Volumetric Modeling and Experimental Validation of Normal Contact Dynamic Forces

Boos, Michael; McPhee, John

doi:10.1115/1.4006836

Cited by 11 publications

(6 citation statements)

References 21 publications

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“…Since volumetric contact considers the pressure developed across the whole contact surface, it is more accurate than point contact models for complex and conforming geometries [21]. This also means that the pressure across the contact surface can be calculated naturally with volumetric contact, unlike point contact models.…”

Section: Vmentioning

confidence: 99%

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A 3D ellipsoidal volumetric foot–ground contact model for forward dynamics

Brown

McPhee

2017

Multibody Syst Dyn

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Foot-ground contact models are an important part of forward dynamic biomechanic models, particularly those used to model gait, and have many challenges associated with them. Contact models can dramatically increase the complexity of the multibody system equations, especially if the contact surface is relatively large or conforming. Since foot-ground contact has a large potential contact area, creating a computationally efficient model is challenging. This is particularly problematic in predictive simulations, which may determine optimal performance by running a model simulation thousands of times. An ideal contact model must find a balance between accuracy for large, conforming surfaces, and computational efficiency.Volumetric contact modelling is explored as a computationally efficient model for footground contact. Previous foot models have used volumetric contact before, but were limited to 2D motion and approximated the surfaces as spheres or 2D shapes. The model presented here improves on current work by using ellipsoid contact geometry and considering 3D motion and geometry. A gait experiment was used to parametrise and validate the model. The model ran over 100 times faster than real-time (in an inverse simulation at 128 fps) and matched experimental normal force and centre of pressure location with less than 7% root-mean-square error.In most gait studies, only the net reaction forces, centre of pressure, and body motions are recorded and used to identify parameters. In this study, contact pressure was also recorded and used as a part of the identification, which was found to increase parameter optimisation time from 10 s to 164 s (due to the additional time needed to calculate the pressure distribution) but helped the results converge to a more realistic model. The model matched experimental pressures with 33-45% root-mean-square error, though some of this was due to measurement errors.The same parametrisation was done with friction included in the foot model. It was determined that the velocity-based friction model that was used was inappropriate for use in an inverse-dynamics simulation. Attempting to optimise the model to match experimental friction resulted in a poor match for friction forces, inaccurate values for the coefficient of friction, and a poorer match to the experimental normal force.

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Section: Vmentioning

confidence: 99%

“…Similarly, the centre of pressure (COP) is at the centroid of this volume of penetration, and all other contact forces (rolling resistance and friction) can be related to the volume of penetration and its properties [21], [22]. The equations for the other contact forces are not given here, but a general derivation is in Gonthier's thesis [22].…”

Section: Vmentioning

confidence: 99%

A 3D ellipsoidal volumetric foot–ground contact model for forward dynamics

Brown

McPhee

2017

Multibody Syst Dyn

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“…How should DEM-P handle these cases? Various computational geometry heuristics exist for producing surrogates for the contact point, normal contact direction, and relative penetration speed, see, for instance, [49][50][51]. Against this backdrop, one can regard DEM-P as either an approach that considers elastic deformation and no penetration, with the frictional contact force modulated by geometric (R andm) and material (K n , K t , C n , C t ) parameters -see Eq.…”

Section: E Flow Sensitivity With Respect To Element Shapementioning

confidence: 99%

“…Against this backdrop, one can regard DEM-P as either an approach that considers elastic deformation and no penetration, with the frictional contact force modulated by geometric (R andm) and material (K n , K t , C n , C t ) parameters -see Eq. (2) [8]; or, an ad-hoc approach not concerned with the local elastic deformation but rather with the mutual penetration, in which case a penetration metric, e.g., the intersection volume for the two geometries in contact, and additional empirical parameters, dictate the frictional contact force [49][50][51]. At the price of not being able to handle arbitrary geometries, we embrace the elastic deformation "orthodoxy" for DEM-P and root the frictional contact force computation in an analytical argument as done in the Herzian contact the-ory [8].…”

