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294 results on '"Shen, Hayley"'

3. On the ocean wave attenuation rate in grease-pancake ice, a comparison of viscous layer propagation models with field data

Author

De Santi, Francesca, De Carolis, Giacomo, Olla, Piero, Doble, Martin, Cheng, Sukun, Shen, Hayley H., and Thomson, Jim

Subjects
Physics - Atmospheric and Oceanic Physics, Physics - Fluid Dynamics
Abstract

The ability of viscous layer models to describe the attenuation of waves propagating in grease-pancake ice covered ocean is investigated. In particular, the Keller's model Keller [1998], the two-layer viscous model [De Carolis and Desiderio 2002] and the close-packing model [De Santi and Olla 2017] are extensively validated by using wave attenuation data collected during two different field campaigns (Weddell Sea, Antarctica, April 2000; western Arctic Ocean, autumn 2015). We use these data to validate the three models by minimizing the differences between the measured and model wave attenuation; the retrieved ice thickness is then compared with measured data. The three models allow to fit the observation data, but with important differences in the three cases. The close-packing model shows good agreement with the data for values of the ice viscosity comparable to those of grease ice in laboratory experiments. For thin ice, the Keller's model performance is similar to that of the close-packing model, while for thick ice much larger values of the ice viscosity are required, which reflects the different ability of the two models to take into account the effect of pancakes. The improvement of performance over the Keller's model achieved by the two-layer viscous model is minimal, which reflects the marginal role in the dynamics of a finite eddy viscosity in the ice-free layer. A good ice thickness retrieval can be obtained by considering the ice layer as the only source in the wave dynamics, so that the wind input can be disregarded.

Published
2018
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7. An Experimental Study on Surface Wave Modulation Due to Viscoelastic Bottom

Author

Sree, Dharma, Law, Adrian Wing-Keung, Shen, Hayley H., di Prisco, Marco, Series Editor, Chen, Sheng-Hong, Series Editor, Vayas, Ioannis, Series Editor, Kumar Shukla, Sanjay, Series Editor, Solari, Giovanni, Series Editor, Sharma, Anuj, Series Editor, Kumar, Nagesh, Series Editor, Wang, Chien Ming, Series Editor, Murali, K., editor, Sriram, V., editor, Samad, Abdus, editor, and Saha, Nilanjan, editor

Published
2019
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16. Emerging trends in the sea state of the Beaufort and Chukchi seas

Author

Thomson, Jim, Fan, Yalin, Stammerjohn, Sharon, Stopa, Justin, Rogers, W. Erick, Girard-Ardhuin, Fanny, Ardhuin, Fabrice, Shen, Hayley, Perrie, Will, Shen, Hui, Ackley, Steve, Babanin, Alex, Liu, Qingxiang, Guest, Peter, Maksym, Ted, Wadhams, Peter, Fairall, Chris, Persson, Ola, Doble, Martin, Graber, Hans, Lund, Bjoern, Squire, Vernon, Gemmrich, Johannes, Lehner, Susanne, Holt, Benjamin, Meylan, Mike, Brozena, John, and Bidlot, Jean-Raymond

Published
2016
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34. Two-dimensional simulation of the angle of repose for a particle system with electrostatic charge under lunar and earth gravity

Author

Ji, Shunying and Shen, Hayley H.

Subjects
Gravity -- Influence, Dynamics of a particle -- Research, Electrostatic interactions -- Observations, Aerospace engineering -- Research, Aerospace and defense industries, Engineering and manufacturing industries, Science and technology
Abstract

This paper presents a study of the angle of repose of a two-dimensional particle system under the Earth and Moon gravity fields. The particles interact with electrostatic forces in addition to friction. A two-dimensional discrete element method is used in this analysis with two particle shapes, circular and noncircular. The noncircular shape is constructed with overlapping pairs of disks. For the range of parameters studied, the angle of repose shows little sensitivity to gravity. The sensitivity to friction and electrostatic charges can be either significant or negligible, depending on the range of these values. For each contact friction, there is a threshold of electric charge on the particle such that the angle of repose suddenly drops to zero when the charge exceeds this threshold. The existence of this threshold, once validated in three-dimensional systems, may provide an opportunity to measure the electrostatic charges of the lunar dust in situ. DOI: 10.1061/(ASCE)0893-1321(2009)22:1(10) CE Database subject headings: Moon: Simulation: Particles: Gravity.

Published
2009

35. Spectral attenuation of ocean waves in pack ice and its application in calibrating viscoelastic wave-in-ice models

Author

Cheng, Sukun, Stopa, Justin, Ardhuin, Fabrice, Shen, Hayley H., Cheng, Sukun, Stopa, Justin, Ardhuin, Fabrice, and Shen, Hayley H.

