Optimal design on the drag reduction structure for the cylinder of percussion-compact DTH hammer

In order to reduce the frictional resistance of the percussion-compact DTH hammer which was used for trenchless pipeline laying and improve its drilling efficiency, a series of cylinders with the drag reduction structural were designed. Then the progress of the cylinder drilling was simulated by ANSYS/LS-DYNA finite element analysis software. Lastly, their respective drilling efficiencies were analyzed scientifically. The results show that: the cylinder with the drag reduction structural applied to percussion-compact DTH hammer is feasible and its drilling efficiency is much better than the conventional cylinder, Furthermore, the effect of the drag reduction was influenced by the angel of blade cone (Anc), the number of the thick segment (N), the diameter of thick segment (D), the slenderness ratio of the thick segment (Sr) and the location of the thick segment (Los); As to the 130mm cylinder, Anc =20, N=1, D=134mm, Sr=1. 5, and Los at the bottom of the cylinder is an ideal parameter combination. 2013 American Society of Civil Engineers.