Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads. This study investigates the effects of bottom bracings on the torsional dynamic characteristics of CTIGBs...Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads. This study investigates the effects of bottom bracings on the torsional dynamic characteristics of CTIGBs. Five types of bottom bracings are designed to investigate their effects on the dynamic characteristics of CTIGBs with different curvatures under free and forced vibrations. To perform numerical investigations, three-dimensional (3-D) finite element (FE) bridge and vehicle models are established using commercial ANSYS code, and then a vehicle-bridge interaction analysis approach is proposed. Road roughness profiles generated from power spectral density and cross spectral functions are also taken into account in the analyses. The numerical results show that torsional frequencies increase significantly after providing bottom bracings, and the increasing rate depends on the type of bottom bracings and their locations of installation. Bottom bracings can act as load transmitting members from one main girder to the others. Large negative bearing forces that have occurred in bridges with small radii of curvatures can be remarkably reduced by providing bottom bracing systems. It is found that the performances of several bottom bracing systems are effective in improving the torsional dynamic characteristics of the bridges in this study.展开更多
In order to predict the plate curvature during snake rolling, FE model was constructed based on plane strain assumption. The accuracy of the FE model was verified by the comparison between the plate curvature conducte...In order to predict the plate curvature during snake rolling, FE model was constructed based on plane strain assumption. The accuracy of the FE model was verified by the comparison between the plate curvature conducted by FE model and experiment respectively. By using FE model, the effect of offset distance, speed ratio, reduction, roll radius and initial plate thickness on the plate curvature during snake rolling was investigated. The experimental results show that, a proper offsetting distance can efficiently decrease plate curvature, however an excessive offsetting distance will increase plate curvature. A larger speed ratio, reduction will cause a large plate curvature, however a larger roll radius has effect to reduce plate curvature. Plate which undergoes a larger reduction and plate with a larger initial thickness always need a larger offset distance to keep the plate the minimum plate curvature, but for a larger roll radius a smaller offset distance is needed.展开更多
A simple modified analytic EAM model for bcc Fe and fcc Al was used to calculate the lattice constant and elastic constants of B2 FeAl and DO3 Fe3Al alloys. The formation energies of vacancy and antisite were also cal...A simple modified analytic EAM model for bcc Fe and fcc Al was used to calculate the lattice constant and elastic constants of B2 FeAl and DO3 Fe3Al alloys. The formation energies of vacancy and antisite were also calculated. The present calculations are in agreement with the experimental data and the theoretical results obtained by other authors.展开更多
The internal temperature of cast-in-place concrete bridges undergoes strong variations during the construction as a result of environmental factors.In order to determine precisely such variations,the present study rel...The internal temperature of cast-in-place concrete bridges undergoes strong variations during the construction as a result of environmental factors.In order to determine precisely such variations,the present study relies on the finite element method,used to model the bridge box girder section and simulate the internal temperature distribution during construction.The numerical results display good agreement with measured temperature values.It is shown that when the external temperature is higher,and the internal and external temperature difference is relatively small,the deviation of the fitting line from existing specifications(Chinese specification,American specification,New Zealand specification)is relatively large and vice versa.展开更多
We investigate the accuracy and robustness of moment tensor(MT)and stress inversion solutions derived from acoustic emissions(AEs)during the laboratory fracturing of prismatic Barre granite specimens.Pre-cut flaws in ...We investigate the accuracy and robustness of moment tensor(MT)and stress inversion solutions derived from acoustic emissions(AEs)during the laboratory fracturing of prismatic Barre granite specimens.Pre-cut flaws in the specimens introduce a complex stress field,resulting in a spatial and temporal variation of focal mechanisms.Specifically,we consider two experimental setups:(1)where the rock is loaded in compression to generate primarily shear-type fractures and(2)where the material is loaded in indirect tension to generate predominantly tensile-type fractures.In each test,we first decompose AE moment tensors into double-couple(DC)and non-DC terms and then derive unambiguous normal and slip vectors using k-means clustering and an unstructured damped stress inversion algorithm.We explore temporal and spatial distributions of DC and non-DC events at different loading levels.The majority of the DC and the tensile non-DC events cluster around the pre-cut flaws,where macro-cracks later develop.Results of stress inversion are verified against the stress field from finite element(FE)modeling.A good agreement is found between the experimentally derived and numerically simulated stress orientations.To the best of the authors’knowledge,this work presents the first case where stress inversion methodologies are validated by numerical simulations at laboratory scale and under highly heterogeneous stress distributions.展开更多
