Many analytical solutions and experimental techniques have been developed which attempt to characterize the dynamics of a structure. In this study, the dynamics of the structure under test are characterized by the spatial representation of the energy flowing through the structure. The spatial representation of the energy or power flow may be used to define the flow of energy from the energy sources to sinks. Conceptually, once the energy path in the structure can be characterized, the structure can be designed to channel or dissipate energy to meet design goals. This concept is analogous to designing the load path of a structure in static design. In order to obtain an accurate spatial model of the power flow and determine points of energy sources and sinks, a high spatial density of the structure response is required. It is impractical to obtain a high spatial density of the response with the use of accelerometers or other structurally mounted measuring devices. In this experimental approach, a scanning laser Doppler vibrometer (LDV) acquires data used in developing a spatial three dimensional model of the steady-state dynamic response. The system response is represented by the three-dimensional complex valued velocity field. From this experimentally derived spatial dynamics model, an accurate representation of the structure's actual energy and power flow can be extracted. In this research, the underlying assumptions in the analytical methods of power flow for beams are discussed and their effects are quantified. A scanning LDV is used to make velocity measurements by scanning the entire beam structure from multiple scan positions. The experimental spatial dynamics modeling technique is used to solve for the three-dimensional complex velocity field of the vibrating beam. From this spatial representation of the dynamic response, the components of power flow due to the shear force and the bending moment are extracted and used to determine the total power flow along the beam. With the methods presented in this paper, a spatial model of the experimental energy and power flow can be determined.

A vibrating sound source causes periodic pressure variations in the air. The pressure variations lead to corresponding variations in the refractive index of the air which can be measured using interferometric techniques like TV- holography. Each measurement maps a cross-section of the integrated sound fields. To obtain a complete map of the volume distribution of sound field we record cross-sections from different directions. Using topographical backprojection of these recordings, we reconstruct the amplitude and phase of the sound field in any plane of the volume.

The laboratory's test facilities are used to characterize the mechanical behavior of fuel assemblies of Pressurized Water Reactors (PWR). These structures are submitted to the excitation of the cooling fluid whose transverse and axial velocity fields are also measured. Fuel assemblies are made of long fuel rods (approximately 4 m) containing depleted uranium pellets. The rods are maintained together using structural grids located at different elevations. The LHC (Laboratoire d'Hydraulique de Coeur) is equipped with special test sections along with hydraulic loops to test these full scale mockups. In order to make measurement on the tested structure with optical devices, the test sections are equipped with a plexiglas front panel or viewports. The use of non contacting methods of measurement such as laser techniques are imposed by: (1) the inaccessibility of the structure studied due to the containment of the assembly in the test section, (2) the fact that the fluid (source of excitation) flowing around the rods should no be disturbed. A laser vibrometer equipped with optic fibers is used to make velocity measurements on the assemblies at different levels. In order to evaluate the level of vibration of the structure tested (fuel assembly or fuel rod), a differential laser vibrometer is used to measure the relative displacement of the assembly with respect to the test section or the relative displacement of the fuel rod with respect to the structural grids of the assembly. The differential technique is important because the higher structural modes of the assembly are mixed up in terms of frequency with the lower structural modes of vibration of the fuel rods.

A laser Doppler vibrometer prototype has been designed in order to get a simple and relatively inexpensive architecture of both the optical part of the system and the signal analysis electronics. In order to improve its operating performances fiber optic components have also been used. The metrological characteristics (measuring range, accuracy, signal to noise ratio, resolution, etc.) of the vibrometer have been evaluated by means of experimental results, comparing them with high performance commercial vibrometers. Some guidelines to develop the system for field applications are also discussed.

Discussed is the unique application of design of experiment (DOE) to structure and test a Taguchi L₉ (3²) factorial experimental matrix (nine tests to study two factors, each factor at three levels), utilizing an HeNe laser Doppler vibrometer and piezocrystal accelerometers to monitor the explosively induced vibrations through the frequency range of 10 to 10⁵ Hz on a flat steel plate (96 X 48 X 0.25 in.). An initial discussion is presented of pyrotechnic shock, or pyroshock, which is a short-duration, high-amplitude, high-frequency transient structural response in aerospace vehicle structures following firing of an ordnance item to separate, sever missile skin, or release a structural member. The development of the shock response spectra (SRS) is detailed. The use of a laser doppler for generating velocity- acceleration-time histories near and at a separation distance from the explosive and the resulting generated shock response spectra plots is detailed together with the laser doppler vibrometer setup as used. The use of DOE/Taguchi as a means of generating performance metrics, prediction equations, and response surface plots is presented as a means to statistically compare and rate the performance of the NeHe laser Doppler vibrometer with respect to two different piezoelectric crystal accelerometers of the contact type mounted directly to the test plate at the frequencies in the 300, 3000, and 10,000 Hz range. Specific constructive conclusions and recommendations are presented on the totally new dimension of understanding the pyroshock phenomenon with respect to the effects and interrelationships of explosive charge weight, location, and the laser Doppler recording system. The use of these valuable statistical tools on other experiments can be cost-effective and provide valuable insight to aid understanding of testing or process control by the engineering community. The superiority of the HeNe laser Doppler vibrometer performance is demonstrated.

