Simulacó numérica directa de la dispersió turbulenta de plomalls amb flotació en un flux en un canal Alexandre Fabregat Tomás, Tarragona, octubre del 2006 1 IntroduccióL'objectiu d'aquest treball és estudiar la dispersió turbulenta de calor en diferents configuracions basades en el canal desenvolupat mitjançant DNS (Direct Numerical Simulations). Aquesta eina ha demostrat ser de gran utilitat a l'hora d'estudiar fluxos turbulents ja que permet, donada una malla computacional capaç de capturar totes les estructures del flux i un esquema que minimitzi els errors i la dissipació numérica, descriure acuradament l'evolució temporal del flux. Permet a més, donada la descripció tridimensional i temporal del flux, determinar amb precisió qualsevol quantitat que seria impossible d'obtenir experimentalment.En el flux en un canal, el fluid esmou entre dues parets planes, llises i paral·leles separades una distància 2d impulsat per un gradient constant mitjà de pressió. El flux s'anomena desenvolupat quan ja no hi ha efectes de regió d'entrada i la única inhomogeneïtat es troba en la direcció normal a la paret. Sota aquestes condicions, les quantitats promitjades esdevenen estacionàries en el temps.En aquest treball s'ha validat el codi computacional mitjançant la reproducció d'algunes configuracions de flux prèviament estudiades per altres autors. Els nous coneixements en l'estudi de la dispersió turbulenta de calor s'han obtingut a l'incloure, en un flux totalment desenvolupat en un canal, una font lineal centrada verticalment que provoca l'aparició d'un plomall amb una temperatura més alta que la del flux del fons i que per tant, al tenir una menor densitat, experimenta flotació i es deflecteix. L'amitjanament temporal del flux permet estudiar les diferents contribucions dels diferents termes rellevants en les equacions de transport.És d'especial interés la comparativa d'aquests resultats amb els corresponents a la formació d'un plomall a partir d'una font lineal d'un escalar passiu.Per altra banda també s'ha estudiat l'eficiència en paral·lel dels mètodes multigrid en la resolució d'equacions de Poisson. Aquestes equacions són d'especial interés ja que apareixen en el càlcul de la pressió i representen un coll d'ampolla en termes de costos computacionals. Aquest mètode numèric ha estat comparat amb els mètodes de gradient conjugat (anteriorment emprats en el codi 3DINAMICS) en la resolució de diferents problemes comparant els costos en termes de temps de CPU i la seua escalabilitat en la màquina multiprocessador de memòria distribuïda del grup de recerca de Mecànica de Fluids de Tarragona.2 Descripció matemàticaUn cop adimensionalitzades mitjançant les escales adequades, les equacions de transport de quantitat de moviment i energia han estat discretitzades sobre una malla desplaçada mitjançant el mètode de volums finits emprant un esquema centrat de segon ordre. La discretització dels termes advectius en els casos amb fonts lineals ha requerit, però, d'un cura especial ja que la no-linealitat d'aquests termes pot provocar oscil·lacions artificials en el camp dels escalars. La difusió numèrica dels mètodes upwind, com el QUICK, ha estat quantificada i comparada amb resultats obtinguts per a esquemes centrats de segon ordre. Les equacions han estat integrades en el temps mitjançant un esquema implícit de segon ordre tipus Crank-Nicholson. També ha estat necessari implementar condicions de sortida per a la temperatura en els casos A i C del tipus no reflectant per tal de garantir la conservació i evitar l'aparició d'estructures artificials en el flux.3 Descripció físicaLa figura 1 presenta un esquema del domini computacional corresponent al canal desenvolupat. De l'esquema es desprén que x, y i z corresponen a les direccions principal del flux, la perpendicular i la normal a les parets respectivament. Les configuracions del flux estudiades es troben resumides a la taula 1 on s'indica la resolució de la xarxa computacional, el nombre de Reynolds (basat en la velocitat de fricció ut) i en el casos amb flotació, el nombre de Grashof, la temperatura de referència i la direcció de flotació (la direcció del vector gravetat).Les dimensions del canal s´on 8pd×2pd×2d en les direccions x, y i z respectivament.En el cas A la temperatura representa un escalar de manera que el plomall format és passiu, és a dir, no hi ha acoblament entre les equacions de quantitat de moviment i energia. A diferència d'aquest, en els casos B i C totes dues equacions queden acoblades pel terme de flotació. Aquest terme apareix quan les diferències de temperatura en el si del fluid generen diferències de densitat. En el cas B, el canal vertical amb convecció mixta, cada paret del canal es troba a una temperatura constant però diferent. El vector gravetat i la direcció del corrent estan alineades de manera que aquesta direcció continua sent homogènia. En la zona propera a la paret calenta la flotació actua en la direcció del corrent imposada pel gradient mitjà de pressió. En canvi, en la zona propera a la paret freda, la flotació s'oposa al moviment del flux.El cas C és similar al cas A però en aquesta ocasió la temperatura no es considera un escalar passiu i per tant la flotació acobla el camp dinàmic amb el de temperatures. El vector gravetat actua en aquest cas en la direcció normal. La inhomogeneïtat en la direcció del flux no permet continuar emprant condicions de contorn periòdiques i per tant, al domini presentat en la figura 1, se li ha acoblat una regió auxiliar a l'entrada on es resolen únicament les equacions de quantitat de moviment. Els camps de velocitat i pressió per a un canal totalment desenvolupat obtinguts en aquest domini auxiliar s'empraran com a condició de contorn a l'entrada del domini de computació. No és necessari cap tipus d'interpolació ja que la resolució del a xarxa d'aquest domini auxiliar és la mateixa que l'emprada en el domini de computació.4 ResultatsEls resultats per a les simulacions presentades en la taula 1 contenen, principalment, els perfils de velocitat i temperatura mitjans així com la intensitat de les fluctuacions. A més, es presenten els perfils de les diferents contribucions dels termes relevants de les equacions de transport amitjanades. Per al cas C, els camps dinàmics i de temperatura no