bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Tuned and Damped Gyrostatic Vibration Absorber
Authors: Arnold R. N. 
Published: October 2007

The vibration absorber described in this paper consists of a gyrostat suspended symmetrically about an axis perpendicular to that of the torsional vibration which it is desired to suppress. The gyrostat is fitted with springs and a viscous damping mechanism which allow limited vibration about its axis. This device is a modification of that employed by Schlick (1904)†, in his attempt to stabilize the rolling of ships at sea. The new arrangement, however, is more efficient, is not restricted to very low frequencies, and is, in general, capable of application to vibration superposed on a mean velocity. A theoretical study is made of the response of such an absorber to one- and two-mass vibratory systems under both forced and self-induced vibration, and design methods are derived by which the essential dimensions for any given application may be readily determined. Experimental investigations with a gyrostatic absorber applied to a one-mass system under forced vibration are recorded, and the results compared with theoretical prediction. The design of a full-scale absorber built to suppress vibration of the table of a heavy planing machine is also given, together with the results obtained with the apparatus on trial.
Centrifugal Pumps—An Alternative Theory
Authors: Anderson H. H. 
Published: October 2007

The hydraulic design of centrifugal pumps has in the past been almost entirely empirical, since there is a large discrepancy between conventional theory and actual tests. Several papers† have already considered this problem of providing a reconciliation of theory and practice. The author suggests that a possible solution may be obtained by considering the total head as being made up of ( a) head due to impact between impeller blade and water; and ( b) head due to centrifugal force. It is assumed that the flow conditions may be such that the impeller blades shear the water without accelerating it. This is suggested as representing the maximum quantity-zero head state where the increase in velocity from branch to casing throat is obtained at the expense of suction pressure. Neglecting losses there will be no torque on the shaft and therefore no head generated. At less quantities the velocity differences between blade and water will cause impact and therefore generate a head. It is also assumed that at less quantities the “pressure” existing between blade and water will transmit to the water the additional energy of the centrifugal head. This latter assumption is supported in some measure by the fact that in practice the head is affected by variation of the ratio of impeller diameter to eye diameter. Head and quantity values are calculated for zero head quantity QF, maximum efficiency quantity Qf, half maximum efficiency quantity Qf/2, and zero quantity. These results compare very reasonably with actual test curves.
Discharge Tests on an Archimedean Screw
Authors: Donaldson A. C. 
Published: October 2007

The paper records a series of tests carried out on an Archimedean Screw in use in a chemical plant. The main object of the tests was to increase, if possible, the overall throughput of the screw and to decide at what speed the screw should be run so as to give a maximum discharge under existing working conditions, thus increasing the production of the plant. It was found that by a slight modification to the existing screw a much more uniform throughput could be obtained and the discharge increased considerably by increasing the speed. The paper also includes some notes and formulae which, it is hoped, will be helpful in determining suitable proportions for similar screws.
The Flow of Metals under Various Stress Conditions
Authors: Nadai A. L. 
Published: October 2007

The phenomena associated with the permanent deformations of the metals have attracted the attention of investigators during the last 100 to 150 years, and have inspired mathematically-minded observers in their endeavour to formulate mechanical rules or laws by which ductile metals flow under prescribed conditions. While the theory of elasticity is mostly concerned with very small strains, a theoretical treatment of the permanent or plastic deformations of metals must also frequently take account of strains of an order of ten to a hundred—and even more—times larger than the strains that can be sustained by them elastically. The engineering means for dealing with finite strains of this order will be reviewed in the lecture, and certain new types of strains that seem to offer possibilities for expressing the stress-strain relations required for developing the theories of the flow of metals under various conditions will be introduced. Several ideal substances, representing behaviour of metals or of other materials under different conditions, may be considered. For a perfectly plastic substance a special solution is quoted for a plane problem and for plastic shells with rotational symmetry. A case of the creep of metals at eleyated temperatures will be mentioned. Experiments made during the war years on the propagation of the plastic zone along mild-steel bars tested under tension, on the flow of copper and of medium carbon steel under combined stresses in the strain hardening range (including observations regarding the ensuing types of fractures which were observed), and experiments on the effect of the speed of deformation in these metals under normal and at elevated temperatures over a wide range of the rates of strain, will be reported.
The Development of Gas Turbine Power Plants for Traction Purposes in Germany
Authors: Bright R. H. 
Published: October 2007

