scholarly journals A LABORATORY EXPERIMENT OF BEACH CUSPS

1984 ◽  
Vol 1 (19) ◽  
pp. 90
Author(s):  
Arata Kaneko
Keyword(s):  
Dimensionless Parameter ◽  
Breaking Point ◽  
Breaking Wave ◽  
Horizontal Distance ◽  
Edge Waves ◽  
Continuous Action ◽  
Bed Materials ◽  
Beach Cusps ◽  
Incident Waves ◽  
Good Agreement

Beach cusps with a longshore spacing of 20 to 150 cm have been built by the continuous action of incident waves on a steep laboratory beach. In the formation stage of beach cusps, all bed materials on the beach moved shoreward. The backwash vortex, which was found first by Matsunaga and Honji (16,18) on a laboratory beach, gave a good explanation of the shoreward movement of bed materials. Beach cusps formed when the value of a dimensionless parameter H^Lk/h^L, which controls swash motion on a steep beach, became larger than 1.12; H)-, is the height of the breaking wave, Ljj its wavelength, h^ the water depth at the breaking point and L the horizontal distance from the shoreline for still water level to the breaking point. The observational spacing of beach cusps formed regularly were in quite good agreement with half a wavelength of the zero-mode subharmonic edge wave generated on a sloping flat beach. As a result of this study, the contribution of edge waves on cusp formation becomes more undoubted.

scholarly journals Fluctuation of magnitude of wave loads for a long array of bottom-mounted cylinders

2019 ◽  
Vol 868 ◽  
pp. 244-285 ◽  
Author(s):  
Xiaohui Zeng ◽  
Fajun Yu ◽  
Min Shi ◽  
Qi Wang
Keyword(s):  
Incidence Angle ◽  
Local Maximum ◽  
Destructive Interference ◽  
Horizontal Distance ◽  
Wave Loads ◽  
Wave Load ◽  
Intrinsic Mechanism ◽  
Fluctuation Phenomenon ◽  
Analytical Formulae ◽  
Incident Waves

For wave loads on cylinders constituting a long but finite array in the presence of incident waves, variations in the magnitude of the load with the non-dimensional wavenumber exhibit interesting features. Towering spikes and nearby secondary peaks (troughs) associated with trapped modes have been studied extensively. Larger non-trapped regions other than these two are termed Region III in this study. Studies of Region III are rare. We find that fluctuations in Region III are regular; the horizontal distance between two adjacent local maximum/minimum points, termed fluctuation spacing, is constant and does not change with non-dimensional wavenumbers. Fluctuation spacing is related only to the total number of cylinders in the array, identification serial number of the cylinder concerned and wave incidence angle. Based on the interaction theory and constructive/destructive interference, we demonstrate that the fluctuation characteristics can be predicted using simple analytical formulae. The formulae for predicting fluctuation spacing and the abscissae of every peak and trough in Region III are proposed. We reveal the intrinsic mechanism of the fluctuation phenomenon. When the diffraction waves emitted from the cylinders at the ends of the array and the cylinder concerned interfere constructively/destructively, peaks/troughs are formed. The fluctuation phenomenon in Region III is related to solutions of inhomogeneous equations. By contrast, spikes and secondary peaks are associated with solutions of the eigenvalue problem. This study of Region III complements existing understanding of the characteristics of the magnitude of wave load. The engineering significances of the results are discussed as well.

scholarly journals GROIN LENGTH AND THE GENERATION OF EDGE WAVES

1976 ◽  
Vol 1 (15) ◽  
pp. 85 ◽  
Author(s):  
Michael K. Gaughan ◽  
Paul D. Komar
Keyword(s):  
Incident Wave ◽  
Wave Length ◽  
Critical Length ◽  
Beach Erosion ◽  
Rip Currents ◽  
Edge Waves ◽  
Normal Waves ◽  
Wave Basin ◽  
Incident Waves ◽  
Selection Of

A series of wave basin experiments were undertaken to better understand the selection of groin spacings and lengths. Rather than obtaining edge waves with the same period as the normal incident waves, subharmonic edge waves were produced with a period twice that of the incoming waves and a wave length equal to the groin spacing. Rip currents were therefore not formed by the interactions of the synchronous edge waves and normal waves as proposed by Bowen and Inman (1969). Rips were present in the wave basin but their origin is uncertain and they were never strong enough to cause beach erosion. The generation of strong subharmonic edge waves conforms with the work of Guza and Davis (1974) and Guza and Inman (1975). The subharmonic edge waves interacted with the incoming waves to give an alternating sequence of surging and collapsing breakers along the beach. Their effects on the swash were sufficient to erode the beach in some places and cause deposition in other places. Thus major rearrangements of the sand were produced between the groins, but significant erosion did not occur as had been anticipated when the study began. By progressively decreasing the length of the submerged portions of the groins, it was found that the strength (amplitude) of the edge waves decreases. A critical submerged groin length was determined whereby the normally incident wave field could not generate resonant subharmonic edge waves of mode zero with a wavelength equal to the groin spacing. The ratio of this critical length to the spacing of the groins was found in the experiments to be approximately 0.15 to 0.20, and did not vary with the steepness of the normal incident waves.

