Applied sciences

Bulletin of the Polish Academy of Sciences: Technical Sciences

Content

Bulletin of the Polish Academy of Sciences: Technical Sciences | Early Access |

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Abstract

The rotating machines with overhung rotors form a broad class of devices used in many types of industry. For this kind of rotor machine in the paper, there is investigated an influence of dynamic and static unbalance of a rotor, parallel and angular misalignments of shafts, and inner anisotropy of rigid couplings on system dynamic responses. The considerations are performed through a hybrid structural model of the machine rotor-shaft system, consisting of continuous beam finite elements and discrete oscillators. Numerical calculations are carried out for parameters characterizing a heavy blower applied in the mining industry. The main goal of the research is to assess the sensitivity of the imperfections mentioned above on excitation severity of rotor-shaft lateral vibrations and motion stability of the machine in question.
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Authors and Affiliations

Tomasz Szolc
Robert Konowrocki
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Abstract

A gyroscopic rotor exposed to unbalance is studied and controlled with an active piezoelectrical bearing. A model is required in order to design a suited controller. Due to the lack of related publications utilizing piezoelectrical bearings and obtaining a modal model purely exploiting experimental modal analysis, this paper reveals a method to receive a modal model of a gyroscopic rotor system with an active piezoelectrical bearing. The properties of the retrieved model are then incorporated into the design of an originally model-free control approach for unbalance vibration elimination, which consists of a simple feedback control and an adaptive feedforward control. After the discussion on the limitations of the model-free control, a modified controller using the priorly identified modal model is implemented on an elementary rotor test-rig comparing its performance to the original model-free controller.
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Authors and Affiliations

Jens Jungblut
Christian Fischer
Stephan Rinderknecht
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Abstract

Rotors of rotating machines are often mounted in hydrodynamic bearings. Loading alternating between the idling and full load magnitudes leads to the rotor journal eccentricity variation in the bearing gap. To avoid taking undesirable operating regimes, its magnitude must be kept in a certain interval. This is offered by the hydrodynamic bearings lubricated with smart oils, the viscosity of which can be changed by the action of a magnetic field. A new design of a hydrodynamic bearing lubricated with magnetically sensitive composite fluid is presented in this paper. Generated in the electric coil, the magnetic flux passes through the bearing housing and the lubricant layer and then returns to the coil core. The action of the magnetic field on the lubricant affects the apparent fluid viscosity and thus the position of the rotor journal in the bearing gap. The developed mathematical model of the bearing is based on applying the Reynolds equation adapted for the case of lubricants exhibiting the yielding shear stress. The results of the performed simulations confirmed that the change of magnetic induction makes it possible to change the bearing load capacity and thus to keep the rotor journal eccentricity in the required range. The extent of control has its limitations. A high increase in the loading capacity can arrive at the rotor forced vibration’s loss of stability and induce large amplitude oscillation.
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Authors and Affiliations

Jaroslav Zapoměl
Petr Ferfecki
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Abstract

In this paper, a new application of the Numerical Assembly Technique is presented for the balancing of linear elastic rotor-bearing systems with a stepped shaft and arbitrarily distributed mass unbalance. The method improves existing balancing techniques by combining the advantages of modal balancing with the fast calculation of an efficient numerical method. The rotating stepped circular shaft is modelled according to the Rayleigh beam theory. The Numerical Assembly Technique is used to calculate the steady-state harmonic response, eigenvalues and the associated mode shapes of the rotor. The displacements of a simulation are compared to measured displacements of the rotor-bearing system to calculate the generalized unbalance for each eigenvalue. The generalized unbalances are modified according to modal theory to calculate orthogonal correction masses. In this manner, a rotor-bearing system is balanced using a single measurement of the displacement at one position on the rotor for every critical speed. Three numerical examples are used to show the accuracy and the balancing success of the proposed method.
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Authors and Affiliations

Georg Quinz
Marcel S. Prem
Michael Klanner
Katrin Ellermann
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Abstract

Vibration in rotating machinery leads to a series of undesired effects, e.g. noise, reduced service life or even machine failure. Even though there are many sources of vibrations in a rotating machine, the most common one is mass unbalance. Therefore, a detailed knowledge of the system behavior due to mass unbalance is crucial in the design phase of a rotor-bearing system. The modelling of the rotor and mass unbalance as a lumped system is a widely used approach to calculate the whirling motion of a rotor-bearing system. A more accurate representation of the real system can be found by a continuous model, especially if the mass unbalance is not constant and arbitrarily oriented in space. Therefore, a quasi-analytical method called Numerical Assembly Technique is extended in this paper, which allows for an efficient and accurate simulation of the unbalance response of a rotor-bearing system. The rotor shaft is modelled by the Rayleigh beam theory including rotatory inertia and gyroscopic effects. Rigid discs can be mounted onto the rotor and the bearings are modeled by linear translational/rotational springs/dampers, including cross-coupling effects. The effect of a constant axial force or torque on the system response is also examined in the simulation.
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Authors and Affiliations

