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The urban underlying surface may affect the thunderstorm process. However, current research on this phenomenon is still in its infancy. This paper aimed to analyze the influence of the urban underlying surface on the evolution of thunderstorm organization through ground observation and numerical simulation. The results indicated that when the thunderstorm system with strong synoptic conditions passed through the built-up area of Beijing, it exhibited obvious bifurcation and detour. The dynamic field of near-surface cold pools could serve as diagnostic indicators for understanding how the urban underlying surface affects the thunderstorm process. The large-scale compact-rise clusters in the city center could alter the movement direction and path of the cold pool outflow, thereby influencing the thunderstorm organization process. In addition to the spatial configuration of the building complex, the city size might also be an important factor influencing the thunderstorm process. This study might provide a fundamental foundation and technical support for predicting and assessing urban thunderstorm disasters. [ABSTRACT FROM AUTHOR]

The aim of this paper is to clarify the negative pressure distribution in drainage structures of soft foundations reinforced by vacuum preloading. The focus of this study was an actual engineering project, the Beijing–Shanghai high-speed railway; four different soil consolidation models were established using FLAC3D to consider various loading conditions. The consolidation process of the soft foundation was calculated and analyzed in detail. The results show that (1) the settlement developed rapidly within the first 30 days, slowed during the period between 20 and 30 days, and finally stabilized. (2) The settlement curves obtained from the four different models were highly consistent with the site monitoring curve for the first 5 days, after which point significant differences appeared. (3) During the first 20 days, the pore water pressure decreased noticeably within the depth range of 0–18 m. Between days 20 and 30, the rate of pore water pressure decrease slowed down, and after the 30th day, the pore water pressure remained constant at all depths. (4) Vacuum preloading affected the soil to a depth of approximately 16 m. A concave or linear distribution of negative pressure in the drainage structure was found to be a reasonable assumption, providing a reference for the numerical analysis of vacuum preloading. [ABSTRACT FROM AUTHOR]

The Pile-beam-arch (PBA) method is a new and effective construction method for the urban metro station. It is the key to ensuring the safe construction of the station to clarify the influence of PBA method construction on surface deformation under unfavorable geological and large span conditions. Based on a station of Beijing subway, this paper studies the surface deformation law of the large-span PBA method in different construction stages under silty clay–pebble composite stratum by means of FLAC 3D numerical analysis and field monitoring of level. Then the influence of the excavation scheme of the pilot tunnel and the construction scheme of the secondary lining of the arch on the surface deformation is simulated and analyzed. The results show that, through numerical simulation, the ratio of pilot tunnel excavation: pile-beam construction: vault initial support construction: vault secondary lining construction is about 5:1.1:3.3:0.6. The settlement deformation mainly occurs in the excavation stage of the pilot tunnel. Through the comparative analysis of the field monitoring results and the numerical simulation results, it can be seen that the two results are highly consistent, which verifies the accuracy of the numerical simulation results. The pilot tunnel excavation scheme of excavating the middle first and then excavating both sides, first through the upper layer and then through the lower layer, and the scheme of one-time construction of the secondary lining of the arch are better. The research results promote the further maturity and perfection of large-span PBA method construction under unfavorable geology and provide reference for similar projects. [ABSTRACT FROM AUTHOR]

To analyze the extent of fire risk in historic Chinese wooden structure buildings, the fire load characteristics of a historic temple in Beijing were studied. In this paper, thermogravimetric and cone calorimeter experiments were conducted on raw wood collected from historic Chinese buildings. Based on the experiment results, temple fire experiments were conducted in a full-scale model temple with high fire load in a historic Chinese wooden structure temple. FDS software was used to explore the characteristics of fire growth and spread in the initial fire. The results demonstrated that the pyrolysis kinetics parameters of historical wood were smaller than those of fresh wood. The reference temperature at 150°C with wood density of 410 kg/m3 in wooden structure building fire simulation was relatively credible. Flashovers are more likely to occur in historic wooden structure buildings of lower wood density and pyrolysis parameters. [ABSTRACT FROM AUTHOR]

Focuses on the collection of research papers on numerical acoustics during the International Congress of Theoretical and Computational Acoustics in Beijing, China. Discussion of the problems of contemporary research; Assessment of the accuracy problems of the boundary-element collocation method; Description of the appearance of viscoelastic material.

