Operational Modal Analysis Tutorial
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, Palle
analysis in an easier way and in many cases more effectively than traditional modal analysis methods. It can be applied for modal testing and analysis on a wide range of structures and not only for problems generally investigated using traditional modal analysis, but also for those requiring load......In this paper the basic principles in operational modal testing and analysis are presented and discussed. A brief review of the techniques for operational modal testing and identification is presented, and it is argued, that there is now a wide range of techniques for effective identification...... estimation, vibration level estimation and fatigue analysis....
Operational Modal Analysis Tutorial
Brincker, Rune; Andersen, Palle
2007-01-01
In this paper the basic principles in operational modal testing and analysis are presented and discussed. A brief review of the techniques for operational modal testing and identification is presented, and it is argued, that there is now a wide range of techniques for effective identification of modal parameters of practical interest - including the mode shape scaling factor - with a high degree of accuracy. It is also argued that the operational technology offers the user a number of advanta...
Fully automated (operational) modal analysis
Reynders, Edwin; Houbrechts, Jeroen; De Roeck, Guido
2012-05-01
Modal parameter estimation requires a lot of user interaction, especially when parametric system identification methods are used and the modes are selected in a stabilization diagram. In this paper, a fully automated, generally applicable three-stage clustering approach is developed for interpreting such a diagram. It does not require any user-specified parameter or threshold value, and it can be used in an experimental, operational, and combined vibration testing context and with any parametric system identification algorithm. The three stages of the algorithm correspond to the three stages in a manual analysis: setting stabilization thresholds for clearing out the diagram, detecting columns of stable modes, and selecting a representative mode from each column. An extensive validation study illustrates the accuracy and robustness of this automation strategy.
Special issue on Operational Modal Analysis
DEFF Research Database (Denmark)
Kirkegaard, Poul Henning; Brincker, Rune
2010-01-01
Operational Modal Analysis (OMA) is not really a new discipline; it has been present from the very beginning of the development of modal testing and analysis going back to the sixties and early seventies.......Operational Modal Analysis (OMA) is not really a new discipline; it has been present from the very beginning of the development of modal testing and analysis going back to the sixties and early seventies....
Uncertainty calculation in (operational) modal analysis
Pintelon, R.; Guillaume, P.; Schoukens, J.
2007-08-01
In (operational) modal analysis the modal parameters of a structure are identified from the response of that structure to (unmeasurable operational) perturbations. A key issue that remains to be solved is the calculation of uncertainty bounds on the estimated modal parameters. The present paper fills this gap. The theory is illustrated by means of a simulation and a real measurement example (operational modal analysis of a bridge).
An application of operational modal analysis in modal filtering
Energy Technology Data Exchange (ETDEWEB)
Kurowski, Piotr; Mendrok, Krzysztof; Uhl, Tadeusz, E-mail: mendrok@agh.edu.pl [AGH University of Science and Technology in Krakow, Al. Mickiewicza 30, 30-059, Krakow (Poland)
2011-07-19
Modal filtration in the field of damage detection has many advantages, including: its autonomous operation (without the interaction of qualified staff), low computational cost and low sensitivity to changes in external conditions. However, the main drawback of this group of damage detection methods is its limited applicability to operational data. In this paper a method of modal filter formulation from the in-operational data is described. The basis for this approach is FRFs synthesis using knowledge of the operational modal model. For that purpose a method of operational mode shape scaling is described. This is based on the measurements of several FRFs of the object. The method is then applied to the construction of modal filters and modal filtration. Additionally, the study presents verification of the method using data obtained from simulation and laboratory experiments. Verification consisted of comparing the results of modal filtering based on classical experimental modal analysis with the results of the approach proposed in the work.
An application of operational modal analysis in modal filtering
Kurowski, Piotr; Mendrok, Krzysztof; Uhl, Tadeusz
2011-07-01
Modal filtration in the field of damage detection has many advantages, including: its autonomous operation (without the interaction of qualified staff), low computational cost and low sensitivity to changes in external conditions. However, the main drawback of this group of damage detection methods is its limited applicability to operational data. In this paper a method of modal filter formulation from the in-operational data is described. The basis for this approach is FRFs synthesis using knowledge of the operational modal model. For that purpose a method of operational mode shape scaling is described. This is based on the measurements of several FRFs of the object. The method is then applied to the construction of modal filters and modal filtration. Additionally, the study presents verification of the method using data obtained from simulation and laboratory experiments. Verification consisted of comparing the results of modal filtering based on classical experimental modal analysis with the results of the approach proposed in the work.
Operational Modal Analysis of Large Bridges
Schanke, Sindre Aavik
2015-01-01
As a part of the new coastal highway E39 which is being planned and built along the west coast of Norway by the Norwegian Public Roads Administration, state of the art methods of structural dynamics needs to be developed and used to cross the deep and wide fjords. Operational modal analysis aims to find the modal properties; natural frequencies, damping ratios and mode shapes of a structure while it is under operating conditions using its vibration data. Several methods of operati...
Operational modal analysis with non stationnary inputs
Gouache, Thibault; Morlier, Joseph; Michon, Guilhem; Coulange, Baptiste
2013-01-01
Operational modal analysis (OMA) techniques enable the use of in-situ and uncontrolled vibrations to be used to lead modal analysis of structures. In reality operational vibrations are a combination of numerous excitations sources that are much more complex than a random white noise or a harmonic. Numerous OMA techniques exist like SSI, NExT, FDD and BSS. All these methods are based on the fundamental hypothesis that the input or force applied to the structure to be analyzed is a stationary w...
Some Elements of Operational Modal Analysis
Rune Brincker
2014-01-01
This paper gives an overview of the main components of operational modal analysis (OMA) and can serve as a tutorial for research oriented OMA applications. The paper gives a short introduction to the modeling of random responses and to the transforms often used in OMA such as the Fourier series, the Fourier integral, the Laplace transform, and the Z-transform. Then the paper introduces the spectral density matrix of the random responses and presents the theoretical solutions for correlation f...
Operational modal analysis by updating autoregressive model
Vu, V. H.; Thomas, M.; Lakis, A. A.; Marcouiller, L.
2011-04-01
This paper presents improvements of a multivariable autoregressive (AR) model for applications in operational modal analysis considering simultaneously the temporal response data of multi-channel measurements. The parameters are estimated by using the least squares method via the implementation of the QR factorization. A new noise rate-based factor called the Noise rate Order Factor (NOF) is introduced for use in the effective selection of model order and noise rate estimation. For the selection of structural modes, an orderwise criterion called the Order Modal Assurance Criterion (OMAC) is used, based on the correlation of mode shapes computed from two successive orders. Specifically, the algorithm is updated with respect to model order from a small value to produce a cost-effective computation. Furthermore, the confidence intervals of each natural frequency, damping ratio and mode shapes are also computed and evaluated with respect to model order and noise rate. This method is thus very effective for identifying the modal parameters in case of ambient vibrations dealing with modern output-only modal analysis. Simulations and discussions on a steel plate structure are presented, and the experimental results show good agreement with the finite element analysis.
Applicability Limits of Operational Modal Analysis to Operational Wind Turbines
DEFF Research Database (Denmark)
Tcherniak, D.; Chauhan, Shashank; Hansen, Morten Hartvig
2011-01-01
Operational Modal Analysis (OMA) is one of the branches of experimental modal analysis which allows extracting modal parameters based on measuring only the responses of a structure under ambient or operational excitation which is not needed to be measured. This makes OMA extremely attractive...... to modal analysis of big structures such as wind turbines where providing measured excitation force is an extremely difficult task. One of the main OMA assumption concerning the excitation is that it is distributed randomly both temporally and spatially. Obviously, closer the real excitation...... is to the assumed one, better modal parameter estimation one can expect. Traditionally, wind excitation is considered as a perfect excitation obeying the OMA assumptions. However, the present study shows that the aeroelastic phenomena due to rotor rotation dramatically changes the character of aerodynamic...
OPERATIONAL MODAL ANALYSIS SCHEMES USING CORRELATION TECHNIQUE
Institute of Scientific and Technical Information of China (English)
Zheng Min; Shen Fan; Chen Huaihai
2005-01-01
For some large-scale engineering structures in operating conditions, modal parameters estimation must base itself on response-only data. This problem has received a considerable amount of attention in the past few years. It is well known that the cross-correlation function between the measured responses is a sum of complex exponential functions of the same form as the impulse response function of the original system. So this paper presents a time-domain operating modal identification global scheme and a frequency-domain scheme from output-only by coupling the cross-correlation function with conventional modal parameter estimation. The outlined techniques are applied to an airplane model to estimate modal parameters from response-only data.
Some Elements of Operational Modal Analysis
Directory of Open Access Journals (Sweden)
Rune Brincker
2014-01-01
Full Text Available This paper gives an overview of the main components of operational modal analysis (OMA and can serve as a tutorial for research oriented OMA applications. The paper gives a short introduction to the modeling of random responses and to the transforms often used in OMA such as the Fourier series, the Fourier integral, the Laplace transform, and the Z-transform. Then the paper introduces the spectral density matrix of the random responses and presents the theoretical solutions for correlation function and spectral density matrix under white noise loading. Some important guidelines for testing are mentioned and the most common techniques for signal processing of the operating signals are presented. The algorithms of some of the commonly used time domain and frequency domain identification techniques are presented and finally some issues are discussed such as mode shape scaling, and mode shape expansion. The different techniques are illustrated on the difficult case of identifying the three first closely spaced modes of the Heritage Court Tower building.
Condition Monitoring Of Operating Pipelines With Operational Modal Analysis Application
Directory of Open Access Journals (Sweden)
Mironov Aleksey
2015-12-01
Full Text Available 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.
Placement of sensors in operational modal analysis for truss bridges
Debnath, N.; Dutta, A.; Deb, S. K.
2012-08-01
A modal approach is considered for sensor placement evaluation in operational modal analysis (OMA) where modal participation at individual degree of freedom (DOF) is evaluated separately for the target modes and subsequently locations are identified using these participation profiles. Modal contribution in output energy (MCOE) is proposed as modal measure to evaluate modal participation and has been applied in this modal approach framework for sensor placement evaluation. MCOE is evaluated using observability grammian for any types of response measurement (displacement, velocity or acceleration), while a system is released from any initial condition. Further, existing modal measures e.g. modal Hankel singular value (MHSV) and system norms (H2, H∞ and Hankel) are explained in perspective of OMA. To understand the efficiency of this proposed technique, MCOE is compared in terms of modal participation with existing modal measures as well as with other techniques like effective independence (EI) and modal kinetic energy (MKE). Analytical similarity is found for participation of a mode with EI method. Further, an existing large truss bridge structure is considered for comparative study based on modal participation of individual target modes along each DOF with acceleration measurement. In this comparison, MCOE technique is found to be in very good agreement with EI method as expected, while good agreement is observed with MHSV as well as norms and reasonable agreement with MKE method. Further, the adopted modal approach uses a flexible and insightful methodology for sensor location evaluation for multiple target modes.
Palanivelu, Sakthivel; Narasimha Rao, K. V.; Ramarathnam, Krishna Kumar
2015-12-01
In order to address various noise generation mechanisms and noise propagation phenomena of a tyre, it is necessary to study the tyre dynamic behaviour in terms of modal parameters. This paper enumerates a novel method of finding the modal parameters of a rolling tyre using an Explicit Finite Element Analysis and Operational Modal Analysis (OMA). ABAQUS Explicit, a commercial Finite Element (FE) software code has been used to simulate the experiment, a tyre rolling over a semi-circular straight and inclined cleat. The acceleration responses obtained from these simulations are used as input to the OMA. LMS test lab has been used for carrying out the Operational Modal Analysis. The modal results are compared with the published results of Kindt [22] and validated. Also, the modal results obtained from OMA are compared with FE modal results of stationary unloaded tyre, stationary loaded tyre and Steady State Transport rolling tyre.
Modal Parameters from a Wind Turbine Wing by Operational Modal Analysis
DEFF Research Database (Denmark)
Herlufsen, H.; Møller, N.; Brincker, Rune;
2002-01-01
Operational Modal Analysis also known as Ambient Modal Analysis has an increasing interest in mechanical engineering. Especially on big structures where the excitation and not less important the determination of the forces is most often a problem. In a structure like a wind turbine wing where...... the modes occur both close in frequency and bidirectional the Ambient excitation has big advantages. In this paper modal parameters are identified from the wing by operational modal analysis. For the parameter identification both parametric and non-parametric techniques are used. Advantages...
Operational Modal Analysis of Wind Turbine Speed-increase Gearbox
Directory of Open Access Journals (Sweden)
LI Yafeng
2013-11-01
Full Text Available Speed increase transmission gear box is the primary vibration and noise source of wind turbine, Operational modal method was adopted to collect impact data and response data of each point based on the gearbox test model. ANSYS finite element model is established to simulate the wind turbine gearbox. Then the modal frequencies of the two methods were compared to ensure the test model is correct. The results show that operational modal method can be applied in wind turbine gearbox modal analysis and it has important guiding significance to gearbox fault diagnosis and reliability and maintainability improving.
Operational modal analysis in the presence of harmonic excitation
Mohanty, P.; Rixen, D. J.
2004-02-01
Modal operational analysis methods are procedures to identify modal parameters of structures from the response to unknown random excitations existing on buildings and in machines during operation. In many practical cases, in addition to the random loads, harmonic excitations are also present due for instance to rotating components. If the frequency of the harmonic component of the input is close to an eigenfrequency of the system, operational modal analysis procedures fail to identify the modal parameters accurately. Therefore, we propose a modification of the least-square complex exponential identification procedure to include explicitly the harmonic component. In that way, the modal parameters can be identified properly. We illustrate the efficiency of the proposed approach on the example of a beam structure excited by multi-harmonic loads superposed on random excitation.
Cara, Javier
2016-05-01
Modal parameters comprise natural frequencies, damping ratios, modal vectors and modal masses. In a theoretic framework, these parameters are the basis for the solution of vibration problems using the theory of modal superposition. In practice, they can be computed from input-output vibration data: the usual procedure is to estimate a mathematical model from the data and then to compute the modal parameters from the estimated model. The most popular models for input-output data are based on the frequency response function, but in recent years the state space model in the time domain has become popular among researchers and practitioners of modal analysis with experimental data. In this work, the equations to compute the modal parameters from the state space model when input and output data are available (like in combined experimental-operational modal analysis) are derived in detail using invariants of the state space model: the equations needed to compute natural frequencies, damping ratios and modal vectors are well known in the operational modal analysis framework, but the equation needed to compute the modal masses has not generated much interest in technical literature. These equations are applied to both a numerical simulation and an experimental study in the last part of the work.
Operational Modal Analysis using Expectation Maximization Algorithm
Cara Cañas, Francisco Javier; Carpio Huertas, Jaime; Juan Ruiz, Jesús; Alarcón Álvarez, Enrique
2011-01-01
This paper presents a time-domain stochastic system identification method based on Maximum Likelihood Estimation and the Expectation Maximization algorithm. The effectiveness of this structural identification method is evaluated through numerical simulation in the context of the ASCE benchmark problem on structural health monitoring. Modal parameters (eigenfrequencies, damping ratios and mode shapes) of the benchmark structure have been estimated applying the proposed identification method...
An operational modal analysis method in frequency and spatial domain
Wang, Tong; Zhang, Lingmi; Tamura, Yukio
2005-12-01
A frequency and spatial domain decomposition method (FSDD) for operational modal analysis (OMA) is presented in this paper, which is an extension of the complex mode indicator function (CMIF) method for experimental modal analysis (EMA). The theoretical background of the FSDD method is clarified. Singular value decomposition is adopted to separate the signal space from the noise space. Finally, an enhanced power spectrum density (PSD) is proposed to obtain more accurate modal parameters by curve fitting in the frequency domain. Moreover, a simulation case and an application case are used to validate this method.
An operational modal analysis method in frequency and spatial domain
Institute of Scientific and Technical Information of China (English)
Wang Tong; Zhang Lingmi; Tamura Yukio
2005-01-01
A frequency and spatial domain decomposition method (FSDD) for operational modal analysis (OMA) is presented in this paper, which is an extension of the complex mode indicator function (CMIF) method for experimental modal analysis (EMA). The theoretical background of the FSDD method is clarified. Singular value decomposition is adopted to separate the signal space from the noise space. Finally, an enhanced power spectrum density (PSD) is proposed to obtain more accurate modal parameters by curve fitting in the frequency domain. Moreover, a simulation case and an application case are used to validate this method.
Eliminating the Influence of Harmonic Components in Operational Modal Analysis
DEFF Research Database (Denmark)
Jacobsen, Niels-Jørgen; Andersen, Palle; Brincker, Rune
2007-01-01
on the well-known Enhanced Frequency Domain Decomposition (EFDD) technique for eliminating these harmonic components in the modal parameter extraction process. For assessing the quality of the method, various experiments were carried out where the results were compared with those obtained with pure stochastic......Operational modal analysis is used for determining the modal parameters of structures for which the input forces cannot be measured. However, the algorithms used assume that the input forces are stochastic in nature. While this is often the case for civil engineering structures, mechanical...
Automatic Operational Modal Analysis for Aeroelastic Applications
Schwochow, Jan; Jelicic, G.
2015-01-01
The development of new aircraft requires the evaluation of the aeroelastic stability to avoid the phenomenon of flutter, a self-excited oscillation of the airframe. Since the rational analysis of the flutter stability comprises coupled simulations using numerical structural models and unsteady aerodynamic loads, the accomplishment is complex and the implementations must be checked for their validity by comparison of analytical and experimental results. In the so-called Ground Vibration Test (...
Explaining operational modal analysis with data from an arch bridge
Magalhães, Filipe; Cunha, Álvaro
2011-07-01
This tutorial paper aims to introduce the topic of operational modal analysis to non-specialists on the subject. First of all, it is stressed the relevance of this experimental technique particularly in the assessment of important civil infrastructure. Then, after a synthesis of required theoretical background, three of the most powerful algorithms for output-only modal identification are presented. The several steps of these identification procedures are illustrated with the processing of data collected on a concrete arch bridge with a span of 280 m. As the use of operational modal analysis in the context of structural health monitoring is a subject under active research, this theme is also introduced and briefly exemplified with data continuously recorded at the same bridge.
Transmissibility-Based Operational Modal Analysis: Enhanced Stabilisation Diagrams
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Gert De Sitter
2012-01-01
Full Text Available Recently it has been shown that also transmissibilities can be used to identify the modal parameters. This approach has several advantages: because of the deterministic character of the transmissibility functions, the estimated parameters are more accurate than the results obtained with the power spectra based operational modal analysis techniques. Another advantage is that the transmissibility functions do not depend on the colouring of the unknown forces. A disadvantage of the transmissibility based operational modal analysis techniques is that non-physical modes show up in the stabilisation diagrams. In this contribution it will first be shown that those non-physical modes will show up when traditional stabilisation diagrams are used. In a second step, a new approach of selecting the physical modes out of a set of estimated modes will be discussed and the new approach will be validated using data generated with an acoustical Finite Element Model. Finally, the approach will be validated using real acoustical data.
Automated Frequency Domain Decomposition for Operational Modal Analysis
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, Palle; Jacobsen, Niels-Jørgen
2007-01-01
The Frequency Domain Decomposition (FDD) technique is known as one of the most user friendly and powerful techniques for operational modal analysis of structures. However, the classical implementation of the technique requires some user interaction. The present paper describes an algorithm for au...
Operational modal analysis applied to the concert harp
Chomette, B.; Le Carrou, J.-L.
2015-05-01
Operational modal analysis (OMA) methods are useful to extract modal parameters of operating systems. These methods seem to be particularly interesting to investigate the modal basis of string instruments during operation to avoid certain disadvantages due to conventional methods. However, the excitation in the case of string instruments is not optimal for OMA due to the presence of damped harmonic components and low noise in the disturbance signal. Therefore, the present study investigates the least-square complex exponential (LSCE) and the modified least-square complex exponential methods in the case of a string instrument to identify modal parameters of the instrument when it is played. The efficiency of the approach is experimentally demonstrated on a concert harp excited by some of its strings and the two methods are compared to a conventional modal analysis. The results show that OMA allows us to identify modes particularly present in the instrument's response with a good estimation especially if they are close to the excitation frequency with the modified LSCE method.
Modal Indicators for Operational Modal Identification
DEFF Research Database (Denmark)
Zhang, L.; Brincker, Rune; Andersen, P.
2001-01-01
Modal validation is of paramount importance for all two-stage time domain modal identification algorithms. However, due to a higher noise/signal ratio in operational/ambient modal analysis, being able to determine the right model order and to distinguish between structural modes and computational...... modes become more significant than in traditional modal analysis. The two major modal indicators, i.e. Modal Confidence Factor (MCF) and Modal Amplitude Coherence (MAmC) are extended to two-stage time domain modal identification algorithms, together with a newly developed indicator, named as Modal...... Participation Indicator (MPI). The application of the three indicators is illustrated on different cases of operational/ambient modal identification. Three major time domain modal identification algorithms are used the Polyreference Complex Exponential (PRCE), Extended Ibrahim Time Domain (EITD), Eigensystem...
Evaluation of Damping Using Frequency Domain Operational Modal Analysis Techniques
DEFF Research Database (Denmark)
Bajric, Anela; Georgakis, Christos T.; Brincker, Rune
2015-01-01
Operational Modal Analysis (OMA) techniques provide in most cases reasonably accurate estimates of structural frequencies and mode shapes. In contrast though, they are known to often produce uncertain structural damping estimates, which is mainly due to inherent random and/or bias errors...... domain techniques, the Frequency Domain Decomposition (FDD) and the Frequency Domain Polyreference (FDPR). The response of a two degree-of-freedom (2DOF) system is numerically established with specified modal parameters subjected to white noise loading. The system identification is evaluated with well...
Towards an automatic spectral and modal identification from operational modal analysis
Vu, V. H.; Thomas, M.; Lafleur, F.; Marcouiller, L.
2013-01-01
A method is developed for the automatic identification of the spectrum and modal parameters of an operational modal analysis using multi sensors. A multivariate autoregressive model is presented, and its parameters are estimated by least squares via the implementation of QR factorization. A noise-independent minimum model order, from which all available physical modes may be identified, is developed. This so-called optimal model order is selected from the convergence of a global order-wise signal-to-noise ratio index. At this model order or higher, the modes are classified based on a decreasing damped modal signal-to-noise (DMSN) criterion. This decreasing order classification allows for easy identification of all the physical modes. A significant change in the DMSN index enables the determination of the number of physical modes in a specific frequency range, and thus, an automatic procedure for identifying the modal parameters can be developed to discriminate harmonic and natural frequencies from spurious ones. Furthermore, a multispectral matrix can be constructed from selected frequencies by introducing a powered amplification factor, which provides a smooth, balanced, noise-free spectrum with all main peaks. The proposed method has been performed on simulated multi-degree-of-freedom systems, on a laboratory test bench, and on an industrial operating high power hydro-electric generator offering the potential for automatic operational modal analysis and structural health monitoring.
Harmonic component detection: Optimized Spectral Kurtosis for operational modal analysis
Dion, J.-L.; Tawfiq, I.; Chevallier, G.
2012-01-01
This work is a contribution in the field of Operational Modal Analysis to identify the modal parameters of mechanical structures using only measured responses. The study deals with structural responses coupled with harmonic components amplitude and frequency modulated in a short range, a common combination for mechanical systems with engines and other rotating machines in operation. These harmonic components generate misleading data interpreted erroneously by the classical methods used in OMA. The present work attempts to differentiate maxima in spectra stemming from harmonic components and structural modes. The detection method proposed is based on the so-called Optimized Spectral Kurtosis and compared with others definitions of Spectral Kurtosis described in the literature. After a parametric study of the method, a critical study is performed on numerical simulations and then on an experimental structure in operation in order to assess the method's performance.
Model validity and frequency band selection in operational modal analysis
Au, Siu-Kui
2016-12-01
Experimental modal analysis aims at identifying the modal properties (e.g., natural frequencies, damping ratios, mode shapes) of a structure using vibration measurements. Two basic questions are encountered when operating in the frequency domain: Is there a mode near a particular frequency? If so, how much spectral data near the frequency can be included for modal identification without incurring significant modeling error? For data with high signal-to-noise (s/n) ratios these questions can be addressed using empirical tools such as singular value spectrum. Otherwise they are generally open and can be challenging, e.g., for modes with low s/n ratios or close modes. In this work these questions are addressed using a Bayesian approach. The focus is on operational modal analysis, i.e., with 'output-only' ambient data, where identification uncertainty and modeling error can be significant and their control is most demanding. The approach leads to 'evidence ratios' quantifying the relative plausibility of competing sets of modeling assumptions. The latter involves modeling the 'what-if-not' situation, which is non-trivial but is resolved by systematic consideration of alternative models and using maximum entropy principle. Synthetic and field data are considered to investigate the behavior of evidence ratios and how they should be interpreted in practical applications.
Operational modal analysis of vehicle system based on SSI under operational conditions
Zhou, Suxia; Xie, Yunye; Xie, Jilong; Li, Fang
2010-03-01
The modal parameters of linear vehicle system are analyzed by the theoretical modal parameter analysis method first, and then SSI based on operational conditions is presented to form the estimation formula of modal parameters of linear vehicle system. At last, the modal parameters of linear vehicle system are identified by SSI after its vibration test under operational conditions, and are simultaneously compared to the results obtained by the theoretical modal parameter analysis method. Comparison results show discrepancies of 0.61~8.32 percent on modal frequencies and 3.86~11.61 percent on modal damping ratios, which implies that SSI based on the operational condition is feasible and effective, and has comparatively higher precision to meet the needs of engineering.
De Vivo, A.; Brutti, C.; Leofanti, J. L.
2013-08-01
Research efforts during recent decades qualify Operational Modal Analysis (OMA) as an interesting tool that is able to identify the modal characteristic parameters of structures excited randomly by environmental loads, eliminating the problem of measuring the external exciting forces. In this paper, an existing OMA technique, the Natural Excitation Technique (NExT) was studied and implemented in order to achieve, from the wind force, the modal parameters of Vega Launcher, the new European launcher vehicle for small and medium satellites. Following a brief summary of the fundamental equations of the method, the modal parameters of Vega are calculated using the OMA technique; the results are then compared with those achieved using a traditional Experimental Modal Analysis under excitation induced by shakers. The comparison shows there is a very good agreement between the results obtained by the two different methods, OMA and the traditional experimental analysis, proving that OMA is a reliable tool to analyse the dynamic behaviour of large structures. Finally, this approach can be used for any type of large structure in civil and mechanical fields and the technique appears to be very promising for further applications.
Operational modal analysis modeling, Bayesian inference, uncertainty laws
Au, Siu-Kui
2017-01-01
This book presents operational modal analysis (OMA), employing a coherent and comprehensive Bayesian framework for modal identification and covering stochastic modeling, theoretical formulations, computational algorithms, and practical applications. Mathematical similarities and philosophical differences between Bayesian and classical statistical approaches to system identification are discussed, allowing their mathematical tools to be shared and their results correctly interpreted. Many chapters can be used as lecture notes for the general topic they cover beyond the OMA context. After an introductory chapter (1), Chapters 2–7 present the general theory of stochastic modeling and analysis of ambient vibrations. Readers are first introduced to the spectral analysis of deterministic time series (2) and structural dynamics (3), which do not require the use of probability concepts. The concepts and techniques in these chapters are subsequently extended to a probabilistic context in Chapter 4 (on stochastic pro...
Identification of Historical Veziragasi Aqueduct Using the Operational Modal Analysis
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E. Ercan
2014-01-01
Full Text Available This paper describes the results of a model updating study conducted on a historical aqueduct, called Veziragasi, in Turkey. The output-only modal identification results obtained from ambient vibration measurements of the structure were used to update a finite element model of the structure. For the purposes of developing a solid model of the structure, the dimensions of the structure, defects, and material degradations in the structure were determined in detail by making a measurement survey. For evaluation of the material properties of the structure, nondestructive and destructive testing methods were applied. The modal analysis of the structure was calculated by FEM. Then, a nondestructive dynamic test as well as operational modal analysis was carried out and dynamic properties were extracted. The natural frequencies and corresponding mode shapes were determined from both theoretical and experimental modal analyses and compared with each other. A good harmony was attained between mode shapes, but there were some differences between natural frequencies. The sources of the differences were introduced and the FEM model was updated by changing material parameters and boundary conditions. Finally, the real analytical model of the aqueduct was put forward and the results were discussed.
Identification of Historical Veziragasi Aqueduct Using the Operational Modal Analysis
Ercan, E.; Nuhoglu, A.
2014-01-01
This paper describes the results of a model updating study conducted on a historical aqueduct, called Veziragasi, in Turkey. The output-only modal identification results obtained from ambient vibration measurements of the structure were used to update a finite element model of the structure. For the purposes of developing a solid model of the structure, the dimensions of the structure, defects, and material degradations in the structure were determined in detail by making a measurement survey. For evaluation of the material properties of the structure, nondestructive and destructive testing methods were applied. The modal analysis of the structure was calculated by FEM. Then, a nondestructive dynamic test as well as operational modal analysis was carried out and dynamic properties were extracted. The natural frequencies and corresponding mode shapes were determined from both theoretical and experimental modal analyses and compared with each other. A good harmony was attained between mode shapes, but there were some differences between natural frequencies. The sources of the differences were introduced and the FEM model was updated by changing material parameters and boundary conditions. Finally, the real analytical model of the aqueduct was put forward and the results were discussed. PMID:24511287
Operational modal analysis of road-rail bridge
Directory of Open Access Journals (Sweden)
Cardoso M.
2015-01-01
Full Text Available In this paper, we describe an Operational Modal Analysis (OMA of the Bridge over the Tocantins River, a composite road-rail bridge located in the city of Marabá, state of Pará, northern Brazil. The bridge is part of the Carajás Railway, which is used by VALE Company to transport iron ore from “Serra dos Carajás”, the largest mineral reserve of the planet. The bridge has a length of 2310m, being the second longest road-rail bridge in Brazil. The study focused on the bridge central span (with 77 m of length and two adjacent spans (with 44 m of length. We employed Piezo-electric accelerometers to measure the dynamic response of the bridge under ambient excitation, which consisted of the passage of loaded and unloaded trains, road traffic, wind and river current. For modal identification, to avoid the influence of the train mass over the bridge system, we only considered acceleration signals of road traffic and signals corresponding to intervals after the passage of loaded trains, i.e., the study disregarded the intervals during which the trains were over the monitored spans. We obtained modal parameters through two identification methods: one in the time domain and other in the frequency domain. We also performed a comparative analysis between the experimental modal parameters, and the numerical results obtained with a finite element model provided by a third-part company.
Operational modal analysis of road-rail bridge
Cardoso M.; Sampaio R. A. C.; de Souza R. M.; Silva E.
2015-01-01
In this paper, we describe an Operational Modal Analysis (OMA) of the Bridge over the Tocantins River, a composite road-rail bridge located in the city of Marabá, state of Pará, northern Brazil. The bridge is part of the Carajás Railway, which is used by VALE Company to transport iron ore from “Serra dos Carajás”, the largest mineral reserve of the planet. The bridge has a length of 2310m, being the second longest road-rail bridge in Brazil. The study focused on the bridge central span (with ...
Fully Automated Operational Modal Analysis using multi-stage clustering
Neu, Eugen; Janser, Frank; Khatibi, Akbar A.; Orifici, Adrian C.
2017-02-01
The interest for robust automatic modal parameter extraction techniques has increased significantly over the last years, together with the rising demand for continuous health monitoring of critical infrastructure like bridges, buildings and wind turbine blades. In this study a novel, multi-stage clustering approach for Automated Operational Modal Analysis (AOMA) is introduced. In contrast to existing approaches, the procedure works without any user-provided thresholds, is applicable within large system order ranges, can be used with very small sensor numbers and does not place any limitations on the damping ratio or the complexity of the system under investigation. The approach works with any parametric system identification algorithm that uses the system order n as sole parameter. Here a data-driven Stochastic Subspace Identification (SSI) method is used. Measurements from a wind tunnel investigation with a composite cantilever equipped with Fiber Bragg Grating Sensors (FBGSs) and piezoelectric sensors are used to assess the performance of the algorithm with a highly damped structure and low signal to noise ratio conditions. The proposed method was able to identify all physical system modes in the investigated frequency range from over 1000 individual datasets using FBGSs under challenging signal to noise ratio conditions and under better signal conditions but from only two sensors.
Energy Technology Data Exchange (ETDEWEB)
Huang, Zhenyu; Zhou, Ning; Tuffner, Francis K.; Chen, Yousu; Trudnowski, Daniel J.; Diao, Ruisheng; Fuller, Jason C.; Mittelstadt, William A.; Hauer, John F.; Dagle, Jeffery E.
2010-10-18
Small signal stability problems are one of the major threats to grid stability and reliability in the U.S. power grid. An undamped mode can cause large-amplitude oscillations and may result in system breakups and large-scale blackouts. There have been several incidents of system-wide oscillations. Of those incidents, the most notable is the August 10, 1996 western system breakup, a result of undamped system-wide oscillations. Significant efforts have been devoted to monitoring system oscillatory behaviors from measurements in the past 20 years. The deployment of phasor measurement units (PMU) provides high-precision, time-synchronized data needed for detecting oscillation modes. Measurement-based modal analysis, also known as ModeMeter, uses real-time phasor measurements to identify system oscillation modes and their damping. Low damping indicates potential system stability issues. Modal analysis has been demonstrated with phasor measurements to have the capability of estimating system modes from both oscillation signals and ambient data. With more and more phasor measurements available and ModeMeter techniques maturing, there is yet a need for methods to bring modal analysis from monitoring to actions. The methods should be able to associate low damping with grid operating conditions, so operators or automated operation schemes can respond when low damping is observed. The work presented in this report aims to develop such a method and establish a Modal Analysis for Grid Operation (MANGO) procedure to aid grid operation decision making to increase inter-area modal damping. The procedure can provide operation suggestions (such as increasing generation or decreasing load) for mitigating inter-area oscillations.
Automated eigensystem realisation algorithm for operational modal analysis
Zhang, Guowen; Ma, Jinghua; Chen, Zhuo; Wang, Ruirong
2014-07-01
The eigensystem realisation algorithm (ERA) is one of the most popular methods in civil engineering applications for estimating modal parameters. Three issues have been addressed in the paper: spurious mode elimination, estimating the energy relationship between different modes, and automatic analysis of the stabilisation diagram. On spurious mode elimination, a new criterion, modal similarity index (MSI) is proposed to measure the reliability of the modes obtained by ERA. On estimating the energy relationship between different modes, the mode energy level (MEL) was introduced to measure the energy contribution of each mode, which can be used to indicate the dominant mode. On automatic analysis of the stabilisation diagram, an automation of the mode selection process based on a hierarchical clustering algorithm was developed. An experimental example of the parameter estimation for the Chaotianmen bridge model in Chongqing, China, is presented to demonstrate the efficacy of the proposed method.
Modal contribution and state space order selection in operational modal analysis
Cara, F. Javier; Juan, Jesús; Alarcón, Enrique; Reynders, Edwin; De Roeck, Guido
2013-07-01
The estimation of modal parameters of a structure from ambient measurements has attracted the attention of many researchers in the last years. The procedure is now well established and the use of state space models, stochastic system identification methods and stabilization diagrams allows to identify the modes of the structure. In this paper the contribution of each identified mode to the measured vibration is discussed. This modal contribution is computed using the Kalman filter and it is an indicator of the importance of the modes. Also the variation of the modal contribution with the order of the model is studied. This analysis suggests selecting the order for the state space model as the order that includes the modes with higher contribution. The order obtained using this method is compared to those obtained using other well known methods, like Akaike criteria for time series or the singular values of the weighted projection matrix in the Stochastic Subspace Identification method. Finally, both simulated and measured vibration data are used to show the practicability of the derived technique. Finally, it is important to remark that the method can be used with any identification method working in the state space model.
DEFF Research Database (Denmark)
Dalgaard Ulriksen, Martin; Tcherniak, Dmitri; Kirkegaard, Poul Henning
2016-01-01
This study demonstrates an application of a previously proposed modal and wavelet analysis-based damage identification method to a wind turbine blade. A trailing edge debonding was introduced to an SSP 34-m blade mounted on a test rig. Operational modal analysis was conducted to obtain mode shapes...
DEFF Research Database (Denmark)
Ulriksen, Martin Dalgaard; Tcherniak, Dmitri; Kirkegaard, Poul Henning
2014-01-01
The presented study demonstrates an application of a previously proposed modal and wavelet analysis-based damage identification method to a wind turbine blade. A trailing edge debonding was introduced to a SSP 34m blade mounted on a test rig. Operational modal analysis (OMA) was conducted to obtain...
Pintelon, R.; Peeters, B.; Guillaume, P.
2010-01-01
Recently [R. Pintelon, B. Peeters, P. Guillaume, Continuous-time operational modal analysis in the presence of harmonic disturbances, Mechanical Systems and Signal Processing 22 (5) (2008) 1017-1035] a single-output algorithm for continuous-time operational modal analysis in the presence of harmonic disturbances with time-varying frequency has been developed. This paper extends the results of Pintelon, et al. [Continuous-time operational modal analysis in the presence of harmonic disturbances, Mechanical Systems and Signal Processing 22 (5) (2008) 1017-1035] to multi-output signals. The statistical performance of the proposed maximum likelihood estimator is illustrated on simulations and real helicopter data.
Energy Technology Data Exchange (ETDEWEB)
Friedmann, A.; Mayer, D.; Koch, M.; Kauba, M.; Melz, T. [Fraunhofer-Institut fuer Betriebsfestigkeit und Systemzuverlaessigkeit LBF, Darmstadt (Germany)
2010-07-01
A state monitoring of mechanical structures is possible based on the modal parameters natural frequency, self-oscillation form and modal damping. Beyond the damage recognition such a monitoring also can be used to the localization of damages. During the monitoring of large structures (such as blades or towers of wind power plants) problems arise with the instrumentation realization: However the execution of a unique data acquisition requires an expenditure which goes beyond logistic questions such as sensor assembly, grid connection and excitation. The presented solution covers two components whose combination can overcome the described problem definition. On the one hand a network of intelligent sensors will be used, on the other hand the received data are evaluated according to the methods of operational modal analysis. So the temporal development of the modal parameters can be supervised with a firmly installed sensor network based on the data received in the normal operation of the structure. The contribution under consideration contains a description of the Random Decrement Method used for the spectral estimation in the sensors. Subsequently, the function mode of the sensor network is presented from the data capture up to the modal dismantling with the help of a numeric system simulation. The realization of the sensor network at a mechanical, wind-excited test-structure is described. The results of the investigation of the test-structure with the sensor network are presented and compared with the results of conventional procedures. The innovation of the presented technology exists in the combination of known methods of random decrement and operational modal analysis with the possibilities of a network of intelligent sensors.
Higher order statistical frequency domain decomposition for operational modal analysis
Nita, G. M.; Mahgoub, M. A.; Sharyatpanahi, S. G.; Cretu, N. C.; El-Fouly, T. M.
2017-02-01
Experimental methods based on modal analysis under ambient vibrational excitation are often employed to detect structural damages of mechanical systems. Many of such frequency domain methods, such as Basic Frequency Domain (BFD), Frequency Domain Decomposition (FFD), or Enhanced Frequency Domain Decomposition (EFFD), use as first step a Fast Fourier Transform (FFT) estimate of the power spectral density (PSD) associated with the response of the system. In this study it is shown that higher order statistical estimators such as Spectral Kurtosis (SK) and Sample to Model Ratio (SMR) may be successfully employed not only to more reliably discriminate the response of the system against the ambient noise fluctuations, but also to better identify and separate contributions from closely spaced individual modes. It is shown that a SMR-based Maximum Likelihood curve fitting algorithm may improve the accuracy of the spectral shape and location of the individual modes and, when combined with the SK analysis, it provides efficient means to categorize such individual spectral components according to their temporal dynamics as coherent or incoherent system responses to unknown ambient excitations.
Transmissibilty-Based Operational Modal Analysis for Flight Flutter Testing Using Exogenous Inputs
Directory of Open Access Journals (Sweden)
Christof Devriendt
2012-01-01
Full Text Available During the recent years several new tools have been introduced by the Vrije Universiteit Brussel in the field of Operational Modal Analysis (OMA such as the transmissibility based approach and the the frequency-domain OMAX concept. One advantage of the transmissibility based approach is that the ambient forces may be coloured (non-white, if they are fully correlated. The main advantage of the OMAX concept is the fact that it combines the advantages of Operational and Experimental Modal Analysis: ambient (unknown forces as well as artificial (known forces are processed simultaneously resulting in improved modal parameters. In this paper, the transmissibility based output-only approach is combined with the input/output OMAX concept. This results in a new methodology in the field of operational modal analysis allowing the estimation of (scaled modal parameters in the presence of arbitrary ambient (unknown forces and artificial (known forces.
Mohanty, P.; Rixen, D. J.
2004-08-01
Operational modal analysis procedures are efficient techniques to identify modal properties of structures excited through unknown random noise produced during operation. In many practical cases, harmonic excitations are often present in addition to the white-noise and, if the harmonic frequency is close to structural frequencies, standard identification techniques fail. Here, a method is presented to take into account the harmonic excitations while doing modal parameter identification for operational modal analysis (OMA). The proposed technique is based on the Ibrahim Time Domain method and explicitly includes the harmonic frequencies known a priori. Therefore, the modified technique allows proper identification of eigenfrequencies and modal damping even when harmonic excitation frequencies are close to the natural frequencies of the structures. Experimental results are shown in the presence of multi-harmonic loads for a steel plate to validate the method.
Monitoring historical masonry structures with operational modal analysis: Two case studies
Ramos, L. F.; Marques, L.; Lourenço, P. B.; De Roeck, G.; Campos-Costa, A.; Roque, J.
2010-07-01
The paper addresses two complex case studies of modal and structural identification of monuments in Portugal: the Clock Tower of Mogadouro and the Church of Jerónimos Monastery, in Lisbon. These are being monitored by University of Minho with vibration, temperature and relative air humidity sensors. Operational modal analysis is being used to estimate the modal parameters, followed by statistical analysis to evaluate the environmental effects on the dynamic response. The aim is to explore damage assessment in masonry structures at an early stage by vibration signatures, as a part of a health monitoring process that helps in the preservation of historical constructions. The paper presents the necessary preliminary dynamic analysis steps before the monitoring task, which includes installation of the monitoring system, system identification and subsequent FE model updating analysis, automatic modal identification and investigation of the influence of the environment on the identified modal parameters.
Automated Modal Parameter Estimation for Operational Modal Analysis of Large Systems
DEFF Research Database (Denmark)
Andersen, Palle; Brincker, Rune; Goursat, Maurice;
2007-01-01
In this paper the problems of doing automatic modal parameter extraction and how to account for large number of data to process are considered. Two different approaches for obtaining the modal parameters automatically using OMA are presented: The Frequency Domain Decomposition (FDD) technique and...... and a correlation-driven Stochastic Subspace Identification (SSI) technique. Special attention is given to the problem of data reduction, where many sensors are available. Finally, the techniques are demonstrated on real data....
DEFF Research Database (Denmark)
Najafi, Nadia; Schmidt Paulsen, Uwe; Belloni, F.
are mounted at different points on the projection of the centroid line of the blade structure. Measurements are set up in PULSE LabShop software (product of Brüel & Kjær Company). In each measurement set, one reference point is subjected to an impulse force, and acceleration responses are recorded at three...... different points. This process continues until the data set contains all the points with their degrees of freedom. Finally the frequency response function (FRF) is obtained for all points, and the natural frequencies and the mode shapes are estimated by peak picking method. Operational Modal Analysis (OMA......) is the second approach used in this project in parallel with stereo vision technique. In this method, only the output is required to be measured; actually the input is random and unknown. In this experiment markers are put on the blade centroid projection line (the same place as the accelerometer positions...
DEFF Research Database (Denmark)
Najafi, Nadia; Schmidt Paulsen, Uwe; Belloni, F.
2014-01-01
are mounted at different points on the projection of the centroid line of the blade structure. Measurements are set up in PULSE LabShop software (product of Brüel & Kjær Company). In each measurement set, one reference point is subjected to an impulse force, and acceleration responses are recorded at three...... different points. This process continues until the data set contains all the points with their degrees of freedom. Finally the frequency response function (FRF) is obtained for all points, and the natural frequencies and the mode shapes are estimated by peak picking method. Operational Modal Analysis (OMA......) is the second approach used in this project in parallel with stereo vision technique. In this method, only the output is required to be measured; actually the input is random and unknown. In this experiment markers are put on the blade centroid projection line (the same place as the accelerometer positions...
DEFF Research Database (Denmark)
Ulriksen, Martin Dalgaard; Tcherniak, Dmitri; Kirkegaard, Poul Henning;
2014-01-01
The presented study demonstrates an application of a previously proposed modal and wavelet analysis-based damage identification method to a wind turbine blade. A trailing edge debonding was introduced to a SSP 34m blade mounted on a test rig. Operational modal analysis (OMA) was conducted to obtain....... Since only a limited number of measurement points were utilized in the experiments, valid damage identification can only be obtained when employing high-frequency modes....
Reynders, Edwin; Roeck, Guido De
2008-04-01
The modal analysis of mechanical or civil engineering structures consists of three steps: data collection, system identification and modal parameter estimation. The system identification step plays a crucial role in the quality of the modal parameters, that are derived from the identified system model, as well as in the number of modal parameters that can be determined. This explains the increasing interest in sophisticated system identification methods for both experimental and operational modal analysis. In purely operational or output-only modal analysis, absolute scaling of the obtained mode shapes is not possible and the frequency content of the ambient forces could be narrow banded so that only a limited number of modes are obtained. This drives the demand for system identification methods that take both artificial and ambient excitation into account so that the amplitude of the artificial excitation can be small compared to that of the ambient excitation. An accurate, robust and efficient system identification method that meets this requirements is combined deterministic-stochastic subspace identification. It can be used both for experimental modal analysis and for operational modal analysis with deterministic inputs. In this paper, the method is generalized to a reference-based version which is faster and, if the chosen reference outputs have the highest SNR values, more accurate than the classical algorithm. The algorithm is validated with experimental data from the Z24 bridge that overpassing the A1 highway between Bern and Zurich in Switzerland, that have been proposed as a benchmark for the assessment of system identification methods for the modal analysis of large structures. With the presented algorithm, the most complete set of modes reported so far is obtained.
Sparse Component Analysis Using Time-Frequency Representations for Operational Modal Analysis
Directory of Open Access Journals (Sweden)
Shaoqian Qin
2015-03-01
Full Text Available Sparse component analysis (SCA has been widely used for blind source separation(BSS for many years. Recently, SCA has been applied to operational modal analysis (OMA, which is also known as output-only modal identification. This paper considers the sparsity of sources’ time-frequency (TF representation and proposes a new TF-domain SCA under the OMA framework. First, the measurements from the sensors are transformed to the TF domain to get a sparse representation. Then, single-source-points (SSPs are detected to better reveal the hyperlines which correspond to the columns of the mixing matrix. The K-hyperline clustering algorithm is used to identify the direction vectors of the hyperlines and then the mixing matrix is calculated. Finally, basis pursuit de-noising technique is used to recover the modal responses, from which the modal parameters are computed. The proposed method is valid even if the number of active modes exceed the number of sensors. Numerical simulation and experimental verification demonstrate the good performance of the proposed method.
Sparse Component Analysis Using Time-Frequency Representations for Operational Modal Analysis
Qin, Shaoqian; Guo, Jie; Zhu, Changan
2015-01-01
Sparse component analysis (SCA) has been widely used for blind source separation(BSS) for many years. Recently, SCA has been applied to operational modal analysis (OMA), which is also known as output-only modal identification. This paper considers the sparsity of sources' time-frequency (TF) representation and proposes a new TF-domain SCA under the OMA framework. First, the measurements from the sensors are transformed to the TF domain to get a sparse representation. Then, single-source-points (SSPs) are detected to better reveal the hyperlines which correspond to the columns of the mixing matrix. The K-hyperline clustering algorithm is used to identify the direction vectors of the hyperlines and then the mixing matrix is calculated. Finally, basis pursuit de-noising technique is used to recover the modal responses, from which the modal parameters are computed. The proposed method is valid even if the number of active modes exceed the number of sensors. Numerical simulation and experimental verification demonstrate the good performance of the proposed method. PMID:25789492
Optical monitoring and operational modal analysis of large wind turbines
Özbek, M.
2013-01-01
Identification of the dynamic properties and the corresponding structural response of wind turbines is essential for optimizing the energy produced, ensuring safe and reliable operation and increasing the life-time of the system. As the sizes of modern wind turbines increase, their dynamic behaviors
Optical monitoring and operational modal analysis of large wind turbines
Özbek, M.
2013-01-01
Identification of the dynamic properties and the corresponding structural response of wind turbines is essential for optimizing the energy produced, ensuring safe and reliable operation and increasing the life-time of the system. As the sizes of modern wind turbines increase, their dynamic behaviors
Hanson, D.; Randall, R. B.; Antoni, J.; Thompson, D. J.; Waters, T. P.; Ford, R. A. J.
2007-08-01
This paper presents a new technique for operational modal analysis (OMA) of multiple input multiple output (MIMO) systems excited by at least one cyclostationary input with a unique cyclic frequency. The technique is based on two signal separation steps; the cyclostationary properties of the input are exploited to estimate the cyclic spectral density, effectively reducing the system from a MIMO to a single input multiple output (SIMO) situation, and curve-fitted in the cepstrum domain, which allows for the separation of the input and transfer function. This technique is demonstrated using measurements taken on a steel beam test rig and a passenger rail vehicle. The performance of this technique is discussed and compared to traditional input/output modal analysis and an existing cepstrum-based OMA technique. It is shown that the technique is able to correctly identify modal parameters, but like other spectrum-based OMA techniques, long time records are required in order to obtain both smooth cyclic spectrum estimates and sufficient resolution for accurate damping estimates. The nature of the input may also inhibit its performance in the very low-frequency region.
Using EFDD as a Robust Technique for Deterministic Excitation in Operational Modal Analysis
DEFF Research Database (Denmark)
Jacobsen, Niels-Jørgen; Andersen, Palle; Brincker, Rune
2007-01-01
The algorithms used in Operational Modal Analysis assume that the input forces are stochastic in nature. While this is often the case for civil engineering structures, mechanical structures, in contrast, are subject inherently to deterministic forces due to the rotating parts in the machinery. Th...
Modal Testing and Analysis of Structures Under Operational Conditions: Industrial Applications
Hermans, L.; van der Auweraer, H.
1999-03-01
Experimental identification of structural dynamics models is usually based on the modal analysis approach. In the classical modal parameter estimation approach, the baseline data which are processed are frequency response functions measured under laboratory conditions. However, in many applications, the real operating conditions may differ significantly from those applied during the modal test. Hence, the need arises to identify a modal model in operational conditions. This issue is even more complicated by the fact that in most cases, only response data are measurable while the actual loading conditions are unknown. Therefore, the system identification process will need to base itself on output-only data. In the last decade, the problem of output-only modal analysis has typically been approached by applying a peak-picking technique to the auto- and cross-powers of the measured responses, resulting in operational deflection shapes and approximate estimates for the resonance frequencies. These shapes were then compared to or even decomposed into the laboratory modal results. Over the past years, several modal parameter estimation techniques have been proposed and studied for modal parameter extraction from output-only data. They include autoregressive moving averaging models, natural excitation technique (NExT) and stochastic subspace methods. In this paper, the capabilities and limitations of the NExT technique and two subspace techniques, referred to as the balanced realization and the canonical variate analysis, are evaluated for its applicability to industrial cases. The theory of the methods is briefly outlined. Subsequently, the performance of the methods is critically evaluated and compared for three industrial cases: the modal characterisation of the rear suspension system of a family car during road tests in order to understand a booming noise problem, flight flutter analysis of a commercial aircraft and the identification of the modes of a three
DEFF Research Database (Denmark)
/S and the Department of Building Technology and Structural Engineering at Aalborg University. It is the first conference ever to focus solely on experimental modal analysis for cases where only the responses are measured. It was decided to hold the conference to generate interest in operational modal analysis (also......These proceedings contain approximately 100 papers presented at the 1st International Operational Modal Conference, Copenhagen, Denmark, April 26 - 27, 2005. The conference is jointly organised by Structural Vibration Systems (SVS), Aalborg, Brüel & Kjær Sound and Vibration Measurement A...... known as ambient modal analysis, output-only modal analysis and natural input modal analysis) which has been around since the beginning of the development of traditional modal analysis in the early seventies. From the beginning, these techniques proved to have several advantages, due to less testing...
DEFF Research Database (Denmark)
López-Aenlle, Manuel; Brincker, Rune; Pelayo, F.
2012-01-01
When operational modal analysis (OMA) is used to estimate modal parameters, mode shapes cannot be mass normalized. In the past few years, some equations have been proposed to scale mode shapes using the mass-change method, which consists of repeating modal testing after changing the mass at diffe...
DEFF Research Database (Denmark)
Bajric, Anela; Brincker, Rune; Thöns, Sebastian
2015-01-01
The Operational Modal Analysis (OMA) techniques provide in most cases reasonably accurate estimates of structural frequencies and mode shapes. They are however known to produce erroneous structural damping estimates, which are presumably thought to be due to inherent random- or bias errors......). The evaluation is based on identification using random response from white noise loading of a three degree-of-freedom (3DOF) system numerically established from specified modal parameters for a range of natural frequencies. The numerical model provides comparisons of the effectiveness of damping estimation...
On the vibro-acoustical operational modal analysis of a helicopter cabin
Pierro, E.; Mucchi, E.; Soria, L.; Vecchio, A.
2009-05-01
This paper aims to present a modal decomposition formulation for a vibro-acoustical operational modal analysis (OMA). In literature many works can be found on this topic, but until now no attention has been focused on the analytical form of the cross-power spectra (CPs) between the system outputs when a fluid-structure coupling is present. In this work it is shown that the CPs modal decomposition depends on the choice of the references, i.e. acoustical or structural. At first it is theoretically pointed out that the CP formulation for the acoustical and structural case is formally identical if appropriately pre-processed. Then, this theoretical result is verified through the results of an extensive experimental testing on the helicopter EUROCOPTER EC-135. The CPs between the structural output velocities and the acoustical response of the microphone inside the helicopter cabin are considered as inputs of an OMA. In order to verify the effectiveness of the modal model so obtained a classical modal analysis is also performed. The acoustical reference choice reveals to be suitable for a vibro-acoustical OMA. It is highlighted, indeed, that the acoustical pressure measurement inside the enclosure can be used as reference instead of the commonly used structural sensors, both from the theoretical and practical point of view. This is useful for high scale structures where the structural responses are usually measured by means of moving sensor arrays and additional fixed reference sensors should be positioned on the surface.
Energy Technology Data Exchange (ETDEWEB)
Ibsen, Lars Bo; Liingaard, M.
2006-12-15
This technical report concerns the basic theory and principles for experimental modal analysis. The sections within the report are: Output-only modal analysis software, general digital analysis, basics of structural dynamics and modal analysis and system identification. (au)
Modified ERA method for operational modal analysis in the presence of harmonic excitations
Mohanty, Prasenjit; Rixen, Daniel J.
2006-01-01
Operational modal analysis (OMA) is a procedure which allows to extract modal parameters of structures from measured responses to unknown excitation arising in operation. It is based on the assumption that the input to the structure is stationary white noise. In practice, however, structural vibration observed in operation cannot always be considered as pure white-noise excitation. In many practical cases, vibrations are induced by a combination of white-noise and harmonic excitations. Harmonic excitations in addition to random inputs can occur due to rotating components or fluctuating forces in electric actuators for instance. The usual way to compute modal parameters in the presence of harmonic excitations is to consider harmonically excited frequencies as being virtual eigenfrequencies of the structure. However, if the frequencies of the harmonic inputs are close to an eigenfrequency of the system, OMA procedures fail to identify the modal parameters properly. In this paper a modified ERA method is proposed, which can be applied as an identification procedure to include the effect of purely harmonic vibrations, assuming the harmonic frequencies are known a priori. The efficiency of the proposed approach is evaluated for an experimental example of a pinned-pinned beam structure excited by multi-harmonic loads superposed on random excitation.
Harmonics elimination algorithm for operational modal analysis using random decrement technique
Modak, S. V.; Rawal, Chetan; Kundra, T. K.
2010-05-01
Operational modal analysis (OMA) extracts modal parameters of a structure using their output response, during operation in general. OMA, when applied to mechanical engineering structures is often faced with the problem of harmonics present in the output response, and can cause erroneous modal extraction. This paper demonstrates for the first time that the random decrement (RD) method can be efficiently employed to eliminate the harmonics from the randomdec signatures. Further, the research work shows effective elimination of large amplitude harmonics also by proposing inclusion of additional random excitation. This obviously need not be recorded for analysis, as is the case with any other OMA method. The free decays obtained from RD have been used for system modal identification using eigen-system realization algorithm (ERA). The proposed harmonic elimination method has an advantage over previous methods in that it does not require the harmonic frequencies to be known and can be used for multiple harmonics, including periodic signals. The theory behind harmonic elimination is first developed and validated. The effectiveness of the method is demonstrated through a simulated study and then by experimental studies on a beam and a more complex F-shape structure, which resembles in shape to the skeleton of a drilling or milling machine tool. Cases with presence of single and multiple harmonics in the response are considered.
Operational modal analysis via image based technique of very flexible space structures
Sabatini, Marco; Gasbarri, Paolo; Palmerini, Giovanni B.; Monti, Riccardo
2013-08-01
Vibrations represent one of the most important topics of the engineering design relevant to flexible structures. The importance of this problem increases when a very flexible system is considered, and this is often the case of space structures. In order to identify the modal characteristics, in terms of natural frequencies and relevant modal parameters, ground tests are performed. However, these parameters could vary due to the operative conditions of the system. In order to continuously monitor the modal characteristics during the satellite lifetime, an operational modal analysis is mandatory. This kind of analysis is usually performed by using classical accelerometers or strain gauges and by properly analyzing the acquired output. In this paper a different approach for the vibrations data acquisition will be performed via image-based technique. In order to simulate a flexible satellite, a free flying platform is used; the problem is furthermore complicated by the fact that the overall system, constituted by a highly rigid bus and very flexible panels, must necessarily be modeled as a multibody system. In the experimental campaign, the camera, placed on the bus, will be used to identify the eigenfrequencies of the vibrating structure; in this case aluminum thin plates simulate very flexible solar panels. The structure is excited by a hammer or studied during a fast attitude maneuver. The results of the experimental activity will be investigated and compared with respect to the numerical simulation obtained via a FEM-multibody software and the relevant results will be proposed and discussed.
