The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform

L. S. Rozhok - One of the best experts on this subject based on the ideXlab platform.

Ya. M. Grigorenko - One of the best experts on this subject based on the ideXlab platform.

  • Layered Inhomogeneous Hollow Cylinders with Concave Corrugations Under Internal Pressure
    International Applied Mechanics, 2018
    Co-Authors: Ya. M. Grigorenko, L. S. Rozhok
    Abstract:

    The stress problem for layered hollow inhomogeneous cylinders with concave semi-corrugations is solved in spatial statement, and their stress state is studied depending on the stiffness of the core layer. To solve the problem, the analytical methods of variable separation, approximation of functions by Discrete Fourier Series, and the numerical Discrete-orthogonalization method are used. Numerical results are analyzed.

  • Effect of Change in the Curvature Parameters on the Stress State of Concave Corrugated Hollow Cylinders
    International Applied Mechanics, 2018
    Co-Authors: Ya. M. Grigorenko, L. S. Rozhok
    Abstract:

    The effect of change in the curvature parameters of the stress state of concave corrugated hollow cylinders is studied. The change is attributed to variations in the radius of a moving circle and in the distance to its center. The problem is solved in spatial statement using analytical methods of separation of variables, approximation of functions by Discrete Fourier Series, and the numerical Discrete-orthogonalization method. Results are presented in the form of plots demonstrating distributions of displacement and stress fields and are analyzed.

  • Equilibrium of Elastic Hollow Inhomogeneous Cylinders with Cross Sections in the Form of Convex Semicorrugations
    Journal of Mathematical Sciences, 2017
    Co-Authors: Ya. M. Grigorenko, L. S. Rozhok
    Abstract:

    We present the solution of a three-dimensional boundary-value problem of stresses in the theory of elasticity for hollow inhomogeneous orthotropic cylinders with cross sections in the form of convex semicorrugations with zones of large curvature. The boundary conditions at the ends of the cylinder make it possible to separate variables along the length. The additional functions are included in the resolving system of differential equations. These functions make it possible to separate the variables along the directrix by using Discrete Fourier Series. The boundary-value problem obtained for the system of ordinary differential equations is solved by the stable numerical method of Discrete orthogonalization over the thickness of the cylinder. The results are presented in the form of plots and tables.

  • stress state of longitudinally corrugated hollow cylinders with different cross sectional curvature
    International Applied Mechanics, 2016
    Co-Authors: Ya. M. Grigorenko, L. S. Rozhok
    Abstract:

    The effect of the change in the curvature due to changes in the epicycle radius on the stress state of longitudinally corrugated hollow cylinders is studied using a spatial problem statement, the variable separation method, Discrete Fourier Series, and the Discrete-orthogonalization method. The results presented in the form of graphs of distribution of displacements and stresses are analyzed

  • Influence of Curvature on the Stress State of Longitudinally Corrugated Hollow Cylinders
    International Applied Mechanics, 2016
    Co-Authors: Ya. M. Grigorenko, L. S. Rozhok
    Abstract:

    The effect of the changes in the curvature caused by variations in the radius of the epicycle and the distance to its center on the stress state of longitudinally corrugated hollow cylinders is studied using a three-dimensional problem statement, the variable separation method, Discrete Fourier Series, and the Discrete-orthogonalization method. The results obtained are presented in the form of graphs of displacement and stress fields and analyzed

Patrick Guillaume - One of the best experts on this subject based on the ideXlab platform.

  • determining the power flow in a rectangular plate using a generalized two step regressive Discrete Fourier Series
    Journal of Vibration and Acoustics, 2012
    Co-Authors: Cedric Vuye, Steve Vanlanduit, Patrick Guillaume, Flavio Presezniak, Gunther Steenackers
    Abstract:

    The evaluation of structural power flow (or structural intensity (SI)) in engineering structures is a field of increasing interest in connection with vibration analysis and noise control. In contrast to classical techniques such as modal analysis, the SI indicates the magnitude and direction of the vibratory energy traveling in the structures, which yields information about the positions of the sources/sinks, along with the energy transmission path. In this paper, a new algorithm is proposed to model operational deflection shapes (ODS). The model is a two-dimensional Fourier domain model that is estimated by using a weighted nonlinear least-squares method. From the wave number-frequency domain data thus obtained, the spatial derivatives that are necessary to determine the structural power flow are easily computed. The proposed method is less sensitive to measurement noise than traditional power flow estimation techniques. A numerical model of a simply supported plate excited by two shakers, phased to act as an energy source and sink, is used as a simulation case. Measurements are executed on a clamped plate excited by an electromagnetic shaker in combination with a damper.

