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Wyświetlanie 1-9 z 9
Tytuł:
Nonlinear degradation modeling and maintenance policy for a two-stage degradation system based on cumulative damage model
System charakteryzujący się dwuetapowym procesem degradacji: nieliniowe modelowanie degradacji oraz wyznaczanie strategii eksploatacji systemu na podstawie modelu sumowania uszkodzeń
Autorzy:
Ni, X.
Zhao, J.
Song, W.
Guo, C.
Li, H.
Powiązania:
https://bibliotekanauki.pl/articles/301523.pdf
Data publikacji:
2016
Wydawca:
Polska Akademia Nauk. Polskie Naukowo-Techniczne Towarzystwo Eksploatacyjne PAN
Tematy:
two-stage
nonlinear
degradation modeling
cumulative damage model
maintenance policy
dwu-etapowy
nieliniowy
modelowanie degradacji
model sumowania uszkodzeń
strategia eksploatacji
Opis:
This paper attempts to take into account a two-stage degradation system which degradation rate is non-stationary and change over time. The system degradation is thought to be caused by shocks, and system degradation model is established based on cumulative damage model. The nonlinear degradation process is expressed by different shock damage and shock counting. And shock damage and shock counting are assumed to be Gamma distribution and non-homogeneous Poisson process, respectively. On the basis of these, system reliability model and nonlinear degradation model are given. In order to optimal maintenance policy for considered system, adaptive maintenance policy and time-dependent maintenance policy are studied, and mean maintenance cost rate is established to evaluate the maintenance policies. Numerical examples are given to analyze the influences of degradation model parameters and find optimal maintenance policy for considered system.
W przedstawionym artykule badano system, w którym proces degradacji zachodzi dwuetapowo, a szybkość degradacji jest zmienna w czasie. Przyjęto, że do degradacji systemu dochodzi w wyniku wstrząsów. Model degradacji systemu oparto na modelu sumowania uszkodzeń. Nieliniowy proces degradacji określono jako taki, w którym uszkodzenie powodowane wstrząsem oraz częstotliwość wstrząsów są wartościami zmiennymi. Przyjęto, że uszkodzenie powodowane wstrząsem ma rozkład gamma a częstotliwość wstrząsów jest niejednorodnym procesem Poissona. Na tej podstawie utworzono model niezawodności systemu oraz model degradacji nieliniowej. W celu opracowania optymalnej strategii eksploatacji dla rozpatrywanego systemu, rozważono dwa typy strategii utrzymania ruchu: strategię adaptacyjną oraz strategię czasowo-zależną. Strategie te oceniano określając średni poziom kosztów eksploatacji. Przykłady numeryczne posłużyły do analizy wpływu parametrów modelu degradacji oraz pozwoliły określić optymalną strategię utrzymania dla rozpatrywanego systemu.
Źródło:
Eksploatacja i Niezawodność; 2016, 18, 2; 171-180
1507-2711
Pojawia się w:
Eksploatacja i Niezawodność
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
An Early Miocene microtoid cricetid rodent from the Junggar Basin of Xinjiang, China
Autorzy:
Maridet, O.
Wu, W.
Ye, J.
Meng, J.
Bi, S.
Ni, X.
Powiązania:
https://bibliotekanauki.pl/articles/21577.pdf
Data publikacji:
2014
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Opis:
Microtoid cricetids are widely considered to be the ancestral form of arvicoline rodents, a successful rodent group includ− ing voles, lemmings and muskrats. The oldest previously known microtoid cricetid is Microtocricetus molassicus from the Late Miocene (MN9, ca. 10–11 Ma) of Europe. Here, we report a new microtoid cricetid, Primoprismus fejfari gen. et sp. nov., from the Junggar Basin of Xinjiang, northwestern China. The rodent assemblage found in association with this specimen indicates a late Early Miocene age, roughly estimated at 18–17 Ma, and thus more than 6 million years older than M. molassicus. While morphological comparisons suggest that the new taxon is most closely related to M. molas− sicus, it differs from the latter in a striking combination of primitive characters, including a lower crown, smaller size, a differentiated posterolophid and hypolophid, a faint anterolophid, the absence of an ectolophid, and the presence of a stylid on the labial border of the tooth. Arid conditions prevailing across the mid−latitude interior of Eurasia during the Early Miocene, enhanced by the combined effects of the Tibetan uplift and the gradual retreat of the Tethys Ocean, likely played a role in the appearance of grasslands, which in turn triggered the evolution of microtoid cricetids and, ultimately, the origin of arvicoline rodents.
Źródło:
Acta Palaeontologica Polonica; 2014, 59, 1
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Signature of Hot Phonons in Reliability of Nitride Transistors and Signal Delay
Autorzy:
Matulionis, A.
Liberis, J.
Matulionienė, I.
Šermukšnis, E.
