bluuebunny/crossref_metadata_2025_split huggingface dataset:
Piezoelectric energy enhancement strategy for active fuzzy harvester with time-varying and intermittent switching
Authors: Hara Yushin , Zhou Meng , Li An , Otsuka Keisuke , Makihara Kanjuro 
Published: November 2020

Abstract
This study aims to increase the amount of electrical energy harvested from a piezoelectric vibration energy harvester under unloaded and high-load resistance conditions. Although increased piezoelectric charge due to the synchronized switch harvesting on inductor (SSHI) strategy damps mechanical vibrations, the mechanical vibration amplitude of a mechanical element in a harvester is assumed to be constant for most discussions regarding the active harvester with SSHI strategy. However, this assumption is not valid under excessive switching actions, in which case the performance of the harvester deteriorates. This problem is known as the vibration suppression effect. To address this problem, in this study, two switching strategies for the charge inversion circuit—namely, switching considering vibration suppression-threshold (SCVS-t) and adaptive SCVS-t (ASCVS-t)—are proposed through intermittent switching actions. During the harvesting process, intermittent switching using these strategies is performed based on the output voltage threshold, thus maintaining high mechanical vibration amplitude and excellent harvesting performance by avoiding excess switching. The ASCVS-t adopts a tuning algorithm for the time-varying threshold and can achieve appropriate intermittent switching and effective harvesting under various vibration conditions without pre-tuning. Experimental comparisons with conventional strategies confirm that the proposed strategies achieve 2.9 times and 2.0 times greater harvested energy storages than a standard harvester and conventional switching strategy, respectively.
Receptor-mediated endocytosis of nanoparticle based on the co-rotational grid method
Authors: Xu Wu , Jia Kangyu , Liu Xiaohu 
Published: November 2020

Abstract
Endocytosis is a cellular process in which the nanoparticle can be internalized to form a vesicle. Receptor-mediated transport is a mainly endocytic pathway, and many theoretical models have been proposed to study the physiochemical mechanism underlying this specific endocytic pathway. Traditional methods mainly focus on the interactions between the nanoparticles and the plasma membrane. The role that actin force plays during endocytosis of nanoparticle is neglected. However, recent extraordinary studies show that the actin force is the main driving force in endocytosis. Based on previous instructive models and configurations of the actin network observed in literature, there mainly exist oblique push and pull forces generated by the growth of actin network at the endocytic site and the lateral contraction force produced by proteins such as myosin at the concave neck of membrane. Considering these two different actin force-generation mechanisms, a new actin force model is proposed in this paper. Then, a numerical analysis is performed based on the co-rotational grid method. Besides, and the influence of osmotic pressure, the plasma membrane stiffness, actin force containing growth process and asymmetry of the actin network have been investigated. Meanwhile, the relative importance of the two actin force-generation mechanism is obtained, which is consistent with the theoretical and experimental results in literature. Our model can obtain the critical nanoparticle radius that can be absorbed most efficiently by considering the force that actin filaments could provide. And our results show that there exist a critical size for nanoparticle which could only be absorbed by tumor cell. In addition, the effects of growth process and asymmetry of the actin network are discussed. This method has the potential to reveal the underlying mechanisms of the complex dynamic behaviors of the endocytosis process.
Influence of formation activation induced by fracturing fluid on casing deformation during hydraulic fracturing operation in shale gas wells
Authors: Zeng Y J , Du J L , Zhou S M , Qian Q Tao , Liu K 
Published: November 2020

Abstract
Sichuan Basin in China is rich in shale gas resources and has great exploration and development capacity. It is the main area of shale gas exploration and production in China. The proved shale gas reserves discovered by Sinopec in Weirong area exceed 100 billion m3, and they play an important role in the development of shale gas in China. In Sichuan Basin, the use of traditional shale gas production methods such as multi-stage hydraulic fracturing is hampered by serious casing deformation. By December 2019, Sinopec performed hydraulic fracturing operations in 20 wells in this area, where casing deformation was encountered in 10 wells, resulting in an increase of up to 5.69% in the proportion of invalid fracture sections. In order to explain the mechanism of casing deformation during hydraulic fracturing, the geological structures of a shale gas production site in Sichuan Basin with frequent casing deformation were examined, and the geological reasons for this deformation were revealed. In addition, a geological model was established to calculate the influence of formation activation induced by fracturing fluid on the casing load, and formation activation during hydraulic fracturing was studied. The results reported in this paper are of great significance for optimizing hydraulic fracturing parameters and reducing the influence of formation activities on the casing of horizontal wells.
DEM analysis on the triaxial behaviour of mudstone considering water disintegration
Authors: Cao Zhensheng , Jia Tong , Zhang Shaoqiang , Ouyang Xun , Jiang Chuanbin , Huang Xin 
Published: November 2020

