Structural dynamics is an essential aspect of mechanical engineering and a key module in the master's program in automotive engineering at the Universidad Autónoma de Nuevo León. Since this ...discipline requires a strong theoretical foundation coupled with significant practical application, it is essential to provide students with the necessary tools and content to gain a comprehensive understanding of the subject through engaging and applied case studies. This article presents the teaching methodology of a structural dynamics course, incorporating practical real-world cases that cover the most crucial components of the syllabus. Simulation tools and numerical analysis are applied through the course as support. Additionally, experimental activities are designed to complement the theoretical knowledge, ranging from simple student-conducted experiments to more complex laboratory activities involving specialized equipment and real-life field measurements. The discussion highlights how this approach is more engaging and practical for students, aiding their comprehension and application of theoretical concepts.
While data-driven model reduction techniques are well-established for linearizable mechanical systems, general approaches to reducing nonlinearizable systems with multiple coexisting steady states ...have been unavailable. In this paper, we review such a data-driven nonlinear model reduction methodology based on spectral submanifolds. As input, this approach takes observations of unforced nonlinear oscillations to construct normal forms of the dynamics reduced to very low-dimensional invariant manifolds. These normal forms capture amplitude-dependent properties and are accurate enough to provide predictions for nonlinearizable system response under the additions of external forcing. We illustrate these results on examples from structural vibrations, featuring both synthetic and experimental data.
This article is part of the theme issue ‘Data-driven prediction in dynamical systems’.
•Radial internal clearance in self-aligning ball bearings is studied,•The optimal radial clearance is looked for,•Recurrence-based methods are applied for the analysis of acceleration time ...series,•The sensitivity analysis for recurrence quantificators is conducted,•3 recurrence quantificators show high sensitivity to the change of radial clearance.
In this work, we present a quantitative and qualitative analysis of the dynamic response of ball bearings dependent on radial internal clearance. We measured the vibrations of a rotating system based on self-aligning ball bearings for different clearances and rotating speeds. The analysis of vibration spectra was conducted considering a set of different recurrence indicators in order to describe the response of the bearing to the optimal clearance. It comes out that indicators have different sensitivity to the changes of the internal clearance. Few quantificators, i.e. entropy, trapping time, and recurrence period density entropy demonstrate the highest sensitivity to the change of radial clearance. The proposed quantificators are useful for real-time monitoring of operating clearance.
Weakly damped mechanical systems under small periodic forcing tend to exhibit periodic response in a close vicinity of certain periodic orbits of their conservative limit. Specifically, ...amplitude-frequency plots for the conservative limit have often been noted, both numerically and experimentally, to serve as backbone curves for the near resonance peaks of the forced response. In other cases, such a relationship between the unforced and forced response was not observed. Here, we provide a systematic mathematical analysis that predicts which members of conservative periodic orbit families will serve as backbone curves for the forced–damped response. We also obtain mathematical conditions under which approximate numerical and experimental approaches, such as energy balance and force appropriation, are justifiable. Finally, we derive analytic criteria for the birth of isolated response branches (isolas) whose identification is otherwise challenging from numerical continuation.
•A rope-spun rotor is proposed to convert low-frequency vibrations to rotation motion.•High-speed rotation is achieved by the rotor under ultralow-frequency vibrations.•A harvester with the rotor ...generates high power under ultralow-frequency excitations.•8-minute running of the harvester sustains 60-minute operation of a wireless sensor.•Three electronics are simultaneously operated by the harvester as tapped by hand.
Ultralow-frequency kinetic energy mainly in the form of vibrations is omnipresent in the environment, but its effective exploitation remains a challenge. To tackle this problem, this paper presents a rope-spun rotor structure to transform ultralow-frequency vibrations/linear motions to rapid rotations through a piece of rope. The superior performance of the rotor is demonstrated by applying it to electromagnetic energy harvesting from ultralow-frequency vibrations and irregular human body motions. When the rope-spun rotor based harvester is periodically pushed down 10.5 mm at 1.5 Hz, it produces 9.7 mW electric power. When embedded in a shoe insole, the harvester delivers 8 mW power to a matched load as a male participant walks with the shoe at 6.5 km/h. When positioned under a piece of floorboard, the harvester can charge a supercapacitor (220 mF) from 0 to 3.5 V within 8 min. The harvester can also sustain the continuous operation of multiple electronics simultaneously by scavenging energy from gentle finger tapping motions. This study demonstrates a new mechanism for realizing vibration-to-rotation conversion and a promising way for efficient harvesting of ultralow-frequency energy.
The paper presents the results of the bench tests to measure mechanical vibrations of a new aircraft opposed piston engine with reciprocating pistons. The PLZ-100 engine is a three-cylinder, ...six-piston, two-shaft drive unit with a two-stroke diesel cycle. This type of engine is dedicated for powering light aircraft, e.g. autogyros. The tests were carried out on a test bench at the Lublin University of Technology. The engine was loaded with constant torque, for several fixed values of rotational speed of a crankshaft. The angle of the start of diesel injection was changed for each of the rotational speeds. The mechanical vibrations that accompanied the operation of this drive unit were recorded with three measurement transducers and a National Instruments conditioning system. Each of the transducers was mounted on a different axis of the engine. The signals were analyzed from their courses with the DIAdem software. The results were the courses of effective speed and vibration acceleration to conduct a vibration-acoustic evaluation of the PLZ-100, detect and prevent various types of defects or failures.
In this paper, the principal time-domain system identification methods are studied and used to carry out the experimental modal analysis of a single-link flexible manipulator with curved geometry in ...a comparative fashion. The identification process carried out in this study is aimed at deriving first-order state-space dynamical models and second-order configuration-space dynamical models of the single-link flexible manipulator by using an array of fundamental system identification procedures, which includes the ARX (AutoRegressive eXogenous method), SSEST (State-Space ESTimation method), N4SID (Numerical Algorithm for Subspace State-Space System Identification), ERA/OKID (Eigensystem Realization Algorithm combined with the Observer/Kalman Filter Identification method), and TFEST (Transfer Function ESTimation method) methods. The main goal of this paper is, therefore, to perform a comparative study between the most fundamental system identification procedures applied to the numerical and experimental analysis of the structural vibrations of a flexible manipulator having a curved geometric shape. First, this paper poses the theoretical foundations for the development of the numerical study and the experimental testing to be performed for the case study. Subsequently, the flexible manipulator analyzed in this work is modeled with various levels of complexity, which range from a simple lumped parameter model to a linear finite element model developed by integrating the interconnections between the SOLIDWORKS and ANSYS software. By doing so, the computational procedures applied to the time-domain experimental measurements of the dynamic behavior of the flexible manipulator allow for reconstructing first-order and second-order mechanical models of the structural system of interest in the MATLAB simulation environment. The numerical results and the experimental tests reported in this investigation demonstrate the effectiveness of all the time-domain system identification approaches considered in the paper.
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