384 research outputs found
Simultaneous detection of the nonlinear restoring and excitation of a forced nonlinear oscillation: an integral approach
We address in this article, how to calculate the restoring characteristic and the excitation of a nonlinear forced oscillating system. Under the assumption that the forced nonlinear oscillator has a periodic solution with period, we constructed a system of linear equations by introducing time-dependent multipliers. The periodicity assumption helps simplify the system of linear equations. The stability and uniqueness are also presented for the inverse problem. Numerical testing is conducted to show the effectiveness of our presented methodology.Peer ReviewedPostprint (author's final draft
Controller optimization with constraints on probabilistic peak responses
Peak response is a more suitable index than mean response in the light of structural safety. In
this study, a controller optimization method is proposed to restrict peak responses of building structures
subject to earthquake excitations, which are modeled as partially stationary stochastic process. The
constraints are given with specified failure probabilities of peak responses. LQR is chosen to assure
stability in numerical process of optimization. Optimization problem is formulated with weightings on
controlled outputs as design variables and gradients of objective and constraint functions are derived. Full
state feedback controllers designed by the proposed method satisfy various design objectives and output
feedback controllers using LQG also yield similar results without significant performance deterioration.The work presented in this paper was partially supported by Research Fund of the National
Research Laboratory Program (Project No. M1-0203-00-0068) from the Ministry of Science and
Technology in Korea. The authors also gratefully acknowledge the support of this research by the
Smart Infra-Structure Technology Center (SISTeC) (Project No. R11-2022-101-03004-0(2002))
Theory of magnetic field-induced metaelectric critical end point in BiMnO
A recent experiment on the multiferroic BiMnO compound under a strong
applied magnetic field revealed a rich phase diagram driven by the coupling of
magnetic and charge (dipolar) degrees of freedom. Based on the
exchange-striction mechanism, we propose here a theoretical model with the
intent to capture the interplay of the spin and dipolar moments in the presence
of a magnetic field in BiMnO. Experimentally observed behavior of the
dielectric constants, magnetic susceptibility, and the polarization is, for the
most part, reproduced by our model. The critical behavior observed near the
polarization reversal point in the phase diagram is interpreted as
arising from the proximity to the critical end point.Comment: Theory; relevant experiment uploaded as arXiv:0810.190
Spontaneous phase oscillation induced by inertia and time delay
We consider a system of coupled oscillators with finite inertia and
time-delayed interaction, and investigate the interplay between inertia and
delay both analytically and numerically. The phase velocity of the system is
examined; revealed in numerical simulations is emergence of spontaneous phase
oscillation without external driving, which turns out to be in good agreement
with analytical results derived in the strong-coupling limit. Such
self-oscillation is found to suppress synchronization and its frequency is
observed to decrease with inertia and delay. We obtain the phase diagram, which
displays oscillatory and stationary phases in the appropriate regions of the
parameters.Comment: 5 pages, 6 figures, to pe published in PR
Draft genome sequence of a caprolactam degrader bacterium: Pseudomonas taiwanensis strain SJ9
AbstractPseudomonas taiwanensis strain SJ9 is a caprolactam degrader, isolated from industrial wastewater in South Korea and considered to have the potential for caprolactam bioremediation. The genome of this strain is approximately 6.2 Mb (G+C content, 61.75%) with 6,010 protein-coding sequences (CDS), of which 46% are assigned to recognized functional genes. This draft genome of strain SJ9 will provide insights into the genetic basis of its caprolactam-degradation ability
Cyclic Loading Test of Structural Walls with Small Openings
This study aimed to investigate the effects of small openings on the structural performance of reinforced-concrete (RC) structural walls. Cyclic lateral loading tests were conducted on five RC walls with an aspect ratio of 2.6 and small openings. The main test parameter was the size of the small openings. The specimens were designed to fail after flexural yielding, considering the typical failure mode of slender RC walls. The structural performances of the test specimens were analyzed based on the test results in terms of the load-carrying capacity (flexural strength), hysteretic behavior, strain distribution, and the size of the openings. The specimens showed flexural yielding regardless of the size of the openings, and the flexural strength and deformation capacity were not significantly affected by the small openings. This result indicates that small openings do not affect the flexural behavior of slender walls if the walls have sufficient shear resistance and the small openings are located away from the extreme compressive end and in the compression zone where compressive stress does not decrease.This work was fnancially supported by the National Research Foundation of Korea (NRF) Grant funded by the Korea Government (MSIT) (No. 2018R1A2B6007559
Seismic analysis, design, and retrofit of built-environments: a procedural review of current practices and case studies
Abstract
This paper presents a synthesis of current practices in regard to the seismic analysis, design, and retrofit of built-environments. Background information on the behavior of existing buildings subjected to earthquake loadings is gathered and rehabilitation methodologies are elaborated. The first part of the review examines design standards and guidelines that are used in the structural engineering community. These documents are mandatory for the legal adoption of a model code by the governing jurisdiction where the building in question is to be located. The second part discusses retrofit procedures alongside specific provisions dominating the requirements and techniques appertaining to ground motions. The third part handles case studies emphasizing an upgrade of school buildings that are non-conforming to contemporary specifications and guidelines. For substantiating the performance of proposed methodologies, laboratory tests are conducted in conjunction with finite element analysis, which form the technical foundation of site implementations
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