The investigation on the mechanical mechanism of the retaining and protection structure of superdeep excavations is an important subject, and its deformation control research is particularly important. Taking the deepest foundation pit with full-section overall excavation in Beijing as an example, this paper studies the stress and deformation characteristics of composite soil nailing wall and anchored soldier pile wall combined retaining system under complex geological conditions of multi-layer groundwater during the process of excavating 31.4 m deep. The Midas simulation software and monitoring data are used to analyze the construction process of foundation excavation. The simulated results and monitored values of anchor force, ground settlement, and soil deformation during foundation excavation are analyzed and discussed to verify the reliability of the model. The spatial effect of internal force and deformation of composite retaining and protection structure for superdeep foundation excavation is discussed, and the parameters affecting the retaining structure are analyzed and investigated. The research shows that with the increase of excavation depth, both the extremum of the bending moment and the extremum of lateral displacement of retaining piles are increasing, and the position of the extremum of bending moment is located near the excavation face; then, the bending moment reaches the maximum when the foundation pit is excavated to the bottom. Within a certain range, increasing the rigidity or the embedded depth of the retaining pile or the prestress of the anchor can effectively control the lateral displacement of the excavation. However, when the rigidity of retaining pile is too large, its lateral displacement does not change significantly. Similarly, when the embedded depth is too long or the prestress of the anchor is too powerful, the effect of controlling deformation is also not obvious. The research results will provide theoretical basis and practical experience for the design and construction of superdeep excavations. [ABSTRACT FROM AUTHOR]

• A two-population 3-strategy evolutionary game model for subway network operation extension. • Theoretical analysis and numerical simulation of Evolutionary Equilibria for the replicator dynamics system. • The best long-term strategies of networks and key factors (motivations) analysis. • An extended game model for investigating the impact of adjustment minutes. With the growing demand for night travel and the development of the night-time economy, extending the operation time of metropolitan subway networks has become essential. This paper proposes a 2-population 3-strategy evolutionary game model for subway network operation extension decisions, which considers the interests of subway companies, passengers, and the government while addressing transfer failure between lines due to uncoordinated subway operation time adjustments. The study resolves the Evolutionary Equilibria (EEs) of the replicator dynamics system and identifies key factors influencing the evolutionary path using theoretical calculations and a ternary phase diagram. Additionally, an extended game model investigates the impact of adjustment minutes. To verify the models, a case study based on the Beijing subway network is conducted. We show that the rule of maximum total fitness ensures the priority of EE strategies for all lines, selecting Nash equilibrium strategies for the lines which cannot select EE in a vastly reduced network strategy profile space (from 729 to 2). The study concludes that combining subsidy measures can eliminate multiple equilibria produced by implementing only penalty measures, and combining penalty measures can have the effect of making small subsidies as effective as large subsidies. The variation of the satisfaction/loyalty affects the system equilibrium only when both game players value passenger satisfaction/loyalty. Finally, we find that the proper adjustment minutes not only can make operation extension a long-term best strategy but also increase the payoff (106,158 RMB/year) and enhance the occupancy rate (20 %) of the last train. The study provides a theoretical foundation for the government to regulate the operation extension of subway companies from multiple perspectives. [ABSTRACT FROM AUTHOR]

