Updating the Craig–Bampton reduction basis for efficient structural reanalysis

A Combined Approximation (CA) based reanalysis technique is proposed for updating the static modes in a reduction basis which can be used for sizing optimization problems. Although the proposed technique is utilized under the framework of the Craig–Bampton (CB) method, it can be employed with any condensation procedure that involves the computation of the static modes. An automated update scheme is also presented that switches the proposed technique with the exact analysis when the computational efficiency is lost. Moreover, the Enriched Craig–Bampton (ECB) method is studied for the reanalysis of the normal modes. The ECB‐ and the CA‐based techniques are merged for efficient update of the CB reduction basis. An academic test problem is utilized for the demonstration of the introduced concepts. Copyright © 2010 John Wiley & Sons, Ltd.     

Development of new wood treatments combining boron impregnation and thermo modification: effect of additives on boron leachability

Environmental pressures in France and in most European countries during the last decade have led to the development of more environmentally acceptable preservation methods. In this context, wood heat treatment is one of the most investigated alternative methods. Important chemical modifications resulting from thermo-degradation reactions confer new properties to wood, like increased decay resistance or higher dimensional stability, while mechanical properties like tensile strength decrease after treatment. However, the improved durability of heat treated wood is not sufficient to allow its utilization in ground contact, where it is subjected to insect and fungi attacks. Impregnation with borax before thermal treatment could be an interesting method to improve the properties of thermally modified wood. Boron is a relatively harmless biocide that improves resistance to fungi and insects like termites. Additionally, borax can also improve wood fire resistance due to its fire retardant effect. To reduce boron leachability, two additives previously developed in the laboratory corresponding to water soluble polymerizable polyglycerol derivatives were added to the borax solution, taking advantage of thermal treatment to fix the latter through polymerization within the wood structure limiting boron leachability.     

Microwave‐assisted synthesis of polyglycerol from glycerol carbonate

Microwave irradiation of glycerol carbonate allows formation of glycidol, which readily polymerizes to form polyglycerol under mild conditions comparatively to the classical polyetherification reaction involving high temperature and basic conditions. Analysis of the crude reactional mixture indicated the presence of low‐molecular weight oligomers constituted mainly of di, tri, and tetraglycerols with small quantities of higher molecular weights oligomers. Molecular size distribution was relatively similar to that of polyglycerols obtained under basic condition, even if these latter contained slightly higher amounts of high‐molecular weight oligomers. Structure of oligomers differs slightly according to the conditions of polymerization, and polyglycerols are obtained under microwave activation containing higher contents of cyclic isomers, whereas polyglycerols obtained under basic conditions contain more ramified isomers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Noise analysis of a zero power critical line reactor using Langevin's technique

Noise analysis of a critical, infinite-length, zero-power line reactor is given using the Langevin technique. A one-speed model is used and delayed neutrons are ignored. Stochastic analysis is carried out starting from the Boltzman equation with the assumption that neutrons move only in both directions in the line reactor. The power spectrum of neutron fluctuations is obtained and compared with that computed from diffusion approximation. Exact expressions for auto and cross-power spectrums of non-fission neutron detectors' outputs are also obtained.     

The least-squares identification of FIR systems subject to worst-case noise

The least-squares identification of FIR systems is analyzed assuming that the noise is a bounded signal and the input signal is a pseudo-random binary sequence. A lower bound on the worst-case transfer function error shows that the least-square estimate of the transfer function diverges as the order of the FIR system is increased. This implies that, in the presence of the worst-case noise, the trade-off between the estimation error due to the disturbance and the bias error (due to unmodeled dynamics) is significantly different from the corresponding trade-off in the random error case: with a worst-case formulation, the model complexity should not increase indefinitely as the size of the data set increases.     

Comprehensive stability design of planar steel members and framing systems via inelastic buckling analysis

This paper presents a comprehensive approach for the design of planar structural steel members and framing systems using a direct computational buckling analysis configured with appropriate column, beam and beam-column inelastic stiffness reduction factors. The stiffness reduction factors are derived from the ANSI/AISC 360-16 Specification column, beam and beam-column strength provisions. The resulting procedure provides a rigorous check of all member in-plane and out-of-plane design resistances accounting for continuity effects across braced points as well as lateral and/or rotational restraint from other framing. The method allows for the consideration of any type and configuration of stability bracing. With this approach, no member effective length (K) or moment gradient and/or load height (C _b ) factors are required. The buckling analysis rigorously captures the stability behavior commonly approximated by these factors. A pre-buckling analysis is conducted using the AISC Direct Analysis Method (the DM) to account for second-order effects on the in-plane internal forces. The buckling analysis is combined with cross-section strength checks based on the AISC Specification resistance equations to fully capture all the member strength limit states. This approach provides a particularly powerful mechanism for the design of frames utilizing general stepped and/or tapered I-section members.     

