Search results for "Modell"
showing 10 items of 2134 documents
Modelling polycarbonate synthesis rates on the example of bulk heteropolyaddition of diphenyl carbonate and bisphenol A diglycidyl ether
2016
This paper investigates the effects of increased reaction mixture viscosity on the kinetics of linear polymer creation in a bulk polyaddition process of diphenyl carbonate and bisphenol A diglycidyl ether. The paper presents a method for solving a system of bulk polyaddition of diphenyl carbonate and bisphenol A diglycidyl ether process balance equations, allowing the determinatiof the process kinetic parameters. Determination of polymerisation reaction kinetic parameters was also made possible by the use of the so-called partial reaction rate constant. Such an approach enabled a significant simplification of the mathematical expressions describing the heteropolyaddition process and provide…
Non-linear inductor modelling for a DC/DC buck converter
2017
The paper is focused on the modelling of an inductor to exploit its non-linear behaviour in the roll-off region when it is employed in a DC/DC converter. The model is set up on the basis of experimental data measured in operating conditions, which are fitted to a polynomial curve describing the inductance variations. The analysis of the buck converter, performed by including the proposed model, is validated by experimental tests.
Stochastic resonance in a metal-oxide memristive device
2021
Abstract The stochastic resonance phenomenon has been studied experimentally and theoretically for a state-of-art metal-oxide memristive device based on yttria-stabilized zirconium dioxide and tantalum pentoxide, which exhibits bipolar filamentary resistive switching of anionic type. The effect of white Gaussian noise superimposed on the sub-threshold sinusoidal driving signal is analyzed through the time series statistics of the resistive switching parameters, the spectral response to a periodic perturbation and the signal-to-noise ratio at the output of the nonlinear system. The stabilized resistive switching and the increased memristance response are revealed in the observed regularities…
Empirical model for stress ratio effect on fatigue delamination growth rate in composite laminates
2004
An empirical model is proposed for the stress ratio effect on the fatigue delamination growth rate in composite laminates under single-mode loading, intending to provide a simple and accurate description tool in engineering application. The model is based on heuristic considerations of damage accumulation ahead of the crack. Linear cumulative assumption is used for damage estimation. Comparison of the prediction based on the proposed model with the test results for different carbon, glass, and alumina fibre-reinforced composites at several stress ratios shows reasonable agreement.
Interfacial energy effects within the framework of strain gradient plasticity
2009
AbstractIn the framework of strain gradient plasticity, a solid body with boundary surface playing the role of a dissipative boundary layer endowed with surface tension and surface energy, is addressed. Using the so-called residual-based gradient plasticity theory, the state equations and the higher order boundary conditions are derived quite naturally for both the bulk material and the boundary layer. A phenomenological constitutive model is envisioned, in which the bulk material and the boundary layer obey (rate independent associative) coupled plasticity evolution laws, with kinematic hardening laws of differential nature for the bulk material, but of nondifferential nature for the layer…
Numerical modeling and validation of hydrothermal liquefaction of a lignin particle for biocrude production
2021
Abstract Lignin liquefaction process under catalyst-free conditions in a temperature range from 573 K to 647 K is investigated with this mathematical model. Based on the theoretical understanding of the physical and chemical processes of the liquefaction process in subcritical temperatures, a comprehensive mathematical model for the decomposition of lignin by hydrolysis reaction pathway is developed on the results of a series of batch experiments. The model consists of four main sections. They are liquefaction of lignin particle, oily film, and inorganic (ash) layer formation behavior during the liquefaction, kinetic model to model further liquefaction process of initial products, and the l…
The interphase finite element
2011
Mesomodelling of structures made of heterogeneous materials requires the introduction of mechanical models which are able to simulate the interactions between the adherents. Among these devices is quite popular the zero thickness interface (ZTI) model where the contact tractions and the displacement discontinuities are the primary static and kinematic variables. In some cases the joint response depends also on the internal stresses and strains within the thin layer adjacent to the joint interfaces. The interphase model, taking into account these additional variables, represents a sort of enhanced ZTI. In this paper a general theoretical formulation of the interphase model is reported and an…
Shallow flow stability analysis with applications in hydraulics
2016
Šķidruma plūsmas stabilitātes analīze ar pielietojumiem hidraulikā Promocijas darbā tiek veikta plūsmu l ineārā un vāji nelineārā stabilitātes analīze seklos sajaukšanās slāņos. Plūsma tiek pieņemta kā nedaudz izliekta garenvirzienā . Berzes koe ficients mainās šķērsvirzienā . Lineārā stabilitāte tiek analizēta no laika un telpas aspektiem. Turklāt problēma ir vispārināta divu komponenšu seklām plūsmām. Tiek izskatītas divas pieejas vāji nelineārās stabilitātes analīzei. Parādīts, ka amplitūdas vie nādojums ir kompleksais Ginzburga - Landau vienādojums (paralēlu plūsmu pieņēmums). Otra pieeja ņem vērā lēno garenvirziena bāzes plūsmas izmaiņ u . Tiek iegū ts pirmās kārtas amplitūdas attīstīb…
Matemātiskā modelēšana: Matemātiskās fizikas lietišķās problēmas
1998
Krājums veltīts skaitlisko metožu izstrādei, pamatošanai un pielietošanai konkrētu matemātiskās fizikas problēmu risināšanā
Mathematical models and their solutions for different heat exchange processes in environment with layered structure
2012
Promocijas darbā tiek apskatīti 3D, 2D un 1D risinājumi stacionārām siltuma vadīšanas problēmām cilindriskā sistēmā ar ribu. Kā arī iztirzāti nestacionāru problēmu risinājumi hiperboliskām siltuma vadīšanas problēmām 1D cilindram un 2D cilindriskai sistēmai ar ribu. Iegūti kvazi-analītiski risinājumi cilindriskai sistēmai ar ribu, izmantojot konservatīvās viduvēšanas metodi. Izmantojot vispārinātu Grīna funkcijas metodi ir konstruēts precīzais analītiskais atrisinājums vairākām cilindriskām sistēmām ar ribu. Daži no stacionāriem modeļiem ir skaitliski konstruēti un sniegti aprēķinu piemēri. Darbā ir analizēti un salīdzināti iegūtie rezultāti. Atslēgas vārdi: konservatīvā viduvēšana, Grīna f…