Bodies Of Complex Shape Research Articles

The use of groups of drones for diagnostics of subsurface objects in the radio range

Diagnostics of objects that are bodies of complex shape can be based on representing their boundaries of such objects (including subsurface ones) in the form of a set of paraboloids. It is shown that the determination of specific geometric characteristics of such paraboloids is ensured through the artificial synthesis of a distributed lens, the individual elements of which are placed on individual unmanned aerial vehicles. Technically, lens synthesis is achieved by changing the phase of radio frequency radiation, carried out using phase shifters. The method is implemented through scanning the object under study by adjusting the effective optical power and its orientation in space. Model calculations are presented that prove the prospects of using the proposed method. Specific examples of radio-electronic circuits that ensure the implementation of the proposed approach are presented. A feature of the phase shifters used is the preliminary detection of the phase of the signal arriving at each of the elements of the distributed lens, and the subsequent introduction of an additional phase difference due to the weighted summation of harmonic signals that are in antiphase.

Analysis of the stress-strain state of the rotary device fastening part by the semi-analytical finite element method

The possibilities of the numerical apparatus developed on the basis of the semi-analytical finite element method are shown on the example of solving a specific problem. In the areas of maximum values, the parameters of the stress-strain state of the re-device fastening part were compared. It is worth noting the relatively complex configuration of the cross-section of the object, which led to a thorough study of the principles of constructing a grid area. The surface of interaction between the axis and the hull was modeled by a fairly thin layer of elements in relation to their thickness, which absorb only normal stresses. Analysis of the stress-strain state of the rotary device fastening part should be carried out from the standpoint of a spatial problem. Moreover, according to the results of the elastic calculation, the transition section between the body and the base plate turned out to be more loaded compared to the zone of contact interaction between the body and the axle. The data of the calculation performed in the elastic-plastic formulation made it possible to clarify the idea of the operating conditions of individual sections of the object and to draw a conclusion about the uniformity of the hull. The carried out studies confidently demonstrated the wide possibilities of the developed approach in solving new, practically important problems of elastic deformation of prismatic bodies of complex shape in the spatial formulation of new ones. To substantiate the reliability of the results of the calculation of the elements under consideration, a sequential increase in the number of FE in the cross-section and the number of retained terms of the decomposition along the length of the body, as well as an increase in the accuracy of solving systems of equations, are given. In addition, an assessment of the satisfaction of natural boundary conditions on the surface of the body and the conditions of equilibrium in the integral sense is given according to the characteristic sections within the region, which showed their fairly good performance. New data on the regularities of behavior of critical structures in the process of loading, due to the consideration of their physical and geometric parameters, have been obtained.

Suitability of different machine learning methods for high-speed flow modeling issues

In the present study, machine learning algorithms are applied for modeling transport coefficients in strongly nonequilibrium reacting gas flows. As a model case, the problem of a hypersonic flow of a five-component air mixture around a sphere is considered. Various approaches for an application of machine learning methods, such as linear regression, k-nearest neighbors, support vector machine, regression tree, random forest, gradient boosting, and neural network (multilayer perceptron) are investigated. For the transport coefficients regression modeling the combination of machine learning methods with the finite volume method is constructed. The machine learning regressors are trained on the accurate numerical data given by one-temperature approach of the kinetic theory. The results of trained models are compared with approximate formulae of Blottner-Eucken-Wilke model. The results of different machine learning methods are analyzed in terms of the relationship between the obtained accuracy of calculations and the overall speed of calculations. The overall time of dataset formation and model training is estimated. The design of the constructed multilayer perceptron is discussed. The machine learning methods considered in the article can be used for the engineering problem such as design of high-speed aircraft, as well as for modeling of flows around complex shape bodies.

