Dissertations / Theses on the topic 'Direct field'
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Bai, Kun. "Direct field-feedback control for permanent magnet spherical motors." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/50141.
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There are emerging requirements for high accuracy multi-DOF actuators in numerous applications. As one of the novel motors capable of multi-DOF manipulation, permanent magnet spherical motors (PMSMs) that can provide continuous and dexterous motion in one joint have been widely studied for their advantages in structure and energy efficiency. The demands to bring forward the performance of PMSMs for precision applications have motivated this thesis to develop a closed-loop orientation control system with high accuracy and bandwidth. Unlike traditional control methods for PMSMs, which rely on explicit orientation feedback, a new control method (referred to here as direct field-feedback control or in short DFC) directly utilizing the magnetic fields for feedback have been developed in this thesis. Because magnetic field measurements are almost instantaneous and the need for real-time orientation estimation is eliminated in DFC, the system sampling time is greatly reduced. Meanwhile, several field-based methods have been developed for the major components in the DFC system and each component can be processed independently and concurrently with the magnetic field measurements. The parallel computation further improves the system bandwidth and also reduces accumulated error. The DFC system has been experimentally implemented and evaluated. The results show excellent control performances in terms of accuracy and bandwidth. To facilitate the design and analysis of the DFC system, several new algorithms have been developed, which include the modeling and computing of magnetic fields as well as forces and torques, an analysis of bijective relationship between orientation and magnetic fields, and a method for calibration and reconstruction of the rotor magnetic field in 3 dimensional space. These algorithms not only enable the implementation of the DFC system for a PMSM, but also benefit the PMSM studies in design, modeling and field-based sensing. While the immediate outcome of this research is a control system for PMSMs, this new control method can be applied to a broad spectrum of electromagnetic motion systems.
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Andrikopoulos, Pavlos. "Direct electric field visualization in semiconductor planar structures." Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FAndrikopoulos.pdf.
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Thesis (M.S. in Applied Physics and M.S. in Systems Engineering)--Naval Postgraduate School, December 2006.Thesis Advisor(s): Nancy M. Haegel, David Jenn. "December 2006." Includes bibliographical references (p. 125). Also available in print.
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Källström, Petter. "Direct Digital Frequency Synthesis in Field-Programmable Gate Arrays." Thesis, Linköping University, Department of Electrical Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-56550.
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This thesis is about creation of a Matlab program that suggests and automatically generates a Phase to Sine Amplitude Converter (PSAC) in the hardware language VHDL, suitable for Direct Digital Frequency Synthesis (DDFS). Main hardware target is Field Programmable Gate Arrays (FPGAs).
Focus in this report is how an FPGA works, different methods for sine amplitude generation and their signal qualities vs the hardware resources they use.
Detta exjobb handlar om att skapa ett Matlab-program som föreslår och implementerar en sinusgenerator i hårdvaruspråket VHDL, avsedd för digital frekvenssyntes (DDFS). Ämnad hårdvara för implementeringen är en fältprogrammerbar grindmatris (FPGA).
Fokus i denna rapport ligger på hur en FPGA är uppbyggd, olika metoder för sinusgenerering och vilka kvaliteter på sinusvågen de ger och vilka resurser i hårdvaran de använder.
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Mahaffey, Joshua Vincent. "A Direct Approach at Field Computation Using the FMM Framework." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1330913863.
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Sitapati, Kartik. "Mixed-Field Finite-Element Computations." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11195.
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A new method called the Direct Method is developed to solve for the propagating modes in waveguides via the finite-element method. The variational form of the Direct method is derived to ensure that an extremum is reached. The Direct method uses Maxwell's equations directly, both zero and first-order, scalar and vector bases that are used in the finite-element formulation. The direct solution method solves for both the magnetic and electric fields simultaneously. Comparisons are made with the traditionally used vector-Helmholtz equation set. The advantages and disadvantages of the newly developed method is described as well as several results displayed using the WR-90 waveguide and a circular waveguide as test waveguides. Results include a partially filled dielectric loaded rectangular waveguide. The effects of including the divergence of the fields in the functional as penalty terms on the quality of results obtained by the Direct method and the vector-Helmholtz method is explored. The quality of results is gauged on the accuracy of the computed modes as well as the elimination or a significant reduction in the number of 'spurious modes' that are often encountered in solutions to waveguide problems. It is shown that computational time for the solution and computer storage requirements exceed the typically used Helmholtz equation method but the results obtained can be more accurate. Future work may include developing a sparse eigenvalue solution method that could reduce the solution time and storage requirements significantly.
The Direct method of solution in dynamics resulted after an initial search in magnetostatics for methods to solve for the magnetic field without using the magnetic-vector potential using finite-element methods. A variational derivation that includes the boundary conditions is developed for the magnetic-vector potential method. Several techniques that were used to attempt accurate solutions for the magnetostatic fields with multiple materials and without the use of the magnetic-vector potential are described. It was found that some of the newly developed general techniques for magnetostatics are only accurate when homogeneous media are present. A method using two curl equations is developed which is a Direct method in magnetostatics and reveals the interaction between the bases used. The transition from magnetostatics to dynamics is made and similar Direct methods are applied to the waveguide problem using different bases.Ph. D.
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Vedula, Prakash. "Study of scalar transport in turbulent flows using direct numerical simulations." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/12119.
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Shih, Chun Yu. "Direct numerical simulation of charged colloids in an oscillating electric field." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/200506.
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Jing, Hengzhen. "Direct antenna modulations for UWB pulse transmission and near field communications." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1835265221&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Varjo, S. (Sami). "A direct microlens array imaging system for microscopy." Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526213828.
