循环载荷作用下船体结构极限承载性能研究

发布时间：2018-06-16 04:26

本文选题：循环载荷 + 应力—应变关系　；参考：《武汉理工大学》2014年硕士论文

【摘要】：在船舶安全性评估中，船体梁极限承载能力的研究是其中一个非常重要的方面，而如今的评估方法都是以静力极限强度为准则的。当船体结构遭受到较大的交变载荷的作用时，会导致船体梁危险断面处某些纵向构件发生一定程度的屈服或屈曲破坏及塑性变形，从而使得该断面的极限承载能力降低。其最终结果是，船体梁在某一次未达到一次性纵向极限弯矩的载荷作用下就有可能发生破坏，基于静力极限强度准则会过高评估船体结构的极限强度，不符合实际情形。因此需要引入基于循环载荷作用下的船体极限承载能力的递增塑性破坏准则，考虑循环载荷下船体结构响应。船体加筋板是船舶的主要承载构件，其一次性加载下极限强度已经被广泛研究，而对循环载荷作用下的加筋板的性能分析研究还很少。本文通过大量的有限元计算，修正了Rahman法的加筋板应力-应变公式，并推导出了循环载荷下加筋板的应力-应变关系，这对于循环载荷载荷下加筋板变形性能的研究具有重要意义。最后以循环载荷下加筋板单元性能为基础，进而探讨循环载荷下船体梁弯矩-曲率变化关系，本文的主要研究工作如下： 1）介绍一次性加载下加筋板单元应力-应变关系的两种计算方法：Rahman法和FEM非线性有限元法。将两种方法计算结果进行对比，验证其准确性和可靠性，，并分析两种方法的优劣。 2）基于FEM非线性有限元方法的结果，修正Rahman法的理论计算公式，并进行误差分析，得到更为准确的计算加筋板单元应力-应变曲线的简单关系式。 3）分析循环载荷作用下加筋板的变形性能，基于修正Rahman法的简单计算公式，得到循环载荷作用下加筋板单元的应力-应变关系。并提出了两种典型的循环加载历程：单向递增循环模式和双向递增循环模式。给出算例分别计算两种循环历程下加筋板单元的应力-应变曲线，并与有限元结果进行比较验证。 4）在传统逐步破坏法基础上，引入循环载荷下结构的递增累积塑性破坏概念，采用循环载荷下结构单元的应力-应变关系，改进计算程序，得到循环弯曲简化方法计算程序。使用修改后的程序对两个箱型梁模型和一条散货船实船算例进行计算，探讨两种典型循环历程下船体梁的极限承载性能，并与非线性有限元软件的计算结果进行对比，验证本文程序的准确性。
[Abstract]:In ship safety assessment, the study of ultimate load-bearing capacity of hull girder is one of the most important aspects, and the present assessment methods are based on static ultimate strength. When the hull structure is subjected to a large alternating load, it will lead to some longitudinal members in the dangerous section of the hull beam to yield or buckle to a certain extent and plastic deformation, thus reducing the ultimate bearing capacity of the section. The ultimate result is that the hull beam may be destroyed under a load which does not reach the one-off longitudinal ultimate bending moment, and the ultimate strength of the hull structure will be evaluated too high based on the static ultimate strength criterion, which is not in line with the actual situation. Therefore it is necessary to introduce an incremental plastic failure criterion based on the ultimate load-carrying capacity of the ship under cyclic load and to consider the response of the hull structure under cyclic load. Hull stiffened plate is the main bearing member of the ship. The ultimate strength under one-time loading has been widely studied, but the performance analysis of stiffened plate under cyclic load is rare. In this paper, the formula of stress-strain of stiffened plate by Rahman method is modified by a lot of finite element calculation, and the stress-strain relation of stiffened plate under cyclic load is deduced. This is of great significance to the study of deformation properties of stiffened plates under cyclic loading. Finally, based on the performance of stiffened plate element under cyclic load, the relationship between bending moment and curvature of hull girder under cyclic load is discussed. The main research work of this paper is as follows: 1) two calculation methods of stress-strain relationship of stiffened plate element under one time loading are introduced: the method of: Rahman and the nonlinear finite element method of FEM. The calculation results of the two methods are compared to verify their accuracy and reliability. 2) based on the results of FEM nonlinear finite element method, the theoretical calculation formula of Rahman method is modified, and the error analysis is carried out. A more accurate formula for calculating the stress-strain curves of stiffened plate elements is obtained. 3) the deformation performance of stiffened plates under cyclic loading is analyzed, based on the simple formula of modified Rahman method. The stress-strain relationship of stiffened plate elements under cyclic loading is obtained. Two typical cyclic loading processes are proposed: unidirectional incremental cycle mode and bidirectional incremental cyclic mode. Examples are given to calculate the stress-strain curves of stiffened plate elements under two cycles, and the results are compared with those of the finite element method. 4) on the basis of the traditional progressive failure method, The concept of incremental cumulative plastic failure of structure under cyclic load is introduced. The stress-strain relationship of structural elements under cyclic load is adopted to improve the calculation program, and the simplified method of cyclic bending is obtained. The modified program is used to calculate two box girder models and a bulk carrier real ship, and the ultimate load-bearing performance of the hull girder under two typical cyclic histories is discussed, and the results are compared with the results of nonlinear finite element software. Verify the accuracy of this program.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U661.4

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