Modelling spanwise heterogeneous roughness through a parametric forcing approach

Inhomogeneous rough surfaces in which strips of roughness alternate with smooth-wall strips are known to generate large-scale secondary motions. Those secondary motions are strongest if the strip width is of the order of the half-channel height and they generate a spatial wall shear stress distribution whose mean value can significantly exceed the area-averaged mean value of a homogeneously smooth and rough surface. In the present paper it is shown that a parametric forcing approach (Busse & Sandham, J. Fluid Mech., vol. 712, 2012, pp. 169–202; Forooghi et al., Intl J. Heat Fluid Flow, vol. 71, 2018, pp. 200–209), calibrated with data from turbulent channel flows over homogeneous roughness, can capture the topological features of the secondary motion over protruding and recessed roughness strips (Stroh et al., J. Fluid Mech., vol. 885, 2020, R5). However, the results suggest that the parametric forcing approach roughness model induces a slightly larger wall offset when applied to the present heterogeneous rough-wall conditions. Contrary to roughness-resolving simulations, where a significantly higher resolution is required to capture roughness geometry, the parametric forcing approach can be applied with usual smooth-wall direct numerical simulation resolution resulting in less computationally expensive simulations for the study of localized roughness effects. Such roughness model simulations are employed to systematically investigate the effect of the relative roughness protrusion on the physical mechanism of secondary flow formation and the related drag increase. It is found that strong secondary motions present over spanwise heterogeneous roughness with geometrical height difference generally lead to a drag increase. However, the physical mechanism guiding the secondary flow formation, and the resulting secondary flow topology, is different for protruding roughness strips and recessed roughness strips separated by protruding smooth surface strips.

Preparing Datasets of Surface Roughness for Constructing Big Data from the Context of Smart Manufacturing and Cognitive Computing

In smart manufacturing, human-cyber-physical systems host digital twins and IoT-based networks. The networks weave manufacturing enablers such as CNC machine tools, robots, CAD/CAM systems, process planning systems, enterprise resource planning systems, and human resources. The twins work as the brains of the enablers; that is, the twins supply the required knowledge and help enablers solve problems autonomously in real-time. Since surface roughness is a major concern of all manufacturing processes, twins to solve surface roughness-relevant problems are needed. The twins must machine-learn the required knowledge from the relevant datasets available in big data. Therefore, preparing surface roughness-relevant datasets to be included in the human-cyber-physical system-friendly big data is a critical issue. However, preparing such datasets is a challenge due to the lack of a steadfast procedure. This study sheds some light on this issue. A state-of-the-art method is proposed to prepare the said datasets for surface roughness, wherein each dataset consists of four segments: semantic annotation, roughness model, simulation algorithm, and simulation system. These segments provide input information for digital twins’ input, modeling, simulation, and validation modules. The semantic annotation segment boils down to a concept map. A human- and machine-readable concept map is thus developed where the information of other segments (roughness model, simulation algorithm, and simulation system) is integrated. The delay map of surface roughness profile heights plays a pivotal role in the proposed dataset preparation method. The successful preparation of datasets of surface roughness underlying milling, turning, grinding, electric discharge machining, and polishing shows the efficacy of the proposed method. The method will be extended to the manufacturing processes in the next phase of this study.

CFD Analysis of Journal Bearing with a Heterogeneous Rough/Smooth Surface

In the present study, a computational investigation into acoustic and tribological performances in journal bearings is presented. A heterogeneous pattern, in which a rough surface is engineered in certain regions and is absent in others, is employed to the bearing surface. The roughness is assumed to follow the sand-grain roughness model, while the bearing noise is solved based on broadband noise source theory. Three types of heterogeneous rough/smooth journal bearings exhibiting different placement and number of the rough zone are evaluated at different combinations of eccentricity ratio using the CFD method. Numerical results show that the heterogeneous rough/smooth bearings can supply lower noise and larger load-carrying capacity in comparison with conventional bearings. Moreover, the effect on the friction force is also discussed.

