35 research outputs found
Frequency-dependent attenuation and elasticity in unconsolidated earth materials: effect of damping
We use the Discrete Element Method (DEM) to understand the underlying
attenuation mechanism in granular media, with special applicability to the
measurements of the so-called effective mass developed earlier. We consider
that the particles interact via Hertz-Mindlin elastic contact forces and that
the damping is describable as a force proportional to the velocity difference
of contacting grains. We determine the behavior of the complex-valued normal
mode frequencies using 1) DEM, 2) direct diagonalization of the relevant
matrix, and 3) a numerical search for the zeros of the relevant determinant.
All three methods are in strong agreement with each other. The real and the
imaginary parts of each normal mode frequency characterize the elastic and the
dissipative properties, respectively, of the granular medium. We demonstrate
that, as the interparticle damping, , increases, the normal modes exhibit
nearly circular trajectories in the complex frequency plane and that for a
given value of they all lie on or near a circle of radius centered on
the point in the complex plane, where . We show that each
normal mode becomes critically damped at a value of the damping parameter , where is the (real-valued) frequency when
there is no damping. The strong indication is that these conclusions carry over
to the properties of real granular media whose dissipation is dominated by the
relative motion of contacting grains. For example, compressional or shear waves
in unconsolidated dry sediments can be expected to become overdamped beyond a
critical frequency, depending upon the strength of the intergranular damping
constant.Comment: 28 pages, 7 figure
PROACTIVE MANAGEMENT OF CUSTOMER NETWORKS FOR STABILITY AND RELIABILITY LEVERAGING APPDY INTEGRATION INTO NETWORK SERVICE PRODUCTS
Techniques are described for leveraging the integration of the AppDynamics (AppDy) Software Development Kit (SDK) with network service products that allows for run-time retrieval of key process data on an AppDy platform. The run-time retrieval of key process data will be managed by a network service provider\u27s customer support teams, which can proactively detect customer network degradations before they have an impact on end user experience
Dynamic effective mass of granular media
We develop the concept of frequency dependent effective mass, M(omega), of
jammed granular materials which occupy a rigid cavity to a filling fraction of
48%, the remaining volume being air of normal room condition or controlled
humidity. The dominant features of M(omega) provide signatures of the
dissipation of acoustic modes, elasticity and aging effects in the granular
medium. We perform humidity controlled experiments and interpret the data in
terms of a continuum model and a "trap" model of thermally activated capillary
bridges at the contact points. The results suggest that attenuation in the
granular materials is influenced significantly by the kinetics of capillary
condensation between the asperities at the contacts.Comment: 4 pages, 3 figure
Use of an Online Photo Management and Sharing Application to Create a Searchable Digital Dental Radiograph Repository
Problem: Dental radiographs generally display one or more findings/diagnoses, and are linked to a unique set of patient demographics, medical history and other findings not represented by the image. However, this information is not associated with radiographs in any type of meta format, and images are not searchable based on any clinical criteria (1,2). The purpose of this pilot study is to create an online, searchable data repository of dental radiographs to be used for patient care, teaching and research. [See PDF for complete abstract
The Use of Social Media by Dental Students for Communication and Learning: Two Viewpoints
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153760/1/jddjde019072.pd
Ultrasonic Study of Water Adsorbed in Nanoporous Glasses
Thermodynamic properties of fluids confined in nanopores differ from those
observed in the bulk. To investigate the effect of nanoconfinement on water
compressibility, we performed water sorption experiments on two nanoporous
glass samples while concomitantly measuring the speed of longitudinal and shear
ultrasonic waves in these samples. These measurements yield the longitudinal
and shear moduli of the water laden nanoporous glass as a function of relative
humidity that we utilized in the Gassmann theory to infer the bulk modulus of
the confined water. This analysis shows that the bulk modulus (inverse of
compressibility) of confined water is noticeably higher than that of the bulk
water at the same temperature. Moreover, the modulus exhibits a linear
dependence on the Laplace pressure. The results for water, which is a polar
fluid, agree with previous experimental and numerical data reported for
non-polar fluids. This similarity suggests that irrespective of intermolecular
forces, confined fluids are stiffer than bulk fluids. Accounting for fluid
stiffening in nanopores may be important for accurate interpretation of wave
propagation measurements in fluid-filled nanoporous media, including in
petrophysics, catalysis, and other applications, such as in porous materials
characterization
Origins of pressure dependent permeability in unconventional hydrocarbon reservoirs
Abstract Unconventional hydrocarbon assets represent a rapidly expanding proportion of North American oil and gas production. Similar to the incipient phase of conventional oil production at the turn of the twentieth century, there are ample opportunities to improve production efficiency. In this work we demonstrate that pressure dependent permeability degradation exhibited by unconventional reservoir materials is due to the mechanical response of a few commonly encountered microstructural constituents. In particular, the mechanical response of unconventional reservoir materials may be conceptualized as the superposed deformation of matrix (or ~ cylindrical/spherical), and compliant (or slit) pores. The former are representative of pores in a granular medium or a cemented sandstone, while the latter represent pores in an aligned clay compact or a microcrack. As a result of this simplicity, we demonstrate that permeability degradation is accounted for through a weighted superposition of conventional permeability models for these pore architectures. This approach permits us to conclude that the most severe pressure dependence is due to imperceptible bedding parallel delamination cracks in the oil bearing argillaceous (clay-rich) mudstones. Finally, we demonstrate that these delaminations tend to populate layers that are enriched with organic carbon. These findings are a basis for improving recovery factors through the development of new completion techniques to exploit, then mitigate pressure dependent permeability in practice
Small-amplitude acoustics in bulk granular media
We propose and validate a three-dimensional continuum modeling approach that predicts small-amplitude acoustic behavior of dense-packed granular media. The model is obtained through a joint experimental and finite-element study focused on the benchmark example of a vibrated container of grains. Using a three-parameter linear viscoelastic constitutive relation, our continuum model is shown to quantitatively predict the effective mass spectra in this geometry, even as geometric parameters for the environment are varied. Further, the model's predictions for the surface displacement field are validated mode-by-mode against experiment. A primary observation is the importance of the boundary condition between grains and the quasirigid walls.Schlumberger-Doll Research Cente