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On August 20, 2019, many catastrophic debris flows broke out in meizoseismal area of Wenchuan M s 8.0 earthquake in China under the influence of continuous heavy rainfall. This paper takes the Chutou gully debris flow event occurred on August 20, 2019 as an example. The 3-D numerical simulation software, RAMMS, is used to back calculate the event and predict the future hazard. Coulomb and viscous turbulent friction, μ and ξ are calibrated in RAMMS. Numerical simulation reveals the movement process of Chutou gully from the aspects of flow depth, velocity, discharge, and run-out solid materials volume. The simulation results show that more than two-thirds of the solid materials are still deposited in the main channel, which could provide material basis for the re-occurrence of high hazard debris flow. In addition, based on the intensity and probability of debris flow, the hazard of debris flow is divided into high, middle, and low degrees. According to the simulation results and hazard assessment model, the hazard map of Chutou gully debris flow in various rainstorm return periods (20, 50, 100, and 200 years) is established, which can provide guidance for the future land-use planning and debris flow prevention works. [ABSTRACT FROM AUTHOR]

Microscopic seepage characteristics are critical for the evaluation of tight sandstone reservoirs. In this study, a digital core approach integrating microscopic seepage simulation and CT scanning was developed to characterize microscopic seepage and fracture effectiveness (the ratio of micro-fractures that contributes to fluid flow) of tight sandstones. Numerical simulations were carried out for characterizations of tight sandstones. The results show that the axial permeability of the investigated cylindrical tight sandstone from Junggar Basin in China is 0.460 μm2, while the radial permeability is 0.3723 μm2, and the axial and radial effective fracture ratios are 0.4387 and 0.4806, respectively, indicating that cracks are not fully developed and the connectivity between micro-cracks is poor. Directional permeability that is difficult to measure by laboratory experiments can be obtained readily using the proposed method in this paper. The results provide important information for improving the exploration and development of tight sandstone reservoirs. [ABSTRACT FROM AUTHOR]

Landslides are one of the most common geological hazards in many parts of the world, which have brought catastrophic consequences to mankind. Seismic shaking can be an important trigger factor generally resulting in large-scale landslides. For some paleolandslides triggered by earthquakes, despite the lack of historical records, certain paleoseismic parameters can be back-analyzed. In this paper, the discrete element method (DEM) was applied to back-analyze the peak ground acceleration (PGA) triggering the Tahman landslide, a paleolandslide located in eastern Pamir, northwest China. Firstly, detailed field geological and geomorphological investigation was conducted to reveal the natural and seismic characteristics of the landslide. Subsequently, discrete element modeling was carried out. Simulation results suggested that the Tahman rock slope was stable under natural conditions. Owing to arid climate and water shortage of the study area, the influence of water was ignored. Additionally, from the perspective of the occurrence time of the landslide and geomorphologic feature of the deposits, the landslide was not caused by glacier activity and freeze–thaw events, and thus, must have been triggered by an earthquake. A peak ground acceleration (PGA) of 0.55 g was found to be a critical value for triggering landslides, and a PGA of 0.76 g could best simulate the kinematic process of a landslide when the simulation results were calibrated against the current geomorphological features of the landslide deposits. It can be concluded from the present study that: (1) PGA amplification in the rock slope was related to the topography during earthquake excitation; (2) the effective duration of the seismic wave had a considerable impact on the back-analyzed PGA, which decreased with increasing effective duration; and (3) the long runout of the Tahman landslide was due to its large volume and the interaction of the slide mass with moraines. [ABSTRACT FROM AUTHOR]

In this paper, an actual landslide process that occurred in Southern China is simulated by a continuum approach, the particle finite element method (PFEM). The PFEM attempts to solve the boundary-value problems in the framework of solid mechanics, satisfying the governing equations including momentum conservation, displacement-strain relation, constitutive relation as well as the frictional contact between the sliding mass and the slip surface. To warrant the convergence behaviour of solutions, the problem is formulated as a mathematical programming problem, while the particle finite element procedure is employed to tackle the issues of mesh distortion and free-surface evolution. The whole procedure of the landslide, from initiation, sliding to deposition, is successfully reproduced by the continuum approach. It is shown that the density of the mass has little influence on the sliding process in the current landslide, whereas both the geometry and the roughness of the slip surface play important roles. Comparative studies are also conducted where a satisfactory agreement is obtained. [ABSTRACT FROM AUTHOR]

