|
Towards fully automatic modelling of the fracture process in quasi-brittle and ductile materials: a unified crack growth criterion
Zhen-jun YANG, Guo-hua LIU
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(7): 867-877.
https://doi.org/10.1631/jzus.A071540
Fully automatic finite element (FE) modelling of the fracture process in quasi-brittle materials such as concrete and rocks and ductile materials such as metals and alloys, is of great significance in assessing structural integrity and presents tremendous challenges to the engineering community. One challenge lies in the adoption of an objective and effective crack propagation criterion. This paper proposes a crack propagation criterion based on the principle of energy conservation and the cohesive zone model (CZM). The virtual crack extension technique is used to calculate the differential terms in the criterion. A fully-automatic discrete crack modelling methodology, integrating the developed criterion, the CZM to model the crack, a simple remeshing procedure to accommodate crack propagation, the J2 flow theory implemented within the incremental plasticity framework to model the ductile materials, and a local arc-length solver to the nonlinear equation system, is developed and implemented in an in-house program. Three examples, i.e., a plain concrete beam with a single shear crack, a reinforced concrete (RC) beam with multiple cracks and a compact-tension steel specimen, are simulated. Good agreement between numerical predictions and experimental data is found, which demonstrates the applicability of the criterion to both quasi-brittle and ductile materials.
|
|
Calculations of plastic collapse load of pressure vessel using FEA
Peng-fei LIU, Jin-yang ZHENG, Li MA, Cun-jian MIAO, Lin-lin WU
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(7): 900-906.
https://doi.org/10.1631/jzus.A0820023
This paper proposes a theoretical method using finite element analysis (FEA) to calculate the plastic collapse loads of pressure vessels under internal pressure, and compares the analytical methods according to three criteria stated in the ASME Boiler Pressure Vessel Code. First, a finite element technique using the arc-length algorithm and the restart analysis is developed to conduct the plastic collapse analysis of vessels, which includes the material and geometry non-linear properties of vessels. Second, as the mechanical properties of vessels are assumed to be elastic-perfectly plastic, the limit load analysis is performed by employing the Newton-Raphson algorithm, while the limit pressure of vessels is obtained by the twice-elastic-slope method and the tangent intersection method respectively to avoid excessive deformation. Finally, the elastic stress analysis under working pressure is conducted and the stress strength of vessels is checked by sorting the stress results. The results are compared with those obtained by experiments and other existing models. This work provides a reference for the selection of the failure criteria and the calculation of the plastic collapse load.
|
|
Experimental study on the spatial distribution of particle rotation in the upper dilute zone of a cold CFB riser
Xue-cheng WU, Qin-hui WANG, Chen TIAN, Zhong-yang LUO, Meng-xiang FANG, Ke-fa CEN
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(7): 922-931.
https://doi.org/10.1631/jzus.A0820034
Particle rotation plays an important role in gas-solid flows. This paper presents an experimental investigation on the spatial distribution of average rotation speed for glass beads in the upper dilute zone of a cold circulating fluidized bed (CFB) riser. It is shown that in the horizontal direction, the average rotation speed in the near-wall area is larger than that in the center area, while in the vertical direction, it decreases as the height increases. The reason resulting in this distribution is analyzed by considering several factors including particle size, particle shape, particle number density, particle collision behavior, and the surrounding flow field, etc. The effects of CFB operation conditions on the spatial distribution of average rotation speed are also studied. The results show that the increasing superficial gas velocity increases the average rotation speed of particles in the near wall area but takes nearly no effect on that in the center area. The external solids mass flux, however, takes the opposite effect. It is found that the average rotation speeds of particles in both areas are increased as the total amount of bed material increases.
|
|
Numerical simulation of a direct internal reforming solid oxide fuel cell using computational fluid dynamics method
Jun LI, Ying-wei KANG, Guang-yi CAO, Xin-jian ZHU, Heng-yong TU, Jian LI
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(7): 961-969.
