Showing papers by "Leibniz University of Hanover published in 1985"

Fundamentals of lubrication in refrigerating systems and heat pumps

Abstract: The fundamentals concerning the influence of oil on the various components of a refrigeration plant are discussed; especially the favourable and unfavourable influences of the lubricant. The requirements for lubricating oils are also described, as they can be deduced from fundamentals. Requirements for oil are considered with respect to new developments, for example, large heat pumps, high temperature heat pumps, and plants with refrigerant mixtures for cooling systems as well as for heat pumps.

Flavanone glucosides in callus and phloem of Prunus avium: Identification and stimulation of their synthesis

Abstract: The flavanone glucosides dihydrowogonin-7-glucoside, eriodictyol-7-giucoside and prunin (naringenin-7-glucoside) were isolated, identified and quantitatively determined in callus cultures and phloem of Prunus avium L. cvs. Sam and Schneiders. These substances were isolated from callus tissue, where they were most abundant. The identification included TLC, HPLC and spectrophotometry in conjunction with hydroxylation and benzoylation. Elevation of sucrose concentrations in the media from 1 to 4% (w/w) resulted in a 3- to 4-fold increase in prunin. A similar response, although much less pronounced, was observed for eriodictyol-7-glucoside, while dihydrowogonin-7-glucoside was not enhanced under these conditions. Addition of benzyladenine to media of tissue cultures also caused an increase in prunin and eriodictyol-7-glucoside levels. Both of these flavanones also increased in phloem above and below a constriction of Prunus stems. Administration of benzyladenine into Prunus stems resulted in a 4-fold increase of prunin in the phloem.

Noise generation in railway wheels due to rail-wheel contact forces

Abstract: SUMMARY In urban rapid transit systems the squealing noise of railway wheels during the passage through narrow curves is very troublesome to passengers and city dwellers. Frequency analyses of measured curving-noise levels show that the bending vibrations of the wheel disks excited by stick-slip motion between the wheel rim and the rail are the main sources of this sound radiation. To get insight into the dynamics of the noise generation it is necessary to understand the bending vibration behaviour of a wheel disk as well as the sound radiation mechanism and the generation of self-sustained oscillations in the contact area. The present paper deals with a theoretical model which comprises all three parts of the problem. In the first part the natural bending vibrations of the wheel are calculated by means of a finite element model. In the second part the forced and self-sustained oscillations are determined using modal expansion techniques. The third part deals with the calculation of the radiated sound pre...

Resistance Calculation from Mask Artwork Data by Finite Element Method

Abstract: Traditional methods for resistance calculation suffer from some unfavourable features, that make them uncomfortable to use. Although requiring a lot of manual processing, they are rather inaccurate and often claim for severe artwork restrictions (e.g. orthogonal geometry) which conflict with the desire for most dense layouts. This paper describes a resistance calculation program called REX (Resistance Extractor), which is based on the well-known Finite Element Method (FEM). Highly flexible in use, it is able to process designed and parasitic resistors of any shape and material with adjustable precision. REX is part of the layout verification system ALAS, designed for mask artwork analysis of bipolar circuits.

On the Contact Problem of Tires, Including Friction

Abstract: The mathematical description of tires does not usually consider frictional interaction between the tire and the surface over which it moves. An approach for doing so is presented in the present paper for a homogeneous tire without grooves and which is loaded axially. The tire footprint area is divided into smaller areas that either stick or slide at the interface between the tire and its supporting structure when frictional forces are applied. Discretization of the contact problem into finite elements leads to a nonlinear system of equations for the nodal displacements. The algorithm applied to compute the normal and tangential forces in the contact zone is described. The Newton‐Raphson method and the modern quasi‐Newton methods BFGS (Broyden, Fletcher, Goldfarb, Shanno) and DFP (Davidon, Fletcher, Powell) proved to be the most effective. Normal and tangential forces in the footprint area were computed by the Lagrange multiplier method or directly by calculation of the stress tensor in the contac...

A method for determining the K-uptake from subsoil by plants

Abstract: Rb was applied to the topsoil in order to trace the potassium which was taken up from the topsoil by plants. The resulting K/Rb ratio in plants increased when plants came into contact with the Rb free subsoil. This change in the K/Rb ratio enables the calculation of the K uptake from the subsoil. the average of the K uptake from the subsoil by spring wheat was 35% of the total uptake.

The Reaction to Political Radicalism and the Popularisation of Political Economy in Early Nineteenth-Century Britain

Abstract: The popularisation of the new discipline of political economy was, with the fierce debate which accompanied the publication of Darwin’s Origin of Species, perhaps the most deeply contested development in nineteenth-century intellectual history. From the publication of Adam Smith’s Wealth of Nations (1776) through the mid-Victorian period, political economy grew to become one of the most important ideological forces in the nineteenth century, welding together a system of morals, a philosophy of government and politics, and an account of the best state for mankind as well as its characteristic economic doctrines, and deeply affecting in the process the rise and development of popular educational institutions and ideas, the evolution of trades’ unions, reform and working class movements, the pattern of popular emigration, and millions of individuals’ conceptions of how life might and ought to be lived.

Increasing the availability of assembly systems

Abstract: Detailed study of the causes of stoppages in 40 automatic assembly systems has led to the development of guidelines for improving their availability

Computerized Information Systems in Personnel

Abstract: In the highly developed industrialized countries computer-assisted information systems in personnel have been set up for many reasons and purposes. My research study showed empirically how and to what extend the large German enterprises are introducing computerized systems for administration and planning. The individual data on each employee serve basically for accounting, but more and more for statements about capabilities, achievements, promotions, and profiles. Chances and dangers with respect to decisionmaking, communication, data privacy, and participation arise and should lead to a legal framework.