  • tomographic reconstruction using a generalized regressive Discrete Fourier Series
    Mechanical Systems and Signal Processing, 2008
    Co-Authors: Joris Vanherzeele, Steve Vanlanduit, Roberto Longo, Patrick Guillaume
    Abstract:

    When measuring three-dimensional phenomena such as flow fields or acoustic fields using an interferometric technique, one is proneto measure different angles of view to obtain a full three-dimensional representation of the phenomenon under investigation.This is due to the fact that an interferometric technique measures a line integral across the optical path. To obtain the full three-dimensional view the different angles of view are passed through a tomographic algorithm. The most widely used tomographic method is the so-called filtered back projection. However, this process suffers from a Series of drawbacks, the most important one being the fact that substantial truncation errors occur in the back projection step. In this article a method is devised to eliminate these errors, based on a parametric frequency-domain approach called generalized regressive Discrete Fourier Series (GRDFS). The method will be applied both to simulated acoustic fields as to real acoustic fields measured using laser doppler vibrometry. The acoustic source will be rotated to obtain continuous angle views of the acoustic field, hence eliminating the tedious process of rotating the measurement setup.

  • Spatial data reduction for laser vibrometry using advanced regressive Fourier Series
    Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, 2008
    Co-Authors: Joris Vanherzeele, Steve Vanlanduit, R. Longo, Patrick Guillaume
    Abstract:

    With the development of optical measurement techniques it is possible to obtain vast amounts of data. In vibrometry applications in particular operational deflection shapes are often obtained with very high spatial resolution. Fortunately, many techniques exist to reduce (approximate) the measurement data. One of the most common techniques for evaluating optical measurement data is by means of a Fourier analysis. However, this technique suffers from what is known as leakage when a non-integer number of periods is considered. This gives rise to non-negligible errors, which will obviously hamper the accuracy of the synthesized shape. Another technique such as a Discrete Cosine Transform, used in the widely spread -jpeg standard does not suffer these anomalies but can still prove erroneous at times. One of the more recent approaches is via a so-called Regressive Discrete Fourier Series (introduced by Arruda) which suffers one disadvantage. The problem statement is non-linear in the parameters and needs a priori information about the deflection shape. This can be resolved by using the Optimized Regressive Discrete Fourier Series (ORDFS), introduced in this article, which uses a non-linear least squares approach. In this article the method will be applied in particular to the reduction of data for laser vibrometer measurements performed on an Inorganic Phosphate Cement (IPC) beam (1D), as well as on a car door (2D). The proposed technique will also be validated on simulations to illustrate the properties concerning compression ration and synthesized mode shape error. The introduced method will be bench marked for compression ratio and synthesized deflection shape error with all prior mentioned techniques as well as to the more novel generalized regressive Discrete Fourier Series (GRDFS).

  • reducing spatial data using an optimized regressive Discrete Fourier Series
    Journal of Sound and Vibration, 2008
    Co-Authors: Joris Vanherzeele, Steve Vanlanduit, Patrick Guillaume
    Abstract:

    Abstract With the development of optical measurement techniques it is possible to obtain vast amounts of data. In vibrometry applications in particular operational deflection shapes are often obtained with very high spatial resolution. Fortunately, many techniques exist to reduce (approximate) the measurement data. One of the most common techniques for evaluating optical measurement data is by means of a Fourier analysis. However, this technique suffers from what is known as leakage when a non-integer number of periods is considered. This gives rise to non-negligible errors, which will obviously hamper the accuracy of the synthesized shape. Another technique such as a Discrete cosine transform, used in the widely spread -jpeg standard does not suffer these anomalies but can still prove erroneous at times. One of the more recent approaches is via a so-called regressive Discrete Fourier Series (introduced by Arruda) which suffers one disadvantage. The problem statement is nonlinear in the parameters and needs a priori information about the deflection shape. This can be resolved by using the optimized regressive Discrete Fourier Series (ORDFS), introduced in this article, which uses a nonlinear least squares approach. In this article the method will be applied in particular to the reduction of data for laser vibrometer measurements performed on an inorganic phosphate cement (IPC) beam (1D), as well as on a car door (2D). The proposed technique will also be validated on simulations to illustrate the properties concerning compression ratio and synthesized mode shape error. The introduced method will be bench marked for compression ratio and synthesized deflection shape error with all prior mentioned techniques.

