On local stabilities of pp-K\"ahler structures

By use of a natural extension map and a power series method, we obtain a local stability theorem for p-K\"ahler structures with the $(p,p+1)$-th mild $\partial\bar\partial$-lemma under small differentiable deformations.Comment: Several typos have been fixed. Final version to appear in Compositio Mathematica. arXiv admin note: text overlap with arXiv:1609.0563

Effects of Low Suction Temperature on the Boil-off Gas compressor

The Boil-off Gas (BOG) compressor is used as a key facility in the liquefied natural gas (LNG) terminal, to recycle the excessive boiled gas for re-liquefaction or direct application. The low suction temperature down to -162? brings about big challenges in design of the BOG compressor. In this paper, the three-dimensional finite element model was used to simulate both the static and periodic transient temperature distribution in the cylinder of a BOG compressor, and a computational fluid dynamics (CFD) model was established to calculate the flow and heat transfer inside the compression chamber and suction/discharge pockets. A test rig was built up to validate the simulated results. The results showed that, the average temperatures in the suction and discharge pockets were about -109? and -60?, respectively, and the temperature of the compression chamber was in-between. The maximum temperature difference between outer and inner surface of the compressor cylinder reached up to 84? during start-up of the compressor, which yielded a thermal strain and stress in the cylinder much larger than those during steady operation of the compressor with only 31? of temperature difference. A variety of pre-cooling temperatures ranging from -20? to -60? were examined, and the results showed pre-cooling down to -20? before start-up was good enough. The amplitude of temperature fluctuation due to the periodic movement of the piston was less than 0.1? in the cylinder wall. The temperature coefficient tended to decrease at lower suction temperature. As the suction temperature decreased from -54.2?to -142.2?, the suction coefficient dropped drastically by 24.4%

Investigation On Premature Failure Of the Self-lubricated Piston Rings in Oil-free Compressor

Abstract: This paper presents the numerical simulation and experimental investigation on impact factors on premature failure of the self-lubricated piston rings in oil-free compressor. In this paper, the finite element method (FEM) was applied to study the non-uniform pressure distributions among the piston rings and the friction process between the self-lubricating piston rings and the cylinder wall, which influence the failure of the self-lubricated piston rings most. In order to verify the mathematic model, a test rig was built to measure the dynamic pressure distributions and temperature field between the piston rings. Both the theoretical and experimental results showed that the first piston ring afford more than 75% of the total pressure difference which was the main reason for the non-uniform wear and thus lead to early invalidation. The friction heat produced between the first piston ring and the cylinder was far more than the rest, which cannot be diffused rapidly through the low conductivity self-lubricating plastics and led to thermal failure of the self-lubricating piston rings. The results provide the theoretical basis to determine the design parameters and the thermal performance of piston rings reasonably