Pantelis G. Nikolakopoulos

Pantelis G. Nikolakopoulos
University of Patras | UP · Department of Mechanical Engineering and Aeronautics

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144
Publications
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1,438
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Publications

Publications (144)
Article
Full-text available
The purpose of this study is to build a parametric algorithm combining analytical results and Machine Learning in order to improve the tribological performance of coated piston rings and thrust bearings in mixed lubrication using different synthetic lubricants. The friction models for piston ring conjunction and pivoted pad thrust bearing consider...
Presentation
The purpose of this paper was to understand how axial distortions could affect on the tribological performance of ring-liner conjunction. If piston rings and cylinder bore wear out, it might be a potential threat to the engine. A detailed investigation of the worn area will help to diagnose and to correct the symptoms, assisting to mitigate the har...
Article
Utilization of smart systems, i.e. software tools that incorporate artificial intelligence (AI), in engineering applications increases. This fact is due to their ability to study the performance of complicated systems, producing results quicker and easier than typical analytical models. This article is focused on the advantages of using Artificial...
Conference Paper
Type of lubricant used for fluid film bearings is one of the most important factors to consider. Bearing characteristics have to maintain steady throughout a wide range of conditions. However, viscosity, which is one of the primary lubricant properties, highly deviates depending on environmental and operational conditions. Macro-molecular micro-str...
Conference Paper
Full-text available
Turbocharged engines with direct injection offer a significant contribution to engine downsizing technology. However, there remain many unsolved and ambitious issues concerning knocking and pre-ignition. Therefore, detailed understanding of the top compression ring lubrication and fuel economy is critical. This paper focuses on the tribological per...
Conference Paper
Full-text available
Hydrodynamic thrust bearings are machine elements used in many rotating machinery in order to support axial loads. The investigation of the lubrication in such mechanisms using numerical analysis methods has been the major subject of many studies over the years. Furthermore, the evolution of technology in the last decade brought the concept of indu...
Article
The paper contains the results of the transient flow of piston ring conjunction of a single-cylinder motorbike engine. Calculations of piston ring forces, asperity contact and gas blow-by are determined in computational fluid dynamics. The stochastic model of Greenwood-Tripp approach is used to predict the load of asperities. The hydrodynamic frict...
Article
The driveshafts can be an important contributor to vehicle interior noise including low-frequency (booming) noise where the vibrations, originating in the powerplant, travel to the vehicle body through the driveshafts. A suitable Key Performance Indicator (KPI) for the driveshaft performance is the transmissibility, which is an output/input acceler...
Article
Full-text available
The influence of operating conditions of the compression rings on the engine power losses affects confoundedly the design of the Internal Combustion Engines (ICEs). Normalized parameters such as Friction Mean Effective Pressure (FMEP) were used to regulate power losses. The purpose of this work was to create a primary control model of the friction...
Article
Full-text available
Despite the high thermal efficiency achieved by modern heavy-duty diesel engines, over 40% of the energy contained in the fuel is wasted as heat either in the cooling or the exhaust gases. By recovering part of the wasted energy, the overall thermal efficiency of the engine increases and the pollutant emissions are reduced. Organic Rankine cycle (O...
Article
The engine power losses and sealing behaviour through compression rings have become a priority for engine manufactures in view of future stringent emissions standards. Historically, compression rings have great application in small road vehicles and high-performance engines. The sealing behaviour of the compression ring has a significant effect on...
Article
The purpose of this paper was to investigate the wear rate and the temperature distribution of a single-layer TiN coated drill in H13 steel alloy workpiece, with the use of a numerical procedure and through relevant experiments. Simulation models were developed, and an experiment was conducted to evaluate the wear rate, as well as the wear mechanis...
Article
Thrust bearings are machine elements designed to support axial loads in rotating machinery. The hydrodynamic lubrication analysis of such bearings has been a major subject for many studies over the years, leading to important conclusions for design parameters that affect their optimal operating conditions. Furthermore, the last few years, the influ...
Article
Engineers and engine manufactures have known for years that piston rings account as the main source of the friction in internal combustion engines, as much as seventy-five percent in many cases. Excessive engine wear is also, very often caused by poor vehicle operation, and subsequent momentary poor lubrication. The paper presents a numerical metho...
Conference Paper
This study contains ring-liner mixed hydrodynamics using a two-phase flow and a gas blow-by model. A 2D CFD model is built to investigate the characteristics of compression ring for different engine conditions. Low, medium, and high driving speeds are examined related to the World-wide harmonised Light vehicles Test Cycle (WLTC). The influence of r...