Directory of Open Access Journals (Sweden)
Wang Liang
2016-01-01
Full Text Available Operational modal analysis (OMA is prevalent in large structure modal identification for that it asks for output measurements only. To guarantee identification accuracy, theoretically, OMA data need to be a random process of Gaussian white noise (GWN. Although numerous OMA applications are found in practice, few have particularly discussed the data distribution and to what extent it would blur the modal judgement. This paper presents a method to sieve segments mostly obeying the GWN distribution out of a recording. With a windowing technique, the data segments are evaluated by the modified Kurtosis value. The process has been demonstrated on the monitoring data of two case study structures: one is a laboratory truss bridge excited by artificial forces, the other is a real cable-stayed bridge subject to environmental loads. The results show that weak randomness data may result in false peaks that would possibly mislead the non-parametric modal identification, such as using the Frequency Domain Decomposition method. To overcome, cares on selecting the optimal segment shall be exercised. The proposed method is verified effective to find the most suitable data for modal identification of structural health monitoring systems.
Continuous-time operational modal analysis in the presence of harmonic disturbances
Pintelon, R.; Peeters, B.; Guillaume, P.
2008-07-01
Operational modal analysis (OMA) allows to identify the modal parameters from the measured response to unknown random perturbations of a mechanical structure in operation. However, in all applications with rotating components (e.g. helicopters, turbines, diesel motors,…,) the structural vibration in operation is a combination of the response to the random perturbation and the harmonic excitation due to the rotating components. Classical OMA methods fail if the harmonic disturbance is close to, or coincides with a resonance frequency of the structure. Therefore, these methods have been extended to deal with harmonic disturbances with a known, fixed frequency. However, in many applications (e.g. helicopters, wind turbines, diesel motors,…) the frequencies of the harmonic disturbances vary in time. This paper presents three methods for suppressing the influence of harmonic disturbances with unknown varying frequencies in operational modal analysis. Two of these methods can handle the case where the peak of the harmonic disturbance and the resonance peak completely overlap. The performance of the three methods is illustrated on simulations and real helicopter data. The present paper handles the single output case only.
Repressing the effects of variable speed harmonic orders in operational modal analysis
Randall, R. B.; Coats, M. D.; Smith, W. A.
2016-10-01
Discrete frequency components such as machine shaft orders can disrupt the operation of normal Operational Modal Analysis (OMA) algorithms. With constant speed machines, they have been removed using time synchronous averaging (TSA). This paper compares two approaches for varying speed machines. In one method, signals are transformed into the order domain, and after the removal of shaft speed related components by a cepstral notching method, are transformed back to the time domain to allow normal OMA. In the other simpler approach an exponential shortpass lifter is applied directly in the time domain cepstrum to enhance the modal information at the expense of other disturbances. For simulated gear signals with speed variations of both ±5% and ±15%, the simpler approach was found to give better results The TSA method is shown not to work in either case. The paper compares the results with those obtained using a stationary random excitation.
Operational modal analysis of a rectangular plate using non-contact excitation and measurement
Xu, Y. F.; Zhu, W. D.
2013-09-01
Operational modal analysis (OMA), or output-only modal analysis, has been extensively developed in the past decades and widely used especially when the input is unknown and difficult to measure. This paper presents a non-contact experimental technique for measuring modal parameters of a rectangular aluminum plate with free boundaries using only the output data, with the intention to apply the technique to turbine blades. OMA is used to analyze both the out-of-plane and in-plane vibrations of the plate in the frequency range of up to 15,000 Hz, which can be an operation frequency range of a turbine blade, under white noise acoustic excitation in a direction of interest. It is shown that OMA can be performed when the types of measurement at the measurement and reference points are different, since the associated cross-correlation functions contain modal characteristics of the test structure. A single-point laser vibrometer and a free-field microphone are used to simultaneously measure the responses of the plate in a non-contact manner, with the microphone measurement serving as the reference. The pressure measured by the microphone near the reference point is shown to be proportional to the normal surface acceleration at the reference point, and the cross power spectral densities obtained by the current test method can be used for modal parameter estimation. A method for measuring the in-plane modes of the plate by shining the laser beam on the plate surface with an incident angle is developed. Experimental modal analysis (EMA) is also performed on the plate using an impact hammer and the laser vibrometer. The measured natural frequencies and mode shapes of the out-of-plane and in-plane modes of the plate using OMA and EMA are compared with those calculated using commercial finite element software. The maximum error between the measured and calculated natural frequencies of the plate is 1.53 percent for the first 18 elastic modes, including 16 out-of-plane and two in
DEFF Research Database (Denmark)
Skafte, Anders; Aenlle, Manuel L.; Brincker, Rune
2016-01-01
measuring the in-plane deformation. This paper proposes a method in which the displacement mode shapes and responses can be predicted using only strain measurements. The method relies on the newly discovered principle of local correspondence, which states that each experimental mode can be expressed....... The method is validated with experimental tests on a scaled model of a two-span bridge installed with strain gauges. Random load was applied to simulate a civil structure under operating condition, and strain mode shapes were identified using operational modal analysis....
Devriendt, Christof; De Sitter, Gert; Vanlanduit, Steve; Guillaume, Patrick
2009-04-01
Operational modal analysis (OMA) is based on the assumption that the forces on the structure are the result of a stochastic process, so being white noise. In practice, however, structural vibrations observed in operation cannot always be considered as pure white-noise excitation. In many mechanical structures the loading forces are often more complex and even harmonic components can be present in the response. This is especially true, when measuring on mechanical structures containing rotating parts (e.g. cars, turbines, windmills), but also civil engineering structures may have responses superimposed by harmonic components. OMA procedures are, strictly speaking, not applicable in these situations. Current techniques may encounter difficulties to correctly identify the modal parameters, especially for modes with eigenfrequencies close to the harmonic frequencies. In this paper a recently proposed OMA technique based on transmissibility measurements will be applied. This method reduces the risk to wrongly identify the modal parameters due to the presence of harmonics. The unknown operational forces can be arbitrary (coloured noise, swept sine, impact, etc.) as long as they are persistently exciting in the frequency band of interest.
Kromulski, J.; Hojan, E.
1996-10-01
Two methods are presented for the determination of operational deflection shapes (ODSs). The first method allows one to determine the ODSs by measuring mechanical vibrations at test points of the operating machine (created by the forces occurring in the actual work cycle). The second method is based on the modal model of the machine, including the forces which occur in the operation process, and yields the operational modes of vibration. The forces introduced into the model are determined by methods of pseudo-inversion of the matrix of the spectral transmissibility functions of the mechanical system and the vector of operating vibrations. The determination of the forces involved is necessary for the definition of the paths of energy transfer and the analysis of the noise emitted by the mechanical system (machine).
An approach to operational modal analysis using the expectation maximization algorithm
Cara, F. Javier; Carpio, Jaime; Juan, Jesús; Alarcón, Enrique
2012-08-01
This paper presents the Expectation Maximization algorithm (EM) applied to operational modal analysis of structures. The EM algorithm is a general-purpose method for maximum likelihood estimation (MLE) that in this work is used to estimate state space models. As it is well known, the MLE enjoys some optimal properties from a statistical point of view, which make it very attractive in practice. However, the EM algorithm has two main drawbacks: its slow convergence and the dependence of the solution on the initial values used. This paper proposes two different strategies to choose initial values for the EM algorithm when used for operational modal analysis: to begin with the parameters estimated by Stochastic Subspace Identification method (SSI) and to start using random points. The effectiveness of the proposed identification method has been evaluated through numerical simulation and measured vibration data in the context of a benchmark problem. Modal parameters (natural frequencies, damping ratios and mode shapes) of the benchmark structure have been estimated using SSI and the EM algorithm. On the whole, the results show that the application of the EM algorithm starting from the solution given by SSI is very useful to identify the vibration modes of a structure, discarding the spurious modes that appear in high order models and discovering other hidden modes. Similar results are obtained using random starting values, although this strategy allows us to analyze the solution of several starting points what overcome the dependence on the initial values used.
Skafte, Anders; Aenlle, Manuel L.; Brincker, Rune
2016-02-01
Measurement systems are being installed in more and more civil structures with the purpose of monitoring the general dynamic behavior of the structure. The instrumentation is typically done with accelerometers, where experimental frequencies and mode shapes can be identified using modal analysis and used in health monitoring algorithms. But the use of accelerometers is not suitable for all structures. Structures like wind turbine blades and wings on airplanes can be exposed to lightning, which can cause the measurement systems to fail. Structures like these are often equipped with fiber sensors measuring the in-plane deformation. This paper proposes a method in which the displacement mode shapes and responses can be predicted using only strain measurements. The method relies on the newly discovered principle of local correspondence, which states that each experimental mode can be expressed as a unique subset of finite element modes. In this paper the technique is further developed to predict the mode shapes in different states of the structure. Once an estimate of the modes is found, responses can be predicted using the superposition of the modal coordinates weighted by the mode shapes. The method is validated with experimental tests on a scaled model of a two-span bridge installed with strain gauges. Random load was applied to simulate a civil structure under operating condition, and strain mode shapes were identified using operational modal analysis.
Insights on the Bayesian spectral density method for operational modal analysis
Au, Siu-Kui
2016-01-01
This paper presents a study on the Bayesian spectral density method for operational modal analysis. The method makes Bayesian inference of the modal properties by using the sample power spectral density (PSD) matrix averaged over independent sets of ambient data. In the typical case with a single set of data, it is divided into non-overlapping segments and they are assumed to be independent. This study is motivated by a recent paper that reveals a mathematical equivalence of the method with the Bayesian FFT method. The latter does not require averaging concepts or the independent segment assumption. This study shows that the equivalence does not hold in reality because the theoretical long data asymptotic distribution of the PSD matrix may not be valid. A single time history can be considered long for the Bayesian FFT method but not necessarily for the Bayesian PSD method, depending on the number of segments.
Modak, S. V.
2013-12-01
Operational Modal Analysis (OMA) is used to extract modal parameters of a structure on the basis of their output response measured during operation. OMA, when applied to mechanical engineering structures is often faced with the problem of harmonics present in the output response. A complex structure may have many dominant frequency components in its response frequency spectrum. These may contain frequency components associated with resonant frequencies of the structure, which and the associated mode shapes and the damping factors represent the data of interest, but may also contain frequencies or harmonics associated with the excitation sources. Since in OMA the characteristics of the excitation sources are not known, one of the problems lies in separating the resonant frequencies from the harmonic excitation frequencies. Any error in this regard may lead to an error in modal identification with the consequence that a harmonic may be construed as a structural mode and vice versa. This issue is addressed in this paper and a method is presented for separating resonant frequencies from harmonic excitation frequencies using random decrement of the response. The principle of the method is presented using an analytical study on a single degree of freedom system. The effectiveness of the method is then demonstrated through numerical studies on a lumped parameter multi-degree of freedom system and a simulated plate structure. Detection of single and multiple harmonics in the response that are well separated as well as close to resonant frequencies are considered.
A method for the harmonic removal in operational modal analysis of rotating blades
Agneni, Alessandro; Coppotelli, Giuliano; Grappasonni, Chiara
2012-02-01
The operational modal analysis, OMA, allows estimating the dynamic properties of a structure, natural frequencies, damping ratios, and mode shapes, without measuring the input forces. According to the main hypothesis concerning the input excitation, i.e., stochastic with frequency independent spectra (at least in the frequency band of interest), it is not theoretically possible to apply the OMA procedures in structures characterized by the presence of harmonic components in the excitation loading. In this paper, an approach capable to identify the presence of harmonic excitations, acting together with a broad band stochastic loading, and then to remove their effects in the modal parameter estimate is presented. The approach is based on the joint use of the statistical parameter called "entropy" and the already developed output-only procedure based on the application of the Hilbert transform properties to the output response signals. The capability to improve the OMA procedures is investigated numerically and through whirl tower experimental tests of a rotating blade in which both stochastic and harmonic contributions to the dynamic excitations have been provided by the perturbations arising from the operative conditions. A sensitivity analysis has been also performed to evaluate the effects of the filtered responses, in the time domain, on the statistical characterization, required to distinguish the operational frequencies from the natural ones.
Operational Modal Analysis Based on Subspace Algorithm with an Improved Stabilization Diagram Method
Directory of Open Access Journals (Sweden)
Shiqiang Qin
2016-01-01
Full Text Available Subspace-based algorithms for operational modal analysis have been extensively studied in the past decades. In the postprocessing of subspace-based algorithms, the stabilization diagram is often used to determine modal parameters. In this paper, an improved stabilization diagram is proposed for stochastic subspace identification. Specifically, first, a model order selection method based on singular entropy theory is proposed. The singular entropy increment is calculated from nonzero singular values of the output covariance matrix. The corresponding model order can be selected when the variation of singular entropy increment approaches to zero. Then, the stabilization diagram with confidence intervals which is established using the uncertainty of modal parameter is presented. Finally, a simulation example of a four-story structure and a full-scale cable-stayed footbridge application is employed to illustrate the improved stabilization diagram method. The study demonstrates that the model order can be reasonably determined by the proposed method. The stabilization diagram with confidence intervals can effectively remove the spurious modes.
Energy Technology Data Exchange (ETDEWEB)
Ovseychuk, V.A.; Shesteren, V.Ye.
1983-01-01
Studies are conducted using statistical and mathematical methods of the schedules of electrical loads and correlated modal and operational indicators of regional 100 to 750 kilovolt substations (PS) of the country's electric power system (EES). An analysis is conducted of the graphs and correlated modal and operational indicators of step down regional 110 to 750 kilovolt substations and the tendencies in the configuration of the daily schedules and the modal operational indicators are established. Probabilistic and statistical models of the loads of substations are developed. Adequate regression models of the daily schedules of reactive loads of substations are obtained.
Operational Modal Analysis and the Performance Assessment of Vehicle Suspension Systems
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L. Soria
2012-01-01
Full Text Available Comfort, road holding and safety of passenger cars are mainly influenced by an appropriate design of suspension systems. Improvements of the dynamic behaviour can be achieved by implementing semi-active or active suspension systems. In these cases, the correct design of a well-performing suspension control strategy is of fundamental importance to obtain satisfying results. Operational Modal Analysis allows the experimental structural identification in those that are the real operating conditions: Moving from output-only data, leading to modal models linearised around the more interesting working points and, in the case of controlled systems, providing the needed information for the optimal design and verification of the controller performance. All these characters are needed for the experimental assessment of vehicle suspension systems. In the paper two suspension architectures are considered equipping the same car type. The former is a semi-active commercial system, the latter a novel prototypic active system. For the assessment of suspension performance, two different kinds of tests have been considered, proving ground tests on different road profiles and laboratory four poster rig tests. By OMA-processing the signals acquired in the different testing conditions and by comparing the results, it is shown how this tool can be effectively utilised to verify the operation and the performance of those systems, by only carrying out a simple, cost-effective road test.
Scaling of mode shapes from operational modal analysis using harmonic forces
Brandt, A.; Berardengo, M.; Manzoni, S.; Cigada, A.
2017-10-01
This paper presents a new method for scaling mode shapes obtained by means of operational modal analysis. The method is capable of scaling mode shapes on any structure, also structures with closely coupled modes, and the method can be used in the presence of ambient vibration from traffic or wind loads, etc. Harmonic excitation can be relatively easily accomplished by using general-purpose actuators, also for force levels necessary for driving large structures such as bridges and highrise buildings. The signal processing necessary for mode shape scaling by the proposed method is simple and the method can easily be implemented in most measurement systems capable of generating a sine wave output. The tests necessary to scale the modes are short compared to typical operational modal analysis test time. The proposed method is thus easy to apply and inexpensive relative to some other methods for scaling mode shapes that are available in literature. Although it is not necessary per se, we propose to excite the structure at, or close to, the eigenfrequencies of the modes to be scaled, since this provides better signal-to-noise ratio in the response sensors, thus permitting the use of smaller actuators. An extensive experimental activity on a real structure was carried out and the results reported demonstrate the feasibility and accuracy of the proposed method. Since the method utilizes harmonic excitation for the mode shape scaling, we propose to call the method OMAH.
Devriendt, C.; Weijtjens, W.; De Sitter, G.; Guillaume, P.
2013-10-01
In recent years, the authors have proposed an innovative approach for Operational Modal Analysis based on transmissibility measurements. A method was proposed based on combining 2 single-reference transmissibility functions that were obtained during 2 different loading conditions. However in practice one in general has access to multiple transmissibility functions and perhaps even multiple loading conditions. In this paper a new method is introduced that combines all the measured single-reference transmissibility functions in a unique matrix formulation in order to identify system poles. It will be shown that each element of the pseudo-inverse of this matrix is a rational function with poles equal to the system poles. The proposed method reduces the risk to miss system poles and to identify extra non-physical poles. Therefore the method increases the usability and reliability of transmissibility based operational modal analysis (TOMA). The method will be demonstrated and validated by means of an experiment on a beam excited at multiple inputs for three different loading conditions.
Operational modal analysis on a VAWT in a large wind tunnel using stereo vision technique
DEFF Research Database (Denmark)
Najafi, Nadia; Schmidt Paulsen, Uwe
2017-01-01
This paper is about development and use of a research based stereo vision system for vibration and operational modal analysis on a parked, 1-kW, 3-bladed vertical axis wind turbine (VAWT), tested in a wind tunnel at high wind. Vibrations were explored experimentally by tracking small deflections ...... in picking very closely spaced modes. Finally, the uncertainty of the 3D displacement measurement was evaluated by applying a generalized method based on the law of error propagation, for a linear camera model of the stereo vision system.......This paper is about development and use of a research based stereo vision system for vibration and operational modal analysis on a parked, 1-kW, 3-bladed vertical axis wind turbine (VAWT), tested in a wind tunnel at high wind. Vibrations were explored experimentally by tracking small deflections...... of the markers on the structure with two cameras, and also numerically, to study structural vibrations in an overall objective to investigate challenges and to prove the capability of using stereo vision. Two high speed cameras provided displacement measurements at no wind speed interference. The displacement...
DEFF Research Database (Denmark)
Ibsen, Lars Bo; Liingaard, Morten
This technical report concerns the basic theory and principles for experimental modal analysis. The sections within the report are: Output-only modal analysis software (section 1.1), general digital analysis (section 1.2), basics of structural dynamics and modal analysis (section 1.3) and system ...
Operational Modal Analysis of Bridge Structures with Data from GNSS/Accelerometer Measurements.
Xiong, Chunbao; Lu, Huali; Zhu, Jinsong
2017-02-23
Real-time dynamic displacement and acceleration responses of the main span section of the Tianjin Fumin Bridge in China under ambient excitation were tested using a Global Navigation Satellite System (GNSS) dynamic deformation monitoring system and an acceleration sensor vibration test system. Considering the close relationship between the GNSS multipath errors and measurement environment in combination with the noise reduction characteristics of different filtering algorithms, the researchers proposed an AFEC mixed filtering algorithm, which is an combination of autocorrelation function-based empirical mode decomposition (EMD) and Chebyshev mixed filtering to extract the real vibration displacement of the bridge structure after system error correction and filtering de-noising of signals collected by the GNSS. The proposed AFEC mixed filtering algorithm had high accuracy (1 mm) of real displacement at the elevation direction. Next, the traditional random decrement technique (used mainly for stationary random processes) was expanded to non-stationary random processes. Combining the expanded random decrement technique (RDT) and autoregressive moving average model (ARMA), the modal frequency of the bridge structural system was extracted using an expanded ARMA_RDT modal identification method, which was compared with the power spectrum analysis results of the acceleration signal and finite element analysis results. Identification results demonstrated that the proposed algorithm is applicable to analyze the dynamic displacement monitoring data of real bridge structures under ambient excitation and could identify the first five orders of the inherent frequencies of the structural system accurately. The identification error of the inherent frequency was smaller than 6%, indicating the high identification accuracy of the proposed algorithm. Furthermore, the GNSS dynamic deformation monitoring method can be used to monitor dynamic displacement and identify the modal
Operational Modal Analysis of Bridge Structures with Data from GNSS/Accelerometer Measurements
Directory of Open Access Journals (Sweden)
Chunbao Xiong
2017-02-01
Full Text Available Real-time dynamic displacement and acceleration responses of the main span section of the Tianjin Fumin Bridge in China under ambient excitation were tested using a Global Navigation Satellite System (GNSS dynamic deformation monitoring system and an acceleration sensor vibration test system. Considering the close relationship between the GNSS multipath errors and measurement environment in combination with the noise reduction characteristics of different filtering algorithms, the researchers proposed an AFEC mixed filtering algorithm, which is an combination of autocorrelation function-based empirical mode decomposition (EMD and Chebyshev mixed filtering to extract the real vibration displacement of the bridge structure after system error correction and filtering de-noising of signals collected by the GNSS. The proposed AFEC mixed filtering algorithm had high accuracy (1 mm of real displacement at the elevation direction. Next, the traditional random decrement technique (used mainly for stationary random processes was expanded to non-stationary random processes. Combining the expanded random decrement technique (RDT and autoregressive moving average model (ARMA, the modal frequency of the bridge structural system was extracted using an expanded ARMA_RDT modal identification method, which was compared with the power spectrum analysis results of the acceleration signal and finite element analysis results. Identification results demonstrated that the proposed algorithm is applicable to analyze the dynamic displacement monitoring data of real bridge structures under ambient excitation and could identify the first five orders of the inherent frequencies of the structural system accurately. The identification error of the inherent frequency was smaller than 6%, indicating the high identification accuracy of the proposed algorithm. Furthermore, the GNSS dynamic deformation monitoring method can be used to monitor dynamic displacement and identify the
Robust optimal sensor placement for operational modal analysis based on maximum expected utility
Li, Binbin; Der Kiureghian, Armen
2016-06-01
Optimal sensor placement is essentially a decision problem under uncertainty. The maximum expected utility theory and a Bayesian linear model are used in this paper for robust sensor placement aimed at operational modal identification. To avoid nonlinear relations between modal parameters and measured responses, we choose to optimize the sensor locations relative to identifying modal responses. Since the modal responses contain all the information necessary to identify the modal parameters, the optimal sensor locations for modal response estimation provide at least a suboptimal solution for identification of modal parameters. First, a probabilistic model for sensor placement considering model uncertainty, load uncertainty and measurement error is proposed. The maximum expected utility theory is then applied with this model by considering utility functions based on three principles: quadratic loss, Shannon information, and K-L divergence. In addition, the prior covariance of modal responses under band-limited white-noise excitation is derived and the nearest Kronecker product approximation is employed to accelerate evaluation of the utility function. As demonstration and validation examples, sensor placements in a 16-degrees-of-freedom shear-type building and in Guangzhou TV Tower under ground motion and wind load are considered. Placements of individual displacement meter, velocimeter, accelerometer and placement of mixed sensors are illustrated.
A study and extension of second-order blind source separation to operational modal analysis
Antoni, J.; Chauhan, S.
2013-02-01
Second-order blind source separation (SOBSS) has gained recent interest in operational modal analysis (OMA), since it is able to separate a set of system responses into modal coordinates from which the system poles can be extracted by single-degree-of-freedom techniques. In addition, SOBSS returns a mixing matrix whose columns are the estimates of the system mode shapes. The objective of this paper is threefold. First, a theoretical analysis of current SOBSS methods is conducted within the OMA framework and its precise conditions of applicability are established. Second, a new separation method is proposed that fixes current limitations of SOBSS: It returns estimate of complex mode shapes, it can deal with more active modes than the number of available sensors, and it shows superior performance in the case of heavily damped and/or strongly coupled modes. Third, a theoretical connection is drawn between SOBSS and stochastic subspace identification (SSI), which stands as one of the points of reference in OMA. All approaches are finally compared by means of numerical simulations.
Luczak, M. M.; Mucchi, E.; Telega, J.
2016-09-01
The goal of the research is to develop a vibration-based procedure for the identification of structural failures in a laboratory scale model of a tripod supporting structure of an offshore wind turbine. In particular, this paper presents an experimental campaign on the scale model tested in two stages. Stage one encompassed the model tripod structure tested in air. The second stage was done in water. The tripod model structure allows to investigate the propagation of a circumferential representative crack of a cylindrical upper brace. The in-water test configuration included the tower with three bladed rotor. The response of the structure to the different waves loads were measured with accelerometers. Experimental and operational modal analysis was applied to identify the dynamic properties of the investigated scale model for intact and damaged state with different excitations and wave patterns. A comprehensive test matrix allows to assess the differences in estimated modal parameters due to damage or as potentially introduced by nonlinear structural response. The presented technique proves to be effective for detecting and assessing the presence of representative cracks.
Rainieri, Carlo
2014-01-01
This book covers all aspects of operational modal analysis for civil engineering, from theoretical background to applications, including measurement hardware, software development, and data processing. In particular, this book provides an extensive description and discussion of OMA methods, their classification and relationship, and advantages and drawbacks. The authors cover both the well-established theoretical background of OMA methods and the most recent developments in the field, providing detailed examples to help the reader better understand the concepts and potentialities of the technique. Additional material is provided (data, software) to help practitioners and students become familiar with OMA. Covering a range of different aspects of OMA, always with the application in mind, the practical perspective adopted in this book makes it ideal for a wide range of readers from researchers to field engineers; graduate and undergraduate students; and technicians interested in structural dynamics, system iden...
Gómez Araújo, Iván; Laier, Jose Elias
2015-09-01
In recent years, transmissibility functions have been used as alternatives to identify the modal parameters of structures under operating conditions. The scalar power spectrum density transmissibility (PSDT), which relates only two responses, was proposed to extract modal parameters by combining different PSDTs with different transferring outputs. In this sense, this paper proposes extending the scalar PSDT concept to multivariable PSDT by relating multiple responses instead of only two. This extension implies the definition of a transmissibility matrix, relating the cross-spectral density matrix among the responses at coordinates Z and U with the cross-spectral density matrix among the responses at coordinates Z and K. The coordinates in Z are known as the transferring outputs. By defining the same coordinates K and U, but with different transferring outputs Z, we prove that the multivariable PSDT converges to the same matrix when it approaches the system poles. This property is used to define only one matrix with different multivariable PSDTs with same coordinates K and U, but with different transferring outputs. The resulting matrix is singular at the system poles, meaning that by applying the inverse of the matrix, the modal parameters can be identified. Here, a numeric example of a beam model subjected to excitations and data from an operational vibration bridge test shows that the proposed method is capable of identifying modal parameters. Furthermore, the results demonstrate the possibility of estimating the same modal parameters by changing only the coordinates K and U, providing greater reliability during modal parameter identification.
Operational modal analysis of a ship model in the presence of harmonic excitation
Xu, Junchen; Hong, Ming; Liu, Xiaobing
2013-03-01
A ship is operated under an extremely complex environment, and waves and winds are assumed to be the stochastic excitations. Moreover, the propeller, host and mechanical equipment can also induce the harmonic responses. In order to reduce structural vibration, it is important to obtain the modal parameters information of a ship. However, the traditional modal parameter identification methods are not suitable since the excitation information is difficult to obtain. Natural excitation technique-eigensystem realization algorithm (NExT-ERA) is an operational modal identification method which abstracts modal parameters only from the response signals, and it is based on the assumption that the input to the structure is pure white noise. Hence, it is necessary to study the influence of harmonic excitations while applying the NExT-ERA method to a ship structure. The results of this research paper indicate the practical experiences under ambient excitation, ship model experiments were successfully done in the modal parameters identification only when the harmonic frequencies were not too close to the modal frequencies.
Stochastic subspace identification for operational modal analysis of an arch bridge
Loh, Chin-Hsiung; Chen, Ming-Che; Chao, Shu-Hsien
2012-04-01
In this paer the application of output-only system identification technique, known as Stochastic Subspace Identification (SSI) algorithms, for civil infrastructures is carried out. The ability of covariance driven stochastic subspace identification (SSI-COV) was proved through the analysis of the ambient data of an arch bridge under operational condition. A newly developed signal processing technique, Singular Spectrum analysis (SSA), capable to smooth noisy signals, is adopted for pre-processing the recorded data before the SSI. The conjunction of SSA and SSICOV provides a useful criterion for the system order determination. With the aim of estimating accurate modal parameters of the structure in off-line analysis, a stabilization diagram is constructed by plotting the identified poles of the system with increasing the size of data Hankel matrix. Identification task of a real structure, Guandu Bridge, is carried out to identify the system natural frequencies and mode shapes. The uncertainty of the identified model parameters from output-only measurement of the bridge under operation condition, such as temperature and traffic loading conditions, is discussed.
Perspectives of Second-Order Blind Identification for Operational Modal Analysis of Civil Structures
Directory of Open Access Journals (Sweden)
C. Rainieri
2014-01-01
Full Text Available Innovative methods for output-only estimation of the modal properties of civil structures are based on blind source separation techniques. In the present paper attention is focused on the second-order blind identification (SOBI algorithm and the influence of its analysis parameters on computational time and accuracy of modal parameter estimates. These represent key issues in view of the automation of the algorithm and its integration within vibration-based monitoring systems. The herein reported analyses and results provide useful hints for reduction of computational time and control of accuracy of estimates. The latter topic is of interest in the case of single modal identification tests, too. A criterion for extraction of accurate modal parameter estimates is identified and applied to selected experimental case studies. They are representative of the different levels of complexity that can be encountered during real modal tests. The obtained results point out that SOBI can provide accurate estimates and it can also be automated, confirming that it represents a profitable alternative for output-only modal analysis and vibration-based monitoring of civil structures.
Weijtjens, Wout; Lataire, John; Devriendt, Christof; Guillaume, Patrick
2014-12-01
Periodical loads, such as waves and rotating machinery, form a problem for operational modal analysis (OMA). In OMA only the vibrations of a structure of interest are measured and little to nothing is known about the loads causing these vibrations. Therefore, it is often assumed that all dynamics in the measured data are linked to the system of interest. Periodical loads defy this assumption as their periodical behavior is often visible within the measured vibrations. As a consequence most OMA techniques falsely associate the dynamics of the periodical load with the system of interest. Without additional information about the load, one is not able to correctly differentiate between structural dynamics and the dynamics of the load. In several applications, e.g. turbines and helicopters, it was observed that because of periodical loads one was unable to correctly identify one or multiple modes. Transmissibility based OMA (TOMA) is a completely different approach to OMA. By using transmissibility functions to estimate the structural dynamics of the system of interest, all influence of the load-spectrum can be eliminated. TOMA therefore allows to identify the modal parameters without being influenced by the presence of periodical loads, such as harmonics. One of the difficulties of TOMA is that the analyst is required to find two independent datasets, each associated with a different loading condition of the system of interest. This poses a dilemma for TOMA; how can an analyst identify two different loading conditions when little is known about the loads on the system? This paper tackles that problem by assuming that the loading conditions vary continuously over time, e.g. the changing wind directions. From this assumption TOMA is developed into a time-varying framework. This development allows TOMA to not only cope with the continuously changing loading conditions. The time-varying framework also enables the identification of the modal parameters from a single dataset
Modal Testing of Mechanical Structures Subject to Operational Excitation Forces
DEFF Research Database (Denmark)
Møller, N.; Brincker, Rune; Herlufsen, H.;
2000-01-01
Operational Modal Analysis also known as Output Only Modal Analysis has in the recent years been used for extracting modal parameters of civil engineering structures and is now becoming popular for mechanical structures. The advantage of the method is that no artificial excitation need...... to the Operational Modal Analysis. For Operational Modal Analysis two different estimation techniques are used: a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identification (SSI) algorithm....... These are compared to other methods such as traditional Modal Analysis....
Devriendt, Christof; De Sitter, Gert; Guillaume, Patrick
2010-07-01
In this contribution the approach to identify modal parameters from output-only (scalar) transmissibility measurements [C. Devriendt, P. Guillaume, The use of transmissibility measurements in output-only modal analysis, Mechanical Systems and Signal Processing 21 (7) (2007) 2689-2696] is generalized to multivariable transmissibilities. In general, the poles that are identified from (scalar as well as multivariable) transmissibility measurements do not correspond with the system's poles. However, by combining transmissibility measurements under different loading conditions, it is shown in this paper how model parameters can be identified from multivariable transmissibility measurements.
Directory of Open Access Journals (Sweden)
Carlo Ruzzo
2016-10-01
Full Text Available System identification of offshore floating platforms is usually performed by testing small-scale models in wave tanks, where controlled conditions, such as still water for free decay tests, regular and irregular wave loading can be represented. However, this approach may result in constraints on model dimensions, testing time, and costs of the experimental activity. For such reasons, intermediate-scale field modelling of offshore floating structures may become an interesting as well as cost-effective alternative in a near future. Clearly, since the open sea is not a controlled environment, traditional system identification may become challenging and less precise. In this paper, a new approach based on Frequency Domain Decomposition (FDD method for Operational Modal Analysis is proposed and validated against numerical simulations in ANSYS AQWA v.16.0 on a simple spar-type structure. The results obtained match well with numerical predictions, showing that this new approach, opportunely coupled with more traditional wave tanks techniques, proves to be very promising to perform field-site identification of the model structures.
Operational modal analysis of flow-induced vibration of nuclear fuel rods in a turbulent axial flow
Energy Technology Data Exchange (ETDEWEB)
De Pauw, B., E-mail: bdepauw@vub.ac.be [Vrije Universiteit Brussel (VUB), Brussels Photonics Team (B-Phot), Brussels (Belgium); Vrije Universiteit Brussel (VUB), Department of Mechanical Engineering (AVRG), Brussels (Belgium); Belgian Nuclear Research Centre (SCK-CEN), Boeretang 200, Mol (Belgium); Weijtjens, W.; Vanlanduit, S. [Vrije Universiteit Brussel (VUB), Department of Mechanical Engineering (AVRG), Brussels (Belgium); Van Tichelen, K. [Belgian Nuclear Research Centre (SCK-CEN), Boeretang 200, Mol (Belgium); Berghmans, F. [Vrije Universiteit Brussel (VUB), Brussels Photonics Team (B-Phot), Brussels (Belgium)
2015-04-01
Highlights: • We describe an analysis technique to evaluate nuclear fuel pins. • We test a single fuel pin mockup subjected to turbulent axial flow. • Our analysis is based on operational modal analysis (OMA). • The accuracy and precision of our method is higher compared to traditional methods. • We demonstrate the possible onset of a fluid-elastic instability. - Abstract: Flow-induced vibration of nuclear reactor fuel pins can result in mechanical noise and lead to failure of the reactor's fuel assembly. This problem can be exacerbated in the new generation of liquid heavy metal fast reactors that use a much denser and more viscous coolant in the reactor core. An investigation of the flow-induced vibration in these particular conditions is therefore essential. In this paper, we describe an analysis technique to evaluate flow-induced vibration of nuclear reactor fuel pins subjected to a turbulent axial flow of heavy metal. We deal with a single fuel pin mockup designed for the lead–bismuth eutectic (LBE) cooled MYRRHA reactor which is subjected to similar flow conditions as in the reactor core. Our analysis is based on operational modal analysis (OMA) techniques. We show that the accuracy and precision of our OMA technique is higher compared to traditional methods and that it allows evaluating the evolution of modal parameters in operational conditions. We also demonstrate the possible onset of a fluid-elastic instability by tracking the modal parameters with increasing flow velocity.
A frequency-spatial domain decomposition (FSDD) method for operational modal analysis
Zhang, Lingmi; Wang, Tong; Tamura, Yukio
2010-07-01
Following a brief review of the development of operational modal identification techniques, we describe a new method named frequency-spatial domain decomposition (FSDD), with theoretical background, formulation and algorithm. Three typical applications to civil engineering structures are presented to demonstrate the procedure and features of the method: a large-span stadium roof for finite-element model verification, a highway bridge for damage detection and a long-span cable-stayed bridge for structural health monitoring.
Tajaldini, Mehdi; Mat Jafri, Mohd Zubir Mat
2013-05-01
In this study, we propose a novel approach that is called nonlinear modal propagation analysis method (NMPA) in MMI coupler via the enhances of nonlinear wave propagation in terms of guided modes interferences in nonlinear regimes, such that the modal fields are measurable at any point of coupler and output facets. Then, the ultra-short MMI coupler is optimized as a building block in micro ring resonator to investigate the method efficiency against the already used method. Modeling results demonstrate more efficiency and accuracy in shorter lengths of multimode interference coupler. Therefore, NMPA can be used as a method to study the compact dimension coupler and for developing the performance in applications. Furthermore, the possibility of access tothe all-optical switching is assumed due to one continuous MMI for proof of the development of performances in nonlinear regimes.
Hanson, D.; Waters, T. P.; Thompson, D. J.; Randall, R. B.; Ford, R. A. J.
2007-01-01
anti-resonances. It is found that the addition of anti-resonance information improves the updating performance for some combinations of parameter values, but does not improve the update in significant other regions. The simulated results are verified using resonance and anti-resonance frequencies measured on a steel beam test rig. The investigation is extended to include the updating of parameters of a petrol generator set. It is found that the contribution of the anti-resonances to the model update is heavily dependent on the geometry of the model and the choice of variables to be updated, suggesting that, for some models, the pursuit of anti-resonance information through expensive operational modal analysis may be inappropriate.
Operational modal analysis using SVD of power spectral density transmissibility matrices
Araújo, Iván Gómez; Laier, Jose Elias
2014-05-01
This paper proposes the singular value decomposition of power spectrum density transmissibility matrices with different references, (PSDTM-SVD), as an identification method of natural frequencies and mode shapes of a dynamic system subjected to excitations under operational conditions. At the system poles, the rows of the proposed transmissibility matrix converge to the same ratio of amplitudes of vibration modes. As a result, the matrices are linearly dependent on the columns, and their singular values converge to zero. Singular values are used to determine the natural frequencies, and the first left singular vectors are used to estimate mode shapes. A numerical example of the finite element model of a beam subjected to colored noise excitation is analyzed to illustrate the accuracy of the proposed method. Results of the PSDTM-SVD method in the numerical example are compared with obtained using frequency domain decomposition (FDD) and power spectrum density transmissibility (PSDT). It is demonstrated that the proposed method does not depend on the excitation characteristics contrary to the FDD method that assumes white noise excitation, and further reduces the risk to identify extra non-physical poles in comparison to the PSDT method. Furthermore, a case study is performed using data from an operational vibration test of a bridge with a simply supported beam system. The real application of a full-sized bridge has shown that the proposed PSDTM-SVD method is able to identify the operational modal parameter. Operational modal parameters identified by the PSDTM-SVD in the real application agree well those identified by the FDD and PSDT methods.
Operational modal identification using variational Bayes
Li, Binbin; Der Kiureghian, Armen
2017-05-01
Operational modal analysis is the primary tool for modal parameter identification in civil engineering. Bayesian statistics offers an ideal framework for analyzing uncertainties associated with the identified modal parameters. However, the exact Bayesian formulation is usually intractable due to the high computational demand in obtaining the posterior distributions of modal parameters. In this paper, the variational Bayes method is employed to provide an approximate solution. Unlike the Laplace approximation and Monte Carlo sampling, the variational Bayes approach provides a gradient-free algorithm to analytically approximate the posterior distributions. Working with the state-space representation of a dynamical system, the variational Bayes approach for identification of modal parameters is derived by ignoring statistical correlation between latent variables and the model parameters. In this approach, the joint distribution of the state-transition and observation matrices as well as the joint distribution of the process noise and measurement error are firstly calculated analytically using conjugate priors. The distribution of modal parameters is extracted from these obtained joint distributions using a first-order Taylor series expansion. A robust implementation of the method is discussed by using square-root filtering and Cholesky decomposition. The proposed approach is illustrated by its application to an example mass-spring system and the One Rincon Hill Tower in San Francisco.
OPERATIONAL MODAL ANALYSIS OF VEHICLE SYSTEM BASED ON OPERATIONAL CONDITIONS%基于运行工况的车辆系统工作模态分析
Institute of Scientific and Technical Information of China (English)
孙志春; 周志立; 李言; 谢基龙; 谢云叶
2012-01-01
Based on the theoretical modal parameter analysis method, the modal parameters of one special vehicle system were analyzed first, and then stochastic subspace identification method based on operational conditions was presented to form the estimation formula of operational modal parameters of linear vehicle system. At last, the modal parameters of linear vehicle system were identified by SSI after its vibration test under operational conditions, and were simultaneously compared to the results obtained by the theoretical modal parameter analysis method. Comparison results of the former 8 order operational modals of the vehicle system show discrepancies of 3.86-11.61 percent on modal damping ratios and0. 61 ~ 8.32 percent on modal frequencies, which implies that stochastic subspace identification method based on the operational condition is feasible and effective, and has comparatively higher precision to meet the needs of the analysis of vehicle system under operational conditions.%对运行工况下某一特种车辆系统的模态参数,基于计算模态分析方法进行了计算分析;推导了基于运行工况的该车辆系统随机子空间模态识别算法,得到了其工作模态参数的估算公式.同时,对该车辆系统进行了实际运行工况下的模态识别试验,用上述算法估算公式计算了其工作模态参数,并与计算模态分析结果作了比较.对比结果表明,该车辆系统需要考虑的前8阶工作模态的阻尼比和模态频率等参数的识别结果误差分别为:3.86％～11.61％和0.61％～8.32％,由此说明该识别方法具有较高的识别精度,分析方法可行、有效,能满足运行工况下车辆系统振动分析需要.
Analysis on Modals and Semi-Modals
Institute of Scientific and Technical Information of China (English)
陈力
2014-01-01
The modal is a type of auxiliary verb that is used to indicate modality. There are thirteen modal auxiliaries including some past tense forms. In this paper, the modals and semi-modals will be studied through analyzing fifteen sample sentences and referring some grammar books. At last, some suggestions for ESL or ESL teacher to teach modals will be provided.
Operational modal analysis with uncertainty quantification for SDDLV-based damage localization
Directory of Open Access Journals (Sweden)
Döhler Michael
2015-01-01
Full Text Available The Stochastic Dynamic Damage Locating Vector (SDDLV approach is a vibration-based damage localization method based on a finite element model of a structure in a reference state and output-only measurements in both reference and damaged states. A stress field is computed for loads in the null space of a surrogate of the change in the transfer matrix at the sensor positions, where the null space is obtained based on the identified modal parameters in both structural states. Then, the damage location is related to positions where the stress is close to zero. The localization results of this generic approach are perturbed by mainly two sources: modal truncation (not all modes of the structure are available and modal parameter identification errors (estimation is subject to statistical uncertainties. In this paper, we show how damage localization with the SDDLV approach is improved by taking into account the estimation uncertainties of the underlying identified modal parameters.
Effect of sensor placement on operational modal analysis of steel girder bridges
Whelan, Matthew J.; Gangone, Michael V.; Janoyan, Kerop D.
2011-04-01
With the advent and development of low-cost wireless structural health monitoring systems, the task of routinely assessing the in-service condition of highway bridges through distributed sensor-based measurements is an increasingly feasible component of bridge safety and management practice. Bridge monitoring encompasses placement of often a limited number of distributed sensors across a relatively large and complex structural system. Consequently, the selection of proper sensor locations is imperative to extraction of the most value from the recorded measurements. An experimental investigation is presented wherein sensor placement on the superstructure girders or primary beams is contrasted to the response measured on the surface of the bridge deck. The effect on the dataset richness, as evidenced by the modal content, is presented and conclusions regarding optimal placement for this structure type are presented. To affirm the plausibility of the observed responses and conclusions drawn, a finite element analysis is also performed on a model developed from the as-built drawings.
Brewick, P. T.; Smyth, A. W.
2013-12-01
Simulations of estimating the modal damping on a bridge from hour-long records of traffic loading were conducted by combining physics-based finite element modeling and signal processing. The finite element method was used to model a bridge consisting of a series of stringer beams resting atop a larger girder. The traffic loads were separated into trains and cars, with the trains modeled as partially distributed moving masses traveling along the girder and the cars modeled as point loads moving along the stringers. From the acceleration time histories, different operational modal analysis (OMA) techniques were used to find estimates for the modal coefficients of damping. The results demonstrated that a quasi-periodic component in the traffic loading introduces significant error to the damping estimates. This error could be observed in the distortion of the peaks for the power spectral densities (PSD) generated from the responses to the traffic simulations. The main OMA technique explored for the damping estimates was Enhanced Frequency Domain Decomposition (EFDD), but it could not compensate or correct for any alterations to the PSD. Other techniques such as the Stochastic Subspace Identification (SSID) method and curve-fitting frequency domain analysis were evaluated, but they produced comparable damping ratio estimates to EFDD and similarly resulted in large errors for the distorted modes. The influence of quasi-periodic loads was perceptible, which means that for certain cases, the nature of traffic loads may result in damping estimates that are considerably inaccurate no matter what OMA technique is chosen.
Modal Testing of Mechanical Structures subject to Operational Excitation Forces
DEFF Research Database (Denmark)
Møller, N.; Brincker, Rune; Herlufsen, H.;
2001-01-01
to the Operational Modal Analysis. For Operational Modal Analysis two different estimation techniques are used: a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identification (SSI) algorithm...
Modal Testing of Mechanical Structures Subject to Operational Excitation Forces
DEFF Research Database (Denmark)
Møller, N.; Brincker, Rune; Herlufsen, H.;
2000-01-01
to the Operational Modal Analysis. For Operational Modal Analysis two different estimation techniques are used: a non-parametric technique based on Frequency Domain Decomposition (FDD), and a parametric technique working on the raw data in time domain, a data driven Stochastic Subspace Identification (SSI) algorithm...
Reynders, Edwin; Maes, Kristof; Lombaert, Geert; De Roeck, Guido
2016-01-01
Identified modal characteristics are often used as a basis for the calibration and validation of dynamic structural models, for structural control, for structural health monitoring, etc. It is therefore important to know their accuracy. In this article, a method for estimating the (co)variance of modal characteristics that are identified with the stochastic subspace identification method is validated for two civil engineering structures. The first structure is a damaged prestressed concrete bridge for which acceleration and dynamic strain data were measured in 36 different setups. The second structure is a mid-rise building for which acceleration data were measured in 10 different setups. There is a good quantitative agreement between the predicted levels of uncertainty and the observed variability of the eigenfrequencies and damping ratios between the different setups. The method can therefore be used with confidence for quantifying the uncertainty of the identified modal characteristics, also when some or all of them are estimated from a single batch of vibration data. Furthermore, the method is seen to yield valuable insight in the variability of the estimation accuracy from mode to mode and from setup to setup: the more informative a setup is regarding an estimated modal characteristic, the smaller is the estimated variance.
DEFF Research Database (Denmark)
Jacobsen, Niels-Jørgen; Andersen, Palle; Brincker, Rune
2006-01-01
Enhanced Frequency Domain Decomposition technique for eliminating the influence of these harmonic components in the modal parameter extraction process. For various experiments, the quality of the method is assessed and compared to the results obtained using broadband stochastic excitation forces. Good...
Full-Scale Modal Analysis of a Ro-Lo Vessel in Operation
DEFF Research Database (Denmark)
Orlowitz, Esben
Et skib udsættes for en kompleks vibration miljø, påvirket a have såvel som selve operationen af skibet. Særligt hydrodynamiske og -elastiske effekter er svære at bestemme teoretisk. Derfor er eksperimentelle resultater vigtige for verificering. I denne poster visses præliminære resultater fra en...... fuld skala modal test af et Ro-Lo skib....
Modal Parameters Analysis from Operational Responses in Broaching%拉床工作模态参数分析
Institute of Scientific and Technical Information of China (English)
林绿高; 应申舜
2011-01-01
研究了LG51 SH立式拉床工作模态参数,以考察拉床机械结构对其动态特性的影响.在拉床主要结构上布置测点,进行拉刀工作激励下的模态试验,利用LMS振动测试设备SCADAIII - 105,获得实测的频响数据.采用多参考最小二乘复频域( PolyM AX)法,分析拉床工作模态参数.给出了模态识别稳态图,以及前10阶典型振型、模态阻尼比和固有频率等拉床工作模态参数.分析结果表明,LG51 SH拉床整机模态中有38Hz、192Hz的固有频率,与6Hz的拉削力基频的整数倍很接近,应合理安排拉削速度,避免出现激励固有频率的拉削力基频.%Modal parameters for LG51SH broaching machine from operational responses is studied to examine the dynamic properties of mechanical structure. The operational modal is analyzed using PolyMAX method with responsive data of key point in broaching machine, which is excited in practical broaching operation and tested by LMS SCADAIII-105 system. The identified steady state modal、representative modal shape、modal damping ratio and natural frequency in broaching are presented. The test and analysis result shows that there are natural frequency of 38Hz and 192Hz, which are close to multiple of the fundamental frequency of cutting force in broaching, 6Hz, therefore, reasonable cutting velocity should be adopted to void producing fundamental frequency of cutting force in broaching.
DEFF Research Database (Denmark)
Santos, Ilmar; Svendsen, Peter Kjær
2016-01-01
In recent years, theoretical and experimental efforts have transformed the conventional tilting pad journal bearing (TPJB) into a smart mechatronic machine element. The application of electromechanical elements into rotating systems makes feasible the generation of controllable forces over...... forces, resulting from a strong coupling between hydrodynamic, hydrostatic and controllable lubrication regimes, can be used either to control or to excite rotor lateral vibrations. If non-invasive forces are generated via lubricant fluid film, in situ parameter identification can be carried out...... in rotordynamics, i.e. estimation of damping ratio and natural frequencies.The experimental analysis is carried out on a rigid rotor level system supported by one single pair of pads. The estimation of damping and natural frequencies is performed using classical experimental modal analysis (EMA) and operational...
López-Aenlle, M.; Brincker, R.; Pelayo, F.; Canteli, A. F.
2012-01-01
When operational modal analysis (OMA) is used to estimate modal parameters, mode shapes cannot be mass normalized. In the past few years, some equations have been proposed to scale mode shapes using the mass-change method, which consists of repeating modal testing after changing the mass at different points of the structure where the mode shapes are known. In this paper, the structural-dynamic-modification theory is used to derive a set of equations, from which all the existing formulations can be derived. It is shown that the known equations can be divided into two types, the exact and the approximated equations, where the former type does in fact fulfill the equations derived from the theory of structural modification, whereas the remaining equations do not, mainly because the change of the mode shapes of the modified structure is not properly taken into account. By simulations, the paper illustrates the large difference in accuracy between the approximate and the exact formulations. The paper provides two new exact formulations for the scaling factors, one for the non-modified structure and - for the first time in the literature - one for the modified structure. The simulations indicate the influence of errors from the measured natural frequencies and mode shapes on the estimation of the scaling factors using the two exact formulations from the literature and the new exact formulation proposed in this paper. In addition, the paper illustrates statistics of the errors on mode-shape scaling. All simulations were carried out using a plate with closely spaced modes.
Modal Analysis Using Operating Modal Identification Method%采用工作模态识别法进行模态分析
Institute of Scientific and Technical Information of China (English)
郑敏; 申凡; 史东锋; 陈怀海
2004-01-01
Sometimes it is very difficult for some large-scale operating structures to measure the input forces. Modal parameters must be estimated on response-only. A poly-reference time-domain operating modal identification complex exponential method is presented since cross-correlation functions have the same form as impulse response functions. Then a poly-reference frequency-domain operating modal identification method is proposed in this paper. An experiment on an aircraft model is performed to verify the proposed schemes. The results show that both outlined schemes can extract the parameters from outputonly and the modal parameters extracted by proposed frequency-domain method are more accurate than those by presented time-domain complex exponential method.%对于一些大型工作结构,有时很难测得输入信号,只能单独利用实测响应数据进行工作模态识别.本文针对工程实际中的这一情况,首先利用响应间互相关函数同脉冲响应函数在表达形式上的相似性,推导出了多参考点时域工作模态复指数法,继而又从响应间的互相关函数入手,推导出了多参考点频域工作模态识别法.最后采用一飞机模型对这两种方法进行了试验验证,并将所得结果做了对比分析,结果表明,两种多参考点方法都能较有效地单独从实测响应数据提取结构的模态参数,且频域工作模态识别法比时域工作模态复指数法识别精度更高.
Zhang, P. Q.; Tang, X. L.; Shan, B. X.; Brandon, J. A.; Kwan, A. S. K.
1998-07-01
The development of micromechanical sensors poses new challenges in design, calibration and operation. The paper reports a study where analytical and experimental techniques are applied to a prototype sensor. Analytically, a substructuring method is used together with a proprietary finite element package. Experimentally, novel excitation and response transducers are used to provide input data for specialised time domain identification algorithms. The resulting comparisons provide confidence in the combination of techniques used in the study.
Directory of Open Access Journals (Sweden)
Bart Peeters
2007-01-01
Full Text Available During a football game, the ambient vibrations at the roof of a football stadium were recorded. A very large data set consisting of 4 hours of data, sampled at 80 Hz, is available. By a data reduction procedure, the complete data set could be analysed at once in a very short time. The data set was also split in shorter segments corresponding to certain events before, during and after the game to investigate the influence of varying operational conditions on the dynamic properties.
Gkoktsi, Kyriaki; Giaralis, Agathoklis; TauSiesakul, Bamrung
2016-04-01
Motivated by a need to reduce energy consumption in wireless sensors for vibration-based structural health monitoring (SHM) associated with data acquisition and transmission, this paper puts forth a novel approach for undertaking operational modal analysis (OMA) and damage localization relying on compressed vibrations measurements sampled at rates well below the Nyquist rate. Specifically, non-uniform deterministic sub-Nyquist multi-coset sampling of response acceleration signals in white noise excited linear structures is considered in conjunction with a power spectrum blind sampling/estimation technique which retrieves/samples the power spectral density matrix from arrays of sensors directly from the sub-Nyquist measurements (i.e., in the compressed domain) without signal reconstruction in the time-domain and without posing any signal sparsity conditions. The frequency domain decomposition algorithm is then applied to the power spectral density matrix to extract natural frequencies and mode shapes as a standard OMA step. Further, the modal strain energy index (MSEI) is considered for damage localization based on the mode shapes extracted directly from the compressed measurements. The effectiveness and accuracy of the proposed approach is numerically assessed by considering simulated vibration data pertaining to a white-noise excited simply supported beam in healthy and in 3 damaged states, contaminated with Gaussian white noise. Good accuracy is achieved in estimating mode shapes (quantified in terms of the modal assurance criterion) and natural frequencies from an array of 15 multi-coset devices sampling at a 70% slower than the Nyquist frequency rate for SNRs as low as 10db. Damage localization of equal level/quality is also achieved by the MSEI applied to mode shapes derived from noisy sub-Nyquist (70% compression) and Nyquist measurements for all damaged states considered. Overall, the furnished numerical results demonstrate that the herein considered sub
Modal sensitivity analysis for single mode operation in large mode area fiber
Sévigny, Benoit; Zhang, Xiaoxing; Garneau, Marc; Faucher, Mathieu; Lizé, Yannick Keith; Holehouse, Nigel
2008-02-01
Most of the current large mode area (LMA) fibers are few-moded designs using a large, low numerical aperture (N.A.) core, which promotes mode coupling between core modes and increases bending losses (coupling with claddingmodes), which is undesirable both in terms ofmode area and beamquality. Furthermore, short LMA fiber lengths and small cladding diameters are needed to minimize nonlinear effects and maximize pump absorption respectively in high-power pulsed laser systems. Although gain fiber coiling is a widely used technique to filter-out unwanted modes in LMA fibers, coupling between modes can still occur in component leads and relay fibers. In relay fiber, light coupled into higher-order modes can subsequently be lost in the coiling or continue as higher-order modes, which has the overall effect of reducing the effective transmission of the LP 01 mode and degrading the beam quality. However, maximum transmission of the LP 01 mode is often required in order to have the best possible beam quality (minimal M2). Launching in an LMA fiber with a mode field adapter (MFA)1 provides an excellent way of ensuring maximum LP 01 coupling, but preservation of this mode requires highmodal stability in the output fiber. Small cladding, low N.A. LMA fibers have the disadvantage of being extremely sensitive to external forces in real-life applications, which is unwanted for systems where highly sensitive mode coupling can occur. In this paper, we present a detailed experimental and theoretical analysis of mode coupling sensitivity in LMA fibers as a function of fiber parameters such as N.A., core diameter and cladding diameter. Furthermore, we present the impact of higher N.A. as a solution to increase mode stability in terms of its effect on peak power, effective mode area and coupling efficiency.
Cury, Alexandre; Cremona, Christian; Dumoulin, John
2012-11-01
For reliable performance of vibration-based damage detection algorithms, it is important to distinguish abnormal changes in modal parameters caused by structural damage from normal changes due to environmental fluctuations. This paper firstly addresses the modeling of temperature effects on modal frequencies of a PSC box girder bridge located on the A1 motorway in France. Based on a six-month monitoring experimental program, modal frequencies of the first seven mode shapes and temperatures have been measured at three hour intervals. Neural networks are then introduced to formulate regression models for quantifying the effect of temperature on modal parameters (frequencies and mode shapes). In 2009, this bridge underwent a strengthening procedure. In order to assess the effect of strengthening on the vibration characteristics of the bridge, modal properties had to be corrected from temperature influence. Thus, the first goal is to assess the changes on the vibration signature of this bridge induced by the strengthening. For this purpose, classical statistical analysis and clustering methods are applied to the data recorded over the period after strengthening. The second goal is to evaluate the influence of temperature effects on the clustering results. It comes that the temperature correction significantly improves the confidence in the novelty detection and in the strengthening efficiency.
