海洋工程结构物局部结构疲劳行为基础研究
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摘要
随着海洋资源开发的大规模发展，各类海洋工程结构物应运而生。在海上作业的海洋工程结构物，由于受到不断变化的波浪载荷的作用，使得结构内部产生了不断变化的应力，这将造成结构的疲劳损伤，因此疲劳破坏一直被认为是海洋工程结构物的一种主要破坏形式。
目前，海洋平台中大多数结构是由钢管焊接而成。在这些钢管的连接部位，即管节点处，由于结构形式和焊接的影响，很容易在其相贯线附近产生极大的应力集中。因此，管节点局部结构是海洋平台结构中最关键的部位，也是抵抗破坏最薄弱的环节。为此，有必要研究节点局部结构形式对疲劳行为的影响，通过控制节点局部结构区域内热点应力的产生部位，控制疲劳裂纹的产生，同时，对由疲劳造成的裂纹尖端区进行打磨，以延缓裂纹扩展速度，实现延长维修周期、减小维修难度、节省维修费用的目的。
本文试图在上述方面做一些工作，以考虑节点局部结构形式对疲劳行为的影响。文章主要内容包括以下几个方面。
首先，在对该课题研究领域做了简要回顾的基础上，提出了本文研究的意义所在。其次，考虑到本文所要模拟分析的是海洋工程结构物中的构件，因此在第一章里作者主要对海洋工程结构物的总体情况作以简要介绍，包括海洋平台结构系统、设计载荷、工作原理及结构特征等。第二、三章则主要是对有关结构疲劳损伤机理和管节点疲劳分析的介绍，其中涉及到疲劳的基本概念和分析方法，以及在管节点应力分析中应力和应力集中系数(SCF)的选取和计算方法。本文的工作重点在第四章，该章详细地介绍了典型K型管节点疲劳分析的全过程，从模型的建立、网格的划分、载荷及边界条件的选取，到热点应力和SCF的确定，以及最后疲劳寿命的计算。最后，通过数值模拟分析，采取对由疲劳造成的裂纹尖端区进行打磨以延缓裂纹扩展速度的方式，确实延长了节点的疲劳寿命。
With the development of large-scaled exploitation of ocean resources, diverse offshore structures have been being developed. Offshore structures are constantly subjected to the varied wave-induced loads, which accounts for the changing stress of the internal members and due to which structural fatigue damage would surely occur. Therefore, it is always considered as a main form of damage in ocean platforms.
Presently, most structures of platforms are fabricated by steel tubes. In the connection of these tubes, tubular joints, high stress concentration is easily emerged in the vicinity of the intersection owing to the influence of structure and welds. Hence the tubular joints are the most critical but the weakest members of platforms. It is obviously necessary to study the fatigue behavior caused by detailed structures of the joints, and to control the occurrence of fatigue cracks through determination of the hot spot stress location in the joint. Meanwhile, grinding the crack tip to hold up the propagation speed makes it possible to extend the maintenance period, to decrease the maintenance difficulty and to save the maintenance expenses.
Regarding the fatigue behavior resulted from the local structure, the above mentioned aspects are dealt with in the thesis as follows.
Firstly, based on the literature review in this research field, the significance of the study is presented. Then a brief introduction to the general situation of offshore structures is outlined in Chapter 1, including the ocean platform structure system, designed loads, work principle and structural fatigue characteristics. Chapter 2 and Chapter 3 mainly concern the structural fatigue damage mechanism and fatigue analyses for the joint, which covers the basic concept of fatigue and analyses methods, choice of stress and stress concentration factor (SOF). Chapter 4 emphasizes the whole procedure of fatigue analyses for the typical tubular K-joint, from modeling, meshing, choice of loads and boundary conditions to definition of hot spot stress and SCF, and final calculation of fatigue life. In the end, numerical simulation analyses are carried out and the fatigue lifetime does extend through grinding of the crack tip.
