A multiscale method for optimising surface topography in elastohydrodynamic lubrication (EHL) using metamodels

Water-lubricated bearings (WLB), due to their pollution-free nature and low noise, are increasingly becoming critical components in aerospace, marine applications, high-speed railway transportation, precision machine tools, etc. However, in practice, water-lubricated bearings suffer severe friction and wear due to low-viscosity water, harsh conditions, and contaminants like sediment, which can compromise the lubricating film and shorten their lifespan. The implementation of micro-textures has been demonstrated to improve the tribological performance of water-lubricated bearings to a certain extent, leading to their widespread adoption for enhancing the frictional dynamics of sliding bearings. The shape, dimensions (including length, width, and depth), and distribution of these micro-textures have a significant influence on the frictional performance. Therefore, this study aims to explore the coupling effect of different micro-texture shapes and distributions on the frictional performance of water-lubricated sliding, using the computational fluid dynamics (CFD) analysis. The results indicate that strategically arranging textures across multiple regions can enhance the performance of the bearing. Specifically, placing linear groove textures in the outlet of the divergent zone and triangular textures in the divergent zone body maximize improvements in the load-carrying capacity and frictional performance. This specific configuration increases the load-carrying capacity by 7.3% and reduces the friction coefficient by 8.6%. Overall, this study provided critical theoretical and technical insights for the optimization of WLB, contributing to the advancement of clean energy technologies and the extension of critical bearing service life.

Monte Carlo (MC) simulation of most spatially distributed systems is plagued by several problems, namely, execution of one process at a time, large separation of time scales of various processes, and large length scales. Recently, a coarse-grained Monte Carlo (CGMC) method was introduced that can capture large length scales at reasonable computational times. An inherent assumption in this CGMC method revolves around a mean-field closure invoked in each coarse cell that is inaccurate for short-ranged interactions. Two new approaches are explored to improve upon this closure. The first employs the local quasichemical approximation, which is applicable to first nearest-neighbor interactions. The second, termed multiscale CGMC method, employs singular perturbation ideas on multiple grids to capture the entire cluster probability distribution function via short microscopic MC simulations on small, fine-grid lattices by taking advantage of the time scale separation of multiple processes. Computational strategies for coupling the fast process at small length scales (fine grid) with the slow processes at large length scales (coarse grid) are discussed. Finally, the binomial tau-leap method is combined with the multiscale CGMC method to execute multiple processes over the entire lattice and provide additional computational acceleration. Numerical simulations demonstrate that in the presence of fast diffusion and slow adsorption and desorption processes the two new approaches provide more accurate solutions in comparison to the previously introduced CGMC method.

The properties of wavelet spectra of kinetic and magnetic energies, as well as of helicities, are considered by the example of a three-dimensional dynamo model in a rapidly rotating a plane layer and heated from below. It is shown that the transition from the kinematic mode to the full dynamo mode is accompanied by a decrease in the magnetic energy of the system. The hydrodynamic helicity changes its sign by height and has the same sign for all scales. The current and magnetic helicities also have the dipole form of symmetry in the physical space; however, their sign at small and large scales is different—the so-called effect of separation in scales. The cross-helicity has no separation in scales, but it can change the sign with time so that its averaged value is small.

Dynamics of inertial particles is addressed in a homogeneous shear flow as the prototype of statistically steady anisotropic flows. In this simple flow, velocity fluctuations are strongly anisotropic at the largest scales where production of turbulent kinetic energy is active i.e. at scale separation \( r > L_S \left( {L_S } \right) = \sqrt {\varepsilon /S^3 } \) denote the shear scale) while re-isotropization is expected for smaller separations \( r < L_S \) [6]. Since anisotropy is strongly depleted through the inertial range, the advecting field anisotropy may be expected in-influential for the small scale features of particle dynamics. We find instead that the small scales of the particle distribution and particles velocity fluctuations are strongly affected by the geometry of turbulent fluctuations at large scales even in the range of scales where isotropization of velocity statistics occurs.

