Using the complex variable method and conformal mapping,scat- tering of flexural waves and dynamic stress concentrations in Mindlin's thick plates with a cutout have been studied.The general solution of the stress...Using the complex variable method and conformal mapping,scat- tering of flexural waves and dynamic stress concentrations in Mindlin's thick plates with a cutout have been studied.The general solution of the stress problem of the thick plate satisfying the boundary conditions on the contour of cutouts is obtained. Applying the orthogonal function expansion technique,the dynamic stress problem can be reduced into the solution of a set of infinite algebraic equations.As examples, numerical results for the dynamic stress concentration factor in Mindlin's plates with a circular,elliptic cutout are graphically presented in sequence.展开更多
Fault is a common geological structure that has been revealed in the process of underground coal excavation and mining.The nature of its discontinuous structure controls the deformation,damage,and mechanics of the coa...Fault is a common geological structure that has been revealed in the process of underground coal excavation and mining.The nature of its discontinuous structure controls the deformation,damage,and mechanics of the coal or rock mass.The interaction between this discontinuous structure and mining activities is a key factor that dominates fault reactivation and the coal burst it can induce.This paper first summarizes investigations into the relationships between coal mining layouts and fault occurrences,along with relevant conceptual models for fault reactivation.Subsequently,it proposes mechanisms of fault reactivation and its induced coal burst based on the superposition of static and dynamic stresses,which include two kinds of fault reactivations from:mining-induced quasi-static stress(FRMSS)-dominated and seismic-based dynamic stress(FRSDS)-dominated.These two kinds of fault reactivations are then validated by the results of experimental investigations,numerical modeling,and in situ microseismic monitoring.On this basis,monitoring methods and prevention strategies for fault-induced coal burst are discussed and recommended.The results show that fault-induced coal burst is triggered by the superposition of high static stress in the fault pillar and dynamic stress from fault reactivation.High static stress comes from the interaction of the fault and the roof structure,and dynamic stress can be ascribed to FRMSS and FRSDS.The results in this paper could be of great significance in guiding the monitoring and prevention of fault-induced coal bursts.展开更多
Current research on the operational reliability of centrifugal pumps has mainly focused on hydrodynamic instability. However, the interaction between the fluid and structure has not been sufficiently considered; this ...Current research on the operational reliability of centrifugal pumps has mainly focused on hydrodynamic instability. However, the interaction between the fluid and structure has not been sufficiently considered; this interaction can cause vibration and dynamic stress, which can affect the reliability. In this study, the dynamic stresses in a single-blade centrifugal pump impeller are analysed under different operating conditions; the two-way coupling method is used to calculate the fluid-structure interaction. Three-dimensional unsteady Reynolds-averaged Navier-Stokes equations are solved with the SST k-o9 turbulence model for the fluid in the whole flow passage, while transient structure dynamic analysis is used with the finite element method for the structure side. The dynamic stresses in the rotor system are computed according to the fourth strength theory. The stress results show that the highest stress is near the loose bearing and that the equivalent stress increases with the flow rate because the dynamic stresses are closely related to the pressure load. The stress distributions on the blade pressure side, suction side, leading edge, and trailing edge are each analysed for different flow rates; the highest stress distribution is found on the pressure side. On the blade pressure side, a relatively large stress is found near the trailing edge and hub side. Based on these results, a stress distribution prediction method is proposed for centrifugal pumps, which considers the interaction between the fluid and structuxe. The method can be used to check the dynamic stress at different flow rates when optimising the pump design to increase the pump reliability.展开更多
In this study,the tomography of dynamic stress coefficient(TDSC)was established based on a mechanical model of stress wave propagation in bedding planes and a mathematical model of the stress wave attenuation in rock ...In this study,the tomography of dynamic stress coefficient(TDSC)was established based on a mechanical model of stress wave propagation in bedding planes and a mathematical model of the stress wave attenuation in rock masses.The reliability of the TDSC was verified by a linear bedding plane model and field monitoring.Generally,the TDSC in the dynamic stress propagation of bedding planes increases with the following conditions:(1)the increase of the normal stiffness of the bedding plane,(2)the increase of the incident angle of the stress wave,(3)the decrease of the incident frequency of the stress wave,or(4)the growth of three ratios(the ratios of rock densities,elastic moduli,and the Poisson’s ratios)of rocks on either side of bedding planes.The additional stress weakens TDSC linearly and slowly during the stress wave propagation in bedding planes,and the weakening effect increases with the growth of the three ratios.Besides,the TDSC decreases exponentially in the rock mass as propagation distance increases.In a field case,the TDSC decreases significantly as vertical and horizontal distances increase and its wave range increases as vertical distance increases in the sedimentary rock layers.展开更多
