Engineering structures are often subjected to the influences of performance deterioration and multiple hazards during their service lives,and consequently may suffer from damage/failure as a result of external loads.S...Engineering structures are often subjected to the influences of performance deterioration and multiple hazards during their service lives,and consequently may suffer from damage/failure as a result of external loads.Structural reliability and resilience assessment is a powerful tool for quantifying the structural ability to withstand these environmental or operational attacks.This paper proposes new formulas for structural time-dependent reliability and resilience analyses in the presence of multiple hazards,which are functions of the duration of the reference period of interest.The joint impacts of nonstationarities in multiple hazards due to a changing environment,as well as the deterioration of structural performance,are explicitly incorporated.The correlation between the structural resistances/capacities associated with different hazard types is modeled by employing a copula function.It is observed that,under the context of multiple hazards and aging effects,the time-dependent resilience takes a generalized form of time-dependent reliability.The proposed formulas can be used to guide the adaptive design of structures,where adaptive strategies are identified across a range of possible future service conditions.An example is presented to demonstrate the applicability of the proposed method for structural reliability and resilience analyses.展开更多
The strategy on repair and strengthening of existing bridges based on time-dependent reliability was analyzed with the maximum expected benefit as the objective function. A sample of risk-ranking decision was illustra...The strategy on repair and strengthening of existing bridges based on time-dependent reliability was analyzed with the maximum expected benefit as the objective function. A sample of risk-ranking decision was illustrated based on updated inspection information with 35 survival age. The effect of improvement of live loads and difference of repair methods on time-dependent reliability of existing bridges are considered. The results show that the decision method can be used in real project, with the cost of failure consequence and the risk of failure considered.展开更多
In practical engineering, many uncertain factors in loading or degradation of material properties may vary with time. Stochastic process modeling constitutes a suitable approach for describing these time-dependent unc...In practical engineering, many uncertain factors in loading or degradation of material properties may vary with time. Stochastic process modeling constitutes a suitable approach for describing these time-dependent uncertainties. By adopting this approach, however, the timedependent reliability calculation is a great challenge owing to the complexity and the huge computational burden. This paper presents a new instantaneous response surface method t-IRS for time-dependent reliability analysis. Different from the adaptive extreme response surface approach, the proposed method does not need to build and update surrogate models separately at each time node. It first uses the expansion optimal linear estimation method to discretize the stochastic processes into a set of independent standard normal variables together with some deterministic functions of time. Time is then treated as an independent one-dimensional variable. Next, initial samples are generated by Latin hypercube sampling, and the corresponding response values are calculated and utilized to construct an instantaneous response surrogate model of the Kriging type. The active learning method is applied to update the Kriging surrogate model until satisfactory accuracy is achieved. Finally, the instantaneous response surrogate model is used to compute the time-dependent reliability via Monte Carlo simulation. Four case studies are utilized to demonstrate the effectiveness of the ^-IRS method for time-dependent reliability analysis.展开更多
During the life of an offshore structure, its structural strength declines due to various kinds of damages related to the time factor. In this paper, four major kinds of damages, including damages caused by fatigue, d...During the life of an offshore structure, its structural strength declines due to various kinds of damages related to the time factor. In this paper, four major kinds of damages, including damages caused by fatigue, dent, corrosion and marine life, are discussed. Based on these analyses, formulas for the evaluation of the damaged structure reliability are derived. Furthermore the computer program ISM for the analysis of structural reliability is developed by the use of Advanced First Order Second Moment method and Monte-Carlo Importance Sampling method. The reliability of a turbular joint and a beam are studied as numerical examples. The results show that the theory and the analysis method given in this paper are reasonable and effective.展开更多
Reliability is a crucial metric in aerospace engineering.The results of reliability assessments for components like aerospace electromagnetic relays directly impact the development and operational reliability of aeros...Reliability is a crucial metric in aerospace engineering.The results of reliability assessments for components like aerospace electromagnetic relays directly impact the development and operational reliability of aerospace engineering systems.Current methods for analyzing the reliability of aerospace electromagnetic relays have limitations,such as neglecting the combined effects of multiple uncertain factors,degradation of key component properties,and the influence of fluctuations in aerospace environments.Additionally,these methods often assume a single-type uncertainty in the manufacturing process,leading to significant deviations between the analysis results and actual measurement results.To address these issues,this study proposes an efficient timedependent reliability analysis method based on the HL-RF algorithm,considering a hybrid of probabilistic and interval uncertainty that accounts for degradation and environmental conditions.The proposed method is applied to the reliability analysis of actual aerospace electromagnetic relay products and compared with traditional methods,demonstrating significant advantages.The proposed method has been applied to the time-dependent reliability analysis of actual aerospace electromagnetic relay products under different environmental conditions.The analysis results exhibit an error margin within 5.12% compared to actual measurement results.Compared to analysis methods solely based on probabilistic uncertainty quantification or interval uncertainty quantification,this method reduces the analysis error by 52% and 67% respectively.When compared to two other state-of-the-art methods that integrate probabilistic and interval uncertainty quantification,the error reduction is 23%.These demonstrate the superiority of the proposed method and validates its effectiveness.The presented approach has the potential to be extended for reliability analysis in other aerospace electromechanical systems.展开更多
