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The driving and resistance torques of some rotating machinery for industrial applications are nonstationary and affect system dynamics. Under such operating conditions, coupling between torsional and lateral vibrations may become significant for drive lines supported by hydrodynamic bearings in particular design configurations. Indeed, the occurrence of fluid–structure interactions causes a reduction in the stability threshold of the journal bearings. A hypothesis based on Hopf bifurcation theory (HBT), which justifies how the coupling phenomenon develops, is validated by means of overall experimental observations and a suitable numerical model. When the pulsating driving torque induces significant angular speed oscillation, the rotor-bearing system lateral operating response becomes more complex, and bearing instability onset is detected. Such observation proves the influence of bearings in converting torsional oscillations to lateral vibrations. Particularly, during run-up and run-down tests, localized hysteresis is observed in trends of fundamental order contents. The numerical model of the hydrodynamic bearings solves the Reynolds equation in unsteady conditions to quantify the lateral vibrations amplitude in the presence of both angular speed oscillation and dynamic perturbation. The proposed approach proves the onset of torsional–lateral vibration coupling due to hydrodynamic bearings, to a certain extent. The detected hysteresis phenomena can also be explained by the onset of journal bearing instability.

The present work features post-processing methods applied to vibro-acoustic data acquired from a T100 micro gas turbine (mGT) plant coupled with different volume interposed plenums. Such experimental campaign was conducted by relying on a test bench developed at the University of Genoa for hybrid systems emulation. Nonetheless, the obtained results can be generalized to all advanced cycles in which a mGT is coupled with further external elements which cause an increase of plant overall volume size. Since in this case a 100 kW mGT was employed, the interposed vessel was placed between heat recovery system outlet and combustor inlet, such as in common cases relevant to small size plants. Post-processing techniques carried out on acoustic and vibrational measurements can make available innovative diagnostic tools and predictive solutions by relying on appropriate instability indicators which are defined basing only on microphone and accelerometer experimental data. The main results presented in this work are relevant to rotating stall and incipient surge proper identification. Such investigation has been performed to increase the knowledge about such dangerous compressor working conditions; indeed, energy systems characterized by significant interposed volumes coupled with centrifugal compressors feature issues relevant to structural damaging due to surge and rotating stall.

High-speed centrifugal compressors are commonly exploited to pressurize fuel cell-based hybrid energy systems. In such complex plants, because of significant interposed volumes due to fuel cells, dynamic compressor response can induce severe vibrations caused by low mass flow rates instability. In particular, surge strongly limits centrifugal compressors stable working region when moving towards low mass flow rate due to a change in system operating point. Consequently, a complete system identification is performed in order to adequately characterize compressor dynamic response for early surge detection. To this goal, a tailored experimental activity has been carried out at the Thermochemical Power Group of the University of Genoa on a vaneless diffuser compressor turbocharger used for the pressurization of an innovative solid oxide fuel cell (SOFC) emulator plant. Several post-processing methods have been performed on system vibro-acoustic responses to better predict and classify compressor status as stable or unstable. The obtained results provide original diagnostic insights for monitoring systems capable of preventing surge and other low mass flow unstable phenomena, such as rotating stall cells inception. Low mass flow rate fluid-dynamic instabilities prevention can extend compressor operating range, performance, and reliability to allow better integration with other plant components.

Smart Polygeneration Grids integrate different prime movers, such as traditional generators, renewable energy sources and energy storage systems to locally supply electrical and thermal power to achieve high conversion efficiencies and increase self-consumption. Integrating different energy systems poses some challenges on the plant Energy Management Systems (EMS), which must accommodate different operational requirements while following the electrical and thermal loads. Battery Energy Storage Systems (BESSs) can provide additional flexibility to the system. This paper intends to evaluate the impact of integrating a Ni-Zn-based BESS into an existing cogeneration plant through a dedicated sensitivity analysis over the operative characteristics of the BESS itself (maximum power and capacity). The IES LAB of the Savona’s Campus already contains different energy systems: a cogenerative micro gas turbine, a heat-pump, solar thermal panels and two thermal energy storage systems that provide electricity and thermal power to the Smart Polygeneration Grid of the Campus. A new developed energy scheduler accommodates the integration of the new battery and meets the electrical and thermal demands. The aim is to demonstrate that integrating the BESS provides additional benefits in the system management and can reduce fuel usage and OPEX.

