B. Ulrych

Limit Operation Regimes of Actuators Working on the Principle of Thermoelasticity

Actuators working on the principle of thermoelasticity exhibit specific properties (particularly very high forces at small shifts) and may be used, for example, as prospective fixing elements in numerous industrial applications. However, huge mechanical strains and stresses in their active structural parts may lead to irreversible damage or even destruction of the whole device. This paper deals with the limit operation regimes of a typical actuator of this kind that are influenced by geometry of the device, materials, and parameters of the field current. The task is solved as a coupled problem where the electromagnetic field is supposed to be independent of the fields of the temperature and mechanical strains and stresses. On the other hand, the two last fields are solved simultaneously. The methodology is illustrated on a typical example.

Modelling of continual induction hardening in quasi‐coupled formulation

Purpose – As far as the authors know, no sufficiently complete model of continual induction hardening was developed and solved so far. The paper presents both mathematical model of the process and algorithm of its solution in the quasi‐coupled formulation.Design/methodology/approach – Computation of electromagnetic and temperature fields is based on the finite element method, while time variable boundary conditions are determined by means of an original theoretically‐empirical procedure.Findings – Substantial are backgrounds for design of the inductor and parameters of the field current as well as parameters of the cooling medium.Research/limitations/implications – The model reached a good level of accuracy validated by suitable experiments. Nevertheless, next work in the field will also have to respect history of the heating before cooling itself (the austenitizing temperature is a function of the velocity of heating). Very important is also appropriate meshing of the investigated region to suppress nume...

Optimized regime of induction heating of a disk before its pressing on shaft

The paper deals with induction heating of a metal disk before its pressing on a shaft with the aim to find the optimum parameters of its regime. The velocity and efficiency of the process is affected by the arrangement of the inductor, its position with respect to the heated disk, orientation of its windings, amplitude and frequency of the field current and material of the disk that may be ferromagnetic or nonmagnetic. The task is formulated as a weakly coupled problem. The computations are mostly carried out by the FEM-based professional programs OPERA and QuickField supplemented by special user procedures.

Modelling of induction heating and consequent hardening of long prismatic bodies

The paper deals with the problem of induction hardening of long prismatic ferromagnetic bodies. The body is first heated to the austenitizing temperature typically in a cylindrical inductor fed from a source of harmonic current and then merged into a cooling medium. In specific cases, equalisation of temperatures within the body before its cooling may also be required. The mathematical model of the induction heating consists of two non‐linear second order differential equations of the parabolic type describing the distribution of the electromagnetic and non‐stationary temperature fields while the cooling is described by the heat equation and a theoretically empirical algorithm for mapping the process of hardening. The suggested methodology partially takes into account the temperature dependencies of all material parameters. The theoretical analysis is supplemented with an illustrative example and discussion of the results. Computations have been performed by means of professional codes and single‐purpose user programs developed by the authors.

Numerical model of a thermoelastic actuator solved as a coupled contact problem

Purpose – The purpose of this paper is to investigate the parameters and operation characteristics of an actuator working on the principle of thermoelasticity whose structure was designed by the authors.Design/methodology/approach – The mathematical model of the system describes the effects of three physical fields (electromagnetic field, temperature field, and field of mechanical strains and stresses due to thermoelasticity). While the electromagnetic field was solved independently, the thermomechanical task in common with the contact problem was solved in the hard‐coupled formulation. The computations were mostly carried out by own codes.Findings – This type of actuator is characterized by extremely high forces acting in its dilatation element.Research limitations/implications – The parameters of the system may still be improved using a longer field coil and dilatation element. Attention has to be paid, however to the mechanical stability of the system. Another improvement could be achieved by suitably ...

Design of joint between disk and shaft based on induction shrink fit

The problem of fixing a disk on shaft by means of induction shrink fit is analyzed. The analysis consists of two principal parts. The first task is to propose an appropriate interference of the shaft and check the von Mises stress in the disk and shaft in acceptable operation regimes. The second task is to map the process of induction heating of the disk before its putting on the shaft (which represents a nonlinear and nonstationary coupled problem that is solved numerically, in the hard-coupled formulation). The methodology is illustrated with an example of the active wheel of a gas turbine whose results are discussed.

On a fieldless method for the computation of induction-generated heat in 3D non-ferromagnetic metal bodies

The paper deals with the mathematical and computer modeling of the induction heating of non-ferromagnetic metal bodies in harmonic electromagnetic fields. One of the main advantages of the presented method is the elimination of the surrounding air from the electromagnetic model, which strongly reduces the necessity of meshing and simplifies the computation. The task is formulated as a non-stationary quasi-coupled problem, with respect to the temperature dependencies of all important material parameters. Distribution of the eddy currents and Joule losses in the metal body is solved by a system of second-kind Fredholm integral equations. Existence and uniqueness of solution for the continuous as well as discrete problem is shown. Convergence results for the numerical scheme are presented. The theoretical analysis is supplemented with two illustrative examples.

Numerical modelling of cylindrical induction shrink fits

A complete model of a cylindrical induction shrink fit between the disk and shaft is presented. The model consists of two independent parts. The first part is aimed at the purely mechanical aspects of the shrink fit (determination of the interference between both parts necessary for transferring the prescribed torque and reduced stress in both parts for the assumed range of revolutions of the system). The second part maps the process of induction heating of the disk before its setting on the shaft. The methodology is then used for an analysis of a typical example whose results are discussed.

Combined Actuator for Accurate Setting of Position Based on Thermoelasticity Produced by Induction Heating

A novel possibility of accurate control of position is proposed, based on the thermoelastic effect. This paper presents the relevant device together with its complete mathematical model and methodology of its numerical solution. The theoretical analysis is supplemented with the description of the basic operation characteristics of the device.

Numerical simulation of electrical engineering devices: Magneto‐thermo‐mechanical coupling

Purpose – The paper seeks to present a methodology of computer simulation of coupled magneto‐thermo‐mechanical processes in various electrical engineering devices. The methodology allows determining their parameters, characteristics and behaviour in various operation regimes.Design/methodology/approach – The mathematical model consisting of three equations describing magnetic field, temperature field and field of mechanical strains and stresses (or thermoelastic displacements) is solved numerically, partially in the hard‐coupled formulation.Findings – The methodology seems to be sufficiently robust, reliable and applicable to a wide spectrum of devices.Research limitations/implications – At this stage of research, the hard‐coupled formulation of thermo‐mechanical (or thermoelastic) problems is still possible only in 2D.Practical implications – The methodology can successfully be used for design of numerous machines, apparatus and devices from the area of low‐frequency electrical engineering ranging from s...