Accurate stress analysis on rigid central buckle of long-span suspension bridges based on submodel method

Runyang Suspension Bridge (RSB) with the main span of 1490 m is the longest bridge in China and the third longest one in the world. In this bridge the rigid central buckle is employed for the first time in the mid-span of the suspension bridge in China. For such a super-long-span bridge, the traditional finite element (FE) modeling technique and stress analysis methods obviously cannot satisfy the needs of conducting accurate stress analysis on the central buckle. In this paper, the submodel method is introduced and for the first time used in analyzing the stresses of the central buckle. After an accurate FE submodel of the central buckle was specially established according to the analysis results from the whole FE model, the connection technique between the two-scale FE models was realized and the accurate stresses of the central buckle under various vehicle load cases were then conducted based on the submodel method. The calculation results were testified to be accurate and reliable by the field measurements, which show the efficiency and reliability of the submodel method on analyzing the mechanical condition of the central buckle of long-span suspension bridges. Finally, the working behavior and mechanical characteristics of the central buckle of the RSB under vehicle loads were analyzed based on the calculation and measurement results. The results obtained in this paper can provide theoretic references for analyzing and designing the rigid central buckle in long-span suspension bridges in future. Supported by the National High Technology Research and Development Program (“863” Project) (Grant No. 2006AA04Z416), the Key Project of the National Natural Science Foundation of China (Grant No. 50538020), the National Natural Science Foundation of China for Young Scholars (Grant No. 50608017) and the Ph.D. Programs Foundation of Ministry of Education of China (Grant No. 200802861012)     

Environmental variability study on the measured responses of Runyang Cablestayed Bridge using wavelet packet analysis

The structural damage alarming method based on wavelet packet energy spectrum (WPES) for long-span cable-stayed bridges is presented through combination of ambient vibration test and wavelet packet analysis. The environmental variability in the measured WPES and damage alarming indices ERVD of the Runyang Cable-stayed Bridge are discussed in detail using the wavelet packet analysis of the measured acceleration responses of the bridge under daily environmental conditions. The analysis results reveal that the actual environmental conditions including traffic loadings, environmental temperature and typhoon loadings have remarkable correlations with the measured WPES. The changes of environmental temperature have a long-term trend influence on the WPES, while the influences of traffic and typhoon loadings on the measured WPES of the bridge present instantaneous changes because of the nonstationary properties of the loadings. The analysis results of the measured responses further reveal that the damage alarming indices ERVD can sensitively reflect the influences of environmental temperature and typhoon loadings on the dynamic properties of Runyang Cable-stayed Bridge. Therefore, the proposed structural damage alarming indices ERVD under ambient vibrations are suitable for real-time damage alarming for long-span cable-stayed bridges. Supported by the National Hi-Tech Research and Development Program of China (Grant No. 2006AA04Z416) and the National Natural Science Foundation of China (Grant No. 50538020)     

Risk assessment method of major unsafe hydroelectric project

Based on the characteristics of major unsafe hydroelectric projects and the data from field detection, in situ monitoring, and regular safety inspection, the fundamental principles of operation risk assessment are proposed in this paper. Meanwhile, a three layer hierarchical system is constructed, and an improved analytical hierarchical process combining genetic algorithm and analytical hierarchical process is established, with corresponding program. The operation risk of some unsafe dam was assessed with the principles, method and program presented in this paper and the major factors which would affect the operation of the dam were pointed out. Supported by Key Project of NNSF and Yalongjiang Hydroelectric Development Joint Research Fund (Grant No. 50539110), Science and Technology Support Plan (Grant No. 20006BAC14B03), National Natural Science Foundation Major Project (Grant Nos. 50539010, 50539030) and National Natural Science Foundation of China (Grant No. 50579010)     

Ultralight X-type lattice sandwich structure (II): Micromechanics modeling and finite element analysis

The methods of homogenization and finite elements are employed to predict the effective elastic constants and stress-strain responses of a new type of lattice structure, the X-structure proposed by the authors in a companion paper. It is shown that in most cases the predictions by the equivalent homogenization theory agree well with the experimental and 3-dimensional finite element calculated results. The theoretical and numerical study supports the argument that the X-structure is superior to the pyramid lattice structure in terms of mechanical strength. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10632060, 10825210), the National “111” Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519)     

Compensation for time-delayed feedback bang-bang control of quasi-integrable Hamiltonian systems