目前，海洋平台中大多数结构是由钢管焊接而成。在这些钢管的连接部位，即管节点处，由于结构形式和焊接的影响，很容易在其相贯线附近产生极大的应力集中。因此，管节点局部结构是海洋平台结构中最关键的部位，也是抵抗破坏最薄弱的环节。为此，有必要研究节点局部结构形式对疲劳行为的影响，通过控制节点局部结构区域内热点应力的产生部位，控制疲劳裂纹的产生，同时，对由疲劳造成的裂纹尖端区进行打磨，以延缓裂纹扩展速度，实现延长维修周期、减小维修难度、节省维修费用的目的。
本文试图在上述方面做一些工作，以考虑节点局部结构形式对疲劳行为的影响。文章主要内容包括以下几个方面。
首先，在对该课题研究领域做了简要回顾的基础上，提出了本文研究的意义所在。其次，考虑到本文所要模拟分析的是海洋工程结构物中的构件，因此在第一章里作者主要对海洋工程结构物的总体情况作以简要介绍，包括海洋平台结构系统、设计载荷、工作原理及结构特征等。第二、三章则主要是对有关结构疲劳损伤机理和管节点疲劳分析的介绍，其中涉及到疲劳的基本概念和分析方法，以及在管节点应力分析中应力和应力集中系数(SCF)的选取和计算方法。本文的工作重点在第四章，该章详细地介绍了典型K型管节点疲劳分析的全过程，从模型的建立、网格的划分、载荷及边界条件的选取，到热点应力和SCF的确定，以及最后疲劳寿命的计算。最后，通过数值模拟分析，采取对由疲劳造成的裂纹尖端区进行打磨以延缓裂纹扩展速度的方式，确实延长了节点的疲劳寿命。
With the development of large-scaled exploitation of ocean resources, diverse offshore structures have been being developed. Offshore structures are constantly subjected to the varied wave-induced loads, which accounts for the changing stress of the internal members and due to which structural fatigue damage would surely occur. Therefore, it is always considered as a main form of damage in ocean platforms.
Presently, most structures of platforms are fabricated by steel tubes. In the connection of these tubes, tubular joints, high stress concentration is easily emerged in the vicinity of the intersection owing to the influence of structure and welds. Hence the tubular joints are the most critical but the weakest members of platforms. It is obviously necessary to study the fatigue behavior caused by detailed structures of the joints, and to control the occurrence of fatigue cracks through determination of the hot spot stress location in the joint. Meanwhile, grinding the crack tip to hold up the propagation speed makes it possible to extend the maintenance period, to decrease the maintenance difficulty and to save the maintenance expenses.
Regarding the fatigue behavior resulted from the local structure, the above mentioned aspects are dealt with in the thesis as follows.
Firstly, based on the literature review in this research field, the significance of the study is presented. Then a brief introduction to the general situation of offshore structures is outlined in Chapter 1, including the ocean platform structure system, designed loads, work principle and structural fatigue characteristics. Chapter 2 and Chapter 3 mainly concern the structural fatigue damage mechanism and fatigue analyses for the joint, which covers the basic concept of fatigue and analyses methods, choice of stress and stress concentration factor (SOF). Chapter 4 emphasizes the whole procedure of fatigue analyses for the typical tubular K-joint, from modeling, meshing, choice of loads and boundary conditions to definition of hot spot stress and SCF, and final calculation of fatigue life. In the end, numerical simulation analyses are carried out and the fatigue lifetime does extend through grinding of the crack tip.
引文
[1] 任贵永海洋活动式平台[M]天津大学出版社．天津．1989．
[2] 崔维成，蔡新刚，冷建兴 船舶结构疲劳强度校核研究现状及我国的进展[J]船舶力学．1998．Vol．2(4)：63-81．
[3] A. Almar-Naess Fatigue Handbook—Offshore Steel Structure [M] Tapir. 1985.
[4] T.R. Gurney Fatigue of Welded Structures [M] Cambridge University Press. London. 1979.
[5] S.M. Cheng An experimental investigation of tubular T-joints under cyclic loads [J] Journal of Offshore Mechanics and Arctic Engineering. 1999. Vol. 121: 137-143.
[6] 汪广海，陈伯真国产Z向钢制造的海洋平台管节点的疲劳性能[J]海洋工程．1992．Vol．10(2)：1-7．
[7] 姚木林，石理国 内环加强管节点疲劳性能研究[J]舰船性能研究．1994．Vol．3：83-92．
[8] M.R. Morgan, M. M. K. Lee New parametric equations for stress concentration factors in tubular K-joints under balanced axial loading [J] International Journal of Fatigue. 1997. Vol. 19(4): 309-317.
[9] M.R. Morgan, M. M. K. Lee Prediction of stress concentrations and degrees of bending in axially loaded tubular K-joints [J] Journal of Constructional Steel Research. 1998. Vol. 45(1): 67-97.
[10] M. R. Morgan, M. M. K. Lee Stress concentration factors in tubular K-joints under in-plane moment loading [J] Journal of Structural Engineering. 1998. Vol. 124(4): 382-390.
