<div style="text-align:justify;"> Currently, coupled mode theory (CMT) is widely used for calculating the coupling coefficient of twin-core fibers (TCFs) that are used in a broad range of important app...<div style="text-align:justify;"> Currently, coupled mode theory (CMT) is widely used for calculating the coupling coefficient of twin-core fibers (TCFs) that are used in a broad range of important applications. This approach is highly accurate for scenarios with weak coupling between the cores but shows significant errors in the strong coupling scenarios, necessitating the use of a more accurate method for coupling coefficient calculations. Therefore, in this work, we calculate the coupling coefficients of TCFs using the supermode theory with finite element method (FEM) that has higher accuracy than CMT, particularly for the strong coupling TCF. To investigate the origin of the differences between the results obtained by these two methods, the modal field distributions of the supermodes of TCF are simulated and analyzed in detail. </div>展开更多
The boundary dement method was improved for the 2D elastic composites with randomly distributed inclusions. This problem can be reduced to a boundary integral equation for a multi-connected domain. Further, considerin...The boundary dement method was improved for the 2D elastic composites with randomly distributed inclusions. This problem can be reduced to a boundary integral equation for a multi-connected domain. Further, considering the matrices of the tractions and displacements for each group of the identical inclusion were the same, an effective computational scheme was designed, since the orders of the resulting matrix equations can be greatly reduced. Numerical examples indicate that this boundary element method scheme is more effective than the conventional multi-domain boundary element method for such a problem. The present scheme can be used to investigate the effective mechanical properties of the fiber-reinforced composites.展开更多
A two-dimensional axisymmetric finite element model based on an improved cohesive element method was developed to simulate interfacial debonding, sliding friction, and residual thermal stresses in SiC composites durin...A two-dimensional axisymmetric finite element model based on an improved cohesive element method was developed to simulate interfacial debonding, sliding friction, and residual thermal stresses in SiC composites during single-fiber push-out tests to extract the interfacial bond strength and frictional stress. The numerical load–displacement curves agree well with experimental curves,indicating that this cohesive element method can be used for calculating the interfacial properties of SiC composites.The simulation results show that cracks are most likely to occur at the ends of the experimental sample, where the maximum shear stress is observed and that the interfacial shear strength and constant sliding friction stress decrease with an increase in temperature. Moreover, the load required to cause complete interfacial failure increases with the increase in critical shear strength, and the composite materials with higher fiber volume fractions have higher bearing capacities. In addition, the initial failure load increases with an increase in interphase thickness.展开更多
To meet the demand for an accurate and highly efficient damage model with a distinct physical meaning for performance-based earthquake engineering applications, a stiffness degradation-based damage model for reinforce...To meet the demand for an accurate and highly efficient damage model with a distinct physical meaning for performance-based earthquake engineering applications, a stiffness degradation-based damage model for reinforced concrete （RC） members and structures was developed using fiber beam-column elements. In this model, damage indices for concrete and steel fibers were defined by the degradation of the initial reloading modulus and the low-cycle fatigue law. Then, section, member, story and structure damage was evaluated by the degradation of the sectional bending stiffness, rod-end bending stiffness, story lateral stiffness and structure lateral stiffness, respectively. The damage model was realized in Matlab by reading in the outputs of OpenSees. The application of the damage model to RC columns and a RC frame indicates that the damage model is capable of accurately predicting the magnitude, position, and evolutionary process of damage, and estimating stow damage more precisely than inter-story drift. Additionally, the damage model establishes a close connection between damage indices at various levels without introducing weighting coefficients or force-displacement relationships. The development of the model has perfected the damage assessment function of OpenSees, laying a solid foundation for damage estimation at various levels of a large-scale structure subjected to seismic loading.展开更多
The main objective of this study was to compare the results obtained with both virtual and experimental research methods, when the biomechanical behavior of teeth restored with esthetic posts was investigated. The fin...The main objective of this study was to compare the results obtained with both virtual and experimental research methods, when the biomechanical behavior of teeth restored with esthetic posts was investigated. The finite element method was used to develop models of healthy maxillary canines and maxillary canines restored with definitive crowns and glass-fiber posts, quartzfiber posts, and titanium posts. Stress distribution was observed when external loads were applied. Load was applied in-vitro to analyse the fracture resistance of 48 maxillary canines restored in the same way as it was considered in the virtual method. The analysis of results using the finite element method led to the conclusion that restored teeth, in which the elastic modulus of the post was similar to that of the dentine and the material of the core had the best biomechanical performance. The experimental study validated the virtual analysis.展开更多
