Numerical Modeling of Explosively Loaded

Concrete Structures Using a Coupled CFD-

CSD Methodology

Michael E. Giltrud, Joseph D. Baum, Orlando A. Soto

Fumiya Togashi; Applied Simulations Inc.

Rainald Löhner; George Mason University

International Explosive Safety Symposium, 9 August 2018

2

Outline

• Methodology

• Background

• Kasun Finite Element Model

• Kasun Finite Element Analysis• 1 - 6.9kg Bare Charge

• 16 - 6.9kg Bare Charges

• 1 - 155mm Cased Charge

• 16 - 155mm Cased Charges

• Summary and Conclusions

3

Flow Solver: FEFLO

Adaptive, unstructured grids (triangles/tetrahedra)

Compressible & incompressible flows

Inviscid, laminar & turbulent flow

Several turbulence models (MILES, Smagorisnky, Baldwin-Lomax, Spalart-Allmaras, K-Epsilon)

Explicit and implicit time stepping

EOS: Real air, water (Tate), SESAME, polynomials, tables

State-of-the-art shock capturing numerical schemes (Roe, FCT, HLLC, ENO, WENO, DG…..)

Body-fitted ALE or embedded for moving bodies/change of topology

Edge-based FE data structure

Kinetic combustion modeling

JWL (HE, non-ideal HE), Miller after-burn models, Cheetah

Particles as a dilute phase

Exchange of mass/momentum/energy with flow

Extensive benchmarking and validation

International group of users (in many disciplines)

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Structural Dynamics Solver: ASICSD

ASICSD:

CSD solver: specifically for large, plastic deformations

Beams, shells & solid elements

Elastic, plastic, viscoelastic materials

Various concrete models

Rivets, bolts etc.

Erosion model, but

Cracking, rather than erosion for structural break-up

Mott’s model for weapon case break

Johnson and Cook model for thermal softening

Non-reflecting BC

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MASTER: FEMAP

Find Interpolating Parameters

Between CFD & CSD Meshes

Faces and Nodes

Use Octree for fast Search

Impose stress Loads

(p, v), heat flux

CFD -> CSD

Impose Boundary

Displacement,

Velocities

CSD -> CFD

CFD/CSD Loose Coupling Approach

CFD - FEFLO

CSD: ASICSD

Transfer Interface Mesh

Transfer Interface Mesh

6

Background

• Background:• In 2008, a joint Norwegian and Swedish

experimental program was conducted to examined the detonation of explosives within concrete ammunition storage structures

• The program focused on pressure occurring from detonation and the debris thrown caused by the detonation

• The concrete structure known as Kasun III was 2m x 2m x 2m having nominal wall thickness of 150mm

7

Kasun Finite Element Mesh

8

Kasun III Configuration and Charge

1 – 6.9kg Bare Charge

9

Pressure Comparisons

1 – 6.9kg Bare Charge

Pressure gauges located

on internal wall

P1-Pressure on Lower Left

P4-Pressure on Upper Left

Experimental Pressure

Experimental Impulse

Calculated Pressure

Calculated Impulse

10

Peak Pressure Versus Range

1 – 6.9kg Bare Charge

Range (cm)

Pea

k P

ress

ure

(psi

)

Pressure Off The Side

200 300 400 500 600 700 800 1000 2000 3000 4000 50000.20.2

0.3

0.5

0.7

1

2

3

5

7

10

FEFLO Pmax (psi)Exp Pmax (psi)

Range (cm)

Pea

k P

ress

ure

(psi

)Pressure Off The Back

200 300 400 500 600 700 800 1000 2000 3000 4000 50000.2

0.3

0.5

0.7

1

2

3

5

7

10

FEFLO Pmax (psi)Exp Pmax (psi)

