The current national criteria cannot accurately reflect the multi-crack interference effect of defective gas pipelines,and thus result in conservative assessment results.In order to improve the safety assessment accur...The current national criteria cannot accurately reflect the multi-crack interference effect of defective gas pipelines,and thus result in conservative assessment results.In order to improve the safety assessment accuracy of defective gas pipelines,we compared the singular element method with the three-dimensional virtual crack closure technology(3D-VCCT),then,selected the 3D-VCCT to build a multi-crack interference model of gas pipelines,and finally,studied the interference effect of subsidiary cracks on the front points of the main crack by analyzing the variation of the interference factors between cracks.The following research results were obtained:first,as the subsidiary crack size changes,the strongest interference effect of a parallel collinear crack occurs near the surface of the crack,exhibiting an enhances effect;second,under certain conditions,the interference effect of a parallel coaxial crack is more significant at the deepest point and the surface point of the crack,and exhibits an enhanced effect at the deepest point and a weakened effect at the surface point;third,when the horizontal spacing between cracks is 6 times greater than the major semi-axis of the main crack,the interference effect of parallel collinear cracks and parallel bias cracks is very little,and multi-cracks can be simplified as a single crack for analysis.The research results not only can provide technical references for fracture analysis of multi-crack gas pipelines,but also can provide theoretical basis for the safety assessment of multi-cracks of the gas pipelines.展开更多
The numerical quadrature methods for dealing with the problems of singular and near-singular integrals caused by Burton-Miller method are proposed, by which the conventional and fast multipole BEMs （boundary element ...The numerical quadrature methods for dealing with the problems of singular and near-singular integrals caused by Burton-Miller method are proposed, by which the conventional and fast multipole BEMs （boundary element methods） for 3D acoustic problems based on constant elements are improved. To solve the problem of singular integrals, a Hadamard finite-part integral method is presented, which is a simplified combination of the methods proposed by Kirkup and Wolf. The problem of near-singular integrals is overcome by the simple method of polar transformation and the more complex method of PART （Projection and Angular ＆ Radial Transformation）. The effectiveness of these methods for solving the singular and near-singular problems is validated through comparing with the results computed by the analytical method and/or the commercial software LMS Virtual.Lab. In addition, the influence of the near-singular integral problem on the computational precisions is analyzed by computing the errors relative to the exact solution. The computational complexities of the conventional and fast multipole BEM are analyzed and compared through numerical computations. A large-scale acoustic scattering problem, whose degree of freedoms is about 340,000, is implemented successfully. The results show that, the near singularity is primarily introduced by the hyper-singular kernel, and has great influences on the precision of the solution. The precision of fast multipole BEM is the same as conventional BEM, but the computational complexities are much lower.展开更多
Many researchers have focused their efforts on fatigue failures occurring on weld toes. In recent years, more and more fatigue failures occur on weld roots. Therefore, it is important to explore the behaviour of weld ...Many researchers have focused their efforts on fatigue failures occurring on weld toes. In recent years, more and more fatigue failures occur on weld roots. Therefore, it is important to explore the behaviour of weld root fatigues. This paper investigates numerically the Magnification factors （Mk） for types of semi-elliptical cracks on the weld root of a T-butt joint. The geometry of the joint is determined by four important parameters： crack depth ratio, crack shape ratio, weld leg ratio and weld angle. A singular element approach is used to generate the corresponding finite element meshes. For each set of given four parameters of the semi-elliptical root crack, the corresponding T-butt joint is numerically simulated and its Mk at the deepest point of the weld root crack is obtained for the respective tension and shear loads. The variation range of the four parameters covers 750 cases for each load, totaling 1500 simulations are completed. The numerical results obtained are then represented by the curve to explore the effects of four parameters on the Mk. To obtain an approximate equation representing Mk as a function of the four parameters for each load, a multiple regression method is adopted and the related regression analysis is performed. The error distributions of the two approximate equations are compared with the finite element data. It is confirmed that the obtained approximate functions fit very well to the database from which they are derived. Therefore, these two equations present a valuable reference for engineering applications in T-butt joint designs.展开更多
基金Project supported by National Science and Technology Infrastructure Program“Risk-based key technologies for preventing pipeline accidents”(No.:2011BAK06B01-11).
