Finite element modelling of creep process - steady state stresses and strains

Finite element modelling of steady state creep process has been described. Using an analogy of visco-plastic problem with a described procedure, the finite element method has been used to calculate steady state stresses and strains in 2D problems. An example of application of such a procedure have been presented, using real life problem - cylindrical pipe with longitudinal crack at high temperature, under internal pressure, and estimating its residual life, based on the C* integral evaluation

Numerical simulation of multiphase flow around suction plates of ventilation mill in the function of extending its remaining working life

Ovaj rad prestavlja mogućnost korišćenja rezltata numeričkih simulacija, za smanjenje habanja radnih delova ventilacionog mlina za mlevenje uglja u termoelektrani Kostolac B. Mogućnost revitalizacije usisnih ploča ventilacionog mlina je zasnovan na 3D numeričkoj simulaciji multifaznog strujanja u ventilacionom mlinu. Čvrste čestice smeše ugalj, mineralne materije, pesak tokom procesa mlevenja izazivaju veliko habanje usisnih ploča. Primenom softverskog paketa ANSYS FLUENT 12, dobiće se detaljniji prikaz multifaznog strujanja i brzine mešavine koja omogućuje da se na osnovu intenziteta i smera brzine, preciznije odrede kritične zone u kojima će se pojaviti oštećenja kod usisnih ploča ventilacionog mlina. Korišćen je Euler-Euler model mešavine. Rezultati dobijeni pomoću numeričke simulacije koristiće se za izbor optimalne tehnologije revitalizacije usisnih ploča ventilacionog mlina. Primenom ovog pristupa rešavanja problema smanjio bi se broj mogućih interventnih popravki i produžio bi se period između neophodnih kompletnih remonta postrojenja, čime bi se ostvarili značajni ekonomski efekti i ujedno povećala energetska efikasnost termoenergetskih agregata.This paper presents results of the analyses obtained by numerical simulation for the possibilities of increasing the wear resistance of the ventilation mill working parts for coal grinding in the Kostolac B power plant. The possibilities for modification are based on 3D numerical simulation of multiphase flow of ventilation mill. Mineral materials during the process of milling in the ventilation mill cause strong wear of the suction plates. The multiphase flow simulations are performed in order to obtain the mineral materials paths and velocity vectors. The mixture model of the Euler-Euler approach is used. The results obtained in the numerical simulation serve for the selection of an optimal redesign of the suction plates. The application of this approach can reduce the number of possible repairs and extends the period between them, resulting in significant economic effects

Numerical simulation of multiphase flow around suction plates of ventilation mill in the function of extending its remaining working life

Ovaj rad prestavlja mogućnost korišćenja rezltata numeričkih simulacija, za smanjenje habanja radnih delova ventilacionog mlina za mlevenje uglja u termoelektrani Kostolac B. Mogućnost revitalizacije usisnih ploča ventilacionog mlina je zasnovan na 3D numeričkoj simulaciji multifaznog strujanja u ventilacionom mlinu. Čvrste čestice smeše ugalj, mineralne materije, pesak tokom procesa mlevenja izazivaju veliko habanje usisnih ploča. Primenom softverskog paketa ANSYS FLUENT 12, dobiće se detaljniji prikaz multifaznog strujanja i brzine mešavine koja omogućuje da se na osnovu intenziteta i smera brzine, preciznije odrede kritične zone u kojima će se pojaviti oštećenja kod usisnih ploča ventilacionog mlina. Korišćen je Euler-Euler model mešavine. Rezultati dobijeni pomoću numeričke simulacije koristiće se za izbor optimalne tehnologije revitalizacije usisnih ploča ventilacionog mlina. Primenom ovog pristupa rešavanja problema smanjio bi se broj mogućih interventnih popravki i produžio bi se period između neophodnih kompletnih remonta postrojenja, čime bi se ostvarili značajni ekonomski efekti i ujedno povećala energetska efikasnost termoenergetskih agregata.This paper presents results of the analyses obtained by numerical simulation for the possibilities of increasing the wear resistance of the ventilation mill working parts for coal grinding in the Kostolac B power plant. The possibilities for modification are based on 3D numerical simulation of multiphase flow of ventilation mill. Mineral materials during the process of milling in the ventilation mill cause strong wear of the suction plates. The multiphase flow simulations are performed in order to obtain the mineral materials paths and velocity vectors. The mixture model of the Euler-Euler approach is used. The results obtained in the numerical simulation serve for the selection of an optimal redesign of the suction plates. The application of this approach can reduce the number of possible repairs and extends the period between them, resulting in significant economic effects

Position and speed control of electromechanical actuator for aerospace applications

