1,721,139 research outputs found
Boundary integral methods for sound propagation with subsonic potential mean flows
No full textThis work deals with including non-uniform mean flow effects into boundary integral solutions to acoustic wave propagation. A time harmonic boundary integral solution is proposed for low Mach number potential flows with small non-uniform mean flow velocities and a free-field Green’s function is recovered to solve the corresponding kernel. The boundary integral formulation can be used as a means of solving both wave extrapolation and boundary element problems. For boundary element solutions to external sound propagation, the non-uniqueness issue is worked around by extending the conventional combined Helmholtz integral equation formulation and the Burton–Miller approach to non-uniform mean flows. Nonetheless, the proposed integral formulation is shown to be consistent with a combination of the physical models associated with the Taylor and Lorentz transforms. The combined Taylor–Lorentz transformation allows mean flow effects on acoustic wave propagation to be resolved by using a standard boundary integral formulation for the Helmholtz problem with quiescent media in a transformed space.Numerical experiments are performed to benchmark the proposed integral formulations against finite element solutions based on the linearised potential equation. Numerical examples are also used to validate a weakly-coupled approach exploiting the proposed integral formulations in order to predict forward fan noise installation effects. Nonetheless, the integral formulations in a transformed space are used to simulate mean flow effects based on standard boundary element solvers for quiescent media. The results suggest that, for low Mach numbers, boundary element solutions to wave propagation with non-uniform mean flows represent a good approximation of finite element solutions based on the linearised potential equation. It is shown that the boundary element solutions including non-uniform mean flow effects improve on the corresponding approximations assuming a uniform flow in the whole computational domain. This is observed when sound propagation is predicted in the near field and in a region where the non-uniformity in the mean flow velocity is significant
SimplETAS: A Benchmark Earthquake Forecasting Model Suitable for Operational Purposes and Seismic Hazard Analysis
No full textThe epidemic‐type aftershock sequence (ETAS) model is the most effective mathematical description of the short‐term space–time earthquake clustering. However, the use of such a model is sometimes hampered by the difficulty in estimating the high number of its unknown correlated parameters. Moreover, the most recent ETAS formulations introduce the space–time variability of some parameters that makes their estimation even more arduous. Here, we investigate the model in an opposite perspective, looking for the simplest ETAS parameterization that can satisfactorily describes the earthquake clustering in crustal tectonic regions; we named this model simplETAS. We show that simplETAS calibrated with the Italian seismicity of the last decades adequately describes the space–time occurrence of the out‐of‐sample largest earthquakes in the instrumental and historical catalog, confirming the validity of the assumptions made to build the model. Owing to its simplicity, simplETAS is easily applicable in most regions, and it has some important properties that are worth being remarked. First, simplETAS can be used as a benchmark model to assess the relative predictive skill of more complex earthquake forecasts. Second, it may be used for operational earthquake forecasting purposes in regions with limited earthquake catalogs. Third, it provides a straightforward, flexible, and effective approach to generate synthetic earthquake catalogs of variable length to be implemented in seismic hazard and risk analysis, overcoming all the declustering‐related problems and the controversial Poisson assumption
Towards CFD guidelines for planing hull simulations based on the Naples Systematic Series
No full textDue to their higher motion amplitudes and instabilities, numerical simulations of planing hulls using Computational Fluid Dynamics (CFD) codes are more difficult than that of displacement ships. Indeed, for an accurate evaluation of the hydrodynamic performances of planing craft, the high-fidelity estimation of the pressure field around the hull is crucial. For this reason, validations and comparisons with experimental data are still important to identify the guidelines for both simulation settings and mesh generation. In this paper, two commercial packages will be compared focusing on a resistance case for the parent hull model (C1 hull) from the Naples Systematic Series (NSS) at four Froude numbers (Fr).
The NSS is a new systematic series of hard chine hulls intensively tested in planing and semiplaning speed range, De Luca et al. [1]. It has been chosen for the hull form: it is characterized by a warped bottom and a sectional area curve significantly different from the prismatic hulls. These differences amplify the difficulties in finding out the exact pressure distribution on the bottom and, consequently, make the evaluation more stringent.