Lower limb injures are frequently observed in passenger car traffic accidents.Previous studies of the injuries focus on long bone fractures by using either cadaver component tests or simulations of the long bone kinem...Lower limb injures are frequently observed in passenger car traffic accidents.Previous studies of the injuries focus on long bone fractures by using either cadaver component tests or simulations of the long bone kinematics,which lack in-depth study on the fractures in stress analysis.This paper aims to investigate lower limb impact biomechanics in real-world car to pedestrian accidents and to predict fractures of long bones in term of stress parameter for femur,tibia,and fibula.For the above purposes,a 3D finite element(FE) model of human body lower limb(HBM-LL) is developed based on human anatomy.The model consists of the pelvis,femur,tibia,fibula,patella,foot bones,primary tendons,knee joint capsule,meniscus,and ligaments.The FE model is validated by comparing the results from a lateral impact between simulations and tests with cadaver lower limb specimens.Two real-world accidents are selected from an in-depth accident database with detailed information about the accident scene,car impact speed,damage to the car,and pedestrian injuries.Multi-body system(MBS) models are used to reconstruct the kinematics of the pedestrians in the two accidents and the impact conditions are calculated for initial impact velocity and orientations of the car and pedestrian during the collision.The FE model is used to perform injury reconstructions and predict the fractures by using physical parameters,such as von Mises stress of long bones.The calculated failure level of the long bones is correlated with the injury outcomes observed from the two accident cases.The reconstruction result shows that the HBM-LL FE model has acceptable biofidelity and can be applied to predict the risk of long bone fractures.This study provides an efficient methodology to investigate the long bone fracture suffered from vehicle traffic collisions.展开更多
Lateral spread of frozen ground crust over liquefied soil has caused extensive bridge foundation damage in the past winter earthquakes.A shake table experiment was conducted to investigate the performance of a model p...Lateral spread of frozen ground crust over liquefied soil has caused extensive bridge foundation damage in the past winter earthquakes.A shake table experiment was conducted to investigate the performance of a model pile in this scenario and revealed unique pile failure mechanisms.The modelling results provided valuable data for validating numerical models.This paper presents analyses and results of this experiment using two numerical modeling approaches: solid-fluid coupled finite element(FE) modeling and the beam-on-nonlinear-Winkler-foundation(BNWF) method.A FE model was constructed based on the experiment configuration and subjected to earthquake loading.Soil and pile response results were presented and compared with experimental results to validate this model.The BNWF method was used to predict the pile response and failure mechanism.A p-y curve was presented for modelling the frozen ground crust with the free-field displacement from the experiment as loading.Pile responses were presented and compared with those of the experiment and FE model.It was concluded that the coupled FE model was effective in predicting formation of three plastic hinges at ground surface,ground crust-liquefiable soil interface and within the medium dense sand layer,while the BNWF method was only able to predict the latter two.展开更多
This paper aims at investigating brain injury mechanisms and predicting head injuries in real world accidents. For this purpose, a 3D human head finite element model (HBM-head) was developed based on head-brain anat...This paper aims at investigating brain injury mechanisms and predicting head injuries in real world accidents. For this purpose, a 3D human head finite element model (HBM-head) was developed based on head-brain anatomy. The HBM head model was validated with two experimental tests. Then the head finite element(FE) model and a multi-body system (MBS) model were used to carry out reconstructions of real world vehicle-pedestrian accidents and brain injuries. The MBS models were used for calculating the head impact conditions in vehicle impacts. The HBM-head model was used for calculating the injury related physical parameters, such as intracranial pressure, stress, and strain. The calculated intracranial pressure and strain distribution were correlated with the injury outcomes observed from accidents. It is shown that this model can predict the intracranial biomechanical response and calculate the injury related physical parameters. The head FE model has good biofidelity and will be a valuable tool for the study of injury mechanisms and the tolerance level of the brain.展开更多
An inflatable cuff wrapped around the upper arm is widely used in noninvasive blood pressure measurement.However, the mechanical interaction between cuff and arm tissues, a factor that potentially affects the accuracy...An inflatable cuff wrapped around the upper arm is widely used in noninvasive blood pressure measurement.However, the mechanical interaction between cuff and arm tissues, a factor that potentially affects the accuracy of noninvasive blood pressure measurement, remains rarely addressed. In the present study, finite element(FE) models were constructed to quantify intra-arm stresses generated by cuff compression, aiming to provide some theoretical evidence for identifying factors of importance for blood pressure measurement or explaining clinical observations. Obtained results showed that the simulated tissue stresses were highly sensitive to the distribution of cuff pressure on the arm surface and the contact condition between muscle and bone. In contrast, the magnitude of cuff pressure and small variations in elastic properties of arm soft tissues had little influence on the efficiency of pressure transmission in arm tissues. In particular, it was found that a thickened subcutaneous fat layer in obese subjects significantly reduced the effective pressure transmitted to the brachial artery, which may explain why blood pressure overestimation occurs more frequently in obese subjects in noninvasive blood pressure measurement.展开更多
