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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Reologické vlastnosti žloutků slepičích vajec v průběhu skladování

Pavková, Lucie January 2016 (has links)
The thesis deals with the influence of storage time on particular physical and rheolo-gical properties of a yolk of chicken eggs. Monitored eggs were stored at 6 °C for 8 weeks. The thesis describes the influence of storage time on physical characteristics of a whole egg, such as weight and shape index. As expected, the weight loss of chicken eggs was demonstrated during eight weeks storing. Egg yolk (colour, height, width, weight, index and density) was also described and evaluated in detail. According to our estimates, there are no significant changes in weight during yolk storing. But yolk index is distinctly decreased. During the final part of monitoring rheological properties were evaluated - apparent viscosity, time dependence of viscosity and dependence of shear stress on the shear rate (flow curves). The experiments have proved Newtonian behaviour of egg yolk throughout the storage. The storage time has also clear impact on flow properties of yolk. The results of each experiment were modelled using the power law (Ostwald-de Waele) model.
2

Reologické vlastnosti kravského, kozího a ovčího mléka

Písaříková, Veronika January 2016 (has links)
This thesis is focused on the rheological properties of cow, goat and sheep milk. These kinds of milk are described and compared in the first part. The thesis describes physical properties and technology of milk transport. Next part deals with legislation about milk in the European Union and in the Czech Republic. Special attention is given to the requirements of warehouse equipment and heat treatment of milk. Another part deals with analytical properties of milk (dry matter, protein, fat, lactose, acidity of the milk, electrical conductivity and density). In the last part are monitored rheological properties of these three types of milk. Selected samples are measured with shear stress depending on the strain rate. It is important because it helps us to determine what type of fluid is milk. Then, there is monitored dependence of the dynamic viscosity at the shear stress and effect of temperature on viscosity. These experiments demonstrated that milk belongs to liquids with Newtonian behavior. To evaluation the results was used Newton's law of viscosity and Ostwald de Waele model.
3

Pevnostní vlastnosti lepidlových filmů v závislosti na klimatických podmínkách lepených spojů

Knápková, Adéla January 2018 (has links)
The diploma thesis deals with influence of climatic conditions on the strength properties of adhesive bonded joints of outdoor wood furniture by using dispersion-based PVAc adhesive for assembly joints. Samples of acacia, beech and larch wood were glued with waterborne polyvinyl acetate adhesive. The glued joints were exposed to various humidity and temperature conditions in order to monitor the influence of climatic conditions on the shear tensile strength of adhesive film of individual wood species.
4

Reologické vlastnosti smetany

Škopíková, Miroslava January 2017 (has links)
This diploma thesis deals with rheological properties of cream in this theoretical part. The first part describes the composition of milk as a basic product in the production of cream, and the definition of cream according to legislation and its composition. Another part of the thesis is focused on the production of cream and its distribution by kind. In the next chapter, attention is paid to the rheological properties of food, esspecially viscosity and density. The practical part is focused on the measurement of rheological properties of 10 whipping cream samples available on market. The fat proportion of the samples ranged between 30 - 33 %. For all of these samples, viscosiy and density were measured. For chosen samples was also determined the dependency of shear stress to shear rate. This dependence, using Ostwald-de Waele model, determines what type of fluid is involved. Another observed parameter was the dependency of the dynamic viscosity on the shear rate and the relation of this viscosity to the temperature changes. All samples were subjected to analytical determination of cream (dry matter, fat, titration acidity, active acidity, electrical conductivity). From the analysis of the fat proportion proportion, we are able to compare our measured data to the projected data declared by producers.
5

Porovnání metod hodnocení pevnosti desek z masivního dřeva

Drga, Tomáš January 2015 (has links)
The main aim of the thesis is the comparison of methods that are focused on assessment of solid woods boards' strength. The assessment is considered from a point of view of normative methods and it is determined at industrial oak and beech solid wood panels with PVAC dispersion glue. The thesis consists of two main parts. The first part is theoretical and it is focused on solid wood materials, wood bonding, technological factors and circumstances that influence the quality of adhesive joints. There are also mentioned basic types of adhesives used in furniture and wood industry as well as overview of standards dealing with quality of adhesive joints of wood materials in the theoretical part. The theoretical knowledge is used in the second part where is the methodology created. The methodology helps to find out the density, shear bond strength and percentage violation of adhesive joints of test samples. Finally, the results of analytical part are statistically evaluated and mutually compared and also compared with specialized literature.
6

Činitelé ovlivňující vlastnosti lepených spojů u lepidel používaných v dřevařském průmyslu / Factors affecting the properties of glued joints for glues used in the wood industry

