Lift generation in a soft porous medium under rapid compaction is a new concept for porous media flow. This concept is of extraordinarily broad interest since it applies to such diverse problems as the motion of a red cell in a tightly fitting capillary [8] , the lifting forces generated during skiing or snowboarding [22] , and the design of a futuristic train track [18] , [19] , in addition to classical lubrication theory applications [13] , [14] . In this paper, we developed a systematic, experimental approach to examine the pore pressure generation inside a deformable porous medium. To accomplish this task, a novel porous-walled cylinder–piston apparatus was developed. This apparatus was fully instrumented with pressure transducers, an accelerometer and a displacement sensor. Two synthetic fibers with different microstructures and mechanical properties were tested under various, precisely-controlled loading conditions. Enhanced lift was observed for both of them. The results indicated that lift generation inside a compressible porous medium strongly depends on the material properties and loading conditions. Softer material with lower Darcy permeability was able to generate higher pore pressure, although lowering the permeability of a porous medium was usually accompanied by the increase in the solid phase contribution to the total lift and thus led to the decrease in the pore fluid pressure. It was also observed that higher pore pressure was generated if the porous layer thickness was increased. The study presented herein has provided a rigorous approach for experimentally examining the lift generation in a deformable porous medium. It is of significant importance for the designs of rotational squeeze dampers and shock absorbers, as well as for the application of highly compressible porous media for enhanced lubrication.

In recent studies about lift generation in porous media, dynamic compression experiments have been performed using a porous-walled cylinder-piston apparatus, where the air trapped inside a porous layer underneath the loaded piston was forced out through the porous wall to the ambient, namely, "finite domain," oversimplifying real applications where transiently trapped fluid is squeezed out to the surrounding porous structures, that is, "infinite domain." In the current paper we treat this shortcoming experimentally. A soft, polyester, fibrous, porous material was chosen for the study. Its microstructure was characterized using a scanning electronic microscope. Its porosity was measured using a water-displacement method, and its permeability was determined using a permeameter. The cylinder-piston apparatus was first used in a quasi-static experiment to examine the material's stiffness and was then used in the dynamic compaction experiments in the infinite domain. Detailed pressure distribution was examined. The results indicate that the air lifting force is enhanced by 25 to 30% for the infinite domain over the finite domain due to the existence of the surrounding porous material. The pore pressure, however, relaxes rapidly in the undeformed surroundings. These observations improve our understanding of the dynamic response of soft porous media under rapid compression.