scholarly journals FIELD MEASUREMENTS OF NEARSHORE VELOCITIES

1974 ◽  
Vol 1 (14) ◽  
pp. 30
Author(s):  
David A. Huntley ◽  
Anthony J. Bowen
Keyword(s):  
Wave Motion ◽  
Field Measurements ◽  
Wave Form ◽  
Edge Waves ◽  
Free Standing ◽  
Frequency Wave ◽  
Storm Waves ◽  
Circulation Patterns ◽  
Two Component ◽  
Base Side

Two component electromagnetic flowmeters are being used as the basis of an apparatus to measure nearshore velocities on natural beaches. The flowmeters are mounted on free standing tripods, 1 m. base side and 0.3 m. high, to measure the two components of horizontal flow, and have been used in depths of up to 4 m. and up to 150 m. from the shoreline. The apparatus has proved both flexible and reliable on beaches ranging from steep shingle (slope ^ 0.13) to very shallow sand (slope'*' 0.01) and under a wide variety of wave conditions, including full storm waves on a beach of intermediate slope ( ^ 0.04). Results show that a single flowmeter can be used on a tidal beach to measure the variation of the flow field along a line perpendicular to the shoreline. In this way edge waves and steady nearshore circulation patterns have been detected. If several flowmeters are placed on a line perpendicular to the shoreline, the progress of individual waves can be followed as they pass over each flowmeter in turn, and hence propagation speeds, changes of wave form and the development of lower frequency wave motion close to the shoreline can be studied.

scholarly journals BEACH CUSPS AND EDGE WAVES

1978 ◽  
Vol 1 (16) ◽  
pp. 81 ◽  
Author(s):  
D.A. Huntley ◽  
A.J. Bowen
Keyword(s):  
Incident Wave ◽  
Wave Motion ◽  
Field Measurements ◽  
Convincing Evidence ◽  
Edge Wave ◽  
Wave Frequency ◽  
Edge Waves ◽  
Wide Range ◽  
Beach Cusps ◽  
Resonant Waves

Beach cusps are very common, concave-seaward cuspate patterns at the shoreline of a beach, which tend to occur with a regular longshore spacing, but which can have a wide range of longshore wavelengths from a few centimeters to several kilometers or more. Edge waves, resonant waves trapped at the shoreline by refraction, have been suggested as the cause of beach cusps but it has proved difficult to establish a definitive link on natural beaches . This paper describes field measurements of nearshore velocities, in all three orthogonal directions, that show the presence of edge wave motion just before the formation of beach cusps of the corresponding wavelength, and thus provides convincing evidence that edge waves are responsible for beach cusps. The magnitude of the observed edge wave oscillatory and drift velocities are found to be large and apparently well able to form cusps of the observed size. The observed edge waves are at the subharmonic of the incident wave frequency and thus are the field equivalent of the laboratory observations of Guza and Inman (1975) and Guza and Bowen (1977). It is not clear, however, whether the developing cusp topography enhanced or suppressed the edge wave motion.

scholarly journals FIELD MEASUREMENTS AND MODELLING OF NEARSHORE CURRENTS AT A HIGH-ENERGY GEOLOGICALLY-CONSTRAINED BEACH

2020 ◽  
pp. 18
Author(s):  
Arthur Mouragues ◽  
Philippe Bonneton ◽  
Bruno Castelle ◽  
Vincent Marieu
Keyword(s):  
Surf Zone ◽  
Low Frequency ◽  
Field Measurements ◽  
High Energy ◽  
Oblique Wave ◽  
Wave Forcing ◽  
Circulation Patterns ◽  
Wave Conditions ◽  
Nearshore Currents ◽  
Set Up

We present field measurements of nearshore currents at a high-energy mesotidal beach with the presence of a 500-m headland and a submerged reef. Small changes in wave forcing and tide elevation were found to largely impact circulation patterns. In particular, under 4-m oblique wave conditions, our measurements indicate the presence of an intense low-frequency fluctuating deflection rip flowing against the headland and extending well beyond the surf zone. An XBeach model is further set up to hindcast such flow patterns.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/EiqnjBIkWJE

scholarly journals Geomagnetic activity and local time dependence of the distribution of ultra low-frequency wave power in azimuthal wavenumbers, <i>m</i>

2017 ◽  
Vol 35 (3) ◽  
pp. 629-638 ◽  
Author(s):  
Theodore E. Sarris ◽  
Xinlin Li
Keyword(s):  
Phase Difference ◽  
Low Frequency ◽  
Field Measurements ◽  
Resonant Interaction ◽  
Total Power ◽  
Ulf Waves ◽  
Quiet Time ◽  
Frequency Wave ◽  
Drift Frequency ◽  
Diffusion Rates

