<p dir="ltr">This thesis presents a comprehensive analysis of liquid injection through plain-orifice injectors into high-speed gaseous crossflows. Experimental data is collected for more than 1,000 injection events into a blowdown wind tunnel with Mach numbers ranging from 0.3 to 2.5, and sophisticated methodologies are developed and employed to quantify spray penetration and jet breakup behaviors. Despite the simplicity of a plain-orifice injector design, the flow field induced by the transverse streams is complex and three-dimensional, and the rapid jet breakup and high advection speeds of the resulting droplet cloud make for a difficult diagnostic environment. This results in a present need for accurate tools to predict the performance of plain-orifice injectors in high-speed crossflows and for specific details of jet breakup behaviors and of the resulting droplet distributions. The experiments conducted for this work constitute a substantial database of high-speed images and flow diagnostics, and the analyses conducted thereof provide critical new understandings of this class of flows. Transmittance images have been used extensively to characterize spray penetration profiles, but new analyses presented here use transmittance to quantify time-averaged droplet distributions and their variations with various flow properties. A novel combination of these with cross-sectional Mie-scatter images also enables the generation of three-dimensional spray profiles. A previously unidentified jet-in-crossflow breakup mode is found and distinguished from the catastrophic breakup mode by its instantaneous spray structures; additionally, both regimes are mapped with respect to momentum flux ratio and Weber number by analyzing peak frequencies in modal decompositions. Finally, a spray penetration correlation is developed that spans both subsonic and supersonic crossflows by applying a novel shock correction. Each of these contributions represents a significant advancement in the scientific understanding of liquid jets in high-speed crossflows and a valuable resource for engine design and model validation.</p>

A typical problem in traffic control is the steering over a network of vehicles with different origins and destinations. In this report this scenario is formulated as a multi-commodity network flow problem, a linear programming problem whose objective is to transport, with minimum cost, different commodities from their respective sources to their sinks through a network, while respecting the capacity constraints of the roads. The dynamic network flow formulation of the problem is also presented, extending the network over time to incorporate the temporal dimension. Different algorithms for solving the multi-commodity network flow problem are examined. First, the simplex method, more precisely its revised version, is considered, and then the Dantzig-Wolfe decomposition is illustrated, an optimization algorithm which exploits specific block structures in the constraints. These methods are applied using state-of-the-art linear programming solvers and evaluated with a simulation based on the road network in central Stockholm. The results show that both methods allow for solving the traffic flow problem, with limitations given by the specifics of the solvers and by the space and time discretization of the problem. In particular, the revised simplex algorithm results the faster method.

Fast breeder nuclear reactors use liquid metals such as Sodium (Na), Sodium-Potassium (Na-K), and Lead (Pb) as coolants since these liquids have high thermal conductivity, high thermal diffusivity, and lower heat capacity compared to water and air, thus involving low Prandtl numbers (Pr). However, liquid metals solidify at room temperature which poses challenges for experimental studies, making computational fluid dynamics (CFD) is considered a valuable analysis and design tool. Furthermore, the accurate modeling of turbulent heat transfer in low Pr flows remains one of the main challenges due to the gap between momentum and turbulent thermal diffusion. The study aims to address this challenge by enhancing the understanding of liquid metal coolant behavior and improving the accuracy of turbulence models in these types of fluids under different convective conditions. This research consists of two main parts, where the first one encompasses generating a DNS dataset for Reτ = 640, Pr = 0.004, 0.025, and 0.71, and Gr = 0 and 17.4×106 to supplement existing DNS databases, providing a more comprehensive foundation for turbulence models validation, and the second one envelop assessing the predictive capabilities of linear eddy viscosity-based Reynolds average Navier Stokes (RANS), Partially-average Navier stokes (PANS), and large eddy simulation (LES). The assessment covers four test cases ranging from canonical turbulent flow to more complex flow regimes involving separating and reattaching flows under different convective conditions for Reynolds numbers (Re) ranging from 640 to 40,341 and Pr varying from 0.004 up to 0.71. DNS results improve the understanding of Re, Pr, and buoyancy effects on both mean turbulent flows. Analysis reveals that buoyancy enhances heat transfer more significantly for lower Re and Pr. Furthermore, buoyancy alters flow and thermal structures by enhancing and reducing turbulence on both aiding and opposing sides, affecting heat transport. In addition, the assessment of different turbulence models demonstrates the superiority of LES compared to other models where the average of the prediction errors is 6% over all the cases aligning with findings from the excessive literature review.

