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Number of results: 42
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Abstract

An intelligent boundary switch is a three-phase outdoor power distribution device equipped with a controller. It is installed at the boundary point on the medium voltage overhead distribution lines. It can automatically remove the single-phase-to-ground fault and isolation phase-to-phase short-circuit fault. Firstly, the structure of an intelligent boundary switch is studied, and then the fault detection principle is also investigated. The single-phase-to-ground fault and phase-to-phase short-circuit fault are studied respectively. A method using overcurrent to judge the short-circuit fault is presented. The characteristics of the single-phase-to-ground fault on an ungrounded distribution system and compositional grounded distribution system are analyzed. Based on these characteristics, a method using zero sequence current to detect the single-phase-to-ground fault is proposed. The research results of this paper give a reference for the specification and use of intelligent boundary switches.
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Abstract

The instability characteristics of a dielectric fluid layer heated from below under the influence of a uniform vertical alternating current (AC) electric field is analyzed for different types of electric potential (constant electric potential/ electric current), velocity (rigid/free) and temperature boundary conditions (constant temperature/heat flux or a mixed condition at the upper boundary). The resulting eigenvalue problem is solved numerically using the shooting method for various boundary conditions and the solution is also found in a simple closed form when the perturbation heat flux is zero at the boundaries. The possibility of a more precise control of electrothermal convection (ETC) through various boundary conditions is emphasized. The effect of increasing AC electric Rayleigh number is to hasten while that of Biot number is to delay the onset of ETC. The system is more stable for rigid-rigid boundaries when compared to rigid-free and least stable for free-free boundaries. The change of electric potential boundary condition at the upper boundary from constant electric potential to constant electric current is found to instill more stability on the system. Besides, increase in the AC electric Rayleigh number and the Biot number is to reduce the size of convection cells.
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Abstract

One of the most effective designs to control the road traffic noise is the T-shaped barrier. The aim of this study was to examine the performance of T-shape noise barriers covered with oblique diffusers using boundary element method. A 2D simulation technique based on the boundary element method (BEM) was used to compute the insertion loss at the center frequency of each one-third octave band. In designed barriers, the top surface of the T-shaped noise barriers was covered with oblique diffusers. The width and height of the barrier stem and the width of its cap were 0.3, 2.7, and 1 m, respectively. Angles of he oblique diffusers were 15, 30, and 45 degrees. The oblique diffusers were placed on the top surface with two designs including same oblique diffusers (SOD) and quadratic residue oblique diffusers (QROD). Barriers considered were made of concrete, an acoustically rigid material. The barrier with characteristics of QROD, forward direction, and sequence of angles (15, 30, and 45 degrees) had the greatest value of the overall A-weighted insertion loss equal to 18.3 to 21.8 dBA at a distance of 20 m with various heights of 0 to 6 m.
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Abstract

In this paper a three-dimensional model for determination of a microreactor's length is presented and discussed. The reaction of thermocatalytic decomposition has been implemented on the base of experimental data. Simplified Reynolds-Maxwell formula for the slip velocity boundary condition has been analysed and validated. The influence of the Knudsen diffusion on the microreactor's performance has also been verified. It was revealed that with a given operating conditions and a given geometry of the microreactor, there is no need for application of slip boundary conditions and the Knudsen diffusion in further analysis. It has also been shown that the microreactor's length could be practically estimated using standard models.
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Abstract

Instantaneous acoustic heating of a viscous fluid flow in a boundary layer is the subject of investigation. The governing equation of acoustic heating is derived by means of a special linear combination of conservation equations in the differential form, which reduces all acoustic terms in the linear part of the final equation but preserves terms belonging to the thermal mode. The procedure of decomposition is valid in a weakly nonlinear flow, it yields the nonlinear terms responsible for the modes interaction. Nonlinear acoustic terms form a source of acoustic heating in the case of the dominative sound. This acoustic source reflects the thermoviscous and dispersive properties of a fluid flow. The method of deriving the governing equations does not need averaging over the sound period, and the final governing dynamic equation of the thermal mode is instantaneous. Some examples of acoustic heating are illustrated and discussed, and conclusions about efficiency of heating caused by different waveforms of sound are made.
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Abstract

In this article the authors investigated and presented the experiments on the sentence boundaries annotation from Polish speech using acoustic cues as a source of information. The main result of the investigation is an algorithm for detection of the syntactic boundaries appearing in the places of punctuation marks. In the first stage, the algorithm detects pauses and divides a speech signal into segments. In the second stage, it verifies the configuration of acoustic features and puts hypotheses of the positions of punctuation marks. Classification is performed with parameters describing phone duration and energy, speaking rate, fundamental frequency contours and frequency bands. The best results were achieved for Naive Bayes classifier. The efficiency of the algorithm is 52% precision and 98% recall. Another significant outcome of the research is statistical models of acoustic cues correlated with punctuation in spoken Polish.
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Abstract

