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Wyświetlanie 1-15 z 207
Tytuł:
The experimental identification of the dynamic coefficients of two hydrodynamic journal bearings operating at constant rotational speed and under nonlinear conditions
Autorzy:
Breńkacz, Ł.
Żywica, G.
Drosińska-Komor, M.
Powiązania:
https://bibliotekanauki.pl/articles/259675.pdf
Data publikacji:
2017
Wydawca:
Politechnika Gdańska. Wydział Inżynierii Mechanicznej i Okrętownictwa
Tematy:
bearing dynamic coefficients
experimental research
nonlinear coefficients
impact excitation
hydrodynamic bearing
Opis:
Hydrodynamic bearings are commonly used in ship propulsion systems. Typically, they are calculated using numerical or experimental methods. This paper presents an experimental study through which it has been possible to estimate 24 dynamic coefficients of two hydrodynamic slide bearings operating under nonlinear conditions. During the investigation, bearing mass coefficients are identified by means of a newly developed algorithm. An impact hammer was used to excite vibration of the shaft. The approximation by means of the least squares method was applied to determine bearing dynamic coefficients. Based on the performed research, the four (i.e. two main and two crosscoupled) coefficients of stiffness, damping and mass for each bearing were obtained. The mass coefficients add up to the complex shaft weight. These values are not required for modeling dynamics of the machine because the rotor mass is usually known, however, they may serve as a good indicator to validate the correctness of the stiffness and damping coefficients determined. Additionally, the experimental research procedure was described. The signals of displacements in the bearings and the excitation forces used for determination of the bearing dynamic coefficients were shown. The study discussed in this article is about a rotor supported by two hydrodynamic bearings operating in a nonlinear manner. On the basis of computations, the results of bearing dynamic coefficients were presented for a selected speed.
Źródło:
Polish Maritime Research; 2017, 4; 108-115
1233-2585
Pojawia się w:
Polish Maritime Research
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Various signs in asymmetry coefficiens in empirical distributions
O różnych znakach współczynników asymetrii w rozkładach empirycznych
Autorzy:
Wesołowska-Janczarek, M.
Kornacki, A.
Powiązania:
https://bibliotekanauki.pl/articles/2052019.pdf
Data publikacji:
2016
Wydawca:
Akademia Bialska Nauk Stosowanych im. Jana Pawła II w Białej Podlaskiej
Tematy:
empirical distributions
coefficients of asymmetry As and γ
signs of coefficients
Opis:
Subject and purpose of work: The work concerns coefficients of asymmetry As and γ the values of which are marked based on coefficients obtained from the sample and serve the description of empirical distributions. These coefficients inform of the strength and direction of asymmetry of distribution. The direction is ruled by the sign of coefficient while the strength-by its absolute value. Since for certain empirical distributions these coefficients have different signs an attemt was made to define the conditions in which such a situation may occur. Materials and methods: Within the conducted research different examples of empirical distributions were considered and simulation methods were applied to establish the condition for occurrence of various signs, including coefficients. This condition is based on the location of arithmetical mean of observation in terms of the range , where D is a dominant of data set and Z is a certain volume also indicated on the basis of the same set of observations. Results: As a result of conducted research it was agreed that both analysed coefficients of asymmetry have the same signs where arithmetical mean is located inside the range and different when it is located outside this range. Conclusions: Within the specific research of the selected feature one should calculate only one of these coefficients.
Przedmiot i cel pracy: Praca dotyczy współczynników asymetrii As i γ , których wartości wyznaczane są na podstawie wyników uzyskanych z próby, i służą do opisu empirycznych rozkładów. Współczynniki te informują o sile i kierunku asymetrii rozkładu. O kierunku decyduje znak współczynnika, a o sile jego wartość bezwzględna. Ponieważ dla pewnych rozkładów empirycznych współczynniki te mają różne znaki podjęto próbę określenia warunków w jakich taka sytuacja może mieć miejsce. Materiały i metody: W przeprowadzonych badaniach uwzględniono różne przykłady rozkładów empirycznych i symulacyjnymi metodami ustalono warunek występowania różnych znaków tych współczynników. Warunek ten opiera się na położeniu średniej arytmetycznej obserwacji względem przedziału , gdzie D jest dominantą zbioru danych, a Z pewną wielkością także wyznaczoną na podstawie tego samego zbioru obserwacji. Wyniki: W wyniku przeprowadzonych badań ustalono, że oba rozważane współczynniki asymetrii mają te same znaki, gdy średnia arytmetyczna znajduje się wewnątrz tego przedziału, a różne wtedy gdy leży poza tym przedziałem. Wnioski: W konkretnym badaniu wybranej cechy należy obliczać tylko jeden z tych współczynników.
