Complex-shaped Objects Research Articles

Laser-Induced Full-Matrix Ultrasonic Imaging of Complex-Shaped Objects.

We present laser-induced full-matrix imaging of complex-shaped objects that combines the advantages of noncontact laser ultrasound inspection and high-contrast array imaging based on total focusing method (TFM). Full-matrix data were acquired by synthesizing a laser ultrasonic array through an alternate scanning of the generation and detection laser beams. Taking advantage of the simultaneous generation of all wave modes, surface Rayleigh waves were extracted for surface profiling, and longitudinal waves were utilized for imaging. To gain a better understanding, we analyzed the full-wave dynamics in generation, propagation, and scattering by using numerical simulations. TFM was adapted to accommodate complex surface and suppress interference from other waves, including surface waves and straightforward traveling bulk waves between emission and reception. Numerical and experimental studies on an aluminum sample with a sinusoidal surface and side-drilled holes were conducted, and results agreed well.

Structural properties of graphene on copper substrates

Introduction. Studies of the substrate influence on graphene properties are relevant due to the high sensitivity of this two-dimensional material to the smallest effects. At the same time, studies dedicated to the separation of direct substrate influence and residual synthesis effects on graphene properties are not described in the literature in sufficient detail. Materials and methods. This paper presents the results of a study of the structural properties of as-grown and transferred graphene on copper substrates by Raman spectroscopy and atomic force microscopy. Results and discussion. Using Raman spectroscopy, we found that the mechanical strain in the as-grown grapheme is increased, while negligibly small in transferred graphene, the strain coefficients being of 0.22– 0.33 and ∼ 0 %, respectively. Using atomic force microscopy, we showed that this effect does not relate to the copper surface irregularities: the average roughness of the substrate surface for as-grown graphene was of 20.4 nm, while for the transferred graphene it was of 62.0 nm, the height difference being of almost an order of magnitude greater for the latter. This contradiction was explained in terms of residual synthesis effects present in case of as-grown graphene. Conclusion. Taking into account the analyzed substrate effects is important both for the refinement of methods for the initial characterization of as-grown graphene, and for practical applications requiring graphene transfer to corrugated and perforated substrates, membranes and objects of complex shape.

Combining Stereo and Fourier Transform Profilometry for 3D Scanning in Dynamic Environments

Fast 3D optical sensing of complex shapes remains challenging. While in the passive techniques, there is the correspondence problem, in the active techniques based on fringe projection, there is the challenge of phase recovery and disambiguation. We propose a stereo system that combines active and passive approaches in a complete 3D measurement system. A modified version of the Fourier transform profilometry technique is combined with the beating technique for absolute phase estimation. Stereo correspondence is performed using the obtained phase images. The results demonstrate that one or two frames are enough to estimate the 3D shape of complex objects, and therefore, the proposed approach can be applied for fast shape characterization.

STUDYING THE INFLUENCE OF MICROWAVE RADIATION ON THE THERMOPHYSICAL CHARACTERISTICS OF REVERSED POLYMER COMPOSITION MATERIALS REINFORCED BY CARBON FIBERS

Objectives. The aim of the research is to study the influence of the microwave electromagnetic field on the thermophysical characteristics of PCM reinforced with carbon fibers as one of the factors indicating a certain restructuring of the material, leading to a change in its operational properties.Method. The use of modifying hardening effects that do not lead to excessive destructuring heating of materials.Result. Based on the analysis of scientific and technical literature and trends in the development of technical transport and energy systems, a steady increase in the cons umption of fibrous polymeric composite materials (PCM) in their structures has been revealed. The prospects of applying the effects of microwave radiation (microwave electromagnetic field) on the formation of the required properties of products from PCM and the feasibility of studying the mechanisms of interaction of microwave radiation with the structure of solidified PCM are shown. Experimental studies of the thermophysical interaction of PCM reinforced with carbon fibers with a microwave electromagnetic field with a frequency of 2450 MHz were performed.Conclusion. The fact of more intensive heating of samples of greater thickness and their greater shielding capacity was established. In the study of the thermophysical parameters of PCM subjected to preliminary processing in the microwave electromagnetic field by the modified Parker method, an increase in certain exposure modes of the thermal and thermal conductivities by 20% was observed, which indicates an increase in adhesive bonds in the interfacial zones and an increase in the structure density. This fact can be used in the development of technologies for modifying products from PCM, designed to work in conditions of elevated temperature gradients, which will reduce the magnitude of thermal stresses.Acknowledgment. The research was supported by RFBR grant No. 17-03-00720 «Methodology of optimising microconstruction of composite materials for complex shape objects with increased dynamic strength, formed layer-by-layer by electrotechnological methods».

