On exact and approximated formulations for scaling-mode shapes in operational modal analysis by mass and stiffness change

Bayesian operational modal analysis and modal strain energy are employed for determining the damage and looseness of bolted joints in beam structures under ambient excitation. With this ambient modal identification technique, mode shapes of a damaged beam structure with loosened bolted connections are obtained based on Bayesian theory. Then, the corresponding modal strain energy can be calculated based on the mode shapes. The modal strain energy of the structure with loosened bolted connections is compared with the theoretical one without bolted joints to define a damage index. This approach uses vibration-based nondestructive testing of locations and looseness of bolted joints in beam structures with different boundary conditions by first obtaining modal parameters from ambient vibration data. The damage index is then used to identify locations and looseness of bolted joints in beam structures with single or multiple bolted joints. Furthermore, the comparison between damage indexes due to different looseness levels of bolted connections demonstrates a qualitatively proportional relationship.

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Analysis of Instabilities in Railway Vehicles Employing Operational Modal Analysis

2015 Joint Rail Conference ◽

10.1115/jrc2015-5697 ◽

2015 ◽

Author(s):

Lara Erviti Calvo ◽

Gorka Agirre Castellanos ◽

Germán Gimenez

Keyword(s):

Numerical Model ◽

Modal Analysis ◽

Mode Shape ◽

Operational Modal Analysis ◽

Mode Shapes ◽

Correct Identification ◽

Unstable Condition ◽

Static Tests ◽

Railway Vehicles ◽

Damping Rate

The application of Operational Modal Analysis (OMA) in the railway sector opens a broad field of opportunities. The validation of the numerical model employed in the design phase is usually performed employing data obtained in static tests. The drawback is that some suspension parameters, such as dampers, only have an influence in the dynamic behavior and not in the static behavior. Because of that, the use of the mode shapes identified from track measurements in combination with the static tests leads to a more accurate validation of the numerical model. Apart from that, most passenger comfort and dynamic problems are associated to slightly damped modes. A correct identification of the modal parameters can be used as a continuous design improvement tool to improve the comfort and dynamic characteristics of future designs. Another valuable application of OMA techniques is the identification of the mode shapes corresponding to instabilities, due to the safety impact that they have. In railway vehicles, instabilities are associated to mode shapes that present a damping rate which decreases with the increase of the running speed. Above a certain speed value, the excitation coming from track cannot be damped by the vehicle and it reaches an unstable condition. This unstable condition leads to high acceleration levels experienced by the passengers and high interaction forces between the wheel and the rail that may lead to safety hazards. The speed above which the vehicle is unstable is known as critical speed, and has to be greater than the maximum speed of the vehicle with a reasonable safety margin. The use of OMA techniques allows identifying the mode shape that causes the instability. This paper presents the application of OMA techniques to measurements performed on a passenger vehicle, in which the speed was increased until the vehicle was unstable. The mode shape that caused the instability was identified as well as its corresponding natural frequency and damping rate.

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

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4048879 ◽

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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Determination of characteristic Parameters of masonry Structures via Operational Modal Analysis

International Journal of Engineering Sciences ◽

10.36224/ijes.120304 ◽

2019 ◽

Vol 12 (3) ◽

Author(s):

Ali Koçak ◽

Burak Toydemir ◽

Melih Bulgur

Keyword(s):

Modal Analysis ◽

Operational Modal Analysis ◽

Physical Models ◽

Mode Shapes ◽

Modal Parameters ◽

Model Parameters ◽

Masonry Structures ◽

Characteristic Parameters ◽

Characteristic Model

Commonly, material and vibration characteristics of masonry structures remain uncertain in the evaluation of existing structures under external loads such as earthquake, heat, wind, etc. In addition, determination of compressive and tensile strength of a masonry walls is not straightforward. However, it is very important to know the characteristic parameters such as eigen values, periods and mode shapes of a structure beforehand in order to create accurate and reliable physical models. Since each historical structure has its own unique wall and bearing characteristics, it is not possible to accept random initial values for the bearing capacity and other parameters of the structure. Besides, conducting vertical and lateral loading experiments is costly and time consuming. An alternative way to determine these parameters that govern the structural behavior is to carry out experimental vibration tests using accelerometers. This method, which is also called as Operational Modal Analysis (OMA), is used to obtain the free and forced vibration response of structures by experimental means and to determine the modal parameters of the structure. OMA is very important for the appropriate use of an analysis method and the model parameters used in the analysis. In this study, two masonry buildings, one of which is historical, are discussed and the modal parameters of buildings are determined experimentally with OMA. Characteristic values obtained from OMA were compared with the three dimensional finite element method by adjusting characteristic model parameters.

