Single Point Laser Doppler Vibrometer Research Articles

Deflections and frequencies of long-span steel railroad truss bridges under passenger train excitation using laser Doppler vibrometer

ABSTRACT Given the critical challenge of aging infrastructure, it is imperative to adopt novel techniques that utilize modern technology to assess the structural integrity of existing bridges. This study presents a methodology to estimate the loading frequency of the train passing over the bridge and bridge dynamic responses, such as the acceleration and displacement response of long-span open-deck steel railroad truss-type bridge under the passenger train excitation using a Laser Doppler Vibrometer. The selected bridges for this study were the Cos Cob and Devon Railroad bridges in southern Connecticut, both in the Northeast Corridor. The structural response of the bridge floor system was collected during the field test using a single-point laser Doppler vibrometer and uniaxial accelerometers for reference under passenger trains, such as Metro-North M8, Amtrak Regional, and Amtrak Acela. The recorded data were analyzed using the moving load theory, interpreted, and discussed in the time and frequency domain. The study findings indicate that the bridge response and displacement align with the theoretical and vehicle axle loads. Also, it should provide valuable information about the behavior of the considered bridges under typical operating conditions.

Detection of Barely Visible Impact Damage in Composite Structures Using Backward Sweep Vibro-thermography Technique Utilizing Asymmetry in Local Defect Resonance

ABSTRACT In this article, local defect resonance-based vibrothermography has been studied for different sweep direction and ranges. Two different carbon fiber-reinforced polymer (CFRP) composite plate has been fabricated from vacuum assisted resin transfer molding. In the first plate, a flat bottom hole has been made and two barely visible impact damages are created in other plate. The area of delamination has been determined from phased array ultrasound testing. Laser doppler vibrometry (LDV) has been performed first for different sweep ranges and directions. The CFRP plate is excited with a piezoelectric element at 150 Vpp and the vibration over defect area is captured using a single point laser doppler vibrometer, operating in scanning mode. It has been found that vibration amplitude at local defect resonance (LDR) frequency increases in narrow sweep range compared to a wideband excitation. Again, in both cases, it has been found that backward sweep produces more amplitude compared to forward one due to softening nonlinearity. An asymmetry in LDR frequency is also been observed when the sweep range is further narrowed. An uncooled microbolometer camera is used for reception in case of vibrothermography. Backward sweep is found to be more effective as compared to the forward one and the temperature increment increases in case of narrowband excitation range.

Measurement of the full wave field on a shell using a single-point laser Doppler vibrometer

To experimentally measure the complicated vibration and wave characteristics of a shell, a 3D scanning laser Doppler vibrometer is a competent but costly instrument due to the requirement of exactly aligning each point when scanning the shell. Here we propose a simplified measuring method just by utilizing a single-point laser vibrometer fixed on a motorized positioning system. The clamp can be rotated to adjust the incident angles and translated to capture the whole tested region. During each test in a specific incident angle, the signals are interpolated to generate a continuous wave field in both the time domain and the frequency domain, eliminating the need for alignment. The in-plane and out-of-plane wave fields are obtained from the measured 3D signal using the projection relationship, and then verified both experimentally and numerically. Furthermore, we show that the present method can be used to test complex wave fields, such as the scattering field by obstacles on a cylindrical shell. The present work may stimulate systematically experimental studies on the wave propagation and vibration on shells.

A novel demodulation method with a reference signal for operational modal analysis and baseline-free damage detection of a beam under random excitation

