Implementation of pressurized air injection system in a Kaplan prototype for the reduction of vibration caused by tip vortex cavitation

Blade tip cavitation is a well-known phenomenon that affects the performance of large-diameter Kaplan turbines and induces structural vibration. Injection of pressurized air has been found to yield promising results in reducing those damaging effects. In this work, the results of an experimental test of air injection on a 9.5-m-diameter Kaplan turbine are reported. Experiments were performed for several load conditions and for two different net heads. Accelerations, pressure pulsation and noise emission were monitored for every tested condition. Results show that, at the expense of a maximum efficiency drop of 0.2%, air injection induces a decrease on the level of vibration from 57% up to 84%, depending on the load condition. Such decrease is seen to be proportional to the air flow rate, in the range from 0.06 to 0.8‰ (respect to the discharge at the best efficiency point).Facultad de Ingenierí

Implementation of pressurized air injection system in a Kaplan prototype for the reduction of vibration caused by tip vortex cavitation

Blade tip cavitation is a well-known phenomenon that affects the performance of large-diameter Kaplan turbines and induces structural vibration. Injection of pressurized air has been found to yield promising results in reducing those damaging effects. In this work, the results of an experimental test of air injection on a 9.5-m-diameter Kaplan turbine are reported. Experiments were performed for several load conditions and for two different net heads. Accelerations, pressure pulsation and noise emission were monitored for every tested condition. Results show that, at the expense of a maximum efficiency drop of 0.2%, air injection induces a decrease on the level of vibration from 57% up to 84%, depending on the load condition. Such decrease is seen to be proportional to the air flow rate, in the range from 0.06 to 0.8‰ (respect to the discharge at the best efficiency point).Facultad de Ingenierí

Implementation of pressurized air injection system in a Kaplan prototype for the reduction of vibration caused by tip vortex cavitation

Blade tip cavitation is a well-known phenomenon that affects the performance of large-diameter Kaplan turbines and induces structural vibration. Injection of pressurized air has been found to yield promising results in reducing those damaging effects. In this work, the results of an experimental test of air injection on a 9.5-m-diameter Kaplan turbine are reported. Experiments were performed for several load conditions and for two different net heads. Accelerations, pressure pulsation and noise emission were monitored for every tested condition. Results show that, at the expense of a maximum efficiency drop of 0.2%, air injection induces a decrease on the level of vibration from 57% up to 84%, depending on the load condition. Such decrease is seen to be proportional to the air flow rate, in the range from 0.06 to 0.8‰ (respect to the discharge at the best efficiency point).Facultad de Ingenierí

Board characteristics and the amount of capital raised in the Malaysian IPO market

This study examines the impact of board characteristics on the amount of capital raised through an IPO for a sample of 220 Malaysian IPOs over the period of 2005–2015, applying both ordinary least squares (OLS) and quantile regression (QR) techniques. The OLS results show that board with ethnic Malay directors has a significant and positive association with the amount of capital raised, while a weak significance is found for board size. However, the QR results reveal that other than board ethnicity, other board characteristics namely board size, board independence and CEO duality are significantly associated with the amount of capital raised. The additional results suggest that QR provides a more insightful and full picture into the association than does OLS. The overall empirical evidence lends support to the resource dependence role of the board of directors at the time of an IPO

La poesia araba Studi e prospettive di ricerca

La presente raccolta di articoli è frutto di un incontro sulla poesia araba svoltosi presso l’Università degli Studi di Napoli “L’Orientale” nell’ aprile 2015.Tale giornata di studi è nata dalla volontà di dare vita a un momento di riflessione e di incontro sulla poesia araba in un’ottica di scambio, di dialogo e di confronto sulle proprie ricerche e sulle prospettive di studio. In un momento storico in cui la cultura araba e le sue espressioni artistiche appaiono sovrastate e spesso oscurate dagli eventi dalla contemporaneità, si è scelto di ripercorrere il deserto attingendo al prezioso patrimonio poetico arabo, proponendo un differente itinerario in versi. Un viaggio che inizia dalla tenda per estendersi sino alle corti e alle città; lungo la piana di sabbia che ha custodito il sapere, tramandato il vissuto e riportato alla luce composizioni di poeti fecondi, pietre miliari nella storia della letteratura araba

"Una tenda di parole" Osservazioni sulla terminologia della metrica araba

The lexicon of the Arabic prosody has a symbolic value that often draws inspiration from the pre-Islamic Bedouin experience in the desert, evoking actions or conditions in a specific context. In 1959, Blachère wondered if it was possible to trace the guidelines indicating the path through which the terminology of the ancient Arab prosody had taken form. The philologists who formulated the principles of Arabic prosody believed that lexicon has not been created from the scratch, but most took inspiration from the Bedouin vocabulary (bayt, ‘arūḍ, ikfā’, iqwā’). Starting from the study of Blachère, this article focuses attention on the ziḥāf term and his multiple applications, highlighting the special relation they have with the daily-life terms of the desert. Through the study of some of the most important sources such as Lisān al-‘arab by Ibn Manẓūr, or the works by Ibn Rašīq al-Qayrawānī, Ibn Barrī, Qudāma ibn Ǧa‘far and al-Aṣma‘ī, among others, we can presume that this term is related to the meaning “to walk on the belly, slithering”. The snake slithering in the sand creates a movement which changes the existing landscape, giving a different look to the dunes on which the snake slithers on. Metaphorically the ziḥāfāt would recall the idea of something slithering (like a snake) into a given prosodic form and changing it. Many other terms used in the prosody with a specific meaning have a connection with the desert. For this reason the article is supported by a table from which it is possible to get the close meaning, sometimes only metaphorical, between the terms borrowed from the Bedouin life and their corresponding prosodic use, showing their symbolic representation (ḥabn, iḍmār, ṭayy, qabḍ, ‘aql, ‘aṣb, kaff, ḫabl, ḫazl, šakl, naqṣ). al-Ḫalīl, the first who created an Arabic prosodic lexicon, linked some of technical terms to the Bedouin tents. His choice is dictated by the desire to maintain a strong linkage between the poetry of the early centuries and the poetry of the following periods. The idea behind that was probably to entrust the old Arabic language with an original meaning applicable to different realities

Il Mediterraneo raccontato da Edmondo De Amicis

Il contributo presenta il viaggio che De Amicis svolse in Marocco nel 1875. Nell’Ottocento gli scrittori cominciano ad accompagnare le missioni all’estero. L’alterità è il metro con cui De Amicis affronta il viaggio; si tratta dunque di un percorso individuale che, affermando la propria identità, ne delinea una seconda. Ma le descrizioni dei luoghi, delle persone, della società e della vita sono solo il quadro entro il quale si muovono le percezioni dell’autore. Ad arricchire e impreziosire la visione di De Amicis si accompagnano i disegni di Stefano Ussi (1822-1901) e Cesare Biseo (1843-1909). L’itinerario del viaggio è ben dettagliato, ogni tappa segna un confine e una scoperta. Da Tangeri a Fez e ritorno passando per Had el-Garbìa, Tleta de Reissana, al-Kazar-el-Kibir, Ben- Auda, Karia-el-Abbassi, Beni-Hassen, Sidi-Hassem, Zeguta, Fez, Mechinez, Sebù, Arzilla e Tangeri. Il ricordo di quella terra non si dileguò nel cuore e nella mente di De Amicis che, nel 1882, dedicò a quel viaggio una nostalgica poesia mostrando, a distanza di anni, un vivido ritratto di una intensa emozione