2008 International ANSYS Conference

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2008 International ANSYS Conference NUMERICAL OPTIMIZATION UTILIZING FLUID, THERMAL AND STRUCTURAL MODELING OF THE 155 MM NLOS-C MUZZLE BRAKE Robert Carson

1 2008 International ANSYS Conference NUMERICAL OPTIMIZATION UTILIZING FLUID, THERMAL AND STRUCTURAL MODELING OF THE 155 MM NLOS-C MUZZLE BRAKE Robert Carson RDECOM/ARDEC/WSEC Benet Labs Jeffrey Greer RDECOM/ARDEC/WSEC Benet Labs Mark Witherell RDECOM/ARDEC/WSEC Benet Labs 2008 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

3 NLOS-C Muzzle Brake 3.5 Caliber Length Optimized Muzzle Brake Improved Efficiency over M284 Designed for Maximum Recoil Reduction Compatibility with all 155mm Ammunition 2008 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary

4 Problem Statement The high rate of fire steady state temperature for the NLOS- C muzzle brake is unknown. Therefore, the muzzle brake was structurally modified to increase material where stress concentrations were highest as shown in previous ambient condition analyses as to ensure survivability at extreme high temperatures. A coupled thermal/structural analysis will provide accurate temperatures allowing for the optimization of the muzzle brake potentially reducing weight by approximately 5-10% ANSYS, Inc. All rights reserved. 4 ANSYS, Inc. Proprietary

5 Outline One-Way Coupling Structural-Thermal Analysis Approach Design of Experiment Setup Fluent Steady-State Convection Heat Transfer Analysis ABAQUS Unsteady Thermal Analysis Fluent Unsteady Structural Loading Analysis ABAQUS Unsteady Structural Analysis ABAQUS Weight Reduction and Optimization Conclusions 2008 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary

6 Fluent to ABAQUS One-Way Coupling Fluent ABAQUS Steady Heat Fluxes Unsteady Temperature Unsteady Pressures Dynamic & Static Stress Analyses 2008 ANSYS, Inc. All rights reserved. 6 ANSYS, Inc. Proprietary

7 One-Way Coupling Structural-Thermal Analysis Approach Step 1 Steady-State Fluent CFD Surface Convection Heat Flux at Various Wall Temperature and Inlet Pressure Conditions. Fluid Only Modeled. Step 2 Step 3 Polynomial Models of Surface-Average Heat Flux Constructed Using Designed Experiments For 33 Different Surface Locations. Polynomial Models Utilized in Unsteady ABAQUS Thermal Analysis Model of Solid to Determine End Temperature Condition after Firing 96 Rounds. Natural Convection Assumed Between Rounds. Step 6 Weight Reduction Based on Removing Material in Areas of Low Stress. Rerun Unsteady Thermal and Structural ABAQUS Models. Step 5 Unsteady ABAQUS Structural Model to Determine Stress vs. Time on the Muzzle Brake. Unsteady Surface Average Input from Fluent Utilized for Loads. Step 4 Un-steady Fluent CFD Analysis to Determine Surface- Average Pressure vs. Time Loading of Muzzle Brake at 33 Different Surface Locations 2008 ANSYS, Inc. All rights reserved. 7 ANSYS, Inc. Proprietary

8 Design Of Experiment (DOE) Setup Controllable Factors Determining our Design Our design will contain curvature, therefore a Response Surface Method (RSM) is chosen to approximate the shape of the surface with a polynomial. 2 Factors are of interest that will have an impact on heat flux. 33 Responses are chosen. Each represents heat flux area-weighted averages. PROCESS (4 step process) Noise Factors Iterative Experimentation Analysis Factors Process Responses ANOVA Contour Plots Optimization Conjecture Experiment Subject Matter Knowledge Empirical Models (Polynomials) RSM Flow Chart Design Responses 2008 ANSYS, Inc. All rights reserved. 8 ANSYS, Inc. Proprietary

9 Design of Experiment (DOE) Setup Identifying Response Surfaces The heat flux was averaged over the segregated surfaces. Each surface was a response for the given factors. In the D-Optimal architecture, 24 runs populated the DOE 2008 ANSYS, Inc. All rights reserved. 9 ANSYS, Inc. Proprietary

059 mm Density-based, Explicit, Steady, Node-based Propellant Modeled,

11 CFD Heat Transfer Setup Gambit One-eighth Section 1,112,178 Tet-Cells Fluent 11 row boundary layer applied. 1 st Row Height = mm Density-based, Explicit, Steady, Node-based Propellant Modeled, Volumetric Reactions Deactivated k-epsilon Turbulence Model 2008 ANSYS, Inc. All rights reserved. 11 ANSYS, Inc. Proprietary

