DOCSLIB.ORG

Experimental Modeling of a Rip Current System

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Experimental Modeling of a Rip Current System Reprinted from WAVES Proceedings of the Third International Symposium on Ocean Wave Measurement and Analysis Virginia Beach VA Nov Exp erimental Mo deling of a Rip Current System Merrick C Haller R A Dalrymple and I A Svendsen Abstract Results from an exp erimental investigation of a rip current system in a lab o ratory wave basin are presented The mo deled system includes a planar b each with a sup erimp osed longshore bar containing two rip channels Dense mea surements of water surface elevation crossshore and longshore currents are presented The exp erimental results indicate that in addition to the steady mean water level gradients which drive the steady nearshore circulation time varying pressure gradients are generated in the rip current system and these gradients are directly related to measured current oscillations in the rips Os cillations in the rip currents are shown to have multiple scales A simple calculation shows that classical jet instability theory can predict the order of magnitude of the measured short time scale rip current oscillations Background Shepard rst intro duced the concept of the rip current In the obser vations of Shepard et al and Shepard and Inman those authors describ ed three characteristics of rip currents they are driven by longshore variations in wave height they exhibit p erio dic uctuations in time and are often p erio dically spaced in the longshore direction and they increase in strength with increasing wave height Later observers also noted that many rip currents are not stationary McKenzie Short The oshore end of the rips the rip head can op around like an untended garden hose and the entire rip current can migrate in the longshore direction generation is nearshore One commonly observed mechanism of rip current wave height variations induced by longshore varying b ottom bathymetry In this pap er we will investigate in the lab oratory the waves and currents gen erated in a nearshore system characterized by a longshore varying bathymetry all at Center for Applied Coastal Research Ocean Engineering Lab University of Delaware Newark DE USA Corresp ondence email merrickcoastaludeledu y 3.6 m 1.8 m 18.2 m 7.3 m 1.8 m 3.6 m x 20 m 6 cm 1:30 1:5 Figure Plan view and crosssection of the exp erimental basin and p erio dic rip currents A limited set of eld measurements of rip current systems do es exist Sonu Bowman et al Tang and Dalrymple however due to their transient nature rip currents tend to elude eld in vestigators intent on measuring them with stationary instrumentdeployments In contrast the lab oratory has proven to b e very conducive to the study of rip currents since the environment is more easily controlled Preliminary results from this exp erimentwere given in Haller et al the presentwork utilizes all the data obtained during this exp eriment therefore providing more detailed rip current measurements than rep orted previously and provides an indepth discussion of the low frequency motion observed Physical Mo del t was conducted in the m m directional wave basin at The exp erimen the Center for Applied Coastal Research at the University of Delaware The basin Figure contains a planar concrete b each of slop e along with a steep er to e structure A discontinuous longshore bar made of molded plastic was attached directly onto the b eachslope The crest of the bar is cm ab ove the planar b each and it has a parab olic shap e in the crossshore The discontinuities result from the two gaps in the bar which act as rip channels and tend to x the lo cation of oshore directed rip currents dep ending on the wave conditions These rip channels are lo cated at and of the width of the basin and are each m wide with slop ed sides Separate arrays of ten capacitance wave gages and acousticdoppler velo city meters ADV were used to measure the generated wave elds mean water levels and circulation patterns u u v Details of the exp erimental pro cedure can b e found in Haller et al Most of the exp erimental runs lasted for minutes after the onset of wave generation However a limited set of additional tests were conducted with longer runs of minutes and these will also be discussed here a) Wave Gages b) Current Meters 20 20 15 15 10 10 x (m) x (m) x 5 5 x 0 0 15 10 5 0 15 10 5 0 y (m) y (m) Figure Sampling lo cations for awave gages and b current meters Figure shows the measurement lo cations for the measuring runs describ ed in this pap er The measurement lo cations were densely concentrated around one rip channel in order to resolve the strong pressure and velo city gradients near the rip current However measurements did span a large area of the basin and covered all regions of interest The ADV measurements taken shoreward of x m were taken cm from the b ottom The oshore ADV measure ment lines at x m and m were taken cm and cm from the b ottom resp ectively The still water line was at x m the wave generator at x m and the water depth at the bar crest x m was cm Results Steady circulation The waves were generated normally incident to the shoreline and the oshore wave heightwas cm at x m y m with a frequency ofHz The spatial variations of wave height and water level timeaveraged over the last half of the data collection p erio d s are shown in Figure The mea surements show that there