Źródło:
Economic and Regional Studies; 2016, 09, 1; 63-67
2083-3725
2451-182X
Pojawia się w:
Economic and Regional Studies
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Resource Tuned Optimal Random Network Coding for Single Hop Multicast future 5G Networks
Autorzy:
Dong, Dhawa Sang
Pokhrel, Yagnya Murti
Gachhadar, Anand
Qamar, Faizan
Amiri, Iraj Sadegh
Maharjan, Ram Krishna
Powiązania:
https://bibliotekanauki.pl/articles/226605.pdf
Data publikacji:
2019
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
coding coefficients
computational complexity
lower triangular matrix
random network coding
sparse coding
coefficients
Opis:
Optimal random network coding is reduced complexity in computation of coding coefficients, computation of encoded packets and coefficients are such that minimal transmission bandwidth is enough to transmit coding coefficient to the destinations and decoding process can be carried out as soon as encoded packets are started being received at the destination and decoding process has lower computational complexity. But in traditional random network coding, decoding process is possible only after receiving all encoded packets at receiving nodes. Optimal random network coding also reduces the cost of computation. In this research work, coding coefficient matrix size is determined by the size of layers which defines the number of symbols or packets being involved in coding process. Coding coefficient matrix elements are defined such that it has minimal operations of addition and multiplication during coding and decoding process reducing computational complexity by introducing sparseness in coding coefficients and partial decoding is also possible with the given coding coefficient matrix with systematic sparseness in coding coefficients resulting lower triangular coding coefficients matrix. For the optimal utility of computational resources, depending upon the computational resources unoccupied such as memory available resources budget tuned windowing size is used to define the size of the coefficient matrix.
Źródło:
International Journal of Electronics and Telecommunications; 2019, 65, 3; 463-469
2300-1933
Pojawia się w:
International Journal of Electronics and Telecommunications
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Variability in and correlations among selected physical properties of European larch (Larix decidua Mill.) seeds
Autorzy:
Kaliniewicz, Z.
Tylek, P.
Anders, A.
Markowski, P.
Rawa, T.
Powiązania:
https://bibliotekanauki.pl/articles/297835.pdf
Data publikacji:
2014
Wydawca:
Uniwersytet Warmińsko-Mazurski w Olsztynie
Tematy:
seeds
physical properties
coefficients
correlation
Opis:
Selected physical attributes of European larch seeds harvested from 2 seed plantations and 2 commercial seed stands in north-eastern Poland were determined. The physical properties of seeds were measured, and the results were used to calculate indicators of seed weight and the frictional and geometric properties of seeds. Physical attributes and indicators were compared by Student’s t-test for independent samples, analysis of variance, correlation analysis and linear regression analysis. The average values of physical properties and indicators were determined at: critical transport velocity - from 5.93 to 6.13 m • s-1, thickness - from 1.25 to 1.43 mm, width - from 2.29 to 2.71 mm, length - from 3.71 to 4.57 mm, angle of sliding friction - from 27.85 to 31.98o, weight - from 4.03 to 6.14 mg, coefficient of sliding friction - from 0.54 to 0.63, arithmetic mean diameter - from 2.42 to 2.90 mm, geometric mean diameter - from 2.20 to 2.60 mm, aspect ratio - from 59.60 to 62.38%, sphericity index - from 57.27 to 59.40%, specific weight - from 1.81 to 2.33 g • m-1, volume - from 4.60 to 7.59 mm3 and density - from 0.82 to 0.91 g • cm-3. The material harvested in seed plantations differed from seeds from commercial seed stands in all parameters, excluding critical transport velocity. Seed weight was most correlated with the remaining parameters. The highest value of the correlation coefficient and the equation with the highest value of the coefficient of determination were reported for the dependence between seed weight and seed length. Seed weight was also relatively highly correlated with seed width, therefore, the use of mesh screens with round openings and/or cylindrical grain graders is recommended in seed sorting processes.
Źródło:
Technical Sciences / University of Warmia and Mazury in Olsztyn; 2014, 17(2); 123-134
1505-4675
2083-4527
Pojawia się w:
Technical Sciences / University of Warmia and Mazury in Olsztyn
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Coefficients of shear correction in transveresly nonhomogeneous moderately thick plates
Autorzy:
Jemielita, G.