Hollow-core negative curvature fibers(HC-NCFs)have become one of the research hotspots in the field of optical fiber because of their potential applications in the data and energy transmissions.In this work,a new kind...Hollow-core negative curvature fibers(HC-NCFs)have become one of the research hotspots in the field of optical fiber because of their potential applications in the data and energy transmissions.In this work,a new kind of single-polarization single-mode HC-NCF with nested U-type cladding elements is proposed.To achieve the single-polarization single-mode transmission,we use two different silica tubes in thickness,which satisfy the resonance and anti-resonance conditions on the U-type cladding elements and the cladding tubes,respectively.Besides,the elliptical elements are introduced to achieve good single-mode performance.By studying the influences of the structure parameters on the propagation characteristics,the optimized structure parameters are obtained.The simulation results show that when the wavelength is fixed at 1550 nm,the single-polarization single-mode transmission is achieved,with the polarization extinction ratio of 25749 and minimum high-order mode extinction ratio of 174.Furthermore,the confinement loss is only 0.0015 dB/m.展开更多
Shield tunnel,composed of several segments,is widely used in urban underground engineering.When the tunnel is under load,relative displacement occurs between adjacent segments.In the past,distributed optical fiber sen...Shield tunnel,composed of several segments,is widely used in urban underground engineering.When the tunnel is under load,relative displacement occurs between adjacent segments.In the past,distributed optical fiber sensing technology was used to perform strain monitoring,but there is an urgent need to determine how to transform strain into displacement.In this study,optical frequency domain reflectometry was applied in laboratory tests.Aiming at the shear process and center settlement process of shield tunnel segments,two kinds of quantitative calculation methods were put forward to carry out a quantitative analysis.Meanwhile,the laboratory test process was simulated numerically utilizing the discrete element numerical analysis method.Optical fiber,an atypical geotechnical material,was innovatively applied for discrete element modeling and numerical simulation.The results show that the measured displacement of the dial gauge,the calculated results of the numerical model,and the displacement quantitatively calculated from the optical fiber data agree with each other in general.The latter two methods can potentially be utilized in engineering application of deformation monitoring at shield tunnel joints,but need to be further calibrated and adjusted in detail.展开更多
A simple type of photonic crystal fiber （PCF） for supercontinuum generation is proposed for the first time. The proposed PCF is composed of a solid silica core and a cladding with square lattice uniform elliptical a...A simple type of photonic crystal fiber （PCF） for supercontinuum generation is proposed for the first time. The proposed PCF is composed of a solid silica core and a cladding with square lattice uniform elliptical air holes, which offers not only a large nonlinear coefficient but also a high birefringence and low leakage losses. The PCF with nonlinear coefficient as large as 46 W-1 · km-1 at the wavelength of 1.55 um and a total dispersion as low as ±2.5 ps. nm-1 · km -1 over an ultra-broad waveband range of the S-C-L band （wavelength from 1.46 um to 1.625 um） is optimized by adjusting its structure parameter, such as the lattice constant A, the air-filling fraction f, and the air-hole ellipticity η. The novel PCF with ultra-flattened dispersion, highly nonlinear coefficient, and nearly zero negative dispersion slope will offer a possibility of efficient super-continuum generation in telecommunication windows using a few ps pulses.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
In this paper,a Voronoi cell finite element model is developed to study the microscopic and macroscopic mechanical behaviors of heterogenous materials,including arbitrary distributed heterogeneity(inclusions or fibers...In this paper,a Voronoi cell finite element model is developed to study the microscopic and macroscopic mechanical behaviors of heterogenous materials,including arbitrary distributed heterogeneity(inclusions or fibers)coated with interphase layers,based on linear elasticity theory.The interphase between heterogeneity and a matrix are regarded as in the third phase(elastic layers),in contrast to the perfect interface of the spring-like Voronoi cell finite element model(VCFEM)in the literature.In this model,both stress and the displacement field are assumed to be independent in an element.Formulations of stress are derived for each of the three phases in an element,as is the type of functional.Numerical examples were used to study the microscopic and macroscopic properties,such as the effective modulus,of the composites.The results of the proposed VCFEM were compared with analytical solution and numerical results obtained from a standard finite element analysis to confirm its effectiveness.展开更多
