18 research outputs found
Microtomography of Soil and Soot Deposits: Analysis of Three-Dimensional Structures and Surface Morphology
No full textThe detrimental effects generated by the gas turbine fouling phenomenon are well known. Due to soil and soot particles ingestion, gas turbines experience performance drops related to greater fuel consumption and even lower efficiency. These effects are related to the modification of the shape and surface roughness of relevant surfaces (compressor and turbine blades and vanes, especially) due to the presence of a thin layer generated by micro/nano-sized particle adhesion. Such contaminants are swallowed by the unit and, as a function of the operating conditions, adhere to the surface, causing a sort of dangerous coating to the surface. In this work, a microtomography analysis of the deposited layer is reported. The deposited layer has been generated using micro-sized soil and soot powders under specific impact conditions and substrate surface roughness similar to those in the cold section of a gas turbine compressor. The microtomography analysis has been carried out using the beamline at the ELETTRA Sincrotrone research center. Thanks to the resolution of the beamline, the detection of the threedimensional internal structure of the soil and soot layers has revealed that within the layer, the structure is characterized by discontinuities. Soot and soil particles, even characterized by similar diameter distributions and test conditions, generate layer structures that differ by the magnitude, orientation, location of the internal discontinuities, and surface morphology (i.e., roughness). The comprehension of the packing process allows to understand the adhesion process and define general guidelines to predict the fouling phenomenon
Microtomography of Soil and Soot Deposits: Analysis of Three-Dimensional Structures and Surface Morphology
No full textThe detrimental effects generated by the gas turbine fouling phenomenon are well known. Due to soil and soot particles ingestion, gas turbines experience performance drops related to greater fuel consumption and even lower efficiency. These effects are related to the modification of the shape and surface roughness of relevant surfaces (compressor and turbine blades and vanes, especially) due to the presence of a thin layer generated by micro/nanosized particle adhesion. Such contaminants are swallowed by the unit and, as a function of the operating conditions, adhere to the surface, causing a sort of dangerous coating to the surface. In this work, a microtomography analysis of the deposited layer is reported. The deposited layer has been generated using microsized soil and soot powders under specific impact conditions and substrate surface roughness similar to those in the cold section of a gas turbine compressor. The microtomography analysis has been carried out using the beamline at the ELETTRA Sincrotrone research center. Thanks to the resolution of the beamline, the detection of the three-dimensional internal structure of the soil and soot layers have revealed that within the layer, the structure is characterized by discontinuities. Soot and soil particles, even characterized by similar diameter distributions and test conditions, generate layer structures that differ by the magnitude, orientation, location of the internal discontinuities, and surface morphology (i.e., roughness). The comprehension of the packing process allows us to understand the adhesion process and define general guidelines to predict the fouling phenomenon
An Evolutionary Variant of Q-learning for Global Optimization
No full textThe design of complex aeronautical systems requires the solution of multidisciplinary design optimization (MDO) problems. Despite the considerable technological progress of the last decades, MDO is still computationally expensive and involves a large number of high-fidelity simulations to evaluate the objective functions. This paper describes a derivative-free optimization method, based on reinforcement learning, for global unconstrained optimization problems. Specifically, an evolutionary variant of the well-known Q-learning (QL) algorithm, namely the Evolutionary Q-learning (EVQL), is developed to reduce the computational cost needed to find the optimal solution. Both single- and multi-agent formulations’ performance are assessed on six analytical benchmark problems, showing how EVQL outperforms the QL in terms of learning process acceleration and accuracy. Furthermore, EVQL is also compared with a deterministic particle swarm optimization, providing comparable results. Finally, the EVQL algorithm is used for the solution of an aeroacoustic problem, pertaining to the identification of optimal engine installation to maximize noise shielding. Specifically, the multi-agent EVQL is used to find the minimum of the insertion loss (IL), conditional to the noise source location and the Mach number. The IL is given by a surrogate model, based on stochastic radial basis functions, and trained by a boundary element method solver. The EVQL has a double use for the present application: a) it is used to find the minimum of the objective function, b) it defines where to add new training points based on the surrogate uncertainty, which is used to define algorithm trust regions. to find the optimal solution of the surrogate function and to identify new samples to update the metamodel
Erosive wear behavior of a high-chromium cast iron: effect of different destabilization heat treatments
No full textHigh-chromium cast irons are typically used in high demanding applications, where low production costs and wear performance are key factors. The excellent resistance of these alloys to both abrasion and erosion results from the overall microstructural features, i.e. type, morphology and distribution of hard primary and secondary carbides, along with the matrix constituents. More specifically, it has been suggested that erosive wear resistance is strongly affected by the behavior of the matrix. Hence, according to the specific chemical composition, the microstructure can be tuned, e.g. by increasing its hardness and toughness, to enhance the lifetime of such wear- resistant materials. Heat treatments performed to destabilize the austenite promote its transformation into martensite, the coalescence and thickening of secondary carbides thus increasing the overall hardness of the material.
