Caltech Authors
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Repository of works by Caltech published authors.
Mostrando recursos 1 - 20 de 71
1.
Cavitation and Other Free Surface Phenomena - Brennen, C.
This thesis develops a method of solving axisymmetric cavity flow problems using a relaxation or numerical technique.
Chapter 1 contains a general review of the phenomenon of cavitation in fluids. Special reference is then made to fully developed cavities in an Euler or ideal fluid for both plane and axisymmetric flow. The basic theorems and equations are presented, with the various types of mathematical model which have been suggested. Details of the fundamental feature of this type of flow, namely the phenomenon of flow separation, are given. At the conclusion of the chapter the analytic methods of solution of plane cavitating...
3.
On the theory of surface waves in water generated by moving disturbances - De Prima, C. R.; Wu, T. Y.
The wave profile generated by an obstacle moving at constant veiocity U over a water surface of infinite extent appears to be stationary with respect to the moving body provided, of course, the motion has been maintained for a long time. When the gravitational and capillary effects are both taken into account, the surface waves so generated may possess a minimum phase velocity c[sub]m characterized by a certain wave length, say [lambda][sub]m (see Ref. 1, p. 459). If the velocity U of the solid body is greater than c[sub]m, then the physically correct solution of this two-dimensional problem requires that...
4.
General Formulation of a Perturbation Theory for Unsteady Cavity Flows - Wang, D. P.; Wu, T. Yao-tsu
The problem of a two-dimensional cavity flow of an ideal fluid with small unsteady disturbances in a gravity free field is considered. By regarding the unsteady motion as a small perturbation of an established steady cavity flow, a fundamental formulation of the problem is presented. It is shown that the unsteady disturbance generates a surface wave propagating downstream along the free cavity boundary, much in the same way as the classical gravity waves in water, only with the centrifugal acceleration owing to the curvature of the streamlines in the basic flow playing the role of an equivalent gravity effect. As...
5.
An Approximate Numerical Scheme for the Theory of Cavity Flows Past Obstacles of Arbitrary Profile - Wu, T. Yao-tsu; Wang, D. P.
Recently an exact theory for the cavity flow past an obstacle of arbitrary profile at an arbitrary cavitation number has been developed by adopting a free-streamline wake model. The analysis in this general case leads to a set of two functional equations for which several numerical methods have been devised; some of these methods have already been successfully carried out for several typical cases on a high speed electronic computer.
In this paper an approximate numerical scheme, somewhat like an engineering principle, is introduced which greatly shortens the computation of the dual functional equations while still retaining a high degree...
6.
Viscous Effect on Surface Waves Generated by Steady Disturbances - Wu, T. Yao-tsu; Messick, R. E.
A linearized theory is applied here to investigate the viscous effect on water waves generated and maintained by a system of external disturbances which is distributed over the free surface of an otherwise uniform flow. The flow is taken to be in the steady state configuration. The analysis is carried out to yield the asymptotic expressions for the surface wave when the Reynolds number of the flow is either large or small.
7.
Final Report: Wall Effects in Cavity Flows - Wu, T. Yao-tsu; Whitney, Arthur K.; Lin, J. D.
The wall effects in cavity flows past an arbitrary two-dimensional body is investigated for both pure-drag and lifting cases based on an inviscid nonlinear flow theory. The over-all features of various theoretical flow models for inviscid cavity flows under the wall effects are discussed from the general momentum consideration in comparison with typical viscous, incompressible wake flows in a channel. In the case of pure drag cavity flows, three theoretical models in common use, namely, the open-wake, Riabouchinsky and re-entrant jet models, are applied to evaluate the solution. Methods of numerical computation are discussed for bodies of arbitrary shape, and...
8.
