The inertial coefficient for fluctuating flow through a dominant opening in a building

Xu, Haiwei,Yu, Shice,Lou, Wenjuan Techno-Press 2014 Wind and Structures, An International Journal (WAS Vol.18 No.1

For a building with a dominant windward wall opening, the wind-induced internal pressure response can be described by a second-order non-linear differential equation. However, there are two ill-defined parameters in the governing equation: the inertial coefficient $C_I$ and the loss coefficient $C_L$. Lack of knowledge of these two parameters restricts the practical use of the governing equation. This study was primarily focused on finding an accurate reference value for $C_I$, and the paper presents a systematic investigation of the factors influencing the inertial coefficient for a wind-tunnel model building including: opening configuration and location, wind speed and direction, approaching flow turbulence, the model material, and the installation method. A numerical model was used to simulate the volume deformation under internal pressure, and to predict the bulk modulus of an experimental model. In considering the structural flexibility, an alternative approach was proposed to ensure accurate internal volume distortions, so that similarity of internal pressure responses between model-scale and full-scale building was maintained. The research showed 0.8 to be a reasonable standard value for the inertial coefficient.

The loss coefficient for fluctuating flow through a dominant opening in a building

Xu, Haiwei,Yu, Shice,Lou, Wenjuan Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.24 No.1

Wind-induced fluctuating internal pressures in a building with a dominant opening can be described by a second-order non-linear differential equation. However, the accuracy and efficiency of the governing equation in predicting internal pressure fluctuations depend upon two ill-defined parameters: inertial coefficient $C_I$ and loss coefficient $C_L$, since $C_I$ determines the un-damped oscillation frequency of an air slug at the opening, while $C_L$ controls the decay ratio of the fluctuating internal pressure. This study particularly focused on the value of loss coefficient and its influence factors including: opening configuration and location, internal volumes, as well as wind speed and approaching flow turbulence. A simplified formula was presented to predict loss coefficient, therefore an approximate relationship between the standard deviation of internal and external pressures can be estimated using Vickery's approach. The study shows that the loss coefficient governs the peak response of the internal pressure spectrum which, in turn, will directly influence the standard deviation of the fluctuating internal pressure. The approaching flow characteristic and opening location have a remarkable effect on the parameter $C_L$.

The inertial coefficient for fluctuating flow through a dominant opening in a building

Haiwei Xu,Shice Yu,Wenjuan Lou 한국풍공학회 2014 한국풍공학회지 Vol.18 No.1

For a building with a dominant windward wall opening, the wind-induced internal pressureresponse can be described by a second-order non-linear differential equation. However, there are twoill-defined parameters in the governing equation: the inertial coefficient CI and the loss coefficient CL. Lack of knowledge of these two parameters restricts the practical use of the governing equation. This studywas primarily focused on finding an accurate reference value for CI, and the paper presents a systematicinvestigation of the factors influencing the inertial coefficient for a wind-tunnel model building including:opening configuration and location, wind speed and direction, approaching flow turbulence, the modelmaterial, and the installation method. A numerical model was used to simulate the volume deformationunder internal pressure, and to predict the bulk modulus of an experimental model. In considering thestructural flexibility, an alternative approach was proposed to ensure accurate internal volume distortions, sothat similarity of internal pressure responses between model-scale and full-scale building was maintained. The research showed 0.8 to be a reasonable standard value for the inertial coefficient.

The loss coefficient for fluctuating flow through a dominant opening in a building

Haiwei Xu,Shice Yu,Wenjuan Lou 한국풍공학회 2017 Wind and Structures, An International Journal (WAS Vol.24 No.1

Wind-induced fluctuating internal pressures in a building with a dominant opening can be described by a second-order non-linear differential equation. However, the accuracy and efficiency of the governing equation in predicting internal pressure fluctuations depend upon two ill-defined parameters: inertial coefficient CI and loss coefficient CL, since CI determines the un-damped oscillation frequency of an air slug at the opening, while CL controls the decay ratio of the fluctuating internal pressure. This study particularly focused on the value of loss coefficient and its influence factors including: opening configuration and location, internal volumes, as well as wind speed and approaching flow turbulence. A simplified formula was presented to predict loss coefficient, therefore an approximate relationship between the standard deviation of internal and external pressures can be estimated using Vickery\'s approach. The study shows that the loss coefficient governs the peak response of the internal pressure spectrum which, in turn, will directly influence the standard deviation of the fluctuating internal pressure. The approaching flow characteristic and opening location have a remarkable effect on the parameter CL.

