Natural gas hydrates have been treated as a potential energy resource for decades. Understanding geomechanical properties of hydrate-bearing porous media is an essential to protect the safety of individuals and devices during hydrate production. In this work, a numerical simulator named GrapeFloater is developed to study the deformation behavior of hydrate-bearing porous media during depressurization, and the numerical simulator couples multiple processes such as conductive-convective heat transfer, two-phase fluid flow, intrinsic kinetics of hydrate dissociation, and deformation of solid skeleton. Then, a depressurization experiment is carried out to validate the numerical simulator. A parameter sensitivity analysis is performed to discuss the deformation behavior of hydrate-bearing porous media as well as its effect on production responses. Conclusions are drawn as follows: the numerical simulator named GrapeFloater predicts the experimental results well; the modulus of hydrate-bearing porous media has an obvious effect on production responses; final deformation increases with decreasing outlet pressure; both the depressurization and the modulus decrease during hydrate dissociation contribute to the deformation of hydrate-bearing porous media.
The semicrystalline polyethylene (PE) and amorphous poly(ethylene-co-norbornene) copolymer have been used in a wide variety of applications, especially in packaging. It is a big challenge to improve the transparency of...
The synthesis of isotactic polypropylene (iPP)-based block copolymers by means of controlled isoselective polymerization of propylene with high turnover frequencies is an ongoing challenge in industry and academia. Herein, we report a new strategy for reversible coordinative chain transfer polymerization of propylene and propylene−ethylene with a pyridylamido hafnium/[Ph 3 C][B(C 6 F 5 ) 4 ] catalyst system and iBu 3 Al as a chain transfer agent under conditions that were optimized so that the rate constants for chain transfer and chain propagation were similar (k p ≈ k ct ). Using this new strategy, we could obtain iPP-b-poly(ethylene-co-propylene) and iPP-b-poly(ethylene-co-propylene)-b-iPP block copolymers with controlled molecular weights, hard/soft block ratios, and compositions via a continuous-monomer-feeding approach like that used in living polymerization systems. The polymerization reactions produced uniform block copolymers with previously inaccessible microstructures. The copolymers have both a semicrystalline iPP block ([mmmm] > 99%, melting temperature > 155 °C) and soft ethylene−propylene copolymer blocks (glass transition temperature < −30 °C), with tunable high molecular weights (∼210 kDa) and Schulz−Flory distributions (PDI < 2.5). These promising block copolymers possess dramatically improved tensile properties (30−50-fold increase in elongation at break) relative to those of the iPP homopolymer, whereas the yield strength and strength at break were similar to those of the iPP homopolymer. By tuning the block composition and hard/soft block ratio, we could obtain block copolymers ranging from ductile elastomers to tough plastics. Our new strategy not only sheds significant light on olefin CCTP but also has great potential utility for the industrial production of high-performance polyolefin materials.
Accurately quantifying the aerodynamic forces acting on vehicles and long-span bridges is critical for assessing the safety of moving vehicles on bridges which are subjected to strong wind. It is necessary to consider the aerodynamic interference between vehicles and the bridge, especially for this with the bluff body section and wind barriers. However, very few investigations have been carried out to find aerodynamic coefficients of vehicles on a bridge with the bluff body section and considering the effect of wind barrier. This article therefore carried out wind tunnel tests to determine aerodynamic coefficients of container truck on a bridge with a π-cross section and wind barriers. The influence of vehicle position in different road lanes of the bridge deck and the aerodynamic interference between vehicles on the aerodynamic characteristics of the vehicle and the bridge are investigated. Different heights and ventilation ratios of wind barrier are taken into consideration to examine variations of aerodynamic coefficients with different wind barriers. Furthermore, the change mechanism in the aerodynamic coefficients of the vehicles is observed by analyzing the wind pressure distribution on the surface of the vehicles. The test results show that the different lane locations of the vehicle affect the aerodynamic coefficients significantly, as well as the aerodynamic interference between vehicles with transverse arrangement or longitudinal arrangement, especially for the side force coefficient. The existence of wind barrier reduces the side force coefficients of the vehicle remarkably. Such effects also vary with the ventilation ratio and height of wind barrier.
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