An error indicator for the element free Galerkin method

In this paper we present an error indicator for the Element Free Galerkin (EFG) method, whose evaluation is computationally so simple that it can be readily implemented in existing EFG codes. The error indicator works very well in all numerical examples for 2-D potential and elasticity problems that are presented here, for regular and irregular grid of nodes. Moreover, it was demonstrated that this method is very simple in terms of economy and gives a good performance. The results show the error in EFG approximation may be estimated via the error indicator described in this paper. The indicator allows the global energy norm error to be estimated and also gives a good evaluation of local errors. It can thus be combined with a full adaptive process of refinement or, more simply, provide guidance for cloud of points redesign.     

An electronic heart-beat recorder

Summary An apparatus permitting to record the heart-beats of working persons is described. The input signal is obtained from a barrier layer photocell and a lamp at the ear-lobe. The signal is amplified by a differential amplifier with symmetrical input and feed-back.     

An extended continuum model incorporating the electronic throttle dynamics for traffic flow

This study develops a novel continuum model with consideration of the effect of electronic throttle (ET) dynamics to capture the behaviour of vehicles in traffic flow. In particular, the continuum model is proposed by incorporating the opening angle of ET based on the throttle-based full velocity difference model. Theoretical analyses including stability, negative velocity and shock wave are performed systematically. Numerical experiments and comparisons are conducted to verify the performance of the proposed continuum model. Results show that the steady-state performance of the proposed model is improved with respect to the stability. In addition, the proposed model is effective to rapidly dissipate the effect of external perturbation. Also, the phenomenon of negative velocity can be avoided by the proposed model.     

An eigenanalysis-based bifurcation indicator proposed in the framework of a reduced-order modeling technique for non-linear structural analysis

The Koiter–Newton method is a reduced order modeling technique which allows us to trace efficiently the entire equilibrium path of a non-linear structural analysis. In the framework of buckling the method is capable to handle snap-back and snap-through phenomena but may fail to predict reliably bifurcation branches along the equilibrium path. In this contribution we extend the original Koiter–Newton approach with a reliable and accurate bifurcation indicator which is based on an eigenanalysis of the reduced order tangent stiffness matrix. The proposed indicator has a negligible numerical effort since all computations refer to the reduced order model which is typically of very small dimension. The extension allows the identification of bifurcation points and a tracing of corresponding bifurcation branches in each sector of the equilibrium path. The performance of the method in terms of reliability, accuracy and computational effort is demonstrated with several examples.     

Assessment of electronic shearography for structural inspection

Electronic shearography (ES), a laser interferometry technique, has the potential for large-scale structural inspection and for identifying cracks and strain anomalies. A system based on this technology could possibly be used for noninvasive inspection of structures with high insensitivity and robustness. One major problem is the existence of largerigid body motions in typical engineering structures such as bridges and high-rise buildings. These rigid-body motions are large enough to cause a complete decorrelation of the characteristic speckle pattern that is obtained by illuminating the object surface. This nullifies any possibility of interference between speckled images obtained at different stages of loading, as is necessary for interferometry applications. A systematic study was conducted to characterize the speckle pattern obtained from typical civil structures as a function of the illumination and imaging system. Experiments were carried out to quantify speckle decorrelation as a function of object motion and instrumentation characteristics. A fracture mechanics based finite element (FEM) analysis was carried out on an existing fractured bridge to determine the strains and displacements. The results of these studies were subsequently used to define the parameters of a structural inspection system based on ES for field applications.     

Technology showcase electronic penetrometer for field tests

The design and construction of a cone penetrometer for field use is described. The penetrometer is mounted on a frame to which two wheels are fitted for towing the device from one test site to the next. An electric motor drives the penetrometer during the test and simultaneous readings are performed of both cone depth and penetration resistance. The device weighs 70 kg and the maximum force on the cone typically exceeds 1.2 kN. The acquired data are transferred to a microcomputer and after each penetration the result is presented to the operator in graphic form. The microcomputer is equipped with a fairly large RAM memory which serves as storage medium for data during measuring work. Afterwards, data are easily moved to a mainframe computer for analysis.     

A new smoothness indicator for third‐order WENO scheme

We present a new reference smoothness indicator for third‐order weighted essentially non‐oscillatory scheme to recover its design‐order convergence at critical points. This reference smoothness indicator, which involves both the candidate and global smoothness indicators in the weighted essentially non‐oscillatory framework, is devised according to a sufficient condition on the weights for third‐order convergence. The recovery of design‐order is verified by standard tests. Meanwhile, numerical results demonstrate that the present reference smoothness indicator produces sharper representation of the discontinuity owing to the combined effects of larger weight assignment to the discontinuous stencils and convergence rate recovery. Copyright © 2015 John Wiley & Sons, Ltd.     