Michael Klanner
Marcel S. Prem
Katrin Ellermann
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Abstract

The analysis of subsonic stall flutter in turbomachinery blade cascade is carried out using a medium-fidelity reduced-order aeroelastic numerical model. The model is a type of field mesh-free approach and based on a hybrid boundary element method. The medium-fidelity flow solver is developed on the principle of viscous-inviscid two-way weak-coupling approach. The hybrid flow solver is employed to model separated flow and stall flutter in the 3D blade cascade at subsonic speed. The aerodynamic damping coefficient w.r.t. inter blade phase angle in traveling-wave mode is estimated along with other parameters. The same stability parameter is used to analyze the cascade flutter resistance regime. The estimated results are validated against experimental measurements as well as Navier-Stokes based high fidelity CFD model. The simulated results show good agreement with experimental data. Furthermore, the hybrid flow solver has managed to bring down the computational cost significantly as compared to field-based CFD models. Therefore, all the prime objectives of the research have been successfully achieved.
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Authors and Affiliations

Chandra Shekhar Prasad
Pavel Šnábl
Luděk Pešek
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Abstract

Full-floating ring bearings are state of the art at high speed turbomachinery shafts like in turbochargers. Their main feature is an additional ring between shaft and housing leading to two fluid films in serial arrangement. Analogously, a thrust bearing with an additional separating disk between journal collar and housing can be designed. The disk is allowed to rotate freely only driven by drag torques, while it is radially supported by a short bearing against the journal. This paper addresses this kind of thrust bearing and its implementation into a transient rotor dynamic simulation by solving the Reynolds PDE online during time integration. Special attention is given to the coupling between the different fluid films of this bearing type. Finally, the differences between a coupled and an uncoupled solution are discussed.
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Authors and Affiliations

Steffen Nitzschke
Christian Ziese
Elmar Woschke
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Abstract

This paper deals with research on the subject of magnetic bearing control systems for a high-speed rotating machine. Theoretical and experimental characteristics of the control systems with the model algorithmic control (MAC) algorithm and the proportional-derivative (PD) algorithm are presented. The MAC algorithm is the non-parametric predictive control method that uses an impulse response model. A laboratory model of the rotor-bearing unit under study consists of two active radial magnetic bearings and one active axial (thrust) magnetic bearing. The control system of the rotor position in air gaps consists of the fast prototyping control unit with a signal processor, the input and output modules, power amplifiers, contactless eddy current sensors and the host PC with dedicated software. Rotor displacement and control current signals were registered during investigations using a data acquisition (DAQ) system. In addition, measurements were performed for various rotor speeds, control algorithms and disturbance signals generated by the control system. Finally, the obtained time histories were presented, analyzed and discussed in this paper.
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Authors and Affiliations

Paulina Kurnyta-Mazurek
Tomasz Szolc
Maciej Henzel
Krzysztof Falkowski
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Abstract

Squeeze film dampers (SFDs) are commonly used in turbomachinery in order to introduce external damping, thereby reducing rotor vibrations and acoustic emissions. Since SFDs are of similar geometry as hydrodynamic bearings, the REYNOLDS equation of lubrication can be utilised to predict their dynamic behaviour. However, under certain operating conditions, SFDs can experience significant fluid inertia effects, which are neglected in the usual REYNOLDS analysis. An algorithm for the prediction of these effects on the pressure build up inside a finite-length SFD is therefore presented. For this purpose, the REYNOLDS equation is extended with a first-order perturbation in the fluid velocities to account for the local and convective inertia terms of the NAVIER-STOKES equations. Cavitation is taken into account by means of a mass conserving two-phase model. The resulting equation is then discretized using the finite volume method and solved with an LU factorization. The developed algorithm is capable of calculating the pressure field, and thereby the damping force, inside an SFD for arbitrary operating points in a time-efficient manner. It is therefore suited for integration into transient simulations of turbo machinery without the need for bearing force coefficient maps, which are usually restricted to circular centralized orbits. The capabilities of the method are demonstrated on a transient run-up simulation of a turbocharger rotor with two semi-floating bearings. It can be shown that the consideration of fluid inertia effects introduces a significant shift of the pressure field inside the SFDs, and therefore the resulting damper force vector, at high oil temperatures and high rotational speeds. The effect of fluid inertia on the kinematic behaviour of the whole system on the other hand is rather limited for the examined rotor.
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Authors and Affiliations

Thomas Drapatow
Oliver Alber
Elmar Woschke
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Abstract

State-of-the-art analyses for the rotordynamic assessment of pumps and specific requirements for the simulation tools are described. Examples are a horizontal multistage pump with two fluid film bearings in atmospheric pressure, a horizontal submerged multistage pump with many bearings, and a submerged vertical single-stage pump with water-lubricated bearings. The rotor of the horizontal pump on two bearings is statically overdetermined by the seals and the static bearing forces depend on the deflection in the seals and the bearings. The nonlinear force-displacement relation in the bearings is considered in this paper. The stability of pumps is assessed by Campbell diagrams considering linear seal and bearing properties. Cylindrical bearings can have a destabilizing effect in the case of low loads as in the examples of the submerged pumps. For the pump with many bearings, the influence of the bearing ambient pressure and the bearing specific load on the stability is analyzed. For the vertical pump, the limit cycle, i.e. the vibration level of stabilization, is determined with a nonlinear analysis. All examples have a practical background from engineering work, although they do not exactly correspond to real cases. Analyses were performed with the rotordynamic software MADYN 2000.
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Authors and Affiliations

