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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
361

Controle de perdas na ensilagem de capim Tanzânia (Panicum maximum Jacq. cv. Tanzânia) sob os efeitos do teor de matéria seca, do tamanho de partícula, da estação do ano e da presença do inoculante bacteriano. / Losses of tanzania grass silage (panicum maximum, jacq. cv. tanzania) affected by dry matter level, particle size, season and bacterial inoculant addition.

Mauricio Scoton Igarasi 14 March 2002 (has links)
O objetivo do presente projeto de pesquisa foi a caracterização do processo de ensilagem de capim Tanzânia (Panicum maximum, Jacq.), avaliando a eficiência de colheita da forragem, as perdas durante o processo fermentativo, e o valor nutritivo da silagem. Para a colheita e captação da forragem foi utilizada uma colhedora de forragem comercial, efetuando cortes no inverno e no verão, em uma área destinada a produção de silagem. Para cada corte foram estabelecidos 12 tratamentos com 4 repetições, sendo analisados os efeitos da alteração do teor de matéria seca (forragem na umidade original, pré-emurchecida e a adição de polpa cítrica), do tamanho de partículas (2 níveis), e da aplicação ou não de aditivo bacteriano (1 milhão UFC viáveis/g de forragem ensilada). Nas amostras do material ensilado (forragem) e da silagem (após 120 dias do fechamento dos silos experimentais), foram analisadas o tamanho de partícula, atividade de água, condutividade elétrica,MS, EE, PB, MM, N-NH3, FDA, FDN, N-FDN, N-FDA, Lignina, nitrogênio amoniacal, pH e poder tampão. Também foram avaliadas as perdas de matéria seca na forma de gases, a produção de efluente, recuperação de matéria seca, além da determinação da estabilidade aeróbia da silagem. A análise estatística caracteriza-se em arranjo em parcelas subdivididas (split-plot), sendo que as principais causas de variação foram atribuídas à parcela (alteração do teor de matéria seca, tamanho de partícula, e inoculante bacteriano), e a estação do ano (inverno ou verão), foi atribuída na sub-parcela. A adição de polpa cítrica melhorou as características fermentativas (pH, nitrogênio amoniacal); diminuiu as perdas no processo fermentativo (efluente e gases), aumentou a recuperação de matéria seca, entretanto piorou a estabilidade aeróbica da silagem; aumentou o teor e a taxa de recuperação do NDT, contudo elevou o custo relativo do NDT. O pré emurchecimento elevou as perdas na colheita, entretanto diminuiu as perdas na fermentação (gases, efluente e recuperação de matéria seca) e a estabilidade aeróbica da silagem; diminuiu também o teor de nitrogênio amoniacal, mas não alterou o pH; e apresentou os menores índices de recuperação de NDT. A redução no tamanho da partícula promoveu o aumento na densidade da silagem, entretanto não refletiu na produção de efluente e gases, porém houve a redução na recuperação de matéria seca; melhorou a estabilidade aeróbica da silagem; diminuiu o pH, entretanto elevou o teor de nitrogênio amoniacal; não ocasionou efeito no teor, na taxa de recuperação e no custo relativo do NDT. A adição do inoculante bacteriano não refletiu em alterações nos parâmetros fermentativos (pH e nitrogênio amoniacal), na produção de efluentes e na recuperação de matéria seca, porém promoveu a redução na produção de gases; contudo, houve a elevação no custo relativo do NDT. No corte de verão, a melhoria no processo de ensilagem pode ser alcançado através da elevação do teor de matéria seca. A maior eficiência de recolhimento de forragem pré-emurchecida e a redução no tamanho de partícula, constitui-se em áreas promissoras para o desenvolvimento da indústria de equipamentos de colheita para ensilagem de forragens. / The present trial aimed to evaluate the ensiling process of Tanzania grass (Panicum maximum, Jacq. cv. Tanzania), focusing on efficiency of forage chopping and harvesting, fermentation losses and nutritive value. A pull-type forage chopper was used for harvesting the winter and the following summer cuts in a commercial grass field. In both cuts (sub-plot), twelve treatments, with four replicates each, were assigned to a split plot experimental design, where main (plot) effects were combined into three factors: dry matter level (green chopped, wilted and pelleted citrus pulp -PCP added); particle size (small and large) and lactic acid bacteria (LAB, 1 million CFU. g -1 forage) inoculant, (w or w/o). Forage recovery was measured in the field by using 1x1 m quadrats. Silage fermentation losses were evaluated in 20L plastic buckets provided with Bunsen type valve and effluent absorbent substrate. Forage and silage samples were sieved in a Penn State Forage Separator for particle size measurements and analyzed for water activity (Aw), electrical conductivity (EC), DM, CP, NDF, ADF,EE, ash, N-NH3,, ADIN, NDIN, pH and buffering capacity (BC). After the silos were unloaded, dry matter losses, recovery and aerobic stability were measured. The addition of PCP enhanced the fermentation parameters (lower pH, N-NH3, effluent and gases yield), dry matter and TDN recovery rates and the observed aerobic stability was offset by the improved fermentation profile. Wilting also improved fermentation parameters and aerobic stability, with no changes in silage pH, however, led to a poor TDN recovery rate as a result of increased chopping and harvesting losses. Smaller silage particle size determined increases in fresh and dry matter bulk densities, and lower pH levels, which were associated with better aerobic stability. Gases and effluent yields as well TDN recovery rate and cost, remained unchanged with particle size reduction even tough, higher N-NH3 levels and decreased dry matter recovery rates were observed. LAB inoculant resulted in higher forage TDN cost, mainly due to unchanged silage fermentation profile, except for lowered gases yield. In the summer cut, an improved Ta nzania grass ensiling process might be achieved either by lowering forage moisture content and/or reducing particle size. The machinery industry should play a major role in accomplishing the upgraded needs in forage choppers market.
362

