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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.
311

Om betalningen stannar / When the payment system stops

Steinholz, Tove, Burholt, Johanna January 2022 (has links)
Betalsystemet är en av de viktigaste delarna vi har i den finansiella infrastrukturen, störningar i systemet skulle snabbt kunna leda till allvarliga konsekvenser för både individen, företagen och samhället i stort. Syftet med studien är att ge inblick i hur beredskapen ser ut idag, att hantera dessa störningar. Vidare syftar studien till att reda i vilka åtgärder som behövs för att säkerställa betalsystemets funktion vid en allvarlig störning, där digitala betalmetoder inte är fungerande. För att utföra studien har en kvalitativ metod använts, underlaget för studien har varit intervjuer med sju sakkunniga personer från Finansinspektionen, Riksbanken, Swedbank, Bankomat AB, Regeringskansliet, MSB och Bankgirot. Detta i kombination med relevant teori. Av resultatet kan vi se att genom att skapa en starkare motståndskraft och bättre förmåga för systemen att återhämta sig, blir samhället mer förberett på hanteringen av en framtida kris. Vidare framgår det att samhället inte skulle klara av ett längre avbrott i betalsystemet i dagsläget. Det blir också tydligt att bristande rutiner och en oklar fördelning av ansvaret leder till ett instabilt betalsystem i ett krisläge. Det är oklart vem som står för kostnaderna, om aktörer och myndigheter behöver rusta upp sina system, men detta förväntas bli tydligare i samband med ny kommande lagstiftning. För att säkerställa ett fungerande betalsystem både i ett krisläge och i ett normalläge, behövs ett mer robust system, med tydligare rutiner och ansvarsfördelning. / The payment system is one of the most important functions in our society’s financial infrastructure. Disruptions in the system would rapidly lead to serious consequences for individuals, businesses, and society as a whole. The purpose of the thesis is to provide a better understanding of what the emergency preparedness process looks like in dealing with mentioned disruptions, what actions are needed, and how the different actors address the issue and what risks society faces in the event of prolonged interruptions in the payment system. The study was conducted using a qualitative method, with interviews with seven experts from Finansinspektionen, Riksbanken, Swedbank, Bankomat AB, Government Offices of Sweden, The Swedish Civil Contingencies Agency and Bankgirot as the primary foundation and combining this with the relevant theory. Conclusions that can be drawn are that by strengthening the resilience and preparing society we give our systems a better ability to recover from a future crisis in our payment systems. Furthermore, that the society would not manage to retain control of the payment system in case of extensive disruption. It also became clear that insufficient routines and an indistinct division of responsibilities, lead to an unstable payment system in the event of a crisis. At this time, it is not clear who would pay the costs, if actors and authorities need to enhance their payment systems, but this uncertainty is intended to diminish with forthcoming new legislation. To ensure a functioning payment system in both a crisis and a normal situation, a sturdier system is required, with adequate routines and a division of responsibilities.
312