The simpler and cheaper construction, and the prospect of using fuel of low quality and of considerably increasing the power-to-weight and power-to-volume ratios of the power unit, led the Germans towards the end of the war to investigate the possibility of using gas turbines for land traction units. It was expected by them that they would be able to employ this new type of power plant for a variety of ground traction purposes, but, owing to their total national mobilization, the most important immediate applications they had in mind were for war purposes. It is considered that the information obtained and given in this paper may prove a useful background when considering the possibilities of future development of gas turbine power plants. The various arrangements possible, using either one single turbine, or separate turbines to drive the compressor and provide the output of useful work, were considered by the Germans and a résumé is therefore made of the characteristics of each. In addition, the salient features of the components—compressor, turbines, and combustion chamber—and their development for the purposes which the Germans had in mind, are given.
Radiology of Joints in Welded Piping for Power Plants
Authors: Thomas E. 
Published: October 2007

The type of equipment needed for the examination by radiology of joints in welded piping may vary considerably, especially when the work is carried out both in the shops and on the installation site. Portable X-ray equipment should be robust and improvements in present equipment could be made. The portability of gamma-ray apparatus is a great advantage, but it has disadvantages in its inferior absorption factor. The examination of large and of small pipes calls for different procedure as do also the methods of assessing the radiographs. The determination of the size of fine cracks is largely dependent upon the film-screen combination and there is a need for high-speed fine-grain film. Care should be taken on length of exposure and good facilities should be available for processing work. The location of large faults can be accurately obtained by a technique of double exposure. Of the various types of penetrameters, the “postage stamp” type is considered to be the most suitable for the examination of the welds of pipes.
The Norwich Heat Pump
Authors: Sumner J. A. 
Published: October 2007

The paper provides the history and constructional details and working results of what is believed to be the first large heat pump used for building heating in Great Britain. This machine was constructed and installed as an experimental machine for heating a large block of municipal buildings in Norwich. A brief explanation indicating the principle upon which the heat pump works is given. Reference is also made to the differences between the reversed heat engine when working as a refrigerator and when working as a heat pump. In the latter case there is a deliberate increase in the final temperature T1, from approximately 85 deg. F. to temperatures which may be of the order of 150–200 deg. F. The unsuitability of the term “coefficient of performance”—normally used as a criterion of refrigerator performance—when used as a coefficient relating to the heat pump is pointed out; and the use of a new, alternative term is suggested. The results are shown of operating the Norwich Heat Pump for two winter heating seasons. When using an unsuitable compressor the heat delivered to the building was found to be 3·45 times greater than the equivalent heat (electric) energy required to operate the machine, averaged over the 1945–6 winter heating season. With a more efficient compressor, installed later in 1946, a still better performance is anticipated. The actual costs of heating the building, with coal-fired boilers and a heat pump respectively, are shown in the form of a table. Conclusions indicated are that the heat pump can show a financial saving, as compared with the use of coal-fired boilers, and that it is practicable to use the heat pump in Great Britain for building heating throughout normal English winters.
The Prospects of the Steam Cycle in the Central Power Station
Authors: Martin G. H. 
Published: October 2007

The advent of the gas turbine and its effect on the position of the steam turbine for the central power station is briefly discussed. In the opinion of the author the steam turbine will hold the field for large power generation for many years to come, and there is no immediate prospect of any other form of prime mover becoming a serious competitor for the generation of electricity in the central power station. Data are given indicating the gain in thermal efficiency that can be expected from increased steam conditions up to 2,000 lb. per sq. in., and 1,000 deg. F. with and without reheating. The advantages of reheating as a means of obtaining higher efficiency are strongly emphasized. Methods of operation to enable quick starting are discussed. Some of the principal constructional problems created by high steam conditions are briefly discussed and methods of overcoming the difficulties are indicated. The essence of the paper is to examine, in as simple a manner as possible, the means available for improving the efficiency of the central power station; and in an effort to achieve this, detailed methods of calculation are not included, as it is considered they would detract from a clear appreciation of the results. The minimum of assumptions have been made, so that the curves represent a true picture of the actual gains that could be obtained in practice.
The Gas Turbine as Applied to Marine Propulsion
Authors: Crowe T. A. 
Published: October 2007

The paper commences with an historical survey of gas-turbine development, and deals briefly with the constant-volume and constant-pressure principles. Under the latter are included the open, closed, and semi-closed cycles. Notes are added on air heaters and heat exchangers, materials required for gas-turbine components, and systems of control. The latter portion of the paper covers the application to marine purposes, and describes some current marine-turbine installations. In view of the small number of the moving parts, gas turbines should eventually prove as reliable as older forms of propulsion machinery. Life should not be less than 100,000 hours at full load and temperature, but, as creep tests of this duration are impracticable, the designer must at present base his calculation on rather meagre data. Up-keep costs should, once the initial difficulties have been overcome, compare favourably with those of other forms. A gas turbine of 5,000-10,000 s.h.p. per shaft can be constructed to give a fuel consumption of 0·44-0·46 lb. per s.h.p.-hr. (giving a thermal efficiency of more than 30 per cent on the gross calorific value of the fuel), and the figure should improve to 0·38 lb. (comparable with the Diesel consumption) when metallurgical developments allow the initial air temperature to be raised by 150 deg. F. It should be able to burn the cheaper grades of boiler oil. The gas turbine is lighter in weight and occupies less space than the corresponding steam-turbine or Diesel installation. The author concludes that it will earn a fundamental place in marine propulsion during the course of the next few years.
Modern Applications of Photo-Elasticity
Authors: Heywood R. B. 
Published: October 2007

