Showing papers in "Bulletin of The Polish Academy of Sciences-technical Sciences in 2017"
TL;DR: A number of special cases which can be used to optimize the calcu-lation speed for some classes of integrals of the IntU package for Mathematica computer algebra system are described.
82 citations
TL;DR: In this article, the influence of temperature changes on measurement results during topography measurements of surface texture with the use of profilometry methods is analyzed, and the main drawback of such measurements is the lengthy measurement, which depends on the measurement area, measurement speed in X axis, and sampling interval in Y axis (resulting from the number of measured profiles and the area to cover).
Abstract: The subject of the research described in this paper is the analysis of influence of temperature changes on measurement results during topography measurements of surface texture with the use of profilometry methods. In industrial reality, more and more often areal analysis is used for surface texture description, and it is because of the fact that measurement of a single profile does not give complete information about surface texture of the researched object. One of the methods used in areal measurements of surface texture are the ones coming from profilometry, based on measurement data acquisition by scanning the surface in two perpendicular directions. The main drawback of profilometry in general is the lengthy measurement, which depends on the measurement area, measurement speed in X axis (this axis should be perpendicular to traces of machining) and sampling interval in Y axis (resulting from the number of measured profiles and the area to cover). Dimensions of the area to measure come from the surface roughness of the inspected object. Surfaces with greater roughness usually require performing measurements on a bigger area. Typical probe movement speed in profilometry varies from 0.1 to 2 mm/s, although for some optical probes it can be higher if the converter is good enough. In contact profilometers the use of measurement speed above 0.5 mm/s is risky, because of the possibility of the flight phenomenon, i.e. a loss of contact between tip and surface. BULLETIN OF THE POLISH ACADEMY OF SCIENCES TECHNICAL SCIENCES, Vol. 65, No. 1, 2017 DOI: 10.1515/bpasts-2017-0007
38 citations
TL;DR: In this paper, a lock-in amplifier uses phase-sensitive detection to improve the SNR in continuous wave (cw) experiments, and the integration of detector current pulses is performed using preamplifier based on charge-sensitive amplifier (CSA).
Abstract: The birth of photodetectors can be dated back to 1873 when Smith discovered photoconductivity in selenium. There are two general types of photon detectors without internal gain: photoconductive and junction devices. The majority of optical detectors can be classified in two broad categories: photon detectors and thermal detectors. The practical operating limit for most IR detectors is the background fluctuation limit also known as the background limited infrared photodetector (BLIP) limit. A common problem of any type of photon detector is how to terminate the photodetector with a suitable load resistor and to trade off the performance between bandwidth and signal-to-noise ratio (SNR). A lock-in amplifier uses phase-sensitive detection to improve the SNR in continuous wave (cw) experiments. In energy spectroscopy, the integration of detector current pulses is performed using preamplifier based on charge-sensitive amplifier (CSA).
34 citations
TL;DR: The essence of the proposed algorithms rests on the method of unicoding dedicated to sharing resources, searching non-disjoint decomposition on the basis of the partition of root tables, and choosing the levels of diagram cutting that will guarantee the best mapping to complex logic blocks.
Abstract: *e-mail: mkubica@ath.bielsko.pl Abstract. The main goal of the paper is to present a logic synthesis strategy dedicated to an LUT-based FPGA. New elements of the proposed synthesis strategy include: an original method of function decomposition, non-disjoint decomposition, and technology mapping dedicated to configurability of logic blocks. The aim of all of the proposed synthesis approaches is the sharing of appropriately configured logic blocks. Innovation of the methods is based on the way of searching decomposition, which relies on multiple cutting of an MTBDD diagram describing a multi-output function. The essence of the proposed algorithms rests on the method of unicoding dedicated to sharing resources, searching non-disjoint decomposition on the basis of the partition of root tables, and choosing the levels of diagram cutting that will guarantee the best mapping to complex logic blocks. The methods mentioned above were implemented in the MultiDec tool. The efficiency of the analyzed methods was experimentally confirmed by comparing the synthesis results with both academic and commercial tools.
33 citations
TL;DR: In this article, a magneto-micropolar nanofluid flow with suction or injection in a porous medium over a stretching sheet for the heat and mass transfer is analyzed numerically.
