M/G/1 vacation model with limited service discipline and hybrid switching-on policy

The author studies an M/G/1 queueing system with multiple vacations. The server is turned off in accordance with the K-limited discipline, and is turned on in accordance with the T-N-hybrid policy. This is to say that the server will begin a vacation from the system if either the queue is empty or K customers were served during a busy period. The server idles until it finds at least N waiting units upon return from a vacation. Formulas for the distribution generating function and some characteristics of the queueing process are derived. An optimization problem is discussed.</p

Modeling of autoresonant control of a parametrically excited screen machine

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Modelling of nonlinear dynamic response of a screen machine described by the nonlinear coupled differential equations and excited by the system of autoresonant control is presented. The displacement signal of the screen is fed to the screen excitation directly by means of positive feedback. Negative feedback is used to fix the level of screen amplitude response within the expected range. The screen is anticipated to vibrate with a parametric resonance and the excitation, stabilization and control response of the system are studied in the stable mode. Autoresonant control is thoroughly investigated and output tracking is reported. The control developed provides the possibility of self-tuning and self-adaptation mechanisms that allow the screen machine to maintain a parametric resonant mode of oscillation under a wide range of uncertainty of mass and viscosit

Nonlinear Dynamic Structures with Developing Discontinuity

AbstractDiscontinuity is one of the most important nonlinear factors challenging both methods of nonlinear analysis and its applications. The problem becomes more complicated when the discontinuity is developing under the influence of dynamic processes in the structures. This paper presents the methodology for analysis and simulation of the systems with the developing discontinuity. It is based on the combination of analytical technique using nonlinear integral equations and the Matlab-Simulink computation. This methodology is applied to analysis of nonlinear dynamics of the cracked bar. Some new nonlinear phenomena have been revealed and validated

Finite element simulations of ultrasonically assisted turning

Finite element simulations of ultrasonically assisted turnin

Nonlinear dynamics of structures with propagating cracks

The aim of this paper is to study the evolution of nonlinear dynamics of structures with a propagating crack. A method of simulation used for analysis of dynamics of the cracked structure is based on a combination of an analytical technique and Matlab-Simulink-based simulations. As an example, a model of a cracked bar subjected to longitudinal excitation is used to analyse its nonlinear response as a way to monitor the structural health as crack propagates

The essence and differences of the organizational and economic mechanism of enterprise management

У статті розглянуто сутність поняття організаційно-економічний механізм та його відмінності від інших інструментів управління діяльністю суб’єктів підприємницької діяльності. Предмет дослідження – сучасні теоретичні та методологічні проблеми сутнісного виокремлення механізмів управління, зокрема організаційно-економічного механізму. Метою статті є дослідження існуючих підходів до визначення організаційно-економічного механізму, їх узагальнення та встановлення відмінностей організаційно-економічного механізму від інших видів механізмів управління. Основні методи, які були використані під час проведення дослідження: загальнофілософський (для викладення власних думок); структурно-логічний (при побудові логіки та структури роботи); порівняльний (у процесі аналізу поглядів різних вчених щодо сутності поняття «організаційно-економічний механізм»); метод декомпозиції та синтезу (для вивчення предмету та взаємозв’язку його складових частин). Досліджено розбіжності у розумінні сутності механізмів в економіці, зокрема економічних, організаційних та організаційно-економічних механізмів. Розглянуто сутнісне наповнення кожного з видів механізмів та сформульовано відмінності між ними. Наголошено, що у визначеннях економічного механізму повинен бути наголос на врахування економічних інтересів і потреб суб’єкту та об’єктів управління, а при визначенні сутності організаційного механізму слід приділяти увагу структуризації форм та методів впливу суб’єкта на об’єкт управління. Запропоноване авторське визначення організаційно-економічного механізму управління, яке дозволяє врахувати відмінності кожної зі складових (організаційної та економічної) та наголосити на їх сумісності. Результатом дослідження сутності та відмінності організаційно-економічних механізмів є можливість їх чіткого виокремлення від інших інструментів управління підприємницькою діяльністю, що дозволяє більш якісно їх використовувати у практичній діяльності суб’єктів господарювання.The article considers the essence of the concept of organizational and economic mechanism and its differences from other tools for managing the activities of business entities. The subject of research - modern theoretical and methodological problems of the essential separation of management mechanisms, in particular organizational and economic. The aim of the article is to study the existing approaches to the definition of organizational and economic mechanism, their generalization and to establish differences from other types of management mechanisms. The main methods that were used during the study: general philosophical (to present their own opinions); structural and logical (when building the logic and structure of work); comparative (in the process of considering different views of scientists and scholars on the essence of the concept of "organizational and economic mechanism"); method of decomposition and synthesis (to study the subject and the relationship of its components). Differences in the understanding of the essence of mechanisms in the economy, in particular economic, organizational and organizational-economic mechanisms, have been studied. The essential content of each of the types of mechanisms is considered and the differences between them are formulated. It is emphasized that the definitions of the economic mechanism should emphasize the economic interests and needs of objects and the subject of management, and in determining the essence of the organizational mechanism should pay attention to structuring the forms and methods of influence of the subject on the object of management. The author's definition of the organizational and economic mechanism of management is offered, which allows to take into account the differences of each of the components (organizational and economic) and emphasize their compatibility. The result of the study of the nature and differences of organizational and economic mechanisms is the possibility of their clear separation from other tools of business management, which allows for better use in the practical activities of economic entities

