The water-drop-shaped pressure hull has a good streamline,which has good application prospect in the underwater observatory.Therefore,this study conducted analytical,experimental and numerical investigation of the buc...The water-drop-shaped pressure hull has a good streamline,which has good application prospect in the underwater observatory.Therefore,this study conducted analytical,experimental and numerical investigation of the buckling properties of water-drop-shaped pressure hulls under hydrostatic pressure.A water-drop experiment was conducted to design water-drop-shaped pressure hulls with various shape indices.The critical loads for the water-drop-shaped pressure hulls were resolved by using Mushtari’s formula.Several numerical simulations including linear buckling analysis and nonlinear buckling analysis including eigenmode imperfections were performed.The results indicated that the critical loads resolved by Mushtari's formula were in good agreement with the linear buckling loads from the numerical simulations.This formula can be extended to estimate the buckling capacity of water-drop-shaped pressure hulls.In addition,three groups of pressure hulls were fabricated by using stereolithography,a rapid prototyping technique.Subsequently,three groups of the pressure hulls were subjected to ultrasonic measurements,optical scanning,hydrostatic testing and numerical analysis.The experimental results were consistent with the numerical results.The results indicate that the sharp end of the water-drop-shaped pressure hulls exhibited instability compared with the blunt end.This paper provides a new solution to the limitations of experimental studies on the water-drop-shaped pressure hulls as well as a new configuration and evaluation method for underwater observatories.展开更多
This study aims to improve the performances of the high-pressure water descaling technology used in steel hot rolling processes.In particular,a 2050 mm hot rolling line is considered,and the problem is investigated by...This study aims to improve the performances of the high-pressure water descaling technology used in steel hot rolling processes.In particular,a 2050 mm hot rolling line is considered,and the problem is investigated by means of a fluid–structure interaction(FSI)method by which the descaling effect produced by rolling coils with different section sizes is examined.Assuming a flat fan-shaped nozzle at the entrance of the R1R2 roughing mill,the outflow field characteristics and the velocity distribution curve on the strike line(at a target distance of 30–120 mm)are determined.It is found that the velocity in the center region of the water jet with different target distances is higher than that in the boundary region.As the target distance increases,the velocity of the water jet in the central region decreases.Through comparison with experimental results,it is shown that the simulation model can accurately predict the impact position of the high-pressure water on the impact plate,thereby providing a computational scheme that can be used to optimize the nozzle space layout and improve the slabs’descent effect for different rolling specifications.展开更多
Nuclear power plants exhibit non-linear and time-variable dynamics.Therefore,designing a control system that sets the reactor power and forces it to follow the desired load is complicated.A supercritical water reactor...Nuclear power plants exhibit non-linear and time-variable dynamics.Therefore,designing a control system that sets the reactor power and forces it to follow the desired load is complicated.A supercritical water reactor(SCWR)is a fourth-generation conceptual reactor.In an SCWR,the non-linear dynamics of the reactor require a controller capable of control-ling the nonlinearities.In this study,a pressure-tube-type SCWR was controlled during reactor power maneuvering with a higher order sliding mode,and the reactor outgoing steam temperature and pressure were controlled simultaneously.In an SCWR,the temperature,pressure,and power must be maintained at a setpoint(desired value)during power maneuvering.Reactor point kinetics equations with three groups of delayed neutrons were used in the simulation.Higher-order and classic sliding mode controllers were separately manufactured to control the plant and were compared with the PI controllers speci-fied in previous studies.The controlled parameters were reactor power,steam temperature,and pressure.Notably,for these parameters,the PI controller had certain instabilities in the presence of disturbances.The classic sliding mode controller had a higher accuracy and stability;however its main drawback was the chattering phenomenon.HOSMC was highly accurate and stable and had a small computational cost.In reality,it followed the desired values without oscillations and chattering.展开更多
Numerous engineering cases have demonstrated that the expansive soil channel slope remains susceptible to damage with the implementation of a rigid or closed protective structure. It is common for the protective struc...Numerous engineering cases have demonstrated that the expansive soil channel slope remains susceptible to damage with the implementation of a rigid or closed protective structure. It is common for the protective structure to experience bulging failure due to excessive swelling pressure. To investigate the swelling pressure properties of expansive soil, the constant volume test was employed to study the influence of water content and reserved expansion deformation on the characteristics of swelling pressure in strong expansive soils, and also to explore the evolution mechanism of the swelling pressure. The findings demonstrate that the swelling pressure-time curve can be classified into swelling pressure-time softening and swelling pressure-time stability type. The swelling pressuretime curve of the specimen with low water content is the swelling pressure-time softening type, and the softening level will be weakened with increasing reserved expansion deformation. Besides, the maximum swelling pressure Psmax decreases with increasing water content and reserved expansion deformation, especially for expansion ratio η from 24% to 37%. The reserved deformation has little effect on reducing Psmax when it is beyond 7% of the expansion rate. The specimen with low water content has a more homogeneous structure due to the significant expansion-filling effect, and the fracture and reorganization of the aggregates in the specimens with low water content cause the swelling pressure-time softening behavior. In addition, the proposed swelling pressure-time curve prediction model has a good prediction on the test results. If necessary, a deformation space of about 7% expansion rate is recommended to be reserved in the engineering to reduce the swelling pressure except for keeping a stable water content.展开更多