This study aims to understand the impact of organizational learning on project portfolio success in a multinational Oil and Gas company operated in Indonesia. The Organizational Learning and Project Portfolio Success have been proven to have contribution to business performance and they might possess a relationship where enhancing one of them will strengthen the other. Exploring on this relationship might give beneficial input to the organization in order to maximize their success.  Thus, our research question is formulated as: To what extent does Organizational Learning impact the Project Portfolio Success? We developed the study’s conceptual model based on the relevant previous literature. The conceptual model depicted the aim of the study to test the potential positive impact of each Learning Stocks (Individual, Group, and Organizational) on Project Portfolio Success, as well as the aim to test the potential negative impact of the misalignment between Learning Stocks and Learning Flows on Project Portfolio Success in the studied company. We adopted quantitative research method due to the nature of research question and the ontological and epistemological assumptions we hold toward the studied phenomena. Accordingly, we used a questionnaire as an instrument to collect the required data to test the hypotheses. The questionnaire was subject to a pilot test to ensure the clarity of statements before it was distributed to the targeted respondents which are the managers and the Project Management Office personnel in the studied company. The research hypotheses were tested by applying single and multi-regression analyses using SPSS software. Our findings showed that, independently, each learning stock type (Individual, Group and organizational) has a significant positive impact to project portfolio success. When we looked for the best model that gives the highest explanatory power, the result showed that the combination of all three learning stocks in one model can explain project portfolio success construct the most. Lastly, the study proved that the misalignment between learning stocks and flows gives negative impact to the project portfolio success. We concluded the study by stating the theoretical contribution and practical recommendations based on the results such as the need to have a balanced investment in the individual, group and organizational learning stocks; ensure the alignment between the organizational units’ strategies and goals; develop an “Internal Strategy Awareness Index”; and conduct a revision of the alignment between the company’s strategy and the project portfolio.

While worker flow analysis has grown in importance in many countries, Austria still lacks a specific longitudinal dataset as a prerequisite to perform similar analyses. For this reason, this article provides a coherent procedure to construct a longitudinal dataset based on the rotational panel structure of the Austrian quarterly LFS from 2004 to 2014. The procedure, which is available for researcher, is grounded on the discussion of several related and important issues inherent in constructing this sort of longitudinal data: First, it deals with the construction of the quarterly-matched dataset and the quality-of-measurement of several labour market variables. Second, the paper analyses non-response as a sample selection process, and shows that the selected (quarterly-matched) dataset causes biased estimates of worker flows. Third, the article proposes an iterative raking procedure to obtain survey weights as a bias-correcting device for any future analysis. Based on these adjustments, we present unbiased time-series of worker flows and transition rates, and conclude that the employment-unemployment margin is highly sensitive to economic shocks and that the Austrian labour market is additionally shaped by large movements within the participation margin. (authors' abstract) / Series: Department of Economics Working Paper Series

