Unified modelling of aerospace systems: a bond graph approach

Systems Integration is widely accepted as the basis for improving the efficiency and performance of many engineering products. The aim is to build a unified optimised system not a collection of subsystems that are combined in some ad hoc manner. This moves traditional design boundaries and, in so doing, enables a structured evolution from an integrated system concept to an integrated system product. It is recognised that the inherent complexity cannot be handled effectively without mathematical modelling. The problem is not so much the large number of components but rather the very large number of functional interfaces that result. The costs involved are high and, if the claims of improved efficiency and performance are to be affordable (or even achievable), predictive modelling and analysis will play a major role in reducing risk. A modelling framework is required which can support integrated system development from concept through to certification. This means building a 'system' inside a computer and demonstrating the feasibility of an entire development cycle. The objective is to provide complete coverage of system functionality so as to gain confidence in the design before becoming locked into a full development programme with associated capital investment and contractual arrangements. With these points in mind the purpose of this thesis is threefold. First, to demonstrate the application of bond graphs as a unified modelling framework for aerospace systems. Second, to review the main principles involved with the modelling of engineering systems and to justify the selection of the bond graph notation as a suitable means of representing the power flow (i.e. the dynamics) of physical systems. Third, to present an exposition of the bond graph method and to evolve it into a versatile notation for integrated systems. The originality of the work is based on the recognition that systems integration is a relatively new field of interest without a mature body of academic literature or reported research. Apparently, there is no open literature on the modelling of complete air vehicles plus their embedded vehicle systems which deals with issues of integrated dynamics and control. To this end, bond graph concepts need to be developed and extended in new direction in order to facilitate an intuitive approach to the modelling of integrated systems

Potentials and challenges of the fuel cell technology for ship applications. A comprehensive techno-economic and environmental assessment of maritime power system configurations

The decarbonization of the global ship traffic is one of the industry’s greatest challenges for the next decades and will likely only be achieved with new, energy-efficient power technologies. To evaluate the performances of such technologies, a system modeling and optimization approach is introduced and tested, covering three elementary topics: shipboard solid oxide fuel cells (SOFCs), the benefits of decentralizing ship power systems, and the assessment of potential future power technologies and synthetic fuels. In the following, the analyses’ motivations, scopes, and derived conclusions are presented. SOFCs are a much-discussed technology with promising efficiency, fuel versatility, and few operating emissions. However, complex processes and high temperature levels inhibit their stand-alone dynamic operation. Therefore, the operability in a hybrid system is investigated, focusing on component configurations and evaluation approach corrections. It is demonstrated that moderate storage support satisfies the requirements for an uninterrupted ship operation. Depending on the load characteristics, energy-intensive and power-intensive storage applications with diverging challenges are identified. The analysis also emphasizes to treat degradation modeling with particular care, since technically optimal and cost-optimal design solutions differ meaningfully when assessing annual expenses. Decentralizing a power system with modular components in accordance with the load demand reduces both grid size and transmission losses, leading to a decrease of investment and operating costs. A cruise-ship-based case study considering variable installation locations and potential component failures is used to quantify these benefits. Transmission costs in a distributed system are reduced meaningfully with and without component failure consideration when compared to a central configuration. Also, minor modifications ensure the component redundancy requirements, resulting in comparably marginal extra expenses. Nowadays, numerous synthetic fuels are seen as candidates for future ship applications in combination with either combustion engines or fuel cells. To drive an ongoing technology discussion, performance indicators for envisioned system configurations are assessed in dependence on mission characteristics and critical price trends. Even if gaseous hydrogen is often considered not suitable for ship applications due to its low volumetric energy density, resulting little operating costs are accountable for its superior performance on short passages. For extended missions, fuel cells operating on methanol or ammonia surpass hydrogen economically

Definition of an object oriented library for the dynamic simulation of advanced energy systems: methodologies, tools and application to combined ICE-ORC power plants