is little variation in the mean quantities H rms oshore but near x m the waveheight decays sharply due to strong break ing induced by the bar Corresp ondingly the intense wave breaking over the bar drives a sharp increase in the mean water level in this region and a wave induced setup of mm at the shoreline in the center of the basin y m In the rip channel wave breaking is less intense and mostly o ccurs shore ward of x m Therefore there is a lo cal elevation hill of wave height in the channel and the contours of in the rip channel show a lo cal depression valley trending in the oshore direction a) b) 14 14 13 13 12 12 x (m) 11 x (m) 11 10 10 9 9 8 8 18 16 14 12 10 8 18 16 14 12 10 8 y (m) y (m) Figure Contours of a H contour interval cm and b contour rms interval cm H is computed from bandpassed f Hz rms water surface elevation records Figure compares the crossshore variations of H and measured through rms the rip channel and in the center of the basin Notice the largest measured longshore gradients are near x m which is just shoreward of the bar in what would be considered the bar trough It is also interesting to note that close to the shoreline at x m the longshore gradients are reversed from those in the trough The time average of the mean ows are shown in Figure It can b e seen that the longshore setup gradient induces strong longshore currents in the troughs and exit oshore as rip which are driven towards the rip where they converge currents However due to the reversal of the longshore setup gradient near the shoreline the ow at the shoreline is driven away from the rip channels Figure ab shows crossshore proles of the longshore currents measured near the rip channel and in the center of the basin areas enclosed by dashed lines in c resp ectively There is very little longshore ow in the surf zone at the basin center which implies the dynamics are dominated by the crossshore momentum balance in this region Near the rip channel the longshore currents a) 6 4 cm s m 2 r H 0 4 6 8 10 12 14 14.9 b) 0.4 0.2 cm 0 −0.2 4 6 8 10 12 14 14.9 c) 0.8 0.6 h (m) 0.4 0.2 4 6 8 10 12 14 14.9 x (m) Figure Crossshore variation of a H b measured in rip channel rms dashed line and in center of basin solid line c crossshore prole of bathymetry in center of basin are considerably stronger Also the reversal of longshore ow at the shoreline induces a pronounced shear on the shoreward face of the prole The entire measured circulation is shown in Figure c The current vectors indicate that the dominant feature of the nearshore circulation is the strong oshore directed jet in the rip channel In addition there are two separate h circulation patterns The rst is the classical rip current circulation whic encompasses the longshore feeder currents at the base of the rip the narrow rip neck where the currents are strongest and the rip head where the current spreads out and diminishes Oshore of the rip head the ow diverges and returns shorewards over the bars The secondary circulation is the reverse ows just shoreward of the base of the rips Here the waves which have shoaled through the rip channels break again at the shoreline driving ows is opp osite from the primary circulation away from the rip channels which Figure shows the spatial variation of the timeaveraged ows measured in the rip channel At the entrance to the rip channel abthe rip current is a narrow oshore directed jet which is being fed by converging feeder currents a) b) 14 14 13 13 12 12 x (m) 11 x (m) 11 10 10 9 9 10 0 −10 10 0 −10 v (cm/s) v (cm/s) c) 14 13 12 x (m) 11 10 9 18 16 14 12 10 8 6 4 2 0 y (m) Figure Crossshore proles of longshore current measured near a the rip channel y m b the basin center y m Measuring lo cations for a and b corresp ond to those enclosed by dashed lines in c cvectors of time averaged measured currentvelo cities Dashed line at x m represents still water line as shown by the opp osite sign of the longshore velo city on each side of the rip Figure cd shows that as the rip current exits the channel the sign of the v velo cities has reversed which indicates the ow is starting to diverge oshore comp onent of the ow u has a triangular longshore In addition the prole Results
Load more

Recommended publications
  • Well-Balanced Schemes for the Shallow Water Equations with Coriolis Forces
    Well-balanced schemes for the shallow water equations with Coriolis forces Alina Chertock, Michael Dudzinski, Alexander Kurganov & Mária Lukáčová- Medvid’ová Numerische Mathematik ISSN 0029-599X Volume 138 Number 4 Numer. Math. (2018) 138:939-973 DOI 10.1007/s00211-017-0928-0 1 23 Your article is protected by copyright and all rights are held exclusively by Springer- Verlag GmbH Germany, part of Springer Nature. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Numer. Math. (2018) 138:939–973 Numerische https://doi.org/10.1007/s00211-017-0928-0 Mathematik Well-balanced schemes for the shallow water equations with Coriolis forces Alina Chertock1 · Michael Dudzinski2 · Alexander Kurganov3,4 · Mária Lukáˇcová-Medvid’ová5 Received: 28 April 2014 / Revised: 19 September 2017 / Published online: 2 December 2017 © Springer-Verlag GmbH Germany, part of Springer Nature 2017 Abstract In the present paper we study shallow water equations with bottom topog- raphy and Coriolis forces. The latter yield non-local potential operators that need to be taken into account in order to derive a well-balanced numerical scheme.
