Wind tunnel tests and CFD simulations for snow redistribution on 3D stepped flat roofs

Zhixiang Yu,Fu Zhu,Ruizhou Cao,Xiaoxiao Chen,Lei Zhao,Shichun Zhao 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.28 No.1

The accurate prediction of snow distributions under the wind action on roofs plays an important role in designing structures in civil engineering in regions with heavy snowfall. Affected by some factors such as building shapes, sizes and layouts, the snow drifting on roofs shows more three-dimensional characteristics. Thus, the research on three-dimensional snow distribution is needed. Firstly, four groups of stepped flat roofs are designed, of which the width-height ratio is 3, 4, 5 and 6. Silica sand with average radius of 0.1 mm is used to model the snow particles and then the wind tunnel test of snow drifting on stepped flat roofs is carried out. 3D scanning is used to obtain the snow distribution after the test is finished and the mean mass transport rate is calculated. Next, the wind velocity and duration is determined for numerical simulations based on similarity criteria. The adaptive-mesh method based on radial basis function (RBF) interpolation is used to simulate the dynamic change of snow phase boundary on lower roofs and then a time-marching analysis of steady snow drifting is conducted. The overall trend of numerical results are generally consistent with the wind tunnel tests and field measurements, which validate the accuracy of the numerical simulation. The combination between the wind tunnel test and CFD simulation for three-dimensional typical roofs can provide certain reference to the prediction of the distribution of snow loads on typical roofs.

Graded-Three-Dimensional Cell-Encapsulating Hydrogel as a Potential Biologic Scaffold for Disc Tissue Engineering

Li Zhixiang,Zhang Yiwen,Zhao Yupeng,Gao Xubin,Zhu Zhonglian,Mao Yingji,Qian Taibao 한국조직공학과 재생의학회 2022 조직공학과 재생의학 Vol.19 No.5

BACKGROUND: Intervertebral disk (IVD) degeneration, which can cause lower back pain, is a major predisposing factor for disability and can be managed through multiple approaches. However, there is no satisfactory strategy currently available to reconstruct and recover the natural properties of IVDs after degeneration. As tissue engineering develops, scaffolds with embedded cell cultures have proved critical for the successful regeneration of IVDs. METHODS: In this study, an integrated scaffold for IVD replacement was developed. Through scanning electron microscopy and other mechanical measurements, we characterized the physical properties of different hydrogels. In addition, we simulated the physiological structure of natural IVDs. Nucleus pulposus (NP) cells and annulus fibrosusderived stem cells (AFSCs) were seeded in gelatin methacrylate (GelMA) hydrogel at different concentrations to evaluate cell viability and matrix expression. RESULTS: It was found that different concentrations of GelMA hydrogel can provide a suitable environment for cell survival. However, hydrogels with different mechanical properties influence cell adhesion and extracellular matrix component type I collagen, type II collagen, and aggrecan expression. CONCLUSION: This tissue-engineered IVD implant had a similar structure and function as the native IVD, with the inner area mimicking the NP tissue and the outer area mimicking the stratified annulus fibrosus tissue. The new integrated scaffold demonstrated a good simulation of disc structure. The preparation of efficient and regeneration-promoting tissueengineered scaffolds is an important issue that needs to be explored in the future. It is hoped that this work will provide new ideas and methods for the further construction of functional tissue replacement discs.

Airflow over low-sloped gable roof buildings: Wind tunnel experiment and CFD simulations

Ruizhou Cao,Zhixiang Yu,Zhixiang Liu,Xiaoxiao Chen,Fu Zhu 한국풍공학회 2020 Wind and Structures, An International Journal (WAS Vol.31 No.4

In this study, the impact of roof slope on the flow characteristics over low-sloped gable roofs was investigated using steady computational fluid dynamics (CFD) simulations based on a k- SST turbulence model. A measurement database of the flow field over a scaled model of 15° was created using particle image velocimetry (PIV). Sensitivity analyses for the grid resolutions and turbulence models were performed. Among the three common Reynolds-averaged Navier-Stokes equations (RANS) models, the k- SST model exhibited a better performance, followed by the RNG model and then the realizable k- model. Next, the flow properties over the differently sloped (0° to 25°) building models were determined. It was found that the effect of roof slope on the flow characteristics was identified by changing the position and size of the separation bubbles, 15° was found to be approximately the sensitive slope at which the distribution of the separation bubbles changed significantly. Additionally, it is suggested additional attention focused on the distributions of the negative pressure on the windward surfaces (especially "5" ° and "10" ° roofs) and the possible snow redistribution on the leeward surfaces.

