A real-time structural parameter modification, approach for random vibration reduction: Part II. Experimental verification

Earthquake induced structural vibrations are stochastic in nature. In this paper, we present a novel structural control methodology for earthquake vibration reductions in two parts. Part I summarizes the efforts of the authors toward the development of real-time structural parameter modification (RSPM) control between 1993 and 1996. The operating control principle is minimization of conservative energy. The control hierarchy is realized by low-power-consuming devices (functional switches) with multiple ranked loops. The control method is to optimally adjust the physical parameters (mass, damping and stiffness) of the structure in real time. This method is therefore described as RSPM. It may be called variable passive control or parametric control. In Part I of this paper, the basic thesis of RSPM is presented, together with a discussion of the minimal principle of conservative energy of a vibrating system and the RSPM control hierarchy which contains four ranked loops. Variable passive control is capable of handling the stochastic nature of earthquake ground motion and it does not have certain major drawbacks of conventional active control methods. Part II of this paper describes experimental verifications of RSPM. It will be shown that RSPM can dissipate considerably more energy than existing passive energy dissipation devices. In addition, RSPM can reduce vibrations resulting from multidirectional excitations.     

Designing a laser scanning picoprojector. Part 2: laser-safety-related issues

Laser scanning picoprojectors present a new challenge in the field of laser safety with methods of calculating accessible emission limits still in their infancy. We present a laser safety analysis and a calculation of an example picoprojector. We show that, due to its scanning operation, a picoprojector should be considered an extended laser source, and we also show that a picoprojector with two separate one-axis microelectromechanical systems mirrors offers a higher safe power limit than a projector with a single scanning mirror. Finally, a safety analysis is done under conditions of mirror failure. We show that, if the projector fails to scan in just one of the axes, the ocular hazard rises sharply, highlighting the need for a fail-safe system to be built into laser scanning picoprojectors.     

On the overall elastic moduli of polymer-clay nanocomposite materials using a self-consistent approach. Part II: Experimental verification

Polyamide-6 (PA6) based nanocomposites were prepared using a modified montmorillonite (MMT) Cloisite 20A as nanofillers. The silicate weight fraction of the prepared nanocomposites, determined by burning off the PA6 matrix, was ranged from 0.2 wt% up to 7.5 wt%. The thermomechanical properties of both the neat PA6 and the PA6 filled with MMT nanoclay were measured by means of uniaxial tension tests and dynamic mechanical thermoanalysis, their crystallinity analyzed by differential scanning calorimetry and their morphology observed by transmission electron microscopy. The elastic stiffness of PA6-clay nanocomposites was examined under two moisture levels and was analyzed with the theory formulated in the Part I of this work. Predicted results are found in good agreement with our experiments. The model capabilities are also critically discussed by comparisons with both experiments issued from the literature and the Mori-Tanaka approach widely used in recent literature. It is demonstrated that the proposed micromechanical model is more efficient than the Mori-Tanaka approach. Moreover, the obtained results support the idea that the elastic stiffness of polymer-clay nanocomposites is governed by the same mechanisms as microcomposites, the effects of particle dimension or constrained region being of a second order.     

TaSi2 nanowires: A potential field emitter and interconnect

TaSi2 nanowires have been synthesized on a Si substrate by annealing NiSi2 films at 950 degrees C in an ambient containing Ta vapor. The nanowires could be grown up to 13 microm in length. Field-emission measurements show that the turn-on field is low at 4-4.5 V/microm and the threshold field is down to 6 V/microm with the field enhancement factor as high as 1800. The metallic TaSi2 nanowires exhibit excellent electrical properties with a remarkable high failure current density of 3 x 10(8) A cm(-2). In addition, effects of annealing temperatures and capability of metal silicide mediation layer on the growth of nanowires are addressed. This simple approach promises future applications in nanoelectronics and nano-optoelectronics.     