In this paper,the dynamic stress concentration and scattering of SH-waves by bi-material structures that possess an interface elliptic cavity are investigated.First,by using the complex function method,the Green's...In this paper,the dynamic stress concentration and scattering of SH-waves by bi-material structures that possess an interface elliptic cavity are investigated.First,by using the complex function method,the Green's function is constructed.This yields the solution of the displacement field for an elastic half space with a semi-elliptic canyon impacted by an anti-plane harmonic line source loading on the horizontal surface.Then,the problem is divided into an upper and lower half space along the horizontal interface,regarded as a harmony model.In order to satisfy the integral continuity condition, the unknown anti-plane forces are applied to the interface.The integral equations with unknown forces can be established through the continuity condition,and after transformation,the algebraic equations are solved numerically.Finally,the distribution of the dynamic stress concentration factor(DSCF)around the elliptic cavity is given and the effect of different parameters on DSCF is discussed.展开更多
A mathematical model was developed for layout optimization of truss structures with discrete variables subjected to dynamic stress, dynamic displacement and dynamic stability constraints. By using the quasi-static met...A mathematical model was developed for layout optimization of truss structures with discrete variables subjected to dynamic stress, dynamic displacement and dynamic stability constraints. By using the quasi-static method, the mathematical model of structure optimization under dynamic stress, dynamic displacement and dynamic stability constraints were transformed into one subjected to static stress, displacement and stability constraints. The optimization procedures include two levels, i.e., the topology optimization and the shape optimization. In each level, the comprehensive algorithm was used and the relative difference quotients of two kinds of variables were used to search the optimum solution. A comparison between the optimum results of model with stability constraints and the optimum results of model without stability constraint was given. And that shows the stability constraints have a great effect on the optimum solutions.展开更多
This paper studies the dynamic stress intensity factor (DSIF) at the interface in an adhesive joint under shear loading. Material damage is considered. By introducing the dislocation density function and using the i...This paper studies the dynamic stress intensity factor (DSIF) at the interface in an adhesive joint under shear loading. Material damage is considered. By introducing the dislocation density function and using the integral transform, the problem is reduced to algebraic equations and can be solved with the collocation dots method in the Laplace domain. Time response of DSIF is calculated with the inverse Laplace integral transform. The results show that the mode Ⅱ DSIF increases with the shear relaxation parameter, shear module and Poisson ratio, while decreases with the swell relaxation parameter. Damage shielding only occurs at the initial stage of crack propagation. The singular index of crack tip is -0.5 and independent on the material parameters, damage conditions of materials, and time. The oscillatory index is controlled by viscoelastic material parameters.展开更多
Since a self-elevating platform often works in water for a long time, the lattice leg is largely influenced by wave and current. The amplitude of leg joint stresses is a very important factor for the fatigue life of t...Since a self-elevating platform often works in water for a long time, the lattice leg is largely influenced by wave and current. The amplitude of leg joint stresses is a very important factor for the fatigue life of the platform. However, there are not many researches having been done on the mechanism and dynamic stress analysis of these leg joints. This paper focuses on the dynamic stress analysis and suppression methods of the leg joints of self-elevating platforms. Firstly, the dynamic stresses of the lattice leg joints are analyzed for a self-elevating platform by use of the 5th-order Stokes wave theory. Secondly, the axial and bending stresses are studied due to their large contributions to total stresses. And then, different joint types are considered and the leg-hull interface stiffness is analyzed for the improvement of the joint dynamic stress amplitude. Finally, some useful conclusions are drawn for the optimization design of the self-elevating platform.展开更多
By using the complex variable method and conformal mapping, the diffraction of flexural waves and dynamic stress concentrations in thick plates with a cavity have been studied. A general solution of the stress problem...By using the complex variable method and conformal mapping, the diffraction of flexural waves and dynamic stress concentrations in thick plates with a cavity have been studied. A general solution of the stress problem of the thick plate satisfying the boundary conditions on the contour of an arbitrary cavity is obtained. By employing the orthogonal function expansion technique, the dynamic stress problem can be reduced to the solution of an infinite algebraic equation series. As an example, the numerical results for the dynamic stress concentration factor in thick plates with a circular, elliptic cavity are graphically presented. The numerical results are discussed.展开更多