Groundwater denitrification by fluidized bioelectrochemical systems

Bonin, Lena January 2020 (has links)
Groundwater (GW) accounting for most of the freshwater available around the World, finding sustainable techniques to depollute it is of crucial importance for safe drinking water supply. The extensive use of fertilizers in the agriculture, as well as other anthropogenic activities, are contributing to the excessive nitrate levels in some aquifers. These levels need to be reduced to obtain potable water. Bioelectrochemical systems (BES), using microorganisms to catalyze a desired electrochemical reaction, recently proved to be a very promising technology for water remediation. Groundwater denitrification using Microbial Electrolysis Cell (MEC) needs to be improved for further scaled-up on-site system. The advantages conferred by fluidized bed reactor (FBR), as well as the outstanding electrochemical properties of reduced graphene oxide (rGO), are two potential enhancements of such bioelectrochemical denitrification system that were investigated in this thesis. Some essential parameters could be determined during the preliminary steps' experiments. The fluidization trials gave us a clear insight that Coconut-based Activated Carbon (CAC) particles were resistant carrier particles, nicely fluidized within a 39.27cm3 circular cathodic chamber for a flow rate ranging between 450ml/min to 590ml/min. For the same flow rate of 500ml/min, we could obtain CAC particles fluidization for the upstream fluidized configuration, and still bed particles for the fixed bed downstream configuration, which would be very useful for later unbiased comparison. The denitrifying bacteria showed during their enrichment, a nitrate removal rate of up to 1.986ppm NO3-N/h in serum bottles, with an average of 0.38ppm NO2-N/h accumulation. The parallel running of fixed bed versus fluidized bed denitrifying reactor in order to compare their denitrification performances, was planned, but could not be performed due to COVID-19. The graphene oxide (GO) batch experiments showed a good biocompatibility between GO/rGO and our autotrophic denitrifying bacteria. A change of morphology within about 20 hours was observed, probably suggesting the reduction of GO to rGO by the bacteria. During a first test, the presence of GO led to a 2.7 folds less efficient denitrification performance as compared with the GO/rGO-free condition, likely due to the competition between nitrate and GO for being reduced. However, the denitrification rate in presence of GO/rGO increased up to 1.873ppm NO3-N/h after the second pulse of groundwater and flush with H2/CO2 gas, which is almost 2.3 folds higher than initially in the same condition. This suggests that GO needs some time to get fully reduced to rGO, and the denitrification rate might reach the same or higher levels as in the GO/rGO-free conditions, when GO is fully reduced. Improved denitrification would indicate that rGO facilitates the electron transfer between bacteria and nitrate, as it can be expected from its electrochemical properties previously studied. This would be worth being investigated in the scope of a longer