Combined Feed
https://feeds.library.caltech.edu/people/Ellis-A-T/combined.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenWed, 06 Dec 2023 14:30:43 +0000Production of Accelerated Cavitation Damage by an Acoustic Field in a Cylindrical Cavity
https://resolver.caltech.edu/CaltechAUTHORS:20140829-142252356
Authors: Ellis, A. T.
Year: 1955
DOI: 10.1121/1.1908074
A convenient and economical method for the production of cavitation damage is described. Cavitation is generated in the region of the maximum pressure amplitude of an acoustic field in a resonant cylindrical container. The specimen surface to be damaged is a stationary boundary in the system and is therefore not subject to accelerations such as occur in conventional magnetostriction devices for cavitation damage study. The absence of these accelerations eliminates any possibility of premature material removal from cavitation weakened surfaces. Mathematical analysis of the dynamics of cavitation should also be facilitated. It is shown that simple assumptions lead to an acoustical theory agreeing with experiment to within the accuracy required. Examples are given of the application of this technique to the study of both easily damaged and highly resistant materials. Relatively uniform damage is achieved which is particularly suitable for x‐ray diffraction study of the surface. Alternatively, perturbation of the acoustic field to permit concentrated damage is obtained by forming the specimen surface as the end of a small cylinder. Photomicrographic studies of damage to both monocrystalline and polycrystalline materials have been initiated with the aid of this apparatus. Cavitation experiments have been done in water with an air atmosphere and in toluene with a helium atmosphere. These experiments show that severe damage can result even if a chemically inert environment is employed.https://authors.library.caltech.edu/records/eh5cb-ajp42On the Mechanism of Cavitation Damage
https://resolver.caltech.edu/CaltechAUTHORS:20140826-140952946
Authors: Plesset, M. S.; Ellis, A. T.
Year: 1955
A new method for producing cavitation damage in the
laboratory is described in which the test specimen has no
mechanical accelerations applied to it in contrast with the
conventional magnetostriction device. Alternating pressures
are generated in the water over the specimen by exciting
a resonance in the "water cavity." By this means
the effects of cavitation have been studied for a variety of
materials. Photomicrographs have been taken of several
ordinary (polycrystalline) specimens and also of zinc
monocrystals. The zinc monocrystal has been exposed to
cavitation damage on its basal plane and also on its
twinning plane. X-ray analyses have been made of polycrystalline specimens with various exposures to cavitation. The results show that plastic deformation occurs in the specimens so that the damage results from cold-work of the material which leads to fatigue and failure. A variety of materials has been exposed to intense cavitation for extended periods to get a relative determination of their resistance to cavitation damage. It is found that, roughly speaking, hard materials of high tensile strengths are the most resistant to damage. While this survey is not complete, it has been found that titanium 150-A and tungsten are the most resistant to damage of the materials tested. Cavitation-damage studies, which have been carried out in liquid toluene and in a helium atmosphere, show that chemical effects can be, at most, of secondary significance.https://authors.library.caltech.edu/records/8djmb-yct20On the Mechanism of Cavitation Damage by Nonhemispherical Cavities Collapsing in Contact With a Solid Boundary
https://resolver.caltech.edu/CaltechAUTHORS:20140826-135701608
Authors: Naudé, Charl F.; Ellis, Albert T.
Year: 1961
DOI: 10.1115/1.3662286
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/ypkea-8vw93Some New Approaches to the Study of Cavitation
https://resolver.caltech.edu/CaltechAUTHORS:20140902-155508306
Authors: Ellis, A. T.; Slater, M. E.; Fourney, M. E.
Year: 1963
The design of some experiments to check the assumptions of and to extend existing transient cavitation bubble theory is described. New developments in instrumentation
are discussed and preliminary examples of their application to the problem are given.https://authors.library.caltech.edu/records/vhzta-nzs95Longitudinal Strain Pulse Propagation in Wide Rectangular Bars: Part 2—Experimental Observations and Comparisons With Theory
https://resolver.caltech.edu/CaltechAUTHORS:20140825-164331744
Authors: Jones, O. E.; Ellis, A. T.
Year: 1963
DOI: 10.1115/1.3630106
The plane-stress theory presented in Part 1 is shown to predict qualitatively the warping of plane sections observed in transient fringe patterns obtained using birefringent coatings and in dynamic photoelastic pictures obtained in other investigations. Measurements using conventional techniques are described in which wide rectangular bars were subjected to a longitudinal step-function 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 short-wavelength, second-mode disturbances arrive very early. Experimentally it is observed that these disturbances are accomplished by thickness-mode activity which cannot be accounted for by the plane-stress theory.https://authors.library.caltech.edu/records/k9y65-gvn70Longitudinal Strain Pulse Propagation in Wide Rectangular Bars: Part 1—Theoretical Considerations
https://resolver.caltech.edu/CaltechAUTHORS:20140825-163257337
Authors: Jones, O. E.; Ellis, A. T.
Year: 1963
DOI: 10.1115/1.3630105
The propagation of a longitudinal elastic strain pulse in a wide rectangular bar is considered on the basis of approximate plane-stress equations of motion. Asymptotic expressions are obtained which, for large distances of travel, describe the pulse propagation in a semi-infinite strip with stress-free lateral edges, subject to the conditions that a uniform normal stress with a step-function 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/210bs-vz269Application of a ruby laser to high-speed photography
https://resolver.caltech.edu/CaltechAUTHORS:20140806-103358059
Authors: Ellis, A. T.; Fourney, M. E.
