International Journal of Human Factors Modelling and Simulation (8 papers in press)

Special Issue on: "Dynamics in Digital Human Modelling and Simulation"
Guest Editors: Dr. Yujiang Xiang, The University of Iowa, USADr. Xianlian Zhou, CFD Research Corporation, USA Dr. Jingzhou (James) Yang, Texas Tech University, USA

• A general framework for lumbar spine modeling and simulation
  by Ahmed Sameh, Ayman Kassem 
  Abstract: A general framework for modeling and simulation of the dynamic, three-dimensional motion response of the human lumbar-spine is presented. Lumbar vertebrae were modeled as rigid bodies and all other flexible joint structures (i.e. ligaments, cartilage, muscles, and tendons) were modeled collectively as massless springs and dampers. Coupling coefficients, providing additional constraints, were incorporated in the model. Unknown model coefficients (nominally spring, damping and coupling coefficients) were automatically determined by systematically matching the model predictions to spine forced displacement-time data. A robust parameter optimization module (Monte Carlo routine and genetic algorithm) was developed for this purpose. Two test cases were included for parameters estimation and model verification.
  Keywords: Lumbar spine, Optimization, Genetic Algorithms, Simulation, Parameter estimation.
   
• Child Neck FE Model Development and validation
  by Frank Meyer, Sebastien Roth, Remy Willinger 
  Abstract: Despite of recent progresses in occupant safety, the protection of children is not still optimal. To offer a better understanding of child injury mechanisms, the present study proposes a human-like finite element model of a three years old child’s neck. The subject was scanned with a medical scanner. The images were first semi-automatically segmented in order to extract the soft tissues and the bones. In a second step, the different bones were separated slice by slice on the geometry previously reconstructed. The anatomic structures are identified and each vertebra is reconstructed independently with special attention for the articular process. Finally, an original meshing on the previous geometry was generated to obtain a finite element model of the child’s neck. For validation purpose, the FEM response was superimposed with time corridors available in the literature for different impact cases, which have been scaled down using adapted scale factors from Irwin and Mertz (1997).
  Keywords: Finite element neck model; Scaling Method; Child biomechanics
   
• Classic JACK modelling of driver posture and line-of-sight for operators of lift-trucks
  by Alison Godwin, Sylvain Grenier, Tammy Eger, Linde Corrigan 
  Abstract: Several reports indicate that lift-truck (LT) drivers may be at higher risk for developing musculoskeletal injuries due to postures that must be adopted in order to maneuver the LT in industrial workplaces. This research uses a human simulation program to quantify changes to line-of-sight (LOS) using driving simulations acquired from actual drivers in a closed arena setting. Video files acquired during the mock-up were decimated to 3Hz and the resulting video files were coded in 3D Match. The resulting posture file was used to drive the animation tool in Classic JACK v4.1 human simulation software while quantifying LOS with additional virtual tools. On average, the drivers adopted awkward postures with increased levels of compression in order to have less overall LOS on both LT models. The method introduced was deemed a success at simulating human motion in a virtual environment from a simple, video record of the original motion.
  Keywords: line-of-sight, ergonomics, lift truck, Classic JACK, human simulation, visibility, 3D Match, low-back analysis, industrial, computer animation
   

• Development of an Optimum Bicycle Shifting Strategy Based on Human Factors Modelling
  by T. Y. LIN, Y. C. Chen, H. C. Ping 
  Abstract: According to ergonomic studies, cyclists can be in an optimum state during cycling with a fixed output power and cadence. This study proposes an intelligent shifting strategy, which can be adjusted automatically according to different environmental conditions, and by cyclists according to human factor aspects. The gear-shifting suggestions can also allow riders to maintain output power and optimum cadence during cycling. The output power change during the gear-shifting process can be reduced, and riders will feel comfortable and efficient during cycling
  Keywords: bicycle; derailleur system; gear-shifting strategy; ergonomic.
   