Previous failure analyses of bridges typically focus on substructure failure or superstructure failure separately. However, in an actual bridge, the seismic induced substructure failure and superstructure failure may ...Previous failure analyses of bridges typically focus on substructure failure or superstructure failure separately. However, in an actual bridge, the seismic induced substructure failure and superstructure failure may influence each other. Moreover, previous studies typically use simplified models to analyze the bridge failure; however, there are inherent defects in the calculation accuracy compared with using a detailed three-dimensional (3D) finite element (FE) model. Conversely, a detailed 3D FE model requires more computational costs, and a proper erosion criterion of the 3D elements is necessary. In this paper, a multi-scale FE model, including a corresponding erosion criterion, is proposed and validated that can significantly reduce computational costs with high precision by modelling a pseudo-dynamic test of an reinforced concrete (RC) pier. Numerical simulations of the seismic failures of a continuous RC bridge based on the multi-scale FE modeling method using LS-DYNA are performed. The nonlinear properties of the bridge, various connection strengths and bidirectional excitations are considered. The numerical results demonstrate that the failure of the connections will induce large pounding responses of the girders. The nonlinear deformation of the piers will aggravate the pounding damages. Furthermore, bidirectional earthquakes will induce eccentric poundingsto the girders and different failure modes to the adjacent piers.展开更多
This study focuses on advanced finite element(FE)analyses on The Church of Nativity located in Bethlehem(Palestine),one of the most historic structures in the world.To ensure the model quality,a 3D FE model was create...This study focuses on advanced finite element(FE)analyses on The Church of Nativity located in Bethlehem(Palestine),one of the most historic structures in the world.To ensure the model quality,a 3D FE model was created using two types of typical commercial software,DIANA FEA and SAP2000.From analyses,one of the expected behaviors for this kind of masonry structure“low modal period”was found.The seismic behavior of the church was studied using pushover analyses,which were conducted using DIANA FEA.The first unidirectional mass proportional load pattern was created in both directions,X-direction as a longitudinal direction and Y-direction as the transversal direction.An incremental iterative procedure was used with monotonically increasing horizontal loads,using constant gravity loads.The results showed that the transversal direction is the most vulnerable and the damage concentrates at the main lateral(longitudinal)walls,mainly at the south and north alignment walls,and also at the vaults and at the connections of the vaults to the apse.Crack width was at the upper limit in the in-plane direction(X-direction).While,in Y-direction,it exceeded the limits of IBC code in width and length with a maximum width of 13.7 mm.A more accurate nonlinear dynamic analysis is recommended in the near future,which takes into account the material nonlinearity for more reasonable seismic behavior simulation.展开更多
Two linked models have been developed to explore the relationship between the amount of porosity arising in service from both radiolytic oxidation and fast neutron damage that influences both the strength and the forc...Two linked models have been developed to explore the relationship between the amount of porosity arising in service from both radiolytic oxidation and fast neutron damage that influences both the strength and the force-displacement(load-displacement)behaviour and crack propagation in pile grade A graphite used as a nuclear reactor moderator material.Firstly models of the microstructure of the porous graphite for both unirradiated and irradiated graphite are created.These form the input for the second stage,simulating fracture in lattice-type finite element models,which predicts force(load)-displacement and crack propagation paths.Microstructures comprising aligned filler particles,typical of needle coke,in a porous matrix have been explored.The purpose was to isolate the contributions of filler particles and porosity to fracture strength and crack paths and consider their implications for the overall failure of reactor core graphite.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
