The electromagnetic wave absorption characteristics of composite cement-based building material have attracted much interest in recent times. Researchers have mainly focused on the 2 GHz to 12 GHz frequency range. Mobile and wireless communication systems use frequencies from 800 MHz upwards. The determination of characteristics such as reflection loss, absorption, attenuation and shielding effectiveness are crucial in the evaluation and development of these materials for the building industry. Absorption is an indication of how much of the EMW energy enters the material. Attenuation indicates how much of the absorbed energy is converted into other forms of energy by the material. Shielding effectiveness (SE) is a combination of reflection loss, attenuation and multiple internal reflections and attenuations. This research determined these characteristics by measuring the S11 and S21 parameters of the composite cement-based material in the GSM and WiFi frequency bands. The time domain gating function of a vector network analyser is applied to measure the reflection from the material. The data was then used to obtain the reflection and absorption losses in the frequency bands. The transmission loss was measured by placing the sample in the propagation path between two antennas. MnZn-ferrite and electrolytic manganese dioxide in powder form were evaluated as absorber material to increase the permeability of the cement-based material to improve absorption and attenuation capabilities to create a cost-effective practical electromagnetic wave absorber. The compound of the cement-based material was cement, sifted river sand and filler powder. The results achieved in the research showed the uniqueness of electrolytic manganese dioxide as filler in composite cement based material for electromagnetic wave shielding effectiveness improvement. The combined measurement techniques used in this research were uniquely used to determine the required electromagnetic wave absorption characteristics and shielding effectiveness of 10 dB was measured in the GSM850 and GSM900 frequency bands. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Electrical, Electronic and Computer Engineering / unrestricted

L’un des éléments clé pour atteindre de hauts rendements dans les centrales solaires à récepteur volumétrique est l’absorbeur. Sa structure poreuse permet au rayonnement solaire de pénétrer à l’intérieur, où l'énergie absorbée doit être transférée efficacement par convection au fluide qui la traverse. Dans ce travail, deux types d’absorbeurs innovants sont présentés et analysés : l’un constitué par une série d’éléments empilés avec une structure en forme de grille, l’autre par des éléments similaires à des stores vénitiens. A titre de référence, un absorbeur classique à nid d’abeilles est aussi évalué. La propagation du rayonnement solaire au sein des absorbeurs est modélisée au moyen de la technique de lancer de rayons, basée sur la méthode de Monte Carlo. Leur comportement thermo-hydraulique est simulé par la méthode des éléments finis. Les caractéristiques géométriques des deux absorbeurs proposés améliorent le transfert thermique par convection par rapport aux absorbeurs alvéolaires et la modification des leurs principaux paramètres géométriques nous a permis d’augmenter la longueur d’extinction du rayonnement solaire. Cependant, l’accroissement de leur surface frontale apparente augmente les pertes par réflexion. A l’issu des résultats théoriques, l’absorbeur à stores vénitiens a été retenu pour l’analyser expérimentalement. Ses performances thermiques sont comparées avec celles d’un absorbeur alvéolaire. Ces résultats montrent également que la structure de l’absorbeur proposé intensifie les échanges thermiques vers le fluide. De plus, ce type d’absorbeur atteint un meilleur comportement thermique à de hauts flux radiatifs et à des débits élevés. / One of the key elements for achieving a high efficiency in solar power plants with volumetric receiver is the absorber. Its porous structure allows the solar radiation to penetrate inside it, where the absorbed energy should be transferred efficiently by convection to the fluid which crosses through it. In this work, two types of innovative absorbers are presented and analyzed: one consisting of a set of stacked elements with a grid-like structure, the other with elements similar to venetian blinds. As a reference, a conventional honeycomb absorber is also evaluated. The solar radiation propagation within the absorbers is modeled through the ray tracing technique, based on the Monte Carlo method. Their thermohydraulic behavior is simulated by the finite element method. The geometrical characteristics of the two proposed absorbers improve convective heat transfer compared to honeycomb absorbers and the modification of their main geometric parameters allowed us to increase the extinction length of solar radiation. However, the increase of their apparent frontal surface rises up reflection losses. Based on the theoretical results, the venetian blind absorber was selected to analyze it experimentally. Its thermal performance is compared with that of a honeycomb absorber. These results also indicate that the structure of the proposed absorber intensifies the heat exchange to the fluid. Moreover, this kind of absorber reaches a better thermal behavior at high heat flux and at high flow rates.