The dissertation analyses the scale effects on the tensile strength of materials. By the term scale effects it is meant the variation in a mechanical property as a function of structural size. In particular, it has been observed by numerous investigators that the nominal tensile strength of many materials decreases with increasing size of the specimen tested. This phenomenon is more evident in disordered materials, that is, materials that are macroscopically heterogeneous and damaged. On the basis of Weibull's statistical theory and the principles of Linear Elastic Fracture Mechanics, a self-similarity distribution for defect size is presented (Chapter 4). With this distribution the length of the most critical defect is taken to be proportional to the linear size of the specimen. It is shown that the assumption of self-similarity represents the instance of maximum disorder that can be encountered in real materials, and it supplies, in a strength-size bilogarithmic plane, a linear scaling law with an inclination of -1/2, corresponding to the power of the stress singularity envisaged by LEFM. This formulation contains the fractal concept of self-similarity, even though it is limited to maximum defect dimension. In order to consider the real nature of the micro-structure of the materials, a more complex fractal model is presented (Chapter 5) in which the property of self-similarity is extended to the entire population of defects. This topological law, based on fractal theory and on the so-called renormalisation procedure, states that in order to obtain a nominal constant strength for the material it is necessary to refer to surface areas with non integer physical dimensions. For disordered materials, such as for instance concrete and rocks, renormalised tensile strength is given by a force acting on a surface having a fractal dimension lower than 2. The dimensional decrease, always comprised in the [0, 1/2] range, represents self-similar vacancies in the undamaged section associated with the presence of pores, voids, defects, cracks, aggregate and inclusions, and it approaches the 1/2 limit only for extremely brittle and disordered materials, as is assumed, incidentally, in statistical approaches. As a rule, the scale variation taken into consideration in experimental investigations does not exceed one order of magnitude. In such circumstances, it is only possible to determine a single tangential inclination in the bilogarithmic diagram. Only by taking into account scale variations higher than one order of magnitude it proves possible to detect the transition from disordered to ordered conditions, and a continuous transition from -1/2 to zero inclination may be seen to appear. In physical reality, the peak load resistant section can be viewed as multifractal, of dimension 1.5 on small scales and dimension 2 at large scales. This clearly shows a transition from the extreme disorder that is associated with small scales, where a self-similar distribution of Griffith cracks predominates, to the extreme order of large scales, where the disorder of the microstructure is no longer visible, on account of the limited dimensions of the defects and heterogeneities. The assumption of multifractality for the microstructure of the damaged material (Chapter 7) is the basis of the so-called Multifractal Scaling Law (MFSL). Such law consists of an approximation method which imposes the concavity of the bilogarithmic curve facing upward, which contradicts Bazant's size effect law (SEL). To verify this scaling law and to determine experimentally the variation in nominal tensile strength and fracture energy, a totally innovative testing set-up has been created, involving the use of three servo-controlled jacks (Chapter 5). The interaction of the three jacks, arranged in L formation, makes it possible to centre instant by instant the resultant of the load with the respect to the undamaged section even in the presence of

A S-containing additive, sulfuration modified soybean oil (named as SSO), was prepared by chemical modification of soybean oil with sulfur compounds. The friction and wear performances of AZ91D magnesium alloy against GCr15 bearing steel under the lubrication of rapeseed oil formulated with SSO were evaluated on a SRV tribotester. The topographies and the chemical species of the worn surfaces of magnesium alloy were analyzed by a scanning electron microscope (SEM) and an X-ray photoelectron spectroscope (XPS), respectively. The results indicated that the friction and wear of the magnesium alloy-steel tribomates could be effectively reduced by formulating SSO into rapeseed oil lubricant. The friction coefficients and the wear volumes of magnesium alloy decreased with increasing contents of SSO. The surface lubricated with SSO-doped rapeseed oil was characterized by less wear as compared with that lubricated with neat rapeseed oil. The enhanced anti-wear and friction-reducing abilities of rapeseed oil by SSO in the lubrication of magnesium alloy against steel were ascribed to the formation of a composite boundary lubrication film due to the strong adsorption of SSO and rapeseed oil onto the lubricated surfaces and their tribochemical reactions with magnesium alloy.