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Abstract This work presents the development of a new optical imaging system. Previous objections have claimed that it is easier to build a single good quality field lens than a large number of good microlenses and it is therefore better to use a field objective. The possible benefits from a field lens are here traded for a more compact and cost-efficient design that would be suitable for field diagnostics. The new imaging setup described in this work is based on a microlens array capable of capturing light field data and no other refractive optics are used. Hundreds of lenses with a diameter range 100 to 200 µm are used to capture small elementary images containing a small part of the sample. The design uses a single light source aperture enabling signal separation between the elementary images from the neighboring lenses. Prior art uses, for example, physical structures behind lenses for signal separation, making the suggested approach less complex. Further, the possibility for using printed microlens arrays for imaging instead of expensive glass lenses is studied. The captured light field data consisting of elementary images must be rendered for human viewing. A new method is developed where the rendering is based on gathering the resulting pixel values on a plane set freely in object space, enabling single pass rendering with possibilities to apply statistics to the contributing data improving the rendering quality. Commonly used projection or mosaicing based integration approaches do not allow this. The developed system has its resolution limited by the camera sensor pixel size and objects a few micrometers in size can be resolved. The results show that the imaging setup can be used to capture semi-microscopic images without expensive magnifying optics and it is useful in selected applications. For example, it is shown that the eggs of parasites causing Schistosomiasis can be detected automatically in a microscope sample. It is estimated that the system could be mass produced at low cost. The new system has no moving parts making it less susceptible to mechanical failures and it is compact in comparison with conventional microscopes. It could be a part of a point of care solution needed in diagnostic fieldworkTiivistelmä Tässä väitöskirjassa kuvataan ja tarkastellaan uutta mikrolinsseihin perustuvaa mikroskooppista kuvantamismenetelmää. Aiemmin mikrolinssejä on käytetty tavanomaisten mikroskooppien ominaisuuksien laajentamiseen. Tässä työssä perinteiset mikroskooppiobjektit korvataan linssimatolla, kompaktin ja kustannustehokkaan rakenteen saavuttamiseksi. Käyttökohteena laitteelle on kenttädiagnostiikka. Uusi kuvausjärjestelmä perustuu mikrolinssimattoihin, joilla pystytään näytteistämään valokenttää. Muuta taittavaa optiikka ei käytetä. Sadat halkaisijaltaan 100-200 µm olevat linssit kuvaavat kukin pienen osan näytteestä. Linssien välisten signaalien sekoittumisen estämiseen käytetään hyvin kontrolloitua valonlähdettä. Aiemmin esitetyissä ratkaisuissa käytetään esimerkiksi fyysisiä rakenteita yksittäisten linssien takana. Nyt esitetty ratkaisu on yksinkertaisempi. Työssä esitetään uusi menetelmä osakuvista muodostuvan datan rekonstruktioon. Tuloskuvien muodostamiseksi pikselien arvot kerätään rekonstruktiopinnalle, joka on sijoitettu vapaasti esineavaruuteen. Tämä mahdollistaa laskennallisesti tehokkaan tuloskuvan muodostuksen, sekä tilastollisten menetelmien käytön tuloksen laadun parantamiseen. Kehitetyn järjestelmän resoluutiota rajoittaa kameran pikselikoko ja sillä voidaan havaita muutaman mikrometrin kokoisia kohteita. Tulokset osoittavat, että kuvausmenetelmä sopii mikroskooppisten kohteiden kuvaamiseen ilman kalliita suurentavia linssejä. Menetelmän käyttökelpoisuutta havainnollistetaan, muun muassa, automaattisella Schistosoma parasiitin munien tunnistuksella virtsanäytteestä. Uusi kuvausjärjestelmä on mahdollista toteuttaa edullisesti, siinä ei ole liikkuva osia ja se on pieni verrattuna tavanomaiseen mikroskooppiin. Esitetty ratkaisu soveltuu yhdeksi vaihtoehdoksi kenttädiagnostiikan tarpeisiin
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Wu, Guangyu 1972. "Direct simulation and deterministic prediction of large-scale nonlinear ocean wave-field." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/33450.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2004.Includes bibliographical references (p. 251-258).
Despite its coarse approximation of physics, the phase-averaged wave spectrum model has been the only type of tool available for ocean wave prediction in the past 60 years. With the rapid advances in sensing technology, phase-resolved nonlinear wave modeling, and high performance computing capability in recent years, the time has come to start developing a new generation tool for ocean wave prediction using direct phase-resolved simulations. The key issues in developing such a tool are: (i) proper specification of initial/boundary conditions of the nonlinear ocean wave-field; (ii) development of efficient algorithm for simulation of large-scale wave-field evolution on high performance computing platforms; (iii) modeling of nonlinear physics in ocean wave evolution such as wave-wave, wave-current, wave-bottom and wave-wind interactions. The objective of this thesis is to address (i), (ii) and part of (iii). For (i), a multi-level iterative wave reconstruction tool is developed to deter- ministically reconstruct a nonlinear ocean wave-field based on single or multiple wave probe records, using both analytic low-order Stokes solutions and High-Order-Spectral (HOS) nonlinear wave model.
(cont.) With the reconstructed wave-field as the initial conditions, the ocean wave-field can then be simulated and forecasted into the future deterministically with the physics-based phase-resolved wave model. A theoretical framework is developed to provide the validity of the reconstructed wave-field and the predictability of future evolution of the reconstructed wave-field for given wave conditions. The effects of moving probe, ambient current and finite water depth on the predictable region are studied respectively. To demonstrate its efficacy and useful- ness, the wave reconstruction tool is applied to reconstruct the full kinematics of steep two- and three-dimensional irregular waves using both wave-basin measurements and synthetic data. Excellent agreements between the reconstructed nonlinear wave-field and the original specified wave data are obtained. In particular, it is shown that the inclusion of high-order effects in wave reconstruction is of significance, especially for the prediction of the wave kinematics such as velocity and acceleration. For (ii), a highly scalable HOS wave model is developed and applied to study both two- and three-dimensional ocean wave-field evolution for a realistic space and time scale.
(cont.) Effective filtering tools are developed to model the wave breaking process in wave evolution. For (iii), the HOS wave model is enhanced to account for not only nonlinear wave-wave interactions, but also nonlinear wave interaction with variable ambient current. With this tool, the effects of variable ambient current on nonlinear wave-field evolution are investigated. As a final illustration, this tool is applied in practical ship motion control. Based on the deterministically forecasted wave-field provided by this tool, an optimal path is obtained to reduce the RMS heave motion of ship in point-to-point transit.
by Guangyu Wu.
Ph.D.
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Strik, Philip Philip Frederik Jozef Simon. "Shaping the single European market in the field of foreign direct investment." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610031.
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Pang, Jing. "Direct global positioning system P-code acquisition field programmable gate array prototyping." Ohio University / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1177700503.
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Rossek, Sacha J. "Direct optical control of a microwave phase shifter using GaAs field-effect transistors." Thesis, Middlesex University, 1995. http://eprints.mdx.ac.uk/10682/.
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The design and analysis of a novel optical-to-microwave transducer based upon direct optical control of microwave gallium arsenide (GaAs) field-effect transistor (FET) switches is the subject of this thesis. The switch is activated by illuminating the gate depletion region of the FET device with laser light having a photon energy and wavelength appropriate to the generation of free carriers (electron-hole pairs) within GaAs. The effects of light on the DC and microwave properties of the GaAs FET are explored and analyzed to permit the characterization of the switching performance and transient response of a reflective microwave switch. The switch is novel in that it utilizes direct optical control, whereby the optically controlled GaAs FET is directly in the path of the microwave signal and therefore relies on optically-induced variations in the microwave characteristics of the switch. This contrasts with previous forms of optically controlled switches which rely on indirect methods with the optical stimulus inducing variations in the DC characteristics of the GaAs FET, such that there is no direct interaction between the optically illuminated GaAs FET and the microwave signal. Measured and simulated results relating to the switching performance and transient response of the direct optically controlled microwave switch have been obtained and published as a result of this work. For the first time, good agreement is achieved between the measured and simulated results for the rise and fall times associated with the transient response of the gate photovoltaic effect in optically controlled GaAs FET switches. This confirms that the GaAs FET, when used as an optically controlled microwave switch, has a transient response of the order of several micro-seconds. An enhanced model of the GaAs FET switch has been developed, which represents a more versatile approach and leads to improved accuracy in predicting switching performance. This approach has been shown to be valid for both optical and electrical control of the GaAs FET. This approach can be used to model GaAs FET switches in discrete or packaged forms and predicts accurately the occurrence of resonances which may degrade the switch performance in both switching states. A novel method for tuning these resonances out of the switch operating band has been developed and published. This allows the switch to be configured to operate over the frequency range 1 to 20 GRz. The agreement between the models and measured data has been shown to hold for two very different GaAs FET structures. The results of the direct optically controlled microwave GaAs FET switch have been used as the basis for the design of a novel direct optically controlled microwave phase shifter circuit; Measured and simulated results are in good agreement and verify that the performance of the optically controlled phase shifter is comparable with previously published results for electrically controlled versions of the phase shifter. The 10 GRz phase shifter was optically controlled over a 1 GRz frequency range and exhibited a mid-band insertion loss of 0.15 dB. The outcome of the work provides the basis for directly controlling the phase of a microwave signal using the output of an optical sensor, with the GaAs FET acting as an optical-to-microwave transducer through a monolithic interface.
