In order to analyze mechanism of casing damage,the uniaxial compression experiment and creep experiment of interbedded mudstone samples from Sanan development area of Daqing Oilfield under different water contents wer...In order to analyze mechanism of casing damage,the uniaxial compression experiment and creep experiment of interbedded mudstone samples from Sanan development area of Daqing Oilfield under different water contents were carried out.The changes of the mudstone's mechanical parameters and creep characteristics with the increment of water saturation were studied.The results indicate that the rock strength and elastic modulus decrease rapidly with the increment of water content,at the same time,the creep strain and creep strain rate of steady state increase with the increment of water content,and also the steady state creep strain rate is enhanced with the increment of deviatoric stress.Through the creep characteristic curves,a non-linear creep constitutive equation of mudstone considering the change of water contents is established,which will be used in future numerical analysis.展开更多
Based on the detailed computer .simulation of the indentation testing on the thin-film systems, the present paper explores the detailed procedure of determining elastic properties (elastic modulus E(f) and Poisson rat...Based on the detailed computer .simulation of the indentation testing on the thin-film systems, the present paper explores the detailed procedure of determining elastic properties (elastic modulus E(f) and Poisson ratio v(f) ) and creep parameters (CCREEP (f) and nCREEP (f)) for a simple Norton law (ε=CCREEP (f)σnCREEP(f), where ε is creep strain rate, and σ is the stress) material for a thin film coated on a creep substrate, whose elastic properties(E(s) and v(s)) and creep properties (CCREEP(s) and nCREEP(s) ) of the substrate are known, from indentation elastic and creep testing, respectively. The influences of the thickness of the thin-film and the size of the indenter on the indentation behavior have been discussed. It is shown that the boundary between the thin film and the substrate has great influence on the indentation creep behavior. The relative sizes of indentation systems are chosen so that the behavior of the indentation on the film is influenced by the substrate. The two elastic parameters E(f) and v(f) of the film are coupled on the influence of the elastic behavior of indentation. With the two different size indenters, the two elastic parameters E(f) and v(f) of the film can be uniquely determined by the indentation experimental slopes of depth to applied net section stress results. The procedure of determining of the two Norton law parameters CCREEP (f) and nCREEP(f) includes the following steps by the steady indentation rate d. The first step to calculate the creep indentation rate on certain loads of the two different sizes of indenters on a set of assumed values of CCREEP (f) and nCREEP (f). Then to build relationship between the creep indentation rate and the assumed CCREEP(f) and nCREEP(f). With the experimental creep indentation rate to intersect two sets of CCREEP (f) and nCREEP(f), which have the same values of d. The last step is to build the CCREEP(f) and nCREEP(f)curves from the intersection points for the two indenters.These two curves CCREEP and nCREEP(f) will intersect at one point. The axial values of the point are what we want. The procedure presented in the paper to determine the elastic parameters and creep parameters from the indentation experiments can be applied to any material systems.展开更多
The viscoelastic-plastic creep experiments on soft ore-rock in Jinchuan Mine Ⅲ were performed under circular increment step load and unload. The experimental data were analyzed according to instantaneous elastic stra...The viscoelastic-plastic creep experiments on soft ore-rock in Jinchuan Mine Ⅲ were performed under circular increment step load and unload. The experimental data were analyzed according to instantaneous elastic strain, visco-elastic strain, instantaneous plastic strain and visco-plastic strain. The result shows that instantaneous deformation modulus tends to increase with the increase of creep stress; soft rocks enhance the ability to resist instantaneous elastic deformation and instantaneous plastic deformation during the multi-level of load and unload in the cyclic process. In respect of specimen JC1099, the ratio of visco-elastic strain to visco-plastic strain varies from 3.15 to 6.58, and the ratio has decreasing tendency with stress increase as a whole; creep deformation tends to be a steady state at low stress level; soft rocks creep usually embodies accelerated creep properties at high stress level. With the damaging variable and the hardening function introduced, a nonlinear creep model of soft rocks is established, in which the decay creep is described by the nonlinear hardening function H of viscidity coefficient. The model can describe the accelerated creep of soft rocks since the nonlinear damaging evolvement variable D of deformation parameter of rocks is introduced. Three stages of soft rocks creep can be described with the uniform creep equation in the nonlinear creep model. With this nonlinear creep model applied to the creep experiments of the ore-rock of Jinchuan Mine Ⅲ, the nonlinear creep model’s curves are in good agreement with experimental data.展开更多
