Program and Abstracts of the Annual Meeting of the Georgia Academy of Science, 2009

The annual meeting of the Georgia Academy of Science took place April 3-4, 2009, at Spelman College, Atlanta, Georgia. Presentations were provided by members of the Academy who represented the following sections: I. Biological Sciences II Chemistry III. Earth & Atmospheric Sciences IV. Physics, Mathematics, Computer Science, Engineering & Technology V. Biomedical Sciences VI. Philosophy & History of Science VII. Science Education VIII. Anthropology

A two-dimensional, non-equilibrium numerical model of an alkali seeded hydrogen arcjet thruster

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1998.Includes bibliographical references (p. 158-162).by Darrel Kim Robertson.M.S

Radiometric impact assessments and shielding of CubeSat class satellites in interaction with orbital radiation fields and representativity of the calibration procedure and radiation damage tests in the ground facility

Using FLUKA and MCNP Monte Carlo nuclear particle transport codes, support for radiation shielding design and assessing damage to aerospace components and systems has been developed. To this aim, many comparisons between the simulation of irradiation of aerospace components and systems with accelerators, nuclear research reactors, and spontaneous decay sources with the orbital sources were obtained from the design of a CubeSat mission

Selvitys käytännönläheisistä kuumalämpöpumpputekniikoista ja käyttökohteista tarkoituksena kierrättää energiaa

