Peculiarities associated with testing polyetheretherketone (PEEK) in a model rolling contact

Commonly used four-ball testing configuration when used to investigate rolling contact behavior of polyetheretherketone (PEEK) produced some unexpected peculiarities, namely direct contact between ceramic balls. Direct contact between lower three balls is normally not expected to take place when elastic materials (ferrous or ceramics) are tested. However, due to the viscoelastic nature of PEEK surface damage of the ceramic balls were observed leading to the production of wear debris which in turn facilitated premature failure of PEEK components of the assembly. It is postulated that caution is required when using the four-ball testing configuration to assess rolling contact performance of viscoelastic materials, such as engineering polymers.Gdansk University of Technology, Gdansk, Poland(Grant DS-2012)

Steady wind forcing of a density front over a circular bank

The response of a density front along the edge of a circular bank to steady wind forcing is examined using a primitive equation numerical model. Initially, the fluid is at rest with relatively light, vertically homogeneous water over the bank. The density field is allowed to adjust geostrophically and frictionally for ten days, after which a spatially uniform wind stress is applied for three days. The resulting surface velocity field over the bank is asymmetrical, with a relative maximum on the downwind side of the bank to the left of the wind direction and a relative minimum on the upwind side of the bank to the right of the wind direction. For the small Ekman number considered here, the density-driven flow persists beneath the surface Ekman layer. Light fluid is advected off the bank near the surface in the direction of Ekman transport, weakening the surface density gradients. On the opposite side of the bank, the vertical structure of the density field is weakened and the surface density gradients remain relatively constant. When the wind stress is abruptly turned off, the anti-cyclonic surface velocity is restored within one inertial period, and some light fluid remains off the bank. The loss of neutrally buoyant near-surface particles released over the bank primarily occurs from the region of the bank downwind and to the right. The presence of the density front slightly increases the number of particles lost from the bank. A simple formula for the particle loss is presented

Seasonal characteristics of bottom boundary layer detachment at the shelfbreak front in the Middle Atlantic Bight

Author Posting. © American Geophysical Union, 2004. 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 109 (2004): C03049, doi:10.1029/2003JC002032.The seasonality of various characteristics of the detached bottom boundary layer of the Middle Atlantic Bight shelfbreak front is examined using a collection of high-resolution transects across the front. The analysis follows previous methodology in which accumulated temperature change along isopycnals within the front is used to infer the location of the detached layer. The seasonal mean isopycnal at which detachment occurs (approximately 26.0 kg m−3) is fairly constant throughout the year. However, the vertical scale of the detached layer varies significantly with season, extending 60−80 m above the bottom in winter and spring, but only 20−40 m above the bottom in summer. The vertical scale is controlled by the strength and depth of the seasonal pycnocline. The observations suggest that the detached layer is capable of extending into the euphotic zone during winter and spring.This work was funded by the Office of Naval Research under contracts N00014-01-1-0931 (C. L. and G. G.) and N00014-01-1-0772 (C. L. and G. G.) and by the National Science Foundation under grant OCE-0095261 (R. P.

Drivers of spring and summer variability in the coastal ocean offshore of Cape Cod, MA

Author Posting. © American Geophysical Union, 2016. 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: Oceans 121 (2016): 1789–1805, doi:10.1002/2015JC011252.The drivers of spring and summer variability within the coastal ocean east of Cape Cod, Massachusetts, a critical link between the Gulf of Maine and Mid-Atlantic Bight, are investigated using 2 years of shipboard and moored hydrographic and velocity observations from 2010 and 2011. The observations reveal sharp differences in the spring transition and along-shelf circulation due to variable freshwater and meteorological forcing, along with along-shelf pressure gradients. The role of the along-shelf pressure gradient is inferred using in situ observations of turbulent momentum flux, or Reynolds stresses, estimated from the ADCP-based velocities using recently developed methods and an inversion of the along-shelf momentum balance. During spring, the locally relevant along-shelf pressure gradient contains a sizable component that is not coupled to the along-shelf winds and often opposes the regional sea level gradient. Together with the winds, local pressure gradients dominate along-shelf transport variability during spring, while density-driven geostrophic flows appear to match the contribution of the local winds during summer. These results suggest that local effects along the Outer Cape have the potential to cause significant changes in exchange between the basins.NOAA. Grant Number: NA10OAR4170083; Woods Hole Oceanographic Institution2016-09-1

