In this study a setup is designed and constructed in the Hydromechanics Laboratory of Middle East Technical University in order to observe the flow through grate inlets under different flow and geometry conditions. The rate of interception of flow is determined over a rectangular channel through preliminary experiments run on the tilting flume. The performance of the new set setup has been examined and grate efficiency is obtained both in terms of longitudinal slope and the Froude number. The results which are obtained show that the setup can be used to conduct experiments to obtain a general expression for grate efficiency.

Satellites have become absolute necessity in the growing modern space technology. At present, launch pads are the only means for launching of satellites or any other space vehicles. Due to the large magnitude of current and the associated rate of rise, a lightning strike to launch pads can be quite disastrous. Satellite launch complex forms typically the tallest object in that region. This makes them the more vulnerable to cloud-to-ground lightning. In addition, most of the launch pads are situated near the coastal area, where the isokeraunic levels are quite high. In view of these, almost all the satellite launch pads are provided with suitable Lightning Protection Systems (LPS). The LPS is basically intended for protecting against a direct lightning hit. The present work is related with the LPS to Indian satellite launch pads, Pad-I and Pad-II. The protection system for Pad-I consists of three 120 m tall towers placed approximately at the vertices of an equilateral triangle of 180 m. The same for Pad-II consist of 120 m tall towers placed at vertices of rectangle of size 90 m x 105 m. Towers are interconnected by 6 shield wires at the top. A mast of 10m length forms the top of the tower. Significant work on the analysis of interception efficacy of these protection systems has been reported in the literature. The lightning surge response of these systems have also been analysed and reported. The interception efficacy of these LPS in field can be ascertained by pertinent measurements. Measuring the lightning current on LPS seems to be one of the most suitable choices for this purpose. It would also greatly facilitate collection of local lightning current statistics, data on which is almost absent. Several considerations suggest that the tower bases form ideal place for such measurement. However, such lightning current records would involve mainly the current resulting from stroke interception, as well as, induced current due to strokes nearby. Literature on categorisation of measured currents to the type of stroke and correlation of measured currents to the incident stroke currents is rather limited. This is especially true for interconnected protection system of the type dealt in the present work. Considering these the present work is taken up and its scope is defined as: (i) Evolve a suitable model for study of current distribution in LPS due to Lightning and using the same deduce the current due to stroke interception and that due to stroke nearby. (ii) For the purpose of categorization identify the salient characteristics of current due to the intercepted strokes and that due to bypass/nearby strokes (iii) For the intercepted strokes, develop a processor for estimating the injected stroke current from the measured tower base currents. Lightning event, apart from other associated physical phenomena, is strongly governed by electromagnetic fields. Any method employed for the analysis, either theoretical or experimental, should satisfy the governing electromagnetic equations. As experimentation on actual system, as well as, their laboratory simulation is nearly impossible, theoretical modelling approach is selected. Modelling involves modelling of the channel along with its excitation, modelling of the LPS and modelling of the ground. Channel, following the literature, is represented as a loaded conductor with a lumped current source at the junction point. Such models have quite successfully predicted the electromagnetic fields and current in other places on the down conductor. For the LPS, some simplifications on the geometry are very essential. Tower lattice elements of dimensions much smaller than the wavelength of highest dominant frequency component of lightning current spectrum are neglected. Suitable modification is made for the tower top involving a plate and interconnection of several short members. For the close range within 200 – 400 m, even for the induced currents, the influence of ground in the literature has been reported to be small. Also, there is an extensive grounding network in these systems. In view of the same, a perfectly conducting ground along with suitable ground termination impedance is considered. Only the numerical solution of the problem is feasible and for the same, following the literature, NEC-2 is employed. All the guidelines of NEC are respected in the discretisation. Geometric mean radius is employed for modelling the complex tower elements. Fourier Transform Techniques are employed for time domain conversion of the computed frequency domain quantities. Occasionally, numerical inversion error of