Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5066 

ARL-TR-2462 April 2001 

A Novel Soft Recovery System for the 

155-mm Projectile and Its 

Numerical Simulation 

Avi Birk and Douglas E. Kooker 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
Abstract 

There is a requirement to soft catch, without exceeding a deceleration rate of 1,600 g, 

and within less than 300 m, an unmodified 102~lb SADARM (Sense and Destroy Armor) 

projectile fired at 840 m/s. This report presents a soft-recovery concept and its 

numerical simulation. The concept entails aerodynamic deceleration of the projectile in 

a long tube attached to the gun barrel. The midsection of the tube is bound between a 

diapluagm and a free piston and is prepressurized to about 2 MPa. As the projectile 

enters the tube, the shock wave preceding it ruptures the diaphragm and the projectile 

decelerates as high pressure builds between it and the free piston. The piston 

disengages and travels forward scooping water. The waterlog that forms in front of the 

piston effectively increases the piston’s mass and also induces braking force because of 

the water friction with the tube wall. The projectile’s deceleration is controlled, and 

eventually the projectile exits the tube with a velocity of 10 m/s. The numerical 

simulation, based on the method of characteristics, incorporates unsteady 

one-dimensional fluid dynamics that captures the extensive wave dynamics- This 

report details the effects on the projectile’s deceleration of the midsection length, initial 

pressure, and the water mass. From the simulation, it is possible to soft capture the 

SADARM projectile within 120 m. 

, 

ii 
l 

Contents 

List of Figures V 

List of Tables vii 

1. Introduction 1 

1.1 The Requirement for a Soft Recovery System . . . . . . . . . . . . ..-. e .. . . . . . . . . . . . . . . . . . . . . -1 

1.2 Soft Recovery Concepts and Systems . . . . . . . .._..._.......... _ . . . . . . . . . . . . . . . . . . . ..**.......-. 1 

2. The Proposed Soft Recovery System 3 

3. Mathematical Model of the Flow Dynamics in the SRS Tube 

Sections 5 

3.1 Solution Methodology . . . . . . . . . . . . . . . ..___.............. e .__................_.-*-.................--..... 8 

3.1.1 The Projectile Boundary Conditions (Figure 4) . . . . . . . .._.............-... 8 

3.1.2 The Free-Piston Boundary Conditions (Figure 5) . . . . . . . . . . . . . . .._....... 9 

3.1.3 Solution for a Grid Point in the Inner Flow (Figure 6) . . ..-..... 11 

3.1.4 The Shock Wave Boundary Jump Conditions (Figure 7) . . . . . . . . . 12 

3.1.5 The Tube Exit Boundary (Figure 8) m . .. . . . . . . . . . . ..*..*...................*...... 13 

3.1.6 The Shock Wave Reflection (Figure 9) . ..I_*......................l_.....f..... 14 

3.2 The Initial Values of the Flow in the Tube . . ..- e .. . . . . . . . . . .._I....................__.... 15 

4. Simulation Results 16 

4.1 Coding and Run Parameters ~...~.~.~..._*....~...~~......*..,.~..~...~..~.......*......~~~~..~..-. 16 

4.2 Typical Flow Dynamics With and Without Inclusion of 

the Rupture Disc Process (Figure 10) . . . ..~~~~~~..~.1..........~~~~..~..~.*..*......f.~.~.f....*....~. 17 

4.3 Effects of the Water Friction (Figure 11) . . . . . . . . . . . . . . . . . . ..--...................--....... 18 

4.4 Flow Dynamics for Various Length and Pressure 

Parameters . . . . . . . . . ..l.l.._..***...............-.. e . . . ..-.......* ..~...~~~.~....~*..~......~*.~....~..** . . . . . . . . . . . . 18 

5. Summary and Conclusions 19 

. . . 

lu 

6. References 23 
Distribution List 

Report Documentation Page 

25 

27 

iv 
List of Figures 

Figure 1. The proposed soft recovery system concept. ..,,.. I . . . . . . . . . . . . . . . . .._.................. 4 

Figure 2. The zonal construction of the SIis tube flow . . . . _ .. . . . . . . . . . . . . . .._ I . . . . . . . . . . . . . . . . . . . . . 5 

