A deterministic agent-based path optimization method by mimicking the spreading of ripples

Inspirations from nature have fundamentally contributed to the development of evolutionary computation (EC). This paper, by learning from the natural ripple-spreading phenomenon, proposes a novel ripple-spreading algorithm (RSA) for the path optimization problem (POP). In nature, a ripple spreads at a constant speed in all directions, and the node closest to the source will be the first to be reached. This very simple principle forms the foundation of the proposed RSA. In contrast to most deterministic top-down centralized path optimization methods, such as Dijkstra's algorithm, the RSA is a bottom-up decentralized agent-based simulation model. Moreover, it is distinguished from other agent-based algorithms, such as genetic algorithms and ant colony optimization, by being a deterministic method that can always guarantee the global optimal solution with very good scalability. Here, the RSA is specifically applied to four different POPs. The comparative simulation results presented clearly illustrate the advantages of the RSA in terms of effectiveness and efficiency. Thanks to the combination of both agent-based and deterministic features, the RSA opens new opportunities to attack some problems, such as calculating the exact complete Pareto front in multi-objective optimization and determining the kth shortest project time in project management, which are very difficult, if not impossible, for existing methods to resolve. The ripple-spreading optimization principle, aswell as the new distinguishing features and capacities of RSA, enriches the theoretical foundations of EC

Epidemic modelling by ripple-spreading network and genetic algorithm

Mathematical analysis and modelling is central to infectious disease epidemiology. This paper, inspired by the natural ripple-spreading phenomenon, proposes a novel ripple-spreading network model for the study of infectious disease transmission. The new epidemic model naturally has good potential for capturing many spatial and temporal features observed in the outbreak of plagues. In particular, using a stochastic ripple-spreading process simulates the effect of random contacts and movements of individuals on the probability of infection well, which is usually a challenging issue in epidemic modeling. Some ripple-spreading related parameters such as threshold and amplifying factor of nodes are ideal to describe the importance of individuals’ physical fitness and immunity. The new model is rich in parameters to incorporate many real factors such as public health service and policies, and it is highly flexible to modifications. A genetic algorithm is used to tune the parameters of the model by referring to historic data of an epidemic. The well-tuned model can then be used for analyzing and forecasting purposes. The effectiveness of the proposed method is illustrated by simulation results

Development and use of bioanalytical instrumentation and signal analysis methods for rapid sampling microdialysis monitoring of neuro-intensive care patients

This thesis focuses on the development and use of analysis tools to monitor brain injury patients. For this purpose, an online amperometric analyzer of cerebral microdialysis samples for glucose and lactate has been developed and optimized within the Boutelle group. The initial aim of this thesis was to significantly improve the signal-to-noise ratio and limit of detection of the assay to allow reliable quantification of the analytical data. The first approach was to re-design the electronic instrumentation of the assay. Printed-circuit boards were fabricated and proved very low noise, stable and much smaller than the previous potentiostats. The second approach was to develop generic data processing algorithms to remove three complex types of noise that commonly contaminate analytical signals: spikes, non-stationary ripples and baseline drift. The general strategy consisted in identifying the types of noise, characterising them, and subsequently subtracting them from the otherwise unprocessed data set. Spikes were effectively removed with 96.8% success and ripples were removed with minimal distortion of the signal resulting in an increased signal-to-noise ratio by up to 250%. This allowed reliable quantification of traces from ten patients monitored with the online microdialysis assay. Ninety-six spontaneous metabolic events in response to spreading depolarizations were resolved. These were characterized by a fall in glucose by -32.0 μM and a rise in lactate by +23.1 μM (median values) for over a 20-minute time-period. With frequently repeating events, this led to a progressive depletion of brain glucose. Finally, to improve the temporal coupling between the metabolic data and the electro-cortical signals, a flow-cell was engineered to integrate a potassium selective electrode into the microdialysate flow stream. With good stability over hours of continuous use and a 90% response time of 65 seconds, this flow cell was used for preliminary in vivo experiments the Max Planck Institute in Cologne

Optimal operation and design of modular multilevel converter for HVDC applications

