Methodologies for the optimisation, control and consideration of uncertainty of reactive distillation

The work presented in this thesis is motivated by the current obstacles hindering the implementation of reactive distillation in industry, mainly related to the complexities of its design and control, as well as the impact of uncertainties thereupon. This work presents a rigorous methodology for the optimal design and control under uncertainty of reactive distillation. The methodology can also be used to identify and investigate mitigation strategies for process failures arising due to design and/or operation deficiencies under changed processing conditions, based on the evaluation of different design and/or control alternatives. The first step of the methodology is the simultaneous (MINLP) optimisation of the design and operation of a reactive distillation process superstructure, used to explore the possible steady-state design alternatives available, including ancillary equipment such as pre- and side-reactors, side-strippers and additional distillation columns, based on product-related constraints and a detailed objective cost function. The next step is the investigation of the dynamic control performance of this optimal system, where conventional and advanced process control strategies are considered in order to investigate how robust the system is towards operational disturbances, or whether revising the optimal steady-state design is required. As the optimisation depends heavily on accurate data for reaction kinetics and separation performance, the final step of the methodology is the evaluation of the impact of parameter uncertainty on the performance of the optimal controlled system, including redesigning the controlled system if required. The methodology is demonstrated using a number of industrially relevant case studies with different reaction and separation characteristics in order to investigate how these determine the design and control of an economically attractive and rigorous reactive distillation process. It is demonstrated that the process characteristics have a significant impact on the design of the system, and that auxiliary equipment may be required to meet production specifications and/or to ensure robust controlled behaviour. It is also shown that, under parameter uncertainty, an optimal controlled system may nevertheless face performance issues, and revising the design and/or operation of the process may be required in order to mitigate such situations

Using Digital Hydraulics in Secondary Control of Motor Drive

Due to the increased focus on pollution and global warming, there is a demand for energy efficient systems. This also applies to the offshore oil and gas industry. Normally used hydraulic systems tend to suffer from low energy efficiency, especially when operating with part loads. In the last decades, a new pump and motor technology has experienced increased interest due to the potential of high energy efficiency in a wide range of operation conditions. This new technology is called digital displacement machine technology. Nowadays, there is a desire from the offshore oil and gas industry to use this digital displacement machine technology to design highly efficient hydraulic winch drive systems. The main objectives of the work presented in this thesis are to design a controller for a digital displacement winch drive system and evaluate its control performance. The design of a controller is one part of the work needed to realizing a winch drive system with digital displacement machines. A winch with a lifting capacity of 20000 kg and a drum capacity of 3600 m of wire rope is used as a case study. Digital displacement machines have strict requirements for the on/off valves used to control each cylinder chamber. It is important to activate the valves at optimal times to ensure operation with high energy efficiency and low pressure and flow peaks. Only a small mistiming of the valves will affect the performance of the digital displacement machine significantly. One of the first contributions presented in this thesis is a method for defining how early or late the valves can be timed without reducing the energy efficiency significantly. The control of digital displacement machines is complicated and non-conventional. Each cylinder can be controlled individually and multiple displacement strategies can be used to achieve the same displacement. Each displacement strategy has its dynamic response characteristics and energy efficiency characteristics. The dynamic response characteristics of the drive system are highly relevant when designing control systems. Therefore, in addition to the conventional classical controller, also a suitable displacement strategy must be designed. Designing controllers for digital displacement machines are therefore more complex than designing controllers for conventional hydraulic machines. One of the main focuses of this project has been to analyze the transient and steady state response characteristics of different displacement strategies. In all, three displacement strategies are examined: full stroke displacement strategy, partial stroke displacement strategy and sequential partial stroke displacement strategy. Also, during this work, a new version of the partial stroke displacement strategy has been developed and included in the dynamic response analysis. The dynamic response analysis is a simulation study, where the simulation model is experimentally validated. The experimental work is conducted on a prototype of a single cylinder digital displacement machine. The prototype consists of a five cylinder radial piston motor where one cylinder is modified to operate with the digital displacement technology. The rest of the cylinders are not changed and not used. In addition to validating the simulation model, the prototype is used to test all of the analyzed displacement strategies in low speed operation. The results from the dynamic response analysis are used to select the displacement strategy that is most suited for use in a winch drive system. Then, controllers for the digital displacement winch drive system are developed. The main focus in the control design phase is not to design a new type of controller but to examine already developed controllers and fit them to a winch system driven by digital displacement machines. In the end, the simulation results of the designed controllers are shown and the results are discussed. The simulation results show that digital displacement machines can be used in winch drive systems and achieve both high motion control performance and wire tension control performance.publishedVersio