Figure 3. Illustration of numerical coordinate motion with time. .f............,...._....... 7 

Figure 4. Construct of the projectile’s boundary. ..,...................................-...,.......... 8 

Figure 5. Construct of the free-piston boundaries. . _. . . . . . . . . . . . . . . . . . . _ _ ._. . . . . . . . . . . . . . . . . _._... 9 

Figure 6. Construct of an inner flow point. ..** . . . . . . . . . . . . ..~~.~.........~~......~~~_.~~............... 11 

Figure 7. Construct of the traveling shock waves ._................._........*..........,.,......... 12 

Figure 8. The tube exit boundary. .._.................,.....................-................-................ 13

Figure 9. Flow regions in a reflecting shock wave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Figure 10. Dynamics in the SRS-effects of the transition tube/rupture 

diaphragm process. . . . . . . .._.........................--................*-.................-..................... 17 

Figure 11. Dynamics in the SRS-effects of the water column friction . . . . ...__..+. . ...18 

Figure 12. Dynamics for 100-60 SRS tube charged initially to 200 and 300 psi. . ..20 

Figure 13. Dynamics for 7CL50 SRS tube charged initially to 2p and 300 psi. . ...20 

Figure 14. Dynamics for SO-50 SE tube charged initially to 200 and 300 psi . ...21 

Figure 15. Dynamics for 80-60 SRS tube charged initially to 200 and 300 psi . . ...21 

Figure 16. Snap shots of pressure and velocity distribution in the 

80-60/300-psi tube * .*......,.-..-...........*.*.....**...................~.................--..*.~.*............. 22 
vi 
List of Tables 

Table 1. Selected 155~mm SIX!3 parameters. . . . . ..f..___............_._.-.............-.................. 22 
, 

. . . Vlll 
1. Introduction 

f 

1.1 The Requirement for a Soft Recovery System 

With advances in microelectionic and electco/optic sensors, smart projectiles 

have become a reality. Such a projectile is the U.S. Army’s xM898 SADARM 

(Sense and Destroy Armor) 155 mm. Because of the sensitive components and 

packaging inherent to these designs, projectile tests to evaluate performance 

and/or failure analysis are very expensive. Owing to the projectile’s complexity 

and thin-wall construction, a dummy or malfunctioned projectile recovered after 

being fired downrange may be too damaged for useful analysis. Hence arose the 

need for a soft recovery system (SRS) for the XM898 and similar projectiles. Soft 

recovery is defined here as the recovery of the projectile in a manner that the 

projectile does not exceed certain deceleration limits and damage thresholds. 

The foremost proponents of the SRS have been Ami Frydman [l] and Donald 

Carlucci [2]. The major specifications for the SRS are (1) the projectile is to be 

fired from a standard gun barrel with standard propellant charge, (2) the 

projectile shall not be modified in any way, (3) the SRS shall be able to softly 

catch a projectile fired at 840 m/s within 200 M from the muzzle without 

exceeding a deceleration level of 1,600 g, and (4) the SRS shall have a 

rapid-turnaround. The utilization of the SRS will enable the verification of 

launch integrity and functionality of the projectile’s components, by measuring 

the functional and/or structural performance of the components during the first 

1,200 Cal. of the projectile’s travel. The principal author of this report has 

proposed a novel SRS concept that f&ills the SRS specifications and is believed 

to have important advantages when compared to other concepts. This report 

details a numerical model and its predictions for the flow dynamics in the 

proposed SRS-work funded by the SADARM Program Management Office to 

verify the feasibility of the concept and provide a tool for its engineering. 

