Development of algorithms in open-source Elmer FEM for frequency response and biased modal analysis of MEMS cantilever

2021 ◽  
Vol 20 (2) ◽  
pp. 1020-1031
Author(s):  
Serdar Tez ◽  
Mehmet Kaya
Keyword(s):  
Frequency Response ◽  
Modal Analysis ◽  
Open Source

scholarly journals Simulation of the frequency response of the ERC 1400 Bucket Wheel Excavator boom, during the excavation process

2019 ◽  
Vol 2 (1) ◽  
pp. 153-167
Author(s):  
Florin Dumitru Popescu ◽  
Sorin Mihai Radu ◽  
Andrei Andraș ◽  
Ildiko Kertesz Brînaș
Keyword(s):  
Frequency Response ◽  
Modal Analysis ◽  
High Variability ◽  
Response Analysis ◽  
Virtual Model ◽  
Frequency Response Analysis ◽  
Existing Structures ◽  
Excavation Process ◽  
Simulation Based ◽  
Cyclical Variability

Abstract The paper deals with the modal analysis and frequency response analysis of a bucket wheel excavator (BWE) boom, obtained by simulation, based on a virtual model of an existing BWE boom. The boom, which generally is realized as a spatial truss, is the most vulnerable subsystem of the BWE, being submitted to severe operational loads characterized by very pronounced cyclical, dynamic and stochastic variability. This vulnerability is the consequence of its shape and constructive parameters and the nature, source and character of the external exciting loads to which it is exposed. The classical approach recommended by standards and norms cannot predict the occurrence of failures caused by vibration, which produces fatigue due to the load’s cyclical variability and the deformation produced by resonant vibration of some constitutive elements. As exciting load we considered the operational forces acting on the bucket wheel. In this manner we can take into account the constructive features – with modal analysis, and the vibration regime – with frequency response analysis. The proposed method is useful both in the design phase of new load-bearing structures of truss type subjected to high-variability forces, and also in refurbishment or improvement phases of the existing structures of this kind.

Influence of Tip Shroud Modeling on the Flutter Stability of a Low Pressure Turbine Rotor

2019 ◽  
Author(s):  
Lorenzo Pinelli ◽  
Federico Vanti ◽  
Andrea Arnone ◽  
Benjamin Beßling ◽  
Damian M. Vogt
Keyword(s):  
Modal Analysis ◽  
Open Source ◽  
Linear Method ◽  
Turbine Blades ◽  
Low Pressure ◽  
Turbine Rotor ◽  
Contact Interface ◽  
Aerodynamic Damping ◽  
Low Pressure Turbine ◽  
Tip Shroud

Abstract Since the modern design trend of low pressure turbine blades for aeronautical propulsion leads to lighter and more loaded blades, thus prone to flutter induced vibrations; flutter assessment is now a standard verification within the design loop of these components. Flutter stability assessment requires FEM and CFD tools able to predict the pressure response of fluid flow due to blade oscillation in order to compute the aerodynamic damping. Such tools are mature and validated, yet some geometrical aspects of the blade-row as contact interfaces at the blade tip shroud have to be carefully simulated to obtain accurate flutter results. The aim of this paper is to demonstrate the capability of the Open Source FEM tool (CalculiX) to deal with complex interlocked rotor geometries when performing modal analysis and to show the influence of different contact interface modeling on flutter stability. The solid mesh of a single-pitch row sector has been generated by using the Open Source suite Salome and the modal analysis has been carried out with CalculiX with cyclic symmetry conditions. The following uncoupled flutter simulations have been performed with the CFD TRAF code, an in-house solver developed at the University of Florence, which implements a non-linear method for flutter evaluation. An in-depth comparison among the FEM models with different boundary conditions in terms of mode shape frequency and aerodynamic damping curves are reported. These results show the effect of different contact interface models, especially on the first bending mode family, and confirm the overall row stability detected during a dedicated experimental flutter campaign.

scholarly journals Cepstrum-based damage identification in structures with progressive damage

2018 ◽  
Vol 18 (1) ◽  
pp. 87-102 ◽  
Author(s):  
Ulrike Dackermann ◽  
Wade A Smith ◽  
Mehrisadat Makki Alamdari ◽  
Jianchun Li ◽  
Robert B Randall
Keyword(s):  
Frequency Response ◽  
Modal Analysis ◽  
Response Function ◽  
Principle Component Analysis ◽  
Frequency Response Function ◽  
Component Analysis ◽  
Operational Modal Analysis ◽  
Progressive Damage ◽  
Response Functions ◽  
Principle Component

This article aims at developing a new framework to identify and assess progressive structural damage. The method relies solely on output measurements to establish the frequency response functions of a structure using cepstrum-based operational modal analysis. Two different damage indicative features are constructed using the established frequency response functions. The first damage feature takes the residual frequency response function, defined as the difference in frequency response function between evolving states of the structure, and then reduces its dimension using principle component analysis; while in the second damage indicator, a new feature based on the area under the residual frequency response function curve is proposed. The rationale behind this feature lies in the fact that damage often affects a number of modes of the system, that is, it affects the frequency response function over a wide range of frequencies; as a result, this quantity has higher sensitivity to any structural change by combining all contributions from different frequencies. The obtained feature vectors serve as inputs to a novel multi-stage neural network ensemble designed to assess the severity of damage in the structure. The proposed method is validated using extensive experimental data from a laboratory four-girder timber bridge structure subjected to gradually progressing damage at various locations with different severities. In total, 13 different states of the structure are considered, and it is demonstrated that the new damage feature outperforms the conventional principle component analysis–based feature. The contribution of the work is threefold: first, the application of cepstrum-based operational modal analysis in structural health monitoring is further validated, which has potential for real-life applications where only limited knowledge of the input is available; second, a new damage feature is proposed and its superior performance is demonstrated; and finally, the comprehensive test framework including extensive progressive damage cases validates the proposed technique.

Newton’s Third Law is not a Dogma but a Computational Hypothesis

2020 ◽  
pp. 36-50
Author(s):  
S.V. Arinchev
Keyword(s):  
Frequency Shift ◽  
Frequency Response ◽  
Modal Analysis ◽  
Structural Model ◽  
Particle Interaction ◽  
Experimental Modal Analysis ◽  
Vibration Machine ◽  
Amplitude Frequency Response ◽  
Third Law ◽  
Shift Effect

Experimental modal analysis is an important stage in the development of a flying vehicle structure. In the experiment, the eigenfrequency of the structure is identified by a corresponding resonance peak of its amplitude-frequency response characteristic. Different sensors in the vibration machine provide different amplitude-frequency response characteristics. The resonance peaks obtained through different sensors for one and the same eigenfrequency of the structure are located with a frequency shift of approximately 1 Hz. This frequency-shift effect is an obstacle for the experimental modal analysis of structures with closely located oscillation modes. This paper explains the frequency-shift effect using the particle approach. A particle is a point mass, and a structure is a system of particles connected by springs, with each particle associated with its own structural model. Each particle has a “right” for its own resonance and “lives” in its own parallel reality. Each particle is associated with an acceleration sensor. The number of simultaneously considered models is equal to the number of sensors. The obtained modal-analysis results are related only to the corresponding particle. Newton’s third law of the particle interaction is not used in full when assessing the particles’ interaction. The action and reaction forces are still applied to different particles along the same line in the opposite directions, but these forces are different. Modal-analysis simulation is limited to the 2-DOF and the 3-DOF oscillation models.

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