In this paper a general overview of the applications of the double pulse holographic interferometry technique in CRF (FIAT Research Center) is presented, ranging from vibrational study of simple structures (panel) to dynamical characterization of mechanical structures undergone transient excitation (e.g. slamming car-doors). A comparison with some results obtained by EMA (Experimental Modal Analysis) is also shown.

An experimental procedure for measuring angular rotation vibration as well as translation, using a continuously-scanning Laser Doppler Vibrometer, is described. Sinusoidal scanning enables one angular vibration component to be measured but, by circular scanning, two principal angular vibrations and their direction can be derived directly from the frequency response sidebands. Examples of sine excitation measurements on a rigid cube are given. Processes of narrow-band random excitation and modal analysis are illustrated with reference to measurements on a freely-suspended beam. The laser beam was scanned by using x-y axis deflection mirrors; if this facility was not available, circular scanning could probably be achieved by using a rotating tilted mirror. Sideband frequency response references were obtained by using multiplied excitation force and mirror-drive signals.

This paper describes a laser-based system for measuring vibration on rotating discs. The setup allows the user to track an arbitrary periodic path at any multiple of the disc's rotational speed. In particular, the laser can be rotationally-locked to the disc and thus track a circle in space allowing continuous measurement of the response at a defined point on the disc for both constant and varying rotation speed. An electro-magnetic non-contacting shaker provides the forcing excitation to the rotating disc. Due to rotation, the vibration spectrum of the rotating disc becomes very complex. In particular, the disc vibrates at several frequencies other than the applied excitation frequency. A stepped sine method has been developed to measure and for parameter identification of the rotating disc vibration properties.

Acoustic intensity measurement techniques have been widely used for finding the acoustic power of a sound source from the acoustic energy flux in the space around it. Similar methods have been tried for measuring the vibration intensity or energy flux in plate structures, which require multi-point measurements with accurate information on phase differences. The present study extends the technique to web flutter in paper and plastic film manufacturing. The fundamental concepts of wave intensity are discussed, and the use of two laser-Doppler vibrometers is demonstrated. This study has application to flutter problems in paper dryers and in air-flotation ovens for plastic films.

Vibration of catalyst cell, which is inside the casing of the catalyst, is difficult to measure with usual measuring instrumentation. When catalyst is in use, there is hot exhaust gas flow though the catalyst cell and temperature of the cell is approximately +900 degree(s)C. Therefore non-contact Laser- Doppler-Vibrometer was used to measure vibration velocity of the catalyst cell. The laser beam was directed towards the cell through pipe which was put through and welded to the casing of the catalyst. The outer end of the pipe was screw down with a tempered class to prevent exhaust gas flow from the pipe. The inner end of the pipe was open and few millimeters away from the measuring point. Catalyst was attached to the engine with two ways, rigidly close to the engine and flexible under the engine. The engine was running in test bench under controlled conditions. Vibration measurements were carried out during constant running speeds of the engine. Vibration signals were captured and analyzed with FFT-analyzer. Vibration of catalyst cell was strongest at running speed of 5000 rpm, from 10 to 20 g (1 g equals 9.81 ms^-2), when catalyst was attached rigidly close to the engine. At running speed of 3000 rpm, vibration of catalyst cell was from 2 to 3 g in most cases, when catalyst was attached either rigidly or flexible to the engine. It is estimated that in real life, i.e. when catalyst is attached to car with same engine, vibration of catalyst cell at running speed of 5000 rpm is somewhere between 1 and 10 g. At running speed of 3000 rpm, which may be more often used when driving car (car speed approximately 100 kmh^-1), vibration of catalyst cell is probably few g's.

The Scanning Laser Doppler Vibrometry (SLDV) technique has brought modal testing into a new era. A galvanometer-based laser scanning system for SLDV provides the position accuracy, speed, and flexibility for data acquisition. Testing and calibrating such a scanning system to meet the precision requirements of modal testing has led to the development of the novel parallel-shift method for testing and calibration of the scanning system. This parallel-shift method can provide a cost-effect means for systematic laser scanning accuracy test. However, a number of measurement errors could be involved during the scanning accuracy test. These errors could severally affect the accuracy of the test itself. It is necessary to quantitatively determine the effects of the measurement errors to evaluate and to improve the accuracy of the test. This paper gives a detailed analysis for all the errors involved in the galvanometer-based laser scanning accuracy test using the parallel-shift method. Improvements of the test setup and test procedure are also proposed.