• Safety assessment of wheelchaired occupants in paratransit buses
  by Cezary Bojanowski, Leslaw Kwasniewski, Jerry Wekezer 
  Abstract: A plan for a comprehensive safety assessment of passengers with disabilities traveling in their wheelchairs in paratransit buses is presented in this paper. Computational mechanics and LS-DYNA non-linear finite element code were used as primary tools in this study. All finite element models were partially validated using data available from experimental sled tests. The results of the validation process correlate well with the experimental test. The validated dummy-wheelchair-bus system which was developed allowed for quantitative assessment of injury criteria in several accident scenarios, and in forward- versus backward facing seating configuration for wheelchair passengers. Conclusions and practical recommendations were presented. Although backward seating was found generally beneficial in reducing severity of injuries during accidents, the outcome was proven to be too sensitive to imperfect initial conditions during accidents. Material presented in this paper allows for detailed assessment of benefits and shortcomings of each configuration considered.
  Keywords: Wheelchair occupant safety assessment; paratransit bus; frontal impact; injury criteria; finite element analysis
   
• Uniformity in manikin posturing: A comparison between posture prediction and manual joint manipulation.
  by Dan Lämkull, Lars Hanson, Roland Örtengren 
  Abstract: This paper presents the results of a comparison of manikin posturing within and between simulation engineers. Five simulation engineers were asked to simulate and visualize four manual assembly cases. They repeated each task six times, three times with a posture prediction tool and three times with manual adjustment of the body angles. The results show that the posture prediction tool was not used in an optimal manner. Although the prediction tool was quick at suggesting a likely posture, the simulation engineers were reluctant to consider a simulation task completed until the manikin’s posture was realistic in all aspects, not only in the configurations for the major body joints postures but also for fingers, wrists and feet. This fine tuning of fingers is performed with manual manipulation of joints and cancels out the time gained with the posture prediction tool. The fine tuning does not affect the results in object evaluation methods. Therefore, a lower acceptance level of correctness among managers, simulation engineers and ergonomic specialists is desired, or a shift from visualization to simulation is necessary. Manikin postures differ between simulation engineers. A posture variation exists and this variation in working behaviour should be accepted and simulated. However, simulation engineers also need more extensive knowledge of how workers actually behave on the assembly line; study visits are thus recommended. A shift is also recommended from simulations and visualizations of normal working behaviours to that of ergonomically correct behaviours. This comparison of manikin posturing within and between simulation engineers is an attempt to understand the use of the tool in a practical sense. The comparison indicates that if a posture prediction tool is to be beneficial for the whole organisation, all disciplines involved in the use of manikins must accept simulation results with postures containing some non-cosmetic elements. It is not until such an acceptance is achieved that the successful use of a posture prediction tool will become a reality.
  Keywords: virtual manufacturing, manikin posturing, digital human modelling, posture prediction, manual manipulation, posture variation.
   
• Simulation of Manual Material Handling Tasks in Three Dimensional Spaces
  by Yanxin Zhang, Simon Hsiang 
  Abstract: A novel biomechanical simulation model was developed to simulate and investigate complex manual material handling (MMH) activities. To deal with the large number of degrees of freedom required to simulate MMH tasks, in this model, a non-linear optimization method based on inverse kinematics formulation was developed to simulate MMH tasks. Mathematically, the approach was expressed as a system of nonlinear equations with an objective function and a set of constraints, which was solved using an iterative numerical algorithm. To test and compare the simulation results, a factorial experiment was conducted to obtain the kinematics data for different task conditions. The experimental results showed that the simulated data fit well with the experimental data for all experiment conditions. This model, together with a video based coding system, showed a very promising capability for human–workstation modelling and analysis, layout design of workstation. The proposed methods could be used for the real industrial workstation design/layout and evaluation if the test and training data are not collected in industrial environment. It can also be used for manual assembly workstation prototyping both in a virtual and real design environment.
  Keywords: Manual Materials Handling; Biomechanical Simulation; Non-linear Optimization
   
• Probabilistic Modeling of the Role of Human Factor in Helicopter Landing Ship Situation
  by Ephraim Suhir 
  Abstract: Our analysis contains an attempt to quantify, on the probabilistic basis, the role that a human factor plays, in terms of the operation time, in the helicopter-landing-ship (HLS) situation. The operation time includes the time required for the officer-on-ship-board and the helicopter pilot to make their decisions, and the time required for actual landing. It is assumed that these times could be approximated by the Raleigh’s law of probability distribution, while the duration of the lull follows the normal law. Safe landing can be expected if the probability that it takes place during the lull time is sufficiently high. We develop a simple and easy-to-use model to evaluate this probability. This model can be used in the risk analysis of the landing situation, as well as in the probabilistic assessment of the strength of the helicopter undercarriage. It can be employed also when developing guidelines for personnel training and particularly to establish the decision making time that needs to be met to land the helicopter safely. Certainly, plenty of additional risk analysis and human psychology related effort is needed to make such guidelines practical. It is the author’s belief that the taken approach, with some appropriate modifications and generalizations, is applicable to many other situations affected by the human-equipment-environment interaction.
  Keywords: humaactor, probabilistic model, helicer landing ship