Section: E Flow Sensitivity With Respect To Element Shapementioning

confidence: 99%

Compliant contact versus rigid contact: A comparison in the context of granular dynamics

et al. 2017

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We summarize and numerically compare two approaches for modeling and simulating the dynamics of dry granular matter. The first one, the discrete-element method via penalty (DEM-P), is commonly used in the soft matter physics and geomechanics communities; it can be traced back to the work of Cundall and Strack [P. Cundall, Proc. Symp. ISRM, Nancy, France 1, 129 (1971); P. Cundall and O. Strack, Geotechnique 29, 47 (1979)GTNQA80016-850510.1680/geot.1979.29.1.47]. The second approach, the discrete-element method via complementarity (DEM-C), considers the grains perfectly rigid and enforces nonpenetration via complementarity conditions; it is commonly used in robotics and computer graphics applications and had two strong promoters in Moreau and Jean [J. J. Moreau, in Nonsmooth Mechanics and Applications, edited by J. J. Moreau and P. D. Panagiotopoulos (Springer, Berlin, 1988), pp. 1-82; J. J. Moreau and M. Jean, Proceedings of the Third Biennial Joint Conference on Engineering Systems and Analysis, Montpellier, France, 1996, pp. 201-208]. The DEM-P and DEM-C are manifestly unlike each other: They use different (i) approaches to model the frictional contact problem, (ii) sets of model parameters to capture the physics of interest, and (iii) classes of numerical methods to solve the differential equations that govern the dynamics of the granular material. Herein, we report numerical results for five experiments: shock wave propagation, cone penetration, direct shear, triaxial loading, and hopper flow, which we use to compare the DEM-P and DEM-C solutions. This exercise helps us reach two conclusions. First, both the DEM-P and DEM-C are predictive, i.e., they predict well the macroscale emergent behavior by capturing the dynamics at the microscale. Second, there are classes of problems for which one of the methods has an advantage. Unlike the DEM-P, the DEM-C cannot capture shock-wave propagation through granular media. However, the DEM-C is proficient at handling arbitrary grain geometries and solves, at large integration step sizes, smaller problems, i.e., containing thousands of elements, very effectively. The DEM-P vs DEM-C comparison is carried out using a public-domain, open-source software package; the models used are available online.

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“…2, to supply wider contact areas and therefore produce smoother normal contact forces. The contact model is based on a volumetric approach [4,12]. This model assumes a linear elastic foundation for the material.…”

Section: Linear Volumetric Contact Modelmentioning

confidence: 99%

Foot–ground contact modeling within human gait simulations: from Kelvin–Voigt to hyper-volumetric models

Shourijeh

McPhee

2015

Multibody Syst Dyn

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This study describes the development of a multibody foot-ground contact model consisting of spherical volumetric models for the surfaces of the foot. The developed model is two-dimensional and consists of two segments, the hind-foot, mid-foot, and fore-foot as one rigid body and the phalanges collectively as the second rigid body. The model has four degrees of freedom: ankle x and y, foot orientation, and metatarsal-phalangeal joint angle. Three different types of contact elements are targeted: Kelvin-Voigt, linear volumetric, and hyper-volumetric. The models are kinematically driven at the ankle and the metatarsal joints, and simulated horizontal and vertical ground reaction forces as well as center of pressure location are compared against experimental quantities, acquired from barefoot measurements during a human gait cycle. Parameter identification is performed for finding optimal contact parameters and locations of the contact elements. The hyper-volumetric foot-ground contact model was found to be a suitable choice for foot/ground interaction modeling within human gait simulations; this model showed 75% and 62% improvement on the matching quality over the point contact and linear volumetric models, respectively.

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Volumetric Modeling and Experimental Validation of Normal Contact Dynamic Forces

Cited by 11 publications

References 21 publications

A 3D ellipsoidal volumetric foot–ground contact model for forward dynamics

A 3D ellipsoidal volumetric foot–ground contact model for forward dynamics

Compliant contact versus rigid contact: A comparison in the context of granular dynamics

Foot–ground contact modeling within human gait simulations: from Kelvin–Voigt to hyper-volumetric models

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