207 research outputs found
Operational ocean models in the Adriatic Sea: a skill assessment
No full textIn the framework of the Mediterranean Forecasting System (MFS) project, the performance of regional numerical ocean forecasting systems is assessed by means of model-model and model-data comparison. Three different operational systems considered in this study are: the Adriatic REGional Model (AREG); the Adriatic Regional Ocean Modelling System (AdriaROMS) and the Mediterranean Forecasting System General Circulation Model (MFS-GCM). AREG and AdriaROMS are regional implementations (with some dedicated variations) of POM and ROMS, respectively, while MFS-GCM is an OPA based system. The assessment is done through standard scores. In situ and remote sensing data are used to evaluate the system performance. In particular, a set of CTD measurements collected in the whole western Adriatic during January 2006 and one year of satellite derived sea surface temperature measurements (SST) allow to asses a full three-dimensional picture of the operational forecasting systems quality during January 2006 and to draw some preliminary considerations on the temporal fluctuation of scores estimated on surface quantities between summer 2005 and summer 2006. <br><br> The regional systems share a negative bias in simulated temperature and salinity. Nonetheless, they outperform the MFS-GCM in the shallowest locations. Results on amplitude and phase errors are improved in areas shallower than 50 m, while degraded in deeper locations, where major models deficiencies are related to vertical mixing overestimation. In a basin-wide overview, the two regional models show differences in the local displacement of errors. In addition, in locations where the regional models are mutually correlated, the aggregated mean squared error was found to be smaller, that is a useful outcome of having several operational systems in the same region
Amorphous Carbon Coatings at Cryogenic Temperatures with LHC Type Beams: First Results with the COLDEX Experiment
No full textExtrapolations of electron cloud data from the Large Hadron Collider (LHC) Run 1 to the High Luminosity upgrade (HL-LHC) beam parameters predict an intolerable increase of heat load on the beam screens of the inner triplets. Amorphous carbon (a-C) coating of the beam screen surface is proposed to reduce electron cloud production, thereby minimising its dissipated power. To validate this solution, the COLDEX experiment has been re-commissioned. Such equipment mimics the performance of the LHC cold bore and beam screen cryogenic vacuum system in presence of LHC beams in the Super Proton Synchrotron (SPS). The main objective of the study is the performance evaluation of a-C coatings while operating the beam screen in the 10 to 60 K temperature range and cold bore below 3 K. This paper reviews the status of COLDEX and the results obtained during its first experimental runs
Impact of storms along the coastline of Emilia-Romagna: The morphological signature on the Ravenna coastline (Italy)
No full textThe coastal zone of the Emilia-Romagna region in Italy is exposed to risk from coastal flooding and erosion during storms. The vulnerability of this coastline is a topic of interest for future planning as this area provides large revenue for coastal communities and the whole region. An assessment of the historical record of storm events for the period 2000-2004 was carried out using a wave prediction model, forced by archived atmospheric circulation data. High-resolution air-borne laser detection technology (LIDAR) and video-monitoring (ARGUS) were used to undertake a feasibility study for the assessment of coastal erosion and flooding patterns along one of the best-preserved dune systems of the area. The object of the work was the comparison between two LIDAR flights at an interval of one year (July, 2003-September, 2004) with the second flight carried out after a major storm occurred in September, 2004. Following this event the whole coastal system was severely eroded. The study presented in this paper suggests that for the coast of the Emilia-Romagna region the critical factor that controls dune destruction and inland flooding is the joint occurrence of storm waves and surges. Beach slope is the main morphological control on wave run-up and the impact evaluation for the exceptional event has proved that a wide beach can provide a factor of safety. A small beach replenishment (33,000 m3) was undertaken on the test site but this resulted to be ineffective because of the small volume. Larger-scale beach recharge schemes should be undertaken at the site on a regular basis to provide wider beaches at the dune toe
Novel C-Shaped Shape Memory Alloy Connectors for Vacuum Flanges: Modeling and Tests
No full textShape memory alloy (SMA)-based fasteners and connectors represent a class of successful SMA components that are increasingly used especially in marine or aerospace applications. The present paper aims to investigate novel C-Shaped SMA connectors for room-temperature vacuum pipes within particle accelerators. The proposed connectors exhibit the two-way shape memory effect (TW-SME), so they can generate significant axial recovery forces and they can be dismounted by temperature variations. Proper thermo-mechanical training procedures were performed to tune the mechanical and functional response of the connectors to make them suitable for the investigated application. The thermo-mechanical and functional response of the SMA fasteners in both free and constrained recovery conditions were assessed by strain gauge and extensometer tests as well as by finite element analyses based on a constitutive model, recently developed by the authors, accounting for TW-SME and plasticity. Comparison between experimental and numerical results validates the proposed model. Moreover, results give useful, important information in terms of SMA transformation temperatures, generated recovery forces as well as shape recovery capabilities
