In this work,a method is put forward to obtain the dynamic solution efficiently and accurately for a large-scale train-track-substructure(TTS)system.It is called implicit-explicit integration and multi-time-step solut...In this work,a method is put forward to obtain the dynamic solution efficiently and accurately for a large-scale train-track-substructure(TTS)system.It is called implicit-explicit integration and multi-time-step solution method(abbreviated as mI-nE-MTS method).The TTS system is divided into train-track subsystem and substruc-ture subsystem.Considering that the root cause of low effi-ciency of obtaining TTS solution lies in solving the alge-braic equation of the substructures,the high-efficient Zhai method,an explicit integration scheme,can be introduced to avoid matrix inversion process.The train-track system is solved by implicitly Park method.Moreover,it is known that the requirement of time step size differs for different sub-systems,integration methods and structural frequency response characteristics.A multi-time-step solution is pro-posed,in which time step size for the train-track subsystem and the substructure subsystem can be arbitrarily chosen once satisfying stability and precision demand,namely the time spent for m implicit integral steps is equal to n explicit integral steps,i.e.,mI=nE as mentioned above.The numeri-cal examples show the accuracy,efficiency,and engineering practicality of the proposed method.展开更多
The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident...The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident wave into equivalent loads on the cutoff boundaries. The wave method has high precision, but the implementation is complicated, especially for three-dimensional models. By deducing another form of equivalent input seismic loads in the fi nite element model, a new seismic wave input method is proposed. In the new method, by imposing the displacements of the free wave fi eld on the nodes of the substructure composed of elements that contain artifi cial boundaries, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Subsequently, the equivalent input seismic loads are imposed on the artifi cial boundary nodes to complete the seismic wave input and perform seismic analysis of the soil-structure dynamic interaction model. Compared with the wave method, the new method is simplifi ed by avoiding the complex processes of calculating the equivalent input seismic loads. The validity of the new method is verifi ed by the dynamic analysis numerical examples of the homogeneous and layered half space under vertical and oblique incident seismic waves.展开更多
In the strengthened layer of stainless steel after shot peening,there are a great amount ofdeformation microtwins which may act as structural strengthening factor and prevent thegradual relaxation of surface residual ...In the strengthened layer of stainless steel after shot peening,there are a great amount ofdeformation microtwins which may act as structural strengthening factor and prevent thegradual relaxation of surface residual stress during fatigue,so as to keep its rather high levelof bending fatigue strength.However,in the strengthened surface layer of low carbon steel,dislocation cell structure is so unstalbe during fatigue that its surface residual stress relaxationcannot be retarded.Therefore,the bending fatigue strength of the low carbon steel can not beimprored by shot peening.展开更多
Combining the advantages of numerical simulation with experimental testing,real-time dynamic substructure(RTDS)testing provides a new experimental method for the investigation of engineered structures.However,not all ...Combining the advantages of numerical simulation with experimental testing,real-time dynamic substructure(RTDS)testing provides a new experimental method for the investigation of engineered structures.However,not all unmodeled parts can be physically tested,as testing is often limited by the capacity of the test facility.Model updating is a good option to improve the modeling accuracy for numerical substructures in RTDS.In this study,a model updating method is introduced,which has great performance in describing this nonlinearity.In order to determine the optimal parameters in this model,an Unscented Kalman Filter(UKF)-based algorithm was applied to extract the knowledge contained in the sensors data.All the parameters that need to be identified are listed as the extended state variables,and the identification was achieved via the step-by-step state prediction and state update process.Effectiveness of the proposed method was verified through a group of experimental data,and results showed good agreement.Furthermore,the proposed method was compared with the Extended Kalman Filter(EKF)-based method,and better accuracy was easily found.The proposed parameter identification method has great applicability for structural objects with nonlinear behaviors and could be extended to research in other engineering fields.展开更多
In this paper,a new method for dealing with substructure chain is presented.Here,asubstructure chain means a structure consisting of a number of identical substructures connected in series.Thismethod is parallel to th...In this paper,a new method for dealing with substructure chain is presented.Here,asubstructure chain means a structure consisting of a number of identical substructures connected in series.Thismethod is parallel to the expansion method in the structural analysis according to the transverse section.Themethod of shift invariance and that of initial parameter and transfer matrix,their mutual-relation and com-bined use,as well as the analysis of the eigenproblem on the transverse section,and the expansion methodbased on the eigenvectors are described in this paper.展开更多
