Novel thermal barrier coatings that are resistant to high-temperature attack by glassy deposits

Airborne sand particles that deposit on thermal barrier coatings (TBCs) in gas-turbine engines melt and form calcium–magnesium–aluminosilicate (CMAS) glass, which attacks the TBCs. A new approach for mitigating CMAS attack on TBCs is presented, where up to 20 mol.% Al₂O₃ and 5 mol.% TiO₂ in the form of a solid solution is incorporated into Y₂O₃-stabilized ZrO₂ (YSZ) TBCs. The fabrication of such TBCs with engineered chemistries is made possible by the solution-precursor plasma spray (SPPS) process, which is uniquely suited for depositing coatings of metastable ceramics with extended solid-solubilities. Here, the TBC serves as a reservoir of Al and Ti solutes, which are incorporated into the molten CMAS glass that is in contact with the TBC. This results in the crystallization of the CMAS glass and the attendant arrest of the penetrating CMAS front. This approach could also be used to mitigate attack by other types of foreign deposits (salt, ash, and contaminants) on TBCs.     

State controllability computation technique for linear time‐varying systems by using Taylor series approximation

This article presents a technique to determine the controllability Grammian matrix (CGM) for linear time‐varying systems by using truncated Taylor polynomial vector and the operational matrix of integration. An important property of this algorithm is that it starts by integrating the Lyapunov differential matrix equation in terms of the CGM. However, the algorithm does not use the mathematical integration processes actually, but uses the truncated Taylor polynomial vector and the operational matrix of integration. Thus, the problem is reduced to solving a linear set of algebraic equations with constant coefficients consisting of the Taylor polynomial constant coefficients of each of the CGM elements. Numerical results and error curves are given to illustrate the improvements achieved by the proposed algorithm. Copyright © 2008 John Wiley & Sons, Ltd.     

The role of umbrella arch and face bolt as deformation preventing support system in preventing building damages

Ground settlement is the most significant environmental impact of the tunnels excavated in intensively urbanized regions. A Considerable amount of ground settlement occurs by pre-convergence, formed during the time of support setting followed by the excavation, and movement of tunnel face into the tunnel. The risk of damage on the buildings by the ground settlement can be catastrophically high. Therefore, rock engineers bear an important duty to prevent the potential damage on buildings by controlling the ground settlement while excavating the tunnels. This has been accomplished by applying umbrella arch with face bolt technique recently in various important areas. In this method, the ground settlements can substantially be decreased by limiting the tunnel face movement into the tunnel, by creating a pseudo shell around the tunnel face with umbrella arch and then increasing the stability with face bolts. In this study, as part of the 2nd phase of Izmir metro construction in densely populated Poligon district of Izmir the effects of umbrella arch-face bolt applications on ground settlements have been determined using numerical modeling and in situ measurements. Results indicated that the umbrella arch and face bolt applications have significantly diminished the risk of settlement damage on buildings by reducing the ground settlements and convergence as 69% and 57%, respectively.     

The investigation of the effect of thermal barrier coating on the performance of Stirling engine

The shuttle heat transfer is one of the reasons reducing the performance of Stirling engines. This study is concerned with the reduction in shuttle heat transfer by coating the displacer. The displacer of a gamma type Stirling engine was coated with a layer of yttria‐stabilized zirconia (YSZ), and the effect of the coating on the engine performance was evaluated by comparing speed‐power and speed‐torque characteristics of the engine with coated and uncoated displacers. Characteristics were obtained for 700, 800 and 900°C heater temperatures. At each stage of the heater temperature, the charge pressure ranged from 1 to 3.5 bars with 0.5 bar increments. At 900°C heater temperature and 3 bars charge pressure, the shaft power before coating was 34.9 W, after coating the power increased to 43.8 W, which corresponds to a 25% increment. The temperature applied to the engine did not cause any damage on the coating layer. Copyright © 2008 John Wiley & Sons, Ltd.     

