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LS Dyna Ice Contact Load Tutorial

By Claude Daley

This tutorial is a step-by-step description of how to perform an ice contact simulation in LS-Dyna. In this

case the interaction will be between an angular ice edge and an inclined rigid plate. This example

illustrates a number of features and approaches. Many variations are possible.

The plate will move as a rigid body into the ice.

The ice is a simple elasto-plastic material.

The total ice force will be extracted to permit the calculation of the Process Pressure-Area curve.

The surface of the rigid plate will be used to sense the contact pressures to calculate the spatial

pressure-area curves, and an alternate estimate of the process pressure-area curve.

Rhino is used to create the iges geometry file, which is imported into LS-PrePost.

Data will be saved to .csv files for analysis and plotting in excel.

Entries in Bold signify selection in LS-PrePost.

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Step 1: Rhino Geometry

The ice block is 8m x 4m x 3m as shown

The plate is inclined by 20 deg, and offset from the ice by

3D view

side view

close-up of side view - 10 mm gap.

These two layers are exported as test.igs, into its own folder called Ice_Test.

Now open LS-PrePost (ver 4.1)

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Step 2: Import the iges file:

in this case stich options don’t matter. Normally you select stitch to indicate what

part should be welded to what.

this is what the imported geometry files look like

So for this is just cad, not F.E. mesh.

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Step 3 – meshing

Select Element and Mesh on right side

Next select Solid Mesher

With solid meshing open – click on Try Meshing Automatically

If it works you will see a draft mesh – note that the element size is 0.16 m

Now select Accept

Now by unselecting the Geometry parts in the upper left you will just see the mesh, colored uniquely for

each part. By selecting the FEM parts, we can see that part 1 is the plate and part 2 is the ice.

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These next steps don’t need to be done in exactly this order, but this order works fine.

Step 4 – Mat Cards

The Material models will define the ice as an elasto-plastic solid, and the plate is rigid. Start by selecting

Model and Part and then Keyword Manager

The Keyword Manager window lists all the keyword (k) cards. Select the All option.

Now scroll down to the MAT card, click the to see all the options. Select Material 3,

. When the input form opens, click and fill it in as shown below

Hit Accept , then Done to complete the definition.

Now for the plate select , hit New and fill the form as below. The plate is rigid, but for contact

purpose it has steel-like parameters. CMO =1 means that constraints act globally. CON1 = 5 means that

there will be no global movement in y or z. CON2 = 7 mean no global rotations. With these constraints,

we can impose movement in x and the body will move rigidly in x alone. (it’s odd that a constraint is in a

material card – but it is.) Hit Accept and Done to complete the definition.

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Step 5 – Section Card

The Section cards will define both ice and plate as solids (vs shell or …). In the Keyword manager select

SECTION and SOLID , click and fill it in as shown below. There is not

much info needed – just a TITLE and a SECID.

Step 6 – Part Card

The Part Card lets us tell the part which MAT and SECTION properies apply to which parts. We can also

rename the parts. Two parts exist but with the correct properties yet. So select PART to see

Two parts are listed (right) – Solid1 is selected. Remember that Solid1 is the plate and Solid2 is the ice.

Edit this card by renaming the part and selecting

Click the dot beside the SECID to select the solid section. Click the dot beside MID and select the Rigid

Plate material. Then hit ACCEPT and the card will look like;

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Now select the 2 Solid2 part and fill the card as shown. Be sure to hit Accept and Done;

Hit Done to Close the Keyword Manager for now.

Step 7 – Apply Fixed Boundary

Click on Create Entity This will let us fix a full set of node easily. Select the Boundary option

and Spc. Then Click Cre to Create new SPC nodes

Click to get a perfect top view. A node section menu will pop up. Select the Area option and

ByNode.

Now use the selection tool (elastic band) to select all the nodes at the back of the ice.

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With all the decrees of freedom selected , Hit Apply and a new NSet will be

listed (the (111111) means that x y z rx ry rz are all fixed for the selected nodes) .