The objective of this thesis was to find out practical high temperature heat pump (HTHP) technologies and potential applications for heat sinks at least up to 100 °C within a heating capacity range of 50…1000 kW along with to find out the profitability of HTHPs. A literature survey was executed to find out the technologies and applications. The survey was focusing on both the state-of-the-art research and practices. The profitability was found out via a Finnish case study. According to the survey, there are at least 32 commercialized HTHP models currently from which several can produce heat sinks of at least 100 °C. Several industrial sectors have some processes whose heat demand could be supplied with HTHPs that can produce heat sinks up to 100 °C. In addition, current district heating networks are a promising application for HTHPs since the heat demand is generally at temperatures below 100 °C. According to the survey, the refrigerant, the compressor and the cycle configuration are the most critical considerations as for HTHPs. There is both scientific and practical evidence on that the HTHP technology exists for heat sinks of at least 100 °C, even up to around 165 °C. The refrigerant should be selected such that its critical temperature is at least 10…15 °C higher than that of the condensation temperature and the vapor pressures should be such that the compressor can withstand those, both at the suction and at the discharge. In principle, the refrigerant selection determines the higher temperature limit that could be supplied with a HTHP, at least up to 165 °C. If considering higher temperatures, the maximum compressor discharge temperature of around 180 °C seems to be a limiting factor that is a technological challenge. In outline, the temperature difference between the condensation and evaporation temperatures (temperature lift) determine whether to use a single-stage or a two-stage compression. As for most of suitable refrigerants, the use of an internal heat exchanger (IHX) is suggested to provide the minimum superheat and to increase both the coefficient of performance and the volumetric heating capacity at least up to 20 % along with this improvement is the same in the operational emissions and the energy efficiency. In general, temperature lifts up to 60 °C can be feasible with the single-stage compression. Higher temperature lifts, up to even 120 °C, should be implemented with the two-stage compression to avoid a decrease in the performance. In addition, the two-stage compression can be used to limit the discharge temperature that is especially important as for some refrigerants along with when using the IHX. According to the conditions of the case study, HTHPs can be currently on average around 4.5 times more environmentally friendly and around 1.5…5.5 times more energy efficient when compared to the Finnish average district heating. As for the case study, the HTHPs are economically profitable as well because the simple payback period was estimated to be around two years. However, the profitability is highly sensitive with respect to the source information.Työn tavoitteena oli selvittää käytännönläheisiä kuumalämpöpumppu (HTHP) tekniikoita ja niiden mahdollisia käyttökohteita lämpötiloissa ainakin 100 °C saakka lämmitystehoalueella 50…1000 kW sekä selvittää HTHP:jen kannattavuutta. Tekniikat ja käyttökohteet selvitettiin kirjallisuusselvityksellä. Selvitys keskittyi sekä tuoreimpaan tutkimukseen että käytäntöihin. Kannattavuutta selvitettiin Suomalaisen tapaustutkimuksen avulla. Selvityksen perusteella, kaupallisia HTHP malleja on ainakin 32 kappaletta, joista useat voivat tuottaa ainakin 100 °C lämpötilaa. Useissa teollisuuden sektoreissa on prosesseja, joiden lämmöntarvetta voitaisiin kattaa lämpötiloja 100 °C saakka tuottavilla HTHP:illa. Lisäksi, nykyiset kaukolämpöverkot ovat lupaava käyttökohde HTHP:ille, koska lämmöntarve on yleisesti alle 100 °C lämpötiloissa. Selvityksen perusteella, kylmäaine, kompressori ja kiertoprosessin kokoonpano ovat kriittisimmät huomioonotettavat seikat HTHP:illa. On sekä tieteellisiä ja käytännöllisiä merkkejä siitä, että HTHP-tekniikka on olemassa ainakin 100 °C lämpötiloille, jopa 165 °C lämpötiloihin saakka. Kylmäaine tulisi valita siten, että sen kriittinen lämpötila on vähintään 10…15 °C lauhtumislämpötilaa korkeampi ja höyrynpaineet pitäisivät olla sellaiset, että kompressori voi kestää ne, sekä imu- että painepuolella. Periaatteessa, kylmäainevalinta määrittelee korkeimman lämpötilan, jota voidaan tuottaa HTHP:lla, ainakin lämpötilaan 165 °C saakka. Korkeampien lämpötilojen suhteen, kompressorin suurin sallittu lämpötila (kuumakaasu), noin 180 °C, näyttäisi olevan rajoittava tekijä ollen kompressoritekninen haaste. Pääpiirteissään, lauhtumis- ja höyrystymislämpötilojen ero (lämpötilan nousu) määrittelee sen, että tulisiko käyttää yksi- vai kaksiasteista puristusta. Useimpien kylmäaineiden tapauksessa, sisäisen lämmönsiirtimen (IHX) käyttö on suositeltavaa minimitulistuksen tuottajaksi sekä, koska lämpökerroin ja lämmityksen tilavuustuotto voivat parantua ainakin 20 %. IHX parantaa saman verran HTHP:jen ympäristöystävällisyyttä ja energiatehokkuutta. Yleistäen, lämpötilan nousut 60 °C saakka voivat olla toteuttamiskelpoisia yksiasteisella puristuksella. Korkeammat lämpötilan nousut, jopa 120 °C saakka, pitäisi toteuttaa kaksiasteisella puristuksella välttääkseen suorituskyvyn heikkenemistä. Lisäksi, kaksiasteista puristusta voidaan käyttää alentamaan kuumakaasun lämpötilaa ollen erityisen tärkeää muutamien kylmäaineiden tapauksessa sekä käytettäessä IHX. Tapaustutkimuksen olosuhteiden mukaan, HTHP:t voivat olla tällä hetkellä keskimäärin 4,5 kertaa ympäristöystävällisempiä ja noin 1,5…5,5 kertaa energiatehokkaampia Suomalaiseen keskinkertaiseen kaukolämmitykseen verrattuna. Tapaustutkimuksen tapauksessa, HTHP:t ovat myös taloudellisesti kannattavia, koska investoinnin koroton takaisinmaksuaika olisi arviolta noin kaksi vuotta. Kuitenkin, kannattavuus on erittäin herkkä lähtötietojen suhteen

Performance analysis and dynamics of innovative SOFC hybrid systems based on turbocharger-derived machinery