Abstract: *e-mail: me.bilal.786@gmail.com Abstract. In the present article, magneto-micropolar nanofluid flow with suction or injection in a porous medium over a stretching sheet for the heat and mass transfer is analyzed numerically. Both Hall and ion-slip effects are considered along with variable thermal diffusivity. The governing partial differential equations are transformed to ordinary differential equations using usual similarity transformations. These coupled non-linear differential equations are solved using the shooting method. Effects of prominent parameter on velocities, temperature and concentration are discussed graphically. Numerical values of skin-friction coefficient, local Nusselt number and local Sherwood number are also tabulated and discussed.
32 citations
TL;DR: The obtained results show that the early fault diagnostic method can be used for monitoring electrical DC motors and can also support other fault diagnosis methods based on thermal, current, and vibration signals.
Abstract: *e-mail: adglow@agh.edu.pl Abstract. Diagnosis of electrical direct current motors is essential for industrial plants. The emphasis is put on the development of diagnostic methods of solutions for capturing, processing and recognition of diagnostic signals. This paper presents a technique of early fault diagnosis of a DC motor. The proposed approach is based on acoustic signals. A real-world data of the DC motor were used in the analysis. The work provides an original feature extraction method called the shortened method of frequencies selection (SMoFS-15). The obtained results of the presented analysis show that the early fault diagnostic method can be used for monitoring electrical DC motors. The proposed method can also support other fault diagnosis methods based on thermal, current, and vibration signals.
32 citations
TL;DR: An important task of classification is presented, i.e. mapping surfaces which separate patterns in feature space in the scope of radar emitter recognition (RER) and classification, and the author suggests a RER system which consists of a few independent channels.
Abstract: *e-mail: j.dudczyk@wb.com.pl Abstract. This article presents an important task of classification, i.e. mapping surfaces which separate patterns in feature space in the scope of radar emitter recognition (RER) and classification. Assigning a tested radar to a particular class is based on defining its location from the discriminating areas. In order to carry out the classification process, it is necessary to define metrics in the feature space as it is essential to estimate the distance of a classified radar from the centre of the class. The method presented in this article is based on extraction and selection of distinctive features, which can be received in the process of specific emitter identification (SEI) of radar signals, and on the minimum distance classification. The author suggests a RER system which consists of a few independent channels. The task of each channel is to calculate the distance of the tested radar from a given class and finally, set the correct identification coefficient for each recognized radar. Thus, a multichannel system with independent distance measurement is obtained, which makes it possible to recognize particular radar copies. This system is implemented in electronic intelligence (ELINT) system and tested in real battlefield conditions.
31 citations
TL;DR: In this article, a fractional-order model of supercapacitor impedance is proposed to evaluate the IEC standard recommendation on the conditions of superCapacitor capacitance measurements, which probably result from the use of inaccurate dynamics model.
Abstract: At the beginning of the paper the fractional calculus is briefly presented. Then the models of dielectric relaxation in supercapacitors are described. On the basis of the Cole-Cole model a fractional-order model of supercapacitor impedance is formulated. The frequency characteristics of selected supercapacitors and their voltage response to a current step are assumed as basis to the analysis of their dynamics. An example of the fractional dynamic model application was used for a critical assessment of the IEC standard recommendation on the conditions of supercapacitor capacitance measurements. The presented study shows some imperfections of the IEC standard recommendations , which probably result from the use of inaccurate dynamics model. At the end of the paper the authors propose a solution to this problem by changing the measurement conditions and introducing a concept of dynamic c pacit nce. The conclusions of the paper indi ate that the mod ls of frac ional-order dynamics may be useful not only for the control purposes but also in other domains.
29 citations
TL;DR: In this article, a qualitative assessment of the surface morphology based on SEM studies and methodology that allows for quantitative assessment of stereometric structure based on micro-tomographic measurements is presented.
Abstract: *e-mail: joanna.maszybrocka@us.edu.pl Abstract. Construction of metallic implants with a porous structure that mimics the biomechanical properties of bone is one of the challenges of orthopedic regenerative medicine. The selective laser sintering technique (SLS) allows the production of complex geometries based on three-dimensional model, which offers the prospect of preparing porous metal implants, in which stiffness and porosity can be precisely adjusted to the individual needs of the patient. This requires an interdisciplinary approach to design, manufacturing and testing of porous structures manufactured by selective sintering. An important link in this process is the ability to assess the surface topography of the struts of porous structure. The paper presents a qualitative assessment of the surface morphology based on SEM studies and methodology that allows for quantitative assessment of stereometric structure based on micro-tomographic measurements.