SOLUTION OF PHYSICALLY NONLINEAR PROBLEMS OF DEFORMATION OF MASSIVE AND THIN-WALLED PRISMATIC BODIES

The results of a numerical study on test examples of the convergence of the developed version of the semi-analytical method of finite elementsare presented. A comparison of machine time and accuracy of solving elastic and plastic problems obtained on the basis of finite elements with variableand averaged mechanical parameters was performed.The convergence of the finite element method and the semianalytical finite element method in the calculation of prismatic bodies loaded with localized and distributed external influences was studied. An effective numerical approach to the study of arbitrarily loaded massive and thin-walled prismatic bodies of complex shape, the deformation of which can pass beyond theelastic limit of the material, is being developed based on the finite element moment scheme and the semianalytical variant of the finite element method. Due to the representation of displacements by polynomials and the use of iterative methods of solving systems of equations, this approach is developed in relation to the calculation of objects with arbitrary boundary conditions on the ends, which made it possible to expand the area of effective application of the semi-analytical method of finite elements to a new class ofproblems.A number of new complex problems of elastic and elastic-plastic deformation of massive and thinwalled prismatic bodies, which have an independentapplied value, have been solved.

ФОРМОУТВОРЕННЯ НАМОТУВАННЯМ АНІЗОГРИДНИХ КОМПОЗИТНИХ СІТЧАСТИХ КОРПУСНИХ КОНСТРУКЦІЙ ЛІТАЛЬНИХ АПАРАТІВ

The process of modeling the trajectory of laying the reinforcing material (RM) during the formation of anisogrid composite mesh hull structures (MHS) has been developed. The paper gives a brief description of the types of aircraft structures of complex shape according to the criterion of the possibility of manufacturing by winding, in which certain types of surface shapes are distinguished from the condition of determining the laying trajectory and developing a winding control program (WCP) for CNC machines. It is shown that the process of developing manufacturing technology for structures of complex shape (SCS) has significant differences from the process of developing technology for axisymmetric products. The general technique for determining the trajectory of laying the reinforcing material is shown and new approaches to setting the reinforcement scheme are described. A general method for calculating the WCP for winding SCS is described. Calculation of displacements of the working bodies of the winding machine (WM) includes several subtasks: choosing the sequence of individual turns of the RM, calculating the displacements of the working bodies of the WM when laying each turn, and determining the transition program from turn to turn. It is shown that the most important stage in the development of a general type of SCS winding technology is the choice of a winding scheme that determines the structural power scheme (SPS) of the structure. For this, the concepts are introduced - the base point and the base angle of reinforcement. The winding scheme of any type of products can be described using an array of base point coordinates and base reinforcement angles. An algorithm for calculating the RM stacking trajectory on the mandrel surface is presented. The features of the choice of the order of the turns are described. The order of the turns affects the number of weaves in the structure of the composite material obtained during the winding process and the strength of the resulting product. The optimal sequence of turns according to the strength criterion is determined experimentally by repeated development tests. The features of the choice of programs for the transition from coil to coil are described. The algorithm of actions of the WM during the transition from one turn to another - the transition program consists of two programs: the program for entering the coil and the program for exiting the coil. The algorithm of the transition programs depends on the chosen order of the turns and, in each particular case, depends on the design features of the product. To test the developed methodology, a trial calculation of a general hull SCS was carried out. As a result of the work done, it was possible to solve the problem of the process of modeling the RM laying trajectory for bodies of complex shape with a fixed type of section, made by winding from a polymer composite material (PCM). This technology can be used to produce aircraft structures such as the "wing", "fuselage" of an aircraft, etc. Thus, the possibility of winding SCS of a general type has been proved using the example of mesh hull structures. As a result, the range of production of coiled products has expanded - bodies with an arbitrary convex section and a straight generatrix.