Step 8 – Create Segment Set for the Pressure Sensor

Start to looking at the plate with the palte edge vertical. This is done by looking from the right, setting

the angle inrement to -10 and setting the rotation to be about the y axis (right clic changes the rotation

axis, left clic rotates the model). Then by clicking twicem the model looks like;

The area selection tool is dragged to select the front of the plate.

If you then rotate the model you will see that all the front faces of the solid elements on the plate have

been selected as segments. Segments can be created from solid or shell elemts and are a kind of ‘skin’.

Hit Apply and Done.

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Step 9 – Define a Curve

We need a curve for use with the ridged body motion. A simple ramp will be used.

Click DEFINE and then CURVE . This gives a form;

On the form select NEW and provide a TITLE (such as “ramp”). The curve is defined by entering data for

abscissa (X) and ordinates (Y) ;

each time you hit Insert the two values are added to the list. So enter (0,0), and (1,1).

The form will look like;

If you want, you can Delete or Replace any entries. Before you can plot you must hit Accept. The Plot

button shows you your plot. Hit Done.

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Step 10 – Describe the Rigid Body Motion

We will use the ramp curve to move the plate into the ice. The unit curve work fine in this case. We can

move the plate one meter in one second, but we will stop the analysis at 0.41 seconds. In this way the

plate will have moved a total of 0.41m. The initial gap is 0.01m so this means 0.4m horizontal

penetration into the ice.

In the Keyword Manager under BOUNDARY, select PRESCRIBED_MOTION_RIGID

In our case we will move the plate in the X direction, and have its position controlled by the ramp curve.

Fill in the form exactly as shown below. Hit Accept and Done.

. The PID is the part ID for the plate. The DOF of 1 means X translation. VAD of 2 means displacement is

controlled. The meaning of the selections is shown at the bottom of the form.

Step 11 – Set Termination Time

As mentioned above we will set the termination time to 0.41 seconds. This will give us a total ice

penetration of 0.4 m. This way we don’t need to scale the curve. In the Keyword Manager select

CONTROL and then scroll down to TERMINATION

Enter 0.41 as ENDTIM Then clic Accept and Done

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Step 12 – Create Contact

In the Keyword Manager select CONTACT

Select the AUTOMATIC_SINGLE_SURFACE option

Clic NEW and enter a TITLE (e.g. “contact”) To extract forces later we need to set SPR and MPR to 1.

Nothing else need be entered. Clic Accept and Done.

Step 13 – Create the Force Transducer

This feature will allow us to extract the contact pressures. We will extract them from the segments on

the rigid plate.

In the Keyword Manager again select CONTACT

Select the FORCE_TRANSDUCER_PENALTY option

Fill in the form as shown. The SSTYP=0 is for segments, with SSID referring to the segment set. SPR and

MPR are set to 1 to include the segment output and master side in the Database results. Click Accept

and Done.

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Step 14 – Set Database options

These options will determine what ouput LSDYNA creates.

In the Keyword Manager again select DATABASE

Select BINARY_D3PLOT

Enter 0.004 in the DT box.

This will give us 100 steps for the 3D video of the simulation.

Click Accept and Done.

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Select BINARY_INTFOR

Click NEW and enter 0.004 in the DT box.

This will give us 100 steps for the interface forces (segment pressures) in the simulation.

Click Accept and Done.

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Select the ASCII_option

You can now enter .004 as the default DT

Select the RCFORC to get the contact force in the contact zone (total force, not pressures)

Select SPCFPORCE to get the total reaction force from the ridgid support begind the ice.

Click Accept and Done.

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Step 15 – Check Model

In the Keywod Manager check to see

the full list or card entered. It should include all

the components shown at right.

You can do a Model Check and a Keyword

check. It should show no errors.

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Step 16 – Save Keyword File

Now save the whole keyword file;

Under File select Save As and Save Keyword As;

Enter a name such as test.k and save the file.

The .k file is a simple text file and can be reviewed and edited with any good text editor.

For example Notepad++ is a good free Windows editor. .

Part of the test.k file is shown below.

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Step 17 – Run LS-DYNA

With the test.k file in its folder, Run the LS-DYNA Program Manager.

