Reliability analysis of hydraulic systems of LHD machines using the power law process model

Earlier, a preliminary study of the reliability characteristics of a fleet of load-haul-dump (LHD) machines deployed at Kiruna mine showed that the engine and the hydraulics are the two most critical subsystems. Hydraulic systems are selected for further study because such systems are still under a development phase. Maintenance data for two years for these machines are analyzed. The tests for trends and serial correlation showed that times between successive failures for the hydraulic systems are in most cases not independent and identically distributed. Goodness-of-fit tests showed that the power law process model provides a good fit to the failure data of the hydraulic systems. Methods for parameter estimation in the power law process model and estimation of optimal maintenance intervals for such systems are presented. Emphasis is on the use of graphical methods for data analysis.     

Orthonormal polynomials in wavefront analysis: analytical solution

Zernike circle polynomials are in widespread use for wavefront analysis because of their orthogonality over a circular pupil and their representation of balanced classical aberrations. In recent papers, we derived closed-form polynomials that are orthonormal over a hexagonal pupil, such as the hexagonal segments of a large mirror. We extend our work to elliptical, rectangular, and square pupils. Using the circle polynomials as the basis functions for their orthogonalization over such pupils, we derive closed-form polynomials that are orthonormal over them. These polynomials are unique in that they are not only orthogonal across such pupils, but also represent balanced classical aberrations, just as the Zernike circle polynomials are unique in these respects for circular pupils. The polynomials are given in terms of the circle polynomials as well as in polar and Cartesian coordinates. Relationships between the orthonormal coefficients and the corresponding Zernike coefficients for a given pupil are also obtained. The orthonormal polynomials for a one-dimensional slit pupil are obtained as a limiting case of a rectangular pupil.     

Interacting dissimilar semi-elliptical surface flaws under tension and bending

Stress intensity factors for two dissimilar interacting semi-elliptical coplanar surface flaws (cracks) in a semi-infinite elastic body are obtained under overall tension and bending. First the basic equations for a general planar crack normal to the free surface are established, using the method of equivalent eigen- or transformation strains (the body force method). Then the results are specialized for application to elliptical cracks. Numerical values are obtained for various configurations and crack shapes. Results are compared with those of two-dimensional collinear cracks. Finally, an approximate procedure for estimating the stress intensity factors for a general three-dimensional crack is suggested.     

Double-pulse electronic speckle interferometry for vibration analysis

We describe a double-pulse electronic-speckle-interferometry system. Two separate speckle patterns of an object being tested are recorded within a few microseconds with a CCD camera. Their two images are stored in a frame grabber. The fringes obtained from subtraction are quantitatively analyzed by the spatial-carrier phase-shift method. Using three directions of illumination and one direction of observation, one can record at the same time all the information necessary for the reconstruction of the three-dimensional deformation vector. Applications of this system for measuring the rotating objects are discussed for the case for which a derotator needs to be used. Experimental results are presented.     

Unstable resonator misalignment in ring and linear toroidal resonators

Optical axis motion in a ring resonator is investigated as a function of resonator mirror misalignment by constructing an equivalent paraxial model and applying the ray matrix formalism. Analytical expressions are derived for the optical axis motion. The paraxial model of the ring is shown to imply a linear resonator as a specific case, and the ring resonator expressions collapse to the familiar Krupke-Sooy results for that case. Using this method, new misalignment expressions are determined for more complex linear resonators. Uncorrectable misalignment conditions caused by toroidal mirror parameter errors are studied analytically and with a geometric optics code, and resulting phase front errors are given for a special case. These results are also examined as a basis for toroidal mirror quality specifications.     

Transient Heat Conduction in a Functionally Graded Cylindrical Panel Based on the Dual Phase Lag Theory

The transient heat conduction in a functionally graded cylindrical panel is investigated based on the dual phase lag (DPL) theory in this article. Except for the phase lags which are assumed to be constant, all the other material properties of the panel are assumed to change continuously along the radial direction according to a power-law formulation with different non-homogeneity indices. The heat conduction equations based on the DPL theory in the cylindrical coordinate system are written in a general form which are then used for the analyses of four different geometries: (1) a hollow cylinder of an infinite length; (2) a hollow cylinder of a finite length; (3) a cylindrical panel of an infinite length; and (4) a cylindrical panel of a finite length. Using the Laplace transform, the analytical solutions for temperature and heat flux are obtained in the Laplace domain. The solutions are then converted into the time domain by employing the fast Laplace inversion technique. The exact expressions for the radial thermal wave speed are obtained for the four different geometries. The numerical results are displayed to reveal the effect of different approximations of the DPL theory on the temperature distribution for various non-homogeneity indices. The results are verified with those reported in the literature.     