Complex-shaped TiC/Ti(C,N)-based cermet prepared via rheological press molding using highly-filled granular feedstock

Production of complex-shaped cermet faces challenges owing to its high hardness and brittleness. Plastic shaping is a good solution because the complex-shaped body can be directly formed without machining. In this work, a facile method named rheological press molding (RPM) was raised up, which showed the capability of fabricating TiC/Ti(C,N)-based gear parts with relatively uniform microstructure and high dimensional accuracy. The characteristics of wettability, rheological property and morphology of the polyformaldehyde-based feedstock was measured, and the molding effect including green part molding, debinding and sintering was investigated. The feedstock containing 60 vol% composite powders showed a shear-thinning behavior, with a viscosity lower than 200 Pa·S at 100 S−1. Confirmed by the SEM and XRD results, TiC/Ti(C,N)-based cermets with typical core-rim structure and two phases of Ni-Co metal and Ti(C,N)-based solid solutions were achieved after vacuum sintering at 1500 °C. Good qualified gear parts with polished mirror surface and relative density of 95% were obtained, which showed a linear shrinkage of 12% and the Vicker's hardness of 1482 N/mm2 (Hv10). This method offered an easy and low-cost way to form complex-shaped cermet based on high-filled feedstock.

INTEGRATED CALCULATION AND EXPERIMENTAL TECHNOLOGY FOR ANALYSIS OF CONTACT INTERACTION WITH ACCOUNT OF ELASTIC INTERMEDIATE LAYER

The work delivers solution to a relevant scientific problem of solid mechanics. It consists in developing theoretical basis for computational and experimental research of contact interaction of complex-shaped bodies with account for micromechanical models of roughness and other intermediate or surface layers. New methods and models have been developed for the analysis of contact interaction of complex-shaped bodies with account for the micromechanical properties of surface and intermediate layers characterized by nonlinear local contact stiffness. The developed methods and models as well as the numerical analysis tools have been applied to a series of model and applied problems. The deformation behaviour of novel materials with network microstructures of one-dimensional elements has been determined. Macroscopical properties of these materials have been evaluated based on the special microscopic models and the homogenization methods. Regularities in contact distribution and its dependence on geometrical and physical factors have been determined for various complexshaped bodies. New design solutions for machine elements that improve their strength and durability have been justified. The developed methods and analysis tools have been introduced into the design of new engineering products. Their implementation resulted in improved technical characteristics of protection, structural and functional elements of transport vehicles of special purpose, gear transmissions, technical equipment, hydrovolumetric drives and so on. The conducted computational and experimental studies showed good agreement with the real response of network materials and the observed behavior of interacting elastic bodies with intermediate contact layer. Keywords: solid mechanics, complex-shaped body, contact interaction, contact pressure, intermediate layer

Grid-Stamping on a Polygon Model for Implementing Arbitrary-Shaped Boundary Conditions in a Moving Particle Semi-Implicit Method

This study proposes a new wall boundary condition for the grid-stamping on a polygon (G-StoP) model, which enables a simpler and more efficient handling of boundary surfaces of arbitrarily complex-shaped bodies represented using polygons (or meshes). For example, computer-aided design surface data can be used to analyze flow using a particle-based fluid-solver moving particle semi-implicit method. For coupling simulations of fluid–multibody dynamics, the Pusan-National-University-modified MPS method is improved, and the coupling analysis is performed using RecurDyn, a commercial software package for multibody (or flexible multibody) dynamics. To confirm the applicability of the developed G-StoP model, hydrostatic pressure simulations are conducted in a rectangular tank at various corner angles. Then, the hydrostatic pressure results are compared with previously proposed polygonal wall boundary model results and theoretical solutions. That is, in the case with a corner angle of 30°, it was confirmed that the relative error to the experiment of the polygon model was 11.3%, while that of the G-StoP model was 1.3%. This demonstrates that the proposed G-StoP model is exceptional for numerical stability and robustness even when it is difficult to secure information on neighboring particles as the corner angle of the object becomes small. In addition, the G-StoP model was applied to dam breaking, subaerial landslide tsunami, and wine sloshing problems, and its accuracy and applicability were tested through comparison with experimental and other simulation results. As a result, it was shown that the present simulation results were much closer to the experiments than other simulations.