Frédéric Gaulard
Joachim Schmied
Andreas Fuchs
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Abstract

Designing touch-down bearings (TDB) for outer rotor flywheels operated under high vacuum conditions constitutes a challenging task. Due to their large diameters, conventional TDB cannot not suited well, and a planetary design is applied, consisting of a number of small rolling elements distributed around the stator. Since the amplitude of the peak loads during a drop-down lies close to the static load rating of the bearings, it is expected that their service life can be increased by reducing the maximum forces. Therefore, this paper investigates the influence of elastomer rings around the outer rings in the TDB using simulations. For this purpose, the structure and the models used for contact force calculation in the ANEAS simulation software are presented, especially the modelling of the elastomers. Based on the requirements for a TDB in a flywheel application, three different elastomers (FKM, VMQ, EPDM) are selected for the investigation. The results of the simulations show that stiffness and the type of material strongly influence the maximum force. The best results are obtained using FKM, leading to a reduction of the force amplitude in a wide stiffness range.
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Authors and Affiliations

Benedikt Schüßler
Timo Hopf
Stephan Rinderknecht
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Abstract

In the domain of affective computing different emotional expressions play an important role. To convey the emotional state of human emotions, facial expressions or visual cues are used as an important and primary cue. The facial expressions convey humans affective state more convincingly than any other cues. With the advancement in the deep learning techniques, the convolutional neural network (CNN) can be used to automatically extract the features from the visual cues; however variable sized and biased datasets are a vital challenge to be dealt with as far as implementation of deep models is concerned. Also, the dataset used for training the model plays a significant role in the retrieved results. In this paper, we have proposed a multi-model hybrid ensemble weighted adaptive approach with decision level fusion for personalized affect recognition based on the visual cues. We have used a CNN and pre-trained ResNet-50 model for the transfer learning. VGGFace model’s weights are used to initialize weights of ResNet50 for fine-tuning the model. The proposed system shows significant improvement in test accuracy in affective state recognition compared to the singleton CNN model developed from scratch or transfer learned model. The proposed methodology is validated on The Karolinska Directed Emotional Faces (KDEF) dataset with 77.85% accuracy. The obtained results are promising compared to the existing state of the art methods.
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Authors and Affiliations

Nagesh Jadhav
Rekha Sugandhi
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Abstract

The following paper presents wind tunnel investigation of aerodynamic characteristics of hovering propellers. This propulsion system may be applied on a lightweight Quad Plane VTOL (Vertical Take-Off and Landing) UAV (Unmanned Aerial Vehicle). A Quad Plane is a configuration consisting of a quadcopter design combined with a conventional twin-boom airplane. This kind of design should therefore incorporate the advantages of both types of vehicles in terms of agility and long endurance. However, those benefits may come with a cost of worse performance and higher energy consumption. The characteristics of a fixed-wing aircraft and propellers in axial inflow are well documented, less attention is put to non-axial flow cases. VTOL propellers of a hybrid UAV are subject to a multitude of conditions – various inflow speeds and angles, changing RPMs, interference between propellers and between nearby aerodynamic structures. The tested system presented in this article consists of four electric motors with two coaxial pairs of propellers mounted on one of the fuselage beams. Such a configuration is often chosen by designers of small and medium hybrid UAVs. There is a need for studies of clean, efficient ways of transporting, and this article can aid future designers of a new type of electric UAVs.
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Authors and Affiliations

Katarzyna Pobikrowska
Tomasz Goetzendorf-Grabowski
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Abstract

The paper presents an analysis of the influence of the shape of the rigid body pressed into the micro-periodic composite half-space on the examples of two punch shapes – parabolic and rectangular. The presented material is a layered body that consists of infinitely many thin alternately arranged homogenous layers. Layers of the presented composite are oblique to the boundary surface. Two cases of punch tip shape are examined – parabolic and rectangular. The presented problem has been formulated within the framework of a homogenized model with microlocal parameters and solved using the elastic potentials method and averaged boundary condition. Fourier integral transform method has been used to obtain the solution and the inverse integrals have been calculated numerically. Solutions in terms of contact pressure and maximum pressure characteristics were shown in the form of figures.
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Authors and Affiliations

Piotr Sebestianiuk
Dariusz M. Perkowski
Roman Kulchytsky-Zhyhailo
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Abstract

