Andrzej DYKA and Henryk UGOWSKI
The aim of this paper is to show that in the case of even input signals with sidelobes of equal amplitude and arbitrary sign the D‐algorithm introduced in the first part of this…
Abstract
The aim of this paper is to show that in the case of even input signals with sidelobes of equal amplitude and arbitrary sign the D‐algorithm introduced in the first part of this paper subtitled “Theory”, may give a solution which is equal to that with the Chebyshev minimax norm for the approximation error. It is proved that, with some restrictions, in the case of two, four, and six sidelobe even input signals, the algorithm discussed gives exactly the Chebyshev minimax solution—CMS. Also, properties of the algorithm in the case of more general input signal are discussed.
Andrzej DYKA and Henryk UGOWSKI
A new computational noniterative algorithm which gives the solution to a linear deconvolution‐inverse filtering problem is proposed and its properties are studied. It is proved…
Abstract
A new computational noniterative algorithm which gives the solution to a linear deconvolution‐inverse filtering problem is proposed and its properties are studied. It is proved, in some specific cases of input signal, that the algorithm discussed gives the solution, which is equal to that with the Chebyshev minimax norm for the approximation error. In a general case of input signal the solution obtained provides a good prompt for determining an “appropriate subsystem” of n + 1 linear equations of n unknowns, which directly gives the Chebyshev minimax norm based solution.
H. UGOWSKI and A. DYKA
A solution of a discrete minimax problem is derived, using the standard methods of approximation theory. It represents a problem of the deconvolution‐inverse filtering of a…
Abstract
A solution of a discrete minimax problem is derived, using the standard methods of approximation theory. It represents a problem of the deconvolution‐inverse filtering of a three‐element discrete even signal, subject to a constraint on the output signal sidelobe level. Consequently, properties of this solution, in particular the asymptotic behaviour of the parameter, which represents the degradation of signal‐to‐noise ratio due to the filtering are examined.
This paper presents a closed form analytic solution for the impulse response of an optimum FIR deconvolution filter intended for a pair of discrete pulses of arbitrary amplitude…
Abstract
This paper presents a closed form analytic solution for the impulse response of an optimum FIR deconvolution filter intended for a pair of discrete pulses of arbitrary amplitude and sign, subject to the minimisation of Chebyshev maximum norm for the approximation error. The tradeoff between the approximation error and the degradation of signal‐to‐noise ratio, is examined.
Esmail Lakzian, Mostafa Ramezani, Sima Shabani, Fahime Salmani, Miroslaw Majkut and Heuy Dong Kim
The purpose of this study is to model steam condensing flows through steam turbine blades and find the most suitable condensation model to predict the condensation phenomenon.
Abstract
Purpose
The purpose of this study is to model steam condensing flows through steam turbine blades and find the most suitable condensation model to predict the condensation phenomenon.
Design/methodology/approach
To find the most suitable condensation model, five nucleation equations and four droplet growth equations are combined, and 20 cases are considered for modelling the wet steam flow through steam turbine blades. Finally, by the comparison between the numerical results and experiments, the most suitable case is proposed. To find out whether the proposed case is also valid for other boundary conditions and geometries, it is used to simulate wet steam flows in de Laval nozzles.
Findings
The results indicate that among all the cases, combining the Hale nucleation equation with the Gyarmathy droplet growth equation results in the smallest error in the simulation of wet steam flows through steam turbine blades. Compared with experimental data, the proposed model’s relative error for the static pressure distribution on the blade suction and pressure sides is 2.7% and 2.3%, respectively, and for the liquid droplet radius distribution it totals to 1%. This case is also reliable for simulating condensing steam flows in de Laval nozzles.
Originality/value
The selection of an appropriate condensation model plays a vital role in the simulation of wet steam flows. Considering that the results of numerical studies on condensation models in recent years have not been completely consistent with the experiments and that there are still uncertainties in this field, further studies aiming to improve condensation models are of particular importance. As condensation models play an important role in simulating the condensation phenomenon, this research can help other researchers to better understand the purpose and importance of choosing a suitable condensation model in improving the results. This study is a significant step to improve the existing condensation models and it can help other researchers to gain a revealing insight into choosing an appropriate condensation model for their simulations.
