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Smoothed Particle Hydrodynamics (SPH)

Bird strike example

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These instructions were created using Abaqus 6.11

Use Smoothed Particle Hydrodynamics (SPH) to simulate a bird strike example in which

a bird (in the form of a cylindrical projectile) hits an airplane engine blade.

Run script v_sph_birdstrike.py to create the blade model, which is built using

conventional shell elements.

Proceed with the creation of the bird, to be modeled with SPH elements, as described

below.

1. Create the BIRD geometry

First, create a deformable part to model the bird. Use an aproximat part size of 1.

Sketch a circle and specify a radial dimension of 0.04 m. The height of the extruded

cylinder will be 0.076 m.

For more information (including the model files),

see the associated SIMULIA e-Learning Resource

https://swym.3ds.com/#post:8663

© Dassault Systèmes, 2012 www.3ds.com/simulia-learning

2. Create an auxiliary continuum solid mesh

Before meshing the newly created part, partition the cylinder in half using the Normal To

Edge method.

Once this is done, I can mesh the BIRD using continuum brick elements (C3D8R).

Set the approximate global mesh size to 0.005 (equal to the size of a small cube at each

SPH particle.) To produce as uniform a mesh as possible

use the Medial axis mesh algorithm with minimized mesh transitions.

3. Create a node set that includes all the BIRD nodes

Next, Create a part-level set containing all the BIRD nodes; this will be used in the next

step to create point masses and later to define a node-based BIRD surface.

Note that the SPH method can be used to model

bodies of any size.

The particle size used in SPH applications is

arbitrary.

o However, the smaller the particle size the

more detailed the result.

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4. Create mass elements at the nodes of the auxiliary mesh

Switch to the Property module and create point masses with an arbitrary mass value at

each node of the auxiliary mesh.

Note that Abaqus/CAE displays green square glyphs to indicate the presence of mass

elements at the nodes.

5. Create material

In this example, the material properties of the bird are described by a tabular equation of

state, which is not directly supported by Abaqus/CAE. The Keyword editor was used in

the setup script to define the tabular equation of state material.

© Dassault Systèmes, 2012 www.3ds.com/simulia-learning

6. Instance the BIRD part

Next, instance the BIRD part in the Assembly module and translate it using a start point

of 0,0,0 and an end point of 0.6514, -0.1354, -0.048

7. Apply initial velocity to the BIRD

Now, apply translation velocity to all the nodes of the BIRD in the global 3-direction.

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8. Request the field and history output

Next, create a part-level node set, to request history output at a central point on the

projectile base that is closest to the blade.

Once the set is defined, create a History output request for displacements.

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This completes the Abaqus/CAE portion of the model preparation.

Switch to the Job module, write the input file, and leave Abaqus/CAE open for later

visualization of the analysis results.

9. Now manually modify the input file produced by Abaqus/CAE.

1. In a text editor, start by Removing the auxiliary continuum solid elements

(C3D8R) from the file

2. Then Change the MASS elements to PC3D particle elements

Becomes:

3. Remove the dummy *MASS keyword option from the file

© Dassault Systèmes, 2012 www.3ds.com/simulia-learning

and in its place use the *SOLID SECTION option to associate the particle elements

with the material defined previously in Abaqus/CAE.

Recall that when I meshed the bird, I specified an approximate global mesh size of 5

mm, so the characteristic length given here is 2.5 mm

4. Next, define a node-based surface that includes all the SPH particles using the

part level node set defined earlier Abaqus/CAE

5. Finally, define contact interactions between the particle surface and the aircraft

engine blade.

Now the input data preparation is complete.

10. run the analysis using the command line.

>abaqus –job birdStrike

Recall that particle elements do not have faces or edges;

therefore, I must use a node-based surface rather than an

element-based surface.

Note that the characteristic length associated with the

particle volume is half the side of the small cube

associated with each SPH particle.

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11. After the job completes, study the results in the Abaqus/CAE Visualization

module.

First, visualize the blade deformation as a result of the impact with the bird using the time

history animation.

Note that the elements in the set Part-1-1.CONTACTOUTERBOX have been removed

from the view.

Next, contour the stress distribution in the cylindrical projectile at specific time points.

© Dassault Systèmes, 2012 www.3ds.com/simulia-learning

Use symbol plots to visualize distributions of various vector fields such as velocity.

Finally, create a history plot of the turbine hub displacement. The plot clearly shows that

for the blade design under consideration, the hub displacements resulting from the bird

impact are formidable.

Note that the values of field output variables are shown

as circular patches of color in contour plots.