The state-of-the-art Scanning Laser Doppler Vibrometry (SLDV) technique provides an efficient data acquisition method for modal testing, especially on a large structure with high spatial data density. Two-dimensional angularly evenly spaced (in the laser beam scanning sense) data point distribution are generated. This causes an unevenly spaced data point distribution on the surface of the test structure in the most cases. The interval variations between data points can be quite large if the surface of the structure is not flat, such as an aircraft fuselage. The grid of data points will also become non-square. However, in many cases evenly spaced data point distribution with square or rectangular grids is highly desirable. One such case is when the structure is too large for one scan. A few separate scans are required to be patched together to describe the entire structure. The second example is when a structure needs to be scanned from different viewing angles and data points from different scans need to be coincident to extract 3-D velocity data of the surface of the structure. The third example is where the data points are used to obtain the wavenumber of the vibrating surface of the structure. In this paper, the original velocity data of a partial surface area of an aircraft fuselage were acquired to busing the SLDV technique with a high spatial density. The 2-D angular evenly spaced data then were mapped to a truly spatial evenly spaced coordinates by using the spatial DFT-IDFT technique. This DFT-IDFT technique can preserve original measured velocity information (even including the noise) during the mapping process. This 2-D data mapping technique certainly is not only limited to the fuselage, but also can be very useful for any 3-D structures, large or small, that require more than one scan to compleate surface velocity data acquisition.

In this paper, a geometrical method is presented to determine the pose (position and orientation) of a scanning laser vibrometer with respect to a structural coordinate system. Multiple registration points are simultaneously used to determine the pose in a least squares sense. The known information from each registration point is the structural coordinate and the corresponding scanning coordinate. Three steps are involved in the determination of the pose. The least squares method is applied to each of the three steps. The implementation of the geometrical method has been tested by simulated data and experimental data. The results have shown that this method and its implementation are correct and effective.

A design parameter based update methodology for updating finite models based on the results of experimental dynamics tests is presented. In the proposed method, analyst-selected design parameters are updated with the objective of making realistic changes to a finite element model that will enable the model to more accurately predict the behavior of the structure. This process of 'reconciling' the finite element model with experimental data seeks to bring uncertainty in design parameters into the formulation for realistic updates of the model parameters. The reconciliation process becomes a problem of system identification. Since the finite element model is a spatial model, the high spatial density measurement of the structure's operating shape by the scanning laser-Doppler vibrometer is highly desirable. The reconciliation process updates the selected design parameters by solving a non-linear least-squares problem in which the differences between laser-based velocity measurements and analytically derived structural velocity fields are minimized over the entire structure. In the formulation, design or model parameters with greatest uncertainty are identified first, retaining statistical qualification on the estimates. This method lends itself to cross-validation of the model over the entire structure as well as at several frequencies of interest or over a frequency range. Model order analysis can also be performed within the process to ensure that the correct model is identified. The experimental velocity field is obtained by sinusoidally exciting the test structure at a given frequency and acquiring steady-state velocity data with a scanning laser-Doppler vibrometer. Conceptually, the laser-based measurements are samples of the structure's velocity field of operating shape. The finite element formulation used to generate the analytical steady-state velocity field is derived using either a dynamic stiffness finite element formulation or a static stiffness/mass matrix formulation. The emphasis on operating shapes is a key concept in the process, as it focuses reconciling the finite element model directly with the laser-based measurements. This process avoids the process of comparing mode shapes extracted from the experimental data with eigenvalues and eigenvectors extracted from the finite element model. Thus, the intermediate modal model is eliminated from the reconciliation process. Non-linear optimization algorithms such as sequential quadratic programming or the Nelder-Mead simplex method are used to perform the parameter updates. The ability to impose constraints on parameter changes is useful for keeping the parameters at reasonable values and for preserving system characteristics such as total structure mass. Statistical knowledge of the parameters could also be utilized in this context to penalize large changes from prior parameter estimates.

An application of experimental spatial dynamics modeling is demonstrated for predicting the direct acoustic radiation of a vibrating structure based on experimental velocity response data. A scanning LDV was used to measure velocity response at thousands of locations on a operating reciprocating Freon compressor. Positionally registered data was acquired at multiple scanning positions of the LDV. A weighted least-squares discrete finite element formulation was applied to reconstruct the continuous 3-D velocity response field from the experimental data for a single frequency. The 3-D surface velocity model provided the data necessary for predicting acoustic radiation with a Finite Element/Boundary Element acoustic code. Experimental verification was achieved by acquiring acoustic measurements all around the compressor and comparing the results to the predicted response. The primary motivation for acoustic analysis of the compressor is to reduce the operating noise. This is the first time experimental dynamics analysis has been linked directly to the acoustic analysis of the operational compressor.

A scanning laser Doppler vibrometer (LDV) was used to model one frequency of the spatially continuous 3-D dynamic response of an operating Freon compressor using a finite element formulation. The geometry from a pre-existing finite element model provided the static shape model of a compressor. The scanning LDV measured the velocity response at thousands of locations on the pressurized operating compressor. Positionally registered velocity data was acquired at multiple scanning positions of the laser. A weighted least- squares discrete finite element model was used to reconstruct the continuous 3-D velocity response field from the experimental data. Dynamic 3-D angular velocities, displacements, and accelerations were easily computed from the full field velocity response model. Finally, dynamic strain and stress fields across the shell elements were extracted by directly postprocessing the dynamic response.

