Skewed bridges have exhibited poorer performance during lateral earthquake loading in comparison to non-skewed bridges (Apirakvorapinit et al. 2012; Elnashai et al. 2010). Results from numerical modeling by Shamsabadi et al. (2006), small-scale laboratory tests by Rollins and Jessee (2012), and several large-scale tests performed by Rollins et al. at Brigham Young University (Franke 2013; Marsh 2013; Palmer 2013; Smith 2014; Frederickson 2015) led to the proposal of a reduction curve used to determine a passive force skew reduction factor depending on abutment skew angle (Shamsabadi and Rollins 2014). In all previous tests, a uniform longitudinal load has been applied to the simulated bridge abutment. During seismic events, however, it is unlikely that bridge abutments would experience pure longitudinal loading. Rather, an inclined loading situation would be expected, causing rotation of the abutment backwall into the backfill. In this study, a large-scale test was performed where inclined loading was applied to a 30 skewed bridge abutment with sand backfill and compared to a baseline test with uniform loading and a non-skewed abutment. The impact of rotational force on the passive resistance of the backfill and the skew adjust factor was then evaluated. It was determined that inclined loading does not have a significant effect on the passive force skew reduction factor. However, the reduction factor was somewhat higher than predicted by the proposed reduction curve from Shamsabadi and Rollins 2014. This can be explained by a reduction in the effective skew angle caused by the friction between the side walls and the back wall. The inclined loading did not change the amount of movement required to mobilize passive resistance with ultimate passive force developing for displacements equal to 3 to 6% of the wall height. The rotation of the pile cap due to inclined loading produced higher earth pressure on the obtuse side of the skew wedge, as was expected.These findings largely resolve the concern that inclined loading situations during an earthquake may render the proposed passive force skew reduction curve invalid. We suggest that the proposed reduction curve remains accurate during inclined loading and should be implemented in current codes and practices to properly account for skew angle in bridge design.

No description available.

Thesis (MEng (Mechanical and Mechatronic Engineering))--Stellenbosch University, 2007. / ENGLISH: The design, construction and testing of a passive thermal system, a roof solar chimney, for a loft is considered. Unlike conventional solar chimneys the solar collector is constructed from corrugated iron roof sheets with the aim that it can be integrated into existing buildings at a lower cost or used in low cost housing developments. The main objective of the study was to determine the feasibility of such low-cost design to regulate thermal conditions in a loft, that is heating the loft during winter and enhancing natural ventilation during summer, by carrying out an experimental and analytical study. The results obtained from the experimental study showed that for winter the solar chimney, having a channel width, depth and length of 0.7 m, 0.1 m and 1.8 m respectively and with a peal solar radiation of 850 W/m², heated the room air 5°C higher than the ambient temperature during the hottest periods of the day, which is only marginally better than a loft with conventional roof insulation. At night, it was found that reverse airflow occurred through the chimney, cooling the loft down to ambient temperature, due to radiation heat loss from the roof collector to the night sky. For summer operation, the experimental data showed that the chimney was able to maintain the loft at ambient temperature and the analytical study found that the chimney was able to enhance natural ventilation effectively, reaching air exchange rate of 6.6 per hour for the 4.6 m³ volume space. It was also found that the chimney’s performance dropped rapidly and significantly during periods of low solar radiation and at night. A sensitivity analysis illustrated that for both summer and winter operation, the size, tilt angle and absorptivity of the roof collector greatly effected the efficiency and mass flow rates of the system, agreeing well with other literature. These results prove that this low cost solar chimney cooling design was feasible to enhance natural ventilation mainly during hot summer conditions with high solar radiation. Compared to a loft with only conventional roof insulation, the chimney did not perform effectively during the winter to heat the loft up, meaning that winter operation for this specific design is not feasible. Possible improvements to the design include using construction materials with higher thermal capacities to retain heat energy and ensure continued operation during periods of low solar radiation, as well as using selective absorber coatings on the collector surface. It is recommended that further work on the project include the integration of these improvements into the present design and to use the findings obtained from the sensitivity analysis to improve system efficiencies. CFD analysis of the test-rig will be insightful as an additional means to validate and compare with the analytical and experimental data obtained in this report. With the continuation of these studies, this low-cost solar chimney design can be optimised, validated on a commercial scale and built into existing and new housing developments. Incorporating such a passive thermal device will aid homeowners in air regulation and thermal comfort of their living space as well as saving on energy requirements. / Sponsored by the Centre for Renewable and Sustainable Energy Studies, Stellenbosch University