The present Thesis covers part of the work that has been carried out during the three year Ph.D. course in Industrial Engineering at the University of Parma. Scope of the work is developing theoretical methodologies and a full library of dynamic models that can represent the components that usually appear in energy conversion systems. The proposed library should endorse the possibility to create any desire arrangement of the studied systems, to overcome the lack of testing facilities in order to create full virtual machines capable of representing the main phenomena that occur in the real systems to get a full and deep understanding on the way they operate and respond to transients and off design operating condition. In Chapter Two an overview and classification of modeling techniques, suitable for energy systems analysis, is presented. Among the different classification criteria introduced, it is crucial to define whether state variables can be used for the considered component. This option leads to very different ways of developing the model: if the component modeled displays some “storage” capabilities (i.e. it is assumed to be able to store mass, energy, momentum, or moment of momentum) it is intended as a “state determined” system and state variables are defined through the introduction of cardinal physical laws in differential form. From a mathematical viewpoint this implies integrating in time (time is the only domain considered within this work) ordinary differential equations (ODE) expressed in term of the state variables, whose evolution hence will not depend only on the system inputs but on its complete “history”, that starts with the initialization at simulation time t=0. If the storage capabilities of the model are neglected it will be defined as “not state determined” and only algebraic equations (AE) will be introduced. Often the equations used in this case are derived from steady state performance data, gathered either from experimental investigations or by more complex model tools, thus simplifying the description of their transient behaviour as a continuous progression of steady state operating conditions. This modelling approach is known as “quasi-steady”. The models that will be created should be proper (i.e. models that achieve the accuracy required by the application with minimal complexity) scalable and flexible. The approach is followed is typical of object-oriented modeling and each realized component refers to a physical part (or a physical phenomena) of the system. Particular attention is also paid to causality, i.e. every model should be created in such a way to properly represent the cause-effect correlation between inputs and outputs. Another issue faced is the modeling environment to be chosen. After assessing some of the most widely known softwares that looked suitable for the scope, the choice has fallen on the Matlab®/Simulink® package. Simulink® is appreciated for modelling, simulation and analysis of dynamic systems by use of standard or customized blocks that allow great flexibility in model designing and are suitable for control purposes. Matlab® is exploited for its graphical and result analysis capabilities and the possibility to write specific functions which can be called during simulation. The potentialities in matrix calculation of the Matlab® language are also often exploited. In Chapter Three the complete library of components is presented. According to what seen previously the components created have been split in the two main sub-libraries depending if dealing with “state determined” or “not state determined” components. A full complete system model should comprise a proper alternation of components coming from the two libraries to guarantee a better numerical solvability of the system of equations generated and to avoid algebraic loops. The two realized libraries have been enclosed in the Simulink® library root from where the realized custom blocks can be choosen, analogously to the way the standard blocks are employed. This option not only allows easy access to the developed block in creating any new lay-out, but turns useful since the models picked up from the library, if improved or modified, extend the changes to any Simulink® lay-out where they are employed. For each component a detailed description of the inputs, outputs and state variables (if present) is provided. The realized Simulink® models are also shown along with the specific dialog windows realized to introduce model parameters. Nearly all the models are based on s-functions, which allows executing the compiled Matlab® code while Simulink® is performing the simulation of a system. The sub-library ‘state determined components’ will contain the following components:  thermal solar collectors;  single phase heat exchangers;  heat exchangers with phase change;  drums;  constant pressure combustion chambers;  rotating shafts dynamics;  General fluid Receivers;  ICE intercoolers. Among these particular emphasis is given on the models of heat exchangers. This component has been characterized through the adoption of finite volume approach where a set of differential equations, expressing the energy balances in the axial nodes, is introduced and solved numerically adopting a forward finite difference method. Peculiarity of the proposed procedure is the degree of accuracy that may be tuned by the user defining the precision of the component discretization. The approach has also been applied to model an heat exchanger with phase change (evaporator or condenser) where also mass balances are considered in the component control volumes. The ‘not state determined’ library contains the following models:  compressors;  turbines;  pumps;  valves;  heat exchangers with no thermal dynamics;  in cylinder combustion processes (in ICE). As seen the library features all the “flow control devices’ that may appear in a fluid system, such as turbines, compressors, pumps and valves. Among the elements introduced, a special one in the “ICE in-cylinder processes”. The component is based on characteristic maps that allow to know the state of gases trapped inside an ICE cylinder at the end of expansion stroke. This model will turn useful in realizing a full dynamic model of an ICE. The maps are not based on experimental data, as common practice, but are obtained by means of a specifically developed computer code that resolves the chemical equations that refer to species dissociation at chemical equilibrium. Even though it is just an approximation of the real combustion process, the procedure has been believed to be a useful way to gather information of the engine combustion processes when no (or limited) experimental data are available. In Chapter Four examples of applications of the realized models for fluid components are provided, with reference to power systems widely diffused and of known and proven design. The scope is to display the ease of creating new full models from the base component blocks, and the way to properly couple and link them together. Besides a simple example of a cogenerative micro gas turbine system, deeper insight is provided to the models of an organic Rankine power cycle and an alternative stationary internal combustion engine used for cogeneration purposes. These models will be employed for further analysis in Chapter Five. Results of simulations are presented for all the full models described under transient operating conditions inducted by some changes in the main model inputs. All the presented models have been introduced in a further Simulink® sub-library (‘complete power systems’). To be noted that the example presented are not exhaustive of the capabilities of the presented set of computer models discussed in Chapter Three, but new systems can be easily created depending on the research needs. Chapter Five show the way the developed models are intended for system design purposes. It is author’s belief that a full validated computer model for the dynamic simulation of energy systems can constitute a proper tool aimed at developing, assessing and optimizing new system design configurations, developed to increase energy conversion efficiency and reducing primary energy consumption. In this case a combined ICE-ORC system (intended for stationary applications) is proposed as solution to improve the second principle efficiency of the engine generating unit. Many configurations are proposed and discussed through a comprehensive energy and exergy analysis of the system, in order to highlight the theoretical benefits in terms of energy conversion efficiency that can be achieved in some cases. To prove the feasibility of the design and to deeply assess the mutual interactions that exist between the two prime engines, a complete dynamic model of the system has been proposed and some results, under transient operational conditions are reported. The dynamic model of the full system therefore constitute a virtual test bench for development and enhancement of the new proposed energy conversion unit, relieving the energy system researcher from the costly and demanding real testing that, at least in the first stages of development, can thus be substituted by the simulation model