This study employs similar simulation testing and discrete element simulation coupling to analyze the failure and deformation processes of a model coal seam's roof. The caving area of the overburden rock is divided into three zones: the delamination fracture zone, broken fracture zone, and compaction zone. The caving and fracture zones' heights are approximately 110 m above the coal seam, with a maximum subsidence of 11 m. The delamination fracture zone's porosity range is between 0.2 and 0.3, while the remainder of the roof predominantly exhibits a porosity of less than 0.1. In addition, the numerical model's stress analysis revealed that the overburden rock's displacement zone forms an 'arch-beam' structure starting from 160 m, with the maximum and minimum stress values decreasing as the distance of advancement increases. In the stress beam interval of the overburden rock, the maximum value changes periodically as the advancement distance increases. Based on a comparative analysis between observable data from on-site work and numerical simulation results, the stress data from the numerical simulation are essentially consistent with the actual results detected on-site, indicating the validity of the numerical simulation results. [ABSTRACT FROM AUTHOR]

Similar to the squeezing soft-rock tunnel, the surrounding rock pressure for a deep-buried hard-rock tunnel under high geo-stress also possesses certain long-term evolution characteristics, which have a significant impact on the safety performance of the supporting structures. This paper investigated the evolution characteristics and transfer mechanism of the surrounding rock pressure for a deep-buried hard-rock tunnel through the combinations of the field measurements and numerical simulation. Firstly, the triaxial compression and uniaxial creep tests for granite samples indicated that the hard-brittle rock could exhibit the rheological properties under high geo-stress. Secondly, the field measurements showed that the surrounding rock pressure continued to increase throughout a period of 1200 days. Thirdly, a new composite viscoelastic-plastic creep constitutive model was used to calculate the creep damage degree and scope of the surrounding rock. The results showed that the evolution characteristics of the surrounding rock pressure can be divided into three typical stages, i.e., phase I: rapid growth stage; phase I : decelerating growth stage; and phase III: basically stable stage. From the beginning of phase II to the end of phase III (about 1100 days), the pressure on the supporting structures increased by nearly 40% compared to phase I (about 50 ~ 150 days), and the average pressure-sharing proportions of the primary support and the secondary lining finally were stabilized at 0.6 and 0.4, respectively. The damage of surrounding rock was distributed mainly from the haunch to the vault and the bottom, with the degree and scope of the bottom being the most serious. [ABSTRACT FROM AUTHOR]

Measles remain to be an important global public health issue in China. In spite of large coverage rates of the first dose of Measles mumps rubella (MMR) combination vaccines (MMR1), large numbers of measles cases continue to be reported in China in recent years due to the high incidence and the low coverage of the second MMR vaccine dose (MMR2). This paper is devoted to modeling the combined effects of MMR1 and MMR2 coverage rates on the controlling of measles. To do that, we propose and study a robust time-delayed compartment measles infection model where MMR2 is followed after a fixed time interval of MMR1, and the combined elements of infection and mass immunization are also considered. By using the methods of Lyapunov functional and the uniform theory for infinite-dimensional dynamical systems, a threshold dynamics determined by the basic reproduction number $\Re_{0}$ is established: the measles can be eradicated if $\Re_{0}<1$ , whereas the disease persists if $\Re_{0}>1$ . Moreover, it is shown that the endemic equilibrium is locally asymptotically stable once $\Re_{0}>1$ . Numerical simulations are performed to support the theoretical results and to consider the effects of MMR2 on the controlling of measles. Our results show that to eliminate measles in China, we should have MMR1 coverage rates larger than 88.01% based on perfect MMR2 coverage, and have MMR2 coverage rates larger than 92.63% based on perfect MMR1 coverage; Moreover, our simulations suggest that there is a risk that paradox of vaccination against measles in China may occur: that is, the final size of infected individuals may even increase in spite of the increase of MMR2 coverage rates. [ABSTRACT FROM AUTHOR]

Introduction: The use of Top Coal Caving for exploiting the thick coal seam with shallow buried depth most likely has a strong negative impact on the stability. Case description: Anjialing No. 1 Underground Mine is located in Shuozhou City, Shanxi Province of China. The 4# Coal Seam of this coal mine is the thick coal seam with shallow buried depth, which has the thickness of 12 m and the depth of 180 m in average. This paper focuses on predicting the distribution of ground fissures and water-conducted fissures induced by the exploiting of the 4# Coal Seam. Discussion and evaluation: We first create a 3D computational model, and then use FLAC $$^{3D}$$ software to simulate the mining of coal seam. We then calculate the displacements and tensile strain of the ground surface and strata, and predict the distribution of the ground fissures and water-conducted fissures. Finally, we further analyze the possibility of the perviousness and air leakage of the coal mine on the basis of the predicted distribution of fissures. Conclusions: The prediction results indicate that: (1) the water-conducted fissures are strongly developed and go through the Neogene aquifuge in some region; thus, it may lead to potential perviousness of coal mine; (2) part of these water-conducted fissures connect with the ground fissures; and this behavior may cause the risk of air leakage. [ABSTRACT FROM AUTHOR]