Ni, Yanchun; Lu, Xilin; Lu, Wensheng
2017-03-01
The field non-destructive vibration test plays an important role in the area of structural health monitoring. It assists in monitoring the health status and reducing the risk caused by the poor performance of structures. As the most economic field test among the various vibration tests, the ambient vibration test is the most popular and is widely used to assess the physical condition of a structure under operational service. Based on the ambient vibration data, modal identification can help provide significant previous study for model updating and damage detection during the service life of a structure. It has been proved that modal identification works well in the investigation of the dynamic performance of different kinds of structures. In this paper, the objective structure is a high-rise multi-function office building. The whole building is composed of seven three-story structural units. Each unit comprises one complete floor and two L shaped floors to form large spaces along the vertical direction. There are 56 viscous dampers installed in the building to improve the energy dissipation capacity. Due to the special feature of the structure, field vibration tests and further modal identification were performed to investigate its dynamic performance. Twenty-nine setups were designed to cover all the degrees of freedom of interest. About two years later, another field test was carried out to measure the building for 48 h to investigate the performance variance and the distribution of the modal parameters. A Fast Bayesian FFT method was employed to perform the modal identification. This Bayesian method not only provides the most probable values of the modal parameters but also assesses the associated posterior uncertainty analytically, which is especially relevant in field vibration tests arising due to measurement noise, sensor alignment error, modelling error, etc. A shaking table test was also implemented including cases with and without dampers, which assists
An Introduction to Operational Modal Identification of Offshore Wind Turbine Structures
DEFF Research Database (Denmark)
Damgaard, Mads
to experimental modal analysis of complex dynamically loaded structures. A huge number of papers have been published in the last years within traditional experimental modal analysis. However, for large civil engineering structures accurate model identification under actual operating conditions is difficult...... to extract by traditional experimental technologies. Operational modal analysis allows extracting modal parameters based on measuring only the response of a structure and using the ambient or natural operating forces as unmeasured input. Originally, operational modal analysis was developed for modal...... excitation originating from the rotating rotor and broadband excitation from air turbulence is present, which sets limitations on the applicability of operational modal analysis to wind turbine structures. The technical memorandum contains an introduction to the theory within experimental modal analysis and...
汽车顶棚约束模态与工作模态分析与比较%Analysis and Comparison of Constraint Modal and Operation Modal of a Car Roof
Institute of Scientific and Technical Information of China (English)
周鋐; 曹阳光; 刘浩; 李冰杰
2016-01-01
The constraint modal and operation modal of a car roof were obtained by testing and analysis. In the constraint modal test the car was impacted by a vibration exciter while in the operation modal test it was impacted by a hub in an anechoic chamber. Comparing the results with the auto power spectrum of the noise at driver’s right ear (driver’s noise), it was found that the noise frequency resulted from the operation modal analysis was closer to the noise peak frequency than that from the constraint modal analysis. By the comparison of the auto power spectrum of the driver’s noise with the average of auto power spectrum of the vibration acceleration at all the measurement points, the roof vibration was found to be the main cause of the driver’s noise in 100 Hz to 400 Hz frequency range. Finally, by adjusting the roof structure, the driver’s noise was restrained.%通过试验分析分别得到汽车顶棚约束模态和工作模态，其中约束模态试验采用激振器激励，工作模态试验采用室内转鼓激励；对比驾驶员右耳处噪声自功率谱密度函数，发现通过工作模态分析得到的频率更加贴近噪声峰值频率；将驾驶员右耳处噪声自功率谱和所有测点振动加速度自功率谱平均值相比较，发现100 Hz到400 Hz内顶棚振动对车内噪声起主要作用。最后，通过调整顶棚结构实现车内噪声的降低。
Institute of Scientific and Technical Information of China (English)
金广文; 缪旭弘; 匡贡献; 章林柯
2011-01-01
To overcome the difficulties in the modal analysis of large-scale complex submerged structures based on the conventional experiment method, a new modal analysis method is presented in this paper which combines the operational modal analysis and finite element calculation.The response signals in different positions are decomposed by empirical mode decomposition (EMD), and the modal parameters are identified by using the time domain peak picking method, then the identified modal parameters are used to guide and revise the calculated results of the finite element model.To avoid the modal mixing in EMD, wavelet packets analysis is introduced to decompose the response signal into different frequency bands.The underwater experiment results of ribbed cylindrical double-shell show that the presented methods can effectively identify integrated modal parameters, and engineering availability is validated.%针对传统实验方法很难对水下复杂结构进行模态分析,提出了工作模态参数辨识与有限元计算相结合的模态分析方法.对工作状态下的测点振动响应信号进行EMD分解,用时域峰值序列法进行模态参数辨识,辨识出的模态参数与计算模态结果进行匹配,以指导修正有限元模型,计算得到完整的模态参数.为解决EMD分解出现的模态混叠,提出先对信号进行小波包分解预处理的 方法.双层加肋圆柱壳体模型水下振动试验研究结果表明,该方法现实可行,能有效辨识出比较完整的模态参数.
自行火炮工作模态分析试验技术%Operational Modal Analysis Experimental Technique Used for Self-propelled Gun
Institute of Scientific and Technical Information of China (English)
王宝元; 刘朋科; 衡刚; 周发明; 杨东; 李明涛
2009-01-01
The experimental modal analysis of the selected self-propelled gun was completed with operational modal analysis experimental technique; the modal frequencies distribution and modal modes were obtained; the analyzed result by the proposed method was compared with that by the traditional one. The compared result shows that obtained result by the proposed method is in agreement with that by the traditional method.%利用工作模态分析试验技术完成了自行火炮全炮试验模态分析,得到了所选择自行火炮全炮模态频率分布及其模态振型,并和传统试验模态分析方法进行对比.结果表明:对相同试验对象,工作模态分析试验结果与传统试验模态分析结果一致.
Analysis of Gearbox Performance based on LMS Operating Modal Test%基于LMS工作模态测试的齿轮箱性能分析
Institute of Scientific and Technical Information of China (English)
楼江雷; 唐进元; 陈思雨; 唐健杰; 吴丽娟
2012-01-01
基于LMS测试分析系统,对某试验齿轮箱进行工作模态测试和分析；采用最小二乘复频域法对齿轮箱各阶模态进行参数识别,并对工作模态分析过程中额外输入峰进行了辨识,剔除了谐波引起的虚假模态；通过对测试结果进行分析及讨论,发现齿轮安装偏心导致齿轮啮合频率及其谐波的分布；根据各阶模态振型的特性,对齿轮箱运行状况进行评价,提出对该齿轮箱结构设计的改进措施.%The operating modal of a gearbox is investigated experimentally based on the LMS system. With the least square complex frequency (LSCF) method, the parametric identification of each gearbox modal is deduced. Subsequently , the additional input peaks are identified with the analyses of operating modal, and the fake modals caused by harmonic are removed. Through the analysis and discussion of experimental results, assembly eccentricity lead to the spread of gear meshing frequency and harmonic. Finally, according to the characteristics of each modal shape, the running states of gearbox are evaluated, and improved method for the design of gearbox structures is proposed.
Forms of Address as Discrete Modal Operators
Directory of Open Access Journals (Sweden)
Wojciech Paweł Sosnowski
2016-12-01
Full Text Available Forms of Address as Discrete Modal Operators The category of expressions of politeness includes, among others, forms of address. Forms of address express honorification. Honorification can be defined as a special type of meaning that consists of information about the social and interpersonal relations between the speaker and the addressee, the speaker and the hearer, and the speaker and the protagonist of the predication. As far as their place in the syntactic structure is concerned, forms of address can either be integrated with the other elements of a predication or not. However, they are always part of a predication’s semantic structure. Moreover, forms of address convey the speaker’s attitude to the meaning of the predicate that they want to convey, which consequently means that forms of address also carry a modal element. Modality can be defined as a situation in which an individual is in a particular mental state, i.e. exhibits some kind of attitude to a situation or a type of situations. Forms of address can be categorised as modal operators conveying imperatives, requests, suppositions, etc. The term "operator" can be used for a unit of language when it changes the semantic structure of the predication. My research on honorification is mainly based on contemporary corpora, both monolingual and multilingual. In the present study, I analyse forms of address which carry imperative and optative meanings. Formy adresatywne jako dyskretne operatory modalne W obrębie wyrażeń realizujących funkcje grzecznościowe znajduje się grupa form adresatywnych. Są one częścią kategorii honoryfikatywności rozumianej jako szczególny rodzaj znaczenia zawartego w treści wypowiedzi, informację o towarzysko-społecznej relacji między nadawcą a odbiorcą, nadawcą a słuchaczem oraz nadawcą a bohaterem wypowiedzi. Gramatycznie formy adresatywne mogą być zarówno zintegrowane, jak i niezintegrowane syntaktycznie z resztą wypowiedzi, ale
Rainieri, Carlo; Fabbrocino, Giovanni
2015-08-01
In the last few decades large research efforts have been devoted to the development of methods for automated detection of damage and degradation phenomena at an early stage. Modal-based damage detection techniques are well-established methods, whose effectiveness for Level 1 (existence) and Level 2 (location) damage detection is demonstrated by several studies. The indirect estimation of tensile loads in cables and tie-rods is another attractive application of vibration measurements. It provides interesting opportunities for cheap and fast quality checks in the construction phase, as well as for safety evaluations and structural maintenance over the structure lifespan. However, the lack of automated modal identification and tracking procedures has been for long a relevant drawback to the extensive application of the above-mentioned techniques in the engineering practice. An increasing number of field applications of modal-based structural health and performance assessment are appearing after the development of several automated output-only modal identification procedures in the last few years. Nevertheless, additional efforts are still needed to enhance the robustness of automated modal identification algorithms, control the computational efforts and improve the reliability of modal parameter estimates (in particular, damping). This paper deals with an original algorithm for automated output-only modal parameter estimation. Particular emphasis is given to the extensive validation of the algorithm based on simulated and real datasets in view of continuous monitoring applications. The results point out that the algorithm is fairly robust and demonstrate its ability to provide accurate and precise estimates of the modal parameters, including damping ratios. As a result, it has been used to develop systems for vibration-based estimation of tensile loads in cables and tie-rods. Promising results have been achieved for non-destructive testing as well as continuous
Operational modal analysis of harbor crane under ambient excitation%基于环境激励的港口起重机工作模态分析
Institute of Scientific and Technical Information of China (English)
龚凌诸; 杨晓翔; 钟舜聪; 郭金泉; 许忠福; 梁崇忠
2011-01-01
Aiming at solving the excitation problems of a 40 t harbor crane, operational modal analysis using natural excitation technique (NEXT) were investigated. Ambient excitation, such as that caused by wind, was employed to excite the crane. With the unknown input (excitation) signal, only the response signals were recorded. Taking one of the response signals as the reference, the cross power spectra of response signals were calculated and used for modal identification of the crane. The first four lower modal parameters ( frequencies, damping ratios and mode shapes) were obtained. The results indicate that operational modal analysis of harbor cranes using NExT is applicable.Therefore, NExT could bo recommended in modal testing and analysis of other special equipments.%针对港口起重机难以施加激振力的问题,采用自然环境激励技术(NExT)对港口起重机进行了工作模态分析.在自然风的随机激励下,对某港口40t位起重机进行了模态试验.采用响应点与参考点之间的互功率谱的幅值图代替集总传递函数的幅值图进行了模态分析.由所有测点和参考点间的互功率谱,通过拟合各响应点同参考点之间的互功率谱来识别起重机前4阶低阶模态参数(振型、频率和阻尼).研究结果表明,利用环境激励法对港口起重机的模态参数识别是行之有效的,该方法可推广应用于其他大型特种设备的模态试验和分析.
Zhou, Si-Da; Heylen, Ward; Sas, Paul; Liu, Li
2014-05-01
This paper investigates the problem of modal parameter estimation of time-varying structures under unknown excitation. A time-frequency-domain maximum likelihood estimator of modal parameters for linear time-varying structures is presented by adapting the frequency-domain maximum likelihood estimator to the time-frequency domain. The proposed estimator is parametric, that is, the linear time-varying structures are represented by a time-dependent common-denominator model. To adapt the existing frequency-domain estimator for time-invariant structures to the time-frequency methods for time-varying cases, an orthogonal polynomial and z-domain mapping hybrid basis function is presented, which has the advantageous numerical condition and with which it is convenient to calculate the modal parameters. A series of numerical examples have evaluated and illustrated the performance of the proposed maximum likelihood estimator, and a group of laboratory experiments has further validated the proposed estimator.
Uncertainty quantification for operational modal analysis of bridge structures%桥梁结构工作模态分析的不确定度量化
Institute of Scientific and Technical Information of China (English)
秦世强; 勾红叶; 贾宏宇; 蒲黔辉
2015-01-01
In order to quantify the uncertainty for operational modal analysis (OMA),two methods were employed to estimate the uncertainty of natural frequencies and damping ratios identified by using stochastic subspace identification (SSI).Firstly,mathematical expectation and standard deviation of modal parameters identified from different sets were used to measure the overall size and dispersion, and the overall confidence intervals of modal parameters were constructed.Secondly,a method to quantify the uncertainty of modal parameters obtained from a single set through matrix sensitivity analysis was introduced,and the stabilization diagram with confidence intervals was established.The ambient vibration test of an arch rib of Caiyuanba Yangtze River Bridge was taken as an example.The study showed that the overall confidence intervals is a supplement to the existing single mode to assess modal parameters;the stabilization diagram with confidence intervals can help testers to distinguish the spurious modes from the system actual modes;two methods introduced can measure the uncertainty of the modal parameters from overall and local viewpoints,respectively;they provide a basis for assessing the credibility of the estimated modal parameters from OMA.%为了量化工作模态分析的不确定度，以随机子空间识别为例，用两种方法对识别的固有频率和阻尼比不确定度进行量化：①用不同测试组识别的模态参数的数学期望和标准差衡量其整体大小和离散程度，构建模态参数的整体置信区间；②引入了以矩阵敏感性分析的单个测试组识别的模态参数不确定度量化方法，并构造带置信区间的稳定图。以菜园坝桥拱肋试验数据作为工程实例进行了验证。研究表明：构建的整体置信区间弥补了目前对模态参数的单一评价模式；带置信区间的稳定图能让测试者分辨出结构真实模态和虚假模态；两种方法能分别从整体
Noise elimination algorithm for modal analysis
Energy Technology Data Exchange (ETDEWEB)
Bao, X. X., E-mail: baoxingxian@upc.edu.cn [Department of Naval Architecture and Ocean Engineering, China University of Petroleum (East China), Qingdao 266580 (China); Li, C. L. [Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071 (China); Xiong, C. B. [The First Institute of Oceanography, State Oceanic Administration, Qingdao 266061 (China)
2015-07-27
Modal analysis is an ongoing interdisciplinary physical issue. Modal parameters estimation is applied to determine the dynamic characteristics of structures under vibration excitation. Modal analysis is more challenging for the measured vibration response signals are contaminated with noise. This study develops a mathematical algorithm of structured low rank approximation combined with the complex exponential method to estimate the modal parameters. Physical experiments using a steel cantilever beam with ten accelerometers mounted, excited by an impulse load, demonstrate that this method can significantly eliminate noise from measured signals and accurately identify the modal frequencies and damping ratios. This study provides a fundamental mechanism of noise elimination using structured low rank approximation in physical fields.
网壳结构运行模态分析的模型试验%Experimental study of the operational modal analysis of latticed domes
Institute of Scientific and Technical Information of China (English)
王卓; 闫维明; 叶列平
2011-01-01
研究网壳结构在环境激励下的模态参数识别问题。采用模型试验的方法,通过试验模态和运行模态的分析方法和结果的对比,分析自然激励下参与网壳结构振动的模态阶次和参与程度、虚假模态的辨别以及频域分解法识别模态参数的准确度等问题。试验结果表明：对于具有密集模态的网壳结构,高阶模态主要参与环境激励下的结构响应,得到如下结论：使用频域分解法得到的模态频率识别值准确度高,对于参与结构振动程度强的模态,振型识别的准确度高;提出可以根据模态频率对应的奇异值大小进行虚假模态的辨别,奇异值最大的模态,识别准确度最高,可被认为是真实%Modal parameter identification of latticed domes with ambient excitation was analyzed in model tests.Analytical results are compared with experimental and operational modals to analyze the structural response of latticed domes during ambient excitation to indentify false modals and to calculate the identification accuracy of frequency domain decomposition（FDD）.The analyses show that the participating modals in structural response with ambient excitation are mainly high-order modals for latticed domes with intensive modals.The FDD model accurately identifies modal frequencies.The FDD identification accuracy is also high for modes strongly participating in the structural response.The false modals identification is based on the magnitude of singular value.The modal corresponding to the maximum singular value can be treated as the real structural modal with the highest identification accuracy.
History of Civil Engineering Modal Analysis
DEFF Research Database (Denmark)
Brincker, Rune
2008-01-01
techniques are available for civil engineering modal analysis. The testing of civil structures defers from the traditional modal testing in the sense, that very often it is difficult, or sometimes impossible, to artificially excite a large civil engineering structure. Also, many times, even though...
History of Civil Engineering Modal Analysis
DEFF Research Database (Denmark)
Brincker, Rune
2008-01-01
techniques are available for civil engineering modal analysis. The testing of civil structures defers from the traditional modal testing in the sense, that very often it is difficult, or sometimes impossible, to artificially excite a large civil engineering structure. Also, many times, even though...
Hanson, D.; Randall, R. B.; Antoni, J.; Waters, T. P.; Thompson, D. J.; Ford, R. A. J.
2007-08-01
This paper presents a new technique for scaling mode shapes, obtained from cepstrum-based operational modal analysis (OMA) techniques, such as that described in the companion paper, using finite element model updating. This OMA technique estimated frequency response functions (FRFs) between a cyclostationary input and response measurements. If the input is frequentially white, the resulting FRFs can be obtained up to an overall scaling constant using the in-band poles and zeros identified in the OMA process and employing the response autospectrum as a reference to correct for the effect of out of band modes. In this way, the mode shapes would be scaled correctly relative to each other but would still have arbitrary overall magnitude. If the input is not white, then no reference is available to correct FRF regenerated from in-band poles and zeros, and so these FRFs will exhibit both an overall slope resulting from the effect of out-of-band poles and zeros, and an arbitrary magnitude. This overall slope will differ between measurement locations so even the relative scaling between the mode shapes will be lost. This paper describes a simple technique for recovering both the relative and overall scaling of the FRFs, and hence the mode shapes, based on finite element model updating.
Modal analysis of PATHFINDER unmanned air vehicle
Energy Technology Data Exchange (ETDEWEB)
Woehrle, T.G.; Costerus, B.W.; Lee, C.L.
1994-10-19
An experimental modal analysis was performed on PATHFINDER, a 450-lb, 100-ft wing span, flying-wing-design aircraft powered by solar/electric motors. The aircraft was softly suspended and then excited using random input from a long-stroke shaker. Modal data was taken from 92 measurement locations on the aircraft using newly designed, lightweight, tri-axial accelerometers. A conventional PC-based data acquisition system provided data handling. Modal parameters were calculated, and animated mode shapes were produced using SMS STARStruct{trademark} Modal Analysis System software. The modal parameters will be used for validation of finite element models, optimum placement of onboard accelerometers during flight testing, and vibration isolation design of sensor platforms.
Vibration measurement and modal analysis for tunneller
Institute of Scientific and Technical Information of China (English)
HUANG Min; WU Miao; WEI Ren-zhi
2001-01-01
In this paper, the method of vibration measurement and modal analysis for AM~50 Tunneller machine is presented. When the machine was used for cutting man-made coal bed and real coal bed, the vibration of the machine was measured and the results of signal analysis show that the vibration characteristics under the two kinds of working situations are similar. The modal model of the machine is established, and then, the intrinsic vibration characteristics of AM50 tunneller are investigated by means of the method of experimental modal analysis. The vibration response simulation under a set of loading spectra measured is carried out by force response simulation software.
Smith, Wade A.; Randall, Robert B.
2016-10-01
Operational modal analysis (OMA) seeks to determine a structure's dynamic characteristics from response-only measurements, which comprise both excitation and transmission path effects. The cepstrum has been used successfully in a number of applications to separate these source and path effects, after which the poles and zeros of the transfer function can be obtained via a curve-fitting process. The contributions from the individual poles and zeros can then be added (in log magnitude) to regenerate the frequency response function (FRF). Cepstrum-based OMA was originally developed in the 1980s and 90s, but there have been a number of recent developments that warrant discussion and explanation, and this is the basis of the present paper, which focusses on the FRF regeneration process and on a number of broader points explaining FRFs from a pole-zero perspective. The FRF regenerated from identified poles and zeros is subject to magnitude distortion from the effects of truncation, i.e., from the residual effects of out-of-band poles and zeros. As long as a reference FRF is available - for example from conventional experimental modal analysis or from a finite element model - this distortion can be corrected for using a magnitude equalisation curve. This paper discusses the nature of this equalisation curve, and gives recommendations on how best to obtain it. Other topics covered in the discussion are: the required distribution of poles and zeros for the successful regeneration of FRFs; node points and weak modes in a pole-zero model; the differences in pole-zero distribution between receptance, mobility and accelerance FRF forms; and, how to deal with the very low frequency region when regenerating FRFs. Special consideration is given to the identification of zeros - often masked by noise in response measurements - using transmissibility estimation. It is hoped that the discussion will assist in the application of cepstrum-based OMA methods and will lead to improved
Institute of Scientific and Technical Information of China (English)
林贤坤; 覃柏英; 张令弥; 郭勤涛
2013-01-01
以张家港河大桥为对象,在不中断交通条件下对该桥实施模态试验,建立和修正其有限元模型,由此对试验模态振型质量归一化.利用振型已质量归一化的试验模态参数,计算该桥已知静荷载作用下的试验模态挠度,通过模态挠度与静挠度实测值的比较、关键问题的仿真研究和模态振型对模态挠度影响的误差分析,探讨和说明了基于不中断交通运行模态分析的模态挠度法在实际工程中应用于桥梁状态评估的可行性与有效性.%Zhangjiagang bridge was taken as a studying object,its finite element model was built and updated based on the results of traffic excitation modal test without interrupting traffic,and it was applied to obtain the massnormalized test modal shapes.Using the natural frequencies and the mass-normalized modal shapes,the test modal deflection values of the bridge under given loads were calculated.Through the comparison between the test modal deflection values and the measured values of static deflection,simulation study of some key issues and error analysis for the effect of modal shape on modal deflection,the feasibility and effectiveness of applying the modal deflection method based on operational modal analysis (OMA) without interrupting traffic in condition assessment of a bridge were explored and presented.
Asymptotic modal analysis and statistical energy analysis
Dowell, Earl H.
1988-07-01
Statistical Energy Analysis (SEA) is defined by considering the asymptotic limit of Classical Modal Analysis, an approach called Asymptotic Modal Analysis (AMA). The general approach is described for both structural and acoustical systems. The theoretical foundation is presented for structural systems, and experimental verification is presented for a structural plate responding to a random force. Work accomplished subsequent to the grant initiation focusses on the acoustic response of an interior cavity (i.e., an aircraft or spacecraft fuselage) with a portion of the wall vibrating in a large number of structural modes. First results were presented at the ASME Winter Annual Meeting in December, 1987, and accepted for publication in the Journal of Vibration, Acoustics, Stress and Reliability in Design. It is shown that asymptotically as the number of acoustic modes excited becomes large, the pressure level in the cavity becomes uniform except at the cavity boundaries. However, the mean square pressure at the cavity corner, edge and wall is, respectively, 8, 4, and 2 times the value in the cavity interior. Also it is shown that when the portion of the wall which is vibrating is near a cavity corner or edge, the response is significantly higher.
Institute of Scientific and Technical Information of China (English)
张家雄; 何咏梅; 张华山; 张辉; 李飞
2015-01-01
飞行器在大气中飞行时经历严酷的力热环境，结构动力学问题显著，而模态特性是分析这些问题的重要输入。传统地面模态试验很难准确模拟飞行环境，而工作模态分析技术能够得到飞行器实际飞行中的模态参数。文章首先简要介绍了工作模态分析技术的背景和发展现状，说明了PolyMAX法的基本原理，然后对飞行器飞行试验测量数据进行了处理和分析，采用PolyMAX法成功识别出该飞行器的模态参数，并进行了模态验证。%A flying vehicle is in serious physical and thermal environment when passing through aerosphere, which might be treated as a structural elastic problem, where the modal characteristics are very important inputs of the problem. Traditionally, it is difficult to simulate the environment in the modal testing, however, the realistic modal parameters of a hypersonic flying vehicle could be obtained easily by the operational modal analysis (OMA) technology. The background and the development of the operational modal analysis are reviewed in the paper, and the PolyMAX algorithm is specially addressed. The load measurement data from a flight test of a flying vehicle is processed, the modal parameters are identified successfully based on the PolyMAX method, and the modal parameters are validated.
基于小波变换的车门运行模态分析%Operational modal analysis for vehicle door based on wavelet transform
Institute of Scientific and Technical Information of China (English)
王超峰; 林建辉
2012-01-01
The door in high-speed trans is an important component for evaluating the safety and it effects on the sealing and the noise control. Modal analysis is a significant method for structural design, vibration control and fault diagnosis. Traditional modal analysis methods based on transmission function has characteristics of using excitation signal and response signal for modal recognition. However, modal parameters recognition methods based on natural excitation only use the response from the system. Among different methods, wavelet transform based method is very promising because of its good time frequency property and band-pass filtering for automatically decoupling of the system. Then the modal parameters could be recognized by the wavelet ridges of the map from free vibration signal after wavelet transform. The wavelet-based modal analysis method is presented for the door in high-speed trains and the result is very satisfactory%高速列车车门是评价高速列车安全性的一个很重要的部件，它对高速列车的密封性及噪声控制有很关键的作用。模态分析是结构动态设计，振动和噪声控制及设备故障诊断的重要方法。传统的传递函数模态分析方法的特点是同时利用激励和响应信号进行参数识别，而基于环境激励下的模态参数识别方法仅根据系统的响应就可以进行参数识别。其中，基于小波变换的模态分析方法非常有前景，它利用其良好的时频分辨能力以及带通滤波性质可以使系统自动解耦，然后从自由振动信号的小波变换谱图的小波脊线出发识别模态参数。本文利用基于小波分析的运行模态分析方法，对高速列车车门进行模态参数识别，效果良好。
Impeller deflection and modal finite element analysis.
Energy Technology Data Exchange (ETDEWEB)
Spencer, Nathan A.
2013-10-01
Deflections of an impeller due to centripetal forces are calculated using finite element analysis. The lateral, or out of plane, deflections are an important design consideration for this particular impeller because it incorporates an air bearing with critical gap tolerances. The target gap distance is approximately 10 microns at a rotational velocity of 2500 rpm. The centripetal forces acting on the impeller cause it deflect in a concave fashion, decreasing the initial gap distance as a function of radial position. This deflection is characterized for a previous and updated impeller design for comparative purposes. The impact of design options such as material selection, geometry dimensions, and operating rotational velocity are also explored, followed by a sensitivity study with these parameters bounded by specific design values. A modal analysis is also performed to calculate the impeller's natural frequencies which are desired to be avoided during operation. The finite element modeling techniques continue to be exercised by the impeller design team to address specific questions and evaluate conceptual designs, some of which are included in the Appendix.
Modal test results of a ship under operational conditions
DEFF Research Database (Denmark)
Orlowitz, Esben; Brandt, Anders
2014-01-01
Skibe er udsat for et komplekst vibration miljø, påvirket af havet, samt driftsforholdene. Især er det vanskeligt at anslå analytisk værdier for de hydrodynamiske påvirkninger. Eksperimentelle resultater er derfor vigtigt for at kontrollere de analytiske modeller. I den foreliggende artikel præse...... fokuserer på driftsforhold påvirkning af de modal parametre og viser en betydelig variation af modal dæmpning af skibet i drift, med cirka 400%, 200% og 400% forskel i de første tre globale lodrette bøjning modes, ved forskellige operations hastigheder....
Applied modal analysis of wind turbine blades
DEFF Research Database (Denmark)
Pedersen, H.B.; Kristensen, O.J.D.
2003-01-01
In this project modal analysis has been used to determine the natural frequencies, damping and the mode shapes for wind turbine blades. Different methods to measure the position and adjust the direction of the measuring points are discussed. Differentequipment for mounting the accelerometers...... is investigated by repeated measurement on the same wind turbine blade. Furthermore the flexibility of the test set-up is investigated, by use ofaccelerometers mounted on the flexible adapter plate during the measurement campaign. One experimental campaign investigated the results obtained from a loaded...... and unloaded wind turbine blade. During this campaign the modal analysis are performed on ablade mounted in a horizontal and a vertical position respectively. Finally the results obtained from modal analysis carried out on a wind turbine blade are compared with results obtained from the Stig Øyes blade_EV1...
EXPERIMENTAL MODAL ANALYSIS OF VISCO-ELASTICALLY DAMPED STRUCTURES
Institute of Scientific and Technical Information of China (English)
1998-01-01
The form of the modal analysis of viscoelastically damped structures is simplified and this simplified form is similar to the form of the modal analysis of linear viscously damped structures. As a result of this simplified form, the experimental modal analysis methods of linear viscously damped structures are applied to the experimental modal analysis of viscoelastically damped structures.
Finite Dynamic Elements and Modal Analysis
Directory of Open Access Journals (Sweden)
N.J. Fergusson
1993-01-01
Full Text Available A general modal analysis scheme is derived for forced response that makes use of high accuracy modes computed by the dynamic element method. The new procedure differs from the usual modal analysis in that the modes are obtained from a power series expansion for the dynamic stiffness matrix that includes an extra dynamic correction term in addition to the static stiffness matrix and the consistent mass matrix based on static displacement. A cantilevered beam example is used to demonstrate the relative accuracies of the dynamic element and the traditional finite element methods.
Operational modal analysis of a large wind turbine%大型风力机系统运行模态分析研究
Institute of Scientific and Technical Information of China (English)
钟灿堂; 李德源; 汪显能; 莫文威; 刘雄
2016-01-01
Aiming at the vibration modes and its variation characteristics of a large wind turbine under static status and various rotational speeds,the variations of each mode caused by elastic deformation,inertia and gyroscopic effect and their effects on aeroelastic stability of the wind turbine system were studied.Considering the large wind turbine system's non-linear characteristics and time-varying characteristics caused by the rotational wind rotor,the linear eigenvalue problems of the wind turbine were analyzed by using the dynamics software ADAMS,based on the dynamics theory of multi-body system and the modeling methodology of hybrid multi-body system (HMBS).A stiff integral method was then employed to solve the non-linear control equations of the system numerically considering the elastic deformation of flexible components and the rotation of the wind rotor.The operational modal identification was performed through Fourier spectral analysis.The variations of the system's first ten modes and their influence factors were discussed and analyzed in detail. The results can be used as aeroelastic stability criteria,which offer an effective solution and analysis method to avoid resonance and improve operating efficiency of the wind turbine system.%针对大型风力机在风轮静止、变速转动下振动模态及变化特点，研究弹性变形、惯性及陀螺效应引起的系统各阶模态变化及对系统气弹稳定性影响。通过研究现有线性特征值分析方法，考虑大型风力机非线性特性及风轮转动所致系统时变特性，基于多体系统动力学理论及混合多体系统 HMBS（Hybrid Multi-body Systems）建模方法，结合动力学分析软件 ADAMS，分析静止状态整机系统线性特征值问题；考虑构件弹性变形及风轮旋转，用刚性积分方法对系统非线性控制方程进行数值求解，通过傅里叶谱分析方法实现风轮旋转下系统运转模态识别，并讨论、分析系统前十
Modal analysis of wind turbine blades
DEFF Research Database (Denmark)
Larsen, Gunner Chr.; Hansen, M.H.; Baumgart, A.
2002-01-01
The modal analysis technique has been used to identify essential dynamic properties of wind turbine blades like natural frequencies, damping characteristics and mode shapes. Different experimental procedures have been considered, and the most appropriateof these has been selected. Although...... the comparison is based on measurements on a LM 19 m blade, the recommendations given are believed to be valid for other wind turbine blades as well. The reliability of the selected experimental analysis has beenquantified by estimating the unsystematic variations in the experimental findings. Satisfactory....... The experimental analysis of the LM 19 m blade has been compared with results from a state-of-the-art FE-modeling ofthe same blade. For some of the higher modes substantial discrepancies between the natural frequencies originating from the FE-modeling and the modal analysis, respectively, are observed. In general...
Institute of Scientific and Technical Information of China (English)
单德山; 徐敏
2011-01-01
以某自锚式悬索桥模型试验为研究背景,采用数据驱动随机子空间识别算法和改进稳定图方法对桥梁结构运营模态分析进行研究.为解决数据驱动随机子空间识别中的系统定阶和虚假模态问题,采用奇异熵增量进行系统定阶,并对稳定图进行改进,实现了虚假模态的识别与剔除,最终达到了精确识别桥梁结构模态参数的目的.采用模型试验在不同数据采集方案下的测试数据,识别该模型桥相应测试条件下的模态参数,将识别结果分别与ANSYS理论计算值、DASY-Lab模态参数识别结果进行比较,验证了所提方法及自编程序的正确性,该方法可应用于桥梁结构的运营模态分析中.%The model test of a self-anchored suspension bridge is taken as the research background, the data-driven stochastic subspace identification (Data-Driven SSI) algorithm and the improved stabilization diagram method are employed to study the operational modal analysis of bridge structure. For solving the problem of the system order determination and false modal parameters in the Data-Driven SSI, the singular entropy increment is introduced to determine the system order and to improve the stability diagram, the false modal parameters are therefore identified and eliminated and eventually the goal of accurately identifying the modal parameters of the bridge structure is attained. By using the testing data of the model test under different data acquisition cases, the modal parameters of the bridge structure Under the corresponding testing condi-tions are identified, the identified modal parameters are respectively compared to the values of the ANSYS theoretic calculation and to the results of DASYLab modal parameter identification. The correctness of the method proposed herewith and the self-complied program has been verified and the method can be applied to the operational model analysis of the bridge structure.
Energy Technology Data Exchange (ETDEWEB)
Helsen, J.; Weijtjens, W.; Guo, Y.; Keller, J.; McNiff, B.; Devriendt, C.; Guillaume, P.
2015-02-01
This paper experimentally investigates a worst case grid loss event conducted on the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC) drivetrain mounted on the 2.5MW NREL dynamic nacelle test-rig. The GRC drivetrain has a directly grid-coupled, fixed speed asynchronous generator. The main goal is the assessment of the dynamic content driving this particular assess the dynamic content of the high-speed stage of the GRC gearbox. In addition to external accelerometers, high frequency sampled measurements of strain gauges were used to assess torque fluctuations and bending moments both at the nacelle main shaft and gearbox high-speed shaft (HSS) through the entire duration of the event. Modal analysis was conducted using a polyreference Least Squares Complex Frequency-domain (pLSCF) modal identification estimator. The event driving the torsional resonance was identified. Moreover, the pLSCF estimator identified main drivetrain resonances based on a combination of acceleration and strain measurements. Without external action during the grid-loss event, a mode shape characterized by counter phase rotation of the rotor and generator rotor determined by the drivetrain flexibility and rotor inertias was the main driver of the event. This behavior resulted in significant torque oscillations with large amplitude negative torque periods. Based on tooth strain measurements of the HSS pinion, this work showed that at each zero-crossing, the teeth lost contact and came into contact with the backside flank. In addition, dynamic nontorque loads between the gearbox and generator at the HSS played an important role, as indicated by strain gauge-measurements.
DEFF Research Database (Denmark)
Klinge, Alex; Müller, Henrik Høeg
Modality: Studies in Form and Function reflects the diversity of theoretical frameworks and the heterogeneity of linguistic phenomena under the general heading of modality. Researchers in the fields of logic, philosophy and linguistics have for many years been pondering the elusive nature...
Experimental modal analysis of components of the LHC experiments
Guinchard, M; Catinaccio, A; Kershaw, K; Onnela, A
2007-01-01
Experimental modal analysis of components of the LHC experiments is performed with the purpose of determining their fundamental frequencies, their damping and the mode shapes of light and fragile detector components. This process permits to confirm or replace Finite Element analysis in the case of complex structures (with cables and substructure coupling). It helps solving structural mechanical problems to improve the operational stability and determine the acceleration specifications for transport operations. This paper describes the hardware and software equipment used to perform a modal analysis on particular structures such as a particle detector and the method of curve fitting to extract the results of the measurements. This paper exposes also the main results obtained for the LHC Experiments.
Modal Analysis of Drilling Machine Derrick
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
In this paper, the finite element analysis software ( ANSYS ) is applied to the modal analysis of a ZJ30/1700CZ 's drilling machine derrick under a natural condition and a loaded condition, respectively. The preceding nine step natural frequencies and the corresponding mode shapes of the derrick are calculated. By means of the comparison of the natural frequency of the derrick with the design work frequency of the drilling machine and the analysis of the step mode shape of the derrick, the drilling machine derrick structure design is proved to be correct.
Modal analysis of wind turbine blades
Energy Technology Data Exchange (ETDEWEB)
Larsen, G.C.; Hansen, M.H.; Baumgart, A.; Carlen, I.
2002-02-01
The modal analysis technique has been used to identify essential dynamic properties of wind turbine blades like natural frequencies, damping characteristics and mode shapes. Different experimental procedures have been considered, and the most appropriate of these has been selected. Although the comparison is based on measurements on a LM 19 m blade, the recommendations given are believed to be valid for other wind turbine blades as well. The reliability of the selected experimental analysis has been quantified by estimating the unsystematic variations in the experimental findings. Satisfactory results have been obtained for natural frequencies, damping characteristics and for the dominating deflection direction of the investigated mode shapes. For the secondary deflection directions, the observed experimental uncertainty may be considerable - especially for the torsional deflection. The experimental analysis of the LM 19 m blade has been compared with results from a state-of-the-art FE-modeling of the same blade. For some of the higher modes substantial discrepancies between the natural frequencies originating from the FE-modeling and the modal analysis, respectively, are observed. In general the qualitative features of measured and computed modes shapes are in good agreement. However, for the secondary deflection directions, substantial deviations in the absolute values may occur (when normalizing with respect to the primary deflection direction). Finally, suggestions of potential future improvements of the experimental procedure are discussed. (au)
Institute of Scientific and Technical Information of China (English)
徐洪; 王扬渝; 东辉
2014-01-01
主轴系统的模态参数是加工稳定性预测及参数优化等的重要依据。针对主轴系统难以实施有效激励的问题，提出了基于多点脉冲激励的运行模态分析(Operational modal analysis，OMA)方法，对刀具、刀柄及主轴分别施加脉冲激励，获取测点的振动响应及互相关函数，采用多参考最小二乘复指数法(poly-reference least square complex exponential method, pLSCE)识别了模态参数。通过模态置信判据方法剔除识别过程所衍生的虚假模态，提高了模态参数识别的准确性。与锤击模态试验结果的对比表明，识别的固有频率与阻尼比的最大相对误差分别为4.57%和11.02%，一致性较好，表明由多点激励下响应信号的互相关函数可准确识别主轴系统模态参数，为主轴系统运行模态分析提供了一种新思路。%Modal parameters of the spindle system is an important basis for the prediction of processing stability and parameters optimization. Aiming at the difficulty in the implementation of effective incentive for the spindle system, a new operational modal analysis (OMA) method based on multiple pulse excitation is brought forward, pulse excitations are respectively applied on the tool, toolholder and spindle, response and cross-correlation functions of vibration signals are achieved and modal parameters are identified through the poly-reference least square complex exponential (pLSCE) method. False modes derived from the recognition process is removed to improve the accuracy of modal parameters identification by the modal assurance criterion method. Comparative analysis shows that the maximum relative error of the natural frequency and damping ratio is 4.57% and 11.02%respectively and the OMA results are in good agreement with the hammer modal test results. Results indicate the modal parameters of spindle system can be accurately identified by the cross-correlation functions of response signals under
Natural Characteristics and Operational Modal Analysis of Wind Turbine Gearbox%风电齿轮箱固有特性分析及工作模态测试
Institute of Scientific and Technical Information of China (English)
石万凯; 郑站强; 宋丽鸽
2012-01-01
The drive and structure system coupled dynamics model of wind turbine gearbox was built using finite element method, in which four spring elements was used to simulate each bearing connection.The inherent characteristics of the gearbox under practical constraint were analyzed to get its first 20 modal frequencies and modal shapes.Meanwhile a test was also carried out to obtain the gearbox's modal parameters in 5 different conditions using operational modal identification technique based on response data.The results of test and finite element analysis were consistent by comparison.It indicated that the coupled dynamics model was correct, so the model could be used to analyze gearbox instead of physical model.%采用有限元的方法建立了风电齿轮箱传动系统与结构系统的耦合动力学模型.在轴承连接处采用4个弹簧单元进行模拟,分析了齿轮箱在实际约束条件下的固有特性,得到了其前20阶模态频率与振型.同时对齿轮箱进行了实验,采用基于响应数据的工作模态辨识技术,得到其在5种不同工况下的模态参数,并把得到的参数和有限元的分析结果进行对比,两者的结果基本吻合.结果表明建立的耦合动力学模型是正确的,可以用它来替代实物模型对齿轮箱进行分析.
Multi-modal cockpit interface for improved airport surface operations
Arthur, Jarvis J. (Inventor); Bailey, Randall E. (Inventor); Prinzel, III, Lawrence J. (Inventor); Kramer, Lynda J. (Inventor); Williams, Steven P. (Inventor)
2010-01-01
A system for multi-modal cockpit interface during surface operation of an aircraft comprises a head tracking device, a processing element, and a full-color head worn display. The processing element is configured to receive head position information from the head tracking device, to receive current location information of the aircraft, and to render a virtual airport scene corresponding to the head position information and the current aircraft location. The full-color head worn display is configured to receive the virtual airport scene from the processing element and to display the virtual airport scene. The current location information may be received from one of a global positioning system or an inertial navigation system.
Energy Technology Data Exchange (ETDEWEB)
Moore, L.M.; Byers, F.M. Jr.; Broxton, D.E.
1989-06-01
A thin-section operator-variance test was given to the 2 junior authors, petrographers, by the senior author, a statistician, using 16 thin sections cut from core plugs drilled by the US Geological Survey from drill hole USW VH-2 standard (HCQ) drill core. The thin sections are samples of Topopah Spring devitrified rhyolite tuff from four textural zones, in ascending order: (1) lower nonlithophysal, (2) lower lithopysal, (3) middle nonlithophysal, and (4) upper lithophysal. Drill hole USW-VH-2 is near the center of the Crater Flat, about 6 miles WSW of the Yucca Mountain in Exploration Block. The original thin-section labels were opaqued out with removable enamel and renumbered with alpha-numeric labels. The sliders were then given to the petrographer operators for quantitative thin-section modal (point-count) analysis of cryptocrystalline, spherulitic, granophyric, and void textures, as well as phenocryst minerals. Between operator variance was tested by giving the two petrographers the same slide, and within-operator variance was tested by the same operator the same slide to count in a second test set, administered at least three months after the first set. Both operators were unaware that they were receiving the same slide to recount. 14 figs., 6 tabs.
Holmén, Britt A; Qu, Yingge
2004-04-15
monitor particle emissions with high-resolution real-time instruments and account for the operating regime of the vehicle using time-series analysis to develop predictive number emissions models.
Institute of Scientific and Technical Information of China (English)
管晓明; 傅洪贤; 王梦恕; 崔堃鹏; 林凡涛
2014-01-01
依托重庆新红岩隧道工程，选典型2层砌体结构进行隧道施工爆破振动激励的OMA试验，采用等效体积单元法建立能准确反映砌体结构真实动力特性的有限元模型；探讨砌体用不同材料模型所得分析频率与实测频率误差及二者振型相关性；据OMA试验模态参数，基于砌体与混凝土材料参数的结构固有频率灵敏度分析，选择合适的修正参数进行有限元模型修正研究。结果表明，二层砌体结构前4阶固有频率位于9～25 Hz；较用各向同性模型而言，砌体采用各向异性模型时计算所得前4阶频率与实测频率值更接近，振型相关性更好；修正有限元模型中材料密度、弹性模量、剪切模量后频率与实测频率间误差明显减小，结构模型动力特性更符合实际，正交各向异性材料模型修正最准确。%Based on the engineering background of New Hongyan Tunnel in Chongqing,an operational modal analysis was carried out on a typical 2-story brick masonry structure under tunnel blast excitation.An accurate finite element model which could reflect the actual dynamic characteristics of the brick masonry structure was built by using the representative volume element. Furthermore, the numerical structural natural frequencies and modal shapes were compared with the experimental modal data.According to the first four modal parameters obtained from the operational modal analysis (OMA ) and based on the structural natural frequencies sensitivity analysis of masonry and concrete material parameters,the appropriate modifying parameters were selected and the model of the brick masonry structure was updated.The first four natural frequencies of the brick masonry structure are in 9 ~25Hz.The analysed natural frequencies by using anisotropic model match much better with the experimental modal parameters than by using isotropic model for the brick masonry.Besides,the correlation between the analyzed and
Modal Analysis Based on the Random Decrement Technique
DEFF Research Database (Denmark)
Asmussen, J. C.
The thesis describes and develops the theoretical foundations of the Random Decrement technique, while giving several examples of modal analysis of large building constructions (bridges). The connection between modal parameters and Random Decrement functions is described theoretically...... is expanded to include both a vector formulation that increases speed considerably, and a new method for the prediction of the variance of the estimated Random Decrement functions. The thesis closes with a number of examples of modal analysis of bridges exposed to natural (ambient) load....
MODAL ANALYSIS OF QUARTER CAR MODEL SUSPENSION SYSTEM
Viswanath. K. Allamraju *
2016-01-01
Suspension system is very important for comfort driving and travelling of the passengers. Therefore, this study provides a numerical tool for modeling and analyzing of a two degree of freedom quarter car model suspension system. Modal analysis places a vital role in designing the suspension system. In this paper presented the modal analysis of quarter car model suspension system by considering the undamped and damped factors. The modal and vertical equations of motions describing the su...
Supervised Cross-Modal Factor Analysis for Multiple Modal Data Classification
Wang, Jingbin
2015-10-09
In this paper we study the problem of learning from multiple modal data for purpose of document classification. In this problem, each document is composed two different modals of data, i.e., An image and a text. Cross-modal factor analysis (CFA) has been proposed to project the two different modals of data to a shared data space, so that the classification of a image or a text can be performed directly in this space. A disadvantage of CFA is that it has ignored the supervision information. In this paper, we improve CFA by incorporating the supervision information to represent and classify both image and text modals of documents. We project both image and text data to a shared data space by factor analysis, and then train a class label predictor in the shared space to use the class label information. The factor analysis parameter and the predictor parameter are learned jointly by solving one single objective function. With this objective function, we minimize the distance between the projections of image and text of the same document, and the classification error of the projection measured by hinge loss function. The objective function is optimized by an alternate optimization strategy in an iterative algorithm. Experiments in two different multiple modal document data sets show the advantage of the proposed algorithm over other CFA methods.
Energy Technology Data Exchange (ETDEWEB)
Calderon-Guizar, J.G [Instituto de Investigaciones Electricas, Cuernavaca, Morelos (Mexico)]. E-mail: jgcg@iie.org.mx
2008-10-15
The presence of electromechanical oscillations in any electrical power system is a typical characteristic of this kind of systems. Provided the damping associated with these oscillations lies above of a minimum specified value, the occurrence of these oscillations is not considered as a threat to the system operation. This paper focuses the attention on the application of modal analysis for assessing the dynamical behavior of a power system subjected to small disturbances for different operating conditions and transmission system topologies, as well. The reported results indicate, that modal analysis enables a straight identification of the causes that contribute negatively to the damping of the electromechanical modes. [Spanish] La presencia de oscilaciones electromecanicas en cualquier Sistema Electrico de Potencia (SEP) es una caracteristica propia de estos sistemas. Mientras el amortiguamiento asociado con este tipo de oscilaciones se encuentre dentro de los limites considerados como aceptables para la operacion continua de este tipo de sistemas, el surgimiento de estas no se considera una amenaza para la operacion segura del SEP. El presente articulo, centra su atencion en la aplicacion del analisis modal para evaluar el comportamiento dinamico de un SEP ante la ocurrencia de disturbios de magnitud pequena para diferentes topologias y condiciones de operacion. Los resultados reportados indican, que la aplicacion del analisis modal permite la identificacion directa de las causas que contribuyen en forma negativa al amortiguamiento asociado con los modos electromecanicos, asi como la ubicacion mas adecuada de controles que contribuyan a mejorar el amortiguamiento de los mismos.
A new scenario-based approach to damage detection using operational modal parameter estimates
Hansen, J. B.; Brincker, R.; López-Aenlle, M.; Overgaard, C. F.; Kloborg, K.
2017-09-01
In this paper a vibration-based damage localization and quantification method, based on natural frequencies and mode shapes, is presented. The proposed technique is inspired by a damage assessment methodology based solely on the sensitivity of mass-normalized experimental determined mode shapes. The present method differs by being based on modal data extracted by means of Operational Modal Analysis (OMA) combined with a reasonable Finite Element (FE) representation of the test structure and implemented in a scenario-based framework. Besides a review of the basic methodology this paper addresses fundamental theoretical as well as practical considerations which are crucial to the applicability of a given vibration-based damage assessment configuration. Lastly, the technique is demonstrated on an experimental test case using automated OMA. Both the numerical study as well as the experimental test case presented in this paper are restricted to perturbations concerning mass change.
Modal Analysis for Crack Detection in Small Wind Turbine Blades
DEFF Research Database (Denmark)
Ulriksen, Martin Dalgaard; Skov, Jonas falk; Dickow, Kristoffer Ahrens
2013-01-01
The aim of the present paper is to evaluate structural health monitoring (SHM) techniques based on modal analysis for crack detection in small wind turbine blades. A finite element (FE) model calibrated to measured modal parameters will be introduced to cracks with different sizes along one edge...... of the blade. Changes in modal parameters from the FE model are compared with data obtained from experimental tests. These comparisons will be used to validate the FE model and subsequently discuss the usability of SHM techniques based on modal parameters for condition monitoring of wind turbine blades....
Modal extraction on a diesel engine in operation
DEFF Research Database (Denmark)
Møller, Nis; Herlufsen, Henrik; Brincker, Rune
2000-01-01
In this paper an output only modal testing and identification of a diesel engine is presented. The only loading on the engine is the unknown loading from the engine itself. Two test cases were considered: engine run-up, and engine Run-Down. The response data were analyzed using two different...
Modal Extraction on a Diesel Engine in Operation
DEFF Research Database (Denmark)
Møller, N.; Brincker, Rune; Andersen, P.
2000-01-01
In this paper an output only modal testing and identification of a diesel engine is presented The only loading on the engine is the unknown loading from the engine itself. Two test cases were considered: engine run-up, and engine Run-down. The response data were analysed using two different...
基于随机减量的运行模态频域分析方法%Operational Modal Analysis Method in Frequency Domain Based on Random Decrement
Institute of Scientific and Technical Information of China (English)
黄琴; 王彤; 张海黎
2011-01-01
A new method based on complex mode indicator function and random decrement technique for operational modal analysis in frequency domain is proposed with a focus on the complex large-scale structures such as high buildings and long-span bridges, which are difficult to be excited artificially. The time-domain random decrement functions are transformed to frequency-domain half power spectral density functions by the Fourier transformation, and then the modal parameters including modal frequencies , damping ratios and mode shapes are identified from the half power spectral density functions, with the classical identification algorithm named as complex mode indicator function. Finally, a simulation example of three-dimensional space structure is utilized to validate the algorithm.%以高层建筑、大跨桥梁等难以进行人工激励的大型复杂结构为对象,提出并实现了一种基于随机减量技术和复模态指示因子函数法的新型频域运行状态模态参数识别方法.由随机运行响应估计随机减量函数,然后通过时频域变换得到频域的半功率谱密度函数,并用复模态指示因子函数法从半功率谱密度函数中识别结构模态参数.最后对1个三维空间结构模型进行算法验证,得到相应的各阶模态参数,证明了将随机减量技术和复模态指示因子函数法相结合的方法识别大型结构模态参数的有效性和合理性.
Nondestructive Damage Detection Based on Modal Analysis
Directory of Open Access Journals (Sweden)
T. Plachý
2004-01-01
Full Text Available Three studies of damage identification and localization based on methods using experimentally estimated modal characteristics are presented. The results of an experimental investigation of simple structural elements (three RC-beams and three RC-slabs obtained in the laboratory are compared with the results obtained on a real structure (a composite bridge – a concrete deck supported by steel girders in situ.
Operational Modal Analysis on laminated glass beams
López Aenlle, Manuel; Fernández, Pelayo; Villa García, Luis Manuel; Barredo Egusquiza, Josu; Hermanns, Lutz Karl Heinz; Fraile de Lerma, Alberto
2011-01-01
Laminated glass is a sandwich element consisting of two or more glass sheets, with one or more interlayers of polyvinyl butyral (PVB). The dynamic response of laminated glass beams and plates can be predicted using analytical or numerical models in which the glass and the PVB are usually modelled as linear-elastic and linear viscoelastic materials, respectively. In this work the dynamic behavior of laminated glass beams are predicted using a finite element model and the analytical model ...
3-D finite element computation and dynamic modal analysis on ultrasonic vibration systems
Institute of Scientific and Technical Information of China (English)
倪金刚; 张学仁; 聂景旭(Department of Jet Propulsion 405; Beijing University of Aeronautics and Astronautics; Beijing 100083; China)
1996-01-01
Stress and modal analyses are performed on an ultrasonic vibration system by means of a 3-dimensional finite element computation and dynamic modal analysis code "Algor" The system consists of an edge-cracked specimen linked elastically with one or two amplifying horns which come into resonant longitudinal vibration at 20kHz.Operating principle of the ultrasonic fatigue machines and experimental procedures for ultrasonic fatigue crack growth studies are briefly presented.
Static Structural and Modal Analysis Using Isogeometric Analysis
Gondegaon, Sangamesh; Voruganti, Hari K.
2016-12-01
Isogeometric Analysis (IGA) is a new analysis method for unification of Computer Aided Design (CAD) and Computer Aided Engineering (CAE). With the use of NURBS basis functions for both modelling and analysis, the bottleneck of meshing is avoided and a seamless integration is achieved. The CAD and computational geometry concepts in IGA are new to the analysis community. Though, there is a steady growth of literature, details of calculations, explanations and examples are not reported. The content of the paper is complimentary to the existing literature and addresses the gaps. It includes summary of the literature, overview of the methodology, step-by-step calculations and Matlab codes for example problems in static structural and modal analysis in 1-D and 2-D. At appropriate places, comparison with the Finite Element Analysis (FEM) is also included, so that those familiar with FEM can appreciate IGA better.
Modal interval analysis new tools for numerical information
Sainz, Miguel A; Calm, Remei; Herrero, Pau; Jorba, Lambert; Vehi, Josep
2014-01-01
This book presents an innovative new approach to interval analysis. Modal Interval Analysis (MIA) is an attempt to go beyond the limitations of classic intervals in terms of their structural, algebraic and logical features. The starting point of MIA is quite simple: It consists in defining a modal interval that attaches a quantifier to a classical interval and in introducing the basic relation of inclusion between modal intervals by means of the inclusion of the sets of predicates they accept. This modal approach introduces interval extensions of the real continuous functions, identifies equivalences between logical formulas and interval inclusions, and provides the semantic theorems that justify these equivalences, along with guidelines for arriving at these inclusions. Applications of these equivalences in different areas illustrate the obtained results. The book also presents a new interval object: marks, which aspire to be a new form of numerical treatment of errors in measurements and computations.
Modal analysis of a 2-cylinder crankshaft using ANSYS
Directory of Open Access Journals (Sweden)
Basavaraj Talikoti
2015-12-01
Full Text Available Crankshaft is a relevant component in an I.C. engine which transforms the reciprocating motion into rotational motion. This makes the crankshaft liable to vibrations due to different types of stresses and loads. Modal analysis when performed on crankshaft, gives the behavior of its structure through different mode shapes at different frequencies. It also helps to determine resonance frequencies. Modal analysis is the primary stage of many useful analysis like harmonic analysis and transient dynamic analysis, which give the dynamic behavior of the crankshaft.
Analysis of modal frequency optimization of railway vehicle car body
Directory of Open Access Journals (Sweden)
Wenjing Sun
2016-04-01
Full Text Available High structural modal frequencies of car body are beneficial as they ensure better vibration control and enhance ride quality of railway vehicles. Modal sensitivity optimization and elastic suspension parameters used in the design of equipment beneath the chassis of the car body are proposed in order to improve the modal frequencies of car bodies under service conditions. Modal sensitivity optimization is based on sensitivity analysis theory which considers the thickness of the body frame at various positions as variables in order to achieve optimization. Equipment suspension design analyzes the influence of suspension parameters on the modal frequencies of the car body through the use of an equipment-car body coupled model. Results indicate that both methods can effectively improve the modal parameters of the car body. Modal sensitivity optimization increases vertical bending frequency from 9.70 to 10.60 Hz, while optimization of elastic suspension parameters increases the vertical bending frequency to 10.51 Hz. The suspension design can be used without alteration to the structure of the car body while ensuring better ride quality.
Ambient Response Analysis Modal Analysis for Large Structures
DEFF Research Database (Denmark)
Brincker, Rune; Andersen, Palle
1999-01-01
In this paper an outline is given of the basic ideas in ambient respons analysis, i.e. when modal analyses is performed on systems based on output only. Some of the most known techniques are briefly introduced, and the basic problems discussed. The introduced techniques are the frequency domain...... based peak-picking methods, the polyreference LSCE method, the stochastic subspace method for estimation of state space systems and the prediction error method for estimation of Auto-Regressive Moving Average Vector models. The techniques are illustrated on an example of ambient response measurments...
Modal analysis of a drumlike silencer.
Huang, Lixi
2002-11-01
Low-frequency duct noise is difficult to deal with by passive methods such as porous duct lining. Reactive methods like expansion chamber are rather bulky, while compact resonators are too narrow banded. This study shows that a suitably stretched thin membrane backed by a slender cavity can achieve a satisfactory performance from low to medium frequencies over an octave band. The present paper focuses on the details of the modal behavior of the fully coupled membrane-cavity system, and examples are given with parameters set in a practical range. Typically, the membrane has a structure to air mass ratio of unity, and is stretched towards the elastic stress limit for a material like aluminum. The backing cavity has a depth equal to the duct height and a length five times the duct height. Three resonant peaks are found in the low to medium frequency range while the transmission loss between adjacent peaks remain above 10 dB. For the first peak, almost complete sound reflection occurs as a result of an out-of-phase combination of the first and second in vacuo modes of simply supported membranes. The second peak is solely contributed to by the first mode, while the third peak features mainly the second mode vibration.
