In the discipline of geotechnical engineering, fiber optic sensor based distributed monitoring has played an increasingly important role over the past few decades. Compared with conventional sensors, fiber optic senso...In the discipline of geotechnical engineering, fiber optic sensor based distributed monitoring has played an increasingly important role over the past few decades. Compared with conventional sensors, fiber optic sensors have a variety of exclusive advantages, such as smaller size, higher precision, and better corrosion resistance. These innovative monitoring technologies have been successfully applied for performance monitoring of geo-structures and early warning of potential geo- hazards around the world. In order to investigate their ability to monitor slope stability problems, a medium-sized model of soil nailed slope has been constructed in laboratory. The fully distributed Brillouin optical time-domain analysis (BOTDA) sensing technology was employed to measure the horizontal strain distributions inside the model slope. During model construction, a specially designed strain sensing fiber was buried in the soil mass. Afterward, the surcharge loading was applied on the slope crest in stages using hydraulic jacks and a reaction frame. During testing, an NBX-6o5o BOTDA sensing interrogator was used to collect the fiber optic sensing data. The test results have been analyzed in detail, which shows that the fiber optic sensors can capture the progressive deformation and failure pattern of the model slope. The limit equilibrium analyses were also conducted to obtain the factors ofsafety of the slope under different surface loadings. It is found that the characteristic maximum strains can reflect the stability of the model slope and an empirical relationship was obtained, This study verified the effectiveness of the distributed BOTDA sensing technology in performance monitoring of slope.展开更多
Machining damage occurs on the surface of carbon fiber reinforced polymer (CFRP) composites during processing. In the current simulation model of CFRP, the initial defects on the carbon fiber and the periodic random d...Machining damage occurs on the surface of carbon fiber reinforced polymer (CFRP) composites during processing. In the current simulation model of CFRP, the initial defects on the carbon fiber and the periodic random distribution of the reinforcement phase in the matrix are not considered in detail, which makes the characteristics of the cutting model significantly different from the actual processing conditions. In this paper, a novel three-phase model of carbon fiber/cyanate ester composites is proposed to simulate the machining damage of the composites. The periodic random distribution of the carbon fiber reinforced phase in the matrix was realized using a double perturbation algorithm. To achieve the stochastic distribution of the strength of a single carbon fiber, a novel method that combines the Weibull intensity distribution theory with the Monte Carlo method is presented. The mechanical properties of the cyanate matrix were characterized by fitting the stress-strain curves, and the cohesive zone model was employed to simulate the interface. Based on the model, the machining damage mechanism of the composites was revealed using finite element simulations and by conducting a theoretical analysis. Furthermore, the milling surfaces of the composites were observed using a scanning electron microscope, to verify the accuracy of the simulation results. In this study, the simulations and theoretical analysis of the carbon fiber/cyanate ester composite processing were carried out based on a novel three-phase model, which revealed the material failure and machining damage mechanism more accurately.展开更多
It is widely recognized that nonlinear time-history analysis constitutes the most accurate way to simulate the response of structures subjected to strong levels of seismic excitation. This analytical method is based o...It is widely recognized that nonlinear time-history analysis constitutes the most accurate way to simulate the response of structures subjected to strong levels of seismic excitation. This analytical method is based on sound underlying principles and has the capability to reproduce the intrinsic inelastic dynamic behavior of structures. Nonetheless, comparisons with experimental results from large-scale testing of structures are still needed, in order to ensure adequate levels of confidence in this numerical methodology. The fiber modelling approach employed in the current endeavor inherently accounts for geometric nonlinearities and material inelasticity, without a need for calibration of plastic hinges mechanisms, typical in concentrated plasticity models. The resulting combination of analysis accuracy and modelling simplicity, allows thus to overcome the perhaps not fully justifiable sense of complexity associated to nonlinear dynamic analysis. The fiber-based modelling approach is employed in the framework of a finite element program downloaded from the Intemet for seismic response analysis of framed structures. The reliability and accuracy of the program are demonstrated by numerically reproducing pseudo-dynamic tests on a four span continuous deck concrete bridge. Modelling assumptions are discussed, together with their implications on numerical results of the nonlinear time-history analyses, which were found to be in good agreement with experimental results.展开更多