Abstract. The azimuthal wavenumber m of ultra low-frequency (ULF) waves in the magnetosphere is a required parameter in the calculations of the diffusion rates of energetic electrons and protons in the magnetosphere, as electrons and protons of drift frequency ωd have been shown to radially diffuse due to resonant interaction with ULF waves of frequency ω = mωd. However, there are difficulties in estimating m, due to lack of multipoint measurements. In this paper we use magnetic field measurements at geosynchronous orbit to calculate the cross-spectrogram power and phase differences between time series from magnetometer pairs. Subsequently, assuming that ULF waves of a certain frequency and m would be observed with a certain phase difference between two azimuthally aligned magnetometers, the fraction of the total power in each phase difference range is calculated. As part of the analysis, both quiet-time and storm-time distributions of power per m number are calculated, and it is shown that during active times, a smaller fraction of total power is confined to lower m than during quiet times. It is also shown that in the dayside region, power is distributed mostly to the lowest azimuthal wavenumbers m = 1 and 2, whereas on the nightside it is more equally distributed to all m that can be resolved by the azimuthal separation between two spacecraft.

South Baltic rip currents detected by a field survey

Baltica ◽  
2020 ◽  
Vol 33 (1) ◽  
pp. 11-20
Author(s):  
Rafał Ostrowski ◽  
Jan Schönhofer ◽  
Magdalena Stella ◽  
Alexey Grave ◽  
Aleksander Babakov ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Maximum Velocity ◽  
Experimental Investigations ◽  
Rip Currents ◽  
The South ◽  
Storm Waves ◽  
Circulation Patterns ◽  
Wave Conditions ◽  
Deep Water Wave ◽  
Russian Research

The paper presents results of experimental investigations of currents in the nearshore region of the south Baltic Sea. The analysis is based on the field data collected near Lubiatowo (Poland) using the measuring equipment which was simultaneously operated both by the Polish and Russian research teams. The venture was aimed at detection of rip currents that are rare and insufficiently explored phenomena in the south Baltic coastal zone. The data include wind velocity and direction, deep-water wave buoy records and currents surveyed by means of drifters. The measurements were carried out in the area whose hydrodynamics, lithodynamics and morphodynamics are typical of the south Baltic sandy coast. It appears that the nearshore water flows are mostly represented by longshore wave-driven currents with mean velocities of 0.22–0.53 m/s, and the maximum velocity of 1.32 m/s. Water circulation patterns resembling rip currents with velocities of up to 0.34 m/s were identified only on one day, when specific wave conditions occurred at the study site. Contrary to strong longshore currents generated by storm waves, rip currents occur under mild or moderate wave conditions, when many beach users are willing to swim in nearshore waters. The present findings can therefore be useful for the improvement of swimmers’ safety in the south Baltic Sea regions.

scholarly journals Small defects reconstruction in waveguides from multifrequency one-side scattering data

2021 ◽  
Vol 0 (0) ◽  
pp. 0
Author(s):  
Éric Bonnetier ◽  
Angèle Niclas ◽  
Laurent Seppecher ◽  
Grégory Vial
Keyword(s):  
Born Approximation ◽  
Field Measurements ◽  
Scattering Data ◽  
Inversion Method ◽  
Local Perturbation ◽  
Fourier Domain ◽  
Fourier Inversion ◽  
Frequency Wave ◽  
Partial Data ◽  
Stable Reconstruction

<p style='text-indent:20px;'>Localization and reconstruction of small defects in acoustic or electromagnetic waveguides is of crucial interest in nondestructive evaluation of structures. The aim of this work is to present a new multi-frequency inversion method to reconstruct small defects in a 2D waveguide. Given one-side multi-frequency wave field measurements of propagating modes, we use a Born approximation to provide a <inline-formula><tex-math id="M1">\begin{document}$ \text{L}^2 $\end{document}</tex-math></inline-formula>-stable reconstruction of three types of defects: a local perturbation inside the waveguide, a bending of the waveguide, and a localized defect in the geometry of the waveguide. This method is based on a mode-by-mode spacial Fourier inversion from the available partial data in the Fourier domain. Indeed, in the available data, some high and low spatial frequency information on the defect are missing. We overcome this issue using both a compact support hypothesis and a minimal smoothness hypothesis on the defects. We also provide a suitable numerical method for efficient reconstruction of such defects and we discuss its applications and limits.</p>

scholarly journals RADIO-FREQUENCY WAVE APPLICATION IN ESTHETIC SURGERY OF HEAD AND NECK

2008 ◽  
Vol 37 (2) ◽  
pp. 137-142
Author(s):  
Vukoje Novak
Keyword(s):  
Head And Neck ◽  
Surgical Procedures ◽  
Soft Tissues ◽  
New Technology ◽  
Surgical Techniques ◽  
Pathological Process ◽  
Wave Form ◽  
Esthetic Surgery ◽  
Frequency Wave ◽  
Radio Frequency Wave