Taking Beijing metro line 5 as the research vehicle model, the influence of different track structure on subway vibration is analyzed. According to the coupling dynamic equations of vehicle rail, the coupling dynamic equations of vehicle body models under integrated rail bed, plate rail bed and floating plate rail structure are established, respectively, and the vibration response of vehicle body models under three kinds of rail structure is calculated. The evaluation indexes of dynamic characteristics of rail coupling are analyzed. The analysis results show that with the increase of subway speed, the vertical displacement and acceleration between the vehicle and the middle point of the track gradually increase, and the vibration response of the fourth wheel to the maximum wheel-rail force also gradually increases. With the increase of the buried depth of subway tunnel, the maximum vertical displacement and ground motion acceleration of the three tracks gradually decrease, which indicates that this method can accurately analyze the vibration response of subway under different track structures. [ABSTRACT FROM AUTHOR]

Abstract: Since the thermophysical properties of water change dramatically at near-critical and pseudocritical point, the instability of natural circulation at supercritical pressure may occur in a loop. To predict the region of instability of natural circulation at supercritical pressure, a test loop was built at Tsinghua University. The paper presents the information of the test loop and a numerical analysis model for the loop. The paper verified the numerical analysis code by experiment results and using the code to analyze the instability of the loop. The paper concludes conclusion that there will be no Ledinegg instability occurring at supercritical pressure in the loop. [Copyright &y& Elsevier]

The Variational Doppler Radar Analysis System (VDRAS) was implemented in Beijing, China, and contributed to the Beijing 2008 Forecast Demonstration Project (B08FDP) in support of the Beijing Summer Olympics. VDRAS is a four-dimensional variational data assimilation system that produces frequently updated analyses using Doppler radar radial velocities and reflectivities, surface observations, and mesoscale model data. The system was tested in real time during the B08FDP pretrials in the summers of 2006 and 2007 and run during the Olympics to assist the 0--6-h convective weather nowcasting. This paper provides a description of the upgraded system and its Beijing implementation, an evaluation of the system performance using data collected during the pretrials, and its utility on convective weather nowcasting through two case studies. Verification of VDRAS wind against a wind profiler shows that the analyzed wind is reasonably accurate with a smaller RMS difference for 2006 than for 2007 due to better radar data coverage in 2006. The analyzed cold pools in three convective episodes are compared with surface observations at selected stations. The result shows good agreement between the analysis and the observations. The two case studies demonstrate the role that VDRAS could play in nowcasting convective initiation. [ABSTRACT FROM AUTHOR]

The Beijing 2008 Forecast Demonstration Project (B08FDP) included a variety of nowcasting systems from China, Australia, Canada, and the United States. A goal of the B08FDP was to demonstrate state-of-the-art nowcasting systems within a mutual operational setting. The nowcasting systems were a mix of radar echo extrapolation methods, numerical models, techniques that blended numerical model and extrapolation methods, and systems incorporating forecaster input. This paper focuses on the skill of the nowcasting systems to forecast convective storms that threatened or affected the Summer Olympic Games held in Beijing, China. The topography surrounding Beijing provided unique challenges in that it often enhanced the degree and extent of storm initiation, growth, and dissipation, which took place over short time and space scales. The skill levels of the numerical techniques were inconsistent from hour to hour and day to day and it was speculated that without assimilation of real-time radar reflectivity and Doppler velocity fields to support model initialization, particularly for weakly forced convective events, it would be very difficult for models to provide accurate forecasts on the nowcasting time and space scales. Automated blending techniques tended to be no more skillful than extrapolation since they depended heavily on the models to provide storm initiation, growth, and dissipation. However, even with the cited limitations among individual nowcasting systems, the Chinese Olympic forecasters considered the B08FDP human consensus forecasts to be useful. Key to the success of the human forecasts was the development of nowcasting rules predicated on the character of Beijing convective weather realized over the previous two summers. Based on the B08FDP experience, the status of nowcasting convective storms and future directions are presented. [ABSTRACT FROM AUTHOR]

In this paper, we propose a traffic flow model to study the effects of the real-time traffic state on traffic flow. The numerical results show that the proposed model can describe oscillation in traffic and stop-and-go traffic, where the speed–density relationship is qualitatively accordant with the empirical data of the Weizikeng segment of the Badaling freeway in Beijing, which means that the proposed model can qualitatively reproduce some complex traffic phenomena associated with real-time traffic state. [ABSTRACT FROM AUTHOR]

