Multibody System Dynamics最新文献

Plates are omnipresent in many industrial machinery and structures, such as tanks and bridges. In industry, the impacted plates represent a significant noise source, often annoying. The models dealing with this research theme are generally limited in literature to one part of the problem. Indeed, some numerical developments have been established to simulate the noise an impacted plate generates without calculating the contact force. This one has always been either estimated by Hertz’s law or experimentally. In this paper, an IGA-based model allowing the prediction of the vibration and radiation of the impacted plate is described. In this model, the plate-sphere impact is introduced using a penalty method based on a physical node-to-surface contact algorithm within an isogeometric framework. Based on Bézier extraction of Bsplines, this model makes isogeometric analysis compatible with existing finite elements codes for node-to-surface contact. The only changes needed are limited to the shape function routine without any additional change in the contact formulation. This same discretization method should also extend the scope of this model to other contact formulations and contacting bodies of more complex geometries than has been done in this work.

The elastic aftereffect phenomenon of viscoelastic materials under low-velocity impact has been widely observed in practical engineering. This paper proposes a new approximated solution for the Wang model, which has relatively high accuracy and simplicity, and is helpful for impact analysis of viscoelastic materials with elastic aftereffect. The approximated solution of the hysteresis damping factor is derived theoretically based on an approximation for the relation between the relative deformation and the relative velocity. The new approximated solution is verified by comparing with the exact solution and two sets of experimental data of previous studies. A series of numerical simulations are conducted to analyze the influence of the coefficient of restitution and the remaining surface-deformation ratio on the system’s dynamic response. The results indicate that the inverse restitution function is almost identical to the exact solution in the whole range of the coefficient of restitution. By comparing with experimental results, it has been proven that the new approximated solution has relatively high accuracy in simulating impacts with elastic aftereffect. The coefficient of restitution has more influence on the systems’ dynamic response than the remaining surface-deformation ratio. The described contact-force model can accurately simulate the impact of viscoelastic materials with elastic aftereffect.

The traditional Lewinnek safe zone used for Total-Hip Arthroplasty (THA) surgery has been found to be inadequate, as dissatisfaction rates have risen after this surgery. It is evident that spinopelvic parameters and spine stiffness, factors that have been overlooked previously, must be taken into account for optimal surgical outcomes. In this paper, a novel predictive dynamic modeling approach was proposed to address this issue. This approach involved the development of a multibody model of a human that contained nonlinear spinal elements, which was validated by comparing it to literature in-vitro experiments and conducting a motion-capture experiment. To simulate human sit-to-stand motion, this model was employed with an optimal control approach based on trajectory optimization. Human joint angles were extracted from conducted simulations of different scenarios: normal, fused, and stiff spines. It was found that spine stiffness had a significant effect on lower-limb motion and the risk of implant impingement. Different scenarios of spine stiffness were examined, such as different levels of spinal fusion or an anatomically stiff spine. The optimal acetabular-cup orientation was calculated based on implant-impingement criteria using predicted motions for different spinal-condition scenarios, and the results compared to the clinically recommended orientation values for the same categories of patients. Our preliminary optimization suggests increasing the anteversion-cup angle from (23 ^{circ }) (normal spine) to (29 ^{circ }) for an anatomically stiff spine. For fused spines, the angle should fall within the range of 27–38^∘, depending on the level of fusion. This research is the first of its kind to examine spine flexibility in different scenarios and its impact on lower-limb motion. The findings of this paper could help improve THA surgical planning and reduce the risk of hip impingement or dislocation after THA.