La crescente consapevolezza su temi quali il cambiamento climatico e l\u2019inquinamento atmosferico ha portato a politiche nazionali ed internazionali mirate allo sviluppo di sistemi energetici innovativi e sostenibili. Tra di essi, le fuel cell sono uno dei pi\uf9 promettenti, essendo caratterizzate da alte efficienze e basse emissioni. In particolare, i sistemi ibridi basati sull\u2019integrazione di fuel cell ad alta temperatura con dispositivi derivati da turbocompressori hanno attirato l\u2019attenzione del mondo accademico e dell\u2019industria negli ultimi decenni. Tuttavia, la complessit\ue0, la fragilit\ue0 e l\u2019alto costo di questi impianti ha rallentato il loro sviluppo, e solo poche grandi aziende sono state in grado di realizzare prototipi completi. Le difficolt\ue0 tecniche affrontate dalla comunit\ue0 scientifica hanno messo in luce l\u2019importanza delle simulazioni per progettare, testare, controllare e analizzare i sistemi ibridi a fuel cell. Sulla base di tale esperienza, questa tesi mira ad espandere la attuale conoscenza sui sistemi ibridi a fuel cell a ossidi solidi, ponendo una particolare attenzione su un innovativo sistema turbocompresso di piccola taglia, alimentato con biogas e recentemente introdotto all\u2019interno del progetto europeo Bio-HyPP. Lo scopo principale della tesi \ue8 determinare se questo tipo di sistema possa essere una valida alternativa ai sistemi basati su microturbine a gas, analizzando il suo comportamento in relazione a diversi scenari, sia stazionari, sia transitori. Per fare ci\uf2, \ue8 necessario definire i vincoli operativi del sistema e sviluppare un sistema di controllo in grado di rispettarli, ottimizzando al tempo stesso le prestazioni dell\u2019impianto. Inoltre, l\u2019affidabilit\ue0 dei sistemi ibridi pu\uf2 essere migliorata grazie all\u2019implementazione di strumenti diagnostici e di procedure per prevenire il pompaggio del compressore. La parte finale della tesi \ue8 mirata allo studio di tali strumenti, al loro sviluppo e alla loro integrazione con il sistema di controllo. Tutte le attivit\ue0 presentate in questa tesi sono state svolte facendo affidamento su strumenti di simulazione. Ci\uf2 \ue8 stato possibile grazie alla collaborazione tra il Laboratorio di Matematica Applicata, Simulazione e Modellistica Matematica e il Thermochemical Power Group dell\u2019Universit\ue0 degli Studi di Genova. Dopo aver presentato il layout del sistema a fuel cell con turbocompressore, un dettagliato modello stazionario dell\u2019impianto sviluppato in Matlab\uae-Simulink\uae \ue8 stato utilizzato per progettare una strategia, basata sul controllo di valvole installate sull\u2019impianto, in grado di rispettare tutti i suoi vincoli operativi. Successivamente, \ue8 stata svolta un\u2019analisi di prestazioni in off-design, considerando allo stesso tempo diverse condizioni di carico di potenza e di temperatura ambiente. Tale analisi \ue8 stata utilizzata per confermare l\u2019efficacia della strategia di controllo proposta, e per valutare le capacit\ue0 del sistema con turbocompressore. Successivamente \ue8 stato creato un modello dinamico utilizzando lo strumento TRANSEO, in modo da studiare il comportamento del sistema durante i transitori. Avendo adottato una strategia di controllo basata sulla valvola di cold bypass, \ue8 stata analizzata la risposta del sistema ad una sua apertura a gradino, al fine di progettare un sistema di controllo efficace e reattivo, in grado di mantenere la massima temperatura di cella costante e, allo stesso tempo, di rispettare i vincoli del sistema. Sono stati progettati quattro diversi controllori, che successivamente sono stati testati su due diversi scenari di variazione di carico e confrontati sulla base di vari parametri operativi. La parte finale della tesi ha riguardato lo sviluppo di innovativi strumenti che possano aumentare l\u2019affidabilit\ue0 dei sistemi ibridi a fuel cell a ossidi solidi, in particolare tecniche di prevenzione del pompaggio e sistemi di diagnostica basati su reti Bayesiane. Un modello semplificato del sistema con turbocompressore \ue8 stato sviluppato in TRANSEO e sono state testate diverse tecniche di prevenzione del pompaggio: condizionamento del flusso d\u2019aria, iniezione di acqua, ricircolo e bleed, installazione di un eiettore all\u2019imbocco del compressore. Le soluzioni pi\uf9 efficaci sono state integrate con il controllore del sistema ibrido e sono state testate durante un transitorio per evitare che il punto operativo del compressore si avvicinasse al pompaggio. Infine, grazie ad una collaborazione tra l\u2019Universit\ue0 degli Studi di Genova e la M\ue4lardalens H\uf6gskola di V\ue4ster\ue5s, in Svezia, sono state sviluppate delle reti Bayesiane per la diagnostica di sistemi ibridi a fuel cell a ossidi solidi con microturbina a gas. Questa attivit\ue0 \ue8 stata svolta simulando il sistema su Matlab\uae-Simulink\uae e creando le reti Bayesiane su Hugin Expert. Due sistemi di diagnostica, uno per la microturbina e uno per la fuel cell, sono stati sviluppati e testati in condizioni stazionarie. Il secondo \ue8 stato anche testato in condizioni dinamiche e integrato con il sistema di controllo per prevenire l\u2019usura della cella. In conclusione, questa tesi ha messo in luce il grande potenziale dei sistemi ibridi SOFC-turbocompressore, mostrando la loro alta efficienza in un ampio intervallo di condizioni operative in termini di carico elettrico e temperatura ambiente. La tesi ha anche dimostrato che \ue8 possibile garantire il corretto funzionamento di questi sistemi durante diversi scenari transitori, implementando controllori a cascata progettati per agire sulla valvola di bypass freddo per controllare la massima temperatura della cella. Per quanto riguarda la possibilit\ue0 di migliorare l\u2019affidabilit\ue0 di tali sistemi, le tecniche basate sul ricircolo del compressore sono risultate essere le pi\uf9 efficaci per allontanare il sistema da una condizione di pompaggio. I risultati delle simulazioni mostrano