1.2 Soft Recovery Concepts and Systems 

Basically, all of the techniques for the soft recovery of fired projectiles had been 

established over 20 years ago. Some of the techniques were actually tried out; 

others existed only in the form of patents. However, only a few of the techniques 

comply with the present specifications for the SRS. Wright [3] gave a 

comprehensive list of techniques that existed up to the early 1970s. Paul Baer [4] 

of the U.S. Army Ballistic Research Laboratory (BRL),* Aberdeen. Proving 

Ground, MD proposed an SRS for the 155-mm cannon. He suggested firing the 

* The U.S. Army Ballistic Research Laboratory (BRL) was deactivated 30 September 1992 and 

subsequently became part of the U.S. Army Researc h Laboratory (ARL) on 1 October 1992 

1 
projectie in a side-vented gun such that the projectile exits with a low velocity 

into a recovery tube filled with compressed air. The rifled gun tube was to be 

connected to the recovery tube via a “rotating band squeezer” followed by a 

diaphragm that would retain the compressed air. Paul Baer simulated 

numerically the flow in his proposed SRS, but used a lumped parameter 

approach that completely ignored the very important wave motion that can 

produce large peaks of projectile deceleration. A major drawback of Baer’s SRS 

is the requirement to modify the gun by the side vent. In the early 198Os, 

Honeywell Inc. [5] constructed an SRS for BRL and the system was tested 

successfully with a 155-mm cannon [6]. Although the Honeywell system had the 

advantage of being able to accommodate multiple calibers, it had a major 

drawback-it required a modification of the projectile. The system employed a 

water scoop mounted to the projectile that slowed the projectile via momentum 

exchange with water in a trough. The projectile also was modified during flight 

because the technique required the stripping of the projectile’s A (rotating) band. 

A physically sound concept for an SRS is the Ballistic Compression Decelerator 

patented by the McDonnell Douglas Corporation in 1972 [q. The projectile is 

fired into a prepressurized succession of “decelerator tubes” that are separated 

by multiple diaphragms such that the pressure builds up ahead of the projectile 

(thus decelerating it), and the diaphragms rupture before being pierced by the 

projectile. 

An SRS based on the McDonnell Douglas patent is presently in operation [l, 21 at 

the German firm Rheinmetall W&M, and this SRS is the main competitor for the 

SRS proposed in this report. It can stop an 840 m/s 155~nun projectile in 200 m. 

The main disadvantage of the multiple decelerator tube concept is that it 

employs long tubes, and multiple diaphragms. Therefore, it is expensive to 

construct and it occupies a large amount of real estate. A variation on the 

ballistic compression concept is the McDonnell Douglas 1976 patent [8] titled 

“Projectile Recovery System With Quick Opening Valves-” Here, quick opening 

valves that unseal the tube as the projectile approaches them replace the 

diaphragms. This concept is considered impractical because of its reliabihty. 

Two patents that do not rely on ballistic compression are the “Rifled Soft 

Recovery System,” [9] and “Multicaliber Projectile Soft Recovery System” [lo]. 

The rifled concept relies on a spinning projectile being accurately reengaged in a 

recoiled rifled tube. This concept requires great precision of the firing cycle and 

tube alignment; it is not proven and will probably subject the projectile to 

balloting and excessive stresses. The multicaliber concept has the advantage 

(unlike ballistic compression) of handling multi calibers for the same SRS. A 

deformable element is placed in the path of the projectile and the projectile 

becomes embedded in the element. Mechanical forces are applied to stop the 

element. This concept lacks the deceleration control that the ballistic 

compression technique has, and it subjects the projectile to excessive forces upon 

embedding. 

2 
2. The Proposed Soft Recovery System 

The proposed SRS concept for the 155-n-u-n projectile is based on the ballistic 

compression principle. It is sketched in Figure 1. Unique to the concept is the 

incorporation of a water-controlled free piston in the decelerator tube. The 

principle of operation is as follows. The atmospheric transition tube (ATT) has 

rifling that continues the barrel’s rifling. The rifling is tapered and it transitions 

to a smooth barrel. The spin-stabilized 155-mm projectile enters the ATT where 

the tapered rifling in the tube gradually compresses the projectile’s rotating band 

such that the band engraving is squeezed out and a good seal is formed between 

the band and the smooth wall portion of the ATT. The tapered rifling is believed 

to alleviate balloting of the projectile in the tube. The band sealing assures that 

compressed gas in front of the projectile will not leak around the projectile. The 

combustion gases behind the projectile escape through the vent holes in the ATT 

and the pressure on the projectile’s rear face effectively drops to atmospheric 

value. The shock wave that precedes the projectile ruptures the 750-psi 

diaphragm that holds the pressurized air and enters into the pressurized ,tube. 

