共查询到20条相似文献,搜索用时 518 毫秒
1.
Henderiekus G. B. Allersma 《Experimental Mechanics》1982,22(9):336-341
An optical measuring method and a calculation procedure for determining the distribution of the stress tensor in a plane-strained three-dimensional assembly of random-shaped photoelastic particles are described. The stress tensor at an arbitrary point of the model is determined by an integration procedure, based on the equations of equilibrium of stresses. The distribution of the principal-stress direction and the relative principal-stress difference and at least two normal stresses in a plane have to be known to perform the integration. The distribution of the principal-stress directions and their difference are measured optically by scanning the model with an optical filter system with a single rotating polarizer. 相似文献
2.
M. P. Golubev A. A. Pavlov Al. A. Pavlov A. N. Shiplyuk 《Journal of Applied Mechanics and Technical Physics》2003,44(4):596-604
A new optical method for heat-flow registration is proposed. The sensor is a plane-parallel plate made of a transparent material. The form of the interference pattern resulting from superposition of waves reflected from the leading and trailing edges of the sensor varies in time depending on the distribution of heat flows. A relation for calculating heat flows by the shift of interference fringes is given. The measurements obtained by the optical method and by a certified thermocouple probe are compared. The results are in good agreement. The sensitivity and spatial resolution of the method are estimated. 相似文献
3.
An optical method for measuring the mass of liquid phase in a spray has been developed into an X-ray method. An X-ray of about 6 keV is used to measure the mass distribution of liquid phase in the spray formed by a concentric injector with water and gaseous nitrogen at one atmosphere of pressure. The possibility of measuring the mass of gaseous oxygen and hydrogen is discussed. 相似文献
4.
An instantaneous phase-stepping and subsequent phase analysis method, using a CCD camera with a form-birefringent micro-retarder
array, is proposed for interferometry. An optical setup of a polarization interferometry using a Twyman-Green interferometer
with two polarizers is constructed to analyze the distribution of out-of-plane displacement. Light emerging from the interferometer
is recorded using a CCD camera that has micro-retarder array on the CCD plane. This micro-retarder array has four different
principal directions. That is, an image obtained by the CCD camera contains four types of data corresponding to four different
optical axes of the retarder. The four images separated from the image recorded by the CCD camera are reconstructed using
gray-level interpolation. Then, the distributions of the Stokes parameters that represent the state of polarization are calculated
from the four images. The phase distribution of the interference fringe pattern produced by the Twyman-Green interferometer
is then obtained from these Stokes parameters. This method is applicable to time-dependent phenomena because multiple exposures
are unnecessary for sufficient data acquisition in the completion of phase analysis. 相似文献
5.
光流测量技术作为一种新的空气动力学实验技术,以其像素级分辨率的矢量场测量优势获得广泛的应用。光流测量技术使用光流约束方程,配合平滑限定条件,可以进行速度场测量,获得高分辨率的全局矢量场。本文首先通过研究积分最小化光流测速理论和算法,采用C++编写光流速度测量程序;然后通过三种典型的人工位移图像对光流计算程序进行了验证,并将结果和标准位移分布进行比对分析,以指导如何在实际应用中获得高精度光流速度场;最后进行小型风洞后向台阶实验,利用高速相机拍摄示踪粒子图像,使用光流计算程序获得速度矢量场,同采用互相关算法的粒子图像测速计算结果相比较,体现出光流计算方法像素级分辨率的矢量场测量优势。 相似文献
6.
It is shown that many of the existing index profiling methods for optical fibre and preform are related to one another through the deflection function from which the index profile is reconstructed. These methods are classified into direct deflection function measurement, integral (or phase) measurement, and differential (or intensity) measurement. The deflection function from the integral method is obtained by measuring the phase distribution of the exit rays followed by numerical differentiation. Thus the reconstructed index profile has Gaussian noise. The deflection function from the differential method is obtained by measuring the light intensity distribution followed by a numerical integration. This process enhances low frequency noise but suppresses high frequency noise. The noise from direct method behaves in the similar manner as in the differential method except that it is less pronounced. Studies of the choice of methods for profiling of preform, multimode fibre and single mode fibre are also given. 相似文献
7.
