Mechanism on suppression in vortex-induced vibration of bridge deck with long projecting slab with countermeasures

Zhou, Zhiyong,Yang, Ting,Ding, Quanshun,Ge, Yaojun Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.5

The wind tunnel test of large-scale sectional model and computational fluid dynamics (CFD) are employed for the purpose of studying the aerodynamic appendices and mechanism on suppression for the vortex-induced vibration (VIV). This paper takes the HongKong-Zhuhai-Macao Bridge as an example to conduct the wind tunnel test of large-scale sectional model. The results of wind tunnel test show that it is the crash barrier that induces the vertical VIV. CFD numerical simulation results show that the distance between the curb and crash barrier is not long enough to accelerate the flow velocity between them, resulting in an approximate stagnation region forming behind those two, where the continuous vortex-shedding occurs, giving rise to the vertical VIV in the end. According to the above, 3 types of wind fairing (trapezoidal, airfoil and smaller airfoil) are proposed to accelerate the flow velocity between the crash barrier and curb in order to avoid the continuous vortex-shedding. Both of the CFD numerical simulation and the velocity field measurement show that the flow velocity of all the measuring points in case of the section with airfoil wind fairing, can be increased greatly compared to the results of original section, and the energy is reduced considerably at the natural frequency, indicating that the wind fairing do accelerate the flow velocity behind the crash barrier. Wind tunnel tests in case of the sections with three different countermeasures mentioned above are conducted and the results compared with the original section show that all the three different countermeasures can be used to control VIV to varying degrees.

Quantile inference for moderate deviations from a unit root model with infinite variance

Zhiyong Zhou,Zheng-Yan Lin 한국통계학회 2015 Journal of the Korean Statistical Society Vol.44 No.2

The limit distribution of the quantile estimate for the moderate deviations from a unit root model with possibly infinite variance errors is derived. Both the mildly integrated case and the mildly explosive case are investigated. Quicker convergence rates than the ordinary least squares estimation are gained. Numerical simulations are conducted to illustrate the performance of our estimation procedure.

Numerical studies on non-shear and shear flows past a 5:1 rectangular cylinder

Zhou, Qiang,Cao, Shuyang,Zhou, Zhiyong Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.17 No.4

Large Eddy Simulations (LES) were carried out to investigate the aerodynamic characteristics of a rectangular cylinder with side ratio B/D=5 at Reynolds number Re=22,000 (based on cylinder thickness). Particular attention was devoted to the effects of velocity shear in the oncoming flow. Time-averaged and unsteady flow patterns around the cylinder were studied to enhance understanding of the effects of velocity shear. The simulation results showed that the Strouhal number has no significant variation with oncoming velocity shear, while the peak fluctuation frequency of the drag coefficient becomes identical to that of the lift coefficient with increase in velocity shear. The intermittently-reattached flow that features the aerodynamics of the 5:1 rectangular cylinder in non-shear flow becomes more stably reattached on the high-velocity side, and more stably separated on the low-velocity side. Both the mean and fluctuating drag coefficients increase slightly with increase in velocity shear. The mean and fluctuating lift and moment coefficients increase almost linearly with velocity shear. Lift force acts from the high-velocity side to the low-velocity side, which is similar to that of a circular cylinder but opposite to that of a square cylinder under the same oncoming shear flow.

Experimental and numerical study on generation and mitigation of vortex-induced vibration of open-cross-section composite beam

Zhou, Zhiyong,Zhan, Qingliang,Ge, Yaojun Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.23 No.1

Open-cross-section composite beam (OCB) tends to suffer vortex-induced vibration (VIV) due to its bluff aerodynamic shape. A cable-stayed bridge equipped with typical OCB is taken as an example in this paper to conduct sectional model wind tunnel test. Vortex-induced vibration is observed and maximum vibration amplitudes are obtained. CFD approach is employed to calculate the flow field around original cross sections in service stage and construction stage, as well as sections added with three different countermeasures: splitters, slabs and wind fairings. Results show that flow separate on the upstream edge and cause vortex shedding on original section. Splitters can only smooth the flow field on the upper surface, while slabs cannot smooth flow field on the upper or lower surface too much. Thus, splitters or slabs cannot serve as valid aerodynamic means. Wind tunnel test results show that VIV can only be mitigated when wind fairings are mounted, by which the flow field above and below the bridge deck are accelerated simultaneously.

Mechanism on suppression in vortex-induced vibration of bridge deck with long projecting slab with countermeasures

Zhiyong Zhou,Ting Yang,Quanshun Ding,Yaojun Ge 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.5

The wind tunnel test of large-scale sectional model and computational fluid dynamics (CFD) are employed for the purpose of studying the aerodynamic appendices and mechanism on suppression for the vortex-induced vibration (VIV). This paper takes the HongKong-Zhuhai-Macao Bridge as an example to conduct the wind tunnel test of large-scale sectional model. The results of wind tunnel test show that it is the crash barrier that induces the vertical VIV. CFD numerical simulation results show that the distance between the curb and crash barrier is not long enough to accelerate the flow velocity between them, resulting in an approximate stagnation region forming behind those two, where the continuous vortex-shedding occurs, giving rise to the vertical VIV in the end. According to the above, 3 types of wind fairing (trapezoidal, airfoil and smaller airfoil) are proposed to accelerate the flow velocity between the crash barrier and curb in order to avoid the continuous vortex-shedding. Both of the CFD numerical simulation and the velocity field measurement show that the flow velocity of all the measuring points in case of the section with airfoil wind fairing, can be increased greatly compared to the results of original section, and the energy is reduced considerably at the natural frequency, indicating that the wind fairing do accelerate the flow velocity behind the crash barrier. Wind tunnel tests in case of the sections with three different countermeasures mentioned above are conducted and the results compared with the original section show that all the three different countermeasures can be used to control VIV to varying degrees.

