Iulian Lupea

Modeling, design, and characterization of multisegment cantilevers for resonant mass detection

The work presents the analytic modeling, design, and the experimental and numerical characterization of multisegment cantilevers’ bending and torsion resonant responses with the aim of evaluating the amount and position of matter which deposits on these elastic structures. The cantilevers may comprise any number of geometrically different segments that are serially connected, and actual results are presented for the two-segment, circularly notched configuration. The generic analytical model, which formulates the bending and torsion resonant frequencies of both the original cantilever and the one with the attached mass, is derived by means of Rayleigh’s quotient approach. Relationships are formulated between nondimensional parameters characterizing the geometry, resonant frequencies, and deposited mass amount and position for both bending and torsion. The sensitivity of the frequency shift to the landing parameters and mass amount are also studied. Analytical model, finite element, and experimental testing...

Fatigue Calculation of a Car Component Subjected to Random Vibrations

In this article, a random vibration simulation approach applied to a car component is presented. The main vibration sources which appear in the automotive body are mentioned as input for random analysis. By using finite element analysis, one can estimate the response of the structure in terms of the probability of the maximum displacement and stress. The normal distribution function was used in the analysis for the statistical interpretation of the results. By using the random vibration simulation method, the response of a structure excited by random vibrations can be estimated, with a good precision for various applications. The resulted stress it is used to perform fatigue evaluation by using Palmgren Miner method.

Random Excitation of a Car Component from the Road

In the present paper aspects regarding the analytical modeling, the simulation and the experiments related to random vibrations, with applications to automotive industry, are discussed. Simplified car dynamical models based on lumped masses, springs and dampers being exposed to random vibrations, are considered. The power spectral density is used to define the excitation produced by the unevenness of the road surface which are correlated to the vehicle speed. Two different approaches are observed in parallel. The analytical one is using the dynamical model of the car, the random excitation estimation, the transfer functions from the excitation sources to the target, and the response at the comfort points or the points of interest. The associated numerical calculations are performed with Matlab. For the second approach the finite element models of the car simplified structure are created and the simulations are performed. Statistical tools are used to describe the excitation sources and the response. Good correlation of the results for the two approached is observed. In the sequel a real car component made of plastic is considered. The estimation of the component structure stress with probability of 1σ, 2σ and 3σ, are coming out from the simulation of the part subjected to random vibrations by using finite element analysis. Frequency response functions (FRF) are experimentally measured in the laboratory by placing the plastic component on a shaker. The measured FRFs and the results are compared to the ones resulted from the simulation, observing a good correlation. The output of the random vibration analysis can be used to estimate the fatigue of the component.

Troubleshooting Technics to Identify the Airborne and Structure-Borne Noise Content inside an Electric Vehicle

An electric vehicle was subjected to on-road acoustic tests. A specific high frequency tone was perceived in a sound field dominated by wind and road noise. The car was instrumented with microphones which measured the noise inside the passenger compartment and with tachometers to record the motors rotational velocity with respect to time. Waterfall diagrams were generated by tracking the spectrums of noise from fixed time samples against the rpm of the motor. The analysis of the diagrams revealed that high orders, like the 24th and 48th were responsible for the sound. These orders represent the acoustic response of the electromagnetic interaction between the stator and the rotor of the electric motor. To analyze the propagation of noise from the source (motor) to the target (driver), a transfer path analysis (TPA), respectively an airborne source quantification (ASQ) were proposed. The TPA focused on the structure borne noise generated by the forces transmitted into the body through the powertrain supports, and the ASQ, on the airborne noise radiated by the surface of the motor and gearbox casing. The conclusion was that the airborne noise is the main contributor to the total pressure level in the passenger compartment, but at lower speeds a strong structure borne noise content is present.

Macro and Nano Serially-Compounded Cantilevers for Resonance-Shift Mass Detection

Detecting extraneous matter that deposits on a compliant receiver platform can be performed by means of the resonance shift method, whereby the original and altered natural frequencies of the host structure are compared to evaluate the amount and/or position of the attached matter. By scaling structural dimensions down to the nanometer range, it becomes possible to discern quantities in the molecular realm. One simple and convenient structural detector is the cantilever, whose out-of-the-plane resonant vibrations can be excited/monitored with relative ease. The proposed paper studies a few aspects of the mass attachment detection through monitoring of the natural frequency change of cantilevers, by focusing on the two ends of the dimensional spectrum: the macro- and nano-scale domains. The paper develops an analytical model that enables predicting the mass of attached matter in case its location is point-like and pre-specified. At nano-scale, locating mass attachment is realized through adequate surface functionalizing, while at macro-scale a displacement sensor can be placed conveniently on the compliant structure. The model accommodates cantilever configurations formed of several single-profile segments that are serially connected. Of all possible combinations, the two-segment, circularly-notched design is explicitly studied. Finite element simulation is utilized to check the analytical model validity. The bending natural frequencies of several macro-scale and nano-scale circularly-notched cantilever specimens have been investigated experimentally. Based on the agreement between analytical, numerical and experimental data, the analytical model was further utilized to study the relationships between geometric parameters, deposited mass, mass attachment position and the change in the bending resonant frequency.Copyright