Modular Multilevel Converters (MMCs) are a type of Voltage Source Converter (VSC) which have become the preferred topology choice for High Voltage Direct Current (HVDC) applications. Compare to its HVDC converter predecessors, such as the Line Commutated Converter (LCC), the MMC can control active and reactive power independently, requires smaller filter reactors and have blackstart capabilities. Regarding classical two- and three-level VSCs, the MMC has improved efficiency, easier scalability to higher voltage levels and better AC output voltage harmonic content. However, they need more complex regulation strategy due to its increased number of degrees of freedom (DOFs). Nevertheless, when these DOFs are fully exploited, the MMC can provide better responses than classical converters, especially during unbalanced network conditions. First, an in-depth steady-state mathematical analysis of the converter is performed to identify all its DOFs. Based on the DOFs and the currents imposed by them, the equations for the power transfer between the DC/AC networks and internally, between the upper and lower arms and among the phase-legs, are obtained. The resultant expressions indicate potential interactions between distinct DOFs. By taking advantage of those interactions, it is possible to improve existing circulating current reference calculation methods. Thus, enhancing the MMC response under balanced and unbalanced AC network conditions. The performance of the MMC can be further improved when optimization algorithms are used to calculate its references, in which this thesis proposed two different methods. In the initial proposal, an optimization-based current reference calculation in the natural $abc$ reference frame is presented. It considers the Transmission System Operator (TSO) requirements during AC network voltage sags in the form of active/reactive current set-points to provide Fault Ride Through (FRT) capability and the converter limitations. However, due its highly nonlinear characteristics it presents a high computation burden not allowing it to be solved in real-time applications. To cope with this issue, a second method is introduced whereby modifications are performed in the previous optimization formulation and linearization techniques are employed. The resultant linearized optimization-based reference calculation is then integrated with an energy-based control for MMCs and different case studies are analyzed to validate its performance compared to classical approaches. Finally, an optimization-based methodology to design the submodule (SM) capacitors is proposed. The algorithm considers all the DOFs of the MMC in order to size the SM capacitor while meeting the TSO's requirements and the converter's design limitations. The suggested method is compared with classical approaches for different operating points, and it is further exploited by considering AC network voltage sag conditions.Els convertidors multinivells modulars (MMC) són un tipus de convertidor de font de tensió (VSC) que s'han convertit en l'opció de topologia preferida per a les aplicacions de corrent continu d'alta tensió (HVDC). En comparació amb els seus predecessors convertidors HVDC, com ara el convertidor de commutació de línia (LCC), l'MMC pot controlar la potència activa i reactiva de manera independent, requereix reactors de filtre més petits i té capacitats d'arrencada en negre. Pel que fa als VSC clássics de dos i tres nivells, l'MMC té una eficiència millorada, una escalabilitat més fàcil a nivells de tensió més alts i un millor contingut harmònic de voltatge CA. Tanmateix, necessiten una estratègia de regulació mès complexa a causa del seu major nombre de graus de llibertat (DOF). No obstant això, quan aquests DOFs exploten completament, l'MMC pot proporcionar millors respostes que els convertidors clàssics, especialment en condicions de xarxa desequilibrades. En primer lloc, es realitza una anàlisi matemàtica en estat estacionari en profunditat del convertidor per identificar tots els seus DOF. A partir dels DOF i dels corrents imposats per aquests, s'obtenen les equacions de la transferència de potència entre les xarxes DC/AC i la transferència de potència interna, entre els braços superior i inferior i entre les potes de fase. Les expressions resultants indiquen interaccions potencials entre diferents DOF. Aprofitant aquestes interaccions, és possible millorar el mètode de càlcul de referència de corrent circulant existent. En fer-ho, es pot millorar el rendiment de l'MMC en condicions desequilibrades i amb errors. El rendiment de l'MMC es pot millorar encara més quan s'utilitzen algorismes d'optimització per calcular les seves referències. A la proposta inicial, es presenta un càlcul de referència actual basat en l'optimització en el marc de referència natural abc. Considera els requisits de l'operador del sistema de transmissió (TSO) durant les caigudes de tensió de la xarxa de CA en forma de punts de consigna de corrent actiu/reactiu per proporcionar la capacitat de transmissió de fallades (FRT) i les limitacions del convertidor. Tanmateix, a causa de les seves característiques altament no lineals, presenta una gran càrrega de càlcul que no permet resoldre'l en aplicacions en temps real. Per fer front a aquest problema, es realitzen modificacions en la seva formulació i s'utilitzen técniques de linealització. A continuació, el càlcul de referència basat en l'optimització linealitzada resultant s'integra amb un control basat en energia per a MMC i s'analitzen diferents casos pràctics per validar el seu rendiment en comparació amb els enfocaments clàssics. Finalment, es proposa una metodologia basada en l'optimització per dissenyar els condensadors de submòduls (SM). L'algorisme considera tots els DOF de l'MMC per tal de dimensionar el condensador SM alhora que compleix els requisits del TSO i les limitacions de disseny del convertidor. El mètode suggerit es compara amb els enfocaments clàssics per a diferents punts de funcionament, i s'aprofita encara més tenint en compte les condicions de caiguda de la tensió de la xarxa de CA.Postprint (published version

Leveraging Structural Health Monitoring Data Through Avatars to Extend the Service Life of Mass Timber Buildings

