Václav Kotlan

Numerical Model of Induction Shrink Fits in Monolithic Formulation

Induction heating-based assembly of axisymmetric shrink fits is modeled. The task represents a triply coupled evolutionary problem characterized by mutual interaction of electromagnetic field, temperature field, and field of thermoelastic displacements. Its numerical solution is performed by a fully adaptive higher-order finite element method in monolithic formulation, using a code developed by the authors. All nonlinearities of the system (magnetic permeability and temperature dependencies of all material parameters) are respected. The methodology is illustrated by a typical example whose results are discussed.

Combined heat treatment of metal materials

Purpose – The purpose of this paper is to propose and analyze a combined heat treatment of metal materials, consisting in classic induction pre-heating and/or post-heating and full heating by laser beam. This technology is prospective for some kinds of surface hardening and welding because its application leads to lowering of temperature gradients at the heated spots, which substantially reduces local residual mechanical strains and stresses. Design/methodology/approach – The task was solved like the 3D hard-coupled problem for electromagnetic field, temperature field and field of displacements. It was solved numerically using the techniques based on the FEM. For solution was used commercial software COMSOL Multiphysics, some parts were solved using own scripts in the software Agros. Findings – In the paper are shown results of the numerical solution and experimental measured data. Due the work the authors found that the influence of the pre-heating and post-heating really leads to limit the temperature g...

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.

Numerical modeling of hybrid laser welding taking into account phase change of material

Purpose This paper aims to present a three-dimensional (3D) model of hybrid laser welding of a steel plate. Before welding, the plate is pre- and/or post-heated by induction to avoid mechanical stresses in material due to high gradients of temperature. Welding itself is realized by laser beam without welding rod. The model takes into account existence of both solid and liquid phases in the weld. Design/methodology/approach Presented is the complete mathematical model of the above heat treatment process, taking into account all relevant nonlinearities (saturation curve of the processed steel material and temperature dependences of its physical parameters). Its numerical solution is realized by the finite element method. Some important results are compared with experimental data. Findings In comparison with the former model developed by the authors that did not take into account the phase change, the results are more realistic and exhibit a better accordance with measurements. On the other hand, they strongly depend on sufficiently accurate knowledge of material parameters in both solid and liquid levels (that represent the input data). Research limitations/implications The quality of calculated results strongly depends on the material properties and their temperature dependencies. In case of alloys (whose chemical composition may vary in some range), such data are often unavailable and must be estimated on the basis of experiments. Another quantity that has to be calibrated is the time dependence of power delivered by the laser beam, which is due to the production of a plasma cloud above the exposed spot. Practical implications The presented model and methodology of its solution may represent a basis for design of the complete technology of laser welding with induction pre-heating and/or post-heating. Originality/value Fully 3D model of hybrid laser welding (supplemented with pre- and/or post-heating by magnetic induction) taking into account both solid and liquid phases of welded metal and influence of the plasma cloud is presented.

Fast algorithm for evaluation of critical parameters of smart overalls

A fast and efficient algorithm is presented allowing a firefighter dressed in a smart firefighter protective suit continuously informing him about the time that he can still safely spend in a burning bulding, which is characterized by an dynamic environment of time-variable temperature. The algorithm starts from precalculated time evolution of temperature at selected places of the overall (mostly along its internal surface) for a number of values of the delivered external heat power that are then approximated by simple exponential functions. The prediction is then based on successive measurements of three or more temperatures in time and finding such a precalculated exponential function that best fits them. This function is important for predicting the maximum time of stay that is still safe for the firefighter in the current conditions.

Model of laser heating with induction pre- and post-heating and its experimental verification

Mathematical model of laser heating with induction pre- and/or post-heating is presented and solved. The purpose of this combined way of heat treatment is to reduce residual mechanical stresses in the surface layers of the processed material produced by high temperature gradients at the spots heated by the laser beam. The 3D model takes into account all important nonlinearities including the temperature dependencies of physical parameters of involved materials (such as the magnetic permeability, electric or thermal conductivity, specific heat capacity etc.). Its numerical solution is carried out by the finite element method. The methodology is illustrated with a practical example whose selected results are verified by measurements.

High-speed rotation induction heating in thermal clamping technology

The clamping technology based on high-speed induction heating of the fixing part of the system is proposed and analyzed. The continuous mathematical model of the clamping process is given by three partial differential equations (PDEs) describing the distributions of electromagnetic field, temperature field and field of thermoelastic displacements. Their coefficients containing the physical parameters of the materials are nonlinear temperature-dependent functions. The system is solved numerically in the hard-coupled formulation using a fully adaptive higher-order finite element method developed by the hp-FEM group and implemented in the application Agros2D. The methodology is illustrated with a practical example of fixing the shank of a high-revolution drilling tool in the clamping head. The results are verified by experiments.

New approach to surge phenomena analysis in transformer winding

The paper deals with very fast transient phenomena in a transformer winding connected to a transmission line. The model of this system is created as a circuit with distributed parameters and it is solved numerically using FDTD method in time domain. It results in the time-space distribution of voltage and current waves along the transmission line and the transformer winding. An influence of the line length and rate of surge wave shape was studied. The obtained results provide a deeper insight into very fast transients in the transformer winding and can be used for more advanced design of insulation and a protection system.

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.