1,235 research outputs found

    High performance DSP-based servo drive control for a limited-angle torque motor

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    This thesis describes the analysis, design and implementation of a high performance DSP-based servo drive for a limited-angle torque motor used in thermal imaging applications. A limited-angle torque motor is an electromagnetic actuator based on the Laws' relay principle, and in the present application the rotation required was from - 10° to + 10° in 16 ms, with a flyback period of 4 ms. To ensure good quality picture reproduction, an exceptionally high linearity of ±0.02 ° was necessary throughout the forward sweep. In addition, the drive voltage to the exciting winding of the motor should be less than the +35 V ceiling of the drive amplifier. A research survey shows that little literature was available, probably due to the commercial sensitivity of many of the applications for torque motors. A detailed mathematical model of the motor drive, including high-order linear dynamics and the significant nonlinear characteristics, was developed to provide an insight into the overall system behaviour. The proposed control scheme uses a multicompensator, multi-loop linear controller, to reshape substantially the motor response characteristic, with a non-linear adaptive gain-scheduled controller to compensate effectively for the nonlinear variations of the motor parameters. The scheme demonstrates that a demanding nonlinear control system may be conveniently analysed and synthesised using frequency-domain methods, and that the design techniques may be reliably applied to similar electro-mechanical systems required to track a repetitive waveform. A prototype drive system was designed, constructed and tested during the course of the research. The drive system comprises a DSP-based digital controller, a linear power amplifier and the feedback signal conditioning circuit necessary for the closed-loop control. A switch-mode amplifier was also built, evaluated and compared with the linear amplifier. It was shown that the overall performance of the linear amplifier was superior to that of the switch-mode amplifier for the present application. The control software was developed using the structured programming method, with the continuous controller converted to digital form using the bilinear transform. The 6- operator was used rather than the z-operator, since it is more advantageous for high speed sampling systems. The gain-scheduled control was implemented by developing a schedule table, which is controlled by the DSP program to update continuously the controller parameters in synchronism with the periodic scanning of the motor. The experimental results show excellent agreement with the simulated results, with linearity of ±0.05 ° achieved throughout the forward sweep. Although this did not quite meet the very demanding specifications due to the limitations of the experimental drive system, it clearly demonstrates the effectiveness of the proposed control scheme. The discrepancies between simulated and experimental results are analyzed and discussed, the control design method is reviewed, and detailed suggestions are presented for further work which may improve the drive performance

    The minimum capacity of HVAC secondary systems (with capacity reduction by interzonal airflow) (RP-1049)

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    To date, the performance of alternative HVAC secondary systems has been compared using either the systems’ energy use directly or by a life-cycle cost analysis. This paper introduces the concept of rating a system’s performance by comparing its capacity at a particular operating point to the thermodynamic minimum capacity. A simple ratio, termed the “system effectiveness,” is also introduced to indicate the extent to which the system operates with the minimum possible capacity. This paper describes the calculation of the minimum system capacity as a nonlinear, single- criterion, constrained optimization problem. In particular, it describes the case for the minimization of the system capacity by use of interzonal airflow (the interzonal airflow rates and zone thermal conditions being variables of the optimization). This optimization problem is multi-modal in that the same system capacity can result from more than one interzonal airflow configuration. The optimization problem has been solved here using a genetic algorithm (GA) search method. This paper illustrates the use of the minimum system capacity as a benchmark for the performance of a typical multizone heating, ventilating, and air-conditioning (HVAC) system. The example also illustrates the potential benefit of using interzonal airflow to reduce the required capacity of a system. It can be concluded from the example that the arrangement of the system components is a significant factor in determining the thermal effectiveness of HVAC systems

    Simulation of human thermal responses in a confined space

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    Latest human thermal comfort models, such as the IESD-Fiala model, are active multi-nodal thermal models that simulate physiological regulatory responses, e.g. changing metabolic rate and skin blood flow, shivering and sweating. Commercial CFD packages, such as ANSYS CFX, are widely used in studying transient thermal environment. The purpose of this study is to develop and demonstrate the method for integrating human thermal comfort models with the CFD environment for detailed transient simulations. Different integration strategies are discussed in this paper, as well as the technical problems with using detailed (clothed) 3-D model in the coupled simulation. It is highlighted that further research is required to exploit the full potential of the integrated model in environmental design

    Energy aspects of HVAC system configurations — problem definition and test cases

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    This paper reports on the energy implications of HVAC system configuration by analyzing the energy balance and psychrometrics of typical and innovative systems. Three criteria were shown to be significant: (1) the ability to minimize outside air load, (2) the ability to eliminate simultaneous cooling and heating and use mixing effectively, and (3) the availability of interzonal airflow. Configurations that meet these criteria would be able to deliver the desired indoor air quality with reduced energy consumption. The performance of ten two-zone system configurations, including single-duct, dual-duct, fan-coil-based variations, and other specialized systems in the literature, were analyzed for a number of operational conditions. The results confirmed that fan-coil-based configurations with interzonal airflow paths perform better than other configurations. The conclusion of this study may be used as a guideline for multi-zone system designs