The Unsteady Reynolds-Averaged Navier-Stokes flow solvers results are validated using these benchmark experimental data. Also, grid independence, iteration, and time-step convergence analysis for response variables (resistance coefficients, wetted surfaces, and dynamic trim angles) follow the recommendations published in the verification and validation (V&V) study from De Luca et al. [2]. Hence, the two software are more compared on different features such as the mesh deformation, the overset method, and the correction of numerical ventilation classically observed below the hull. The results show that both software can provide consistent values and that new guidelines are now identified to improve the reliability of the simulations
Rabbit meat quality with an approach to its processing using spices or specific ingredients as antioxidants
Full text linkDue to its low lipid content and high amounts of essential amino acids, rabbit meat is known for its excellent nutritional qualities, being very digestible and ideal for use in healthy diets. Unfortunately, rabbit meat has one of the highest lipid peroxidation susceptibilities, which restricts its use in processed food. Additionally, rabbit meat has some technological peculiarities that make it more challenging to incorporate into processed meat products, such as fragile bones, poor juiciness and a marginal anise-like flavour. But there may still be a demand for rabbit meat today. It might also be suggested as a substitute for traditional meat-based products, which are typically made with beef and pork, particularly for young children and the elderly. Moreover, ready-to-cook products, such as meatballs and burgers, may be well received by customers and new market trends could also emerge. The addition of spices can help improve the flavour and appeal of processed products made from rabbit meat while also increasing the antioxidant content and boosting nutritious value and shelf life. Furthermore, the use of natural antioxidants (spices) responds to the growing attention shown by consumers and food industries to avoid the use of synthetic molecules that diminish the products’ appeal
Effect of dietary Curcuma longa L. powder on lipid oxidation of frozen pork
Full text linkIntroduction - Modification of the eating habits incremented the consumption of ready-to-eat, ready-to-cook and frozen foods. Meat can be store up as frozen for different time in relation to the animal species, to the cut or to a previous processing. Several researches were conducted to evaluate the use of antioxidant products as dietary supplementation in order to produce modification in chemical composition of meat and lead to a positive influence on the length of shelf life of the products. Aim - The aim of this research was to study the effect of the supplementation with Curcuma longa L. powder in pig diet on the lipid oxidation after common frozen storage (-18 °C) of meat for long time (up to 135 days). Materials and methods - Pigs were fed with two different diets, control and turmeric, for 30 days before been slaughtered. Longissimus lumborum chops were frozen at -18 °C and lipid oxidation was evaluated with the thiobarbituric acid reactive substances (TBARS) method after 45, 60, 75, 90, 105, 120 and 135 days of storage. Results and discussion - The addition of the natural antioxidant did not modify the meat quality of the evaluated samples (P > 0.05). Nor the time of storage increased the TBARS value of the meat (P > 0.05). Our results are in accordance with other similar research studies on antioxidant dietary supplementations. Conclusion - Pigs, as large animal, probably need a bigger amount of antioxidant supplementation in order to modified meat characteristics. Thus, the lack of difference in lipid oxidation of frozen meat showed by Control and Turmeric diets could be associated both to the small dose of dietary turmeric powder and to the length of the diet period
Analyses of Different Approaches for Virtual Towing Tank Uncertainty Assessment
No full textThe assessment for the resistance of a new ship under design can be performed through
the Experimental Fluid Dynamics (EFD) or the Computational Fluid Dynamics (CFD)
approach; both have their own Uncertainty Assessment (UA). In CFD field, the Verification
and Validation (V&V) procedures take into account the approximations for numerical
issues and the assumptions adopted to describe the physical phenomena to assess UA.
Different theoretical approaches have become available over time; nevertheless, a single
comprehensive solution to achieve the UA remains still unknown because as the theoret-
ical methodology varies, the outcome changes. In current work, four different literature
approaches will be augmented to perform a V&V analysis for two kinds of model hulls,
tested at different speeds and compared with the experimental data. The investigations
performed among results lead to the division of all the approaches into the three and four
solutions families and to define a robust procedure to identify a reasonable value for the
numerical uncertainty assessment. Regarding the robustness and the UA of the approaches,
the first family proved successful in only 55% of cases with a UA mean value below 2.01%,
while the second one always provides a quantification but with a mean value of 6.65%
Stop culling male layer-type chick: an overview of the alternatives and public perspective
No full text
An extended verification and validation study of CFD simulations for planing hulls
No full textIn the context of marine application of computational fluid dynamic (CFD), it is well known that the numerical simulations of planing craft are significantly less reliable than that of displacement ships. For this reason, it is important to perform a comprehensive approach to the verification and validation (V&V) methodology and procedures for simulating CFD planing craft. In the first part of this paper, an assessment of the accuracy and effectiveness of different simulation setups and techniques for planing craft is performed. In the second part, the results of the V&V study are reported for three different hull models at four Froude numbers (Fr). The Unsteady Reynolds-Averaged Navier-Stokes code results were validated using benchmark experimental data obtained for three hull models characterized by systematic variation of the length to beam ratio. Grid independence, iteration, and time-step convergence analysis for response variables (resistance coefficients, wetted surfaces, and dynamic trim angles) were conducted using the main error and uncertainty estimation methods available in the literature. The same procedures were followed for the profiles of the wave patterns. The results showed that there was improved reliability of the numerical simulation of the planing craft in terms of the errors and uncertainties, related to the predictions of resistance, running attitude, and wave pattern. The results of the V&V study highlighted the fact that modeling of the planing craft is a critical point to improve the reliability of the numerical simulation. © 2016, Society of Naval Architects and Marine Engineers. All rights reserved
Rendimento a scuola: quanto penalizza essere stranieri? Un’indagine nella provincia di Pisa
Full text linkI grandi flussi di immigrazione iniziati dopo gli anni ottanta stanno trasformando l’Italia in una
società multietnica. Nell’attuale fase storica in cui, a causa della persistente crisi economica e dei
conflitti internazionali, l’intolleranza e l’integralismo stanno aumentando è prioritario promuovere
un’efficace interazione tra differenti culture, in un quadro di reciproco rispetto. In questa
prospettiva, la scuola può giocare un ruolo fondamentale contrastando le discriminazioni contro i
nati stranieri, attraverso il contenimento delle disuguaglianze nell’istruzione, come premessa per
ridurre le frustrazioni e l’emarginazione ed alimentare un’armonia sociale e culturale
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