Experimental and numerical life prediction of thermally cycled thermal barrier coatings

This article addresses the predominant degradation modes and life prediction of a plasma-sprayed thermal barrier coating (TBC). The studied TBC system consists of an air-plasma-sprayed bond coat and an air-plasma-sprayed, yttria partially stabilized zirconia top layer on a conventional Hastelloy X substrate. Thermal shock tests of as-sprayed TBC and pre-oxidized TBC specimens were conducted under different burner flame conditions at Volvo Aero Corporation (Trollhättan, Sweden). Finite element models were used to simulate the thermal shock tests. Transient temperature distributions and thermal mismatch stresses in different layers of the coatings during thermal cycling were calculated. The roughness of the interface between the ceramic top coat and the bond coat was modeled through an ideally sinusoidal wavy surface. Bond coat oxidation was simulated through adding an aluminum oxide layer between the ceramic top coat and the bond coat. The calculated stresses indicated that interfacial delamination cracks, initiated in the ceramic top coat at the peak of the asperity of the interface, together with surface cracking, are the main reasons for coating failure. A phenomenological life prediction model for the coating was proposed. This model is accurate within a factor of 3.     

Optimal recursive state estimation with quantized measurements

A set of exact nonlinear filters is derived and analyzed. The filters perform recursive state estimation when only coarsely quantized output signals are available. A system with the dynamics given by n integrators, together with a uniform prior on the state vector, form the model assumptions. In the case with one integrator, properties of the quantizer allows the construction of an exact recursive algorithm for the updating of the probability density function (p.d.f.), using only the corners of a convex polygon defining the region where the p.d.f. is nonzero. It is also shown how to generalize the algorithm to handle multiple measurements quantized with vector quantizers     

Circle criteria in recursive identification

Positive real conditions and differential sector conditions have recently been shown to imply global convergence w.p. 1, for recursive identification schemes based on a class of single-input/single-output linear Wiener models. The models consist of linear dynamics followed by a static output nonlinearity. The model structure is hence closely related to that of the Lure problem in the stability theory of feedback systems. This paper proves that the conditions for convergence can be transformed to graphical circle criteria, depending on the sector conditions and on the Nyquist plot of a transfer function related to the prior knowledge of the poles of the identified system     

Evaluation of on-line flue gas measurements by MISiCFET and metal-oxide sensors in boilers

Metal insulator silicon carbide field-effect transistor sensors, metal-oxide sensors, and a linear Lambda sensor in an electronic nose was used to measure on-line in hot flue gases from a boiler. Flue gas from a 100-MW pellets-fuelled boiler has been used to feed the experimental setup. Several reference instruments, which measure the flue gases in parallel to the sensor array, are connected to the electronic nose. Data was collected during six weeks and then evaluated. Using principal component analysis as the data evaluation method, different operating modes for the boiler have been identified in the data set. The different modes could be described in terms of high or low O/sub 2/ and CO concentration. Furthermore, we have shown that it seems possible to use a sensor array to determine the operating mode of the boiler and, by partial least-squares models, measure the CO concentration when the boiler operates in its optimum mode.     

Convergence analysis of recursive identification algorithms basedon the nonlinear Wiener model

Recursive identification algorithms, based on the nonlinear Wiener model, are presented. A recursive identification algorithm is first derived from a general parameterization of the Wiener model, using a stochastic approximation framework. Local and global convergence of this algorithm can be tied to the stability properties of an associated differential equation. Since inversion is not utilized, noninvertible static nonlinearities can be handled, which allows a treatment of, for example, saturating sensors and blind adaptation problems. Gauss-Newton and stochastic gradient algorithms for the situation where the static nonlinearity is known are then suggested in the single-input/single-output case. The proposed methods can outperform conventional linearizing inversion of the nonlinearity when measurement disturbances affect the output signal. For FIR (finite impulse response) models, it is also proved that global convergence of the schemes is tied to sector conditions on the static nonlinearity. In particular, global convergence of the stochastic gradient method is obtained, provided that the nonlinearity is strictly monotone. The local analysis, performed for IIR (infinite impulse response) models, illustrates the importance of the amplitude contents of the exciting signals     