Microdamage accumulation and adaptation of subchondral bone subjected to intensive cyclic loading are important processes associated with catastrophic bone failure,and joint degeneration in athletic humans and racehor...Microdamage accumulation and adaptation of subchondral bone subjected to intensive cyclic loading are important processes associated with catastrophic bone failure,and joint degeneration in athletic humans and racehorses.At the tissue-level,they lead to a spatial variation in bone tissue mineral density(TMD)which affects the response of the bone to mechanical load.Quantifying the spatial distribution of mechanical load within the subchondral bone is critical for understanding the mechanism of the joint failure.Previously,a gradient of TMD and mechanical properties has been reported under unconfined compression in osteochondral plugs.In the present study,we used micro computed tomography(μCT)-based finite element(FE)models of cartilage-bone to investigate the gradient of strain in the subchondral bone(SCB)from the third metacarpal(MC3)condyle of racehorses under simulated in situ compression.Non-destructive mechanical testing of specimens under high-rate compression provided the apparent-level modulus of SCB.FE models were analysed using unconfined and confined boundary conditions.Unconfined FE-predicted apparent-level gradient of modulus across the SCB thickness correlated well with the experimental results(R^(2)=0.72,p<0.05).The highest strain occurred in the most superficial SCB(0.5–2.5 mm deep to the cartilage-bone interface)under the simulated in-situ compression through articular cartilage.The findings of this study provide an estimation for the spatial distribution of mechanical strain within SCB in-situ in the presence of heterogeneous bone tissue which is commonly observed in joints subjected to intensive cyclic loading.展开更多
Vibration at the stern area is generally the most severe of the entire ship hull,which has always attracted special attention by ship designers and researchers.With reference to a real ship structural layout,a scaled...Vibration at the stern area is generally the most severe of the entire ship hull,which has always attracted special attention by ship designers and researchers.With reference to a real ship structural layout,a scaled stern model of steel structure was innovatively designed to carry out the mode and response tests.Corresponding finite element(FE)model representing the tested structure was established for verification of commonly-used calculation methods of modal parameters and response.Good agreement between experimental and numerical results demonstrates the credibility of FE method,and some key points of modeling and calculating are discussed.In addition,with the combination of the experiment and calculation,some vibration characteristics of ship stern structure are summarized for future ship design guideline.展开更多
The mathematical models for dynamic distributed parameter systems are given by systems of partial differential equations. With nonlinear material properties, the corresponding finite element (FE) models are large syst...The mathematical models for dynamic distributed parameter systems are given by systems of partial differential equations. With nonlinear material properties, the corresponding finite element (FE) models are large systems of nonlinear ordinary differential equations. However, in most cases, the actual dynamics of interest involve only a few of the variables, for which model reduction strategies based on system theoretical concepts can be immensely useful. This paper considers the problem of controlling a three dimensional profile on nontrivial geometries. Dynamic model is obtained by discretizing the domain using FE method. A nonlinear control law is proposed which transfers any arbitrary initial temperature profile to another arbitrary desired one. The large dynamic model is reduced using proper orthogonal decomposition (POD). Finally, the stability of the control law is proved through Lyapunov analysis. Results of numerical implementation are presented and possible further extensions are identified.展开更多
During spinal fusion surgery,angled screw insertion can provide a more favorable stress distribution reducing failure events(screw breakage and loosening).Finite element(FE)analysis can be employed for identifying the...During spinal fusion surgery,angled screw insertion can provide a more favorable stress distribution reducing failure events(screw breakage and loosening).Finite element(FE)analysis can be employed for identifying the optimal insertion path,preventing stress concentrations,and ensuring a lower failure incidence.In this work,a patient-specific FE model of L4 vertebra,virtually implanted with two pedicle screws,was obtained from diagnostic images and numerically investigated.Linearly elastic,inhomogeneous,and isotropic material properties were assigned to bone based on density distributions reconstructed from the medical images.The mechanical response of the screws-vertebra system was analyzed through a progressive damage procedure,considering a stress-based criterion.Different screws insertion angles were simulated,as well as physiological loading conditions.In each loading case,screw orientation influences the fracture mechanism(i.e.,brittle or ductile one),as well as the fracture pattern and load.Besides,stresses in trabecular bone and pedicle screws are significantly affected by the screw configuration.The caudomedial trajectory indicates the most safe case,significantly reducing the stress concentrations in both trabecular bone and screws.Our findings aim to furnish a useful indication to surgeons regarding the screws insertion angle,further reducing the failure risk and improving the clinical outcome of the fixation procedure.展开更多
