Research On Truth-preserving Technique Of Deep-sea Pressure Tight Sediment Sampler

In Hydrothermal Vent's plume areas, the seafloor sediments may contain high concentration of high pressure-hobby microbe and gases, specifically H₂S and H₂. Sealing the sediment core at in-situ pressure is essential for colleting the microbe and gases, which would otherwise die or escape from the sediment due to decreasing pressure during recovery the samples from depth. In this thesis, a pressure tight corer technique, which could be introduced in the modification of traditional multiple corer, is put forward.First of all, an additional thick-wall cylinder is introduced to contain the sediment core and keep its pressure. A series setup is provided to transfer the core into the thick-wall cylinder as soon as the main cable becoming tight. Secondly, the two opening is tightly sealed as soon as the sediment core entering the thick-wall cylinder. The seal could be self-tightened under inner pressure while increasing the difference in pressure during recovery the samples from depth. At last, a hydraulic accumulator is introduced to compensate some mini leakage during the process. Underwater electric power supply is not needed during the whole process.The pressure tight multiple corer have been developed and successfully obtained a pipe of pressure tight sediment core under 3400m deep-sea last summer. The pressure is kept at 34.4MPa 6 hours later. The results show that the corer has a good ability in sampling and pressure holding.The thesis includes senven chapers.Chaper 1 introduces the development of the sediment sampler in the ocean resource exploring fields, the analysis of the present state and the development of the domestic and oversea sampling technique, and the application and the developing trend of the pressure tight sampling technique in the deep-sea resource exploration.In chapter 2, through the geotechnical characteristics study of the bottom sediments, we could find out the influence of the sediments' physical and mechanical characteristics to the column sampling. The process analysis of the contact sampling clarified the mechanics of the "stake effection".The piston-sampling could put off the "stake effection" and increased the sampling length. On this base, the design rules of the sampling cutter-cylinder are put forwardto confirm the ideal dimention in order to reduce the sample disturb and the pressure variation during the samping process.Chapter 3 analyzes that the differencial pressure caused during the deepsea pressure tight sampling requires the comparatively mobile configuration between the pressure-tight cylinder and the sample lining cylinder. Here, the lock of the lining cylinder could easily resolve the conflict between the sampling act and the sample transfer act. The seal method from inner to outer and the special flap valve configuration could achieve the credible seal. It could be through ANSYS finite element simulation to study the potential plastic deformation of the material around the pressure-tight sealing-off under high pressure, and then bring forward to the optima] seal mode.Chapter 4 mainly illuminates the relation between the quantitis of the compensatory seawater and the pressure variation, the valumn of the pressure-tight cylinder and the inner and outer diameter ratio of the cylinder during the differential pressure increment process. Then, a design rule of the pressure compensator was put forward to achieve the half-automatic pressure compensation.Chapter 5 introduces the structure of the sample cylinder and brings forward that the pressure-tight cylinder with reliable seal and steady pressure-withstand is the key to realize the truth-preserving sampling. Through the anlysis of the pressure cylinder's stress, it could be come out to the thickness of the cylinder and the design configuration of the upper and lower lid. The actual sea-test results show that the pressure-tight cylinder based on the former theory has a good ability in sampling and pressure holding.In chapter 6, through the comparation between the two differential trigger theories, which are the theory based on the stroke trigger control and the theory based on the holding opposite force trigger control, the structures are analyzed in detail. The result concludes that the theory based on the holding opposite force trigger control is more adapt to the deep-sea sampling, so it has more abroad meaning.The last chapter looks back to the whole thesis and presents out the fruits of the study. At last, the further explore direction would be carried out in the end of this thesis.