Temperature and pressure play key roles in Global Navigation Satellite System(GNSS) precipitable water vapor(PWV) retrieval. The National Aeronautics and Space Administration(NASA) and European Center for Medium-Range...Temperature and pressure play key roles in Global Navigation Satellite System(GNSS) precipitable water vapor(PWV) retrieval. The National Aeronautics and Space Administration(NASA) and European Center for Medium-Range Weather Forecasts(ECMWF) have released their latest reanalysis product: the modern-era retrospective analysis for research and applications, version 2(MERRA-2) and the fifthgeneration ECMWF reanalysis(ERA5), respectively. Based on the reanalysis data, we evaluate and analyze the accuracy of the surface temperature and pressure products in China using the the measured temperature and pressure data from 609 ground meteorological stations in 2017 as reference values.Then the accuracy of the two datasets and their performances in estimating GNSS PWV are analyzed. The PWV derived from the pressure and temperature products of ERA5 and MERRA-2 has high accuracy. The annual average biases of pressure and temperature for ERA5 are-0.07 hPa and 0.45 K, with the root mean square error(RMSE) of 0.95 hPa and 2.04 K, respectively. The annual average biases of pressure and temperature for MERRA-2 are-0.01 hPa and 0.38 K, with the RMSE of 1.08 h Pa and 2.66 K, respectively.The accuracy of ERA5 is slightly higher than that of MERRA-2. The two reanalysis data show negative biases in most regions of China, with the highest to lowest accuracy in the following order: the south,north, northwest, and Tibet Plateau. Comparing the GNSS PWV calculated using MERRA-2(GNSS MERRA-2 PWV) and ERA5(GNSS ERA5 PWV) with the radiosonde-derived PWV from 48 co-located GNSS stations and the measured PWV of the co-location radiosonde stations, it is found that the accuracy of GNSS ERA5 PWV is better than that of GNSS MERRA-2 PWV. These results show the different applicability of surface temperature and pressure products from MERRA-2 and ERA5 data, indicating that both have important applications in meteorological research and GNSS water vapor monitoring in China.展开更多
To solve the problems of rock strength increase caused by high in-situ stress,the stress release method with rock slot in the bottom hole by an ultra-high-pressure water jet is proposed.The stress conditions of bottom...To solve the problems of rock strength increase caused by high in-situ stress,the stress release method with rock slot in the bottom hole by an ultra-high-pressure water jet is proposed.The stress conditions of bottom hole rock,before and after slotting are analyzed and the stress release mechanism of slotting is clarified.The results show that the stress release by slotting is due to the coupling of three factors:the relief of horizontal stress,the stress concentration zone distancing away from the cutting face,and the increase of pore pressure caused by rock mass expansion;The stress concentration increases the effective stress of rock along the radial distance from O.6R to 1R(R is the radius of the well),and the presence of groove completely releases the stress,it also allows the stress concentration zone to be pushed away from the cutting face,while significantly lowering the value of stresses in the area the drilling bit acting,the maximum stress release efficiency can reach 80%.The effect of slotting characteristics on release efficiency is obvious when the groove location is near the borehole wall.With the increase of groove depth,the stress release efficiency is significantly increased,and the release range of effective stress is enlarged along the axial direction.Therefore,the stress release method and results of simulations in this paper have a guiding significance for best-improving rock-breaking efficiency and further understanding the technique.展开更多
Sand production is a critical issue during the development of offshore oil and gas fields.Certain gas fields(e.g.the AB gas field)have high porosity and high permeability,and with water at the bottom of the reservoir,...Sand production is a critical issue during the development of offshore oil and gas fields.Certain gas fields(e.g.the AB gas field)have high porosity and high permeability,and with water at the bottom of the reservoir,the risk of sand production greatly increases at high differential pressures.Based on reservoir properties,geological conditions,production requirements,and well logging data,in this study an ultrasonic time difference method,a B index method,and a S index method are used together with a model of rock mass failure(accounting for water influx and pressure depletion)to qualitatively predict sand production.The results show that considered sample gas field has an overall high risk of sand production.The critical differential pressure(CDP)without water influx is in the range of 1.40 to 2.35 MPa,the CDP after water influx is from 0.60 to 1.41MPa.The CDP under pressure depletion is in the range of 1.20 to 1.92 MPa.The differential pressure charts of sand production are plotted,and the safe differential pressure windows with or without water influx are obtained.The model calculation results and the experimental results are consistent with the field production data,which indicates that the implemented prediction method could be taken as a reference for sand production prediction in similar deep water gas fields.展开更多
In today’s society, with the continuous growth of energy demand, Bohai Oilfield, as an important offshore oil resource base in China, is facing increasingly severe challenges while contributing to national energy sec...In today’s society, with the continuous growth of energy demand, Bohai Oilfield, as an important offshore oil resource base in China, is facing increasingly severe challenges while contributing to national energy security. In order to improve the quality of water injection in the oilfield and gradually achieve efficient and stable production, Bohai Oilfield has launched a water injection well pressure optimization project, focusing on improving the efficiency and quality of water injection in the water injection wells, in order to achieve the optimal water injection plan. In practical work, P Oilfield continues to promote the development of water injection well pressure optimization projects, emphasizing practical exploration and continuous optimization of work plans. However, during the project implementation process, there were some problems, one of which was that the statistics of cumulative injection volume were not scientific enough, resulting in a more comprehensive and accurate presentation of the actual results of pressure optimization work. In the context of continuous improvement work, after careful analysis and research, P Oilfield has decided to optimize the cumulative injection rate algorithm to guide the oilfield’s water injection work in a more refined way, ensuring sufficient and good water injection, and enhancing the oilfield’s production efficiency and comprehensive competitiveness.展开更多
