scholarly journals EFFECTS OF WAVE GROUPING ON BREAKWATER STABILITY

1978 ◽  
Vol 1 (16) ◽  
pp. 134 ◽  
Author(s):  
R.R. Johnson ◽  
E.P.D. Mansard ◽  
J. Ploeg
Keyword(s):  
Wave Train ◽  
Similar Degree ◽  
New Wave ◽  
Wave Groups ◽  
Model Scale ◽  
Correct Model ◽  
Rubble Mound

It has been found that certain sequences of waves, such as occurring within well defined wave groups, can cause greater damage to rubble mound structures, than equally high individual waves dispersed throughout a wave train. It has therefore been necessary to develop a new wave synthesizing technique, which allows control of the phasing of the wave frequencies, so that a similar degree of wave grouping can be produced in the laboratory as is expected to occur at a particular location in the prototype. Also, during the course of this investigation, an attempt was made to simulate the strength of concrete armour units to the correct model scale. The breaking of armour units, due to their rocking or being displaced, resulted in a much higher percentage of damage, than would have been possible to predict from tests with commonly used model armour units.

Alternative Methodologies for Subsea Flexible Strength Analysis

2018 ◽  
Author(s):  
Anskey A. Miranda ◽  
Fred P. Turner ◽  
Nigel Barltrop
Keyword(s):  
Real World ◽  
Wave Train ◽  
Irregular Waves ◽  
Wave Crest ◽  
Strength Analysis ◽  
New Wave ◽  
Regular Wave ◽  
Wave Analysis ◽  
Sea State ◽  
Irregular Wave

This paper presents a study of the analysis methodologies used to predict the most likely response of flexibles in a subsea environment, with the aim of determining an efficient and reliable prediction methodology. The most accurate method involves simulating multiple wave realisations of a real world sea state, i.e. irregular waves, and post-processing the results to determine the most probable maximum (MPM). Due to the computationally intensive nature of this approach, however, regular wave analysis is typically used to determine flexible response. This approach considers the maximum wave within a design storm at a desired period; the choice of periods may leave room for uncertainty in the conservatism of the approach. With proper screening, regular wave analysis can be a valid yet overly conservative approach resulting in over design and additional cost. However, if screened incorrectly, there is a possibility that the choice of periods could give results that are under conservative. In addition to regular wave analysis, the paper presents two alternative methodologies to determine the most likely response, with the focus on reducing the computational resources required. The first alternative is an ‘Irregular Wave Screen’ approach in which the wave train is screened at areas of interest for waves within a user defined threshold of the maximum wave height, in addition to other user defined parameters. Only waves within these parameters are simulated to determine responses. The second alternative is the ‘New Wave’ approach, which models the most probable wave elevation around the maximum wave crest. The calculated new wave is then placed at the desired location to determine responses. The responses of the Regular, Irregular Wave Screen and New Wave methodologies are compared with the Irregular MPM approach to determine their feasibility to predict the response of flexibles in a real world irregular sea state with lower computational requirements.

scholarly journals The Topos of Childhood in Modern Poetry (1939–1989)

2020 ◽  
Vol nr specjalny 1(2020) ◽  
pp. 364-394
Author(s):  
Robert Mielhorski ◽  
Keyword(s):  
20Th Century ◽  
New Wave ◽  
Wave Groups ◽  
Polish Literature ◽  
Research Paradigms ◽  
Political Events ◽  
The World ◽  
Literary Process ◽  
Poetic Texts

The paper problematises the literary image of childhood in poetry in relation to external historical and socio-political events. The material analysed covers Polish poetry from 1939 – 1989 (a clearly distinguished segment of the historical-literary process). The choice and ordering of the case studies results from the application of two research paradigms: (i) the paradigm concerned with autobiographical motifs, which refers to such topics of 20th century writings as exile (poetry of return by Łobodowski, Wierzyński etc.) immigration (nostalgic [pansentimentalism] and emotionally neutral motifs), Holocaust (motifs of fear, division between now and then, the role of imagination) and (ii) a generation-related paradigm, which allows us to follow the topos of childhood viewed from the perspective of history according to the order of generations entering Polish literature (from the 1920 Generation to the New Wave Groups) up to the succession of consecutive literary trends in the second half of the 20th century (e.g. soc-realism and soc-plans). Poetic texts concerning childhood in the light of history are viewed as records of “rites of passage” operating from the child’s phase of the pre-personalisation area – the child’s sense of being one with the world, experiencing the harmony of being – to the period of personalisation – when history leaves its mark on this period; characterised by the sense of one’s distinctiveness from reality, individual alienation, the need for rationalisation of one’s own existence and the existence of the surrounding reality. The role of history is to lead the child from the pre-personalistic period to the experience of personalisation.

