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Model Documentation

Model Versions

VIVA+ follows Semantic Versioning, where the version numbers follows the format MAJOR.MINOR.PATCH.

  • MAJOR: Backwards incompatible mesh and major updates to model definitions
  • MINOR: Minor updates to the model definitions
  • PATCH: Bugs fixes

Modeling workflow

VIVA+ development followed a workflow where the seated average female model serves as the base model. All the model updates and enhancements are primarily carried out on the seated female model1. The geometry of the average female is based on several statistical shape models (for the outer body shape2, the ribcage3, the femur4, the tibia and pelvis5).

VIVA+ Development Workflow

The other models representing the male and standing postures are created by morphing the nodes of the base model and hence are derivatives of the base model. Each derivative has a list of parameters in the main file, that are used to define the model-specific property (such as sex-dependent properties or posture related variables).

The benefit with this unique VIVA+ workflow is that all model enhancements and bug fixes are carried out on a single model - the base model. These updates are automatically and consistently shared among all the models in the VIVA+ lineup.

The numerical robustness is evaluated in a number of robustness load cases. These load cases, which subject the models to loads of relatively high severity, include crash tests with a generic vehicle interior for the seated models and a pedestrian load case for the standing model.

Model Nomenclature

Model parameters

The model parameters are defined in the main key files (vivaplus-50F.key/vivaplus-50M.key for the occupant models and vivaplus-50F-standing.key for the standing model).

Sex differences

The sex differences are implemented using SEX parameter, with SEX = 0 for female and SEX = 1 for male.

Properties currently controlled by SEX parameters:

  • Head mass and inertia properties
  • Soft tissues densities (scaling the total mass to match the target mass)
  • Knee ligaments (set unstretched ligament length)
  • Quadriceps muscle (set unstretched muscle length)

Model identifiers

The parts and materials, and associated definitions carry a 6-digit identifier. More information can be found on the Model Data Structure page.

References

  1. Jobin D. John, Johan Iraeus, and Mats Y. Svensson. A framework for continuous integration in human body finite element model lineup. In XXVIII Congress of the International Society of Biomechanics (ISB). 2021. ↩

  2. Matthew P Reed and Sheila M Ebert. Elderly occupants: posture, body shape, and belt fit. Technical Report, University of Michigan, Ann Arbor, Transportation Research Institute, 2013. ↩

  3. Yulong Wang, Libo Cao, Zhonghao Bai, Matthew P Reed, Jonathan D Rupp, Carrie N Hoff, and Jingwen Hu. A parametric ribcage geometry model accounting for variations among the adult population. Journal of biomechanics, 49(13):2791–2798, 2016. ↩

  4. Katelyn F. Klein, Jingwen Hu, Matthew P. Reed, Carrie N. Hoff, and Jonathan D. Rupp. Development and validation of statistical models of femur geometry for use with parametric finite element models. Annals of Biomedical Engineering, 43(10):2503–2514, mar 2015. doi:10.1007/s10439-015-1307-6. ↩

  5. Katelyn Frances Klein. Use of Parametric Finite Element Models to Investigate Effects of Occupant Characteristics on Lower-Extremity Injuries in Frontal Crashes. PhD thesis, University of Michigan, 2015. ↩