Analytical Solution for Borehole Contraction Caused by Radial Unloading

Chunfeng Zhao,Yanzong Yang,Cheng Zhao,Changguang Zhang 대한토목학회 2013 KSCE JOURNAL OF CIVIL ENGINEERING Vol.17 No.1

The elastoplastic analysis of a borehole was conducted using the elasto-brittle-plastic softening model and the Mohr-Coulomb strength theory, combined with earth pressure formulas derived from the cavity wall formula and Berezantsev’s formula. The analytical solutions for the plastic zone radius and radial displacement are presented. Using the curves of the plastic zone radius and the wall displacement of the borehole versus borehole depth, the influence of various factors such as different earth pressure calculation methods, the unloading process, the borehole radius, and the dilatation and softening effects are discussed in detail. According to the results, the use of the cavity wall formula leads to convergence easily and both the knee points for the plastic zone radius and the wall displacement of the borehole occur in the shallower part of the borehole. On the other hand, according to Berezantsev’s formula, the earth pressure increases along the shaft, following a hyperbolic curve, and continues to increase at the bottom of the borehole. Because there is a significant difference between the results of the previous two methods, an integrated method for estimating the earth pressure should be derived using the in situ results. The unloading process, borehole radius used in the design, dilatation and softening effects, etc., also have a great influence on the plastic zone radius and the wall displacement of the borehole. Moreover, the borehole radius has huge impact on the boundary force.

Free-Standing Mesoporous Silica/Carbon Composite Film with Crystalline Silica Wall from Ethyl-Bridged Organosilane

박성수,정유인,Chunfeng Xue,Dongyuan Zhao,하창식 한국고분자학회 2008 한국고분자학회 학술대회 연구논문 초록집 Vol.33 No.2

Big data platform for health monitoring systems of multiple bridges

Wang, Manya,Ding, Youliang,Wan, Chunfeng,Zhao, Hanwei Techno-Press 2020 Structural monitoring and maintenance Vol.7 No.4

At present, many machine leaning and data mining methods are used for analyzing and predicting structural response characteristics. However, the platform that combines big data analysis methods with online and offline analysis modules has not been used in actual projects. This work is dedicated to developing a multifunctional Hadoop-Spark big data platform for bridges to monitor and evaluate the serviceability based on structural health monitoring system. It realizes rapid processing, analysis and storage of collected health monitoring data. The platform contains offline computing and online analysis modules, using Hadoop-Spark environment. Hadoop provides the overall framework and storage subsystem for big data platform, while Spark is used for online computing. Finally, the big data Hadoop-Spark platform computational performance is verified through several actual analysis tasks. Experiments show the Hadoop-Spark big data platform has good fault tolerance, scalability and online analysis performance. It can meet the daily analysis requirements of 5s/time for one bridge and 40s/time for 100 bridges.

Modal parameter estimation of civil structures based on improved variational mode decomposition

Lun-hai Zhi,Feng Hu,Chunfeng Zhao,Jingfeng Wang 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.79 No.6

This paper proposes an improved variational mode decomposition (IVMD) algorithm for structural modal parameter estimation based on non-stationary responses. In this improved VMD, the mean envelope entropy (MEE) and particle swarm optimization (PSO) are first employed to determine the optimal decomposition parameters for the subsequent VMD analysis. Then the VMD algorithm is used to decompose the non-stationary data into a number of intrinsic mode functions (IMFs). After obtaining the IMFs based on the IVMD, structural modal parameters such as natural frequencies and damping ratios of civil structures can be determined by using Natural Excitation Technique (NExT) and Direct Interpolating approach (DI). The feasibility and accuracy of the proposed procedure are evaluated by both numerical and full-scale examples. The natural frequencies and damping ratios are successfully identified from the vibration responses with high noise and nonstationary characteristics. The results of this study illustrate that the proposed procedure provides a powerful approach to identify the modal parameters of civil structures using non-stationary responses.