Increasing the bending capacity of reinforced concrete(RC)elements is one of important topics in structure engineering.The goal of this study is to develop a transferred stress system(TSS)on longitudinal reinforcement...Increasing the bending capacity of reinforced concrete(RC)elements is one of important topics in structure engineering.The goal of this study is to develop a transferred stress system(TSS)on longitudinal reinforcement bars for increasing the bending capacity of RC frames.The study is divided into two parts,i.e.,experimental tests and nonlinear FE analysis.The experiments were carried out to determine the load-deflection curves and crack patterns of the ordinary and TSS fixed frame.The FE models were developed for simulating the fixed frames.The obtained load-deflection results and the observed cracks from the FE analysis and experimental tests are compared to evaluate the validation of the FE nonlinear models.Based on the validated FE models,the stress distribution on the ordinary and TSS bars were evaluated.We found the load carrying capacity and ductility of TSS fixed beam are 29.39%and 23.69%higher compared to those of the ordinary fixed beams.The crack expansion occurs on the ordinary fixed beam,although there are several crack openings at mid-span of the TSS fixed beam.The crack distribution was changed in the TSS fixed frame.The TSS fixed beam is proposed to employ in RC frame instead of ordinary RC beam for improving the performance of RC frame.展开更多
文摘Curved twin I-girder bridges (CTIGBs) have low torsional stiffness that makes them vulnerable to dynamic loads. This study investigates the effects of bottom bracings on the torsional dynamic characteristics of CTIGBs. Five types of bottom bracings are designed to investigate their effects on the dynamic characteristics of CTIGBs with different curvatures under free and forced vibrations. To perform numerical investigations, three-dimensional (3-D) finite element (FE) bridge and vehicle models are established using commercial ANSYS code, and then a vehicle-bridge interaction analysis approach is proposed. Road roughness profiles generated from power spectral density and cross spectral functions are also taken into account in the analyses. The numerical results show that torsional frequencies increase significantly after providing bottom bracings, and the increasing rate depends on the type of bottom bracings and their locations of installation. Bottom bracings can act as load transmitting members from one main girder to the others. Large negative bearing forces that have occurred in bridges with small radii of curvatures can be remarkably reduced by providing bottom bracing systems. It is found that the performances of several bottom bracing systems are effective in improving the torsional dynamic characteristics of the bridges in this study.
基金Funded by the Chinese "973" Project (No.2010CB735811)
文摘In order to predict the plate curvature during snake rolling, FE model was constructed based on plane strain assumption. The accuracy of the FE model was verified by the comparison between the plate curvature conducted by FE model and experiment respectively. By using FE model, the effect of offset distance, speed ratio, reduction, roll radius and initial plate thickness on the plate curvature during snake rolling was investigated. The experimental results show that, a proper offsetting distance can efficiently decrease plate curvature, however an excessive offsetting distance will increase plate curvature. A larger speed ratio, reduction will cause a large plate curvature, however a larger roll radius has effect to reduce plate curvature. Plate which undergoes a larger reduction and plate with a larger initial thickness always need a larger offset distance to keep the plate the minimum plate curvature, but for a larger roll radius a smaller offset distance is needed.
文摘A simple modified analytic EAM model for bcc Fe and fcc Al was used to calculate the lattice constant and elastic constants of B2 FeAl and DO3 Fe3Al alloys. The formation energies of vacancy and antisite were also calculated. The present calculations are in agreement with the experimental data and the theoretical results obtained by other authors.
基金supported by National Natural Science Foundation of China(Grant No.51778314).
文摘The internal temperature of cast-in-place concrete bridges undergoes strong variations during the construction as a result of environmental factors.In order to determine precisely such variations,the present study relies on the finite element method,used to model the bridge box girder section and simulate the internal temperature distribution during construction.The numerical results display good agreement with measured temperature values.It is shown that when the external temperature is higher,and the internal and external temperature difference is relatively small,the deviation of the fitting line from existing specifications(Chinese specification,American specification,New Zealand specification)is relatively large and vice versa.
文摘We investigate the accuracy and robustness of moment tensor(MT)and stress inversion solutions derived from acoustic emissions(AEs)during the laboratory fracturing of prismatic Barre granite specimens.Pre-cut flaws in the specimens introduce a complex stress field,resulting in a spatial and temporal variation of focal mechanisms.Specifically,we consider two experimental setups:(1)where the rock is loaded in compression to generate primarily shear-type fractures and(2)where the material is loaded in indirect tension to generate predominantly tensile-type fractures.In each test,we first decompose AE moment tensors into double-couple(DC)and non-DC terms and then derive unambiguous normal and slip vectors using k-means clustering and an unstructured damped stress inversion algorithm.We explore temporal and spatial distributions of DC and non-DC events at different loading levels.The majority of the DC and the tensile non-DC events cluster around the pre-cut flaws,where macro-cracks later develop.Results of stress inversion are verified against the stress field from finite element(FE)modeling.A good agreement is found between the experimentally derived and numerically simulated stress orientations.To the best of the authors’knowledge,this work presents the first case where stress inversion methodologies are validated by numerical simulations at laboratory scale and under highly heterogeneous stress distributions.
