simulation of snowboarding falls: the back edge catch · 2016-10-05 · snowboarding injuries •...
TRANSCRIPT
Simulation of Snowboarding Falls: The Back Edge Catch
Nicholas Yang, PhD, PE Irving Scher, PhD, PE
Lenka Stepan, PhD Jasper Shealy, PhD, CPE
Snowboarding Injuries
• Shealy et al., 2015 – 2010/2011 NSAA incident report
data – Head injuries = 13.4% of all
injuries – Suspected concussion = 11.4%
of all injuries
Linear Acceleration Injuries
Linear Acceleration
• Skull fracture
• Coup brain injuries Near site of impact
• Contrecoup brain injuries Opposite side from impact
Localized injuries
Rotational Acceleration Injuries
Angular Acceleration
Shearing injuries – Bridging vein rupture
(subdural hematoma) – Diffuse axonal injury
Injury not necessarily at or opposite to site of impact
Diffuse injury
Back Edge Catch
The majority of severe snowboarding head injuries were caused by the
�opposite-edge phenomenon��
where the snowboarder falls backwards and contacts the occiput.
— Nakaguchi et al. (2002)
Previous Research – Scher et al., 2005
• Physical testing of back edge catch
• Hybrid III 50th percentile male
• Hard and soft snow
• 30 kph (18.6 mph) impact speed
• Measured linear head acceleration
Objective
Develop a model to simulate a snowboarding back edge catch
Methods • Developed snowboarder model – LS DYNA coupling
• Validate kinematics to video of a real world back edge catch – Modify joint friction torque
• Validate head-snow contact from Scher et al., 2010 ATD experiments
• Human Body Model
(HBM) – 50th percentile male
• LS DYNA Coupling – Snowboard meshed
in LS DYNA
Snowboarder Virtual Model
Back Edge Catch Simulation • Initial snowboarder speed – 17.1 kph (10.5 mph) – Parallel to surface
• 8 degree slope
Back Edge Catch Video
Kinematics Comparison
Unmodified HBM
Modify HBM Joint Friction Torques
Used joint friction torques determined during isometric conditions – Sandler and Robinovitch, 2001 • Lower extremity maximum joint friction torque – Ankle: 90 N-m – Knee: 155 N-m
– Hip: 130 N-m
– van der Horst et al., 1997 • Cervical spine maximum joint friction torque – 20 - 44 N-m depending on cervical spine level
Simulations with Modified Joint Friction Torques
Max Torque 25% of Max Torque
Kinematics Matched to Video Modified HBM 25% max joint friction torque
Validate Head-Snow Contact Properties
• Define snow surface characteristics
• Compare head injury metrics to physical testing – Scher et al., 2005
Snow Contact Characteristics • Federolf et al., 2006 – Measured resistance pressure
of snow • Hard, icy snow • Average snow • Soft groomed snow
• Modeled as FE-FE contact – Defined surface char. – Hard, icy snow – Soft groomed snow
Compare Injury Metrics to Testing Simulate Scher et al., 2005
• Snowboarder HBM with modified joint friction torques
• 20 degree slope
• ~30 kph velocity
• Hard and soft snow
Examined Fall Kinematics
Normal HBM
Modified Joint Friction Torque
Results – Hard Icy Snow Peak Resultant Head Acceleration
Linear
G Angular rad/sec2
Scher et al., 2005 391 ± 105 --
MADYMO HBM 485 23,602
MADYMO modified HBM 379 21,245
Results – Soft Snow Peak Resultant Head Acceleration
Linear
G Angular rad/sec2
Scher et al., 2005 182 ± 105 --
MADYMO HBM 251 10,368
MADYMO modified HBM 147 8,882
Conclusions
Validated snowboarder back edge catch fall simulation - Matched real world fall kinematics
by modifying joint torques
- Similar head linear accelerations to physical back edge catch tests
Further Research
• Joint Torques – Optimize % of max friction torque for
each joint – Sensitivity analysis – Lumbar and thoracic spine
• Match videos of higher speed falls
Relative Velocity Angle - Jumps
Normal Velocity
Tangential Velocity
Resultant Velocity
2014 Olympics: Back Edge Catch
2014 Olympics: Back Edge Catch
THANK YOU
Relative Velocity Angle - Jumps
10 degrees 30 degrees