Dynamic Analysis of Flexible Structures Using Component Mode Synthesis

1989 ◽  
Vol 56 (4) ◽  
pp. 874-880 ◽  
Author(s):  
M. De Smet ◽  
C. Liefooghe ◽  
P. Sas ◽  
R. Snoeys
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Degrees Of Freedom ◽  
Flexible Structures ◽  
Element Model ◽  
Component Mode Synthesis ◽  
Mode Shapes ◽  
Flexible Robot ◽  
Preliminary Calculation ◽  
Resonance Frequencies

In this paper a dynamic model of a flexible robot is built out of a finite element model of each of its links. The number of degrees-of-freedom of these models is strongly reduced by applying the Component Mode Synthesis technique which involves the preliminary calculation of a limited number of mode shapes of the separate links. As can be seen from examples, the type of boundary conditions thereby imposed in the nodes in which one link is connected to the others, strongly determines the accuracy of the calculated resonance frequencies of the robot. The method is applied to an industrial manipulator. The reduced finite element model of the robot is changed in order to match the numerically and experimentally (modal analysis) determined resonance data. Further, the influence of the position of the robot on its resonance frequencies is studied using the optimized numerical model.

Verification of a Finite Element Model of an Unmanned Aerial Vehicle Wing Torque Box via Experimental Modal Testing

2012 ◽  
Author(s):  
Levent Unlusoy ◽  
Melin Sahin ◽  
Yavuz Yaman
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Unmanned Aerial Vehicle ◽  
Natural Frequencies ◽  
Element Model ◽  
Modal Testing ◽  
Mode Shapes ◽  
Resonance Frequencies ◽  
Aerial Vehicle ◽  
Experimental Modal Testing

In this study, the detailed finite element model (FEM) of an unmanned aerial vehicle wing torque box was verified by the experimental modal testing. During the computational studies the free-free boundary conditions were used and the natural frequencies and mode-shapes of the structure were obtained by using the MSC® Software. The results were then compared with the experimentally obtained resonance frequencies and mode-shapes. It was observed that the frequencies were in close agreement having an error within the range of 1.5–3.6%.

Quantify Resonance Inspection With Finite-Element-Based Modal Analyses

2010 ◽  
Author(s):  
K. Lai ◽  
X. Sun ◽  
C. Dasch
Keyword(s):  
Finite Element ◽  
High Stress ◽  
Mesh Size ◽  
Element Model ◽  
Sensitivity Study ◽  
Production Level ◽  
Mode Shapes ◽  
Resonance Spectroscopy ◽  
Frequency Spectra ◽  
Resonance Frequencies

Resonance inspection uses the natural acoustic resonances of a part to identify anomalous parts. Modern instrumentation can measure the many resonant frequencies rapidly and accurately. Sophisticated sorting algorithms trained on sets of good and anomalous parts can rapidly and reliably inspect and sort parts. This paper aims at using finite-element-based modal analysis to put resonance inspection on a more quantitative basis. A production-level automotive steering knuckle is used as the example part for our study. First, the resonance frequency spectra for the knuckle are measured with two different experimental techniques. Next, scanning laser vibrometry is used to determine the mode shape corresponding to each resonance. The material properties including anisotropy are next measured to high accuracy using resonance spectroscopy on cuboids cut from the part. Then, finite element model (FEM) of the knuckle is generated by meshing the actual part geometry obtained with computed tomography (CT). The resonance frequencies and mode shapes are next predicted with a natural frequency extraction analysis after extensive mesh size sensitivity study. The good comparison between the predicted and the experimentally measured resonance spectra indicate that finite-element-based modal analyses have the potential to be a powerful tool in shortening the training process and improving the accuracy of the resonance inspection process for a complex, production level part. The finite element based analysis can also provide a means to computationally test the sensitivity of the frequencies to various possible defects such as porosity or oxide inclusions especially in the high stress regions that the part will experience in service.

Finite Element Model of the Human Knee Joint to Study Tibio-Femoral Contact Mechanics

2000 ◽  
Author(s):  
Tammy Haut Donahue ◽  
Maury L. Hull ◽  
Mark M. Rashid ◽  
Christopher R. Jacobs
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Degrees Of Freedom ◽  
Soft Tissues ◽  
Element Model ◽  
Human Knee ◽  
Human Knee Joint ◽  
Solid Models ◽  
Flexion Extension ◽  
A New Technique

Abstract A finite element model of the tibio-femoral joint in the human knee was created using a new technique for developing accurate solid models of soft tissues (i.e. cartilage and menisci). The model was used to demonstrate that constraining rotational degrees of freedom other than flexion/extension when the joint is loaded in compression markedly affects the load distribution between the medial and lateral sides of the joint. The model also was used to validate the assumption that the bones can be treated as rigid.