11

Kasun III Configuration and Charge

16 – 6.9kg Bare Charges

12

Pressure Comparisons

16 – 6.9kg Bare Charges

Pressure gauges located

on internal wall

P3-Pressure on Lower Right

P6-Pressure on Upper Right

Experimental Pressure

Experimental Impulse

Calculated Pressure

Calculated Impulse

13

Pressure/Impulse Versus Range

16 – 6.9kg Bare Charges

Range (cm)

Pea

k P

ress

ure

(psi

)

KASUN 110kg Bare ChargeBack Radial

200 300 400 500 700 1000 2000 3000 4000 5000 7000 100000.50.7

1

2

3

57

10

20

30

5070

100

200

300

500

Pmax (psi) FEFLO CalculationPmax (psi) Experiment

Peak Pressure vs Range Peak Impulse vs Range

14

Kasun III Configuration and Charge

1 – 155mm Cased Charge

15

Kasun Structural Response1 – 155mm Cased Charge: 14 ms

Model reproduces:

• Bulging in middle bottom of wall

• Separation of walls from floor

• Crack in corner to roof

• Initial separation of roof from walls

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Pressure Comparisons

1 – 155mm Cased Charge

Time (ms)

Pre

ssur

e (k

Pa)

x 1

000

Impu

lse

(kP

a-se

c)

Station 1 - Lower Right

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5-2 -3

-1 -1.5

0 0

1 1.5

2 3

3 4.5

4 6

5 7.5

6 9

7 10.5

8 12

9 13.5

10 15

11 16.5

12 18Comparison P1

ExprimentCalculationImpulse ExprimentImpulse Calculation

Pressure gauges

located on internal

wall

Upper Left

Lower Left

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Peak Pressure Versus Range

1 – 155mm Cased Charge

Peak Pressure vs Range

Range (m)

Pea

k P

essu

re (

psi)

Kasun 1 - 155mm Charge

2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 1000.02

0.03

0.05

0.07

0.1

0.2

0.3

0.5

0.7

1

2

3

5

7

10

2020CalculationExperiment

Big Percentage though

only 1 psi

18

Kasun III Configuration and Charge

16-155mm Cased Charges

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Kasun Structural Response16 – 155mm Cased Charges: 2.8 ms

Model reproduces:

• Bulging in middle bottom of wall

• Separation of walls from floor

• Crack in corner to mid height

• Initial separation of roof from walls

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Pressure Comparisons

16 – 155mm Cased Charges

Time (msec)

Pre

ssu

re (

kP

a x

1000)

P5 - Upper Middle

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-5

-2.5

0

2.5

5

7.5

10

12.5

15

17.5

20

22.5

25

27.5

30Comparison P5

ExperimentCalculation

Pressure gauges

located on internal

wall

Upper Right

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Peak Pressure Versus Range

16 – 155mm Cased Charges

Peak Pressure vs Range

Range (m)

Pea

k P

ress

ure

(psi

)Kasun 8 - 155mm Cased Carges

2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 1000.5

0.7

1

2

3

5

7

10

20

30

50

70

100

200

300

500CalculationExperiment

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Summary of Kasun Analyses

• Bare Charge Analyses– Calculated internal pressure data represent the TNO experimental data

reasonably well though there are differences

– Computed pressure vs range attenuation is nearly identical to the

experimental though the magnitude is slightly greater

• Cased charge analyses– Calculated internal pressure data represent the TNO experimental data

reasonably well though there are differences

– Computed pressure vs range attenuation has the correct trend

compared to the experimental though the magnitude is greater

– Fragments do considerably more damage to the lower structure than the

bare charge

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Conclusions/Recommendation for

Kasun Analyses

Conclusions

– Bare Charge Analyses

• The results of the calculation generally reproduce the experimental results

following trends and amplitudes within about 20% or a few psi at far field.

– Cased charge analyses

• The results of the calculation generally reproduce the experimental results

following trends and amplitudes within about 30% or a few psi at far field.

Recommendation

– Though pressures and debris launch velocity are useful, the

primary metric for these test is the observed debris field.

• The ability to automatically load the coupled-code fragment data into an

accepted trajectory code would be helpful.

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Questions?