A novel demodulation method with a reference signal is developed for operational modal analysis and damage detection of a beam structure under random excitation. The novel demodulation method can process measurements of the beam by a continuously scanning laser Doppler vibrometer (CSLDV) system and measurements of a reference point on the beam by a single-point laser Doppler vibrometer to estimate its modal parameters, such as damped natural frequencies and undamped mode shapes. Damped natural frequencies of the beam are estimated from fast Fourier transforms of measurements of the CSLDV system. A cross-correlation function between a measurement of the CSLDV system and a measurement of a single-point laser Doppler vibrometer is calculated, and the cross-correlation function is multiplied by a sinusoidal signal whose frequency is an estimated damped natural frequency of the beam. The processed cross-correlation function is filtered by a low-pass filter to obtain the undamped mode shape of the beam that corresponds to the estimated damped natural frequency of the beam. Smooth polynomials are used to fit estimated undamped mode shapes, which can be considered as undamped mode shapes of an undamaged beam. Curvatures of estimated undamped mode shapes and polynomials are compared by curvature damage indices to determine the location of a damage in the beam. The novel demodulation method with a reference signal is investigated for baseline-free damage detection from both finite element simulation and experiment. Modal parameters of a finite element model of the damaged beam and a damaged beam specimen, which are under random excitation, are successfully estimated, and locations of damages in the beam model and beam specimen are accurately determined.

Stress and strain calculation method for orthotropic polymer composites under axial and bending ultrasonic fatigue loads

Accelerated fatigue testing is one potential solution to evaluate the very high cycle fatigue behavior of composite materials within a reasonable amount of time. The ultrasonic fatigue testing methodology can be adopted to realize fatigue experiments up to 109 cycles at 20 kHz, compared to conventional fatigue experiments usually carried out between 5–50 Hz. The determination of cyclic stresses during ultrasonic loading remains to be one of the major challenges. The cyclic stresses during ultrasonic fatigue loading were investigated for a carbon fiber 5H satin fabric reinforced in Polyetherketoneketone (CF-PEKK) composite material. Two experimental setups were developed to perform ultrasonic testing under uni-axial and three-point bending loading conditions. A 3D-Scanning Laser Doppler Vibrometer (3D-SLDV) and a single-point Laser Doppler Vibrometer (LDV) were integrated into the test systems to measure the oscillation displacement of the CF-PEKK specimens during ultrasonic cyclic loading. These displacement measurements were used to calculate the resulting strains and stresses under elastic loading conditions. The experimental results were found to be in good agreement with those obtained from finite element models, providing evidence for applying the proposed method.

Effect of freezing and embalming of human cadaveric whole head specimens on bone conduction

Background and aimsConserved specimens do not decay and therefore permit long-term experiments thereby overcoming limited access to fresh (frozen) temporal bones for studies on middle ear mechanics. We used a Thiel conservation method which is mainly based on a watery solution of salts. In contrast to pure Formalin, Thiel conservation aims to preserve the mechanical proprieties of human tissue. The aim of this study is to examine the effect of Thiel conservation on bone conduction in the same specimen before and after conservation. MethodsNine ears of five defrosted whole heads were stimulated with a direct, electrically driven, bone anchored hearing system (Baha, Baha SuperPower). The motion produced by bone conduction stimulation was measured with a single point laser Doppler vibrometer (LDV) at the promontory, the ossicular chain, and the round window through a posterior tympanotomy. After the initial experiments, the entire whole heads were placed in Thiel solution. In order to enable direct comparison between fresh frozen and Thiel specimens, our Thiel conservation did not include intravascular and intrathecal perfusion. The measurements were repeated 3 and 12 months later.To determine the effect of freezing, defrosting, and embalming on the whole heads, CT scans were performed at different stages of the experimental procedure. Additionally, three extracted temporal bones were stimulated a Baha, motion of the promontory measured by LDV and embalmed in Thiel solution to investigate the direct impact of Thiel solution on the bone. ResultsThe averaged magnitude of motion on the promontory increased in whole head specimens by a mean of 10.3 dB after 3 months of Thiel embalming and stayed stable after 12 months. A similar effect was observed for motion at the tympanic membrane (+7.2 dB), the stapes (+9.5 dB), and the round window (+4.0 dB). In contrast to the whole head specimens, the motion of the extracted temporal bones did not change after 3 months of Thiel embalming (-0.04 dB in average). CT scans of the whole heads after conservation showed a notable brain volume loss mostly >50% as well as a remarkable change in the consistency and structure of the brain. Partial changes could already be observed before the Thiel embalming but after 1–2 days of defrosting. In an additional experiment, a substitution of brain mass and weight by Thiel fluid did not lead to new deterioration in sound transmission. In contrast, a frozen (non-defrosted) whole head showed a distinctively reduced magnitude of promontory motion before defrosting. DiscussionFor our setup, the vibration of the ear due to bone conduction in the same whole head specimens significantly increased after Thiel conservation. Such an increase was not observed in extracted temporal bone specimens.Due to brain changes in the CT scans, we investigated the consequences of the brain volume changes and structure loss on the frozen brain before defrosting. The loss of brain volume alone could not explain the increase of ear vibrations, as we did not observe a difference when the volume was replaced with Thiel fluid. However, freezing and defrosting of the entire brain seems to have a major influence. Beside the destructive effect of freezing on the brain, the modified conservation method without perfusion changed the brain structure.In conclusion, bone conduction in whole heads depends on the physical condition of the brain, rather than on the conservation.

