archives@tulane.edu / 1 / Ross Stephen Ransom

Realistic predictions of service life of steel catenary risers (SCR) require an accurate characterization of seafloor stiffness in the region where the riser contacts the seafloor, the so-called touchdown zone. This thesis presents the initial stage of development of a simplified seafloor support model. This model simulates the seafloor-pipe interaction as a flexible pipe supported on a bed of springs. Constants for the soil springs were derived from finite element studies performed in a separate, parallel investigation. These supports are comprised of elasto-plastic springs with spring constants being a function of soil stiffness and strength, and the geometry of the trench within the touchdown zone. Deflections and bending stresses in the pipe are computed based on a finite element method and a finite difference formulation developed in this research project. The finite difference algorithm has capabilities for analyzing linear springs, non-linear springs, and springs having a tension cut-off. The latter feature simulates the effect of a pipe pulling out of contact with the soil. The model is used to perform parametric studies to assess the effects of soil stiffness, soil strength, trench geometry, amplitude of pipe displacements, pipe stiffness, and length of touchdown zone on pipe deflections and bending stresses. In conclusions, the seafloor stiffness (as characterized by the three spring parameters), the magnitude of pipe displacement, and the length of the touchdown zone all influence bending stresses in the pipe. Also, the tension cutoff effect, i.e., the pipe pulling away from the soil, can have a very large effect on bending stresses in the pipe. Neglecting this effect can lead to serious over-estimate of stress levels and excessive conservatism in design.

The selective catalytic reduction (SCR) of nitric oxide (NO) with ammonia over vanadia-based (V2O5-WO3/TiO2) and pillared interlayer clay-based (V2O5/Ti-PILC) monolithic honeycomb catalysts using a laboratory laminar-flow reactor was investigated. The experiments used a number of gas compositions to simulate different combustion gases. A Fourier transform infrared (FTIR) spectrometer was used to determine the concentrations of the product species. The major products were nitric oxide (NO), ammonia (NH3), nitrous oxide (N2O), and nitrogen dioxide (NO2). The aim was to delineate the effect of various parameters including reaction temperature, oxygen concentration, NH3-to-NO ratio, space velocity, heating area, catalyst arrangement, and vanadium coating on the removal of nitric oxide. The investigation showed that the change of the parameters significantly affected the removals of NO and NH3 species, the residual NH3 concentration (or NH3 slip), the temperature of the maximum NO reduction, and the temperature of complete NH3 conversion. The reaction temperature was increased from the ambient temperature (25°C) to 450 °C. For both catalysts, high NO and NH3 removals were obtained in the presence of a small amount of oxygen, but no significant influence was observed from 0.1 to 3.0% O2. An increase in NH3-to-NO ratio increased NO reduction but decreased NH3 conversions. For V2O5-WO3/TiO2, the decrease of space velocity increased NO and NH3 removals and broadened the active temperature window (based on NO > 88% and NH3 > 87%) about 50°C. An increase in heating area decreased the reaction temperature of the maximum NO reduction from 350 to 300°C, and caused the active reaction temperature window (between 250 and 400°C) to shift toward 50°C lower reaction temperatures (between 200 and 350°C). The change of catalyst arrangements resulted slight improvement for NO and NH3 removals, therefore, the change might contribute to more gas removals. The catalyst with extra vanadium coating showed higher NO reductions and NH3 conversions than the catalyst without the extra vanadium coating.

Realistic predictions of service life of steel catenary risers (SCR) require an accurate characterization of seafloor stiffness in the region where the riser contacts the seafloor, the so-called touchdown zone. This thesis presents the initial stage of development of a simplified seafloor support model. This model simulates the seafloor-pipe interaction as a flexible pipe supported on a bed of springs. Constants for the soil springs were derived from finite element studies performed in a separate, parallel investigation. These supports are comprised of elasto-plastic springs with spring constants being a function of soil stiffness and strength, and the geometry of the trench within the touchdown zone. Deflections and bending stresses in the pipe are computed based on a finite element method and a finite difference formulation developed in this research project. The finite difference algorithm has capabilities for analyzing linear springs, non-linear springs, and springs having a tension cut-off. The latter feature simulates the effect of a pipe pulling out of contact with the soil. The model is used to perform parametric studies to assess the effects of soil stiffness, soil strength, trench geometry, amplitude of pipe displacements, pipe stiffness, and length of touchdown zone on pipe deflections and bending stresses. In conclusions, the seafloor stiffness (as characterized by the three spring parameters), the magnitude of pipe displacement, and the length of the touchdown zone all influence bending stresses in the pipe. Also, the tension cutoff effect, i.e., the pipe pulling away from the soil, can have a very large effect on bending stresses in the pipe. Neglecting this effect can lead to serious over-estimate of stress levels and excessive conservatism in design.

