In this paper,an advanced satellite navigation filter design,referred to as the Variational Bayesian Maximum Correntropy Extended Kalman Filter(VBMCEKF),is introduced to enhance robustness and adaptability in scenario...In this paper,an advanced satellite navigation filter design,referred to as the Variational Bayesian Maximum Correntropy Extended Kalman Filter(VBMCEKF),is introduced to enhance robustness and adaptability in scenarios with non-Gaussian noise and heavy-tailed outliers.The proposed design modifies the extended Kalman filter(EKF)for the global navigation satellite system(GNSS),integrating the maximum correntropy criterion(MCC)and the variational Bayesian(VB)method.This adaptive algorithm effectively reduces non-line-of-sight(NLOS)reception contamination and improves estimation accuracy,particularly in time-varying GNSS measurements.Experimental results show that the proposed method significantly outperforms conventional approaches in estimation accuracy under heavy-tailed outliers and non-Gaussian noise.By combining MCC with VB approximation for real-time noise covariance estimation using fixed-point iteration,the VBMCEKF achieves superior filtering performance in challenging GNSS conditions.The method’s adaptability and precision make it ideal for improving satellite navigation performance in stochastic environments.展开更多
In the past few decades,the navigation performance of ships and structures in ice-covered waters has not been fully studied,especially the influence of ice mechanical properties on icebreaking ability.Ice bending stre...In the past few decades,the navigation performance of ships and structures in ice-covered waters has not been fully studied,especially the influence of ice mechanical properties on icebreaking ability.Ice bending strength is a key ice parameter for predicting ship ice loads,and accurate ice bending strength is also the key to scaling model tests results to real ship.However,numerical simulation studies on model ice bending strength of ice tanks are often neglected.In this paper,an explicit finite element method model is used to simulate the ice cantilever beam test,and the failure load and bending strength of the ice are obtained.In this model,the Tsai-Wu failure criterion is used as the material constitutive model,and the required simulation parameters are obtained from the model ice test in ice tank.Parameter sensitivity analysis shows that the cantilever beam size of the model ice has a significant effect on the flexural strength.The results show that proper rounding at the root of the cantilever beam is beneficial to reduce stress concentration and obtain more accurate bending strength;the thickness,width and length of the cantilever beam should conform to a certain ratio,and consistent with the ITTC recommended reference.Therefore,the results of this study can promote model ice experiments and numerical studies and provide ice strength data support for ship design and polar ship maneuvering.展开更多
Ground reinforcement is crucial for tunnel construction, especially in soft rock tunnels. Existing analytical models are inadequate for predicting the ground reaction curves (GRCs) for reinforced tunnels in strain-sof...Ground reinforcement is crucial for tunnel construction, especially in soft rock tunnels. Existing analytical models are inadequate for predicting the ground reaction curves (GRCs) for reinforced tunnels in strain-softening (SS) rock masses. This study proposes a novel analytical model to determine the GRCs of SS rock masses, incorporating ground reinforcement and intermediate principal stress (IPS). The SS constitutive model captures the progressive post- peak failure, while the elastic-brittle model simulates reinforced rock masses. Nine combined states are innovatively investigated to analyze plastic zone development in natural and reinforced regions. Each region is analyzed separately, and coupled through boundary conditions at interface. Comparison with three types of existing models indicates that these models overestimate reinforcement effects. The deformation prediction errors of single geological material models may exceed 75%. Furthermore, neglecting softening and residual zones in natural regions could lead to errors over 50%. Considering the IPS can effectively utilize the rock strength to reduce tunnel deformation by at least 30%, thereby saving on reinforcement and support costs. The computational results show a satisfactory agreement with the monitoring data from a model test and two tunnel projects. The proposed model may offer valuable insights into the design and construction of reinforced tunnel engineering.展开更多
The swinging-loading process is essential for automatic artillery loading systems.This study focuses on the problems of reliability analysis that affect swinging-loading positioning accuracy.A dynamic model for a mult...The swinging-loading process is essential for automatic artillery loading systems.This study focuses on the problems of reliability analysis that affect swinging-loading positioning accuracy.A dynamic model for a multi degree-of-freedom swinging-loading-integrated rigid-flexible coupling system is established.This model is based on the identification of key parameters and platform experiments.Based on the spatial geometric relationship between the breech and loader during modular charge transfer and the possible maximum interference depth of the modular charge,a new failure criterion for estimating the reliability of swinging-loading positioning accuracy is proposed.Considering the uncertainties in the operation of the pendulum loader,the direct probability integration method is introduced to analyze the reliability of the swinging-loading positioning accuracy under three different charge numbers.The results indicate that under two and four charges,the swinging-loading process shows outstanding reliability.However,an unstable stage appears when the swinging motion occurred under six charges,with a maximum positioning failure probability of 0.0712.A comparison between the results obtained under the conventional and proposed criteria further reveals the effectiveness and necessity of the proposed criterion.展开更多
