Development of a Dynamic Biomechanical Model for Load Carriage: Phase 4, Parts A and B: Development of a Dynamic Biomechanical Model Version 2 of Human Load Carriage

Abstract : The overall purpose of this is to improve the understanding of human load carriage capabilities. Earlier phases of the dynamic biomechanical model have lead to a new modeling approach that treats the pack person interface as a dynamic suspension system. In the current study, both 2D and 3D dynamic modeling software packages were selected to permit multiple models of the pack person suspension characteristics. The selected software both permit full user control of model geometry, inertial properties, have extensive libraries of existing dynamic elements for modeling constraints, allow the user to construct complex constraint equations and allow the user to input complex forcing functions. For both the 2D and 3D models, two types of dynamic tests were conducted to determine the impulse response and the natural frequencies. For the 2D model, the impulse response test showed typical results for a mildly under damped system with the amplitude ratio plot showing a modest peak at approximately 8 Hz, higher than the estimated natural frequency of 4.8 Hz. On the other hand, the impulse response test for the 3D model gave a vertical displacement typical of an over damped system and an amplitude ratio plot with several resonant frequencies at approximately 2.5 Hz and again at 5 Hz. With the damping reduced by a factor of 100, there were some initial oscillations of the system followed by a slow decay in the vertical position and as expected, the minimally damped 3D model displayed a dominant natural frequency at approximately 5 Hz. Overall, the 2D model required much higher damping coefficients to bring about a pack displacement pattern similar to that of the 3D model. In addition, the 3D model behaviour was more consistent with the physical system. The next stage in model development is to integrate a waist belt model (Hadcock, 2002) being developed separately into the 3D model.