A Performance Study of Controlled Impact Timing on Harmonics Reduction in Operational Modal Testing

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Hong Cheet Lim ◽  
Zhi Chao Ong ◽  
Zubaidah Ismail ◽  
Shin Yee Khoo
Keyword(s):  
Modal Analysis ◽  
Modal Testing ◽  
Mode Shapes ◽  
Performance Study ◽  
Modal Assurance Criterion ◽  
Structural Dynamic ◽  
Impact Device ◽  
Load Component ◽  
Phase Angles ◽  
The Impact

As an alternative to operational modal analysis and classical experimental modal analysis (EMA), a novel method was introduced previously, namely impact-synchronous modal analysis (ISMA). The effectiveness ISMA on rotor and structural dynamic systems has been proven in previous literature. More recently, an automated impact device (AID) was introduced which utilized tachometer pulse as initiation signal and its effectiveness on ISMA was proven. An attempt to further enhance this device in term of equipment and cost is then proposed by replacing the tachometer with the in-use tri-axial accelerometer through utilizing the filtered response of cyclic load component as an initiation signal to control the impact device, which is also the primary aim for this study. Prior to modal testing, accuracy of this device is illustrated at desired phase angles of 0 deg, 90 deg, 180 deg, and 270 deg. Subsequently, frequency response function (FRF) estimations obtained for ISMA using enhanced AID has demonstrated the suppression capabilities of this device on disturbances, i.e., reduction of 93.58% at 30 Hz and 57.78% at 60 Hz, resulting in a high correlation for signature assurance criterion (SAC) and cross signature assurance criterion (CSAC). Modal parameters extracted from the EMA and ISMA using impact device are presented and compared, for the first three natural modes of the test rig. It is found that natural frequencies are deviating by less than 6%, whereas modal assurance criterion (MAC) values between the mode shapes of the two tests are found to be above 0.9.

Investigation of Impact Profile and Isolation Effect in Automated Impact Device Design and Control for Operational Modal Analysis

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Z. C. Ong ◽  
C. C. Lee
Keyword(s):  
Modal Analysis ◽  
Isolation Effect ◽  
Time Averaging ◽  
Impact Device ◽  
Lack Of Information ◽  
Analysis Technique ◽  
And Control ◽  
Phase Angles ◽  
Synchronous Time

A novel modal analysis technique called impact-synchronous modal analysis (ISMA) was introduced in previous research. With the utilization of impact-synchronous time averaging (ISTA), this modal analysis can be performed in presence of ambient forces whereas the conventional analysis method requires machines to be totally shut down. However, lack of information of phase angles with respect to impact in ISMA has caused it to be labor-intensive and time-consuming. An automated impact device (AID) is introduced in this study in the effort to replace the manually operated impact hammer and prepare it to be used in the current practice of ISMA on the purpose of enhancing its effectiveness and practicability. Impact profile and isolation effect are noted to be the contributing parameters in this study. This paper devoted on calibrating and controlling of the AID which gives the desired impact profiles as compared to the manual impact hammer. The AID is found effective in the determination of dynamic characteristics when the device is isolated from the boundary condition of the test structure.

scholarly journals Dynamic Modal Analysis of Vertical Machining Centre Components

2009 ◽  
Vol 2009 ◽  
pp. 1-10 ◽  
Author(s):  
Anayet U. Patwari ◽  
Waleed F. Faris ◽  
A. K. M. Nurul Amin ◽  
S. K. Loh
Keyword(s):  
Modal Analysis ◽  
Mode Shape ◽  
Modal Testing ◽  
Machine Component ◽  
Vibration Modes ◽  
Structural Dynamic ◽  
Element Simulation ◽  
Analysis Technique ◽  
Design Software

The paper presents a systematic procedure and details of the use of experimental and analytical modal analysis technique for structural dynamic evaluation processes of a vertical machining centre. The main results deal with assessment of the mode shape of the different components of the vertical machining centre. The simplified experimental modal analysis of different components of milling machine was carried out. This model of the different machine tool's structure is made by design software and analyzed by finite element simulation using ABAQUS software to extract the different theoretical mode shape of the components. The model is evaluated and corrected with experimental results by modal testing of the machine components in which the natural frequencies and the shape of vibration modes are analyzed. The analysis resulted in determination of the direction of the maximal compliance of a particular machine component.