It has long been known that polarized light may be employed to analyse the stresses occurring in engineering parts. Recent modifications have simplified the apparatus required, so giving a wider scope to the application of photo-elasticity to engineering. The method of preparing transparent models for stress analysis is discussed, and the significance of the photo-elastic fringes is explained. Only the boundary stresses in the model are considered, and their importance is demonstrated by means of examples, such as the modification of the design of aero-engine parts so that a substantial increase in strength is attained. The procedure for evolving the best shape of fillet for a particular set of conditions is given. The three-dimensional “freezing” technique is described, a technique which enables the boundary stresses in parts of complicated shape to be determined, and has the further advantage that an assessment of the elastic distortions may be made. Examples of the application of photo-elasticity include a connecting rod, crankshaft, poppet valve, and gear wheel.
A Theoretical Discussion of Pitting Failures in Gears
Authors: Beeching R. , Nicholls W. 
Published: October 2007

This paper is primarily concerned with the theoretical consideration of the stresses that cause surface failure of gear teeth. Methods of calculating the permissible line load between contacting cylindrical surfaces for static or cyclic conditions are considered, and the probable effects of friction are discussed qualitatively. Maximum permissible case thicknesses are suggested for case-hardened steel components of varying core strength when subjected to contact stresses of the type encountered in gears, rollers, and cams. In the Appendix is given an account of the derivation (from Hertz's general solution) of expressions for the principal stresses at any point in the neighbourhood of the zone of contact between parallel cylinders. These expressions, which lend themselves to ready computation, reduce to the same form as those derived by Thomas and Hoersch for stresses in the plane of symmetry, but they are more widely applicable.
Thrusts and Stresses in Two-Dimensional Pipe Expansion Bends
Authors: Finniecome J. R. 
Published: October 2007

The primary aim of the paper is to present the fundamental theory on the thrusts and stresses of two-dimensional pipe expansion bends incorporating the Karman flexibility factor. The application of this theory to a series of typical expansion bends is demonstrated for three well-established methods of fixing the ends: fixed at one end and free at the other, fixed at one end and guided at the other, and fixed at both ends. A series of tables summarizes the formulae and data on the expansions, thrusts, and bending stresses for 90 deg. bends, 180 deg. U-bends, and 45 deg. lyre expansion-bends for the three methods of fixing the ends indicated above. The importance of the methods of fixing the ends of expansion bends on the thrusts and bending stresses for four typical cases is indicated in a table that gives the ratio of the resultant thrusts and maximum bending stresses due to expansion for bends fixed at one end and guided at the other end, and for those fixed at both ends, in relation to the corresponding amounts for bends fixed at one end and free at the other. The detailed analysis for typical cases shows distinctly that the thrusts and bending stresses are greatly increased for a pipe bend fixed at both ends or fixed at one end and guided at the other, as compared with those fixed at one end and free at the other.
Basic Principles of Automatic Control Systems
Authors: Porter A. 
Published: October 2007

The importance of automatic control systems in a wide field of industrial and military applications has been accentuated during the past few years. The object of this paper is to review some of the basic principles of the subject, with special reference to automatic regulating systems. A major difficulty at present is the lack of standardization of the terminology associated with automatic control systems; in this paper an attempt has been made to co-ordinate, albeit on a small scale, generally recognized industrial usage with the recommendations of the Ministry of Supply Servo Nomenclature Panel. It is convenient, for example, to consider an automatic regulator system as a special type of servo-system. In order to present the nomenclature in a manner which may be readily assimilated, the operation of a simple automatic speed regulator is described in detail. The performance of an automatic control system is usually assessed by ( a) the speed of response of the system subsequent to a sudden disturbance, ( b) the nature of the response, and ( c) the magnitude of the steady-state errors. In the case of complex control systems, such as fire-control systems, it is sometimes desirable to study, in addition, the frequency response characteristics of each main element, and to determine the overall performance of the system by the application of vector methods. The latter have been used widely in the solution of acoustical problems, and in the design of electronic feed-back amplifiers, and their adaptation to the analogous problems of servo-system design has considerably facilitated progress. The stabilization of automatic control systems, and the elimination of steady-state errors can often be achieved by the incorporation of subsidiary feed-back loops. For example, a comparison of the basic operation of a typical position control servo-system with that of a typical automatic regulator shows that certain lags in the operation of the latter can be short-circuited by introducing “disturbance feed-back”. This approach to the problem of improving the performance of these systems does not appear to have been treated extensively in the literature. Its value is demonstrated in the paper by comparing the responses of certain idealized automatic thermal regulating systems, some incorporating “disturbance feed-back”, and others with straightforward controllers.
An Electrical Potential Analyser
Authors: Redshaw S. C. 
Published: October 2007

