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Strengthening an in-service reinforcement concrete bridge with prestressed CFRP bars
Hai-long WANG, Wei-liang JIN, David J. CLELAND, Ai-hui ZHANG
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2009, 10(5): 635-644.
https://doi.org/10.1631/jzus.A0820836
Carbon fiber reinforced polymer (CFRP) bars were prestressed for the structural strengthening of 8 T-shaped reinforced concrete (RC) beams of a 21-year-old bridge in China. The ultimate bearing capacity of the existing bridge after retrofit was discussed on the basis of concrete structures theory. The flexural strengths of RC beams strengthened with CFRP bars were controlled by the failure of concrete in compression and a prestressing method was applied in the retrofit. The field construction processes of strengthening with CFRP bars—including grouting cracks, cutting groove, grouting epoxy and embedding CFRP bars, surface treating, banding with the U-type CFRP sheets, releasing external prestressed steel tendons—were introduced in detail. In order to evaluate the effectiveness of this strengthening method, field tests using vehicles as live load were applied before and after the retrofit. The test results of deflection and concrete strain of the T-shaped beams with and without strengthening show that the capacity of the repaired bridge, including the bending strength and stiffness, is enhanced. The measurements of crack width also indicate that this strengthening method can enhance the durability of bridges. Therefore, the proposed strengthening technology is feasible and effective.
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Machining distortion prediction of aerospace monolithic components
Yun-bo BI, Qun-lin CHENG, Hui-yue DONG, Ying-lin KE
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2009, 10(5): 661-668.
https://doi.org/10.1631/jzus.A0820392
To predict the distortion of aerospace monolithic components, a model is established to simulate the numerical control (NC) milling process using 3D finite element method (FEM). In this model, the cutting layer is simplified firstly. Then, the models of cutting force and cutting temperature are established to gain the cutting loads, which are applied to the mesh model of the part. Finally, a prototype of machining simulation environment is developed to simulate the milling process of a spar. Key factors influencing the distortion, such as initial residual stress, cutting loads, fixture layout, cutting sequence, and tool path are considered all together. The total distortion of the spar is predicted and an experiment is conducted to validate the numerical results. It is found that the maximum discrepancy between the simulation results and experiment values is 19.0%.
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Penetration of disk fragments following impact on thin plate
Juan-juan LI, Hai-jun XUAN, Lian-fang LIAO, Wei-rong HONG, Rong-ren WU
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2009, 10(5): 677-684.
https://doi.org/10.1631/jzus.A0820746
To investigate the ballistic resistance and failure pattern of aeroengine casing following the impact of disk fragments, and to determine the optimum case structure, the phenomena of a 1/3rd disk fragment impact on single and double-layered thin plate targets were simulated using nonlinear dynamical analysis software MSC.Dytran. Strain rate effect was introduced in a Johnson-Cook (JC) material model for the disk fragment and the plate. Impact modeling was based on the Arbitrary Lagrange-Eulerian method, and simulated using explicit finite element method (FEM). Simulation results showed that the major failure pattern of the plate is shearing and tensile fracture with large plastic deformation. It was also concluded that the ballistic limit velocity increases with the standoff distance when it is beyond a certain value, and that greater resistance is obtained when the front plate has either a proportionately low or high thickness. The impact resistance of a double-layered plate may exceed that of a single plate if the thicknesses and standoff distance of the two plates are set appropriately.
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Measurement of boiling heat transfer coefficient in liquid nitrogen bath by inverse heat conduction method
Tao JIN, Jian-ping HONG, Hao ZHENG, Ke TANG, Zhi-hua GAN
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2009, 10(5): 691-696.
https://doi.org/10.1631/jzus.A0820540
Inverse heat conduction method (IHCM) is one of the most effective approaches to obtaining the boiling heat transfer coefficient from measured results. This paper focuses on its application in cryogenic boiling heat transfer. Experiments were conducted on the heat transfer of a stainless steel block in a liquid nitrogen bath, with the assumption of a 1D conduction condition to realize fast acquisition of the temperature of the test points inside the block. With the inverse-heat conduction theory and the explicit finite difference model, a solving program was developed to calculate the heat flux and the boiling heat transfer coefficient of a stainless steel block in liquid nitrogen bath based on the temperature acquisition data. Considering the oscillating data and some unsmooth transition points in the inverse-heat-conduction calculation result of the heat-transfer coefficient, a two-step data-fitting procedure was proposed to obtain the expression for the boiling heat transfer coefficients. The coefficient was then verified for accuracy by a comparison between the simulation results using this expression and the verifying experimental results of a stainless steel block. The maximum error with a revised segment fitting is around 6%, which verifies the feasibility of using IHCM to measure the boiling heat transfer coefficient in liquid nitrogen bath.