The deformation behavior of dispersion strengthened copper alloy Cu-Al2O3 was studied by TEM. The results show that nano-scaled dispersed second phase not only increases dislocation density in matrix, but also has an ...The deformation behavior of dispersion strengthened copper alloy Cu-Al2O3 was studied by TEM. The results show that nano-scaled dispersed second phase not only increases dislocation density in matrix, but also has an important influence on the dislocation substructure. The presence of fine dispersed Al2 O3 particles results in a uniform and random dislocation distribution in matrix copper and causes the difficulty in formation of dislocation cell structure and the decrease in the amount of cell structure during deformation. Deformation gives rise to much more dislocations and dislocation cells form more difficultly and the decrease in the cell size with the increase of dispersion degree.展开更多
Train–track–substructure dynamic interaction is an extension of the vehicle–track coupled dynamics.It contributes to evaluate dynamic interaction and performance between train–track system and its substructures.Fo...Train–track–substructure dynamic interaction is an extension of the vehicle–track coupled dynamics.It contributes to evaluate dynamic interaction and performance between train–track system and its substructures.For the first time,this work devotes to presenting engineering practical methods for modeling and solving such large-scale train–track–substructure interaction systems from a unified viewpoint.In this study,a train consists of several multi-rigid-body vehicles,and the track is modeled by various finite elements.The track length needs only satisfy the length of a train plus boundary length at two sides,despite how long the train moves on the track.The substructures and their interaction matrices to the upper track are established as independent modules,with no need for additionally building the track structures above substructures,and accordingly saving computational cost.Track–substructure local coordinates are defined to assist the confirming of the overlapped portions between the train–track system and the substructural system to effectively combine the cyclic calculation and iterative solution procedures.The advancement of this model lies in its convenience,efficiency and accuracy in continuously considering the vibration participation of multi-types of substructures against the moving of a train on the track.Numerical examples have shown the effectiveness of this method;besides,influence of substructures on train–track dynamic behaviors is illustrated accompanied by clarifying excitation difference of different track irregularity spectrums.展开更多
Free-interface dual-compatibility modal synthesis method(compatibility of both force and displacement on interfaces)is introduced to large-scale civil engineering structure to enhance computation efficiency. The basic...Free-interface dual-compatibility modal synthesis method(compatibility of both force and displacement on interfaces)is introduced to large-scale civil engineering structure to enhance computation efficiency. The basic equations of the method are first set up, and then the mode cut-off principle and the dividing principle are proposed. MATLAB is used for simulation in different frame structures. The simulation results demonstrate the applicability of this substructure method to civil engineering structures and the correctness of the proposed mode cut-off principle. Studies are also conducted on how to divide the whole structure for better computation efficiency while maintaining better precision. It is observed that the geometry and material properties should be considered, and the synthesis results would be more precise when the inflection points of the mode shapes are taken into consideration. Furthermore, the simulation performed on a large-scale high-rise connected structure further proves the feasibility and efficiency of this modal synthesis method compared with the traditional global method. It is also concluded from the simulation results that the fewer number of DOFs in each substructure will result in better computation efficiency, but too many substructures will be time-consuming due to the tedious synthesis procedures. Moreover, the substructures with free interface will introduce errors and reduce the precision dramatically, which should be avoided.展开更多
The morphologic,substructural and crystallographic characteristics of martensite in steels 60and 60Si2Mn have been investigated by means of optical and transmission electronmicroscopy combined with B-M phenomenologica...The morphologic,substructural and crystallographic characteristics of martensite in steels 60and 60Si2Mn have been investigated by means of optical and transmission electronmicroscopy combined with B-M phenomenological crystallographic theory.The average hab-it plane of martensite in medium carbon iron alloys is{225}_f.Experimental data on the habitplane and the orientation relationship between the austenite and martensite are in agreementwith the B-M theoretical calculation of using the Bain strain and lattice invariant shear on(100)[011]_f.展开更多
β-quenching a Zr-1.15 wt％Cr-0.10 wt％Fe alloy produces a martensitic or a Widmanst(a|¨)tten transforma-tion morphology,or a mixture of the two,depending on the cooling rate.For the Widmanst(a|¨)tten struct...β-quenching a Zr-1.15 wt％Cr-0.10 wt％Fe alloy produces a martensitic or a Widmanst(a|¨)tten transforma-tion morphology,or a mixture of the two,depending on the cooling rate.For the Widmanst(a|¨)tten structure,orthe mixed martensitic-Widmanst(a|¨)itten structure,a grain boundary phase is observed at most prior-β grainboundaries.X-ray line broadening analysis and the thermoelectric power(TEP)measurements of thesequenched samples show that not only the solubility of alloying elements in α-Zr matrix,but also substructure(microstrain,crystallite size and dislocation density)have an effect on TEP.Thus,TEP measurements are verywell suited for following the structural transformations taking place in Zr alloys during fabrication.展开更多
