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

An Efficient Design of the Piezoresistive Pressure Sensor Applied for Micro Aerial Vehicle

In this research, the developing process of a piezoresistive pressure sensor working in the atmosphere environment applied in micro aerial vehicle using the MEMS fabrication method is introduced. The sensor consists of four Au/Cr piezoresistors in a Wheatstone bridge configuration on a wet oxidized silicon diaphragm. To fabricate the sensor, three lithographic steps were conducted: the first one is to define the resistors and Au/Cr lines/pads, the second and the third ones are to determine the width and the thickness of the square SiO2/Si diaphragm, respectively. The sensor diaphragm shape and thickness were defined by the anisotropic etching of Si in tetramethylammonium hydroxide (TMAH) solution, and the resistors array are formed by sputtering and wet etching method. The sensor size is ~6000 µm by 6000 µm. The sensor output voltage was measured for various applied pressure levels from 0 to 1.2 bar with 5V voltage supply. The fabricated sensor also exhibits a sensitivity of 50.01 mV/bar

An Efficient Design of the Piezoresistive Pressure Sensor Applied for Micro Aerial Vehicle

In this research, the developing process of a piezoresistive pressure sensor working in the atmosphere environment applied in micro aerial vehicle using the MEMS fabrication method is introduced. The sensor consists of four Au/Cr piezoresistors in a Wheatstone bridge configuration on a wet oxidized silicon diaphragm. To fabricate the sensor, three lithographic steps were conducted: the first one is to define the resistors and Au/Cr lines/pads, the second and the third ones are to determine the width and the thickness of the square SiO2/Si diaphragm, respectively. The sensor diaphragm shape and thickness were defined by the anisotropic etching of Si in tetramethylammonium hydroxide (TMAH) solution, and the resistors array are formed by sputtering and wet etching method. The sensor size is ~6000 µm by 6000 µm. The sensor output voltage was measured for various applied pressure levels from 0 to 1.2 bar with 5V voltage supply. The fabricated sensor also exhibits a sensitivity of 50.01 mV/bar

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

Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial

Background Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population. Methods AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921. Findings Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months. Interpretation Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke

Static Characteristics of a Tilting Five-Pad Journal Bearing with an Asymmetric Geometry

In this paper, static characteristics of a tilting five‐pad rocker‐backed journal bearing with an asymmetric geometry, i.e., different clearance for each pad, are investigated. A thermo‐elastohydrodynamic (TEHD) model considering the elasticity of the pad and pivot is used for the simulation. The pivot stiffness of each pad obtained by experiment is also introduced in the model. The experimental tests were carried out on a tilting pad journal bearing (TPJB) with a nominal diameter of 100 mm and a length‐to‐diameter (L/D) ratio of 0.7 with load‐between‐pad (LBP) and load‐on‐pad (LOP) arrangements. Several analyses, including numerical simulations and experimental measurements, are implemented in order to obtain the static behaviors of the tiltingpad bearing under variations of rotational speed, amplitude and direction of applied static load, such as clearance distribution profile, static eccentricity, temperature and pressure distribution. The results show that the effect of asymmetric geometry on the static characteristics is not negligible

The Effect of the Pivot Stiffness on the Performances of Five-Pad Tilting Pad Bearings

The role of the pivot flexibility in tilting-pad journal bearings (TPJBs) has become essential, particularly for bearings working at high applied load and relatively high rotor speeds. Predictions from a simple bearing model with rigid pivots show incorrect estimation of the dynamic coecients in comparison with the experimental results. Normally, the more flexible the pad pivot, the lower the dynamic coecients because the stiness of the pivot takes in series with the stiness and damping of the oil film. This paper investigates the influence of pivot stiness on the dynamic force coecients of two dierent five-pad TPJBs as a function of the applied static load and excitation frequency: rocker-backed pivot and spherical pivot bearings. In order to highlight the eect of the pivot stiness in the spherical pivot bearing, displacement restriction components and elastic copper made shims have been used. Firstly, a thermo-elasto-hydrodynamic model for the static and dynamic characteristics of the two bearings is described. This model takes into account the flexibility of both pad and pivot. The pivot stinesses calculated by means of the Hertz theory and those obtained by experiments have been introduced and compared in the model. The clearance profiles of two tested bearing and the shaft center loci obtained by measurement and prediction are also shown. The dynamic coecients of the two bearings obtained from the numerical simulation were compared with the experimental results. By the analysis it can be concluded that the eect of the pivot flexibility on the clearance profile, the shaft locus and on the dynamic coecients is very significant. More important, it is important to estimate the pivot stiness of each single pad using experimental measurements

Effect of the load direction on non-nominal five-pad tilting-pad journal bearings

In this paper, a theoretical analysis of the influence of the load direction on the characteristics of a five-pad tilting-pad journal bearing (TPJB) is investigated. An analysis is performed for a TPJB using a non- nominal geometry, that is, with a different preload factor for each pad. The analytical results are then compared with the experimental measurements for a real bearing having pads with different geometries due to manufacturing errors. The results show that the load direction has considerable effects on both the static and dynamic characteristics of the TPJB. A robust estimation method is introduced for the calculation of experimental dynamic coefficients. The procedure for the bearing geometry estimation from the experimental measurement of the clearance profile is also described

Behaviour of tilting-pad journal bearings in case of large manufacturing errors

The behavior of five-pad tilting-pad journal bearings in case of large manufacturing errors, is investigated by means of a parametric analysis in this paper. The sensitivity analysis was performed for several combinations of pad thickness in both load-on-pad (LOP) and load-between-pad (LBP) configuration using a TEHD model. Pad thickness machining errors cause different preload factor or clearance for each pad. Several cases of thickness variation and different rotational speed were studied. Numerical results show that machining errors have a strong influence on the dynamic coefficients and on the static behaviour

Numerical investigation of the effect of manufacturing errors in pads on the behaviour of tilting-pad journal bearings

In this study, the effect of the manufacturing tolerances of the pad thickness or the assembly errors on the characteristics of a five-pad tilting-pad journal bearing is analysed. In fact, the pad thickness errors correspond to a different preload factor or clearance for each pad. A sensitivity analysis was performed for several combinations of pad thickness for both load-on-pad and load-between-pad configurations using a thermo-elasto-hydro-dynamic model. Three cases of thickness variations were studied. The numerical results show that these manufacturing or assembly errors considerably affect on both the static and dynamic behaviours of the bearing