Applied sciences

Bulletin of the Polish Academy of Sciences: Technical Sciences

Content

Bulletin of the Polish Academy of Sciences: Technical Sciences | 2021 | 69 | No. 1 |

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Abstract

In this paper, a novel Power-Frequency Droop Control (PFDC) is introduced to perfectly bring back the system frequency and share the reactive power in isolated microgrid with virtual power plant (VPP). The frequency-based power delivery must be essentially implemented in VPP which can operate as a conventional synchronous generator. It has been attained by enhancing the power processing unit of each VPP to operate as an active generator. The inverter coupling impedance which has been assigned by the virtual impedance technique has reduced the affected power coupling resulting from line resistance. The reference has been subsequently adjusted to compensate the frequency deviation caused by load variation and retrieve the VPP frequency to its nominal value. In addition, the line voltage drop has compensated the voltage drop and load sharing error to obliterate the reactive power sharing imprecision resulting from the voltage deviation. The voltage feedback confirms the correct voltage after compensating the voltage drop. As an illustration, conventional PFDC after a load change cannot restore the system frequency which is deviated from 50 Hz and rested in 49.9 Hz while, proposed PFDC strategy fades away the frequency deviation via compensating the variation of the frequency reference. Likewise, the frequency restoration factor ( γ) has an effective role in retrieving the system frequency, i.e., the restoration rate of the system frequency is in proportion with γ. As a whole, the simulation results have pointed to the high performance of proposed strategy in an isolated microgrid.
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Authors and Affiliations

Amir Khanjanzadeh
Soodabeh Soleymani
Babak Mozafari
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Abstract

The paper presents an analytical solution of levitation problem for conductive, dielectric and magnetically anisotropic ball. The levitation exerts either an AC or impulse magnetic field. Both the Lorentz and material electromagnetic forces (of magnetic matter) could lift the ball in a gravitational field. The electromagnetic field distribution is derived by means of variables separation method. The total force is evaluated by Maxwell stress tensor (generalized), co-energy and Lorentz methods. Additionally, power losses are calculated by means of Joule density and the Poynting vector surface integrals. High frequency asymptotic formulas for the Lorentz force and power losses are presented. All analytical solutions derived could be useful for rapid analysis and design of levitations systems. Finally, some remarks about considered levitations are formulated.
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Authors and Affiliations

Dariusz Spałek
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Abstract

Load profiles of residential consumers are very diverse. This paper proposes the usage of a continuous wavelet transform and wavelet coherence to perform analysis of residential power consumer load profiles. The importance of load profiles in power engineering and common shapes of profiles along with the factors that cause them are described. The continuous wavelet transform and wavelet coherence has been presented. In contrast with other studies, this research has been conducted using detailed (not averaged) load profiles. Presented load profiles were measured separately on working day and weekend during winter in two urban households. Results of applying the continuous wavelet transform for load profiles analysis are presented as coloured scalograms. Moreover, the wavelet coherence was used to detect potential relationships between two consumers in power usage patterns. Results of coherence analysis are also presented in a colourful plots. The conducted studies show that the Morlet wavelet is slightly better suitable for load profiles analysis than the Meyer’s wavelet. Research of this type may be valuable for a power system operator and companies selling electricity in order to match their offer to customers better or for people managing electricity consumption in buildings.
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Authors and Affiliations

Piotr Kapler
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Abstract

This paper presents a concept of a shunt active power filter, which is able to provide more precise mapping of its input current drawn from a power line in a reference signal, as compared to a typical filter solution. It can be achieved by means of an interconnection of two separate power electronics converters making, as a whole, a controlled current source, which mainly determines the quality of the shunt active filter operation. One of these power devices, the “auxiliary converter”, corrects the total output current, being a sum of output currents of both converters, toward the reference signal. The rated output power of the auxiliary converter is much lower than the output power of the main one, while its frequency response is extended. Thanks to both these properties and the operation of the auxiliary converter in a continuous mode, pulse modulation components in the filter input current are minimized. Benefits of the filter are paid for by a relatively small increase in the complexity and cost of the system. The proposed solution can be especially attractive for devices with higher output power, where, due to dynamic power loss in power switches, a pulse modulation carrier frequency must be lowered, leading to the limitation of the “frequency response” of the converter. The concept of such a system was called the “hybrid converter topology”. In the first part of the paper, the rules of operation of the active filter based on this topology are presented. Also, the results of comparative studies of filter simulation models based on both typical, i.e. single converter, and hybrid converter topologies, are discussed.
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Authors and Affiliations