  • acoustic source identification using a generalized regressive Discrete Fourier Series for tomographic reconstruction
    Journal of the Acoustical Society of America, 2007
    Co-Authors: Joris Vanherzeele, Steve Vanlanduit, Roberto Longo, Patrick Guillaume
    Abstract:

    When measuring three‐dimensional phenomena such as acoustic fields using an interferometric technique, one is prone to measure different angles of view to obtain a full three‐dimensional representation of the phenomenon under investigation. This is due to the fact that an interferometric technique measures a line integral across the optical path. To obtain the full three‐dimensional view, the different angles of view are passed through a tomographic algorithm. The most widely used tomographic method is filtered back projection. However, this process suffers from a Series of drawbacks, the most important one being the fact that substantial truncation errors occur in the back projection step. In this article, a method is devised to eliminate these errors, based on a parametric frequency domain approach called generalized regressive Discrete Fourier Series (GRDFS). The method will be applied to laser doppler vibrometer measurements on a loudspeaker. This source will be rotated to obtain continuous angle views of the acoustic field, hence eliminating the tedious process of rotating the measurement set‐up. By demodulation of a measured signal, it is possible to determine the position of the loudspeaker in space. The results obtained with the GRDFS will be compared to the classical filtered back projection method.

Jose Roberto De Franca Arruda - One of the best experts on this subject based on the ideXlab platform.

  • a robust one dimensional regressive Discrete Fourier Series
    Mechanical Systems and Signal Processing, 2010
    Co-Authors: Jose Roberto De Franca Arruda
    Abstract:

    The regressive Discrete Fourier Series (RDFS) proposed in the early nineties can be used to smooth signals in one or two dimensions and to compute derivatives (e.g., spatial or time). This can be useful in applications where there is a need to compute derivatives of noisy data. The choice of the period and number of frequency lines of the Fourier Series in the RDFS is empirical, based on the a priori information available about the data being treated. When the chosen period is larger that the data extension and the number of frequency lines increase, the RDFS may present numerical instability. In this paper a more robust RDFS is proposed to avoid such numerical instability. This robust version of the RDFS may be useful when a priori information is not available to guide the choice of the RDFS parameters.

  • identification of the bending stiffness matrix of symmetric laminates using regressive Discrete Fourier Series and finite differences
    Journal of Sound and Vibration, 2009
    Co-Authors: F B Batista, Jose Roberto De Franca Arruda, E L Albuquerque, M Dias
    Abstract:

    Abstract It is known that the elastic constants of composite materials can be identified by modal analysis and numerical methods. This approach is nondestructive, since it consists of simple tests and does not require high computational effort. It can be applied to isotropic, orthotropic, or anisotropic materials, making it a useful alternative for the characterization of composite materials. However, when elastic constants are bending constants, the method requires numerical spatial derivatives of experimental mode shapes. These derivatives are highly sensitive to noise. Previous works attempted to overcome the problem by using special optical devices. In this study, the elastic constant is identified using mode shapes obtained by standard laser vibrometers. To minimize errors, the mode shapes are first smoothed by regressive Discrete Fourier Series, after which their spatial derivatives are computed using finite differences. Numerical simulations using the finite element method and experimental results confirm the accuracy of the proposed method. The experimental examples reported here consist of an isotropic steel plate and an orthotropic carbon–epoxy plate excited with an electromechanical shaker. The forced response is measured at a large number of points, using a laser Doppler vibrometer. Both numerical and experimental results were satisfactory.

  • Localizing Energy Sources and Sinks in Plates Using Power Flow Maps Computed From Laser Vibrometer Measurements
    Shock and Vibration, 1998
    Co-Authors: Jose Roberto De Franca Arruda
    Abstract:

    This paper presents an experimental method especially adapted for the computation of structural power flow using spatially dense vibration data measured with scanning laser Doppler vibrometers. In the proposed method, the operational deflection shapes measured over the surface of the structure are curve-fitted using a two-dimensional Discrete Fourier Series approximation that minimizes the effects of spatial leakage. From the wavenumber-frequency domain data thus obtained, the spatial derivatives that are necessary to determine the structural power flow are easily computed. Divergence plots are then obtained from the computed intensity fields. An example consisting of a rectangular aluminum plate supported by rubber mounts and excited by a point force is used to appraise the proposed method. The proposed method is compared with more traditional finite difference methods. The proposed method was the only to allow the localization of the energy source and sinks from the experimental divergence plots.