In this paper, direct stiffness correction methods (Berman-Baruch methods) are revisited for use as a tool for localizing structural faults based on spatially dense mode shapes obtained experimentally using laser Doppler velocimeters. Besides the standard Berman-Baruch formulation and a recently proposed iterative formulation which preserves sparsity, three other alternative formulations are proposed by the authors. The methods are evaluated using both numerically simulated and experimental data. The numerical example results (clamped-free beam) show that some of the formulations indicated clearly the fault location. With the experimental example (free-free beam), however, the fault localization wasn't so evident. The experimental modal test was done with conventional instrumentation. The authors expect that better results can be obtained using laser data.

Many reports concerning Laser Doppler Vibration Sensing describe the detection systems as 'High-Sensitivity', and imply this is a correct manner of specifying the performance of the optical system. In this paper, we describe how the performance of a vibrometer is determined by two parameters, which we have (arbitrarily) defined sensitivity and resolution. An analysis of these performance parameters for two different Vibrometer configurations shows that a fiber-optic based system which provides marginally lower sensitivity than its bulk optic counterpart, can actually provide a better resolution. An analysis of various applications and their system requirements, shows that Vibrometer users must understand which of these parameters is the most important. For example, NDT testing using an Ultrasonic Detecting LDV is shown to be mostly critical to resolution (small signal detection) and not so critical in terms of sensitivity (performance from poor quality surfaces). In this paper we present a method of defining sensitivity and resolution and outline the results obtained with fiber and non-fiber systems.

In view of stricter future statutory requirements concerning noise emissions by motor vehicles, the acoustic optimization of noise emitting components will become increasingly important. Customers complain about transmission noise when for example gears excite individual resonances (eigenfrequencies) of the transmission housing. Normally the eigenfrequencies and also the excitation frequencies are not moveable out of narrow limits. Therefore, in addition to optimizing gear geometry, the transmission housing must be designed so that dynamic forces acting through the gears onto the shaft bearing points lead to minimum level of radiated sound power from the transmission housing. For this reason, the resonance vibration shapes induced on a car transmission under operating conditions were measured using the laser-transmission test rig. Additionally, a comparison was made between the inspection of an empty transmission housing (using finite element calculation and experimental modal analysis).

The development of a systematic, whole body, visual recording process and its application to the study of disc brake noise and its recent adaptation to investigate drum brake noise is discussed. It is demonstrated that amplitude and vibration phase information my be obtained using classical double pulsed holographic techniques. Additionally it is demonstrated that details of a moving mode of vibration may be obtained in a rotating body. The application to drum brake noise show how low frequency noise (1 kHz) is related to backplate excitation whereas higher frequency noise (6 kHz) relates to drum excitation.

Previously described interferometric techniques for the measurement of rotational motion include the use of a differential mode interferometer directly acquiring the difference of two parallel velocity vectors at separate points of the rotating object. The difference value is immediately obtained in the optical domain and thus the resulting beat frequency at the detector output is directly proportional to the absolute value of the angular velocity. Despite the ingeniously simple design, this technique has some disadvantages: (1) Due to the direct heterodyning, the reflected beams must have a sufficient intensity to generate a useful signal at the interferometer's output. This results in the necessity of a retroreflective coating at the surface under investigation. (2) Acquisition of rotational vibrations is only possible if the rotational speed exceeds a certain value, because no useful carrier frequency will be generated at lower velocities. (3) This technique does not provide directional information. With the new approach described here, the two tangential velocity components needed are acquired separately using the principle of optical heterodyne interferometry and combined to provide rotational information after having been converted into electrical signals. Due to the heterodyning with the reference beam, this provides an optical amplification of each measurement beam and thus significantly increases the optical sensitivity of the system. As a result, measurements from most uncooperative surfaces are possible without any retroreflective coating. Furthermore, this technique allows us to define rotational direction and to acquire rotational vibrations at zero RPM as well.

Precision surfaces are needed in many fields. Usually they should be finished with nm order surface roughness as well as with a highly form accuracy. In order to know the textures of the machining surface and diagnose the machining process, the measurement should be carried out in the condition which is usually influenced by vibration disturbances. The purpose of this paper is to describe a new precision surface profiling probe - Integrated Holographic Optical Probe (IHOP) for precision surfaces profile measurement which is nearly insensitive to vertical vibrations. IHOP is an integrated sensor which serves a four sensors. It can be used in the differential mode to eliminate or to minimize errors caused by vibrations. In this first report, the computer simulation and experimental results are obtained. They show the sensitivity with the order of nanometers for this probe. The complexity and the size of the probe can be significantly reduced.

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.

