Microseismic data shows that some unconventional reservoirs comprise well-developed natural fractures and complex hydraulic fracture networks.It is neither practical nor advantageous to simulate a huge number of natur...Microseismic data shows that some unconventional reservoirs comprise well-developed natural fractures and complex hydraulic fracture networks.It is neither practical nor advantageous to simulate a huge number of natural and hydraulic fractures with numerical models.Given that the conventional dual-porosity models are not applicable to the highly discrete natural fractures,the paper develops a semianalytical well testing model for horizontal wells with hydraulic fracture networks and randomly-distributed discretely natural fractures.The proposed model has the capability to analyze the pressure behaviors by considering complex fracture networks and isolated natural fractures rapidly and efficiently.The model includes diffusivity equations in three domains:(1)matrix,(2)discretely natural fractures,and(3)hydraulic fracture networks.The pressure transient solution of these diffusivity equations is obtained by using Laplace transforms and super-position principle.We verify the presented model by performing a case study with a numerical simulator for complex natural fractures.It is found that there are some interestingflow behaviors for fracture-network horizontal well with discretely natural fractures like bilinearflow,“V-shape”caused byfluid supply,pseudo boundary-dominatedflow,impact of natural fractures,etc.The pseudo boundary-dominatedflow provides us the information about how large the area covered by hydraulic fracture networks.The impact of natural fracture shows the pa-rameters of natural fractures.This work provides a good understanding of transient pressure behaviors in unconventional reservoirs and guidelines for the producer optimizefield development and well economics.展开更多
Slopes are likely to fail in areas with frequent rainfall and earthquakes.The deformation characteristics of unsaturated slopes subjected to post-rainfall earthquakes are investigated using centrifuge model tests and ...Slopes are likely to fail in areas with frequent rainfall and earthquakes.The deformation characteristics of unsaturated slopes subjected to post-rainfall earthquakes are investigated using centrifuge model tests and finite element analyses.Three tests of the slope deformation under earthquake and post-rainfall earthquakes are first studied using image analysis techniques.Then,based on an elastoplastic constitutive model,numerical simulations are carried out using the finite element method and compared with the centrifuge test results.Finally,a parametric study is performed to clarify the effects of antecedent rainfall on earthquake-induced slope deformation.The results show that slope deformation caused by post-rainfall earthquakes differs from that caused by earthquakes without antecedent rainfall.The seepage flow and soil strength of the slope are affected by previous rainfall conditions,such as intensity and duration,which directly influence the slope deformation caused by the subsequent earthquake.Soil displacement and strain become greater and the slip surface is more noticeable during the post-rainfall earthquake of higher intensity.In addition,the time interval between the rainfall and the earthquake has a considerable impact on the detailed characteristics of the slope deformation,and the significant deformation occurs at the time of lowest soil strength when seepage flow reaches the lower part of the slope.Moreover,the repeated intermittent rainfall greatly affects the subsequent earthquake-induced slope deformation,the main characteristics of which are closely related to the changes in saturation and strength of the slope.However,with the prolonged time gap between each round of rainfall,the earthquake-induced slope deformation becomes insignificant.展开更多
Modeling technology has been introduced into software testing field.However,how to carry through the testing modeling effectively is still a difficulty.Based on combination of simulation modeling technology and embedd...Modeling technology has been introduced into software testing field.However,how to carry through the testing modeling effectively is still a difficulty.Based on combination of simulation modeling technology and embedded real-time software testing method,the process of simulation testing modeling is studied first.And then,the supporting environment of simulation testing modeling is put forward.Furthermore,an approach of embedded real-time software simulation testing modeling including modeling of cross-linked equipments of system under testing(SUT),test case,testing scheduling,and testing system service is brought forward.Finally,the formalized description and execution system of testing models are given,with which we can realize real-time,closed loop,mad automated system testing for embedded real-time software.展开更多
In this paper, an inner turret moored FPSO which works in the water of 320 m depth, is selected to study the socalled ＂passively-truncated ＋ numerical-simulation＂ type of hybrid model testing technique while the tn...In this paper, an inner turret moored FPSO which works in the water of 320 m depth, is selected to study the socalled ＂passively-truncated ＋ numerical-simulation＂ type of hybrid model testing technique while the tnmcated water depth is 160 m and the model scale ）, = 80. During the investigation, the optimization design of the equivalent-depth truncated system is performed by using the similarity of the static characteristics between the truncated system and the full depth one as the objective function. According to the truncated system, the corresponding physical test model is made. By adopting the coupling time domain simulation method, the tnmcated system model test is numerically reconstructed to carefully verify the computer simulation software and to adjust the corresponding hydrodynamic parameters. Based on the above work, the numerical extrapolation to the full depth system is performed by using the verified computer software and the adjusted hydrodyrmmic parameters. The full depth system model test is then performed in the basin and the results are compared with those from the numerical extrapolation. At last, the implementation procedure and the key technique of the hybrid model testing of the deep-sea platforms are summarized and printed. Through the above investigations, some beneficial conclusions are presented.展开更多
Bedding slope is a typical heterogeneous slope consisting of different soil/rock layers and is likely to slide along the weakest interface.Conventional slope protection methods for bedding slopes,such as retaining wal...Bedding slope is a typical heterogeneous slope consisting of different soil/rock layers and is likely to slide along the weakest interface.Conventional slope protection methods for bedding slopes,such as retaining walls,stabilizing piles,and anchors,are time-consuming and labor-and energy-intensive.This study proposes an innovative polymer grout method to improve the bearing capacity and reduce the displacement of bedding slopes.A series of large-scale model tests were carried out to verify the effectiveness of polymer grout in protecting bedding slopes.Specifically,load-displacement relationships and failure patterns were analyzed for different testing slopes with various dosages of polymer.Results show the great potential of polymer grout in improving bearing capacity,reducing settlement,and protecting slopes from being crushed under shearing.The polymer-treated slopes remained structurally intact,while the untreated slope exhibited considerable damage when subjected to loads surpassing the bearing capacity.It is also found that polymer-cemented soils concentrate around the injection pipe,forming a fan-shaped sheet-like structure.This study proves the improvement of polymer grouting for bedding slope treatment and will contribute to the development of a fast method to protect bedding slopes from landslides.展开更多