Time-dependent reliability-based design optimization(TRBDO)has received extensive attention because of its ability to achieve optimal solutions that help meet the requirement for whole lifecycle reliability by quantit...Time-dependent reliability-based design optimization(TRBDO)has received extensive attention because of its ability to achieve optimal solutions that help meet the requirement for whole lifecycle reliability by quantitatively considering dynamic uncertainties.However,directly solving TRBDO problems is computationally expensive,if not prohibitive,owing to the need to repeatedly evaluate time-dependent probabilistic constraints.To address this challenge,an efficient decoupled method called sequential optimization and time-dependent reliability assessment(SOTRA)is proposed in this study.This method transforms the original TRBDO problem,initially formulated probabilistically,into a problem using percentile formulation after discretizing time-dependent performance functions.By adopting the equivalent minimum performance target point(EMPTP)concept,the TRBDO problem is further converted into an equivalent deterministic optimization problem,which is subsequently solved through a sequential iteration process involving deterministic optimization and time-dependent reliability analysis.To efficiently and robustly search an EMPTP for reliability analysis,a time-dependent self-adaptive finite-step length method is developed.To verify the proposed SOTRA method against existing TRBDO methods,a numerical example,a benchmark structural design case of a simply supported beam,and an engineering application for flexible wheel design are exemplified in this study.The results demonstrate that the proposed SOTRA method exhibits high efficiency and robustness in solving TRBDO problems.展开更多
Backfill is routinely adopted as a ground support measure for underground mines.However,ground stability enhancement by backfill has received limited research attention.This is likely to be because of the conventional...Backfill is routinely adopted as a ground support measure for underground mines.However,ground stability enhancement by backfill has received limited research attention.This is likely to be because of the conventional assumption that the fill material exhibits a significantly lower stiffness than the host rocks.Significantly,a recent pioneering work revealed the time-dependent ground stability around a backfilled stope with vertical walls through numerical modeling.In practice,underground stopes typically exhibit a higher or lower degree of inclination.This alters the stress state in peripheral rocks and may induce severe instability and dilution,particularly in stope-hanging walls.Hence,it is imperative to analyze the time-dependent ground stability of inclined backfilled stopes for backfill structure design.Therefore,comprehensive numerical simulations were performed using FLAC3D to address this knowledge deficiency by incorporating a coupled analysis of the backfill consolidation behavior and long-term creep deformation in surrounding rocks.The ground stability was evaluated based on the confinement effectiveness,strength-stress ratio,stress path relative to the yield surface,and time-dependent stress redistribution in the rocks.A parametric study revealed that the inclination angle of the backfilled stope reduced the confinement effectiveness in the host rocks when the wall creep was minor.This exacerbated the rock mass sloughing potential.However,a backfilled stope with a shallower dip angle achieved superior ground stability enhancement when the creep deformation was substantial,by applying a more significant compression on the backfill and effectively mobilizing its passive support performance during consolidation.Additional simulations were conducted to analyze the effects of stope height and width,mine depth,mechanical properties of rocks,backfill compressibility,and filling gap on the time-dependent stress redistribution and stability around the inclined backfilled stope.展开更多
A multi-stage stress relaxation test was performed on a granodiorite sample to understand the deformation process prior to the macroscopic failure of brittle rocks,as well as the transient response during stress relax...A multi-stage stress relaxation test was performed on a granodiorite sample to understand the deformation process prior to the macroscopic failure of brittle rocks,as well as the transient response during stress relaxation.Distributed optical fiber sensing was used to measure strains across the sample surface by helically wrapping the single-mode fiber around the cylindrical sample.Close agreement was observed between the circumferential strains obtained from the optical fibers and the extensometer.The reconstructed full-field strain contours show strain heterogeneity from the crack closure phase,and the strains in the later deformation phase are dominantly localized within the former high-strain zone.The Gini coefficient was used to quantify the degree of strain localization and shows an initial increase during the crack closure phase,a decrease during the linear elastic phase,and a subsequent increase during the post-yielding phase.This behavior corresponds to a process of initial localization from an imperfect boundary condition,homogenization,and eventual relocalization prior to the macroscopic failure of the sample.The transient strain rate decay during the stress relaxation phase was quantified using the p-value in the“Omori-like"power law function.A higher initial stress at the onset of relaxation results in a lower p-value,indicating a slower strain rate decay.As the sample approaches macroscopic failure,the lowest p-value shifts from the most damaged zone to adjacent areas,suggesting stress redistribution or crack propagation in deformed crystalline rocks under stress relaxation conditions.展开更多
In-situ stress is a key parameter for underground mine design and rock stability analysis.The borehole overcoring technique is widely used for in-situ stress measurement,but the rheological recovery deformation of roc...In-situ stress is a key parameter for underground mine design and rock stability analysis.The borehole overcoring technique is widely used for in-situ stress measurement,but the rheological recovery deformation of rocks after stress relief introduces errors.To improve accuracy,this study proposes an in-situ stress solution theory that incorporates time-dependent stress relief effects.Triaxial stepwise loadingunloading rheological tests on granite and siltstone established quantitative relationships between instantaneous elastic recovery and viscoelastic recovery under different stress levels,confirming their impact on measurement accuracy.By integrating a dual-class elastic deformation recovery model,an improved in-situ stress solution theory was derived.Additionally,accounting for the nonlinear characteristics of rock masses,a determination method for time-dependent nonlinear mechanical parameters was proposed.Based on the CSIRO hollow inclusion strain cell,time-dependent strain correction equations and long-term confining pressure calibration equations were formulated.Finally,the proposed theory was successfully applied at one iron mine(736 m depth)in Xinjiang,China,and one coal mine(510 m depth)in Ningxia,China.Compared to classical theory,the calculated mean stress values showed accuracy improvements of 6.0%and 9.4%,respectively,validating the applicability and reliability of the proposed theory.展开更多