In[1],the exact analytic method for the solution of differential equation with variablecoefficients was suggested and an analytic expression of solution was given by initialparameter algorithm.But to some problems suc...In[1],the exact analytic method for the solution of differential equation with variablecoefficients was suggested and an analytic expression of solution was given by initialparameter algorithm.But to some problems such as the bending,free vibration andbuckling of nonhomogeneous long cylinders,it is difficult to obtain their solutions by theinitial parameter algorithm on computer.In this paper,the substructure computationalalgorithm for the exact analytic method is presented through the bending of non-homogeneous long cylindrical shell.This substructure algorithm can be applied to solve theproblems which can not be calculated by the initial parameter algorithm on computer.Finally,the problems can be reduced to solving a low order system of algebraic equationslike the initial parameter algorithm.Numerical examples are given and compared with theinitial para-algorithm at the end of the paper,which confirms the correcthess of thesubstructure computational algorithm.展开更多
Peridynamics(PD)is a widely used theory to simulate discontinuities,but its application in real-world structural problems is somewhat limited due to the relatively low-efficiency.The numerical substructure method(NSM)...Peridynamics(PD)is a widely used theory to simulate discontinuities,but its application in real-world structural problems is somewhat limited due to the relatively low-efficiency.The numerical substructure method(NSM)presented by the authors and co-workers provides an efficient approach for modeling structures with local nonlinearities,which is usually restricted in problems of continuum mechanics.In this paper,an approach is presented to couple the PD theory with the NSM for modeling structures with local discontinuities,taking advantage of the powerful capability of the PD for discontinuities simulation and high computational efficiency of the NSM.The structure is simulated using liner elastic finite element(FE)model while the local cracking regions are isolated and simulated using a PD substructure model.A force corrector calculated from the PD model is applied on the FE model to consider the effect of discontinuities.The PD is integrated in the substructure model using interface elements with embedded PD nodes.The equations of motions of both the NSM system and the PD substructure are solved using the central difference method.Three examples of two-dimensional(2D)concrete cantilever beams under the concentrated force are investigated to verify the proposed coupling approach.展开更多
The alteration of substructure of an austenitic stainless steel has been investigated during con-stant strain fatigue.No plateau stage on the cyclic stress-strain curve was observed for thestainless steel in contrast ...The alteration of substructure of an austenitic stainless steel has been investigated during con-stant strain fatigue.No plateau stage on the cyclic stress-strain curve was observed for thestainless steel in contrast with a monocrystalline pure copper specimen.This may relate to itslow stacking fault energy.During strain fatigue under various amplitudes the substructure ofdislocation in austenite alterates correspondingly.It revealed to associate with the appearancechange of the cyclic stress-strain curve.展开更多
To improve the computational efficiency in large-scale problems,the substructure method was proposed in the finite element analysis(FEA)of constructions,electronics devices,auto parts,etc.The effect of random vibratio...To improve the computational efficiency in large-scale problems,the substructure method was proposed in the finite element analysis(FEA)of constructions,electronics devices,auto parts,etc.The effect of random vibration on an electronic chassis was analyzed by the substructure method via the ANSYS FEA.The basic principles of the substructure methods were briefly discussed,and then modeling and FEA,including model analysis and power spectral density(PSD)analysis,of the electronic chassis was conducted with substructure method via the ANSYS.Finally vibration experiment was done to verify the accuracy of FEA with substructure method,which proved that the substructure method,with adequate accuracy,could improve the computational efficiency for large-scale electronic chassis.Based on the stress distribution from FEA and experimental results,a comprehensive structural optimization was proposed.展开更多
An efficient computational approach based on substructure methodology is proposed to analyze the viaduct-pile foundation-soil dynamic interaction under train loads.Thetrain-viaductsubsystemissolvedusingthe dynamic sti...An efficient computational approach based on substructure methodology is proposed to analyze the viaduct-pile foundation-soil dynamic interaction under train loads.Thetrain-viaductsubsystemissolvedusingthe dynamic stiffness integration method,and its accuracy is verified by the existing analytical solution for a moving vehicle on a simply supported beam.For the pile foundation-soil subsystem,the geometric and material properties of piles and soils are assumed to be invariable along the azimuth direction.By introducing the equivalent stiffness of grouped piles,the governing equations of pile foundation-soil interaction are simplified based on Fourier decomposition method,so the three-dimensional problem is decomposedintoseveraltwo-dimensionalaxisymmetricfinite element models.The pile foundation-soil interaction model is verified by field measurements due to shaker loading at pile foundation top.In addition,these two substructures are coupled with the displacement compatibility condition at interface of pier bottom and pile foundation top.Finally,the proposed train-viaduct-pile foundation-soil interaction model was validated by field tests.The results show that the proposed model can predict vibrations of pile foundation and soil accurately,thereby providing a basis for the prediction of pile-soil foundation settlement.The frequency spectra of the vibration in Beijing-Tianjin high-speed railway demonstrated that the main frequencies of the pier top and ground surface are below 100 and 30 Hz,respectively.展开更多
