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Tan, Wee Choon. "Numerical Investigation of Ammonia-fueled Planar SOFC Stack－Internal and External Cooling Effects." Kyoto University, 2018. http://hdl.handle.net/2433/235990.
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Marra, Dario. "Development of solid oxide fuel cell stack models for monitoring, diagnosis and control applications." Doctoral thesis, Universita degli studi di Salerno, 2013. http://hdl.handle.net/10556/1014.
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2011 - 2012In the present thesis different SOFC stack models have been presented. The results shown were obtained in the general framework of the GENIUS project (GEneric diagNosis Instrument for SOFC systems), funded by the European Union (grant agreement n° 245128). The objective of the project is to develop “generic” diagnostic tools and methodologies for SOFC systems. The “generic” term refers to the flexibility of diagnosis tools to be adapted to different SOFC systems. In order to achieve the target of the project and to develop stack models suitable for monitoring, control and diagnosis applications for SOFC systems, different modeling approaches have been proposed. Particular attention was given to their implementability into computational tools for on-board use. In this thesis one-dimensional (1-D), grey-box and blackbox stack models, both stationary and dynamic were developed. The models were validated with experimental data provided by European partners in the frame of the GENIUS project. A 1-D stationary model of a planar SOFC in co-flow and counter-flow configurations was presented. The model was developed starting from a 1- D model proposed by the University of Salerno for co-flow configuration (Sorrentino, 2006). The model was cross-validated with similar models developed by the University of Genoa and by the institute VTT. The crossvalidation results underlined the suitability of the 1-D model developed. A possible application of the 1-D model for the estimation of stack degradation was presented. The results confirmed the possibility to implement such a model for fault detection. A lumped gray-box model for the simulation of TOPSOE stack thermal dynamics was developed for the SOFC stack of TOPSOE, whose experimental data were made available in the frame of the GENIUS project. Particular attention was given to the problem of heat flows between stack and surrounding and a dedicated model was proposed. The black-box approach followed for the implementation of the heat flows and its reliability and accuracy was shown to be satisfactory for the purpose of its applications. The procedure adopted turned out to be fast and applicable to other SOFC stacks with different geometries and materials. The good results obtained and the limited calculation time make this model suitable for implementation in diagnostic tools. Another field of application is that of virtual sensors for stack temperature control. Black-box models for SOFC stack were also developed. In particular, a stationary Neural Network for the simulation of the HEXIS stack voltage was developed. The analyzed system was a 5-cells stack operated up to 10 thousand hours at constant load. The neural network exhibited very good prediction accuracy, even for systems with different technology from the one used for training the model. Beyond showing excellent prediction capabilities, the NN ensured high accuracy in well reproducing evolution of degradation in SOFC stacks, especially thanks to the inclusion of time among model inputs. Moreover, a Recurrent Neural Network for dynamic simulation of TOPSOE stack voltage and a similar one for a short stack built by HTc and tested by VTT were developed. The stacks analyzed were: a planar co-flow SOFC stack (TOPSOE) and a planar counter-flow SOFC stack (VTT-HTc). All models developed in this thesis have shown high accuracy and computation times that allow them to be implemented into diagnostic and control tool both for off-line (1-D model and grey-box) and for on-line (NN and RNNs) applications. It is important noting that the models were developed with reference to stacks produced by different companies. This allowed the evaluation of different SOFC technologies, thus obtaining useful information in the models development. The information underlined the critical aspects of these systems with regard to the measurements and control of some system variables, giving indications for the stack models development. The proposed modeling approaches are good candidates to address emerging needs in fuel cell development and on-field deployment, such as the opportunity of developing versatile model-based tools capable to be generic enough for real-time control and diagnosis of different fuel cell systems typologies, technologies and power scales. [edited by author]
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Al-Masri, Ali [Verfasser], Detlef [Akademischer Betreuer] Stolten, and Wilfried [Akademischer Betreuer] Becker. "Numerische Modellierung der thermomechanischen Fluid-Struktur-Interaktion im SOFC-Stack / Ali Al-Masri ; Detlef Stolten, Wilfried Becker." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/113059064X/34.
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BRUNACCINI, GIOVANNI. "Investigation on low and high temperature fuel cell components and their evaluation in short stack configuration." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2010. http://hdl.handle.net/2108/1300.
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La ricerca sulle celle a combustibile ad ossidi solidi (SOFC) ed a membrana ad elettrolita polimerico è attualmente indirizzata al miglioramento delle performance e della loro vita utile, così come alla riduzione dei costi. Tali aspetti sono importanti per rendere questi dispositivi più interessanti per il mercato, sia nelle applicazioni stazionarie che automotive.
Da questo punto di vista, per la tecnologia PEMFC sembra necessario un incremento della temperatura (da 80°C a 110-120°C, high temperature PEMFC o HT-PEMFC).
Ciò porterebbe ad una migliore resistenza alle impurezze di CO nel fuel, un migliore thermal and water management ed una migliore efficienza per la co-generazione.
Al contrario, la tecnologia SOFC va verso temperature intermedie (IT-SOFC); ciò permetterebbe una riduzione dei costi nello sviluppo di celle planari, grazie a processi di fabbricazione meno onerosi ed ad un incremento della stabilità.
Questi modi di estendere l'applicazione sono ben studiati per celle singole, ma il processo di scale-up verso dispositivi di potenza necessita di ulteriori specifici approfondimenti. Inoltre, tecnologie differenti necessitano di procedure di test differenti, adattate a specifici settori applicativi.
In questa tesi di Dottorato, sono stati testati dispositivi a celle a combustibile basati su tecnologia ad ossidi solidi od ad elettrolita polimerico per applicazioni specifiche. In particolare, sono stati studiati stack di fuel cells di potenza nominale pari ad 1kW, per verificare la possibilità dell'utilizzo di fuel cell per applicazioni di piccola taglia.
Attualmente, i dispositivi basati su HT-PEMFC stanno suscitando interesse per lo sviluppo delle celle a combustibile. Nonostante una profonda conoscenza delle proprietà dei materiali, la valutazione degli stessi a livello di stack è stata oggetto di un piccolo numero di studi. In questa attività di ricerca è stato approfondito proprio questo aspetto.
La tecnologia IT-SOFC è considerata adatta per applicazioni stazionarie e per la produzione di energia distribuita, poiché può usare combustibile poco costoso in processi elettrochimici ad elevata efficienza. Inoltre, per applicazioni relative ad utenze residenziali, i dispositivi studiati possono essere considerati come la base per lo sviluppo di un sistema turn-key e non come la versione downscaled per studi da laboratorio.
Questa tesi di Dottorato include considerazioni per applicazioni sia stazionarie che automotive, analizzando stack di fuel cells di potenza sufficiente per essere considerati come proof-of-concept. In altre parole, la potenza è sufficiente per studiare i principali fenomeni che appaiono in stack di dimensioni superiori orientate ad applicazioni pratiche.
L'intera attività può essere suddivisa in due parti:
1) test di short stack HT-PEMFC per la valutazione delle performance in condizioni tipiche del settore automovtive (corrente, temperatura, umidificazione, pressione) e per individuare il punto di lavoro ottimale;
2) test di stack IT-SOFC in gas naturale per valutare la perdita di prestazioni per fenomeni legati a cicli redox che possono avvenire durante l'uso reale.
Tecniche di diagnosi, come il metodo di interruzione di corrente e la spettrocopia d'impedenza hanno completato lo studio fornendo informazioni circa l'ottimizzazione dell'assemblaggio degli stack.
La sperimentazione è stata interamente condotta in laboratorio, per controllare in maniera accurata le variabili di processo; nonostante ciò, le prestazioni ottenute sono comunque utili per applicazioni concrete, una volta che siano state definite condizioni di lavoro appropriate come compromesso tra prestazioni e costi.Research activities on solid oxide (SOFC) or polymer electrolyte membrane (PEMFC) fuel cells are currently focused on performance and lifetime enhancement as well as costs reduction. These aspects are relevant to make such systems more attractive for the market, both for stationary and automotive applications. From this point of view, an increase of temperature (from 80°C to 110-120°C) appears necessary for PEMFC technology (high temperature PEMFC, or HTPEMFC). This would allow more resistance to CO contaminants in the fuel, better thermal and water management and a better efficiency for co-generation. On the contrary, SOFC technology is moving towards intermediate temperature (IT-SOFC); this would allow cost reduction while developing planar cells, due to less critical construction processes and an increase of stability. These ways to enhance the fuel cells applications are well studied for single cell but the scale-up process to significant power production devices needs specific investigations. Moreover, different technologies need different field test procedures, tailored on the specific application sectors. In this Ph.D. thesis, fuel cell devices exploiting either solid oxide or polymer electrolyte technologies, were tested for specific applications. In particular, 1kW fuel cell stacks were tested in order to verify the possibility of fuel cell use in small size applications. Nowadays, HT-PEMFC devices are creating lot of interest for FC technology development. Anyway, despite a deep knowledge of material properties, the assessment of the new materials at stack level have undergone only few studies. In this research activity this aspect was investigated. Moreover, IT-SOFC technology is considered valuable for stationary applications and distributed energy production, using cheap fuels and a highly efficient electrochemical process. Nevertheless, for residential energy consumption, the studied SOFC device can be considered not as a downscaled device for laboratory study, but as the base to develop a complete system. This Ph.D. thesis involves considerations for both stationary and automotive applications, by analysing fuel cells stack with a size large enough to be considered a proof-of-concept. In other words, the size appears sufficient to investigate main phenomena visible in larger stack oriented to real world applications. The whole activity can be divided in two lines: 1) tests of HT-PEMFC short stacks that were carried out to evaluate their performance in typical automotive working conditions (current, temperature, humidification, pressure) and to establish an optimal operating point. 2) tests of IT-SOFC stacks in natural gas, in order to evaluate performance decay and its response to detrimental effects due to thermal and redox cycles that can appear in "out of laboratory" usage. Diagnostic analysis such as current interrupt method and electrochemical impedance spectroscopy completed the study by supplying information about the optimization of stack assembling procedure. The whole experimental activities were carried out in laboratory, to accurately control the process variables; nevertheless, the recorded performances are anyway meaningful with respect to real world applications, once defined tailored working conditions by a good compromise between performances and costs.
