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Mircea D. Pascovici

Mircea D. Pascovici

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79
Publications
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878
Citations

Publications

Publications (79)
Article
Full-text available
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...
Conference Paper
Full-text available
It is generally accepted that actual high performance brush seals are interference seals and therefore, tribological behavior at the bristle-to-shaft interface is a major concern. As in any other sliding contact, contact temperature is an important topic, which must be addressed. In a recent paper, Pascovici & Cicone [15] proposed a simplified elas...
Article
During last two decades it was theoretically and experimentally proved that the fluid squeeze out from a soft and porous layer under the action of an external impact load produces high lifting forces. For high porosity, the elastic forces generated by the solid phase are negligible. The mechanism, strongly dependent on permeability variation with l...
Article
Full-text available
During last decade a series of theoretical studies revealed the high pressures generated in highly porous soft materials imbibed with fluids and subjected to compression, with possible application to impact damping. The mechanism, named eXPoroHydroDynamic (XPHD) Lubrication, combines the resistance to flow inside the porous matrix with its variable...
Article
Many published studies on the behaviour of imbibed porous materials reveal a good potential in shock absorption. This phenomenom studied until now only in contact with rigid surfaces is based on a complex process that involves the squeeze of fluid from the porous layer at different levels of permeability. This innovative process which is strongly d...
Article
Full-text available
Theoretical and experimental evidences show that high lift forces can be generated when a porous layer imbibed with a fluid is subjected to compression by a rigid and impermeable component in normal (approaching) relative motion. If the porous layer is soft enough to neglect its solid structure reaction to compression then the pressure increase can...
Article
Full-text available
This paper presents an original theoretical model for squeeze flow of a Bingham fluid between a multiple-disk stack. The volume of fluid and the speed of the squeeze process are constant. Low and high squeeze speeds were considered in accordance with Covey-Stanmore theory adapted for the constant volume fluid conditions. The case for low speed was...
Article
The fluid film pressure and temperature fields have been measured simultaneously under laboratory conditions at one land of a Circumferential Groove Journal Bearing (CGJB), together with friction torque and oil flow rate, during a time span from stand-still start-up to the development of a thermally stabilized steady operating regime. A very fine m...
Article
Full-text available
The present paper proposes a theoretical and experimental approach to predict the imbibition process into a fibrous porous media where the displacement of air by the liquid is seen to be characterized by the presence of a clearly-defined liquid front. The imbibition process is defined as the absorption of liquid in a porous media, mainly due to sur...
Article
Full-text available
This paper presents an original theoretical model for the axisymmetric squeeze flow of a Newtonian fluid imbibed in the central region of a highly compressible porous layer. The fluid flow is studied for three squeezing conditions: constant speed, constant force and given impulse. The experimental validation of the model is made for reticulated pol...
Article
Full-text available
It has been shown before that liquids can slip at a solid boundary, which prompted the idea that parallel-surfaces bearings can be achieved just by alternating slip and non-slip regions in the direction of fluid flow. The amount of slip at the wall depends on the surface tension at the liquid–solid interface, which in turn depends on the chemical s...
Conference Paper
Full-text available
An innovative solution for damping of residual energy after the impact of a bullet on a protective vest, based on the flow of a fluid through a porous material that is placed under the protective Kevlar layers, has been recently proposed. The fluid flow through the open pores is produced by the compression of the porous material, during impact, i.e...
Conference Paper
Simultaneous measurements of the fluid film pressure and temperature fields have been performed during the start-up regime for a lightly loaded two-land symmetrical circumferential groove journal bearing (specific pressure: 0.25 MPa; diameter: 100 mm; acceleration and nominal speed: 0 to 4000 rpm in 20 s). The measurements grid consists in 4 axial...
Article
Full-text available
Surface texturing has been shown to reduce friction and increase the film thickness in various tribological applications (hydrodynamic bearings, mechanical seals, and cylinder–liner contacts). However, only few studies discuss optimal texturing properties, and most of them focus on the optimal dimple shape. This article proposes an in-depth study o...
Conference Paper
This paper presents experimental and theoretical results for squeeze flow of a non-Newtonian fluid between parallel surfaces at constant speed. A mathematical model for circular plates squeeze (disc configuration) is proposed for a fluid with a rheological behavior described by power law. Experiments were conducted on CETR UMT 2 test rig for a shea...
