685 research outputs found
Energetic and exergetic analysis of combined cycle power plant: Part-1 operation and performance
Energetic and exergetic analyses are conducted using operating data for Sabiya, a combined cycle power plant (CCPP) with an advanced triple pressure reheat heat recovery steam generator (HRSG). Furthermore, a sensitivity analysis is carried out on the HRSG using a recent approach to differentiate between the sources of irreversibility. The proposed system was modelled using the IPSEpro software and further validated by the manufacturer’s data. The performance of the Sabiya CCPP was examined for different climatic conditions, pressure ratios, pinch point temperatures, high-pressure steam, and condenser pressure values. The results confirmed that 60.9% of the total exergy destruction occurs in the combustion chamber, which constitutes the main source of irreversibilities within a system. The exergy destruction was significantly affected by both the pressure ratio and the high-pressure steam, where the relation between them was seen to be inversely proportional. The high-pressure stage contributes about 50% of the exergy destruction within the HRSG compared to other stages and the reheat system, due to the high temperature difference between the streams and the large number of components, which leads to high energy loss to the surroundings. Numerous possibilities for improving the CCPP’s performance are introduced, based on the obtained results
Exergetic, exergoeconomic and exergoenvironmental analysis of intercooled gas turbine engine
Exergetic and exergoeconomic and exergoenvironmental analyses have been performed for an advanced aero-derivative intercooled gas turbine engine. The proposed system was modelled using the IPSEpro software package and validated using manufacturer’s published data. The exergoeconomic model evaluates the cost-effectiveness of the gas turbine engine based on the Specific Exergy Costing [SPECO] method. The CO2 emissions per KWh were estimated using a generic combustor model, HEPHAESTUS, developed at Cranfield University. It is well known that the exergetic analysis can determine the magnitudes, locations and types of losses within an energy system. The effect of load and ambient temperature variations on gas turbine performance were investigated for two different configurations. The first system, Case-I, was a simple gas turbine (SCGT) engine, and the second, Case-II, an intercooling gas turbine (ICGT) system. The latter enhances gas turbine efficiency but, at the same time, has an adverse effect on the combustion chamber due to reduced compressed air temperature. It was confirmed that full load and low ambient temperature are preferable due to the low waste exergy. The unit exergy cost rate for both SCGT and ICGT have been calculated as 8.59 and 8.32 US$/GJ respectively. The exergoenvironmental results show the ICGT achieved lower emission levels and is more environmentally friendly than the SCGT
Optimal fault-tolerant flight control for aircraft with actuation impairments
Current trends towards greater complexity and automation are leaving modern
technological systems increasingly vulnerable to faults. Without proper action, a
minor error may lead to devastating consequences. In flight control, where the
controllability and dynamic stability of the aircraft primarily rely on the control
surfaces and engine thrust, faults in these effectors result in a higher extent of risk for
these aspects. Moreover, the operation of automatic flight control would be suddenly
disturbed. To address this problem, different methodologies of designing optimal
flight controllers are presented in this thesis. For multiple-input multiple-output
(MIMO) systems, the feedback optimal control is a prominent technique that solves
a multi-objective cost function, which includes, for instance, tracking requirements
and control energy minimisation.
The first proposed method is based on a linear quadratic regulator (LQR) control
law augmented with a fault-compensation scheme. This fault-tolerant system handles
the situation in an adaptive way by solving the optimisation cost function and
considering fault information, while assuming an effective fault detection system is
available. The developed scheme was tested in a six-degrees-of-freedom nonlinear
environment to validate the linear-based controller. Results showed that this fault
tolerant control (FTC) strategy managed to handle high magnitudes of the actuator’s
loss of effciency faults. Although the rise time of aircraft response became slower,
overshoot and settling errors were minimised, and the stability of the aircraft was
maintained.