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Allen, Jeremy L. "The Effect of Baffle Arrangements on Flow Uniformity in a Manifold for a Unique Solid Oxide Fuel Cell Stack Design." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1320851931.
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Sivasankaran, Visweshwar. "Manufacturing and characterization of single cell intermediate-temperature solid oxide fuel cells for APU in transportation application." Thesis, Dijon, 2014. http://www.theses.fr/2014DIJOS027/document.
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La fabrication de cellules de piles à combustible IT-SOFC de large dimension par un nouveau procédé simple et peu coûteux est présentée dans ce manuscrit. L’optimisation de ce nouveau procédé en regard de l’utilisation d’agents de porosité, d’épaisseur de couches et de température de frittage a été réalisée. Les résultats des tests électrochimiques sur des cellules de surface active 10 cm2 réalisés dans le dispositif Fiaxell semi-ouvert ont été détaillés pour différentes cellules. Des tests de performance de longue durée ont également été menés sur le dispositif Fiaxell, présentés et discutés. La préparation et la réalisation d’un nouveau banc de test de stack a également été mené et présenté dans ces travauxThe fabrications of large area IT-SOFC planar cell by new simple and cost effective process were explained. The optimization of the new process with respect to pore formers, thickness of layers, sintering temperature were performed. The electrochemical results of 10cm2 performed in Fiaxell open flange set up were detailed with respect to different configuration. Long term ageing performance tests of single cells were conducted in Fiaxell device and results are discussed. Preparation of new test bench and stacking process performed till now were briefed
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Price, Robert. "Metal/metal oxide co-impregnated lanthanum strontium calcium titanate anodes for solid oxide fuel cells." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16018.
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Solid Oxide Fuel Cells (SOFC) are electrochemical energy conversion devices which allow fuel gases, e.g. hydrogen or natural gas, to be converted to electricity and heat at much high efficiencies than combustion-based energy conversion technologies. SOFC are particularly suited to employment in stationary energy conversion applications, e.g. micro-combined heat and power (μ-CHP) and base load, which are certain to play a large role in worldwide decentralisation of power distribution and supply over the coming decades. Use of high-temperature SOFC technology within these systems is also a vital requirement in order to utilise fuel gases which are readily available in different areas of the world. Unfortunately, the limiting factor to the long-term commercialisation of SOFC systems is the redox instability, coking intolerance and sulphur poisoning of the state-of-the-art Ni-based cermet composite anode material. This research explores the ‘powder to power' development of alternative SOFC anode catalyst systems by impregnation of an A-site deficient La0.20Sr0.25Ca0.45TiO3 (LSCT[sub](A-)) anode ‘backbone' microstructure with coatings of ceria-based oxide ion conductors and metallic electrocatalyst particles, in order to create a SOFC anode which exhibits high redox stability, tolerance to sulphur poisoning and low voltage degradation rates under operating conditions. A 75 weight percent (wt. %) solids loading LSCT[sub](A-) ink, exhibiting ideal properties for screen printing of thick-film SOFC anode layers, was screen printed with 325 and 230 mesh counts (per inch) screens onto electrolyte supports. Sintering of anode layers between 1250 °C and 1350 °C for 1 to 2 hours indicated that microstructures printed with the 230 mesh screen provided a higher porosity and improved grain connectivity than those printed with the 325 mesh screen. Sintering anode layers at 1350 °C for 2 hours provided an anode microstructure with an advantageous combination of lateral grain connectivity and porosity, giving rise to an ‘effective' electrical conductivity of 17.5 S cm−1 at 850 °C. Impregnation of this optimised LSCT[sub](A-) anode scaffold with 13-16 wt. % (of the anode mass) Ce0.80Gd0.20O1.90 (CGO) and either Ni (5 wt. %), Pd, Pt, Rh or Ru (2-3 wt. %) and integration into SOFC resulted in achievement of Area Specific Resistances (ASR) of as low as 0.39 Ω cm−2, using thick (160 μm) 6ScSZ electrolytes. Durability testing of SOFC with Ni/CGO, Ni/CeO2, Pt/CGO and Rh/CGO impregnated LSCT[sub](A-) anodes was subsequently carried out in industrial button cell test rigs at HEXIS AG, Winterthur, Switzerland. Both Ni/CGO and Pt/CGO cells showed unacceptable levels of degradation (14.9% and 13.4%, respectively) during a ~960 hour period of operation, including redox/thermo/thermoredox cycling treatments. Significantly, by exchanging the CGO component for the CeO2 component in the SOFC containing Ni, the degradation over the same time period was almost halved. Most importantly, galvanostatic operation of the SOFC with a Rh/CGO impregnated anode for >3000 hours (without cycling treatments) resulted in an average voltage degradation rate of < 1.9% kh−1 which, to the author's knowledge, has not previously been reported for an alternative, SrTiO3-based anode material. Finally, transfer of the Rh/CGO impregnated LSCT[sub](A-) anode to industrial short stack (5 cells) scale at HEXIS AG revealed that operation in relevant conditions, with low gas flow rates, resulted in accelerated degradation of the Rh/CGO anode. During a 1451 hour period of galvanostatic operation, with redox cycles and overload treatments, a voltage degradation of 19.2% was observed. Redox cycling was noted to briefly recover performance of the stack before rapidly degrading back to the pre-redox cycling performance, though redox cycling does not affect this anode detrimentally. Instead, a more severe, underlying degradation mechanism, most likely caused by instability and agglomeration of Rh nanoparticles under operating conditions, is responsible for this observed degradation. Furthermore, exposure of the SOFC to fuel utilisations of >100% (overloading) had little effect on the Rh/CGO co-impregnated LSCT[sub](A-) anodes, giving a direct advantage over the standard HEXIS SOFC. Finally, elevated ohmic resistances caused by imperfect contacting with the Ni-based current collector materials highlighted that a new method of current collection must be developed for use with these anode materials.
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Hyde, Andrew Justin. "A Portable Generator Incorporating Mini-Tubular Solid Oxide Fuel Cells." The University of Waikato, 2008. http://hdl.handle.net/10289/2582.
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Modern society has become reliant on battery powered electronic devices such as cell phones and laptop computers. The standard way of recharging these devices is by connecting to a reticulated electricity supply. In situations with no electricity supply some other recharging method is required. Such a possibility is a small, portable, generator based on fuel cell technology, specifically mini-tubular solid oxide fuel cells (MT-SOFC). MT-SOFCs have been developed since the 1990s but there is limited analysis, discussion or research on developing and constructing a portable generator based on MT-SOFC technology. Such a generator, running on a portable gas supply, requires combining the key aspects of cell performance, a heating and fuel reforming system, and cell manifolds. Cell design, fuel type, fuel flow rate, current-collection method and operating temperature all greatly affected MT-SOFCs performance. Segmenting the cathode significantly increased the power output. Maximum power density from an electrolyte supported MT-SOFC was 140 mW/cm2. The partial oxidation reactor (POR) developed provided the required heat to maintain the MT-SOFCs at an operating temperature suitable for generating electricity. The exhaust gas from the POR was a suitable fuel for MT-SOFCs, having sufficient carbon monoxide and hydrogen to generate electricity. Various manifold materials were evaluated including solid metal blocks and folded sheet metal. It was found that manifolds made from easily worked alumina fibre board decreased the thermal stresses and therefore the fracture rate of the MT-SOFCs. The final prototype developed comprised a partial oxidation reactor and MT-SOFCs mounted in alumina fibre board manifolds within a well-insulated enclosure, which could be run on LPG. Calculated efficiency of the final prototype was 4%. If all the carbon monoxide and hydrogen produced by the partial oxidation reactor were converted to electrical energy, efficiency would increase to 39%. Under ideal conditions, efficiency would be 78%. Efficiency of the prototype can be improved by increasing the fuel and oxygen utilisation ratios, ensuring heat from the exhaust gases is transferred to the incoming gases, and improving the methods for collecting current at both the anode and cathode.
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Kornely, Michael [Verfasser], and E. [Akademischer Betreuer] Ivers-Tiffée. "Elektrische Charakterisierung und Modellierung von metallischen Interkonnektoren (MIC) des SOFC-Stacks / Michael Kornely ; Betreuer: E. Ivers-Tiffée." Karlsruhe : KIT Scientific Publishing, 2012. http://d-nb.info/1184493332/34.
