[Ren, Wei-Xin] Cent S Univ, Dept Civil Engn, Changsha 410075, Hunan, Peoples R China.;Natl Engn Lab High Speed Railway Construct, Changsha 410075, Hunan, Peoples R China.
[Ren, Wei-Xin] Cent S Univ, Dept Civil Engn, Changsha 410075, Hunan, Peoples R China.
Response surface;Finite element;Model updating;Optimization;Design of experiment;Regression analysis
Fast-running response surface models that approximate multivariate input/output relationships of time-consuming physical-based computer models enable effective finite element (FE) model updating analyses. In this paper, a response surface-based FE model updating procedure for civil engineering structures in structural dynamics is presented. The key issues to implement such a model updating are discussed such as sampling with design of experiments, selecting the significant updating parameters and constructing a quadratic polynomial response surface. The objective function is formed by the residuals between analytical and measured natural frequencies. Single-objective optimization with equal weights of natural frequency residual of each mode is used for optimization computation. The proposed procedure is illustrated by a simulated simply supported beam and a full-size precast continuous box girder bridge tested under operational vibration conditions. The results have been compared with those obtained from the traditional sensitivity-based FE model updating method. The real application to a full-size bridge has demonstrated that the FE model updating process is efficient and converges fast with the response surface to replace the original FE model. With the response surface at hand, an optimization problem is formulated explicitly. Hence, no FE calculation is required in each optimization iteration. The response surface-based FE model updating can be easily implemented in practice with available commercial FE analysis packages. (C) 2010 Elsevier Ltd. All rights reserved.
Journal of Fluid Mechanics,2009年638:453-490 ISSN：0022-1120
[Zhou, Y.; Wang, H. F.] Hong Kong Polytech Univ, Dept Mech Engn, Kowloon, Hong Kong, Peoples R China.;[Wang, H. F.] Huazhong Univ Sci & Technol, State Key Lab Coal Combust, Wuhan 430074, Peoples R China.;[Wang, H. F.] Cent S Univ, Sch Engn & Architecture, Changsha, Hunan, Peoples R China.
[Zhou, Y.] Hong Kong Polytech Univ, Dept Mech Engn, Kowloon, Hong Kong, Peoples R China.
Shear waves propagating along the imperfectly bonded interface of a magnetoelectric composite consisting of Piezoelectric (PE) and Piezomagnetic (PM) phases are considered. An exact dispersion relation is obtained. It is found that the interfacial imperfection strongly affects the velocity of interfacial shear waves. The existence condition of the interfacial shear waves is derived. In particular, for certain combined magnetoelectric composites, interfacial shear waves do no exist for perfect interface and exist only for imperfect interface. Moreover, the corresponding waves are dispersive, and the range of the phase velocity is derived, lying between the smaller of the Bleustein-Gulyaev waves of two PE and PM materials and the interfacial waves for the perfect bonding. These findings are useful for PE/PM composites in the microwave technology.
The objective of this study is to evaluate the rheological properties and chemical bonding of nano-modified asphalt binders blended with nanosilica. In this study, the nanosilica was added to the control asphalt at contents of 4% and 6% based on the weight of asphalt binders. Superpave binder and mixture tests were utilized in this study to estimate the characteristics of the nano-modifed asphalt binder and mixture. The rotational viscosity (RV), dynamic shear rheometer (DSR), bending beam rhometer (BBR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), asphalt pavement analyzer (APA), dynamic modulus (DM) and flow number (FN) tests were used to analyze rheological properties and chemical bonding changes of the nano-modified asphalt binder and the performance of the nano-modified asphalt mixture. In addition, the performance of nano-modified asphalt after rolling thin-film oven (RTFO) short-term and pressure-aging vessel (PAV) long-term aging was assessed as well. The dissipated work per load cycle for the asphalt binder was used to evaluate the rheological properties of the nano-modified asphalt binder. Based on the binder test results, it was found that the additional nanosilica in the control asphalt binder slightly decreased the viscosity of the control asphalt binder, maintained low dissipated work per load cycle, held a similar low-temperature performance to the control asphalt, and had a positive effect on antioxidation. From the mixture test results, the dynamic modulus and flow number of nano-modified asphalt mixtures improved, and the rutting susceptibility of nano-modified asphalt mixtures was reduced compared to the control asphalt mixture. In general, the findings from this study show that the antiaging property and rutting and fatigue cracking performance of nanosilica modified asphalt binders are enhanced, and the addition of nanosilica in the control asphalt mixture significantly improves the dynamic modulus, flow number, and rutting resistance of asphalt mixtures.