magnitude less than 5% is encountered. For the validation of the numerical modelling for both direct stroke and that nearby, time domain experimentation on electromagnetically reduced scale models (35:1) is employed. As the channel electrical and geometrical parameters are stochastic in nature, it is necessary to ensure that the deduction made using the model is practically relevant. For this, some parametric studies are conducted. The influence of channel length and inclination, stroke current velocity etc. has been shown to be insignificant for the case of intercepted strokes. Simulations are carried out for the stroke intercepted (i.e. direct strikes) by the LPS. The characteristics of the tower base currents are investigated. The base currents indicate a dispersive propagation along the towers and further a frequency dependent current division at the tower-shield wire junctions. Base currents contain superimposed oscillations, which basically originate from various junctions of the system. The magnitude of the oscillations is obviously dependent on the rise time of the incident currents. The tower base currents settle within about 10 -15 µs, which is shorter than that for isolated tower. Further, the full-frequency model could be limited to this time period. The corresponding current transfer functions are deduced. For the stroke interception by shield wires, based on the earlier work, only stroke to midspan is found to be relevant and hence it is considered. The nature of tower base currents for a stroke to midspan of the shield wires seem to be similar. However there are some distinct features, which are helpful in identifying the stroke location on the LPS. From the time correlated tower base currents, a suitable methodology for identifying the stroke interception location on LPS is developed. Next, simulations for induced current due to a bypass stroke, as well as, stroke to ground outside the LPS, however, within 1 km radius are taken up. In fact, it is estimated that latter is nearly 5 – 13 times higher than the strokes collected by LPS, indicating it as the most probable event. The objective here is characterization, rather than correlation. In this study, the influence of charge induced on the LPS by the descending leader is neglected and the upward leader activity is approximately considered. To the best of author’s knowledge, studies on such induced currents in down conductors are very scarce. Considering this and noting that the number of parameters is quite large, first the basic study is taken up on simple cylindrical down conductors. Many important and interesting deductions are made. The nature of the induced current is highly dependent on the rate of rise as well as the velocity of propagation of the stroke current. The magnitude and to some extent, the wave shape of the induced current is found to depend on the average as well as maximum di/dt of the stroke current. For a given wave shape, the magnitude of the induced current increases with rate of rise of the wave front; however, saturating trend will onset after some point. The height of the down conductor mainly governs the frequency of the oscillatory component of the induced current. The dependency of the induced current on the radius of the down conductor seems to be logarithmic (which is in accordance with the antenna theory). Based on these results, the parameters for the corresponding study on LPS under consideration, is chosen. The results of the investigation on the induced currents in LPS show that they have quite distinct waveform. They are basically bipolar and oscillatory in nature, with relatively short duration. These unique features facilitate clear distinction of the induced currents from that due to stroke interception. Basic characteristics are reasonably insensitive to the separation distance of the protection system and the channel, current propagation velocity along the channel, channel inclination and shape of the current front. The salient features of the induced current due to a bypass stroke are also enumerated. • The noise, if any, in the measured current can be addressed only after acquiring sufficient data. Based on the above, the following procedure is suggested for the stroke classification and estimation. • By employing the distinct features of the resulting tower base currents, analyze the measured tower base currents and classify the strokes into the intercepted stroke or stroke to ground. • For the latter case, using the salient features of the bypass strokes, further classify the strokes to bypass strokes and stroke to ground outside the protected volume. • For the intercepted strokes, using the relative strengths and wave shapes, identify the interception point to either tower top or the midspan of the shield wires. • Then by using the corresponding transfer functions and Fourier Transform techniques, compute the injected stroke current. • Using the above, other tower base currents are computed and compared with the measured currents. This gives quantification for the accuracy of the method. In summary the present work has made some original contribution to the classification and estimation of stroke currents measured on the interconnected LPS.

