Analysis Of Rotordynamic Forces On Cavitating/Noncavitating Turbopumps

The present work illustrates the main results of an experimental campaign conducted in the Cavitating Pump Rotordynamic Test Facility (CPRTF) at Alta S.p.A., Pisa, on a three bladed, tapered-hub, variable-pitch inducer, named DAPROT3, and on a mixed flow pump, named VAMPDAP. The latter consists of the combination between the DAPROT3 inducer and a centrifugal pump placed downstream, called VAMPIRE. As a consequence of a displacement of the rotation axis, fluid induced rotordynamic forces arise, leading to a secondary motion of the shaft axis here referred as whirl motion. This precession of the shaft can be both unstable or stable depending on the direction of the rotordynamic force and the whirl frequency ratio. The combined effects of rotordynamic fluid forces and cavitation represent the dominant fluid mechanical phenomena that adversely affects the dynamic stability and pumping performance of turbopumps. In the experimental campaign, the rotordynamic forces and the hydraulic efficiency have been measured both in noncavitating and cavitating conditions, at different flow rates and temperatures, by means of a rotating dynamometer placed just behind the inducer. Two different methods have been exploited for the evaluation of fluid-induced rotordynamic forces. Indeed, in addition to the classic approach of discrete tests, a series of continuous tests have been performed in order to obtain a continuous spectra, allowing the possibility of accurately and unambiguously identifying the spectral minima and maxima, which are of special interest in the identification of the most dangerous operational condition of the test item. It has been found that the DAPROT3 inducer presents a different behavior of rotordynamic forces with respect to the typical trend observed in centrifugal pump impellers in presence of a whirl motion concordant with impeller rotation, according to previous experimental campaigns. It has been observed also that cavitation does not affect the rotordynamic forces in a significant way. Nevertheless particular situations may arise in which a certain level of cavitation is capable to alter the stability regions and in which the presence of a cold or hot flow may play an important role. Conversely the flow rate has a great influence and its variation may destabilize a pump that is stable at design condition. An increasing deviation has been obtained for decreasing flow rate as a consequence of the interaction between rotating backflow and whirl motion. The effect of cavitation on hydraulic efficiency has been found to be negligible with variations within 1%. On the other hand, the presence of rotordynamic forces may affect the efficiency up to 2% depending on the whirl speed both for cold and hot flow conditions. For what concerns the VAMPDAP pump, a deviation from the typical trend of fluid-induced rotordynamic forces has been observed as a consequence of the presence of the inducer placed upstream with respect to a radial pump, whose experimental diagrams respect the expectations. The effect of cavitation on this pump is relevant only at high flow rates, where for discordant whirl motion a decrease in rotordynamic force appears, whereas in other operating conditions it can be considered almost negligible. The experimental campaign has included the evaluation of thermal cavitation effect by performing tests at two different temperatures also for VAMPDAP pump. From the results it has been observed that no significant thermal effects are found in terms of rotordynamic forces. Moreover, the hydraulic efficiency is not affected from cavitation since the maximum variations are in the order of 0.9 % only at design and even lower at off-design conditions. At the same time the rotordynamic forces influence the efficiency in the order of 1% depending on whirl speed

Rivalutazione clinica delle osteosintesi nelle fratture di femore del cane

Le fratture femorali presentano un 'incidenza piuttosto alta nel cane soprattutto in seguito traumi ad alta velocità dovuti a incidenti automobilistici o cadute. Il trattamento di tale tipo di lesione richiede solitamente la riduzione e la stabilizzazione chirurgica mediante l'impiego di diverse tecniche di osteosintesi, quali fissatori esterni, placche e viti a compressione dinamica, chiodi centro midollari, cerchiaggi ecc. scelti di volta in volta in funzione di fattori quali: l'età e la mole dell'animale, il tipo e la localizzazione della frattura, l'indole e la disponibilità del proprietario. Il recupero funzionale postoperatorio si presenta solitamente buono per ciascuna tecnica impiegata; le principali complicazioni che sono state osservate sono rappresentate da malunioni e pseudoartrosi, dovute per lo più al cedimento degli impianti, e osteomieliti. Scopo del presente lavoro di tesi è stato quello di rivalutare in senso critico i risultati ottenuti dal trattamento delle fratture di femore del cane con diversi mezzi di osteosintesi. A tale scopo sono state prese in esame le cartelle cliniche dei soggetti, afferiti presso il Dipartimento di Clinica Veterinaria dell'Università di Pisa nel periodo compreso tra gennaio 2001 e settembre 2008, per i quali è stata emessa diagnosi di frattura di femore. In particolare sono stati presi in considerazione la razza e la mole del soggetto; l’eziologia; le caratteristiche della frattura; il tipo di osteosintesi messa in atto; i dati riguardanti il follow-up, e l'eventuale insorgenza di complicazioni. La miglior opzione terapeutica è risultata l'osteosintesi con placche a compressione dinamica che è esitata in un maggior numeri di guarigioni ossee corrette. Le principali complicazioni riscontrate sono riferibili ad una cattiva gestione del periodo post-operatorio, con mobilizzazione o cedimento dei mezzi di fissazione, in un caso evolute in pseudoartrosi, o, anchilosi dell'articolazione del ginocchio. Come per tutte le fratture delle ossa lunghe, anche per quelle femorali, il corretto management e il buon esito del trattamento dipendono da diversi fattori. In particolare la scelta del mezzo di osteosintesi più appropriato e una buona gestione del periodo post-operatorio rappresentano i punti critici nel trattamento delle fratture di femore del cane

