Bubbly flows are ubiquitously found in natural systems and are widely used in (bio)-chemical and energy-producing processes. A variety of design options, ease of maintenance, and a large operability window make bubble columns a commonplace across industries, ranging from oil processing to biotechnology and electrolyzers. Despite their wide applicability and advantages, the complexity of designing and optimizing largescale bubble columns arises from inherent multiphysics - multiscale phenomena. The design and scale-up methodologies, from laboratory to large-scale, require a detailed understanding of the interplay between the different physical phenomena and processes, for a variety of fluid compositions and operation conditions, at various scales: from single bubbles to dense bubbly flows in industrial situations. For example: (i) the interplay between rheology, hydrodynamics and interfacial phenomena for a single bubble; (ii) the interplay between the collective dynamics of the bubbles inside the column, the bubble size distribution and the bubble generation process....

Dit onderzoek bestudeert het energieverlies van het barotroop getij aan de opwekking van intern getij. Dit energieverlies vindt plaats bij stroming van de gestratificeerde oceaan over steile topografieën, zoals ruggen in de oceaan en bij de randen van continentale platen. Zo'n 25-30% van de totale getij-energie, die wordt opgewekt door de zon en de maan gaat zo verloren.

In een wereldwijd getijmodel wordt alleen het dieptegemiddelde gedrag van de getijstroming beschouwd, waardoor de opwekking van intern getij niet expliciet gemodelleerd kan worden. Om het effect daar wel in mee te nemen, wordt het verlies van barotroop getij aan de opwekking van intern getij geparametriseerd aan de hand van variabelen, die in dat model wel meegenomen zijn.

Het onderzoek is numeriek uitgevoerd met het hydrostatisch oceaanmodel Delft3D-Flexible Mesh. In het 3D model is expliciet de opwekking van intern getij gesimuleerd en vergeleken met analytische resultaten voor de opwekking van intern getij. Daarnaast zijn deze resultaten gebruikt om de huidige geïmplementeerde parametrisering, van de opwekking van intern getij, in het 2D model te toetsen.

De expliciete simulering van de opwekking van intern getij in Delft3D-FM is succesvol gedaan. Het energieverlies van barotroop getij aan de opwekking van intern getij was in overeenstemming de literatuur. Voor smalle topografieën hoger dan (ongeveer) een halve oceaandiepte lijkt de hydrostatische aanname in het model te worden overschreden waardoor numerieke dissipatie van intern getij optreedt.

De huidige geïmplementeerde parametrisering van het verlies van barotroop getij aan de opwekking van intern getij is voor een beperkte verzameling topografieën en stratificaties getest. De resultaten geven indicaties, dat de huidige parametrisering niet in staat is om de conversie over een breder scala van topografieën in de oceanen goed te benaderen. Het voorspelbare gedrag van de conversie voor steile, superkritische topografieën wijst erop dat zo'n parametrisering wel mogelijk is.

Aanbevelingen voor verder onderzoek zijn het uitbreiden van het gebruikte model met stromingen in x- en y-richting en het effect van de Coriolis parameter. Om de parametrisering beter te testen kan het bestaande model op meer verschillende typische topografieën en stratificaties in de oceaan worden toegepast.

Plastic pollution is a big problem all over the world. Every year more plastic is produced, a lot of plastic litter is mismanaged and enters the ocean. It’s important to know where these plastics accumulate. With this information the problem can be quantified and the plastic litter can be cleaned up. In this project, the transport of micro plastics will be studied. These are plastic particles with a diameter smaller than 5 mm.

To model micro plastics in an accurate way, it is important to include the physical properties of plastics in a transport model. Plastic particles have an extra upwards buoyancy force in the vertical direction, this force has to be taken into account in the model. Therefore, the two-dimensional vertical behavior of plastic particles is studied in this project. Two common transport models are explored: the advection-diffusion equation and a stochastic random walk model. The properties of plastics are discussed and how the transport models can be adapted to be adequate to model micro plastics.

