scholarly journals Quantifying Optically Derived Two-Dimensional Wave-Averaged Currents in the Surf Zone

2021 ◽  
Vol 13 (4) ◽  
pp. 690
Author(s):  
Dylan Anderson ◽  
A. Spicer Bak ◽  
Katherine L. Brodie ◽  
Nicholas Cohn ◽  
Rob A. Holman ◽  
...  
Keyword(s):  
Surf Zone ◽  
Spatial Scales ◽  
Low Cost ◽  
Breaking Waves ◽  
Two Dimensional ◽  
Rip Currents ◽  
Circulation Patterns ◽  
Passive Tracers ◽  
A New Technique ◽  
Incident Waves

Complex two-dimensional nearshore current patterns are generated by feedbacks between sub-aqueous morphology and momentum imparted on the water column by breaking waves, winds, and tides. These non-stationary features, such as rip currents and circulation cells, respond to changing environmental conditions and underlying morphology. However, using fixed instruments to observe nearshore currents is limiting due to the high costs and logistics necessary to achieve adequate spatial sampling resolution. A new technique for processing surf-zone imagery, WAMFlow, quantifies fluid velocities to reveal complex, multi-scale (10 s–1000 s meters) nearshore surface circulation patterns. We apply the concept of a wave-averaged movie (WAM) to measure surf-zone circulation patterns on spatial scales of kilometers in the alongshore and 100 s of meters in the cross-shore. The approach uses a rolling average of 2 Hz optical imagery, removing the dominant optical clutter of incident waves, to leave the residual foam or water turbidity features carried by the flow. These residual features are tracked as quasi-passive tracers in space and time using optical flow, which solves for u and v as a function of image intensity gradients in x, y, and t. Surf zone drifters were deployed over multiple days with varying nearshore circulations to validate the optically derived flow patterns. Root mean square error are reduced to 0.1 m per second after filtering based on image attributes. The optically derived patterns captured longshore currents, rip currents, and gyres within the surf zone. Quantifying nearshore circulation patterns using low-cost image platforms and open-source computer vision algorithms presents the potential to further our understanding of fundamental surf zone dynamics.

scholarly journals Diffusion and the formation of vorticity staircases in randomly strained two-dimensional vortices

2009 ◽  
Vol 638 ◽  
pp. 49-72 ◽  
Author(s):  
MATTHEW R. TURNER ◽  
ANDREW P. BASSOM ◽  
ANDREW D. GILBERT
Keyword(s):  
Diffusion Equation ◽  
Surf Zone ◽  
Spatial Scales ◽  
Effective Diffusion ◽  
Effective Diffusivity ◽  
Angular Frequency ◽  
Asymptotic Model ◽  
Two Dimensional ◽  
Fine Scale ◽  
Long Time

The spreading and diffusion of two-dimensional vortices subject to weak external random strain fields is examined. The response to such a field of given angular frequency depends on the profile of the vortex and can be calculated numerically. An effective diffusivity can be determined as a function of radius and may be used to evolve the profile over a long time scale, using a diffusion equation that is both nonlinear and non-local. This equation, containing an additional smoothing parameter, is simulated starting with a Gaussian vortex. Fine scale steps in the vorticity profile develop at the periphery of the vortex and these form a vorticity staircase. The effective diffusivity is high in the steps where the vorticity gradient is low: between the steps are barriers characterized by low effective diffusivity and high vorticity gradient. The steps then merge before the vorticity is finally swept out and this leaves a vortex with a compact core and a sharp edge. There is also an increase in the effective diffusion within an encircling surf zone.In order to understand the properties of the evolution of the Gaussian vortex, an asymptotic model first proposed by Balmforth, Llewellyn Smith & Young (J. Fluid Mech., vol. 426, 2001, p. 95) is employed. The model is based on a vorticity distribution that consists of a compact vortex core surrounded by a skirt of relatively weak vorticity. Again simulations show the formation of fine scale vorticity steps within the skirt, followed by merger. The diffusion equation we develop has a tendency to generate vorticity steps on arbitrarily fine scales; these are limited in our numerical simulations by smoothing the effective diffusivity over small spatial scales.

