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The Ffowcs-Williams and Hawkings acoustic analogy is utilized to analyze the signature of a system consisting of a propeller and a downstream hydrofoil, mimicking a rudder at [Formula: see text] incidence. This study is carried out exploiting the database generated by Large-Eddy Simulations on a cylindrical mesh consisting of almost 2 × 109 grid points. Three rotational speeds of the propeller are considered. The analysis reveals that the major sources of sound are located at the leading edge of the hydrofoil, due to the impingement by the propeller wake. With the exception of small radial coordinates around the propeller wake, between two and four diameters from the propeller axis, where the non-linear sources of sound have the lead, most noise comes from the linear, loading sources on the surface of the hydrofoil, due to fluctuations of the hydrodynamic pressure. As a result, the azimuthal directivity of the sound pressure levels develops a dipole-like distribution, elongated in the direction of the span of the hydrofoil. The attenuation of the acoustic pressure along the radial direction is initially cubic, then quadratic, and eventually, within less than ten diameters away from the system, linear.

International audience; Training the next generation of aeroacoustic researchers is vital for addressing some difficult yet very important societal challenges, such as the provision of environmentally sustainable air transport operations, both for what concerns airport noise pollution and cabin noise. Sustained demand for more fuel efficient, environmentally friendly, and quieter aircraft power plants is promoting the development of ultra-high bypass engines for large transport aircraft. These turbofan engines require trained aero-acousticians and improved industrial design tools, to tackle some of the difficult design challenges posed by the larger diameter and by the larger fraction of the thrust delivered through the secondary (annular) nozzle. Whilst aeroacoustics is a well-established discipline in its own right, it tends not to be offered as an undergraduate course. This creates a recruitment challenge in doctoral training, with new post-graduate students being recruited across a range of qualifications, including Physics (physical acoustics), Mathematics, and Engineering (aerodynamics). A doctorate in aeroacoustics therefore poses the dual challenge of developing the underpinning basic knowledge in the researchers while pursuing advances in the state of the art. Seven European doctoral schools have teamed up in an Integrated Training Network of the 7th Framework Programme, AeroTraNet 2, in an effort to create an aeroacoustic doctoral training experience with greater critical mass, in which doctoral candidates could avail themselves of training facilities and courses across the network, to address their start-up knowledge gap. This 1ICSV24, London, 23-27 July 2017 four-year experience generated a wealth of lessons learnt, from sharing doctoral training practices, as well as from bottom-up initiatives led by the Early Stage Researchers involved in the project.

The present paper describes two "unconventional" approaches to experimentally address the diagnostics, analysis and solution of hydroacoustic problems in naval engineering. The first approach, based on direct pressure fluctuation measurements combined with detailed flow measurements in the proximity of the noise source, provides a direct estimate of the flow phenomena at the origin of sound generation and emission. The second approach concerns the use of an acoustic analogies in combination with a time resolved velocimetry technique capable of resolving all the velocity gradients at an instant. The abilities of the two approaches are investigated with reference to the analysis of the noise sources in some reference case studies.

A sample of 14 water maser sources associated with young stellar objects (YSOs) has been monitored over 13 years with the Medicina 32-m antenna. The YSOs have been selected with bolometric luminosities from 20 L⊙ to 2 × 106 L⊙ with the aim of investigating the relationship between H2O maser variability and stellar mass. The results are presented in various graphical forms which allow to follow the variation of the different spectral components. In particular, four quantities have been considered in our analysis: the intensity of the maser lines as a function of time and velocity; the flux integrated over the observed velocity range as a function of time; the maximum flux ever observed at each velocity; and the frequency of occurrence of the maser emission at any given velocity.

The present work concerns the experimental measurements of the velocity field around a catamaran advancing in static drift. The purpose of this paper is twofold: - firstly the study aims at characterizing the dynamics of the keel vortices generated along the demihulls and their interaction with both the free surface and the breaking vortices; - secondly, detailed flow measurements are used to collect a valuable experimental dataset for CFD benchmarking in severe off design conditions. To reach these goals, measurements are performed on some cross-planes along and downstream of the catamaran, for different Froude and drift angle combinations. In all the tests, the model was fixed at the dynamical values of trim and sinkage, measured in a preliminary PMM experiment. Major geometrical and kinematical characteristics of the keel vortices were documented in the paper though the analysis of the mean and fluctuating components of the velocity and vorticity fields.

