1,720,961 research outputs found
A modal based reduction technique for wide loose interfaces and application to a turbine stator
Full text linkAim of this research is the prediction of the non-linear forced response of a stator bladed disk for aeronautical applications in the presence of friction contacts at the hook joints (casing – vane segment contact). Due to the large extension of the contact interfaces the use of classic node-to-node contact elements based on the Coulomb friction law becomes cumbersome. Although such approach appears convenient for problems involving small contact regions, it is computationally expensive when large contact interfaces with refined meshes are present between components. In this research, a novel modal interface reduction method is combined with a layer of Jenkins contact elements in order to efficiently predict the effects of friction on the non-linear forced response of the stator bladed disk. The wide rail/hook contact regions are therefore suitable for the application of the presented technique. The goodness of the proposed methodology is quantified both in terms of accuracy and time costs savings on the calculation of non-linear forced responses by exploiting cyclic symmetry hypotheses and the Harmonic Balance Method
Reduced order modeling of large contact interfaces to calculate the non-linear response of frictionally damped structures
Full text linkHigh-frequency nonlinear vibration analysis through low-frequency stereo-camera systems
Full text linkThis paper describes a new methodology that expands the capabilities of low-frame, high-resolution stereo-camera systems in studying the dynamic behavior of components in the presence of nonlinear phenomena. A new downsampling technique called the Smoothed Harmonics Analysis (SHA) is proposed. This technique addresses the limitations due to the low-frame rate cameras for the study of high-frequency periodic steady-state nonlinear oscillations. SHA enables accurate reconstruction of downsampled signals, thus opening up numerous potential applications. The feasibility of this technique is demonstrated by analyzing the motion of a beam with nonlinear behavior. The nonlinearity is caused by intermittent contact while the beam is subjected to harmonic excitation
A parametric study of Limit Cycle Oscillation of a bladed disk caused by flutter and friction at the blade root joints
No full textDIC vibration measurement through smartphone devices
Full text linkDigital Image Correlation (DIC) stands as a promising non-contact method for assessing the complete dynamics of vibrating structures. Utilizing one or two cameras, DIC can capture either 2D or 3D dynamics. Through subsequent post-processing of images, structural points are correlated across different time frames to derive displacement information. Given the abundance of camera options available, spanning frame rate, resolution, versatility, and quality, the selection process is dictated by specific application needs and financial considerations. This study seeks to explore the feasibility of utilizing the cameras integrated into a ubiquitous device of everyday life: the smartphone. The proposed approaches offer straightforward procedures suitable for educational purposes or early investigation of structure dynamics. The paper presents case studies and discusses simple experiments that students or DIC beginners can conduct on simple vibrating structures. Initially, a simple 2D dynamics was investigated by recording the vibration of a clamped beam with moving constraints using just a single smartphone. The L-type cross section of the beam emphasizes its in-plane motion. The frames were post-processed with open-source software and the deformed shapes were extracted. This assignment serves as an introductory exercise in DIC fundamentals. Subsequently, the focus shifts to investigating the 3D dynamics of the beam. Given the challenges associated with synchronizing multiple smartphone video acquisitions, the image of the beam was instead reflected by two mirrors, and these reflected images were recorded by a single smartphone. Then, the recorded images were split and processed to obtain the full-field 3D dynamics of the beam
Vibration parameters identification of turbomachinery rotor blades under transient condition using Blade Tip-Timing measurements
Full text linkDuring run ups and run downs, the rotating blades are subjected to fluctuating forces with time dependent
frequencies and the dynamic response of the blades around the resonance crossings deviates from the stationary
response. This paper presents a procedure to identify the vibration parameters of rotating blades under this
non-stationary condition. An analytically based solution of a single degree of freedom (SDOF) system exposed
to a transient harmonic excitation with linear time varying frequency is used for parameters identification. This
analytical model is fitted into the Blade Tip-Timing (BTT) data and the vibration parameters are determined
by a least square optimization technique. A numerical simulator based on a lumped parameter model of the
bladed disk assembly is employed to demonstrate the method performance. Afterwards, the accuracy of the
method is proved by testing it on the experimental data acquired by BTT and strain gauges on a rotating
bladed disk
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
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