In this paper, a novel damage detection approach for the spring connection of the double beam system using the dynamic response of the beam and genetic algorithm is presented. The double beam system is regarded as both Bernoulli-Euler beams with simply supported ends, the upper and lower beams are connected by a series of linear springs with certain intervals. With the genetic algorithm, the dynamic acceleration response of double beam system under moving load, which can be solved by the Newmark-β integration procedure, is used as the input data to detect the connection damage. Thus the dynamic response of the double beam system with a certain damage pattern can be calculated employing the moving load model. If the calculated result is quite close to the recorded response of the damaged bridge, this damage pattern will be the solution. The connection damage detection process of the proposed approach is presented herein, and its feasibility is studied from the numerical investigation with simple and multiple damages detection. It is concluded that the sophisticated damage conditions need much longer time to detect successfully.
The paper deals wirh rhe problem of reconsrrucrion of nonlineariries in a certain class of nonlinear dynamical sysrems of rhe mulri-channel form. Each channel of rhe system has a nonlinearity being in series connection wirh a linear rime-invariant system. Such model is ofen referred fo as rhe Hammerstein sysrem. The a priori information abour the sysfem nonlinearities is very limired excluding any parametric approach fo the problem. The mode m statistical theory of nonparamerric regression along wirh the marginal inregmrion approach are applied ro fomz estimates of rhe nonlineariries. In particular the kernel regression techniques are used ro consrmcr rhe identificarion olgorifhms. The proposed esrimares are able to decouple the esrimarion problem relared ro each channel. This is a surprising result since rhe input signals are dependenr wirh complerely unknown joinr probability densiry function. Pointwise convergence properties of rhe proposed esrimarion procedures are esrablished and convergence rares are evaluated. Compurer simulations are included ro verib rhe rheory.
When people stay in the vibrating environment for a long time, the body may produce a series of physiological and psychological diseases. In order to evaluate the impact of vibration on the human body, the establishment of evaluation method or evaluation system is necessary. At present, most countries usually evaluate whole-body vibration based on the international standard ISO 2631-1 "Mechanical vibration and shock-Evaluation of human exposure to whole-body vibration-Part 1: General requirements". In this paper, the experiments of perception threshold of whole-body vibration were taken as the breakthrough point of evaluation method, and 12 subjects participated in the experiments. Through the experiments, comparing the provisions of ISO 2631-1, we get some different conclusions about the distribution law of perception thresholds. This also provides some data support for further experimental research.
A simplified approach is proposed to reduce computational cost in conventional parametric optimization of open or in-filled trenches isolating rail-induced structural vibrations. In particular, it stands on an FEM-based hybrid optimization scheme consisting of multiple two-dimensional models and one global three-dimensional model. First, representative planar FE (finite element) models orthogonal to the rail-direction are identified. For each section, the sensitivity of the trench's design parameters, such as geometry and backfill materials, to its vibration screening effect is respectively evaluated. Second, a full trench along the rail-direction is determined according to the two-dimensional optimization result. The global performance of the optimal trench is simulated in the three-dimensional model and finally becomes a reference for practical design. By optimizing the design parameters of a case study project, the proposed approach has shown the capability of solving complex engineering problems at a minimum computational cost, therefore is applicable in determining design parameters of rail-induced vibration isolation trenches.
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