15 April 2016, Volume 56 Issue 4

    

• Select all
  |

CIVIL ENGINEERING
• Select
  Simplified theoretical model for self-centering concrete bridge piers with stiffness deterioration

  LIU Hui, HE Minghua, XIN Kegui, GUO Jia, LIU Wen

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 341-347. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.001

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Self-centering concrete bridge piers (SCCP), which have been used to retrofit bridge piers to give better seismic response, effectively reduce residual displacements during severe earthquakes. This study gives a simplified theoretical model for self-centering concrete bridge piers including a stiffness deterioration analysis and lateral force-displacement analysis. The stiffness deterioration analysis introduces 3 damage factors for γ_u, γ_c and γ_r. These damage factors illustrate the damage caused by increasing lateral displacements. The theoretical model has been validated against existing experimental data with good agreement.
• Select
  Key-value cache based IFC model implementation for web environments

  LIU Qiang, ZHANG Jianping, HU Zhenzhong

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 348-353,359. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.002

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Industry foundation class (IFC) based building information modeling (BIM) systems has developed rapidly in recent years. However, there are still few methods and tools supporting web-oriented transmissions and queries of IFC model data. This paper describes a web-enabled IFC object model using the JSON format and the IFC data cache with the Redis distributed key-value store for IFC applications in web environment. Stepwise and dynamic parsing of the IFC data enables lightweight, standardized network data transmission with large-capacity, high-speed dynamic parsing of the IFC data. Tests show that the object model and the parsing method are able to support web BIM applications and significantly enhance the efficiency of parsing IFC data files, with double the parsing speed of large (over 30 MB) IFC files.
HYDRAULIC ENGINEERING
• Select
  Game analysis of design incentives for delivering international hydropower EPC projects

  TANG Wenzhe, WANG Tengfei, SUN Hongxin, QI Dashan

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 354-359. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.003

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  China's hydropower construction companies need to strengthen their design management for international EPC (engineering-procurement-construction) project delivery. Gaming theory was used to develop single-period and multi-period incentive models to investigate the incentive mechanisms between contractors and designers. The models were used to analyze 7 international EPC projects. The results show that:1) Design incentives promote optimum designs which add value to the project and benefit both contractors and designers. 2) Single-period incentives can lead to opportunistic behaviour, which may reduce the effectiveness of the design incentives. 3) The introduction of strategic benefits in multi-period incentives effectively strengthens the stability of long-term cooperation and maximize the benefits to contractors and designers in the long run. 4) EPC contractors should establish partnering relationships with qualified designers based on incentive evaluations.
• Select
  Enhancing design management in international EPC projects based on partnering

  WANG Tengfei, TANG Wenzhe, QI Dashan, DU Lei

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 360-364,372. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.004

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  China's hydropower construction companies need to improve their design management skills to compete in the international engineering-procurement-construction (EPC) market. A design management model was used to identify the relationships between partnering with stakeholders, design management and project performance. Data from 7 hydropower EPC projects in 6 countries was evaluated using reliability tests, factor analyses and path analyses to show that design management is dependent on system building, dispute settlements, value adding and technology promotion. Partnering with stakeholders, design management and project performance are positively related. Partnering not only enhances project performance by promoting effective design management, but also directly improves project performance.
• Select
  Comparison of water and land policies for agriculture water conservation in arid areas based on a coupled socio-hydrological model

  LIU Ye, TIAN Fuqiang

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 365-372. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.005