Based on complex variables and conformal mapping, the elastic wave scat- tering and dynamic stress concentrations in the plates with two holes are studied by the refined dynamic equation of plate bending. The problem ...Based on complex variables and conformal mapping, the elastic wave scat- tering and dynamic stress concentrations in the plates with two holes are studied by the refined dynamic equation of plate bending. The problem to be solved is changed to a set of infinite algebraic equations by an orthogonM function expansion method. As examples, under free boundary conditions, the numerical results of the dynamic moment concen- tration factors in the plates with two circular holes are computed. The results indicate that the parameters such as the incident wave number, the thickness of plates, and the spacing between holes have great effects on the dynamic stress distributions. The results are accurate because the refined equation is derived without any engineering hypothese.展开更多
A dynamic weight function method is presented for dynamic stress intensity factors of circular disk with a radial edge crack under external impulsive pressure. The dynamic stresses in a circular disk are solved under ...A dynamic weight function method is presented for dynamic stress intensity factors of circular disk with a radial edge crack under external impulsive pressure. The dynamic stresses in a circular disk are solved under abrupt step external pressure using the eigenfunction method. The solution consists of a quasi-static solution satisfying inhomogeneous boundary conditions and a dynamic solution satisfying homogeneous boundary conditions. By making use of Fourier- Bessel series expansion, the history and distribution of dynamic stresses in the circular disk are derived. Furthermore, the equation for stress intensity factors under uniform pressure is used as the reference case, the weight function equation for the circular disk containing an edge crack is worked out, and the dynamic stress intensity factor equation for the circular disk containing a radial edge crack can be given. The results indicate that the stress intensity factors under sudden step external pressure vary periodically with time, and the ratio of the maximum value of dynamic stress intensity factors to the corresponding static value is about 2.0.展开更多
The time-domain BEM was developed to analyze the dynamic stress intensity factor ( DSIF) of 3-D elastodynamic crack problems. To simulate the stress singularity along the front of a crack, eight-node isoparametric sin...The time-domain BEM was developed to analyze the dynamic stress intensity factor ( DSIF) of 3-D elastodynamic crack problems. To simulate the stress singularity along the front of a crack, eight-node isoparametric singular elements were used, and the DSIF for a semi-circular surface crack was firstly calculated based on displacement equation using the time-domain BEM formulation. The new scheme to determine the time step was brought forward. By the dynamic analysis program of time-domain BEM compiled by its, several numerical examples are presented, which demonstrate the unconditional stability and high accuracy of time-domain BEM applied to 3-D elastodynamic crack problems.展开更多
Dynamic stress intensity factors are evaluated for thick-walled cylinder with a radial edge crack under internal impulsive pressure. Firstly, the equation for stress intensity factors under static uniform pressure is ...Dynamic stress intensity factors are evaluated for thick-walled cylinder with a radial edge crack under internal impulsive pressure. Firstly, the equation for stress intensity factors under static uniform pressure is used as the reference case, and then the weight function for a thick-walled cylinder containing a radial edge crack can be worked out. Secondly, the dynamic stresses in uncracked thick-walled cylinders are solved under internal impulsive pressure by using mode shape function method. The solution consists of a quasi-static solution satisfying inhomogeneous boundary conditions and a dynamic solution satisfying homogeneous boundary condi- tions, and the history and distribution of dynamic stresses in thick-walled cylinders are derived in terms of Fourier-Bessel series. Finally, the dynamic stress intensity factor equations for thick-walled cylinder containing a radial edge crack sub- jected to internal impulsive pressure are given by dynamic weight function method. The finite element method is utilized to verify the results of numerical examples, showing the validity and feasibility of the proposed method.展开更多
Based on the motion equations of flexural wave in Ambartsumian' s plates including the effects of transverse shear deformations,by using perturbation method of small parameter,the scatter- ing of flexural waves an...Based on the motion equations of flexural wave in Ambartsumian' s plates including the effects of transverse shear deformations,by using perturbation method of small parameter,the scatter- ing of flexural waves and dynamic stress concentrations in the plate with a cutout have been studied. The asypmtotic solution of the dynamic stress problem is obtained.Numerical results for the dynamic stress concentration factor in Ambartsumian's plates with a circular cutout are graphically presented and discussed.展开更多
A new formula is obtained to calculate dynamic stress intensity factors of the three-point bending specimen containing a single edge crack in this study. Firstly, the weight function for three-point bending specimen c...A new formula is obtained to calculate dynamic stress intensity factors of the three-point bending specimen containing a single edge crack in this study. Firstly, the weight function for three-point bending specimen containing a single edge crack is derived from a general weight function form and two reference stress intensity factors, the coefficients of the weight function are given. Secondly, the history and distribution of dynamic stresses in uncracked three-point bending specimen are derived based on the vibration theory. Finally~ the dynamic stress intensity factors equations for three-pointing specimen with a single edge crack subjected to impact loadings are obtained by the weight function method. The obtained formula is verified by the comparison with the numerical results of the finite element method (FEM). Good agreements have been achieved. The law of dynamic stress intensity factors of the three-point bending specimen under impact loadings varing with crack depths and loading rates is studied.展开更多
