Materiały konferencyjne, referaty (WM)
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Pozycja Ogólnopolska Konferencja Naukowa Inżynieria Materiałowa - Materiały i Technologie(Wydawnictwo Politechniki Łódzkiej, 2022) Sawicki, Jacek - Redaktor naukowyPozycja Numerical analysis of the dynamic thread stretching process(Wydawnictwo Politechniki Łódzkiej, 2022) Prążyńska, Aleksandra; Mikołajczyk, Zbigniew; Kuchar, MaciejThe subject of the paper is the analysis of the dynamic thread stretching process under extreme conditions of the excitation speed with the physical phenomena described in terms of rheological models. The analysis was carried out using three basic models relating to viscoelastic bodies, i.e. the Maxwell, Kelvin-Voigt and Standard 2 models. The relationships between the reaction forces of the stretched threads and the input parameters of the process were included both in an analytical form and in a numerical model. The theoretical analysis was related to the experimental tests carried out on polyester threads with a linear mass of 84, 110 and 334 dtex, assuming the tensile speed ranging from 0.6 to 1.5 m / s. The experiment was carried out on a custom designed test stand. In the conclusion of the obtained research, it can be stated that the most appropriate model for the description of the analysed thread stretching process is the Standard model 2 and it should be emphasized that the traditional analysis based on analytical relationships coincides with the results of numerical analysis. This proves the correctness of the adopted numerical model with specific boundary conditions.Pozycja 1D, 2D and 3D dosimetry – a brief overview of the DosLab group’s research work(Wydawnictwo Politechniki Łódzkiej, 2022) Sąsiadek-Andrzejczak, Elżbieta; Jaszczak, Malwina; Maras, Piotr; Dudek, Mariusz; Piotrowski, Michał; Kozicki, MarekDosLab is a research group from the Lodz University of Technology, Poland. The research topics carried out by the DosLab group are innovative and interdisciplinary, covering the area of textile engineering, materials engineering, radiation chemistry and medical physics. This study is intended to present an overview of the group's work related to 1D, 2D and 3D dosimetry of UV and ionizing radiation.Pozycja Investigation of wettability measurements of protective gloves materials(Wydawnictwo Politechniki Łódzkiej, 2022) Irzmańska, Emilia; Adamus-Włodarczyk, Agnieszka; Jastrzębska, Aleksandra; Litwicka, NataliaWettability measurements of the polymeric materials that are designed to be used for protective gloves are the key aspect in the evaluation of their potential safety of use. The gloves made of polymeric materials that will be resistant to chemical or biological contamination should exhibit low wettability and good adhesive properties to reduce the possibility of accumulation of hazardous substances on the surfaces of the gloves together with losing dexterity of hand movement during work. Currently, in laboratory practice, there is no method to investigate thoroughly the wetting properties of polymeric surfaces taking into consideration parameters like water permeability index, non-wettability index, and absorption index. The presented research concerns the novel way of measuring the wettability of polymeric protective gloves, and the validation of the proposed method. Based on the series of performed measurements, a thorough assessment of the uncertainty budgets for individual components of performed metrological analysis of obtained results was performed. Based on these findings, the measurement errors that could affect the reliability, repeatability, and quality of the performed investigation have been identified.Pozycja Dynamics of Energy Harvesting Mechanical System in the Vicinity of 1:1 Resonance(Wydawnictwo Politechniki Łódzkiej, 2021) Puzyrov, Volodymyr; Awrejcewicz, Jan; Losyeva, NataliyaEnergy harvesting provides a useful way to power electronic devices without using batteries or electrical wiring. Energy harvesting can be defined as the conversion of environmental energy, such as mechanical, thermal, light energies into usable electrical energy. Conventional mechanical energy harvesting devices use a line harvester to generate electricity through vibrations or other mechanical motion. However, linear generators generate significant power in a narrow band around resonance, and the power is limited by the internal damping factor and the driving force at the resonant frequency. Such devices implementing a linear (resonant) generator cannot generate sufficient specific power. In present paper the mechanical system is considered which consists of two coupled oscillators (nonlinear absorber connected with primary mass) and a piezoelectric element attached. Two goals are pursued: the mitigation of the responses of the main mass and maximizing the amount of energy extracted from vibrations. The influence of nonlinear stiffness's component is discussed. It is shown that the piezoelectric element allows the effective energy harvesting and at the same has very limited influence on reducing the amplitude of oscillations of the main mass.Pozycja Influence of a relatively high frequency structure vibrations on the dynamics of real stick-slip motion(Wydawnictwo Politechniki Łódzkiej, 2021) Olejnik, Paweł; Górniak vel Górski, Adrian; Cebulak, Maciej; Awrejcewicz, JanThe work concerns the research on the impact of structure vibrations on the dynamics of frictional contact of bodies moving in relation to each other and remaining in frictional contact, causing a stick-slip motion. A literature review was carried out, describing mainly the phenomena concerning friction, but also the dynamics of vibrations and non-ideal energy sources that induce system oscillations. In the next step an experimental station for investigation of friction equipped with a new subsystem inducing high-frequency vibrations is presented to propose a modified physical model of the investigated frictional system. After analysing the most important factors influencing the behavior of the tested system, a mathematical description was prepared, which in theory showed the potential influence of the attached subsystem on the dynamics of the movement of the tested object - the frictional connection. Various