Abstract
Mudstone is a typical type of soft rocks. It is stable and has high strength in its natural state. However, in presence of water the constituent minerals dissolve and the inter-grain bonds are weakened, which thereby greatly reduces the strength of mudstone. As one of the most prevailing geological formations in the southwestern China, understanding the mechanical behaviour of mudstone at different degrees of disintegration is of great importance to practical engineering. This paper presents a micro-mechanical analysis on the mechanical behaviour of mudstone at different degrees of disintegration using the discrete element method (DEM). The laboratory triaxial tests carried out on mudstone samples that have been merged in water for different time periods are simulated. The dissolution of minerals and weakening of bonds between grains are considered by reducing the selected input parameters of parallel bonds at random locations. Different degrees of disintegration are obtained by multiplying the selected input parameters of parallel bonds with different reducing factors. The stress-strain curves obtained using the proposed approach are in good agreements with the experimental data. The progressive failure mechanism of mudstone at different degrees of disintegration is investigated considering the characteristics of particle motion, contact variation and bond breakage. Micro-scale analysis shows that with the increasing of confining pressure, the fraction of shear breakage of parallel bonds increases but the declining rate of coordination number post peak decreases. These underlie the fundamental mechanism of the change of failure mode of mudstone from brittleness to ductileness. Regardless of its spatial locations, the majority of broken bonds for the disintegrated specimens are those bonds with reduced input parameters. And the fraction of altered bonds within the broken bonds increases with the increasing degree of disintegration. The current research provides insightful understanding of the fundamental behaviour of mudstone in the presence of water.
Regulation functions in the Beilun estuary by tidal numerical simulation
Authors: Guo Y Q , Ma J R , Huang L Y , Zou G L 
Published: November 2020

Abstract
It is a relatively short distance from mountains to the sea for the Beilun river. Its runoff seasonally varies with strong flooding and less sand. The mangroves are unique and spread wildly in the estuary to maintain a stable riverbed by scouring the waves and currents. However, the regulation structures built along the estuary by both China and Vietnam were not well-designed according to the laws of flow and sediment movement. A numerical model has been developed to simulate the functions of the regulations in this paper. Today, the shape of the estuary is mostly formed by the regulation structures. The discharge ratio and velocity changes are displayed to reveal the effects of the regulations. Coriolis force is intended to drive the flooding and ebbing flow in different ways, so the south passage usually becomes deeper and larger while the river island usually connects to the north shore in the northern portion of the earth. However, this phenomenon has not properly worked in this region, likely due to other manmade activities and the mangroves defending the shallows from scouring while the regulations are directing the flow currents.
A Simulation Study of the Emergency Double-Row Micropile Reinforcement of the Xituo Landslide
Authors: Liu ZhongShuai , Zou Wukun , Deng Sangen , Fu Yu , Tang Shengchuan , Gou Dongyuan , Xu Feng 
Published: November 2020

Abstract
This paper studies the suitability of a double-row anti-slide micropile solution for the emergency reinforcement project of the Xituo landslide. The FLAC3D program was used to simulate the stability of the landslide before and after micropile installation. Several key parameters were monitored in the simulation such as the landslide displacement, the shear strain rate at the slip surface, as well as the bending moments and the shear forces exerted on the piles. Both the displacement graph and the shear strain rate cloud map of the landslide before reinforcement indicate that the Xituo landslide is in an unstable state and tends toward accelerated collapse. After the double-row anti-slide micropiles were installed, the displacement of the slope toe gradually stabilized, and the displacement on the river side of the highway was significantly reduced. Moreover, the shear strain rate cloud diagram at the location of the micropiles developed upward, and the shear strain rate was small. These changes indicate that the double-row anti-slide micropiles could effectively restrain further deformation and damage because of the Xituo landslide. Furthermore, the simulated maximum shear forces exerted on the piles, 115.5 and 75.8 kN, are much lower than the maximum micropile design value of 260 kN. The simulated maximum pile body bending moments, 3173.8 and 1170.0 kNm, also fall below the recommended maximum value of 4500 kNm. Therefore, double-row anti-slide micropiles are an effective and practical solution for stabilizing the Xituo landslide.
Seismic stability of an underground cavern in jointed rock mass based on the discrete fracture network
Authors: Cun Chu , Peishuai Chen , Qing Yuan , Hong Jiang , Deding Feng 
Published: November 2020

Abstract
In the construction of underground structures in high seismic intensity areas, it is inevitable that a fault fracture zone will pass through the construction site. Therefore, it is very important to evaluate and analyze the stability of the unstable block, which is cut by the fault and the dominant joint group. In this study, the discrete element method was used to simulate the seismic response of an underground powerhouse of a hydropower station near a high seismic zone. The discrete fracture network (DFN) model was introduced to simulate the joint group. Moreover, to optimize the number of joints and improve computational efficiency under dynamic conditions, the joints in the DFN with little influence on the stability of the cavity, were deleted by the algorithm, and a nonlinear time-history response analysis method was used for dynamic calculation. Based on the simulation results obtained, it was possible to classify the instability of the unstable block, and corresponding suggestions for construction were provided. Additionally, these results can be used as a reference for the seismic design of similar underground structures.
Modeling investigation of the impacts of dead-end fracture on heat transfer of water flowing through rough fractured rocks
Authors: Chen Yuedu 
Published: November 2020

