15 December 2015, Volume 55 Issue 12

    

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CIVIL ENGINEERING
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  BIM-based design method for prefabricated pipeline components

  HU Zhenzhong, CHEN Xiangxiang, WANG Liang, HE Tianfeng

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1269-1275. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.001

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  The industrialization of China is creating prefabricated pipelines instead of pipeline made on site. However, prefabricated pipeline design methods are not entirely suitable for manufacturing in the factory and assembling on site. A building information model (BIM) is introduced here for designing prefabricated pipelines. An automatic prefabricated pipeline design method was developed for dividing the pipelines with a semi-automatic design method for pipeline supports and an intelligent assembling method for pipeline groups. A general purpose prefabricated pipeline design system was then developed. The method addresses three core issues for model visualization, progressive parametric modeling and information sharing.The model is applied to two real-world projects to show the enhanced design efficiency and reduced material waste.
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  Numerical model for a single pile with negative friction and soil consolidation

  YANG Jun, ZHANG Dafeng

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1276-1280. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.002

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  This paper describes a numerical model for predicting the pile foundation conditions with negative friction and soil consolidation. The geotechnical finite element software Plaxis was used to create the numerical model and soil replacement method to simulate initial soil state before acceleration of the centrifuge. Then, the development of negative friction was simulated, and the results are quite accurate. The predicted soil settlement error after consolidation is within 6.8% of the test data, the pile settling error is within 34.7% and the piling force error is within 18.3%. In addition, the excess pore pressure and relative maximum axial piling force are consistent with centrifuge test data for various consolidation times and axial force is approximately linearly related with the square root of time. This model provides reference data for calculating single pile foundations with negative friction and soil consolidation.
HYDRAULIC ENGINEERING
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  Design wind loads on hyperbolic cooling towers during construction

  ZHANG Ming, WANG Fei, LI Qingbin, TANG Dongsheng

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1281-1288. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.003

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  The fundamental theory of structural reliability was used to predict the design wind load on hyperbolic cooling towers during construction to give the same reliability during construction as for the design reference period. The relationships between the reliability for the design reference period for various time intervals and the reliability during construction for various time intervals are given based on the time interval method for analyzing the structural reliability using the stationary binomial stochastic process model for wind loads. The structural resistance during construction is found to be proportional to that of the design reference period. The characteristic wind loads also preserve the proportionality relation with the wind load factor during construction defined in this paper using partial safety factor design expressions for these two periods. A general wind load factor solution procedure was given and the predicted wind load factors were computed for typical probabilistic distributions of the random variables. The wind load factor increases with the extension of the construction cycle or with a lower resistance partial safety factor. The relationship between the wind load factor and the construction time is well fit by a logarithmic function. The design wind load for hyperbolic cooling towers during construction can be determined with the correlations or simplified tables of the wind load factor.
  
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  Numerical simulation of multidirectional irregular wave group propagation

  LIU Si, ZHANG Yongliang

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1289-1295. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.004

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  Irregular wave group motion was simulated for comparison with physical model tests. Real waves are multidirectional waves. A numerical method was developed to simulate multidirectional irregular wave groups for various wave parameters, grouping factors and directional spreading parameters for use in designing an experimental wave basin for multidirectional irregular wave groups. The simulations of the wave time series of the incident waves was based on the numerical model of modified Boussinesq equations solved by finite element. Examples show that multidirectional waves containing the desired wave groupiness can be generated at a specified position in the numerical wave basin. Transformations of the wave groupings in the basin are also numerically analyzed.
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  Influence of rubber cultivation on the aquatic ecology of the Naban River

  ZHAO Na, WANG Zhaoyin, XU Mengzhen, ZHOU Xiongdong, ZHANG Chendi

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1296-1302. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.005

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  Xishuangbanna in southern Yunnan is one of the global hotspots of biodiversity protection. Large-scale rubber cultivation has altered the river conditions by changing the hydraulics, sediment conditions, and water quality. Research about the influence of rubber cultivation on the aquatic ecology is very important for regional ecology and sustainable utilization of resources in this region. Field sampling, measurements and indoor identification were used in this research with the Naban River chosen as the research stream. Macroinvertebrates were used as indicators to assess the ecological status of the river and the influence of rubber cultivation on the ecology. The results show that the rubber cultivation has little impact on the water quality in the survey section with Grade Ⅱwater quality. With the increase of rubber cultivation intensity, the biodiversity of macroinvertebrates trended to decrease. The abundance ratio of sensitive species (Ephemeroptera, Trichoptera and Plecoptera) to the total macroinvertebrates trended to decrease. The abundance ratio of Diptera trended to increase. With the increase of rubber cultivation intensity, the abundance ratio of shredders trended to increase. The abundance ratio of predators trended to decrease.
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  Reservoir resettlement compensation standard based on living standards

