130,387 research outputs found
Una procedura per la stima delle tensioni termo-meccaniche in alberi intagliati
No full textNei componenti meccanici dalla geometria complessa l’analisi delle tensioni termomeccaniche è comunemente
effettuata tramite FEM. Questa analisi risulta onerosa a livello computazionale e la validità dei
risultati è limitata ai casi specifici considerati. Per tali motivi può risultare utile un approccio analitico,
seppure semplificato, che sia in grado di fornire una ragionevole stima delle tensioni termo-meccaniche
per classi di geometrie simili.
Nel presente lavoro, è stato considerato il caso di alberi intagliati; in particolare, si è preso a riferimento
un albero a due diametri soggetto a convezione con fluido sulla superficie esterna. Ci si è quindi proposti
di verificare se fosse possibile definire un fattore di concentrazione delle tensioni termo-meccaniche per
stimare lo stato di tensione nella zona di raccordo a partire dalla soluzione numerica nota per il cilindro
infinito. È stato verificato che è possibile esprimere tale coefficiente tramite il rapporto tra i picchi delle
tensioni misurate durante il transitorio nella zona di intaglio ed in quella cilindrica. Nel lavoro viene
inoltre discusso l’effetto delle dimensioni del componente sullo stato di sollecitazione, tramite il numero
di Biot. Nel caso delle tensioni termomeccaniche, infatti, l’effetto della concentrazione di tensione non
è riconducibile ad un semplice problema di forma
A model-based prediction of balancing behavior of rotors above the speed range in available balancing systems
No full textRotor balancing is probably the most discussed topic in the entire literature about rotor dynamics. It would therefore seem that, from the point of view of theory, this is a problem of little interest, however, balancing is very relevant in the industrial practice and sometimes there are very particular cases that cannot be addressed and solved by traditional methods. Moreover, many papers deal with only simulated results or with small-scale tests-rigs, which can hardly reproduce the behavior of real rotors. The case described in this paper is just one of these and presents what could be defined as “predicting the effect of balancing” at rotational speeds that are higher than those possible on balancing machines. Rotordynamics modeling, identification techniques developed by the authors and the available vibration measurements allow the simulation of the behavior, i.e. the vibrations, of the considered turbine rotor on the balancing machine,even at rotational speeds higher than those are possible to be reached, but that correspond to the trip speed in the plant
A Navigation Interface Based on Head Tracking by Accelerometers
No full textThis work presents a novel user interface for navigation in virtual environments and remote control of devices. The proposed system is head-mounted, allowing for the control of up to six degrees of freedom while leaving the user with free hands. The device is composed of six linear accelerometers arranged on a couple of glasses and a specific embedded controller that allows for the measuring of glass acceleration information. This is then translated in motion control information for navigation in virtual environments and/or as other devices input. The specific algorithms to integrate the motion acceleration cues sensed from the glasses while filtering the drifting errors and effect related to head rotations are presented herein
Full-scale vibration testing of nozzle guide vanes
No full textAn increasing number of turboexpanders are equipped with Nozzle Guide Vane (NGV) as the first stator stage. By varying the throat area of the first stator vane the NGV enables an additional control methodology to the line-up power output allowing higher operational flexibility and higher efficiency at partial load and partial speed. The design of this component might become critical for enabling high expander availability considering its exposure to high temperature, thermal loading, and fluid induced vibrations. This is especially true also considering that the vibration frequencies of this sub-assembly are influenced by internal clearances and by the value of the friction coefficient, which leaves a relevant margin of error when using numerical methods (such as FEM) for predicting the actual structural behavior of this component. In this paper, the design of a full-scale test bench for the determination of both friction coefficients and modal behavior of a nozzle guide vane geometry is described. The bench enables us to simulate the pre-load due to aerodynamic forces on the NGV airfoil simulating the actual working conditions of bushes and bearings
Steam turbine rotor stress control through nonlinear model predictive control
