1,721,173 research outputs found
Analisi sperimentale e teorica dell'effetto degli smorzatori sottopala sullo smorzamento delle vibrazioni nelle palette di turbina.
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Measurement of contact parameters on under-platform dampers coupled with blade dynamics
No full textIn the field of turbomachinery, one of the prime design aspects is to avoid high cycle fatigue failure commonly caused by fluctuating forces on the blades. These fluctuating forces render a high amplitude vibration of the blades that can be mitigated by introducing devices such as under-platform dampers and shrouds in the blade assembly. These devices are quite efficient in limiting the vibration amplitude of the blade even at the high temperatures that are typical of turbines. However, nonlinear forces are developed at the contact and these nonlinear forces make numerical simulations challenging for the designers. Therefore, along with numerical computations, experimental evidences are necessary to understand the actual physics of the damper-blade interactions. This paper represents an experimental study of the effect of these nonlinear contact forces on the vibration amplitude of the blade The present investigation explores, for the first time, the contact forces and relative displacement between the damper-blade contact interface measured directly using a recently developed experimental setup. These measured forces and relative displacement are further post processed to compute the equivalent contact characteristics, namely equivalent contact stiffness and damping. The contact characteristics are then associated with the classically measured performance of the dampers defined by the variation in frequency response of the blade. The experimental work presented here provides one of the first investigations to relate the macro/global behavior of the blade-damper with the micro/local behavior of their contact
A novel test rig to investigate under-platform damper dynamics
Full text linkIn the field of turbomachinery, vibration amplitude is often reduced by dissipating the kinetic energy of the blades with devices that utilize dry friction. Under-platform dampers, for example, are often placed in the underside of two consecutive turbine blades. Dampers are kept in contact with the under-platform of the respective blades by means of the cen-trifugal force. If the damper is well designed, vibration of blades instigate a relative motion between the under-platform and the damper. A friction force, that is a non-conservative force, arises in the contact and partly dissipates the vibration energy. Several contact mod-els are available in the literature to simulate the contact between the damper and the under-platform. However, the actual dynamics of the blade-damper interaction have not fully understood yet. Several test rigs have been previously developed to experimentally investigate the performance of under-platform dampers. The majority of these experimen-tal setups aim to evaluate the overall damper efficiency in terms of reduction in response amplitude of the blade for a given exciting force that simulates the aerodynamic loads. Unfortunately, the experimental data acquired on the blade dynamics do not provide enough information to understand the damper dynamics. Therefore, the uncertainty on the damper behavior remains a big issue.
In this work, a novel experimental test rig has been developed to extensively investigate the damper dynamic behavior. A single replaceable blade is clamped in the rig with a speci-fic clamping device. With this device the blade root is pressed against a groove machined in the test rig. The pushing force is controllable and measurable, to better simulate the actual centrifugal load acting on the blade. Two dampers, one on each side of the blade, are in con-tact with the blade under-platforms and with platforms on force measuring supports. These supports have been specifically designed to measure the contact forces on the dam-per. The contact forces on the blade are computed by post processing the measured forces and assuming the static equilibrium of the damper. The damper kinematics is rebuilt by using the relative displacement, measured with a differential laser, between the damper and the blade under-platform.
