In the field of seismic protection of structures, it is crucial to be able to diminish ‘as much as possible’ and dissipate
‘as fast as possible’ the load induced by seismic (vibration-shock) energy imparted to a structure by an earthquake. In this
context, the concept of passive nonlinear energy pumping appears to be natural for application to seismic mitigation. Hence, the overall problem discussed in this paper can be formulated
as follows: Design a set of nonlinear energy sinks (NESs) that are locally attached to a main structure, with the purpose of passively
absorbing a significant part of the applied seismic energy, locally confining it and then dissipating it in the smallest possible
time. Alternatively, the overall goal will be to demonstrate that it is feasible to passively divert the applied seismic energy
from the main structure (to be protected) to a set of preferential nonlinear substructures (the set of NESs), where this energy
is locally dissipated at a time scale fast enough to be of practical use for seismic mitigation. It is the aim of this work to show that the concept of nonlinear energy pumping is feasible for seismic mitigation. We consider
a two degree-of-freedom (DOF) primary linear system (the structure to be protected) and study seismic-induced vibration control
through the use of Vibro-Impact NESs (VI NESs). Also, we account for the possibility of attaching to the primary structure additional alternative NES configurations
possessing essential but smooth nonlinearities (e.g., with no discontinuities). We study the performance of the NESs through
a set of evaluation criteria. The damped nonlinear transitions that occur during the operation of the VI NESs are then studied
by superimposing wavelet spectra of the nonlinear responses to appropriately defined frequency – energy plots (FEPs) of branches
of periodic orbits of underlying Conservative systems. 相似文献
Summary In this paper, the performance of a nonlinear base-isolation system, comprised of a nonlinearly sprung subfoundation tuned
in a 1∶1 internal resonance to a flexible mode of the linear primary structure to be isolated, is examined. The application
of nonlinear localization to seismic isolation distinguishes this study from other base-isolation studies in the literature.
Under the condition of third-order smooth stiffness nonlinearity, it is shown that a localized nonlinear normal mode (NNM)
is induced in the system, which confines energy to the subfoundation and away from the primary or main structure. This is
followed by a numerical analysis wherein the smooth nonlinearity is replaced by clearance nonlinearity, and the system is
excited by ground motions representing near-field seismic events. The performance of the nonlinear system is compared with
that of the corresponding linear system through simulation, and the sensitivity of the isolation system to several design
parameters is analyzed. These simulations confirm the existence of the localized NNM, and show that the introduction of simple
clearance nonlinearity significantly reduces the seismic energy transmitted to the main structure, resulting in significant
attenuation in the response.
This work was supported in part by the National Science Foundation Grant CMS 00-00060. The authors are grateful for this support. 相似文献
Based on a theoretical foundation for empirical mode decomposition, which dictates the correspondence between the analytical
and empirical slow-flow analyses, we develop a time-domain nonlinear system identification (NSI) technique. This NSI method
is based on multiscale dynamic partitions and direct analysis of measured time series, and makes no presumptions regarding
the type and strength of the system nonlinearity. Hence, the method is expected to be applicable to broad classes of applications
involving time-variant/time-invariant, linear/nonlinear, and smooth/non-smooth dynamical systems. The method leads to nonparametric
reduced order models of simple form; i.e., in the form of coupled or uncoupled oscillators with time-varying or time-invariant coefficients forced by nonhomogeneous
terms representing nonlinear modal interactions. Key to our method is a slow/fast partition of transient dynamics which leads
to the identification of the basic fast frequencies of the dynamics, and the subsequent development of slow-flow models governing
the essential dynamics of the system. We provide examples of application of the NSI method by analyzing strongly nonlinear
modal interactions in two dynamical systems with essentially nonlinear attachments. 相似文献
We propose a model of our universe as a 3-sphere resting on the surface of a black hole which exists in a spacetime consisting
of four space dimensions and one time dimension. The matter and energy within our universe exist as stationary solutions to
the field equations in the Rindler coordinates just above the horizon of the black hole. Each solution may be though of as
a standing wave consisting of a wave propagating toward the horizon superposed with its time-reversed twin propagating away
from the horizon. As matter and energy from the greater five-dimensional spacetime fall into the black hole, its radius increases
and our universe expands. This mechanism of expansion allows the model to describe a universe which is older than its oldest
stars and homogeneous without inflation. It also predicts galaxy counts at high redshift which agree with observation. 相似文献
Thiophene was polymerized in high yield on exposure to aluminum chloride in solvent under mild conditions. Experimental evidence [IR, NMR, UV, and mass spectra, elemental analyses, reductive desulfurization, and comparison with the literature trimer of thiophene (prepared with phosphoric acid)] suggests the following structure: From gel permeation chromatography an average weight of 1290 was obtained, which corresponded to the presence of 15 rings; the highest-molecular-weight chains contained about 192 rings. Mechanistically, participation of cationic intermediates is proposed. Apparently chain extension can occur by various routes, including participation of neutral oligomer molecules. 相似文献
A FNAL E799 Collaboration has carried out a search for the lepton-family number violating decay π0 → μ±e using π0's produced from KL → π0π0π0 decays in flight. No events were observed. Assuming that lepton-family number violation is charge independent, the 90% confidence level upper limit on
We deposit Pt particles electrochemically on an electrode covered with a Nafion membrane. Platinum ions travel through the hydrophilic channels of the membrane, and platinum deposits are formed at the place where the channels make contact with the planar electrode. This procedure deposits the catalyst only at the end of the hydrophilic channels that cross the membrane; no catalyst is placed under the hydrophobic domains, where it would not be in contact with the electrolyte. By performing a series of cyclic voltammograms with this system, we show that deposition of the platinum through the membrane achieves better platinum utilization than deposition of platinum on the naked electrode followed by the placement of the membrane on top. 相似文献