To investigate the specific creep behavior of ultra-deep buried salt during oil and gas exploitation,a set of triaxial creep experiments was conducted at elevated temperatures with constant axial pressure and unloadin...To investigate the specific creep behavior of ultra-deep buried salt during oil and gas exploitation,a set of triaxial creep experiments was conducted at elevated temperatures with constant axial pressure and unloading confining pressure conditions.Experimental results show that the salt sample deforms more significantly with the increase of applied temperature and deviatoric loading.The accelerated creep phase is not occurring until the applied temperature reaches 130℃,and higher temperature is beneficial to the occurrence of accelerated creep.To describe the specific creep behavior,a novel three-dimensional(3D)creep constitutive model is developed that incorporates the thermal and mechanical variables into mechanical elements.Subsequently,the standard particle swarm optimization(SPSO)method is adopted to fit the experimental data,and the sensibility of key model parameters is analyzed to further illustrate the model function.As a result,the model can accurately predict the creep behavior of salt under the coupled thermo-mechanical effect in deep-buried condition.Based on the research results,the creep mechanical behavior of wellbore shrinkage is predicted in deep drilling projects crossing salt layer,which has practical implications for deep rock mechanics problems.展开更多
The systematic experiment regarding the general uniaxial compression test and the creep deformations of the typical limestones from the surrounding rock of the highway tunnels were made.The relationship between the ax...The systematic experiment regarding the general uniaxial compression test and the creep deformations of the typical limestones from the surrounding rock of the highway tunnels were made.The relationship between the axial stress and the delayed deformation steady value was obtained from the creep tests under low loading stresses.By the least square method,the parameters of Nishihara creep model were calculated from the creep curves.The results indicate that the strain change always lags behind the increase of stress,and the long-term strength of the limestone is about 80.6% of the stress at the volumetric strain reversal which is obtained from the conventional uniaxial compression test.展开更多
Healthcare organizations rely on patients’feedback and experiences to evaluate their performance and services,thereby allowing such organizations to improve inadequate services and address any shortcomings.According ...Healthcare organizations rely on patients’feedback and experiences to evaluate their performance and services,thereby allowing such organizations to improve inadequate services and address any shortcomings.According to the literature,social networks and particularly Twitter are effective platforms for gathering public opinions.Moreover,recent studies have used natural language processing to measure sentiments in text segments collected from Twitter to capture public opinions about various sectors,including healthcare.The present study aimed to analyze Arabic Twitter-based patient experience sentiments and to introduce an Arabic patient experience corpus.The authors collected 12,400 tweets from Arabic patients discussing patient experiences related to healthcare organizations in Saudi Arabia from 1 January 2008 to 29 January 2022.The tweets were labeled according to sentiment(positive or negative)and sector(public or private),and thereby the Hospital Patient Experiences in Saudi Arabia(HoPE-SA)dataset was produced.A simple statistical analysis was conducted to examine differences in patient views of healthcare sectors.The authors trained five models to distinguish sentiments in tweets automatically with the following schemes:a transformer-based model fine-tuned with deep learning architecture and a transformer-based model fine-tuned with simple architecture,using two different transformer-based embeddings based on Bidirectional Encoder Representations from Transformers(BERT),Multi-dialect Arabic BERT(MAR-BERT),and multilingual BERT(mBERT),as well as a pretrained word2vec model with a support vector machine classifier.This is the first study to investigate the use of a bidirectional long short-term memory layer followed by a feedforward neural network for the fine-tuning of MARBERT.The deep-learning fine-tuned MARBERT-based model—the authors’best-performing model—achieved accuracy,micro-F1,and macro-F1 scores of 98.71%,98.73%,and 98.63%,respectively.展开更多
A uniaxial viscoelastoplastic model that can describe whole creep behaviors of asphalt sand at different temperatures was presented.The model was composed of three submodels in series,which describe elastoplastic,visc...A uniaxial viscoelastoplastic model that can describe whole creep behaviors of asphalt sand at different temperatures was presented.The model was composed of three submodels in series,which describe elastoplastic,viscoelastic and viscoplastic characteristics respectively.The constitutive equation was established for uniaxial loading condition,and the creep representation was also obtained.The constitutive parameters were determined by uniaxial compression tests under controlled-stress of 0.1 MPa with five different test temperatures of 20,40,45,50 and 60 ℃.Expressions of the model parameters in terms of temperatures were also given.The model gave prediction at various temperatures consistent with the experimental results,and can reflect the total deformation characterization of asphalt sands.展开更多
The lithology of the strata in the Gobi region of the Xinjiang autonomous region of China is mainly composed of mudstone,silty mudstone,and other soft rocks.Because of the low strength of the rock mass and the serious...The lithology of the strata in the Gobi region of the Xinjiang autonomous region of China is mainly composed of mudstone,silty mudstone,and other soft rocks.Because of the low strength of the rock mass and the serious effects of physical weathering in this area,the slope stability in open-pit mines is poor,and creep deformation and instability can readily occur.Taking the Dananhu No.2 open-pit mine as a typical example,the creep test of a mudstone sample under different stress levels was studied.Then,based on a bottom friction experiment and a FLAC3D numerical simulation,the deformation and failure processes of the slope were analyzed.The stress–displacement curve and the displacement–time curve for the monitoring points were plotted to obtain the relationship between the stress and displacement for the slope of the soft rock.The results showed that the long-term strength of the mudstone was between 8.0 and 8.8 MPa,and that stable creep occurred when the slope was under low stress.The potential failure mode for this type of slope is that the front edge creeps along the weak layer and then a crack is formed at the trailing edge of the slope.When the crack penetrates the weak layer,cutting bedding and bedding sliding occur.The deformation process of the stable creep slope includes an initial deformation stage,an initial creep stage,a constant velocity creep stage and a deceleration creep stage.展开更多
