Auswahl der wissenschaftlichen Literatur zum Thema „Anti-surge device“

Gas pressure plays an important role in the economic efficiency and stability of the operation of gas-fired boiler. However, because of the inherent characteristic of gas booster which is introduced to regulate the pressure of gas, there is surge happened in gas booster, resulting in deviation of gas pressure from set value, even damage to device. To settle the problem of surge, an anti-surge control is designed based on the characteristic curves of gas booster. And the control strategy is applied in a thermal power plant with gas-fired boiler. The practical operating result shows the effect of the proposed method.

Osteoarthritis (OA) is a global health issue with myriad pathophysiological factors and is one of the most common causes of chronic disability in adults due to pain and altered joint function. The end stage of OA develops from a destructive inflammatory cycle, driven by the pro-inflammatory cytokines interleukin-1β (IL-1β) and tumour necrosis factor alpha (TNFα). Owing to the less predictable results of total knee arthroplasty (TKA) in younger patients presenting with knee OA, there has been a surge in research evaluating less invasive biological treatment options, one of which is autologous protein solution (APS). APS is an autologous blood derivative obtained by using a proprietary device, made of APS separator, which isolates white blood cells (WBCs) and platelets in a small volume of plasma, and APS concentrator, which further concentrates platelets, WBCs and plasma proteins, resulting in a concentrated solution with high levels of growth factors including the anti-inflammatory mediators against IL-1β and TNFα. A single intraarticular injection of APS appears to be a promising solution for treatment of early-stage OA from current evidence, the majority of which comes from preclinical studies. More clinical studies are needed before APS can be widely accepted as a treatment modality for OA. Cite this article: EFORT Open Rev 2021;6:716-726. DOI: 10.1302/2058-5241.6.200040

The AlGaN/GaN materials with a wide band gap, high electron mobility, and high breakdown voltage are suitable for manufacturing high-power and high-frequency electronic devices. In this study, metal Schottky contact electrodes of different dimensions are prepared on AlGaN/GaN wafers to fabricate metal–semiconductor–metal (MSM) varactors. Voltage-dependent capacitance and breakdown voltages of the varactors are measured and studied. The corresponding breakdown mechanisms of varactors with different electrode gaps are proposed. Furthermore, an anti-surge application using GaN-based MSM varactors in a signal transmission module is demonstrated, and its surge suppression capability is shown. We believe that our study will be beneficial in developing surge protection circuits for RF applications.

As abordagens actuais do preconceito e racismo têm sugerido que as manifestações racistas, apesar de condenáveis à luz das normas vigentes, não têm diminuído, o racismo surge agora com uma aparência diferente (indirecta e subtil), mesmo naqueles que se declaram manifestamente anti-racistas (e.g. Gaertner & Dovidio, 1986; Dovidio & Gaertnes, 1998; Devine, 1989). A explicação para este fenómeno parece passar pelo pressuposto da existência de duas estruturas distintas de conhecimento: as crenças culturais (estereótipos) facilmente activadas, e as crenças individuais, apenas activadas em algumas circunstâncias (Devine, 1989). A natureza dos julgamentos subsequentes será função da estrutura de conhecimentos que tiver sido activada. Esta hipótese foi abordada em dois estudos, um contextualizado ao nível de comportamentos criminosos (Estudo 1) e outro ao nível de transgressões no emprego (Estudo 2). A activação destas duas estruturas de conhecimento foi operacionalizada elo objectivo de processamento fornecido aos participantes, que ora se centrava no “que eu penso” ora no que “as pessoas em geral pensam”. Como esperado, a activação das crenças culturais geraram respostas mais discriminatórias que as crenças individuais.DOI: http://dx.doi.org/10.17575/rpsicol.v16i2.486

Abstract This paper presents an oscillating wave surge converter (OWSC)-type attachment, comprising a submerged vertical flap connected to the fore edge of a very large floating structure (VLFS) with hinges and linear power take-off (PTO) systems, for extracting wave energy while reducing hydroelastic responses of VLFS. In terms of reductions in hydroelastic responses of VLFS, the OWSC-type attachment is better than the recently proposed raft wave energy converter (WEC)-type attachment for relatively short waves (T < 7 s) and better than the conventional anti-motion device comprising a submerged vertical flap rigidly connected to the fore edge of VLFS for all wave periods. Importantly, the horizontal wave force acting on the submerged flap for the OWSC-type attachment is smaller than that for the conventional anti-motion device, leading to a more economical mooring system. In terms of wave energy extraction, the OWSC-type attachment is better than the raft WEC-type attachment for intermediate and long waves (T ≥ 7 s). In addition, for maximizing power production, the required flap length for the OWSC-type attachment is much smaller than the required pontoon length for the raft WEC-type attachment (about λ/10 as compared to about λ/3, where λ is the incident wavelength).