When the shock wave reaches the free piston and reflects from it, the free piston 

overcomes the shear ring that holds it against the pressurized air. The free piston 

then moves down the guide tube pushing ahead a growing column of water. 

The free piston is made of light material, e.g., plastic such as high-density 

polyethylene. The free piston has to be light enough so that initially it accelerates 

quickly and thus prevents high-pressure spikes from developing in the 

pressurized tube section. The water effectively increases the free piston mass 

with time and also adds frictional force due to the water boundary layer on the 

tube wall. The growth of the free piston mass and the added water friction 

retard the free piston motion and thus regulate the air pressure between the free 

piston and the projectile to a sustained level between 2,000 and 4,000 psi. This 

pressure is enough to slow the projectile from 840 m/s to 10 m/s within 100 m 

without exceeding the 1600-g deceleration limit. The water and compressed air 

escape in the slotted brake tube, and the projectile is stopped in the tapered 

lining of the brake tube. In operation of the SRS, the initial pressure and water 

mass are easily adjusted to allow fine control of the projectile exit velocity into 

the brake tube. 

The expendable parts in this SRS concept are the diaphragm, the shear ring, and 

the free piston. Because the proposed SRS length is much shorter than the 

aforementioned Rheinmetall’s SRS and it employs fewer expendable parts, it is 

believed that the construction and operation of the proposed SRS is significantly 

cheaper than Rheinmetall’s SRS. 

3 


The time-dependent governing equations in each zone assume isentropic flow of 

a Noble-Abel gas with constant molecular weight, covolume, and ratio of specific 

heats. Furthermore, the flow is assumed to be one-dimensional and inviscid, 

which of course neglects heat transfer to the tube wall. The one-dimensional 

treatment of the problem necessarily assigns a flat front to the projectile, a front 

that in reality is an elongated ogive. Obviously, boundary layer effects are not 

accounted for. In practice, the growth of boundary layers in the long sections of 

the tube will,constrict the flow and modify the strength of the traveling shock 

waves. Intuitively, viscosity and boundary layer effects will tend to dissipate the 

wave motion in the tube thus resulting in lower peak pressure loading (and 

hence deceleration) on the projectile, Thus, the simplified assumptions are likely 

to result in conservative peak pressure values, The present model incorporates 

the most important aspects of the flow physics and it is therefore adequate for 

the purpose of feasibility studies of the SRS concept, and for a parametric study 

of the concept. 

With pressure P, density p, velocity u (with respect to laboratory coordinates), 

and sound speed a, these equations can be written in characteristic form as 

du %p.a.-0, 

dt dt 

which are integrated, respectively, along the right (+) and left (-) running 

directions, 

dz --=U+a, 

dt 

where U is the material velocity relative to the coordinate velocity V,, i.e., U = u - 

VC. The energy equation can be written in the form 

-- dP dp-() &. a2 ‘x- ’ 

which is integrated along the streamline 

dz -U. dt- 

(3) 

With the temperature T, covolume b, ratio of specific heats y (=cp/cv), and gas 

constant ‘3 (= universal gas constant/molecular weight), the Noble-Abel 

equation of state is simply 

P 5JI.T 

-- 

;- 1-p.b’ (5) 

6 

3.1 Solution Methodology 

In general, the flow is solved sequentially from zones 1 to 4. For each zone, the 

boundary conditions must be solved first before the interior flow solution, The 

solution is known at time t=O and it is marched from time t to time t+dt using the 

characteristic/free-stream construct shown in Figures 4-8. All notations are 

noted in these figures. 

3.1.1 The Projectile Boundary Conditions (Figure 4) 

PROJECTILE 

Figure 4. Construct of the projectile’s boundary. 

From equations 1 and 2, upstream along the 4-1 left-running characteristic: 

PI-P,-(p-a),,.(u,-u,)=O, 

where 

(7) 

b- ) -( a 41 _ (P’4-44 

2 1 - 

From Newton’s Second Law: 

yF= ‘tMaV) 

dt ’ L- 

{ 

50 t- p2 PI0 + p* -- 

2 2 

Y 

(8) 

8 

From equations 1 and 2, downstream along the 2-3 right-running characteristic: 

P, -P3 +(P-a),, .(uz -u3)=0, (10) 

where 

( ) P+b,= i (Pa), +b42 

2 I - 

From equations 3 and 4, along the streamline 20-2: 

P2 -P20 -aZzo .(P2 -Pzo)=% 

where 

2 

a220 = ai f ai, i 2 I . 