The aim of the present paper is to reveal the influence of different fiber orientations on the tool wear evolution and wear mechanism. Side-milling experiments with large-diameter milling tools are conducted. A finite...The aim of the present paper is to reveal the influence of different fiber orientations on the tool wear evolution and wear mechanism. Side-milling experiments with large-diameter milling tools are conducted. A finite element(FE) cutting model of carbon fiber reinforced plastics(CFRP)is established to get insight into the cutting stress status at different wear stages. The results show that different fiber orientations bring about distinct differences in the extent, profile and mechanism of tool wear. Severer wear occurs when cutting 45° and 90° plies, followed by 0°, correspondingly,the least wear is obtained when θ = 135°(θ represents the orientation of fibers). Moreover, the worn profiles of cutting tools when θ = 0° and 45° are waterfall edge, while round edge occurs whenθ = 135° and a combined shape of waterfall and round edge is obtained when θ = 90°. The wear mechanisms under different fiber orientations are strongly dependent on the cutting stress distributions. The evolution of tool wear profile is basically consistent with the stress distribution on the tool surface at different wear stages, and the extent of tool wear is determined by the magnitude of stress on the tool surface. Besides, the worn edges produce an actual negative clearance angle,which decreases the actual cutting thickness and leads to compressing and bending failure of fibers beneath the cutting region as well as low surface qualities.展开更多
A dual-guided photonic crystal fiber(PCF) with low and flattened dispersion is designed, which can support a large number of orbital angular momentum(OAM) modes. The properties of the proposed PCF are systematically a...A dual-guided photonic crystal fiber(PCF) with low and flattened dispersion is designed, which can support a large number of orbital angular momentum(OAM) modes. The properties of the proposed PCF are systematically analyzed through the finite element method. The results show that the proposed PCF can support up to 84 OAM modes with 600 nm bandwidth ranging from 1000 to1600 nm. All values of mode purity are above 91.7%, the isolation parameters are larger than 67 dB and the maximum value up to 145 dB, the lowest confinement loss is only 5×10^(-13) dB·m^(-1).More importantly, the values of dispersion for all modes are less than 40 ps·km-1·nm-1, and the lowest dispersion variation is only 0.7 ps·km^(-1)·nm^(-1). These superior optical properties make the proposed PCF have great advantage in stable transmissions of data and long-distance optical fiber communication system with large capacity.展开更多
Stress-induced birefringence and modal birefringence of single-mode specialty optical fibers with three stress regions are numerically analyzed by the vector finite element method. Stress distribution and stress-induc...Stress-induced birefringence and modal birefringence of single-mode specialty optical fibers with three stress regions are numerically analyzed by the vector finite element method. Stress distribution and stress-induced birefringence distribution of three kinds of optical fibers with different cross structures are presented and compared, and the influence on the stress- induced birefringence by temperature change are analyzed as well. The results show that the fibers with three-stress regions have a lower linear birefringence, which is very important for the fabrication of the circular polaxization-maintalning fiber with high performance drawn from the same fiber preform by using the spinning method.展开更多
This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations.A Weibull distribution model was estab...This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations.A Weibull distribution model was established to describe the fiber strength dispersion based on single-fiber tensile tests for carbon fibers extracted from the composite.The constitutive models for the matrix and interface were established based on the uniaxial tensile and single-fiber push-out tests,respectively.Then,a 3D micromechanical numerical model,innovatively considering the fiber strength dispersion by use of the weakest link and Weibull distribution theories,was estab-lished to simulate the progressive failure behavior of the composite under longitudinal tension.Due to the dispersion of fiber strength,the weakest link of the fiber first fractures,and stress concentra-tion occurs in the surrounding fibers,interfaces,and matrix.The maximum stress concentration fac-tor for neighboring fibers varies nonlinearly with the distance from the fractured fiber.Both isolated and clustered fractured fibers are present during the progressive failure process of the composite.The expansion of fractured fiber clusters intensifies stress concentration and material degradation which in turn enlarges the fractured fiber clusters,and their mutual action leads to the final collapse of the composite.展开更多
In this paper, an adaptive boundary element method （BEM） is presented for solving 3-D elasticity problems. The numerical scheme is accelerated by the new version of fast multipole method （FMM） and parallelized on ...In this paper, an adaptive boundary element method （BEM） is presented for solving 3-D elasticity problems. The numerical scheme is accelerated by the new version of fast multipole method （FMM） and parallelized on distributed memory architectures. The resulting solver is applied to the study of representative volume element （RVE） for short fiberreinforced composites with complex inclusion geometry. Numerical examples performed on a 32-processor cluster show that the proposed method is both accurate and efficient, and can solve problems of large size that are challenging to existing state-of-the-art domain methods.展开更多
