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Numerical Simulations of Dynamic Behavior of Polyurea Toughened Steel Plates under Impact Loading
Chien-Chung Chen,Daniel G. Linzell
Journal of Computational Engineering , 2014, DOI: 10.1155/2014/416049
Abstract: The objective of the work discussed herein is to develop a nonlinear 3D finite element model to simulate dynamic behavior of polyurea toughened steel plates under impact loading. Experimental and numerical work related to model development are presented. Material properties are incorporated into numerical models to account for strain-rate effects on the dynamic behavior of polyurea and steel. One bare steel plate and four polyurea toughened steel plates were tested under impact loading using a pendulum impact device. Displacement time-history data from experimental work was used to validate the numerical models. Details on material model construction, finite element model development, and model validation are presented and discussed. Results indicate that the developed numerical models can reasonably predict dynamic response of polyurea toughened steel plates under impact loading. 1. Introduction Extreme natural and man-made hazards have always posed threats to civil infrastructure. Typical natural threats include earthquakes and hurricanes and man-made hazards can include malicious events caused by explosions or vehicle collisions. As conventional structures designed primarily based on strength and serviceability criteria can, in some instances, be vulnerable to impulsive and impact loads, it was of interest to examine new structural systems and materials that might better protect important structural components against these loads. This paper summarizes portions of a study that investigated the effectiveness with which an innovative coating material helped improve steel structural component impact resistance. Polyurea is a coating material that has received research interest due to its effective energy absorption properties. Davidson et al. [1] utilized polyurea as a blast load retrofitting material for masonry wall systems in residential or low-rise office structures. Fatt Hoo et al. [2] investigated the performance of polyurea strengthened concrete masonry walls subjected to blast loading. Results suggested that polyurea coated concrete masonry walls could improve blast resistance and reduce fragmentation. Also, Porter et al. [3] indicated that polyurea can be used to increase blast resistance of timber-framed structures. Nevertheless, the performance of various substrate materials coated with polyurea, from brittle materials like the aforementioned concrete and masonry to more ductile materials like steel, may vary widely because of the inherent different material behavior between brittle and ductile materials, and, as a result, approaches for
Nonlinear Seismic Response Analysis of Curved and Skewed Bridge System with Spherical Bearings
Junwon Seo,Daniel G. Linzell,Jong Wan Hu
Advances in Civil Engineering , 2013, DOI: 10.1155/2013/248575
Abstract: A three-dimensional (3D) modeling approach to investigate nonlinear seismic response of a curved and skewed bridge system is proposed. The approach is applied to a three-span curved and skewed steel girder bridge in the United States. The superstructure is modeled using 3D frame elements for the girders, truss elements for the cross-frames, and equivalent frame elements to represent the deck. Spherical bearings are modeled with zero-length elements coupled with hysteretic material models. Nonlinear seismic responses of the bearings subjected to actual ground motions are examined in various directions. Findings indicate that the bearings experience moderate damage for most loading scenarios based on FEMA seismic performance criteria. Further, the bearing responses are different for the loading scenarios because of seismic effects caused by interactions between excitation direction and radius of curvature. 1. Introduction Studies related to the design and analysis of curved and skewed steel bridges have focused on modeling and design for static and pseudo-static loads [1–4], and only a few investigations have looked at seismic behavior [5]. To design and assess curved steel bridges in high and moderate seismic zones, it is of interest to more extensively examine seismic analysis methods so that reliable 3D modeling approaches are developed. Studies have been undertaken that applied modeling approaches to predict the seismic response of straight steel girder bridges [6]. Similar simplified modeling approaches have been proposed for curved steel bridges, but the approaches were applied to static events [1]. These studies have shown that modeling using a 3D approach can provide improved accuracy relative to line girder analyses by incorporating member depths. For a curved and skewed bridge, where significant lateral displacements may be induced at the bearings under a seismic event, modeling structural component depths would be assumed to be important. For these reasons, a 3D modeling approach is used herein to investigate seismic responses of a curved steel I-girder bridge system with skewed supports. The 3D approach is applied to a three-span continuous curved steel I-girder bridge system in the United States. Following the approach recommended by previous research [1], the bridge is modeled using elastic frame elements for the I-girders, truss elements for the cross-frames, and elastic frame elements for the deck. Preliminary seismic responses at the bearings are presented for the bridge under El Centro ground motions. 2. Modeling Approach All elements
Output-only Structural Health Monitoring of a Riveted Steel Railway Bridge utilizing Proper Orthogonal Decomposition, Artificial Neural Network, and Strain Measurements？
Ahmed Rageh,Daniel Linzell,Saeed Eftekhar Azam
Proceedings | An Open Access Journal from MDPI , 2019, DOI: https://doi.org/10.3390/ecsa-5-05834
