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Abstract

The motion of a ring pack on a thin oil film covering a cylinder liner has been analysed. In contrast to the previous paper [8], which considered only hydrodynamic phenomena, in the present paper a mixed lubrication case is also taken into account. Equations describing the mixed lubrication problem based on the empirical mathematical model formulated in works of Patir, Cheng [5], [6] and Greenwood, Trip [2] have been combined and used in this paper. Results of numerical simulations of this phenomenon have been presented. The model of ring motion considered takes the following phenomena into account: hydrodynamic and contact forces, spring and gas forces and the local motion of each ring in piston grooves. Differences between the motion of the ring on a thick and thin oil film are analysed and discussed.
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Authors and Affiliations

Andrzej Wolff
Janusz Piechna
ORCID: ORCID
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Abstract

The motion of a ring pack on a thin film covering a cylinder liner has been analysed. In contrast to the previous papers [30], [31], which considered a primary hydrodynamic phenomena (including mixed lubrication), in the present paper an additional degree of freedom of a ring i.e. a twist motion is also taken into account. Equations describing the twist of rings are presented and used in simulation. The twist phenomena of a single ring have been analysed in the past [25]. In this paper, the twist effects of separate rings forming a ring pack are considered. In the pack configuration, the twist of the upstream ring strongly influences the operation of the downstream ring. The phenomenon commonly treated as secondary effect seems to be influencing the ring motion strongly. Differences between results obtained applying and neglecting ring twist motion are analysed and discussed.

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Authors and Affiliations

Andrzej Wolff
Janusz Piechna
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Abstract

The human environment consists of a large variety of mechanical and biomechanical systems in which different types of contact can occur. In this work, we consider a monopedal jumper modelled as a three-dimensional rigid multibody system with contact and simulate its dynamics using a structure preserving method. The applied mechanical integrator is based on a constrained version of the Lagrange-d’Alembert principle. The resulting variational integrator preserves the symplecticity and momentum maps of the multibody dynamics. To ensure the structure preservation and the geometric correctness, we solve the non-smooth problem including the computation of the contact configuration, time and force instead of relying on a smooth approximation of the contact problem via a penalty potential. In addition to the formulation of non-smooth problems in forward dynamic simulations, we are interested in the optimal control of the monopedal high jump. The optimal control problem is solved using a direct transcription method transforming it into a constrained optimisation problem, see [14].

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Authors and Affiliations

Michael W. Koch
Sigrid Leyendecker

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