Injury Evaluation Application - Fall

This demonstration problem examines the injury producing mechanics during several fall scenarios. A human model is generated with passive joint created from the Hybrid III crash dummy database in LifeMOD/BodySIM. Contact elements are created between the segments of the model and the floor.

The model is then given initial velocity conditions and the dynamics simulation is performed. A second simulation is performed where the joint stiffness are scaled down to represent a more flaccid human or someone not prepared for the fall.

Injuries are accessed by examining the impact forces, joint torques, and the deceleration of the head.

Features of this example problem include:

• Parametric analysis
• Creating body segments from the Chinese PeopleSize Anthropometric database
• Contact elements between body segments and environment
• Hybrid III Crash Dummy strength characteristics at the joints
• Posture manipulation
• Passive simulation

Sections

• Generating the Body Segments
• Generating the Joints
• Posing the Human Model
• Creating Contact Forces
• Running the Passive Simulation
• Running the Parameter Variation Study
• Interrogating the Results
• Further

Generating the Body Segments

In this phase the human body models are generated. The body consists of 19 segments and 18 joints with the mass properties of a 95% Chinese male and the joint characteristics of the Hybrid III crash dummy.

Figure 1: Body segment creation panel

Step 2: Create the body
Enter "World" for the world model name and "Connor" for the human body name. Units are Inch-Lbm-Lbf and the color is set to red. Hands are set to grip and the full body model is specified. The model is created from an anthropometric database named "PeopleSize". The body will be constructed for a 95th percentile Chinese male. Select OK to set parameters and select Create Body Parameter Table to create the segment measurement table and Create Human Model from Parameter Table to create the model.

Generating the Joints

In this phase, the human segments created in the first phase are connected together with kinematic joints. At the same time torque functions are created at each joint degree of freedom. The torque function is created from the Hybrid III database of torque functions. The torque is based on a nonlinear joint stiffness, damping, friction and hysteresis (losses), specific to each DOF for each joint as derived from the physical Hybrid III crash dummy. A scale factor of 1.0 us used which represents the baseline stiffness of the Hybrid III crash dummy.

Figure 2: Panel to create HIII joints on the body model.

Step 3: Bring up joint create panel
Select JOINTS in the main-menu and CREATE BASE JOINT SET in the sub-menu. Select HYBRID III CRASH DUMMY STRENGTH CHARACTERISTICS. Enter a scale factor of 1.0 to use the default stiffness of the crash dummy.

Step 4: Create Hybrid III strength joints on the model
SELECT ALL body regions and select EXECUTE. From this six panels will appear to create the joint/torque sets for each region of the body (spinal, left arm, left leg, right arm, right leg).

Posing the Human Model

After the joints are created on the model the posture of the model may be adjusted, and the model moved into place. The posture may be adjusted by recalling one of several postures in the posture library then further modify the joint angles if necessary. The body is moved into place by selecting the Lower_Torso segment and changing the location.

Figure 3: Connor Model after adjusting the posture

Figure 4: Using the standard ADAMS/View control panel to reposition the human model in the environment

Step 5: Bring up posture panel
Select POSTURE on the main-menu and CONFIGURE BASE MODEL on the sub-menu.

Step 6: Update the left/right shoulder joints
Enter -100 for the right and left shoulder, sagittal joint angle. Then select the SHOULDER button for both arms.

Step 7: Update the left/right elbow joints
Enter -70 for the right and left elbow, sagittal joint angle. Then select the ELBOW button for both arms.

Step 8: Update the upper_neck joint
Enter 30 for the thoracic sagittal joint angle. Then select the UPPERNECK button to update the joint angle.

Step 9: Update the lower_neck joint
Enter 30 for the thoracic sagittal joint angle. Then select the LOWERNECK button to update the joint angle.

Step 10: Update the thoracic joint
Enter 30 for the thoracic sagittal joint angle. Then select the THORACIC button to update the joint angle.

Step 11: Update the lumbar joint
Enter 30 for the lumbar sagittal joint angle. Then select the LUMBAR button to update the joint angle.