27 citations
TL;DR: In this paper, the authors present a necessary aspect in the answer that the construction industry must provide to solve its negative impact on the environment, which is referred to as innovation in construction, where tradition is strongly rooted in society and safety and long term reliability are required.
Abstract: Manuscript submitted 2017-11-23, initially accepted for publication 2017-11-24, published in December 2017. Abstract. Innovation in construction is presented as a necessary aspect in the answer that the construction industry must provide to solve its negative impact on the environment. Original and innovative research is only part of the work to be accomplished. More important is the implementation of innovation in practice, where traditions are strongly rooted in society, and safety and long term reliability are required. Lessons from nature and study of durable examples handed down from the pasts serve as guidelines to innovative approaches that contribute to sustainability.
27 citations
TL;DR: In this article, the Pearson linear correlation coefficients were determined to analyze the relationship between the waviness parameters and the level of vibration, and the test results showed that an increase in the surface WAViness on the inner and outer raceways causes an increase of the vibration level.
Abstract: Manuscript submitted 2016-07-22, revised 2016-12-23, 2017-01-18 and 2017-01-23, initially accepted for publication 2017-01-27, published in August 2017. Abstract. This paper provides a quantitative analysis of how raceway waviness (RONt) in 6304-type bearings affects their vibration. The waviness of bearing races was measured at the actual points of contact between the balls and the races. The measurements were conducted in the range of 16–50 undulations per revolution (UPR). The bearing vibration was analyzed in three bandwidths of frequency: low (LB) (50 ÷ 300 Hz), medium MB (300 ÷ 1800 Hz) and high HB (1800 ÷ 10 000 Hz), as well as in the full RMS bandwidth. The paper also presents the procedure used to determine the actual points of contact between the ball and each race to specify the point of waviness measurement. The method of calculation of the contact angle for a ball bearing is also discussed. The Pearson linear correlation coefficients were determined to analyze the relationships between the waviness parameters and the level of vibration. The test results show that an increase in the surface waviness on the inner and outer raceways causes an increase in the vibration level. The influence is most visible for the medium frequency bandwidth.
TL;DR: In this article, a method for finding the decentralized controller for the class of positive descriptor fractional discrete-time linear systems with different fractional orders is presented. But the method is not suitable for the case of positive descriptors.
Abstract: Positive descriptor fractional discrete-time linear systems with fractional different orders are addressed. Decomposition of the regular pencil is used for extending necessary and sufficient conditions for positivity of the descriptor fractional discrete-time linear system with different fractional orders. Method for finding the decentralized controller for the class of positive systems is given and its effectiveness is demonstrated on numerical example.
TL;DR: It was observed that as the model using ANN provided quite satisfactory results, and that it can be used for online tool wear estimation, which is essential for maintaining the surface quality and minimizing the manufacturing cost.
Abstract: Manuscript submitted 2016-10-05, revised 2017-01-19, 2017-02-15, 2017-02-16 and 2017-02-17, initially accepted for publication 2017-02-17, published in August 2017. Abstract. Nowadays, finishing operation in hardened steel parts which have wide industrial applications is done by hard turning. Cubic boron nitride (CBN) inserts, which are expensive, are used for hard turning. The cheaper coated carbide tool is seen as a substitute for CBN inserts in the hardness range (45–55 HRC). However, tool wear in a coated carbide tool during hard turning is a significant factor that influences the tolerance of machined surface. An online tool wear estimation system is essential for maintaining the surface quality and minimizing the manufacturing cost. In this investigation, the cutting tool wear estimation using artificial neural network (ANN) is proposed. AISI4140 steel hardened to 47 HRC is used as a work piece and a coated carbide tool is the cutting tool. Experimentation is based on full factorial design (FFD) as per design of experiments. The variations in cutting forces and vibrations are measured during the experimentation. Based on the process parameters and measured parameters an ANN-based tool wear estimator is developed. The wear outputs from the ANN model are then tested. It was observed that as the model using ANN provided quite satisfactory results, and that it can be used for online tool wear estimation.
