Dynamic Deformation Measurement Research Articles

An optical fibre sensor for dynamic deformation measurements based on the intensity modulation of a low-coherence source

An optical fibre sensing technique for the measurement of dynamic deformations using a Michelson interferometer is reported. The method applied to interferometers with an initial path unbalance of around 1 cm is based on the rf intensity modulation of a low-coherence source. A large measurement range of 1 cm is intrinsic to the method and with an adequate demodulation process sensitivity better than 10 μm is obtained. This novel approach allows for measuring dynamic deformations with a bandwidth up to 100 Hz.

Measurement of out-of-plane static and dynamic deformations by processing digital speckle pattern interferometry fringes using wavelet transform

In this paper, we are presenting measurement of static and dynamic deformations in rectangular plate fixed at one end using digital speckle pattern interferometry (DSPI). To improve the measurement accuracy, we have developed a new filtering scheme based on combination of average/median filtering and Symlet wavelet filtering which enhances the signal-to-noise ratio (SNR) in the speckle interferogram obtained from DSPI. Experimental results show that our filtering scheme is quite effective in improving SNR of the speckle interferogram. The measurements by DSPI and calculations from beam theory in the case of out-of-plane static deformation and the measurements by DSPI and accelerometer in the case of dynamic deformation are in good agreement.

713 液柱マランゴニ対流の動的表面変形と表面温度変動の相関(オーガナイズドセッション7 流れの可視化応用解析)

Some recent studies (e.g., Kamotani & Ostrach 1998) on the onset of oscillation of thermocapillary flow (Marangoni convection) of a simulated half-floating zone have shown that the onset is not determined by the Marangoni number alone and dynamic surface deformation is conjectured to play an important role in the onset mechanisms. The present paper is aiming at obtaining a direct clue to the physical significance of the dynamic surface deformation by performing a series of simultaneous measurements of surface temperature oscillation and dynamic surface deformation. An IR camera with a framing rate of 30 fps is used to measure unsteady temperature distributions on the surface of liquid bridge after the onset of oscillation. Simultaneously, the dynamic surface deformation along an edge of the liquid bridge is measured by a microscopic imaging technique with a spatial resolution of 0.37 μm and a temporal resolution of 30 Hz. Their synchronous operation permits measurement of phase relationship between surface temperature oscillation and dynamic surface deformation. It is revealed that (1) the surface temperature exhibits a rotational oscillation of mode 1 with a period of 1.2 s under the present conditions (d=5 mm, Ar=0.5, V/V_0=0.62 and ΔT=ΔT_c+1 K), (2) there is about 180 deg phase difference between surface temperature oscillation and dynamic surface deformation, and (3) the rotational surface temperature oscillation has a spatial distribution inclined to the axis of liquid bridge in such a way that the phase of oscillation near the lower cooled disk proceeds to that near the upper heated disk.

Simultaneous three-dimensional dynamic deformation measurements with pulsed digital holography

The three deformation components x, y, z of a vibrating object are measured simultaneously by use of digital holography with a double-pulse ruby laser source. The object is illuminated from three different directions, each optically path matched with three reference beams such that three independent digital holograms are formed and added incoherently in one single CCD image. The optical phase difference between the two recordings taken for each hologram is quantitatively evaluated by the Fourier-transform method so that a set of three phase maps is obtained, representing the deformation along three sensitivity vectors. The total object deformation is obtained as a vector resultant from the data of the three phase maps. To give the full three-dimensional (3-D) description, the shape of the object is measured by the two-wavelength contouring method. Experiments are performed with a cylinder as the test object, transiently and harmonically excited. The 3-D deformation and shape measurement results are presented graphically.

Spatial phase-stepped interferometry using a holographic optical element

We describe two new techniques for spatial phase stepping using a computer-generated holographic optical element (HOE). The techniques are implemented with electronic speckle pattern interferom- etry, although they could be applied to other optical metrology methods. The first technique uses an HOE that introduces a known phase step between the 61 diffracted orders, without being translated. The interfer- ence phase corresponding to object deformation can be calculated from a single TV frame, and the technique is therefore suitable for the mea- surement of transient deformations. We apply the technique to measure the phase changes caused by refractive index variations in an evolving thermal plume. The second technique requires the HOE to be used in conjunction with a phase grating. In this technique, the HOE and the phase grating are used sequentially for the two exposures required in speckle interferometry (made before and after object deformation) and is therefore suitable for making dynamic deformation measurements with a double-pulsed interferometer. A root mean square (rms) precision of 2p/20 rad for the phase measurements is obtained. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)00712-6)

Amplitude modulation of a low-coherence source, applications to distance and dynamic displacement sensing

The possibilities of the radio-frequency amplitude modulation of a low-coherence source for distance and displacement measurements are discussed. This intensity-based method, used within a Michelson interferometer, is a novel alternative to perform dynamic deformation measurements. The theoretical background is presented, together with the experimental verification of the principle. Besides, the results of the first quasi-dynamic tests are shown and the perspectives of the technique discussed. This method is specially useful for the dynamic monitoring of civil structures, where large measurements bases are needed. Furthermore, the application of the amplitude modulation for distance measurements is demonstrated experimentally.