An investigation into hybrid power trains for vehicles with regenerative braking

Imperial Users onl

CBR and MBR techniques: review for an application in the emergencies domain

The purpose of this document is to provide an in-depth analysis of current reasoning engine practice and the integration strategies of Case Based Reasoning and Model Based Reasoning that will be used in the design and development of the RIMSAT system. RIMSAT (Remote Intelligent Management Support and Training) is a European Commission funded project designed to: a.. Provide an innovative, 'intelligent', knowledge based solution aimed at improving the quality of critical decisions b.. Enhance the competencies and responsiveness of individuals and organisations involved in highly complex, safety critical incidents - irrespective of their location. In other words, RIMSAT aims to design and implement a decision support system that using Case Base Reasoning as well as Model Base Reasoning technology is applied in the management of emergency situations. This document is part of a deliverable for RIMSAT project, and although it has been done in close contact with the requirements of the project, it provides an overview wide enough for providing a state of the art in integration strategies between CBR and MBR technologies.Postprint (published version

Gas Turbines

This book is intended to provide valuable information for the analysis and design of various gas turbine engines for different applications. The target audience for this book is design, maintenance, materials, aerospace and mechanical engineers. The design and maintenance engineers in the gas turbine and aircraft industry will benefit immensely from the integration and system discussions in the book. The chapters are of high relevance and interest to manufacturers, researchers and academicians as well