A laser Doppler velocimeter (LDV) based on laser heterodyne interferometry is described in this paper and has been used to measure the dynamic characteristics of disks. The digital linear phase low pass filter and differential filter are designed and used in the data processing system. The measurement results on the dynamic characteristics, velocity, acceleration and runout in axial direction of the hard disk at 3600 rpm are given.

A new-type active vibration isolation system is developed for ultra-precision measuring system. It is composed of three sets of 3D Laser interferometer transducer and six groups of piezoelectric displacement executor to constrain six degrees of space movement and to realize real-time compensation of vibration. The active vibration isolation system can effectively eliminate low-frequency vibrations. Combined with passive vibration isolation system, it gives better vibration isolation effect.

Digital Speckle Pattern Interferometry (DSPI) is a non destructive testing optical method allowing the visualization of the defects of the deformations of an object submitted to static deformation or to vibration. This method can be applied to a lot of cases within a range of displacements between tens of nanometers and tens of micrometers. DSPI can be applied to detect the natural frequencies and to visualize the mode shapes of a vibrating object. It is very convenient to study small and weak objects because no contact is required comparing the classical modal analysis using accelerometers. DSPI was successfully applied to study a cantilever aluminum plate (5 cm X 10 cm X 1 mm). The experimental iso-displacement fringe maps are compared to computational results using a finite element method.

The aim of this work is to present an overview about the speckles produced from many surfaces used in automotive industries using different illuminating wavelengths e.g. white light, Hg and Na light sources. In order to minimize the effect of the reflected speckle grains from such surfaces one has to calculate the speckle grain size and contrast at different wavelengths and the visibility of interference fringes obtained and also the roughness of the rough surface used. The speckles recorded at different angle of incidence for light used to achieve the proper scattering angles which gives minimum speckle brightness causing distortion of the formed image for a moment. Speckles produced from non-spectral light sources were photographed also to identify the difference between such pattern and the speckle pattern obtained with He- Ne laser light source and purely spectral light sources. The visibility of the interference fringe pattern obtained by speckle photography technique with different wavelengths has been investigated experimentally and theoretically.

The need to predict the dynamic behavior of a structure is of paramount importance in many engineering applications. To achieve this goal a certain number of measurements of the structure under study are needed. Unfortunately, not all the measuring problems can be solved with traditional techniques: on small and light structures the mass loading effect of the instrumentation can yield to incorrect estimation; similarly, in case of high temperature surfaces and magnetically or electrically noisy environment the use of normal sensors, like accelerometers, might be unmanageable. The use of a non-contacting technique, like the Laser Doppler Vibrometer seems to be a way to overcome efficiently and elegantly these problems.

The paper describes a remote measurement technique by using laser to illuminate the moving grating (scattering object) which produces the Doppler effect of diffracted light to measure the tangential displacement (velocity). The optical systems that can realize the measurement are presented and their characteristics are compared. The principle of measurement is analyzed, and the foundation of selecting the grating and laser is discussed also. The result of experiment proves that the method produces qualified signal, and it can be used to measure the remote tangential displacement precisely. At the distance of 3,000 mm, the maximum accumulative error in the measurement range of 5 mm is less than 3 micrometers .

Ductile cast iron containers for transportation and deposition of radioactive waste have to be designed carefully in order to avoid unacceptable damages and leakages in case of an accident. Therefore various calculation and experimental methods are used during development and licensing of the containers. Besides others the container has to suffer severe impacts (e.g. falling from a height of several meters onto a concrete base). The level of strains must not exceed a value which would adversely affect the package in such a way that it would fail to meet the applicable requirements. In practice complex events as an impact are very difficult to calculate. Both the position of maximum stress and the time of its occurrence are not easy to be predicted with conventional methods. Therefore holography as an integral measuring technique was combined with strain gauge techniques and FEM calculations to analyze the integral and local loads of the container at drop tests. In this paper we explain the experimental and analytical proceedings and the combination of the results.

In this work we describe an optical sensor to determine the stress applied at a concrete structure. The optical sensor is a monomode fiber optic, that is embedded in the concrete. The principle of these sensors is based on photoelastic effect, that produces a birefringence in the optical fiber and induces a rotation on the polarization angle of the guided polarized light. The photoelastic effect is produced due to a controlled applied charge in the center of the concrete structure. The shift of polarization is analyzed by a polaroid analyzer.

The paper deals with the development and realization of diffraction grating interferometers for the accurate dynamic measurement of angular acceleration, angular velocity, and rotation angle. Comparison investigations between holographically and lithographically manufactured diffraction gratings are described and the influences of disturbing quantities leading to errors of measurement of the rotation angle are investigated.

At the PTB, two-beam interferometry has been further developed to accurately measure translational and rotational motion quantities at various time dependences over wide ranges of intensity. A uniform description is given of the interferometric method of measuring both translational and rotational motion quantities such as accelerations and angular accelerations. The paper focusses on an analysis of the dynamic behavior of an interferometric measurement system with regard to the measurement errors due to deterministic and stochastic disturbing quantities.