scholarly journals COMPUTATION OF LONGSHORE CURRENTS

1974 ◽  
Vol 1 (14) ◽  
pp. 40 ◽  
Author(s):  
Ivar G. Jonsson ◽  
Ove Skovgaard ◽  
Torben S. Jacobsen
Keyword(s):  
Surf Zone ◽  
Numerical Algorithms ◽  
Field Measurements ◽  
Breaking Waves ◽  
Bottom Friction ◽  
Rip Currents ◽  
Longshore Current ◽  
Lateral Mixing ◽  
Set Up ◽  
The Given

The steady state profile of the longshore current induced by regular, obliquely incident, breaking waves, over a bottom with arbitrary parallel bottom contours, is predicted. A momentum approach is adopted. The wave parameters must be given at a depth outside the surf zone, where the current velocity is very small. The variation of the bottom roughness along the given bottom profile must be prescribed in advance. Depth refraction is included also in the calculation of wave set-down and set-up. Current refraction and rip-currents are excluded. The model includes two new expressions, one for the calculation of the turbulent lateral mixing, and one for the turbulent bottom friction. The term for the bottom friction is non-linear. Rapid convergent numerical algorithms are described for the solution of the governing equations. The predicted current profiles are compared with laboratory experiments and field measurements. For a plane sloping bottom, the influence of different eddy viscosities and constant values of bottom roughness is examined.

scholarly journals GPU-ACCELERATED SPH MODEL FOR WATER WAVES AND FREE SURFACE FLOWS

2011 ◽  
Vol 1 (32) ◽  
pp. 9 ◽  
Author(s):  
Robert Anthony Dalrymple ◽  
Alexis Herault ◽  
Giuseppe Bilotta ◽  
Rozita Jalali Farahani
Keyword(s):  
Water Waves ◽  
Graphics Processing Unit ◽  
Low Cost ◽  
Breaking Waves ◽  
Free Surface Flows ◽  
Nonlinear Phenomena ◽  
Processing Unit ◽  
Rip Currents ◽  
Nearshore Circulation ◽  
Sph Model

This paper discusses the meshless numerical method Smoothed Particle Hydrodynamics and its application to water waves and nearshore circulation. In particularly we focus on an implementation of the model on the graphics processing unit (GPU) of computers, which permits low-cost supercomputing capabilities for certain types of computational problems. The implementation here runs on Nvidia graphics cards, from off-the-shelf laptops to the top-of-line Tesla cards for workstations with their current 480 massively parallel streaming processors. Here we apply the model to breaking waves and nearshore circulation, demonstrating that SPH can model changes in wave properties due to shoaling, refraction, and diffraction and wave-current interaction; as well as nonlinear phenomena such as harmonic generation, and, by using wave-period averaged quantities, such aspects of nearshore circulation as wave set-up, longshore currents, rip currents, and nearshore circulation gyres.

TWO-DIMENSIONAL STATIC AND DYNAMIC DISPLAY SYSTEM OF BOWEL SOUND MAGNITUDE MAP FOR EVALUATION OF INTESTINAL MOTILITY

2009 ◽  
Vol 21 (05) ◽  
pp. 333-342 ◽  
Author(s):  
Chia-Hung Chien ◽  
Hsiang-Ting Huang ◽  
Cheng-Yi Wang ◽  
Fok-Ching Chong
Keyword(s):  
Real Time ◽  
Intestinal Motility ◽  
Low Cost ◽  
Activity Level ◽  
Bowel Sound ◽  
Two Dimensional ◽  
Dynamic Display ◽  
Before And After ◽  
Abdominal Surface ◽  
A New Technique

The aim of this work is to develop a new technique of two-dimensional (2D) bowel sound magnitude map (BSMM) with multichannel electronic stethoscopes to evaluate the location, intensity, and track of intestinal motility from the abdominal surface in real time. The static BSMM, obtained from the interpolation of captured one-dimensional (1D) signals, demonstrated an activity level of intestinal motility with different colors. It enabled spatial visualization of the sound origin to locate the peristaltic position of bowels. The dynamic BSMM, displayed in either time series or continuous mode, clearly showed the tracking pattern of intestinal motility on the whole abdomen. Our results verified the validation of this system with a computer simulation and the specific detection of bowel sounds (BSs). The detection of physiologic intestinal motility, including that before and after meal or before defecation, is also available with BSMMs. A simple, noninvasive, low-cost, visualizable, and real-time device has been successfully developed in this work.