Denna studie har sammanställt kunskap och erfarenhet från drift av SCR-anläggningar påfartyg med syftet att fastställa de huvudsakliga orsakerna bakom problem som uppstår ikatalysatoranläggningar inom Nord- och Östersjöfarten. Undersökningen utfördes meden kvalitativ intervjumetod. För att få en bra täckning riktade sig undersökningen motbåde rederier och fartyg med erfarenhet av SCR, samt tillverkare av systemen.Intervjuerna utfördes per telefon och analyserades sedan mot frågeställningarna. Iresultatet framkom att ett stort antal anläggningar genomgått modifieringar eftersomproblem uppstått. Ett antal vanligt förekommande problem identifierades. Någrakomponenter är särskilt kritiska att designa och dimensionera, såsom utrusning förureainjicering och magnetventiler för sotblåsning. Vidare framkom att avgastemperatursåväl som bränslet och ureans kvalité var viktiga faktorer för att uppnå god prestandaoch livslängd. Studien visar även att ökad kompetens krävs både hos befintlig ochblivande maskinpersonal för att underhållsåtgärder ska ske på rätt sätt och i rätt tid. Föratt möta eventuella framtida behov av SCR kombinerat med scrubberteknik krävs fortsattteknikutveckling. / The objective of the project was to compile knowledge and experience from the operationof SCR-installations on vessels in order to determine the main causes behind theproblems that arise in the catalyst systems within North- and Baltic Sea shipping. Thestudy was performed as a qualitative interview method. In order to get a good coverage,the study was directed against both companies and ships with experience of SCR andmanufacturers of systems. The interviews were conducted by telephone, and thenanalyzed against the objective. The result showed that a large number of plants haveundergone modifications since problems has occurred. A number of common problemswere identified. The study identified some components that are particularly critical todesign and dimension, such as equipment for urea injection and solenoid valves for sootblowing. It was also found that the exhaust temperature as well as fuel and urea qualitywere important factors in achieving good performance and lifetime. Increasedcompetence is required from both existing and future engine personnel so thatmaintenance can be done the right way and at the right time. To meet future demands ofSCR combined with scrubber technique further technical development is required.

The goal of the project is to evaluate a new setup for the company Iberobot Svenska AB, using HMI and PLC, for resistance spot welding equipment controller. The purpose of the controller is to control the weld process; weld power and time. One of the question raised is if this setup could be used as an RWE controller and thereby be able to re-place an old proprietary controller called TEC6000. A prototype is built compatible with current single phase RWE and literature study is conducted to answer this question.  The new setup is based on Beijer iX T7B Softmotion which includes an HMI and a PLC with EtherCAT support. EtherCAT input and output modules from Beckhoff are chosen because they can handle the speed required by the weld process. The controller is implemented using theory for RMS value, timing diagram and state diagram based on weld process. The prototype is revised three times. A zero crossing detector is implemented. A control element driver using opto-triac is implemented. Measurements using oscillo-scope are conducted which shows that the controller is able to start a weld, but zero crossing detection is unstable and further research into this and current regulation is needed before an end user product can be made.

This thesis titled Impact of driving mode on urea consumption describes the influence between different drive modes and conditions of urea injection into the selective catalytic reduction system. The first half of the thesis deals with the theoretical part. Introduction deals with the theory of formation of harmful pollution in exhaust emissions, the effects of pollutants and legislative regulations. There are also explained key parts of different systems, reduction of harmful exhaust gas components . The main emphasis is put on the selective catalytic reduction. Other chapters are devoted to the methodology and testing procedures . The aim of this thesis is a presentation of the system regulation, its pros and cons under various operational modes.