TL;DR: The paper shows that the number of solution granules can be higher than 2 and that in certain problems division does not occur explicitly, and shows how to realize the fuzzy division when its denominator contains zero.
Abstract: Manuscript submitted 2016-01-26, revised 2016-07-08, 2016-10-26 and 2016-12-30, initially accepted for publication 2017-01-20, published in August 2017. Abstract. The paper presents difficulties connected with fuzzy and interval division. If operations such as fuzzy addition, subtraction and multiplication provide as a result one compact, multidimensional granule, then a result of the fuzzy division can consists of few separated granules. Such results are more difficult to use in next calculations. The paper shows that the number of solution granules can be higher than 2 and that in certain problems division does not occur explicitly. In certain problems, separation of particular solution granules can be considerable. The paper also shows how to realize the fuzzy division when its denominator contains zero. Most types of fuzzy arithmetics forbid such operation. However, the paper shows that it is possible. Multidimensional fuzzy RDM arithmetic and horizontal membership functions which facilitate detecting of solution granules are also described. The considered problems are visualized by examples.
TL;DR: Analysis of selected noise reduction methods used in optical coherence tomography (OCT) retina images (the socalled B-scans) includes median and averaging filtering, anisotropic diffusion, soft wavelet thresholding, and multiframe wavelets thresholding.
Abstract: *e-mail: tomasz.marciniak@put.poznan.pl Abstract. This paper presents analysis of selected noise reduction methods used in optical coherence tomography (OCT) retina images (the socalled B-scans). The tested algorithms include median and averaging filtering, anisotropic diffusion, soft wavelet thresholding, and multiframe wavelet thresholding. Precision of the denoising process was evaluated based on the results of automated retina layers segmentation, since this stage (vital for ophthalmic diagnosis) is strongly dependent on the image quality. Experiments were conducted with a set of 3D low quality scans obtained from 10 healthy patients and 10 patients with vitreoretinal pathologies. Influence of each method on the automatic image segmentation for both groups of patients is thoroughly described. Manual annotations of investigated retina layers provided by ophthalmology experts served as reference data for evaluation of the segmentation algorithm.
TL;DR: In this article, a split S-shaped composite meta atom is described, which exhibits double negative characteristics at resonance frequency and exhibits an almost 3.70 GHz bandwidth when the operating frequency from 8 to 14 GHz (X-band).
Abstract: Manuscript submitted 2016-08-30, revised 2016-10-27, initially accepted for publication 2016-11-02, published in August 2017. Abstract. The aim of this paper is to describe a split S-shaped composite meta atom which shows double negative characteristics at resonance frequency. The proposed meta-atom structure exhibits an almost 3.70 GHz bandwidth when the operating frequency from 8 to 14 GHz (X-band). In this study, the ring width, split width, size of substrate material, and the substrate material itself are varying to investigate their effect on the resonance frequencies. Metal strips of the outer resonator are the splits and the inner ring resonator is designed in a way that it forms a split S-shaped structure on the epoxy resin fibre (FR-4) substrate material. The CST Microwave Studio electromagnetic simulator software was used for the design and simulation purposes, and an Agilent N5227A vector network analyser was used for practical measurements.
TL;DR: In this paper, the assessment of marking LED sources with the power of an equivalent light bulb was studied both on the basis of calculations and measurements performed, and the results indicated that for only 4 from among the 13 LED sources studied, the given value of the power may be recognized as in accordance with the actual state of affairs and still with a reservation that specified ambient temperature shall be required.
Abstract: This article presents considerations on the assessment of marking LED sources with the power of an equivalent light bulb. This problem was studied both on the basis of calculations and measurements performed. 17 LEDs of different powers and luminous fluxes were tested. Calculations assessing conformity with the declared power showed that an important disadvantage for most of the LED sources results from the method of marking them with the power of an equivalent light bulb from the point of view of the luminous flux emitted. Manufacturers do not do this correctly, misleading the potential user. Meanwhile, measurements performed in different ambient temperatures indicated that for only 4 from among the 13 LED sources studied the given value of the power of an equivalent light bulb may be recognized as in accordance with the actual state of affairs and still with a reservation that specified ambient temperature shall be required. In other cases the values of power quoted are either understated or overstated.