    [Show full text]
  • Part II-1 Water Wave Mechanics
    Chapter 1 EM 1110-2-1100 WATER WAVE MECHANICS (Part II) 1 August 2008 (Change 2) Table of Contents Page II-1-1. Introduction ............................................................II-1-1 II-1-2. Regular Waves .........................................................II-1-3 a. Introduction ...........................................................II-1-3 b. Definition of wave parameters .............................................II-1-4 c. Linear wave theory ......................................................II-1-5 (1) Introduction .......................................................II-1-5 (2) Wave celerity, length, and period.......................................II-1-6 (3) The sinusoidal wave profile...........................................II-1-9 (4) Some useful functions ...............................................II-1-9 (5) Local fluid velocities and accelerations .................................II-1-12 (6) Water particle displacements .........................................II-1-13 (7) Subsurface pressure ................................................II-1-21 (8) Group velocity ....................................................II-1-22 (9) Wave energy and power.............................................II-1-26 (10)Summary of linear wave theory.......................................II-1-29 d. Nonlinear wave theories .................................................II-1-30 (1) Introduction ......................................................II-1-30 (2) Stokes finite-amplitude wave theory ...................................II-1-32
    [Show full text]
  • Beach Safety in Atypical Rip Current Systems: Testing Traditional Beach Safety Messages in Non-Traditional Settings
    Beach safety in atypical rip current systems: testing traditional beach safety messages in non-traditional settings Benjamin Robert Van Leeuwen A thesis in fulfilment of the requirements for the degree of Master of Science School of Biological, Earth and Environmental Science (BEES) Faculty of Science Supervisors: Associate Professor Robert Brander, School of Biological, Earth and Environmental Sciences, UNSW Australia, Sydney, NSW, 2052, Australia Professor Ian Turner, Water Research Laboratory, School of Civil and Environmental Engineering, UNSW Australia, Manly Vale, NSW, 2093, Australia July 2015 PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Van Leeuwen First name: Benjamin Other name/s: Robert Abbreviation for degree as given in the University calendar: MSc School: School of Biological, Earth and Environmental Sciences Faculty: Science Title: Beach safety in atypical rip current systems: testing traditional beach safety messages in non-traditional settings Abstract 350 words maximum: (PLEASE TYPE) As a major coastal process and hazard, rip currents are a topic of considerable interest from both a scientific and safety perspective. Collaborations between these two areas are a recent development, yet a scientific basis for safety information is crucial to better understanding how to avoid and mitigate the hazard presented by rip currents. One such area is the field of swimmer escape strategies. Contemporary safety advice is divided on the relative merits of a ‘Stay Afloat’ versus ‘Swim Parallel’ strategy, yet conceptual understanding of both these strategies is largely based on an idealised model of rip current morphology and flow dynamics where channels are incised in shore-connected bars.
    [Show full text]
  • Fluid Simulation Using Shallow Water Equation
    Fluid Simulation using Shallow Water Equation Dhruv Kore Itika Gupta Undergraduate Student Graduate Student University of Illinois at Chicago University of Illinois at Chicago [email protected] [email protected] 847-345-9745 312-478-0764 ABSTRACT rivers and channel. As the name suggest, the main In this paper, we present a technique, which shows how characteristic of shallow Water flows is that the vertical waves once generated from a small drop continue to ripple. dimension is much smaller as compared to the horizontal Waves interact with each other and on collision change the dimension. Naïve Stroke Equation defines the motion of form and direction. Once the waves strike the boundary, fluids and from these equations we derive SWE. they return with the same speed and in sometime, depending on the delay, you can see continuous ripples in In Next section we talk about the related works under the the surface. We use shallow water equation to achieve the heading Literature Review. Then we will explain the desired output. framework and other concepts necessary to understand the SWE and wave equation. In the section followed by it, we Author Keywords show the results achieved using our implementation. Then Naïve Stroke Equation; Shallow Water Equation; Fluid finally we talk about conclusion and future work. Simulation; WebGL; Quadratic function. LITERATURE REVIEW INTRODUCTION In [2] author in detail explains the Shallow water equation In early years of fluid simulation, procedural surface with its derivation. Since then a lot of authors has used generation was used to represent waves as presented by SWE to present the formation of waves in water.
