Buckling Properties of Water-Drop-Shaped Pressure Hulls with Various Shape Indices Under Hydrostatic External Pressure

The water-drop-shaped pressure hull has a good streamline,which has good application prospect in the underwater observatory.Therefore,this study conducted analytical,experimental and numerical investigation of the buckling properties of water-drop-shaped pressure hulls under hydrostatic pressure.A water-drop experiment was conducted to design water-drop-shaped pressure hulls with various shape indices.The critical loads for the water-drop-shaped pressure hulls were resolved by using Mushtari’s formula.Several numerical simulations including linear buckling analysis and nonlinear buckling analysis including eigenmode imperfections were performed.The results indicated that the critical loads resolved by Mushtari's formula were in good agreement with the linear buckling loads from the numerical simulations.This formula can be extended to estimate the buckling capacity of water-drop-shaped pressure hulls.In addition,three groups of pressure hulls were fabricated by using stereolithography,a rapid prototyping technique.Subsequently,three groups of the pressure hulls were subjected to ultrasonic measurements,optical scanning,hydrostatic testing and numerical analysis.The experimental results were consistent with the numerical results.The results indicate that the sharp end of the water-drop-shaped pressure hulls exhibited instability compared with the blunt end.This paper provides a new solution to the limitations of experimental studies on the water-drop-shaped pressure hulls as well as a new configuration and evaluation method for underwater observatories.

Multi-objective design optimization of composite submerged cylindrical pressure hull for minimum buoyancy and maximum buckling load capacity

This paper presents the design optimization of composite submersible cylindrical pressure hull subjected to 3 MPa hydrostatic pressure.The design optimization study is conducted for cross-ply layups[0_(s)/90_(t)/0_(u)],[0_(s)/90_(t)/0_(u)]s,[0_(s)/90_(t)]s and[90_(s)/0_(t)]s considering three uni-directional composites,i.e.Carbon/Epoxy,Glass/Epoxy,and Boron/Epoxy.The optimization study is performed by coupling a Multi-Objective Genetic Algorithm(MOGA)and Analytical Analysis.Minimizing the buoyancy factor and maximizing the buckling load factor are considered as the objectives of the optimization study.The objectives of the optimization are achieved under constraints on the Tsai-Wu,Tsai-Hill and Maximum Stress composite failure criteria and on buckling load factor.To verify the optimization approach,optimization of one particular layup configuration is also conducted in ANSYS with the same objectives and constraints.

Multi‑Crack Interaction and Influence on the Spherical Pressure Hull for a Deep‑Sea Manned Submersible

This study investigates the interaction and influence of surface cracks on the spherical pressure hull of a deep-sea manned submersible.The finite element model of the spherical hull is established,and a semi-elliptical surface crack is inserted in the welding toe of the spherical hull as the main crack.Considering the combined effect of external uniform pressure and welding residual stress at the weld toe,the stress intensity factor(SIF)is obtained based on the M-integral method.Inserting disturbing cracks at different positions on the spherical hull surface,the interaction and influence between multi-cracks are revealed by numerical calculation.The results show that the existence of the disturbing crack has a great influence on the stress intensity factor of the main crack,and the influence is different with the different location of disturbing crack.The study of the interaction of multiple cracks under different interference factors and the influence of disturbing cracks on the main crack can provide some reference for future engineering applications.

Design optimization of composite egg-shaped submersible pressure hull for minimum buoyancy factor

This paper describes a design optimization study of the composite egg-shaped submersible pressure hull employing optimization and finite element analysis(FEA)tools as a first attempt to provide an optimized design of the composite egg-shaped pressure hull for manufacturing or further investigations.A total of 15 optimal designs for the composite egg-shaped pressure hull under hydrostatic pressure are obtained in terms of fibers’angles and the number of layers for 5 lay-up arrangements and 3 unidirectional(UD)composite materials.The optimization process is performed utilizing a genetic algorithm and FEA in ANSYS.The minimization of the buoyancy factor eB:FT is selected as the objective for the optimization under constraints on both material failure and buckling strength.Nonlinear buckling analysis is conducted for one optimal design considering both geometric nonlinearity and imperfections.A sensitivity study is also conducted to further investigate the influence of the design variables on the optimal design of the egg-shaped pressure hull.

Numerical simulation and analysis of the underwater implosion of spherical hollow ceramic pressure hulls in 11000 m depth

Pressure hulls play an important role in deep-sea underwater vehicles.However,in the ultra-high pressure environment,a highly destructive phenomenon could occur to them which is called implosion.To study the characteristics of the flow field of the underwater implosion of hollow ceramic pressure hulls,the compressible multiphase flow theory,direct numerical simulation,and adaptive mesh refinement are used to numerically simulate the underwater implosion of a single ceramic pressure hull and multiple linearly arranged ceramic pressure hulls.Firstly,the feasibility of the numerical simulation method is verified.Then,the results of the flow field of the underwater implosion of hollow ceramic pressure hulls in 11000 m depth is analyzed.There are the compression-rebound processes of the internal air cavity in the implosion.In the rebound stage,a shock wave that is several times the ambient pressure is generated outside the pressure hull,and the propagation speed is close to the speed of sound.The pressure peak of the shock wave has a negative exponential power function relationship with the distance to the center of the sphere.Finally,it is found that the obvious superimposed effect between spheres exists in the chain-reaction implosion which enhances the implosion shock wave.

Non-linear buckling analysis of imperfect thin spherical pressure hull for manned submersible

Thin spherical pressure hulls are used as a human occupancy in deep water applications.DNV and other standards specify the imperfection allowed for pressure hulls.Numerical analyses are carried out to find the buckling pressure for both perfect and imperfect thin spherical pressure hulls,considering the geometric and material non-linearities.It is observed that there is a huge variation in the elastic and inelastic buckling pressure in perfect spherical pressure hulls.Moreover,if the manufacturing imperfections are considered in the inelastic numerical analysis,still there is a reduction in the buckling pressure.Design criteria,for deep water pressure hulls,is that both buckling pressure and yield pressure must be greater than the design pressure.In the elastic analysis,if t/D>0.006 buckling pressure is always greater than the yield pressure whereas in the inelastic analysis,the buckling pressure is falling below the yield pressure for all t/D ratios.Hence,inelastic numerical analysis with manufacturing imperfection has to considered in the design of deep water spherical pressure hulls of manned submersibles.

Depth control for a deep-sea self-holding intelligent buoy system based on active disturbance rejection control method

The net buoyancy of the deep-sea self-holding intelligent buoy(DSIB)will change with depth due to pressure hull deformation in the deep submergence process.The net buoyancy changes will affect the hovering performance of the DSIB.To make the DSIB have better resistance to the external disturbances caused by the net buoyancy and water resistance,a depth controller was designed to improve the depth positioning based on the active disturbance rejection control(ADRC).Firstly,a dynamic model was established based on the motion analysis of the DSIB.In addition,the extended state observer(ESO)and nonlinear state error feedback controller were designed based on the Lyapunov stability principle.Finally,semi-physical simulations for the depth control process were made by using the ADRC depth controller and traditional PID depth controller,respectively.The results of the semi-physical simulations indicate that the depth controller based on the ADRC can achieve the predefined depth control under the external disturbances.Compared with the traditional PID depth controller,the overshoot of the ADRC depth controller is 1.74%,and the depth error is within 0.5%.It not only has a better control capability to restrain the overshoot and shock caused by the external disturbances,but also can improve intelligence of the DSIB under the depth tracking task.