Powiązania:
https://bibliotekanauki.pl/articles/282079.pdf
Data publikacji:
2002
Wydawca:
Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:
moderately thick plates
shear coefficients
Opis:
A method of determination of the shear stiffness of an anisotropic nonhomogeneous plate of moderate thickness has been presented in the paper. The set of shear coefficients for the plates has been formulated and determined by the author.
Współczynniki ścinania poprzecznie niejednorodnych płyt średniej grubości. W pracy przedstawiono sposób wyznaczania współczynników ścinania anizotropowych, poprzecznie niejednorodnych płyt średniej grubości o poprzecznrej niejednorodności. Korzystając z założeń kinematycznych Hencky-Bolle'a podano podstawowe równania teorii płyt średniej grubości. Korzystając z zasady równoważności prac wirtualnych wyznaczono wzory na współczynniki ścinania i podano ich jawną postać.
Źródło:
Journal of Theoretical and Applied Mechanics; 2002, 40, 1; 73-84
1429-2955
Pojawia się w:
Journal of Theoretical and Applied Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Experimental and numerical determination of the hydrodynamic coefficients of an autonomous underwater vehicle
Autorzy:
Sakaki, Abdollah
Kerdabadi, Mohsen Sadeghian
Powiązania:
https://bibliotekanauki.pl/articles/135543.pdf
Data publikacji:
2020
Wydawca:
Akademia Morska w Szczecinie. Wydawnictwo AMSz
Tematy:
Reynolds averaged Navier–Stokes
computational fluid dynamics
linear coefficients
non-linear coefficients
underwater vehicle
Opis:
Computational fluid dynamics (CFD) has progressed rapidly in the past fifty years and is now used in many industrial fields, such as air, space, and marine engineering. CFD has an irreplaceable role in marine design and scientific research, and its applications within this field continue to grow with the development of computers. CFD is used to quickly and inexpensively simulate fluid behaviour using the Reynolds Averaged Navier–Stokes (RANS) equations to calculate hydrodynamic coefficients, which are needed in manoeuvrability studies of underwater vehicles (UWV). Here, these computations are performed for six geometrical shapes that represent typical autonomous underwater vehicles (AUVs) currently in use. Resistance test simulations at up to 20o drift angles were conducted for AUVs with different length-to-diameter ratios. The results were compared with the experimental data and current quasi-experimental relationships, which suggested that the CFD predictions were adequately precise and accurate. These predictions indicated that there was a non-linear relationship between forces and moments and the lateral speed. Moreover, both linear and non-linear hydrodynamic coefficients were calculated.
Źródło:
Zeszyty Naukowe Akademii Morskiej w Szczecinie; 2020, 62 (134); 124-135
1733-8670
2392-0378
Pojawia się w:
Zeszyty Naukowe Akademii Morskiej w Szczecinie
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Efficient Calculation of the Reed-Muller Form by Means of the Walsh Transform
Autorzy:
Porwik, P.
Powiązania:
https://bibliotekanauki.pl/articles/908505.pdf
Data publikacji:
2002
Wydawca:
Uniwersytet Zielonogórski. Oficyna Wydawnicza
Tematy:
informatyka
Reed-Muller coefficients
Walsh coefficients
coefficient distribution
Boolean function
synthesis of Boolean functions
Opis:
The paper describes a spectral method for combinational logic synthesis using the Walsh transform and the Reed-Muller form. A new algorithm is presented that allows us to obtain the mixed polarity Reed-Muller expansion of Boolean functions. The most popular minimisation (sub-minimisation) criterion of the Reed-Muller form is obtained by the exhaustive search of all the polarity vectors. This paper presents a non-exhaustive method for Reed-Muller expansions. The new method allows us to build the Reed-Muller form based on the analysis of Walsh-Hadamard coefficients. The presented method has much less complexity than the procedures which have been applied until now. Both the transforms and the presented Walsh-Hadamard spectral characterization of the Reed-Muller expansion are compared. An analysis of the properties of the spectra obtained from these transforms is made.
Źródło:
International Journal of Applied Mathematics and Computer Science; 2002, 12, 4; 571-579
1641-876X
2083-8492
Pojawia się w:
International Journal of Applied Mathematics and Computer Science
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The models for the comparison of roundness profiles
Autorzy:
Tichá, S.
Adamczak, S.
