A simple method for evaluating the maximum slip of anchorages

The analytical solutions to the bond problem for monotonically increasing loads are developed for a monomial exponential local bond stress-slip relationship (law) – “exact solution” –, a linear local law – “proposed solution” – and a constant bond stress distribution, such as that recommended by the Eurocode. The three solutions are thoroughly developed for the pull-out of a bar embedded in a cylindrical element, with longitudinal concrete in tension. For short anchorages, which undergo a rigid motion and whose “exact solution” requires a complex iterative procedure, the “proposed solution” explicitly provides very accurate bond stress distributions. On the basis of this accuracy, an approximate expression for the slip distribution is derived. The proposed approximate solution is the first one providing a direct slip expression for short anchorages. Approximate explicit expressions for the maximum bond stress and the maximum slip are also given. The comparison between the maximum slip values measured during experimental tests and the corresponding values obtained from the proposed approximate expression demonstrates the accuracy of the latter.     

A method for evaluating shockwave propagation in snow

Shockwaves in snow are analyzed by developing and then solving a set of governing jump equations which are defined in terms of the jump in certain material parameters across the shockwave. This method represents an alternative means to studying shockwaves, since most previous solution techniques have involved direct integration of the governing differential wave equations. However, since this classical means is normally difficult, the use of jump equations represents a viable means of determining stress wave properties. The two methods are compared for propagation of plastic shockwaves in snow, and some comparison to data is made. The use of jump equations is shown to give results which are similar to those obtained with the direct method.     

A variable hysteresis aperturing method for superconductingcounting A/D conversion

The authors present an aperturing method for superconducting counting A/D (analog/digital) converters. The scheme, called TRAP (time release after aperturing of pulses), utilizes a large β_L two-junction SQUID (superconducting quantum interference device) quantizer and plays on the ability to control the amount of hysteresis available in such a SQUID. Incoming information from the analog signal can be either immediately processed by the quantizer or trapped and outputted at a later time. The author explains how this control can be used to form a picosecond aperture for counting A/D converters, eliminating pulse-skipping problems. SPICE simulations confirm the ideal behaviour of the TRAP     

A method for raising the accuracy of frequency measurement

A method is considered for making high-precision frequency measurements with simple, inexpensive, and inexact frequency meters.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 53–54, October, 1993.     

A method for evaluating dynamic tensile damage of rock

This paper presents two evolution laws for dynamic tensile damage of brittle rock based on light gas gun (LGG) tests. By analyzing the attenuation of sound-wave propagation in the rock samples before and after impact tests, one evolution law for dynamic tensile damage of rock is introduced and incorporated into the finite element code LS-DYNA through a user-defined subroutine. The improved code is then applied to the simulation of the tensile damage and blast crater near free face of rock mass, and the resulting crater geometry is compared with empirical formula. In addition, based on the phenomenological point of view and the velocity–time histories recorded in LGG tests, another evolution law of tensile damage is proposed to consider the nucleation and growth of microflaws in rock. Parametric analyses are carried out with the self-developed finite difference code and an optimization procedure for the parameter determination is suggested.     

A quantitative method for evaluating the performances of hyperspectral image fusion

Hyperspectral image fusion is a key technique of hyperspectral data processing. In recent years, many fusion methods have been proposed, but there is little work concerning evaluation of the performances of different image fusion methods. In this paper, a method called quantitative correlation analysis (QCA) is proposed, which provides a quantitative measure of the information transferred by an image fusion technique into the output image. Using the proposed method, the performances of different image fusion methods can be compared and analyzed directly based on the images of before and after performing the fusion. The correlation information entropy, based on the developed QCA, is also proposed and testified by numerical simulations. Typical hyperspectral data are applied to the proposed method. The results show that the method is effective, and its conclusions agree with the classification results in applications.     