Operational Modal Parameter Identification Based on ICA%基于ICA的工作模态参数识别
Institute of Scientific and Technical Information of China (English)
张锐; 黄晋英; 郎忠宝
2015-01-01
The paper expounds the principle of independent component analysis and the operational modal analysis based on the principle of ICA. The analysis demonstrates the consistency between ICA separation model and structural vibration modal analysis model. The ICA algorithm and the software OMA developed by Belgian LMS are applied to identify the condition of gear box and broken tooth through modal parameters respectively. This paper finds that the algorithm of ICA, comparing with Op.PolyMAX which is the most commonly used, has strong anti-noise performance. Besides, it is easy to operate and the identification is accurate, this kind of algorithm provides a new basis of work modal parameters identification.%本文分别阐述了独立分量分析和基于ICA的工作模态分析原理，发现了ICA分离模型与结构振动模态分析模型的一致性。应用ICA算法和比利时LMS公司的OMA分析软件分别对齿轮箱正常和断齿工况进行模态参数识别，对比发现，ICA算法与目前最常用的Op. PolyMAX算法相比抗噪性强，识别简便精准,为工作模态参数识别提供新的识别依据。
Institute of Scientific and Technical Information of China (English)
刘佳; 赵悦; 凌亮; 圣小珍
2015-01-01
In order to learn the dynamic characteristics of the bogie frames of high-speed trains in traveling status, an operational modal test of the bogie was carried out. The cross spectra between the response points of the bogie frame were obtained and the modal parameters were identified by using the Least Square Complex-Frequency Method. According to the results of the identification, the pseudo modals corresponding to the obvious vibration peaks in the acceleration of the bogie induced by the excitation of the axle box were removed so that the true modal parameters were obtained. According to the measured frequency spectrum of the axle box and floor vibration, sources of the floor vibration peak frequencies were found, and the effect of the bogie frame’s operational modes on the prominent peaks was analyzed. The measured data is very useful for understanding the dynamic characteristics of the train bogie frames in operation status and the mechanism of obvious peaks of the carriage’s floor vibration. The methods of the test and modal parameter identification may provide a reference for part’s operational modal test of high-speed trains.%为进一步了解运行过程中转向架构架的真实动态特性，对实际线路运行的某高速列车进行工作模态测试，获取构架响应点之间的互谱信号并进行模态参数识别。模态参数识别方法采用最小二乘复频域法。根据其识别结果，剔除由轴箱传至构架且引起构架显著峰值的虚假模态，获得构架真实工作模态参数。结合轴箱、车体外地板振动实测频谱，找到车体外地板显著振动频率来源，进而分析转向架工作模态对车体外地板振动显著峰值的影响。本文的相关实测结果为了解运行过程中转向架构架真实动力学行为、研究车体外地板振动显著频率的产生、传递机理提供依据；同时，测试及模态参数识别方法为车体运行部件工作模态试验提供参考。
Dynamic Modal Analysis of Vertical Machining Centre Components
Directory of Open Access Journals (Sweden)
Anayet U. Patwari
2009-01-01
Full Text Available 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.
The Transient Modal Dynamic Analysis of a Coke Tower
Institute of Scientific and Technical Information of China (English)
XIE Teng-teng; SUN Tie; XING Ling; ZHANG Su-xiang
2012-01-01
Dynamic analysis must be performed when the duration of the applied load is short or if the load is dynamic in nature. Wind load, as a random load, can lead to the vibration of the coke tower. In order to study the influence to the strength of the coke tower by wind, ABAQUS was used to conduct the transient modal dynamic analysis of the wind load. The response of the structure during loading and unloading was mainly observed. The results indicate that, with the effect of wind, the maximal nodal displacement appears at the top of the tower, which is 0.79 mm; while the maximal stress locates at the node around the skirt, the maximum is 3.26 MPa. Both of the displacement and stress cannot cause the failure of the structure. After loading and unloading, the structure engenders vibration along the loading direction. The frequency is 10 Hz, under the effect of external loads, it may easily cause the resonance of the structure, which can cause damage to the structure. So it must be taken into consideration during the process of design and operation.
Experimental Modal Analysis of a Flat Plate Subjected To Vibration
Directory of Open Access Journals (Sweden)
Owunna Ikechukwu
2016-07-01
Full Text Available Modal analysis is significant in evaluating the mode shapes generated by a component under vibrational excitation, as the mode shapes can be used to determine the displacement or response of the component under the influence vibration in real life application. Result obtained from the modal analysis will generate a number of resonances which the frequency and damping effect can be determined by measurement. However, determining the accuracy of modal analysis result is somewhat difficult as the experimental results and the results generated by Finite Element Analysis (FEA solvers can be affected by a number of factors pointed out in this paper. In this study, a flat plate was mounted on an electromagnetic shaker which enabled the excitation of the plate, while results of the response were measured using a transducer attached to the plate. The plate was also modelled using CATIA software and the files transferred to the different FEA solvers such as HYPERMESH, ANSYS 6 Degree of Freedom (DOF as well as ANSYS 5 degree of freedom, in which the same analysis was carried out to obtain a set of results other than the experimental results. Each FEA solver generated results that were in close proximity with the experimental results, particularly the results generated by ANSYS 5 Degree of freedom. Hence, to ascertain the accuracy of the results obtained from modal analysis experimental procedure, it is important to match up the results generated from different FEA solvers with the experimental results.
Modal analysis of kagome-lattice structures
Perez, H.; Blakley, S.; Zheltikov, A. M.
2015-05-01
The first few lowest order circularly symmetric electromagnetic eigenmodes of a full kagome lattice are compared to those of a kagome lattice with a hexagonal defect. This analysis offers important insights into the physics behind the waveguiding properties of hollow-core fibers with a kagome-lattice cladding.
Model Checking Is Static Analysis of Modal Logic
DEFF Research Database (Denmark)
Nielson, Flemming; Nielson, Hanne Riis
2010-01-01
Flow Logic is an approach to the static analysis of programs that has been developed for functional, imperative and object-oriented programming languages and for concurrent, distributed, mobile and cryptographic process calculi. In this paper we extend it; to deal with modal logics and prove...
Model Checking Is Static Analysis of Modal Logic
DEFF Research Database (Denmark)
Nielson, Flemming; Nielson, Hanne Riis
2010-01-01
Flow Logic is an approach to the static analysis of programs that has been developed for functional, imperative and object-oriented programming languages and for concurrent, distributed, mobile and cryptographic process calculi. In this paper we extend it; to deal with modal logics and prove...
Modal analysis of beam with piezoelectric sensors a actuators
Directory of Open Access Journals (Sweden)
Zemčík R.
2007-10-01
Full Text Available One dimensional finite element is developed for the analysis of structures with applied piezoelectric sensors and actuators, i.e. smart structures, mechanical behavior of which can be controlled in real-time. The element is based on Euler-Bernoulli theory and it assumes bilinear distribution of electric field potential. Mathematical model was implemented in MATLAB environment. Sensitivity analysis is carried out for the case of modal analysis with and without piezo patches.
A machine learning approach to nonlinear modal analysis
Worden, K.; Green, P. L.
2017-02-01
Although linear modal analysis has proved itself to be the method of choice for the analysis of linear dynamic structures, its extension to nonlinear structures has proved to be a problem. A number of competing viewpoints on nonlinear modal analysis have emerged, each of which preserves a subset of the properties of the original linear theory. From the geometrical point of view, one can argue that the invariant manifold approach of Shaw and Pierre is the most natural generalisation. However, the Shaw-Pierre approach is rather demanding technically, depending as it does on the analytical construction of a mapping between spaces, which maps physical coordinates into invariant manifolds spanned by independent subsets of variables. The objective of the current paper is to demonstrate a data-based approach motivated by Shaw-Pierre method which exploits the idea of statistical independence to optimise a parametric form of the mapping. The approach can also be regarded as a generalisation of the Principal Orthogonal Decomposition (POD). A machine learning approach to inversion of the modal transformation is presented, based on the use of Gaussian processes, and this is equivalent to a nonlinear form of modal superposition. However, it is shown that issues can arise if the forward transformation is a polynomial and can thus have a multi-valued inverse. The overall approach is demonstrated using a number of case studies based on both simulated and experimental data.
Comparison of Different Independent Component Analysis Algorithms for Output-Only Modal Analysis
Directory of Open Access Journals (Sweden)
Jianying Wang
2016-01-01
Full Text Available From the principle of independent component analysis (ICA and the uncertainty of amplitude, order, and number of source signals, this paper expounds the root reasons for modal energy uncertainty, identified order uncertainty, and modal missing in output-only modal analysis based on ICA methods. Aiming at the problem of lack of comparison and evaluation of different ICA algorithms for output-only modal analysis, this paper studies the different objective functions and optimization methods of ICA for output-only modal parameter identification. Simulation results on simply supported beam verify the effectiveness, robustness, and convergence rate of five different ICA algorithms for output-only modal parameters identification and show that maximization negentropy with quasi-Newton iterative of ICA method is more suitable for modal parameter identification.
Operation modes of a liquid-crystal modal wave-front corrector.
Loktev, Mikhail; Vdovin, Gleb; Guralnik, Igor
2004-04-10
Liquid-crystal modal wave-front correctors provide much better wave-front correction than do piston correctors with the same number of actuators; moreover, use of additional degrees of freedom of the driving ac voltage signals may further improve device performance. Some practical aspects of the operation of liquid-crystal modal wave-front correctors are discussed. Special attention is paid to the interference of various contact responses and to the formation of required phase shapes through wider control of signal frequencies and electric phase shifts. The study is based on an analytic approach and numerical investigation; major theoretical conclusions are verified experimentally.
Vibration measurement and modal analysis of boom type tunneller
Energy Technology Data Exchange (ETDEWEB)
Min, H.; Gong, L.; Miao, W.; Wei, A. [China University of Mining & Technology, Jiangsu (China)
2003-04-01
The vibrations of an AM50 boom tunnelling machine have been measured in real time when cutting a man-made and a real coal bed. The vibration characteristics were similar in these working conditions, i.e. the man-made coal bed can be used as a realistic simulation of real cutting conditions. A modal model of the machine was then established and the intrinsic vibration characteristics were investigated by experimental modal analysis. Vibration response simulations under a set of measured load spectra and structural dynamics modification were also carried out using structural analysis software. The results not only facilitate the structural dynamics modification of the AM50 tunneller but also provide a foundation for optimising the design of new types of tunnelling machine.
Numerical Analysis of Modal Instability Onset in Fiber Amplifiers
2014-03-11
Evolution of the logarithmic frequency spectrum of the off-center optical intensity probe along the length of the co-pumped amplifier for the case of...Evolution of the logarithmic frequency spectrum of the off-center optical intensity probe along the length of the counter-pumped amplifier for the...ABSTRACT 16. SECURITY CLASSIFICATION OF: Numerical analysis of the onset of modal instability in fiber amplifiers is presented. Specifically calculations
Generalised Modal Analysis with the Pad\\'e-Laplace transform
Tannous, C
2003-01-01
We present the G-MAPLE (Generalised Modal Analysis from the Poles of the Laplace Expansion) software that allows decomposing data depending on a single parameter (such as time series data) into a set of exponential functions having complex amplitudes and arguments. The novelty is that G-MAPLE determines the unknown number of exponentials in the data along with the corresponding complex amplitudes and arguments.
Why Output Only Modal Analysis is a Desirable Tool for a Wide Range of Practical Applications
DEFF Research Database (Denmark)
Brincker, Rune; Ventura, C.; Andersen, P.
2003-01-01
In this paper the basic principles in output modal testing and analysis are presented and discussed. A brief review of the techniques for output-only modal testing and identification is presented, and it is argued, that there is now a wide range of techniques for effective identification of modal...... in an easier way and in many cases more effectively than traditional modal analysis methods. It can be applied for modal testing and analysis on a wide range of structures and not only for problems generally investigated using traditional modal analysis, but also for those requiring load estimation, vibration...
Structural optimization of precision instruments through modal analysis
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
In order to improve the dynamic stability of precision instruments during the design process,a compositive design method based on modal analysis of structure is proposed.With uniform boundary conditions and material characters,the results of Finite Element Analysis(FEA)vary with models.It should be checked whether the model is correctly simplified.Modal experiments can be used for such purpose.The method combines the high efficiency and agility of FEA with the reliability and accuracy of experiments,and avoids the drawbacks of FEA or experiments,such as uncertainty of FEA and high cost of experiments.Taking rotor-frame structure as an example,this method is applied as follows: First the modal characters of structure are analyzed with FEA,and then the natural frequencies of the structure are tested by experiments to check the reliability of FEA method,and finally the design scheme is optimized by modifying structure parameters with confirmed FEA.
Generalized modal analysis for closed-loop piezoelectric devices
Giraud-Audine, Christophe; Giraud, Frédéric; Amberg, Michel; Lemaire-Semail, Betty
2015-08-01
Stress in a piezoelectric material can be controlled by imposing an electrical field. Thanks to feedback, this electrical field can be a function of some strain-related measurement so as to confer on the piezoelectric device a closed-loop macroscopic behaviour. In this paper we address the modelling of such a system by extending the modal decomposition methods to account for the closed loop. To do so, the boundary conditions are modified to include the electrical feedback circuit, hence allowing a closed-loop modal analysis. A case study is used to illustrate the theory and to validate it. The main advantage of the method is that design issues such as the coupling factor of the device and closed-loop stability are simultaneously captured.
Miles, Jeffrey Hilton
2007-01-01
A treatment of the modal decomposition of the pressure field in a combustor as determined by two pressure time history measurements is developed herein. It is applied to a Pratt and Whitney PW4098 engine combustor over a range of operating conditions. For modes other than the plane wave the assumption is made that there are distinct frequency bands in which the individual modes, including the plane wave mode, overlap such that if circumferential mode m and circumferential mode m-1 are present then circumferential mode m-2 is not. In the analysis used herein at frequencies above the first cutoff mode frequency, only pairs of circumferential modes are individually present at each frequency. Consequently, this is a restricted modal analysis. As part of the analysis one specifies mode cut-on frequencies. This creates a set of frequencies that each mode spans. One finding was the successful use of the same modal span frequencies over a range of operating conditions for this particular engine. This suggests that for this case the cut-on frequencies are in proximity at each operating condition. Consequently, the combustion noise spectrum related to the circumferential modes might not change much with operating condition.
An Analysis of Modal Verbs in Language Teaching
Institute of Scientific and Technical Information of China (English)
邵阳
2011-01-01
Through classifying modal verbs from the semantic aspect and the pragmatic aspect, this paper discusses difficulties that students may encounter in modal verb learning. It indicates that modal verbs have complicacy, and a deductive approach and inductive approach should intermingle as an appropriate method to improve students’ accuracy in use of modal verbs.
A modal analysis for the acoustic radiation problems,I.Theory
Institute of Scientific and Technical Information of China (English)
JIANG Zhe
2004-01-01
For the acoustic radiation problems from a complex vibrating body surface, a modal analysis approach is put forward. All the normal vibration velocities on a vibrating surface form the Hilbert space. In the Hilbert space, an operator is defined, which includes the radiation property of the vibrating surface and is linear, self-adjoint and positive. Using the operator, a set of basis functions in the Hilbert space are obtained, which describe the radiation patterns and are called the radiation modes. Based on the radiation modes, a set of basis functions of the radiation field are obtained by the Helmholtz simple layer potentials,which describe the distribution patterns of the radiation field and are called the field distribution modes. The radiation behavior can be expressed by expansions of the radiation modes and the field distribution modes. The modal analysis approach is introduced into the acoustic radiation problems.
Bruin, Marieke; Nevøy, Anne
2014-07-01
After pediatric cochlear implantation, parents have to make decisions concerning which communication modality the child and the child's family will use. The choice has to be made against a background of opposing views on communication modality in follow-up after pediatric cochlear implantation. The opposing views form a discourse that has been a core issue in the international body of literature for a long time. For hearing parents caught up in this ongoing controversy, the choice can be a difficult one. The study reported in this article explores the discourse on communication modality and is based on 27 written parental accounts on experiences with follow-up. From the perspective of Foucault's thinking, discourses exert knowledge and power. Drawing on Foucault, the study explores how the discourse on communication modality is constructed, how it operates, and how it governs thinking and acting. The Foucauldian analysis brings to the fore the complex nature of the discourse and states that follow-up, which is intended to be helpful for parents, may induce insecurity and frustration. The study brings into conversation a broader understanding of the discourse on communication modality and addresses a need for increased awareness on how the discourse governs thinking and acting in follow-up.
Directory of Open Access Journals (Sweden)
Oegik Soegihardjo
2014-01-01
Full Text Available Experimental modal analysis (EMA is one among other methods to analyze dynamics characteristics of the structure. EMA is used widely in structural, automotive engineering, design and machining proccess for determination of modal parameters. EMA measures excitation force and frequency response function of the structure in time domain and then converts these data into frequency domain using Fast Fourier Transfrom (FFT. In this research EMA is applied to analyze the dynamics characteristics of wood structures that would be used as stiffener for boxed shaped work-piece or as a frame for traditional wood ship. The availability of the characteristics dynamics' data for wood are limited, so EMA is very useful tool to determine modal parameters for specific wood structures.Experiments was conducted using modal hammer to excite the wood structure and an accelerometer to measurse the response of the structure as acceleration data. The data acquired by EMA are used to determine modal parameters of wood structure in the terms of natural frequency, mode shapes and damping ratio. The dimension of wood being analyze (length x width x height is 860 mm x 50 mm x 50 mm. Simulation of modal analysis using finite element method was carried out as a comparison to the experimental data. Four points or locations along the wood's length are excited using modal hammer to get data for determination ofmodal parameters of the wood structure. Several curves such as FRF, amplitude and phase angle are presented for modal parameters determination. Analysis based on those curves provide the modal parameter of the structure. The natural frequencies of the first three modes of wood structures are 56 Hz, 334 Hz and 854 Hz. Damping ratio for those natural frequencies are 0,0178; 0,0139 and 0,012. The natural frequencies of the first three modes of wood structures from modal analysis simulation are 55,37 Hz,339,71 Hz and 921,71Hz.Differences between experimental and simulation
Automated SEM Modal Analysis Applied to the Diogenites
Bowman, L. E.; Spilde, M. N.; Papike, James J.
1996-01-01
Analysis of volume proportions of minerals, or modal analysis, is routinely accomplished by point counting on an optical microscope, but the process, particularly on brecciated samples such as the diogenite meteorites, is tedious and prone to error by misidentification of very small fragments, which may make up a significant volume of the sample. Precise volume percentage data can be gathered on a scanning electron microscope (SEM) utilizing digital imaging and an energy dispersive spectrometer (EDS). This form of automated phase analysis reduces error, and at the same time provides more information than could be gathered using simple point counting alone, such as particle morphology statistics and chemical analyses. We have previously studied major, minor, and trace-element chemistry of orthopyroxene from a suite of diogenites. This abstract describes the method applied to determine the modes on this same suite of meteorites and the results of that research. The modal abundances thus determined add additional information on the petrogenesis of the diogenites. In addition, low-abundance phases such as spinels were located for further analysis by this method.
Modal Analysis of MARS Solar Panel and Planar Vibrations
Simonyan, Andranik; Williams, R. Brett
2007-01-01
This slide presentation reviews the modal analysis of MARS solar panels and the planar vibrations. Included are views of the solar panels mock-up assembly, a view of the test seup,a view of the plot from the test, with the raw numbers of the frequencies in Hz values with the mode number, the spatial acceleration plots of Center sub panel at resonant frequencies, predictions from the Finite element models, an explanation of the two test that were done on the plate and the results from both tests,
Modal Analysis Based on the Random Decrement Technique
DEFF Research Database (Denmark)
Asmussen, J. C.; Brincker, Rune
1998-01-01
This article describes the work carried out within the project: Modal Analysis Based on the Random Decrement Technique - Application to Civil Engineering Structures. The project is part of the research programme: Dynamics of Structures sponsored by the Danish Technical Research Counsil. The planned...... contents and the requirement for the project prior to its start are described together with thee results obtained during the 3 year period of the project. The project was mainly carried out as a Ph.D project by the first author from September 1994 to August 1997 in cooperation with associate professor Rune...
Modal Analysis of MARS Solar Panel and Planar Vibrations
Simonyan, Andranik; Williams, R. Brett
2007-01-01
This slide presentation reviews the modal analysis of MARS solar panels and the planar vibrations. Included are views of the solar panels mock-up assembly, a view of the test seup,a view of the plot from the test, with the raw numbers of the frequencies in Hz values with the mode number, the spatial acceleration plots of Center sub panel at resonant frequencies, predictions from the Finite element models, an explanation of the two test that were done on the plate and the results from both tests,
Non normal modal analysis of oscillations in boiling water reactors
Energy Technology Data Exchange (ETDEWEB)
Suarez-Antola, Roberto, E-mail: roberto.suarez@miem.gub.uy [Ministerio de Industria, Energia y Mineria (MIEM), Montevideo (Uruguay); Flores-Godoy, Jose-Job, E-mail: job.flores@ibero.mx [Universidad Iberoamericana (UIA), Mexico, DF (Mexico). Dept. de Fisica Y Matematicas
2013-07-01
The first objective of the present work is to construct a simple reduced order model for BWR stability analysis, combining a two nodes nodal model of the thermal hydraulics with a two modes modal model of the neutronics. Two coupled non-linear integral-differential equations are obtained, in terms of one global (in phase) and one local (out of phase) power amplitude, with direct and cross feedback reactivities given as functions of thermal hydraulics core variables (void fractions and temperatures). The second objective is to apply the effective life time approximation to further simplify the nonlinear equations. Linear approximations for the equations of the amplitudes of the global and regional modes are derived. The linearized equation for the amplitude of the global mode corresponds to a decoupled and damped harmonic oscillator. An analytical closed form formula for the damping coefficient, as a function of the parameters space of the BWR, is obtained. The coefficient changes its sign (with the corresponding modification in the decay ratio) when a stability boundary is crossed. This produces a supercritical Hopf bifurcation, with the steady state power of the reactor as the bifurcation parameter. However, the linearized equation for the amplitude of the regional mode corresponds always to an over-damped and always coupled (with the amplitude of the global mode) harmonic oscillator, for every set of possible values of core parameters (including the steady state power of the reactor) in the framework of the present mathematical model. The equation for the above mentioned over damped linear oscillator is closely connected with a non-normal operator. Due to this connection, there could be a significant transient growth of some solutions of the linear equation. This behavior allows a significant shrinking of the basin of attraction of the equilibrium state. The third objective is to apply the above approach to partially study the stability of the regional mode and
Miles, Jeffrey Hilton
2006-01-01
A treatment of the modal decomposition of the pressure field in a combustor as determined by two Kulite pressure measurements is developed herein. It is applied to a Pratt & Whitney PW4098 engine combustor over a range of operating conditions. For modes other than the plane wave the new part of the treatment is the assumption that there are distinct frequency bands in which the individual modes, including the plane wave mode, overlap such that if circumferential mode m and circumferential mode m-1 are present than circumferential mode m 2 is not. Consequently, in the analysis used herein at frequencies above the first cut-off mode frequency, only pairs of circumferential modes are individually present at each frequency. Consequently, this is a restricted modal analysis. A new result is that the successful use of the same modal span frequencies over a range of operating conditions for this particular engine suggests that the temperature, T, and the velocity, v, of the flow at each operating condition are related by c(sup 2)-v(sup 2) = a constant where c is the speed of sound.
Terahertz mechanical vibrations in lysozyme: Raman spectroscopy vs modal analysis
Carpinteri, Alberto; Lacidogna, Giuseppe; Piana, Gianfranco; Bassani, Andrea
2017-07-01
The mechanical behaviour of proteins is receiving an increasing attention from the scientific community. Recently it has been suggested that mechanical vibrations play a crucial role in controlling structural configuration changes (folding) which govern proteins biological function. The mechanism behind protein folding is still not completely understood, and many efforts are being made to investigate this phenomenon. Complex molecular dynamics simulations and sophisticated experimental measurements are conducted to investigate protein dynamics and to perform protein structure predictions; however, these are two related, although quite distinct, approaches. Here we investigate mechanical vibrations of lysozyme by Raman spectroscopy and linear normal mode calculations (modal analysis). The input mechanical parameters to the numerical computations are taken from the literature. We first give an estimate of the order of magnitude of protein vibration frequencies by considering both classical wave mechanics and structural dynamics formulas. Afterwards, we perform modal analyses of some relevant chemical groups and of the full lysozyme protein. The numerical results are compared to experimental data, obtained from both in-house and literature Raman measurements. In particular, the attention is focused on a large peak at 0.84 THz (29.3 cm-1) in the Raman spectrum obtained analyzing a lyophilized powder sample.
UNDERSTANDING FLOW OF ENERGY IN BUILDINGS USING MODAL ANALYSIS METHODOLOGY
Energy Technology Data Exchange (ETDEWEB)
John Gardner; Kevin Heglund; Kevin Van Den Wymelenberg; Craig Rieger
2013-07-01
It is widely understood that energy storage is the key to integrating variable generators into the grid. It has been proposed that the thermal mass of buildings could be used as a distributed energy storage solution and several researchers are making headway in this problem. However, the inability to easily determine the magnitude of the building’s effective thermal mass, and how the heating ventilation and air conditioning (HVAC) system exchanges thermal energy with it, is a significant challenge to designing systems which utilize this storage mechanism. In this paper we adapt modal analysis methods used in mechanical structures to identify the primary modes of energy transfer among thermal masses in a building. The paper describes the technique using data from an idealized building model. The approach is successfully applied to actual temperature data from a commercial building in downtown Boise, Idaho.
Mathematical modeling of spinning elastic bodies for modal analysis.
Likins, P. W.; Barbera, F. J.; Baddeley, V.
1973-01-01
The problem of modal analysis of an elastic appendage on a rotating base is examined to establish the relative advantages of various mathematical models of elastic structures and to extract general inferences concerning the magnitude and character of the influence of spin on the natural frequencies and mode shapes of rotating structures. In realization of the first objective, it is concluded that except for a small class of very special cases the elastic continuum model is devoid of useful results, while for constant nominal spin rate the distributed-mass finite-element model is quite generally tractable, since in the latter case the governing equations are always linear, constant-coefficient, ordinary differential equations. Although with both of these alternatives the details of the formulation generally obscure the essence of the problem and permit very little engineering insight to be gained without extensive computation, this difficulty is not encountered when dealing with simple concentrated mass models.
Bi-Modal and Mixture Distributions in Circular Data Analysis
Directory of Open Access Journals (Sweden)
Muhammet Burak KILIC
2016-10-01
Full Text Available Objective: Circular statistics is a special area which is analyzed by observed angular data on the unit circle. In many various studies, such as environment, biology or medicine, circular (angular data is an important part of the research. For illustration, to determine the secondary structure of the proteins by utilizing dihedral angles or to asses physical disorders such as gait disturbances between the bones in the geometric morphology or the organization of the beach after leaving the eggs of sea turtles, are the important applications of this area. The uses of linear statistical methods in this area lead to misleading results because of the geometric shape of the circular data. Therefore, when it is analyzing such angular data, circular statistical methods should be used. The objective of this study is compared with the bi-modal and mixture distributions in circular data analysis. Material and Methods: The bi-modal mixture von Mises, wrapped Normal, wrapped Cauchy and the generalisations of von Mises distributions were used and it was performed by iterative methods to obtain aximum likelihood estimators. These iterative methods were applied in R programming and the R codes were given for the circular distribution of the parameter estimation. These distributions were examined for analyzing dihedral angles in proteins and turtles rotations, and model selection was performed by using Akaike and Bayesian information criteria. Results: For dihedral angles in protein, two mixture wrapped Cauchy distribution was given the better fit. For turtle rotations, the generalizations of von Mises distribution and two mixture von Mises distribution were given the better fit. Conclusion: If there is observed an excessive concentration in one or more modes in analyzing circular data, the bimodal mixture von Mises and the generalisations of von Mises distribution for modeling may not be preferred. If there is not observed an excessive concentration in
Analysis on the Modality of English News Report
Institute of Scientific and Technical Information of China (English)
肖蓉
2011-01-01
Modality is used to express subjective judgment as well as the speaker’s opinions and attitudes.This paper aims to analyze the reporters’orientation reflected by linguistic modal expressions in English news reports from the perspective of Systemic-Functio
Static Structural and Modal Analysis of Gas Turbine Blade
Ranjan Kumar, Ravi; Pandey, K. M., Prof.
2017-08-01
Gas turbine is one of the most versatile items of turbo machinery nowadays. It is used in different modes such as power generation, oil and gas, process plants, aviation, domestic and related small industries. This paper is based on the problems concerning blade profile selection, material selection and turbine rotor blade vibration that seriously impact the induced stress-deformation and structural functioning of developmental gas turbine engine. In this paper for generating specific power by rotating blade at specific RPM, blade profile and material has been decided by static structural analysis. Gas turbine rotating blade RPM is decided by Modal Analysis so that the natural frequency of blade should not match with the excitation frequency. For the above blade profile has been modeled in SOLIDWORKS and analysis has been done in ANSYS WORKBENCH 14. Existing NACA6409 profile has been selected as base model and then it is modified by bending it through 72.5° and 145°. Hence these three different blade profiles have been analyzed for three different materials viz. Super Alloy X, Nimonic 80A and Inconel 625 at three different speed viz. 20000, 40000 and 60000RPM. It is found that NACA6409 with 72.5° bent gives best result for all material at all speed. Among all the material Inconel 625 gives best result. Hence Blade of Inconel 625 having 72.5° bent profile is the best combination for all RPM.
Stability and modal analysis of shock/boundary layer interactions
Nichols, Joseph W.; Larsson, Johan; Bernardini, Matteo; Pirozzoli, Sergio
2016-06-01
The dynamics of oblique shock wave/turbulent boundary layer interactions is analyzed by mining a large-eddy simulation (LES) database for various strengths of the incoming shock. The flow dynamics is first analyzed by means of dynamic mode decomposition (DMD), which highlights the simultaneous occurrence of two types of flow modes, namely a low-frequency type associated with breathing motion of the separation bubble, accompanied by flapping motion of the reflected shock, and a high-frequency type associated with the propagation of instability waves past the interaction zone. Global linear stability analysis performed on the mean LES flow fields yields a single unstable zero-frequency mode, plus a variety of marginally stable low-frequency modes whose stability margin decreases with the strength of the interaction. The least stable linear modes are grouped into two classes, one of which bears striking resemblance to the breathing mode recovered from DMD and another class associated with revolving motion within the separation bubble. The results of the modal and linear stability analysis support the notion that low-frequency dynamics is intrinsic to the interaction zone, but some continuous forcing from the upstream boundary layer may be required to keep the system near a limit cycle. This can be modeled as a weakly damped oscillator with forcing, as in the early empirical model by Plotkin (AIAA J 13:1036-1040, 1975).
Stability and modal analysis of shock/boundary layer interactions
Nichols, Joseph W.; Larsson, Johan; Bernardini, Matteo; Pirozzoli, Sergio
2017-02-01
The dynamics of oblique shock wave/turbulent boundary layer interactions is analyzed by mining a large-eddy simulation (LES) database for various strengths of the incoming shock. The flow dynamics is first analyzed by means of dynamic mode decomposition (DMD), which highlights the simultaneous occurrence of two types of flow modes, namely a low-frequency type associated with breathing motion of the separation bubble, accompanied by flapping motion of the reflected shock, and a high-frequency type associated with the propagation of instability waves past the interaction zone. Global linear stability analysis performed on the mean LES flow fields yields a single unstable zero-frequency mode, plus a variety of marginally stable low-frequency modes whose stability margin decreases with the strength of the interaction. The least stable linear modes are grouped into two classes, one of which bears striking resemblance to the breathing mode recovered from DMD and another class associated with revolving motion within the separation bubble. The results of the modal and linear stability analysis support the notion that low-frequency dynamics is intrinsic to the interaction zone, but some continuous forcing from the upstream boundary layer may be required to keep the system near a limit cycle. This can be modeled as a weakly damped oscillator with forcing, as in the early empirical model by Plotkin (AIAA J 13:1036-1040, 1975).
Yi, Pengxing; Huang, Peng; Shi, Tielin
2016-12-01
Wind turbine gearbox (WTG), which functions as an accelerator, ensures the performance and service life of wind turbine systems. This paper examines the distinctive modal properties of WTGs through finite element (FE) and experimental modal analyses. The study is performed in two parts. First, a whole system model is developed to investigate the first 10 modal frequencies and mode shapes of WTG using flexible multibody modeling techniques. Given the complex structure and operating conditions of WTG, this study applies spring elements to the model and quantifies how the bearings and gear pair interactions affect the dynamic characteristics of WTGs. Second, the FE modal results are validated through experimental modal analyses of a 1.5 WM WTG using the frequency response function method of single point excitation and multi-point response. The natural frequencies from the FE and experimental modal analyses show favorable agreement and reveal that the characteristic frequency of the studied gearbox avoids its eigenfrequency very well.
MODAL TEST AND ANALYSIS OF CANTILEVER BEAM WITH TIP MASS
Institute of Scientific and Technical Information of China (English)
肖世富; 杜强; 陈滨; 刘才山; 向荣山; 周为华; 徐友钜; 徐有刚
2002-01-01
The phenomenon of dynamic stiffening is a research field of general interest for flexible multi-body systems. In fact, there are not only dynamic stiffening but also dynamic softening phenomenon in the flexible multi-body systems. In this paper, a non-linear dynamic model and its linearization characteristic equations of a cantilever beam with tip mass in the centrifugal field are established by adopting the general Hamilton Variational Principle. Then, the problems of the dynamic stiffening and the dynamic softening are studied by using numerical simulations. Meanwhile,the modal test is carried out on our centrifuge. The numerical results show that the system stiffness will be strengthened when the centrifugal tension force acts on the beam (i.e. the dynamic stiffening). However, the system stiffness will be weakened when the centrifugal compression force acts on the beam (i.e. the dynamic softening).Furthermore, the equilibrium position of the system will lose its stability when the inertial force reaches a critical value. Through theoretical analysis, we find that this phenomenon comes from the effect of dynamic softening resulting from the centrifugal compression force. Our test results verify the above conclusions and confirm that both dynamic stiffening and softening phenomena exist in flexible multi-body systems.
Travel modal choice analysis for traffic corridors based on decision-theoretic approaches
Institute of Scientific and Technical Information of China (English)
郭伟; 张毅; 尤佳轩; 胡坚明; 裴欣
2016-01-01
The rapid development of multimodal transportation system prompts travellers to choose multiple transportation modes, such as private vehicles or taxi, transit (subways or buses), or park-and-ride combinations for urban trips. Traffic corridor is a major scenario that supports travellers to commute from suburban residential areas to central working areas. Studying their modal choice behaviour is receiving more and more interests. On one hand, it will guide the travellers to rationally choose their most economic and beneficial mode for urban trips. On the other hand, it will help traffic operators to make more appropriate policies to enhance the share of public transit in order to alleviate the traffic congestion and produce more economic and social benefits. To analyze the travel modal choice, a generalized cost model for three typical modes is first established to evaluate each different travel alternative. Then, random utility theory (RUT) and decision field theory (DFT) are introduced to describe the decision-making process how travellers make their mode choices. Further, some important factors that may influence the modal choice behaviour are discussed as well. To test the feasibility of the proposed model, a field test in Beijing was conducted to collect the real-time data and estimate the model parameters. The improvements in the test results and analysis show new advances in the development of travel mode choice on multimodal transportation networks.
Totaro, N.; Guyader, J. L.
2012-06-01
The present article deals with an extension of the Statistical modal Energy distribution Analysis (SmEdA) method to estimate kinetic and potential energy density in coupled subsystems. The SmEdA method uses the modal bases of uncoupled subsystems and focuses on the modal energies rather than the global energies of subsystems such as SEA (Statistical Energy Analysis). This method permits extending SEA to subsystems with low modal overlap or to localized excitations as it does not assume the existence of modal energy equipartition. We demonstrate that by using the modal energies of subsystems computed by SmEdA, it is possible to estimate energy distribution in subsystems. This approach has the same advantages of standard SEA, as it uses very short calculations to analyze damping effects. The estimation of energy distribution from SmEdA is applied to an academic case and an industrial example.
Directory of Open Access Journals (Sweden)
Hua Jian
2015-09-01
Full Text Available A statically designed derrick of deep oil well drilling rig may have poor dynamic characteristics, which can cause earlier structure failure of the drilling rig and harsh working condition. One such designed derrick is found to vibrate severely in operation while the rotation speed of rotary table is about 120 r/min with the working frequency of 2.0 Hz. To solve this problem, an experimental modal test of the derrick is conducted and the modal frequencies and vibration shapes are obtained. Through comparison of modal frequencies with that of exciting devices, it is found that the severe vibration of the drilling rig is caused by the resonance of second modal frequency (1.96 Hz and the working frequency of rotary table. Based on principles of sensitivity analysis and structural dynamics modification method, the frequency sensitivities of all nodes on the derrick are calculated and compared, and then seven nodes with high-frequency sensitivity are selected on which corresponding mass are added to vary the modal frequency. Result shows that the second modal frequency of the derrick is reduced to 1.42 Hz and is out of the normal working frequency range of rotary table, which demonstrates that the dynamic characteristics of the derrick is improved and severe vibration can be avoided.
Experimental modal analysis on damage of skeleton in brake of airplane
Institute of Scientific and Technical Information of China (English)
无
1999-01-01
The relation between damage and modal parameters of skeleton has been discussed and analysed.Some significant results for detecting damage have been obtained by using experimental data of ωdi and ζi· Then, the modal experiments of four type of skeleton have been performed, the modal bifurcation phenomenon is discovered. It follows that this method for studying skeleton damage is a very promising method through theoretical and experimental analysis.
Application of experimental modal analysis technique to structural design of linear vibrating screen
Institute of Scientific and Technical Information of China (English)
LI Wen-ying(李文英); MI Zhao-yang(米朝阳); WU Wang-guo(武望国); XIONG Shi-bo(熊诗波)
2004-01-01
A large model of the screen was mounted in the laboratory for studying its modal performance. The model is suspended with steel ropes. Modal test was carried out with artificially exciting by 500 g impacting hammer and 100 kg exciting force shaker respectively. Synthesis and correction of the modal parameters are obtained from both testing methods. Design faults of vibrating screen were determined based on the analysis and dynamic correction of structure approaches about the screen was put forward finally.
Modal Analysis in Lined Wedge-Shaped Ducts
Mechel, F. P.
1998-10-01
It has been suggested to describe the sound field in a wedge-shaped duct in a cylindrical co-ordinate system in which the boundaries of the wedge lie in a co-ordinate surface. This suggestion was developed in a companion paper [1]. The wave equation can be separated only if the boundaries are ideally reflecting (rigid or soft). Two solutions were proposed in reference [1] for absorbing boundaries. In the first solution the sound field is composed of “ideal modes” (modes in a wedge with ideally reflecting boundaries); the boundary condition at the absorbing boundary then leads to a system of equations for the mode amplitudes. The problem with this method lies in the fact that there is no radial orthogonality of the ideal modes so that the precision of the field synthesis by ideal modes is doubtful. In the second method in reference [1] one defines “fictitious modes” which satisfy the boundary conditions at the flanks exactly and which are based on hypergeometric functions as radial functions, but which produce a “rest” in the wave equation. It was described how this rest can be minimized; this procedure leads to slow numerical integrations. In the present paper, the wedge is subdivided into duct sections with parallel walls (the boundary is stepped); the fields in the sections are composed of duct modes (modes in a straight lined duct); the mode amplitudes are determined from the boundary conditions at the section limits. The advantages of the present method are (analytically) the duct modes are orthogonal across the sections, so the mode amplitudes can be determined with the usual precision of a modal analysis, and (numerically) no numerical integrations are needed.
Output-Only Modal Analysis by Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Zhang, Lingmi; Andersen, Palle
2000-01-01
approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using...
Is Synthesizing MRI Contrast Useful for Inter-modality Analysis?
DEFF Research Database (Denmark)
Iglesias, Juan Eugenio; Konukoglu, Ender; Zikic, Darko
2013-01-01
Availability of multi-modal magnetic resonance imaging (MRI) databases opens up the opportunity to synthesize different MRI contrasts without actually acquiring the images. In theory such synthetic images have the potential to reduce the amount of acquisitions to perform certain analyses. However...
Modal Analysis of Worm and Worm Gear Based on ANSYS Workbench
Directory of Open Access Journals (Sweden)
Liu Yichang
2015-01-01
Full Text Available To establish the three-dimensional model of the worm and worm gear by using SolidWorks. On the worm and worm gear modal analysis is carried out by using finite element analysis software ANSYS Workbench. Obtain the first 6 order natural frequency and vibration mode characteristics of worm and worm gear. Modal analysis laid the foundation for further study on dynamics analysis, Also for the worm and worm gear structure optimization design provides a reference.
Modal analysis based equivalent circuit model and its verification for a single cMUT cell
Mao, S. P.; Rottenberg, X.; Rochus, V.; Czarnecki, P.; Helin, P.; Severi, S.; Nauwelaers, B.; Tilmans, H. A. C.
2017-03-01
This paper presents the lumped equivalent circuit model and its verification of both transmission and reception properties of a single cell capacitive micromachined ultrasonic transducer (cMUT), which is operating in a non-collapse small signal region. The derivation of this equivalent circuit model is based on the modal analysis techniques, harmonic modes are included by using the mode superposition method; and thus a wide frequency range response of the cMUT cell can be simulated by our equivalent circuit model. The importance of the cross modal coupling between different eigenmodes of a cMUT cell is discussed by us for the first time. In this paper the development of this model is only illustrated by a single circular cMUT cell under a uniform excitation. Extension of this model and corresponding results under a more generalized excitation will be presented in our upcoming publication (Mao et al 2016 Proc. IEEE Int. Ultrasonics Symp.). This model is verified by both finite element method (FEM) simulation and experimental characterizations. Results predicted by our model are in a good agreement with the FEM simulation results, and this works for a single cMUT cell operated in either transmission or reception. Results obtained from the model also rather match the experimental results of the cMUT cell. This equivalent circuit model provides an easy and precise way to rapidly predict the behaviors of cMUT cells.
Modal analysis of coupled vibration of belt drive systems
Institute of Scientific and Technical Information of China (English)
LI Xiao-jun; CHEN Li-qun
2008-01-01
The modal method is applied to analyze coupled vibration of belt drive systems. A belt drive system is a hybrid system consisting of continuous belts modeled as strings as well as discrete pulleys and a tensioner arm. The characteristic equation of the system is derived from the governing equation. Numerical results demenstrate the effects of the transport speed and the initial tension on natural frequencies.
Output-only Modal Analysis by Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Zhang, L.; Andersen, P.
2000-01-01
approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using...... this decomposition technique close modes can be identified with high accuracy even in the case of strong noise contamination of the signals. Also, the technique clearly indicates harmonic components in the response signals....
Output-Only Modal Analysis by Frequency Domain Decomposition
DEFF Research Database (Denmark)
Brincker, Rune; Zhang, Lingmi; Andersen, Palle
2000-01-01
approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using...... this decomposition technique close modes can be identified with high accuracy even in the case of strong noise contamination of the signals. Also, the technique clearly indicates harmonic components in the response signals....
Analysis on rotational Doppler Effect based on modal expansion method
Zhou, Hailong; Zhang, Pei; Zhang, Xinliang
2015-01-01
We theoretically investigate the optical rotational Doppler Effect using modal expansion method. We find that the frequency shift content is only determined by the surface of spinning object and the reduced Doppler shift is linear to the change of mode index. The theoretical model makes us better understand the physical processes of rotational Doppler Effect. It can provide theoretical guidance for many related applications, such as detection of rotating bodies, detection of OAM and frequency shift.
Strain Modal Analysis of Small and Light Pipes Using Distributed Fibre Bragg Grating Sensors.
Huang, Jun; Zhou, Zude; Zhang, Lin; Chen, Juntao; Ji, Chunqian; Pham, Duc Truong
2016-09-25
Vibration fatigue failure is a critical problem of hydraulic pipes under severe working conditions. Strain modal testing of small and light pipes is a good option for dynamic characteristic evaluation, structural health monitoring and damage identification. Unique features such as small size, light weight, and high multiplexing capability enable Fibre Bragg Grating (FBG) sensors to measure structural dynamic responses where sensor size and placement are critical. In this paper, experimental strain modal analysis of pipes using distributed FBG sensors ispresented. Strain modal analysis and parameter identification methods are introduced. Experimental strain modal testing and finite element analysis for a cantilever pipe have been carried out. The analysis results indicate that the natural frequencies and strain mode shapes of the tested pipe acquired by FBG sensors are in good agreement with the results obtained by a reference accelerometer and simulation outputs. The strain modal parameters of a hydraulic pipe were obtained by the proposed strain modal testing method. FBG sensors have been shown to be useful in the experimental strain modal analysis of small and light pipes in mechanical, aeronautic and aerospace applications.
A modal approach for vibration analysis and condition monitoring of a centrifugal pump
Directory of Open Access Journals (Sweden)
Ramana Podugu
2011-08-01
Full Text Available The modal analysis of the centrifugal pump and its assembly is performed using FEM technology. The mathematical model and FEA model are built for the original centrifugal casing and simulation is made to find the pump natural frequencies. The first ten natural frequencies were compared to pump operating speed and their multiples up to pump vane passing frequency as per HIS (Hydraulic Institute Standards -9.6.4-2000 guidelines. In the original design, the first natural frequency in vertical direction of the pump is found to be thecause for resonance at the first multiple speed of the pump. The first natural frequency of the original model was found to be 63.25 Hz which is very close to 62.5 Hz of the pump operating speed by a margin of 1.2%. As per HIS clause 9.6.4.4, the first natural frequency should be 10% above or below the pump operating speed. Finally, the model was modified by stiffening the pump pedestals and again FEA analysis was carried out to find the natural frequencies. As a result of modification in design, the first natural frequency was increased to 74.31Hz which is above 10% the pump operating speed i.e., 62.5 Hz. Hence, the results of the modified design aresatisfied with HIS clause. The results also show that the higher the stiffness of the pump, higher the natural frequency is.
VoxelStats: A MATLAB Package for Multi-Modal Voxel-Wise Brain Image Analysis.
Mathotaarachchi, Sulantha; Wang, Seqian; Shin, Monica; Pascoal, Tharick A; Benedet, Andrea L; Kang, Min Su; Beaudry, Thomas; Fonov, Vladimir S; Gauthier, Serge; Labbe, Aurélie; Rosa-Neto, Pedro
2016-01-01
In healthy individuals, behavioral outcomes are highly associated with the variability on brain regional structure or neurochemical phenotypes. Similarly, in the context of neurodegenerative conditions, neuroimaging reveals that cognitive decline is linked to the magnitude of atrophy, neurochemical declines, or concentrations of abnormal protein aggregates across brain regions. However, modeling the effects of multiple regional abnormalities as determinants of cognitive decline at the voxel level remains largely unexplored by multimodal imaging research, given the high computational cost of estimating regression models for every single voxel from various imaging modalities. VoxelStats is a voxel-wise computational framework to overcome these computational limitations and to perform statistical operations on multiple scalar variables and imaging modalities at the voxel level. VoxelStats package has been developed in Matlab(®) and supports imaging formats such as Nifti-1, ANALYZE, and MINC v2. Prebuilt functions in VoxelStats enable the user to perform voxel-wise general and generalized linear models and mixed effect models with multiple volumetric covariates. Importantly, VoxelStats can recognize scalar values or image volumes as response variables and can accommodate volumetric statistical covariates as well as their interaction effects with other variables. Furthermore, this package includes built-in functionality to perform voxel-wise receiver operating characteristic analysis and paired and unpaired group contrast analysis. Validation of VoxelStats was conducted by comparing the linear regression functionality with existing toolboxes such as glim_image and RMINC. The validation results were identical to existing methods and the additional functionality was demonstrated by generating feature case assessments (t-statistics, odds ratio, and true positive rate maps). In summary, VoxelStats expands the current methods for multimodal imaging analysis by allowing the
Lv, Wei; Winters, Michael; Weinberg, Gil; Henry, Asegun
2016-01-01
We used molecular dynamics simulations, the Green-Kubo Modal Analysis (GKMA) method and sonification to study the modal contributions to thermal conductivity in individual polythiophene chains. The simulations suggest that it is possible to achieve divergent thermal conductivity and the GKMA method allowed for exact pinpointing of the modes responsible for the anomalous behavior. The analysis showed that transverse vibrations in the plane of the aromatic rings at low frequencies ~ 0.05 THz ar...
Modal analysis of an aircraft engine fan noise
Gorodkova, Natalia; Chursin, Valeriy; Bersenev, Yuliy; Burdakov, Ruslan; Siner, Aleksandr; Viskova, Tatiana
2016-10-01
The fan is one of the main noise sources of an aircraft engine. To reduce fan noise and provide liner optimization in the inlet it is necessary to research modal structure of the fan noise. The present paper contains results of acoustic tests on installation for mode generation that consists of 34-channel generator and the inlet updated for mounting of 100 microphones, the experiments were provided in new anechoic chamber of Perm National Research Polytechnic University, the engine with the same inlet was also tested in the open test bench conditions, and results of the fan noise modal structure are presented. For modal structure educting, all 100 channels were synchronously registered in a given frequency range. The measured data were analyzed with PULSE analyzer using fast Fourier transform with a frequency resolution 8..16 Hz. Single modes with numbers from 0 to 35 at frequencies 500; 630; 800; 1000; 1250; 1600 Hz and different combinations of modes at frequencies 1000, 1600, 2000, 2500 Hz were set during tests. Modes with small enough numbers are generated well on the laboratory installation, high-number modes generate additional modes caused by a complicated interference pattern of sound field in the inlet. Open test bench results showed that there are also a lot of harmonic components at frequencies lower than fan BPF. Under 0.65 of cut off there is only one distinct mode, other modes with close and less numbers appear from 0.7 of cut off and above. At power regimes 0.76 and 0.94 of cut off the highest mode also changes from positive to negative mode number area. Numbers of the highest modes change smoothly enough with the growth of power regime. At power regimes with Mach>1 (0.7 of cut off and above) on circumference of blade wheel there is a well-defined noise of shock waves at rotor frequency harmonics that appears at the range between the first rotor frequency and fan blade passing frequency (BPF). It is planned to continue researching of sound field
Operational Analysis in the Launch Environment
James, George; Kaouk, Mo; Cao, Tim; Fogt, Vince; Rocha, Rodney; Schultz, Ken; Tucker, Jon-Michael; Rayos, Eli; Bell,Jeff; Alldredge, David; Howsman, Tom
2012-01-01
The launch environment is a challenging regime to work due to changing system dynamics, changing environmental loading, joint compression loads that cannot be easily applied on the ground, and control effects. Operational testing is one of the few feasible approaches to capture system level dynamics since ground testing cannot reproduce all of these conditions easily. However, the most successful applications of Operational Modal Testing involve systems with good stationarity and long data acquisition times. This paper covers an ongoing effort to understand the launch environment and the utility of current operational modal tools. This work is expected to produce a collection of operational tools that can be applied to non-stationary launch environment, experience dealing with launch data, and an expanding database of flight parameters such as damping. This paper reports on recent efforts to build a software framework for the data processing utilizing existing and specialty tools; understand the limits of current tools; assess a wider variety of current tools; and expand the experience with additional datasets as well as to begin to address issues raised in earlier launch analysis studies.
Operational Modal Analysis in the Presence of Harmonic Excitations
Mohanty, P.
2005-01-01
The dynamic behavior of structures is a primordial factor determining its structural stability, reliability and lifespan. Therefore, in many advanced engineering applications, it has become essential to predict the dynamics of new designs through simulations, to identify the dynamic characteristics
Operational Modal Analysis in the Presence of Harmonic Excitations
Mohanty, P.
2005-01-01
The dynamic behavior of structures is a primordial factor determining its structural stability, reliability and lifespan. Therefore, in many advanced engineering applications, it has become essential to predict the dynamics of new designs through simulations, to identify the dynamic characteristics
Effects of Joint Controller on Analytical Modal Analysis of Rotational Flexible Manipulator
Institute of Scientific and Technical Information of China (English)
CHU Ming; ZHANG Yanheng; CHEN Gang; SUN Hanxu
2015-01-01
Modal analysis is a fundamental and important task for modeling and control of the flexible manipulator. However, almost all of the traditional modal analysis methods view the flexible manipulator as a pure mechanical structure and neglect feedback action of joint controller. In order to study the effects of joint controller on the modal analysis of rotational flexible manipulator, a closed-loop analytical modal analysis method is proposed. Firstly, two exact boundary constralnts, namely servo feedback constralnt and bending moment constralnt, are derived to solve the vibration partial differential equation. It is found that the stiffness and damping galns of joint controller are both included in the boundary conditions, which lead to an unconventional secular term. Secondly, analytical algorithm based on Ritz approach is developed by using Laplace transform and complex modal approach to obtaln the natural frequencies and mode shapes. And then, the numerical simulations are performed and the computational results show that joint controller has pronounced influence on the modal parameters:joint controller stiffness reduces the natural frequency, while joint controller damping makes the shape phase non-zero. Furthermore, the validity of the presented conclusion is confirmed through experimental studies. These findings are expected to improve the performance of dynamics simulation systems and model-based controllers.
Comparison of Modal Analysis Methods Applied to a Vibro-Acoustic Test Article
Pritchard, Jocelyn; Pappa, Richard; Buehrle, Ralph; Grosveld, Ferdinand
2001-01-01
Modal testing of a vibro-acoustic test article referred to as the Aluminum Testbed Cylinder (ATC) has provided frequency response data for the development of validated numerical models of complex structures for interior noise prediction and control. The ATC is an all aluminum, ring and stringer stiffened cylinder, 12 feet in length and 4 feet in diameter. The cylinder was designed to represent typical aircraft construction. Modal tests were conducted for several different configurations of the cylinder assembly under ambient and pressurized conditions. The purpose of this paper is to present results from dynamic testing of different ATC configurations using two modal analysis software methods: Eigensystem Realization Algorithm (ERA) and MTS IDEAS Polyreference method. The paper compares results from the two analysis methods as well as the results from various test configurations. The effects of pressurization on the modal characteristics are discussed.
A finite element solver for modal analysis of multi-span offshore pipelines
2014-01-01
Accurate determination of pipeline eigenfrequencies and mode shapes is essential to free span design. For pipelines resting on rough seabeds, multiple free spans are commonly located sufficiently close to be interacting, and finite element analysis (FEA) is then conventionally required to determine the modal response. In the present report, a tailor-made (specific purpose) FEA tool is developed to carry out modal analyses of multi-span offshore pipelines. The specific purpose FEA tool is thor...
Experimental Modal Analysis and Dynamic Component Synthesis. Volume 6. Software User’s Guide.
1987-12-01
theTechnical Reports should be referenced. V.4 20. OISTRIBUTION/ AVAILABIlTY OF ABSTRACT 21 ABSTRACT SECURITY CLASSIFICATION UNCLASSIFIED/UNLIMITED...documentation is consistent with prevailing usage in the modal analysis area. Certain conventions that are used are based upon previous practice in...the BCS Modal Program (User Program Nine) or based upon common usage in the HP-5451-A/B/C Fourier Systems. A specific example of this is the use of the
Finite Element Modeling and Modal Analysis of Complicated Structure with Bolted Joints
Institute of Scientific and Technical Information of China (English)
PU Da-yu; LIAO Ri-dong; ZUO Zheng-xing; FENG Hui-hua
2009-01-01
A contact bolt model is proposed as a new modeling technique to investigate the complex structure with bolted joints for modal analysis and compared with the coupled bolt model, and the test results are given. Among these models, the coupled bolt model provides the best accurate responses compared with the experimental results. The contact bolt model shows the best effectiveness and usefulness in view of operational time. The bolt models proposed in this study are adopted for a dynamic characteristic analysis of a large diesel engine consisting of several parts which are connected by many bolts. The dynamic behavior of the entire engine structure was investigated by experiment. The coupled bolt model and the contact bolt model were applied to model the assembly of engine with high preload. The experimental results are in good agreement with the finite element method (FEM) results. Compared with the other models, the contact bolt model presented in this paper is more effective and useful in view of operational time and experience of analysts.
Determination of replicate composite bone material properties using modal analysis.
Leuridan, Steven; Goossens, Quentin; Pastrav, Leonard; Roosen, Jorg; Mulier, Michiel; Denis, Kathleen; Desmet, Wim; Sloten, Jos Vander
2017-02-01
Replicate composite bones are used extensively for in vitro testing of new orthopedic devices. Contrary to tests with cadaveric bone material, which inherently exhibits large variability, they offer a standardized alternative with limited variability. Accurate knowledge of the composite's material properties is important when interpreting in vitro test results and when using them in FE models of biomechanical constructs. The cortical bone analogue material properties of three different fourth-generation composite bone models were determined by updating FE bone models using experimental and numerical modal analyses results. The influence of the cortical bone analogue material model (isotropic or transversely isotropic) and the inter- and intra-specimen variability were assessed. Isotropic cortical bone analogue material models failed to represent the experimental behavior in a satisfactory way even after updating the elastic material constants. When transversely isotropic material models were used, the updating procedure resulted in a reduction of the longitudinal Young's modulus from 16.00GPa before updating to an average of 13.96 GPa after updating. The shear modulus was increased from 3.30GPa to an average value of 3.92GPa. The transverse Young's modulus was lowered from an initial value of 10.00GPa to 9.89GPa. Low inter- and intra-specimen variability was found. Copyright © 2016 Elsevier Ltd. All rights reserved.
Modal seismic analysis of a nuclear power plant control panel and comparison with SAP 4
Pamidi, M. R.; Pamidi, P. R.