Chemical expansion of CeO2−δ and Ce0.8Zr0.2O2−δ thin films determined by laser Doppler vibrometry at high temperatures and different oxygen partial pressures

The chemical expansion of ceria (CeO2−δ) and ceria-zirconia (Ce0.8Zr0.2O2−δ, CZO80) thin films is investigated by high-temperature laser Doppler vibrometry (LDV) at temperatures from 600 to 950 °C. The films are deposited on single-crystalline 8 mol-% yttria-stabilized zirconia substrates, which act as pumping cells to adjust oxygen non-stoichiometry in the thin films. Oxygen deficiency causes film expansion, leading to mechanical strain that bends the sample. The total displacement, i.e., the sum of bending and film-thickness change, is determined contact-less by LDV. A differential laser Doppler vibrometer (D-LDV) is realized to enable measurements on a very long time scale, which is necessary due to the long equilibrium times of the ceramic films. These displacements are compared to those acquired with a commercial single-point laser Doppler vibrometer (SP-LDV) for motions above 1 Hz. Here, both devices yield similar results. CZO80 films are found to bend a substrate much more than ceria films under similar experimental conditions. A model describing the displacement of the sample is derived from the Stoney model and applied to calculate deflections using literature data. The displacements at the center of the CZO80 sample measured with the SP-LDV increase from 0.18 nm at 10 Hz and 600 °C to 32.7 nm at 0.1 Hz and 800 °C. For ceria, the displacements range from 1.6 nm (10 Hz, 800 °C) to 79.4 nm (0.1 Hz, 900 °C). The D-LDV enables the detection of quasi-static displacements at very low frequencies. The ceria sample exhibits 218 nm at 0.001 Hz and 800 °C.

Vibration Measurements of the Gerbil Eardrum Under Quasi-static Pressure Sweeps.

Tympanometry provides an objective measurement of the status of the middle ear. During tympanometry, the ear-canal pressure is varied, while the response of the ear to sound pressure is measured. The effects of the pressure on the mechanics of the middle ear are not well understood. This study is a continuation of our previous work in which the vibration response of the gerbil eardrum was measured in vivo under quasi-static pressure steps. In this study, we delivered a continuous pressure sweep to the middle ear and measured the vibration response at four locations for six gerbils. Vibrations were recorded using a single-point laser Doppler vibrometer and glass-coated reflective beads (diameter ~ 40µm) at the umbo and on the mid-manubrium, posterior pars tensa and anterior pars tensa.The vibration magnitudes were similar to those in the previous step-wise pressurization experiments. Most gerbils showed repeatability within less than 10dB for consecutive cycles. As described in the previous study, as the frequency was increased at ambient pressure, the vibration magnitude on the manubrium increased slightly to a broad peak (referred to as R1) and then decreased until a small peak appeared (referred to as R2), followed by multiple peaks and troughs as the magnitude decreased further. The low-frequency vibration magnitude (at 1kHz) decreased monotonically as the pressure became more negative except for a dip (about 500Pa wide) that occurred between - 700 and - 1800Pa. The lowest overall magnitude was recorded in the dip at mid-manubrium. The vibration magnitudes also decreased as the middle-ear pressure was made more positive and were larger than those at negative pressures. R1 was only visible at negative and small positive middle-ear pressures, while R2 was visible for both positive and negative pressures. R2 split into multiple branches after the middle-ear pressure became slightly positive. No magnitude dip was visible for positive middle-ear pressures.The low-frequency vibration magnitudes at negative middle-ear pressures on the pars tensa were higher than those on the manubrium. R1 was not visible for large negative middle-ear pressures on the pars tensa. R2 appeared as a multi-peak feature on the pars tensa as well, and a higher-frequency branch on the posterior pars tensa appeared as a trough on the anterior pars tensa. The magnitude dip was not present on the pars tensa. The largest overall magnitude was recorded at the R2 peak on the posterior pars tensa.The results of this study expand on the findings of the step-wise pressurization experiments and provide further insight into the evolution of the vibration response of the eardrum under quasi-static pressures.