Anisotropic Adaptation of Moving Unstructured Mesh to Bodies of Complex Shapes Described by an Interpolation Octree

Anisotropic Adaptation of Moving Unstructured Mesh to Bodies of Complex Shapes Described by an Interpolation Octree

Creep of Complex-Shaped Bodies of Revolution Made of Functionally Gradient Materials

Creep of Complex-Shaped Bodies of Revolution Made of Functionally Gradient Materials

Modeling of bodies with spherical pores by generalized linear interpolation

The article offers a description of parametric objects with spherical pores by generalized linear interpolation. Increasing the volume of high-resolution image data requires the development of algorithms capable of processing large images with reduced computational costs. Numerical data on the geometry of the pores of the object under study are transformed into the geometry of bodies consisting of octagonal portions of cubic shape. Parametric porous objects can model both the shape and the isoparametric interior. Often, this type of parametric bodies is used as initial or boundary conditions in numerical modeling to demonstrate internal modeling. To form a body of complex shape, parametric solid-state elements can be connected together. The continuity between the elements can be determined in the same way as when modeling cubic parametric splines. A lot of research is devoted to the reconstruction of the geometric structure of porous materials based on digital images of objects for a better understanding and representation of physical processes in a porous medium. A detailed understanding of the microstructure can be used to determine physical properties, and then to evaluate and improve the characteristics of simulated objects and processes in them. The article presents the results of the proposed algorithm in the MathCAD environment and software processing of a porous body based on digital images.

Turbulent flow simulation near fixed drone propeller using immersed boundary method

Current paper investigates the possibility of modeling the flow near the drone propeller on a simply connected mesh using the immersed boundary method and calculating its aerodynamic characteristics. An important part of the technique is the moving mesh adaptation to the surface of a streamlined body that retains its topology. The position and shape of the body are given by an interpolation grid, which stores the function of the distance to the body surface, as well as a number of geometry parameters. The method described in this paper is usually used to simulate flow near moving bodies, but here a stationary formulation is considered to assess the possibilities of using the proposed method for modeling flow near bodies of complex shapes where there are areas of high curvature and thin edges. For the proposed formulation of the problem, the results of the calculation carried out by the classical method on a body-fitted mesh and the results of modeling obtained using the method of immersed boundaries on a simply connected mesh are presented. The paper compares the results of these approaches, evaluates the possibility of using the immersed boundary method in combination with mesh adaptation to simulate the flow around bodies of complex shapes, and identifies the weaknesses of the proposed approach.

Problems of the Mathematical Theory of Diffraction by Bodies of Complex Shape

Problems of the Mathematical Theory of Diffraction by Bodies of Complex Shape

CONSTRUCTION OF SOLVING EQUATIONS OF SEMI-ANALYTICAL METHOD OF FINISHED ELEMENTS FOR PRISMATIC BODIES OF COMPLEX SHAPE

The article presents an effective numerical approach to the study of arbitrarily loaded massive and thin-walled prismatic bodies of complex shape, the deformation of which can take place beyond the elasticity of the material. The equations of the semi-analytical finite element method (SAFEM) when used to decompose the displacements of Fourier series. The main relations between the spatial problem of the theory of elasticity in a curvilinear coordinate system and the theory of plastic flow for an isotropically reinforcing material under the Mises fluidity condition are presented. In accordance with the method of the moment scheme of finite elements (MSFE), the expressions of deformations of the prismatic finite element due to the nodal values of amplitude displacements are obtained. Formulas for calculating the stiffness matrix coefficients of a finite element (FE) with variable and averaged in the cross-sectional plane mechanical and geometric parameters are derived.

