scholarly journals SOLID AND PERMEABLE SUBMERGED BREAKWATERS

1968 ◽  
Vol 1 (11) ◽  
pp. 72 ◽  
Author(s):  
T. Milne Dick ◽  
A. Brebner
Keyword(s):  
Reflection Coefficient ◽  
Standing Wave ◽  
Deep Water ◽  
Incident Wave ◽  
Wave Energy ◽  
Incident Energy ◽  
Wave Length ◽  
Wave Number ◽  
Frequency Range ◽  
Thin Barrier

The behaviour of thin and rectangular solid submerged breakwaters is re-examined. Dean's theory is found to be correct for a thin barrier in infinitely deep water. An empirical and theoretical relationship for the reflection coefficient of a thin breakwater across the wave number spectrum is proposed. Rectangular solid breakwaters have a maximum reflection when the incident wave has the same period as a standing wave on top of the breakwater and with a wave length equal to the crest width. A submerged permeable breakwater for depths of submergence greater than 5% of the total depth transmits less wave energy than the solid over a certain frequency range. The minimum is transmitted when the criterion above for solid breakwaters is also met. Both permeable and solid rectangular breakwaters cause a substantial loss in wave energy and at least 501 of the incident energy is lost to turbulence. A substantial proportion, 30 to 601 of the energy transmitted is transferred to higher frequencies than the incident wave.

scholarly journals Optimization of Wave Energy Converter Arrays by an Improved Differential Evolution Algorithm

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3522 ◽  
Author(s):  
Hong-Wei Fang ◽  
Yu-Zhu Feng ◽  
Guo-Ping Li
Keyword(s):  
Differential Evolution ◽  
Incident Wave ◽  
Wave Energy ◽  
Differential Evolution Algorithm ◽  
Wave Energy Converter ◽  
Wave Number ◽  
Adaptive Mutation ◽  
Energy Converter ◽  
De Algorithm ◽  
Evolution Algorithm

Since different incident waves will cause the same array to perform differently with respect to the wave energy converter (WEC), the parameters of the incident wave, including the incident angle and the incident wave number, are taken into account for optimizing the wave energy converter array. Then, the differential evolution (DE) algorithm, which has the advantages of simple operation procedures and a strong global search ability, is used to optimize the wave energy converter array. However, the traditional differential evolution algorithm cannot satisfy the convergence precision and speed simultaneously. In order to make the optimization results more accurate, the concept of an adaptive mutation operator is presented to improve the performance of differential evolution algorithm. It gives the improved algorithm a faster convergence and a higher precision ability. The three-float, five-float, and eight-float arrays were optimized, respectively. It can be concluded that the larger the size of the array is, the greater the interaction between the floats is. Hence, a higher efficiency of wave energy extraction for wave energy converter arrays is achieved by the layout optimization of the array of wave energy converters. The results also show that the optimal layout of the array system is inhomogeneously distributed and that the improved DE algorithm used on array optimization is superior to the traditional DE algorithm.

scholarly journals Bi-Ellipse Microstripline Antenna Array Varians

2021 ◽  
Author(s):  
Putu Artawan
Keyword(s):  
Reflection Coefficient ◽  
Antenna Array ◽  
Standing Wave ◽  
Microstrip Antenna ◽  
Communication Systems ◽  
Return Loss ◽  
Voltage Standing Wave Ratio ◽  
Frequency Range ◽  
X Band ◽  
Working Frequency

The objectives of this research include obtaining and verifying the impedance formula of the designed bi-ellipse microstrip antenna and correlating the results obtained through simulation and experimentation. The research also aims to obtain the structure and dimensions that provide optimal characteristics of the designed bi-ellipse microstrip antenna and produce a prototype at S, C and X-Band frequencies. This research produced the structure and dimensions of a bi-ellipse microstrip antenna that provide optimal characteristics of antenna. The characteristics results of the antenna parameters in this research include a 8x2 array, with a bandwidth value of around 100.0 MHz obtained at a working frequency of 7.09GHz (7.04 GHz - 7.14 GHz), with a reflection coefficient value of 0.02, Voltage Standing Wave Ratio (VSWR) of 1.06, return loss of −30.00 dB and a gain of 7.30 dB. For the 8x4 array, a bandwidth value of approximately 210.0 MHz is obtained at a working frequency range of 2.85GHz, which ranges from 2.74GHz - 2.95GHz, with a reflection coefficient value of 0.04, Voltage Standing Wave Ratio (VSWR) of 1.09, return loss of −27.06 dB and a gain of 8.19 dB. The results presented above fulfill the indicators of good antenna characteristics parameters applicable to radar communication systems.