scholarly journals Analysis of Rip Current Characteristics Using Dye Tracking Method

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 719
Author(s):  
Hyun Dong Kim ◽  
Kyu-Han Kim
Keyword(s):  
Surf Zone ◽  
Breaking Waves ◽  
Rip Current ◽  
Rip Currents ◽  
Induced Current ◽  
Tracking Method ◽  
Survey Techniques ◽  
Current Characteristics ◽  
Bed Material ◽  
Wave Induced

Rip currents are strong water channels flowing away from the shoreline. They can occur on any shore with breaking waves. Rip currents play a significant role in changing the topography of shallow water regions by transporting large amounts of bed material offshore. Moreover, they pose a significant danger for people living in nearshore zones and surfers and cause hundreds of deaths annually worldwide. Therefore, rip current generation characteristics have been investigated to prevent casualties. In this study, a GPS drifter survey was chosen as the investigation method; however, a few drawbacks were discovered, such as low accuracy due to the GPS drifter becoming trapped in the surf zone. Therefore, drones and dyes were used to overcome the drawbacks of drifter methods. The results of dye tracking and the 3D wave-induced current numerical simulation were compared; the velocity and formation of the rip current were found to be relatively similar. With the technological advancements and invention of new survey equipment, the survey techniques also evolve, and this paper shows that the disadvantages of the GPS-based Lagrangian method can be overcome using a dye-mounted drone, which observes the rip current easily and accurately.

Techniques for assessing the performance of circuit materials at microwave and millimetre-wave frequencies

2003 ◽  
Vol 783 ◽  
Author(s):  
Charles E Free
Keyword(s):  
Loss Tangent ◽  
Good Accuracy ◽  
Low Cost ◽  
Resonant Cavity ◽  
New Technique ◽  
Millimetre Wave ◽  
A New Technique

This paper discusses the techniques that are available for characterising circuit materials at microwave and millimetre wave frequencies. In particular, the paper focuses on a new technique for measuring the loss tangent of substrates at mm-wave frequencies using a circular resonant cavity. The benefits of the new technique are that it is simple, low cost, capable of good accuracy and has the potential to work at high mm-wave frequencies.

Ti3C2-MXene/Bismuth Ferrite Nanohybrids for Efficient Degradation of Organic Dye and Colorless Pollutant

2019 ◽  
Author(s):  
Ayesha Tariq ◽  
M. Abdullah Iqbal ◽  
S. Irfan Ali ◽  
Muhammad Z. Iqbal ◽  
Deji Akinwande ◽  
...  
Keyword(s):  
Surface Area ◽  
Low Cost ◽  
Bismuth Ferrite ◽  
Organic Dye ◽  
Two Dimensional ◽  
Electron Hole ◽  
Photocatalytic Application ◽  
Electron Hole Pair ◽  
Pair Generation ◽  
Photocatalytic Applications

<p>Nanohybrids, made up of Bismuth ferrites/Carbon allotropes, are extensively used in photocatalytic applications nowadays. Our work proposes a nanohybrid system composed of Bismuth ferrite nanoparticles with two-dimensional (2D) MXene sheets namely, the BiFeO<sub>3</sub> (BFO)/Ti<sub>3</sub>C<sub>2</sub> (MXene) nanohybrid for enhanced photocatalytic activity. We have fabricated the BFO/MXene nanohybrid using simple and low cost double solvent solvothermal method. The SEM and TEM images show that the BFO nanoparticles were attached onto the MXene surface and in the inter-layers of two-dimensional (2D) MXene sheets. The photocatalytic application is tested for the visible light irradiation which showed the highest efficiency among all pure-BFO based photocatalysts, i.e. 100% degradation in 42 min for organic dye (Congo Red) and colorless aqueous pollutant (acetophenone) in 150 min, respectively. The present BFO-based hybrid system exhibited the large surface area of 147 m<sup>2</sup>g<sup>-1</sup>measured via Brunauer-Emmett-Teller (BET) sorption-desorption technique, and is found to be largest among BFO and its derivatives. Also, the photoluminescence (PL) spectra indicate large electron-hole pair generation. Fast and efficient degradation of organic molecules is supported by both factors; larger surface area and lower electron-hole recombination rate. The BFO/MXene nanohybrid presented here is a highly efficient photocatalyst compared to other nanostructures based on pure BiFeO<sub>3</sub> which makes it a promising candidate for many future applications.</p>

