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Newsletter Volume 5 - 1st Quarter 2005

Human Motorcycle Control: Stabilizing and De-Stabilizing, Part II

CONTENTS

Case Study: Human Motorcycle Control: Stabilizing and De-Stabilizing, Part II

Software: LifeMOD™ v2005.1 New Product Release!

Other News : Recorded Keynote Address, New Publication: "A Study of the Human Impulse Response from the Standing Shooting Posture"



This issue presents the second part of the two part newsletter investigating the biomechanics of a motorcycle crash. In the first issue (Volume 4) we examined the rider's actions which led to the unsafe handling of the motorcycle. In this issue we will examine the biomechanics of the resulting motorcycle crash and study various injury producing mechanisms.


Also in this issue, learn how BRG.LifeMOD™ makes this technology accessible to all researchers and students of biomechanics. Additionally, we are pleased to announce the release of LifeMOD Version 2005.1 with many new functions and features including a new scalable muscle geometry database for the entire body and scaling muscle graphics. We invite you to download a free trial version of the software; try out one of our 17 easy-to-follow tutorials and begin building physics-based human models today.



HUMAN MOTORCYCLE CONTROL:
STABILIZING AND DE-STABILIZING, PART II

Introduction

A motorcycle rider must be constantly attentive to environmental disturbances - potholes, insects, wind, etc. These disturbances can cause crashes, and crashes usually result in injury.

The first part (Volume 4 issue) in this two-part series, discussed the execution of the lane change maneuver at 50 mph, both in a steady state condition and when encountering a pothole (disturbance) during the apex of the first turn. In that issue we examined the rider's response to stabilize the motorcycle in a healthy condition with the proper neuroactuation time delays and in an impaired condition with an extended time delay.

This second issue in the 2-part newsletter explores the results when the rider-cycle model becomes unstable due to the extended response delay and results in a injury-producing crash. It also provides an evaluation of the biomechanics response of the rider to the resulting crash conditions [McGuan, 93].

See the Volume 4 issue for a discussion of the development of the rider-cycle simulation model.

Human Model

The human component of the rider-cycle model consists of a 2-phase model. The first phase is the motorcycle control phase, discussed at length in Newsletter Volume 4. The second phase, the crash phase, is the topic of the current discussion.

For both phases, the human model was built using BRG.LifeMOD™ [McGuan, 04]. The segment geometry, mass properties and joints were all generated for a 50 percentile male from internal anthropometric databases. The model is then represented as a skeletal, skin or crash dummy.

For a 2-phase human model that will both control the motorcycle and respond to the crash, the joints of the model consisted of both active elements (controlling phase) and passive elements (reactive phase). The type of elements were dependent on the instantaneous state of the model. See Figure 1. The phase of the human model was directed by the state of the break-away force attachments between the feet and hands of the human model and the foot pegs and grips respectively. Break-away attachments (springs) are used between the hands and the grips and will release at a certain threshold [Mathiowetz, 86] to allow the human model to detach from the motorcycle during a crash event.


Figure 1: Human joints switch from active controlling to passive response, depending on the state of attachment of the rider to the motorcycle.Figure 1: Human joints switch from active controlling to passive response, depending on the state of attachment of the rider to the motorcycle.

During the crash phase, the human model must also interact in an impact sense with the motorcycle and the environment. To model this interaction, a contact algorithm in LifeMOD is employed to calculate the impact and frictional forces between the various segments of the human model and the motorcycle and the ground. Contact elements are also created between the motorcycle structure and ground. Body segment to environment contact properties were developed from [SAE, 86].

The crash phase of the human model uses torques acting at the joints between the segments of the human model to simulate the proper kinematic rebound during a ballistic impact. The joint torques generated from LifeMOD are based on stiffness, damping and friction data measured at the Armstrong Aerospace Medical Research Laboratory, Wright Patterson Air Force Base [Kelps] from the mechanical Hybrid III [Foster, 77] crash dummy. The non-linear stiffnesses are included in look-up table form for each of the three rotational degrees-of-freedom for each of the 18 joints in the human model.


Figure 2: Anthropometric joint torque curve form.Figure 2: Anthropometric joint torque curve form.

These data can be typically represented by the curve form shown in Figure 2. This curve describes a small (or non-existent) stiffness throughout the normal operating range for a particular joint at a particular degree of freedom. The sharp inclines and declines of the curve are a result of the joint encountering hard-tissue (or soft tissues limitations) resistance, resulting in the exceeding of the biological limit of the joint. It is within this range that injury can occur to the joint.

These joint torque data, derived from the Hybrid III crash dummy, are generally considered a passive response model for the kinematic rebound simulation, representing a rider being unaware of the impending crash. The slope of the curve form in Figure 2 may be altered for the rider, using a scale factor to represent the rider recognizing the pending crash and "freezing".

Motorcycle Model

The vehicle dynamics can be characterized analytically via a system of differential equations and studied using classical mechanics. Practical limitations necessitate the usage of "automated" mechanics programs which generate and solve the equations of controlled motion. For this inquiry, the motorcycle will be modeled using MSC/ADAMS (MSC software).

