95 research outputs found
Sandwich Town Neck Beach UAS Aerial Imagery 2018-01-04 (Peter Traykovski, Woods Hole Oceanographic Intitution)
No full textAerial Images from a DJI Phantom 4 with FC330 Camera and Kinematic GPS Marker Flag Locations, in support of coastal morphology studies
Using Unmanned Survey Vehicles to Measure Coastal Morphodynamic Processes and Improve Models
No full textThis talk will describe the development of a small surf capable USV and its use in conducting bathymetric surveys to improve sand bar migration models. Surveys were conducted at Pea Island, NC, South shore of Martha’s Vineyard MA, and East facing beaches of Cape Cod. Surveys strategies were adapted to the unique challenges of each environment and new features such as real-time data transmission and map generation were developed to ensure successful outcomes. Along with the bathymetric data structure from motion topography from a tethered blimp or GNSS track line data from a back-pack system was usually collected to create bathy-topo maps from –10 m depths to + 3 m elevations. Data from the surveys documented both offshore sandbar migration during a highly energetic wave event at Martha’s Vineyard (4 m wave height) and onshore migration at Pea Island in response to moderate energy waves.
Coupled nearshore hydrodynamic, sediment transport and morphology models such as Xbeach typically require different scaling coefficients for wave skewness and acceleration sand transport terms to hindcast onshore or offshore sand bar migration, e.g., the direction of migration needs to be known a-priori for successful hindcasts. The talk will describe implementing a new bedload model based on measurements of wave formed ripple migration into Xbeach and the implication for sand bar migration prediction. The new bedload model has enhanced transport rates at low stresses compared to those currently included in XBeach which results in improved ability to predict on and offshore sand bar migration events with a single set of tuning coefficients.
Presenter Bio
Peter Traykovski received his B.S. degree in mechanical engineering from Duke University in Durham, NC in 1988, an M.S. & Ocean Engineer degree from the Massachusetts Institute of Technology & Woods Hole Oceanographic Institution Join Program (MIT&WHOI) in Cambridge and Woods Hole, MA in 1994, and a Ph.D. in Applied Ocean Sciences and Engineering from the MIT & WHOI Joint program in 1998.
He was a post-doctoral investigator at WHOI from 1998 to 2000 and has been employed there as a scientist since 2000. He currently holds the position of Associate Scientist with Tenure in the department of Applied Ocean Physics and Engineering. His research interests include Sediment Transport, Coastal Processes, and Acoustical Oceanography. In sediment transport, his research has focused on measurements and modeling of time dependent bedform morphology and the dynamics of high concentration fine sediment (fluid mud) flows in the wave boundary layer. One of his most important contributions was the discovery of wave supported turbidity flows of fluid mud on relatively flat continental shelves in the late 1990’s. In addition to his scientific interests, he has also focused on developing technology for measuring sediment transport processes and coastal morphology. This has included adapting high frequency imaging sonars for autonomous use in the ocean and development of pulse-coherent Doppler profilers for measuring turbulent flows. More recently he has been active in developing low cost autonomous surface vessels (ASVs) for coastal oceanographic and bathymetric survey. Combining measurements from with topography generated with unmanned aerial system (UAS) photogrammetric techniques allows high resolution and rapid repeat interval surveying of coastal systems.
Dr. Traykovski a member of the Acoustical Society of America, American Geophysical Union and Institute of Electrical and Electronics Engineers
Horizontal directional spectrum estimation of the Heard Island transmissions
No full textThesis (Ocean. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, and Woods Hole Oceanographic Institution, 1994.Includes bibliographical references.by Peter Traykovski.Ocean.E
Observations and modeling of sand transport in a wave dominated environment
No full textThesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 1998.Includes bibliographical references.by Peter Traykovski.Ph.D
High and variable drag in a sinuous estuary with intermittent stratification
No full text© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bo, T., Ralston, D. K., Kranenburg, W. M., Geyer, W. R., & Traykovski, P. High and variable drag in a sinuous estuary with intermittent stratification. Journal of Geophysical Research: Oceans, 126(10), (2021): e2021JC017327, https://doi.org/10.1029/2021JC017327In field observations from a sinuous estuary, the drag coefficient C based on the momentum balance was in the range of 5-20 X10-3, much greater than expected from bottom friction alone. C also varied at tidal and seasonal timescales. CD was greater during flood tides than ebbs, most notably during spring tides. The ebb tide CD was negatively correlated with river discharge, while the flood tide CD showed no dependence on discharge. The large values of CD are explained by form drag from flow separation at sharp channel bends. Greater water depths during flood tides corresponded with increased values of CD, consistent with the expected depth dependence for flow separation, as flow separation becomes stronger in deeper water. Additionally, the strength of the adverse pressure gradient downstream of the bend apex, which is indicative of flow separation, correlated with CD during flood tides. While CD generally increased with water depth, CD decreased for the highest water levels that corresponded with overbank flow. The decrease in CD may be due to the inhibition of flow separation with flow over the vegetated marsh. The dependence of CD during ebbs on discharge corresponds with the inhibition of flow separation by a favoring baroclinic pressure gradient that is locally generated at the bend apex due to curvature-induced secondary circulation. This effect increases with stratification, which increases with discharge. Additional factors may contribute to the high drag, including secondary circulation, multiple scales of bedforms, and shallow shoals, but the observations suggest that flow separation is the primary source.The research leading to these results was funded by NSF awards OCE-1634480, OCE-1634481, and OCE-2123002.2022-03-2
Travel-time perturbations due to internal waves : equivalence of modal and ray solutions