Measurement of NEG Coating Performance Variation in the LHC after the First Long Shutdown
No full textDuring the Long Shutdown 1 (LS1) of the Large Hadron Collider, 90% of the Non-Evaporable Getter (NEG) coated beam pipes in the Long Straight Sections (LSS) were vented to undertake the planned upgrade and consolidation programmes. After each intervention, an additional bake-out and NEG activation were performed to reach the vacuum requirements. An analysis of the coating performance variation after the additional activation cycle has been carried out by using ultimate pressure and pressure build-up measurements. In addition, laboratory measurements have been carried out to mimic the LHC coated beam pipe behaviour. The experimental data have been compared with calculation obtained by Molflow+
A three-dimensional phenomenological model for shape memory alloys including two-way shape memory effect and plasticity
No full textThe one-way and two-way shape memory effects (SMEs) as well as the thermal hysteresis represent fundamental properties when dealing with the design of detachable and thermally-stable connection systems based on shape memory alloys (SMAs). Such properties can be induced and tuned by thermo-mechanical processes that include thermal treatments and severe pre-deformation in martensitic state, causing the onset of plastic strains. In such complex conditions, material modeling is of great importance to support the design. This paper proposes a generalization of the three-dimensional phenomenological constitutive model by Souza et al. (1998), in order to describe the behavior of severely pre-strained NiTi-based SMAs. The proposed model allows to describe pseudoelasticity, one-way and two-way SMEs, as well as additional physical phenomena evidenced experimentally, such as transformation temperatures’ evolution, thermal hysteresis, phase transformations at low stresses, thermal strains, and phase-dependent elastic properties. Several numerical simulations, ranging from uniaxial tests to the finite element analysis of two case-studies, are performed. Model results are in good agreement with the results of a performed experimental campaign and allow to discuss SMA behavior under such complex loading conditions
Carbon film deposition on polyethylene terephtalate by pulsed-plasma technology
No full textElastic amorphous carbon films were deposited by continuous and pulsed-plasma sputtering on polyethylene terephtalate (PET) for gas barrier applications. A study was done of the influence of the plasma parameters on the morphological, mechanical, structural properties of the films. Graphite was used as the sputtering target either in argon-hydrogen RF plasmas. In the pulsed mode operation (on/off), pulse frequencies within the (1-100) kHz range were applied. Pulsing resulted in an enhanced deposition rate and in changes in the ion population composition of the plasma, namely an increase of the hydrogenic ion proportion with the low frequencies. This influenced both the elasticity of the films and the disorder in the atomic structure. Correlations between the plasma process parameters and the permeation properties of the films to He were also mad
Impact of storms along the coastline of Emilia-Romagna: the morphological signature on the Ravenna coastline (Italy)
No full textThe coastal zone of the Emilia-Romagna region in Italy is exposed to risk from coastal flooding and erosion during storms. The vulnerability of this coastline is a topic of interest for future coastal planning as this area provides large revenue for coastal communities and the whole region. An assessment of the historical record of storm events for the period 2000-2004 was carried out using a wave prediction model, forced by archived atmospheric circulation data. High-resolution air-borne laser detection technology (LIDAR) and video-monitoring (ARGUS) were used to undertake a feasibility study for the assessment of coastal erosion and flooding patterns along one of the best-preserved dune systems of the area. The object of the work was the comparison between two LIDAR flights at an interval of one year (July 2003-September 2004) with the second flight carried out after a major storm occurred in September 2004. Following this event the whole coastal system was severely eroded. The study presented in this paper suggests that for the coast of the Emilia-Romagna region the critical factor that controls dune destruction and inland flooding is the joint occurrence of storm waves and surges. Beach slope is the main morphological control on wave run-up and the impact evaluation for the exceptional event has proved that a wide beach can provide a factor of safety. A small beach replenishment (33,000 m3) was undertaken on the test site but this resulted to be ineffective because of the small volume. Larger-scale beach recharge schemes should be undertaken at the site on a regular basis to provide wider beaches at the dune toe
Study of the discharge gas trapping during thin film growth
No full textDischarge gas trapping in thin films produced by sputtering is known to be due to high energy neutrals bouncing back from the cathode. Qualitatively, the phenomenon is enhanced by raising the discharge voltage and is strongly dependent on the atomic masses of the discharge gas and of the cathode material. In addition to these known effects it is shown that, for a given gas, the trapped amount decreases with increasing the melting temperature of the deposited material. The results obtained both by sample melting and laser ablation are presented and discussed
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