We complete the publication of all microlensing planets (and “possible planets”) identified by the uniform approach of the KMT AnomalyFinder system in the 21 KMT subprime fields during the 2019 observing season, namely, KMT-2019-BLG-0298, KMT-2019-BLG-1216, KMT-2019-BLG-2783, OGLE-2019-BLG-0249, and OGLE-2019-BLG-0679 (planets), as well as OGLE-2019-BLG-0344 and KMT-2019-BLG-0304 (possible planets). The five planets have mean log mass ratio measurements of (−2.6, −3.6, −2.5, −2.2, −2.3), median mass estimates of (1.81, 0.094, 1.16, 7.12, 3.34) M _Jup , and median distance estimates of (6.7, 2.7, 5.9, 6.4, 5.6) kpc, respectively. The main scientific interest of these planets is that they complete the AnomalyFinder sample for 2019, which has a total of 25 planets that are likely to enter the statistical sample. We find statistical consistency with the previously published 33 planets from the 2018 AnomalyFinder analysis according to an ensemble of five tests. Of the 58 planets from 2018–2019, 23 were newly discovered by AnomalyFinder. Within statistical precision, half of the planets have caustic crossings, while half do not; an equal number of detected planets result from major- and minor-image light-curve perturbations; and an equal number come from KMT prime fields versus subprime fields.

In bacteria functionally related genes comprising metabolic pathways and protein complexes are frequently encoded in operons and are widely conserved across phylogenetically diverse species. The evolution of these operon-encoded processes is affected by diverse mechanisms such as gene duplication, loss, rearrangement, and horizontal transfer. These mechanisms can result in functional diversification, increasing the potential evolution of novel biological pathways, and enabling pre-existing pathways to adapt to the requirements of particular environments. Despite the fundamental importance that these mechanisms play in bacterial environmental adaptation, a systematic approach for studying the evolution of operon organization is lacking. Herein, we present a novel method to study the evolution of operons based on phylogenetic clustering of operon-encoded protein families and genomic-proximity network visualizations of operon architectures. We applied this approach to study the evolution of the synthase dependent exopolysaccharide (EPS) biosynthetic systems: cellulose, acetylated cellulose, poly-β-1,6-N-acetyl-D-glucosamine (PNAG), Pel, and alginate. These polymers have important roles in biofilm formation, antibiotic tolerance, and as virulence factors in opportunistic pathogens. Our approach revealed the complex evolutionary landscape of EPS machineries, and enabled operons to be classified into evolutionarily distinct lineages. Cellulose operons show phyla-specific operon lineages resulting from gene loss, rearrangement, and the acquisition of accessory loci, and the occurrence of whole-operon duplications arising through horizonal gene transfer. Our evolution-based classification also distinguishes between PNAG production from Gram-negative and Gram-positive bacteria on the basis of structural and functional evolution of the acetylation modification domains shared by PgaB and IcaB loci, respectively. We also predict several pel-like operon lineages in Gram-positive bacteria and demonstrate in our companion paper (Whitfield et al PLoS Pathogens, in press) that Bacillus cereus produces a Pel-dependent biofilm that is regulated by cyclic-3',5'-dimeric guanosine monophosphate (c-di-GMP).

Our understanding of the biofilm matrix components utilized by Gram-positive bacteria, and the signalling pathways that regulate their production are largely unknown. In a companion study, we developed a computational pipeline for the unbiased identification of homologous bacterial operons and applied this algorithm to the analysis of synthase-dependent exopolysaccharide biosynthetic systems. Here, we explore the finding that many species of Gram-positive bacteria have operons with similarity to the Pseudomonas aeruginosa pel locus. Our characterization of the pelDEADAFG operon from Bacillus cereus ATCC 10987, presented herein, demonstrates that this locus is required for biofilm formation and produces a polysaccharide structurally similar to Pel. We show that the degenerate GGDEF domain of the B. cereus PelD ortholog binds cyclic-3',5'-dimeric guanosine monophosphate (c-di-GMP), and that this binding is required for biofilm formation. Finally, we identify a diguanylate cyclase, CdgF, and a c-di-GMP phosphodiesterase, CdgE, that reciprocally regulate the production of Pel. The discovery of this novel c-di-GMP regulatory circuit significantly contributes to our limited understanding of c-di-GMP signalling in Gram-positive organisms. Furthermore, conservation of the core pelDEADAFG locus amongst many species of bacilli, clostridia, streptococci, and actinobacteria suggests that Pel may be a common biofilm matrix component in many Gram-positive bacteria.

