There are few works that have studied the sealing mechanism between two rough surfaces. In the present article, an elastohydrodynamic one-dimensional model of the U-cup hydraulic seal is performed by taking into account both the shaft and the lip roughness. The numerical results are compared with the inverse hydrodynamic lubrication (IHL) theory and are validated with previously published experiments. Differences confirm the accuracy of the elastohydrodynamic lubrication (EHL) modeling with a gap of about 5% between numerical and experimental results. The study of the textured shaft effect is performed in three steps: by first changing the shape of the grooves, then changing their amplitudes, and finally by varying their densities. The results demonstrate that a dry contact could occur for some pattern profiles, whereas full-film lubrication is verified for other profiles. The numerical simulations confirm that the asymmetric groove shape affects the friction and show a significant impact of the pattern amplitude on the power loss. Additionally, a slight effect of the groove density is observed on the friction force.

Since the sixties, most of numerical studies that model the rotary lip seal lubrication have been restricted by assuming that one of the two opposing surfaces is smooth: either the lip or the shaft. This hypothesis, although it is verified only for a shaft roughness ten times smaller than that of the seal, is the best solution to avoid the transient term “∂h/∂t” in the deterministic approach. Thus, the subject of the present study is twofold. The first part validates the current hydrodynamic model with the international literature by assuming the asperities on the lip and shaft as a two-dimensional cosine function. In the second part the Reynolds equation for rough surfaces with relative motion is solved. The numerical results show that the relative motion between rough surfaces impacts significantly the load support and the leakage rate, but affects slightly the friction torque.

It is generally agreed that radial lip seals are used in systems with a rotating shaft and a stationary lip. However, according to previous work, it was demonstrated that relative motion between the shaft and the lip has substantial effects on the hydrodynamic lifting load and sealing performances. Nowadays, new generations of textured shafts have emerged in order to reduce friction torque and improve reverse pumping, but no study has confirmed the effect of the relative motion between the rough lip and the shaft grooves on the rotary lip seal performances. In this work, an isothermal hydrodynamic lubrication was performed in transient conditions to investigate the effect of the relative velocity between an oblique grooved shaft and a rough lip. After confirming the validity of the current model with respect to previous works, simulations have underlined the effect of the grooved shaft with relative lip motion on the rotary lip seal performance. Indeed, by keeping the same relative velocity between surfaces, it is shown that moving the shaft with a rate higher than that of the lip surface could produce an important reverse pumping and reduce the friction torque significantly, in comparison with cases where the shaft velocity is weaker.

In the last years, the new research papers piezoelectric energy harvesting from vortex-induced vibration (PEH-VIV) are focused on indirect contact between airflow and piezoelectric transducer. Where some researchers have noticed that is difficult to establish an accurate analytical model that could describe precisely the behavior of the piezoelectric generator including the indirect interaction with airflow. Due to these difficulties, new studies are concentrating directly on the experimental investigations to get results of energy harvesters of the indirect-contact piezoelectric wind energy harvesters (IC-PWEHs). However, this paper presents an analytical model that can provide good results according to experimental tests. The obtained results concern the displacement of the piezoelectric transducer indirectly excited by a vortex-induced vibration (VIV) and the generated voltage according to a different mass of cylindrical shell. The numerical results of the model show a significant agreement with the experimental results due to the good estimation of the system’s parameters, where the computing is done numerically using the MATLAB Simulink. Additionally, the optimal mass value of the piezoelectric transducer was determined approximately by the proposed analytical model. Where this mass is equivalent to the highest voltage amplitude according to the experimental tests.

It is commonly known that the sealing performance of dynamic seals is significantly influenced by the surface finish. To reduce friction effect and leakage ratio, new generations of grooved lip or shaft have emerged, but only two computational models were performed up to now with a textured elastomeric lip: spiral groove in the axial direction or micro-cavities according to the circumferential direction. However, if the numerical results have confirmed the slight effect of the grooved lip on the rotary lip seal performances, it seems relevant to investigate the influence of such grooves on the reciprocating hydraulic rod seal behavior. Thus, the scope of this work is to perform a parametric study of the grooved lip throughout a one-dimensional elastohydrodynamic model by taking into account the elasticity of the lip and the shaft roughness. After confirming the validity of the current model, numerical simulations have been performed and compared with experiments. The effect of lip grooves on the hydraulic rod seal behavior in outstroke and instroke shaft motion has been underlined. Thereby, it is shown that the leakage and the average film thickness are sensible to both the depth and the density of the lip groove. Additionally, a slight effect of the pattern shape is observed on the friction force.

Since the 1960s, all studies have assumed that a film thickness “h” provides a unique pressure field “p” by resolving the Reynolds equation. However, it is relevant to investigate the film thickness unicity under a given hydrodynamic pressure within the inverse theory. This paper presents a new approach to deduce from an initial film thickness a widespread number of thicknesses providing the same hydrodynamic pressure under a specific condition of gradient pressure. For this purpose, three steps were presented: 1) computing the hydrodynamic pressure from an initial film thickness by resolving the Reynolds equation with Gümbel’s cavitation model, 2) using a new algorithm to generate a second film thickness, 3) comparing and validating the hydrodynamic pressure produced by both thicknesses with the modified Reynolds equation. Throughout three surface finishes: the macro-shaped, micro-textured, and rough surfaces, it has been demonstrated that under a specific hydrodynamic pressure gradient, several film thicknesses could generate the same pressure field with a slight difference by considering cavitation. Besides, this paper confirms also that different ratios of the averaged film thickness by the root mean square (RMS) similar hydrodynamic pressure could be generated, thereby the deficiency of this ratio to define the lubrication regime as commonly known with Patir and Cheng theory.