Velocity vectors show good flow movement and turning in the

12 Step 1: CFD Heat Transfer Analysis Velocity Magnitude shows excellent shock structure in the critical vane areas. Velocity vectors show good flow movement and turning in the vanes as well ANSYS, Inc. All rights reserved. 12 ANSYS, Inc. Proprietary

Step 1: CFD Heat Transfer Analysis Total Temperature is the temperature at the thermodynamic state that would exist if the fluid were brought to zero

13 Step 1: CFD Heat Transfer Analysis Total Temperature is the temperature at the thermodynamic state that would exist if the fluid were brought to zero velocity. Shows relative temperature distribution on the different sections of the brake ANSYS, Inc. All rights reserved. 13 ANSYS, Inc. Proprietary

Step 2: DOE Analysis Significant Model: F-value of 8951 with p-value < 0.0001.

9995 is in reasonable agreement with Adj R-Squared of 0.9992.

14 Step 2: DOE Analysis Significant Model: F-value of 8951 with p-value < R-Squared, Adj R-Squared and Pred R-Squared: Pred R-Squared of is in reasonable agreement with Adj R-Squared of Adeq Precision: Measures signal to noise ratio. A ratio greater than 4 is desired. Our ratio is 297. F1-u 2008 ANSYS, Inc. All rights reserved. 14 ANSYS, Inc. Proprietary

15 Predicted Normal % Probability Step 2: DOE Analysis Residuals should follow a straight line which, on this specially scaled graph, indicates a normal distribution Predicted vs. Actual shows how the model predicts over the range of data Random scatter should occur about the 45 degree line Clusters below or above indicate under or over prediction E E E E E+08 Normal Plot of Residuals Internally Studentized Residuals Predicted vs. Actual Actual -9.96E E E E E ANSYS, Inc. All rights reserved. 15 ANSYS, Inc. Proprietary

f1-u DOE Export Model Graph shows non-linearity The output used is the polynomial of the two factors ABAQUS will use these 33 polynomials for the

16 f1-u DOE Export Model Graph shows non-linearity The output used is the polynomial of the two factors ABAQUS will use these 33 polynomials for the heat flux 1E E+7-4.5E E+7-1E ANSYS, Inc. All rights reserved. 16 ANSYS, Inc. Proprietary

Step 3: ABAQUS Thermal FEA (Gen 4) Maximum Muzzle Brake High Rate of Fire Operating Temperature Firing Sequence: Fire 1 full magazine Rate: 6 shots per minute Magazine reload of 12 minutes Repeat

17 Step 3: ABAQUS Thermal FEA (Gen 4) Maximum Muzzle Brake High Rate of Fire Operating Temperature Firing Sequence: Fire 1 full magazine Rate: 6 shots per minute Magazine reload of 12 minutes Repeat firing process for 4 magazines Boundary Conditions Worst-Case high temperature conditions Temperature dependant natural convection (no wind) h 7.5 C W Solar radiation heat flux 1,100 2 m Radiation to ambient (exterior facing surfaces only): Emissivity 0.88 Assuming perfect conduction between gun tube and muzzle brake threads and pilots Ambient air temperature 54ºC Mesh: utilized linear tetrahedron elements W 2 m 2008 ANSYS, Inc. All rights reserved. 17 ANSYS, Inc. Proprietary

18 Static Pressure (psi) Step 3: ABAQUS Thermal FEA (Gen 4) Maximum Muzzle Brake High Rate of Fire Operating Temperature Thermal Loading: 33 surfaces were loaded with the pressure and wall temperature dependent heat fluxes provided from the DoE results Example: Surface F1L A polynomial equation for pressure vs. time was used to calculate pressures during the firing heating steps f 2 3 ( x) a bx cx dx ANSYS, Inc. All rights reserved. 18 ANSYS, Inc. Proprietary Time (s)

19 Step 3: ABAQUS Thermal FEA (Gen 4) Maximum Muzzle Brake High Rate of Fire Operating Temperature The maximum temperature of the Gen 4 muzzle brake 10 seconds after the 95 th shot = 467ºC = 872ºF Max Temp after 95 th shot = 467 C 2008 ANSYS, Inc. All rights reserved. 19 ANSYS, Inc. Proprietary

20 Step 4: Fluent Unsteady Loading Model Temperature and pressure patched into gun barrel based on projectile ready to enter muzzle brake. Flow allowed to expand using unsteady, coupledexplicit inviscid model. Surface average pressure vs. time recorded during run for multiple surfaces. Used as input for unsteady ABAQUS Model 2008 ANSYS, Inc. All rights reserved. 20 ANSYS, Inc. Proprietary