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Experimental study on rehydration conditions of freeze-dried platelets
Ju-li FAN, Xian-guo XU, Shao-zhi ZHANG, Fa-ming ZHU, Guang-ming CHEN, Li-xing YAN
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2009, 10(5): 697-703.
https://doi.org/10.1631/jzus.A0820549
A rehydration process for freeze-dried human platelets was studied on 1 ml of samples. The effects of prehydration duration, prehydration temperature, and rehydration solution on the recovery rate, mean platelet volume (MPV), and platelet distribution width (PDW) were investigated. The mass changes during the prehydration process were also studied. Three prehydration durations: 0, 1.5, and 3.5 h, and two rehydration solutions: platelet-poor plasma and phosphate-buffered saline (PBS), were tested. It was found that: (1) the prehydration was of significance; (2) 1.5 h of prehydration had better effects than 3.5 h of prehydration; (3) as a rehydration solution, the platelet-poor plasma behaved better than the PBS. The impacts of prehydration duration and temperature on the results were studied. There was almost no difference between 35 and 37 °C. Among all the prehydration durations tested, 15, 30, 60, 90, and 120 min, the best result was achieved with the time duration of 15 min. The weights of prehydrated platelets at the end of each test were measured and the water contents were calculated. After 15 min of prehydration, the water contents in the samples were about (4.8±0.01)% and (5.27±0.29)% (w/w) corresponding to the conditions of 35 and 37 °C, respectively. These results will be helpful for further studies on the freeze-drying of mammalian cells.
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Critical review in adsorption kinetic models
Hui QIU, Lu LV, Bing-cai PAN, Qing-jian ZHANG, Wei-ming ZHANG, Quan-xing ZHANG
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2009, 10(5): 716-724.
https://doi.org/10.1631/jzus.A0820524
Adsorption is one of the most widely applied techniques for environmental remediation. Its kinetics are of great significance to evaluate the performance of a given adsorbent and gain insight into the underlying mechanisms. There are lots of references available concerning adsorption kinetics, and several mathematic models have been developed to describe adsorption reaction and diffusion processes. However, these models were frequently employed to fit the kinetic data in an unsuitable or improper manner. This is mainly because the boundary conditions of the associated models were, to a considerable extent, ignored for data modeling. Here we reviewed several widely-used adsorption kinetic models and paid more attention to their boundary conditions. We believe that the review is of certain significance and improvement for adsorption kinetic modeling.
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Novel photocatalytic reactor for degradation of DDT in water and its optimization model
Wei-hai PANG, Nai-yun GAO, Yang DENG, Yu-lin TANG
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2009, 10(5): 732-738.
https://doi.org/10.1631/jzus.A0820501
A novel photocatalytic reactor was developed to remove (1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane) (DDT) from water. In the reactor, a cenosphere was used to support TiO2 film made by means of sol-gel. Because the cenospheres were coated with TiO2, their specific gravity was slightly increased from the original 0.6~0.8 to 0.8~0.9, so that they were able to be suspended in water. With the mixed operation of a bubbler, the water in the reactor was in a well-fluidized state. The bottom of the reactor is a sand filter bed, which can be used to prevent the photocatalyst from being lost. A mathematical model of the reactor has been developed in the two primary influential factors: ultraviolet (UV) light intensity and photocatalyst concentration. With such a model, the reactor can be designed more reasonably.
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Theoretical relationships between first flush of roof runoff and influencing factors
Biao WANG, Tian LI
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2009, 10(5): 746-757.
https://doi.org/10.1631/jzus.A0820718
Considering the short length of building roofs, a theoretical analysis of the first flush of roof runoff was conducted based on the kinematic wave and pollutant erosion equations. This mathematical derivation with analytical solutions predicts pollutant mass first flush (MFF), mean concentration of initial runoff (MCIF), mean concentration of roof runoff (MCRR) with diversion of initial portion and residual mass available on the bed surface (RS) after the entire runoff under the condition of constant excess rainfall. And the effects of the associated influencing factors (roof length, roof gradient, roof surface roughness, rainfall intensity, rainfall duration, and erosion coefficients) on them were discussed while the values of parameters referred to the previous studies. The results showed that for roofs whose length is shorter than 20 m, both the increase in roof length and roof gradient and the decrease in roof surface roughness result in larger MFF and MCIF and smaller MCRR and RS, which is beneficial to water reuse and pollution reduction. The theoretical relationship between the first flush and the influencing factors may aid the planning and design of roof in terms of rainwater utilization or diffuse pollution control.
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Simulated moving bed separation of tocopherol homologues: simulation and experiments
Yu-bin LÜ, Bao-gen SU, Yi-wen YANG, Qi-long REN, Ping-dong WU
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2009, 10(5): 758-766.
https://doi.org/10.1631/jzus.A0850108
Chromatograms of tocopherol homologues were obtained by a column of analytical size (inner diameter (ID) 0.46 cm cm×10 cm) packed with silica gel. Adsorption isotherms and film mass-transfer coefficient were estimated from the chromatograms by using a general rate model, which considers axial dispersion, external mass-transfer and intraparticle diffusion. Based on the obtained isotherms and mass-transfer coefficient, the separation process of tocopherol homologues on simulated moving bed (SMB) was simulated using the same model. According to the simulated results, a mixture of α-, γ-, δ-tocopherols and other impurities was separated on an SMB equipment. The SMB equipment was composed of 8 columns of ID 2 cm×10 cm, with 2 columns in each section. The solid phase was silica gel, and the mobile phase was n-hexane/2-propanol (99/1 by volume). γ- and δ-tocopherols of purity greater than 98% were obtained with recovery greater than 98%. The effects of operating conditions (flow rates and switching time) on the performance of SMB were studied by both simulation and experiments. It was found that all the simulation results were quite close to the experimental results. We conclude that process development and optimization of operating conditions of SMB by simulation are feasible.
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18 articles
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