Basic Characteristics And Theory Of Impact Damage Of Submarine Double Tube

Because of its good heat preservation ability,outstanding in place stability and thermal stability,as well as excellent resistance to external loads,the double tube has been more and more widely used.The existing structural design and damage assessment generally ignore the contact effect between the inner pipe and the outer pipe,adopt the simplification method of two-layer single wall tube,and ignore the influence of the special structure of the double tube on the overall resistance,resulting in the conservative design and assessment of the double tube.Because the outer pipe is not affected by the internal transportation load and the inner pipe is isolated from the submarine environment,the double tube can appropriately reduce the safety level and the wall thickness of the inner and outer pipes,greatly improving the economy of the double pipe..In this paper,basic characteristics and theory of impact damage of submarine double tube are studied.Based on the basic theory of the single wall tube impact damage and the structural characteristics of the double tube,a double tube impact damage test device is designed independently,and the experimental research on the impact damage process of the double tube is completed.The impact damage mechanism of the double tube is revealed,and the calculation method of critical point and the impact damage process of the double tube under the condition of rotation constraint and rotation freedom support are proposed.Based on the different deformation and support conditions of the inner tube,the theoretical model of the double tube impact damage is put forward,including the three stages theoretical model of the double tube impact damage with rotation restraint,the two stages theoretical model of the double tube impact damage with rotation freedom and the impact damage of the double tube non-compliant system considering the influence of bulkhead.The model predicts the large plastic deformation of the double tube under low-velocity impact load.The impact damage process and critical point of the double tube are verified by the finite element analysis method,and the impact of bulkhead on the double tube is explored.The finite element simulation method reflecting the impact damage mechanism and large deformation process of the double tube is proposed.Based on the study of the structural and material characteristics,it is found that the theoretical model of impact damage of the double tube is suitable for the single wall tube.Compared with the single wall weight model and the single wall equivalent stiffness model,the theoretical model of impact damage of the double tube is the best in all stages.It is found that the wall thickness directly affects the resistance of the double tube,and the outer diameter indirectly affects the resistance of the double tube by affecting the critical point.The effects of the new structure and material properties,such as yield strength ratio,wall thickness ratio and outer diameter ratio,are studied and analyzed.The wall thickness ratio and yield strength ratio determine the resistance to the external load,while the outer diameter ratio determines the critical point.The impact damage model of the double tube non-compliant system is related to the distance between the impact point and the bulkhead.With the increase of the distance,its resistance to the external load decreases rapidly.The research results show that the theoretical model of the double tube impact damage proposed in this paper can effectively predict the depression depth of the double tube under external force,reflect the mechanical characteristics of the double tube structure in different stages,and lay a theoretical basis for the design of the double tube structure and the formulation of damage assessment standards.