This paper presents the design of a versatile mechanism that can enable new directions in amphibious, all-terrain locomotion. The simple, passive, flapped-paddle can be integrated with several structures that are well-suited for locomotion in terrestrial applications. The flapped-paddle overcomes a serious limitation of the conventional flipper where the net lateral forces generated during oscillatory motion in aquatic environments averages out to zero. The flapped-paddle and its mounting, collectively, rests in natural positions in the aquatic environment so as to maximize hydrodynamic force utilization and consequently the propulsive efficiency. The simplicity of the design enabled us to develop a simulation model that concurs well with experimental results. The results reported in the paper are based on integrating the flapped-paddle with the curved leg of the RHex hexapod robot.
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Authors and Affiliations

Piotr Burzynski
Ashutosh Simha
Ülle Kotta
Ewa Pawluszewicz
Shivakumar Sastry
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Abstract

The above-threshold operation of a Fabry-Perot laser with a nonlinear PT (parity time) mirror is investigated. For the first time, the analysis accounts for gain saturation of an active medium as well as gain and loss saturation effects in the PT mirror. The obtained laser output intensity characteristics have been demonstrated as a function of various PT mirror parameters such as: the ratio of the PT structure period to laser operating wavelength, number of PT mirror primitive cells, and gain and loss saturation intensities of the PT mirror gain and loss layers. Two functional configurations of the laser have been considered: laser operating as a discrete device, and as a component of an integrated circuit. It has been shown that, in general, the laser operation depends on the PT mirror orientation with respect to the active medium of the laser. Moreover, when the laser radiation is outcoupled through the PT mirror to the free space, bistable operation is possible, when losses of the mirror’s loss layer saturate faster than gain of the gain layer. Furthermore, for a given saturation intensity of the mirror loss layers, the increase of the saturation intensity of the mirror gain layers causes increasing output intensity, i.e., the PT mirror additionally amplifies the laser output signal.
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Authors and Affiliations

Agnieszka Mossakowska-Wyszyńska
Piotr Witoński
Paweł Szczepański
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Abstract

This article deals with the effect of selected machining parameter values in hard turning of tested OCHN3MFA steel in terms of SEM microstructural analysis of workpiece material, cutting forces, long-term tests, and SEM observations of flank wear VB and crater wear KT of used changeable coated cemented carbide cutting inserts in the processes of performed experiments. OCHN3MFA steel was selected as an experimental (workpiece) material. The selected experimental steel was analyzed prior to hard turning tests to check the initial microstructure of bulk material and subsurface microstructure after hard turning and chemical composition. Study of workpiece material’s microstructure and worn cemented carbide cutting inserts was performed with Tescan Vega TS 5135 scanning electron microscope (SEM) with the X-Ray microanalyzer Noran Six/300. The chemical composition of workpiece material was analyzed with Tasman Q4 surface analyzer. All hard turning experiments of the used specimens were performed under the selected machining parameters in the SU 50A machine tool with the 8th selected individual geometry of coated cementite carbide cutting inserts clamped in the appropriate DCLNR 2525M12-M type of cutting tool holder. During the hard turning technological process of the individual tested samples made of OCHN3MFA steel, cutting forces were measured with a Kistler 9257B piezoelectric dynamometer, with their subsequent evaluation using Dynoware software. After the long-term testing, other experiments and results were also realized, evaluating the influence of selected machining parameters with different cutting insert geometry on the achieved surface quality.
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Authors and Affiliations

Jozef Majerík
Igor Barényi
Zdenek Pokorný
Josef Sedlák
Vlastimil Neumann
David Dobrocký
Aleš Jaroš
Michal Krbaťa
Jozef Jambor
Robert Kusenda
Miroslav Sagan
Jiri Procházka
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Abstract

The article discusses the applicability of a novel method to determine horizontal curvature of the railway track axis based on results of mobile satellite measurements. The method is based on inclination angle changes of a moving chord in the Cartesian coordinate system. In the presented case, the variant referred to as the method of two virtual chords is applied. It consists in maneuvering with only one GNSS (Global Navigation Satellite System) receiver. The assumptions of the novel method are formulated, and an assessment of its application in the performed campaign of mobile satellite measurements is presented. The shape of the measured railway axis is shown in the national spatial reference system PL-2000, and the speed of the measuring trolley during measurement is calculated based on the recorded coordinates. It has been observed that over the test section, the curvature ordinates differ from the expected waveform, which can be caused by disturbances of the measuring trolley trajectory. However, this problem can easily be overcome by filtering the measured track axis ordinates to obtain the correct shape – this refers to all track segments: straight sections, circular arcs and transition curves. The virtual chord method can also constitute the basis for assessing the quality of the recorded satellite signal. The performed analysis has shown high accuracy of the measuring process.
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Authors and Affiliations

Władysław Koc
Andrzej Wilk
Cezary Specht
Krzysztof Karwowski
Jacek Skibicki
Krzysztof Czaplewski
Slawomir Judek
Piotr Chrostowski
Jacek Szmagliński
Paweł Dąbrowski
Mariusz Specht
Sławomir Grulkowski
ORCID: ORCID
Roksana Licow
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Abstract