The stochastic averaging method for quasi-integrable Hamiltonian systems with time-delayed feedback bang-bang control is first introduced. Then, two time delay compensation methods, namely the method of changing control force amplitude (CFA) and the method of changing control delay time (CDT), are proposed. The conditions applicable to each compensation method are discussed. Finally, an example is worked out in detail to illustrate the application and effectiveness of the proposed methods and the two compensation methods in combination. Supported by the National Natural Science Foundation of China (Grant No. 10772159), the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20060335125), Zhejiang Natural Science Foundation (Grant No. Y7080070), and Fujian Provincial Science and Technology Project (Grant No. 2005YZ1021)     

Research on polyfluorene derivatives end-capped by N-hexyl-carbazole and benzene

Copolymers of 9,9-dioctylfluorene (DOF) and 2-thienyl-benzothiadiazole (DBT) were synthesized by Suzuki reaction and end-capped by N-hexyl-carbazole and benzene, which were abbreviated as PDOF-DBT-Cz and PDOF-DBT-B, respectively. The photophysical, electrochemical and thermal properties of the copolymers were studied. The results indicated that replacement of N-hexyl-carbazole as end-capping group of PDOF-DBT can vary light color and improve luminescence efficiency. Supported by the Major Project of Science Foundation Ministry of Education of China (Grant No. 207015) and the National Natural Science Foundation of China (Grant No. 20671068)     

A hybrid-stress solid-shell element for non-linear analysis of piezoelectric structures

This paper presents eight-node solid-shell elements for geometric non-linear analyze of piezoelectric structures. To subdue shear, trapezoidal and thickness locking, the assumed natural strain method and an ad hoc modified generalized laminate stiffness matrix are employed. With the generalized stresses arising from the modified generalized laminate stiffness matrix assumed to be independent from the ones obtained from the displacement, an extended Hellinger-Reissner functional can be derived. By choosing the assumed generalized stresses similar to the assumed stresses of a previous solid element, a hybrid-stress solid-shell element is formulated. The presented finite shell element is able to model arbitrary curved shell structures. Non-linear numerical examples demonstrate the ability of the proposed model to analyze nonlinear piezoelectric devices. Supported by the National Natural Science Foundation of China (Grant No. 10672111) and the Major Project of the Natural Science Foundation of Jiangsu Province (Grant No. BK2006725)     

Relaxor behavior and electrical properties of high dielectric constant materials

Several typical high dielectric constant materials are reviewed to study the electrical properties and relaxation mechanism. It is found that a Lorenz-type law can be used to describe the dielectric permittivity of either the normal ferroelectrics with or without diffuse phase transitions (DPT) or the typical ferroelectric relaxors. The ferroelectric DPT can be well described by just one fitting process using the Lorenz-type law, while the relaxor ferroelectric transition needs two independent fitting processes. The Lorenz-type law fails at the low temperature side of the dielectric maximum of a first-order ferroelectric phase transition. Above the transition temperature, the dielectric curves of all the studied materials can be well described by a Lorenz-type law. Supported by the National Natural Science Foundation of China (Grant No. 50672075), New Century Excellent Talents (Grant No. 05-087), Natural Science Foundation of Northwestern Polytechnical University (Grant No. 200703), Xi’an Science & Technology Foundation (Grant No. CXY08006) and 111 Project (Grant No. B08040)     

Dynamic substructure model for multiple impact responses of micro/nano piezoelectric precision drive system

A dynamic substructure technique which considers the electromechanical coupling effect of the PZT and the inertial effect of flexible components is presented to study the multiple impact dynamic be- havior of micro/nano piezoelectric impact drive systems. It can investigate the step-like motion of ob- ject body and the multiple impacts behaviors reasonably by the comparison of the experimental data and the numerical solution of the spring-mass model. It is expected to have higher accuracy in the numerical s...     

BRVAAF and performance analysis for target detection

A bistatic range-velocity-acceleration ambiguity function (BRVAAF) is proposed. The model of radar measurements of an accelerating target involving the time delay, Doppler frequency and Doppler rate is given. The relationships between these measurements and the parameters of the bistatic geometry, target position, velocity and acceleration are derived. Moreover, the effects of the bistatic geometry factors on these measurements are analyzed. Besides, the two relationships of the bistatic integration loss and the bistatic optimum integration time with these factors are built and their change trends are described respectively. This research is helpful to analyze the influences of the bistatic geometry factors on the target detection and signal processing. Supported by the National Natural Science Foundation of China (Grant No. 60232010), the National Natural Science Foundation of China for Distinguished Young Scholars (Grant No. 60625104) and the Advanced Research Project (Grant Nos. 51307060504, 9140A07040806BQ01)     