Aphysical model facility was designed, built, and setup for conducting model tests on a composite foundation in a soil ground. The model tests were carried out on a composite foundation with different combinations of ...Aphysical model facility was designed, built, and setup for conducting model tests on a composite foundation in a soil ground. The model tests were carried out on a composite foundation with different combinations of vertical reinforcement elements in the same soil ground. Via the analysis of the collected data the characteristics of the composite foundation with different reinforcing elements were obtained, including the characteristics of load-settlement curves, column stresses, stresses of the intercolumn soil, pile-soil stress ratio, and load-sharing ratios of columns and soil. Results from the model tests reveal the mechanism of a composite foundation with different reinforcing elements quantitatively. It is concluded that both a composite foundation with a combination of steel pipe pile and sand column and that with a combination of concrete pile and lime column have a higher bearing capacity than the composite foundation with only sand columns with the same conditions of soil ground and loading. A composite foundation with lime column and sand column embodies no much better performance than that with sand colunms only.展开更多
Conducting model experiments is an effective and reliable way in the investigation of ship hydrodynamic and hydroelastic behaviors. A survey of model testing techniques for ship hydroelasticity and its prospect are pr...Conducting model experiments is an effective and reliable way in the investigation of ship hydrodynamic and hydroelastic behaviors. A survey of model testing techniques for ship hydroelasticity and its prospect are presented in this paper. The research highlights with respect to ship hydroelasticity and key points in model testing are summarized at first. Then testing techniques including laboratory tank test and full-scale sea trial are reviewed, and both their advantages and disadvantages are analyzed comprehensively. Based on the conventional testing approaches, a state-of-the-art testing approach which includes performing tests using large-scale model at sea is proposed. Furthermore, recommendations towards the further development of ship hydroelasticity tests are forecasted and discussed.展开更多
Shotcrete is one of the common solutions for shallow sliding.It works by forming a protective layer with high strength and cementing the loose soil particles on the slope surface to prevent shallow sliding.However,the...Shotcrete is one of the common solutions for shallow sliding.It works by forming a protective layer with high strength and cementing the loose soil particles on the slope surface to prevent shallow sliding.However,the solidification time of conventional cement paste is long when shotcrete is used to treat cohesionless soil landslide.The idea of reinforcing slope with polyurethane solidified soil(i.e.,mixture of polyurethane and sand)was proposed.Model tests and finite element analysis were carried out to study the effectiveness of the proposed new method on the emergency treatment of cohesionless soil landslide.Surcharge loading on the crest of the slope was applied step by step until landslide was triggered so as to test and compare the stability and bearing capacity of slope models with different conditions.The simulated slope displacements were relatively close to the measured results,and the simulated slope deformation characteristics were in good agreement with the observed phenomena,which verifies the accuracy of the numerical method.Under the condition of surcharge loading on the crest of the slope,the unreinforced slope slid when the surcharge loading exceeded 30 k Pa,which presented a failure mode of local instability and collapse at the shallow layer of slope top.The reinforced slope remained stable even when the surcharge loading reached 48 k Pa.The displacement of the reinforced slope was reduced by more than 95%.Overall,this study verifies the effectiveness of polyurethane in the emergency treatment of cohesionless soil landslide and should have broad application prospects in the field of geological disasters concerning the safety of people's live.展开更多
Ice load on underwater vehicles breaking through ice covers from underneath is a significant concern for researchers in polar exploration,and the research on this problem is still in its early stages.Both mechanical e...Ice load on underwater vehicles breaking through ice covers from underneath is a significant concern for researchers in polar exploration,and the research on this problem is still in its early stages.Both mechanical experimental measurement and numerical simulation pose research challenges.This study focuses on the ice load of a cylinder structure breaking upward through the ice sheet form underneath in the Small Ice Model Basin of China Ship Scientific Research Center(CSSRC SIMB).A high-speed camera system was employed to observe the ice sheet failure during the tests,in which,with the loading position as center,local radial cracks and circumferential cracks were generated.A load sensor was used to measure the overall ice load during this process.Meanwhile,a numerical model was developed using LS-DYNA for validation and comparison.With this model,numerical simulation was conducted under various ice thicknesses and upgoing speeds to analyze the instantaneous curves of ice load.The calculation results were statistically analyzed under different working conditions to determine the influence of the factors on the ice load of the cylinder.The study explores the measurement method about ice load of objects vertically breaking through model ice sheet and is expected to provide some fundamental insights into the safety design of underwater structures operating in ice waters.展开更多
Polymer flooding is an important means of improving oil recovery and is widely used in Daqing,Xinjiang,and Shengli oilfields,China.Different from conventional injection media such as water and gas,viscoelastic polymer...Polymer flooding is an important means of improving oil recovery and is widely used in Daqing,Xinjiang,and Shengli oilfields,China.Different from conventional injection media such as water and gas,viscoelastic polymer solutions exhibit non-Newtonian and nonlinear flow behavior including shear thinning and shear thickening,polymer convection,diffusion,adsorption,retention,inaccessible pore volume,and reduced effective permeability.However,available well test model of polymer flooding wells generally simplifies these characteristics on pressure transient response,which may lead to inaccurate results.This work proposes a novel two-phase numerical well test model to better describe the polymer viscoelasticity and nonlinear flow behavior.Different influence factors that related to near-well blockage during polymer flooding process,including the degree of blockage(inner zone permeability),the extent of blockage(composite radius),and polymer flooding front radius are explored to investigate these impacts on bottom hole pressure responses.Results show that polymer viscoelasticity has a significant impact on the transitional flow segment of type curves,and the effects of near-well formation blockage and polymer concentration distribution on well test curves are very similar.Thus,to accurately interpret the degree of near-well blockage in injection wells,it is essential to first eliminate the influence of polymer viscoelasticity.Finally,a field case is comprehensively analyzed and discussed to illustrate the applicability of the proposed model.展开更多