Powiązania:
https://bibliotekanauki.pl/articles/384343.pdf
Data publikacji:
2012
Wydawca:
Sieć Badawcza Łukasiewicz - Przemysłowy Instytut Automatyki i Pomiarów
Tematy:
roundness
correlation coefficients
mathematical models
comparison
Opis:
Roundness is one of the mostly frequently observed geometrical deviations. A profile of a machine part consisting of simple harmonic courses or their sums depends on a number of factors. Modeling of geometrical deviations requires applying the Fourier to extend each periodical function into an infinite series of harmonic components. Using of harmonic analysis we are able to determine the values of amplitudes of single components and their phase shifts. These parameters can be used for example for comparison of roundness profiles by means of correlation coefficients. The obtained correlation coefficients are concrete parameters, on the basis of which it is possible to determine the degree of conformity and unity between the compared profiles. The comparison of evaluated roundness profiles can be represented as mathematical statistical models. In these models is detected sequence of single steps, which are necessary for determination of required correlation coefficients [1, 2] .
Źródło:
Journal of Automation Mobile Robotics and Intelligent Systems; 2012, 6, 3; 27-29
1897-8649
2080-2145
Pojawia się w:
Journal of Automation Mobile Robotics and Intelligent Systems
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On the asymptotic behavior of thermal Taylor dispersion processes in periodic media
O asymptotycznej naturze procesu termicznej dyspersji Taylora w ośrodkach periodycznych
Autorzy:
Timofte, C.
Powiązania:
https://bibliotekanauki.pl/articles/281111.pdf
Data publikacji:
2003
Wydawca:
Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:
macrotransport equation
macroscale coefficients
scale parameters
Opis:
Using the generalized method of moments and a central limit theorem, we shall describe a large class of thermal dispersion phenomena occurring in some macrohomogeneous systems. We shall be interested in computing the macroscale coefficients in terms of the microscale coefficients and the system geometry. Also, the functional dependence of the effective coefficients on the velocity and the spatial scale parameters is analyzed.
W pracy dokonano przeglądu szerokiej klasy zjawisk związanych z termiczną dyspersją w wybranych układach jednorodnych w skali makro. W opisie wykorzystano uogólnioną metodę momentów i twierdzenie o granicy centralnej. Jako szczególnie interesujący przedstawiono problem obliczania współczynników makroskali w funkcji współczynników mikroskali i geometrii badanego układu. Ponadto przeanalizowano funkcjonalną zależność współczynników efektywnych od pola prędkości i przestrzennych parametrów skali.
Źródło:
Journal of Theoretical and Applied Mechanics; 2003, 41, 1; 75-88
1429-2955
Pojawia się w:
Journal of Theoretical and Applied Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Determination of pseudo-viscosity coefficients for visco-elastic lubricants
Autorzy:
Wierzcholski, K.
Powiązania:
https://bibliotekanauki.pl/articles/247504.pdf
Data publikacji:
2010
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
pseudo elastic coefficients
method of determination
Opis:
In this paper we assume determination of pseudo-viscosity coefficients of visco-elastic non-Newtonian fluid flow directly near the cooperating micro-bearing surface. We show the constitutive stress-strain dependencies of non-Newtonian visco-elastic media with regard to the content of addition of nano-particles. The greater content of nano-particles and influences of superficial layer of cooperating surfaces on the dynamic oil viscosity, the more distinct non-Newtonian properties. The non-Newtonian properties create non-linear dependencies between strain and stress. Moreover the dynamic viscosity or apparent dynamic viscosity of oil often decreases along with shear rate increasing during motion. dynamic viscosity of oil inside very thin boundary layers depends on Young's modulus of the cell body being in contact with the oil. Considered visco-elastic oils with nano-particles have non-Newtonian pseudo-plastic properties, described in the beginning by means of Rivlin-Ericksen constitutive relations. Hence their stress-strain dependencies presented in this paper have the modified Rivlin-Ericksen form. Scientific efforts brought into this elaboration represent an impact to the considered domain by providing for some data on comparisons between boundary conditions for lubrication flow in super thin boundary layer lying on the external surface of biological cells of joint cartilage and boundary conditions for lubrication of micro-bearing of shaft diameter smaller than 2 mm.
Źródło:
Journal of KONES; 2010, 17, 2; 491-496
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Wpływ parametrów systemu budowlano-instalacyjnego na wskaźniki energetyczne budynków jednorodzinnych
Influence of building-installation system parameters on the building energetic coefficients
Autorzy:
Wójcikiewicz, M.
Sanytsky, M.
Sekret, R.