Article
This paper tries to display complete thermo-hydrodynamic research in journal bearings, investigating the growing pressure and temperature rise inside the bearing during operation. The narrow and infinitely long bearings are extensively investigated including analytical solutions either for plain journal bearing, or journal bearing with an axial gro...
Article
Full-text available
Nowadays, the technology of internal combustion engines plays an important role, towards the energy consumption, since it is estimated that one third of the consumed fuel is aimed to counterbalance the friction. Special contribution at this issue has the piston ring – liner system and therefore, the finding of friction and minimum lubricant thickne...
Article
Purpose The purpose of this paper is to focus on the creation of an isothermal elastic ring-liner model to highlight, through stresses, the occurrence of the plastic deformation in certain crank angles under extreme dry lubrication conditions. Design/methodology/approach The stresses that are exported from this analysis are pointing out not only t...
Article
This paper focuses on the creation of an isothermal elastic ring-liner model to highlight, the occurrence of plastic deformation in certain crank angles under extreme dry lubrication conditions. The results that are exported from the current analysis show the importance of the proposed model to predict the correct stresses and friction coefficient,...
Article
This study focuses on the dynamic and tribological characterisation of a single‐layer graphene sheet (SLGS). A 10 × 10 nm graphene model is developed, which is modally analysed for both zigzag and armchair lattices, thus enabling the examination of chirality effect on the SLGS' eigenfrequencies. The tribological analysis consists of the same SLGS m...
Article
To further improve efficiency in automotive engine systems, it is important to understand the generation of friction in its components. Accurate simulation and modeling of friction in machine components is, amongst other things, dependent on realistic lubricant rheology and lubricant properties, where especially the latter may change as the machine...
Article
In this paper, a CFD model combined with experimental measurements of the ring deformations, in a single-cylinder fired engine, using a strain gauge through the cylinder bore is presented. The strain gauge data is analysed to measure the primary reflection due to friction between the thin compression ring and the cylinder wall. The findings show th...
Conference Paper
This study focuses on the creation of an isothermal elastic model to highlight, through stresses, the occurrence of plastic deformation in certain crank angles under extreme dry conditions inside an internal combustion engine. The stresses that are exported from this analysis are pointing out not only the necessity for an elastoplastic model to be...
Conference Paper
This study aims on the dynamic and tribological characterization of a Single Layer Graphene Sheet (SLGS) including the effects of a graphene cantilever’s deflection. A 10 x 10 nm graphene model is developed, which is modally analyzed for both Zigzag and Armchair lattices. A typical Atomic Force Microscope (AFM) cantilever with carbon coated tip is...
Article
The production of surface topography by artificial pockets is introduced as a well-known method to reduce friction and wear between conjugating surfaces under different lubrication regimes. As a result, the proper design and position of the pockets are of prime importance. This paper supports that goal and focuses on the contribution of the square-...
Article
This study focuses on the contribution of the square-shaped textures in several inlet positions and densities on film thickness and wear of line contacts under mixed lubricated conditions. The applied load, the sliding speed and the lubricant oil are set on a custom-built block-on-ring test rig. The lubricant film thickness is measured in real time...
Article
Full-text available
The hydrodynamic lubrication and thermal analysis of tilting pad thrust bearings has been a major subject for many studies in the field of tribology. There is only a limited number of studies regarding thrust bearings with coated surfaces. The purpose of this study is to build a parametric, iterative algorithm in order to perform a complete thermal...
Article
Full-text available
This study aims on the dynamic and tribological characterization of a Single Layer Graphene Sheet (SLGS) including the effects of a graphene cantilever’s deflection. A 10 x 10 nm graphene model is developed, which is modally analyzed for both Zigzag and Armchair lattices. A typical Atomic Force Microscope (AFM) cantilever with carbon coated tip is...
Article
Full-text available
This study focuses on the creation of an isothermal elastic model to highlight, through stresses, the occurrence of plastic deformation in certain crank angles under extreme dry conditions inside an internal combustion engine. The stresses that are exported from this analysis are pointing out not only the necessity for an elastoplastic model to be...
Article
Full-text available
The main objective of the current paper is to present the electromagnetic and thermal analysis of an AMB which is controlled by a non-linear controller, taking into account the weight of the rotor. The system consists of a rotor and two pairs of electromagnets, each one placed on the vertical and horizontal axis respectively. A Fuzzy PID controller...