The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep...The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep behavior and the material micro geometric parameters. The unit cell models were used to calculate the macroscopic creep behavior with different micro geometric parameters of fibers on different loading directions. The influence of the geometric parameters of the fibers and loading directions on the macroscopic creep behavior had been obtained, and described quantitatively. The matrix/fiber interface had been considered by a third layer, matrix/fiber interlayer, in the unit cells with different creep properties and thickness. Based on the numerical results of the unit cell models, a statistic model had been presented for the plane randomly-distributed-fiber MMCs. The fiber breakage had been taken into account in the statistic model for it starts experimentally early in the creep life. With the distribution of the geometric parameters of the fibers, the results of the statistic model agree well with the experiments. With the statistic model, the influence of the geometric parameters and the breakage of the fibers as well as the properties and thickness of, the interlayer on the macroscopic steady creep rate have been discussed.展开更多
Finite element method is used to simulate the high-speed melt spinning process, based on the equation system proposed by Doufas et al. Calculation predicts a neck-like deformation, as well as the related profiles of v...Finite element method is used to simulate the high-speed melt spinning process, based on the equation system proposed by Doufas et al. Calculation predicts a neck-like deformation, as well as the related profiles of velocity, diameter, temperature, chain orientation, and crystallinity in the fiber spinning process. Considering combined effects on the process such as flow-induced crystallization, viscoelasticity, filament cooling, air drag, inertia, surface tension and gravity, the simulated material flow behaviors are consistent with those observed for semi-crystalline polymers under various spinning conditions, The structure change of polymer coils in the necking region described by the evolution of conformation tensor is also investigated. Based on the relaxation mechanism of macromolecules in flow field different types of morphology change of polymer chains before and in the neck are proposed, giving a complete prospect of structure evolution and crystallization of semi-crystalline polymer in the high speed fiber spinning process.展开更多
文摘<div style="text-align:justify;"> Currently, coupled mode theory (CMT) is widely used for calculating the coupling coefficient of twin-core fibers (TCFs) that are used in a broad range of important applications. This approach is highly accurate for scenarios with weak coupling between the cores but shows significant errors in the strong coupling scenarios, necessitating the use of a more accurate method for coupling coefficient calculations. Therefore, in this work, we calculate the coupling coefficients of TCFs using the supermode theory with finite element method (FEM) that has higher accuracy than CMT, particularly for the strong coupling TCF. To investigate the origin of the differences between the results obtained by these two methods, the modal field distributions of the supermodes of TCF are simulated and analyzed in detail. </div>
文摘The boundary dement method was improved for the 2D elastic composites with randomly distributed inclusions. This problem can be reduced to a boundary integral equation for a multi-connected domain. Further, considering the matrices of the tractions and displacements for each group of the identical inclusion were the same, an effective computational scheme was designed, since the orders of the resulting matrix equations can be greatly reduced. Numerical examples indicate that this boundary element method scheme is more effective than the conventional multi-domain boundary element method for such a problem. The present scheme can be used to investigate the effective mechanical properties of the fiber-reinforced composites.
基金supported by the National Natural Science Foundation of China(No.11405124)Science Challenge Project(No.TZ2018004)+1 种基金Natural Science Basic Research Plan in Shaanxi Province of China(No.2015JQ1030)the Shaanxi Province Postdoctoral Science Foundation(2014)
文摘A two-dimensional axisymmetric finite element model based on an improved cohesive element method was developed to simulate interfacial debonding, sliding friction, and residual thermal stresses in SiC composites during single-fiber push-out tests to extract the interfacial bond strength and frictional stress. The numerical load–displacement curves agree well with experimental curves,indicating that this cohesive element method can be used for calculating the interfacial properties of SiC composites.The simulation results show that cracks are most likely to occur at the ends of the experimental sample, where the maximum shear stress is observed and that the interfacial shear strength and constant sliding friction stress decrease with an increase in temperature. Moreover, the load required to cause complete interfacial failure increases with the increase in critical shear strength, and the composite materials with higher fiber volume fractions have higher bearing capacities. In addition, the initial failure load increases with an increase in interphase thickness.