experience. / Grundvatten (GW) som står för det mesta av det sötvatten som finns tillgängligt runt om i världen och att hitta hållbara tekniker för att förorena det är av avgörande betydelse för en trygg dricksvattenförsörjning. Den omfattande användningen av gödselmedel i jordbruket, liksom andra antropogena aktiviteter, bidrar till de överdrivna nitratnivåerna i vissa vattenfiskare. Dessa nivåer måste sänkas för att erhålla dricksvatten. Bioelektrokemiska system (BES), med användning av mikroorganismer för att katalysera en önskad elektrokemisk reaktion, visade sig nyligen vara en mycket lovande teknik för sanering av vatten. Grundvatten denitrifikation med hjälp av Microbial Electrolysis Cell (MEC) måste förbättras för att ytterligare skala upp systemet på plats. Fördelarna med fluidiserad bäddreaktor (FBR) såväl som de enastående elektrokemiska egenskaperna hos reducerad grafenoxid (rGO) är två potentiella förbättringar av ett sådant bioelektrokemiskt denitrifikationssystem som undersöktes i denna avhandling. Vissa väsentliga parametrar kan bestämmas under de preliminära stegens experiment. Fluidiseringsstudierna gav oss en klar insikt om att kokosnötbaserade aktiverade kolpartiklar (CAC) -partiklar var resistenta bärarpartiklar, trevligt fluidiserade i en cirkulär katodisk kammare på 39,27 cm3 för en flödeshastighet mellan 450ml/min till 590ml/min. För samma flödeshastighet på 500ml/min kunde vi få CAC-partikelfluidisering för uppströms fluidiserad konfiguration och stillbäddspartiklar för den fixerade bädden nedströms konfiguration, vilket skulle vara mycket användbart för senare opartisk jämförelse. De denriffriserande bakterierna visade under deras anrikning en nitratborttagningshastighet av upp till 1,986 ppm NO3-N/h i serumflaskor, med ett genomsnitt på 0,38 ppm NO2-N / h ackumulering. Den parallella körningen av denitrifierande reaktorn med fast bädd kontra fluidiserad bädd för att jämföra deras denitrifikationsprestanda planerades, men kunde inte utföras på grund av COVID-19. Diagramexperimenten av grafenoxid (GO) visade en god biokompatibilitet mellan GO/rGO och våra autotrofiska denitrifierande bakterier. En förändring av morfologin inom cirka 20 timmar observerades, vilket antagligen antydde att bakterierna minskade GO till rGO. Under ett första test ledde närvaron av GO till 2,7 gånger mindre effektiv denitrifikationsprestanda jämfört med GO/rGO-fritt tillstånd, troligtvis på grund av konkurrensen mellan nitrat och GO för att ha minskat. Denitrifikationsgraden i närvaro av GO/rGO ökade emellertid upp till 1,873 ppm NO3-N/h efter den andra grundvattenspulsen och spolades med H2/CO2-gas, vilket är nästan 2,3 gånger högre än ursprungligen i samma tillstånd. Detta antyder att GO behöver lite tid för att helt reduceras till rGO, och denitrifikationsgraden kan nå samma eller högre nivåer som i GO/rGO-fria förhållanden, när GO är helt reducerad. Förbättrad denitrifikation skulle indikera att rGO underlättar elektronöverföring mellan bakterier och nitrat, som det kan förväntas av dess elektrokemiska egenskaper som tidigare studerats. Detta skulle vara värt att undersökas inom ramen för en längre upplevelse.
313

