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Discrete element modeling of sand behavior in a biaxial shear test
Zhi-yi HUANG, Zhong-xuan YANG, Zhen-yu WANG
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1176-1183.
https://doi.org/10.1631/jzus.A0720059
The mechanical behavior of sand is very complex, and depends on factors including confining pressure, density, and drainage condition. A soil mass can be contractive or dilative when subjected to shear loading, and eventually reaches an ultimate state, referred to as the critical state in soil mechanics. Conventional approach to explore the mechanical behavior of sand mainly relies on the experimental tests in laboratory. This paper gives an alternative view to this subject using discrete element method (DEM), which has attracted much attention in recent years. The implementation of the DEM is carried out by a series of numerical tests on granular assemblies with varying initial densities and confining pressures, under different test configurations. The results demonstrate that such numerical simulations can produce correct responses of the sand behavior in general, including the critical state response, as compared to experimental observations. In addition, the DEM can further provide details of the microstructure evolutions during shearing processes, and the resulting induced anisotropy can be fully captured and quantified in the particle scale.
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Nonlinear dynamic response of stay cables under axial harmonic excitation
Xu XIE, He ZHANG, Zhi-cheng ZHANG
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1193-1200.
https://doi.org/10.1631/jzus.A0720132
This paper proposes a new numerical simulation method for analyzing the parametric vibration of stay cables based on the theory of nonlinear dynamic response of structures under the asynchronous support excitation. The effects of important parameters related to parametric vibration of cables, i.e., characteristics of structure, excitation frequency, excitation amplitude, damping effect of the air and the viscous damping coefficient of the cables, were investigated by using the proposed method for the cables with significant length difference as examples. The analysis results show that nonlinear finite element method is a powerful technique in analyzing the parametric vibration of cables, the behavior of parametric vibration of the two cables with different Irvine parameters has similar properties, the amplitudes of parametric vibration of cables are related to the frequency and amplitude of harmonic support excitations and the effect of distributed viscous damping on parametric vibration of the cables is very small.
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Tensile force correction calculation method for prestressed construction of tension structures
Xin ZHUO, Guo-fa ZHANG, Koichiro ISHIKAWA, Dao-an LOU
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1201-1207.
https://doi.org/10.1631/jzus.A0720090
Factors such as errors during the fabrication or construction of structural components and errors of calculation assumption or calculation methods, are very likely to cause serious deviation of many strings’ actual prestressing forces from the designed values during tension structure construction or service period, and further to threaten the safety and reliability of the structure. Aiming at relatively large errors of the prestressing force of strings in a tension structure construction or service period, this paper proposes a new finite element method (FEM), the “tensile force correction calculation method”. Based on the measured prestressing forces of the strings, this new method applies the structure from the zero prestressing force status approach to the measured prestressing force status for the first phase, and from the measured prestressing force status approach to the designed prestressing force status for the second phase. The construction tensile force correction value for each string can be obtained by multi-iteration with FEM. Using the results of calculation, the strings’ tensile force correction by group and in batch will be methodic, simple and accurate. This new calculation method can be applied to the prestressed correction construction simulation analysis for tension structures.
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Deformation-based freeform feature reconstruction in reverse engineering
Qing WANG, Jiang-xiong LI, Ying-lin KE
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1214-1228.
https://doi.org/10.1631/jzus.A0820244
For reconstructing a freeform feature from point cloud, a deformation-based method is proposed in this paper. The freeform feature consists of a secondary surface and a blending surface. The secondary surface plays a role in substituting a local region of a given primary surface. The blending surface acts as a bridge to smoothly connect the unchanged region of the primary surface with the secondary surface. The secondary surface is generated by surface deformation subjected to line constraints, i.e., character lines and limiting lines, not designed by conventional methods. The lines are used to represent the underlying information of the freeform feature in point cloud, where the character lines depict the feature’s shape, and the limiting lines determine its location and orientation. The configuration of the character lines and the extraction of the limiting lines are discussed in detail. The blending surface is designed by the traditional modeling method, whose intrinsic parameters are recovered from point cloud through a series of steps, namely, point cloud slicing, circle fitting and regression analysis. The proposed method is used not only to effectively and efficiently reconstruct the freeform feature, but also to modify it by manipulating the line constraints. Typical examples are given to verify our method.
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Determination of rock resistant coefficient based on Mohr-Coulomb criterion for underwater tunnel
Zhong-ren TU, Qiang YANG, Qi-ming SHEN, Xiao-wen WANG
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1239-1244.
https://doi.org/10.1631/jzus.A071390
According to the load-structure method, the wall rock with lining can bear the load caused by the surrounding rock, and the rock resistant coefficient (RRC) is a key parameter for evaluating the capacity of this wall rock. Based on the Mohr-Coulomb yield criterion, this paper develops a formula for calculating the RRC, which has been applied to the real engineering project, such as Xiamen Xiang’an East Passage Underwater Tunnel Project. The fact shows that this formula is helpful for designers to determine the RRC value.