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Li, Shaopeng. "Development of algorithms for the direct multi-configuration self-consistent field (MCSCF) method." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6945.
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In order to improve the performance of the current parallelized direct multi-configuration self-consistent field (MCSCF) implementations of the program package Gaussian [42], consisting of the complete active space (CAS) SCF method [43] and the restricted active space (RAS) SCF method [44], this thesis introduces a matrix multiplication scheme as part of the CI eigenvalue evaluation of these methods. Thus highly optimized linear algebra routines, which are able to use data in a sequential and predictable way, can be used in our method, resulting in a much better performance overall than the current methods. The side effect of this matrix multiplication scheme is that it requires some extra memory to store the additional intermediate matrices. Several chemical systems are used to demonstrate that the new CAS and RAS methods are faster than the current CAS and RAS methods respectively. This thesis is structured into four chapters. Chapter One is the general introduction, which describes the background of the CASSCF/RASSCF methods. Then the efficiency of the current CASSCF/RASSCF code is discussed, which serves as the motivation for this thesis, followed by a brief introduction to our method. Chapter Two describes applying the matrix multiplication scheme to accelerate the current direct CASSCF method, by reorganizing the summation order in the equation that generates non-zero Hamiltonian matrix elements. It is demonstrated that the new method can perform much faster than the current CASSCF method by carrying out single point energy calculations on pyracylene and pyrene molecules, and geometry optimization calculations on anthracene+ / phenanthrene+ molecules. However, in the RASSCF method, because an arbitrary number of doubly-occupied or unoccupied orbitals are introduced into the CASSCF reference space, many new orbital integral cases arise. Some cases are suitable for the matrix multiplication scheme, while others are not. Chapter Three applies the scheme to those suitable integral cases that are also the most time-consuming cases for the RASSCF calculation. The coronene molecule - with different sizes of orbital active space - has been used to demonstrate that the new RASSCF method can perform significantly faster than the current Gaussian method. Chapter Four describes an attempt to modify the other integral cases, based on a review of the method developed by Saunders and Van Lenthe [95]. Calculations on coronene molecule are used again to test whether this implementation can further improve the performance of the RASSCF method developed in Chapter Three.
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Parackal, Bhavana. "An Investigation of Low Temperature Direct Propane Fuel Cells." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35896.
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This research is directed toward the investigation of a low temperature direct propane fuel cell (DPFC). Modeling included a parametric study of a direct propane fuel cell using computational fluid dynamics (CFD), specifically FreeFem++ software. Polarization curves predicted by the CFD model were used to understand fuel cell performance. The predictions obtained from the computational fluid dynamics mathematical model for the fuel cell were compared with experimental results. The computational work identified some critical parameters (exchange current density, pressure, temperature) for improving the overall performance of the fuel cell. The model predictions clearly highlighted the role of catalysts in significantly enhancing the overall performance of a DPFC. Experiments were performed using commercial Nafion-Pt based membrane electrode assemblies (MEAs) to obtain a basis for comparison. It is the first report in the literature that a Pt-Ru (Platinum-Ruthenium) MEA was used in the investigation of a DPFC. Also, it was the first study that fed liquid water continuously to a DPFC by using interdigitated flow field (IDFF) at the anode to humidify the dry propane feed gas. During the experiments oscillations were observed at very low current densities i.e. in nA/cm2, which is a rare case and not reported in the literature to date. This observation has raised serious concerns about the existence of absolute open-circuit cell potential difference for a DPFC. The cycling behaviour observed with DPFC indicated the presence of a continuous degradation-regeneration process of the catalyst surface near open-circuit potential. The experimental work further evaluated the performance of fuel cell by measurement of polarization curves.
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Swartling, Gustaf, and William Johansson. "Foreign Direct Investment in Cuba : A study on the 2014 reforms." Thesis, Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-70589.
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Since the Soviet collapse in 1991, Cuba tried intensively to attract foreign direct investments in order to improve the economic situation. The first reform was made in 1995, which was not a success, since both foreign direct investment and joint ventures decreased in the beginning of the 21st Century. In response, the government implemented a new law concerning foreign direct investment in 2014, with more relaxed regulations and increased benefits for the investors. This study aimed to examine whether the 2014 reform had solved the problems that existed under the previous law and the new reforms had helped Cuba’s exports. The purpose was therefore to investigate to which industry foreign direct investment should be allocated. The study took two approaches. First, it applied the Revealed Comparative Advantage model to distinguish effective from ineffective industries. It included a field study that aimed to gain understanding of the effect the new law has had so far, and whether it could improve exports. In addition, the field study attempted to determine where foreign direct investment should be allocated. The results indicated that Cuba has a comparative advantage in two industries: mining and agriculture. These industries were therefore examined in the field study. Key findings showed that ongoing issues, such as bureaucracy, lack of legal security and the wage policies of government employment agencies still exist, despite the introduction of new legislation. However, the new law may create increasing export possibilities in the food and mining industries, since Cuba has an outwardly-orientated policy and large factor proportions in agriculture and mining that could be exploited.Minor Field Study (MFS)
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Johansson, Malin. "Foreign direct investment as a source of skill-upgrading : -a minor field study in Dakar." Thesis, Växjö University, School of Management and Economics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:vxu:diva-5263.
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The last two centuries have been distinguished by technological innovation, liberalization and globalization of the world economy. Out of this environment the multinational enterprises (MNEs) have arisen -seeking the best profit opportunities around the world without consideration to poverty and equality in the host countries. This has raised the interest of the present study where the objective is to assess the impact MNEs have on the host country in terms of transferring know-how. By testing two hypotheses, the study attempts to analyze whether MNEs entail a transfer of skills and also identifies the extent to which MNEs are a potential source of skill-upgrading. The research is realized by a qualitative minor field study in Dakar where 24 semi-structured interviews are carried out at three MNEs and three Senegalese enterprises. The interviews are jointly analyzed with a theoretical framework in order to determinate if there are significant differences between the two types of enterprises concerning the wage-setting, working conditions as well as transfer of know-how. The result shows that MNEs have more training opportunities then local enterprises, the working conditions do not differ significantly. Further there is no evidence found for MNEs paying higher wages then local enterprises judged by the general attitude of the interviewees. It is therefore assumed to be some labor mobility, implying that the training contributed by MNEs might work a source of skill-upgrade for the workforce in Dakar.