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Condition Monitoring Of Operating Pipelines With Operational Modal Analysis Application

Transport and Telecommunication Journal ◽

10.1515/ttj-2015-0028 ◽

2015 ◽

Vol 16 (4) ◽

pp. 305-319 ◽

Cited By ~ 7

Author(s):

Aleksey Mironov ◽

Pavel Doronkin ◽

Aleksander Priklonsky ◽

Igor Kabashkin

Keyword(s):

Modal Analysis ◽

Condition Monitoring ◽

Dynamic Properties ◽

Operational Modal Analysis ◽

Mode Shapes ◽

Special Focus ◽

Dynamic Features ◽

Modal Shape ◽

Reliability Models ◽

Study Results

Abstract In the petroleum, natural gas and petrochemical industries, great attention is being paid to safety, reliability and maintainability of equipment. There are a number of technologies to monitor, control, and maintain gas, oil, water, and sewer pipelines. The paper focuses on operational modal analysis (OMA) application for condition monitoring of operating pipelines. Special focus is on the topicality of OMA for definition of the dynamic features of the pipeline (frequencies and mode shapes) in operation. The research was conducted using two operating laboratory models imitated a part of the operating pipeline. The results of finite-element modeling, identification of pipe natural modes and its modification under the influence of virtual failure are discussed. The work considers the results of experimental research of dynamic behavior of the operating pipe models using one of OMA techniques and comparing dynamic properties with the modeled data. The study results demonstrate sensitivity of modal shape parameters to modification of operating pipeline technical state. Two strategies of pipeline repair – with continuously condition-based monitoring with proposed technology and without such monitoring, was discussed. Markov chain reliability models for each strategy were analyzed and reliability improvement factor for proposed technology of monitoring in compare with traditional one was evaluated. It is resumed about ability of operating pipeline condition monitoring by measuring dynamic deformations of the operating pipe and OMA techniques application for dynamic properties extraction.

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Operational Modal Analysis of Damage Gear

International Journal of Innovative Technology and Exploring Engineering - Special Issue ◽

10.35940/ijitee.c9210.019320 ◽

2020 ◽

Vol 9 (3) ◽

pp. 2778-2783

Keyword(s):

Domain Decomposition ◽

Modal Analysis ◽

Frequency Domain ◽

Dynamic Characteristics ◽

Natural Frequencies ◽

Helical Gear ◽

Operational Modal Analysis ◽

Mode Shapes ◽

Identification Algorithm ◽

Frequency Domain Decomposition

As natural frequencies and mode shapes are often a key to understanding dynamic characteristics of structural elements, modal analysis provides a viable means to determine these properties. This paper investigates the dynamic characteristics of a healthy and unhealthy condition of a commercially used helical gear using the Frequency Domain Decomposition (FDD) identification algorithm in Operational Modal Analysis (OMA). For the unhealthy condition, a refined range of percentage of defects are introduced to the helical gear starting from one (1) tooth being defected (1/60 teeth) to six (6) teeth being defected (6/60 teeth). The specimen is tested under a free-free boundary condition for its simplicity and direct investigation purpose. Comparison of the results of these varying conditions of the structure will be shown to justify the validity of the method used. Acceptable modal data are obtained by considering and accentuating on the technical aspects in processing the experimental data which are critical aspects to be addressed. The natural frequencies and mode shapes are obtained through automatic and manual peak-picking process from Singular Value Decomposition (SVD) plot using Frequency Domain Decomposition (FDD) technique and the results are validated using the established Modal Assurance Criterion (MAC) indicator. The results indicate that OMA using FDD algorithm is a good method in identifying the dynamic characteristics and hence, is effective in detection of defects in this rotating element

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Operational Modal Analysis, Testing and Modelling of Prefabricated Steel Modules with Different LSF Composite Walls

Materials ◽

10.3390/ma13245816 ◽

2020 ◽

Vol 13 (24) ◽

pp. 5816

Author(s):

Maria Rashidi ◽

Pejman Sharafi ◽

Mohammad Alembagheri ◽

Ali Bigdeli ◽

Bijan Samali

Keyword(s):