The selective catalytic reduction (SCR) of NO_X (x = 1,2) using Cu-exchanged zeolites is used commercially for the abatement of NO_X from on-road lean-burn diesel engines. At the low exhaust temperatures during cold-start and idle operation (<523 K), the SCR reaction proceeds via a Cu²⁺/Cu⁺ redox cycle of NH₃-solvated and mobilized Cu ions. Reduction of Cu²⁺ species proceeds via NO-assisted reduction of isolated NH₃-solvated Cu²⁺ ions. To complete Cu⁺ to Cu²⁺ oxidation, two [Cu(NH₃)₂]⁺ species react together with O₂ to form a dimeric O₂-bridged Cu²⁺ species that is subsequently reduced by NO and NH₃ to complete the SCR catalytic turnover. NH₃-solvated Cu ion species are nominally isolated under <i>ex-situ</i> conditions, however, motivating the critical research question studied in this work regarding how Cu ion mobility and dynamic interconversion of mononuclear and binuclear active sites facilitate SCR chemistry. In particular, this work focuses on understanding how active site proximity, zeolite pore connectivity and dimensionality, and catalyst poisons impact the number and reactivity of active Cu sites.<br> Steady-state SCR kinetics (473 K) measured at fixed gas conditions (10 kPa O₂) on a series of Cu-chabazite (CHA) zeolites with varied density of isolated Cu ions (0.078-0.35 Cu per 10³ ų) exhibit non-single site behavior because of changes in the kinetic relevance of Cu⁺ oxidation and Cu²⁺ reduction half-cycles, and the non-mean field nature of the Cu⁺ oxidation process. Measurement of SCR rates at dioxygen pressures (1-60 kPa O₂) far removed from typical operating conditions (3-17 kPa O₂) allows isolating the kinetic behavior under primarily Cu⁺ oxidation-limited and Cu²⁺ reduction-limited conditions, and estimating rate parameters for these two regimes by regressing SCR rates as a function of O2 pressure to an empirical Langmuirian rate expression. Apparent rate constants that are first-order in O₂ (k_first) increase systematically with Cu density, consistent with the dual-site Cu⁺ oxidation mechanism. Apparent rate constants that are zero-order in O2 (k_zero) show a weak dependence on Cu density, similar to the fraction of Cu that can be oxidized by O₂ at 473 K in transient experiments, suggesting that changes in k_zero reflect changes in the fraction of active Cu given the single-site nature of Cu²⁺ reduction mechanisms. The measured apparent activation energy in the Cu⁺ oxidation limit (E_app,first) increases systematically with Cu density, highlighting the non-mean field nature of Cu⁺ oxidation over the range of Cu densities studied. The measured apparent activation energies in the Cu²⁺ reduction limit are constant above a threshold Cu density (0.17 Cu per 10³ ų), consistent with mean-field behavior, but begin to deviate at lower densities (0.084-0.10 Cu per 10³ ų).<br> A series of Cu-zeolites with 2D (LEV, FER) and 1D (MOR) pore connectivity were synthesized to quantify how the framework topology and pore structure influences the mobility and reactivity of Cu ions during SCR. When compared to Cu-CHA, a 3D pore structure, values of k_first and k_zero (per total Cu) were several factors lower on the 2D and 1D zeolites, indicating that decreasing the effective volumetric footprint of Cu ions during SCR decreases both the rate of dual-site Cu⁺ oxidation and the fraction of Cu⁺ that oxidizes. When compared to other 3D double-six membered ring (d6r) zeolites with different pore shape (AEI) and size (AFX), rates (per total Cu) were generally a factor of 1.5 to 2 times higher on Cu-CHA, indicating that the open pore structure of cylindrical cages in CHA are favorable for low-temperature SCR reactivity.<br> The arrangement and density of framework Al atoms in CHA influences low-temperature SCR, as the framework Al atoms mediate Cu ion mobility and the arrangement of Al in the framework determines the chemical identity of the Cu active site precursors as either [CuOH]⁺ exchanged at an isolated framework Al center or Cu²⁺ exchanged at paired framework Al in a six-membered ring (6-MR). Synthesis of CHA zeolites with mixtures of Na⁺ and TMAda⁺ provides a strategy to alter the amount of Al centers in 6-MR paired configurations, because Na+ co-occludes in 6-MR voids adjacent to TMAda⁺ occluded within the cha cage. In contrast, synthesis of CHA zeolites with mixtures of K⁺ and TMAda⁺ results in primarily 6-MR isolated Al configurations because K⁺ cations displace TMAda⁺ from residing in cha cages. Thus, the use of different mixtures of organic and inorganic structure directing agents (SDAs) provide routes to synthesize CHA zeolites that favor the formation of either [CuOH]⁺ or Cu²⁺ species. The Cu speciation influences both hydrothermal stability and resistance to sulfur poisoning. SO₂ is a catalyst poison ubiquitous in automotive exhaust and is found to bind to [CuOH]⁺ sites more strongly than Cu²⁺ sites, both before and after high-temperature de-sulfation treatments. <br> Together, these findings reveal several of the important structural and active site requirements for low-temperature NO_X SCR with NH₃ on Cu-zeolites. The non-mean field nature of the SCR redox cycle on Cu²⁺/Cu⁺ ion sites, and the requirement for Cu ions to be located in proximal and accessible locations of zeolite void spaces becomes more favorable in 3D highly connected pore structures, highlighting a primary reason why low-temperature SCR rates (per Cu) are higher on Cu-CHA than on other Cu-zeolites. The synthetic procedures presented here to influence the Al arrangement in CHA zeolites provide new strategies to alter the speciation and density of isolated Cu ion sites, even among Cu-CHA zeolites of nominally identical elemental composition, which have implications for the stability and resistance to poisons of the catalyst under realistic operating conditions. Together, synthetic strategies to manipulate the proximity of active sites, methods to quantify transient and steady-state kinetics, and <i>in situ</i> and <i>operando</i> characterization are invaluable tools to study and understand the non-mean field dynamic interconversion of isolated and multinuclear sites during low-temperature SCR catalysis.<br>