In a repairable consecutive C(k,n:F)system,after the system operates for a certain time,some components may fail,some failed components may be repaired and the state of the system may change.The models developed in th...In a repairable consecutive C(k,n:F)system,after the system operates for a certain time,some components may fail,some failed components may be repaired and the state of the system may change.The models developed in the existing literature usually assume that the state of the sys-tem varies over time depending on the values of n and k and the state of the system is known.Since the system reliability will vary over time,it is of great interest to analyse the time-dependent system reliability.In this paper,we develop a novel and simple method that utilizes the eigen-values of the transition rate matrix of the system for the computation of time-dependent system reliability when the system state is known.In addition,the transition performance probabilities of the system from a known state to the possible states are also analysed.Computational results are presented to illustrate the applicability and accuracy of the proposed method.展开更多
Blade vibration failure is one of the main failure modes of compressor wheel of turbocharger for vehicle application. The existing models for evaluating the reliability of blade vibration of compressor wheel are stati...Blade vibration failure is one of the main failure modes of compressor wheel of turbocharger for vehicle application. The existing models for evaluating the reliability of blade vibration of compressor wheel are static, and can not reflect the relationship between the reliability of compressor wheel with blade vibration failure mode and the life parameter. For the blade vibration failure mode of compressor wheel of turbocharger, the reliability evaluation method is studied. Taking a compressor wheel of turbocharger for vehicle application as an example, the blade vibration characteristics and how they change with the operating parameters of turbocharger are analyzed. The failure criterion for blade vibration mode of compressor wheel is built with the Campbell diagram, and taking the effect of the dispersity of blade natural vibration frequency and randomness of turbocharger operating speed into account, time-dependent reliability models of compressor wheel with blade vibration failure mode are derived, which embody the parameters of blade natural vibration frequency, turbocharger operating speed, the blade number of compressor wheel, life index and minimum number of resonance, etc. Finally, the rule governing the reliability and failure rate of compressor wheel and the method for determining the reliable life of compressor with blade vibration is presented. A method is proposed to evaluate the reliability of compressor wheel with blade vibration failure mode time-dependently.展开更多
Catastrophic failure in engineering structures of island reefs would occur when the tertiary creep initiates in coral reef limestone with a transition from short-to long-term load.Due to the complexity of biological s...Catastrophic failure in engineering structures of island reefs would occur when the tertiary creep initiates in coral reef limestone with a transition from short-to long-term load.Due to the complexity of biological structures,the underlying micro-behaviors involving time-dependent deformation are poorly understood.For this,an abnormal phenomenon was observed where the axial and lateral creep deformations were mutually independent by a series of triaxial tests under constant stress and strain rate conditions.The significantly large lateral creep deformation implies that the creep process cannot be described in continuum mechanics regime.Herein,it is hypothesized that sliding mechanism of crystal cleavages dominates the lateral creep deformation in coral reef limestone.Then,approaches of polarizing microscope(PM)and scanning electronic microscope(SEM)are utilized to validate the hypothesis.It shows that the sliding behavior of crystal cleavages combats with conventional creep micro-mechanisms at certain condition.The former is sensitive to time and strain rate,and is merely activated in the creep regime.展开更多
With respect to oceanic fluid dynamics,certain models have appeared,e.g.,an extended time-dependent(3+1)-dimensional shallow water wave equation in an ocean or a river,which we investigate in this paper.Using symbolic...With respect to oceanic fluid dynamics,certain models have appeared,e.g.,an extended time-dependent(3+1)-dimensional shallow water wave equation in an ocean or a river,which we investigate in this paper.Using symbolic computation,we find out,on one hand,a set of bilinear auto-Backlund transformations,which could connect certain solutions of that equation with other solutions of that equation itself,and on the other hand,a set of similarity reductions,which could go from that equation to a known ordinary differential equation.The results in this paper depend on all the oceanic variable coefficients in that equation.展开更多
The field of diffusion micro structural magnetic resonance(MR)aims to probe timedependent diffusion,i.e.,an ensemble-averaged mean-squared displacement that is not linear in time.This time-dependence contains rich inf...The field of diffusion micro structural magnetic resonance(MR)aims to probe timedependent diffusion,i.e.,an ensemble-averaged mean-squared displacement that is not linear in time.This time-dependence contains rich information about the surrounding microenvironment.MR methods to measure time-dependent diffusion quantitatively,however,require either non-standard pulse sequences,such as oscillating gradients,or make non-physical assumptions,such as infinitely narrow gradient pulses.Here,we argue that standard spin echo and stimulated echo MR sequences can be used to probe directly.In particular,we propose a framework in which the log-signal ratio obtained from a pair of measurements with different inter-pulse spacingΔis proportional to the MSD between these twoΔvalues along the gradient direction x:-.The framework is quantitative for short,finite-duration gradient pulses and under the Gaussian phase approximation(GPA).To validate the framework,we consider onedimensional diffusion between impermeable,parallel planes,as well as periodicallyspaced,permeable planes.Excellent agreement is obtained between the estimation and the ground truth in the regime where the GPA is expected to hold.Importantly,the GPA can be made to hold for any underlying microstructure,making the proposed framework widely applicable.展开更多
This article first outlines the fundamental definitions of Mycoplasma pneumoniae and the basic principles of antibiotics. It then analyzes and discusses the progress in antibiotic application and time-eff ect studies ...This article first outlines the fundamental definitions of Mycoplasma pneumoniae and the basic principles of antibiotics. It then analyzes and discusses the progress in antibiotic application and time-eff ect studies for neonatal pneumonia treatment, specifically comparing conventional antibiotic therapy with stepwise treatment regimens, and contrasting monotherapy with penicillin, monotherapy with cephalosporins, and combination therapy. Finally, it offers a prospective outlook on antibiotic application and time-effect research in neonatal pneumonia treatment, aiming to provide valuable reference for further scholarly investigations.展开更多