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Improper water and land policies to encourage water conservation may lead to increased agricultural water use, which is called the irrigation efficiency paradox. This study assesses the impact of water and land policies on water-conservation in agriculture development. This study uses a coupled socio-hydrological model which includes water and land policies, irrigated land area, irrigation water use and an environmental indicator. The interactions between the human responses to the policies and the environmental changes are reflected in the model. The model is used to analyze the agriculture water-conservation development during 1998-2010 in Bayinguoleng Mongol Autonomous Prefecture, Xinjiang as an example with four policy scenarios including weak irrigation land control, low irrigation land control, medium irrigation land control and strong irrigation land control to analyze how agriculture water-conservation develops with different policy scenarios. With the weak irrigation land control scenario which represents the actual situation, the model effectively represents the process mechanism for the irrigation efficiency paradox. The analyses further shows that the low and medium irrigation land control scenarios stabilize the total irrigation water use after 2005 while the irrigation area quickly increases. The strong irrigation control severely limits the ability and the initiative of the water users. The total irrigation water use increased during 1998-2010 with small increases in the amount of irrigated land and the irrigation areas with water-conservation. These slowed the agricultural economic development. The results show that this framework of the water-use policies based on the coupled socio- hydrological model can be used to capture the mechanism that leads to the irrigation efficiency paradox as an effective evaluation method with theoretical support for making proper water and land policies for agriculture water-conservation in semi-arid areas.
  
• Select
  Response of soil salinity and crop growth to irrigation methods in Xinjiang

  HU Hongchang, ZHANG Zhi, TIAN Fuqiang, YANG Pengju, NI Guangheng, YAO Xinhua

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 373-380. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.006

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Mulched drip irrigation has gradually replaced flood irrigation and is now widely used in Xinjiang. This study explores the effects of the irrigation methods on the soil salt dynamics and the crop growth using experiments conducted from 2011 to 2012 in a cotton field with mulched drip and flood irrigation systems. The 6 900 samples was observed. The results show that the salinity increased during the growth period by 25% within the top 50 cm of the soil depth with mulched drip irrigation. With flood irrigation, the soil salinity markably decreased due to the large amount of irrigation water. The salt leaching depth was 50 cm for drip irrigation, but more than 150 cm for flood irrigation. The root density with drip irrigation was 1.6 times that of flood irrigation. The water use efficiency was 0.68 kg/m³ with mulched drip irrigation and 0.22 kg/m³ with flood irrigation. Thus, the mulched drip irrigation significantly enhances the water use efficiency; however, the salinization risk induced by the lack of leaching water must also be addressed.
• Select
  Snowfall changes in China during 1956-2010

  ZHANG Danwu, CONG Zhentao, NI Guangheng

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 381-386,393. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.007

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Changes in snowfall not only alter the temporal distribution of intra-annual runoff, but also the available annual water resources. The characteristics and temporal trend of snowfall were evaluated during the past five decades in China. Based on daily observations from 743 national meteorological stations for the period 1956-2010, an empirical relationship was used to identify precipitation types. The interpolated 10 km grid snowfall data was then analyzed at different time scales. The results indicate that the annual snowfall shows inter-decadal variations of "less-more-less" in the regions other than the Yangtze River region. The evenly distributed snowfalls in these regions during the cold season result in significant accumulation, which tends to yield more total annual runoff. Differently, decreasing annual snowfalls in the mid-and lower-reaches of the Yangtze River region are due to several single day snowfalls. So, the snowfall results in little runoff in these regions.
• Select
  Numerical simulation of the hydraulic characteristics of hilly irrigation systems

  LIU Jiahong, ZHOU Jinjun, WANG Hao, LV Hongxing

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 387-393. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.008

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The hydraulic characteristics of pressurized pipelines are important for irrigation system designs. The hydrodynamics irrigation pipes in a hilly terrain were analyzed here using a computational fluid dynamics model. The energy losses in the pipeline were calculated with the input discharge as the control variable. The relationship between the Reynolds number and flow resistance coefficient of a convex section (a 135° elbow) was analyzed. The pressure and velocity distributions are presented for the pipeline. The results show that:1) when the Reynolds number is less than 5.0×10⁴, the flow coefficient of the elbow decreases rapidly with increasing Reynolds number; 2) when the Reynolds number is more than 7.0×10⁴, the flow coefficient is nearly constant; 3) when the Reynolds number is in the range of 2.3×10⁴ and 7.0×10⁴, the flow coefficient ranges in 4.12~0.37. The pressure on the backside of the elbow is high, while the inside pressure is low. The velocity distribution is just the opposite with a low velocity near the backside of the elbow and higher velocities near the inside.
CONSTRUCTION MANAGEMENT
• Select
  Scale-economy conditions of China's listed real estate companies based on cost elasticity

