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[Objectives] This paper aims to study the influence of welding defects on fatigue life of aluminum alloy plate frame.[Methods] Firstly,use X-ray to detect the welds of the test aluminum alloy plate frames with two gusset joints,and then select two plate frames with and without welding defects respectively. Then obtain main types of the welding defects through the analysis on the X-ray images. Then,carry out fatigue tests for these two plate frames with and without welding defects under different loads,so as to obtain the fatigue life of the plate frames. Finally,establish local FE models for the test plate frames with three types of welding defects by using ABAQUS software,and analyze and reveal the failure mechanism of the plate frames with welding defects.[Results] The test results show that,the failure of the test plate frame with welding defects is caused by the fracture on the longitudinal web due to the extension of the crack in the welding defect at the end of the weld;the failure of the test plate frame without welding defects,which is related to the gusset joint,is caused by the fracture on the longitudinal web due to the extension of the fatigue crack generated under the cyclic loads on the longitudinal web.[Conclusions] This study results can provide a reference for the assessment of the fatigue life and for the influence of the welding defects on the fatigue life.

With the global temperature continuing to rise, the Arctic ice is melting. The development of the Arctic route and exploitation of Arctic resources are drawing the wide attention of international society. Many countries are starting a new round of the construction of polar ships. In recent years, domestic and foreign researchers have begun to focus on the numerical study of ice loads on structure. However, the current commercial finite element software lacks a specialized element used for simulating the mechanical properties of sea ice. This lack increases the difficulty of the numerical study of ice loads on structure. In this paper, based on Reinicke and Remer's elliptic failure criteria and Winkler's elastic foundation, an element has been developed to simulate the bending failure of isotropic granular ice. The ice loads of typical marine structures, such as slope structure and conical structure, are calculated through the direct analysis method with the developed element. A comparison between the results of the direct analysis method and analytical method show good agreement. In brief, the proposed direct analysis method may provide tools and certain references for structural design in an ice environment.

[Objectives] A concept named ‘component contribution rate’ is proposed to solve problems concerning the influence of ship structure components on ship structure performance.[Methods] First, a hierarchical structure is elaborated and mapped from structural components to structural performance. Second, the component contribution rate is defined in order to describe the contribution rate for a component in structural performance to fulfill its structural purpose. Next, the grey target theory is applied to quantify the component contribution rate.[Results] Finally, the application of the proposed method is demonstrated through a SWATH case study.[Conclusions] This method can be applied in the evaluation of the ship structural schemes,in order to support the optimal design of ship structure.

Due to the wave and hydrodynamic interaction between two ships advancing parallel on the ocean, their six-degrees-of-freedom motions are much more complex during replenishment. The seakeeping performance of two vessels is analyzed with AQWA. On the basis of the RAO functions of the two parallel vessels, spectrum analysis and time-domain analysis were carried out, and the significant amplitudes were obtained using the computed time-history and correlation function method. The significant amplitudes are compared with the results of the spectrum analysis and good agreement is observed. It is found that hydrodynamic interaction between two ships has a great impact on the process of replenishment. Depending on the results of the analysis, dangerous conditions during the replenishment process could be avoided, thereby ensuring the safety of supply work.

[Objectives] This paper aims to study the effects of initial cracks on the dynamic response of aluminum alloy plate under repeated impacts.[Methods] Through the repeated impact test and finite element simulation of the aluminum alloy plate, we analyze the dynamic response characteristics of the aluminum alloy plate under repeated impacts, and compare the impact loads and failure modes of the aluminum alloy plate with and without initial cracks.[Results] The test results are in good agreement with the simulation calculations. The results show that the aluminum alloy plate is sensitive to initial cracks under repeated impacts;the initial cracks can reduce the load carrying capacity of the aluminum alloy plate,resulting in the reduced impact load and the reduced number of the repeated impacts for failure; the failure modes are also influenced by the initial cracks under repeated impacts.[Conclusions] The research in this paper provides a certain basis and reference for calculating and evaluating the structure strength of aluminum alloy hull plate.