3,163 research outputs found
Spaces of finite element differential forms
We discuss the construction of finite element spaces of differential forms
which satisfy the crucial assumptions of the finite element exterior calculus,
namely that they can be assembled into subcomplexes of the de Rham complex
which admit commuting projections. We present two families of spaces in the
case of simplicial meshes, and two other families in the case of cubical
meshes. We make use of the exterior calculus and the Koszul complex to define
and understand the spaces. These tools allow us to treat a wide variety of
situations, which are often treated separately, in a unified fashion.Comment: To appear in: Analysis and Numerics of Partial Differential
Equations, U. Gianazza, F. Brezzi, P. Colli Franzone, and G. Gilardi, eds.,
Springer 2013. v2: a few minor typos corrected. v3: a few more typo
correction
Tests of propellers for Alvin side propulsion units
Full scale dynamometer tests were run on a series of
unshrouded propellers in the range of propeller diameters considered
practical for use on the side propulsion units of the
research submarine ALVIN. Measurements taken included static
thrust, torque, and RPM for various values of hydraulic power
input to the driving motor.
In other tests, propellers having 14 inch diameter and
20 inch pitch (the present ALVIN configuration) were compared
for static thrust as follows: conventional blade shape, unshrouded;
conventional blade shape in ALVIN flow-accelerating
nozzle unit; square-ended blades in ALVIN nozzle unit.
Recommendations are given concerning the proposed new
ALVIN side propulsion units
Torque tests of a full size model of the Alvin/AUTEC emergency sphere release
Laboratory torque tests were perfoirmed using an actual emergency sphere
release shaft of the type used in the research submarines ALVIN, SEA CLIFF and
TURTLE. A test fixture was constructed which permitted laboratory simulation
of the side (squeezing) forces applied to the release shaft came as a result of
forebody buoyancy. Estimated full-scale side forces were applied to the cam by
a laboratory compression testing machine, and the torque required to rotate the
shaft was measured. Tests were run with contacting surfaces (a) clean and dry,
(b) greased, and (c) immersed in sea water. From the test results, values of
release torque were calculated for the submarines in question. Coefficient of
friction values of the contrating materials (Monel K-500 on phosphor bronze)
also are reported.Submitted to the Office of Naval Research
under contract Ndnr-3484(00); NR 260-107
Experimental stress analysis of model of emergency forebody release device used in deep diving research submarines Alvin, Sea Cliff and Turtle
Originally issued as Reference No. 69-68, series later renamed WHOI-Technical ReportsTests were conducted on a full-scale model of the emergency
forebody release used in the deep-diving submarines ALVIN, SEA CLIFF
and TURTLE. The model was machined from metal to the same dimensional
tolerances as the prototype. Resistance strain gages, attached
to the model, permitted measurement of forces on component parts of
the device. Of primary concern was the bending stress which might
be set up in the release operating shaft when the submarine is submerged
in an inclined position. Tests were arranged to simulate three possible
conditions of loading of the release device at a 30 degree vehicle list
angle: case (1) righting moment of inclined forebody resisted by release components only; case (2) righting moment resisted by release
with assistance from lower guides; and (3) righting moment resisted
by couple set up by release and rubber support ring. Test results show that shaft bending stresses (for ALVIN) are high (200,000 psi)
for the case (1) condition, lower (400,000 - 90,000 psi) for case (2)
and essentially zero for case (3). The conclusion is that the present
forebody release design is adequate for all submarine attitudes
encountered
in normal operation, provided the vehicle has been assembled so
that contact between sphere and rubber ring is assured at all times.Submitted to the Office of Naval Research
under Contract Nonr-3484(00); NR 260-107
A pendulum inclinometer for use with small deep-submersibles
The authors developed a pendulum inclinometer suitable for use with small deepsubmersibles
or surface craft. The instrument uses a relatively short heavy pendulum and a
viscous damping system for minimizing the effects of unwanted oscilatory motion. The
pendulum relative motion is transmitted to the dial pointer through a flexible cord. The
mechanism is designed so that the inclinometer gives a direct reading of the tangent of the
angle of inclination. Adjustments are provided for leveling the instrument and for setting the
dial to zero. Upper and lower clamping devices protect the pendulum suspension from damage
during transit. The inclinometer has been used successfully in recent inclining experiments
for the small research submarine Alvin.Prepared for the Office of Naval Research under
Contract N00014-73-C-0097; NR 083-383
Micromechanics of Spray-On Foam Insulation
Understanding the thermo-mechanical response of the Space Shuttle External Tank spray-on foam insulation (SOFI) material is critical, to NASA's Return to Flight effort. This closed-cell rigid polymeric foam is used to insulate the metallic Space Shuttle External Tank, which is at cryogenic temperatures immediately prior to and during lift off. The shedding of the SOFI during ascent led to the loss of the Columbia, and eliminating/minimizing foam lass from the tank has become a priority for NASA as it seeks to resume scheduled space shuttle missions. Determining the nature of the SOFI material behavior in response to both thermal and mechanical loading plays an important role as any structural modeling of the shedding phenomenon k predicated on knowledge of the constitutive behavior of the foam. In this paper, the SOFI material has been analyzed using the High-Fidelity Generalized Method of Cells (HFGMC) micromechanics model, which has recently been extended to admit a triply-periodic 3-D repeating unit cell (RUC). Additional theoretical extensions that mere made in order to enable modeling of the closed-cell-foam material include the ability to represent internal boundaries within the RUC (to simulated internal pores) and the ability to impose an internal pressure within the simulated pores. This latter extension is crucial as two sources contribute to significant internal pressure changes within the SOFI pores. First, gas trapped in the pores during the spray process will expand or contract due to temperature changes. Second, the pore pressure will increase due to outgassing of water and other species present in the foam skeleton polymer material. With HFGMC's new pore pressure modeling capabilities, a nonlinear pressure change within the simulated pore can be imposed that accounts for both of these sources, in addition to stmdar&-thermal and mechanical loading; The triply-periodic HFGMC micromechanics model described above was implemented within NASA GRC's MAC/GMC software package, giving the model access to a range of nonlinear constitutive models for the polymeric foam skeleton material. A repeating unit cell architecture was constructed that, while relatively simple, still accounts for the geometric anisotropy of the porous foam microstructure and its thin walls and thicker edges. With the lack of reliable polymeric foam skeleton materia1 properties, many simulations were executed aimed at backing out these material properties. Then, using these properties, predictions of the thermo-mechanical behavior of the foam, including calculated internal applied pressure profiles, were performed and compared with appropriate experimental data
An Experimental Approach to Examining Psychological Contributions to Multisite Musculoskeletal Pain.
The present study examined the prospective value of pain catastrophizing, fear of pain, and depression in the prediction of multisite musculoskeletal pain following experimentally induced delayed-onset muscle soreness (DOMS). The study sample consisted of 119 (63 females, 56 males) healthy university students. Measures of pain catastrophizing, fear of pain, and depression were completed prior to the DOMS induction procedure. Analyses revealed that pain catastrophizing and fear of pain prospectively predicted the experience of multisite pain following DOMS induction. Analyses also revealed that women were more likely to experience multisite pain than men. There was no significant relation between depressive symptoms and the experience of multisite pain. The discussion addresses the mechanisms by which pain catastrophizing and fear of pain might contribute to the spreading of pain. Clinical implications of the findings are also addressed. Perspective: The results of this experimental study suggest that pain catastrophizing and fear of pain might increase the risk of developing multisite pain following musculoskeletal injury
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