Flow Measurements in Two Cambered Vane Diffusers With Different Passage Widths

Abstract: To investigate the influence of the vaneless space between impeller exit and the diffuser vanes, datailed flow measurements in two diffusers with the same vane geometry but different passage width are compared.The three-dimensional character of the flow changes between impeller exit and the entry to the two dimensional vanes depending on the shape of the shroud. After initial measurements with a constant area vaneless space, the width of the vaned diffuser was later on reduced by 10%. The compressor maps show an increase in overall pressure rise and efficiency with the width reduction.To get further details of the flow field, measurements of the static pressure distribution at hub and shroud have been performed at several operation points for both diffusers. At the same points the flow angle and total pressure distribution between hub and shroud upstream and downstream of the vanes have been measured with probes. The maximum efficiency of the narrow diffuser is nearly 2% higher than for the wide diffuser. The measurements give further details to explain this improvements.Copyright © 1985 by ASME

A Coupled Analysis of Plastic Deformation and Heat Transfer

Abstract: In industrial forming processes, the deformation power is mostly transformed into heat. This causes a temperature increase within the workpiece and as a result a varying thermomechanical behaviour of the material. In an inhomogeneous process, the friction losses also raise the temperature at the interface die/workpiece. Therefore, the influence of temperature change on the material behaviour and, hence, on the accuracy of the final shape and on the forming load must be taken into account in the mathematical formulation.

Meßtechnik zur Charakterisierung von Gas/Flüssigkeits‐Reaktoren

Abstract: Measuring techniques for characterizing gas/liquid reactors. The article considers measuring techniques for the characterization of the phases in gas/liquid reactors. These include the velocity profile and turbulence in the continuous phase as well as holdup, size, and velocity of the dispersed phase. Also, methods for the determination of the specific interfacial area and the volumetric mass transfer coefficients are discussed. Measuring methods have made enormous advances in recent years. In spite of this, there is a lack of reliable methods, especially for use during reactions without disturbing the state of the reactor. It is suspected that probe technique will gradually fall into disuse and more and more attention will be focussed on contractless methods. This calls for further development of ultrasonic methods and methods relying on emission of light.

Blade Vibration on Centrifugal Compressors: Blade Response to Different Excitation Conditions

Abstract: Results and analysis of blade vibration measurements on a high pressure ratio / high mass flow centrifugal compressor made with strain gages and using multichannel telemetry are described for compressors with 3 different types of vaned diffusers. Considerable high frequency blade excitation and vibration of the shallow region near the impeller outlet were observed. Initial progress to predict this dangerous excitation caused by the diffuser vanes was made with the help of FE computations using a simplified element system consisting of the vibrating zones of a 90° sector of the impeller. Satisfactory agreement with measured vibration data was achieved.The influence of rotating stall on blade excitation was investigated using different types of vaned diffusers leading to different numbers of rotating stall zones and variations in the rotational speed of the cells. Blade vibration intensity due to surge in conjunction with variations of the diffuser is also considered.Holographic interferometry was successfully applied to blade vibration measurements on compressors in operation. The investigation was aimed at studying the occurrence of blade modes and the vibratory behavior of the different blades near the interesting inlet zone. The occurrence of different constellations of blade modes at a resonance point and at an operating point far from resonance was demonstrated.Copyright © 1985 by ASME

Hybrid vibration-mode analysis of rotating turbine-blade models

Abstract: In the field of turbomachinery special attention is devoted to the dynamic behavior of the blading, because from time to time vibrations are transferred to the machine. Numerical calculations of eigenfrequencies and eigenmodes are often made during design, but verification of these numerical processes by experiment is necessary. In addition to several holographic measuring methods, a new method has been developed to determine the vibration modes of blades in general, especially for a rotating blade. This is the object-related laser triggering method (OLT method), which yields interferograms without using an image derotator, thus avoiding special alignment of the derotator axis and machine axis. Some brief remarks are given on the well known numerical method. The experimental equipment is described and the results are discussed.

Blade Vibration on Centrifugal Compressors: Fundamental Considerations and Initial Measurements

Abstract: Blade vibration has to be considered in the design of high pressure ratio / high mass flow centrifugal compressors with increasing rotational speed values due to the reduced blade thickness. Results of a theoretical and experimental investigation concerning this problem are described. FE calculations of the stress distribution on the blade for the lower natural frequencies and various vibration tests at rest were carried out to investigate resonance and damping effects. This preparatory work was aimed at determining blade vibration behavior and acquiring fundamental experience for measurements on compressors in operation.Results of blade vibration measurements on compressors with a vaneless diffuser carried out with semiconductor strain gages and an 8-channel telemetry system are presented for constant rotational speed and for constant throttle valve position, and indicate considerable blade excitation during stall effects. Simultaneous flow measurements complete the investigation to determine the causes of blade vibration. For example, investigations were made of the extent of blade resonance excitation due to non-uniformity of the flow downstream of the impeller or due to flow disturbances caused by carrier blades for bearings in the compressor inlet and simulated by spoilers.Copyright © 1985 by ASME

Research on Ram Guide Accuracy of Forming Presses

Abstract: Growing competition in technology of industrial production will set up strong demands in forming processes concerning obtainable precision of the workpieces. In addition to the direct influence of the tool the mediate interaction of the machine/tool system gets more important. To improve the precision of parts by increasing the rigidity of machines, it is indispensable to obtain knowledge of machine characteristics. Besides practical measurements the complexity of the machine geometry leads us to apply numerical analysing techniques, especially the Finite-Element-Method (FEM). It helps the producer and the machine’s user to take profit out of favourable working parameters of the whole machine design.