Augmenting a single-point laser Doppler vibrometer to perform scanning measurements

Laser Doppler vibrometers (LDV) are used for non-contact vibration measurements of various structures and are frequently used for stringed instrument measurements. Single-point LDVs can be used with the roving hammer or LDV method for mode shape measurements, but this is time-consuming and requires constant attention. Scanning LDVs exist but are expensive and often out of reach of musical acoustics researchers. An inexpensive apparatus to modify a common single-point LDV such that it can perform automated scanning measurements is presented. The augmentation consists of a mirror galvanometer, impact hammer controller, and 3D printed mounting hardware. The scanning system is controlled by a microprocessor and can be easily automated. The total cost of the system, excluding the LDV and impact hammer, is under two hundred dollars. Measurements of guitars are presented to validate the scanning system and discuss any shortcomings.

Vibration Measurements of the Gerbil Eardrum Under Quasi-static Pressure Steps.

Tympanometry is a relatively simple non-invasive test of the status of the middle ear. An important step towards understanding the mechanics of the middle ear during tympanometry is to make vibration measurements on the eardrum under tympanometric pressures. In this study, we measured in vivo vibration responses in 11 gerbils while varying the middle-ear pressure quasi-statically, with the ear canal at ambient pressure. Vibrations were recorded using a single-point laser Doppler vibrometer with five glass-coated reflective beads (diameter ~ 40μm) as targets. The locations were the umbo, mid-manubrium, posterior pars tensa, anterior pars tensa and pars flaccida. As described in earlier studies, the unpressurized vibration magnitude was flat at low frequencies, increased until a resonance frequency at around 1.8-2.5kHz, and became complex at higher frequencies. At both the umbo and mid-manubrium points, when the static pressure was decreased to the most negative middle-ear pressure (- 2500Pa), the low-frequency vibration magnitude (measured at 1.0kHz) showed a monotonic decrease, except for an unexpected dip at around - 500 to - 1000Pa. This dip was not present for the pars-tensa and pars-flaccida points. The resonance frequency shifted to higher frequencies, to around 7-8kHz at - 2500Pa. For positive middle-ear pressures, the low-frequency vibration magnitude decreased monotonically, with no dip, and the resonance frequency shifted to around 5-6kHz at + 2500Pa. There was more inter-specimen variability on the positive-pressure side than on the negative-pressure side. The low-frequency vibration magnitudes on the negative-pressure side were higher for the pars-tensa points than for the umbo and mid-manubrium points, while the magnitudes were similar at all four locations on the positive-pressure side. Most gerbils showed repeatability within less than 10dB for consecutive cycles. The results of this study provide insight into the mechanics of the gerbil middle ear under tympanometric pressures.