Heat transfers at the interface of adjacent saturated soil primarily through the soil particles and the water in the voids.The presence of water induces the contraction of heat flow lines at the interface,leading to t...Heat transfers at the interface of adjacent saturated soil primarily through the soil particles and the water in the voids.The presence of water induces the contraction of heat flow lines at the interface,leading to the emergence of the thermal contact resistance effect.In this paper,four thermal contact models were developed to predict the thermal contact resistance at the interface of multilayered saturated soils.Based on the theory of thermal-hydro-mechanical coupling,semi-analytical solutions of thermal consolidation subjected to time-dependent heating and loading were obtained by employing Laplace transform and its inverse transformation.Thermal consolidation characteristics of multilayered saturated soils under four different thermal contact models were discussed,and the effects of thermal resistance coefficient,partition thermal contact coefficient,and temperature amplitude on the thermal consolidation process were investigated.The outcomes indicate that the general thermal contact model results in the most pronounced thermal gradient at the interface,which can be degenerated to the other three thermal contact models.The perfect thermal contact model overestimates the deformation of the saturated soil during the thermal consolidation.Moreover,the effect of temperature on consolidation properties decreases gradually with increasing interfacial contact thermal resistance.展开更多
The Zagros Basin in southwestern Iran is a significant source of coal,with numerous coal mines operating in the region.Ensuring the stability of coal mines is crucial for safe and efficient mining operations.This stud...The Zagros Basin in southwestern Iran is a significant source of coal,with numerous coal mines operating in the region.Ensuring the stability of coal mines is crucial for safe and efficient mining operations.This study investigates the time-varying response of rocks and roof resistance in coal mines in the Zagros Mountains using a novel approach that combines numerical simulation,relaxation testing,and rock displacement studies.The results show that rocks exhibit significant time-dependent behavior,with changes in rock mechanical properties over time.A comprehensive viscoelastic-plastic model is devel-oped to accurately describe the time-varying strain-softening response of rocks and simulate laboratory tests.The model integrates the Burgers and strain-softening models,simulating stress relaxation curves and rock displacement over time.The study reveals that the rock mass displays significant nonlinear behavior,with changes in rock mechanical properties over time.The findings of this study highlight the importance of considering the time-varying response of rocks and roof resistance in coal mine stability analysis.The results provide valuable insights into the time-dependent behavior of rock mass in coal mines in Iran,which can inform mining practices and mitigate potential hazards.Results in this study can contribute to developing strategies for improving roof stability and reducing the likelihood of roof collapses.展开更多
We present a fully time-dependent quantum wave packet evolution method for investigating molecular dynamics in intense laser fields.This approach enables the simultaneous treatment of interactions among multiple elect...We present a fully time-dependent quantum wave packet evolution method for investigating molecular dynamics in intense laser fields.This approach enables the simultaneous treatment of interactions among multiple electronic states while simultaneously tracking their time-dependent electronic,vibrational,and rotational dynamics.As an illustrative example,we consider neutral H_(2)molecules and simulate the laser-induced excitation dynamics of electronic and rotational states in strong laser fields,quantitatively distinguishing the respective contributions of electronic dipole transitions(within the classical-field approximation)and non-resonant Raman processes to the overall molecular dynamics.Furthermore,we precisely evaluate the relative contributions of direct tunneling ionization from the ground state and ionization following electronic excitation in the strong-field ionization of H_(2).The developed methodology shows strong potential for performing high-precision theoretical simulations of electronic-vibrational-rotational state excitations,ionization,and dissociation dynamics in molecules and their ions under intense laser fields.展开更多
In this work,we demonstrated the InSnO(ITO)TFTs passivated with SiO_(2)via the PECVD process compatible with large-area production for the first time.The passivated ITO TFTs with various channel thicknesses(t_(ch)=4,5...In this work,we demonstrated the InSnO(ITO)TFTs passivated with SiO_(2)via the PECVD process compatible with large-area production for the first time.The passivated ITO TFTs with various channel thicknesses(t_(ch)=4,5,6 nm)exhibit excellent electrical performance and superior uniformity.The reliability properties of ITO TFTs were evaluated in detail under positive bias stress(PBS)conditions before and after passivation.Compared to the devices without passivation,the passivated devices have only 50%threshold voltage degradation(ΔV_(th))and 50%newly generated traps due to excellent isolation of the ambient atmosphere.The negligible performance degradation of ITO TFTs with passivation during negative bias stress(NBS)and negative bias temperature stress(NBTS)verifies the outstanding immunity to the water vapor of the SiO_(2)passivation layer.Overall,the ITO TFT with the t_(ch)of 6 nm and with SiO_(2)passivation exhibits the best performance in terms of electrical properties,uniformity,and reliability,which is promising in large-area production.展开更多
This paper investigates the reliability of internal marine combustion engines using an integrated approach that combines Fault Tree Analysis(FTA)and Bayesian Networks(BN).FTA provides a structured,top-down method for ...This paper investigates the reliability of internal marine combustion engines using an integrated approach that combines Fault Tree Analysis(FTA)and Bayesian Networks(BN).FTA provides a structured,top-down method for identifying critical failure modes and their root causes,while BN introduces flexibility in probabilistic reasoning,enabling dynamic updates based on new evidence.This dual methodology overcomes the limitations of static FTA models,offering a comprehensive framework for system reliability analysis.Critical failures,including External Leakage(ELU),Failure to Start(FTS),and Overheating(OHE),were identified as key risks.By incorporating redundancy into high-risk components such as pumps and batteries,the likelihood of these failures was significantly reduced.For instance,redundant pumps reduced the probability of ELU by 31.88%,while additional batteries decreased the occurrence of FTS by 36.45%.The results underscore the practical benefits of combining FTA and BN for enhancing system reliability,particularly in maritime applications where operational safety and efficiency are critical.This research provides valuable insights for maintenance planning and highlights the importance of redundancy in critical systems,especially as the industry transitions toward more autonomous vessels.展开更多
基金supported by the Vice-Chancellor’s Postdoctoral Research Fellowship from the University of Wollongong.