Torsional seismic response control of asymmetric-plan systems by using viscous dampers

A new approach to locating viscous dampers optimally is herein presented in order to control the torsional seismic response of asymmetric-plan buildings. Firstly, the effects of the plan-wise distribution of supplemental damping on torsionally dynamic behavior have been investigated by using modal analysis techniques in the state space representation in order to highlight the main physical aspects of the problem. Optimal design criteria have then been carried out by evaluating the H1 and H2 norms of the transfer function relating the maximum edge displacement to the input seismic excitation. These norms represent suitable performance indexes to investigate the optimal plan-wise distribution of extra-structural dampers by means of parametrical analysis on varying the dynamic characteristics of the asymmetric-plan system. The numerical constraints on the mechanical parameters related to the practical application of the proposed control strategy are taken into account. Simple design formulae to model the results for the H2 norm are proposed and positively verified through broad numerical experimentation which compared the seismic response of asymmetric systems to synthetic and real excitations for different design strategies in a plan-wise arrangement of supplemental damping

An advanced 3D multi-body system model for the human lumbar spine

Series : Mechanisms and machine science, ISSN 2211-0984, vol. 24A novel 3D multi-body system model of the human lumbar spine is presented, allowing the dynamic study of the all set but also to access mechanical demands, characteristics and performance under work of the individual intervertebral discs. An advanced FEM analysis was used for the most precise characterization of the disc 6DOF mechanical behavior, in order to build up a tool capable of predicting and assist in the design of disc recovery strategies – namely in the development of replace-ment materials for the degenerated disc nucleus – as well as in the analysis of variations in the me-chanical properties (disorders) at disc level or kinematic structure (e.g. interbody fusion, pedicle fixa-tion, etc.), and its influence in the overall spine dynamics and at motion segments individual level. Preliminary results of the model, at different levels of its development, are presented

Analysis and robust decentralized control of power systems using FACTS devices

Today\u27s changing electric power systems create a growing need for flexible, reliable, fast responding, and accurate answers to questions of analysis, simulation, and design in the fields of electric power generation, transmission, distribution, and consumption. The Flexible Alternating Current Transmission Systems (FACTS) technology program utilizes power electronics components to replace conventional mechanical elements yielding increased flexibility in controlling the electric power system. Benefits include decreased response times and improved overall dynamic system behavior. FACTS devices allow the design of new control strategies, e.g., independent control of active and reactive power flows, which were not realizable a decade ago. However, FACTS components also create uncertainties. Besides the choice of the FACTS devices available, decisions concerning the location, rating, and operating scheme must be made. All of them require reliable numerical tools with appropriate stability, accuracy, and validity of results. This dissertation develops methods to model and control electric power systems including FACTS devices on the transmission level as well as the application of the software tools created to simulate, analyze, and improve the transient stability of electric power systems.;The Power Analysis Toolbox (PAT) developed is embedded in the MATLAB/Simulink environment. The toolbox provides numerous models for the different components of a power system and utilizes an advanced data structure that not only increases data organization and transparency but also simplifies the efforts necessary to incorporate new elements. The functions provided facilitate the computation of steady-state solutions and perform steady-state voltage stability analysis, nonlinear dynamic studies, as well as linearization around a chosen operating point.;Applying intelligent control design in the form of a fuzzy power system damping scheme applied to the Unified Power Flow Controller (UPFC) is proposed. Supplementary damping signals are generated based on local active power flow measurements guaranteeing feasibility. The effectiveness of this controller for longitudinal power systems under dynamic conditions is shown using a Two Area - Four Machine system. When large disturbances are applied, simulation results show that this design can enhance power system operation and damping characteristics. Investigations of meshed power systems such as the New England - New York power system are performed to gain further insight into adverse controller effects

Adaptive torque control of a diesel engine for transient test cycles

Adaptive control techniques have been applied to the problem of diesel engine torque control. Adaptive control has the potential of greater versatility than classical control techniques. Three adaptive control strategies are tested and compared to each other: self-tuning control with one-shot parameter identification and controller design, self-tuning gain-scheduling control, and self-tuning control with continuous adaptation of system and controller parameters. A continuous-time parameter identification approach, namely the Poisson Moment Functional (PMF) method, is employed due to its superior noise rejection capability. To ensure the applicability of time delay systems, a Smith predictor is employed. The controller design is implemented using a new pole-zero placement algorithm to ensure closed-loop stability. Comparisons with constant parameter controllers reveal that adaptive control provides equal or better torque control than a constant parameter controller. The results of the transient cycle tests also prove that the self-tuning control can be successfully applied to systems with dramatically different dynamic characteristics, and hence show the versatility of the self-tuning adaptive control

Urban typologies and heat energy demand. A case-study in the Italian context.

