Study On Strengthening Of Buckling Resistance Of Torispherical Shell And Repairing Method Of Defect

Pressure hull is an important component needed in deep-sea resources development and scientific exploration.It is usually used to ensure the normal working environment of engineering equipment and scientific instruments.In practical engineering applications,in order to realize the access and maintenance of personnel and equipment,it is necessary to open holes in the pressure shell and seal it with a head with good mechanical properties.Commonly used head are spherical head,oval head and torispherical head.Among them,the torispherical head is the most widely used because of its advantages such as simple structure,easy processing and high space utilization rate.However,due to the discontinuity of its geometric curvature,it is easy to produce stress concentration phenomenon,and its bearing capacity is easily affected by geometric defects.However,during the production,transportation and working process of the dish-shaped head,there may be pitting defects on the shell due to collision or impact,which reduces the pressure resistance of the pressure hull.At this time,it is necessary to repair the pitting defects to ensure the stability of the pressure hull.Therefore,this thesis studies the improvement of buckling strength of the dish-shaped head and the repair of pitting defects.The contents are as follows:Firstly,the buckling characteristics of the dishing head without defects are studied,and the influence of the defect amplitude on the buckling load of the dishing head is analyzed.According to the national standard dimensions,four identical dished heads were manufactured by stamping,and the geometric parameters were measured and the finite element model was established.The buckling performance and buckling characteristics of the torispherical head were studied by combining nonlinear buckling simulation with hydrostatic pressure test.Secondly,according to the buckling characteristics of the torispherical head,two strengthening schemes are designed to optimize the compression capacity of the torispherical head.The same volume thickening method is used to strengthen the torispherical head and carbon fiber composite material is used to strengthen part of the torispherical head.In this thesis,the strengthening effect and strengthening performance of the two strengthening methods are studied by numerical analysis.It is found that both strengthening methods can effectively increase the ultimate buckling load of the torispherical head.Then,considering that the ultimate buckling load of the pressure shell is easily affected by the pitting defect,the influence of the pitting defect on the buckling performance of the torispherical head and the repair method were studied.The pitting defects were made on the upper surface of four dished heads,and two of the dished heads affected by the pitting defects were repaired by carbon fiber wrapping.Through the hydrostatic pressure test and numerical analysis of four dishing heads,the influence of the pit defect on the ultimate bearing capacity of the dishing head and the effect and feasibility of repairing the pit defect with carbon fiber were studied.The results show that the influence of pit defects on the ultimate load of the torispherical head varies with different positions,and the reasonable carbon fiber repair method can effectively repair the influence of pit defects on the torispherical head.Finally,on the basis of the previous research,a larger torispherical head hatchcover was redesigned which could adapt to the water depth of 500 meters.The same volume thickening and strengthening were carried out to study the changes of the ultimate bearing capacity of the torispherical head hatchcover before and after thickening.Then,the effect of the pit defect on the bearing capacity of the thickened torispherical head cover and the effect and feasibility of carbon fiber repair under the influence of the pit defect are studied.It is found that the ultimate load of the dished head can be effectively increased by equal volume thickening and strengthening,and the influence of the pitting defects on the ultimate load of the thickened hatchcover can be effectively remedied by carbon fiber wrapping.