Use of electronic speckle interferometry for recording nanodisplacements

Advancement of nanomechanics and nanotechnologies assumes creation of adequate tools for measuring displacements in the nanoscale range. In the present paper, for these purposes we propose to use the method and hardware of electronic speckle interferometry, which have several advantages over the other known measurement means. We present an idea based on which the method of electronic speckle interferometry, primarily designed to be used to measure displacements in the submicron range, can be used to measure displacements that are hundreds of times smaller, i.e., of the order of 1 nanometer. We consider the theoretical justification of this idea and the program algorithm for its implementation and describe the methods, the test specimens, and the results of experimental metrological test of the possibility of measuring displacements in the nanoscale range by using the existing model of the electronic speckle interferometer.     

Calibrated multichannel electronic interferometry for quantitative flow visualization

Calibrated multichannel electronic interferometry, a new technique for quantitative flow visualization of transient phenomena, is discussed. This technique uses an interferometer combined with diffraction gratings to generate three phase shifted interferograms simultaneously which are used to perform multichannel phase shifting. The optical system is calibrated with no phase object present using standard piezoelectric phase shifting, and this calibration information is stored as an electro-optic hologram. The calibration information is used along with the three phase-shifted interferograms that exist with a phase object present to perform time-resolved phase shifting. Examples using natural convection and separated flows are presented.     

Bifurcation indicator for geometrically nonlinear elasticity using the Method of Fundamental Solutions

In the present work, we propose a numerical analysis of instability and bifurcations for geometrically nonlinear elasticity problems. These latter are solved by using the Asymptotic Numerical Method (ANM) associated with the Method of Fundamental Solutions (MFS). To compute bifurcation points and to determine the critical loads, we propose three techniques. The first one is based on a geometrical indicator obtained by analyzing the Taylor series. The second one exploits the properties of the Padé approximants, and the last technique uses an analytical bifurcation indicator. Numerical examples are studied to show the efficiency and the reliability of the proposed algorithms.     

Adaptive mesh refinement for two-phase slug flows with an a priori indicator

The purpose of this paper is to present a novel adaptive mesh refinement AMR technique for computing unstable one dimensional two-phase flows in pipelines. In multiphase flows, the prediction and localisation of inter-facial waves, slugs and instabilities related to flow conditions under study require high levels of accuracy. This is more apparent in systems at industrial scales, where flow lines possess highly distorted regions and irregular topologies.Uniform fine meshes for these long devices are costly and in general situations the optimum space discretisation could not be determined a priori.Adaptive mesh refinement AMR procedure provides a remedy to this problem by refining the mesh locally, allowing to capture regions where sharp discontinuities and steep gradients are present. With appropriate algorithm and data organisation, AMR helps to reduce CPU time and speeds up simulations of flows in long pipes. The effectiveness of AMR methods relies on estimators that determine where refinement is required. We show in this work that for transient flows combining gradient-based error estimator with Kelvin–Helmholtz stability condition can improve the acceleration of computation and locate regions where refinements are required. The Kelvin–Helmholtz is a local condition and is an a priori indicator for the refinement.     

Experimental study for reliability of electronic packaging under vibration

An automated fatigue-testing system was developed for an experimental study on the integrity of the electronic packaging subjected to mechanical vibration. The fatigue-testing machine utilized the electromagnetic device as an actuator. A data acquisition system was developed for the fatigue test of the electronic board. The fixture for the specimen was designed to be suitable for measuring the fatigue life of a typical module/lead/card electronic system subjected to vibration. With this automated fatiguetesting machine, the mechanical integrity of surface mount component with the spider gullwing leads has been studied by a mechanical flexural fatigue test. An experimental method was developed to measure the changes in electrical resistance in the lead, which is used to indicate a fatigue failure. Finally, a relationship between the loading force and the fatigue life of high-cycle region was discussed for the lead of spider gullwing type surface-mounted component. With the relation, the fatigue life of the surface-mounted component (SMC) subjected to vibration environment was predicted successfully.This paper was presented at the 1995 SEM Spring Conference on Experimental Mechanics, Grand Rapids, MI, June 12–14.     