Shelf water and chlorophyll export from the Hatteras slope and outer shelf

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 4291–4304, doi:10.1002/2014JC009809.Using high-resolution data acquired from a shipboard ADCP and a towed Scanfish equipped with a CTD and fluorometer, we examine the properties and transport of Middle Atlantic Bight (MAB) shelf water over a region of the Hatteras outer shelf and slope where MAB shelf water is commonly deflected offshore and entrained into the Gulf Stream. The data are from a period in early August 2004 when the seasonal pycnocline of the MAB is well developed and situated over a weakly stratified, near-bottom shelf water mass commonly referred to as the cold pool. Our data show chlorophyll-rich cold pool water carried rapidly southward over the slope and outer shelf, at a rate of up to 60 cm s−1, as part of the shelf-edge frontal jet. This southward transport of chlorophyll-rich cold pool water is shunted eastward and entrained into the Gulf Stream. However, the latitude band over which this export occurs varies significantly over the 7 day course of our study, a variation which is linked to an order 50 km shift in the latitude at which the Gulf Stream separates from the continental margin. The coupled rapid translation of the Gulf Stream frontal separation and the cold pool export zone is likely to have a significant impact on the movement and accumulation of biogenic material over the Hatteras slope and rise.This work was supported by the U.S. National Science Foundation through grants OCE-03–27249 and OCE-0926999

Richard W. Garvine (1940 –2007)

Richard Garvine passed away on December 10, 2007 of pancreatic cancer, and the ocean science community lost a respected, humane leader whose impact will endure on several levels. Rich was born in 1940 in Pottstown, Pennsylvania. His undergraduate degree in aerospace engineering at M.I.T. was followed by a Ph.D. at Princeton University in 1965, also in aerospace engineering. He was hired by the General Electric Space Sciences Laboratory as a theoretical aerodynamicist, but in 1969, perhaps prodded by a downturn in the aerospace field, he made the rather dramatic shift to a position as an Assistant Professor of Oceanography at the University of Connecticut. At this time, oceanography was booming, with growing budgets and overwhelming optimism about its future. For example, Vice President Humphrey had just visited an oceanographic institution, the Stratton Commission had recently completed its historical work calling for a greater investment in ocean activities, and the National Science Foundation was responding by the creation of the International Decade for Ocean Exploration (IDOE). It was a splendid time to enter the field, and Rich was one of many talented scientists entering with a doctorate in a specialty other than oceanography..

Scientific rationale and conceptual design of a process-oriented shelfbreak observatory: the OOI pioneer array

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gawarkiewicz, G., & Plueddemann, A. J. Scientific rationale and conceptual design of a process-oriented shelfbreak observatory: The OOI pioneer array. Journal of Operational Oceanography, 13(1), (2019): 19-36, doi: 10.1080/1755876X.2019.1679609.The Ocean Observatories Initiative (OOI) of the National Science Foundation in the USA includes a coastal observatory called the OOI Pioneer Array, which is focused on understanding shelf/slope exchange processes. The OOI Pioneer Array has been designed and constructed and is currently in operation. In order to fully understand the design principles and constraints, we first describe the basic exchange processes and review prior experiments in the region. Emphasis is placed on the space and time scales of important exchange processes such as frontal meandering and warm core ring interactions with the Shelfbreak Front, the dominant sources of variability in the region. The three major components of the Pioneer Array are then described, including preliminary data from the underwater gliders and Autonomous Underwater Vehicle (AUV) deployments. The relevance of the Pioneer Array to important recent scientific issues in the area, including enhanced warming of the continental shelf and increasing frequency and spatial extent of Gulf Stream interactions with the continental shelf is discussed. Finally, similar observatories in Asia are briefly described, and general conclusions regarding principles that should guide the design of shelfbreak observatories in other geographic regions are presented.Financial support for this work was provided by the National Science Foundation under grant number OCE-1657853 (GG) and OCE-1026342 (AJP). GG was also supported by a Senior Scientist Chair from the Woods Hole Oceanographic Institution

Dynamics of the direct intrusion of Gulf Stream ring water onto the Mid-Atlantic Bight shelf

