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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenWed, 06 Dec 2023 14:30:44 +0000On the Mechanism of Cavitation Damage by Non-Hemispherical Cavities Collapsing in Contact with a Solid Boundary
https://resolver.caltech.edu/CaltechETD:etd-06302006-081114
Authors: Naudé, Charl François
Year: 1960
DOI: 10.7907/QACP-9A29
A perfect fluid perturbation 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 non-hemispherical, but axially symmetric cavity which collapses in contact with a solid boundary. The theory suggests the possibility that such cavities may deform to the extent that the cavity wall strikes the solid surface before minimum cavity volume is reached.
High speed motion pictures of cavities generated by spark methods are used to test the theory experimentally. It is found that the theory describes the change of shape of such cavities fairly well, and that the phenomenon of the cavity wall striking the solid boundary does indeed occur.
By studying the damaging effects of various cavities of this type on aluminum samples, it is shown that pressures resulting from the cavity wall striking the surface are much higher than pressures caused by compression of gases inside the cavity. It is furthermore found that the estimated impact velocities of the cavity walls on the solid boundary can account for water hammer pressures sufficiently large to have caused the observed damage.https://thesis.library.caltech.edu/id/eprint/2787Theoretical and Experimental Studies on the Propagation of Longitudinal Elastic Strain Pulses in Wide Rectangular Bars
https://resolver.caltech.edu/CaltechETD:etd-06142006-103619
Authors: Jones, Orval Elmer
Year: 1961
DOI: 10.7907/KXTS-1Y59
The method of birefringent coatings is considered as an experimental means of studying wave propagation phenomena in metals. Experiments using the Ellis ultra-high-speed camera and a rectangular aluminum bar having a birefringent coating of PhotoStress indicate that transient fringe patterns resulting from impact can be successfully photographed using existing film and light sources at exposure times of 0.05 microseconds. Pronounced fringe curvatures, indicating the warping of plane sections, were observed in the pictures during the passage of the strain pulse.
The propagation of a longitudinal elastic strain pulse in a wide rectangular bar is considered on the basis of the approximate plane-stress equations of motion. Asymptotic expressions are obtained which, for large distances of travel, describe the 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 undergoes no lateral extension. These expressions are shown to qualitatively predict the warping of plane sections observed in the high-speed pictures and in the dynamic photoelastic pictures obtained by other investigators.
Measurements using conventional measuring techniques are described in which wide rectangular aluminum bars of several thicknesses were subjected to a 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 plane-stress 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 two-dimensional plane-stress theory.https://thesis.library.caltech.edu/id/eprint/2586I. On the application of a laser to high speed photography. II. Torsional magnetoelastic waves in a circular cylinder
https://resolver.caltech.edu/CaltechETD:etd-12082005-131705
Authors: Fourney, Michael E.
Year: 1963
DOI: 10.7907/6M9E-V056
The first part of this thesis deals with the application of a ruby laser to high speed photography. The light that is emitted from a ruby laser is monochromatic, collimated, coherent, linearly polarized, and highly intense. It has been demonstrated that these properties make the laser a very useful tool for research in areas involving photographic techniques.
A method has been devised by which the output of the laser is controlled and is emitted in the form of a series of light pulses. The rate at which these pulses are generated can be controlled and repetition rates of over 1.6 Mc/sec have been achieved. The 30 nsec duration of an individual pulse represents the exposure time for a high speed laser camera which has been developed. Pictures have been taken at rates of over 1.2 million frames per second. This exposure time represents a reduction of an order of magnitude over that previously possible, with an increase of three orders of magnitude in intensity. In applications where a particular characteristic of the laser light is required, such as the monochromatic nature desired in photoelasticity, this improvement of four orders of magnitude is further increased.
When a series of light pulses is generated in the manner described above it is found that the amplitude of the pulse train becomes stable above a certain critical frequency. This critical frequency is determined to be a function of the laser cavity length. The amplitude of the stabilized pulse train is a function of the repetition rate and the cavity length. The nature of this variation is established and a mechanistic explanation of the phenomena involved is presented.
https://thesis.library.caltech.edu/id/eprint/4860On the added mass of sphere in a circular cylinder considering real fluid effects
https://resolver.caltech.edu/CaltechTHESIS:10052015-161503645
Authors: Mellsen, Stanley Brun
Year: 1966
DOI: 10.7907/63N8-1N50
<p>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.</p>
<p>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.</p>
<p>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. </p>
https://thesis.library.caltech.edu/id/eprint/9202Formation of jets by implusive acceleration of a curved free surface
https://resolver.caltech.edu/CaltechTHESIS:12072015-132454281
Authors: Gruber, William Paul
Year: 1968
DOI: 10.7907/SWXB-0X23
<p>The sudden axial acceleration of a column of liquid bounded at one end by a concave free surface has been found, experimentally, to produce a jet which issues from the free surface with a speed several times that imparted to the column. </p>
<p>Theoretical approximations to such flows, valid for small time, are formulated subject to the assumption that the fluid is inviscid and incompressible. In a special two-dimensional case, it is found that, for vanishingly small time, the velocity at the point on the free surface from which the jet emanates is π/2 times the velocity imparted to the column. The solutions to several problems in two and three dimensions assuming that the initial curvature of the free surface is small, lead to values for this ratio dependent upon the curvature—the initial velocity in the case of axial symmetry exceeding that of the analogous two-dimensional problem by approximately 25%.</p>
<p>Experiments conducted upon the phenomenon give values systematically in excess of those predicted by the theory, although theory and experiment are in qualitative agreement with respect to the displacement of the free surface. It is suggested that the discrepancy is attributable to effects of finite curvature having been imperfectly accounted for in the axially-symmetric analysis. </p>
<p>Photographic materials on pp. 115, 120, and 121 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered. </p>
https://thesis.library.caltech.edu/id/eprint/9310