Improved prediction model for time-dependent deformations of concrete: Part 2—Basic creep

The second part of this series presents the formulae for the prediction of basic creep of concrete, i.e. creep at no moisture exchange. The formulae give the secant uniaxial compliance function which depends on the stress level, and, as a special case, the compliance function for linear structural analysis according to the principle of superposition. The formulae are based on the recently developed solidification theory for concrete creep which takes into account simultaneous ageing, satisfies all the basic thermodynamic requirements, and avoids divergence of creep curves. The formulae, which describe both creep and elastic properties, involve only four free material parameters. All four appear linearly, so that optimum data fits can be obtained by linear regression. For the frequent situations where no test data for the particular concrete to be used are available, empirical formulae for predicting these four parameters from the concrete mix composition and the standard compressive strength are given. These formulae, however, involve considerable error. To avoid it, one should, whenever possible, carry out measurements of the elastic modulus and, if possible, also the short-time creep of 7 to 28 days duration. With such measurements, greatly improved predictions can be achieved. The predictions are compared with 17 extensive data sets taken from the literature, and the coefficients of variation of the deviations are found to be smaller than with previous models.     

A dynamic simulation model for transient absorption chiller performance. Part II: Numerical results and experimental verification

This paper is the second paper out of two which present the development of a dynamic model for single-effect LiBr/water absorption chillers. The first part describes the model in detail with respect to the heat and mass balances as well as the dynamic terms. This second part presents a more detailed investigation of the model performance, including performance analysis, sensitivity checks and a comparison to experimental data. General model functionality is demonstrated.A sensitivity analysis gives results which agree very well to fundamental expectations: it shows that an increase in both external and internal thermal mass results in a slower response to the step change but also in smaller heat flow oscillations during the transient period. Also, the thermal mass has been found to influence the heat flow transients more significantly if allocated internally. The time shift in the solution cycle has been found to influence both the time to reach steady-state and the transients and oscillations of the heat flow. A smaller time shift leads to significantly faster response.A comparison with experimental data shows that the dynamic agreement between experiment and simulation is very good with dynamic temperature deviations between 10 and 25 s. The total time to achieve a new steady-state in hot water temperature after a 10 K input temperature step amounts to approximately 15 min. Compared to this, the present dynamic deviations are in the magnitude of approximately 1–3%.     

A mixed-variable continuously deforming finite element method for parabolic evolution problems. Part III: Numerical implementation and computational results

In Part I of this paper,¹ the conceptual framework of a rate variational least squares formulation of a continuously deforming mixed-variable finite element method was presented for solving a single evolution equation. In Part II² a system of ordinary differential equations with respect to time was derived for solving a system of three coupled evolution equations by the deforming grid mixed-variable least squares rate variational finite element method. The system of evolution equations describes the coupled heat flow, fluid flow and trace species transport in porous media under conditions when the flow velocities and constituent phase transitions induce sharp fronts in the solution domain. In this paper, we present the method we have adopted to integrate with respect to time the resulting spatially discretized system of non-linear ordinary differential equations. Next, we present computational results obtained using the code in which this deforming mixed finite element method was implemented. Because several features of the formulation are novel and have not been previously attempted, the problems were selected to exercise these features with the objective of demonstrating that the formulation is correct and that the numerical procedures adopted converge to the correct solutions.     

Global behaviour of a composite stiffened panel in buckling. Part 2: Experimental investigation

The present study analyses an aircraft composite fuselage structure manufactured by the Liquid Resin Infusion (LRI) process and subjected to a compressive load. LRI is based on the moulding of high performance composite parts by infusing liquid resin on dry fibres instead of prepreg fabrics or Resin Transfer Moulding (RTM). Actual industrial projects face composite integrated structure issues as a number of structures (stiffeners, …) are more and more integrated onto the skins of aircraft fuselage.A post-buckling test of a composite fuselage representative panel is set up, from numerical results available in previous works. Two stereo Digital Image Correlation (DIC) systems are positioned on each side of the panel, that are aimed at correlating numerical and experimental out-of-plane displacements (corresponding to the skin local buckling displacements of the panel). First, the experimental approach and the test facility are presented. A post-mortem failure analysis is then performed with the help of Non-Destructive Techniques (NDT). X-ray Computed Tomography (CT) measurements and ultrasonic testing (US) techniques are able to explain the failure mechanisms that occured during this post-buckling test. Numerical results are validated by the experimental results.     