This paper presents the results of velocity field measurements around the Delft catamaran 372 advancing in steady drift course. The purposes of the work are the characterization of the strong vortical structures generated along the keel of each demihull and to provide a valuable experimental data set for CFD benchmarking in severe off design conditions. To this aim, a stereo PIV system has been used to measure the velocity field around the model on several cross planes; two speeds, corresponding to Fr=0.4 and Fr=0.5 and to drift angle, 6° and 9°, have been tested. To prevent damages to the PIV system, measurements were taken only on planes where ventilation and/or air bubble entrapment did not occur. For the same reason, measurements could not be taken at higher Froude and/or drift angle. PIV measurements have been conducted fixing the model at the dynamical trim and sinkage, which have been measured in a preliminary PMM experimental campaign.

The present paper deals with the problem of the propeller induced perturbation on the rudder . The study aims at providing insights on the key mechanisms governing the complex interaction between the propeller wake structures and the rudder. In this regard, a wide experimental activity that concerned PIV and LDV velocity measurements and wall-pressure-measurements on the two faces of the rudder was performed in a cavitation tunnel. The major flow features that distinguish the flow field around a rudder operating in the race of a propeller, were highlighted, such as the complex dynamics of the propeller tip votices and the re-storing mechanism of the tip vortex downstream of the rudder. Wall-pressure signals were Fourier decomposed and, then, reconstructed isolating the contributions of the more energetic harmonics when both the propeller phase and the rudder deflection change.

We report on new aspects of the star-forming region S235AB revealed through high-resolution observations at radio and mid-infrared wavelengths. Using the Very Large Array, we carried out sensitive observations of S235AB in the cm continuum (6, 3.6, 1.3, and 0.7) and in the 22 GHz water maser line. These were complemented with Spitzer Space Telescope Infrared Array Camera archive data to clarify the correspondence between radio and IR sources. We made also use of newly presented data from the Medicina water maser patrol, started in 1987, to study the variability of the water masers found in the region. S235A is a classical HII region whose structure is now well resolved. To the south, no radio continuum emission is detected either from the compact molecular core or from the jet-like structure observed at 3.3 mm, suggesting emission from dust in both cases. We find two new compact radio continuum sources (VLA-1 and VLA-2) and three separate maser spots. VLA-1 coincides with one of the maser spots and with a previously identified IR source (M1). VLA-2 lies towards S235B and represents the first radio detection from this peculiar nebula that may represent an ionized wind from a more evolved star. The two other maser spots coincide with an elongated structure previously observed within the molecular core in the C34S line. This structure is perpendicular to a bipolar molecular outflow observed in HCO+(1-0) and may trace the associated equatorial disk. The Spitzer images reveal a red object towards the molecular core. This is the most viable candidate for the embedded source originating the outflow and maser phenomenology. The picture emerging from these and previous data shows the extreme complexity of a small (< 0.5 pc) star-forming region where widely different stages of stellar evolution are present., 15 pages, 16 figures, to be published in Astronomy & Astrophysics

Isolated iliac artery aneurysm is a rare pathology that is often asymptomatic for long periods; this late diagnosis exposes patients to a high risk of death following aneurysm rupture. The aim of this study was to establish the most suitable diagnostic approach, the correct indications for treatment, and the most appropriate tactics and surgical technique.Twenty-eight patients were observed over 13 years. Aneurysmal involvement was unilateral in 22 cases and bilateral in the remaining 6 patients. Preoperative diagnostic tests included eco-colour Doppler (ECD) and angio-CT in all cases, with angio-MR and angiography as more selective procedures. Seventeen patients underwent conventional open surgery with prosthetic replacement of the aneurysmatic tract, 7 patients were treated using endovascular exclusion, and lastly 4 were monitored over time.There was no perioperative mortality for either treatment. During the postoperative period following conventional open surgery, complications included one case of severe respiratory failure, one microembolism of the lower limb, and 2 periprosthetic hematoma. During the follow-up, we observed one pseudo-aneurysm, 3 cases of retrograde ejaculation and one patient with erectile dysfunction after traditional surgery; there was one minor endoleak after endovascular exclusion.Our experience suggests that ECD is a useful method for arriving at an early diagnosis, while angio-CT imaging is essential for a correct preoperative study. Aneurysms with a diameter equal or greater than 3 cm or that present annual increases in excess of 5 mm represent a correct indication for treatment. Conventional open surgery is the treatment of choice for young patients in good general conditions. Endovascular exclusion is indicated when the patient's clinical conditions contraindicate open surgery and the morphology of the aneurysmal arterial district allows the endoprosthesis to be safely implanted.