Abstract: This study presents a new scheme for autonomous health monitoring of railroad infrastructure using a continuous stream of structural health monitoring data. The study utilized measured strains from an optimized sensor set deployed on a double track, steel, railway, truss bridge located in central Nebraska. The most common failure mode for the superstructure of this structural system is the stringer-to-floor beam connection failure, which was the focus of this study. However, the proposed methodology could be used to assess the condition of a wide range of structural elements and details. The damage feature adopted in this framework was the variations of Proper Orthogonal Modes (POMs) of the measured structural response. To automatically detect the occurrence, location, and intensity of deficiencies from the POMs, Artificial Neural Networks (ANN) were adopted. POM variations, which are traditionally input (load) dependent, were ultimately utilized as damage indicators. To alleviate the variability of POMs due to non-stationarity of the train loads, a preset windowing of measured output was completed in conjunction with automated peak-picking. Furthermore, input variability necessitated implementing ANNs to help decouple POM changes due to load variations from those caused by deficiencies, changes that would render the proposed framework input independent; a significant advancement. Damage “scenarios” were artificially introduced into select output (strain) datasets recorded while monitoring train passes across the selected bridge. This information, in turn, was used to train ANNs using MATLAB’s Neural Net Toolbox. Trained ANNs were tested against monitored loading events and artificial damage scenarios. Applicability of the proposed, output-only framework was investigated via studies of the bridge under operational conditions. To account for the effects of potential deficiencies at the stringer-to-floor beam connections, measured signal amplitudes were artificially decreased at select locations. Finally, to validate the applicability of the proposed method using low-cost measurement devices, the measured signals were corrupted by high levels of white, Gaussian noises featuring spatial correlations. It was concluded that the proposed framework could successfully identify 20 damage indices, which were artificially imposed on measured signals under operational conditions
Pomeranchuk-Nematic instability in the presence of a weak magnetic field
Daniel G. Barci,Daniel Reyes
Physics , 2012, DOI: 10.1103/PhysRevB.87.075147
Abstract: We analyze a two-dimensional Pomeranchuk-Nematic instability, trigger by the Landau parameter $F_2<0$, in the presence of a small magnetic field. Using Landau Fermi liquid theory in the isotropic phase, we analyze the collective modes near the quantum critical point $F_2=-1,\omega_c=0$ (where $\omega_c$ is the cyclotron frequency). We focus on the effects of parity symmetry breaking on the Fermi surface deformation. We show that, for studying the critical regime, the linear response approximation of the Landau-Silin equation is not sufficient and it is necessary to compute corrections at least of order $\omega_c^2$. Identifying the slowest oscillation mode in the disordered phase, we compute the phase diagram for the isotropic/nematic phase transition in terms of $F_2$ and $\omega_c$.
Biology of Genomes: making sense of sequence
Daniel G MacArthur
Genome Medicine , 2009, DOI: 10.1186/gm61
Abstract: The Cold Spring Harbor Laboratory Biology of Genomes meeting is one of the most eagerly awaited events in the genomics calendar, and this year's meeting [1] did not disappoint: participants were treated to four days of cutting-edge research on a diverse array of topics. This report focuses on the major themes of the meeting relevant to the field of medical genomics.The single dominant message emerging from this year's meeting was simple: advances in DNA sequencing technology are now enabling the generation of biological data at a frightening (and accelerating) pace. Increasing sequencing capacity promises rapid advances in biological understanding, but it also brings tremendous challenges in terms of storing, disseminating and analyzing vast quantities of data.Both the power and the challenges of large-scale sequencing data were evident in the first session of the meeting, which focused on cancer genomics. Several speakers in this session, including Mike Stratton (Wellcome Trust Sanger Institute, Hinxton, UK), Elaine Mardis (Washington University, St Louis, USA) and Gad Getz (Broad Institute, Cambridge, USA), discussed progress in the use of large-scale sequencing to develop comprehensive catalogs of the genetic changes underlying cancer progression.The general strategy is to generate sequence data from both tumor samples and normal tissue from the same patient; genetic differences between the two samples represent candidates for somatic changes occurring during cancer progression. Stratton presented results from low-coverage sequencing of 24 breast cancer genomes, illustrating the power of this approach for the detection of structural variants (SVs); Mardis and Getz both presented high-coverage sequencing of smaller numbers of cancer samples for combined analysis of SVs and smaller-scale genetic variation.These approaches have successfully generated high-resolution snapshots of genetic variation in tumors, but many challenges remain. For instance, there are many di
Parasitic diseases: opportunities and challenges in the 21st century
Colley, Daniel G;
Memórias do Instituto Oswaldo Cruz , 2000, DOI: 10.1590/S0074-02762000000700015
Abstract: the opportunities and challenges for the study and control of parasitic diseases in the 21st century are both exciting and daunting. based on the contributions from this field over the last part of the 20th century, we should expect new biologic concepts will continue to come from this discipline to enrich the general area of biomedical research. the general nature of such a broad category of infections is difficult to distill, but they often depend on well-orchestrated, complex life cycles and they often involve chronic, relatively well-balanced host/parasite relationships. such characteristics force biological systems to their limits, and this may be why studies of these diseases have made fundamental contributions to molecular biology, cell biology and immunology. however, if these findings are to continue apace, parasitologists must capitalize on the new findings being generated though genomics, bioinformatics, proteomics, and genetic manipulations of both host and parasite. furthermore, they must do so based on sound biological insights and the use of hypothesis-driven studies of these complex systems. a major challenge over the next century will be to capitalize on these new findings and translate them into successful, sustainable strategies for control, elimination and eradication of the parasitic diseases that pose major public health threats to the physical and cognitive development and health of so many people worldwide.