Drifting Rogue Packets

2018 ◽  
Author(s):  
Amin Chabchoub ◽  
Norbert Hoffmann ◽  
Nail Akhmediev ◽  
Takuji Waseda
Keyword(s):  
Modulation Instability ◽  
Wave Train ◽  
Modulation Frequency ◽  
Phase Speed ◽  
Periodic Wave ◽  
Unstable Wave ◽  
Extreme Waves ◽  
Wave Groups ◽  
The Waves ◽  
Good Agreement

Modulation instability (MI) is one possible mechanism to explain the formation of extreme waves in uni-directional and narrow-banded seas. It can be triggered, when side-bands around the main frequency are excited and subsequently follow an exponential growth. In physical domain this dynamics translates to periodic pulsations of wave groups that can reach heights up to three times the initial amplitude of the wave train. It is well-known that these periodic wave groups propagate with approximately half the waves phase speed in deep-water. We report an experimental study on modulationally unstable wave groups that propagate with a velocity that is higher than the group velocity since the modulation frequency is complex. It is shown that when this additional velocity to the wave groups is small a good agreement with exact nonlinear Schrödinger (NLS) models, that describe the nonlinear stage of MI, is reached. Otherwise a significant deviation is observed that could be compensated when increasing accuracy of the water wave modeling beyond NLS.

Forecast of Critical Wave Groups From Surface Elevation Snapshots

2007 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Daniel Testa ◽  
Sascha Kosleck ◽  
Robert Stu¨ck
Keyword(s):  
Wave Train ◽  
Wave Length ◽  
Wave Spectrum ◽  
Amplitude Spectrum ◽  
Response Spectra ◽  
Phase Spectrum ◽  
Surface Elevation ◽  
Fast Fourier Transformation ◽  
Wave Groups ◽  
The Impact

Reports on damages of ships, cargo and structures during heavy seas have been increasing within the last years. The impact of single extreme waves or wave groups on marine structures and ships causes enormous forces often leading to critical situations or even loss of crew, ship and cargo. Dangerous situations can be predicted by a forecast of encountering wave trains and the identification of critical wave groups. The paper presents a method to calculate the wave train a ship will encounter from surface elevation snapshots of the surrounding sea, taken by the ship radar. The time-dependent surface elevation snapshot far ahead of the ship is transferred into frequency domain by the use of Fast Fourier Transformation (FFT). The resulting complex Fourier spectrum given over the inverse wave length 1/L is converted into an amplitude spectrum and a phase spectrum. By shifting the phase spectrum to the position of the cruising ship the encountering waves can in turn be calculated in advance — depending on speed. The permanent processing of incoming snapshots delivers a continuous prediction of the water surface elevation at the position of the cruising ship. Based on these data the expected ship motion behaviour can be calculated continuously in time domain. In addition the response spectra, resulting from the wave spectrum and the relevant RAOs, are also evaluated. As wave data far ahead of the ship are used, it allows a forward glance, and dangerous situations, particularly resonance and parametric resonance are detectable before the ship is encountering this wave train. Consequently, the procedure can be used by the master as an assistance support system.

Experimental Variation of Focusing Wave Groups for the Investigation of Their Predictability

2009 ◽  
Author(s):  
Janou Hennig ◽  
Christian E. Schmittner
Keyword(s):  
Deterministic Model ◽  
Focal Point ◽  
Wave Train ◽  
Wave Crest ◽  
Intermediate Water ◽  
Test Results ◽  
Wave Groups ◽  
Experimental Variation ◽  
Wave Phase Velocity ◽  
Target Wave

In deterministic model testing, focusing wave groups are used for the simulation of dedicated wave environments. They are characterized by the transient appearance of one relatively steep wave crest. The phasing of the wave components which leads to an exact focusing in one point in time and space is strongly dependent on the correct modeling of the wave phase velocity while the position of the focusing point depends on the wave group celerity. For wave generation purposes, the calculation of a wave maker control signal based on a target wave train at a desired position in the tank (inverse or backward modeling) is of crucial importance. Numerical wave tanks and empirical approaches are often calibrated based on wave characteristics measured in a particular tank. This paper presents model test results for the variation of frequency range, steepness and focal point of focusing wave groups at intermediate water depth. The measured characteristics are compared to predicted parameters.