  QIANG Maoshan, WANG Jie

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1303-1308. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.006

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  Reservoir resettlement compensation should be in conformity with the reservoir resettlement compensation principle. This study uses the per capita annual net income as the living standard measurement index with a calculational method based on the measurement index for compensation for reservoir resettlement relocation. The method resolves the gap between the required compensation and the current compensation. An actual reservoir resettlement case is analyzed to show that even though the current reservoir resettlement compensation standard based on “filling the loss” gives living standard resettlement compensation that reaches and exceeds the living standard without relocation from the present value of the long-term cumulative cash flow, the resettlement compensation living standard does not reach that without relocation in the short time. Therefore, the insufficient reservoir resettlement compensation leads to short-term social instabilities, so the compensation standard must be calculated from the perspective of reconstructing the reservoir resettlement living standard.
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  Core competency model for mega Chinese international contractors

  LIN Zhenghang, QIANG Maoshan, YUAN Shangnan

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1309-1314,1323. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.007

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  The status quo of 54 mega Chinese International Contractors' (CICs) core competencies were investigated to develop a competency evaluation and measurement table for mega international contractors. A multi-dimensional project management model was used to correlate the hierarchy structure and core competency factors to create a competency evaluation model for mega international contractors. The model relates culture, strategy, organization, project management, professional technique, human resources, risk management, capital operation, market expanding and basic competences to provide guidance for core competency evaluation and strategic planning for mega international contractors.
NUCLEAR AND NEW ENERGY ENGINEERING
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  Chinese carbon market: Current status and future perspectives

  LIN Wenbin, LIU Bin

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1315-1323. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.008

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  Faced with the increasingly serious problem of global climate change, China has developed pilot carbon markets at the provincial level and is actively exploring pilot market linkage and a national market. This study compares the current status of the pilot carbon markets in terms of their legal basis, system design, institutional arrangement and regulatory policies. Then, the economic development, industrial structure and abatement costs of the different pilot provincial and city markets are analyzed to provide guidance for a national market. This paper advises policy makers to start building a national carbon market once the pilot markets are operating steadily and that the pilot markets should be gradually linked to the national system. While constructing national market, central government should consider maneuverable policy for different provinces, as well as the coexistence of carbon market and other energy, environment and climate policies.
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  Boost pressure mechanism in hydraulic cylinders for control rod hydraulic drive systems

  LIU Qianfeng, BO Hanliang, QIN Benke

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1324-1331. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.009

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  The stepping of a hydraulic cylinder was analyzed based on the fluid mechanics for a control rod hydraulic drive system (CRHDS). The pressure transient was analyzed experimentally and theoretically for abnormal operating conditions. The results show that as the cylinder pressure increases, the pressure has an inflexion point when the inner cylinder reaches the top. The inner cylinder displacement increases while the speed of the inner cylinder decrease as the pressure increases. The flow velocity at the sealing ring increases due to the higher pressure between the two surfaces of the inner cylinder. This mechanism can be used to analyze the cylinder performance.
  
PHYSICS AND ENGINEERING PHYSICS
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  Measurement of indoor natural neutron spectrum with a Bonner sphere spectrometer

  HU Qingdong, ZENG Zhi, MA Hao, CHENG Jianping, LI Junli, ZHANG Hui, WANG Xin, WU Zhen

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1332-1334,1341. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.010

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  A Bonner sphere spectrometer was used to measure indoor natural neutron spectra in Beijing with the neutron energy spectrum obtained using an unfolding procedure with a genetic algorithm. The spectra and fluence-to-dose conversion coefficients gave a neutron flux of 2.83×10^-3 cm^-2·s^-1 and a neutron ambient dose equivalent of (1.5±0.1) nSv/h for neutron energy below 20 MeV. The total neutron flux was 3.54×10^-3 cm^-2·s^-1 and the total neutron ambient dose equivalent was (2.1±0.1) nSv/h which are comparable with the dose of (2.3±0.2) nSv/h measured by a ³He neutron monitor. The results are consistent with other measurements at similar latitudes, which verifies the reliability of this instrument and the indoor neutron dose equivalent in Beijing.
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  Mosaic designs for extending PET axial fields of view