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Liu, Zhengyang. "Characterization and Failure Mode Analysis of Cascode GaN HEMT." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/49580.
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Recent emerging gallium nitride (GaN) high electron mobility transistor (HEMT) is expected to be a promising candidate for high frequency power conversion techniques. Due to the advantages of the material, the GaN HEMT has a better figure of merit (FOM) compared to the state-of-the-art silicon (Si) power metal oxide silicon field effect transistor (MOSFET), which allows the GaN HEMT to switch with faster transition and lower switching loss. By applying the GaN HEMT in a circuit design, it is possible to achieve high frequency, high efficiency, and high density power conversion at the same time.
To characterize the switching performance of the GaN HEMT, an accurate behavior-level simulation model is developed in this thesis. The packaging related parasitic inductance, including both self-inductance and mutual-inductance, are extracted based on finite element analysis (FEA) methods. Then the accuracy of the simulation model is verified by a double-pulse tester, and the simulation results match well with experiment in terms of both device switching waveform and switching energy.
Based on the simulation model, detailed loss breakdown and loss mechanism analysis are made. The cascode GaN HEMT has high turn-on loss due to the body diode reverse recovery of the low voltage Si MOSFET and the common source inductance (CSI) of the package; while the turn-off loss is extremely small attributing to the cascode structure.
With this unique feature, the critical conduction mode (CRM) soft switching technique are applied to reduce the dominant turn on loss and increase converter efficiency significantly. The switching frequency is successfully pushed to 5MHz while maintaining high efficiency and good thermal performance.
Traditional packaging method is becoming a bottle neck to fully utilize the advantages of GaN HEMT. So an investigation of the package influence on the cascode GaN HEMT is also conducted. Several critical parasitic inductors are identified, which cause high turn on loss and high parasitic ringing which may lead to device failure. To solve the issue, the stack-die package is proposed to eliminate all critical parasitic inductors, and as a result, reducing turn on loss by half and avoiding potential failure mode of the cascode GaN device effectively.
Utilizing the proposed stack-die package and ZVS soft switching, the GaN HEMT high frequency, high efficiency, and high density power conversion capability can be further extended to a higher level.Master of Science
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Sarda, Venkatesh Verfasser], Lorenz [Akademischer Betreuer] Singheiser, and Werner [Akademischer Betreuer] [Lehnert. "Degradation phenomena in the anode side of solid oxide fuel cell (SOFC) stacks / Venkatesh Sarda ; Lorenz Singheiser, Werner Lehnert." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1156924243/34.
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TARALASHVILI, TAMAR. "Interstate soft conflicts, trade and FDI." Doctoral thesis, Università Politecnica delle Marche, 2021. http://hdl.handle.net/11566/291111.
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Questa tesi contribuisce alla letteratura sull'impatto economico dei conflitti tra stati. La tesi contribuisce concentrandosi sull'analisi empirica dell'effetto dei conflitti "soft" sui flussi commerciali e sugli IDE bilaterali. I conflitti "soft" tra stati derivanti dal fallimento della diplomazia, quando un'operazione militare sembra troppo radicale, possono agire come uno strumento politico e avere un impatto negativo sulle relazioni bilaterali. E poiché oggigiorno i paesi tendono a evitare la violenza e l'intervento militarizzato, i conflitti “soft” interstatali diventano esplicitamente interessanti da studiare.
L'approccio empirico si basa sull'uso di dati panel bilanciati con osservazioni annuali e sull'adozione del modello gravitazionale coerente con la teoria, aumentato da una nuova misura del conflitto "soft" interstatale.
I risultati ottenuti per mezzo di stimatori standard del modello gravitazionale mostrano che i conflitti “soft” hanno un impatto negativo statisticamente significativo e prolungato sia sul commercio bilaterale che sugli stock di IDE, indipendentemente dal controllo per le variabili omesse (presenza di accordi commerciali regionali, diversi tipi di sanzioni e controversie interstatali militarizzate) e diverse specificazioni del modello. I nostri risultati dimostrano che l'impatto di diversi tipi (indiretto: contro il paese in generale e diretto: contro una specifica organizzazione) dei conflitti “soft" interstatali è abbastanza eterogeneo tra commercio e IDE. Entrambi i tipi di conflitti “soft” hanno un significato impatto negativo sul commercio, mentre nel caso degli IDE, abbiamo trovato rilevanza solo per i casi diretti.
I risultati dimostrano che l'impatto dei diversi tipi di conflitti “soft" interstatali - indiretto, ossia contro il paese in generale e diretti, contro una specifica organizzazione o impresa - è abbastanza eterogeneo tra commercio e IDE. Entrambi i tipi di conflitti “soft” hanno un significativo impatto negativo sul commercio, mentre nel caso degli IDE, l'evidenza riguarda solo i conflitti diretti. This thesis contributes to the literature on the economic impact of interstate conflicts. The thesis contributes by focusing on the empirical analysis of effect of soft conflicts on bilateral trade and FDI. Interstate soft conflicts arising from the failure of diplomacy, when a military operation seems too radical, can act as a policy tool and have a negative impact on bilateral relations. And since nowadays countries tend to avoid violence and militarized intervention, interstate soft conflicts become explicitly interesting to study. The empirical approach is based on the use of balanced panel data with annual observations and on a theory-consistent structural gravity framework augmented by a new measure of interstate soft conflict. The results from standard gravity estimators show that interstate soft conflicts have a statistically significant and sustained negative impact on both bilateral trade and FDI stocks, regardless of the control for omitted variables (presence of regional trade agreements, different types of sanctions and militarized interstate disputes) and different model specifications. The results demonstrate that the impact of different types of interstate soft conflicts – indirect, against the country in general and direct, against a specific organization or firm - is quite heterogeneous between trade and FDI. Both types of soft conflicts have a significant negative impact on trade, while in case of FDI, we found significance only for direct cases.
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Ferreira, Ronaldo Rodrigues. "The transactional HW/SW stack for fault tolerant embedded computing." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/114607.
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O desafio de implementar tolerância a falhas em sistemas embarcados advém das restrições físicas de ocupação de área, dissipação de potência e consumo de energia desses sistemas. A necessidade de otimizar essas três restrições de projeto concomitante à computação dentro dos requisitos de desempenho e de tempo-real cria um problema difícil de ser resolvido. Soluções clássicas de tolerância a falhas tais como redundância modular dupla e tripla não são factíveis devido ao alto custo em potência e a falta de um mecanismo para se recuperar erros. Apesar de algumas técnicas existentes reduzirem o overhead de potência e área, essas incorrem em alta degradação de desempenho e muitas vezes assumem um modelo de falhas que não é factível. Essa tese introduz a Pilha de HW/SW Transacional, ou simplesmente Pilha, para gerenciar de maneira eficiente as restrições de área, potência, cobertura de falhas e desempenho. A Pilha introduz uma nova estratégia de compilação que organiza os programas em Blocos Básicos Transacionais (BBT), juntamente com um novo processador, a Arquitetura de Blocos Básicos Transacionais (ABBT), a qual provê detecção e recuperação de erros de grão fino e determinística ao usar o BBT como um contâiner de erros e como unidade de checkpointing. Duas soluções para prover a semântica de execução do BBT em hardware são propostas, uma baseada em software e a outra em hardware. A área, potência, desempenho e cobertura de falhas foram avaliadas através do modelo de hardware do ABBT. A Pilha provê uma cobertura de falhas de 99,35%, com overhead de 2,05 em potência e 2,65 de área. A Pilha apresenta overhead de desempenho de 1,33 e 1,54, dependento do modelo de hardware usado para suportar a semântica de execução do BBT.Fault tolerance implementation in embedded systems is challenging because the physical constraints of area occupation, power dissipation, and energy consumption of these systems. The need for optimizing these three physical constraints while doing computation within the available performance goals and real-time deadlines creates a conundrum that is hard to solve. Classical fault tolerance solutions such as triple and dual modular redundancy are not feasible due to their high power overhead or lack of efficient and deterministic error recovery. Existing techniques, although some of them reduce the power and area overhead, incur heavy perfor- mance penalties and most of the time do not assume a feasible fault model. This dissertation introduces the Transactional HW/SW Stack, or simply Stack, to effi- ciently manage the area, power, fault coverage, and performance conundrum. The Stack introduces a new compilation strategy that assembles programs into Transac- tional Basic Blocks, together with a novel microprocessor, the TransactiOnal Basic Block Architecture (ToBBA), which provides fine-grained error detection and deter- ministic error rollback and elimination using the Transactional Basic Blocks (TBBs) both as a container for errors and as a small unit of data checkpointing. Two so- lutions to sustain the TBB semantics in hardware are introduced: software- and hardware-based. Stack’s area, power, performance, and coverage were evaluated using ToBBA’s hardware implementation model. The Stack attains an error correc- tion coverage of 99.35% with 2.05 power overhead within an area overhead of 2.65. The Stack also presents a performance overhead of 1.33 or 1.54, depending on the hardware model adopted to support the TBB.
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Weisser, Peter. "The Admiral's Carrot and Stick: Zheng He and the Confucius Institute." CSUSB ScholarWorks, 2018. https://scholarworks.lib.csusb.edu/etd/625.