Micro plastics are assumed as spheres in fluid. With this assumption, the flow regime around a plastic particle is estimated with the Reynolds number. These assumptions make it possible to calculate a terminal buoyancy velocity, due to the floating character of plastic. This velocity is added in the vertical direction to
both transport models. To model the turbulence in the ocean, the eddy diffusivity coefficient is defined. This is a variable that states how turbulent the flow is, it can be described as an enhanced diffusion coefficient. The eddy diffusivity coefficient can be estimated with the model Prandlt defined. Here we used a simplified turbulence model for the tests described. In combination with Delft3D-FM the eddy diffusivity from the turbulence model in there can be used.

Both models are implemented in Matlab. The characteristics of the model match with the expected behavior of floating plastics. Plastic particles will perfectly follow the velocity field, except for the extra vertical velocity. When this term is non-zero, the particles will float. Both models have some limitations in efficiency
for modeling plastic particles. The advection-diffusion equation is not suitable for high concentration gradients. The random walk model is not suitable for big areas or long timescales. The choice between both models is depending on the sort of case that someone wants to model.

This project has been carried out at Deltares, an independent water research institute. At Deltares there is a two-dimensional horizontal model available to model particles in the ocean. In the future the existing model of Deltares and the model in this project could be combined. This combined model can be tested for
real-life situations in the ocean. With this combined model, the physical properties of plastics are included in a three-dimensional particle model.

Multiphase flows are often opaque. This makes it hard to obtain experimental data to expand our knowledge about them. Even doing small scale experiments is hard, since most techniques that are used to investigate fluid flows use visible light. Therefore new techniques are being developed. One of them is Radioactive Particle Tracking using Single Photon Emission Computed Tomography, better known as SPECT. SPECT is already used for medical purposes, like locating tumors.
In this research we investigated with what accuracy a radioactive tracer particle, emitting gamma rays, can be tracked while moving in a stirred tank filled with 2.5 L of water. Therefore we did some experiments using a 2 mm polystyrene sphere with a golden core. The gold is activated in the reactor of the Reactor Institute Delft (RID) of the TU Delft, after which it will start to emit gamma rays. The gamma rays are detected by three gamma cameras placed around the tank. Each has a collimator with a cross slit in front of the detector plate, to obtain information about the location of the particle, such that by combining the information from the three detectors, its position can be reconstructed. First we did an experiment with a cobalt source, with a low activity, at multiple fixed positions in air, to test the setup. After that we did some experiments with the particle with gold, with a high activity, at multiple fixed positions in air,moving along a known circular trajectory in water and when moving freely in a stirred tank. The last two experiments are also carried out with the tank being aerated.
We found out that the inaccuracy in the reconstructions increases when: the tracer particle is positioned farther away from the center of the setup, the frame rate that is used is increased or the velocity of the tracer particle increases. The error ranges from 0.5 up to 4 mm depending on the settings. The injection of air
bubbles at the bottom of the tank with different air flow rates, did not seem to influence the accuracy. Although the accuracy is not that high, there are still a lot of improvements that can be made in order to increase the accuracy.

The broth in industrial scale fermentors may contain significant gradients in, for example, substrate concentration, dissolved oxygen and shear rates. From the perspective of microbes in this fermentor, these gradients translate to temporal variations in their environment that may affect their metabolic response. As a result, there may be differences in process yield between laboratory scale fermentations and their industrial counterpart. Rather than scaling-up bioprocesses based on equivalence, it is recommended to scale-down: mimic the large-scale environment in lab scale setups, to account for hydrodynamic-metabolic interaction from the start. In this thesis, the use of Euler-Lagrange computational fluid dynamics to capture the large-scale fermentation environment is explored. Lagrangian simulations offer to study processes from the microbial perspective (so-called “lifelines”), and enable coupling of metabolic models describing the response to external variations. With this, it is possible to take the history of the trajectory of the microbe into account, as organisms may not adapt to their surroundings instantaneously. Guidelines for the setup of fermentor simulations are presented, and several means for processing the lifelines are discussed. The obtained information is used to design lab-scale fermentations that mimic large-scale conditions. It is furthermore shown how coupled hydrodynamic-metabolic simulations can be used to predict yield-loss, assess process improvements, and study the onset of population heterogeneity in large-scale fermentors. Additionally, a more fundamental towards the role of the turbulent Schmidt number in multi-impeller mixing is included.