Another FTC approach has been developed utilising the features of controller
robustness against the system parametric uncertainties, without the need for reconfiguration
or adaptation. Two types of control laws were established under this scheme,
the
H∞
and µ-synthesis controllers. Both were tested in a nonlinear environment
for three points in the flight envelope: ascending, cruising, and descending. The
H∞
controller maintained the requirements in the intact case; while in fault, it yielded
non-robust high-frequency control surface deflections. The µ-synthesis, on the other
hand, managed to handle the constraints of the system and accommodate faults
reaching 30% loss of effciency in actuation. The final approach is based on the control allocation technique. It considers the tracking requirements and the constraints of
the actuators in the design process. To accommodate lock-in-place faults, a new
control effort redistribution scheme was proposed using the fuzzy logic technique,
assuming faults are provided by a fault detection system. The results of simulation
testing on a Boeing 747 multi-effector model showed that the system managed to
handle these faults and maintain good tracking and stability performance, with some
acceptable degradation in particular fault scenarios. The limitations of the controller
to handle a high degree of faults were also presented
Development of a survey instrument for measuring the perceptions and attitudes of the managers of Saudi public organisations on the benefits of Saudi labour rights and laws
The procedure adopted for development of a survey instrument to measure the perceptions and attitudes of Saudi managers on the benefits laws has been described in this paper. The commonly adopted procedure of determining the
scales and items for the survey was followed. The context-specific requirements were considered in determining the items to be included in the two scales. The full questionnaire contained relevant demographic items, eight items each for perceptions and attitudes measurement and a final open question for whatever the survey participants wished to say about the topic of survey. A pilot trial was done using the developed survey instrument to measure perceptions and attitudes of Saudi public sector managers on the benefits
enjoyed by their workforce due to favourable labour laws. The results showed both perceptions and attitudes of managers to be positive. The results were explained in a number of different ways with the support of literature. Some
limitations of this research, as scope for further research, have also been listed
Managing security and compliance risks of outsourced IT projects
PhD ThesisSeveral sources of constraints, such as business, financial and legal, can lead
organisations to outsource some of their IT services. As a consequence, different
security risks may be introduced, such as confidentiality, integrity and
availability risks. Analysing and managing the potential security risks in the
early stages of project execution allow organisations to avoid or mitigate the
impact of these security risks. Several organisations have adopted ISMS
standards and frameworks in an endeavour to manage outsourced IT project
security risks. In this thesis, existing ISMS standards and frameworks have been
reviewed and analysed to assess their ability to effectively manage the security
and compliance risks of outsourced IT projects and satisfy their security needs.
The review reveals that existing ISMS standards and frameworks represent only
general security recommendations and do not consider variation in security
requirements from one organisation to another. There is also a lack of adequate
guidance for implementing or complying with these standards and frameworks,
and they are not designed to manage the security and compliance risks of
outsourced IT projects. To overcome these weaknesses, a new framework has
been introduced. The framework is a structured approach that is designed to
manage variation in security requirements, as well as provide a methodology to
guide organisations for the purpose of security management and implementation.
The framework was evaluated using different evaluation methods including a
focus group, questionnaire, and case study, which were also used to generate
recommendations and suggestions for improvements. The evaluation results
confirmed that the framework provided the participants with an effective
approach for managing security and compliance risks in the outsourcing context.
It was understandable, easy to use, and independent from different constraints
such as project size, cost or execution time. The framework is now ready to be put
into practice by organisations that intend to outsource their IT services partially
or totally
Strategic management role in boosting hotel performance
The foremost aim of this paper is to examine the right linkage of specific market orientation, innovation strategy and organizational performance of 114 hotels in Malaysia. Data were drawn from census method on 475 hotels’ top and middle managers who are responsible for the progress of innovation and market orientation of their hotel. These research findings confirmed that all hypotheses give valuable indications on the strategic linkage of specific market orientation and innovation strategy to pursue for improved organizational performance. The results highlighted hotels pursuing competitor orientation focused on process innovation. Hotels that pursue customer orientation focused on service innovation. The result shows that competitor orientation, customer orientation, process innovation and service innovation have a significant effect on organizational performance. Remarkably, this research found process innovation partially mediates the association between competitor orientation and performance, while service innovation partially mediates the association of customer orientation and performance. The paper develops an integrated model that link specific market orientation, innovation strategy and organizational performance of hotels in Malaysia
Quality Measurements on Quantised Meshes
In computer graphics, triangle mesh has emerged as the ubiquitous shape rep- resentation for 3D modelling and visualisation applications. Triangle meshes, often undergo compression by specialised algorithms for the purposes of storage and trans- mission. During the compression processes, the coordinates of the vertices of the triangle meshes are quantised using fixed-point arithmetic. Potentially, that can alter the visual quality of the 3D model. Indeed, if the number of bits per vertex coordinate is too low, the mesh will be deemed by the user as visually too coarse as quantisation artifacts will become perceptible. Therefore, there is the need for the development of quality metrics that will enable us to predict the visual appearance of a triangle mesh at a given level of vertex coordinate quantisation
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Harmonics mitigation based on the minimization of non-linearity current in a power system
Harmonic issues in power systems are becoming an important topic for industrial customers and power suppliers alike due to their adverse effects in both consumer appliances as well as for utility suppliers. Consumers should seek to reduce harmonic pollution, regardless of voltage or current distortion already present in the network. This article suggests a new method for suppressing distortions by using the non-linearity current index (NLCI) to determine the shunt single-tuned passive filter (STPF) compensator value in non-sinusoidal power systems, with the objective of maintaining the power factor within desired limits. The objective of the proposed method is to minimize the nonlinear current of customer’s loads in the power system at the point of common coupling (PCC). Moreover, the proposed design takes into consideration other practical constraints for the total voltage and individual harmonic distortion limits, ensuring compliance with (Institute of Electrical and Electronics Engineers) IEEE 519-2014 guidelines, maintaining distortions at an acceptable level while also abiding by the capacitor loading constraints established in IEEE 18-2012. The performance of the optimally designed compensator is assessed using well documented IEEE standards based on numerical examples of nonlinear loads taken from previous publications
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