1,720,964 research outputs found
Quantifying Epistemic and Aleatoric Uncertainty in the Ampair 600 Wind Turbine
No full textDetermining the uncertainty in a mechanical joint is very important and very difficult. This paper presents two methods of determining the uncertainty in the joint: maximum entropy approach and sampling methods. Maximum entropy is an approach that can quantify the aleatoric and epistemic uncertainty independently. This approach is applied on a rigid connection of the Ampair 600 Wind Turbine and shows that the epistemic uncertainty of the system is very high. Sampling methods are used on an simplified representation of the wind turbine as a lumped mass approximation. The sampling methods are able to treat the joint in a nonlinear sense by using a discrete four-parameter Iwan model as the joint model. This is able to predict accurately the data within the uncertainty bounds when considering epistemic uncertainty. The Iwan joint model is then implemented on the high fidelity model and preliminary results are presente
Quantifying Epistemic and Aleatoric Uncertainty in the Ampair 600 Wind Turbine
No full textThe goal of this chapter is to demonstrate a practical application of the maximum entropy method. While there are multiple approaches to quantifying uncertainty (both aleatoric and epistemic), the maximum entropy method is commonly used to study joint mechanics due to the high epistemic uncertainty in these systems. The maximum entropy method is applied to the Ampair 600 Wind Turbine. Experimental data is used to drive the development of several numerical models. Results demonstrate that accounting for aleatoric uncertainty alone will lead to nonconservative predictions of the system response. However, once epistemic uncertainty is included in the model, results span the complete set of measured responses
Visualization and Identification of Nonlinear Structural Dynamics Via Phase-Based Motion Magnification
No full textThe identification and analysis of nonlinear dynamics in structural systems remain critical challenges in engineering, particularly when subtle vibrational phenomena are involved. Phase-Based Motion Magnification (PBMM) has emerged as a powerful noncontact technique for visualizing fine-scale motions in complex systems, yet its application to nonlinear structural behavior remains underexplored. This study investigates the dynamic response of a beam–spring system with intentional nonlinearities, focusing on the characterization of superharmonic components and mode shapes using PBMM. Experimental tests under force-controlled stepped-sine excitation reveal pronounced hardening effects at the first resonant frequency, attributed to the geometric nonlinearity of the spring, and minimal nonlinear behavior at the second resonant frequency. High-speed video recordings were processed with PBMM, enabling the visualization of subtle energy redistribution into higher harmonics and the extraction of mode shapes across multiple frequency ranges. To enhance structural boundary visualization, a novel Visualization of Edge Detection (VED) method combining DexiNed edge detection and bilateral filtering was employed. Comparisons between PBMM results and accelerometer data validated the effectiveness of this approach in capturing nonlinear responses. These findings highlight the potential of PBMM, combined with advanced post-processing techniques, to revolutionize non-contact modal analysis and provide new insights into the nonlinear dynamics of engineering structures
A New Tool for Investigating Mesoscale Contact
Get PDFThis thesis presents a body of work undertaken to develop a new contact test rig for the Tribomechadynamics Lab. Motivated by a continued interest in the design and modeling of joined structures, the need for a mesoscale contact testing capability is uncovered by a discussion of several research areas. Built upon the science of instrumented indentation, the test rig is capable of a maximum applied load of 4,000 N over a contact displacement of less than 90 microns. Resolution in the load - displacement data is 2 N and 100 nm, respectively. Interchangeable contact tips and a custom built height positioning stage contribute to the flexibility of the tool. The accompanying controller and user interface allow for high test throughput by even inexperienced users. The construction, validation, and initial testing of the rig are described in depth. The development of the post-processing methods and derivation of several material properties from the load-displacement data are covered as well.
The functionality of the rig is illustrated by the results of three unique applications: an indentation and flattening study on multiple materials, a study of the influence of coating thickness on the properties of layered solids, and a proof of concept for a future rough contact study. Data from high fidelity surface characterization is integrated with the contact data. A tool for maximizing productivity and capability by stitching surface scans into a complete surface of interest is developed as well. The promising results of the initial testing motivates a discussion of future additions to the rig and applications not yet explored
Multi-Scale Modeling in Bolted Interfaces
No full textThe thesis develops a framework for modeling the dynamics of bolted
structures in a multi-scale manner. Understanding that most of the
challenges faced by the joints community is around the reconciliation
of contact response with physical parameters of the system, the
current work is an attempt for this reconciliation using properties
identified from interfacial scans of the structure. The basic idea of
statistical averaging as conducted in rough contact studies is used
here for achieving this in a segment-by-segment fashion. Thus, the
response characterization may be done in a manner that represents the
micro-level asperity distributions while also preserving a meso-level
understanding of possible local variations. Since all of these are
used, through the framework, for macro-level simulations of the
dynamics, the approach links the micro-, meso-, and the macro-length
scales (in that order).
For the dynamical simulations, a modified modal quasi-static approach
is proposed, which is capable of representing amplitude-dependent
nonlinear modal characteristics of nonlinear dynamical systems with
linear limit cases. Since the fully stuck and the fully slipped cases
may be taken as the limit cases, this is well applicable for the cases
with frictional contacts. The results for the modified approach are
compared with the responses characterized from other time- and
frequency-domain approaches for a simple example in order to validate
its efficacy.
Finally, the approach is applied for a three bolt lap-joint benchmark
(the so-called ``Brake-Reu{\ss}-Beam''). Since the characterization of
the interface is conducted in a full-field manner on top of a finite
element mesh, the framework is also demonstrated to be applicable for
conducting full-field micro-scale interface evolution
studies. Validating this would enable models with
backward-evolutionary dependence (macro- influencing meso- influencing
micro-scale attributes). To this end, preliminary statistical studies
are conducted to establish and/or understand correlations of local
changes in relevant roughness parameters with predicted local
tractions and dissipation fluxes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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