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In view of fluid flow in cracks and rock deformation, the mathematical model for shale hydraulic crack propagation was established. The crack flow field and the rock stress field were solved with the finite element method and the extended finite element method respectively, and the two fields were coupled through the Picard iteration. The presented model gave results consistent with those of the classic model, which verified correctness of the former. Based on the model, the effects of the rock elasticity modulus, Poisson's ratio and injection rate on the crack geometry, and the dynamic process of a hydraulic crack approaching a natural crack at an arbitrary angle, were simulated. The numerical results show that the elasticity modulus and injection rate have significant influence on the crack geometry, while the Poisson's ratio has little effect; the more brittle the shale is, the longer and narrower the hydraulic crack will grow; the greater the principal stress difference and the approaching angle are, the easier the hydraulic crack crosses the natural crack; there is a relatively large decrease in the crack width at the intersection between a hydraulic crack and a natural crack; the extended finite element method avoids mesh reconstruction and refinement during computation, and reduces the computing time. The presented model provides an effective theoretical tool for the shale fracturing design. [ABSTRACT FROM AUTHOR]

In this paper, the decision-making behavior is introduced into the queuing models, starting from the customer to maximize the interests, the customer optimal balking strategies in the Geom/G/1 (ES, MV) has been studied. On the premise of unobservable queue, based on a natural reward-cost structure, the overall profit function about the individual customer and the whole customers are constructed by a method of mean value analysis, then the customer equilibrium balking strategies and socially optimal balking strategies are analyzed and determined within the parameters of different ranges. At last, the conclusion is improved by numerical simulation. [ABSTRACT FROM AUTHOR]

Wind characteristics of hurricane Gustavo (2008) in the whole process of making landing on Louisiana State of USA is observed and analyzed, including wind speed, wind pressure, temperature, air moisture, rainfall, etc, on the height of 2.5m, 4m, 5m, 7m, 10m. Then, observation data are divided into three stages: pre-hurricane, in-hurricane and post-hurricane. Thereafter, gust factor, turbulence intensity, integral scale, correlation function, and probability distribution function are obtained in time domain on 10min samples. Power spectrum of wind speed in horizontal direction is fitted and averaged in frequency domain. The calculation and observation of HHT spectrum for wind speed on the height of 10m are conducted in time and frequency hybrid domain. Research shows that: Gust factors and turbulence intensities tend to be larger during the pre-hurricane period, while the integral scale shows opposite trend; the averaged values of gust factor is 1. 67; Gust factor increases exponentially with turbulence intensity; The probability density function of fluctuating wind speed of Gustavo (2008) follows a Gaussian distribution; The averaged power spectrum for wind speed in horizontal direction is higher in low-frequency region and lower in high-frequency region compared with the current power spectrums; The fluctuating wind speed for hurricane is shown to be a nonlinearity and instability stochastic process. [ABSTRACT FROM AUTHOR]

The flow characteristics around the hyperbolic cooling tower model with circular cross section in the wind tunnel experiments are sensitive to Reynolds number. How to get the accurate Reynolds number effects in the wind tunnel tests for super large cooling towers is still a tough task for structural wind engineers. Up to now, engineers have not been able to get the precise values of some dynamic characteristic parameters induced by fluctuating wind due to the shortcomings of early quasi-dynamic sensors. Meanwhile, it is noted that these parameters play important roles in the design process of super large cooling towers which are higher than 165m. This research is based on a 235m high super large cooling tower on the planning. By external pressure wind tunnel tests of the rigid model with scale of 1 : 200, a detailed study on the super high Reynolds number effects of the tower are carried out and some valuable conclusions are gotten after the tests. (1) The influence of the surface roughness to Reynolds numbers effects is sensitive to the flow characteristics; (2) The higher wind speed should be firstly chosen in the wind tunnel tests on the same condition; (3) The best simulation measurements should consider the distribution of mean and fluctuating wind pressures of the model's critical sections, drag coefficients and Strouhal number together; (4) Whether the Strouhal number-Reynolds numbers curve of circular cylinder is suitable to super large hyperbolic cooling towers with changing sections in altitude direction should be checked by field tests in the future. [ABSTRACT FROM AUTHOR]

An effective stress calculation formula was proposed for coal containing gas with considering the swelling stress of gas adsorption based on the effective stress principles for porous media. Referring to dynamic model of porosity and permeability in coal containing gas, solid-gas coupling model which could describe the skeleton deformability of coal containing gas and the compressibility of gas under the solid-gas interaction condition was built. First we made excavation on the three-dimensional model based on the physical parameters of Pingdingshan tenth coal mine to obtain the stress distribution of coal seam after excavated instead of easy uniform loading. Then we simulated the gas drainage from boreholes based on constructed mathematical model. From the results we got: (1) Negative pressure didn't have a great influence on gas drainage. (2) The porosity of coal seam decreased gradually over time. (3) The effective radius increased gradually to a fixed value over time. [ABSTRACT FROM AUTHOR]

In this paper, a high temperature resistant crosslinking acid for high temperature acid fracturing operation in the carbonate reservoir is developed through screening the crosslinking acid thickener and crosslinker and remixing with acid additives. Acid thickener and crosslink-er are crucial to the comprehensive performances of the crosslinking acid under high temperature. DM3802 and JL-10 were screened as the best thickener and the best crosslinker respectively through analyzing of acid solubility, thermostability, crosslinking time, crosslinked viscosity and time of temperature resistance. The dosages were also determined. The compatibility experiment with acid additives also showed the excellent compatibility of this crosslinking acid system. It shows that the crosslinking acid system possesses the characteristics of good high temperature resistance, superb rheological profiles, good prop-carrying capacity, controlled leak-off and good gel breaking property under 120 °C. [ABSTRACT FROM AUTHOR]