TL;DR: This paper proposes a new type of interior composite-rotor bearingless permanent magnet synchronous motors (BPMSMs) with two layer permanent magnets (PMs) to reduce the torque ripple of this kind of motors.
Abstract: Manuscript submitted 2016-12-22, revised 2017-02-24 and 2017-03-23, initially accepted for publication 2017-03-24, published in December 2017. Abstract. In this paper, a new type of interior composite-rotor bearingless permanent magnet synchronous motors (BPMSMs) with two layer permanent magnets (PMs) is proposed. In order to reduce the torque ripple of this kind of motors, the sizes of PMs are optimized. Moreover, the magnetic field analysis of the interior composite-rotor BPMSM with two layer PMs is carried out by the finite element method (FEM). The corresponding static electronic magnetic characteristics at no load, including magnetic field, PM flux linkage and inductance, are studied in detail. In addition, electromagnetic torque characteristics and suspension force characteristics are also investigated thoroughly. The results of the analysis and simulation lay a significant foundation for further research on the interior composite-rotor BPMSMs with two layer PMs.
TL;DR: In this article, a modified wet chemical precipitation method is used for HAp synthesis and experiments are performed in batches to observe the effect of cobalt adsorption on HAp matrix.
Abstract: *e-mail: rskhairnarsps@gmail.com Abstract. Cobalt radionuclide is one of the prime contaminants generated during operation of pressurized heavy water. The paper reports the study of cobalt adsorption on hydroxyapatite (HAp) nanoceramic. A modified wet chemical precipitation method is used for HAp synthesis. The HAp nano-material is characterized by XRD, FTIR, TG/DTA, AFM, SEM, and EDAX. Experiments are performed in batches to observe the effect of cobalt adsorption on HAp matrix. The adsorption of cobalt on HAp is examined at room temperature. The isotherm and kinetic studies showed that the Freundlich isotherm and pseudo-second order model are the best choices to describe the nature of adsorption.
TL;DR: An application of the ant algorithm and bees algorithm in optimization of QAP problem as an example of NPhard optimization problem and an influence of particular elements of algorithms, including neighbourhood size and neighbourhood search method will be determined.
Abstract: Manuscript submitted 2016-11-23, revised 2017-01-23, 2017-02-20 and 2017-03-19, initially accepted for publication 2017-03-22, published in August 2017. Abstract. This paper presents an application of the ant algorithm and bees algorithm in optimization of QAP problem as an example of NPhard optimization problem. The experiments with two types of algorithms: the bees algorithm and the ant algorithm were performed for the test instances of the quadratic assignment problem from QAPLIB, designed by Burkard, Karisch and Rendl. On the basis of the experiments results, an influence of particular elements of algorithms, including neighbourhood size and neighbourhood search method, will be determined.
TL;DR: In this article, a duality between stabilizability and detectability is established between the concepts of observability and stabilizeability of a dynamical system, and the concept of controllability is used to simplify the analysis and synthesis of the solution to many problems of control theory.
Abstract: dynamical system are unstable, the concepts of observability and detectability are equivalent. On the other hand, stabilizability means controllability of at least all unstable modes of the dynamical system. Once again, if all modes of the system are unstable, notions of controllability and stabilizability coincide. If the system is stabilizable, it is possible to stabilize it by the appropriate state feedback, whereas if the system is stabilizable and detectable, it is possible to stabilize it by the appropriate output feedback. In the same way as for controllability and observability, there is a formal duality between stabilizability and detectability concepts. Controllability is also strongly related to the theory of realization and so called minimal realization [8–10]. Realization theory makes clear the relationship between input-output description in the operator domain (transfer-function) and statespace representation (system of differential equations) in the time domain. The aim of the minimal state-space realization problem is to find a state-space model of minimal size of the given system. Realization theory has also shown the importance of using the right system model for a particular problem. The transfer function formulation does not reveal the behavior inside the system, such as unobservable unstable modes. Therefore, the transfer function matrix cannot always be used to study the stability properties of the time-invariant systems, since it describes only the controllable and observable part of the dynamical system. This is because of so-called hidden polezero cancellations [11, 4]. Different properties of dynamical systems stand out more clearly in some special descriptions of the system referred to as canonical forms. That is why they are often used to simplify the system analysis and synthesis of the solution to many problems of control theory. Controllability is strongly related to Kalman, Jordan and Luenberger canonical forms for linear time-invariant control systems [3, 12, 13]. Moreover, the concept of controllability plays an important role in determining the solution to the optimal control problem, in particular to the so called minimum energy control problem for many classes of linear finite dimensional, infinite dimensional and delayed dynamical systems, both deterministic and stochastic [14–17]. Therefore, controllability criteria are useful
TL;DR: A new sensorless control structure for the PMSM drive is presented, to utilize as a reference a model of the whole drive, including speed and current controllers and motor model, which produces reference voltage for the real inverter.