Fluid structure interaction by means of variational multiscale reduced order models

A reduced order model designed by means of a variational multiscale stabilized formulation has been applied successfully to fluid-structure interaction problems in a strongly coupled partitioned solution scheme. Details of the formulation and the implementation both for the interaction problem and for the reduced models, for both the off-line and on-line phases, are shown. Results are obtained for cases in which both domains are reduced at the same time. Numerical results are presented for a semistationary and a fully transient case.     

Cell control research— current status and development trends

A critical literature review on cell controller research is presented in this paper. Different definitions of a flexible manufacturing cell and cell controller are analysed, and comprehensive cell and cell controller definitions are given. Based on the requirements for a cell control system suggested by practitioners, users and researchers, a new set of general requirements for the development of a cell control system is proposed. After many well-known cell control systems are reviewed, a general structure of a cell controller and the general architecture of the cell control system, which includes a cell controller and a sub-system for the generation and configuration of a cell controller, are suggested. The scheduling approaches used in cell control are also discussed. The tools employed for modelling the cell control logic are examined. The trends and potential research directions in cell controller development are addressed.     

Interfacial stress singularities in a bimaterial wedge

In this paper stress intensity factors are presented for a bimaterial wedge in which plasticity effects are allowed for. Results are presented for a range of materials and for wedges in which each material occupies a sector of angle equal to one half that of the wedge. The calculations are an extension of previous work in which only a 180° wedge was considered and an entirely different numerical scheme is used that leads to analytic fits to the stress parameters.     

Flow field due to a row of vortex and source lines spanning a conical annular duct

Analytical expressions are derived for the incompressible flow due to a row of vortex and source lines spanning a duct whose walls are coaxial conical surfaces of revolution with a common vertex. The singularity lines have the shape of an arc of circle meeting the walls perpendicularly, and are defined by the intersection of a spherical surface with a series of equally spaced meridional planes. Although source lines of spanwisely varying strength are in general assumed, only vortex lines of constant circulation are considered. Simpler expressions are derived for the limiting two-dimensional cases when the flow is axisymmetric (actuator disc), and when the angular distance between the conical walls becomes vanishingly small. The expressions for the latter case are used in an example to obtain numerical results by a panel method for the velocity distribution of the flow about the inlet guide vane system of a water turbine of bulb type.     

Diffraction and refraction of surface waves using finite and infinite elements

The wave problem is introduced and a derivation of Berkhoff's surface wave theory is outlined. Appropriate boundary conditions are described, for finite and infinite boundaries. These equations are then presented in a variational form, which is used as a basis for finite and infinite elements. The elements are used to solve a wide range of unbounded surface wave problems. Comparisons are given with other methods. It is concluded that infinite elements are a competitive method for the solution of such problems.     

Metamodels of production line transient behaviour for sudden machine breakdowns

Production controls based on mean value analysis and steady-state conditions are incapable of making on-time decisions that cope with unexpected dynamic events which are due to interruptions in complex work flow characteristic of modern production lines. One of the most significant dynamic events in production situations is a sudden machine/operator breakdown/outage. Computer simulation is known to be a useful tool for modelling the dynamic response of a system to machine breakdown, but it takes too long to perform its analysis to provide the response time necessary for control procedures. Analytical methods provide formulae which are suitable for real-time analysis, but there are no results available for transient behaviour associated with machine breakdown. Metamodelling is the process of summarizing the results of a simulation study in analytical form. In this paper, we present our metamodels for the dynamic behaviour of both time in system and number in system for a general arrival time, general service time, multi-station, multi-server production line system. The formulae are exponential in nature and are developed through a study of first-order differential equations from system control theory. The constants used in our results are determined off-line through discrete-event simulation analysis. The metamodels themselves are available to on-line users as a predictor of parts that will be delayed because of breakdown(s) as a function of time in the future. The integrated approach of using simulation for modelling system details and analytic method for describing the revealed system transient behaviour is a powerful methodology for analysing large-scale production systems.     