Maglev trains experience significant aerodynamic effects when passing through tunnels.A moving model test was conducted to explore the practical effects of speed reduction and entrance buffer structures on mitigating ...Maglev trains experience significant aerodynamic effects when passing through tunnels.A moving model test was conducted to explore the practical effects of speed reduction and entrance buffer structures on mitigating tunnel/maglev aerodynamic effects.It is found that both have an overall positive effect on mitigating the aerodynamic environment inside and outside the tunnel.Trains operating at 200 km/h show a 49.8%decrease in peak-to-peak pressure and a 50.7%decrease in transient pressure instability on inner walls compared to those at 280 km/h.Lower speeds resulted in a 65.6%decrease in amplitude and a 24.5%decrease in decay rate,both of which are parameters for exponential fittings of pressure peaks that decay naturally after the train leaves.The buffer structures result in a reduction of up to 25.7%in the maximum positive pressure and a 29.0%decrease in transient pressure instability.Additionally,a reduction in amplitude of up to 21.2%and a 32.2%increase in decay rate were observed with the use of buffer structures.Nevertheless,it is difficult to conclude direct correlations between the maximum pressure,peak-to-peak values,etc.,and the speeds or buffer structures due to the complex wave propagation in tunnels.However,speed reduction and buffer structures are proven to be effective in reducing the micro-pressure wave levels with a simpler monotonic relationship.展开更多
The bolted flange structure finds significant applications in fields such as aerospace,shipbuilding,and pipeline transportation.The investigation of its dynamic characteristics has consistently been a focal point for ...The bolted flange structure finds significant applications in fields such as aerospace,shipbuilding,and pipeline transportation.The investigation of its dynamic characteristics has consistently been a focal point for researchers;however,there remains a deficiency in the development of robust analytical models.This paper introduces a novel analytical model based on the finite element methods and the Timoshenko beam theory to accurately simulate the bolted flange structure.The stiffness,mass,damping,and inertia matrices of the rotor system are individually derived,and the dynamic equation is subsequently formulated.The model’s validity and accuracy are validated through both the experimental testing and the finite element analysis.This study aims to elucidate the relationship between the external loads and the influence of the geometric configuration on the stiffness and contact behavior of the bolted flange structure,thereby enabling a thorough and precise prediction of the static and dynamic load transfer pathways,as well as the distribution of vibrational energy within the structure,while also facilitating the incorporation of friction and slip effects.Simultaneously,this work provides a foundational framework for the optimization design of bolted flange structures,addressing the factors such as the number,size,and geometric distribution of bolts.展开更多
Understanding the stress distribution derived from monitoring the principal stress(PS)in slopes is of great importance.In this study,a miniature sensor for quantifying the two-dimensional(2D)PS in landslide model test...Understanding the stress distribution derived from monitoring the principal stress(PS)in slopes is of great importance.In this study,a miniature sensor for quantifying the two-dimensional(2D)PS in landslide model tests is proposed.The fundamental principle and design of the sensor are demonstrated.The sensor comprises three earth pressure gages and one gyroscope,with the utilization of three-dimensional(3D)printing technology.The difficulties of installation location during model preparation and sensor rotation during testing can be effectively overcome using this sensor.Two different arrangements of the sensors are tested in verification tests.Additionally,the application of the sensor in an excavated-induced slope model is tested.The results demonstrate that the sensor exhibits commendable performance and achieves a desirable level of accuracy,with a principal stress angle error of±5°in the verification tests.The stress transformation of the slope model,generated by excavation,is demonstrated in the application test by monitoring the two miniature principal stress(MPS)sensors.The sensor has a significant potential for measuring primary stress in landslide model tests and other geotechnical model experiments.展开更多
To ensure the operational safety of railways in the landslide-prone areas of mountainous regions,a large-scale model test and numerical simulation were conducted to study the bending moment distribution,internal force...To ensure the operational safety of railways in the landslide-prone areas of mountainous regions,a large-scale model test and numerical simulation were conducted to study the bending moment distribution,internal force distribution,deformation development,and crack propagation characteristics of a framed anti-sliding structure(FAS)under landslide thrust up to the point of failure.Results show that the maximum bending moment and its increase rate in the fore pile are greater than those in the rear pile,with the maximum bending moment of the fore pile approximately 1.1 times that of the rear pile.When the FAS fails,the displacement at the top of the fore pile is significantly greater,about 1.27 times that of the rear pile in the experiment.Major cracks develop at locations corresponding to the peak bending moments.Small transverse cracks initially appear on the upper surface at the intersection between the primary beam and rear pile and then spread to the side of the structure.At the failure stage,major cracks are observed at the pil-beam intersections and near the anchor points.Strengthening flexural stiffness at intersections where major cracks occur can improve the overall thrust-deformation coordination of the FAS,thereby maximizing its performance.展开更多
This paper presents a dynamic modeling method to test and examine the minimum mass of pressurized pore-gas for triggering landslides in stable gentle soil slopes.A stable gentle soil slope model is constructed with a ...This paper presents a dynamic modeling method to test and examine the minimum mass of pressurized pore-gas for triggering landslides in stable gentle soil slopes.A stable gentle soil slope model is constructed with a dry cement powder core,a saturated clay middle layer,and a dry sand upper layer.The test injects H_(2)O_(2)solution into the cement core to produce new pore-gas.The model test includes three identical H_(2)O_(2)injections.The small mass of generated oxygen gas(0.07%of slope soil mass and landslide body)from the first injection can build sufficient pore-gas pressure to cause soil upheaval and slide.Meanwhile,despite the first injection causing leak paths in the clay layer,the generated small mass of gas from the second and third injections can further trigger the landslide.A dynamic theoretical analysis of the slope failure is carried out and the required minimum pore-gas pressure for the landslide is calculated.The mass and pressure of generated gas in the model test are also estimated based on the calibration test for oxygen generation from H_(2)O_(2)solution in cement powder.The results indicate that the minimum mass of the generated gas for triggering the landslide is 2 ppm to 0.07%of the landslide body.Furthermore,the small mass of gas can provide sufficient pressure to cause soil upheaval and soil sliding in dynamic analysis.展开更多
During fully mechanized caving mining of thick coal seams,a large amount of strain energy accumulates in the roof,especially when the roof is thick and hard,making it difficultfor the roof to collapse naturally.When t...During fully mechanized caving mining of thick coal seams,a large amount of strain energy accumulates in the roof,especially when the roof is thick and hard,making it difficultfor the roof to collapse naturally.When the roof eventually collapses,the accumulated energy is released instantaneously,exerting a strong impact on the roadway.To address this issue,we proposed the synergistic control method of directional comprehensive pressure relief and energy-absorbing support(PREA)for roadways with hard roofs.In this study,we developed a three-dimensional physical model test apparatus for roof cutting and pressure relief.The 122108 ventilation roadway at the Caojiatan Coal Mine,which has a thick and hard roof,was taken as the engineering example.We analyzed the evolution patterns of stress and displacement in both the stope and the roadway surrounding rocks under different schemes.The PREA reinforcement mechanism for the roadway was investigated through comparative model tests between the new and original methods.The results showed that,compared to the original method,the new method reduced surrounding rock stress by up to 60.4%,and the roadway convergence decreased by up to 52.1%.Based on these results,we proposed corresponding engineering recommendations,which can guide fieldreinforcement design and application.The results demonstrate that the PREA method effectively reduces stress and ensures the safety and stability of the roadway.展开更多
