Equidensometry applied to photoelasticity

Agfacontour film has simplified photographic procedures so that equidensity techniques can now be applied in photoelastic practice and other work requiring evaluation of optical fringes for fractional orders. Direct photography and copying from conventional negatives are described and practical considerations indicated.     

On the effect of quarter-wave-plate errors in stress-holo-interferometry

The purpose of this paper is to analyze the influence of imperfect quarter-wave plates on the fringe configuration which is obtained in holographic interferometry. It has been found that isopachics may be substantially shifted by very small errors in the retardation of the quarter-wave plates. An alternative multiexposure technique using plane-polarized light is proposed. This technique eliminates the quarter-wave-plate error and preserves the full-field character of the interferometic method. The technique is proven analytically and experimentally.     

Speckle technique for dynamic drop profile measurement on rough surfaces

A technique has been developed for measuring three-dimensional instantaneous drop profiles on rough surfaces. The surface is illuminated using a laser and images are captured of the resulting speckle pattern with and without the drop in place. The analysis consists of finding the contact line, measuring the deformation of the speckle field caused by refraction of light at the drop surface, then reconstructing the drop using simulated annealing optimization to find the drop shape whose shift vector field best matches the one measured. An error analysis of the technique was performed using a Monte Carlo technique and comparisons to sideview drop images for a large sample of drops. Mean contact angle measurement error was found to be −1.6° with a 1 − σ error bound of −6.9°, +2.0°.     

Shear layer instabilities in low-density transverse jets

The near-field shear layer instabilities forming in round transverse jets of variable (reduced) densities relative to the crossflow are investigated through gas-phase experiments. Jets composed of helium and nitrogen mixtures are injected from a converging nozzle mounted flush with an injection wall into air crossflow, allowing the jet-to-crossflow density ratio S to be varied between 1.00, the equidensity case, and 0.14, at constant jet Reynolds number Re _j ?=?1,800. Jet-to-crossflow momentum flux ratios J are examined in the range $\infty>J\geq5$ at incremental values of the density ratio S. The results of single-component hotwire measurements in the jet shear layer indicate that a transition to global instability likely occurs as J is brought below approximately 10, and/or as S is brought below approximately 0.45?C0.40. This observation appears to link many previous independent studies of both equidensity transverse jets and low-density free jets, which may become globally unstable under alteration of J and S, respectively. However, the dynamical character of the transition to global instability in the low-density transverse jet displays differences under independent variation of J and S, which may indicate the predominance of different modes.     

A laser induced fluorescence technique for quantifying transient liquid fuel films utilising total internal reflection

This paper describes the development of a laser induced fluorescence (LIF) technique to quantify the thickness and spatial distribution of transient liquid fuel films formed as a result of spray–wall interaction. The LIF technique relies on the principle that upon excitation by laser radiation the intensity of the fluorescent signal from a tracer like 3-pentanone is proportional to the film thickness. A binary solution of 10% (v/v) of 3-pentanone in iso-octane is used as a test fuel with a Nd:YAG laser as the excitation light source (utilising the fourth harmonic at wavelength 266 nm) and an intensified CCD camera is used to record the results as fluorescent images. The propagation of the excitation laser beam through the optical piston is carefully controlled by total internal reflection so that only the fuel film is excited and not the airborne droplets above the film, which had been previously shown to induce significant error. Other known sources of error are also carefully minimised. Calibrated temporally resolved benchmark results of a transient spray from a gasoline direct injector impinging on a flat quartz crown under atmospheric conditions are presented, with observations and discussion of the transient development of the fuel film. The calibrated measurements are consistent with previous studies of this event and demonstrate the applicability of the technique particularly for appraisal of CFD predictions. The potential utilisation of the technique under typical elevated ambient conditions is commented upon.     