Coupling of Sloshing and Ship Motions

2003 ◽  
Vol 47 (03) ◽  
pp. 208-221 ◽  
Author(s):  
Olav F. Rognebakke ◽  
Odd M. Faltinsen
Keyword(s):  
Steady State ◽  
Transient Behavior ◽  
Frequency Domain Analysis ◽  
Ship Motions ◽  
Steady State Motion ◽  
Constant Coefficients ◽  
Incident Waves ◽  
Violent Sloshing ◽  
Different Levels ◽  
Good Agreement

The coupled effect between ship motions and sloshing is studied. Two-dimensional experiments of a hull section containing tanks filled with different levels of water excited in sway by regular waves have been conducted. Steady-state results are obtained for the sway amplitude. Even if violent sloshing occurs in the tanks, the steady-state motion is almost linear and sinusoidal with the frequency of the linear incident waves. This implies that higher-order harmonics of the sloshing force are filtered out by the system. Simulations of the modeled case are performed using a linear and a nonlinear sloshing model and mainly assuming linear external flow. For steady-state motion, a convolution formulation does not improve the results relative to using constant coefficients in the equation of motion. However, in order to properly model the transient behavior in an irregular sea, a convolution formulation must be included. The treatment of the retardation function for the external problem is discussed in detail. A good agreement between experiments and computations is reported. The calculated coupled motion is sensitive to the damping of the sloshing motion in a certain frequency range where the coupled sloshing and ship motions cause resonant ship motions. A quasilinear frequency domain analysis is used to explain this by introducing the sloshing loads as a frequency dependent spring.

Numerical Simulations of Ship Bow and Shoulder Wave Breaking in Different Advancing Speeds

2018 ◽  
Author(s):  
Zhen Ren ◽  
Jianhua Wang ◽  
Decheng Wan
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Wave Breaking ◽  
Wave Pattern ◽  
Breaking Wave ◽  
Wake Field ◽  
Bow Wave ◽  
Calm Water ◽  
Wave Phenomena ◽  
Good Agreement

The KCS model is employed for the numerical simulations to investigate the wave breaking phenomena of the bow and shoulder wave. RANS approach coupled with high resolution VOF technique is used to resolve the free surface. In order to study the speed effects on the phenomena of ship wave breaking, four different speeds, i.e. Fr = 0.26, 0.30, 0.32, 0.35, are investigated in calm water. Predicted resistance and wave patterns under Fr = 0.26 are validated with the available experiment data, and good agreement is achieved. For the Fr = 0.26 case, the wave pattern is steady, and the alternate variation of vorticity appear near the free surface is associated with the wake field. The breaking wave phenomena can be observed when the Froude number is over 0.32 and the Fr = 0.35 case shows most violent breaking bow wave. For the Fr = 0.35 case, the process of overturning and breaking of bow wave is observed clearly, and at the tail of bow wave, some breaking features of free surface are also captured. The reconnection of the initial plunger with the free surface results in a pair of counter-rotating vortex that is responsible for the second plunger and scar.

scholarly journals TRANSMISSION OF RANDOM WAVES THROUGH PILE BREAKWATERS

1986 ◽  
Vol 1 (20) ◽  
pp. 169 ◽  
Author(s):  
Clifford L. Truitt ◽  
John B. Herbich
Keyword(s):  
Random Waves ◽  
Pile Spacing ◽  
Transmission Coefficients ◽  
Pile Diameter ◽  
Model Pile ◽  
Incident Waves ◽  
Good Agreement ◽  
Monochromatic Waves

Several previous investigators have conducted experiments leading to expressions for predicting the transformation of waves passing through closely-spaced pile breakwaters. The present study extends those earlier experiments using monochromatic waves to the case of a spectrum of random waves. Records of incident waves and of waves after transmission through a model pile breakwater were compared to determine a coefficient of transmission. Results are presented for several cases of pile spacing and pile diameter. Good agreement is found between observed transmission coefficients and those predicted using the expression proposed by Hayashi et al. (1966).

Beach Cusps and Edge Waves

1978 ◽  
Author(s):  
D. A. Huntley ◽  
A. J. Bowen
Keyword(s):  
Edge Waves ◽  
Beach Cusps

Numerical Simulation of Pre-Crack Propagation in ZrB2-SiC-AlN Ceramics Subjected to Thermal Shock

2013 ◽  
Vol 833 ◽  
pp. 154-158
Author(s):  
Xiao Yang Wan ◽  
Jun Liang ◽  
Guo Dong Fang ◽  
Ling Ling Wang
Keyword(s):  
Numerical Simulation ◽  
Thermal Stress ◽  
Crack Propagation ◽  
Thermal Shock ◽  
Dimensionless Parameter ◽  
Experimental Results ◽  
Force Model ◽  
Quenching Temperature ◽  
Depth Direction ◽  
Good Agreement

The present work examines the pre-indented crack propagation in ZrB2-SiC-AlN ceramics subjected to thermal shock under different temperature differences. A cohesive force model is applied according to the shape and characteristics of the crack in the indentation - quenching experiments. A dimensionless parameter is introduced to characterize the effect of depth on thermal stress which considers the cracks propagate along both the surface and the depth direction. The modified numerical results are 11.3%, 16.6%, 20.8% 27.1% and 64.6% at the quenching temperature differences of 240°C, 280°C, 320°C and 360°C, respectively, which are in good agreement with the experimental results.

