No abstract

This paper aimed to research the effects of inertial mass coefficient on knotless netting models used in tuna purse seine. Knotless nettings were modeled and simulated using mathematical and mechanical models. In the simulation, the marine environment was imitated in the computer. The results demonstrated that inertial mass coefficient was a key factor to affect the stability of knotless model, especially in the sinking process, and the model presented more stable and quicker convergent as the inertial mass coefficient increased. During fishing operation at sea, the instability of the sinking of purse seine with knotless nettings, especially in the area with complicated currents and waves, might be due to the smaller inertial mass coefficient of knotless nettings.

According to the dynamic theory and characteristics of the bridge modal analysis theories and methods for bridge were introduced which mainly included solving the nature frequency, mode shape, and damping ratio with the Rayleigh-Ritz method, subspace iteration method. And the application of bridge modal shape sequences and frequencies with their changes were illustrated in the diagnosis of the bridge disaster. Dynamic testing of the bridge should be measured for vibration mode and frequency which could be used to analyze the change of supports, constraints and other facilities of the bridge and to predict the working condition of the structure.

Hydraulic fracturing is the main method to increase the output of coal-bed methane wells, however, the hydraulic fracturing result of coal-bed methane well is usually affected by large number of factors such as the conditions of coal-bed, the conditions of coal-bed methane well, fracturing operation parameters and so on. As a result, the fracturing operation result is difficult to predict. This paper assumed coal seam thickness, the depth of coal seam, coal seam gas content and other six main factors which affect hydraulic fracturing results by analysis various factors. Membership function of the expert system was established to divide the level of each factor. The established method which applies the expert system to predict the hydraulic fracturing results of coal-bed methane wells was based on expert database. Using the established expert system to calculate 200 groups of test data and the prediction error rate is only 3.5%. The prediction results are accurate and reliable, and can provide guidance for coal-bed methane wells fracturing optimization.

Considering pore pressure variation of sidewall rock, which is caused by drilling fluid filtering, the porosity variation model of sidewall rock in sandstone reservoir and effective stress factor variation model are established, and according to relationship between pore pressure and total volume strain of sandstone, the calculation model of safe window of drilling fluid density on sandstone reservoir, with which considered variation of porosity and effective stress factor are finally established. Applying the calculation of this model shows that: with increased function of drilling fluid filtering, which is as increased as pore pressure of sidewall rock, caving pressure that ensures well hole stability is increased, fracturing pressure is decreased, safe window of drilling fluid is narrowing, and that is against of safety drilling.