In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature(HPHT)curing conditions,various influencing factors,including cement sour...In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature(HPHT)curing conditions,various influencing factors,including cement sources,particle sizes of silica flour,and additions of silica fume,alumina,colloidal iron oxide and nano-graphene,were investigated.To simulate the environment of cementing geothermal wells and deep wells,cement slurries were directly cured at 50 MPa and 200?C.Mineral compositions(as determined by X-ray diffraction Rietveld refinement),water permeability,compressive strength and Young’s modulus were used to evaluate the qualities of the set cement.Short-term curing(2e30 d)test results indicated that the adoption of 6 m m ultrafine crystalline silica played the most important role in stabilizing the mechanical properties of oil well cement systems,while the addition of silica fume had a detrimental effect on strength stability.Long-term curing(2e180 d)test results indicated that nano-graphene could stabilize the Young’s modulus of oil well cement systems.However,none of the ad-mixtures studied here can completely prevent the strength retrogression phenomenon due to their inability to stop the conversion of amorphous to crystalline phases.展开更多
A new numerical model for low-permeability reservoirs is developed.The model incorporates the nonlinear characteristics of oil-water two-phase flows while taking into account the initiation pressure gradient.Related n...A new numerical model for low-permeability reservoirs is developed.The model incorporates the nonlinear characteristics of oil-water two-phase flows while taking into account the initiation pressure gradient.Related numerical solutions are obtained using a finite difference method.The correctness of the method is demonstrated using a two-dimensional inhomogeneous low permeability example.Then,the differences in the cumulative oil and water production are investigated for different starting water saturations.It is shown that when the initial water saturation grows,the water content of the block continues to rise and the cumulative oil production gradually decreases.展开更多
Cyclic triaxial tests and numerical analyses were undertaken, in order to evaluate the wave-induced pore water pressure in seabed sediments in the Hangzhou Bay. The cyclic triaxial tests indicate that the rate of pore...Cyclic triaxial tests and numerical analyses were undertaken, in order to evaluate the wave-induced pore water pressure in seabed sediments in the Hangzhou Bay. The cyclic triaxial tests indicate that the rate of pore water pressure generation in cohesive soils decreases with time, and the development of the pore water pressure can be represented by a hyperbolic curve. Numerical analyses, taking into account the generation and dissipation of pore water pressure simultaneously, suggest that the pore water pressure buildup in cohesive soils may increase with time continuously until the pore water pressure ratio approaches to 1, or it may decrease after a certain time, which is controlled by drain conditions. These phenomena are different from those in sands. For waves with a retum period of 100 a in the Hangzhou Bay, if the wave duration is more than 60 h, then the pore water pressure ratio will be close to 1 and soil fabric failure will take place.展开更多
When perforating with an abrasive water jet, it is possible that the pressure in the hole (perforation) will be higher than that in the annulus because of water jet blasting against the hole wall, which also is the ...When perforating with an abrasive water jet, it is possible that the pressure in the hole (perforation) will be higher than that in the annulus because of water jet blasting against the hole wall, which also is the theoretical basis for the technology of hydro-jet fracturing. This paper analyzes the mechanism of generating pressure stagnation in water jet hole, and puts forward a new concept of hydroseal. Then, the distribution of pressure in the hole was simulated with the finite element method. The simulation results showed that the pressure in the hole was higher than that in the annulus. Also, the lower the annular pressure (confining pressure) and the higher the blasting pressure, the greater the pressure difference. An experiment indicated that the cement sample was lifted up under the pressure stagnation in the hole, which proved the finite element simulation results obviously.展开更多
Explicit finite difference code was used to calculate the stability factors of shallow tunnels without internal support in limit state. The proposed method was formulated within the nonassociative plasticity. For the ...Explicit finite difference code was used to calculate the stability factors of shallow tunnels without internal support in limit state. The proposed method was formulated within the nonassociative plasticity. For the shallow tunnels in soft clay, without considering the influences of pore water pressure and dilatancy, numerical results were compared with the previously published solutions. From the comparisons, it is found that the present solutions agree well with the previous solutions. The accuracy of the strength reduction technique was demonstrated through the comparisons. The influence of the pore water pressure was discussed. For the shallow tunnels in dilatant cohesive-frictional soils, the dilatant analysis was carried out.展开更多
In the process of rock breaking, the conical pick bears great cutting force and wear, as a result, high-pressure water jet technology is used to assist with cutting. However, the effect of the water jet position has n...In the process of rock breaking, the conical pick bears great cutting force and wear, as a result, high-pressure water jet technology is used to assist with cutting. However, the effect of the water jet position has not been studied for rock breaking using a pick. Therefore, the models of rock breaking with different configuration modes of the water jet are established based on SPH combined with FEM. The effect of the water jet pressure, distance between the jet and the pick bit, and cutting depth on the rock breaking performance as well as a comparison of the tension and compression stress are studied via simulation; the simulation results are verified by experiments. The numerical and experimental results indicate that the decrease in the rates of the pick force obviously increases from 25 MPa to 40 MPa, but slowly after 40 MPa, and the optimal distance between the jet and the pick bit is 2 mm under the JFP and JSP modes. The JCP mode is proved the best, followed by the modes of JRP and JFP, and the worst mode is JSP. The decrease in the rates of the pick force of the JCP, JRP, JFP, and JSP modes are up to 30.96%, 28.96%, 33.46%, 28.17%, and 25.42%, respectively, in experiment. Moreover, the JSP mode can be regarded as a special JFP model when the distance between the pick-tip and the jet impact point is 0 mm. This paper has a dominant capability in introducing new numerical and experimental method for the study of rock breaking assisted by water jet and electing the best water jet position from four different configuration modes.展开更多