Hydraulic fracture(HF)formed in rock significantly helps with the development of geo-energy and georesources.The HF formation condition was challenging to understand,with obscure rock micro-cracking mechanisms being a...Hydraulic fracture(HF)formed in rock significantly helps with the development of geo-energy and georesources.The HF formation condition was challenging to understand,with obscure rock micro-cracking mechanisms being a key factor.The rock micro-cracking mechanism under gradient pore water pressure was analyzed on the scale of mineral particles and it was combined with macroscopic boundary conditions of rock hydraulic fracturing,obtaining the propagation criterion of HF in rock based on the rock micro-cracking mechanism which was verified by experiment.The results show that the disturbed skeleton stress induced by the disturbance of gradient pore water pressure in rock equals the pore water pressure difference.The overall range of the defined mechanical shape factor a/b is around 1,but greater than0.5.Under the combined influence of pore water pressure differences and macroscopic boundary stresses on the rock micro-cracking,micro-cracks form among rock mineral particles,micro-cracks connect to form micro-hydraulic fracture surfaces,and micro-hydraulic fracture surfaces open to form macrohydraulic fractures.HF begins to form at the micro-cracking initiation pressure(MCIP),which was tested by keeping the HF tip near the initiation point.The theoretical value of MCIP calculated by the proposed propagation criterion is close to MCIP tested.展开更多
In this paper,we study normal families of meromorphic functions.By using the idea in[16],we obtain some normality criteria for families of meromorphic functions concerning the wandering multiple functions,which extend...In this paper,we study normal families of meromorphic functions.By using the idea in[16],we obtain some normality criteria for families of meromorphic functions concerning the wandering multiple functions,which extend and improve the well-known Montel's criterion,Bloch-Valiron's theorem,and the related results due to Carathéodory,and Grahl-Nevo et al..展开更多
This study investigates the instability characteristics of dynamic disasters resulting from disruption caused by extracting resources underground. Utilizing the split Hopkinson pressure bar (SHPB) system, the dynamic ...This study investigates the instability characteristics of dynamic disasters resulting from disruption caused by extracting resources underground. Utilizing the split Hopkinson pressure bar (SHPB) system, the dynamic response mechanism of coal energy evolution is examined, and the energy instability criterion is established. The validity of the instability criterion is explored from the standpoint of damage progression. The results demonstrate that the energy conversion mechanism undergoes a fundamental alternation under impact disturbance. Moreover, the energy release rate as well as the energy dissipation rate undergo comparable changes across distinct levels of impact disturbance. The distinction between the energy release rate and the energy dissipation rate (DRD) increases as coal mass deformation grows. Prior to coal facing instability and failure, the DRD experienced an inflection point followed by a sharp decrease. In conjunction with the discussion on the damage evolution, the physical and mechanical significance of DRD remains clear, which can essentially describe the whole impact loading process. The phenomenon that the inflection point appears and DRD subsequently suddenly decreases can be employed as the energy criterion prior to the failure of instability. Furthermore, this paper provides significant reference for the prediction of dynamic instability of coal under dynamic disturbance.展开更多
This paper presents a new criterion for determining the unloading points quantitatively and consistently in a multi-stage triaxial test.The radial strain gradient(RSG)is first introduced as an arc tangent function of ...This paper presents a new criterion for determining the unloading points quantitatively and consistently in a multi-stage triaxial test.The radial strain gradient(RSG)is first introduced as an arc tangent function of the rate of change of radial strain to time.RSG is observed to correlate closely with the stress state of a compressed sample,and reaches a horizontal asymptote as approaching failure.For a given rock type,RSG value at peak stress is almost the same,irrespective of the porosity and permeability.These findings lead to the development of RSG criterion:Unloading points can be precisely determined at the time when RSG reaches a pre-determined value that is a little smaller than or equal to the RSG at peak stress.The RSG criterion is validated against other criteria and the single-stage triaxial test on various types of rocks.Failure envelopes from the RSG criterion match well with those from single-stage tests.A practical procedure is recommended to use the RSG criterion:an unconfined compression or single-stage test is first conducted to determine the RSG at peak stress for one sample,the unloading point is then selected to be a value close to the RSG at peak stress,and the multi-stage test is finally performed on another sample using the pre-selected RSG unloading criterion.Generally,the RSG criterion is applicable for any type of rocks,especially brittle rocks,where other criteria are not suitable.Further,it can be practically implemented on the most available rock mechanical testing instruments.展开更多
The generalized Zhang-Zhu(GZZ)strength criterion was proposed as an extension to the Hoek-Brown criterion and the Mogi criterion.The introduction to mean normal stress results in a non-smooth and non-convex yield surf...The generalized Zhang-Zhu(GZZ)strength criterion was proposed as an extension to the Hoek-Brown criterion and the Mogi criterion.The introduction to mean normal stress results in a non-smooth and non-convex yield surface,which presents a challenge for updating plastic stress.Current research primarily focuses on modified smooth GZZ criteria or approximate solutions,which inevitably lead to increased computational costs or inaccuracies.In this paper,an accurate stress updating algorithm is proposed based on the original GZZ criterion.The algorithm operates entirely in the principal stress space,where numerical singularities at the intersection of yield surfaces are avoided by defining four different types of stress updating.This approach simplifies the GZZ criterion compared to its formulation in general stress space.The return mapping is employed to compute the updated stress and consistent stiffness matrix,facilitating calculations using both finite element implicit and explicit algorithms.Finally,the accuracy of the proposed method is validated using rock true triaxial test data and semianalytical solutions for stresses and displacement around a circular opening under the GZZ criterion.展开更多