The importance of atmospheric electricity research has been increasingly recognized in recent decades. Research on atmospheric electricity has been actively conducted since the 1980s in China. Lightning physics and its effects, as important branches of atmospheric electricity, have received more attention because of their significance both in scientific research and lightning protection applications. This paper reviews atmospheric electricity research based primarily on ground-based field experiments at different regions in China in the last decade. The results described in this review include physics and effects of lightning, rocket-triggered lightning and its physical processes of discharge, thunderstorm electricity on the Tibetan Plateau and its surrounding areas, lightning activity associated with severe convective storms, the effect and response of lightning to climate change, numerical simulation of thunderstorm electrification and lightning discharge, lightning detection and location techniques, and transient luminous events above thunderstorms. [ABSTRACT FROM AUTHOR]

This paper provides a review of paleoclimate modeling activities in China. Rather than attempt to cover all topics, we have chosen a few climatic intervals and events judged to be particularly informative to the international community. In historical climate simulations, changes in solar radiation and volcanic activity explain most parts of reconstructions over the last millennium prior to the industrial era, while atmospheric greenhouse gas concentrations play the most important role in the 20th century warming over China. There is a considerable model-data mismatch in the annual and boreal winter temperature change over China during the mid-Holocene [6000 years before present (ka BP)], while coupled models with an interactive ocean generally perform better than atmospheric models. For the Last Glacial Maximum (21 ka BP), climate models successfully reproduce the surface cooling trend over China but fail to reproduce its magnitude, with a better performance for coupled models. At that time, reconstructed vegetation and western Pacific sea surface temperatures could have significantly affected the East Asian climate, and environmental conditions on the Qinghai-Tibetan Plateau were most likely very different to the present day. During the late Marine Isotope Stage 3 (30-40 ka BP), orbital forcing and Northern Hemisphere glaciation, as well as vegetation change in China, were likely responsible for East Asian climate change. On the tectonic scale, the Qinghai-Tibetan Plateau uplift, the Tethys Sea retreat, and the South China Sea expansion played important roles in the formation of the East Asian monsoon-dominant environment pattern during the late Cenozoic. [ABSTRACT FROM AUTHOR]

It is inevitable to build hydropower stations in the rivers with high sediment content, especially in China. In this study, numerical simulation of a hydraulic turbine with long and short blades under the conditions of sediment-containing water was carried out based on the Euler-Euler method using ANSYS CFX software. The flow characteristics inside the turbine under different particle diameters and inlet volume fractions of sediment were analysed and studied. The calculation results show the wear area increased as the sediment particle diameter increased with constant sediment volume fraction. The larger the particle diameter was, the more serious the sediment accumulation was in the lower local area along the direction of gravity, which is likely to cause wear in the turbine flow passage components. In the case of a constant sediment particle diameter, the wear area of the turbine flow passage components increased with increased sediment volume fraction. The wear intensity of a Francis turbine runner during a one-year operation period under four different sediment contents was predicted. The results show that the total wear of the long blades was approximately 9.09 mm, and the total wear of the short blades was approximately 2.33 mm; these values can seriously affect the stable operation of a hydraulic turbine. The scientific prediction of the blade wear intensity and location provides a reliable and quantifiable basis for determining the operation status and maintenance needs of turbine units. [ABSTRACT FROM AUTHOR]

As a result of deep burial depth, small pore throat, poor connectivity between pores, different clay mineral contents in reservoirs, and strong reservoir sensitivity, injection wells often have problems such as rapidly increasing water-injection pressure and insufficient water-injection quantity in the process of water-injection development. The main measures used to solve the difficulties of water injection in low-permeability reservoirs include fracturing, acidizing, and surfactant depressurization and injection increase, all of which have some disadvantages of high cost and environmental damage. In recent years, depressurization and injection-increase environment-safe bio-nano-materials have been introduced into low-permeability reservoirs and have achieved good application results in China. On the other hand, although there have been many researches on EOR (enhanced oil recovery) of nano-materials, the numerical simulation field of nano-depressurization and injection-augmenting technology is still a blank that the wettability mechanism of nano-materials and EOR nano-materials used in bio-nano-depressurization and injection-augmenting technology are almost completely opposite, and the influence of adsorption on formation is almost completely opposite. The adsorption of nanoparticles in other EOR studies will reduce the porosity and make the reservoir more hydrophilic. Nanoparticles used in biological nano-technology will produce hydrophobic film near the well, which will reduce the seepage resistance through the slip of water phase. In this study, a set of water flooding model of numerical simulation technology for depressurization and injection-augmenting of biological nano-materials considering adsorption characteristics and reservoir physical properties was established, the sensitivity analysis of key injection parameters was carried out, and the application effect prediction chart of biological nano-technology was drawn, and the model and prediction chart were verified by real oilfield data. As far as we know, this is the first numerical simulation study on biological nano-technology that has been applied in oil fields. [ABSTRACT FROM AUTHOR]