This article describes the main concepts behind this new approach and explains the design and working of this novel test rig. Moreover, the influence of the damper contact forces on the dynamic behavior of the blade is discussed in the result section
Friction damping and forced-response of vibrating structures: an insight into model validation
Full text linkDry friction is widely incorporated in turbomachinery, in the form of under-platform dampers, to limit vibrations at resonance and reduce risks of high-cycle fatigue failures. Most of the test rigs that were used to investigate the behavior of under-platform dampers aim at evaluating the damper performance in terms of reduction of forced-response amplitude in blades. This approach could be insufficient to understand local nonlinearities in the contact and the influence of dampers on blade dynamics. A recently developed test rig provides the authors with an unprecedented set of information. It is capable to measure contact forces and relative displacements between dampers and blade in addition to the overall blade dynamic response. This controlled environment, together with an effective model of the blade/dampers system, is used to provide an insight into the subject of model validation. The presented experimental and numerical study of the damper is used to highlight the relevance of an accurate representation of the constraints induced by friction contacts and to discuss the adequacy of state-of-the-art contact models
Synergizing Financial Inclusion and Green Finance: Advancing Sustainable Development Goals 2030 and 2050 in Alignment With COP 29 Commitments
No full textFinancial inclusion (FI) and green finance (GF) are critical enablers for achieving the United Nations’ Sustainable Development Goals (UNSDGs) and fulfilling objectives outlined in COP 29 related to climate action. FI and GF drive capital mobilization, green investments, and emissions reduction. A comprehensive literature review on FI and GF was conducted on the Web of Science and Scopus databases using VoSviewer and the Bibliometrix package in R. Analysis revealed that GF is mainly connected with digital finance, environmental economics, economic development, human capital, and blockchain. FI is intricately linked to multiple dimensions of sustainable development, including environmental quality, green growth, climate change, urbanization, and trade openness. Moreover, we identified seven clusters underscoring the strong interrelationships between FI, GF, and UN SDGs. Future research can explore key enablers of FI, such as digital technologies, regulatory frameworks, financial literacy, and public-private partnerships, and examine the interplay between FI and monetary policy
COVID-19: Automatic Detection of the Novel Coronavirus Disease from CT Images Using an Optimized Convolutional Neural Network
No full textIt is widely known that a quick disclosure of the COVID-19 can help to reduce its spread dramatically. Transcriptase polymerase chain reaction could be a more
useful, rapid, and trustworthy technique for the evaluation and classification of the COVID-19 disease. Currently, a computerized method for classifying computed tomography (CT) images of chests can be crucial for speeding up the detection while the COVID-19 epidemic is rapidly spreading. In this article, the authors have proposed an optimized convolutional neural network model (ADECOCNN) to divide infected and not infected patients. Furthermore, the ADECO-CNN approach is compared with pretrained convolutional neural network (CNN)-based VGG19, GoogleNet, and ResNet models. Extensive analysis proved that the ADECO-CNN-optimized CNN model can classify CT images with 99.99% accuracy, 99.96% sensitivity, 99.92%
precision, and 99.97% specificity
Tribological Characterization of Electrical Discharge Machined Surfaces for AISI 304L
Full text linkSurface treatments are normally carried out after machining. Surface treatment is a costly and time-consuming process. Hence, it makes sense to reduce the requirement of surface treatment as much as possible. Electrical Discharge Machining (EDM) is a frequently used machining process. EDM produces a recast layer on the surface of machined components. The tribological performance of this recast layer is not very well understood. The properties of the recast layer formed as a result of EDM depend upon the discharge current, electrodes and dielectrics. This work aims to study the effects of each on the tribological performance – in terms of the wear depth, friction coefficient, friction force and contact surface temperature of recast layers. Subsequent improvement in the quality of surfaces will significantly reduce the cost and time required to treat surfaces after machining. Hence, various combinations of discharge current, dielectrics and electrodes have been used to characterize and deduce their effects. The tribo-tests are performed in the boundary lubrication regime under pin-on-disc configuration to analyze sliding friction, contact surface temperature and the wear of the recast layers formed on AISI 304L. The surface morphology of the test pins has been performed by Scanning Electron Microscopy (SEM) before and after the tests. The results show that indeed it is possible to control the tribological performance of the recast layers by varying EDM parameters. This approach promises to be a useful methodology to improve the tribological performance of the layers formed after EDM and reduce the time and costs required for surface treatments post machining
An Experimental Investigation of the Dynamics of a Blade with Two Under-Platform Dampers
No full textSeveral experimental apparatus have been designed in the past to evaluate the effectiveness of under-platform dampers. Most of these experimental setups allow to measure the overall damper efficiency in terms of reduction of vibration amplitude in turbine blades. The experimental data collected with these test rigs do not increase the knowledge about the damper dynamics and therefore the uncertainty on the damper behavior remains a big issue. In this paper a different approach to evaluate the damper-blade interaction has been put forward. A test rig has been purposely designed to accommodate a single blade and two under-platform dampers. One side of each damper is in contact with a ground support specifically designed to measure two independent forces on the damper. In this way both the normal and the tangential force components in the damper-blade contact can be inferred. Damper kinematics is rebuilt by using the relative displacement measured between damper and blade. This paper describes the concept behind the new approach, shows the details of the new test rig and discuss the blade frequency response from a new point of view
Student academic success prediction in multimedia-supported virtual learning system using ensemble learning approach
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