To evaluate the effect of phase change materials (PCMs) on the indoor thermal environment of greenhouses under different weather conditions and over a long time in the heating season, a study was carried out using both experimental method and numerical method. The study was conducted in a typical greenhouse located in Beijing, China, and important parameters have been monitored continuously for 61 days, including indoor air temperature, outdoor air temperature, solar radiation, surface temperature of greenhouse envelopes and soil temperature. Based on these parameters, a number of indicators, namely, operative temperature, daily effective accumulative temperature, irradiated surface temperature of the north wall, average temperature of PCMs, and daily heat storage and release, have been used to evaluate the performance of PCMs in greenhouses. All indicators have provided consistent results that confirm the positive effect of PCMs on improving the indoor thermal environment of greenhouses over a long time. Additionally, the paper has demonstrated that a sunny weather could help to promote the efficiency of PCMs, comparing to a cloudy weather. [ABSTRACT FROM AUTHOR]

The impacts of anthropogenic heat emissions, urban land use, and aerosols on a snowfall event in Beijing were investigated by using the Weather Research and Forecasting model. The results show that urban land use and anthropogenic heat emissions can reduce the accumulation of snowfall by 17%–22% within the fifth ring road, which depends on the aerosol number concentration and size. The increase in aerosols (same land use and anthropogenic heat emissions) can increase the accumulated snowfall within fifth ring road, especially for accumulated and coarse mode. Urban land use, anthropogenic heat emissions, and aerosols have different effect on snowfall, which depend mainly on relatively humidity. Urban land use and anthropogenic heat emissions lead to the formation of an "urban heat and dry island," which is not favorable to snowfall processes during the initial snowfall processes and leads to a decrease in ice crystals and snow by 47% averaged. At this time, the increase in aerosol number concentrations has less impact (increase by 5% averaged) on snowfall because of higher supersaturation required for activation. With the development of snowfall processes, the feedback of cloud microphysics decrease temperature and increase relative humidity, which is favorable to snowfall process and increase snowfall slightly by 5% averaged. Meanwhile, the critical radius of aerosols that can be activated decrease, smaller particle aerosols are activated to form supercooled cloud water and further to form ice crystals and snow, which leads to an increase in accumulated snowfall by 11% averaged. Plain Language Summary: Urban are places where humans live, but human activities including urban land use changing, anthropogenic heat, and aerosols emissions can change local weather, especially local precipitation. It's important to know how human activities affect precipitation to avoid urban flooding and provide a theoretical basis for artificial impact weather. We analyzed the impact of urban land use, anthropogenic heat, and aerosols emissions on a snowfall over Beijing by using numerical simulation. Urban land use and anthropogenic heat emissions lead to the formation of the "urban heat and dry island," which leads to a decrease in the initial snowfall but slightly increase snowfall in the later period. The effect of aerosols on snowfall is related to number concentration and size. And the increase in aerosol number concentrations has less impact on snowfall at the initial period due to the lower supersaturation produced by the urban heat and dry island but increase snowfall in the later period due to higher supersaturation caused by the feedback of the cloud microphysics. Key Points: The interaction effects of urban environment, aerosol, large‐scale environment, and cloud microphysical processes reduce 16%–22% snowfallThe urban heat and dry island reduce 47% snowfall at the initial period and slightly increase 5% snowfall at the later periodThe increase of aerosols has the increase effects on snowfall, which increases about 5% and 11% at the different periods, respectively [ABSTRACT FROM AUTHOR]