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As the People’s Republic of China begins to accumulate influence on the international stage through strategic usage of soft power, the history and application of soft power throughout the history of China will be important to future scholars of the politics of Beijing. This study will examine Beijing and its government official’s perceptions of its soft power and how there have been historical parallels between the modern People’s Republic of China and the Ming Dynasty (1368-1644) in regard to soft power politics and China’s search for its legitimacy as a rising global power. This study will use two examples that have similar parallels: The eunuch admiral Zheng He (1371-1433) and his journey’s through the South China Sea, the Indian Ocean and the Middle East and the Confucius Institute, a teaching and cultural exchange program under the auspices of the Office of Chinese Language International, known colloquially as Hanban, an organization under the direct control of the Chinese Communist Party’s leadership.
What connects these two topics is the subject of soft power, a term coined by Joseph S. Nye, relating to the kind of power wielded by countries that does not involve military force and uses a “Charm Strategy” to support favorable treatment amongst its trading partners. Zheng He sailed the oceans to neighboring countries, in an attempt to give legitimacy to Ming China through the imperial tribute trade system. The Confucius Institute continues that legacy today, teaching a view of China that is shaped in Beijing. I will show the parallels between this historical figure and that of the Confucius Institute, showing that the pursuit of soft power is not a recent phenomenon in Chinese politics but a theory and a motivation that has existed in China since medieval times in China’s endless search for legitimacy in the eyes of its neighbors. I will be researching the life and journeys of Zheng He, along with the controversies surrounding the Confucius Institute and how all of these factors relate to China attempting to re-instate a legacy that the nation has was lost over since the nineteenth century’s “Century of Humiliation”. This loss of prestige was a result of European colonial power’s ambitions in the area. I will also use evidence to prove the importance of Confucianism in regard to the development of soft power in China. As China seeks to find its legitimacy, we will see that this has been some centuries in the making and plays a crucial part of Chinese politics today. The re-assertion of China’s place in the world as a rising world power will have geopolitical implications for decades to come.
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Yan, Yulin Verfasser], Werner [Akademischer Betreuer] [Lehnert, and Lorenz [Akademischer Betreuer] Singheiser. "Degradation study of SOC stacks with impedance spectroscopy / Yulin Yan ; Werner Lehnert, Lorenz Singheiser." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1186069570/34.
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Yan, Yulin [Verfasser], Werner [Akademischer Betreuer] Lehnert, and Lorenz [Akademischer Betreuer] Singheiser. "Degradation study of SOC stacks with impedance spectroscopy / Yulin Yan ; Werner Lehnert, Lorenz Singheiser." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1186069570/34.
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Fürthauer, Sebastian [Verfasser], Frank [Akademischer Betreuer] Jülicher, and Holger [Akademischer Betreuer] Stark. "Active Chiral Processes in Soft Biological Matter / Sebastian Fürthauer. Gutachter: Frank Jülicher ; Holger Stark. Betreuer: Frank Jülicher." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://d-nb.info/1068148063/34.
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Longbottom, Todd L. M. S. "Climatic and topographic controls on soil carbon storage and dynamics in the Indian Himalaya: Potential carbon cycle and climate change feedbacks." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1342106746.
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Cicero, Simone. "Modelli statistici per il calcolo dello stock di carbonio nei suoli: applicazione al database della Regione Emilia Romagna." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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Lo scopo principale della tesi è stato quello di verificare se l’Agricoltura Conservativa è in grado di aumentare nel tempo le quantità di Carbonio Organico del Suolo (SOC) in modo più efficiente rispetto alle comuni pratiche di Agricoltura Convenzionale. Utilizzando i dati del progetto Europeo LifeHelpSoil, sono state effettuate delle simulazioni predittive delle dinamiche del carbonio in diversi tipi di suoli presenti nelle 4 aziende di progetto tramite RothC un modello molto utilizzato in ambito scientifico a livello internazionale. La prima parte del lavoro ha riguardato il reperimento di tutti i dati di input per il modello ovvero: A) dati climatici storici e proiezioni future di valori medi mensili relativi ai siti aziendali provenienti da ARPAE e JRC; B) dati relativi al tipo di suolo (% Argilla e Stock di Carbonio Organico); C) dati riguardanti gli ordinamenti colturali e le pratiche agricole nelle tre annualità del progetto Life (2014-2016): tipo di coltura; irrigazione; lavorazioni del terreno; cover-crops; concimazioni; inoltre a partire dai quantitativi in peso del prodotto raccolto sono stati calcolati prima i diversi residui colturali e poi i relativi apporti in termini di carbonio organico al suolo. La seconda parte si è sviluppata con le simulazioni utilizzando diversi archi temporali. Il modello richiede una prima fase di parametrizzazione utilizzando dati climatici del passato e dati di input di materiale organico tali da portare la simulazione all’equilibrio ossia ottenere valori di SOC simulati pari al valore di carbonio misurato in campo; segue poi la fase di simulazione futura utilizzando gli schemi di gestione agronomica del suolo adottati nel progetto Life e i dati climatici di climate change. I risultati ottenuti hanno confermato l’ipotesi che l’Agricoltura Conservativa aumenti il contenuto di Carbonio organico nel terreno (quindi di Sostanza Organica) il quale è un parametro importante in quanto principale indicatore di qualità del suolo.
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Russi, Luigi. "modeling the pressure drop and thermal profile of a novel solid oxide fuel cell stack design with a homogenized approach." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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Le celle a combustibile a ossidi solidi (SOFCs) rappresentano una tecnologia chiave in uno scenario di decarbonizzazione delle attività umane per i prossimi anni.
Gli stack attualmente disponibili presentano elevati gradienti di temperatura e grandi perdite di carico attraverso lo stack, così come distribuzioni di corrente disuniformi, problemi di perdita di contatto e di deterioramento.
Un innovativo design dello stack, detto"Chessboard", è stato ideato al DTU Energy.
La determinazione dei campi di temperatura, pressione e velocità nello stack tramite simulazione risulta fondamentale per valutare la qualità di un certo design. Infatti non sempre è possibile misurare sperimentalmente grandezze fisiche locali all'interno dello stack.
In questo lavoro un modello tridimensionale (3D) dello stack è stato costruito. L'approccio modellistico utilizzato si basa sulla tecnica di omogenizzazione. Un metodo efficiente a livello computazionale basato sull'utilizzo di una geometria semplificata, ma con proprietà termofisiche anisotropiche che rispecchino la vera geometria dello stack per reincrementare il livello di dettaglio.
Fra tutte le fisiche che descrivono i fenomeni in una SOFC, solo il moto dei fluidi e la trasmissione del calore sono effettivamente risolte dal modello nell'attuale stadio di sviluppo, mentre i fenomeni elettrochimici sono definiti come parametri in ingresso.
Una volta impostato il modello, è stato eseguito uno studio parametrico, con lo scopo di ottenere i profili di temperatura e pressione in funzione delle dimensioni dello stack, dell'eccesso d'aria, della pressione in ingresso dell'aria e della dimensione dei pori. Individuando quindi una finestra di esercizio sicura per i 4 parametri considerati.
Dai risultati si evince che è possibile trovare diverse combinazioni di parametri che soddisfino l'obiettivo di progetto dato da limiti sui materiali costituenti lo stack, tutto questo con dei tempi di risoluzione nell'ordine dei minuti.
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Thull, Jean-Paul. "Management of stock effluent spillage from trucks in New Zealand." Lincoln University, 1999. http://hdl.handle.net/10182/778.
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The key objective of this multi-disciplinary research was to seek for feasible solutions to avoid effluent from livestock trucks spilling onto roads. Stock effluent spillage mainly poses road safety hazards and environmental damage, and also causes offence to road users and tourists. This task required reviewing previous institutional actions, assessing the power of the existing legislation, and evaluating the interests and attitudes of the stakeholder groups involved in the overall livestock supply chain. It was also necessary to consider politics, administration, public policy and economics, gaining the willing cooperation and confidence of the stakeholder groups through application of 'Soft Systems Methodology' (SSM). A key component was the creation of a 13 minute video and its associated brochure as a primary tool for a stakeholder educational awareness programme. It was necessary to analyse the complex relationships between livestock preparation prior to transport; effluent produced in-transit; and end product quality factors. Detailed information pertaining to the nature of livestock shipments by truck in the South Island of New Zealand had to be collected and verified. All the above information were fed into the calculation of an ideal network of in-transit effluent discharge sites on State Highways in the South Island of New Zealand. Assuming the adoption of best practice throughout the supply chain, it was possible to recommend sustainable solutions. The problem is amenable to solution. Adoption of a strong Industry Code of Practice, coupled with the construction of a strategic network of dump sites will enable the industry to avoid the heavy-handed legal consequences of allowing the status quo to continue.
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Huling, Kelsey Rose Stark. "Tubules to Tracebacks: Animating sensation through material." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555451814841903.
