Measurement of angular vibrations of electrical machines for performing vibrational diagnostics of their technical state

The present state of vibration measurement for precision rotor systems is analyzed. A method is proposed and described for using hardware and software to measure and perform a spectral analysis of vibrational angular displacements of electrical machines. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 40–42, November, 1997.     

Probabilistic durability analysis methods for metallic airframes

Probabilistic-based deterministic and stochastic crack growth approaches are compared and evaluated for durability analysis applications dealing with fatigue cracking in metallic fastener holes. Crack exceedance predictions for the deterministic crack growth approach correlated well with experimental results. Correlations for the stochastic crack growth approach were more conservative and less accurate than those for the deterministic crack growth approach.     

Use of inverse problems for spatial diagnostics of the heat transfer of aircraft models

A theoretical-experimental approach to the diagnostics of nonsteady heat transfer using a scale model of an aircraft prepared by heat-flux sensors is proposed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 3, pp. 362–368, March, 1989.     

A statistical view of iterative methods for linear inverse problems

In this article, we study the problem of recovering the unknown solution of a linear ill-posed problem, via iterative regularization methods, from a statistical point of view. The basic purpose of the paper is to develop adaptive model selection techniques for determining the regularization parameters, i.e., the iteration index. We assume observations are taken over a fixed grid and we consider solutions over a sequence of finite-dimensional subspaces. Based on concentration inequalities techniques, we derive non-asymptotic optimal upper bounds for the mean square error of the proposed estimator.     

Mathematical models, methods, and algorithms used for the radio-wave diagnostics of multilayer dielectrics

We present the results of investigations carried out at the Karpenko Physicomechanical Institute of the Ukrainian Academy of Sciences and devoted to the development of the methods of nondestructive testing of multilayer dielectric objects with plane interfaces. These methods make it possible to determine the thicknesses of the layers, the depths and thicknesses of the interlayers, and their permittivities by analyzing the frequency dependence of the reflection coefficient of superhigh-frequency electromagnetic waves. The procedure of determination is based on the solution of direct and inverse problems of reflection from the tested objects. We describe and discuss some of these methods and algorithms. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 5, pp. 49–57, September–October, 1997.     

Probabilistic methods for assessing current and future performance of concrete structures in nuclear power plants

Concrete safety-related structures and components in nuclear plants may be exposed to aggressive service and environmental effects that may cause their strength and stiffness to deteriorate over an extended period of service. A performance assessment of an existing structure subject to deterioration requires a consideration of likely degradation mechanisms, a framework for managing the inevitable uncertainties in operating or environmental loads, capacities, and nondestructive evaluation technologies, and tools for determining whether the observed degradation impacts the remaining service life or safety margin of the plant to any significant degree. Research is in progress to support the development of condition assessment tools and guidelines using modern structural reliability analysis methods.     

Probabilistic structural analysis methods for space propulsion system components

NASA Lewis Research Center is currently developing probabilistic structural analysis methodology for select Space Shuttle Main Engine (SSME) components. This methodology consists of the following program elements: (1) composite load spectra, (2) probabilistic structural analysis methods, (3) probabilistic finite element theory - new variational principles, and (4) probabilistic structural analysis application. The methodology has led to significant technical progress in several important aspects of probabilistic structural analysis. The program and significant accomplishments to date are summarized in this paper.     

Classification of washing machines vibration signals using discretewavelet analysis for feature extraction

Wavelets provide a powerful tool for nonstationary signal analysis. In vibration monitoring, the occurrence of occasional transient disturbances makes the recorded signal nonstationary, especially during the start-up of an engine. Through the wavelet analysis, transients can be decomposed into a series of wavelet components, each of which is a time-domain signal that covers a specific octave frequency band. Disturbances of small extent (duration) are amplified relative to the rest of the signal when projected to similar size wavelet bases and, thus, they can be easily detected in the corresponding frequency band. This paper presents a new method for extracting features in the wavelet domain and uses them for classification of washing machines vibration transient signals. The discrete wavelet transform (DWT), in conjunction with statistical digital signal processing techniques, is used for feature extraction. The Karhunen Loeve transform (KLT) is used for feature reduction and decorrelation of the feature vectors. The Euclidean, Mahalanobis, and Bayesian distance classifiers, the learning vector quantization (LVQ) classifier, and the fuzzy gradient classifier are used for classification of the resulting feature space. Classification results are illustrated and compared for the rising part of vibration velocity signals of a variety of real washing machines with various defects     