Abstract: Manuscript submitted 2016-07-08, revised 2016-10-12, 2016-11-20 and 2017-01-06, initially accepted for publication 2017-01-30, published in August 2017. Abstract. In the paper a new sensorless control structure for the PMSM drive is presented. Such a structure is especially recommended for speed in the range of single revolutions per second (excluding standstill). The method uses a back EMF observer for position estimation. However, there is no need to estimate the speed. This is a big advantage because of possible irregularity of estimated back EMF in this speed range, which makes the calculation of speed difficult or impossible. The proposed structure is similar to the model following control, but the reference model attempts to track the motor operating point. The main idea is to utilize as a reference a model of the whole drive, including speed and current controllers and motor model. Such a model produces reference voltage for the real inverter. However, an extra unit – called rotator – is needed to provide precise control of direct axis current, which is sensitive to the improper position of the voltage vector. The rotator acts as a kind of compensator for error of position estimation.
TL;DR: Wieczorowski et al. as mentioned in this paper applied an elastic-plastic contact model to machined two-process steel textures with a smooth, flat steel surface, and calculated parameters characterizing the summits important in contact mechanics for different sampling intervals.
Abstract: *e-mail: michal.wieczorowski@put.poznan.pl Abstract. Contact of random machined two-process steel textures with a smooth, flat steel surface is discussed in this paper. Two-process surfaces were machined by vapour blasting followed by lapping. An elastic-plastic contact model was applied, assuming distributed radius of asperities. Calculation procedures allowed the mean surface separation, contact pressure, and area fraction to be computed as functions of sampling intervals. Parameters characterizing the summits important in contact mechanics were calculated for different sampling intervals. Plasticity index of two-process textures was calculated using the modified procedure. It was found that the influence of sampling interval on normal contact depended on the rough surface ability to plastic deformation. The use of a traditional method of calculation overestimated the plasticity index. Peaks from plateau surface region governed contact characteristics of two-process surfaces.
TL;DR: This paper investigates the formation control problem of multiple agents and uses the technique of nonlinear disturbance observer to tackle the issue and some simulation results are presented to show the feasibility and validity of the proposed control scheme through a multi-agent platform.
Abstract: *e-mail: dianwei.qian@ncepu.edu.cn Abstract. This paper investigates the formation control problem of multiple agents. The formation control is founded on leader-following approaches. The method of integral sliding mode control is adopted to achieve formation maneuvers of the agents based on the concept of graph theory. Since the agents are subject to uncertainties, the uncertainties also challenge the formation-control design. Under a mild assumption that the uncertainties have an unknown bound, the technique of nonlinear disturbance observer is utilized to tackle the issue. According to a given communication topology, formation stability conditions are investigated by the observer-based integral sliding mode formation control. From the perspective of Lyapunov, not only is the formation stability guaranteed, but the desired formation of the agents is also realized. Finally, some simulation results are presented to show the feasibility and validity of the proposed control scheme through a multi-agent platform.
TL;DR: In this article, the stagnation point flow of electrically conducting micro nanofluid towards a shrinking sheet, considering a chemical reaction of first order is investigated, and the numerical technique is utilized to discuss the results for velocity, microrotation, temperature, and concentration fields.