Structural components may enter an initial-elastic state,a plastic-hardening state and a residual-elastic state during strong seismic excitations.In the residual-elastic state,structural components keep in an unloadin...Structural components may enter an initial-elastic state,a plastic-hardening state and a residual-elastic state during strong seismic excitations.In the residual-elastic state,structural components keep in an unloading/reloading stage that is dominated by a tangent stiffness,thus structural components remain residual deformations but behave in an elastic manner.It has a great potential to make model order reduction for such structural components using the tangent-stiffness-based vibration modes as a reduced order basis.In this paper,an adaptive substructure-based model order reduction method is developed to perform nonlinear seismic analysis for structures that have a priori unknown damage distribution.This method is able to generate time-varying substructures and make nonlinear model order reduction for substructures in the residual-elastic phase.The finite element program OpenSees has been extended to provide the adaptive substructure-based nonlinear seismic analysis.At the low level of OpenSees framework,a new abstract layer is created to represent the time-varying substructures and implement the modeling process of substructures.At the high level of OpenSees framework,a new transient analysis class is created to implement the solving process of substructure-based governing equations.Compared with the conventional time step integration method,the adaptive substructure-based model order reduction method can yield comparative results with a higher computational efficiency.展开更多
BACKGROUND Radiation dose to specific cardiac substructures can have a significant on treatment related morbidity and mortality,yet definition of these structures is labor intensive and not standard.Autosegmentation s...BACKGROUND Radiation dose to specific cardiac substructures can have a significant on treatment related morbidity and mortality,yet definition of these structures is labor intensive and not standard.Autosegmentation software may potentially address these issues,however it is unclear whether this approach can be broadly applied across different treatment planning conditions.We investigated the feasibility of autosegmentation of the cardiac substructures in four-dimensional(4D)computed tomography(CT),respiratory-gated,non-contrasted imaging.AIM To determine whether autosegmentation can be successfully employed on 4DCT respiratory-gated,non-contrasted imaging.METHODS We included patients who underwent stereotactic body radiation therapy for inoperable,early-stage non-small cell lung cancer from 2007 to 2019.All patients were simulated via 4DCT imaging with respiratory gating without intravenous contrast.Generated structure quality was evaluated by degree of required manual edits and volume discrepancy between the autocontoured structures and its edited sister structure.RESULTS Initial 17-structure cardiac atlas was generated with 20 patients followed by three successive iterations of 10 patients using MIM software.The great vessels and heart chambers were reliably autosegmented with most edits considered minor.In contrast,coronary arteries either failed to be autosegmented or the generated structures required major alterations necessitating deletion and manual definition.Similarly,the generated mitral and tricuspid valves were poor whereas the aortic and pulmonary valves required at least minor and moderate changes respectively.For the majority of subsites,the additional samples did not appear to substantially impact the quality of generated structures.Volumetric analysis between autosegmented and its manually edited sister structure yielded comparable findings to the physician-based assessment of structure quality.CONCLUSION The use of MIM software with 30-sample subject library was found to be useful in delineating many of the heart substructures with acceptable clinical accuracy on respiratory-gated 4DCT imaging.Small volume structures,such as the coronary arteries were poorly autosegmented and require manual definition.展开更多
In this paper,a substructure method of three-dimensional semi-analytic boundary element is established.The seismic scattering by three-dimensional topography of a hill can be analyzed by the method in frequency domain...In this paper,a substructure method of three-dimensional semi-analytic boundary element is established.The seismic scattering by three-dimensional topography of a hill can be analyzed by the method in frequency domain.Using this method,the computational effort and storage space are reduced considerably.Finally,analytic results are given.展开更多
On assuming that weak substructure has a dynamics which is similar to quantum chromodynamics but much stronger, we conclude that unquenching is indispensable for predictions on the spectrum of weak-substructure resona...On assuming that weak substructure has a dynamics which is similar to quantum chromodynamics but much stronger, we conclude that unquenching is indispensable for predictions on the spectrum of weak-substructure resonances[1].展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.52008404,U1934217 and 11790283)Science and Technology Research and Development Program Project of China Railway Group Limited(Major Special Project,No.2020-Special-02)the National Natural Science Foundation of Hunan Province(Grant No.2021JJ30850).
