No abstract

Purpose -The purpose of this paper is to introduce a method for evaluating the production tolerances influence on the practically realized optimal solution of electrotechnical devices. The influence is estimated by the optimal solution range defined with a given probability. Design/methodology/approach -Because of the tolerances nature, the paper is in probabilistic categories. The accent is put on the cases when the mathematical description of the cost function is analytical, for example polynomial found on the basis of the design of experiments and response surface methodology. The optimal solution range is defined with a given probability. The governing equation is Chebychev's inequality. In some cases, Chebychev's inequality would be rather weak but the advantage is that it is valid for all kinds of probabilistic distributions. Findings -A numerical example -an electrical machine -is considered with respect to variances in the magnetic characteristics of the stator and rotor core electrotechnical steel and tolerances in the geometrical dimensions of the machine. An analytical expression for the variance of the optimal solution is obtained in the case of a second order polynomial cost function. It is found that the energetic characteristic of the realized optimal design is expected to be negligibly different from its value in the proposed optimal project. Originality/value -Although the example concerns the field of electrical machines, the methodology can be of interest for other domains and for different electrotechnical devices.

The aim of this work is the modeling of coupled electric and heat processes in a system for spot resistance welding of cross-wire reinforced steel bars. The real system geometry, dependences of material properties on the temperature, and changes of contact resistance and released power during the welding process have been taken into account in the study.The 3D analysis of the coupled AC electric and transient thermal field distributions is carried out using the finite element method. The novel feature is that the processes are modeled for several successive time stages, corresponding to the change of contact area, related contact resistance, and reduction of the released power, occurring simultaneously with the creation of contact between the workpieces. The values of contact resistance and power changes have been determined on the basis of preliminary experimental and theoretical investigations.The obtained results present the electric and temperature field distributions in the system. Special attention has been paid to the temperature evolution at specified observation points and lines in the contact area. The obtained information could be useful for clarification of the complicated nature of interrelated electric, thermal, mechanical, and physicochemical welding processes. Adequate modeling is also an opportunity for proper control and improvement of the system.

No abstract

The aim of the work is the investigation of induction heating system used for longitudinal, high frequency pipe welding.Coupled electromagnetic and temperature field distribution has been studied in order to estimate system efficiency and factors influencing the quality of the welding process and required energy. The problem was considered as three dimensional. Time harmonic electromagnetic and transient thermal field has been solved using finite element method and COMSOL 4.2 software package.