Performance of large-diameter pneumatic down-the-hole (DTH) hammers: A focus on influences of the hammer structure

Pneumatic down-the-hole (DTH) hammer has been extensively used in air drillings through hard and ultra-hard geological formations. Numerical modeling can offer close observation on the working behaviors by visualizing internal pressure status as well as provide reliable performance predictions for large-diameter DTH hammers to which conventional empirical and experimental approaches cannot be applied. In this study, CFD simulations coupled with dynamic meshing are utilized to simulate the air flow and piston movement inside the large-diameter DTH hammers. The numerical modeling scheme is verified against a theoretical model published in literature. Effects of structural parameters on hammer performance, including piston mass, piston upper-end diameter, piston groove diameter, and lengths of intake and exhaust stroke in both front and rear chambers, are analyzed in detail by virtue of sets of numerical simulations. The simulations suggest that changing the intake stroke of front chamber has a negligible influence on hammer performance while increasing the piston groove would lower all the four indicators of hammer performance, including impact energy, impact frequency, maximum stroke, and air consumption rate. Changing the other structural parameters demonstrates mixed effects on the performance indicators. Based on the numerical simulations, a large GQ-400 DTH hammer has been designed for reduced air consumption rate and tested in a field drilling practice. The air drilling test with the designed hammer provided a penetration rate 1.7 times faster than that of conventional mud drilling.

Surgical treatment for both-column acetabular fractures using pre-operative virtual simulation and three-dimensional printing techniques

Background:Surgical treatment of both-column acetabular fractures is challenging because of the complex acetabular fracture patterns and the curved surface of the acetabulum.Seldom study has compared the application of three-dimensional(3D)printing technology and traditional methods of contouring plates intra-operatively for the surgical treatment of both-column acetabular fractures.We presented the use of both 3D printing technology and a virtual simulation in pre-operative planning for both-column acetabular fractures.We hypothesized that 3D printing technology will assist orthopedic surgeons in shortening the surgical time and improving the clinical outcomes.Methods:Forty patients with both-column acetabular fractures were recruited in the randomized prospective case-control study from September 2013 to September 2017 for this prospective study(No.ChiCTR1900028230).We allocated the patients to two groups using block randomization(3D printing group,n=20;conventional method group,n=20).For the 3D printing group,1:1 scaled pelvic models were created using 3D printing,and the plates were pre-contoured according to the pelvic models.The plates for the conventional method group were contoured during the operation without 3D printed pelvic models.The operation time,instrumentation time,time of intra-operative fluoroscopy,blood loss,number of times the approach was performed,blood transfusion,post-operative fracture reduction quality,hip joint function,and complications were recorded and compared between the two groups.Results:The operation and instrumentation times in the 3D printing group were significantly shorter(130.8±29.2 min,t=-7.5,P<0.001 and 32.1±9.5 min,t=-6.5,P<0.001,respectively)than those in the conventional method group.The amount of blood loss and blood transfusion in the 3D printing group were significantly lower(500[400,800]mL,Mann-Whitney U=74.5,P<0.001 and 0[0,400]mL,Mann-Whitney U=59.5,P<0.001,respectively)than those in the conventional method group.The number of the approach performed in the 3D printing group was significantly smaller than that in the conventional method group(pararectus+Kocher-Langenbeck[K-L]approach rate:35%vs.85%;x2=10.4,P<0.05).The time of intra-operative fluoroscopy in the 3D printing group was significantly shorter than that in the conventional method group(4.2±1.8 vs.7.7±2.6 s;t=-5.0,P<0.001).The post-operative fracture reduction quality in the 3D printing group was significantly better than that in the conventional method group(good reduction rate:80%vs.30%;x2=10.1,P<0.05).The hip joint function(based on the Harris score 1 year after the operation)in the 3D printing group was significantly better than that in the conventional method group(excellent/good rate:75%vs.30%;χ^2=8.1,P<0.05).The complication was similar in both groups(5.0%vs.25%;χ^2=3.1,P=0.182).Conclusions:The use of a pre-operative virtual simulation and 3D printing technology is a more effective method for treating bothcolumn acetabular fractures.This method can shorten the operation and instrumentation times,reduce blood loss,blood transfusion and the time of intra-operative fluoroscopy,and improve the post-operative fracture reduction quality.