To get fiber motion in condensing zone of compact spinning,velocity of this area is achieved by simulation,and then a bead-elastic rod fiber model is established.Based on simulation and dynamic analysis on this zone,g...To get fiber motion in condensing zone of compact spinning,velocity of this area is achieved by simulation,and then a bead-elastic rod fiber model is established.Based on simulation and dynamic analysis on this zone,governing equations are constructed and Runge-Kutta approach is used.Lastly,trajectories of fibers are calculated by specially designed Matlab procedure according to the principles mentioned above.Results show that fiber motions at different initial positions are different;X-axis velocity component makes fibers gathering on sides of suction slot;Y-axis airflow gets fibers gradually close and then stick to the surface of lattice apron.Fiber motions also reflect that the compact spinning process in condensing zone can be divided into three parts:fast convergence zone,adjustment convergence zone,and steady convergence zone.展开更多
Accurate acid placement constitutes a major concern in matrix stimulation because the acid tends to penetrate the zones of least resistance while leaving the low-permeability regions of the formation untreated.Degrada...Accurate acid placement constitutes a major concern in matrix stimulation because the acid tends to penetrate the zones of least resistance while leaving the low-permeability regions of the formation untreated.Degradable materials(fibers and solid particles)have recently shown a good capability as fluid diversion to overcome the issues related to matrix stimulation.Despite the success achieved in the recent acid stimulation jobs stemming from the use of some products that rely on fiber flocculation as the main diverting mechanism,it was observed that the volume of the base fluid and the loading of the particles are not optimized.The current industry lacks a scientific design guideline because the used methodology is based on experience or empirical studies in a particular area with a particular product.It is important then to understand the fundamentals of how acid diversion works in carbonates with different diverting mechanisms and diverters.Mathematical modeling and computer simulations are effective tools to develop this understanding and are efficiently applied to new product development,new applications of existing products or usage optimization.In this work,we develop a numerical model to study fiber dynamics in fluid flow.We employ a discrete element method in which the fibers are represented by multi-rigid-body systems of interconnected spheres.The discrete fiber model is coupled with a fluid flow solver to account for the inherent simultaneous interactions.The focus of the study is on the tendency for fibers to flocculate and bridge when interacting with suspending fluids and encountering restrictions that can be representative of fractures or wormholes in carbonates.The trends of the dynamic fiber behavior under various operating conditions including fiber loading,flow rate and fluid viscosity obtained from the numerical model show consistency with experimental observations.The present numerical investigation reveals that the bridging capability of the fiber–fluid system can be enhanced by increasing the fiber loading,selecting fibers with higher stiffness,reducing the injection flow rate,reducing the suspending fluid viscosity or increasing the attractive cohesive forces among fibers by using sticky fibers.展开更多
Probability of detection(POD)graphics allow for a change from qualitative to quantitative assessment for every damage detection system,and as such it is a main request for conventional non-destructive testing(NDT)tech...Probability of detection(POD)graphics allow for a change from qualitative to quantitative assessment for every damage detection system,and as such it is a main request for conventional non-destructive testing(NDT)techniques.Its availability can greatly help towards the industrialization of the corresponding Structural health monitoring(SHM)system.But having in mind that for SHM systems the sensors are at fixed positions,and the location of a potential damage would change its detectability.Consequently robust simulation tools are required to obtain the model assisted probability of detection(MAPOD)which is needed to validate the SHM system.This tool may also help for the optimization of the sensor distribution,and finally will allow a probabilistic risk management.INDEUS,simulation of ultrasonic waves SHM system,was a main milestone in this direction.This article deals with the simulation tools for a strain based SHM system,using fiber optic sensors(FOS).FOS are essentially strain/temperature sensors,either with multi-point or with distributed sensing.The simulation tool includes the finite element model(FEM)for the original and damaged structure,and algorithms to compare the strain data at the pre-established sensors locations,and