estan desenvolupats. Els perfils mitjans a diferents posicions aigües avall permeten estudiar l'evolució del plomall ascendent a més d'analitzar com la flotació afecta al balanç de les diferents contribucions. La figure 2 presenta el camp mitjà de temperatures per al cas C amb les tres posicions en la direcció principal del flux per a les quals s'han inclòs els perfils.Finalment, es presenten els resultats corresponents a la comparativa entre els diferents solvers per a una equació de Poisson. Tots els mètodes numèrics han es-3Figura 2: Camp mitjà de temperatures per al cas C tat paral·lelitzats mitjançant les llibreries Message Passing Interface. En la figura 3 es presenten com a exemple els resultats (en termes de temps de CPU i speedup) per a la resolució de l'equació de Poisson per al desacoblament de pressió i velocitat en el cas del flux desenvolupat en un canal.Els resultats de speed-up per als diferents mètodes mostren la baixa escalabilitat del solver multigrid comparat amb els altres mètodes del tipus gradient conjugat. La raó radica en les grans necessitats de comunicació d'un algoritme construït sobre un esquema de relaxació tipus SOR. Tanmateix, multigrid és el mètode numèric que requereix menys temps de CPU per concloure la tasca. El factor respecte als mètodes de gradient conjugat pot arribar a ser de 30 i per tant és el millor candidat per a la resolució d'aquests tipus de problemes. / The main goal of this work is to study the turbulent heat transfer in a developed channel flow using Direct Numerical Simulations (DNS). These simulations solve explicitly all the scales present in the turbulent flow so, even for moderate Reynolds numbers, the discretization grids need to be fine enough to capture the smallest structures of the flow and, consequently, DNS demands large computational resources. The flow, driven by a mean constant pressure gradient in the streamwise direction, is confined between two smooth, parallel and infinite walls separated a distance 2d.The turbulent heat transport is studied for three different flow configurations.Some of them are used as benchmark results for this work. The three cases reported can be summarized as:· case A: Scalar plume from a line source in a horizontal channel.· case B:Mixed convection with the gravity vector aligned with the streamwise direction (vertical channel).· case C: Buoyant plume from a line source in a horizontal channel.In addition, preliminary results for a turbulent reacting flow in a fully developed channel are also presented.In the case B heat flux results from a temperature difference between the channel walls. The gravity vector is aligned with the streamwise direction and the Grashof, Reynolds and Prandtl numbers are Gr = 9.6 · 106, Ret = 150 and Pr = 0.71 respectively. Close to the hot wall, buoyancy acts aligned to the flow direction imposed by the mean pressure gradient so velocities are generally increased in comparison with a purely forced convection flow. Oppositely, near the cold wall, buoyancy is opposed to the flow and consequently velocities are decreased.Cases A and C are similar because in both cases a hot fluid is released within a cold background flow through a line source vertically centered in the wall-normal direction located at the inlet. The height of the source is 0.054d. The injected hot fluid disperses forming a hot plume that is convected downstream between the two adiabatic walls of the channel.The difference between cases A and C lies in the fact that for case A heat and momentum are decoupled and temperature acts as an scalar. Advection and diffusion are the only phenomena responsible for the evolution of the plume. On the other hand, in case C, buoyancy couples heat and momentum and, consequently, the plume floats drifting upward as it advances in the channel due to its lower density. In case C, the streamwise direction is not homogenous because of the coupling between heat and momentum. To guarantee developed conditions at the inlet of the channel it has been necessary to attach a buffer domain just before the computational domain. In this buffer domain, the momentum transport equations for a fully developed channel are solved with the same resolution used in the main domain.The results of cases A and B have been used to validate the 3DINAMICS CFD code by comparison with data reported in the literature. This code is written in FORTRAN 90 and parallelized using the Message Passing Interface (MPI-CHlibrary). It uses the second order in time Crank-Nicholson scheme to integrate numerically the transport equations which are discretized spatially using the centered second-order finite volume approach.The analysis of averaged turbulent quantities and the contributions of the different terms of the time-averaged transport equations is used to show how buoyancy affects the turbulent transport of momentum and heat along the channel.Finally, following a similar configuration than that of case A, a chemical reactantA released through line source reacts with a background reactant B following a second order chemical reaction with Damkh¨oler number of 1. Preliminary results for turbulent species transport are also included in this work.Special attention have been devoted to the discretization of the advective terms to avoid non-realistic values of the variables because of the non-linearities of the transport equations. The conservative non-reflecting boundary conditions have been implemented at the outlet to simulate the convected outflow when the streamwise direction can not be considered homogeneous, as in case C. For homogeneous directions, periodic boundary conditions have been used.Large grid resolutions (up to 8 million grid nodes for case C including the buffer region) demand important computational resources. A parallel Multigrid solver has substituted the previous conjugate gradient method to solve the Poisson equation in the pressure calculation. This step was the most expensive in terms of CPU costs. The Multigrid method efficiency has been compared with two different versions of the conjugate gradient approach and it has been demonstrated that this method is the most efficient in terms of CPU time although the current algorithmcan be improved to enhance the scalability inmultiprocessor computers.