This paper introduces two models. First, it introduces a model for geometric pressure loss in horizontal pipe junctions with arbitrary amounts of in-/outlets, under assumption of steady-state, incompressible, single phase flow and no wall friction. The model is shown to be in agreement with experimental data via another model. Second, the junction model is incorporated in a pipe flow network model under the same assumptions as the junction model. The resulting pipe flow network model is compared to a pipe flow network model in which pressure loss due to junctions is neglected. The results show that for long pipes L 600 m the addition of junction pressure has negligible influence on the total static pressure drop in the network. However, for L < 600 m the influence is bigger than 10%.

In 2011, Royal Dutch Shell plc (Shell) took the final investment decision to develop the Prelude gas field using the world’s first Floating Liquefied Natural Gas (FLNG) facility. FLNG poses some new technical challenges. For example, as the vessel is moored to the seabed, it is subject to movements induced by waves, winds and tides. Therefore, flexible instead of rigid risers are used to bring the gas from the seabed to the surface. However, these risers are limited in diameter. For Prelude each flowline is connected to a single riser. In new future projects it might be beneficial to have a single (larger diameter) subsea flowline at the sea floor which is split into two or more flexible risers. This flow split is complicated as gas wells produce a multiphase mixture of gas, hydrocarbon condensates and/or water. There thus is a need to understand how the different phases will distribute over the multiple risers, and how this will influence the whole operation. In previous lab experiments [1], a horizontal symmetric impacting T-junction was used to divide the multiphase mixture from the horizontal flowline into two vertical risers. It was found that at low gas flow rates, for which the flow regime in the risers is hydrodynamic slug flow, non-symmetric distributions in the phase split are the rule rather than the exception. These maldistributions exhibit transient behaviour, and exhibit hysteresis. However, in gas production from dry fields with low Liquid to Gas Ratios (LGR), the gas flow rates generally are higher and the flow regime in the vertical risers is annular flow. In this flow pattern, liquids flow in the upward direction and no liquid buildup occurs at the riser base. As annular flow is more stable in time, it is expected that for these conditions the phase splits are evenly distributed over the two risers and no transient behaviour is present. The main aim of the present study was to verify the hypothesis that if the gas flow rate is sufficiently high to sustain annular flow in both risers the phases will distribute evenly. Thereto experiments were performed in the Severe Slugging Loop (SSL) at the Shell Technology Centre Amsterdam. The loop consists of a 100 [m] horizontal flowline connected via an impacting T-junction to two 1.25 [in] diameter vertical risers of 16.8 [m] height. The facility is operated with an air-water mixture at atmospheric pressure and ambient temperature. As the SSL is not equipped with flow meters to measure the phase flow in the risers, a new method is developed to identify maldistribution in the phase split. In two phase flow in a vertical riser, the flow rates in the pipe are not uniquely determined by the pressure drop. However, in the current dual riser experiments the total flow rate in the setup is known. It is found that, with the use of single riser benchmark data and visual inspection, one can distinguish between an equal and an unequal phase split. Experiments are performed to test the stability of the phase split, and the effect of hysteresis for various gas and liquid flow rate combinations. It is observed that five different states exist for the flow split in the single flowline dual riser geometry. Out of these, only two are stable, which occur on opposite sides of a certain gas flow rate transition point. This point is identified as the minimum in the pressure gradient curve for a single vertical riser. This minimum can be linked to the transition from churn flow to annular flow. In addition to the experiments, a computational model is proposed to predict the phase split. In this model, the Shell Flow Correlations (SFC) for multiphase pipe flow are used to propagate the boundary conditions of the system from the riser tops to the corresponding outlets of the splitter at the base of the risers. Next, all possible phase splits which satisfy the extended Bernoulli equation and the conservation of momentum in the splitter are identified. The model conserves mass implicitly. The extended Bernoulli equation is implemented as the Advanced Double Stream Model (ADSM) [2], the control volume approach is used for the conservation of momentum. All three sub-models assume 1D steady state fully developed flow in the different parts of the geometry. By imposing different back pressures on the risers, for a constant gas and liquid flow, the model can generate phase split curves. These are compared to experimental data available in the literature and experimental results by Van de Gronden. It is found that the write-up of the derivations in the original ADSM paper [2] contains typos or errors. Therefore we have derived new relations, but they do not exhibit the same behaviour as the modelling results presented in the paper. From the comparison with the experimental results, it is concluded that the proposed computational model, which assumes 1D steady state fully developed flow, predicts a much too symmetric phase split. The modelling effort has not yet resulted in a reliable for the phase split prediction model.