Wolfram Kirchweger Rainer Haslacher Michael Hallmannsegger Udo Gerke 《Experiments in fluids》2007,43(2-3):329-340
Within the underlying project, the task was to develop methods for optical measurements in a hydrogen-fuelled engine with
direct-injection, with the goal of measuring the jet patterns during injection, the stratification of the charge at ignition
point and the propagation of the flame during combustion. Therefore, the method of planar laser-induced-fluorescence (PLIF)
was chosen. In order to apply this technique for the named tasks, particular methods the visualisation of fuel distribution
and the flame front were developed. The measurements were carried out on a single cylinder research engine installed at the
Institute for Internal Combustion Engines at Graz University of Technology. This engine features optical access through a
quartz-glass liner and a window in the piston while providing a layout equivalent to modern passenger car engines and the
possibility to operate in fired mode. As it is hardly feasible to directly excite molecular hydrogen by means of laser light,
it is necessary to add a tracer substance to the fuel that provides high fluorescence intensity while not changing the properties
of the fuel. Consequently, Triethylamine was chosen as a tracer to be mixed with hydrogen at 200 ppm, which allows it to be
used up to a maximum pressure of 200 bar while still providing a strong LIF signal. Due to the excellent linearity of the
signal to the local air/fuel-ratio it was possible to develop a method for the calibration of the images in order to compensate
for inhomogeneities of the laser beam and staining of the optical access and to ultimately allow a quantification of the fuel
distribution. The results are images scaled on air/fuel-ratio which can be used for a direct optimisation of mixture formation
processes and the validation of CFD-models. For the analysis of the combustion process the method was adapted with two different
approaches. For homogeneous charges a new method was applied by marking the flame front using the tracer within the fuel,
so that both are burned together. However, as this method is limited to measurements with a homogeneous distribution of tracer
within the measured volume, an alternative technique had to be applied for the measurement of stratified charges. In this
case, a direct visualisation of the flame front was achieved by exciting the OH-radicals formed during combustion. As this
method has significantly increased demands on measuring equipment and is more time consuming, both methods are used in parallel
on specific measuring tasks. 相似文献
8.
In this study,the optical flow method is used to measure the velocity distribution of a granular flow in a rectangular quasi-two-dimensional silo.Using the velocity gradient,a free-fall arch(FFA)is obtained and its geometric characteristics are calculated.A parabola-shaped FFA structure is discovered above the orifice in the steady flow state.The shape of the FFA affects the flow rate through the orifice.Furthermore,as jamming begins to occur,the geometry of the FFA disappears gradually from both sides and then from the middle;finally,the FFA disappears completely in the state of jamming.As the boundary between finite-stress and stress-free regions,the FFA facilitates further studies regarding the discontinuity of the stress area above the orifice. 相似文献
9.
In heat-loaded structures of energy equipment at the moment of crisis of heat exchange in working elements, the ultimate state of the material occurs. Thermal stresses were studied experimentally in a bulk porous material with a groove on the surface with a view to finding out the distribution of deformations and thermal stresses due to the location of the heat source. It appeared efficient to apply optical methods. Using holographic interferometry, a pattern of distribution of thermal deformations over the surface of the specimens was obtained. Using the photoelastic method to investigate a grooved porous structure, a physical pattern of the distribution of thermal stresses inside the block and in the groove was obtained. Ways are outlined for designing and reducing the probability of occurrence of destructive cracks. A similarity is observed in the distribution of strains and stresses that indicates the interrelatedness of surface and internal processes. The application of optical methods made it possible to discover a physical pattern of destruction. The results are expected to be used in the future to investigate other porous materials. 相似文献
10.
目前高温环境中材料的变形测量是研究的热点,基于数字图像特征识别的非接触测量方法促进了高温环境变形测量的发展,但由于高温环境的复杂性,存在很多测量影响因素,其中高温环境中热流场的存在对数字图像法的影响尤为明显。本文提出了一种对高温变形测量中热流场造成畸变影响的修正方法。针对基于光学成像方法的材料高温变形测量中常见的热流场扰动,通过数值仿真得到热流场模型及热流场分布状况,再结合光线追迹原理对热流场造成的图像畸变影响进行分析,用数值分析结果对高温变形测量实验结果进行修正。对比扰动修正结果与真实位移有很好的一致性,从而证明了所提方法的可行性和有效性。 相似文献
11.
G. A. Papadopoulos 《Experimental Mechanics》2004,44(4):440-443
The objective of this paper is the experimental estimation of the load distribution in roller-bearing by the metrhod of caustics.