A method for topological optimization of structures with discrete variables subjected to dynamic stress and displacement constraints is presented. By using the quasistatic method, the structure optimization problem un...A method for topological optimization of structures with discrete variables subjected to dynamic stress and displacement constraints is presented. By using the quasistatic method, the structure optimization problem under dynamic stress and displacement constraints is converted into one subjected to static stress and displacement constraints. The comprehensive algorithm for topological optimization of structures with discrete variables is used to find the optimum solution.展开更多
The problem of a Griffith crack in an unbounded orthotropic functionally graded material subjected to antipole shear impact was studied. The shear moduli in two directions of the functionally graded material were assu...The problem of a Griffith crack in an unbounded orthotropic functionally graded material subjected to antipole shear impact was studied. The shear moduli in two directions of the functionally graded material were assumed to vary proportionately as definite gradient. By using integral transforms and dual integral equations, the local dynamic stress field was obtained. The results of dynamic stress intensity factor show that increasing shear moduli's gradient of FGM or increasing the shear modulus in direction perpendicular to crack surface can restrain the magnitude of dynamic stress intensity factor.展开更多
The variation characteristics of dynamic stress in crustal blocks and its relationship with earthquakes are comprehensively studied by analyzing geophysical data and calculating the dynamic response of crustal blocks ...The variation characteristics of dynamic stress in crustal blocks and its relationship with earthquakes are comprehensively studied by analyzing geophysical data and calculating the dynamic response of crustal blocks in North China to the tide level change of Bohai Sea and Yellow Sea using a 3D nonlinear dynamic finite element simulation. This study has noticed some new features of crustal dynamic stress: (a) High stress level appears at the place where the stress waves superpose and interference during the process of propagation, and the enhancement of dynamic shear stress is more significant as compared with that of compressive stress; (b) Variation of dynamic stress has influence on seismogenic environment and hence earthquake occurrence; (c) As viewed from the variation characteristics of crustal dynamic stress, the superimposing process of shear stress manifests the preparation process of earthquakes.展开更多
The analysis of the dynamic stress on the particle-matrix interface in particle-reinforced composite for the reason that this stress may lead to the microvoids' nucleation due to the interfacial debonding were stu...The analysis of the dynamic stress on the particle-matrix interface in particle-reinforced composite for the reason that this stress may lead to the microvoids' nucleation due to the interfacial debonding were studied. For simplification, a sphere containing a concentric rigid spherical particle was taken as the representative volume element (RVE). The Laplace transformation was used to derive the basic equations, and the analytical solutions were obtained by means of Hankel transformation. Moreover, the influences of the inertia and viscosity on the debonding damage were also discussed.展开更多
A series of hydraulic model tests with horizontal movable seabed under regular wave actions have been carried out to investigate the dynamic interactions between water waves and seabed soil. Seabed dynamic stresses fr...A series of hydraulic model tests with horizontal movable seabed under regular wave actions have been carried out to investigate the dynamic interactions between water waves and seabed soil. Seabed dynamic stresses from experiments are, tound to differ from theoretical resuhs. The response of p0 in permeable seabed has a small decay and phase shift to the nonlinear wave actions, and the dynamic stresses, σs/p0, σh/p0 and u/p0, contain different phase shift characteristics. Such phenomena will strongly affect the dynamic stress path in seabed. If the phase shifts of σs. and σh are neglected, the stress path will become a straight line; otherwise, it will become an elliptical curve. In phase shift cases, the long axis of the p - q diagram will be shortened when the depth increases, and the short axis will become longer when the phase shift increases. For the p' - q' diagram, the larger the phase lag of u, the longer the short axis. Relative results offer useful information for the analysis of seabed stability.展开更多
基金The project supported by the National Natural Science Foundation of China
文摘Using the complex variable method and conformal mapping,scat- tering of flexural waves and dynamic stress concentrations in Mindlin's thick plates with a cutout have been studied.The general solution of the stress problem of the thick plate satisfying the boundary conditions on the contour of cutouts is obtained. Applying the orthogonal function expansion technique,the dynamic stress problem can be reduced into the solution of a set of infinite algebraic equations.As examples, numerical results for the dynamic stress concentration factor in Mindlin's plates with a circular,elliptic cutout are graphically presented in sequence.