Probabilistic asymptotic analysis of stochastic online scheduling problems

In the stochastic online scheduling environment, jobs with unknown release times and weights arrive over time. Upon arrival, the information on the weight of the job is revealed but the processing requirement remains unknown until the job is finished. In this paper we consider the objective of minimizing the total weighted completion time. With the assumptions that job weights are bounded, machine capacity is adequate, and processing requirements are bounded and identical and independently distributed across the machines and jobs, we show that any nondelay algorithm is asymptotically optimal for the stochastic online single machine problem, flow shop problem, and uniform parallel machine problem. Our simulation studies of these stochastic online scheduling problems show that two generic nondelay algorithms perform very well as long as the number of jobs is larger than 100.     

Application of statistical methods to solve global reconstruction problems

A solution of the problem of reconstructing a mathematical model using statistical methods to specify the evolution operator is optimized. It is shown that this procedure can be used for modeling with short time series, so that the metric and dynamic characteristics of an attractor can be determined with a knowledge of the reconstructed model equations. Direct methods of analyzing scalar time series are less effective in this situation. Pis’ma Zh. Tekh. Fiz. 23, 7–13 (April 26, 1997)     

Probabilistic modeling of chloride-induced corrosion in concrete structures using first- and second-order reliability methods

Concrete structures are subjected to chloride-induced corrosion that can lead to shortened service life. Reliable predictions of life cycle performance of concrete structures are critical to the optimization of their life cycle design and maintenance to minimize their life cycle costs. This paper presents two simplified semi-analytical probabilistic models based on the first- and second-order reliability methods to model the uncertainty of the key parameters including surface chloride concentration, chloride threshold, cover depth and diffusion coefficient, which govern the chloride ingress into concrete and corrosion of reinforcing steel. A case study of a reinforced concrete highway bridge deck is used to illustrate the capability and efficiency of these simplified probabilistic models in modeling the uncertainty and predicting the time-dependent probability of corrosion. The models enable to quantify the impact of the different governing parameters on probability of corrosion and service life, which can be used to develop cost-effective management strategies.     

BEM analysis of thin structures for thermoelastic problems

A new boundary element method is developed for solving thin-body thermoelastic problems in this paper. Firstly, the novel regularized boundary integral equations (BIEs) containing indirect unknowns are proposed to cancel the singularity of fundamental solutions. Secondly, a general nonlinear transformation available for high-order geometry elements is introduced in order to remove or damp out the near singularity of fundamental solutions, which is crucial for accurate solutions of thin-body problems. Finally, the domain integrals arising in both displacement and its derivative integral equations, caused by the thermal loads, are regularized using a semi-analytical technique. Six benchmark examples are examined. Results indicate that the proposed method is accurate, convergent and computationally efficient. The proposed method is a competitive alternative to existing methods for solving thin-walled thermoelastic problems.     

Spectral analysis of acoustic signals in linear space-time structures

An experimental-analytical method is proposed for estimating the generalized radial velocity in the form of a set of discrete values for a set of discrete times.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 50–52, June, 1994.     

Dynamic analysis of framed structures with statistical uncertainties

The forced harmonic vibration analysis of portal frames consisting of viscously damped beams with spatial stochastic variation of mass and stiffness properties is considered. The analysis is based on the assembly of element stochastic dynamic stiffness matrices. The solution involves inversion of the global dynamic stiffness matrix, which, in this case, turns out to be a complex‐valued symmetric random matrix. Three alternative approximate procedures, namely, random eigenfunction expansion method, complex Neumann expansion method and combined analytical and simulation method are used to invert the matrix. The performance of these approximate procedures is evaluated using Monte Carlo simulation results. Copyright © 1999 John Wiley & Sons, Ltd.     

Probabilistic analysis of linear elastic cracked structures with uncertain damage

This paper presents a simple and reliable method for the probabilistic characterization of the linear elastic response of cracked structures with uncertain damage. In particular, truss and frame structures with edge cracks of uncertain depth and location are considered. The method of analysis originates from an approach recently appeared in the literature, which is generalized to treat structures with cracks affected by uncertainty. According to this approach, the uncertainties are transformed into superimposed deformations depending on the distribution of internal forces and an iterative procedure is established to solve the resultant equations. The procedure is optimally tuned based on the convergence analysis. Several numerical tests evidence excellent accuracy and convergence qualities also in the case of multicracked structures with large fluctuation of damage.