Analysis Of Axial Displacement Variation Of Multi-type Observation Windows For Manned Submersibles

With the sustainable development of human society and the construction of the marine resources demand,the deep-sea resources development was included in the national strategy,and the development of deep-sea exploration technology and equipment is the premise to realize resources development,which has been expressed in the medium and long-term science and technology development planning of our country,the development of Chinese manufacturing planning,and the national science and technology innovation planning.Moreover,the development of deep-sea manned submersible is still the frontier technology of deep-sea equipment development.Manned cabin is an important part in the design of deep manned submersible.The structure of Polymethyl methacrylate(PMMA)observation window is a weak part in the design of manned cabin,which is very important to the overall reliability and safety of manned submersible.In this theis,the material characteristics,structural characteristics and creep deformation characteristics of three common forms of acrylic observation windows used in deep-sea manned submersibles are studied.By considering two key factors of the load level and the load-holding time of diving operation,the axial displacement of the observation window with different diameter depth ratio is analyzed.Based on a series of analysis results,an explicit calculation formula is established to quickly evaluate the displacement,which will provide support for the design of the strengthened part of the observation window opening in the manned cabin.The research contents mainly include the following aspects:(1)By comparing the material characteristics and structure characteristics that can be used in the manufacture of the observation window of submersible,the working environment and load spectrum characteristics of the window are simplified described.The constitutive model used to describe the viscoelastic and creep properties of PMMA is comparative analyzed,and the viscoelastic model adopted the finite element analysis is identified.The properties of PMMA affected by temperature were analyzed,and the elastic modulus of PMMA at different temperatures was predicted based on the time-temperature equivalence principle of WLF.(2)Based on the analysis of the stress characteristics of the conical frustum observation window with different diameter depth ratio,the variation of stress distribution and stress concentration level in axial direction with the increase of window thickness is studied.Based on the original calculation formula of axial displacement of conical frustum observation window based on load holding time,the load influence factor is added to optimize the calculation formula of axial displacement.(3)Based on the study of the properties of PMMA materials,the influence of different transition angle depth and transition radius on the mechanical properties of the90-degree conical frustum PMMA observation window was analyzed.By comparing the stress and deformation distribution of the observation window under different transition radius,the optimization effect of transition angle on the uneven stress distribution of the contact surface between the observation window and the window seat and the stress concentration at the edge of the inner surface of the window is analyzed.(4)Parametric analysis of creep deformation of spherical sector observation windows with different boundary friction coefficients and opening angles was carried out.By comparing the distribution of axial displacement under different boundary friction coefficients,the influence law of friction coefficient on the axial displacement and deformation of observation window is analyzed.By comparing the axial displacement of spherical sector observation window with different opening angles,the influence trend of increasing opening angle on the axial displacement of window is analyzed,and the optimal opening design of spherical fan type observation window is determined.(5)Based on a series of finite element simulation results of spherical sector observation window and flat disk window,the calculation formula of axial displacement of conical frustum observation windows with different thickness,different inner diameter ratio and load holding time is obtained,which considers the viscoelastic characteristics of PMMA and the influence of load holding time and load level on axial displacement.In this conclusion,in this thesis,the influence of the material,structure type,boundary conditions,load and working environment of the observation window on the creep deformation of the PMMA observation window under the pressure is considered.The creep characteristics and axial displacement variation of the three common types of observation windows are analyzed systematically,which lays a foundation for the optimization design of the observation window and the strengthened part of the hull in the future's designs of manned submersible.