Facile synthesis of mesoporous carbon nitrides using the incipient wetness method and the application as hydrogen adsorbent

Park, Sung Soo,Chu, Sang-Wook,Xue, Chunfeng,Zhao, Dongyuan,Ha, Chang-Sik Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.29

<P>Highly nitrogen-enriched mesoporous carbon nitride materials with 2-dimensional (2-D) (2D-meso-CN) and 3-dimensional (3-D) mesostructures (3D-meso-CN) were synthesized using mesoporous silica as a hard template and cyanamide as a precursor <I>via</I> the incipient wetness process without using any solvent. The materials were characterized by small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) for the mesostructure analysis, N<SUB>2</SUB> adsorption–desorption isotherms for surface area and pore size distribution, and X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FT-IR) spectroscopy for the composition analysis of frameworks. The mesoporous carbon nitride replicas have graphitic-like stacking of carbon nitride sheets in mesopore walls. The N/C ratio of the mesoporous carbon nitride replicas is 1.13 after the carbonization at 550 °C for 3 h. 2D-meso-CN and 3D-meso-CN have the BET surface area of 361 and 343 m<SUP>2</SUP> g<SUP>−1</SUP>, large pore volume of 0.50 and 0.67 cm<SUP>3</SUP> g<SUP>−1</SUP>, and pore diameter of 27.8 Å (for 2D-meso-CN), 24.5 and 80.3 Å (for 3D-meso-CN), respectively. It was found that the 3D-meso-CN has higher capacity of hydrogen uptake of 0.25 wt% than the pure mesoporous carbon FDU-15 (0.16 wt%) at 50 bar under room temperature (298 K).</P> <P>Graphic Abstract</P><P>Highly nitrogen-enriched mesoporous carbon nitride materials with 2-dimensional (2-D) (2D-meso-CN) and 3-dimensional (3-D) mesostructures (3D-meso-CN) were synthesized using mesoporous silica as a hard template and cyanamide as a precursor <I>via</I> the incipient wetness process without using any solvent. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1jm10849b'> </P>

Simulation of Earthquake Motion Phase considering Its Fractal and Auto-covariance Features

Adam A. Abdelrahman,Tadanobu Sato,Chunfeng Wan,Lei Zhao 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.9

The earthquake motion phase (EMP) is decomposed into linear delay and fluctuation parts. In this paper, the peculiar stochastic characteristics of the fluctuation part of the phase (FPP) are discussed. First, we show that the FPP has self-affine similarity and should be expressed as a fractal stochastic process by using several observed earthquake motion time histories, as well as the FPP has a long term memory in the frequency domain. Moreover, the possibility of simulating FPP using the simple fractional Brownian motion (fBm) is discussed and conclude that this is not possible. To overcome this problem, we develop a new stochastic process, the modified fBm that is able to simulate a stochastically rigorous sample FPP. This newly developed algorithm represents the phase characteristics of the observed EMP well.

Dynamic Analysis of AP1000 Shield Building Considering Fluid and Structure Interaction Effects

Qiang Xu,Jianyun Chen,CHAOBI ZHANG,Jing Li,Chunfeng Zhao 한국원자력학회 2016 Nuclear Engineering and Technology Vol.48 No.1

The shield building of AP1000 was designed to protect the steel containment vessel of thenuclear reactor. Therefore, the safety and integrity must be ensured during the plant life inany conditions such as an earthquake. The aim of this paper is to study the effect of waterin the water tank on the response of the AP1000 shield building when subjected to threedimensionalseismic ground acceleration. The smoothed particle hydrodynamics method(SPH) and finite element method (FEM) coupling method is used to numerically simulatethe fluid and structure interaction (FSI) between water in the water tank and the AP1000shield building. Then the grid convergence of FEM and SPH for the AP1000 shield building isanalyzed. Next the modal analysis of the AP1000 shield building with various water levels(WLs) in the water tank is taken. Meanwhile, the pressure due to sloshing and oscillation ofthe water in the gravity drain water tank is studied. The influences of the height of water inthe water tank on the time history of acceleration of the AP1000 shield building are discussed,as well as the distributions of amplification, acceleration, displacement, andstresses of the AP1000 shield building. Research on the relationship between the WLs in thewater tank and the response spectrums of the structure are also taken. The results showthat the high WL in the water tank can limit the vibration of the AP1000 shield building andcan more efficiently dissipate the kinetic energy of the AP1000 shield building by fluidstructureinteraction.