基金the National Natural Science Foundation of China under Grant Nos.51278218 and 51078166
文摘To meet the demand for an accurate and highly efficient damage model with a distinct physical meaning for performance-based earthquake engineering applications, a stiffness degradation-based damage model for reinforced concrete （RC） members and structures was developed using fiber beam-column elements. In this model, damage indices for concrete and steel fibers were defined by the degradation of the initial reloading modulus and the low-cycle fatigue law. Then, section, member, story and structure damage was evaluated by the degradation of the sectional bending stiffness, rod-end bending stiffness, story lateral stiffness and structure lateral stiffness, respectively. The damage model was realized in Matlab by reading in the outputs of OpenSees. The application of the damage model to RC columns and a RC frame indicates that the damage model is capable of accurately predicting the magnitude, position, and evolutionary process of damage, and estimating stow damage more precisely than inter-story drift. Additionally, the damage model establishes a close connection between damage indices at various levels without introducing weighting coefficients or force-displacement relationships. The development of the model has perfected the damage assessment function of OpenSees, laying a solid foundation for damage estimation at various levels of a large-scale structure subjected to seismic loading.
文摘The main objective of this study was to compare the results obtained with both virtual and experimental research methods, when the biomechanical behavior of teeth restored with esthetic posts was investigated. The finite element method was used to develop models of healthy maxillary canines and maxillary canines restored with definitive crowns and glass-fiber posts, quartzfiber posts, and titanium posts. Stress distribution was observed when external loads were applied. Load was applied in-vitro to analyse the fracture resistance of 48 maxillary canines restored in the same way as it was considered in the virtual method. The analysis of results using the finite element method led to the conclusion that restored teeth, in which the elastic modulus of the post was similar to that of the dentine and the material of the core had the best biomechanical performance. The experimental study validated the virtual analysis.
基金supported by the National Natural Science Foundation of China(Grant No.61935007)。
文摘Hollow-core negative curvature fibers(HC-NCFs)have become one of the research hotspots in the field of optical fiber because of their potential applications in the data and energy transmissions.In this work,a new kind of single-polarization single-mode HC-NCF with nested U-type cladding elements is proposed.To achieve the single-polarization single-mode transmission,we use two different silica tubes in thickness,which satisfy the resonance and anti-resonance conditions on the U-type cladding elements and the cladding tubes,respectively.Besides,the elliptical elements are introduced to achieve good single-mode performance.By studying the influences of the structure parameters on the propagation characteristics,the optimized structure parameters are obtained.The simulation results show that when the wavelength is fixed at 1550 nm,the single-polarization single-mode transmission is achieved,with the polarization extinction ratio of 25749 and minimum high-order mode extinction ratio of 174.Furthermore,the confinement loss is only 0.0015 dB/m.
基金National Natural Science Foundation of China,Grant/Award Numbers:41977218,42222707State Key Laboratory for GeoMechanics and Deep Underground Engineering,Grant/Award Number:SKLGDUEK2117。
文摘Shield tunnel,composed of several segments,is widely used in urban underground engineering.When the tunnel is under load,relative displacement occurs between adjacent segments.In the past,distributed optical fiber sensing technology was used to perform strain monitoring,but there is an urgent need to determine how to transform strain into displacement.In this study,optical frequency domain reflectometry was applied in laboratory tests.Aiming at the shear process and center settlement process of shield tunnel segments,two kinds of quantitative calculation methods were put forward to carry out a quantitative analysis.Meanwhile,the laboratory test process was simulated numerically utilizing the discrete element numerical analysis method.Optical fiber,an atypical geotechnical material,was innovatively applied for discrete element modeling and numerical simulation.The results show that the measured displacement of the dial gauge,the calculated results of the numerical model,and the displacement quantitatively calculated from the optical fiber data agree with each other in general.The latter two methods can potentially be utilized in engineering application of deformation monitoring at shield tunnel joints,but need to be further calibrated and adjusted in detail.