This thesis is a study of multiple access schemes for satellite land mobile systems that provide a domestic or regional service to a large number of small terminals. Three orbit options are studied, namely the geostationary, elliptical (Molniya) and inclined circular orbits. These are investigated for various mobile applications and the choice of the Molniya orbit is justified for a U. K. system. Frequency, Time and Code Division Multiple Access (FDMA, TDMA and CDMA) are studied and their relative merits in the mobile environment are highlighted. A hybrid TDMA/FDMA structure is suggested for a large system. Reservation ALOHA schemes are appraised in a TDMA environment and an adaptive reservation multiple access protocol is proposed and analysed for a wide range of mobile communication traffic profiles. The system can cope with short and long data messages as well as voice calls. Various protocol options are presented and a target system having 100,000 users is considered. Analyses are presented for the steady state of protocols employing pure and slotted ALOHA and for the stabilty of the slotted variant, while simulation techniques were employed to validate the steady state analysis of the slotted ALOHA protocol and to analyse the stability problem of the pure ALOHA version. An innovative technique is put forward to integrate the reservation and the acquisition processes. It employs the geographical spread of the users to form part of the random delay in P-ALOHA. Finally an economic feasibility study is performed for the spacesegment. For costs of capital (r) less than 23 % the discounted payback period is less than the project's lifetime (10 years). At r- 8% the payback period is about 5.6 years, while the internal-rate-of-return is 22.2 %. The net present value at the end of the projects lifetime is £M 70 at r-8%.

[pt] O compartilhamento de frequências entre sistemas de comunicações por satélite e sistemas terrestres tem sido objeto de estudos desde o aparecimento dos primeiros sistemas comerciais de comunicações por satélite. Um caso particular que tem despertado o interesse dos operadores de sistemas terrestres diz respeito à interferência produzida pelos enlaces descendentes de sistemas de satélite que utilizam orbitas elípticas altamente inclinadas (Highly Elliptical Orbit - HEO) nos receptores do Serviço Fixo Terrestre (Fixed Service - FS). Os trabalhos encontrados na literatura, envolvendo este tipo de interferência, apresentam análises que consideram a hipótese simplificadora de que todos os receptores vítima do Serviço Fixo Terrestre têm suas antenas receptoras com elevação zero graus. No presente trabalho é feita uma análise probabilística da interferência agregada produzida por satélites de múltiplos sistemas HEO sobre receptores do Serviço Fixo Terrestre na faixa de 18 GHz, na qual o ângulo de elevação da antena receptora dos sistemas FS considerados é modelado por uma variável aleatória com função densidade de probabilidade conhecida. A modelagem matemática desenvolvida é aplicada a dois cenários envolvendo múltiplos sistemas HEO interferentes. Mais especificamente, um dos cenários considera três sistemas HEO com satélites operando apenas no hemisfério norte e o outro, três sistemas HEO com satélites operando tanto no hemisfério norte quanto no sul. Os resultados obtidos são comparados àqueles que utilizam a hipótese de que as antenas receptoras de todos os sistemas FS considerados têm angulo de elevação zero. / [en] Frequency sharing between satellite systems and terrestrial fixed service (FS) systems has been object of studies since the onset of commercial satellite communication systems. A particular case of interest refers to the interference produced by the downlink of highly elliptical orbit satellite systems (HEO) into fixed service receivers. In the literature, studies involving this type of interference have presented analyzes that consider the simplifying assumption that all victim fixed service receivers have their receiving antennas with zero degree elevation angle. In this work a probabilistic analysis is used to evaluate the aggregate interference produced by the satellites of multiple highly elliptical orbit satellite systems into fixed service receivers operating in the 18 GHz frequency band. The FS receiving antenna elevation angle is modeled as a random variable with known probability density function. The proposed mathematical model is applied to two scenarios involving multiple interfering HEO systems. More specifically, the first scenario considers three interfering HEO systems having satellites that operate only in the northern hemisphere. In the second scenario, three HEO systems with satellites that operate in both the northern and southern hemisphere are considered. The obtained results are compared to those resulting from analyses that use the hypothesis that the receiving antennas of all the FS victim systems have a zero degree elevation angle.