Jinping traffic tunnel is one of the deepest traffic tunnels in the world with a maximum overburden of 2 375 m and the overburden over 73% of its total length is larger than 1 500 m. The tunnel is 17.5 km long and des...Jinping traffic tunnel is one of the deepest traffic tunnels in the world with a maximum overburden of 2 375 m and the overburden over 73% of its total length is larger than 1 500 m. The tunnel is 17.5 km long and designed to provide a shortcut road between two hydropower stations: Jinping I and Jinping II of the Jinping Hydropower Project, located on Yalong River, Liangshan State, Sichuan Province, China. The tunnel is so deep that building any shafts is impossible. The construction starts from both ends (east and west ends), and the construction length from the west end is 10 km with a blind heading. This paper deals with an overview of this project and analysis of the engineering features, as well as key technologies developed and applied during the construction, including geological prediction, rock burst prevention under a super high in-situ stress, sealing of groundwater with a high pressure and big flow rate, ventilation for a blind heading of 10 km, wet spraying of shotcrete at zones of rock burst and rich water, etc. The application of the new technologies to the construction achieved a high quality tunnel within the contract period.展开更多
The coupling numerical model of wave interaction with porous medium is used to study wave- induced pore water pressure in high permeability seabed. In the model, the wave field solver is based on the two dimensional R...The coupling numerical model of wave interaction with porous medium is used to study wave- induced pore water pressure in high permeability seabed. In the model, the wave field solver is based on the two dimensional Reynolds-averaged Navier-Stokes (RANS) equations with a k-s closure, and Forchheimer equations are adopted for flow within the porous media. By introducing a Velocity-Pressure Correction equation for the wave flow and porous flow, a highly efficient coupling between the two flows is implemented. The numerical tests are conducted to study the effects of seabed thickness, porosity, particle size and intrinsic permeability coefficient on regular wave and solitary wave-induced pore water pressure response. The results indicate that, as compared with regular wave-induced, solitary wave-induced pore water pressure has larger values and stronger action on seabed with different parameters. The results also clearly show the flow characteristics of pore water flow within seabed and water wave flow on seabed. The maximum pore water flow velocities within seabed under solitary wave action are higher than those under regular wave action.展开更多
Objective The effects of arsenic exposure from drinking water, arsenic metabolism, and arsenic methylation on blood pressure(BP) were observed in this study. Methods The BP and arsenic species of 560 participants we...Objective The effects of arsenic exposure from drinking water, arsenic metabolism, and arsenic methylation on blood pressure(BP) were observed in this study. Methods The BP and arsenic species of 560 participants were determined. Logistic regression analysis was applied to estimate the odds ratios of BP associated with arsenic metabolites and arsenic methylation capability. Results BP was positively associated with cumulative arsenic exposure(CAE). Subjects with abnormal diastolic blood pressure(DBP), systolic blood pressure(SBP), and pulse pressure(PP) usually had higher urinary i As(inorganic arsenic), MMA(monomethylated arsenic), DMA(dimethylated arsenic), and TAs(total arsenic) than subjects with normal DBP, SBP, and PP. The i As%, MMA%, and DMA% differed slightly between subjects with abnormal BP and those with normal BP. The PMI and SMI were slightly higher in subjects with abnormal PP than in those with normal PP. Conclusion Our findings suggest that higher CAE may elevate BP. Males may have a higher risk of abnormal DBP, whereas females have a higher risk of abnormal SBP and PP. Higher urinary i As may increase the risk of abnormal BP. Lower PMI may elevate the BP. However, higher SMI may increase the DBP and SBP, and lower SMI may elevate the PP.展开更多
A novel fiber Bragg grating(FBG)sensor with three-dimensional(3D)fused deposition modeling(FDM)approach is proposed for effective stress measurement in soil mass.The three-diaphragm structure design is developed to me...A novel fiber Bragg grating(FBG)sensor with three-dimensional(3D)fused deposition modeling(FDM)approach is proposed for effective stress measurement in soil mass.The three-diaphragm structure design is developed to measure earth and water pressures simultaneously.The proposed transducer has advantages of small size,high sensitivity,low cost,immunity to electromagnetic interference and rapid prototyping.The working principle,design parameters,and manufacturing details are discussed.The proposed transducer was calibrated for earth and water pressures measurement by using weights and a specially designed pressure chamber,respectively.The calibration results showed that the wavelength of the transducer was proportional to the applied pressure.The sensitivity coefficients of the earth and water pressures were 12.633 nm/MPa and 6.282 nm/MPa,respectively.Repeated tests and error analysis demonstrated the excellent stability and accuracy of the earth and water pressure measurements.The performance of the proposed transducer was further verified by a model experimental test and numerical analysis,which indicated that the proposed transducer has great potential for practical applications.展开更多
Based on statistical analysis on the situation of casing damage and water injection pressure in Pubei Oilfield, it shows that the main forms of casing damage in Pubei Oilfield are deformation and dislocation. Dip angl...Based on statistical analysis on the situation of casing damage and water injection pressure in Pubei Oilfield, it shows that the main forms of casing damage in Pubei Oilfield are deformation and dislocation. Dip angle and faults have a significant impact on casing damage and casing damage is closely related to water injection pressure. Through laboratory simulating experiment and theoretical calculation, the formula of critical injection pressure giving rise to casing damage is obtained and the preventive measures are drafted.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52071160 and 52071203)the 333-Key-Industry Talent Project of Jiangsu Scientific Committee(Grant No.JTO 2022-21).
