In order to study buckling propagation mechanism in deep sea pipelines, the contact between pipeline's inner walls in buckling process was studied. A two-dimensional ring model was used to represent the pipeline a...In order to study buckling propagation mechanism in deep sea pipelines, the contact between pipeline's inner walls in buckling process was studied. A two-dimensional ring model was used to represent the pipeline and a nonlinear spring model was adopted to simulate the contact between inner walls. Based on the elastoplastic constitutive relationship and the principle of virtual work theory, the coupling effect of pipeline's nonlinear large deformation and wall contact was included in the theoretical analysis with the aid of MATLAB, and the application scope of the theoretical model was also discussed. The calculated results show that during the loading process, the change in external pressure is closely related to the distribution of section stress, and once the walls are contacting each other, the external pressure increases and then remains stable after it reaches a specific value. Without fracture, the pipeline section will stop showing deformation. The results of theoretical calculations agree well with those of numerical simulations. Finally, in order to ensure reliability and accuracy of the theoretical results, the collapse pressure and propagation pressure were both verified by numerical simulations and experiments. Therefore, the theoretical model can be used to analyze pipeline's buckling deformation and contact between pipeline's inner walls, which forms the basis for further research on three-dimensional buckling propagation.展开更多
In order to theoretically study the buckle propagation of subsea pipelines with slip-on buckle arrestors, a two-dimensional ring model was set up to represent the pipeline and a nonlinear spring model was adopted to s...In order to theoretically study the buckle propagation of subsea pipelines with slip-on buckle arrestors, a two-dimensional ring model was set up to represent the pipeline and a nonlinear spring model was adopted to simulate the contact between pipeline's inner walls and between pipeline's outer wall and slip-on buckle arrestor's inner wall during buckle propagation. In addition, some reverse springs are added to prevent the wall of left and right sides separating from the inner wall of slip-on buckle arrestors. Considering large deformation kinematics relations and the elastic-plastic constitutive relation of material, balance equations were established with the principle of virtual work. The variation of external pressure with respect to the cross-sectional area of pipelines was analyzed, and the lower bound of the crossover pressure of slip-on buckle arrestors was calculated based on Maxwell's energy balance method. By comparing the theoretical results with experiment and finite element numerical simulation, the theoretical method is proved to be correct and reliable.展开更多
This study provides a comprehensive analysis of collision and impact problems’ numerical solutions, focusing ongeometric, contact, and material nonlinearities, all essential in solving large deformation problems duri...This study provides a comprehensive analysis of collision and impact problems’ numerical solutions, focusing ongeometric, contact, and material nonlinearities, all essential in solving large deformation problems during a collision.The initial discussion revolves around the stress and strain of large deformation during a collision, followedby explanations of the fundamental finite element solution method for addressing such issues. The hourglassmode’s control methods, such as single-point reduced integration and contact-collision algorithms are detailedand implemented within the finite element framework. The paper further investigates the dynamic responseand failure modes of Reinforced Concrete (RC) members under asymmetrical impact using a 3D discrete modelin ABAQUS that treats steel bars and concrete connections as bond slips. The model’s validity was confirmedthrough comparisons with the node-sharing algorithm and system energy relations. Experimental parameterswere varied, including the rigid hammer’s mass and initial velocity, concrete strength, and longitudinal and stirrupreinforcement ratios. Findings indicated that increased hammer mass and velocity escalated RC member damage,while increased reinforcement ratios improved impact resistance. Contrarily, increased concrete strength did notsignificantly reduce lateral displacement when considering strain rate effects. The study also explores materialnonlinearity, examining different materials’ responses to collision-induced forces and stresses, demonstratedthrough an elastic rod impact case study. The paper proposes a damage criterion based on the residual axialload-bearing capacity for assessing damage under the asymmetrical impact, showing a correlation betweendamage degree hammer mass and initial velocity. The results, validated through comparison with theoreticaland analytical solutions, verify the ABAQUS program’s accuracy and reliability in analyzing impact problems,offering valuable insights into collision and impact problems’ nonlinearities and practical strategies for enhancingRC structures’ resilience under dynamic stress.展开更多
The lack of research on flexible drilling tool leads to limited application of ultra-short radius horizontal wells.The flexible drilling tool is different from the conventional drilling tool.The flexible drilling pipe...The lack of research on flexible drilling tool leads to limited application of ultra-short radius horizontal wells.The flexible drilling tool is different from the conventional drilling tool.The flexible drilling pipe involves a mutual transition between the structure and the mechanism during the deformation process.At the same time,the flexible drilling pipe and the eccentric guide tube,the guide tube and the wellbore generate random contact.In this paper,3-D beam elements,universal joint elements,rigid beam elements and the beam-beam contact elements are combined to establish a two-layer contact nonlinear finite element model of the flexible drilling tool in the wellbore.The dynamic relaxation method is introduced for numerical solution.The feasibility of the model and the algorithm is verified by an example.The mechanical analysis of flexible drilling tool under the four hole inclinations in the oblique section is carried out.It is found that the flexible drilling pipe has a“folded line”deformation.The contact force between the flexible drilling pipe and the guide tube is randomly distributed.The contact force between the guide tube and the wellbore in the oblique section is greater than that in the vertical section.As the hole inclinations increase,the torque and axial force transmitted to the drill bit gradually decrease.展开更多