The excavation of deep tunnels crossing faults is highly prone to triggering rockburst disasters,which has become a significant engineering issue.In this study,taking the fault-slip rockbursts from a deep tunnel in so...The excavation of deep tunnels crossing faults is highly prone to triggering rockburst disasters,which has become a significant engineering issue.In this study,taking the fault-slip rockbursts from a deep tunnel in southwestern China as the engineering prototype,large-scale three-dimensional(3D)physical model tests were conducted on a 3D-printed complex geological model containing two faults.Based on the selfdeveloped 3D loading system and excavation device,the macroscopic failure of fault-slip rockbursts was simulated indoors.The stress,strain,and fracturing characteristics of the surrounding rock near the two faults were systematically evaluated during excavation and multistage loading.The test results effectively revealed the evolution and triggering mechanism of fault-slip rockbursts.After the excavation of a highstress tunnel,stress readjustment occurred.Owing to the presence of these two faults,stress continued to accumulate in the rock mass between them,leading to the accumulation of fractures.When the shear stress on a fault surface exceeded its shear strength,sudden fault slip and dislocation occurred,thus triggering rockbursts.Rockbursts occurred twice in the vault between the two faults,showing obvious intermittent characteristics.The rockburst pit was controlled by two faults.When the faults remained stable,tensile failure predominated in the surrounding rock.However,when the fault slip was triggered,shear failure in the surrounding rock increased.These findings provide valuable insights for enhancing the comprehension of fault-slip rockbursts.展开更多
In the physical model test of landslides,the selection of analogous materials is the key,and it is difficult to consider the similarity of mechanical properties and seepage performance at the same time.To develop a mo...In the physical model test of landslides,the selection of analogous materials is the key,and it is difficult to consider the similarity of mechanical properties and seepage performance at the same time.To develop a model material suitable for analysing the deformation and failure of reservoir landslides,based on the existing research foundation of analogous materials,5 materials and 5 physical-mechanical parameters were selected to design an orthogonal test.The factor sensitivity of each component ratio and its influence on the physical-mechanical indices were studied by range analysis and stepwise regression analysis,and the proportioning method was determined.Finally,the model material was developed,and a model test was carried out considering Huangtupo as the prototype application.The results showed that(1)the model material composed of sand,barite powder,glass beads,clay,and bentonite had a wide distribution of physical-mechanical parameters,which could be applied to model tests under different conditions;(2)the physical-mechanical parameters of analogous materials matched the application prototype;and(3)the mechanical properties and seepage performance of the model material sample met the requirements of reservoir landslide model tests,which could be used to simulate landslide evolution and analyse the deformation process.展开更多
Structure-type rockbursts frequently occur in deep tunnels,with structural planes and stress conditions being critical factors in their formation.In this study,we utilized specially developed analogous materials that ...Structure-type rockbursts frequently occur in deep tunnels,with structural planes and stress conditions being critical factors in their formation.In this study,we utilized specially developed analogous materials that exhibit the high brittleness and strength characteristics of deep hard rock to construct physical models representing different types of structural planes,including composite,exposed,non-exposed,and throughgoing structural planes.Physical simulation experiments were conducted on structuretype rockbursts in deep horseshoe-shaped tunnels,focusing on strain differentiation characteristics,critical triggering conditions,critical crack opening displacement,the incubation process,the reduction effects of structural planes on failure intensity,and formation mechanisms.These experiments were complemented by acoustic and optical monitoring,as well as discrete element numerical simulations,to provide a comprehensive analysis.The results revealed that the most significant strain heterogeneity in the surrounding rock occurs at the tip of the structural plane along the tunnel's minimum principal stress direction,driven by the combined effects of tensile and shear forces.We quantitatively determined the critical stress and strain conditions for structure-type rockbursts and evaluated the intensity of rockbursts induced by different structural planes using critical crack opening displacement(COD)values,the uniformity coefficient,and the curvature coefficient.Analysis of acoustic emission events,including frequency,amplitude,and b-value,indicated that the macro-fracture process is governed by both the principal stress differential and the characteristics of the structural plane.Furthermore,using the bearing capacity reduction coefficient,we found that exposed structural planes have the most significant weakening effect on rock mass strength,followed by non-exposed and throughgoing structural planes.The analysis of average frequency(AF)and rise angle(RA)parameters revealed a close correlation between the failure modes of structure-type rockbursts,the rock mass structure,and the stress levels.These findings provide critical theoretical support for the prediction and prevention of structure-type rockburst disasters.展开更多
Captive model tests are one of the most common methods to calculate the maneuvering hydrodynamic coefficients and characteristics of surface and underwater vehicles.Considerable attention must be paid to selecting and...Captive model tests are one of the most common methods to calculate the maneuvering hydrodynamic coefficients and characteristics of surface and underwater vehicles.Considerable attention must be paid to selecting and designing the most suitable laboratory equipment for towing tanks.A computational fluid dynamics(CFD)-based method is implemented to determine the loads acting on the towing facility of the submarine model.A reversed topology is also used to ensure the appropriateness of the load cells in the developed method.In this study,the numerical simulations were evaluated using the experimental results of the SUBOFF benchmark submarine model of the Defence Advanced Research Projects Agency.The maximum and minimum loads acting on the 2.5-meter submarine model were measured by determining the body’s lightest and heaviest maneuvering test scenarios.In addition to having sufficient endurance against high loads,the precision in measuring the light load was also investigated.The horizontal planar motion mechanism(HPMM)facilities in the National Iranian Marine Laboratory were developed by locating the load cells inside the submarine model.The results were presented as a case study.A numerical-based method was developed to obtain the appropriate load measurement facilities.Load cells of HPMM test basins can be selected by following the two-way procedure presented in this study.展开更多
基金supported by National Key S&T Special Projects(2016ZX05047-004 and 2016ZX05030)National Natural Science Foundation of China(U1762210)+1 种基金Beijing Natural Science Foundation(3204052)Post-doctoral Program for Innovation Talents(BX20180380).