In the article the results of simulation and experimental studies of the movement of a four-wheeled mobile platform, taking into account wheel slip have been presented. The simulation results have been based on the dynamics of the four-wheel mobile platform. The dynamic model of the system motion takes into account the relationship between the active and passive forces accompanying the platform motion, especially during wheel slip. The formulated initial problem describing the motion of the system has been solved by the Runge-Kutta method of the fourth order. The proposed computational model including the platform dynamics model has been verified in experimental studies using the LEO Rover robot. The motion parameters obtained on the basis of the adopted computational model in the form of trajectories, velocities and accelerations have been compared with the results of experimental tests, and the results of this comparison have been included in the paper. The proposed computational model can be useful in various situations, e.g., real-time control, where models with a high degree of complexity are useless due to the computation time. The simulation results obtained on the basis of the proposed model are sufficiently compatible with the results of experimental tests of motion parameters obtained for the selected type of mobile robot.
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Authors and Affiliations

Anna Jaskot
Bogdan Posiadała
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Abstract

Modern industry requires an increasing level of efficiency in a lightweight design. To achieve these objectives, easy-to-apply numerical tests can help in finding the best method of topological optimization for practical industrial applications. In this paper, several numerical benchmarks are proposed. The numerical benchmarks facilitate qualitative comparison with analytical examples and quantitative comparison with the presented numerical solutions. Moreover, an example of a comparison of two optimization algorithms was performed. That was a commonly used SIMP algorithm and a new version of the CCSA hybrid algorithm of topology optimization. The numerical benchmarks were done for stress constraints and a few material models used in additive manufacturing.
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Authors and Affiliations

Grzegorz Fiuk
Mirosław W. Mrzygłód
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Abstract

The increasing concern for worldwide energy production is the result of global industrialization and decreasing energy resources. Despite the cost factor, solar energy continues to become more popular due to its long-term nature as a resource and growing conversion efficiency. A dye-sensitized solar cell converts visible light into electricity. The efficient use of dye as a sensitizer is the critical factor in enhancing the performance of the dye-sensitized solar cell. Natural dyes are found in abundance in leaves, flower petals, roots, and other natural resources. Due to the advantages of natural dyes such as cost-effectiveness, the simpler extraction process, and being environmentally friendly, etc., researchers are working extensively to replace synthetic dyes with natural ones. This paper highlights the various types of natural dyes and their effect on the efficiency of the dye-sensitized solar cell.
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Authors and Affiliations

Cherry Bhargava
Pardeep Kumar Sharma
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Abstract

The goal of the research was to analyze the acoustic emission signal recorded during heat treatment. On a special stand, samples prepared from 27MnCrB5-2 steel were tested. The steel samples were heated to 950°C and then cooled continuously in the air. Signals from phase changes occurring during cooling were recorded using the system for registering acoustic emission. As a result of the changes, Widmanstätten ferrite and bainite structures were observed under a scanning microscope. The recorded acoustic emission signal was analyzed and assigned to the appropriate phase transformation with the use of artificial neural networks.
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Authors and Affiliations

Andrzej Trafarski
Małgorzata Łazarska
Zbigniew Ranachowski
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Abstract

The paper presents the results of experimental verification on using a zero-sum differential game and H control in the problems of tracking and stabilizing motion of a wheeled mobile robot (WMR). It is a new approach to the synthesis of input-output systems based on the theory of dissipative systems in the sense of the possibility of their practical application. This paper expands upon the problem of optimal control of a nonlinear, nonholonomic wheeled mobile robot by including the reduced impact of changing operating condtions and possible disturbances of the robot’s complex motion. The proposed approach is based on the H∞ control theory and the control is generated by the neural approximation solution to the Hamilton-Jacobi-Isaacs equation. Our verification experiments confirm that the H∞ condition is met for reduced impact of disturbances in the task of tracking and stabilizing the robot motion in the form of changing operating conditions and other disturbances, which made it possible to achieve high accuracy of motion.
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Authors and Affiliations

Zenon Hendzel
Paweł Penar
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Abstract

Numerous examples of physically unjustified neural networks, despite satisfactory performance, generate contradictions with logic and lead to many inaccuracies in the final applications. One of the methods to justify the typical black-box model already at the training stage involves extending its cost function by a relationship directly inspired by the physical formula. This publication explains the concept of Physics-guided neural networks (PGNN), makes an overview of already proposed solutions in the field and describes possibilities of implementing physics-based loss functions for spatial analysis. Our approach shows that the model predictions are not only optimal but also scientifically consistent with domain specific equations. Furthermore, we present two applications of PGNNs and illustrate their advantages in theory by solving Poisson’s and Burger’s partial differential equations. The proposed formulas describe various real-world processes and have numerous applications in the area of applied mathematics. Eventually, the usage of scientific knowledge contained in the tailored cost functions shows that our methods guarantee physics-consistent results as well as better generalizability of the model compared to classical, artificial neural networks.
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Authors and Affiliations