Innovationer inom fastighetsförvaltning : Lönsamheten i att komplettera regleringen av uppvärmningen i en byggnad med mobilstyrning / Innovations within property management : The profitability of complementing the regulation of heating in a building with mobile control

Marefat, Emil, Valdani, Sandra January 2018 (has links)
I takt med att samhället digitaliseras allt mer förändras våra liv på olika plan, inte minst i det egna hemmet. Idén om smarta hem har funnits ett tag, men nya innovationer fortsätter att dyka upp på marknaden. Samtidigt är det ofta aktuellt för människor att spara pengar om de kan, och ett sätt att spara pengar är att minska energiförbrukningen i den egna bostaden.Att via en SmartPhone kunna reglera temperaturen i en bostad är i dagsläget tekniskt möjligt, men är ändå inte fullt etablerat på bostadsmarknaden. Många människor befinner sig på arbetsplatser flera timmar av dagen, och det är inte nödvändigt att bostaden håller en komfortabel temperatur när ingen är hemma. I den här undersökningen utreds det av den anledningen lönsamheten i att addera mobilstyrning som ett komplement till regleringen av uppvärmningen i en byggnad, men även själva intresset för ett sådant här system på marknaden.För att kunna uppfylla syftet med undersökningen utfördes bland annat intervjuer av allmänheten och en fastighetsägare för att undersöka intresset på marknaden. För att undersöka den ekonomiska lönsamheten i att addera mobilstyrning som ett komplement till regleringen av uppvärmningen i en byggnad gjordes även hypotetiska kassaflöden. Efter undersökningen var slutförd kunde det konstateras att det fanns ett tydligt intresse för mobilstyrning på marknaden. Från kassaflödena kunde även utläsas att det på sikt är potentiellt ekonomiskt lönsamt för en fastighetsägare att installera mobila styrenheter. Lönsamheten beror dock på olika faktorer, däribland mänskliga faktorer och byggnadsteknik. / As society is increasingly digitalized our lives are changing rapidly in many areas of everyday life, one of them is the homes in which we live. The concept of a smart home has been around for some time and new innovations continue to appear on the market to define the modern homes of the future. Also, people often want to save money at given opportunity, and reducing the daily home energy consumption is a way to accomplish that.To be able to regulate the temperature of the home with a SmartPhone is currently technically possible, but it’s still not fully established in the housing market. As most people leave their homes for several hours a day during the average week a constant heating level is unnecessary. Because of this it could be interesting to investigate the potential market interest as well as the profitability of adding mobile control as a complement to the ordinary regulation of heating in a building.In order to conduct this study, interviews of the public and a property owner were conducted to get an overview of the level of potential market interest. In order to investigate the profitability of adding the mobile controlled system, a hypothetical cash flow calculation was made. After the interviews were completed, it was noted that there was a clear interest in using this kind of mobile controlling in the market. From the cash flow calculation it could also be seen that in the long term it is likely to be economically profitable for a property owner to invest in this system as well. The profitability, however, depends on a number of factors, including human behavioral patterns and building technology.
314