21 Step 5: ABAQUS Structural FEA (Gen 4) FEA Boundary Conditions Mesh: Same mesh as Thermal FEA. Added mid-side nodes to create quadratic elements (allows for import of 95 th shot temperature field) Modeled with temperature dependant material properties Modulus of Elasticity Poisson s Ratio Yield Strength Ultimate Strength Specific Heat Thermal Conductivity 2008 ANSYS, Inc. All rights reserved. 21 ANSYS, Inc. Proprietary

22 Step 5: ABAQUS Structural FEA (Gen 4) Maximum Muzzle Brake High Rate of Fire Operating Temperature Collar Boundary Condition (simulated twice) Modeled statically Modeled including gun system dynamics Muzzle Brake Accel Collar BC Gun Tube Accel Pressure Loading: Utilized 3-D CFD transient CFD results for the 33 surfaces 2008 ANSYS, Inc. All rights reserved. 22 ANSYS, Inc. Proprietary

Step 5: ABAQUS Structural FEA (Gen 4) Results:

and Yield Strength Approved for public release;

23 Step 5: ABAQUS Structural FEA (Gen 4) Results: Von Mises Stress Results: Factor of Safety Max Stress Lowest Factor of Safety = 1.53 Notes: - FOS based upon Temp, Mises Stress, and Yield Strength Approved for public release; distribution is unlimited. Case GOVT - All Gray areas 7 August have 2008 a FOS > ANSYS, Inc. All rights reserved. 23 ANSYS, Inc. Proprietary

24 Step 6: Weight Reduction Initiative (Gen 5) Examples of Changes from Gen 4 (~12 in all) 1.) Reduce Lock Key Boss Height Gen 4 Gen 5 2.) Reduced in Supports on the last 2 Vanes (increased ID of support) Gen 4 Gen ANSYS, Inc. All rights reserved. 24 ANSYS, Inc. Proprietary

brake 10 seconds after the 95 th shot = 475ºC = 888ºF Max Temp after 95

25 Step 7: ABAQUS Thermal FEA (Gen 5) Maximum Muzzle Brake High Rate of Fire Operating Temperature The maximum temperature of the Gen 5 muzzle brake 10 seconds after the 95 th shot = 475ºC = 888ºF Max Temp after 95 th shot = 475 C 2008 ANSYS, Inc. All rights reserved. 25 ANSYS, Inc. Proprietary

26 Step 8: ABAQUS Structural FEA (Gen 5) Results: Von Mises Stress Results: Factor of Safety Reference: Stress = 73% Max Stress Max Stress Lowest Factor of Safety = 1.39 Notes: - FOS based upon Temp, Mises Stress, and Yield Strength - All Gray areas have a FOS > ANSYS, Inc. All rights reserved. 26 ANSYS, Inc. Proprietary

27 One-Way Coupling Structural-Thermal Analysis Approach Step 1 Steady-State Fluent CFD Surface Convection Heat Flux at Various Wall Temperature and Inlet Pressure Conditions. Fluid Only Modeled. Step 2 Step 3 Polynomial Models of Surface-Average Heat Flux Constructed Using Designed Experiments For 33 Different Surface Locations. Polynomial Models Utilized in Unsteady ABAQUS Thermal Analysis Model of Solid to Determine End Temperature Condition after Firing 96 Rounds. Natural Convection Assumed Between Rounds. Step 6 Weight Reduction Based on Removing Material in Areas of Low Stress. Rerun Unsteady Thermal and Structural ABAQUS Models. Step 5 Unsteady ABAQUS Structural Model to Determine Stress vs. Time on the Muzzle Brake. Unsteady Surface Average Input from Fluent Utilized for Loads. Step 4 Un-steady Fluent CFD Analysis to Determine Surface- Average Pressure vs. Time Loading of Muzzle Brake at 33 Different Surface Locations 2008 ANSYS, Inc. All rights reserved. 27 ANSYS, Inc. Proprietary

28 Conclusions Seven percent (7%) Reduction of Weight on the Gen 5 Muzzle Brake Structural viability of both Gen 4 and Gen 5 verified with FOS measurements. Gen 4 Lowest FOS 1.53 Gen 5 Lowest FOS 1.39 Applicability of the procedure to other components is possible and encouraged. Current work on another platform for a tube analysis is underway ANSYS, Inc. All rights reserved. 28 ANSYS, Inc. Proprietary

NDIA 2010 Numerical Prediction of Large Caliber Cannon Impulse. Bob Carson Mechanical Engineer Fluid Dynamics Analyst Date: 19 May 2010

NDIA 2010 Numerical Prediction of Large Caliber Cannon Impulse Bob Carson Mechanical Engineer Fluid Dynamics Analyst Date: 19 May 2010 AGENDA Where is Benet Laboratories? What is a Large Caliber Cannon?