Powiązania:
https://bibliotekanauki.pl/articles/271072.pdf
Data publikacji:
2010
Wydawca:
Centralny Ośrodek Badawczo-Rozwojowy Aparatury Badawczej i Dydaktycznej, COBRABiD
Tematy:
budownictwo
wskaźniki energetyczne
buildings
energetic coefficients
Opis:
W artykule przedstawiono wyniki badań, dotyczących wpływu parametrów systemu budowlano-instalacyjnego na wartość wskaźników energetycznych budynków jednorodzinnych. Do przeprowadzenia analizy przyjęto trzy rodzaje budynków: standardowy, energooszczędny oraz pasywny. Wśród tych kategorii przyjęto dodatkowo trzy powierzchnie użytkowe, tj. 100 m2,150 m2 i 200 m2. Wymienione kategorie budynków różnią się między sobą izolacyjnością przegród zewnętrznych pełnych i przeszklonych oraz sprawnością użytkową systemu ogrzewczego. Do porównania wytypowanych obiektów wykorzystano bilans energetyczny, oparty o metodologię wykonywania świadectw charakterystyki energetycznej budynków. Przedstawiono ponadto modele matematyczne wpływu parametrów przegród zewnętrznych omawianych budynków oraz powierzchni ogrzewanej na ich wskaźniki energetyczne, tj. zapotrzebowanie na energię końcową Ek i energię pierwotną Ep.
In this paper experimental results of influence of building-installation system parameters on the building energetic coefficients are presented. Three types of buildings: standard, energy-saving and passive with heating surface of 100 m2,150 m2 i 200 m2 have been used. The above types of buildings differ on thermal barrier and heating system efficiency. Certificate for energy characteristic of building has been used. Mathematics models of influence of thermal barrier parameters and heating surface on the energy characteristic, namely final energy Ek and primary energy Ep have been established.
Źródło:
Aparatura Badawcza i Dydaktyczna; 2010, 15, 2; 69-73
2392-1765
Pojawia się w:
Aparatura Badawcza i Dydaktyczna
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A combined numerical-experimental model of air foil bearing compliant structure
Autorzy:
Łagodziński, J.
Zieliński, P.
Powiązania:
https://bibliotekanauki.pl/articles/175400.pdf
Data publikacji:
2016
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
airfoil bearing
numerical model
gas bearing coefficients
Opis:
The paper concerns the development process of numerical-experimental model of air foil bearing compliant structure. Theoretically, static and dynamic characteristics of the foil bearing are the result of elastic combined properties of the two serially connected elements. One of them is a thin gas film of very small thickness and relatively high static and dynamic stiffness. The second elastic element is a pretensioned bump foil spring. This paper focuses on the properties of compliant foil structure and leaves aside the gas film behavior. At the beginning of the model development, the global stiffness and damping properties of compliant structure were obtained from the test stand measurements. In the next step, some assumptions concerning the model were made. The main one was the replacememy of the single bumps of the corrugated foil by the set of elastic-damping numerical elements. At last, the fine-tuning of the model was carried out. The tuning involved changing of subelements local damping and stiffness properties, which in effect influenced the global properties of foil bearing. The tuning criterion for the model was defined as follows: the bearing global stiffness and damping properties of the model should not differ from the experimentally obtained values more than 10%.
Źródło:
Transactions of the Institute of Fluid-Flow Machinery; 2016, 133; 117-129
0079-3205
Pojawia się w:
Transactions of the Institute of Fluid-Flow Machinery
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
An experimental investigation conducted in order to determine bearing dynamic coefficients of two hydrodynamic bearings using impulse responses
Autorzy:
Breńkacz, Ł.
Żywica, G.
Powiązania:
https://bibliotekanauki.pl/articles/175435.pdf
Data publikacji:
2016
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
hydrodynamic bearings
bearing dynamic coefficients
experimental study
Opis:
The paper presents the experimental investigation carried out in order to identify bearing dynamic coefficients of two hydrodynamic bearings from impulse responses. In this method the stiffness, damping and mass coefficients of two hydrodynamic bearings were calculated in a single algorithm. For each rotational speed, were obtained 12 dynamic coefficients which enable to fully describe the dynamic state of the rotor. Exciting force signals, applied using an impact hammer were shown. Displacements of the shaft were measured by eddy current sensors. The measurements were carried out at various rotational speeds, including resonance speeds. The vibration amplitude in a resonance case increases significantly with time after the excitation was induced by an impact hammer. Excitations of the rotor with an impact hammer were recorded using a high-speed camera. These unique recordings and simultaneous analysis of the trajectory of the bearing journals depict the contact phenomena that occur during impulse excitation of the rotor.
Źródło:
Transactions of the Institute of Fluid-Flow Machinery; 2016, 133; 39-54
0079-3205
Pojawia się w:
Transactions of the Institute of Fluid-Flow Machinery
Dostawca treści:
Biblioteka Nauki
Artykuł
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