  CHENG Li, WEI Qingyang, XIA Yan, SHANG Hong, LIU Yaqiang, WU Chaoxia, MA Tianyu

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1335-1341. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.011

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  There positron emission tomography (PET) mosaic designs were developed from a traditional PET design based on GATE (Geant4 Application for Emission Tomography) simulations using axial sensitivity, volume sensitivity and spatial resolutions with various energy thresholds of 0 keV, 250 keV and 350 keV. The results indicate that without the effect of the energy threshold, the axial sensitivity of the mosaic designs is increased 24%-50%, while the volume sensitivity is increased 47%-62%. With an appropriate energy threshold (250 keV), the axial sensitivity is increased by 12% while the volume sensitivity is increased by 8% to give similar image quality as the traditional design.
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  Prediction of retweet counts by a back propagation neural network

  DENG Qing, MA Yefeng, LIU Yi, ZHANG Hui

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1342-1347. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.012

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  Twitter has become a major platform for expressing and gathering information to change people's opinions and lives. Retweets are a key mechanism for information diffusion. The retweet mechanism can be a useful method to guide public opinion and contribute to emergency responses. This paper considers a case study of the conflicts between urban management officials (known as Chengguan in China) and the public. This study focused on factor analysis and prediction of a tweet's popularity based on a back propagation (BP) neural network during a crisis. The weighted analysis of various factors from the perspectives of the posters and the content of the microblog messages shows how some factors, including the user's activity, hashtag, visual information, mentioning others and posting time, influences a message's popularity. The results show that followers are more attracted by a tweet's content rather than its poster. The prediction problem is changed into a pattern classification problem to predict the retweet count using a back propagation (BP) neural network. The stability of the results was tested by changing the number of samples.
CHEMISTRY AND CHEMICAL ENGINEERING
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  Experiments and simulations of carbon dioxide absorption process in packed columns of different sizes

  CHEN Jian, TONG Chuan, PENG Yong, TANG Zhigang

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1348-1353. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.013

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  The development of absorption processes for carbon capture needs studies of process scale-up and modeling CO₂ absorption was measured in 200 mm and 600 mm diameter packed columns. An effective mass transfer area correlation for structured packings was used to simulate the process with a rate-based method and different mass transfer models. The results show that the most suitable mass transfer model is the film resistance model with average relative errors in the CO₂ mole fraction of 1% and 3% in the two columns. Thus, this mass transfer model and mass transfer area correlation are valid for structured packings and CO₂ absorption in various size columns could be predicted by this simulation.
ECONOMICS AND MANAGEMENT
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  CEO power, corporate social responsibility, and corporate performance

  TAO Wenjie, JIN Zhanming

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1354-1360. https://doi.org/10.16511/j.cnki.qhdxxb.2015.24.014

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  The chief executive officer (CEO) plays an irreplaceable role in the corporate social responsibility (CSR) decision-making and implementation process, but the effect of CEO's power relationships on corporate social performance is less mentioned. A-share listed companies who released CSR reports from 2009 to 2011 were studied using the OLS (ordinary least squares) method to test the relationships among CEO power, CSR and corporate finance performance (CFP). The results show that structural power can help CEOs more effectively solve social-environmental problems, but it is not sufficient to improve CFP with the influence of ownership power having opposite effects on CSR and CFP. CEOs with prestige power and expert power can better relate social and business interests. The results show that companies should carefully structure the CEO's power with effective power restrictions to protect the owner's equity and maintain sustainable development.
THERMAL ENGINEERING
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  Comparison investigation of axial flow compressors with and without shrouded stators

  LI Xiang, GU Chunwei

  Journal of Tsinghua University(Science and Technology). 2015, 55(12): 1361-1366. https://doi.org/10.16511/j.cnki.qhdxxb.2015.23.001

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  The stator design was changed from shrouded to unshrouded for the Tsinghua 1.5-stage transonic axial flow compressor test rig to study whether the unshrouded stator met the design requirements. Both shrouded and unshrouded configurations were simulated using CFD, with the influence of the stator gap size also investigated. The results show that the efficiency is 1.8% higher at the design point and the stall margin increases by 1.5% for the compressor with the unshrouded stator. The leakage flow and endwall secondary flow are balanced at a smaller gap, but the clearance flow tends to be dominant near the endwall at a larger gap, e.g. 0.8 mm. Therefore, the gap size should strictly be controlled in the manufacturing process.