The Doppler shift spectrum of coherent radiation scattered from rough vibrating body is studied. The analytical expression for temporal correlation function of scattered field is obtained whereby the different types of scattering surface motion can be analyzed. Estimates of harmonic amplitudes were made the correlation properties of the spectrum were studied. It is found that when vibration amplitude is sufficiently small the set of harmonic amplitudes will fluctuate as a whole and will be highly correlated. With the rise of vibration amplitude the set of odd harmonic amplitudes remains to be highly correlated and so is the set of even harmonics. On further increasing the vibration amplitude the correlation between two sets diminishes and two sets become uncorrelated altogether.

The statistical properties of scattered coherent radiation from a rough body arbitrarily moving in its own plane are analyzed. Three cases of the optical geometry are considered: the free space, image plane of an optical system, and the focal plane of an optical system. The expressions for the space-time intensity correlation function and the corresponding power spectrum are derived. It is shown that in the case of small-amplitude vibrations, a contribution to the power spectrum of each mechanical vibration is proportional to the square of the mechanical vibration amplitude. An experiment carried out at (lambda) equals 0.63 micrometers by using the optical geometry of focal plane has verified the feasibility of noncontact measurement of mechanical vibration spectrum.

In the article the light beam behavior of a long distance laser collimation is experimentally studied and theoretically analyzed. The method of multiple- point monitoring and error correction is put forward to established a highly stable collimation datum line. The multiple-point sampling measurement system controlled by a microcomputer has been designed and established. A model of correcting the light beam drift by the method of mixed multivariable variance has been gotten. The influences of the light beam drift, the light beam incurve, the light beam random tremble, and etc. are comprehensively considered in the correcting model. The correcting model can be suited to different measurement conditions. The experiment result indicates that the light beam drift corrected by the mixed multivariable variance model makes form 45% to 80% reduction under different experiment conditions.

Two types of exciters have been investigated experimentally. One of the exciters uses a small permanent magnet fastened on the object. The force is introduced by the change in the electromagnetic field from a coil via an air gap. The second exciter is an eddy-current electromagnet one. The amplitude of the forces from these exciters are calibrated by using dynamic reciprocity in conjunction with electronic holography. These forces strongly depend upon the distance between the exciter and the object.

This paper summarizes the history of using acousto-optics to investigate ultrasonic fields both continuous and pulsed. There are a variety of methods yielding images of the fields and others yielding quantitative information.

One of the major objectives of industry is to curtail costs. An element, among others, that enables to achieve such goal is the efficiency of the production cycle machines. Such efficiency lies in the reliability of the upkeeping operations. Among maintenance procedures, measuring and analyzing vibrations is a way to detect structure modifications over the machine's lifespan. Further, the availability of a mathematical model describing the influence of each individual part of the machine on the total dynamic behavior of the whole machine may help localizing breakdowns during diagnosis operations. The paper hereof illustrates an analytical-numerical model which can simulate the behavior of a rolling housing. The aforesaid mathematical model has been obtained by FEM techniques, the dynamic response by mode superposition and the synthesis of the vibration time sequence in the frequency versus by FFT numerical techniques.

The application of a transportable electronic speckle pattern shearing instrument, based on multiple laser sources is presented. Uniform illumination over a wide surface is assured by inexpensive and multiple laser diodes. High visibility deformation and vibration patterns have been obtained using a modified Michelson interferometer, prisms, and diffractive components as shearing optics.

Modal tests were conducted on three annular plates with different ratio between inner and outer radius, both in air, a condition very close to vacuum, and completely immersed in water, in order to obtain modal properties. It is to note that only data on natural frequencies of vibration in vacuum are available in scientific literature. An advanced experimental apparatus based on a single-beam laser vibrometer and on a scanning laser vibrometer was satisfactorily used for tests in air and in water. Experiments confirmed that natural frequencies are strongly reduced due to the interaction between water and plate. Therefore the NAVMI factors for annular plates are introduced and experimentally evaluated for the test plates; these data are adimensional and could be used for applications. The boundary conditions of the plates are both free edges and the plates' material is low carbon steel.

The paper presents the application of a laser Doppler vibrometer as a nonintrusive measurement technique to detect damage of frescoes paintings. Experimental verification is carried on a wall where detachment of the external layer from the inner substrate is artificially introduced. Impulse excitation shows that frequency response functions identify the presence of any damage. Laser beam scanning provides a way to remotely investigate large areas of paintings. Acoustic excitation is also tested; it allows to excite resonant vibrations on detached areas. A measurement procedure is proposed and tested on the experimental wall and on field tests performed on a real fresco inside a church.