Michał Gwóźdź
Łukasz Ciepliński
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Abstract

The article presents an identification method of the model of the ball-and-race coal mill motor power signal with the use of machine learning techniques. The stages of preparing training data for model parameters identification purposes are described, as well as these aimed at verifying the quality of the evaluated model. In order to meet the tasks of machine learning, additive regression model was applied. Identification of the additive model parameters was performed on the basis of iterative backfitting algorithm combined with nonparametric estimation techniques. The proposed models have predictive nature and are aimed at simulation of the motor power signal of a coal mill during its regular operation, startup and shutdown. A comparative analysis has been performed of the models structured differently in terms of identification quality and sensitivity to the existence of an exemplary disturbance in the form of overhangs in the coal bunker. Tests carried out on the basis of real measuring data registered in the Polish power unit with a capacity of 200 MW confirm the effectiveness of the method.
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Authors and Affiliations

Zofia Magdalena Łabęda-Grudziak
Mariusz Lipiński
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Abstract

Speech emotion recognition (SER) is a complicated and challenging task in the human-computer interaction because it is difficult to find the best feature set to discriminate the emotional state entirely. We always used the FFT to handle the raw signal in the process of extracting the low-level description features, such as short-time energy, fundamental frequency, formant, MFCC (mel frequency cepstral coefficient) and so on. However, these features are built on the domain of frequency and ignore the information from temporal domain. In this paper, we propose a novel framework that utilizes multi-layers wavelet sequence set from wavelet packet reconstruction (WPR) and conventional feature set to constitute mixed feature set for achieving the emotional recognition with recurrent neural networks (RNN) based on the attention mechanism. In addition, the silent frames have a disadvantageous effect on SER, so we adopt voice activity detection of autocorrelation function to eliminate the emotional irrelevant frames. We show that the application of proposed algorithm significantly outperforms traditional features set in the prediction of spontaneous emotional states on the IEMOCAP corpus and EMODB database respectively, and we achieve better classification for both speaker-independent and speaker-dependent experiment. It is noteworthy that we acquire 62.52% and 77.57% accuracy results with speaker-independent (SI) performance, 66.90% and 82.26% accuracy results with speaker-dependent (SD) experiment in final.
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Authors and Affiliations

Hao Meng
Tianhao Yan
Hongwei Wei
Xun Ji
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Abstract

Sharing research data from public funding is an important topic, especially now, during times of global emergencies like the COVID-19 pandemic, when we need policies that enable rapid sharing of research data. Our aim is to discuss and review the revised Draft of the OECD Recommendation Concerning Access to Research Data from Public Funding. The Recommendation is based on ethical scientific practice, but in order to be able to apply it in real settings, we suggest several enhancements to make it more actionable. In particular, constant maintenance of provided software stipulated by the Recommendation is virtually impossible even for commercial software. Other major concerns are insufficient clarity regarding how to finance data repositories in joint private-public investments, inconsistencies between data security and user-friendliness of access, little focus on the reproducibility of submitted data, risks related to the mining of large data sets, and sensitive (particularly personal) data protection. In addition, we identify several risks and threats that need to be considered when designing and developing data platforms to implement the Recommendation (e.g., not only the descriptions of the data formats but also the data collection methods should be available). Furthermore, the non-even level of readiness of some countries for the practical implementation of the proposed Recommendation poses a risk of its delayed or incomplete implementation.
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Authors and Affiliations

Lech Madeyski
Tomasz Lewowski
Barbara Kitchenham
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Abstract

In this present study, the effect of the shot peening process on fatigue life, surface hardness and corrosion properties of a low carbon alloy steel is examined at room temperature. The research article addresses the effect of shot peening by varying the process parameters such as peening distance and pressure with amachrome as shots. The experiment is designed by means of full factorial design. The experimental result reveals that the pressure and distance are the most significant factors in the shot peening process. The results illustrate that the average pressure of 7 bar and distance of 100 mm improves fatigue life by 1.5% of unpeened material under 20 Hz frequency while corrosion resistance improves by 4% with unpeening of the low carbon alloy steel by using amachrome as a shot.
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Authors and Affiliations