基金This research was carried out by the following funded projects:National Natural Science Foundation of China(51604270,51874292,and 51804303)Fundamental Research Funds for the Central Universities(2017QNA26)+2 种基金Natural Science Foundation of Jiangsu Province(BK20180643)Independent Research Projects of State Key Laboratory of Coal Resources and Safe Mining,China University of Mining and Technology(SKLCRSM15X04)The first author also acknowledges the China Postdoctoral Council International Postdoctoral Exchange Fellowship Program(20170060).
文摘Fault is a common geological structure that has been revealed in the process of underground coal excavation and mining.The nature of its discontinuous structure controls the deformation,damage,and mechanics of the coal or rock mass.The interaction between this discontinuous structure and mining activities is a key factor that dominates fault reactivation and the coal burst it can induce.This paper first summarizes investigations into the relationships between coal mining layouts and fault occurrences,along with relevant conceptual models for fault reactivation.Subsequently,it proposes mechanisms of fault reactivation and its induced coal burst based on the superposition of static and dynamic stresses,which include two kinds of fault reactivations from:mining-induced quasi-static stress(FRMSS)-dominated and seismic-based dynamic stress(FRSDS)-dominated.These two kinds of fault reactivations are then validated by the results of experimental investigations,numerical modeling,and in situ microseismic monitoring.On this basis,monitoring methods and prevention strategies for fault-induced coal burst are discussed and recommended.The results show that fault-induced coal burst is triggered by the superposition of high static stress in the fault pillar and dynamic stress from fault reactivation.High static stress comes from the interaction of the fault and the roof structure,and dynamic stress can be ascribed to FRMSS and FRSDS.The results in this paper could be of great significance in guiding the monitoring and prevention of fault-induced coal bursts.
基金supported by National Natural Science Foundation of China(Grant Nos.51239005,51009072)National Science & Technology Pillar Program of China(Grant No.2011BAF14B04)
文摘Current research on the operational reliability of centrifugal pumps has mainly focused on hydrodynamic instability. However, the interaction between the fluid and structure has not been sufficiently considered; this interaction can cause vibration and dynamic stress, which can affect the reliability. In this study, the dynamic stresses in a single-blade centrifugal pump impeller are analysed under different operating conditions; the two-way coupling method is used to calculate the fluid-structure interaction. Three-dimensional unsteady Reynolds-averaged Navier-Stokes equations are solved with the SST k-o9 turbulence model for the fluid in the whole flow passage, while transient structure dynamic analysis is used with the finite element method for the structure side. The dynamic stresses in the rotor system are computed according to the fourth strength theory. The stress results show that the highest stress is near the loose bearing and that the equivalent stress increases with the flow rate because the dynamic stresses are closely related to the pressure load. The stress distributions on the blade pressure side, suction side, leading edge, and trailing edge are each analysed for different flow rates; the highest stress distribution is found on the pressure side. On the blade pressure side, a relatively large stress is found near the trailing edge and hub side. Based on these results, a stress distribution prediction method is proposed for centrifugal pumps, which considers the interaction between the fluid and structuxe. The method can be used to check the dynamic stress at different flow rates when optimising the pump design to increase the pump reliability.