基金supported by National Hi-tech Research and Development Program of China (863 Program,Grant No. 2006AA110101)"111 Program" of Ministry of Education and State Administration of Foreign Experts Affairs of China (Grant No. 111-2-11)+1 种基金General Motors Research and Development Center (Grant No. RD-209)Project of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body,Hunan University,China (Grant No. 60870004)
文摘Lower limb injures are frequently observed in passenger car traffic accidents.Previous studies of the injuries focus on long bone fractures by using either cadaver component tests or simulations of the long bone kinematics,which lack in-depth study on the fractures in stress analysis.This paper aims to investigate lower limb impact biomechanics in real-world car to pedestrian accidents and to predict fractures of long bones in term of stress parameter for femur,tibia,and fibula.For the above purposes,a 3D finite element(FE) model of human body lower limb(HBM-LL) is developed based on human anatomy.The model consists of the pelvis,femur,tibia,fibula,patella,foot bones,primary tendons,knee joint capsule,meniscus,and ligaments.The FE model is validated by comparing the results from a lateral impact between simulations and tests with cadaver lower limb specimens.Two real-world accidents are selected from an in-depth accident database with detailed information about the accident scene,car impact speed,damage to the car,and pedestrian injuries.Multi-body system(MBS) models are used to reconstruct the kinematics of the pedestrians in the two accidents and the impact conditions are calculated for initial impact velocity and orientations of the car and pedestrian during the collision.The FE model is used to perform injury reconstructions and predict the fractures by using physical parameters,such as von Mises stress of long bones.The calculated failure level of the long bones is correlated with the injury outcomes observed from the two accident cases.The reconstruction result shows that the HBM-LL FE model has acceptable biofidelity and can be applied to predict the risk of long bone fractures.This study provides an efficient methodology to investigate the long bone fracture suffered from vehicle traffic collisions.
基金US Department of Transportation through Alaska University Transportation Centerthe State of Alaska Department of Transportation and Public Facilities(AK DOT&PF)under Project AUTC#410015
文摘Lateral spread of frozen ground crust over liquefied soil has caused extensive bridge foundation damage in the past winter earthquakes.A shake table experiment was conducted to investigate the performance of a model pile in this scenario and revealed unique pile failure mechanisms.The modelling results provided valuable data for validating numerical models.This paper presents analyses and results of this experiment using two numerical modeling approaches: solid-fluid coupled finite element(FE) modeling and the beam-on-nonlinear-Winkler-foundation(BNWF) method.A FE model was constructed based on the experiment configuration and subjected to earthquake loading.Soil and pile response results were presented and compared with experimental results to validate this model.The BNWF method was used to predict the pile response and failure mechanism.A p-y curve was presented for modelling the frozen ground crust with the free-field displacement from the experiment as loading.Pile responses were presented and compared with those of the experiment and FE model.It was concluded that the coupled FE model was effective in predicting formation of three plastic hinges at ground surface,ground crust-liquefiable soil interface and within the medium dense sand layer,while the BNWF method was only able to predict the latter two.
基金National Natural Science Foundation of China(No. 10472031).
文摘This paper aims at investigating brain injury mechanisms and predicting head injuries in real world accidents. For this purpose, a 3D human head finite element model (HBM-head) was developed based on head-brain anatomy. The HBM head model was validated with two experimental tests. Then the head finite element(FE) model and a multi-body system (MBS) model were used to carry out reconstructions of real world vehicle-pedestrian accidents and brain injuries. The MBS models were used for calculating the head impact conditions in vehicle impacts. The HBM-head model was used for calculating the injury related physical parameters, such as intracranial pressure, stress, and strain. The calculated intracranial pressure and strain distribution were correlated with the injury outcomes observed from accidents. It is shown that this model can predict the intracranial biomechanical response and calculate the injury related physical parameters. The head FE model has good biofidelity and will be a valuable tool for the study of injury mechanisms and the tolerance level of the brain.
