2008 international ansys · pdf file2008 international ansys conference ... step 3: abaqus...

© 2008 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

2008 International

ANSYS Conference

Approved for public release; distribution is unlimited. Case GOVT 08-8120. 7 August 2008

NUMERICAL OPTIMIZATION UTILIZING FLUID,

THERMAL AND STRUCTURAL MODELING OF

THE 155 MM NLOS-C MUZZLE BRAKE

Robert Carson – RDECOM/ARDEC/WSEC – Benet LabsJeffrey Greer – RDECOM/ARDEC/WSEC – Benet LabsMark Witherell – RDECOM/ARDEC/WSEC – Benet Labs

© 2008 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. ProprietaryApproved for public release; distribution is unlimited. Case GOVT 08-8120. 7 August 2008

Non-Line-of-Sight Cannon

• FCS NLOS-C

• 155mm Self-Propelled Howitzer

• 6 Rounds/Min

• 24 Round Magazine


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


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%.


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


Fluent to ABAQUS One-Way Coupling

Steady Heat Fluxes Unsteady Temperature

Fluent ABAQUS

Unsteady PressuresDynamic & Static

Stress Analyses


One-Way Coupling Structural-Thermal

Analysis Approach

Steady-State Fluent

CFD Surface

Convection Heat Flux

at Various Wall

Temperature and Inlet

Pressure Conditions.

Fluid Only Modeled.

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.

Un-steady Fluent

CFD Analysis to

Determine Surface-

Average Pressure

vs. Time Loading

of Muzzle Brake at

33 Different

Surface Locations

Unsteady ABAQUS

Structural Model to

Determine Stress vs.

Time on the Muzzle

Brake. Unsteady

Surface Average

Input from Fluent

Utilized for Loads.

Weight Reduction

Based on

Removing Material

in Areas of Low

Stress. Rerun

Unsteady Thermal

and Structural

ABAQUS Models.

Step 1 Step 2 Step 3

Step 4Step 5Step 6


Design Of Experiment (DOE) Setup

• 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

Controllable Factors

Noise Factors

Responses

(4 step process)

Analysis

Conjecture

Design

Experiment

Iterative Experimentation

Optimization

Contour Plots

ANOVA

Empirical Models (Polynomials)

Responses

Process

Factors

Subject Matter Knowledge

RSM Flow Chart


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


DOE Populated CFD Runs

• Two Factors

– Wall Temperature

– Static Pressure


CFD Heat Transfer Setup

• Gambit

– One-eighth Section

– 1,112,178 Tet-Cells

• 11 row boundary layer applied.

• 1st Row Height = 0.059 mm

• Fluent

– Density-based, Explicit, Steady,

Node-based

– Propellant Modeled, Volumetric

Reactions Deactivated

– k-epsilon Turbulence Model


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.


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.


Step 2: DOE Analysis

• Significant Model: F-value of 8951 with p-value <

0.0001.

• R-Squared, Adj R-Squared and Pred R-Squared:

Pred R-Squared of 0.9995 is in reasonable

agreement with Adj R-Squared of 0.9992.

• Adeq Precision: Measures signal to noise ratio. A

ratio greater than 4 is desired. Our ratio is 297.

F1-u


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

Internally Studentized Residuals

No

rma

l %

Pro

ba

bili

ty

Normal Plot of Residuals

-2.06 -1.04 -0.03 0.98 2.00

1

51020305070809095

99

Actual

Pre

dic

ted

Predicted vs. Actual

-1.00E+08

-7.25E+07

-4.50E+07

-1.75E+07

1.00E+07

-9.96E+07 -7.46E+07 -4.96E+07 -2.46E+07 3.88E+05


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

-45

216

477

738

1000

1892088

39875886

7785

-1E+8

-7.25E+7

-4.5E+7

-1.75E+7

1E+7

f1-u


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

– Solar radiation heat flux ≈ 1,100

– 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

Step 3: ABAQUS Thermal FEA (Gen 4)

Cm

W2

2m

W




– 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

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 0.01 0.02 0.03 0.04 0.05 0.06

Time (s)

Sta

tic

Pre

ss

ure

(p

si)

32)( dxcxbxaxf



Max Temp after

95th shot = 467 C


– The maximum temperature of the Gen 4 muzzle brake 10 seconds after the 95th shot = 467ºC = 872ºF


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, coupled-

explicit inviscid model.

• Surface average pressure vs. time recorded

during run for multiple surfaces.

• Used as input for unsteady ABAQUS Model


FEA Boundary Conditions

– Mesh: Same mesh as Thermal FEA. Added “mid-side” nodes to create quadratic elements (allows for import of 95th shot temperature field)

– Modeled with temperature dependant material properties

• Modulus of Elasticity

• Poisson’s Ratio

• Yield Strength

• Ultimate Strength

• Specific Heat

• Thermal Conductivity

Step 5: ABAQUS Structural FEA (Gen 4)



– Collar Boundary Condition (simulated twice)

• Modeled statically

• Modeled including gun system dynamics

– Pressure Loading:

• Utilized 3-D CFD transient CFD results for the 33 surfaces


Collar BC

Muzzle Brake Accel

Gun Tube Accel



Lowest Factor

of Safety = 1.53 Max Stress

Results: Von Mises Stress Results: Factor of Safety

Notes:

- FOS based upon Temp, Mises Stress, and Yield Strength

- All Gray areas have a FOS > 3.0


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 5




– The maximum temperature of the Gen 5 muzzle brake 10 seconds after the 95th shot = 475ºC = 888ºF

Max Temp after

95th shot = 475 C



Results: Von Mises Stress Results: Factor of Safety

Reference: Stress = 73% Max Stress

Max Stress

Notes:

- FOS based upon Temp, Mises Stress, and Yield Strength

- All Gray areas have a FOS > 3.0

Lowest Factor of

Safety = 1.39


One-Way Coupling Structural-Thermal

Analysis Approach

Steady-State Fluent

CFD Surface

Convection Heat Flux

at Various Wall

Temperature and Inlet

Pressure Conditions.

Fluid Only Modeled.

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.

Un-steady Fluent

CFD Analysis to

Determine Surface-

Average Pressure

vs. Time Loading

of Muzzle Brake at

33 Different

Surface Locations

Unsteady ABAQUS

Structural Model to

Determine Stress vs.

Time on the Muzzle

Brake. Unsteady

Surface Average

Input from Fluent

Utilized for Loads.

Weight Reduction

Based on

Removing Material

in Areas of Low

Stress. Rerun

Unsteady Thermal

and Structural

ABAQUS Models.

Step 1 Step 2 Step 3

Step 4Step 5Step 6


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.

2008 international ansys · pdf file2008 international ansys conference ... step 3: abaqus...

Documents