Step 12: Update the left/right hip joints
Enter -90 for the right and left hip, sagittal joint angle. Then select the HIP button for both legs.

Step 13: Update the left/right knee joints
Enter 120 for the right and left knee], sagittal joint angle. Then select the KNEE button for both legs.

Step 14: Rotate and reposition model
Reposition the model by modifying the location of the Lower_Torso segment. Use the ADAMS/View movement panel as displayed in figure 4 or by entering the ADAMS/View command:

part mod rigid name part=.World.Connor_Lower_Torso location=-15,-20, 63.0 orientation=270, 150, 210 rel=.World

Or you can select the right vu and rotate the lower_torso by an angle of 110, like shown in figure 4.

Creating Contact Forces

Contact forces are created on the model to provide an interaction between the human model and the environment. LifeMOD/BodySIM™ contact forces utilize an ellipsoid-plate contact algorithm for efficient calculation of the reaction of the body segments to impact with the environment. The general form of the contact force function is

F n =k *(g**e)+Step (g,0,0,d max ,c max )*dg/dt

where:

g represents the penetration the ellipsoid into the plate
dg/dt is the penetration velocity at the contact point.
e is a positive real value denoting the force exponent.
dmax is a positive real value specifying the boundary penetration to apply the maximum damping coefficient cmax.

Figure 5: Contact set creation panel with parameters set for Connor model.

Step 15: Create contact marker on floor
Create a marker to identify the location and orientation of the contact surface (floor). Use the ADAMS/View command:

marker create marker=.World.ground.MARKER_1946 &
location=-10, -31, 0 &
orientation=0,-90,0

Or you can create a marker using the icon.

Place the marker anywhere in the screen, than modify its coordinates and orientation (0, -90, 0). The markers location is (-10, -31, 0).

Step 16: Bring up contact panel
Select CONTACTS on the main-menu and CREATE BASE CONTACT SET on the sub-menu. Enter .World.ground.MARKER_1946 in the contact surface marker field and set the parameters as in Figure 5.

Step 17: Create contact between body segments and floor
Select Head, Upper_Torso, Central_Torso, Lower_Torso, Right_Scapular, Right_Upper_Arm, Right_Lower_Arm, Right_Hand, Left_Scapular, Left_Upper_Arm, Left_Lower_Arm, Left_Hand, Right_Upper_Leg, Right_Lower_Leg, Right_Foot_Single, Left_Foot_Single as the contact segments. Then select APPLY.

Running the Passive Simulation

With the models generated, joints created, contact forces applied, and set in the right posture, the dynamic analysis will be performed. This simulation is termed "passive", since the human model will be responding to forces from the environment. Two cases will be performed; each with varying initial velocity conditions.

Figure 6: Setting the initial conditions for the body

Figure 7: Gravity and integrator settings for passive simulation.

Step 18: Bring up the initial conditions panel
Select ANALYZE from the main-menu and BODY VELOCITY INITIAL CONDITIONS from the sub-menu.

Step 19: Set the initial conditions for the model
Set the initial velocity conditions as in the panel in figure 6.

Step 20: Bring up the analyze panel
Select ANALYZE from the main-menu and DYNAMICS from the sub-menu.

Step 21: Run the dynamics simulation
Set the gravity vector at -386 in the negative Y direction. Run the simulation for 1.0 seconds and 100 time steps using the default integrator settings.

Step 22: Display simulation
When the simulation is complete, animate the model by using the animation tool in Main Tools panel.

Running the Parameter Variation Study

To evaluate the effects of "bracing" the joint strength is modified and compared between successive runs.

Figure 8: Decreasing the joint stiffness for all the joints in the body model

Step 23: Save the first analysis
Select SAVE ANALYSIS and enter the name Case_1. Select OK.

Step 24: Bring up Parameters panel
Select PARAMETERS in the main-menu and JOINTS in the sub-menu.

Step 25: Decrease Hybrid III Scale factor
Decrease the scale factor for .6, effectively reducing the stiffness in the joints.