You can clic on the button or select the Solver menu and select Start LS-DYNA Analysis

You will see the Input window. Select Browse and select the test.k file

Select the number of CPUs you want (8 in my case)

Select the Advaned button and select the S= option. Give a name for the Inteface force data file (Ive

called it Press)

Now say OK and RUN . You should see the program running and it all is well it will say

N o r m a l t e r m i n a t i o n

In my case the analysis took 34 seconds on my 8-core new DELL 7810 workstation.

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Step 18 – Review LS-DYNA Results in D3Plot

Your folder should now look something like

If you open the D3plot file you will see the mesh. You can rune the animation control to see an

animation in time. There will be 100 frames in the video. With POST selected, you can select

fringe plots . Then you can select a variety of output plots. The von-Mises stress plot if shown

below. Notive that the plate is stressless – because its rigid.

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Now select the Ascii plot button and you will see . The items with * have data

available. The spcforc item has all the fixed boundary reaction forces. Select the spcforc * item and hit

Load. . Now select All and Total to add all the reaction force values.

Select and hit

The plot looks like

After applying a 4 point moving average the plot is much smoother.

.

Now Save the plot data in a FT.csv file

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Step 19 – Analyze SPC Results in Excel

The FT.csv file contains two columns of information; time and force, highlighted in blue and orange

below. The penetration X-pen can ve computed from the time variable, because velocity wa s1m/s and

there was a 0.01m offset. So x_pen = time - .01

The area can ve found from the penetration. For this particular shape the area gows with the square of

the penetration and the equation is 10.91 x^2 (in this case 10.91 = tan(150/2)/sin20. With different

wedge and tilt angles the constant would be different). The average pressure is computed by dividing

the force by the nominal area. This should be the process pressure-arae curve. A power fit shows a

curve of P=5.42 A-.115 which is something like the PC1 PA curve.

Step 20 – Review LS-DYNA Results in Press File

The Press file contains the interface pressures. We will examine the pressures on the plate. Open the

Press file in LSPrePost. The first view will look something like;

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Select the Fringe Component and then select interface pressures from the Segment options.

By selecting Assembly and Select Part, you can just show the segments.

Select the Pressure Transducer Part

At the final timestep the Pressure looks like;

The maximum contact pressures are around 8 MPa in the center of the contact.

To extract detailed surface pressure information we will select some of the segments and plot the time

histories of the segment pressures. With the contact pressures displayed on the segments as shown

above, select History plots . Then choose Segment and Interface Pressure.

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Now you can select segments (ByElem), which will look like;

Now on the History sub-window you can clic on Plot.

Now for all the segments selected you will see a Pressure-Time plot;

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You can save all this data to a file, e.g Seg_Pres.csv.

Step 21 – Analyze Interface Pressure Results in Excel

The Seg_Pres.csv file contains a column for time multiple columns of pressure. Each of the elements is

approx 0.157m x 0.157m (found by using measurement tool ) for an area of .025m2 .

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The .csv file looks like;

Each row represents a moment in time. We can compute a spatial pressure-area curve for each moment

in time. To save excessive analysis, we will delete most of the rows and create 4 PA curves (at t=.1, .2, .3,

.4 s). The pressure data can be raked and the spatial pressure-are curves can be computed as shown in

the spreadsheet below;

The data plots as follows. The segment pressures show the spatial PA curves.

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The end points on the spatial curves are the acreage pressure as measured by the segments. These are a

kind of process pressure-area curve. Unfortunately this way of estimating the process curve produces a

very different result from the direct calculation of the process curve from the SPC data abaove. The fig

below compares the two approaches.

This table show the area, force and average pressure as computed from the segment sensors vs the

nominal values from the spc data. The forces are almost inentical, but the nominal areas are quite

different from the segment estimate.

time A_seg Pav_seg Force_seg [MN]

A_nom Pav_nom Force_spc [MN]

0.100057 0.591576 0.859761 0.508614267 0.088483 5.874972 0.519835

0.200061 1.207801 1.848185 2.232239336 0.394104 5.633844 2.22032

0.30009 2.366304 2.255062 5.336162671 0.918101 5.822488 5.34563

0.400076 3.155072 3.105695 9.798691429 1.660058 5.94557 9.86999

The End