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Machine component design has become a prominent topic for researchers in recent years. The analysis of bearing systems has received considerable attention in order to avoid detrimental contact. Among the most important studies in this area are the transient problems of journal bearings, which are usually performed by coupling the Reynolds equation with the motion equations. Many techniques have been presented in the literature and are still being explored to ensure the accurate findings and efficient solution prediction of unsteady state Reynolds equation. In this paper, the Proper Generalized Decomposition (PGD) approach is expanded for the analysis of the lubricant behavior of dynamically loaded journal bearing considering Swift-Stieber boundary conditions. The PGD model is applied in this problem, seeking the approximate solution in its separated form of the partial differential Reynolds equation at each time step during the load applied cycle employing the alternating direction strategy. Compared to the classical resolution, the PGD solution has a considerably low computational cost. To verify the accuracy and efficiency of this approach, three cases have been considered, infinitely short, infinitely long and finite journal bearings under the dynamic load. The results of the suggested methodology when compared to the full discretized model (FDM) show that, the new scheme is more efficient, converges quickly, and gives the accurate solutions with a very low CPU time consumption.

The influence of counter-rotation between the inducer and impeller, along with a newly introduced system for their independent rotation on the pump cavitation characteristics, has been studied experimentally. Remarkably, this pump allows users to select between co-rotation and counter-rotation modes, providing significant operational adaptability. The high-speed camera is used to analyze vaporization structures and closely monitor the stability of the head pressure delivered by the pump during the cavitation testing phase. For both co-rotation and counter-rotation modes, different types of cavitation within the inducer and between the inducer and the impeller at three varied flow rates have been studied using image analysis. The results reveal improved cavitation performance and comparable efficiency at consistent pressure–flowrate combinations, emphasizing the advantages of counter-rotation across the three tested flow rates. In counter-rotation mode, the tangential velocity of the flow at the output of the inducer is opposite to that of the co-rotation mode. Consequently, the tangential velocity of the flow entering the impeller is reduced, leading to enhanced flow stability and increased pump pressure. The findings from image analysis demonstrate that the structure of cavitation varies between co-rotation and counter-rotation modes. Reversing the rotation direction of the inducer not only improves the pump cavitation characteristics but also changes the vapor structure due to changes in the flow pattern. [ABSTRACT FROM AUTHOR]

The use of a counter-rotating rotor in turbomachines can be a solution to improve performances by allowing reduction in size and weight, especially compared to multistage configuration. The present study aims are to demonstrate another advantage of the counter-rotating rotors: their application to expand the operating range of centrifugal compressors toward extremely low flow rates based on an active control method. This method was performed on two different counter-rotating configurations. The principle of the active control method is to adjust independently the rotation speed of each rotor to push back the instability appearance. Experimental results show that reducing the rotation speed of the upstream-rotor while fixing the speed of the downstream rotor can push the instability phenomenon toward a lower mass flow rate while decreasing the pressure rise and efficiency. Co-rotating mode is applied to push further the stable region toward low mass flow rates allowing a significant extension of the operating range. The experimental results reveal that the map width is shifted by about 50% over the studied range toward a lower mass flow rate for both counter-rotating centrifugal compressors when using the control method. This can be achieved when the absolute value of the upstream-rotor speed is within the range of 48%–61% of the rotational speed of the downstream rotor. [ABSTRACT FROM AUTHOR]

In this article, the overall mechanical properties of a short glass fiber-reinforced polyphenylene sulfide (PPS) composite were tested after oxidation at different temperatures (140, 160, 180, and 200[degrees]C), with a maximum oxidation time of approximately 5,300 h. In aspect of thermal aging process, the oxidation rates in 200 and 180[degrees]C are considerably harsher and faster than the case in 160 and 140[degrees]C, according to the concentration evolution of [C=O]. In aspect of mechanical properties, for virgin samples, due to an excellent fiber-matrix adhesion, no progressive damage is developed. Moreover, the fatigue results of aged samples show that the fatigue lifetime of PPS composites decreases more and more obviously with the oxidation time increasing while no significant loss of stiffness is observed. In addition, both monotonie and cyclic loadings are basically driven by the PPS matrix deformation. In the end, the relationship between fatigue lifetime and concentration of [CO] is built and discussed., INTRODUCTION In the past several decades, glass fiber-reinforced polyphenylene sulfide (PPS) composites are widely used to lighten automotive parts and other application sections [1-15]. The main reason to use this [...]

