passage of waves around the end of a semi-infinite impermeable breakwater (Putnam and Arthur, 1948), and, second, the passage of waves through a gap in a breakwater (Blue and Johnson, 1949t Carr and Stelzriede, 1951). In general, the theoretical solutions have been found to apply with conservative results, that is, the predicted wave heights in the lee of a breakwater are found to be slightly larger than the height of waves that may be expected under actual conditions. The use of the diffraction theory in breakwater design is made convenient when summarized in the form of diagrams with curves of equal values of diffraction coefficients on a coordinate system in which the origin of the Bystem is at the tip of a single breakwater (Figs. 2a-2b, and 3) or at the center of a gap (Figs. 2c, and 4-6). The diffraction coefficient in this instance is defined as the ratio of the diffracted wave height to the incident wave height and usually is designated by the symbol K». The procedure in preparing diffraction diagrams appears elsewhere (Johnson, 1950). The purpose of this paper is to present diffraction diagrams to supplement the material of Dunham (1951). For complete details on the application of diffraction diagrams to typical harbor problems the reader is referred to this latter paper.


Fluids ◽  
2021 ◽  
Vol 6 (3) ◽  
pp. 122
Author(s):  
Harvey Segur ◽  
Soroush Khadem

An ocean swell refers to a train of periodic or nearly periodic waves. The wave train can propagate on the free surface of a body of water over very long distances. A great deal of the current study in the dynamics of water waves is focused on ocean swells. These swells are typically created initially in the neighborhood of an ocean storm, and then the swell propagates away from the storm in all directions. We consider a different kind of wave, called seas, which are created by and driven entirely by wind. These waves typically have no periodicity, and can rise and fall with changes in the wind. Specifically, this is a two-fluid problem, with air above a moveable interface, and water below it. We focus on the local dynamics at the air-water interface. Various properties at this locality have implications on the waves as a whole, such as pressure differentials and velocity profiles. The following analysis provides insight into the dynamics of seas, and some of the features of these intriguing waves, including a process known as white-capping.


Author(s):  
Zhivelina Cherneva ◽  
M. Aziz Tayfun ◽  
C. Guedes Soares

Modulational instabilities induced by third-order nonlinear interactions among freely propagating waves can cause the statistics of various surface features to deviate significantly from the predictions based on the linear Gaussian and second-order models. This study analyzes deep-water waves simulated in a wave basin and characterized with such instabilities, and compares the statistics of the wave heights, crests and troughs amplitudes observed with a variety of theoretical approximations based on Gram-Charlier expansions. The results indicate that the theoretical approximations describe the empirical distributions observed reasonably well, for the most part. Further comparisons also show that the heights and crests of the largest waves do not exceed Miche-Stokes type upper limits.


Author(s):  
Xiaojing Niu ◽  
Yixiang Chen ◽  
Haojie Zhou

A moving atmospheric pressure disturbance can induce a system of forced water waves. As predicted by the linear theory, an infinite wave height will be induced when the Froude number Fr=1, which is known as the Proudman resonance. Fr is defined as the ratio between the moving speed of an atmospheric pressure disturbance and the phase velocity of shallow water wave. The Proudman resonance is thought to be one of main mechanisms for the destructive meteotsunami (Monserrat et al., 2006). In this study, the nonlinear shallow water equations are used to describe the waves induced by a moving pressure disturbance, and the impact factors to the maximum water elevation in the case of Fr=1 are discussed.