1976-01-01
The application of NASTRAN to seismic analysis by considering the example of a nuclear power plant control panel was considered. A modal analysis of a three-dimensional model of the panel, consisting of beam and quadri-lateral membrane elements, is performed. Using the results of this analysis and a typical response spectrum of an earthquake, the seismic response of the structure is obtained. ALTERs required to the program in order to compute the maximum modal responses as well as the resultant response are given. The results are compared with those obtained by using the SAP IV computer program.
Energy Technology Data Exchange (ETDEWEB)
Leon Rodriguez, Daniel
2000-12-15
The economic development of the countries has taken implicit a growing industrialization the one which, joined to those every time bigger resident's necessities, it has caused a constant and progressive increment in the electric power demand. However, in the last years the growth of the electric network of these systems has been more and more limited for diverse such factors as the ecology and the economy, as well as for the social and political costs that implies each new construction in the system. With the presence of these restrictions the electric systems in many cases, have been forced to satisfy the increments in the demand making a more exhaustive use of the infrastructure that they have available and the incorporation of only a few new system elements or constructions. These aspects have caused such systems to operate with more limited security margins and that their stability has to be analyzed in a reliable and precise way. Taking into account the previously mentioned aspects, as the electric systems have had the necessity of operating under forced conditions to satisfy the load demand, voltage stability problems have been presented with more frequency causing serious disturbances and in some cases, total blackouts. With these problems, the voltage stability analysis has taken bigger importance in the studies that the electric utilities carry out. This issue has caused that bigger resources are dedicated for the investigation of this phenomenon with the purpose of understanding and developing tools that allow studying it in a more complete and more truthful way. Modal analysis is one of the most recent and popular steady techniques the one that, from its appearance has had a great peak due to the valuable and quick information that provides, besides its implementation easiness and the little effort computational that it requires. In this work is carried out the voltage stability evaluation of a real electric system applying in a combined way the
Multi-modal Discourse Analysis of Peng Liyuan’s Dress
Institute of Scientific and Technical Information of China (English)
顾伟红
2016-01-01
Traditional discourse analysis basically focuses on language rather than non-linguistic symbol resources in terms of meaning construction. The latter emerging multi-modal discourse analysis breaks this limitation into a large extent. This paper analyzed Peng Liyuan’s dress with semiotics of Saussure and visual grammar of Kress and Van Ixeuwen as theoretical framework.
Static Analysis, Design Modification and Modal Analysis of Structural Chassis Frame
Directory of Open Access Journals (Sweden)
Madhu Ps
2014-05-01
Full Text Available The chassis frame is an important part in a truck and it carries the whole load acting on the truck as well as different parts of the automobile. So it must be strong enough to resist the shock, twist, vibration and other stresses. Maximum stress and maximum deflection are important criteria for design of the chassis. The objective of present is to determine the maximum stress, maximum deflection and to recognize critical regions under static loading condition. Static structural analysis of the chassis frame is carried out by FEA Method. The structural chassis frame is modeled using PRO-E wildfire 4.0 software. The Pre-processing has done with HYPERMESH software; then the problem has been solved through RADIOSS and the post processing was done by HYPERVIEW. The results obtained like maximum shear stress, Von-mises stress and maximum deflections are used for improving design modification. Modal analysis of the chassis frame done using ANSYS WORKBENCH. Through modal analysis, natural frequencies and corresponding vibration mode shapes of the structure are obtained.
Dryginin, N. V.; Krasnoveikin, V. A.; Filippov, A. V.; Tarasov, S. Yu.; Rubtsov, V. E.
2016-11-01
Additive manufacturing by 3D printing is the most advanced and promising trend for making the multicomponent composites. Polymer-based carbon fiber reinforced composites demonstrate high mechanical properties combined with low weight characteristics of the component. This paper shows the results of 3D modeling and experimental modal analysis on a polymer composite framework obtained using additive manufacturing. By the example of three oscillation modes it was shown the agreement between the results of modeling and experimental modal analysis with the use of laser Doppler vibrometry.
Modal Analysis on the Wind Tunnel Test Bed based on Workbench
Directory of Open Access Journals (Sweden)
Shao Zi-yan
2015-01-01
Full Text Available This paper shows a wind tunnel test bed with parallelogram structure. The three-dimensional model was built by Solidworks after analyzing the movement principle. Then the model was imported to Workbench and carried out modal analysis according to the theory of finite element modal analysis. Finally the first six vibration mode and the natural frequency were got. This result provides theoretical support for the further research of the stability of the structure, and it also provides theoretical basis for the optimal design of the institution.
Data Processing And Machine Learning Methods For Multi-Modal Operator State Classification Systems
Hearn, Tristan A.
2015-01-01
This document is intended as an introduction to a set of common signal processing learning methods that may be used in the software portion of a functional crew state monitoring system. This includes overviews of both the theory of the methods involved, as well as examples of implementation. Practical considerations are discussed for implementing modular, flexible, and scalable processing and classification software for a multi-modal, multi-channel monitoring system. Example source code is also given for all of the discussed processing and classification methods.
Sensitivity analysis and dynamic modification of modal parameter in mechanical transmission system
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
Sensitivity analysis is one of the effective methods in the dynamic modification. The sensitivity of the modal parameters such as the natural frequencies and mode shapes in undamped free vibration of mechanical transmission system is analyzed in this paper.In particular,the sensitivities of the modal parameters to physical parameters of shaft system such as the inertia and stiffness are given.A calculation formula for dynamic modification is presented based on the analysis of modal parameter.With a mechanical transmission system as an example, the sensitivities of natural frequencies and modes shape are calculated and analyzed. Furthermore, the dynamic modification is also carried out and a good result is obtained.
Numerical Modal Analysis of Vibrations in a Three-Phase Linear Switched Reluctance Actuator
Directory of Open Access Journals (Sweden)
José Salvado
2017-01-01
Full Text Available This paper addresses the problem of vibrations produced by switched reluctance actuators, focusing on the linear configuration of this type of machines, aiming at its characterization regarding the structural vibrations. The complexity of the mechanical system and the number of parts used put serious restrictions on the effectiveness of analytical approaches. We build the 3D model of the actuator and use finite element method (FEM to find its natural frequencies. The focus is on frequencies within the range up to nearly 1.2 kHz which is considered relevant, based on preliminary simulations and experiments. Spectral analysis results of audio signals from experimental modal excitation are also shown and discussed. The obtained data support the characterization of the linear actuator regarding the excited modes, its vibration frequencies, and mode shapes, with high potential of excitation due to the regular operation regimes of the machine. The results reveal abundant modes and harmonics and the symmetry characteristics of the actuator, showing that the vibration modes can be excited for different configurations of the actuator. The identification of the most critical modes is of great significance for the actuator’s control strategies. This analysis also provides significant information to adopt solutions to reduce the vibrations at the design.
A custom multi-modal sensor suite and data analysis pipeline for aerial field phenotyping
Bartlett, Paul W.; Coblenz, Lauren; Sherwin, Gary; Stambler, Adam; van der Meer, Andries
2017-05-01
Our group has developed a custom, multi-modal sensor suite and data analysis pipeline to phenotype crops in the field using unpiloted aircraft systems (UAS). This approach to high-throughput field phenotyping is part of a research initiative intending to markedly accelerate the breeding process for refined energy sorghum varieties. To date, single rotor and multirotor helicopters, roughly 14 kg in total weight, are being employed to provide sensor coverage over multiple hectaresized fields in tens of minutes. The quick, autonomous operations allow for complete field coverage at consistent plant and lighting conditions, with low operating costs. The sensor suite collects data simultaneously from six sensors and registers it for fusion and analysis. High resolution color imagery targets color and geometric phenotypes, along with lidar measurements. Long-wave infrared imagery targets temperature phenomena and plant stress. Hyperspectral visible and near-infrared imagery targets phenotypes such as biomass and chlorophyll content, as well as novel, predictive spectral signatures. Onboard spectrometers and careful laboratory and in-field calibration techniques aim to increase the physical validity of the sensor data throughout and across growing seasons. Off-line processing of data creates basic products such as image maps and digital elevation models. Derived data products include phenotype charts, statistics, and trends. The outcome of this work is a set of commercially available phenotyping technologies, including sensor suites, a fully integrated phenotyping UAS, and data analysis software. Effort is also underway to transition these technologies to farm management users by way of streamlined, lower cost sensor packages and intuitive software interfaces.
Validation of VARK learning modalities questionnaire using Rasch analysis
Fitkov-Norris, E. D.; Yeghiazarian, A.
2015-02-01
This article discusses the application of Rasch analysis to assess the internal validity of a four sub-scale VARK (Visual, Auditory, Read/Write and Kinaesthetic) learning styles instrument. The results from the analysis show that the Rasch model fits the majority of the VARK questionnaire data and the sample data support the internal validity of the four sub-constructs at 1% level of significance for all but one item. While this suggests that the instrument could potentially be used as a predictor for a person's learning preference orientation, further analysis is necessary to confirm the invariability of the instrument across different user groups across factors such as gender, age, educational and cultural background.
Full vector modal analysis of microstructured optical fiber propagation characteristics
Zghal, Mourad; Bahloul, Faouzi; Chatta, Rihab; Attia, Rabah; Pagnoux, Dominique; Roy, Philippe; Melin, Gilles; Gasca, Laurent
2004-10-01
Microstructured optical fibers (MOFs) are optical fibers having a periodic air-silica cross-section. The air holes extend along the axis of the fiber for its entire length. The core of the fiber is formed by a missing hole in the periodic structure. Remarkable properties of MOFs have recently been reported. This paper presents new work in the modeling of the propagation characteristics of MOFs using the Finite Element Method (FEM) and the Galerkin Method (GM). This efficient electromagnetic simulation package provides a vectorial description of the electromagnetic fields and of the associated effective index. This information includes accurate determination of the spectral extent of the modes, cutoff properties and mode-field distributions. We show that FEM is well adapted for describing the fields at abrupt transitions of the refractive index while GM has the advantage to accurately analyze MOFs of significant complexity using only modest computational resources. This presentation will focus on the specific techniques required to determine single mode operation, dispersion properties and effective area through careful choice of the geometrical parameters of the fibers. We demonstrate that with suitable geometrical parameters, the zero dispersion wavelength can be shifted. This tool can also provide design criteria for fabricating MOFs and a corresponding map of effective area. This approach is validated by comparison with experimental results and measurements on actual MOFs fabricated at IRCOM and at Alcatel Research and Innovation Center.
Guan, Cheng; Zhang, Houjiang; Wang, Xiping; Miao, Hu; Zhou, Lujing; Liu, Fenglu
2017-01-01
Key elastic properties of full-sized wood composite panels (WCPs) must be accurately determined not only for safety, but also serviceability demands. In this study, the modal parameters of full-sized WCPs supported on four nodes were analyzed for determining the modulus of elasticity (E) in both major and minor axes, as well as the in-plane shear modulus of panels by using a vibration testing method. The experimental modal analysis was conducted on three full-sized medium-density fiberboard (MDF) and three full-sized particleboard (PB) panels of three different thicknesses (12, 15, and 18 mm). The natural frequencies and mode shapes of the first nine modes of vibration were determined. Results from experimental modal testing were compared with the results of a theoretical modal analysis. A sensitivity analysis was performed to identify the sensitive modes for calculating E (major axis: Ex and minor axis: Ey) and the in-plane shear modulus (Gxy) of the panels. Mode shapes of the MDF and PB panels obtained from modal testing are in a good agreement with those from theoretical modal analyses. A strong linear relationship exists between the measured natural frequencies and the calculated frequencies. The frequencies of modes (2, 0), (0, 2), and (2, 1) under the four-node support condition were determined as the characteristic frequencies for calculation of Ex, Ey, and Gxy of full-sized WCPs. The results of this study indicate that the four-node support can be used in free vibration test to determine the elastic properties of full-sized WCPs. PMID:28773043
An improved method for and error evaluation of modal pushover analysis%Modal Pushover的改进方法及误差评估
Institute of Scientific and Technical Information of China (English)
杨红; 臧登科; 闻奇光; 王志军
2009-01-01
在对Modal Pushover方法的原理及误差进行评价的基础上,结合与整体目标位移延性系数相对应的钢筋混凝土框架构件刚度折减系数的合理取值,提出了Modal Pushover的改进方法.为考察高阶振型参与程度的影响规律,以10层和16层钢筋混凝土平面框架为例,将框架在7条地震动波不同峰值加速度作用下的非线性地震反应统计结果作为对比基准点,研究Modal Pushover方法、改进Modal Pushover方法的分析结果随框架周期、地震动强度增加的误差变化规律.研究表明,Modal Pushover方法、改进Modal Pushover方法的误差并不随着框架周期加大而增加,表明该方法能合理地考虑高振型参与反应的影响;框架非线性程度加深后,改进Modal Pushover方法可在一定程度上降低MPA(Model Pushover Analysi)方法的误差.
Modal Analysis of a Single-Structure Multiaxis MEMS Gyroscope
Directory of Open Access Journals (Sweden)
Muhammad Ali Shah
2016-01-01
Full Text Available This paper reports on designing a single-structure triaxes MEMS capacitive gyroscope which is capable of measuring the three angular velocities on a single drive. A Z-shaped beam for the support of folded coupling spring has been applied to suppress the unwanted mode and decrease the stress effect at the spring ends. The unique coupling spring has changed the driving motion, due to which slide film damping in the driving mode has been reduced. This reduction can lead to higher performance of the sensor with less requirements on vacuum level which decreases the cost of fabrication. Simulation analysis has been performed in COMSOL Multiphysics and Matlab Simulink to finalize the design for fabrication. After finite element analysis, the driving, x-sensing, z-sensing, and y-sensing are, respectively, found to be 13.30 KHz, 13.40 KHz, 13.47 KHz, and 13.51 KHz.
Energy Technology Data Exchange (ETDEWEB)
Dumeige, Yannick; Feron, Patrice [Universite Europeenne de Bretagne, Laboratoire Foton and CNRS, UMR 6082 Foton, Enssat, BP 80518, F-22305 Lannion Cedex (France)
2011-10-15
Coupled nonlinear resonators have potential applications for the integration of multistable photonic devices. The dynamic properties of two coupled-mode nonlinear microcavities made of Kerr material are studied by linear stability analysis. Using a suitable combination of the modal coupling rate and the frequency detuning, it is possible to obtain configurations where a hysteresis loop is included inside other bistable cycles. We show that a single resonator with two modes both linearly and nonlinearly coupled via the cross-Kerr effect can have a multistable behavior. This could be implemented in semiconductor nonlinear whispering-gallery-mode microresonators under modal coupling for all optical signal processing or ternary optical logic applications.
Self-organized Hydrodynamics in an Annular Domain: Modal Analysis and Nonlinear Effects
Degond, Pierre; Yu, Hui
2014-01-01
The Self-Organized Hydrodynamics model of collective behavior is studied on an annular domain. A modal analysis of the linearized model around a perfectly polarized steady-state is conducted. It shows that the model has only pure imaginary modes in countable number and is hence stable. Numerical computations of the low-order modes are provided. The fully non-linear model is numerically solved and nonlinear mode-coupling is then analyzed. Finally, the efficiency of the modal decomposition to a...
Fluid-Structure Interaction Effects Modeling for the Modal Analysis of a Steam Generator Tube Bundle
Energy Technology Data Exchange (ETDEWEB)
Sigrist, J.F. [DCNS Prop, Serv Tech et Sci, F-44620 La Montagne, (France); Broc, D. [CEA Saclay, Serv Etud Mecan et Sism, F-91191 Gif Sur Yvette, (France)
2009-07-01
Seismic analysis of steam generator is of paramount importance in the safety assessment of nuclear installations. These analyses require, in particular, the calculation of frequency, mode shape, and effective modal mass of the system Eigenmodes. As fluid-structure interaction effects can significantly affect the dynamic behavior of immersed structures, the numerical modeling of the steam generator has to take into account FSI. A complete modeling of heat exchangers (including pressure vessel, tubes, and fluid) is not accessible to the engineer for industrial design studies. In the past decades, homogenization methods have been studied and developed in order to model tubes and fluid through an equivalent continuous media, thus avoiding the tedious task to mesh all structure and fluid sub-domains within the tube bundle. Few of these methods have nonetheless been implemented in industrial finite element codes. In a previous paper (Sigrist, 2007, 'Fluid-Structure Interaction Effects Modeling for the Modal Analysis of a Nuclear Pressure Vessel', J. Pressure Vessel Technol., 123, p. 1-6), a homogenization method has been applied to an industrial case for the modal analysis of a nuclear rector with internal structures and coupling effects modeling. The present paper aims at investigating the extension of the proposed method for the dynamic analysis of tube bundles with fluid-structure interaction modeling. The homogenization method is compared with the classical coupled method in terms of eigenfrequencies, Eigenmodes, and effective modal masses. (authors)
Marques dos Santos, Fábio Luis; Peeters, Bart
2016-10-01
This paper discusses the use of optical fiber Bragg grating (FBG) and piezo strain sensors for structural dynamic measurements. For certain industrial applications, there is an interest to use strain sensors rather than in combination with accelerometers for experimental modal analysis. Classical electrical strain gauges can be used hereto, but other types of strain sensors are an interesting alternative with some very specific advantages. This work gives an overview of two types of dynamic strain sensors, applied to two industrial applications (a helicopter main rotor blade and an F-16 aircraft), FBG sensors and dynamic piezo strain sensors, discussing their use and benefits. Moreover, the concept of strain modal analysis is introduced and it is shown how it can be beneficial to apply strain measurements to experimental modal analysis. Finally, experimental results for the two applications are shown, with an experimental modal analysis carried out on the helicopter main rotor blade using FBG sensors and a similar experiment is done with the aircraft but using piezo strain sensors instead.
Jaipal, Kamini
2010-01-01
The teaching of science is a complex process, involving the use of multiple modalities. This paper illustrates the potential of a multimodal semiotics discourse analysis framework to illuminate meaning-making possibilities during the teaching of a science concept. A multimodal semiotics analytical framework is developed and used to (1) analyze the…
Yamahata, Christophe; Stranczl, Marc; Sarajlic, Edin; Krijnen, Gijsbertus J.M.; Gijs, Martin A.M.
A simple optical method is proposed for performing in-plane experimental modal analysis of micromachined struc- tures with a conventional charge-coupled device (CCD) camera. The motion of a micromechanical device actuated by high- frequency sinusoidal forces (kilohertz range) is recorded at the
Yamahata, Christophe; Stranczl, Marc; Sarajlic, Edin; Krijnen, Gijs J.M.; Gijs, Martin A.M.
2012-01-01
A simple optical method is proposed for performing in-plane experimental modal analysis of micromachined struc- tures with a conventional charge-coupled device (CCD) camera. The motion of a micromechanical device actuated by high- frequency sinusoidal forces (kilohertz range) is recorded at the fixe
Asymptotic modal analysis of a rectangular acoustic cavity excited by wall vibration
Peretti, Linda F.; Dowell, Earl H.
1992-01-01
Asymptotic modal analysis, a method that has recently been developed for structural dynamical systems, has been applied to a rectangular acoustic cavity. The cavity had a flexible vibrating portion on one wall, and the other five walls were rigid. Banded white noise was transmitted through the flexible portion (plate) only. Both the location along the wall and the size of the plate were varied. The mean square pressure levels of the cavity interior were computed as a ratio of the result obtained from classical modal analysis to that obtained from asymptotic modal analysis for the various plate configurations. In general, this ratio converged to 1.0 as the number of responding modes increased. Intensification effects were found due to both the excitation location and the response location. The asymptotic modal analysis method was both efficient and accurate in solving the given problem. The method has advantages over the traditional methods that are used for solving dynamics problems with a large number of responding modes.
Study on Operational Modal Parameters Identification of Ship Structures%船舶结构运行模态参数辨识研究
Institute of Scientific and Technical Information of China (English)
姜大正; 洪明; 周力
2011-01-01
Operational modal analysis is a procedure which allows extracting modal parameters from a structure only based on response data under ambient excitation. It is based on the assumption that input to the structure is stationary white noise. In this paper, the application feasibility of operational modal analysis on ship structures is discussed. And band stop filter is proposed to filter the obvious harmonic energy to improve the identification precision of real modes. Then the auto-cross spectrum density method is discussed and verified by a simply supported beam experiment with white noise and harmonic excitations. This method is testified to be effective to identify the natural frequencies and operating deflection shapes. So it isfeasible and significant to identify modal parameters of ship structures under ambient excitations.%运行模态分析是仅基于结构运行状态下的响应来提取结构模态参数的一种方法,通常假设环境激励为白噪声进行分析.实际上,船舶航行过程所受激励十分复杂,不能简单地假设为白噪声激励,由主机和螺旋桨等产生的确定频率激励同样存在.因此,航行中船舶所受激励可以假设为白噪声和简谐激励同时存在.进一步讨论了运行模态技术在船舶结构振动分析中应用的可行性和前景.研究使用带阻数字滤波技术滤除激励中的简谐成分来提高结构真实模态的辨识精度.讨论了自互功率谱密度法,并研究使用此方法提取同时受白噪声和简谐激励作用的简支梁的模态参数.实验结果表明该方法能够较准确地识别出同时受白噪声和简谐激励的结构模态参数.这对于分析航行中船舶有害振动结构的模态特征,并实施有效的减振优化措施具有很广泛的实际意义.
Arunkumar, S.; Baskaralal, V. P. M.; Muthuraman, V.
2017-03-01
The rudimentary steps of the modal analysis and simulation are carried out. The modal analysis is carried out on the different Aluminum Alloys cantilever beam. The cantilever beam is designed in the graphical environment of the ANSYS. The cantilever beam was fine-tuned on one end with all degree of liberation on this end were taken, beam cannot move and rotate. Mode shapes and natural frequencies are premeditated in platforms ANSYS with arithmetical formulation of the direct solver including the block Lanczos method. Aluminum alloys are widely utilized in much application due to their estimable weight to vigor property. Many examination works have been distributed out to make developments the mechanical properties of aluminum alloys. The composition of alloying elements plays a consequential role in deciding the properties of an alloy. In this study a numerical analysis implement i.e., finite element analysis (FEA) is utilized. The work obtainable in this paper is aimed at the study of effect of modal analysis of different aluminum alloys. The modeling and analysis is carried out utilizing ANSYS FEA software. A modal analysis is carried out to understand the modes of frequency demeanor of the material considered. The modal analysis play a vital role in the design of components subjected to high vibration.
Comparative Modal Analysis of Gasketed and Nongasketed Bolted Flanged Pipe Joints: FEA Approach
Directory of Open Access Journals (Sweden)
Muhammad Abid
2012-01-01
Full Text Available It is widely known that resonance can quickly lead to failure in vibrating bolted flanged pipe joints. Condition monitoring is performed time to time in some industries for smooth operation of a system, whereas mostly trial-and-error tests are performed to control vibration. During all this process, the inherent design problems are not considered. A bolted flange joint in piping system is not a simple problem, being the combination of flange, gasket, bolts, and washers. The success of a bolted flanged pipe joint is defined by the “static mode of load” in the joint. However, it has been recognized that a “dynamic mode of load” governs in a gasketed bolted flanged pipe joint, which leads to its failure due to flange rotation, providing flange yielding, fatigue of bolts, and gasket crushing. This paper presents results of detailed 3D finite element and mathematical modal analysis under bolt up to determine natural frequencies and mode shapes of gasketed flanged joints with and without raised face in comparison to the nongasketed flange joint.
Rukes, Lothar; Paschereit, Oliver; Oberleithner, Kilian
2016-01-01
Modal linear stability analysis has proven very successful in the analysis of coherent structures of turbulent flows. Formally, it describes the evolution of a disturbance in the limit of infinite time. In this work we apply modal linear stability analysis to a turbulent swirling jet undergoing a control parameter transient. The flow undergoes a transition from a non-vortex breakdown state to a state with a strong recirculation bubble and the associated global mode. High-speed Particle Image Velocimetry (PIV) measurements are the basis for a local linear stability analysis of the temporarily evolving base flow. This analysis reveals that the onset of the global mode is strongly linked to the formation of the internal stagnation point. Several transition scenarios are discussed and the ability of a frequency selection criterion to predict the wavemaker location, frequency and growth rate of the global mode are evaluated. We find excellent agreement between the linear global mode frequency and the experimental ...
Modal analysis of two identical circular plates coupled with fluid
Energy Technology Data Exchange (ETDEWEB)
Jeong, Kyeong Hoon; Lee, Gyu Mahn; Park, Keun Bae; Chang, Moon Hee
2001-01-01
An analytical method for evaluating the free vibration of two identical circular plates coupled with fluid was developed by assuming the clamped boundary condition of the plates and an ideal fluid. The method was based upon the finite Fourier-Bessel series expansion and the Rayleigh-Riz method. The proposed method is verified by finite element analyses using commercial software, ANSYS (release 5.6) with good accuracy. Two transverse vibration modes, namely in-phase and out-of-phase, are observed alternately in the fluid-coupled system when the number of nodal circles increases for the fixed nodal diameter. It is found that the normalized natural frequency of the fluid-coupled system monotonically increases with an increase in the number of nodal diameters and circles by virtue of a decrease in relative hydrodynamic mass. The effect of distance between the circular plates and the effect of fluid bounding on the fluid-coupled natural frequencies are also investigated. The theory developed in this report can be applicable to the dynamic analysis of a bottom screen assembly in SMART integral reactor.
Modal analysis of cable-stayed UHPC bridge
Directory of Open Access Journals (Sweden)
Tej Petr
2017-01-01
Full Text Available This paper deals with the dynamic analysis of cable-stayed UHPC bridge over the Vltava river near town Melnik in Czech Republic, Europe. Bridge serves for pedestrians and cyclists. This work aims to familiarize the reader with dynamic calculations carried out and the results obtained, describing the dynamic properties of proposed bridge. The construction of bridge is designed as a cable-stayed structure with prestressed bridge deck consisting of prefabricated UHPC panels and reversed “V” shaped steel pylon with height of approximately 40 meters. The deck is anchored using 24 steel hangers in one row in a steel pylon - 17 ropes in the main span and 7 cables on the other side. Range of the main span is 99.18 meters and the secondary span is 31.9 m. Deck width is 4.5 meters with 3.0 meters passing space. The bridge is designed for the possibility of passage of vehicles weighting up to 3.5 tonnes. Deck panels are made of UHPC with reinforcement. At the edge of the bridge on the side of the shorter span the bridge deck is firmly connected with abutment and on the other deck it is stored using a pair of sliding bearings.
DEFF Research Database (Denmark)
Tan, Jin; Wang, Xiao Ru; Chen, Zhe
2013-01-01
In order to study the stability of a grid-connected direct-drive permanent magnet synchronous generator (PMSG) wind turbine systems, this paper presents the modal analysis of a PMSG wind turbine system. A PMSG model suitable for small signal stability analysis is presented. The modal properties o...
Energy Technology Data Exchange (ETDEWEB)
Aguirre Romano, Jorge E.; Preciado Delgado, Eduardo [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)
1991-12-31
In applying the modal analysis to rotor balancing, it is frequent to find technical matters that are hardly developed in text books or that can only be deducted through a profound and complex study. For this reason, an engineer dedicated to the practice that wishes to deepen in the subject of rotor balancing, can hardly understand these matters, unless they are developed with the specific orientation that relate them with the balancing practice. In this paper two of these subjects related to the definition and recollection of modal parameters are presented: a) the fundamental form of the polar diagrams of response, that can be perfectly circular in certain cases and b) the relationship that exists among the modal forms of a rotor and the distribution of weights that must be placed to balance them in a given way. [Espanol] Al aplicar el analisis modal al balanceo de rotores, es frecuente encontrar temas tecnicos que dificilmente se desarrollan en los libros de texto, o que solo pueden deducirse mediante un estudio profundo y complejo. Por esta razon, un ingeniero dedicado a la practica que desee profundizar en el tema de balanceo de rotores, dificilmente podra comprender estos temas, a no ser que estos sean desarrollados con la orientacion especifica que los relacionen con la practica del balanceo. En este trabajo se presentan dos de esos temas relacionados con la definicion y obtencion de los parametros modales: a) la forma fundamental de los diagramas polares de respuesta, que puede ser circular perfecta en ciertos casos, y b) la relacion que existe entre las formas modales de un rotor y la distribucion de pesos que se deben colocar para balancear un modo dado.
Non-modal linear stability analysis of miscible viscous fingering in a Hele-Shaw cell
Hota, Tapan Kumar; Mishra, Manoranjan
2015-01-01
For miscible viscous fingering (VF) in a Hele-Shaw cell or in two dimensional homogeneous porous media, the transient growth of disturbances is investigated by non-modal linear stability analysis (NMA). Due to the non-autonomous nature of the linearized perturbed equations, the linear stability theory prohibits using the normal mode analysis. The linearized perturbed equations for Darcy's law coupled with a convection-diffusion equation is discretized using finite difference method. The resultant matrix valued initial value problem is then solved by fourth order Runge-Kutta method, followed by a singular value decomposition (SVD) of the propagator matrix. We demonstrate the dominant perturbation that experiences the maximum amplification within the linear regime which lead to the transient growth. This feature was previously unattained in the existing linear stability methods for miscible VF. To explore the relevance of the optimal perturbation obtained from non-modal analysis of the physical system, we perfo...
MODAL ANALYSIS OF REAL TIMBER FRAME HOUSES WITH DIFFERENT INSULATION MATERIALS
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Marcin Szczepański
2016-09-01
Full Text Available The aim of this article is to present the results of a numerical modal analysis of two actual structures of timber frame buildings and the different behaviour due to the used insulation material. One model of the timber structure was filled with mineral wool, while the other with polyurethane foam. During the modal analysis, eigenvalues for both models have been determined. The results of the analysis clearly show the increase of stiffness and damping properties of skeletal constructions achieved by the use of polyurethane foam as the skeleton filling. The numerical model was based on prior experimental test on real scale single frame elements, therefore the result can be assumed to be adequate.
Eigenanatomy: sparse dimensionality reduction for multi-modal medical image analysis.
Kandel, Benjamin M; Wang, Danny J J; Gee, James C; Avants, Brian B
2015-02-01
Rigorous statistical analysis of multimodal imaging datasets is challenging. Mass-univariate methods for extracting correlations between image voxels and outcome measurements are not ideal for multimodal datasets, as they do not account for interactions between the different modalities. The extremely high dimensionality of medical images necessitates dimensionality reduction, such as principal component analysis (PCA) or independent component analysis (ICA). These dimensionality reduction techniques, however, consist of contributions from every region in the brain and are therefore difficult to interpret. Recent advances in sparse dimensionality reduction have enabled construction of a set of image regions that explain the variance of the images while still maintaining anatomical interpretability. The projections of the original data on the sparse eigenvectors, however, are highly collinear and therefore difficult to incorporate into multi-modal image analysis pipelines. We propose here a method for clustering sparse eigenvectors and selecting a subset of the eigenvectors to make interpretable predictions from a multi-modal dataset. Evaluation on a publicly available dataset shows that the proposed method outperforms PCA and ICA-based regressions while still maintaining anatomical meaning. To facilitate reproducibility, the complete dataset used and all source code is publicly available. Copyright © 2014 Elsevier Inc. All rights reserved.
A Modal Pushover Analysis on Multi-Span Concrete Bridges to Estimate Inelastic Seismic Responses
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Pennung Warnitchai
2007-01-01
Full Text Available The performance of Modal Pushover Analysis (MPA in predicting the inelastic seismic response of multi-span concrete bridges is investigated. The bridge is subjected to lateral forces distributed proportionally over the span of the bridge in accordance to the product of mass and displaced shape. The bridge is pushed up to the target displacement determined from the peak displacement of the nth mode inelastic Single Degree of Freedom System derived from Uncoupled Modal Response History Analysis (UMRHA. The peak response from each mode is combined using Square-Root of Sum-of-Square (SRSS rule. Although the use of SRSS rule is not appropriate in this bridge and the displaced pattern is shifted from the elastic shape due to yielding, MPA can predict well the total peak response of the bridge in inelastic range.
MODAL ANALYSIS OF HEAVY VEHICLE TRUCK TRANSMISSION GEARBOX HOUSING MADE FROM DIFFERENT MATERIALS
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ASHWANI KUMAR
2016-02-01
Full Text Available Heavy vehicle truck transmission gearbox housing is subjected to load fluctuations, harmonic excitation, gear meshing excitation, gear defects, varying speed and torque conditions. Transmission errors and internal excitations are the root cause of vibration and noise. The main objective of this research work is weight calculation and modal analysis of gearbox housing. For weight calculation four different materials have been selected, apart from weight calculation the material mechanical properties influence on natural frequency and mode shape of transmission gearbox housing was also simulated using modal analysis. Grey cast iron FG260, Grey cast iron HT200, structural steel and Al alloys are the four materials used for the weight calculation process. Zero displacement constraint based boundary condition was applied for simulation. FEA based numerical simulation method was used to find the natural frequency, mode shapes and weight calculation of housing. The FEA simulation results show that the natural frequency of all materials varies (1669-4655 Hz. In weight calculation the weight of Al alloys housing is minimum (21.102 kg.The housing weight of Grey cast iron HT200 and FG260 is same, 54.85 kg. The density of structural steel is high, which increases the weight of housing as 59.80 kg. The modal analysis results show the lateral vibration, axial bending vibration, torsional vibration, and axial bending with torsional vibration. The vibration signature patterns for first twenty modes were studied for four different materials. Solid Edge and Pro-E software have good feature suited for complex geometric modeling. FEA based software Ansys 14.5 is used for modal analysis. The result of this research work has been verified with experimental result available in literature.
Modal analysis of untransposed bilateral three-phase lines -- a perturbation approach
Energy Technology Data Exchange (ETDEWEB)
Faria, J.A.B. [Inst. Superior Tecnico, Lisboa (Portugal). Centro de Electrotecnia Teorica e Medidas Electricas; Mendes, J.H.B. [Univ. de Los Andes, Merida (Venezuela). Escuela de Ingenieria Electrica
1997-01-01
Model analysis of three-phase power lines exhibiting bilateral symmetry leads to modal transformation matrices that closely resemble Clarke`s transformation. The authors develop a perturbation theory approach to justify, interpret, and gain understanding of this well known fact. Further, the authors show how to find new frequency dependent correction terms that once added to Clarke`s transformation lead to improved accuracy.
Material model of pelvic bone based on modal analysis: a study on the composite bone.
Henyš, Petr; Čapek, Lukáš
2017-02-01
Digital models based on finite element (FE) analysis are widely used in orthopaedics to predict the stress or strain in the bone due to bone-implant interaction. The usability of the model depends strongly on the bone material description. The material model that is most commonly used is based on a constant Young's modulus or on the apparent density of bone obtained from computer tomography (CT) data. The Young's modulus of bone is described in many experimental works with large variations in the results. The concept of measuring and validating the material model of the pelvic bone based on modal analysis is introduced in this pilot study. The modal frequencies, damping, and shapes of the composite bone were measured precisely by an impact hammer at 239 points. An FE model was built using the data pertaining to the geometry and apparent density obtained from the CT of the composite bone. The isotropic homogeneous Young's modulus and Poisson's ratio of the cortical and trabecular bone were estimated from the optimisation procedure including Gaussian statistical properties. The performance of the updated model was investigated through the sensitivity analysis of the natural frequencies with respect to the material parameters. The maximal error between the numerical and experimental natural frequencies of the bone reached 1.74 % in the first modal shape. Finally, the optimised parameters were matched with the data sheets of the composite bone. The maximal difference between the calibrated material properties and that obtained from the data sheet was 34 %. The optimisation scheme of the FE model based on the modal analysis data provides extremely useful calibration of the FE models with the uncertainty bounds and without the influence of the boundary conditions.
Likins, P.; Ohkami, Y.; Wong, C.
1976-01-01
The paper examines the validity of the assumption that certain appendage-distributed (modal) coordinates can be truncated from a system model without unacceptable degradation of fidelity in hybrid coordinate dynamic analysis for attitude control of spacecraft with flexible appendages. Alternative truncation criteria are proposed and their interrelationships defined. Particular attention is given to truncation criteria based on eigenvalues, eigenvectors, and controllability and observability. No definitive resolution of the problem is advanced, and exhaustive study is required to obtain ultimate truncation criteria.
A new analysis methodology for estimating the eigenfrequencies of systems with high modal damping
Ozbek, Muammer; Rixen, Daniel J.
2016-01-01
Contemporary system identification algorithms are well proven to provide accurate eigenfrequency estimates in analyzing the systems with low modal damping. Since most engineering structures usually have low damping ratios the corresponding response characteristics can easily be obtained by conventional methods. Indeed, these modes can be extracted by using relatively short measurement durations (150-200 cycles of the lowest frequency included in the data block). However, some specific applications such as analyzing the in-operation vibration behavior of MW scale large wind turbines also require an accurate estimation of the modes with high damping. For a rotating wind turbine, some important turbine modes (e.g. flapwise rotor modes) have very high aeroelastic damping, which make them very difficult (if not impossible) to be detected. Extracting these high damping modes is a challenging task for almost all system identification techniques that are currently in use. In this work, a new method, which is based on Natural Excitation Technique (NExT), is proposed as an alternative approach for extracting the eigenfrequencies of high damping modes in an efficient way. NExT is a well established experimental dynamic analysis tool which was specifically developed to extract the dynamic characteristics of wind turbines in the early 90s. However, during the analyses it was observed that conventional NExT algorithm requires analyzing very long measurement durations (4500-5000 cycles) to be able to estimate the high damping modes accurately. A new method proposed in this work enables the eigenfrequencies of high damping modes to be estimated by using data series which are approximately 30 times shorter (around 150 cycles) than those required for a standard NExT algorithm.
Comparative analysis of carotid endarterectomy late outcomes related to intervention modality.
Pokrovskiĭ, A V; Kuntsevich, G I; Beloiartsev, D F; Timina, I E; Kolosov, R V
2005-01-01
The paper presents a comparative analysis of late outcomes after 105 carotid endarterectomies (CEA) performed in 89 patients from 1997 to 2003, including 95 patients (90.5%) operated for atherosclerotic stenosis of internal carotid artery (ICA) and 7 patients (6.6%)--for combined ICA stenosis and tortuosity. The severity distribution of cerebrovascular insufficiency (CVI) was the following: grade I--in 22.8%, grade II--in 12.4%, grade III--in 25.7% and grade IV--in 38.1% of patients. CEA methods included eversion endarterectomy in 50.4% cases and open (classic) surgical CEA with PTFE patch angioplasty in 49.6% cases. Mean follow-up period was 31.8 months for the eversion CEA group and 37 months--for the open CEA group (from 3 to 72 months). In 76.4% patients the duration of follow-up period exceeded 1 year. During the follow-up period all patients underwent clinical examination and color duplex scanning of reconstructed CA segment with assessment of diameter, vascular wall thickness and blood flow. TIA was registered in 1 patient from eversion CEA group and in 1 patient from open CEA group. Thus, in the long-term postoperative period 98% of patients were free from neurological complications. Hemodynamically significant restenoses developed in 8 cases (7.6%), including 4 patients from the eversion CEA group and 4 patients from the open CEA group. Myointimal hyperplasia (> 3 mm) accompanied by hemodynamical alterations occurred in 1 patient from the eversion CEA group and in 2 from the open CEA group. In the rest of cases restenoses were related to atherosclerotic plaque formation. In conclusion, the long-term outcomes indicate that CEA is effective in the prevention of cerebrovascular events regardless of carotid angioplasty strategy. The rate of late postoperative restenoses was similar for eversion and open CEAs. Both modalities can be promising for the surgical correction of CA stenoses.
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Si-Da Zhou
2015-01-01
Full Text Available Real-time estimation of modal parameters of time-varying structures can conduct an obvious contribution to some specific applications in structural dynamic area, such as health monitoring, damage detection, and vibration control; the recursive algorithm of modal parameter estimation supplies one of fundamentals for acquiring modal parameters in real-time. This paper presents a vector multistage recursive method of modal parameter estimation for time-varying structures in hybrid time and frequency domain, including stages of recursive estimation of time-dependent power spectra, frozen-time modal parameter estimation, recursive modal validation, and continuous-time estimation of modal parameters. An experimental example validates the proposed method finally.
Transient analysis mode participation for modal survey target mode selection using MSC/NASTRAN DMAP
Barnett, Alan R.; Ibrahim, Omar M.; Sullivan, Timothy L.; Goodnight, Thomas W.
1994-01-01
Many methods have been developed to aid analysts in identifying component modes which contribute significantly to component responses. These modes, typically targeted for dynamic model correlation via a modal survey, are known as target modes. Most methods used to identify target modes are based on component global dynamic behavior. It is sometimes unclear if these methods identify all modes contributing to responses important to the analyst. These responses are usually those in areas of hardware design concerns. One method used to check the completeness of target mode sets and identify modes contributing significantly to important component responses is mode participation. With this method, the participation of component modes in dynamic responses is quantified. Those modes which have high participation are likely modal survey target modes. Mode participation is most beneficial when it is used with responses from analyses simulating actual flight events. For spacecraft, these responses are generated via a structural dynamic coupled loads analysis. Using MSC/NASTRAN DMAP, a method has been developed for calculating mode participation based on transient coupled loads analysis results. The algorithm has been implemented to be compatible with an existing coupled loads methodology and has been used successfully to develop a set of modal survey target modes.
Finite element modeling and modal analysis of the human spine vibration configuration.
Guo, Li-Xin; Zhang, Yi-Min; Zhang, Ming
2011-10-01
This study was designed to investigate the modal characteristics of the human spine. A 3-D finite element model of the spine T12-Pelvis segment was used to extract resonant frequencies and modal modes of the human spine. By finite element modal analysis and harmonic response analysis, several lower vibration modes in the flexion-extension, lateral bending, and vertical directions were obtained and its vibration configurations were shown in this paper. The results indicate that the lowest resonant frequency of the model is in the flexion-extension direction. The second-order resonant frequency is in the lateral bending direction and the third-order resonant frequency of the T12-Pelvis model is in the vertical direction. The results also show that lumbar spinal vertebrae conduct the rotation action during whole body vibration (WBV). The vibration configurations of the lumbar spine can explore the motion mechanism of different lumbar components under WBV and make us to understand the vibration-induced spine diseases. The findings in this study will be helpful to understand WBV-related injury of the spine in clinics and the ergonomics design and development of mechanical production to protect human spine safety.
Barton, E.; Middleton, C.; Koo, K.; Crocker, L.; Brownjohn, J.
2011-07-01
This paper presents the results from collaboration between the National Physical Laboratory (NPL) and the University of Sheffield on an ongoing research project at NPL. A 50 year old reinforced concrete footbridge has been converted to a full scale structural health monitoring (SHM) demonstrator. The structure is monitored using a variety of techniques; however, interrelating results and converting data to knowledge are not possible without a reliable numerical model. During the first stage of the project, the work concentrated on static loading and an FE model of the undamaged bridge was created, and updated, under specified static loading and temperature conditions. This model was found to accurately represent the response under static loading and it was used to identify locations for sensor installation. The next stage involves the evaluation of repair/strengthening patches under both static and dynamic loading. Therefore, before deliberately introducing significant damage, the first set of dynamic tests was conducted and modal properties were estimated. The measured modal properties did not match the modal analysis from the statically updated FE model; it was clear that the existing model required updating. This paper introduces the results of the dynamic testing and model updating. It is shown that the structure exhibits large non-linear, amplitude dependant characteristics. This creates a difficult updating process, but we attempt to produce the best linear representation of the structure. A sensitivity analysis is performed to determine the most sensitive locations for planned damage/repair scenarios and is used to decide whether additional sensors will be necessary.
Energy Technology Data Exchange (ETDEWEB)
Barton, E; Crocker, L [Structural health monitoring, National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW (United Kingdom); Middleton, C; Koo, K; Brownjohn, J, E-mail: elena.barton@npl.co.uk, E-mail: C.J.Middleton@sheffield.ac.uk, E-mail: k.koo@sheffield.ac.uk, E-mail: louise.crocker@npl.co.uk, E-mail: j.brownjohn@sheffield.ac.uk [University of Sheffield, Department of Civil and Structural Engineering, Vibration Engineering Research Section, Sir Frederick Mappin Building Mappin Street, Sheffield, S1 3JD (United Kingdom)
2011-07-19
This paper presents the results from collaboration between the National Physical Laboratory (NPL) and the University of Sheffield on an ongoing research project at NPL. A 50 year old reinforced concrete footbridge has been converted to a full scale structural health monitoring (SHM) demonstrator. The structure is monitored using a variety of techniques; however, interrelating results and converting data to knowledge are not possible without a reliable numerical model. During the first stage of the project, the work concentrated on static loading and an FE model of the undamaged bridge was created, and updated, under specified static loading and temperature conditions. This model was found to accurately represent the response under static loading and it was used to identify locations for sensor installation. The next stage involves the evaluation of repair/strengthening patches under both static and dynamic loading. Therefore, before deliberately introducing significant damage, the first set of dynamic tests was conducted and modal properties were estimated. The measured modal properties did not match the modal analysis from the statically updated FE model; it was clear that the existing model required updating. This paper introduces the results of the dynamic testing and model updating. It is shown that the structure exhibits large non-linear, amplitude dependant characteristics. This creates a difficult updating process, but we attempt to produce the best linear representation of the structure. A sensitivity analysis is performed to determine the most sensitive locations for planned damage/repair scenarios and is used to decide whether additional sensors will be necessary.
Modal analysis of sailplane and transport aircraft wings using the dynamic stiffness method
Banerjee, J. R.
2016-05-01
The purpose of this paper is to provide theory, results, discussion and conclusions arising from an in-depth investigation on the modal behaviour of high aspect ratio aircraft wings. The illustrative examples chosen are representative of sailplane and transport airliner wings. To achieve this objective, the dynamic stiffness method of modal analysis is used. The wing is represented by a series of dynamic stiffness elements of bending-torsion coupled beams which are assembled to form the overall dynamic stiffness matrix of the complete wing. With cantilever boundary condition applied at the root, the eigenvalue problem is formulated and finally solved with the help of the Wittrick-Williams algorithm to yield the eigenvalues and eigenmodes which are essentially the natural frequencies and mode shapes of the wing. Results for wings of two sailplanes and four transport aircraft are discussed and finally some conclusions are drawn
Modal and harmonic response analysis of cutter head of juice extractor
Li, Jinkuan; Liu, Zaixin; Zhou, Dingli; Li, Zhao
2017-01-01
A cutter head is one of the most important parts in juice extractor, because whether the juice extractor is reliable or secure enough is directly to the cutter head natural frequency as well as its mode shape size. Cutter head is took as an example in this paper. By establishing the vibration dynamics equations and using finite element method, the 6 modal of the cutter head is analyzed. The range of the rotate speed to keep safety is obtained when it is working. The result shows that the highest rotate speed of the cutter head is far lower than its first order critical speed which avoids the sympathetic vibration efficiently, and the cutter head is designed relatively rational. The harmonic response of the cutter head is analyzed based on the result of modal analysis. The resonant frequency and amplitude of cutter head are obtained. They can provide a theoretical basis for the further design optimization of the cutter head.
Effect of perfectly matched layer reflection coefficient on modal analysis of leaky waveguide modes.
Lai, Chih-Hsien; Chang, Hung-chun
2011-01-17
The reflection coefficient is one important parameter of the perfectly matched layer (PML). Here we investigate its effect on the modal analysis of leaky waveguide modes by examining three different leaky waveguide structures, i.e., the holey fiber, the air-core terahertz pipe waveguide, and the gain-guided and index-antiguided slab waveguide. Numerical results reveal that the typical values 10(-8) ~10(-12) are inadequate for obtaining the imaginary part of the complex propagation constant, and the suggested reflection coefficient would be much smaller, for example, 10(-50) or 10(-100). With such a small coefficient, both the computational window size and the PML thickness can be significantly reduced without loss of stability. Moreover, in some cases, the modal field profiles can only be accurately obtained with such a small coefficient.
Enunciative analysis of modals in libras-portuguese simultaneous interpretation's corpus
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Anderson Almeida-Silva
2015-12-01
Full Text Available This paper focuses on the work of the sign Language interpreter in the condition of a second speaker within the speech production. These professionals, when interpreting, they look for re-create [actualize] the emanated concepts from the source language into the target language, creating, then, a second enunciative instance. The theoretical basis is situated in the perspective of the theory of enunciation (BENVENISTE, 1989; FLORES, 2008, 2009a, 2009b, 2010 and in the study of the modals in spoken languages and LIBRAS. We aim to find what are the marks left in the discourse by the second speaker of the text, in this case, the interpreter, regarding specifically to the use of modals, and additionally, to analyze their choices for using one or other type of modal (in the target text, which might have been made explicit or implicit in the first enunciative context (source text. In order to reach these goals, sampling was composed by a transcription of a video-recorded speech of a deaf person with the length of 40’ (forty minutes that was being simultaneously interpreted into spoken Portuguese. Six excerpts from the total speech, in which modal’s occurrences were attested within the source or target language, were submitted to the analysis. The main findings are: 1. the tendency of the deontic modality being almost always interpreted in the same way of the source language; 2. the interpreting choices are always guided by enunciative clues that are left in the speech of the first speaker, to which the interpreters must to demonstrate expertise in recognizing these language-specific aspects; 3. in the absence of explicit modals in the speech, the interpreters appears to be sensible to the modal’s notions spread by the whole text’s surface; 4. the temporal omission of epistemic modals with a high degree of certainty is understood as an interpretative strategy and not as an infidelity with the original information; 5. the term “tempo de
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Yu. V. Vasilevich
2014-01-01
Full Text Available The aim of the paper is to reveal and analyze resonance modes of a large-scale milling-drilling-boring machine. The machine has a movable column with vertical slot occupied by a symmetrical carriage with horizontal ram. Static rigidity of the machine is relatively low due to its large dimensions. So it is necessary to assess possible vibration activity. Virtual and operational trials of the machine have been carried out simultaneously. Modeling has been executed with the help of a finite element method (FEM. The FEM-model takes into account not only rigidity of machine structures but also flexibility of bearings, feed drive systems and guides. Modal FEM-analysis has revealed eight resonance modes that embrace the whole machine tool. They form a frequency interval from 12 to 75 Hz which is undesirable for machining. Three closely located resonances (31-37 Hz are considered as the most dangerous ones. They represent various combinations of three simple motions: vertical oscillations of a carriage, horizontal vibrations of a ram and column torsion. Reliability of FEM- estimations has been proved by in-situ vibration measurements.An effect for stabilization of resonance modes has been detected while making variations in design parameters of the machine tool. For example, a virtual replacement of cast iron for steel in machine structures practically does not have any effect on resonance frequencies. Rigidity increase in some parts (e.g. a ram has also a small effect on a resonance pattern. On the other hand, resonance stability makes it possible to avoid them while selecting a spindle rotation frequency.It is recommended to set double feed drives for all axes. A pair of vertical screws prevents a “pecking” resonance of the carriage at frequency of 54 Hz. It is necessary to foresee an operation of a main drive of such heavy machine tool in the above resonance interval with the spindle frequency of more than 75 Hz. For this purpose it is necessary
The Study of Some Cracks on the Panels of a Minibus Body Using Modal Analysis
Iozsa, D.; Micu, D. A.
2016-11-01
The body vibrations caused by the disturbing forces which acts on this one cause many problems connected, generaly, with the passengers confort (mechanical vibrations, noises) and also connected with the body reliability. The paper presents the study of some craks appeared on the roof panels of the body of a minibus and the study of some attempts to improve the behaviour. The study was made using the modal analysis in two steps. First was studied the behaviour of the hole structure and than was studied only the panel where cracks appear. The analysis of the first four eigenmodes confirmed cause of the cracks. Finally, it was offered an improved solution.
Generalized Modal Analysis of Electromagnetic - and Quantum-Waveguide Structures and Discontinuities
Weisshaar, Andreas
Generalized modal analysis techniques for the characterization and modeling of dissipationless planar waveguide structures and discontinuities encountered in microwave and optical integrated circuits, as well as of quantum waveguide structures and devices, are presented. The frequency-dependent transmission properties of the curved microstrip bend are derived by utilizing a second-order perturbation analysis of the equivalent modified curved waveguide model and a mode-matching method which includes the higher order modes. An extension of the mode-matching method for characterization of microstrip right-angle bends and T junctions having a rectangular notch is formulated. The modal solutions for an arbitrary graded-index dielectric slab waveguide are derived by applying the generalized telegraphist's equations to the equivalent inhomogeneous parallel-plate waveguide model with electric or magnetic walls. These modal solutions are employed in a mode-matching procedure to calculate the transmission properties of a step discontinuity in typical diffused optical dielectric slab waveguides. Power loss calculations for an abrupt offset in a diffused optical waveguide show a smooth increase in radiation loss whereas a sharp transition from almost zero to nearly total radiation loss is found for an abrupt change in diffusion depth. In the analysis of quantum waveguide structures, the modal expansions of the wave function together with a mode-matching technique are utilized. The computed generalized scattering matrices (GSMs) of junctions and uniform waveguide sections are combined via an extended GSM technique to obtain the scattering parameters of composite quantum waveguide structures. Results for cascaded right-angle bends and periodic multi-waveguide structures in a split-gate configuration are presented assuming hard wall confinement. For the multisection structures, strong resonant behavior similar to that in resonant tunneling diodes is found. Calculated current
Poggi, Valerio; Ermert, Laura; Burjanek, Jan; Michel, Clotaire; Fäh, Donat
2015-01-01
Frequency domain decomposition (FDD) is a well-established spectral technique used in civil engineering to analyse and monitor the modal response of buildings and structures. The method is based on singular value decomposition of the cross-power spectral density matrix from simultaneous array recordings of ambient vibrations. This method is advantageous to retrieve not only the resonance frequencies of the investigated structure, but also the corresponding modal shapes without the need for an absolute reference. This is an important piece of information, which can be used to validate the consistency of numerical models and analytical solutions. We apply this approach using advanced signal processing to evaluate the resonance characteristics of 2-D Alpine sedimentary valleys. In this study, we present the results obtained at Martigny, in the Rhône valley (Switzerland). For the analysis, we use 2 hr of ambient vibration recordings from a linear seismic array deployed perpendicularly to the valley axis. Only the horizontal-axial direction (SH) of the ground motion is considered. Using the FDD method, six separate resonant frequencies are retrieved together with their corresponding modal shapes. We compare the mode shapes with results from classical standard spectral ratios and numerical simulations of ambient vibration recordings.
Zhou, Hao; Hirose, Mitsuhito; Greenwood, William; Xiao, Yong; Lynch, Jerome; Zekkos, Dimitrios; Kamat, Vineet
2016-04-01
Unmanned aerial vehicles (UAVs) can serve as a powerful mobile sensing platform for assessing the health of civil infrastructure systems. To date, the majority of their uses have been dedicated to vision and laser-based spatial imaging using on-board cameras and LiDAR units, respectively. Comparatively less work has focused on integration of other sensing modalities relevant to structural monitoring applications. The overarching goal of this study is to explore the ability for UAVs to deploy a network of wireless sensors on structures for controlled vibration testing. The study develops a UAV platform with an integrated robotic gripper that can be used to install wireless sensors in structures, drop a heavy weight for the introduction of impact loads, and to uninstall wireless sensors for reinstallation elsewhere. A pose estimation algorithm is embedded in the UAV to estimate the location of the UAV during sensor placement and impact load introduction. The Martlet wireless sensor network architecture is integrated with the UAV to provide the UAV a mobile sensing capability. The UAV is programmed to command field deployed Martlets, aggregate and temporarily store data from the wireless sensor network, and to communicate data to a fixed base station on site. This study demonstrates the integrated UAV system using a simply supported beam in the lab with Martlet wireless sensors placed by the UAV and impact load testing performed. The study verifies the feasibility of the integrated UAV-wireless monitoring system architecture with accurate modal characteristics of the beam estimated by modal analysis.
Ozer, Ekin; Feng, Dongming; Feng, Maria Q.
2017-10-01
State-of-the-art multisensory technologies and heterogeneous sensor networks propose a wide range of response measurement opportunities for structural health monitoring (SHM). Measuring and fusing different physical quantities in terms of structural vibrations can provide alternative acquisition methods and improve the quality of the modal testing results. In this study, a recently introduced SHM concept, SHM with smartphones, is focused to utilize multisensory smartphone features for a hybridized structural vibration response measurement framework. Based on vibration testing of a small-scale multistory laboratory model, displacement and acceleration responses are monitored using two different smartphone sensors, an embedded camera and accelerometer, respectively. Double-integration or differentiation among different measurement types is performed to combine multisensory measurements on a comparative basis. In addition, distributed sensor signals from collocated devices are processed for modal identification, and performance of smartphone-based sensing platforms are tested under different configuration scenarios and heterogeneity levels. The results of these tests show a novel and successful implementation of a hybrid motion sensing platform through multiple sensor type and device integration. Despite the heterogeneity of motion data obtained from different smartphone devices and technologies, it is shown that multisensory response measurements can be blended for experimental modal analysis. Getting benefit from the accessibility of smartphone technology, similar smartphone-based dynamic testing methodologies can provide innovative SHM solutions with mobile, programmable, and cost-free interfaces.
What Modals Are: Modal Verbs, Modal Words, and Auxiliary Modals
Directory of Open Access Journals (Sweden)
Fazira A. Kakzhanova
2013-01-01
Full Text Available The modals are a complicated grammatical phenomenon. As of today, the status of modals is still not precisely defined in the linguistics literature, and they are described under different names: modal verbs, modal words, auxiliary modals, or defective verbs. Modals express the result of the conversion of thought processes (deep structure about the realization of actions into surface structure. As articles determine the status of nouns as indefinite or definite things, modals determine the relation of a person to actions or the quality of an action as realizable or unrealizable. Modals cannot truly be ‘modal verbs’, because they lack the morphological characteristics of verbs (aspect, voice, mood, and tense, and the term ‘defective verb’ is flawed for the same reason. Furthermore, they cannot be ‘auxiliary modals’, because they don’t neutralize their main meanings when they become auxiliary. Thus, I propose to refer to these elements only as modals or modal words.