Real-time polarization phase shifting technique for dynamic deformation measurement

By using a special Ronchi phase grating and polarization phase shifting method, four phase shifted patterns can be captured simultaneously, and then the dynamic deformation can be measured. The analysis and experiments are given.

The dynamic deformation measurement of the high speed heated LY12 aluminium plate with moire interferometry

Using the moire interferometry method, the dynamic deformation of a pre-loaded LY12 aluminium tensile specimen under a thermal heating was studied. The dynamic deformation of the specimen under high speed heating procedures was recorded with a film video camera. The experimental results showed that it is feasible to use moire interferometry for measuring dynamic deformations under conditions of fast heating.

Measurement of gear tooth dynamic deformation using dynamic speckle photography

A new method of measuring gear tooth dynamic deformation is proposed. Dynamic speckle photographs of the rotating gear tooth have been achieved by combining the pulsed ruby laser with the out-syn-signal. Double speckle patterns of the whole mesh period of gear tooth are obtained by accurate time delay of the ruby laser. Gear tooth dynamic deformation of the whole mesh period is achieved using the automatic image processing. Testing results show that the trends of gear tooth deformation coincides with the calculation by the finite element method. The success of this new trying provides a new technique for the measurement of gear tooth dynamic deformation.

Three-Dimensional Deformation Comparison Between F-16 Bias and Radial Aircraft Tires

Abstract This paper presents an optical technique called fringe projection to measure 3D tire deformation subjected to different loads, percentages of deflection, and yaw angles. Unlike the well-known Moiré method, the proposed technique uses a single light source and one grating, thus requiring no image superposition. As a result, the measurement is not as sensitive to vibration as the Moiré method. The fringe projection also differs from the commonly used optical inspection technique in manufacturing industry via line scanning known as structured light, which cannot be applied to dynamic deformation measurements. The recently developed subpixel resolution was employed to accurately locate the optical fringe centers, which in turn improves the accuracy in 3D geometry determination. A fiber-optic displacement sensor was also placed close to the tire sidewall to measure the deformational change of the selected reference point. Finally, the deformations are compared between F-16 bias and radial aircraft tires when subjected to the same loading conditions.

Relationship of Pressure Wave Velocity to Self-Excited Oscillation of Collapsible Tube Flow

o investigate the causes of self-excited oscillations of collapsible tube flow, measurements of dynamic tube deformation were conducted using a laser displacement meter supported on a pulse-motor stage together with an electromagnetic flow meter. The results have clarified that fluid velocity approaches pressure wave velocity, which is estimated from the tube law, at the throat around the stability boundaries and that a supercritical flow and subcritical flow occur alternately during oscillations. By contrast, a linearized lumped parameter model has been developed. The model demonstrates that slight supercritical flow leads to instability of the negative stiffness type and also suggests that negative dynamic resistance induces instability of the negative damping type. Although causes such as unsteady flow separation were not examined here, a self-excited oscillation caused by supercritical flow close to choking has been verified experimentally and theoretically.

Relation of Pressure Wave Velocity to Self-Excited Oscillation of Collapsible Tube Flow.

To investigate causes of self - excited oscillations of collapsible tube flow, measurements of dynamic tube deformation were conducted with a laser displacement meter carried on a pulse-motor stage together with an electromagnetic flow meter. The results have clarified that fluid velocity approaches pressure wave velocity, which is estimated from the tube law, at the throat around the stability boundaries and that supercritical flow and subcritical flow occur alternately during oscillations. On the other hand, a linearized lumped parameter model has been developed. The model explains that slight supercritical flow leads to jnstability of negative stiffness type and also suggests that dynamic negative resistance induces instability of negative damping type. Though the causes such as unsteady flow separation were not examined here, a self-excited oscillation caused by supercritical flow close to choking has been verified experimentally and theoretically.

Measurements for dynamic deformation by mismatch white speckle method

This paper presents a simple method for measurements of dynamic deformation by mismatch white speckle method using dynamic photoelastic device. The method is able to measure not only large dynamic deformation[1], but also small dynamic deformation. Combined with dynamic isochromate pattern, the elastic modulus Poisson's ratio and dynamic material fringe value of the material measured can be obtained by the method.

HOLOGRAPHIC INTERFEROMETRY FOR ROTATING SUBJECT

Holographic interferometry has been applied to the measurement of dynamic deformation taking place over an object during rotation. An exact match of the reconstructed images, one recorded in rotation and the other in repose, is achieved by an optical arrangement designed for the purpose and ensures clear interference fringes over the object. A Q-switched ruby laser is used for the recording. A preliminary experiment is described.