With the constant diversification of cropping systems and the constant increase in farm size, new trends are observed for agricultural machinery. The increase in size of the machinery and the increasing number of contractors has opened the market to selfpropelled forage harvesters equipped with headers that can harvest row crops in any direction, at any spacing. High-capacity pull-type forage harvesters are also in demand but no commercial model offers non-row sensitive corn headers. The objectives of this research were to collect data and develop models of specific energy requirements for a prototype non-row sensitive corn header. The ability to better understand the processes involved during the harvesting and the modeling of these allowed the formulation of recommendations to reduce the loads on the harvester and propelling tractor. Three sets of experiments were performed. The first experiment consisted of measuring specific energy requirements of a non-row sensitive header, in field conditions, and to compare them with a conventional header. The prototype tested was found to require approximately twice the power than a conventional header of the same width, mostly due to high no-load power. Some properties of corn stalk required for the modeling of the energy needs, that were not available in literature, were measured in the laboratory. Those include the cutting energy with a specific knife configuration used on the prototype header and the crushing resistance of corn stalk. Two knife designs were compared for required cutting energy and found not to be significantly different with values of 0.054 J/mm2 of stalk cross-section area and 0.063 J/mm2. An average crushing resistance of 6.5 N per percent of relative deformation was measured. Three mathematical models were developed and validated with experimental data to predict and understand the specific energy needs of the non-row sensitive header. An analytical model was developed based on the analysis of the processes involved in the harvesting. A regression model was developed based on throughput and header speed and a general model suggested in literature was also validated with the data. All three models were fitted with coefficient of correlation between 0.88 to 0.90.

With the constant diversification of cropping systems and the constant increase in farm size, new trends are observed for agricultural machinery. The increase in size of the machinery and the increasing number of contractors has opened the market to selfpropelled forage harvesters equipped with headers that can harvest row crops in any direction, at any spacing. High-capacity pull-type forage harvesters are also in demand but no commercial model offers non-row sensitive corn headers. The objectives of this research were to collect data and develop models of specific energy requirements for a prototype non-row sensitive corn header. The ability to better understand the processes involved during the harvesting and the modeling of these allowed the formulation of recommendations to reduce the loads on the harvester and propelling tractor. Three sets of experiments were performed. The first experiment consisted of measuring specific energy requirements of a non-row sensitive header, in field conditions, and to compare them with a conventional header. The prototype tested was found to require approximately twice the power than a conventional header of the same width, mostly due to high no-load power. Some properties of corn stalk required for the modeling of the energy needs, that were not available in literature, were measured in the laboratory. Those include the cutting energy with a specific knife configuration used on the prototype header and the crushing resistance of corn stalk. Two knife designs were compared for required cutting energy and found not to be significantly different with values of 0.054 J/mm2 of stalk cross-section area and 0.063 J/mm2. An average crushing resistance of 6.5 N per percent of relative deformation was measured. Three mathematical models were developed and validated with experimental data to predict and understand the specific energy needs of the non-row sensitive header. An analytical model was developed based on the analysis of the processes involved in the harvesting. A regression model was developed based on throughput and header speed and a general model suggested in literature was also validated with the data. All three models were fitted with coefficient of correlation between 0.88 to 0.90.

An analytical transport/reaction model was developed to simulate the catalytic performance of ZnO nanowires as a catalyst support. ZnO nanowires were chosen because they have easily characterized, controllable features and a spatially uniform morphology. The analytical model couples convection in the catalyst flow channel with reaction and diffusion in the porous substrate material; it was developed to show that a simple analytical model with physics-based mass transport and empirical kinetics can be used to capture the essential physics involved in catalytic conversion of hydrocarbons. The model was effective at predicting species conversion efficiency over a range of temperature and flow rate. The model clarifies the relationship between advection, bulk diffusion, pore diffusion, and kinetics. The model was used to optimize the geometry of the experimental catalyst for which it predicted that maximum species conversion density for fixed catalyst surface occurred at a channel height of 520 [mu]m. A modeling study of thermoelectric (TE) vehicle waste heat recovery was conducted based on abundant and inexpensive Mg₂ Si[subscript 0.5] Sn[subscript 0.5] and MnSi[subscript 1.75] TE materials with consideration of performance at the system and TE device levels. The modeling study identified a critical TE design space of fill fraction, leg length, n-/p-type leg area ratio, and current; these parameters needed to be optimized simultaneously for positive TE power output. The TE power output was sensitive to this design space, and the optimal design point was sensitive to engine operating conditions. The maximum net TE power for a 29.5 L strip fin heat exchanger with an 800 K exhaust flow at 7.9 kg/min was 2.25 kW. This work also includes two generations of TE waste heat recovery systems that were built and tested in the exhaust system of a Cummins 6.7 L turbo Diesel engine. The first generation was a small scale heat exchanger intended for concept validation, and the second generation was a full scale heat exchanger that used the entire exhaust flow at high speed and torque. The second generation heat exchanger showed that the model could accurately predict heat transfer, and the maximum experimental heat transfer rate was 15.3 kW for exhaust flow at 7.0 kg/min and 740 K. / text

