1,721,044 research outputs found
Chasing the high-resolution mapping of rotational and strain FRFs as receptance processing from different full-field optical measuring technologies
No full textThanks to the recent advances in digital vision systems, a question might arise about where the full-field optical and contactless methods can bring modern design procedures. An answer lies on the methodologically detailed comparison of the results, processed from different full-field optical techniques, in exploring consistent and high-resolution maps of rotational and strain FRFs that is done through this paper.
Great exertions were first put in thoroughly testing a thin aluminium plate, in its real dynamics as a lightweight structure with broad frequency band dynamics and high modal density, in a unique comparative set-up, to obtain Receptance FRF maps of displacements-over-force by means of 3 different full-field optical techniques (SLDV, DIC, ESPI). There resulted superior quality Receptance maps in a broad and dense frequency domain, with high-resolution and continuity-wise consistent mapping at each frequency line.
This paper exploits the here detailed robust numerical differentiation and signal processing in order to calculate the Impedance-based models of rotational and strain FRFs. Especially for DIC and for ESPI, both rarely used on many frequency lines, the fully populated FRFs for rotations and strains are a clear novelty, with rotational Coherence functions as added quality assessment features.
The systematic comparison of the results obtained in the same location of the sample, by means of spatial and frequency domain metrics, is possible because of the proposed pointwise procedure, permitting the first numerical matching assessment of the 3 optical technologies on these awaited experiment-based quantities, as the full-field rotational and strain FRFs
Mapping the defect acceptance for dynamically loaded components by exploiting DIC-based full-field receptances
Full text linkPotential defect acceptance can be seen dependable upon the mapping of effective strains on the whole surface, due to dynamic loading of the components as they are mounted. With proper constitutive models and loading spectra, the experiment-based mapping of the equivalent stresses can be achieved from optical full-field receptances in an extremely dense grid, also for lightweight parts, without inertia distortions thanks to contactless measurements. Fatigue spectral methods turn this mapping into components’ life distributions, for a clear assessment of the material’s utilisation: a risk grading mapping for potential defects can be formulated in the area of inquiry in order to discriminate between safe and dangerous locations. By following this experiment-based approach, potential defects in exercise and production might be tolerated in safer locations, under the chosen dynamic task, with great savings in costs and maintenance. Among the image-based full-field measurement techniques, Hi-Speed DIC has proved to work in many environments, to be able to estimate full-field receptances of real components in their effective assembling and loading conditions, in different cases of industrial interest. The quality achieved by DIC in the receptance maps helps in numerically deriving the strain FRFs on the sensed surface. Extended scenarios – with newly modelled coloured noises for an advanced excitation definition from two shakers – and a vibrating rectangular plate, as real mounted component, are highlighted in details to prove the effectiveness of DIC-based risk index mapping under defect acceptance criteria
Broad frequency band full field measurements for advanced applications: Point-wise comparisons between optical technologies
No full textThe progress of optical systems gives nowadays at disposal on lightweight structures complex dynamic measurements and modal tests, each with its own advantages, drawbacks and preferred usage domains.
It is thus more easy than before to obtain highly spatially defined vibration patterns for many applications in vibration engineering, testing and general product development.
The potential of three completely different technologies is here benchmarked on a common test rig and advanced applications.
SLDV, dynamic ESPI and hi-speed DIC are here first deployed in a complex and unique test on the estimation of FRFs with high spatial accuracy from a thin vibrating plate.
The latter exhibits a broad band dynamics and high modal density in the common frequency domain where the techniques can find an operative intersection.
A peculiar point-wise comparison is here addressed by means of discrete geometry transforms to put all the three technologies on trial at each physical point of the surface.
Full field measurement technologies can not estimate only displacement fields on a refined grid, but can exploit the spatial consistency of the results through neighbouring locations by means of numerical differentiation operators in the spatial domain to obtain rotational degrees of freedom and superficial dynamic strain distributions, with enhanced quality, compared to other technologies in literature.
Approaching the task with the aid of superior quality \textit{receptance} maps from the three different full field gears, this work calculates and compares rotational and dynamic strain FRFs.
