Publications

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A number of methods for non-linear system identification in the time and frequency domain have been developed in the past. These methods have been applied to many systems, ranging from micro-scale devices to macro-scale systems, sometimes with uncertain results. The aim of this paper is to assess the efficiency of a subset of methods and understand their range of usability. The methods considered in this study are the restoring force surface (RFS), Hilbert transform (HT), zero-crossing (ZC), direct quadrature (DQ), short-time Fourier transform (SFT) and zero-crossing for systems with asymmetric restoring forces (ZCA). The accuracy and robustness of the methods against measured noise were evaluated using simulated data from a SDOF system. The application of the selected methods to a simulated non-linear MDOF system was also investigated. It could be shown that under certain conditions these methods may still provide reliable results for MDOF systems although generally their use should be avoided. The methods were also applied to data from a micro-electro-mechanical-systems (MEMS). Unfortunately, due to lack of symmetry in the experimental data, only the RFS and ZCA could have been used, leading to the finding that the MEMS device may be modelled using quadratic stiffness.

Overhead collisions of trucks with low-clearance railway bridges cause more than half of the railway traffic interruptions over bridges in the United States. Railroad owners are required to characterize the damage caused by such events and assess the safety of subsequent train crossings. However, damage characterization is currently visual (subjective) and becomes difficult in remote locations where collisions are not reported and inspections are not performed following the impact. To mitigate these shortcomings, this paper presents a new impact definition and rating strategy for automatically and remotely quantify damage. This research proposes an impact rating strategy based on the information that best describes the consequences of vehicle-railway bridge collisions. A series of representative impacts were simulated using numerical finite element models of a steel railway bridge. Railway owners provided information about the bridge and impact characterization based on railway industry experience. The resulting nonlinear dynamic responses were evaluated with the proposed rating strategy to assess the effect of these impacts. In addition, a neural network methodology was implemented on a simplified numerical model to identify spatial characteristics of the impact damage.

Bolted joints are prevalent in most assembled structures; however, predictive models for their behavior do not exist. Calibrated models, such as the Iwan model, are able to predict the response of a jointed structure over a range of excitations once calibrated at a nominal load. The Iwan model, though, is not widely adopted due to the high computational expense of implementation. To address this, an analytical solution of the Iwan model is derived under the hypothesis that for an arbitrary load reversal, there is a new distribution of dry friction elements, which are now stuck, that approximately resemble a scaled version of the original distribution of dry friction elements. The dry friction elements internal to the Iwan model do not have a uniform set of parameters and are described by a distribution of parameters, i.e., which internal dry friction elements are stuck or slipping at a given load, that ultimately governs the behavior of the joint as it transitions from microslip to macroslip. This hypothesis allows the model to require no information from previous loading cycles. Additionally, the model is extended to include the pinning behavior inherent in a bolted joint. Modifications of the resulting framework are discussed to highlight how the constitutive model for friction can be changed (in the case of an Iwan–Stribeck formulation) or how the distribution of dry friction elements can be changed (as is the case for the Iwan plasticity model). Finally, the reduced Iwan plus pinning model is then applied to the Brake–Reuß beam in order to discuss methods to deduce model parameters from experimental data.

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This report analyzes the results of a study on culture and its capability to influence research. The study occurred during the 2016 Nonlinear Mechanics and Dynamics Summer Research Institute, a six-week research program sponsored by Sandia National Laboratories and the University of New Mexico consisting of 27 graduate students participating in ten different projects. Two separate surveys were administered at the beginning and end of the Institute, in addition to interviews and observation, in order to study the effects of various cultural factors on engineering processes and maintaining professional interactions. The results of this study indicate that cultural differences are not a significant barrier to engineering progress and most cultural issues are minor. A variety of cultures instead provide new perspectives, advancing universal understanding.

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The Fourth International Workshop on Jointe d Structures was held from October 19-21, 2015, in Dartington, UK. Forty five researchers from both the United States and international locations convened to discuss the recent progress of mechanical joints related research and associated efforts in addition to developing a ne w roadmap for the evoluti on of joints research from academic to industrial appli cations over the next five to te n years. The workshop itself was organized around four themes: applications that ca n benefit from joints research (applicability), repeatability and variability issues in experi ments (repeatability), challenges in developing predictive models (predictability), and potential paths forward (way forward). The outcomes of the workshop are still in progress as the joints community develops a new roadmap for joints research; however, there are many aspects that are related here within. The ultimate goal of this research community is to deve lop a validated method for the de sign and analysis of dynamically loaded structures with frictional joints. Acknowledgement The authors thank all of the participants of the workshop for their contributions to the discussion and goals laid out herein. Additio nally, we would like to thank Sandia National Laboratories, the National Scie nce Foundation, and the Atomic Weapons Establishment for their support of this workshop.

The Reduced Order Modeling Unlimited Localized Interface Simulator (ROMULIS) is a set of toolbox scripts in MATLAB designed to perform nonlinear transient integration on a system of reduced order st ructural models that interact with each other at localized interfaces. ROMULIS is meant to provide a us er-friendly interface for applying the latest developments in numerical techniques and modeling in structural dynamics analysis while also giving the freedom to implement new technologies from forthcoming research. This report documents how to use and interpret the toolbox sc ripts. The theory behind th e code is given, followed by a manual for interacting with the scripts to perform simulations. Lastly, a high-level introduction that explains how the scripts in teract with each other is given for aspiring developers.

The 2016 Parameterized Reduced Order Modeling (PROM) Workshop was held in June, 2016, in Albuquerque, NM. This workshop included 30 researchers who took part in a two day discussion regarding the state of the art for PROMs, complimentary reduced order modeling (ROM) theories, and discussion of the future di rections of PROM research. The goals of the workshop were three-fold: to assess the relative accuracy, efficiency, and merits of the different PROM methods; to discuss the state of the art for ROMs and how PROMs can benefit from these advances; and to define the pressing challenges for PROMs and a path for future research collaborations.

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