空间飞行器故障诊断技术的发展和展望

由于空间飞行器需要高指标的安全保障，故障诊断成为极紧迫的任务，本文将评述空间飞行器故障诊断的重要性和特点，讨论空间飞行器故障诊断系统的结构和故障诊断技术，展望空间飞行器智能故障诊断技术的前景。     

Hydrodynamics of deformable contiguous spherical shapes in an incompressible inviscid fluid

Summary An exact solution to the two-body interaction problem is presented for the case of spherical shapes moving in an incompressible and inviscid fluid. The spheres are assumed to translate in an arbitrary manner and to undergo radial deformation (or pulsation). The problem is formulated in terms of spherical harmonics and the force experienced by the spheres is obtained by employing the Lagally theorem. The expressions for the force are given as an infinite sum of coefficients which are found by solving an infinite set of linear equations. Three main geometries are considered, namely, two spheres exterior to each other, one sphere in the interior of the other and sphere in a rectangular channel. Numerical values for the added-mass coefficients as well as for the hydrodynamic forces are found for the case of rigid sphere moving toward or parallel to a rigid wall or a free surface, and a pulsating sphere in the proximity of these boundaries. Also given are numerical values for the transverse and the longitudinal addedmass coefficients for a sphere moving in a rectangular channel for different channel-blockage ratios.     

Optimal Projective Three-Level Designs for Factor Screening and Interaction Detection

Orthogonal arrays (OAs) are widely used in industrial experiments for factor screening. Suppose that only a few of the factors in the experiments turn out to be important. An OA can be used not only for screening factors, but also for detecting interactions among a subset of active factors. In this article a set of optimality criteria is proposed to assess the performance of designs for factor screening, projection, and interaction detection, and a three-step approach is proposed to search for optimal designs. Combinatorial and algorithmic construction methods are proposed for generating new designs. Permutations of levels are used for improving the eligibility and estimation efficiency of the projected designs. The techniques are then applied to search for best three-level designs with 18 and 27 runs. Many new, efficient, and practically useful nonregular designs are found and their properties are discussed.     

Hydrodynamic principles of wave power extraction

The hydrodynamic principles common to many wave power converters are reviewed via two representative systems. The first involves one or more floating bodies, and the second water oscillating in a fixed enclosure. It is shown that the prevailing basis is impedance matching and resonance, for which the typical analysis can be illustrated for a single buoy and for an oscillating water column. We then examine the mechanics of a more recent design involving a compact array of small buoys that are not resonated. Its theoretical potential is compared with that of a large buoy of equal volume. A simple theory is also given for a two-dimensional array of small buoys in well-separated rows parallel to a coast. The effects of coastline on a land-based oscillating water column are examined analytically. Possible benefits of moderate to large column sizes are explored. Strategies for broadening the frequency bandwidth of high efficiency by controlling the power-takeoff system are discussed.     

Analysis of inverse heat-conduction problems by means of similarity solutions

Similarity solutions are given for a linear heat-conduction equation for a wide class of boundary conditions. The solutions are used for analyzing inverse problems that are applied to the determination of external heating conditions.     

四边形单元面积坐标理论

本文建立了四边形单元面积坐标的系统理论，包括：（１）给出四边形单元两个特征参数ｇ１，ｇ２的定义以及四边形退化为平行四边形（含矩形），梯形，三角形时相应的特征条件；（２）给出四边形单元面积坐标的定义及其与直角坐标和四边形等参坐标之间的变换关系；（３）给出四边形单元四个面积坐标分量之间应满足的两个恒等式并予以证明；（４）给出相关的一些重要公式。可以看出，四边形面积坐标是构造四边形单元的有效工具。它既是自然坐标，具有不变性；同时它与直角坐标之间为线性关系，易于得出单元刚度矩阵的积分显式，无需依赖于数值积分。     

Interaction between crack and arbitrarily shaped hole with stress and displacement boundaries

The interaction between a crack and an arbitrarily shaped hole under stress and displacement boundaries in an infinite plane subjected to a remote uniform load is studied. The Green's functions of a point dislocation for the problems are derived and are then used to analyze the interaction problem. The superposition principle is employed to reduce the original problem to two subsidiary problems. The complex stress functions of each problem are composed of two parts, in which the second parts are always holomorphic. Using analytical continuation in conjunction with rational mapping function, the stress functions are obtained in closed form. The interaction of a hole or an inclusion with a crack is solved using dislocations to model the crack and solving a system of singular integral equations. Stress intensity factors for crack tips and stress concentration factors for inclusion corner are determined and plotted for various cases. The affecting ranges of hole and inclusion are investigated.     

Neural networks for cost estimation: Simulations and pilot application

Neural networks in a multilayer perceptron architecture are able to classify data and approximate functions based on a set of sample data (curve fitting). These properties are used to investigate experimentally the applicability of neural networks for cost estimation in early phases of product design. Experiments are based on pilot cost data from a manufacturing company. In addition, artificially created simulative data are used for benchmarking. The cost estimation performance is compared to conventional methods, i.e. linear and non-linear parametric regression. Neural networks achieve lower deviations in their cost estimations. Beyond the use of standard neural architectures, simple modifications for a performance improvement are suggested and tested. Finally, a profile for situations where neural networks are appropriate is derived from the results.