Study on the Damage Model of Coal Rock Caused by Hydraulic Pressure and Electrical Impulse in Borehole

The purpose of this study is to study the damage and fracturing effects of high-voltage discharge on coal-rock mass under the action of hydrostatic pressure. Based on the traditional damage evolution model and the change of the effective bearing area and stress around the microcrack of coal-rock mass on a microscopic scale, the expression of macroscopic damage variation of coal-rock mass under the action of electrohydraulic coupling was derived, and its damage constitutive relation was established. The high-voltage pulse water shock stress test of coal-rock mass under the conditions of different water pressures and voltages was carried out, and its damage numerical model was established by the ABAQUS/XFEM. The damage variable values of coal-rock mass with different electrohydraulic parameters were compared to characterize the generation and expansion of internal macroscopic cracks. From the results, it is shown that the damage variable based on the effective bearing area and stress around the crack can represent the morphology and expansion change of crack of coal-rock mass with different electrohydraulic parameters clearly and quantitatively. Different hydrostatic pressures and discharge voltages have influence on the damage variables of coal-rock mass, but different influencing degrees cause different damages on coal-rock mass. The damage of coal rock can be characterized by the change of the effective bearing area and stress around microcracks in coal body. So, stress testing and numerical simulation have verified the correctness of the damage model.

Numerical modelling of percussion water jets driven by multiple collisions

A numerical model is proposed in this research to analyse the behaviour of the pulse jet driven by percussion hammer. The mass of the hammer is usually larger than that of the piston and the resistance of compressed water can low down the piston, thus multiple collisions occur each time when the hammer strikes the piston. The proposed model has the merit to consider various striking possibilities to simulate the process of pulse water jet generated by multiple hammer collisions. In addition, a hammer-driven percussion pulse jet is developed and the corresponding experiments are carried out for verifying the reliability of the numerical model. Comparison results show that the predicted pressure and velocity values match well with the experimental data. The simulation of the generation of pulsed jet reveals the collisions and motions of the hammer and the piston and provides understanding of the mechanism of the pulse jet generation. The design of the hammer-driven pulse water jet device can be optimised through modelling different combinations of the parameters of the chamber, hammer, piston and nozzle for a specific purpose of rock fragmentation.

Assessment of four different media for the mass culture of Ceriodaphnia reticulata (Jurine) as a live fish feed

Experiments on the mass culture of Ceriodaphnia reticulata (Jurine) were carried out in aquarium water for 54 days with different media like cowdung (1.5g/L), pulse bran water (50g/L), poultry manure (0.45g/L) and snail faeces (faeces of six apple snails). All the media were fertilized by 50-100% of the initial amount of feed in every 7 days. About 100 individuals of C. reticulata were inoculated as starter in 50 litres of water (2 individuals/ml).The temperature of the media ranged from 24-30oC during study period. pH of the culture media varied i.e., 9.1 ± 0.40 in cowdung; 8.72 ± 0.73 in pulse bran water, 8.82 ± 0.72 in poultry manure and 7.5 ± 0.55 in snail faeces. The highest average population of C. reticulata was observed in cowdung (8.56 ± 4.11individuals/ml), moderate in poultry manure (4.21 ± 2.97 individuals/ml) and snail faeces (2.52 ± 3.01individuals/ml). The lowest growth of C. reticulata was recorded in pulse water (0.37 ± 0.69 individuals/ml). The culture media with cowdung as well as poultry manure and snail faeces were found to be useful for artificial mass production of C. reticulata. DOI: http://dx.doi.org/10.3329/jasbs.v39i2.17849 J. Asiat. Soc. Bangladesh, Sci. 39(2): 129-138, December 2013