This paper presents an overview of basic concepts, features and difficulties of the boundary element method (BEM) and examples of its application to exterior and interior problems. The basic concepts of the BEM are explained firstly, and different methods for treating the non-uniqueness problem are described. The application of the BEM to half-space problems is feasible by considering a Green's Function that satisfies the boundary condition on the infinite plane. As a special interior problem, the sound field in an ultrasonic homogenizer is computed. A combination of the BEM and the finite element method (FEM) for treating the problem of acoustic-structure interaction is also described. Finally, variants of the BEM are presented, which can be applied to problems arising in flow acoustics.
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Abstract

Excitation of the entropy mode in the field of intense sound, that is, acoustic heating, is theoretically considered in this work. The dynamic equation for an excess density which specifies the entropy mode, has been obtained by means of the method of projections. It takes the form of the diffusion equation with an acoustic driving force which is quadratically nonlinear in the leading order. The diffusion coefficient is proportional to the thermal conduction, and the acoustic force is proportional to the total attenuation. Theoretical description of instantaneous heating allows to take into account aperiodic and impulsive sounds. Acoustic heating in a half-space and in a planar resonator is discussed. The aim of this study is to evaluate acoustic heating and determine the contribution of thermal conduction and mechanical viscosity in different boundary problems. The conclusions are drawn for the Dirichlet and Neumann boundary conditions. The instantaneous dynamic equation for variations in temperature, which specifies the entropy mode, is solved analytically for some types of acoustic exciters. The results show variation in temperature as a function of time and distance from the boundary for different boundary conditions.
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Abstract

An isogeometric boundary element method is applied to simulate wave scattering problems governed by the Helmholtz equation. The NURBS (non-uniform rational B-splines) widely used in the CAD (computer aided design) field is applied to represent the geometric model and approximate physical field variables. The Burton-Miller formulation is used to overcome the fictitious frequency problem when using a single Helmholtz boundary integral equation for exterior boundary-value problems. The singular integrals existing in Burton-Miller formulation are evaluated directly and accurately using Hadamard’s finite part integration. Fast multipole method is applied to accelerate the solution of the system of equations. It is demonstrated that the isogeometric boundary element method based on NURBS performs better than the conventional approach based on Lagrange basis functions in terms of accuracy, and the use of the fast multipole method both retains the accuracy for isogeometric boundary element method and reduces the computational cost.
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Abstract

During the 1920s and 1930s Gdynia transformed from a small fishing village into a dynamically developing city through the construction in its vicinity of the largest seaport of interwar Poland. The city’s first expansion plan (1926, Adam Kuncewicz, Roman Feliński), designed for approximately 100 000 inhabitants, had to be revised already within a few years because development of the port has proved to be faster and the terrain requirements of the port substantially greater than originally predicted. In effect grounds originally planned for general city functions were yielded to the rapidly developing port. It was not until 2003 when the port boundaries shifted significantly as a result of restrictions and changes in the nature of port activity. These changes freed around 53 ha of post-harbour sites for new development, attractively located in the immediate vicinity of the existing city centre and waterfront. In 2015 the port boundaries shifted again adding 3 ha more of post-harbour sites. The changes also spurred investment in the north of downtown Gdynia – in accordance with the intentions of first city planners. Ideas how to make good use of post-harbour areas have been invented and evolved since 1990s. The concept which is currently under development was prepared in 2008 by the City Planning Offi ce of Gdynia. Since 2010 analyses and studies of future development have been conducted using 3D model. The concept is continuously updated and new details are added based on projects obtained through architectural competitions. Since 2015 development areas of the northern part of the city center were rebranded as Gdynia Sea City. In accordance with this concept Gdynia Sea City will be the modern city centre with areas designed for leisure, relaxation and business and will be inhabited by more than 10 thousand people. The area’s new grid is a continuation of the urban grid of historical downtown Gdynia and draws upon unrealized city plans of the interwar period. The scale of new buildings in the area is reminiscent of the historical buildings in the area. Groups of higher buildings are allowed outside of a protected area of the historic center, in areas selected through view and cityscape analysis. The residential and commercial complex Sea Towers together with two other newly constructed tall buildings is currently the dominant in this area. Several new development complexes are under construction. Planning concepts assume public availability of quays around the port basins and maintaining spacious openings towards the sea. Construction of marinas is expected using part of the docks and the ability to expand and reduce existing wharves, movement of pedestrians and cyclists between Fishermen Pier and South Pier will be facilitated through the construction of a bridge or a ferry connection. The planned enlargement into the post-harbour areas will double the current potential of Gdynia downtown, and enlarge the scope of representative areas and change the panorama from the historic city center and from the sea. Attractive downtown sites can provide an answer to the issue of uncontrolled urban spill into peripheral areas of adjacent municipalities.
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Abstract

