As part of the rock mass, both the mesoscopic and macroscopic flaws will affect the creep mechanical behavior of the rock mass with nonpersistent joints. This study focuses on this kind of rock mass and establishes a creep damage model to account for the effect of the joint on its creep mechanical behavior. First, on basis of analyzing the rock element creep mechanism and the typical creep deformation curve, a new creep damage constitutive model for the rock element is set up by introducing the damage theory and Kachanov damage evolution law into the classic creep constitutive model such as J body model. Second, the determination method of the proposed model parameters is studied in detail. Third, the calculation method of the macroscopic damage caused by the joint proposed by others is introduced which can consider the joint geometry, strength, and deformation parameters at the same time. Finally, the creep damage model for the rock mass with nonpersistent joints under uniaxial compression is proposed. The calculation examples indicate that it can present the effect of the joint on the rock mass creep mechanical behavior.

Coalbed methane development represents a complex system engineering operation that involves complex technology, many links, long cycles, and various risks. If risks are not controlled in a timely and effective manner, project operators may easily cause different levels of casualties, resource waste and property loss. To evaluate the risk status of coalbed methane development projects, this paper constructs a coalbed methane development risk assessment index system that consists of six first grade indexes and 45 second grade indexes. The weight of each index is calculated based on the structure entropy weight method. Then, a theoretical model for risk assessments of coalbed methane development is established based on the matter-element extension method. Finally, the model is applied to analyze a coalbed methane development project in the southern Qinshui Basin of China. The results show that the overall risk level of the coalbed methane development project is Grade II, indicating that the overall risk of the project is small, but the local risk of the project needs to be rectified in time. The assessment results are consistent with the actual operation of the project, indicating that the established risk assessment model has good applicability and effectiveness.

To explore the diffusion law of harmful gases near the excavation face in tunnel construction on plateaus, select the optimal ventilation parameters, and improve the ventilation efficiency, Ansys Fluent was used to set the environmental parameters according to the highland, where the tunnel is located, and simulate and curve fit the diffusion phenomenon of CO and NO₂ based on the fluid control equations and species transport model. The effects of air velocity, ventilation time, and duct position on the diffusion law of harmful gases were analyzed, from which the optimal ventilation conditions were selected, and the ventilation effects under the optimal conditions were compared with those under the original conditions. The study shows that after the fresh airflow passes through the outlet, part of it flows out along the tunnel wall toward the cave entrance, and the other part interacts with the return air to form a vortex; when the air supply speed is 10 m/s and the distance from the duct outlet to the excavation face is 25 m, the maximum concentration of harmful gases decreases by 92-99% after 20 min of ventilation compared with that before optimization and the smoke exhaust efficiency increases by 2.5% per minute.

Although underground pipeline transportation of crude oil is critical, very few studies have been found in the literature addressing the effects of the pipeline leakage position. To fill the gap, in this study, the influences of the leakage position of a pipeline on the underground diffusion of crude oil were investigated numerically. The results showed that the leakage position largely affects the shape of crude oil diffusion. The diffusion contour of the crude oil changes from shapes of inverted U and ellipse to circle when the leakage positions are located at the top, side and bottom sections of the pipeline. It was known based on numerical results that the leakage position shows limited influence on axial diffusion width and radial diffusion depth of crude oil. Empirical relationships were developed to predict the axis diffusion width and radial diffusion depth. The outcomes of this study provide a technical guidance for the underground pipeline transportation safety and the related emergency management.

In order to analyze the research hotspots of marine energy, the Citespace III software was used to visually analyze marine energy. The database was collected on the criteria of marine energy as the keyword, and time span extended from 2007 to 2016 on the basis of the “Web of Sciencetm core collection database”. The scientific knowledge maps analysis of marine energy has been conducted based on the Citespace III software, and analyzes the active countries/regions, institutions and research hotspots in related research fields. Active countries/regions, institutions and research hotspots of relevant research areas have been studied, and University of Chinese Academy of Sciences is at the first place of whole research institutions in marine energy field. Keywords co-occurrence analysis results show that coast, corrosion, kinetics, evolution and sediments have the highest centralities which are the focal keywords in marine energy research field. The results of the co-citation analysis show that wave energy, tidal stream energy, tidal stream turbines, and the microalgae biofuels are the hotspots in marine energy research field.

The explosion of the combustible gas within the restricted space in the city wells will endanger the people's life and fortune. The syncretic gas detector of MX4 and MX6 are used in this study to detect the harmful gas in the well. The result shows that the main harmful gases are mainly CH₄, H₂S and CO₂, and their content range is given. Then the explosion test of the combustible gas is done in the spherical explosion vessel of 20L in volume in the lab, which studies the effect of the content of the methane and CO₂ on the explosion maximum pressure and its increase rate. Finally, FLACS code is adopted to study the effect of the inert gas CO₂ in the well on effectively restricting the methane combustion and explosive reaction. It is found that CO₂ has the restrict effect on the methane explosion.