To solve the problem of time difference of arrival(TDOA)positioning and tracking of targets by the unmanned aerial vehicles(UAV)swarm in future air combat,this paper adopts the TDOA positioning method and uses time di...To solve the problem of time difference of arrival(TDOA)positioning and tracking of targets by the unmanned aerial vehicles(UAV)swarm in future air combat,this paper adopts the TDOA positioning method and uses time difference sensors of the UAV swarm to locate target radiation sources.Firstly,a TDOA model for the target is set up for the UAV swarm under the condition that the error variance varies with the received signal-to-noise ratio.The accuracy of the positioning error is analyzed by geometric dilution of precision(GDOP).The D-optimality criterion of the positioning model is theoretically derived.The target is positioned and settled,and the maximum value of the Fisher information matrix determinant is used as the optimization objective function to optimize the track of the UAV in real time.Simulation results show that the track optimization improves the positioning accuracy and stability of the UAV swarm to the target.展开更多
To understand the strengths of rocks under complex stress states,a generalized nonlinear threedimensional(3D)Hoek‒Brown failure(NGHB)criterion was proposed in this study.This criterion shares the same parameters with ...To understand the strengths of rocks under complex stress states,a generalized nonlinear threedimensional(3D)Hoek‒Brown failure(NGHB)criterion was proposed in this study.This criterion shares the same parameters with the generalized HB(GHB)criterion and inherits the parameter advantages of GHB.Two new parameters,b,and n,were introduced into the NGHB criterion that primarily controls the deviatoric plane shape of the NGHB criterion under triaxial tension and compression,respectively.The NGHB criterion can consider the influence of intermediate principal stress(IPS),where the deviatoric plane shape satisfies the smoothness requirements,while the HB criterion not.This criterion can degenerate into the two modified 3D HB criteria,the Priest criterion under triaxial compression condition and the HB criterion under triaxial compression and tension condition.This criterion was verified using true triaxial test data for different parameters,six types of rocks,and two kinds of in situ rock masses.For comparison,three existing 3D HB criteria were selected for performance comparison research.The result showed that the NGHB criterion gave better prediction performance than other criteria.The prediction errors of the strength of six types of rocks and two kinds of in situ rock masses were in the range of 2.0724%-3.5091%and 1.0144%-3.2321%,respectively.The proposed criterion lays a preliminary theoretical foundation for prediction of engineering rock mass strength under complex in situ stress conditions.展开更多
Deep metal mines are often mined using the high-level pillars with subsequent cementation backfilling(HLSCB)mining method.At the design stage,it is therefore important to have a reasonable method for determining the s...Deep metal mines are often mined using the high-level pillars with subsequent cementation backfilling(HLSCB)mining method.At the design stage,it is therefore important to have a reasonable method for determining the shear strength of the high-level pillars(i.e.cohesion and internal friction angle)when they are supported by cemented backfilling.In this study,a formula was derived for the upper limit of the confining pressure σ3max on a high-level pillar supported by cemented backfilling in a deep metal mine.A new method of estimating the shear strength of such pillars was then proposed based on the Hoek eBrown failure criterion.Our analysis indicates that the horizontal stress σhh acting on the cemented backfill pillar can be simplified by expressing it as a constant value.A reasonable and effective value for σ3max can then be determined.The value of s3max predicted using the proposed method is generally less than 3 MPa.Within this range,the shear strength of the high-level pillar is accurately calculated using the equivalent MohreCoulomb theory.The proposed method can effectively avoid the calculation of inaccurate shear strength values for the high-level pillars when the original HoekeBrown criterion is used in the presence of large confining pressures,i.e.the situation in which the cohesion value is too large and the friction angle is too small can effectively be avoided.The proposed method is applied to a deep metal mine in China that is being excavated using the HLSCB method.The shear strength parameters of the high-level pillars obtained using the proposed method were input in the numerical simulations.The numerical results show that the recommended level heights and sizes of the high-level pillars and rooms in the mine are rational.展开更多
Based on existing triaxial compression experimental data,a new empirical failure criterion with wide applicability was proposed considering hydrostatic pressure,second stress invariance,and maximum shear stress.Four f...Based on existing triaxial compression experimental data,a new empirical failure criterion with wide applicability was proposed considering hydrostatic pressure,second stress invariance,and maximum shear stress.Four fitting evaluation indicators were used to verify the consistency of the new failure criterion,and the differences with the other 6 failure criteria were discussed.The characteristics of the new failure criteria in the principal stress space were finally analyzed.The results indicate that(1)the new failure criterion exhibits strong predictive ability for triaxial experiments and has good applicability for both intact and jointed rocks;(2)the influence of hydrostatic pressure on the failure surface exhibits a non-linear trend,and different hydrostatic pressure also exhibits different distribution patterns on the deviatoric stress plane,with a distribution characteristic pattern of hexagonal snowflake-regular hexagon.The maximum shear stress has a torsional effect on the new criterion,in the three-dimensional failure surface.The parameters a and b of the rock have an impact on the failure surface morphology of the new criterion function on the offset surface.展开更多