from this comparison to extract information about damage occurrence and location.The study has been applied to the structure of an all-composite unmanned aircraft vehicle(UAV)now under construction,designed at Universidad Politecnica de Madrid for the inspection of electrical utilities networks.Distributed sensing optical fibers were internally bonded at the fuselage and wing.Routine inspection is planned to be done with the aircraft at the test bench by imposing known loads.From the acquired strain data,damage occurrence may be calculated as slight deviations from the baselines.This is a fast inspection procedure without requiring trained specialists,and it would allow for detection of hidden damages.Simulation indicates that stringer partial debondings are detected before they become critical,while small delaminations as those produced by barely visible impact damages would require a prohibited number of sensing lines.These simulation tools may easily be applied to any other complex structure,just by changing the FEM models.From these results it is shown how a fiber optic based SHM system may be used as a reliable damage detection procedure.展开更多
By taking into account the effect of the bi-modulus for tension and compression of the fiber reinforced polymer (FRP) sheet in the reinforcement layer, a general mathematical model for the nonlinear bending of a sle...By taking into account the effect of the bi-modulus for tension and compression of the fiber reinforced polymer (FRP) sheet in the reinforcement layer, a general mathematical model for the nonlinear bending of a slender timber beam strengthened with the FRP sheet is established under the hypothesis of the large deflection deformation of the beam. Nonlinear governing equations of the second order effect of the beam bending are derived. The nonlinear stability of a simply-supported slender timber column strengthened with the FRP sheet is then investigated. An expression of the critical load of the simply-supported FRP-strengthened timber beam is obtained. The existence of postbuckling solution of the timber column is proved theoretically, and an asymptotic analytical solution of the postbuckling state in the vicinity of the critical load is obtained using the perturbation method. Parameters are studied showing that the FRP reinforcement layer has great influence on the critical load of the timber column, and has little influence on the dimensionless postbuckling state.展开更多
A theoretical model concerning active Q-switching of an Fe:ZnSe laser pumped by a continuous-wave(CW)2.8μm fiber laser is developed.Calculations are compared with the recently reported experiment results,and good agr...A theoretical model concerning active Q-switching of an Fe:ZnSe laser pumped by a continuous-wave(CW)2.8μm fiber laser is developed.Calculations are compared with the recently reported experiment results,and good agreement is achieved.Effects of principal parameters,including pump power,output reflectivity,ion concentration and temperature of crystal,on the laser output performance are investigated and analyzed.Numerical results demonstrate that similar to highly efficient CWFe:ZnSe laser,low temperature of the crystal is significant to obtain high peak power Q-switched pulses.The numerical simulation results are useful for optimizing the design of actively Q-switched Fe:ZnSe laser.展开更多
Carbon fiber is a kind of new polymer material with excellent mechanical properties and being applied widely.The process of carbon fiber prepared by bamboo tar,including extraction,condensation,spinning,oxidation and ...Carbon fiber is a kind of new polymer material with excellent mechanical properties and being applied widely.The process of carbon fiber prepared by bamboo tar,including extraction,condensation,spinning,oxidation and carbonation,is influenced by the pyrolysis kinetics significantly.In this paper,the thermogravimetric analysis(TGA)of bamboo tar produced in the process of pyrolysis and gasification of the bamboo which is known as Phylostachys sulphurea,was analyzed by the distributed activation energy model(DAEM)to understand the kinetic properties and parameters of bamboo tar.The thermogravimetric analysis of bamboo tar which is used as the raw material of carbon fiber was conducted under 5 different heating rates(i.e.5,10,15,30 and 50℃/min,etc.)in nitrogen atmosphere.The results show that the activation energy of bamboo tar and the exponential factor increased significantly with the increase of the heating rate,and the low heating rate is advantageous to the extraction of bamboo tar solvent and the thermal polycondensation,which can provide scientific reference for the optimization of carbon fiber technology.The thermal weight results show that the temperature range of bamboo tar being decomposed rapidly is 213℃-410℃.The ranges of the activation energy were calculated by DAEM,which have small difference in comparisons with five heating rates when the conversion rate is at 0.1-0.6 and the average value of the activation energy is 119 kJ/mol.The stability range of the activation energy is enlarged when the conversion rate is greater than 0.6 and heating rate increases.展开更多
