Elimination of Back Influences of Renewable Sources with Using Storage Devices

Import 22/07/2015V této bakalářské práci jsou popsány zpětné vlivy obnovitelných zdrojů, především fotovoltaických elektráren, na distribuční soustavu. Cílem práce je tyto zpětné vlivy eliminovat a to s použitím akumulačního zařízení elektrické energie. Především se jedná o akumulaci elektrické energie pomocí akumulátorů. V první kapitole jsou definovány negativní zpětné vlivy, kterými může fotovoltaická elektrárna působit na distribuční soustavu, také jsou zde uvedeny požadavky na kvalitu elektrické energie z hlediska jednotlivých parametrů. Další kapitola je věnována akumulaci elektrické energie, především pomocí akumulátorů. Jsou zde popsány i nejčastěji používané baterie a jejich výhody či nevýhody pro jednotlivé typy akumulací. Poslední kapitola je věnována eliminaci zpětných vlivů pomocí akumulačního zařízení. Popisovány jsou zde dva druhy akumulací a to výkonová a energetická akumulace s případným řešením výkonové bilance v místě připojení fotovoltaické elektrárny do sítě. V závěru práce je provedeno zhodnocení, s následným doporučením použití jednotlivých typů akumulátorů pro daný způsob akumulace.This bachelor thesis deals with the back influences of renewable sources, especially photovoltaic power plants, on the distribution system. The aim of this work is to eliminate these back influences by using an accumulative device of electric power. It primarily covers the accumulation of electric power via accumulators. The first chapter defines the negative back influences by which the photovoltaic power plant can affect the distribution system. It also defines the requirements on quality of electric power from the perspective of the individual parameters. The next chapter is dedicated to accumulation of electric power, especially via accumulators. The most used batteries and their advantages and disadvantages for the individual types of accumulations are being described here. This entails two types of accumulations, namely output and energetic accumulation with potential output balance solution of the access point of the photovoltaic power plant into the system. The summary of the paper provides an evaluation with subsequent recommendation of usage of the individual types of accumulators for the given type of accumulation.410 - Katedra elektroenergetikyvelmi dobř

Measurements and modeling of temperature-strain rate dependent uniaxial and planar extensional viscosities for branched LDPE polymer melt

In this work, novel rectangle and circular orifice (zero-length) dies have been utilized for temperature-strain rate dependent planar and uniaxial extensional viscosity measurements for the LDPE polymer melt by using standard twin bore capillary rheometer and Cogswell model and the capability of five different constitutive equations (novel generalized Newtonian model, original Yao model, extended Yao model, modified White-Metzner model, modified Leonov model) to describe the measured experimental data has been tested. It has been shown that chain branching causes the strain hardening occurrence in both uniaxial and planar extensional viscosities and its maximum is shifted to the higher strain rates if the temperature is increased. The level of uniaxial extensional strain hardening for the branched LDPE sample has been found to be higher in comparison with the planar extensional viscosity within wide range of temperatures. (C) 2016 Elsevier Ltd. All rights reserved.Grant Agency of the Czech Republic [16-05886S

Effect of viscoelastic stress state at die exit on extrusion film casting process: Theoretical study

In this work, viscoelastic, isothermal extrusion film casting modeling utilizing 1D membrane model and modified Leonov model was performed in order to understand the role of viscoelastic stress state at the die exit on the polymer melt film stretching in the post die area. Experimental data for LDPE and theoretical predictions based on the eXtended Pom-Pom (XPP) model taken from the open literature were used for the validation purposes. It was found that predicting capabilities of 1D membrane model utilizing XPP and modified Leonov model are comparable for the given processing conditions and material. Consequent theoretical parametric study revealed that increase in the viscoelastic stress state at the die exit, characterized as the ratio of second and first normal stress differences, -N-2/N-1, leads to increase in neck-in phenomenon. This suggests that specific attention should be paid to optimization of the extrusion die design in order to stabilize polymer melt film stretching in the post die area

Influence of long chain branching on fiber diameter distribution for polypropylene nonwovens produced by melt blown process