A ética e a luta pela equidade social e melhoria da qualidade de vida das populações impulsiona a busca pela universalização do atendimento do serviço energético e pela utilização racional dos recursos renováveis existentes em cada local. Nesse sentido, o aproveitamento da energia solar apresenta-se como uma excelente alternativa, seja para disponibilizar pequenas quantidades de energia elétrica, utilizando-se de geradores fotovoltaicos, seja para o aquecimento de água ou ainda para o condicionamento ambiental de edificações. Em qualquer desses casos, são necessárias informações confiáveis sobre o recurso solar disponível. O presente trabalho se insere nesse contexto buscando, além de propor um padrão para instalação de estações solarimétricas, para o sistema de unidades utilizado e para a rotina de calibração e manutenção dos equipamentos, caracterizar a radiação solar no Estado de São Paulo, tendo como um de seus objetivos oferecer dados de irradiação solar diária média mensal, centrando a atenção na cidade de São Paulo e no Vale do Ribeira, no litoral sul do Estado de São Paulo. Esta última área, localizada no município de Cananéia, possui baixos índices de eletrificação rural e grande potencial de utilização de sistemas fotovoltaicos para suprir a demanda de residências isoladas. Como, em geral, os painéis para aproveitamento do recurso solar são instalados em uma determinada inclinação, para se dimensionar corretamente um sistema é necessário transformar os dados de irradiação solar de plano horizontal para plano inclinado. Assim, foram testados os diversos modelos presentes na literatura para o cálculo da irradiação global diária mensal em plano inclinado a partir de dados em plano horizontal. Todos esses modelos necessitam de dados de irradiação difusa, ou seja, a irradiação proveniente de toda a esfera celeste, menos diretamente do Sol, para poderem ser utilizados. Dessa maneira, o presente trabalho buscou testar os diversos modelos que calculam a irradiação difusa a partir da irradiação global e, com a verificação da inadequação desses, propõe uma nova correlação, mais apropriada para nossa realidade. / Ethics, and the struggle both for social equity and the improvement of the standard of living of populations, drive the efforts for both the universalization of energy provision and the rational utilization of existing renewable resources. Accordingly, utilizing solar energy presents itself as an excellent alternative, whether it is to make available small quantities of electric energy, utilizing photovoltaic generators, for heating water, or for environmental conditioning. Whatever the case, it is necessary to have reliable information on available solar resource. This work seeks to develop standards for implementation of solarimetric stations, for the unit system to be utilized and for the routine of calibration and maintenance of equipment. It also seeks to characterize solar radiation in the state of São Paulo, with one of its objectives being the supply of data of monthly average daily irradiation in the city of São Paulo and the Ribeira Valley (south coast of São Paulo state). The latter has low levels of rural electrification and great potential for utilizing photovoltaic systems in the supply of energy for isolated residences. As solar panels are generally installed on a sloped surface, the correct dimensioning of systems requires converting solar irradiation data from horizontal plane to tilted plane. Thus, several models presented in the literature that calculate monthly average daily irradiation on inclined plane from available data measured on horizontal plane were tested. All such models need diffuse irradiation data, that is, irradiation originating from the entire sky, except that originating directly from the sun, to be utilized. For this reason, this work sought to test several models that establish correlations for the calculation of diffuse solar irradiation from global solar irradiation. As the inadequacy of such models was verified, this proposes a new correlation that is more appropriate for the conditions of the state of São Paulo.