Water-slide manufacturers are constantly searching for innovative designs that maximize the rider’s fun while complying with safety requirements. However, the current state-of-the-art does not offer any simulation tool capable of aiding the design phase before manufacture in an affordable computational time. In this paper, we present a novel approach using smooth surface models together with Saint Venant’s filament theory to predict the water channel and, by this, a realistic estimation of passenger/water-slide interaction. The paper covers the theory and the experimental validation for the case of circular slide cross-sections. It is shown that the predicted water channel follows very well the measurement even without the influence of Saint Venant’s water-height terms and of the elliptical correction of the water cross-section for slanted water streamlines with respect to the centerline of the circular tube. Thus, for this kind of applications, a simple Bernoulli streamline model with proper water-slide friction parameters is shown to be sufficient. On the other hand, parameter identification of fluid-surface friction shows that three terms must be considered: a static one, a curvature-dependent correction, and a third correction factor for changes from low to large curvature (splashing effect). The results are also compared with fluid simulations using OpenFOAM. It is shown that the results of the simple model are not less accurate than the fluid-dynamics model, while needing only 1/100.000 of the computational time. The paper shows also the passenger/slide interaction by a multibody model including contact and passenger/fluid interactions. It is shown that the interaction between the passenger and water is significant for correct reproduction of real motion, showing that the water channel is relevant for computer-based water-slide layouts. As the water-channel parameters can be sufficiently modeled by Bernoulli’s streamline theory, the approach is independent of the slide cross-section and thus extendable to general cases. Also, as the computations run at 7/10 of real time, they can be used for online optimizations and passenger-specific actions on site.

A numerical model for the deterministic analysis of adhesive rough contacts down to the nano-scale

The surface electronic structure of ReO 3 is investigated by the discrete-variational (DV)-Xα cluster method. Two models of the neutral (001) surface are proposed; a) rough surface model and b) smooth surface model. In the former model one half of the top Re ions are covered by oxygen ions, while in the latter model the formal charge of the top Re ion is varied from that of the bulk Re ions. The level position, the orbital components and the electron occupation number of the intrinsic surface state are found to differ greatly according to the surface model. The electronic state of the defect level induced by the surface O vacancy is investigated in detail and discussed in relation to the catalytic activity.

Theoretical interpretation of infrared measurements at Deimos in the framework of crater radiation

A method is proposed to track the full hand motion from 3D points reconstructed using a stereoscopic set of cameras. This approach combines the advantages of methods that use 2D motion (e.g. optical flow), and those that use a 3D reconstruction at each time frame to capture the hand motion. Matching either contours or a 3D reconstruction against a 3D hand model is usually very difficult due to self-occlusions and the locally-cylindrical structure of each phalanx in the model, but our use of 3D point trajectories constrains the motion and overcomes these problems.

Industrial Teratology is the scientific and engineering discipline focused on the interaction of surfaces in relative motion, covering friction, lubrication, and wear. Its significance in industry is immense, as it contributes to the efficiency, longevity, and performance of machinery and mechanical systems. a crucial role in enhancing the efficiency, reliability, and lifespan of machinery and components. Industrial teratology is significant for several key reasons, impacting various sectors and contributing to technological, economic, and environmental advancements: Improved tribological practices reduce wear and tear on machinery and components, extending their operational life and reducing the frequency of replacements. Enhanced lubrication and friction management lead to lower energy consumption, decreasing operational costs in industries ranging from manufacturing to transportation. tribological systems lower energy consumption, leading to lower greenhouse gas emissions and a reduced carbon footprint. The development of environmentally friendly lubricants and tribological materials reduces the reliance on harmful chemicals and promotes sustainability. Industrial tribology is the study of the interactions between surfaces that are in motion relative to each other, including aspects such as friction, wear, and lubrication. Its significance in research and industry is multifaceted, influencing a broad range of applications and contributing to technological advancements and economic efficiency. Here are some key aspects highlighting the significance of industrial tribology research Alternative: A, B, C, D, E. Evaluation Preference: Cost ($), Durability (hrs), Environmental Impact (scale 1-5), Wear Rate (mm³/hr). The results indicate that E Attained the top position, while B had the lowest position achieved. “The dataset's significance regarding Industrial Tribology, according to the MOORA Method, E achieves the highest ranking.

We inquire about the properties of 2D Navier-Stokes turbulence simultaneously forced at small and large scales. The background motivation comes by observational results on atmospheric turbulence. We show that the velocity field is amenable to the sum of two auxiliary velocity fields forced at large and small scale and exhibiting a direct enstrophy and an inverse-energy cascade, respectively. Remarkably, the two auxiliary fields reconcile universal properties of fluxes with positive statistical correlation in the inertial range.

