PRIMER 22.1

Dummy Positioning using Ansys LS-DYNA

The Ansys LS-DYNA dummy positioning tool in PRIMER allows the user to create an Ansys LS-DYNA analysis automatically to position a dummy. This works in a similar way to the PRIMER seatsquash Ansys LS-DYNA method. This method of positioning is appropriate for those who wish to capture deformations in the foam/rubber parts of the dummy that occur due to the positioning, that are not captured by PRIMER's traditional dummy positioning methods. The Ansys LS-DYNA positioning method is illustrated below:

Starting point - dummy in original position.

Through using the PRIMER Ansys LS-DYNA positioning tool, an Ansys LS-DYNA analysis is created that will "pull" the dummy into the desired position.

A DYNAIN file is produced by the Ansys LS-DYNA analysis. PRIMER can now import the DYNAIN data back into the original model. This will mean updated coordinates capturing the deformation of the dummy foam/rubber parts will be updated in the original model.

The tool works through a series of steps to create the Ansys LS-DYNA analysis. Before using this tool, the user must save the target position using PRIMERs traditional dummy positioning methods, as the saved position is used to create the entities required to "pull" the dummy into position. The initial model should contain just the dummy.

Step 1

Step 1 is a reminder to ensure you have a saved position using the traditional PRIMER positioning methods. See Further Positioning Commands for information on saving positions.

Once you have a saved position, press Position.

Step 2

To position the dummy, PRIMER requires three nodes per dummy assembly. These nodes are used to "pull" each assembly into their final position in a Ansys LS-DYNA analysis. The nodes selected should be on a rigid or stiff part of the assembly. The nodes can be set manually, however it is recommended to use Automatically determine nodes . This will find rigid nodes in each assembly to use during positioning.

Note you can specify to ignore parts below a certain mass when automatically determining the nodes. This is so that small rigid parts that you do not want to be "pulled" (for example, the dummy may contain small rigid target marker parts) are not considered.

You also have the option to rigidify any assembly for the Ansys LS-DYNA analysis. This may be beneficial for soft extremities, such as hands and feet, which may become excessively deformed during the Ansys LS-DYNA positioning. If the R switch next to the assembly is toggled on, PRIMER will rigidify the assembly when setting up the analysis in the final step. Note that when toggling the R switch, PRIMER will automatically recalculate the 3 nodes for that assembly, as there will now be more/less "rigid" nodes in the assembly.

You can also chose to ignore any assembly so that cables are not attached. This may be beneficial if the model is over constrained. Removing cables from certain assemblies may help to solve this. Press the I switch next to the assembly to ignore it.

Once you have selected the nodes for each assembly, chosen which assemblies you wish to rigidify and/or ignore, click Next.

Step 3

The next step is optional and allows you to select any part from the assemblies you have chosen to rigidify that you may wish to remain deformable.

Once you have made any selection, or to skip this step, click Next.

Step 4

When the analysis model is created, PRIMER will move the dummy to the desired H-Point. PRIMER will then use the neck base node to rotate the dummy around it's local Y axis to the approximate final position. This helps to reduce the overall movement of the assemblies during the analysis and hence can reduce run times. It is recommended that the neck node be set to a node at the top of the torso/base of the neck. PRIMER will also use the hip node to rotate the dummy around it's local Z axis to the approximate final position. It is recommended that this be set to a node on the right or left hip (outer surface). See images below for examples of this.

Once you have selected the two nodes, click Next.

Step 5

The next step is to choose the position saved earlier. This is the position you want to achieve through the Ansys LS-DYNA analysis.

Once you have chosen the position, click Next.

Step 6

At this point you may wish to save the model. The nodes chosen in the previous steps can be saved to the dummy tree in the keyword file. Leave the Dummies tab open, and click on Model->Write to save the model.

The Ansys LS-DYNA method works by creating cables and dampers that pull the assemblies into the final position. A number of inputs relating to the analysis can be set on the final panel:

Force applied in cables - The force that is applied to the cables to pull the assemblies into position.
Force ramp up time - The time taken to ramp the force up from zero.
Damping applied with cables - This is the damping applied in-line with the cables used to pull the assemblies into position.
Total analysis time - Termination time for the analysis. This is also used during creation of a *DEFINE_CONSTRUCTION_STAGES card which is used to create a DYNAIN file to import back into PRIMER .
Global damping - Global damping applied in the analysis (can also be turned off).
Remove *CONSTR_RIG_BODY across assem - turn this on if your dummy model has rigid body constraints across assemblies. Sometimes rigid body constraints are created in the model across assemblies to simulate the locking of assemblies relative to each other during a crash test. During positioning these would not be locked so should be removed during the setup of the pre-simulation analysis model.
Units - Specify the units system you are working in to update the above values accordingly.

It is recommended to use the default settings to start with. These can then be modified with subsequent analysis is required.

Once you have set the values you want, click Next , the Apply.

The analysis is now ready to run. Once complete, the analysis will produce a DYNAIN file, which will have a name similar to "end_stage001_dynain". This contains coordinate and initial stress information from the analysis which can be imported back into the original model using PRIMER . To import the DYNAIN file back into the original model, use the following steps:

Step 1

Step 1 is a reminder to ensure you have a saved position using the traditional PRIMER positioning methods. You need the original saved position for the import tool should you wish to further modify the position of the dummy using PRIMER's traditional rigid body dummy positioning methods. See Position: Positioning Dummies for information on saving positions.

To continue with the import procedure, press Import.

Step 2

Step 2 is to select the position you used when creating the Ansys LS-DYNA analysis. This is the position saved using PRIMER's traditional rigid body positioning methods. The position needs to be chosen here to ensure any further positioning is possible.

Once you have chosen the position, click Next.

Step 3

Step 3 is where you select the DYNAIN file produced by the Ansys LS-DYNA analysis.

Here you can choose to just read the nodes and the elements (which is faster) or read all entities (slower) from the DYNAIN files.

Once you have chosen the DYNAIN file, click Next.

Step 4

Step 4 is where you select what data you wish to import from the DYNAIN file.

Once you have made your selection of what you want to import, click Apply to import the data into your model.

Previous | Next