The natural property of rock material,whether impact occurs,is the key influencing factor of the occurrence of rock burst disaster.To accurately assess rock burst proneness,this study focuses on typical sandstone as t...The natural property of rock material,whether impact occurs,is the key influencing factor of the occurrence of rock burst disaster.To accurately assess rock burst proneness,this study focuses on typical sandstone as the research object.Uniaxial cyclic loading and unloading tests were conducted to measure the elastic strain energy accumulated in sandstone under different stress levels and a relationship between elastic strain energy and stress level was established.The results show that:(1)The peak stress under cyclic loading and unloading conditions is slightly lower than the uniaxial compressive strength.With an increase in the number of cycles,the internal damage of sandstone continues to accumulate,and the mechanical properties such as compressive strength continue to deteriorate;(2)With an increase in stress,the input strain energy,elastic strain energy,and dissipated strain energy also increase;(3)When the stress is low,the increase in elastic strain energy is large and shows a steady growth;with an increase in stress,the increase of elastic strain energy decreases;(4)The square of stress at any time has a good linear relationship with elastic strain energy.According to the relationship obtained from the test,the elastic strain energy at the peak stress time can be obtained;(5)A new criterion for assessing rock burst proneness is proposed:residual energy release rate index W_(T),which characterizes the energy release per unit time when the rock burst occurs.The intervals for evaluating the rock burst proneness of the residual energy release rate index W_(T) are as follows:W_(T)<0.025,indicating no rock burst proneness;0.025≤W_(T)<0.15,indicating weak rock burst proneness;0.15≤W_(T)<2,indicating medium rock burst proneness;W_(T)>2,indicating strong rock burst proneness;and(6)The rationality of the proposed residual energy release rate index W_(T) is verified by the multi-index method and the multi-sample method,and the proposed residual energy release rate index is used to determine the rock burst proneness of 10 kinds of rock samples.The evaluation accuracy is shown to be high,and it can reflect the actual rock burst proneness.展开更多
Rock masses in high-elevation or cold regions are vulnerable to the combined effects of freeze-thaw(F-T)weathering and dynamic mixed-mode loading,posing a serious threaten to the safety and stability of geotechnical e...Rock masses in high-elevation or cold regions are vulnerable to the combined effects of freeze-thaw(F-T)weathering and dynamic mixed-mode loading,posing a serious threaten to the safety and stability of geotechnical engineering.In this study,a series of dynamic fracture tests were conducted on notched semi-circular bend(NSCB)granite specimens subjected to different mixed-mode loading and F-T cycles using a split Hopkinson pressure bar(SHPB)test system.The effects of F-T treatment and dynamic mixed-mode loading on the fracture properties of granite,including effective fracture toughness,progressive fracture process,and macroscopic morphology of fracture surface,were comprehensively revealed.The experimental results suggest that the dynamic effective fracture toughness of NSCB specimens is dependent on the loading rate,particularly when the mode I loading is dominant.Additionally,the fracture toughness decreases as the number of F-T cycles increases,with an inflection point at 30 F-T cycles.All granite specimens subjected to mixed-mode loading exhibit a curved fracture path,with faster crack propagation speed and more fine cracks in specimens exposed to higher F-T cycles.Macroscopic morphology of fracture surface obtained using three-dimensional(3D)scanning indicates that the fractal dimension of the fracture surface increases with increasing F-T cycles,and the increment is more pronounced for specimens subjected to a higher mode II loading component.Moreover,this study compared the fracture resistance of F-T treated granite subjected to dynamic mixed loading using the maximum tangential stress(MTS)criterion and the generalized maximum tangential stress-based semi-analytical(SA-GMTS)criterion.Compared with the MTS criterion,the SA-GMTS criterion shows a more reasonable consistency with the experimental results,with a root mean square error within±7%.展开更多
For the sake of solving the problem that it is difficult to be integrated for the Mises specific plastic power due to its nonlinearity,a new linear criterion,named the globally optimal approximation criterion,is const...For the sake of solving the problem that it is difficult to be integrated for the Mises specific plastic power due to its nonlinearity,a new linear criterion,named the globally optimal approximation criterion,is constructed by the polygonal approximation to the Mises circle.The new criterion is proved to be the linear function of the principal stress componentsσ1,σ2 andσ3 and the trajectory of it on theπ-plane is a non-equiangular but equilateral dodecagon intersecting the Mises circle.The theoretical results of the current criterion described by the Lode stress parameters are in excellent accordance with the experimental results.Meanwhile,according to the trend that the metallic flow velocity between rollers aggrandizes gradually from the inlet to the outlet during the hot rolling of a thick plate,a biomimetic velocity field is proposed in which the horizontal velocity component fits the egg-circular curve distribution.The velocity field and its simulated results agree quite well.Subsequently,using the determined linear criterion,energy analysis of the constructed velocity field is utilized to obtain the interior deformation power,while the vector decomposition approach is utilized to obtain the frictional power and shear power.On this basis,the overall power is obtained and the analytical solutions are generated for the rolling torque,rolling force and the coefficient of the stress state under different egg curves by minimizing the neutral angle.Furthermore,the parameter optimization of the characteristic parameterρwhich affects the slope of the egg-circular curve is carried out and the best egg-circular curve which can minimize the energy consumption is determined.The best agreement between the theoretical and observed values of rolling force and rolling torque is under this curve,and the mean relative errors of the rolling torque and rolling force are no more than 2.93%,while the maximum error is no more than 8.35%.展开更多
1.Introduction Material fracture is a primary mode of failure for engineer-ing components,often resulting in severe safety incidents due to its sudden nature.Therefore,predicting material fracture becomes crucial both...1.Introduction Material fracture is a primary mode of failure for engineer-ing components,often resulting in severe safety incidents due to its sudden nature.Therefore,predicting material fracture becomes crucial both in science and engineering.Scientists have been con-tinuously engaged in this research field for centuries[1-3],propos-ing fracture criteria with different equation forms[2,3],such as the classical maximum tensile and shear stress criteria,etc.展开更多
基金supported by the National Science and Technology Council,Taiwan under grants NSTC 111-2221-E-019-047 and NSTC 112-2221-E-019-030.