Preparation and properties of ZnO nano-whiskers

By a novel controlled combustion synthesis method, a large amount of ZnO nano-whiskers with different morphologies like nanotetrapods, long-leg nanotetrapod and multipods, were prepared without any catalysts and additives in open air at high temperature. Their morphologies, structures and optical properties were investigated by using SEM, XRD and PL spectrum. The possible growth mechanisms on the ZnO nano-whiskers were proposed in this paper. Supported by the National Natural Science Foundation of China (Grant Nos. 50572010, 50742007 and 10672020), National Defense Founds of China (Grant Nos. 51420205BQ0154 and A2220061080), “863” Project of China (Grant No. 2007AA03Z103), and the Scientific Research Foundation of Graduate School of BIT (Grant No. AA200802)     

Thermoelastic properties of sandwich materials with pin-reinforced foam cores

Pin-reinforced foam is a novel type of sandwich core materials formed by inserting pins (trusses) into a foam matrix to create a truss-like network reinforced foam core. Upon loading, the pins deform predominantly by local stretching whilst the deformation of foam is governed by local bending. This paper presents a theoretical study on the thermoelasticity of pin-reinforced foam sandwich cores. To calculate the effective thermoelastic properties of pin-reinforced foam cores, the energy-based homogenization approach is employed to develop a micromechanicsbased model, calibrated by the existing experimental data. It is found that the stiffness of the sandwich core is mainly governed by pin reinforcements: the foam matrix contributes little to sandwich stiffness. Compared with traditional foam cores without pin reinforcements, the changes in in-plane thermal expansion coefficients are not vigorous as a result of pin reinforcements, while the throughthickness thermal expansion coefficient changes significantly. It is also demonstrated that it is possible to design materials with zero or negative thermal expansion coefficients under such a context. Supported by the National Basic Research Program of China (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10572111, 10632060), the National 111 Project of China (Grant No. B06024), the National High Technology Research Development Program (Grant No. 2006AA03Z519), the NPU Foundation for Fundamental Research, the Open Foundation of State Key Laboratory of Structural Analysis of Industrial Equipment (Grant No. GZ0701), and the NPU Foundation for Scientific Innovation     

Real-time measurement of temperature field with ICCD as sensor (II)

The colorimetric method for real-time measurement of temperature field using ICCD as sensor was developed. In order to ensure the accuracy and sensitivity, the relationship between the ratio response of two-color images and radiant property of body, transmission property of filter, spectral response of ICCD is discussed. The analysis is based on computer calculation of the established mathematical model. On the basis of the analysis, optimum wavelengths are obtained for a given sensor system. Experimental work was carried out to check the correctness of the theoretical resutls. The method is useful for general purpose of study and design of the developed system. Project supported by the National Natural Science Foundation of China (Grant No. 59475064) and the Natural Science Foundation of Jiangxi Province.     

Ultralight X-type lattice sandwich structure (I): Concept,fabrication and experimental characterization

A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10632060,10825210), the National “111” Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519)     

A level set method for reliability-based topology optimization of compliant mechanisms

Based on the level set model and the reliability theory, a numerical approach of reliability-based topology optimization for compliant mechanisms with multiple inputs and outputs is presented. A multi-objective topology optimal model of compliant mechanisms considering uncertainties of the loads, material properties, and member geometries is developed. The reliability analysis and topology optimization are integrated in the optimal iterative process. The reliabilities of the compliant mechanisms are evaluated by using the first order reliability method. Meanwhile, the problem of structural topology optimization is solved by the level set method which is flexible in handling complex topological changes and concise in describing the boundary shape of the mechanism. Numerical examples show the importance of considering the stochastic nature of the compliant mechanisms in the topology optimization process. Supported by the National Natural Science Foundation of China (Grant No. 50775073), the Teaching and Research Award Program for Outstanding Young Teacher in Higher Education Institutions of the Ministry of Education of China, the Guangdong Hong Kong Technology Cooperation Funding (Dongguan Project 20061682), the Research Project of Ministry of Education and Guangdong Province (Grant No. 2006D90304001), and the Natural Science Foundation of Guangdong Province, China (Grant No. 05006494)     

A novel random phase-shifting digital holographic microscopy method

This paper proposes a new method that reconstructs the information of specimen by using random phase shift step in digital holographic microscopy (DHM). The principles of the method are described and discussed in detail. In practical experiment, because the phase shifter is neither perfectly linear nor calibrated, digital holograms with inaccurate phase shift step are recorded by the charge-coupled device (CCD). The phase could be accurately reconstructed from the recorded digital holograms by using the random phase-shifting algorithm, which makes up for reconstructed phase error caused by ordinary phase-shifting algorithm. The phase aberration compensation is also discussed. In order to verify the flexibility of the proposed method, numerical simulation of random phase-shifting DHM was carried out. The simulation results illustrated that the presented method is effective when the phase shift step is unknown or random in DHM. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2004CB619304), the National Natural Science Foundation of China (Grant Nos. 10625209, 10472050, 10732080), the Project of Beijing Natural Sciences Foundation (Grant No. 3072007), the Program for New Century Excellent Talents (NCET) in Chinese University Ministry of Education (Grant No. NCET-05-0059), and the Opening Funds from the State Key Laboratory of Explosion Science and Technology     