文摘In this work,a method is put forward to obtain the dynamic solution efficiently and accurately for a large-scale train-track-substructure(TTS)system.It is called implicit-explicit integration and multi-time-step solution method(abbreviated as mI-nE-MTS method).The TTS system is divided into train-track subsystem and substruc-ture subsystem.Considering that the root cause of low effi-ciency of obtaining TTS solution lies in solving the alge-braic equation of the substructures,the high-efficient Zhai method,an explicit integration scheme,can be introduced to avoid matrix inversion process.The train-track system is solved by implicitly Park method.Moreover,it is known that the requirement of time step size differs for different sub-systems,integration methods and structural frequency response characteristics.A multi-time-step solution is pro-posed,in which time step size for the train-track subsystem and the substructure subsystem can be arbitrarily chosen once satisfying stability and precision demand,namely the time spent for m implicit integral steps is equal to n explicit integral steps,i.e.,mI=nE as mentioned above.The numeri-cal examples show the accuracy,efficiency,and engineering practicality of the proposed method.
基金National Natural Science Foundation of China under Grant No.51478247National Key Research and Development Program of China under Grant No.2016YFC1402800
文摘The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident wave into equivalent loads on the cutoff boundaries. The wave method has high precision, but the implementation is complicated, especially for three-dimensional models. By deducing another form of equivalent input seismic loads in the fi nite element model, a new seismic wave input method is proposed. In the new method, by imposing the displacements of the free wave fi eld on the nodes of the substructure composed of elements that contain artifi cial boundaries, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Subsequently, the equivalent input seismic loads are imposed on the artifi cial boundary nodes to complete the seismic wave input and perform seismic analysis of the soil-structure dynamic interaction model. Compared with the wave method, the new method is simplifi ed by avoiding the complex processes of calculating the equivalent input seismic loads. The validity of the new method is verifi ed by the dynamic analysis numerical examples of the homogeneous and layered half space under vertical and oblique incident seismic waves.
文摘In the strengthened layer of stainless steel after shot peening,there are a great amount ofdeformation microtwins which may act as structural strengthening factor and prevent thegradual relaxation of surface residual stress during fatigue,so as to keep its rather high levelof bending fatigue strength.However,in the strengthened surface layer of low carbon steel,dislocation cell structure is so unstalbe during fatigue that its surface residual stress relaxationcannot be retarded.Therefore,the bending fatigue strength of the low carbon steel can not beimprored by shot peening.
基金National Natural Science Foundation of China under Grant Nos.61903009,51978016 and 61673002Beijing Municipal Education Commission under Grant No.KM201810011005。
文摘Combining the advantages of numerical simulation with experimental testing,real-time dynamic substructure(RTDS)testing provides a new experimental method for the investigation of engineered structures.However,not all unmodeled parts can be physically tested,as testing is often limited by the capacity of the test facility.Model updating is a good option to improve the modeling accuracy for numerical substructures in RTDS.In this study,a model updating method is introduced,which has great performance in describing this nonlinearity.In order to determine the optimal parameters in this model,an Unscented Kalman Filter(UKF)-based algorithm was applied to extract the knowledge contained in the sensors data.All the parameters that need to be identified are listed as the extended state variables,and the identification was achieved via the step-by-step state prediction and state update process.Effectiveness of the proposed method was verified through a group of experimental data,and results showed good agreement.Furthermore,the proposed method was compared with the Extended Kalman Filter(EKF)-based method,and better accuracy was easily found.The proposed parameter identification method has great applicability for structural objects with nonlinear behaviors and could be extended to research in other engineering fields.
