Unrelieved pressure on load-bearing muscle tissues of humans can produce pressure ulcers. In a seated upright posture, the highest pressures occur inferior to the ischial tuberosities (ITs). Moreover, the vibration can initiate the development of pressure ulcer. Therefore, the seat cushion is not only used to lower the maximum seating pressure on buttocks but also minimize the transmission of vibration to human body. The purpose of this study was to investigate the effects of varying vertical vibration frequencies on seat-interface contact pressure during sitting on three different seat cushions by using a finite element modeling approach. A simplified two-dimensional human buttock-thigh model was developed to simulate the mechanical response of the muscle of buttocks and thigh under vertical vibration. Static and vibrational loads with five different frequencies of 0.1, 1, 10, 30 and 50 Hz and the same amplitude of 3 mm were applied to different seat cushions. The result showed that the “SAF 6060” seat cushion with both hyperelastic and viscoelastic behaviors could be effective in reducing the amplitude of varying maximum contact pressure, especially for the frequency of 10-20 Hz. This method could help in design of seat cushions with appropriate material properties and shape so as to reduce vibrations transmitted to human body at a certain frequency range.
KeywordsFinite Element AnalysisSeat CushionVibrationButtock-Thigh
M. M. Verver, J. van Hoof, C. W. J. Oomens, J. S. H. M. Wis-mans and F. P. T. Baaijens, “A Finite Element Model of the Human Buttocks for Prediction of Seat Pressure Distributions,” Computer Methods in Biomechanics and Biomedical Engi-neering, Vol. 7, No. 4, 2004, pp. 193- 203.
D. M. Brienza, P. E. Karg, M. J. Geyer, S. Kelsey and E. Trefler, “The Rela-tionship between Pressure Ulcer Incidence and Buttock-Seat Cushion Interface Pressure in At-Risk Elderly Wheelchair Us-ers,” Archives of Physical Medicine and Rehabilitation, Vol. 82, No. 4, 2002, pp. 529-533.
J. M. Black, “Moving toward Consensus on Deep Tissue Injury and Pressure Ulcer Staging,” Advances in Skin & Wound Care: The Journal for Prevention and Healing,” Vol. 18, No. 8, 2005, pp. 415-421.
M. R. Bliss, “Acute Pressure Area Care: Sir James Paget’s Legacy,” Lancet, Vol. 339, No. 8792, 1992, pp. 221-223.
M. Gru-jicic, B. Pandurangan, G. Arakere, W. C. Bell, T. He and X. Xie, “Seat-Cushion and Soft-Tissue Material Modeling and a Finite Element Investigation of the Seating Comfort for Pas-senger-Vehicle Occupants,” Materials & Design, Vol. 30, No. 10, 2009, pp. 4273-4285.
E. Linder-Ganz, N. Shabshin, Y. Itzchak, Z. Yizhar, I. Siev-Ner and A. Gefen, “Strains and Stresses in Sub- Dermal Tissues of the Buttocks are Greater in Paraplegics than in Healthy During Sitting,” Journal of Biome-chanics, Vol. 41, No. 3, 2008, pp. 567-580.
M. Makhsous, D. Lim, R. Hendrix, J. Bankard, W. Z. Rymer and L. Fang, “Finite Element Analysis for Evaluation of Pressure Ulcer on the Buttock: Development and Vvalidation,” IEEE Transactions on Neural Systems and Rehabilitation Engineering, Vol. 15, No. 4, 2007, pp. 517-525.
R. Ragan, T. W. Kernozek, M. Bidar and J. W. Matheson “Seat-Interface Pressures on Various Thicknesses of Foam Wheelchair Cushions: A Finite Modeling Approach,” Archives of Physical Medicine and Rehabilitation, Vol. 83, No. 6, 2002, pp. 872-875.
A. Siefert, S. Pankoke and H. P. W?lfel, “Virtual Optimisation of Car Passenger Seats: Simulation of Static and Dynamic Effects on Drivers’ Seating Comfort,” International Journal of Industrial Ergonomics, Vol. 38, No. 5-6, 2008, pp. 410-424.
Q. Sun, F. Lin, L. Ruberte, E. Nam, R. Hendrix and M. Makhsous, “FE Modeling and Analysis of Compressed Human Buttock-Thigh Tissue,” Proceeding of ASB 29th Annual Meeting, Georgia, 2005.
B. A. Todd and J. G. Thacker, “Three-Dimensional Computer Model of the Human Buttocks, In Vivo,” Journal of Rehabilitation Research, Vol. 31, No. 2, 1984, pp. 111- 118.