基金Project supported by the China Scholarship Council Western Talent Project, China (Grant No. 20095004)the Key Science and Technology Program of Shaanxi Province, China (Grant No. 2010K01-078)+2 种基金the Natural Science Foundation of the Education Department of Shaanxi Province, China (Grant No. 2010JK403)the Science and Technology Program of Baoji, China (Grant No. 2010BJ02)the Key Program of Scientific Research of Baoji College of Arts and Science,China (Grant No. ZK11016)
文摘A simple type of photonic crystal fiber （PCF） for supercontinuum generation is proposed for the first time. The proposed PCF is composed of a solid silica core and a cladding with square lattice uniform elliptical air holes, which offers not only a large nonlinear coefficient but also a high birefringence and low leakage losses. The PCF with nonlinear coefficient as large as 46 W-1 · km-1 at the wavelength of 1.55 um and a total dispersion as low as ±2.5 ps. nm-1 · km -1 over an ultra-broad waveband range of the S-C-L band （wavelength from 1.46 um to 1.625 um） is optimized by adjusting its structure parameter, such as the lattice constant A, the air-filling fraction f, and the air-hole ellipticity η. The novel PCF with ultra-flattened dispersion, highly nonlinear coefficient, and nearly zero negative dispersion slope will offer a possibility of efficient super-continuum generation in telecommunication windows using a few ps pulses.
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 National Natural Science Foundation of China(Grants 11402103 and 11572142).
文摘In this paper,a Voronoi cell finite element model is developed to study the microscopic and macroscopic mechanical behaviors of heterogenous materials,including arbitrary distributed heterogeneity(inclusions or fibers)coated with interphase layers,based on linear elasticity theory.The interphase between heterogeneity and a matrix are regarded as in the third phase(elastic layers),in contrast to the perfect interface of the spring-like Voronoi cell finite element model(VCFEM)in the literature.In this model,both stress and the displacement field are assumed to be independent in an element.Formulations of stress are derived for each of the three phases in an element,as is the type of functional.Numerical examples were used to study the microscopic and macroscopic properties,such as the effective modulus,of the composites.The results of the proposed VCFEM were compared with analytical solution and numerical results obtained from a standard finite element analysis to confirm its effectiveness.
基金supported by the National Natural Science Foundation of China(No.52075380)the Natural Science Foundation of Tianjin(Nos.21JCYBJC00610 and 19JCYBJC19000).
文摘The aim of the present paper is to reveal the influence of different fiber orientations on the tool wear evolution and wear mechanism. Side-milling experiments with large-diameter milling tools are conducted. A finite element(FE) cutting model of carbon fiber reinforced plastics(CFRP)is established to get insight into the cutting stress status at different wear stages. The results show that different fiber orientations bring about distinct differences in the extent, profile and mechanism of tool wear. Severer wear occurs when cutting 45° and 90° plies, followed by 0°, correspondingly,the least wear is obtained when θ = 135°(θ represents the orientation of fibers). Moreover, the worn profiles of cutting tools when θ = 0° and 45° are waterfall edge, while round edge occurs whenθ = 135° and a combined shape of waterfall and round edge is obtained when θ = 90°. The wear mechanisms under different fiber orientations are strongly dependent on the cutting stress distributions. The evolution of tool wear profile is basically consistent with the stress distribution on the tool surface at different wear stages, and the extent of tool wear is determined by the magnitude of stress on the tool surface. Besides, the worn edges produce an actual negative clearance angle,which decreases the actual cutting thickness and leads to compressing and bending failure of fibers beneath the cutting region as well as low surface qualities.
基金the Fundamental Research Funds for the Central Universities(2020YJ005,2021MS072,2019MS085)the Natural Science Foundation of Hebei Province(E2019502177,E2020502010)the National Natural Science Foundation of China(51607066,61775057)。
文摘A dual-guided photonic crystal fiber(PCF) with low and flattened dispersion is designed, which can support a large number of orbital angular momentum(OAM) modes. The properties of the proposed PCF are systematically analyzed through the finite element method. The results show that the proposed PCF can support up to 84 OAM modes with 600 nm bandwidth ranging from 1000 to1600 nm. All values of mode purity are above 91.7%, the isolation parameters are larger than 67 dB and the maximum value up to 145 dB, the lowest confinement loss is only 5×10^(-13) dB·m^(-1).More importantly, the values of dispersion for all modes are less than 40 ps·km-1·nm-1, and the lowest dispersion variation is only 0.7 ps·km^(-1)·nm^(-1). These superior optical properties make the proposed PCF have great advantage in stable transmissions of data and long-distance optical fiber communication system with large capacity.