  ZHANG Hong, CHEN Jiawei, WANG Yue, Vera Li

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 394-398,405. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.009

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Accurate understanding of the scale-economy conditions for real estate companies is the precondition for optimizing the company scale. Annual data from 38 listed real estate companies during 2005-2011 was used to calculate the cost elasticity with the translog cost function (TCF) model to judge the overall scale-economy conditions of listed real estate companies. The model is used to analyze the scale economy characteristics for different types of listed real estate companies in terms of asset size, ownership property and business coverage. The results show that there is an general scale economy for China's listed real estate companies and the scale-economy conditions improve over time. The results also show that during 2005-2011, scale economies existed in 26 listed real estate companies, 68.4% of the total. The scale-economy conditions show that listed real estate companies with asset values of 5×10⁹-10×10⁹ yuan are more successful than other companies, privately-owned companies are better than state-owned companies, and companies which cover less than 10 cities are better than the others.
• Select
  Simulated comparisons of resale housing sales brokerage patterns

  ZHANG Hong, ZHANG Yang, LI Vera, XU Zhao

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 399-405. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.010

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The effects of resale housing sales brokerage patterns on buyer's utility were investigated by the buyer's utility for different brokerage patterns. Actual resale housing trading processes were used to develop mathematical models of the buyer's utility for "single broker" and "double broker" patterns. Matlab was then used to simulate the buyer's utility and related indexes. The findings show that the "single broker" pattern has smaller buyer to broker incentives than the "double broker" pattern, but the broker's search efforts and buyer's utility are bigger. From buyer's utility perspective, the buyer should select the "single broker" pattern to promote the resale housing trading process when all other variables are unchanged.
  
PHYSICS AND ENGINEERING PHYSICS
• Select
  Optimization of a coil design for magnetic hyperthermia treatment based on the finite element method

  WU Jian'an, WU Zuhe, WANG Heng, LI Liya, TANG Jintian

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 406-410,416. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.011

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  A D-shaped coil improved the magnetic intensity and magnetic field uniformity over a circular coil for tumors in the head. The coil was designed using computer simulations and evaluated in trials with the center magnetic field intensity increased by 5.9%, and the valid treatment space increased by 4.6%. The coil also meets the design requirements.
• Select
  Information transfer efficiency based small-world assessment methodology for metro networks

  WANG Zhiru, SU Guofeng, LIANG Zuolun

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 411-416. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.012

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  This study presents an improved algorithm for the clustering coefficient in a metro network model. The algorithm is based on the information transfer efficiency that considers the differences between the directly and indirectly connected origin-to-destination stations. The algorithm was evaluated using 52 metro networks in the world. The information transfer efficiency based clustering coefficients for the 52 metro networks are between 0.195 and 0.407 (average 0.29), which is lower than the value given by P-Space (Space-of-Stops), but still considerably higher than the values for random networks (0.01 to 0.16, the average is 0.06) with the same size. Therefore, metro networks are small-world networks, although with a stricter evaluation model.
ECONOMICS AND MANAGEMENT
• Select
  CO₂ emissions in coastal and inland regions in China:Perspectives based on the final products

  PAN Wenqing, ZHANG Runjun, PAN Yuange

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 417-423. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.013