文摘Microseismic data shows that some unconventional reservoirs comprise well-developed natural fractures and complex hydraulic fracture networks.It is neither practical nor advantageous to simulate a huge number of natural and hydraulic fractures with numerical models.Given that the conventional dual-porosity models are not applicable to the highly discrete natural fractures,the paper develops a semianalytical well testing model for horizontal wells with hydraulic fracture networks and randomly-distributed discretely natural fractures.The proposed model has the capability to analyze the pressure behaviors by considering complex fracture networks and isolated natural fractures rapidly and efficiently.The model includes diffusivity equations in three domains:(1)matrix,(2)discretely natural fractures,and(3)hydraulic fracture networks.The pressure transient solution of these diffusivity equations is obtained by using Laplace transforms and super-position principle.We verify the presented model by performing a case study with a numerical simulator for complex natural fractures.It is found that there are some interestingflow behaviors for fracture-network horizontal well with discretely natural fractures like bilinearflow,“V-shape”caused byfluid supply,pseudo boundary-dominatedflow,impact of natural fractures,etc.The pseudo boundary-dominatedflow provides us the information about how large the area covered by hydraulic fracture networks.The impact of natural fracture shows the pa-rameters of natural fractures.This work provides a good understanding of transient pressure behaviors in unconventional reservoirs and guidelines for the producer optimizefield development and well economics.
基金supported by the China Postdoctoral Science Foundation(CPSF)(Grant No.2024M762769)the Natural Science Basic Research Program of Shaanxi(Grant No.2024JC-YBQN-0333)the Postdoctoral Fellowship Program of CPSF(Grant No.GZC20232230).
文摘Slopes are likely to fail in areas with frequent rainfall and earthquakes.The deformation characteristics of unsaturated slopes subjected to post-rainfall earthquakes are investigated using centrifuge model tests and finite element analyses.Three tests of the slope deformation under earthquake and post-rainfall earthquakes are first studied using image analysis techniques.Then,based on an elastoplastic constitutive model,numerical simulations are carried out using the finite element method and compared with the centrifuge test results.Finally,a parametric study is performed to clarify the effects of antecedent rainfall on earthquake-induced slope deformation.The results show that slope deformation caused by post-rainfall earthquakes differs from that caused by earthquakes without antecedent rainfall.The seepage flow and soil strength of the slope are affected by previous rainfall conditions,such as intensity and duration,which directly influence the slope deformation caused by the subsequent earthquake.Soil displacement and strain become greater and the slip surface is more noticeable during the post-rainfall earthquake of higher intensity.In addition,the time interval between the rainfall and the earthquake has a considerable impact on the detailed characteristics of the slope deformation,and the significant deformation occurs at the time of lowest soil strength when seepage flow reaches the lower part of the slope.Moreover,the repeated intermittent rainfall greatly affects the subsequent earthquake-induced slope deformation,the main characteristics of which are closely related to the changes in saturation and strength of the slope.However,with the prolonged time gap between each round of rainfall,the earthquake-induced slope deformation becomes insignificant.
文摘Modeling technology has been introduced into software testing field.However,how to carry through the testing modeling effectively is still a difficulty.Based on combination of simulation modeling technology and embedded real-time software testing method,the process of simulation testing modeling is studied first.And then,the supporting environment of simulation testing modeling is put forward.Furthermore,an approach of embedded real-time software simulation testing modeling including modeling of cross-linked equipments of system under testing(SUT),test case,testing scheduling,and testing system service is brought forward.Finally,the formalized description and execution system of testing models are given,with which we can realize real-time,closed loop,mad automated system testing for embedded real-time software.
基金This work was financially supported by the National Natural Science Foundation of China (Grant No10602055)Nature Science Foundation of China Jiliang University (Grant No XZ0501)
文摘In this paper, an inner turret moored FPSO which works in the water of 320 m depth, is selected to study the socalled ＂passively-truncated ＋ numerical-simulation＂ type of hybrid model testing technique while the tnmcated water depth is 160 m and the model scale ）, = 80. During the investigation, the optimization design of the equivalent-depth truncated system is performed by using the similarity of the static characteristics between the truncated system and the full depth one as the objective function. According to the truncated system, the corresponding physical test model is made. By adopting the coupling time domain simulation method, the tnmcated system model test is numerically reconstructed to carefully verify the computer simulation software and to adjust the corresponding hydrodynamic parameters. Based on the above work, the numerical extrapolation to the full depth system is performed by using the verified computer software and the adjusted hydrodyrmmic parameters. The full depth system model test is then performed in the basin and the results are compared with those from the numerical extrapolation. At last, the implementation procedure and the key technique of the hybrid model testing of the deep-sea platforms are summarized and printed. Through the above investigations, some beneficial conclusions are presented.
基金supported by the Fujian Science Foundation for Outstanding Youth(Grant No.2023J06039)the National Natural Science Foundation of China(Grant No.41977259 and No.U2005205)Fujian Province natural resources science and technology innovation project(Grant No.KY-090000-04-2022-019)。
文摘Bedding slope is a typical heterogeneous slope consisting of different soil/rock layers and is likely to slide along the weakest interface.Conventional slope protection methods for bedding slopes,such as retaining walls,stabilizing piles,and anchors,are time-consuming and labor-and energy-intensive.This study proposes an innovative polymer grout method to improve the bearing capacity and reduce the displacement of bedding slopes.A series of large-scale model tests were carried out to verify the effectiveness of polymer grout in protecting bedding slopes.Specifically,load-displacement relationships and failure patterns were analyzed for different testing slopes with various dosages of polymer.Results show the great potential of polymer grout in improving bearing capacity,reducing settlement,and protecting slopes from being crushed under shearing.The polymer-treated slopes remained structurally intact,while the untreated slope exhibited considerable damage when subjected to loads surpassing the bearing capacity.It is also found that polymer-cemented soils concentrate around the injection pipe,forming a fan-shaped sheet-like structure.This study proves the improvement of polymer grouting for bedding slope treatment and will contribute to the development of a fast method to protect bedding slopes from landslides.