Provision of clean drinking water to poor can prevent a large number of deaths and illnesses amongst children around the world. In 2010, about 0.75 million child deaths were caused due to diarrhea, and a further 22.5 million years of life were lost due to ill-health, disability or early death caused by unimproved water and inadequate sanitation around the world. Most of these people live in regions with limited or no electricity, and abundance of sunshine and salt water or unclean water. Solar thermal distillation using solar stills is the most potent way of cleaning the salt water in the absence of electricity. Several products, such as the inflatable stills for life rafts, water-cone and water pyramid have been demonstrated for the purification of salt water. None of these is specifically targeting a single family. We found that simple ways of natural cooling improve the production considerably. Moreover, dripping from cleaned water from the condensing area reduced the production. A simple rule could be formulated that provides an estimate of the maximum length before dripping starts. With this a more clever design of the collection of clean water allows stills of larger scale that still produce efficiently. The work of this thesis we aim at a plastic based solar stills capable of providing at least 2.5 liters/day of drinking water, an amount put forward by the UNICEF. The results are being used by Dr Ten B.V. for the development of a simple and replicable mass manufacturing process for plastic based stills. Future projects for the use of solar stills are under consideration with several governments and organizations like UNHCR

High speed X-ray tomography is a promising tool to visualize the time-resolved gas distribution for fluidized beds. The tomography unit at Delft University of Technology is composed of three X-ray tubes and three double-layer detector arrays. The X-ray tubes are places at 120? around the fluidized bed. The detector arrays are placed opposite to the X-ray tubes. The full angle scanning can be done simultaneously, without mechanically rotating the X-ray tube as in traditional medical CT. The temporal resolution can be up to 2500 fps. By using this high speed X-ray tomographic system in my dissertation, we study tomographic reconstruction algorithms and measure different gas jets in the fluidized beds. To evaluate the performance of the novel reconstruction algorithms for high speed X-ray tomography, Simultaneous Algebraic Reconstruction Technique (SART) and Adaptive Genetic Algorithm (AGA) are compared in Chapter 3. The reconstruction quality of AGA is better than SART at low resolutions, but SART performs better at high resolution in finding the right shape. The system noise influences AGA less than SART. SART is much faster and does not have reproducibility problems; poor reproducibility influences the reliability of AGA. The features of the reconstruction quality for SART and AGA are further discussed in Chapter 4. AGA is better than SART in distinguishing small phantoms and small distance between phantoms. SART, on the other hand, is better at reconstructing the shapes than AGA. We developed a hybrid approach to combine the advantages of AGA and SART. The result of AGA is used as initial guess for SART in this hybrid algorithm, by which the reconstruction accuracy is indeed improved. A flat-base spouted bed is studied with the high speed X-ray tomography system in Chapter 5. We focus on the spout diameter and position. The hybrid algorithm is used to visualize the spout in the cross sectional area of the spouted bed. For a more accurate quantitative study, we developed a method to process the raw data directly. The time-averaged results of the spout diameters are validated with the literature. A simple model for the particle circulation is developed based on the time-averaged spout diameter. The model is also validated by measurement of the fountain height. The time-resolved results of the spout diameter are analyzed by the Power Spectral Density (PSD). The stability of the spout diameter is discussed for different measurement heights and gas flowrates by comparing the average PSD. We find that the most stable spout diameter happens at U/Ums ? 