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Increasing Ejector Efficiency via Diffuser Shape Optimization
Kubíčková, Lucie; Isoz, Martin; Haidl, Jan
2021 - English
An ejector is a technologically simple and yet wide-application fluid machine. While it has favorable characteristics for a signifficant number of technological processes, its main downside is probably its high operational energy demands. The present paper is an initial result of an ongoing research aimed at improving energy e ciency of the ejector via optimization of its geometry. In the paper, we focus mostly on presenting a general multi-objective optimization framework usable for an ejector shape optimization. The approach applicability is illustrated on a simpli ed problem comprising only a single phase flow in an ejector mixing tube and diffuser. Nevertheless, the achieved simulation and optimization results are validated against experimental data. The proposed optimization method itself is based on multi-objective evolutionary algorithms (MOEAs) combined with computational fluid dynamics (CFD) for evaluation of the vector-valued objective function.
Keywords:
CFD; MOEA; ejector; OpenFOAM
Available at various institutes of the ASCR
Increasing Ejector Efficiency via Diffuser Shape Optimization
An ejector is a technologically simple and yet wide-application fluid machine. While it has favorable characteristics for a signifficant number of technological processes, its main downside is ...
Accuracy of the analytical methods developed for blade tip-timing analysis
Maturkanič, Dušan; Procházka, Pavel; Kozánek, Jan
2021 - English
Within the research of methods for precision solution of rotor blade vibration based on the philosophy of Blade Tip-Timing at the Institute of Thermomechanics AS CR, v.v.i., the effort was concentrated on the decomposition of measured data. This paper describes the accuracy of analytical methods taking into consideration the errors of the measured sensors or the influence of the measurement conditions on the results.
Keywords:
harmonic function; analytical method; blade vibration; accuracy; error; distortion; frequency
Available at various institutes of the ASCR
Accuracy of the analytical methods developed for blade tip-timing analysis
Within the research of methods for precision solution of rotor blade vibration based on the philosophy of Blade Tip-Timing at the Institute of Thermomechanics AS CR, v.v.i., the effort was ...
Dynamics of a magnetically excited blade: theoretical and experimental analysis
Tchawou Tchuisseu, Eder Batista; Procházka, Pavel; Mekhalfia, Mohammed Lamine; Hodboď, Robert; Maturkanič, Dušan
2021 - English
This work dealt with the theoretical and experimental analysis of a static blade subjected to a magnetic excitation. The theoretical analysis combines the modeling and design of the blade via ANSYS in whih the modal analysis is done. Both methods showed qualitative agreement of the results.
Keywords:
turbine blade; magnetic excitation; turbo-machinery; finite element method
Available at various institutes of the ASCR
Dynamics of a magnetically excited blade: theoretical and experimental analysis
This work dealt with the theoretical and experimental analysis of a static blade subjected to a magnetic excitation. The theoretical analysis combines the modeling and design of the blade via ANSYS in ...
Deep learning methods for acoustic emission evaluation
Kovanda, M.; Chlada, Milan
2021 - English
The goal of this paper is to show the possibilities of state-of-the-art deep learning methods for ultrasound signals evaluation. Several neural network architectures are applied to\nacoustic emission signals measured during the tensile tests of metallic specimen to determine the beginning of plasticity in the material. Plastic deformation is accompanied by microscopic\nevents such as a slip of atomic plane dislocations which is hardly detectable by other methods. The potential of machine learning is demonstrated on two tensile tests where the material is\nstrained until it collapses. The examined networks proved well to reliably predict the risk of collapse together with changes in the ultrasound emission signals.
Keywords:
acoustic emission; deep learning; machine learning; plastic deformation; time series classification
Available at various institutes of the ASCR
Deep learning methods for acoustic emission evaluation
The goal of this paper is to show the possibilities of state-of-the-art deep learning methods for ultrasound signals evaluation. Several neural network architectures are applied to\nacoustic emission ...
Nucleation criteria detection as a mean to investigate metastable state
Celný, David; Span, R.; Vrabec, J.
2021 - English
Focus is given to the core problematic, reaching the nucleation region and sample the relevant data for selected pure substance. This termodynamic condition required for nucleation are found in so called metastable region. Metastable region is found between binodal and spinodal line separating it from the stable and unstable system condition respectively.\nObtaining the data in this area proves to be an experimental challenge, therefore the data has to be gathered using other means. Proposed setup relies two part approach combining equation of state (EoS) and molecular simulation. The computational core is done with molecular dynamics tool combined with on the fly performing decision cluster criterion utilized is already available in previously published work. These cluster criteria ensure that the system is only calculated within targeted conditions and the sampled micro-states remain valid observations. To capture whole metastable region two criteria are present for both cluster and void case as illustrated below. Remaining part utilize the equation of state for the initial system condition sampling of the metastable region by calculating the stability line and predicting the instability line for the LJ fluid as show in Linhart et.al. . These thermodynamic condition probes are evaluated afterwards with the established simulation method. Intermediate result from simulations are collected in form of both Helmholtz energy temperature and density derivatives descriptors as well as time averages of system properties for fluids like LJ, Oxygen and Nitrogen.
