Bionic Design And Buckling Mechanism Reseach Of Longan-shaped Pressure Hulls

The pressure-resistant structure is a key component and buoyancy unit of marine engineering equipment.And it play an important role in ensuring the normal work of non-pressure equipment or the health and safety of personnel.The spherical structure is the best choice for the traditional pressure hull,which is sensitive to initial imperfections and the location of the instability is unknown.Therefore,in view of the above problems,this paper takes the dried longan as the bionic prototype,and carries out the bionic design of the longan-shaped pressure hull and studies its buckling mechanism.This paper designs a new pressure hull,which has many advantages,such as insensitive to the initial imperfections,predictable instability position and high bearing capacity.The main research contents of this paper are as follows:(1)The bionic design of longan-shaped pressure hulls are carried out.Firstly,in order to study the geometric characteristic of the longan,the size,shape and thickness of the dried longan were measured.Then,the pressure resistance test was carried out on dried longan to study the compressive properties of longans.Finally,according to the contour equation describing the longan shell,the contour shape of the longanshaped pressure hull is designed,and the principle of general bionic design is expounded.Results show that the length,width,height and shape index of the dired longan are close to the normal distribution,and the width and height are approximately equal;the contour shape of the longan shell can be described by the Cassini oval equation;the collapse pressure of the longan shell increases monotonously with an increase in the wall thickness-to-equivalent radius ratio.(2)Effect of shape indices on buckling of longan-shaped pressure hulls are carried out.Firstly,the mathematical models of longan-shaped pressure hulls with different shape indices are established by using the principle of equal volume.and then the linear elastic and nonlinear buckling analysis of the mathematical models of each longanshaped pressure hull is carried out.Results show that the linear elastic buckling load of the ideal longan-shaped pressure hulls decreases monotonously with the increase of the shape indices,but after the inflection point,although the linear elastic buckling load has some fluctuation,it increases significantly overall.The influence of shape indices on nonlinear buckling load of longan-shaped pressure hulls is basically consistent with that of shape indices on linear elastic buckling load of longan-shaped pressure hulls,except for longan-shaped pressure hull with a shape indice of 0.1.The equilibrium path of the hull with defects can be divided into three types: unstable path,metastable path and stable path.(3)Optimization of Contour shape of of longan-shaped pressure hulls is carried out.Firstly,based on the spherical pressure hull with a diameter of 2m,the mathematical models of longan-shaped pressure hull were established by using the principle of equal volume.Secondly,the linear elastic and elastic-plastic buckling analysis of longan-shaped pressure hulls were carried out.And then the optimum range of the contour shape of the longan-shaped pressure hull is obtained.Results show that the optimal range of the contour of longan-shaped pressure hulls is 0.09~0.15,and the optimal interval is 0.10~0.11.(4)The buckling test research of longan-shaped pressure hulls is carried out.the longan-shaped pressure hull scale models were made by using the punch forming technology and the rapid prototyping technology.Secondly,the three-dimensional scanning test,the thickness measurement test and the pressure resistance test were carried out on the scale models.Finally,the scanned models were analyzed by numerical method to study their buckling characteristics.Results show that buckling of the longan-shaped metal pressure hulls is an elastic-plastic buckling regime,and the experimental results are in good agreement with the numerical results.And the critical buckling load of longan-shaped pressure hulls with a shape indice of 0.1 is higher than that of the spherical one.Moreover,buckling of the longan-shaped resin pressure hulls is close to an elastic buckling regime,and the test results are consistent with the numerical results.The traditional mindset of spherical structure is the optimal choice of pressure shell is broken.