Wind characteristics at Sutong Bridge site using 8-year field measurement data

Xu, Zidong,Wang, Hao,Wu, Teng,Tao, Tianyou,Mao, Jianxiao Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.25 No.2

Full-scale wind characteristics based on the field measurements is an essential element in structural wind engineering. Statistical analysis of the wind characteristics at Sutong Cable-stayed Bridge (SCB) site is conducted in this study with the recorded long-term wind data from structural health monitoring system (SHMS) between 2008 and 2015. Both the mean and turbulent wind characteristics and power spectra are comprehensively investigated and compared with those in the current codes of practice, such as the measured wind rose diagram, monthly maximum mean wind speed, turbulence intensity, integral length scale. Measurement results based on the monitoring data show that winds surrounding the SCB site are substantially influenced by the southeast monsoon in summer and strong northern wind in winter. The measured turbulence intensity is slightly higher than the recommended values in specifications, while the measured ratio of lateral to longitudinal turbulence intensity is slightly lower. An approximately linear relationship between the measured turbulence intensities and gust factors is obtained. The mean value of the turbulence integral length scale is smaller than that of typical typhoon events. In addition, it is found that the Kaimal spectrum is suitable to be adopted as the power spectrum for longitudinal wind component at the SCB site. This contribution would provide important wind characteristic references for the wind performance evaluation of SCB and other civil infrastructures in adjacent regions.

High-Precision Position Tracking Control of Giant Magnetostrictive Actuators Using Fractional-Order Sliding Mode Control with Inverse Prandtl-Ishlinskii Compensator

Zidong Liu,Weike Liu,Pan Wang,Zhi Li,Yunlang Xu,Xiaofeng Yang,Feng Shu 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.3

Giant magnetostrictive actuators (GMAs) are increasingly being applied in ultra-precision motion platforms due to its high energy density, fast response and high displacement resolution. However, due to the inherent hysteresis nonlinearity of giant magnetostrictive materials, high-precision position tracking control of GMAs becomes very challenging. In this paper, a fractional-order sliding mode control (FSMC) strategy based on inverse Prandtl-Ishlinskii (PI) model (FSMC-PI) is proposed for GMAs. The inverse PI model is established to compensate for the hysteresis nonlinearity. Besides, based on the traditional sliding mode control (SMC), the proposed FSMC-PI introduces the fractional calculus term into the sliding surface, which ensures that the state converges to the fractional-order sliding manifold with fast response and small overshoot, and the position tracking performance of GMAs is enhanced. Moreover, as a feedback control method, FSMC can further effectively suppress the uncertainties and external disturbances that the inverse PI model cannot deal with. The stability of FSMC is analyzed and proved according to the Lyapunov Theorem. In addition, a double integrator is connected in series after the FSMC system, which can further improve the dynamic characteristics of the GMA system so as to guarantee the overall position tracking control performance. Finally, experiments are conducted on a GMA system with very low load, and the results demonstrate that the proposed approach can improve the position tracking performance and disturbance suppression capability more effectively, compared with four different control schemes.

Numerical Analysis on Buffeting Performance of a Long-Span Four-Tower Suspension Bridge Using the FEM Model

Hao Wang,Zidong Xu,Min Yang,Tianyou Tao,Jianxiao Mao,Hui Gao 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.3

The multi-tower suspension bridge (MTSB), which is a considerable choice for the cross-river and even cross-sea bridges, has attracted intensive attentions by researchers in recent years. However, the static and dynamic performance of the MTSB becomes more complicated due to its super long spans and the multiple middle towers. The wind-induced vibration becomes the critical issue when constructs the MTSBs due to their low rigidity. In this work, a finite element model (FEM) of a MTSB with four towers and three spans is presented. Several major parameters such as the stiffness of the main girder and the middle towers, the sag-to-span ratios, the self-excited forces, and the spectral model of turbulence are selected to investigate their effects on buffeting performance of the MTSB. Results show that the rigid main girder can decrease the buffeting displacements in lateral and torsional directions, while the vertical buffeting displacement significantly decreases with the increasing stiffness of middle towers. In addition, the buffeting displacements of the main girder increase with the decreasing sag-to-span ratio. Besides, it can be concluded that the self-excited forces should be considered and the turbulent power spectrum should be carefully chosen in analyzing buffeting responses of the MTSB.

Effects of Floating Gate Structures on the Two-Dimensional Electron Gas Density and Electron Mobility in AlGaN/AlN/GaN Heterostructure Field-Effect Transistors

Jingtao Zhao,Zhenguo Zhao,Zidong Chen,Zhaojun Lin,Fukai Xu 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.12

In this study, we have investigated the electrical properties of the AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with floating gate structures using the measured capacitancevoltage (C-V) and current-voltage (I-V) characteristics. It is found that the two-dimensional electron gas (2DEG) density under the central gate cannot be changed by the floating gate structures. However, the floating gate structures can cause the strain variation in the barrier layer, which lead to the non-uniform distribution of the polarization charges, then induce a polarization Coulomb field and scatter the 2DEG. More floating gate structures and closer distance between the floating gates and the central gate will result in stronger scattering effect of the 2DEG.

Performance of structures and infrastructure facilities during an EF4 Tornado in Yancheng

Tianyou Tao,Hao Wang,Chengyuan Yao,Zhongqin Zou,Zidong Xu 한국풍공학회 2018 Wind and Structures, An International Journal (WAS Vol.27 No.2

Heavy damages to properties with attendant losses were frequently caused by tornadoes in recent years. This natural hazard is one of the most destructive wind events that must be fully studied and well understood in order to keep the safety of structures and infrastructure facilities. On June 23, 2016, a severe tornado, which is an Enhanced Fujita (EF) 4 storm, occurred in the rim of a coastal city named as Yancheng in China. Numerous low-rise buildings as well as facilities (e.g., transmission towers) were destroyed or damaged. In this paper, damages to structures and infrastructure facilities by the severe tornado are reviewed. The collapses of residential buildings, industrial structures and other infrastructure facilities are described. With an overview of the damages, various possible mechanisms of the collapse are then discussed and utilized to reveal the initiation of the damage to various facilities. It is hoped that this paper can provide a concise but comprehensive reference for the researchers and engineers to help understand the tornado effects on structures and expose the vulnerabilities that need to be improved in current wind-resistant design practices.

Performance of structures and infrastructure facilities during an EF4 Tornado in Yancheng

Tao, Tianyou,Wang, Hao,Yao, Chengyuan,Zou, Zhongqin,Xu, Zidong Techno-Press 2018 Wind and Structures, An International Journal (WAS Vol.27 No.2

Heavy damages to properties with attendant losses were frequently caused by tornadoes in recent years. This natural hazard is one of the most destructive wind events that must be fully studied and well understood in order to keep the safety of structures and infrastructure facilities. On June 23, 2016, a severe tornado, which is an Enhanced Fujita (EF) 4 storm, occurred in the rim of a coastal city named as Yancheng in China. Numerous low-rise buildings as well as facilities (e.g., transmission towers) were destroyed or damaged. In this paper, damages to structures and infrastructure facilities by the severe tornado are reviewed. The collapses of residential buildings, industrial structures and other infrastructure facilities are described. With an overview of the damages, various possible mechanisms of the collapse are then discussed and utilized to reveal the initiation of the damage to various facilities. It is hoped that this paper can provide a concise but comprehensive reference for the researchers and engineers to help understand the tornado effects on structures and expose the vulnerabilities that need to be improved in current wind-resistant design practices.