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Quibel, Edouard. "Impacts de la préparation du sol lors de la phase de plantation sur la dynamique des matières organiques et la fonction de stockage du Carbone dans les sols forestiers Impact du travail du sol localisé sur le stock de carbone organique du sol et la communauté microbienne en condition de plantation en forêt tempérée Changes in soil organic carbon stock by mechanical site preparation in oak and pine plantations on an acidic soil Impact du travail du sol localisé sur le stock de carbone organique du sol et la communauté microbienne en condition de plantation sur sol à engorgement temporaire en eau." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMR017.
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Dans le contexte actuel de changement climatique, la forêt est vue comme un puits de carbone, c’est-à-dire qu’elle contribue à stocker du C. Ce stockage peut s’effectuer à moyen terme dans la biomasse ligneuse et à plus long terme dans les sols. Afin de préserver les forêts et leur capacité de stockage, les gestionnaires forestiers se voient contraints d’effectuer de la régénération artificielle, c’est-à-dire de la plantation pour adapter les peuplements aux conditions futures. Pour assurer le succès de cette étape de plantation, il est parfois nécessaire de lever certaines contraintes comme la présence de végétation bloquante, de tassement ou d’engorgement en eau des sols. Pour ce faire, une Préparation Mécanique des Sols (PMS) peut être effectuée avant la plantation. Ces travaux de PMS sont susceptibles de provoquer une perte de Carbone Organique du Sol (COS). Afin de limiter les effets négatifs de la PMS, des outils ont été développés afin de ne préparer le sol que de manière localisée, sur la future ligne de plants. Ces outils ont été développés pour répondre à certaines situations. Les outils Scarificateur Réfersible® et le sous-soleur multifonction® (MFSS) sont faits pour préparer des sols tassés et/ou envahis par la fougère aigle (Pteridium aquilinum). Les outils Razherb® (RAZ) et Culti 3B® (C3B) sont, quant à eux, utilisés pour préparer des sols tassés et/ou engorgés en eau envahis par la molinie (Molinia caerulea). Dans un premier temps, appuyé sur 6 sites du réseau ALTER, l’impact de l’outil RS, seul ou en combinaison avec MFSS, sur le COS a été évalué 5 ans après la PMS. Leur impact a été évalué sur le COS de manière quantitative et qualitative mais également sur le fonctionnement microbien du sol. Cette étude a montré, sur la zone travaillée, une baisse du stock de C sur le profil de sol complet (L-60 cm) et du C minéralisé par la communauté microbienne en conditions contrôlées. Cependant, il a également été démontré que les caractéristiques du sol modulent l’impact de ces outils à l’échelle de la parcelle forestière. Dans un deuxième temps, appuyé sur 3 sites du réseau PILOTE, l’impact de la combinaison d’outils RAZ+C3B a été évalué sur les stocks de COS et sur la minéralisation potentielle. Sur ces sols à engorgement temporaire, une baisse de stock de COS a été observée dans la zone travaillée uniquement dans le topsoil (L-30 cm). En revanche, le stock de COS sur le profil complet comme la minéralisation potentielle ne présentaient pas d’effet significatif sur la zone travaillée. A l’échelle de la parcelle forestière, la combinaison RAZ+C3B n’a pas présenté d’effet sur les stocks de COS ni sur la minéralisation potentielle. Dans son ensemble, ce travail de thèse suggère que bien qu’ayant un impact sur la zone préparée, les outils utilisés dans cette étude n’influençaient que peu le sol à l’échelle de la parcelle forestière. Toutefois, ces observations peuvent varier selon le type de sol en présence et avoir un impact importantIn the current context of climate change, forests are seen as a carbon sinj, i. e. they can contribute to C storage. This storage can take place in the medium term in woody biomass and in the longer term in soils. In order to preserve forests and their C storage capacity, foresters have to carry out artificial regeneration (i. e. planting) to adapt stands to future conditions. To ensure the success of this planting stage, it is sometimes necessary to remove some constraints such as the presence of blocking vegetation, compaction or waterlogging of soil. To do this, a Mechanical Soil Preparation (MSP) can be carried out prior to plantin. This PMS work may cause a Soil Organic Carbon (SOC) loss by mineralization. In order to limit the negative effects of PMS, tools have been developed to prepare the soil only in a localized area, on the future line of plants. These tools have been developed to respond to some situations. The Reversible Scarifier® (RS) tool and the Multifunction Subsoiler (MFSS) are designed to prepare soils compacted and/or invaded by eagle fern (Pteridium aquilinum). The Razherb® (RAZ) and the Culti 3B® (C3B) tools are designed to prepare compacted and/or waterlogged soils invaded by Molinia caerulea (Molinia caerulea). First, based on 6 sites belonging to the ALTER network, the impact of the RS tool alone and in combination with MFSS on COS was evaluated 5 years after the PMS. This evaluation therefore focused on the quantity and quality of SOC. The impact of the tools on the microbial functioning of the soil was also tested. This part showed a decrease in the stock of C and mineralized C by the microbial community under controlled conditions localized to the prepared area but impacts at the forest stand scale depend on soil characteristics. Second, based on 3 sites belonging to the PILOTE network, the impact of the combination of RAZ+C3B tools on SOC stocks and potential mineralization was evaluated. On these soils with temporary waterlogging, adecrease in SOC stock was observed in the prepared area only in the topsoil (0-30 cm). On the other hand, both SOC stock on the full profile and the potential mineralization did not have a significant effect on the prepared area. At the forest stand scale, the RAZ+C3B combination had no effect on SOC stock or potential mineralization. This thesis work suggests that although they had an impact on the prepared area, the tools used in this study had low influence on the soil at the forest plot scale. However, these observations may vary according to the soil type and have a significant impact on the forest plot
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Oliveira, Daniele Costa de. "Potencial de sequestro de carbono no solo e dinâmica da matéria orgânica em pastagens degradadas no Brasil." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/11/11140/tde-17072018-184226/.
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As pastagens são o principal uso da terra no mundo, ocupando dois terços de sua área agricultável e três quartos da área agricultável do Brasil. Quando bem manejadas, as pastagens possuem alta capacidade de estocar C no solo, porém podem perder até 50% do C do solo quando em avançado estágio de degradação. Os objetivos desse trabalho foram quantificar o potencial de sequestro de C e avaliar a dinâmica da matéria orgânica no solo em locais de conversão de pastagens degradadas para bem manejadas no Brasil. Para tanto, foram avaliadas as alterações dos estoques de C no solo nas pastagens do Brasil através de uma meta-análise, bem como os fatores de manejo e as taxas de variações do estoque de C no solo em diferentes status de pastagens. Em sete cronossequências situadas em Vila Bela da Santíssima Trindade (MT), Nova Xavantina (MT), Conquista D\'Oeste (MT), Dueré (TO), Carmolândia (TO) e Paraíso (TO), foram determinadas as alterações na quantidade e na qualidade da Matéria Orgânica do Solo (MOS). Foram determinados os estoques de C e N e as taxas de variação locais. A qualidade da MOS foi avaliada por meio de análise isotópica, fracionamento físico, Índice de Manejo do C (IMC), grau de humificação (HFIL) e teor de C na Biomassa Microbiana (C-BM). Através da meta-análise, estimou-se que no Brasil os solos sob pastagens degradadas apresentam redução dos estoques de C de 0,13 Mg ha-1 ano-1. As pastagens nominais foram capazes de aumentar o estoque de C no solo, enquanto as pastagens melhoradas nem sempre mantiveram os estoques semelhantes aos da vegetação nativa. A recuperação das pastagens promove acúmulo de C no solo na faixa de 0,40 Mg ha-1 ano-1. O cumprimento da meta de recuperação dos 30 milhões de hectares de pastagens resultará no acumúlo de 12 Tg ha-1 ano-1 de C. A degradação das pastagens nos estados do Mato Grosso e Tocantins reduziu os estoques de C no solo numa faixa de -0,06 Mg ha-1 ano-1, enquanto a recuperação das mesmas proporcionou aumento de 0,12 Mg ha-1 ano-1. Nas pastagens avaliadas, cerca de 54% do C é originado das gramíneas cultivadas. A fração orgânica foi a mais sensível às Mudanças de Uso da Terra (MUT), promovendo diminuição dos estoques de C nessa fração. A implantação de pastagens tem impacto negativo na qualidade da MOS, com diminuição do IMC de até 70%. Contudo, se bem manejadas, o IMC das pastagens pode ser superior ao da vegetação nativa, como acontece quando a pastagem é consorciada com Pueraria spp. O C-BM e o grau de humificação não foram alterados após a implantação ou a recuperação das pastagens, não sendo bons indicadores de qualidade da MOS. As alterações dos estoques de C nas frações da MOS e o IMC foram os indicadores mais eficientes de alterações da qualidade da MOS em pastagens. As recuperação de pastagens degradadas promove aumento no estoque de C no solo e melhoria da qualidade da MOS.Pastures are the main land use in the world, occupying two-thirds of the world\'s arable land and three quarters of agricultural areas of Brazil. When well-managed, pastures have a high capacity to store SOC, but they may lose up to 50 % of stock SOC when in an advanced stage of degradation. The objective of this work was to quantify the potential of carbon sequestration and to evaluate soil organic matter dynamics in the conversion of degraded pastures to well-managed in Brazil. We evaluated changes in stocks SOC in pastures in Brazil through a meta-analysis, determining the management factors and the rates of stocks SOC changes in different pasture status. In seven cronossequences located in Vila Bela da Santíssima Trindade (MT), Nova Xavantina (MT), Conquista D\'Oeste (MT), Dueré (TO), Carmolândia (TO) and Paraíso (TO) were determined the changes in the quantity and quality of soil organic matter (SOM). C and N stocks and rates of local variations were determined. The quality of the SOM was evaluated through isotopic analysis, physical fractionation, C management index (CMI), degree of humification (HFIL) and C content in microbial biomass (MB-C). Through the meta-analysis it was estimated that in Brazil degraded pastures present a reduction of stocks SOC of 0.13 Mg ha-1 year -1. Nominal pastures were able to increase stock SOC, while improved pastures did not always maintain stocks similar to native vegetation. The recovery of pastures promotes the accumulation of C in the soil at the rate of 0.40 Mg ha-1 year -1. Meeting the recovery goal of 30 million ha of pasture will result in the accumulation of 12 Tg C ha-1year -1. The degradation of pastures in the states of Mato Grosso and Tocantins reduces C stocks in the soil at a rate of 0.06 Mg C ha-1 year-1. While the recovery of degraded pastures has the potential to increase C stocks in the soil with rate of 0.12 Mg C ha-1 year-1. In the pastures evaluated, about 54% of the C originates from the cultivated grasses. The organic fraction was the most sensitive to LUC, promoting the decrease of C stocks in this fraction. Pasture implantation has a negative impact on SOM quality, with a reduction in the CMI of up to 70%; however, if managed well, the CMI of pastures may be higher than that of native vegetation. The MB-C and degree of humification were not altered after the implantation or the recovery of the pastures. Changes in C stocks in SOM fractions and CMI were the most efficient indicators of changes in SOM quality in pastures. The recovery of degraded pastures promotes an increase in C stock in the soil and an improvement in the quality of the MOS.