Loss Aversion : A Study of Changes in Loss Aversion Towards a 50/50 Gamble

Smedensjö Myhre, Mauritz, Nilsson, David January 2020 (has links)
Loss aversion is a theory which states that losses loom larger than gains. Negative outcomes are weighted heavier than positive outcomes in decision making but could this weight change when different prospects are evaluated? This thesis focuses on how the loss aversion changes toward different magnitudes of a loss for young individuals when they are faced with a 50/50 chance of winning or losing a gamble. The loss aversion is tested toward six different magnitudes of a potential loss ranging from 100 kr to 4 000 kr. The loss aversion toward these six different magnitudes is then compared to examine how the loss aversion changes. This data was collected using a survey experiment that was digitally distributed to economics students at Linnaeus University in Växjö.The results from the subsequent analysis showed that the loss aversion was not constant towards all six losses. The loss aversion was different in ten out of fifteen pairwise comparisons. Respondents became more loss averse when the loss increased but the loss aversion did however seem to be less sensitive to increases in losses above the 1 000 kr mark.
363

Coordinated active power reduction strategy for voltage rise mitigation in LV distribution network

Ainah, Priye 16 August 2018 (has links)
Integration of renewable energy systems by the utility, customers, and the third party into the electric power system, most especially in the MV and LV distribution networks grew over the last decade due to the liberalization of the electricity market, rising energy demand, and increasing environmental concern. The distributed rooftop PV system contributes to relieve the overall load, reduce losses, avoid conventional generation upgrade, and better matching of demand on the LV distribution network. Originally, the LV distribution network is designed for unidirectional current flow, that is from the substation to customers. However, a high penetration of rooftop solar PVs (with power levels typically ranging from 1 – 10 kW) may lead to the current flowing in the reverse direction and this could result in a sudden voltage rise. These negative impacts on the network have discouraged the distribution network operators (DNOs) to allow increased PV penetration in the LV distribution network because some customers load, and equipment are sensitive to voltage perturbation. Presently, the most applied voltage rise mitigation strategy for high rooftop solar PV penetration is the total disconnect from the LV distribution network when the voltage at the point of common coupling (PCC) goes above statutory voltage limits. However, the sudden disconnection of the PV system from the grid can cause network perturbation and affect the security of the network. This action may also cause voltage instability in the network and can reduce the lifetime of grid equipment such as voltage regulators, air conditioner etc. Due to this negative impact, different voltage rise mitigation strategies such as the active transformer with on load tap changers (OLTC), distributed battery energy storage system and reactive power support (D-STATCOM, etc.) have been used to curtail voltage rise in the distribution network. However, the implementation of D-STATCOM device on a radial LV distribution network results in high line current and losses. This may be detrimental to the distribution network. Therefore, in this thesis, a coordinated active power reduction (CAPR) strategy is proposed using a modified PWM PI current control strategy to ramp down the output power and voltage of a grid-tied voltage source inverter (VSI). In the proposed strategy, a reactive reference is generated based on the measured voltage level at the PCC using a threshold voltage algorithm to regulate the amplitude of the modulating signal to increase the off time of the high frequency signal which shut down the PV array momentary in an extremely short time and allow the VSI to absorb some reactive power through the freewheeling diode and reduce voltage. The proposed CAPR strategy was designed and simulated on a scaled down simple radial LV distribution network in MATLAB®/Simulink® software environment. The results show that the CAPR can ramp down the PV output power, reduce reverse power flow and reduce the sudden voltage rise at the point of common coupling (PCC) within ±5% of the standard voltage limit. The study also compares the performance of the proposed CAPR strategy to that of the distributed static compensator (D-STATCOM) and battery energy storage system (BESS) with respect to response time to curtail sudden voltage rise, losses and reverse power flow. The investigation shows that the D-STATCOM has the faster response time to curtail voltage rise. However, the voltage rise reduction is accompanied by high current, losses and reverse active power flow. The introduction of the BESS demonstrates better performance than the D- STATCOM device in terms of reverse power flow and losses. The CAPR strategy performs better than both D-STATCOM and BESS in terms of line losses and reverse power flow reduction.
364