Abstract: The use of groundwater flow models is prevalent in the field of environmental hydrogeology. Models have been applied to investigate a wide variety of hydrogeological conditions. Recently, groundwater models have been applied to predict the fate and transport of contaminants for risk evaluation purposes. In this paper, a transient groundwater flow model in Daxing district of Beijing, China was developed. The conceptual model was built by analyzing the hydrogeological data. Hydraulic conductivities have been calibrated by the steady state model. The storage coefficients are calibrated by the transient model based on the available data observed from 1995 to 2000, which provides insights to understand the dynamic behavior of groundwater systems and to predict spatial-temporal distributions of groundwater levels in responding to changes. The model results help to identify the aquifer properties and to analyze the groundwater flow dynamics, the changes of groundwater levels, in addition, the improvement of the groundwater level monitoring network will be proposed through the analysis of groundwater levels. The calibrated transient model will be used later to predict the impacts of water resources management schemes on groundwater in the study area. [Copyright &y& Elsevier]

Abstract: The groundwater heat pump (GWHP) system utilizes groundwater as alternative renewable and clean energy source for space heating and cooling, which is an open-loop system that withdraws water from a production well, passes it through a heat exchanger and discharges the water into an injection well. By utilizing the relatively stable temperature of groundwater, GWHP system can work with a higher coefficient of performance. It is necessary to evaluate the aquifer capacity for the proper design and application of GWHP. In this paper, a numerical method of underground heat transfer, energy balance method and thermal storage method were presented to calculate the load capacity of a unit area of shallow aquifer. The model results indicate that the numerical method, which is based on performance efficiency of groundwater heat pump, reflects the behavior of groundwater pumping and recharging processes, and better than energy balance method and thermal storage method, additionally it has the advantages of energy saving and environmental protect. The capacity is positively related to aquifer thickness. The final results show that it is easy for ground water recharging in alluvial and pluvial fan located at the piedmont, while load capacity is relatively smaller. In contrast, it is difficult for groundwater recharging in south-east plain where a larger load capacity is obtained. [Copyright &y& Elsevier]

Abstract: An elasto-plastic model originally developed at Tsinghua University (Tsinghua elasto-plastic model) for soils reflects the observed non-linearity and dilatancy of soils in laboratory tests. The model incorporates a yield criterion, an associated flow rule and a work-hardening law, which can be determined by laboratory tests. This paper presents a modified Tsinghua elasto-plastic constitutive model, which incorporates a function of plastic work as the hardening parameter in the original Tsinghua elasto-plastic model. The modified model has 12 parameters, which are easily determined using conventional triaxial shearing and isotropic compression tests. It can be used to describe strain hardening followed by strain-softening behaviour and to simulate dilatancy during shear application. The modified model was used to determine the relationship between load and settlement for a shallow footing founded on dense Yongding River sand. The results of the numerical analyses were in agreement with the results of hydraulic gradient laboratory tests. The results showed in a preliminary way that the modified model developed in this study was effective for simulating the strain-softening boundary-value problems common in geotechnical engineering. [Copyright &y& Elsevier]

In this paper, a numerical method of the rising groundwater level is presented through an elastoplastic constitutive model for the unsaturated soil and a numerical realization method for the rising groundwater level. A model test of the rising groundwater level is conducted to validate the rationality of the presented numerical method. Taking an interval subway tunnel in Beijing as the background, a numerical simulation with a homogeneous soil layer, which contians the existing tunnel, is conducted according to the presented numerical method of the rising groundwater level. Based on the numerical simulation results, the variations of the ground saturation, the ground stress state, and the ground vertical deformation under the condition of the rising groundwater level are studied through a homogeneous soil layer, and the normal contact pressure on the outer surface of the lining, the radial deformation, the bending moment, the hoop thrust, and the shear force of the lining under the condition of the rising groundwater level are analyzed through a homogeneous soil layer with the existing tunnel. [ABSTRACT FROM AUTHOR]