基金supported in part by the National Natural Science Foundation of China (Grant 81370438)the SJTU Medical-Engineering Cross-cutting Research Project (Grant YG2015MS53)supported by the Hui-Chun Chin and Tsung-Dao Lee Chinese Undergraduate Research Program Endowment
文摘An inflatable cuff wrapped around the upper arm is widely used in noninvasive blood pressure measurement.However, the mechanical interaction between cuff and arm tissues, a factor that potentially affects the accuracy of noninvasive blood pressure measurement, remains rarely addressed. In the present study, finite element(FE) models were constructed to quantify intra-arm stresses generated by cuff compression, aiming to provide some theoretical evidence for identifying factors of importance for blood pressure measurement or explaining clinical observations. Obtained results showed that the simulated tissue stresses were highly sensitive to the distribution of cuff pressure on the arm surface and the contact condition between muscle and bone. In contrast, the magnitude of cuff pressure and small variations in elastic properties of arm soft tissues had little influence on the efficiency of pressure transmission in arm tissues. In particular, it was found that a thickened subcutaneous fat layer in obese subjects significantly reduced the effective pressure transmitted to the brachial artery, which may explain why blood pressure overestimation occurs more frequently in obese subjects in noninvasive blood pressure measurement.
基金National Program on Key Basic Research Project of China(973) under Grant No.2011CB013603the National Natural Science Foundation of China under Grant Nos.51427901,91315301 and 51408410the Natural Science Foundation of Tianjin,China under Grant No.15JCQNJC07200
文摘Previous failure analyses of bridges typically focus on substructure failure or superstructure failure separately. However, in an actual bridge, the seismic induced substructure failure and superstructure failure may influence each other. Moreover, previous studies typically use simplified models to analyze the bridge failure; however, there are inherent defects in the calculation accuracy compared with using a detailed three-dimensional (3D) finite element (FE) model. Conversely, a detailed 3D FE model requires more computational costs, and a proper erosion criterion of the 3D elements is necessary. In this paper, a multi-scale FE model, including a corresponding erosion criterion, is proposed and validated that can significantly reduce computational costs with high precision by modelling a pseudo-dynamic test of an reinforced concrete (RC) pier. Numerical simulations of the seismic failures of a continuous RC bridge based on the multi-scale FE modeling method using LS-DYNA are performed. The nonlinear properties of the bridge, various connection strengths and bidirectional excitations are considered. The numerical results demonstrate that the failure of the connections will induce large pounding responses of the girders. The nonlinear deformation of the piers will aggravate the pounding damages. Furthermore, bidirectional earthquakes will induce eccentric poundingsto the girders and different failure modes to the adjacent piers.
文摘This study focuses on advanced finite element(FE)analyses on The Church of Nativity located in Bethlehem(Palestine),one of the most historic structures in the world.To ensure the model quality,a 3D FE model was created using two types of typical commercial software,DIANA FEA and SAP2000.From analyses,one of the expected behaviors for this kind of masonry structure“low modal period”was found.The seismic behavior of the church was studied using pushover analyses,which were conducted using DIANA FEA.The first unidirectional mass proportional load pattern was created in both directions,X-direction as a longitudinal direction and Y-direction as the transversal direction.An incremental iterative procedure was used with monotonically increasing horizontal loads,using constant gravity loads.The results showed that the transversal direction is the most vulnerable and the damage concentrates at the main lateral(longitudinal)walls,mainly at the south and north alignment walls,and also at the vaults and at the connections of the vaults to the apse.Crack width was at the upper limit in the in-plane direction(X-direction).While,in Y-direction,it exceeded the limits of IBC code in width and length with a maximum width of 13.7 mm.A more accurate nonlinear dynamic analysis is recommended in the near future,which takes into account the material nonlinearity for more reasonable seismic behavior simulation.
文摘Two linked models have been developed to explore the relationship between the amount of porosity arising in service from both radiolytic oxidation and fast neutron damage that influences both the strength and the force-displacement(load-displacement)behaviour and crack propagation in pile grade A graphite used as a nuclear reactor moderator material.Firstly models of the microstructure of the porous graphite for both unirradiated and irradiated graphite are created.These form the input for the second stage,simulating fracture in lattice-type finite element models,which predicts force(load)-displacement and crack propagation paths.Microstructures comprising aligned filler particles,typical of needle coke,in a porous matrix have been explored.The purpose was to isolate the contributions of filler particles and porosity to fracture strength and crack paths and consider their implications for the overall failure of reactor core graphite.
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funded by Racing Victoria Limited and the Victorian Racing Industry Fund of the Victorian State Government and The University of Melbourne.
