Double-pulsed Holographic Interferometry Research Articles

The measurement of the absolute displacement of a noisy disc brake

The investigation of in-plane vibration of a noisy disc brake is problematic because it is difficult both to measure and to verify. Because of the disc structure and the inability to visualize disc in-plane vibration, there has been reluctance by researchers to accept the contribution of a displacement parallel to the surface of the object, or in-plane displacement, to noise generation. In addition to measuring absolute displacement, it has been difficult to isolate the in-plane and out-of-plane components of displacement using either non-contact or conventional displacement measurement techniques. This paper investigates absolute displacement of a brake disc during noise generation. Double-pulsed holographic interferometry is used to record a series of time-related images of the brake head from three different angles of observation. Because each image views the brake head from a different perspective, each of them records a different degree of in-plane and out-of-plane displacement. By careful analysis of the three images, it is possible to isolate the in-plane displacement from the out-of-plane displacement. The time-related series allows the displacement to be investigated over a full cycle of excitation and so create an animation of the mode of vibration. It is seen that the in-plane displacement is complex and that its amplitude may be about twice that of the out-of-plane displacement.

Experimental study of micro shock wave focusing for precise medical applications

For applying shock waves to sensitive medical procedures like cranioplasty in a close vicinity of the brain or treatment of myocardial dysfunction, generation of micro underwater shock waves plays an important role. Such delicate applications make limits on usage of conventional shock wave (SW) sources. In the present research a half‐ellipsoidal cavity with 20.0‐mm minor diameter and the ratio of major to minor diameters of 1.41 was designed as a compact extracorporeal SW source. Silver azide AgN3 pellets ranging from 1.0 to 20 μg with their energy ranging from 1.9 to 38 mJ were used to generate shock waves at the first focal point F1 inside the reflector. Irradiation of a Q‐switched Nd:YAG laser beam through a 400‐μm optical fiber was used to ignite the pellet. The whole sequences of the shock wave generation, propagation, and focusing were visualized by quantitative double pulse holographic interferometry and time‐resolved high speed shadowgraph methods. Pressure histories were measured at the shock wav...

Four-pulse interferometric recordings of transient events by pulsed TV holography

With traditional double-pulsed holographic interferometry or pulsed TV holography, the experiment usually has to be repeated to allow the recording of a time sequence of interferograms of the event. With the proposed technique a sequence of four interferograms of a solitary transient event is measured. A twin oscillator, injection-seeded, pulsed Nd:YAG laser is incorporated into a pulsed TV holography set-up. With orthogonal polarisation and double pulsing of each of the two channels of the laser, four pulses are recorded on two separate CCD-frames. Four interferograms of a laser-impacted plate obtained from the same experiment, show how the bending waves develop and propagate in the plate.

Micro-Shock Waves Generated Inside a Fluid Jet Impinging on Plane Wall

An Nd:glass laser pulse (18 ns, 1.38 J) is focused in a tiny area of about 100-mum diam under ambient conditions to produce micro-shock waves. The laser is focused above a planar surface with a typical standoff distance of about 4 mm, The laser energy is focused inside a supersonic circular jet of carbon dioxide gas produced by a nozzle with internal diameter of 2.9 mm and external diameter of 8 mm, Nominal value of the Mach number of the jet is around 2 with the corresponding pressure ratio of 7.5 (stagnation pressure/static pressure at the exit of the nozzle), The interaction process of the micro-shock wave generated inside the supersonic jet with the plane wall is investigated using double-pulse holographic interferometry. A strong surface vortex field with subsequent generation of a side jet propagating outward along the plane wail is observed. The interaction of the micro-shock wave with the cellular structure of the supersonic jet does not seem to influence the near surface features of the flowfield. The development of the coherent structures near the nozzle exit due to the upstream propagation of pressure waves seems to be affected by the outward propagating micro-shock wave. Mach reflection is observed when the micro-shock wave interacts with the plane wall at a standoff distance of 4 mm, The Mach stem is slightly deflected, indicating strong boundary-layer and viscous effects near the wall. The interaction process is also simulated numerically using an axisymmetric transient laminar Navier-Stokes solver. Qualitative agreement between experimental and numerical results is good.