An online air pollutant tagged module has been developed in the Nested Air Quality Prediction Model System (NAQPMS) to investigate the impact of local and regional sources on the air pollutants in Beijing during the Campaign of Air Quality Research in Beijing 2006 (CAREBeijing-2006). The NAQPMS model shows high performance in simulating sulfur dioxide (SO2), particulate matter (PM10), nitrogen dioxide (NO2), and ozone (O3) with overall better agreements with the observations at urban sites than rural areas. With the tagged module, the air pollutant contributions from local and regional sources to the surface layer (about 30m) and the upper layer (about 1.1 km) in Beijing are differentiated and estimated. The air pollutants at the surface layer in Beijing are dominated by the contributions from local sources, accounting for 65% of SO2, 75% of PM10 and nearly 90% of NO2, respectively, comparatively, the 1.1 km layer has large source contributions from the surrounding regions (e.g., southern Beijing), accounting for more than 50% of the SO2 and PM 10 concentrations. County scale analysis is also performed and the results suggest that Tianjin is the dominant source of SO2 in Pinggu County, and Langfang, Hebei is the most important regional contributor to PM10 in Beijing. Moreover, the surrounding regions show larger impact on SO2, PM10 and NO2 in the eastern counties of Beijing (e.g., Pinggu, Tongzhou and Daxing) than those in western Beijing, which is likely due to the Beijing's semi-basin topography and the summer monsoon. Our results indicate that the efforts to control the air pollutants in Beijing should focus on controlling both local and regional emissions. [ABSTRACT FROM AUTHOR]

Under strong earthquakes, long-span spatial latticed structures may collapse due to dynamic instability or strength failure. The elasto-plastic dynamic behaviors of three spatial latticed structures, including two double-layer cylindrical shells and one spherical shell constructed for the 2008 Olympic Games in Beijing, were quantitatively examined under multi-support excitation (MSE) and uniform support excitation (USE). In the numerical analyses, several important parameters were investigated such as the peak acceleration and displacement responses at key joints, the number and distribution of plastic members, and the deformation of the shell at the moment of collapse. Analysis results reveal the features and the failure mechanism of the spatial latticed structures under MSE and USE. In both scenarios, the double-layer reticulated shell collapses in the 'overflow' mode, and the collapse is governed by the number of invalid plastic members rather than the total number of plastic members, beginning with damage to some of the local regions near the supports. By comparing the numbers and distributions of the plastic members under MSE to those under USE, it was observed that the plastic members spread more sufficiently and the internal forces are more uniform under MSE, especially in cases of lower apparent velocities in soils. Due to the effects of pseudo-static displacement, the stresses in the members near the supports under MSE are higher than those under USE. [ABSTRACT FROM AUTHOR]

In this study, an extreme rainstorm that occurred in the Beijing–Tianjin–Hebei (BTH) region in China on 19–20 July 2016 is simulated and analyzed using the Weather Research and Forecasting model, coupled with a multilayer urban canopy scheme, to reveal the impact of urbanization on the extreme precipitation process in the region. The results show that the urban heat island effect (that is, surface warming and an increased near-ground sensible heat flux, which leads to increased vertical motion and atmospheric instability layer strengthening) plays a dominant role in the urban modification of rainfall during the early stages of urbanization, resulting in an increase of 6–10 mm in average hourly precipitation in urban and downwind areas. With the further development of urbanization in the BTH region, particularly in the big cities of Beijing and Tianjin, the large-scale expansion of the urban surface reduces the surface moisture, the evaporation of surface water from the ground, and the height of the atmospheric boundary layer, leading to an urban dry island effect brought about by the lack of near-surface water vapor, which inhibits an increase in precipitation. The positive effect of the urban heat island on precipitation was offset by the urban dry island effect, so the increase in precipitation in the urban areas was not obvious, but an increased range of 8–10 mm was noted. The existence of large cities changes the position of the strong upward movement of air, and convective upward movement is more likely to occur between the suburbs. With the further expansion of the underlying surface of the adjacent cities of Beijing and Tianjin, the upward movement between the two cities coincides, leading to an obvious increase in precipitation between the two cities. [ABSTRACT FROM AUTHOR]