Simulazione CFD della dinamica di una barca a vela di Coppa America in presenza di moto ondoso

L’obiettivo principale del lavoro è l’elaborazione di una procedura generale per la simulazione CFD della dinamica di una barca a vela in presenza di moto ondoso, che permetta di calcolare l’andamento temporale delle forze fluidodinamiche agenti sull’imbarcazione. In particolare questa procedura è utilizzata per lo uno studio della bolina di una imbarcazione di classe Coppa America. Assegnate la geometria di riferimento e le condizioni operative, sono ricavate le principali prestazioni della barca a vela, come la velocità di avanzamento e gli angoli di beccheggio, di rollio e di scarroccio. Per il calcolo fluidodinamico si utilizza un modello non stazionario a sei gradi di libertà, 6 DOF Motion, nel quale la griglia di calcolo si muove in modo solidale al corpo. Nella simulazione la barca a vela è considerata come un corpo rigido che, sotto l’azione delle forze agenti sullo scafo e sul piano velico, può traslare e ruotare liberamente intorno agli assi di riferimento. Il moto ondoso del mare è implementato in accordo con il modello di Stokes per le onde periodiche approssimato al quinto ordine. Nell’ambito di validità di questo modello è possibile rappresentare molteplici condizioni del mare assegnando il valore della corrente marina e del vento, l’altezza dell’onda, il suo periodo e la profondità del fondale. Le due diverse fasi aria-acqua sono realizzate con il modello Volume of Fluid (VOF) che bene si adatta alla simulazione di flussi di fluidi immiscibili su griglie di calcolo capaci di calcolare l’interfaccia fra le varie fasi. Il modello di turbolenza scelto è il k-e standard. Il software CAD per la realizzazione della geometria della barca a vela è CATIA V5R19 e la relativa mesh di superficie è generata con ANSA 13.0.2. Per la realizzazione della mesh di volume e dell’analisi CFD è utilizzato Star CCM+ v4.04.011

A growth scale for the phasic development of common buckwheat

Growth scales give a standardized definition of crop development and increase the understanding among researchers and growers. In this research we defined a growth scale for the phasic development of common buckwheat that was mainly based on a sequence of easily recognizable changes occurring on the first and the terminal clusters of inflorescences formed on the main stem. Observations were carried out on plants grown in two years throughout spring. In an attempt to uniform the duration of phasic development across sowing dates, the length of phases and sub-phases was calculated in days and in thermal time using nine combinations of cardinal temperatures. A sequence of stages and various patterns of coordinated development were maintained throughout all sowings and years. Specifically, (1) the first inflorescence became visible after three true leaves had fully expanded on the main stem; (2) flowering reached the terminal inflorescence cluster before full-sized green fruits became visible in the first inflorescence, and (3) fruit ripening in the whole plant ended within two weeks of the end of ripening in the oldest inflorescence. Plant size was increased with the delay of sowing, and the length of the growth cycle was by approximately 400°Cd longer when plants experienced a day length longer than 15 h. This changed the correspondence between flowering and ripening stages, so that full flowering was associated with the development of green fruits in the first inflorescence when the cycle was short, but with their development in the terminal cluster when it was long. Trends in grain yield did not correspond to those in plant size and phase length. We are confident that this growth scale will be a valuable tool for following the progress of buckwheat development and to predict growth patterns and harvest time in response to temperature and photoperiod

Forage and grain yield of common buckwheat in Mediterranean conditions: Response to sowing time and irrigation

With the view to extending the cultivation of common buckwheat to Mediterranean environments, we investigated the responses of two varieties to three sowing times, early spring, late spring and late summer, in rainfed and irrigated conditions. Plants were harvested at two ripening stages for forage production and at maturity for grain yield. The crop cycle lasted 82-88 days independent of sowing time, whereas the thermal time was ∼1000 degree-days in early spring and late summer sowings, and 1200 degree-days when sown in late spring. Forage yield increased up to 75% between ripening stages. Early spring was the best sowing time for forage (4tha-1 dry weight) and grain yield (2tha-1 dry weight) in rainfed conditions. Late spring sowings give the highest forage yield when irrigated (6tha-1 dry weight), but were not suitable for producing grain, for the adverse effect of high summer temperatures on seed set and seed filling. Late summer sowings produced acceptable grain yield (1.5tha-1 dry weight), whereas short days and low temperatures limited forage production. Thus, in Mediterranean environments, buckwheat could be profitably introduced as a minor summer crop, sown in early spring for grain production and in late spring for forage production

