"Analysis of dynamic responses and instabilities in rotating machinery\u201d

The first task 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., micro Gas 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 were 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 work, 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 RK, 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. The second main task of the present work is the development and the implementation of a suitable analytical model to correctly capture rolling bearing radial stiffness, particularly nearby the critical speeds of the investigated rotor-bearings system. In this work, such bearing non-linear stiffness lumped parameter model is firstly validated on the commercial RK and then it is applied to both air bladeless turbines (or Tesla turbines) and to an innovative microturbine, in order to assess their global rotodynamic behavior when they are mounted on ball bearings. In order to properly investigate all the issues related to critical speeds and stiffness, an adequate number of experimental tests was performed by exploiting an experimental air Tesla turbine prototype located at TPG experimental facility of the University of Genoa. The correlation between measured flexural critical speeds and their numerical predictions is markedly conditioned by the correct identification of ball bearings dynamic characteristics; in particular, bearings stiffness effect may play a significant role in terms of rotor-bearings system natural frequencies and therefore it must be properly assessed. Indeed, Tesla turbine rotor FE model previously employed for numerical modal analysis relies on rigid bearings assumption and therefore it does not account for bearings stiffness overall contribution, which may become crucial in case of \u201chard mounting\u201d of rotor-bearings systems. Subsequently, high-speed air Tesla rotor is investigated by means of an enhanced FE model for numerical modal analysis within Ansys\uae environment, where ball bearings are modelled as non-linear springs whose stiffness is expressed according to the analytic model implemented in Matlab\uae. Two different numerical FE models are devised for microturbine rotor modelling which respectively rely on beam elements and on three-dimensional solid elements for mechanical system spatial discretization. The obtained results in terms of rotor-bearings system modal analysis exhibit an improvement in experimental-numerical results correlation by relying on such ball bearing stiffness model; moreover, beam-based FE model critical speeds predictions are coherent with experimental evidence and with respect to solid elements model it is characterized by lower computational time and it is more easily interpretable. Thus, such experimentally validated numerical model represents a reliable and easily adaptable tool for highspeed rotating machinery critical speeds prediction in practical industrial application cases. Finally In this work, several signal processing techniques performed on vibro-acoustic signals acquired from a T100 Turbec microturbine (which is furnished with a centrifugal compressor) are illustrated. Research activity goal focuses on the investigation different kinds of system response starting from non-intrusive probes signals like accelerometers and microphones; this is made by means of techniques such as HOSA and Wavelet Transform, developed in Matlab\uae environment, for early detection of the onset of unstable phenomena in centrifugal compressors. These new and different methods have been applied to the same set of data to get sufficiently independent information useful to synergistically improve knowledge in the diagnostic system. Data were acquired by means of an experimental facility based on a T100 turbine developed by the Thermochemical Power Group (TPG) at the University of Genoa. Sampling rate and sensor placement were carefully taken into account, basing both on the physical phenomena to be observed and on the sensor dynamic characteristics. In this context, it is meant to study microphones and accelerometers signals not from an isolated centrifugal turbomachine installed in a dedicated line, but from a whole compressor placed in a mGT system for energy generation. Indeed, the investigated machine is not operating in standalone mode, but its working point and angular velocity depend on the coupling with several elements. In particular, compressor working point and then its vibro-acoustic signals are expected to convey vibration and sound contributions coming from all the plant components; thus, they are more representative of machine realistic behavior in the energy system

Energy management and load profile optimisation of 10 kWh BESS integrated into a Smart Polygeneration Grid subnetwork

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

Early surge detection on a turbocharger used to pressurize a SOFC plant emulator

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

Early surge detection in a mGT plant coupled with large volumes

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

Stem cell therapy for severe autoimmune diseases

Intense immunosuppresion followed by alogenic or autogenic hematopoietic stem cell transplantation is a relatively recent procedure which was used for the first time in severe, refractory cases of systemic lupus erythematosus. Currently three agressive procedures are used in the treatment of autoimmune diseases: high dose chemotherapy without stem cell rescue, intense immunosuppression with subsequent infusion of the alogenic hematopoietic stem cell transplantation combined with or without the selection of CD34+ cells, and the autogenic hematopoietic stem cell transplantation. Proof of the graft-versus-leukemia effect observed define SCT as a form of immunotherapy, with additional evidence of an similar Graft-vs-Autoimmunity effect which is suggestive of a cure for autoimmune diseases in this type of therapy. The use of alogenic SCT improved due to its safety compared to autogenic transplantations. In this report, data of multiply sclerosis and systemic lupus erythematosus are reported, with the conclusion that Immunoablation followed by SCT is clearly indicated in such cases

Nonmyeloablative hematopoietic stem cell transplantation for systemic lupus erythematosus,”

Two streams of research are at the origin of the utilization of hematopoietic stem cell transplantation (HSCT) for severe autoimmune diseases (SADs). The allogeneic approach came from experimental studies on lupus mice, besides clinical results in coincidental diseases. The autologous procedure was encouraged by researches on experimental neurological and rheumatic disorders. At present the number of allogeneic HSCT performed for human SADs can be estimated to not over 100 patients, and the results are not greatly encouraging, considering the significant transplant-related mortality (TRM) and the occasional development of a new autoimmune disorder and/or relapses notwithstanding full donor chimerism. Autologous HSCT for refractory SLE has become a major target. Severe cases have been salvaged, TRM is low and diminishing, and prolonged clinical remissions are obtainable. Two types of immune resetting have been established, "re-education" and regulatory T cell (Tregs) normalization. Allogeneic HSCT for SLE seems best indicated for patients with disease complicated by an oncohematologic malignancy. Autologous HSCT is a powerful salvage therapy for otherwise intractable SLE. The duration of remission in uncertain, but a favorable response to previously inactive treatments is a generally constant feature. The comparison with new biological agents, or the combination of both, are to be ascertained

Hematopoietic Stem Cell Transplantation for Systemic Lupus Erythematosus

Two streams of research are at the origin of the utilization of hematopoietic stem cell transplantation (HSCT) for severe autoimmune diseases (SADs). The allogeneic approach came from experimental studies on lupus mice, besides clinical results in coincidental diseases. The autologous procedure was encouraged by researches on experimental neurological and rheumatic disorders. At present the number of allogeneic HSCT performed for human SADs can be estimated to not over 100 patients, and the results are not greatly encouraging, considering the significant transplant-related mortality (TRM) and the occasional development of a new autoimmune disorder and/or relapses notwithstanding full donor chimerism. Autologous HSCT for refractory SLE has become a major target. Severe cases have been salvaged, TRM is low and diminishing, and prolonged clinical remissions are obtainable. Two types of immune resetting have been established, “re-education” and regulatory T cell (Tregs) normalization. Allogeneic HSCT for SLE seems best indicated for patients with disease complicated by an oncohematologic malignancy. Autologous HSCT is a powerful salvage therapy for otherwise intractable SLE. The duration of remission in uncertain, but a favorable response to previously inactive treatments is a generally constant feature. The comparison with new biological agents, or the combination of both, are to be ascertained