Details
Keywords
Novel necessary and sufficient existence conditions for convolution inverses of real finite sequences are derived. These conditions are obtained with the aid of well known…
Abstract
Novel necessary and sufficient existence conditions for convolution inverses of real finite sequences are derived. These conditions are obtained with the aid of well known conditions expressed in terms of the Fourier and z‐transforms. The conditions given in the paper imply suitable algorithms, which are convenient for checking the existence of convolution inverses of any real finite sequences.
Henryk UGOWSKI and Andrzej DYKA
The aim of this paper is to prove the existence and unicity of the convolution inverse for a certain class of real functions of the discrete argument. The properties of these…
Abstract
The aim of this paper is to prove the existence and unicity of the convolution inverse for a certain class of real functions of the discrete argument. The properties of these inverses, in particular the errors that arise from the truncation of the infinite sequences that represent them, are examined. In the second part of this paper subtitled “Application in solving convolution equations” the possibility of using convolution inverses for determining the solution to the Fredholm equations of the first kind is discussed.
Henryk UGOWSKI and Andrzej DYKA
In the first part of this paper subtitled ‘Theory and estimation of the truncation error’ we have examined the existence and unicity of the convolution inverse. In this part of…
Abstract
In the first part of this paper subtitled ‘Theory and estimation of the truncation error’ we have examined the existence and unicity of the convolution inverse. In this part of the paper we discuss the application of convolution inverses for determining the solution to the Fredholm equation of the first kind. Particular attention is paid to the errors that arise from both the truncation of the infinite sequence that represents the inverse and the inaccuracy in input data.
Filip Wasilczuk, Pawel Flaszynski, Piotr Kaczynski, Ryszard Szwaba, Piotr Doerffer and Krzysztof Marugi
The purpose of the study is to measure the mass flow in the flow through the labyrinth seal of the gas turbine and compare it to the results of numerical simulation. Moreover the…
Abstract
Purpose
The purpose of the study is to measure the mass flow in the flow through the labyrinth seal of the gas turbine and compare it to the results of numerical simulation. Moreover the capability of two turbulence models to reflect the phenomenon will be assessed. The studied case will later be used as a reference case for the new, original design of flow control method to limit the leakage flow through the labyrinth seal.
Design/methodology/approach
Experimental measurements were conducted, measuring the mass flow and the pressure in the model of the labyrinth seal. It was compared to the results of numerical simulation performed in ANSYS/Fluent commercial code for the same geometry.
Findings
The precise machining of parts was identified as crucial for obtaining correct results in the experiment. The model characteristics were documented, allowing for its future use as the reference case for testing the new labyrinth seal geometry. Experimentally validated numerical model of the flow in the labyrinth seal was developed.
Research limitations/implications
The research studies the basic case, future research on the case with a new labyrinth seal geometry is planned. Research is conducted on simplified case without rotation and the impact of the turbine main channel.
Practical implications
Importance of machining accuracy up to 0.01 mm was found to be important for measuring leakage in small gaps and decision making on the optimal configuration selection.
Originality/value
The research is an important step in the development of original modification of the labyrinth seal, resulting in leakage reduction, by serving as a reference case.
Details
Keywords
Krzysztof Piotrowski, Peter Langendörfer, Oliver Maye and Zoya Dyka
To enhance security and privacy of e‐cash systems that apply revocable anonymity by presenting a statistical attack that reveals the hidden ID and suitable protection means…
Abstract
Purpose
To enhance security and privacy of e‐cash systems that apply revocable anonymity by presenting a statistical attack that reveals the hidden ID and suitable protection means against this kind of attack.
Design/methodology/approach
The feasibility of a statistical attack that reveals the ID of user of e‐cash schemes with revocable anonymity is shown. To avoid such attacks the application of modulo operations while constructing e‐cash coins is proposed. Measurement results are used to back up the suitability of this approach.
Findings
Revocable anonymity systems can successfully be attacked. Applying modulo operations can prevent such attacks.
Practical implications
The recommendations given in this paper should be applied whenever an e‐cash scheme or similar system with revocable anonymity is designed. Otherwise the promised feature may be compromised very easily.
Originality/value
The paper identifies a formerly unknown attack against systems with revocable identities, and presents a mathematical solution to protect such systems against the attack presented.