文摘The water-drop-shaped pressure hull has a good streamline,which has good application prospect in the underwater observatory.Therefore,this study conducted analytical,experimental and numerical investigation of the buckling properties of water-drop-shaped pressure hulls under hydrostatic pressure.A water-drop experiment was conducted to design water-drop-shaped pressure hulls with various shape indices.The critical loads for the water-drop-shaped pressure hulls were resolved by using Mushtari’s formula.Several numerical simulations including linear buckling analysis and nonlinear buckling analysis including eigenmode imperfections were performed.The results indicated that the critical loads resolved by Mushtari's formula were in good agreement with the linear buckling loads from the numerical simulations.This formula can be extended to estimate the buckling capacity of water-drop-shaped pressure hulls.In addition,three groups of pressure hulls were fabricated by using stereolithography,a rapid prototyping technique.Subsequently,three groups of the pressure hulls were subjected to ultrasonic measurements,optical scanning,hydrostatic testing and numerical analysis.The experimental results were consistent with the numerical results.The results indicate that the sharp end of the water-drop-shaped pressure hulls exhibited instability compared with the blunt end.This paper provides a new solution to the limitations of experimental studies on the water-drop-shaped pressure hulls as well as a new configuration and evaluation method for underwater observatories.
基金The research was funded by Science and Technology Project of Hebei Education Department(Project Number:QN2022198).Y.C.received the grant.
文摘This study aims to improve the performances of the high-pressure water descaling technology used in steel hot rolling processes.In particular,a 2050 mm hot rolling line is considered,and the problem is investigated by means of a fluid–structure interaction(FSI)method by which the descaling effect produced by rolling coils with different section sizes is examined.Assuming a flat fan-shaped nozzle at the entrance of the R1R2 roughing mill,the outflow field characteristics and the velocity distribution curve on the strike line(at a target distance of 30–120 mm)are determined.It is found that the velocity in the center region of the water jet with different target distances is higher than that in the boundary region.As the target distance increases,the velocity of the water jet in the central region decreases.Through comparison with experimental results,it is shown that the simulation model can accurately predict the impact position of the high-pressure water on the impact plate,thereby providing a computational scheme that can be used to optimize the nozzle space layout and improve the slabs’descent effect for different rolling specifications.
文摘Nuclear power plants exhibit non-linear and time-variable dynamics.Therefore,designing a control system that sets the reactor power and forces it to follow the desired load is complicated.A supercritical water reactor(SCWR)is a fourth-generation conceptual reactor.In an SCWR,the non-linear dynamics of the reactor require a controller capable of control-ling the nonlinearities.In this study,a pressure-tube-type SCWR was controlled during reactor power maneuvering with a higher order sliding mode,and the reactor outgoing steam temperature and pressure were controlled simultaneously.In an SCWR,the temperature,pressure,and power must be maintained at a setpoint(desired value)during power maneuvering.Reactor point kinetics equations with three groups of delayed neutrons were used in the simulation.Higher-order and classic sliding mode controllers were separately manufactured to control the plant and were compared with the PI controllers speci-fied in previous studies.The controlled parameters were reactor power,steam temperature,and pressure.Notably,for these parameters,the PI controller had certain instabilities in the presence of disturbances.The classic sliding mode controller had a higher accuracy and stability;however its main drawback was the chattering phenomenon.HOSMC was highly accurate and stable and had a small computational cost.In reality,it followed the desired values without oscillations and chattering.
基金financially supported by the National Key R&D Program of China (Grant No. 2019YFC1509901)。
文摘Numerous engineering cases have demonstrated that the expansive soil channel slope remains susceptible to damage with the implementation of a rigid or closed protective structure. It is common for the protective structure to experience bulging failure due to excessive swelling pressure. To investigate the swelling pressure properties of expansive soil, the constant volume test was employed to study the influence of water content and reserved expansion deformation on the characteristics of swelling pressure in strong expansive soils, and also to explore the evolution mechanism of the swelling pressure. The findings demonstrate that the swelling pressure-time curve can be classified into swelling pressure-time softening and swelling pressure-time stability type. The swelling pressuretime curve of the specimen with low water content is the swelling pressure-time softening type, and the softening level will be weakened with increasing reserved expansion deformation. Besides, the maximum swelling pressure Psmax decreases with increasing water content and reserved expansion deformation, especially for expansion ratio η from 24% to 37%. The reserved deformation has little effect on reducing Psmax when it is beyond 7% of the expansion rate. The specimen with low water content has a more homogeneous structure due to the significant expansion-filling effect, and the fracture and reorganization of the aggregates in the specimens with low water content cause the swelling pressure-time softening behavior. In addition, the proposed swelling pressure-time curve prediction model has a good prediction on the test results. If necessary, a deformation space of about 7% expansion rate is recommended to be reserved in the engineering to reduce the swelling pressure except for keeping a stable water content.
