Bionic Research On Deep-sea Pressure Hulls Based On Biological Characteristic Of Eggshell

Deep submersible is an important equipment for oceanic exploration and deep-sea research.As the most critical component of the submersible,the pressure hull provides a safe living and working space for crews and scientists and equipments.The weight of the manned pressure hull accounts for almost 1/3 of the total weight of a submersible.Spherical preesure hulls are most used as the component of the existing deep submersibles.However,spherical preesure hulls have disadvantages of difficult interior arrangement/low space efficiency,weak hydraulic performance,and are highly sensitive to geometric imperfections.As a solution of above problems,egg-shaped pressure hulls are designed to replace the spherical one.Eggshell is a thin-walled multi-focus structure of revolution with positive gaussian curve.It has many advantages,such as weight-strength ratio,span-thickness ratio,streamline,aesthetic characteristics and reasonable distribution of material.In addition,the eggshell has an extremely good capacity of pressure resistance under uniform external pressure.Therefore,this paper carried out a bionic research on deep pressure hull based on biological characteristic of eggshell by combination of analytical calculation,numerical simulation and experimental study.Some main research contents and conclusions of this paper are in the following:(1)Investigation on bionic characteristic of eggshells by experiment.The geometric characteristic of eggshells was researched by carrying out the mearsurement of size,shape and thickness.Also,the collapse pressure and shape of eggshells were studied by conducting the mechanical performance and pressure resistance tests.Results show that the major axis length,minor axis length and shape index of eggshells are close to normal distribution,and its thickness is thin at both end and thick at the equator area.What’s more,eggshell has an extremely good capacity of pressure resistance under hydrostatic pressure and could be approximately bearing the load of 2t.The collapse shape of eggshells is in the form of breaking at the equator area,which agrees well with the result abtained from numerical simulation.(2)Based on general theory of thin-walled shells of revolution,the structure of the egg-shaped shell was designed.Firstly,strength and buckling equations of the egg-shaped shell were derived according to thin-walled theory.Next,according to the N-R function,the shape of egg-shaped pressure hull was described briefly.At last,based on the strength and buckling equations of the egg-shaped shell,both of uniform and variable thicknesses of the egg-shaped pressure hull were designed with equivalent strength or buckling loads.Two types of material were considered as follows: plastic and hard brittle material.Above design formulas of thickness could lay a solid foundation for the application of egg-shaped pressure hulls to deep submersible in the future.(3)Research on buckling of egg-shaped pressure hulls by numerical simulation.Firstly,both of uniform and variable thicknesses of egg-shaped pressure hull were determined with the depth of 4km.Both of elastic and elastic-plastic buckling behaviors of egg-shaped pressure hulls were analyzed numerically.For a like-for-like comparison,the volume and strength equivalent spherical pressure hull was proposed.Besides,effects of shape and wall thickness on buckling of egg-shaped pressure hulls were explored.Results show that overall performance of egg-sheped pressure hull is superior to that of spherical one.Moreover,geometric imperfection of the egg-shaped pressure hull would be more sensitive when the egg-shaped pressure hull is close to a spherical pressure hull.Likewise,with equivalent thickness,geometric imperfection of the egg-shaped pressure hull is less sensitive to that of spherical pressure hull.These findings indicate that egg-shaped pressure hull is more suitable than spherical one for application to deep manned/unmanned submersible.(4)Buckling regime of egg-shaped pressure hulls was verified by Laboratory scale tests.The Laboratory scale egg-shaped pressure hulls were manufactured by using rapid prototyping and punch forming technology respectively.Tests of the finished egg-shaped metal/resin pressure hulls subjected to hydrostatic pressure were conducted.The collapse pressure and shape of the egg-shaped metal/resin pressure hulls were studied.Results show the egg-shaped resin pressure hull obtained from rapid prototyping technology is close to an ideal model than the egg-shaped metal pressure hulls obtained from punch forming.Moreover,buckling of the egg-shaped resin pressure hull is close to an elastic buckling regime,while buckling of the egg-shaped metal pressure hull is an elastic-plastic buckling regime.The results agree well with those obtained from numerical and analytical analyses.