A method for evaluating Hunter whiteness of mixed powders

The Hunter whiteness (HW) is an important quality index of powder in agricultural, food and pigment industries. Relationship between HW of mixed powder and mass percent of each individual powder was investigated. We found a linear relationship expressed by a corresponding equation. According to this equation, the HW of mixed powder was only related to the HW and mass percent of each kind of individual power. Therefore, such equation can simply and rapidly evaluate HW of the mixed powder during the powder matching process.     

A thermoelectric method of evaluating the purity of platinum for standard thermocouples

Conclusions Strict tolerances with respect to the stability of standard thermocouples require the checking of the value of W=R₁₀₀/R₀ of the electrode platinum. Direct measurements of R₁₀₀ and R₀ are complicated and require considerable expenditure of time. The thermoelectric method of indirect determination of R₁₀₀/R₀ provides a sufficiently accurate and speedy check of this characteristic of the platinum electrode.     

A quantitative method for evaluating the detectability of lesions in digital mammography

This study presents a quantitative method for evaluating the detectability of microcalcifications in digital mammography. Four hundred and twenty microcalcifications (with various morphology, size and contrast), simulated with a previously validated method, were used for the creation of image datasets. Lesions were inserted into 163 regions of interests of 59 selected raw digital mammograms with various anatomical backgrounds and acquired with a Siemens Novation DR. After processing, these composite images were scored by experienced radiologists, who located multiple simulated lesions and rated them under conditions of free-search. For statistical analysis, free-response receiver-operating characteristic curves are plotted; the use of jackknife free-response receiver-operating characteristic method has also been investigated. The main advantage of this methodology is that the exact number of inserted microcalcifications is well known and that the lesions are fully characterised in terms of pathology, size, morphology and peak contrast. A first application has been the evaluation of the effect of anatomical background on microcalcifications detection. Preliminary findings in this study indicate that this method may be a promising tool to evaluate factors that have an influence on the detectability of lesions, such as the clinical processing or the viewing conditions.     

A new method for evaluating fracture toughness of brittle materials

A new testing procedure is suggested for measuring the fracture toughness of brittle materials as superconductors and ceramics. The idea is to perform a compression test on a subcompact square specimen which contains a central hole. The presence of the hole induces a tensile stress at a certain small region attached to the hole. In this region an artificial notch is introduced such that the fracture path satisfies a pure tensile opening mode (mode I) to which the linear fracture mechanics rules apply. The stress distribution on the fracture plane guarantees a certain amount of stable crack extension. The relationship between the critical compressive load and the stress intensity factor is formulated via an available Green function along with a numerical solution (FEM with ANSYS code). The testing procedure is demonstrated with specimens made of two types of tungsten carbide which differ by their grain size only. Test results are examined via fracture toughness and strength values produced by other conventional methods and the agreement is very good. The geometry and loading direction enable the fracture toughness results to be relatively insensitive to the notch tip radius and the crack length, thereby relaxing the requirements for accurate measurements.The small size of the suggested specimen (12.70mm×12.70mm×5mm) and the avoidance of gripping interfaces provide the major cost-wise advantages.     

New variable transformations for evaluating nearly singular integrals in 3D boundary element method

This work presents new variable transformations for accurate evaluation of the nearly singular integrals arising in the 3D boundary element method (BEM). The proposed method is an extension of the variable transformation method in Ref. [4] for 2D BEM to 3D BEM. In this paper, first a new system denoted as $(\alpha ,\beta )$ is introduced compared with the polar coordinate system. So the original transformations in Ref. [4] can be developed to 3D in $(\alpha ,\beta )$ or the polar coordinate system. Then, the new transformation is performed by four steps in case the source point coincides with the projection point or five steps otherwise. For each step, a new transformation is proposed based on the approximate distance function, so that all steps can finally be unified into a uniform formation. To perform integration on irregular elements, an adaptive integration scheme combined with the transformations is applied. Numerical examples compared with other methods are presented. The results demonstrate that our method is accurate and effective.     

