Chapter 42: Mine Blast Under a Vehicle

42 Mine Blast Under a Vehicle

Summary 716

Introduction 717

Solution Requirements 718

Results 722

Input File(s) 727

Video Examples 727

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SummaryTitle Chapter 42: Mine Blast Under a Vehicle

Features • Using Dummy boundary to make closed volume• Using Leakage to make free flow between two Euler meshes• Explosive modeled by ideal gas

Geometry

Material properties • Vehicle Structure

Density = 7.85E-9 ton/mm3

Young’s Modulus = 2.1E5 ton/mm/s2

Poisson’s ratio = 0.3

Yield stress = 250. ton/mm/s2

• Euler (Air)

Density = 1.29E-12 ton/mm3; Gamma = 1.4

• Specific Internal Energy = 1.9385E8 ton-mm2/s2

• Euler (Explosive - equivalent to TNT of 7kg and radius of .25 meter)

Density = 107.E-12 ton/mm3; Specific Internal Energy = 3.9E12 ton/mm2/s2

• Ground – Rigid

Analysis characteristics Transient explicit dynamic analysis (SOL 700)

Boundary conditions • Fixed boundary condition of ground• In and out directional flow boundary of outer euler zone

Element types • 2-node bar element for stiffener of vehicle • 4-node shell element for vehicle, dummy elements and ground• 8-node hex element for euler which is automatically generated by MESH option

FE results 1. Acceleration plot at 0.0008 seconds 2. Stress Distribution plot at 0.0008 seconds

Inner Euler Zone

Vehicle

Ground

Explosive

Outer Euler Zone

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IntroductionThis is a simulation of an explosion under a vehicle. The vehicle has triggered a mine that is exploding underneath the bottom shield. In this example, the actual explosion of the mine is not modeled. Instead, the simulation is started moments after the mine explodes. This is called the blast wave approach. At the location of the mine, a high density and high specific energy is assumed in the shape of a small sphere. During the simulation, this region of high density, energy, and high pressure, expands rapidly. The blast wave interacts with the bottom shield and causes an acceleration of parts of the flexible body. The intent of this simulation is to find the location and the value of the maximum acceleration.

SOL 700 Model

An outline of the basic numerical model is shown in Figure 42-1 below. It is composed of the following main components:

a. Vehicle Structure

b. Euler Domain 1 - air outside vehicle and compressed air (explosive)

c. Euler Domain 2 - air inside vehicle

d. Ground

e. Fluid Structural Coupling

Figure 42-1 Outline of Basic Numerical Model

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Solution RequirementsA. The Vehicle:

Vehicle structure is modeled by QUAD, TRIA shell elements and some BAR elements.

Figure 42-2 Vehicle Structure

Material properties are taken as follows:

Assumed that there will be no failure of the structure. In a part of the structure, there is a hole through which air and pressure waves can freely flow. This hole will be modeled with dummy shell elements.

B. Euler Domain 1:

The first Euler domain is the air on the outside of the vehicle. The properties of air at rest are:

Density 7.85E-9 tonne/mm3

Modulus of elasticity 210000. tonne/mm/s2

Poison ratio 0.3

Yield stress 250. tonne/mm/s2

Density 1.29E-12 tonne/mm3

Gamma 1.4

Specific internal energy 1.9385E8 tonne-mm2/s2

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In the input file:

MATDEUL,230,1.29e-12,203,,,,,,++,,1.01TICVAL,5,,DENSITY,1.29E-12,SIE,1.938e11

At the location of the mine, a small region will be modeled with high density and specific internal energy equivalent to TNT of 7kg when the sphere has a radius of .25 meter:

The input file will show:

TICVAL,4,,DENSITY,107E-12,SIE,3.9e12SPHERE,400,,1797.5,0.,-450.,250.