come la loro integrazione con strumenti di monitoraggio possa prevenire diverse situazioni di pericolo. La parte finale della tesi ha mostrato come il deterioramento dei sistemi ibridi a SOFC possa essere limitato grazie a reti Bayesiane, che sono state utilizzate per diagnosticare accuratamente le condizioni di un sistema SOFC-microturbina a gas, ma potrebbero ugualmente essere applicate su impianti con turbocompressore.The growing awareness on climate change and pollution has brought to national and international policies aimed at promoting the development of innovative and environmentally sustainable energy systems. Among these systems, fuel cells are one of the most promising technologies, characterized by high energy conversion efficiencies and low emissions. In particular, hybrid systems based on the integration of a high temperature fuel cell with turbocharger-derived machinery have drawn the interest of academia and industry over the past decades. However, the complexity, fragility and high cost of these plants have slowed down their development, and only a few big companies were able to build complete prototypes. The technological challenges faced by the scientific community have highlighted the importance of simulations to design, test, control and analyse fuel cell hybrid systems. Based on this experience, this thesis wants to expand the current knowledge on solid oxide fuel cell hybrid systems, with a particular focus on an innovative small-scale biofueled turbocharged layout, which was introduced recently within the Bio-HyPP European project. The main goal of this thesis is to determine if this kind of system can be a viable alternative to micro gas turbine-based systems, analysing its steady-state and transient behaviour in various operating conditions. To do this, it is necessary to define the system operative constraints, and to develop a control system capable of ensuring their compliance, while optimizing the plant performance. The possibility of increasing the reliability of solid oxide fuel cell hybrid systems is finally investigated, considering the implementation of surge prevention techniques and diagnostic tools. All these activities strongly relying on simulation tools. This was possible thanks to the collaboration between the Laboratory of Applied Mathematics, Simulation and Mathematical Modelling with the Thermochemical Power Group of the University of Genoa. After introducing the layout of the turbocharged fuel cell system, a detailed steady-state model of the plant is developed in Matlab\uae-Simulink\uae and used to design a strategy, based on the control of valves installed on the plant, able to comply with its many operative constraints. Then, an off-design performance analysis of the system is performed, considering simultaneously various conditions of power load and ambient temperature. This analysis is used to confirm the effectiveness of the proposed control strategy and to assess the capabilities of the turbocharged system. A dynamic model is created using the TRANSEO tool to study the transient behaviour of the system. Having adopted a control strategy based on the cold bypass valve, the response of the system to a valve opening step change is analysed in order to design an effective and responsive control system, able to keep the fuel cell maximum temperature constant while complying with the system constraints. Four different controllers are designed, tested on two different load variation scenarios and compared on the basis of many parameters. The final part of the thesis regards the development of innovative tools aimed at improving the reliability of solid oxide fuel cell hybrid system, in particular surge prevention techniques and Bayesian belief network-based diagnosis systems. A simplified dynamic model of the turbocharged SOFC system is developed in TRANSEO, and various surge prevention techniques are tested on it: intake air conditioning, water spray at compressor inlet, air bleed and recirculation, and installation of an ejector at the compressor intake. The most effective procedures are integrated with the controller of the hybrid system and tested during a transient scenario to prevent the compressor operative point from approaching a surge condition. Bayesian belief networks aimed at diagnosing the status of SOFC hybrid systems are developed thanks to a collaboration between the University of Genoa and the M\ue4lardalens H\uf6gskola of V\ue4ster\ue5s, Sweden. A micro gas turbine \u2013 solid oxide fuel cell system is considered for this study, but the methodology could be easily extended to turbocharged plants. The activity is carried out simulating the system on Matlab\uae-Simulink\uae and designing the Bayesian networks on Hugin Expert. Two different diagnosis systems, one for the turbomachinery and one for the fuel cell stack, are developed and tested on stationary conditions. The second one is also tested during transients and integrated with the control system to prevent degradation of the fuel cells. In conclusion, this thesis highlighted the great potential of turbocharged SOFC hybrid systems, showing high energy conversion efficiencies in a wide operative range in terms of load and ambient conditions. It also showed that the proper operation of the system is possible during various transient scenarios, implementing cascade controllers designed to act on a cold bypass valve to control the SOFC maximum temperature. Regarding the possibility of improving the reliability of these systems, surge prevention techniques based on compressor recirculation appeared as the most effective ones. Simulation results suggest that their integration with a surge precursors detection tool could avoid the occurrence of many potentially dangerous scenarios. The final part of this thesis showed that the durability of SOFC hybrid systems could be further improved thanks to Bayesian belief networks, which were proved to effectively diagnose the status of SOFC-MGT systems but could be applied to turbocharged plants as well