This thesis analyses and compares the performance, performance persistence and fund flows for UK equity unit trusts/OEICs and UK equity unit-linked personal pensions over the sample period January 1980 to December 2007. Unit-linked personal pension funds are an illiquid investment from the investor’s perspective since any invested capital is inaccessible until retirement whereas for unit trusts/OEICs capital invested can be withdrawn at any time. Since decreasing returns to scale from fund flows are the equilibrating mechanism in Berk and Green (2004) that results in no persistence in performance the illiquid nature of unit-linked personal pension funds should ensure more evidence of performance persistence in comparison to unit trusts/OEICs. I find significant evidence using performance ranked portfolio strategies that underlying portfolios that are only composed of unit-linked personal pension funds have greater performance persistence than unit-linked personal pension funds that have underlying portfolios that also include at least a unit trust/OEIC. This evidence is consistent with Berk and Green (2004) since the illiquid nature of personal pension funds results in an attenuated performance fund flow relationship restricting the equilibrating mechanism. However, there are anomalies in the performance persistence results in relation to Berk and Green (2004) but it could be due to the differential between the number of non-surviving unit trusts/OEICs and non-surviving unit-linked personal pension funds. I also find that the performance fund flow relationship based on abnormal returns from a Carhart four factor model for both UK equity unit trusts/OEICs and UK unit-linked personal pensions is convex but the performance fund flow relationship is more attenuated for the unit-linked personal pension funds. For the worst performing unit trusts/OEICs there are outflows on average whereas for unit-linked personal pensions there are fund inflows on average. For performance persistence tests conditional on underlying portfolio fund flows unit trusts/OEICs that have the worst performance but the lowest net fund flows in the ranking period have significantly greater subsequent performance in comparison to the unit trusts/OEICs that have the worst performance but the highest net fund flows in the ranking period. This empirical evidence provides support for Berk and Green (2004) but for the unit-linked personal pension funds the evidence is less convincing. There is very little evidence that UK equity unit-trusts/OEICs or UK equity unit-linked personal pensions produce abnormal returns. These results are robust across the single index (CAPM) model, the Fama and French three factor model and the Carhart four factor model for both conditional and unconditional models. There is also no evidence that unit trusts/OEICs or unit-linked personal pension funds can time the market. There is a significantly negative timing effect across unconditional factor models which becomes insignificant for the conditional models. There is also no evidence that unit trusts/OEICs have significantly different performance than unit-linked personal pension funds.

Downslope flows and regions of enhanced cooling have important impacts on society and the environment. Parameterisation of these often subgrid-scale phenomena in numerical models requires a sound understanding of the underlying physical processes, which has been the overarching aim of this work. A numerical model has been used to characterise the development of a region of enhanced cooling in an idealised alpine valley with width and depth of order 10 and 1 km, respectively, under stable, decoupled, poorly-drained conditions. A focus of this work has been to remove the uncertainty surrounding the forcing mechanisms behind the development of regions of enhanced cooling. The average valley-atmosphere cooling has been found to be almost equally partitioned between radiative and dynamics effects. Complex interactions between the downslope flows and the region of enhanced cooling have been quantified for the first time. For example, relatively large variations in the downslope flows are generally restricted to the region of enhanced cooling and cannot solely be attributed to the analytical model of [McNider, 1982a]. These flow variations generally coincide with return flows above the downslope flows, where a thin region of unstable air occurs, as well as coinciding with elongated downslope flow structures. The impact of these interactions on the dispersion of passive pollutants has been investigated. For example, pollutants are generally trapped within the region of enhanced cooling. The concentration of pollutants within the region of enhanced cooling, emitted over the lower half of the slopes, increase as the emission source moves away from the ground-based inversion that expands from the bottom of the valley. The concentration of pollutants within the region of enhanced cooling is very similar when varying the location of the emission source over the top half of the valley slopes. This work includes a test of the effects of varying the horizontal numerical grid resolution on average valley-atmosphere temperature changes.

Energy audit and calculation strategies for energy flows in buildings: a case study of Vallongatan 1   This thesis involves an energy audit of a building with offices and laboratories in Uppsala, Sweden. The calculations are performed in Microsoft Excel and were later used as the basis for developing calculation strategies for similar, future, energy audits.   The building was erected in the early 1990s and the heating requirement of just above 700 MWh is covered by district heating from the city network. The total gross floor area is about 8400 m2 and is served by an air conditioning system consisting of seven ventilation units with rotary heat exchangers, heating and cooling coils, as well as water radiators throughout the building.   No significant improvement measures have been implemented since the construction, and the building therefore has a potential to improve its energy performance. The report addresses a number of measures that could be taken, as well as an evaluation of each one. The most economically viable of these would be to clean the rotary heat exchangers, which is deemed to have a potential to save about 70 MWh or 48 700 SEK annually. In comparison to the estimated cost of between 35 000 and 42 000 SEK this is likely to become profitable as early as the first year.   The calculation templates that were developed cover three different building standards, these are categorized as low, improved and advanced standard. Here, the desired areas and types of activities are typed in easily for either individual rooms or entire offices or buildings. The templates provide estimates regarding power and energy needs for heating and comfort cooling, recommended air flows, heat development and dissipation as well as carbon dioxide concentration in the room air.