OVERVIEW OF MODERN APPROACHES TO SOLVING THE PROBLEM OF EXTENDED RADAR TARGETS RECOGNITION

The development of the theory and technology of radio location indicates the need to solve problems of radar recognition of targets by spatial parameters. This is due to the need to provide in promising radar stations (complexes) with a software overview of the required resolution to obtain three-dimensional images in all spatial coordinates.
 The task of radar targets recognition, which is to assign the observed objects to the appropriate classes and types, is of considerable and growing interest. Different classes (types) of targets make up a certain alphabet, the choice of which determines not only the effectiveness of the use of recognition, but also the difficulties that arise in its implementation.
 Currently, there are a large number of radar recognition algorithms. They differ in the stages of decision-making, the degree and nature of accounting for statistics of signs, obstacles and signals. Due to the fact that the secondary emission pattern of extended targets is multi-lobed, statistical algorithms are preferred.
 The information used for radar recognition is contained in the set of received radar signals. However, most often for target recognition certain measured target features are used, which are compared in accordance with the recognition algorithms with known (reference) features.
 The choice of recognition features is usually made heuristically. This set of parameters does not always allow providing the required quality of recognition. The synthesized algorithms work unstable or require unreasonably large computational costs due to a significant increase in the dimensionality of the feature space.
 Analysis of known radar recognition algorithms of extended targets shows that they were developed under significant constraints.
 At present, the tasks of point targets radar surveillance are most fully solved. The tasks of processing signals reflected from bodies of complex shape, given the difficulties of their formulation and solution are not fully explored.
 It is promising to consider a set of radar surveillance tasks and the criteria used in them as a multicriteria task, the solution of which is associated with vector optimization of the location system as a whole.

SUBSTANTIATION OF APPROPRIATE OPTIONS FOR APPLICATION OF METHODS OF OBSERVABILITY ATTENUATION OF UKRAINIAN ARMED FORCES’ MILITARY EQUIPMENT, PROTECTION OF PERSONNEL AND EQUIPMENT FROM TECHNICAL MEANS OF RADIOLOCATING AND OPTICAL-ELECTRONIC INTELLIGENCE

Development of technologies for creating materials, environments and coatings with specified electrophysical characteristics for practical implementation in production and widespread use of observability attenuation technologies of surface, air, space, abovewater objects, surface-based installations, troops for the needs of Armed Forces of Ukraine and other military formations, impacts of artificial sources of electromagnetic radiation on the human body today is especially relevant.
 Nowadays, "stealth technologies" include the following main areas: the theory of diffraction on bodies of complex shape, research and development of radio-absorbing materials, coating technology and, finally, radiophysical experiment, which is used for control in each of these areas. One of the most important tasks is to reduce the level of signals generated by the reflection of electromagnetic waves emitted by radars, since radars still remain the most "long-range" means of detecting targets and air defense systems aiming.
 To date, "stealth technology" begins with mathematical modeling of electromagnetic wave scattering on an object, the radar visibility of which should be reduced. This step is essential for a preliminary assessment of the possible result and allows optimizing the shape and electrophysical characteristics of the object.
 The world leading countries have developed absorbing materials that capable to provide electromagnetic compatibility of the electronic equipment, camouflaging and counteraction to radio technical intelligence, use in designs of the radio electronic equipment.
 The comparative analysis of the developings that are promising for usage as radio-absorbing materials and radio-absorbing covering is carried out in the work.
 In the future, it is planned to expand the shielding frequency range and the range of use of absorbing coatings to protect personnel and equipment from electromagnetic emission.

CONTACT INTERACTION OF COMPLEX-SHAPED BODIES WITH ACCOUNT FOR NONLINEAR CHARACTERISTICS OF THE INTERMEDIATE LAYER MATERIAL

The paper describes the analysis of stress-strain state of complex-shaped bodies that come into contact over surfaces of conforming shape. The intermediate layer placed between these bodies has nonlinear properties depending on the load history. These properties may be associated with the microstructure of the surface layers of the materials of the contacting bodies. They can also be determined by the properties of network structure materials, polymers, rubber-like materials, sprays, gaskets, etc. The effect of these properties on the contact pressure distribution is illustrated by the example of hydraulic pistons. It is established that with the change of properties of intermediate layers the character of contact pressure distribution changes together with the locations of minima and maxima of contact pressure. Moreover, the contact area itself changes size and shape. Peculiarities of the stress-strain state of the contacting bodies are also determined. Possibilities of control of contact pressure distributions and stress-strain state of contacting bodies by special choice of intermediate layer properties are established.