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Khakdaman, Hamidreza. "A Two Dimensional Model of a Direct Propane Fuel Cell with an Interdigitated Flow Field." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/22732.
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Increasing environmental concerns as well as diminishing fossil fuel reserves call for a new generation of energy conversion technologies. Fuel cells, which convert the chemical energy of a fuel directly to electrical energy, have been identified as one of the leading alternative energy conversion technologies. Fuel cells are more efficient than conventional heat engines with minimal pollutant emissions and superior scalability. Proton Exchange Membrane Fuel Cells (PEMFCs) which produce electricity from hydrogen have been widely investigated for transportation and stationary applications.
The focus of this study is on the Direct Propane Fuel Cell (DPFC), which belongs to the PEMFC family, but consumes propane instead of hydrogen as feedstock. A drawback associated with DPFCs is that the propane reaction rate is much slower than that of hydrogen. Two ideas were suggested to overcome this issue: (i) operating at high temperatures (150-230oC), and (ii) keeping the propane partial pressure at the maximum possible value. An electrolyte material composed of zirconium phosphate (ZrP) and polytetrafluoroethylene (PTFE) was suggested because it is an acceptable proton conductor at high temperatures. In order to keep the propane partial pressure at the maximum value, interdigitated flow-fields were chosen to distribute propane through the anode catalyst layer.
In order to evaluate the performance of a DPFC which operates at high temperature and uses interdigitated flow-fields, a computational approach was chosen. Computational Fluid Dynamics (CFD) was used to create two 2-D mathematical models for DPFCs based on differential conservation equations. Two different approaches were investigated to model species transport in the electrolyte phase of the anode and cathode catalyst layers and the membrane layer. In the first approach, the migration phenomenon was assumed to be the only mechanism of proton transport. However, both migration and diffusion phenomena were considered as mechanisms of species transport in the second approach. Therefore, Ohm's law was used in the first approach and concentrated solution theory (Generalized Stefan-Maxwell equations) was used for the second one. Both models are isothermal.
The models were solved numerically by implementing the partial differential equations and the boundary conditions in FreeFEM++ software which is based on Finite Element Methods. Programming in the C++ language was performed and the existing library of C++ classes and tools in FreeFEM++ were used. The final model contained 60 pages of original code, written specifically for this thesis.
The models were used to predict the performance of a DPFC with different operating conditions and equipment design parameters. The results showed that using a specific combination of interdigitated flow-fields, ZrP-PTFE electrolyte having a proton conductivity of 0.05 S/cm, and operating at 230oC and 1 atm produced a performance (polarization curve) that was (a) far superior to anything in the DPFC published literature, and (b) competitive with the performance of direct methanol fuel cells. In addition, it was equivalent to that of hydrogen fuel cells at low current densities (30 mA/cm2).
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Qi, Yusheng Ph D. Massachusetts Institute of Technology. "Phase-resolved reconstruction and forecast of nonlinear irregular wave field based on direct numerical simulations." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111739.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 241-249).
The problem of phase-resolved reconstruction and forecast of ocean wave field based on measurements is of basic scientific interest and practical importance in ocean science and marine engineering. This capability aids and expands the use and interpretation of field and wave basin measurements, contributing to the study of fundamental wave mechanics. It also expands the operational envelope and improves survivability and efficiency of ships and marine facilities in severe seas. We develop theoretical and computational capabilities to solve this problem, which can be applied to both ocean wave field and wave basin experiments. Given limited wave measurement data, there exists specific space and time domain( s) (the "predictable zone") where the wave-field can be reconstructed and forecasted. In this thesis, using linearized wave theory and reasonable assumptions of the frequency and directional extent of the wave field, we obtain closed-form expressions for (linear) predictable zone PL in terms of set notation involving the individual measurement. We derive and illustrate PL obtained for ("probe") measurements at one or more fixed locations over time, for moving probes, for whole-area wave measurements, and combinations of these. We also consider the problem of optimal deployment of these measurements to maximize the volume of PL in space-time. For J probes, we show that this volume scales as J³ (in contrast to J when the predictable zones of individual measurements are simply summed). With the knowledge of the predictable zone, we develop and validate a high-order reconstruction (HOR) method for the phase-resolved reconstruction of nonlinear wave field given a set of wave measurements. HOR optimizes the amplitude and phase of L free-wave components of the nonlinear wave field, accounting for nonlinear wave interactions up to order M in the evolution to obtain a nonlinear wave field that minimizes the reconstruction error between reconstructed wave field and the given measurements. For a given reconstruction tolerance, L and M are provided in the HOR scheme itself. To demonstrate the validity and efficacy of HOR, we perform extensive tests of general two- and three-dimensional wave fields specified by theoretical Stokes waves, nonlinear simulations, and physical wave fields in tank experiments. The necessary L, for general broad banded wave fields, is shown to be relatively small and substantially less than the free and locked modes needed for the nonlinear evolution. We find that, even for relatively small wave steepness, the inclusion of high-order effects in HOR is important for prediction of wave kinematics not in the measurements. For all the cases we consider, HOR converges to the underlying wave field within a nonlinear spatial-temporal predictable zone PNL (dependent on the measurements and wave nonlinearity). PNL generally extends in time (and space) beyond the measurements, thus obtaining reliable forecast/predictions of the wave field. For linear waves, PNL=PL, verifying the predictable zone theory. With increasing wave nonlinearity, we show that PNL contains and is generally greater than PL. Thus PL provides a (conservative) estimate of PNL when the underlying wave field is not known. For nonlinear steep wave-field, wave breaking plays an important role in the evolution of the wave field. We develop a phenomenological wave breaking model that can be incorporated into the nonlinear evolution engine of HOR to predict breaking onset and simulate proper amount of energy dissipation. Thus HOR can properly reconstruct and forecast nonlinear wave field which may contain breaking events. The breaking model is developed in the spectra domain and based on analysis of simulated two-dimensional wave breaking caused by different wave-wave interaction mechanism, including modulation instability and wave focusing. The developed wave breaking model is calibrated, validated and verified by different wave breaking measurements and excellent agreement is obtained between simulated wave breaking results and measured ones. The wave breaking model can be further used to simulate the locations of breaking events, which is validated statistically by calculating the Phillips statistics. This thesis does not address the issue of wave-body interaction nor the control problem for scale models in the wave basin, but it provides necessary nonlinear whole-field data for intense CFD analysis of wave-body interaction at a level heretofore not possible. The presence of imposed current or wind is not considered at this stage but can be incorporated in the future using the same framework.
by Yusheng Qi.
Ph. D.
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Vaithianathan, Elangovan. "Field verification of Standard Installation Direct Design (SIDD) method for 610-mm diameter concrete pipes." Ohio University / OhioLINK, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1176237149.
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Dever, Timothy P. "Direct Torque Control of Resonant Inverter Driven Permanent Magnet Synchronous Motor." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1586426523199448.
