empirical behavior well. The use of the Dynamic Analysis and Design System (DADS) software 

 and the modeling techniques developed under this tasking has extended the Navy's capability to 

 design complex seawater hydraulic system components. 



3. The model predicts a small improvement in impact mechanism performance from an 

 increase in the supply poppet valve size. Validation testing confirmed that the groove in the seat 

 of the supply poppet valve is not necessary. Elimination of the grooved feature from the 

 production drill and substitution of a larger valve seat can reduce component cost. 



4. The seawater motor, presently plumbed in series with the impact mechanism, produces 

 unacceptable back pressure variations to the impact mechanism resulting in erratic behavior and 

 poor impact mechanism performance. Model results confirm that the motor supply must be 

 decoupled from the linear impact mechanism drive chamber pressure if the impact mechanism 

 is to cycle properly. 



5. The smaller, single diameter plunger resulted in a significant reduction in impact 

 energy with a corresponding reduction in drill body motion. Extending plunger length and 

 eliminating the dead band portion of the piston stroke improved impact mechanism efficiency. 

 Use of a single diameter plunger and plunger sleeve can reduce component fabrication cost while 

 improving impact mechanism performance. 



6. The cause of the two distinct modes of drill body motion observed during drill 

 operation has not been identified. Impact mechanism performance continues to show dependence 

 on drill body motion. Test results confirm that minimizing drill body displacement is necessary 

 to maximize impact mechanism performance. Reducing the supply pressure, increasing the 

 applied force on the drill body, and changing the cycle timing have made demonstrable 

 improvements to impact mechanism performance because of small drill body displacement. 



7. The model predicts impact energy values close to the design goal of 7 foot-pounds for 

 a plunger area of 0.34 square inches. The oversize plunger produced a slow return stroke and 

 maintained the drill body position within 0.15 inches. This allowed consistent impact energy. 

 Further improvements were predicted by the model for a lengthened plunger cutout which 

 successfully prevented double impacting, without decreasing impact energy. 



RECOMMENDATIONS 



A goal of this effort was to produce design data for a linear impact mechanism that could 

 be transitioned into a usable diver-operated rock drill. Complete realization of this goal has not 

 been attained. The single poppet-kicker port impact mechanism has proven to be a complex 

 mechanism. There is still much that is not understood such as the observed dual mode drill body 

 displacement behavior. The validated model now serves as a tool that can be used in the 

 optimization process to reach the design requirement of 7 foot-pounds impact energy. Because 

 it is more cost effective to conduct the optimization process using the validated computer model, 

 further optimization of the impact mechanism model is recommended prior to any hardware 

 testing. The following recommendations, based on observed model results, should provide the 

 basis for achieving the design requirement: 



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