Research On Global Strength And Local Structural Improvement Of Longitudinal Pontoon Of Very Large Floating Structure

The Very Large Floating Structure(VLFS)can be used as an airport,seaport,and energy savings base,etc.,and is currently one of the hot spots in marine engineering research.VLFS adapts to the strategic needs of China's marine development,which is of great scientific and strategic significance.In the current study of VLFS,there are many studies on hydroelasticity,but there are few studies on the global strength of the structure,and there is no standard for checking the strength of VLFS,so the global strength of VLFS needs to be researched for further exploration.In this paper,longitudinal pontoon of VLFS is taken as study subject,the global strength of the structure is analyzed by direct calculating method to determine the high stress region of the structure,and various schemes are adopted to improve the high stress area structure.Then the global strength of these improved schemes is analyzed and compared.Finally we will obtain a more reasonable and feasible scheme of longitudinal pontoon of VLFS.The main works and conclusions are as follows:(1)A hydrodynamic model of longitudinal pontoon of VLFS is established and analyzed,and the transfer function of motion response and wave load were obtained.The results show that the vertical force of midship section and vertical bending moment of longitudinal mid-section are the largest.Among them,the vertical force of midship section reaches the maximum in the condition of head sea,and the vertical bending moment of longitudinal mid-section reaches the maximum in the condition of oblique seas.(2)Based on the design wave approach,wave loading prediction of the longitudinal pontoon of VLFS is carried out,the parameters of design waves and the dangerous condition are obtained;Then the global strength of the structure is analyzed with the different software under the dangerous condition and the stress distribution of the structure could be got.The results show that the high stress region of the structure obtained by the two kinds of software are the same,that is,the connection parts between columns and the cross brace,the connection parts between columns and the upper shell,and the connection parts between columns and the floating body.Among these parts,the max Von Mises stress occurs at the connection parts between columns and the upper shell.(3)The global strength of longitudinal pontoon and horizontal pontoon of VLFS under the same design sea conditions is compared.The results show that the high stress region of longitudinal pontoons and horizontal pontoons of VLFS is similar and it is the connection parts between the columns(floating body)and the cross brace,the connection parts between the columns and the upper shell,and the connection parts between the columns and the floating body.The max Von Mises stress of longitudinal pontoon of VLFS occurs at the connection parts between columns and the upper shell,but the max Von Mises stress of horizontal pontoon of VLFS occurs at the connection parts between the cross brace and the floating body.(4)According to the analysis results of the global strength of the longitudinal pontoon of VLFS,several schemes such as increasing the thickness of plate of the high stress region,increasing the number of stiffened and increasing local column structure are used to improve the structure of longitudinal pontoon of VLFS.Then,the global strength of the improved structure are compared.Finally,a more reasonable and feasible structure reinforcement scheme of longitudinal pontoon of VLFS is obtained.The results show that the schemes such as increasing the thickness of plate and the number of aggregates in the high stress region etc.have a greater impact on the global strength of longitudinal pontoon of VLFS,and the scheme that increasing the thickness of plate and the number of aggregates and local column structure is the most obvious to reduce the Von Mises stress and the most reasonable.