scholarly journals Morphological development of rip channel systems: Normal and near-normal wave incidence

2005 ◽  
Vol 110 (C10) ◽  
Author(s):  
D. Calvete
Keyword(s):  
Normal Wave ◽  
Morphological Development ◽  
Wave Incidence ◽  
Channel Systems

scholarly journals On beach cusp formation

2008 ◽  
Vol 597 ◽  
pp. 145-169 ◽  
Author(s):  
NICHOLAS DODD ◽  
ADAM M. STOKER ◽  
DANIEL CALVETE ◽  
ANURAK SRIARIYAWAT
Keyword(s):  
Evolution Equation ◽  
Shallow Water Equations ◽  
Normal Wave ◽  
Feedback Mechanism ◽  
Physical Mechanisms ◽  
Wave Cycle ◽  
Bed Evolution ◽  
Positive Feedback Mechanism ◽  
Beach Cusp ◽  
Wave Incidence

A system of shallow water equations and a bed evolution equation are used to examine the evolution of perturbations on an erodible, initially plane beach subject to normal wave incidence. Both a permeable (under Darcy's law) and an impermeable beach are considered. It is found that alongshore-periodic morphological features reminiscent of swash beach cusps form after a number of incident wave periods on both beaches. On the permeable (impermeable) beach these patterns are accretional (erosional). In both cases flow is ‘horn divergent’. Spacings of the cusps are consistent with observations, and are close to those provided by a standing synchronous linear edge wave. An analysis of the processes leading to bed change is presented. Two physical mechanisms are identified: concentration gradient and flow divergence, which are dominant in the lower and upper swash respectively, and their difference over a wave cycle leads to erosion or deposition on an impermeable beach. Infiltration enters this balance in the upper swash. A bed wave of elevation is shown to advance up the beach at the tip of the uprush, with a smaller wave of depression on the backwash. It is found that cusp horns can grow by a positive feedback mechanism stemming from decreased (increased) backwash on positive (negative) bed perturbations.

Oscillating Wave Surge Converters: Interactions in a Wave Farm

2014 ◽  
Author(s):  
Dripta Sarkar ◽  
Emiliano Renzi ◽  
Frederic Dias
Keyword(s):  
Normal Wave ◽  
Linear Potential ◽  
Hypersingular Integrals ◽  
Wave Energy Converters ◽  
Hydrodynamic Behaviour ◽  
Integral Equation Formulation ◽  
Novel Method ◽  
Wave Farm ◽  
Special Case ◽  
Wave Incidence

The hydrodynamic behaviour of a wave farm comprising of Oscillating Wave Surge Converters (OWSC) is investigated using a mathematical model based on linear potential flow theory. The developed method can analyse a large number of wave energy converters in arbitrary configurations with oblique wave incidence and considers the hydrodynamic interactions amongst all the devices. The highly efficient novel method is based on Greens Integral Equation formulation, yielding hypersingular integrals which are finally solved using Chebyshev polynomials of the second kind. Using the semi -analytical approach, some possible configurations of a wave farm are studied. In the case of an inline configuration of the OWSCs with normal wave incidence, the occurrence of a near resonant behaviour already observed for 3 flaps is confirmed. A strong wave focussing effect is observed in some special configurations comprising of a large number of such devices. In general, the flaps located on the front of the wave farm are found to exhibit an enhanced performance behaviour in average, due to the mutual interactions arising within the array. A special case of two back to back flaps, oscillating independently, is also analysed using the above approach.

scholarly journals On the influence of lateral cells and local perforation of resonance liner samples on the accuracy of determining their acoustic characteristics in experimental studies

2020 ◽  
Vol 320 ◽  
pp. 00018
Author(s):  
Oleg Kustov ◽  
Igor Khramtsov
Keyword(s):  
Sound Pressure ◽  
Experimental Studies ◽  
Normal Wave ◽  
Single Layer ◽  
Frequency Range ◽  
Acoustic Characteristics ◽  
Layer Sample ◽  
Honeycomb Cell ◽  
Research Recommendations ◽  
Wave Incidence