methods of implementing the unbalance of rotors, being the source of highfrequency excitation, have been considered. At the final stage, a series of measurements of the displacement of the vibrating block on the moving belt was performed with the highfrequency excitation turned on and off. The prepared graphs were used to analyse the dynamics of frictional contact and the impact of non-autonomous vibrations on the occurrence of the stick-slip phenomenon.Pozycja Determination of global damping and stiffness coefficients of journal foil bearing(Wydawnictwo Politechniki Łódzkiej, 2021) Łagodziński, Jakub; Tkacz, Eliza; Kozanecki, ZbigniewFor the few last years, in modern low-power generation systems, a demand for oilfree compressors has appeared. The development of reliable bearing technology for this relatively high-speed small turbomachinery could be crucial. In order to implement this technology more widely, a selection of the optimal design from the viewpoint of machine reliability must be conducted. A high speed turbomachinery with nominal speed of tens of thousands rpm strongly depends on the proper rotordynamic design. This is especially important when the foil bearings are taken to consideration. These compliant surface gas bearings are a class of hydrodynamic bearings that use the ambient gas as their working fluid and, thus, require no dedicated lubrication system. On the other hand, due to their relatively low damping, a designer should analyze thoroughly the dynamics of the rotor-bearing-casing system in the whole operating rpm range. A correctly operating rotor supported in foil bearings is a design solution that have wide possibilities of applications, unavailable for conventionally supported one. In the turbomachinery, a dynamic behaviour of the machine is related mostly to the stiffness and damping coefficients of system components like rotor, bearings and casing. The foil bearings, although simple in design, indicate complex behaviour resulting from Coulomb friction between their elements. This Coulomb friction affects the damping and stiffness of a given bearing support. Gas film, as a bearing part with relatively high stiffness, plays less role in the rotordynamics than the elastic structure of corrugated foils. So far, many more or less reliable numerical models of this phenomenon have been built and their experimental verification results have been described in literature. The research approach presented in this paper is different. The authors suggested obtaining the data experimentally from the bearing isolated on a test bench, where, the shaft is stationary (fixed), and the gas film is not present. The shaker excites the bearing sleeve while the damping and stiffness are provided to the system by the foil structure. The test bench can be described mathematically as system with single degree of freedom with damping and external forcing. The information collected about the bearing’s global coefficients can be implemented afterwards to the rotordynamic software as a tabular data. This will allow to prepare reliable models that will shorten the design process of newly developed compressors with these oilfree supports.Pozycja Higher order asymptotic homogenization for dynamical problems(Wydawnictwo Politechniki Łódzkiej, 2021) Awrejcewicz, J.; Andrianov, I.I.; Diskovsky, A.A.In general, asymptotic homogenization methods are based on the hypothesis of perfect scale separation. In practice, this is not always the case. The problem arises of improving the solution in such a way that it becomes applicable if inhomogeneity parameter is not small. Our study focuses on the higher order asymptotic homogenization for dynamical problems. Systems with continuous and piecewise continuous parameters, discrete systems, and also continuous systems with discrete elements are considered. Both low-frequency and highfrequency vibrations are analyzed. For low-frequency vibrations, several approximations of the asymptotic homogenization method are constructed. The influence of the boundary conditions, the system parameters is investigated.Pozycja Anisotropic friction sliding rule influence on the mechanical systems dynamics(Wydawnictwo Politechniki Łódzkiej, 2021) Wijata, Adam; Stańczyk, Bartosz; Awrejcewicz, JanAnisotropic friction can produce friction force which is not collinear with a sliding direction. How much friction deviates from a sliding direction is described with a so-called sliding potential or equivalently a sliding rule. A sliding potential is often described with an ellipse or a superellipse. In this paper we propose an oval curve which provides piecewise continuous mathematical description for a sliding rule and fits better to the experimental results than a typical superepllipse. For an exemplary mechanical system it is shown, that an anisotropic sliding potential can lead to an unstable equilibrium position in the system. Furthermore, for what parameters the unstable equilibrium occurs differs between sliding potential models. We have tested four different geometrical models of sliding potential in this regard.Pozycja Estimation the Domain of Attraction for a System of Two Coupled Oscillators with Weak Damping(Wydawnictwo Politechniki Łódzkiej, 2021) Awrejcewicz, Jan; Puzyrov, Volodymyr; Losyeva, Nataliya; Savchenko, Nina; Nikolaieva, OksanaWhen solving a wide class of problems of nonlinear dynamics, the stability property of a given system regime is a prerequisite for design. An important role is played by the concept of the domain of attraction (DoA) of the equilibrium point (or limit cycle). However, as a rule, this domain is difficult to find and describe in explicit form. Therefore, the search for DoA estimate has been a fundamental problem in the control theory since the middle of the last century. Currently, methods based on Lyapunov functions predominate in the literature. We have studied the problem of obtaining the estimates of the DoA for equilibrium of the mechanical systems. The method for using Lyapunov function of special kind for a system with polynomial right-hand side to find the estimates for DoA is proposed. This procedure is illustrated by the example of a mechanical system which consists of two coupled nonlinear oscillators with weak damping.