An 8-bars linkage, formed by two four-bars and one slider-crank mechanisms connected in series, designed to obtain a rectilinear motion of the output link with two dwell periods, has been tested to validate the desired output motion. The input crank is powered, using a belt transmission, by an asynchronous motor fed by a voltage source inverter. The displacement in the dwells, measured with a Laser Doppler Vibrometer, has been recorded for different values of the input crank speed. By comparison to theoretical results it is shown that, for high input crank speed, link elasticity and joint clearances strongly influence the displacement amplitude in the dwells.

This paper describes the invention of an entirely new interferometric transducer for remote measurement of vibration acceleration. Compared to Laser Doppler Velocimetry, the device will offer more straightforward operation for the engineering user by incorporating an optical configuration in which path lengths are inherently matched. The Laser Doppler Accelerometer will complement use of piezoelectric accelerometers in all situations where noncontact operation is necessary but its most important applications lie beyond the working range of piezoelectric accelerometers where extremely high accelerations or high shocks are encountered.

A new technique for real-time contrast enhancement and phase control of fringes in additive stroboscopic TV Holography applied to out-of-plane vibration analysis and its implementation of a fiber optic electronic speckle pattern interferometer (FOESPI) are presented. Synchronous stroboscopic illumination, firing two pulses per object's vibration period, is combined with simultaneous interpulse (high frequency) and interframe (low frequency) phase modulation in the reference arm of the ESPI yielding a sequence of frames (interferograms) that are grabbed and processed in real-time. With this artifice both speckle and fringes phases are independently controlled by means of the parameters of modulation enabling speckle contrast inversion, as required to enhance the visibility of fringes by sequential subtraction, as well as dynamic fringe phase shifting to solve peak-valley ambiguity.

Experiments were performed in a water tunnel to measure vibrations on a model hull appendage. The model was especially constructed to be in hydroelastic similitude. A scanning laser vibrometer system has been developed for these experiments. It is able to scan a 3D-grid map. The optical head was mounted on a displacement table controlled by the system. For each point of the model surface, the laser focus, the dynamic range are monitored by a personal computer and the vibration velocity signal is recorded automatically. The data are then processed. Multiple FFT averaging is done on each point for the vibrometer and for a reference accelerometer located on the model. The different frequencies corresponding to the structural resonances of the model are provided. For each of these frequencies, the system gives the amplitude of the vibration after integration of the velocity signal. The vibration map of the scan area can be displayed. The results of the different vibration modes were similar to those predicted by simulation.

Measurement systems based on image processing are used more and more in quality control. With aid of the interference ability of laserlight it is possible to gain the lost third dimension of 'normal' images in form of a phase relation. At the Lehrstuhl fur Feingeratebau der TU Munchen an electronic-speckle-pattern-interferometry (ESPI)-camera was constructed and continuously developed. The new arrangement enables to evaluate vibrations and deformations by ESPI and by Shearing Interferometry. Enjoyable are also the small dimensions of the camera.

Temporal and spatial evolution of shock waves generated during drilling processes of optical materials by a high repetition rate copper vapor laser were investigated by means of a CW probe beam deflection technique. Experimental results of the cinematic behavior and of the air density distribution of the shock wave were compared to respect a theoretical model of shock wave expansion providing also quantitative information on the main physical functions associated to laser-induced acoustic phenomena.

As the result of free surface deformation during laser-induced thermocapillary convection process near-surface flow velocity vector has a non-zero projection on direction laser beam spreads. This property of liquid flow allows to measure the velocity of near-surface mass flow using the backscatter signal from surface particle inclusions and rippling induced by surface tension gradient. Similar to coherent Doppler wind lidar scheme measurements can be formed by high intensity irradiating a target surface (with consequent phase transition in the boundary layer zone) and observing the Doppler shift in the frequency of the radiation backscattered from scatters within interaction region. We have proposed the monostatic interaction scheme. In this case interaction and probe regions are equivalent precisely. Our paper is devoted in investigation of laser-induced-near-surface thermocapillary convection flow in such target materials as water, paraffin, naphthalene, ehyl alcohol and oil using Doppler backscattered signal detected by heterodyne method.

In this paper a new measurement technique to analyze hand-arm vibration is proposed. The methodology is based on a laser scanning vibrometer, a new instrument that measures, without contact, vibration on grid points on a surface. The technique can be applied in laboratory tests and also to perform in field tests on hand-guided vibrating tools, vehicles, machine. Tests with sinusoidal vibrations up to 250 Hz have been performed on different subjects with their hand on three test devices, designed accordingly to ISO standards, has been used to verify the measurement technique. Further work has been started in order to develop a measurement system for mapping the mechanical impedance measurements in some points of the hand of different subjects are illustrated. These techniques prove to be very powerful to analyze hand-arm dynamic characteristics.

This paper describes a noncontact fiber optic probe for measuring tangential velocity of a surface and its normal displacement. The developed sensor is based on the intensity modulation of back-scattered light achieved by interaction of collimated laser beams with the moving surface; the probe has been realized using optical fibers and micro-lenses in order to miniaturize the system. Both the measurements of velocity and displacement are simultaneously obtained by using cross-correlation techniques. The device is tested on a specially prepared belt drive and its performance is compared with two different commercial measurement systems.