The Euler region will be modeled by using the MESH entry. The region will have to be large enough to contain the entire vehicle, including when the vehicle is in motion:

MESH,1,BOX,,,,,,,++,-2623.,-1403.,-903.,6100.,2800.,2150.,,,++,30,10,10,,,,EULER,201

For the most accurate blastwave simulations, it is advised to use the Second-order Euler solver of SOL 700. This is activated by specifying the second-order option on the Euler property entry and specifying the parameter to use the second-order Range Kutta integration method:

PARAM,RKSCHEME,3PEULER1,201,,2ndOrder,101

To initialize the whole first Euler mesh, a TICEUL entry will be defined. To initialize the Euler domain, other than within the sphere of the explosion, a second large sphere is used. Because it has lower priority, the Euler elements within the mine blast are will still initialized with high density and energy:

TICEUL1,101,11TICREG,1,11,SPHERE,400,230,4,20.TICREG,2,11,SPHERE,501,230,5,1.SPHERE,400,,1797.5,0.,-450.,250.SPHERE,501,,0.,0.,-5000.,10000.

The Euler domain has infinite boundaries. This can be achieved by defining a zero gradient flow boundary on the outside of the Euler mesh. Use an empty FLOWDEF entry:

FLOWDEF,202,,HYDRO,,,,,,++,FLOW,BOTH

Density 107E-12 tonne/mm3

Specific Internal Energy 4.9E12 tonne-mm2/s2

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C. Euler Domain 2:

The second Euler region represents the air inside the vehicle. Also for the second Euler region, a MESH entry is used. The air is at rest again, so the same properties apply:

PEULER1,202,,2ndOrder,102TICEUL1,102,12TICREG,3,12,SPHERE,502,230,5,5.SPHERE,502,,0.,0.,-5000.,10000.

Many of the previous cards will be used to initialize the density and energy (TICVAL) and material (DMAT/EOSGAM) in this Euler region:

TICVAL,4,,DENSITY,107E-12,SIE,3.9e12TICVAL,5,,DENSITY,1.29E-12,SIE,1.938e11

MATDEUL,230,1.29e-12,203,,,,,,++,,1.01EOSGAM,203,1.4

D. The Ground:

The ground is modeled as rigid body using dummy QUAD elements. It is used to close the Euler boundary under the vehicle so the blast wave will reflect on this boundary:

PSHELL,999,999,1.MATRIG,999,,,,1.0E10,0.00,0.00,-800.,++,1.E10,0.0,0.0,1.E10,0.0,1.E10,,,++,,,,,,,,,++,,,,1,7,7

E. Fluid Structure Interaction:

In order to make fluid structure interaction possible, a closed volume needs to be defined. The car model itself is not closed, so a dummy boundary will be defined to close the volume. This extra surface consists of three parts:

Part 1 resides on the back,

Part 2 is the top cover, and

Part 3 is the vent on the bottom of the vehicle.

For all these parts, dummy shell elements are defined and hole definitions will be defined.

Figure 42-3 Dummy Shell Elements Defined to Close the Volume

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The input for dummy shell elements

PSHELL,900,901,1.PSHELL,910,901,1.PSHELL,920,901,1.MATD009,901,1.E-20

With this closed volume, the coupling surface can be defined. For each Euler domain, a separate surface is required. However, in this model, the interaction surface consists of the same elements, except for the extra ground elements (pid=999) for the outer Euler domain region 1. The surface definition will make use of the properties of the elements.

The outer surface:

BCPROP,97,60,61,62,110,135,150,900,++,910,920,999

The inner surface:

BCPROP,98,60,61,62,110,135,150,900,++,910,920

Now the coupling surfaces can be defined. For the outer region, all elements inside the volume are not active. The covered option will, therefore, be set to INSIDE. Attached to this surface will be the first Euler MESH:

COUPLE,1,97,INSIDE,ON,ON,11,,,++,,,,,,,,,++,,1

The inner Euler domain is constrained by surface 2. For this volume, the outer Euler elements will be covered:

COUPLE,2,98,OUTSIDE,ON,ON,,,,++,,,,,,,,,++,,2

As discussed before, there are holes in the coupling surface. To this end, a flow definition is required for one of the coupling surfaces. In this example, the flow cards are referenced from the first coupling surface. The input to define flow between the regions is:

LEAKAGE,1,11,1,PORFCPL,84,CONSTANT,1.0BCPROP,1,900

Also, for each of the other two flow surfaces, these set of cards are repeated

$LEAKAGE,2,11,2,PORFCPL,84,CONSTANT,1.0BCPROP,2,910$LEAKAGE,3,11,3,PORFCPL,84,CONSTANT,1.0BCPROP,3,920$

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Finally, the flow definition itself prescribes that the Euler region from coupling surface 1 is interacting with the Euler region from coupling surface 2:

PORFCPL,84,LARGE,,BOTH,2

F. Miscellaneous:

a. Because this model uses the coupling surface interface, the time step safety factor for Eulerian elements has to be .6. However, the Lagrangian elements (the quadratic and triangular elements) determine the time-step, and it is beneficial to use a higher time step safety factor for the Lagrangian elements:

PARAM,STEPFCTL,0.9

b. To show results every .0002 seconds the following output request was added:

DYPARAM, LSDYNA, BINARY, D3PLOT,.0002

PARAM, CPLSARC,.0002

ResultsThe Figure 42-4 below shows the location, value, and time of the maximum acceleration. The stress distribution at this time is also in Figure 42-5.

Figure 42-4 Acceleration Plot

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Figure 42-5 Stress Distribution Plot

Abbreviated SOL 700 Input FileSOL 700,NLTRAN STOP=1CENDTITLE= Job name: mine blast (mm/tonne/s/K)IC=1SPC=1$TSTEPNL=1$------- BULK DATA SECTION -------BEGIN BULK$------- Parameter Section ------$DYPARAM,RKSCHEME,3DYPARAM,FASTCOUPDYPARAM,STEPFCTL,0.9PARAM*,DYINISTEP,.5E-7PARAM*,DYMINSTEP,1.E-13$$DYPARAM,LSDYNA,BINARY,D3PLOT,.0002PARAM,CPLSARC,.0002$MESH,1,BOX,,,,,,,++,-2623.,-1403.,-903.,6100.,2800.,2150.,,,++,30,10,10,,,,EULER,201$MESH,2,BOX,,,,,,,++,-2621.,-1201.,-251.,5900.,2400.,1250.,,,++,30,10,10,,,,EULER,202$PEULER1,201,,2ndOrder,101$TICEUL1,101,11

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$TICREG,1,11,SPHERE,400,230,4,20.TICREG,2,11,SPHERE,501,230,5,1.$SPHERE,400,,1797.5,0.,-450.,250.SPHERE,501,,0.,0.,-5000.,10000.$PEULER1,202,,2ndOrder,102$TICEUL1,102,12$TICREG,3,12,SPHERE,502,230,5,5.$SPHERE,502,,0.,0.,-5000.,10000.$TICVAL,4,,DENSITY,107E-12,SIE,3.9e12TICVAL,5,,DENSITY,1.29E-12,SIE,1.938e11$MATDEUL,230,1.29e-12,203,,,,,,++,,1.01$EOSGAM,203,1.4$FLOWDEF,202,,HYDRO,,,,,,++,FLOW,BOTH$COUPLE,1,97,INSIDE,ON,ON,11,,,++,,,,,,,,,++,,1$$ Define flow thru the holes$LEAKAGE,1,11,1,PORFCPL,84,CONSTANT,1.0BCPROP,1,900$LEAKAGE,2,11,2,PORFCPL,84,CONSTANT,1.0BCPROP,2,910$LEAKAGE,3,11,3,PORFCPL,84,CONSTANT,1.0BCPROP,3,920$PORFCPL,84,LARGE,,BOTH,2$COUPLE,2,98,OUTSIDE,ON,ON,,,,++,,,,,,,,,++,,2$BCPROP,97,60,61,62,110,135,150,900,++,910,920,999$BCPROP,98,60,61,62,110,135,150,900,++,910,920$$ ========== PROPERTY SETS ==========