Article
Full-text available
This paper presents a thorough experimental study of piston assembly friction and noise in a single-cylinder motorbike engine operating at low speeds. The friction of the piston ring pack is evaluated using a foil strain gauge with minimal cylinder modification on the thrust side. The technique involves transmitting deformations through the cylinde...
Article
Full-text available
A planetary gearbox model comprising five spur gears (sun, ring and three planets) and the carrier has been developed and analysed. The influence of gear teeth backlash and friction during mixed regime of lubrication has been taken into consideration. Greenwood and Tripp model is employed, while viscous friction is calculated analytically using the...
Article
Full-text available
This paper is a presentation of a linear model of a magnetic bearing and a comparison of two controllers concerning their control performance. Initially, the benefits obtained by the use of magnetic bearings in the electromechanical systems are presented. Afterwards, the necessity for a suitable controller design is discussed in terms of the instab...
Article
Smart machines are defined here as machines with properties adaptable to measurements of some external situations. In this paper, a rotor supported by two or more journal bearings is considered as a rotating system. As an external situation the magnitude of the rotor vibrations is considered here, and the smartness of the system is the possibility...
Conference Paper
Full-text available
This paper refers to active magnetic bearings that they are disturbed by round off errors due to the rotor’s nominal diameter machining defects. It is proved that the roundness effects are quite intense in this problem because of the nonlinear nature of the electromagnetism laws. , A finite element code was developed in a Multiphysics environment,i...
Conference Paper
Full-text available
Compression rings are mechanical components with specific interest for the internal combustion engines. Various studies focusing on the tribology of compression rings have been used in order to estimate friction and lubricant film thickness, including gas blow-by, surface treatments and thermal effects. In this paper, a combined experimental and nu...
Conference Paper
Full-text available
In this paper, a FEA model was created in order to simulate a SLGS-Graphene Tip tribo pair under 10, 50 and 70nN vertical at contact. Zigzag and Armchair lattices were used. The static friction forces were calculated according to the Prandtl-Tomlinson model, as well as the corresponding friction coefficients.
Article
Purpose Compression rings are the main sources of frictional losses in internal combustion engines. The present paper aims to present a thermo-mixed hydrodynamic analysis for coated top compression rings. To understand the coating effects, the main tribological parameters are investigated into a ring-cylinder conjunction in a motorbike engine. Fur...
Conference Paper
Full-text available
The ring-pack is the main part of parasitic losses in the engine. In particular, the major contribution of the top compression ring friction is approximately 15-20% of the total friction due to the piston-ring pack. The object of this paper is to measure the piston-ring pack friction during the cold start-up period of a single-cylinder motorbike en...
Conference Paper
Dynamic and Tribological Study of a Planetary Gearbox with Backlash and Gear Meshing Non-linearity Konstantina Salagianni1, Pantelis Nikolakopoulos2*, Mahdi Mohammadpour3 and Stephanos Theodossiades3 1,2Machine Design Laboratory, Department of Mechanical Engineering and Aeronautics, University of Patras, Patras, Greece, 26504 3Wolfson School of...
Article
Journal bearings are machine elements with widespread application. The extent of their use, from the automobile engines to gas turbines, gives a significant incentive for improvement of their performance. Various approaches focusing on the journal bearing design have been used in the past in order to reduce power losses and increase load carrying c...
Article
This paper presents the modeling and the computer simulation of a continuously variable transmission (CVT), applicable to a (2 kWatt power) wind turbine, as well as the evaluation of the suggested mechanism. Transmission in conventional wind turbines offers a constant ratio, as a result the rotational speed of the generator's shaft varies depending...
Article
The integrity and reliability of a rotor depend significantly on the dynamic characteristics of its bearings. Bearing design has been altered in many ways in order to achieve improvement in terms of damping and stiffness. A promising field in terms of vibration control and overall performance improvement for the journal bearings is the use of smart...
Article
Thin lubricant films and cavitation to ring–bore contact have a directly correlation between wear and emissions output of internal combustion engines. Thus, there is a need to develop innovate engineering solutions such as surface texturing. In particular, micro textures are manufactured in order to keep more lubricant in weakly lubricated contact....
Article
The top compression ring design of an internal combustion engine has an impact on ring in-plane motion and its lubrication conditions at the ring-cylinder liner contact. In this paper, the geometrical dimensions of the top compression piston ring-cylinder system were obtained from an actual four-stroke motorbike engine. The top ring tribological be...