This work aims to improve the rutting and fatigue cracking resistance of asphalt binders using selected nano- or micro-sized materials and to shed light on the microstructure changes induced by such modification to asphalt binders. The four modifiers (Nanomer I.44P, carbon microfiber, non-modified nanoclay and polymer modified nanoclay) were added into the control asphalt binder (PG 58-34). The Superpave (TM) tests and Fourier transform infrared spectroscopy (FTIR) measurements were conducted for obtaining the complex shear modulus G(+) and microstructure distribution of modified asphalt binders. Meanwhile, the short-term and long-term aging processes of asphalt binders are simulated by rolling thin film oven (RTFO) and pressure aging vessel (PAV) tests. From the dynamic shear rheometer (DSR) and FTIR tests results, the complex shear modulus G(+) values of nano- or micro-materials (Nanomer I.44P, non-modified nanoclay and carbon microfiber) modified asphalt binders increase, and the performance of resistance to rutting is improved compared to the control asphalt binder. The addition of polymer modified nanoclay (PMN) into the control asphalt binder decreases the complex shear modulus, and enhances the resistance to fatigue cracking. Moreover, the addition of four modifiers into the control asphalt binder can delay and weaken the aging and oxidation effect. (C) 2012 Elsevier Ltd. All rights reserved.
Collapse shape of shallow circular tunnel is derived using a new curved failure mechanism within the framework of upper bound theorem. Nonlinear Hoek-Brown failure criterion is adopted in the present analysis. With the consideration of supporting pressure, the energy dissipations of the new failure mechanism are calculated by employing integral technique. Equating the rate of energy dissipation to the external rate of work, the objective function is formulated, and is optimized with the variational approach. Numerical results are presented, and collapse mechanisms of shallow tunnel taking into account supporting pressure are obtained. The present results are compared with the previous solutions, and the agreement shows that the present method is valid. The effects of different parameters on the failure mechanisms are discussed, and a critical depth expression is proposed for classifying shallow and deep tunnels. (C) 2011 Elsevier Ltd. All rights reserved.
In this paper, a novel method is proposed for the first time to obtain static pull-in voltages with fringing field effects in electrostatically actuated cantilever and clamped-clamped micro-beams where the mid-plane stretching and the residual axial load are taken into account for clamped-clamped boundary conditions. The non-classical Euler–Bernoulli beam model containing one material length scale parameter is adopted to effectively capture the size effect. In the solution procedure, the governing fourth-order differential equation of variable coefficients is converted into a Fredholm integral equation. By adopting the first natural mode of the cantilever and clamped-clamped micro-beams as a deflection shape function, the resulting equation is solved for the static pull-in voltages. The accuracy of the present analytical closed-form solution is verified through comparing with the experimentally measured and numerical data conducted in the published works. From the experimental data available in the literature, the value of the material length scale parameter for the (poly)silicon is estimated to be in the order of magnitude of 10−1 μm. Then, the effect of the material length scale parameter on the pull-in voltages of the cantilever and clamped-clamped micro-beams is investigated. The results indicate that the tensile residual stress can extend the validity range of the classical continuum mechanics to lower beam thicknesses. It is also found that microcantilever beams are more sensitive to the size effect than their corresponding clamped-clamped micro-beams.
This paper investigates the buoyancy-driven smoke flow layering length (both upstream and downstream) beneath the ceiling with combination of point extraction and longitudinal ventilation in tunnel fires. A theoretical model is developed based on previous back-laying model with only longitudinal ventilation, with modified actual heat release rate, as well as modified upstream and downstream opposing longitudinal air flow velocities by the induced flow velocity due to point extraction. Experiments are carried out in a reduced scale model tunnel with dimensionless of 72 m x 1.5 m x 1.3 m. A LPG porous gas burner is used as fire source. The smoke flow layering length both upstream and downstream are identified based on temperature profiles measured along the ceiling, for different experiment conditions. CFD simulations with FDS are also performed for the same scenarios. Results show that with combination of point extraction and longitudinal ventilation, the smoke flow layering length is not symmetric where it is longer downstream than that upstream. The upstream smoke layering length decreases, while the downstream layering length increases with increase in longitudinal ventilation velocity; and they both decrease with increase in point extraction velocity. The predictions by the proposed theoretical model agree well with the measurements and simulation results. (c) 2013 Elsevier Ltd. All rights reserved.