In this work, linear isotactic polypropylene (L-PP) and long-chain branched polypropylene (LCB-PP) miscible blend, both having comparable weight average molecular weight, zero-shear viscosity, and polydispersity index, were used to produce nonwovens via melt blown technology in order to understand the role of long chain branching in the fiber diameter distribution. Basic morphological characteristics of produced nonwoven samples have been determined using digital image analysis of scanning electron microscope images considering different magnifications to capture nanofibers as well as microfibers. At the same air flow rate, polymer flow rate, and temperature, the average fiber diameters were the same, 1.6 μm, but the coefficient of variation, CV, was greater for the linear PP than for the blend. Material elasticity was assessed by reptation-mode relaxation time, λ, determined by fitting of deformation rate dependent shear viscosity by Cross and Carreau-Yasuda models as well as via fitting of frequency dependent loss and storage moduli master curve by a two-mode Maxwell model. It was found that λ is higher for LCB-PP in comparison with L-PP and the Cross model gives a meaningful relaxation time while the Carreau-Yasuda model does not despite giving a better numerical fit. Extensional rheology was assessed by the strain rate dependent uniaxial extensional viscosity (estimated from the entrance pressure drop using the Gibson method). The infinite shear to zero-shear shear viscosity ratio η ∞ /η 0 (obtained directly from the shear viscosity data measured in a very wide shear rate range) was shown to be proportional to the maximum normalized extensional viscosity at very high extensional strain rates, ηE, ∞ /(3η 0 ). η ∞ /η 0 was related to temperature and basic molecular characteristics of given polymers via simple equation. It was observed that extensional viscosity for both samples first decreases with increased extensional strain rate to its minimum value at 200 000-400 000 1/s and then increases to plateau value, ηE, ∞ (corresponding to the maximum chain stretch) at about 2 10 6 1/s. At low deformation rates, extensional viscosity is higher for LCB-PP in comparison with L-PP, but the trend is switched at very high deformation rates; ηE, ∞ (and also ηE, ∞ /3η 0 ) becomes lower for LCB-PP in comparison with L-PP. These results suggest that high stability of LCB-PP blend can be explained by its higher stretchability at very high deformation rates (occurring at the die exit where an intensive fiber attenuation takes the place) and its lower stretchability at medium and low deformation rates, at which melt/air inertia driven bending instability called whipping occurs. © 2019 The Society of Rheology.Grant Agency of the Czech RepublicGrant Agency of the Czech Republic [16-05886S

Heat transfer model verification for thermal monitoring system of integral bridges

Thermal actions considered on abutments of integral bridges by the European standard (Eurocode 1) might be in variety of certain situations underestimated. Based on this assumption, thermal monitoring system has been designed and installed into structure of bridge No. 27-117. Temperature profiles in five certain spots are being measured to provide sufficient basis for evaluation of real thermal actions on abutments of integral bridges. For purpose of measurement verification, elementary heat transfer models for finite element method solver were created. These models are being loaded by simplified temperature profiles reached in real time in-situ. Evaluated models provide verification data to compare with measured temperature profiles in structure and might provide information about temperature profiles probably reached during extreme weather situations

Effect of die exit stress state, Deborah number, uniaxial and planar extensional rheology on the neck-in phenomenon in polymeric flat film production

In this work, effect of the second to first normal stress difference ratio at the die exit, −N2/N1, uniaxial extensional strain hardening, [Formula presented], planar-to-uniaxial extensional viscosity ratio, [Formula presented], and Deborah number, De, has been investigated via viscoelastic isothermal modeling utilizing 1D membrane model and a single-mode modified Leonov model as the constitutive equation. Based on the performed parametric study, it was found that there exists a threshold value for De and [Formula presented], above which, the neck-in starts to be strongly dependent on −N2/N1. It was found that such critical De decreases if −N2/N1, [Formula presented] increases and/or [Formula presented] decreases. Numerical solutions of the utilized model were successfully approximated by a dimensionless analytical equation relating the normalized maximum attainable neck-in with [Formula presented], [Formula presented], −N2/N1 and De. Suggested equation was tested by using literature experimental data considering that −N2/N1 depends on die exit shear rate, temperature and utilized constitutive model parameters for given polymer melt. It was found that approximate model predictions are in a very good agreement with the corresponding experimental data for low as well as very high Deborah numbers, at which neck-in strongly depends on −N2/N1. It is believed that the obtained knowledge together with the suggested simple model can be used for optimization of the extrusion die design (influencing flow history and thus die exit stress state), molecular architecture of polymer melts and processing conditions to suppress neck-in phenomenon in production of very thin polymeric flat films. © 2018 Elsevier B.V.1 6-05886S, GACR, Grantová Agentura České RepublikyGrant Agency of the Czech Republic [16-05886S

Effect of heat transfer coefficient, draw ratio, and die exit temperature on the production of flat polypropylene membranes

In this work, a stable numerical scheme has been developed for the 1.5-dimensional film casting model of Silagy et al. [Polym. Eng. Sci. 36, "Study of the stability of the film casting process," 2614-2625 (1996)] utilizing the viscoelastic modified Leonov model as the constitutive equation and energy equation coupled with the crystallization kinetics of semicrystalline polymers taking into account actual temperature as well as cooling rate. The model has been successfully validated on the experimental data for linear isotactic polypropylene taken from the open literature. Drawing distance, draw ratio, heat transfer coefficient, and die exit melt temperature were systematically varied in the utilized model in order to understand the role of process conditions in the neck-in phenomenon (unwanted film width shrinkage during stretching in the post die area) and crystalline phase development during flat film production. It is believed that the utilized numerical model together with the suggested stable numerical scheme as well as obtained research results can help to understand a processing window for the production of flat porous membranes from linear polypropylene considerably. © 2019 Author(s).Grant Agency of the Czech RepublicGrant Agency of the Czech Republic [16-05886S