基金Project (No.50478090) supported by the National Natural Science Foundation of China
文摘Aphysical model facility was designed, built, and setup for conducting model tests on a composite foundation in a soil ground. The model tests were carried out on a composite foundation with different combinations of vertical reinforcement elements in the same soil ground. Via the analysis of the collected data the characteristics of the composite foundation with different reinforcing elements were obtained, including the characteristics of load-settlement curves, column stresses, stresses of the intercolumn soil, pile-soil stress ratio, and load-sharing ratios of columns and soil. Results from the model tests reveal the mechanism of a composite foundation with different reinforcing elements quantitatively. It is concluded that both a composite foundation with a combination of steel pipe pile and sand column and that with a combination of concrete pile and lime column have a higher bearing capacity than the composite foundation with only sand columns with the same conditions of soil ground and loading. A composite foundation with lime column and sand column embodies no much better performance than that with sand colunms only.
基金the National Natural Science Foundations of China(Nos.51679049 and 51079034)
文摘Conducting model experiments is an effective and reliable way in the investigation of ship hydrodynamic and hydroelastic behaviors. A survey of model testing techniques for ship hydroelasticity and its prospect are presented in this paper. The research highlights with respect to ship hydroelasticity and key points in model testing are summarized at first. Then testing techniques including laboratory tank test and full-scale sea trial are reviewed, and both their advantages and disadvantages are analyzed comprehensively. Based on the conventional testing approaches, a state-of-the-art testing approach which includes performing tests using large-scale model at sea is proposed. Furthermore, recommendations towards the further development of ship hydroelasticity tests are forecasted and discussed.
基金the financial support from the Fujian Science Foundation for Outstanding Youth(2023J06039)the National Natural Science Foundation of China(Grant No.41977259,U2005205,41972268)the Independent Research Project of Technology Innovation Center for Monitoring and Restoration Engineering of Ecological Fragile Zone in Southeast China(KY-090000-04-2022-019)。
文摘Shotcrete is one of the common solutions for shallow sliding.It works by forming a protective layer with high strength and cementing the loose soil particles on the slope surface to prevent shallow sliding.However,the solidification time of conventional cement paste is long when shotcrete is used to treat cohesionless soil landslide.The idea of reinforcing slope with polyurethane solidified soil(i.e.,mixture of polyurethane and sand)was proposed.Model tests and finite element analysis were carried out to study the effectiveness of the proposed new method on the emergency treatment of cohesionless soil landslide.Surcharge loading on the crest of the slope was applied step by step until landslide was triggered so as to test and compare the stability and bearing capacity of slope models with different conditions.The simulated slope displacements were relatively close to the measured results,and the simulated slope deformation characteristics were in good agreement with the observed phenomena,which verifies the accuracy of the numerical method.Under the condition of surcharge loading on the crest of the slope,the unreinforced slope slid when the surcharge loading exceeded 30 k Pa,which presented a failure mode of local instability and collapse at the shallow layer of slope top.The reinforced slope remained stable even when the surcharge loading reached 48 k Pa.The displacement of the reinforced slope was reduced by more than 95%.Overall,this study verifies the effectiveness of polyurethane in the emergency treatment of cohesionless soil landslide and should have broad application prospects in the field of geological disasters concerning the safety of people's live.
文摘Ice load on underwater vehicles breaking through ice covers from underneath is a significant concern for researchers in polar exploration,and the research on this problem is still in its early stages.Both mechanical experimental measurement and numerical simulation pose research challenges.This study focuses on the ice load of a cylinder structure breaking upward through the ice sheet form underneath in the Small Ice Model Basin of China Ship Scientific Research Center(CSSRC SIMB).A high-speed camera system was employed to observe the ice sheet failure during the tests,in which,with the loading position as center,local radial cracks and circumferential cracks were generated.A load sensor was used to measure the overall ice load during this process.Meanwhile,a numerical model was developed using LS-DYNA for validation and comparison.With this model,numerical simulation was conducted under various ice thicknesses and upgoing speeds to analyze the instantaneous curves of ice load.The calculation results were statistically analyzed under different working conditions to determine the influence of the factors on the ice load of the cylinder.The study explores the measurement method about ice load of objects vertically breaking through model ice sheet and is expected to provide some fundamental insights into the safety design of underwater structures operating in ice waters.
基金supported by the National Natural Science Foundation of China(52104049)the Young Elite Scientist Sponsorship Program by Beijing Association for Science and Technology(BYESS2023262)。
文摘Polymer flooding is an important means of improving oil recovery and is widely used in Daqing,Xinjiang,and Shengli oilfields,China.Different from conventional injection media such as water and gas,viscoelastic polymer solutions exhibit non-Newtonian and nonlinear flow behavior including shear thinning and shear thickening,polymer convection,diffusion,adsorption,retention,inaccessible pore volume,and reduced effective permeability.However,available well test model of polymer flooding wells generally simplifies these characteristics on pressure transient response,which may lead to inaccurate results.This work proposes a novel two-phase numerical well test model to better describe the polymer viscoelasticity and nonlinear flow behavior.Different influence factors that related to near-well blockage during polymer flooding process,including the degree of blockage(inner zone permeability),the extent of blockage(composite radius),and polymer flooding front radius are explored to investigate these impacts on bottom hole pressure responses.Results show that polymer viscoelasticity has a significant impact on the transitional flow segment of type curves,and the effects of near-well formation blockage and polymer concentration distribution on well test curves are very similar.Thus,to accurately interpret the degree of near-well blockage in injection wells,it is essential to first eliminate the influence of polymer viscoelasticity.Finally,a field case is comprehensively analyzed and discussed to illustrate the applicability of the proposed model.