The present study investigates the effects of different destabilization heat treatments performed on a hypereutectic white cast iron, with 21 % Cr and 4 % Nb, applied as an hardface coating to a low carbon steel substrate to improve its erosive wear resistance. The hardfacing plate was made by the open-arc welding of a flux- cored wire: high-chromium cast iron electrodes were deposited onto the substrate. The as-received and the heat- treated material was analyzed through optical and scanning electron microscopy, X-Ray diffraction and hardness tests to determine the relationship between microstructural variations and heat-treatment parameters. The erosive resistance was evaluated per the ASTM G76 standard in a purpose-built air blast test rig: experiments were performed with clinker powder (with a d90 of 9.73 μm) as erodent particles at an impingement angle of 90°. The tribological performance was assessed through weight loss measurements and analyses of the worn surfaces. The results suggest that erosion is dependent on carbide volume fraction and hardness along with the matrix microstructure: the hardest martensitic matrix gave the greatest erosion resistance
Successful treatment of pure red cell aplasia in systemic lupus erythematosus with cyclosporin A : a case report
No full textWe report a patient with longstanding systemic lupus erythematosus (SLE) who developed pure red cell aplasia (PRCA). This condition is rare in connective tissue diseases and is reported in 32 previous cases of SLE in literature. Our patient recovered, apparently in response to treatment with high dosage of corticosteroids, but relapse occurred when the prednisone dosage was tapered down to 10 mg/day. The patient was successfully treated with cyclosporin A with no recurrence of the disease in the last 2 years
Analysis of soil and soot deposits by X-ray computed microtomography
No full textEngineering systems continuously interact with nano-sized particles coming from natural or artificial sources. Considering nano-sized contaminants the detrimental effects are known as soiling and fouling phenomena. The objective of the present work is to gather morphological and three-dimensional quantitative information of discontinuities such as voids and pores within the nano-sized particle layer and in correspondence to the substrate/layer interface using microtomography. Deposits are obtained through impact tests using fine powder (soil and soot), and there are realized on a low-density material substrate characterized by different surface roughness values. The packing process and the discontinuities at the substrate-to-layer interfaces explain macroscopic effects as detachment and spallation but at the same time, give the possibility to understand more in detail the process related to the deposition mechanisms involved in this type of test defining general guidelines to predict the fouling phenomenon and to improve the capability of the removal process
The Italian version of the Fibrofatigue Scale, a reliable tool for the evaluation of fibromyalgia symptoms
No full textObjective: To validate a translated Italian version of the Fibrofatigue Scale (FFS). Methods: The Italian version of FFS was administered to 60 patients affected by fibromyalgia (FM) (57 patients were interviewed again 10 days later) together with the Italian version of the Fibromyalgia Impact Questionnaire (FIQ), the Stanford Health Assessment Questionnaire (HAQ) and the Medical Outcome Survey Short Form-36 (SF-36). All patients were asked about the severity of pain today (10-cm visual analogue scale) and the duration of symptoms. Test-retest reliability was assessed using Spearman correlations. Internal consistency was evaluated with Cronbach's alpha of reliability. Construct validity of the FFS was evaluated by correlations among the FFS, the FIQ and the subscales of the SF-36. Results: Mean duration of symptoms was 7.6 years, and mean age of participants was 56.3 years. Test-retest reliability was between 0.70 and 0.95 for the single items as well as for the total FFS and other components. Internal consistency was 0.90 for the overall FFS. Significant correlations were obtained between the FFS items and the SF-36. Conclusions: The Italian FFS is a reliable and valid instrument for detecting and measuring functional disability and symptoms severity in Italian patients with FM
Reward (BIS/BAS) mechanisms and fatigue in patients on chronic hemodialysis
No full textRecently, it has been demonstrated that chronic inflammation could have a role on fatigue onset in chronic hemodialysis (HD). Research on neuro-immune interactions highlighted that an alteration of basal ganglia functioning, secondary to chronic inflammation, may translate in a reduced motivation and altered reward processes in chronic diseases. This study investigated a possible correlation between fatigue severity and reward mechanisms, that regulate motivational dispositions, in HD patients. Evaluation scales were administered to ninety-four patients on HD (54 Male, 40 Female; Mdage = 67±26.5; Dialytic Mdage in years = 4±6.3. Fatigue was assessed by using Fatigue Severity Scale (FSS). Behavioural Inhibition System (BIS) and Behavioural Activation System (BAS) Scale was administered to investigate approach/avoidance behaviours. Anxiety and depression were measured by State-Trait Anxiety Inventory (STAI-Y) and Beck Depression Inventory (BDI-II). Results show that the distribution of HD patients for FSS score did not show a normal pattern. FSS score was significantly higher in patients with high BIS Z-score than in patients with low and medium BIS Z-score. BDI score and STAI-Y scores were similar among BIS Z-score groups of patients. Findings suggest that in patients on chronic hemodialysis there is a correlation between fatigue severity symptoms and motivational disposition mechanisms that predispose to action inhibition