CFD-DEM modeling of snowdrifts on stepped flat roofs

Lei Zhao,Zhixiang Yu,Fu Zhu,Xin Qi,Shichun Zhao 한국풍공학회 2016 Wind and Structures, An International Journal (WAS Vol.23 No.6

Snowdrift formation on roofs should be considered in snowy and windy areas to ensure the safety of buildings. Presently, the prediction of snowdrifts on roofs relies heavily on field measurements, wind tunnel tests and numerical simulations. In this paper, a new snowdrift modeling method by using CFD (Computational Fluid Dynamics) coupled with DEM (Discrete Element Method) is presented, including material parameters and particle size, collision parameters, particle numbers and input modes, boundary conditions of CFD, simulation time and inlet velocity, and coupling calculation process. Not only is the two-way coupling between wind and snow particles which includes the transient changes in snow surface topography, but also the cohesion and collision between snow particles are taken into account. The numerical method is applied to simulate the snowdrift on a typical stepped flat roof. The feasibility of using coupled CFD with DEM to study snowdrift is verified by comparing the simulation results with field measurement results on the snow depth distribution of the lower roof.

Adaptive Cooperation for Bidirectional Communication in Cognitive Radio Networks

( Yuan Gao ),( Changping Zhu ),( Zhixiang Deng ),( Yibin Tang ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.3

In the interweave cognitive networks, the interference from the primary user degrades the performance of the cognitive user transmissions. In this paper, we propose an adaptive cooperation scheme in the interweave cognitive networks to improve the performance of the cognitive user transmissions. In the proposed scheme for the bidirectional communication of two end-source cognitive users, the bidirectional communication is completed through the non-relay direct transmission, the one-way relaying cooperation transmission, and the two-way relaying cooperation transmission depending on the limited feedback from the end-sources. For the performance analysis of the proposed scheme, we derive the outage probability and the finite-SNR diversity multiplexing tradeoff (f-DMT) in a closed form, considering the imperfect spectrum sensing, the interference from the primary user, and the power allocation between the relay and the end-sources. The results show that compared with the direct transmissions (DT), the pure one-way relaying transmissions (POWRT), and the pure two-way relaying transmissions (PTWRT), the proposed scheme has better outage performance. In terms of the f-DMT, the proposed scheme outperforms the full cooperation transmissions of the POWRT and PTWRT.

CFD-DEM modeling of snowdrifts on stepped flat roofs

Zhao, Lei,Yu, Zhixiang,Zhu, Fu,Qi, Xin,Zhao, Shichun Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.23 No.6

Snowdrift formation on roofs should be considered in snowy and windy areas to ensure the safety of buildings. Presently, the prediction of snowdrifts on roofs relies heavily on field measurements, wind tunnel tests and numerical simulations. In this paper, a new snowdrift modeling method by using CFD (Computational Fluid Dynamics) coupled with DEM (Discrete Element Method) is presented, including material parameters and particle size, collision parameters, particle numbers and input modes, boundary conditions of CFD, simulation time and inlet velocity, and coupling calculation process. Not only is the two-way coupling between wind and snow particles which includes the transient changes in snow surface topography, but also the cohesion and collision between snow particles are taken into account. The numerical method is applied to simulate the snowdrift on a typical stepped flat roof. The feasibility of using coupled CFD with DEM to study snowdrift is verified by comparing the simulation results with field measurement results on the snow depth distribution of the lower roof.

The improved Shark Search Approach for Crawling Large-scale Web Data

Youwei Yuan,Dou Chen,Yong Li,Dongjin Yu,Lamei Yan,Zhixiang Zhu 보안공학연구지원센터 2014 International Journal of Multimedia and Ubiquitous Vol.9 No.8