Application of time reversal mirror technique in microwave-induced thermo-acoustic tomography system

Microwave-induced thermo-acoustic tomography (MITAT) is a promising technique with great potential in biomedical imaging. It has both the high contrast of the microwave imaging and the high resolution of the ultrasound imaging. In this paper, the proportional relationship between the absorbed microwave energy distribution and the induced ultrasound source distribution is derived. Further, the time reversal mirror (TRM) technique based on the pseudo-spectral time domain (PSTD) method is applied to MITAT system. The simulation results show that high contrast and resolution can be achieved by the TRM technique based on PSTD method even for the received signals with very low signal-to-noise ratio (SNR) and the model parameter with random fluctuation. Supported by the National Natural Science Foundation of China (Grant No. 60771042), the National Hi-Tech Research and Development Program (“863” Project) (Grant No. 2007AA12Z159), 111 Project (Grant No. B07046), SiChuan Excellent Youth Foundation (Grant No. 08ZQ026-039), Program for New Century Excellent Talents in University of China and Program for Changjiang Scholars     

桥梁风工程2020年度研究进展

随着土耳其恰纳卡莱大桥、中国张皋过江通道以及西堠门公铁两用大桥等超大跨度桥梁的建造,桥梁风工程研究面临新的挑战。继2019年研究进展后,聚焦桥梁颤振、桥梁涡激振动和桥梁抖振等桥梁抗风设计关键问题,通过对风工程领域主流学术期刊论文的梳理,介绍和评述了2020年以来相关领域主要研究进展。     

Development of ecohydrological assessment tool and its application

The development of Hydro-Informatic Modelling System (HIMS) provides an integrated platform for hydrological simulation. To extend the application of HIMS, an ecohydrological modeling system named ecohydrological assessment tool (EcoHAT) has been developed. Integrating parameter-management tools, RS (remote sensing) inversion tools, module-design tools and GIS analysis tools, the EcoHAT provides an integrated tool to simulate ecohydrological processes on regional scale, which develops a new method on sustainable use of water. EcoHAT has been applied to several case studies, such as, the Yellow River Basin, the acid deposition area in Guizhou province and the riparian catchment of Guanting reservoir in Beijing. Results prove that EcoHAT can efficiently simulate and analysis the ecohydrological processes on regional scale and provide technical support to integrated water resources management on basin scale. Supported by the National Key Technology R&D Program in the 11th Five-year Plan of China (Grant No. 2006BAB06B07), the National Natural Science Foundation of China (Grant No. 40671123), the National Basic Research Program of China (“973” Project) (Grant Nos. 2005CB422207, G19990436), and the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA12Z145)     

Design and fabrication of erbium doped photosensitive fibers

A kind of erbium doped photosensitive fiber (EDPF) was proposed and fabricated, whose core was made of double layers named photosensitive layer and erbium doped layer. The double-layer core design can overcome difficulties in fabrication of EDPF with single core design, i.e. the conflict between the high consistency rare earth doping and high consistency germanium doping. A sample was fabricated through the modified chemical vapor deposition method combined with solution doping technique. The peak absorption coefficient was 48.80 dB/m at 1.53 μm, the background loss was lower than 0.1 dB/m, and the reflectivity of the fiber Brag gratings (FBG) written directly on the sample fiber was up to 97.3% by UV-writing technology. Moreover, a C band tunable fiber laser was fabricated using the sample fiber, in which a uniform FBG was written directly on EDPFs as a reflector. A single wavelength lasing with a maximum wavelength tuning range of 1555.2–1558.0 nm was achieved experimentally. Within this tuning range, the full-width at half maximum (FWHM) of the laser output was smaller than 0.015 nm and the side mode suppression ratio (SMSR) was better than 50 dB. Supported by the National High Technology Research and Development Program of China (863 Project) (Grant No. 2007AA01Z258), the National Natural Science Foundation of China (Grant No. 60771008), Program for New Century Excellent Talents in University (Grant No. NCET-06-0076), Beijing Natural Science Foundation (Grant No. 4052023), and the Beijing Jiaotong University Foundation (Grant No. 2006XM003)