基金Project supported by the Shanghai Leading Academic Discipline Project (Grant No.S30108)the Science and Technology Commission of Shanghai Municipality (Grant No.08DZ2231100)
文摘Stress-induced birefringence and modal birefringence of single-mode specialty optical fibers with three stress regions are numerically analyzed by the vector finite element method. Stress distribution and stress-induced birefringence distribution of three kinds of optical fibers with different cross structures are presented and compared, and the influence on the stress- induced birefringence by temperature change are analyzed as well. The results show that the fibers with three-stress regions have a lower linear birefringence, which is very important for the fabrication of the circular polaxization-maintalning fiber with high performance drawn from the same fiber preform by using the spinning method.
基金the National Natural Science Foundation of China(No.52165018)the Jiangxi Key Laboratory of Forming and Joining Technology for Aerospace Component,China(No.EL202303270)the Jiangxi Provincial Department of Science and Technology,China(No.20225BCJ22002)
文摘This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations.A Weibull distribution model was established to describe the fiber strength dispersion based on single-fiber tensile tests for carbon fibers extracted from the composite.The constitutive models for the matrix and interface were established based on the uniaxial tensile and single-fiber push-out tests,respectively.Then,a 3D micromechanical numerical model,innovatively considering the fiber strength dispersion by use of the weakest link and Weibull distribution theories,was estab-lished to simulate the progressive failure behavior of the composite under longitudinal tension.Due to the dispersion of fiber strength,the weakest link of the fiber first fractures,and stress concentra-tion occurs in the surrounding fibers,interfaces,and matrix.The maximum stress concentration fac-tor for neighboring fibers varies nonlinearly with the distance from the fractured fiber.Both isolated and clustered fractured fibers are present during the progressive failure process of the composite.The expansion of fractured fiber clusters intensifies stress concentration and material degradation which in turn enlarges the fractured fiber clusters,and their mutual action leads to the final collapse of the composite.
基金The project supported by the National Natural Science Foundation of China (10472051)
文摘In this paper, an adaptive boundary element method （BEM） is presented for solving 3-D elasticity problems. The numerical scheme is accelerated by the new version of fast multipole method （FMM） and parallelized on distributed memory architectures. The resulting solver is applied to the study of representative volume element （RVE） for short fiberreinforced composites with complex inclusion geometry. Numerical examples performed on a 32-processor cluster show that the proposed method is both accurate and efficient, and can solve problems of large size that are challenging to existing state-of-the-art domain methods.
文摘The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep behavior and the material micro geometric parameters. The unit cell models were used to calculate the macroscopic creep behavior with different micro geometric parameters of fibers on different loading directions. The influence of the geometric parameters of the fibers and loading directions on the macroscopic creep behavior had been obtained, and described quantitatively. The matrix/fiber interface had been considered by a third layer, matrix/fiber interlayer, in the unit cells with different creep properties and thickness. Based on the numerical results of the unit cell models, a statistic model had been presented for the plane randomly-distributed-fiber MMCs. The fiber breakage had been taken into account in the statistic model for it starts experimentally early in the creep life. With the distribution of the geometric parameters of the fibers, the results of the statistic model agree well with the experiments. With the statistic model, the influence of the geometric parameters and the breakage of the fibers as well as the properties and thickness of, the interlayer on the macroscopic steady creep rate have been discussed.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.20204007,50390090,20490220,10590355)the Doctoral Foundation of National Education Committee of China(No.20030248008)the 863 Project of China(No.2002AA336120).
文摘Finite element method is used to simulate the high-speed melt spinning process, based on the equation system proposed by Doufas et al. Calculation predicts a neck-like deformation, as well as the related profiles of velocity, diameter, temperature, chain orientation, and crystallinity in the fiber spinning process. Considering combined effects on the process such as flow-induced crystallization, viscoelasticity, filament cooling, air drag, inertia, surface tension and gravity, the simulated material flow behaviors are consistent with those observed for semi-crystalline polymers under various spinning conditions, The structure change of polymer coils in the necking region described by the evolution of conformation tensor is also investigated. Based on the relaxation mechanism of macromolecules in flow field different types of morphology change of polymer chains before and in the neck are proposed, giving a complete prospect of structure evolution and crystallization of semi-crystalline polymer in the high speed fiber spinning process.