基金the financial support provided by the National Basic Research Program of China (973 Program) (Grant No. 2011CB710605)the National Natural Science Foundation of China (Grant Nos. 41102174, 41302217)supported by the National Key Technology R&D Program of China (Grant No. 2012BAK10B05)
文摘In the discipline of geotechnical engineering, fiber optic sensor based distributed monitoring has played an increasingly important role over the past few decades. Compared with conventional sensors, fiber optic sensors have a variety of exclusive advantages, such as smaller size, higher precision, and better corrosion resistance. These innovative monitoring technologies have been successfully applied for performance monitoring of geo-structures and early warning of potential geo- hazards around the world. In order to investigate their ability to monitor slope stability problems, a medium-sized model of soil nailed slope has been constructed in laboratory. The fully distributed Brillouin optical time-domain analysis (BOTDA) sensing technology was employed to measure the horizontal strain distributions inside the model slope. During model construction, a specially designed strain sensing fiber was buried in the soil mass. Afterward, the surcharge loading was applied on the slope crest in stages using hydraulic jacks and a reaction frame. During testing, an NBX-6o5o BOTDA sensing interrogator was used to collect the fiber optic sensing data. The test results have been analyzed in detail, which shows that the fiber optic sensors can capture the progressive deformation and failure pattern of the model slope. The limit equilibrium analyses were also conducted to obtain the factors ofsafety of the slope under different surface loadings. It is found that the characteristic maximum strains can reflect the stability of the model slope and an empirical relationship was obtained, This study verified the effectiveness of the distributed BOTDA sensing technology in performance monitoring of slope.
基金Supported by Research Innovation Fund Project “Research on micro machining mechanism of fiber reinforced composites”(Grant No.HIT.NSRIF.2014055)of Harbin Institute of Technology,China
文摘Machining damage occurs on the surface of carbon fiber reinforced polymer (CFRP) composites during processing. In the current simulation model of CFRP, the initial defects on the carbon fiber and the periodic random distribution of the reinforcement phase in the matrix are not considered in detail, which makes the characteristics of the cutting model significantly different from the actual processing conditions. In this paper, a novel three-phase model of carbon fiber/cyanate ester composites is proposed to simulate the machining damage of the composites. The periodic random distribution of the carbon fiber reinforced phase in the matrix was realized using a double perturbation algorithm. To achieve the stochastic distribution of the strength of a single carbon fiber, a novel method that combines the Weibull intensity distribution theory with the Monte Carlo method is presented. The mechanical properties of the cyanate matrix were characterized by fitting the stress-strain curves, and the cohesive zone model was employed to simulate the interface. Based on the model, the machining damage mechanism of the composites was revealed using finite element simulations and by conducting a theoretical analysis. Furthermore, the milling surfaces of the composites were observed using a scanning electron microscope, to verify the accuracy of the simulation results. In this study, the simulations and theoretical analysis of the carbon fiber/cyanate ester composite processing were carried out based on a novel three-phase model, which revealed the material failure and machining damage mechanism more accurately.
文摘It is widely recognized that nonlinear time-history analysis constitutes the most accurate way to simulate the response of structures subjected to strong levels of seismic excitation. This analytical method is based on sound underlying principles and has the capability to reproduce the intrinsic inelastic dynamic behavior of structures. Nonetheless, comparisons with experimental results from large-scale testing of structures are still needed, in order to ensure adequate levels of confidence in this numerical methodology. The fiber modelling approach employed in the current endeavor inherently accounts for geometric nonlinearities and material inelasticity, without a need for calibration of plastic hinges mechanisms, typical in concentrated plasticity models. The resulting combination of analysis accuracy and modelling simplicity, allows thus to overcome the perhaps not fully justifiable sense of complexity associated to nonlinear dynamic analysis. The fiber-based modelling approach is employed in the framework of a finite element program downloaded from the Intemet for seismic response analysis of framed structures. The reliability and accuracy of the program are demonstrated by numerically reproducing pseudo-dynamic tests on a four span continuous deck concrete bridge. Modelling assumptions are discussed, together with their implications on numerical results of the nonlinear time-history analyses, which were found to be in good agreement with experimental results.