Resonant tuning of Langevin transducers for ultrasonically assisted machining applications

This paper provides a fundamental study into the trade-offs between the location of piezoceramic elements, resonant frequency, and achievable ultrasonic vibration amplitude at the working end of the Bolted Langevin-style Transducers (BLT) for Ultrasonically Assisted Machining (UAM) applications. Analytical models and Finite Element (FE) models are established for theoretical study, which are then validated by experiments on four real electro-mechanical transducers. Results suggest that resonant frequency and oscillation amplitude of the BLTs depend essentially on the dimensions of the system and the location of piezoceramic elements. The highest resonant frequency and the maximal vibration are achieved when the piezoceramic elements are at the longitudinal displacement node, where the highest effective electro-mechanical coupling coefficient value is exhibited. However, the minimal resonant frequency and the lowest vibration, which is almost equal to zero, are observed when the piezoceramic elements are located at the displacement anti-node. In addition, the longitudinal displacement node locations are dependent on the resonant frequency of the devices rather than the locations of the piezoceramic elements

Vibration Control of Linear Split Stirling Cryogenic Cooler for Airborne Infrared Application

Modern infrared imagers often rely on the split Stirling cryogenic coolers the linear compressors of which are the well-known sources of harmonic disturbance. The traditional method of their passive isolation fails to meet the restraints on the static and dynamic deflections which are originated by the combined action of the airborne g-loading and harsh random vibration

Theoretical background for the bionic substantiation of parameters of the stubble cultivator working bodies

In the southern regions of Russia, the technology of cultivation of grain crops in the variant of partial sowing has been widely used. In this regard, it became necessary to create effective working bodies of a stubble cultivator that would have fundamentally new resource-saving ways of influencing the area under cultivating and meet the requirements of modern advanced technologies. The shapes of the working bodies surfaces of the cultivators were improved taking into account the mechanic-bionic approach. The main parameters of the toothed cutting surface were determined by the method of bionic comparisons, with a scarab beetle as a bionic prototype. Use of the serrated shape of the cutting edge is consistent with the bionic principle of multi-contact exposure and leads to the fact that the tops of the teeth become stress concentrators and, with a significantly smaller indentation force, cause soil destruction processes, which reduces the energy costs of cutting the soil layer. The optimal curvilinear shape of the working surface made in the form of a logarithmic spiral, is characterized by a constant value of the angle between the normal and the radius vector, and the value of this angle, equal to the angle of internal friction of the soil φ2, will ensure the sliding of the soil and plant residues with minimal energy consumption. The number (n = 4), height (h = 5...7 mm) and tooth placement step (S = 10...12 mm) of the bit tip of the stubble cultivator are analytically justified. The shape of the profile of the working surface of the stubble cultivator bit in the form of a logarithmic spiral with a variable angle of crumbling is proposed. The studies were conducted in the period from September to October 2018 in the soil channel of the research Laboratory of Bionic Agroengineering of the Department of Mechanization and Technical Service in Agro-Industrial Complex. They have shown the decrease in the traction resistance of the proposed working body of the stubble cultivator by 16.5% in comparison with the traction resistance of the serial sample

Application of smooth-particle hydrodynamics in metal machining

The finite element (FE) method has been extensively used to model complex cutting processes. However, due to large strains in a process zone, leading to increased element distortions, such simulations are confronted with numerical difficulties. Smooth-particle hydrodynamics (SPH) is a mesh-free computational method, which has been used to simulate multi-body problems. In this paper we present a 3D hybrid modelling approach for orthogonal micro-machining of a copper single crystal with the use of SPH and continuum FE. The model is implemented in a commercial FE software ABAQUS/Explicit. The study is used to gain insight into the effects of crystallographic anisotropy on the machining response of f.c.c. cubic metals