Experimental Modal Analysis of a Half-Scale Model Twin-Engine Aircraft Rear Fuselage Engine Mount Support Frame

2017 ◽  
Author(s):  
Diego A. Chamberlain ◽  
Chris K. Mechefske
Keyword(s):  
Modal Analysis ◽  
Natural Frequencies ◽  
Testing Procedure ◽  
Modal Testing ◽  
Scale Model ◽  
Mode Shapes ◽  
Component Testing ◽  
Fitting Procedures ◽  
Engine Mount ◽  
Set Up

Experimental modal testing using an impact hammer is a commonly used method for obtaining the modal parameters of any structure for which the vibrational behavior is of interest. Natural frequencies and associated mode shapes of the structure can be extracted directly from measured FRFs (Frequency Response Functions) through various curve fitting procedures. This paper provides an overview of the modal testing conducted on an aerospace component. Testing set-up, experimental equipment and the methodology employed are all described in detail. Further validation of the testing procedure was done by ensuring that the experimental results satisfy the requirements of repeatability, reciprocity and linearity. The relevant ISO standard has been referenced and important concepts to modal analysis are expanded upon. Recorded natural frequencies, coherence and a description of the observed mode shapes are presented along with notable trends.

Vibrations Analysis of Cable-Harnessed Plates: Continuum Modeling and Experimental Validation

2020 ◽  
pp. 1-34
Author(s):  
Pranav Agrawal ◽  
Armaghan Salehian
Keyword(s):  
Dynamic Modelling ◽  
Dry Mass ◽  
Linear Displacement ◽  
Modal Testing ◽  
Analytical Models ◽  
Mode Shapes ◽  
Power Cables ◽  
Dynamic Effects ◽  
Lumped Mass ◽  
Modal Assurance Criterion

Abstract Dynamic modelling of spacecraft structures is imperative to their successful design for flight missions. A large number of these structures' dry mass consists of signal and power cables, dynamics of which is not well-predicted using ad hoc cable lumped mass models. Hence, accurate modeling techniques are required to understand these cable dynamics effects. In the past, efforts towards developing analytical models for cable-harnessed structures have been primarily focused on beam-like host structures. The presented paper is aimed to fill this gap by obtaining analytical solutions through an energy equivalent homogenization approach for cable harnessed plate-like structures and to ultimately help with understanding the dynamic effects of signal and power cables on two-dimensional plate-like structures. As a first step, systems of periodic geometries with parallel cable configurations are considered. The strain and kinetic energy expressions for the fundamental repeated elements are found using linear displacement fields and Green-Lagrange strain tensors. The governing partial differential equation (PDE) for the out-of-plane motion of the cable-harnessed system is then found using Hamilton's principle. Experimental modal testing is performed for the purpose of validations of the frequency response functions (FRFs) obtained from the model for the cable-harnessed plates under clamped-free-free-free boundary conditions. The results clearly show the dynamic effects of the cables which are also well-predicted by the model. Finally, Modal Assurance Criterion (MAC) analysis has been used for further validations of the mode shapes obtained from the model.

Improved Results in Structural Dynamic Calculations by Linking Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA)

1995 ◽  
Author(s):  
Ulrich Gabbert ◽  
Manfred Zehn ◽  
Friedrich Wahl
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Modal Analysis ◽  
Numerical Models ◽  
Mass Matrix ◽  
Computer Time ◽  
Experimental Modal Analysis ◽  
Mode Shapes ◽  
Element Analysis ◽  
Structural Dynamic

Abstract The paper deals with improvements of accuracy of structural dynamic calculations by using both the advantages of Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA). The basis for such improvements are reasonable mechanical and numerical models and accurate frequency response measurements (eigenfrequencies and mode shapes). The paper deals first with reasons for and estimations of errors in numerical and experimental analysis. It can be shown by theory and experiment that neither FEA nor EMA models are unique, due to inevitable incompleteness of the mode shapes and eigenfrequencies from a vibration test. Verification and updating of FE models by linking FEA with EMA are discussed in the paper and mainly focussed on FE models with a large number of degrees of freedom. Hence an update method has been introduced, which leads to an improved model in a relatively small quantity of computer time. It can be shown, that based on measured eigenfrequencies and calculated eigenvectors, an updating of FE-models for real engineering problems, by changing the mass matrix only, is a very efficient procedure with a surprisingly good quality updated model.