Introduction: Four-megahertz radiowave surgery is a relatively new technology usage of which rapidly expands reaching superior results compared to other surgical techniques. Radiosurgery is an atraumatic metod of cutting and coagulation of soft tissues that uses optimal low heat 4.0 MHz source for numerous plastic,esthetic and cosmetic interventions which reguires surgical precision, penetration control and low temperature. This technology allows us to simultaneously cut and coagulate the tissue with minimal lateral tissue alteration, without burning damage and with better wounds healing.This mode is used by the author in high vascularity anatomical areas and for the deeper tissue of the head and neck. The pure cutting wave-form is ideal for skin excision with otoplasty and blepharoplasty when we expect ideal esthetic result. Coagulation is obviously paramount for any surgeon and can make the difference between a good and poor result. When he coagulates tissues in the head and neck, the surgen is frequently close to significant structures such as nerves and vessels which we must protect. Ellman Sugitron 4.0 offers great advantages. One of the stronges point of the Ellman system is the large array of specialized electrodes. By bending the malleable electrodes we can use them at any angle or even around corners. Material and Methods: The Author has done surgical procedures on over 600 patients using this technique on different esthetic problems with satisfying results. In operative material dominate various skin growths (hemangioma, fibroma, naevus, wart) blepharoplasy, otoplasty, rhinoplasty and other minor surgical procedures. Interventions were done in local anesthesy. The aim of this work is to present our observations about radioablation in heterogenous pathological process on head and neck based of our own experience. Results: Our results show that this technology have great advantage over other techniques (scalpel, electrocouter, laser) from which the most important are simultaneous cutting and coagulation,coagulation in liquid medium, minimal termal damage of latteral tissues, faster healing of wounds with excellent cosmetic results. If we want surgery without cut,cut without scar, Ellman Sugitron is the best choice.

scholarly journals WAVE-FORMED RIPPLES IN NEARSHORE SANDS

1976 ◽  
Vol 1 (15) ◽  
pp. 122 ◽  
Author(s):  
John R. Dingler ◽  
Douglas L. Inman
Keyword(s):  
Wave Motion ◽  
Wave Spectrum ◽  
Fine Sand ◽  
Wave Form ◽  
Flow Sheet ◽  
Sheet Flow ◽  
Stress Criterion ◽  
Relative Stress ◽  
La Jolla ◽  
Relict Ripples

Ripples are generated and modified by wind-generated waves and their profiles are controlled by the nature of the near-bottom wave motion and by the size of the bed material. Wave-formed ripples develop under a definable set of conditions called the ripple regime. The ripple regime is bounded by those conditions that initiate grain motion, low-wave intensity, and by those that cause the disappearance of ripples, onset of sheet flow. Sheet flow occurs when intense wave motion causes several grain layers to be in motion. Three distinct ripple types occur in nearshbre areas of fine sand - relict ripples, vortex ripples, and transition ripples. Vortex and transition ripples lie within the active ripple regime, whereas relict ripples do not. Ripples in fine sand were studied in the field at La Jolla, California, where profiles were obtained using a newly developed high-resolution sonar capable of vertical resolution of the order of one millimeter. Simultaneous profile and wave-pressure measurements permit correlation of the ripple profiles with individual waves and with the wave spectrum. The sonar, with its rapid scan capability (^ one meter per second), gives instantaneous measurement of the actively changing bed features in nearshore waters. The combination of bottom scans and wavepressure measurements extends previous wave-ripple studies to include all of the nearshore ripple regime. The relation between the wave and ripple data from this study is best shown by plotting ripple steepness n/A against the wave form of the Shields relative stress criterion 0. Vortex ripples (n /\ ^_ 0.15) occur for 0 values less than 40 but greater than the minimum value which is determined by the onset of grain motion.

scholarly journals STABILITY ANALYSIS OF SEAFLOOR FOUNDATIONS

1980 ◽  
Vol 1 (17) ◽  
pp. 109 ◽  
Author(s):  
Tokuo Yamamoto ◽  
Tasumasa Suzuki
Keyword(s):  
Stability Analysis ◽  
Wave Length ◽  
Field Measurements ◽  
Senior Author ◽  
Effective Stresses ◽  
Design Storm ◽  
Storm Waves ◽  
Effective Stress Analysis ◽  
Concrete Blocks ◽  
Wave Induced

Stability analysis of homogeneous and inhomogeneous seabed foundations under attack by storm waves are made by calculating the wave induced effective stresses. Wave induced effective stress analysis of homogeneous seabed is made using the theory previously developed by the senior author which is based on the poro-elastic theory by Biot. Effective stresses in inhomogeneous seabeds induced by waves are calculated by approximating an inhomogeneous bed by many layers of homogeneous soils each of which has different geotechnical properties of soils. A good agreement is obtained between the theory and the pore pressure data in situ field measurements. For a given wave length, it is found that there exists a most unstable thickness of homogeneous seabed when the seabed thickness is one-fifth of the wave length. As a realistic example of an inhomogeneous bed, the effective stresses in a typical seabed formation at the Mississippi Delta area of the Gulf of Mexico under the attack of design storm waves are calculated. The numerical results indicate that the storm waves induce a continuous submarine landslide which extends as deep as 9 m from the mud line. Numerical calculations also indicate that such landslides and liquefaction of seabeds can be prevented by placing a layer of concrete blocks or rubbles on the top of the seabeds.

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