基金Project(52202426)supported by the National Natural Science Foundation of ChinaProjects(15205723,15226424)supported by the Research Grants Council of the Hong Kong Special Administrative Region,China。
文摘Maglev trains experience significant aerodynamic effects when passing through tunnels.A moving model test was conducted to explore the practical effects of speed reduction and entrance buffer structures on mitigating tunnel/maglev aerodynamic effects.It is found that both have an overall positive effect on mitigating the aerodynamic environment inside and outside the tunnel.Trains operating at 200 km/h show a 49.8%decrease in peak-to-peak pressure and a 50.7%decrease in transient pressure instability on inner walls compared to those at 280 km/h.Lower speeds resulted in a 65.6%decrease in amplitude and a 24.5%decrease in decay rate,both of which are parameters for exponential fittings of pressure peaks that decay naturally after the train leaves.The buffer structures result in a reduction of up to 25.7%in the maximum positive pressure and a 29.0%decrease in transient pressure instability.Additionally,a reduction in amplitude of up to 21.2%and a 32.2%increase in decay rate were observed with the use of buffer structures.Nevertheless,it is difficult to conclude direct correlations between the maximum pressure,peak-to-peak values,etc.,and the speeds or buffer structures due to the complex wave propagation in tunnels.However,speed reduction and buffer structures are proven to be effective in reducing the micro-pressure wave levels with a simpler monotonic relationship.
基金Project supported by the National Defense Technology Foundation Under the State Administration of Science,Technology,and Industry for National Defense of China(No.JSZL2022213A001)the Special Funds for Basic Research in Central Universities of China(No.HYGJZN202322)。
文摘The bolted flange structure finds significant applications in fields such as aerospace,shipbuilding,and pipeline transportation.The investigation of its dynamic characteristics has consistently been a focal point for researchers;however,there remains a deficiency in the development of robust analytical models.This paper introduces a novel analytical model based on the finite element methods and the Timoshenko beam theory to accurately simulate the bolted flange structure.The stiffness,mass,damping,and inertia matrices of the rotor system are individually derived,and the dynamic equation is subsequently formulated.The model’s validity and accuracy are validated through both the experimental testing and the finite element analysis.This study aims to elucidate the relationship between the external loads and the influence of the geometric configuration on the stiffness and contact behavior of the bolted flange structure,thereby enabling a thorough and precise prediction of the static and dynamic load transfer pathways,as well as the distribution of vibrational energy within the structure,while also facilitating the incorporation of friction and slip effects.Simultaneously,this work provides a foundational framework for the optimization design of bolted flange structures,addressing the factors such as the number,size,and geometric distribution of bolts.
基金supported by the National Nature Science Foundation of China(Grant No.42207216)the Major Program of the National Natural Science Foundation of China(Grant No.42090055)the National Nature Science Foundation of China(Grant No.42377182).
文摘Understanding the stress distribution derived from monitoring the principal stress(PS)in slopes is of great importance.In this study,a miniature sensor for quantifying the two-dimensional(2D)PS in landslide model tests is proposed.The fundamental principle and design of the sensor are demonstrated.The sensor comprises three earth pressure gages and one gyroscope,with the utilization of three-dimensional(3D)printing technology.The difficulties of installation location during model preparation and sensor rotation during testing can be effectively overcome using this sensor.Two different arrangements of the sensors are tested in verification tests.Additionally,the application of the sensor in an excavated-induced slope model is tested.The results demonstrate that the sensor exhibits commendable performance and achieves a desirable level of accuracy,with a principal stress angle error of±5°in the verification tests.The stress transformation of the slope model,generated by excavation,is demonstrated in the application test by monitoring the two miniature principal stress(MPS)sensors.The sensor has a significant potential for measuring primary stress in landslide model tests and other geotechnical model experiments.
基金The National Natural Science Foundation of China(No.52078427).
文摘To ensure the operational safety of railways in the landslide-prone areas of mountainous regions,a large-scale model test and numerical simulation were conducted to study the bending moment distribution,internal force distribution,deformation development,and crack propagation characteristics of a framed anti-sliding structure(FAS)under landslide thrust up to the point of failure.Results show that the maximum bending moment and its increase rate in the fore pile are greater than those in the rear pile,with the maximum bending moment of the fore pile approximately 1.1 times that of the rear pile.When the FAS fails,the displacement at the top of the fore pile is significantly greater,about 1.27 times that of the rear pile in the experiment.Major cracks develop at locations corresponding to the peak bending moments.Small transverse cracks initially appear on the upper surface at the intersection between the primary beam and rear pile and then spread to the side of the structure.At the failure stage,major cracks are observed at the pil-beam intersections and near the anchor points.Strengthening flexural stiffness at intersections where major cracks occur can improve the overall thrust-deformation coordination of the FAS,thereby maximizing its performance.
基金supported by grants from the Research Grant Council of the Hong Kong Special Administrative Region,China(Project No.HKU 17207518).
文摘This paper presents a dynamic modeling method to test and examine the minimum mass of pressurized pore-gas for triggering landslides in stable gentle soil slopes.A stable gentle soil slope model is constructed with a dry cement powder core,a saturated clay middle layer,and a dry sand upper layer.The test injects H_(2)O_(2)solution into the cement core to produce new pore-gas.The model test includes three identical H_(2)O_(2)injections.The small mass of generated oxygen gas(0.07%of slope soil mass and landslide body)from the first injection can build sufficient pore-gas pressure to cause soil upheaval and slide.Meanwhile,despite the first injection causing leak paths in the clay layer,the generated small mass of gas from the second and third injections can further trigger the landslide.A dynamic theoretical analysis of the slope failure is carried out and the required minimum pore-gas pressure for the landslide is calculated.The mass and pressure of generated gas in the model test are also estimated based on the calibration test for oxygen generation from H_(2)O_(2)solution in cement powder.The results indicate that the minimum mass of the generated gas for triggering the landslide is 2 ppm to 0.07%of the landslide body.Furthermore,the small mass of gas can provide sufficient pressure to cause soil upheaval and soil sliding in dynamic analysis.
基金supported by the National Natural Science Foundation of China(Grant Nos.U24A2088 and 42277174)the Fundamental Research Funds for the Central Universities,China(Grant No.2024JCCXSB01).