Based on the rock creep experiment, the data of aftershock sequence and post-earth- quake deformation are used to estimate the viscosity of crust medium near earthquake focus. Firstly 9 samples that belong to 3 kinds ...Based on the rock creep experiment, the data of aftershock sequence and post-earth- quake deformation are used to estimate the viscosity of crust medium near earthquake focus. Firstly 9 samples that belong to 3 kinds of rock are conducted in creep experiment under constant pressure to obtain the creep curves directly. Inversion results show that the standard linear model is the best one to present the earth medium. It exhibits obvious elasticity within a short time, while it exhibits obvious rheology within a long time. The relationship between element module μ 2 and the whole module μ of standard linear model or the module of real earth medium is calculated and analyzed. On the basis of μ 2 = 25 μ, the sequence of aftershock of Gonghe earthquake in Qinghai Province is analyzed and the relationship between accumulated released strain and the time is obtained, which, combined with the creep experiment results, is used to estimate the viscosity of crustal medium in this area. The measured vertical deformation after the same earthquake also is combined with the creep experiment results, then it is used to calculate the relaxation time and viscosity through three different methods respectively, i.e. inversion of Kelvin model, difference method of deformation and viscoelastic dislo- cation theory. The viscosity of crustal medium in 32 km depth of earthquake focus of Gonghe area deduced from the different data and methods is about 1019 Pa·s, which is the same as the research results by other authors at home and abroad.展开更多
基金Project(2002CB412704) supported by the Major State Basic Research Development Program of China
文摘In order to analyze mechanism of casing damage,the uniaxial compression experiment and creep experiment of interbedded mudstone samples from Sanan development area of Daqing Oilfield under different water contents were carried out.The changes of the mudstone's mechanical parameters and creep characteristics with the increment of water saturation were studied.The results indicate that the rock strength and elastic modulus decrease rapidly with the increment of water content,at the same time,the creep strain and creep strain rate of steady state increase with the increment of water content,and also the steady state creep strain rate is enhanced with the increment of deviatoric stress.Through the creep characteristic curves,a non-linear creep constitutive equation of mudstone considering the change of water contents is established,which will be used in future numerical analysis.
基金the Alexander von Humboldt FOundation. GE would liketo aCknowledge funding from Deutsche Forschungsgemeinschaft (SFB 526: Rheo
文摘Based on the detailed computer .simulation of the indentation testing on the thin-film systems, the present paper explores the detailed procedure of determining elastic properties (elastic modulus E(f) and Poisson ratio v(f) ) and creep parameters (CCREEP (f) and nCREEP (f)) for a simple Norton law (ε=CCREEP (f)σnCREEP(f), where ε is creep strain rate, and σ is the stress) material for a thin film coated on a creep substrate, whose elastic properties(E(s) and v(s)) and creep properties (CCREEP(s) and nCREEP(s) ) of the substrate are known, from indentation elastic and creep testing, respectively. The influences of the thickness of the thin-film and the size of the indenter on the indentation behavior have been discussed. It is shown that the boundary between the thin film and the substrate has great influence on the indentation creep behavior. The relative sizes of indentation systems are chosen so that the behavior of the indentation on the film is influenced by the substrate. The two elastic parameters E(f) and v(f) of the film are coupled on the influence of the elastic behavior of indentation. With the two different size indenters, the two elastic parameters E(f) and v(f) of the film can be uniquely determined by the indentation experimental slopes of depth to applied net section stress results. The procedure of determining of the two Norton law parameters CCREEP (f) and nCREEP(f) includes the following steps by the steady indentation rate d. The first step to calculate the creep indentation rate on certain loads of the two different sizes of indenters on a set of assumed values of CCREEP (f) and nCREEP (f). Then to build relationship between the creep indentation rate and the assumed CCREEP(f) and nCREEP(f). With the experimental creep indentation rate to intersect two sets of CCREEP (f) and nCREEP(f), which have the same values of d. The last step is to build the CCREEP(f) and nCREEP(f)curves from the intersection points for the two indenters.These two curves CCREEP and nCREEP(f) will intersect at one point. The axial values of the point are what we want. The procedure presented in the paper to determine the elastic parameters and creep parameters from the indentation experiments can be applied to any material systems.