文摘Engineering structures are often subjected to the influences of performance deterioration and multiple hazards during their service lives,and consequently may suffer from damage/failure as a result of external loads.Structural reliability and resilience assessment is a powerful tool for quantifying the structural ability to withstand these environmental or operational attacks.This paper proposes new formulas for structural time-dependent reliability and resilience analyses in the presence of multiple hazards,which are functions of the duration of the reference period of interest.The joint impacts of nonstationarities in multiple hazards due to a changing environment,as well as the deterioration of structural performance,are explicitly incorporated.The correlation between the structural resistances/capacities associated with different hazard types is modeled by employing a copula function.It is observed that,under the context of multiple hazards and aging effects,the time-dependent resilience takes a generalized form of time-dependent reliability.The proposed formulas can be used to guide the adaptive design of structures,where adaptive strategies are identified across a range of possible future service conditions.An example is presented to demonstrate the applicability of the proposed method for structural reliability and resilience analyses.
基金TheLiaoningProviceCommunicationDe partmentKeyScienceFoundation (No .0 10 1)
文摘The strategy on repair and strengthening of existing bridges based on time-dependent reliability was analyzed with the maximum expected benefit as the objective function. A sample of risk-ranking decision was illustrated based on updated inspection information with 35 survival age. The effect of improvement of live loads and difference of repair methods on time-dependent reliability of existing bridges are considered. The results show that the decision method can be used in real project, with the cost of failure consequence and the risk of failure considered.
基金supported by the National Natural Science Foundation of China (Nos.11572134 and 11832013).
文摘In practical engineering, many uncertain factors in loading or degradation of material properties may vary with time. Stochastic process modeling constitutes a suitable approach for describing these time-dependent uncertainties. By adopting this approach, however, the timedependent reliability calculation is a great challenge owing to the complexity and the huge computational burden. This paper presents a new instantaneous response surface method t-IRS for time-dependent reliability analysis. Different from the adaptive extreme response surface approach, the proposed method does not need to build and update surrogate models separately at each time node. It first uses the expansion optimal linear estimation method to discretize the stochastic processes into a set of independent standard normal variables together with some deterministic functions of time. Time is then treated as an independent one-dimensional variable. Next, initial samples are generated by Latin hypercube sampling, and the corresponding response values are calculated and utilized to construct an instantaneous response surrogate model of the Kriging type. The active learning method is applied to update the Kriging surrogate model until satisfactory accuracy is achieved. Finally, the instantaneous response surrogate model is used to compute the time-dependent reliability via Monte Carlo simulation. Four case studies are utilized to demonstrate the effectiveness of the ^-IRS method for time-dependent reliability analysis.
文摘During the life of an offshore structure, its structural strength declines due to various kinds of damages related to the time factor. In this paper, four major kinds of damages, including damages caused by fatigue, dent, corrosion and marine life, are discussed. Based on these analyses, formulas for the evaluation of the damaged structure reliability are derived. Furthermore the computer program ISM for the analysis of structural reliability is developed by the use of Advanced First Order Second Moment method and Monte-Carlo Importance Sampling method. The reliability of a turbular joint and a beam are studied as numerical examples. The results show that the theory and the analysis method given in this paper are reasonable and effective.
基金supported by the National Natural Science Foundation of China(No.52277141).
文摘Reliability is a crucial metric in aerospace engineering.The results of reliability assessments for components like aerospace electromagnetic relays directly impact the development and operational reliability of aerospace engineering systems.Current methods for analyzing the reliability of aerospace electromagnetic relays have limitations,such as neglecting the combined effects of multiple uncertain factors,degradation of key component properties,and the influence of fluctuations in aerospace environments.Additionally,these methods often assume a single-type uncertainty in the manufacturing process,leading to significant deviations between the analysis results and actual measurement results.To address these issues,this study proposes an efficient timedependent reliability analysis method based on the HL-RF algorithm,considering a hybrid of probabilistic and interval uncertainty that accounts for degradation and environmental conditions.The proposed method is applied to the reliability analysis of actual aerospace electromagnetic relay products and compared with traditional methods,demonstrating significant advantages.The proposed method has been applied to the time-dependent reliability analysis of actual aerospace electromagnetic relay products under different environmental conditions.The analysis results exhibit an error margin within 5.12% compared to actual measurement results.Compared to analysis methods solely based on probabilistic uncertainty quantification or interval uncertainty quantification,this method reduces the analysis error by 52% and 67% respectively.When compared to two other state-of-the-art methods that integrate probabilistic and interval uncertainty quantification,the error reduction is 23%.These demonstrate the superiority of the proposed method and validates its effectiveness.The presented approach has the potential to be extended for reliability analysis in other aerospace electromechanical systems.
