Brunel University Research Archive

    Analytical grid generation and numerical assessment of tip leakage flows in sliding vane rotary machines

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    © 2021 The Author(s). The research presents a new analytical grid generation methodology for computational fluid dynamics studies in positive displacement sliding vane rotary machines based on the user defined nodal displacement approach. This method is more inclusive than state of the art ones since it enables the investigation of a broader range of design configurations, such as single, double and multiple-acting vane machines with non-circular housing, slanted blade and asymmetric blade tip profiles. Node number and radial divisions of blade tip are the parameters that affect most the mesh quality. The method was validated against indicated pressure measurements on a rotary vane expander resulting in a confidence interval within 4.31%. The benchmark analysis showed that the proposed method is as accurate as the manual ANSYS ICEM one but more than 1500 times faster (111s instead of 48h to generate 360 grids). The paper further proposes a novel method to track the leakage flows at the blade tip gaps of vane machines through a post-processing routine in ANSYS CFD-Post based on rotating monitoring planes. The leakage assessment on the vane expander case study showed that a 10 μm gap between blade tip and the 76 mm stator led to a 0.06 unit increase of the expander filling factor.Research Councils UK (RCUK) Centre for Sustainable Energy Use in Food Chains (Grant No. EP/K011820/1); National Science Foundation of China (NSFC, Grant No. 21978227) and the China Scholarship Council (CSC, Grant No. 201906280153)

    Nonlinear multi-scale homogenization with different structural models at different scales

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    We present an extension of the computational homogenization theory to cases where different structural models are used at different scales and no energy potential can be defined at the small scale. We observe that volumetric averaging, which is not applicable in such cases unless similarities exist in the macro-scale and micro-scale models, is not a necessary prerequisite to carry out computational homogenization. At each material point of the macro-model, we replace the conventional representative volume element with a representative domain element (RDE). To link the large-scale and small-scale problems, we then introduce a linear operator, mapping the smooth part of the small-scale displacement field of each RDE to the large-scale strain field and a trace operator to impose boundary conditions in the RDE. The latter is defined on the basis of engineering judgement, analogously to the conventional theory. A generalized Hill’s condition, rather than being invoked, is derived from duality principles and is used to recover the stress measures at the large scale. For the implementation in a nonlinear finite-element analysis, ‘control nodes’ and constraint equationsare used. The effectiveness of the procedure is demonstrated for three beam-to-truss example problems, for which multi-scale convergence is numerically analysed.Lloyd’s Register EME

    Delivering knowledge in the field: A telecommunications service provision and maintenance case

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    This paper proposes a novel approach to providing knowledge management services in a business process wherein field engineers are the main process actors, providing and maintaining telecommunications services. Cooperating multi-agents play a central role for the provision of knowledge management services by integrating heterogeneous systems to collect related knowledge for the execution of mobile tasks. The proposed system is expected to increase both the performance of the mobile workforce and customer satisfaction by supporting and encouraging knowledge sharing

    Non-fragile state estimation for discrete Markovian jumping neural networks

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    In this paper, the non-fragile state estimation problem is investigated for a class of discrete-time neural networks subject to Markovian jumping parameters and time delays. In terms of a Markov chain, the mode switching phenomenon at different times is considered in both the parameters and the discrete delays of the neural networks. To account for the possible gain variations occurring in the implementation, the gain of the estimator is assumed to be perturbed by multiplicative norm-bounded uncertainties. We aim to design a non-fragile state estimator such that, in the presence of all admissible gain variations, the estimation error converges to zero exponentially. By adopting the Lyapunov–Krasovskii functional and the stochastic analysis theory, sufficient conditions are established to ensure the existence of the desired state estimator that guarantees the stability of the overall estimation error dynamics. The explicit expression of such estimators is parameterized by solving a convex optimization problem via the semi-definite programming method. A numerical simulation example is provided to verify the usefulness of the proposed methods

    Modified finite-difference approximations near the singularitiy in the problem of motz

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    A simple, modified finite-difference method is described for solving Laplace's equation with boundary singularities of the infinite derivative type. Modified approximations for the derivatives of the Laplacian equation are employed near the singularity. These are developed from a truncated series form of the local analytical solution. The method is applied to the problem of Motz. The numerical results compare favourably with those obtained by other techniques

    “Sticking jewels in your life”: Exploring women’s strategies for negotiating an acceptable quality of life with multiple sclerosis

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    This study explored women’s strategies for living with multiple sclerosis (MS). Twenty-seven women were interviewed, most of whom had lived with MS for more than five years. Analysis of the semi-structured interviews followed the interpretative phenomenological approach. The women portrayed living with MS as an ongoing process of negotiation, and described gaining quality of life through looking after their health; maintaining a familiar self-image, particularly through meaningful occupations, and adapting pre-illness skills and interests to their changing levels of physical functioning; actively valuing positive life experiences, including finding benefits in adversity; clarifying values, priorities and philosophy of life; and maintaining mutual, caring relationships. Some regarded MS as presenting opportunities for personal growth. Without minimizing the very substantial difficulties that MS presents, the findings suggest that well-being derives from both managing the illness and also embracing life’s wider experiences, including change and growth. Implications for rehabilitation and counseling professionals are considered

    Three efficient numerical models to analyse the step problem in shallow water

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    In this paper, the problem of acoustic wave propagation in a waveguide of infinite extent is modelled, taking into account constant depth in each section of the sea. Efficient numerical strategies in the frequency domain are addressed to investigate two-dimensional acoustic wave propagation in a shallow water configuration, considering a step in the rigid bottom and a flat free surface. The time domain responses are obtained by means of an inverse Fast Fourier Transform (FFT) of results computed in the frequency domain. The numerical approaches used here are based on the Boundary Element Method (BEM) and the Method of Fundamental Solutions (MFS). In the numerical models only the inclined or vertical interface between the sub-regions of different depth are discretized, as Green׳s functions that take into account the presence of free and rigid surfaces are used. These Green׳s functions are obtained either by eigenfunction expansion or by Ewald׳s method. A detailed discussion on the performance of these formulations is carried out, with the aim of finding an efficient numerical formulation to solve the step problem in shallow water

    Multimedia content delivery for emerging satellite networks

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    Multimedia content delivery over satellite systems is considered as a promising service in the emerging networks. The aim of this work is to design a novel radio resource management (RRM) algorithm for efficiently managing multicast multimedia content transmission over satellite network. The proposed approach performs the spectrum management on a per-group basis, by splitting multicast terminals into different subgroups according to the experienced channel qualities. We demonstrate that subgrouping policy defined by the authors as multicast subgrouping-maximum satisfaction index (MS-MSI), is based on a new metric (i.e., MSI), which overcomes the weakness of the previous techniques proposed in literature and provides the best trade-off between user throughput and fairness. As a further result, we demonstrate that MS-MSI is robust to the long propagation delay of satellite links. An extensive simulation campaign has been conducted by considering several satellite environments

    On the comparison of two numerical methods for conformal mapping

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    Let G be a simply-connected domain in the t—plane (t = x + iy), bounded by the three straight lines x = 0, y = 0, x =1 and a Jordan arc with cartesian equation y = τ (X). Also, let g be the function which maps conformally a rectangle R onto G, so that the four corners of R are mapped onto those of G. In this paper we show that the method con-sidered recently by Challis and Burley [2], for determining approx- imations to g, is equivalent to a special case of the well-known method of Garrick [8] for the mapping of doubly-connected domains, Hence, by using results already available in the literature, we provide some theoretical justification for the method of [2]
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