Research On Key Techniques Of Pressure-retaining Sampling Of A Novel Full-ocean-depth Sediment Sampler

Seabed sediments are rich in polymetallic crusts,oil,natural gas and other mineral resources all of which are of important economic value.Besides,they hold evolutionary records of paleoclimate and paleoenvironment information,which can be used for scientific research such as inversion of history of land and ocean,speculation of ocean circulation mode and evolution of life process.The premise of resource exploitation and scientific research is to obtain sediment samples with in-situ characteristics among which pressure retention is an important index.However,due to the existence of high-pressure water-layers,the acquisition of original samples depends completely on advanced sediment collection methods and technical equipment.Only a few existing sampling techniques are available to obtain pressure-retaining sediment samples,usually at depths less than 7,000 m,and pressure-retaining rates need to be further improved.In this paper,with the objective of achieving pressure-retaining sampling of sediments,the key technologies such as effective sampling,ultra-high pressure sealing and pressure retention are studied.A novel pressure-retaining sediment samplerwhich can be mounted on submersibles is developed.(1)The design scheme of a novel pressure-retaining sediment sampler which can be mounted on submersibles is proposed.The design scheme of self-sealing structure of floating piston is determined,and the design scheme of piston pressure-compensation suitable for the sampling of full-ocean-depth sediments is put forward and its feasibility is studied.The pressure-retaining transfer scheme for the double piston samples is proposed and the experimental research is carried out.(2)In order to realize highly-efficient sampling,a method of sediment sampling modeling and numerical model calculation is proposed,which equates the sediments to non-Newtonian Herschel Bulkleyviscoplastic fluid and the sediment sampling calculation model is established by using the multiphase flow Volume of Fluid(VOF)method.Finite element method and multiphase flow model are used for the three-dimensional flow field dynamic simulation and solution of the calculation model.The influence rules of structural parameters(sampling tube diameter,inlet and outlet drainage area rates)and working parameters(sampling velocity,dynamic viscosity of sediment)on sampling volume and coring ratesare studied in detail.A sampling experiment platform is built and a sampling simulation experiment is carried out to verify the validity the model.This research can provide a theoretical basis for the structural design of the sampler’s sampling device and the determination of sampling parameters oriented to efficient sampling technology.(3)The design criteria of the pressure-bearing system of the sediment sampler are studied and the pressure-bearing system is then designed.The calculation model of rubber composite seal structure under ultra-high pressure is established.The influence rules of seawater pressure,compression ratio of sealing rings and material hardness on sealing performance are studied in detail.The sealing mechanism of composite seal structure is revealed,and the preconditions for self-sealing are obtained.The experimental research on the bearing and sealing performance of the sampler is carried out.The results show that the sealing structure of the sampler can realize reliable sealing under ultra-high pressure.This research can provide scientific basis for the determination of ultra-high pressure seal structures and structural parameters.(4)In order to achieve high pressure-retaining rate,a mathematical model of piston pressure compensation based on the real gas equation of state is established.The heat transfer and thermodynamic calculation analysis of the whole sampling process are carried out,and the variation law of seawater and nitrogen temperature in the sampler varying with time under different diving and recovery velocities is studied.The pressure-retaining mechanism of the sampler is studied,and the influence rules of structural parameters and working conditions on the pressure-retaining performance are examined.The ultra-high pressure test platform is built and the experiments to examine the pressure-retaining performance are carried out,and the experimental results verify the validity of the model.The userguideline of pressure compensator of the sampler is put forward,which provides guidance for pressure-retaining sampling.This research can provide theoretical basis for the geometric structure design of sediment samplers and the determination of pressure compensation parameters.(5)The lake tests of the sampler are carried out to examine the coordination between the sampler and the mechanical arm.The deep-sea tests of the sampler are also carried out,and its sampling performance,bearing performance,sealing performance and pressure-retaining performance under ultra-high pressure are tested.The results show that the sediment sampler developed in this paper is capable of obtaining pressure-retaining samples,and its working principle and structural design are reasonable and feasible,which can be applied to pressure-retaining sampling of deep-sea sediments.