基金This work is supported by the National Natural Science Foundation of China(Nos.51804099 and U1704129)the Focus Research and Special Development for Scientific and Technological Project of Henan Province(No.202102310542)+1 种基金the Fundamental Research Funds for the Central Universities(No.2018ZDPY02ZDPY02)the research fund of State Key Laboratory of Coal Resources and Safe Mining,CUMT(SKLCRSM19KF011).
文摘In this study,the tomography of dynamic stress coefficient(TDSC)was established based on a mechanical model of stress wave propagation in bedding planes and a mathematical model of the stress wave attenuation in rock masses.The reliability of the TDSC was verified by a linear bedding plane model and field monitoring.Generally,the TDSC in the dynamic stress propagation of bedding planes increases with the following conditions:(1)the increase of the normal stiffness of the bedding plane,(2)the increase of the incident angle of the stress wave,(3)the decrease of the incident frequency of the stress wave,or(4)the growth of three ratios(the ratios of rock densities,elastic moduli,and the Poisson’s ratios)of rocks on either side of bedding planes.The additional stress weakens TDSC linearly and slowly during the stress wave propagation in bedding planes,and the weakening effect increases with the growth of the three ratios.Besides,the TDSC decreases exponentially in the rock mass as propagation distance increases.In a field case,the TDSC decreases significantly as vertical and horizontal distances increase and its wave range increases as vertical distance increases in the sedimentary rock layers.
文摘In this paper,the dynamic stress concentration and scattering of SH-waves by bi-material structures that possess an interface elliptic cavity are investigated.First,by using the complex function method,the Green's function is constructed.This yields the solution of the displacement field for an elastic half space with a semi-elliptic canyon impacted by an anti-plane harmonic line source loading on the horizontal surface.Then,the problem is divided into an upper and lower half space along the horizontal interface,regarded as a harmony model.In order to satisfy the integral continuity condition, the unknown anti-plane forces are applied to the interface.The integral equations with unknown forces can be established through the continuity condition,and after transformation,the algebraic equations are solved numerically.Finally,the distribution of the dynamic stress concentration factor(DSCF)around the elliptic cavity is given and the effect of different parameters on DSCF is discussed.
基金Project supported by the National Natural Science Foundation of China (Nos. 10002005 and 10421002)the Natural Science Foundation of Tianjin (No.02360081)the Education Committee Foundation of Tianjin (No.20022104)the Program for Changjiang Scholars and Innovative Research Team in University of China and the 211 Foundation of Dalian University of Technology
文摘A mathematical model was developed for layout optimization of truss structures with discrete variables subjected to dynamic stress, dynamic displacement and dynamic stability constraints. By using the quasi-static method, the mathematical model of structure optimization under dynamic stress, dynamic displacement and dynamic stability constraints were transformed into one subjected to static stress, displacement and stability constraints. The optimization procedures include two levels, i.e., the topology optimization and the shape optimization. In each level, the comprehensive algorithm was used and the relative difference quotients of two kinds of variables were used to search the optimum solution. A comparison between the optimum results of model with stability constraints and the optimum results of model without stability constraint was given. And that shows the stability constraints have a great effect on the optimum solutions.
基金the National Natural Science Foundation of China(No.10672027)the National Basic Research Program of China(No.2006CB601205)the National Science Fund for Distin-guished Young Scholars of China(No.50625414)
文摘This paper studies the dynamic stress intensity factor (DSIF) at the interface in an adhesive joint under shear loading. Material damage is considered. By introducing the dislocation density function and using the integral transform, the problem is reduced to algebraic equations and can be solved with the collocation dots method in the Laplace domain. Time response of DSIF is calculated with the inverse Laplace integral transform. The results show that the mode Ⅱ DSIF increases with the shear relaxation parameter, shear module and Poisson ratio, while decreases with the swell relaxation parameter. Damage shielding only occurs at the initial stage of crack propagation. The singular index of crack tip is -0.5 and independent on the material parameters, damage conditions of materials, and time. The oscillatory index is controlled by viscoelastic material parameters.