COMPARISON OF FREQUENCY RESPONSE AND NEURAL NETWORK TECHNIQUES FOR SYSTEM IDENTIFICATION OF AN ACTIVELY CONTROLLED STRUCTURE
GóMEZ PIZANO,DANIEL;
DYNA , 2011,
Abstract: system identification methodsare generally used to obtain the dynamic properties of structural systems. the dynamic properties are used for various purposes, such as model updating, structural health monitoring, and control synthesis. this paper presents the identification of an actively controlled structure with an active mass damper based on input-outputrelationships.the input signals include accelerations in the base of the structure and control force inputs while the output signals are the accelerations of the structure due to the inputs. in this paper, the system identification using frequency response functions iscompared with non-linear relationships obtained by using artificial neural networks (ann) for bothasingle-input, single-output, and multiple-inputsingle-output (miso) system. the results indicate that for the miso structural system,the ann technique providesa more accurate identification than identifications obtained with frequency responsemethods.
Transplante de medula óssea em leucemia mielóide aguda
Tabak, Daniel G.;
Revista Brasileira de Hematologia e Hemoterapia , 2000, DOI: 10.1590/S1516-84842000000100008
Abstract: bone marrow transplantation represents an effective therapy for acute myelogenous leukemia. despite its initial use in patients in late stages of their disease, the best results have been documented when the procedure is undertaken while in first complete remission. recent advances in the management of the neutropenic patient have guaranteed the safe use of aggressive chemoterapy regimens, resulting in a prolonged disease free survival, similar to what is documented after myeloablative regimens. doubts still remain as of which patients should be submitted to marrow transplantation and at which stage of their disease. cytogenetics and a better definition of other biological characteristics will allow a better selection of patients. the control of graft versus host disease, improvement in the management of infectious complications, the use of nonmyeloablative conditioning regimens and a greater availability of unrelated marrow donors will permit a greater use of allogeneic marrow transplantation in acute myelogenous leukemia, including elderly patients. the role of autologous transplantation must be better defined.
Transplante de medula óssea nas síndromes mielodisplásicas
Tabak, Daniel G.;
Revista Brasileira de Hematologia e Hemoterapia , 2002, DOI: 10.1590/S1516-84842002000300003
Abstract: around 40% of patients suffering from myelodisplastic syndromes can be cured by allogeneic bone marrow transplantations. the most favorable results are observed in patients with refractory anemia who present an event free survival of up to 65% at 5 years. the main restrictions in the application of this strategy for the majority of the patients are the advanced age of diagnosis and the availability of a compatible donor. the higher risk of relapse in patients with an increased rate of blasts and high-risk cytogenetic alterations mainly identified in secondary myelodisplastias further limit its use. although some patients can be benefited by the utilization of pre-transplantation cytoreductive chemotherapy, there is still insufficient proof of a clear benefit for the majority of patients. not one preparatory regime has shown to be superior, however the increased use of non-myeloablative regimes favor the treatment of a greater number of over 60-year-old patients. preliminary studies also indicated that specific patients can be benefited by a autogenic transplantation and these results should be compared with those from unrelated donors. recent studies also demonstrated more favorable results with the utilization of hematopoietic stem cells from peripheral blood in patients high risk of relapse. better definition of prognostic factors will allow an ideal selection of patients and the optimal time for the procedure.
SBTMO: Presente e futuro. Ainda há muito a fazer...
Tabak Daniel G.
Revista Brasileira de Hematologia e Hemoterapia , 2002,
Abstract:
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