模态分析是水电机组故障诊断的重要方法,但其传统方法缺少对接触部分非线性接触的模拟手段,直接影响模态分析的准确性,也无法对链接部位的失效过程及趋势进行分析。该文基于用户自定义单元子程序接口(user-defined element subroutine i...模态分析是水电机组故障诊断的重要方法,但其传统方法缺少对接触部分非线性接触的模拟手段,直接影响模态分析的准确性,也无法对链接部位的失效过程及趋势进行分析。该文基于用户自定义单元子程序接口(user-defined element subroutine interface,UEL),建立了结合部三维非线性专用分析单元模型。推导所提模型有限元格式的基本方程,获得表征材料非线性特性的本构关系;给出螺栓连接的固定结合部的静态分析,以及立式水轮发电机导轴承支架的模态分析算例;给出导轴承支架的支臂末端螺栓连接变刚度计算的工程应用实例。实验与仿真对比结果表明了建立的UEL三维非线性接触分析专用单元模型的正确性;连接失效分析表明了随着导轴承支架接触刚度的下降,会在整机模态频率计算中引入新的频率段这一结果的重要性。展开更多
A mathematical program is proposed for the highly nonlinear problem involving frictional contact. A program-pattern using the fast multipole boundary element method (FM- BEM) is given for 3-D elastic contact with fric...A mathematical program is proposed for the highly nonlinear problem involving frictional contact. A program-pattern using the fast multipole boundary element method (FM- BEM) is given for 3-D elastic contact with friction to replace the Monte Carlo method. A new optimized generalized minimal residual (GMRES) algorithm is presented. Numerical examples demonstrate the validity of the program-pattern optimization model for node-to-surface contact with friction. The GMRES algorithm greatly improves the computational efciency.展开更多
Nonlinear dynamic response represents the most important studies for structures subjected to a dynamic mo-tion so that it provides the researcher by an excellent information especially at critical design levels. The u...Nonlinear dynamic response represents the most important studies for structures subjected to a dynamic mo-tion so that it provides the researcher by an excellent information especially at critical design levels. The un-predictable nonlinearity in the structure appears when damage is inherited. Most times, the failure of the structure is related to the dynamic nonlinearity. With regard to the breathing phenomena for nonlinear struc-tural systems, very little is known about how the nonlinearities influence the response and the dynamic char-acteristics of cracked structures. In this research, dynamic nonlinearity is presented in damaged structure due to presence of a crack. The crack is assumed to be open and close simultaneously and then breathing. Effect of breathing phenomenon was studied deeply. Crack breathing is simulated at the crack surfaces using con-tact elements. The contact, geometrical, penalty, and spin stiffnesses are taken in consideration. In addition, effect of several important parameters such as rotor angular velocity and crack ratio are studied. The study showed that the breathing natural frequency of any structure is ranged between opened (no contact) and closed crack natural frequencies. The larger crack length, the more nonlinear disturbance in the dynamic re-sponse behavior. Also, at a critical crack length, some mode shapes tend to exchange and pass over with other modes. The presence of the mode interchanging and mode crossover was a guide on the nonlinear re-sponse for the cracked structure. The numerical modeling is achieved using ANSYS finite element program. Experimental data are used for validating the accurate use of contact elements in ANSYS environment.展开更多
To study the dynamic characteristics and damping mechanism of impact-contact between the tips of blades further more,the impact-contact between the tips of a pair of blades was studied through numerical simulation.In ...To study the dynamic characteristics and damping mechanism of impact-contact between the tips of blades further more,the impact-contact between the tips of a pair of blades was studied through numerical simulation.In this paper,the dynamic equation of contact-impact between the tips was established and Newmark direct integration method was adopted in numerical simulation.The nonlinear response characteristics and damping mechanism of impact-contact system are obtained.The results of numerical simulation were obtained as follows:As the clearance between blade shrouds is smaller,the vibration amplitude is smaller.The clearance between blade shrouds has a great influence on the input energy of the aerodynamic-excitation-vibration force.As the clearance of blade shrouds increases,the input energy of the aerodynamic-excitation-vibration force increases rapidly.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 51239008 and 51179126)the National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2011ZX05026-005)
文摘In order to study buckling propagation mechanism in deep sea pipelines, the contact between pipeline's inner walls in buckling process was studied. A two-dimensional ring model was used to represent the pipeline and a nonlinear spring model was adopted to simulate the contact between inner walls. Based on the elastoplastic constitutive relationship and the principle of virtual work theory, the coupling effect of pipeline's nonlinear large deformation and wall contact was included in the theoretical analysis with the aid of MATLAB, and the application scope of the theoretical model was also discussed. The calculated results show that during the loading process, the change in external pressure is closely related to the distribution of section stress, and once the walls are contacting each other, the external pressure increases and then remains stable after it reaches a specific value. Without fracture, the pipeline section will stop showing deformation. The results of theoretical calculations agree well with those of numerical simulations. Finally, in order to ensure reliability and accuracy of the theoretical results, the collapse pressure and propagation pressure were both verified by numerical simulations and experiments. Therefore, the theoretical model can be used to analyze pipeline's buckling deformation and contact between pipeline's inner walls, which forms the basis for further research on three-dimensional buckling propagation.
