Assessment of a quintuple hotwire measurement technique for highly turbulent flows

A five-wire calibration and measurement technique is presented, which is an extension of the four-wire method developed by Döbbeling et al. (1990a, b). From numerical simulations of the uniqueness domain and the angular resolution it is concluded that the uniqueness domain of the quintuple technique can be expanded to a hemisphere as opposed to the four-wire techniques which are restricted to a conical domain of about 40° half angle. Measurements of the mean velocities and Reynolds stresses in a low-turbulence jet and in grid turbulence confirm and complement the results of the numerical simulations. It is thus shown that the quintuple method achieves increased accuracy in an expanded measurement range.The work of D. Hölzer, student of engineering at the University of Karlsruhe, and the support of W. Paulat and W. Pfeffinger in writing the data aquisition software, and H. Klette who manufactured the probe, is gratefully acknowledged. This work was supported by the Deutsche Forschungsgemeinschaft within the framework of the Sonderforschungsbereich 167, Hochbelastete Brennräume- Stationäre Gleichdruckverbrennung, Teilprojekt A10.     

Design and stress evaluation of a nonsymmetric pressure vessel

Presently, the large variation in demand for electrical power at different periods of the day imposes new considerations in the evaluation of pressure components in large steam-generating equipment. In the past, pressure components such as valve bodies have been designed for static pressure conditions against bursting with sufficient stiffness to assure operation ability. In today's plant operation, the response of the valve body to thermal transients will have a major influence on the life of the valve. Since the valve body is a compact nonsymmetric body, the direct calculation of stresses is very complex. The evaluation of the behavior of nonsymmetric pressure components under the loads imposed by various operational modes requires information from both analytical and experimental methods of analysis. The contributions from modern computer-calculation programs and three-dimensional photoelasticity are discussed as applied to the evaluation of a valve body used in a large, supercritical steam generator. In the analysis, computer procedures are used to develop the preliminary geometry for pressure loading. Because of the close proximity of the nonsymmetrical openings, a three-dimensional photoelastic analysis is used to calibrate the computer model. Once a satisfactory computer model has been developed for pressure loading, it is used to calculate the thermal stresses. Since stresses have little meaning in themselves, a design basis is necessary to evaluate the significance of the calculated stresses. The design basis must consider the types of failures which are possible and is thus dependent on the temperature at which the valve must operate. A design basis is discussed for the evaluation of pressure components in a boiler system.     

Das mechanische Verhalten von Thermoplasten bei mittlerer und hoher Deformation bis zum Bruch

Zusammenfassung Es wird versucht, den Deformationsvorgang bis zum Bruch an einem unvernetzten thermoplastischen Material zu analysieren. Dabei zeigt es sich, daß das makroskopische Bruchverhalten des Materials durch die beiden konkurrierenden Vorgänge des mikroskopischen Fehlstellenwachstums und der aufgezwungenen makroskopischen Deformation bestimmt wird. Da das Fehlstellenwachstum wiederum von der molekularen Reaktion des Materials auf die Deformation abhängt, ergeben sich enge Zusammenhänge zwischen dem Dehnungs- und Bruchverhalten und den molekularen Relaxationsprozessen.Diese Zusammenhänge werden an einem Weichmacherfreien PVC erstens mit Hilfe von Zugversuchen in einem weiten Geschwindigkeits- und Temperaturbereich und zweitens mit einer indirekten Methode zur Verfolgung des Fehlstellenwachstums untersucht.Wenn mit niedrigeren Geschwindigkeiten die zur Verfügung stehende Zeit und bzw. oder die Versuchstemperatur zunehmen, steigt die mittlere Dehnbarkeit erstmalig an, wenn die Neben-Relaxationsmechanismen die Streckspannung abbauen können, und erreicht sehr hohe Werte, wenn die Hauptrelaxationsmechanismen die lokalen Spannungen an den Fehlstellen herabsetzen.

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Summary An attempt is made to analyse the deformation process of a non-crosslinked thermoplastic material until fracture occurs. It is shown that the macroscopic fracture behaviour is determined by the competition of the microscopic flaw growing with the macroscopic elongation. The flaw growing itself depends on the molecular reaction of the specimen against the elongation forced upon it. This causes certain relations between the strain- and fracture-behaviour and the molecular relaxation processes of the material.These relations were investigated by means of tensile tests on unplastified PVC in a wide speed and temperature range. Moreover the flaw growing during the tensile tests is examined by a new indirect method.With increasing test time and temperature the mean elongation increases for the first time, when the secondary relaxation processes are able to reduce the yield stress. A further marked increase of the elongation is to be stated when the main relaxation processes diminish the local stresses at the microscopic flaws.

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Vorgetragen auf der Jahrestagung der Deutschen Rheologen in Berlin-Dahlem am 22. Mai 1968.     