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Ai, Yong-le. "Novel direct field and torque control of six-phase induction machine with special phase current waveform." Thesis, Link to the online version, 2006. http://hdl.handle.net/10019/489.
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Harle, Thomas. "Radio frequency plasma thrusters : performance evaluation of low magnetic field mode operation through direct thrust measurements." Thesis, University of Surrey, 2015. http://epubs.surrey.ac.uk/807990/.
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This thesis describes an experimental investigation into the performance of a radio frequency plasma thruster (RFPT). This type of thruster does not rely on the use of high voltage ion acceleration grids or beam neutralisers which are typically life limiting elements of an electric thruster. The RFPT excites an atomic or molecular gas into a plasma using an external RF antenna. This plasma is contained by a cylindrical dielectric source tube which is open at one end. An axial magnetic field is applied to the plasma using one or more solenoids or a permanent magnet source. The magnetic field is usually applied such that it is constant throughout the length of the source tube, after which the field diverges. The plasma couples with the imposed magnetic field, generating internal field structures, which can be used to regulate both the power coupling and the rate at which the plasma diffuses out of the source tube. In this study, the thruster performance is measured directly, thus providing missions designers with accurate performance data which can be used to assess applicability of the technology to future missions. A re-configurable lab prototype thruster was constructed and a pendulum type thrust balance was developed in order to make direct measurements of the thrust produced by the Surrey Space Centre (SSC) RFPT. The balance has been developed to allow mounting of the thruster together with the necessary RF and DC electrical feeds as well as the propellant feeds and incorporates sensors which allow measurements to be made in an RF plasma environment. A low magnetic field mode of RFPT operation was investigated in order to assess whether this mode of operation may be able to provide performance increases at reduced imposed magnetic fields (< 20 mT), which could enable the serious consideration of this technology for future flight opportunities. The lowered magnetic fields used here may reduce the risk of interference with spacecraft subsystems and perturbation to the spacecraft orbit, when compared to many of the proposed plasma thrusters which use fields in excess of 40 mT. Direct thrust measurements of an RFPT operating in a low field mode are presented as a function of the propellant flow, RF power and for two source tube lengths. The thrust is shown to peak at a field strength, B_0, which is demonstrated to vary with RF power and propellant flow. The peaks are also shown to correspond generally to peaks in the source plasma density, plasma potential and in some cases to exhaust ion beam current. Ion energy distribution function measurements show that strong beams are not present in thruster configurations which use a 170 mm length source tube but are shown to increase in strength when using a shorter 85 mm length tube. The low field mode is shown to generally provide performance increases over the non-magnetised case by a factor of 4. Low field mode thrust measurements using the shorter 85 mm source tube and matching double saddle antenna revealed enhanced peak performance gains over the 170 mm length case, resulting in an increase of the thrust efficiency by up to a factor of 15. The performance of the RFPT operating in this configuration is shown to produce enhanced or equivalent performance, when compared to similar state of the art configurations but at generally lower imposed magnetic fields. This particular optimisation may make possible a first flight opportunity for the RFPT as weak magnetic fields may be supplied easily by electromagnets. Electromagnets can be easily deactivated or field reversed to avoid interference with spacecraft subsystems and orbital parameters unlike permanent magnets which may be required to generate higher magnetic fields. Operation of the RFPT in the low field mode with an 85~mm source has also revealed new low field mode behaviour compared to the 170 mm case, producing sudden, large reductions in the performance of the thruster for imposed fields beyond B_0 which are shown to correspond to drops in source plasma density, plasma resistance and exhaust beam current.
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Thornton, Corinne. "DIRECT SUPPORT STAFF RETENTION AND TURNOVER IN THE FIELD OF APPLIED BEHAVIOR ANALYSIS: A NATIONAL SURVEY." Master's thesis, Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/531037.
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Applied Behavioral AnalysisEd.M.
This paper explores the current rates and correlates of turnover among direct support staff working with individuals with developmental disabilities. While the United State Department of Labor, Bureau of Labor Statistics collects data on annual separation rates by a variety of industry sectors, there is not a recognized sector for the field of Applied Behavior Analysis. Other data sources similarly do not include Applied Behavior Analysis as its own industry sector, which produces a gap in knowledge. This study uses data obtained from providers of services for individuals with developmental disabilities in a national online survey to obtain rates of turnover for the field of Applied Behavior Analysis. Results indicate a lower rate of turnover than what is reported in the fields of education, and social services in general. The results also indicate that pay rate and amount of supervision offered increase retention while training offered pre and post hire has little correlation to rate of turnover.
Temple University--Theses
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Tiwale, Nikhil. "Zinc oxide nanowire field effect transistors for sensor applications." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/268227.
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A wide variety of tunable physio-chemical properties make ZnO nanowires a promising candidate for functional device applications. Although bottom-up grown nanowires are producible in volume, their high-throughput device integration requires control over dimensions and, more importantly, of precise placement. Thus development of top-down fabrication routes with accurate device positioning is imperative and hence pursued in this thesis. ZnO thin film transistors (TFT) were fabricated using solution based precursor zinc neodecanoate. A range of ZnO thin films were prepared by varying process parameters, such as precursor concentrations and annealing temperatures, and then analysed for their optical and electrical characteristics. ZnO TFTs prepared from a 15 % precursor concentration and annealing at 700 $^\circ$C exhibited best device performance with a saturation mobility of 0.1 cm$^2$/V.s and an on/off ratio of 10$^7$. Trap limited conduction (TLC) transport was found to be dominant in these devices. A direct-write electron beam lithography (EBL) process was developed using zinc naphthenate and zinc neodecanoate precursors for the top-down synthesis of ZnO nanowires. Nanoscale ZnO patterns with a resolution of 50 nm and lengths up to 25 $\mu$m were fabricated. A linear mobility of 0.5 cm$^2$/V.s and an on/off ratio of $\sim$10$^5$ was achieved in the micro-FETs with 50 $\mu$m channel width. Interestingly, on scaling down the ZnO channel width down to 100 nm, almost two orders of magnitude enhancement in the linear mobility was observed, which reached $\sim$33.75 cm$^2$/V.s. Such increment in the device performance was attributed to the formation of larger grains and thus reduction in the grain-boundary scattering. Six volatile organic compounds (VOCs) were sensed at room temperature using the direct-write EBL fabricated ZnO devices under UV sensitisation. As the surface-to-volume ratio increases with the decreasing channel width (from 50 $\mu$m to 100 nm), sensing response of the ZnO devices becomes more significant. Ppm level detection of various VOCs was observed; with a 25 ppm level Anisole detection being the lowest concentration. Additionally, using 100 nm device, detection of 10 ppm NO$_2$ was achieved at room temperature. The sensing response towards NO$_2$ was found to be increased with UV illumination and sensor temperature. This led to exhibit $\sim$171 % sensing response for a 2.5 ppm level of NO$_2$.
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Miller, Kelsey, Olivier Guyon, and Jared Males. "Spatial linear dark field control: stabilizing deep contrast for exoplanet imaging using bright speckles." SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2017. http://hdl.handle.net/10150/626442.