Topologically protected broadband rerouting of propagating waves around complex objects

Abstract Achieving robust propagation and guiding of electromagnetic waves through complex and disordered structures is a major goal of modern photonics research, for both classical and quantum applications. Although the realization of backscattering-free and disorder-immune guided waves has recently become possible through various photonic schemes inspired by topological insulators in condensed matter physics, the interaction between such topologically protected guided waves and free-space propagating waves remains mostly unexplored, especially in the context of scattering systems. Here, we theoretically demonstrate that free-space propagating plane waves can be efficiently coupled into topological one-way surface waves, which can seamlessly flow around sharp corners and electrically large barriers and release their energy back into free space in the form of leaky-wave radiation. We exploit this physical mechanism to realize topologically protected wave-rerouting around an electrically large impenetrable object of complex shape, with transmission efficiency exceeding 90%, over a relatively broad bandwidth. The proposed topological wave-rerouting scheme is based on a stratified structure composed of a topologically nontrivial magnetized plasmonic material coated by a suitable isotropic layer. Our results may open a new avenue in the field of topological photonics and electromagnetics, for applications that require engineered interactions between guided waves and free-space propagating waves, including for complex beam-routing systems and advanced stealth technology. More generally, our work may pave the way for robust defect/damage-immune scattering and radiating systems.

Origami-Inspired Fabrication: Self-Folding or Self-Unfolding of Cross-Linked-Polyimide Objects in Extremely Hot Ambience

A methodology that integrates a folding step into the conventional poly(amic acid)/polyimide film fabrication scheme is developed. It enables fabricating cross-linked polyimide (XCP2) films into a host of complex-shaped objects. Particularly unprecedented is that these origami (3D) objects can be unfolded into a 2D temporary shape under externally applied stress at T ∼ Tg and remain in the free-standing, 2D configuration at room temperature until spontaneously returning to the original 3D configuration at T > 200 °C. This 3D/2D/3D cycle can be repeated >20× without showing any sign of fatigue, as exemplified by a cubic box that shows visually no dimensional change after each cycle, and even after having been immersed in a 215 °C oil bath for 3 days. The enabling materials are two series XCP2s that are cross-linked by either a phosphine oxide-containing triamine (POTAm) or a trianhydride (POTAn). These cross-linked polyimides form tough and creasable films that possess ∼100% shape memory recovery and 99% shape memory fixity and withstand over 100 fatigue-prone, strain-stress-temperature cycles, while the linear version LCP2 film exhibits much lower shape memory recovery and fails after only 7 cycles.

Laser surface texturing with shifted method—Functional surfaces at high speed

Laser surface texturing is a promising technology for future wide applications of functional surfaces with specific properties like hydrophobic, antibacterial, adhesive, self-cleaning, anticorrosion, light absorbing, low friction, etc. Great advancements have been made in this field in the last few years, but in most cases, it takes from minutes up to 1 h to produce 1 cm2 of a functional surface. Even the availability of high-power ultrashort pulsed lasers in the last few years did not dramatically increase productivity, because there are physical limitations of current processing methods: heat accumulation and oxidation, plasma shielding effect, and precision at high speeds. In order to solve these limitations, there have been developed a new method called a shifted laser surface texturing (sLST) method. The new method has a potential to be at least 100 times more productive with no heat accumulation effect and virtually unlimited number of complex shape objects produced with high precision on the surface. In the present work, the principle and advantages of the method are described. The results of the method are compared with two standard methods (path filling of objects and hatch over all objects). The sLST method is presented in both single pulse and burst variants. Examples of its application on different materials for increased adhesion of surface coatings are shown.