基金supported by the National Natural Science Foundation of China (Grant No. 51609222)the Natural Science Foundation of Shandong Province (Grant No. ZR2016EEB03)+2 种基金the Opening Fund of State Key Laboratory of Coastal and Offshore Engineering (Dalian University of Technology) (Grant No. LP1505)the Opening Fund of State Key Laboratory of Hydraulic Engineering Simulation and Safety (Tianjin University) (Grant No. HESS-1602)the Fundamental Research Funds for the Central Universities (Grant No. 201513039)
文摘In order to theoretically study the buckle propagation of subsea pipelines with slip-on buckle arrestors, a two-dimensional ring model was set up to represent the pipeline and a nonlinear spring model was adopted to simulate the contact between pipeline's inner walls and between pipeline's outer wall and slip-on buckle arrestor's inner wall during buckle propagation. In addition, some reverse springs are added to prevent the wall of left and right sides separating from the inner wall of slip-on buckle arrestors. Considering large deformation kinematics relations and the elastic-plastic constitutive relation of material, balance equations were established with the principle of virtual work. The variation of external pressure with respect to the cross-sectional area of pipelines was analyzed, and the lower bound of the crossover pressure of slip-on buckle arrestors was calculated based on Maxwell's energy balance method. By comparing the theoretical results with experiment and finite element numerical simulation, the theoretical method is proved to be correct and reliable.
基金the authority of the National Natural Science Foundation of China(Grant Nos.52178168 and 51378427)for financing this research work and several ongoing research projects related to structural impact performance.
文摘This study provides a comprehensive analysis of collision and impact problems’ numerical solutions, focusing ongeometric, contact, and material nonlinearities, all essential in solving large deformation problems during a collision.The initial discussion revolves around the stress and strain of large deformation during a collision, followedby explanations of the fundamental finite element solution method for addressing such issues. The hourglassmode’s control methods, such as single-point reduced integration and contact-collision algorithms are detailedand implemented within the finite element framework. The paper further investigates the dynamic responseand failure modes of Reinforced Concrete (RC) members under asymmetrical impact using a 3D discrete modelin ABAQUS that treats steel bars and concrete connections as bond slips. The model’s validity was confirmedthrough comparisons with the node-sharing algorithm and system energy relations. Experimental parameterswere varied, including the rigid hammer’s mass and initial velocity, concrete strength, and longitudinal and stirrupreinforcement ratios. Findings indicated that increased hammer mass and velocity escalated RC member damage,while increased reinforcement ratios improved impact resistance. Contrarily, increased concrete strength did notsignificantly reduce lateral displacement when considering strain rate effects. The study also explores materialnonlinearity, examining different materials’ responses to collision-induced forces and stresses, demonstratedthrough an elastic rod impact case study. The paper proposes a damage criterion based on the residual axialload-bearing capacity for assessing damage under the asymmetrical impact, showing a correlation betweendamage degree hammer mass and initial velocity. The results, validated through comparison with theoreticaland analytical solutions, verify the ABAQUS program’s accuracy and reliability in analyzing impact problems,offering valuable insights into collision and impact problems’ nonlinearities and practical strategies for enhancingRC structures’ resilience under dynamic stress.
基金support from the Natural Science Foundation of China(Grant numbers:51674088)supported by National Natural Science Foundation of China(Grant No.51674088).