文摘Microdamage accumulation and adaptation of subchondral bone subjected to intensive cyclic loading are important processes associated with catastrophic bone failure,and joint degeneration in athletic humans and racehorses.At the tissue-level,they lead to a spatial variation in bone tissue mineral density(TMD)which affects the response of the bone to mechanical load.Quantifying the spatial distribution of mechanical load within the subchondral bone is critical for understanding the mechanism of the joint failure.Previously,a gradient of TMD and mechanical properties has been reported under unconfined compression in osteochondral plugs.In the present study,we used micro computed tomography(μCT)-based finite element(FE)models of cartilage-bone to investigate the gradient of strain in the subchondral bone(SCB)from the third metacarpal(MC3)condyle of racehorses under simulated in situ compression.Non-destructive mechanical testing of specimens under high-rate compression provided the apparent-level modulus of SCB.FE models were analysed using unconfined and confined boundary conditions.Unconfined FE-predicted apparent-level gradient of modulus across the SCB thickness correlated well with the experimental results(R^(2)=0.72,p<0.05).The highest strain occurred in the most superficial SCB(0.5–2.5 mm deep to the cartilage-bone interface)under the simulated in-situ compression through articular cartilage.The findings of this study provide an estimation for the spatial distribution of mechanical strain within SCB in-situ in the presence of heterogeneous bone tissue which is commonly observed in joints subjected to intensive cyclic loading.
文摘Vibration at the stern area is generally the most severe of the entire ship hull,which has always attracted special attention by ship designers and researchers.With reference to a real ship structural layout,a scaled stern model of steel structure was innovatively designed to carry out the mode and response tests.Corresponding finite element(FE)model representing the tested structure was established for verification of commonly-used calculation methods of modal parameters and response.Good agreement between experimental and numerical results demonstrates the credibility of FE method,and some key points of modeling and calculating are discussed.In addition,with the combination of the experiment and calculation,some vibration characteristics of ship stern structure are summarized for future ship design guideline.
文摘The mathematical models for dynamic distributed parameter systems are given by systems of partial differential equations. With nonlinear material properties, the corresponding finite element (FE) models are large systems of nonlinear ordinary differential equations. However, in most cases, the actual dynamics of interest involve only a few of the variables, for which model reduction strategies based on system theoretical concepts can be immensely useful. This paper considers the problem of controlling a three dimensional profile on nontrivial geometries. Dynamic model is obtained by discretizing the domain using FE method. A nonlinear control law is proposed which transfers any arbitrary initial temperature profile to another arbitrary desired one. The large dynamic model is reduced using proper orthogonal decomposition (POD). Finally, the stability of the control law is proved through Lyapunov analysis. Results of numerical implementation are presented and possible further extensions are identified.
基金The authors acknowledge the support of the Italian National Group for Mathematical Physics(GNFM-INdAM).
文摘During spinal fusion surgery,angled screw insertion can provide a more favorable stress distribution reducing failure events(screw breakage and loosening).Finite element(FE)analysis can be employed for identifying the optimal insertion path,preventing stress concentrations,and ensuring a lower failure incidence.In this work,a patient-specific FE model of L4 vertebra,virtually implanted with two pedicle screws,was obtained from diagnostic images and numerically investigated.Linearly elastic,inhomogeneous,and isotropic material properties were assigned to bone based on density distributions reconstructed from the medical images.The mechanical response of the screws-vertebra system was analyzed through a progressive damage procedure,considering a stress-based criterion.Different screws insertion angles were simulated,as well as physiological loading conditions.In each loading case,screw orientation influences the fracture mechanism(i.e.,brittle or ductile one),as well as the fracture pattern and load.Besides,stresses in trabecular bone and pedicle screws are significantly affected by the screw configuration.The caudomedial trajectory indicates the most safe case,significantly reducing the stress concentrations in both trabecular bone and screws.Our findings aim to furnish a useful indication to surgeons regarding the screws insertion angle,further reducing the failure risk and improving the clinical outcome of the fixation procedure.
文摘Increasing the bending capacity of reinforced concrete(RC)elements is one of important topics in structure engineering.The goal of this study is to develop a transferred stress system(TSS)on longitudinal reinforcement bars for increasing the bending capacity of RC frames.The study is divided into two parts,i.e.,experimental tests and nonlinear FE analysis.The experiments were carried out to determine the load-deflection curves and crack patterns of the ordinary and TSS fixed frame.The FE models were developed for simulating the fixed frames.The obtained load-deflection results and the observed cracks from the FE analysis and experimental tests are compared to evaluate the validation of the FE nonlinear models.Based on the validated FE models,the stress distribution on the ordinary and TSS bars were evaluated.We found the load carrying capacity and ductility of TSS fixed beam are 29.39%and 23.69%higher compared to those of the ordinary fixed beams.The crack expansion occurs on the ordinary fixed beam,although there are several crack openings at mid-span of the TSS fixed beam.The crack distribution was changed in the TSS fixed frame.The TSS fixed beam is proposed to employ in RC frame instead of ordinary RC beam for improving the performance of RC frame.