Similarly, along the streamline 10-l: 

where 

Upstream along the 7-1 left-running characteristics: 

PI -P7 -(p-a)71 .(q -u,)= 0, 

where 

From Newton’s Second Law: 

co + p* I P,o +P, 

2 2 

-$p, .(Lw -u2 +f *AFp =+{(M, +M,,)a~, 

(11) 

(13) 

where M,,, and MWl are the masses of the water column at time t and t+dt, L, 

is the water column length, and M, and A, = A, are the free piston mass and 

cross- section area. 

10 
The frictional force due to the water cohunn, 

Pw * (Lw a2 * fX,, $Am = pw .(L,, eu; vfi -LW2,, $,, ef,,).;A,, 

where the friction coefficient is taken from [13] for turbulent flow in a 

Prandtl universal law for smooth circular tube). 

tube (the 

f= 1 

16 - log,, Re&)- 0.4 

where Re= Pw-U*D is the Reynolds number. 

PW 

There are six unknowns in equations 10-14, namely: u, , PI, p1 , and u2, P2, p2, 

where, of course, sound speeds al and a2 are found from equation 6. The 

remaining equation relates u, to u,, i.e., u, = (1 + K) * u2, where the factor K is 

the inil& ratio of water to air volumes in the guide tube. This solution requires 

iteration similar to the projectile solution. 

3.1.3 Solution for a Grid Point in the Inner Flow (Figure 6) 

tA A POINT IN THE INNER FLOW 

0 1 

#19, a- , ,‘I ‘\ 

7 - 

/* i 

,a’ . 

i, 

** 1 ‘. s 

a’ I ; 

,*’ 

, 

i ‘. 

tit 

*’ 1 ‘. 

---I---------- Characteristic 

I’ 

u ~‘a I! 

* 

. -a-.-.-.- Streamline 

U -,a 

i i ‘. \ 

,*’ iu , 

.’ i 

; 

/ 

‘. 

i t 

5 z 

A h 

Figure 6. Construct of an inner flow point. 

The inner flow solution is based on two characteristics lines (right-running and 

left-running) and one streamline. The unknowns are I+, p,, and PI which are 

found from equations similar to equations 10, 11, and 13. (where, again, the 

sound speed is found from equation 6). 

11 
3.1.4 The Shock Wave Boundary Jump Conditions (Figure 7) 

-__----------_----.-Characteris

TRAVELING SHOCK WAVE -. I d -. -. - m I. -. - Streamline 

x-- Shock Wave 

_ . _ . ” _ ” _ . . 

f 

Figure 7. Construct of the traveling shock waves. 

Because of the projectile’s supersonic velocity, a shock wave leads the projectile’s 

motion. Once the projectile enters the catch-tube (that has the same diameter as 

the projectile), the shock wave detaches from the projectile and becomes a 

traveling wave. A traveling shock wave will also originate in front of the free 

piston as the piston accelerates to supersonic velocity. 

The values at point 1 (Figure 7) are uniquely determined by the upstream flow 

field and are found identically to the inner-point solution. The remaining 

unknowns are ug, p2, Pz, and u,, (the shock wave velocity), requiring four 

equations for a solution. The characteristic line trailing the shock wave on the 

high-pressure side provides one equation. The remaining three equations are 

jump conditions across the discontinuity to conserve mass, momentum, and 

energy. 

12 
Mass: 

Momentum: 

Energy: 

p2 *(u2 -usw>= Pl++ -%v); (15) 

p* f&U2 ‘(U2 -u,)=p1 +Plul4+ -hv); (16) 

e2 +S+$(u2 -Q) = e, + 

Pz 

:++.(u, -u&J; (17) 

where e = cv . (T - TO) and T is related to P and p through the equation of state 

(equation 5). 

Equations 15-17 can be rearranged such that together with the characteristic 

equatiori, they result in two nonlinear algebraic equations that include only usW 

and Pz as unknowns. The numerical solution is obtained by iteration. 