What is the countercultural potential of citizen science? As a participant in the wider citizen science movement, I can attest that contemporary citizen science initiatives rarely characterise themselves as countercultural. Rather, the goal of most citizen science projects is to be seen as producing orthodox scientific knowledge: the ethos is respectability rather than rebellion (NERC). I will suggest instead that there are resonances with the counterculture that emerged in the 1960s, most visibly through an emphasis on participatory experimentation and the principles of environmental sustainability and social justice. This will be illustrated by example, through two citizen science projects that have a commitment to combining social values with scientific practice. I will then describe the explicitly countercultural organisation, Science for the People, which arose from within the scientific community itself, out of opposition to the Vietnam War. Methodological and conceptual weaknesses in the authoritative model of science are explored, suggesting that there is an opportunity for citizen science to become anti-hegemonic by challenging the hegemony of science itself. This reformulation will be expressed through Deleuze and Guattari's notion of nomadic science, the means through which citizen science could become countercultural. Counterculture Before examining the countercultural potential of citizen science, I set out some of the grounds for identifying a counterculture drawing on the ideas of Theodore Roszak, who invented the term counterculture to describe the new forms of youth movements that emerged in the 1960s (Roszak). This was a perspective that allowed the carnivalesque procession of beatniks, hippies and the New Left to be seen as a single paradigm shift combining psychic and social revolution. But just as striking and more often forgotten is the way Roszak characterised the role of the counterculture as mobilising a vital critique of the scientific worldview (Roszak 273-274). The concept of counterculture has been taken up in diverse ways since its original formation. We can draw, for example, on Lawrence Grossberg's more contemporary analysis of counterculture (Grossberg) to clarify the main concepts and contrast them with a scientific approach. Firstly, a counterculture works on and through cultural formations. This positions it as something the scientific community would see as the other, as the opposite to the objective, repeatable and quantitative truth-seeking of science. Secondly, a counterculture is a diverse and hybrid space without a unitary identity. Again, scientists would often see science as a singular activity applied in modulated forms depending on the context, although in practice the different sciences can experience each other as different tribes. Thirdly, a counterculture is lived as a transformative experience where the participant is fundamentally changed at a psychic level through participation in unique events. Contrast this with the scientific idea of the separation of observer and observed, and the objective repeatability of the experiment irrespective of the experimenter. Fourthly, a counterculture is associated with a unique moment in time, a point of shift from the old to the new. For the counterculture of the 1960s this was the Age of Aquarius. In general, the aim of science and scientists is to contribute to a form of truth that is essentially timeless, in that a physical law is assumed to hold across all time (and space), although science also has moments of radical change with regard to scientific paradigms. Finally, and significantly for the conclusions of this paper, according to Roszak a counterculture stands against the mainstream. It offers a challenge not at the level of detail but, to the fundamental assumptions of the status quo. This is what “science” cannot do, in as much as science itself has become the mainstream. It was the character of science as the bedrock of all values that Roszak himself opposed and for which he named and welcomed the counterculture. Although critical of some of the more shallow aspects of its psychedelic experimentation or political militancy, he shared its criticism of the technocratic society (the technocracy) and the egocentric mode of consciousness. His hope was that the counterculture could help restore a visionary imagination along with a more human sense of community. What Is Citizen Science? In recent years the concept of citizen science has grown massively in popularity, but is still an open and unstable term with many variants. Current moves towards institutionalisation (Citizen Science Association) are attempting to marry growth and stabilisation, with the first Annual General Meeting of the European Citizen Science Association securing a tentative agreement on the common principles of citizen science (Haklay, "European"). Key papers and presentations in the mainstream of the movement emphasise that citizen science is not a new activity (Bonney et al.) with much being made of the fact that the National Audubon Society started its annual Christmas Bird Count in 1900 (National Audubon Society). However, this elides the key role of the Internet in the current surge, which takes two distinct forms; the organisation of distributed fieldwork, and the online crowdsourcing of data analysis. To scientists, the appeal of citizen science fieldwork follows from its distributed character; they can research patterns over large scales and across latitudes