Vortex dynamics in the wake of a mechanical fish

A novel Stereo PIV technique, with improvements over other techniques, is presented. The key feature of the new technique is the direct measurement of calibration data at each point in space on the measurement grid, so that no interpolation is necessary. This is achieved through the use of a contiguous target which can be analysed using standard PIV processing software. The technique results in three-dimensional measurements of high accuracy with a significantly simpler calibration phase. This has the benefit of improving ease of use and reducing the time taken to obtain data. Thorough error analysis shows that while previously-described error trends are correct, additional facets of the technique can be optimised to allow highly accurate results. The new technique is rigorously validated here using pure translation and rotation test cases. Finally, the technique is used to measure a complex swirling flow within a cylindrical vessel.     

A-posteriori error estimation for second order mechanical systems

One important issue for the simulation of flexible multibody systems is the reduction of the flexible bodies degrees of freedom.As far as safety questions are concerned knowledge about the error introduced by the reduction of the flexible degrees of freedom is helpful and very important.In this work,an a-posteriori error estimator for linear first order systems is extended for error estimation of mechanical second order systems.Due to the special second order structure of mechanical systems,an improvement of the a-posteriori error estimator is achieved.A major advantage of the a-posteriori error estimator is that the estimator is independent of the used reduction technique.Therefore,it can be used for moment-matching based,Gramian matrices based or modal based model reduction techniques.The capability of the proposed technique is demonstrated by the a-posteriori error estimation of a mechanical system,and a sensitivity analysis of the parameters involved in the error estimation process is conducted.     

A New Procedure to Measure Near Yield Residual Stresses Using the Deep Hole Drilling Technique

Mechanical strain relief techniques for estimating the magnitude of residual stress work by measuring strains or displacements when part of the component is machined away. The underlying assumption is that such strain or displacement changes result from elastic unloading. Unfortunately, in components containing high levels of residual stress, elastic-plastic unloading may well occur, particularly when the residual stresses are highly triaxial. This paper examines the performance of one mechanical strain relief technique particularly suitable for large section components, the deep hole drilling (DHD) technique. The magnitude of error is calculated for different magnitudes of residual stress and can be substantial for residual stress states close to yield. A modification to the technique is described to allow large magnitudes of residual stress to be measured correctly. The new technique is validated using the case of a quenched cylinder where use of the standard DHD technique leads to unacceptable error. The measured residual stresses using the new technique are compared with the results obtained using the neutron diffraction technique and are shown to be in excellent agreement.     

Whole field measurement of temperature in water using two-color laser induced fluorescence

 A technique is described that measures the instantaneous three-dimensional temperature distribution in water using two-color laser-induced fluorescence (LIF). Two fluorescent dyes, Rhodamine B and Rhodamine 110, are used as temperature indicators. A laser light sheet scanned across the entire measurement volume excites the fluorescent dye, and an optical system involving a color beam splitter gives the intensity distribution of the individual fluorescent dyes on two separate monochrome CCD cameras. The ratio of these fluorescence intensities at each point of the image is calibrated against the temperature to eliminate the effect of the fluctuation of illuminating light intensity. A stable thermally stratified layer was measured by this system to evaluate the total accuracy of the measurement system. The random error of the measurement was ±1.4 K with 95% confidence. Measurements of thermal convection over a heated horizontal surface show temperature iso-surfaces having typical structures such as plumes, ridges and thermals. Received: 1 October 1997/Accepted: 23 March 1998     

Assessment of quantitative imaging of contaminant distributions in porous media

In this article an experimental setup designed to assist in the characterization of complex solute transport problems in porous media is described. Glass beads representing the medium are confined in a 2-D transparent Perspex box and a water flow transports a fluorescent dye. Under suitable illumination, the dye emits visible light which is collected by a CCD camera. The image acquired by this non-invasive optical technique is processed to estimate the 2-dimensional distribution of tracer concentrations by using an appropriate calibration curve that links fluorescent intensity and solute concentration. Details about the dye choice and discussion about photobleaching are reported. An analysis of the experimental error on the concentration profile is also presented. A few recent results of a study on contaminant plume within a homogenous porous matrix constituted by glass beads having mean diameter of 1 mm or 2 mm shows the performance of constructed model.     