Study of possibility of using axisymmetric body as heat sink for cooling machine parts

The paper presents the results of the study of possibility using a body with an optimized shape with a minimum aerodynamic drag force as a heat sink in a convective gas flow for cooling machine parts. The relevance of cooling or heat sink systems for mechanical engineering is not in doubt. Maintaining the optimum thermal state of machine parts within the specified limits is necessary to prevent heating, which can cause violations of normal operating conditions, and, as a result, increased wear, jamming and breakage of parts. To ensure the normal operation of the system, it is necessary to cool the parts contacting the hot gases, removing heat from them to the atmosphere directly, or using an intermediate body (water, low-freezing liquid). Heat sink is an aerodynamic process, a process of heat mass transfer of a substance, and aerodynamic characteristics and, in particular, the nature of streamlining of bodies of the simplest forms are of great scientific and practical interest. Bodies of complex shape can always be represented as a combination of simpler ones, for which it is easy to explore and calculate the flow paths, on the basis of which analytical methods for calculating aerodynamic characteristics are compiled. A computational experiment was conducted in the software product Ansys Fluent. The conditions of the experiment (comparison of heat removal bodies) during numerical modeling are the preservation of constants: the volume and shape of the working zone; distances from the sources, drains and centers of bodies; aerodynamic flow rates; masses of compared bodies; thermal power of the source and other parameters in addition to the shape of the surface. The resulting optimized shape of the body coincides with the current lines, which is the main advantage, since no separation from the surface is observed when streamlining the flow. Thus, the entire surface area will be the effective surface area of the heatsink as opposed to other known shapes of bodies, whereby the temperature of the heat loaded element placed in the center of the heatsink will decrease.

Processing of large and complex-shaped fine-grained alumina bodies with high transparency

The paper presents the development of unique processing methods for large alumina windows, domes, and thin sheets with a fine-grained structure and high optical transmission. Gelcasting combined with post-hot isostatic pressing proved to be a suitable processing method for windows and domes. This method provided alumina ceramics with a real in-line transmission of up to 72 % at a wavelength of 633 nm and with a theoretical in-line transmission in the infrared region between 1500 and 4000 nm for 0.8 mm thick bodies. Complex-shaped bodies, domes, were prepared with minimum warping during sintering. Thin transparent alumina sheets were prepared by gel-tape casting. This novel tape casting method utilized the advantages of the gelcasting method. The real in-line transmission of the tapes was lower compared with the windows. Nevertheless, the thin tapes with a thickness below 350 μm exhibited reasonable transparency even after pressureless sintering and without a polishing of sintered samples.

The Algorithm of the Vortex Sheet Intensity Determining in 3D Incompressible Flow Simulation around a Body

An original algorithm is developed for vortex methods of computational fluid dynamics for determining the intensity of the vortex sheet on the surface of a body in the flow of an incompressible medium. Unlike the common in the vortex methods approach to satisfying the no-slip boundary condition on a streamlined surface, which is based on ensuring that the normal velocity component of the medium is zero, the proposed procedure is based on a mathematically equivalent condition of equality to zero of the tangent velocity component on the body surface. The unknown intensity of the vortex sheet is assumed to be piecewise constant on triangular panels that approximate the surface of the body. The resulting integral equation is approximated by a system of linear algebraic equations, which dimension is twice the number of panels. The coefficients of the system matrix are expressed through double integrals over the panels. An algorithm is proposed for calculating these integrals for the case of neighboring panels, when these integrals are improper. An additive singularity exclusion is performed and analytical expressions for the integrals of them are obtained. The smooth parts of integrands are integrated numerically using Gaussian quadrature formulae. The proposed algorithm makes it possible to improve significantly the accuracy of the vortex sheet intensity reconstruction when flow simulating around complex-shaped bodies by using vortex methods for arbitrary triangular surface meshes, including essentially non-uniform and having cells with high aspect ratio.