Lukáš Koudela

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.

Modeling of loudspeaker using hp-adaptive methods

Numerical modeling of harmonic acoustic field produced by a common commercial loudspeaker is carried out. The goal is to obtain the directional characteristic of the device. So far, these characteristics could only be obtained by measurements, which was very complicated and also expensive. Another benefit of the model consists in obtaining a reference mathematical model for other acoustic devices, such as diffusors or resonators. The continuous mathematical model is derived from the physical laws and is considered for the ideal fluids with properties of a perfect continuum. The model of the loudspeaker in the axial symmetry (2D) is described by the Helmholtz differential equation for harmonic acoustic field and for the correct solution the appropriate boundary conditions and material properties are also defined. The task is solved numerically by a fully adaptive higher-order finite element method developed by the hp-FEM group. The convergence of results is discussed for the different adaptive techniques and the advantages of the use of

Numerical analysis for reducing negative impact of power transformers on the environment

hp

Numerical calculation and experimental verification of forces during regulation of permanent magnet

-adaptivity are demonstrated. Selected results of the computations are then compared with experiments performed in an anechoic chamber at the University of West Bohemia and based on the standard CSN EN 60268-5.

Surge phenomena in system of transmission line and transformer winding

Purpose The paper aims to deal with shape optimization of a novel thermoelastic clutch working on the principle of induction heating. The clutch consists of a driving part, with a ferromagnetic ring, and a driven part. The driving part rotates in a static field produced by appropriately arranged static permanent magnet. Currents induced in the rotating ferromagnetic ring cause its temperature to rise and increase its internal and external radii. As soon as its external diameter reaches the diameter of head of the driven part, it starts also rotating because of mechanical friction between both parts. Design/methodology/approach Presented is the complete mathematical model of the device, taking into account all relevant nonlinearities (saturation curve of the processed steel material and temperature dependences of its physical parameters). The forward solution is realized by the finite element method, and the shape optimization is solved using heuristic algorithms. Findings The clutch was found to be fully functional and may be used in applications with limited access into the device. Research limitations/implications The coefficient of expansion of material of the driven part must be substantially lower than the same coefficient of the driving part to keep the necessary friction torque. The clutch can be only used in applications where higher temperatures (such as 300°C) are not dangerous to the environment. Practical implications The presented model and methodology of its solution may represent a basis for design of devices for transfer of generally mechanical forces and torques. Originality/value This paper presents an idea of induction-produced thermoelastic connection of two parts capable of transferring mechanical forces and torques.

Numerical modeling of transient acoustic field using finite element method

The goal of this paper is to present a methodology for numerical analysis of 3D numerical model of a transformer for reducing negative noise impact on the environment. The task is to map structural dynamics and vibrations of its selected parts. The main aim of this paper is to describe the numerical analysis of natural frequencies and demonstrate the impact of transformer construction in three-phase transformer core. The model taking into account the real arrangement of the device is solved numerically by the finite element method. All results are compared with experimental measurement on a real device.

Monolithic model of induction shrink fit for high-speed tools

Thermal clamping of high-speed machine tools is modeled. The process is based on induction heating of rotating clamping head in static magnetic field produced by suitably arranged permanent magnets fixed in magnetic circuit. The mathematical model of the process consists of three mutually coupled partial differential equations that are solved numerically in the monolithic formulation. All important material nonlinearities are taken into account. Selected results are verified experimentally on a laboratory model of the device.

Numerical modeling of sound propagation in anechoic chamber with Quadratic Residue Diffuser

Many technical applications (manipulators, actuators, clamping devices, etc.) take advantage from the fact that the magnetic field strength and thus magnetic holding force of permanent magnets may temporarily be affected (decreased or increased) by suitably oriented external magnetic field. This field is usually generated by an appropriate direct current carrying coil. In this paper, this fact is quantified by numerical analysis and the results are verified by experimental measurement on a real device. The particular attention is given to the dependence of the holding force of the permanent magnet on the excitation current.