Abstract

We investigate a case of ocean waves through a pack ice cover captured by Sentinel-1A synthetic aperture radar (SAR) on 12 October 2015 in the Beaufort Sea. The study domain is 400 km by 300 km, adjacent to a marginal ice zone (MIZ). The wave spectra in this domain were reported in a previous study (Stopa et al., 2018b). In that study, the authors divided the domain into two regions delineated by the first appearance of leads (FAL) and reported a clear change of wave attenuation of the total energy between the two regions. In the present study, we use the same dataset to study the spectral attenuation in the domain. According to the quality of SAR-retrieved wave spectrum, we focus on a range of wave numbers corresponding to 9–15 s waves from the open-water dispersion relation. We first determine the apparent attenuation rates of each wave number by pairing the wave spectra from different locations. These attenuation rates slightly increase with increasing wave number before the FAL and become lower and more uniform against wave number in thicker ice after the FAL. The spectral attenuation due to the ice effect is then extracted from the measured apparent attenuation and used to calibrate two viscoelastic wave-in-ice models. For the Wang and Shen (2010b) model, the calibrated equivalent shear modulus and viscosity of the pack ice are roughly 1 order of magnitude greater than that in grease and pancake ice reported in Cheng et al. (2017). These parameters obtained for the extended Fox and Squire model are much greater, as found in Mosig et al. (2015) using data from the Antarctic MIZ. This study shows a promising way of using remote-sensing data with large spatial coverage to conduct model calibration for various types of ice cover. Highlights. Three key points: The spatial distribution of wave number and spectral attenuation in pack ice are analyzed from SAR-retrieved surface wave spectra. The spectral attenuation rate of 9–15 s waves varies around 10−5 m2 s−1, with

Published
2020
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37. Effect of contact force models on granular flow dynamics

Author

Ji, Shunying and Shen, Hayley H.

Subjects
Granular materials -- Mechanical properties, Stress-strain curves -- Analysis, Science and technology
Abstract

The contact force model consisting of a linear spring dashpot with a frictional glider has been widely adapted to simulate granular flows. Real contact mechanics between two solid bodies is very complicated. Extensive theoretical and experimental studies exist for binary contacts. Very little work has been reported that addresses the effect of contact mechanics on the bulk behavior of granular materials. We first briefly summarize the difference of binary contacts between a linear spring--dasbpot model and the Hertzian nonlinear spring with two nonlinear dashpot models. We then compare the constitutive behaviors of a granular material using a linear and a nonlinear model. The stress- and strain-rate relation in simple shear flow and the resulting coordination number are calculated using the discrete element method. It is found that although at the grain level binary contact between two particles depends on whether a linear or a nonlinear model is used, the bulk behavior of granular materials is qualitatively similar with either model. DOI: 10.1061/(ASCE)0733-9399(2006)132:11(1252) CE Database subject headings: Models; Granular materials; Solids flow; Stress strain relations.

Published
2006

38. Fluid mechanics: an essential part of an environmental engineering curriculum

Author

Cheng, Alexander H.-D., Liu, Clark C.K., Shen, Hayley, Teng, Michelle H., and Wang, Keh-Han

Subjects
Fluid mechanics -- Study and teaching, Civil engineering -- Study and teaching, Environmental engineering -- Study and teaching, Business, Education, Engineering and manufacturing industries
Abstract

In this paper we discuss teaching fluid mechanics to civil and environmental engineering majors at both the undergraduate and graduate levels. Fluid mechanics is a key course in environmental engineering that ties together the physical aspects with chemical and biological aspects. We survey the historical development of the role of fluid mechanics in environmental engineering, discuss current needs and curriculum, and point out areas for potential improvements. CE Database keywords: Fluid mechanics; Engineering education; Curricula.

Published
2002

42. Overview of the Arctic Sea state and boundary layer physics program

Author

Thomson, Jim, Ackley, Stephen, Girard-Ardhuin, Fanny, Ardhuin, Fabrice, Babanin, Alexander, Boutin, Guillaume, Brozena, John, Cheng, Sukun, Collins, Clarence, Doble, Martin, Fairall, Christopher W., Guest, Peter, Gebhardt, Claus, Gemmrich, Johannes, Graber, Hans C., Holt, Benjamin, Lehner, Susanne, Lund, Björn, Meylan, Michael, Maksym, Ted, Montiel, Fabien, Perrie, Will, Persson, Ola, Rainville, Luc, Rogers, W. Erick, Shen, Hui, Shen, Hayley, Squire, Vernon, Stammerjohn, Sharon E., Stopa, Justin, Smith, Madison M., Sutherland, Peter, Wadhams, Peter, Thomson, Jim, Ackley, Stephen, Girard-Ardhuin, Fanny, Ardhuin, Fabrice, Babanin, Alexander, Boutin, Guillaume, Brozena, John, Cheng, Sukun, Collins, Clarence, Doble, Martin, Fairall, Christopher W., Guest, Peter, Gebhardt, Claus, Gemmrich, Johannes, Graber, Hans C., Holt, Benjamin, Lehner, Susanne, Lund, Björn, Meylan, Michael, Maksym, Ted, Montiel, Fabien, Perrie, Will, Persson, Ola, Rainville, Luc, Rogers, W. Erick, Shen, Hui, Shen, Hayley, Squire, Vernon, Stammerjohn, Sharon E., Stopa, Justin, Smith, Madison M., Sutherland, Peter, and Wadhams, Peter