The rider-cycle system can be viewed as a closed-loop mechanical system. The controlled element, the motorcycle, consists of four parts: the two wheels, the steering assembly, and the body, connected with revolute joints. The effects of the suspension system are not included in this inquiry. This results in a system with eight degrees-of-freedom, including the six components of vehicle gross motion and the rotational freedoms of the front wheel and the steering assembly.


Figure 3: Exploded view of the simple motorcycle model.Figure 3: Exploded view of the simple motorcycle model.

Rider-Cycle Mechanical System - Crash Phase

To simulate rider error (or inattentiveness to the pothole) the time constant (τ) in the neuromuscular actuation equation is changed from a healthy alert rider [Eaton, 73] to an impaired rider or from O.2 to O.4. See Human Motorcycle Control: Stabilizing and De-Stabilizing, Part I. This causes the response rate of the rider to be delayed causing an instability in the control system. During this instability the relative motion between the rider and the motorcycle is large enough to cause the hand-grip and foot-peg break-away forces to release. This event triggers the change in control phase to passive phase in the human joints.

Figure 4 illustrates the resulting crash event due to rider instability. It may be apparent from the kinematic rebound sequence that the rider does not react to the impending crash with any defensive posturing. For the purposes of this inquiry, it is assumed that the event occurs over such a short duration, 0.76 seconds, that the only posturing that the rider has time for is to "freeze". This effect is accounted for in the model by scaling the curve forms in Figure 2 for each joint.


Figure 4: Crash sequence from the moment of instability to the final resting position.Figure 4: Crash sequence from the moment of instability to the final resting position.
  • Stage 1 (time=0.0): This is the instant when the motorcycle/rider model goes unstable and a crash is imminent. At this point the hands and feet are still attached to the vehicle since the forces have not yet surpassed the established limits. There is relatively minor loading on the joints, with the largest on the lumbar spine at 33600 N-mm (200 in-lbs).
  • Stage 2 (time=0.15): At this time step, the connections between the rider and the vehicle surpass the predefined limits (> 180 lbs) and the human model now detaches from the vehicle. This is the major impact event of the crash, where the model absorbs most of the energy. The rider first impacts the ground with the head, and shoulders. The head impacts the ground with a load of 6672 N (1500 lbs) cause a neck torque of 384200 N-mm (3400 in-lbs). The load is reduced by the impact with the shoulder at 13344 N (3000 lbs). This blow to the shoulder causes the joint to flex rapidly. With the blow to the head, the torque on the neck is at its highest point of 395500 N-mm (3500 in-lbs). There are also impacts between the rider and the motorcycle including a substantial impact of 4314 N (970 lbs) between the chest and the gas tank.
  • Stage 3 (time=0.60): At this time step, the human model is completely ballistic (rebound) without any external forces acting on it at this time. The right arm is displaced due to the friction of the road surface during the impact. Also, the body is rotating due to the frictional effects of the interaction between the right side of the body and ground. Since there is no contact with ground at this time, there is no impact loading on the human model.
  • Stage 4 (time=1.0): The human model impacts the ground again for the second head impact. At this stage the impact is to the anterior (front) portion of the skull resulting in a head load of 3322 N (746 lbs) and a neck torque of 188500 N-mm (1668 in-lbs). The substantial load is due to the fact that the body is now rotating during this phase, effectively increasing the impact velocity.
  • Stage 5 (time=1.6): At this point, the human model now remains in contact with the ground for the third head contact. Energy from the impact is being dissipated through contact friction. This contact is now to the posterior of the skull at a load of 1621 N (364 lbs).
  • Stage 6 (time=3.0): This stage represents the final resting position of the human surrogate at the end of the simulation period. The forces and torques at this point are at a minimum.

Injury Analysis

Major injuries resulting from a vehicle crash, are generated by a change in velocity. That change in velocity may occur on a localized part of the body as a result of a specific blow, or it may be a whole-body velocity change. The actual response of the human frame, depends not only on the overall velocity change but on the varying accelerations which may occur during the impact phase. In addition, the external loading produces a biological response, which causes various relative motions and reactions to develop inside the human body. It is that human response which is, in essence, the biodynamics of trauma.

To determine if the human surrogate model is experiencing trauma during the simulated crash event, the resulting forces and reactions must be recorded and compared against established injury tolerance criteria. Much data are available for head injuries, [SAE, 86, Ommaya, 84, Thibault, 90] including skull fracture data due to blows and brain injury data due to the forces resulting from translational and rotational acceleration. There are also data [SAE, 86, Ommaya, 84, McKenzie, 71] for neck injury tolerance.


Figure 5: Major injury-causing stage of the accident (stage 2) causing a shoulder injury (left) and and neck and skull injury (right).Figure 5: Major injury-causing stage of the accident (stage 2) causing a shoulder injury (left) and and neck and skull injury (right).