Vliv nastavení regulátoru servopohonu na energetickou náročnost / Influence of servodrive controller settings on energy consumption

Kura, Ondřej January 2021 (has links)
The aim of this work is to investigate the energy consumption of the servo drive at different control settings. First, the theoretical part describes the servo drive as a mechatronic system with subsequent disassembly in terms of losses and efficiency, where all the losses that occur in the servo drives are defined. Subsequently, the theoretical part concludes with a chapter on controllers, thanks to which it is possible to control servo drives and describes their influence on the resulting control. In the practical part, a model of a DC motor with a linear axis and regulation was first created in the Simulink program. Subsequently, the Matlab program defined motion with linear acceleration and motion using S-curves, which controlled the model. Then the model was measured at different settings of the controllers and the resulting waveforms together with the energy values were compared with each other. In the second half of the practical part of this work, a real servo drive was then measured with a subsequent comparison with the created model. In this comparison, the resulting waveforms and energy values were also compared. The result of this work is then to determine the effect of changes on the resulting control, which are made in the controller settings. The functional models can then be used to determine how the various servo drives will behave under the given control conditions.
365

Zlepšení energetických parametrů asynchronních strojů malého výkonu / Improvement Power Parameter of Small Induction Motors

Kuda, Roman January 2011 (has links)
This master´s thesis treats of all asynchronous motor. The project is about type and distribution motors, about differences between three-phase and single-phase machines and efficiency. In one of the chapters describes a particular type of engine with all the parametersfrom the manufacturer. This engine is completely analyzed and it is measured in detail. Then the project deals with the division, the calculation of losses and subsequent possibilities to increase the efficiency of induction motor. In the last chapter is calculation of single-phase motors, based on the engine produced.
366

Vytápění a větrání výrobní a skladové haly / Ventilation and heating system of a production and storage hall

Bližňák, Jakub January 2009 (has links)
The objective of this master thesis is to design heating and ventilation systems for a production and storage hall and a contiguous administrative part of the building. The basis of design is in calculation of thermal losses and gains of the building. The objective of design is to reach requisite microclimate for single spaces and operations. System of heating, ventilation and cooling are elaborated in drawing documentation.
367

Výpočtové modelování mechanických ztrát v klikovém mechanismu / Computational modeling of cranktrain mechanical losses

Smetana, Roman January 2010 (has links)
In the introduction of master’s thesis is introduced the common identification with basics of friction, wear and mechanical losses. Master’s thesis includes description of solving losses by help of the MBS software and analysis of mechanical losses in the crank train. In the last part of work is introduced design for decrease mechanical losses in the crank train. At the close of master’s thesis are reviewed records.
368

Stanovení ztrát při nestacionárním proudění kapaliny v trubici / Hydraulic losses during unsteady flow of liquid in a pipe

Svoboda, Jakub January 2011 (has links)
This thesis is focused on solving hydraulic losses during unsteady flow of liquid in pipe for both laminar and turbulent flow in smooth pipes. Radial viscosity distribution is assumed to be the same as for steady flow. Viscosity distribution is derived from velocity profile, which is mathematically described with suitably chosen function. Laplace images of unsteady velocity profile and mean velocity in cross-section are derived depending on pressure difference. Loss coefficient is derived and on base of transfer matrix method, self-numbers are calculated. Self-numbers represent attenuation and own frequency. Self-numbers are compared to values from software called “F-ACHAR” and loss coefficient is compared to the one for quasi-steady method.
369

Výpočtový model kotle KWH / Computational Model of KWH Boiler

Koiš, Jiří January 2014 (has links)
The subject of this thesis is the computational model of existing KWH boiler. There is a short research in the introduction, which deals with combustion heat of considered boiler.  The stoichiometric and balance calculations of gasification chamber ZKG are performed first. The Balance calculations are based on the boiler thermal loss calculations, the losses were determined experimentally. The entire calculation is processed in a computational program for purposses of debugging and manipulation with partial calculations. The computational model that is proposed in this thesis provide better boiler proces understandig. The real boiler measurement is performed for evaluation. The next point is the result analyses, that shows potential boiler efficiency improvements.
370

Ztráty ve valivých ložiscích / Power Losses of a Rolling Bearing

Šedo, Matej January 2015 (has links)
Subject of this thesis is analysis of friction power losses in rolling bearings and design and implementation of computing program. Thesis is divided into six chapters. At the beginning there is overview of different types of rolling bearings and their system of lubrication. Fundamentals of elastohydrodynamic lubrication are described together with effects that occur in lubricant. Remaining part is focused on friction in rolling bearing its sources and calculation. Other programs for computing friction losses are shown and own program is designed. Designed program is applied on bearings of chosen type and results are compared with existing models.

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