Težište ovog rada je upravljanje elektromehaničkim aktuatorom (EMA) za primjene u zračnom prostoru. Upravljanje EMA je ostvareno uporabom pozicijskog regulatora i upravljanja koje kombinira položaj i brzinu regulatora. Osnovna smjernica bila je smanjenje gubitaka snage, zagrijavanja i potrošnje struje u sustavu. Jedno od važnih područja u okviru pogona promjenljivim brzinama motora su operativne granice sustava. Danas se operativne granice pogona s promjenljivim brzinama motora postavljaju na osnovu operativnih granica pogona na bazi prosječnih vrijednosti, npr. ograničenjima struje i snage na preporučene vrijednosti. To dovodi do nedovoljne iskorištenosti sustava i velikih gubitaka korisne snage. U ovom radu, u prvom dijelu je predstavljen osnovni koncept elektromehaničkog aktuatora (EMA) i njegov matematički model, zatim je prikazano upravljanje položajem i brzinom elektromehaničkog actuatora uporabom PID regulatora. U drugom dijelu usporedo se daje prikaz simulacija vlastite konstrukcije upravljanja položajem i brzinom pomoću PID regulatora, uporabom SIMULINK-a u MATLAB-u.Main focus of this paper is control of electromechanical actuator (EMA) for aerospace applications. Control of EMA done using position regulator and control which combine position and speed regulator is shown. The main guideline is to decrease power losses, heating and current consumption in the system. One of the important areas within the field of variable speed motor drives are the system’s operational boundaries. Presently, the operational boundaries of variable speed motor drives are set based on the operational boundaries of single speed motors, i.e. by limiting current and power to rated values. This results in under-utilization of the system, and places the motor at risk of excessive power losses. In this paper, the first part represents general concept of electromechanical actuators and mathematical modelling of the system; then the control of position and speed of electromechanical actuator (EMA) by using PID controller is presented. The second part shows simulations of our own design of control speed and position by PID controller using SIMULINK and MATLAB software

Heat generation during plunge stage in friction stir welding

This paper deals with the heat generation in the Al alloy Al2024-T3 plate under different rotating speeds and plunge speeds during the plunge stage of friction stir welding. A 3-D finite element model is developed in the commercial code ABAQUS/Explicit using the arbitrary Lagrangian-Eulerian formulation, the Johnson- Cook material law, and Coulomb's Law of friction. The heat generation in friction stir welding can be divided into two parts: frictional heat generated by the tool and heat generated by material deformation near the pin and the tool shoulder region. Numerical results obtained in this work indicate a more prominent influence from the friction-generated heat. The slip rate of the tool relative to the workpiece material is related to this portion of heat. The material velocity, on the other hand, is related to the heat generated by plastic deformation. Increasing the plunging speed of the tool decreases the friction-generated heat and increases the amount of deformation-generated heat, while increasing the tool rotating speed has the opposite influence on both heat portions. Numerical results are compared with the experimental ones, in order to validate the numerical model, and a good agreement is obtained

Comparison of various optimization criteria for actuator placement for active vibration control of smart composite beam

Position of piezoelectric actuators and sensors on a smart structure directly affects the control performances of a smart structure. In order to improve efficiency of active vibration control of a smart structure, optimization of piezoelectric actuators and sensors placement has been performed. There are various optimization criteria for optimal placement of piezoelectric actuator. The ‘state-of-the-art’ of optimization criteria is presented in [1]. The aim of this paper is to compare control effectiveness of smart composite cantilever beam, where optimal configurations of actuator-sensor pairs were found by using four optimization criteria (LQR based optimization, grammian matrices, performance index and fuzzy optimization strategy). The problem is formulated as multi-input-multi-output (MIMO) model. The beam is discretized by using the finite element method (FEM). The particle swarm optimization (PSO) method is used to find optimal configurations for each configuration

Comparison of various optimization criteria for actuator placement for active vibration control of smart composite beam

Position of piezoelectric actuators and sensors on a smart structure directly affects the control performances of a smart structure. In order to improve efficiency of active vibration control of a smart structure, optimization of piezoelectric actuators and sensors placement has been performed. There are various optimization criteria for optimal placement of piezoelectric actuator. The ‘state-of-the-art’ of optimization criteria is presented in [1]. The aim of this paper is to compare control effectiveness of smart composite cantilever beam, where optimal configurations of actuator-sensor pairs were found by using four optimization criteria (LQR based optimization, grammian matrices, performance index and fuzzy optimization strategy). The problem is formulated as multi-input-multi-output (MIMO) model. The beam is discretized by using the finite element method (FEM). The particle swarm optimization (PSO) method is used to find optimal configurations for each configuration

Heat generation during plunge stage in friction stir welding

This paper deals with the heat generation in the Al alloy Al2024-T3 plate under different rotating speeds and plunge speeds during the plunge stage of friction stir welding (FSW). A three-dimensional finite element model (FEM) is developed in the commercial code ABAQUS/Explicit using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law and Coulomb’s Law of friction. The heat generation in FSW can be divided into two parts: frictional heat generated by the tool and heat generated by material deformation near the pin and the tool shoulder region. Numerical results obtained in this work indicate a more prominent influence from the friction-generated heat. The slip rate of the tool relative to the workpiece material is related to this portion of heat. The material velocity, on the other hand, is related to the heat generated by plastic deformation. Increasing the plunging speed of the tool decreases the friction-generated heat and increases the amount of deformation-generated heat, while increasing the tool rotating speed has the opposite influence on both heat portions. Numerical results are compared with the experimental ones, in order to validate the numerical model, and a good agreement is obtained

BRACHISTOCHRONIC MOTION OF A NONLINEAR NONHOLONOMIC MECHANICAL SYSTEM MODEL

The paper analyzes the brachistochronic motion of a nonlinear nonholonomic mechanical system [1] in a horizontal plane, between two specified positions. Differential equations of motion are created based on the general theorems of dynamics. The formulated brachistochrone problem is solved applying the variational calculus. The two-point boundary value problem (TPBVP) of the system of nonlinear differential equations is solved by the shooting method. Special attention is directed to the realization of thus obtained brachistochronic motion