Research On Influential Parameters Of PMMA Window Performance For Deep-Sea Manned Cabin

Faced with the increasingly scarce land resources,limited human living space and deteriorating ecological environment,the international community has gradually focused on the ocean.The increase in exploration activities in the deep sea(depth interval of6000-11000 meters)has promoted the development of large-scale manned submersibles.The manned cabin is the main pressure-bearing component in deep-sea manned submersibles,and the observation window design is one of the key technologies for manned cabin research.In the deep sea ultra-high pressure working environment,the manned cabin opening structure represented by the observation window is essential for ensuring the safety and reliability of the submersible.In this paper,the observation window of the deep-sea manned cabin is taken as the research object By considering its basic mechanical properties,structural optimization and creep characteristics.The current research status of the observation window at home and abroad is briefly summarized,and the unsolved technical problems in this field are summarized.The research content and main results of this paper include the following aspects:(1)The material properties and structural forms of the observation window are compared.The working environment and load spectrum characteristics and its simplified description method are analyzed and the specific structural form and the material of the frustum-shaped PMMA observation window used for the current study are determined.(2)Based on the law of refraction of light,the observation fields of the two frustum observation windows of plane and single curved surface are analyzed,and the influence of structural form and structural parameters on the observation field is discussed.The analysis results show that the coverage of the observation field of the plane frustum-shaped observation window with the cone angle greater than 83.68 degrees is the best.The most widely used 90-degree plane frustum shape will be taken as the analysis object to further study its strength,optimization and creep characteristics.(3)Parametric analysis is carried out on the influence of material propertyparameters in linear elastic calculation,considering the influence of potential factors such as temperature and material nonlinearity on the observation window design.By comparing the pressure test results and the finite element simulation results are found to be better matched when the elastic modulus and Poisson’s ratio the PMMA are 2400 MPa and 0.35 respectively.According to the actual temperature range tested in the pressure chamber,the effect of temperature effect can be considered in the preliminary design of the observation window.(4)Based on the observation window and the performance of PMMA materials,the influence of different transition radii on the mechanical properties of the 90-degree plane frustum-shaped PMMA observation window was analyzed.Comparing the stress and deformation distribution of the observation window under different transition radii,it is found that setting the reasonable transition fillet can effectively improve the uneven stress distribution at the contact surface between the observation window and the window seat and decrease the stress concentration at the edge of the inner surface of the window,but when the transition radius exceeds 5000 mm,the degree of stress concentration decrease is not obvious and the observation field is seriously reduced.(5)In order to overcome the shortcomings of the linear elastic model which can not accurately characterize the constitutive relation of PMMA,this paper proposes a finite element analysis method based on viscoelastic model to simulate the viscous creep of PMMA,which is applied in analysis the axial displacement of the window under different types of load spectrum.In addition,the influence of thickness-inner diameter ratio(t/D)and load-holding time T on axial displacement is analyzed.The results show that there is a large interaction between thickness-inner diameter ratio and load-holding time.on the axial displacement.When the thickness-to-inner diameter ratio is greater than1.5 and the load-bearing time exceeds 100 h,the axial displacement change tends to converge.The influence of the thickness-inner diameter ratio should be considered when optimizing the observation window structure.(6)Based on the finite element calculation results of a series of observation windows,an explicit fitting formula for calculating the axial displacement of the frustum-shaped observation window under a specified high pressure which can be used to describe and calculate different thickness-inner diameter ratio and load-holding time is obtained.The influence of the creep characteristics on the axial displacement is closer to the actual deformation of the observation window.The fitting validity of the formula isverified by comparing the correlation between the formula and the finite element simulation results.To be summarized,this thesis studied the view scope,optimized form,structural strength and creep characteristics of the frustum-shaped PMMA observation window by use of finite element analysis considering the interaction effects of various factors such as material properties,load and environment.The research results will lay a theoretical foundation for the establishment of a relatively complete research process on the performance of PMMA observation windows for deep-sea manned cabin.