The aim of the present research is to characterize both experimentally and numerically journal bearings with low radial clearances for rotors in small-scale applications (e.g., microgas turbines); their diameter is in the order of ten millimetres, leading to very small dimensional clearances when the typical relative ones (order of 1/1000) are employed; investigating this particular class of journal bearings under static and dynamic loading conditions represents something unexplored. To this goal, a suitable test rig was designed and the performance of its bearings was investigated under steady load. For the sake of comparison, numerical simulations of the lubrication were also performed by means of a simplified model. The original test rig adopted is a commercial rotor kit (RK), but substantial modifications were carried out in order to allow significant measurements. Indeed, the relative radial clearance of RK4 RK bearings is about 2/100, while it is around 1/1000 in industrial bearings. Therefore, the same original RK bearings are employed in this new test rig, but a new shaft was designed to reduce their original clearance. The new custom shaft allows to study bearing behaviour for different clearances, since it is equipped with interchangeable journals. Experimental data obtained by this test rig are then compared with further results of more sophisticated simulations. They were carried out by means of an in-house developed finite element (FEM) code, suitable for thermoelasto-hydrodynamic (TEHD) analysis of journal bearings both in static and dynamic conditions. In this paper, bearing static performances are studied to assess the reliability of the experimental journal location predictions by comparing them with the ones coming from already validated numerical codes. Such comparisons are presented both for large and small clearance bearings of original and modified RKs, respectively. Good agreement is found only for the modified RK equipped with small clearance bearings (relative radial clearance 8/1000), as expected. In comparison with two-dimensional lubrication analysis, three-dimensional simulation improves prediction of journal location and correlation with experimental results.

High-speed centrifugal compressors may be exploited to pressurize fuel cell systems. Nonetheless, due to fuel cells significant interposed volumes, compressor behavior can lead to severe vibrations related to fluid-dynamic instabilities during part load operating conditions. In particular, surge strongly limits centrifugal compressors stable operating region when moving toward low mass flow rates due to a change in system working point. Therefore, compressor dynamic response must be adequately characterized for early surge detection. To this aim, a dedicated experimental activity was conducted on a vaneless diffuser turbocharger coupled to a solid oxide fuel cell emulator plant; compressor evolution toward surge was investigated. Several signal processing techniques were applied to pressure signals as well as vibro-acoustic responses to better predict compressor behavior and classify its status as stable or unstable. Cepstrum, cross-correlation, and wavelet transform have been identified as suitable techniques to define precursors able to early detect surge. By means of cross-correlation function, propagation phenomena in the ducts can be investigated to assess how they interact near compressor low-mass flowrate unstable conditions. Cepstrum provides a convenient way to determine pressure signal spectrum distortion in terms of further periodic components onset. These harmonic components are due to complex system responses generated by transient phenomena; indeed, cepstrum allows to identify hidden anomalous contributions in system response spectra which may arise in incipient surge conditions. Wavelet transform was performed on both structural and pressure response signals to observe their dominant energy contents temporal evolution; indeed, such spectral pattern time-dependent variation can detect the rise of unstable conditions. By exploiting all these techniques, a complete system identification is performed which allows a deeper investigation of the physical phenomena involved; moreover, a more complete set of surge precursors extracted from different probes' physical signals were defined. The results obtained provide original diagnostic insights for monitoring systems suited to perform early surge detection. Compressor instability prevention can extend its operating range, performance, and reliability to allow better integration with other plant components. Finally, cepstrum application for compressor instability identification can be regarded as a novel method in the fluid machinery field. [ABSTRACT FROM AUTHOR]

The use of computational structural models that include geometrical non-linearity in many application cases may require high reliability in prediction of displacements. Nevertheless, large differences up to 60% on maximum total displacement have been found among results of static large-deformation analyses performed by means of the major commercial software packages in a simple benchmark study with linear material properties. In order to investigate the causes of such disagreement, the present work compares different finite element formulations including well-established stress update schemes. The various formulations are tested, and results are compared in three test cases. Rodriguez stress update algorithms have shown the best performance among methods reported in literature. Finally, the cause of the large differences found in the predictions of commercial codes is identified. It is linked to the energetic inconsistency of some stress update methods in the simulation of extension/compression loading conditions. Such inaccuracy is reproduced analytically by formulating and integrating the corresponding inconsistent constitutive equations. The identified problem is very important for designers, as it affects almost all the static simulations, which are the most common type of large-deformation analyses and usually involve extension/compression loading. [ABSTRACT FROM AUTHOR]