Recyclability assessment of Al 7075 chips produced by cold comminution and consolidation using spark plasma sintering

A solid-state recycling route for processing aluminium alloy 7075 chips is proposed. This process involves pulverizing the chips using an industrial scale comminution line to produce a broad particle size distribution of granulated products and powders. Upon sieving, the ?140 mesh fraction of the pulverised material was consolidated by spark plasma sintering into fully dense compacts, i.e. >99%. The properties of the pulverised powders and compacts were compared to commercially available aluminium alloy 7075 powder used in industrial press-sinter applications. The comminution line produced powder particles which possessed a 7·9?±?0·6-nm thick native oxide layer with adhering exogenous contaminants, and aluminium oxide particles dispersed throughout the powder. The presence of the oxide layer and exogenous contaminants was found to be deleterious to the powder consolidation and mechanical properties. A flexural strength and strain and hardness of 94·7?±?7·2?MPa, 2·1?±?0·3% and 69·3?±?5·2 HV were obtained, respectively.     

The vibration and stability of a three-layered conical shell containing an FGM layer subjected to axial compressive load

Summary In this paper, the vibration and stability of a three-layered conical shell containing a functionally graded material (FGM) layer subjected to axial compressive load are studied. The material properties of the functionally graded layer are assumed to vary continuously through the thickness of the shell. The variation of properties follows an arbitrary distribution in terms of the volume fractions of the constituents. The fundamental relations, the dynamic stability and compatibility equations of three-layered truncated conical shells containing an FGM layer are obtained first. Applying Galerkin's method, these equations are transformed to a pair of time dependent differential equations, and critical axial load and frequency parameter are obtained. The results show that the critical parameters are affected by the configurations of the constituent materials and the variation of the shell geometry. Comparing results with those in the literature validates the present analysis.     

Multibase scalar multiplications in cryptographic pairings

The efficient computation of the Tate pairing is crucial for various cryptographic applications. In the computation the Tate pairing, two types of costs should be considered: that of scalar multiplication and the evaluations of Miller’s line functions for elliptic curves. In this paper we optimize the calculation of \((f_{2j\pm 1}(Q),[2j\pm 1]P)\), \((f_{3j}(Q),[3]P)\), \((f_{3j\pm 1}(Q),[3j\pm 1]P)\) given the points P and Q in an elliptic curve, to improve the efficiency of the Tate pairing, when using the representation of the scalar n in NAF, in signed ternary base, and in double-base chain. Finally we compare their computational costs. In the case of a double-base chain, a general comparison is not simple, so we consider a few examples.     

The Effect of Iron Content on Microstructure and Mechanical Properties of A356 Cast Alloy

In the present study, microstructure and mechanical properties of A356 alloy including various amounts (0.2 to 1.2 wt pct) of iron were investigated. The alloys were produced by conventional gravity sand casting method. In order to determine the effect of iron addition to A356, optical and scanning electron microscopes (SEM/EDS) were used for microstructural examinations, and X-ray diffraction (XRD) analysis was carried out for phase characterization. Tensile tests were also conducted in order to determine effect of the Fe content on mechanical properties. It was found that as the Fe content of A356 was increased, the secondary dendrite arm spacing (SDAS) was decreased and the morphology of Al-Si eutectic became finer. From XRD examinations, different iron-based intermetallic compounds (β-Al₅FeSi and α-Al₈Fe₂Si) formations were observed. It was also observed that as iron content increased, α-Al₈Fe₂Si intermetallic was transformed into β-Al₅FeSi intermetallic. The tensile test results revealed that tensile strength and elongation values were reduced by increasing Fe content. It was also determined that β-Al₅FeSi intermetallics were more negatively effective on tensile strength than α-Al₈Fe₂Si intermetallics.