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Steam as coolant and lubricant in turning of metal matrix composites
Raviraj SHETTY, Raghuvir PAI, Vasanth KAMATH, Shrikanth S. RAO
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1245-1250.
https://doi.org/10.1631/jzus.A072203
Green cutting has become focus of attention in ecological and environmental protection. Steam is cheap, pollution-free and eco-friendly, and then is a good and economical coolant and lubricant. Steam generator and steam feeding system were developed to generate and feed steam. Comparative experiments were carried out in cutting AA6061-15 vol.% SiC (25 µm particle size), with cubic boron nitride (CBN) insert KB-90 grade under the conditions of compressed air, oil water emulsion, steam as coolant and lubricant, and dry cutting, respectively. The experimental results show that, with steam as coolant and lubricant, gradual reduction in the cutting force, friction coefficient, surface roughness and cutting temperature values were observed. Further, there was reduction in built up edge formation. It is proved that use of water steam as coolant and lubricant is environmentally friendly.
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Study on a 5.0 W/80 K single stage Stirling type pulse tube cryocooler
Zhi-hua GAN, Guo-jun LIU, Ying-zhe WU, Qiang CAO, Li-min QIU, Guo-bang CHEN, J.M. PFOTENHAUER
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1277-1282.
https://doi.org/10.1631/jzus.A0820220
A single stage Stirling pulse tube cryocooler was designed based on REGEN 3.2 and fabricated for testing. The experimental results show that the cooler can provide a cooling capacity of 5.0 W at 79.1 K, and produce a no-load temperature of 57.0 K, operating with an average pressure of 2.50 MPa and a frequency of 60 Hz, performance results that are very close to the calculated values. The cryocooler can be cooled from room temperature to 80 K in 8.5 min. The fast cooldown time is a result of the small regenerator.
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Attrition resistant catalyst for dimethyl ether synthesis in fluidized-bed reactor
Li-hua TENG
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1288-1295.
https://doi.org/10.1631/jzus.A0820155
Fluidized-bed reactor is a candidate for dimethyl ether (DME) synthesis from syngas because of its excellent heat removal capability. In order to improve the attrition resistance of catalyst, an amount of silica sol as binder was added to the catalyst composed of methanol synthesis component CuO/ZnO/Al2O3 and methanol dehydration component HZSM-5, which was prepared by coprecipitation and shaped by spray drying to get spherical particles. The effect of silica sol on the catalytic activity was investigated in a fixed-bed flow microreactor. Based on the experiment results, silica sol in the range of 0~20wt% had small effect on the catalytic activity. Generally, the CO conversion and DME yield decreased with the increase in concentration of silica sol, while the attrition resistance of catalysts increased with increasing silica sol, indicating that it was feasible to improve the attrition resistance without greatly sacrificing the activity of catalyst. In addition, the characterizations of catalysts were carried out using Brunauer-Emmett-Teller (BET), X-ray powder diffraction (XRD) and temperature programmed reduction (TPR).
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Polychlorinated dibenzo-p-dioxins and dibenzofurans in flue gas emissions from municipal solid waste incinerators in China
Tong CHEN, Yue-ling GU, Jian-hua YAN, Xiao-dong LI, Sheng-yong LU, Hui-fen DAI, Ke-fa CEN
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1296-1303.
https://doi.org/10.1631/jzus.A0720144
Polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) emissions in flue gas from two types of municipal solid waste incinerators (MSWIs) most commonly used in China were investigated in this study. The selected incinerators include two grate-type MSWIs: MSWI-A (350 t/d) and MSWI-B (150 t/d), and two fluidized bed MSWIs: MSWI-C (400 t/d) and MSWI-D (400 t/d), which are all equipped with semi-dry lime scrubber and bag filter except MSWI-D equipped with cyclone and wet scrubber (WS) as air pollutant control device (APCD). Results indicated that the emission concentration and the international toxic equivalents (I-TEQs) of the PCDD/Fs from the stacks were in the range of 1.210~10.273 ng/Nm3 and 0.019~0.201 ng I-TEQ/Nm3, respectively. They were greatly lower than the emission regulation standard of PCDD/Fs in China (1.0 ng I-TEQ/Nm3). However, only the PCDD/Fs emission level from MSWI-C was below 0.1 ng I-TEQ/Nm3. Although the homologue profiles were distinct, the contributions of the 2,3,7,8-subsituted congeners to the total I-TEQ were similar among all the investigated MSWIs. Two major 2,3,7,8-substituted congeners, 2,3,4,7,8-PeCDF and 1,2,3,7,8-PeCDD, account for 47% and 9% (average values) of the total I-TEQ values, respectively. The correlation between PCDD/Fs levels and composition of flue gas was also discussed.
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Synthesis of poly[methyl(3,3,3-trifluoropropyl)siloxane]-b-poly(ethylene oxide) block copolymers
Xiao-li ZHAN, Bi CHEN, Qing-hua ZHANG, Ling-min YI, Bo JIANG, Feng-qiu CHEN
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(9): 1304-1308.
https://doi.org/10.1631/jzus.A0820162
A series of new amphiphilic poly[methyl(3,3,3-trifluoropropyl)siloxane]-b-poly(ethylene oxide) (PMTFPS-b-PEO) diblock copolymers with different ratios of hydrophobic segment to hydrophilic segment were prepared by coupling reactions of end-functional PMTFPS and PEO homopolymers. Copolymers were shown to be well defined and narrow molecular weight distribution (MWD) (1.07~1.3) by characterizations such as gel permeation chromatography (GPC) and 1H-nudear magnetic resonance (1H-NMR).
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20 articles
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