https://doi.org/10.1631/jzus.A0720054
A detailed mathematical model of a direct internal reforming solid oxide fuel cell (DIR-SOFC) incorporating with simulation of chemical and physical processes in the fuel cell is presented. The model is developed based on the reforming and electrochemical reaction mechanisms, mass and energy conservation, and heat transfer. A computational fluid dynamics (CFD) method is used for solving the complicated multiple partial differential equations (PDEs) to obtain the numerical approximations. The resulting distributions of chemical species concentrations, temperature and current density in a cross-flow DIR-SOFC are given and analyzed in detail. Further, the influence between distributions of chemical species concentrations, temperature and current density during the simulation is illustrated and discussed. The heat and mass transfer, and the kinetics of reforming and electrochemical reactions have significant effects on the parameter distributions within the cell. The results show the particular characteristics of the DIR-SOFC among fuel cells, and can aid in stack design and control.
|
|
Numerical study of PV/T-SAHP system
Gang PEI, Jie JI, Ke-liang LIU, Han-feng HE, Ai-guo JIANG
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(7): 970-980.
https://doi.org/10.1631/jzus.A0720143
In order to utilize solar energy effectively and to achieve a higher electrical efficiency by limiting the operating temperature of the photovoltaic (PV) panel, a novel photovoltaic/thermal solar-assisted heat pump (PV/T-SAHP) system was proposed and constructed. The hybrid solar system generates electricity and thermal energy simultaneously. A distributed parameters model of the PV/T-SAHP system was developed and applied to analyze the system dynamic performance in terms of PV action, photothermal action and Rankine cycle processes. The simulation results indicated that the coefficient of performance (COP) of the proposed PV/T-SAHP can be much better than that of the conventional heat pump. Both PV-efficiency and photothermic efficiency have been improved considerably. The results also showed that the performance of this PV/T-SAHP system was strongly influenced by the evaporator area, tube pitch and tilt angle of the PV/T evaporator, which are the key factors in PV/T-SAHP system optimization and PV/T evaporator design.
|
|
Fibrous TiO2 prepared by chemical vapor deposition using activated carbon fibers as template via adsorption, hydrolysis and calcinations
Hui-na YANG, Li-fen LIU, Feng-lin YANG, Jimmy C. YU
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(7): 981-987.
https://doi.org/10.1631/jzus.A0720089
TiO2 fibers were prepared via alternatively introducing water vapor and Ti precursor carried by N2 to an APCVD (chemical vapor deposition under atmospheric pressure) reactor at ≤200 °C. Activated carbon fibers (ACFs) were used as templates for deposition and later removed by calcinations. The obtained catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer, Emmett and Teller (BET) and X-ray diffraction (XRD) analysis. The pores within TiO2 fibers included micro-range and meso-range, e.g., 7 nm, and the specific surface areas for TiO2 fibers were 141 m2/g and 148 m2/g for samples deposited at 100 °C and 200 °C (using ACF1700 as template), respectively. The deposition temperature significantly influenced TiO2 morphology. The special advantages of this technique for preparing porous nano-material include no consumption of organic solvent in the process and easy control of deposition conditions and speeds.
|
|
Removal and transformation of dissolved organic matter in secondary effluent during granular activated carbon treatment
Liang-liang WEI, Qing-liang ZHAO, Shuang XUE, Ting JIA
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2008, 9(7): 994-1003.
https://doi.org/10.1631/jzus.A071508
This paper focused on the removal and transformation of the dissolved organic matter (DOM) in secondary effluent during the granular activated carbon (GAC) treatment. Using XAD-8/XAD-4 resins, DOM was fractionated into five classes: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N) and hydrophilic fraction (HPI). Subsequently, the water quality parameters of dissolved organic carbon (DOC), absorbance of ultraviolet light at 254 nm (UV-254), specific ultraviolet light absorbance (SUVA) and trihalomethane formation potential (THMFP) were analyzed for the unfractionated and fractionated water samples. The results showed that the order of the DOC removal with respect to DOM fractions was observed to be HPI>HPO-A>HPO-N>TPI-A>TPI-N. During the GAC treatment, the THMFP of the unfractionated water samples decreased from 397.4 µg/L to 176.5 µg/L, resulting in a removal efficiency of 55.6%. The removal order of the trihalomethanes (THMs) precursor was as follows: HPO-A>TPI-A>TPI-N>HPO-N>HPI. By the GAC treatment, the specific THMFP of HPO-A, TPI-A, TPI-N and the original unfractionated water samples had a noticeable decrease, while that of HPO-N and HPI showed a converse trend. The Fourier transform infrared (FTIR) results showed that the hydroxide groups, carboxylic acids, aliphatic C–H were significantly reduced by GAC treatment.
|
19 articles
|