基金Project supported by National Natural Science Foundation of China.
文摘In this paper,a new method for dealing with substructure chain is presented.Here,asubstructure chain means a structure consisting of a number of identical substructures connected in series.Thismethod is parallel to the expansion method in the structural analysis according to the transverse section.Themethod of shift invariance and that of initial parameter and transfer matrix,their mutual-relation and com-bined use,as well as the analysis of the eigenproblem on the transverse section,and the expansion methodbased on the eigenvectors are described in this paper.
文摘The deformation behavior of dispersion strengthened copper alloy Cu-Al2O3 was studied by TEM. The results show that nano-scaled dispersed second phase not only increases dislocation density in matrix, but also has an important influence on the dislocation substructure. The presence of fine dispersed Al2 O3 particles results in a uniform and random dislocation distribution in matrix copper and causes the difficulty in formation of dislocation cell structure and the decrease in the amount of cell structure during deformation. Deformation gives rise to much more dislocations and dislocation cells form more difficultly and the decrease in the cell size with the increase of dispersion degree.
基金This work was supported by the National Natural Science Foundation of China(Grant No.52008404)the National Natural Science Foundation of Hunan Province(Grant No.2021JJ30850).
文摘Train–track–substructure dynamic interaction is an extension of the vehicle–track coupled dynamics.It contributes to evaluate dynamic interaction and performance between train–track system and its substructures.For the first time,this work devotes to presenting engineering practical methods for modeling and solving such large-scale train–track–substructure interaction systems from a unified viewpoint.In this study,a train consists of several multi-rigid-body vehicles,and the track is modeled by various finite elements.The track length needs only satisfy the length of a train plus boundary length at two sides,despite how long the train moves on the track.The substructures and their interaction matrices to the upper track are established as independent modules,with no need for additionally building the track structures above substructures,and accordingly saving computational cost.Track–substructure local coordinates are defined to assist the confirming of the overlapped portions between the train–track system and the substructural system to effectively combine the cyclic calculation and iterative solution procedures.The advancement of this model lies in its convenience,efficiency and accuracy in continuously considering the vibration participation of multi-types of substructures against the moving of a train on the track.Numerical examples have shown the effectiveness of this method;besides,influence of substructures on train–track dynamic behaviors is illustrated accompanied by clarifying excitation difference of different track irregularity spectrums.
基金Supported by the National Natural Science Foundation of China(No.51108089)Doctoral Programs Foundation of Ministry of Education of China(No.20113514120005)the Foundation of the Education Department of Fujian Province(No.JA14057)
文摘Free-interface dual-compatibility modal synthesis method(compatibility of both force and displacement on interfaces)is introduced to large-scale civil engineering structure to enhance computation efficiency. The basic equations of the method are first set up, and then the mode cut-off principle and the dividing principle are proposed. MATLAB is used for simulation in different frame structures. The simulation results demonstrate the applicability of this substructure method to civil engineering structures and the correctness of the proposed mode cut-off principle. Studies are also conducted on how to divide the whole structure for better computation efficiency while maintaining better precision. It is observed that the geometry and material properties should be considered, and the synthesis results would be more precise when the inflection points of the mode shapes are taken into consideration. Furthermore, the simulation performed on a large-scale high-rise connected structure further proves the feasibility and efficiency of this modal synthesis method compared with the traditional global method. It is also concluded from the simulation results that the fewer number of DOFs in each substructure will result in better computation efficiency, but too many substructures will be time-consuming due to the tedious synthesis procedures. Moreover, the substructures with free interface will introduce errors and reduce the precision dramatically, which should be avoided.
文摘The morphologic,substructural and crystallographic characteristics of martensite in steels 60and 60Si2Mn have been investigated by means of optical and transmission electronmicroscopy combined with B-M phenomenological crystallographic theory.The average hab-it plane of martensite in medium carbon iron alloys is{225}_f.Experimental data on the habitplane and the orientation relationship between the austenite and martensite are in agreementwith the B-M theoretical calculation of using the Bain strain and lattice invariant shear on(100)[011]_f.
