Table of Content

30 December 2016, Volume 22 Issue 6

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Monte Carlo simulation of pyrocarbon deposition process based on graphite crystallite surface model

LIU Binglin1, MA Xiao1, FANG Jinming2, TANG Zhepeng1, LI Aijun1, SUN Jinliang1

2016, 22(6):  691-700.  doi:10.3969/j.issn.1007-2861.2015.04.005

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The base plane of graphite crystallite was proposed as the surface model of pyrocarbon prepared in chemical vapor infil-tration (CVI) processes. The Particle-Filler(P-F) model and Langmuir-Hinshelwood (L-H) mechanism of CVI processes were applied to simulate the texture formation in the process of pyrocarbon growth using the Monte Carlo (MC) method, and the process of textural interface formation was studied. The results showed that the texture formation mechanism of pyrocarbon deposition presented an S-shape curve with bi-stability transition by variation of the ration of C₆ species to C₂ species in the gas phase. Moreover, there was a hysteresis in the bi-stability transition of pyrocarbon textures, and the hysteresis was clearly influenced by the composition of the gas-phase species.

Analysis of liquid metal flow with electromagnetic braking in continuous casting of slab by three-dimensional simulation

ZHOU Ran, FAN Yafu, DENG Kang, ZHANG Zhenqiang, REN Zhongming

2016, 22(6):  701-709.  doi:10.3969/j.issn.1007-2861.2015.02.006

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Using mercury as working medium in the earlier study, physical simulation was intended to investigate the liquid flow in a mold of slab in continuous casting with electromagnetic braking (EMBr). From the restrictions on the size and quantity of the sensors, the result of mercury model was limited to analysis in a two-dimensional flow field. Based on the previous physical simulation, a three-dimensional flow was simulated numerically with a standard k-ε turbulence model to investigate influences of the magnetic field intensity, and distribution on the metal flow in the mold of slab in continuous casting with and without EMBr. Simulation results were compared with the physical results. It was found that the simulation could reveal more detailed phenomena and flow behaviors. These could not be observed in physical simulation as restricted by the quantity of sensors. The results indicated that a flow field in a crystallizer had a complex three-dimensional flow field characteristic with a flow control mold (FC Mold) EMBr mode. More attention must be paid to mold slow liquid level caused by surface inclusions, transverse crack and other factors. Appropriate and effective EMBr should match the continuous casting process.

Precipitation and growth of Nd₂Fe₁₄B/α-Fe during amorphous crystallized process and its magnetic properties

XUE Yun1, HOU Xueling1, HAN Ning2, LU Qianqian1, XU Hui1

2016, 22(6):  710-718.  doi:10.3969/j.issn.1007-2861.2015.04.002

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The crystal structure, magnetic properties of the Nd_9.5Fe₇₆Co₅Ti₃B_6.5  amorphous alloys annealed at different temperatures were investigated by X-ray diffraction(XRD), vibrating sample magnetometer (VSM), and differential scanning calorimeter (DSC). The results indicated that the Nd₂Fe₁₄B phase was precipitated prior to that of α-Fe phase from the amorphous matrix. Nd₂Fe₁₄B phase and α-Fe phase were precipitated at 600 and 680 ℃, respectively. α-Fe phase grain growed up more obviously than Nd₂Fe₁₄B phase with increasing annealing temperature. The grain sizes of α-Fe phase and Nd₂Fe₁₄B phase growed from 22.4 and 32.8 nm to 33.3 and 39.8 nm when they annealed at 690 to 700 ℃. When annealing at 690 ℃, there were strong exchange coupling effects between hard magnetic phase Nd₂Fe₁₄B with 32.8 nm and soft magnetic phase α-Fe with 22.4 nm. MeanwhileNd_9.5Fe₇₆Co₅Ti₃B_6.5 alloy obtained the best magnetic properties with B_r =0.88 T, H_ci =523.76 kA/m, and (BH)_max=100.01 kJ/m³.

Preparation and properties of (TA)₅T-structured TiO₂/Ag assembly films

HAN Wei, WANG Yue, TANG Haotian, YU Jingjing, YU Shengwen

2016, 22(6):  719-726.  doi:10.3969/j.issn.1007-2861.2015.04.006

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(TA)₅T-structured TiO₂/Ag assembly films with different Ag contents were prepared by magnetron sputtering, and its phase constitution and properties were studied. The film structure of TiO₂/Ag assembly films was analyzed with X-ray diffraction(XRD), and surface morphology was observed with scanning electron microscope (SEM). Absorption spectrums of the films were measured with ultraviolet-visible spectrophotometry(UV-VIS). Resistivities of the films were calculated from I-V curves measured with a Keithley 2400. The results showed that anatase phase of TiO₂ was formed in all (TA)₅Tstructured TiO₂/Ag assembly films annealed at 500 ℃ for 60 min in an N₂ furnace. The main crystalline size of TiO₂ increased with the increasing Ag content. Irregular-shaped and different-sized Ag nanoparticles distributed unevenly on the film surface. Compared with pure TiO₂ films, the absorption edges of (TA)₅T-structured TiO₂/Ag assembly films shifted toward blue and had surface plasmon resonance (SPR) absorption peaks. Resistivities of the films decreased with the increasing Ag content. In (TA)₅T-structured TiO₂/Ag assembly films, the position of surface plasmon resonance could be regulated roughly through changing the Ag content.

