The Lumped Parameter Theory And Modeling Method Of The DTH Hammer Drilling System

In the vibration analysis of the pneumatic DTH hammer drilling system, the impact characteristics of DTH need to research. An authentic simulation relies on the accuracy of the impact model and boundary conditions. The application of the lumped parameter theory is limited in multi-body dynamics because it affects the accuracy of the impact model. In response to the above issue, this paper makes the following work:Firstly, the piston-bit impact process is simplified to the axial impact of two flexible rods. The axial impact of flexible rods with Hertz contact and a spring as the substitution of the Hertz contact are maily studied. By means of LS-DYNA the longitudinal impact of a hammer with a rounded end of different curvature radii on a drill rod is numerically simulated The FE simulation and the impact experiment validate the linear spring model. Service conditions are also given.Secondly, the lumped parameter model is studied. To breaks down the limitations that the stiffness and damp of the contact and the penetration can not be ascertained, a parameter estimation program of the lumped model is compiled.The problem of ascertaining contact parameter in impact model is solved.Finally, aiming at the problems of the model of the pneumatic DTH hammer drilling system, by accurately defining the impact contact of the piston with the bit, setting the bit-rock boundary conditions and investigating the effect of drillstring modal truncation method and the time step on the simulation accuracy, optimize the dynamic model of drill string. It provides a basis for the further vibration response analysis of the DTH hammer.This paper makes an in-depth analysis of DTH impact process. The limitations in lumped parameter theory are broken down and the impact parameters of the DTH impact model are ascertained with the parameter estimation program. The DTH hammer model provides a basis for the further vibration response analysis of the drillstring.