APPLICATION OF SQUEEZE FILM DAMPERS

The level of the vibrations and the presence of instability are the two most critical aspects regarding the operations of turbomachinery. To cope with this issues that may compromise the operation of the machines, squeeze film dampers (SFD) are often used in many industrial applications. Unfortunately, many complex phenomena characterize the dynamic behavior of these compo-nents and determine the high complexity of the modeling of these components. The most relevant phenomena involved in the characterization of SFDs are indi-viduated after a comprehensive investigation of the state of the art. Among them, the oil film cavitation, the air ingestion, and the effect of the inertia are intro-duced. A modeling strategy based on the Reynolds equation is then presented. The boundary conditions to be adopted for the feeding and discharging of oil are investigated and implemented. Eventually, the finite difference model is applied to a practical example to evaluate the possibility to minimize the vibration level and to reduce the effect of the instability if a SFD is added to a rotodynamic system. Meaningful information about the modeling of SFDs is provided in this work. The critical aspects of these components and their modeling are high-lighted and discussed

Diagnostics Of Traction System Of Very High Speed trains: Experimental Results And Selection Of The Most Suitable Signal Processing Techniques

Traction equipment of very high speed trains (VHST) is characterized by high complexity and quality of the components and requires high reliability. An efficient maintenance approach like condition based maintenance (CBM) should be implemented to reduce the costs of preventive maintenance program. For this purpose, an experimental full scale test rig for the CBM of VHST traction equipment has been designed to investigate in detail, failures in the main mechanical components of system, i.e. motor, bearings and gearbox. The paper describes first the main characteristics of the testrig. Then, the results of a long test campaign is described in detail. Several damaged bearings, intentionally and artificially or owing to field use, have been installed (more than 60 configurations) and 12 different operating conditions, in terms of motor torque and speed, have been tested. Moreover, several signal processing techniques have been used, including the more traditional frequency and statistically based and the more sophisticated exploiting multi-domain and cyclostationarity approaches. Very positive results have been obtained and they prove, for the first time to best of authors’ knowledge, that, by positioning suitably the sensor and by using an appropriate signal analysis technique, bearing defects can be identified, even under heavy environmental noise. The results allow defining: i) the most suitable sensor position and type to be installed for each component and ii) the most suitable technique for signal analysis in order to monitor the distinct signature of impending faults of the bearings, gearbox and motor

Comportamento sperimentale di cuscinetti portanti lubrificati operanti a bassi numeri di Sommerfeld

In questa memoria viene descritto il comportamento sperimentale di un cuscinetto cilindrico portante lubrificato in condizioni di funzionamento critiche, ovvero a velocità di rotazione molto basse ed in presenza di elevata pressione specifica. Il cuscinetto utilizzato ha diametro nominale di 160 mm e lunghezza pari a 145 mm. La velocità di rotazione considerata è pari a 60 rpm (1 Hz), mentre i carichi applicati in direzione verticale variano da 20 kN a 350 kN, il che corrisponde a numeri di Sommerfeld variabili tra 0,1314 e 0,0086. Verranno presentati e discussi i dati ottenuti per la posizione di equilibrio statico, per la pressione idrodinamica, per la distribuzione di temperatura e per i coefficienti di rigidezza e smorzamento dinamici

Accurate modelling of bearings and seals for rotating machines for power generation

This paper reviews the most recent achievements obtained in the modelling of oil-film bearings and of labyrinth seals at Politecnico di Milano. These two topics are receiving increasing interest in nowadays rotor dynamics, in particular by OEM, owing to the increasing demand of high-performances/efficiencies and to the remarkable effect that they have on the stability of rotating machinery. The precise evaluation of dynamic coefficients, for both oil-film tilting-pad journal bearings and labyrinth seals, allows reliable evaluation of machine stability in the design phase. At this aim, several models are available in the literature. On the contrary, there are not so many cases, in which the models are validated by means of experimental tests. The bearing and labyrinth seal models presented here are supported by experimental validation

A novel method of frequency band selection for squared envelope analysis for fault diagnosing of rolling element bearings in a locomotive powertrain

The development of diagnostics for rolling element bearings (REBs) in recent years makes it possible to detect faults in bearings in real-time. Squared envelope analysis (SEA), in which the statistical characteristics of the squared envelope (SE) or the squared envelope spectrum (SES) are analysed, is widely recognized as both an effective and the simplest method. The most critical step of SEA is to find an optimal frequency band that contains the maximum defect information. The most commonly used approaches for selecting the optimal frequency band are derived from measuring the kurtosis of the SE or the SES. However, most methods fail to cope with the interference of a single or a few impulses in the corresponding domain. A new method is proposed in this paper called “PMFSgram”, which just calculates the kurtosis of the SES in the range centred at the first two harmonics with a span of three times the modulation frequency rather than the entire SES of the band filtered signals. It is possible to avoid most of the interference from a small number of undesired impulses in the SES. PMFSgram uses several bandwidths from 1.5 times to 4.5 times the fault frequency and for each bandwidth has the same number of central frequencies. The frequency setting method is able to select an optimal frequency band containing most of the useful information with less noise. The performance of the new method is verified using synthesized signals and actual vibration data

Numerical Evaluation of Alford Forces Acting on an Axial Expander for Supercritical CO2 Application