An Ovariectomy-Induced Rabbit Osteoporotic Model: A New Perspective

Nathan Robert Wanderman,Cindy Mallet,Hugo Giambini,Nirong Bao,Chunfeng Zhao,Kai-Nan An,Brett A. Freedman,Ahmad Nassr 대한척추외과학회 2018 Asian Spine Journal Vol.12 No.1

Study Design: Experimental Animal Model. Purpose: The aim of our study was to validate a pure bilateral ovariectomy (OVX) female New Zealand white rabbit model of postmenopausal osteoporosis utilizing animal-sparing in vivo techniques for evaluating bone mineral density (BMD). We also sought to demonstrate that bilateral OVX in female New Zealand white rabbits can produce diminished BMD in the spinal column and simulate osteoporosis, without the need for adjuvant chemotherapeutic agents (i.e., no additional glucocorticosteroids or other drugs were used for stimulating accelerated BMD loss), which can be assessed by in vivo BMD testing. Overview of Literature: Multiple animal models of postmenopausal osteoporosis have been described. Rat ovariectomy models have been successful, but are limited by rats’ inability to achieve true skeletal maturity and a slight morphology that limits surgical instrumentation. Rabbit models have been described which do not have these limitations, but previous models have relied on adjunctive steroid therapy to achieve osteoporosis and have required animal sacrifice for bone mineral density assessment. Methods: Thirty-six skeletally mature female rabbits underwent bilateral OVX. BMD was measured using dual-energy X-ray absorptiometry on the metaphysis of the proximal tibia and distal femur, at baseline and 17 weeks postoperatively. Results: Mean BMD values were significantly reduced by 21.9% (p <0.05) in the proximal tibia and 11.9% (p <0.001) in the distal femur at 17 weeks. Conclusions: This study is the first to demonstrate a significant bone loss within four months of pure OVX in rabbits using animalsparing validation techniques. We believe that this OVX model is safe, reproducible, and can be employed to longitudinally evaluate the effect of anti-osteoporosis therapeutics and surgical interventions.

Dynamic Analysis of AP1000 Shield Building Considering Fluid and Structure Interaction Effects

Xu, Qiang,Chen, Jianyun,Zhang, Chaobi,Li, Jing,Zhao, Chunfeng Korean Nuclear Society 2016 Nuclear Engineering and Technology Vol.48 No.1

The shield building of AP1000 was designed to protect the steel containment vessel of the nuclear reactor. Therefore, the safety and integrity must be ensured during the plant life in any conditions such as an earthquake. The aim of this paper is to study the effect of water in the water tank on the response of the AP1000 shield building when subjected to three-dimensional seismic ground acceleration. The smoothed particle hydrodynamics method (SPH) and finite element method (FEM) coupling method is used to numerically simulate the fluid and structure interaction (FSI) between water in the water tank and the AP1000 shield building. Then the grid convergence of FEM and SPH for the AP1000 shield building is analyzed. Next the modal analysis of the AP1000 shield building with various water levels (WLs) in the water tank is taken. Meanwhile, the pressure due to sloshing and oscillation of the water in the gravity drain water tank is studied. The influences of the height of water in the water tank on the time history of acceleration of the AP1000 shield building are discussed, as well as the distributions of amplification, acceleration, displacement, and stresses of the AP1000 shield building. Research on the relationship between the WLs in the water tank and the response spectrums of the structure are also taken. The results show that the high WL in the water tank can limit the vibration of the AP1000 shield building and can more efficiently dissipate the kinetic energy of the AP1000 shield building by fluid-structure interaction.