2021 ◽  
Author(s):  
Cormac Byrne ◽  
Ronadh Cox

&lt;p&gt;It is difficult to educate the public about geoscience and to create a message that will be heard in a noisy world. Coastal geoscience in particular&amp;#8212;despite its growing importance as sea-level rises and storminess increases&amp;#8212;has not penetrated effectively into the public sphere. High-energy coasts attract increasing numbers of visitors, most unaware of hazards related to stochastic wave behaviour. Photo-seekers in the Instagram era are driving up accidents in extreme environments, and it&amp;#8217;s increasingly common for people to be caught off guard and dragged into the ocean by rogue waves. Creative ways are needed to build awareness of the hazards, as well as the beauty, of high-energy coasts.&lt;/p&gt;&lt;p&gt;&quot;Drumming the Waves&quot;, a musical representation of wave interactions with boulder beaches, is an NSF-funded musician-geoscientist collaboration. Informed by the shared physics of sound and water waves, the composition will showcase how mutual interference among wave sets gives rise to chaotic seas, rogue waves, and ocean swell; and how waves can be amplified unpredictably in the coastal zone. Minimalist compositional techniques are employed to overlap and superimpose multiple series of small and seemingly inconsequential rhythmic and melodic musical events, leading to composite results that are unpredictable, sometimes chaotic, and occasionally extreme.&lt;/p&gt;&lt;p&gt;A visceral artistic approach helps capture the &amp;#8216;feeling&amp;#8217; of coastal waves and the impact of their interaction with boulder beaches, conveying sea states from serene calm to extreme chaos. Audio samples recorded at coastal locations in Ireland and the UK, both in air and beneath the ocean surface, are interwoven in the soundscape. We use wave sounds both in their natural audio state and in processed form. Creating new sounds by interacting field recordings of waves with electronic audio processers provides an artistic representation of the ubiquitous power and energy present in coastal environments. The temporal and erratic nature of coastal waves informs the musical structures on a macro level, exploring the contrast between the simple rhythm of tides and swell, and the irregular ephemerality of turbulent sea conditions. On a micro level, parallels between ocean and audio waves shapes are exploited to create novel musical events by shaping LFO (low frequency oscillator) and noise gates to mimic two-dimensional coastal wave models. Periodic emergence of unexpectedly large sound events mimics hazardous rogue wave generation.&lt;/p&gt;&lt;p&gt;We will build educational content around the music, to contextualise and explain it, and to draw attention specifically to boulder beaches, wave hazards, and the science of high-energy coasts. Simple worksheets showing wave spectra will be paired with percussion rhythms and melody that can be layered by students, either drumming and singing together, or mixing audio loops within a DAW (Digital Audio Workstation) such as GarageBand. This will permit students to build complex spectra from simple underlying wave forms. PowerPoint slides and explanatory text, pitched at the appropriate level, will be distributed to teachers for combined music/science learning. Using music to convey the science of wave interactions and wave amplification opens new doors and prospects for engaging and educating the public.&lt;/p&gt;


Author(s):  
Amy E. Nivette ◽  
Renee Zahnow ◽  
Raul Aguilar ◽  
Andri Ahven ◽  
Shai Amram ◽  
...  

AbstractThe stay-at-home restrictions to control the spread of COVID-19 led to unparalleled sudden change in daily life, but it is unclear how they affected urban crime globally. We collected data on daily counts of crime in 27 cities across 23 countries in the Americas, Europe, the Middle East and Asia. We conducted interrupted time series analyses to assess the impact of stay-at-home restrictions on different types of crime in each city. Our findings show that the stay-at-home policies were associated with a considerable drop in urban crime, but with substantial variation across cities and types of crime. Meta-regression results showed that more stringent restrictions over movement in public space were predictive of larger declines in crime.


2010 ◽  
Vol 67 (8) ◽  
pp. 2537-2546 ◽  
Author(s):  
John F. Scinocca ◽  
Bruce R. Sutherland

Abstract A new effect related to the evaluation of momentum deposition in conventional parameterizations of orographic gravity wave drag (GWD) is considered. The effect takes the form of an adjustment to the basic-state wind about which steady-state wave solutions are constructed. The adjustment is conservative and follows from wave–mean flow theory associated with wave transience at the leading edge of the wave train, which sets up the steady solution assumed in such parameterizations. This has been referred to as “self-acceleration” and it is shown to induce a systematic lowering of the elevation of momentum deposition, which depends quadratically on the amplitude of the wave. An expression for the leading-order impact of self-acceleration is derived in terms of a reduction of the critical inverse Froude number Fc, which determines the onset of wave breaking for upwardly propagating waves in orographic GWD schemes. In such schemes Fc is a central tuning parameter and typical values are generally smaller than anticipated from conventional wave theory. Here it is suggested that self-acceleration may provide some of the explanation for why such small values of Fc are required. The impact of Fc on present-day climate is illustrated by simulations of the Canadian Middle Atmosphere Model.


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