Submitted by Rafael Santana (rafael.silvasantana@ufpe.br) on 2017-07-12T18:01:48Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Aida Avendano_Dissertacao_Eng Mecanica_UFPE.pdf: 2879829 bytes, checksum: 90b10e461eb8407986cea09be582a591 (MD5) / Made available in DSpace on 2017-07-12T18:01:48Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Aida Avendano_Dissertacao_Eng Mecanica_UFPE.pdf: 2879829 bytes, checksum: 90b10e461eb8407986cea09be582a591 (MD5) Previous issue date: 2016-01-29 / PRH-PB203 EQUIPAMENTOS/PETROBRAS / O processo de transferência de calor e massa dentro de um absorvedor tubular em espiral de Brometo de Lítio-Água (LiBr/H2O), resfriado com água em contracorrente, foi simulado usando um modelo matemático não linear. Para a simulação criou-se um programa em Matlab, usando o método numérico iterativo. Na calibração da malha física foram utilizadas condições de trabalho do absorvedor e o coeficiente de transferência de massa efetivo, Kef, obtidos da literatura. O coeficiente de transferência de calor global, U, foi calculado usando a resistência térmica global dentro do absorvedor. Para o cálculo do coeficiente de transferência de massa e de calor da interface solução-vapor se utilizaram correlações de analogia de transferência de calor e massa. As distribuições da temperatura e concentração da solução de LiBr/H2O, e a temperatura da água de resfriamento ao longo do comprimento do absorvedor foram determinadas utilizando o programa desenvolvido e os resultados obtidos apresentaram uma boa concordância quando comparados com dados reportados na literatura. Finalmente, foi analisada a influência da variação de alguns dos parâmetros, tais como temperatura e vazão de entrada da água de resfriamento, comprimento do absorvedor e material do tubo absorvedor dentro do absorvedor utilizando o programa desenvolvido. Os resultados obtidos mostraram que o programa desenvolvido permite predizer o comportamento do processo de transferência de massa e calor dentro do absorvedor em espiral de LiBr/H2O, além de representar uma ferramenta para o dimensionamento e/ou otimização deste componente. / The mass and heat transfer process in a spiral tubular absorber of the Water/Lithium Bromide (LiBr/H2O), cooled with in counter-current, was simulated using a nonlinear mathematical model. For the simulation was developed a program in Matlab, using the iterative numerical method. For the calibration of physical mesh were used absorber working condition and effective mass transfer coefficient, Kef, obtained from the literature. The global heat transfer coefficient, U, was calculated using the global thermal resistance within the absorber. For the calculation of the mass and heat transfer coefficient of the interface vapor-solution are used analogy correlations of mass and heat transfer. The temperature distribution and concentration of LiBr/H2O, and the cooling water temperature along of the length of the absorber were determined using the program developed, and the result obtained showed good agreement when compared to the data reported in the literature. Finally, the influence of the variation the some parameters were analyzed, such as inlet temperature and mass flow of cooling water, length of the absorber and material absorber tube within the absorber using the developed program. The result obtained showed that this program allowed to predict the behavior of the mass and heat transfer process in the absorber spiral of the LiBr/H2O, also represents a tool for the design and/or optimization of this component.