A Three-way Handshaking Access Mechanism for Point to Multipoint In-band Full-duplex Wireless Networks

( Haiwei Zuo ),( Yanjing Sun ),( Changlin Lin ),( Song Li ),( Hongli Xu ),( Zefu Tan ),( Yanfen Wang ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.7

In-band Full-duplex (IBFD) wireless communication allows improved throughput for wireless networks. The current Half-duplex (HD) medium access mechanism Request to Send/Clear to Send (RTS/CTS) has been directly applied to IBFD wireless networks. However, this is only able to support a symmetric dual link, and does not provide the full advantages of IBFD. To increase network throughput in a superior way to the HD mechanism, a novel three-way handshaking access mechanism RTS/SRTS (Second Request to Send)/CTS is proposed for point to multipoint (PMP) IBFD wireless networks, which can support both symmetric dual link and asymmetric dual link communication. In this approach, IBFD wireless communication only requires one channel access for two-way simultaneous packet transmissions. We first describe the RTS/SRTS/CTS mechanism and the symmetric/asymmetric dual link transmission procedure and then provide a theoretical analysis of network throughput and delay using a Markov model. Using simulations, we demonstrate that the RTS/SRTS/CTS access mechanism shows improved performance relative to that of the RTS/CTS HD access mechanism.

Non-stationary statistical modeling of extreme wind speed series with exposure correction

Mingfeng Huang,Qiang Li,Haiwei Xu,Wenjuan Lou,Ning Lin 한국풍공학회 2018 Wind and Structures, An International Journal (WAS Vol.26 No.3

Extreme wind speed analysis has been carried out conventionally by assuming the extreme series data is stationary. However, time-varying trends of the extreme wind speed series could be detected at many surface meteorological stations in China. Two main reasons, exposure change and climate change, were provided to explain the temporal trends of daily maximum wind speed and annual maximum wind speed series data, recorded at Hangzhou (China) meteorological station. After making a correction on wind speed series for time varying exposure, it is necessary to perform non-stationary statistical modeling on the corrected extreme wind speed data series in addition to the classical extreme value analysis. The generalized extreme value (GEV) distribution with time-dependent location and scale parameters was selected as a non-stationary model to describe the corrected extreme wind speed series. The obtained non-stationary extreme value models were then used to estimate the non-stationary extreme wind speed quantiles with various mean recurrence intervals (MRIs) considering changing climate, and compared to the corresponding stationary ones with various MRIs for the Hangzhou area in China. The results indicate that the non-stationary property or dependence of extreme wind speed data should be carefully evaluated and reflected in the determination of design wind speeds.

Wind-induced conductor response considering the nonproportionality of generalized aerodynamic damping

Wenjuan Lou,Dengguo Wu,Haiwei Xu 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7

Aerodynamic damping is a key factor that influences the wind-induced responses of transmission conductors. The inaccurate estimation of aerodynamic damping leads to misunderstanding of conductor response to wind actions. For dynamic response analysis in the frequency domain, the generalized aerodynamic damping matrix used to solve conductor motion is diagonal. This study reanalyzed the conductor generalized aerodynamic damping matrix by considering its horizontal and vertical motions and the coupling effects of different modes. The derived generalized aerodynamic damping was a nondiagonal matrix, and we defined it as nonproportional generalized aerodynamic damping. Variations in the aerodynamic damping ratio and the nonproportionality of generalized aerodynamic damping with wind speed were investigated through numerical studies of single- and triple-span conductors. Triple-span conductors with different span lengths, hanging heights, and initial pretension forces were adopted to discuss the effects of the nonproportionality of generalized aerodynamic damping on estimating the dynamic responses of conductors. Results showed that neglecting the vertical motion of a conductor leads to an overestimation of the aerodynamic damping ratio, especially under high wind speed conditions. The nonproportionality of generalized aerodynamic damping is highest when the incoming wind speed at 10 m is 25 m/s. Ignoring such nonproportionality leads to an overestimation of the resonant responses of conductors but exerts minimal effects on total fluctuating responses mainly contributed by background components. Therefore, for a transmission conductor with a significant resonant response, the nonproportionality effect of generalized aerodynamic damping must be considered. Increasing span length and conductor height or reducing initial pretension force seems to enhance nonproportionality effects on conductor responses.