基金Project(2007CB209400) supported by the Major State Basic Research and Development Program of ChinaProject(50774093) supported by the National Natural Science Foundation of ChinaProject(200801) supported by Open Research Fund of Hunan Provincial Key of Safe Mining Techniques of Coal Mines
文摘The viscoelastic-plastic creep experiments on soft ore-rock in Jinchuan Mine Ⅲ were performed under circular increment step load and unload. The experimental data were analyzed according to instantaneous elastic strain, visco-elastic strain, instantaneous plastic strain and visco-plastic strain. The result shows that instantaneous deformation modulus tends to increase with the increase of creep stress; soft rocks enhance the ability to resist instantaneous elastic deformation and instantaneous plastic deformation during the multi-level of load and unload in the cyclic process. In respect of specimen JC1099, the ratio of visco-elastic strain to visco-plastic strain varies from 3.15 to 6.58, and the ratio has decreasing tendency with stress increase as a whole; creep deformation tends to be a steady state at low stress level; soft rocks creep usually embodies accelerated creep properties at high stress level. With the damaging variable and the hardening function introduced, a nonlinear creep model of soft rocks is established, in which the decay creep is described by the nonlinear hardening function H of viscidity coefficient. The model can describe the accelerated creep of soft rocks since the nonlinear damaging evolvement variable D of deformation parameter of rocks is introduced. Three stages of soft rocks creep can be described with the uniform creep equation in the nonlinear creep model. With this nonlinear creep model applied to the creep experiments of the ore-rock of Jinchuan Mine Ⅲ, the nonlinear creep model’s curves are in good agreement with experimental data.
基金This research was financially supported by the Scientific and technological research projects in Sichuan province(Grant Nos.2022YFSY0007 and 2021YFH0010)the National Scientific Science Foundation of China(Grant No.U20A20266).
文摘To investigate the specific creep behavior of ultra-deep buried salt during oil and gas exploitation,a set of triaxial creep experiments was conducted at elevated temperatures with constant axial pressure and unloading confining pressure conditions.Experimental results show that the salt sample deforms more significantly with the increase of applied temperature and deviatoric loading.The accelerated creep phase is not occurring until the applied temperature reaches 130℃,and higher temperature is beneficial to the occurrence of accelerated creep.To describe the specific creep behavior,a novel three-dimensional(3D)creep constitutive model is developed that incorporates the thermal and mechanical variables into mechanical elements.Subsequently,the standard particle swarm optimization(SPSO)method is adopted to fit the experimental data,and the sensibility of key model parameters is analyzed to further illustrate the model function.As a result,the model can accurately predict the creep behavior of salt under the coupled thermo-mechanical effect in deep-buried condition.Based on the research results,the creep mechanical behavior of wellbore shrinkage is predicted in deep drilling projects crossing salt layer,which has practical implications for deep rock mechanics problems.
基金Project(50774090) supported by the National Natural Science Foundation of China
文摘The systematic experiment regarding the general uniaxial compression test and the creep deformations of the typical limestones from the surrounding rock of the highway tunnels were made.The relationship between the axial stress and the delayed deformation steady value was obtained from the creep tests under low loading stresses.By the least square method,the parameters of Nishihara creep model were calculated from the creep curves.The results indicate that the strain change always lags behind the increase of stress,and the long-term strength of the limestone is about 80.6% of the stress at the volumetric strain reversal which is obtained from the conventional uniaxial compression test.