基金supported by the National Science Foundation for Excellent Young Scholars(Grant No.52422507)the National Natural Science Foundation of China(Grant Nos.52305256,52275244)+1 种基金Postdoctoral Fellowship Program of CPSF(Grant No.GZC20230661)China Postdoctoral Science Foundation(Grant Nos.2024T170211,2023M740970)。
文摘Time-dependent reliability-based design optimization(TRBDO)has received extensive attention because of its ability to achieve optimal solutions that help meet the requirement for whole lifecycle reliability by quantitatively considering dynamic uncertainties.However,directly solving TRBDO problems is computationally expensive,if not prohibitive,owing to the need to repeatedly evaluate time-dependent probabilistic constraints.To address this challenge,an efficient decoupled method called sequential optimization and time-dependent reliability assessment(SOTRA)is proposed in this study.This method transforms the original TRBDO problem,initially formulated probabilistically,into a problem using percentile formulation after discretizing time-dependent performance functions.By adopting the equivalent minimum performance target point(EMPTP)concept,the TRBDO problem is further converted into an equivalent deterministic optimization problem,which is subsequently solved through a sequential iteration process involving deterministic optimization and time-dependent reliability analysis.To efficiently and robustly search an EMPTP for reliability analysis,a time-dependent self-adaptive finite-step length method is developed.To verify the proposed SOTRA method against existing TRBDO methods,a numerical example,a benchmark structural design case of a simply supported beam,and an engineering application for flexible wheel design are exemplified in this study.The results demonstrate that the proposed SOTRA method exhibits high efficiency and robustness in solving TRBDO problems.
基金funding support from the National Natural Science Foundation of China(Nos.52304101 and 52204153)the China Postdoctoral Science Foundation(No.2023MD734215)+2 种基金the Youth Talent Support Program of Xi’an Association for Science and Technology(No.959202413070)the Key Research and Development Program of Shaanxi(No.2023-LL-QY-07)the Key Research and Development Program of Zhejiang(No.2023C03182).
文摘Backfill is routinely adopted as a ground support measure for underground mines.However,ground stability enhancement by backfill has received limited research attention.This is likely to be because of the conventional assumption that the fill material exhibits a significantly lower stiffness than the host rocks.Significantly,a recent pioneering work revealed the time-dependent ground stability around a backfilled stope with vertical walls through numerical modeling.In practice,underground stopes typically exhibit a higher or lower degree of inclination.This alters the stress state in peripheral rocks and may induce severe instability and dilution,particularly in stope-hanging walls.Hence,it is imperative to analyze the time-dependent ground stability of inclined backfilled stopes for backfill structure design.Therefore,comprehensive numerical simulations were performed using FLAC3D to address this knowledge deficiency by incorporating a coupled analysis of the backfill consolidation behavior and long-term creep deformation in surrounding rocks.The ground stability was evaluated based on the confinement effectiveness,strength-stress ratio,stress path relative to the yield surface,and time-dependent stress redistribution in the rocks.A parametric study revealed that the inclination angle of the backfilled stope reduced the confinement effectiveness in the host rocks when the wall creep was minor.This exacerbated the rock mass sloughing potential.However,a backfilled stope with a shallower dip angle achieved superior ground stability enhancement when the creep deformation was substantial,by applying a more significant compression on the backfill and effectively mobilizing its passive support performance during consolidation.Additional simulations were conducted to analyze the effects of stope height and width,mine depth,mechanical properties of rocks,backfill compressibility,and filling gap on the time-dependent stress redistribution and stability around the inclined backfilled stope.
基金support of her postdoctoral research at the GFZ Helmholtz Centre for Geosciences.P.Pan acknowledges the financial support of the National Natural Science Foundation of China(Grant No.52339001)H.Hofmann and Y.Ji acknowledge the financial support of the Helmholtz Association's Initiative and Networking Fund for the Helmholtz Young Investigator Group ARES(contract number VH-NG-1516).
文摘A multi-stage stress relaxation test was performed on a granodiorite sample to understand the deformation process prior to the macroscopic failure of brittle rocks,as well as the transient response during stress relaxation.Distributed optical fiber sensing was used to measure strains across the sample surface by helically wrapping the single-mode fiber around the cylindrical sample.Close agreement was observed between the circumferential strains obtained from the optical fibers and the extensometer.The reconstructed full-field strain contours show strain heterogeneity from the crack closure phase,and the strains in the later deformation phase are dominantly localized within the former high-strain zone.The Gini coefficient was used to quantify the degree of strain localization and shows an initial increase during the crack closure phase,a decrease during the linear elastic phase,and a subsequent increase during the post-yielding phase.This behavior corresponds to a process of initial localization from an imperfect boundary condition,homogenization,and eventual relocalization prior to the macroscopic failure of the sample.The transient strain rate decay during the stress relaxation phase was quantified using the p-value in the“Omori-like"power law function.A higher initial stress at the onset of relaxation results in a lower p-value,indicating a slower strain rate decay.As the sample approaches macroscopic failure,the lowest p-value shifts from the most damaged zone to adjacent areas,suggesting stress redistribution or crack propagation in deformed crystalline rocks under stress relaxation conditions.
基金supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China(No.2024ZD1700201)the National Natural Science Foundation of China(Nos.U2034206,51974014 and 51574014)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(No.2024A1515011631)the National Key Research and Development Project of China(No.2022YFC3004601)。
文摘In-situ stress is a key parameter for underground mine design and rock stability analysis.The borehole overcoring technique is widely used for in-situ stress measurement,but the rheological recovery deformation of rocks after stress relief introduces errors.To improve accuracy,this study proposes an in-situ stress solution theory that incorporates time-dependent stress relief effects.Triaxial stepwise loadingunloading rheological tests on granite and siltstone established quantitative relationships between instantaneous elastic recovery and viscoelastic recovery under different stress levels,confirming their impact on measurement accuracy.By integrating a dual-class elastic deformation recovery model,an improved in-situ stress solution theory was derived.Additionally,accounting for the nonlinear characteristics of rock masses,a determination method for time-dependent nonlinear mechanical parameters was proposed.Based on the CSIRO hollow inclusion strain cell,time-dependent strain correction equations and long-term confining pressure calibration equations were formulated.Finally,the proposed theory was successfully applied at one iron mine(736 m depth)in Xinjiang,China,and one coal mine(510 m depth)in Ningxia,China.Compared to classical theory,the calculated mean stress values showed accuracy improvements of 6.0%and 9.4%,respectively,validating the applicability and reliability of the proposed theory.
