ABSTRACT
The mechanisms of the strain rate dependence of closed-cell PVC foams under shock were numerically studied based on a cell-based model combined with the Coupled Eulerian-Lagrangian (CEL) method in this paper. The strain rate effect of the base material and the entrapped gas effect were focused. The results show that the strain rate effect of the base material has a significant influence on the stress magnitude in the regions before and after the shock front, and the entrapped gas mainly affects the velocity field. Both the strain rate effect of the base material and the entrapped gas have a notable influence on the strain distribution. Taking PVC foam with a relative density of 0.07 as an example, the strain rate effect of the base material will increase the impact stress by 45% and reduce the impact strain by 0.04. The entrapped gas will reduce the impact strain by 0.18, and its effect on the impact stress can be ignored. Finally, two constitutive laws considering the strain rate effect and entrapped gas effect were proposed and compared for the PVC foam under shock with one based on the Hugoniot relationship and the other based on the D-RPH model.
ABSTRACT
The underwater nonwetted state on a superhydrophobic surface is hardly maintained in flowing water because the entrapped gas dissolves into the water or is carried off by flow. Therefore, a source gas is necessary to maintain a superhydrophobic state for its applications under realistic conditions. As detailed in this paper, based on the gas entrapped on a hydrophobic structured surface, the gas regeneration was experimentally achieved to replenish the losses of gas carried off by the flowing and reduced through dissolution. Furthermore, the mechanism of mass transfer at the liquid-gas interface was investigated by simulation. The results indicated that water molecules at a liquid-gas interface should escape to entrapped gas when water content didn't reach saturation. This phenomenon could be due to the evaporation at the liquid-gas interface. With the increasing water content in the entrapped gas, the evaporation rate at the liquid-gas interface descended gradually. Under the action of flowing, the substances containing high concentrations of water molecule was washed away at the liquid-gas interface. Therefore, the low concentration of the water molecule at the liquid-gas interface was created. As a result, the equilibrium of water and gas at the liquid-gad interface was broken, and the evaporation continued to replenish the lost gas. Overall, the presented results in this study could be considered a promising candidate for replenishing the lost gas in hydrophobic structured surfaces by mass transfer at the liquid-gas interface.
ABSTRACT
Peat is a kind of special material rich in organic matter. Because of the high content of organic matter, it shows different deformation behaviors from conventional geotechnical materials. Peat grain has a non-negligible compressibility due to the presence of organic matter. Biogas can generate from peat and can be trapped in form of gas bubbles. Considering the natural properties of peat, a special three-phase composition of peat is described which indicates the existence of organic matter and gas bubbles in peat. A stress-strain-time model is proposed for the compression of organic matter, and the surface tension effect is considered in the compression model of gas bubbles. Finally, a mathematical model has been developed to simulate the deformation behavior of peat considering the compressibility of organic matter and entrapped gas bubbles. The deformation process is the coupling of volume variation of organic matter, gas bubbles and water drainage. The proposed model is used to simulate a series of peat laboratory oedometer tests, and the model can well capture the test results with reasonable model parameters. Effects of model parameters on deformation of peat are also analyzed.