3.1.5 The Tube Exit Boundary (Figure 8) 

This characteristic exists if the exit 

flow is supersonic 

Figure 8. The tube exit boundary. 

If the exit flow is supersonic or sonic, the unknowns are ul, p1 , PII the solution is 

like an inner-point solution. If the flow is subsonic, PI is atmospheric, and 

u1 and p, are found from the solution of the right-running 3-l characteristic and 

the streamline. 
The solution methodology is as follows. An initial value of p1 is guessed, the 

equations are solved, p, is updated, and the point 4 is found. If the point lies left 

of the exit plane, the flow is supersonic, and the equations are re-solved using the 

two characteristics 3-l and 4-1 until p1 converges. If the point 4 lies right of the 

exit plane, the flow is subsonic, and the equations are re-solved using only the 

3-1 characteristic and the assumption that the static pressure at the exit plane is 

atmospheric. 

3.1.6 The Shock Wave Reflection (Figure 9) 

0 r- reflected 

Cl .- -- b 

0 fbehind 

front 

Figure 9. Flow regions in a reflecting shock wave. 

The shock wave that separates zone 1 from zone 2 will reflect from the rupture 

disc, thereby causing a pressure differential across the disc that is sufficient for 

its rupture. During the flow process, the wave also reflects from both the 

projectile’s face and the free piston’s rear. 

Figure 9 shows schematically the shock wave reflection process from a boundary 

that may have a velocity u, . The flow conditions in the “front” and “behind” 

regions are known from the preceding shock wave boundary solution. The 

boundary velocity, u r, which is also the gas velocity in the reflected region at the 

boundary, is known from the projectile or free piston boundary solutions. Thus, 

the unknowns are p,, P,, and uSWr (the reflected shock wave velocity). These 

unknowns are easily solved using the conservation of mass, momentum, and 

energy as in equations 15-17. 

14 
Mass: 

Pb .(ub -USWr)=& ‘b, -%d; (18) 

Momentum: 

p~+Pr.Ur.(Ur-Uswr)=Pb+Pb-Ub’(Ub-U5Wr); (19) 

Energy: 

3.2 The Initial Values of the Flow in the Tube 

At time t=O, the projectile enters the tube with supersonic velocity (uP = 

840 m/s). The velocity, uSW , of the resultant shock wave is obtained by 

employing an impulsive piston-motion equation [14] 

where M, = u, and the subscript 2 denotes zone 2 (Figure 2). 

The jump conditi%s across the shock wave (equations 15-17) yield the initial 

flow parameters in zone 1. 

As stated before, the rupture disc is designed to rupture once the shock wave 

reflects from it. At this time, the flow conditions at the location occupied by the 

rupture disc are found using shock-tube equations [14]. 

(22) 

(23) 

15 
where the subscript r refers to the conditions at the reflected region of the 

incident shock wave (Figure 9), the subscript 2P refers to pressurized zone 

between the ruptured disc and the free piston, and the subscript rup refers to the 

conditions initiated at the rupture disc location. In equations 22-24, the 

unknowns are Pmp , u rup, and M rup . 

U swrup -%p ‘a2P is the speed of the shock wave generated by rupturing the disc. 

In reality, at the time of the rupturing, the projectile is very close to the rupture 

disc, and hence, the shock wave that reflects from the rupture disc, reflects 

shortly from the projectile and overtakes/overwhelms the rupture disc shock 

wave. 

4. Simulation Results 

4.1 Coding and Run Parameters 

The numerical solution was coded in FORTRAN 77 using the Watcom [15] 

Compiler. The code is run via an executable file in Microsoft Windows 

(Windows NT 4.0, Windows 95, or greater) environment. The program input is 

done interactively, and output data is automatically stored in ASCII files on the 

computer hard disc. The program prompts for lengths of the SRS tube sections; 

the weights of the projectile, free piston, and water; the initial pressure in zone 3; 

the projectile velocity; the hold pressures of the rupture diaphragm and shear 

ring. Other input parameters include the number of grid points per 

computational zone, time constants, run options, and output frequency. 

