A frequency–spatial domain decomposition (FSDD) method for operational modal analysis

Zhang, Lingmi; Wang, Tong; Tamura, Yukio

doi:10.1016/j.ymssp.2009.10.024

Cited by 113 publications

(83 citation statements)

References 7 publications

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“…Although there are many applications of OMA to civil structures in the literature, such as [11], there are not many applications to wind turbines. James et al [12] used NExT on a horizontal-axis wind turbine (HAWT) with the rotor diameter of 17.8 m. A successful modal extraction below 10 Hz was shown, including elastic vibration and blade rotation harmonics.…”

Section: Literature Reviewmentioning

confidence: 99%

Contribution of Small Wind Turbine Structural Vibration to Noise Emission

2013

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A major barrier to the acceptance of small wind turbines is that they are perceived to be noisy. This paper investigates an aspect of noise emission that has not been considered; vibration and noise generation from the tower. First, vibration measurements were made using accelerometers placed on the 10.2 m monopole tower of a Skystream 2.4 kW wind turbine, and natural frequencies and corresponding deflection shapes were calculated. Second, the results from the survey were used to verify the predictions of a finite element model of the tower structure. Lastly, the tower's acoustic emission was simulated computationally, as it was not possible to measure it accurately. Most vibration energy occurred in the very low frequency band (≤10 Hz). It was found that wind itself can only excite the first two bending modes. On the other hand, emitted noise from the tower at large distances can be neglected, as close to the tower, the noise can reach 30 dB.

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Section: Literature Reviewmentioning

confidence: 99%

Contribution of Small Wind Turbine Structural Vibration to Noise Emission

2013

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“…12,14 The earliest manifestations of FDD were peak picking and half-power bandwidth estimation schemes operating on the Power Spectral Density (PSD) functions. 13 However the advanced FDD algorithms refine the modal parameter estimates using powerful tools like the Singular Value Decomposition (SVD). 4,13 An interesting direction for frequency domain approaches involves the use of Hilbert transforms applied to PSD's to obtain biased Frequency Response Function (FRF) estimates.…”

Section: Technical Backgroundmentioning

confidence: 99%

“…13 However the advanced FDD algorithms refine the modal parameter estimates using powerful tools like the Singular Value Decomposition (SVD). 4,13 An interesting direction for frequency domain approaches involves the use of Hilbert transforms applied to PSD's to obtain biased Frequency Response Function (FRF) estimates. 4,19 There is another direction in operational testing that involves estimating the forces acting on the system.…”

Section: Technical Backgroundmentioning

confidence: 99%

Progress in Operational Analysis of Launch Vehicles in Nonstationary Flight

James

Kaouk

Cao

2013

Special Topics in Structural Dynamics, Volume 6

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This paper presents recent results in an ongoing effort to understand and develop techniques to process launch vehicle data, which is extremely challenging for modal parameter identification. The primary source of difficulty is due to the nonstationary nature of the situation. The system is changing, the environment is not steady, and there is an active control system operating. Hence, the primary tool for producing clean operational results (significant data lengths and data averaging) is not available to the user. This work reported herein uses a correlation-based two step operational modal analysis approach to process the relevant data sets for understanding and development of processes. A significant drawback for such processing of short time histories is a series of beating phenomena due to the inability to average out random modal excitations. A recursive correlation process coupled to a new convergence metric (designed to mitigate the beating phenomena) is the object of this study. It has been found in limited studies that this process creates clean modal frequency estimates but numerically alters the damping. KEYWORDS Operational Modal Analysis, Signal Processing, Hilbert Transform, Correlation Function, Damping Estimation INTRODUCTIONThe spacecraft launch environment is a highly complex and non-stationary event that is characterized by high amplitude input forces, highly variable loads, a wide spectrum of responses, constantly changing vehicle mass, active control interactions, staging, and limited instrumentation. At the same time, structural response analyses and loads estimations must be performed with models that are only partially validated using ground test data due to the fact that access to diagnostic and environmental ground tests are limited. To compound matters, project managers tend to reduce uncertainty factors designed to protect for loads increases and model unknowns. As a result, the designs progress rapidly before loads and structural problems are uncovered. This means that there are very few tools available to recover from structural dynamics issues in such a highly dynamic environment without costly redesigns late in the design cycle or in early operations.

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“…Hence a major activity involved the development of individual modules to implement a single technique for integration into the MIDOS framework. The techniques currently developed, in development, or under consideration include: correlation function processing [1,2], Stochastic Subspace Identification (SSI) [3], Frequency Domain Decomposition (FDD) [4], wavelet processing [5], Hilbert-Huang [6], force reconstruction [7,8] as well as other supporting techniques such as mode shape extraction [9], harmonic removal [10], Maximum Entropy Method (MEM) [11,12], random decrement [13,14], etc. Currently, there are limited modules built for standard OMA processing as well as unsteady launch processing based on correlation functions.…”

Section: Module Developmentmentioning

confidence: 99%

“…The analysis activities related to datasets #8 and #11 above will be discussed in more detail in this paper. Special emphasis will be paid to lessons-learned by previous 4 insights driven by analysis activities related to datasets #4,#5, #6, and #7. A question of particular interest to this paper are the indications from the previous database processing exercises that the control system is affecting the estimated modal properties of the lowest bending modes during launch [1].…”

Section: Data Processingmentioning

confidence: 99%

Operational Analysis in the Launch Environment

James

Kaouk

Cao

et al. 2012

Topics in Modal Analysis I, Volume 5

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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. INTRODUCTIONThe spacecraft launch environment is a highly complex and non-stationary event that is characterized by high amplitude input forces, highly variable loads, a wide spectrum of responses, constantly changing vehicle mass, active control interactions, staging, and limited instrumentation. At the same time, structural response analyses and loads estimations must be performed with models that are only partially validated using ground test data due to the fact that access to diagnostic and environmental ground tests are limited. To compound matters, projects are tending to use reduced uncertainty factors designed to protect for loads increases and model unknowns. As a result, the designs progress rapidly before loads and structural problems are uncovered. This means that there are very few tools available to recover from structural dynamics issues in such a dynamic environment without costly redesigns late in the design cycle or in early operations.

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A frequency–spatial domain decomposition (FSDD) method for operational modal analysis

Cited by 113 publications

References 7 publications

Contribution of Small Wind Turbine Structural Vibration to Noise Emission

Contribution of Small Wind Turbine Structural Vibration to Noise Emission

Progress in Operational Analysis of Launch Vehicles in Nonstationary Flight

Operational Analysis in the Launch Environment

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