The knowledge of the effects of the wakes from Dynamic Positioning (DP) thrusters and the practical need to describe and predict their impact is fundamental in the assessment of design loading on slipstream-submerged equipment associated with offshore floating systems. In particular, with the increasing importance and application of DP thrusters in the offshore industry, the designer as well as the operator must have more information about the momentum in the wake from the thruster. This paper presents wake measurements from cavitation tunnel tests carried out on a ducted propeller model at the Italian Ship Model Basin (INSEAN), Rome, Italy. Through these experiments, DP thruster wake velocity components at different downstream axial planes were obtained experimentally using a Stereo Particle Image Velocimetry (SPIV) system in the INSEAN cavitation tunnel, up to 15 diameters downstream. These experiments were carried out with and without the nozzle in the bollard pull condition. This paper presents the results from these tests and discusses their importance for structures placed in the slipstream.

An experimental investigation of the propeller wake in a cavitation tunnel has been performed using particle image velocimetry (PIV). A PIV image analysis algorithm implementing iterative window offset and stretching has been adopted. The main characteristics of the propeller wake at different loading conditions have been pointed out by using phase sampling techniques. Longitudinal evolution of the blade viscous wake, developing from the blade surface boundary layers, of the trailing vortex sheets, due to the radial gradient of the bound circulation, is discussed up to 1 diameter downstream. In the near field the effects of turbulent diffusion and viscous dissipation, which cause a rapid space broadening of the velocity gradients in the trailing edge wake, are also examined. In the far wake the development of the slipstream instability and the breakdown of the hub and tip vortices are outlined.

The knowledge of the effects of the wakes from Dynamic Positioning (DP) thrusters and the practical need to describe and predict their impact is fundamental in the assessment of design loading on slipstream-submerged equipment associated with offshore floating systems. In particular, with the increasing importance and application of DP thrusters in the offshore industry, the designer as well as the operator must have more information about the momentum in the wake from the thruster. This paper presents wake measurements from cavitation tunnel tests carried out on a ducted propeller model at the Italian Ship Model Basin (INSEAN), Rome, Italy. Through these experiments, DP thruster wake velocity components at different downstream axial planes were obtained experimentally using a Stereo Particle Image Velocimetry (SPIV) system in the INSEAN cavitation tunnel, up to 15 diameters downstream. These experiments were carried out with and without the nozzle in the bollard pull condition. This paper presents the results from these tests and discusses their importance for structures placed in the slipstream., 25th Symposium on Naval Hydrodynamics, 8-13 August, St. John's, NL

We present the analysis of the properties of water maser emission in 14 star forming regions (SFRs), which have been monitored for up to 13 years with a sampling rate of about once every 2-3 months. The 14 regions were chosen to span a range in luminosity Lfir of the associated Young Stellar Object (YSO) between 20 Lsun and 1.8 x 106 Lsun. The general scope of the analysis is to investigate the dependence of the overall spectral morphology of the maser emission and its variability on the luminosity of the YSO. We find that higher-luminosity sources tend to be associated with stronger and more stable masers. Higher-luminosity YSOs can excite more emission components over a larger range in velocity, yet the emission that dominates the spectra is at a velocity very near that of the molecular cloud in which the objects are embedded. For Lfir >~ 3 x 104 Lsun the maser emission becomes increasingly structured and more extended in velocity with increasing Lfir. Below this limit the maser emission shows the same variety of morphologies, but without a clear dependence on Lfir and with a smaller velocity extent. Also, for sources with Lfir above this limit, the water maser is always present above the 5sigma -level; below it, the typical 5sigma detection rate is 75-80%. Although the present sample contains few objects with low YSO luminosity, we can conclude that there must be a lower limit to Lfir (~ 1840% (with an absolute maximum of ~ 820 Jy over 63 days). The ranges found in burst- intensity and -duration are biased by our minimum sampling interval, while the lifetime of the burst is furthermore affected by the fact that bursts of very long duration may not be recognized as such. In addition to the flux density variations in individual emission components, the H2O maser output as a whole is found to exhibit a periodic long-term variation in several sources. This may be a consequence of periodic variations in the wind/jets from the exciting YSO.

We present the results of more than 10 years of monitoring of the water vapor maser emission in 14 star forming regions obtained with the Medicina 32-m radiotelescope. The sample of objects covers a large range of luminosities of the associated FIR sources. In order to present in a compact and representative way the large amount of data available, we give for each source: a time-velocity-flux density plot, the time dependent integrated flux, the lower and upper envelopes of the maser emission, the frequency of the maser occurrence as a function of velocity, and the mean velocity averaged over the observing period. A brief morphological description of the environment of the maser source is also given. The present data form the basis for a discussion of the main properties of the water vapor maser emission to be presented in a forthcoming paper.