Modal Modeling of Micro-Machining Center

2012 ◽  
Author(s):  
Marcin Chodźko ◽  
Krzysztof Marchelek
Keyword(s):  
Machine Tool ◽  
Model Updating ◽  
Dynamic Properties ◽  
Modal Testing ◽  
Mode Shapes ◽  
Experimental Investigations ◽  
Micro Machining ◽  
Machining Center ◽  
Modal Model ◽  
The Impact

Modeling of dynamic properties of machine tools has a significant influence on improvement of its construction. This process is extremely important when a new construction of machine tool is under development. Experimental modal analysis provides information about frequency bandwidths with significant amplitudes of resonances, damping values and mode shapes. This information can be used in FEM model updating, stability prediction or finding weak elements of the machine tool structure as well. In the paper the modal model of prototype of the micro machining center is presented. Polymax algorithm was used to estimate the poles (frequency, damping) of modal model and modal shapes. Modal model was built on the basis of the impact test results. Methodology of conducted experimental test is presented. Tested machine tool was made of different materials (steel, aluminum, stone and others) which causes difficulties during experimental investigations. In the construction different types of guideways were implemented — rolling, slide and pneumatic ones. Maximum rotational speed of the tool is about 100 000 rev/min, so the frequency range where poles of modal model are estimated is wide (high frequencies of excitation during machining). Weight of sensors used during testing is an important issue due to a low mass of the structure. Also the excitation of the structure is troublesome because of vulnerability of precise guideways and forces sensors used in machine tool construction. Validation of the modal model is also presented in the paper and practical problems of modal testing are discussed.

Hydraulic Modal Analysis in Theory and Practice

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Gudrun Mikota ◽  
Bernhard Manhartsgruber ◽  
Franz Hammerle ◽  
Andreas Brandl
Keyword(s):  
Frequency Response ◽  
Theory And Practice ◽  
Mode Shapes ◽  
Pipeline System ◽  
Response Functions ◽  
Hydraulic Systems ◽  
Modal Assurance Criterion ◽  
Frequency Response Functions ◽  
Practical Applications ◽  
The Impact

Theoretical and experimental modal analyses are treated for hydraulic systems modeled by discrete capacities, inductances, resistances, and fluid lines with dynamic laminar flow. Based on an approximate multi-degrees-of-freedom description, it is shown how hydraulic natural frequencies, damping ratios, and mode shapes can be identified from measured frequency response functions between flow rate excitation and pressure response. Experiments are presented for a pipeline system that includes three side branches and an accumulator. In view of practical applications, two different types of servovalve excitation as well as impact hammer excitation are considered. Pressure is measured by 19 sensors throughout the system. Results are compared in terms of frequency response functions between 50 and 850 Hz, the first five hydraulic modes, and weighted auto modal assurance criteria of experimental mode shapes. Out of the tested excitation devices, the servovalve is clearly preferred; if valves cannot be used, the impact hammer offers a reasonable workaround. For a reduced number of five sensors, different sensor arrangements are assessed by the respective weighted auto modal assurance criteria of experimental mode shapes. A theoretical hydraulic modal model provides a similar assessment. The quality of the theoretical model is confirmed by the weighted modal assurance criterion of theoretical and experimental mode shapes from servovalve excitation.

