1,721,190 research outputs found
Operational vibration of a waterjet focuser as means for monitoring its wear progression
Full text linkAbrasive waterjet cutting is a competitive manufacturing technology in the aerospace, defense, and automotive industries. End-user requirements are currently pushing machine builders to improve the automation of their processes, in an effort to reduce costs and downtimes, as well as increase robustness and stability. On this regard, the waterjet focuser is a critical component, as its fast wear progression requires constant human supervision, for promptly detecting detrimental effects on the cutting performance. This paper describes an innovative approach for in-line monitoring the wear progression of a waterjet focuser, by means of an accelerometer installed on its tip. This result is allowed by two separate studies of the focuser, of which the first investigates the sensitivity of its first mode frequency to the wear progression, while the second demonstrates the possibility of tracking said frequency from the in-line vibration signal delivered by the accelerometer, during operation. The presented setup makes use of low-cost sensing hardware that can be easily retrofitted into the design of waterjet focusers. The information delivered is expected to tackle end-user requirements for improved process automation
The dynamic behaviour of submerged floating tunnels
No full textpubblicazione su DVD + abstract su libro p. 25-2
Strutture Dati per la Progettazione di Circuiti Integrati
No full textLa progettazione di circuiti integrati VLSI richiede strumenti CAD sempre piu' sofisticati ed efficienti. In particolare e' di primaria importanza la scelta di strutture dati efficienti per la gestione del layout sia a livello simbolico che fisico. In questo lavoro vengono analizzate e valutate le principali strutture dati utilizzabili in ambito CAD e viene descritta in dettaglio la struttura dati Corner Stitching a 45o e gli algoritmi per la gestione di Poligoni
Modeling of two-dimensional water motion field during a seaquake
No full textThis study investigates seaquake phenomena, analyzing the role of P-waves in generating seismic waves in water. Different modeling approaches for understanding the dynamic water motion during seaquake are addressed and one-dimensional P-wave propagation in the frequency domain is compared to two dimensional propagation models in frequency and time domain. The comparison is specifically carried out for structures like Submerged Floating Tunnels focusing on the effect of water depth, self-damping and resonance on the water motion field. The two dimensional propagation model in frequency domain is extended to account for a non-flat seabed. The results obtained are critically compared to the ones delivered by a time domain approach utilizing a Finite Element discretization and exploiting the Domain Reduction Method for soil-structure interaction analysis
On the estimation of von mises equivalent stress in random vibration analysis
Full text linkLinear random vibration analysis aims to the probabilistic characterization of response functions; classical procedures are targeted to the time histories of output kinematic variables, such as displacement, velocity and acceleration, and to parameters which are linearly related to them, such as internal forces, deformations, stress components ecc. Much less attention has been devoted, by researcher and developers, to the case of response variables which are non-linearly dependent of the lagrangian coordinates or their derivatives; the most typical among these is the Von Mises equivalent stress, whose square value is quadratic in the components of the stress tensor, and thus in the lagrangian coordinates. The topic is of relevance especially for the structural safety of industrial equipment and systems, which is usually based on local stress integrity assessment. In the paper an innovative analytical procedure to deal with the probabilistic characterization of the VM stress is proposed as an extension of the classical approach adopted for linear output parameters. To this aim the matrix of the quadratic form delivering is decomposed into the sum of suitable factors; each of them deserves the same treatment as for linear parameters. The various features related to the numerical implementation of the procedure for stationary or non-stationary (evolutionary) random excitation are discussed, with reference to both the application via direct frequency domain treatment and to the modal superposition approach; an example is finally shown and commented
Numerical models for the dynamic response of submerged floating tunnels under seismic loading
No full textThe modeling of tethering elements of seabed anchored floating structures is addressed, with particular
reference to the so-called Archimedes Bridge (submerged floating tunnel, SFT) solution for deep water
crossing; attention is devoted to the design solution encompassing slender bars as anchor elements. Two
numerical tools are proposed: firstly, a geometrically nonlinear finite element (NWB model), developed
in previous work, has been refined in order to capture the effect of higher flexural modes of anchor
bars. Secondly, a 3D beam element, based on the classical corotational formulation (CR model), has
been developed and coded. Both elements are implemented in a numerical procedure for the dynamic
time domain step-by-step analysis of nonlinear discretized systems; seismic loading is introduced by
generating artificial time histories of spatially variable seismic motion. An example of application of the
NWB element is shown regarding the behavior of the dynamic model of a complete SFT. The model
was subjected to extreme multiple-support seismic loading. The seismic behavior is here illustrated and
commented, especially in light of the effect of higher local vibration modes of the anchor bars. Finally, a
comparison between the performances of the two modeling approaches is presented. Both harmonic and
seismic excitations are considered in the test; the results justify the use of the simpler NWB approach,
especially in the SFT design phase
Dynamic response of submerged floating tunnel to seismic excitation: modelling aspects
No full textPubblicazione su CD-ROM, 10 pp
Investigation of the influence of the AWJ-specific energy on the cutting kerf profile on aluminium 6082
Full text linkThis study introduces the abrasive waterjet specific energy as a novel physical quantity to characterize the taper ratio in abrasive waterjet cutting. Said quantity was defined as a proper combination of the most influential control factors. A series of abrasive waterjet cutting experiments on aluminium 6082, were conducted, according to the design of experiments methodology. For each experimental run, the width of the kerf profile was measured and characterized in terms of taper ratio. The effect of the abrasive waterjet specific energy and the main process parameters on the measured quantities were investigated. Results showed that inside the experimental range of the process parameters, the abrasive waterjet specific energy correlates well with the taper ratio. As a conclusion, different combinations of the control factors (water pressure, abrasive mass flow rate, feed rate), corresponding to the same level of abrasive waterjet specific energy, produced the same cutting kerf geometry as well as the same taper ratio. This result gives freedom to the waterjet users in selecting the best parameter combination according to some criteria (e.g., time or cost) for achieving the target AWJ-specific energy and the consequent kerf quality
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