Round window and promontory movements during bone conduction with different middle ear conditions in Thiel embalmed specimens

Background: Thiel conservation is mainly based on a watery solution of salts. We have shown that bone conduction (BC) evokes motion in normal middle ears of Thiel embalmed specimens that is comparable to the motion for other cadaveric models.Aims/Objectives: We evaluated whether promontory and round window (RW) motion identifies differences in BC transmission for different middle ear conditions.Methods: We investigated the conditions of mobile ossicle chain, cement-fixed stapes and stapedectomy in seven ears. A retroauricular bone anchored hearing system provided BC stimulation. The motions of the promontory and the RW were measured using single point laser Doppler vibrometer (LDV, HLV1000, Polytec).Results: The averaged differences between the conditions were small for RW motion and for promontory motion. However, for RW motion we found differences of more than one standard deviation at some frequencies. These differences in RW motion were more apparent when we limited the analysis to three selected specimens.Conclusions and Significance: Extracochlear measurement of the RW motion with LDV allowed differentiation between BC for different middle ear conditions. These changes could be detected best in a small frequency range in selected specimens. Promontory motion could not be used to differentiate between different conditions of the middle ear.ABBREVIATIONS: LDV: laser Doppler vibrometry; Prom: cochlear promontory; RW: round window; ST: stapes; TM: tympanic membrane; VProm: velocity of the promontory; VRW: velocity of the round window

Three-dimensional full-field vibration measurements using a handheld single-point laser Doppler vibrometer

The laser Dopper vibrometer (LDV) has become a standard instrument to perform high spatial resolution 3D vibration measurements of complex structures. An important step in the LDV measurement procedure is the estimation of the pose of the instrument relative to the test object. Existing LDV pose estimation methods rely on the use of 3D range sensors to perform this task. These sensors are costly and often their spatial resolution and accuracy is too limited for an accurate LDV pose estimation. But most importantly, existing LDV pose estimation techniques are slow. In this paper, we present a novel LDV pose estimation method based on matching of a 2D camera image and a CAD model of the test object. In contrast to existing pose estimation techniques, our method is able to track the pose of the LDV in real-time (up to about 30 LDV positions per second). This means that our method also allows LDV pose estimation when either the LDV or the object is moving. Using the real-time LDV pose tracking we present a new LDV measurement methodology where we hold instrument in our hand while moving around the test structure. This allows us to perform full-field scanning and 3D velocity measurements with a low-cost single point LDV sensor. We show that the measurement accuracy of a stationary handheld LDV measurement is about 40 dB (which is about 10 dB lower than in the case of measurements on a tripod). Furthermore, we demonstrate that the 3D vibrations measurements using the handheld vibrometer have an error of about 20% compared to classical measurements performed by combining three LDV measurements on a tripod. We illustrate our method on vibration measurements of a composite bicycle frame.

Laser doppler vibrometer validation of an optical flow motion tracking algorithm

Abstract Background The use of single point laser Doppler vibrometer is well established for evaluating displacement or validation in many applications such as scientific research, defence, manufacturing, and biomedicine with other techniques. In this research, breast shaped fabricated phantoms are used in laser Doppler vibrometery to validate the optical flow motion measuring algorithm used in a mechanical vibration based breast cancer screening system. Methods Three different silicone phantoms were used: healthy; 10 mm inclusion and 20 mm inclusion. The overall goal was to use single point laser Doppler vibrometer data to validate digital image-based elasto-tomography (DIET) motion data from optical flow tracking at frequencies of 16 Hz, 24 Hz, 32 Hz, and 40 Hz. Summary of findings Results show excellent validation with errors less than 6% for healthy phantom, and errors less than 8% for 10 mm inclusion and 20 mm inclusion. Conclusions The overall results from the optical flow motion algorithm used with DIET and a laser Doppler vibrometer at every frequency show the optical flow algorithm captures surface motion of breast shaped silicone phantoms with good accuracy. The optical flow algorithm is thus suitable and robust enough for use in clinical breast screening. Finally, the errors presented quantify explicitly the error of this algorithm verses this laser-based gold standard.