Keywords:
metastable state; equation of state; molecular dynamics; cluster criterion
Available at various institutes of the ASCR
Nucleation criteria detection as a mean to investigate metastable state
Focus is given to the core problematic, reaching the nucleation region and sample the relevant data for selected pure substance. This termodynamic condition required for nucleation are found in so ...
Modal analysis of a container with measuring equipment for space mission
Zolotarev, Igor; Bula, Vítězslav
2021 - English
This paper continues investigations of some measuring equipment for space mission. The frequency-modal properties a container with several slots and measured desks are studied. The natural frequencies and corresponded modes obtained using measuring methods are presented for several combinations of the container components.
Keywords:
modal analysis; natural frequencies; modes of vibration
Available at various institutes of the ASCR
Modal analysis of a container with measuring equipment for space mission
This paper continues investigations of some measuring equipment for space mission. The frequency-modal properties a container with several slots and measured desks are studied. The natural frequencies ...
Numerical and Experimental Investigation of the Flow Field in Five Blade Linear Cascade in Subsonic Flow
Šnábl, Pavel; Chindada, Sony; Bublík, O.; Procházka, Pavel P.; Prasad, Chandra Shekhar
2021 - English
In large steam turbines, last stage blades are very long and must be designed very thin and with no shroud to minimize the centrifugal force which leads to low eigenfrequencies and low structural damping. In this case, aero-elastic damping plays important role on last stage bladed disc’s dynamics. Three major aero-elastic issues found in turbomachinery are forced response, non-synchronous vibrations, and flutter. Flutter is an unstable, self-excited vibration resulting from coupling between the structural vibrations and unsteady aerodynamic forces. It is clear that this unstable behaviour must be avoided and predictions of flutter behaviour need to be performed during design stage of the turbine.\n
Keywords:
subsonic flow; flow field; blade linear cascade; ansys fluent; FlowPro
Available at various institutes of the ASCR
Numerical and Experimental Investigation of the Flow Field in Five Blade Linear Cascade in Subsonic Flow
In large steam turbines, last stage blades are very long and must be designed very thin and with no shroud to minimize the centrifugal force which leads to low eigenfrequencies and low structural ...
Use of advanced kinematic hardening rules for prediction of multiaxial ratcheting
Klepač, Vilém; Parma, Slavomír; Feigenbaum, H. P.; Marek, René; Plešek, Jiří; Svárovský, Jiří
2021 - English
The cumulation of plastic deformation due to cyclic loading, so called ratcheting, is considered as critical process for purpose of simulation. For this reason, many of advanced models of plasticity have been developed to capture the evolution of material during the load reversals. Historically, these models are based on concept of multicomponent back-stress, that provides the prediction of phenomenon of kinematic hardening (KH) [Chaboche 1979]. The key for accurate prediction is, besides well designed model, identification of model parameters. To present results on prediction of multiaxial ratcheting by FEA, the multicomponent Armstrong-Frederick with a threshold with r Modification was implemented via the UMAT interface of Abaqus Standart. Model parameters were identified on experimental data presented in [Hassan, Kyriakides 1992] and [Hassan et. al. 1992]. To prove the performance of the model subroutine, other numerical examples will be presented and their computational costs will be discussed.
Keywords:
plasticity; ratcheting; low-cycle fatigue
Available at various institutes of the ASCR
Use of advanced kinematic hardening rules for prediction of multiaxial ratcheting
The cumulation of plastic deformation due to cyclic loading, so called ratcheting, is considered as critical process for purpose of simulation. For this reason, many of advanced models of plasticity ...
Assessment of post-processing capabilities in selected software for topology optimization
Ježek, Ondřej; Kopačka, Ján; Gabriel, Dušan
2021 - English
Topology optimization (TO) has come to the fore in recent years, especially with the development of 3D printing. Finite element systems often include TO functionality based on either\ndensity-based or level set methods. In the case of the first-mentioned method, the results of TO are further processed into geometry suitable for additive manufacturing. However, current\nprograms only include basic post-processing capabilities with minimal customization options. This paper will first briefly summarize the theoretical background of TO and post-processing\nmethods. Next, selected commercial TO programs will be compared from the perspective of shape post-processing. The final part will be devoted to applying the level set method for shape\npost-processing of a topologically optimized industrial robot gripper.
Keywords:
post-processing; topology optimization; level set method
Available at various institutes of the ASCR
Assessment of post-processing capabilities in selected software for topology optimization
Topology optimization (TO) has come to the fore in recent years, especially with the development of 3D printing. Finite element systems often include TO functionality based on either\ndensity-based or ...
Acoustic resonances can support self-oscillations of a dynamic system.
Horáček, Jaromír; Radolf, Vojtěch; Košina, Jan; Laukkanen, A. M.
2021 - English
Flutter instability of human vocal folds is a necessary condition for speaking, because airflow induced vibrations of the vocal folds create the voice source. The present study shows that the vocal fold self-oscillations can be strongly influenced by interaction with acoustic resonances of the human vocal tract.
Keywords:
biomechanics of voice; modelling of human voice
Available at various institutes of the ASCR
Acoustic resonances can support self-oscillations of a dynamic system.
Flutter instability of human vocal folds is a necessary condition for speaking, because airflow induced vibrations of the vocal folds create the voice source. The present study shows that the vocal ...
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