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Analysis and optimal synthesis of single loop spatial mechanisms
Med Amine Laribi, Lotfi Romdhane, Sa?d Zeghloul
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(9): 665-679.
https://doi.org/10.1631/jzus.A1000052
In this work, a systematic approach is presented to obtain the input-output equations of a single loop 4-bar spatial mechanisms. The dialytic method along with Denavit-Hartenberg parameters can be used to obtain these equations efficiently. A genetic algorithm (GA) has been used to solve the problem of spatial mechanisms synthesis. Two types of mechanisms, e.g., RSCR and RSPC (R: revolute; S: spherical; C: cylindrical; P: prismatic), have illustrated the application of the GA to solve the problem of function generation and path generation. In some cases, the GA method becomes trapped in a local minimum. A combined GA-fuzzy logic (GA-FL) method is then used to improve the final result. The results show that GAs, combined with an adequate description of the mechanism, are well suited for spatial mechanism synthesis problems and have neither difficulties inherent to the choice of the initial feasible guess, nor a problem of convergence, as it is the case for deterministic methods.
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One and two dimensional chloride ion diffusion of fly ash concrete under flexural stress
Yun-sheng Zhang, Wei Sun, Zhi-yong Liu, Shu-dong Chen
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(9): 692-701.
https://doi.org/10.1631/jzus.A1100006
A preloading frame is firstly designed to accurately apply external flexural stress to concrete specimens. Then a method is developed to measure one and two dimensional (1D and 2D) chloride ion concentrations at different distances from the surface of concrete under flexural stress. Using this method and the preloading frame, 1D and 2D stress-diffusion is systematically investigated for fly ash concretes made with different fly ash contents (0%, 10%, 20%, 40%, and 60%), and water to binder ratios (0.3, 0.35, and 0.4). The stress accelerating effect on 1D and 2D chloride ion diffusion is also quantitatively analyzed through a comparison between stress-diffusion and nonstress-diffusion. A diffusion accelerating effect caused by external flexural stress can clearly be observed through the comparison. In order to quantify the stress accelerating effect, a stress accelerating factor is proposed in this paper. The relationship between stress accelerating factor and external stress-to-ultimate stress ratio is given as an exponential function. Finally, the process of the initiation, prorogation, and distribution of microcracks on the tensile face of specimen is observed in-situ by using a small-sized loading frame and scanning electron microscope (SEM). The above research provides an insight into chloride attack on the edge reinforcing bars of concrete structures under flexural stress, such as large-span beam and board in the field of civil engineering.
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Mortality weighting-based method for aggregate urban air risk assessment
Qing-yu Zhang, Guo-jin Sun, Wei-li Tian, Yu-mei Wei, Si-mai Fang, Jin-feng Ruan, Guo-rong Shan, Yao Shi
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(9): 702-709.
https://doi.org/10.1631/jzus.A11b0043
This paper deals with a mortality-weighted synthetic evaluation (MWSE) method for evaluating urban air risk. Sulphur dioxide (SO2), nitrogen oxide (NOx), and particulate matter (PM10) were used as pollution indices. The urban area of Hangzhou, China is divided into 756 grid cells, with a resolution of 1 km×1 km, and is evaluated using the MWSE and the air quality index (AQI), a widely-used method to evaluate ambient air quality and air risk. In an evaluation of one day in April 2004, the surface areas categorized as levels I and III, as defined by the integrated air risk evaluation, were 27.3% and 3.3% lower, respectively, than grades I and III defined by the AQI evaluation. Meanwhile, the areas classified as level II or above level III by the integrated air risk evaluation were 55.1% and 101.1% higher, respectively, than grade II or above grade III when using the AQI evaluation. From this comparison, we find that the MWSE method is more sensitive than the AQI method. The AQI method uses a single index to assess integrated air quality and is therefore unable to evaluate integrated air risks due to multiple pollutants. The MWSE method overcomes this problem, providing improved accuracy in air risk assessment.
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Measuring the value of water quality improvements in Lake Tai, China
Wei-wen Zhang
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(9): 710-719.
https://doi.org/10.1631/jzus.A11b0157
Despite widespread concerns and elevated policy debates, little is known about the Chinese public’s perceptions of water pollution and willingness to cooperate with government policies. Based on survey data, this study examined Lake Tai resident perception of water pollution, willingness to pay (WTP) for water quality improvements, and its influencing factors. Contingent valuation (CV) results showed that respondents would prefer to pay 141 CNY per household a year, approximately 0.70% of their annual per capita disposable income, as an environmental fee to improve water quality in Lake Tai. Aggregate WTP for all five lakeside cities of Lake Tai was estimated at about 3.8 billion CNY, without discounts, in the next ten years. WTP was found to increase with income and female respondents were willing to pay more than males. Those respondents who were dissatisfied with water quality were more likely to pay more. The usage of Lake Tai did not strongly affect WTP.
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Temperature and thermodynamic deformation analysis of the rotors on a twin screw multiphase pump with high gas volume fractions
Tie-yu Gao, Dong-fang Yang, Feng Cao, Jin-cheng Jiao
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2011, 12(9): 720-730.
https://doi.org/10.1631/jzus.A1000485
The pressure increasing process within a twin screw multiphase pump, under the condition of high gas volume fractions (GVFs), induces large temperature and pressure changes that cause the rotors to deform. Rotor deformations heavily influence the backflow of the multiphase fluid through clearances within the twin screw multiphase pump and these deformations may even lead to pump failures. An accurate temperature and pressure distribution on the screw rotors need be obtained before the deformation analysis can be carried out. By means of small temperature and pressure sensors embedded into the groove at the root of the rotors, the temperatures of 12 points on the rotors and the pressure distributions of a twin screw multiphase pump under high GVFs conditions were recorded. Temperature test results were adopted to perform a heat transfer analysis for determining the temperature distribution on the screw rotors. Then deformation analyses, including thermal deformation, force deformation, and total deformation, were conducted according to the pressure and temperature distributions. Deformation analysis for different materials was also conducted under the same boundary conditions. A material was suggested for the manufacturing of rotors in a twin screw multiphase pump under the condition of high gas volume fractions.
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7 articles
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