    [Show full text]
  • Shallow Water Waves and Solitary Waves Article Outline Glossary
    Shallow Water Waves and Solitary Waves Willy Hereman Department of Mathematical and Computer Sciences, Colorado School of Mines, Golden, Colorado, USA Article Outline Glossary I. Definition of the Subject II. Introduction{Historical Perspective III. Completely Integrable Shallow Water Wave Equations IV. Shallow Water Wave Equations of Geophysical Fluid Dynamics V. Computation of Solitary Wave Solutions VI. Water Wave Experiments and Observations VII. Future Directions VIII. Bibliography Glossary Deep water A surface wave is said to be in deep water if its wavelength is much shorter than the local water depth. Internal wave A internal wave travels within the interior of a fluid. The maximum velocity and maximum amplitude occur within the fluid or at an internal boundary (interface). Internal waves depend on the density-stratification of the fluid. Shallow water A surface wave is said to be in shallow water if its wavelength is much larger than the local water depth. Shallow water waves Shallow water waves correspond to the flow at the free surface of a body of shallow water under the force of gravity, or to the flow below a horizontal pressure surface in a fluid. Shallow water wave equations Shallow water wave equations are a set of partial differential equations that describe shallow water waves. 1 Solitary wave A solitary wave is a localized gravity wave that maintains its coherence and, hence, its visi- bility through properties of nonlinear hydrodynamics. Solitary waves have finite amplitude and propagate with constant speed and constant shape. Soliton Solitons are solitary waves that have an elastic scattering property: they retain their shape and speed after colliding with each other.
    [Show full text]
  • Shallow-Water Equations and Related Topics
    CHAPTER 1 Shallow-Water Equations and Related Topics Didier Bresch UMR 5127 CNRS, LAMA, Universite´ de Savoie, 73376 Le Bourget-du-Lac, France Contents 1. Preface .................................................... 3 2. Introduction ................................................. 4 3. A friction shallow-water system ...................................... 5 3.1. Conservation of potential vorticity .................................. 5 3.2. The inviscid shallow-water equations ................................. 7 3.3. LERAY solutions ........................................... 11 3.3.1. A new mathematical entropy: The BD entropy ........................ 12 3.3.2. Weak solutions with drag terms ................................ 16 3.3.3. Forgetting drag terms – Stability ............................... 19 3.3.4. Bounded domains ....................................... 21 3.4. Strong solutions ............................................ 23 3.5. Other viscous terms in the literature ................................. 23 3.6. Low Froude number limits ...................................... 25 3.6.1. The quasi-geostrophic model ................................. 25 3.6.2. The lake equations ...................................... 34 3.7. An interesting open problem: Open sea boundary conditions .................... 41 3.8. Multi-level and multi-layers models ................................. 43 3.9. Friction shallow-water equations derivation ............................. 44 3.9.1. Formal derivation ....................................... 44 3.10.
    [Show full text]
  • Waves in Water from Ripples to Tsunamis and to Rogue Waves
    Waves in Water from ripples to tsunamis and to rogue waves Vera Mikyoung Hur (Mathematics) (Image from Flickr) The motion of a fluid can be very complicated as we know whenever we see waves break on a beach, (Image from the Internet) The motion of a fluid can be very complicated as we know whenever we fly in an airplane, (Image from the Internet) The motion of a fluid can be very complicated as we know whenever we look at a lake on a windy day. (Image from the Internet) Euler in the 1750s proposed a mathematical model of an incompressible fluid. @u + (u · r)u + rP = F, @t r · u = 0. Here, u(x; t) is the velocity of the fluid at the point x and time t, P(x; t) is the pressure, and F(x; t) is an outside force. The Navier-Stokes equations (adding ν∆u) allow the fluid to be viscous. It is concise and captures the essence of fluid behavior. The theory of fluids has provided source and inspiration to many branches of mathematics, e.g. Cauchy's complex function theory. Difficulties of understanding fluids are profound. e.g. the global-in-time solution of the Navier-Stokes equations in 3 dimensions is a Clay Millennium Problem! Waves, jets, drops come to mind when thinking of fluids. They involve one or more fluids separated by an unknown surface. In the mathematical community, they go by free boundary problems. (Image from the Internet) Free boundaries are mathematically challenging in their own right. They occur in many other situations, such as melting of ice stretching a membrane over an obstacle.