The addition of Tier 2 standards by United States Environmental Protection Agency (EPA) has increased focus on light-duty vehicle emissions. In this study, a diesel-electric hybrid vehicle was used for testing under the Challenge X program. The diesel engine was powered by a 20% soy-based biodiesel - 80% diesel blend, and the electric motor received its energy from a 330 volt Nickle Metal Hydride battery pack. The diesel engine, notorious for high emissions of nitrogen oxides (NOx) and particulate matter (PM), requires aftertreatment of these emissions to achieve Tier 2 EPA compliance. The primary focus of this thesis is use of a urea injection selective catalytic reduction (SCR) system to reduce NOx emissions. Also, a diesel particulate filter (DPF) was employed for PM reduction purposes. Significant decreases in both NOx and PM emissions were achieved.

The fatigue life of a Steel Catenary Riser (SCR) near its touch-down zone is substantially affected by its interaction with the seabed. Hence, accurate estimate of its fatigue life requires the understanding and realistic modeling of the interaction between them. The interaction between SCR and the seabed depends on many factors, such as soil properties, riser characteristics, and the development of trenching at the seafloor. Existing approaches for modeling the seabed in interaction with a SCR approximate the seabed soil by a linear or nonlinear spring and a dashpot which respectively represent the stiffness and damping of the soil. However, they do not take into account certain phenomena resulting from plastic deformation or degradation of the seabed soil, such as trenching. In this study, a more realistic approach is developed for simulating the interaction between a SCR and the seabed soil. In addition to the use of a realistic P-y curve (where P stands for the supporting or resistance force of the seafloor and y for the vertical penetration of the riser into the soil) to simulate the soil deformation during its interaction with a riser, it considers the development of a trench caused by continuous poundings of a riser on the seabed and then its feedback effect on the variation of the bending moment along the riser. In this study, it has been found that trenching underneath a SCR may decrease the maximum variation of bending moment near its touch-down zone. Since the variation of the moment dictates the fatigue damage to the SCR, the results based on this approach indicate that the trenching development at the seabed may increase the fatigue life of a SCR and therefore, it may have important application to the design of a SCR.