Mining relationships among knowledge, attitude, and practice of drivers using self-organizing map and decision tree: The case of Bandar Abbas city taxi drivers

Background and Objectives: Traffic accidents are the leading causes of fatal or nonfatal work-related injuries in many countries. Analyzing influencing factors on knowledge, attitude, and practice of drivers is a topic of interest for policymakers to decrease traffic accident injury victims. Materials and Methods: In this article, a two-stage data mining approach was presented for determining the mining relationships among knowledge, attitude, and practice of drivers. In the first stage, because of existing multidimensional practice variables, self-organizing map neural network was utilized to automatically arrange drivers into two safe and unsafe driving practice clusters. In the second stage, a decision tree was used to model relationships among knowledge and attitude of drivers and practice clusters. The authors' designed questionnaires were used to collect data in 235 male taxi drivers of Bandar Abbas city in Iran regarding the drivers' knowledge and attitude toward traffic regulations. The driving practices were assessed using a prepared checklist. Results: The most important attribute affecting practice of drivers was the maximum safe speed in the city. Conclusions: The results of this investigation showed that drivers' knowledge toward traffic regulations had a dramatic impact on safe driving practices. Levels of drivers' education can influence practice of drivers

Decision tree-based modelling for identification of potential interactions between type 2 diabetes risk factors: A decade follow-up in a Middle East prospective cohort study

Objective: The current study was undertaken for use of the decision tree (DT) method for development of different prediction models for incidence of type 2 diabetes (T2D) and for exploring interactions between predictor variables in those models. Design: Prospective cohort study. Setting: Tehran Lipid and Glucose Study (TLGS). Methods: A total of 6647 participants (43.4 men) aged >20 years, without T2D at baselines ((1999- 2001) and (2002-2005)), were followed until 2012. 2 series of models (with and without 2-hour postchallenge plasma glucose (2h-PCPG)) were developed using 3 types of DT algorithms. The performances of the models were assessed using sensitivity, specificity, area under the ROC curve (AUC), geometric mean (G-Mean) and F-Measure. Primary outcome measure: T2D was primary outcome which defined if fasting plasma glucose (FPG) was �7 mmol/L or if the 2h-PCPG was �11.1 mmol/L or if the participant was taking antidiabetic medication. Results: During a median follow-up of 9.5 years, 729 new cases of T2D were identified. The Quick Unbiased Efficient Statistical Tree (QUEST) algorithm had the highest sensitivity and G-Mean among all the models for men and women. The models that included 2h-PCPG had sensitivity and G-Mean of (78 and 0.75) and (78 and 0.78) for men and women, respectively. Both models achieved good discrimination power with AUC above 0.78. FPG, 2h-PCPG, waist-toheight ratio (WHtR) and mean arterial blood pressure (MAP) were the most important factors to incidence of T2D in both genders. Among men, those with an FPG�4.9 mmol/L and 2h-PCPG�7.7 mmol/L had the lowest risk, and those with an FPG>5.3 mmol/L and 2h-PCPG>4.4 mmol/L had the highest risk for T2D incidence. In women, those with an FPG�5.2 mmol/L and WHtR�0.55 had the lowest risk, and those with an FPG>5.2 mmol/L and WHtR>0.56 had the highest risk for T2D incidence. Conclusions: Our study emphasises the utility of DT for exploring interactions between predictor variables

Forecasting U.S. Tourist arrivals using optimal Singular Spectrum Analysis

This study examines the potential advantages of using Singular Spectrum Analysis (SSA) for forecasting tourism demand. To do this it examines the performance of SSA forecasts using monthly data for tourist arrivals into the United States over the period 1996 to 2012. The SSA forecasts are compared to those from a range of other forecasting approaches previously used to forecast tourism demand. These include ARIMA, exponential smoothing and neural networks. The results presented show that the SSA approach produces forecasts which perform (statistically) significantly better than the alternative methods in forecasting total tourist arrivals into the U.S. Forecasts using the SSA approach are also shown to offer a significantly better forecasting performance for arrivals into the U.S. from individual source countries. Of the alternative forecasting approaches exponential smoothing and feed-forward neural networks in particular were found to perform poorly. The key conclusion is that Singular Spectrum Analysis (SSA) offers significant advantages in forecasting tourist arrivals into the US and is worthy of consideration for other forecasting studies of tourism demand