Non-stationary statistical modeling of extreme wind speed series with exposure correction

Huang, Mingfeng,Li, Qiang,Xu, Haiwei,Lou, Wenjuan,Lin, Ning Techno-Press 2018 Wind and Structures, An International Journal (WAS Vol.26 No.3

Extreme wind speed analysis has been carried out conventionally by assuming the extreme series data is stationary. However, time-varying trends of the extreme wind speed series could be detected at many surface meteorological stations in China. Two main reasons, exposure change and climate change, were provided to explain the temporal trends of daily maximum wind speed and annual maximum wind speed series data, recorded at Hangzhou (China) meteorological station. After making a correction on wind speed series for time varying exposure, it is necessary to perform non-stationary statistical modeling on the corrected extreme wind speed data series in addition to the classical extreme value analysis. The generalized extreme value (GEV) distribution with time-dependent location and scale parameters was selected as a non-stationary model to describe the corrected extreme wind speed series. The obtained non-stationary extreme value models were then used to estimate the non-stationary extreme wind speed quantiles with various mean recurrence intervals (MRIs) considering changing climate, and compared to the corresponding stationary ones with various MRIs for the Hangzhou area in China. The results indicate that the non-stationary property or dependence of extreme wind speed data should be carefully evaluated and reflected in the determination of design wind speeds.

Electroless Cu/Ni Plating on Graphite Flake and the Effects to the Properties of Graphite Flake/Si/Al Hybrid Composites

Ying Huang,Xuanyi Peng,Yiwen Yang,Haiwei Wu,Xu Sun,Xiaopeng Han 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.5

Proper process and parameter were investigated to coat Cu or Ni on graphite fl ake (G f ) by electroless plating. Microstructuralcharacterization indicated that the Cu/Ni was coated on the G f uniformly and comprehensively. Then aluminum matrixcomposites reinforced with Si and graphite were fabricated by a unique vacuum gas pressure infi ltration. The thermal conductivityand mechanical properties of the composites, both with and without Cu or Ni coating layers on the graphite surface,have been studied. The obtained results indicated that the mechanical property of the Cu or Ni coated G f /Si/Al compositesdramatically increased, as compared with the non-coated G f /Si/Al composite. In the meantime, Cu or Ni coated G f provedto have better wettability and interfacial bonding with the aluminum matrix, which were expected to be a highly sustainableand dispersible reinforcement for metal matrix composites.

Lane Detection Algorithm for Night-time Digital Image Based on Distribution Feature of Boundary Pixels

Feng You,Ronghui Zhang,Lingshu Zhong,Haiwei Wang,Jianmin Xu 한국광학회 2013 Current Optics and Photonics Vol.17 No.2

This paper presents a novel algorithm for nighttime detection of the lane markers painted on a road at night. First of all, the proposed algorithm uses neighborhood average filtering, 8-directional Sobel operator and thresholding segmentation based on OTSU’s to handle raw lane images taken from a digital CCD camera. Secondly, combining intensity map and gradient map, we analyze the distribution features of pixels on boundaries of lanes in the nighttime and construct 4 feature sets for these points, which are helpful to supply with sufficient data related to lane boundaries to detect lane markers much more robustly. Then, the searching method in multiple directions- horizontal, vertical and diagonal directions, is conducted to eliminate the noise points on lane boundaries. Adapted Hough transformation is utilized to obtain the feature parameters related to the lane edge. The proposed algorithm can not only significantly improve detection performance for the lane marker, but it requires less computational power. Finally, the algorithm is proved to be reliable and robust in lane detection in a nighttime scenario.