The Shinkai 6500, which boasted the deepest submergence vehicle in the world at her completion, is the culmination of Japanese submarines. The Shinkai 6500 has dives more than 1, 500 times after completion in 1989. I will mainly introduce the structure and performance of the Shinkai 6500, especially the structure against water pressure.
It is more than 60 years since certain microbial populations were first discovered in deep-sea environments such as abyssal and hadal zones (>4000m) of ocean. According to the development of deep-sea technology and various sampling tools, the microbiological explorations have renewed our view of deep-sea microbial ecosystems: it was previously considered to be the static habitats and communities composed of minor extremophilic and long-surviving populations successively from the surface and overlying ocean environments while it is being recognized as the dynamic habitats and communities composed of genetically diverse and functionally active populations responding to variable oceanographic, geological and geochemical events and impacts. The most outstanding examples are discoveries of dark energy ecosystems in the deep-sea and subseafloor environments, represented by various types of chemosynthetic microbial communities completely independent of photosynthetic production in the deep-sea hydrothermal systems, an enormous biomass and diversity of deep subseafloor microbial communities beneath the global oceanfloor, and unique hadal biosphere at great depths of >6000m in ultradeep trenches. The findings have revolutionized our understanding of limits of life and biosphere and the origin and early evolution of life in the Earth. Even very recently, the previously unknown microbial ecosystem has been being found in the deep-sea and subseafloor environments. I can be proud that Japanese deep-sea exploration techniques and microbiologists have greatly contributed to these findings. In this article, the brief history and recent advance are reviewed.
Ocean drilling project has historically been commenced by Project MoHole in 1961drilling into mantle through the Mohorovicic discontinuity at 6km below seafloor at the same timing of the Apollo project sending human to the Moon. It has been more than 50 years since then, and it has been just 50 years since the launch of Deep Sea Drilling Project (DSDP) in 1968 after Project MoHole. A compilation of holes into the ocean crust cored by scientific ocean drilling since the beginning of DSDP to 2018 highlights that only 38 holes deeper than 100m have been cored in oceanic crust and the total recovered ocean crustal material represents <2% of the cores. However, despite this relative paucity of material, scientific ocean drilling has provided essential and hitherto unavailable observations for advancing our understanding of the processes that repave nearly 70% of Earth's surface over short geological time scales (<200 million years) : these include better knowledge of ocean crust architecture and the accretion in processes in the axial zone of mid-ocean ridge spreading centers. It is still our ambition to explore the deep interior of our planet by scientific drilling in ocean, the most successful, long-term international scientific collaboration in any field. The Mohole-to-Mantle (M2M) project will sample for the first time upper mantle peridotites at a fast-spreading mid-ocean ridge. This will be achieved by drilling by D⁄V Chikyu through intact fast-spread oceanic crust, and ∼500m into the mantle lithosphere.
For the girth flange of heat exchangers, the circumferential temperature distribution of shell and connecting flange due to inside fluid will affect tightness of the girth flange, however this effect is not considered in present design codes. It is important to know the key characteristics of flange tightness to minimize the risk of leakage. In past studies, the effects of circumferential temperature distribution on flange tightness were investigated at high temperature operations. The effects of partial cooling on flange tightness might be severer than circumferential high temperature distribution. In this paper, the effects of partial cooling on flange tightness were studied. The flange tightness was evaluated by wideness of partially cooled region (liquid level) of heat exchanger and gasket recovery characteristics parametrically. Based on these studies, it was concluded that the gasket contact pressure was decreased by the partial cooling of heat exchanger and the effects of the above mentioned factors were summarized quantitatively.
In this study, semi-destructive methods of conventional deep hole drilling (DHD) and incremental DHD (iDHD) techniques and destructive method using strain gauge were applied, respectively, to measure through-thickness residual stress in multi-pass welded joints of 100mm thick plate. Meanwhile, welding thermal elastic-plastic analysis with the finite element methods was performed to calculate the distribution of residual stress in the multi-pass welded joints. The calculated weld penetration, temperature profiles and through-thickness residual stresses in the welds were compared, respectively, with those measured. Through the comparison among them, the applicability and measurement accuracy of conventional and incremental DHD techniques for the welds were discussed. The results showed that the applicability of both DHD techniques was not too bad to estimate the distribution of residual stress induced by welding. In particular, the iDHD technique showed better accuracy of measurement of through-thickness residual stress in the welds, even though it takes more time and effort for measurement process. A reasonable balance of accuracy and effort might have to be taken into consideration for the application of DHD techniques for the welds.