文摘β-quenching a Zr-1.15 wt％Cr-0.10 wt％Fe alloy produces a martensitic or a Widmanst(a|¨)tten transforma-tion morphology,or a mixture of the two,depending on the cooling rate.For the Widmanst(a|¨)tten structure,orthe mixed martensitic-Widmanst(a|¨)itten structure,a grain boundary phase is observed at most prior-β grainboundaries.X-ray line broadening analysis and the thermoelectric power(TEP)measurements of thesequenched samples show that not only the solubility of alloying elements in α-Zr matrix,but also substructure(microstrain,crystallite size and dislocation density)have an effect on TEP.Thus,TEP measurements are verywell suited for following the structural transformations taking place in Zr alloys during fabrication.
文摘In[1],the exact analytic method for the solution of differential equation with variablecoefficients was suggested and an analytic expression of solution was given by initialparameter algorithm.But to some problems such as the bending,free vibration andbuckling of nonhomogeneous long cylinders,it is difficult to obtain their solutions by theinitial parameter algorithm on computer.In this paper,the substructure computationalalgorithm for the exact analytic method is presented through the bending of non-homogeneous long cylindrical shell.This substructure algorithm can be applied to solve theproblems which can not be calculated by the initial parameter algorithm on computer.Finally,the problems can be reduced to solving a low order system of algebraic equationslike the initial parameter algorithm.Numerical examples are given and compared with theinitial para-algorithm at the end of the paper,which confirms the correcthess of thesubstructure computational algorithm.
基金Financial support by the National Key Research and Development program of China under Grant No.2016YFC0701106the National Natural Science Foundation of China under grants No.51578473the program of China Scholarship Council(CSC,No.201606060083)are gratefully acknowledged.
文摘Peridynamics(PD)is a widely used theory to simulate discontinuities,but its application in real-world structural problems is somewhat limited due to the relatively low-efficiency.The numerical substructure method(NSM)presented by the authors and co-workers provides an efficient approach for modeling structures with local nonlinearities,which is usually restricted in problems of continuum mechanics.In this paper,an approach is presented to couple the PD theory with the NSM for modeling structures with local discontinuities,taking advantage of the powerful capability of the PD for discontinuities simulation and high computational efficiency of the NSM.The structure is simulated using liner elastic finite element(FE)model while the local cracking regions are isolated and simulated using a PD substructure model.A force corrector calculated from the PD model is applied on the FE model to consider the effect of discontinuities.The PD is integrated in the substructure model using interface elements with embedded PD nodes.The equations of motions of both the NSM system and the PD substructure are solved using the central difference method.Three examples of two-dimensional(2D)concrete cantilever beams under the concentrated force are investigated to verify the proposed coupling approach.
文摘The alteration of substructure of an austenitic stainless steel has been investigated during con-stant strain fatigue.No plateau stage on the cyclic stress-strain curve was observed for thestainless steel in contrast with a monocrystalline pure copper specimen.This may relate to itslow stacking fault energy.During strain fatigue under various amplitudes the substructure ofdislocation in austenite alterates correspondingly.It revealed to associate with the appearancechange of the cyclic stress-strain curve.
文摘To improve the computational efficiency in large-scale problems,the substructure method was proposed in the finite element analysis(FEA)of constructions,electronics devices,auto parts,etc.The effect of random vibration on an electronic chassis was analyzed by the substructure method via the ANSYS FEA.The basic principles of the substructure methods were briefly discussed,and then modeling and FEA,including model analysis and power spectral density(PSD)analysis,of the electronic chassis was conducted with substructure method via the ANSYS.Finally vibration experiment was done to verify the accuracy of FEA with substructure method,which proved that the substructure method,with adequate accuracy,could improve the computational efficiency for large-scale electronic chassis.Based on the stress distribution from FEA and experimental results,a comprehensive structural optimization was proposed.