A pragmatic analysis framework for the description of modality usage in academic English contexts
Piqué, Jordi; Posteguillo, Santiago; Andreu-Besó, J. Vicent
2001-01-01
In our pragmatic approach to research articles (RAs), we take a look at one of the main characteristics of academic writing: the use of modalized statements. Modalization, in the form of modal verbs, has been extensively studied by ESP researchers and practitioners. Most of their studies, however, have slightly touched upon the distinction between epistemic modality, which questions the certainty or probability of a statement, and deontic modality, which lays obligations or gives permission t...
An Investigation into the Potential Application of Wavelets to Modal Testing and Analysis
Gwinn, A. Fort, Jr.
2002-01-01
The analysis of transient data of the type found in vibrating mechanical systems has been greatly improved through the use of modern techniques such as Fourier analysis. This is especially true when considered in conjunction with the development of the so-called Fast Fourier Transform algorithm by Cooley and the tremendous strides in computational power of the last several decades. The usefulness of the discrete Fourier Transform is its ability to transform sampled data from the "time-domain" to the "frequency domain," thereby allowing the analyst to decompose a signal into its frequency content. More recent developments have led to the wavelet transform. The strength of wavelet analysis is its ability to maintain both time and frequency information, thus making it an attractive candidate for the analysis of non-stationary signals. This report is an overview of wavelet theory and the potential use of the wavelet transform as an alternative to Fourier analysis in modal identification.
A consistent concept for high- and low-frequency dynamics based on stochastic modal analysis
Pradlwarter, H. J.; Schuëller, G. I.
2005-12-01
Accurate expressions for the kinetic energy in substructure excited by white noise and broad-band spectra, based on classical random vibration theory and modal analysis, are presented. The approach is accurate, general and valid for all frequency ranges, since no simplifying are needed to arrive at the presented power flow relations. Strong coupling, local energies and energies in substructures can be analyzed for uncorrelated as well as for correlated excitation. The results are compared with statistical energy analysis (SEA) which is applicable for the high-frequency range. It is shown, that the SEA representations is only suitable for very weak coupling between substructures, while an inverse representation does not show the observed limitations. Energies in substructures are not sensitive to variations of the eigenfrequencies or mode shapes due to the summation over frequency ranges and over the domain of the substructure. Hence, modal analysis will lead to accurate estimates even in case FE analysis fails to provide accurate eigenfrequencies and mode shapes, since the coupling between substructures is still represented with acceptable accuracy. Uncertain structural properties will affect the coupling between substructures and therefore the power flow. It is suggested to assess this influence by using Monte Carlo simulation.
Institute of Scientific and Technical Information of China (English)
赵威; 张永杰; 王喆; 韦冰峰
2013-01-01
To solve some problems of the operational modal identification of large missile launch vehicle, a model reflecting the main dynamic characteristics of large missile launch vehicle was made. Modal experiments were conducted and dynamic characteristics of the model were identified using the Least Square Complex Exponent (LSCE) method. Modal identification results were compared and analyzed to evaluate the LSCE method. It was applied to the operational modal identification of large missile launch vehicle. It is of significance to provide references for the dynamic characteristics analysis of large missile launch vehicle.%针对大型导弹车在运输状态下的动态特性识别问题，设计制作了能够反映大型导弹车主要动力学特征的简化模型，使用最小二乘复指数法（LSCE）对简化模型进行了动态特性识别，对识别结果进行了分析和评估，并将最小二乘复指数法应用到真实大型导弹车运输状态的模态识别中。可为大型导弹车运输状态下的动力学特性分析提供参考。
Koning, G G; Adang, E M M; Stalmeier, P F M; Keus, F; Vriens, P W H E; van Laarhoven, C J H M
2013-12-01
The transinguinal preperitoneal (TIPP) technique using a soft mesh with a memory ring was developed recently for inguinal hernia repair. To compare TIPP with the Lichtenstein method, a randomised trial was conducted (ISRCTN93798494). The aim of this study was to perform an economic evaluation of the TIPP modality compared to the Lichtenstein modality from both a hospital and societal perspective alongside the clinical trial. The TULIP study was a double-blind randomised clinical trial comparing two techniques for inguinal hernia repair (TIPP and Lichtenstein). Correct generation of the allocation sequence, allocation concealment, blinding, and follow-up were used/applied according to the recommendations of the Cochrane Handbook. Next to the cost drivers, the short-form-36 health survey (SF-36) data from the TULIP trial was used to determine utility. The SF-36 data from the TULIP trial were revised using the SF-6D algorithm according to Brazier. Two scenarios-a hospital and a societal perspective-were presented. If the analyses showed no difference in effects (on the SF-6D) the cost effectiveness decision rule to cost minimisation was altered. No significant difference in SF-6D utility between both modalities was found (mean difference: 0.888, 95% CI -1.02 to 1.23); consequently, the economic decision rule became cost minimisation. For the hospital perspective no significant differences in costs were found (mean difference: euro -13, 95% CI euro -130 to euro 104). However, when including productivity gains in the analysis, significant differences (P = 0.037) in costs favouring the TIPP modality (mean saving: euro 1,472, 95% CI euro 463- euro 2,714) were found. The results show that TIPP is a cost-saving inguinal hernia repair technique compared to the Lichtenstein modality against equal effectiveness expressed as quality adjusted life week at 1 year given a societal perspective. In the trial, TIPP patients showed on average a quicker recovery of 6.5 days compared to
Advantages and Drawbacks of Applying Periodic Time-Variant Modal Analysis to Spur Gear Dynamics
DEFF Research Database (Denmark)
Pedersen, Rune; Santos, Ilmar; Hede, Ivan Arthur
2010-01-01
A simplified torsional model with a reduced number of degrees-of-freedom is used in order to investigate the potential of the technique. A time-dependent gear mesh stiffness function is introduced and expanded in a Fourier series. The necessary number of Fourier terms is determined in order...... to ensure sufficient accuracy of the results. The method of time-variant modal analysis is applied, and the changes in the fundamental and the parametric resonance frequencies as a function of the rotational speed of the gears, are found. By obtaining the stationary and parametric parts of the time...
SELECTIVE MODAL ANALYSIS OF POWER FLOW OSCILLATION IN LARGE SCALE LONGITUDINAL POWER SYSTEMS
Directory of Open Access Journals (Sweden)
Wirindi -
2009-06-01
Full Text Available Novel selective modal analysis for the determination of low frequency power flow oscillation behaviour based on eigenvalues with corresponding damping ratio, cumulative damping index, and participation factors is proposed. The power system being investigated consists of three large longitudinally interconnected areas with some weak tie lines. Different modes, such as exciter modes, inter area modes, and local modes of the dominant poles are fully studied to find out the significant level of system damping and other factors producing power flow instability. The nature of the energy exchange between area is determined and strategic power flow stability improvement is developed and tested.
A modal analysis method to describe weak nonlinear effects in metamaterials
Zeng, Y; O'Hara, J; Trugman, S A
2012-01-01
We apply a rigorous eigenmode analysis to study the electromagnetic properties of linear and weakly nonlinear metamaterials. The nonlinear response can be totally described by the linear eigenmodes when weak nonlinearities are attributed to metamaterials. We use this theory to interpret intrinsic second-harmonic spectroscopy on metallic metamaterials. Our study indicates that metamaterial eigenmodes play a critical role in optimizing a nonlinear metamaterial response to the extent that a poorly optimized modal pattern overwhelms the widely recognized benefits of plasmonic resonant field enhancements.
Dynamic analysis and modal test of long-span cable-stayed bridge based on ambient excitation
Institute of Scientific and Technical Information of China (English)
CHEN Chang-song; YAN Dong-huang
2007-01-01
To study the stifilless distilbution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the girder with double ribs.Based on the simplified model four stiffness formulae were deduced according to Hamilton principle.These formulae reflect well the contribution of the flexural, shearing, free torsion and restricted torsion deformation, respectively.An identification method about modal parameters was put forward by combining method of peak value and power spectral density according to modal test under ambient excitation.The dynamic finite element method analysis and modal test were carried out in a long-span concrete cable-stayed bridge.The results show that the errors of frequencies between theoretical analysis and test results are less than 10%mostly,and the most important modal parameters for cable-stayed bridge are determined to be the longitudinal floating mode, the first vertical flexural mode and the first torsional mode, which demonstrate that the method of stifiness distribution for three beams model is accurate and method to identify modal parameters is effective under ambient excitation modal test.
Modal and Dynamic Analysis of a Vehicle with Kinetic Dynamic Suspension System
Directory of Open Access Journals (Sweden)
Bangji Zhang
2016-01-01
Full Text Available A novel kinetic dynamic suspension (KDS system is presented for the cooperative control of the roll and warp motion modes of off-road vehicles. The proposed KDS system consists of two hydraulic cylinders acting on the antiroll bars. Hence, the antiroll bars are not completely replaced by the hydraulic system, but both systems are installed. In this paper, the vibration analysis in terms of natural frequencies of different motion modes in frequency domain for an off-road vehicle equipped with different configurable suspension systems is studied by using the modal analysis method. The dynamic responses of the vehicle with different configurable suspension systems are investigated under different road excitations and maneuvers. The results of the modal and dynamic analysis prove that the KDS system can reduce the roll and articulation motions of the off-road vehicle without adding extra bounce stiffness and deteriorating the ride comfort. Furthermore, the roll stiffness is increased and the warp stiffness is decreased by the KDS system, which could significantly enhance handing performance and off-road capability.
On the Force Drop Off Phenomenon in Shaker Testing in Experimental Modal Analysis
Directory of Open Access Journals (Sweden)
Paulo Sergio Varoto
2002-01-01
Full Text Available The Electrodynamic Vibration Exciter (shakers has been one of the most employed excitation sources in modal tests. The shaker is an electromechanical device that provides a mechanical motion due to the input signal sent to its coil. Despite being widely used, it is well known that the shaker interacts with the structure under test. In particular, when the structure passes through a given resonance, the force delivered by the shaker abruptly decreases, causing the so called drop off phenomenon. This paper aims to study this force drop off phenomenon in the single shaker modal testing. Analytical models are developed to help in understanding the physical principles involved in the interaction between the shaker and the structure under test. Experimental analyses are performed using different shakers as well as excitation signals, in order to evaluate the effects of the input signal, as well as the power amplifier operational modes, on the structure dynamics. Preliminary tests revealed that significant distortions might occur during vibration tests using shakers and these distortions significantly affect the determination of the structure response.
MPCV Exercise Operational Volume Analysis
Godfrey, A.; Humphreys, B.; Funk, J.; Perusek, G.; Lewandowski, B. E.
2017-01-01
In order to minimize the loss of bone and muscle mass during spaceflight, the Multi-purpose Crew Vehicle (MPCV) will include an exercise device and enough free space within the cabin for astronauts to use the device effectively. The NASA Digital Astronaut Project (DAP) has been tasked with using computational modeling to aid in determining whether or not the available operational volume is sufficient for in-flight exercise.Motion capture data was acquired using a 12-camera Smart DX system (BTS Bioengineering, Brooklyn, NY), while exercisers performed 9 resistive exercises without volume restrictions in a 1g environment. Data were collected from two male subjects, one being in the 99th percentile of height and the other in the 50th percentile of height, using between 25 and 60 motion capture markers. Motion capture data was also recorded as a third subject, also near the 50th percentile in height, performed aerobic rowing during a parabolic flight. A motion capture system and algorithms developed previously and presented at last years HRP-IWS were utilized to collect and process the data from the parabolic flight [1]. These motions were applied to a scaled version of a biomechanical model within the biomechanical modeling software OpenSim [2], and the volume sweeps of the motions were visually assessed against an imported CAD model of the operational volume. Further numerical analysis was performed using Matlab (Mathworks, Natick, MA) and the OpenSim API. This analysis determined the location of every marker in space over the duration of the exercise motion, and the distance of each marker to the nearest surface of the volume. Containment of the exercise motions within the operational volume was determined on a per-exercise and per-subject basis. The orientation of the exerciser and the angle of the footplate were two important factors upon which containment was dependent. Regions where the exercise motion exceeds the bounds of the operational volume have been
Institute of Scientific and Technical Information of China (English)
WANG Zheng; ZHU Dianxiang
2007-01-01
This paper took the upper-lower wide belt sander B229 with four-feet wide belts,manufactured in China,as the study target.By means of framework dynamic design,we study its vibration characteristics by commencing from the place having horizontal defects and used experimental modal analysis (EMA) and power spectrum density (PSD) to observe the sanding parts and the whole machine,respectively.In the modal test,we mainly adopted the cross spots testing method to get the frequency response function of the fixed spots to every excitation vibration spot,then applied the SISO frequency response function and the frequency response function fitting method to identify and complete parameter recognition,respectively.The typical frequency response function chart of the whole machine and its sanding parts,as well as its second-order mode charts of contacting roller,were obtained.Through PSD analysis,we can get the amplitude-frequency spectrum and drive frequency.
Sepahvand, K.
2017-07-01
Damping parameters of fiber-reinforced composite possess significant uncertainty due to the structural complexity of such materials. Considering the parameters as random variables, this paper uses the generalized polynomial chaos (gPC) expansion to capture the uncertainty in the damping and frequency response function of composite plate structures. A spectral stochastic finite element formulation for damped vibration analysis of laminate plates is employed. Experimental modal data for samples of plates is used to identify and realize the range and probability distributions of uncertain damping parameters. The constructed gPC expansions for the uncertain parameters are used as inputs to a deterministic finite element model to realize random frequency responses on a few numbers of collocation points generated in random space. The realizations then are employed to estimate the unknown deterministic functions of the gPC expansion approximating the responses. Employing modal superposition method to solve harmonic analysis problem yields an efficient sparse gPC expansion representing the responses. The results show while the responses are influenced by the damping uncertainties at the mid and high frequency ranges, the impact in low frequency modes can be safely ignored. Utilizing a few random collocation points, the method indicates also a very good agreement compared to the sampling-based Monte Carlo simulations with large number of realizations. As the deterministic finite element model serves as black-box solver, the procedure can be efficiently adopted to complex structural systems with uncertain parameters in terms of computational time.
Interface conductance modal analysis of lattice matched InGaAs/InP
Gordiz, Kiarash; Henry, Asegun
2016-05-01
We studied the heat conduction at InGaAs/InP interfaces and found that the total value of interface conductance was quite high ˜830 MW m-2 K-1. The modal contributions to the thermal interface conductance (TIC) were then investigated to determine the mode responsible. Using the recently developed interface conductance modal analysis method, we showed that more than 70% of the TIC arises from extended modes in the system. The lattice dynamics calculations across the interface revealed that, unlike any other interfaces previously studied, the different classes of vibration around the interface of InGaAs/InP naturally segregate into distinct regions with respect to frequency. In addition, interestingly, the entire region of frequency overlap between the sides of the interface is occupied by extended modes, whereby the two materials vibrate together with a single frequency. We also mapped the correlations between modes, which showed that the contribution by extended modes to the TIC primarily arises from coupling to the modes that have the same frequencies of vibration (i.e., autocorrelations). Moreover, interfacial modes despite their low population still contribute more than 6% to interfacial thermal transport. The analysis sheds light on the nature of heat conduction by different classes of vibration that exist in interfacial systems, which has technological relevance to applications such as thermophotovoltaics and optoelectronics.
Lv, Wei; Winters, R Michael; DeAngelis, Freddy; Weinberg, Gil; Henry, Asegun
2017-08-03
We used molecular dynamics simulations and the Green-Kubo modal analysis (GKMA) method as well as sonification to study the modal contributions to thermal conductivity in individual polythiophene chains. The simulations suggest that it is possible to achieve divergent thermal conductivity in individual polythiophene chains of certain lengths, with periodic boundary conditions. Application of the GKMA method further allowed for exact pinpointing of the modes responsible for the anomalous behavior. The analysis showed that transverse vibrations in the plane of the aromatic rings at low frequencies ∼0.05 THz are primarily responsible for the divergence. Within the integration time, one mode in particular exhibits a thermal conductivity contribution greater than 100 W m(-1) K(-1). Further investigation showed that the divergence arises from persistent correlation between the three lowest frequency modes on chains that have exact multiples of 30 unit cells in length. Sonification of the mode heat fluxes revealed regions where the heat flux amplitude yields a somewhat sinusoidal envelope with a long period similar to the relaxation time. This characteristic in the divergent mode heat fluxes gives rise to the overall thermal conductivity divergence, which strongly supports earlier hypotheses that attribute the divergence to correlated phonon-phonon scattering/interactions as opposed to a lack of scattering/interaction among modes (e.g., infinite relaxation time/ballistic transport).
Non-modal stability analysis and transient growth in a magnetized Vlasov plasma
Ratushnaya, Valeria
2014-01-01
Collisionless plasmas, such as those encountered in tokamaks, exhibit a rich variety of instabilities. The physical origin, triggering mechanisms and fundamental understanding of many plasma instabilities, however, are still open problems. We investigate the stability properties of a collisionless Vlasov plasma in a stationary homogeneous magnetic field. We narrow the scope of our investigation to the case of Maxwellian plasma. For the first time using a fully kinetic approach we show the emergence of the local instability, a transient growth, followed by classical Landau damping in a stable magnetized plasma. We show that the linearized Vlasov operator is non-normal leading to the algebraic growth of the perturbations using non-modal stability theory. The typical time scales of the obtained instabilities are of the order of several plasma periods. The first-order distribution function and the corresponding electric field are calculated and the dependence on the magnetic field and perturbation parameters is s...
Sinou, Jean-Jacques; Thouverez, Fabrice; Jezequel, Louis
2006-01-01
International audience; Herein, a novel non-linear procedure for producing non-linear behaviour and stable limit cycle amplitudes of non-linear systems subjected to super-critical Hopf bifurcation point is presented. This approach, called Complex Non-Linear Modal Analysis (CNLMA), makes use of the non-linear unstable mode which governs the non-linear dynamic of structural systems in unstable areas. In this study, the computational methodology of CNLMA is presented for the systematic estimatio...
Fein, Howard
1999-03-01
Holographic Interferometry has been successfully employed to characterize the materials and behavior of diverse types of structures under stress. Specialized variations of this technology have also been applied to define dynamic and vibration related structural behavior. Such applications of holographic technique offer some of the most effective methods of modal and dynamic analysis available. Real-time dynamic testing of the modal and mechanical behavior of aerodynamic control and airfoil structures for advanced aircraft has always required advanced instrumentation for data collection in either actual flight test or wind-tunnel simulations. Advanced optical holography techniques are alternate methods which result in actual full-field behavioral data on the ground in a noninvasive environment. These methods offer significant insight in both the development and subsequent operational test and modeling of advanced exotic metal control structures and their integration with total vehicle system dynamics. Structures and materials can be analyzed with very low amplitude excitation and the resultant data can be used to adjust the accuracy mathematically derived structural and behavioral models. Holographic Interferometry offers a powerful tool to aid in the developmental engineering of exotic metal structures for high stress applications. Advanced Titanium alloy is a significant example of these sorts of materials which has found continually increased use in advanced aerodynamic, undersea, and other highly mobil platforms. Aircraft applications in particular must consider environments where extremes in vibration and impulsive mechanical stress can affect both operation and structural stability. These considerations present ideal requisites for analysis using advanced holographic methods in the initial design and test of structures made with such advanced materials. Holographic techniques are nondestructive, real- time, and definitive in allowing the identification of
An improved modal pushover analysis procedure for estimating seismic demands of structures
Institute of Scientific and Technical Information of China (English)
Mao Jianmeng; Zhai Changhai; Xie Lili
2008-01-01
The pushover analysis (POA) procedure is difficult to apply to high-rise buildings, as it cannot account for the contributions of higher modes. To overcome this limitation, a modal pushover analysis (MPA) procedure was proposed by Chopra et al. (2001). However, invariable lateral force distributions are still adopted in the MPA. In this paper, an improved MPA procedure is presented to estimate the seismic demands of structures, considering the redistribution of inertia forces after the structure yields. This improved procedure is verified with numerical examples of 5-, 9- and 22-story buildings. It is concluded that the improved MPA procedure is more accurate than either the POA procedure or MPA procedure. In addition, the proposed procedure avoids a large computational effort by adopting a two-phase lateral force distribution..
Modal and nonmodal stability analysis of electrohydrodynamic flow with and without cross-flow
Zhang, Mengqi; Wu, Jian; Schmid, Peter J; Quadrio, Maurizio
2015-01-01
We report the results of a complete modal and nonmodal linear stability analysis of the electrohydrodynamic flow (EHD) for the problem of electroconvection in the strong injection region. Convective cells are formed by Coulomb force in an insulating liquid residing between two plane electrodes subject to unipolar injection. Besides pure electroconvection, we also consider the case where a cross-flow is present, generated by a streamwise pressure gradient, in the form of a laminar Poiseuille flow. The effect of charge diffusion, often neglected in previous linear stability analyses, is included in the present study and a transient growth analysis, rarely considered in EHD, is carried out. In the case without cross-flow, a non-zero charge diffusion leads to a lower linear stability threshold and thus to a more unstable low. The transient growth, though enhanced by increasing charge diffusion, remains small and hence cannot fully account for the discrepancy of the linear stability threshold between theoretical a...
Institute of Scientific and Technical Information of China (English)
LI Sheng; ZHAO Deyou
2004-01-01
Modal analysis of structural acoustic radiation from a vibrating structure is discussed using structural vibration modes and acoustic radiation modes based on the quadratic form of acoustic power. The finite element method is employed for discretisizing the structure.The boundary element method and Rayleigh integral are used for modeling the acoustic fluid.It is shown that the power radiated by a single vibration mode is to increase the radiated power and the effect of modal interaction can lead to an increase or a decrease or no change in the radiated power, moreover, control of vibration modes is a good way to reduce both vibration and radiated sound as long as the influence of interaction of vibration modes on sound radiation is insignificant. Stiffeners may change mode shapes of a plate and thus change radiation efficiency of the plate's modes. The CHIEF method is adopted to obtain an acoustic radiation mode formulation without the nonuniqueness difficulty at critical frequencies for three-dimensional structures by using Moore-Penrose inverse. A pulsating cube is involved to verify the formulation. Good agreement is obtained between the numerical and analytical solutions. The shapes and radiation efficiencies of acoustic radiation modes of the cube are discussed. The structural acoustic control using structural vibration modes and acoustic radiation modes are compared and studied.
Energy Technology Data Exchange (ETDEWEB)
Lee, Y [University of Kansas Hospital, Kansas City, KS (United States); Fullerton, G; Goins, B [University of Texas Health Science Center at San Antonio, San Antonio, TX (United States)
2015-06-15
Purpose: In our previous study a preclinical multi-modality quality assurance (QA) phantom that contains five tumor-simulating test objects with 2, 4, 7, 10 and 14 mm diameters was developed for accurate tumor size measurement by researchers during cancer drug development and testing. This study analyzed the errors during tumor volume measurement from preclinical magnetic resonance (MR), micro-computed tomography (micro- CT) and ultrasound (US) images acquired in a rodent tumor model using the preclinical multi-modality QA phantom. Methods: Using preclinical 7-Tesla MR, US and micro-CT scanners, images were acquired of subcutaneous SCC4 tumor xenografts in nude rats (3–4 rats per group; 5 groups) along with the QA phantom using the same imaging protocols. After tumors were excised, in-air micro-CT imaging was performed to determine reference tumor volume. Volumes measured for the rat tumors and phantom test objects were calculated using formula V = (π/6)*a*b*c where a, b and c are the maximum diameters in three perpendicular dimensions determined by the three imaging modalities. Then linear regression analysis was performed to compare image-based tumor volumes with the reference tumor volume and known test object volume for the rats and the phantom respectively. Results: The slopes of regression lines for in-vivo tumor volumes measured by three imaging modalities were 1.021, 1.101 and 0.862 for MRI, micro-CT and US respectively. For phantom, the slopes were 0.9485, 0.9971 and 0.9734 for MRI, micro-CT and US respectively. Conclusion: For both animal and phantom studies, random and systematic errors were observed. Random errors were observer-dependent and systematic errors were mainly due to selected imaging protocols and/or measurement method. In the animal study, there were additional systematic errors attributed to ellipsoidal assumption for tumor shape. The systematic errors measured using the QA phantom need to be taken into account to reduce measurement
Renardel de Lavalette, Gerard R.
2004-01-01
The dynamic modal logic DML is presented, featuring actions that change the interpretation of a propositional variable or a modality. The semantics is defined both in terms of modal structures and of labelled transition systems (Kripke models). The extension µDML with recursively defined actions aim
DEFF Research Database (Denmark)
Luczak, Marcin; Manzato, Simone; Peeters, Bart;
2014-01-01
of model parameters was selected for the model updating process. Design of experiment and response surface method was implemented to find values of model parameters yielding results closest to the experimental. The updated finite element model is producing results more consistent with the measurement...... is to validate finite element model of the modified wind turbine blade section mounted in the flexible support structure accordingly to the experimental results. Bend-twist coupling was implemented by adding angled unidirectional layers on the suction and pressure side of the blade. Dynamic test and simulations...... were performed on a section of a full scale wind turbine blade provided by Vestas Wind Systems A/S. The numerical results are compared to the experimental measurements and the discrepancies are assessed by natural frequency difference and modal assurance criterion. Based on sensitivity analysis, set...
Directory of Open Access Journals (Sweden)
J.Jithendranath
2013-07-01
Full Text Available This paper presents an evolutionary based algorithm for solving optimal reactive power dispatch problem in power system. The problem was designed as a Multi-Objective case with loss minimization and voltage stability as objectives. Generator terminal voltages, tap setting of transformers and reactive power generation of capacitor banks were taken as optimization variables. Modal analysis method is adopted to assess the voltage stability of system. The above presented problem was solved on basis of efficient and reliable technique among all evolutionary based algorithms, the Differential Evolution Technique. The proposed method has been tested on IEEE 30 bus system where the obtained results were found satisfactorily to a large extent that of reported earlier.
THE STUDY OF MODAL VERBS FROM A PEDAGOGICAL PERSPECTIVE: AN ANALYSIS OF TEXTBOOKS AND GRAMMARS
Directory of Open Access Journals (Sweden)
María Jesús Sánchez
2007-05-01
Full Text Available This paper shows how the indiscriminate combination of the form-function criterion in the traditional presentation of modal verbs brings more confusion than light to the subject due mostly to the fact that the grammatical simplicity of modal verbs clashes with their semantic complexity. In order to verify the treatment of modals in the EFL classroom, both a reduced but representative sample of textbooks and English grammar books will be analysed. Based on the findings of research conducted in this field, this article concludes that when studying modals in the EFL classroom the pragmatic uses of modal verbs should be primed over potential polysemic often indeterminate semantic values and/or grammatical criteria based on a higher or lower rank of graded modality.
NIF Periscope Wall Modal Study Comparison of Results for 2 FEA Models with 2 Modal Tests
Energy Technology Data Exchange (ETDEWEB)
Eli, M W; Gerhard, M A; Lee, C L; Sommer, S C; Woehrle, T G
2000-10-26
This report summarizes experimentally and numerically determined modal properties for one of the reinforced concrete end walls of the NIF Periscope Support Structure in Laser Bay 1. Two methods were used to determine these modal properties: (1) Computational finite-element analyses (modal extraction process); and (2) Experimental modal analysis based on measured test data. This report also includes experimentally determined modal properties for a prototype LM3/Polarizer line-replaceable unit (LRU) and a prototype PEPC LRU. Two important parameters, used during the design phase, are validated through testing [ref 1]. These parameters are the natural frequencies and modal damping (of the system in question) for the first several global modes of vibration. Experimental modal testing provides these modal values, along with the corresponding mode shapes. Another important parameter, the input excitation (expected during normal operation of the NIF laser system) [ref 1], can be verified by performing a series of ambient vibration measurements in the vicinity of the particular system (or subsystem) of interest. The topic of ambient input excitation will be covered in a separate report. Due to the large mass of the Periscope Pedestal, it is difficult to excite the entire series of Periscope Pedestal Walls all at once. It was decided that the experimental modal tests would be performed on just one Periscope End Wall in Laser Bay 1. Experimental modal properties for the Periscope End Wall have been used to validate and update the FE analyses. Results from the analyses and modal tests support the conclusion that the Periscope Pedestal will not exceed the stability budget, which is described in reference 1. The results of the modal tests for the Periscope End Wall in Laser Bay 1 have provided examples of modal properties that can be derived from future modal tests of the entire Periscope Assembly (excluding the LRU's). This next series of larger modal tests can be
DEFF Research Database (Denmark)
Skjoldan, P.F.; Hansen, Morten Hartvig
2009-01-01
Structures with isotropic bladed rotors can be modally analyzed by eigenvalue analysis of time-invariant Coleman transformed equations of motion related to the inertial frame or by Floquet analysis of the periodic equations of motion. The Coleman transformation is here shown to be a special case ...
Information content and analysis methods for multi-modal high-throughput biomedical data.
Ray, Bisakha; Henaff, Mikael; Ma, Sisi; Efstathiadis, Efstratios; Peskin, Eric R; Picone, Marco; Poli, Tito; Aliferis, Constantin F; Statnikov, Alexander
2014-03-21
The spectrum of modern molecular high-throughput assaying includes diverse technologies such as microarray gene expression, miRNA expression, proteomics, DNA methylation, among many others. Now that these technologies have matured and become increasingly accessible, the next frontier is to collect "multi-modal" data for the same set of subjects and conduct integrative, multi-level analyses. While multi-modal data does contain distinct biological information that can be useful for answering complex biology questions, its value for predicting clinical phenotypes and contributions of each type of input remain unknown. We obtained 47 datasets/predictive tasks that in total span over 9 data modalities and executed analytic experiments for predicting various clinical phenotypes and outcomes. First, we analyzed each modality separately using uni-modal approaches based on several state-of-the-art supervised classification and feature selection methods. Then, we applied integrative multi-modal classification techniques. We have found that gene expression is the most predictively informative modality. Other modalities such as protein expression, miRNA expression, and DNA methylation also provide highly predictive results, which are often statistically comparable but not superior to gene expression data. Integrative multi-modal analyses generally do not increase predictive signal compared to gene expression data.
Modal Analysis of a Centrifugal Pump Impeller Using Finite Element Method
Directory of Open Access Journals (Sweden)
Ashri Muhammad
2014-07-01
Full Text Available The turbo machinery design has evolved rapidly in the last 50 years. The development in the design of any turbo machinery involves interdisciplinary process, namely stress analysis, vibration analysis, fluid dynamics, thermodynamics and the material selection. One of the major and common analyses used in the development of any mechanical part subjected to dynamic loading is the modal analysis. In this paper, the dynamic characteristics of an impeller of a centrifugal pump were studied. The dynamics characteristics studied were limited to the natural frequencies and the mode shapes. The impeller chosen for the study was a single-entry impeller with radial vanes. Finite element method (FEM was used since it has proven to be an alternative approach to the experimental method for the vibrational behavior analysis of a component or a system. Modeling and simulation of the impeller have been carried out using ANSYS Bladegen and ANSYS Workbench software, respectively. The eigenvalues and the eigenvectors were observed, and they represent the frequencies and the corresponding mode shapes of the impeller, respectively. The results showed that the varying number of impeller blades and impeller blade thickness had minimal effect on frequencies. However, the change to the impeller disk thickness had significant effects on the natural frequency of the impeller.
Operant Variability: A Conceptual Analysis
Barba, Lourenco de Souza
2012-01-01
Some researchers claim that variability is an operant dimension of behavior. The present paper reviews the concept of operant behavior and emphasizes that differentiation is the behavioral process that demonstrates an operant relation. Differentiation is conceived as change in the overlap between two probability distributions: the distribution of…
The Difference Between Modal Verbs in Deontic and Epistemic Modality
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Menik Winiharti
2012-10-01
Full Text Available Modality is always interesting to discuss. Understanding it is crucial for both language teachers and learners. This essay discusses the concept of modality, its types and uses. It has a goal to find the difference between deontic and epistemic modality that is indicated by their modal verbs. It also provides the readers a better understanding of modality, particularly of its types and uses. The result of the analysis shows that in general, deontic modality indicates obligation and permission, while epistemic modality expresses possibility and prediction. However, the difference between deontic and epistemic modality is not a clear cut, since one single modal verb can express both types, and one single proposition can be expressed by more than one modal verb.
Molina-Viedma, Ángel J.; López-Alba, Elías; Felipe-Sesé, Luis; Díaz, Francisco A.
2017-10-01
In recent years, many efforts have been made to exploit full-field measurement optical techniques for modal identification. Three-dimensional digital image correlation using high-speed cameras has been extensively employed for this purpose. Modal identification algorithms are applied to process the frequency response functions (FRF), which relate the displacement response of the structure to the excitation force. However, one of the most common tests for modal analysis involves the base motion excitation of a structural element instead of force excitation. In this case, the relationship between response and excitation is typically based on displacements, which are known as transmissibility functions. In this study, a methodology for experimental modal analysis using high-speed 3D digital image correlation and base motion excitation tests is proposed. In particular, a cantilever beam was excited from its base with a random signal, using a clamped edge join. Full-field transmissibility functions were obtained through the beam and converted into FRF for proper identification, considering a single degree-of-freedom theoretical conversion. Subsequently, modal identification was performed using a circle-fit approach. The proposed methodology facilitates the management of the typically large amounts of data points involved in the DIC measurement during modal identification. Moreover, it was possible to determine the natural frequencies, damping ratios and full-field mode shapes without requiring any additional tests. Finally, the results were experimentally validated by comparing them with those obtained by employing traditional accelerometers, analytical models and finite element method analyses. The comparison was performed by using the quantitative indicator modal assurance criterion. The results showed a high level of correspondence, consolidating the proposed experimental methodology.
Verification of BModes: Rotary Beam and Tower Modal Analysis Code; Preprint
Energy Technology Data Exchange (ETDEWEB)
Bir, G.
2010-04-01
This paper describes verification of BModes, a finite-element code developed to provide coupled modes for the blades and tower of a wind turbine. The blades, which may be rotating or non-rotating, and the towers, whether onshore or offshore, are modeled using specialized 15-dof beam finite elements. Both blade and tower models allow a tip attachment, which is assumed to be rigid body with six moments of inertia, and a mass centroid that may be offset from the blade or tower axis. Examples of tip attachments are aerodynamic brakes for blades and nacelle-rotor subassembly for towers. BModes modeling allows for tower supports including tension wires, floating platforms, and monopiles on elastic foundations. Coupled modes (implying coupling of flap, lag, axial, and torsional motions) are required for modeling major flexible components in a modal-based, aeroelastic code such as FAST1. These are also required for validation of turbine models using experimental data, modal-based fatigue analysis, controls design, and understanding aeroelastic-stability behavior of turbines. Verification studies began with uniform tower models, with and without tip inertia, and progressed to realistic towers. For the floating turbine, we accounted for the effects of hydrodynamic inertia, hydrostatic restoring, and mooring lines stiffness. For the monopole-supported tower, we accounted for distributed hydrodynamic mass on the submerged part of the tower and for distributed foundation stiffness. Finally, we verified a model of a blade carrying tip mass and rotating at different speeds (verifications of other blade models, rotating or non-rotating, have been reported in another paper.) Verifications were performed by comparing BModes-generated modes with analytical results, if available, or with MSC.ADAMS results. All results in general show excellent agreement.
Zhong, Jianfeng; Zhong, Shuncong; Zhang, Qiukun
2016-10-01
A high-speed camera-based two-dimensional optical coherence vibration tomography (2DOCVT) system with a subnanometre displacement resolution was developed and employed for low-frequency vibration measurement and modal analysis. Experimental results demonstrated the ability of low-frequency absolute displacement measurement of structural line vibrations without scanning. Three-dimensional (3D) surface displacement of a vibrating structure could also be obtained using the developed 2DOCVT by scanning the structure. The scanning 2DOCVT system acted like a 3D optical coherence vibration tomography system. The developed 2DOCVT system could capture structural modal parameters without vibration excitation input information, and therefore, it is a response-only method. The 2DOCVT could be recommended in the application of low-frequency vibration measurement and modal analysis of beam and plate structures, especially when the vibration amplitude is at nanometre or micrometre scale.
Some Remarks on the Transformational Analysis of Sentences with Modal Adverbs
Zabrocki, Tadeusz
1973-01-01
A deep structure underlying sentences with modal adverbs and verbs in English is discussed. Semantic and syntactic similarities are pointed out in support of a suggestion that both surface structures have a common deep structure source. Possible ways of dealing with modality in a generative grammar are presented. (Available from: See FL 508 214.)…
Directory of Open Access Journals (Sweden)
Junghwan Kook
2014-12-01
Full Text Available The aim of this paper is to investigate the enhancement of the damping ratio of a structure with embedded microbeam resonators in air-filled internal cavities. In this context, we discuss theoretical aspects in the framework of the effective modal damping ratio (MDR and derive an approximate relation expressing how an increased damping due to the acoustic medium surrounding the microbeam affect the MDR of the macrobeam. We further analyze the effect of including dissipation of the acoustic medium by using finite element (FE analysis with acoustic-structure interaction (ASI using a simple phenomenological acoustic loss model. An eigenvalue analysis is carried out to demonstrate the improvement of the damping characteristic of the macrobeam with the resonating microbeam in the lossy air and the results are compared to a forced vibration analysis for a macrobeam with one or multiple embedded microbeams. Finally we demonstrate the effect of randomness in terms of position and size of microbeams and discuss the difference between the phenomenological acoustic loss model and a full thermoacoustic model.
Modal and Probabilistic Analysis of Wind Turbine Blade under Air-Flow
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Ismaïl Sossey-Alaoui
2017-01-01
Full Text Available Wind power is one of the most important sources of renewable energy. Wind-turbines extract kinetic energy from the wind and convert it into mechanical energy. Therefore wind turbine power production depends on the interaction between the blade and the wind. The fluid-structure interaction, that means the interaction of some deformable structure with a surrounding or internal fluid flow, belong nowadays to the most important and challenging multi-physics problems which are aimed to treat by numerical simulations. The topic fluid-structure interaction plays a dominant role in many fields of engineering. Therefore, a strong need for appropriate numerical simulation tools exists with a variety of numerical and physical aspects. The present paper takes care about fluid-structure interaction using modern simulation techniques such as coupled field analysis. This work illustrates the use of load transfer coupled physics analysis to solve a steady-state air flow-blade interaction problem, followed by modal analysis where natural frequency are obtained with two different approaches: deterministic and probabilistic. The numerical results are deduced from a finite element approximation of the coupled problem with a non-symmetric pressure/displacement formulation. Deterministic and probabilistic results are given and discussed.
Multidimensional modal analysis of liquid nonlinear sloshing in right circular cylindrical tank
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The multidimensional modal theory proposed by Faltinsen, et al. (2000) is applied to solve liquid nonlinear free sloshing in right circular cylindrical tank for the first time. After selecting the leading modes and fixing the order of magnitudes based on the Narimanov-Moiseev third order asymptotic hypothesis, the general infinite dimensional modal system is reduced to a five dimensional asymptotic modal system (the system of second order nonlinear ordinary differential equations coupling the generalized time dependent coordinates of free surface wave elevation). The numerical integrations of this modal system discover most important nonlinear phenomena, which agree well with both pervious analytic theories and experimental observations. The results indicate that the multidimensional modal method is a very good tool for solving liquid nonlinear sloshing dynamics and will be developed to investigate more complex sloshing problem in our following work.
Non-modal stability analysis and transient growth in a magnetized Vlasov plasma
Ratushnaya, V.
2014-12-01
Collisionless plasmas, such as those encountered in tokamaks, exhibit a rich variety of instabilities. The physical origin, triggering mechanisms and fundamental understanding of many plasma instabilities, however, are still open problems. We investigate the stability properties of a 3-dimensional collisionless Vlasov plasma in a stationary homogeneous magnetic field. We narrow the scope of our investigation to the case of Maxwellian plasma and examine its evolution with an electrostatic approximation. For the first time using a fully kinetic approach we show the emergence of the local instability, a transient growth, followed by classical Landau damping in a stable magnetized plasma. We show that the linearized Vlasov operator is non-normal leading to the algebraic growth of the perturbations using non-modal stability theory. The typical time scales of the obtained instabilities are of the order of several plasma periods. The first-order distribution function and the corresponding electric field are calculated and the dependence on the magnetic field and perturbation parameters is studied. Our results offer a new scenario of the emergence and development of plasma instabilities on the kinetic scale.
Identiﬁcation of honeycomb sandwich properties by high-resolution modal analysis
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Rebillat M.
2010-06-01
Full Text Available A method is proposed to identify the mechanical properties of the skin and core materials of honeycomb sandwich. All the elastic coeﬃcients and loss-factors that matter in the dynamics of a panel in the thick-plate approximation are identiﬁed. To this end, experimental natural modes (i.e. eigenmodes of the damped system are compared to the numerical modes of a large sandwich panel (lx,y/h ≃ 80. The chosen generic model for the visco-elastic behaviour of the materials is E (1 + jη. The numerical modes are computed by means of a Rayleigh-Ritz procedure and their dampings are predicted according to the visco-elastic model. The frequencies and dampings of the natural modes of the panel are estimated experimentally by means of a high-resolution modal analysis technique. An optimisation procedure yields the desired coeﬃcients. A sensitivity analysis assess the reliability of the method.
Directory of Open Access Journals (Sweden)
K. Y. Kim
2009-06-01
Full Text Available The guided modal properties of double-positive and double-negative metamaterial slab waveguides are numerically analyzed and compared when varying the dielectric and magnetic constants. As the cutoff frequencies of both slab waveguides remained unchanged when the absolute value of the refractive index was kept invariant, this enabled an effective comparison of the respective guided modes. Thus, the guided mode dispersion characteristics of the double-positive and double-negative slab waveguides were analyzed and compared, including several higher order modes. As a result, this comparative analysis provides greater physical insights and a better understanding of the guided modal characteristics of double-negative metamaterial slab waveguides.
Kosko, Karl W.; Herbst, Patricio
2012-01-01
Analysis of teacher-to-teacher talk provides researchers with useful information regarding the teaching profession and teachers' perspectives. This article provides a description of a method, with accompanying example, examining teacher-to-teacher talk by incorporating semantic modality and examining trends of its usage in a quantitative manner.…
CSIR Research Space (South Africa)
Britz, K
2013-01-01
Full Text Available with a preference ordering on worlds in Kripke models. The resulting family of modal logics allow for the elegant expression of defeasible modalities. We also propose a tableau calculus which is sound and complete with respect to our preferential...
Scholte, Johannes B J; van Dessel, Helke A; Linssen, Catharina F M; Bergmans, Dennis C J J; Savelkoul, Paul H M; Roekaerts, Paul M H J; van Mook, Walther N K A
2014-10-01
Authoritative guidelines state that the diagnosis of ventilator-associated pneumonia (VAP) can be established using either endotracheal aspirate (ETA) or bronchoalveolar lavage fluid (BALF) analysis, thereby suggesting that their results are considered to be in accordance. Therefore, the results of ETA Gram staining and semiquantitative cultures were compared to the results from a paired ETA-BALF analysis. Different thresholds for the positivity of ETAs were assessed. This was a prospective study of all patients who underwent bronchoalveolar lavage for suspected VAP in a 27-bed university intensive care unit during an 8-year period. VAP was diagnosed when ≥ 2% of the BALF cells contained intracellular organisms and/or when BALF quantitative culture revealed ≥ 10(4) CFU/ml of potentially pathogenic microorganisms. ETA Gram staining and semiquantitative cultures were compared to the results from paired BALF analysis by Cohen's kappa coefficients. VAP was suspected in 311 patients and diagnosed in 122 (39%) patients. In 288 (93%) patients, the results from the ETA analysis were available for comparison. Depending on the threshold used and the diagnostic modality, VAP incidences varied from 15% to 68%. For the diagnosis of VAP, the most accurate threshold for positivity of ETA semiquantitative cultures was moderate or heavy growth, whereas the optimal threshold for BALF Gram staining was ≥ 1 microorganisms per high power field. The Cohen's kappa coefficients were 0.22, 0.31, and 0.60 for ETA and paired BALF Gram stains, cultures, and BALF Gram stains, respectively. Since the ETA and BALF Gram stains and cultures agreed only fairly, they are probably not interchangeable for diagnosing VAP.
Energy Technology Data Exchange (ETDEWEB)
Lee, Jongsuh; Hussain, Syed Hassaan; Wang, Semyung, E-mail: smwang@gist.ac.kr; Park, Kyihwan [School of Mechatronics, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of)
2014-09-15
Generally, it is time consuming to experimentally identify the operating deflection shape or mode shape of a structure. To overcome this problem, the Hilbert Huang transform (HHT) technique has been recently proposed. This technique is used to extract the mode shape from measurements that continuously measure the vibration of a region of interest within a structure using a non-contact laser sensor. In previous research regarding the HHT, two technical processes were needed to obtain the mode shape for each mode. The purpose of this study is to improve and complement our previous research, and for this purpose, a modal analysis approach is adapted without using the two technical processes to obtain an accurate un-damped impulse response of each mode for continuous scanning measurements. In addition, frequency response functions for each type of beam are derived, making it possible to make continuously scanned measurements along a straight profile. In this paper, the technical limitations and drawbacks of the damping compensation technique used in previous research are identified. In addition, the separation of resonant frequency (the Doppler effect) that occurs in continuous scanning measurements and the separation of damping phenomenon are also observed. The proposed method is quantitatively verified by comparing it with the results obtained from a conventional approach to estimate the mode shape with an impulse response.
Lee, Jongsuh; Hussain, Syed Hassaan; Wang, Semyung; Park, Kyihwan
2014-09-01
Generally, it is time consuming to experimentally identify the operating deflection shape or mode shape of a structure. To overcome this problem, the Hilbert Huang transform (HHT) technique has been recently proposed. This technique is used to extract the mode shape from measurements that continuously measure the vibration of a region of interest within a structure using a non-contact laser sensor. In previous research regarding the HHT, two technical processes were needed to obtain the mode shape for each mode. The purpose of this study is to improve and complement our previous research, and for this purpose, a modal analysis approach is adapted without using the two technical processes to obtain an accurate un-damped impulse response of each mode for continuous scanning measurements. In addition, frequency response functions for each type of beam are derived, making it possible to make continuously scanned measurements along a straight profile. In this paper, the technical limitations and drawbacks of the damping compensation technique used in previous research are identified. In addition, the separation of resonant frequency (the Doppler effect) that occurs in continuous scanning measurements and the separation of damping phenomenon are also observed. The proposed method is quantitatively verified by comparing it with the results obtained from a conventional approach to estimate the mode shape with an impulse response.
Prognostic Analysis System and Methods of Operation
MacKey, Ryan M. E. (Inventor); Sneddon, Robert (Inventor)
2014-01-01
A prognostic analysis system and methods of operating the system are provided. In particular, a prognostic analysis system for the analysis of physical system health applicable to mechanical, electrical, chemical and optical systems and methods of operating the system are described herein.
Directory of Open Access Journals (Sweden)
Kenichi eOishi
2011-08-01
Full Text Available Background: Alterations of the gray and white matter have been identified in Alzheimer’s disease (AD by structural MRI and diffusion tensor imaging (DTI. However, whether the combination of these modalities could increase the diagnostic performance is unknown.Methods: Participants included 19 AD patients, 22 amnestic mild cognitive impairment (aMCI patients, and 22 cognitively normal elderly (NC. The aMCI group was further divided into an aMCI-converter group (converted to AD dementia within three years, and an aMCI-stable group who did not convert in this time period. A T1-weighted image, a T2 map, and a DTI of each participant were normalized, and voxel-based comparisons between AD and NC groups were performed. Regions-of-interest, which defined the areas with significant differences between AD and NC, were created for each modality and named disease-specific spatial filters (DSF. Linear discriminant analysis was used to optimize the combination of multiple MRI measurements extracted by DSF to effectively differentiate AD from NC. The resultant DSF and the discriminant function were applied to the aMCI group to investigate the power to differentiate the aMCI-converters from the aMCI-stable patients. Results: The multi-modal approach with AD-specific filters led to a predictive model with an area under the receiver operating characteristic curve (AUC of 0.93, in differentiating aMCI-converters from aMCI-stable patients. This AUC was better than that of a single-contrast-based approach, such as T1-based morphometry or diffusion anisotropy analysis. Conclusion: The multi-modal approach has the potential to increase the value of MRI in predicting conversion from aMCI to AD.
ON THE MORPHOLOGICAL ANALYSIS OF THE SERMON: THE MODALITY OF PERSUASION
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TARABRINA T.B.
2015-01-01
Full Text Available The article dwells upon morphological aspects of the modality of persuasion as exemplified in the sermons by Metropolitan Anthony of Sourozh and provides the results of the author’s the research work.
Determination of Stress Histories in Structures by Natural Input Modal Analysis
DEFF Research Database (Denmark)
Hjelm, Henrik P.; Brincker, Rune; Graugaard-Jensen, Jesper;
2005-01-01
In this paper it is shown that stress histories can be estimated with high accuracy by integrating measured accelerations to obtain displacement and then performing a modal decomposition of the so estimated displacements. The relation between the modal coordinate and the stress in an arbitrary po....... It is shown that the so estimated stress histories can replace strain gauge measurements in many cases, and it allows for an accurate estimation of fatigue damage....
Gulati, Mamta; Saini, Tarun Deep
2017-02-01
We present a modal analysis of instabilities of counter-rotating, self-gravitating collisionless stellar discs, using the recently introduced modified WKB formulation of spiral density waves for collisionless systems by Gulati & Saini. The discs are assumed to be axisymmetric and in coplanar orbits around a massive object at the common centre of the discs. The mass in both discs is assumed to be much smaller than the mass of the central object. For each disc, the disc particles are assumed to be in near circular orbits. The two discs are coupled to each other gravitationally. The perturbed dynamics of the discs evolves on the order of the precession time-scale of the discs, which is much longer than the Keplerian time-scale. We present results for the azimuthal wavenumber m = 1 and 2, for the full range of disc mass ratio between the prograde and retrograde discs. The eigenspectra are in general complex, therefore all eigenmodes are unstable. Eigenfunctions are radially more compact for m = 1 as compared to m = 2. Pattern speed of eigenmodes is always prograde with respect to the more massive disc. The growth rate of unstable modes increases with increasing mass fraction in the retrograde disc, and decreases with m; therefore, m = 1 instability is likely to play the dominant role in the dynamics of such systems.
Gulati, Mamta
2016-01-01
We present a modal analysis of instabilities of counter-rotating, self-gravitating collisionless stellar discs, using the recently introduced modified WKB formulation of spiral density waves for collisionless systems (Gulati \\& Saini). The discs are assumed to be axisymmetric and in coplanar orbits around a massive object at the common center of the discs. The mass in both discs is assumed to be much smaller than the mass of the central object. For each disc, the disc particles are assumed to be in near circular orbits. The two discs are coupled to each other gravitationally. The perturbed dynamics of the discs evolves on the order of the precession time scale of the discs, which is much longer than the Keplerian time scale. We present results for the azimuthal wave number $m=1$ and $m=2$, for the full range of disc mass ratio between the prograde and retrograde discs. The eigenspectra are in general complex, therefore all eigenmodes are unstable. Eigenfunctions are radially more compact for $m = 1$ as co...
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Marcin Luczak
2014-01-01
Full Text Available This paper presents selected results and aspects of the multidisciplinary and interdisciplinary research oriented for the experimental and numerical study of the structural dynamics of a bend-twist coupled full scale section of a wind turbine blade structure. The main goal of the conducted research is to validate finite element model of the modified wind turbine blade section mounted in the flexible support structure accordingly to the experimental results. Bend-twist coupling was implemented by adding angled unidirectional layers on the suction and pressure side of the blade. Dynamic test and simulations were performed on a section of a full scale wind turbine blade provided by Vestas Wind Systems A/S. The numerical results are compared to the experimental measurements and the discrepancies are assessed by natural frequency difference and modal assurance criterion. Based on sensitivity analysis, set of model parameters was selected for the model updating process. Design of experiment and response surface method was implemented to find values of model parameters yielding results closest to the experimental. The updated finite element model is producing results more consistent with the measurement outcomes.
Fourier spectral-based modal curvature analysis and its application to damage detection in beams
Yang, Zhi-Bo; Radzienski, Maciej; Kudela, Pawel; Ostachowicz, Wieslaw
2017-02-01
In this paper, a simple Fourier spectral-based method is proposed to calculate the modal curvature (MC) of beams instead of the traditional central difference method. Based on the present method, damages in beam-like structures are localized. The present method provides an alternative selection to estimate MC in damage detection. There are two advantages of the present method. Firstly, the spectral calculation of spatial derivatives is conducted globally, which provides the suppression for noise. In addition, signal processing in the wavenumber domain provides an alternative choice for spatial filtering for mode shapes. Secondly, the proposed method provides a precise estimation of the MC which is related to original definition. With the absence of numerical derivative, the estimated results can be more stable and robust. Statistical analysis is conducted to show the effectiveness and noise immunity of the proposed method. In order to obtain the better identification, the MC calculated by the proposed method is employed as the input of continuous wavelet transform, and then the hybrid method is generated. The validations of the present method and comparison with the traditional central difference method are numerically and experimentally demonstrated.
Predicting wind-induced vibrations of high-rise buildings using unsteady CFD and modal analysis
Zhang, Yue
2015-01-01
This paper investigates the wind-induced vibration of the CAARC standard tall building model, via unsteady Computational Fluid Dynamics (CFD) and a structural modal analysis. In this numerical procedure, the natural unsteady wind in the atmospheric boundary layer is modeled with an artificial inflow turbulence generation method. Then, the turbulent flow is simulated by the second mode of a Zonal Detached-Eddy Simulation, and a conservative quadrature-projection scheme is adopted to transfer unsteady loads from fluid to structural nodes. The aerodynamic damping that represents the fluid-structure interaction mechanism is determined by empirical functions extracted from wind tunnel experiments. Eventually, the flow solutions and the structural responses in terms of mean and root mean square quantities are compared with experimental measurements, over a wide range of reduced velocities. The significance of turbulent inflow conditions and aeroelastic effects is highlighted. The current methodology provides predictions of good accuracy and can be considered as a preliminary design tool to evaluate the unsteady wind effects on tall buildings.
Li, Hongbo; Lee, Jai-Bong; Liu, Hongchen; Han, Jung-Suk; Yang, Jae-Ho; Koak, Jai-Young
2010-01-01
PURPOSE The aim of this article is to analyze the preference for treatment modality of dentists. MATERIAL AND METHODS Data of 20,038 patients was involved. Data analysis were done by distribution according to the various kinds of prosthesis, including complete denture, removable partial denture, fixed partial denture, implant-supported dental prosthesis as well as distribution according to the professional titles of the dentists finishing the treatment, including resident and professors. RESULTS The number of cases of dental prosthesis increased year by year. 61.06% of the patients accepted fixed partial denture restoration. The number of patients who accepted implant supported restoration is also increasing year by year. The number of complete denture, implant-supported dental prosthesis finished by professors was larger than that done by residents, while it was contrary for removable partial denture, fixed partial denture, and the difference was statistically significant (P<.05). CONCLUSION Professors and residents have some difference in the categorization of prosthesis finished. Fixed partial denture and implant-supported dental prosthesis are preferred. PMID:21165180
Modal analysis of the SCALPEL mask using experimental and numerical methods
Semke, William H.; Schlax, Michael P.; Engelstad, Roxann L.; Lovell, Edward G.; Liddle, James A.
1999-06-01
Controlling the dynamic response of the SCALPEL mask is important to ensure high throughput consistent with the stringent error budgets allocated for sub-130 nm lithography. In this paper experimental and numerical modal analysis result for the SCALPEL mask are presented and compared. These experimental result are used to verify and benchmark the finite element modeling efforts. The mode shapes and their respective frequencies provide valuable information for characterizing the out-of-plane and in-plane oscillations of the mask. The out-of-plane mode shapes were found experimentally with the use of both a Zygo interferometer and a Polytec scanning laser vibrometer. An additional application for out-of-plane oscillations involves a SCALPEL mask cleaning procedure, called the PLAMAX process, where the mask is resonated at its natural frequencies while surface particles are electrostatically charged in the present of a plasma and removed. The in-plane vibrations of the SCALPEL mask have also been investigated, since this is the primary excitation mode of the mask during exposure stepping. For experimental data, the in-plane modes were excited mechanically and detected using a MTI Fotonic sensor fiber-optic probe.