基金supported by the Shanghai Science Foundation of Important Projects for Post Doctoral Research, China (Grant No. 09R21421600)
文摘Since a self-elevating platform often works in water for a long time, the lattice leg is largely influenced by wave and current. The amplitude of leg joint stresses is a very important factor for the fatigue life of the platform. However, there are not many researches having been done on the mechanism and dynamic stress analysis of these leg joints. This paper focuses on the dynamic stress analysis and suppression methods of the leg joints of self-elevating platforms. Firstly, the dynamic stresses of the lattice leg joints are analyzed for a self-elevating platform by use of the 5th-order Stokes wave theory. Secondly, the axial and bending stresses are studied due to their large contributions to total stresses. And then, different joint types are considered and the leg-hull interface stiffness is analyzed for the improvement of the joint dynamic stress amplitude. Finally, some useful conclusions are drawn for the optimization design of the self-elevating platform.
文摘By using the complex variable method and conformal mapping, the diffraction of flexural waves and dynamic stress concentrations in thick plates with a cavity have been studied. A general solution of the stress problem of the thick plate satisfying the boundary conditions on the contour of an arbitrary cavity is obtained. By employing the orthogonal function expansion technique, the dynamic stress problem can be reduced to the solution of an infinite algebraic equation series. As an example, the numerical results for the dynamic stress concentration factor in thick plates with a circular, elliptic cavity are graphically presented. The numerical results are discussed.
基金Project supported by the National Natural Science Foundation of China(Nos.51378451 and 51378245)
文摘Based on complex variables and conformal mapping, the elastic wave scat- tering and dynamic stress concentrations in the plates with two holes are studied by the refined dynamic equation of plate bending. The problem to be solved is changed to a set of infinite algebraic equations by an orthogonM function expansion method. As examples, under free boundary conditions, the numerical results of the dynamic moment concen- tration factors in the plates with two circular holes are computed. The results indicate that the parameters such as the incident wave number, the thickness of plates, and the spacing between holes have great effects on the dynamic stress distributions. The results are accurate because the refined equation is derived without any engineering hypothese.
文摘A dynamic weight function method is presented for dynamic stress intensity factors of circular disk with a radial edge crack under external impulsive pressure. The dynamic stresses in a circular disk are solved under abrupt step external pressure using the eigenfunction method. The solution consists of a quasi-static solution satisfying inhomogeneous boundary conditions and a dynamic solution satisfying homogeneous boundary conditions. By making use of Fourier- Bessel series expansion, the history and distribution of dynamic stresses in the circular disk are derived. Furthermore, the equation for stress intensity factors under uniform pressure is used as the reference case, the weight function equation for the circular disk containing an edge crack is worked out, and the dynamic stress intensity factor equation for the circular disk containing a radial edge crack can be given. The results indicate that the stress intensity factors under sudden step external pressure vary periodically with time, and the ratio of the maximum value of dynamic stress intensity factors to the corresponding static value is about 2.0.
文摘The time-domain BEM was developed to analyze the dynamic stress intensity factor ( DSIF) of 3-D elastodynamic crack problems. To simulate the stress singularity along the front of a crack, eight-node isoparametric singular elements were used, and the DSIF for a semi-circular surface crack was firstly calculated based on displacement equation using the time-domain BEM formulation. The new scheme to determine the time step was brought forward. By the dynamic analysis program of time-domain BEM compiled by its, several numerical examples are presented, which demonstrate the unconditional stability and high accuracy of time-domain BEM applied to 3-D elastodynamic crack problems.
基金supported by the China Aviation Industry Corporation I Program (ATPD-1104-02).
文摘Dynamic stress intensity factors are evaluated for thick-walled cylinder with a radial edge crack under internal impulsive pressure. Firstly, the equation for stress intensity factors under static uniform pressure is used as the reference case, and then the weight function for a thick-walled cylinder containing a radial edge crack can be worked out. Secondly, the dynamic stresses in uncracked thick-walled cylinders are solved under internal impulsive pressure by using mode shape function method. The solution consists of a quasi-static solution satisfying inhomogeneous boundary conditions and a dynamic solution satisfying homogeneous boundary condi- tions, and the history and distribution of dynamic stresses in thick-walled cylinders are derived in terms of Fourier-Bessel series. Finally, the dynamic stress intensity factor equations for thick-walled cylinder containing a radial edge crack sub- jected to internal impulsive pressure are given by dynamic weight function method. The finite element method is utilized to verify the results of numerical examples, showing the validity and feasibility of the proposed method.
基金the National Natural Science Foundation of China.