Error-compensating phase-calculation algorithm in rapid-switching double-pulsed holographic interferometry

An algorithm is presented for calculating the phase difference that is obtained with rapid-switching, double-pulsed holographic interferometry. Imperfect switching between reference beams in between two laser pulses causes a distortion in the phase-stepped interferograms that results in erroneous phase calculation when conventional phase-calculating algorithms are used. Instead of estimating the error that is involved, an extra step is added to a more conventional algorithm such as Carré's algorithm, so that this leakage effect is compensated for. Thus the desired phase difference is found. Also, a measure is found for excluding unreliable calculations, based on the light intensities and phase steps for each pixel and the leakage ratios.

Shock waves in an elliptical cavity with varying height

Transient shock waves in a confined elliptical chamber are experimentally investigated. Quantitative results of the pressure distribution are obtained for an air-filled cavity. Lower bounding surfaces of different geometrical shapes can be inserted making it possible to get chambers with varying height. An electrical discharge across a pair of electrodes inside the cavity gives rise to the shock waves. Double pulsed holographic interferometry is used to study the propagation and focusing process of the waves. The results are quantitatively evaluated by using the method of two-reference-beam holography. The angular pressure distribution behind the converging wave front is presented for different geometries of an air-filled cavity. The pressure distribution is non-homogeneous but symmetric along the wave front. The pressure level is higher for the geometry where the height of the chamber decreases with the radial distance from the outgoing focus and lower for increasing height of the chamber. In addition, shock waves in a water-filled cavity are studied. In this case qualitative results are obtained.

Transient acoustic near field in air generated by impacted plates

The transient acoustic near field in air from impacted cantilever plates of two different geometrical shapes and materials is studied using two-reference-beam double-pulsed holographic interferometry. The acoustic waves, observed in two directions simultaneously, are generated by traveling flexural waves in the plates and by the impact process itself. A subsequent phase-stepping procedure is used for quantitative evaluation of the registered two-dimensional projections of the acoustic fields. An interesting observation is the acoustic radiation at the free end of the plate, where sound waves propagate into the air in oblique directions from the plate. At the region right above the free end no acoustic waves are observed. Supersonic flexural waves in the plates generate trace-matched acoustic waves in the surrounding air. Calculations of the corresponding two-dimensional transient acoustic fields are performed. Those are based on an analytical solution of the Kirchhoff plate equation. Calculated results reproduce the character of the observed transient acoustic waves quite well.

Digital Double-Pulse Holographic Interferometry for Vibration Analysis

Different arrangements for double-pulsed holographic and speckle interferometry for vibration analysis will be described. Experimental results obtained with films (classical holographic interferometry) and CCD cameras (digital holographic interferometry) as storage materials are presented. In digital holography, two separate holograms of an object under test are recorded within a few microseconds using a CCD camera and are stored in a frame grabber. The phases of the two reconstructed wave fields are calculated from the complex amplitudes. The deformation is obtained from the phase difference. In the case of electronic speckle pattern interferometry (or image plane hologram), the phase can be calculated by using the sinusoid-fitting method. In the case of digital holographic interferometry, the phase is obtained by digital reconstruction of the complex amplitudes of the wave fronts. Using three directions of illumination and one direction of observation, all the information necessary for the reconstruction of the 3-dimensional deformation vector can be recorded at the same time. Applications of the method for measuring rotating objects are discussed where a derotator needs to be used.

Digital Double-Pulse Holographic Interferometry for Vibration Analysis

Different arrangements for double-pulsed holographic and speckle interferometry for vibration analysis will be described. Experimental results obtained with films (classical holographic interferometry) and CCD cameras (digital holographic interferometry) as storage materials are presented. In digital holography, two separate holograms of an object under test are recorded within a few microseconds using a CCD camera and are stored in a frame grabber. The phases of the two reconstructed wave fields are calculated from the complex amplitudes. The deformation is obtained from the phase difference. In the case of electronic speckle pattern interferometry (or image plane hologram), the phase can be calculated by using the sinusoid-fitting method. In the case of digital holographic interferometry, the phase is obtained by digital reconstruction of the complex amplitudes of the wave fronts. Using three directions of illumination and one direction of observation, all the information necessary for the reconstruction of the 3-dimensional deformation vector can be recorded at the same time. Applications of the method for measuring rotating objects are discussed where a derotator needs to be used.