FEM Simulation of Torque Characteristic of Asynchronous Motor

V této diplomové práci je popsán asynchronní motor a jeho konstrukční uspořádání. Jsou popsány a uvedeny díly, ze kterých se asynchronní motor skládá, princip jeho činnosti, náhradní schéma a zapojení svorkovnice pro připojení motoru k síti. Diplomová práce se zabývá simulací momentové charakteristiky pomocí metody konečných prvků v program ANSYS Maxwell. Momentová charakteristika je zde teoreticky rozebrána a popsána s uvedenými možnostmi měření momentové charakteristiky v praxi. Po provedení simulace je následně momentová charakteristika vyhodnocena z hlediska synchronních a asynchronních momentů, které jsou taktéž popsány v teoretické části. Dále jsou uvedeny příklady, jak potlačit parasitní momenty a synchronní momenty. Simulováno bylo natočení drážek rotoru o 10° a srovnání s rotorem bez natočených drážek.Diploma thesis is focused to asynchronous motor and its mechanical design. Principle of operation, equivalent circuit, terminal block wiring and the parts of alternating current motor are described within as well. The main objective of thesis deal with simulation of torque characteristic using the finite element method in ANSYS Maxwell software. Theoretical analysis of torque characteristic is, along with mentioned real measurement methods, described. Simulation implementation was followed by the evaluation of torque characteristic which is based on synchronous and asynchronous moments. These are described in theoretical part of thesis. In examples are mentioned methods for suppressing parasitic and synchronous moments. Simulation was performed on one skew width of the rotor grooves and rotor positional matching without any rotation of grooves.410 - Katedra elektroenergetikyvýborn

Analysis of Manufacturing Technology of Long Gun Stocks

Import 29/09/2010Bakalářská práce pojednává ve všech částech o výrobě a konstrukci pažeb sportovních a loveckých dlouhých zbraní. Je zde provedena rešerše v oblasti dlouhých zbraní na současném trhu; jednotlivé pažby jsou klasifikovány, uveden popis jednotlivých konstrukčních částí, jejich účel a vliv na funkci, konstrukci a použití zbraně. V práci je kladen důraz na proces výroby s uvedením všech možných výrobních metod pažby. Také jsou uvedeny možnosti ručních úprav pažeb, a to buď úpravy podle potřeb a rozměrů střelce nebo úpravy sportovní podle zaměření na jednotlivé střelecké disciplíny. Závěrem je vytvořen podrobný technologický postup výroby pažeb s rozborem jednotlivých operací, s uvedením potřebných měřidel, strojů, nástrojů a pomůcek. Práce zhodnocuje stav a možnosti výroby pažeb, reakce na trh a požadavky zákazníků České zbrojovky Uherský Brod a.s.This thesis deals with production and construction of sporting and hunting arms gunstocks. It includes the background research in the current market, classification of gunstocks, description of structural features and their impact on construction, function and using of the guns. The thesis places emphasis on all possibilities of production process. There are also handmade modifications (due to the needs or proportions and dicsiplines of gunman) included. In conclusion there is the technological process of sporting and hunting arms gunstock constuction with description of single operations including all indicators, machines, instruments and tools. This thesis evaluates state and position of gunstock production, its reaction on current market and requirements of „Česká zbrojovka Uherský Brod Inc“. customers.Prezenční340 - Katedra výrobních strojů a konstruovánívýborn

Strength Analysis and Design of Formula Student Front Stabiliser Arm

Bakalářská práce se zabývá vhodnou úpravou páky předního stabilizátoru vozu Formule Student. Nejprve je probrán teoretický základ únavového lomu. Zdůrazněná je nízkocyklová únava potřebná k výpočtu životnosti. Následně je proveden odhad charakteristického zatížení a předpokládaný počet cyklů do poruchy. Poté je vytvořena simulace současné konstrukce, která slouží jako výchozí stav pro porovnávání s novými řešeními. Matematické modelování je provedeno pomocí metody konečných prvků v prostředí Ansys Workbench. V práci jsou uvedeny 2 varianty úprav, z nichž každá dosahuje předem stanovené životnosti. Životnost je vypočtena pomocí simulace v programu Ansys Mechanical a také v tabulkovém procesoru Excel numerickým výpočtem. Každá z variant má určité přednosti a nedostatky. Srovnání variant je uvedeno v tabulce v závěru práce.The bachelor thesis deals with the suitable modification of the front stabilizer lever of a Formula Student car. First, the theoretical basis of fatigue fracture is discussed. The low-cycle fatigue is emphasized due to calculate of lifetime. Subsequently, an estimate of the characteristic load and the expected number of cycles to failure is made. A simulation of the current design is then prepared for the following comparison with the new solutions. Mathematical modelling is performed using the finite element method in Ansys Workbench. The work presents 2 variants of the modifications each of which achieves a predetermined lifetime. The service life is calculated by simulation in Ansys Mechanical and also in an Excel spreadsheet by numerical calculation. Each of the variants has certain advantages and disadvantages. A comparison of the variants is given in the table at the end of the paper.330 - Katedra aplikované mechanikyvýborn