No full textAuthor Posting. © Acoustical Society of America, 1996. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 99 (1996): 822-830, doi:10.1121/1.414563.In a recent paper, Lynch et al. used modal and ray based perturbation techniques to compare predicted variances of acoustic travel times due to internal waves to measured variances in the Barents Sea Polar Front experiment [Lynch et al., J. Acoust. Soc. Am. 99, 803–821 (1996)]. One of the interesting results of this work is that the modal and ray travel-time variances are substantially different for rays and modes with the same grazing angle. Specifically, the maximum modal travel-time variance shows a resonant effect in which the variance increases with increasing frequency. Unlike the modal solution, the ray travel-time variance has a geometrically constrained maximum, independent of frequency. In this paper, the linear first-order solutions for the ray and modal variances due to the internal waves are reviewed, and in an Appendix the effects of the linearizing assumptions are examined. The ray and mode solutions are then shown to be consistent by considering a truncated sum of modes that constructively interfere along a geometric ray path. By defining the travel-time perturbation due to a truncated sum of modes, the travel-time variance of the modal sum is derived. With increasing frequency the maximum value of this variance converges to a frequency-independent result with a similar magnitude to the ray maximum variance
Observations of wave orbital scale ripples and a nonequilibrium time-dependent model
No full textAuthor Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C06026, doi:10.1029/2006JC003811.Measurements of seafloor ripples under wave-dominated conditions from the LEO15 site and the Martha’s Vineyard coastal observatory were used to develop a time-dependent model for ripple geometry. The measurements consisted of backscatter imagery from rotary side-scan sonars, centimeter resolution bathymetric maps from a two-axis rotary pencil-beam sonar, and forcing hydrodynamics. During moderate energy conditions the ripple wavelength typically scaled with wave orbital diameter. In more energetic conditions the ripples reached a maximum wavelength of 0.8 to 1.2 m and did not continue to increase in wavelength or decrease in height. The observations showed that the relict ripples left after storms typically had wavelengths close to the maximum wavelength. The time-dependent model is based on an equilibrium model that allows the ripples to maintain wavelength proportional to wave orbital diameter until a suspension threshold determined by wave velocity and grain size is reached. The time-dependent model allows the ripple spectra to follow the equilibrium solution with a temporal delay that is based on the ratio of the ripple cross-sectional area to the sediment transport rate. The data was compared to the equilibrium model, a simplified version of the time-dependent model (where the ripples were assumed to follow the equilibrium model only when the bed stress was sufficient to move sediment), and the complete time-dependent model. It was found that only the complete time-dependent model was able to correctly predict the long wavelength relict ripples and that the other approaches underpredicted relict ripple wavelengths.This work was funded under ONR grants N00014-01-
10564 and N00014-06-10329
Observations and modeling of wave-supported sediment gravity flows on the Po prodelta and comparison to prior observations from the Eel shelf
No full textAuthor Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 27 (2007): 375-399, doi:10.1016/j.csr.2005.07.008.A mooring and tripod array was deployed from the fall of 2002 through the spring of 2003 on the Po prodelta to measure sediment transport processes associated with sediment delivered from the Po River. Observations on the prodelta revealed wave-supported gravity flows of high concentration mud suspensions that are dynamically and kinematically similar to those observed on the Eel shelf (Traykovski et al., 2000). Due to the dynamic similarity between the two sites, a simple one-dimensional across-shelf model with the appropriate bottom boundary condition was used to examine fluxes associated with this transport mechanism at both locations. To calculate the sediment concentrations associated with the wave-dominated and wave-current resuspension, a bottom boundary condition using a reference concentration was combined with an “active layer” formulation to limit the amount of sediment in suspension. Whereas the wave-supported gravity flow mechanism dominates the transport on the Eel shelf, on the Po prodelta flux due to this mechanism is equal in magnitude to transport due to wave resuspension and wind-forced mean currents in cross-shore direction. Southward transport due to wave resuspension and wind forced mean currents move an order of magnitude more sediment along-shore than the downslope flux associated wave-supported gravity flows.This work funded by the U.S. Office of Naval Research under grant number #N00014-02-10378, under the direction of program manager, Tom Drake
Coupled dynamics of interfacial waves and bed forms in fluid muds over erodible seabeds in oscillatory flows
No full text© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 5698–5709, doi:10.1002/2015JC010872.Recent field investigations of the damping of ocean surface waves over fluid muds have revealed waves on the interface between the thin layer of fluid mud and the overlying much thicker column of clear water, accompanied by bed forms on the erodible seabed beneath the fluid mud. The frequencies and wavelengths of the observed interfacial waves are qualitatively consistent with the linear dispersion relationship for long interfacial waves, but the forcing mechanism is not known. To understand the forcing, a linear model is proposed, based on the layer-averaged hydrostatic equations for the fluid mud, together with the Meyer-Peter-Mueller equation for the sediment transport within the underlying seabed, both subject to oscillatory forcing by the surface waves. If the underlying seabed is nonerodible and flat, the model indicates parametric instability to interfacial waves, but the threshold for instability is not met by the observations. If the underlying seabed is erodible, the model indicates that perturbations to the seabed elevation in the presence of the oscillatory forcing create interfacial waves, which in turn produce stresses within the fluid mud that force a net transport of sediment within the seabed toward the bed form crests, thus causing growth of both bed forms and interfacial waves. The frequencies, wavelengths, and growth rates are in qualitative agreement with the observations. A competition between mixing created by the interfacial waves and gravitational settling might control the thickness, density, and viscosity of the fluid muds during periods of strong forcing.This study was supported by the Coastal Geodynamics Program at the Office of Naval Research and by the Physical Oceanography Program at the National Science Foundation
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