C. Selva Senthil Prabhu
P. Ashoka Varthanan
T. Ram Kumar
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Abstract

In the present research, the wear behaviour of magnesium alloy (MA) AZ91D is studied and optimized. MA AZ91D is casted using a die-casting method. The tribology experiments are tested using pin-on-disc tribometer. The input parameters are sliding velocity (1‒3 m/s), load (1‒5 kg), and distance (0.5‒1.5 km). The worn surfaces are characterized by a scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). The response surface method (RSM) is used for modelling and optimising wear parameters. This quadratic equation and RSM-optimized parameters are used in genetic algorithm (GA). The GA is used to search for the optimum values which give the minimum wear rate and lower coefficient of friction. The developed equations are compared with the experimental values to determine the accuracy of the prediction.
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Authors and Affiliations

M. Beniyel
M. Sivapragash
S.C. Vettivel
P. Senthil Kumar
K.K. Ajith Kumar
K. Niranjan
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Abstract

In this work, conversion coatings based on nitrates Ca(NO 3) 2 and Zn(NO 3) 2 were produced on the surface of MgZn49Ca4 to protect against corrosion. The main aim of this study was to prepare dense and uniform coatings using a conversion method (based on nitrates Ca(NO 3) 2 and Zn(NO 3) 2) for resorbable Mg alloys. The scientific goal of the work was to determine the pathway and main degradation mechanisms of samples with nitrate-based coatings as compared with an uncoated substrate. Determining the effect of the coatings produced on the Mg alloy was required to assess the protective properties of Mg alloy-coating systems. For this purpose, the morphology and chemical composition of coated samples, post corrosion tests and structural tests of the substrate were performed (optical microscopy, SEM/EDS). Immersion and electrochemical tests of samples were also carried out in Ringer’s solution at 37°C. The results of immersion and electrochemical tests indicated lower corrosion resistance of the substrate as compared with coated samples. The hydrogen evolution rate of the substrate increased with the immersion time. For coated samples, the hydrogen evolution rate was more stable. The ZnN coating (based on Zn(NO 3) 2) provides better corrosion protection because the corrosion product layer was uniform, while the sample with a CaN coating (based on Ca(NO 3) 2) displayed clusters of corrosion products. It was found that pitting corrosion on the substrate led to the complete disintegration and non-uniform corrosion of the coated samples, especially the CaN sample, due to the unevenly-distributed products on its surface.
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Authors and Affiliations

Katarzyna Cesarz-Andraczke
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Abstract

In the paper, a design method of a static anti-windup compensator for systems with input saturations is proposed. First, an anti-windup controller is presented for system with cut-off saturations, and, secondly, the design problem of the compensator is presented to be a non-convex optimization problem easily solved using bilinear matrix inequalities formulation. This approach guarantees stability of the closed-loop system against saturation nonlinearities and optimizes the robust control performance while the saturation is active.
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Authors and Affiliations

Dariusz Horla
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Abstract

In the paper a new, state space, fully discrete, fractional model of a heat transfer process in one dimensional body is addressed. The proposed model derives directly from fractional heat transfer equation. It employes the discrete Grünwald-Letnikov operator to express the fractional order differences along both coordinates: time and space. The practical stability and numerical complexity of the model are analysed. Theoretical results are verified using experimental data.
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Authors and Affiliations

Krzysztof Oprzędkiewicz
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Abstract

The paper presents the results of analyses concerning a new approach to approximating trajectory of mining-induced horizontal displacements. Analyses aimed at finding the most effective method of fitting data to the trajectory of mining-induced horizontal displacements. Two variants were made. In the first, the direct least square fitting (DLSF) method was applied based on the minimization of the objective function defined in the form of an algebraic distance. In the second, the effectiveness of differential-free optimization methods (DFO) was verified. As part of this study, the following methods were tested: genetic algorithms (GA), differential evolution (DE) and particle swarm optimization (PSO). The data for the analysis were measurements of on the ground surface caused by the mining progressive work at face no. 698 of the German Prospel-Haniel mine. The results obtained were compared in terms of the fitting quality, the stability of the results and the time needed to carry out the calculations. Finally, it was found that the direct least square fitting (DLSF) approach is the most effective for the analyzed registration data base. In the authors’ opinion, this is dictated by the angular range in which the measurements within a given measuring point oscillated.
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Authors and Affiliations