基金the National Natural Science Foundation of China(Grant No.42204006)the Guangxi Natural Science Foundation of China(2020GXNSFBA297145)+1 种基金the“Ba Gui Scholars”program of the provincial government of Guangxi,and Innovation Project of GuangXi Graduate Education(Grant No.YCSW2022322)Open Research Fund Program of the Key Laboratory of Geospace Environment and Geodesy,Ministry of Education,China(GrantNo.20-01-03,21-01-04)
文摘Temperature and pressure play key roles in Global Navigation Satellite System(GNSS) precipitable water vapor(PWV) retrieval. The National Aeronautics and Space Administration(NASA) and European Center for Medium-Range Weather Forecasts(ECMWF) have released their latest reanalysis product: the modern-era retrospective analysis for research and applications, version 2(MERRA-2) and the fifthgeneration ECMWF reanalysis(ERA5), respectively. Based on the reanalysis data, we evaluate and analyze the accuracy of the surface temperature and pressure products in China using the the measured temperature and pressure data from 609 ground meteorological stations in 2017 as reference values.Then the accuracy of the two datasets and their performances in estimating GNSS PWV are analyzed. The PWV derived from the pressure and temperature products of ERA5 and MERRA-2 has high accuracy. The annual average biases of pressure and temperature for ERA5 are-0.07 hPa and 0.45 K, with the root mean square error(RMSE) of 0.95 hPa and 2.04 K, respectively. The annual average biases of pressure and temperature for MERRA-2 are-0.01 hPa and 0.38 K, with the RMSE of 1.08 h Pa and 2.66 K, respectively.The accuracy of ERA5 is slightly higher than that of MERRA-2. The two reanalysis data show negative biases in most regions of China, with the highest to lowest accuracy in the following order: the south,north, northwest, and Tibet Plateau. Comparing the GNSS PWV calculated using MERRA-2(GNSS MERRA-2 PWV) and ERA5(GNSS ERA5 PWV) with the radiosonde-derived PWV from 48 co-located GNSS stations and the measured PWV of the co-location radiosonde stations, it is found that the accuracy of GNSS ERA5 PWV is better than that of GNSS MERRA-2 PWV. These results show the different applicability of surface temperature and pressure products from MERRA-2 and ERA5 data, indicating that both have important applications in meteorological research and GNSS water vapor monitoring in China.
基金support of the National Key Research and Development Program of China(2021YFE0111400)the Shandong provincial natural science foundation(No.ZR2019MEE120)the horizon programme of the EU's funding of the ORCH YD project,EU-H2020(101006752-ORCHYD).
文摘To solve the problems of rock strength increase caused by high in-situ stress,the stress release method with rock slot in the bottom hole by an ultra-high-pressure water jet is proposed.The stress conditions of bottom hole rock,before and after slotting are analyzed and the stress release mechanism of slotting is clarified.The results show that the stress release by slotting is due to the coupling of three factors:the relief of horizontal stress,the stress concentration zone distancing away from the cutting face,and the increase of pore pressure caused by rock mass expansion;The stress concentration increases the effective stress of rock along the radial distance from O.6R to 1R(R is the radius of the well),and the presence of groove completely releases the stress,it also allows the stress concentration zone to be pushed away from the cutting face,while significantly lowering the value of stresses in the area the drilling bit acting,the maximum stress release efficiency can reach 80%.The effect of slotting characteristics on release efficiency is obvious when the groove location is near the borehole wall.With the increase of groove depth,the stress release efficiency is significantly increased,and the release range of effective stress is enlarged along the axial direction.Therefore,the stress release method and results of simulations in this paper have a guiding significance for best-improving rock-breaking efficiency and further understanding the technique.
基金This research is financially supported by the National Natural Science Foundation of China(Grant No.52174015)supported by the Program for Changjiang Scholars and Innovative Research Team in University(IRT_14R58).
文摘Sand production is a critical issue during the development of offshore oil and gas fields.Certain gas fields(e.g.the AB gas field)have high porosity and high permeability,and with water at the bottom of the reservoir,the risk of sand production greatly increases at high differential pressures.Based on reservoir properties,geological conditions,production requirements,and well logging data,in this study an ultrasonic time difference method,a B index method,and a S index method are used together with a model of rock mass failure(accounting for water influx and pressure depletion)to qualitatively predict sand production.The results show that considered sample gas field has an overall high risk of sand production.The critical differential pressure(CDP)without water influx is in the range of 1.40 to 2.35 MPa,the CDP after water influx is from 0.60 to 1.41MPa.The CDP under pressure depletion is in the range of 1.20 to 1.92 MPa.The differential pressure charts of sand production are plotted,and the safe differential pressure windows with or without water influx are obtained.The model calculation results and the experimental results are consistent with the field production data,which indicates that the implemented prediction method could be taken as a reference for sand production prediction in similar deep water gas fields.
文摘In today’s society, with the continuous growth of energy demand, Bohai Oilfield, as an important offshore oil resource base in China, is facing increasingly severe challenges while contributing to national energy security. In order to improve the quality of water injection in the oilfield and gradually achieve efficient and stable production, Bohai Oilfield has launched a water injection well pressure optimization project, focusing on improving the efficiency and quality of water injection in the water injection wells, in order to achieve the optimal water injection plan. In practical work, P Oilfield continues to promote the development of water injection well pressure optimization projects, emphasizing practical exploration and continuous optimization of work plans. However, during the project implementation process, there were some problems, one of which was that the statistics of cumulative injection volume were not scientific enough, resulting in a more comprehensive and accurate presentation of the actual results of pressure optimization work. In the context of continuous improvement work, after careful analysis and research, P Oilfield has decided to optimize the cumulative injection rate algorithm to guide the oilfield’s water injection work in a more refined way, ensuring sufficient and good water injection, and enhancing the oilfield’s production efficiency and comprehensive competitiveness.
