Dynamic Response Of Steel Tubes In Ocean Engineering

Steel tubes are widely used in the ocean engineering,such as brace of platforms or subsea pipelines.With the development of the exploitation of resources in the sea,some platforms are equipped with protection structures constituted by tubes to prevent devices on the platforms from impact.Final deformation especially global deformation should be limited to these kind of tubes so that the devices will not be affected.Thus,it is of great importance to study the dynamic response of tubes.The deformation of tubes and the way to distinguish global and local deformation should be focused.In this paper,the investigation for steel tubes subjected to lateral impact is based on the experimental,numerical and theoretical study in which the damage of tubes,deformation modes and mechanical mechanism are focused.The major elements of this paper are as follows:(1)Experimental study is carried out using drop hammer rig on about 100 tubes which are divided in to 5 groups according to their different diameters.The velocity and the acceleration during impact and the deformation of tubes after impact are measured with measurement equipment in the lab.Based on the analysis for characters of upper and lower surface deformation of tubes,the quantitative and qualitative way to calculate local and global deformation is raised.The longitudinal deformation mode which is closer to the real condition is raised by analyzing the contour line and section deformation of the tube.In addition,the effect of different impact positions to the deformation is studied.(2)The software ABAQUS is used for numerical simulation of lateral impact on tubes.With the comparison of finite element and experiment results,the finite element method is verified to simulate the impact process.Moreover,the simulation is carried out on every tubes in the experiment to make further analysis.By the analysis of the experiment results and finite elements results with a larger range of the impact energy,experienced equation is raised for practical use.(3)The method to study mechanism of dynamic response theoretically is developed based on the research of rigid plastic beam model.The drawback of the rigid plastic beam theory is analyzed by comparing the theoretical results with experimental results.Moreover,experienced equations raised by Amdahl,Ellinas and Oliveira respectively are analyzed and the drawbacks and advantages of those methods are discussed.(4)The beam-on-foundation model is developed for calculating the final deformation of tubes.By keeping the upper surface of the tube while transferring the section force to spring after choosing the suitable section deformation mode identical with experiments,the appropriate beam-on-foundation model is established.The results calculated by the beam-on-foundation model are closed to the experiment results,proving the validation of this model.