Investigation on the Mechanical, Microstructural, and Electrical Properties of Graphene Oxide-Cement Composite

Al Muhit, Baig Abdullah 01 January 2015 (has links)
Nanotechnology refers to the use of the materials or particles ranging from a few nanometers (nm) to 100 nanometers (nm) in a wide range of applications. Use of nanomaterials in cement composite to enhance the mechanical properties, fracture toughness and other functionalities has been studied for decades. In this regard, one of the carbon-based nanomaterials, Graphene Oxide (GO), has received attentions from researchers for its superior mechanical properties (e.g. tensile strength, yield strength, and Young's modulus). Although GO is not lucrative in increasing electrical conductivity (EC) of cement paste compared to that of graphene- another derivative of GO, reduced graphene oxide (rGO), might be a solution to increase EC. Another derivative of GO is the solution to the problem. In this research, the compressive strength and flexural strength of GO-cement composite (GOCC) and rGO-cement composite (rGOCC) have been investigated with 0.01% and 0.05% GO and rGO content. GOCC-0.05% showed 27% increase in compressive strength compared to the control cement paste after 28 days (d) of hydration. GOCC-0.01% showed only 3.4% increase in compressive strength compared to the control. rGOCC-0.05% showed 21% increase in compressive strength and 15.5% increase in Modulus of Rupture (MOR) compared to the control cement paste after 28 d of hydration. On the other hand, rGOCC-0.01% showed 7% increase in compressive strength and 0.35% increase in MOR after 28 d. GOCC-0.05% showed increasing trends in compressive strength after 28 d indicating continuation of hydration. Similarly, rGOCC-0.05% also showed increasing trends in compressive and flexural strength after 28 d, possibly due to the reason described earlier. Microstructural investigation on GOCC-0.05% and GOCC-0.01% by X-ray Diffraction (XRD) illustrated that the crystallite sizes of tobermorite-Å and jennite, which are mineralogical counterpart of disordered Calcium-Silicate-Hydrate (C-S-H), increases from 3 d to 28 d, representing the crystallite growth due to continued hydration. However, the crystallite size of GOCC-0.05% was smaller than that of GOCC-0.01% at both 3 d and 28 d, indicating finer nucleated grains. According to Hall-Petch equation, mechanical strength increases with decreasing particle size. Finer particles or grains can increase the strength in cement composites in several other ways: (1) GO acted as heterogeneous nucleation sites because of reactive functional groups. Activation energy was decreased by these "defects" in the cement paste, and consequently, numerous nuclei of C-S-H. with high surface area were formed, (2) because of finer grains, cracks are forced to move along a tortuous path, which makes the structure difficult to fail, and strength increased consequently (3) Finer grains of GOCC-0.05% created compacted hydration products decreasing porosity which can indirectly increase the strength. The above reasons, separately or in conjunction, might increase the strength of GOCC-0.05% and proved that GO is responsible for increasing heterogeneous nucleation sites during cement hydration. Early age hydration (EAH) characteristics were investigated for rGOCC specimens with 0.1% and 0.5% rGO content. Scanning Electron Microscope (SEM), Energy Dispersive X-ray analysis (EDX), and X-ray Diffraction (XRD) were employed to study the EAH characteristics. SEM/EDX, and XRD analysis were performed after 15 min, 1 h, 3 h and 24 h of hydration. (EAH) study on rGOCC-0.1% showed that at 15 min hydration, numerous precipitates of, possibly, C-S-H formed along the grain boundary (GB) of unhydrated cement grains. This served as visual confirmation of Thomas and Scherer's Boundary Nucleation and Growth (BNG) model that hydration of cement grains was initiated by the short burst of nucleation of C-S-H embryos along GB. EDX on rGOCC-0.1% and rGOCC-0.5% showed that Ca/Si ratio in C-S-H was ~2.0. This finding indicated that C-S-H structure in this study was concurrent with that of impure jennite. XRD analysis also evidently showed that jennite was present, possibly possessing a short range ordered (SRO) structure, referring to local crystalline structure in a very short area. After consulting Chen's work, it would be appropriate to say that C-S-H found in this study resembled more as C-S-H (II), which is disordered jennite. It was also observed that as expected with cement with nanomaterials, with continuing hydration, pore spaces were filled with hydration products such as C-S-H, ettringite, CH, sulfoaluminates etc,. Lastly, Electrical resistivity (ER) testing on 9 sets of rGOCC specimens was conducted. The specimen includes 0.5%, 1%, 5% rGO content, and the control conditioned in both oven dry (OD) and saturated surface dry (SSD). ER increased with the increase of rGO content from 0.5% and 1% compared to that of the control. However, the ER of rGOCC-5% was significantly decreased, showing 93% reduction compared to the control, which can be interpreted as a threshold value for sensing applications to be explored. As expected, large reduction of ER value occurred on the specimens with the SSD condition. This reduction can be attributed to the ionic conduction though the pore solution of the composites. As the rGO content increased, so did the potential nucleation sites for hydration (as can be seen in SEM images), which might block the number of contact points among the rGO, resulting in low conduction and high resistivity. However, as rGO content increased to 5%, the contact areas/points increased to a degree that could trump the nucleation seeding sites, resulting in decreased ER. The ER measured with the rGOCC specimens was comparable to that of cement composites incorporating carbon fibers (CF), and steel fibers, but higher content of rGO are required to have a similar ER range of those fiber cement composites. This might be due to smaller sizes of rGO sheets and lower aspect ratio compared to other nanofibers causing drastic reduction of electron tunneling mechanism compared to other fibers.
315

