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Wed, 06 Dec 2023 13:13:54 +0000

An Experimental Study of Longitudinal Strain Pulse Propagation in Wide Rectangular Bars
https://resolver.caltech.edu/CaltechAUTHORS:20150511105940240
Authors: Jones, Orval; Ellis, Albert T.
Year: 2015
The planestress theory presented in Part I is shown to qualitatively predict the warping of plane sections observed in transient fringe patterns obtained
using birefringent coatings and in dynamic photoelastic pictures obtained by other investigators. Measurements using conventional techniques are described in which wide rectangular bars were subjected to a longitudinal stepfunction pressure loading produced by a shock tube. Comparisons show that the gross features of the experimental records for the head of the pulse are qualitatively predicted by the theory. Both theory and experiment show that shortwavelength second mode disturbances arrive very early. Experimentally it is observed that these disturbances are accompanied by thickness mode activity which cannot be accounted for by the planestress theory.
https://authors.library.caltech.edu/records/qjpyzc6s74

Torsional Magnetoelastic Waves in a Circular Cylinder
https://resolver.caltech.edu/CaltechAUTHORS:20150527133101786
Authors: Fourney, M. E.; Ellis, A. T.
Year: 2015
In this paper the effect of an electromagnetic field on the propagation of a pure torsional elastic wave in a conducting circular cylinder is investigated. The general field equations and boundary conditions are linearized and the equations of motion for an infinitely long
circular rod are obtained for the particular electromagnetic field configurations considered.
The torsional motion of a solid rod in a steady axial magnetic field with and without a steady electric field is considered. In the first case it is found that a pure torsional mode will not propagate. In the
second case a pure torsional mode will propagate and its frequency equation is obtained. The results for a perfect conductor are compared to a real material.
The torsional motion of a hollow rod in a steady tangential
magnetic field with and without a steady axial electric field is considered. Without the electric field the equations are completely uncoupled
and the solution is the standard elastic one. The electric field introduces coupling via the induced magnetic field. The equations of motion are obtained, however the actual solutions are not obtained due to the mathematical complexity involved.
https://authors.library.caltech.edu/records/ba0ysddy38

Parameters Affecting Cavitation and Some New Methods for Their Study [Final Report]
https://resolver.caltech.edu/CaltechAUTHORS:20150527141909361
Authors: Ellis, A. T.
Year: 2015
New experimental observations are presented which
support the high speed jet mechanism of cavitation damage.
A general discussion of the basic hydrodynamic theory involved is given and the importance of certain parameters on damage are pointed out. New techniques for studying the collapse of single cavities are described and the concept and development of a high speed photographic system using a ruby laser is outlined. Magnifications of up to fifty times at picture repetition rates as high as 1,600,000 per second and exposure times of 20 billionths of a second have been achieved.
https://authors.library.caltech.edu/records/kg7vzt2w54

On the Mechanism of Cavitation Damage by NonHemispherical Cavities Collapsing in Contact with a Solid Boundary
https://resolver.caltech.edu/CaltechAUTHORS:20150526144122096
Authors: NaudÃ©, Charl F.; Ellis, Albert T.
Year: 2015
A perfect fluid theory, which neglects the effect of gravity, and which assumes that the pressure inside a cavitation bubble remains
constant during the collapse process, is given for the case of a nonhemispherical, but axially symmetric cavity which collapses in contact with a solid boundary. The theory suggests the possibility that such a cavity may deform to the extent that its wall strikes the solid boundary
before minimum cavity volume is reached. High speed motion pictures of cavities generated by spark methods are used to test the theory experimentally. Agreement between theory and experiment is good for the range of experimental cavities considered, and the phenomenon of
the cavity wall striking the solid boundary does indeed occur. Studies of damage by cavities of this type on soft aluminum samples reveals that pressures caused by the cavity wall striking the boundary are
higher than those resulting from a compression of gases inside the cavity, and are responsible for the damage.
https://authors.library.caltech.edu/records/dc13jh7s60