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 42 (2015): 7687–7695, doi:10.1002/2015GL065530.Onshore intrusions of offshore waters onto the Mid-Atlantic Bight shelf can greatly affect shelf circulation, biogeochemistry, and fisheries. Previous studies have concentrated on onshore intrusions of slope water. Here we present a direct intrusion of Gulf Stream warm-core ring water onto the shelf representing a previously unknown exchange process at the shelfbreak. Impingement of warm-core rings at the shelfbreak generates along-isobath intrusions that grow like Pinocchio's nose, extending hundreds of kilometers to the southwest. By combining satellite and Ocean Observatory Initiative Pioneer Array data and idealized numerical simulations, we discover that the intrusion results from topographically induced vorticity variation of the ring water, rather than from entrainment of the shelfbreak frontal jet. This intrusion of the Gulf Stream ring water has important biogeochemical implications and could facilitate migration of marine species across the shelfbreak barrier and transport low-nutrient surface Gulf Stream ring water to the otherwise productive shelfbreak region.National Science Foundation Grant Number: OCE-112912

Pathways of shelf water export from the Hatteras shelf and slope

Author Posting. © American Geophysical Union, 2012. 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 117 (2012): C08023, doi:10.1029/2012JC007995.It has long been recognized that a massive flow of Middle Atlantic Bight (MAB) shelf water is exported to the deep ocean in the region near Cape Hatteras, North Carolina. We examine the details of this export using data from an extensive array of 26 moorings, deployed over the shelf and slope between Cape Hatteras and the Chesapeake Bay mouth (from 35° 27′ to 36° 40′ N) as part of the U.S. Department of Energy's Ocean Margins Program. Our analysis indicates that the flow of the MAB shelf-edge frontal jet, which typically extends over the MAB slope, falls victim to export over the length of the mooring array, essentially vanishing by the southern extreme of the array. By contrast, the flow of MAB shelf water entering the study region over the inner and middle shelf (to roughly the 40-m isobath) tends to experience very little loss over the extent of the OMP array. Based on our findings and those of previous studies, we hypothesize that this inner and middle shelf flow is diverted seaward upon encountering the Hatteras Front, which separates MAB and South Atlantic Bight shelf waters. Some fraction of this flow appears to return to the OMP array, moving northeastward over the upper slope en route to the deep ocean. Our analysis also suggests that the export of MAB shelf water is enhanced as the Gulf Stream approaches the shelf-edge near Diamond Shoals, a process we deem to be a high priority for future study.The Ocean Margins Program was funded by the U.S. Department of Energy through various grants. Our analysis was supported by a grant (OCE-0926999) from the National Science Foundation.2013-02-2

Length scale of the finite-amplitude meanders of shelfbreak fronts

Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2598–2620, doi:10.1175/JPO-D-14-0249.1.Through combining analytical arguments and numerical models, this study investigates the finite-amplitude meanders of shelfbreak fronts characterized by sloping isopycnals outcropping at both the surface and the shelfbreak bottom. The objective is to provide a formula for the meander length scale that can explain observed frontal length scale variability and also be verified with observations. Considering the frontal instability to be a mixture of barotropic and baroclinic instability, the derived along-shelf meander length scale formula is [b1/(1 + a1S1/2)]NH/f, where N is the buoyancy frequency; H is the depth of the front; f is the Coriolis parameter; S is the Burger number measuring the ratio of energy conversion associated with barotropic and baroclinic instability; and a1 and b1 are empirical constants. Initial growth rate of the frontal instability is formulated as [b2(1 + a1S1/2)/(1 + a2αS1/2)]NH/L, where α is the bottom slope at the foot of the front, and a2 and b2 are empirical constants. The formulas are verified using numerical sensitivity simulations, and fitting of the simulated and formulated results gives a1 = 2.69, b1 = 14.65, a2 = 5.1 × 103, and b2 = 6.2 × 10−2. The numerical simulations also show development of fast-growing frontal symmetric instability when the minimum initial potential vorticity is negative. Although frontal symmetric instability leads to faster development of barotropic and baroclinic instability at later times, it does not significantly influence the meander length scale. The derived meander length scale provides a framework for future studies of the influences of external forces on shelfbreak frontal circulation and cross-frontal exchange.WGZ and GGG were supported by the National Science Foundation through Grant OCE-1129125.2016-04-0