Liquid Droplet Impact Over Hydrophobic Mesh Surfaces and Assessment of Weber Number Dependent Characteristics

Impacting droplets and droplet ejection from hydrophobic mesh surfaces have interest in biomedicine, heat transfer engineering, and self-cleaning of surfaces. The rate and the size of newborn droplets can vary depending on, the droplet fluid properties, Weber number, mesh geometry, and surface wetting states. In the present study, impacting water droplets onto hydrophobic mesh surface is investigated and impact properties including, spreading, rebounding, and droplet fluid penetration and ejection rates are examined. Droplet behavior is assessed using high recording facilities and predicted in line with the experiments. The findings reveal that the critical Weber number for droplet fluid penetrating/ejecting from mesh screen mainly depends on the droplet fluid capillary length, and hydrophobic mesh size. The contact time of impacting droplet over mesh surface reduces with increasing droplet Weber number, which opposes the case observed for impacting droplets over flat hydrophobic surfaces. The restitution coefficient attains lower values for impacting droplets over mesh surfaces than that of flat surfaces. The rate and diameter of the ejected droplet from the mesh increases as droplet Weber increases. At the onset of impact, streamline curvature is formed inside droplet fluid, which creates a stagnation zone with radially varying pressure at the droplet fluid mesh interface. This reduces the ejected droplet diameter from mesh cells as mesh cells are located away from the impacting vertical axis.

Analysis of Magnetic Forces in the Working Clearance with Magnetic-Abrasive Treatment of Inductors on Standing Magnets

The authors describe the method of calculating the magnetic forces in the working gap in the case of magnetically abrasive machining of flat surfaces of billets from magnetic materials by the periphery of a circular inductor on permanent magnets. The application of the software package ANSIS Maxwell for the calculation of the magnetic induction method in the working gap and the magnetic forces of the magnetically abrasive powder acting on the grain is shown. As a result of the work, the magnetic induction in the working gap was calculated for magnetically abrasive machining of flat surfaces of billets from magnetic materials by an inducer on permanent magnets. Also, calculations showed the distribution of the magnetic abrasive powder in the working gap, depending on the material of the workpiece being processed. In the case of magnetically abrasive machining of a magnetic workpiece, the powder in the working gap is concentrated in the zones with the greatest density of force lines - under the inductor poles. An analysis is made of the distribution of magnetic forces in the working gap during magnetic abrasive machining.

Formal grammar methodology for digital visualization of Islamic geometric patterns

In the oriental practice of art and architecture, and among the regions under their influence, Islamic geometric patterns (IGPs) have been widely used, not only due to aesthetics and decoration but also to make it possible to cover wide flat surfaces, curved surface of domes, and perforated surfaces of window and partitions, with perfectly tessellated shapes. However, with advances in time and technology, these techniques could not connect to the new technologies and benefit from the capacities of digitalization. Recent progress in science and technology tends to open new doors to study geometrical patterns by digitalizing the old ones and developing new variations. This study looks at formal grammar and computer science to introduce a new approach to digital visualization of available IGPs, particularly, star patterns. We investigate the potentials of developing a re-writing system for simulation of IGPs to provide a flexible platform, which allows introducing IGP to CAD/CAM software without previous knowledge on their design or drawing techniques. This methodology allows designers to directly develop various scenarios of IGP applications and implement them on related CAD/CAM tools. Formal language and grammar theories, based on applied mathematics are contributing to the advancements of computer science and digital modeling. They can provide an opportunity to express relational definition and written equivalents of the geometries by using strings and symbols. It is supposed that by using the formal grammar frameworks, certain languages could be developed to visualize IGPs in a machine-friendly way, and consequently, this computational interpretation of IGPs facilitates their application and further developments, for example, regards to digital fabrication. The presented method of IGP visualization is developed as a C#-based add-on for Grasshopper in Rhino3D, one of the main modeling tools used by architects and product designers.

A NUMERICAL APPROACH TO THE CONTACT OF NOMINALLY FLAT SURFACES

Machined surfaces can be described by heights and wavelengths of the surface asperities that show a statistical variation. Considering that a regular wavy surface with a sinusoidal profile is the crudest model for a rough surface, studying the contact of regular wavy surfaces is a good approximation for the contact of nominally flat surfaces. Such contact problems exhibit periodicity that can be simulated with the aid of computational techniques derived for contact mechanics in the frequency domain. The displacement calculation, which is a necessary step in the resolution of the contact problem, is mathematically a convolution product that can be calculated in the frequency domain with increased computational efficiency. The displacement induced by a unit surface load can be expressed in the frequency domain by the frequency response functions, which are counterparts of the space domain solutions to half-space fundamental problems such as the Boussinesq problem. The displacement induced by a periodic pressure distribution can be computed by executing the convolution product between the frequency response function and pressure on a single period. It should be noted that the convolution calculation in the spectral domain implies that the contributions of all neighbouring pressure periods are accounted for. The need to treat numerically only a single period results in remarkable computational efficiency, allowing for high density meshes that can capture the essential features of any textured real surface. The displacement calculation promotes the solution of the contact problem by an iterative approach. The advanced method is benchmarked against existing analytical solutions for the 3D contact of surfaces possessing two-dimensional waviness. This essentially deterministic model, supported by a direct numerical solution that can be obtained for samples of real rough surfaces, presents itself as a worthy alternative to the existing statistical models for rough contact interaction.