Optimization of milling parameters for pre-hardened plastic mould steel SDP1

LIU Liang1,2, MIN Yongan1, ZHANG Zheng1, WU Xiaochun1

2016, 22(6):  727-736.  doi:10.3969/j.issn.1007-2861.2014.05.001

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Milling parameters of a new pre-hardened plastic mould steel SDP1 were optimized using the Taguchi method and model analysis. The optimization model for rough milling was set up. Based on signal-to-noise ratio (SNR) and analysis of variance, influences of milling force, milling speed, feed rate and axial milling depth on the /Fn value were discussed. Optimal parameters were obtained and confirmed.

Exit choice behavior of pedestrians evacuating from a two-exit room

DONG Liyun1,2, CHEN Li1, LI Xiang1

2016, 22(6):  737-745.  doi:10.3969/j.issn.1007-2861.2015.02.004

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Pedestrian evacuation from a two-exit room was investigated using a cellular automaton model based on the floor field. To depict the exit choice behavior, a decaying floor field was introduced, taking into account the degree of congestion near exits. Since the number of pedestrians in the exit areas varied over time, the decaying floor field was dynamical. In evacuation, a pedestrian might turn to another exit according to the varying floor field. The decay factor might be regarded as a measure of the pedestrians’ sensitivity to the exit congestion. Numerical results showed that more pedestrians left the room from the large exit and fewer from the small exit. Two groups of pedestrians almost completed their evacuation from the two exits simultaneously. However, large decay factors led to undulation of the pedestrian flow and a prolonged evacuation time. The optimal decay factor was then determined, which minimized the evacuation time and maximized the usage of exits. It was shown that the decaying floor field played a vital role in capturing the essential features of exit choice behavior during evacuation.

Determination of bisphenol A in soybean milk by dispersive liquid-liquid microextraction coupled with high performance liquid chromatography

ZHA Yiming, WANG Xinxiu, FAN Yong, WANG Tianlin, LUO Liqiang

2016, 22(6):  746-752.  doi:10.3969/j.issn.1007-2861.2015.03.010

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A novel method was developed for determination of bisphenol A in soybean milk using dispersive liquid-liquid microextraction coupled with high performance liquid chromatography (DLLME-HPLC). Under the optimal conditions, the peak area had a linear relation with the concentration of bisphenol A over the range of 1~100 μg/L. The detection limit was 0.3 μg/L and recovery was among 91.6%~97.5%. The method had good accuracy and reproducibility, and was appropriate for determination of bisphenol A in soybean milk.

Simulation of slurry flow with high sediment concentration based on two-fluid model

LIANG Chengpeng, CHEN Hongxun, QIAN Tao

2016, 22(6):  753-762.  doi:10.3969/j.issn.1007-2861.2015.01.007

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Since sediment usually has a negative effect on hydropower project, it is necessary to develop appropriate methods to analyze sediment transport. Due to complexity of high concentration granular flow, a three dimensional two-fluid model was proposed to study slurry flows of both suspended load and traction load. The model took into account interaction between particles and water, as well as inter-particle collision and fluctuation of the two phase volume fraction. Numerical simulation of an open-channel sediment experiment of Coleman was used to validate the two-fluid model. Based on the model validation, the deposition effect of a specific desander was analyzed.

A new proof of the Brunn-Minkowski inequality

LIAO Ting

2016, 22(6):  763-774.  doi:10.3969/j.issn.1007-2861.2015.03.001

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Several important properties of Knöthe map were obtained, and then the Knöthe maps between certain specific convex bodies were calculated. As an application, a new proof of Brunn-Minkowski inequality using Knöthe map was given.

Preparation, performance and recovery of expanded graphite loaded with lanthanum hydroxide

SU Yang, JIN Suwan, ZHANG Ling

2016, 22(6):  776-783.  doi:10.3969/j.issn.1007-2861.2015.02.017

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Expanded graphite-LaOH (EG-LaOH) was fabricated successfully using an immersion method. The best synthesis conditions were studied. Influences of initial phosphate concentration, interfering anions and dosage were investigated as well. The best condition of EG-LaOH preparation was La concentration of 0.10 mol/L and immersion time of 40 min. Removal capacity of EG-LaOH was gradually improved and then kept unchanged with the increase of phosphate concentration but decreased with the rise of dosage. F⁻ and Cl⁻ had only limited impact on phosphorus removal of EG-LaOH. After the first recovery under the condition of 25 and 90 ℃, removal capacities of EG-LaOH could still reach 9.48 and 14.40 mg/g, respectively.