A temperatura do solo influencia a maioria dos processos físicos, químicos e biológicos que ocorrem no solo. O modelo analítico exponencial-senoidal em uma dimensão descreve razoavelmente bem a temperatura no solo, T (oC), como função do tempo, t (s), e da profundidade, z (m), 0 &#8804; z < &#8734;. A temperatura da superfície pode ser representada pela soma de duas senóides, uma relacionada com variações de temperatura anuais, outra com variações diárias, cada uma tendo uma amplitude constante. Uma correção para a variação temporal de amplitude diária é aqui introduzida. A equação do calor é resolvida analiticamente, com pouco aumento em complexidade em relação à solução tradicional. Predições de temperatura obtidas pela nova solução analítica foram comparadas com predições obtidas da solução usual, que trata a amplitude diária como constante. Para comparar as predições, foram necessários valores experimentais de certos parâmetros que aparecem nestas equações; foi suficiente usar valores típicos, obtidos na literatura. Predições são comparadas utilizando quatro conceitos: (i) profundidade de amortecimento, D; (ii) profundidade de penetração, zM; (iii) erro quadrático médio (EQM); e (iv) erro quadrático médio na forma de uma integral (EQMI). O conceito de zM foi aqui introduzido, acompanhado por uma equação simples que permite calcular qual é a profundidade zm tal que, se temperatura T(zM,t) for aproximada como Ta (valor médio da temperatura ao longo do ano, em zM), o erro em tal aproximação será igual ou menor um certo valor previamente definido, por exemplo, de 0,1 oC. O conceito de EQMI, também introduzido nesta tese, substitui o somatório que aparece no EQM por uma integral definida, e serve para comparar dois modelos analíticos, o que era o caso desta tese. Valores de D e zM mostram que a correção é desprezível para z > 0,6 m. Valores de EQM mostram que a correção é considerável para z = 0,1 m. Nesta profundidade, o valor máximo foi EQM = 0.30 oC para dias inteiros, e EQM = 0.29 oC para meses inteiros. Valores de EQMI foram praticamente iguais aos valores de EQM. Para qualquer profundidade a correção introduzida, ainda que considerável, é pequena. Entretanto, a única informação adicional requerida para aplicar a equação nova é a informação de variação temporal da amplitude diária. Desta forma, pode-se sugerir que a nova equação seja preferida, quando esta informação esteja facilmente disponível a partir de dados experimentais. / Soil temperature influences many physical, chemical and biological processes that occur in soil. The exponential-sinusoidal one-dimensional analytical model reasonably describes soil temperature, T (oC), as a function of time, t (s), and depth, z (m), 0 &#8804; z < &#8734;. Surface temperature may be represented by the sum of two sinusoids, one related to annual and the other to daily temperature variations, each one having constant amplitude. A correction for the temporal variation of daily amplitude is introduced here. The heat equation is solved analytically, with minimal increase in complexity compared to the traditional solution. Temperature predictions obtained from the novel analytical solution are compared with predictions from the usual solution that treats the daily amplitude as a constant. Comparisons demanded experimental parameters, which were obtained from scientific literature. Predictions are compared using four concepts: (i) damping depth, D; (ii) penetration depth, zM; (iii) root mean squared error (RMSE); and (iv) root mean squared error defined by a definite integral (RMSEI). The concept of zM was introduced here, through a simple equation, which allows calculation of the depth zm, at which T(zM,t) can be approximated to Ta (average annual value of soil temperature at zM). The concept of RMSEI was also introduced here, and replaces a sum by a definite integral. The RMSEI can be used to compare analytical models, as it was the case here. Values of D and zM show that the correction is negligible for z > 0,6 m. Values of RMSE show that the correction is considerable for z = 0,1 m. For individual days, at a depth z = 0,1 m, the maximum value was RMSE = 0.30 oC; for whole months, the maximum value was RMSE = 0.29 oC. RMSEI values were practically the same as RMSE values. The correction introduced here was small at all depths. However, the only additional information required to apply the novel equation is information on temporal variation of daily amplitude, so this equation should be preferred when such data are readily available.