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Chen, Tsung-Ting, and 陳宗廷. "Thermal stress analysis of a planar SOFC stack." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/a2gy3r.
Full textAbstract:
碩士國立中央大學
機械工程研究所
94
Solid oxide fuel cells (SOFCs) utilize ceramics as the anode, electrolyte, and cathode (often called a positive electrode-electrolyte-negative electrode, PEN) and operate at high temperatures such that they have the highest efficiencies of all fuel cells. The high-temperature operation, however, gives rise to significant thermal stresses caused from the mismatch of coefficient of thermal expansion (CTE) and temperature gradients in the SOFC system. Therefore, a comprehensive thermal stress analysis of SOFC stack is necessary for the success in design and operation of a SOFC system. The aim of this study is, by using finite element simulation, to characterize the thermal stress distribution in a planar SOFC stack during transients and steady operation. An integrated electrochemical and thermal analysis was first conducted to generate the temperature profiles in a 3-cell SOFC stack during various start-up and steady stages. The obtained temperature fields within the cell stack were subsequently applied to a thermal stress analysis using a 3-D finite element model of a 3-cell stack. Each unit cell consists basically of a PEN assembly, interconnect, nickel mesh, and gas-tight glass-ceramic seals. Incorporation of the glass-ceramic sealant, which was never considered in other previous studies, into the 3-cell FEA model would produce more realistic results in thermal stress analysis. In particular, the effect of viscous behavior of glass-ceramic sealant on thermal stress distribution within the cell stack was investigated. In addition, the effects of stack support condition, temperature gradient, cyclic operation were also characterized. Modeling results indicated that a change in the support condition at the bottom frame of the 3-cell stack would not cause significant changes in the thermal stress distribution. Thermal stress distribution did not differ significantly in each unit cell within the 3-cell stack due to a negligible out-of-plane thermal stress gradient. By considering the viscous characteristics of glass-ceramic sealant at temperatures above the glass-transition temperature (Tg), relaxation of thermal stresses in PEN and glass-ceramic sealant was predicted. Effect of operating cycles on the variation of thermal stress was also simulated and the results indicated that a significant increase in thermal stress in PEN and glass-ceramic sealant would be expected with increasing cycle number.
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Chen, Chen-yin, and 陳貞吟. "Development and Modification of Interconnet Materials for SOFC Cell Stack." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/41798682149762083371.
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碩士國立中央大學
能源工程研究所
95
Two choices for interconnect materials are ceramic and metallic alloy materials. To combine the advantages of these materials, we’ll coat high electronic conductivity ceramic materials, such as lanthanide series metal oxides (La1-xCaxCrO3, LCC). LCC powder materials were synthesized by the glycine-nitrate-process(GNP). Our study included different sintering times and temperatures, concentrations of coating ceramic materials, and thickness of coating. The effects of different test conditions are related to performance. From XRD results, longer sintering time could also induce the undesired formation of FeCr¬2O4. From SEM results, we clearly saw that the coating layer was quite smooth and the LCC20-coated Crofer22 composite was suitable as an interconnect in SOFC since it could prevent Cr from oxidation and volatilization at high internal temperatures under SOFC operation conditions. For ASR measurements, the ASR of fresh Crofer22 was measured at 1.0361 mΩ-cm2. After 100 hr oxidation, the result of non-coated sample was 3.0740 mΩ-cm2. With a similar setup to LCC20-coated samples, results were 0.9263 mΩ-cm2. These results improved the ability of the composite interconnect to promote electronic conductivity at high internal temperatures. Through comprehensive studies, we seek to develop ceramic/metal composite interconnect materials with low cost, high electronic conductivity, great high temperature characteristics, high oxidation resistance, puncture resistance, and stability under multiple chemical gases.
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邱重銘. "Cold Start-up Dynamic Simulation of a Micro SOFC Stack." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/23912456521776763420.
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Chen, An-Hsin, and 陳安信. "Thermal Stress Analysis of a Planar SOFC Stack with Mica Sealants." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/46605163957270321781.
Full textAbstract:
碩士國立中央大學
機械工程研究所
95
The aim of this study is, by using finite element analysis (FEA), to characterize the thermal stress distribution in a planar solid oxide fuel cell (SOFC) stack with a compressive sealing design at various stages. The temperature profiles generated by an integrated thermo-electrochemical model were applied to calculate the thermal stress distributions in a multiple-cell SOFC stack by using a three-dimensional (3-D) FEA model. The constructed 3-D FEA model consists of the complete components used in a practical SOFC stack, including positive electrode-electrolyte-negative electrode (PEN) assembly, interconnect, nickel mesh, glass-ceramic seals, and compressive mica seals. Incorporation of the compressive mica sealant, which was never considered in previous studies, into the 3-D FEA model would produce more realistic results in thermal stress analysis and enhance the reliability of predicting potential failure locations in an SOFC stack. The stress fields at different assembly temperatures and the effect of anisotropic elastic moduli of mica sealant were investigated. The thermal stresses in each component at room temperature after assembly were increased when the assembly temperature was increased form 200 oC to 300 and 400 oC. However, the assembly temperature did not affect the thermal stress distributions significantly at steady-operation and shutdown stages. Two different elastic moduli of mica material were used in the FEA model and the simulation results indicated that the critical stresses in each component at a specific stage were comparable except for the mica sealants. Thermal stress distributions obtained in the current study were also made a comparison with those in a rigid-bonding sealing design. The thermal stresses in each component were larger at the after-assembly and shutdown stages but lower in the operation condition for the rigid-bonding type of sealing design. That trend of stress distribution was opposite to that for a compressive sealing design used in the current study.
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Huang, Ling-Hao, and 黃令豪. "Effect of Sealing Design on the Thermal Stresses in SOFC Stack." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/gxsju4.
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碩士國立中央大學
機械工程研究所
96
Solid oxide fuel cell (SOFC) usually operates at a high temperature with a good fuel flexibility and a high efficiency. However, the coefficient of thermal expansion mismatch between ceramic electrodes and metallic components under this high temperature gives rise to a large amount of stresses in the cell stack. In order to predict the durability and reliability of a SOFC stack, a comprehensive three-dimensional finite element analysis (FEA) model based on a stack design being developed at the Institute of Nuclear Energy Research (INER) was constructed. The model was designed for using mica sealant in a compressive sealing design. The first objective of this study is using FEA to calculate the thermal stress distribution in a three-cell planar SOFC stack with a compressive mica sealing design under cyclic thermal loading and to investigate the effects of the applied assembly load on the stress distribution. Simulation results indicate that an applied compressive load of 0.6 MPa could eliminate the bending deformation of the PEN and frame leading to a well joined structure. For a greater applied load, the critical stresses in the glass-ceramic and mica sealants were increased. The glass-ceramic and mica sealants might fail for an applied compressive load of 6 MPa. In this regard, a 0.6 MPa compressive load might be an optimal assembly load. When the SOFC stack was subjected to cyclic thermal loading, the stress accumulation behavior was observed at the inner corners of the frames. The critical stress in the metallic interconnect/frame was increased with increasing number of operating cycles. However, the critical stresses in the PEN, nickel mesh, mica gasket, and glass-ceramic sealant barely changed with cycle number. The second objective of the current study is to make a comparison of the stress distributions between two sealing designs, namely the rigid and compressive seals. Changing a rigid type of glass-ceramic sealant to a compressive type of mica gasket would influence the stress distribution, especially in the PENs. The critical stress in the PEN was decreased at room temperature but significantly increased at operation temperature. Such difference in the stress distribution could be ascribed by the difference in the constrained conditions at the interface of connecting components under various sealing designs. The third objective of this work is to assess the structural reliability of the PEN subjected to such a high thermal stress by measuring the flexural strength of two anode materials, namely Slip-41 and Slip-48. The Slip-48 anode material has a higher flexural strength than does the Slip-41 anode material. The difference in the strength might be caused by their different porosity. Fractography analysis results indicate the Slip-48 anode has a smoother fracture surface and a less amount of defects, compared to the Slip-41. Both anode materials have no obvious temperature dependence on the flexural strength. By importing the mechanical properties of the Slip-48 anode material into stress analysis, the critical stress in the PENs at steady-operation stage would exceed its strength. Therefore, the strength of the tested anode materials needs to be improved for future use in the given SOFC stack design.