A new electronic circuit for a hot-cathode ionization gauge

Summary Details are given of a circuit, capable of measuring pressures in the range 10⁻³ mm Hg to 10⁻¹⁰ mm Hg. As the quotient of ion current over emission current is measured, which is proportional to the pressure in the above-mentioned range, the need for an emission stabilizer has been eliminated. At pressures lower than 10⁻⁴ mm Hg, meter indication varies by not more than 3% at emission currents between 10μA and 1 mA. The author wishes to thank Prof. Dr. J. Kistemaker for his stimulating interest, and J. Los, H. Zaaiman, C. Visser, R. Wunnink and T. Heise for carrying out many measurements. This work is part of the research program of the Stichting voor Fundamenteel Onderzoek der Materie and was made possible by financial support from the Nederlandse Organisatie voor Zuiver Wetenschappelijk Onderzoek.     

Single amplifier biquad based autonomous electronic oscillators for chaos generation

Two simple autonomous chaotic electronic circuits have been proposed in this paper. The core of each of the circuits consists of a single amplifier biquad (SAB). We have proposed two configurations of converting this SAB into chaotic oscillators using suitable passive nonlinear element and a storage element in the form of an inductor. The mathematical models of the proposed chaotic circuits have been constructed, which are fourth order autonomous nonlinear differential equations. The behavior of the proposed circuits has been investigated through numerical simulations, Spice-based circuit simulations and electronic hardware experiments and they agree well with each other. It has been found that both the circuits show complex behaviors like bifurcations and chaos for a certain range of circuit parameters.     

Spectral entropy as a flow state indicator

In many practical applications, the flow state (laminar, transitional, turbulent) might vary in space and/or in time for a given configuration. The aim of the current study is to show that the spectral entropy S_d, obtained from solving the eigenvalue problem for the temporal autocorrelation function, can be used in order to uniquely quantify the flow state and differentiate between laminar, transitional, or turbulent regimes; as such, it delivers a direct measure of turbulence level. Therefore, this quantity might support hybrid numerical simulations by determining the local flow state, identifying in this way the most suitable computational model and switching, e.g., from RANS to LES. The first test of the suggested approach relies on Direct Numerical Simulations (DNS) for decaying Homogeneous Isotropic Turbulence (HIT) performed for ten different Taylor Reynolds numbers. Results obtained by analyzing DNS indicate that S_d is an excellent candidate to quantify turbulence level and transition. To check the robustness of the corresponding analysis, the impact of different resolutions has been investigated, revealing that a correct state estimate is still obtained with a coarser spatial or temporal resolution. Finally, to check the generality of the approach, the entropy thresholds obtained from the DNS analysis have been used with the same algorithm to analyze 1) DNS results obtained for the Taylor-Green vortex benchmark at Re=1600 as well as 2) results obtained through Large Eddy Simulations in a blood nozzle, revealing in both cases a perfect agreement with a traditional, user-based analysis of the flow conditions. Hence, S_d appears to be an excellent quantitative indicator of laminar, transitional, or turbulent flow, allowing an automatic, user-independent analysis of the flow state for a variety of conditions. In principle, it could be used without modification to analyze experimental measurements as well.     

A new interferometric method for vibration measurement by electronic holography

Electronic holography is a well-established technique used in real-time, non-contact, whole-field displacement measurements. When using the real-time, time-averaged method for vibration measurments, the quantitative interpretation of dense fringe patterns is difficult because of speckle noise. Even when speckle-reducing procedures are used, such as multiple-frame averaging or rotation of the illumination beam, the remaining speckles and decreasing visibility of higher-order Bessel fringes are serious limitations. The primary objective of this paper is to present a new realtime, interferometric method for mechanical vibration measurements and the associated quantitative interpretation. The fringe pattern obtained by this method is quasi-binary and half as dense as in the time-averaged method. The method greatly improves the overall visibility (contrast, resolution) of vibration fringe patterns without any sacrifice in the real-time capabilities. Quantitative fringe interpretation is straightforward and based on binary fringe tracking. It allows quantitative measurements in situations where the time-averaged fringe processing fails.     

Partial drift compensation in electronic d-c analog computers for differential equations

Summary The most serious errors in electronicd-c analog computers for differential equations arise from drifts due to unbalances in the amplifiers. We will describe a certain method of reducing these errors: partial drift compensation. Here the analog computer as a whole is compensated for with regard to certain drifts, i.e. certain drifts in the way they appear in the differential equation. The sources of one drift may be located in several elements of the computer. The number of points where the compensation has to be applied is usually much smaller than the number of sources. Thus the partial compensation is an economic solution of the drift problem if it can be realized. This question is treated in the paper and it is shown that this kind of compensation is well suited for analog computers with time-shared elements. An example is finally given where the number of compensation points is nine, although the number of drift sources is forty-five.