The resistance to flow of imbibed fluids in soft porous structures subjected to compression can be a solution for impact attenuation. The mechanism, named ex-poro-hydrodynamic (XPHD) lubrication, is based on permeability variation with porosity, which, at its turn, depends on the compression degree of the porous structure. A literature survey revealed scarce information regarding the permeability of compressed reticulated foams or 3D fiber-based structures, used in XPHD applications. Moreover, the permeability depends on the fluid and its velocity. This paper presents experimental data of the permeability of glycerine for an in-plane, axisymmetric flow through a porous material subjected to various degrees of compression. The experiments were done on an in-house made radial permeameter with pressure differentials up to 6 bars. The experimental data was compared with the predicted results, using the well-known Kozeny-Carman equation and related formulations.

The paper presents experimental and theoretical results for the planar squeeze flow of a finite volume of viscoplastic material through a highly deformable porous layer. The central zone of an annular disc made of a reticulated polyurethane foam with high porosity (ε > 0.97) was fully filled with tooth paste. The porous disc placed between two flat, impermeable, parallel, and rigid discs was subjected to compression and the normal force was recorded. After compression, the radial extension of the squeezed fluid was measured. The visualisation of the compressed disc managed to provide evidence of a tortuous flow inside the porous structure. An original analytical model is proposed for the prediction of the front of the flow inside the porous layer and corresponding resistant normal force. The model combines the Covey and Stanmore (1981) model for squeeze flow of a Bingham fluid inside the central zone, with an original approach for flow through the reticulated foams, based on the concept of “equivalent flow tubes” with variable tortuosity. This explorative investigation is of interest for innovative shock absorbers. The model validity covers both low and high plasticity numbers and was experimentally validated for low speed.

It is well known since the pioneering work of Dowson and Castelli that load capacity increases in compliant (elastic pad) hydrostatic bearings, compared to their rigid counterparts. In a recently published paper, a new design solution of a flexible pad hydrostatic bearing was proposed and analysed theoretically. A simplified analytical model was proposed for the fluid-structure interaction. The model was based on two important simplifications: linear pressure distribution on the bearing land, used to calculate the deformation of the pad, and parabolic variation of film thickness in the Reynolds equation. The analysis was made for isothermal conditions and constant pressure in the recess. This new approach relaxes the two simplifications by considering a linearly elastic model for the flexible pad and including its deformation in the Reynolds equation. A finite differences scheme is proposed for both the fluid flow and elastic deformation, considering the flexible plate simply supported. The consistency and convergence of the iterative solution are analysed, and comparisons with previous analytical solutions are shown. These results show the limits of the accuracy of the simplified analytical model and allow the selection of the design parameters of a test rig.

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The present study is dedicated to the innovative 3-bar torsion spring used as suspension solution for the first time at Lunokhod-1, the first autonomous vehicle sent for the exploration of the Moon in the early 70-ies by the former USSR. The paper describes a simple analytical model for calculation of spring static characteristics, taking into account both torsion and bending effects. Closed form solutions of this model allows quick and elegant parametric analysis. A comparison with a single torsion bar with the same stiffness reveal an increase of the maximum stress with more than 50%. A 3D finite element (FE) simulation is proposed to evaluate the accuracy of the analytical model. The model was meshed in an automated pattern (sweep for hubs and tetrahedrons for bars) with mesh morphing. Very close results between analytical and numerical solutions have been found, concluding that the analytical model is accurate. The 3-D finite element simulation was used to evaluate the effects of design details like fillet radius of the bars or contact stresses in the hex hub.

Aerostatic bearings were proven to be an optimal choice in situations where low friction, cleanliness, and high motion accuracy are required. Their functionality relies heavily on flow restrictors, which are responsible for regulating and controlling the supply flow, and consequently, the thickness and stiffness of the fluid film. A diverse range of restrictors with varying characteristics is used, among which are the porous restrictors. The current work introduces a novel solution involving a porous, highly compressible restrictor, whose element of novelty compared to its predecessors consists of its variable thickness and corresponding permeability, regulated by the load on the bearing. The gas is supplied through an annular, elastic, deformable, porous disc, which is compressed by a metal plate, subjected to compression by the recess pressure on one side and by the supply pressure on the other side. One or more springs are used in parallel with the porous disc to obtain the optimum elastic response. The objective of this study is to evaluate the performance characteristics and compare them to a conventional restrictor. A parametric analysis is performed to define the size and properties of the porous restrictor.