Development of surface roughness model in turning process of 3X13 steel using TiAlN coated carbide insert

Surface roughness that is one of the most important parameters is used to evaluate the quality of a machining process. Improving the accuracy of the surface roughness model will contribute to ensure an accurate assessment of the machining quality. This study aims to improve the accuracy of the surface roughness model in a machnining process. In this study, Johnson and Box-Cox transformations were successfully applied to improve the accuracy of surface roughness model when turning 3X13 steel using TiAlN insert. Four input parameters that were used in experimental process were cutting velocity, feed rate, depth of cut, and insert-nose radius. The experimental matrix was designed using Central Composite Design (CCD) with 29 experiments. By analyzing the experimental data, the influence of input parameters on surface roughness was investigated. A quadratic model was built to explain the relationship of surface roughness and the input parameters. Box-Cox and Johnson transformations were applied to develop two new models of surface roughness. The accuracy of three surface roughness models showed that the surface roughness model using Johnson transformation had the highest accuracy. The second one model of surface roughness is the model using Box-Cox transformation. And surface roughness model without transformation had the smallest accuracy. Using the Johnson transformation, the determination coefficient of surface roughness model increased from 80.43 % to 84.09 %, and mean absolute error reduced from 19.94 % to 16.64 %. Johnson and Box-Cox transformations could be applied to improve the acuaracy of the surface roughness prediction in turning process of 3X13 steel and can be extended with other materials and other machining processes

THE PHENOMENON OF INK DUSTING TAKING INTO ACCOUNT THE SURFACE ROUGHNESS OFFSET PRINTING PLATE

The paper investigates the influence of the mechanics of a friction printing pair on ink dusting in the printing process, taking into account the surface roughness of the printing plate. The aim of the study is to determine the influence of the surface roughness of the printing plate on the deformation of the deckle, as well as on the value of the total force in the area of the printed contact, the relative gear ratio and the relative speed of sliding of the deckle along the surface of the cylinder, which directly affects the dusting of the ink. It was found that when studying the mechanics of a printed pair, the influence of the microgeometry of the contacting surfaces on the parameters under study was not taken into account. The influence of microprotrusions of the surface roughness of the printing plate on the deformation of the deckle in the area of the printed contact has been substantiated and established. To determine the introduction of surface roughness irregularities, a discrete roughness model is used, presented as a set of identical spherical segments. To determine the influence of the surface roughness of the printing plate on the friction force arising in the contact zone, a calculation scheme is proposed that differs from analogs. A method is developed for calculating the parameters of a friction pair in the printing process, taking into account the roughness. Expressions are obtained for determining the total moment of tangential friction forces in the sliding sections when spherical irregularities are introduced. According to the proposed technique, the corresponding graphical dependences of the gear ratio on different parameters of the friction printed pair are shown. The advantages of this study in comparison with analogs are that at certain values of the parameters of the friction pair, taking into account the surface roughness of the printing plate, also at known values of the mechanical characteristics and thickness of the deckle, it is possible to determine the change in the length of the deckle of a given composition, which is necessary in the printing process. The proposed calculation method, which is carried out without taking into account the pressure in the printed contact zone, allows predicting the quality of printed impressions and the amount of ink involved in the formation of ink dusting, as well as correctly adjusting the printing press before the printing process.

The Effect of Interfacial Roughness on Residual Stresses in Electron Beam-Physical Vapor Deposition of Thermal Barrier Coatings

Residual stresses play an essential role in determining the failure mechanisms and life of an electron beam-physical vapour deposition thermal barrier coating (EB-PVD TBC) system. In this paper, a new transitional roughness model was proposed and applied to describe the interfacial roughness profile during thermal cycles. Finite element models were implemented to calculate residual stresses at specific positions close to the interface of TBCs using temperature process-dependent model parameters. Combining stresses evaluated at valleys of the topcoat (TC) and excessive sharp tip roughness profiles, positions where the maximum out-of-plane residual stresses occur were identified and used to explain possible cracking routes of EB-PVD TBCs as interfacial roughness evolves during thermal cycling.