АЛГОРИТМ ПРОЕКТУВАННЯ АВТОМАТИЗОВАНИХ ЗМІШУВАЛЬНИХ КОМПЛЕКСІВ БЕЗПЕРЕРВНОЇ ДІЇ ДЛЯ СИПКИХ МАТЕРІАЛІВ

Purpose. Creation of design algorithm of continuous action mixing complexes that will allow defining parameters of the equipment proceeding from requirements to quality, productivity and the set compounding of mixture.Methodology. The method of discrete elements, classical mechanics positions, theory of solids contact interaction, method of mathematical modeling are used in the work.Findings. The paper proposes a generalized algorithm for designing a continuous mixing complex for bulk materials. The procedure for designing a centrifugal mixer, the flow shapers, plate feeders and conical-cylindrical hoppers are presented. Calculations of design and technological parameters are carried out on the basis of information about the physical and mechanical properties of bulk components particles, requirements for equipment performance and the mixture homogeneity. The results of calculations of the mixing complex for the three-component mixture used for the production of polyethylene film are presented. To test the proposed algorithm, a mathematical model based on the discrete elements method is created. The mixing process is modeled and the coefficients of inhomogeneity of each of the components in the finished mixture are determined. The obtained results confirmed that the proposed algorithm allows to determine the parameters of the mixing complex, which ensure compliance with the specified requirements for the quality and the equipment performance.Originality. Mathematical models of bulk motion dynamics in mixing complexes are improved, which include bunker devices, plate feeders, flow shapers and continuous centrifugal mixer, taking into account the bulk motion discrete nature.Practical value. The obtained results allow calculating the design and technological parameters of the equipment that is a part of the continuous mixing complex according to the set productivity, recipe and requirements to the mixture homogeneity.

Ductile fracture modeling of metallic materials: a short review

Since the end of the last century a lot of research on ductile damaging and fracture process has been carried out. The interest and the attention on the topic are due to several aspects. The margin to reduce the costs of production or maintenance can be still improved by a better knowledge of the ductile failure, leading to the necessity to overcome traditional approaches. New materials or technologies introduced in the industrial market require new strategies and approaches to model the metal behavior. In particular, the increase of the computational power together with the use of finite elements (FE), extended finite elements (X-FE), discrete elements (DE) methods need the formulation of constitutive models capable of describing accurately the physical phenomenon of the damaging process. Therefore, the recent development of novel constitutive models and damage criteria. This work offers an overview on the current state of the art in non-linear deformation and damaging process reviewing the main constitutive models and their numerical applications.

HULLFORM & HYDRODYNAMIC CONSIDERATIONS IN THE DESIGN OF THE UK FUTURE AIRCRAFT CARRIER (CVF)

The author is to be congratulated in producing a paper for the journal on an important aspect (hydrodynamics) of a design, which was taken to a considerable level of definition before not being proceeded with. The fact that we so rarely get visibility of the thinking and effort behind “abortive” designs – so very little was allowed to be preserved of the cancelled CVA01 of the 1960s – and that this can be compared to the separately evolved, subsequently fully design and, now in 2017, about to go into service QUEEN ELIZABETH (QEC) carrier, makes this a very worthwhile document for the Transactions. Not only can the various detailed conclusions on the hydrodynamically related design choices be read for their input to the BAE Systems alternative to the Thales design, that was finally developed into the QEC (see S Knight’s 2009 RINA Conference paper), the paper also provides general insights into the interaction of one specific topic (hydrodynamics) with wider design developments. This can be instructive to future designers of complex ships – not just aircraft carriers. It could be argued that despite the growing capabilities of CFD tools, that there still appears to be a need for substantial model testing of discrete elements of the hydrodynamic design, as described. Would the author like to comment as to whether he sees this dual need for CFD and physical model testing likely to continue whenever new designs “are just that little bit too different” and how one might judge the latter?

Compact silencers with discrete baffle elements for new-generation light small arms

This paper presents the results of the development of silencers, whose design features discrete baffle elements. The advisability of silencers of this type is confirmed by their operational reliability and shot sound suppression efficiency in their actual service as part of light small arms of different types. To design advanced silencers, technical requirements for their design were developed. The paper describes the possibility of using discrete elements (cones, hemispheres, flat baffles, etc.) as the key component of a powder gas spreader. Differently shaped elements are used as additional elements that form a powder gas flow inside a silencer: for example, cylindrical elements, including perforated ones to provide a powder gas flow between the expansion chambers. One way to increase silencer efficiency is an additional expansion chamber that embraces the external part of the barrel and is gas-dynamically connected to a traditional muzzle silencer. In deciding on an optimum design for compact silencers, the following was redetermined: the number of expansion chambers and the dimensions thereof, the powder gas energy converter design, the baffle type, the presence of a gas flow between the chambers near the inner surface of the silencer body, and, if so, the gas flow rate. The silencer design was optimized based on simulating the processes inside the silencer using the authors’ efficiency calculation procedure for silencers with different internal components. Comparison tests of the silencers developed and foreign silencers confirmed a high efficiency of the former. The silencers with discrete baffles for light small arms developed at the Institute of Technical Mechanics of the National Academy of Ukraine and the State Space Agency of Ukraine compare well in performance with their best foreign counterparts. The designs of some of them are covered by Ukrainian patents.

