523 research outputs found

    Computer aided design of twin screw compressors

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    The twin screw refrigeration compressor is required to run over a large range of working conditions. In order to design an advanced and high-efficiency compressor economically, computer aided design techniques are required. This thesis presents such techniques, which include profile generation, geometrical characteristic calculation, working process simulation, rotor cutter blade calculation and optimisation techniques. All the basic theory and equations and the derived equations are presented. Four important computer programs, ie the profile generation program, the geometrical characteristics calculation program, the working process simulation program and the cutter blade calculation program, are developed and presented in the thesis. A few other support programs are also developed by the author to display the calculated results. All the programs developed form a program library for the CAD of twin screw compressors. All the programs except the profile generation program are universal, which means that they can be used for any shape of rotor profile. For the working process simulation program, only refrigeration twin screw compressors are considered, but it is easy to extend the use of the programs to other kinds of compressor. The thermodynamic effects of the following are discussed and taken into account: internal leakage of gas through all paths; oil, injected and drained from bearings; refrigerant injection, both gaseous and liquid; the flashing of injected refrigerant and that dissolved in oil; friction effects, in both end and main casings; the use of measured performance data in the determination of essential empirical coefficients in the mathematical model. The application of the programs and the design optimisation technique are presented, which include leakage analysis, compressor geometrical parameter optimisation, rotor-to-rotor clearance distribution optimisation and cutter blade shape optimisation etc. The author believes that the research work presented in this thesis is of practical value. Further, it presents new knowledge: of the compression start blow hole and its influence; of leakage quantitative analysis; of compressor design optimisation; of the quantitative analysis of the influence of different determination procedures of inter-rotor clearances.The twin screw refrigeration compressor is required to run over a large range of working conditions. In order to design an advanced and high-efficiency compressor economically, computer aided design techniques are required. This thesis presents such techniques, which include profile generation, geometrical characteristic calculation, working process simulation, rotor cutter blade calculation and optimisation techniques. All the basic theory and equations and the derived equations are presented. Four important computer programs, ie the profile generation program, the geometrical characteristics calculation program, the working process simulation program and the cutter blade calculation program, are developed and presented in the thesis. A few other support programs are also developed by the author to display the calculated results. All the programs developed form a program library for the CAD of twin screw compressors. All the programs except the profile generation program are universal, which means that they can be used for any shape of rotor profile. For the working process simulation program, only refrigeration twin screw compressors are considered, but it is easy to extend the use of the programs to other kinds of compressor. The thermodynamic effects of the following are discussed and taken into account: internal leakage of gas through all paths; oil, injected and drained from bearings; refrigerant injection, both gaseous and liquid; the flashing of injected refrigerant and that dissolved in oil; friction effects, in both end and main casings; the use of measured performance data in the determination of essential empirical coefficients in the mathematical model. The application of the programs and the design optimisation technique are presented, which include leakage analysis, compressor geometrical parameter optimisation, rotor-to-rotor clearance distribution optimisation and cutter blade shape optimisation etc. The author believes that the research work presented in this thesis is of practical value. Further, it presents new knowledge: of the compression start blow hole and its influence; of leakage quantitative analysis; of compressor design optimisation; of the quantitative analysis of the influence of different determination procedures of inter-rotor clearances

    Atomisers for the Aerial Application of Pesticides in Tsetse (Glossina sp) and Armyworm (Spodoptera exempta) Control