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Daniel P Bray
2014-12-01
Full Text Available The sand fly Phlebotomus argentipes is arguably the most important vector of leishmaniasis worldwide. As there is no vaccine against the parasites that cause leishmaniasis, disease prevention focuses on control of the insect vector. Understanding reproductive behaviour will be essential to controlling populations of P. argentipes, and developing new strategies for reducing leishmaniasis transmission. Through statistical analysis of male-female interactions, this study provides a detailed description of P. argentipes courtship, and behaviours critical to mating success are highlighted. The potential for a role of cuticular hydrocarbons in P. argentipes courtship is also investigated, by comparing chemicals extracted from the surface of male and female flies.P. argentipes courtship shared many similarities with that of both Phlebotomus papatasi and the New World leishmaniasis vector Lutzomyia longipalpis. Male wing-flapping while approaching the female during courtship predicted mating success, and touching between males and females was a common and frequent occurrence. Both sexes were able to reject a potential partner. Significant differences were found in the profile of chemicals extracted from the surface of males and females. Results of GC analysis indicate that female extracts contained a number of peaks with relatively short retention times not present in males. Extracts from males had higher peaks for chemicals with relatively long retention times.The importance of male approach flapping suggests that production of audio signals through wing beating, or dispersal of sex pheromones, are important to mating in this species. Frequent touching as a means of communication, and the differences in the chemical profiles extracted from males and females, may also indicate a role for cuticular hydrocarbons in P. argentipes courtship. Comparing characteristics of successful and unsuccessful mates could aid in identifying the modality of signals
CoSMoMVPA: multi-modal multivariate pattern analysis of neuroimaging datain Matlab / GNU Octave
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Nikolaas N Oosterhof
2016-07-01
Full Text Available Recent years have seen an increase in the popularity of multivariate pattern (MVP analysis of functional magnetic resonance (fMRI data, and, to a much lesser extent, magneto- and electro-encephalography (M/EEG data. We present CoSMoMVPA, a lightweight MVPA (MVP analysis toolbox implemented in the intersection of the Matlab and GNU Octave languages, that treats both fMRI and M/EEG data as first-class citizens.CoSMoMVPA supports all state-of-the-art MVP analysis techniques, including searchlight analyses, classification, correlations, representational similarity analysis, and the time generalization method. These can be used to address both data-driven and hypothesis-driven questions about neural organization and representations, both within and across: space, time, frequency bands, neuroimaging modalities, individuals, and species.It uses a uniform data representation of fMRI data in the volume or on the surface, and of M/EEG data at the sensor and source level. Through various external toolboxes, it directly supports reading and writing a variety of fMRI and M/EEG neuroimaging formats, and, where applicable, can convert between them. As a result, it can be integrated readily in existing pipelines and used with existing preprocessed datasets. CoSMoMVPA overloads the traditional volumetric searchlight concept to support neighborhoods for M/EEG and surface-based fMRI data, which supports localization of multivariate effects of interest across space, time, and frequency dimensions. CoSMoMVPA also provides a generalized approach to multiple comparison correction across these dimensions using Threshold-Free Cluster Enhancement with state-of-the-art clustering and permutation techniques.CoSMoMVPA is highly modular and uses abstractions to provide a uniform interface for a variety of MVP measures. Typical analyses require a few lines of code, making it accessible to beginner users. At the same time, expert programmers can easily extend its functionality
Repository operational criteria comparative analysis
Energy Technology Data Exchange (ETDEWEB)
Hageman, J.P.; Chowdhury, A.H. [Southwest Research Inst., San Antonio, TX (United States). Center for Nuclear Waste Regulatory Analyses
1994-06-01
The objective of the ``Repository Operational Criteria (ROC) Feasibility Studies`` (or ROC task) was to conduct comprehensive and integrated analyses of repository design, construction, and operations criteria in 10 CFR Part 60 regulations considering the interfaces among the components of the regulations and impacts of any potential changes to those regulations. The ROC task addresses regulatory criteria and uncertainties related to the preclosure aspects of the geologic repository. Those parts of 10 CFR Part 60 that require routine guidance or minor changes to the rule were addressed in Hageman and Chowdhury, 1992. The ROC task shows a possible need for further regulatory clarity, by major changes to the rule, related to the design bases and siting of a geologic repository operations area and radiological emergency planning in order to assure defense-in-depth. The analyses, presented in this report, resulted in the development and refinement of regulatory concepts and their supporting rationale for recommendations for potential major changes to 10 CFR Pan 0 regulations.
Tank Farm Operations Surveillance Automation Analysis
Energy Technology Data Exchange (ETDEWEB)
MARQUEZ, D.L.
2000-12-21
The Nuclear Operations Project Services identified the need to improve manual tank farm surveillance data collection, review, distribution and storage practices often referred to as Operator Rounds. This document provides the analysis in terms of feasibility to improve the manual data collection methods by using handheld computer units, barcode technology, a database for storage and acquisitions, associated software, and operational procedures to increase the efficiency of Operator Rounds associated with surveillance activities.
New type of potassium deposit: Modal analysis and preparation of potassium carbonate
Institute of Scientific and Technical Information of China (English)
MA; Hongwen; FENG; Wuwei; MIAO; Shiding; WANG; Yingbin; TI
2005-01-01
A kind of dolomitic mudstone newly found in North China has high amounts of K2O up to 10wB% in average, and potassium reserve is at superior scale. Mineral assemblage of the potassium ore indicates a specific and complicated geological environment under which the potassium deposit formed. Modal analysis of the potassium host rock shows that the principal minerals in the ore include microcline, dolomite, and clay minerals such as illite, illite/smectite mixed layer, and kaolinite, attributable to a new type of insoluble potassium deposits in ore genesis. The experiments in this research demonstrated that with sodium carbonate as flux agent, the potassium ore could be decomposed with a proportion as high as 99.4% by calcinations at moderate temperature for no more than 1.5―2.0 h; more than 70% of K2O in the calcined materials were leached into the liquor, and by acidification reaction of the filter liquor, a large amount of impurities such as Fe3+, Ti4+, Mn2+, Mg2+, and Ca2+ were removed with precipitation of alumino-silicious colloid residue, which makes it possible to prepare potassium carbonate of electronic grade from the filter liquor, whereas the alumino-silicious residue could be utilized to make mineral polymer, a new type of inorganic construction structural materials. The current research shows that industrial exploitation and comprehensive utilization of this new type of insoluble potassium resource are feasible both in economic benefits and environmental kindness with the fairly clean production process as sketched in this paper.
Du, Ting-Ting; Xiao, Xiu-Bin; Su, Hang; Da, Yong; Chen, Xin-Lin; Zhong, Kai-Li; Zhao, Shi-Hua; Lu, Yun; Wang, Shuang; Zhang, Wei-Jing
2012-04-01
This paper explored the curative effect of combined modality therapy and extended field radiotherapy for early-stage Hodgkin's Lymphoma. 104 cases of early-stage Hodgkin's Lymphoma from Jan 1987 to Dec 2010 in PLA Hospital 307 were retrospectively analyzed, including 76 cases in combined modality therapy group and 28 cases in extended field radiotherapy group, and the long-term efficacy and toxicity of two therapy modalities were evaluated. The results showed that the median survival time of 104 cases was 85.42 months, the complete remission rates of combined modality therapy and extended field radiotherapy groups were 72.4 and 71.4 respectively (P = 0.924); the overall response rates of combined modality therapy and extended field radiotherapy groups were 97.4 and 96.4 respectively (P = 0.779); the 5-year overall survival (OS) rates in the 2 groups were 89.5 and 89.1 respectively, and the 8-year OS rates of the 2 groups were 81.3 and 70.6. No statistical difference was found in above-mentioned 2 groups. Moreover, the 5-year progression free survival (PFS) rates of these 2 groups were 84.2 and 69.0 (P = 0.04), and 8-year PFS rates of these 2 groups were 80.0 and 55.5 (P = 0.04) respectively, the 5-year relapse rates of these 2 groups were 28.1 and 45.6 (P = 0.023) respectively. It is concluded that the combined modality therapy can raise the PFS rate and reduce the relapse rate as compared with extended field radiotherapy for early-stage Hodgkin's Lymphoma, but there is no difference in the overall survival rate between the 2 groups.
Bozzelli, Laura; French, Tim; Hales, James; Pinchinat, Sophie
2012-01-01
In this paper we present refinement modal logic. A refinement is like a bisimulation, except that from the three relational requirements only 'atoms' and 'back' need to be satisfied. Our logic contains a new operator 'forall' in additional to the standard modalities 'Box' for each agent. The operator 'forall' acts as a quantifier over the set of all refinements of a given model. We call it the refinement operator. As a variation on a bisimulation quantifier, it can be seen as a refinement quantifier over a variable not occurring in the formula bound by the operator. The logic combines the simplicity of multi-agent modal logic with some powers of monadic second order quantification. We present a sound and complete axiomatization of multiagent refinement modal logic. We also present an extension of the logic to the modal mu-calculus, and an axiomatization for the single-agent version of this logic. Examples and applications are also discussed: to software verification and design (the set of agents can also be s...
Numerical modeling on the interaction of internal solitary wave with slope-shelf and modal analysis
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
On the basis of a nonhydrostatic numerical model, the interaction of internal solitary wave with slope-shelf was studied. The breaking and polarity transformation were analyzed. A "kink" structure, due to shoaling topography and higher nonlinear effect, was found to be generated by the leading wave before breaking. Coherent vortex shedding behind the leading wave was presented. The evolution characteristics of the modal structure were analyzed based on the empirical orthogonal function method. The modal structure was complicated due to the effect of the variable topography, especially when breaking occurred. In the performed experiments, the contributions to the total variance from higher mode jumped from no more than 20% to over 40%.
Tapered Simplified Modal Method for Analysis of Non-rectangular Gratings
Li, Shuai; Barbastathis, George
2016-01-01
The Simplified Modal Method (SMM) provides a quick and intuitive way to analyze the performance of gratings of rectangular shapes. For non-rectangular shapes, a version of SMM has been developed, but it applies only to the Littrow-mounting incidence case and it neglects reflection. Here, we use the theory of mode-coupling in a tapered waveguide to improve SMM so that it applies to non-rectangular gratings at arbitrary angles of incidence. Moreover, this new 'Tapered Simplified Modal Method' (TSMM) allows us to properly account for reflected light. We present here the analytical development of the theory and numerical simulations, demonstrating the validity of the method.
Ctyroký, Jirí; Richter, Ivan; Kwiecien, Pavel
2008-06-01
The performance of three bidirectional modal methods the "classical" bidirectional eigenmode expansion propagation method, the aperiodic rigorous coupled wave analysis (known also as the Fourier modal method), and the mode expansion method based on harmonic expansion are mutually compared using modeling tasks that include eigenmode calculation of a relatively high-contrast planar waveguide, spectral transmittance of a one-dimensional "photonic crystal" filter in a photonic wire, spectral transmittance of a surface plasmon based optical sensor, and a reflectance from a double-groove structure in a high-contrast waveguide. All methods exhibit generally comparable performance, as follows from good mutual agreement of the results and generally comparable computational time. Although all methods use perfectly matched layers as absorbing boundary conditions, their implementation in the aperiodic rigorous coupled wave analysis exhibits significantly stronger attenuation than that used in the other two methods. Thus, significant improvement of the latter methods seems possible.
Panopoulou, A.; Fransen, S.; Gomez-Molinero, V.; Kostopoulos, V.
2013-09-01
The objective of this work is to develop a new structural health monitoring system for composite aerospace structures based on dynamic response strain measurements and experimental modal analysis techniques. Fiber Bragg grating (FBG) optical sensors were used for monitoring the dynamic response of the composite structure. The structural dynamic behavior has been numerically simulated and experimentally verified by means of vibration testing. The hypothesis of all vibration tests was that actual damage in composites reduces their stiffness and produces an eigenfrequency shifting to lower values in the same sense as mass increase produces. Thus, damage was simulated by slightly varying locally the mass of the structure at different zones. The correlation between the simulated damage and the loss of stiffness was analytically defined. Experimental modal analysis based on the strain responses was conducted and the extracted strain mode shapes were the input for the damage detection expert system. A feed-forward back propagation neural network was the core of the damage detection system. The features-input to the neural network consisted of the strain mode shapes, extracted from the experimental modal analysis. Dedicated training and validation activities were carried out based on the experimental results. The system showed high reliability, confirmed by the ability of the neural network to recognize the size and the position of damage on the structure. The experiments were performed on a real structure i.e. a lightweight antenna sub-reflector, manufactured and tested at EADS CASA ESPACIO. An integrated FBG sensor network, based on the advantage of multiplexing, was mounted on the structure with optimum topology. Numerical simulation was used as a support tool at all the steps of the work. Potential applications for the proposed system are during ground qualification extensive tests of space structures and during the mission as modal analysis tool on board, being able
Panopoulou, A.; Fransen, S.; Gomez Molinero, V.; Kostopoulos, V.
2012-07-01
The objective of this work is to develop a new structural health monitoring system for composite aerospace structures based on dynamic response strain measurements and experimental modal analysis techniques. Fibre Bragg Grating (FBG) optical sensors were used for monitoring the dynamic response of the composite structure. The structural dynamic behaviour has been numerically simulated and experimentally verified by means of vibration testing. The hypothesis of all vibration tests was that actual damage in composites reduces their stiffness and produces the same result as mass increase produces. Thus, damage was simulated by slightly varying locally the mass of the structure at different zones. Experimental modal analysis based on the strain responses was conducted and the extracted strain mode shapes were the input for the damage detection expert system. A feed-forward back propagation neural network was the core of the damage detection system. The features-input to the neural network consisted of the strain mode shapes, extracted from the experimental modal analysis. Dedicated training and validation activities were carried out based on the experimental results. The system showed high reliability, confirmed by the ability of the neural network to recognize the size and the position of damage on the structure. The experiments were performed on a real structure i.e. a lightweight antenna sub- reflector, manufactured and tested at EADS CASA ESPACIO. An integrated FBG sensor network, based on the advantage of multiplexing, was mounted on the structure with optimum topology. Numerical simulation of both structures was used as a support tool at all the steps of the work. Potential applications for the proposed system are during ground qualification extensive tests of space structures and during the mission as modal analysis tool on board, being able via the FBG responses to identify a potential failure.
Non-linear modal analysis of structural components subjected to unilateral constraints
Attar, M.; Karrech, A.; Regenauer-Lieb, K.
2017-02-01
In this paper, we present a detailed numerical study of the non-linear dynamics in structural components under unilateral contact constraints. Here, the unilateral term characterises the constitutive law of the restoring force in the constraints as they only sustain elastic reactions in one direction, either compressive or tensile. Thus, the non-differentiability of the contact law at the discontinuity point is the only source of non-linearity. In our approach, the discrete lattice method (DLM) is used to treat the continuous system as a piecewise linear model. Thus, the trajectory of each node in the discrete model would be a sequence of smooth solutions with the switching times between them. The application of the one-step integration scheme allows us to detect the occurrence of contact (i.e. the instants that the lattice nodes cross the discontinuity boundary) and consequently update the active constraints. We also consider embedding the bisection algorithm into the time integration procedure to localise the instants at which the nodes cross the boundary and minimise the accumulative error. Subsequently, the resulting unconditionally stable integration scheme is utilised as the modelling tool in combination with the shooting technique to perform a novel non-smooth modal analysis. In analogy with the smooth non-linear systems, the evolution of non-smooth periodic motions is presented in the frequency-stiffness plots. We apply our method to obtain non-linear normal modes (NNMs) for a number of representative problems, including a bar-obstacle system, a beam-substrate system and a granular chain with tensionless interactions. These numerical examples demonstrate the efficiency of the solution procedure to trace the family of energy-independent non-linear modes across the range of contact stiffnesses. Moreover, the stability analysis of the modes on the plot backbone reveal that they may become unstable due to the interaction with the higher modes or bifurcation of
Seismic response of a full-scale wind turbine tower using experimental and numerical modal analysis
Kandil, Kamel Sayed Ahmad; Saudi, Ghada N.; Eltaly, Boshra Aboul-Anen; El-khier, Mostafa Mahmoud Abo
2016-09-01
Wind turbine technology has developed tremendously over the past years. In Egypt, the Zafarana wind farm is currently generating at a capacity of 517 MW, making it one of the largest onshore wind farms in the world. It is located in an active seismic zone along the west side of the Gulf of Suez. Accordingly, seismic risk assessment is demanded for studying the structural integrity of wind towers under expected seismic hazard events. In the context of ongoing joint Egypt-US research project "Seismic Risk Assessment of Wind Turbine Towers in Zafarana wind Farm Egypt" (Project ID: 4588), this paper describes the dynamic performance investigation of an existing Nordex N43 wind turbine tower. Both experimental and numerical work are illustrated explaining the methodology adopted to investigate the dynamic behavior of the tower under seismic load. Field dynamic testing of the full-scale tower was performed using ambient vibration techniques (AVT). Both frequency domain and time domain methods were utilized to identify the actual dynamic properties of the tower as built in the site. Mainly, the natural frequencies, their corresponding mode shapes and damping ratios of the tower were successfully identified using AVT. A vibration-based finite element model (FEM) was constructed using ANSYS V.12 software. The numerical and experimental results of modal analysis were both compared for matching purpose. Using different simulation considerations, the initial FEM was updated to finally match the experimental results with good agreement. Using the final updated FEM, the response of the tower under the AQABA earthquake excitation was investigated. Time history analysis was conducted to define the seismic response of the tower in terms of the structural stresses and displacements. This work is considered as one of the pioneer structural studies of the wind turbine towers in Egypt. Identification of the actual dynamic properties of the existing tower was successfully performed
Seismic response of a full-scale wind turbine tower using experimental and numerical modal analysis
Kandil, Kamel Sayed Ahmad; Saudi, Ghada N.; Eltaly, Boshra Aboul-Anen; El-khier, Mostafa Mahmoud Abo
2016-12-01
Wind turbine technology has developed tremendously over the past years. In Egypt, the Zafarana wind farm is currently generating at a capacity of 517 MW, making it one of the largest onshore wind farms in the world. It is located in an active seismic zone along the west side of the Gulf of Suez. Accordingly, seismic risk assessment is demanded for studying the structural integrity of wind towers under expected seismic hazard events. In the context of ongoing joint Egypt-US research project "Seismic Risk Assessment of Wind Turbine Towers in Zafarana wind Farm Egypt" (Project ID: 4588), this paper describes the dynamic performance investigation of an existing Nordex N43 wind turbine tower. Both experimental and numerical work are illustrated explaining the methodology adopted to investigate the dynamic behavior of the tower under seismic load. Field dynamic testing of the full-scale tower was performed using ambient vibration techniques (AVT). Both frequency domain and time domain methods were utilized to identify the actual dynamic properties of the tower as built in the site. Mainly, the natural frequencies, their corresponding mode shapes and damping ratios of the tower were successfully identified using AVT. A vibration-based finite element model (FEM) was constructed using ANSYS V.12 software. The numerical and experimental results of modal analysis were both compared for matching purpose. Using different simulation considerations, the initial FEM was updated to finally match the experimental results with good agreement. Using the final updated FEM, the response of the tower under the AQABA earthquake excitation was investigated. Time history analysis was conducted to define the seismic response of the tower in terms of the structural stresses and displacements. This work is considered as one of the pioneer structural studies of the wind turbine towers in Egypt. Identification of the actual dynamic properties of the existing tower was successfully performed
Imaging modalities for the classification of gout: systematic literature review and meta-analysis
Ogdie, A.; Taylor, W.J.; Weatherall, M.; Fransen, J.; Jansen, T.L.; Neogi, T.; Schumacher, H.R.; Dalbeth, N.
2015-01-01
BACKGROUND: Although there has been major progress in gout imaging, no gout classification criteria currently include advanced imaging techniques. OBJECTIVE: To examine the usefulness of imaging modalities in the classification of gout when compared to monosodium urate (MSU) crystal confirmation as
EMERGING MODALITIES FOR SOIL CARBON ANALYSIS: SAMPLING STATISTICS AND ECONOMICS WORKSHOP.
Energy Technology Data Exchange (ETDEWEB)
WIELOPOLSKI, L.
2006-04-01
The workshop's main objectives are (1) to present the emerging modalities for analyzing carbon in soil, (2) to assess their error propagation, (3) to recommend new protocols and sampling strategies for the new instrumentation, and, (4) to compare the costs of the new methods with traditional chemical ones.
DEFF Research Database (Denmark)
Kook, Junghwan; Jensen, Jakob Søndergaard
2014-01-01
The aim of this paper is to investigate the enhancement of the damping ratio of a structure with embedded microbeam resonators in air-filled internal cavities. In this context, we discuss theoretical aspects in the framework of the effective modal damping ratio (MDR) and derive an approximate rel...
The Verb in Philippine English: A Preliminary Analysis of Modal Would
Bautista, Ma. Lourdes S.
2004-01-01
Taking its inspiration from a study conducted by Svalberg of Brunei English verb usage (1998), this paper examines the responses of a sample of 205 Filipino university freshmen to grammatically correct and incorrect verb forms in a 20-item Grammaticality Judgment Test. The test covered tense harmony, verb forms, tenses, and modals. Except in the…
Integration of Pulsed-Laser ESPI with Spatial Domain Modal Analysis
Directory of Open Access Journals (Sweden)
H. Van der Auweraer
2002-01-01
Full Text Available The present paper discusses the various critical elements of a modal testing system based on pulsed-laser holographic ESPI measurements. Such system allows making very high spatial resolution measurements on panel-like structures at frequencies that are of relevance for the vibro-acoustic behavior.
The Teodorescu Operator in Clifford Analysis
Institute of Scientific and Technical Information of China (English)
F.BRACKX; H.De SCHEPPER; M.E.LUNA-ELIZARRAR(A)S; M.SHAPIRO
2012-01-01
Euclidean Clifford analysis is a higher dimensional function theory centred around monogenic functions,i.e.,null solutions to a first order vector valued rotation invariant differential operator (θ) called the Dirac operator.More recently,Hermitian Clifford analysis has emerged as a new branch,offering yet a refinement of the Euclidean case; it focuses on the simultaneous null solutions,called Hermitian monogenic functions,to two Hermitian Dirac operators (θ)z_ and (θ)z_(+) which are invariant under the action of the unitary group.In Euclidean Clifford analysis,the Teodorescu operator is the right inverse of the Dirac operator (θ).In this paper,Teodorescu operators for the Hermitian Dirac operators (θ)z_ and (θ)z(+) are constructed.Moreover,the structure of the Euclidean and Hermitian Teodorescu operators is revealed by analyzing the more subtle behaviour of their components.Finally,the obtained inversion relations are still refined for the differential operators issuing from the Euclidean and Hermitian Dirac operators by splitting the Clifford algebra product into its dot and wedge parts.Their relationship with several complex variables theory is discussed.
Directory of Open Access Journals (Sweden)
Chifu Yang
2013-02-01
Full Text Available The workspace of a spatial 6‐DOF electro‐hydraulic parallel manipulator is strongly coupled, due to its multi‐closed‐loop kinematic structure and the coupling complicates motion planning and control of the parallel manipulator. This paper clearly analyses the strong dynamic coupling property in the workspace of a spatial 6‐DOF parallel manipulator, using modal decoupling theory and a frequency responses characteristics analysis method. The dynamic model of a spatial 6‐DOF electro‐hydraulic parallel manipulator is expressed with the Kane method and hydromechanics principles. The modal analysis method is used to establish the map between strong coupling workspace and decoupled modal space and the dynamic coupling relationship and coupling strength between workspaces are exactly revealed. The quantitative evaluation index of dynamic coupling is presented. Moreover, the relationship between dynamic coupling effects and input is discussed through applying frequency characteristics analysis. Experimental results show the workspace of the parallel manipulator is strongly coupled and the coupling property is coincident with theoretical results.
Potter, Jennifer L.
2011-12-01
Noise and vibration has long been sought to be reduced in major industries: automotive, aerospace and marine to name a few. Products must be tested and pass certain levels of federally regulated standards before entering the market. Vibration measurements are commonly acquired using accelerometers; however limitations of this method create a need for alternative solutions. Two methods for non-contact vibration measurements are compared: Laser Vibrometry, which directly measures the surface velocity of the aluminum plate, and Nearfield Acoustic Holography (NAH), which measures sound pressure in the nearfield, and using Green's Functions, reconstructs the surface velocity at the plate. The surface velocity from each method is then used in modal analysis to determine the comparability of frequency, damping and mode shapes. Frequency and mode shapes are also compared to an FEA model. Laser Vibrometry is a proven, direct method for determining surface velocity and subsequently calculating modal analysis results. NAH is an effective method in locating noise sources, especially those that are not well separated spatially. Little work has been done in incorporating NAH into modal analysis.
Stochastic Modelling and Analysis of Warehouse Operations
Y. Gong (Yeming)
2009-01-01
textabstractThis thesis has studied stochastic models and analysis of warehouse operations. After an overview of stochastic research in warehouse operations, we explore the following topics. Firstly, we search optimal batch sizes in a parallel-aisle warehouse with online order arrivals. We employ a
Operational morbidity analysis: ophthalmic presentations during Operation TELIC.
Ollerton, J E; Hodgetts, T J
2010-03-01
This paper analyses all ophthalmic attendances to a deployed emergency department (ED) in Iraq to identify patterns of injury to optimise patient care, plan equipment tables for future operations and emphasise need for prevention of ocular morbidity. The Academic Department of Military Emergency Medicine at the Royal Centre for Defence Medicine in Birmingham maintains an electronic database with derails on all attendances to the emergency departments deployed on Operations. This Operational Emergency Department Attendance Register (OpEDAR) was searched for all patients with medical classification of Ophthalmology over a 52 month period between 1 March 2003 and 30 June 2007. During this period 30,195 patients were seen in the ED on Operation Telic and are available for analysis. Patients with ophthalmic complaints account for 5.3% of all presentations to the ED and rank as the 7th most common reason for attendance. This paper identifies patterns of injury to enable future planning of equipment tables and identifies the need for prevention of injury wherever possible. Implications on days lost from full active duty for the injured can be extrapolated. More data needs to be collated on the use of eye protection and the relevance of contact lenses in deployed personnel with eye injuries.
Mourka, A.; Mazilu, M.; Wright, E. M.; Dholakia, K.
2013-01-01
The modal characterization of various families of beams is a topic of current interest. We recently reported a new method for the simultaneous determination of both the azimuthal and radial mode indices for light fields possessing orbital angular momentum. The method is based upon probing the far-field diffraction pattern from a random aperture and using the recorded data as a ‘training set'. We then transform the observed data into uncorrelated variables using the principal component analysis (PCA) algorithm. Here, we show the generic nature of this approach for the simultaneous determination of the modal parameters of Hermite-Gaussian and Bessel beams. This reinforces the widespread applicability of this method for applications including information processing, spectroscopy and manipulation. Additionally, preliminary results demonstrate reliable decomposition of superpositions of Laguerre-Gaussians, yielding the intensities and relative phases of each constituent mode. Thus, this approach represents a powerful method for characterizing the optical multi-dimensional Hilbert space. PMID:23478330
Assessment of nonlinear distortions in modal testing and analysis of vibrating automotive structures
Verboven, P.; Guillaume, P.; Vanlanduit, S.; Cauberghe, B.
2006-05-01
In this paper, new developments for the nonparametric processing of modal test data are presented. Classically, random noise signals are applied to deal with possible nonlinear distortions during frequency response function measurements of linear dynamic systems. However, the use of multisine excitation signals allows the engineer to control much more his experiments. First of all, the nonparametric estimation of multivariable frequency response functions can be more easily based on an "errors-in-variables" stochastic framework. In addition, the application of a well-chosen multisine excitation permits improvement of the data quality, as well as the detection, qualification and quantification of nonlinear distortions during FRF measurements. To make the presented techniques available for multi-input modal testing, attention is paid to the design of optimal multi-input excitations by maximizing the Fisher information matrix as well as minimizing the crest factor of the applied excitation.
Modal analysis of the scattering coefficients of an open cavity in a waveguide
Tong, Yuhui
2016-01-01
The characteristics of an acoustic scatterer are often described by scattering coefficients. The understanding of the mechanisms involved in the frequency dependent features of the coefficients has been a challenge task, owing to the complicated coupling between the waves in open space and the modes inside the finite scatterer. In this paper, a frequency-dependent modal description of the scattering coefficient is utilized to study the modal properties of the scatterer. The important role that eigenmodes play in defining the features of the scattering coefficients is revealed via an expansion of the coefficients by the eigenmodes. The results show the local extrema of the scattering coefficients can be attributed to the constructive/destructive interference of resonant and non-resonant modes. In particular, an approximated equation, which is equivalent to the standard Fano formula, is obtained to describe the sharp anti-symmetric Fano characteristics of the scattering coefficients. The special cases where sca...
Modal analysis and SHM investigation of CX-100 wind turbine blade
Energy Technology Data Exchange (ETDEWEB)
Deines, Krystal E [Los Alamos National Laboratory; Marinone, Timothy [Los Alamos National Laboratory; Schultz, Ryan A [Los Alamos National Laboratory; Farinholt, Kevin R [Los Alamos National Laboratory; Park, Gyuhae [Los Alamos National Laboratory
2010-11-08
This paper presents the dynamic characterization of a CX-100 wind turbine blade using modal testing. Obtaining a thorough dynamic characterization of turbine blades is important because they are complex structures, making them very difficult to accurately model without supplementing with experimental data. The results of this dynamic characterization can be used to validate a numerical model and understand the effect of structural damage on the performance of the blades. Also covered is an exploration into Structural Health Monitoring (SHM) techniques employed on the blade surface to detect changes in the blade dynamic properties. SHM design parameters such as traveling distance of the wave were examined . Results obtained during modal and SHM testing will provide a baseline for future work in blade damage detection and mitigation.
Energy Technology Data Exchange (ETDEWEB)
Mohd, Shukri [Nondestructive Testing Group, Industrial Technology Division, Malaysian Nuclear Agency, 43000, Bangi, Selangor (Malaysia); Holford, Karen M.; Pullin, Rhys [Cardiff School of Engineering, Cardiff University, Queen' s Buildings, The Parade, CARDIFF CF24 3AA (United Kingdom)
2014-02-12
Source location is an important feature of acoustic emission (AE) damage monitoring in nuclear piping. The ability to accurately locate sources can assist in source characterisation and early warning of failure. This paper describe the development of a novelAE source location technique termed 'Wavelet Transform analysis and Modal Location (WTML)' based on Lamb wave theory and time-frequency analysis that can be used for global monitoring of plate like steel structures. Source location was performed on a steel pipe of 1500 mm long and 220 mm outer diameter with nominal thickness of 5 mm under a planar location test setup using H-N sources. The accuracy of the new technique was compared with other AE source location methods such as the time of arrival (TOA) techniqueand DeltaTlocation. Theresults of the study show that the WTML method produces more accurate location resultscompared with TOA and triple point filtering location methods. The accuracy of the WTML approach is comparable with the deltaT location method but requires no initial acoustic calibration of the structure.
Mobile, Multi-modal, Label-Free Imaging Probe Analysis of Choroidal Oximetry and Retinal Hypoxia
2016-10-01
regions in injured eyes 4) Measure TRPM7 and cellular/apoptosis biomarkers in retinas 5) Measure neuronal death and cell-specific biomarker in retinas...modal label-free imaging system and calibrating our system to measure blood oxygen levels in the eye . The reported problems with our coherent anti...now ready to test human hemoglobin with our CARS system. 3) Detect and map hypoxic regions in injured eyes In Quarter 1-2: We optimized our
Optimal sensor placement for multi-setup modal analysis of structures
Zhang, Jie; Maes, Kristof; De Roeck, Guido; Reynders, Edwin; Papadimitriou, Costas; Lombaert, Geert
2017-08-01
Modal tests on large structures are often performed in multiple setups for practical reasons. Several sensors are kept fixed as reference sensors over all setups, while the other, so called roving sensors, are moved from one setup to another. This paper develops an optimal sensor placement strategy for multi-setup modal identification, which simultaneously optimizes the locations of the reference sensors and roving sensors. As an optimality criterion, the Information Entropy is adopted, which is a scalar measure of uncertainty in the Bayesian framework. The focus in the application goes to repetitive structures where modes typically occur in clusters, with closely spaced natural frequencies and similar wavelengths. The proposed strategy is illustrated for selecting optimal positions of uni-axial sensors for a repetitive frame structure. The influence of the number of reference sensors and two strategies for positioning roving sensors, i.e. a cluster and a uniform distribution of roving sensors, are investigated. The number of reference sensors is found to be preferably equal to or larger than the number of modes to be identified. In this case, the information content, as quantified by the Information Entropy, is not very sensitive to the roving sensor strategy. If less reference sensors are used, it is highly preferred to distribute the roving sensors uniformly over the structure instead of clustering them. The proposed strategy has been validated by an experimental modal test on a floor of an office building of KU Leuven, which has a nearly repetitive structural layout. The results show how optimally locating sensors allows extracting more information from the data. Though the focus is on applications involving repetitive structures, the proposed strategy can be applied to multi-setup modal identification of any large structure.
Numerical and experimental modal analysis of the reed and pipe of a clarinet
Facchinetti, Matteo L.; Boutillon, Xavier; Constantinescu, Andrei
2003-05-01
A modal computation of a complete clarinet is presented by the association of finite-element models of the reed and of part of the pipe with a lumped-element model of the rest of the pipe. In the first part, we compare modal computations of the reed and the air inside the mouthpiece and barrel with measurements performed by holographic interferometry. In the second part, the complete clarinet is modeled by adjoining a series of lumped elements for the remaining part of the pipe. The parameters of the lumped-resonator model are determined from acoustic impedance measurements. Computed eigenmodes of the whole system show that modal patterns of the reed differ significantly whether it is alone or coupled to air. Some modes exhibit mostly reed motion and a small contribution of the acoustic pressure inside the pipe. Resonance frequencies measured on a clarinet with the mouthpiece replaced by the cylinder of equal volume differ significantly from the computed eigenfrequencies of the clarinet taking the actual shape of the mouthpiece into account and from those including the (linear) dynamics of the reed. This suggests revisiting the customary quality index based on the alignment of the peaks of the input acoustical impedance curve.
On Modal Refinement and Consistency
DEFF Research Database (Denmark)
Nyman, Ulrik; Larsen, Kim Guldstrand; Wasowski, Andrzej
2007-01-01
Almost 20 years after the original conception, we revisit several fundamental question about modal transition systems. First, we demonstrate the incompleteness of the standard modal refinement using a counterexample due to Hüttel. Deciding any refinement, complete with respect to the standard...... notions of implementation, is shown to be computationally hard (co-NP hard). Second, we consider four forms of consistency (existence of implementations) for modal specifications. We characterize each operationally, giving algorithms for deciding, and for synthesizing implementations, together...
Analysis and Synthesis of Delta Operator Systems
Yang, Hongjiu; Shi, Peng; Zhao, Ling
2012-01-01
This book is devoted to analysis and design on delta operator systems. When sampling is fast, a dynamical system will become difficult to control, which can be seen in wide real world applications. Delta operator approach is very effective to deal with fast sampling systems. Moreover, it is easy to observe and analyze the control effect with different sampling periods in delta operator systems. The framework of this book has been carefully constructed for delta operator systems to handle sliding mode control, time delays, filter design, finite frequency and networked control. These problems indeed are especially important and significant in automation and control systems design. Through the clear framework of the book, readers can easily go through the learning process on delta operator systems via a precise and comfortable learning sequence. Following this enjoyable trail, readers will come out knowing how to use delta operator approach to deal with control problems under fast sampling case. This book should...
Noncommutative analysis, operator theory and applications
Cipriani, Fabio; Colombo, Fabrizio; Guido, Daniele; Sabadini, Irene; Sauvageot, Jean-Luc
2016-01-01
This book illustrates several aspects of the current research activity in operator theory, operator algebras and applications in various areas of mathematics and mathematical physics. It is addressed to specialists but also to graduate students in several fields including global analysis, Schur analysis, complex analysis, C*-algebras, noncommutative geometry, operator algebras, operator theory and their applications. Contributors: F. Arici, S. Bernstein, V. Bolotnikov, J. Bourgain, P. Cerejeiras, F. Cipriani, F. Colombo, F. D'Andrea, G. Dell'Antonio, M. Elin, U. Franz, D. Guido, T. Isola, A. Kula, L.E. Labuschagne, G. Landi, W.A. Majewski, I. Sabadini, J.-L. Sauvageot, D. Shoikhet, A. Skalski, H. de Snoo, D. C. Struppa, N. Vieira, D.V. Voiculescu, and H. Woracek.
英语情态动词的语用释解%Pragmatic Analysis of English Modal Verb
Institute of Scientific and Technical Information of China (English)
漆舒琴; 诸惜时
2012-01-01
情态动词的使用不仅使话语变得更委婉、礼貌，而且能达到交际目的的成功实现。运用Austin和Searle的言语行为理论对英语情态动词的语用特征进行初步的分析，可以加深对情态动词的理解和使用，提高语言使用的正确性，达到实际的交际意图。%The use of modal verb can not only make the utterance more euphemistic and polite, but also achieve the communicative goal successfully. By using the speech act theory of Austin and Searle to give a preliminary analysis of modal verb's pragmatic features, we can deepen our understanding and use of modal verb, improve the correctness of language use and reach the communicative intention.
Hu, Sau-Lon James; Yang, Wen-Long; Liu, Fu-Shun; Li, Hua-Jun
2014-12-01
All time-domain methods for experimental modal analysis (EMA) begin with a mathematical model. Based on either a high-order matrix polynomial model or a first-order state-space model, this paper emphasizes the comparison of numerical conditioning and stability, as well as the modal parameter estimation, among EMA methods. Numerical conditioning pertains to the perturbation behavior of a mathematical problem (model) itself and stability pertains to the perturbation behavior of an algorithm used to solve that problem on a computer. As various EMA methods are modeled differently with distinct solution algorithms, implementing these methods would have different conditioning and stability. In this paper, both deterministic and stochastic EMA methods are covered. Three different scenarios for the response signal are considered: (1) clean response from impulse loading, (2) noisy response from impulse loading, and (3) noisy response from ambient noise excitation. Comparing the numerical conditioning of various EMA methods, this paper theoretically illustrates that methods based on first-order state-space models are more likely to be well-conditioned (with a smaller conditioning number) than those based on high-order polynomial models. Furthermore, the numerical observation of a case study for a 6 degree-of-freedom system also suggests that first-order state-space model methods are more robust and accurate for the estimation of modal frequency and damping.
Constraint methods for modal satisfiability
Brand, S.; Gennari, R.; de Rijke, M.; Apt, K.R.; Fages, F.; Rossi, F.
2004-01-01
Modal and modal-like formalisms such as temporal or description logics go beyond propositional logic by introducing operators that allow for a guarded form of quantication over states or paths of transition systems. Thus, they are more expressive than propositional logic, yet computationally better
Yang, Y.; Sciacchitano, A.; Veldhuis, L. L. M.; Eitelberg, G.
2016-10-01
During the ground operation of aircraft, there is potentially a system of vortices generated from the ground toward the propulsor, commonly denoted as ground vortices. Although extensive research has been conducted on ground vortices induced by turbofans which were simplified by suction tubes, these studies cannot well capture the properties of ground vortices induced by propellers, e.g., the flow phenomena due to intermittent characteristics of blade passing and the presence of slipstream of the propeller. Therefore, the investigation of ground vortices induced by a propeller is performed to improve understanding of these phenomena. The distributions of velocities in two different planes containing the vortices were measured by high frequency Particle Image Velocimetry. These planes are a wall-parallel plane in close proximity to the ground and a wall-normal plane upstream of the propeller. The instantaneous flow fields feature highly unsteady flow in both of these two planes. The spectral analysis is conducted in these two flow fields and the energetic frequencies are quantified. The flow fields are further evaluated by applying the Proper Orthogonal Decomposition analysis to capture the coherent flow structures. Consistent flow structures with strong contributions to the turbulent kinetic energy are noticed in the two planes.
Institute of Scientific and Technical Information of China (English)
2013-01-01
Halliday categorizes modal operators as three values, the low, the middle and the high, and with the usage of Modal operators, different modal meanings will be expressed, and dif-ferent roles of the spokesperson will be represented. This paper studies the values of modal operators in the Whitehouse press briefing discourses which are used by the spokespersons, and tries to discover how the spokesperson functions in the establish-ing of relationship between the government and the public, by analyzing the appearance of modal operators in the discourses.% 韩礼德把情态动词分为三个量值，低值、中值和高值，使用不同量值情态动词可以表达不同的情态意义，表现出说话者的角色定位。本文研究了白宫新闻发布会语篇中发言人所使用的情态动词的量值，通过分析不同量值的情态动词在语篇中出现的频率，由此揭示出在新闻发布会中，发言人是如何运用情态动词来发挥不同作用的。
Uncertainty analysis of strain modal parameters by Bayesian method using frequency response function
Institute of Scientific and Technical Information of China (English)
Xu Li; Yi Weijian; Zhihua Yi
2007-01-01
Structural strain modes are able to detect changes in local structural performance, but errors are inevitably intermixed in the measured data. In this paper, strain modal parameters are considered as random variables, and their uncertainty is analyzed by a Bayesian method based on the structural frequency response function (FRF). The estimates of strain modal parameters with maximal posterior probability are determined. Several independent measurements of the FRF of a four-story reinforced concrete frame structural model were performed in the laboratory. The ability to identify the stiffness change in a concrete column using the strain mode was verified. It is shown that the uncertainty of the natural frequency is very small. Compared with the displacement mode shape, the variations of strain mode shapes at each point are quite different. The damping ratios are more affected by the types of test systems. Except for the case where a high order strain mode does not identify local damage, the first order strain mode can provide an exact indication of the damage location.
Model Design of Piezoelectric Micromachined Modal Gyroscope
Directory of Open Access Journals (Sweden)
Xiaojun Hu
2011-01-01
Full Text Available This paper reports a novel kind of solid-state microgyroscope, which is called piezoelectric micromachined modal gyroscope (PMMG. PMMG has large stiffness and robust resistance to shake and strike because there is no evident mass-spring component in its structure. This work focused on quantitative optimization of the gyroscope, which is still blank for such gyroscope. The modal analysis by the finite element method (FEM was firstly conducted. A set of quantitative indicators were developed to optimize the operation mode. By FEM, the harmonic analysis was conducted to find the way to efficiently actuate the operational mode needed. The optimal configuration of driving electrodes was obtained. At last, the Coriolis analysis was conducted to show the relation between angular velocity and differential output voltage by the Coriolis force under working condition. The results obtained in this paper provide theoretical basis for realizing this novel kind of micromachined gyroscope.
Human reliability analysis of control room operators
Energy Technology Data Exchange (ETDEWEB)
Santos, Isaac J.A.L.; Carvalho, Paulo Victor R.; Grecco, Claudio H.S. [Instituto de Engenharia Nuclear (IEN), Rio de Janeiro, RJ (Brazil)
2005-07-01
Human reliability is the probability that a person correctly performs some system required action in a required time period and performs no extraneous action that can degrade the system Human reliability analysis (HRA) is the analysis, prediction and evaluation of work-oriented human performance using some indices as human error likelihood and probability of task accomplishment. Significant progress has been made in the HRA field during the last years, mainly in nuclear area. Some first-generation HRA methods were developed, as THERP (Technique for human error rate prediction). Now, an array of called second-generation methods are emerging as alternatives, for instance ATHEANA (A Technique for human event analysis). The ergonomics approach has as tool the ergonomic work analysis. It focus on the study of operator's activities in physical and mental form, considering at the same time the observed characteristics of operator and the elements of the work environment as they are presented to and perceived by the operators. The aim of this paper is to propose a methodology to analyze the human reliability of the operators of industrial plant control room, using a framework that includes the approach used by ATHEANA, THERP and the work ergonomics analysis. (author)
Energy Technology Data Exchange (ETDEWEB)
Martinez-Ponce, G.; Solano, Cristina [Centro de Investigaciones en Optica A.C, Guanajuato (Mexico)
2001-02-01
The propagation of a plane electromagnetic wave through a grating using the modal theory is analyzed. The eigenproblem is solved in function of the ratio illumination wavelength {lambda} to grating period (d). When this ratio is much greater than one (quasiestatic limit), the grating shows a response similar to an uniaxial film. It is possible to approximate the eigenfunction for calculating the effective refractive indices of the birefringent element. This effect is called form birefringence and can be used to design retardation plates. [Spanish] En este trabajo se analiza la propagacion de una onda electromagnetica plana a traves de una rejilla utilizando la teoria modal. Estableciendo el problema de valor caracteristico se determina que la solucion es dependiente de la razon longitud de onda de iluminacion {lambda} y el periodo de la rejilla (d). En el caso {lambda}/d mayor que 1, conocido como el limite cuasiestatico, la rejilla se comporta como una pelicula uniaxial, obteniendose los indices ordinario y extraordinario a partir de una aproximacion a la ecuacion caracteristica. Este fenomeno, llamado birrefringencia de forma, puede emplearse para disenar elementos birrefringentes.
Modal Identification Using OMA Techniques: Nonlinearity Effect
Directory of Open Access Journals (Sweden)
E. Zhang
2015-01-01
Full Text Available This paper is focused on an assessment of the state of the art of operational modal analysis (OMA methodologies in estimating modal parameters from output responses of nonlinear structures. By means of the Volterra series, the nonlinear structure excited by random excitation is modeled as best linear approximation plus a term representing nonlinear distortions. As the nonlinear distortions are of stochastic nature and thus indistinguishable from the measurement noise, a protocol based on the use of the random phase multisine is proposed to reveal the accuracy and robustness of the linear OMA technique in the presence of the system nonlinearity. Several frequency- and time-domain based OMA techniques are examined for the modal identification of simulated and real nonlinear mechanical systems. Theoretical analyses are also provided to understand how the system nonlinearity degrades the performance of the OMA algorithms.
Staffing for Cyberspace Operations: Summary of Analysis
2016-08-01
information , including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services , Directorate for Information Operations...Analysis and Integration , Office of the Secretary of Defense Cost Assessment and Program Evaluation; and the Director, Acquisition Resources and...findings and recommendations of a full-length report containing classified information .1 It is meant to make the key elements of the analysis accessible
Design and analysis of annulus core few mode EDFA for modal gain equalization
Gaur, Ankita
2016-01-01
Few-mode fiber amplifier is widely under study to overcome the issue of internet traffic in optical communication. This article proposes annulus core few-mode erbium doped fiber (FM-EDF) with annulus or extra annulus doping for amplification of the LP01, LP11, LP21, and LP31 signal mode groups with low differential modal gain (DMG). Our simulations confirm that extra annulus doping helps in reducing DMG of higher order mode groups. We have achieved less than 2.2 dB DMG over C-band for 4-mode groups using extra annulus doping. The proposed EDF would be useful for space division multiplexing (SDM) based optical fiber communication system.
Design and Analysis of Annulus Core Few Mode EDFA for Modal Gain Equalization
Gaur, Ankita; Rastogi, Vipul
2016-05-01
Few-mode fiber amplifier is widely under study to overcome the issue of internet traffic in optical communication. This article proposes annulus core few-mode erbium doped fiber (FM-EDF) with annulus or extra annulus doping for amplification of the LP01, LP11, LP21, and LP31 signal mode groups with low differential modal gain (DMG). Our simulations confirm that extra annulus doping helps in reducing DMG of higher order mode groups. We have achieved less than 2.2 dB DMG over C-band for 4-mode groups using extra annulus doping. The proposed EDF would be useful for space division multiplexing (SDM) based optical fiber communication system.
Direct method for second-order sensitivity analysis of modal assurance criterion
Lei, Sheng; Mao, Kuanmin; Li, Li; Xiao, Weiwei; Li, Bin
2016-08-01
A Lagrange direct method is proposed to calculate the second-order sensitivity of modal assurance criterion (MAC) values of undamped systems. The eigenvalue problem and normalizations of eigenvectors, which augmented by using some Lagrange multipliers, are used as the constraints of the Lagrange functional. Once the Lagrange multipliers are determined, the sensitivities of MAC values can be evaluated directly. The Lagrange direct method is accurate, efficient and easy to implement. A simply supported beam is utilized to check the accuracy of the proposed method. A frame is adopted to validate the predicting capacity of the first- and second-order sensitivities of MAC values. It is shown that the computational costs of the proposed method can be remarkably reduced in comparison with those of the indirect method without loss of accuracy.
River bedform inception by flow unsteadiness: A modal and nonmodal analysis
Caruso, Alice; Vesipa, Riccardo; Camporeale, Carlo; Ridolfi, Luca; Schmid, Peter J.
2016-05-01
River bedforms arise as a result of morphological instabilities of the stream-sediment interface. Dunes and antidunes constitute the most typical patterns, and their occurrence and dynamics are relevant for a number of engineering and environmental applications. Although flow variability is a typical feature of all rivers, the bedform-triggering morphological instabilities have generally been studied under the assumption of a constant flow rate. In order to partially address this shortcoming, we here discuss the influence of (periodic) flow unsteadiness on bedform inception. To this end, our recent one-dimensional validated model coupling Dressler's equations with a refined mechanistic sediment transport formulation is adopted, and both the asymptotic and transient dynamics are investigated by modal and nonmodal analyses.
Multi-Source Learning for Joint Analysis of Incomplete Multi-Modality Neuroimaging Data.
Yuan, Lei; Wang, Yalin; Thompson, Paul M; Narayan, Vaibhav A; Ye, Jieping
2012-01-01
Incomplete data present serious problems when integrating largescale brain imaging data sets from different imaging modalities. In the Alzheimer's Disease Neuroimaging Initiative (ADNI), for example, over half of the subjects lack cerebrospinal fluid (CSF) measurements; an independent half of the subjects do not have fluorodeoxyglucose positron emission tomography (FDG-PET) scans; many lack proteomics measurements. Traditionally, subjects with missing measures are discarded, resulting in a severe loss of available information. We address this problem by proposing two novel learning methods where all the samples (with at least one available data source) can be used. In the first method, we divide our samples according to the availability of data sources, and we learn shared sets of features with state-of-the-art sparse learning methods. Our second method learns a base classifier for each data source independently, based on which we represent each source using a single column of prediction scores; we then estimate the missing prediction scores, which, combined with the existing prediction scores, are used to build a multi-source fusion model. To illustrate the proposed approaches, we classify patients from the ADNI study into groups with Alzheimer's disease (AD), mild cognitive impairment (MCI) and normal controls, based on the multi-modality data. At baseline, ADNI's 780 participants (172 AD, 397 MCI, 211 Normal), have at least one of four data types: magnetic resonance imaging (MRI), FDG-PET, CSF and proteomics. These data are used to test our algorithms. Comprehensive experiments show that our proposed methods yield stable and promising results.
Framework for the analysis of crystallization operations
DEFF Research Database (Denmark)
Meisler, Kresten Troelstrup; Abdul Samad, Noor Asma Fazli Bin; Gernaey, Krist
Crystallization is often applied in the production of salts and/oractive pharmaceutical ingredients (API), and the crystallization step is an essential part of the manufacturing process for many chemicals-based products.In recent years the monitoring and analysis of crystallization operations has...
Feedback analysis of transimpedance operational amplifier circuits
DEFF Research Database (Denmark)
Bruun, Erik
1993-01-01
The transimpedance or current feedback operational amplifier (CFB op-amp) is reviewed and compared to a conventional voltage mode op-amp using an analysis emphasizing the basic feedback characteristics of the circuit. With this approach the paradox of the constant bandwidth obtained from CFB op...
Army Information Operations Officer Needs Analysis Report
2016-03-01
helping with formatting the final report iv ARMY INFORMATION OPERATIONS OFFICER NEEDS ANALYSIS REPORT EXECUTIVE SUMMARY Research...time.” One IO officer suggested the IPO try to get a access the database that has all the old APA reports archived as a way to look at assessment
Mohammadi-Nejad, Ali-Reza; Hossein-Zadeh, Gholam-Ali; Soltanian-Zadeh, Hamid
2017-07-01
Multi-modal data fusion has recently emerged as a comprehensive neuroimaging analysis approach, which usually uses canonical correlation analysis (CCA). However, the current CCA-based fusion approaches face problems like high-dimensionality, multi-collinearity, unimodal feature selection, asymmetry, and loss of spatial information in reshaping the imaging data into vectors. This paper proposes a structured and sparse CCA (ssCCA) technique as a novel CCA method to overcome the above problems. To investigate the performance of the proposed algorithm, we have compared three data fusion techniques: standard CCA, regularized CCA, and ssCCA, and evaluated their ability to detect multi-modal data associations. We have used simulations to compare the performance of these approaches and probe the effects of non-negativity constraint, the dimensionality of features, sample size, and noise power. The results demonstrate that ssCCA outperforms the existing standard and regularized CCA-based fusion approaches. We have also applied the methods to real functional magnetic resonance imaging (fMRI) and structural MRI data of Alzheimer's disease (AD) patients (n = 34) and healthy control (HC) subjects (n = 42) from the ADNI database. The results illustrate that the proposed unsupervised technique differentiates the transition pattern between the subject-course of AD patients and HC subjects with a p-value of less than 1×10(-6) . Furthermore, we have depicted the brain mapping of functional areas that are most correlated with the anatomical changes in AD patients relative to HC subjects.
Koška, Pavel; Doya, Valérie; Peterka, Pavel
2017-03-01
High-power fiber lasers became important devices in many industrial and health care fields. The key for high-power operation of fiber lasers is the double-clad fiber technology transforming lower-brightness pumps into high-brightness laser beams. Efficient pump absorption in the active core of the double-clad fiber is crucial for reliable and economic operation of high power fiber lasers. In our recent work we extensively studied the dependence of the pump absorption efficiency on bending and twisting of the fiber. For the first time we theoretically predicted and later experimentally demonstrated significant enhancement of pump absorption efficiency by simultaneous bending and twisting of the double-clad fiber. In this contribution we provide extension of our previous theoretical studies using beam propagation model incorporating laser rate equations. The effect of bending and twisting on signal amplification in the double-clad fiber is analyzed for different input signal powers, and moreover, pump field modal spectra are evaluated. The results show that in correspondence with pump absorption efficiency the gain of the amplifier is enhanced under the conditions of simultaneously bent and twisted fiber. The key to understand the effect of bending and twisting on pump absorption efficiency consists in modal spectra of pump field propagating in the first clad of the double clad fiber. Three cases of straight, bent only, and simultaneously bent and twisted fiber are compared. The comparison shows that bending causes increase of the spectral range of propagating modes, but does not bring about mode-mixing. Substantial mode-mixing is established only in simultaneously bent and twisted fiber.
Operational amplifier circuits analysis and design
Nelson, J C C
1995-01-01
This book, a revised and updated version of the author's Basic Operational Amplifiers (Butterworths 1986), enables the non-specialist to make effective use of readily available integrated circuit operational amplifiers for a range of applications, including instrumentation, signal generation and processing.It is assumed the reader has a background in the basic techniques of circuit analysis, particularly the use of j notation for reactive circuits, with a corresponding level of mathematical ability. The underlying theory is explained with sufficient but not excessive, detail. A range of compu
Non-overlapped random decrement technique for parameter identification in operational modal analysis
Zhang, Y.; Song, H. W.
2016-03-01
The random decrement technique (RDT) is used to estimate free vibration response from output data generated by Gaussian white noise. The principle is to decay the excitation via averaging of segments in output data. With RDT, the triggering condition for determining the initial points of segments causes overlap during averaging; the consequence is a residual excitation, peaking at the first natural frequency. This paper presents a modified RDT with non-overlapped segments to eliminate this peak. Numerical comparison between non-overlapped RDT (NRDT) and RDT shows the accuracy improvement of damping. However, time history data is sometimes not long enough in NRDT, which results in an inevitable overlap. In order to keep the accuracy of NRDT, the first natural period is viewed as the critical length between adjacent initial points to distinguish the inevitable overlap from that in RDT.
Operational modal analysis of a tyre using a PU probe based scanning technique
Tijs, E.; Makwana, B.K.; Peksel, O.; Amarnath, S.K.P.; Bekke, D.A.; Dr. K.S. Krishnan,
2013-01-01
Tyre vibration can be studied with several experimental and simulation techniques. An important goal for a tyre manufacturer is to “tune” the resonant frequency of the tyre subsystem to reduce the structure-borne noise in the car interior. In this paper, a novel measurement technique is applied to d
Institute of Scientific and Technical Information of China (English)
董霄峰; 练继建; 杨敏; 王海军
2015-01-01
To solve the problem in identifying modal parameters accurately and retraining false modes induced by severe disruption due to the electromagnetic frequency signals,rotational frequency signals and environmental noise usually mixed in the acceleration data observed from prototype test of offshore wind turbine structure,a compound de-noising method,combining self-adaptive filter and ensemble empirical mode decomposition,was put forward to achieve filtering,noise reduction and modal identification for the first time. By means of testing signal processing in the new way including filtering,decomposing,de-noising and refactoring,much noise interference was reduced and full information of the structural vibration was reserved. Then the modal information will be identified preliminar-ily using both random decrement technique and eigensystem realization algorithm,and the false modes were elimi-nated by vibration mode analysis in order to obtain the operation modal parameters of offshore wind power structure correctly. Besides,the method presented here not only shows better accuracy and higher efficiency in noise reduction compared to the classic approaches which are lack of the statistical characteristics of noise,but also provides opera-tional modal identification of wind turbine structure with a preferable applied value in engineering based on measured signals.%海上风机结构现场原型观测所获取的振动加速度信号中，往往混有大量的电磁工频、机组转频及环境噪声等成分，这些干扰信号处理不当易导致模态识别失真与产生虚假模态等问题。针对这一问题提出了基于自适应滤波与集成经验模态分解(EEMD)法的组合降噪方法。通过对测试信号采取滤波、分解、降噪及重组等过程可以更有效地降低各种噪声干扰，以完整地保留结构自身的振动信息；再利用随机减量法(RDT)和特征系统实现法(ERA)完成模态信息的初步识别，并结合振型
Feng, Sheng; Lotz, Thomas; Chase, J Geoffrey; Hann, Christopher E
2010-01-01
Digital Image Elasto Tomography (DIET) is a non-invasive elastographic breast cancer screening technology, based on image-based measurement of surface vibrations induced on a breast by mechanical actuation. Knowledge of frequency response characteristics of a breast prior to imaging is critical to maximize the imaging signal and diagnostic capability of the system. A feasibility analysis for a non-invasive image based modal analysis system is presented that is able to robustly and rapidly identify resonant frequencies in soft tissue. Three images per oscillation cycle are enough to capture the behavior at a given frequency. Thus, a sweep over critical frequency ranges can be performed prior to imaging to determine critical imaging settings of the DIET system to optimize its tumor detection performance.
Load Estimation from Modal Parameters
DEFF Research Database (Denmark)
Aenlle, Manuel López; Brincker, Rune; Fernández, Pelayo Fernández;
2007-01-01
In Natural Input Modal Analysis the modal parameters are estimated just from the responses while the loading is not recorded. However, engineers are sometimes interested in knowing some features of the loading acting on a structure. In this paper, a procedure to determine the loading from a FRF...... matrix assembled from modal parameters and the experimental responses recorded using standard sensors, is presented. The method implies the inversion of the FRF which, in general, is not full rank matrix due to the truncation of the modal space. Furthermore, some ecommendations are included to improve...
Analysis of Predictive Values Based on Individual Risk Factors in Multi-Modality Trials
Directory of Open Access Journals (Sweden)
Katharina Lange
2013-03-01
Full Text Available The accuracy of diagnostic tests with binary end-points is most frequently measured by sensitivity and specificity. However, from the clinical perspective, the main purpose of a diagnostic agent is to assess the probability of a patient actually being diseased and hence predictive values are more suitable here. As predictive values depend on the pre-test probability of disease, we provide a method to take risk factors influencing the patient’s prior probability of disease into account, when calculating predictive values. Furthermore, approaches to assess confidence intervals and a methodology to compare predictive values by statistical tests are presented. Hereby the methods can be used to analyze predictive values of factorial diagnostic trials, such as multi-modality, multi-reader-trials. We further performed a simulation study assessing length and coverage probability for different types of confidence intervals, and we present the R-Package facROC that can be used to analyze predictive values in factorial diagnostic trials in particular. The methods are applied to a study evaluating CT-angiography as a noninvasive alternative to coronary angiography for diagnosing coronary artery disease. Hereby the patients’ symptoms are considered as risk factors influencing the respective predictive values.
