1,721,004 research outputs found
Nuove tecniche sperimentali per la caratterizzazione dei fenomeni cavitativi
No full textArticolo su Rivista Tecnologie trasporto mare - n°2.2008 - ISSN 1721-758
Evaluation of Slamming Loads on Ship Bow Section Adopting SPH and RANSE Method
No full textDifferent numerical methods have been applied to the evaluation of slamming loads on a typical ship bow section, for which experimental data of drop tests has been made available within MARSTRUCT thematic network. Experimental data cover different drop cases, with variable speed and different heel angles. Numerical techniques adopted are a commercial
CFD VOF program and Smoothed Particles Hydrodynamics Method (SPH) currently under development at DINAV; results from both methods are presented and compared with available experimental data, allowing to make an assessment of these different techniques and to stress their relative merits and shortcomings.
Regarding SPH, most of calculations are performed using a conventional treatment of boundaries with repulsive forces, while a few tests have been performed with a novel boundary treatment which adopts variable smoothing length ghost particles (VSLGP), with promising results in terms of computational efficiency
SPH Analysis of a Planing Surface
No full textIn the present study SPH method was applied in order to study the peculiar flow around a 2D flat planing surface. Results were compared with analytical solutions and RANSE calculations. For the application of the method to this particular case an SPH code with an inlet and an outlet of particles was developed
Comparison of SPH and RANSE methods for the evaluation of impact problems in the marine field
No full textThis paper relates to the comparison of two different numerical methods applied for the evaluation of slamming and sloshing problems. In particular, a CFD VOF program and Smoothed Particles Hydrodynamics (SPH) currently under development at DINAV have been applied
Evaluation of slamming loads using smoothed particle hydrodynamics and Reynolds-averaged Navier-Stokes methods
No full textA free surface Reynolds-averaged Navier–Stokes solver and a smoothed particle hydrodynamics method, the latter currently under development by the authors, have been applied to the evaluation of slamming loads (global forces and local pressures) over a series of two-dimensional cases for which experimental data (drop tests with a free falling rig) were
available. In particular, numerical simulations were conducted on a wedge-shaped section with 30u deadrise and on a ship bow section; in both cases, different heel angles and different drop speeds have been considered, to analyse a wide range of cases and to assess not only the accuracy of the numerical methods in a single case, but also their capability to capture
significantly different conditions. Results from both methods are presented and compared with available measurements, allowing an assessment of these different techniques to be made and their relative merits and shortcomings to be observed
Propeller Cavitation 3d Reconstruction through Stereo-Vision Algorithms
No full textIn recent years an increasing interest towards innovative techniques to be applied in usual experimental facilities has grown. From cavitation tunnel point of view, attention has been given to measurement of dimensions of propeller cavitation bubbles. The need arises from the increase in ship performance and environmental/comfort requirements, leading to new standards in propeller design. In addition Computer Fluid Dynamics developed in recent years new tools to investigate these phenomena, but they still lack in validation with experimental data. Therefore the usual simple human observation seems to be no more adequate to determine propeller behaviour with respect to cavitation. Moreover it does not supply data directly and objectively comparable with numerical results.
In this scenario computer vision seems to be a promising research tool, because of relative limited hardware cost and of the availability of many software libraries. Additionally, computer vision is continuously spreading in many fields providing new algorithms and techniques. In this paper the experimental setup and software tools currently under development in the cavitation tunnel of Genoa University are presented. In particular three standard video surveillance cameras are adopted, while the OpenCv computer vision library is used for software development. Although this library provides a good support to 3D reconstruction its application in this environment is not straightforward, mainly because the optical path is not standard. Currently a volume reconstruction method based on [1] and an active stereo technique, with source light produced by a triggered laser, are studied. In present paper both techniques are presented along with preliminary results, clearly outlining their merits and shortcomings
Evaluation of slamming loads on V-shape ship sections with different numerical methods
No full textThis work deals with the application of different numerical methods for the evaluation of slamming loads on V-shape sections, namely a commercial CFD VOF program and Smoothed Particles Hydrodynamics Method (SPH) currently under development at DINAV; preliminary results from both methods are presented, together with a comparison between the two methodologies, stressing their relative merits and shortcomings
Evaluation of Slamming Loads on a Wedge-Shaped Section at Different Heel Angles adopting SPH and RANSE Methods
No full textIn the present work different numerical methods, namely a free surface RANSE solver and Smoothed Particles Hydrodynamics (SPH) method, this last currently under development at DINAV, have been applied to the evaluation of slamming loads (global forces and local pressures) on a typical wedge shaped section with 30° deadrise, for which experimental data (drop tests with a free falling rig) at different heel angles (ranging from 0° to about 30°) were available. Results from both methods are presented and compared with available experiments, allowing to make an assessment of these different techniques and to stress their relative merits and shortcomings
Experimental characterization of two CP propellers at different pitch settings, considering cavitating behaviour and related noise phenomena
No full textPropeller design has evolved significantly in last years, with the introduction of numerical methods which can provide a very reliable assessment of propeller characteristics, not only in correspondence to the usual design conditions, but also to off-design conditions. Nevertheless, problems still exist if “very off-design conditions” are considered, and if interest is posed on cavitation related problems such as radiated noise. Interest in radiated noise phenomenon is constantly increasing, not involving anymore only naval vessels, but affecting also design of other “high added value ships”, such as cruise ships and megayachts, for which comfort problem and environmental impact are a key element. One of the most significant problems related to radiated noise, is the rather low amount of experimental data available, and this is particularly significant for CPP propellers at off design conditions. In present paper, the experimental characterization of two alternative designs of a CP propeller in terms of usual mechanical characteristic, cavitation and radiated noise is presented. Experimental campaign has been conducted considering two very different pitch settings, allowing to analyse propeller behaviour also in correspondence to very off design conditions
Implants with a laser-microgrooved Collar Placed in Grafted Posterior Maxillary Extraction Sockets and in Crestally Grafted Sinuses: a 5-Year Multicentre Retrospective Study
Full text linkThe aim of this retrospective multicentre cohort study was to compare clinical outcomes, soft tissues conditions and differences in marginal bone loss between implants with a laser-microgrooved collar placed in posterior maxillary extraction sockets grafted by 4 to 5 months, and in posterior maxillary pristine bone (spontaneously healed posterior maxillary extraction sockets) by means of osteotome-mediated sinus floor elevation, over a period of 5 years after functional loading
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