1.3 in the middle part of the spout. The time-resolved spout position is plotted by polar coordinates. We found that the spout position is more stable when the diameter is less stable, and vice versa. Another gas jet, i.e. the gas distribution below a downward facing micro-nozzle in a fluidized bed, is also measured using the high speed X-ray tomography in Chapter 6. The improved SART method is used for the reconstruction because we need to consider the transition area between the gas voids and bulk phase. Time-averaged 3-D images of the gas distribution below the nozzle are obtained. The results are compared with direct analysis of the raw data. A bubbling area, a diluted area, and a compacted area are found. We analyzed the dynamics of the gas voids by employing a cross-correlation technique and inspecting the reconstructed pseudo 3-D image. The cross-correlation estimates the direction of bubble motion, and also helps to calculate the bubble velocity and bubble size. The pseudo 3-D image shows the pattern of the gas voids. We found that single bubbles are regularly formed by the nozzle, and move upwards. The expansion, splitting and coalescence of the bubbles were also observed. The gas injected from the nozzle mainly ends up in bubbles. We compared the fluidized bed results with those obtained for a similar nozzle in a gas-water system, and found a similar flow pattern and penetration depth. In summary, we improved the accuracy of high speed X-ray tomography by developing novel data processing approaches, such as the hybrid algorithm and raw data processing. We evaluated the dynamics of the spout in a flat-base spouted bed from the tomographic measurements, and developed a model for particle circulation based on these measurements. We also measured the time-resolved gas distribution below the downward facing micro-nozzle using the high speed X-ray tomography. The obtained results illustrate that X-ray tomography is a valuable tool to study gas-solids distribution – both time-averaged and time-resolved in fluidized beds.

The polytropic model to describe air expansion, has been used for years to describe the behavior of surge vessels. In this thesis the alternative to describe this behavior, the Rational Heat Transfer (RHT) equation developed by Graze (1968), is extended with an estimation of all heat terms in surge vessels. The RHT model is compared to the poly- tropic model for isolated and non-isolated vessels and is shown to give a good estimation for the air expansion, which has been checked with measurement data from Shuweihat, a location in Abu Dhabi in the United Arab Emirates where a large pumping station is located. Calculations for the size of the surge vessel point out that the minimal volume of a surge vessel calculated with the RHT model is 10 % smaller than if the volume is calculated with the polytropic model. Furthermore, the heating of the air pocket in a surge vessel has been modeled by a numerical solution of the one-dimensional heat equa- tion with a convective and a non linear source term. From this models can be concluded that the air in a surge vessel warms up slower than the expansion time of that vessel.

One of the vital safety mechanisms in the reactor core of most nuclear power plants is the negative feedback from the core temperature on the power output. An increased temperature will reduce the power output of the reactor, 'automatically' cooling the it and preventing the nuclear reaction to spin out of control. For this reason, it is important to have a good understanding of the temperature distribution within the reactor core. The water that flows through the core is the main reason for the transport of heat, hence it is of interest to have a good understanding of the behavior of the flow. On of the aspects that defines the flow properties is the geometry of the reactor, a so called 'rod-bundle geometry'. It is the presumption that a large shear in the fluid, induced by the geometry, causes the formation of largescale coherent structures. These structures affect the mixing of heat in the reactor and are, therefore, of interest.

