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Increasing Ejector Efficiency via Diffuser Shape Optimization
Kubíčková, Lucie; Isoz, Martin; Haidl, Jan
2021 - anglický
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.
Klíčová slova:
CFD; MOEA; ejector; OpenFOAM
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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.
Klíčová slova:
harmonic function; analytical method; blade vibration; accuracy; error; distortion; frequency
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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.
Klíčová slova:
turbine blade; magnetic excitation; turbo-machinery; finite element method
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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.
Klíčová slova:
acoustic emission; deep learning; machine learning; plastic deformation; time series classification
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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.
Klíčová slova:
metastable state; equation of state; molecular dynamics; cluster criterion
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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.
Klíčová slova:
modal analysis; natural frequencies; modes of vibration
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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
Klíčová slova:
subsonic flow; flow field; blade linear cascade; ansys fluent; FlowPro
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Boundary Layer on the Flat Plate with Roughness Strip
Skála, Vladislav
2021 - anglický
Effect of the roughness strip on the boundary layer development on a flat plate was studied experimentally. A special model of a flat plate was designed. Experiment was made in non perturbed flow. Smooth flat plate (with super elliptical leading edge) was equipped with short roughness strip (close to the leading edge). Profiles of total pressure along the boundary layer were measured using flattened Pitot tube. First basic results of experiments are presented.
Klíčová slova:
boundary layer; transition to turbulence; roughness strip
Dokument je dostupný na externích webových stránkách.
Boundary Layer on the Flat Plate with Roughness Strip
Effect of the roughness strip on the boundary layer development on a flat plate was studied experimentally. A special model of a flat plate was designed. Experiment was made in non perturbed flow. ...
CFD Analysis of Flow in a Blade Cascade Deformed Due to Forced Torsional Vibration
Vomáčko, V.; Šidlof, P.; Šimurda, David; Hála, Jindřich
2021 - anglický
The paper presents a 3D numerical simulation of flow in a blade cascade, whose geometry models the test section of a new experimental facility for blade flutter research. In the experimental setup, the middle blade of the cascade undergoes high-frequency forced sinusoidal pitching oscillation. Due to inertial forces, the slender blade deforms elastically to certain degree. The goal of this study is to assess the influence of the elastic deformation on the flow field. To compute the deformed geometry, a transient structural analysis was performed. In the second part, the CFD model of flow past a 3D blade cascade with deformed and undeformed blade is presented and these two configurations are compared. For the deformed configuration the incidence angle increases along the blade span from -1.8° to -2.7°. However, the Mach number distribution along the span varies less than expected. blade cascade, flutter, turbomachinery, CFD
Klíčová slova:
blade cascade; flutter; turbomachinery; CFD
Dokument je dostupný na externích webových stránkách.
CFD Analysis of Flow in a Blade Cascade Deformed Due to Forced Torsional Vibration
The paper presents a 3D numerical simulation of flow in a blade cascade, whose geometry models the test section of a new experimental facility for blade flutter research. In the experimental setup, ...
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 - anglický
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.
Klíčová slova:
plasticity; ratcheting; low-cycle fatigue
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
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