Applied Mechanics and Materials Vols. 568-570

Abstract: Quadri-wave lateral shearing interferometry (QWLSI) is a new and powerful technique for wave-front measurement. This paper deduced the principle of QWLSI in details, showed a Fourier analysis of the resulting interferogram, then obtained a wave-front with high accuracy and minimum reconstruction error by using the least square method. Finally a 532nm laser was measured to validate the reconstruction, and the error analysis was discussed in practical laser metrology. It is concluded that QWLSI provides a better choice for the adaptive optics as compared with traditional lateral shearing interferometer (TLSI) and Shack-Hartmann (S-H) wave-front sensor.

Abstract: The phase characteristics of the high frequency pulse tube cryocooler which include the mass flows, the pressure amplitudes, and the phase angles between them significantly affect the cooler performance. A measurement method by using pressure sensors, temperature sensors and linear variable differential transformer rods is presented to evaluate and estimate the phase characteristics for the key components within the cooler such as the compressor, the regenerator, the inertance tube. etc, also the construction method of the phasor diagram based on the measurement is given. The constructed phasor diagram can be used to compare with the design values and provide the optimization direction of the prototype.

Abstract: Gamma densitometry is a widespread nonintrusive method for measuring the void fraction among all the methods. Void fraction is a fundamental parameter and generally obtained by the logarithmic and linear equations by means of single-beam gamma-densitometry. However, using these two equations in large diameter pipeline is a hard goal to reach because of the limitation of the radioactive source. In this paper, we proposed a formula for the void fraction measurements in large diameter pipeline and this formula can be also utilized in small diameter pipeline. Deviations between the calculated and actual void fraction of the methods in this paper are demonstrated. The theoretical errors of the new formulae are relatively insignificant in comparison to the logarithmic and linear equations. The method for large diameter pipe has even a smaller theoretical error than multi-beam gamma-densitometry. Disadvantages of the logarithmic equation are analyzed and the modification of the void fraction measurement formulae is proved to be progressive in mathematics. We discussed the simplifications in the novel methods and they have negligible effect on the measurements. Measurement positions and areas are optimized based on the theoretical deduction. In addition, we formulated the experimental requirements of different void fraction expressions.

Abstract: This study presented a novel non-contact optical measuing method for grape stem diameter in fields. The main algorithm contained 3 steps: saperation of the stem from background, determination of the stem segment, and the computation of stem diameter. The experiments conducted in field not only validated the effectiveness, but also proved the high accuracy of the optical measuring system. And our further experimental results showed that the continuous measurement of grape stem diameter can provide periodic data for the analysis of physiological disorders in grapes.

Abstract: Light is a transverse electromagnetic wave, which has the volatility and particles. When light waves are added up in the spatial uniform medium, different conditions will produce interference effects in the meeting area. Optical path difference affects the distribution of the interference pattern directly, and the light interference pattern gives information of phase and amplitude in turn. Due to the measurement precision and extremely high sensitivity of response, the principle of optical coherence has been studied based on measuring the related physical quantity indirectly.

Abstract: The random-fuzzy variables (RFVs) method based on the theory of evidence is studied, for the need of ADC uncertainty evaluation and the limitations of existing approaches. The connotation of RFVs adopted for expression of measurement result together with its associated uncertainty is discussed, and the RFVs mathematics for uncertainty propagation is analyzed. RFVs can naturally separate the contributions to the measurement uncertainty of the systematic and random effects. Taking power measurements as an example, RFVs method is applied to the presentation and propagation of the measurement uncertainty of ADC, and the results are compared with those obtained by GUM, which shows the RFVs method can be effectively employed in evaluating uncertainty of ADC, and is capable of providing the interval of confidence for all possible levels of confidence, within which the measurement result is supposed to lie.

Abstract: The AC magnetic susceptibility is a fundamental method in materials science, which allows to probe the dynamic magnetic response of magnetic materials and superconductors. The LAMPS laboratory at the Laboratori Nazionali di Frascati of the INFN hosts an AC multi-harmonic magnetometer that allows performing experiments with an AC magnetic field ranging from 0.1 to 20 Gauss and in the frequency range from 17 to 2070 Hz. A DC magnetic field from 0 to 8 T produced by a superconducting magnet can be applied, while data may be collected in the temperature range 4.2-300 K using a liquid He cryostat under different temperature cycles setups. The first seven AC magnetic multi-harmonic susceptibility components can be measured with a magnetic sensitivity of 1x10^-6 emu and a temperature precision of 0.01 K. Here we will describe in detail about schematic of the magnetometer, special attention will be dedicated to the instruments control, data acquisition framework and the user-friendly LabVIEW-based software platform.

Abstract: This paper mainly analyzes the effects of solar storms on GPS measurement errors. Solar storms produce a lot of charged particles, which makes the electron density in ionosphere increase, and in further affects the ionosphere delay errors. Ionosphere delay errors are one of the main sources of GPS measurement error, which is a direct impact on measurement precision of GPS. GPS distance errors are caused by ionosphere delay errors. In the case of solar storms, dual frequency observation cannot completely remove ionosphere delay, so in measurement process appropriate methods will be used to reduce errors in GPS measurement, for example, during the observation in the night and increased observation period. By comparing and analyzing the GPS observation data in solar storms and under normal conditions with GAMIT/GLOBK software, a conclusion is made in this paper that observing in the night and the increased observation period can reduce the GPS measurement errors.

Abstract: The diameter and the shape of particle were the important characteristics of solid particle. The purpose of this paper was to observe the shape and to measure the diameter of bulk material particles included ferroferric oxide, silicon dioxide and sodium chloride, and to explore the most suitable calculation method of these bulk material particles. The studied results showed that the calculation formulas of the equivalent diameter of equal volume sphere and the equivalent diameter of equal surface area sphere were both applicable to the particle with micro-shape approximated to spheroid, such as ferroferric oxide particle. And the formula of the equivalent diameter of equal surface area sphere was more applicable to the particle with micro-shape approximated to regular tetrahedron, such as silicon dioxide particle. As for the particle with micro-shape approximated to regular hexahedron, such as sodium chloride particle, the formula of the equivalent diameter of equal volume sphere was more applicable.

Abstract: This paper presented a method of the displacement measurement of ground wind loads for launch vehicle based on laser and Digital Image Processing Technology. The launch vehicle structure model was built by calculating the wind pressure. Measurement model and algorithm for single laser were given. In view of nonrigid component, a method for computing the centroid displacement was presented. Error analysis and error reducing measures were preliminarily discussed.