This thesis is about the beginning of a global tide model in DFlow-FM, a project by Deltares. The first focus lay on finding the best grid that can be used for this model. We tried to grids, a rotated lat-lon grid and a squarely grid with local refinement. After calculating the RMS-value it was found that the local refined grid gave the best results and should therefore be used. The second part of the thesis was about internal tide, how it should be included in the model. This needs future work to improve the results but the way it should be included was found to be a linear friction coefficient.

Separation of oil and water is an essential step in the treatment of the production streams from fossil oil wells. Settling by gravity is a robust though voluminous process and therewith expensive method at remote locations, leading to a need for smaller separation equipment. In this thesis, we describe the research performed on the development of an inline axial cyclone for oil/water separation. This work is part of ISPT project OG-00-004 and has an experimental nature: a flowrig has been constructed to test different cyclones at flow rates up to 60 m3/h in a 10 cm diameter tube in which brine and low-viscosity lubricant oil can be mixed in almost any proportion. Results are compared with numerical datasets resulting from the same ISPT project. Three different swirl elements have been developed for this project: a strong swirl element and a weak swirl element with 10 cm diameter, and one element with a 26 cm diameter in combination with a tapered tube section. For all three swirl elements, the velocity profile of water has been measured with Laser Doppler Anemometry (LDA). The strong swirl element has a swirl number of 3.7, the weak of 2.3 and the large diameter element of 3.9. The axial velocity profile normalized with the bulk velocity shows vortex breakdown (upstream flow in the center), where the severeness of the breakdown normalized with the upstream bulk velocity shows proportionality with the swirl number. For the azimuthal velocity, the velocity profile was proportional to the bulk velocity. The non-dimensional azimuthal velocity was similar for all three swirl elements in the region |r/D| < 0.2. Outside that region the relative velocity is strongly influenced by the swirl element. Time series obtained with single phase LDA studies were used to estimate the effect of turbulent dispersion on droplet trajectories. A simplified equation of motion based on centrifugal buoyancy, drag and turbulent dispersion was solved for many fictitious droplet paths. The measured, chaotic axial velocity time series was used to mimic the radial component of the velocity fluctuations. With this model, we can predict the smallest droplet size that can be separated with a certain cyclone and the largest droplet size before it is broken by the flow. Model results show good agreement with overall bulk data obtained in the experimental flow rig. With an intrusive endoscope technique, we measured the droplet size distribution at various positions in the axial cyclone. From this, Hinze’s theory for the droplet size in turbulent pipe flow is confirmed. Furthermore, the inverse correlation between azimuthal velocity and median droplet size is shown and quantified: a lower velocity allows larger droplets to survive. Different designs were tested to understand which parameters have a large influence on the industrially relevant parameter of separation performance. This question is answered by variation of the swirl element, swirl tube length, pickup tube diameter, flow rate and droplet size. Changes that affect the droplet size have a severe effect on separation, these are the swirl element and flow rate. Changes that increase the droplet size lead to better phase separation. The other geometrical changes can be used to optimize performance, but are not identified as parameters leading to breakthrough improvements. Two non-dimensional numbers can be used to explain the behavior of the cyclone: the Weber number (We) based on the droplet size upstream of the swirl element and the maximum velocity obtained in the gaps of the swirl element, and the Reynolds number (Re_?) for the droplets downstream of the swirl element based on their median diameter and the azimuthal liquid velocity. Separation is better for a smaller We number, because droplets are less vulnerable for breakup under that condition. A large Re? number is beneficial since the droplets then experience a large centrifugal acceleration which is larger than turbulent dispersion. Both trends are confirmed with experimental data obtained in this project. We propose that there is a function for the maximum possible separation efficiency based on both non-dimensional numbers. The inverse coupling between We and Re_? via the azimuthal velocity makes optimization of separation efficiency difficult. Application of a large diameter swirl element (low velocity and therefore limited droplet breakup) in combination with a gradual tapering of the tube (increasing the azimuthal velocity) is a possibility to obtain both a large We and Re? number. Another option is to place multiple axial cyclones in series, with a stepwise increase of the swirl strength in each subsequent cyclone. In such a configuration, each step is capable of separating smaller droplets than the previous step, without immediate breakup of large droplets. This method should increase the overall quality of the phase separation.