The cuboidal room acoustics field is modelled with the Fourier method. A combination of uniform, impedance boundary conditions imposed on walls is assumed, and they are expressed by absorption coefficient values. The absorption coefficient, in the full range of its values in the discrete form, is considered. With above assumptions, the formula for a rough estimation of the cuboidal room acoustics is derived. This approximate formula expresses the mean sound pressure level as a function of the absorption coefficient, frequency, and volume of the room separately. It is derived based on the least-squares approximation theory and it is a novelty in the cuboidal room acoustics. Theoretical considerations are illustrated via numerical calculations performed for the 3D acoustic problem. Quantitative results received with the help of the approximate formula may be a point of reference to the numerical calculations.
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Abstract

The paper presents a tool for accurate evaluation of high field concentrations near singular lines, such as contours of cracks, notches and grains intersections, in 3D problems solved the BEM. Two types of boundary elements, accounting for singularities, are considered: (i) edge elements, which adjoin a singular line, and (ii) intermediate elements, which while not adjoining the line, are still under strong influence of the singularity. An efficient method to evaluate the influence coefficients and the field intensity factors is suggested for the both types of the elements. The method avoids time expensive numerical evaluation of singular and hypersingular integrals over the element surface by reduction to 1D integrals. The method being general, its details are explained by considering a representative examples for elasticity problems for a piece-wise homogeneous medium with cracks, inclusions and pores. Numerical examples for plane elements illustrate the exposition. The method can be extended for curvilinear elements.
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Abstract

A hybrid artificial boundary condition (HABC) that combines the volume-based acoustic damping layer (ADL) and the local face-based characteristic boundary condition (CBC) is presented to enhance the absorption of acoustic waves near the computational boundaries. This method is applied to the prediction of aerodynamic noise from a circular cylinder immersed in uniform compressible viscous flow. Different ADLs are designed to assess their effectiveness whereby the effect of the mesh-stretch direction on wave absorption in the ADL is analysed. Large eddy simulation (LES) and FW-H acoustic analogy method are implemented to predict the far-field noise, and the sensitivities of each approach to the HABC are compared. In the LES computed propagation field of the fluctuation pressure and the frequency-domain results, the spurious reflections at edges are found to be significantly eliminated by the HABC through the effective dissipation of incident waves along the wave-front direction in the ADL. Thereby, the LES results are found to be in a good agreement with the acoustic pressure predicted using FW-H method, which is observed to be just affected slightly by reflected waves.
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Abstract

During fieldwork in the early 1990s at the then still active quarry near Nasiłów, on the left bank of the River Vistula (Wisła), accompanied by Professor Andrzej Radwański, some lobster remains were collected. A fragmentary anterior portion of a decapod crustacean carapace, recovered from a level about 2 m below the Cretaceous–Paleogene (K/Pg) boundary, in a siliceous chalk unit locally referred to as ‘opoka’, constitutes the oldest record of the thaumastocheliform genus Dinochelus Ahyong, Chan and Bouchet, 2010, D. radwanskii sp. nov. The other, more complete, individual is from c. 3 m above the K/Pg boundary, coming from marly gaizes or ‘siwak’; this is ascribed to a new species of Hoploparia M’Coy, 1849, H. nasilowensis sp. nov., the first to be recorded from Danian (lower Paleocene) strata. Although both ‘opoka’ and ‘siwak’ facies in the Nasiłów area are very rich in diverse biota, including some brachyurans, no macruran remains had so far been recorded from the region.
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Abstract

A parcel is the most important object of real estate cadastre. Its primary spatial attribute are boundaries, determining the extent of property rights. Capturing the data on boundaries should be performed in the way ensuring sufficiently high accuracy and reliability. In recent years, as part of the project “ZSIN – Construction of Integrated Real Estate Information System – Stage I”, in the territories of the participating districts, actions were taken aimed at the modernization of the register of land and buildings. In many cases, this process was carried out basing on photogrammetric materials. Applicable regulations allow such a possibility. This paper, basing on the documentation from the National Geodetic and Cartographic Documentation Center and on the authors’ own surveys attempts to assess the applicability of the photogrammetric method to capture data on the boundaries of cadastral parcels. The scope of the research, most importantly, included the problem of accuracy with which it was possible to determine the position of a boundary point using photogrammetric surveys carried out on the terrain model created from processed aerial photographs. The article demonstrates the manner of recording this information in the cadastral database, as well as the resulting legal consequences. Moreover, the level of reliability of the entered values of the selected attributes of boundary points was assessed.
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Abstract

The paper contains a description of a multiscale algorithm based on the boundary element method (BEM) coupled with a discrete atomistic model. The atomic model uses empirical pair-wise potentials to describe interactions between atoms. The Newton-Raphson method is applied to solve a nanoscale model. The continuum domain is modelled by using BEM. The application of BEM reduces the total number of degrees of freedom in the multiscale model. Some numerical results of simulations at the nanoscale are shown to examine the presented algorithm.
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Abstract

