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百年期刊
ISSN 1000-0585
CN 11-1848/P
Started in 1982
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Table of Content
, Volume 61 Issue 6
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DISASTER PREVENTION AND MITIGATION
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Coupled disaster scenario evaluation and response method based on the E-LVC technology
DENG Qing, SHI Chenghao, WANG Chenyang, CHEN Bin, GAO Yang, ZHANG Hui
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 487-493. DOI: 10.16511/j.cnki.qhdxxb.2021.22.002
Abstract
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An E-LVC (enhanced, live, virtual simulation, constructive simulation) technology based coupled disaster scenario evaluation and response method is developed to improve responses to large coupled disasters. The method maps the complex disaster environments using bionic navigation and positioning systems with the dynamic interactions of E-LVC based disaster rescue robots and data from large experiments and simulations. In a coupled disaster scenario, rescue robots can enter disaster sites to explore the site environments and report front-line field data which can be used to map the disaster site conditions as a foundation for emergency disaster response. The system is used with a case study of a hypothetical major earthquake scenario in Beijing that creats many fires driven by high winds to evaluate emergency evacuation responses including personnel evacuation and large-scale traffic evacuation to verify the ability of this system to support emergency response decision-making.
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Experimental research on extinguishing paraffin wax fires
GAO Yang, DENG Qing, LI Yu, ZHANG Hui
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 494-501. DOI: 10.16511/j.cnki.qhdxxb.2020.22.041
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This study developed an experimental model for extinguishing paraffin wax fires. The model used a standard tube gun fire extinguisher and a standard fire extinguisher. The paraffin pan fire extinguishing experiment evaluated the extinguishing effects of typical extinguishing agents, including direct water flow, foam, hydrogels, dry powders, and carbon dioxide. The experiments yielded data for the thermal radiation and temperature changes during the paraffin fires. The extinguishing efficiency was then assessed from the data. The assessments included the extinguishing time, the needed amount of extinguishing agent, the cooling effect, the effect of radiation and the ability to prevent boil over, splashing and rekindling of the fire. This study then compared the fire extinguishing efficiencies, advantages and disadvantages of various extinguishing agents, and application methods for the various extinguishing agents. This study develops the theory of fusible solid fires and improves fire-fighting techniques and personnel protection capabilities.
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Characterization of
n
-heptane annular pool fires based on flame shape and texture features
LI Cong, MA Xun, YANG Rui, ZHANG Hui
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 502-508. DOI: 10.16511/j.cnki.qhdxxb.2020.22.042
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The key characteristics of various size
n
-heptane annular pool fires were experimentally analyzed in this study. The experiments controlled the inner and outer diameters of the annular pool fires. The annular fire flame structures were then analyzed with measurements of the shape and texture features of the flame images. The results show that the flame generates from the outer edge of the annular pool and spreads toward the center. A hollow area develops inside the flame with this area growing as the ratio of the inner to outer diameters increases. For a constant outer diameter, the flame area, perimeter, contrast, entropy, and correlation all decrease with increasing diameter ratio, while the energy increases. A principal component analysis shows that the first two principal components related to the ratio of the inner to outer diameters have high contribution rates larger than 95%, so they can be used to quantify annular flames.
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Construction and deduction of rainstorm disaster scenarios based on Bayesian networks
JIANG Bo, ZHANG Chao, CHEN Tao, YUAN Hongyong, FAN Weicheng
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 509-517. DOI: 10.16511/j.cnki.qhdxxb.2020.22.039
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Rainstorm disasters are characterized by high intensity and long duration that lead to secondary events and difficult emergency response. This study analyzed rainstorm risks from a global perspective. An emergency scenario was constructed that considered the complexity of the secondary events to analyze the entire development of a rainstorm scenario. A Bayesian network (BN) was used with various risk factor probabilities to analyze the flood risks caused by various rainstorms. The key nodes in the network were then identified by a sensitivity analysis of the risk factors. The results show that the rainstorm risk analysis based on this BN model can help decision makers evaluate storm conditions, develop response plans, identify key risk factors, and improve the timeliness and effectiveness of emergency responses.