Year: 1963
DOI: 10.1109/PROC.1963.2340
Multiple pulsing of a ruby laser has been achieved and incorporated into a high-speed camera. The pulsing is accomplished by means of cavity Q spoiling techniques utilizing a Kerr cell. a rotating mirror camera is used with the laser acting as a stroboscopic light source to record the events. Framing rates of over a million frames per second with exposure times of less than 30 nsec are easily obtainable. This in conjunction with the highly intense monochromatic, cohere and collimated nature of the laser light makes the high-speed laser camera desirable in many areas of research.https://authors.library.caltech.edu/records/fz9xq-yew61The Variable-Atmosphere Wave Tank
https://resolver.caltech.edu/CaltechAUTHORS:20140905-104321840
Authors: Waugh, J. G.; Ellis, A. T.
Year: 1964
A facility was constructed for the study of water-entry,
water-exit, and underwater trajectory behavior of
small momentum-propelled missiles for varied trajectory
launching angles, missile accelerations and velocities,
wave fields and conditions of cavitation. A unique feature
is the electromagnetic missile propulsion system.
The facility is made principally of non-magnetic and
electrically non-conducting materials to permit the determination of missile accelerating force from the reactive force on the launching coil.https://authors.library.caltech.edu/records/70xmh-sgn68The Unsteady Flow Cavitation Tunnel at the California Institute of Technology
https://resolver.caltech.edu/CaltechAUTHORS:20140707-103051551
Authors: Barnard, J. S.; Ellis, A. T.; Slater, M. E.
Year: 1964
In the Blow-down Water Tunnel at the California Institute
of Technology, velocities of the order of 100
ft / sec are readily obtainable in a 2-3/ 4-in. square working section. The apparatus is described and several of
its features which make it particularly suitable for cavitation studies are emphasized. Operation is automatic and a device is described whereby the controls may be preset
to yield a desired combination of tunnel static pressure
and velocity.https://authors.library.caltech.edu/records/rd2t2-p8b31Techniques for Metric Photography
https://resolver.caltech.edu/CaltechAUTHORS:20140729-110919819
Authors: Waugh, J. G.; Ellis, A. T.; Mellsen, S. B.
Year: 1966
DOI: 10.5594/J15361
Three techniques for metric photography are described. In the first, missile position-time data are obtained from measurement of photographs of the virtual image
produced in a precision-ground sphere by a timed stroboscopic point-source lamp. In the second, a rotating circular film disc is covered with sector-shaped exposures
using a timed stroboscopic lamp. In the third, the previously described techniques are combined to obtain data simultaneously.https://authors.library.caltech.edu/records/am01s-xcq69Real Fluid Effects on an Accelerated Sphere Before Boundary-Layer Separation
https://resolver.caltech.edu/CaltechAUTHORS:20140903-155819036
Authors: Mellsen, S. B.; Waugh, J. G.; Ellis, A. T.
Year: 2014
Studies were made on the apparent increase in mass on acceleration (added mass) of a sphere accelerated from rest and before boundary-layer separation, in cylinders
of various diameters filled with water or oil. From a comparison of theoretical and experimentally obtained added masses, the following conclusions were drawn: In the
absence of wall effects on the boundary layer, the wall shear stress over elements of the sphere can be approximated by the solution for the flat plate moving parallel to itself and the potential flow over the elements outside the boundary layer. The impulse on the elements is obtained by integration with respect to time, and the wall
drag and drag impulse on the sphere by integration over the sphere surface. Good theoretical and experimental agreement obtains under the assumption that a mass of fluid, estimated from the wall drag impulse, is carried in the boundary layer and may be university distributed over the sphere.https://authors.library.caltech.edu/records/zbk2s-d8t60An Experimental Study of Longitudinal Strain Pulse Propagation in Wide Rectangular Bars
https://resolver.caltech.edu/CaltechAUTHORS:20150511-105940240
Authors: Jones, Orval; Ellis, Albert T.
Year: 2015
The plane-stress 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 step-function 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 short-wavelength 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 plane-stress theory.https://authors.library.caltech.edu/records/qjpyz-c6s74Torsional Magnetoelastic Waves in a Circular Cylinder
https://resolver.caltech.edu/CaltechAUTHORS:20150527-133101786
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/ba0ys-ddy38Parameters Affecting Cavitation and Some New Methods for Their Study [Final Report]
https://resolver.caltech.edu/CaltechAUTHORS:20150527-141909361
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/kg7vz-t2w54On the Mechanism of Cavitation Damage by Non-Hemispherical Cavities Collapsing in Contact with a Solid Boundary
https://resolver.caltech.edu/CaltechAUTHORS:20150526-144122096
Authors: Naudé, 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/dc13j-h7s60Observations on Cavitation Bubble Collapse
https://resolver.caltech.edu/CaltechAUTHORS:20150527-141321349
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 High-Speed 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 high-speed 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/fkb3g-63m14A Theoretical Study of Longitudinal Strain Pulse Propagation in Wide Rectangular Bars
https://resolver.caltech.edu/CaltechAUTHORS:20150526-140944534
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 plane-stress equations of motion.
Asymptotic expressions are obtained which, for large distances of travel, describe the pulse propagation in a semi-infinite strip with stress-free lateral
edges, subject to the conditions that a uniform normal stress with a step-function 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/e6ze2-79e05Fluid Free Surface Proximity Effect on a Sphere Vertically Accelerated from Rest
https://resolver.caltech.edu/CaltechAUTHORS:20150603-093212131
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/qw5xq-cpd75On the Added Mass of a Sphere in a Circular Cylinder Considering Real Fluid Effects
https://resolver.caltech.edu/CaltechAUTHORS:20150603-152348259
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 short-arc 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/yr9e8-qx875