Zur Rheologie der Torfbearbeitung

Zusammenfassung Zur rheologischen Charakterisierung nordwestdeutschen Hochmoortorfes genügt allein die Fließgrenze. Sie ist abhängig von der Torfart und bei mechanischer Vorbehandlung von der Gesamtzahl der Rührerumdrehungen. Die Erniedrigung der Fließgrenze durch Bearbeitung wird mit Hilfe eines einfachen Strukturmodells gedeutet.Der Vergleich zweier Bearbeitungsmaschinen bei jeweils gleichen Fließgrenzen des Torfes ergibt, daß das Momentenverhältnis nur von der Rührerbauart, nicht von der Torfart abhängt. Damit ist die Bestimmung der Fließgrenze durch Rührertypen möglich, bei denen die Meßsehwierigkeiten des Rotationsviskosimeters nicht auftreten. Weiter folgt daraus, daß das Verhältnis der spezifischen Arbeiten zweier Rührer, die gleichen Torf bis zur gleichen Fließgrenze bearbeiten, ebenfalls von der Torfart unabhängig ist. Die Abhängigkeit von der Rührerbauart ist relativ gering.Die kraftwirtschaftliche Bewertung verschiedener Rührerkonstruktionen läßt sieh infolge der geringen Unterschiede der spezifischen Arbeiten und der großen Versuchsstreuung nur durch sehr viele Einzelmessungen sichern.     

An actuator-disc model for the prediction of abrupt stall in an axial compressor rotor

The representation of loss in a cascade by the appearance of blockage has been extended to deal with blade rows by the use of a source distribution to represent this blockage, and in the case of the actuator disc approximation, the presence of sources is confined to an axi-symmetric dìstribution over the actuator disc. It is found that if a typical dependence of loss (and consequently diffusion ratio) upon incidence for each section of an axial compressor rotor is represented in this manner, the influence of blockage on the axial velocity distribution may be found using the potential equation combined with the usual actuator disc approximation. Study of the behaviour of the controlling ordinary differential equation for the axial velocity ahead of the disc reveals that as the flow is reduced, the equation contains a singularity within the range of radius and a meaningful solution does not exist. This result is interpreted as the limit to continuous operation and reasonable agreement between this predicted limit and the appearance of abrupt stall (experimentally) is found.     

Determination of the critical loads of shells by nondestructive methods

Two methods for determining the location of and load level to produce instability of compressed cylindrical shells are presented. The first relates the variation in the wall normal stiffness as a function of applied compressive force to the critical load. It uses the distribution of stiffness over the surface of the shell as a guide to buckle location. The second method associates the local dynamic mass with instability behavior. The test data presented show that either method will give excellent prediction capability from low-load-level data for shells of orthodox form. Neither method appears to apply to spirally stiffened shells. This is thought to be due to the fact that there is a substantial difference between the buckle pattern under axial compression and the imperfection shape induced by the normal displacement which is used to ascertain the wall stiffness and the dynamic mass.     

A note on duality in finite elasticity

The duality between stress and deformation fields for plane deformations of a compressible isotropic hyperelastic material established by J. M. Hill [1]is generalized to deformations of a homogeneous elastic material without the restrictions of isotropy and hyperelasticity. At the same time a clarification of Hill's results is achieved.     

The buckling load of an elastically supported cantilevered column with continuously varying cross section and distributed axial load

Summary The solution for the buckling load of an elastic supported cantilevered column with continuously varying cross section and distributed axial load is developed. Boundary conditions are formulated for fixed and elastic support. The critical loads are tabled for an usual variation in cross section and axial load distribution as function of the ratio between respectively rigidities and axial forces at fixed and free end, the variation of the rigidity and axial forces given by their degrees of the polynomial variation and rotation stiffness of the elastic support.

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Übersicht Es wird die Knicklast für eine elastisch gelagerte, freitragende Säule mit stetig veränderlichem Querschnitt und stetig verteilter Axiallast berechnet. Die Randbedingungen sind für feste sowie für elastische Lagerung formuliert worden. Für einen übliczen Bereich von Querschnitten und Axiallasten werden die kritischen Lasten in Tabellen angegeben. Dabei wurde das Verhältnis zwischen der Steifigkeit und den Axiallasten am festen und freien Ende variiert.

     

The diffractographic strain gage

A method for measuring strain using diffraction of light from a single aperture is described, and results of a comparison tensile test with an electrical-resistance strain gage are presented. The “diffractographic strain gage” is shown to have high sensitivity, linearity, accuracy and temperature compensation and the ability to operate in a variety of hostile environments. It is furthermore simple, inexpensive, and the data can be collected by eye without assistance from further instrumentation.     

Radiation effects on creep rupture and fatigue strength of pure aluminum

Paper describes an experimental investigation on the effect of nuclear radiation on the creep rupture and fatigue strength of pure aluminum for the ratios of alternating stress to mean stress ranging from zero to infinity. It was found that not only was the strength of the material tested affected by radiation over a range of ratios of stresses, but also the brittle-ductile transition was influenced.Based upon the experimental results obtained, an analytical model was developed to correlate creep rupture, fatigue strength and radiation effect for various ratios of stresses. This information may prove to be valuable in dealing with the stress analysis of nuclear reactors.Paper was presented at 1966 SESA Annual Meeting held in Pittsburgh, Pa., on November 6–9.