PM_2.5 and its heavy metal contents in Shanghai and the assessment of health risk to residents

ZHANG Chunchun1,2, HE Chiquan1

2016, 22(6):  784-792.  doi:10.3969/j.issn.1007-2861.2016.05.006

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PM_2.5 concentration and its heavy metal contents in a typical mixing area in Shanghai with industrial units and residents were monitored from summer to winter. The trend of PM_2.5 concentration and its heavy metal contents were found. Human exposure health risk assessment method was used to evaluate potential health risk of PM_2.5 concentration and its heavy metal contents. The results showed that PM_2.5 concentration in residential sites was equal to the average value of Shanghai. Pollution levels in each point showed a strong seasonal pattern, which was significantly higher in winter than in summer and in autumn. Concentrations of Pb and Cd did not exceed the standard limit, but that of As was more than doubled compared to the standard. Both non-cancer risk and cancer risk of heavy metal exposure were at an acceptable level, without increasing health risks to local residents.

Job shop scheduling with uncertainty based on genetic algorithm

PENG Yunfang1, GAO Ya1, XIA Beixin2

2016, 22(6):  793-803.  doi:10.3969/j.issn.1007-2861.2015.05.008

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A mathematical model representing uncertain processing time by triangular fuzzy number was built to deal with the job shop scheduling problem with different due date windows. An improved genetic algorithm was developed to solve the problem. The algorithm generated initial population using an integer coding method combined with a roulette method and the elitist strategy in the selection operator. Precedence operation crossover (POX) and swap mutation methods were used in crossover and mutation operators. Meanwhile, crossover and mutation probabilities were dynamically adjusted to improve the algorithm’s performance. An example was given to verify validity of the model and algorithm.

Analysis of shipping network of Southeast-Asian route along maritime Silk Road based on complex networks

CHEN Fuying, HU Zhihua

2016, 22(6):  804-812.  doi:10.3969/j.issn.1007-2861.2016.04.017

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To promote the strategical construction of the maritime Silk Road, a data platform of maritime Silk Road for the Southeast-Asian shipping network was built. Based on the theory of complex networks, the features of the port network of Southeast-Asian route from the degree and its centrality, closeness centrality and node betweenness were analyzed. The results showed that the shipping network of the Southeast-Asian route had a small average distance and high average clustering coefficient with a near exponential density distribution, showing a small-world effect and scale-free property. Along its ports, Port Singapore, Port Klang and Port Tanjung Pelepas all had larger degrees and centralities. These ports could be referred when China constructs core ports along the “One Belt and One Road”.

Analysis of deformation of existing tunnel overlapped by new shield tunnel

CAI Weiyang1, ZHANG Mengxi1, WU Huiming2

2016, 22(6):  813-820.  doi:10.3969/j.issn.1007-2861.2015.02.021

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As the newly-built Metro Line 11 in Shanghai went through Line 4, a method of data monitoring was used to analyze the deformation of the existing tunnel overlapped by Line 11 under construction with lower- and upper-shields. Cubic spline interpolation was used to simulate the deformation curve. A deformation curve of the full-length profile of the cross section was obtained. Based on an improved longitudinal equivalent continuous model of the tunnel, the relationship between the tunnel’s longitudinal deformation curve and the amount of stretching of the circular seam was calculated. Combined with the specifications, control indicators of deformation for the existing tunnel caused by Line 11 were proposed. The results showed that the maximum deformation in excavation engineering should be controlled first when the lower-shield was constructed, and then the upper-shield. At the same time, deformation of the inside and outside circle should be concentrated in its centerline around 2.5 times the outer diameter of the shield tunnel. In constructing the lower part, subsidence in the outer circle was larger because the outer circle was more influenced and the pre-disturbance was mainly concentrated in the outer center region. The results provided a theoretical basis for constructing overlapped metro lines, especially for protecting an existing tunnel when the lower-shield was constructed first.

Influences of the water conservancy revetment structure construction to the adjacent underground raw water pipeline

CAI Yu

2016, 22(6):  821-828.  doi:10.3969/j.issn.1007-2861.2016.05.014

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Combined with the 2nd Da Lu waterway regulation project, water conservancy revetment constructions on the existing adjacent underground water supply pipelines were investigated. Besides the squeezing soil effect of the piles, the project also influenced the settlement of the structure and soil vibration, pre-drilling hole collapse, change of upper load, and so forth. To reduce the influence, some measures were taken, including in situ monitoring, control of sink rate of pile, and seperate pilling of neighboring pile foundations, restrictions on piling quantity, pre-drilled piling, considering the front pile curtain effect,
and pre-borehole wall protection. The practice results showed that these measures were effective and could be used for the similar projects.