Showing papers by "Cranfield University published in 1977"

The determination of stress and strain concentrations at an ellipsoidal inclusion in an anisotropic material

Abstract: The aim of this paper is to produce elementary yet explicit formulae for the evaluation of stress and strain concentration factors at an ellipsoidal inclusion, for arbitrary anisotropy, under uniform loading at infinity. The results are such that the required formulae do not involve the solution of any boundary value prolems or the knowledge of any Green's functions. An important feature of the analysis is that the solution of the interface problem is intimately related to the solution of the inclusion problem.

Ignition and flame quenching in flowing gaseous mixtures

Abstract: The influence of pressure, velocity, turbulence intensity, turbulence scale and mixture composition on minimum ignition energy and quenching distance in flowing gaseous mixtures is examined experimentally for methane and propane fuels. In some experiments, the nitrogen in the air is replaced by various inert gases such as carbon dioxide, helium or argon, while in others the nitrogen is either partly or totally replaced by oxygen. The tests are conducted at room temperature in a 9 cm square working section through which the combustible mixture is arranged to flow at various levels of pressure, turbulence and velocity. At each test condition, the spark energy required to ignite the flowing mixture is measured for several gap widths in order to establish the optimum gap width corresponding to minimum ignition energy. From analysis of the relevant combustion and heat transfer processes involved, expressions for the prediction of quenching distance in flowing mixtures are derived. Support for the model employed in this analysis is demonstrated by a close level of agreement between theoretical predictions of quenching distance and corresponding values calculated from the experimental data on minimum ignition energy obtained over a wide range of mixture compositions and flow conditions.

Vortex Excited Oscillations of Yawed Circular Cylinders

Abstract: Yawed cylinders are cylinders inclined forward or backwards in the plane of the flowing fluid. They are used in many practical situations such as braced frame members and raked marine piles. This paper describes an examination of three aspects of the yawed cylinder-fluid interactions over a range of yaw angles ±45° from the vertical for the Reynolds number range 2,000 < Re < 20,000. viz. 1. Establishment of the stability criteria of vortex-excited oscillations. 2. Measurement of ‘steady’ drag forces and equivalent drag coefficients. 3. Visualization of the local flow over stationary and oscillating cylinder. After a brief review of previous experimental and theoretical work, the results of the three items listed above are presented and discussed. Vortex-excited oscillations were recorded in the in-line and crossflow directions throughout the range of yaw angles and the results of items 2, 3 were used to justify the forms of the stability criteria proposed for these oscillations.

Goal Programming and Agricultural Planning

Abstract: Goal Programming is similar in structure to linear programming, but offers a more flexible approach to planning problems by allowing a number of goals which are not necessarily compatible to be taken into account, simultaneously. The use of linear programming in farm planning is reviewed briefly. Consideration is given to published evidence of the goals of farmers, and ways in which these goals can be represented. A goal programming model of a 600 acre mixed farm is described and evaluated. Advantages and shortcomings of goal programming in relation to linear programming are considered. It is found that goal programming can be used as a means of generating a range of possible solutions to the planning problem.

Tracing insecticide spray droplets by sizes on natural surfaces. The state of the art and its value

Abstract: Recent trends in integrated chemical and biological pest control call for further refinement of the effectiveness of existing chemical pesticides by more efficient spray application. One aspect of improving spray efficiency is by the use of the correct range of droplet sizes. In this way the volume of spray, and the amount of active ingredient used, particularly in ultra-low volume techniques, can be further optimised, and when combined with correct application time, gives maximum biological efficiency with minimum disturbance of the environment. This necessitates a study of the size spectrum of droplets deposited on rigorously defined biological targets which in turn calls for an investigation of suitable tracer methodology. Additional details of the previously published fluorescent particle method are discussed, and its reappraisal shows that it is a unique method capable of estimating droplet sizes on all biological surfaces, especially insect larvae. The reversibly soluble fluorescent pigment method based on the relative balance between soluble and insoluble state of the pigment proves highly successful in imprinting fluorescent droplets on broad leaves, particularly on cotton.

Manufacture of Toughened Plastics

Abstract: There are several different routes to toughened plastics. The most important processes are bulk or bulk-suspension polymerisation, emulsion polymerisation and the Ziegler-Natta process. Significant amounts of toughened plastics are also made by melt blending. Each process has its own technical and economic advantages, which are often specific to the type of material being produced. The bulk and bulk-suspension processes are especially suitable for HIPS, whilst emulsion polymerisation is preferred for ABS, MBS and related products. Ziegler-Natta catalysis has been adapted for the manufacture of toughened polypropylene, and melt blending is used extensively to make toughened PVC. Each of these processes is analysed in this chapter, with particular reference to the relationship between method of manufacture and structure of product.

A Survey of Representations of Spatial Rotation about a Fixed Point

Abstract: This paper presents a comparison of five methods of representing a general spatial rigid-body rotation about a fixed point. The following representations are considered: the real orthogonal 3 × 3 matrix; the special unitary 2 × 2 matrix; the Pauli spin matrices; the unit quaternion; and the special unitary 3 × 3 matrix together with spherical harmonics of the first degree. Although the first of these representations is certainly the most commonly used, particularly in engineering and technological applications, it is shown that it is not the best or most efficient representation. The conclusion reached is that the most concise and efficient representation in practice is the unit quaternion, although the special unitary 2 × 2 matrices follow closely behind.