    [Show full text]
  • Modified Shallow Water Equations for Significantly Varying Seabeds Denys Dutykh, Didier Clamond
    Modified Shallow Water Equations for significantly varying seabeds Denys Dutykh, Didier Clamond To cite this version: Denys Dutykh, Didier Clamond. Modified Shallow Water Equations for significantly varying seabeds: Modified Shallow Water Equations. Applied Mathematical Modelling, Elsevier, 2016, 40 (23-24), pp.9767-9787. 10.1016/j.apm.2016.06.033. hal-00675209v6 HAL Id: hal-00675209 https://hal.archives-ouvertes.fr/hal-00675209v6 Submitted on 26 Apr 2016 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution - NonCommercial| 4.0 International License Denys Dutykh CNRS, Université Savoie Mont Blanc, France Didier Clamond Université de Nice – Sophia Antipolis, France Modified Shallow Water Equations for significantly varying seabeds arXiv.org / hal Last modified: April 26, 2016 Modified Shallow Water Equations for significantly varying seabeds Denys Dutykh∗ and Didier Clamond Abstract. In the present study, we propose a modified version of the Nonlinear Shal- low Water Equations (Saint-Venant or NSWE) for irrotational surface waves in the case when the bottom undergoes some significant variations in space and time. The model is derived from a variational principle by choosing an appropriate shallow water ansatz and imposing some constraints.
    [Show full text]
  • ATM 500: Atmospheric Dynamics End-Of-Semester Review, December 4 2018 Here, in Bullet Points, Are the Key Concepts from the Second Half of the Course
    ATM 500: Atmospheric Dynamics End-of-semester review, December 4 2018 Here, in bullet points, are the key concepts from the second half of the course. They are not meant to be self-contained notes! Refer back to your course notes for notation, derivations, and deeper discussion. Static stability The vertical variation of density in the environment determines whether a parcel, disturbed upward from an initial hydrostatic rest state, will accelerate away from its initial position, or oscillate about that position. For an incompressible or Boussinesq fluid, the buoyancy frequency is g dρ~ N 2 = − ρ~dz For a compressible ideal gas, the buoyancy frequency is g dθ~ N 2 = θ~dz (the expressions are different because density is not conserved in a small upward displacement of a compressible fluid, but potential temperature is conserved) Fluid is statically stable if N 2 > 0; otherwise it is statically unstable. Typical value for troposphere: N = 0:01 s−1, with corresponding oscillation period of 10 minutes. Dry adiabatic lapse rate g −1 Γd = = 9:8 K km cp The rate at which temperature decreases during adiabatic ascent (for which Dθ Dt = 0) \Dry" here means that there is no latent heating from condensation of water vapor. Static stability criteria for a dry atmosphere Environment is stable to dry con- vection if dθ~ dT~ > 0 or − < Γ dz dz d and otherwise unstable. 1 Buoyancy equation for Boussinesq fluid with background stratification Db0 + N 2w = 0 Dt where we have separated the full buoyancy into a mean vertical part ^b(z) and 0 2 d^b 2 everything else (b ), and N = dz .