Conference Paper
The aim of this study is to present distributions of the film pressure and temperature measured at one land of a two-land Circumferential Groove Journal Bearing (CGJB) during start-up and steady state operating conditions. Simultaneous pressure and temperature measurements are performed in both axial and circumferential directions. Five axial plane...
Article
Fluid flow through highly compressible porous layers (HCPL) subjected to external loads is known as ex-poro-hydrodynamic (XPHD) lubrication. Several models have been proposed for squeeze in XPHD conditions and analytical solutions were obtained based on a significant number of simplifications. Consequently, an analysis of these simplifications effe...
Conference Paper
Full-text available
Steady-state tests are performed on a 100 mm, in diameter, Circumferential Groove Journal Bearing (CGJB), consisting of two 20 mm lands. The supply groove’s depth is adjustable by mounting special adapters. The lubricant pressure and temperature values are measured in five, respectively four, axial planes in one of the lands with high accuracy tran...
Conference Paper
Full-text available
A theoretical model for thermally induced seizure, based on a lumped model analysis, has been previously developed by Cristea et al. in 2010 [1]. Due to the increase of the average global temperature, the system encounters clearance loss, which ultimately can lead to seizure. This study presents a series of experiments designed to validate the tran...
Article
This study presents a new simple lumped model for analyzing the thermally induced seizure of fully lubricated eccentric circumferential groove journal bearings (CGJB). The model represents a significant upgrade of a previous seizure lumped model developed by Pascovici & Kucinschi, in 2002. Main upgrades consist of: eccentric operation, introduction...
Article
The current study presents the experimental determination of the lubricant film pressure and temperature distributions on one land of a symmetrical two-land circumferential groove journal bearing (CGJB) operating under low-load steady-state conditions. Film pressure and temperature measurements are done both in axial and circumferential directions....
Article
The objective of this article is the study of the load-carrying capacity of a Rayleigh step slider (RSS) for both direct motion (+RSS – which generates lifting effects) and reverse motion (−RSS – which generates suction or cavitational effects). Normal force was measured on a pin-on-disc test rig, with two lubricants (SAE-20 W-50 oil and glycerin)...
Article
Squeeze film dampers are widely used technical components for turbomachinery as a means to reduce the amplitude of rotor vibration owing to unbalance. This article proposes a different type of circular damper using highly compressible porous layers (HCPL) imbibed with Newtonian liquids. The elastic forces of the HCPL solid phase are negligible comp...
Conference Paper
The study concerns experimental investigations of lubricant film temperature distributions in one land of a two-land Circumferential Groove Journal Bearing (CGJB) operating in steady-state conditions. Temperature measurements are performed both in axial and circumferential directions. Four axial planes, with three equally spaced temperature tapings...
Article
Ex-poro-hydrodynamic (XPHD) lubrication, a mechanism that generates self-sustained films when highly compressible porous layers (HCPL) imbibed with liquids are squeezed, is strongly dependent on permeability variation of the porous structure. The present paper analyzes the variation of the permeability with layer compression. The experiments were p...
Conference Paper
A recent experimental investigation of the complete pressure field for a circumferential groove journal bearing (CGJB) under steady state operating conditions has been performed by the authors and presented elsewhere. The present paper presents, in more detail, the divergent zone pressure field measurements on one land of the symmetrical CGJB and c...
Article
Full-text available
Despite a large amount of work dedicated to the study of the effects of textured surfaces in tribological pairs, there is still a need for accurate and convincing experimental results to prove the benefic effects predicted theoretically. This paper presents an original experimental set-up with a partially textured flat pin sliding on a rotating dis...
Conference Paper
Full-text available
This study presents a new simple lumped model designed to analyze the thermally induced seizure of fully lubricated eccentric circumferential groove journal bearings (CGJB). The current model represents an upgrade of a previous seizure analysis lumped model developed by Pascovici & Kucinschi, in 2002, and considers an eccentric bearing operation, i...
Article
A theoretical model that evaluates the frictional properties of an infinitely wide rigid cylinder rotating over a grooved surface in a hydrodynamic lubrication regime is presented in this article. The parabolic approximation of the film thickness is used in order to analytically compute the pressure distribution in the fluid film. At the discontinu...
Article
The process of liquid flow takes place inside a highly compressible porous layer (HCPL) many times. In these cases, elastic forces of the HCPL solid phase are negligible, compared with hydrodynamic (HD) forces. Such processes were named ex-poro-HD (XPHD). A study of the impact process under XPHD conditions for circular and rectangular aligned plate...