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Comparative research on disasters evolution of over-flow and dam-break mode based on conditional judgment model
CHEN Changkun, XU Tong, JI Lulu, ZHANG Yulun, LEI Peng
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 518-526. DOI: 10.16511/j.cnki.qhdxxb.2020.21.014
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A model was developed to describe the evolution of over-flow and dam-break disasters based on critical judgments of the disaster evolution. The model accounts for the effects of various types of causes, self-recovery characteristics, repairs, internal noise and impacts from outside the system. The model was then used in a parametric study of critical disaster parameter values and disaster evolution delay coefficients. The results indicate that the destructive impact of dam-breaks is far greater than that of overflows. In addition, increasing the critical value of the disaster significantly affects the evolution of an over-flow disaster. The disaster losses at a given time, especially the event evolution following a dam break, are reduced by a larger delay coefficient. This models gives insights on disaster evolution that can be used to improve preparedness and disaster response management.
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Emergency warning information repost behavior of Weibo users
CHEN Anying, ZHU Haoran, SU Guofeng
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 527-535. DOI: 10.16511/j.cnki.qhdxxb.2020.26.045
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Online social networks, such as Sina Weibo, are playing increasingly important roles in disseminating early warning information. This paper uses disaster warning information as an example to analyze the motivation of users for spreading emergency warning information on Sina Weibo from the perspectives of interest correlation, rational thinking and user interest. The results show that a regional index and an interest index predict user warning information repost behavior. The prediction accuracy of this model is similar to related research and is interpretable. This research can predict and identify user repost behavior which can facilitate delivery of emergency warning information and expand the information spread.
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Community evacuation scheme based on multi-objective programming and agent simulations
ZHANG Jing, CHEN Tao, HUANG Lida, SU Guofeng, SUN Zhanhui, CHEN Jianguo
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 536-542. DOI: 10.16511/j.cnki.qhdxxb.2020.22.032
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Residents need to be quickly evacuated from buildings after earthquakes. However, shelters need to be built in advance and community evacuation schemes need to be developed to provide effective emergency response after an earthquake. This paper presents a community evacuation scheme design method using multi-objective programming and agent simulations. The optimal evacuation schemes are developed based on the accessibility of rescue agencies, traffic conditions, shelter capacity and other factors based on various numbers of earthquake shelters using multi-objective programming with the evacuation behavior simulated using the Pathfinder software. The results show that the particle swarm optimization algorithm has good convergence for the multi-objective programming problem of location selection and allocation of earthquake shelters, and is suitable for quick modeling and calculation. The evacuation scheme of designated earthquake shelters is instructive, which can greatly alleviate the "overload" phenomenon of free evacuation scheme and ensure that all personnel can arrive at the shelters as soon as possible.
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Rockburst prediction based on oversampling and objective weighting method
TANG Zhili, WANG Xue, XU Qianjun
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 543-555. DOI: 10.16511/j.cnki.qhdxxb.2021.22.013
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Machine learning rockburst predictions seek to solve the data imbalance problem and improve the prediction accuracy and model generalization. This work optimized a rockburst prediction algorithm using a dataset containing 246 rockburst cases and 6 rockburst indicators,
B
1
, MTS, SCF, UCS, UTS and
W
et
. Nine rockburst prediction models were developed based on machine learning algorithms to study the effects of 5 oversampling methods and 5 objective weighting methods on the model predictions. The results show that data oversampling improves the model accuracy by 11.8% to 52.3% and increases the macro average
F
1
by 13.0% to 50.0%. Random oversampling gives the best improvements to resolve the data imbalance problem. After randomly oversampling the data set, objective date weighting only increases the accuracy and the macro average
F
1
of the extreme gradient boosting algorithm (XGBoost) model by 1.1% and 1.2%, the random forest (RF) model by 2.1% and 2.3%, the decision tree (DT) model by 10.7% and 11.8%, and the extremely randomized trees (ET) model by 12.9% and 12.8%. The multi-layer perception (MLP) algorithm model based on random oversampling is the best rockburst prediction model with an accuracy of 0.917 and a macro average
F
1
of 0.920.