Analytisk lyssning : Hur påverkar bilder vad vi hör och kan vi träna vår hörsel? / Analytic Listening : How do pictures effect what we hear and is it possible to practice hearing?

Östblad, Per Anders January 2011 (has links)
Denna studie har undersökt huruvida det är möjligt att träna sin hörsel i att lyssna analytiskt. Den har också syftat till att undersöka huruvida bilder påverkar hur människor identifierar och bedömer ljud. Efter en litteraturstudie samt en hypotestestande undersökning på området har jag sett tendenser som tyder på att det går att träna sin hörsel i denna typ av lyssning. Jag har också sett indikationer på att bilder kan påverka hur vi identifierar ljud.
316

Adaptation of Nontraditional Control Techniques to Nonlinear Micro and Macro Mechanical Systems

Daqaq, Mohammed F. 15 August 2006 (has links)
We investigate the implementation of nontraditional open-loop and closed-loop control techniques to systems at the micro and macro scales. At the macro level, we consider a quay-side container crane. It is known that the United States relies on ocean transportation for 95% of cargo tonnage that moves in and out of the country. Each year over six million loaded marine containers enter U.S. ports. Current growth predictions indicate that container cargo will quadruple in the next twenty years. To cope with this rapid growth, we develop a novel open-loop input-shaping control technique to mitigate payload oscillations on quay-side container cranes. The proposed approach is suitable for automated crane operations, does not require any alterations to the existing crane structure, uses the maximum crane capabilities, and is based on an accurate two-dimensional four-bar-mechanism model of a container crane. The shaped commands are based on a nonlinear approximation of the two-dimensional model frequency and, unlike traditional input-shaping techniques, our approach can account for large hoisting operations. For operator-in-the-loop crane operations, we develop a closed-loop nonlinear delayed-position feedback controller. Key features of this controller are that it: does not require major modifications to the existing crane structure, accounts for motion inversion delays, rejects external disturbances, and is superimposed on the crane operator commands. To validate the controllers, we construct a 1:10 scale model of a 65-ton quay-side container crane. The facility consists of a 7-meter track, 3.5-meter hoisting cables, a trolley, a traverse motor, two hoisting motors, and a 50-pound payload. Using this setup, we demonstrated the effectiveness of the controllers in mitigating payload oscillations in both of the open-loop and closed-loop modes of operation. At the micro level, we consider a micro optical device known as the torsional micromirror. This device has a tremendous number of industrial and consumer market applications including optical switching, light scanning, digital displays, etc. To analyze this device, we develop a comprehensive model of an electrically actuated torsional mirror. Using a Galerkin expansion, we develop a reduced-order model of the mirror and verify it against experimental data. We investigate the accuracy of representing the mirror using a two-degrees-of-freedom lumped-mass model. We conclude that, under normal operating conditions, the statics and dynamics of the mirror can be accurately represented by the simplified lumped-mass system. We utilize the lumped-mass model to study and analyze the nonlinear dynamics of torsional micromirrors subjected to combined DC and resonant AC excitations. The analysis is aimed at enhancing the performance of micromirrors used for scanning applications by providing better insight into the effects of system parameters on the microscanner's optimal design and performance. Examining the characteristics of the mirror response, we found that, for a certain DC voltage range, a two-to-one internal resonance might be activated between the first two modes. Due to this internal resonance, the mirror exhibits complex dynamic behavior. This behavior results in undesirable vibrations that can be detrimental to the scanner performance. Torsional micromirrors are currently being implemented to provide all-optical switching in fiber optic networks. Traditional switching techniques are based on converting the optical signal into electrical signal and back into optical signal before it can be switched into another fiber. This reduces the rate of data transfer substantially. To realize fast all-optical switching, we enhance the transient dynamic characteristics and performance of torsional micromirrors by developing a novel technique for preshaping the voltage commands applied to activate the mirror. This new approach is the first to effectively account for inherent nonlinearities, damping effects, and the energy of the significant higher modes. Using this technique, we are able to realize very fast switching operations with minimal settling time and almost zero overshoot. / Ph. D.
317

Modeling and Simulation of MEMS Devices

Zhao, Xiaopeng 19 August 2004 (has links)
The objective of this dissertation is to present a modeling and simulation methodology for MEMS devices and identify and understand the associated nonlinearities due to large deflections, electric actuation, impacts, and friction. In the first part of the dissertation, we introduce a reduced-order model of flexible microplates under electric excitation. The model utilizes the von Karman plate equations to account for geometric nonlinearities due to large plate deflections. The Galerkin approach is employed to reduce the partial-differential equations of motion and associated boundary conditions into a finite dimensional system of nonlinearly coupled ordinary-differential equations. We use the reduced-order model to analyze the mechanical behavior of a simply supported microplate and a fully clamped microplate. Effect of various design parameters on both the static and dynamic characteristics of microplates is studied. The second part of the dissertation presents comprehensive modeling and simulation tools for impact microactuators. Nonsmooth dynamics due to impacts and friction are studied, combining various approaches, including direct numerical integration, root-finding technique for periodic motions, continuation of grazing periodic orbits, and local analysis of the near grazing dynamics. The transition between nonimpacting and impacting long term motions, referred to as grazing bifurcations, indicates the transition between on and off states of an impact microactuator. Three different on-off switching mechanisms are identified for the Mita microactuator. These mechanisms also generalize to arbitrary impacting systems with a similar nonlinearity. A local map based on the concept of discontinuity mapping provides an effcient and accurate tool for the grazing bifurcation analysis. Nonlinear impacting dynamics of the microactuator are studied in detail to identify various bifurcations and parameter ranges corresponding to chaotic motions. We find that the frequency-response curves of the impacting dynamics are significantly different from those of the nonimpacting dynamics. / Ph. D.
318

Parallel Simulations, Reduced-Order Modeling, and Feedback Control of Vortex Shedding using Fluidic Actuators