scholarly journals On the Rapid Spectral Evolution of Steep Wave Groups with Directional Spreading at Intermediate Depths

2020 ◽  
Author(s):  
Dylan Barratt ◽  
Harry B. Bingham ◽  
Paul H. Taylor ◽  
Ton S. van den Bremer ◽  
Thomas A. A. Adcock
Keyword(s):  
Wave Train ◽  
Three Dimensional ◽  
Finite Depth ◽  
Wave Group ◽  
Spectral Evolution ◽  
Wave Groups ◽  
Return Current ◽  
Resonant Interactions ◽  
Energy Transfers ◽  
Steep Wave

<p>We have performed numerical simulations of steep three-dimensional wave groups, formed by dispersive focusing, using the fully-nonlinear potential flow solver <em>OceanWave3D</em>. We find that third-order resonant interactions result in directional energy transfers to higher-wavenumber components, forming steep wave groups with augmented kinematics and a prolonged lifespan. If the wave group is initially narrow banded, <em>quasi-degenerate interactions</em> resembling the instability band of a regular wave train arise, characterised by unidirectional energy transfers and energy transfers along the resonance angle, ±35.26°, of the Phillips ‘figure-of-eight’ loop. Spectral broadening due to the quasi-degenerate interactions eventually facilitates <em>non-degenerate interactions</em>, which dominate the spectral evolution of the wave group after focus. The non-degenerate interactions manifest primarily as a high-wavenumber sidelobe, which forms at an angle of ±55° to the spectral peak. We consider finite-depth effects in the range of deep to intermediate waters (5.592 ≥ <em>k<sub>p</sub>d</em> ≥ 1.363), based on the characteristic wavenumber (<em>k<sub>p</sub></em>) and the domain depth (<em>d</em>), and find that all forms of spectral evolution are suppressed by depth. However, the quasi-degenerate interactions exhibit a greater sensitivity to depth, suggesting suppression of the modulation instability by the return current, consistent with previous studies. We also observe sensitivity to depth for <em>k<sub>p</sub>d</em> values commonly considered "deep", indicating that the length scales of the wave group and return current may be better indicators of dimensionless depth than the length scale of any individual wave component. The non-degenerate interactions appear to be depth resilient with persistent evidence of a ±55° spectral sidelobe at a depth of <em>k<sub>p</sub>d</em> =1.363. Although the quasi-degenerate interactions are significantly suppressed by depth, the interactions do not entirely disappear for <em>k<sub>p</sub>d</em> =1.363 and show signs of biasing towards oblique, rather than unidirectional, wave components at intermediate depths. The contraction of the wavenumber spectrum in the <em>k<sub>y</sub></em>-direction has also proved to be resilient to depth, suggesting that lateral expansion of the wave group and the "wall of water" effect of Gibbs & Taylor (2005) may persist at intermediate depths.</p>

scholarly journals On the interaction of wind and steep gravity wave groups using Miles' and Jeffreys' mechanisms

2008 ◽  
Vol 15 (6) ◽  
pp. 1023-1031 ◽  
Author(s):  
J. Touboul ◽  
C. Kharif ◽  
E. Pelinovsky ◽  
J.-P. Giovanangeli
Keyword(s):  
Wave Packet ◽  
Physical Model ◽  
Linear Theory ◽  
Water Wave ◽  
Wave Train ◽  
Wave Group ◽  
Fully Nonlinear Equations ◽  
Wave Groups ◽  
Nonlinear Approach ◽  
Steep Wave

Abstract. The interaction of wind and water wave groups is investigated theoretically and numerically. A steep wave train is generated by means of dispersive focusing, using both the linear theory and fully nonlinear equations. The linear theory is based on the Schrödinger equation while the nonlinear approach is developed numerically within the framework of the potential theory. The interaction between the chirped wave packet and wind is described by the Miles' mechanism. The differences between both approaches are discussed, and the influence of nonlinearity is emphasized. Furthermore, a different mechanism is considered, described by the modified Jeffreys' sheltering theory. From comparison between the two mechanisms, it is found that the persistence of the steep wave group depends on the physical model used, and is significantly increased when we use the latter mechanism.

