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RESEARCH PAPERS

J. Basic Eng. 1968;90(4):435-440. doi:10.1115/1.3605157.

This investigation was conducted to define the plastic stress distribution at a section 90 degrees from the point of load application on a ring. The elastic and plastic stress distribution was determined experimentally by using postyield strain gages and the stress-strain relationship obtained from a uniaxial tensile test. The experimental results in the elastic range were found to agree with presently available theoretical predictions. A theoretical plasticity analysis of the ring was made by assuming that it deforms to the shape of an ellipse and that plane sections remain plane. The strains determined in this manner were used to calculate stresses off the tensile stress-strain curve. The experimental results indicated that this initial analysis gave a good approximation of the stress distribution for large deflections of the ring.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):441-444. doi:10.1115/1.3605158.

A theoretical buckling load for a strut with a single-edge notch at its mid point is calculated assuming that the effect of the notch is to produce a discontinuity in the slope of the strut. This buckling load is not likely to be reached if the material of the strut is at all brittle and it is shown that the fracture load can be calculated from the critical stress intensity factor of the material. Some justification to the theoretical treatment is obtained from the analysis of previous experimental results.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):445-452. doi:10.1115/1.3605159.

The investigation deals with the “spin-up” of the liquid partially filling a right circular cylinder which is impulsively accelerated from rest to a constant angular velocity. By application of certain simplifying assumptions, a simplification of the Navier-Stokes equations is obtained and numerically solved, obtaining the unsteady angular velocity distribution of the liquid and the configuration of the liquid’s free surface, as it approaches, asymptotically with time, a paraboloid. The simplifying assumptions are qualitatively verified by experiment. Measurement of the theoretically predicted free-surface configuration is obtained by an electrohydraulic servosystem designed and developed for the problem. Good agreement between experiment and theory is obtained.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):455-467. doi:10.1115/1.3605163.

The fully developed incompressible turbulent boundary layer in a channel has been explored using constant-temperature hot-wire anemometry. Particular attention was paid to measurements well into the viscous sublayer, yielding results which are believed to be new. Frequency spectral analyses of the fluctuating velocity components have been obtained for the inner layers. The mean velocity distribution in the sublayer has been determined with sufficient accuracy for a reasonable estimate of skin friction to be made. The results are compared with those of Laufer [11] and Comte-Bellot [4].

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):469-475. doi:10.1115/1.3605168.

A study is made of the ratcheting growth of an elastic-plastic one-dimensional element subjected to thermal cycling in the presence of a sustained axial load. The cyclic temperature distribution across the element is taken as either linear or parabolic. The cyclic growth of the element is computed as a function of the cyclic temperature and sustained axial load.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):476-483. doi:10.1115/1.3605169.

The flow in the near-wake of a circular cylinder was measured with hot-wire anemometry. Processing of the large body of data on unsteady features of the flow was aided with a digital computer. The major sets of results are for Reynolds numbers of 10,600 and 53,000. The results are presented in several complementary forms. In discussion of the results it is shown how they relate to the generation and maintenance of the Strouhal frequency, the existence and discussion of velocity spikes, the control of heat transfer, and to greater irregularity at lower Reynolds numbers. Some issues are raised in the processing of nonstationary random data.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):485-493. doi:10.1115/1.3605172.

Two parallel straight cascades moving against one another with constant velocity are considered within plane incompressible potential flow. The position of the exciting active cascade is assumed upstream as well as downstream of the passive cascade. Free vortex sheets start only from the trailing edge of the passive cascade. Assuming infinite thin blades with small camber, small elongation and harmonic excitement, amplitudes of instationary lift and moment in relation to the corresponding stationary quantities are calculated as a function of pitch ratio of the two cascades, stagger angles of both cascades, and ratio of plate circulation to total circulation. These amplitudes reach up to 20 percent of the corresponding values in stationary flow but do not form a pronounced maximum in case of equal pitches. This effect increases if the vortex sheets from the neighboring passive profiles are neglected; it also increases with increasing pitch-chord ratio and decreasing number of harmonics. A comparison with the theoretical results of Kemps and Sears [15] shows up to 30 percent smaller lift amplitudes. Downstream position of the active cascade increases the amplitudes, especially in the case of increasing angle of attack.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):494-500. doi:10.1115/1.3605173.

