Zhang Jialin Sun Xinyi Dalian Maritime University, Dalian 116000
Abstract: With the rapid development of the maritime transport industry, the number of ships continues to increase, the scope and scale of shipping continues to increase, so the maritime transport accidents are also gradually increasing. In order to ensure the safety of maritime transport, it is necessary to improve the rationality of the structure of ships and Marine engineering, and improve the ultimate strength of the structure. There are many links in the design of ships and ocean engineering, among which the design of structural ultimate pressure is the last one. The calculation of structural ultimate strength of ships and ocean engineering is the most complicated link in the whole process, so it is necessary to find a reasonable method to analyze it.
Key words: ultimate strength; Ocean Engineering; Calculation method
When we analyze the ultimate strength of ships and offshore engineering structures, we need to understand the calculation method of calculating the ultimate strength of structures and determine the accurate value of the ultimate strength of hull modules. To calculate it, it is necessary to establish a reasonable hull model to determine the ultimate strength, and the finite element analysis method is used in the calculation. However, this method is applicable in theory but has various limitations in practice. Full consideration of various influencing factors to conduct accurate analysis, so as to carry out safe and orderly offshore engineering operations, to ensure the safety of the maritime transport industry.
Ⅰ. Overview of the basic content of the ultimate strength of the structure
Ultimate strength refers to the maximum bearing capacity and level that hull structure can resist overall hull stiffness and complete loss of bearing capacity when hull is damaged to a certain degree. In order to avoid the occurrence of accidents, certain protective measures must be taken to minimize the damage when the ship is damaged by huge external impact in the process of operation and reaches the limit state of the structure.
1. Calculation of the ultimate strength of the structure
As an important step in ship design, in order to accurately calculate the ultimate strength of ship structure, it is necessary to establish a certain suitable hull model as a carrier, and obtain accurate data by using finite element analysis. However, this method has its limitations. When applied to the actual situation, there are many influencing factors, which are difficult to calculate, consuming huge manpower and time to calculate, and producing large errors. Therefore, now this method is less calculated, and the results are not accurate. At present, the more commonly used method is the progressive failure method, which is simple to calculate and can accurately calculate the ultimate strength of the structure. At the same time, the calculation process also shows the whole analysis process, which is representative. In this method, the hull structure is analyzed and calculated according to the horizontal and vertical dimensions respectively. First, the calculation and analysis are performed step by step, and then the results of each part are integrated and analyzed to improve the accuracy of the overall calculation process.
2. Structural limit state analysis
The limit state of structure is an instantaneous process, which is difficult to grasp accurately. To judge the limit state of structure, it is necessary to determine it according to clear characteristics. The limit state is preliminarily determined, and then the calculation is carried out on this basis. When this process is the system impacted by external force, the structure rigidity and bearing capacity of the complete loss of status, the process does not use certain formula for the calculation of one pace reachs the designated position, data of image is not a straight line, so need to be adopted gradually destroy method section is calculated first, and then each step results are integrated, the final analysis results. The results obtained by this method are not affected by various external factors, and can be applied to the actual Marine transportation environment, so as to obtain a more accurate structural strength calculation, which can be better applied to ships, improve the rationality of ships and Marine engineering structures, and reduce the occurrence of accidents.
Ⅱ. Carry out the calculation and analysis of structural ultimate strength failure
In order to get the ultimate strength of the structure accurately, the step by step analysis method is used for piecewise analysis, and the suitable formula is used for approximate linear calculation at each section, and the optimal result is obtained.
1. Use Hughes formula to calculate
According to the actual situation, the hull model is divided into different sections and different structural units to find the law between the stress and strain of the scattered part of the ship. When the first reinforced reinforcement plate is destroyed, the curvature at the beginning is determined to find the change data of the whole hull model. When the data is determined, the calculation is carried out. According to the force balance equation applied to the hull truncation surface, the data is put into the calculation formula of each unit to determine the single part, and then these separate parts are summarized and integrated to calculate the overall bending moment. The whole calculation process needs to be repeated to determine the ultimate bending moment data.
2. Finite element method is used for analysis and calculation
Due to the ship and ocean engineering environment is different, is not an ideal state, influenced by many factors, not the ideal linear equation, for the convenience of calculation, the whole process of segmentation analysis, so each segment can be seen as the ideal condition, the image can be seen as a linear equation, the complex problem of simplification, the nonlinear problem into a linear problem, use linear equation to calculate, is now often used Newton - posen method, this method has a wide application scope, calculation more accurate and reasonable, to establish a certain model, and applies this method can obtain accurate results, The law between linear change and nonlinear change is obtained.
Ⅲ. Conclusion
About the calculation of ultimate strength of ship and ocean engineering structure is complicated, influenced by various environmental factors in real situations, not to be regarded as ideal condition, adopting the method of segmentation step by step, therefore, in order to conform to the reality of laws for the principle, using assumptions and decomposition method to calculate step by step, the whole structure is divided into different parts, each part of the calculation, finally to consolidate and get the most accurate structure ultimate strength. It is applied to ship and ocean engineering to make its structure reach the most reasonable state and ensure the safety and smooth progress of sea navigation.