Qiusheng Li

Bio: Qiusheng Li is an academic researcher from City University of Hong Kong. The author has contributed to research in topics: Wind speed & Wind tunnel. The author has an hindex of 47, co-authored 429 publications receiving 8830 citations. Previous affiliations of Qiusheng Li include Chinese Ministry of Education & Guangzhou University.

Analytical Evaluation of Dynamic Responses of Time-varying Systems:

Abstract: An analytical approach for forced vibration of single-degree-of-freedom (SDOF) systems with arbitrary time-dependent parameters is presented. Unlike most of the previous studies on this topic, the function for describing the variation of mass of a SDOF system with time is an arbitrary continuous or piecewise real-valued function, and the variation of stiffness with time is expressed as a functional relation with the variation of mass and vice versa. Using appropriate functional transformation, the closed-form homogeneous solutions of the governing differential equations for forced vibrations of such a SDOF system with continuous time variable parameters (mass and stiffness) are derived for 10 important cases. The particular solutions of the non-homogeneous differential equations are determined based on the Lagrange method. Furthermore, the proposed exact method and solutions are developed to analyze the forced vibration of SDOF systems with multi-step (piecewise) non-periodical variable parameters. A nume...

Free longitudinal vibrations of tall buildings and high-rise structures

Abstract: In this paper, tall buildings and high-rise structures are considered as cantilever bars with variable cross-section for the analysis of their free vibrations. The differential equations of free longitudinal vibrations of bars with variable cross-section are reduced to Bessel's equations by selecting suitable expressions, such as power functions and exponential functions, for the distribution of stiffness and mass. An approach is proposed for determining the natural frequencies and mode shapes in the vertical direction for tall buildings and high-rise structures with variably distributed stiffness and variably distributed mass. The derived solutions are expressed in terms of Bessel functions. A numerical example shows that the value of the natural frequency computed by the proposed method is close to full scale measured data. It is shown that the selected expressions are suitable for describing the distributions of stiffness and mass of tall buildings and high-rise structures. It is demonstrated that the proposed method has practical significance for free longitudinal vibration analysis. © 1998 John Wiley & Sons, Ltd.

Dynamic Wind Load Combination for a Tall Building Based on Copula Functions

Abstract: Dynamic wind loads on tall buildings can be decomposed into three components, i.e. two translational components and one torsional component. When one component reaches its maximum, the other two components have low probability to take their maximum values. It is common to use combination coefficients for estimating the mean extremes of linearly combined wind loads. The traditional design practice for determining wind load combinations relies partly on some approximate combination rules and lacks a systematic and reliable method. Based on the high frequency force balance (HFFB) testing results, wind loads can be acquired in terms of time history data, which provides necessary information for the more rigorous determination of combination coefficients by probabilistic methods. In this paper, a 3D copula-based approach is proposed for determining the combination coefficients for three stochastic wind loads associated with a specific exceedance probability and a set of 3D realizable equivalent static wind loads (ESWLs) on tall buildings. Using the measured base moment and torque data by the HFFB wind tunnel test, a case study is presented to illustrate the effectiveness of the proposed framework to determine the dynamic wind load combinations and associated 3D realizable ESWLs on a full-scale 60-story building.

Switchable terahertz broadband absorption and linear-to-circular polarization conversion

Abstract: We proposed a switchable bifunctional metasurface for broadband absorber and linear-to-circular polarization converter (LTCPC) in terahertz regime. When vanadium dioxide (VO2) is in the metallic state, the designed metasurface acts as a broadband terahertz absorber. The results demonstrate that the absorptance is above 90% and the bandwidth ratio is 68.6% from 0.981 to 2.011 THz. When VO2 is in the insulated state, the proposed structure behaves as an LTCPC with ellipticities 1 and −1 in frequency bands of 0.391∼0.517 and 0.673∼2.363 THz, respectively. The axis ratio is lower than 3 dB. The designed metasurface provides a new method for designing multifunctional terahertz devices.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Nonlinear Time Series Analysis.

Abstract: : This thesis applies neural network feature selection techniques to multivariate time series data to improve prediction of a target time series. Two approaches to feature selection are used. First, a subset enumeration method is used to determine which financial indicators are most useful for aiding in prediction of the S&P 500 futures daily price. The candidate indicators evaluated include RSI, Stochastics and several moving averages. Results indicate that the Stochastics and RSI indicators result in better prediction results than the moving averages. The second approach to feature selection is calculation of individual saliency metrics. A new decision boundary-based individual saliency metric, and a classifier independent saliency metric are developed and tested. Ruck's saliency metric, the decision boundary based saliency metric, and the classifier independent saliency metric are compared for a data set consisting of the RSI and Stochastics indicators as well as delayed closing price values. The decision based metric and the Ruck metric results are similar, but the classifier independent metric agrees with neither of the other metrics. The nine most salient features, determined by the decision boundary based metric, are used to train a neural network and the results are presented and compared to other published results. (AN)