The Kyoto related mechanism – clean development mechanism (CDM) – can be used to generate certified emission reductions (CERs) for climate mitigating projects indeveloping countries. These credits provide an opportunity for additional project financing. This thesis has investigated the feasibility of using the CDM for off-grid solar home systems in order to electrify health centers in Uganda. The investigated scope includes two scenarios; one related to a particular project, ICT4MPOWER, and another one related to a national scenario of health center electrification. Two dimensions of feasibility have been targeted; legal prerequisites – various regulations that govern CDM projects – and value creating potential. The latter dimension has primarily focused on whether sufficient CDM-specific profit can be generated, but also looked at broader perspectives of value creation. Calculated break-even scenarios show that the expected scope of the ICT4MPOWER project is far too small to benefit from CDM. A national scenario improves the chances of generating a sufficient profit but would most likely still be too small. A project with broader national coverage would likely need to be arranged as a CDM program of activites (PoA). Such an arrangement has organizational benefits but does further worsen the financial outlook. Apart from the unfortunate value creating prospects, there are also obstacles related to legal prerequisites. To establish a baseline – the business as usual scenario which reflect the emission reduction potential of a project – may be difficult and somewhat ad-hoc. To demonstrate additionality – that the project would not have been carried out anyway – is another potential obstacle which applies to the PoA scenario. All in all, there are clear doubts that CDM would be a feasible solution for the investigated scenarios.