Дискретные геометрические модели оценки степени затененности в гелиоэнергетике

Geometric simulation and its software for estimating the efficiency of deployment of solar panels on spacecraft and solar concentrators on the ground are considered in this work. Both the physical and mathematical set up of the problem for estimating the energy efficiency of solar panels, taking into account their shading both by each other and by other elements of a space station has been described in this paper. It has been shown that the known methods for mechanization and automation of such calculations are focused on objects of relatively simple geometric shapes (such as buildings), and are inefficient for objects of complex and diverse geometric shape, characteristic both for spacecraft themselves and their solar panels. Therefore, to solve this problem, a receptor (voxel) geometric model digitizing the computational space has been chosen. The receptor model’s uniqueness is that comparing the values of receptor codes allows easy determine the intersection of objects. Has been described a developed receptor geometric model for estimating the effective area of solar panels, taking into account their shading when the object (for example, a spacecraft) is illuminated by a flow of solar energy from a given direction. The essential difference between the developed receptor geometric model and the classical one is that the former is multiform, i.e. uses not the 2-digit code (0 and 1), but the 4-digit one (0, 1, 2 and 3). Has been demonstrated a software implementation of the described geometric model in C#, and a graphical shell developed for this problem, allowing see the obtained results’ numerical values. Have been provided examples of its implementation in solving of practical problems. The results of verification for the described receptor geometric model have been demonstrated. All this allows speak about efficiency of using receptor geometric models both in singular computation calculations and for creating the appropriate algorithmic, mathematical support and software for the corresponding CAD systems.

ГЕОМЕТРИЧНЕ МОДЕЛЮВАННЯ СКЛАДНИХ ОБ’ЄКТІВ НА ОСНОВІ ПОЛІТОЧКОВИХ ВІДОБРАЖЕНЬ ВІДРІЗКІВ ПРЯМИХ

In this paper, we propose a method of polypointed mappings of line segments in geometric modeling of complex objects, which differs from ordinary polypointed mappings in that you can set straight lines as an inverse image, not in an implicit form, but as a set of points and obtain a transformed object as a set of points. In addition, it is proposed to use weights for each base point, which allows you to control the shape of the transformed curve in such a way that the curve is somehow attracted to a point with a higher weight compared to other base points. Polypoint transformations are used in the design of complex geometric shapes in mechanical engineering. Enhancing the capabilities of polypoint transformations is an important issue at the present time. The aim of the article is the use of line segments in the method of polypoint mappings for geometric modeling of complex objects. The proposed process of weighted political dot mapping can be applied in the implementation of geometric modeling of complex shape objects with the ability to control the shape of a simulated object by changing the weights of the points. As shown in test examples, the shape of the transformed figure changes in such a way that it seems to be attracted to points with increased weight and, conversely, is repelled from points with reduced weight. As the disadvantages of the proposed method, one can indicate an insufficient level of predictability of the result. Further research is proposed in identifying the properties of using weighted polypoint mappings in the direction of increasing the level of predictability of the results for effective use in geometric modeling of complex objects. Key words: discrete-given curve, line segment, polypoint mapping of lines, geometric modeling.

Исследование условий возникновения эолова микрорельефа

The possibilities of numerical modeling of the motion of hydrodynamic flows around objects of complex shape allow us to consider the results of calculations as one of the ways to understand the mechanisms of wind removal of sand particles. To study the conditions for the occurrence of microrelief, a number of numerical experiments are carried out using the open package OpenFOAM. Over inhomogeneities of the surface, determined by the features of the mutual arrangement of particles, there are areas of pressure reduction, near which the wind removal of particles is more likely. The reason for this decrease in pressure is a different kind of rarefaction of the spatial arrangement of surface elements: a change in distance, a change in the orientation of the structure in space, a change in the angle between planes containing particles. Due to the decrease in pressure, an increase in the air velocity at the surface and the occurrence of microvortices occur.

Evaluation of Object Surface Edge Profiles Detected with a 2-D Laser Scanning Sensor.

Canopy edge profile detection is a critical component of plant recognition in variable-rate spray control systems. The accuracy of a high-speed 270° radial laser sensor was evaluated in detecting the surface edge profiles of six complex-shaped objects. These objects were toy balls with a pink smooth surface, light brown rectangular cardboard boxes, black and red texture surfaced basketballs, white smooth cylinders, and two different sized artificial plants. Evaluations included reconstructed three-dimensional (3-D) images for the object surfaces with the data acquired from the laser sensor at four different detection heights (0.25, 0.50, 0.75, and 1.00 m) above each object, five sensor travel speeds (1.6, 2.4, 3.2, 4.0, and 4.8 km h−1), and 8 to 15 horizontal distances to the sensor ranging from 0 to 3.5 m. Edge profiles of the six objects detected with the laser sensor were compared with images taken with a digital camera. The edge similarity score (ESS) was significantly affected by the horizontal distances of the objects, and the influence became weaker when the objects were placed closer to each other. The detection heights and travel speeds also influenced the ESS slightly. The overall average ESS ranged from 0.38 to 0.95 for all the objects under all the test conditions, thereby providing baseline information for the integration of the laser sensor into future development of greenhouse variable-rate spray systems to improve pesticide, irrigation, and nutrition application efficiencies through watering booms.