Conference Paper
Under high and super-high speed or loads, the oil film produced in journal bearings is easy to collapse causing cavitation of the lubricant film. The existence of cavitation has an important effect on the tribological characteristics of the journal bearing. In this paper an analytical investigation, based on CFD technique, of the cavitation charact...
Article
Full-text available
This paper presents the study of magnetic bearings regarding a linear model. Initially, the advantages of magnetic bearings are referenced, in relation to the existing technology. Subsequently, the linearized model of the system is presented and the need for closed loop and control of the system is clarified. This need leads to further analysis of...
Conference Paper
Full-text available
Up to 90% of the combustion chamber pressure applied on the top compression ring during the combustion cycle. The main functions of the compression rings are to prevent the passage of the combustion gas and to absorb the heat between piston and cylinder wall. Thus, the main priority is to improve the structural integrity and the shape of top rings....
Article
Full-text available
A 2D axisymmetric hydrodynamic model was developed considering fluid structure interaction analysis in order to solve the Navier–Stokes equations. The effect of lubricants viscosities in terms of both monograde and multigrade oils, on the produced piston ring friction force are compared, using smooth and textured piston rings. The novelty of the cu...
Article
A proportional–integral–derivative (PID) control model of an active hydromagnetic journal bearing (AHJB) is presented here and its design guidelines are explicitly described. The nonlinear rotor equations of motion, is introduced. Then, the linearization of these equations in the bearing specific equilibrium point is performed and presented along w...
Article
Purpose – Continuous on-line monitoring of structural integrity are in priority in many engineering fields such as aerospace, automotive, civilian structures, and industrial applications. Of all these possible applications, the aerospace industry has one of the highest payoffs. Possible damage can lead to catastrophic failures and costly inspection...
Article
Full-text available
Slow speed slew bearings are widely used in many applications such us radar, aviation and aerospace units, bogie bearings for vehicles, harbor and shipyard cranes. Slew bearings are design to carry out high axial and radial loads, they have high titling rigidity and they lubricated with grease. Slew bearings consist of the rollers, the inner and th...
Conference Paper
Full-text available
The design of piston ring pack is a major subject on the internal combustion engines. The current trend focused on thin piston rings and the improvements of profile to oil consumption and lubrication in each engine stage. In this paper, an investigation of piston ring shapes in modern combustion engines was performed. The geometrical dimensions of...
Conference Paper
The hydrodynamic lubrication and thermal analysis of tilting pad thrust bearings has been a major subject for many studies in the field of tribology [1,2]. There is only a limited number of studies regarding thrust bearings with coated surfaces [3].The purpose of this study is to build a parametric, iterative algorithm in order to perform a complet...
Conference Paper
Full-text available
Smart machines are defined here as machines with properties adaptable to measurements of some external situations. In this paper a rotor on two or more journal bearings is considered as a rotating system. As external situation the magnitude of the rotor vibrations is considered here, and the smart of the system is the possibility to change the char...
Article
Full-text available
The environmental impact of many industrial and naval applications is becoming increasingly important. Journal bearings are crucial components related with the reliable, safe and environmentally friendly operation of rotating machinery in many applications, e.g., in hydroplants, ships, power generation stations. The maintenance activities in certai...
Conference Paper
Active control of vibrations is an important capability of bearings using magnetorheological fluids as lubricants. Magnetorheological fluids are a suspension of micron sized iron particles in a carrier fluid, usually a mineral oil. These particles, polarized under the influence of a magnetic field, form chains inside the lubricant volume, they hind...
Article
The rotordynamic behavior of a system supported by journal bearings is critical to its reliability. A suitable method of control of the orbital motion of a shaft in a journal bearing is the use of smart lubricants, in effect fluids with controllable physical properties. There are various categories of smart lubricants. One class of smart lubricants...
Article
Full-text available
Tribological behaviour of sliding surfaces under boundary/mixed and fully lubrication conditions is an important aspect of tribo pair design. At the same time, artificially textured surfaces have a worth noted tribological behaviour in piston ring tribology. In this paper, experiments were performed in a custom made block-on-ring test rig calibrate...
Conference Paper
Previous studies of journal bearings with artificial texturing on the bearing surface show potential benefits in certain cases. These benefits are usually focused on a specific operating area of the bearing, whereas under certain operating conditions the performance of the bearing is deteriorating due to the surface texturing. Gaining control over...