基金Financial support comes from China National Natural Science Foundation(Grant No.51974352)as well as from China University of Petroleum(East China)(Grant Nos.2018000025 and 2019000011)。
文摘In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature(HPHT)curing conditions,various influencing factors,including cement sources,particle sizes of silica flour,and additions of silica fume,alumina,colloidal iron oxide and nano-graphene,were investigated.To simulate the environment of cementing geothermal wells and deep wells,cement slurries were directly cured at 50 MPa and 200?C.Mineral compositions(as determined by X-ray diffraction Rietveld refinement),water permeability,compressive strength and Young’s modulus were used to evaluate the qualities of the set cement.Short-term curing(2e30 d)test results indicated that the adoption of 6 m m ultrafine crystalline silica played the most important role in stabilizing the mechanical properties of oil well cement systems,while the addition of silica fume had a detrimental effect on strength stability.Long-term curing(2e180 d)test results indicated that nano-graphene could stabilize the Young’s modulus of oil well cement systems.However,none of the ad-mixtures studied here can completely prevent the strength retrogression phenomenon due to their inability to stop the conversion of amorphous to crystalline phases.
文摘A new numerical model for low-permeability reservoirs is developed.The model incorporates the nonlinear characteristics of oil-water two-phase flows while taking into account the initiation pressure gradient.Related numerical solutions are obtained using a finite difference method.The correctness of the method is demonstrated using a two-dimensional inhomogeneous low permeability example.Then,the differences in the cumulative oil and water production are investigated for different starting water saturations.It is shown that when the initial water saturation grows,the water content of the block continues to rise and the cumulative oil production gradually decreases.
基金This work was supported by the National Natural Science Foundation of China under the contract Nos 10372089 and 40476032.
文摘Cyclic triaxial tests and numerical analyses were undertaken, in order to evaluate the wave-induced pore water pressure in seabed sediments in the Hangzhou Bay. The cyclic triaxial tests indicate that the rate of pore water pressure generation in cohesive soils decreases with time, and the development of the pore water pressure can be represented by a hyperbolic curve. Numerical analyses, taking into account the generation and dissipation of pore water pressure simultaneously, suggest that the pore water pressure buildup in cohesive soils may increase with time continuously until the pore water pressure ratio approaches to 1, or it may decrease after a certain time, which is controlled by drain conditions. These phenomena are different from those in sands. For waves with a retum period of 100 a in the Hangzhou Bay, if the wave duration is more than 60 h, then the pore water pressure ratio will be close to 1 and soil fabric failure will take place.
文摘When perforating with an abrasive water jet, it is possible that the pressure in the hole (perforation) will be higher than that in the annulus because of water jet blasting against the hole wall, which also is the theoretical basis for the technology of hydro-jet fracturing. This paper analyzes the mechanism of generating pressure stagnation in water jet hole, and puts forward a new concept of hydroseal. Then, the distribution of pressure in the hole was simulated with the finite element method. The simulation results showed that the pressure in the hole was higher than that in the annulus. Also, the lower the annular pressure (confining pressure) and the higher the blasting pressure, the greater the pressure difference. An experiment indicated that the cement sample was lifted up under the pressure stagnation in the hole, which proved the finite element simulation results obviously.
基金Project(200550) supported by the Foundation for the Author of National Excellent Doctoral Dissertation of ChinaProject (09JJ1008) supported by the Natural Science Foundation of Hunan Province, China
文摘Explicit finite difference code was used to calculate the stability factors of shallow tunnels without internal support in limit state. The proposed method was formulated within the nonassociative plasticity. For the shallow tunnels in soft clay, without considering the influences of pore water pressure and dilatancy, numerical results were compared with the previously published solutions. From the comparisons, it is found that the present solutions agree well with the previous solutions. The accuracy of the strength reduction technique was demonstrated through the comparisons. The influence of the pore water pressure was discussed. For the shallow tunnels in dilatant cohesive-frictional soils, the dilatant analysis was carried out.
基金Supported by National Natural Science Foundation of China(Grant No.51375478)the Fundamental Research Funds for the Central Universities,China(Grant No.2014ZDPY12)the Priority Academic Program Development of Jiangsu High Education Institute of China
文摘In the process of rock breaking, the conical pick bears great cutting force and wear, as a result, high-pressure water jet technology is used to assist with cutting. However, the effect of the water jet position has not been studied for rock breaking using a pick. Therefore, the models of rock breaking with different configuration modes of the water jet are established based on SPH combined with FEM. The effect of the water jet pressure, distance between the jet and the pick bit, and cutting depth on the rock breaking performance as well as a comparison of the tension and compression stress are studied via simulation; the simulation results are verified by experiments. The numerical and experimental results indicate that the decrease in the rates of the pick force obviously increases from 25 MPa to 40 MPa, but slowly after 40 MPa, and the optimal distance between the jet and the pick bit is 2 mm under the JFP and JSP modes. The JCP mode is proved the best, followed by the modes of JRP and JFP, and the worst mode is JSP. The decrease in the rates of the pick force of the JCP, JRP, JFP, and JSP modes are up to 30.96%, 28.96%, 33.46%, 28.17%, and 25.42%, respectively, in experiment. Moreover, the JSP mode can be regarded as a special JFP model when the distance between the pick-tip and the jet impact point is 0 mm. This paper has a dominant capability in introducing new numerical and experimental method for the study of rock breaking assisted by water jet and electing the best water jet position from four different configuration modes.
