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Forced movement of a ball in spherical cavity under kinematic excitation
Náprstek, Jiří; Fischer, Cyril
2018 - English
In the paper the response of a heavy ball rolling inside a semi-spherical cavity under horizontal kinematic excitation is investigated. The system with six degrees of freedom with three non-holonomic constraints is considered. The contact between the ball and the cavity surface is supposed to be perfect without any sliding. The mathematical model using the Appel-Gibbs function of acceleration energy is developed and discussed. The most important post-critical regimes are outlined and qualitatively evaluated on the frequency axis. Numerical experiments have been performed when excitation frequency is slowly swept up and down. Results obtained by means of semi-analytical investigation and numerical simulation are evaluated and physically interpreted. Some applications in civil engineering as a tuned mass damper used on slender structures is outlined. Strengths and weaknesses of solution method are evaluated.
Keywords:
nonlinear dynamics; non-holonomic systems; Appell-Gibbs formulation; singular states; tuned mass damper
Fulltext is available at external website.
Forced movement of a ball in spherical cavity under kinematic excitation
In the paper the response of a heavy ball rolling inside a semi-spherical cavity under horizontal kinematic excitation is investigated. The system with six degrees of freedom with three non-holonomic ...
Accuracy and numerical efficiency of approximate method for complex eigensolution of structure with specialized damping device
Hračov, Stanislav
2018 - English
The paper provides a detailed parametric analysis of the recently proposed approximate method for complex eigensolution of non-classically damped structures. This method is based on a combination of perturbation and incremental approaches and is applicable to the classically damped structures equipped with a specialized passive damping device. The numerical efficiency in terms of the required calculation times and the accuracy is demonstrated on a model of an existing structure for various combination of computational parameters. Wide numerical simulations revealed the selection of real eigenmodes of undamped system used in the approximate eigensolution as the most important parameter affecting the final accuracy.
Keywords:
non-classical damping; complex eigensolution; perturbation method; passive damper
Fulltext is available at external website.
Accuracy and numerical efficiency of approximate method for complex eigensolution of structure with specialized damping device
The paper provides a detailed parametric analysis of the recently proposed approximate method for complex eigensolution of non-classically damped structures. This method is based on a combination of ...
Crystallization force of sodium chloride
Koudelková, Veronika; Wolf, Benjamin
2018 - English
Soluble salts are one of the most deteriorating factor causing damage of historical building materials due to generation of crystallization pressure inside pore space. Direct measurement of crystallization force is quite challenging, hence we developed at our institute a novel device able to detect the force of growing crystal. The device is based on the monitoring of force developed with upper microscopic glass on the growing crystal to maintain constant position. The crystal could generate force because of the existence of thin liquid layer of solution between both surfaces come into contact. The driving force for the subsequent growth of crystal against obstacle is supersaturation, which is mainly induced by evaporation of the salt solution. In this experiment, the crystal of sodium chloride generated force 16.8 mN and the corresponding crystallization pressure was equal to the value 0.48 MPa.
Keywords:
crystallization force; sodium chloride; salt deterioration
Fulltext is available at external website.
Crystallization force of sodium chloride
Soluble salts are one of the most deteriorating factor causing damage of historical building materials due to generation of crystallization pressure inside pore space. Direct measurement of ...
Analysis of Baroque sculpture based on X-ray fluorescence imaging and X-ray\ncomputed tomography data fusion
Vavřík, Daniel; Kumpová, Ivana; Vopálenský, Michal; Lauterkranc, J.
2017 - English
It is advantageous to combine information about geometry and the inner structure of historical artifacts with information about the elemental composition of decorative layers, typically covering historical wooden sculptures. X-ray computed tomography describing artifact structure is quite common and easy. Standard X-ray fluorescence (XRF) analysis of decorative layers is typically done for several selected spots of the artifact’s surface utilizing single pad detector. XRF imaging fully describing the surface’s elemental composition is commonly done for flat objects, while time consuming XRF tomography is applied to relatively small objects. It will be shown in this work that an effective fusion combination of XRF imaging and X-ray tomography describing the whole object can be realized even when using a limited number of XRF images.
Keywords:
X-ray computed tomography; X-ray flourescence imaging; cultural heritage; data fusion
Fulltext is available at external website.
Analysis of Baroque sculpture based on X-ray fluorescence imaging and X-ray\ncomputed tomography data fusion
It is advantageous to combine information about geometry and the inner structure of historical artifacts with information about the elemental composition of decorative layers, typically covering ...