scholarly journals WAVE REFLECTION GENERATED BY CAISSONS WITH INTERNAL RUBBLE MOUND OF VARIABLE SLOPE

2012 ◽  
Vol 1 (33) ◽  
pp. 51 ◽  
Author(s):  
Carla Faraci ◽  
Biagio Cammaroto ◽  
Luca Cavallaro ◽  
Enrico Foti
Keyword(s):  
Optimal Design ◽  
Reflection Coefficient ◽  
Analytical Model ◽  
Incident Wave ◽  
Wave Energy ◽  
Wave Reflection ◽  
Energy Reduction ◽  
Experimental Campaign ◽  
Rubble Mound ◽  
Incident Wave Energy

The paper reports on an experimental campaign focused on the performances of prefabricated caissons with internal rubble mound (combined caissons) in terms of incident wave energy reduction. The frontal opening and the chamber width of the caisson were changed in order to find the optimal design dimensions allowing the reflection coefficient to be reduced as much as possible. As expected, the best performances of the combined caisson occur when the rubble mound slope is gentler. The experimental results were also compared with an analytical model available in literature; such a comparison showed that the combined caisson exhibits a smaller reflection than predicted as far as wave periods higher than 8-9 s at a prototype scale are concerned.

Surface-wave propagation over sinusoidally varying topography

1984 ◽  
Vol 144 ◽  
pp. 419-443 ◽  
Author(s):  
A. G. Davies ◽  
A. D. Heathershaw
Keyword(s):  
Reflection Coefficient ◽  
Surface Waves ◽  
Wave Field ◽  
Incident Wave ◽  
Wave Energy ◽  
Bottom Topography ◽  
Finite Depth ◽  
Linear Perturbation ◽  
Linear Perturbation Theory ◽  
Incident Wave Energy

Surface waves travelling in water of finite depth may be scattered by a region of undulating bottom topography. The present study is concerned with the idealized two-dimensional situation in which long-crested surface waves are incident upon a patch of long-crested regular bottom ripples. The principal question examined concerns the amount of incident wave energy that is reflected by the ripple patch. Linear perturbation theory is used to show that the reflection coefficient is both oscillatory in the quotient of the length of the patch and the surface wavelength, and also strongly dependent upon the quotient of the surface and bed wavelengths. In particular, there is a Bragg resonance between the surface waves and the ripples, which is associated with the reflection of incident wave energy. A secondary question concerns the nature of the wave field in the immediate vicinity of the ripple patch. In resonant cases, it is shown how the partially standing wave on the upwave side of the ripple patch gives way, in an almost linear manner over the patch itself, to a progressive transmitted wave on the downwave side. The theoretical predictions are compared with an extensive set of laboratory observations made in a wave tank. Comparisons relating both to the reflection coefficient, and also to the wave field over the ripple patch, are shown to give consistently good agreement. Finally, the implications of the results for sediment transport on an erodible bed are examined.

scholarly journals Energy Analysis on Dynamic Fragmentation Degree of Cemented Sand Specimens under Confining Pressure

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Ying Xu ◽  
Jinjin Ge ◽  
Wei Huang
Keyword(s):  
Fracture Energy ◽  
Incident Wave ◽  
Wave Energy ◽  
Incident Energy ◽  
Confining Pressure ◽  
Energy Ratio ◽  
Energy Conditions ◽  
Absorbed Energy ◽  
Cemented Sand ◽  
Incident Wave Energy

In order to study the fragmentation energy dissipation characteristics of cemented sand specimens under confining pressure and impact loads, the energy consumption of cemented sand specimens was analyzed through an impact compression and split test performed at different loading rates with different impact pressures by using a variable cross section SHPB (split Hopkinson pressure bar) with an active confining pressure loading apparatus. The results show that (1) the absorbed energy and incident energy were in a linear relationship and the proportion between them was relatively constant under confining pressure, and the absorbed energy had a quadratic relationship with the incident energy under zero confining pressure. (2) The fracture energy ratio increased with the increase in incident energy, the damage energy ratio decreased with the increase in incident energy, and the damage energy ratio were always higher than the fracture energy ratio under confining pressure. (3) The energy absorbed by the cemented sand specimens decreased sharply with the increase of confining pressure under the same incident wave energy conditions, and the reflected wave energy and transmitted wave energy increased. (4) When the incident wave energy was constant, the ratio of the energy causing surface fractures to the energy absorbed by the cemented sand specimens decreased sharply with the increase of confining pressure, while the energy causing crack growth and damage increased sharply. These conclusions may guide similar models of blasting tests in the future.