An analysis is given for determining the lift fluctuation on an aerofoil due to a gust parallel to the undisturbed flow. By combining the new analysis with an established theory for “transverse” gusts perpendicular to the undisturbed flow, it is possible to obtain the fluctuating lift on a rotating fan or compressor blade moving through a flow disturbance. It is shown that simple design rules may be derived for fans and compressors if the fluctuating lift forces, and possibly therefore the associated noise, are to be reduced.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):501-509. doi:10.1115/1.3605176.

The paper presents an approach for the analysis of low-velocity two and three-dimensional transient fluid-flow problems. The method assumes the continuum can be represented by a latticework of piping elements and that motion in the continuum can be described by solving the one-dimensional transient flow equations in the piping elements. The approach offers the advantage of being able to handle unusual and irregular boundary conditions, fixed or moveable, but restricted to the limitation of low Mach number. Undesirable grid characteristics are identified and comparisons with known hydrodynamic solutions are presented.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):511-518. doi:10.1115/1.3605180.

The forces acting on a circular cylinder by a time-dependent flow are analyzed through the use of a potential flow model. The shear layers which spring from the sides of the body are replaced by a combination of line vortices and infinite number of vortex sheets which connect the nascent vortices to their respective feeding zones. The analysis is then applied to the prediction of the kinematic and dynamic characteristics of symmetric vortex separation on circular cylinders. The results compare favorably with the latest available experimental data. The development of the wake is also traced and the results show the primary and secondary roll-ups of the shear layers as represented by the line vortices and vortex sheets.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):521-530. doi:10.1115/1.3605184.

Results of field measurement of transients in two pump discharge lines show that the pressures were greater than had been predicted during design, and a theory and method of analysis are developed which explains the time-history of the transients measured. The field measurements were undertaken because of the complexity of the phenomena and because very little measured data were available. Results are presented graphically along with analytical solutions. Conclusions drawn were: (a) The inherent difficulty of prediction of water-column separation effects is further complicated by the uncertainty about complete pump operating characteristics and actual moment of inertia of pumps and motors; (b) the effects of air and gases entrained in solution in the water must be considered in the analytical solution; and (c) entrained air can have a detrimental effect on the water-hammer transient, i.e., larger pressure surges in the discharge line and higher reverse speeds of the pumps can be caused by its presence.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):532-540. doi:10.1115/1.3605187.

The dynamic response of liquid flow systems may be grossly affected by motion of the system’s structural supports. Pressure and flow perturbations within the flow system provide the driving forces for the structural supports, and the resulting motion induces further pressure and flow perturbations. In this type of closed-loop system, instabilities are possible. Analysis techniques are developed which enable the analyst to formulate distributed parameter, nonlinear solutions to unsteady flow problems including structural motion. These techniques are based on plane wave theory and require the use of a digital computer. For sinusoidal periodic inputs of small amplitudes, closed-form mathematical solutions are possible if nonlinearities are linearized, and these solutions are carried out. Examples show that resonance points and peak-to-peak pressure amplitudes may be very sensitive to structural properties of the supporting structure. Analytical results obtained with the closed-form linearized model and the nonlinear digital model are compared. It is also shown that the closed-form linearized model gives results which compare favorably with the nonlinear model for the case of sinusoidal inputs, but cannot be applied if the input perturbations are nonsinusoidal or are sufficiently large or if wave shapes are to be computed. Experimental results are shown to agree well with theoretical calculations.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):541-552. doi:10.1115/1.3605188.

This paper describes an experimental study of the incompressible flow through a step expansion in a circular pipe as affected by suction through an annular gap lining the convex corner of the step. A uniform inlet flow with thin boundary layer is considered. Application of suction at a rate greater than some critical value caused the flow to expand rapidly into the larger diameter (basic effect previously termed an “edge suction effect”), the degree of expansion greatly dependent on gap orientation and size. Critical suction rates have been determined and other data collected to evaluate the configuration as a (short) diffuser.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):555-562. doi:10.1115/1.3605192.

The problem of unsteady flow in the blade passage of a partial admission impulse turbine with supersonic nozzle flow is introduced. Previous work carried out at M.I.T. revealed the presence of a shock wave at the entrance to the blade passages and this report sets out to predict the formation of such a shock wave using a one-dimensional theory. The one-dimensional theory is discussed in some detail and a novel method for dealing with the inflow boundary conditions is developed. Details of a characteristic calculation are given, and this is matched with a shock wave analysis to predict the formation of the shock wave. The implications of the theoretical work are discussed and experimental results obtained from a hydraulic analogy are presented which confirm the analysis.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):563-570. doi:10.1115/1.3605193.