Measurement and prediction of cavitating flow-induced vibrations

The objective of this paper is to investigate the unsteady cavitation behaviors and the corresponding cavitating flow-induced vibrations. Results are presented for the modified NACA66 hydrofoils made of stainless steel and POM Polyacetate respectively at Re = 6.0×105 for various cavitation regimes. The high-speed camera and the single point laser Doppler vibrometer (LDV) are used to observe the transient cavitating flow patterns and measure the vibration velocities. The results showed that the vibration amplitude increases dramatically for the cloud cavitation due to the development of large-scale cloud cavity. The main flow-induced frequencies, which are in accordance with the cavity shedding frequency, decrease with the decrease of the cavitation number. As for the effect of the hydroelastic response on the vibration behavior, the lift coefficient for the POM Polyacetate hydrofoil fluctuates more significantly with a larger mean value than that for the stainless steel hydrofoil. Compared with the vaporous cavity along the suction side of the stainless steel hydrofoil, the cavity for POM Polyacetate hydrofoil appears to be fragmentized. The main vibration frequencies for the POM Polyacetate hydrofoil are larger than that for the stainless steel hydrofoil, with the chaotic hydroelastic response with high frequency.

Analytical and experimental investigation of the interaction of Lamb waves in a stiffened aluminum plate with a horizontal crack at the root of the stiffener

This paper addresses an analytical and experimental analysis based on the physics of the Lamb wave propagation and interaction with the discontinuity. An analytical method called “complex modes expansion with vector projection (CMEP)” is used to calculate the scattering coefficients (amplitude of the out-of-plane velocity) of Lamb wave modes from geometric discontinuities. Two cases are considered in this research: (a) a plate with a pristine stiffener and (b) a plate with a cracked stiffener. Complex-valued scattering coefficients are calculated from 50 kHz to 350 kHz for A0 incident waves. Scatter coefficients are compared for both cases to identify a suitable frequency range to excite Lamb waves using a piezoelectric wafer active sensor (PWAS) to detect the crack. The frequency-dependent complex-valued scatter coefficients are then inserted into the global analytical model. The global analytical solution predicts time domain scattered signal from the discontinuity. The crack can be detected by comparing the waveforms for pristine stiffener and cracked stiffener. An experiment was conducted for both pristine stiffener and cracked stiffener to compare with the analytical results. A long PWAS was placed parallel to the waveform to create straight crested Lamb wave modes in the plate. Antisymmetric Lamb wave modes were selectively excited by using two PWAS transducers placed on opposite sides of the plate and energized by out-of-phase signals. A single-point laser Doppler vibrometer (LDV) was used to measure the out-of-plane velocity of scattered Lamb waves on the plate. The obtained experimental results agree well with the analytical predictions.

Mesenchymal stem cell-laden hybrid scaffold for regenerating subacute tympanic membrane perforation

Tympanic membrane (TM) perforation is one of the most common otology complications. To date, there has not been reported TM regeneration using bioprinted scaffold. The purpose of this study was to evaluate the efficacy and feasibility of bioprinted polycaprolactone/collagen/alginate-mesenchymal stem cell (PCAMSC) scaffolds for the regeneration of subacute TM perforation. Sprague-Dawley rats were used in an animal model of subacute TM perforation. In the experimental group (n=7), bioprinted 3D PCAMSC scaffold was placed on the perforation. The control group (n=7) were treated with polycaprolactone/collagen/alginate (PCA) scaffold. Healing time, acoustic-mechanical properties, and morphological analysis were performed by otoendoscopy, auditory brainstem response (ABR), single-point laser doppler vibrometer (LDV), optical coherence tomography (OCT), and light microscopic evaluation. The closure of the TM perforation was achieved in 100% of the experimental group vs. 72% of the control group, and this difference was statistically significant (p<0.05). The ABR threshold at all frequencies of the experimental group was recovered to the normal level compared to the control group. TM vibration velocity in the experimental group recovered similar to the normal control level. The difference are very small and they are not statistically significant below 1kHz (p=0.074). By OCT and light microscopic examination, regenerated TM of the experimental group showed thickened fibrous and mucosal layer. In contrast, the control group showed well regenerated but less thickened than experimental group. From these results, the cell-laden PCAMSC scaffold offers a significant advantage in the TM regeneration in a rat subacute TM perforation model. It may offer attractive opportunities in the conservative clinical treatment.

