Bionic Design And Experimental Study Of Multi-egg-shaped Cross-over Pressure Shell

Deep-sea submersible is an important tool for ocean exploration and exploration,and structure design for pressure hull of which plays a decisive role.Eggshells with multifocal surfaces of positive Gaussian curvature,offer such advantages as excellent safety,load capacity and span-to-thickness ratio.Bionics has been employed to propose egg-shaped pressure hulls based on the geometric properties of goose eggshells,which could optimally coordinate the safety,capacity,and space utility ratio characteristics of deep submersibles.These previous findings motivated us to investigate a multi-segment non-typical pressure hull,the segments of which are egg-shaped shells.It is of great significance to develop modeling and theorization of bionic model,mechanical theory of special-shaped shells,design theory of multi-segment pressure hull,and the buckling theory and experiment of the non-typical moderate thick hulls.The main contents are as follows:(1)Multi-segment egg-shaped pressure hulls were designed on the basis of the best egg-shaped function describing goose egg meridian,which was established according to a series of biological experiments of egg shells.Effects of the main geometric parameters on the performances of the multi-segment egg-shaped pressure hulls were analyzed.The results show that the number of eggshells has little influence on the yield loads and buckling behavior of the multi-segment egg-shaped pressure hulls,which can be reducible to double-segment or three-segment egg-shaped pressure hulls.The optimal multi-segment spherical pressure hull on the basis of the principle of equal displacement in the direction of the minor axis was proposed,in order to avoid two common forms of failure: at intersections between the rib rings and segments,radial deformation of each segment would be consistent with that of a corresponding single spherical pressure hull without openings at the same point.(2)Stress of three-segment egg-shaped pressure hulls was analyzed by theoretical analysis and numerical calculation,in order to verify the principle of deformation coordination.The stress behavior was similar for each segment and single egg-shaped pressure hull,and the difference between the theoretical stress and numerical simulation was only 5.91%.The stress concentration caused by the edge effect could be avoided at the joints,where sudden changes of thickness and curvature exist.These findings indicate that the dimension parameters of the rib-rings are in a reasonablerange.(3)Results for numerical and analytical study into buckling behaviors of the three-segment egg-shaped pressure hull are provided,and single egg-shaped pressure hull with a single piece was also presented for comparison.These results confirmed that for shells with closely spaced Eigen-values,one of the linear combinations of the clustered buckling modes may be the worst imperfection shape,and the single buckling mode was not the worst geometric imperfection.The collapse load of the multi-segment egg-shaped pressure hull can be determined by the collapse load of the egg-shaped pressure hull multiplied by a rational reduction factor.(4)For investigating the collapse behavior of multi-segment egg-shaped hulls loaded with external pressure,the buckling behaviors of optimal double-segment egg-shaped hulls made of resin were determined numerically and verified experimentally.The nonlinear numerical analysis with arc-length method was based on deterministic imperfections obtained from measured geometric shapes and elastic-plastic modeling of true stress–strain curves,which agreed well with experimental one and could be used to predict buckling behaviors of hulls.Moreover,the collapse of multi-segment egg-shaped pressure shell was far away from the rib-ring,which supported further the principle of deformation coordination,and verified that multi-segment egg-shaped hull inherits breakdown characteristics of the single egg-shaped hull.It can simplify multi-segment egg-shaped pressure hull to single egg-shaped pressure hull in analysis of strength and stability.