基金H.K.T.Ng’s work was also supported by a grant from the Simons Foundation[Grant Number 709773]。
文摘In a repairable consecutive C(k,n:F)system,after the system operates for a certain time,some components may fail,some failed components may be repaired and the state of the system may change.The models developed in the existing literature usually assume that the state of the sys-tem varies over time depending on the values of n and k and the state of the system is known.Since the system reliability will vary over time,it is of great interest to analyse the time-dependent system reliability.In this paper,we develop a novel and simple method that utilizes the eigen-values of the transition rate matrix of the system for the computation of time-dependent system reliability when the system state is known.In addition,the transition performance probabilities of the system from a known state to the possible states are also analysed.Computational results are presented to illustrate the applicability and accuracy of the proposed method.
基金supported by National Natural Science Foundation of China(Grant Nos.51375465,50905007)
文摘Blade vibration failure is one of the main failure modes of compressor wheel of turbocharger for vehicle application. The existing models for evaluating the reliability of blade vibration of compressor wheel are static, and can not reflect the relationship between the reliability of compressor wheel with blade vibration failure mode and the life parameter. For the blade vibration failure mode of compressor wheel of turbocharger, the reliability evaluation method is studied. Taking a compressor wheel of turbocharger for vehicle application as an example, the blade vibration characteristics and how they change with the operating parameters of turbocharger are analyzed. The failure criterion for blade vibration mode of compressor wheel is built with the Campbell diagram, and taking the effect of the dispersity of blade natural vibration frequency and randomness of turbocharger operating speed into account, time-dependent reliability models of compressor wheel with blade vibration failure mode are derived, which embody the parameters of blade natural vibration frequency, turbocharger operating speed, the blade number of compressor wheel, life index and minimum number of resonance, etc. Finally, the rule governing the reliability and failure rate of compressor wheel and the method for determining the reliable life of compressor with blade vibration is presented. A method is proposed to evaluate the reliability of compressor wheel with blade vibration failure mode time-dependently.
基金supported by the National Natural Science Foundation of China(Grant Nos.41877267,41877260)the Priority Research Program of the Chinese Academy of Science(Grant No.XDA13010201).
文摘Catastrophic failure in engineering structures of island reefs would occur when the tertiary creep initiates in coral reef limestone with a transition from short-to long-term load.Due to the complexity of biological structures,the underlying micro-behaviors involving time-dependent deformation are poorly understood.For this,an abnormal phenomenon was observed where the axial and lateral creep deformations were mutually independent by a series of triaxial tests under constant stress and strain rate conditions.The significantly large lateral creep deformation implies that the creep process cannot be described in continuum mechanics regime.Herein,it is hypothesized that sliding mechanism of crystal cleavages dominates the lateral creep deformation in coral reef limestone.Then,approaches of polarizing microscope(PM)and scanning electronic microscope(SEM)are utilized to validate the hypothesis.It shows that the sliding behavior of crystal cleavages combats with conventional creep micro-mechanisms at certain condition.The former is sensitive to time and strain rate,and is merely activated in the creep regime.
基金financially supported by the Scientific Research Foundation of North China University of Technology(Grant Nos.11005136024XN147-87 and 110051360024XN151-86).
文摘With respect to oceanic fluid dynamics,certain models have appeared,e.g.,an extended time-dependent(3+1)-dimensional shallow water wave equation in an ocean or a river,which we investigate in this paper.Using symbolic computation,we find out,on one hand,a set of bilinear auto-Backlund transformations,which could connect certain solutions of that equation with other solutions of that equation itself,and on the other hand,a set of similarity reductions,which could go from that equation to a known ordinary differential equation.The results in this paper depend on all the oceanic variable coefficients in that equation.
基金supported by the intramural research program(IRP)of the Eunice Kennedy Shriver National Institute of Child Health and Human Development。
文摘The field of diffusion micro structural magnetic resonance(MR)aims to probe timedependent diffusion,i.e.,an ensemble-averaged mean-squared displacement that is not linear in time.This time-dependence contains rich information about the surrounding microenvironment.MR methods to measure time-dependent diffusion quantitatively,however,require either non-standard pulse sequences,such as oscillating gradients,or make non-physical assumptions,such as infinitely narrow gradient pulses.Here,we argue that standard spin echo and stimulated echo MR sequences can be used to probe directly.In particular,we propose a framework in which the log-signal ratio obtained from a pair of measurements with different inter-pulse spacingΔis proportional to the MSD between these twoΔvalues along the gradient direction x:-.The framework is quantitative for short,finite-duration gradient pulses and under the Gaussian phase approximation(GPA).To validate the framework,we consider onedimensional diffusion between impermeable,parallel planes,as well as periodicallyspaced,permeable planes.Excellent agreement is obtained between the estimation and the ground truth in the regime where the GPA is expected to hold.Importantly,the GPA can be made to hold for any underlying microstructure,making the proposed framework widely applicable.
文摘This article first outlines the fundamental definitions of Mycoplasma pneumoniae and the basic principles of antibiotics. It then analyzes and discusses the progress in antibiotic application and time-eff ect studies for neonatal pneumonia treatment, specifically comparing conventional antibiotic therapy with stepwise treatment regimens, and contrasting monotherapy with penicillin, monotherapy with cephalosporins, and combination therapy. Finally, it offers a prospective outlook on antibiotic application and time-effect research in neonatal pneumonia treatment, aiming to provide valuable reference for further scholarly investigations.