New variable transformations for evaluating nearly singular integrals in 2D boundary element method

This work presents a further development of the distance transformation technique for accurate evaluation of the nearly singular integrals arising in the 2D boundary element method (BEM). The traditional technique separates the nearly hypersingular integral into two parts: a near strong singular part and a nearly hypersingular part. The near strong singular part with the one-ordered distance transformation is evaluated by the standard Gaussian quadrature and the nearly hypersingular part still needs to be transformed into an analytical form. In this paper, the distance transformation is performed by four steps in case the source point coincides with the projection point or five steps otherwise. For each step, new transformation is proposed based on the approximate distance function, so that all steps can finally be unified into a uniform formation. With the new formulation, the nearly hypersingular integral can be dealt with directly and the near singularity separation and the cumbersome analytical deductions related to a specific fundamental solution are avoided. Numerical examples and comparisons with the existing methods on straight line elements and curved elements demonstrate that our method is accurate and effective.     

A dynamic approach for evaluating parameters in a numerical method

A new methodology for evaluating unknown parameters in a numerical method for solving a partial differential equation is developed. The main result is the identification of a functional form for the parameters which is derived by requiring the numerical method to yield ‘optimal’ solutions over a set of finite‐dimensional function spaces. The functional depends upon the numerical solution, the forcing function, the set of function spaces, and the definition of the optimal solution. It does not require exact or approximate analytical solutions of the continuous problem, and is derived from an extension of the variational Germano identity. This methodology is applied to the one‐dimensional, linear advection–diffusion problem to yield a non‐linear dynamic diffusivity method. It is found that this method yields results that are commensurate to the SUPG method. The same methodology is then used to evaluate the Smagorinsky eddy viscosity for the large eddy simulation of the decay of homogeneous isotropic turbulence in three dimensions. In this case the resulting method is found to be more accurate than the constant‐coefficient and the traditional dynamic versions of the Smagorinsky model. Copyright © 2004 John Wiley & Sons, Ltd.     

A variable frequency method for wide-band microwave materialcharacterization

A variable reactance termination method for measurement of the complex permittivity spectra is described. The method uses modern frequency swept sources and is semi-automated. The frequency variable replaces mechanical tuning for improved measurements and optimization of sensitivity. Sources of errors are outlined, and range and limitations on conductivity are discussed. Results of measurements of Teflon and silicon are presented     

二维分布动载荷识别的频域方法

运用频域法在广义正交域中识别二维分布动载荷。基于数学拟合理论，二维动态载荷在广义正交域中可分解为二维正交函数的级数形式，未知的二维分布动载荷就可以表示为各阶正交基函数线性叠加，这时未知的复杂分布动载荷的识别就可以转化为简单的正交拟合系数的识别。根据线性系统的叠加原理，将待识别载荷的分解基函数看成已知分布动载荷作用于结构时，结构的响应与待识别载荷作用下结构的响应成线性关系。只要结构实测的响应点数大于待识别的系数，就能求出各系数，因而就可以识别分布动载荷。通过计算机仿真验证该方法能有效识别二维分布动载荷，且能与有限元方法结合，识别复杂结构上的分布动载荷。该方法具有很好的通用性，能简单方便运用于工程结构，能很好地抑制噪声的干扰。仿真试验说明该方法具有很好的识别精度。进一步的试验验证了该方法工程适用性。     

A model for evaluating the effect of fatigue crack repair by the infiltration method

Infiltration of foreign materials into a fatigue crack has previously been shown to be able to retard the crack and extend fatigue life. Most of the related studies were empirical and phenomenological in nature. To aid engineering decisions, it would be advantageous if the possible outcome of a repair can be evaluated beforehand. To this end, a crack closure model taking into account the additional closure effect of the infiltrant has been developed and verified against experimental results. With this model, the sensitivity of the repair effect to various parameters such as mechanical properties of the infiltrant, depth of penetration and infiltration load level can be assessed.     

A digital method of frequency measurement for harmonic signals

Conclusions A new method and an algorithm are described for determining the frequency or period of a harmonic signal no matter what the period of the signal. The principle can be used in digital measuring systems, particularly at low and infralow frequencies.Translated from Izmeritel'naya Tekhnika, No. 11, pp. 71–73, November, 1973.