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PROJECT AND TRANSACTION MANAGEMENT
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Optimization of PPP project transaction structures based on resilience goals
WANG Yingying, GAN Tian, WANG Shouqing
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 556-564. DOI: 10.16511/j.cnki.qhdxxb.2021.22.006
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Transaction structures are the core mechanisms of public-private partnership (PPP) project governance. These directly affect the interest, risk and responsibility distributions among the stakeholders. Resilience goals optimize the structure to enhance the long-term project sustainability. This paper analyzes the resilience goal definition and its applicability to PPP projects. Then, the optimization principles for risk resilience, self-development, force majeure resilience and crisis resilience are used to develop an optimization framework based on resilience goals for the optimization objectives of the government institutions, social capital, contract system and facility capabilities. Finally, the differences between an incremental project and a stock project are discussed along with how to optimize the project transaction structure based on the optimization framework. The optimization involves setting up a project company through investment in the project transaction, implementing operational projects and continuously supplying infrastructure and public services. The results show that the framework and project transaction structure optimization path identified in this study based on the resilience goals provide flexible optimization principles, support strategies and optimization elements that benefit the long-term risk reduction characteristics of PPP projects.
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Endowment effect in corporate mergers and acquisitions and its impact on takeover premiums
TANG Jian, ZHANG Hong
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 565-572. DOI: 10.16511/j.cnki.qhdxxb.2020.26.039
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The endowment effect is a common behavioral bias in commodity transactions, usually manifested by the owner of an item having a higher evaluation of the item’s worth than the buyer. This study used a multivariate regression analysis to analyze 425 takeovers from 2010—2018 in which both parties were U.S. listed companies to study the endowment effect in mergers and acquisitions and its impact on the takeover premiums. The results show that there is an endowment effect that significantly increases the takeover premiums with the impact varying in different industries and being more prominent in emerging industries. The acquirers should fully consider the high takeover cost caused by the endowment effect when evaluating the target company. Policy makers should pay attention to the welfare loss caused by the endowment effect when making industry organization policies.
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Quantitative analysis of the impact of sponge city construction on housing prices with Suining city in Sichuan Province as an example
SHEN Yang, XU Yuanxin, WU Jing
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 573-581. DOI: 10.16511/j.cnki.qhdxxb.2021.22.005
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The sponge city method is a new concept that has been vigorously advocated in recent years in China's urban construction and renewal. This method improves the construction ecology, reduces urban flood risks and promotes water recycling. Thus, sponge city construction improves the living environment and enhances people's willingness to pay for housing. This study analyzes Suining city in Sichuan Province as an example to study the impact of sponge city construction on the housing market price. The analysis shows that sponge city construction increases the average community housing price per year by 385.2 Yuan/m
2
(or 5.48%) with the pricing premium appearing from the rainy season in Suining. The sponge city construction increases the local economic benefit of Suining by 3.985 billion Yuan from housing price premium. The overall benefit is 6.302 billion Yuan considering all the contributions, which exceeds the construction cost.
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Analysis of households' willingness to pay for residential building seismic resilience
WANG Qiuyi, WU Jing, PAN Peng
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 582-590. DOI: 10.16511/j.cnki.qhdxxb.2020.25.040
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The seismic resilience of buildings has attracted increasing research attention for earthquake prevention and damage mitigation. However, there have been few studies using economic analyses. This study minimized the building life-cycle costs with two models used to quantify the household willingness to pay (WTP) for improved residential building seismic resilience based on two subjective utility models using expected utility theory and prospect theory. Then, the household WTP for residential building seismic resilience was calculated and compared with the corresponding incremental costs using parameters from the
Standard for Seismic Resilience Assessment of Buildings
for selected new residential buildings in Beijing in 2017 as an example. The results show that improving the residential building seismic resilience to the 1 or 2 star levels is financially feasible. However, further development to the 3 star level still relies on government subsidies or other support. This study also provides some policy implications to increase the household WTP for building seismic resilience.