文摘In this paper,an advanced satellite navigation filter design,referred to as the Variational Bayesian Maximum Correntropy Extended Kalman Filter(VBMCEKF),is introduced to enhance robustness and adaptability in scenarios with non-Gaussian noise and heavy-tailed outliers.The proposed design modifies the extended Kalman filter(EKF)for the global navigation satellite system(GNSS),integrating the maximum correntropy criterion(MCC)and the variational Bayesian(VB)method.This adaptive algorithm effectively reduces non-line-of-sight(NLOS)reception contamination and improves estimation accuracy,particularly in time-varying GNSS measurements.Experimental results show that the proposed method significantly outperforms conventional approaches in estimation accuracy under heavy-tailed outliers and non-Gaussian noise.By combining MCC with VB approximation for real-time noise covariance estimation using fixed-point iteration,the VBMCEKF achieves superior filtering performance in challenging GNSS conditions.The method’s adaptability and precision make it ideal for improving satellite navigation performance in stochastic environments.
文摘In the past few decades,the navigation performance of ships and structures in ice-covered waters has not been fully studied,especially the influence of ice mechanical properties on icebreaking ability.Ice bending strength is a key ice parameter for predicting ship ice loads,and accurate ice bending strength is also the key to scaling model tests results to real ship.However,numerical simulation studies on model ice bending strength of ice tanks are often neglected.In this paper,an explicit finite element method model is used to simulate the ice cantilever beam test,and the failure load and bending strength of the ice are obtained.In this model,the Tsai-Wu failure criterion is used as the material constitutive model,and the required simulation parameters are obtained from the model ice test in ice tank.Parameter sensitivity analysis shows that the cantilever beam size of the model ice has a significant effect on the flexural strength.The results show that proper rounding at the root of the cantilever beam is beneficial to reduce stress concentration and obtain more accurate bending strength;the thickness,width and length of the cantilever beam should conform to a certain ratio,and consistent with the ITTC recommended reference.Therefore,the results of this study can promote model ice experiments and numerical studies and provide ice strength data support for ship design and polar ship maneuvering.
基金Projects(52208382, 52278387, 51738002) supported by the National Natural Science Foundation of ChinaProject(2022YJS072) supported by the Fundamental Research Funds for the Central Universities,China。
文摘Ground reinforcement is crucial for tunnel construction, especially in soft rock tunnels. Existing analytical models are inadequate for predicting the ground reaction curves (GRCs) for reinforced tunnels in strain-softening (SS) rock masses. This study proposes a novel analytical model to determine the GRCs of SS rock masses, incorporating ground reinforcement and intermediate principal stress (IPS). The SS constitutive model captures the progressive post- peak failure, while the elastic-brittle model simulates reinforced rock masses. Nine combined states are innovatively investigated to analyze plastic zone development in natural and reinforced regions. Each region is analyzed separately, and coupled through boundary conditions at interface. Comparison with three types of existing models indicates that these models overestimate reinforcement effects. The deformation prediction errors of single geological material models may exceed 75%. Furthermore, neglecting softening and residual zones in natural regions could lead to errors over 50%. Considering the IPS can effectively utilize the rock strength to reduce tunnel deformation by at least 30%, thereby saving on reinforcement and support costs. The computational results show a satisfactory agreement with the monitoring data from a model test and two tunnel projects. The proposed model may offer valuable insights into the design and construction of reinforced tunnel engineering.
文摘The swinging-loading process is essential for automatic artillery loading systems.This study focuses on the problems of reliability analysis that affect swinging-loading positioning accuracy.A dynamic model for a multi degree-of-freedom swinging-loading-integrated rigid-flexible coupling system is established.This model is based on the identification of key parameters and platform experiments.Based on the spatial geometric relationship between the breech and loader during modular charge transfer and the possible maximum interference depth of the modular charge,a new failure criterion for estimating the reliability of swinging-loading positioning accuracy is proposed.Considering the uncertainties in the operation of the pendulum loader,the direct probability integration method is introduced to analyze the reliability of the swinging-loading positioning accuracy under three different charge numbers.The results indicate that under two and four charges,the swinging-loading process shows outstanding reliability.However,an unstable stage appears when the swinging motion occurred under six charges,with a maximum positioning failure probability of 0.0712.A comparison between the results obtained under the conventional and proposed criteria further reveals the effectiveness and necessity of the proposed criterion.
