Analysis of the sealing performance of combined sealing structure under deep-sea high pressure environment

For the requirement of safe and stable operation,the combined sealing structure was used for reciprocating motion in the deep sea high-pressure environment,and the effects of different seawater depths and shaft movement speed on the sealing performance of the combined sealing structure were studied.The change rule of the sealing performance of the combined sealing structure of reciprocating motion under different working conditions is proved.The study shows that in the combined sealing structure of reciprocating movement,the Von Mises stress and the contact stress of the O-ring varies with the direction of the shaft movement.The Von Mises stress and contact stress of the O-ring,the Von Mises stress and the contact stress on each sealing lip of the slip ring gradually increase with the increasing of seawater depths.At the same time,the Von Mises stress of the O-ring which in the process of the shaft upward movement is greater than the shaft downward movement,making the shaft upward movement more likely to cause the O-ring relaxation and fatigue.The shaft movement speed has no significant influence on the Von Mises stress and contact stress of the O-ring.The research results provide theoretical guidance and technical support for the selection and optimization of the geometrical parameters of the combined sealing structure in the deep-sea high-pressure environment.

Spectral characteristics of underwater laser-induced breakdown spectroscopy under high-pressure conditions

Laser-induced breakdown spectroscopy(LIBS) has been proven to be an attractive technique for in situ oceanic applications.However,when applying LIBS into deep-sea,the pressure effect caused by different ocean depths is inescapable and could have great influence on the LIBS signals.In this work,spectral characteristics of underwater LIBS were investigated as a function of pressure in the range of 0.1-45 MPa.A high-pressure chamber built in the laboratory was used to simulate the high-pressure deep-sea environment.Optimal laser energy and detection delay were first determined under different pressure conditions and were shown to be independent of the external pressure.The increase in pressure has a significant impact both on the peak intensity and line broadening of the observed spectra.The peak intensity of Na,Li and K lines increases with the increasing pressure until a maximum intensity is reached at 12.5 MPa.Above this value,the peak intensity decreases gradually up to 45 MPa.For Ca line,the maximum intensity was observed at 30 MPa.The line broadening keeps constant at low pressures from 0.1-10 MPa,while it increases linearly at higher pressures,indicating a higher electron density caused by the compression effect of the high external pressure.We also compared the spectral data obtained from the high-pressure chamber and from the field sea trials,and the good consistency between the laboratory data and sea-trial data suggested the key role of pressure effect on underwater LIBS signals for practical deep-sea applications.

The role of hydrostatic pressure on the metal corrosion in simulated deep-sea environments—a review

This paper reviewed the corrosion behavior of metals in simulated deep-water environments and briefly discussed the effect of hydrostatic pressure on the different corrosion types for the active and the passive alloys.A consensus on the corrosion mechanism is that hydrostatic pressure accelerates the dissolution kinetics,changes the chemical compositions of the product layer or passive films,and promotes the adsorption of Cl^(-)on the metal surface.In addition,a newly-developed mechanism that hydrostatic pressure facilitates the dissolution process by thinning the electric double layer was reviewed,the synergistic effect of hydrostatic pressure and tensile stress on the stress corrosion cracking was discussed,and the modified coating with chemical bonding interface to prolong the service life in this environment was introduced.

Application of the ancient trace fossil group in deep sea to the sedimentology

Extremely abundant trace fossils are associated with the deep-sea deposits, especially in turbidite measure and flysch facies. And these trace groups then become the effective indicators to reconstruct the ancient depositional environment and the palaeogeography. This paper focuses on ( ⅰ ) the formational features of deep-sea fossil and its assemblage feature, and further recongnizes that the coexistence of the shallow and deep water trace group in a depositional sequences is the identification mark of turbidite sequence; ( ⅱ ) thought and methods using the trace fossil to restore their environmental parameters such as the ancient sea depth, oxygenbearing condition and sedimentation rate, etc.; ( ⅲ ) the application and significance of deep-sea ichnofacies in environment interpretation.