&amp;lt;p&amp;gt;&amp;lt;span lang=&amp;quot;EN-US&amp;quot;&amp;gt;Cold (eV) ions of ionospheric origin dominate the number density of most of the volume of the magnetosphere during most of the time. &amp;lt;/span&amp;gt;&amp;lt;span lang=&amp;quot;EN-US&amp;quot;&amp;gt;Supersonic flows of cold positive ions are common and can cause a negatively charged wake behind a positively charged spacecraft. The associated induced electric field can be observed and can be used to study the cold ions. We present observations from the Cluster and MMS spacecraft showing how a charged satellite, and also individual charged wire booms of &amp;amp;#160;an electric field instrument, can be used to investigate cold ion populations. &amp;lt;/span&amp;gt;&amp;lt;span lang=&amp;quot;EN-US&amp;quot;&amp;gt;Ionospheric ions affect large scales, including the Alfv&amp;amp;#233;n velocity and &amp;lt;/span&amp;gt;&amp;lt;span lang=&amp;quot;EN-US&amp;quot;&amp;gt;&amp;amp;#160;&amp;lt;/span&amp;gt;&amp;lt;span lang=&amp;quot;EN-US&amp;quot;&amp;gt;thus energy transport with waves and the magnetic reconnection rate. These ions also affect small-scale kinetic plasma physics, including the Hall physics and wave instabilities associated with magnetic reconnection. Concerning large scales, we summarize observations from several spacecraft and show that a typical total outflow rate of ionospheric ions is 10&amp;lt;sup&amp;gt;26&amp;lt;/sup&amp;gt; ions/s and that many of these ions stay cold also after a long time in the magnetosphere.&amp;amp;#160; Concerning small scales, we show examples of how cold ions modify the Hall physics of thin current sheets, including magnetic reconnection separatrices. On small kinetic scales the cold ions introduce a new length-scale, a gyro radius between the gyro radii of hot (keV) ions and electrons. &amp;lt;/span&amp;gt;&amp;lt;span lang=&amp;quot;EN-US&amp;quot;&amp;gt;The Hall currents carried by electrons can be partially cancelled by the cold ions when electrons and the magnetized cold ions ExB drift together. Also, close to a reconnection X-line an additional diffusion region can be formed (regions associated with hot and cold ions, and with electrons, total of three).&amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt;

Aims Anthropogenic activities have drastically increased nutrient availability, resulting in declines in species richness in many plant communities. However, most previous studies have explored only species-loss patterns and mechanisms over small sampling areas, so their results might overestimate species loss at larger spatial scales. The aim of this research was to explore species diversity change patterns and speciesloss rates at multiple scales in alpine meadow communities following nutrient enrichment. Specifically, we asked two closely related questions: (i) do changes in species diversity and species-loss patterns differ among spatial scales? and (ii) how does community compositional dissimilarity and species turnover change among spatial scale? Methods This study was implemented in an alpine meadow community, which is regarded as one of the most sensitive and vulnerable terrestrial ecosystems to anthropogenic nutrient enrichment. We conducted a fertilization experiment that involved the addition of nitrogen (N), phosphorus (P) and a mixture of both to a series of quadrats ranging from 1 to 16 m~2 over 5 years to study the variations in the patterns of species diversity in response to nutrient additions at different spatial scales. Important Findings Our results showed that the changes in species diversity and species loss were dependent on the type of fertilization and the spatial scale. After N and NP fertilization, species diversity significantly decreased at the small scale but not at the large scale, and the rate of species loss decreased as the spatial scale increased. In contrast, the differences between the P addition and control communities were negligible at both the small and large spatial scales. N fertilization caused species to be lost from the small sampling scale, but because different species were lost from different samples, there was an increase in compositional dissimilarity at larger spatial scales, which reduced the total number of species lost when measured at larger scales. These findings highlight spatial scale in evaluating the biodiversity loss after fertilization and suggest that the compositional dissimilarity might play an important role in mediating species loss after fertilization. Our study significantly improved our understanding of changes in species diversity and species loss at different spatial scales under nutrient-enrichment scenarios.