Clinical audit: Development of the criteria of good practices

Clinical audit is a systematic review of the procedures in order to improve the quality and the outcome of patient care, whereby the procedures are examined against agreed standards for good medical RADIOLOGICAL procedures. The criteria of good procedures (i.e. the good practice) are thus the cornerstones for development of clinical audits: these should be the basis of assessments regardless of the type of the audit--external, internal, comprehensive or partial. A lot of criteria for good practices are available through the recommendations and publications by international and national professional societies and other relevant organisations. For practical use in clinical audits, the criteria need to be compiled, sorted out and agreed on for the particular aims of an audit (comprehensive or partial, external or internal). The national professional and scientific societies can provide valuable contribution to this development. For examination--or treatment-specific criteria--preliminary consensus needs to be obtained with the help of clinical experts, while clinical audits can be useful as a benchmarking tool to improve the criteria.     

Investigation of particle in-flight characteristics during atmospheric plasma spraying of yttria-stabilized ZrO2: Part 1. Experimental

A detailed investigation of the relationship between the parameters of the spray process and the in-flight properties of the particles was carried out using a multivariate statistical approach. A full factorial designed experiment concerning the spray process was performed, the spray gun parameters’ current, argon flow rate, hydrogen flow rate, and powder feed rate being selected to control the process. The particle properties, viz. velocity, temperature, and diameter, were determined using an optical measurement system, DPV 2000. In addition, the standard deviations of, and the correlations between, the measured particle properties were analyzed. The results showed current to have the strongest impact on particle velocity and particle temperature and argon flow rate to be the only parameter with an inverse effect on velocity and temperature.     

Performance of an Adaptive Controller for the Neuromuscular Blockade Based on Inversion of a Wiener Model

An adaptive controller based on a minimally parameterized parsimonious Wiener model for the effect of the muscle relaxant rocuronium in the neuromuscular blockade is presented. The controller structure combines inversion of the recursively identified static nonlinearity of the Wiener model with a positive compartmental control law for the linearized system. The overall strategy exploits the fact that the model has only two parameters, which are estimated by an extended Kalman filter. Due to the fact that the positive control law for total mass conservation of compartmental systems is only proven to be convergent for time‐invariant systems, the identification of the parameter in the linear block of the minimally parameterized parsimonious Wiener model is stopped when the controller is turned on. The controller was implemented in the platform Galeno and tested in simulation and in thirteen real cases of patients under general anesthesia. The good reference tracking results and robustness to noise show the reliability of the proposed strategy.     

ODE analysis and redesign in blind adaptation

In blind adaptation the dynamics of an unknown channel (system) is recovered together with the transmitted symbol sequence (input signal). This paper generalizes the author's previous algorithm (1994, 1997), that is not derived by criterion minimization, to include adaptive regressor filtering. The resulting scheme, which adapts a finite-dimensional IIR channel model, is designed to converge only to a well-defined set of parameters when binary symbols are transmitted over the channel. This provides a partial solution to the recently discussed ill-convergence problem in blind adaptation. Some connections to adaptive control theory are noted     

Quality Considerations for the Evaluation of Thermal Spray Coatings

Revealing the true structural and mechanical properties is of utmost importance for the optimized use of thermal sprayed coatings. Only the true properties can be expected to correlate to the spray parameters. During the recent decade, the gas turbine industry has experienced a focus on the laboratory procedures being the weakest link in a frozen and robust process. This article will show several results indicating that the laboratory procedures are more essential to the evaluation results than the spray parameters themselves. With new and robust laboratory techniques, the true properties of thermal spray coatings are revealed, causing a major problem with respect to the quality standards developed 30-40 years ago. In many cases, these old specifications need updates, which is a difficult task from a cost, time, and quality perspective for OEM’s. Coatings that have been successfully used for almost half a century no longer conform to the specification they were optimized to, because of these new appropriate laboratory techniques and procedures. What is actually meant when stating the following? (1) The coating has 5% porosity; (2) No cracks are allowed; (3) Tensile bond is 50 Mpa; (4) Hardness is 1000 HV; and (5) Coating thickness is 100 μm. This article also initiates a discussion on the measurement inaccuracies, for testing of thermally sprayed coatings, with respect to the commonly used general international standards (such as QS9000, ISO17025, AS9003, and ISO10012), as well as with respect to recommendations from the Six Sigma methodology.