Numerical simulation study of the Reynolds number effect on two bridge decks based on the deterministic vortex method

Zhou, Zhiyong,Ma, Rujin Techno-Press 2010 Wind and Structures, An International Journal (WAS Vol.13 No.4

Researches on the Reynolds number effect on bridge decks have made slow progress due to the complicated nature of the subject. Heretofore, few studies on this topic have been made. In this paper, aerostatic coefficients, Strouhal number ($S_t$), pressure distribution and Reynolds number ($R_e$) of Great Belt East Bridge and Sutong Bridge were investigated based on deterministic vortex method (DVM). In this method, Particle Strength Exchange (PSE) was chosen to implement the simulation of the flow around bluff body and to analyze the micro-mechanism of the aerostatic loading and Reynolds number effect. Compared with the results obtained from wind tunnel tests, reliability of numerical simulation can be proved. Numerical results also showed that the Reynolds number effect on aerostatic coefficients and Strouhal number of the two bridges can not be neglected. In the range of the Reynolds number from $10^5$ to $10^6$, it has great effect on the Strouhal number of Sutong Bridge, while the St is difficult to obtain from wind tunnel tests in this range.

Numerical simulation study of the Reynolds number effect on two bridge decks based on the deterministic vortex method

Zhiyong Zhou,Rujin Ma 한국풍공학회 2010 Wind and Structures, An International Journal (WAS Vol.13 No.4

Researches on the Reynolds number effect on bridge decks have made slow progress due to the complicated nature of the subject. Heretofore, few studies on this topic have been made. In this paper, aerostatic coefficients, Strouhal number (St), pressure distribution and Reynolds number (Re) of Great Belt East Bridge and Sutong Bridge were investigated based on deterministic vortex method (DVM). In this method, Particle Strength Exchange (PSE) was chosen to implement the simulation of the flow around bluff body and to analyze the micro-mechanism of the aerostatic loading and Reynolds number effect. Compared with the results obtained from wind tunnel tests, reliability of numerical simulation can be proved. Numerical results also showed that the Reynolds number effect on aerostatic coefficients and Strouhal number of the two bridges can not be neglected. In the range of the Reynolds number from 105 to 106, it has great effect on the Strouhal number of Sutong Bridge, while the St is difficult to obtain from wind tunnel tests in this range.

Numerical studies on non-shear and shear flows past a 5:1 rectangular cylinder

Qiang Zhou,Shuyang Cao,Zhiyong Zhou 한국풍공학회 2013 한국풍공학회지 Vol.17 No.4

Large Eddy Simulations (LES) were carried out to investigate the aerodynamic characteristics of a rectangular cylinder with side ratio B/D=5 at Reynolds number Re=22,000 (based on cylinder thickness). Particular attention was devoted to the effects of velocity shear in the oncoming flow. Time-averaged and unsteady flow patterns around the cylinder were studied to enhance understanding of the effects of velocity shear. The simulation results showed that the Strouhal number has no significant variation with oncoming velocity shear, while the peak fluctuation frequency of the drag coefficient becomes identical to that of the lift coefficient with increase in velocity shear. The intermittently-reattached flow that features the aerodynamics of the 5:1 rectangular cylinder in non-shear flow becomes more stably reattached on the high-velocity side, and more stably separated on the low-velocity side. Both the mean and fluctuating drag coefficients increase slightly with increase in velocity shear. The mean and fluctuating lift and moment coefficients increase almost linearly with velocity shear. Lift force acts from the high-velocity side to the low-velocity side, which is similar to that of a circular cylinder but opposite to that of a square cylinder under the same oncoming shear flow.

Study on Deformation of Closed-Cell Aluminum Foam in Different Solid–Liquid–Gas Coexisting State

Zhiyong Liu,Ying Cheng,Yanxiang Li,Ningzhen Wang,Xu Zhou 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.3

The deformation of closed-cell aluminum foam (CAF) in different solid–liquid–gas coexisting state was studied in thispaper. The results showed that the most suitable temperature of the CAF deformation was about 635 °C, which made theCAF have maximum deformation, but its characteristic parameters changed slightly. Moreover, the multi-grain cell wall andsmall size cell were helpful to the CAF deformation in the solid–liquid–gas coexisting state. When the CAF deformed at635 °C, the inter-granular solidification microstructure and part of the primary α-Al grain were melted into liquid. The fixedor inter-locked primary α-Al grain was released and changed into the distributed discretely near-spherical grain, making thecell wall have good thixotropy. At the same time, the gas pressure in the cell was recovered to the foaming stage, so the gaspressure could be close to the flow stress of cell wall. During the CAF deformation in the solid–liquid–gas coexisting state,the cell wall deformed in thixotropic under the supporting and coordinating of the gas pressure in the cell, meanwhile, thecell was moved following the cell wall deformation. Therefore, the CAF deformation was affected by the types of the cellwalls and the cell size.

Study on Dynamic Guidance Obstacle Avoidance for UAV

Xiong Zhiyong,Yang Xiuxia,Zhang Yi,Hua Wei,Zhou Weiei 보안공학연구지원센터 2016 International Journal of Future Generation Communi Vol.9 No.8

With the flight environment becoming more and more complex, how to avoid the moving threat for the UAV under the dynamic environment and complete the mission become a key problem. With the idea of guidance, using the method of dimension reduction, the dynamic guidance obstacle avoidance method in three dimensional spaces is given. Considering the collision avoidance completion time and the UAV’s maneuverability, the parameters range of obstacle avoidance navigation law are deduced. Simulation results show the validity of the algorithm.