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Chien, Wei-Ming, and 簡暐珉. "Experimental Simulation and Analysis of Flow Visualization and Uniformity in a Planar SOFC Stack." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/52987355174763757303.
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碩士國立中央大學
能源工程研究所
96
This thesis investigates experimentally flow distributions in a planar SOFC short-stack using various designs of external manifolds and thus increases flow uniformity of the short-stack. A hydraulic platform combined with laser-induced fluorescence (LIF) and dye visualization (DV) techniques are established to obtain flow fields in the short-stack including three layers, each layer having 12 rib-channels. A Matlab-based code is used to process these flow field images by the binary method and thus corresponding velocities in each of 12 channels for all three different layers can be extracted. Results from both LIF and DV methods are roughly the same with the largest difference up to 10 %, when the channel Reynolds number(Re = VDh/???are within 25~100, where V is the velocity, Dh is the hydraulic diameter of the rib channel, and ? is the kinematic viscosity of fluid. The focus is placed on the effect of different flow directions in both the feed header (FH) and the exhaust header (EH) to flow uniformity of the short-stack. There are five arrangements: (1) The Conventional-type, where both FH and EH are in the same streamwise direction of flow channels; (2) Z-type, where FH and EH are in the same spanwise direction of flow channels; (3) TZ-type, both FH and EH in the same transverse direction of flow channels; (4) U-type, similar to (2) but FH and EH are in opposite directions; (5) TU-type, similar to (3) but FH and EH are in opposite directions. These experimental results show that the fourth design (U-type) has the best flow uniformity among all different designs. In attempt to further improve flow uniformity of the U-type design, a triangular pyramid is placed in the feed header, which can further increase flow uniformity in each layer of the short-stack. Based on the best knowledge of the author, the present study is the first experimental measurement on the flow distributions in the short-stack of planar SOFC and should be useful for numerical simulations.
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Huang, Sheng-Wei, and 黃陞緯. "Innovative Solid Oxide Fuel Cell (SOFC) Stack Design For Asymmetric Membrane Electrode Assembly (MEA) Structure." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/69696476351786189161.
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碩士元智大學
機械工程學系
93
This study is focused on the design and evaluation of the solid oxide fuel cell (SOFC) based on asymmetric membrane electrode assembly (MEA). In the beginning, the planar SOFC single cell is built and its performance is evaluated. We found that the ohmic resistance can be decreased with proper pressing between stainless steel current collector and MEA. In addition, the reduction of NiO within anode to Ni under dilute H2 environment also further decreases the ohmic resistance. The decrease of ohmic resistance results in higher performance. Meanwhile, increasing the cell temperature promotes the cell performance due to lower electrolyte resistivity and higher electrode activities as expected. Based on the experience built on the single cell, two-cell stack were further built and its performance is also evaluated. By properly distributing the air and dilute H2 to corresponding parts with proper sealing, the voltage doubles at a certain current density comparing to the single cell. However, the cell performance decays after long-term operation probably due to cathode poison from the Cr oxide formed on the stainless steel current collector.
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Huang, Yau-De, and 黃耀德. "Numerial Analysis of Thermal and Flow Field in SOFC Stacks." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/54359072046629487258.
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徐瑞民. "The Application of Soft Computing in Investing Taiwan Stock Exchange Capitalization Weighted Stock Index Options." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/01854143811981826438.
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碩士明新科技大學
企業管理研究所
100
TAIEX options were launched in the end of 2001. The trading volume of 2001 was 5,137 followed by 1,566,446 in 2002 and 125,767,624 in 2010. With trading volume increasing by 80 times in 10 years, TAIEX options trading has accounted for about 68.73% of the total, making it one of the most important financial derivative commodities. However, TAIEX options trading is involved with combinations of the buyer, the seller, the right to buy and the right to sell coupled with factors including time value and intrinsic value, the operations of TAIEX options are more complex than the stock market or the future market. The buyer of TAIEX options enjoys the power to determine the contract performance or not by paying the royalties. In other words, it can regulate investment risk. To reduce investment risk, general investors tend to take the buyer operations. However, in most cases, Taiwan’ stock market is in the trend of consolidation. Investors in the buyer position may lose royalties due to the special operational characteristics of the options and cannot profit from the TAIEX options market as expected. This paper employs four forecasting methods including the multiple stepwise regression, back-propagation neural networks, support vector regression, and genetic programming. The research period is January 19, 2011 to January 18, 2012. With the daily closing number of the TAIEX index as the subject, this paper divides the research period into 13 intervals to build the forecast model. In forecasting operation, this paper selects the most accurate forecast model from the four forecasting methods to use the stock market index closing number of 10 consecutive days to predict the stock market closing number after five days. Coupled with the simple operational strategies mainly in the buyer position of buying call options when the option forecast value after price gap computation is bullish and buying put options when the option forecast value after price gap computation is bearish, this paper simulates the operations of the entire year in 2011. According to the results, the genetic programming is the most accurate forecasting method, and the Strategy No. 3 of “conservative operating principles” with investment return rate at 45.25% is the best investment strategy. Keywords：TAIEX options, Multiple stepwise regression, Back-propagation neural networks, Support vector regression, Ggenetic programming
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Tang, Shao-Yuan, and 湯韶元. "The Application of Soft Computing for Investing Taiwan Stock Futures." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/69865850882756111669.
Full textAbstract:
碩士明新科技大學
管理研究所
101
With rapid development of Taiwan's economy, the market provides more and more financial products for investors. Among them, stock futures combine stocks and futures, involving the robustness of stocks and high leverage of futures. The stock futures have surprising growth potential and multi-dimension functions. This thesis uses genetic programming and support vector regression with technical indicators. Moreover, three factor model and liquidity indicator are used to construct stock price prediction model, and investment strategies are established to help investors to invest stock futures. The research period is between December 1, 2009 and July 31, 2012. The stock futures derived from stocks is the research object. There are eight investment cases during the research period. The empirical results show that the proposed prediction model combined with investment operation strategies can obtain the average rate of return, which is greater than the market index return rate and interest rate of three-month fixed deposit in the banks of Taiwan.
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Peng, Da-Hsiung, and 彭大雄. "Experimental study on the effect of a stack of rings with soft blades for pier scour prevention." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/58553138137551172006.
Full textAbstract:
碩士國立成功大學
水利及海洋工程學系碩博士班
95
This research proposed a device consisting of a stack of rings with soft blades to prevent pier scouring. The device was tested in the flume under the following four arrangements: Type A- pier has no scour prevention device; Type B-pier surrounded by a device consisting of a stack of rings with soft blades; Type C-a “stack of rings with soft blades” device placed before pier; Type D-a “stack of rings with soft blades” device placed before and after pier. Scour behavior was oberserved, as each configuration was subjected to a passing flood. All scour-prevention configurations effectively decrease scour and vortex phenomenon. But type D devices arrangement which before the pier included a triangular stack of rings with soft blades, while those placed after the pier consisted of a “U” type’s stack of rings with soft blades, does so most effectively.
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Liao, Wen-Hsiang, and 廖文祥. "A Study on the Application of Soft Computing to Trading Timing in Taiwan Stock Market." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/22380791262613501261.
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碩士長庚大學
資訊管理研究所
93
In the recent years, applying artificial intelligence to financial transaction has become more and more popular. This study combines the advantages of genetic algorithm and neural network, and it takes the technical indicators of the stocks as inputs to decide the right time of transaction. It also investigates whether the proposed trading strategy is better than single technical indicator strategy and buy-and-hold strategy. This study adopts moving-window to evaluate TSEC Taiwan 50 between Jan 4, 2000 and Dec 31, 2004 on the proposed trading, single technical indicator, and buy-and-hold strategies. The capability of making profits by the proposed trading strategy is more effective and stable than single indicator and buy-and-hold strategies during the 3-years evaluation. Although the study on technical indicators shows valuable reference for stock exchange, investors should not take it as the best index for trading strategy.
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Shie, Yi-Da, and 謝易達. "Measurements and Analyses of Anode-Supported and Electrolyte-Supported Single-Cell Stacks for Pressurized SOFCs." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/16403717118737202833.