Bartłomiej Borzyszkowski
Karol Damaszke
Jakub Romankiewicz
Marcin Świniarski
Marek Moszyński
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Abstract

Coagulation is a process during which a flocculent suspension may sediment. It is characterized by its polydisperse structure. There are three main fractions of sedimentation particles after coagulation: spherical, non-spherical and porous agglomerates. Each of the fractions sediments in a different manner, for different forces act on them, due to interactions between the particles, inhibition or entrainment of neighboring particles. The existing sedimentation models of polydisperse suspension do not consider the flocculation process, i.e. the change of one particle into another during sedimentation, resulting from their agglomeration. The presented model considers the shape of particles and flocculation, which is a new approach to the description of the mathematical process of sedimentation. The velocity of sedimentation depends on the concentration of particles of a given fraction in a specific time step. Following the time step, the heights of individual fractions are calculated. Subsequently, new concentration values of individual fractions are determined for the correspondingly reduced volume of occurrence of a given fraction in the volume analyzed, taking particle flocculation into consideration. The new concentration values obtained in this way allow to recalculate the total sedimentation rates for the next time step. Subsequent iterations allow for numerical simulation of the sedimentation process.
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Authors and Affiliations

Mariusz Rząsa
Ewelina Łukasiewicz
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Abstract

The article presents the method of magnetron sputtering for the deposition of conductive emitter coatings in semiconductor structures. The layers were applied to a silicon substrate. For optical investigations, borosilicate glasses were used. The obtained layers were subjected to both optical and electrical characterisation, as well as structural investigations. The layers on silicon substrates were tested with the four-point probe to find the dependence of resistivity on the layer thickness. The analysis of the elemental composition of the layer was conducted using a scanning electron microscope equipped with an EDS system. The morphology of the layers was examined with the atomic force microscope (AFM) of the scanning electron microscope (SEM) and the structures with the use of X-ray diffraction (XRD). The thickness of the manufactured layers was estimated by ellipsometry. The composition was controlled by selecting the target and the conditions of the application, i.e. the composition of the plasma atmosphere and the power of the magnetrons. Based on the obtained results, this article aims to investigate the influence of the manufacturing method and the selected process parameter on the optical properties of thin films, which should be characterised by the highest possible value of the transmission coefficient (>85–90%) and high electrical conductivity.
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Authors and Affiliations

Małgorzata Musztyfaga-Staszuk
Dušan Pudiš
Robert Socha
Katarzyna Gawlińska-Nęcek
Piotr Panek
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Abstract

This study proposes a new integrated analytical-field design method for multi-disc magnetorheological (MR) clutches. This method includes two stages, an analytical stage (composed of 36 algebraic formulas) and a field stage based on the finite element method (FEM). The design procedure is presented systematically, step-by-step, and the results of the consecutive steps of the design calculations are depicted graphically against the background of the entire considered clutch. The essential advantage of the integrated method with this two-stage structure is the relatively high accuracy of the first analytical stage of the design procedure and the rapid convergence of the second field stage employing the FEM. The essence of the new method is the introduction of a yoke factor kY (the concept of which is based on the theory of induction machines) that determines the ratio of the total magnetomotive force required to magnetise the entire magnetic circuit of the clutch to the magnetomotive force required to magnetise the movement region. The final value, the yoke factor kY is determined using loop calculations. The simplicity of the developed design method predisposes its use in optimisation calculations. The proposed method can also be adapted to other MR devices analysed in shear mode.
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Authors and Affiliations

Krzysztof Kluszczyński
Zbigniew Pilch
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Abstract

In the paper, the numerical method of solving the one-dimensional subdiffusion equation with the source term is presented. In the approach used, the key role is played by transforming of the partial differential equation into an equivalent integro-differential equation. As a result of the discretization of the integro-differential equation obtained an implicit numerical scheme which is the generalized Crank-Nicolson method. The implicit numerical schemes based on the finite difference method, such as the Carnk-Nicolson method or the Laasonen method, as a rule are unconditionally stable, which is their undoubted advantage. The discretization of the integro-differential equation is performed in two stages. First, the left-sided Riemann-Liouville integrals are approximated in such a way that the integrands are linear functions between successive grid nodes with respect to the time variable. This allows us to find the discrete values of the integral kernel of the left-sided Riemann-Liouville integral and assign them to the appropriate nodes. In the second step, second order derivative with respect to the spatial variable is approximated by the difference quotient. The obtained numerical scheme is verified on three examples for which closed analytical solutions are known.
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Authors and Affiliations

Marek Błasik
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Abstract

This paper addresses the problem of part of speech (POS) tagging for the Tamil language, which is low resourced and agglutinative. POS tagging is the process of assigning syntactic categories for the words in a sentence. This is the preliminary step for many of the Natural Language Processing (NLP) tasks. For this work, various sequential deep learning models such as recurrent neural network (RNN), Long Short-Term Memory (LSTM), Gated Recurrent Unit (GRU) and Bi-directional Long Short-Term Memory (Bi-LSTM) were used at the word level. For evaluating the model, the performance metrics such as precision, recall, F1-score and accuracy were used. Further, a tag set of 32 tags and 225 000 tagged Tamil words was utilized for training. To find the appropriate hidden state, the hidden states were varied as 4, 16, 32 and 64, and the models were trained. The experiments indicated that the increase in hidden state improves the performance of the model. Among all the combinations, Bi-LSTM with 64 hidden states displayed the best accuracy (94%). For Tamil POS tagging, this is the initial attempt to be carried out using a deep learning model.
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Authors and Affiliations