The diploma thesis deals with the application of acoustic methods for evaluating the technical condition of the shock absorbers. Analysis of acoustic radiation during damping operation leads to the definition of a new non-contact diagnostic methodology that can determine the condition of the shock absorbers. The first part of the thesis focuses on the noise radiation of the shock absorbers, which is caused by discontinuous dumping. Further, the methods for the noise source localization available at The Institute of Machine and Industrial Design are described – with their functionalities, advantages and limitations. Based on all the information, an appropriate method is selected and used in the experimental part of this work. Then, aeration and removing the full volume of oil with damage of the shock absorber tube are caused (induced) on several types of the shocks. Noise radiation is measured by a microphone array and by a sound meter; the acoustic maps, frequency spectra and the synchronous filtration graphs are calculated from the measured data. From the differences in the acoustic radiations of each shock condition, a suitable diagnostic criterion for a specific shock absorber is defined. The final part discusses obtained results. Based on these results, a general diagnostic methodology, applicable to any type of shock absorber, is formulated.

The aim of this master thesis is modification of landing gear for accomplishment CS-23 regula-tion from that purpose, because landing gear in the use can't pass this type of certification. The first part examines the alternatives of landing gear with consideration optimal technical and eco-nomical difficulty. After finding optimal type of landing gear with shock absorber is there part of designing and computing the load. Last part of thesis is about stress analysis of whole con-cept and reconsidering final changes.

The diploma thesis titled, Computational model of shock absorber, is concerned with ways to simulate individual actuators of dampening with the goal of obtaining F-v characteristics dependent on the setup of the shock absorber. The work is divided into two halves, the first one being a review of literature and the second half being practical. The review part is focused on ways of shock absorber constructions and the physical principles involved with the present forces. The practical part of the work contains a computational model of a monotube shock absorber in the Matlab programming software.

The aim of this master’s thesis is to evaluate the effect of shock absorber on vehicle limits. At the beginning of the thesis, shock absorber properties were described. Then computational model was created and manoeuvres for shock absorber behaviour were defined. Created mathematical model is based on quarter model of a car and excitation in form of road with a random profile is an essential part of the model. This model was used for evaluation of heave. After heave analysis, shock absorber behaviour during drive was investigated. Drive conditions were defined as set of handling manoeuvres. For the drive investigation, complete multibody virtual model of racing car was used. Based on drive investigation analysis, optimal damping characteristics for each manoeuvre were found. Furthermore, each optimal characteristic was compared for different manoeuvres. Obtained results were compared. As a conclusion, compromise damping characteristic was suggested with the aim to fit the combination of all defined drive conditions. Final part of the thesis was aimed at validation of the computational model. Data measured during real drive were used as an input for this validation.

The diploma thesis deals with basic test procedures conducted by companies Euro NCAP and RCAR. It focuses mainly on insurance impact and describes the creation of a model, simulation and crash on barrier. Moreover, it explores the influence of change of yield strength, thickness and hardening of material of energy-absorber on simulation of insurance impact, especially the amount of absorbed energy by energy-absorber.

This master's thesis deals with an engineering design of an external reservoir for hydraulic shock absorbers with combined filling of oil and magnetorheological fluid. The first part describes existing designes of magnetorheological shock absorbers and characteristics of magnetorheological fluid. Next part describes a design of an experimental external reservoir and a test of its functionality on a prototype. This is followed by an optimalized engineering design of the experimental external reservoir.

The thesis deals with the measurement system for determining the thermal efficiency of the newly developed types of solar absorbers. Measuring equipment allows simultaneous indoor or outdoor thermal efficiency detection of up to four samples absorbers. Emphasis is placed on the flow and heat transfer medium temperature changes. For this purpose is used Biotech FCH-m-POM-LC and LM35DZ sensors. Sensor signal is transferred to a PC using the measuring module NI USB-6221. Here it is further processed by proposed evaluation program. The software is implemented in LabVIEW integrated development environment. In a final part are performed a verification measurements to assess system performance and evaluate the thermal efficiency of various types of solar absorbers. This path is also demonstrated high efficiency applications absorbent layer coating color RABSORB 5.