Dealing with Dependence in Risk Simulations

Abstract: Difficulties arise in choosing a suitable sampling scheme for risk simulations when variables are not judged to be independent of each other. This paper shows that, by considering the unconditional distributions of the variables as transformations of the normal distribution, a model can be constructed to overcome these difficulties. This model takes account of the extent of the dependence between the variables while at the same time keeping to a minimum the total number of individual probability assessments which must be made by management.

Chemical amplification at the wave head of a finite amplitude gasdynamic disturbance

Abstract: Consider a background state which consists of a spatially uniform chemically reactive mixture in a general state of disequilibrium. The analytical method of characteristics is used to show that a plane finite amplitude disturbance propagates through this system at the frozen sound speed and, if the degree of disequilibrium is sufficient, is amplified by the chemical reaction. Some comments are made about the time to shock-wave formation and its relation to the homogeneous explosion ignition time, and also about expansion waves, which are found to have a tendency towards fixed-strength ‘quenching waves’, their strength being proportional to the extent of the ambient disequilibrium.

Flame quenching in turbulent flowing gaseous mixtures

Abstract: A series of tests has been carried out on flowing combustible mixtures in order to examine the influence of various flow parameters, notably pressure, velocity and turbulence, on quenching distance. A wide range of mixture compositions was employed. In some experiments the nitrogen in the air was partially or totally replaced with oxygen, while in others the nitrogen was replaced by various inert gases such as argon, helium and carbon dioxide. The purpose of these variations in chemical composition was to try and distinguish between the relative importance of thermal and diffusional mechanisms in the quenching of hydrocarbon flames. The fuels employed were methane and propane. The tests were conducted in a 9 cm. square working section through which the combustible mixture flowed at various levels of pressure and turbulence intensity and at velocities up to 30 m/sec. At each test condition the spark energy required to ignite the flowing mixture was measured for several different values of electrode gap width. By plotting a graph of ignition energy against gap width, the quenching distance was obtained as the gap width corresponding to minimum ignition energy. The results obtained generally confirmed the importance of thermal diffusion processes, even at the highest flow velocities. Quenching distance was found to increase with increases, in turbulence intensity and to diminish with increases in pressure and laminar flame speed. No appreciable effect of turbulence scale or flow velocity was observed. Analysis of the experimental data showed that for turbulent, flowing mixtures the quenching distance is obtained as the product of the laminar value and a factor containing the term ( u′/S L ) 0.5 which takes into account the additional quenching due to turbulent diffusion.

Response Of Articulated Towers To Waves And Current

Abstract: There has been an increasing use of mobile offshore systems in the North Sea for storing and loading oil into attendant tankers. A typical type of mobile loading and storage system is the articulated buoyant loading tower. This paper analyzes the motion of a single articulated tower without a tanker under the combined action of forces resulting from current and a train of regular linear waves. The dynamic response of the tower is obtained by formulating the equations of motion by Lagrange's method. The wave forces are determined using a modified form of Morison's equation that accounts for the relative motion of the water particles with respect to the structure.

Mechanisms of Rubber Toughening

Abstract: How do small quantities of rubber produce such dramatic increases in the fracture resistance of brittle plastics? What is the mechanism of rubber toughening? The answer to these fundamental questions is far from obvious. The first satisfactory theory of toughening was advanced in 1964, almost 40 years after Ostromislensky’s original discovery, and 15 years after the commercial introduction of HIPS. Since 1964, the subject has developed to the stage at which quantitative theories can be constructed, but there are still many outstanding questions concerning the relationship between structure and fracture resistance. This chapter presents some of the qualitative and quantitative theories of rubber toughening, and discusses the problems that remain unresolved.

Thermal Resistances of Stacks of Thin Layers under Compression

Abstract: Stacks, each comprising a number of thin, ‘flat’ layers of tin-coated steel, were compressed in a direction normal to the individual layers under loadings of up to 8 times 106Nm-2. Two distinct modes of deformation occurred: a layer-flattening region at low loads (P/M < 10-3), and a surface-waviness deformation region under higher loading pressures. The thermal resistance per unit area per unit length of each stack (in a vacuum of better than 7 times 10-2Nm-2) was inversely proportional to the compression per layer for freshly-assembled stacks throughout the loading region corresponding to macroscopic conformity. Hystereses in the thermal resistance and compression characteristics were observed during the initial loading/unloading cycles. A dimensionless correlation relating conductance to applied loading is proposed for stacks of bedded-down thin layers.

Efficiency in Pesticide Application

Abstract: Publisher Summary This chapter presents the efficiency in pesticide application. It is the greatest when the biggest fraction of what is applied is collected by a specified biological target in a specified form, namely, the target dose. The nature of the pest and the nature of the crop or animal to be protected dictate the biological target. The first parameter circumscribing efficiency in pesticide application is the scale of the population of biological targets in space and in time. Efficiency in pesticide application can be achieved only by a more rigorous definition of the biological target that is selected in consideration of knowledge of the pest's habit and the route of entry of the chosen pesticide. The nature of the biological target determines the droplet sizes that must be used to ensure target specific application. Atomizer equipment that maximizes the number of droplets of optimum size and knowledge of the mechanisms of transfer of such droplets to their destination can then be employed to improve efficiency in application.

Modelling of Air Movements in Rooms

Abstract: Dimensionless parameters pertinent to air flows in rooms are examined. Consideration of the limitations of modelling techniques leads to suggestions as to how significant results for full-size systems can be obtained from models of less than one-tenth full scale.

Properties of Liquid Photoresists used in the Photoetching of Stainless Steel

Abstract: In the use of liquid photoresists for photoetching, measurement of coating thickness is important for process control. Relative average thickness can be determined from weight/unit areas, but value...