in ways that would be impossible for a researcher at a single study site (Toomey). Gathering together the volunteer, observations are made possible by an infrastructure of web tools. The role of the citizen in this is to be a careful observer; the eyes and ears of the scientist in cyberspace. In online crowdsourcing, the internet is used to present pattern recognition tasks; enrolling users in searching images for signs of new planets or the jets of material from black holes. The growth of science crowdsourcing is exponential; one of the largest sites facilitating this kind of citizen science now has well in excess of a million registered users (Zooniverse). Such is the force of the technological aura around crowdsourced science that mainstream publications often conflate it with the whole of citizen science (Parr). There are projects within citizen science which share core values with the counterculture as originally defined by Roszak, in particular open participation and social justice. These projects also show characteristics from Grossberg's analysis of counterculture; they are diverse and hybrid spaces, carry a sense of moving from an old era to a new one, and have cultural forms of their own. They open up the full range of the scientific method to participation, including problem definition, research design, analysis and action. Citizen science projects that aim for participation in all these areas include the Extreme Citizen Science research group (ExCiteS) at University College London (UCL), the associated social enterprise Mapping for Change (Mapping for Change), and the Public Laboratory for Open Technology and Science (Public Lab). ExCiteS sees its version of citizen science as "a situated, bottom-up practice" that "takes into account local needs, practices and culture". Public Lab, meanwhile, argue that many citizen science projects only offer non-scientists token forms of participation in scientific inquiry that rarely amount to more that data collection and record keeping. They counter this through an open process which tries to involve communities all the way from framing the research questions, to prototyping tools, to collating and interpreting the measurements. ExCiteS and Public Lab also share an implicit commitment to social justice through scientific activity. The Public Lab mission is to "put scientific inquiry at the heart of civic life" and the UCL research group strive for "new devices and knowledge creation processes that can transform the world". All of their work is framed by environmental sustainability and care for the planet, whether it's enabling environmental monitoring by indigenous communities in the Congo (ExCiteS) or developing do-it-yourself spectrometry kits to detect crude oil pollution (Public Lab, "Homebrew"). Having provided a case for elements of countercultural DNA being present in bottom-up and problem-driven citizen science, we can contrast this with Science for the People, a scientific movement that was born out of the counterculture. Countercultural Science from the 1970s: Science for the People Science for the People (SftP) was a scientific movement seeded by a rebellion of young physicists against the role of US science in the Vietnam War. Young members of the American Physical Society (APS) lobbied for it to take a position against the war but were heavily criticised by other members, whose written complaints in the communications of the APS focused on the importance of scientific neutrality and the need to maintain the association's purely scientific nature rather than allowing science to become contaminated by politics (Sarah Bridger, in Plenary 2, 0:46 to 1:04). The counter-narrative from the dissidents argued that science is not neutral, invoking the example of Nazi science as a justification for taking a stand. After losing the internal vote the young radicals left to form Scientists and Engineers for Social and Political Action (SESPA), which later became Science for the People (SftP). As well as opposition to the Vietnam War, SftP embodied from the start other key themes of the counterculture, such as civil rights and feminism. For example, the first edition of Science for the People magazine (appearing as Vol. 2, No. 2 of the SESPA Newsletter) included an article about leading Black Panther, Bobby Seale, alongside a piece entitled “Women Demand Equality in Science.” The final articles in the same issue are indicators of SftP's dual approach to science and change; both the radicalisation of professionals (“Computer Professionals for Peace”) and the demystification of technical practices (“Statistics for the People”) (Science for the People). Science for the People was by no means just a magazine. For example, their technical assistance programme provided practical support to street health clinics run by the Black Panthers, and brought SftP under FBI surveillance (Herb Fox, in Plenary 1, 0:25 to 0:35). Both as a magazine and as a movement, SftP showed a tenacious longevity, with the publication being produced every two months between August 1970 and May/June 1989. It mutated through a network of affiliated local groups and international links, and was deeply involved in constructing early critiques of nuclear power and genetic determinism. SftP itself seems to have had a consistent commitment to non-hierarchical processes and, as one of the founders expressed it, a “shit kicking” approach to putting its principles in to practice (Al Weinrub, in Plenary 1, 0:25 to 