No full textThe current flexibility of the energy market requires operating steam turbines that have challenging operation requirements such as variable steam conditions and higher number of startups. This article proposes an advanced control system based on the Nonlinear Model Predictive Control (NMPC) technique, which allows to speed up the start-up of steam turbines and increase the energy produced while maintaining rotor stress as a constraint variable. A soft sensor for the online calculation of rotor stress is presented together with the steam turbine control logic. Then, we present how the computational cost of the controller was contained by reducing the order of the formulation of the optimization problem, adjusting the scheduling of the optimizer routine, and tuning the parameters of the controller itself. The performance of the control system has been compared with respect to the PI Controller architecture fed by the soft sensor results and with standard pre-calculated curves. The control architecture was evaluated in a simulation exploiting actual data from a Concentrated Solar Power Plant. The NMPC technique shows an increase in performance, with respect to the custom PI control application, and encouraging results
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Bimonthly chemotherapy with oxaliplatin, irinotecan, infusional 5-fluorouracil/folinic acid in patients with metastatic colorectal cancer pretreated with irinotecan- or oxaliplatin-based chemotherapy
No full textThis study was conducted to assess the tolerability and efficacy of a ternary bimonthly irinotecan (CPT-11) - oxaliplatin (OHP) - infusional 5-fluorouracil (5-FU)/folinic acid (FA) combination in advanced colorectal cancer patients who had received prior CPT-11 and/or OHP-based chemotherapy regimen. Colorectal cancer patients were given bimonthly CPT-11 as a 90-min infusion, followed by OHP (85 mg/m2), FA (200 mg/m2) 2-h infusions and 5-FU (48-h infusion). CPT-11 and 5-FU doses were escalated as reported below. 26 patients were recruited. Fourteen patients had received a prior CPT-11-, 6 patients a prior OHP-based chemotherapy regimen and 6 patients both regimens. Three dose levels were investigated: CPT-11 100, 120 and 140 mg/m2 and 5-FU 1500, 1800 and 2100 mg/m2 in 6, 12 and 8 patients, respectively. All patients were evaluable for toxicity, 24 for antitumor activity. At all dose levels toxicity was acceptable. Grade 4 toxicity occurred in two patients only (neutropenia in one case and stomatitis in another one, 3.8%). Grade 3 toxicities included nausea and vomiting (34.6%), asthenia (26.9%), neurosensory toxicity (15.4%), neutropenia (3.8%) and diarrhea (3.8%). Hematological toxicity was infrequent and generally mild. At the third dose level, a higher, although not significantly different incidence of hematological and neurosensory toxicity (both occurring in 62.5% of cases, all grades) was observed compared to the other two, while nausea and vomiting were significantly less frequent (37.5% vs 100%). Overall, we observed 2 complete responses, 9 partial responses (OR 45.8%), 8 stable disease (33.3%), and 5 disease progression (20.8%). Median overall survival was 18 months and median time-to-progression 5.5 months. This combination showed moderate toxicity and promising antitumor activity in CPT-11 and/or OHP pretreated colorectal cancer patients. The second dose level using CPT-11 at 120 mg/m2 and 5-FU at 1800 mg/m2 is recommended for further phase II studies in this patient population. © E.S.I.F.T. srl - Firenze
A Study of Feasibility for a Macro-Milli Serial-Parallel Robotic Manipulator for Surgery Operated by a 3 Dofs Haptic Device
No full textTheoretical and experimental evaluation of a 2-Channel bilateral Force Reflection teleoperation system
No full textThis paper presents the theoretical and experimental
evaluation of a 2-Channel bilateral Force Reflection
teleoperation system.
The teleoperation system is a master-slave bilateral system
based on two parallel kinematics robots with three degree of
freedom, which has been devised for the validation of robotics
assisted surgery procedures. Both master and slave systems
present an isomorphic kinematics which allow only translational
motion of the end-effector.
The aim of the present work is to evaluate two different
implementations of a Force Reflection control architectures: a
Position Error Based Force Reflection Control and a Direct
Force Reflection Control. The two architectures are compared
in terms of performance, i.e. stability and transparency, on the
basis of both simulations and experimental data. Some novel
theoretical results are presented, which permit a direct evaluation
of performance for both the two architectures
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