The relative merits of frequency domain (FD) electromagnetic transient analysis against the time domain approach are discussed. When used on highly resonant systems, conventional FD methods which rely on the FFT, can yield erroneous results. This is shown to be due to inadequate sampling resolution, which is determined empirically. The collection of analytical tools for FD analysis is reviewed with emphasis on the control of errors. From these principles a systematic and objective methodology to extract a system's transient response from FD data is proposed. The methodology is extended with a further proposal using dynamic adaptive sampling to obtain an accurate frequency response spectrum efficiently. The proposal is based on the adaptive integration principle but uses a relative convergence limit based on the most recently computed value of integral. The frequency samples obtained are non-uniformly spaced and a modified inverse DFT formula is developed. The sampling strategy results in a very substantial reduction in computational demand over the conventional FFT technique. Accurate transient results can be obtained with typically less than 10% of the samples of the conventional approach. The sampling strategy also enables highly resonant structures to be analysed in the frequency domain. To sample an extremely resonant spectrum accurately, resolution in the order of 1 in 10<SUP>6</SUP> is required. This level of computational demand is beyond the practical limit of the conventional FFT methods. The methodology has been used to model transients on resonant wires and transmission lines of various configurations in both antenna and scattering modes. A particular case studied uses an equivalent antenna model of a human body which is standing on a perfect ground and exposed to low frequency radiations. The resulting currents flowing at the feet into the ground, which is adopted as a measure for exposure level, are predicted accurately. The methodology's relative performance in terms of efficiency, accuracy, utility and ease of use against a thin wire time domain integral equation formulation is discussed in some detail.

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.

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