Dynamic stress FRFs can be modelled directly from the latter, by means of a constitutive model, avoiding the costly and time-consuming steps of building and tuning a numerical dynamic model of a flexible component or a structure in real life conditions.
Once dynamic stress FRFs are obtained, spectral fatigue approaches can try to predict the life of a component in many excitation conditions.
Different spectral shaping of the excitation can easily be used to enhance the comparison in the framework of any of the spectral approaches for fatigue life calculations, highlighting benefits and drawbacks of a direct experimental approach to failure and risk assessment in structural dynamics when dealing with complex patterns in real-life testing.
Are optical measurements and spatially dense datasets really effective in advanced model updating of lightweight structures with complex structural dynamics?
The noise shown in the raw signal of some experiments may pose issues in proficiently exploiting the added data in a fruitful model updating procedure.
Model updating results are here compared between scanning and native full field technologies, with comments and details on the test rig, on the advantages and drawbacks of the approaches.
The identification of EMA models highlights the increasing quality of shapes that can be obtained from native full field high resolution gears, against that (some time unexpectedly poor) of SLDV tested
Attempts at Pseudo-Inverse Vibro-Acoustics by Means of SLDV-Based Full-Field Mobilities
Full text linkLightweight components can have structural integrity and reliability concerns, coming from dynamic airborne pressure fields. Hardly tuned numerical structural models may enter into vibro-acoustic simulations of the pressure fields radiated by vibrating plates, potentially masking the forecast of severe outputs. Instead, this paper proposes—for the direct and inverse vibro-acoustic approaches—to characterise the broad frequency band structural dynamics of radiating surfaces by means of experiment-based full-field contactless techniques, with increased spatial resolution, but without the inertia-related distortions of traditional measurement transducers. The SLDV-based mobilities bring the real-life behaviour of the component into the vibro-acoustic simulations, with the actual realisation-related complete structural dynamics and broad frequency band excitation. The paper aims at assessing the procedure for the estimation, in the whole spectrum, of the airborne force, which can be transmitted by an airborne pressure field to known structural locations. The simulation tools revisit the simple Rayleigh integral approximation of sound radiation from a vibrating surface, a real thin flat plate, describable by SLDV-based complex-valued full-field mobilities. Airborne pressure fields and excitation forces concern the early attempts of direct and pseudo-inverse vibro-acoustics. Details, examples and considerations about the whole procedures are thoroughly provided: on the simulation of the vibro-acoustic transfer matrix and of the radiated sound pressures with given excitation forces; on the retrieval of the airborne forces in restraining locations, together with the assessment of the numerical precision of the retrieving procedure
The multirate resource constraint
No full textMany real world cyclic scheduling problems involve applications that need to be repeated with different periodicity. For example, multirate control systems present multiple control loops that are organized hierarchically: The higher-level loop responds to the slower system dynamics and typically its period can be a few orders of magnitude longer than the lowest level. Cyclic scheduling problems can be cast into classical RCPSP instances via a technique called unfolding [4,6], which causes graph expansion. In the case of multirate applications, this expansion can be significantly large. In this context, finding a high-quality allocation and schedule could be very challenging. In this paper, we propose a new Multirate Resource Constraint, modeling unary resources, that avoids graph expansion by exploiting the multirate nature of the schedule in its filtering algorithm. In an experimentation on synthetic and real-world instances, we show that our method drastically outperforms approaches based on state-of-the-art unfolding and constraint based scheduling
Full-field ESPI techniques in structural dynamics
No full textRassegna delle ricerche effettuate dall'autore nel campo delle misure di vibrazioni con ottiche/interferometria laser speckle.
Abstract: "In this paper Electronic Speckle Pattern Interferometry (ESPI) technique
is presented for the structural dynamics of mechanical components. Starting from a
brief description of its principles, ESPI is shown with its potentials for the inquiry in
complex-shaped displacement fields, due to heterogeneous structure or complex vibration
patters, in a wide frequency range. The applications range from integrity inspection, to
vibration analysis and to fatigue life assessment. This paper illustrates a review of the
researches of the author on the ESPI capabilities in experimental dynamics.
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