A study of the use of solution adaptive grid (SAG) method for simulations of incompressible flows is carried out in this work. Both laminar and turbulent types of flows are chosen. Investigation on laminar flow simulation starts with mesh adaptation criteria that are based on strong changes of some selected flow parameters; pressure and velocity components. Three most common laminar types of flows are studied; flow in a circular pipe, flow in a channel with sudden expansion and flow in a cavity with a moving lid. It is found that with the use of SAG, a reduction in both computational grid nodes and CPU time can be obtained when compared to those of fixed grid while satisfactory solutions are also achievable. Nevertheless, the refinement criteria setup procedure reveals inconveniences and requirement for several judgments that have to be defined ‘ad hoc’. This hence, makes the refinement criteria dubious for real engineering applications. For the study of turbulent flows with large eddy simulation (LES) and implicit filtering, examination of literature reveals that the lack of connections between the filter width and a physical scale has made LES somewhat unclosed, i.e. in a physical sense. In addition, it is known that numerical and modelling errors are always combined and it is difficult to study each of them separately making the total error magnitude difficult to control. Since both error types are characterised by the grid size, LES users very often find cases where a finer mesh no longer provides better accuracy. An attempt to address this ‘physical’ enclosure property of LES and its complication to implement/setup in FLUENT begins with the construction of a new refinement variable as a function of the Taylor scale. Then a new SAG algorithm is formed. The requirement to satisfy a condition of the selected subgrid scale (SAG) model, the Smagorinsky model, is taken into consideration to minimize the modeling error. The construction of a new refinement algorithm is also aimed to be the key to studying the interaction between the two types of error and could lead to the means of controlling their total magnitude. The validation in terms of its effectiveness, efficiency and reliability of the algorithm are made based on several criteria corresponding to suitability for practical applications. This includes the simplicity to setup/employ, computational affordability, and the accuracy level. For this, two different turbulent flow types that represent different commonly found turbulent phenomena are chosen; plane free jet and the flow over a circular cylinder. The simulations of the two cases were carried out in two dimensions. It is found that there are two key factors that strongly determine the success of the algorithm. The first factor is the Taylor scale definition, with literature only available for the turbulent plane jet study, for which good level of accuracy is expected. Unfortunately, this is not true for the flow over a circular cylinder, indicating a need for further analytical work. The second encountered difficulty results from limited access to software codes, which makes it impossible to implement the proposed scheme. As a result, the algorithm formulation needs be modified with carful judgment. Nevertheless, overall results are in reasonably good agreement with their corresponding experimental data.

There are four chapters in my dissertation. Chapter one gives a brief introduction of the three essays. Chapter two studies the choice of exchange rate regimes in East Asia using a business-cycle approach. My results suggest that countries in East Asia are driven mainly by country-specific shocks, making more rigid exchange rate regimes less desirable. Neither a yen bloc nor a dollar bloc has been identified in East Asia. However, Japan seems more influential to countries such as Korea and Taiwan. An optimum currency area does not seem feasible for East Asia, at least in the short run. Chapter three applies the cointegration and causality analyses to the real effective exchange rates to study the degree of monetary integration in East Asia. I find that the ASEAN and the NIE countries, respectively, have achieved some degree of integration, but not East Asia as a whole. The yen is found to move closely with the NIE currencies. However, neither the yen nor the dollar imposes a dominant driving force on the East Asian currencies. My results suggest that East Asia is not an optimum currency area. Chapter four expands the traditional monetary model of exchange rate determination into a structural VAR model incorporating various capital flows and the balance of trade in addition to the macroeconomic fundamentals. The model is then applied to the Australian dollar (AUD), the Canadian dollar (CAD), and the US dollar (USD) exchange rates over 19802004. I find that capital flows, especially portfolio investments, explain a major portion of the exchange rate fluctuations in the relatively small and open economies such as Australia and Canada in the short-to-medium run. The impacts of capital flows are limited to the US dollar exchange rates. Among the macroeconomic fundamentals, the interest rate plays an important role in exchange rate determination for all three currencies. The results imply that different capital flows do influence exchange rates differently and are important determinants of exchange rates.