A method is given for the analysis of time dependent two-dimensional incompressible laminar boundary layers. The technique is a combination of the method of weighted residuals and the method of lines, and reduces the boundary-layer equations to an Nth order approximation in terms of a system of ordinary differential equations. The method is demonstrated by solving the transient flow over a semi-infinite flat plate and the results are compared with known asymptotic solutions. For a third approximation, the steady-state skin friction coefficient given by the present method agrees with the Blasius solution within 0.1 percent.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):572-578. doi:10.1115/1.3605196.

This paper presents an extensive review of some recent experimental results for developing turbulent free shear layers in isoenergetic flow with free stream Mach numbers up to eight. Experimental longitudinal variations of a midprofile velocity and a characteristic layer width are compared with corresponding predictions from a recent theory for developing layers and from the well-known asymptotic theory. Using a recent theoretical specification for the variation of spread rate parameter σ with free stream Mach number, it was found that the predictions of the developing layer analysis were in general agreement with measurements. It was demonstrated that the asymptotic theory, in conjunction with the virtual origin technique, can also be utilized to predict developing layer growth. An experimental specification of σ yielded uncertainties ranging from 15 to 50 percent, although the results tended to confirm the general validity of some recent theoretical postulations for the spread rate parameter.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):581-594. doi:10.1115/1.3605199.

A comprehensive study is made of factors influencing the accuracy of predicted thickness effects on the flow due to oscillatory motion of a sweptback wing in supersonic flight. For a delta planform with its leading edge swept at or near the Mach angle, the streamlines and velocity pattern due to thickness are found to be highly three-dimensional. Based on this observation, improvements are suggested to previous approximate second-order theories for the unsteady loading. Numerical examples are presented for a 45 deg della which indicate a substantial difference between the linearized and nonlinear pressure distributions. Although a greater volume of computation is needed to guarantee adequate accuracy, practical means are described for the complete numerical solution of problems of this type.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):596-606. doi:10.1115/1.3605203.

In this shock tube investigation, the passage of a plane normal shock wave and its associated drift flow over a two-dimensional circular cylinder impulsively generated a vortex street. The operating free stream Reynolds and Mach number range was 3.25 × 104 ≤ Rn ≤ 2.03 × 105 and 0.193 ≤ M∞ ≤ 0.483, respectively. The formation of the initial standing pair of vortices, their shedding, and the subsequent establishment of the vortex street were recorded interferometrically using a high speed framing camera. The movement of the initial vortex pair was observed to be significantly altered for Rn > 1.5 × 105 , where a secondary vortex pair was generated and merged with the initial vortex pair well before shedding commenced. During the lifetime of the impulsively generated wake, the Strouhal number, S, approached an average value of 0.16 which is significantly lower than the usual steady-state value of about S ≃ 0.2. Values of spacing ratio were found to decrease with increasing vortex street lifetime for all downstream locations. Other pertinent vortex street characteristics were also reported.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):607-616. doi:10.1115/1.3605204.

A field investigation was made to determine the source and character of pressure pulsations in the boiler feed system of a central power station. By systematic equipment elimination, it was concluded that the oscillation are caused by rotating stall in the boiler feed pump as it enters into resonance with the piping circuit. An analysis is carried out of the equivalent linear system under harmonic conditions. The analytical model provides reasonable agreement with the observations for the three tested piping configurations. Some insight is provided in the mechanism of the pulsations and the dynamic impedances of typical component equipment.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Basic Eng. 1968;90(4):620-622. doi:10.1115/1.3605210.

A brief review of various theories of interaction of inclusions and domain walls in a ferromagnetic material is presented. A postulate concerning the modification of domain patterns by inclusions, based on theory, is described and the various free-energy contributions of the inclusion to the matrix in the vicinity of the inclusion are discussed. Examples of domain wall bending in ingot iron by manganese sulfide inclusions are shown to agree with the postulated model of interaction of a stress field around the inclusion and the domain wall.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1968;90(4):622-625. doi:10.1115/1.3605211.
Abstract
Commentary by Dr. Valentin Fuster

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