Two-Dimensional Local Deep-Level Transient Spectroscopy Imaging Using Super-Higher-Order Scanning Nonlinear Dielectric Microscopy

2016 ◽  
Author(s):  
N. Chinone ◽  
Y. Cho ◽  
R. Kosugi ◽  
Y. Tanaka ◽  
S. Harada ◽  
...  
Keyword(s):  
Deep Level Transient Spectroscopy ◽  
Deep Level ◽  
Higher Order ◽  
Trap Density ◽  
New Technique ◽  
Two Dimensional ◽  
Nonlinear Dielectric ◽  
Annealing Conditions ◽  
Transient Spectroscopy ◽  
A New Technique

Abstract A new technique for local deep level transient spectroscopy (DLTS) imaging using super-higher-order scanning nonlinear dielectric microscopy is proposed. Using this technique. SiCVSiC structure samples with different post oxidation annealing conditions were measured. We observed that the local DLTS signal decreases with post oxidation annealing (POA), which agrees with the well-known phenomena that POA reduces trap density. Furthermore, obtained local DLTS images had dark and bright areas, which is considered to show the trap distribution at/near SiCVSiC interface.

scholarly journals The Accelerations of a Wave Measurement Buoy Impacted by Breaking Waves in the Surf Zone

2021 ◽  
Vol 9 (2) ◽  
pp. 214
Author(s):  
Adam C. Brown ◽  
Robert K. Paasch
Keyword(s):  
Inertial Measurement Unit ◽  
Surf Zone ◽  
Spherical Wave ◽  
Breaking Waves ◽  
Measurement Unit ◽  
High Fidelity ◽  
Wave Measurement ◽  
Near Shore ◽  
Shoaling Waves ◽  
Multiple Deployments

A spherical wave measurement buoy capable of detecting breaking waves has been designed and built. The buoy is 16 inches in diameter and houses a 9 degree of freedom inertial measurement unit (IMU). The orientation and acceleration of the buoy is continuously logged at frequencies up to 200 Hz providing a high fidelity description of the motion of the buoy as it is impacted by breaking waves. The buoy was deployed several times throughout the winter of 2013–2014. Both moored and free-drifting data were acquired in near-shore shoaling waves off the coast of Newport, OR. Almost 200 breaking waves of varying type and intensity were measured over the course of multiple deployments. The characteristic signature of spilling and plunging breakers was identified in the IMU data.

scholarly journals Microfabrication with Very Low-Average Power of Green Light to Produce PDMS Microchips

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 607
Author(s):  
Lucero M. Hernandez-Cedillo ◽  
Francisco G. Vázquez-Cuevas ◽  
Rafael Quintero-Torres ◽  
Jose L. Aragón ◽  
Miguel Angel Ocampo Mortera ◽  
...  
Keyword(s):  
Low Cost ◽  
Average Power ◽  
Green Light ◽  
Microfluidic Devices ◽  
Processing Parameters ◽  
Coating Film ◽  
Two Dimensional ◽  
Dimethyl Siloxane ◽  
Visible Laser ◽  
High Absorption

In this article, we show an alternative low-cost fabrication method to obtain poly(dimethyl siloxane) (PDMS) microfluidic devices. The proposed method allows the inscription of micron resolution channels on polystyrene (PS) surfaces, used as a mold for the wanted microchip’s production, by applying a high absorption coating film on the PS surface to ablate it with a focused low-power visible laser. The method allows for obtaining micro-resolution channels at powers between 2 and 10 mW and can realize any two-dimensional polymeric devices. The effect of the main processing parameters on the channel’s geometry is presented.

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