Step 26: Bring up the analyze panel
Select ANALYZE from the main-menu and DYNAMICS from the sub-menu.

Step 27: Run the dynamics simulation
Set the gravity vector at -386 in the negative Y direction. Run the simulation for 1.0 seconds and 50 time steps using the default integrator settings.

Step 28: Display simulation
When the simulation is complete, animate the model by using the animation tool in Main Tools panel.

Step 29: Display simulation with dummy model
For another method of viewing the animated model, select Dummy as the external representation and none as the internal on the BodySIM Display Toolbox and run the animation.

Step 30: Display simulation with skin/skeletal model
For another method of viewing the animated model, select Skin as the external representation and Skeleton as the internal on the BodySIM Display Toolbox and run the animation.

Step 31: Save the second analysis
Select SAVE ANALYSIS and enter the name Case_2. Select OK.

Interrogating the Results

With the simulations complete, the results may be reviewed in many ways. One of the best ways to understand model performance is to plot the data and view the animation simultaneously. In this final section, results for head impact forces and decelerations are compared for both models and both strength parameters settings.

Figure 9: Animation sequences of the human responses to the fall.

Figure 10: Head acceleration (left), head contact (middle) and neck joint torques for both simulation cases

Figure10 Settings in the ADAMS post processor panel to superimpose animation for both cases. (case_1 in red)

Step 32: Bring up results panel
Select RESULTS on the main-menu and DATA DISPLAY on the sub-menu. Select Contacts as the Data Type and select the post processor button.

Step 33: Plot the head impact for case-1
Select the Z-component of the contact force, Connor_Head_CON_1 for the Connor model for case_1 analysis. Select Create Full Plot to create the data curve.

Step 34: Plot the head impact for case-2
Select the Z-component of the contact force, Connor_Head_CON_1 for the Connor model for case_2 analysis. Select Create Full Plot to create the data curve.

Step 35: Animate case_1
Select ANIMATION from the sub-menu. Set the analysis to .World.Case_1, select Divide Window, right view and select PLAY.

Step 36: Animate case_2
Set the analysis to .World.Case_2 and select PLAY.

Step 37: Animate both cases superimposed
Select Compare Cases and .world.case_1 as Case 1 and .world.case_2 as Case 2. Select PLAY.

Step 38: Bring up Body results panel
Select DATA DISPLAY in the sub-menu and set Body Motion as the Data Type.

Step 39: Plot the head acceleration for case-1
Select y-component of the CM_Acceleration characteristic for the head of the model for Case_1. Use the same filter settings as above. Select Create Full Plot to create the data curve.

Step 40: Plot the head acceleration for case-2
Select y-component of the CM_Acceleration characteristic for the head of the model for Case_2. Use the same filter settings as above. Select Create Full Plot to create the data curve.

Step 41: Animate the skin/skeleton model case_1
Select ANIMATION in the sub-menu. For another method of viewing the animated model, select Skin as the external representation and Skeleton as the internal on the BodySIM Display Toolbox and run the animation.

Step 42: Animate the skin/skeleton model case_2
Set the analysis to .World.Case_2, select PLAY.

Step 43: Animate both cases superimposed
Select none as the external representation and Skeleton as the internal on the BodySIM Display Toolbox. Select Compare Cases and .world.case_1 as Case 1 and .world.case_2 as Case 2. Select PLAY.

Step 44: DEMO COMPLETE

Further

This model was put forth to demonstrate the creation of a passive human model to determine the physical reactions to a human during a fall. Obviously the model can be further refined and improved, from the point developed in this example. The intention with this example was to touch of the various modeling functions of both LifeMOD/BodySIM™ and ADAMS/View necessary to create a human model of this nature for this application.

This model may be refined in many areas including:

• Creating a more biofidelic spine model to examine local loadings on the vertebrae and soft tissues (see Section 4: Non-Standard Model Example - Detailed Cervical Spine).
• Creating simulations with varying boundary conditions such as fall height, initial velocity, impact angle, ground compliance, posture, etc.
• Adding "human reaction" by adding PD controllers to several joints.