基金supported by the National Key Research and Development Program of China (No.2021YFC2902102)the National Natural Science Foundation of China (Nos.52374103 and 52274013)。
文摘Hydraulic fracture(HF)formed in rock significantly helps with the development of geo-energy and georesources.The HF formation condition was challenging to understand,with obscure rock micro-cracking mechanisms being a key factor.The rock micro-cracking mechanism under gradient pore water pressure was analyzed on the scale of mineral particles and it was combined with macroscopic boundary conditions of rock hydraulic fracturing,obtaining the propagation criterion of HF in rock based on the rock micro-cracking mechanism which was verified by experiment.The results show that the disturbed skeleton stress induced by the disturbance of gradient pore water pressure in rock equals the pore water pressure difference.The overall range of the defined mechanical shape factor a/b is around 1,but greater than0.5.Under the combined influence of pore water pressure differences and macroscopic boundary stresses on the rock micro-cracking,micro-cracks form among rock mineral particles,micro-cracks connect to form micro-hydraulic fracture surfaces,and micro-hydraulic fracture surfaces open to form macrohydraulic fractures.HF begins to form at the micro-cracking initiation pressure(MCIP),which was tested by keeping the HF tip near the initiation point.The theoretical value of MCIP calculated by the proposed propagation criterion is close to MCIP tested.
文摘In this paper,we study normal families of meromorphic functions.By using the idea in[16],we obtain some normality criteria for families of meromorphic functions concerning the wandering multiple functions,which extend and improve the well-known Montel's criterion,Bloch-Valiron's theorem,and the related results due to Carathéodory,and Grahl-Nevo et al..
基金Projects(51934007,12072363,52004268) supported by the National Natural Science Foundation of ChinaProject(22KJD440002) supported by the Natural Science Fund for Colleges and Universities in Jiangsu Province,China。
文摘This study investigates the instability characteristics of dynamic disasters resulting from disruption caused by extracting resources underground. Utilizing the split Hopkinson pressure bar (SHPB) system, the dynamic response mechanism of coal energy evolution is examined, and the energy instability criterion is established. The validity of the instability criterion is explored from the standpoint of damage progression. The results demonstrate that the energy conversion mechanism undergoes a fundamental alternation under impact disturbance. Moreover, the energy release rate as well as the energy dissipation rate undergo comparable changes across distinct levels of impact disturbance. The distinction between the energy release rate and the energy dissipation rate (DRD) increases as coal mass deformation grows. Prior to coal facing instability and failure, the DRD experienced an inflection point followed by a sharp decrease. In conjunction with the discussion on the damage evolution, the physical and mechanical significance of DRD remains clear, which can essentially describe the whole impact loading process. The phenomenon that the inflection point appears and DRD subsequently suddenly decreases can be employed as the energy criterion prior to the failure of instability. Furthermore, this paper provides significant reference for the prediction of dynamic instability of coal under dynamic disturbance.
文摘This paper presents a new criterion for determining the unloading points quantitatively and consistently in a multi-stage triaxial test.The radial strain gradient(RSG)is first introduced as an arc tangent function of the rate of change of radial strain to time.RSG is observed to correlate closely with the stress state of a compressed sample,and reaches a horizontal asymptote as approaching failure.For a given rock type,RSG value at peak stress is almost the same,irrespective of the porosity and permeability.These findings lead to the development of RSG criterion:Unloading points can be precisely determined at the time when RSG reaches a pre-determined value that is a little smaller than or equal to the RSG at peak stress.The RSG criterion is validated against other criteria and the single-stage triaxial test on various types of rocks.Failure envelopes from the RSG criterion match well with those from single-stage tests.A practical procedure is recommended to use the RSG criterion:an unconfined compression or single-stage test is first conducted to determine the RSG at peak stress for one sample,the unloading point is then selected to be a value close to the RSG at peak stress,and the multi-stage test is finally performed on another sample using the pre-selected RSG unloading criterion.Generally,the RSG criterion is applicable for any type of rocks,especially brittle rocks,where other criteria are not suitable.Further,it can be practically implemented on the most available rock mechanical testing instruments.
基金the financial support provided by the National Key R&D Program of China(Grant No.2022YFB2302102)the National Natural Science Foundation of China(Grant Nos.42472340 and 42072308).
文摘The generalized Zhang-Zhu(GZZ)strength criterion was proposed as an extension to the Hoek-Brown criterion and the Mogi criterion.The introduction to mean normal stress results in a non-smooth and non-convex yield surface,which presents a challenge for updating plastic stress.Current research primarily focuses on modified smooth GZZ criteria or approximate solutions,which inevitably lead to increased computational costs or inaccuracies.In this paper,an accurate stress updating algorithm is proposed based on the original GZZ criterion.The algorithm operates entirely in the principal stress space,where numerical singularities at the intersection of yield surfaces are avoided by defining four different types of stress updating.This approach simplifies the GZZ criterion compared to its formulation in general stress space.The return mapping is employed to compute the updated stress and consistent stiffness matrix,facilitating calculations using both finite element implicit and explicit algorithms.Finally,the accuracy of the proposed method is validated using rock true triaxial test data and semianalytical solutions for stresses and displacement around a circular opening under the GZZ criterion.
基金This work was supported by the National Natural Science Foundation of China(61502522)the Equipment Pre-Research Field Fund(JZX7Y20190253036101)+1 种基金the Equipment Pre-Research Ministry of Education Joint Fund(6141A02033703)the Hubei Provincial Natural Science Foundation(2019CFC897).
文摘To solve the problem of time difference of arrival(TDOA)positioning and tracking of targets by the unmanned aerial vehicles(UAV)swarm in future air combat,this paper adopts the TDOA positioning method and uses time difference sensors of the UAV swarm to locate target radiation sources.Firstly,a TDOA model for the target is set up for the UAV swarm under the condition that the error variance varies with the received signal-to-noise ratio.The accuracy of the positioning error is analyzed by geometric dilution of precision(GDOP).The D-optimality criterion of the positioning model is theoretically derived.The target is positioned and settled,and the maximum value of the Fisher information matrix determinant is used as the optimization objective function to optimize the track of the UAV in real time.Simulation results show that the track optimization improves the positioning accuracy and stability of the UAV swarm to the target.