Establishment of a simple neutron calibration field using a moderated 252Cf source: Part II. Experimental characterization of simple neutron calibration field

This paper describes the development and experimental standardization of neutron fields simply arranged for detector calibrations used for radiation control and environmental measurement. These fields are the following: (1) bare ²⁵²Cf fission field, (2) iron-moderated ²⁵²Cf field, (3) carbone-moderated Cf field, and (4) polyethylene-moderated ²⁵²Cf field. These fields are most suitable for calibrating the detectors used in and around nuclear and radiation facilities, since the fields are designed to simulate the typical neutron fields in and around the facilities.The direct neutron components of these fields have been standardized by the following two methods: (1) calculation by the ANISN code, and (2) measurements with and without a shadow shield by detectors standardized in the national standard field at the Electrotechnical Laboratory (ETL). The neutron emission rates of the ²⁵²Cf source have been calibrated also at ETL. We have standardized only direct components because of their independence of room size and peripheral structures. The standardized values are energy spectra and dose equivalent rates of the direct neutron components; the accuracies have also been evaluated to be 20% below 100 keV, 15% at 1 MeV, and 50% above 5 MeV. These fields including room scattered components have also been characterized especially to calibrate neutron detectors having sensitivity to low energy room scattered neutrons, because of large errors caused by shadow shield subtraction.     

Experimental and dynamic system simulation and optimization of a centrifugal pump-coupling-engine system. Part 2: System design

A comprehensive theoretical non-linear torsional dynamic model of a pump-coupling-engine assembly has been constructed, with some of the system characteristics evaluated through the finite element method. Coupling elements have non-constant stiffness, which makes the dynamic system non-linear. The resulting model provided information on the torsional vibration response of the system and therefore allowed analysis of the effect of different designs on the torsional system dynamics. Model outputs have been compared to experimental test rig results where system rotational inertia and four different couplings have been studied. The main aim of the work was to improve system design in order to guarantee reliable operation. The model facilitated a dynamic characterization of the system and has been used as predictive tool for subsequent design.     

Adaptive composites incorporating shape memory alloy wires. Part 2: development of internal recovery stresses as a function of activation temperature

Shape memory alloy (SMA) wires have been integrated in composite laminates consisting of an epoxy resin reinforced by aramid fibres. In the first part of this series, a new methodology was proposed for the simultaneous measurement of stress and temperature in the reinforcing fibres during shape memory wire activation. Those tests were conducted at three activation temperatures (40, 60 and 100°C) and the internal compressive stress distribution was extracted for low wire volume fraction composites. It was observed that for higher wire volume fractions the high compressive recovery stresses generated during electrical resistive heating of the wires led to the geometric failure of the composite coupons. In this work, measurements are conducted on hybrid laminate coupons of dimensions that prevent geometric (global) specimen failure. The internal stress distribution is measured at relatively high activation temperatures of 80 and 100°C and a filtering technique based on fast Fourier transform (FFT) is employed to simulate the stress and temperature variability and to filter the associated experimental noise. The results show that the higher stresses appear in the middle of the mid-wire distance and that the values at 100°C activation are not significantly different than those at 80°C indicating the presence of an upper limit in the transmission of wire recovery stresses in these systems.     

Alternating field losses in superconducting wires carrying dc transport currents. Part 2: multifilamentary composite conductors

Investigations of transient field losses in multifilamentary composite conductors carrying dc transport currents, I, are presented. As shown previously, the total loss is best characterized by a normalized transport current i = l/l_c and a dimensionless field-change rate β = τB_e/B_p, where τ is the relaxation time of the coupling current and B_p is the full-penetration field of a solid conductor equivalent to the multifilamentary composite. For β ? 1, the composite conductor behaves like a solid conductor and a saturation effect occurs in both the magnetization and the ac losses. The characteristic feature of the composite appears for β ? 1, and the total losses for transport currents below i < 1 ? β are almost independent of i. Beyond the limit given, losses rise sharply. Experimental results over a wide range of the field change rate and the transport-current level agree sufficiently with the calculations.     

Modelling of Failure of Woven Composites. Part 2: Experimental and Numerical Justification of the Interzone Concept

The failure of woven composites has been examined. This study is presented in two parts:

• Modelling of failure of woven composites. Part 1: nomenclature defining the interzone concept;
• Modelling of failure of woven composites. Part 2: experimental and numerical justification of the interzone concept.