With the aim of optimizing Drug Eluting Stents (DES), particular attention has been laid on computational methods of controlling the drug release profile among researchers. Consequently, various models and simulations are available in the literature. Nevertheless, validations based on biorelevant in-vitro trials are lacking. In the present study, a comparison of drug release from polyurethane samples between calculated results and experimental-data has been carried out. The calculation results are from a numerical simulation and a newly established mathematical model for reproducing the liberation kinetic. Different fluid flow rates and initial drug concentrations in polymer have been taken into account.

In the present study, the static characteristics of hydrodynamic circular journal bearings of finite length are highlighted, using the combined influences of textured surface and non-Newtonian lubricants behavior, obeying to the Rabinowitsch fluid model. The associated nonlinear Rabinowitsch-Reynolds equation has been discretized using finite differences scheme and solved by the mean of Elrod’s algorithm taking into account the presence of cylindrical textures on full/optimum bearing surface. Following to the absence of textures on the bearing surface or the non-Newtonian fluid behavior, the obtained results are in good agreement with the reference ones. The hydrodynamic lubrication static performances are computed for various parameters such as textures location; eccentricity ratio and the rheological coeffcient. The results suggest that texturing the bearing’s convergent zone enhances significantly the load carrying capacity and reduces the friction coeffcient, whereas texturing the full bearing surface may leads to bad performances. It is also noticed that the pseudoplastic lubricant coeffcient decreases the bearing performances (load capacity and pressure) compared to Newtonian fluid cases. Considering the optimal arrangement of textures on the contact surface, a significant improvement in terms of load capacity and friction can be achieved, especially at low pseudoplasticity effect.

Centrifugal compressors are widely used in many industrial applications because of their advantages. However, these turbomachines suffer at a low-flow rate from instabilities, such as rotating stall and surge. That leads to operational failure, pressure fluctuations and vibrations of the thorough system. Many mechanical solutions minimize these instabilities and expand the operating range towards low-flow rates like active control of the flow path, variable inlet guide vane and casing treatment. Currently, our team has developed a new compressor composed of a twin-impeller powered by autonomous systems. We notice the performance improvement and instabilities suppression of this compressor experimentally. In this paper, a CFD study is presented to explain some of these experimental observations by analyzing the inside of twin-impeller, the flow structures and thermodynamic characteristics at low flow rates operating in a co-rotating mode. Numerical results and experimental measurements of compressor maps are consistent.

Drug-eluting stents implanted in blood vessels are subject to various dynamics of blood flow. In this study, we present the evaluation of a mathematical model considering the effect of flow rate, to simulate the kinetic profiles of drug release (Diclofenac Sodium (DS)) from in-vitro from PLGA films. This model solves a set of non-linear equation for modeling simultaneously the burst, diffusion, swelling and erosion involved in the mechanisms of liberation. The release parameters depending on the flow rate are determined using the corresponding mathematical equations. For the evaluation of the proposed model, test data obtained in our laboratory are used. To quantify DS release from drug-carrier PLGA films, we used the flow-through cell apparatus in a closed-loop. Four flow rate values are applied. For each value, the model-substance liberation kinetics showed an increase in drug released with the flow rate. The simulated release profiles show good agreement with the experimental results. Therefore, the use of this model could provide a practical tool to assess in-vitro drug release profiles from polymer matrices under continuous flow rate constraint, and could help improve the design of drug eluting stents.

In recent years, machine component design has been a major concern for researchers. Emphasis has been placed especially on the analysis of bearing systems in order to avoid detrimental contact. The shaft misalignment is one of the most problems that affects directly the operating conditions of these components. In this context, the present study proposes a reduced-order method "Proper Generalized Decomposition" (PGD) using the separation technique through the alternating direction strategy to solve the modified Reynolds equation, taking into account the presence of misalignment in the shafting system. The solution shows the representation of two types of misalignment geometry, especially axial and twisting. A comparison of the results between the proposed approach and the classical method, through several benchmark examples, made it possible to highlight that the new scheme is more efficient, converges quickly and provides accurate solutions, with a very low CPU time expenditure.

In this paper, 3D numerical simulations have been carried out to enhance the understanding of a flow over a passive control device composed of micro cylinder with, d/c = 1.34% placed in the vicinity of NACA0012 aerofoil wing, by means of γ–Reθt transition sensitive turbulence model meant to predict the separation induced by transition achieved for aerofoils operating at moderate Reynolds number (Re = 4.45×105). Results show that the separation of the boundary layer has been eliminated by the passive static vortex generator at stall regime due to the injection of free-stream momentum to the boundary layer. The early transition to turbulent state overcomes the local flow deceleration of an adverse pressure gradient and remains sticked to the wall the boundary layer. Furthermore, the wing aerodynamic performance are improved as drag is reduced and lift is enhanced which is straight forward linked to the lift to drag ratio gain that varies from 22.68% to 134.17% at post stall angles of attack.