Bernardino Barrientos

Measurement of out-of-plane deformation by combination of speckle photography and speckle shearing interferometry

Summary We measure the derivative of out-of-plane deformation in presence of large in-plane rigid body displacement (RBD) by a combination of Electronic Speckle-Shearing Pattern Interferometry (ESSPI) and speckle photography. We use digital speckle photography in order to compensate for the in-plane RBD and eliminate any decorrelation effects. ESSPI techniques are then applied to the compensated speckle images to obtain the derivative of the out-of-plane deformation. The method is tested on an aluminum plate subjected to simultaneous out-of-plane deformation and large in-plane RBD. The results indicate that the proposed method preserves the fringe contrast observed in ESSPI.

Modal vibration analysis of a metal plate by using a laser vibrometer and the POD method

The proper orthogonal decomposition (POD), also known as Karhunen–Loeve expansion, is applied to the modal vibration analysis of a metal plate. The metal plate was subject to vibrations with an electrodynamical shaker in a range of frequencies from 100 to 5000 Hz. The data were obtained from the measurements with a laser vibrometer. The plate vibration measurements were used to calculate the eigenfunctions and the eigenvalues. It was found that a large fraction of the total energy of the vibrations is contained within the first four POD modes. The essential features of the vibrations are thus described by only the first four eigenfunctions.

Measurement of transient deformation by color encoding

We present a method based on color encoding for measurement of transient 3D deformation in diffuse objects. The object is illuminated by structured light that consists of a fringe pattern with cyan fringes embedded in a white background. Color images are registered and information on each color channel is then separated. Surface features appear on the blue channel while fringes on the red channel. The in-plane components of displacement are calculated via digital correlation of the texture images. Likewise, the resulting fringes serve for the measuring of the out-of-plane component. As crossing of information between signals is avoided, the accuracy of the method is high. This is confirmed by a series of displacement measurements of an aluminum plate.

Out-of-plane displacement measurement by electronic speckle pattern interferometry in presence of large in-plane displacement

We measured out-of-plane displacement in presence of large in-plane displacements and deformations by electronic speckle pattern interferometry (ESPI). By means of digital speckle photography (DSP) the large in-plane displacement is measured and then compensated by software from interferometric images, before calculating the phase distribution related to the out-of-plane deformation. This means that decorrelation effects are not present and that the use of intermediate images is not necessary. The optical phase was extracted by spatial phase shifting, which enables the study of rapid transient events. The proposed method was applied to different combinations of out-of-plane deformation and large in-plane displacement. The compensation of large in-plane displacement allows us to maintain the contrast of ESPI fringes.

Multiplicative electronic speckle-pattern interferometry fringes

A theoretical analysis of fringe patterns and its experimental corroboration obtained by multiplication of two speckled images with electronic speckle-pattern interferometry (ESPI) are reported. A specifically designed digital filter is used to enhance the contrast and visibility of the inherently noisy multiplication fringes. Phase retrieval is achieved by a phase-stepping technique. Experimental results are presented for the in-plane-sensitive optical ESPI setup; however, out-of-plane and shearing setups may be used as well. The method represents an alternative to the subtraction and addition techniques in ESPI.

Aeolic vibration of aerial electricity transmission cables

A feasibility study for amplitude and frequency vibration measurement in aerial electricity transmission cable has been made. This study was carried out incorporating a fringe projection method for the experimental part and horizontal taut string model for theoretical one. However, this kind of model ignores some inherent properties such as cable sag and cable inclination. Then, this work reports advances on aeolic vibration considering real cables. Catenary and sag are considered in our theoretical model in such a way that an optical theodolite for measuring has been used. Preliminary measurements of the catenary as well as numerical simulation of a sagged cable vibration are given.

New method for optical object derotation

A new optical method capable of measuring out-of-plane deformations of rotating objects based on the Fourier transform phase decoding technique is presented. Digital holography is used to test the method, which digitally derotates one of the holograms at its phase reconstruction stage to accurately remove object rotation fringes, uniquely rendering phase maps that quantitatively show the out-of-plane deformation. Commonly, object derotators are based on creating standing images of the rotating object under study. Typically, this is achieved by means of a rotating prism that has to be precisely synchronised with the object rotation. In contrast, this new method eliminates the need of using the expensive mechanical servomechanisms contained in the commercially available optomechanical derotators by using double pulsed digital holography in conjunction with Fourier optics.

Non-spherical seeding 3D positioning from CCD images using Lorenz-Mie theory

This paper describes the imaging of spherical and non-spherical particle diffraction patterns using plane-wave illumination. A discussion is presented on both the theoretical analysis of the diffraction pattern of the particle on its image plane using the Lorenz–Mie theory and its applicability to non-spherical particles. The images obtained for both spherical and non-spherical particles are quantitatively compared to calculated results, and implications for particle position estimation of non-spherical particles are discussed.

Three-dimensional displacement in multi-colored objects

Three-dimensional displacement in multi-colored objects is measured by combining fringe projection (FP) and digital image correlation (DIC). Simultaneity of measurements through both techniques is warranted by encoding their signals on the RGB channels of color images. By separating the illuminating sources for each technique and by using ultraviolet light for DIC, contrast and amplitude of the registered signals are enhanced, enabling displacement measurement of multi-colored objects in dynamic events. The objects may even present a relatively large dynamic range of intensity levels. Proper selection of the light sources is supported by spectral analyses of the components of the system and by evaluation of the contrast of the registered images. Experimental results reveal that displacement measurements with relatively high accuracy can be obtained.

Performance comparison of background-oriented schlieren and fringe deflection in temperature measurement, part 2: experimental evaluation

Abstract. In part 1 of the study, background-oriented schlieren (BOS) and fringe deflection (FD) were numerically compared when used for the measurement of temperature. The aim of this part is to experimentally corroborate the obtained numerical results. In this regard, we analyze an axisymmetric flame issued by a gas nozzle. Fringe deflection and BOS images are recorded at two different points in time and the corresponding displacement results are compared. Furthermore, we implement a variation of the techniques that allows us to carry out simultaneous displacement measurements by them. In this case, the signals of the techniques are encoded on the RGB channels of a color background image. The results confirm that FD slightly outperforms BOS, in particular for images that contain relatively high temperature gradients or regions with low contrast.