# Wydział Mechaniczny / Faculty of Mechanical Engineering / W1

Stały URI zbioruhttp://hdl.handle.net/11652/1

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56 wyniki

## Wyniki wyszukiwania

Pozycja Mathematical modelling and investigations of the hexapod robot(Wydawnictwo Politechniki Łódzkiej, 2016) Awrejcewicz, Jan; Grzelczyk, Dariusz; Stańczyk, BartoszLegged locomotion is the most common locomotion form in nature which is used by numerous animal species in order to move on the Earth. It motivated and became the inspiration for many researchers for the construction of walking machines which belong to the most important group of mobile robots met in engineering applications. There are numerous examples of both biological inspirations and constructed prototypes of multi-legged robots (including hexapod robots) investigated. Interesting state-of-the-art in this area can be found in papers . In particular, in reference a summary of biological paragon from nature, methods of investigations of legged locomotion and the constructed multi-legged robots are presented and discussed.Pozycja Guidance of the resonance energy flow in the mechanism of coupled magnetic pendulums(Elsevier, 2022) Pilipchuk, Valery N.; Polczyński, Krystian; Bednarek, Maksymilian; Awrejcewicz, JanThis paper presents a methodology of controlling the resonance energy exchange in mechanical system consisting of two weakly coupled magnetic pendulums interacting with the magnetic field generated by coils placed underneath. It is shown that properly guided magnetic fields can effectively change mechanical potentials in a way that the energy flow between the oscillators takes the desired direction. Studies were considered by using a specific set of descriptive functions characterizing the total excitation level, its distribution between the pendulums, and the phase shift. The developed control strategies are based on the observation that, in the case of antiphase oscillation, the energy is moving from the pendulum subjected to the repelling magnetic field, to the oscillator under the attracting field. In contrast, during the inphase oscillations, the energy flow is reversed. Therefore, closed-loop controller requires only the information about phase shift, which is easily estimated from dynamic state signals through the coherency index. Advantage of suggested control strategy is that the temporal rate of inputs is dictated by the speed of beating, which is relatively slow compared to the carrying oscillations.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 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.Pozycja Dynamic analysis of functionally graded sandwich shells resting on elastic foundations(Wydawnictwo Politechniki Łódzkiej, 2021) Tetyana, Shmatko; Lidiya, Kurpa; Awrejcewicz, JanFree vibrations of sandwich shallow shells resting on elastic foundations are investigated. It is assumed that shell consists of three layers of the different thickness. Different schemes of arrangement of layers are considered. Namely, the core is made of ceramics or metals , and the upper and lower layers are made of FGM. The volume fractions of metal and ceramic are described by the power law. Shear deformation shell theory of the first (FSDT) that includes interaction with elastic foundations is applied. To study shells with an arbitrary plan form the R-functions theory combined with the variational Ritz method are used. Validation of the proposed method and developed software has been examined on test problems for FG shell with rectangular plan form. New results for shallow shells with complex plan form were obtained. Effects of the power law index, boundary conditions, thickness of core and face sheet layers, elastic foundations on fundamental frequencies are studied in this work.Pozycja Construction and 3D model of stand for investigating a non-ideal forcing in a nonlinear chain dynamics of self-excited oscillators with friction(Wydawnictwo Politechniki Łódzkiej, 2021) Rogala, Patryk; Olejnik, Paweł; Awrejcewicz, JanThe research involves application and research on a non-ideal forcing to modelling and identification of vibrating systems with friction. It is still an innovative approach in the numerical analysis of vibrations of mechatronic machines and devices. This will allow to make a much real numerical modelling and more efficient identification of nonlinear dynamic phenomena observed in vibrating systems with friction, and thus, a better modelling of such phenomena in computer programs. To obtain the goal, initial 3D model of the mechanical stand was made in the CAD software. Based on the 3D model, real stand will be built, and experiments will be held to obtain data that will be necessary to ensure correctness of the mathematical model, which also will be studied and developed.Pozycja Mathematical Modelling of an extended Swinging Atwood Machine(Wydawnictwo Politechniki Łódzkiej, 2021) Yakubu, Godiya; Olejnik, Paweł; Awrejcewicz, JanAn extended model for a variable-length pendulum’s mechanical application is being derived from the Swinging Atwood Machine (SAM). An electrical component consisting of an electromagnet and armature coil is attached on the link connected to the counterweight mass on the left-hand side of the modified SAM to provide an excitation force for the system when an electric current is induced. The extended SAM presents a novel SAM concept being derived from a variable-length double pendulum with a suspension between the two pendulums. The equations of motion are simulated to see the trajectory of the two pendulums. The results of original numerical simulations show some compact regions of attraction at some regimes. Therefore, the extended SAM’s nonlinear dynamics presented in the current work can be thoroughly studied, and more modifications can be achieved. The new technique can reduce residual vibrations through damping when the desired level of the crane is reached. It can also be used in simple mechatronic and robotic systems.Pozycja Geometrically nonlinear vibrations of double-layered nanoplates(Wydawnictwo Politechniki Łódzkiej, 2021) Awrejcewicz, Jan; Mazur, OlgaThe geometrically nonlinear vibrations of simply supported double-layered graphene sheet systems are considered in the presented manuscript. The interaction between layers is taken into account due to van der Waals forces. The investigation is based on the nonlocal elasticity theory, Kirchhoff plate theory and von Kármán theory. The governing equations are used in mixed form by introducing the stress Airy function. The analytical presentation of the nonlinear frequency ratio for in-phase vibration and anti-phase vibration modes is presented. It is shown that the nonlocal parameter included in the compatibility equation can significantly change the vibrating characteristics.