    [Show full text]
  • Multilayer Shallow Water Equations with Complete Coriolis Force. Part I: Derivation on a Non-Traditional Beta-Plane
    Accepted for publication in the Journal of Fluid Mechanics °c 2010 Cambridge University Press 1 doi:10.1017/S0022112009993922 Multilayer shallow water equations with complete Coriolis force. Part I: Derivation on a non-traditional beta-plane By ANDREW L. STEWART and PAUL J. DELLAR OCIAM, Mathematical Institute, 24–29 St Giles’, Oxford, OX1 3LB, UK [email protected], [email protected] (Received 22 May 2009; revised 9 December 2009; accepted 9 December 2009) We derive equations to describe the flow of multiple superposed layers of inviscid, incompressible fluids with con- stant densities over prescribed topography in a rotating frame. Motivated by geophysical applications, these equations incorporate the complete Coriolis force. We do not make the widely used “traditional approximation” that omits the contribution to the Coriolis force from the locally horizontal part of the rotation vector. Our derivation is performed by averaging the governing Euler equations over each layer, and from two different forms of Hamilton’s variational principle that differ in their treatment of the coupling between layers. The coupling may be included implicitly through the map from Lagrangian particle labels to particle coordinates, or explicitly by adding terms representing the work done on each layer by the pressure exerted by the layers above. The latter approach requires additional terms in the Lagrangian, but extends more easily to many layers. We show that our equations obey the expected conservation laws for energy, momentum, and potential vorticity. The conserved momentum and potential vorticity are modified by non-traditional effects. The vertical component of the rotation vector that appears in the potential vorticity for each layer under the traditional approximation is replaced by the component perpendicular to the layer’s midsurface.
    [Show full text]
  • A Particle-In-Cell Method for the Solution of Two-Layer Shallow-Water Equations
    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS Int. J. Numer. Meth. Fluids 2000; 32: 515–543 A particle-in-cell method for the solution of two-layer shallow-water equations Benoit Cushman-Roisina,*, Oleg E. Esenkovb and Benedict J. Mathiasc a Thayer School of Engineering, Dartmouth College, Hano6er, NH 03755-8000, U.S.A. b Rosenstiel School of Marine and Atmospheric Science, Uni6ersity of Miami, Miami, FL 33149-1098, U.S.A. c i2 Technologies, 303 Twin Dolphin Dri6e, Redwood City, CA 94065, U.S.A. SUMMARY A particle-in-cell (PIC) numerical method developed for the study of shallow-water dynamics, when the moving fluid layer is laterally confined by the intersection of its top and bottom surfaces, is described. The effect of ambient rotation is included for application to geophysical fluids, particularly open-ocean buoyant vortices in which the underlying density interface outcrops to the surface around the rim of the vortex. Extensions to include the dynamical effect of a second moving layer (baroclinicity) and the presence of a lateral rigid boundary (sidewall) are also described. Although the method was developed for oceanographic investigations, applications to other fluid mechanics problems would be straightforward. Copyright © 2000 John Wiley & Sons, Ltd. KEY WORDS: open-ocean; particle-in-cell; shallow-water equation 1. INTRODUCTION There are a number of situations, mostly geophysical in nature, where fluid flows occur in layers that are much thinner than they are wide. In such cases, hydrostatic equilibrium is invoked in the vertical, and the equations of motion reduce to the so-called St. Venant or shallow-water equations [1].
    [Show full text]
  • Rip Current Detection
    Eurographics Conference on Visualization (EuroVis) (2016) K.-L. Ma, G. Santucci, and J. van Wijk (Guest Editors) Detecting and Visualizing Rip Current Using Optical Flow S. Philip y1 and A. Pang1 1University of California, Santa Cruz, United States Abstract Rip current are fast moving and narrow currents that are strongest near the beach. They are dangerous not only for novice but also experienced swimmers. Once caught in the current, the flow of the water pulls the person away from the beach. Many people in panic try to swim against the current and end up drowning due to exhaustion since these currents are usually faster than the speed at which one can swim. They have led to the drowning deaths of more than 100 beachgoers each year in United States alone [USL16]. For a knowledgeable person, these rip-currents are fairly easy to spot. But they are a threat to most people who are unaware of rip-currents or who do not know how to identify them. In this paper, we discuss a novel approach that uses optical flow to detect rip currents and then visualize them in an intuitive manner. Keywords: Time-dependent, vector fields, and visualization. 1. Introduction Rip currents are very fast moving and narrow channels of water that pose a serious hazard to unwary beach goers. These currents will generally pull a person out to sea. Trying to swim against the current often lead to exhaustion and can lead to drowning. Accord- ing to United States Lifesaving Association, there are four ways to visually identify rip currents: • A channel of churning, choppy water; • A line of sea foam, seaweed, or debris moving steadily seaward; • Different colored water beyond the surf zone; and • A break in the incoming wave pattern as waves roll onto shore [USL16].
    [Show full text]