Embora o escoamento estratificado óleo-água seja comum na indústria do petróleo, existem poucos trabalhos na literatura sobre a estrutura ondulatória encontrada no escoamento em dutos ascendentes ou descendentes. O objetivo deste trabalho é entender e caracterizar as estruturas interfaciais ondulatórias em escoamentos estratificados óleo e água em dutos levemente inclinados e comparar com os resultados retirados da modelagem proposta. Uma primeira tentativa de modelar a onda interfacial óleo-água através da equação da energia bifásica unidimensional para regime permanente é apresentada e comparada aos resultados obtidos experimentalmente. Valores de comprimento de onda foram coletados para quatro ângulos de inclinação a partir da horizontal (-5º, -2º, 2º e 5º) e diversos pares de vazão de óleo e água. Os dados foram extraídos de frames de vídeos de alta resolução através de uma técnica manual. Um software baseado em LabView foi desenvolvido para possibilitar a automação da obtenção do comprimento de onda e amplitude. Os comprimentos de onda obtidos com a técnica automática foram comparados com os dados obtidos através da técnica manual. O mensuramento é bem satisfatório e sugere que a ferramenta experimental proposta possa ser aplicada para o estudo de qualquer padrão de escoamento óleo-água, onde uma estrutura ondulatória possa ser identificada. A validade da modelagem da onda interfacial proposta foi avaliada através da comparação entre os resultados teóricos e dados experimentais. A concordância observada é encorajadora. / Even though the oil-water stratified flow pattern has a common occurrence in the upstream oil industry, quite often in directional wells, there are only a few works in the literature dealing with its interfacial wavy structure. This work has the mean goal of comprehending a characterizing the interfacial wave structure in inclined water-oil stratified pipe flow, comparing it with the proposed model. A model, based on the steady-state one-dimensional two-phase flow energy equation is presented and compared to our experimental data. Wave lengths and amplitude data were collected at four inclinations from the horizontal (-5º, -2º, 2º and 5º) and several oil and water flow rates. The data were extracted form high-resolution video images through a manual technique. A LabView based software was developed in order to obtain the lengths and amplitude automatically. Wave length obtained from it were compared to the manual technique data. The satisfactory measurement suggests the applicability of the experimental tool to any water-oil pipe flow pattern, where a wave structure can be identified. The validity by the comparison between theoretical and experimental data. The agreement observed is promising.

The main objective of this study is to model and analyze a three dimensional inclined semi-elliptic surface crack in a Functionally Graded Material (FGM) coating bonded to a homogeneous substrate with a bond coat. The parametric analyses on FGMs are based upon zirconia-yttria (ZrO2-8wt%-Y2O3) FGM coating bonded to a substrate made of a nickel-based superalloy. It is assumed that there is a nickel-chromium&amp / #8211 / aluminum&amp / #8211 / zirconium (NiCrAlY) bond coat between the FGM coating and substrate. Metal-rich, linear variation, ceramic-rich and homogeneous ceramic FGM coating types are considered in the analyses. The inclined semi-elliptic surface crack problem in the FGM coating-bond coat-substrate system is analyzed under transient thermal loading. This problem is modeled and analyzed by utilizing three dimensional finite elements. Strain singularity around the crack front is simulated using collapsed 20 &amp / #8211 / node quarter &amp / #8211 / point brick elements. Three &amp / #8211 / dimensional displacement correlation technique is utilized to extract the mixed mode stress intensity factors around the crack front for different inclination angles of the semi-elliptic surface crack. The energy release rates around the crack front are also calculated by using the evaluated mixed mode stress intensity factors. The results obtained in this study are the peak values of mixed mode stress intensity factors and energy release rates around the crack front for various inclination angles of the semi-elliptic surface crack embedded in the FGM coating of the composite structure subjected to transient thermal loading.

An X band dual polarized slotted waveguide antenna array is designed with very high polarization purity for both horizontal and vertical polarizations. Horizontally polarized radiators are designed using a novel non-inclined edge wall slots whereas the vertically polarized slots are implemented using broad wall slots opened on baffled single ridge rectangular waveguides. Electromagnetic model based on an infinite array unit cell approach is introduced to characterize the slots used in the array. 20 by 10 element planar array of these slots is manufactured and radiation fields are measured. The measurement results of this array are in very good accordance with the simulation results. The dual polarized antenna possesses a low sidelobe level of -35 dB and is able to scan a sector of &plusmn / 35 degrees in elevation. It also has a usable bandwidth of 600 MHz.

Zur Bemessung und Simulation von flächigen Textilbetonstrukturen werden Berechnungsmodelle benötigt, die das Materialverhalten unter biaxialer Beanspruchung abbilden können. Für eindimensionale Strukturen existieren einige Modelle, zu deren Weiterentwicklung eine Erweiterung zur Abbildung des biaxialen Materialverhaltens vorgeschlagen wird. In diesem Beitrag werden die notwendigen Erweiterungen und deren Umsetzbarkeit bei der Modellierung diskutiert und bewertet. / For design and simulation of plane textile reinforced concrete structures mechanical models representing the material behaviour under biaxial loading are necessary. For one-dimensional structures several models were presented in the past. For their further development an extension for biaxial material behaviour is usually proposed. In this paper the required extensions are discussed and their feasibility for modelling is assessed.