  • Space-frequency regression method for nonmodal modeling of spatially dense data
    First International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, 1994
    Co-Authors: Jose Roberto De Franca Arruda
    Abstract:

    When spatially-dense mobility shapes are measured with laser techniques, it is often impracticable to use Experimental Modal Analysis to model the experimental data. To deal with this situation, a space-frequency regression method using Chebicheff polynomials and two-dimensional Discrete Fourier Series approximation is proposed in this paper. The proposed regressive approach was implemented and verified using a simple experimental example consisting of a freely-suspended rectangular aluminum plate. A reduced and smoothed model, which takes advantage of the sinusoidal spatial pattern of structural mobility shapes and the polynomial frequency domain patter of FRFs, is thus obtained. The reduced model can be economically stored, and, later, used to produce smoothed curves with any desired frequency and spatial resolutions.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

  • surface smoothing and partial spatial derivatives computation using a regressive Discrete Fourier Series
    Mechanical Systems and Signal Processing, 1992
    Co-Authors: Jose Roberto De Franca Arruda
    Abstract:

    Abstract The smoothing of surfaces which can be described as scalar functions of a two-dimensional domain is classical in image processing. Smoothing techniques can be used in experimental modal analysis applications to smooth spatially dense measured operating shapes. When transformation filtering techniques are used, a mathematical model of the smoothed surface is obtained. The mathematical model of the out-of-plane displacement operating shape surface can be used to calculate in-plane angular displacements, thus increasing by threefold the number of degrees-of-freedom obtained from the experimental measurements. In this paper, a surface smoothing method consisting of estimating by least-squares the coefficients of a two-dimensional Discrete Fourier Series with arbitrary period and arbitrary frequency resolution is presented. It is shown that the proposed method called Regressive Discrete Fourier Series (RDFS) minimises the leakage problem and can be used with non-equally-spaced and non-rectangular-domain data. The RDFS method is compared to a more classical approach consisting of using the two-dimensional Discrete Fourier transform (DFT). With the Fourier Series model it is straightforward to calculate partial derivatives. Numerical results are shown to illustrate the proposed method and to compare it to the two-dimensional DFT method, which was enhanced with spline padding to reduce leakage.

Joris Vanherzeele - One of the best experts on this subject based on the ideXlab platform.

  • tomographic reconstruction using a generalized regressive Discrete Fourier Series
    Mechanical Systems and Signal Processing, 2008
    Co-Authors: Joris Vanherzeele, Steve Vanlanduit, Roberto Longo, Patrick Guillaume
    Abstract:

    When measuring three-dimensional phenomena such as flow fields or acoustic fields using an interferometric technique, one is proneto measure different angles of view to obtain a full three-dimensional representation of the phenomenon under investigation.This is due to the fact that an interferometric technique measures a line integral across the optical path. To obtain the full three-dimensional view the different angles of view are passed through a tomographic algorithm. The most widely used tomographic method is the so-called filtered back projection. However, this process suffers from a Series of drawbacks, the most important one being the fact that substantial truncation errors occur in the back projection step. In this article a method is devised to eliminate these errors, based on a parametric frequency-domain approach called generalized regressive Discrete Fourier Series (GRDFS). The method will be applied both to simulated acoustic fields as to real acoustic fields measured using laser doppler vibrometry. The acoustic source will be rotated to obtain continuous angle views of the acoustic field, hence eliminating the tedious process of rotating the measurement setup.

  • Spatial data reduction for laser vibrometry using advanced regressive Fourier Series
    Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, 2008
    Co-Authors: Joris Vanherzeele, Steve Vanlanduit, R. Longo, Patrick Guillaume
    Abstract:

    With the development of optical measurement techniques it is possible to obtain vast amounts of data. In vibrometry applications in particular operational deflection shapes are often obtained with very high spatial resolution. Fortunately, many techniques exist to reduce (approximate) the measurement data. One of the most common techniques for evaluating optical measurement data is by means of a Fourier analysis. However, this technique suffers from what is known as leakage when a non-integer number of periods is considered. This gives rise to non-negligible errors, which will obviously hamper the accuracy of the synthesized shape. Another technique such as a Discrete Cosine Transform, used in the widely spread -jpeg standard does not suffer these anomalies but can still prove erroneous at times. One of the more recent approaches is via a so-called Regressive Discrete Fourier Series (introduced by Arruda) which suffers one disadvantage. The problem statement is non-linear in the parameters and needs a priori information about the deflection shape. This can be resolved by using the Optimized Regressive Discrete Fourier Series (ORDFS), introduced in this article, which uses a non-linear least squares approach. In this article the method will be applied in particular to the reduction of data for laser vibrometer measurements performed on an Inorganic Phosphate Cement (IPC) beam (1D), as well as on a car door (2D). The proposed technique will also be validated on simulations to illustrate the properties concerning compression ration and synthesized mode shape error. The introduced method will be bench marked for compression ratio and synthesized deflection shape error with all prior mentioned techniques as well as to the more novel generalized regressive Discrete Fourier Series (GRDFS).