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HYDRAULIC ENGINEERING
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Simulated power control for doubly-fed pumped storage units
HU Wanfeng, FAN Honggang, WANG Zhengwei
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 591-600. DOI: 10.16511/j.cnki.qhdxxb.2020.22.025
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The control system for doubly-fed pumped storage units used to regulate the grid power was modeled using a hydraulic-mechanical-electric coupled system of the pumped storage power plant for transient process. The power control system modeled a doubly-fed induction machine (DFIM) using the stator voltage oriented vector control strategy. The model was used to study the power regulation of a 300 MW doubly-fed variable speed unit connected to an infinite bus with comparisons to a conventional fixed-speed unit with an electrically excited synchronous machine. The results show that the DFIM stator active power can be controlled directly by the rotor current so that the stator active power of the variable speed unit can accurately track the power reference. The fixed-speed unit output power is the mechanical power generated by the pump turbine, which can be changed by modifying the guide vane opening and adjusting the flow. However, the penstocks are quite long, so the flow rate and the power of the fixed-speed unit change slowly.
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Numerical predictions of the total dissolved air distribution and its effect on fish in a reservoir with the Eulerian-Lagrangian model
HUANG Juping, HUANG Yinghan, OU Yangming, WANG Yuanming, FENG Jingjie, LI Ran
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 601-609. DOI: 10.16511/j.cnki.qhdxxb.2020.26.032
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Flow over a spillway discharge becomes supersaturated with dissolved air. The air slowly dissipatesbut the water remains supersaturated a long distance downstream of the dam, especially in the deep reservoir areas of cascade power stations. The supersaturated air can then be lethal to fish. Current research cannot completely simulate the fish movements and exposure timesin the various gas concentrations; therefore, the total dissolved gas (TDG) residence time was used to characterize the influence of the gas on fish in this study. However, neither the Eulerian model nor the Lagrangian model can simulate both the gas distribution and the residence time. Thus, this study used a combined three dimensional Eulerian-Lagrangian model of the air dissipation including dissipation in the water and mass transfer at the water surface. Particle tracking was used to estimate the tailrace residence time and the gas exposure time. The model was used to estimate the fish injury probability due to supersaturated air in the Tongjiezi reservoir in the Dadu River based on previous experimental data for the fish air tolerance ability. This study provides a method to analyze fish injury from supersaturated air and to optimize spillwaydischarge flows.
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COMPUTER SCIENCE AND TECHNOLOGY
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Approximate computing method based on memristors
JI Yu, ZHANG Youhui, ZHENG Weimin
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 610-617. DOI: 10.16511/j.cnki.qhdxxb.2020.22.027
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Memristors are non-volatile memory devices that are also capable of colocation computations. General-purpose computations can use memristors to approximate arbitrary functions with neural networks or can use memristors to model basic gate circuits that then perform arbitrary Boolean logic calculations. However, the use of memristors to approximate arbitrary functions does not have controllable errors and the use of memristors to model basic gate circuits is slower than conventional digital circuits. This paper presents a general-purpose approximate computing paradigm for memristors and a memristor based hardware architecture, general-purpose field programmable synapse array (GP-FPSA), that combines the advantages of these two methods for efficient general-purpose approximate computing with controllable errors. A universal approximating construction method is used to resolve the large, uncontrollable error of directly training a neural network for approximations. Then, the model control flow splits complicated functions to reduce the construction cost. The memristor-based architecture significantly improves the computational power for general-purpose computing.
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Distributed-optimization-based mix-flow scheduling mechanism for data center networks
ZHANG Tong, REN Fengyuan, SHU Ran
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 618-625. DOI: 10.16511/j.cnki.qhdxxb.2020.21.018
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Data center networks are key cloud computing infrastructure whose performance critically impacts the quality of service. Currently, data centers have multiple services with both deadline and non-deadline flows. This paper presents a distributed-optimization-based mix-flow scheduling (DOMS) mechanism to meet the transmission requirements of both types of flows. First, the optimization goals and transmission constraints are defined for both kinds of flows and the mixed-flow scheduling problem is formalized as a real-time rate allocation problem. Then, a coordinated scheduling structure is designed for the hosts and switches that leverages the dual decomposition characteristics of the problem. This method uses a distributed solution method to solve the problem with the flow rates evolving to a global optimal solution. Simulations show that this method effectively reduces deadline miss rates for deadline flows as well as flow completion times for non-deadline flows.
