| Rock burst is one of the major dynamic hazards encountered in coal mining.In recent years,it has been found that the degree of damage to the support does not correspond exactly to the magnitude of the impact ground pressure,as small magnitudes of impact ground pressure can also produce large impact damage.The degree of damage to the support is related to the frequency of the shock wave and the inherent frequency of the support when the impact pressure occurs.In order to enhance the anti-shock performance of the "support and enclosure" system,this paper uses theoretical analysis and numerical simulation methods from the perspective of resonance of the "support and enclosure" system to investigate the dynamic response law of the energy-absorbing support and the key component,the energy-absorbing anti-shock column,in the time and frequency domains of the step-type roadway.The dynamic response law of the energy-absorbing support and the key component-energy-absorbing anti-scouring column of the marchway is studied from the perspective of resonance of the system.The main results are as follows:(1)The calculation method of the inherent frequency and vibration function of the energy-absorbing anti-surge column is proposed.The energy-absorbing column is simplified into a rod model,and the theoretical equation of the inherent frequency of the energy-absorbing column is obtained,and it is concluded that the inherent frequency of the energy-absorbing column decreases nonlinearly with increasing length,decreases nonlinearly with increasing material density,and increases nonlinearly with increasing material modulus of elasticity,which provides a theoretical basis for the column design.(2)The dynamics model of the stride type energy-absorbing brace-roadway enclosure system was established.The steady-state response of the system is related to the initial dynamic load amplitude,dynamic load frequency,mass matrix,stiffness matrix and damping matrix.The extreme value of the displacement of the top beam of the energy-absorbing support is positively related to the load amplitude and the mass of the energy-absorbing support,and negatively related to the support stiffness and support damping,which provides a theoretical basis for the design of the brace.(3)Dynamic response analysis of the energy-absorbing anti-surge column from the time and frequency domain.The natural frequency of first two orders of energy-absorbing column is within the vibration range of rock burst surrounding rock,and its natural frequency varies with the length,material density and elastic modulus in accordance with theoretical results,and natural frequency decreases slightly with the increase of settcing force.When resonance occurs,the amplitude of displacement,velocity and acceleration response of energy-absorbing column is significantly higher than the response at other frequencies.The dynamic load amplitude is the same,and the smaller the frequency,the greater the give way speed.When designing column,its natural frequency should be adjusted to avoid the rock burst surrounding rock vibration frequency range to prevent resonance from occurring.(4)Dynamic response analysis of the step-type energy-absorbing bracket from the time and frequency domain.The natural frequency of step-type energy-absorbing support slightly decreases with the increase of setting force,and setting force has less influence on vibration mode.When resonance occurs,the displacement,velocity and acceleration response amplitudes increase significantly.The dynamic load amplitude is the same,the smaller the dynamic load frequency,the greater the energy-absorbing bracket gives way to speed,the greater the acceleration amplitude,the greater the peak value of support resistance and the greater the range of change.The low frequency and high amplitude of dynamic load are not conducive to the energy-absorbing bracket’s ability to give way and support.(5)Dynamic response analysis of the step-type energy-absorbing bracket-roadway rock system.Under the dynamic load,the maximum displacement of energy-absorbing support occurs at top beam,the displacement distribution of top beam is large in the middle and small at the two ends.The stress distribution of top beam is high in middle and low at two sides;the acceleration amplitude of surrounding rocks near the top plate and near the source of dynamic load is larger.When dynamic load frequency is natural frequency of energy-absorbing support,the difference between vibration frequency of column and vibration frequency of surrounding rock is small.In the design process of step-type energy-absorbing support,the resonance factor should be taken into consideration to avoid vibration frequency range of surrounding rock under impact pressure and to reduce the dynamic response of support system.The results provide a theoretical basis for the design of step-type energy-absorbing support,which is of great significance for enhancing the impact protection performance of support and surrounding rock system. |
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