Projecting by conical screw lines with constant step

The relevance of the study: The formation of surfaces by analytical methods and their visualization using computer graphics is one of the topical problems of applied geometry. Purpose of the study is to investigate non-traditional projection systems, to select congruence parameters of conical helical lines that cover the entire complex of surface requirements, obtained by projecting with conic rays an arbitrary flat or spatial line and using computer graphics in visualization of the surface. Methods of research: The general analytical theory of applied surface molding, developed by prof. Skidan I A and a single unit, which is based on the mathematical support of computer technologies for designing and creating objects of complex shape. Results of the research: An example of an analytical interpretation of the image of curvilinear projection by conical screw lines of a constant step and an example of congruence of conical screw lines, located on coaxial cones with a common vertex and a variable angle of inclination of the generator to the axis. The properties are investigated, the parameters of the helical line of the congruence, passing through an arbitrary point of space that does not belong to the axis, are determined. A method is proposed for constructing spiral surfaces, the framework of which consists of rays projecting an arbitrary line.

3D Technologies in the Production of Jewelry with Elements of Complicated Design

The article analyzes the objects of complicated shapes and technologies of their exact reproduction in jewelry which allow creating elements of complicated design at the stage of creation of master-models. The possibilities of applying 3D technologies are correlated with the sizes of objects that are complicated in design. The technologies allowing to most accurately convey the shape and texture of objects of complex shape - forming on a small-sized object with a complex design, using a ductile metallic mass and using a scanned 3D model of an object of a large shape with a complicated design - are considered in detail.

Calculation of the Acoustic Field on the Surface of a Complex-Shaped Object within a Radiating Cylindrical Shell

Problems of a decrease in acoustic loads on complex-shaped objects within a cylindrical shell are encountered frequently in practice. A good example is adjustment of a space vehicle to an assembly protection unit of a carrier rocket. This study presents a mathematical model for determining acoustic loads acting on an object and depending on the factor of acoustic energy absorption by surfaces. As a result, the spectra of the root-mean-square levels of the acoustic pressure have been obtained as functions of the area of a shell surface coated with a sound-absorbing material, as well as the area of an object beneath it.

МОДЕЛІ ПОТОЧНИХ ЗОБРАЖЕНЬ, ЩО ФОРМУЮТЬСЯ КАНАЛАМИ КОМБІНОВАНОЇ КОРЕЛЯЦІЙНО-ЕКСТРЕМАЛЬНОЇ СИСТЕМИ НАВІГАЦІЇ БЕЗПІЛОТНОГО ЛІТАЛЬНОГО АПАРАТУ

A refinement of the current image model has been accomplished, which are formed by separate channels of the combined correlation-extreme navigation system depending on the spatial position of the unmanned aerial vehicle and its changes. The model takes into account the influence of the three-dimensional shape of complex objects of the sighting surface on the effective antenna temperature of the radiometric channel, which made it possible to refine the moles of the description of the radiometric and television current image of the sighting surface, depending on the informative features. It is determined that at small viewing altitudes the change in the spatial position of the unmanned aerial vehicle leads to significant differences in the radio brightness temperature within a single sighting object, which causes the blurring and appearance of new interfaces on the current image of the viewing surface. It is established that the discrepancy between the current image and the reference image, which arises from the appearance of new interfaces at the sight of complex three-dimensional objects from low altitudes and with a change in the spatial position and orientation of the unmanned aerial vehicle, leads to the formation of a multi-extremal decision function and a decrease in the accuracy of the location of the correlation-extreme navigation system.

Invisibility on demand based on a generalized Hilbert transform

Designing invisible objects without the usage of extreme materials is a long-sought goal for photonic applications. Invisibility techniques demonstrated so far typically require high anisotropy, gain and losses, while also not being flexible. Here we propose an invisibility approach to suppress the scattering of waves from/to given directions and for particular frequency ranges, i.e. invisibility on demand. We derive a Born approximation-based generalized Hilbert transform for a specific invisibility arrangement relating the two quadratures of the complex permittivity of an object. The theoretical proposal is confirmed by numerical calculations, indicating that near-perfect invisibility can be attained for arbitrary objects with low-index contrast. We further demonstrate the cases where the idea can be extended to high-index objects or restricted to within practical limits by avoiding gain areas. The proposed concept opens a new route for the practical implementation of complex-shaped objects with arbitrarily suppressed scatterings determined on demand.

