No abstract

A floating-type joint applies the entire bolt load to the gasket to generate sealing contact stress, and is prone to leak due to the bolt load loss. Different with the floating type one, a metal-to-metal contact type joint applies only part of the bolt load to the gasket to achieve seating stress, and applies the additional bolt load to the metal-to-metal contact to compensate for the unloading effects due to internal and external loadings. Due to this advantage, metal-to-metal contact type joints are gradually used in chemical industries, nuclear power industries, etc. A flange joint together with a metal-to-metal contact type gasket forms the metal-to-metal contact type joint studied in this article. A threedimensional nonlinear finite element model is developed to highlight the complex behavior of the flange joint under bolting-up, pressure loading and thermal loading conditions. Despite the common perception that gasket stress in a metal-to-metal contact type joint stays constant, reduced gasket stress is concluded due to flange rotation and joint thermal expansion.

Metal-to-metal contact type flange joints (bolted flange joint with metal-to-metal contact) have a constant gasket sealing stress during service, so it is extensively used for ''zero leakage'' design in petrochemical, chemical, or nuclear power industry. XP CEN\TS 1591-3 provides a calculation method for metal-to-metal contact flange joints but the gasket parameters needed in this calculation and their test methods are not given. To determine the gasket parameters of metal-to-metal contact type flange joints, the procedures of the compression-resilience test, the stress relaxation test, and the sealing test at different temperature were described here, and the main mechanical properties and sealing property of a metal-to-metal contact type gasket were obtained from these tests. The methods to determine the metalto-metal contact gasket parameters were introduced. And then, the calculation for a DN80 PN5.0 metal-to-metal contact type flange joint was carried out with two methods, one was the method according to XP CEN\TS 1591-3, the other was finite element method. In these calculations, the assembly condition and service condition were considered. The results of the two methods coincided well. This showed the test methods and test results of metal-to-metal contact type gasket parameters suggested here were available. So, they could be applied for the calculation of metal-tometal contact type flange joints.

The current novel coronavirus disease 2019 (COVID-19) outbreak in global has provided an opportunity to understand the spread of this pandemic linked to healthcare settings. It is very important to predict the trend of epidemic situation for timely response. In this paper, we proposed a Susceptible-Exposed-Infectious-Recovered-Susceptible (SEIRS) model to simulate and forecast the trend of COVID-19 epidemic in China. The simulation results provide a good fit to the actual number and peak time of confirmed epidemic in Hubei province, and the simulation results also show that the epidemic of Hubei province would decline in early June. However, there are some differences between the simulation results and the real situation of other regions in China, because this model does not consider human intervention strategy. In a word, our SEIRS dynamic model is effective in simulating and predicting the COVID-19 epidemic in Hubei province, China, it has meaningful reference for the prevention and control of the pandemic situation which is raging all over the world.

Experimental techniques and identification of dynamic properties of flexible polyurethane foam used in automotive seats are described here. In the experimental fixture a rigid block is mounted on a 3 inch cube of foam material, which serves as the only flexible component. The dynamic system is modeled as a single degree-of -freedom system. The experimental fixture is excited by a small impulse at the top of the block and by a shaker on the basement. For the first situation the foam is simplified as a linear viscoelastic material. By exciting with the shaker the nonlinear and viscoelastic properties of foam materials are considered. For these two different cases not only the model response and the impact of model parameters are analyzed but also the corresponding system parameters are identified during the experimental data.