Digital double-pulse holographic interferometry using Fresnel and image plane holograms

Different arrangements for digital double-pulse holographic and speckle interferometry for vibration analysis are described. In the case of digital double-pulse holographic interferometry, two separate holograms of an object under test are recorded within a few microseconds using a CCD camera and stored in a frame grabber. The phases of the two reconstructed wave fields are calculated from the complex amplitudes which are obtained by digital reconstruction of the wavefront produced by the hologram. The deformation is obtained from the phase difference. In the case of ESPI (or image plane hologram) the phase can be calculated by using the sinusoid-fitting method or the Fourier method. Using three directions of illumination and one direction of observation, all the information necessary for the reconstruction of the three-dimensional deformation vector can be recorded at the same time. Applications of the method for measuring rotating objects are discussed, together with the derotator needed.

Visualization of surface waves propagating over surfaces eroded due to particle impact

The continuous impact of particles onto a material surface results in erosion. In technical applications particles with a diameter from microns up to millimetres impinge onto surfaces with velocities up to 10 m s −1. In order to investigate experimentally the erosion at the surface of crystalline materials plates of austenitic steel were locally damaged owing to the repeated impact of solid particles. The amplitude of the elastic surface deformation which is excited by the impact of a single particle is only 10 −9-10 −7 m. The surface deformation which is caused by such an impact was measured by means of double-pulse holographic interferometry. Because of the small amplitude of the surface waves quasi-heterodyne holographic interferometry was required. The areas of initial wear of the materials can be recognized by the disturbed propagation of the surface waves.

Interferometric study of organized motions in turbulent boundary layers

Double-pulse holographic interferometry has been used to visualize organized structures in zero-pressure-gradient turbulent boundary layers over a flat plate at M=1.8, 2.5, and 3.6 (Re 0 =1.2×10 4 to 2.2×10 4 ) Differential interferograms taken with a pulse interval between 2 to 600 μs at three different Mach numbers show an interesting array of fringe cells that appear inclined downstream in the boundary layers. These fringe cells must be the interferometric images of large-scale outer-layer structures convecting in the main flow direction. On absolute interferograms of the boundary layers, the interferometric images appear as horizontal fringe lines running over the test surface. The wavy fringe pattern frequently exhibits distinct inclined interfaces with a positive upstream density gradient that must be associated with the backs of large-scale outer-layer bulges. Quantitative information of these structures has been extracted from the interferograms that is in agreement with data from other investigators using different experimental techniques. To aid the interpretation of the experimental data, interferograms have been generated numerically with the database from a large-eddy simulation. These interferograms also reveal regular fringe patterns in the boundary layer that are found to be produced by the large-scale structures in the layer

Measuring the deformation of crystalline materials due to the impact of eroding particles

The continuous impact of particles on to a material surface results in erosion. In technical applications particles with a diameter from some microns up to some millimetres impinge on to surfaces with velocities up to some ten metres per second. In order to investigate experimentally the erosion at the surface of crystalline materials plates of austenitic steel are locally damaged due to the repeated impact of solid particles. The amplitude of the surface deformation which is excited by the impact of a single particle is only 10 −9−10 −7 m. The surface deformation which is caused by such an impact is measured by means of double-pulse holographic interferometry. Because of the small amplitude of the surface waves quasi-heterodyne holographic interferometry is required. The areas of initial wear of the materials can be recognized by the disturbed propagation of the surface waves.

On structure-borne sound: Experiments showing the initial transient acoustic wave field generated by an impacted plate

The initial propagating transient acoustic field in air generated by an impacted plate is visualized. The transient traveling flexural waves in the plate created by the impact are shown, simultaneously. The experiments are performed using double pulsed holographic interferometry. It is shown that flexural waves in a plate act as a series of traveling acoustic sources. Since the flexural waves in the plate are dispersive the trace matched acoustical waves further away from the impact source propagate at a smaller angle relative to the plate than those closer to the impact. An observer situated close to the plate and away from the impact point will first receive high-frequency components of the sound. A quantitative evaluation of the acoustic field also shows that if there is a transient increase in pressure on one side of the plate there will be a similar decrease on the other side.

