Appendix A 

 DETAILS OF DADS MODEL 



DYNAMIC MODEL 



The software selected for model development was the Dynamic Analysis and Design 

 System (DADS). The developed computer model of the linear impact mechanism qualitatively 

 mimicked empirical test results obtained during prior rock drill evaluation testing. After model 

 validation, parametric studies were performed for comparison to baseline model results. Model 

 refinements lead to predictions of performance improvements. 



The basic building blocks for the model consisted of bodies, some fixed to an inertial 

 reference frame, and some allowed to move; joints between the bodies; springs; hydraulic 

 accumulators; valves; actuators; line elements; and control functions. The control and hydraulic 

 functions in the model were divided into four sections: 



1 - Supply Pressure Activation 



2 - Poppet Motion 



3 - Plunger Motion 



4 - Piston Motion 



Figure A-l shows the activation of the supply pressure. The nominal supply pressure is 

 supplied by a large accumulator (SOURCE). The switch (VALVE. SWITCH) is initially closed 

 and, at a selected time, is opened to supply pressure to the drill (PS). 



Figure A-2 shows the effects of poppet motion. The poppet is considered to act as a 

 valve (VALVE. POPPET) which controls flow to the drive chamber. A curve is used to translate 

 the displacement of the poppet (DIS.PPHPOl) into a spool setting (SPOOL.POPPET). In the 

 closed position, the supply pressure applies a force on the poppet (ACT.POPPET1). In addition 

 to the supply pressure acting to open the poppet, the kicker port pressure (PK) acts to hold the 

 poppet closed (ACT.POPPET2). Included is a small biasing spring that works to close the poppet 

 when the pressures are balanced. 



When the poppet opens, additional area on the poppet is exposed, and the supply pressure 

 must be applied to the added area. This was initially modeled using a curve to represent the 

 added area and multiplying by the supply pressure to obtain the added force. This was later 

 changed to better reflect a more complex pressure distribution due to the fluid flow velocity 

 decreasing as the flow cross-sectional area increases. A closer approximation was achieved by 

 applying the pressure in the poppet chamber to the added area at all times. This change was 

 made by adding line element (LINE3) discussed below. Poppet chamber pressure (PPO) is 

 applied to the added area to hold the poppet open (ACT.POPPET3). 



Figure A-3 shows the operation of the plunger. Flow from the supply port to the kicker 

 port, and from the kicker port to exhaust, is regulated by the position of the plunger. Curves 

 used to represent the plunger as a spool valve were based on the dimensions of the plunger cutout 

 and galleries in the plunger sleeve. These curves are used to translate the displacement of the 



A-l 