Observations on Cavitation Bubble Collapse
https://resolver.caltech.edu/CaltechAUTHORS:20150527141321349
Authors: Ellis, Albert T.
Year: 2015
Experimental observations are made on collapsing cavitation
bubbles. Bubbles generated by two different methods are studied. The first method consists of bubble generation and collapse by flow over a submerged body. This work is done in the HighSpeed Water Tunnel of the Hydrodynamics Laboratory. Existing photographic equipment and
experimental techniques are employed. The second method consists of bubble generation and collapse by variation of the hydrostatic pressure. Much improved time and space resolution of the collapse is obtained in
the latter case by design and construction of a highspeed photographic system. Bubble collapse pictures are taken at 10^5 frames per sec and an effective exposure time of 5 x 10^(8) sec. A magnification of eight diameters fro.m object to image is attained. This equipment reveals new details of cavitation bubble collapse.
Numerical solutions of the spherical bubble collapse equations are compared with experimental results. A consistently longer collapse time is observed in all cases. Observed bubble asymmetries are shown to be caused by pressure gradients. A large degree of coupling
1s shown to exist between the radial motion and the translational motion of the bubble centroid. Bubble collapse is observed to be much less stable than bubble growth.
https://authors.library.caltech.edu/records/fkb3g63m14

A Theoretical Study of Longitudinal Strain Pulse Propagation in Wide Rectangular Bars
https://resolver.caltech.edu/CaltechAUTHORS:20150526140944534
Authors: Jones, Orval; Ellis, Albert T.
Year: 2015
The propagation of a longitudinal elastic strain pulse in a wide rectangular bar is considered on the basis of approximate planestress equations of motion.
Asymptotic expressions are obtained which, for large distances of travel, describe the pulse propagation in a semiinfinite strip with stressfree lateral
edges, subject to the conditions that a uniform normal stress with a stepfunction time dependence is applied to the end and that the end is laterally
constrained. Particular emphasis is given to describing the warping of plane sections during passage of the strain pulse.
https://authors.library.caltech.edu/records/e6ze279e05

Fluid Free Surface Proximity Effect on a Sphere Vertically Accelerated from Rest
https://resolver.caltech.edu/CaltechAUTHORS:20150603093212131
Authors: Waugh, J. G.; Ellis, A. T.
Year: 2015
Theory is developed to estimate the effect of free
surface proximity on the initial added mass of a sphere
accelerated vertically upward from rest in an ideal fluid.
It is assumed that the acceleration regime is sufficiently
brief that inertial forces predominate and gravitational
effects may be neglected. Results of tests in water indicate
that while there are slight viscous and gravitational effects
over the acceleration regime, the agreement between theory
and experiment is good. It is concluded that over briefer
acceleration regimes these effects would decrease and the
agreement would improve.
https://authors.library.caltech.edu/records/qw5xqcpd75

On the Added Mass of a Sphere in a Circular Cylinder Considering Real Fluid Effects
https://resolver.caltech.edu/CaltechAUTHORS:20150603152348259
Authors: Mellsen, S. B.; Ellis, A. T.; Waugh, J. G.
Year: 2015
An experimental method combined with boundary layer theory
is given for evaluating the added mass of a sphere moving along the axis of a circular cylinder filled with water or oil. The real fluid effects are separated from ideal fluid effects.
The experimental method consists essentially of a magnetic
steel sphere propelled from rest by an electromagnetic coil in which the current is accurately controlled so that it only supplies force for a short time interval which is within the laminar flow regime of the fluid. The motion of the sphere as a function of time is recorded on single frame photographs using a shortarc multiple flash lamp with
accurately controlled time intervals between flashes.
A concept of the effect of boundary layer displacement on the fluid flow around a sphere is introduced to evaluate the real fluid effects on the added mass. Surprisingly accurate agreement between experiment and theory is achieved.
https://authors.library.caltech.edu/records/yr9e8qx875