This thesis analyzes the National Adaptation Programs of Action (NAPA) that aredeveloped for the least developed countries within the United Nations FrameworkConvention of Climate Change. The NAPAs are developed to help the least developedcountries to deal with the challenges that are likely to occur due to climate changeissues. Within the United Nations there is strong consensus that gender mainstreamingmust be a part of all of the strategies implemented within the UN.By analyzing the NAPAs concerning food security and energy using gender theory anddiscourse analysis it is clear that gender is often overlooked when creating solutionsfor future issues that are likely to be caused by climate change. The energy sector inparticular overlook the needs of women in rural areas and have a clear male bias. In theNAPAs concerning food security women’s participation is slightly more present, butthere is a clear lack of gender mainstreaming in the documents.

<p>This dissertation investigates the varied institutional foundations of local governance in rural China with central emphasis on the role of communal structures and rural-urban migration. Instead of treating indigenously developed institutions (IDIs) and externally imposed institutions (EIIs) as competing variables as in most other contemporary research on local governance, this dissertation develops a theoretical framework exploring the interaction between the two types of institutions in sustaining local governance as well as analyzing how community structural features shape this interaction and influence their respective efficacy in sustaining local governance. With the help of a representative national survey in mainland China in 2008 and carefully selected case studies, this dissertation finds that both indigenous institutions and externally imposed institutions can uphold quality governance in local communities, as long as they can efficaciously solve the problems of collective action and accountability. Close-knit communities favor the operation of indigenous institutions; while externally imposed institutions are relatively more competent in half-open communities. However, neither of them can survive and perform effectively in atomized communities due to the lack of a minimal level of coordination among community members. As outward migration challenges rural communities in an uneven way and transforms communal structures to various extents, it is likely to observe a variety of institutional foundations sustaining local governance in Chinese villages.</p> / Dissertation

It is a common method to use mergers and acquisitions to grow for enterprises. Cross-border mergers and acquisitions is one of the ways to expand the oversea marker share, besides mergers and acquisitions in domestic market itself. In the past, the enterprises from developed countries took the role to buy oversee targets. The enterprises from emerging markets gradually become the protagonist for the reason of the rise of emerging markets, especially after the Global Financial Crisis and European Debt Crisis. This study refers to literature presented to look deeply into the motivations of mergers and acquisitions from different acquirers. We classified the motivations we found in the secondary data, with year 2007 to May 2012 as the scope, expecting to figure out the differences between developed-country acquirers and emerging-market acquirers. The result shows that the main motivations for developed-country acquirers are seeking for the resources needed, entering local market and increasing the size of itself. On the other hand, going into international market, reaching economy of scale and seeking for the resources needed are the main motivations for emerging-market acquirers. Furthermore, the motivation of mergers and acquisition differs from one industry to another.

This study investigates the Fisher Effect for a sample of ten developed countries and ten developing countries. The study examines whether the nominal interest rate adjusts to the expected inflation rate in the long run. The distinction between the developed countries and developing countries also enables to identify special conditions under which Fisher Effect is more likely to hold. To analyze the long run relationship between the nominal interest rate and expected inflation rate, Bounds test approach of Pesaran et. al. (2001) is utilized. Estimation results show that the adjustment of nominal interest rate to expected inflation is encountered mostly for the developing countries which have inflationary history in their economies.

This dissertation explores how Internet use impacts four different measures of economic development using several econometric techniques on multi-country panel data. The economic development outcomes investigated are: per capita GDP, per capita export revenues, per capita market capitalization, and societal well-being as measured by the United Nations Human Development Index (HDI). Data from the World Bank, the International Telecommunication Union, and the United Nations -covering 202 countries over the period 1996 to 2007- are combined to allow for empirical investigation using dynamic panel data and finite mixture model estimation techniques on the total sample and subsamples stratified by country income level. The results suggest that countries benefit differently from increasing Internet use and the magnitude of the effect depends on the income level of the country. In low income countries, additional Internet use has a significant positive effect on per capita GDP and overall welfare, as measured by the HDI. Increasing Internet use has a significant positive effect on all four measures of economic development in countries that have achieved middle income status. Since Internet use affects economic development outcomes differently depending on the income level of the country, the policy recommendations must also vary according to the country's income level.