Typically, the number of grid points per computational zone varies from 11 to 51 

points where computational zones 1 and 2 are more finely resolved. These grid 

resolutions were found to be adequate- higher resolution did not produce 

materially different results. The time steps of the solution were determined from 

the Courant-Friedrichs-Lewy condition [16]. When the free piston or the shock 

waves exit the tube, this causes a step pressure drop at the exit plane, and it was 

necessary for numerical stability to represent the step pressure as a time-wise 

exponential function. Typically, the time constant for the exponential function 

was chosen to be from 3 to 7 time steps. Run options include various default 

parameters; and in addition the choices of ignoring the water column friction 

and/or ignoring the transition tube and the rupture disc. Another run option is a 

Regula Falsi [17]-based iteration of either the initial pressure in zone 3, or the 

total mass of the distributed water, for a desired projectile exit velocity. For the 

simulation runs described here, the free-piston weight is fixed at 5 kg that is a 

practical weight for a polyethylene-made piston. Also, the projectile weight and 

muzzle velocity are fixed at the operational values of 46 kg and 840 m/s. The 

16 



900 

800 

700 

I 

600 

g 800 

x 400 

e 300 

200 

100 

0 

Projectile impact velocity: 840 m/s. Tube exit velocity: 10 m/s. 

Initial pressure in tube: 200,300 pai (1.38,2.07 MPa) in a 60-m section 

Total water weight: 36.98, 22.72 kg, distributed in a 40-m section 

Free-Piston weight: 5 kg 

I I, I II 1 I I I L 11 ” 1 L 11 1 1 ’ 

-10 0 10 20 30 40 50 60 70 80 90 100 

35 

30 

25 

20 i 

ii 

15 2 

i 

10 L 

5 

-0 

POSITION, m 

Figure 12. Dynamics for 100-60 SRS tube charged initially to 200 and 300 psi. 

900 

800 

700 

Jr) 600 

E 500 

G 

3 400 

s 300 

200 

100 

0 

Projectile impact velocity: 640 m/s. Tube exit velocity: 10 m/s. 

Initial pressure in tube: 200, 300 psi (1.36, 2.07 MPa) In a 50-m section 

Total water weight: 46.94, 37.13 kg, distributed in a 20-m section 

Pressure on projectile’s front 

.-a-.-*- Free-Plstonvelocitv 

I I I1 ! I I I I 11 I( 

-10 0 10 20 30 40 50 60 70 

POSITION, m 

35 

30 

25 

20 g 

W* 

15 I 

cn 

9 

10 % 

5 

-0 

Figure 13. Dynamics for 7030 SRS tube charged initially to 200 and 300 psi. 

20 


. 

6. References 

1. Frydman, A. Personal communication with A. Birk. U.S. Army Research 

Laboratory, Aberdeen Proving Ground, MD, January 2000. 

2. Carlucci, D. Personal communication with A. Birk, U.S. Army Research, 

Development, and Engineering Center, Dover, NJ, February 2000. 

3. Wright, L. D. “An Investigation of High ‘g’ Launch, So&Recovery Test 

Facihties.” Tank Systems Laboratory Technical Report No. RE-TR-7l-12, U.S. 

Army Weapons Comman d, R&D Directorate, Rock Island, IL, March 1973. 

4. Baer, P. G. “DigitaI Computer Analysis of a 155MM Soft Recovery System.” 

Report No. 1634, U.S. Army BaIlistic Research Laboratory, Aberdeen Proving 

Ground, MD, February 1973. 

5. Clarke, E. V., C. R. Ruth, J. W. Evans, J. E. Bowen, J. R. Hewitt, and J. L. 

Stabile. “Large Cahber ProjectiIe Soft Recovery.” ABRL-MR-03083, U.S. Army 

Ballistic Research Laboratory, Aberdeen Proving Ground, MD, February 

1981. 

6. Evans, J. W., C. R. Ruth, and E. V. Clarke. “Soft Recovery Tests of a 155~MM 

Cannon Launched Guided ProjectiIe Warhead, Type T.” ARBRL-MR-03107, 

US. Army BaIIistic Research Laboratory, Aberdeen Proving Ground, MD, 

May 1981. 

7. Teng, R. N. “Ballistic Compression Decelerator.” U.S. Patent No. 3,678,745, 

issued to McDonnell Douglas Corporation, July 1972. 

