Natural gas (NG) network and electric network are becoming tightly integrated by microturbines in the microgrid. Interactions between these two networks are not well captured by the traditional microturbine (MT) models. To address this issue, two improved models for single-shaft MT and split-shaft MT are proposed in this paper. In addition, dynamic models of the hybrid natural gas and electricity system (HGES) are developed for the analysis of their interactions. Dynamic behaviors of natural gas in pipes are described by partial differential equations (PDEs), while the electric network is described by differential algebraic equations (DAEs). So the overall network is a typical two-time scale dynamic system. Numerical studies indicate that the two-time scale algorithm is faster and can capture the interactions between the two networks. The results also show the HGES with a single-shaft MT is a weakly coupled system in which disturbances in the two networks mainly influence the dc link voltage of the MT, while the split-shaft MT is a strongly coupled system where the impact of an event will affect both networks.Index Terms-Dynamic modeling, hybrid natural gas and electricity system (HGES), interaction, microgrid, microturbine (MT), natural gas network.

The present paper presents a numerical approach to investigate the surface layer characteristics after ultrasonic surface rolling process (USRP), which is a severe plastic deformation process involving complex static extrusion and dynamic impact. Efforts are made in the development of finite element model (FEM), accompanied by assessment of material constitutive relation and meshing accuracy as well as definition of loading condition according to the technological principle of USRP. The majority of processing parameters have been taken into account, and results are discussed in terms of residual stress, surface roughness and workhardening. As supplied 40Cr disc was subjected to ultrasonic surface rolling for validation of FEM, and the residual stresses predicted from the FEM are in good agreement with the measurements obtained by X-ray diffraction method, indicating that the present FEM can be used as a fast prediction tool for the design of ultrasonic surface rolling parameters.

After being subjected to ultrasonic peening treatment (UPT), the resistance of X65 pipeline steel to hydrogen sulphide corrosion was investigated through electrochemical, immersion and slow-strain-rate testing. In addition, the UPT-induced compressive residual stresses layer and related changes in the steel near-surface microstructure and hardness were examined by scanning electron microscopy, optical microscopy and X-ray diffraction. The obtained results revealed that UPT was able to significantly improve the corrosion potential of X65 pipeline steel and reduce its hydrogen sulphide corrosion rate, while the formation of the compressive stress layer increased the steel's tensile strength and inhibited hydrogen blistering.

A method combining ultrasonic impact treatment with electrospark was developed to fabricate ceramic coatings on Ti-6Al-4V alloy. In this paper, the mechanism of the combined process is described in detail. The microstructure, chemical states, phase composition and surface residual stress of the ceramic coated titanium alloy were presented. The coatings mainly consist of carbides of titanium. The hardness of the coating increased significantly owing to the existence of the ceramic phase. Further, the impact process and the narrow space that the shock ball traverses decrease the surface roughness of the sample after the combined process. Finally, the surface residual stress of the sample treated by the combined process is compressive stress.

No abstract