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    Aerial application of insecticides is likely to remain an important component in realistically-costed vector and migratory pest control operations for the foreseeable future. The objective of this work was to identify or design improved atomisers for use in two such operations, tsetse (Glossina sp. ) and African armyworm (Spodoptera exempta) control, the former requiring an insecticide aerosol ýx'ith a VMD of 20 to 30ýim at rates upto 0.5 litres/minute and the latter a fine spray with a VMD of 80 to 120ýtm at rates around 16 litres/minute. In both cases rotary atomisation was confirmed as the most appropriate technique. Assessments were made of seven commerciall%, available atomisers and two existinc, prototypes, on the basis of existing reports and new data generated under simulated flight conditions in a wind tunnel. Droplet sizing was carried out using an optical array probe set to give a resolution of 54m over a range of 3.6 -3) 12.54m. None of the atomisers tested met the specification for tsetse-spraying, the limiting factors being rotation speed and inability to distribute low volumes of liquid across their full atomising surface. The Micronair AU4000 and AU5000 and the Micron X-I were found to be suitable for armyworm control, the Micron X-1 having the additional ability to produce spray with VMDs down to 40ýim. A review of rotary atomiser literature provided design guidelines for the design of an atomiser capable of meeting tsetse specifications. The principle effect of liquid flow 4D within the atomiser was found to be on the uniformity of fluid distribution. Premature ligament formation and formation of cross-flow vortices were identified as factors which could adversely influence fluid distribution under some conditions. Ligzan ment seperation from disks can be aided byI slender teeth, providing that these have a spaciniz similar to the natural spacing of ligaments predicted by Taylor instability theoInry . The effect of rotation speed and atomiser diameter on droIp let diameter is determined by the degree of stretching of the ligament due to its acceleration relative to the atomiser, implying that a finer spray would be achieved using a smaller rotating diameter disc than a larger diameter disc with the same peripheral speed. A series of experimental studies was carried out usinrgD higZDh speed photogZ_r_a phy in conjunction with the droplet sizinaprobe. Disturbancesh a,,i,n, g the forrn predicted for C cross-flow vortices were observed in liquid on a plain spinning disc. A sin(-)'Ieligament generator was constructed. With increasing rotation speed this rt\'taled a series of increasingly unstable ligament disintegration modes in which interaction with the surroundin4g15 air became a controlling-- factor. Complete shattering of the ligament occured at a Weber number of between 4 and 5, similar to reported values for liquid jets in a cross flo%v of cyas. Droplet sizing indicated that the specified performance for tsetse operations could be obtained from 50mm diameter atomisers with a total of around _'30000is suing points at a rotation speed of 26000 RPNI. This Zý sucy(yestecdN l,i ndcr rather than disc-based atomisers. A slit was found to be impractical as a means of distributing liquid unifom-ily at high rotation speeds but distribution was sucýe: ssfully achieved using a porous flow resistor. Prototype wind- and electi-ically-driven atornisers were constructed using rotating porous cylinders fed internally by spray bars designed with the help of finite element methods. Ligament formation was found to occur from a film of liquid on the outer surface of the cylinder, the variation in spacing with feedrate and rotation speed suggesting Taylor instability to be the controlling factor. The prototype atomisers achieved a performance suitable for tsetse control operations. This was not enhanced by the provision of discrete issuing points

    Archives of Data Science, Series A. Vol. 1,1: Special Issue: Selected Papers of the 3rd German-Polish Symposium on Data Analysis and Applications

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    The first volume of Archives of Data Science, Series A is a special issue of a selection of contributions which have been originally presented at the {\em 3rd Bilateral German-Polish Symposium on Data Analysis and Its Applications} (GPSDAA 2013). All selected papers fit into the emerging field of data science consisting of the mathematical sciences (computer science, mathematics, operations research, and statistics) and an application domain (e.g. marketing, biology, economics, engineering)

    Micro-Electro Discharge Machining: Principles, Recent Advancements and Applications

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    Micro electrical discharge machining (micro-EDM) is a thermo-electric and contactless process most suited for micro-manufacturing and high-precision machining, especially when difficult-to-cut materials, such as super alloys, composites, and electro conductive ceramics, are processed. Many industrial domains exploit this technology to fabricate highly demanding components, such as high-aspect-ratio micro holes for fuel injectors, high-precision molds, and biomedical parts.Moreover, the continuous trend towards miniaturization and high precision functional components boosted the development of control strategies and optimization methodologies specifically suited to address the challenges in micro- and nano-scale fabrication.This Special Issue showcases 12 research papers and a review article focusing on novel methodological developments on several aspects of micro electrical discharge machining: machinability studies of hard materials (TiNi shape memory alloys, Si3N4–TiN ceramic composite, ZrB2-based ceramics reinforced with SiC fibers and whiskers, tungsten-cemented carbide, Ti-6Al-4V alloy, duplex stainless steel, and cubic boron nitride), process optimization adopting different dielectrics or electrodes, characterization of mechanical performance of processed surface, process analysis, and optimization via discharge pulse-type discrimination, hybrid processes, fabrication of molds for inflatable soft microactuators, and implementation of low-cost desktop micro-EDM system

    Experimental and numerical investigations of bone drilling for the indication of bone quality during orthopaedic surgery

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    Bone drilling is an essential part of many orthopaedic surgical procedures, including those for internal fixation and for attaching prosthetics. Drilling into bone is a fundamental skill that can be both very simple, such as drilling through long bones, or very difficult, such as drilling through the vertebral pedicles where incorrectly drilled holes can result in nerve damage, vascular damage or fractured pedicles. Also large forces experienced during bone drilling may promote crack formation and can result in drill overrun, causing considerable damage to surrounding tissues. Therefore, it is important to understand the effect of bone material quality on the bone drilling forces to select favourable drilling conditions, and improve orthopaedic procedures. [Continues.