文摘Based on the motion equations of flexural wave in Ambartsumian' s plates including the effects of transverse shear deformations,by using perturbation method of small parameter,the scatter- ing of flexural waves and dynamic stress concentrations in the plate with a cutout have been studied. The asypmtotic solution of the dynamic stress problem is obtained.Numerical results for the dynamic stress concentration factor in Ambartsumian's plates with a circular cutout are graphically presented and discussed.
基金supported by the China Aviation Industry Corporation I Program (No.ATPD-1104-02)the Science Foundation of Nanjing University of Science and Technology (No.2010GJPY026)
文摘A new formula is obtained to calculate dynamic stress intensity factors of the three-point bending specimen containing a single edge crack in this study. Firstly, the weight function for three-point bending specimen containing a single edge crack is derived from a general weight function form and two reference stress intensity factors, the coefficients of the weight function are given. Secondly, the history and distribution of dynamic stresses in uncracked three-point bending specimen are derived based on the vibration theory. Finally~ the dynamic stress intensity factors equations for three-pointing specimen with a single edge crack subjected to impact loadings are obtained by the weight function method. The obtained formula is verified by the comparison with the numerical results of the finite element method (FEM). Good agreements have been achieved. The law of dynamic stress intensity factors of the three-point bending specimen under impact loadings varing with crack depths and loading rates is studied.
文摘A method for topological optimization of structures with discrete variables subjected to dynamic stress and displacement constraints is presented. By using the quasistatic method, the structure optimization problem under dynamic stress and displacement constraints is converted into one subjected to static stress and displacement constraints. The comprehensive algorithm for topological optimization of structures with discrete variables is used to find the optimum solution.
文摘The problem of a Griffith crack in an unbounded orthotropic functionally graded material subjected to antipole shear impact was studied. The shear moduli in two directions of the functionally graded material were assumed to vary proportionately as definite gradient. By using integral transforms and dual integral equations, the local dynamic stress field was obtained. The results of dynamic stress intensity factor show that increasing shear moduli's gradient of FGM or increasing the shear modulus in direction perpendicular to crack surface can restrain the magnitude of dynamic stress intensity factor.
基金National Natural Science Foundation of China(40174024).
文摘The variation characteristics of dynamic stress in crustal blocks and its relationship with earthquakes are comprehensively studied by analyzing geophysical data and calculating the dynamic response of crustal blocks in North China to the tide level change of Bohai Sea and Yellow Sea using a 3D nonlinear dynamic finite element simulation. This study has noticed some new features of crustal dynamic stress: (a) High stress level appears at the place where the stress waves superpose and interference during the process of propagation, and the enhancement of dynamic shear stress is more significant as compared with that of compressive stress; (b) Variation of dynamic stress has influence on seismogenic environment and hence earthquake occurrence; (c) As viewed from the variation characteristics of crustal dynamic stress, the superimposing process of shear stress manifests the preparation process of earthquakes.
文摘The analysis of the dynamic stress on the particle-matrix interface in particle-reinforced composite for the reason that this stress may lead to the microvoids' nucleation due to the interfacial debonding were studied. For simplification, a sphere containing a concentric rigid spherical particle was taken as the representative volume element (RVE). The Laplace transformation was used to derive the basic equations, and the analytical solutions were obtained by means of Hankel transformation. Moreover, the influences of the inertia and viscosity on the debonding damage were also discussed.
基金This research was financially supported by the National Science Council , Taiwan under the project entitled"TheStudy of the Dynamic Behavior of Foundation Soil beneath Nearshore structures under Wave Loading Action (I)"withthe project number of NSC-91-2211-E-019-013
文摘A series of hydraulic model tests with horizontal movable seabed under regular wave actions have been carried out to investigate the dynamic interactions between water waves and seabed soil. Seabed dynamic stresses from experiments are, tound to differ from theoretical resuhs. The response of p0 in permeable seabed has a small decay and phase shift to the nonlinear wave actions, and the dynamic stresses, σs/p0, σh/p0 and u/p0, contain different phase shift characteristics. Such phenomena will strongly affect the dynamic stress path in seabed. If the phase shifts of σs. and σh are neglected, the stress path will become a straight line; otherwise, it will become an elliptical curve. In phase shift cases, the long axis of the p - q diagram will be shortened when the depth increases, and the short axis will become longer when the phase shift increases. For the p' - q' diagram, the larger the phase lag of u, the longer the short axis. Relative results offer useful information for the analysis of seabed stability.