文摘To get fiber motion in condensing zone of compact spinning,velocity of this area is achieved by simulation,and then a bead-elastic rod fiber model is established.Based on simulation and dynamic analysis on this zone,governing equations are constructed and Runge-Kutta approach is used.Lastly,trajectories of fibers are calculated by specially designed Matlab procedure according to the principles mentioned above.Results show that fiber motions at different initial positions are different;X-axis velocity component makes fibers gathering on sides of suction slot;Y-axis airflow gets fibers gradually close and then stick to the surface of lattice apron.Fiber motions also reflect that the compact spinning process in condensing zone can be divided into three parts:fast convergence zone,adjustment convergence zone,and steady convergence zone.
文摘Accurate acid placement constitutes a major concern in matrix stimulation because the acid tends to penetrate the zones of least resistance while leaving the low-permeability regions of the formation untreated.Degradable materials(fibers and solid particles)have recently shown a good capability as fluid diversion to overcome the issues related to matrix stimulation.Despite the success achieved in the recent acid stimulation jobs stemming from the use of some products that rely on fiber flocculation as the main diverting mechanism,it was observed that the volume of the base fluid and the loading of the particles are not optimized.The current industry lacks a scientific design guideline because the used methodology is based on experience or empirical studies in a particular area with a particular product.It is important then to understand the fundamentals of how acid diversion works in carbonates with different diverting mechanisms and diverters.Mathematical modeling and computer simulations are effective tools to develop this understanding and are efficiently applied to new product development,new applications of existing products or usage optimization.In this work,we develop a numerical model to study fiber dynamics in fluid flow.We employ a discrete element method in which the fibers are represented by multi-rigid-body systems of interconnected spheres.The discrete fiber model is coupled with a fluid flow solver to account for the inherent simultaneous interactions.The focus of the study is on the tendency for fibers to flocculate and bridge when interacting with suspending fluids and encountering restrictions that can be representative of fractures or wormholes in carbonates.The trends of the dynamic fiber behavior under various operating conditions including fiber loading,flow rate and fluid viscosity obtained from the numerical model show consistency with experimental observations.The present numerical investigation reveals that the bridging capability of the fiber–fluid system can be enhanced by increasing the fiber loading,selecting fibers with higher stiffness,reducing the injection flow rate,reducing the suspending fluid viscosity or increasing the attractive cohesive forces among fibers by using sticky fibers.
基金supported by the project TRA2014-58263-C2-2-Rfunded by the National Research program of Spain
文摘Probability of detection(POD)graphics allow for a change from qualitative to quantitative assessment for every damage detection system,and as such it is a main request for conventional non-destructive testing(NDT)techniques.Its availability can greatly help towards the industrialization of the corresponding Structural health monitoring(SHM)system.But having in mind that for SHM systems the sensors are at fixed positions,and the location of a potential damage would change its detectability.Consequently robust simulation tools are required to obtain the model assisted probability of detection(MAPOD)which is needed to validate the SHM system.This tool may also help for the optimization of the sensor distribution,and finally will allow a probabilistic risk management.INDEUS,simulation of ultrasonic waves SHM system,was a main milestone in this direction.This article deals with the simulation tools for a strain based SHM system,using fiber optic sensors(FOS).FOS are essentially strain/temperature sensors,either with multi-point or with distributed sensing.The simulation tool includes the finite element model(FEM)for the original and damaged structure,and algorithms to compare the strain data at the pre-established sensors locations,and from this comparison to extract information about damage occurrence and location.The study has been applied to the structure of an all-composite unmanned aircraft vehicle(UAV)now under construction,designed at Universidad Politecnica de Madrid for the inspection of electrical utilities networks.Distributed sensing optical fibers were internally bonded at the fuselage and wing.Routine inspection is planned to be done with the aircraft at the test bench by imposing known loads.From the acquired strain data,damage occurrence may be calculated as slight deviations from the baselines.This is a fast inspection procedure without requiring trained specialists,and it would allow for detection of hidden damages.Simulation indicates that stringer partial debondings are detected before they become critical,while small delaminations as those produced by barely visible impact damages would require a prohibited number of sensing lines.These simulation tools may easily be applied to any other complex structure,just by changing the FEM models.From these results it is shown how a fiber optic based SHM system may be used as a reliable damage detection procedure.