0:35). SftP criticised power, front and centre. It is this opposition to hegemony that puts the “counter” into counterculture, and is missing from citizen science as currently practised. Cracks in the authority of orthodox science, which can be traced to both methodologies and basic concepts, follow in this paper. These can be seen as an opportunity for citizen science to directly challenge orthodox science and thus establish an anti-hegemonic stance of its own. Weaknesses of Scientific Hegemony In this section I argue that the weaknesses of scientific hegemony are in proportion to its claims to authority (Feyerabend). Through my scientific training as an experimental particle physicist I have participated in many discussions about the ontological and epistemological grounds for scientific authority. While most scientists choose to present their practice publicly as an infallible machine for the production of truths, the opinions behind the curtain are far more mixed. Physicist Lee Somolin has written a devastating critique of science-in-practice that focuses on the capture of the institutional economy of science by an ideological grouping of string theorists (Smolin), and his account is replete with questions about science itself and ethnographic details that bring to life the messy behind-the-scenes conflicts in scientific-knowledge making. Knowledge of this messiness has prompted some citizen science advocates to take science to task, for example for demanding higher standards in data consistency from citizen science than is often the case in orthodox science (Haklay, "Assertions"; Freitag, "Good Science"). Scientists will also and invariably refer to reproducibility as the basis for the authority of scientific truths. The principle that the same experiments always get the same results, irrespective of who is doing the experiment, and as long as they follow the same method, is a foundation of scientific objectivity. However, a 2012 study of landmark results in cancer science was able to reproduce only 11 per cent of the original findings (Begley and Ellis). While this may be an outlier case, there are broader issues with statistics and falsification, a bias on positive results, weaknesses in peer review and the “publish or perish” academic culture (The Economist). While the pressures are all-too-human, the resulting distortions are rarely acknowledged in public by scientists themselves. On the other hand, citizen science has been slow to pick up the gauntlet. For example, while some scientists involved in citizen science have commented on the inequality and inappropriateness of orthodox peer review for citizen science papers (Freitag, “What Is the Role”) there has been no direct challenge to any significant part of the scientific edifice. I argue that the nearest thing to a real challenge to orthodox science is the proposal for a post-normal science, which pre-dates the current wave of citizen science. Post-normal science tries to accommodate the philosophical implications of post-structuralism and at the same time position science to tackle problems such as climate change, intractable to reproducibility (Funtowicz and Ravetz). It accomplishes this by extending the domains in which science can provide meaningful answers to include issues such as global warming, which involve high decision stakes and high uncertainty. It extends traditional peer review into an extended peer community, which includes all the stakeholders in an issue, and may involve active research as well as quality assessment. The idea of extended peer review has obvious overlaps with community-oriented citizen science, but has yet to be widely mobilised as a theoretical buttress for citizen-led science. Prior even to post-normal science are the potential cracks in the core philosophy of science. In her book Cosmopolitics, Isabelle Stengers characterises the essential nature of scientific truth as the ability to disqualify and exclude other truth claims. This, she asserts, is the hegemony of physics and its singular claim to decide what is real and what is true. Stengers traces this, in part, to the confrontation more than one hundred years ago between Max Planck and Ernst Mach, whereas the latter argued that claims to an absolute truth should be replaced by formulations that tied physical laws to the human practices that produced them. Planck stood firmly for knowledge forms that were unbounded by time, space or specific social-material procedures (Stengers). Although contemporary understandings of science are based on Planck's version, citizen science has the potential to re-open these questions in a productive manner for its own practices, if it can re-conceive of itself as what Deleuze and Guattari would call nomadic science (Deleuze; Deleuze & Guattari). Citizen Science as Nomadic Science Deleuze and Guattari referred to orthodox science as Royal Science or Striated Science, referring in part to its state-like form of authority and practice, as well as its psycho-social character. Their alternative is a smooth or nomadic science that, importantly for citizen science, does not have the ambition to totalise knowledge. Nomadic science is a form of empirical investigation that has no need to be hooked up to a grand narrative. The concept of nomadic science is a natural fit for bottom-up citizen science because it can valorise truths that are non-dual and that go beyond objectivity to include the experiential. In this sense it is like the extended peer review of