Bionic Study Of Egg-shaped Pressure Dome

Bathyscaphes have poor working environment and long diving time.It is necessary to optimally coordinate the safety,carrying capacity and man-machine link characteristics of bathyscaphes.In this case,higher performance requirements are raised on the strength,stability,reserve buoyancy,in-shell space utilization,passenger comfort and other aspects of pressure shell heads.In addition,there are not enough in-depth studies which comprehensively consider these factors.According to the existing literature related to pressure shell heads,the anti-pressure ability of oblate ellipsoid heads is obviously better than that of prolate spheroidal heads.Therefore,oblate ellipsoid heads are widely applied in the pressure equipment of submarines.However,oblate ellipsoid heads have poor streamline and prolate spheroidal light shells need to be designed to reduce the water resistance of submarines,which will lead to larger transition space between light shell and head.Meanwhile,submarines will carry a lot of water when working underwater.For this purpose,this paper proposes ring-stiffened prolate spheroidal head.With good anti-pressure ability and streamline,this structure is characterized by great design and calculation difficulty,low in-shell space utilization,complicated technology and high processing cost.Therefore,it is very necessary to seek for a type of ribless heads whose safety,hydrodynamics and space utilization efficiency are optimally coordinated.Eggshell is a kind of bionic prototype because it satisfies dome principle and possesses strong pressure characteristic and streamline.Egg-shaped pressure shells can optimally coordinate the safety,speedability,space utilization,man-machine link and other performances of submarines.Hence,this paper designed,studied and developed a kind of new-type prolate ribless heads from the perspective of egg-shaped bionics.Below are specific research contents and conclusions:(1)Through understanding the geometric characteristics of goose egg,we get the long axis,short axis,egg shape coefficient and egg shape function of goose egg shell so as to provide preliminary theoretical basis for the subsequent bionic design of egg-shaped heads.In addition,the bionic design formula of egg-shaped heads was obtained according to egg-shaped contour function relation.The design formula of egg-shaped heads was taken as the basis to derive the mass and volume formula,strength and stability formula as well as equal thickness and thickening design formula of heads.(2)The test method was used to verify the shrinkage ratio model test of egg-shaped pressure heads.The buckling characteristics of 304 stainless steel egg-shaped heads under uniform external pressure were thoroughly studied.An egg-shaped biomimetic head was designed.Using the stamping technology,nine test models with 160 mm in bottom diameter and 121 mm in height were fabricated.On this basis,contour scanning,ultrasonic thickness measurement and hydrostatic pressure testing were performed on each model to study its buckling load and instability mode.According to the scanning and thickness measurement results,the nonlinear buckling analysis of the test head is in good agreement with the test results.(3)The buckling characteristics of egg-shaped heads and spherical heads under 1 mm and 1.5 mm wall thickness were compared and analyzed,which showed that the egg-shaped heads have good stress tolerance and low sensitivity to material plasticity and shape defects.Taking the design of the butterfly-shaped deep-sea seal protection cover as an example,the comparative advantages of the egg-shaped head in the actual production and application and the advantages of the butterfly head,and the hemispherical head in terms of strength and stability are comparatively analyzed.The results showed that the stress of the egg-shaped head was mainly concentrated in the waist area,and the stress distribution uniformity was relatively good.The highest comprehensive performance of the egg-shaped head was the effective choice for the design of pressure heads with a depth of several kilometers.