Akhtar, Imran 02 May 2008 (has links)
In most of the engineering and industrial flow applications, one encounters fluid-structure interaction. This interaction can lead to some undesirable forces acting on the structure, causing its damage or fatigue. The phenomenon, being complex in nature, requires thorough understanding of the flow physics. Analyzing canonical flows, such as the flow past a cylinder, provides fundamental concepts governing the fluid behavior. Despite a simpler geometry, studying such flows are a building block in an effort to comprehend, model, and control complicated flows. For the flow past a circular cylinder, we examine the phenomenon of vortex shedding observed in many bluff body wakes. We develop a parallel computational fluid dynamics (CFD) code to solve the incompressible Navier-Stokes equations on curvilinear coordinates to analyze vortex shedding. The algorithm is implemented on a distributed-memory, message-passing parallel computer, and a domain decomposition technique is employed to partition the grid into various processors. We validate and verify the numerical results with existing experimental and numerical studies. We analyse the performance of the parallel CFD solver by computing the speed-up and efficiency of the solver. We also show that the algorithm is scalable and can be efficiently employed to study other engineering problems requiring larger grid sizes and computational domains. Various other features of the solver, such as the turbulence model, moving boundary techniques, shear, and other canonical flows are also presented. Direct numerical simulations (DNS) are performed to simulate the flow past a circular cylinder to compute the velocity and pressure fields. Based on the flow realizations of the DNS data, we use the proper orthogonal decomposition (POD) tool to determine the minimum degrees of freedom (or modes) required to represent the flow field. For the current nonlinear problem, the dominant POD modes are used in a Galerkin procedure to project the Navier-Stokes equations onto a low-dimensional space, thereby reducing the distributed-parameter problem into a finite-dimensional nonlinear dynamical system in time. We use long-time integration of the reduced-order model to calculate periodic solutions and alternatively use a shooting technique to home on the system limit cycles. We obtain the pressure-Poisson equation by taking the divergence of the Navier-Stokes equation and then project it onto the pressure POD modes. Then, we decompose the pressure into lift and drag components and compare the results with the CFD results. To reduce the fluctuating forces on the structure, we implement full-state feedback control on the low-dimensional model with suction applied aft of the separation point. The control algorithm is successfully simulated using the CFD code and suppression of vortex-shedding is achieved. / Ph. D.
319

Parametric covariance assignment using a reduced-order closed-form covariance model

Zhang, Qichun, Wang, Z., Wang, H. 03 October 2019 (has links)
Yes / This paper presents a novel closed-form covariance model using covariance matrix decomposition for both continuous-time and discrete-time stochastic systems which are subjected to Gaussian noises. Different from the existing covariance models, it has been shown that the order of the presented model can be reduced to the order of original systems and the parameters of the model can be obtained by Kronecker product and Hadamard product which imply a uniform expression. Furthermore, the associated controller design can be simplified due to the use of the reduced-order structure of the model. Based on this model, the state and output covariance assignment algorithms have been developed with parametric state and output feedback, where the computational complexity is reduced and the extended free parameters of parametric feedback supply flexibility to the optimization. As an extension, the reduced-order closed-form covariance model for stochastic systems with parameter uncertainties is also presented in this paper. A simulated example is included to show the effectiveness of the proposed control algorithm, where encouraging results have been obtained. / National Natural Science Foundation of China [grant number 61573022], [grant number 61290323] and [grant number 61333007]
320

Exact/heuristic hybrids using rVNS and hyperheuristics for workforce scheduling

Remde, Stephen M., Cowling, Peter I., Dahal, Keshav P., Colledge, N.J. January 2007 (has links)
In this paper we study a complex real-world workforce scheduling problem. We propose a method of splitting the problem into smaller parts and solving each part using exhaustive search. These smaller parts comprise a combination of choosing a method to select a task to be scheduled and a method to allocate resources, including time, to the selected task. We use reduced Variable Neighbourhood Search (rVNS) and hyperheuristic approaches to decide which sub problems to tackle. The resulting methods are compared to local search and Genetic Algorithm approaches. Parallelisation is used to perform nearly one CPU-year of experiments. The results show that the new methods can produce results fitter than the Genetic Algorithm in less time and that they are far superior to any of their component techniques. The method used to split up the problem is generalisable and could be applied to a wide range of optimisation problems.

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