By understanding current approaches and methods of product development (PD) combined with knowledge of the needs and know-how of customers in the least developed countries (LDCs) associated risks and excessive costs can be avoided. The main purpose of this thesis is to highlight the important need of developing products and services for the LDCs and to look at current practices for PD and to distill these into one method for developing products pertinent to LDC needs and markets. Conversely, the second purpose for this thesis is to examine possible LDC based development tools that can be applicable when designing for the more established markets. There are also crucial social, cultural, economic and political reasons for addressing LDC related issues. The goal is to show companies of all sizes that it can be profitable to expand to new markets in the LDCs and also that the steps used there can help generate new revenue when implemented in their current markets, as well as to provide them a model for it. This thesis includes and clearly demonstrates the importance of development involvement on the local level and the benefit of using complementors. The thesis data and conclusions are based on literature studies and an extended stay in the Dominican Republic. It is here observed that by getting closer to the end customer, a company will get an increased understanding and knowledge that provides an advantage over the competition. And for companies to succeed in the LDCs, the three most significant things to consider are: 1) to find the specific needs of the customer, 2) design for affordability, and 3) to source and manufacture locally. It will be seen that the benefits to such an approach extend outward in essentially all directions.

This thesis examines the need for a multilateral regime for the regulation of foreign direct investment. The absence of such a regime has slowed the growth of foreign direct investment, as investment decisions are difficult to make because of the uncertainty of investment rules. Attempts to establish a multilateral framework for investment have failed due to disagreement between developed and developing countries on its scope. The major source of controversy has been the inclusion of the national treatment standard in the prospective agreement. This thesis analyses the position of both sides, and attempts to find a balance between the positive and negative effects of the multilateral framework for regulating foreign direct investment. It argues that an investment regime modelled after the General Agreement on Trade in Services could be beneficial, as it would provide security for investment, and flexibility for host countries to control the inflow of foreign investment.

Various hazardous chemical substances are used daily as part of manufacturing and processing. Exposure to these hazardous chemical substances (HCSs) can cause adverse health effects in the exposed workers. Occupational exposure limits (OELs) are used to control exposure to these HCSs and thereby protect workers from the adverse effects that exposure may induce. The aim of this study was to compare South African list of OELs as contained in the Hazardous Chemical Substance Regulations (HCSR) to several developed and developing countries based on two aspects: (1) the number of substances that are selected and regulated by the lists of each country (2) and the overall level of the OELs set by the different countries and jurisdictions. Due to the nature and the large amount of data the study is divided into two parts. The first part is a comparison of South African OELs with nine developed countries and jurisdictions along with the Mine Health and Safety Act Regulation 22.9 (MHSR) of South Africa. The second comparison was conducted between South African and the four developing BRICS countries. BRICS is an acronym for: Brazil, Russia, India, China and South Africa, all are leading developing countries. Substance selection and coverage was compared by analysing the number of overlapping and uniquely regulated OELs that existed between countries. The over-all level of OELs was determined and quantified by using the statistical method, the geometric means of ratios. These ratios were compared in order to establish how the levels of OELs of the South African HCSR compare with the level of the various other countries. Results indicated that there are large and unsystematic differences between the selection of HCSs that are regulated by different countries and jurisdictions. Individual coverage and selection of HCSs between the various developing and developed countries and jurisdictions in the study was inconsistent and dissimilar. A high number of HCSs are regulated by only one of the various countries included in this study. Among the developed countries 20.8% of substances are uniquely regulated, whereas 46% of HCSs are regulated by only one of the various developing countries. According to the geometric means of ratios Occupational Safety and Health Administration (OSHA) is the only jurisdiction in a developed country that has a higher overall level of OELs when compared to South Africa as for the rest of the developed countries they all yielded a lower overall level of OELs. American Conference of Governmental Industrial Hygiene (ACGIH) had the lowest overall level of OELs. When compared with the BRICS countries South Africa had a higher overall level of OELs. The average overall level of OELs differs substantially between the BRICS countries; Russia having the lowest, and Brazil having the highest overall limit when compared relative to South African HCSR. Strong similarities were found between South African HCSR and MHSR indicating national similarity. The South African OELs for HCSs have an overall higher level than the majority of developed and developing countries. Various factors may be responsible for these differences among countries and jurisdictions. These factors include, variations in scientific reasoning, the risk acceptance of the negative impact that various HCSs might induce and the time lags that countries have between updates. Further differences may be explained by the difference in consideration of socio-economical and practical feasibility of an OEL and the predominant industries in a country. / Thesis (MSc (Occupational Hygiene))--North-West University, Potchefstroom Campus, 2013