post-normal science but without the need to be limited to high-risk high-stakes questions. As there is no a priori problem with provisional knowledges, it naturally inclines towards the local, the situated and the culturally reflective. The apparent unreliability of citizen science in terms of participants and tools, which is solely a source of anxiety, can become heuristic for nomadic science when re-cast through the forgotten alternatives like Mach's formulation; that truths are never separated from the specifics of the context and process that produced them (Stengers 6-18; 223). Nomadic science, I believe, will start to emerge through projects that are prepared to tackle toxic epistemology as much as toxic pollutants. For example, the Community Based Auditing (CBA) developed by environmental activists in Tasmania (Tattersall) challenges local alliances of state and extractive industries by undermining their own truth claims with regards to environmental impact, a process described in the CBA Toolbox as disconfirmation. In CBA, this mixture of post-normal science and Stenger's critique is combined with forms of data collection and analysis known as Community Based Sampling (Tattersall et al.), which would be recognisable to any citizen science project. The change from citizen science to nomadic science is not a total rupture but a shift in the starting point: it is based on an overt critique of power. One way to bring this about is being tested in the “Kosovo Science for Change” project (Science for Change Kosovo), where I am a researcher and where we have adopted the critical pedagogy of Paulo Freire as the starting point for our empirical investigations (Freire). Critical pedagogy is learning as the co-operative activity of understanding—how our lived experience is constructed by power, and how to make a difference in the world. Taking a position such as nomadic science, openly critical of Royal Science, is the anti-hegemonic stance that could qualify citizen science as properly countercultural. Citizen Science and Counterculture Counterculture, as I have expressed it, stands against or rejects the hegemonic culture. However, there is a strong tendency in contemporary social movements to take a stance not only against the dominant structures but against hegemony itself. They contest what Richard Day calls the hegemony of hegemony (Day). I witnessed this during the counter-G8 mobilisation of 2001. Having been an activist in the 1980s and 1990s I was wearily familiar with the sectarian competitiveness of various radical narratives, each seeking to establish itself as the correct path. So it was a strongly affective experience to stand in the convergence centre and listen to so many divergent social groups and movements agree to support each other's tactics, expressing a solidarity based on a non-judgemental pluralism. Since then we have seen the emergence of similarly anti-hegemonic countercultures around the Occupy and Anonymous movements. It is in this context of counterculture that I will try to summarise and evaluate the countercultural potential of citizen science and what being countercultural might offer to citizen science itself. To be countercultural it is not enough for citizen science to counterpose participation against the institutional and hierarchical aspects of professional science. As an activity defined purely by engagement it offers to plug the legitimacy gap for science while still being wholly dependent on it. A countercultural citizen science must pose a strong challenge to the status quo, and I have suggested that a route to this would be to develop as nomadic science. This does not mean replacing or overthrowing science but constructing an other to science with its own claim to empirical methods. It is fair to ask what this would offer citizen science that it does not already have. At an abstract level it would gain a freedom of movement; an ability to occupy Deleuzian smooth spaces rather than be constrained by the striation of established science. The founders of Science for the People are clear that it could never have existed if it had not been able to draw on the mass movements of its time. Being countercultural would give citizen science an affinity with the bottom-up, local and community-based issues where empirical methods are likely to have the most social impact. One of many examples is the movement against fracking (the hydraulic fracturing of deep rock formations to release shale gas). Together, these benefits of being countercultural open up the possibility for forms of citizen science to spread rhizomatically in a way that is not about immaterial virtual labour but is itself part of a wider cultural change. 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Tahle práce se zaměřila na aerodynamickou analýzu principů zvyšování pumpážních záloh. V první kapitole jsou popsány kompresory leteckých motorů a zavedeny potřebné znalosti kompresorových charakteristik a proti-pumpážních zařízení. V druhé kapitole se nachází detailní popis CFD modelu, jeho nastavení, citlivostní analýzy sítě a korelace výsledků s experimentálním měřením. V třetí kapitole jsou popsány data neupraveného kompresoru a jsou zde popsány problematická místa první stupně kompresoru z pohledu proti-pumpážních zařízení. Ve čtvrté kaptiole jsou popsány CFD výsledky z analýz jednotlivých proti-pumpážních zařízení a také popis jejich optimalizace. Práce je zakončena srovnáním jednotlivých zařízení pomocí dvou objektivních kritérií.