Contact problems have many practical and important applications1. For the solution of such problems, besides mechanical analysis, the experimental method of caustics2 can also be applied. The optical method of caustics is suitable for the experimental study of singularities in stress fields
created either by discontinuities or by loading. Previously, caustics has been applied to the study of singular stress fields
developed near concentrated or uniformly distributed loads which are applied along straight boundaries.3,4 In this work, it is applied to study the load distribution in rollerbearings. 相似文献
12.
An experimental technique based on the optical method of caustics for the solution of the two-dimensional problem of a narrow contact between two elastic disks was developed. In particular, an elliptical pressure distribution of the Hertz type was assumed, as well as a rectilinear contact form according to Muskhelishvili's solution. The method presents the advantage of yielding directly the contact length, from which the load applied on the disks can be readily evaluated. 相似文献
13.
A multi-scale optical imaging technique was developed allowing for the 2D observation of two phase flow in porous media at
two different scales simultaneously: Using two coupled cameras, a 2D flow cell (0.5 × 0.5m2) is recorded entirely at the bench scale and at the pore scale with a spatial resolution of 0.5 and 0.01 mm, respectively.
The technique is applied to study channelized gas flow in saturated glass beads. We analyze the phase distribution at the
pore scale and derive a pixel-based method for the measurement of saturation at the larger scale. This method assumes linearity
between the mean reflected light intensity and the local gas saturation if averaging is performed over representative areas
(REV). The REV depends on the irregularity of the local pore structure and has a lower limit at the correlation length of
the porous medium (somewhat above the size of the glass beads) and an upper limit which correlates with the width of gas channels.
These limits could be quantified through optical analysis. The optical approach to estimate phase saturations was validated
by gravimetric analysis where a characteristic ratio between the optically observed flow cell wall and the saturation within
the bulk material was identified, which corresponds to the expectation based on geometrical considerations of the glass bead
packing. Considering a transient flow experiment the optical method is demonstrated to be able to quantify the temporal evolution
of the residual and the convective gas phase. We conclude that the new technique provides a valuable tool to improve our quantitative
understanding of multiphase phenomena across different scales. 相似文献
14.
A non-destructive experimental procedure is presented which enables the determination of residual thermal stresses in optical
fiber preforms. The procedure is based on integrated photoelasticity. We carry out the measurement of the optical retardation
using the traditional Sénarmont compensation method combined with a fringe shifting technique. The radial distribution of
the axial stress is reconstructed using Abel transform. We have investigated two different refractive-index profiles, adopted
in the realization of monomode and multimode optical fibers. It was shown that in both cases the results obtained experimentally
and those analytically predicted by the Timoshenko elastic model were in good agreement. To obtain accurate experimental results,
it was necessary to apply a correction procedure to take into account the fact that the trafectories of the light rays inside
the preforms are not straight lines. 相似文献
15.
Optical throughput, namely the product of area times subtending solid, is a useful concept in calculations of light coupling to optical fibers. It is invariant through an optical system, thus providing a simple and elegant way to derive the maximum coupling efficiency between a light source and a fiber, regardless of intervening optics. Because throughput is proportional to the number of modes supported by an optical structure, it also yields the distribution of modal power within a fiber.In this paper, we illustrate applications of throughput by calculating light coupling into fibers and mode distribution within. 相似文献
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18.
W. J. Beranek 《Experimental Mechanics》1968,8(6):249-256
The paper describes the possibilities of rapidly and conveniently obtaining results by means of the reflection moiré method. The moiré photographs are produced with the aid of a screen provided with a finely ruled grid. The contrast of the photographs is increased by optical means. By displacement of two equal moiré photographs, moiré fringes of second order for the curvature or the twist are obtained. It is shown how charts can be produced which indicate:
- The distribution of the bending moments
- The distribution of the bending moments for which the reinforcement should be designed
- The distribution of the shear forces and the magnitude of the bearing reactions.
19.
This paper presents a simplified optical method for measuring the residual stresses by rapid cooling in thermosetting resin
strips. First, the fundamental equations for calculating the residual stress from the residual birefringence were obtained
by the linear photoviscoelastic theory. The specimens were then subjected to rapid cooling. After rapid cooling, the residual
stress was measured by two methods, the simplified optical method mentioned above and the well-known layer-removal method.
The effectiveness of the simplified optical method was discussed by comparing results of the two methods. 相似文献