Three-dimensional characterization of polymer foams using X-ray dark-field imaging
Senck, S.; Plank, B.; Gusenbauer, C.; Salaberger, D.; Vavřík, Daniel; Santer, W.; Kastner, J.
2017 - English
Due to the low cost, the ease of processing, and excellent material properties, polymer foams are used in various applications, e.g. packaging, building and construction, furnitures and bedding, and the automotive and aerospace sector. The mechanical response of polymer foams is primarily influenced by density and morphology. While foam density can be determined with high precision, cell morphology is more difficult to determine since the size distribution of foam cells differs in three dimensions. However, using conventional methods, e.g. optical light microscopy or scanning electron microscopy, it is very difficult to obtain three-dimensional information and to differentiate between the strut system and cell walls. An alternative for the three-dimensional characterization of foam morphology is micro-computed tomography (XCT). But even non-destructive techniques like XCT are not able to characterize anisotropic foams if the thickness of single struts and cell walls is below the physcial resolution of the respective XCT system. In this contribution we therefore investigate different polymeric foam samples using a Talbot-Lau grating interferometer XCT (TLGI-XCT) system. We show that the obtained darkfield contrast images show a high contrast and a strong signal at struts and cell walls, facilitating the segmentation of foam cells in various examples.
Keywords:
foam; micro-computed tomography; Talbot-Lau grating interferometer XCT; dark-field imaging
Fulltext is available at external website.
Three-dimensional characterization of polymer foams using X-ray dark-field imaging
Due to the low cost, the ease of processing, and excellent material properties, polymer foams are used in various applications, e.g. packaging, building and construction, furnitures and bedding, and ...
Analytical approach of slender structure vibration due to random component of the wind velocity
Náprstek, Jiří; Hračov, Stanislav
2017 - English
Along wind random vibration of slender structures represents one of the most important aeroelastic effects resulting from wind - structure interaction. The theoretical model being based on one-dimensional elements with continuously distributed mass and stiffness has been introduced in this paper. The system has been considered to be linear self-adjoint with strongly non-proportional linear damping due to both material of the structure and presence of vibration dampers. The additive random excitation continuously distributed in time and space is Gaussian, therefore the response is Gaussian as well. Consequently, mathematical mean value and correlation function are satisfactory for the full description of the generalized solution of the respective PDE in the stochastic meaning. The general results have been obtained mostly in the form of analytical formulae for important cases of input spectral densities. A numerical example dealing with real structure is presented.
Keywords:
random vibrations; slender structures; wind load; non-proportional damping; distributed-parameter systems
Fulltext is available at external website.
Analytical approach of slender structure vibration due to random component of the wind velocity
Along wind random vibration of slender structures represents one of the most important aeroelastic effects resulting from wind - structure interaction. The theoretical model being based on ...
Optimization of acquisition parameters in radiography and tomography
Vopálenský, Michal; Vavřík, Daniel; Kumpová, Ivana
2017 - English
Contrast in radiographic images is one of the most important parameters both in radiography and tomography. This paper investigates the possibility of adjusting the radiographic parameters, in particular the accelerating voltage of the X-ray tube, in order to maximize the difference in the detected intensity in response to the change in the thickness of the investigated object. Simplified model is used that allows finding the optimal operating point for the given material and thickness without an apriory knowledge about the X-ray spectra, detector response and the material composition. It is shown that in case of small changes of thickness, the optimum is met when the detected intensity behind the object of certain thickness is at approx. 37 % of the full range (i.e., of the value that would be measured under the same conditions in the absence of the object). In spite of simplifications made, the theoretical model shows a very good correspondence with the experimental data. A brief consideration is made on the case of a general difference in thicknesses.
Keywords:
X-ray computed tomography; X-ray radiography; X-ray optimization; image processing; contrast
Fulltext is available at external website.
Optimization of acquisition parameters in radiography and tomography
Contrast in radiographic images is one of the most important parameters both in radiography and tomography. This paper investigates the possibility of adjusting the radiographic parameters, in ...
Influence of ice accretion at bridge rope on Strouhal number
Pospíšil, Stanislav; Gorski, P.; Kuznetsov, Sergeii
2015 - English
The paper is concerned with the method and results of wind tunnel investigations of the/nStrouhal number (St) of a stationary iced cable model of cable-supported bridges with/nrespect to different angles of wind attack. The methodology leading to the experimental/nicing of the inclined cable model was prepared in a climatic section of the laboratory./nThe St values were determined within the range of the Reynolds number (Re) between/n2.4·104 and 16.5·104, based on the dominant vortex shedding frequencies measured in/nthe wake of the model.