In the first part, the concepts of the interzone and the geometry of an interzone have been defined in a general way for a large panel of woven composites. In the second part, it has been shown that the failure of woven composites is well described by using the interzone concept. The load transfer between intact interzones and broken interzones has been evaluated for two types of loadings (tensile loading and loading in bending). The analysis of these load transfers explains why in the case of a tensile loading the failure is of a sudden-death type whereas in the case of bending loading the failure is progressive. The concept of failure of an interzone has been also defined.     

Enhanced layerwise model for laminates with imperfect interfaces - Part 2: Experimental validation and failure prediction

In this paper, the layerwise model for laminates with imperfect interfaces and enhanced in Part 1 of this work is confronted with experimental results. The model calculations are validated by comparing its sliding predictions in double lap adhesive joints to the sliding measurements performed in a previous paper. The model predictions agree with the experimental results. Finally, the model is applied to the failure analysis in double lap joints and T-peel joints exhibiting adherend, adhesive and cohesive failures. The model calculations and pertinent failure criteria provide accurate predictions and may become a helpful tool suitable to the design of adhesive joints.     

Characterisation and optimisation of flexible transfer lines for liquid helium. Part I: Experimental results

The transfer of liquid helium (LHe) into mobile dewars or transport vessels is a common and unavoidable process at LHe decant stations. During this transfer reasonable amounts of LHe evaporate due to heat leak and pressure drop. Thus generated helium gas needs to be collected and reliquefied which requires a huge amount of electrical energy. Therefore, the design of transfer lines used at LHe decant stations has been optimised to establish a LHe transfer with minor evaporation losses which increases the overall efficiency and capacity of LHe decant stations. This paper presents the experimental results achieved during the thermohydraulic optimisation of a flexible LHe transfer line. An extensive measurement campaign with a set of dedicated transfer lines equipped with pressure and temperature sensors led to unique experimental data of this specific transfer process. The experimental results cover the heat leak, the pressure drop, the transfer rate, the outlet quality, and the cool-down and warm-up behaviour of the examined transfer lines. Based on the obtained results the design of the considered flexible transfer line has been optimised, featuring reduced heat leak and pressure drop.     

A mixed-variable continuously deforming finite element method for parabolic evolution problems. Part I: The variational formulation for a single evolution equation

The objective of the research presented here was to develop a generic adaptive computational method for porous media evolution problems that involve coupled heat flow, fluid flow and species transport processes with sharply defined phase-change interfaces. In this paper we examine the general least squares variational approach and develop the conceptual framework for a rate least squares variational formulation of a continuously deforming mixed variable finite element method for solving highly non-linear time-dependent partial differential equations. In Part II of this paper¹ we extend the formulation given here for a single evolution equation to a system of coupled evolution equations. In Part III² we discuss in detail the numerical procedures that were implemented in a computer program and present several numerical examples that demonstrate the performance of this computational method.     

Silicon carbide fibres and their potential for use in composite materials. Part 1

The preparation and properties of silicon carbide fibres are reviewed. Particular attention has been paid to multifilament-yarn fibres (Nicalon), but CVD monofilaments and whiskers prepared from rice hulls are also considered. The properties are reviewed mainly from the viewpoint of the use of the fibres in metal matrix composites. Thus, as well as mechanical properties of the fibres, the oxidation behaviour of SiC and its interaction with metals are examined. The review is divided into two parts; part I deals with the preparation, structure and mechanical properties of fibres, while part II will deal with the oxidation of SiC and the interaction of the compound with metals.     

Silicon carbide fibres and their potential for use in composite materials. Part II

In the second part of this review on silicon carbide fibres, the chemical properties of SiC relevant to the use of SiC fibres as a reinforcement in metal matrix composite materials are reviewed. Particular attention is paid to the oxidation of SiC, and to the interaction of SiC with metals and alloys with respect to chemical interactions and fibre/matrix bonding.     

Variable-order variable-step algorithms for second-order systems. Part 2: The codes

In a companion paper, Thomas and Gladwell,⁴ the authors designed a class of multistage methods for second-order systems of ordinary differential equations (ODE's), together with local error estimators based on embedding techniques. Here we provide a set of subroutines implementing the algorithms and discuss our numerical experience with the resulting codes.