Mass timber construction systems, incorporating engineered wood products as structural elements, are gaining acceptance as a sustainable alternative to multi-story concrete or steel-frame structures. The relative novelty of these systems brings uncertainties on whether these buildings perform long-term as expected. Consequently, several structural health monitoring (SHM) projects have recently emerged to document their behavior. A wide and systematic use of this data by the mass timber industry is currently hindered by limitations of SHM programs. These limitations include scalability, difficulty of data integration, diverse strategies for data collection, scarcity of relevant data, complexity of data analysis, and limited usability of predictive tools. This perspective paper envisions the use of avatars as a Web-based layer on top of sensing devices to support SHM data and protocol interoperability, analysis, and reasoning capability and to improve life cycle management of mass timber buildings. The proposed approach supports robustness, high level and large-scale interoperability and data processing by leveraging the Web protocol stack, overcoming many limitations of conventional centralized SHM systems. The design of avatars is applied in an exemplary scenario of hygrothermal data reconstruction, and use of this data to compare different mold growth prediction models. The proposed approach demonstrates the ability of avatars to efficiently filter and enrich data from heterogeneous sensors, thus overcoming problems due to data gaps or insufficient spatial distribution of sensors. In addition, the designed avatars can provide prediction or reasoning capability about the building, thus acting as a digital twin solution to support building lifecycle management

Transformation of Multidirectional Sea Field and Computational Study

A computational model based on the evolution equation for water waves (Li, 1994b) derived from the original Berkhoffs (1972) "Mild Slope Equation" is tested against multidirectional sea data. The model accounts for reflection as well as diffraction-refraction processes, which is important for applications involving coastal structures. The accuracy and convergence of the numerical solution, as well as the possibility of the implementation of an adaptive numerical scheme are investigated and implemented. The model was firstly tested using laboratory measurements (Briggs et al, 1995) of random directional wave diffraction around a semi-infinite breakwater on a flat bottom. These tests confirm the need to use "directional modelling" (using the principle of linear superposition) for the prediction of wave heights behind the breakwater. The model was then tested using directional wave data records, which were chosen from 4500 wave records collected in the field campaign, by the University of Plymouth and the University of Brighton, at Elmer - Sussex, UK from September 1993 - January 1995. The results showed that the representation of the measured random sea by monochromatic wave runs can introduce a significant error in wave height predictions shoreward of the breakwaters in the diffraction region, thus confirming the importance of directional modelling for random wave simulation. Evidence strongly suggests that non-linear wave effects have a significant influence (40-60%) on the accuracy of the model. Consequently, further tests are needed, which should also consider the influence of wave-current interaction, wave breaking, bed fiiction and transmissive boundaries. Over all the model predictions are more accurate for the controlled environment in the laboratory (5-13%), than for field conditions where the directional modelling accuracy varied from 8 - 32%. A summary of the data, collected by the author as a member of the University of Plymouth Research Team and a database of spectral and directional parameters is also presented in this thesis. Field validation of the numerical model required accurate estimates of measured data. Emphasis was placed on identifying a suitable directional analysis method, which accurately predicted direction and directional spread in the far-field from structures where reflection is still present. The non-phase-locked (hfPL) methods developed for a homogeneous sea are found to be appropriate. The anzdysis of two NPL methods, the Maximum Likelihood Method (MLM) and Bayesian Directional Method (BDM), directional estimates for simulated data shows that both methods can predict accurate incident wave height and direction. Both methods tend to overpredict directional spread and give non-accurate reflection estimates. The MLM method is easier to implement than the BDM method, which is sensitive to the chosen starting value of the hyperparameter u. As the difference between estimates of the two methods for numerical data is small, the MLM method's estimates were chosen for model testing

Common-mode voltage cancellation in single- and three-phase transformer-less PV power converters

Electrical Energy generation is an issue that is continuously cause of concern around the world. Many efforts have been done in this sense to cover the requirements of the constantly growing in the electrical energy demand. But not only the electrical energy demand is growing but also clean electrical energy demand. In this sense, many countries are taking advantage from the renewable energy generation systems, considering mainly wind and solar energy. Solar energy systems provide a high percentage of the total energy production, according with the latest report of the International Energy Agency (IEA) regarding Photovoltaic Power System Program (PVPS), the cumulative installed PV power at the end of 2009 it was around 20.3 GW out of which 6.188 GW were installed in 2009. From the total PV power installed in 2009, 6.113 are grid connected systems. The growing of the PV systems is due to the new technologies and developments that have permitted to reduce costs in the total design and installation of a PV source. As the major percentage of the total PV energy installed is from grid connected systems, this thesis work deals with the analysis and proposals in the transformerless grid-connected PV systems which can provide higher efficiencies regarding PV system with transformer. In this sense, when there is not transformer between the electrical grid and the power converter, a problem regarding leakage ground currents appears, this is the main issue in this thesis work. The main research task in this thesis work is to analyze and evaluate the operation of the different transformerless topologies presented in the bibliography and then to provide some solutions to minimize the leakage ground current phenomenon in order to comply with the standard requirements