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$$ * pbar.9988 *$PBAR 9988 222 3600.1000000.1000000.2000000.$$ * pbar.9989 *$PBAR 9989 222 100000. 3.E+8 3.E+8 6.E+8$$ * pbar.9990 *$PBAR 9990 222 3000. 200000.2500000.3000000.$$ * pbar.9993 *$PBAR,9993,111,459.96,25066.,55282.,16543.$$ * pbar.9996 *$PBAR,9996,111,895.52,309450.,55349.,48782.$$ * pbar.9999 *$PBAR,9999,111,736.,490275.,827555.,2095137.$$ * pshell.30 *$PSHELL 30 111 3 $$ * pshell.40 *$PSHELL 40 111 4 $$ * pshell.50 *$PSHELL 50 111 5 $$ * pshell.60 *$PSHELL 60 111 6PSHELL 61 111 6 PSHELL 62 111 6 $ * pshell.80 *$PSHELL 80 111 8 $$ * pshell.110 *$PSHELL 110 111 11 $$ * pshell.120 *$PSHELL 120 111 12 $

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$ * pshell.135 *$PSHELL 135 111 13.5 $$ * pshell.150 *$PSHELL 150 111 15 PSHELL 151 111 15 $$ * pshell.200 *$PSHELL 200 111 20 $$ * pshell.450 *$PSHELL 450 111 45 $$ dummy elements for coupling surface$ holePSHELL,900,901,1.$ top coverPSHELL,910,901,1.$ side coverPSHELL,920,901,1.$MATD009,901,1.E-20$$ groundPSHELL,999,999,1.$MATRIG,999,,,,1.0E10,0.00,0.00,-800.,++,1.E10,0.0,0.0,1.E10,0.0,1.E10,,,++,,,,,,,,,++,,,,1,7,7$$ * conm2 *$CONM2,5000,1145,,1.5 CONM2,5001,1146,,1.7$$ ========= MATERIAL DEFINITIONS ==========$MATD024,111,7.85e-09,210000.,.3,250E10$MAT1,222,210000.,,.3,7.85e-09$INCLUDE model.bdfINCLUDE ground.dat$ENDDATA

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Input File(s)

Video Examples

Import and Inspect ModelTo see a video example of this step, click on the image or caption below to view a streaming video for this section; it lasts approximately four minutes to import and inspect the model.

Figure 42-6 Video of Importing To and Inspecting the Model

File Description

nug_42.dat MD Nastran input file for leakage using dummy element

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Create PropertiesTo see a video example of this step, click on the image or caption below to view a streaming video for this section; it lasts approximately two minutes.

Figure 42-7 Video to Create Properties

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Create Eulerian DomainsTo see a video example of this step, click on the image or caption below to view a streaming video for this section; it lasts approximately five minutes.w

Figure 42-8 Video to Create Eulerian Domains

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Create Eulerian MeshTo see a video example of this step, click on the image or caption below to view a streaming video for this section; it lasts approximately three minutes.

Figure 42-9 Video to Create Eulerian Mesh

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Create Coupling SurfacesTo see a video example of this step, click on the image or caption below to view a streaming video for this section; it lasts approximately two minutes.

Figure 42-10 Video to Create Coupling Surfaces

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Create LeakageTo see a video example of this step, click on the image or caption below to view a streaming video for this section; it lasts approximately two minutes.

Figure 42-11 Video to Create Leakage

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Define Job ParametersTo see a video example of this step, click on the image or caption below to view a streaming video for this section; it lasts approximately two minutes.

Figure 42-12 Video to Define Job Parameters

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Attach and View ResultsTo see a video example of this step, click on the image or caption below to view a streaming video for this section; it lasts approximately eight minutes.

Figure 42-13 Video to View Results