基金supported by the National Natural Science Foundation of China(Grant Nos.51934003,52334004)Yunnan Major Scientific and Technological Projects(Grant No.202202AG050014)。
文摘To understand the strengths of rocks under complex stress states,a generalized nonlinear threedimensional(3D)Hoek‒Brown failure(NGHB)criterion was proposed in this study.This criterion shares the same parameters with the generalized HB(GHB)criterion and inherits the parameter advantages of GHB.Two new parameters,b,and n,were introduced into the NGHB criterion that primarily controls the deviatoric plane shape of the NGHB criterion under triaxial tension and compression,respectively.The NGHB criterion can consider the influence of intermediate principal stress(IPS),where the deviatoric plane shape satisfies the smoothness requirements,while the HB criterion not.This criterion can degenerate into the two modified 3D HB criteria,the Priest criterion under triaxial compression condition and the HB criterion under triaxial compression and tension condition.This criterion was verified using true triaxial test data for different parameters,six types of rocks,and two kinds of in situ rock masses.For comparison,three existing 3D HB criteria were selected for performance comparison research.The result showed that the NGHB criterion gave better prediction performance than other criteria.The prediction errors of the strength of six types of rocks and two kinds of in situ rock masses were in the range of 2.0724%-3.5091%and 1.0144%-3.2321%,respectively.The proposed criterion lays a preliminary theoretical foundation for prediction of engineering rock mass strength under complex in situ stress conditions.
基金Financial support for this work was provided by the General Program and Youth Fund Program of the National Natural Science Foundation of China(Grant Nos.42377175 and 42002292).
文摘Deep metal mines are often mined using the high-level pillars with subsequent cementation backfilling(HLSCB)mining method.At the design stage,it is therefore important to have a reasonable method for determining the shear strength of the high-level pillars(i.e.cohesion and internal friction angle)when they are supported by cemented backfilling.In this study,a formula was derived for the upper limit of the confining pressure σ3max on a high-level pillar supported by cemented backfilling in a deep metal mine.A new method of estimating the shear strength of such pillars was then proposed based on the Hoek eBrown failure criterion.Our analysis indicates that the horizontal stress σhh acting on the cemented backfill pillar can be simplified by expressing it as a constant value.A reasonable and effective value for σ3max can then be determined.The value of s3max predicted using the proposed method is generally less than 3 MPa.Within this range,the shear strength of the high-level pillar is accurately calculated using the equivalent MohreCoulomb theory.The proposed method can effectively avoid the calculation of inaccurate shear strength values for the high-level pillars when the original HoekeBrown criterion is used in the presence of large confining pressures,i.e.the situation in which the cohesion value is too large and the friction angle is too small can effectively be avoided.The proposed method is applied to a deep metal mine in China that is being excavated using the HLSCB method.The shear strength parameters of the high-level pillars obtained using the proposed method were input in the numerical simulations.The numerical results show that the recommended level heights and sizes of the high-level pillars and rooms in the mine are rational.
基金supported by the National Natural Science Foundation of China(Nos.52004289 and U22A20165)the Fundamental Research Funds for the Central Universities(No.2022XJNY01)。
文摘Based on existing triaxial compression experimental data,a new empirical failure criterion with wide applicability was proposed considering hydrostatic pressure,second stress invariance,and maximum shear stress.Four fitting evaluation indicators were used to verify the consistency of the new failure criterion,and the differences with the other 6 failure criteria were discussed.The characteristics of the new failure criteria in the principal stress space were finally analyzed.The results indicate that(1)the new failure criterion exhibits strong predictive ability for triaxial experiments and has good applicability for both intact and jointed rocks;(2)the influence of hydrostatic pressure on the failure surface exhibits a non-linear trend,and different hydrostatic pressure also exhibits different distribution patterns on the deviatoric stress plane,with a distribution characteristic pattern of hexagonal snowflake-regular hexagon.The maximum shear stress has a torsional effect on the new criterion,in the three-dimensional failure surface.The parameters a and b of the rock have an impact on the failure surface morphology of the new criterion function on the offset surface.
基金supported by the National Natural Science Foundation of China(Grant No.52304142)basic scientific research fees of colleges and universities directly under Inner Mongolia Autonomous Region(Grant No.2023QNJS108).