The heavy rainfall caused by Super Typhoon Rammasun (2014), the strongest typhoon that has landed in China since meteorological records began, has caused huge economic and social losses to China. Preliminary analysis showed that the intensity and area of the rainfall were closely related to Wuzhi Mountain, China. However, the physical mechanisms need to be analyzed in depth. Using the WRF V3.9 model, a high-resolution numerical simulation of topographic influence on the heavy rainfall of Typhoon Rammasun was carried out. The results show that the topographic rise significantly weakened the rainfall intensity and changed the location of the heavy rainfall center of Typhoon Rammasun. If the topography of Hainan Island increased to twice the original altitude, the maximum daily rainfall caused by Rammasun decreased by 35.2%, and the heavy rainfall center shifted from western Hainan Island (WHI) to southwestern Hainan Island. On one hand, the topographic rise increased the friction of the topography and weakened the intensity of Rammasun, resulting in a weaker rainfall in WHI (the observed heavy rainfall center). On the other hand, the topographic rise changed the structure of Rammasun. The control experiment showed that the heavy rainfall in WHI was mainly caused by meso-micro scale systems on an outer spiral cloud belt of Rammasun. If the altitude rose, the low-level convergence and the mid-low level ascending movement in WHI were weakened, making it difficult to form long-lasting, quasi-stationary meso-micro scale systems, eventually leading to the rainfall center transferring to southwestern Hainan Island. [ABSTRACT FROM AUTHOR]

ERA5 is the latest fifth-generation reanalysis global atmosphere dataset from the European Centre for Medium-Range Weather Forecasts, replacing ERA-Interim as the next generation of representative satellite-observational data on the global scale. ERA5 data have been evaluated and applied in different regions, but the performances are inconsistent. Meanwhile, there are few precise evaluations of ERA5 precipitation data over long time series have been performed in Chinese mainland. This study evaluates the temporal-spatial performance of ERA5 precipitation data from 1979 to 2018 based on gridded-ground meteorological station observational data across China. The results showed that ERA5 data could capture the annual and seasonal patterns of observed precipitation in China well, with correlation coefficient values ranging from 0.796 to 0.945, but ERA5 slightly overestimated precipitation in the summer. Nonetheless, the results also showed that the accuracy of the precipitation products was strongly correlated with topographic distribution and climatic divisions. The performance of ERA5 shows spatial inherently across China that the highest correlation coefficient values locate in eastern, Northwestern and North China and the lowest biases locate in Southeast China. This study provides a reliable data assessment of the ERA5 data and precipitation trend analyses in China. The results provide accuracy references for the further use of precipitation satellite data for hydrological calculations and climate numerical simulations. [ABSTRACT FROM AUTHOR]

Updating the urban land cover information has been proved a necessary method for the numerical studies of urban climate and urban atmospheric environment in China, a fast urbanizing country. However, there are uncertainties in the urban land use/cover (ULUC) information in different datasets due to the uncertainties in raw data sources and produce methods. In this study, the Weather Research and Forecasting model is used to simulate the summer climate over the Yangtze River Delta in July and August 2013, when a heatwave episode occurred. Five numerical experiments are designed; one is the baseline experiment (non-urban land cover (NOURB)) in which all urban land covers are removed, and different urban land use/cover (ULUC) experiments from four different global land cover datasets are used in other four experiments. The differences between the ULUC experiments and the NOURB experiment are used to observe the urbanization effects. The results show a remarkable urbanization effect in all the ULUC experiments, and the urbanization influences are most different over the union-urban area, which defined as the area marked as urban area by at least one land cover dataset, because the uncertainties in urban land cover information are greatest in this area. All the ULUC experiments show the regional influence of urbanization as well, which means urbanization effects are not limited in cities. The Climate Change Initiative (CCI) experiment using the European Space Agency CCI 2013 dataset showed the greatest urbanization influence and the highest effect index in all analyzed variables, because of the largest urban land cover area in the analysis domain. The urban land cover area in the Global Land Cover experiment is the smallest among the ULUC experiments, but it distributes in a more concentrated way than in other experiments; it indicates that both city size and city shape affect the regional influence. [ABSTRACT FROM AUTHOR]