Janusz Rusek
Krzysztof Tajduś
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Abstract

This paper presents a new form of a mathematical estimation of stochastic bio-hydrodynamic lubrication parameters for real human joint surfaces with phospholipid bilayers. In this work, the authors present the analytical and stochastic considerations, which are based on the measurements of human joint surfaces. The gap is restricted between two cooperating biological surfaces. After numerous experimental measurements, it directly follows that the random symmetrical as well as unsymmetrical increments and decrements of the gap height in human joints influence the hydrodynamic pressure, load-carrying capacity, friction forces, and wear of the cooperating cartilage surfaces in human joints. The main focus of the paper was to demonstrate the influence of variations in the expected values and standard deviation of human joint gap height on the hydrodynamic lubrication parameters occurring in the human joint. It is very important to notice that the new form of apparent dynamic viscosity of synovial fluid formulated by the authors depends on ultra-thin gap height variations. Moreover, evident connection was observed between the apparent dynamic viscosity and the properties of cartilage surface coated by phospholipid cells. The above observations indicate an indirect impact of stochastic changes in the height of the gap and the indirect impact of random changes in the properties of the joint surface coated with the phospholipid layers, on the value of hydrodynamic pressure, load carrying capacity and friction forces. In this paper the authors present a synthetic, comprehensive estimation of stochastic bio-hydrodynamic lubrication parameters for the cooperating, rotational cartilage bio-surfaces with phospholipid bilayers occurring in human joints. The new results presented in this paper were obtained taking into account 3D variations in the dynamic viscosity of synovial fluid, particularly random variations crosswise the film thickness for non-Newtonian synovial fluid properties. According to the authors’ knowledge, the obtained results are widely applicable in spatiotemporal models in biology and health science.
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Authors and Affiliations

Krzysztof Wierzcholski
Andrzej Miszczak
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Abstract

This paper presents material and technological studies on lab-on-chip (LOC) devices as a first step towards biocompatible and reliable research on microscopic fungi and soil organisms on a microscale. This approach is intended to respond to the growing need for environmental control and protection, by means of modern, miniaturized, portable and dependable microfluidics instrumentation. The authors have presented herein long-term, successful cultivation of different fungi representatives (with emphasis put on Cladosporium macrocarpum) in specially fabricated all-glass LOCs. Notable differences were noted in the development of these creatures on polymer, polydimethylosiloxane (PDMS) cultivation substrates, revealing the uncommon morphological character of the fungi mycelium. The utility of all-glass LOCs was verified for other fungi representatives as well –  Fusarium culmorum and Pencilium expansum, showing technical correspondence and biocompatibility of the devices. On that basis, other future applications of the solution are possible, covering, e.g. investigation of additional, environmentally relevant fungi species. Further development of the LOC instrumentation is also taken into consideration, which could be used for cultivation of other soil organisms and study of their mutual relationships within the integrated microfluidic device.
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Authors and Affiliations

Agnieszka Podwin
Tymon Janisz
Katarzyna Patejuk
Piotr Szyszka
Rafał Walczak
Jan Dziuban
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Abstract

The longitudinal automatic carrier landing system (ACLS) control law is designed based on nonlinear dynamic inversion (NDI), which can reject air wake, decouple lateral states, and track the dynamic desired touchdown point (DTP). First of all, the nonlinear landing model of F/A−18 aircraft in the final approach is established, in which the parameters of the aerodynamic, control surfaces, and limited states are acquired. Second, the strategy of tracking the desired longitudinal trajectory through pitch angle control is adopted. The automatic power compensation system (APCS), pitch angle rate, pitch angle, and vertical position control loops are developed based on the adaptive NDI. The stable analysis and the principal description are derived in detail. Deck motion compensation (DMC) algorithm is designed by frequency response method. Third, the control parameters are optimized through the genetic algorithm. A fitness function integrated with velocity, angle of attack (AOA), pitch rate, pitch angle, and vertical position of the aircraft are proposed. Finally, integrated simulations are conducted on a semi-physical simulation platform. The results indicate that the adopted automatic landing control law can achieve both excellent performance and the ability to reject the air wake and lateral coupling.
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Authors and Affiliations

Lipeng Wang
Zhi Zhang
Qidan Zhu
Zixia Wen

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