    Evolutionary synthesis of HVAC system configurations : algorithm development (RP-1049)

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    This paper describes the development of a model-based optimization procedure for the synthesis of novel heating, ventilating, and air-conditioning system configurations. The optimization problem can be considered as having three suboptimization problems: the choice of a component set; the design of the topological connections between the components; and the design of a system operating strategy. In an attempt to limit the computational effort required to obtain a design solution, the approach adopted in this research is to solve all three subproblems simultaneously. The computational effort has been further limited by implementing simplified component models and including the system performance evaluation as part of the optimization problem (there being no need, in this respect, to simulate the system performance). The optimization problem has been solved using a Genetic Algorithm (GA) that has data structures and search operators specifically developed for the solution of HVAC system optimization problems. The performance of the algorithm and various search operators has been examined for a two-zone optimization problem, the objective of the optimization being to find a system design that minimizes system energy use. In particular, the performance of the algorithm in finding feasible system designs has been examined. It was concluded that the search was unreliable when the component set was optimized, but if the component set was fixed as a boundary condition on the search, then the algorithm had an 81% probability of finding a feasible system design. The optimality of the solutions is not examined in this paper but is described in an associated publication (Wright and Zhang 2008). It was concluded that, given a candidate set of system components, the algorithm described here provides an effective tool for exploring the design of novel HVAC systems

    What impacts more on innovation : Organizational context or individual competences ?

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    The present article examines the link between a firm’s organizational context and its capacity to be ambidextrous in terms of innovation. Although the management practices underlying context have a profound effect on innovation, their impact has not previously been investigated. Nor has research looked empirically at the individual competences that should be developed in order to favour specific types of innovation. Using a dataset of 174 firms, the present study shows that firms pursuing exploration and exploitation strategies in terms of innovation should adopt long-term oriented practices that favor risk taking and creativity, thus creating an appropriate organizational context. Competence management was found to have a strong moderating effect on the link between organizational context and innovation ambidexterity. Implications include the need to look at how management may increase innovation ambidexterity, and to chose appropriate combinations of competences and organizational context

    Exploring organisational culture and power in private-run Early Childhood Education and Care (ECEC) institutions in China

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    In the last two decades, increasing numbers of private ECEC institutions have been established in China. However, the quality of these institutions have been criticised. To address this problem and to find out how organisational cultures were constructed in ECEC settings in China, I carried out research in two private ECEC schools which shared the same cultural framework. Three dimensions for deciphering organisational cultures were used as the conceptual framework of this study: three levels of culture as a structural view, along with the notion of power and the notion of small culture as two non-structural views. This conceptual framework offers a new critical approach, to fill the gap between structural and interpretive views for deciphering organisational cultures. Furthermore, it offers the flexibility for exploring the relationship between power, agency and structure, and the role of personal trajectories in constructing small cultures, especially when related to broader contexts. The findings from the study suggest four types of cultural devices were used to create a formal organisational cultural framework: organisational physical structures and decorations, rules, traditions and cultural activities. Additionally, the roles of the main stakeholders including senior management teams and teachers were identified, as the final decision-makers at school, department and classroom level. The multiple roles of parents were discovered, to be customers, allies of schools, as well as practitioners alongside teachers in the classroom. The three external factors that influenced the main stakeholders in constructing organisational cultures were: national curriculum reform, policy change from one-child to two-child, and Confucianism and Collectivism ideologies. The findings of this study provide insights for policy makers of and in ECECs as well as the practitioners in educational settings in terms of how cultures are constructed in ECECs and how these affect the ways in which ECECs work.</div

    Ensemble yield simulations: Using heat-tolerant and later-maturing varieties to adapt to climate warming

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    <div><p>The use of modern crop varieties is a dominant method of obtaining high yields in crop production. Efforts to identify suitable varieties, with characteristics that would increase crop yield under future climate conditions, remain essential to developing sustainable agriculture and food security. This work aims to evaluate potential genotypic adaptations (i.e., using varieties with increased ability to produce desirable grain numbers under high temperatures and with enhanced thermal time requirements during the grain-filling period) to cope with the negative impacts of climate change on maize yield. The contributions of different options were investigated at six sites in the North China Plain using the APSIM model and the outputs of 8 GCMs under RCP4.5 scenarios. It was found that without considering adaptation options, mean maize yield would decrease by 7~18% during 2010–2039 relative to 1976–2005. A large decrease in grain number relative to stabilized grain weight decreased maize yield under future climate scenarios. Using heat-tolerant varieties, maize yield could increase on average by 6% to 10%. Using later maturing varieties, e.g., enhanced thermal time requirements during the grain-filling period, maize yield could increase by 7% to 10%. The optimal adaptation options were site specific.</p></div

    PDFs and CDFs of yield changes for variety <i>Xundan29</i>.

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    <p>PDFs and CDFs of yield changes for variety <i>Xundan29</i>.</p

    Locations of study sites in the North China Plain.

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    <p>Locations of study sites in the North China Plain.</p
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