Abstract

Author Posting. © American Geophysical Union, 2018. 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 123(12), (2018): 8674-8687, doi:10.1002/2018JC013766., A large collaborative program has studied the coupled air‐ice‐ocean‐wave processes occurring in the Arctic during the autumn ice advance. The program included a field campaign in the western Arctic during the autumn of 2015, with in situ data collection and both aerial and satellite remote sensing. Many of the analyses have focused on using and improving forecast models. Summarizing and synthesizing the results from a series of separate papers, the overall view is of an Arctic shifting to a more seasonal system. The dramatic increase in open water extent and duration in the autumn means that large surface waves and significant surface heat fluxes are now common. When refreezing finally does occur, it is a highly variable process in space and time. Wind and wave events drive episodic advances and retreats of the ice edge, with associated variations in sea ice formation types (e.g., pancakes, nilas). This variability becomes imprinted on the winter ice cover, which in turn affects the melt season the following year., This program was supported by the Office of Naval Research, Code 32, under Program Managers Scott Harper and Martin Jeffries. The crew of R/V Sikuliaq provide outstanding support in collecting the field data, and the US National Ice Center, German Aerospace Center (DLR), and European Space Agency facilitated the remote sensing collections and daily analysis products. RADARSAT‐2 Data and Products are from MacDonald, Dettwiler, and Associates Ltd., courtesy of the U.S. National Ice Center. Data, supporting information, and a cruise report can be found at http://www.apl.uw.edu/arcticseastate

Published
2019

43. Collisional restitution dependence on viscosity

Author

Lundberg, Jan and Shen, Hayley H.

Subjects
Viscosity -- Research, Collisions (Physics) -- Research, Science and technology
Abstract

Dense two-phase flows Occur in many material processing Situations. In these flows, particle collision presents a mechanism for internal resistance In the literature, restitution coefficients are given for collisions between dry objects. Little is known about two colliding objects placed in a fluid. Thus, although two-phase flow models exist for dense mixtures, realistic values of the required restitution coefficient are not available. Recent theoretical and experimental analyses of colliding spheres in a viscous fluid show that collisional rebound depends greatly on the interstitial fluid. At very high viscosity, contact may not occur. This paper presents an experimental study of collisional restitution between steel and nylon, and a range of Newtonian viscous fluids. The fluids have a viscosity range from 27 [mm.sup.2]/s to 2,600 [mm.sup.2]/s. The normal impact velocity ranges from 0.015 m/s to 0.75 m/s. Preliminary results show that the behaviour of the impact and the resulting restitution coefficient depend on the interstitial fluid. These results will be useful to the mathematical modeling of dense two-phase flows., A experiment is conducted to determine the restitution coefficient of colliding objects with viscous fluid at the contact surface. Results show that restitution coefficient values are comparable to values from dry collisions, for oil viscosity up to 10 sq mm/s. For greater oil viscosity however, the restitution coefficient can decrease. Softer materials are also more dependent on viscosity changes. For modeling two-phase flows, the restitution coefficient for both the solid and liquid must be taken into account.

Published
1992

44. Constitutive Relation in Transitional Granular Flows

Author

Shen, Hayley H, Hanes, Daniel M, and Jenkins, James T

Subjects
Fluid Mechanics And Thermodynamics
Abstract

To study the constitutive behavior of granular materials, the presence of gravity is detrimental. Although empirical relations have been obtained for engineering designs to control granular flows on Earth, it is not known how well these Earthbound relations can be used in another gravity field. Fundamental understanding must be derived to reliably design for granular flows in space exploration. There are two extremes of granular flows of which significant amount of knowledge is available. One deals with a dense and quasi-static situation where the deformation rate nearly vanishes. The other deals with dilute and rapidly fluctuating grain velocities where particle inertia dominates. This project, funded by the NASA Microgravity Fluid Physics Program, aims to study this transitional regime via physical experiments and computer simulations. A conceptual model has been established as described below. There are two natural time scales in a granular flow. One is the travel time between two consecutive collisions and the other is the duration of a collision contact. At a very low shear-rate, the shear-induced particle velocity is low. Hence the travel time between collisions is longer than the contact time between colliding particles. Binary collisions prevail. As the shear-rate increases, the traveling time between collisions reduces and the probability of multiple collisions goes up. These particle groups disperse shortly after and new groups form. When shear-rate is further increased, clusters grow in size due to an increasing chance for free particles to join before groups have the time to disperse. The maximum cluster size may depend on the global concentration and material properties. As the solid concentration approaches zero, the cluster size goes to one particle diameter. The maximum possible cluster size under any condition is the container size, provided that the shear flow is inside a container. The critical shear-rates that dictate the initiation of the multiple contacts, and the size and lifetime of the collision clusters, are functions of the concentration also. A 'regime' theory has been proposed by Babic et al. This theory suggested that both the solid concentration, C, and the non-dimensional shear-rate, B, are important in determining the regimes of the granular constitutive law. Additional information is included in the original extended abstract.

Published
2002

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