A theory of the origin of microseisms

1950 ◽  
Vol 243 (857) ◽  
pp. 1-35 ◽  
Keyword(s):  
Wave Train ◽  
Wave Length ◽  
Ocean Waves ◽  
Pressure Variation ◽  
Second Order ◽  
Stokes Wave ◽  
Wave Groups ◽  
Infinite Depth ◽  
First Order ◽  
Sea Bed

In the past it has been considered unlikely that ocean waves are capable of generating microseismic oscillations of the sea bed over areas of deep water, since the decrease of the pressure variations with depth is exponential, according to the first-order theory generally used. However, it was recently shown by Miche that in the second approximation to the standing wave there is a second-order pressure variation which is not attenuated with depth and which must therefore ultimately predominate over the first-order pressure variations. In §§ 2 and 3 of the present paper the general conditions under which second-order pressure variations of this latter type will occur are considered. It is shown that in an infinite wave train there is in general a second-order pressure variation at infinite depth which is applied equally over the whole fluid and is associated with no particle motion. In the case of two progressive waves of the same wave-length travelling in opposite directions this pressure variation is proportional to the product of the (first-order) amplitudes of the two waves and is of twice their frequency. The pressure variation at infinite depth is found to be closely related to changes in the potential energy of the wave train as a whole. By introducing the two-dimensional frequency spectrum of the motion it is shown that in the general case variations in the mean pressure over a wide area only occur when the spectrum contains wave groups of the same wave-length travelling in opposite directions. (These are called opposite wave groups.) In § 4 the effect of the compressibility of the water is considered by evaluating the motion of an opposite pair of waves in a heavy compressible fluid to the second order of approximation. In place of the pressure variation at infinite depth, waves of compression are set up, and there is resonance between the bottom and the free surface when the depth of water is about (1/2 n + 1/4) times the length of a compression wave ( n being an integer). The motion in a surface layer whose thickness is of the order of the length of a Stokes wave is otherwise unaffected by the compressibility. Section 5 is devoted to the question whether the second-order pressure variations in surface waves are capable of generating microseisms of the observed order of magnitude. By considering the displacement of the sea bed due to a concentrated force at the upper surface of the water it is shown that the effect of resonance will be to increase the disturbance by a factor of the order of 5 over its value in shallow water. The results of §§ 3 and 4 are used to derive an expression for the vertical displacement of the ground in terms of the frequency characteristics of the waves. The displacement from a storm area of 1000 sq.km, is estimated to be of the order of 6.5μ at a distance of 2000 km. Ocean waves may therefore be the cause of microseisms, provided that there is interference between groups of waves of the same frequency travelling in opposite directions. Suitable conditions of wave interference may occur at the centre of a cyclonic depression or possibly if there is wave reflexion from a coast. In the latter case the microseisms are likely to be smaller, except perhaps locally. Confirmation of the present theory is provided by the observations of Bernard and Deacon, who discovered independently that the period of the microseisms is in many cases about half that of the ocean waves associated with them.

scholarly journals Generation, Transformation, and Scattering of Long Waves Induced by a Short-Wave Group over Finite Topography

2011 ◽  
Vol 41 (10) ◽  
pp. 1842-1859 ◽  
Author(s):  
Qingping Zou
Keyword(s):  
Analytical Solutions ◽  
Wave Train ◽  
Short Wave ◽  
Long Waves ◽  
Wave Group ◽  
Wave Groups ◽  
Long Wave ◽  
Wave Orbital Velocity ◽  
Variable Water ◽  
Horizontal Bottom

Abstract Second-order analytical solutions are constructed for various long waves generated by a gravity wave train propagating over finite variable depth h(x) using a multiphase Wentzel–Kramers–Brillouin (WKB) method. It is found that, along with the well-known long wave, locked to the envelope of the wave train and traveling at the group velocity Cg, a forced long wave and free long waves are induced by the depth variation in this region. The forced long wave depends on the depth derivatives hx and hxx and travels at Cg, whereas the free long waves depend on h, hx, and hxx and travel in the opposite directions at . They interfere with each other and generate free long waves radiating away from this region. The author found that this topography-induced forced long wave is in quadrature with the short-wave group and that a secondary long-wave orbital velocity is generated by variable water depth, which is in quadrature with its horizontal bottom counterpart. Both these processes play an important role in the energy transfer between the short-wave groups and long waves. These behaviors were not revealed by previous studies on long waves induced by a wave group over finite topography, which calculated the total amplitude of long-wave components numerically without consideration of the phase of the long waves. The analytical solutions here also indicate that the discontinuity of hx and hxx at the topography junctions has a significant effect on the scattered long waves. The controlling factors for the amplitudes of these long waves are identified and the underlying physical processes systematically investigated in this presentation.

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