[11] M. R. Morgan, M. M. K. Lee Parametric equations for distributions of stress concentration factors in tubular K-joints under out-of-plane loading [J] International Journal of Fatigue. 1998. Vol. 20(6): 449-461.
[12] E. Chang, W. D. Dover Stress concentration factors parametric equations for tubular X and DT joint [J] International Journal of Fatigue. 1996. Vol. 18(6): 363-387.
[13] E. Chang, W. D. Dover Parametric equations to predict stress distributions along the intersection of tubular X and DT joints [J] International Journal of Fatigue. 1999. Vol. 21(6): 619-635.
[14] E. Chang, W. D. Dover Prediction of stress distributions along the intersection of tubular Y and T-joints [J] Intemational Journal of Fatigue. 1999. Vol. 21 (4): 361-381.
[15] E. Chang, W. D. Dover Prediction of degree of bending in tubular X and DT joints [J]
International Journal of Fatigue. 1999. Vol. 21(2): 147-161.
[16] H. Fessler, P. B. Mockford, J. J. Webster Parametric equations for the flexibility matrices of single brace tubular joint in offshore structure [P] In Proc Instn Civ Engrs. Part 2. 1986.
[17] H. Fessler, P. B. Mockford, J. J. Webster Parametric equations for the flexibility matrices of multi-brace tubular joint in offshore structure [P] In Proc Instn Civ Engrs. Part 2. 1986.
[18] Spyros A. Karamanos, Arie Romeijn, Jaap Wardenier On the fatigue design of K-joint tubular girders [J] International Journal of Offshore and Polar Engineering. 2000. Vol. 10(1): 50-56.
[19] 顾剑民 海洋平台管节点局部柔度的参数分析及其试验研究[J]上海交通大学学报．1994．Vol．28(增刊)：9-15．
[20] Spyros A. Karamanos, Afie Romeijn, Jaap Wardenier Stress concentrations in tubular gap K-joints: mechanics and fatigue design [J] Engineering Structures. 2000. Vol. 22(1): 4-14.
[21] S. P. Chiew, C. K. Soh, N. W. Wu General SCF design equations for steel multiplanar tubular XX-joints [J] International Journal of Fatigue. 2000. Vol. 22(4): 283-293.
[22] S. P. Chiew, C. K. Soh, T. C. Fung, A. K. Soh Numerical study of multiplanar tubular DX-joints subject to axial loads [J] Computers and Structures. 1999. Vol. 72(6): 749-761.
[23] D. Radaj, C. M. Sonsino, D. Flade Prediction of service fatigue strength of a welded tubular joint on the basis of the notch strain approach [J] International Journal of Fatigue. 1998. Vol. 20(6): 471-480.
[24] D. Bowness, M. M. K. Lee Fatigue crack curvature under the weld toe in an offshore tubular joint [J] International Journal of Fatigue. 1998. Vol. 20(6): 481-490.
[25] 钱仍绩管节点与船舶甲板结构中疲劳裂纹扩展方向的研究[J]海洋工程．1996．Vol．14(1)：81-87．
[26] P. Gandhi, Stig Berg Fatigue behavior of T-joints: square chords and circular braces [J] Journal of Structural Engineering. 1998. Vol. 124(4): 399-404.
[27] P. Gandhi, D. S. Ramachandra Murthy, G. Raghava, A. G. Madhava Rao Fatigue crack growth in stiffened steel tubular joints in seawater environment [J] Engineering Structures. 2000. Vol. 22(10): 1390-1401.
[28] P. T. Myers, F. P. Brennan, W. D. Dover The effect of rack/rib plate on the stress concentration factors in jack-up chords [J] Marine Structures. 2001. Vol. 14(4-5): 485-505.
[2] 崔维成，蔡新刚，冷建兴 船舶结构疲劳强度校核研究现状及我国的进展[J]船舶力学．1998．Vol．2(4)：63-81．
[3] A. Almar-Naess Fatigue Handbook—Offshore Steel Structure [M] Tapir. 1985.
[4] T.R. Gurney Fatigue of Welded Structures [M] Cambridge University Press. London. 1979.
[5] S.M. Cheng An experimental investigation of tubular T-joints under cyclic loads [J] Journal of Offshore Mechanics and Arctic Engineering. 1999. Vol. 121: 137-143.