Limitation of fourier transform photoelasticity: Influence of isoclinics

The application of the Fourier transform to photoelasticity was used in the evaluation of the retardation using a carrier system of fringes. In photoelasticity, the light intensity from the analyzer in a circular polariscope depends on both the retardation (isochromatics) and the isoclinic parameter. The theoretical analysis shows that the angle between the principal stresses in the model and in the carrier system of fringes influences the evaluation of the retardation (isochromatics), as occurs when misaligned compensators (namely, Babinet) are used. As a consequence, this method may not be applied as a full-field technique, although the error is small if the angle between the principal stresses in the model and in the carrier is less than 25 deg. Numerical simulations and experimental tests were conducted to corroborate this prediction.     

速率偏频技术提高激光陀螺精度的理论研究

以分析激光陀螺主要误差源出发点,从理论上研究了速率偏频技术的作用,指出它可有效地降低激光陀螺锁区引入的随机游走误差,部分地补偿激光陀螺谐振腔中的光束位移引起的不可控激光陀螺的零偏误差,并可解决拦动激光陀螺在系统使用中的锥形误差（Coning Error)和划桨误差（Sculling Error)。利用激光陀螺的拍频方程和拦动偏频激光陀螺的拍频近似解,得出了速率偏频激光陀螺随机游走误差与速率偏频系统参数的表达式,并指出了速率偏频技术的特点及速率偏频技术要解决的主要技术问题。     

基于无网格Galerkin法求解矩形绝缘管道内的磁流体流动

无量纲磁流体流动控制方程中的哈特曼数较大将导致数值计算发散或误差过大。将无网格Galerkin法引入绝缘管道内的稳定磁流体流动计算中,针对磁流体控制方程中大哈特曼数导致计算误差大的情况,对无网格Galerkin法添加了稳定项。计算结果表明,同等条件下,添加了稳定项的无网格Galerkin法总体相对误差远小于标准无网格Galerkin法的结果,且可以计算哈特曼数最大达50000绝缘管道内的磁流体流动。     

Quantitative limits of thermal and fluid phenomena measurements using the neutron attenuation characteristics of materials

Temporal and spatial resolution of the neutron radiographic technique were investigated in order to apply this technique to the visualization and measurement of thermal and fluid phenomena. The temporal resolution of three imaging methods of temporally resolved neutron radiography-static neutron radiography with a pulsed neutron beam and high frame rate neutron radiography with either a pulsed or steady neutron beam-was studied. It was determined that the temporal resolution was determined by the sensitivity and light decay time of the image detector and statistical variation of neutrons, and the resolution limits of static and dynamic imaging methods were estimated to be a few microseconds and a few hundred microseconds, respectively. An image processing method was proposed to measure flow characteristics such as void fraction. By performing an error analysis to calculate the limit value of liquid film thickness that can be measured by neutron radiography, it was determined that the limit value of a rectangular channel gap or round tube diameter should be smaller than 3.25 or 4.00 mm, respectively, for measuring the void fraction of air-water flow within an error of 10%. The void fraction measuring method was experimentally confirmed by comparing the void fraction values in a rectangular duct with a 2.4-mm gap obtained by neutron radiography with those obtained by optical and conductance probe methods. It was shown quantitatively that the measurement error decreased when consecutive frames were temporally integrated.     

Application of the maximum entropy technique in tomographic reconstruction from laser diffraction data to determine local spray drop size distribution

This work proposes a new deconvolution technique to obtain local drop size distributions from line-of-sight intensity data measured by laser diffraction technique. The tomographic reconstruction, based on the maximum entropy (ME) technique, is applied to forward scattered light signal from a laser beam scanning horizontally through the spray on each plane from the center to the edge of spray, resulting in the reconstructed scattered light intensities at particular points in the spray. These reconstructed intensities are in turn converted to local drop size distributions. Unlike the classical method of the onion peeling technique or other mathematical transformation techniques that yield unrealistic negative scattered light intensity solutions, the maximum entropy constraints ensure positive light intensity. Experimental validations to the reconstructed results are achieved by using phase Doppler particle analyzer (PDPA). The results from the PDPA measurements agree very well with the proposed ME tomographic reconstruction.     