Abstract: *e-mail: ali_qau70@yahoo.com Abstract. In this article the stagnation point flow of electrically conducting micro nanofluid towards a shrinking sheet, considering a chemical reaction of first order is investigated. Involvement of magnetic field occurs in the momentum equation, whereas the energy and concentrations equations incorporated the influence of thermophoresis and Brownian motion. Convective boundary condition on temperature and zero mass flux condition on concentration are implemented. Partial differential equations are converted into the ordinary ones using suitable variables. The numerical technique is utilized to discuss the results for velocity, microrotation, temperature, and concentration fields.
TL;DR: In this paper, an analytical solution to the problem of time-fractional heat conduction in a sphere consisting of an inner solid sphere and concentric spherical layers is presented.
Abstract: *e-mail: stanislaw.kukla@im.pcz.pl Abstract. An analytical solution to the problem of time-fractional heat conduction in a sphere consisting of an inner solid sphere and concentric spherical layers is presented. In the heat conduction equation, the Caputo time-derivative of fractional order and the Robin boundary condition at the outer surface of the sphere are assumed. The spherical layers are characterized by different material properties and perfect thermal contact is assumed between the layers. The analytical solution to the problem of heat conduction in the sphere for time-dependent surrounding temperature and for time-space-dependent volumetric heat source is derived. Numerical examples are presented to show the effect of the harmonically varying intensity of the heat source and the harmonically varying surrounding temperature on the temperature in the sphere for different orders of the Caputo time-derivative.
TL;DR: Computational experiments show that solutions obtained by the stochastic version of metaheuristics are more stable than solutions generated by classic, deterministic version of the algorithm.
Abstract: *e-mail: wojciech.bozejko@pwr.edu.pl Abstract. We consider a stochastic variant of the single machine total weighted tardiness problem jobs parameters are independent random variables with normal or Erlang distributions. Since even deterministic problem is NP-hard, it is difficult to find global optimum for large instances in the reasonable run time. Therefore, we propose tabu search metaheuristics in this work. Computational experiments show that solutions obtained by the stochastic version of metaheuristics are more stable (i.e. resistant to data disturbance) than solutions generated by classic, deterministic version of the algorithm.
TL;DR: This paper investigates a control structure to enhance the DC fault ride-through capability of a full-bridge modular multilevel converter (MMC) station, while ensuring a stable controlled operation as a STATCOM during DC faults without the need for fault isolation.
Abstract: Manuscript submitted 2017-02-28, initially accepted for publication 2017-06-22, published in October 2017. Abstract. This paper investigates a control structure to enhance the DC fault ride-through capability of a full-bridge modular multilevel converter (MMC) station, while ensuring a stable controlled operation as a STATCOM during DC faults without the need for fault isolation. Taking advantage of the switching states of a full-bridge submodule, a DC current controller is proposed, which provides the DC voltage reference for the modulation when a DC fault is detected. By changing the outer controllers strategy from DC voltage or active power control to converter energy control during a fault, the decoupling of the converter operation from the DC side dynamics is realized. In this paper, the focus is on the control methodology at all times of operation and the evaluation of the STATCOM control during a fault. To this end, extensive simulations were performed on a three-terminal high voltage direct current (HVDC) grid in radial configuration and a pole-to-pole DC fault case was investigated. The results showed that the AC voltage and current were controlled within limits at all times, while the full-bridge MMC was able to provide reactive power support to the AC grid. Moreover, using the proposed control methodology, the transients at the operation transition points between STATCOM and inverter/rectifier operation were minimized and the stations were able to safely ride through the fault.
TL;DR: The aim is to find a schedule with a minimum possible length by studying the case of identical jobs subject to some kind of mutual exclusion constraints modeled by a bipartite incompatibility graph of degree $\Delta".
Abstract: In the paper we consider the problem of scheduling n identical jobs on 4 uniform machines with speeds s1 s2 s3 s4; respectively. Our aim is to find a schedule with a minimum possible length. We assume that jobs are subject to some kind of mutual exclusion constraints modeled by a bipartite incompatibility graph of degree , where two incompatible jobs cannot be processed on the same machine. We show that the problem is NP-hard even if s1 = s2 = s3. If, however, 4 and s1 12s2, s2 = s3 = s4, then the problem can be solved to optimality in time O(n 1:5 ). The same algorithm returns a solution of value at most 2 times optimal provided that s1 2s2. Finally, we study the case s1 s2 s3 = s4 and give an O(n 1:5 )-time 32=15-approximation algorithm in