文摘Jinping traffic tunnel is one of the deepest traffic tunnels in the world with a maximum overburden of 2 375 m and the overburden over 73% of its total length is larger than 1 500 m. The tunnel is 17.5 km long and designed to provide a shortcut road between two hydropower stations: Jinping I and Jinping II of the Jinping Hydropower Project, located on Yalong River, Liangshan State, Sichuan Province, China. The tunnel is so deep that building any shafts is impossible. The construction starts from both ends (east and west ends), and the construction length from the west end is 10 km with a blind heading. This paper deals with an overview of this project and analysis of the engineering features, as well as key technologies developed and applied during the construction, including geological prediction, rock burst prevention under a super high in-situ stress, sealing of groundwater with a high pressure and big flow rate, ventilation for a blind heading of 10 km, wet spraying of shotcrete at zones of rock burst and rich water, etc. The application of the new technologies to the construction achieved a high quality tunnel within the contract period.
基金The National Natural Science Foundation of China under contract Nos 50909009,50979008 and 41176072the Open Foundation of the State Key Laboratory of Coastal and Offshore Engineering in Dalian University of Technology of China under contract No. LP1004the Ph.D. Program Foundation of Ministry of Education of China under contract No. 20094316110002
文摘The coupling numerical model of wave interaction with porous medium is used to study wave- induced pore water pressure in high permeability seabed. In the model, the wave field solver is based on the two dimensional Reynolds-averaged Navier-Stokes (RANS) equations with a k-s closure, and Forchheimer equations are adopted for flow within the porous media. By introducing a Velocity-Pressure Correction equation for the wave flow and porous flow, a highly efficient coupling between the two flows is implemented. The numerical tests are conducted to study the effects of seabed thickness, porosity, particle size and intrinsic permeability coefficient on regular wave and solitary wave-induced pore water pressure response. The results indicate that, as compared with regular wave-induced, solitary wave-induced pore water pressure has larger values and stronger action on seabed with different parameters. The results also clearly show the flow characteristics of pore water flow within seabed and water wave flow on seabed. The maximum pore water flow velocities within seabed under solitary wave action are higher than those under regular wave action.
基金supported by the State Key Program of National Natural Science foundation of China(Grant No.41230749)the National Natural Science foundation of China(Grant No.41601559)
文摘Objective The effects of arsenic exposure from drinking water, arsenic metabolism, and arsenic methylation on blood pressure(BP) were observed in this study. Methods The BP and arsenic species of 560 participants were determined. Logistic regression analysis was applied to estimate the odds ratios of BP associated with arsenic metabolites and arsenic methylation capability. Results BP was positively associated with cumulative arsenic exposure(CAE). Subjects with abnormal diastolic blood pressure(DBP), systolic blood pressure(SBP), and pulse pressure(PP) usually had higher urinary i As(inorganic arsenic), MMA(monomethylated arsenic), DMA(dimethylated arsenic), and TAs(total arsenic) than subjects with normal DBP, SBP, and PP. The i As%, MMA%, and DMA% differed slightly between subjects with abnormal BP and those with normal BP. The PMI and SMI were slightly higher in subjects with abnormal PP than in those with normal PP. Conclusion Our findings suggest that higher CAE may elevate BP. Males may have a higher risk of abnormal DBP, whereas females have a higher risk of abnormal SBP and PP. Higher urinary i As may increase the risk of abnormal BP. Lower PMI may elevate the BP. However, higher SMI may increase the DBP and SBP, and lower SMI may elevate the PP.
基金funding support from the National Natural Science Foundation of China(Grant Nos.41972271 and 42177127)Sanya Science and Education Innovation Park of Wuhan University of Technology(Grant No.2020KF0007)。
文摘A novel fiber Bragg grating(FBG)sensor with three-dimensional(3D)fused deposition modeling(FDM)approach is proposed for effective stress measurement in soil mass.The three-diaphragm structure design is developed to measure earth and water pressures simultaneously.The proposed transducer has advantages of small size,high sensitivity,low cost,immunity to electromagnetic interference and rapid prototyping.The working principle,design parameters,and manufacturing details are discussed.The proposed transducer was calibrated for earth and water pressures measurement by using weights and a specially designed pressure chamber,respectively.The calibration results showed that the wavelength of the transducer was proportional to the applied pressure.The sensitivity coefficients of the earth and water pressures were 12.633 nm/MPa and 6.282 nm/MPa,respectively.Repeated tests and error analysis demonstrated the excellent stability and accuracy of the earth and water pressure measurements.The performance of the proposed transducer was further verified by a model experimental test and numerical analysis,which indicated that the proposed transducer has great potential for practical applications.
文摘Based on statistical analysis on the situation of casing damage and water injection pressure in Pubei Oilfield, it shows that the main forms of casing damage in Pubei Oilfield are deformation and dislocation. Dip angle and faults have a significant impact on casing damage and casing damage is closely related to water injection pressure. Through laboratory simulating experiment and theoretical calculation, the formula of critical injection pressure giving rise to casing damage is obtained and the preventive measures are drafted.