Holographic interferometry in wave phenomena visualization

Double-pulsed holographic interferometry and a well controlled impact were employed in visualization of wave phenomena in a steel beam. Heat liberation due to the impact was also visualized.

Transient wave response of the violin body

In this investigation, the dispersive, transient wave propagation field of a complete violin excited by a mechanically induced impulse at the top of the bridge is presented. By means of double pulsed holographic interferometry with a ruby laser as light source the propagating wave field is recorded. From presented interferograms, it is seen that initially the top plate acts mainly as a nonsymmetric dipole with centers at the two bridge feet. The back plate is strongly coupled to the motion of the top plate by the sound post and acts more like a monopole. Thus the position of the sound post is crucial to the performance of the instrument. The free edges at the f-holes are very early reached by the dispersive bending waves of high amplitude probably giving a significant contribution to the sound of the violin family instruments.

Three-dimensional flow visualization of shock wave using double-pulsed holographic interferometry. 1st report, Three-dimensional measurement of shock wave configuration generated from the flying u-shaped pin in a supersonic flow and its date processing.

It is extremely important to obtain basic knowledge of shock waves formed in turbo machines rotating at supersonic speed. The main purpose of this research is to develop an advanced 3-dimensional visualization technique using double-pulsed holographic interferometry with diffused laser light. As the initial step of this research, this technique was applied to observation of the oblique shock waves generated at a "U" -shaped pin, which was utilized in order to get better understanding of the 3-dimensionality of an object flying counter to the supersonic flow in this 1st report. The oblique shock waves generated at each edge could be visualized by the interference fringes and clearly separated in the reconstructed real image. Also by employing the reconstructed process coupled with a spatial filter, it could be verified that this diffused double-pulsed holography is effectively applicable to the 3-dimensional measuring technique of the shock wave. Furthermore, the algorithm for real-time data processing was developed.

Three-dimensional flow visualization of shock wave using double-pulsed holographic interferometry. 2nd report, Flow visualization for three-dimensional shock structures in rotating aeroengine fan blade rows.

The growing demand for more fuel-efficient aero gas turbine engines has led to the need for a detailed understanding of the aerodynamic behavior of components. The optical technique of holography has recently achieved importance as a means of providing the experimental data necessary for the development and validation of relevant design calculation methods. This paper describes the double-pulsed holographic flow visualization technique which has been developed at IHI and provides information on 3-dimensional shock structures of the transonic flow region between the blades and shock/casing wall boundary layer interaction in rotating aeroengine fan at various rotor speeds and throttling conditions.

レーザを用いた噴霧粒子の計測

A basic knowlege for laser speckle photography (LSP) and in-line holographic interferometry is highly essential to obtain two-dimensional velocity distribution of particle jet impinged by the nozzle. LSP can measure the velocity distribution for the entire impinging field. However it is rather difficult to apply this LSP for the high-speed or unsteady flow using CW lasers like Ar-ion or He-Ne gas lasers with the optical chopper due to the intensity of palusive laser light.From this point of view the effort was made to obtain two dimentional velocity field of high-speed particle jet by the giant double pulsed ruby laser in this paper. It is clarified from the results that LSP using double pulsed laser can be masured with high accuracy in the renge of 51-10(m/sec). Parallel with this LSP method, double pulsed holographic interferometry technice is also carried out in order to visualize the two dimensional velocity field of particle, jet. This result agree well with the ones obtained by the LSP method. Through these total considerations, this LSP method is proved to be highly effective for the flow mesurement in a high speed particle jet.

画像処理による衝撃波形状の三次元表示

This paper describes the technique of three-dimensional graphic display for the shock wave structures. The shock waves generated at a U shaped pin which is moving in the supersonic flow field of a converging-diverging nozzle is visualized by the double pulsed holographic interferometry. The hologram obtained by this method is reconstructed and the shock wave profiles at each of the cross-sections of the real image are thinned by image processing. The numerical data which indicated the thinned shock waves are constructed by computer graphics techniques. As a result, the three-dimensional shock wave structures were clearly visualized by graphic display.