Different approach to establish an armament system baseline
Mohan Palathingal Yu Lu US Army, RDECOM-ARDEC Picatinny Arsenal, NJ 07806-5000 Overview
• Conventional design of new armament systems is not fully integrated
• Proposing an integrated approach to provide first order estimate of projectile and gun using optimization methods – Individual models of the projectile and gun are not the primary focus – Emphasis is on the framework for arriving at the baseline system
• The hope is to use this approach to: – Help systems developer narrow down the design space – Provide subject matter experts (projectile and gun) with starting point for further exploration of projectile and gun designs
2 Approach
• Simple Quasi static model set up in ANSYS with constraints imposed due to practical consideration for the bullet and weapon • Full Bore penetrator (base pushed; no sabots) • Simple tapered pressure vessel to simulate Weapon
– Loads on model: • Normalized pressure travel curves from actual Large caliber & Small caliber data (no IB code coupled with the model)
• Design Optimization module in ANSYS is used for iterative design
3 Projectile & Gun Parameters
Gbor Gtor
Gir Pir Pleng Target=25mm Gleng
Range=1000m
4 Algorithm
Working the problem backwards:
1. Begin with Target thickness and Range requirements (say 25mm at 1000m)
2. Projectile design space: Range=1000m • Establish range of penetrator parameters Target=25mm • Establish length range such that penetration does not exceed 1.2 times the length (practical considerations):
• example 0.85L • Establish diameter range such that: • Eg. L/D ratios in the range of 5 Lanz Odermatt fits Pir Pleng 1.0 Striking Velocity 5 Algorithm 3. Calculate striking velocity for that penetrator configuration to defeat the target 4. Calculate velocity falloff, use point mass estimates (from diameter and mass). 5. Calculate muzzle velocity from velocity fall off and the defeat range. 6. Calculate Muzzle energy (from projectile mass and muzzle velocity) 6 Algorithm 3. Weapon Design Space: • Complex gun tube design considerations (auto frettage, critical velocity, thermal considerations etc ) are not considered for this illustration. • Chambrage and breech block features and recoil omitted for simplicity but could be added in other versions. Since we have a full bore projectile, the gun bore is set as the projectile diameter + clearance Gbor Gtor Gir Gleng – Establish a range of acceptable gun tube lengths Gleng (in this model, its set equal to travel) that is acceptable to the customer (say from 0.5m to 2.0m) – Optimization routine picks Gleng from the range 7 Algorithm • Since required muzzle energy is now known, and Gleng is known, the mean base pressure can be calculated • Mean Base Pressure * Travel = Muzzle Energy (Area*Travel) • Breech pressure can then be calculated, since it is on the order of 2/3rd breech pressure (no Lagrange here; no IB code used) • Factor in energy losses (projectile kinetic energy about 29% of chemical energy) 8 Pressurization Model M829A2 Normalized Data Breech Norm vs Travel Norm 1.2 1 0.8 2.5 0.6 0.4 2 0.2 Norm Normalized Pressure Normalized 0 1.5 0 0.2 0.4 0.6 0.8 1 1.2 Normalized Travel 1 Breech 0.5 M919 Normalized Data 0 1.2 1 0 0.2 0.4 0.6 0.8 1 1.2 0.8 0.6 Travel Norm 0.4 0.2 Normalized Pressure Normalized 0 0 0.2 0.4 0.6 0.8 1 1.2 Breech Norm919 Normalized Travel Breech Norm M829A2 Average Breech Norm 919&A2 Tube pressurization data generated from the average of normalized breech pressures 9 Optimization Scheme Optimization Routine Structure Design Variable Constraints: • Projectile Length constraints (penetration cannot exceed 1.2 times length) • Projectile length to Diameter constraints (5 <≤ LD ≤15) • Gun Tube length constraint (set by practical restrictions) • Tube outer diameter constraint (set by practical restrictions) • Tube muzzle diameter constraint (set by practical restrictions) State Variables Constraints: • Projectile axial stress at base not to exceed • Projectile von mises stress not to exceed • von Mises stress at Chamber area not to exceed limit • von Mises stress at Muzzle area not to exceed limit OBJECTIVE Function: • Minimize Volume of Gun Tube (or weight of tube) 10 Sample Results PROJECTILE PARAMETERS (YS 940 MPa, Defeat 0.5 km,Gun tube 1 to 1.5m) 1.5 15 Length (m/s^2*1e6) 1 10 0.5 5 Projectile acceleration 0 0 Projectile 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 Projectile acceleration (m/s^2*1e6) Projectile lengthx10 11 Sample Results Projectile eq. & axial stress (YS 940 MPa, Defeat 0.5 km, Gun tube 1 to 1.5 m) 800 600 (MPa) 400 200 stress 0 ‐200 15 25 35 45 55 65 75 85 95 105 ‐400 ‐600 Projectile ‐800 Target thickness (mm) Ave. projectile eq. stress (Mpa) Ave. projectile axial stress (Mpa) 12 Sample Results GUN PARAMETERS (YS 940 MPa, Defeat 0.5 km, Gun tube length 1.0 to 1.5 m) 25 1.6 1.4 (mm) 20 1.2 (m) Dia 15 1 Bore length & 0.8 10 (kg) 0.6 tube Wt 0.4 5 Gun 0.2 Tube 0 0 15 25 35 45 55 65 75 85 95 105 Gun tube weight Gun bore diameter Gun tube length 13 Summary • A simple model of projectile and gun in an optimization framework has been used to arrive at a first order estimate of the armament system • Future attempts will be focused adding more features to the projectile and gun model to observe if the approach is still feasible for exploring new armament systems 14