    DC and Microwave Analysis of Gallium Arsenide Field-Effect Transistor-Based Nucleic Acid Biosensors

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    Sensitive high-frequency microwave devices hold great promise for biosensor design. These devices include GaAs field effect transistors (FETs), which can serve as transducers for biochemical reactions, providing a platform for label-free biosensing. In this study, a two-dimensional numerical model of a GaAs FET-based nucleic acid biosensor is proposed and simulated. The electronic band structure, space charge density, and current-voltage relationships of the biosensor device are calculated. The intrinsic small signal parameters for the device are derived from simulated DC characteristics and used to predict AC behavior at high frequencies. The biosensor model is based on GaAs field-effect device physics, semiconductor transport equations, and a DNA charge model. Immobilization of DNA molecules onto the GaAs sensor surface results in an increase in charge density at the gate region, resulting from negatively-charged DNA molecules. In modeling this charge effect on device electrical characteristics, we take into account the pre-existing surface charge, the orientation of DNA molecules on the sensor surface, and the distance of the negative molecular charges from the sensor surface. Hybridization with complementary molecules results in a further increase in charge density, which further impacts the electrical behavior of the device. This behavior is studied through simulation of the device current transport equations. In the simulations, numerical methods are used to calculate the band structure and self-consistent solutions for the coupled Schrodinger, Poisson, and current equations. The results suggest that immobilization and hybridization of DNA biomolecules at the biosensor device can lead to measurable changes in electronic band structure and current-voltage relationships. The high-frequency response of the biosensor device shows that GaAs FET devices can be fabricated as sensitive detectors of oligonucleotide binding, facilitating the development of inexpensive semiconductor-based molecular diagnostics suitable for rapid diagnosis of various disease states

    Workshop on the Integration of Finite Element Modeling with Geometric Modeling

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    The workshop on the Integration of Finite Element Modeling with Geometric Modeling was held on 12 May 1987. It was held to discuss the geometric modeling requirements of the finite element modeling process and to better understand the technical aspects of the integration of these two areas. The 11 papers are presented except for one for which only the abstract is given

    Lunar vertical-shaft mining system

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    This report proposes a method that will allow lunar vertical-shaft mining. Lunar mining allows the exploitation of mineral resources imbedded within the surface. The proposed lunar vertical-shaft mining system is comprised of five subsystems: structure, materials handling, drilling, mining, and planning. The structure provides support for the exploration and mining equipment in the lunar environment. The materials handling subsystem moves mined material outside the structure and mining and drilling equipment inside the structure. The drilling process bores into the surface for the purpose of collecting soil samples, inserting transducer probes, or locating ore deposits. Once the ore deposits are discovered and pinpointed, mining operations bring the ore to the surface. The final subsystem is planning, which involves the construction of the mining structure

    Development of low friction coatings for alsi milling

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    Aluminium silicon (AlSi) alloys play an essential role in many industries because of their good machinability characteristics. However, their low degree of plasticity promotes adhesion at the tool edge during machine cutting, leading to a built-up edge (BUE) which reduces tool lifetimes, and the silicon content leads to tool abrasion. Currently, cemented carbide mill inserts coated with titanium diboride (TiB₂)offer the prospects of machining an array of structural metallic alloys including AlSi. However, the brittle nature of TiB₂ leaves it prone to extensive surface damage, particularly during the running-in stage of machining when tool adaptation takes place. An additional coating addressing abrasive wear and preventing BUE could limit TiB₂damage. Fabricating coatings of TiB₂ using arc evaporation remains challenging as an extensive cathode fracture occurs. Thus, the present work aims to address the drawbacks associated with TiB₂ by the deposition of a thin lubricious coating on top of the TiB₂.Secondly, the development of a new cathode, which would allow the deposition of TiB₂ by arc evaporation is investigated. A hybrid Physical Vapor Deposition system combining Filtered Cathodic Vacuum Arc (FCVA) and Magnetron Sputtering was developed forth is study. Three lubricious coating systems of Ti-MoS₂, single layer DLC and DLC-WS₂ were investigated as a top layer. Ti-MoS₂ was optimised for dry machining applications, and a Ti:MoS₂ ratio around 0.39 was found to prevent Al from sticking to the tool edges. The DLC and DLC-WS₂ coatings were designed for machining with coolant. In comparison to the performance of a TiB₂ benchmark, the monolayer DLC coating improved the machining length by ~60% and a two-layer DLC-WS₂ coating decreased wear rate by ~75%, having a measured coefficient of friction of 0.05. The development of TiB₂ cathodes for FCVA required a modification of the chemical composition to improve it’s sinterability and prevent cathode fracture during arc operation. A TiB₂-TiSi₂ (5 wt%)cathode ensured the best balance between arc stability and cathode utilisation while TiB₂-C(1 wt%)has provided exceptional arc stability, although the cathode utilisation was less due to the constant generation of cathode flakes
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