文摘During fully mechanized caving mining of thick coal seams,a large amount of strain energy accumulates in the roof,especially when the roof is thick and hard,making it difficultfor the roof to collapse naturally.When the roof eventually collapses,the accumulated energy is released instantaneously,exerting a strong impact on the roadway.To address this issue,we proposed the synergistic control method of directional comprehensive pressure relief and energy-absorbing support(PREA)for roadways with hard roofs.In this study,we developed a three-dimensional physical model test apparatus for roof cutting and pressure relief.The 122108 ventilation roadway at the Caojiatan Coal Mine,which has a thick and hard roof,was taken as the engineering example.We analyzed the evolution patterns of stress and displacement in both the stope and the roadway surrounding rocks under different schemes.The PREA reinforcement mechanism for the roadway was investigated through comparative model tests between the new and original methods.The results showed that,compared to the original method,the new method reduced surrounding rock stress by up to 60.4%,and the roadway convergence decreased by up to 52.1%.Based on these results,we proposed corresponding engineering recommendations,which can guide fieldreinforcement design and application.The results demonstrate that the PREA method effectively reduces stress and ensures the safety and stability of the roadway.
基金funding support from the National Natural Science Foundation of China(Grant Nos.42177136 and 52309126).
文摘The excavation of deep tunnels crossing faults is highly prone to triggering rockburst disasters,which has become a significant engineering issue.In this study,taking the fault-slip rockbursts from a deep tunnel in southwestern China as the engineering prototype,large-scale three-dimensional(3D)physical model tests were conducted on a 3D-printed complex geological model containing two faults.Based on the selfdeveloped 3D loading system and excavation device,the macroscopic failure of fault-slip rockbursts was simulated indoors.The stress,strain,and fracturing characteristics of the surrounding rock near the two faults were systematically evaluated during excavation and multistage loading.The test results effectively revealed the evolution and triggering mechanism of fault-slip rockbursts.After the excavation of a highstress tunnel,stress readjustment occurred.Owing to the presence of these two faults,stress continued to accumulate in the rock mass between them,leading to the accumulation of fractures.When the shear stress on a fault surface exceeded its shear strength,sudden fault slip and dislocation occurred,thus triggering rockbursts.Rockbursts occurred twice in the vault between the two faults,showing obvious intermittent characteristics.The rockburst pit was controlled by two faults.When the faults remained stable,tensile failure predominated in the surrounding rock.However,when the fault slip was triggered,shear failure in the surrounding rock increased.These findings provide valuable insights for enhancing the comprehension of fault-slip rockbursts.
基金supported by the Major Program of the National Natural Science Foundation of China(No.42090054)the National Key Scientific Instrument and Equipment Development Projects of China(No.41827808)+1 种基金the Major Program of the National Natural Science Foundation of China(No.42090055)the National Science Foundation of China(No.42107194)。
文摘In the physical model test of landslides,the selection of analogous materials is the key,and it is difficult to consider the similarity of mechanical properties and seepage performance at the same time.To develop a model material suitable for analysing the deformation and failure of reservoir landslides,based on the existing research foundation of analogous materials,5 materials and 5 physical-mechanical parameters were selected to design an orthogonal test.The factor sensitivity of each component ratio and its influence on the physical-mechanical indices were studied by range analysis and stepwise regression analysis,and the proportioning method was determined.Finally,the model material was developed,and a model test was carried out considering Huangtupo as the prototype application.The results showed that(1)the model material composed of sand,barite powder,glass beads,clay,and bentonite had a wide distribution of physical-mechanical parameters,which could be applied to model tests under different conditions;(2)the physical-mechanical parameters of analogous materials matched the application prototype;and(3)the mechanical properties and seepage performance of the model material sample met the requirements of reservoir landslide model tests,which could be used to simulate landslide evolution and analyse the deformation process.
基金supported by the National Natural Science Foundation of China(Grant Nos.42307241 and 42107211)the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Independent Research Project(Grant No.SKLGP2022Z008).
文摘Structure-type rockbursts frequently occur in deep tunnels,with structural planes and stress conditions being critical factors in their formation.In this study,we utilized specially developed analogous materials that exhibit the high brittleness and strength characteristics of deep hard rock to construct physical models representing different types of structural planes,including composite,exposed,non-exposed,and throughgoing structural planes.Physical simulation experiments were conducted on structuretype rockbursts in deep horseshoe-shaped tunnels,focusing on strain differentiation characteristics,critical triggering conditions,critical crack opening displacement,the incubation process,the reduction effects of structural planes on failure intensity,and formation mechanisms.These experiments were complemented by acoustic and optical monitoring,as well as discrete element numerical simulations,to provide a comprehensive analysis.The results revealed that the most significant strain heterogeneity in the surrounding rock occurs at the tip of the structural plane along the tunnel's minimum principal stress direction,driven by the combined effects of tensile and shear forces.We quantitatively determined the critical stress and strain conditions for structure-type rockbursts and evaluated the intensity of rockbursts induced by different structural planes using critical crack opening displacement(COD)values,the uniformity coefficient,and the curvature coefficient.Analysis of acoustic emission events,including frequency,amplitude,and b-value,indicated that the macro-fracture process is governed by both the principal stress differential and the characteristics of the structural plane.Furthermore,using the bearing capacity reduction coefficient,we found that exposed structural planes have the most significant weakening effect on rock mass strength,followed by non-exposed and throughgoing structural planes.The analysis of average frequency(AF)and rise angle(RA)parameters revealed a close correlation between the failure modes of structure-type rockbursts,the rock mass structure,and the stress levels.These findings provide critical theoretical support for the prediction and prevention of structure-type rockburst disasters.
文摘Captive model tests are one of the most common methods to calculate the maneuvering hydrodynamic coefficients and characteristics of surface and underwater vehicles.Considerable attention must be paid to selecting and designing the most suitable laboratory equipment for towing tanks.A computational fluid dynamics(CFD)-based method is implemented to determine the loads acting on the towing facility of the submarine model.A reversed topology is also used to ensure the appropriateness of the load cells in the developed method.In this study,the numerical simulations were evaluated using the experimental results of the SUBOFF benchmark submarine model of the Defence Advanced Research Projects Agency.The maximum and minimum loads acting on the 2.5-meter submarine model were measured by determining the body’s lightest and heaviest maneuvering test scenarios.In addition to having sufficient endurance against high loads,the precision in measuring the light load was also investigated.The horizontal planar motion mechanism(HPMM)facilities in the National Iranian Marine Laboratory were developed by locating the load cells inside the submarine model.The results were presented as a case study.A numerical-based method was developed to obtain the appropriate load measurement facilities.Load cells of HPMM test basins can be selected by following the two-way procedure presented in this study.