The ENEL power station of Bargi, Italy, houses a 185 MVA synchronous hydrogenerator/motor. Since three years, the vibrations of the high-voltage stator end-windings are continuously monitored by twelve optical fiber sensor, each consisting of an intensity-modulated proximity-sensor which detects the motion of an elastic cantilever by means of the triangulation technique. The results of vibration measurements over a period of several hours are presented, by considering both the pumping and generating modes of operation.

Build-up and bonding technology is of paramount importance for the manufacture of microelectronic components, since the reliability of electronic circuits depends in an essential manner on the quality of the connections responsible for the exchange of data and signals among the individual system components. A failure at only a single bonding site among as many as several hundred per component often results in failure of the entire system, and thus losses in the form of expenditures for production. The reproducible manufacture of the terminal contacts within very close tolerance limits is thus decisive for the quality and long-term reliability of the system.

For nearly ten years Volkswagen has been applying scanning laser vibrometry for analyzing vibrations and structure-born noise of auto parts, like engines, auxiliaries, gearboxes, and the whole body as well. Compared with holographic interferometry the scanning vibrometry offers the great advantage of measuring operation mode shapes. Operating modes or 'real motions' are unharmonic motions, consisting of more than one frequency component. By applying an FFT- algorithm it is possible to analyze the frequency spectrum of the vibrating structure. This measurement of multiple mode shapes is obtained by only one scanning process, a very time saving procedure. In this paper we present (1) applications of this technique in automotive development, (2) a detailed description of the measurement procedure, (3) a discussion of advantages and disadvantages, and a (4) comparison of specific features of commercially available vibrometers and our own prototype, called SOVAS.

The conventional practice of building quantitative dynamic models from experimental data is based of measurements from surface mounted transducers, accelerometers. In this practice, the accelerometer is mounted on the 'actual' structure under test with known position and orientation completely determining the magnitude and direction of the response. Because of the mass loading and local stiffening of the structure by surface mounted transducers, noncontact measurements of the response by transducers, such as the laser Doppler vibrometer (LDV), are being developed. The scanning LDV is ideal for this task as it also makes it practical to acquire high spatial density dynamic response measurements. However, there are two fundamental problems that are unique to non-contact measurement transducers, like the LDV, that must be resolved before they can be used to develop quantitative dynamic models. The two fundamental issues are determining (1) the point on the structure at which the measurement is acquired and the direction from which it is measured and (2) the 'actual' shape of the structure under test to resolve issue one. This paper describes shape modeling techniques which resolve these fundamental problems and provide the means for reconstructing the three- dimensional (3-D) velocity field of a vibrating structure using a scanning laser Doppler vibrometer.

Holographic and Speckle Interferometry provide full-field inspection of surfaces with high accuracy: these techniques offer some useful advantages (e.g. speed, high-precision,...) over other optical nonintrusive inspection techniques. Although the performance and precision of Holographic and Speckle Interferometry are affected by ambient conditions (temperature gradients, air turbulences, ...), the development of special experimental methods allows the use of these techniques directly in-field. An application of these interferometric methods can be foreseen, for example, in traditional testing laboratories or for a direct industrial production control. A great effort is currently in progress at ENEA-Frascati and at JRC-Ispra in order to develop new methods and computerized optoelectronic systems aiming at the application of Holographic and Speckle Interferometry to structural testing. Our most recent experimental results using time-average holographic interferometry and pulsed holographic interferometry for dynamic displacement measurements are presented. A theoretical background of the time-average ESPI procedure is described and some experimental results are shown.

The use of Laser-Doppler vibrometers for noncontact vibration measurements is increasing to allows the characterization of dynamic behavior of structures where the traditional accelerometers are unusable due to small sized structures, high frequency of high temperatures. Installed on a robotic deplacement system, these vibrometers allow the realization of cartographys. The system developed at CETIM comprises of two vibrometers on one 4 axes robot, and enables the mappings of vibrational velocity and also the measurement of energy flows, that allows the visualization of the of transmission paths and the calculation of the vibrational power for characterizing the forces injected into structures. Some techniques, like modal analysis can be improved by the use of such devices. The paper presents the system and the results obtained and insists on the practical aspects of experimentations. After a reminder of the quantities measured, the influential parameters are put forward: the surface state, the positioning of systems, sensitivity, the phase mismatch, aspects of signal processing on automatic measurements, etc...some examples of application are presented.

The technique of holographic interferometry by double-exposure and double- reference serves as a basis for a new method designed to obtain the magnitude and phase of the vibration field of a plate. The experimental findings in which the plate is excited by two shakers are then used to calculate the structural intensity which describes the transfer of vibrational energy by elastic waves in the structure. This calculation corresponds to a spatial Fourier transform of measurement data and to the processing of these data in the wavenumber domain. The divergence of the structural intensity vector is used to detect mechanical excitations on the plate.