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211.
High-cycle fatigue experiments are performed on welded tubular steel X-joints, with braces and chord of equal diameter. They are scaled-down joints, used extensively in offshore wind platforms. Three different welding procedures are considered in specimen fabrication: manual, fully-automatic and manual with HFMI post-weld treatment. Τwo possible locations for crack initiation were identified: chord “crown” and “in-between location”, also verified by numerical calculations and fractography of failed specimens. Monotonic loading tests on fatigue-cracked specimens showed good performance in terms of ultimate strength and deformation capacity, despite the presence of through-thickness cracks. The results are compared with predictions from relevant design standards. 相似文献
212.
Analysis of flexible marine propellers in terms of their structural response and stress is the key to accurate fatigue prediction. At present, finite element method (FEM) analyses of flexible propellers have been performed as a part of the fluid–structure interaction (FSI) analysis using a numerical method for the flexible structures, which is identical to that used for their rigid counterparts. In this study, the Euler force in a rotating frame is employed as an additional external force on the blades of the marine propeller during the FSI analysis. The Euler force is an inertial force component in the rotating frame due to angular acceleration. Acceleration of the rotating frame arises from large deformations of the propeller due to its flexible characteristics. The angular acceleration of the propeller is obtained for each time step, and the resulting Euler force is accounted for as a body force. The FSI analysis results are compared to experimental results in terms of the structural response, stress, and fatigue. It is clear that the Euler force has a major effect on the fatigue characteristics of the propeller because it amplifies the main response components. In conclusion, incorporating the Euler force in FSI analyses of flexible marine propellers is necessary for adequate prediction of the propeller fatigue. 相似文献
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214.
A new simple and accurate shell FE-based structural Hot Spot Stress (HSS) determination method for web-stiffened cruciform joints has been proposed. Local stress of welded joints in full-scale bulk carrier (BC)’s lower stool models subject to bending and pressure loadings are examined. HSSs determined by the proposed method are compared with those derived by Lotsberg’s method and the conventional 0.5t-1.5t extrapolation. As results, following are found:
- (1)
- The local stress of full-scale BC lower stool models with various stool angle and plate thickness can be calculated accurately solely from shell FE results by means of the proposed method.
- (2)
- HSSs of welded joints in full-scale BC lower stool models subject to bending and pressure loadings derived by the proposed method show good agreement with the target HSSs determined from fine solid models. This demonstrates the validity of the proposed method for actual ship structures under the real load.
- (3)
- The excessive safety allowance of HSS determined by the conventional 0.5t-1.5t extrapolation can be reduced substantially by adopting Lotsberg’s method or our proposal. The proposed HSS determination method gives more accurate estimates compared to Lotsberg’s method under the conditions chosen, and the application range of the proposed method is equal to or wider than Lotsberg’s method.
215.
Marine structures such as ships and offshore platforms are mostly designed with damage tolerance and this design philosophy requires accurate prediction of fatigue crack propagation process. Now more and more people have realized that only a fatigue life prediction method based on fatigue crack propagation (FCP) theory has the potential to satisfy the accuracy requirement and to explain various fatigue phenomena observed. In the past several years, the authors’ group has made some efforts in developing a unified fatigue life prediction (UFLP) method for marine structures. The key issue for this development is to establish a “correct” crack growth rate relation. In this paper the improvement of the crack growth rate model is dealt with first. A new crack growth rate model based on the concept of partial crack closure is presented. The capability of the model is demonstrated. Secondly, studies on the engineering approaches to determine the parameters in the new crack growth rate model are carried out and validated by comparing with the experimental results on a wide range of alloys. Thirdly, the preliminary studies on some significant problems such as load sequence effect are presented. Finally, further studies for the application of the UFLP method to the fatigue strength assessment of marine structures are pointed out. 相似文献
216.
文章根据作者已提出的基于海况频度分布的统计分类及非线性动力学计算的疲劳评估方法,通过进一步改进波浪能的输入,提出了一种更为有效的计算方法。通过将这一方法运用到一典型导管架结构的疲劳计算,文中首先研究了波浪方向对疲劳破坏的影响,进而分析了波浪谱中若干重要参数及HHT-α时间积分中步长对疲劳计算结果的影响。通过对结构反应的统计研究,发现海况的恶劣程度并不直接影响结构响应非高斯趋势的显著程度。文中提出的方法在减少不确定性的同时又不降低安全标准,有效提高了疲劳计算的精确度,从而可以降低相关近海结构建设和维护成本。文中的计算方法已被成功地应用于北海及墨西哥湾数座近海结构在风和波浪荷载作用下的疲劳评估。 相似文献
217.
218.
由于传统的大修模式存在随意性大、标准不统一、经济性差等问题,再制造技术的逐渐成熟为工程机械的修复提供了更多的选择基于再制造技术的大修方案,依托再制造产业的技术、效率、成本优势,将大修的难点转移到再制造企业新的大修方案不但可以有效遏制机械装备性能劣化趋势,减小大修工作量,而且可降低使用维护成本 相似文献
219.
220.
导管架式海洋平台可靠性检测与维修策略研究 总被引:3,自引:0,他引:3
本文提出了导管架式海洋平台在疲劳破损模式下,检测与维修费用最小化的构件及系统可靠性检测与维修最佳策略的研究方法。 相似文献