文摘The natural property of rock material,whether impact occurs,is the key influencing factor of the occurrence of rock burst disaster.To accurately assess rock burst proneness,this study focuses on typical sandstone as the research object.Uniaxial cyclic loading and unloading tests were conducted to measure the elastic strain energy accumulated in sandstone under different stress levels and a relationship between elastic strain energy and stress level was established.The results show that:(1)The peak stress under cyclic loading and unloading conditions is slightly lower than the uniaxial compressive strength.With an increase in the number of cycles,the internal damage of sandstone continues to accumulate,and the mechanical properties such as compressive strength continue to deteriorate;(2)With an increase in stress,the input strain energy,elastic strain energy,and dissipated strain energy also increase;(3)When the stress is low,the increase in elastic strain energy is large and shows a steady growth;with an increase in stress,the increase of elastic strain energy decreases;(4)The square of stress at any time has a good linear relationship with elastic strain energy.According to the relationship obtained from the test,the elastic strain energy at the peak stress time can be obtained;(5)A new criterion for assessing rock burst proneness is proposed:residual energy release rate index W_(T),which characterizes the energy release per unit time when the rock burst occurs.The intervals for evaluating the rock burst proneness of the residual energy release rate index W_(T) are as follows:W_(T)<0.025,indicating no rock burst proneness;0.025≤W_(T)<0.15,indicating weak rock burst proneness;0.15≤W_(T)<2,indicating medium rock burst proneness;W_(T)>2,indicating strong rock burst proneness;and(6)The rationality of the proposed residual energy release rate index W_(T) is verified by the multi-index method and the multi-sample method,and the proposed residual energy release rate index is used to determine the rock burst proneness of 10 kinds of rock samples.The evaluation accuracy is shown to be high,and it can reflect the actual rock burst proneness.
基金support from the National Natural Science Foundation of China(Grant Nos.52225904 and 52039007)the Natural Science Foundation of Sichuan Province(Grant No.2023NSFSC0377).
文摘Rock masses in high-elevation or cold regions are vulnerable to the combined effects of freeze-thaw(F-T)weathering and dynamic mixed-mode loading,posing a serious threaten to the safety and stability of geotechnical engineering.In this study,a series of dynamic fracture tests were conducted on notched semi-circular bend(NSCB)granite specimens subjected to different mixed-mode loading and F-T cycles using a split Hopkinson pressure bar(SHPB)test system.The effects of F-T treatment and dynamic mixed-mode loading on the fracture properties of granite,including effective fracture toughness,progressive fracture process,and macroscopic morphology of fracture surface,were comprehensively revealed.The experimental results suggest that the dynamic effective fracture toughness of NSCB specimens is dependent on the loading rate,particularly when the mode I loading is dominant.Additionally,the fracture toughness decreases as the number of F-T cycles increases,with an inflection point at 30 F-T cycles.All granite specimens subjected to mixed-mode loading exhibit a curved fracture path,with faster crack propagation speed and more fine cracks in specimens exposed to higher F-T cycles.Macroscopic morphology of fracture surface obtained using three-dimensional(3D)scanning indicates that the fractal dimension of the fracture surface increases with increasing F-T cycles,and the increment is more pronounced for specimens subjected to a higher mode II loading component.Moreover,this study compared the fracture resistance of F-T treated granite subjected to dynamic mixed loading using the maximum tangential stress(MTS)criterion and the generalized maximum tangential stress-based semi-analytical(SA-GMTS)criterion.Compared with the MTS criterion,the SA-GMTS criterion shows a more reasonable consistency with the experimental results,with a root mean square error within±7%.
基金support from the National Natural Science Foundation of China(Grant Nos.52074187,U1960105 and 52274388)the Undergraduate Training Program for Innovation and Entrepreneurship,Soochow University,China(Grant No.202210285158Y).
文摘For the sake of solving the problem that it is difficult to be integrated for the Mises specific plastic power due to its nonlinearity,a new linear criterion,named the globally optimal approximation criterion,is constructed by the polygonal approximation to the Mises circle.The new criterion is proved to be the linear function of the principal stress componentsσ1,σ2 andσ3 and the trajectory of it on theπ-plane is a non-equiangular but equilateral dodecagon intersecting the Mises circle.The theoretical results of the current criterion described by the Lode stress parameters are in excellent accordance with the experimental results.Meanwhile,according to the trend that the metallic flow velocity between rollers aggrandizes gradually from the inlet to the outlet during the hot rolling of a thick plate,a biomimetic velocity field is proposed in which the horizontal velocity component fits the egg-circular curve distribution.The velocity field and its simulated results agree quite well.Subsequently,using the determined linear criterion,energy analysis of the constructed velocity field is utilized to obtain the interior deformation power,while the vector decomposition approach is utilized to obtain the frictional power and shear power.On this basis,the overall power is obtained and the analytical solutions are generated for the rolling torque,rolling force and the coefficient of the stress state under different egg curves by minimizing the neutral angle.Furthermore,the parameter optimization of the characteristic parameterρwhich affects the slope of the egg-circular curve is carried out and the best egg-circular curve which can minimize the energy consumption is determined.The best agreement between the theoretical and observed values of rolling force and rolling torque is under this curve,and the mean relative errors of the rolling torque and rolling force are no more than 2.93%,while the maximum error is no more than 8.35%.
基金supported by the National Nat-ural Science Foundation of China(NSFC)under Grant Nos.52130002,52321001,U2241245the KC Wong Education Founda-tion(No.GJTD-2020-09)+2 种基金the Youth Innovation Promotion Asso-ciation CAS(Grant No.2021192)the IMR Innovation Fund(No.2023-ZD01)the National Key R&D Program of China(No.2020YFA0710404).
文摘1.Introduction Material fracture is a primary mode of failure for engineer-ing components,often resulting in severe safety incidents due to its sudden nature.Therefore,predicting material fracture becomes crucial both in science and engineering.Scientists have been con-tinuously engaged in this research field for centuries[1-3],propos-ing fracture criteria with different equation forms[2,3],such as the classical maximum tensile and shear stress criteria,etc.