Nanoscale self-assembly: concepts, applications and challenges

Self-assembly offers unique possibilities for fabricating nanostructures, with different morphologies and properties, typically from vapor or liquid phase precursors. Molecular units, nanoparticles, biological molecules and other discrete elements can spontaneously organise or form via interactions at the nanoscale. Currently, nanoscale self-assembly finds applications in a wide variety of areas including carbon nanomaterials and semiconductor nanowires, semiconductor heterojunctions and superlattices, the deposition of quantum dots, drug delivery, such as mRNA-based vaccines, and modern integrated circuits and nanoelectronics, to name a few. Recent advancements in drug delivery, silicon nanoelectronics, lasers and nanotechnology in general, owing to nanoscale self-assembly, coupled with its versatility, simplicity and scalability, have highlighted its importance and potential for fabricating more complex nanostructures with advanced functionalities in the future. This review aims to provide readers with concise information about the basic concepts of nanoscale self-assembly, its applications to date, and future outlook. First, an overview of various self-assembly techniques such as vapour deposition, colloidal growth, molecular self-assembly and directed self-assembly/hybrid approaches are discussed. Applications in diverse fields involving specific examples of nanoscale self-assembly then highlight the state of the art and finally, the future outlook for nanoscale self-assembly and potential for more complex nanomaterial assemblies in the future as technological functionality increases.

Determination of the coefficient of restitution upon contact of a steel ball with aluminum and steel surfaces

In this work, experimental studies on the rebound of a steel ball from aluminum and steel surfaces have been carried out. Using the ideology of the method of discrete elements, a three-dimensional model of the process was built. By carrying out multivariate calculations with varying the restitution coefficient and subsequent comparison of experimental and calculated data on the ball rebound height, the actual restitution coefficient for contact pairs “steel - steel” and “steel - aluminum” was determined. The results of the work will be used in the development of a complex model of high-energy ball milling.

A Continuity Flow Based Tomographic Reconstruction Algorithm for 4D Multi-Beam High Temporal—Low Angular Sampling

A mathematical framework and accompanying numerical algorithm exploiting the continuity equation for 4D reconstruction of spatiotemporal attenuation fields from multi-angle full-field transmission measurements is presented. The algorithm is geared towards rotation-free dynamic multi-beam X-ray tomography measurements, for which angular information is sparse but the temporal information is rich. 3D attenuation maps are recovered by propagating an initial discretized density volume in time according to the advection equations using the Finite Volumes method with a total variation diminishing monotonic upstream-centered scheme (TVDMUSCL). The benefits and limitations of the algorithm are explored using dynamic granular system phantoms modelled via discrete elements and projected by an analytical ray model independent from the numerical ray model used in the reconstruction scheme. Three phantom scenarios of increasing complexity are presented and it is found that projections from only a few (unknowns:equations > 10) angles can be sufficient for characterisation of the 3D attenuation field evolution in time. It is shown that the artificial velocity field produced by the algorithm sub-iteration, which is used to propagate the attenuation field, can to some extent approximate the true kinematics of the system. Furthermore, it is found that the selection of a temporal interpolation scheme for projection data can have a significant impact on error build up in the reconstructed attenuation field.

A Method for Assessing the Stability of Digital Automatic Control Systems (ACS) with Discrete Elements. Hypothesis and Simulation Results

The article presents a new approach to the analysis of the stability of automatic systems with discrete links. In almost all modern automatic control systems (ACS), there are links that break signals in time. These are power controlled switches—transistors or thyristors operating in a pulsed mode and digital links in regulators. Time discretization significantly affects the stability of processes in the automatic control system. The theoretical analysis of such systems is rather complicated and requires a significant change in engineering approaches to analysis. With the improvement of digital controllers and a significant increase in their performance, this problem has practically been forgotten. However, its mathematical “content” has not changed since the 1980s when discreteness began to play a major role in hindering the transition to digital automatic control systems. In this paper, we propose a new approach that consists of interpreting the sampling operation by a link with the proposed frequency characteristic, which determines the suppression of input high-frequency signals. This link greatly simplifies engineering calculations and demonstrates the new capabilities of sampling systems. These possibilities include the rational distribution of digitalization resources—the number of bits and the sampling interval between the regulator channels, depending on the frequency range of the efficiency of these channels. We verify and confirm our theoretical statements through simulations and show how this approach makes it possible to formulate new principles of construction of seemingly well-known controllers—PID (Proportional Integral Differential) controllers and variable structure systems (VSS).