Dynamic modeling and characteristics analysis of a modal-independent linear ultrasonic motor.
Li, Xiang; Yao, Zhiyuan; Zhou, Shengli; Lv, Qibao; Liu, Zhen
2016-12-01
In this paper, an integrated model is developed to analyze the fundamental characteristics of a modal-independent linear ultrasonic motor with double piezoelectric vibrators. The energy method is used to model the dynamics of the two piezoelectric vibrators. The interface forces are coupled into the dynamic equations of the two vibrators and the moving platform, forming a whole machine model of the motor. The behavior of the force transmission of the motor is analyzed via the resulting model to understand the drive mechanism. In particular, the relative contact length is proposed to describe the intermittent contact characteristic between the stator and the mover, and its role in evaluating motor performance is discussed. The relations between the output speed and various inputs to the motor and the start-stop transients of the motor are analyzed by numerical simulations, which are validated by experiments. Furthermore, the dead-zone behavior is predicted and clarified analytically using the proposed model, which is also observed in experiments. These results are useful for designing servo control scheme for the motor.
Analysis of Predictive Values Based on Individual Risk Factors in Multi-Modality Trials.
Lange, Katharina; Brunner, Edgar
2013-03-15
The accuracy of diagnostic tests with binary end-points is most frequently measured by sensitivity and specificity. However, from the clinical perspective, the main purpose of a diagnostic agent is to assess the probability of a patient actually being diseased and hence predictive values are more suitable here. As predictive values depend on the pre-test probability of disease, we provide a method to take risk factors influencing the patient's prior probability of disease into account, when calculating predictive values. Furthermore, approaches to assess confidence intervals and a methodology to compare predictive values by statistical tests are presented. Hereby the methods can be used to analyze predictive values of factorial diagnostic trials, such as multi-modality, multi-reader-trials. We further performed a simulation study assessing length and coverage probability for different types of confidence intervals, and we present the R-Package facROC that can be used to analyze predictive values in factorial diagnostic trials in particular. The methods are applied to a study evaluating CT-angiography as a noninvasive alternative to coronary angiography for diagnosing coronary artery disease. Hereby the patients' symptoms are considered as risk factors influencing the respective predictive values.
A comparison methodology for measured and predicted displacement fields in modal analysis
Sebastian, C. M.; López-Alba, E.; Patterson, E. A.
2017-07-01
Recent advances in experimental mechanics have enabled full-field measurements of deformation fields and - particularly in the field of solid mechanics - methodologies have been proposed for utilizing these fields in the validation of computational models. However, the comparison of modal shapes and the path from the undeformed shape to the deformed shape at the extreme of a vibration cycle is not straightforward. Therefore a new method to compare vibration data from experiment to simulations is presented which uses full-field experimental data from the entire cycle of vibration. Here, the first three modes of vibration of an aerospace panel were compared, covering a frequency range of 14-59 Hz and maximum out-of-plane displacements of 2 mm. Two different comparison methodologies are considered; the first is the use of confidence bands, previously explored for quasi-static loading, the second is the use of a concordance correlation coefficient, which provides quantifiable information about the validity of the simulation. In addition, three different simulation conditions were considered, representing a systematic refinement of the model. It was found that meaningful conclusions can be drawn about the simulation by comparing individual components of deformation from the image decomposition process, such as the relative phase and magnitude. It was ultimately found that the best performing model did not entirely fall within the confidence bounds for all conditions, but returned a concordance correlation coefficient of nearly 70% for all three modes.
Directory of Open Access Journals (Sweden)
Shitao Tian
2016-01-01
Full Text Available Constrained layer damping treatments promise to be an effective method to control vibration in flexible structures. Cutting both the constraining layer and the viscoelastic layer, which leads to segmentation, increases the damping efficiency. However, this approach is not always effective. A parametric study was carried out using modal strain energy method to explore interaction between segmentation and design parameters, including geometry parameters and material properties. A finite element model capable of handling treatments with extremely thin viscoelastic layer was developed based on interlaminar continuous shear stress theories. Using the developed method, influence of placing cuts and change in design parameters on the shear strain field inside the viscoelastic layer was analyzed, since most design parameters act on the damping efficiency through their influence on the shear strain field. Furthermore, optimal cut arrangements were obtained by adopting a genetic algorithm. Subject to a weight limitation, symmetric and asymmetric configurations were compared. It was shown that symmetric configurations always presented higher damping. Segmentation was found to be suitable for treatments with relatively thin viscoelastic layer. Provided that optimal viscoelastic layer thickness was selected, placing cuts would only be applicable to treatments with low shear strain level inside the viscoelastic layer.
Schulz, Matthias; Chau, Wilkin; Graham, Simon J; McIntosh, Anthony R; Ross, Bernhard; Ishii, Ryouhei; Pantev, Christo
2004-05-01
We develop a novel approach of cross-modal correspondence analysis (CMCA) to address whether brain activities observed in magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) represent a common neuronal subpopulation, and if so, which frequency band obtained by MEG best fits the common brain areas. Fourteen adults were investigated by whole-head MEG using a single equivalent current dipole (ECD) and synthetic aperture magnetometry (SAM) approaches and by fMRI at 1.5 T using linear time-invariant modeling to generate statistical maps. The same somatosensory stimulus sequences consisting of tactile impulses to the right sided: digit 1, digit 4 and lower lip were used in both neuroimaging modalities. To evaluate the reproducibility of MEG and fMRI results, one subject was measured repeatedly. Despite different MEG dipole locations and locations of maximum activation in SAM and fMRI, CMCA revealed a common subpopulation of the primary somatosensory cortex, which displays a clear homuncular organization. MEG activity in the frequency range between 30 and 60 Hz, followed by the ranges of 20-30 and 60-100 Hz, explained best the defined subrepresentation given by both MEG and fMRI. These findings have important implications for improving and understanding of the biophysics underlying both neuroimaging techniques, and for determining the best strategy to combine MEG and fMRI data to study the spatiotemporal nature of brain activity.
Process Analysis of the CV Group's Operation
Wilhelmsson, M
2000-01-01
This report will give an explanation of the internal reorganization that has been done because of the necessity to optimize operation in the cooling and ventilation group. The basic structure for the group was defined at the end of 1998. We understood then that change was needed to accommodate the increased workload due to the LHC project. In addition, we face a relatively large turnover of personnel (retirements and some recruitment) with related integration issues to consider. We would also like to implement new approaches in the management of both operations and maintenance. After some running-in problems during the first half of 1999, we realized that much more could be gained with the analysis and the definition and documenting of each single function and generic activity within the group. The authors will explain how this analysis was carried out and give some feedback of the outcome, so far.
Functional analysis and the Feynman operator calculus
Gill, Tepper L
2016-01-01
This book provides the mathematical foundations for Feynman's operator calculus and for the Feynman path integral formulation of quantum mechanics as a natural extension of analysis and functional analysis to the infinite-dimensional setting. In one application, the results are used to prove the last two remaining conjectures of Freeman Dyson for quantum electrodynamics. In another application, the results are used to unify methods and weaken domain requirements for non-autonomous evolution equations. Other applications include a general theory of Lebesgue measure on Banach spaces with a Schauder basis and a new approach to the structure theory of operators on uniformly convex Banach spaces. This book is intended for advanced graduate students and researchers.
Staffing for Cyberspace Operations: Summary of Analysis
2016-08-01
Service’s current mix with the IDA alternative). The costing was performed in accordance with guidance and cost elements laid out in DoDI 7041.04.5 The...capable of carrying out cyberspace operations is currently a major force planning effort in the Department of Defense (DoD). Determining the...Analysis and Integration, Office of the Secretary of Defense Cost Assessment and Program Evaluation; and the Director, Acquisition Resources and
Peretti, L. F.; Dowell, E. H.
1992-01-01
An experiment was performed on a rigid wall rectangular acoustic cavity driven by a flexible plate mounted in a quarter of one end wall and excited by white noise. The experiment was designed so that the assumptions of Asymptotic Modal Analysis (AMA) were satisfied for certain bandwidths and center frequencies. Measurements of sound pressure levels at points along the boundaries and incrementally into tbe interior were taken. These were compared with the theoretical results predicted with AMA, and found to be in good agreement, particularly for moderate (1/3 octave) bandwidths and sufficiently high center frequencies. Sound pressure level measurements were also taken well into the cavity interior at various points along the 5 totally rigid walls. The AMA theory, including boundary intensification effects, was shown to be accurate provided the assumption of large number of acoustic modes is satisfied, and variables such as power spectra of the wall acceleration, frequency, and damping are slowly varying in the frequency of bandwidth.
Peretti, L. F.; Dowell, E. H.
1992-10-01
An experiment was performed on a rigid wall rectangular acoustic cavity driven by a flexible plate mounted in a quarter of one end wall and excited by white noise. The experiment was designed so that the assumptions of Asymptotic Modal Analysis (AMA) were satisfied for certain bandwidths and center frequencies. Measurements of sound pressure levels at points along the boundaries and incrementally into tbe interior were taken. These were compared with the theoretical results predicted with AMA, and found to be in good agreement, particularly for moderate (1/3 octave) bandwidths and sufficiently high center frequencies. Sound pressure level measurements were also taken well into the cavity interior at various points along the 5 totally rigid walls. The AMA theory, including boundary intensification effects, was shown to be accurate provided the assumption of large number of acoustic modes is satisfied, and variables such as power spectra of the wall acceleration, frequency, and damping are slowly varying in the frequency of bandwidth.
Operational morbidity analysis of soft tissue injuries during Operation TELIC.
Ollerton, J; Hodgetts, T; Russell, R
2007-12-01
Soft tissue injury accounted for one in five of all presentations to the Emergency Department (ED) during Operation TELIC (UK forces in Iraq) from March 2003 to November 2006. This ranks soft tissue complaints as the most frequent cause of attendance to a deployed field hospital ED. This paper analyses the injury patterns, together with implications for future clinical practice and operational planning to prevent injury, optimise patient care and maximize force regeneration.
Analysis of Operational Risks in Shipbuilding Industry
Directory of Open Access Journals (Sweden)
Daniela MATEI
2012-11-01
Full Text Available Our paper emphasizes the opportunities provided both for the academic research and companies by using a proposed model of analyzing the operational risks within business in general and shipbuilding industry in particular. The model aims to display the loss distribution from the operational risk for each business line/ type of event, based on frequency and severity estimation of the events. These estimations are derived mainly from the history logs of internal loss events. The calculations extend over a certain period of time in the future with a certain level of confidence. It should also be mentioned that the proposed model estimates unexpected losses, without making any suppositions concerning the values of the expected and unexpected losses. Several ideas could be extracted by analyzing and synthesizing the theoretical models from available literature. These ideas were analyzed in order to develop a model for operational risk analysis that is adapted to shipbuilding. This paper describes a new model, which can be applied to the naval industry to quantify operational risks.
大学英语课堂中PPT课件的多模态性研究%Multi -modal Analysis of Power Point in the College English Class
Institute of Scientific and Technical Information of China (English)
王馨
2012-01-01
以系统功能语言学为基础的多模态理论是语言学家在长期的外语研究中创立的全新理念，图像、颜色和动作等非语言形式在多模态理论的发展中得到重新认可和重视。PPT课件通过声音、图像、文字、动画等非语言形式成为高校英语重要的多媒体教学手段。本文通过视觉模态、听觉模态和视听模态分析了PPT课件在大学英语课堂中的多模态应用。%Based on the system functional linguistics multi modal is a new concept created by the lin guist in the long term of the foreign language analysis. Nonlinguistic such as pictures, colors and animations gain attention and recognition again with the development of multi modal. PPT becomes an important multi media tool by means of sound, picture, word and animation in English teaching. The paper analyzes the appli cation of PPT in multi modal through the visual modal, acoustical modal and audio visual modal in the col lege English class.
Analysis of economic impact between the modality of renal replacement therapy.
Gouveia, Denise Sbrissia E Silva; Bignelli, Alexandre Tortoza; Hokazono, Silvia Regina; Danucalov, Itamara; Siemens, Tobias August; Meyer, Fernando; Santos, Luiz Sergio; Martins, Ziliane Caetano Lopes; Mierzwa, Tiago César; Furquim, Raquel
2017-04-27
Chronic kidney disease (CKD) is a major health problem, determining the reduction in life expectancy and an increased risk of cardiovascular disease. An observational, cohort, retrospective, based on patient's medical records data with CKD under hemodialysis, peritoneal dialysis and kidney transplantation in the city of Curitiba, in the period from January to June 2014, evacuativo the financial impact on the Unified Health System (SUS) and the supplementary health. The lowest cost of a kidney transplant in the first year was R$ 40,743.03 when cyclosporine was used and the highest was R$ 48,388.17 with the use of tacrolimus. In the second year post-transplant, hemodialysis and peritoneal dialysis have a higher cost compared to kidney transplant. Transplantation with deceased donor, treated with tacrolimus: R$ 67,023.39; Hemodialysis R$ 71,717.51 and automated peritoneal dialysis automatic R$ 69,527.03. After the first two years of renal replacement therapy, transplantation demonstrates lower costs to the system when compared to other modalities evaluated. Based on that, this therapy justifies improvements in government policies in this sector. A doença renal crônica (DRC) é um grande problema de saúde, determina redução na expectativa de vida e aumento dos riscos de doenças cardiovasculares. Estudo observacional, de coorte, retrospectivo, baseado em dados de prontuários de pacientes com DRC em hemodiálise, diálise peritoneal e transplante renal na cidade de Curitiba, no período de janeiro a junho de 2014, avaliando o impacto financeiro no Sistema Único de Saúde (SUS) e na saúde suplementar. O menor custo de um transplante renal no primeiro ano foi de R$ 40.743,03, quando utilizada a ciclosporina, e o maior de R$ 48.388,17, com a utilização do tacrolimo. Já no segundo ano pós-transplante, a hemodiálise e a diálise peritoneal têm valor superior ao transplante renal. Transplante com doador falecido, com tacrolimo: R$ 67.023,39; hemodiálise R$ 71
Energy Technology Data Exchange (ETDEWEB)
Sun, Yu.; Wei, Wei; Yang, Hua-Wei; Liu, Jian-Lun [Affiliated Cancer Hospital of Guangxi Medical University, Department of Breast Surgery of Guangxi Cancer Hospital, Nanning, Guangxi (China)
2013-03-15
The purpose of this study was to assess the diagnostic performance of breast-specific gamma imaging (BSGI) as an adjunct modality to mammography for detecting breast cancer. Comprehensive searches of MEDLINE (1984 to August 2012) and EMBASE (1994 to August 2012) were performed. A summary receiver operating characteristic curve (SROC) was constructed to summarize the overall test performance of BSGI. The sensitivities for detecting subcentimetre cancer and ductal carcinoma in situ (DCIS) were pooled. The potential of BSGI to complement mammography was also evaluated by identifying mammography-occult breast cancer. Analysis of the studies revealed that the overall validity estimates of BSGI in detecting breast cancer were as follows: sensitivity 95 % (95 % CI 93-96 %), specificity 80 % (95 % CI 78-82 %), positive likelihood ratio 4.63 (95 % CI 3.13-6.85), negative likelihood ratio 0.08 (95 % CI 0.05-0.14), and diagnostic odds ratio 56.67 (95 % CI 26.68-120.34). The area under the SROC was 0.9552 and the Q* point was 0.8977. The pooled sensitivities for detecting subcentimetre cancer and DCIS were 84 % (95 % CI 80-88 %) and 88 % (95 % CI 81-92 %), respectively. Among patients with normal mammography, 4 % were diagnosed with breast cancer by BSGI, and among those with mammography suggestive of malignancy or new biopsy-proven breast cancer, 6 % were diagnosed with additional cancers in the breast by BSGI. BSGI had a high diagnostic performance as an excellent adjunct modality to mammography for detecting breast cancer. The ability to identify subcentimetre cancer and DCIS was also high. (orig.)
Framework for the analysis of crystallization operations
DEFF Research Database (Denmark)
Meisler, Kresten Troelstrup; Abdul Samad, Noor Asma Fazli Bin; Gernaey, Krist
received increased attention due to the growing need to control more sophisticated production lines as well asto measure/monitor the final product characteristics. Crystallization operations involve a combination of several phenomena, and different kinetic models are required for their modeling. Growth......Crystallization is often applied in the production of salts and/oractive pharmaceutical ingredients (API), and the crystallization step is an essential part of the manufacturing process for many chemicals-based products.In recent years the monitoring and analysis of crystallization operations has...... of the crystals occurs in multiple dimensions and the relative rates of different growth and other kinetic phenomena control the shape and size distribution of the final product. Including several dimensions in the crystallization will allow a more general description of the kinetic phenomena...
Feedback analysis of transimpedance operational amplifier circuits
Bruun, Erik
1993-01-01
The transimpedance or current feedback operational amplifier (CFB op-amp) is reviewed and compared to a conventional voltage mode op-amp using an analysis emphasizing the basic feedback characteristics of the circuit. With this approach the paradox of the constant bandwidth obtained from CFB op-amps is explained. It is demonstrated in a simple manner that the constant gain-bandwidth product of the conventional op-amp and the constant bandwidth of the CFB op-amp are both in accordance with bas...
Remote-Controlled Rotorcraft Blade Vibration and Modal Analysis at Low Frequencies
2016-02-01
mechanical failures. The system collects data during flight and stores the data for further analysis. HUMSs provide some degrees of health status of...unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT Health and usage monitoring systems (HUMSs) collect sensor data from vehicle mechanical systems...A typical HUMS box collects data during flight and stores the data for further analysis to determine the current state, reliability, and safety of
Bruin, Marieke; Nevøy, Anne
2014-01-01
After pediatric cochlear implantation, parents have to make decisions concerning which communication modality the child and the child's family will use. The choice has to be made against a background of opposing views on communication modality in follow-up after pediatric cochlear implantation. The opposing views form a discourse that has…
Chen, Jie
2010-01-01
This paper is a generic study of schematic structures and the use of modal verbs of 50 English Research Article (RA) abstracts. With Bhatia's (1990) model as the framework, three other move patterns were obtained besides the normal move order. The density of modal verbs varies greatly from move to move with significant differences in the frequency…
Bruin, Marieke; Nevøy, Anne
2014-01-01
After pediatric cochlear implantation, parents have to make decisions concerning which communication modality the child and the child's family will use. The choice has to be made against a background of opposing views on communication modality in follow-up after pediatric cochlear implantation. The opposing views form a discourse that has…
Wada, B. K.; Kuo, C-P.; Glaser, R. J.
1986-01-01
For the structural dynamic analysis of large space structures, the technology in structural synthesis and the development of structural analysis software have increased the capability to predict the dynamic characteristics of the structural system. The various subsystems which comprise the system are represented by various displacement functions; the displacement functions are then combined to represent the total structure. Experience has indicated that even when subsystem mathematical models are verified by test, the mathematical representations of the total system are often in error because the mathematical model of the structural elements which are significant when loads are applied at the interconnection points are not adequately verified by test. A multiple test concept, based upon the Multiple Boundary Condition Test (MBCT), is presented which will increase the accuracy of the system mathematical model by improving the subsystem test and test/analysis correlation procedure.
Tajima, Takuro; Tanaka, Yujiro; Nakamura, Masahito; Seyama, Michiko
2017-03-01
Quantitative analysis of glucose using conventional optical spectroscopy suffers from a lack of repeatability due to high optical scattering in skin tissue. Here we present a multi-modality analysis of glucose aqueous solution using photoacoustic spectroscopy (PAS) and broadband dielectric spectroscopy (BDS). These techniques involve the direct detection of the acoustic and electromagnetic waves propagating through or reflecting from tissue without their being scattered. They therefore have potential for better tolerance to the variation of scattering. For PAS, to differentiate signals induced by water absorption, we select another laser wavelength (1.38 μm) that exhibits the same absorbance for water at 1.61 μm. Furthermore, one of the two photoacoustic signals is used to normalize the variations of acoustic properties in differential signal. Measured results for glucose solutions (0-2 g/dL) showed that the differential signal has a sensitivity of 1.61%/g·dL-1 and a detection limit of 120 mg/dL. We also tested glucose detection with BDS (500 MHz to 50 GHz) by detecting glucose hydration bonding at around 10-20 GHz. Using a partial least square analysis and first derivation on broadband spectra, we obtained an RMS error 19 mg/dL and a detection limit of 59 mg/dL. Using both the low-scattering ultrasonic and microwave detection techniques, we successfully captured the glucose footprint in the physiological range.
Modal analysis of a small vertical axis wind turbine (Type DARRIEUS
Directory of Open Access Journals (Sweden)
Ion NILA
2012-06-01
Full Text Available This paper reports a brief study on free vibration analysis for determining parameters such as natural frequencies and mode shapes for vertical axis wind turbines (VAWT for an urban application. This study is focused on numerical work using available finite element software. For further understanding of the wind turbine dynamic analysis, two vibration parameters of dynamic response have been studied, namely natural frequencies and mode shapes.Block Lanczos method has been used to analyze the natural frequency while wind turbine mode shapes have been utilized because of their accuracy and faster solution. In this problem 12 modes of structure have been extracted.
Plasma physics analysis of SERT-2 operation
Kaufman, H. R.
1980-01-01
An analysis of the major plasma processes involved in the SERT 2 spacecraft experiments was conducted to aid in the interpretation of recent data. A plume penetration model was developed for neutralization electron conduction to the ion beam and showed qualitative agreement with flight data. In the SERT 2 configuration conduction of neutralization electrons between thrusters was experimentally demonstrated in space. The analysis of this configuration suggests that the relative orientation of the two magnetic fields was an important factor in the observed results. Specifically, the opposed field orientation appeared to provide a high conductivity channel between thrusters and a barrier to the ambient low energy electrons in space. The SERT 2 neutralizer currents with negative neutralizer biases were up to about twice the theoretical prediction for electron collection by the ground screen. An explanation for the higher experimental values was a possible conductive path from the neutralizer plume to a nearby part of the ground screen. Plasma probe measurements of SERT 2 gave the clearest indication of plasma electron temperature, with normal operation being near 5 eV and discharge only operation near 2 eV.
Bornstein, Marc H.; Putnick, Diane L.; Lansford, Jennifer E.; Deater-Deckard, Kirby; Bradley, Robert H.
2015-01-01
Caregiving is requisite to wholesome child development from the beginning of life. A cross-sectional microgenetic analysis of six caregiving practices across the child's 1st year (0-12 months) in 42,539 families from nationally representative samples in 38 low- and middle-income countries is reported. Rates of caregiving varied tremendously within…
Analysis of the modal behavior of an antiguide diode laser array with Talbot filter
Eijk, van Pieter D.; Reglat, Muriel; Vassilief, Georges; Krijnen, Gijs J.M.; Driessen, Alfred; Mouthaan, Anton J.
1991-01-01
An analysis of the filtering of the array modes in a resonant optical waveguide (ROW) array of antiguides by a diffractive spatial filter (a Talbot filter) is presented. A dispersion relation is derived for the array modes, allowing the calculation of the field distribution. The filtering is analyze
Modal analysis of measurements from a large-scale VIV model test of a riser in linearly sheared flow
Lie, H.; Kaasen, K. E.
2006-05-01
Large-scale model testing of a tensioned steel riser in well-defined sheared current was performed at Hanøytangen outside Bergen, Norway in 1997. The length of the model was 90 m and the diameter was 3 cm. The aim of the present work is to look into this information and try to improve the understanding of vortex-induced vibrations (VIV) for cases with very high order of responding modes, and in particular to study if and under which circumstances the riser motions would be single-mode or multi-mode. The measurement system consisted of 29 biaxial gauges for bending moment. The signals are processed to yield curvature and displacement and further to identify modes of vibration. A modal approach is used successfully employing a combination of signal filtering and least-squares fitting of precalculated mode-shapes. As a part of the modal analysis, it is demonstrated that the equally spaced instrumentation limited the maximum mode number to be extracted to be equal to the number of instrumentation locations. This imposed a constraint on the analysis of in-line (IL) vibration, which occurs at higher frequencies and involves higher modes than cross-flow (CF). The analysis has shown that in general the riser response was irregular (i.e. broad-banded) and that the degree of irregularity increases with the flow speed. In some tests distinct spectral peaks could be seen, corresponding to a dominating mode. No occurrences of single-mode (lock-in) were seen. The IL response is more broad-banded than the CF response and contains higher frequencies. The average value of the displacement r.m.s over the length of the riser is computed to indicate the magnitude of VIV motion during one test. In the CF direction the average displacement is typically 1/4 of the diameter, almost independent of the flow speed. For the IL direction the values are in the range 0.05 0.08 of the diameter. The peak frequency taken from the spectra of the CF displacement at riser midpoint show approximately
Novel Methods for Surface EMG Analysis and Exploration Based on Multi-Modal Gaussian Mixture Models.
Directory of Open Access Journals (Sweden)
Anna Magdalena Vögele
Full Text Available This paper introduces a new method for data analysis of animal muscle activation during locomotion. It is based on fitting Gaussian mixture models (GMMs to surface EMG data (sEMG. This approach enables researchers/users to isolate parts of the overall muscle activation within locomotion EMG data. Furthermore, it provides new opportunities for analysis and exploration of sEMG data by using the resulting Gaussian modes as atomic building blocks for a hierarchical clustering. In our experiments, composite peak models representing the general activation pattern per sensor location (one sensor on the long back muscle, three sensors on the gluteus muscle on each body side were identified per individual for all 14 horses during walk and trot in the present study. Hereby we show the applicability of the method to identify composite peak models, which describe activation of different muscles throughout cycles of locomotion.
Institute of Scientific and Technical Information of China (English)
HU Ying-chun; LI Shang-ping
2007-01-01
A three-dimensional model of the uplift device of a sugarcane harvester was built up in Pro/Engineer. Simulation and evaluation of its motional and dynamic performance were performed with the automatic dynamic analysis of mechanical system (ADAMS). ANSYS program was applied to the structural analysis of the model. A finite element analytic model was built up with the bottom-up methodology and was meshed. The default Block Lanczos method was used to work out the native frequency. The results indicate that the five lower modes-the transpotaion wheel, the left holding device, the right holding device, the left cutter disk, and the right cutter disk- and displacement of vibratory type only slightly affect the process of sugarcane harvester and harvesting quality. So it is advisable that the optimization of the static intensity other than the dynamic stiffness of uplift device be executed.
Experimental Modal Analysis and Dynamic Component Synthesis. Volume 1. Summary of Technical Work
1987-12-01
Rades. M., "Identification of the Dynamic Characteristics of a Simple System with Quadratic Damping," Serie de Mecanique Appliquee. 28 (4), 1983, pp...Measurement and Analysis Requirements," SAE Paper Number 751066 1975, 17 pp. [261 Prony, R. "Essai Experimental et Analytique sur les Lois de [a...of the Dynamic Characteristics of a Simple System with Quadratic Damping, Serie de Mecanique Appliquee, Vol. 28, Num. 4, 1983, pp. 439-446. 11391
Directory of Open Access Journals (Sweden)
Ajeet Kumar Gandhi
2015-01-01
Full Text Available Background: Adenoid cystic carcinoma (ACC accounts for 1% of all head and neck (HN cancers. Materials and Methods: Demographic, clinical, treatment, and survival details of 66 patients were collected (1995-2011 and analyzed. Disease-free survival (DFS was estimated by Kaplan-Meier method. Results: Primary disease sites were sinonasal (n = 27, salivary gland (n = 30, and others (n = 9. Median follow-up was 23 months (range: 12-211 months. Estimated DFS at 2- and 5-year were 75% and 67.2%, respectively. On univariate analysis, intra-cranial extension (ICE (hazard ratio [HR]: 3.59, P = 0.0071, lymph node involvement (HR: 4.05, P = 0.0065, treatment modality (others vs. surgery plus adjuvant radiotherapy, HR: 2.39, P = 0.0286 and T stage (T3/4 vs. T1/2, HR: 3.27, P = 0.007 had significant impact on DFS. Lymph node involvement (P = 0.038 and ICE (P = 0.038 continued to have significant impact on DFS on multivariate analysis. Conclusion: Surgery followed by adjuvant radiotherapy remains the treatment of choice for HN ACC. Lymph node involvement and ICE confer poor prognosis.
MODALITIES OF LOCAL DEBT ANALYSIS IN THE NORTH-WEST REGION OF ROMANIA
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Ioan BĂTRÂNCEA
2016-12-01
Full Text Available Public debt is a topic of great interest problem tracked over the years and has worsened with the outbreak of the second wave of financial crisis around the world, namely the sovereign debt crisis. After BREXIT the EU must urgently adopt uniform tax measures to prevent a new crisis of sovereign debt in countries like Greece, Italy, Spain, Portugal, and for the meeting the Maastricht criteria on public debt. UE countries have to adopting a pro - active stance by continuing fiscal consolidation measures. That is why in this paper the authors present an analysis of local public debt based on a correlated system of indicators.
POD/MAC-Based Modal Basis Selection for a Reduced Order Nonlinear Response Analysis
Rizzi, Stephen A.; Przekop, Adam
2007-01-01
A feasibility study was conducted to explore the applicability of a POD/MAC basis selection technique to a nonlinear structural response analysis. For the case studied the application of the POD/MAC technique resulted in a substantial improvement of the reduced order simulation when compared to a classic approach utilizing only low frequency modes present in the excitation bandwidth. Further studies are aimed to expand application of the presented technique to more complex structures including non-planar and two-dimensional configurations. For non-planar structures the separation of different displacement components may not be necessary or desirable.
ON THE REDUNDANCY OF COMPLEX MODAL PARAMETERS
Institute of Scientific and Technical Information of China (English)
陈奎孚; 焦群英
2004-01-01
Generating the simulation transfer function (TF) is indispensable to modal analysis, such as examining modal parameters identification algorithm, and assessing modal analysis software. Comparing 3 feasible algorithms to simulate TF shows that, one of them is preperable, which is expressing the TF as the function of the complex modal parameters ( CMPs ) , because the deliberate behaviors of CMPs can be implemented easily,such as, dense modals , large damping, and complex modal shape, etc. Nonetheless, even this preferable algorithms is elected, the complex modal shapes cannot be specified arbitrarily, because the number of CMPs far more exceeds that in physical coordinate. So for physical realizable system, there are redundant constraints in CMPs. By analyzing the eigenvalue problem of a complex modal system, and the inversion equations from CMPs to physical parameters, the explicit redundancy constraints were presented. For the special cases, such as the real modal, the damping free modal, and non-complete identification, the specific forms of the redundancy constraints were discussed, along with the number of independent parameters. It is worthy of noting that, redundancy constraints are automatically satisfied for the real modal case. Their equivalent forms on the transfer matrix and a column of transfer matrix were also provided. These results are applicable to generate TF, to implement identification by optimization and appreciate the identification results, to evaluate residual modal, and to verify the complementary of identified modal orders.
ANALYSIS OF RESPIRATORY DEPOSITION OF INHALED PARTICLES FOR DIFFERENT DOSE METRICS: COMPARISON OF NUMBER, SURFACE AREA AND MASS DOSE OF TYPICAL AMBIENT BI-MODAL AEROSOLS.Chong S. Kim, SC. Hu*, PA Jaques*, US EPA, National Health and Environmental Effects Research Laboratory, ...
基于ANSYS的复合材料飞轮系统模态分析%Modal Analysis of Composite Flywheel System base on ANSYS
Institute of Scientific and Technical Information of China (English)
李文逸; 宋以国; 李翀
2012-01-01
储能飞轮系统在工程中应用广泛,由于飞轮系统转速较高,因此对飞轮系统进行模态分析是非常必要的.利用有限元分析软件ANSYS对复合材料飞轮系统进行模态分析,得到了飞轮的固有频率与模态振型,为飞轮系统的结构设计与优化以及振动特性研究提供了有效的依据.%Flywheel energy storage system is widely used in the engineering field. Because of its high speed, it is necessary for the flywheel system to modal analysis. The modal analysis of the composite flywheel system was carried out with the finite element analysis software ANSYS. The natural frequency and the modal shape of the flywheel system were obtained. The modal analysis results of the flywheel system suspended foundation for the structure optimization of the system and the vibration characteristics study.
Directory of Open Access Journals (Sweden)
Marian-Dumitru Nedeloni
2015-09-01
Full Text Available This paper presents the study of the modal analysis of four types of plates in parallelogram shape, with or without defects, using the SolidWorks program. The results obtained after this study, have targeted the behavior of plates regarding the mesh, the deformation scale, the resultant amplitude, the rotational speeds, respectively the Eigen frequencies according to the vibration modes.
Multi-Body Dynamics and Modal Analysis of Compliant Gear Bodies
Vinayak, H.; Singh, R.
1998-02-01
This paper extends the multi-body dynamics modelling strategy for rigid gears to include compliant gear bodies in multi-mesh transmissions. Only external, fixed center, helical or spur gears are considered. This formulation combines distributed gear mesh stiffness and gear blank compliance models in a multi-body dynamics framework resulting in a set of non-linear differential equations with time-varying coefficients. Linearization and other simplifications are applied to yield the resulting linear time-invariant equations of motion. Several solution techniques are then used to determine eigensolutions and forced harmonic responses. The resulting normal mode solutions are compared to those obtained by the finite element analysis for several examples of transmission containing flexible gears. These include ring-gears and bodies with discontinuities. A parametric study has been performed to assess the effect of gear orientation on the dynamics of transmissions. Finally analytical predictions are compared to the results of a laboratory experiment.
2016-01-01
International audience; An important step in the operational modal analysis of a structure is to infer on its dynamic behavior through its modal parameters. They can be estimated by various modal identification algorithms that fit a theoretical model to measured data. When output-only data is available, i.e. measured responses of the structure, frequencies, damping ratios and mode shapes can be identified assuming that ambient sources like wind or traffic excite the system sufficiently. When ...
Directory of Open Access Journals (Sweden)
Maas Stefan
2015-01-01
Full Text Available Structural Health Monitoring (SHM intends to identify damage by changes of characteristics as for instance the modal parameters. The eigenfrequencies, mode-shapes and damping-values are either directly used as damage indicators or the changes of derived parameters are analysed, such as e.g. flexibilities or updated finite element models. One common way is a continuous monitoring under environmental excitation forces, such as wind or traffic, i.e. the so-called output-only modal analysis. Alternatively, a forced measured external excitation in distinct time-intervals may be used for input-output modal analysis. Both methods are limited by the precision or the repeatability under real-life conditions at site. The paper will summarize several field tests of artificially step-by-step damaged bridges prior to their final demolishment and it will show the changes of eigenfrequencies due to induced artificial damage. Additionally, some results of a monitoring campaign of a healthy bridge in Luxembourg are presented. Reinforced concrete shows non-linear behaviour in the sense that modal parameters depend on the excitation force amplitude, i.e. higher forces lead often to lower eigenfrequencies than smaller forces. Furthermore, the temperature of real bridges is neither constant in space nor in time, while for instance the stiffness of asphalt is strongly dependant on it. Finally, ageing as such can also change a bridge’s stiffness and its modal parameters, e.g. because creep and shrinkage of concrete or ageing of elastomeric bearing pads influence their modulus of elasticity. These effects cannot be considered as damage, though they influence the measurement of modal parameters and hinder damage detection.
Modal analysis of a multilayer dielectric microsphere in a free-space ambient medium.
LaComb, R; Casey, J P
2015-10-01
An analysis of the eigenmodes associated with a dielectric sphere embedded within one or more spherical layers of varying permittivity is presented. A matrix formulation is applied to the general multilayer problem, and the solution is validated by comparison to the complex transcendental equations derived for the homogeneous dielectric spherical resonator and a single-layer spherical dielectric resonator. Although only lossless cases are considered for simplicity, the formulation presented is applicable to resonators (with loss or gain) via the replacement of real permittivities with complex permittivities. The matrix formulation presented for the multilayer dielectric sphere follows a previously published development with the inclusion of some significant corrections. A Wronskian filter effective index approximation is developed for the estimation of Bessel functions of large order (expanding the functionality of the models to evaluation of whispering gallery modes), which is easily integrated into the presented models. Numerical simulations are generated utilizing MATLAB to solve for the complex roots of the characteristic equation, amplitude reflection coefficient, surface impedance of the dielectric layers, Q-factor, and field patterns for both TE and TM modes. Results are presented for single-layer and multilayer spherical geometries and compared to previously published results.
Directory of Open Access Journals (Sweden)
Taehyun Kim
2017-01-01
Full Text Available The modal analysis method (MAM is very useful for obtaining the dynamic responses of a structure in analytical closed forms. In order to use the MAM, accurate information is needed on the natural frequencies, mode shapes, and orthogonality of the mode shapes a priori. A thorough literature survey reveals that the necessary information reported in the existing literature is sometimes very limited or incomplete, even for simple beam models such as Timoshenko beams. Thus, we present complete information on the natural frequencies, three types of mode shapes, and the orthogonality of the mode shapes for simply supported Timoshenko beams. Based on this information, we use the MAM to derive the forced vibration responses of a simply supported Timoshenko beam subjected to arbitrary initial conditions and to stationary or moving loads (a point transverse force and a point bending moment in analytical closed form. We then conduct numerical studies to investigate the effects of each type of mode shape on the long-term dynamic responses (vibrations, the short-term dynamic responses (waves, and the deformed shapes of an example Timoshenko beam subjected to stationary or moving point loads.
Anwar, Abdul Rauf; Mideska, Kidist Gebremariam; Hellriegel, Helge; Hoogenboom, Nienke; Krause, Holger; Schnitzler, Alfons; Deuschl, Günther; Raethjen, Jan; Heute, Ulrich; Muthuraman, Muthuraman
2014-01-01
Owing to the recent advances in multi-modal data analysis, the aim of the present study was to analyze the functional network of the brain which remained the same during the eyes-open (EO) and eyes-closed (EC) resting task. The simultaneously recorded electroencephalogram (EEG) and magnetoencephalogram (MEG) were used for this study, recorded from five distinct cortical regions of the brain. We focused on the 'alpha' functional network, corresponding to the individual peak frequency in the alpha band. The total data set of 120 seconds was divided into three segments of 18 seconds each, taken from start, middle, and end of the recording. This segmentation allowed us to analyze the evolution of the underlying functional network. The method of time-resolved partial directed coherence (tPDC) was used to assess the causality. This method allowed us to focus on the individual peak frequency in the 'alpha' band (7-13 Hz). Because of the significantly higher power in the recorded EEG in comparison to MEG, at the individual peak frequency of the alpha band, results rely only on EEG. The MEG was used only for comparison. Our results show that different regions of the brain start to `disconnect' from one another over the course of time. The driving signals, along with the feedback signals between different cortical regions start to recede over time. This shows that, with the course of rest, brain regions reduce communication with each another.
Institute of Scientific and Technical Information of China (English)
谭谨; 王晓茹; 陈哲
2013-01-01
为研究永磁直驱风电系统（PMSG）并网后自身的稳定性问题，进行了并网风电系统的模态分析。建立了适用于系统小扰动稳定分析的 PMSG 风电系统模型，研究了并网风机无穷大系统的模式特性。采用特征值法分析了轴系模型、轴系刚性参数、运行点、并网距离对并网风电系统模式的影响。并在PSCAD/EMTDC上建立了相应的非线性模型，利用Prony方法对输出功率曲线进行模式识别，验证了模态分析结论。研究从模态分析的角度说明了轴系双质块建模的重要性，以及上述参数对并网PMSG稳定性影响的相关结论，结果有助于了解并网PMSG风电系统稳定性问题的本质。%In order to study the stability of a grid-connected direct-drive permanent magnet synchronous generator (PMSG) wind turbine systems, this paper presents the modal analysis of a PMSG wind turbine system. A PMSG model suitable for small signal stability analysis is presented. The modal properties of a grid-connected PMSG wind turbine system are studied. Then the comprehensive impacts of the shaft model, shaft parameters, operation points and lengths of the transmission line on the modal characteristic of the system are investigated by the eigenvalue analysis method. Meanwhile, the corresponding nonlinear model is set up in the PSCAD/EMTDC, and the output power curve is analyzed by Prony method to validate the modal analysis results. The results show the importance of shaft two-mass model and the relationship between the stability of PMSG system and the system parameters from the angle of modal analysis. It offers a better understanding about the essence of the stability of grid-connected PMSG wind turbine system. This work is supported by National Natural Science Foundation of China (No. 50937002).
Islami Parkoohi, Parisa; Jalli, Reza; Danaei, Mina; Khajavian, Shiva; Askarian, Mehrdad
2014-05-01
Medical imaging has a remarkable role in the practice of clinical medicine. This study intends to evaluate the knowledge of indications of five common medical imaging modalities and estimation of the imposed cost of their non-indicated requests among medical students who attend Shiraz University of Medical Sciences, Shiraz, Iran. We conducted across-sectional survey using a self-administered questionnaire to assess the knowledge of indications of a number of medical imaging modalities among 270 medical students during their externship or internship periods. Knowledge scoring was performed according to a descriptive international grade conversion (fail to excellent) using Iranian academic grading (0 to 20). In addition, we estimated the cost for incorrect selection of those modalities according to public and private tariffs in US dollars. The participation and response rate was 200/270 (74%). The mean knowledge score was fair for all modalities. Similar scores were excellent for X-ray, acceptable for Doppler ultrasonography, and fair for ultrasonography, CT scan and MRI. The total cost for non-indicated requests of those modalities equaled $104303 (public tariff) and $205581 (private tariff). Medical students at Shiraz University of Medical Sciences lacked favorable knowledge about indications for common medical imaging modalities. The results of this study have shown a significant cost for non-indicated requests of medical imaging. Of note, the present radiology curriculum is in need of a major revision with regards to evidence-based radiology and health economy concerns.
Directory of Open Access Journals (Sweden)
Parisa Islami Parkoohi
2015-05-01
Full Text Available Medical imaging has a remarkable role in the practice of clinical medicine. This study intends to evaluate the knowledge of indications of five common medical imaging modalities and estimation of the imposed cost of their non-indicated requests among medical students who attend Shiraz University of Medical Sciences, Shiraz, Iran. We conducted across-sectional survey using a self-administered questionnaire to assess the knowledge of indications of a number of medical imaging modalities among 270 medical students during their externship or internship periods. Knowledge scoring was performed according to a descriptive international grade conversion (fail to excellent using Iranian academic grading (0 to 20. In addition, we estimated the cost for incorrect selection of those modalities according to public and private tariffs in US dollars. The participation and response rate was 200/270 (74%. The mean knowledge score was fair for all modalities. Similar scores were excellent for X-ray, acceptable for Doppler ultrasonography, and fair for ultrasonography, CT scan and MRI. The total cost for non-indicated requests of those modalities equaled $104303 (public tariff and $205581 (private tariff. Medical students at Shiraz University of Medical Sciences lacked favorable knowledge about indications for common medical imaging modalities. The results of this study have shown a significant cost for non-indicated requests of medical imaging. Of note, the present radiology curriculum is in need of a major revision with regards to evidence-based radiology and health economy concerns.
Operator Semigroups meet Complex Analysis, Harmonic Analysis and Mathematical Physics
Chill, Ralph; Tomilov, Yuri
2015-01-01
This proceedings volume originates from a conference held in Herrnhut in June 2013. It provides unique insights into the power of abstract methods and techniques in dealing successfully with numerous applications stemming from classical analysis and mathematical physics. The book features diverse topics in the area of operator semigroups, including partial differential equations, martingale and Hilbert transforms, Banach and von Neumann algebras, Schrödinger operators, maximal regularity and Fourier multipliers, interpolation, operator-theoretical problems (concerning generation, perturbation and dilation, for example), and various qualitative and quantitative Tauberian theorems with a focus on transfinite induction and magics of Cantor. The last fifteen years have seen the dawn of a new era for semigroup theory with the emphasis on applications of abstract results, often unexpected and far removed from traditional ones. The aim of the conference was to bring together prominent experts in the field of modern...
HILBERT-DIRAC OPERATORS IN CLIFFORD ANALYSIS
Institute of Scientific and Technical Information of China (English)
F.BRACKX; H.DE SCHEPPER
2005-01-01
Around the central theme of "square root" of the Laplace operator it is shown that the classical Riesz potentials of the first and of the second kind allow for an explicit expression of so-called Hilbert-Dirac convolution operators involving natural and complex powers of the Dirac operator.
Modal Epistemology and Conceivability
DEFF Research Database (Denmark)
Philosophical argumentation often depends on modal facts, i.e. facts about what is possible, contingent, or necessary. For thought and cognition outside the domain of philosophy modal facts are also often decisive. It seems we have an easy access to modal facts, but how so? Through a presentation...... of the state-of-the-art in modal epistemology I wish to outline a research project based on conceivability that will try to explain how we come to know modal facts....
CoSMoMVPA: Multi-Modal Multivariate Pattern Analysis of Neuroimaging Data in Matlab/GNU Octave.
Oosterhof, Nikolaas N; Connolly, Andrew C; Haxby, James V
2016-01-01
Recent years have seen an increase in the popularity of multivariate pattern (MVP) analysis of functional magnetic resonance (fMRI) data, and, to a much lesser extent, magneto- and electro-encephalography (M/EEG) data. We present CoSMoMVPA, a lightweight MVPA (MVP analysis) toolbox implemented in the intersection of the Matlab and GNU Octave languages, that treats both fMRI and M/EEG data as first-class citizens. CoSMoMVPA supports all state-of-the-art MVP analysis techniques, including searchlight analyses, classification, correlations, representational similarity analysis, and the time generalization method. These can be used to address both data-driven and hypothesis-driven questions about neural organization and representations, both within and across: space, time, frequency bands, neuroimaging modalities, individuals, and species. It uses a uniform data representation of fMRI data in the volume or on the surface, and of M/EEG data at the sensor and source level. Through various external toolboxes, it directly supports reading and writing a variety of fMRI and M/EEG neuroimaging formats, and, where applicable, can convert between them. As a result, it can be integrated readily in existing pipelines and used with existing preprocessed datasets. CoSMoMVPA overloads the traditional volumetric searchlight concept to support neighborhoods for M/EEG and surface-based fMRI data, which supports localization of multivariate effects of interest across space, time, and frequency dimensions. CoSMoMVPA also provides a generalized approach to multiple comparison correction across these dimensions using Threshold-Free Cluster Enhancement with state-of-the-art clustering and permutation techniques. CoSMoMVPA is highly modular and uses abstractions to provide a uniform interface for a variety of MVP measures. Typical analyses require a few lines of code, making it accessible to beginner users. At the same time, expert programmers can easily extend its functionality. Co
Institute of Scientific and Technical Information of China (English)
李长玉; 王丽
2016-01-01
A structural modal parameters testing method (peak picking method )under excitation of operation is presented.Matlab software is used to realize the method.The experimental modal analysis of a metal disc is carried out by using peak picking method and traditional impact method.The result of different method is compared.It is found that in the first two order modes,the normal frequency errors are about 1 .6% and 1 .7% respectively,the damping ratio errors are 7.2% and 1 1% respectively,the mode shapes are approximately the same.Thereby the accuracy of the peak picking method is verified.The method is suitable for the large structure which is not easy to be excited.Moreover,the vibration characteristics of the structure can be analyzed by this method.%提出了一种在结构自身运行激励下只根据响应信号测试结构模态参数的方法—“峰值法”。通过MATLAB软件编程实现了该方法，并且利用传统的锤击方法和“峰值法”对一金属圆盘进行了实验模态分析。通过对比分析发现采用两种不同方法所取得的结果在前两阶模态中固有频率误差分别为1．6％和1．7％，阻尼比误差分别为7．2％和11％，振型整体趋势一致。从而验证了该方法的正确性。该方法适合不容易被激振的大型结构，而且能够分析结构在运行激励情况下的振动特性。
Directory of Open Access Journals (Sweden)
Jorge Gil
2016-02-01
.The integrated multimodal network model combines the various mobility infrastructure networks and the buildings’ land use to create a detailed description of the region, using open spatial data and open source Geographic Information Systems (GIS technologies. The network model’s spatial analysis covers local urban form indicators, such as street layout, network density and land use mix, as well as regional indicators of multimodal accessibility and network configuration (its structure, to give a holistic profile of urban areas across modes and scales of travel.The analysis results go through exploratory data mining and classification procedures to identify urban form typologies of urban areas. It is shown that there is a relation between this ‘urban modality’ of urban areas and the travel patterns of their residents, measured as a set of sustainable mobility indicators related to mode share and distance travelled. For this reason, ‘urban modality’ offers the possibility for ex-ante evaluation of sustainable mobility potential of planned urban areas. Furthermore, when combined with the socio-economic profile of the resident population, ‘urban modality’ defines a context for the ex-post evaluation of sustainable mobility performance of existing urban areas.The evaluation of suburban areas together with the more central historical urban areas gives invariably a high score in sustainable travel to the central areas, and rates the suburban areas negatively. On the other hand, the evaluation of sustainable mobility performance in the context of suburban areas of the same type allows the finer distinction of underperformers that have scope for improvement, and overachievers that provide examples of (relative success. This contextual evaluation can become a decision support instrument for “hard” and “soft” planning measures involving sustainable mobility targets.Applying this method to the set of VINEX neighbourhoods of the Randstad leads to the conclusion that
基于ANSYS对大型钢桁桥的模态分析%MODAL ANALYSIS OF LARGE TRUSS STEEL BRADGE BASED ON ANSYS
Institute of Scientific and Technical Information of China (English)
占智贵
2011-01-01
Modal analysis is the foundation of dynamic analysis, and it takes an important part in structral dynamic analysis. At the beginning of this paper, we diseribed the basic theory of modal analysis,establishing a dynamic model of a large truss steel bradge with ANSYS,and then we got the natrual frequency and mode shape. At last, we used midas/civil to analyze the bradge, and compared the results with ANSYS,and it showed that modal analysis based on ANSYS is credible.%模态分析是动力学分析的基础,在结构动力学分析中具有重要作用.本文对模态分析的理论进行了概述,使用大型通用有限元软件ANSYS建立了某大型钢桁桥的三维动力学模型,得到了该桥的各阶固有频率和振型,最后通过与Midas/civil桥梁专用软件的分析结果进行了对比,表明ANSYS的分析结果是可靠的.
Modal Analysis of the EMU Car-Body in the Preparation Condition Based on Mass Fineness Distribution
Li, Ya-Na; Rao, Ben-Teng; Xie, Su-Ming; Ma, Si-Qun
Analyzing the car-body modal of EMU is the key of assessing EMU dynamic quality at high speed. The car-body modal can be influenced to same degree by the mass fineness distribution and the rationality of coupling stiffness of suspension device. Considering all equipments layout including internal decoration, FEM of the EMU car-body under preparation based on mass fineness distribution was created and the free modal was carried out with FEA software. The vertical bend frequency 10.03Hz, that is closer to the experimental data, satisfies the relative requirement. And on this basis, different vibration frequencies were studied under different elastic hanging stiffness of suspension device. Vibration frequency change is same on three direction with vertical direction stiffness, which indicate vertical stiffness is more important than the other direction stiffness. Thus these results provide some rational references for EMU car-body structural design.
Directory of Open Access Journals (Sweden)
Heather D VanGuilder
Full Text Available BACKGROUND: As a leading cause of adult blindness, diabetic retinopathy is a prevalent and profound complication of diabetes. We have previously reported duration-dependent changes in retinal vascular permeability, apoptosis, and mRNA expression with diabetes in a rat model system. The aim of this study was to identify retinal proteomic alterations associated with functional dysregulation of the diabetic retina to better understand diabetic retinopathy pathogenesis and that could be used as surrogate endpoints in preclinical drug testing studies. METHODOLOGY/PRINCIPAL FINDINGS: A multi-modal proteomic approach of antibody (Luminex-, electrophoresis (DIGE-, and LC-MS (iTRAQ-based quantitation methods was used to maximize coverage of the retinal proteome. Transcriptomic profiling through microarray analysis was included to identify additional targets and assess potential regulation of protein expression changes at the mRNA level. The proteomic approaches proved complementary, with limited overlap in proteomic coverage. Alterations in pro-inflammatory, signaling and crystallin family proteins were confirmed by orthogonal methods in multiple independent animal cohorts. In an independent experiment, insulin replacement therapy normalized the expression of some proteins (Dbi, Anxa5 while other proteins (Cp, Cryba3, Lgals3, Stat3 were only partially normalized and Fgf2 and Crybb2 expression remained elevated. CONCLUSIONS/SIGNIFICANCE: These results expand the understanding of the changes in retinal protein expression occurring with diabetes and their responsiveness to normalization of blood glucose through insulin therapy. These proteins, especially those not normalized by insulin therapy, may also be useful in preclinical drug development studies.
Wöhrer, Stefan; Kiesewetter, Barbara; Fischbach, Julia; Müllauer, Leonhard; Troch, Marlene; Lukas, Julius; Mayerhoefer, Marius E; Raderer, Markus
2014-08-01
We have performed a retrospective analysis of all patients with extragastric mucosa-associated lymphoid tissue (MALT) lymphoma treated at our institution to compare the efficacy of first-line therapeutic modalities including surgery, radiation, systemic therapy, and antibiotics. One hundred eighty-five patients with extragastric MALT lymphoma with a median age of 63 (interquartile range (IQR) 50-74) years and a median follow-up time of 49 (IQR 18-103) months were retrospectively analyzed. Time to progression and time to next therapy were used as surrogate endpoints for efficacy. Patients having either surgery (100 %), chemo/immunotherapy (85.5 %), or radiation (80 %) had significantly (p = 0.01) higher response rates than patients treated with antibiotics (33.3 %). Patients who were irradiated had significantly more progressive disease, but also the longest follow-up time. Stage, elevated LDH, anemia, elevated beta-2 microglobulin, plasmacytic differentiation, monoclonal gammopathy, or autoimmune disease did not influence the rate of disease progression nor did complete remission or partial remission from initial therapy influence time to and rate of progression. There was no significant difference in the median time to progression (p = 0.141), but the estimated time to progression (p = 0.023) as well as the estimated time to next therapy (p = 0.021) was significantly different among the various cohorts favoring surgery, chemo/immunotherapy, and radiation. Our results suggest extragastric MALT lymphoma as a potential systemic disease irrespective of initial stage. Radiation, surgery, and chemo/immunotherapy seem to be equally effective in achieving remissions and prolonged progression free survivals, but a curative potential is questionable. Localized MALT lymphomas affecting the thyroid gland or the lungs have excellent long-term progression-free survivals with surgical treatment only.
Zheng, Minyi; Zhang, Bangji; Zhang, Jie; Zhang, Nong
2016-07-01
Physical parameters are very important for vehicle dynamic modeling and analysis. However, most of physical parameter identification methods are assuming some physical parameters of vehicle are known, and the other unknown parameters can be identified. In order to identify physical parameters of vehicle in the case that all physical parameters are unknown, a methodology based on the State Variable Method(SVM) for physical parameter identification of two-axis on-road vehicle is presented. The modal parameters of the vehicle are identified by the SVM, furthermore, the physical parameters of the vehicle are estimated by least squares method. In numerical simulations, physical parameters of Ford Granada are chosen as parameters of vehicle model, and half-sine bump function is chosen to simulate tire stimulated by impulse excitation. The first numerical simulation shows that the present method can identify all of the physical parameters and the largest absolute value of percentage error of the identified physical parameter is 0.205%; and the effect of the errors of additional mass, structural parameter and measurement noise are discussed in the following simulations, the results shows that when signal contains 30 dB noise, the largest absolute value of percentage error of the identification is 3.78%. These simulations verify that the presented method is effective and accurate for physical parameter identification of two-axis on-road vehicles. The proposed methodology can identify all physical parameters of 7-DOF vehicle model by using free-decay responses of vehicle without need to assume some physical parameters are known.
Aeroelastic modal dynamics of wind turbines including anisotropic effects
DEFF Research Database (Denmark)
Skjoldan, Peter Fisker
, damping, and periodic mode shapes of a rotating wind turbine by describing the rotor degrees of freedom in the inertial frame. This approach is valid only for an isotropic system. Anisotropic systems, e.g., with an unbalanced rotor or operating in wind shear, are treated with the general approaches...... of Floquet analysis or Hill's method which do not provide a unique reference frame for observing the modal frequency, to which any multiple of the rotor speed can be added. This indeterminacy is resolved by requiring that the periodic mode shape be as constant as possible in the inertial frame. The modal...... frequency is thus identified as the dominant frequency in the response of a pure excitation of the mode observed in the inertial frame. A modal analysis tool based directly on the complex aeroelastic wind turbine code BHawC is presented. It uses the Coleman approach in isotropic conditions...
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
In most of real operational conditions only response data are measurable while the actual excitations are unknown, so modal parameter must be extracted only from responses. This paper gives a theoretical formulation for the cross-correlation functions and cross-power spectra between the outputs under the assumption of white-noise excitation. It widens the field of modal analysis under ambient excitation because many classical methods by impulse response functions or frequency response functions can be used easily for modal analysis under unknown excitation. The Polyreference Complex Exponential method and Eigensystem Realization Algorithm using cross-correlation functions in time domain and Orthogonal Polynomial method using cross-power spectra in frequency domain are applied to a steel frame to extract modal parameters under operational conditions. The modal properties of the steel frame from these three methods are compared with those from frequency response functions analysis. The results show that the modal analysis method using cross-correlation functions or cross-power spectra presented in this paper can extract modal parameters efficiently under unknown excitation.
Analysis of the human operator subsystems
Jones, Lynette A.; Hunter, Ian W.
1991-01-01
Except in low-bandwidth systems, knowledge of the human operator transfer function is essential for high-performance telerobotic systems. This information has usually been derived from detailed analyses of tracking performance, in which the human operator is considered as a complete system rather than as a summation of a number of subsystems, each of which influences the operator's output. Studies of one of these subsystems, the limb mechanics system, demonstrate that large parameter variations can occur that can have a profound effect on the stability of force-reflecting telerobot systems. An objective of this research was to decompose the performance of the human operator system in order to establish how the dynamics of each of the elements influence the operator's responses.