For the crash event simulated in this newsletter, the rider absorbs the majority of the crash energy during stage 2. In this stage, the head experiences an impact force of 6672 N (1500 lbs) which is beyond the limit for skull fracture [Ommaya, 84]. If the rider were wearing a helmet during the crash, the possibility of a skull fracture would be greatly reduced, however, the torque on the neck due to the added mass would increased. Due to the head impact, the neck receives a torque of 384200 N-mm (3400 in-lbs) which is far above the volunteer pain threshold of 88149 N-mm (780 in-lbs) [SAE, 86] and is likely to cause tissue damage.

Also in this phase, the surrogate experiences an impact force of 1334 N (3000 lbs) which causes the shoulder joint to rotate and induce a torque of 1356000 N-mm (12,000 in-lbs). This loading causes the joint to exceed its biological limit and causes extreme strain to the joint. The joint torque of 1356000 N-mm is more than enough load to cause injury [SAE, 86]

Conclusion

As illustrated by this crash simulation, the injury potential for this crash occurring at 50 miles per hour on a concrete surface is quite high. Based on the results from this simulation, there is a distinct probability of a skull fracture, a neck soft tissue injury and a shoulder joint hyper-rotation injury. Injuries caused by abrasions were not considered in this inquiry.

References
  • []Eaton , D. J. 1973, "Man-Machine Dynamics in the Stabilization of Single-Track Vehicles." University of Michigan, Ph.D. Thesis.
  • []Foster, J. K. et al. "HYBRID III - A Biomechanically Based Crash Test Dummy", Proceedings of the 21st Stapp Car Crash Conference 1977.
  • []Kelps, I.; et al. "Measurement of HYBRIDIII Dummy Properties and Analytical Simulation Data Base Development", Armstrong Aerospace Medical Research Laboratory Report no. AAMRL-TR-88-005.
  • []Mathiowetz V., et al., 1986, "Grip and pinch strength: norms for 6- to 19-year-olds." Am J Occup Ther. 1986 Oct;40(10):705-11.
  • []McGuan, S. 2004 BRG.LifeMOD™ 2004 Users Manual, Biomechanics Research Group, Inc.
  • []McGuan, S. P. 1993, "Active Human Surrogate Control of a Motorcycle - Stabilizing and De-Stabilizing" Journal of Passenger Cars.
  • []McKenzie, J. A. Williams, J. F."The Dynamic Behavior of the Head and Cervical Spine During Whiplash", Journal of Biomechanics, Vol. 4, 1971.
  • []Ommaya, A. K. Goldsmith, W. "Head and Neck Injury Criteria and Tolerance Levels", The biomechanics of Impact Trauma. Elsevier Science Publishers B. V. Amsterdam, 1984.
  • []SAE, Society of Automotive Engineers, "Human Tolerance to Impact Conditions as Related to Motor Vehicle Design", SAE Information Report no. J885, 1986.
  • []Thibault, L.E.; Gennarelli, T. A."Brain Injury: An analysis of Neural and Neurovascular Trauma in the Nonhuman Primate", Association for the Advancement of Automotive Medicine Conference Proceedings, Scottsdale, Arizona. 1990


SOFTWARE

The BRG is pleased to announce the release of LifeMOD™ version 2005.1. This new release makes state-of-the-art human modeling accessible to every investigator interested in the physics behind human motion. The release includes a new muscle parameters library which includes data on physiological cross sectional areas, maximum tissue stresses, etc. for each of the 212 muscles included in LifeMOD. These properties also scale based on the body size, weight, age and gender. In addition the user may affect the muscle output from 5 times normal to 0 to perform muscle imbalance or weakened studies.


A new graphical animation feature has been introduced which allows for the scaling of the muscle graphics and joint graphics based on force and torque magnitudes.


A new generalized contact algorithm which permits general contact between any two surfaces has been introduced. This allows for sophisticated modeling of knee joints, as well as external contacts between the body and the environment.


Due to the tremendous response we received from our users for our "trainable" muscles, we have introduced several more muscle groups to ensure LifeMOD's position as the most powerful, versatile and ease-to-use full-body human modeling package available today.


This new version is a direct result from an ongoing and rigorous user dialogue, partnerships with our research community, and the inclusion of much functionality developed by our professional staff to solve the world's most demanding biomechanics issues. View Examples...



SERVICES

The Biomechanics Research Group Inc. is a service-based organization chartered to empower our customers to capture a level of ROI from their technology investment in ways they've never imagined. We are committed to customer service, product excellence and continuous quality improvement in all we do. We provide training, modeling and simulation expertise. Contact us for more information.



OTHER NEWS


2005 Korean Cad/Cam Conference Keynote Address "Achieving Commercial Success in Biomechanics Simulation" by Shawn McGuan President/CEO of BRG

Recorded webinar: "Virtual Product Development for Biomechanics Applications" by Shawn McGuan

New publication: "A Study of the Human Response Characteristics During the Standing Shooting Posture", Y. S. Lee, et al., KSME. Feb., 2005 See PDF

Check out our new model repository! We would like to sincerely thank those who have contributed to the LifeMOD™ body of knowledge. We pledge to do our best to increase the technical capabilities of LifeMOD while developing new ways to educate the community.



If you need further information on our software and services, please contact us.


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