  • reducing spatial data using an optimized regressive Discrete Fourier Series
    Journal of Sound and Vibration, 2008
    Co-Authors: Joris Vanherzeele, Steve Vanlanduit, Patrick Guillaume
    Abstract:

    Abstract With the development of optical measurement techniques it is possible to obtain vast amounts of data. In vibrometry applications in particular operational deflection shapes are often obtained with very high spatial resolution. Fortunately, many techniques exist to reduce (approximate) the measurement data. One of the most common techniques for evaluating optical measurement data is by means of a Fourier analysis. However, this technique suffers from what is known as leakage when a non-integer number of periods is considered. This gives rise to non-negligible errors, which will obviously hamper the accuracy of the synthesized shape. Another technique such as a Discrete cosine transform, used in the widely spread -jpeg standard does not suffer these anomalies but can still prove erroneous at times. One of the more recent approaches is via a so-called regressive Discrete Fourier Series (introduced by Arruda) which suffers one disadvantage. The problem statement is nonlinear in the parameters and needs a priori information about the deflection shape. This can be resolved by using the optimized regressive Discrete Fourier Series (ORDFS), introduced in this article, which uses a nonlinear least squares approach. In this article the method will be applied in particular to the reduction of data for laser vibrometer measurements performed on an inorganic phosphate cement (IPC) beam (1D), as well as on a car door (2D). The proposed technique will also be validated on simulations to illustrate the properties concerning compression ratio and synthesized mode shape error. The introduced method will be bench marked for compression ratio and synthesized deflection shape error with all prior mentioned techniques.

  • acoustic source identification using a generalized regressive Discrete Fourier Series for tomographic reconstruction
    Journal of the Acoustical Society of America, 2007
    Co-Authors: Joris Vanherzeele, Steve Vanlanduit, Roberto Longo, Patrick Guillaume
    Abstract:

    When measuring three‐dimensional phenomena such as acoustic fields using an interferometric technique, one is prone to measure different angles of view to obtain a full three‐dimensional representation of the phenomenon under investigation. This is due to the fact that an interferometric technique measures a line integral across the optical path. To obtain the full three‐dimensional view, the different angles of view are passed through a tomographic algorithm. The most widely used tomographic method is filtered back projection. However, this process suffers from a Series of drawbacks, the most important one being the fact that substantial truncation errors occur in the back projection step. In this article, a method is devised to eliminate these errors, based on a parametric frequency domain approach called generalized regressive Discrete Fourier Series (GRDFS). The method will be applied to laser doppler vibrometer measurements on a loudspeaker. This source will be rotated to obtain continuous angle views of the acoustic field, hence eliminating the tedious process of rotating the measurement set‐up. By demodulation of a measured signal, it is possible to determine the position of the loudspeaker in space. The results obtained with the GRDFS will be compared to the classical filtered back projection method.

  • data reduction using a generalized regressive Discrete Fourier Series
    Journal of Sound and Vibration, 2006
    Co-Authors: Joris Vanherzeele, Steve Vanlanduit, Patrick Guillaume, P Verboven
    Abstract:

    Abstract With the development of optical measurement techniques it is possible to obtain vast amounts of data. In vibrometry applications in particular operational deflection shapes are often obtained with very high spatial resolution. It has long been known that it is possible to reduce (approximate) the measurement data by means of a Fourier decomposition. One of the most common techniques for evaluating optical measurement data is by means of a Fourier analysis. It is well known that for periodic and band-limited sequences the Discrete Fourier Transform (DFT) returns the true Fourier coefficients when exactly 1 period (or a multiple) is processed. Leakage will occur when less than 1 period is considered. This gives rise to non-negligible errors, which can be resolved by using the Generalized Regressive Discrete Fourier Series (GRDFS), introduced in this article. The measured signal is represented by a model using sines and cosines. The coefficients of those sines and cosines are then estimated together with the phase and frequency on a global scale by means of a frequency domain system identification technique. By making use of the regressive technique proposed in this paper, it is possible to reduce the data in comparison to the classical Fourier decomposition by a sizeable factor. In this article the method will be applied in particular to the reduction of data for laser vibrometer measurements performed on an Inorganic Phosphate Cement (IPC) beam (1D), as well as on an aluminium plate (2D). The proposed technique will also be validated on both 1D and 2D simulations of varying complexity.