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Direct imaging of exoplanets requires establishing and maintaining a high-contrast dark field (DF) within the science image to a high degree of precision (10(-10)). Current approaches aimed at establishing the DF, such as electric field conjugation (EFC), have been demonstrated in the lab and have proven capable of high-contrast DF generation. The same approaches have been considered for the maintenance of the DF as well. However, these methods rely on phase diversity measurements, which require field modulation; this interrupts the DF and consequently competes with the science acquisition. We introduce and demonstrate spatial linear dark field control (LDFC) as an alternative technique by which the high-contrast DF can be maintained without modulation. Once the DF has been established by conventional EFC, spatial LDFC locks the high-contrast state of the DF by operating a closed loop around the linear response of the bright field (BF) to wavefront variations that modify both the BF and the DF. We describe the fundamental operating principles of spatial LDFC and provide numerical simulations of its operation as a DF stabilization technique that is capable of wavefront correction within the DF without interrupting science acquisition. (c) The Authors.
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Zhao, Jibo. "An Efficient Wide-Speed Direct Torque Control Based on Fuzzy Logic Technique." University of Toledo / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1352922315.
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Simsek, Gunay. "Sensorless Direct Field Oriented Control Of Induction Machine By Flux And Speed Estimation Using Model Reference Adaptive System." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12604965/index.pdf.
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ABSTRACT
SENSORLESS DIRECT FIELD ORIENTED CONTROL OF
INDUCTION MACHINE
BY FLUX AND SPEED ESTIMATORS USING MODEL
REFERENCE ADAPTIVE SYSTEM
This work focuses on an observer design which will estimate flux-linkage and
speed for induction motors in its entire speed control range. The theoretical base of
the algorithm is explained in detail and its both open-loop, and closed-loop
performance is tested with experiments, measuring only stator current and voltage.
Theoretically, the field-oriented control for the induction motor drive can be
mainly categorized into two typesindirect and direct field oriented. The field to be oriented may be rotor, stator, or airgap flux-linkage. In the indirect field-oriented control, the slip estimation based on the measured or estimated rotor speed is required in order to compute the synchronous speed. There is no need for the flux estimation in such a system. For the direct field oriented case the synchronous speed is computed with the aid of a flux estimator. In DFO, the synchronous speed is iv computed from the ratio of dq-axes fluxes. With the combination of a flux estimator and an open-loop speed estimator one can observe stator-rotor fluxes, rotor-flux angle and rotor speed. In this study, the direct (rotor) flux oriented control system with flux and-open-loop speed estimators is described and tested in real-time with the Evaluation Module named TMS320LF21407 and the Embedded Target software named Vissim from Visual Solutions Company.
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Yildirim, Dogan. "Field Oriented Control Of A Permanent Magnet Synchronous Motor Using Space Vector Modulated Direct Ac-ac Matrix Converter." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614302/index.pdf.
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The study designs and constructs a three-phase to three-phase direct AC&ndashAC matrix converter based surface mounted permanent magnet synchronous motor (PMSM) drive system. First, the matrix converter topologies are analyzed and the state-space equations describing the system have been derived in terms of the input and output variables. After that, matrix converter commutation and modulation methods are investigated. A four-step commutation technique based on output current direction provides safe commutation between the matrix converter switches. Then, the matrix converter is simulated for both the open-loop and the closed-loop control. For the closed-loop control, a current regulator (PI controller) controls the output currents and their phase angles. Advanced pulse width modulation and control techniques, such as space vector pulse width modulation and field oriented control, have been used for the closed-loop control of the system. Next, a model of diode-rectified two-level voltage source inverter is developed for simulations. A comparative study of indirect space vector modulated direct matrix converter and space vector modulated diode-rectified two-level voltage source inverter is given in terms of input/output waveforms to verify that the matrix converter fulfills the two-level voltage source inverter operation. Following the verification of matrix converter operation comparing with the diode-rectified two-level voltage source inverter, the simulation model of permanent magnet motor drive system is implemented. Also, a direct matrix converter prototype is constructed for experimental verifications of the results. As a first step in experimental works, filter types are investigated and a three-phase input filter is constructed to reduce the harmonic pollution. Then, direct matrix converter power circuitry and gate-driver circuitry are designed and constructed. To control the matrix switches, the control algorithm is implemented using a DSP and a FPGA. This digital control system measures the output currents and the input voltages with the aid of sensors and controls the matrix converter switches to produce the required PWM pattern to synthesize the reference input current and output voltage vectors, as well. Finally, the simulation results are tested and supported by laboratory experiments involving both an R-L load and a permanent magnet synchronous motor load. During the tests, the line-to-line supply voltage is set to 26 V peak value and a 400 V/3.5 kW surface mounted permanent magnet motor is used.
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Buse, Hauke. "Micro- and sub-microstructuring and characterisation of technical surfaces by means of laser direct writing including a novel approach for laser beam profiling." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/8361.
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Within recent years, numerous fields of engineering, like mechanics, optics and electronics, have been influenced and revolutionised by the technique of microand nano-structuring. For example, special optical elements for beam shaping, surface structures for the reduction of friction or modern "lab on chip" devices have been produced. Within this thesis a universal system has been developed facilitating the production of such structured surfaces with dimensions down to 500 nm. This system is not only capable of structuring surfaces by means of lithographic processes; it further allows the inspection of surfaces by scanning their topography. To realise such a system, two different technologies have been evaluated: Scanning Near-field Optical Lithography (SNOL), a very sophisticated technique which uses a thin fibre tip to expose a photo resist-covered surface, and confocal scanning technology. Here, the confocal scanning is accomplished using an adapted optical component, the optical pickup unit (OPU), from a gaming console, which turned out to be the most suitable and cost-efficient solution for the realisation of this system. Several test series have been carried out during this work, to verify the performance of the confocal system, both to structure photo resist surfaces and to characterise unknown surfaces. This present work will show the ability of the developed system to produce structures down to the sub-micron range and to characterise unknown surfaces with sub- micron precision. Various patterns have been written into photo resistcoated substrates to structure their surface. Beginning with diffractive optical elements (DOE) for beam shaping, followed by Dammann gratings for twodimensional beam shaping and optical gratings for light guidance as well as producing technical surfaces imitating the properties of sharkskin or simple micromechanical structures, the developed confocal system has shown itself to be flexible and widely-applicable. IV During the development of the confocal system, a strong need for a beam profiling system analysing the light beam diverging from the OPU, was recognised. Due to the fact that no commercially available system was capable of characterising beam sizes within the range of the diffraction limit, a novel method for beam profiling was invented. This method makes use of the fibre tips already applied within the SNOL system, producing tomographical scans of the beam spot.
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Skelton, Chanda Lee. "Investigations into gametophyte morphology and population sex ratios through direct comparisons between laboratory-grown and field-grown fern gametophytes." [Ames, Iowa : Iowa State University], 2007.
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Atkinson, Erin C. "Field-testing of a passive surface water flux meter for the direct measurement of water and solute mass fluxes." [Gainesville, Fla.] : University of Florida, 2007. http://purl.fcla.edu/fcla/etd/UFE0021166.