[6] 汪广海，陈伯真国产Z向钢制造的海洋平台管节点的疲劳性能[J]海洋工程．1992．Vol．10(2)：1-7．
[7] 姚木林，石理国 内环加强管节点疲劳性能研究[J]舰船性能研究．1994．Vol．3：83-92．
[8] M.R. Morgan, M. M. K. Lee New parametric equations for stress concentration factors in tubular K-joints under balanced axial loading [J] International Journal of Fatigue. 1997. Vol. 19(4): 309-317.
[9] M.R. Morgan, M. M. K. Lee Prediction of stress concentrations and degrees of bending in axially loaded tubular K-joints [J] Journal of Constructional Steel Research. 1998. Vol. 45(1): 67-97.
[10] M. R. Morgan, M. M. K. Lee Stress concentration factors in tubular K-joints under in-plane moment loading [J] Journal of Structural Engineering. 1998. Vol. 124(4): 382-390.
[11] M. R. Morgan, M. M. K. Lee Parametric equations for distributions of stress concentration factors in tubular K-joints under out-of-plane loading [J] International Journal of Fatigue. 1998. Vol. 20(6): 449-461.
[12] E. Chang, W. D. Dover Stress concentration factors parametric equations for tubular X and DT joint [J] International Journal of Fatigue. 1996. Vol. 18(6): 363-387.
[13] E. Chang, W. D. Dover Parametric equations to predict stress distributions along the intersection of tubular X and DT joints [J] International Journal of Fatigue. 1999. Vol. 21(6): 619-635.
[14] E. Chang, W. D. Dover Prediction of stress distributions along the intersection of tubular Y and T-joints [J] Intemational Journal of Fatigue. 1999. Vol. 21 (4): 361-381.
[15] E. Chang, W. D. Dover Prediction of degree of bending in tubular X and DT joints [J]
International Journal of Fatigue. 1999. Vol. 21(2): 147-161.
[16] H. Fessler, P. B. Mockford, J. J. Webster Parametric equations for the flexibility matrices of single brace tubular joint in offshore structure [P] In Proc Instn Civ Engrs. Part 2. 1986.
[17] H. Fessler, P. B. Mockford, J. J. Webster Parametric equations for the flexibility matrices of multi-brace tubular joint in offshore structure [P] In Proc Instn Civ Engrs. Part 2. 1986.
[18] Spyros A. Karamanos, Arie Romeijn, Jaap Wardenier On the fatigue design of K-joint tubular girders [J] International Journal of Offshore and Polar Engineering. 2000. Vol. 10(1): 50-56.
[19] 顾剑民 海洋平台管节点局部柔度的参数分析及其试验研究[J]上海交通大学学报．1994．Vol．28(增刊)：9-15．
[20] Spyros A. Karamanos, Afie Romeijn, Jaap Wardenier Stress concentrations in tubular gap K-joints: mechanics and fatigue design [J] Engineering Structures. 2000. Vol. 22(1): 4-14.
[21] S. P. Chiew, C. K. Soh, N. W. Wu General SCF design equations for steel multiplanar tubular XX-joints [J] International Journal of Fatigue. 2000. Vol. 22(4): 283-293.
[22] S. P. Chiew, C. K. Soh, T. C. Fung, A. K. Soh Numerical study of multiplanar tubular DX-joints subject to axial loads [J] Computers and Structures. 1999. Vol. 72(6): 749-761.
[23] D. Radaj, C. M. Sonsino, D. Flade Prediction of service fatigue strength of a welded tubular joint on the basis of the notch strain approach [J] International Journal of Fatigue. 1998. Vol. 20(6): 471-480.
[24] D. Bowness, M. M. K. Lee Fatigue crack curvature under the weld toe in an offshore tubular joint [J] International Journal of Fatigue. 1998. Vol. 20(6): 481-490.
[25] 钱仍绩管节点与船舶甲板结构中疲劳裂纹扩展方向的研究[J]海洋工程．1996．Vol．14(1)：81-87．
[26] P. Gandhi, Stig Berg Fatigue behavior of T-joints: square chords and circular braces [J] Journal of Structural Engineering. 1998. Vol. 124(4): 399-404.
[27] P. Gandhi, D. S. Ramachandra Murthy, G. Raghava, A. G. Madhava Rao Fatigue crack growth in stiffened steel tubular joints in seawater environment [J] Engineering Structures. 2000. Vol. 22(10): 1390-1401.
[28] P. T. Myers, F. P. Brennan, W. D. Dover The effect of rack/rib plate on the stress concentration factors in jack-up chords [J] Marine Structures. 2001. Vol. 14(4-5): 485-505.