Exhaust system energy management of internal combustion engines

Today, the investigation of fuel economy improvements in internal combustion engines (ICEs) has become the most significant research interest among the automobile manufacturers and researchers. The scarcity of natural resources, progressively increasing oil prices, carbon dioxide taxation and stringent emission regulations all make fuel economy research relevant and compelling. The enhancement of engine performance solely using incylinder techniques is proving increasingly difficult and as a consequence the concept of exhaust energy recovery has emerged as an area of considerable interest. Three main energy recovery systems have been identified that are at various stages of investigation. Vapour power bottoming cycles and turbo-compounding devices have already been applied in commercially available marine engines and automobiles. Although the fuel economy benefits are substantial, system design implications have limited their adaptation due to the additional components and the complexity of the resulting system. In this context, thermo-electric (TE) generation systems, though still in their infancy for vehicle applications have been identified as attractive, promising and solid state candidates of low complexity. The performance of these devices is limited to the relative infancy of materials investigations and module architectures. There is great potential to be explored. The initial modelling work reported in this study shows that with current materials and construction technology, thermo-electric devices could be produced to displace the alternator of the light duty vehicles, providing the fuel economy benefits of 3.9%-4.7% for passenger cars and 7.4% for passenger buses. More efficient thermo-electric materials could increase the fuel economy significantly resulting in a substantially improved business case. The dynamic behaviour of the thermo-electric generator (TEG) applied in both, main exhaust gas stream and exhaust gas recirculation (EGR) path of light duty and heavy duty engines were studied through a series of experimental and modelling programs. The analyses of the thermo-electric generation systems have highlighted the need for advanced heat exchanger design as well as the improved materials to enhance the performance of these systems. These research requirements led to the need for a systems evaluation technique typified by hardware-in-the-loop (HIL) testing method to evaluate heat exchange and materials options. HIL methods have been used during this study to estimate both the output power and the exhaust back pressure created by the device. The work has established the feasibility of a new approach to heat exchange devices for thermo-electric systems. Based on design projections and the predicted performance of new materials, the potential to match the performance of established heat recovery methods has been demonstrated

An experimental and numerical convective heat transfer analysis over a transonic gas turbine rotor blade.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006.An experimental and numerical investigation of the flow and convective heat transfer distribution around a high turning angle gas turbine rotor blade has been carried out at the University of Kwa-Zulu, Durban campus. This study in gas turbine blade aerothermodynamics was done to meet the research and development requirements of the CSIR and ARMSCOR. The experimental results were generated using an existing continuously running supersonic cascade facility which offers realistic engine conditions at low operating costs. These results were then used to develop and validate a 2-D model created using the commercially available Computational Fluid Dynamics (CFD) software package, FLUENT. An initial phase of the study entailed a restoration of what was an unoperational experimental facility to a state capable of producing test simulation conditions. In the analysis, a 4-blade cascade system with provisions for an interchangeable, test blade was subjected to the steady state conditions set up by the facility. Firstly, the flow was characterised by evaluating the static pressures around the midspan of a pressure measurement test blade. This was done using two pressure transducers, a scanivalve, an upgraded data acquisition system and LABview software. The method for measuring the heat transfer distributions made use of a transient measuring technique, whereby a pre-chilled Macor test blade, instrumented with thin film heat flux gauges was rapidly introduced into the hot cascade flow conditions by displacing an aluminum dummy blade while still maintaining the flow conditions. Measurement of the heat flux and generation of the isothermal heat transfer co-efficient distributions entailed re-instrumentation of the test blade section with gauges of increased temperature sensitivity along with modifications of the associated electrical circuitry to improve on the quality of experimental data. Both the experimental flow and heat transfer data were used to validate the CFD model developed in FLUENT. An investigation into different meshing strategies and turbulence models placed emphasis on the choice of model upon correlation. The outcome of which showed the k -co model's superiority in predicting the flow at transonic conditions. A feasibility study regarding a new means of implementing a film cooled turbine test blade at the supersonic cascade facility was also successfully investigated. The study comprised of experimental facility modifications as well as cascade and blade redesigns, all of which were to account for the requirements of film cooling. The implementation of this project, however, demanded the resources of both time and money of which neither commodity was available