transportation facilities. In an offshore oil and gas production facility, pipeline-riser systems are required to transport two-phase hydrocarbons from subsurface oil and gas wells to a central production platform. Severe slugs reaching several thousands pipe diameters may occur when transporting gas and liquid in these pipeline-riser systems. Severe slugging creates potential problems in the platform facilities, e.g. separators, pumps, and compressors. Severe slugging may cause flooding and overpressurization of the separator, rupture of the pipe, and an increased back pressure at the wellhead. All of these might lead to the complete shutdown of the production facility. Therefore, the accurate predictions of severe slugging characteristics, e.g. slug length, oscillatory period, are essential for the proper design and operation of two-phase flow in the pipeline-riser systems. Pipelines used for the transportation of hydrocarbons in an offshore production facility, are laid out over the seafloor. The uneven seafloor topography forms different pipeline-riser configurations. In this dissertation, we described the severe slugging characteristics in a long downward inclined pipeline-riser system. We carried out experiments in a relatively long pipeline-riser configuration, and also performed numerical simulations using a one-dimensional two-fluid model. It was found experimentally, as also reproduced numerically, that transient slugs were generated in the pipeline upstream of the riser base. These transient slugs effectively contributed to the initial blockage of the riser base. Furthermore, an existing analytical model for the prediction of the flow behaviour in the pipeline-riser system was modified. The modified model, which was tested against our experimental results, showed a better performance than previously published models. We developed a transient drift flux model to simulate the severe slugging characteristics in a pipeline-riser system. The model was tested against experimental data and interestingly, could predict the occurrence of severe slugging in a horizontal pipeline-riser system, which is a subject of debate in the open literature. That motivated us to conduct experiments in a horizontal pipeline-riser configuration. It was observed that severe slugging can develop even in the horizontal pipeline-riser configuration. Moreover, a new class of severe slugging was found and referred to as dual-frequency severe slugging, which corresponds to dual-frequency pressure and flow rate fluctuations. It was found that dual-frequency severe slugging evolves when the pipeline length exceeds a certain threshold. In this dissertation, we also described the severe slugging characteristics in a hilly-terrain pipeline-riser configuration. A hilly-terrain pipeline consists of interconnected horizontal, downhill, and uphill sections. It was observed that, the existence of a hilly-terrain unit in a pipeline-riser system induces a more severe type of slugging, which exhibits longer slugs than that of a horizontal pipeline-riser system. So far we have summarized our work on the characteristics of severe slugging in a pipeline-riser system. In this dissertation, we also discuss the occurrence of severe slugging in an extended reach well. In response to meet the world energy demand, the oil and gas industry has also moved towards development of resources in scattered, isolated oil and gas pockets. Snake wells and fish-hook wells are extended reach wells, which have been used to develop these small hydrocarbon deposits more efficiently than conventional vertical or horizontal wells. The extended reach well resembles the pipeline-riser configuration. The flow conditions, e.g. pressure, and the pipe specifications, e.g. diameter, at the bottom of a well are generally different than the pipeline laid out over the seafloor. It is expected that severe slugging at the bottom of the well is less likely to occur. In this dissertation, we performed numerical simulations to study the possible formation of severe slugging at the bottom of an extended reach well. It was found that severe slugs were initiated at the bottom of the extended reach well. This teaches one to study the well hydrodynamics more carefully when designing an extended reach well.