Application of Ti6Al7Nb Alloy for the Manufacture of Biomechanical Functional Structures (BFS) for Custom-Made Bone Implants.

Unlike conventional manufacturing techniques, additive manufacturing (AM) can form objects of complex shape and geometry in an almost unrestricted manner. AM’s advantages include higher control of local process parameters and a possibility to use two or more various materials during manufacture. In this work, we applied one of AM technologies, selective laser melting, using Ti6Al7Nb alloy to produce biomedical functional structures (BFS) in the form of bone implants. Five types of BFS structures (A1, A2, A3, B, C) were manufactured for the research. The aim of this study was to investigate such technological aspects as architecture, manufacturing methods, process parameters, surface modification, and to compare them with such functional properties such as accuracy, mechanical, and biological in manufactured implants. Initial in vitro studies were performed using osteoblast cell line hFOB 1.19 (ATCC CRL-11372) (American Type Culture Collection). The results of the presented study confirm high applicative potential of AM to produce bone implants of high accuracy and geometric complexity, displaying desired mechanical properties. The experimental tests, as well as geometrical accuracy analysis, showed that the square shaped (A3) BFS structures were characterized by the lowest deviation range and smallestanisotropy of mechanical properties. Moreover, cell culture experiments performed in this study proved that the designed and obtained implant’s internal porosity (A3) enhances the growth of bone cells (osteoblasts) and can obtain predesigned biomechanical characteristics comparable to those of the bone tissue.

Distributed Current Source Method for Modeling Magnetic and Eddy-Current Fields Induced in Nonferrous Metallic Objects

This paper presents a new modeling method to determine the harmonic eddy current (EC) field induced in a nonferrous metal and its corresponding magnetic flux density (MFD) by an EC-based sensing system for geometrical measurements, which accounts for the boundary effects of the object. Modeled using a distributed current source (DCS) method in state-space representation, the EC field is formulated as a two-step constrained least-square problem to solve for its real and imaginary parts. Two practical techniques to improve the efficiency and accuracy of the EC solutions are illustrated. The first refines the DCS distribution based on the skin-depth effects, and the second takes advantages of commercial mesh-generation software to facilitate the modeling of EC induced in complex-shaped objects. The DCS-based EC models are verified numerically by comparing computed results with two-dimensional (2-D) analytical axisymmetric solutions and commercial finite-element analysis, and evaluated experimentally with an EC sensor that measures the MFD generated by the induced EC in different materials and geometrical configurations.

Modelling, simulation and optimisation of pulse-reverse regime of copper, silver and gold electrodeposition

Abstract Pulse-reverse power modes are used in galvanotechniques in order to obtain coatings with better characteristics in terms of gloss, adhesion, tracking sharp edges and uniform distribution of deposits on complex shape objects, compared with the coatings produced by constant current modes. Pulse-reverse modes also allow the use of a higher current density, and thus the production speed of electroplating cells increases. Systems for standard electroplating of copper, silver and gold are optimised by the suitable choice of duration and intensity of the pulses. It is shown that coatings with satisfactory quality can be deposited using higher current density, different modes of pulsed current in a very short period of time, without expensive and often dangerous additives in the electrolyte. Parameters of the model for certain electrochemical systems were determined by modelling and computer simulation, so the system behaviour under different circumstances becomes predictive.

The Frequency-Domain Algorithm for Ultrasonic Imaging of Complex-Shaped Objects

The algorithms based on Synthetic Aperture Focusing Technique are aimed at the determination of the imageries of the flaws in controlled objects. Ultrasonic imaging of complex-shaped objects requires specific algorithms which are able to take into account the complicated character of ultrasonic waves propagation. In this article, we suggested the novel frequency-domain algorithm for ultrasonic imaging of complex-shaped objects. This algorithm is based on Phase –shift migration theory and Stolt transform. The evaluation of suggested technique was done by the application of raw ultrasonic data which was obtained by using computer simulations. Derived results show that proposed algorithm is able to make accurate and precise imaging of flaws in complex-shaped objects.