A Note on the Linear and Nonlinear Theories for Fully Cavitated Hydrofoils - Wu, T. Yao-tsu
The lifting problem of fully cavitated hydrofoils has recently received some attention. The nonlinear problem of two-dimensional fully cavitated hydrofoils has been treated by the author, using a generalized free streamline theory. The hydrofoils investigated in Ref. 1 were those with sharp leading and trailing edges which are assumed to be the separation points of the cavity streamlines. Except for this limitation, the nonlinear theory is applicable to hydrofoils of arbitrary geometric profile, operating at any cavitation number, and for almost all angles of attack as long as the cavity wake is fully developed. By using an elegant linear theory,...
9.
Swimming of a Waving Plate - Wu, T. Yao-tsu
The purpose of this paper is to study the basic principle of fish propulsion. As a simplified model, the two-dimensional potential flow over a waving plate of finite chord is treated. The solid plate, assumed to be flexible and thin, is capable of performing the motion which consists of a progressing wave of given wave length and phase velocity along the chord, the envelope of the wave train being an arbitrary function of the distance from the leading edge. The problem is solved by applying the general theory for oscillating deformable airfoils. The thrust, power required, and the energy imparted...
10.
Small-Time Behavior of Unsteady Cavity Flows - Wang, D. P.; Wu, T. Yao-tsu
A perturbation theory is applied to investigate the small-time behavior of unsteady cavity flows in which the time-dependent part of the flow may be taken as a small-time expansion superimposed on an established steady cavity flow of an ideal fluid. One purpose of this paper is to study the effect of the initial cavity size on the resulting flow due to a given disturbance. Various existing steady cavity-flow models have been employed for this purpose to evaluate the initial reaction of a cavitated body in an unsteady motion. Furthermore, a physical model is proposed here to give a proper representation...
11.
Experiments on Circular Arc and Flat Plate Hydrofoils in Noncavitating and Full Cavity Flows - Parkin, Blaine R.
An investigation in the High Speed Water Tunnel of the two-dimensional hydrodynamic characteristics of sharp-edged hydrofoils is described. The lift, drag, and pitching moment were measured in cavitating and noncavitating flows for flat plate and circular arc profiles. The theory of Wu for the forces on sharp-edged profiles in full cavity flow and the experimental results showed good agreement over a wide range of attack angles.
12.
Deformation Measurements at the Sub-Micron Size Scale: II. Refinements in the Algorithm for Digital Image Correction - Vendroux, G.; Knauss, W. G.
Improvements are proposed in the application of the Digital Image Correlation method, a technique that compares digital images of a specimen surface before and after deformation to deduce its sureface (2-D) displacement field and strains. These refinements, tested on translations and rigid body rotations were significant with regard to the computer efficiency and covergence properties of the method. In addition, the formulation of the algorithm was extended so as to compute the three-dimensional surface displacement field from Scanning Tunneling Microscope tomographies of a deforming specimen. The reolsution of this new displacement measuring method at the namometer scale was assessed on...
13.
Submicron Deformation Field Measurements II: Improved Digital Image Correlation - Vendroux, G.; Knauss, W. G.
This is the second paper in a series of three devoted to the applicaiton of Scanning Tunneling Microscopy to mechanics problems. In this paper improvements to the Digital Image Correlation method are outlined, a technique that compares digital images of a specimen surface before and after deformation to deduce its (2-D) surface displacement field and strains. The necessity of using the framework of large deformation theory for accurately addressing rigid body rotations to reduce associated errors in the strain components is pointed out. In addition, the algorithm is extended to compute the three-dimensional surface displacement field from Scanning Tunneling Microscope...
14.
Final Report to the Air Force Office of Scientific Research on Hygroviscoelasticity of the Human Intervertebral Disc - Knauss, W. G.
In order to gain an improved understanding of the behavior of human intervertebral disc material under various kinds of loads the viscoelastic properties of small specimens excised from human L4-L5 discs were examined. Excisions were made from donated spine segments procured a few hours after death and then frozen. Material examined was in the form of single lamellar specimens as well as specimens containing several lamellae.