The electrical potential analyser provides, in effect, an electrical analogy to the solution of Poisson's and Laplace's equations when expressed in finite difference form. The principal object in designing the instrument was to provide an experimental alternative to the “relaxation” technique which, although invaluable in the solution of many problems, is often very lengthy and tedious. The potential analyser consists essentially of a square mesh, the nodal points of which are interconnected by low value wire resistances, and a base. Corresponding nodes on the mesh and base are connected through high value resistances. A current is applied in such a manner that an electrical potential is provided, as required, to points on the mesh and the mesh boundary; the base being either used or discarded according to the nature of the problem. Readings of potential at each mesh node are recorded by a suitable galvanometer circuit. An analyser having a square mesh, such that the mesh separation is 1/12 the side length, has been constructed and encouraging results have been obtained with its use. The instrument is easily operated and results are rapidly obtained. The use of the analyser is not limited to the solution of Poisson's and Laplace's equations. By a suitable interchange of network resistances, other equations which can be expressed in finite difference form may be solved and solutions to problems involving irregular boundaries present no undue difficulty.
Heat Flow in the Gas Turbine
Authors: Smith A. G. 
Published: October 2007

In this lecture experimental data are presented on turbine-blade heat transfer, which is an important factor in the design of high-temperature turbines. Blade stagger has a considerable effect on blade Nusselt number and on the rate of variation of Nusselt number with Reynolds number. For nozzleblades, theoretical and experimental values of the Nusselt number agree fairly well. A method is proposed for the approximate estimation of Nusselt number by Keynolds analogy. The experimental data are used in the calculation of heat flow in blades cooled at the root, and in internally air-cooled blades. Other methods of cooling have been proposed, including partial admission of cold air or liquid through the nozzle ring; the theoretically advantageous “sweat” cooling by exuding coolant air through a porous skin, or the injection of coolant air through slits; root cooling might include modifications, such as effective increase of blade conductivity by tubes of liquid embedded in the blade or reduction, by an insulating layer, of the amount of heat conducted to the blades; internal liquid cooling by forced or convective circulation is a possible alternative to internal air-cooling. Some of these methods have been successfully used-for example, internal air-cooling of hollow blades in German jet engines; internal liquid-cooling in an experimental German turbine; and a certain degree of “root” cooling in British aircraft turbines. Theoretical analysis of the problem of turbine cooling has been rendered difficult, in the past, by absence of data on blade heat-transfer coefficients. For root-cooled blades of heat-resisting alloy the cooled region is small, but it would be satisfactorily large for nozzle blades of high-conductivity material. Internal air-cooling needs only small quantities of coolant, provided a high internal blade conductance is achieved by subdividing the internal flow passage. The effectiveness of root-cooling diminishes with increase of scale; on the other hand, the relative cooling air quantity necessary to cool a blade internally diminishes with increase of scale. The heat exchanger is a bulky and expensive component of most “plant” gas-turbine systems, and with the aim of size reduction “regenerative” type exchangers have been investigated for some time as an alternative to the bulky recuperative type. The lecture deals with the advantage in bulk of the regenerator, and gives some relevant data on heat-transfer in laminar flow
Large-Scale Torsional Fatigue Testing of Marine Shafting
Authors: Dorey S. F. 
Published: October 2007

The paper describes the design and construction of a new type of torsional fatigue testing machine of the resonance type capable of generating a reversed harmonic torque of up to ±3 × 106 lb.-in. in a stationary test shaft, at a frequency of approximately 2,500 vibrations per minute. Reference is made to a specially developed electronic method of speed control capable of regulating the nominal stress in the specimen to within one per cent. The paper includes the results of a number of fatigue tests carried out on 9 3/4-inch diameter mild steel shafts, and also on “Meehanite” cast-iron specimens of 6 inches diameter, and concludes with some remarks on scale effect, based on results from 1/2-inch diameter specimens subjected to reversed torsional fatigue tests carried out on a combined-stress fatigue testing machine at the National Physical Laboratory.