Abstract
A clear understanding of the convective heat transfer characteristics of fluid in three-dimensional (3D) rock fractures affected by dead-end fractures is important in evaluating heat recovery in fractured geothermal reservoirs. Two 3D cubic fractured rock models with and without rough dead-end fractures are built to conduct flow and heat transfer simulations by solving hydrothermal coupling equations. The rough fractures are upscaled from lab-measured small-scale rock fractures. Injection velocities of 0.002 m/s and 0.02 m/s were imposed to examine how dead-end fractures affect the heat transfer processes within hot fractured rocks. Several characteristic parameters, including outlet water temperature, total heat extraction, and overall permeability, are presented to quantitatively describe the effects of dead-end fractures. Results show that dead-end fractures retard fluid flow through the fractured model and significantly decrease the overall permeability. A low-temperature zone grows rapidly under the effect of dead-end fractures, and the outlet water temperature is lower in this case than in the model without dead-end fractures. Moreover, the total heat extraction is higher in the model without dead-end fractures than in the model with dead-end fractures. This result is mainly ascribed to the former model’s large overall permeability. Results reveal that dead-end fractures cannot be ignored in the evaluation of flow and heat transfer in the modeling of heat extraction from subsurface fractured geothermal reservoirs.
Prediction of water inflow into a tunnel based on three-district zoning of faults
Authors: Wu J , Wu L , Zhao C L 
Published: November 2020

Abstract
Water inflow into a tunnel subject to fault zones and fault effective zones is interpreted in this study using a three-district zoning method. An improved Brinkman model is proposed to investigate the seepage law of the geological defects of a fault. A coupled calculation model of typical Darcy seepage and Brinkman rapid seepage is constructed to establish a mathematical model of nonlinear seepage flow based on three-district zoning and the corresponding numerical implementation. In addition, the influence of the angle between the fault dip and tunneling directions on the water inrush in a tunnel is also studied. The variation characteristics of the pore pressure and velocity fields under various construction stages are analyzed, as is the seepage velocity of pore water at the tunnel heading. Moreover, the effects of the fault dip direction on the seepage field and water inflow are discussed. The following results were obtained. (1) Before excavation to the fault effective zone, the pore pressure at the same depth remained essentially unchanged in front of the tunnel heading. After excavation to the fault effective zone, the pore pressure at the same depth increases linearly with distance in front of the tunnel heading. (2) The seepage velocity changed gently before excavation to the fault effective zone but showed wavy fluctuating after excavation to the fault effective zone. The velocity reached its maximum value in the fault zone before decreasing rapidly and remaining close to zero in the general surrounding rock zones. (3) As the excavation length increased, the water inflow increased gradually, reaching its maximum value in the fault zone. (4) In the fault zone, the seepage velocity decreased with an increase in the fault dip. The water inflow reached maximum and minimum values at angles of 90° and 150°, respectively.
Estimation of REV for Danba schist based on 3D synthetic rock mass technique
Authors: Zhen CUI , Ping-zhi CHEN , Qian SHENG 
Published: November 2020

Abstract
This paper aims to provide a case study of determining the structure and mechanical Representative Elementary Volume (REV) simultaneously for a specific jointed rock mass. The schist of Danba HPP project is taken as the study case here. A Synthetic Rock Mass model (SRM) is firstly constructed based on sophisticated geological loggings. With which the number of joint centers per unit volume (P30), the area of joint per unit volume (P32), and the Young’s modulus (E) are examined for various sample sizes. It is found that the SRM is a powerful tool to address those problems. The P30 reduces gradually with the increase of rock mass scale. As for P32 and E, maximum and minimum value and the variance decrease rapidly with the increase of rock mass size. A comprehensive REV size of 50~60m is then estimated based on the above 3 indexes. According to the SRM simulation, young’s modulus of the REV scale is around 6.8GPa, which is a little bit higher than the recommended value by geologists. This difference is believed to be reasonable as the recommended value usually been significantly undervalued. The procedures and findings of this paper may provide a certain reference for further studies on rock mass scale effects.
Shear strength parameter determination for the single plane of weakness criterion: Implications for wellbore stability
Authors: Ma Tianshou , Qiu Yi , Liu Diancheng , Liu Yang , Zhu Gongsheng , Peng Nian 
Published: November 2020

