This document describes an example of using the Piper Framework to position the human body model THUMS AM50 v4.02 to that of an occupant after a Autonomous Emergency Braking (AEB) performed at 50 km/h. Human body models can be used to study the effect of pre-crash maneuvers on crash safety. In the proposed workflow, the position of the occupant at maximum excursion during the precrash manoeuvre will be reproduced using the Piper simplified physics positioning. The positioned model could be used as an input for a crash simulation. Data from the OM4IS (Occupant Model For Integrated Safety project) were used to generate the targets used for the positioning. During the OM4IS project, the motion of some volunteer during precrash manoeuvres were recorded (kirschbichler 2014). The volunteers were seated on the front passenger seat of a test car equipped with high speed cameras. The Vicon recording system was used to record the motion of some markers positioned at key anatomical locations on the volunteers. The position of those markers at maximum excursion were used as targets position for corresponding landmarks defined on the THUMS AM50 v4.02. We believe that the process described in this tutorial could be generalized and facilitate the use of human body models for studying the impact of precrash motions on the safety of vehicle occupants.
What files are needed for this tutorial?
The tutorial assumes that the User has access to the following:
- A version of the THUMS AM50 v4.02 model
- Piper metadata associated to THUMS AM50 v4.02 (“.pmr) that will describe the component of the model for Piper (see Help on this topic)
- Piper framework (available here) Note: as Piper was designed to be model and code agnostic, this tutorial could be applied to any human body model assuming that the user have access to the necessary Piper metadata files.
- Before starting the Tutorial, please download the target files and the footrest which will be loaded later during the tutorial.
This document will described how to 1)add landmarks to the THUMS v4.02 Metadata 2) position the model using the prepositioning module 3) smooth the model using the smoothing module.
Step 1. add landmarks to the THUMS v4.02 Metadata
Landmarks corresponding to the OM4IS markers have to be added to the THUMS metadata. Please download the following file: THUMS_V4_additional_landmarks_OM4IS.key
Add this file as an include to your master THUMS keyword file (THUMS.dyn).
Add this block in your .pmr file in the model description field:
<landmarks name="Auto" type="point">
<keyword kw="*SET_NODE_LIST_TITLE"> <id>251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 </id> </keyword> </landmarks>
A description of the added landmarks is presented in table 1.
Table 1. Anatomical description of the OM4IS markers.
|Marker name||Anatomical description|
|LFHD||Left front head|
|RFHD||Right front head|
|T1||First thoracic vertebrae|
|C1||First cervical vertebrae|
Step 2. position the model using the prepositioning module
- Run Piper
- Import the THUMS model .pmr file.
- Open the Piper modules parameter window.
- In the Pre-Position parameters set the affine density to 300/m3 and the target stiffness to 1e+9. This will improve the quality of the skin deformation and increase the stiffness of the applied positioning targets during the prepositioning. The affine density will however increase the computing time.
- Click on the Kriging tab and set the maximum control point per box to 40000 and the maximum nodes per box to 300000. Changing those parameters will improve the quality of the smoothing at the expanse of the computing time.
- Select the prepositioning module
We will now proceed to the positioning of the model using the prepositioning module. The positioning will be performed in 2 steps. In the first step, the arms and the legs will be positioned. Joints of the shoulder, elbow, hip and knee will be rotated so that the feet rest on the footrest of the crash environment and the hands be close to the thigh.
- Load the footrest using the environment manager.
- Fix the whole bones of the body proper and head as well as the right and left clavicles and scapulas.
- Use the joint controller option and enter the following joint angle rotations:
Table 2. Rotations of the different joints for the hands and arms positioning.
|Joint name||Joint rotation x,y,z|
|Right_glenohumeral||0.0, 11.0, 0.0|
|Left_glenohumeral||0.0, 11.0, 0.0|
|Right_humeroulnar||0.0, 8.0, 0.0|
|Left_humeroulnar||0.0, 8.0, 0.0|
|Right_radiocarpal||0.0, 0.0, 0.0|
|Left_radiocarpal||0.0, 0.0, 0.0|
|Right_hip||0.0, -10.0, 0.0|
|Left_hip||0.0, -10.0, 0.0|
|Right_knee||0.0, 0.0, 0.0|
|Left_knee||0.0, 0.0, 0.0|
|Right_ankle_joint||0.0, 0.0, 0.0|
|Left_ankle_joint||0.0, 0.0, 0.0|
- Click on positioning on the top right of the window and wait until the model reaches a stabilized position. Then click again on positioning, this will stop the positioning You can now check that the feet lie on the footrest and the hands over the thigh.
We will now perform the second step of the positioning which will consist in blocking the legs and hands and positioning the trunk.
- Remove all the joints and fixed bones targets and clear the imported targets.
- Import and load the target file Targets_OOP_1.
This file contains a first series of constraints consisting mainly of frame to frame controllers and landmarks controllers particularly used to maintain the hands in place.
- Clear the imported targets.
- Open the Piper modules parameter window and modify the target stiffness value from 1e+9 to 1e+4.
- Import and load the target file Targets_OOP_2.
- Click on the landmark icon. Change the x value of the target position for the CHIN landmark from -181.8 to -171.8
- Click on positioning on the top right of the window and wait until the model reaches a stabilized position. Then click again on positioning. The trunk is now positioned according to the target positions defined for the landmarks.
- Activate the all node option in the Update model box on the bottom right of the module window. Then click on update in the same box.
The positioned model needs to be smoothed.
Step 3. smooth the model using the smoothing module.
We will smooth the model using the smooth transformation option. This will use the Kriging algorithm in order to correct the deformation of the mesh using the input model as a reference. We will start by smoothing the legs, pelvis and abdomen.
- Click on the picking button, select Box / Node in the Pickers options and draw a box similar as in the following figure.
- Click on the Smooth Transform button. Then click on Choose the baseline model from current Model History and select the import model.
- Select Body_proper, Right_lower_limb and _Left_lower_limb as targets and click on smooth. Wait until the smoothing operation is finished, this operation could take up to 30 minutes.
- Repeat the same operation with the box shown on the figure below and with the Body_proper, the Left_upper_limb and the Right_upper_limb as targets.
- Repeat the same operation with the box shown on the figure below and with the Head, the Body_proper, the Left_upper_limb and the Right_upper_limb as targets.
- You can now check if the model has some negative volume elements by using the Mesquite. deselect the option Use relative quality and click on Compute quality.
- By clicking on Information grid you can visualize the elements with negative volume on the last column.
- If you are satisfied with the model resulting from the smoothing, you can now export your model by clicking on Project / Export / Export HBM to FE files.