Keywords:
bridge cable; ice accretion; Strouhal number; angle of attack; vortex shedding frequency
Fulltext is available at external website.
Influence of ice accretion at bridge rope on Strouhal number
The paper is concerned with the method and results of wind tunnel investigations of the/nStrouhal number (St) of a stationary iced cable model of cable-supported bridges with/nrespect to different ...
The numerical assessment of a full-scale truss reconstructed employing a traditional all-wooden joints
Milch, J.; Tippner, J.; Sebera, V.; Kunecký, Jiří; Kloiber, Michal; Navrátil, M.
2015 - English
The assessment of mechanical behaviour of all-wooden joints used in historical timber structures such as churches, castles etc. is currently paid a big attention in the Czech Republic, and Central Europe as a whole. The reasons are (a) a high number of such structures; (b) their significance to the national cultural heritage and maintenance for preserving their cultural value; and (c) missing information about global mechanical behaviour of joints and whole truss structures when loaded. Generally, valuable historical monuments need to be evaluated as regards the structure and safety of all timber elements in the structure for their future preservation [1]. The present paper shows a novel methodology for virtual assessment of mechanical behaviour used in a historically valuable gothic truss structure of St. James's Church in Brno, which is very valuable from both structural and architectural points of view. The church was constructed between1220 and 1724, the used styles including the Romanesque, the Gothic and the Neogothic. Also carpentry master Anton Ebenberger participated [2]. The aim of this paper was to describe the real loading of a joint that corresponds to the real function of a joint in the truss structure during the loading owing to new positions of replacement joints in the truss. Currently, the truss of St. James’s church shows large defects including decayed members; therefore, renovation is needed. The restoration of the truss should be carefully implemented in the structure and analyzed beforehand. Therefore, the numerical approaches based on FEM were used to evaluate the mechanical behaviour of the beam truss with a detailed 3D solid joint.
Keywords:
timber structures; all-wooden joints; mechanical behaviour
Fulltext is available at external website.
The numerical assessment of a full-scale truss reconstructed employing a traditional all-wooden joints
The assessment of mechanical behaviour of all-wooden joints used in historical timber structures such as churches, castles etc. is currently paid a big attention in the Czech Republic, and Central ...
Strengthening of weak historic renders with traditional and innovated consolidation treatment
Slížková, Zuzana; Frankeová, Dita
2015 - English
The presented study was aimed to proof consolidation effects of different families of consolidants: inorganic agents (lime -based or silica-based solutions or sols), organic agents (silicic acid ester based consolidant) and their combination on the characteristics of weak mortars prepared in laboratory with different types of aggregates. Besides exploring consolidant-substrate interaction also the pozzolanic activity of the aggregate and the binder mortar component after reaction with lime (calcium hydroxide solution) was investigated in order to understand and describe the strengthening mechanism into consolidated mortars. As the study was based on experimental research, the production of mortar test specimens represented an important preliminary work. Different mortar components (various types of sand in terms of phase composition, clay, lime) and the same ratio of the aggregate and the binder were used in various mortar mixtures. Various mineralogical types of aggregate were used with the same grain size distribution (600 pieces of tubes of 40 mm in outer diameter, of the height of 40 mm and depth of 4 mm were prepared for testing the compressive strength, for the tension tests 550 thin plates of dimensions 40 mm x 100 mm x 4 mm were cast and 600 beams 20 x 20 x100mm were made for testing the flexural strength and other characteristics of reference and consolidated mortars). The sand used for mortar specimens was characterized by microscopic examination of thin section and also by X-ray diffraction, X-ray fluorescence spectroscopy and thermal analysis. The pozzolanic activity of the sands (reactivity with calcium hydroxide) was determined by means of the thermal analysis and supplemented by wet silicate analysis. The amount of the effective matter in the consolidant was the same for all agents per the square unit for all mortar types and specimen shape. One set of specimens was prepared as the reference set the second set was used for the evaluation.
Keywords:
lime mortar; lime render; consolidating products; lime water; nanolime; consolidation; strengthening
Available in a digital repository NRGL
Strengthening of weak historic renders with traditional and innovated consolidation treatment
The presented study was aimed to proof consolidation effects of different families of consolidants: inorganic agents (lime -based or silica-based solutions or sols), organic agents (silicic acid ester ...
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