A modular co-simulation approach for urban energy systems

Cities are the main site of energy consumption, which result in approximately 71% of global CO2 emissions. Therefore, energy planning in cities can play a critical role in climate change mitigation by improving the efficiency of urban energy usage. The energy characteristics of cities are complex as they involve interactions of multiple domains, such as energy resources, distribution networks, storage and demands from various consumers. Such complexity makes urban energy planning a challenging task, which requires an accurate simulation of the interactions and flows between different urban energy subsystems. Co-simulation has been adopted by a number of researchers to simulate dynamic interactions between subsystems. However, the research has been domain specific and could only be used in limited areas. There was no generic approach to tackle the interoperability challenge of a comprehensive simulation for urban energy systems. To address such a gap, the aim of this thesis is to develop a generic and scalable urban energy co-simulation approach to comprehensively model the dynamic, complex and interactive nature of urban energy systems. This was achieved through the development of a generic and scalable urban energy co-simulation architecture and approach for the integration and orchestration of urban energy simulation tools, also called simulators, from different domains. Nine requirements were identified through a literature review of co-simulation, its approaches, standards, middleware and simulation tools. A conceptual co-simulation architecture was proposed that can address the requirements. The architecture has a modular design with four layers. The simulator layer wraps the simulation tools; the interconnection layer enables the communication between tools programmed in different programming languages; the interoperability layer provides a mechanism for the tool composition and orchestration; and the control layer controls the overall simulation sequence and how data is exchanged. Based on the architecture, a Co-simulation Platform for Ecological-urban (COPE) was developed. Suitable co-simulation software libraries were adopted and mapped together to fulfil the requirements of each layer of COPE to achieve the research objectives. For different simulation purposes, subsystem simulation tools from different domains could be selected and integrated into the platform. A master algorithm could then be developed to orchestrate and synchronise the tools by controlling how the tools are run and how data are exchanged among the tools. In order to evaluate COPE’s fundamental functionality and demonstrate its application, two case studies are presented in the thesis: simulating multiple application domains for a single building and multiple (interacting) buildings respectively. From the case studies, it was observed that COPE can successfully synchronise and manage interactions between the co-simulation platform and integrated simulation tools. The simulation results are validated by comparing the results obtained from the direct coupling approach. The applicability of COPE is demonstrated by simulating energy flows in urban energy systems in a neighbourhood context. Computing performance diagnostics also showed that this functionality is achieved with modest overhead. The layered modular co-simulation approach and COPE presented in this thesis provide a generic and scalable approach to simulating urban energy systems. It could be used for decision making to improve urban energy efficiency

AN EXPERIMENTAL INVESTIGATION OF HIGH DOSE RATE ELECTRON BEAM IRRADIATION OF PETROLEUM IN A CONTINUOUS FLOW SYSTEM

High dose rate electron beam (10 MeV, 15 kW, LINAC) irradiation was investigated as a potential technology for heavy oil upgrading. The flow system allows irradiation of crude oils at constant temperature while bubbling natural gas through the oil. Experimental parameters including dose, temperature, shear rate and dose rate were allowed to change in order to find the optimal condition. Pure hydrocarbons were selected and irradiated by the same source at low temperatures. Results revealed that conversion and product yields not only depends on those irradiation conditions, but also relies on the molecular structure of irradiated compounds. Irradiation of petroleum activates hydrocarbon compounds which subsequently undergo a series of chemical reactions including radical initiation, propagation and termination. Two reaction pathways could be initiated by absorbed energy, then compete inside the irradiated compounds and eventually lead to multiple products. Cracking is due to hydrocarbon chain scission and produces products smaller than the parent molecules. Polymerization is caused by molecule recombination and produces products larger than the parent molecules. Cracking and polymerization could be enhanced or suppressed by altering irradiation conditions such as irradiation temperature and total absorbed energy. To selectively favor one of them and suppress the other one requires detailed investigation of many parameters. In general, higher dose rate and higher temperature favor cracking reactions. Fundamental studies were conducted by irradiating pure and neat hydrocarbon compounds with the same electron beam source. Responses from irradiating different compounds varied dramatically. Saturated hydrocarbons tended to produce the most products. The presence of rings on a saturated hydrocarbon greatly enhanced its tendency toward polymerized products which are commonly dimers and trimers. Unsaturated hydrocarbons were less reactive with lower yields of products. One unsaturated ring on a molecule will tremendously suppress its reactivity toward chain scission products and only produce detectable polymerized species. Stability of a hydrocarbon compound and its radiation product pattern are closely related to its molecular structure. The saturation degree of a molecule and its average bond strength could be used to characterize the stability and product yields for a compound. Crude oil is a complex mixture of thousands of hydrocarbon compounds and nonhydrocarbons. Conversion and product yields from irradiating crudes do not simply resemble those from irradiation of pure compounds due to unknown chemical composition and unknown reaction pathways. This explains why it is so challenging to predict heavy oil conversion under electron beam irradiation. Crude oils could be separated into a few fractions, e.g. saturates, aromatics, resin and asphaltene. Irradiation of each fraction may follow the same results obtained from irradiating pure and neat compounds. Saturates should have the highest conversion to light products whereas everything else either is chemically stable or polymerizes. That provides a possibility of improving the total conversion and product yields from crude oil irradiation by separating crudes into different fractions, then selectively irradiating the saturates and avoiding other fractions