Applications of reprogrammability in algorithm acceleration

This doctoral thesis consists of an introductory part and eight appended publications, which deal with hardware-based reprogrammability in algorithm acceleration with a specific emphasis on the possibilities offered by modern large-scale Field Programmable Gate Arrays (FPGAs) in computationally demanding applications. The historical evolution of both the theoretical and technological paths culminating in the introduction of reprogrammable logic devices is first outlined. This is followed by defining the commonly used terms in the thesis. The reprogrammable logic market is surveyed, and the architectural structures and the technological reasonings behind them are described in detail. As reprogrammable logic lies between Application Specific Integrated Circuits (ASICs) and general-purpose microprocessors in the implementation spectrum of electronics systems, special attention has been paid to differentiate these three implementation approaches. This has been done to emphasize, that reprogrammable logic offers much more than just a low-volume replacement for ASICs. Design systems for reprogrammable logic are investigated, as the learning curve associated with them is the main hurdle for software-oriented designers for using reprogrammable logic devices. The theoretically important topic of partial reprogrammability is described in detail, but it is concluded, that the practical problems in designing viable development platforms for partially reprogrammable systems will hinder its wide-spread adoption. The main technical, design-oriented, and economic applicability factors of reprogrammable logic are laid out. The main advantages of reprogrammable logic are their suitability for fine-grained bit-level parallelizable computing with a short time-to-market and low upfront costs. It is also concluded, that the main opportunities for reprogrammable logic lie in the potential of high-level design systems, and the ever-growing ASIC design gap. On the other hand, most power-conscious mass-market portable products do not seem to offer major new market potential for reprogrammable logic. The appended publications are examined and compared to contemporaneous research at other research institutions. The conclusion is that for relatively wide classes of well-defined computation problems, reprogrammable logic offers a more efficient solution than a software-centered approach, with a much shorter production cycle than is the case with ASICs.reviewe

Proceedings of the Scientific-Practical Conference "Research and Development - 2016"

talent management; sensor arrays; automatic speech recognition; dry separation technology; oil production; oil waste; laser technolog