When determining the acoustic characteristics of a single-layer sample of a honeycomb liner by experiments in interferometers with normal wave incidence, a significant effect of incomplete lateral cells of the sample on acoustic characteristics was revealed. The experiments were carried out on two interferometers with channel diameters of 30 and 50 mm in the frequency range 500-3500 Hz at sound pressure levels of 120-155 dB. Based on the results of the experiments, an assessment was made of the effect on the acoustic characteristics of the percentage of perforation, which is the same both for one honeycomb cell and for the entire SAS sample. Based on the results of the research, recommendations were made to improve the accuracy of obtaining the acoustic characteristics of samples of honeycomb liner when testing them in interferometers of normal wave incidence.

scholarly journals Design of Multiple Parallel-Arranged Perforated Panel Absorbers for Low Frequency Sound Absorption

Materials ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2099
Author(s):  
Xin Li ◽  
Qianqian Wu ◽  
Ludi Kang ◽  
Bilong Liu
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
Normal Wave ◽  
Low Frequency ◽  
Approximation Model ◽  
Low Frequencies ◽  
Absorption Bandwidth ◽  
Frequency Sound ◽  
Electrical Analogy ◽  
Wave Incidence

A particular structure that consists of four parallel-arranged perforated panel absorbers (PPAs) is proposed for the low frequency sound absorption within a constraint space. The apertures of the perforated panels are set to ≥1.5 mm, and the number of orifices is much less and therefore easier to be produced in comparison with that of the micro perforated panel (MPP). A simple approximation model by using acoustic-electrical analogy is described to calculate the sound absorption coefficient of such device subject to normal wave incidence. Theoretical and experimental results demonstrate that the device can provide more than one octave sound absorption bandwidth at low frequencies.

scholarly journals Emerging crescentic patterns in modeled double sandbar systems

2019 ◽  
Author(s):  
Giovanni Coco ◽  
Daniel Calvete ◽  
Francesca Ribas ◽  
Huib E. de Swart ◽  
Albert Falques
Keyword(s):  
Stability Analysis ◽  
Normal Wave ◽  
The Other ◽  
Large Variability ◽  
Wave Heights ◽  
The Difference ◽  
Offshore Wave ◽  
Channel Patterns ◽  
Fully Coupled ◽  
Wave Incidence

Abstract. The morphodynamic stability of double-barred beaches is explored using a numerical model based on linear stability analysis. Surfzone hydrodynamics is described by coupling depth and wave averaged conservation of mass and momentum with the wave-energy and phase equations, including roller dynamics. A simplified sediment transport formulation relates flow to seabed changes. Under normal wave incidence an alongshore uniform coast with a cross-shore profile characterized by the presence of two sandbars, can be unstable, thereby resulting in the development of crescentic/rip channel patterns. Our study demonstrates that sandbar coupling can be either in-phase (highs and lows of both sandbars are at the same alongshore position) or out-of-phase (highs and lows of one sandbar correspond to lows and highs of the other sandbar). In line with observations, results of numerical simulations show a large variability in the possible emerging bottom patterns. Our analysis indicates that the inner bar-modes are dominant for large height/depth differences between the two sandbars crests and small offshore wave heights, while patterns related to the outer sandbar dominate for small values of the difference in sandbar depth. For intermediate differences between the two sandbars depths, patterns on both longshore bars appear to be fully coupled. For relatively larger waves and large depth over the outer sandbar, patterns develop close to the shoreline/inner surfzone.

MORPHOLOGICAL DEVELOPMENT OF COASTS AT VERY OBLIQUE WAVE INCIDENCE

2003 ◽  
Author(s):  
Dorthe Petersen ◽  
Rolf Deigaard ◽  
Jørgen Fredsøe ◽  
Nils Drønen
Keyword(s):  
Morphological Development ◽  
Oblique Wave ◽  
Wave Incidence

Reflection and transmission from porous structures under oblique wave attack

1991 ◽  
Vol 224 ◽  
pp. 625-644 ◽  
Author(s):  
Robert A. Dalrymple ◽  
Miguel A. Losada ◽  
P. A. Martin
Keyword(s):  
Porous Medium ◽  
Plane Wave ◽  
Water Waves ◽  
Normal Wave ◽  
Eigenfunction Expansions ◽  
Reflection And Transmission ◽  
Oblique Wave ◽  
Water Region ◽  
Wave Incidence ◽  
Wave Modes