A Method for Reduction in the Start-Up Time of a Bubbling Bed Boiler Combustor

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Vijay Jain ◽  
Prabir Basu ◽  
Dominic Groulx
Keyword(s):  
Fluidized Bed ◽  
Internal Heat ◽  
Peak Temperature ◽  
Fuel Oil ◽  
Start Up ◽  
Bubbling Fluidized Bed ◽  
Bed Materials ◽  
The Mean ◽  
Rate Of Heating ◽  
Good Agreement

A study on the heating of inert bed solids in a bubbling fluidized bed by means of an over-bed start-up oil burner is presented in this paper. Experiments carried out in a 160 mm diameter bed shows that the bed heats up nonlinearly with time. The rate of heating and the peak temperature reached by the bed solids depend on the bed depth, the mean particle size, and the superficial velocity through the bed. It was further noted that premixing a certain amount of biomass with the inert bed solids accelerates the rate of heating, as well as increase the peak temperature attained. The internal heat generation in the biomass is found to start at temperatures as low as 200°C. Thus, premixing some biomass with inert bed materials could reduce the combustion start-up time of a fluidized bed boiler, reducing at the same time the start-up cost by saving on consumption of expensive fuel oil in the burner. Experimental data in the present laboratory-scale unit shows good agreement with those obtained earlier in an industrial fluidized bed tested with waste-coal.

scholarly journals Bubble production by air filament and cavity breakup in plunging breaking wave crests

2021 ◽  
Vol 929 ◽  
Author(s):  
Qiang Gao ◽  
Grant B. Deane ◽  
Lian Shen
Keyword(s):  
Surface Tension ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Interface Instability ◽  
Interface Curvature ◽  
Rayleigh Taylor Instability ◽  
Air Cavities ◽  
Rayleigh Instabilities ◽  
Good Agreement

Air filaments and cavities in plunging breaking waves, generically cylinders, produce bubbles through an interface instability. The effects of gravity, surface tension and surface curvature on cylinder breakup are explored. A generalized dispersion relation is obtained that spans the Rayleigh–Taylor and Plateau–Rayleigh instabilities as cylinder radius varies. The analysis provides insight into the role of surface tension in the formation of bubbles from filaments and cavities. Small filaments break up into bubbles through a Plateau–Rayleigh instability driven through the action of surface tension. Large air cavities produce bubbles through a Rayleigh–Taylor instability driven by gravity and moderated by surface tension, which has a stabilizing effect. Surface tension, interface curvature and gravity are all important for cases between these two extremes. Predicted unstable mode wavenumber and bubble size show good agreement with direct numerical simulations of plunging breaking waves and air cylinders.

scholarly journals Fast radio bursts as electromagnetic radiation from cusps on superconducting cosmic strings

2015 ◽  
Vol 5 (1) ◽  
pp. 43-50 ◽  
Author(s):  
L. Zadorozhna
Keyword(s):  
Electromagnetic Radiation ◽  
Gravitational Constant ◽  
Dimensionless Parameter ◽  
Cosmic Strings ◽  
Unit Length ◽  
Topological Defects ◽  
Energy Scale ◽  
Radio Bursts ◽  
Proposed Model ◽  
Good Agreement

Cosmic strings are topological defects, relicts of the early Universe, which can be formed during phase transitions of fields with spontaneous broken symmetry. There also exists a special class of cosmic strings - superconducting cosmic strings, inside of which the massless charge carriers, so-called zero modes, are presented and can move along the string without any resistance. The superconducting cosmic strings during their relativistic motion through the cosmic plasma could be a powerful source of electromagnetic radiation. The emission of cusps on the superconducting strings is highly beamed and has the nature of bursts. In the present work, it is shown, that the millisecond extragalactic radio bursts, discovered during the last decade, called the fast radio bursts (FRB), with unknown nature, could be explained as radiation from cusps on superconducting cosmic strings. Estimates made for ten FRBs discovered till now show that bursts could be produced by a string with α=ΓGμ/c2∼ 5⋅10-13-10-12, where Γ ∼ 50 is a dimensionless parameter, G is the gravitational constant, c is the speed of light, μ is the mass per unit length of a string, which corresponds to the energy scale of the phase transition η∼1.2⋅1012-1.7⋅1012 GeV. The observed duration, flux and event rate are in a good agreement with the proposed model. In the framework of emission from cusps of superconducting cosmic string loops, probability of FRB detecting is estimated, which is found to be highly close to the probability of detecting, given by observational data.

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