S. Anbukkarasi
S. Varadhaganapathy
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In this paper, the performance and frequency bandwidth of the piezoelectric energy harvester (PZEH) is improved by introducing two permanent magnets, which is attached to the proof mass of a dual beam structure. Both magnets are in the vicinity of each other and attached in such as a way to proof mass of a dual-beam, so that they create a magnetic field around each other. The generated magnetic field develops a repulsive force between the magnets, which improves not only electrical output but also enhances the bandwidth of harvester. The simple rectangular cantilever structure with and without magnetic tip mass has the frequency bandwidth of 4 Hz and 4.5 Hz respectively. The proposed structure generates a peak voltage of 20 V at a frequency of 114.51 Hz at an excitation acceleration of 1g (g = 9.8 m/s2). The peak output power of a proposed structure is 12.2 μW. The operational frequency range of a proposed dual-beam cantilever with magnetic tip mass of 30 mT is from 102.51 Hz to 120.51 Hz i.e., 18 Hz. The operational frequency range of a dual-beam cantilever without magnetic tip mass is from 104.18 Hz to 118.18 Hz i.e., 14 Hz. There is an improvement of 22.22% in the frequency bandwidth of proposed dual-beam cantilever with magnetic tip mass of 30 mT than the dual-beam without magnetic tip mass.
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Authors and Affiliations

Ashutosh Anand
Srikanta Pal
Sudip Kundu
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The blast mitigation in case of military vehicles is still a popular field of research. The main problem is coping with the vehicle global motion consequences after the explosion. The paper presents a possibility of an application of the linear Vacuum Packed Particle (VPP) damper as a supplementation for a viscous shock absorber in a traditional blast mitigation seat design. The paper presents field test results for the underbelly blast explosion and comparing them to the laboratory tests carried out on the impact bench. To collect accelerations, the Anthropomorphic Test Device – Hybrid III dummy was used. The set of numerical simulations of the modified blast mitigation seat with the additional VPP linear damper were revealed. The VPP damper was modeled by the Johnson-Cook model of the viscoplasticity. The Hertzian contact theory was adopted to model the contact between the vehicle and the ground. The reduction of the Dynamic Response Index (DRI) in case of the VPP damper application was proved.
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Authors and Affiliations

Dominik Rodak
Mateusz Żurawski
Michał Gmitrzuk
Lech Starczewski
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Unmanned vehicles are often used in everyday life, mostly by rescue teams or scientist during exploration of new terrains. In those constructions suspension has constant dimensions what leads to many disadvantages and more over limits application area. The solution of these problems can be a creation of a six – wheeled mobile platform which can dynamically change wheel base in relation to the area of action or terrain inclination angle. The active change in location of center of gravity gives a possibility to access sloppy obstacles not available with classical suspensions. The main scope of this study is to investigate an influence of material properties on vibration frequency at different length of suspension members. The obtained results will allow finding the optimum material for production of a prototype unit.
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Authors and Affiliations

Krzysztof Sokół
Maciej Pierzgalski
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Abstract

The following discussion concerns the use of innovative smart materials called vacuum-packed particles (VPP) as active energy absorbers. VPP, also known as a granular jamming system, is a structure composed of granular media contained within an elastomer coating. By changing the vacuum pressure inside the coating, it is possible to control the mechanical properties of the structure. VPP have many applications, e.g. in medicine, robotics and vibration damping. No attempts have yet been made to use VPP to absorb the energy of a collision, although given their properties, this could very well be an interesting application. In the first part of the paper, the general concept of the absorber is presented. Then a protype and the empirical tests conducted are precisely described. The middle part of the paper considers the basic properties of VPP and modeling methodology. A proposal for a constitutive equation is presented, and a numerical simulation using LS-Dyna was performed. In the final section, the concept of a smart parking post is presented.
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Authors and Affiliations

Piotr Bartkowski
Hubert Bukowiecki
Franciszek Gawiński
Robert Zalewski
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This paper presents the concept of the modelling methodology of a payload-vessel system allowing for a comprehensive investigation of mutual interactions of the system dynamics for lifting in air. The proposed model consists of six degrees of freedom (6-DoF) vessel and three degrees of freedom (3-DoF) lifting model that can replace the industrial practice based on a simplified approach adopted for light lifts. Utilising the response amplitude operators (RAO’s) processing methodology provides the ability to incorporate the excitation functions at the vessel crane tip as a kinematic and analyse a wide spectrum of lifted object weights on a basis of regular wave excitation. The analytical model is presented in details and its solution in a form of numerical simulation results are provided and discussed within the article. The proposed model exposes the disadvantages of the models encountered in engineering practice and literature and proposes a novel approach enabling efficient studies addressing a lack of access to reliable modelling tools in terms of coupled models for offshore lifting operations planning.
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Authors and Affiliations