8. Covey, W. B., J. R. Mastandrea, and R. N. Teng. “Projectile Recovery System 

With Quick Opening Valves.” US. Patent No. 3,940,981, issued to McDonnell 

Douglas Corporation, March 1976. 

9. Curchack, H. D. “Rifled Soft Recovery System.” U.S. Patent 4,002,064, issued 

to U.S. Department of the Army, February, 1976. 

10. Curchack, H. D., and A. D. Hahn. “Multi-Caliber Projectile Soft Recovery 

System.” U.S. Patent No. 435,460, issued to U.S. Department of the Army, 

June 1980. 

11. Kooker, D. E. “Modeling of Compaction Wave Behavior in Confined 

Gram&r Energetic Material” BRL-TR-3138, U.S. Army BaIIistic Research 

Laboratory, Aberdeen Proving Ground, MD, August 1990. 

12. IMSL. “User Manual/Math Library.” Ver 1.1, Houston, Texas, 1989. 

13. Bird, R. B., W, E. Stewart, and E. N. Lightfoot. Transport Phenomena. John 

Wiley & Sons, Inc., p. 204,196O. 

23 
14. Thompson, P.A. CompressibZe-Fluid Dynamic. McGraw-Hill Book Company, 

Chapter 8,1972. 

15. Sybase Inc. Watcom FORTRAN77, Version 11.0,1996. 

16. Peyret, R., and T. D. Taylor. Compufafional Methods fiy Fluid Flow. SpringerVerlag, 1985. 

17. Carnahan, B., H. A. Luther, and J-O. Wilkes. AppIied Numerical Methods. John 

Wiley & Sons, Inc., Chapter 3.8,1969. 

24 
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imulation 

vi Birk and Douglas E. Kookex 

AFU-m-2462 

een Proving Ground, MD 2 10055066 

‘M SADARM, Picatinny Arsenal, NJ 07806-5000 

1. SUPPLEMENTARY NOTES 

2a. DISTRlBUTlON/AVAlLABILlTY STATEMENT 

Lpproved for public release; distribution is urilimited. 

- 12b. DlSTRlBUTlON CODE 

3. ABSTRACT(Maximum 200 wwds) 

There is a requirement to soft catch, without exceeding a deceleration rate of 1,600 g, and witbin less than 300 m, ar 

unnodified 102-lb SADARM (Sense and Destroy Armor) projectile tied at 840 m/s. This report presents a 

iofi-recovery concept and its numerical simulation The concept entails aerodynamic deceleration of the projectile in a 

ong tube attached to the gun barrel. The midsection of the tube is bound between a diaphragm and a free piston and ti 

3repressurized to about 2 MPa. As the projectile enters the tube, the shock wave preceding it ruptures the diaphragm 

md the projectile decelerates as high pressure builds between it and the free piston. The piston disengages and travel: 

?orward scooping water. The waterlog that forms in front of the piston effectively increases the piston’s mass and alsc 

nduces braking force because of the water friction with the tube wall. The projectile’s deceleration is controlled, ant 

wentually the projectile exits the tube with a velocity of 10 m/s. The numerical simulation, based on the method o 

haracteristics, incorporates unsteady one-dimensional fluid dynamics that captures the extensive wave dynamics. Thi! 

eport details the effects on the projectile’s deceleration of the midsection length, initial pressure, and the water mass. 

From the simulation, it is possible to soft capture the SADARM projectile within 120 m. 

14. SUBJECTTERMS 

soft recovery, free piston, projectile, SADApM 

15. NUMBER OF PAGES 

33 

16. PRlCE CODE 

17. SECURITY CMSSIFICATION 18. SECURITY CLASSIACATlON 19. SECURIW CLASSIFICATION 20. LIMITATION OF ABSTRACT 

OF REPORT OF THIS PAGE OF ABSTRACT 

UNCLASSIFIED TJNCLASSIFIED UNCLASSIPIED L U-L 

NSN 7m,.snILwnn c,-.n.+.rl cn- ‘y1e IDa., *_L\o\ 

Presaibed by ANSI Std. 23918 298-102 
INTENTIONALLY LEFT BLANK. 

28 
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