Submitted by Bernardo Melo Montes Nogueira Borges null (bernardonog@hotmail.com) on 2016-04-27T20:07:00Z No. of bitstreams: 1 Tese_Bernardo_Melo_Montes_Nogueira_Borges.pdf: 1559546 bytes, checksum: 6d1bf6517586eaeee1a07a41f98d1490 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-04-29T22:10:32Z (GMT) No. of bitstreams: 1 borges_bmmn_dr_jabo.pdf: 1559546 bytes, checksum: 6d1bf6517586eaeee1a07a41f98d1490 (MD5) / Made available in DSpace on 2016-04-29T22:10:32Z (GMT). No. of bitstreams: 1 borges_bmmn_dr_jabo.pdf: 1559546 bytes, checksum: 6d1bf6517586eaeee1a07a41f98d1490 (MD5) Previous issue date: 2016-03-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Forrageiras do gênero Cynodon são conhecidas por sua capacidade de resposta a altas doses de nitrogênio (N). Em condições tropicais o N pode se tornar um problema ambiental e financeiro devido à sua baixa eficiência de uso pelas plantas, principalmente como resultado de perdas por volatilização e/ou lixiviação. Portanto, objetivou-se com este trabalho avaliar fontes e doses de N no crescimento e produção de matéria seca do Tifton 85, bem como mudanças nas frações do carbono (C) no solo. Um experimento foi conduzido de 2012 a 2014, e constituiu de um fatorial em um delineamento de blocos ao acaso, onde os tratamentos foram a associação de duas fontes de N (nitrato de amônio [NA] e ureia), e cinco doses do nutriente (0, 60, 120, 180 e 240 kg ha-1 N por corte) aplicadas a cada 30 dias. Neste experimento foram utilizados NA e ureia enriquecidos com 15N como uma ferramenta para quantificar a recuperação do N advindo do fertilizante, nas plantas e no sistema solo-planta. As plantas foram cortadas para avaliar a produção de matéria seca, concentração de N na parte aérea e recuperação. O índice de área foliar (LAI), radiação fotossinteticamente ativa interceptada (PARi) e índice de clorofila (CI) foram mensurados no dia anterior ao corte. As amostras de solo foram coletadas nas parcelas que receberam NA e foram fracionadas em carbono orgânico particulado (POC), fração leve livre (FLF) e fração mineral (C-min); O teor de C nas frações foi quantificado. Os resultados demonstraram que o NA pode ser uma fonte mais eficiente somente quando a quantidade de precipitação é insuficiente para incorporar o fertilizante ao solo, resultando em maior produção de forragem, na somatória dos dois anos ambas as fontes produziram a mesma quantidade de matéria seca onde a maior produtividade 37,2 Mg ha-1, foi atingida com a dose de 210 kg ha-1 N por corte. Por outro lado, a quantidade de N recuperado pelo sistema de planta+solo foi maior quando a ureia foi utilizada, com destaque para a quantidade de N no solo, onde a ureia foi capaz de manter 10% mais N que o NA, a recuperação do nutriente diminuiu à medida que as doses foram elevadas. Nenhuma alteração no conteúdo de C foi notada devido às diferentes doses de N utilizadas, no entanto o POC e o C-min foram mais sensíveis às mudanças na camada de 0-0,1 m do que na camada de 0,1-0,2 m. / Cynodon hybrids are known by their ability to respond to high rates of nitrogen (N). In tropical conditions, N may become an environmental and financial issue due to its low efficiency of use by plants, mainly as a result of losses by volatilization and/or leaching. Therefore, the aims with this work were to evaluate N sources and rates on growth and dry matter yield of Tifton 85 and to determine changes in soil carbon (C) fractions in response to N fertilization. The 2-yr field experiment was conducted from 2012 to 2014, and consisted of a factorial design. Treatments were a combination of two sources of N (ammonium nitrate [AN] and urea) and five rates of the nutrient (0, 60, 120, 180 and 240 kg ha-1 N per cut) applied broadcast every 30 days. This study used AN and urea enriched with 15N as a tool to quantify the recovery of N derived from fertilizer in plants and the soil-plant system. Forage was cut at 30-d intervals for dry matter yield, shoot N concentration determinations and N recovery. The leaf area index (LAI), photosynthetic active radiation intercepted (PARi) and chlorophyll index (CI) were evaluated on the day before clipping. Soil samples were collected in plots receiving AN and they were fractionated in to particulate organic carbon (POC), free light fraction (FLF) and mineral fraction (C-min); The C concentration of the various fractions was determined. Results showed that AN was a more efficient source only when the amount of precipitation is insufficient to incorporate the fertilizer to the soil, resulting in increased production, in the sum of the two years both sources produced the same amount of dry matter in which the highest productivity, 37.2 t ha-1 , was achieved at the rate of 210 kg ha-1 N per cutting. On the other hand, the amount of N recovered by the plant+soil system was higher when urea was used, especially the amount of N in the soil, where urea was able to maintain 10% more N than AN, the nutrient recovery decreased as the rates were increased. No change in soil C concentration was detected in response to the different N rates used, however the POC and the C-min were more sensitive to changes in the layer of 0-0.1 m than the layer from 0.1-0.2 m.