Finite Element Model Verification for the Use of Piezoelectric Sensor in Structural Modal Analysis

2006 ◽  
Vol 22 (2) ◽  
pp. 107-114 ◽  
Author(s):  
B.-T. Wang ◽  
P.-H. Chen ◽  
R.-L. Chen
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Piezoelectric Materials ◽  
Piezoelectric Sensor ◽  
Model Verification ◽  
Modal Testing ◽  
Mode Shapes ◽  
Response Analysis ◽  
Pvdf Film ◽  
Element Analysis

AbstractThis paper presents the theoretical modal analysis for the use of PVDF sensor in structural modal testing via finite element analysis (FEA). A series of rectangular PVDF films are adhered on the surface of cantilever beam as sensors, while the point impact force is applied as the actuator for experimental modal analysis (EMA). Natural frequencies and mode shapes determined from both FEA and EMA are validated. In FEA, the beam structure is modeled by 3D solid elements, and the PVDF films are modeled by 3D coupled field piezoelectric elements. Both modal analysis and harmonic response analysis are performed to obtain the structural modal parameters and frequency response functions, respectively. Results show that both FEA and EMA results agree well. In particular, the PVDF sensor mode shapes, proportional to the slope difference between the two edges of PVDF film, are numerically and experimentally validated by FEA and EMA, respectively. Therefore, the simulation of PVDF films for vibration analysis in FEA can be verified and easily extended to other complex structures that may contain piezoelectric materials.

Modal Hammering Test and Sensitivity Analysis for BIW Vehicle

2014 ◽  
Vol 599-601 ◽  
pp. 985-991
Author(s):  
Cheng Wu Liu
Keyword(s):  
Sensitivity Analysis ◽  
Modal Analysis ◽  
Structural Parameters ◽  
Low Frequency ◽  
Modal Testing ◽  
Testing System ◽  
Modal Parameter ◽  
Modal Assurance Criterion ◽  
Body In White ◽  
Modal Parameter Estimation

Aiming at the defects of classical modal parameter estimation approach, the impulse hammer modal test during body-in-white (BIW) stage was done through polyMAX method method. Based on modal analysis theory, an experimental model of BIW was established. The compositions of the experimental modal testing system, the design of testing scheme as well as its validation were described in detail in this paper. The collected data were identified via the polyMAX modal analysis method. The dynamic characteristics of BIW were confirmed by Modal Assurance Criterion. Influence of low frequency distribution characteristics on complete vehicle NVH was also analyzed. On the basis of above investigation, sensitivity analysis of the structure of BIW was conducted and sensitive structural parameters were determined. The test results show that the modal testing system can meet the requirement of precision with reliable results of parameter identification and sensitivity analysis, which can serve as a basis for the improvement of BIW structural design.

Structural Modification of a Pipe Under Harmonic Excitation Using an Hybrid Numerical/Experimental Method

2011 ◽  
Author(s):  
Charles Bodel
Keyword(s):  
Modal Analysis ◽  
Nuclear Power ◽  
Natural Frequencies ◽  
Harmonic Excitation ◽  
Experimental Modal Analysis ◽  
Point Of View ◽  
Mode Shapes ◽  
Design Stage ◽  
Centrifugal Pumps ◽  
Structural Dynamic

Vibrations generated by centrifugal pumps are difficult to predict at the design stage, for it is hardly possible to accurately determine the natural frequencies of pipes and to avoid coincidences with the blade pass frequency of the pump and its harmonics. One is often led to modify the existing structure, by adding stiffness, mass or damping. This paper illustrates this point on a pipe connected to a pump in a nuclear power plant operated by EDF (E´lectricite´ de France). In October 2010, abnormal vibrations were measured on a thin pipe at the outlet of a pump in a powerplant in France. The French nuclear regulatory commission asked EDF to perform a diagnosis and to define solutions within a few months. EDF/R&D division has used an original method developed in 2004 based on hybrid data, and called LMME-SDM (for Local Model Mode-shapes Expansion Structural Dynamic Modification). The main objective is to define a structure modification able to remove all natural frequencies close to the harmonic excitation. For the purpose of the study, we need a numerical model, which should be fairly correct from a static point of view, but which is not necessarily updated from a dynamic point of view, and an experimental modal analysis carried out under real conditions on the pipe. During the experimental modal analysis, a test of added mass has been carried out so that the method can be validated by comparing the predicted and the observed frequency. This method has already been used in industrial cases in former studies [3], however the study presented here has reached a higher level in complexity. Even if this method is able to give reasonable results compared to measurements, it is close to its limits.

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