Article
The paper proposes a model for the squeeze process under impact for highly compressible porous layers imbibed with fluids (HCPL). It is assumed that the normal forces generated by elastic compression of the fibers comprising the solid phase are negligible compared to the pressure forces generated in the imbibed fluid, within the porous layer. The p...
Article
The article presents a one-dimensional isothermal flow model with analytical solution for partially textured surfaces, nominally parallel. The model allows a simple and elegant parametric analysis of slider performance characteristics (load-carrying capacity, friction force, and friction coefficient) in terms of texture dimensions. It is shown that...
Article
During the last 10-15 years a new lubrication mechanism applicable to highly compressible porous layers acting as self-sustained films has been developed. This type of lubrication is strongly dependent on porosity variation and consequently on permeability hence the name ex-poro-hydrodynamic-XPHD lubrication was proposed. The objective of the prese...
Article
The present paper presents an original, quasi-analytical, thermoelastohydrodynamic (TEHD) model for a fluid film, parallel surface, elastic slider. Temperature variation along the slider is included in a simplified manner, based on Tipei assumption (viscosity variation along the pad is proportional to film thickness variation) [Tipei N. Theory of l...
Article
L'utilisation des surfaces micro-texturées dans les paliers et butées hydrodynamiques peut avoir des effets positifs sur les performances de ces composants. Cependant, une étude analytique suffit pour montrer qu'une mauvaise distribution ou un dimensionnement inadapté des textures peuvent conduire à des pertes de performance et non à des gains. Afi...
Conference Paper
Surface texturing has been shown to have friction reducing / load capacity increasing effects in parallel sliders, as well as in cylinder-liner contacts and in hydrodynamic seals. However, if texture is to be regarded as the sole mean of hydrodynamic lift in parallel sliders, or as a way of improving hydrodynamic performance in slider, thrust and j...
Article
Full-text available
Lubricated textured surfaces reduce the friction coefficient and the surface wear rate. The present work is dedicated to the analytical and numerical study of load capacity and friction coefficient of a single, square dimple, typical for textured surfaces realized by lithography. The analytical model is based on the pressure linearization while the...
Article
A numerical model is developed to analyze the influence of thermal deformations on the performance of a radially grooved thrust washer. The analysis couples the flow phenomena (including cavitation) in the lubricant with the heat transfer in both the fluid and solid media, as well as with the thermally induced deformations in the solid parts. The f...
Conference Paper
Full-text available
The squeeze film for layered, compliant and porous contacts is a challenging subject with application in Biotribology as well as for a better insight of principles of natural joints for designing of performant artificial joint replacements. The paper presents an original approach of flowing process both in the lubricant film and trough the complian...
Article
Compliant and permeable layered surfaces are used in natural synovial joints and have been proposed for the bearing surface in artificial joint replacements. The squeeze-film lubrication mechanism plays an important role in long-term performance of both natural and artificial joints. The full lubrication solution of the present problem including co...
Article
Thermoelastic instability (TEI) in a mechanical component manifests itself in the form of macroscopic hot spots. To gain insight into the mechanism of hot spotting, an engineering TEI model for two solid surfaces separated by a viscous liquid film in relative sliding motion is developed. The model lends itself to a useful analytical expression for...
Article
Full-text available
A simplified solution of the Reynolds equation for non-isoviscous conditions, based on a 3rd degree polynomial representation of the velocity profile is proposed. It allows uncoupling the energy and momentum equations and leads to an analytical solution, independent of the law of temperature-viscosity dependence. Using the proposed solution, correl...
Article
A novel hydrodynamic system, called torsional fluid film vibrator (TFFV) is proposed. This device is complementary to the Lanchesters absorber and presents a classical response of a one-degree of freedom linear system with a periodical self-excitation. The fluid,film thickness variation produces a variable viscous drag moment, which drives the elas...
Article
Published experimental data and results of numerical modelling have shown that in certain cases the temperature gradient along the radius of the sealing gap of mechanical face seals (MFSs) can be significant. As a consequence, isothermal calculation of seal performance characteristics can induce some errors. In a recent paper, Pascovici and Etsion...
Article
A novel squeeze film damper and vibration generator (SFD&VG) is proposed as an option in the vibration control field. The SFD&VG can be used as an active squeeze film damper (ASFD) or as a vibration generator (vibrator), for unidimensional vibration damping or generation. The SFD&VG concept is connected with current reseal-ch to improve a common in...
