1,721,017 research outputs found
Unbalanced, cracked, and misaligned rotating machines: a comparison between classification procedures throughout the steady-state operation
No full textThis article compares two intelligent methods for automatic detection of unbalancing, cracks, and parallel misalignment in rotary machines. The finite element method is used to model the faults in a rotating system. The modeled system then operates virtually under different conditions in the steady-state operation; the vibrational responses are calculated numerically. To compare the accuracy of different manners in the classification of defective systems, firstly, four distinct types of features, i.e., statistical, frequency, time–frequency, and uncertainty are exploited. The T test process is utilized to test the extracted characteristics; the unreliable features are removed from feature vectors, then the remained ones are used in four supervised machine learning classifiers, i.e., support vector machine, k-nearest neighbors, Naive Bayes, and decision trees. In the following, as the convolution neural networks (CNNs) approach, the persistence spectrums of raw signals are plotted, and these graphs are introduced as input data. Comparing results of the different classification methods, it has been observed that although CNNs based on persistence spectrum graphs are computationally heavy and time-consuming, they provide more accurate results than the other classifiers. The results show that the proposed approach for rotor fault detection is effective, accurate, and robust and that it has promise for real engineering applications
Da une langue – une nation allo schwa. Lingue e language policies tra propaganda e attivismo
No full textThe article aims to investigate the historical processes and linguistic arguments behind language-political interventions in Europe. By analysing, from a multidisciplinary point of view, a series of historical examples of language policies in Europe a paradigm shift is outlined from discourses relating to inter-linguistic phenomena, such as the relationship between standard and minority languages, to intralinguistic ones, e. g. aspects concerning the norm and codification of a standard language or different types of inclusive language and their integration. In addition to this, the contribution aims to identify the ideological nexus of linguistic interventions in order to verify the possibility of conceptualising them as manifestations of propaganda. Through examples, it is assumed that language per se has become a propagandistic political instrument or a means to gain political power.L’articolo intende indagare i processi storici e gli argomenti linguistici alla base delle intervenzioni politico-linguistiche in Europa. Analizzando, da un punto di vista multidisciplinare, una serie di esempi storici di politica linguistica e language policies in Europa, viene delineato un cambio di paradigma dai discorsi relativi a fenomeni interlinguistici, come il rapporto tra lingua standard e lingue minoritarie, a quelli intralinguistici; per esempio, aspetti che riguardano la norma e la codificazione della lingua standard o diversi tipi di linguaggio inclusivo e la loro integrazione. Oltre a ciò, il contributo mira a identificare il nesso ideologico delle intervenzioni linguistiche in modo tale da verificare la possibilità di concepirle come manifestazioni di propaganda. Attraverso gli esempi si ipotizza che la lingua per se sia diventata uno strumento politico propagandistico oppure un mezzo per raggiungere più potere politico
Investigation on composite energy absorbers of a composite fuselage section subjected to vertical drop test
No full textIn the aircraft industry, crashworthiness design and certification phases have been and are going to be the most attractive topics for designers, mostly because of the increasing use of composites for primary structural components. It is well known that the cargo subfloor elements of the fuselage structure play a crucial role in absorbing the kinetic energy during a crash. In particular, the stanchions, or struts, are important parts for the structural response; as a matter of fact, they connect the fuselage frames to the cabin’s floor and, ideally, are expected to crush under a compressive force in order to dissipate the impact energy in a controlled way and, consequently, to minimize the energy transferred to the passengers. The aim of this work is to demonstrate, experimentally and numerically, the energy absorption capability of the stanchions, made of both composite material and aluminium alloy, of a full-scale 95% composites made fuselage section under a critical load condition, such as an emergency landing. A Finite Element model allowing estimating the passive safety capabilities of the designed struts has been developed and herein proposed
Experimental investigation of GFRP plates under LVI phenomena with different impact energy levels
No full textThis paper deals with an experimental tests campaign addressed to investigate the structural behaviour of short Glass Fibre Reinforced Polymers (GFRP) plates (PA66 GF30) under Low Velocity Impact (LVI) phenomena, characterized by different impact energy levels, according to the ASTM D7136 requirement. The scope of this research activity must be found in a wider scenario, in which the experimental characterization can be the key-step to develop an established numerical model for the simulation of the experimental tests. Under a Certification by Analysis (CbA) purpose, an established numerical model can be used, rather than to virtually characterize the behaviour of specimens (reducing the costs related to the experimental tests), to simulate LVI on large structural component difficult to test in a laboratory
FE Analyses of a CFRP–Aluminum Single-Lap Hybrid Bonded/Bolted Joint at Different Tensile Loads
No full textJoints are often unavoidable and can be critical points in a complex structure made up of different sub-elements and materials, e.g., a lightweight aircraft structure. Joining can be performed with different techniques as mechanical fasteners, bonding, or hybrid bonded/bolted (HBB) solutions. HBB solutions are effectively used to join different materials, as metals and composites, leading to composite–metal HBB joint. In this paper, the structural behavior of a carbon fiber reinforced polymer (CFRP)–aluminum single-lap HBB joint is numerically investigated. Specifically, a detailed finite element model (FEM) is developed to study the joint subjected to an external tensile load. Analyses are conducted by considering two different bolt preloads and three external tensile loads (six tests in total). Results are compared with the aim to highlight the behavior of the joint, and in particular the stress–strain state in each component as a consequence of the applied load pair
Enhancing Air Compressor Fault Diagnosis: A Comparative Study of GPT-2 and Traditional Machine Learning Models
No full textThis study investigates the application of GPT-2, a transformer-based model, for fault diagnosis in reciprocating air compressors, highlighting its ability to capture complex patterns in acoustic signals. Two approaches are compared: the first involves extracting time, frequency, and complexity-based features and classifying them using traditional machine learning models, with a narrow neural network achieving the best performance. The second approach reformulates these features as sequential data for GPT-2, which, through meticulous hyperparameter optimization, delivered superior diagnostic accuracy. Additionally, SHapley Additive exPlanations analysis was employed to enhance model interpretability by identifying the most influential features, providing valuable insights into the fault diagnosis process. While GPT-2 demonstrated notable performance gains over conventional models, it required a more precise hyperparameter tuning. This study offers valuable insights into the application of large language models for classifying damaged mechanical systems
Influence of Building Position and Printing Scheme on Mechanical Properties of Fused Filament Fabrication PLA Specimens
No full textThe recent improvement of additive manufacturing (AM) technologies has been attracting the industry and research community attention. This paper aims to investigate the influence of building position and printing scheme on the tensile mechanical properties of Tough polylactic acid (PLA) material, manufactured through a fused deposition modeling (FDM) 3D printing – the S5 ProBundle Ultimaker. FDM 3D printing, also known as fused filament fabrication (FFF), is an AM process within the realm of material extrusion. FDM builds parts Layer by Layer by selectively depositing melted material in a predetermined path, and uses thermoplastic polymers that come in the form of filaments. In this paper, AM Tough PLA specimens are manufactured according to ASTM-D638 requirement considering two different positions on the building plate and two printing schemes. Specimens are tested under static tensile test and the mechanical properties are extracted
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