The dissertation is devoted to analysis of unstable phenomena in the centrifugal blower. These phenomena are known to be a source of serious threat to safety of the machine and the piping system connected to it. The complexity of centrifugal impellers causes that instabilities therein can have various forms and locations and have been subject of interest for over 60 years. The dissertation consists of two main parts: one of them being a result of the experimental investigations, the other one describing an outcome of the numerical simulations. In the experimental part, three methods of data analysis were applied: static, dynamic and a novel approach referred to as the quasi-dynamic one. The blower was examined in two configurations of the outlet pipe corresponding to different outlet plenum volumes. The results were presented in a form of a performance curve, amplitude plots, scalograms, phase trajectories and spectral maps. The machine was found to operate in four different regimes , namely: the stable regime, the inlet recirculation, the transient phase and the deep surge. The inlet recirculation was identifed as the earliest instability present in the inlet zone. It was characterized by strong pressure jumps and a spectral structure of broadband noise. In the transient phase, the pressure oscillation amplitude grew by one order of magnitude and appeared in all points analyzed. In the deep surge, strong pressure oscillations appeared, with one frequency component close to the Helmholtz frequency. A new factor that can be used for real-time monitoring and early detection of unstable flow phenomena was developed as a result of signal phase trajectory analysis. The second part presents results of the transient numerical simulations conducted with FLUENT and then compared to the experimental data. The full impeller geometry was simulated together with the diffuser, the volute and large volumes of the inlet and outlet pipes. Computations were run at different combinations of the boundary conditions corresponding to different operational points. Simulations with a reduced plenum volume were also conducted analogously to the experimental study. The machine was found to operate in four working regimes: stable regime, pre-surge (impeller instability), presurge (inlet recirculation) and the deep surge. An overview on the machine performance was provided together with a detailed description of particular flow structures. The results were compared to the experimental data by means of, a performance curve, phase trajectories and frequency spectra and were found to be in reasonable agreement. The numerical study introduced a possibility of a detailed analysis of unstable flow structures such as the inlet recirculation, the impeller instability, a the deep surge cycle. The study confirmed that computational methods introduce an opportunity to understand the unstable flow structures in detail and provide a missing link between real flow phenomena and mathematical surge and stall models, which is essential for effective anti-surge protection.

This paper recites the non-linear dynamic finite element simulation to the whole collision process of the collision between the anti-collision equipment and the bridge pile cap in the rough waves and surge with an example, basing on the solving technique of explicit non-linear finite element method and the mechanism in bridge-anti-collision equipment collision, including the process of building a reasonable FEA model and the numerical calculation and analysis of the collision process in considering the hydrodynamics influence by non-linear finite element analysis code MSC.Dytran / Patran. Described in detail attached to the collision analysis needs to consider such as determination of element size control, the selection of material models and failure criteria, the definition of contact and friction and so on. It is pointed that local strength of the anti-collision equipments and the bridge pile caps, as well as the collision impact force in the rough seas and surge. On the basis of numerical simulation, the general laws and characteristics of the impulse response of collision are achieved, which can be extended to the design of the bridge anti-collision devices and reinforcement for pier caps with providing a range of meaningful conclusions.

