Multifractal Characteristics Of Electromagnetic Radiation In Coal And Rock

As an important strategic resource,coal plays an important role in the economic development of our country.Safe and effective coal mine production has great social significance.The coal mine dynamic disaster is one of the key factors to restrict the coal mine production safety.Effective disaster prediction is very important for coal mine safety production.Fractal theory is a mathematical tool for quantitative description of natural phenomena.Because of the accurate description of the nonlinear and complex phenomena,the theory has aroused great repercussions in the academic circles.Multifractal can describe the complex nonlinear characteristics of fractal objects completely and accurately.The fixed mass method has the advantages of no starting point effect,size effect and convergence.In this paper,the fixed mass method is used to analyze the electromagnetic radiation signal of pure coal sample and different proportion of coal samples in the process of uniaxial compression.The multi fractal dimension and multifractal spectrum of electromagnetic radiation signal are obtained.Then,the relationship between the multifractal spectrum and the ratio of the composite roof,uniaxial compressive strength,elastic modulus,elastic energy index,impact energy index and residual energy is analyzed.The conclusions are as follows:(1)In the process of coal and rock material loading,the low frequency electromagnetic radiation signal will be transmitted to the outer space.(2)In the process of uniaxial compression,the number of electromagnetic radiation pulses increases substantially when the sample is in the compaction stage;In the elastic stage,the number of electromagnetic radiation pulse signal began to decrease,and remained stable for a period of time;When the stress increases to coal pressure limit,coal near the main rupture stage,electromagnetic radiation pulse signal break stability,suddenly increased and maintained at a high peak,the peak and the peak approximately equal in elastic stage;When the specimen enters the residual deformation stage,it gradually decreases to the previous level.(3)When the coal rock material is subjected to external loads,the electromagnetic radiation signal emitted by the material is discontinuous,and has the characteristics of paroxysmal.(4)When the coal and rock material is subjected to external loads,the maximum value of the radiated electromagnetic emission signal is proportional to the strength of the coal sample.(5)The value of the electromagnetic radiation signal is positively correlated with the proportion of the whole sample.When the proportion of the roof in the combined coal sample increases,the electromagnetic radiation signal generated in the process of uniaxial compression increases with the ratio of positive index.(6)The fractal theory is used to deal with the electromagnetic radiation signal emitted from coal and rock mass.(7)The whole loading process of the specimen was divided into 20 equal parts according to the time average,and the fractal dimension of each part was calculated by the fixed mass method.It is found that in the same period of time,the larger the statistical moment Q value is,the smaller the fractal dimension value is.The specimen in the loading process,multi fractal dimension will change with the change of stress and specimen loading before rupture,multi fractal dimension showed irregular features of shock,the specimen loaded after the bursting of a rapid increase in multi fractal dimension decreased.(8)The whole loading process is divided into five stages: compaction,elasticity,plasticity,main rupture and residual deformation.The multifractal spectrum of each stage is calculated.When the specimen is in the elastic stage,the multifractal spectrum width decreases slightly.With the increase of stress,the specimen enters the plastic stage from the elastic stage,and the multifractal spectrum width increases.Near the main fracture stage,the multifractal spectral width increases and reaches the maximum value.After entering the residual deformation stage,there is a small reduction.Based on the above analysis,we can draw a conclusion that when the spectral width increases sharply,the impact damage will occur.(9)The combination of coal samples under uniaxial compression,the multifractal spectrum width and roof proportion,uniaxial compressive strength,elastic modulus,elastic energy index,impact energy index,residual energy is proportional.