This paper deals with a non-linear mathematical model for simulation and analysis of a dynamic behaviour of a rotorbearing system. The model is used for the simulation of plane motion of a centre of rotor's cross-section which makes the model convenient for the analysis of vibrations generated in a rolling bearing as well as for the analysis of accuracy of the revolution of rotor supported on a rolling bearing. The model takes into account the following quantities: internal radial clearance, external radial load and unbalanced load. Differential equations of a motion are derived using Lagrange's equations. The contacts between the balls and the rings are considered to be non-linear with a stiffness derived by the Hertzian theory of an elastic contact. The proposed model enables direct determination of local contact deformations which significantly reduces needed computations and CPU time. The results obtained by the model are used to reconstruct phase-space trajectories and Poincaré maps and to calculate the largest Lyapunov exponent in order to establish the stability of rotor-bearing system motion. A computer program is developed based on the mathematical model for the simulation and analysis of a dynamic behaviour of a rotor-bearing system.

A computational fluid dynamics (CFD) model of the thermal elastohydrodynamically lubricated (EHL) line contact problem has been developed for the purpose of exploring the physical processes that occur inside a thin EHL film subjected to shearing motion. The Navier-Stokes equations are solved by using the finite volume method (FVM) in a commercial CFD software, ANSYS Fluent. A set of user-defined functions (UDF) are used for computing viscosity, density, heat source, temperature of moving surfaces and elastic deformation of the top roller according to well-established equations commonly used in the EHL theory. The cavitation problem is solved by taking into account multiphase mixture flow. The model combinations of Houpert and Ree-Eyring and of Tait and Carreau were used for modeling the non-Newtonian behavior of Squalane and the results were compared. Both rheological models suggest the existence of shear-band and plug-flow at high fluid pressure. Due to the differences in viscosity at GPa-level pressure, the chosen model has substantial influence on the computed shear stress and temperature distributions in the high-pressure region. This shows the importance of using correct rheology information in the whole range of pressure, temperature, and shear strain rate.

This paper considers the factors that influence the heat generation within ball bearing. Various lubrication regimes are taken into consideration and a mathematical model for determination of the coefficient of heat generation is set up. Due to the complexity of mathematical tools, and in order to perform better and easier analysis of the considered phenomenon, the application that integrates the mathematical models of load distribution and heat generation was developed. The impact of the contact load and angular shaft speed on the level of heat generated in radial ball bearing was analyzed.

Twist drill flute profile design is necessary in order to determine the required grinding wheel profile for a flute production. An accurate drill flute profile design is generated for two-flute conical twist drills using analytical equations to generate a drill flute profile design needed for the production of twist drills with straight lips. The required grinding wheel profile for a flute production was expressed in digitized form as well as in terms of two curve-fitted circular arcs. The drill flute profile geometry can never be precisely generated when required grinding wheel profile is represented by two circular arcs and the generated flute profile is just a very good approximation of the design flute profile. A CAD (computer aided design) software has been developed using MATLAB to determine the required grinding wheel profile for generating a given drill flute profile design.

Original scientific paper In this paper we present a model for the experimental and numerical study of helical shells. Three different forms were chosen for the experiment: Model A forms a helicoidal shell on a cylindrical shell, Model B is an annular shell on a cylindrical shell and Model C a rectangular plate on a cylindrical shell.. Placing a continuous load on the surface of the shell was achieved by normal pressure, thanks to special sealing elements within the construction of the double helical shell.The strain was measured using strain gauges. Comparable results were obtained using the ANSYS Workbench software package for analysis using the finite element method. The experimental investigation confirmed that the numerical modelling provides relevant results for the stress, deformation and deflections of continuously loaded helical shells. Keywords: displacement; FEA; helicoidal shell; radial stress Model ispitivanja helikoidalnih ljuskiIzvorni znanstveni članak U radu su predstavljeni modeli za eksperimentalno i numeričko istraživanje zavojne ljuske. Tri oblika su odabrana za eksperiment: model A predstavlja zavojnu ljusku na cilindričnoj ljuski, model B kružnu ljusku na cilindričnoj ljuski, i model C pravokutnu ljusku na cilindričnoj ljusci. Ostvarenje kontinualnog opterećenja po površini ljuske je izvršeno pomoću normalnog tlaka koga osigurava konstrukcija sa dvostrukom zavojnom ljuskom sa posebnim elementima za brtvljenje. Mjerenje naprezanja je izvršeno korištenjem mjernih traka. Usporedni rezultati su dobiveni uporabom softverskog paketa za analizu pomoću metode konačnih elemenata ANSYS Workbench. Eksperimentalna istraživanja su potvrdila da numeričko modeliranje daje mjerodavne rezultate naprezanja, deformacija i ugiba kontinualno opterećene zavojne ljuske.