Conference Paper
Full-text available
Piston rings are the most complicated component of the internal combustion engine. They are designed to seal the combustion chamber of the engine while minimizing the friction against the cylinder liner. Modern automobiles normally use three rings: two compressions rings and one oil ring. The first compression ring is the closest to the combustion...
Conference Paper
Journal bearings are devices that support a wide range of rotating machinery. Their simple design and their ability to absorb vibrations are significant advantages over other similar bearing solutions. The damping capacity of the journal bearings along with their tribological performance may be improved using magnetorheological fluids (MRF’s). The...
Article
Design of piston rings is a very crucial subject in the field of internal combustion engines. In the present paper, a numerical model is created using the Navier–Stokes equations. Fluid–structure interaction analysis is performed in order to calculate the structural integrity of the ring for several engine operational conditions and texturing patte...
Article
The present study examines the mechanical behavior and corrosion resistance in dual phase B500c reinforced steel used in concrete structures, before and after applying a layer of aluminum coating in intense corrosion environment. The aluminum layer was applied on the steel bars via thermal process with a flame spray gun and an average layer of 100...
Article
Full-text available
Tribological parameters such as friction, lubrication and wear influence strongly the engine component's life. In this study, a piston ring-cylinder system simulated taking into account the surface modifications under fully flooded lubrication and normal engine conditions. The hydrodynamic pressure field solved based on the Navier Stokes equations...
Article
Full-text available
Purpose – The purpose of this paper is to review and to provide a dipper understanding of what happens to piston rings and cylinder surfaces when manufacturing errors depicted, such as waviness and straightness. The mechanism of friction and the piston ring structural integrity, due to the surface irregularities, are analyzed either for smooth ring...
Article
Full-text available
Previous studies of journal bearings with artificial texturing on the bearing surface show potential benefits in certain cases. These benefits are usually focused on a specific operating area of the bearing, whereas under certain operating conditions the performance of the bearing is deteriorating due to the surface texturing. Gaining control over...
Article
The architecture of the electrical actuation module driving a magnetic-hydraulic bearing system is presented. The bearing is intended to be scaled for use in applications of all sizes in industries like shipboard for support of the engine-propeller shaft or in power-plants for the shaft through which the prime mover, e.g. steam or gas turbine, is d...
Conference Paper
Full-text available
The surface condition of the piston ring-cylinder system affects significantly its performance. Simultaneously, the oil condition and its viscosity play an important role in these tribological components. In this study a Fluid Structure Interaction (FSI) analysis is used in order to solve the Navier Stokes equations, calculating the hydrodynamic fi...
Article
A fluid solid interaction model (FSI) developed for two different structural cylinder patterns in order to simulate the frictional performance of piston ring–cylinder liner systems for marine engines. Computational fluid dynamics (CFD) analysis is used to solve the Navier Stokes equations. A fully flooded inlet and outlet conditions are assumed tak...
Chapter
Full-text available
In this work computational models with measured friction on a motor of four stroke engine are compared. Fluid Structure Interaction analysis is performed using the Navier Stokes equations in order to calculate the hydrodynamic friction for several engine operational conditions. The piston ring friction was experimentally measured under different co...
Conference Paper
Continuous on-line monitoring of structural integrity are in priority in many engineering fields such as aerospace, automotive, civilian structures and industrial applications. Of all these possible applications, the aerospace industry has one of the highest payoffs. Possible damage can lead to catastrophic failures and costly inspections. On the...
Conference Paper
The integrity and reliability of a rotor depends significantly on the dynamic characteristics of its bearings. Bearing design has been altered in many ways in order to achieve improvement in terms of damping and stiffness. A promising field in terms of vibrations control and overall performance improvement for the journal bearings is the use of sma...
Article
The integrity and reliability of a rotor depends significantly on the dynamic characteristics of its bearings. Bearing design has been altered in many ways in order to achieve improvement in terms of damping and stiffness. A promising field in terms of vibrations control and overall performance improvement for the journal bearings is the use of sma...
Article
The integrity and reliability of a rotor depend significantly on the dynamic characteristics of its bearings. Bearing design has evolved in many ways in order to achieve higher damping and stiffness. A promising field in terms of vibrations control and overall performance improvement for the journal bearings is the use of smart lubricants. Smart lu...
Article
Full-text available
Rotor dynamics considerations play an important role in the design of a number of machine elements, especially those that operate at high rotational speeds. During system start-up and shutdown, the rotor and bearing materials are subjected to high mean and alternating stresses that cause fatigue, particularly when the rotor is running at critical s...