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ENGINEERING MECHANICS
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C
1
natural element method for plastic limit analyses of thin plates
ZHOU Shutao, MA Binjie, HOU Chuantao, TONG Jun, JU Yatang, LIU Yinghua
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 626-635. DOI: 10.16511/j.cnki.qhdxxb.2020.25.041
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The C
1
natural element method (C
1
NEM) was used to study the limiting loads of circular, rhombic, and equilateral polygon thin plates subjected to various loading conditions. An iterative solution for the upper load limits of the thin plates made the generalized stress fields satisfy the equilibrium equations and the boundary conditions. Iterative solutions were also used to calculate the lower limits of the load multipliers of thin plates using the lower bound theorem to obtain the generalized stress fields. This numerical method overcomes the difficulties introduced by the strong nonlinearity of the constraint condition in the lower bound theorem and reduces the calculations for the lower bound analysis in an easily implemented algorithm. This numerical approach can also be incorporated into upper bound analyses to estimate the limiting loads of thin plates. Numerical examples show that this numerical method can accurately and quickly predict the upper and lower load limits of thin plates.
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Fault tree analysis of an aircraft flap system based on a non-probability model
ZHOU Changcong, CHANG Qi, ZHOU Chunping, ZHAO Haodong, SHI Zhuangke
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 636-642. DOI: 10.16511/j.cnki.qhdxxb.2020.22.44
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A fault tree based system reliability method was developed to predict the failure probabilities of system components by a non-probability interval model. A non-probabilistic reliability index was developed which included reliability or safety criteria to evaluate the system reliability. Then, two sensitivity indices were developed to indicate the contribution of each basic event. This method was then used for a fault tree analysis of the unilateral asymmetric movement of an aircraft flap system. The results show that this method can accurately predict the system reliability and can accurately identify important events to provide references for optimizing the system reliability.
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MECHANICAL ENGINEERING
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Research progress on wear mechanism of hard materials worn by soft polymers
GUO Fei, CHENG Ganlin, ZHANG Zhaoxiang, HUANG Xing, JIA Xiaohong
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 643-652. DOI: 10.16511/j.cnki.qhdxxb.2021.22.011
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Polymer friction and wear has always been important in tribology research. Friction studies of hard material pairs such as metals and ceramics have generally focused on the lower hardness wear due to the order of magnitude difference in hardness. However, the friction can also wear the hard material surface which has led to increasing interest in the wear of hard materials by soft polymers. This paper reviews the research on the wear of hard materials by soft polymer materials for the past 70 years, and summarizes the observed wear mechanism and the factors influencing the hard material wear. This paper then summarizes the challenges and key problems for this special wear phenomenon and future research trends investigating the wear mechanism of hard material worn by soft polymers.
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Ring-diode capacitance detection circuit characteristics
ZHOU Xiaotong, ZHANG Rong
Journal of Tsinghua University(Science and Technology). 2021,
61
(6): 653-658. DOI: 10.16511/j.cnki.qhdxxb.2020.21.012
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The accuracy of micro-capacitance detection systems in gyroscopes directly determines the rotor displacement measurement accuracy, which in turn determines the overall accuracy of the gyroscope. A micro-capacitance detector was developed in this study based on ring-diode demodulation for the special structure of a spinning-rotor gyro. The system output gain variations were studied to develop a gain algorithm based on the leakage minimization principle with a noise reduction algorithm to reduce the output noise. This micro-capacitance detection method based on ring diodes reduces the noise which improves the capacitance detection resolution. Tests show that the optimized circuit gives a capacitance resolution of better than 20.0 aF and a resolution at the unit bandwidth of better than 0.258 aF·Hz
-1/2
which is excellent capacitance measurement accuracy.
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