Directional excitation of sound in an aperiodic finite baffle system is analyzed using a method developed earlier in electrostatics. The solution to the corresponding boundary value problem is obtained in the spatial-frequency domain. The acoustic pressure and normal particle velocity distribution in acoustic media can be easily computed by the inverse Fourier transform from their spatial spectra on the baffle plane. The presented method can be used for linear acoustic phased arrays modeling with finite element size and inter-element interactions taken into account. Some illustrative numerical examples presenting the far-field radiation pattern and wave-beam steering are given.
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Abstract

In slowly flaring horns the wave fronts can be considered approximately plane and the input impedance can be calculated with the transmission line method (short cones in series). In a rapidly flaring horn the kinetic energy of transverse flow adds to the local inertance, resulting in an effective increase in length when it is located in a pressure node. For low frequencies corrections are available. These fail at higher frequencies when cross-dimensions become comparable to the wavelength, causing resonances in the cross-direction. To investigate this, the pipe radiating in outer space is modelled with a finite difference method. The outer boundaries must be fully absorbing as the walls of an anechoic chamber. To achieve this, Berenger's perfectly matched layer technique is applied. Results are presented for conical horns, they are compared with earlier published investigations on flanges. The input impedance changes when the largest cross-dimension (outer diameter of flange or diameter of the horn end) becomes comparable to half a wavelength. This effect shifts the position of higher modes in the pipe, influencing the conditions for mode locking, important for ease of playing, dynamic range and sound quality.
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Abstract

The objective of the present research is to develop the novel multi-compaction technology to produce hybrid structure in powder metallurgy (P/M) components using dissimilar Fe-based alloys. Two distinct powder alloys with different compositions were are used in this study: Fe-Cr-Mo-C pre-alloyed powder for high strength and Fe-Cu-C mixed powder for enhanced machinability and lower material cost. Initially, Fe-Cu-C was pre-compacted using a bar-shaped die with lower compaction pressure. The green compact of Fe-Cu-C alloy was inserted into a die residing a half of the die, and another half of the die was filled with the Fe-Cr-Mo-C powder. Then they subsequently underwent re-compaction with higher pressure. The final compact was sintered at 1120°C for 60 min. In order to determine the mechanical behavior, transverse rupture strength (TRS) and Vickers hardness of sintered materials were measured and correlated with density variations. The microstructure was characterized using optical microscope and scanning electron microscope to investigate the interfacial characteristics between dissimilar P/M alloys.
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Abstract

Presented work considers flow and thermal phenomena occurring during the single minijet impingement on curved surfaces, heated with a constant heat flux, as well as the array of minijets. Numerical analyses, based on the mass, momentum and energy conservation laws, were conducted, regarding single phase and two-phase simulations. Focus was placed on the proper model construction, in which turbulence and boundary layer modeling was crucial. Calculations were done for various inlet parameters. Initial single minijet results served as the basis for the main calculations, which were conducted for two jet arrays, with flat and curved heated surfaces. Such complex geometries came from the cooling systems of electrical devices, and the geometry of cylindrical heat exchanger. The results, regarding Nusselt number, heated surface temperature, turbulence kinetic energy, production of entropy and vorticity, were presented and discussed. For assumed geometrical parameters similar results were obtained.
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Abstract

The grain boundary wetting phase transition in an industrial EZ33A cast alloy is studied. 12% of the grain boundaries are completely wetted at the temperature slightly higher than the eutectic transformation temperature (530°C). The fraction of wetted grain boundaries increases with temperature, reaches a maximum of 85% at 570°C, and does not change further until the alloy melts. In the as-cast state, the alloy has low ductile properties at the ambient temperature. The microstructure in the as-cast state corresponds to the wetting state at about 560°C, which indicates that the cooling rate in casting is almost equal to that in quenching. The volume and the surface fraction of the second phase and the hardness measured at the least wetted state of samples point to its good machinability. The wetting data are used to suggest a sequence of heat treatment and machining for processing EZ33A alloy parts.
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Abstract

Steady state two-dimensional numerical simulation of laminar heat transfer and fluid flow in a scraped surface heat exchanger (SSHE) is presented. Typical SSHE consists of a stator, rotating shaft and scraping blades. Due to symmetry only a quarter of the heat exchanger is modelled. Governing equations for transport of mass, momentum and energy are discretised and solved with the use of commercial CFD code. The results are presented in a nondimensional form for velocity, pressure and temperature distributions. Local and averaged Nusselt number along the stator wall are calculated and depicted in graphs. It was found that the thirty fold increase of the cReynolds number, leads to heat transfer enhancement rate by three times.
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