基金supported by the National Natural Science Foundation of China(Nos.52125803,51988101 and 52008369)。
文摘An efficient computational approach based on substructure methodology is proposed to analyze the viaduct-pile foundation-soil dynamic interaction under train loads.Thetrain-viaductsubsystemissolvedusingthe dynamic stiffness integration method,and its accuracy is verified by the existing analytical solution for a moving vehicle on a simply supported beam.For the pile foundation-soil subsystem,the geometric and material properties of piles and soils are assumed to be invariable along the azimuth direction.By introducing the equivalent stiffness of grouped piles,the governing equations of pile foundation-soil interaction are simplified based on Fourier decomposition method,so the three-dimensional problem is decomposedintoseveraltwo-dimensionalaxisymmetricfinite element models.The pile foundation-soil interaction model is verified by field measurements due to shaker loading at pile foundation top.In addition,these two substructures are coupled with the displacement compatibility condition at interface of pier bottom and pile foundation top.Finally,the proposed train-viaduct-pile foundation-soil interaction model was validated by field tests.The results show that the proposed model can predict vibrations of pile foundation and soil accurately,thereby providing a basis for the prediction of pile-soil foundation settlement.The frequency spectra of the vibration in Beijing-Tianjin high-speed railway demonstrated that the main frequencies of the pier top and ground surface are below 100 and 30 Hz,respectively.
基金supported by the National Nature Science Foundation of China(No.51678210)National Key Research and Development Program of China(No.2016YFC0701400).
文摘Structural components may enter an initial-elastic state,a plastic-hardening state and a residual-elastic state during strong seismic excitations.In the residual-elastic state,structural components keep in an unloading/reloading stage that is dominated by a tangent stiffness,thus structural components remain residual deformations but behave in an elastic manner.It has a great potential to make model order reduction for such structural components using the tangent-stiffness-based vibration modes as a reduced order basis.In this paper,an adaptive substructure-based model order reduction method is developed to perform nonlinear seismic analysis for structures that have a priori unknown damage distribution.This method is able to generate time-varying substructures and make nonlinear model order reduction for substructures in the residual-elastic phase.The finite element program OpenSees has been extended to provide the adaptive substructure-based nonlinear seismic analysis.At the low level of OpenSees framework,a new abstract layer is created to represent the time-varying substructures and implement the modeling process of substructures.At the high level of OpenSees framework,a new transient analysis class is created to implement the solving process of substructure-based governing equations.Compared with the conventional time step integration method,the adaptive substructure-based model order reduction method can yield comparative results with a higher computational efficiency.
文摘BACKGROUND Radiation dose to specific cardiac substructures can have a significant on treatment related morbidity and mortality,yet definition of these structures is labor intensive and not standard.Autosegmentation software may potentially address these issues,however it is unclear whether this approach can be broadly applied across different treatment planning conditions.We investigated the feasibility of autosegmentation of the cardiac substructures in four-dimensional(4D)computed tomography(CT),respiratory-gated,non-contrasted imaging.AIM To determine whether autosegmentation can be successfully employed on 4DCT respiratory-gated,non-contrasted imaging.METHODS We included patients who underwent stereotactic body radiation therapy for inoperable,early-stage non-small cell lung cancer from 2007 to 2019.All patients were simulated via 4DCT imaging with respiratory gating without intravenous contrast.Generated structure quality was evaluated by degree of required manual edits and volume discrepancy between the autocontoured structures and its edited sister structure.RESULTS Initial 17-structure cardiac atlas was generated with 20 patients followed by three successive iterations of 10 patients using MIM software.The great vessels and heart chambers were reliably autosegmented with most edits considered minor.In contrast,coronary arteries either failed to be autosegmented or the generated structures required major alterations necessitating deletion and manual definition.Similarly,the generated mitral and tricuspid valves were poor whereas the aortic and pulmonary valves required at least minor and moderate changes respectively.For the majority of subsites,the additional samples did not appear to substantially impact the quality of generated structures.Volumetric analysis between autosegmented and its manually edited sister structure yielded comparable findings to the physician-based assessment of structure quality.CONCLUSION The use of MIM software with 30-sample subject library was found to be useful in delineating many of the heart substructures with acceptable clinical accuracy on respiratory-gated 4DCT imaging.Small volume structures,such as the coronary arteries were poorly autosegmented and require manual definition.
基金This project was sponsored by the Earthquake Science Foundation, China
文摘In this paper,a substructure method of three-dimensional semi-analytic boundary element is established.The seismic scattering by three-dimensional topography of a hill can be analyzed by the method in frequency domain.Using this method,the computational effort and storage space are reduced considerably.Finally,analytic results are given.
文摘On assuming that weak substructure has a dynamics which is similar to quantum chromodynamics but much stronger, we conclude that unquenching is indispensable for predictions on the spectrum of weak-substructure resonances[1].