Physical and numerical investigation of the flow induced vibration of the hydrofoil

The objective of this paper is to investigate the flow induced vibration of a flexible hydrofoil in cavitating flows via combined experimental and numerical studies. The experiments are presented for the modified NACA66 hydrofoil made of POM Polyacetate in the closed-loop cavitation tunnel at Beijing Institute of Technology. The high-speed camera and the single point Laser Doppler Vibrometer are applied to analyze the transient flow structures and the corresponding structural vibration characteristics. The hybrid coupled fluid structure interaction model is conducted to couple the incompressible and unsteady Reynolds Averaged Navier-Stokes solver with a simplified two-degree-of-freedom structural model. The k-ω SST turbulence model with the turbulence viscosity correction and the Zwart cavitation model are introduced to the present simulations. The results showed that with the decreasing of the cavitation number, the cavitating flows display incipient cavitation, sheet cavitation, cloud cavitation and supercavitation. The vibration magnitude increases dramatically for the cloud cavitation and decline for the supercavitation. The cloud cavitation development strongly affects the vibration response, which is corresponding to the periodically developing and shedding of the large-scale cloud cavity. The main frequency of the vibration amplitude is accordance with the cavity shedding frequency and other two frequencies of the vibration amplitude are corresponding to the natural frequencies of the bending and twisting modes.

Experimental investigation of the flow-induced vibration of hydrofoils in cavitating flows

The objective of this paper is to investigate the correlation between fluid induced vibration and unsteady cavitation behaviours. Experimental results are presented for a modified NACA66 hydrofoil, which is fixed at α=8°. The high-speed camera is synchronized with a single point Laser Doppler Vibrometer to analyze the transient cavitating flow structures and the corresponding structural vibration characteristics. The results showed that, with the decreasing of the cavitation number, the cavitating flows in a water tunnel display several types of cavitation patterns, such as incipient cavitation, sheet cavitation and cloud cavitation. The cavity shedding frequency reduces with the decrease of the cavitation number. As for the cloud cavitation regime, the trend of the vibration velocity goes up with the growth of the attached cavity, accompanied with small amplitude fluctuations. Then the collapse and shedding of the large-scale cloud cavities leads to substantial increase of the vibration velocity fluctuations.

How Geometric Misalignments can affect the Accuracy of Measurements by a Novel Configuration of Self-Tracking LDV

Aim of the paper is to evaluate the reliability of a novel configuration of a Laser Doppler Vibrometer (LDV) for the measurement of vibrations affecting rotating components of machines. In the paper an analysis of errors due to the possible static misalignments of the mirrors utilized in an experimental apparatus has been carried out. This instrument was set up for the estimation of the out of plane vibrations of moving (rotating) objects, in order to give a better characterization of the self-tracking technique employed with the use of a 1D single point LDV and its measurements. The accuracies of the measures are mostly linked to the interaction between environment and instrumentation.

The Tuning Fork Examination: Are You Performing It Correctly?

Objectives: The tuning fork remains a useful diagnostic tool in modern otolaryngology practice. Two important variables help describe the sound generated by the tuning fork: frequency and amplitude. We sought to determine whether the manner in which a tuning fork is activated affects its vibrational response. Methods: A Polytec OFV-5000 single point laser Doppler vibrometer was used to obtain direct velocity measurements after activation of 256 Hz, 512 Hz, and 1024 Hz tuning forks with several striking methods: striking the parietal bone, striking the pisiform bone, striking a wood table, and striking a metal surface. Each method was tested using three separate subjective intensities: softly, medium force, and significant force. Data were analyzed using the Polytec Vibrometer Software to produce a velocity spectrum and measurements of frequency and velocity amplitude. Results: The predominant frequency of motion of all tuning forks was their expected fundamental frequency. Additional nonharmonic frequencies were recorded when striking the 256 Hz and the 512 Hz tuning forks against metal or wood. The aberrant frequencies were of lower intensity relative to the fundamental frequency of the tuning fork. Conclusions: No additional frequencies were seen with activation on the head or pisiform bone or with the 1024 Hz fork using any method. For the 256 Hz and 512 Hz tuning forks, striking a hard surface produced additional and potentially misleading frequencies. As some providers use this test to guide surgical candidacy decisions in stapes surgery, this could have significant impact in clinical decisions.