风力发电机叶片用玻璃纤维织物的渗透率

通过改变纤维层数来改变纤维织物的孔隙率,采用一维饱和流动方法测量了风力发电叶片用玻璃纤维织物(WindstrandTM)三个方向(x、y和z)的饱和渗透率大小.考察了孔隙率、模具尺寸以及纤维方向(平行于和垂直于2％的纤维束两个方向)对其饱和渗透率的影响.结果表明:渗透率随孔隙率的降低而迅速降低；当孔隙率为34.6％～54.7％时,模具尺寸对y向饱和渗透率影响不大；改变2％的纤维束方向(由平行到垂直),当孔隙率为34.6％～54.7％时,对饱和渗透率有一定影响.当孔隙率为45％～55％时,玻璃纤维织物x和y方向的饱和渗透率约为z方向饱和渗透率的3～7倍.     

风力发电机叶片用玻璃纤维织物的渗透率

通过改变纤维层数来改变纤维织物的孔隙率, 采用一维饱和流动方法测量了风力发电叶片用玻璃纤维织物(Windstrand^TM)三个方向(x、y和z)的饱和渗透率大小。考察了孔隙率、模具尺寸以及纤维方向(平行于和垂直于2%的纤维束两个方向)对其饱和渗透率的影响。结果表明: 渗透率随孔隙率的降低而迅速降低; 当孔隙率为34.6%~54.7%时, 模具尺寸对y向饱和渗透率影响不大; 改变2%的纤维束方向(由平行到垂直), 当孔隙率为34.6%~54.7%时, 对饱和渗透率有一定影响。当孔隙率为45%~55%时, 玻璃纤维织物x和y方向的饱和渗透率约为z方向饱和渗透率的3~7倍。     

Measurement of permeability of continuous filament mat glass–fibre reinforcements by saturated radial airflow

The measurement of fibre reinforcement permeability is important for the understanding, optimisation and modelling of RTM and resin infusion processes. This work investigates the use of a saturated radial air flow experiment for measuring the permeability of continuous filament mat (CFM), which is a common reinforcement type used for industrial RTM parts. The use of air, rather than liquid resin, is cleaner, quicker and potentially easier to control. The paper considers the problems inherent in using a compressible fluid, instead of a liquid, for the measurement of permeability, and the requirements for maintaining laminar flow. It describes the instrumentation used for flow and pressure measurement, and the effect of varying flow rate. Results compare favourably with published permeability values based on liquid flow experiments, and are independent of flow rate within the range of values investigated.     

Study of saturated and unsaturated permeability in natural fiber fabrics

The main goal of this work is to understand how the main processing variables are affected when glass fibers are replaced by natural fibers in reinforced plastics. In this publication, a jute fabric was characterized in terms of its saturated and unsaturated permeability. It was found that fluid absorption and swelling are mechanisms present in natural fibers that reduce both permeabilities. Fluid absorption removes fluid from the main stream as it travels through the reinforcement, acting as a sink component and thus decreasing flow velocity during the unsaturated flow. Also, the saturation of the natural fibers cause swelling, reducing the porosity and increasing flow resistance during saturated flow.     

Propagation of unipolar perturbations in hysteretic media with saturation of nonlinear losses

The propagation and evolution of unipolar perturbation pulses in hysteretic media with saturation of nonlinear losses have been theoretically studied. An exact analytical solution that describes the propagation and evolution of initially triangular pulses in these media has been obtained. Numerical and graphic analyses of the obtained solution are presented.     

不同纤维堆积状态下饱和渗透率实验研究

通过调节压力控制纤维体积分数, 用单向饱和流动法对纤维层厚度方向的饱和渗透率进行了测定。考察了纤维体积分数随压力的变化规律, 并分别研究了纤维体积分数、纤维层数、铺层方式和纤维种类对渗透率的影响。结果表明, 当纤维体积分数超过某临界值后其值随压力增大的幅度减小。单向和正交铺层时层数变化对渗透率没有影响, 而平纹布渗透率随着纤维层数的增加而减小。此外, 纤维种类的改变对渗透率有明显影响。      

The effect of transport current and saturation on the losses of multifilamentary superconducting wires

A slab model is used to investigate the effects of saturation of the superconducing filaments on the losses of multifilamentary superconductors exposed to a uniformly changing field. It is necessary to consider not only the saturated region (where J = J_c), and the superconducting region, but also the region in which current is transferred to the copper. The volume of this region can be about double that of the saturated region. The losses are in qualitative agreement with previous models for round wires, but it is shown that these models do not use the correct current distributions. Some analytic features of the correct solution are derived but a complete solution requires numerical computation.     

Measurement of magnetic losses in resonant metallised ferrites

Microwave magnetic losses, far enough from the ferromagnetic resonance, are generally measured by perturbation methods, i.e. by comparing resonance of a cavity with and without magnetic sample. Nevertheless such methods require very accurate apparatuses, for parameters of the resonant cavity are slightly altered by the presence of the sample because of the relative smallness of the latter. The fore-going difficulty can be overcome by using the sample as a resonant cavity. The TM010mode of a cylindrical metallised sample are very convenient to achieve accurate measurement of magnetic losses. This method is quite effectual for materials with low magnetic moments and for low frequencies (from 1 to 5 GHz). Large metallic cavities are avoided and the apparatus is very simple.     