基金Project supported by the National High Technology Research and Development Program(No. 2009AA032303-2)
文摘By taking into account the effect of the bi-modulus for tension and compression of the fiber reinforced polymer (FRP) sheet in the reinforcement layer, a general mathematical model for the nonlinear bending of a slender timber beam strengthened with the FRP sheet is established under the hypothesis of the large deflection deformation of the beam. Nonlinear governing equations of the second order effect of the beam bending are derived. The nonlinear stability of a simply-supported slender timber column strengthened with the FRP sheet is then investigated. An expression of the critical load of the simply-supported FRP-strengthened timber beam is obtained. The existence of postbuckling solution of the timber column is proved theoretically, and an asymptotic analytical solution of the postbuckling state in the vicinity of the critical load is obtained using the perturbation method. Parameters are studied showing that the FRP reinforcement layer has great influence on the critical load of the timber column, and has little influence on the dimensionless postbuckling state.
基金the 2021 Annual Instructional Science and Technology Program of Yongzhou(No.2021YZKJ09)the Science Research Project of Hunan Institute of Science and Technology(No.21xky040)。
文摘A theoretical model concerning active Q-switching of an Fe:ZnSe laser pumped by a continuous-wave(CW)2.8μm fiber laser is developed.Calculations are compared with the recently reported experiment results,and good agreement is achieved.Effects of principal parameters,including pump power,output reflectivity,ion concentration and temperature of crystal,on the laser output performance are investigated and analyzed.Numerical results demonstrate that similar to highly efficient CWFe:ZnSe laser,low temperature of the crystal is significant to obtain high peak power Q-switched pulses.The numerical simulation results are useful for optimizing the design of actively Q-switched Fe:ZnSe laser.
基金This work was financially supported by the National Natural Science Foundation of China(551376056)“Study of regulation mechanisms and photo-thermal properties of photosynthetic hydrogen production under the condition of multiphase biomass flow”.
文摘Carbon fiber is a kind of new polymer material with excellent mechanical properties and being applied widely.The process of carbon fiber prepared by bamboo tar,including extraction,condensation,spinning,oxidation and carbonation,is influenced by the pyrolysis kinetics significantly.In this paper,the thermogravimetric analysis(TGA)of bamboo tar produced in the process of pyrolysis and gasification of the bamboo which is known as Phylostachys sulphurea,was analyzed by the distributed activation energy model(DAEM)to understand the kinetic properties and parameters of bamboo tar.The thermogravimetric analysis of bamboo tar which is used as the raw material of carbon fiber was conducted under 5 different heating rates(i.e.5,10,15,30 and 50℃/min,etc.)in nitrogen atmosphere.The results show that the activation energy of bamboo tar and the exponential factor increased significantly with the increase of the heating rate,and the low heating rate is advantageous to the extraction of bamboo tar solvent and the thermal polycondensation,which can provide scientific reference for the optimization of carbon fiber technology.The thermal weight results show that the temperature range of bamboo tar being decomposed rapidly is 213℃-410℃.The ranges of the activation energy were calculated by DAEM,which have small difference in comparisons with five heating rates when the conversion rate is at 0.1-0.6 and the average value of the activation energy is 119 kJ/mol.The stability range of the activation energy is enlarged when the conversion rate is greater than 0.6 and heating rate increases.