A fuzzy-controlled single-phase active power filter operating with fixed switching frequency for reactive power and current harmonics compensation

This paper introduces a single-phase voltage source current-controlled pulse width modulation rectifier model, acting as an active power filter (APF), with a fuzzy logic controller in the inner loop and a simple proportional-integral (PI) d.c. link voltage controller in the outer loop to compensate reactive power and current harmonic components simultaneously from nonlinear loads. The proposed scheme operates with a fixed switching frequency. The control scheme of the APF is simple, since it has fewer control inputs for determining the desired action. It is easily tunable for different performance criteria and can be achieved by means of low-cost of hardware installation, as it does not need to use more sensitive and accurate measuring devices. The model can also compensate both reactive and harmonic current components from nonlinear loads.     

Boundary layer equations and stretching sheet solutions for the modified second grade fluid

A modified second grade non-Newtonian fluid model is considered. The model is a combination of power-law and second grade fluids in which the fluid may exhibit normal stresses, shear thinning or shear thickening behaviors. The equations of motion are derived for two dimensional incompressible flows. The boundary layer equations are derived from the equations. Symmetries of the boundary layer equations are calculated using Lie Group theory. For a special power law index of m = −1, the principal Lie algebra extends. Using one of the symmetries, the partial differential system is transferred to an ordinary differential system. The ordinary differential equations are numerically integrated for the stretching sheet boundary conditions. Effects of power-law index and second grade coefficient on the boundary layers are shown and solutions are contrasted with the usual second grade fluid solutions. The shear stress on the boundary is also calculated.     

Super-orthogonal space-time-frequency trellis coded OFDM

Super-orthogonal space-time trellis codes (SOSTTCs) given in the literature are full rate and provide full spatial diversity with high coding gain in narrowband quasistatic fading channels. The high number of parallel transitions in their trellis structure restricts their performance in wideband channels where the code performance suffers from multipath. Code design criteria are derived and a computer search based method is proposed to design full-rate optimised SOSTTCs exploiting full spatial and multipath diversity for multiple-input multiple-output orthogonal frequency division multiplexing systems. The proposed codes have codewords defined in space, time, and frequency. We evaluate the codeword error rates of the new 16, 32 and 64-state super-orthogonal space-time-frequency trellis codes for quadrature phase shift keying by computer simulation and show that they provide significant error performance improvement compared to their counterparts with equivalent delay length     

Solar radiation over Turkey and its analysis

Ground-based solar-radiation observations have rather high random errors, which were sourced from maintenance, calibration and/or inaccurate instruments in Turkey. Satellite-based radiation data obtained from the National Aeronautics and Space Administration (NASA) were compared with reliable ground observations, and it was found that the global solar incident insolation data of the NASA Surface Meteorology and Solar Energy (SSE) dataset is usable, with a rather low mean relative error of about 4%. Therefore, monthly and annual spatial distribution over Turkey and solar-radiation time series were analysed in order to detect the potential of solar radiation and to find out variations and trends, respectively.     

New perturbation–iteration solutions for Bratu-type equations

Perturbation–iteration theory is systematically generated for both linear and nonlinear second-order differential equations and applied to Bratu-type equations. Different perturbation–iteration algorithms depending upon the number of Taylor expansion terms are proposed. Using the iteration formulas derived using different perturbation–iteration algorithms, new solutions of Bratu-type equations are obtained. Solutions constructed using different perturbation–iteration algorithms are contrasted with each other as well as with numerical solutions. It is found that algorithms with more Taylor series expansion terms yield more accurate results.     

The effect of niobium on the microstructure of ferritic stainless steel

The effect of different amounts of Nb and of homogenization on the ferritic stainless steels containing 17–18 wt.% Cr was investigated with scanning electron microscopy (SEM), optical microscopy, energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential thermal analysis (DTA). It was observed that M₂₃C₆, NbC and sigma phase formed in these steels. In addition, the formation of Nb₂C was observed in the sample containing 3.0 wt.% Nb. While the amount of Nb increased from 0.5 to 3.0 wt.% Nb, the microhardness of the matrix and the amount of M₂₃C₆ decreased and the toughness of the samples increased. After homogenization, the increase in the toughness of the samples containing 1.5–3.0 wt.%Nb was considerable and impressive.