Article
The present paper proposes an advanced bidimensional model necessary to calculate the temperature field in a journal bearing submitted to both rapid and slow start-ups. The model takes into account realistic thermal boundary conditions at fluid film-solid interfaces, The thermoelastic deformations of both the journal and of the bush are also consid...
Article
Full-text available
The presence of rigid particulate contamination in hydrodynamic bearings is known to lead to considerable damage resulting in failure. This paper presents a model for evaluating the flash temperature between a fixed, rigid particle embedded into the bearing over-layer while in contact with the slider. Scuffing is assumed to occur if the flash tempe...
Article
Thermally induced seizure can lead to a rapid catastrophic bearing failure. An analytical model was developed to study this phenomenon in an unloaded journal bearing. The model consisted of two concentric cylinders containing lubricant in which the inner one rotates at a specified rpm and the outer cylinder is stationary. The appropriate governing...
Article
An experimental apparatus was designed and tested to study the thermally induced seizure in bearing. The setup consists of a simple, unloaded journal bearing configuration which lends itself to useful physical interpretation without the complexities that are present in the control of flow rates and eccentricity in a loaded journal bearing in which...
Article
Full-text available
The boiling interface in a misaligned two-phase mechanical seal is analyzed using a complete thermohydrodynamic approach that requires complex simultaneous iterative solutions of the nonaxisymmetric heat transfer and phase-change problems. It is shown that under certain operating conditions, characterized by a modified Sommerfeld number, several ap...
Article
The problem of vaporization in face seals operating on mixtures where the minority liquid is discontinuous and has the lower boiling point is analyzed. A model based on several simplifications is presented and used to solve a numerical example for water-in-oil mixtures. It is shown that even the smallest amount (in the order of 1 %) of water in the...
Article
A qualitative study of the hydrodynamic effect on the radius at which boiling occurs in two-phase, misaligned, mechanical seals with coning is presented. The more important parameters affecting the problem are identified and analyzed. It is found that hydrodynamic effects depend mainly on a modified Sommerfeld number. It is shown that in most pract...
Article
Full-text available
The accuracy of the isoviscous solution of the Reynolds equation for mechanical seals is examined by comparison with a temperature-dependent solution. It is found that the isoviscous solution produces a radial pressure distribution that always overestimates the more realistic temperature-dependent pressure distribution. The error depends on a singl...
Article
Full-text available
The combination of phase change, coning, and face misalignment in mechanical seals is studied. The seal performance is calculated using an implicit analytical solution of the the thermohydrodynamic problem. It is found that phase change can be detrimental to the seal's angular stiffness. It is also found that the boiling interface is practically ax...
Article
Full-text available
A thermo-hydrodynamic analysis is performed for a face-to-face double seal configuration. Temperature and viscosity variations both across and along the sealing gap are considered and realistic boundary conditions are considered. The energy equation is solved analytically and the radial temperature variation is presented by an implicit equation. Th...
Article
This paper studies the load capacity and power dissipated by friction for grease squeeze films. The problem is solved both analytically (approximately) and numerically. The results are in agreement with experimental observation regarding the increased damping capacity of oils compared with that of greases having the same viscosity.
Article
Full-text available
It is assumed that the existence of some discontinuities in the experimentally determined circumferential temperature distribution of journal bearings is determined by the lubricant-wall heat transfer and the local hydrodynamic flow conditions. From this hypothesis a simplified theoretical model is proposed which uses adequate boundary conditions a...
Article
Using a specially developed test rig a more thorough analysis of discontinuities in the circumferential temperature distribution of complete journal bearings has been carried out. The experimental results contribute to the explanation of the interdependence of temperature distribution in the lubricant film, heat transfer and hydrodynamic flow condi...
Article
This paper is focused on the geometry and operating parameters of the bearing experimentally studied at NASA Glenn Research Center by F. Dimofte. It presents two simple thermoelastohydrodynamic (TEHD) models for two typical mechanisms of seizure of a three-wave journal bearing: seizure during start-up under normal lubrication, respectively seizure...

Projects

Project (1)
Archived project
The present project has as main objective the development of an improved protection equipment for human personnel or vehicles which will contain in the backing an encapsulated highly compressible porous layer (HCPL), imbibed with a liquid, capable to absorb a large part of the energy produced by the bullet impact or the shock waves generated by an explosion.