REMOTE SENSING OF CITY. DIGITAL DATABASES FOR ARCHITECTURE

The study proposes advanced analyses of the monastic citiy of the western coastal area of the Athos Peninsula in Greece. This research is the result of architectural and environmental survey campaigns conducted since July 2020.The current bibliographic documentation is limited, and most of the volumes focus on an art and historical description of the paintings in the monasteries, as well as on visitors’ travel notes.Through the consolidated phases of the discipline of representation, such as digital surveying, point clouds and the processing of flat surfaces, a journey of knowledge of the third arm of the Chalkidiki peninsula is proposed with regard to the religious architecture considered as micro-cities.The initial part of the research was developed with photographic documentation from the sea, while in subsequent survey phase of the monasteries on the west coast was carried out.The instrumental survey activities, carried out with the help of quadrihelix drones and terrestrial photogrammetry, concerned the Monastery of St. Dionysius, the Monastery of Xeropotmus, the Monastery of Zographos, the Monastery of Dochiario, the Monastery of Simonpetra, the Monastery of St. Paul, the Monastery of Xenophon, the Monastery of St. Gregory, the Monastery of St. Pantaleimon and the Monastery of Konstamonitou.The research aims to expose, for the first time, the unpublished instrumental surveys carried out in the Athos community, which has been averse to the access of tourists and curious people for centuries.

Identifying non-pseudo-alternating knots by using the free factor property of minimal genus Seifert surfaces

Pseudo-alternating knots and links are defined constructively via their Seifert surfaces. By performing Murasugi sums of primitive flat surfaces, such a knot or link is obtained as the boundary of the resulting surface. Conversely, it is hard to determine whether a given knot or link is pseudo-alternating or not. A major difficulty is the lack of criteria to recognize whether a given Seifert surface is decomposable as a Murasugi sum. In this paper, we propose a new idea to identify non-pseudo-alternating knots. Combining with the uniqueness of minimal genus Seifert surface obtained through sutured manifold theory, we demonstrate that two infinite classes of pretzel knots are not pseudo-alternating.

Diamond Grinding Technology of Flexural Strength Test Pieces of Super hard, Brittle, Composite-ceramic Materials and Technological Equipment

At the present stage of the revolutionary development of technologies, scientists from the leading countries of the world are working intensively to create qualitatively new materials whose physical-mechanical, electrical, thermal or other properties far exceed the basic constructions, armament or other metals used. Such materials are surface, brittle, composite ceramic materials (based on oxide and carbide ceramics, state-of-the-art surface compositions, polycrystalline diamond + Si  SiC and etc.). A progressive process for diamond grinding test samples from composite ceramic materials to determine the bending strength is discussed. The proposed technological process is based on an original and effective method for polishing the flat surfaces of articles made of difficult-to-process and composite materials - low-temperature precision grinding (LPG). Based on the results of many years and multilateral studies in the field of diamond processing of various non-metallic, composite and ceramic materials, optimum conditions for diamond polishing of mentioned materials have been determined and recommended. Technological equipment and equipment for processing composite and ceramic materials are also disclosed.

Magnetically Deployable Robots Using Layered Lamina Emergent Mechanism

The steady rise of deployable structures and mechanisms based on kirigami and origami principles has brought about design innovations that yield flexible and lightweight robots. These robots are designed based on desirable locomotion mechanisms and often incorporate additional materials to support their flexible structure to enable load-bearing applications and considerable efficient movement. One tetherless way to actuate these robots is via the use of magnets. This paper incorporates magnetic actuation and kirigami structures based on the lamina emergent mechanism (LEM). Three designs of magnetic-actuated LEMs (triangular prism, single LEM (SLEM), alternating mirror dual LEM (AMDLEM)) are proposed, and small permanent magnets are attached to the structures’ flaps or legs that rotate in response to an Actuating Permanent Magnet (APM) to yield stick-slip locomotion, enabling the robots to waddle and crawl on a frictional surface. For preliminary characterization, we actuate the three designs at a frequency of 0.6 Hz. We observed the triangular prism, SLEM, and AMDLEM prototypes to achieve horizontal speeds of 4.3 mm/s, 10.7 mm/s, and 12.5 mm/s on flat surfaces, respectively. We further explore how changing different parameters (actuation frequency, friction, leg length, stiffness, compressibility) affects the locomotion of the different mechanisms.

Development of a technological complex for thermofriction hardening of products with a circular cross section

There are many methods of influencing the structural state of the surface of products of different shapes and different purposes. At the same time, the increase in the relevance of the application of a particular method is closely related to its ability to provide high hardening rates while reducing the cost of such products. The TFН technology has already shown its high efficiency in strengthening surfaces [1]. In addition, studies were conducted on the hardening of surfaces of different profiles [2]. However, the best results are achieved when hardening flat surfaces. In this regard, it is entirely appropriate to conduct research that is related to the development of a technological complex that would include the optimal ratio of processing factors to ensure the necessary level of hardening in the studied objects that have a circular cross-section. Goal. The purpose of this work is to develop a technological complex for processing objects with a circular cross-section. To achieve this goal, metallographic and durometric studies of samples in the initial state and after processing were carried out. At the same time, the changes in the structure and mechanical properties that occur in steel due to processing were studied. Method. The method of thermal friction hardening includes a combined effect of heat and deformation on the treated surface. The peculiarity of this method is the deformation under short-term heating conditions. This makes it possible to further strengthen pre-hardened materials. Results. Under the influence of TFC, significant changes are observed in the structure of cylindrical samples made of 65G steel. This is expressed by the formation of a so-called "white surface layer" in the surface of these samples, which has an ultra-high microhardness [13, 14]. The properties of this layer depend on the initial state of the material, the conditions and modes of conducting TFН.