Leach, J.
Wu, M.
Ni, X.
Morkoç, H.
Powiązania:
https://bibliotekanauki.pl/articles/1506173.pdf
Data publikacji:
2011-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
72.70.+m
73.50.Fq
73.61.Ey
Opis:
Lifetime of non-equilibrium (hot) phonons in biased GaN heterostructures with two-dimensional electron gas channels was estimated from hot-electron fluctuations. Dependence of the lifetime on the electron density is not monotonous - the resonance-type fastest decay serves as a signature of hot phonons. The signature is resolved in nitride heterostructure field effect transistors when the gate voltage is used to change the channel electron density. The transistor cut-off frequency decreases on both sides of the resonance in agreement with the enhanced electron scattering caused by longer hot-phonon lifetimes. The signature is also noted in device reliability experiment: the enhanced temperature of hot phonons, possibly, triggers formation of new defects and accelerates device degradation.
Źródło:
Acta Physica Polonica A; 2011, 119, 2; 225-227
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Agent-based evacuation in passenger ships using a goal-driven decision-making model
Autorzy:
Ni, B.
Li, Z.
Li, X.
Powiązania:
https://bibliotekanauki.pl/articles/258666.pdf
Data publikacji:
2017
Wydawca:
Politechnika Gdańska. Wydział Inżynierii Mechanicznej i Okrętownictwa
Tematy:
ship evacuation analysis
agent-based model
goal-driven decision-making model
social force model
steering behavior
Opis:
A new agent-based model is proposed to support designers in assessing the evacuation capabilities of passenger ships and in improving ship safety. It comprises models for goal-driven decision-making, path planning, and movement. The goal-driven decision-making model determines an agent’s target by decomposing abstract goals into subgoals. The path-planning model plans the shortest path from the agent’s current position to its target. The movement model is a combination of social-force and steering models to control the agent in moving along its path. The utility of the proposed model is verified using 11 tests for passenger ships proposed by the Maritime Safety Committee of the International Maritime Organization.
Źródło:
Polish Maritime Research; 2017, 2; 56-67
1233-2585
Pojawia się w:
Polish Maritime Research
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
An overview of design, control, power management, system stability and reliability in electric ships
Autorzy:
Ni, K.
Hu, Y.
Li, X.
Powiązania:
https://bibliotekanauki.pl/articles/1193412.pdf
Data publikacji:
2017
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
electric ship
control algorithms
power electronics techniques
power drive system
stability
Opis:
With the fast development of power electronics techniques, electrification of shipboard power systems (SPS) is an unstoppable trend, and the concepts of electric ships (ESs) and all-electric ships (AESs) emerge. In order to meet the constantly increasing electricity demand in SPS, the medium voltage direct current (MVDC) SPS becomes a promising shipboard electrical network architecture. This paper aims to present a comprehensive review of the design, control, power management, system stability and reliability in ESs. The most recent technologies and academic achievements in these fields are discussed. In the near future, it is possible that the electric propulsion technology will be widely applied to various types of ships.
Źródło:
Power Electronics and Drives; 2017, 2, 37/2; 5-29
2451-0262
2543-4292
Pojawia się w:
Power Electronics and Drives
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Modelling of ship’s trajectory planning in collision situations by hybrid genetic algorithm
Autorzy:
Ni, S.
Liu, Z.
Cai, Y.
Wang, X.
Powiązania:
https://bibliotekanauki.pl/articles/259640.pdf
Data publikacji:
2018
Wydawca:
Politechnika Gdańska. Wydział Inżynierii Mechanicznej i Okrętownictwa
Tematy:
trajectory planning
Multiple Genetic Algorithm
ship collision avoidance
nonlinear programming
COLREGs
Opis:
Ship collision-avoidance trajectory planning aims at searching for a theoretical safe-critical trajectory in accordance with COLREGs and good seamanship. In this paper, a novel optimal trajectory planning based on hybrid genetic algorithm is presented for ship collision avoidance in the open sea. The proposed formulation is established based on the theory of the Multiple Genetic Algorithm (MPGA) and Nonlinear Programming, which not only overcomes the inherent deficiency of the Genetic Algorithm (GA) for premature convergence, but also guarantees the practicality and consistency of the optimal trajectory. Meanwhile, the encounter type as well as the obligation of collision avoidance is determined according to COLREGs, which is then considered as the restricted condition for the operation of population initialization. Finally, this trajectory planning model is evaluated with a set of test cases simulating various traffic scenarios to demonstrate the feasibility and superiority of the optimal trajectory.
Źródło:
Polish Maritime Research; 2018, 3; 14-25
1233-2585
Pojawia się w:
Polish Maritime Research
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Kinetics of flotation. Order of process, rate constant distribution and ultimate recovery
Autorzy:
Bu, X.
Xie, G.
Peng, Y.