Nowadays, large parts of the world population (50-60%) are living in urban areas, which represent the most energy consuming systems (Buckley et al., 2009). Local governments are therefore asked to take new responsibilities in terms of energy management, adopting the urban scale as level of action, developing new methods and strategies to bring energy sustainability (saving/producing) and environmental quality into the cities. The development of a new energetic and environmental planning approach that can set energy as primary key – leading to a high level of urban efficiency and having a broad effect on other urban areas – is hence highly important. Different studies have pointed out the fundamental energetic role of urban morphology and typology (Ratti et al., 2004). Recognizing the key role of planning and design, and the contribution of modeling, some questions are arising: is it possible to analyze the performances of the built environment in a georeferenced way, considering the effect of urban design/form aspects, in order to achieve a better knowledge of those city characteristics that influence energy demand? Which is the role played by typologies in (re)orienting the energy analyses/model? Which targets can be achieved in reducing cost and energy? The project explore different factors involved in the energy performance of the city, in particular using an innovative evaluation model of heat energy demand, which has urban typologies as starting and key point of the analyses. A dynamic and georeferenced method has been specifically developed, allowing the estimation of the energy behavior of the “real†city. The empirical study is applied at the City of Gorgonzola - Italy, which holds potential both for the dimension of the built environment and the variety of urban typologies, which allow a comparison between them. Purpose of the paper is thus to analyze the results coming from the estimation, that can lead to a strong integration between energy, urban design and planning system.

Wind turbine drive train vibration with focus on gear dynamics under nondeterministic loads

In present-day, the engineering challenge around a drive train design for a wind turbine is not only to enhancesystem reliability but also to reduce the turbine top mass. These requirements together with the trend of upscaling affect many system characteristics and parameters. The proposed contribution presents a model tostudy torsional drive train vibration dynamics of a generic indirect drive multi-MW wind turbine. The mainfocus lies on developing a fully parameterized computational model of a multi-stage gearbox which fulfillsthe requirement of a proper gear dynamic representation appropriate for multibody formalism as well asthe requirement to be computationally efficient. Two different strategies for modeling the gear contact arestudied and compared in time domain. An analysis of a multi-stage gearbox together with a generator load and a turbine specific nondeterministic excitation was carried out. It is believed that the obtained results will help designer to improve drive train components and to enhance wind turbine reliability and cost efficiency

Strategies to design for dynamic usability

Since usability is a property of the interaction between a product, a user and the task that he or she is trying to complete [6], a product’s usability can vary when it is used in varying use situations. We define this as dynamic usability. This study is aimed at exploring how practitioners currently deal with dynamic usability. From a retrospective case study research of three design projects different principles and strategies were formulated for dealing with dynamic use situations. In this paper we present solution principles that are applied to accommodate products to dynamic use situations and we discuss two design process issues with regard to dynamic usability, namely the information sources that are used to get insight in the use situations and the means by which designers try to get insight in the consequence of their design decisions with regard to future use situation

Wind turbine drive train vibration with focus on gear dynamics under nondeterministic loads

In present-day, the engineering challenge around a drive train design for a wind turbine is not only to enhancesystem reliability but also to reduce the turbine top mass. These requirements together with the trend of upscaling affect many system characteristics and parameters. The proposed contribution presents a model tostudy torsional drive train vibration dynamics of a generic indirect drive multi-MW wind turbine. The mainfocus lies on developing a fully parameterized computational model of a multi-stage gearbox which fulfillsthe requirement of a proper gear dynamic representation appropriate for multibody formalism as well asthe requirement to be computationally efficient. Two different strategies for modeling the gear contact arestudied and compared in time domain. An analysis of a multi-stage gearbox together with a generator load and a turbine specific nondeterministic excitation was carried out. It is believed that the obtained results will help designer to improve drive train components and to enhance wind turbine reliability and cost efficiency