158 research outputs found
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
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
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
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
No full textThis 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
The impact of fretting wear on structural dynamics: experiment and simulation
No full textThis paper investigates the effects of fretting wear on frictional contacts. A high frequency friction rig is used to measure the evolution of hysteresis loops, friction coefficient and tangential contact stiffness over time. This evolution of the contact parameters is linked to significant changes in natural frequencies and damping of the rig. Hysteresis loops are replicated by using a Bouc-Wen modified formulation, which includes wear to simulate the evolution of contact parameters and to model the evolving dynamic behaviour of the rig. A comparison of the measured and predicted dynamic behaviour demonstrates the feasibility of the proposed approach and highlights the need to consider wear to accurately capture the dynamic response of a system with frictional joints over its lifetime
Efficient Model Reduction and Prediction of Superharmonic Resonances in Frictional and Hysteretic Systems
No full textModern engineering structures exhibit nonlinear vibration behavior as designs
are pushed to reduce weight and energy consumption. Of specific interest here,
joints in assembled structures introduce friction, hysteresis, and unilateral
contact resulting in nonlinear vibration effects. In many cases, it is
impractical to remove jointed connections necessitating, the understanding of
these behaviors. This work focuses on superharmonic and internal resonances in
hysteretic and jointed systems. Superharmonic resonances occur when a nonlinear
system is forced at an integer fraction of a natural frequency resulting in a
large (locally maximal) response at an integer multiple of the forcing
frequency. When a second vibration mode simultaneously responds in resonance at
the forcing frequency, the combined phenomena is termed an internal resonance.
First, variable phase resonance nonlinear modes (VPRNM) is extended to track
superharmonic resonances in multiple degree of freedom systems exhibiting
hysteresis. Then a novel reduced order model based on VPRNM (VPRNM ROM) is
proposed to reconstruct frequency response curves faster than utilizing the
harmonic balance method (HBM). The VPRNM ROM is demonstrated for a 3 degree of
freedom system with a 3:1 internal resonance and for the jointed Half
Brake-Reuss Beam (HBRB), which exhibits a 7:1 internal resonance. For the HBRB,
new experimental results are used to validate the modeling approaches, and a
previously developed physics-based friction model is further validated,
achieving frequency predictions within 3%. For the considered cases, VPRNM ROM
construction is up to 4 times faster than HBM, and the evaluation of the VPRNM
ROM is up to 780,000 times faster than HBM. The modeling shows that both
tangential slipping and normal direction clapping of the joint play important
roles in exciting the superharmonic resonances in the HBRB.Comment: 84 pages, 53 figures, 4 tables. Under Review at Mechanical Systems
and Signal Processin
The Brake-Reuß Beams: A System Designed for the Measurements and Modeling of Variability and Repeatability of Jointed Structures with Frictional Interfaces
No full text
Constitutive Modeling of Contact for Elastic–Plastic Materials Engaged in Micro/Macroslip
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