Measurement of instantaneous losses in switching power devices

A novel technique is proposed for measuring instantaneous power and energy losses in static switching devices during the different operating intervals (turn-on delay, rise time, on-state, turn-off delay, full time, and off-state) of a switching cycle. To this end, a system for measuring voltages and currents is used, based on sampling at 200 Ms/s for data acquisition. The data are then transferred to a personal computer (PC), where they are conditioned and processed to obtain the instantaneous values and the average values of power losses for any desired duty cycle or single impulse. It is concluded that the high-speed digital acquisitions of voltage and current data along with the possibility of automatically processing on a PC allows the calculation of the losses during the fast switching transients with a greater degree of accuracy and detail than that afforded by classical techniques     

Measurement of optical losses and damage thresholds of multilayer coatings

A correlation between the absorption measured at λ = 514 and 1060 nm and the damage thresholds at λ = 1060 nm is established for evaporated dielectric multilayer stacks. In addition the diffused reflectance of the coatings was measured at λ = 633 nm by means of a Coblentz sphere.     

Measurement of losses in a Stirling cycle cooler

An attempt has been made to identify and measure all the significant power losses in a miniature Stirling cycle refrigerator. Methods of measuring these losses in a working refrigerator using non-invasive instrumentation are described. An energy balance is presented which shows that all the major sources of energy loss have been accounted for quantitatively. This provides a sound basis for optimization of cryocooler design.     

Measurement of thermophysical properties of lead by a submicrosecond pulse-heating method in the range 2000–5000 K

A submicrosecond ohmic pulse-heating technique with heating rates of more than 10⁹K· s^–1 allows the determination of such thermophysical properties as heat capacity and the mutual dependences among enthalpy, electrical resistivity, temperature, and volume up to superheated liquid states for lead. Also, an estimation of the critical point data is given from investigations at elevated static pressures.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.     

Gas permeability of concrete in relation to its degree of saturation

Permeability, along with diffusion and absorption, is used to quantify durability characteristics of a concrete. The measured value of gas permeability of concrete depends strongly on its degree of saturation. Moreover, when the size of pores is of the same order of magnitude as the mean free path of molecules of the percolating gas, there is some molecular flow which violates the assumptions of the Darcy's law. As a result, the coefficient of permeability varies with the applied pressure. In an attempt to take these effects into account, we have tried to quantify different types of flow and we propose a method to calculate the apparent coefficient of permeability and hence the gas flow through concrete having any given degree of saturation and being under a given pressure difference across its extremities. For this purpose, we are characterizing concrete with an intrinsic permeability value. The variation of this intrinsic permeability and that of the contribution of non-viscous flow is studied, for a single concrete mix design in relation to the degree of saturation using a constant head permeametre named as CEMBUREAU and oxygen as the percolating gas.

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Résumé La perméabilité, de même que la diffusion et l'absorption est utilisée dans le but de quantifier la durabilité d'un béton. La mesure de la perméabilité au gaz des bétons dépend fortement de leur taux de saturation. De plus la taille des pores pouvant être de l'ordre de grandeur du libre parcours moyen des molécules du gaz percolant, on a alors apparition d'un écoulement de type moléculaire qui ne respecte pas les hypothèses de la loi de Darcy et conséquemment la perméabilité varie en fonction de la pression moyenne de l'essai. Afin de prendre en compte ces problèmes, nous avons essayé de quantifier les différents types d'écoulement en présence et nous proposons une méthode de calcul de la perméabilité apparente puis du débit gazeux, pour n'importe quel taux de saturation du béton et pour n'importe quel gradient de pression. Pour cela il convient de déterminer la perméabilité intrinsèque du matériau qui est indépendante de la pression d'essai. Pour une composition de béton standard nous étudions les variations de la perméabilité intrinsèque et celle de la part d'écoulement moléculaire en fonction du taux de saturation du matériau. Les perméabilités sont mesurées à l'aide d'un perméamètre à oxygène à charge constante de type CEMBUREAU.

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Editorial note LMDC, The Laboratoire Matériaux et Durabilité des Constructions,is a RILEM Titular Member. It is directed by Prof. Jean-Pierre Ollivier, a RILEM Senior Member who is member of the RILEM Coordinating Committee.     

Counting losses due to saturation effects of scintillation counters at high count rates

The counting statistics of a scintillation counter, with a preamplifier saturated by an overloading input, are investigated. First, the formulae for the variance and the mean number of counts, accumulated within a given gating time, are derived by considering counting-loss effects originating from the saturation and a finite resolving time of the electronic circuit. Numerical examples based on the formulae indicate that the saturation makes a positive contribution to the variance-to-mean ratio and that the contribution increases with count rate. Next the ratios are measured under high count rates when the preamplifier saturation can be observed. By fitting the present formula to the measured data, the counting-loss parameters can be evaluated. Corrections based on the parameters are made for various count rates measured in a nuclear reactor. As a result of the corrections, the linearity between count rate and reactor power can be restored.     

Measurement of ethylene permeability of plastic films

This work presents the development of a method to measure the ethylene permeability of plastic films used in vegetable packaging, by exploiting the adsorption and desorption properties of a synthetic sodium zeolite. In order to establish the best conditions and requirements for the procedure, the ethylene adsorption and desorption by the zeolite was studied at different temperatures and partial pressures. The method was used to study the ethylene permeability of two common cling films (EVA and plasticized PVC) and shown to be both economical and accurate.     

Measurement of harmonic losses in transformers supplyingnonsinusoidal load currents

The spread of the load control techniques based on power electronics is causing the increase of harmonic losses in power distribution systems. A digital method for the evaluation of these losses in power transformers, which only requires measurements taken at the transformer output terminals, is discussed. The accuracy of the method, along with the performance of a virtual-instrumentation-based instrument implementing it, is also discussed. The results of some experimental work are reported