Nowadays, supercritical carbon dioxide (S-CO2) cycles are of great interest in the scientific research especially considering the energy transition that is occurring. The S-CO2 high density and relatively low viscosity make it an interesting fluid for power generation. For large heat sources, large flowrates of fluid can be obtained. Therefore, the development of axial flow expanders can allow large power generations. In the presence of rotor eccentricities, the aerodynamic loading of free-standing blades is not constant tangentially and will promote the lateral vibration of the rotor. The dynamic phenomenon that arises is known as Thomas-Alford force. The Thomas-Alford force determines an increase of the vibration level of the machine and a higher risk of instabilities. In this paper, a preliminary investigation of a S-CO2 axial expander stage is performed. Different correlations proposed in the literature are adopted to estimate the magnitude of the Thomas-Alford force. A mono-dimensional code and a simplified computational fluid dynamics (CFD) model are adopted to obtain the parameters of the stage considered. In this preliminary investigation, only free-standing blades are considered. The results obtained show a good agreement between 1D and CFD inputs required by the different correlation used. Despite this, the cross coupled stiffness calculated are widely dependent on the correlation used; then, this study can be considered as the starting point for more detailed investigations validating the correlations behavior in this environment through an unsteady CFD and/or a proper test campaign

Cooled pads with bioinspired gyroid lattice for tilting pad journal bearings: Experimental validation of numerical model for heat transfer

Hydrodynamic journal bearings are essential components for industrial rotating machineries. Continuously growing specific power allows more compact and efficient machines to be obtained, by reducing the environmental footprint of production plants. The aim of this work is to provide a new design of an innovative pad for Tilting Pad Journal Bearings (TPJBs) with an embedded cooling circuit, able to limit the oil film temperature. As a result, specific load can be increased leading to a possible downsizing of the bearing and reduction of lubricant quantity. The heat exchange in the cooling circuit of the pad has been enhanced using bioinspired gyroid lattice. The thermo-mechanical study of the pad has been performed with both numerical and experimental analysis. The resulting thermal and mechanical performances have been calculated and discussed. The tested components have been manufactured in stainless steel by using a metal 3D printing technology, based on polymer-metal feedstock extrusion. A performance analysis is conducted to catch differences between the nominal and the printed geometry. The prototype is able to dissipate the generated heat with a higher efficiency, and the pressure drop inside the cooling circuit can be estimated with the numerical model here proposed

Ottimizzazione delle Caratteristiche Reologiche di Lubrificanti per l’Industria di Processo Finalizzati alla Riduzione delle Perdite di Potenza

The aim of the paper is to optimize the tribological characteristics of lubricating oils that are used in the process industry during machining. In several cases, the machines employed are organized in several “stands” forming “lines” and are equipped by several spindles supported by journal bearings, fed by the same oil, but operating at different rotational speed. Often, the geometry and the size of the bearings and the loads acting on them are also different. Typically, the spindles supported by the bearings rotate at increasing speeds from the feeding of the blank material to the outlet of the machined one. The power loss on the single spindle is different from the others, not only for the different rotational speed, but also because the oil with which the single bearing is fed has different temperature and, thus, different viscosity. At present, stand-ard mineral oils for typical use are employed. Owing to the large power loss in these kinds of plants, an attractive idea for power saving is, therefore, to formulate a lubricating oil which, globally, along the entire line, has the best rheological characteristics (mainly in terms of vis-cosity) depending on the actual rotational speed of all spindles. In this way, the power dissipated during the machining process can be reduced while maintain-ing sufficient oil-film thicknesses in the various spindle journal bearings. In this paper, the modelling of the line is presented, by using a TEHD model for the calculation of the power dissipated in each journal bearing and the lu-bricating oil characteristics are defined by means of a multivariate optimization on the parameters of viscosity, temperature and thickness of the oil film. Final-ly, the optimized dynamic viscosity curve is obtained and can be used for the formulation of an oil, not necessary of mineral origin, with suitable additives

Analisi teorica e sperimentale dell’effetto della direzione del carico in cuscinetti a pattini oscillanti reali

I cuscinetti portanti a pattini oscillanti sono ampiamente utilizzati nelle macchine rotanti per velocità elevate e carichi sia bassi sia elevati. Data l’importanza di questo componente delle macchine rotanti, molti autori hanno pubblicato diversi studi, teorici e sperimentali, per valutare l’effetto dei giochi, della temperatura del lubrificante, della portata dell’olio e di diversi effetti termici sul comportamento di questo tipo di cuscinetto. Tuttavia, le indagini sull’influenza della direzione di carico sulle proprietà dei cuscinetti a pattini oscillanti sono spesso molto limitate e non considerano le geometria reale del cuscinetto. In questo articolo verrà presentata un’analisi teorica e sperimentale degli effetti delle direzione del carico nei cuscinetti reali a pattini oscillanti

Condition monitoring of the rolling stock and infrastructure: results of a pilot project

The application of Prognostics and Health Monitoring (PHM) concepts in rail vehicles and railway infrastructure is a rapidly growing field of research, and extensive efforts are being spent with the aim of improving the reliability and availability of railway systems and of substantially reducing maintenance costs by switching from time-based to event-driven maintenance policies. This paper presents the results of a research project in which concepts were developed and demonstrated for the health monitoring of the rolling stock (traction equipment) and of the railway infrastructure (track and overhead equipment). A prototype monitoring system was installed on a E464 locomotive and results were gathered across a time span of 14 months from December 2014 to January 2016