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Yang, Hao. "Characteristics of gas-liquid two-phase flow in the anode flow field of liquid feed direct methanol fuel cells /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?MECH%202004%20YANGH.
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Salter, Graeme S. "High contrast limitations of slicer based integral field spectrographs." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:de6d946d-063f-4568-8615-ea5154ac5909.
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The viability of using a slicer based integral field spectrograph (IFS) for high contrast observations has been under scrutiny due to the belief that the one dimensional coherence that persists along the slice to the point of sampling at the detector will cause the creation of secondary speckles that will not have the same characteristics as normal speckles, thus stopping us from calibrating them out. It has also been previously assumed that a suitably low differential wavefront error when moving slice to slice was not guaranteed by design. It was for these reasons that slicer based IFSs were not selected for the current generation of planet finding instruments. As part of the EPICS (Exo Planet Imaging Camera and Spectrograph for the E-ELT) design study it was decided that slicers should be re-investigated due to results from on sky observations suggesting these limitations did not exist. The purpose of this thesis was to determine whether there was validity to the concerns mentioned above and therefore to answer the question; Would implementing a slicer based integral field spectrograph limit the achievable contrast of an instrument designed for the direct detection of exoplanets? Chapter 1 gives a brief introduction into the field of exoplanet research. Charpter 2 describes the noise limiting direct detection of exoplanets and the ways to get around it. Chapter 3 gives an overview of the two types of IFS under investigation by the EPICS consortium. Chapter 4 looks into details of the EPICS instrument and the IFS design study that came about. Chapter 5 shows simulations performed for the aim of achieving better contrasts via post processing methods and accurate data reduction as well as simulations of slicer based integral field spectrographs. Experimental tests using a slicer and a preoptics setup designed to simulate the limiting noise are described in Chapter 6. Chapter 7 looks at using SINFONI for high contrast observations and Chapter 8 details the conclusions drawn from the work presented in this thesis, as well as possible extensions to it. The work performed in this thesis dispels the concerns about the continued one dimensional coherence up to the detecter and suggests that slicer based integral field spectrographs do not inherently limit the contrast achievable; Results from experiments fit well with the requirements for EPICS to achieve its goals. Simulations also supported the idea that secondary speckle noise should not be an issue for the slicer based IFS. This means that a slicer based IFS is a viable option for the EPICS instrument.
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Kronberg, Anders. "Design and Simulation of Field Oriented Control and Direct Torque Control for a Permanent Magnet Synchronous Motor with Positive Saliency." Thesis, Uppsala universitet, Elektricitetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-176343.
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The researchers at the Department of Electricity at Uppsala University has recently entered the field of electric motor design, however no real knowledge of motor control of salient pole permanent magnet motors exists in the department. This thesis will present a general description of the control method of motors that exist today, this has been done by reviewing existing literature. The literature review has shown that there are at least three control methods with a significant different in their control approach, Scalar-, Field Oriented- and Direct Torque- Control. The two last methods were chosen by the author as the most useful and was implemented and simulated together with the newly developed motor in MATLAB Simulink to evaluate their performance. The simulation results show that there is no difference in performance of the two methods, but they show a difference in efficiency. The results show that it's worth to develop both methods further, mainly for reducing the torque and current ripple. This result was not expected according to literature, which suggests that the Field Oriented Control has a lower torque ripple. This could be caused by the choice of hysteresis control for inverter switching, instead of more sophisticated methods with a proportional integral derivative controller (PID) together with Sinusoidal Pulse Width Modulation (SPWM) or Space Vector Modulation (SVM).
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Arias, Escobar Maria Alejandra [Verfasser]. "Direct use of urine as fertilizer : potential risks of loading pharmaceuticals and hormones to field crops / Maria Alejandra Arias Escobar." Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/118563620X/34.
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Park, Jinwon. "A Runge Kutta Discontinuous Galerkin-Direct Ghost Fluid (RKDG-DGF) Method to Near-field Early-time Underwater Explosion (UNDEX) Simulations." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28905.
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A coupled solution approach is presented for numerically simulating a near-field underwater explosion (UNDEX). An UNDEX consists of a complicated sequence of events over a wide range of time scales. Due to the complex physics, separate simulations for near/far-field and early/late-time are common in practice. This work focuses on near-field early-time UNDEX simulations. Using the assumption of compressible, inviscid and adiabatic flow, the fluid flow is governed by a set of Euler fluid equations. In practical simulations, we often encounter computational difficulties that include large displacements, shocks, multi-fluid flows with cavitation, spurious waves reflecting from boundaries and fluid-structure coupling. Existing methods and codes are not able to simultaneously consider all of these characteristics.
A robust numerical method that is capable of treating large displacements, capturing shocks, handling two-fluid flows with cavitation, imposing non-reflecting boundary conditions (NRBC) and allowing the movement of fluid grids is required. This method is developed by combining numerical techniques that include a high-order accurate numerical method with a shock capturing scheme, a multi-fluid method to handle explosive gas-water flows and cavitating flows, and an Arbitrary Lagrangian Eulerian (ALE) deformable fluid mesh. These combined approaches are unique for numerically simulating various near-field UNDEX phenomena within a robust single framework. A review of the literature indicates that a fully coupled methodology with all of these characteristics for near-field UNDEX phenomena has not yet been developed.
A set of governing equations in the ALE description is discretized by a Runge Kutta Discontinuous Galerkin (RKDG) method. For multi-fluid flows, a Direct Ghost Fluid (DGF) Method coupled with the Level Set (LS) interface method is incorporated in the RKDG framework. The combination of RKDG and DGF methods (RKDG-DGF) is the main contribution of this work which improves the quality and stability of near-field UNDEX flow simulations. Unlike other methods, this method is simpler to apply for various UNDEX applications and easier to extend to multi-dimensions.Ph. D.
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Tango, Gerard Joseph. "Applications of a Direct Fast Field/Reflectivity Method to Wave Propagation Modeling in Underwater Acoustic and Solid Earth Seismic Environments." ScholarWorks@UNO, 1985. https://scholarworks.uno.edu/td/2684.
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A new method is discussed for exact rapid computation of the depth-dependent Green's function occuring in full integral solutions to the acoustic and elastic Helmholtz wave equation, allowing calculations of underwater acoustic propagation loss and full wavefield synthetic seismograms, in range-independent plane stratified media.
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Zhou, Qiping. "Near-field microwave imaging with coherent and interferometric reconstruction methods." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1591903415194694.
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Heather, Andrew. "Numerical and physical analysis of liquid break-up and atomisation relating to pressure-swirl gasoline direct injection." Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/14401.