Tensile relaxation tests were performed on single lamellae prepared such that the collagen fibers were a) aligned with the tension axis, b) normal to the tension axis and c) at an angle of about...
15.
A Free Streamline Theory for Two-Dimensional Fully Cavitated Hydrofoils - Wu, T. Yao-tsu
The problem of cavity flows received attention early in the development of hydrodynamics because of its occurrence in high speed motion of solid bodies in water. Many previous works in this field were mainly concerned with the calculation of drag in a cavitating flow. The lifting problem with a cavity (or wake) arose later in the applications of water pumps, marine propellers, stalling airfoils, and hydrofoil crafts. Although several formulations of the problem of lift in cavity flows have been pointed out before, these theories have not yet been developed to yield general results in explicit form so that a...
16.
A Wake Model for Free-Streamline Flow Theory Part I. Fully and Partially Developed Wake Flows and Cavity Flows past an Oblique Flat Plate - Wu, T. Yao-tsu
A wake model for the free-streamline theory is proposed to treat the two-dimensional flow past an obstacle with a wake or cavity formation. In this model the wake flow is approximately described in the large by an equivalent potential flow such that along the wake boundary the pressure first assumes a prescribed constant under-pressure in a region downstream of the separation points (called the near-wake) and then increases continuously from this under-pressure to the given free stream value in an infinite wake strip of finite width (the far-wake). The boundary of the wake trailing a lifting body is allowed to...
17.
Two Dimensional Sink Flow of a Viscous, Heat-Conducting Compressible Fluid; Cylindrical Shock Waves - Wu, Y. T.
The steady two-dimensional sink-type flow of a viscous, heat-conducting perfect gas is investigated. An approximate solution of this problem is given for the case of large Reynolds number Re (cf. the definition given in the text). In obtaining the present solution the values of Prandtl number and the ratio of the first and second viscosity coefficient may be arbitrary. The result shows that the solution has two branches, both of physical significance. On the subsonic branch of the solution the flow speed starts from the stagnation point at infinity, increases monotonically for decreasing radial distance and eventually terminates with maximum...
18.
The growth or collapse of a spherical bubble in a viscous compressible liquid - Gilmore, Forrest R.
With the help of a hypothesis first proposed by Mirkwood and Betbe, the partial differential equations for the flow of a compressible liquid surrounding a spherical bubble are reduced to a single total differential equation for the bubble-wall velocity. The Kirkwood-Bethe hypothesis represents an extrapolation of acoustic theory and would be expected to be most accurate when all liquid velocities are small compared to the velocity of sound in the liquid. However, the present theory is found to agree quite well with the only available numerical solution of the partial differential equations which extends up to a bubble-wall velocity of...
19.
Partial cavity instabilities - Duttweiler, M. E.; Brennen, C. E.
This paper reviews some of the literature on partial cavity instabilities on single hydrofoils and then summarizes the striking differences in the appearance and behavior of partial cavities on swept foils (as opposed to two-dimensional, unswept foils) as rcently highlighted by de Lange et al. (1994) and Laberteaux and Ceccio (1998). These demonstrate the importance of the spanwise evolution of the re-entrant jet, and the consequences for the characteristics of the cavity closure flow. It is suggested in this paper that several variants of this evolution can be seen in the photographs of cavitation on single hydrofoils foils and on...
20.
Anyons in an exactly solved model and beyond - Kitaev, Alexei
A spin-1/2 system on a honeycomb lattice is studied. The interactions between nearest neighbors are of XX, YY or ZZ type, depending on the direction of the link; different types of interactions may differ in strength. The model is solved exactly by a reduction to free fermions in a static Z2 source gauge field. A phase diagram in the parameter space is obtained. One of the phases has an energy gap and carries excitations that are Abelian anyons. The other phase is gapless, but acquires a gap in the presence of magnetic field. In the latter case excitations are non-Abelian...
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