The linear theory for water waves impinging obliquely on a vertically sided porous structure is examined. For normal wave incidence, the reflection and transmission from a porous breakwater has been studied many times using eigenfunction expansions in the water region in front of the structure, within the porous medium, and behind the structure in the down-wave water region. For oblique wave incidence, the reflection and transmission coefficients are significantly altered and they are calculated here.Using a plane-wave assumption, which involves neglecting the evanescent eigenmodes that exist near the structure boundaries (to satisfy matching conditions), the problem can be reduced from a matrix problem to one which is analytic. The plane-wave approximation provides an adequate solution for the case where the damping within the structure is not too great.An important parameter in this problem is Γ2= ω2h(s- if)/g, where ω is the wave angular frequency,hthe constant water depth,gthe acceleration due to gravity, andsandfare parameters describing the porous medium. As the friction in the porous medium,f, becomes non-zero, the eigenfunctions differ from those in the fluid regions, largely owing to the change in the modal wavenumbers, which depend on Γ2.For an infinite number of values of ΓF2, there are no eigenfunction expansions in the porous medium, owing to the coalescence of two of the wavenumbers. These cases are shown to result in a non-separable mathematical problem and the appropriate wave modes are determined. As the two wavenumbers approach the critical value of Γ2, it is shown that the wave modes can swap their identity.

Scanning Electron Microscopy and x-ray analysis of microparticles and early hydration effects

1995 ◽  
Vol 53 ◽  
pp. 692-693
Author(s):  
Yun Lu ◽  
David C. Joy
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
High Resolution ◽  
Morphological Development ◽  
Early Hydration ◽  
X Ray ◽  
Blended Cements ◽  
Powder Particles ◽  
Chemical Wastes ◽  
Scanning Electron

High resolution scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDXA) were performed to investigate microparticles in blended cements and their hydration products containing sodium-rich chemical wastes. The physical appearance of powder particles and the morphological development at different hydration stages were characterized by using high resolution SEM Hitachi S-900 and by SEM S-800 with a EDX spectrometer. Microparticles were dispersed on the sample holder and glued by 1% palomino solution. Hydrated bulk samples were dehydrated by acetone and mounted on the holder by silver paste. Both fracture surfaces and flat cutting sections of hydrating samples were prepared and examined. Some specimens were coated with an 3 nm thick Au-Pd or Cr layer to provide good conducting surfaces. For high resolution SEM S-900 observations the accelerating voltage of electrons was 1-2 KeV to protect the electron charging. Microchemical analyses were carried out by S800/EDS equipped with a LINK detector of take-off angle =40°.

SEM study of the morphological effects of kinetin and zeatin on the growth and development of the apical meristem in wheat

1995 ◽  
Vol 53 ◽  
pp. 978-979
Author(s):  
G. M. Hutchins ◽  
J. S. Gardner
Keyword(s):  
Growth And Development ◽  
Furfuryl Alcohol ◽  
Apical Meristem ◽  
Plant Cells ◽  
Triticum Aestivum L ◽  
Morphological Development ◽  
Naturally Occurring ◽  
Chinese Spring Wheat ◽  
Sem Study ◽  
Moist Environment

Cytokinins are plant hormones that play a large and incompletely understood role in the life-cycle of plants. The goal of this study was to determine what roles cytokinins play in the morphological development of wheat. To achieve any real success in altering the development and growth of wheat, the cytokinins must be applied directly to the apical meristem, or spike of the plant. It is in this region that the plant cells are actively undergoing mitosis. Kinetin and Zeatin were the two cytokinins chosen for this experiment. Kinetin is an artificial hormone that was originally extracted from old or heated DNA. Kinetin is easily made from the reaction of adenine and furfuryl alcohol. Zeatin is a naturally occurring hormone found in corn, wheat, and many other plants.Chinese Spring Wheat (Triticum aestivum L.) was used for this experiment. Prior to planting, the seeds were germinated in a moist environment for 72 hours.

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