scholarly journals Dynamic Analysis of Tapered Thin-Walled Beams Using Spectral Finite Element Method

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Yiping Shen ◽  
Zhijun Zhu ◽  
Songlai Wang ◽  
Gang Wang
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Wind Turbine ◽  
Element Model ◽  
Rotor Blades ◽  
Mode Shapes ◽  
Modal Frequency ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
Spectral Finite Element

Tapered thin-walled structures have been widely used in wind turbine and rotor blade. In this paper, a spectral finite element model is developed to investigate tapered thin-walled beam structures, in which torsion related warping effect is included. First, a set of fully coupled governing equations are derived using Hamilton’s principle to account for axial, bending, and torsion motion. Then, the differential transform method (DTM) is applied to obtain the semianalytical solutions in order to formulate the spectral finite element. Finally, numerical simulations are conducted for tapered thin-walled wind turbine rotor blades and validated by the ANSYS. Modal frequency results agree well with the ANSYS predictions, in which approximate 30,000 shell elements were used. In the SFEM, one single spectral finite element is needed to perform such calculations because the interpolation functions are deduced from the exact semianalytical solutions. Coupled axial-bending-torsion mode shapes are obtained as well. In summary, the proposed spectral finite element model is able to accurately and efficiently to perform the modal analysis for tapered thin-walled rotor blades. These modal frequency and mode shape results are important to carry out design and performance evaluation of the tapered thin-walled structures.

Dynamic Characteristics and Finite Element Model Updating of Micromachined Torsion Structures

2013 ◽  
Vol 284-287 ◽  
pp. 1831-1835
Author(s):  
Wei Hsin Gau ◽  
Kun Nan Chen ◽  
Yunn Lin Hwang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Finite Element Model ◽  
Model Updating ◽  
Speckle Pattern ◽  
Element Model ◽  
Mode Shapes ◽  
Electronic Speckle Pattern Interferometry ◽  
Finite Element Model Updating ◽  
Element Analysis

In this paper, two experimental techniques, Electronic Speckle Pattern Interferometry and Stroboscopic Interferometry, and two different finite element analysis packages are used to measure or to analyze the frequencies and mode shapes of a micromachined, cross-shaped torsion structure. Four sets of modal data are compared and shown having a significant discrepancy in their frequency values, although their mode shapes are quite consistent. Inconsistency in the frequency results due to erroneous inputs of geometrical and material parameters to the finite element analysis can be salvaged by applying the finite element model updating procedure. Two updating cases show that the optimization sequences converge quickly and significant improvements in frequency prediction are achieved. With the inclusion of the thickness parameter, the second case yields a maximum of under 0.4% in frequency difference, and all parameters attain more reliable updated values.

Comparing Measured Responses of an Offshore Structure with Operational Modal Analysis assisted Classical Model Approach

2020 ◽  
pp. 1-10
Author(s):  
Bruna Nabuco ◽  
Sandro D. Amador ◽  
Evangelos I. Katsanos ◽  
Ulf T. Tygesen ◽  
Erik Damgaard Christensen ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Modal Analysis ◽  
Element Model ◽  
Operating Conditions ◽  
Operational Modal Analysis ◽  
Mode Shapes ◽  
Wave Forces ◽  
Wave Load ◽  
Offshore Structure

Abstract Aiming to ensure the structural integrity of an offshore structure, wave-induced responses have been measured during normal operating conditions. Operational Modal Analysis is applied to the data obtained from continuously monitoring the structure. Sensors placed only on the topside of an offshore platform are sufficient to provide information to identify the modal properties of the structure, such as natural frequencies, damping ratios, and mode shapes. A finite element model is created and updated in line with the identified dynamic properties for applying a modal expansion technique in the interest of accessing information at any point of the structure. Wave radars are also placed at the platform from which the wave forces are calculated based on basic industrial standard models. In this way, the wave kinematics are estimated according to the linear wave theory associated with Wheeler stretching. Since this study is related to offshore structures composed by slender elements, the wave forces are estimated using Morison formulation. By assigning typical values to the drag and inertia coefficients, wave loads are estimated and applied to the updated finite element model. For the diffraction effect, the wave load has also been evaluated according to MacCamy and Fuchs theory. The responses obtained from this procedure are compared with measured responses. In addition to describing the process, this paper presents a case study to verify the theory using monitoring data from a tripod jacket. Results indicate realistic response estimation that contributes to the knowledge about the state of the structure.

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