Anna Mackojć
Bogumil Chiliński
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In the work, multi-criteria optimization of phononic structures was performed in order to minimize the transmission in the frequency range of acoustic waves, eliminate high transmission peaks with a small half-width inside of the band gap and what was the most important part of the work to minimizing the number of layers in the structure. Two types of genetic algorithm were compared in the study. The first one was characterized by a constant number of layers (GACL) of the phononic structure of each individual in each population. Then, the algorithm was run for a different number of layers, as a result of which the structures with the best value of the objective function were determined. In the second version of the algorithm, individuals in populations had a variable number of layers (GAVL) which required a different type of target function and crossover procedure. The transmission for quasi one-dimensional phononic structures was determined with the use of the Transfer Matrix Method algorithm. Based on the research, it can be concluded that the developed GAVL algorithm with an appropriately selected objective function achieved optimal solutions in a much smaller number of iterations than the GACL algorithm, and the value of the k parameter below 1 leads to a faster achievement of the optimal structure.
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Authors and Affiliations

Sebastian Garus
Wojciech Sochacki
Mariusz Kubanek
Marcin Nabiałek
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Abstract

Parallel realizations of discrete transforms (DTs) computation algorithms (DTCAs) performed on graphics processing units (GPUs) play a significant role in many modern data processing methods utilized in numerous areas of human activity. In this paper the authors propose a novel execution time prediction model, which allows for accurate and rapid estimation of execution times of various kinds of structurally different DTCAs performed on GPUs of distinct architectures, without the necessity of conducting the actual experiments on physical hardware. The model can serve as a guide for the system analyst in making the optimal choice of the GPU hardware solution for a given computational task involving particular DT calculation, or can help in choosing the best appropriate parallel implementation of the selected DT, given the limitations imposed by available hardware. Restricting the model to exhaustively adhere only to the key common features of DTCAs, enables the authors to significantly simplify its structure, leading consequently to its design as a hybrid, analytically–simulationial method, exploiting jointly the main advantages of both of the mentioned techniques, namely: time-effectiveness and high prediction accuracy, while, at the same time, causing mutual elimination of the major weaknesses of both of the specified approaches within the proposed solution. The model is validated experimentally on two structurally different parallel methods of discrete wavelet transform (DWT) computation, i.e. the direct convolution-based and lattice structure-based schemes, by comparing its prediction results with the actual measurements taken for 6 different graphics cards, representing a fairly broad spectrum of GPUs’ compute architectures. Experimental results reveal the model’s overall average execution time prediction accuracy to be at a level of 97.2%, with global maximum prediction error of 14.5%, recorded throughout all the conducted experiments, maintaining at the same time high average evaluation speed of 3.5 ms for single simulation duration. The results allow to infer model’s generality and possibility of extrapolation to other DTCAs and different GPU architectures, what, along with the proposed model’s straightforwardness, time-effectiveness and ease of practical application, makes it, in the authors’ opinion, a very interesting alternative to the related existing solutions.
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Authors and Affiliations

Dariusz Puchala
Kamil Stokfiszewski
Kamil Wieloch
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Abstract

To better extract feature maps from low-resolution (LR) images and recover high-frequency information in the high-resolution (HR) images in image super-resolution (SR), we propose a new SR algorithm based on deep convolutional neural network (CNN) in this paper. The network structure is composed of the feature extraction part and the reconstruction part. The extraction network extracts the feature maps of LR images and use the sub-pixel convolutional neural network as the up-sampling operator. Skip connection, densely connected neural networks, and feature map fusion are used to extract information from hierarchical feature maps at the end of the network, which can effectively reduce the dimension of the feature maps. In the reconstruction network, we add a 3×3 convolution layer based on the original sub-pixel convolution layer, which can make the reconstruction network have better nonlinear mapping ability. The experiments show that the algorithm has a significant improvement in PSNR, SSIM, and human visual effects compared with some state-of-the-art algorithms based on deep learning.
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Authors and Affiliations

Xin Yang
Yifan Zhang
Dake Zhou
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Abstract

Learning resources are massive, heterogeneous, and constantly changing. How to find the required resources quickly and accurately has become a very challenging work in the management and sharing of learning resources. According to the characteristics of learning resources, this paper proposes a progressive learning resource description model, which can describe dynamic heterogeneous resource information on a fine-grained level by using information extraction technology, then a semantic annotation algorithm is defined to calculate the semantic of learning resource, and add these semantic to the description model. Moreover, a semantic search method is proposed to find the required resources, which calculate the content with the highest similarity to the user query, and then return the results in descending order of similarity. The simulation results show that the method is feasible and effective.
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Authors and Affiliations

Xiaocong Lai
Ying Pan
Xueling Jiang

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