Bichromatic particle streak velocimetry bPSV

We propose a novel technique for three-dimensional three-component (3D3C) interfacial flow measurement. It is based on the particle streak velocimetry principle. A relatively long integration time of the camera is used for capturing the movement of tracer particles as streaks on the sensor. The velocity along these streaks is extracted by periodically changing the illumination using a known pattern. A dye with different absorption characteristics in two distinct wavelengths is used to color the fluid. The depth of particles relative to the fluid interface can then be computed from their intensities when illuminated with light sources at those two different wavelengths. Hence, from our approach, a bichromatic, periodical illumination together with an image processing routine for precisely extracting particle streak features is used for measuring 3D3C fluid flow with a single camera. The technique is applied to measuring turbulent Rayleigh–Bénard convection at the free air--water interface. Using Lagrangian statistics, we are able to demonstrate a clear transition from the Batchelor regime to the Richardson regime, both of which were postulated for isotropic turbulence. The relative error of the velocity extraction of our new technique was found to be below 0.5?%.     

基于方位旋转调制的平台式惯导系统“一点校”

为了提高惯导系统长时间导航精度,需要在导航阶段对系统进行综校。设计了一种基于方位旋转调制技术的平台式惯导系统一点校方案。方位旋转调制技术可以有效地调制水平惯性敏感元件误差,降低其对系统工作精度的不利影响,这为"一点校"方案的实施提供了前提。分析了方位旋转式平台惯导系统的误差模型,得到了系统误差与误差源之间的解析关系。通过分析研究系统的误差传播特性,建立了方位陀螺漂移与系统位置误差的数学模型,完成了方位旋转式平台惯导系统的"一点校"方案设计,通过系统试验验证其有效性,方位陀螺常值漂移为0.003(°)/h的条件下,经10 h一点校,40 h一点校后,72 h定位误差小于1nmile,航向误差小于1′。     

Measurements of admixture concentration fluctuations in a turbulent shear flow using an averaged Talbot image

The present study is concerned with adopting of a Talbot effect-based technique for analyzing flows with random phase inhomogeneities. It is shown that this method is a powerful tool for diagnostics of turbulent flows. The potential of the technique is illustrated by measuring mean and fluctuating values of admixture concentration of two-dimensional turbulent helium jet issuing into the ambient air. Averaged air and helium concentrations throughout the flow field are determined using local light refraction measurements with a high spatial resolution from a long-exposed Talbot image of the jet. The analysis of light intensity distributions in light spots of a Talbot-image shows that the jet turbulence is inhomogeneous and anisotropic. Quantitative information on rms fluctuations of concentration gradients throughout the flow field is obtained from local photometric measurements at the Talbot light spots.     

Adaptive neural novel prescribed performance control for non-affine pure-feedback systems with input saturation

An error constraint control problem is considered for pure-feedback systems with non-affine functions being possibly in-differentiable. A new constraint variable is used to construct virtual control that guarantees the tracking error within the transient and steady-state performance envelopment. The new error transformation avoids non-differentiable problems and complex deductions caused by traditional error constraint approaches. A locally semi-bounded and continuous condition for non-affine functions is employed to ensure the controllability and transform the closed-loop system into a pseudo-affine form. An auxiliary system with bounded compensation term is proposed for nonlinear systems with input saturation. On the basis of backstepping technique, an adaptive neural controller is designed to handle unknown terms and circumvent repeated differentiations of virtual controls. The boundedness and convergence of the closed-loop system are proved by Lyapunov theory. Asymptotic tracking is achieved without violating control input constraint and error constraint. Two examples are performed to verify the theoretical findings.     

A photo-optical technique for measuring flow-induced vibrations in cantilevered tube bundles

A photo-optical technique has been developed for monitoring the dynamic displacement of cantilevered tubes in fluid flow. The technique employs an optical fiber to transmit light through the tube and a phototransistor array to measure the motion of the light beam that is projected from the end of the tube. The device is simple, inexpensive, and very sensitive to small displacements. Details are given for the development of the technique, analysis of performance, and static calibration. The device was tested by monitoring the dynamic response of a bundle of cantilevered tubes in both single-phase and two-phase Freon 11 flows. The results are compared with those of a standard strain gauge bridge.