E. Wagnac, C. Aubin and J. Dansereau, “A New Method to Generate a Patient-specific Finite Element Model of the Human Buttocks,” IEEE transactions on Biomedical Engi-neering, Vol. 55, No. 2, 2008, pp. 774-782.
R. A. Cooper, “Wheelchair Selection and Configuration,” Demos Medical, New York, 1998.
J. L. Minkel, “Seating and Mobility Considerations for People with Spinal Cord Injury,” Physical Therapy, Vol. 80, No. 7, 2000, pp. 701-709.
X. Wu, S. Rakheja and P. é. Boileau, “Distribution of Human-Seat Inter-face Pressure on a Soft Automotive Seat under Vertical Vibra-tion,” International Journal of Industrial Ergonomics, Vol. 24, No. 5, 1999, pp. 545- 557.
C. P. DiGiovine, R. A. Cooper, S. G. Fitzgerald, M. L. Boninger, E. J. Wolf and S. Guo, “Whole-Body Vibration During Manual Wheelchair Propulsion with Selected Seat Cushions and Back Supports,” IEEE Trans-actions on Neural Systems and Rehabilitation Engineering, Vol. 11, No. 3, 2003, pp. 311-322.
International Organization for Standardization, “ISO 2631-1: 1997, Mechanical Vibration and Shock - Evaluation of Human Exposure to Whole-body Vibration,” Switzerland, 1997.
M. M. Verver, J. van Hoof, C. W. J. Oomens, N. van de Wouw and J. S. H. M. Wismans, “Estimation of Spinal Loading in Vertical Vibrations by Nu-merical Simulation,” Clinical Biomechanics, Vol. 18, No. 9, 2003, pp. 800-811.
S. Kitazaki and M. J. Griffin, “A Modal Analysis of Whole-Body Vertical Vibration Using a Finite Element Model of the Human Body,” Journal of Sound and Vibration, Vol. 200, No. 1, 1997, pp. 83-103.
T.-H. Kim, Y.-T. Kim and Y.-S. Yoon, “Development of a Biome-chanical Model of the Human Body in a Sitting Posture with Vibration Transmissibility in the Vertical Direction,” Interna-tional Journal of Industrial Ergonomics, Vol. 35, No. 9, 2005, pp. 817-829.
J. Rosen and M. Arcan, “Modeling the Hu-man Body/Seat System in a Vibration Environment,” Journal of Biomechanical Engineering, Vol. 125, No. 2, 2003, pp. 223- 231.
F. M. L. Amirouche, “Modeling of Human Reactions to Whole-body Vibration,” Journal of Biomechanical Engi-neering, Vol. 109, No. 3, 1987, pp. 210-217.
D. R. Huston, C. C. Johnson, M. A. Wood and X. Zhao, “Vibration Attenuating Characteristics of Air Filled Seat Cushions,” Journal of Sound and Vibration, Vol. 222, No. 2, 1999, pp. 333-340.
E. J. Wolf, M. S. R. A. Cooper, C. P. DiGiovine, M. L. Boninger and S. Guo, “Using the Absorbed Power Me-thod to Evaluate Effectiveness of Vibration Absorption of Se-lected Seat Cushions During Manual Wheelchair Propulsion,” Medical Engineering & Physics, Vol. 26, No. 9, 2004, pp. 799-806.
R. L. Huston, “Principles of biomechanics,” CRC Press, Boca Raton, 2009.
W. Chow and E. Odell, “Deformations and Stresses in Soft Body Tissues of a Sitting Person,” Journal of Biomechanical Engineering, Vol. 100, 1978, pp. 79-87.
A. Lowe and R. S. Lakes, “Negative Poisson’s Ratio Foam as Seat Cushion Material,” Cellular Polymers, Vol. 19, No. 3, 2000, pp. 157-167.
ABAQUS Version 6.9-1, “User Documentation,” Dassault Systems, 2009.
M. Schrodt, G. Benderoth and A. K¨uhhorn, “Hyperelastic Description of Polymer Soft Foams at Finite Deformations,” TECHNISCHE MECHANIK, Vol. 25, No. 3-4, 2005, pp. 162-173.
E. Pennestrì, P. P. Valentini and L. Vita, “Comfort Analysis of Car Occupants: Comparison between Multibody and Finite Element Models,” International Journal of Vehicle Systems Modelling and Testing, Vol. 1, No. 1-3, 2005, pp. 68-78.
C. Y. Tang and C. P. Tsui, “Method of Modeling Muscular Tissue with Active Finite Elements,” U. S. Patent, The Hong Kong Polytechnic University, Kowloon (HK), 2006.
D. B. Chaffin, G. B. J. Andersson and B. J. Martin, “Occupational Biomechanics,” Wiley-Interscience, Hoboken, 2006.