Abstract
Wellbore stability is a classic rock mechanics problem encountered during drilling and completion, which costs the drilling industry more than $100 million per year worldwide. The failure criterion is a very important aspect of the wellbore stability analysis. Accordingly, for shale rich in bedding, fissures, joints, and cuts, we often use the single plane of weakness criterion to describe the compressive shear strength. The anisotropic strength of a rock depends on the strength of the rock matrix and the weak plane (i.e., cohesive strength of the matrix, friction angle in the matrix, cohesion of the weak plane, and friction angle in the weak plane). However, directly and accurately determining the compressive shear strength parameters of the rock matrix and the weak plane using the conventional least square and molar stress circle methods is difficult because of the difference between the rock matrix and the weak plane. This study uses the grid search algorithm to quickly match the optimal matrix cohesion, matrix internal friction angle, weak plane cohesion, and weak plane internal friction angle through the published triaxial test data of two sets of anisotropic rocks. The four parameters of the compressive shear strength materials obtained by the grid search algorithm are used to predict the results, which are very consistent with the experimental results. The correlation coefficient (R
2) above 0.98 is enough to meet the engineering requirements. Taking a shale gas well in the Sichuan Basin as an example, a collapse pressure prediction model is finally established by combining the grid search method to determine the material parameters of the compressive shear strength, shear wellbore instability model, and SWP criterion. Consequently, the model results are found to be in good match with the engineering practice.
Optimization and Establishment of Drillability in Gravel Formation
Authors: Pei Yang , Yan Zhang , Hongbo Wang 
Published: November 2020

Abstract
Rock drillability is a comprehensive index used to evaluate the difficulty of drilling and is a basic factor to determine drilling efficiency. Proper evaluation of rock drillability is vital to achieving high-quality and efficient drilling. Currently, the method for determining the drillability of rocks is primarily based on laboratory micro-bit experiments to measure the core’s resistance to drilling. This method requires a large number of cores and is expensive, takes a long time to start the test, and often lags behind drilling. Moreover, some people analyzed the relationship between the actual drilling parameters and the mechanics’ specific energy of drill bit and established a method to evaluate the rock drillability of rock. Field application proves that the drillability model is poorly correlated with the actual drilling conditions. The value of the actual drilling energy is usually 100–1000 times that of the theoretically calculated mechanics specific energy. Through laboratory experiments, we study the strength and failure characteristics of different gravel sizes and gravel contents with different impact speeds. The matching relationship between rock mass and impact speeds is analyzed. Based on the experimental results, a phase similar to a drill bit and a drilling tool is proposed to support drillability assessment. Under the condition of the same gravel size, with the increase of gravel content, the average cutting speed gradually decreases under the condition of certain cutting force, which is approximately exponential; with the increase of gravel particle size, under the condition of certain cutting force, the average cutting speed rapidly decreases, and the gravel particle size has a decisive impact on the average cutting speed. The above research results can be used to establish a new drillability evaluation model and to optimize the drill bits, drilling tools, and drilling parameters.
Relationship of rockburst and energy dissipation characteristics of brittle rock at great depth
Authors: Huang Shuling , Zhong Pengju , Ding Xiuli 
Published: November 2020

Abstract
Rockburst is defined as a major geological disaster of hard rock mass. At present, rockburst analysis mostly focuses on its mechanism, prediction, and preventive measures, and great progress has been made. However, a few comprehensive analyses on the rockburst mechanism still need to be investigated from different energy perspectives. From the energy perspective, this study analyzes the relationship between a rockburst and the destructive properties of T2b marble in the deep buried tunnel of the Jinping Secondary Hydropower Station. Our analysis includes strain energy accumulation and dissipation, shear fracture, energy release, and acoustic emission (AE). The obtained results show that in the energy release and dissipation processes, three dilatancy mechanisms trigger a rockburst, namely the tensile fracture extension control mechanism, closed fracture friction control mechanism, and their mutual transformation compound control mechanisms. Different mechanisms lead to different energy mutation patterns that determine the rockburst extent and scale. We also found that the strain energy of brittle rocks linearly increases with the increase of the confining pressure during the failure of the brittle rocks. The energy storage rate of the front peak at the lower confining pressure was significantly greater than that of the back peak. However, the difference gradually decreases as the confining pressure increases. The total shear fracture energy with the increase of the confining pressure first increases and then decreases. The peak before the shear fracture energy nonlinearly increases gradually, and the two fractures can be similar until the brittle–ductile transition. Lastly, the AE experiment shows that during the addition and unloading of brittle rocks at a great depth, three types of energy active periods and three types of energy decay periods are observed. The precursor to an instantaneous rockburst is the second type of energy fading period, while that to a delayed rockburst is the third type of energy fading period. The second type of energetically active period refers to the birth of a rockburst. The third type refers to the occurrence of a standard rockburst or a recurrence, such as a discontinuous rockburst.