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This thesis presents detailed fuel spray investigations relating to an automotive Gasoline Direct Injection (GDI) pressure-swirl injector, employing a combination of numerical and physical analyses. The emphasis is placed on the near-nozzle in recognition that all later flow processes are dominated by this critical region. To enable the technology to maximise its potential, it is essential to further our understanding of the fundamental flow physics that govern the injection process, which remain largely unknown. The complexity of the spray process has led to many avenues of research. Simplified models are particularly suitable for parametric studies, allowing fast computation of some of the most important design parameters, such as nozzle discharge coefficient, cone angle and initial velocity. More complex methods such as Computational Fluid Dynamics (CFD) offer significantly more detail including the temporal and spatial evaluation of the flow field and fuel distribution, but at the cost of often lengthy computational time, and the need to tune models against physical evidence. Unfortunately none are able to describe all aspects of the injection event simultaneously. A considerable body of existing experimental data gathered under atmospheric conditions has been condensed and carefully presented to provide a comprehensive picture of injector operation. This comprises global spray performance data, spray imaging, and droplet velocity and size maps as a function of time after the Start Of Injection (SOl). These serve to provide a means to develop physical models and to correlate model predictions. Particular attention is drawn to the challenges faced by numerical methods to successfully predict the complex spray behaviour. A fundamental computational study employing the Volume Of Fluid (VOF) method describes droplet break-up under controlled conditions. By varying the Weber number of the flow the expected break-up mechanisms are recovered, and the numerics and case set-up tuned to offer a practical balance between the resource burden and solution accuracy. This paved the way to a detailed 3-D transient analysis of the near-nozzle region of a pressure-swirl injector. Computed results clearly identify the consecutive phases of the fuel spray development, from the initial unsteady jet through to the stable, swirling hollow cone formation. Comparison with experimental measurements revealed that the computational approach is able to capture the main qualitative features of the spray process.
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Szilas, Casper. "The Tanzanian Minjingu phosphate rock : possibilities and limitations for direct application /." Copenhagen : Royal Veterinary and Agricultural University, Chemistry Department, 2002. http://www.kemi.kvl.dk/c̃asz/thesis_cszilas.pdf.
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Justham, Timothy. "Cyclic variation in the flow field behaviour within a direct injection spark ignition engine : a high speed digital particle image velocimetry study." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/6551.
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Currently environmental concerns are driving internal combustion engine manufacturers to seek greater fuel efficiency, more refinement and lower emissions. Cyclic variation is a known obstacle to achieving the greatest potential against these goals and therefore an understanding of how to reduce these is sought. It is widely accepted that cyclic variation in in-cylinder flow motions is a key contributor to overall cyclic variation and therefore the characterisation of factors affecting these is an important step in the process of achieving a better understanding and ultimately control of cyclic variation. This thesis reports the development of a novel optical engine research facility in which high speed digital particle image velocimetry (HSDPIV) has been applied to the study of flow field behaviour within a direct injection spark ignition (DISI) engine. This study investigates the spatial and temporal development of flow structures over and within many engine cycles. Flow field PIV measurements have been captured with a high spatial resolution and temporal frequencies up to 5 kHz from a number of measurement locations at a large range of crank angles. The major contributions from this work have included the use of the novel measurement technique to investigate spatial and temporal flow field development in the intake runner, valve jet, in-cylinder tumble and swirl planes and the pent roof. The gathered data have been used to investigate cycle by cycle variations in both high and low frequency flow structures. Major findings of this work have included the observation of highly varying flow fields throughout the engine cycle. Frequency analysis of these flows has allowed the low frequency bulk motions and higher frequency turbulent components to be studied. The low frequency flow field components are shown to create varying flow field interactions within the cylinder that also affect the manner in which the flow develops over the course of the cycle. The intensity of the turbulence fluctuations, u , has been calculated based upon the high frequency components within the flow and variations within this are shown to correlate with pressure related combustion parameters.
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Chow, Li Sze. "Investigation of direct detection of nerve firing in the human visual system due to axonal field modulation of the magnetic resonance signal." Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425600.
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Coskun, Nart. "A comparison of configutration arrays for the resistivity and induced polarisation methods and a direct interpretation technique for vertical profiling field data." Thesis, University of York, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261078.
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Libby, Lowell W. "The Effect of Direct Experience on Generating Insight into and Deepending Understanding of Academic Topics Studied by high School Seniors in the Field." Fogler Library, University of Maine, 2001. http://www.library.umaine.edu/theses/pdf/LibbyLW2001.pdf.
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Zeller, Niclas [Verfasser], Uwe [Akademischer Betreuer] Stilla, Franz [Gutachter] Quint, Daniel [Gutachter] Cremers, and Uwe [Gutachter] Stilla. "Direct Plenoptic Odometry - Robust Tracking and Mapping with a Light Field Camera / Niclas Zeller ; Gutachter: Franz Quint, Daniel Cremers, Uwe Stilla ; Betreuer: Uwe Stilla." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1171988001/34.
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Jeon, Hong Young. "Plant specific direct chemical application field robot /." 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3337809.
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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008.Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6956. Adviser: Lei F. Tian. Includes bibliographical references (leaves 119-127) Available on microfilm from Pro Quest Information and Learning.
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Lin, Chia-han, and 林佳翰. "Direct Growth of Single Zinc Oxide Nanowire Field-Effect Transistor." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/30977524735154846147.
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碩士國立臺南大學
材料科學系碩士班
101
Zinc oxide nanowire (ZnO NW) is a promising material for building nano-electronic devices. However, it is difficult to position a single nanowire for device fabrication. In this research, we used a strategy including Electron Beam Lithography and Chemical Bath Deposition to directly grow a single Zinc oxide nanowire across a pair of electrodes at low temperature environment. The field-effect phenomenon of the nanowire was observed. According to the current measurement data, the maximum value of electron mobility can reach 134 cm2/V．s, and device showed a threshold voltage of ~2.75 V with the current ratio over ~1000 between ON and OFF states. Finally, for reducing the nanowires resistance, we covered the electrical contacts with aluminum electrode to overcome the Schottky barrier contact resistance, and also applied argon plasma post-treatment to substantially enhance the nanowire mobility.
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Hung, Te-Sheng, and 洪德昇. "The Development of Spectral Phase Interferometry for Direct Electric-Field Reconstruction." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/57357208988984719719.
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碩士國立中正大學
物理所
94
This thesis describes the development to the spectral phase interferometry for direct electric field reconstruction (SPIDER). We first develop a program to simulate the trace of a pulse on the spectral interferogram and retrieve the spectral phase base on a Fourier transform algorithm. We also build a SPIDER apparatus to measure the phase of a pulse from a CPA (chirped-pulse amplification) laser system by employing the algorithm developed. Finally, we calibrate the SPIDER system by calculating the dispersion induced by changing the distance of two gratings in a compressor system and compare the results to that measured by the SPIDER system.
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Yeh, Lung-Yi, and 葉隆億. "PID-Fuzzy Speed Control of a Direct Field- Oriented Induction Motor." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/62523070706368643403.
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碩士中原大學
電機工程研究所
97
In this paper, we present a PID-Fuzzy Logic (PID-FL) controller for the speed control of a direct field-oriented induction motor (DFOIM). Our PID controller is derived based on the Ziegler-Nichols (Z-N) method. The performance of fixed gains PID is not well under all operating conditions. In order to increase the performance of PID, we apply a fuzzy logic to improve the performance. The process to obtain the PID-FL is easily, systematic and only with three membership functions are used for each input and output for low computational burden, which can achieve very good results. The experimental results show that the proposed controller is robust under the load torque operation, and it can significantly improve the controlled speed performance of a DFOIM.