文摘Healthcare organizations rely on patients’feedback and experiences to evaluate their performance and services,thereby allowing such organizations to improve inadequate services and address any shortcomings.According to the literature,social networks and particularly Twitter are effective platforms for gathering public opinions.Moreover,recent studies have used natural language processing to measure sentiments in text segments collected from Twitter to capture public opinions about various sectors,including healthcare.The present study aimed to analyze Arabic Twitter-based patient experience sentiments and to introduce an Arabic patient experience corpus.The authors collected 12,400 tweets from Arabic patients discussing patient experiences related to healthcare organizations in Saudi Arabia from 1 January 2008 to 29 January 2022.The tweets were labeled according to sentiment(positive or negative)and sector(public or private),and thereby the Hospital Patient Experiences in Saudi Arabia(HoPE-SA)dataset was produced.A simple statistical analysis was conducted to examine differences in patient views of healthcare sectors.The authors trained five models to distinguish sentiments in tweets automatically with the following schemes:a transformer-based model fine-tuned with deep learning architecture and a transformer-based model fine-tuned with simple architecture,using two different transformer-based embeddings based on Bidirectional Encoder Representations from Transformers(BERT),Multi-dialect Arabic BERT(MAR-BERT),and multilingual BERT(mBERT),as well as a pretrained word2vec model with a support vector machine classifier.This is the first study to investigate the use of a bidirectional long short-term memory layer followed by a feedforward neural network for the fine-tuning of MARBERT.The deep-learning fine-tuned MARBERT-based model—the authors’best-performing model—achieved accuracy,micro-F1,and macro-F1 scores of 98.71%,98.73%,and 98.63%,respectively.
基金Project(10672063) supported by the National Natural Science Foundation of China
文摘A uniaxial viscoelastoplastic model that can describe whole creep behaviors of asphalt sand at different temperatures was presented.The model was composed of three submodels in series,which describe elastoplastic,viscoelastic and viscoplastic characteristics respectively.The constitutive equation was established for uniaxial loading condition,and the creep representation was also obtained.The constitutive parameters were determined by uniaxial compression tests under controlled-stress of 0.1 MPa with five different test temperatures of 20,40,45,50 and 60 ℃.Expressions of the model parameters in terms of temperatures were also given.The model gave prediction at various temperatures consistent with the experimental results,and can reflect the total deformation characterization of asphalt sands.
基金The work was Supported by State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology,Beijing(No.SKLGDUEK1923)National Key Research and Development Program(No.2018YFC0808301).
文摘The lithology of the strata in the Gobi region of the Xinjiang autonomous region of China is mainly composed of mudstone,silty mudstone,and other soft rocks.Because of the low strength of the rock mass and the serious effects of physical weathering in this area,the slope stability in open-pit mines is poor,and creep deformation and instability can readily occur.Taking the Dananhu No.2 open-pit mine as a typical example,the creep test of a mudstone sample under different stress levels was studied.Then,based on a bottom friction experiment and a FLAC3D numerical simulation,the deformation and failure processes of the slope were analyzed.The stress–displacement curve and the displacement–time curve for the monitoring points were plotted to obtain the relationship between the stress and displacement for the slope of the soft rock.The results showed that the long-term strength of the mudstone was between 8.0 and 8.8 MPa,and that stable creep occurred when the slope was under low stress.The potential failure mode for this type of slope is that the front edge creeps along the weak layer and then a crack is formed at the trailing edge of the slope.When the crack penetrates the weak layer,cutting bedding and bedding sliding occur.The deformation process of the stable creep slope includes an initial deformation stage,an initial creep stage,a constant velocity creep stage and a deceleration creep stage.
基金supported by the National Natural Science Foundation of China(Grant No.40274057).
文摘Based on the rock creep experiment, the data of aftershock sequence and post-earth- quake deformation are used to estimate the viscosity of crust medium near earthquake focus. Firstly 9 samples that belong to 3 kinds of rock are conducted in creep experiment under constant pressure to obtain the creep curves directly. Inversion results show that the standard linear model is the best one to present the earth medium. It exhibits obvious elasticity within a short time, while it exhibits obvious rheology within a long time. The relationship between element module μ 2 and the whole module μ of standard linear model or the module of real earth medium is calculated and analyzed. On the basis of μ 2 = 25 μ, the sequence of aftershock of Gonghe earthquake in Qinghai Province is analyzed and the relationship between accumulated released strain and the time is obtained, which, combined with the creep experiment results, is used to estimate the viscosity of crustal medium in this area. The measured vertical deformation after the same earthquake also is combined with the creep experiment results, then it is used to calculate the relaxation time and viscosity through three different methods respectively, i.e. inversion of Kelvin model, difference method of deformation and viscoelastic dislo- cation theory. The viscosity of crustal medium in 32 km depth of earthquake focus of Gonghe area deduced from the different data and methods is about 1019 Pa·s, which is the same as the research results by other authors at home and abroad.