Modal Analysis ◽

Dynamic Characteristics ◽

Operational Modal Analysis ◽

Mode Shapes ◽

Infill Wall ◽

Modular Systems ◽

Modal Properties ◽

Modular Units ◽

Composite Walls ◽

Modular Structures

The modal properties of modular structures, such as their natural frequencies, damping ratios and mode shapes, are different than those of conventional structures, mainly due to different structural systems being used for assembling prefabricated modular units onsite. To study the dynamic characteristics of modular systems and define a dynamic model, both the modal properties of the individual units and their connections need to be considered. This study is focused on the former aspect. A full-scale prefabricated volumetric steel module was experimentally tested using operational modal analysis technique under pure ambient vibrations and randomly generated artificial hammer impacts. It was tested in different situations: [a] bare (frame only) condition, and [b] infilled condition with different configurations of gypsum and cement-boards light-steel framed composite walls. The coupled module-wall system was instrumented with sensitive accelerometers, and its pure and free vibration responses were synchronously recorded through a data acquisition system. The main dynamic characteristics of the module were extracted using output-only algorithms, and the effects of the presence of infill wall panels and their material are discussed. Then, the module’s numerical micromodel for bare and infilled states is generated and calibrated against experimental results. Finally, an equivalent linear strut macro-model is proposed based on the calibrated data. The contribution of this study is assessing the effects of different infill wall materials on the dynamic characteristics of modular steel units, and proposing simple models for macro-analysis of infilled module assemblies.

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Operational Modal Analysis for Dynamic Characterization of a Ro-Lo Ship

Journal of Ship Research ◽

10.5957/jsr.2014.58.4.216 ◽

2014 ◽

Vol 58 (04) ◽

pp. 216-224 ◽

Cited By ~ 1

Author(s):

Esben Orlowitz ◽

Anders Brandt

Keyword(s):

Modal Analysis ◽

Natural Frequencies ◽

Operating Conditions ◽

Operational Modal Analysis ◽

Mode Shapes ◽

Dynamic Characterization ◽

Sea Trial ◽

Global Modes ◽

Bending Modes

The dynamic characteristics of ship structures are becoming more important as the flexibility of modern ships increases, for example, to predict reliable design life. This requires an accurate dynamic model of the structure, which, because of complex vibration environment and complex boundary conditions, can only be validated by measurements. In the present paper the use of operational modal analysis (OMA) for dynamic characterization of a ship structure based on experimental data, from a full-scale measurement of a 210-m long Ro-Lo ship during sea trial, is presented. The measurements contain three different data sets obtained under different operating conditions of the ship: 10 knots cruising speed, 18 knots cruising speed, and at anchor. Natural frequencies, modal damping ratios, and mode shapes have been successfully estimated for the first 10 global modes. Damping ratios for the current ship were found within the range 0.9%–1.9% and natural frequencies were found to range from 0.8 to 4.1 Hz for the first 10 global modes of the ship at design speed (18 knots). The three different operating conditions showed, in addition, a speed dependency of the natural frequencies and damping ratios. The natural frequencies were found to be lower for the 18-knots condition compared with the two other conditions, most significantly for the vertical bending modes. Also, for the vertical bending modes, the damping ratios increased by 28%–288% when the speed increased from 10 to 18 knots. Other modes were not found to have the same strong speed dependency.

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Operational Modal Analysis: A Tool for Assessing Changes on Structural Health State of Historical Constructions after Consolidation and Reinforcement Works—Jura Chapel (Jerez de la Frontera, Spain)

Shock and Vibration ◽

10.1155/2018/3710419 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12 ◽

Cited By ~ 3

Author(s):

Manuel Romero ◽

Pablo Pachón ◽

Víctor Compán ◽

Margarita Cámara ◽

Francisco Pinto

Keyword(s):

Modal Analysis ◽

Dynamic Properties ◽

Operational Modal Analysis ◽

Ambient Vibration ◽

Mode Shapes ◽

Health Improvement ◽

Health State ◽

Structural Behaviour ◽

Structural Health ◽

Historical Masonry

Today’s society is sensitive to the architectural heritage conservation. This implies to perform works to maintain these buildings and to assure their structural security. In the last years, the structural analysis of historical masonry constructions has experienced a great progress, thanks to the use of techniques based on the study of the dynamic properties of building structures. In this context, changes on the structural health state of a building are one of the elements that can be assessed considering changes on their dynamic properties. This is useful to evaluate the effectiveness of structural interventions on this kind of buildings by analysing these properties before and after it. This paper focuses on the Jura Chapel, in Jerez de la Frontera (Spain). This chapel is part of San Juan de los Caballeros Church and is dated from the 15th century. In 2015 and after the identification of some structural damages in the chapel vault, an intervention was initiated to improve its structural behaviour and to recover its original appearance. The present work reports the evaluation of the effects that this intervention has on the structural health state of the building, using nondestructive techniques based on ambient vibration tests (AVT) and Operational Modal Analysis (OMA). The AVT were performed for both prerestored and restored states and under environmental loads. A discussion about the validity of doing AVT from extrados when a vault presents disconnection between ribs and web is included in the paper. As a result, the first five natural frequency values have increased while the corresponding mode shapes have not changed significantly. This proves a structural health improvement caused by the repairing process without changing the original behaviour of the structure. This work shows OMA capabilities for evaluating the effectiveness of intervention works on the health state of a historical masonry structure.

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