Abstract In the ocean environment, the ship is prone to motions in six directions of roll, pitch, yaw, sway, surge, and heave under the influence of the waves. It will affect not only the airworthiness of the ship, but also have an adverse impact for the crew and the board’s equipment. In view of this situation, a new type of ship anti-rolling device has been proposed, which is based on the structural characteristics of the Stewart platform with precise adjustment of the position of the load platform and the stability of the gyroscope under the high-speed rotation of the rotor. Firstly, theoretical analysis of the device conducted with theorem of moment of momentum method shows that the device has practical feasibility and effectiveness. Then, a solid model has been established in Creo2.0 software, and the model has been imported into the dynamic analysis software MSC.ADAMS. Finally, using torque as the exciting force to simulate the impact of the wave, the dynamic simulation of the overall model has been analyzed. The simulation results show that such device has good anti-rolling performance under certain waves, indicating that the new anti-rolling device based on the Stewart platform and the three-axis gyroscope has effective reliability and practicability.

Abstract Pressurized solid oxide fuel cell (SOFC) systems are one of the most promising technologies to achieve high energy conversion efficiencies and reduce pollutant emissions. The most common solution for pressurization is the integration with a micro gas turbine, a device capable of exploiting the residual energy of the exhaust gas to compress the fuel cell air intake and, at the same time, generating additional electrical power. The focus of this study is on an alternative layout, based on an automotive turbocharger, which has been more recently considered by the research community to improve cost effectiveness at small size (< 100 kW), despite reducing slightly the top achievable performance. Such turbocharged SOFC system poses two main challenges. On one side, the absence of an electrical generator does not allow the direct control of the rotational speed, which is determined by the power balance between turbine and compressor. On the other side, the presence of a large volume between compressor and turbine, due to the fuel cell stack, alters the dynamic behavior of the turbocharger during transients, increasing the risk of compressor surge. The pressure oscillations associated with such event are particularly detrimental for the system, because they could easily damage the materials of the fuel cells. The aim of this paper is to investigate different techniques to drive the operative point of the compressor far from the surge condition when needed, reducing the risks related to transients and increasing its reliability. By means of a system dynamic model, developed using the TRANSEO simulation tool by TPG, the effect of different anti-surge solutions is simulated: (i) intake air conditioning, (ii) water spray at compressor inlet, (iii) air bleed and recirculation, and (iv) installation of an ejector at the compressor intake. The pressurized fuel cell system is simulated with two different control strategies, i.e. constant fuel mass flow and constant turbine inlet temperature. Different solutions are evaluated based on surge margin behavior, both in the short and long terms, but also monitoring other relevant physical quantities of the system, such as compressor pressure ratio and turbocharger rotational speed.

The sizing of surge protection devices for both compressor and surrounding system may require the knowledge of performance curves in 2nd quadrant with a certain level of accuracy. In particular two performance curves are usually important: the pressure ratio trend versus flow rate inside the compressor and the work coefficient or power absorption law. The first curve allows estimating mass flow in the compressor given a certain pressure level imposed by system, while the second is important to estimate the time required to system blow down during ESD (emergency shutdown). Experimental data are routinely not available in the early phase of anti-surge protection devices and prediction methods are needed to provide performance curves in 2nd quadrant starting from the geometry of both compressor and system. In this paper two different approaches are presented to estimate performance curves in 2nd quadrant: the first is a simple 1D approach based on velocity triangle and the second is a full unsteady CFD computation. The two different approaches are applied to the experimental data more deeply investigated in part I by Belardini E.[3]. The measurement of compressor behavior in 2nd quadrant was possible thanks to a dedicated test arrangement in which a booster compressor is used forcing stable reverse flow. The 1D method showed good agreement with experiments at design speed. In off-design condition a correlation for deviation angle was tuned on experimental data to maintain an acceptable level of accuracy. With very low reverse flow rates some discrepancies are still present but this region plays a secondary role during the dynamic simulations of ESD or surge events. The unsteady CFD computation allowed a deeper insight into the fluid structures, especially close to very low flow rates when the deviation of the 1D method and the experimental data is higher. An important power absorption mechanism was identified in the pre-rotation effect of impeller as also the higher impact of secondary flows. These two methods are complementary in terms of level of complexity and accuracy and to a certain extent both necessary. 1D methods are fast to be executed and more easily calibrated to match the available experiments, but they have limited capability to help understanding the underlying physics. CFD is a more powerful tool for understanding fluid structures and energy transfer mechanisms but requires computational times not always suitable for a production environment. 1D method can be used for standard compressor and applications for which consolidated experience have been already gathered while CFD is more suitable during the development of new products or up to front projects in general.