Connection between base drag, separating boundary layer characteristics and wake mean recirculation length of an axisymmetric blunt-based body

The variation of the base drag of an axisymmetric bluff body caused by modifications of the boundary-layer separating at the sharp-edged contour of its base is analysed through different numerical simulations, and the results are compared with those of a previous experimental investigation. Variational MultiScale Large-Eddy Simulations (VMS-LES) are first carried out on the same nominal geometry and at the same Reynolds number of the experiments. Subsequently, Direct Numerical Simulations (DNS) are performed at Reynolds numbers that are roughly two orders of magnitude lower, in order to investigate on the sensitivity of the main findings to the Reynolds number. The results of experiments, VMS-LES and DNS simulations show that an increase of the base pressure - and thus a decrease of the base drag - may be obtained by increasing the boundary layer thickness before separation, which causes a proportional increase of the length of the mean recirculation region behind the body. In spite of the different setups, Reynolds numbers and turbulence levels in the experiments and numerical simulations, in all cases the base pressure is found to be directly proportional to the length of the mean recirculation region, which is thus a key index of the base drag value. In turn, the recirculation length seems to be connected with the location of the incipient instability of the detaching shear layers, which can be moved downstream by an increase of the thickness of the separating boundary layer and upstream by an increase of the turbulence level

Control of the turbulent flow in a plane diffuser through optimized contoured cavities

A passive control strategy, which consists in introducing contoured cavities in solid walls, is applied to a plane asymmetric diffuser at a Reynolds number that implies fully-turbulent flow upstream of the diffuser divergent part. The analysed reference configuration, for which experimental and numerical data were available, is characterized by an area ratio of 4.7 and a divergence angle of 10 degrees. A large zone of steady flow separation is present in the diffuser without the introduction of the control. One and two subsequent contoured cavities are introduced in the divergent wall of the diffuser and a numerical optimization procedure is carried out to obtain the cavity geometry that maximizes the pressure recovery in the diffuser and minimizes the flow separation extent. The introduction of one optimized cavity leads to an increase in pressure recovery of the order of 6.9% and to a significant reduction of the separation extent, and further improvement (9.6%) is obtained by introducing two subsequent cavities in the divergent wall. The most important geometrical parameters are also identified, and the robustness of the solution to small changes in their values and in the Reynolds number is assessed. The present results show that the proposed control strategy, previously tested in the laminar regime, is effective also for turbulent flows at higher Reynolds numbers. As already found for laminar flow, the success of the control is due both to a virtual geometry modification of the diffuser and to a favourable effect of the cavities in reducing the momentum losses near the wall

OPTICAL PEAKING ON TOP OF SELECTIVE MODE LAUNCH TECHNIQUE FOR EXTENDED REACH SUPPORT ON MULTIMODE FIBER LINKS

Techniques are described herein for implementing optical peaking on top of a selective mode launch technique, thereby providing extended reach support on multimode fiber links. Although this document describes the successful implementation of this solution at 25G, this solution is applicable to all bit rates whenever the link performances are affected by system bandwidth limitations. In this practical implementation, this launch solution for 25G Vertical-Cavity Surface-Emitting Laser (VCSEL) transceivers leverages optical peaking on top of a selective mode launch technique to ensure 300m/400m support over OM3/OM4 optical fibers and therefore smoothless transition from 10G to 25G applications

Forage potential of winter cereal/legume intercrops in organic farming

This research was performed to assess the potential of cereal/legume intercropping to enhance forage yield and quality when compared with cereal sole crops under the constrains imposed by UE organic farming regulations. Sole crops (SC) and intercrops (IC) of two winter cereals, barley (Hordeum vulgare L.) and durum wheat (Triticum durum Desf.), and two legumes, white lupin (Lupinus albus L.) and common vetch (Vicia sativa L.), were evaluated at two harvest times for dry matter yield (DMY), crude protein concentration (CPC), and nitrogen yield (NY). Yield values and dry matter concentration (DMC) were generally higher when cereals were at the hard dough compared to the late milk stage. On average, intercropping increased forage yield by 72%, NY by 190%, and CPC by 40 g kg-1, compared to cereal sole crops, but the choice of legume species affected the yield advantage and the composition of forage. Land equivalent ratio (LER) of intercrops was always higher than 1, ranging from 1.39 to 1.61. Intercropping also enhanced weed suppression, compared to sole crop