Boška, Pavel January 2016 (has links)
Dissertation focuses on the influence of selected factors on the properties of the bond glued by acetate polyvinyl adhesives. Factors such temperature and moisture content of the environment, the pressing pressure and cyclic stress. Despite the same type of adhesive, the properties may vary for different producers of adhesives and according to which the product is not intended. Influence will be compared to the test samples of dried beech timber with regard to shear bond strength. They will be compared properties of adhesives from different manufacturers and different destination. Test samples and test progress carried out in accordance with current standards, or largely based on. This research should help users streamline the process of adhesive bonding and reduce the production costs of the bond.
7

Numerická simulace hluku generovaného nestabilitami ve smykové vrstvě / Numerical Simulation of Noise Generated by Shear Layer Instabilities

Šálený, Vratislav January 2018 (has links)
Predicting and inhibiting aerodynamically generated noise for fast moving vehicles such as cars, aircraft and trains is increasingly important. The tonal noise generated by the shear-layer instability of air flowing around the cavity opening is especially one of the most significant and most intense sources of aerodynamically generated noise. Computational aeroacoustics (CAA) based on the CFD simulations of compressible Navier-Stokes equations offers the most general approach to predicting those aerodynamically induced sounds. Aeroacoustics is practically always associated with turbulent flow and turbulence is the major challenge for CFD simulations. Four different turbulence modelling approaches are examined in this work. Three of them belong to the LES method category and one uses the URANS approach. Appropriate numerical discretization and iteration schemes have been identified for each of these approaches and implemented in the OpenFOAM open source CFD platform. The accuracy, computational performance and convergence reliability of those schemes have been subsequently studied during three-dimensional CFD simulations on a model of a suitable real object. The CFD simulation results are validated by a measurement. An organ pipe has been chosen as the object of this CAA research because it uses self-sustained oscillations, commonly referred as shear-layer (Rossiter) modes, as the source of its tone generation. The numerical simulation of the shear layer modes, respectively the noise generated by instability in the shear layer, is the subject of this work.
8

Využití alternativních výztužných materiálů ve vrstvených lepených materiálech

Svatoň, Kryštof January 2018 (has links)
Thesis deals with possibilities of reinforcement of plywood boards with natural materials in order to improve mechanical and physical properties. 5-layer spruce boards were reinforced under top layer with basalt fabric and jute. There was used environmental friendly glue for plywood fabrication. Results indicate increase in mechanical properties of boards with basalt fabric reinforcement. Mechanical properties of boards reinforced by jute were decreased.
9

Deformační analýza kmene při kácení

Veselý, Jiří January 2019 (has links)
This work deals with strain analysis of tree during felling. The main goal is to describe the origin of the deformation field. Another aim is to explain the effect of individual cuts on the size of deformation forces. Two relatively new methods in the field of wood are used to investigate the experimentally, namely digital image correlation (DIC) and finite element method. The work deals with methodical foundations for tree research during its felling. The DIC method measured seven trees in the forest when felling. Using the results obtained by this experiment, the numerical model was validated. This comparison suggested higher rigidity of the body using the finite element method compared to the actual tree, but the reaction was similar. With respect to the higher stiffness, the model was used to describe the deformation field inside the tree and to describe the effect of each cut on this field. The thesis also draws attention to the methodological errors that can occur during felling and which have been described in the experiment. Another output is an indication of the direction in which further measurements should be made and the errors that occurred during this measurement to avoid repetition.
10

Experimentální stanovení smykové pevnosti zemin z oblasti sesuvu Dobkovičky a vývoj korelačních vztahů mezi pevností zemin a jejich fyzikálními vlastnostmi / Experimental investigation of shear strength of soils from the Dobkovičky landslide area and development of correlations between soil strength and their physical properties

Roháč, Jakub January 2021 (has links)
Critical and residual states are key soil conditions relevant to slope stability. Evaluating the available shear strength in relation to these conditions is crucial for reliable stability analyses. The best way to determine the strength parameters is through properly selected laboratory tests of soil mechanics. However, in specific cases, these parameters can be estimated based on other material properties of soils. The work clarifies the applicability of various correlation equations from the literature and proposes new relationships, created from laboratory- determined results of strength and index parameters of soils from the Bohemian Central Mountains. It shows how different equations or different material properties of soils can predict the required value of strength. The work also describes how the residual strength of soils and its estimation can be affected. This is mainly caused by the clay fraction proportion and by the shear rate used in its laboratory determination. The results are applied to a specific geotechnical problem - to estimate the critical state and the residual friction angle of soils from the selected study area of the D8 motorway, which is well known thanks to the stability problems. Last but not least, various errors and misunderstandings are discussed, which are often...

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