基金Projects(U24B20113,42477162) supported by the National Natural Science Foundation of ChinaProject(2025C02228) supported by the Primary Research and Development Plan of Zhejiang Province,China。
文摘Heat transfers at the interface of adjacent saturated soil primarily through the soil particles and the water in the voids.The presence of water induces the contraction of heat flow lines at the interface,leading to the emergence of the thermal contact resistance effect.In this paper,four thermal contact models were developed to predict the thermal contact resistance at the interface of multilayered saturated soils.Based on the theory of thermal-hydro-mechanical coupling,semi-analytical solutions of thermal consolidation subjected to time-dependent heating and loading were obtained by employing Laplace transform and its inverse transformation.Thermal consolidation characteristics of multilayered saturated soils under four different thermal contact models were discussed,and the effects of thermal resistance coefficient,partition thermal contact coefficient,and temperature amplitude on the thermal consolidation process were investigated.The outcomes indicate that the general thermal contact model results in the most pronounced thermal gradient at the interface,which can be degenerated to the other three thermal contact models.The perfect thermal contact model overestimates the deformation of the saturated soil during the thermal consolidation.Moreover,the effect of temperature on consolidation properties decreases gradually with increasing interfacial contact thermal resistance.
文摘The Zagros Basin in southwestern Iran is a significant source of coal,with numerous coal mines operating in the region.Ensuring the stability of coal mines is crucial for safe and efficient mining operations.This study investigates the time-varying response of rocks and roof resistance in coal mines in the Zagros Mountains using a novel approach that combines numerical simulation,relaxation testing,and rock displacement studies.The results show that rocks exhibit significant time-dependent behavior,with changes in rock mechanical properties over time.A comprehensive viscoelastic-plastic model is devel-oped to accurately describe the time-varying strain-softening response of rocks and simulate laboratory tests.The model integrates the Burgers and strain-softening models,simulating stress relaxation curves and rock displacement over time.The study reveals that the rock mass displays significant nonlinear behavior,with changes in rock mechanical properties over time.The findings of this study highlight the importance of considering the time-varying response of rocks and roof resistance in coal mine stability analysis.The results provide valuable insights into the time-dependent behavior of rock mass in coal mines in Iran,which can inform mining practices and mitigate potential hazards.Results in this study can contribute to developing strategies for improving roof stability and reducing the likelihood of roof collapses.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFA1602502)the National Natural Science Foundation of China(Grant No.12450404)。
文摘We present a fully time-dependent quantum wave packet evolution method for investigating molecular dynamics in intense laser fields.This approach enables the simultaneous treatment of interactions among multiple electronic states while simultaneously tracking their time-dependent electronic,vibrational,and rotational dynamics.As an illustrative example,we consider neutral H_(2)molecules and simulate the laser-induced excitation dynamics of electronic and rotational states in strong laser fields,quantitatively distinguishing the respective contributions of electronic dipole transitions(within the classical-field approximation)and non-resonant Raman processes to the overall molecular dynamics.Furthermore,we precisely evaluate the relative contributions of direct tunneling ionization from the ground state and ionization following electronic excitation in the strong-field ionization of H_(2).The developed methodology shows strong potential for performing high-precision theoretical simulations of electronic-vibrational-rotational state excitations,ionization,and dissociation dynamics in molecules and their ions under intense laser fields.
基金supported in part by the National Natural Science Foundation of China(62404110,62274033)Natural Science Foundation of Jiangsu Province(BK20221453)+1 种基金Fundamental Research Funds for the Central UniversitiesNatural Science Research Start-up Foundation of Recruiting Talents of Nanjing University of Posts and Telecommunications(NY223159)。
文摘In this work,we demonstrated the InSnO(ITO)TFTs passivated with SiO_(2)via the PECVD process compatible with large-area production for the first time.The passivated ITO TFTs with various channel thicknesses(t_(ch)=4,5,6 nm)exhibit excellent electrical performance and superior uniformity.The reliability properties of ITO TFTs were evaluated in detail under positive bias stress(PBS)conditions before and after passivation.Compared to the devices without passivation,the passivated devices have only 50%threshold voltage degradation(ΔV_(th))and 50%newly generated traps due to excellent isolation of the ambient atmosphere.The negligible performance degradation of ITO TFTs with passivation during negative bias stress(NBS)and negative bias temperature stress(NBTS)verifies the outstanding immunity to the water vapor of the SiO_(2)passivation layer.Overall,the ITO TFT with the t_(ch)of 6 nm and with SiO_(2)passivation exhibits the best performance in terms of electrical properties,uniformity,and reliability,which is promising in large-area production.
基金supported by Istanbul Technical University(Project No.45698)supported through the“Young Researchers’Career Development Project-training of doctoral students”of the Croatian Science Foundation.
文摘This paper investigates the reliability of internal marine combustion engines using an integrated approach that combines Fault Tree Analysis(FTA)and Bayesian Networks(BN).FTA provides a structured,top-down method for identifying critical failure modes and their root causes,while BN introduces flexibility in probabilistic reasoning,enabling dynamic updates based on new evidence.This dual methodology overcomes the limitations of static FTA models,offering a comprehensive framework for system reliability analysis.Critical failures,including External Leakage(ELU),Failure to Start(FTS),and Overheating(OHE),were identified as key risks.By incorporating redundancy into high-risk components such as pumps and batteries,the likelihood of these failures was significantly reduced.For instance,redundant pumps reduced the probability of ELU by 31.88%,while additional batteries decreased the occurrence of FTS by 36.45%.The results underscore the practical benefits of combining FTA and BN for enhancing system reliability,particularly in maritime applications where operational safety and efficiency are critical.This research provides valuable insights for maintenance planning and highlights the importance of redundancy in critical systems,especially as the industry transitions toward more autonomous vessels.