文摘The current national criteria cannot accurately reflect the multi-crack interference effect of defective gas pipelines,and thus result in conservative assessment results.In order to improve the safety assessment accuracy of defective gas pipelines,we compared the singular element method with the three-dimensional virtual crack closure technology(3D-VCCT),then,selected the 3D-VCCT to build a multi-crack interference model of gas pipelines,and finally,studied the interference effect of subsidiary cracks on the front points of the main crack by analyzing the variation of the interference factors between cracks.The following research results were obtained:first,as the subsidiary crack size changes,the strongest interference effect of a parallel collinear crack occurs near the surface of the crack,exhibiting an enhances effect;second,under certain conditions,the interference effect of a parallel coaxial crack is more significant at the deepest point and the surface point of the crack,and exhibits an enhanced effect at the deepest point and a weakened effect at the surface point;third,when the horizontal spacing between cracks is 6 times greater than the major semi-axis of the main crack,the interference effect of parallel collinear cracks and parallel bias cracks is very little,and multi-cracks can be simplified as a single crack for analysis.The research results not only can provide technical references for fracture analysis of multi-crack gas pipelines,but also can provide theoretical basis for the safety assessment of multi-cracks of the gas pipelines.
基金supported by the National Natural Science Foundation of China(11304344,11404364)the Project of Hubei Provincial Department of Education(D20141803)+1 种基金the Natural Science Foundation of Hubei Province(2014CFB378)the Doctoral Scientific Research Foundation of Hubei University of Automotive Technology(BK201604)
文摘The numerical quadrature methods for dealing with the problems of singular and near-singular integrals caused by Burton-Miller method are proposed, by which the conventional and fast multipole BEMs （boundary element methods） for 3D acoustic problems based on constant elements are improved. To solve the problem of singular integrals, a Hadamard finite-part integral method is presented, which is a simplified combination of the methods proposed by Kirkup and Wolf. The problem of near-singular integrals is overcome by the simple method of polar transformation and the more complex method of PART （Projection and Angular ＆ Radial Transformation）. The effectiveness of these methods for solving the singular and near-singular problems is validated through comparing with the results computed by the analytical method and/or the commercial software LMS Virtual.Lab. In addition, the influence of the near-singular integral problem on the computational precisions is analyzed by computing the errors relative to the exact solution. The computational complexities of the conventional and fast multipole BEM are analyzed and compared through numerical computations. A large-scale acoustic scattering problem, whose degree of freedoms is about 340,000, is implemented successfully. The results show that, the near singularity is primarily introduced by the hyper-singular kernel, and has great influences on the precision of the solution. The precision of fast multipole BEM is the same as conventional BEM, but the computational complexities are much lower.
基金Project supported by the National Basic Research Program (973 Program) of China (No. 2011CB711102)
文摘Many researchers have focused their efforts on fatigue failures occurring on weld toes. In recent years, more and more fatigue failures occur on weld roots. Therefore, it is important to explore the behaviour of weld root fatigues. This paper investigates numerically the Magnification factors （Mk） for types of semi-elliptical cracks on the weld root of a T-butt joint. The geometry of the joint is determined by four important parameters： crack depth ratio, crack shape ratio, weld leg ratio and weld angle. A singular element approach is used to generate the corresponding finite element meshes. For each set of given four parameters of the semi-elliptical root crack, the corresponding T-butt joint is numerically simulated and its Mk at the deepest point of the weld root crack is obtained for the respective tension and shear loads. The variation range of the four parameters covers 750 cases for each load, totaling 1500 simulations are completed. The numerical results obtained are then represented by the curve to explore the effects of four parameters on the Mk. To obtain an approximate equation representing Mk as a function of the four parameters for each load, a multiple regression method is adopted and the related regression analysis is performed. The error distributions of the two approximate equations are compared with the finite element data. It is confirmed that the obtained approximate functions fit very well to the database from which they are derived. Therefore, these two equations present a valuable reference for engineering applications in T-butt joint designs.