文摘The lack of research on flexible drilling tool leads to limited application of ultra-short radius horizontal wells.The flexible drilling tool is different from the conventional drilling tool.The flexible drilling pipe involves a mutual transition between the structure and the mechanism during the deformation process.At the same time,the flexible drilling pipe and the eccentric guide tube,the guide tube and the wellbore generate random contact.In this paper,3-D beam elements,universal joint elements,rigid beam elements and the beam-beam contact elements are combined to establish a two-layer contact nonlinear finite element model of the flexible drilling tool in the wellbore.The dynamic relaxation method is introduced for numerical solution.The feasibility of the model and the algorithm is verified by an example.The mechanical analysis of flexible drilling tool under the four hole inclinations in the oblique section is carried out.It is found that the flexible drilling pipe has a“folded line”deformation.The contact force between the flexible drilling pipe and the guide tube is randomly distributed.The contact force between the guide tube and the wellbore in the oblique section is greater than that in the vertical section.As the hole inclinations increase,the torque and axial force transmitted to the drill bit gradually decrease.
文摘模态分析是水电机组故障诊断的重要方法,但其传统方法缺少对接触部分非线性接触的模拟手段,直接影响模态分析的准确性,也无法对链接部位的失效过程及趋势进行分析。该文基于用户自定义单元子程序接口(user-defined element subroutine interface,UEL),建立了结合部三维非线性专用分析单元模型。推导所提模型有限元格式的基本方程,获得表征材料非线性特性的本构关系;给出螺栓连接的固定结合部的静态分析,以及立式水轮发电机导轴承支架的模态分析算例;给出导轴承支架的支臂末端螺栓连接变刚度计算的工程应用实例。实验与仿真对比结果表明了建立的UEL三维非线性接触分析专用单元模型的正确性;连接失效分析表明了随着导轴承支架接触刚度的下降,会在整机模态频率计算中引入新的频率段这一结果的重要性。
基金Project(11972112)supported by the National Natural Science Foundation of ChinaProject(N2103024)supported by the Fundamental Research Funds for the Central Universities,China。
基金Project supported by the National Natural Science Foundation of China(No.50075075).
文摘A mathematical program is proposed for the highly nonlinear problem involving frictional contact. A program-pattern using the fast multipole boundary element method (FM- BEM) is given for 3-D elastic contact with friction to replace the Monte Carlo method. A new optimized generalized minimal residual (GMRES) algorithm is presented. Numerical examples demonstrate the validity of the program-pattern optimization model for node-to-surface contact with friction. The GMRES algorithm greatly improves the computational efciency.
文摘Nonlinear dynamic response represents the most important studies for structures subjected to a dynamic mo-tion so that it provides the researcher by an excellent information especially at critical design levels. The un-predictable nonlinearity in the structure appears when damage is inherited. Most times, the failure of the structure is related to the dynamic nonlinearity. With regard to the breathing phenomena for nonlinear struc-tural systems, very little is known about how the nonlinearities influence the response and the dynamic char-acteristics of cracked structures. In this research, dynamic nonlinearity is presented in damaged structure due to presence of a crack. The crack is assumed to be open and close simultaneously and then breathing. Effect of breathing phenomenon was studied deeply. Crack breathing is simulated at the crack surfaces using con-tact elements. The contact, geometrical, penalty, and spin stiffnesses are taken in consideration. In addition, effect of several important parameters such as rotor angular velocity and crack ratio are studied. The study showed that the breathing natural frequency of any structure is ranged between opened (no contact) and closed crack natural frequencies. The larger crack length, the more nonlinear disturbance in the dynamic re-sponse behavior. Also, at a critical crack length, some mode shapes tend to exchange and pass over with other modes. The presence of the mode interchanging and mode crossover was a guide on the nonlinear re-sponse for the cracked structure. The numerical modeling is achieved using ANSYS finite element program. Experimental data are used for validating the accurate use of contact elements in ANSYS environment.
文摘To study the dynamic characteristics and damping mechanism of impact-contact between the tips of blades further more,the impact-contact between the tips of a pair of blades was studied through numerical simulation.In this paper,the dynamic equation of contact-impact between the tips was established and Newmark direct integration method was adopted in numerical simulation.The nonlinear response characteristics and damping mechanism of impact-contact system are obtained.The results of numerical simulation were obtained as follows:As the clearance between blade shrouds is smaller,the vibration amplitude is smaller.The clearance between blade shrouds has a great influence on the input energy of the aerodynamic-excitation-vibration force.As the clearance of blade shrouds increases,the input energy of the aerodynamic-excitation-vibration force increases rapidly.