scholarly journals DISSIPATION OF DEEP WATER WAVES BY HYDRAULIC BREAKWATERS

1968 ◽  
Vol 1 (11) ◽  
pp. 66
Author(s):  
R.E. Nece ◽  
E.P. Richey ◽  
V. Seetharama Rao
Keyword(s):  
Deep Water ◽  
Incident Wave ◽  
Water Waves ◽  
Wave Length ◽  
Surface Current ◽  
Theoretical Predictions ◽  
Excess Power ◽  
Incident Waves ◽  
Deep Water Waves

Experimental results axe presented for a laboratory study of the effectiveness of hydraulic breakwaters in dissipating deep water waves. Test data are reported for a range of wave steepnesses for wave length: water depth ratios ranging from 0.375 to 1.343. It is shown that the effectiveness of hydraulic breakwaters depends upon the steepness of the incident wave and upon the ratio of the momentum of the opposing surface current created by the breakwater to the momentum of the incident waves. Results also are compared with the theoretical predictions of Taylor which are appropriate to deep water waves. Data are presented in a form allowing the determination of hydraulic breakwater manifold discharge characteristics in order to achieve specified attenuation for a particular incident wave. It is concluded that while the hydraulic breakwater is better adapted to deep water waves than to shallow water waves upon which prior studies of the device have concentrated, it is generally inefficient for most practical cases because of excess power requirements. Some possible field applications are indicated.

On characteristics of the water-particle velocity in a plunging breaker

1983 ◽  
Vol 126 ◽  
pp. 251-268 ◽  
Author(s):  
Takeo Nakagawa
Keyword(s):  
Wave Energy ◽  
Wave Breaking ◽  
Separate Flow ◽  
Transverse Flow ◽  
Two Dimensional ◽  
Frequency Range ◽  
Flow Component ◽  
Flow Components ◽  
Flow Drag ◽  
Plunging Breaker

Three velocity components of water particles in a plunging breaker over a horizontal step on the bed of a two-dimensional laboratory wave tank have been determined simultaneously by means of an elaborate flowmeter that measures the flow drag on three ‘tension threads’, with each recording a separate flow component.It is found that all three of the r.m.s. values in the plunging breaker become maximum at x/L ≈ 0·7, where x is the distance from the breaking point to the shore and L is the wavelength. It is found that both the velocity and r.m.s. values of the transverse flow component generated by the shoaling and wave breaking become comparable to those of the other two flow components.On the basis of spectral analyses it is found that major wave frequencies in both the longitudinal and vertical flow components of the original two-dimensional wave survive even after experiencing relatively strong shoaling and wave breaking, and part of the original wave energy is transferred to the transverse flow component and is located at these major frequencies. It is found that the majority of the higher-harmonic-frequency components (or turbulent fluctuations) are generated in the shoaling process and that the wave breaking provides a relatively minor contribution to the generation. Finally, it is found that, through the shoaling and wave breaking, the original wave energy is transported to a frequency range lower than the primary wave frequency (negative cascade), as well as to the higher frequency range (positive cascade) in each flow component.

Theory of Short Wave Excitation

1986 ◽  
Vol 30 (03) ◽  
pp. 147-152
Author(s):  
Yong Kwun Chung
Keyword(s):  
Incident Wave ◽  
Characteristic Length ◽  
Finite Depth ◽  
Short Wave ◽  
The Body ◽  
Wave Number ◽  
Floating Body ◽  
Wave Excitation ◽  
Exciting Forces ◽  
Wave Exciting Forces

When the wavelength of the incident wave is short, the total surface potential on a floating body is found to be 2∅ i & O (m-l∅ i) on the lit surface and O (m-l∅ j) on the shadow surface where ~b i is the potential of the incident wave and m the wave number in water of finite depth. The present approximation for wave exciting forces and moments is reasonably good up to X/L ∅ 1 where h is the wavelength and L the characteristic length of the body.

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