The purpose of this work was to find a suitable calculation method for predicting the function of distribution systems in the design calculations of process and energy equipment. In particular, it aimed at describing the distribution of the working fluid flow in a dividing distribution system and a combined Z-type distribution system (with nozzles located parallel to opposite sides of the system). Analytical and CFD calculation tools validated by data from the performed physical experiments were used in this work. In the CFD method, the prediction of the dividing flow was performed for full 3D and simplified 2D geometry of Z-type distribution systems. The carried-out analyzes show that the prediction of the distribution system function obtained by both analytical and numerical approaches is accurate enough. The relative difference between the experimental and computational relative standard deviations did not exceed 9 %. The main disadvantage of 3D CFD analysis, especially concerning the purpose of the intended application, i.e., the inclusion of a distribution model in a complex modeling system for the initial design of heat transfer equipment, was the extremely long computational time. Analytical models appear to be a reasonable compromise between the accuracy of the flow distribution prediction and the computational times.

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Yes / In this paper, an analytical model that represents the streamwise velocity distribution for open channel flow with submerged flexible vegetation is studied. In the present vegetated flow modelling, the whole flow field has been separated into two layers vertically: a vegetated layer and a non-vegetated free-water layer. Within the vegetated layer, an analysis of the mechanisms affecting water flow through flexible vegetation has been conducted. In the non-vegetated layer, a modified log-law equation that represents the velocity profile varying with vegetation height has been investigated. Based on the studied analytical model, a sensitivity analysis has been conducted to assess the influences of the drag and friction coefficients on the flow velocity. The investigated ranges of drag and friction coefficients have also been compared to published values. The findings suggest that the drag and friction coefficient values are non-constant at different depths and vegetation densities, unlike the constant values commonly suggested in literature. This phenomenon is particularly clear for flows with flexible vegetation, which is characterised by large deflection.

No / Vegetation remains to be an important factor that can hinder the river flow. It needs innovative management scheme, in order to adapt these changes and ensure sustainability of their multiple usages. Vegetation plays an important role in floods and droughts adaptation within river system to alleviate any flood that may propagates from river to its surrounding. Vegetation within river can also retard its flow to cause building-up of deposition, and further adding to uncertainty of water use under extreme droughts. Due to these, it is important to study and understand vegetation drag behaviour toward flow in order to prevent flood risk and water security with hydrological drought in the basin and any other negative impact caused by it. In this study, an analytical approach for river flooding has been studied by improved representation of drag coefficient CD in flow velocity distribution modelling. The analysis of flow parameters, i.e. Reynolds number, on the drag coefficient CD has been conducted. The presented model has been used and analysed in open channel flows with flexible vegetation. In modelling, the flexible vegetated channel layers were divided into vegetation, top of vegetation and water layer zones in the model. The balance of forces for each layer has been established by validation using different reported measured data. The modelling results showed reasonably corresponding prediction of velocity profile in flows with flexible vegetation.

I propose compact models of single-gate (SG) and double-gate (DG) JFETs predicting the current-voltage characteristics for both long and short channel devices. In order to make the current equation continuous through all operating conditions from subthreshold to well-above threshold, without non-physical fitting parameters, mobile carriers in depletion region are considered. For describing the short channel behavior, relevant parameters extracted from the two-dimensional analytical solution of Poisson's equation are used for modifying long channel equations. Comparisons of models with the numerical simulation showing close agreement are presented. Based on models, merits of DG JFET over SG JFET and SG MOSFET are discussed by examining the schematic circuit diagram describing the relation between gate and channel potentials for each device. / text

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