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碩士國立中央大學
能源工程研究所
102
This study applies a recently-established high-pressure double-chamber solid oxide fuel cell (SOFC) testing platform together with the self-assembled single cell stacks (a full cell with flow distributors in both anode and cathode), so that cell performance and electrochemical impedance spectroscopy (EIS) of both anode-supported and electrolyte-supported SOFCs can be measured. Fixed flow rates are used for all experiments, 500 sccm hydrogen and 400 sccm nitrogen for the anode and 900 sccm air for the cathode. To investigate effects of system pressure (p) and temperature (T), five different p varying from 1 atm to 5 atm and four different T varying from 700℃ to 800℃ are independently controlled and varied. The major objective is to compare advantages/disadvantages and similarities/differences between anode-supported and electrolyte-supported SOFC single stacks. Results show that cell performances of both anode-supported and electrolyte-supported SOFC singlel stacks increase with increasing p and T. For example, when T = 850℃ at 0.7 V, the power densities (PD) of anode-supported/electrolyte-supported single-cell stacks are respectively 309/193 mW cm-2 at p = 1 atm, values of PD modestly increase to 422/228 mW cm-2 rather quickly as p increases at 3 atm, and values of PD can only increase modestly to 476/250 mW cm-2 at p = 5 atm. These results reveal that pressurization for the increase of PD is most significant from 1 atm to 3 atm and such enhancement becomes more gradually when p > 3 atm. Furthermore, the aforesaid that cell performance results are to be explained by EIS measurements. We use equivalent an circuit model to analyze EIS data. It is found that the ohmic polarization resistance is independent of p, but it decreases with increasing T. Moreover, both of activation and concentration polarization resistances decrease with increasing T and/or p. Such resistance results due to effects of increasing p and T are similar for both anode-supported and electrolyte-supported single-cell stacks. When compared, it is also found that the increase of PD due to pressurization is more significant in the anode-supported single-cell stack than in the electrolyte-supported SOFC single-cell stack. However, the latter is more sensitive to the temperature effect as compared to the former. Generally speaking, the temperature effect is more effective than the pressurization effect in terms of the increase of cell performance. This is because increasing T can effectively decrease the ohmic polarization resistance. The present study is important, because it is the first step toward the development of pressurized SOFCs combined with micro gas turbines for future power generation.
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Ribeiro, André Filipe da Silva. "Implementação de nó sensor baseado em SoC ARM e ZigBee." Master's thesis, 2018. http://hdl.handle.net/1822/57432.
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Dissertação de mestrado integrado em Engenharia Eletrónica Industrial e ComputadoresOs acidentes rodoviários são uma das principais causas de mortalidade no mundo e representam um custo considerável para a sociedade. A elevada percentagem de autoestradas na rede rodoviária nacional em relação à rede rodoviária europeia levou ao desenvolvimento de instrumentos de avaliação das infraestruturas e de ferramentas de gestão da segurança. Neste sentido, foi criado um sistema de gestão das infraestruturas rodoviárias, em que uma das principais funções é detetar a ocorrência de acidentes em tempo real, alertando os gestores da própria Wireless Sensor Network (WSN) e os utilizadores da autoestrada. O objetivo do presente estudo foi transferir todas as funcionalidades de software do elemento desse sistema de gestão que deteta a ocorrência de acidentes, ou seja, o nó sensor, recorrendo a um System-on-Chip (SoC) que possui um transceiver de rádio frequência (RF) e um processador que pertence à família ARM Cortex M3. Avaliou-se igualmente o consumo energético do nó sensor desenvolvido. Os resultados mostram que as funcionalidades de software foram transferidas com sucesso e que o novo nó sensor apresenta um consumo energético mais baixo do que o anterior. Conclui-se que o nó sensor desenvolvido possui mais autonomia e poderá ser uma boa opção para implementação em sistemas de gestão das infraestruturas rodoviárias. Sugerem-se posteriores análises para otimização e ajustamento do sistema às reais condições de utilização.
Road accidents constitute one of the major’s world mortality cause and represent a considerable cost to society. High percentage of motorways in portuguese national road network compared to european road network has conducted to the development of assessment instruments of infrastructures and safety management tools. In this sense, a road infrastructure management system was created to detect live incidents occurrence and alert Wireless Sensor Netwok (WSN) managers and highroad drivers. The present study aimed to transfer all the software functionalities of a dedicated embedded system in a System-on-Chip (SoC) with a transceiver of Radio Frequency (RF), wherein the processor belongs to family ARM Cortex M3. The developed sensor node energetic consumption was assessed. Results indicate that the functionalities were successfully transfered and the new sensor node consumes lower energy than the previous one. Conclusions about the better autonomy of the developed sensor node indicate that it might constitute a good option to implement in road infrastructures management systems. Further analyses to optimize and adjust the system to real conditions are suggested.
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Yu, Shih-Ban, and 尤仕邦. "The comparison of cluster based Soft – Computing methods on the trend forecasting with the weighted stock price index." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/28777945982161194188.
Full textAbstract:
碩士開南大學
財務金融學系
97
This study utilized Back-Propagation Neural Network (BPNN)、Support Vector Machine(SVM) and Genetic Algorithm Fuzzy Decision Tree (GAFDT) as three primary prediction models to forecast the stock trading signals. And the data clustered or not will be compared in both models. The object of this research was the Weighted Price Index of the Taiwan Stock Exchange. In 25 technical indices, we first used stepwise regression analysis to sieve out relative important factors, and k-means cluster analysis was adopted for data clustering. Then five-full alternation was applied in the experimental design process. Model from one to three are utilized to predict by BPNN, SVM and GAFDT, respectively. GAFDT began with transferring continuous data to discrete data by fuzzy sets so as to increase the comprehensibility of decision tree, and then utilized Genetic Algorithms to optimize the parameters like fuzzy term numbers. Finally, we compare the different intervals between Weighted Price Index of the Taiwan Stock Exchange and S&P 500 by GAFDT. Empirical findings revealed that the highest accurate rate was GAFDT (82.93%), followed by SVM (76.12%) and BPNN (75.53%). The more clusters GAFDT and SVM swarm off, the higher the accurate rate is. The accurate rate of falling of stock was higher than correction and rising in Weighted Price Index of the Taiwan Stock Exchange. The accurate rate of rising of stock is higher than correction and falling in S&P 500. Consequently, the prediction will be affected by training and testing in different stock markets and tendencies.
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Júnior, Eládio João Munar. "Implementação de uma rede de sensores sem fios baseada em SoC Arm e ZigBee." Master's thesis, 2019. http://hdl.handle.net/1822/72246.
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Dissertação de mestrado em Engenharia Eletrónica Industrial e ComputadoresAs vias de comunicação terrestres são elementos fulcrais para o desenvolvimento das sociedades. A sinistralidade rodoviária é uma das principais ameaças à integridade dos elementos que constituem o sistema rodoviário. No sentido de minimizar este impacto negativo, surge esta dissertação cujo objetivo é apresentar um sistema de monitorização que informa com precisão a ocorrência de colisões de veículos com os guardas de segurança das autoestradas e alertar as entidades responsáveis pela gestão do sistema em tempo real sobre o sucedido. A presente dissertação está orientada em melhorar o projeto, Sustainable Infrastructure Management System (SustIMS), desenvolvido pelo grupo de investigação Embedded System Research Group (ESRG) do Centro ALGORITMI da Universidade do Minho em co-promoção com a empresa Ascendi. Através da implementação de uma rede de sensores sem fios baseada em ZigBee, recorrendo a um System-on-Chip (SoC) comtransceiver Radio Frequency (RF) da família Arm Cortex-M3, equipado com sensor acelerómetro Microelectromechanical Systems (MEMS). O ZigBee, é um protocolo que assenta sobre as camadas definidas no standard IEEE 802.15.4, rede de baixo débito, mas com longa autonomia e baixa complexidade. De forma a cumprir com esses requisitos foi utilizado um processador Arm Cortex-M3 e um acelerómetro MEMS, os quais são caracterizados pelo seu baixo consumo energético. Os resultados desta dissertação são: (1) melhorias na solução atual com o principal foco de reduzir o consumo de energia do sistema; (2) o aumento do alcance da comunicação dos dispositivos; (3) o porting da aplicação para nova versão da Z-Stack; e (4) compatibilização do sistema com os microserviços web, desenvolvidos pelo ESRG.
Road communication is an essential component when it comes to society development. Road accidents are one of the main threats to the integrity of the elements that compose the road system. In order to minimize this negative impact, this dissertation aims to present a monitoring system that informs, with precision, the occurrence of vehicle collision against highway security rails and alert the entities responsible for the real-time management of the system about the event. The present dissertation aims to improve the project, Sustainable Infrastructure Management System, developed by the University of Minho’s Embedded System Research Group (ESRG) in co-promotion with the company Ascendi. By implementing a ZigBee-based wireless sensor network (WSN) using an Arm Cortex-M3 family Radio Frequency (RF) transceiver System-on-Chip (SoC) equipped with an Microelectromechanical Systems (MEMS) accelerometer sensor. ZigBee is a protocol based on the layers defined in the IEEE 802.15.4 standard, low speed network, but with long autonomy and low complexity. In order to meet this requirements an Arm Cortex-M processor and MEMS accelerometer were used, which are characterized by their low power consumption. The results of this dissertation are: (1) improvements on the current solution with the main focus on reducing the system energy consumption; (2) increasing the communication range of the devices; (3) the application porting for the new version of Z-Stack; (4) System compatibility with the microservices developed by the ESRG.