Ge, L.
Ni, C.
Powiązania:
https://bibliotekanauki.pl/articles/110034.pdf
Data publikacji:
2017
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
kinetic mode
kinetic order
rate constant distribution
ultimate recovery
overfitting
Opis:
Kinetic models can be used to characterize the flotation process. In this paper, three primary parameters, namely, distribution of flotation rate constant f(K), order of flotation process n and ultimate recovery R∞ are presented to perform analysis of flotation kinetics. The flotation rate constant f(K) is a function of both the size and hydrophobicity of particles. Though the more commonly used distributions are Delta function as well as Rectangular, Kelsall and Gamma models, there is no agreement in the literature as to which distribution function better characterize the floatability distribution. The first-order models can be used to describe most mineral flotation processes, while there is also evidence that the non-integral-order equation is capable of representing the kinetic characteristics of the batch flotation process. The order is lower than 1 in the initial moments of the flotation process. The solution of ultimate recovery calculated by the least squares method is greater than 100% (R∞ >100%). An empirical model was proposed to avoid the improper phenomenon in the solution of ultimate recovery, which can improve the availability and validity of kinetic models. Finally, more attention should be paid to the overfitting resulting from the increase in the number of parameters in the statistical analysis of kinetic models.
Źródło:
Physicochemical Problems of Mineral Processing; 2017, 53, 1; 342-365
1643-1049
2084-4735
Pojawia się w:
Physicochemical Problems of Mineral Processing
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Leaching of heavy metals from MSWI fly ash : experiments vs. simulation
Autorzy:
Qiu, Q
Jiang, X.
Chen, Z.
Lu, S.
Ni, M.
Powiązania:
https://bibliotekanauki.pl/articles/205253.pdf
Data publikacji:
2018
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
simulation
MSWI fly ash
microwave
hydrothermal treatment
Visual MINTEQ
Opis:
In this work, pH-dependence experiments and leaching modeling using Visual MINTEQ were performed to evaluate the stability and simulate the leaching characteristics of heavy metals in municipal solid waste incineration (MSWI) fly ash. Modeling the equilibrium concentration of Cd, Cu, Cr, Ni, Pb and Zn in raw and treated fly ash was the main target and was conducted over a pH range of 0.5–14. In addition, simulation of the leaching behavior of MSWI fly ash with different additives was also conducted. The treated fly ash was solidified by a microwave-assisted hydrothermal process with added phosphate. The initial elemental concentrations of MSWI fly ash, including raw and treated fly ash, were detected by a microwave apparatus and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The ICP-AES analysis showed that most leaching concentrations of treated fly ash decreased considerably compared to the raw fly ash. The simulation results indicated that the dissolution/precipitation simulation models of Zn, Cu and Pb were broadly consistent with the experimental results, while the leaching behaviors of Ni, Cr and Cd were determined by both dissolution/precipitation and surface complexation mechanisms. In addition, the models of reagent solidification revealed that the stabilization effect of Na2S was better than that of Na2CO3. This model will be useful in the evaluation of the leaching concentrations of heavy metals in fly ash.
Źródło:
Archives of Environmental Protection; 2018, 44, 2; 55-61
2083-4772
2083-4810
Pojawia się w:
Archives of Environmental Protection
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Flotation of long flame coal pretreated by polyoxyethylene sorbitan monostearate
Autorzy:
Ni, C.
Xie, G.
Li, Z.
Bu, X.
Peng, Y.
Sha, J.
Powiązania:
https://bibliotekanauki.pl/articles/110299.pdf
Data publikacji:
2016
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
flotation
hydrophobicity
low rank coal
Tween 60
pretreatment
Opis:
In this investigation, polyoxyethylene sorbitan monostearate (Tween 60) was used to improve flotation of fine long flame coal. The flotation recovery of long flame coal could be increased when long flame coal was either pretreated or conditioned with Tween 60 in a flotation cell for a period before the addition of collector. Fourier Transform Infrared (FTIR) technique was used to indicate surface properties of long flame coal. The results of FTIR show that there are many oxygen functional groups on the sur-face. Contact angle measurements were used to indicate changes in hydrophobicity of coal surface before and after Tween 60 and/or diesel pretreatments. The results of contact angle measurements show that hydrophobicity of coal can be increased by Tween 60. Tween 60 can also enhance adsorption of diesel on the coal surface, and hence floatability of long flame coal can be further improved. Tween 60 primarily enhances the flotation recovery of low density coal fractions (<1.5 and 1.5-1.8 kg/dm3). However, the increase in flotatation recovery is less significant with an excessive addition of Tween 60.
Źródło:
Physicochemical Problems of Mineral Processing; 2016, 52, 1; 317-327
1643-1049
2084-4735
Pojawia się w:
Physicochemical Problems of Mineral Processing
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-9 z 9

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