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Data in China's Coastal-Inland Bi-regional Input-Output Table of 2007 was analyzed using the spillover and feedback effects decomposition technique to identify "Who discharges CO₂" and "Who induces CO₂ emission". The inland region discharged 12×10⁸ t more CO₂ than the coastal region, but the coastal region induced 5.7×10⁸t more CO₂ emissions. Thus, there is "carbon leakage" from the coastal region to the inland region in China and policies that those who discharge bear responsibility are not fair. The differences between the actual CO₂ emissions and the cause of the CO₂ emissions from the industry perspective were also studied. The electrical supply and chemical products manufacturing industries, which are traditional high energy-consuming industries, discharged more CO₂but induced little CO₂, while the construction industry induced more CO₂ emissions in both the coastal and inland regions in China.
CHEMISTRY AND CHEMICAL ENGINEERING
• Select
  Molecular reconstruction model for petroleum fractions based on structure oriented lumping

  QIU Tong, CHEN Jincai, FANG Zhou

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 424-429. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.014

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  A molecular reconstruction method is given based on a structure oriented lumping model to predict petroleum fractions at the molecular level to achieve molecular management of refining processes. 22 basic structures were selected with relevant constraints. Then, 1 000 virtual molecules were constructed by the Monte Carlo method. Finally, the virtual molecules were adjusted according to the entropy maximization principle. The molecular reconstruction method predicts the petroleum fractions with relative errors between the properties and calibration data less than 3%.
• Select
  Optimal control of distillation columns based on a multiple model switching strategy

  WANG Zhenlei, CHEN Dengqian, WANG Xin

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 430-436. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.015

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Distillation columns have many features such as their nonlinear control equations and many random disturbances, which contribute to parameter variations in the mathematical model. This paper describes a method that combines multi-model switching control with the linear quadratic regulator (LQR) optimal method to solve the control problems that result from the parameter variation. The method combines the advantages of both methods. The parameter interval is first decomposed into sub-intervals with sub-models then built and combined into a model set. A sub-optimal controller is then designed using the LQR method and the controllers are switched to get the optimal controller based on the performance index function. Comparison of this method with the single LQR optimization method shows that with this method, the output concentrations at the top and the bottom of the distillation column remain stable when parameter Par jumps from 20 to 19.5.
AUTO MATION
• Select
  Lagrangian decomposition approach for solving continuous-time scheduling models of refinery production problems

  SHI Lei, JIANG Yongheng, WANG Ling, HUANG Dexian

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 437-447. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.016

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Continuous-time models need more computational effort to solve refinery production scheduling problems as the scheduling problem size increases. A new Lagrangian decomposition approach was used which divides the whole scheduling problem into nine subproblems. The convergence of Lagrange multipliers is accelerated by adding auxiliary constraints to the subproblems. This paper gives an initialization scheme for the Lagrange multipliers, a hybrid method to update the Lagrange multipliers and a heuristic algorithm to find feasible solutions. Computational results for three cases with different time horizons and different numbers of orders show that the Lagrangian scheme improves the computational efficiency and obtains optimal or near-optimal solutions.
• Select
  Frequency domain design method for decentralized control of multivariable processes

  XU Feng, PAN Qi, WANG Yilan, LUO Xionglin

  Journal of Tsinghua University(Science and Technology). 2016, 56(4): 448-452. https://doi.org/10.16511/j.cnki.qhdxxb.2016.24.017

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The input-output variable pairing and the control-loop configuration are the first steps in designing a decentralized control configuration for multivariable processes. The relative gain array (RGA) method and improved variations have been widely used for control system designs, but they generally utilize time domain process information that create challenges when dealing with long lag times, integrators, and unstable systems. This work describes a relative frequency gain method as the ratio of the open-loop frequency gain to the close-loop frequency gain. An interaction measurement index is given through averaging the differences between the relative frequency gain and (1, j0) in the full frequency domain. The interaction measurement index array is used to create a new control-loop pairing criterion for the control structure selection. This method makes better use of the dynamic process characteristics than existing methods through frequency domain analysis. The method is simple and effective, with long lag times, integrators, and unstable systems.