Assessment of Fracture Propagation in Pipelines Transporting Impure CO2 Streams

Running fractures are considered as most dangerous catastrophic mode of failure of high-pressure transportation pipelines. This paper describes methodology for coupled modelling of an outflow, heat transfer and crack propagation in pipelines. The methodology is validated and applied to investigate the ductile fracture propagation in pipelines transporting impure CO 2 streams to provide recommendations for the fracture control. To assess the propensity of pipelines to brittle fractures, the temperature distribution in the pipe wall in the vicinity of a crack is simulated for various conditions of heat transfer relevant to both overground and buried pipelines

Film boiling and rapid phase transition of liquefied natural gas

When liquefied natural gas (LNG) is spilled onto water there is a possibility that explosive rapid phase transition (RPT) events occur. According to experiments, these vapor explosions are highly unpredictable, with yields up to several kilograms of TNT equivalent. The leading theory of RPT claims that triggering occurs due to a sudden and rapid chain of events involving film-boiling collapse, liquid superheating, rapid nucleation and explosive expansion. Still, after over four decades of research on the topic, it appears that there is no reliable and accepted method for quantitative LNG RPT risk-assessment. The main goal of the present thesis is to remedy this issue through theoretical means. According to the leading theory of RPT, prediction of the triggering event necessitates modelling of two properties: the Leidenfrost temperature and the superheat limit temperature, both of which were investigated herein. The Leidenfrost temperature is by definition the surface temperature below which film-boiling collapse occurs. Therefore, it is necessary to understand film boiling and its stability. While much work has been done in the past on modelling the stability of thin liquid films with the long-wave approximation, these models are not directly applicable to film boiling. The equations describing a vapor film trapped between two dense phases of extremely different temperatures turn out to be different in subtle but important ways. In this project a new model for vapor-film dynamics has been developed within the long-wave approximation methodology. This model crucially involves a coupling to non-equilibrium evaporation models from kinetic theory, which allows for the inclusion of the thermocapillary effect at the evaporating interface. Based on stability analysis of this model, a novel and promising prediction method for the Leidenfrost temperature has been discovered. The method carries with it the surprising theoretical implication that film-boiling collapse occurs when the thermocapillary instability overpowers vapor-thrust stabilization. However, further experimental investigations of the Leidenfrost temperature is needed in order to draw strong conclusions regarding its validity. The superheat limit may be estimated within the framework of classical nucleation theory (CNT). These predictions have been compared with a wide array of relevant experimental data on hydrocarbons, both for pure fluids and binary mixtures. The performance of the CNT model was deemed satisfactory, and thus, no further efforts to improve superheat limit modelling have been made in this project. Finally, a framework for the prediction of RPT risk and consequence during LNG boil-off has been developed. This framework demonstrates how models for the Leidenfrost temperature and the superheat limit temperature as functions of LNG mixture composition may be combined with classical thermodynamics in order to predict when (and if) the conditions for RPT triggering may be met. Additionally, it has been shown how the predicted LNG composition at the time of triggering may be used to estimate the worst case explosive pressure and energy yield through the use of a simplified thermodynamic model. While quite idealized, this framework represents an important step towards practical risk assessment and mitigation for LNG rapid phase transition. The thesis concludes with a series of suggestions on how the framework may be further improved

Optical Properties of truncated and coated spheroidal Nanoparticles on a Substrate

In nanoparticle research it is common to perform optical measurements on particle films during deposition, to help understand the growth process. GranFilm is a software under development which can calculate the optical properties of an array of truncated nanoparticles supported on a substrate. The theory behind these calculations is based on the work of Bedeaux and Vlieger. One feature which was missing from the software until now was the ability to do such simulations on the case of truncated spheroidal nanoparticles with an arbitrary number of coatings of different materials. In the beginning of this work, the equations needed to perform these simulations are derived, and then reduced to previously derived special cases for verification. The new equations are then implemented into GranFilm, and the new code is put through numerical tests. Finally, the new functionality is tested with the help of experimental data from an oxidation process of a silver nanoparticle film. The qualitative evolution of the optical properties of the film is reproduced quite successfully, but some issues remain

Numerical solution of the dynamics of director fields in nematic liquid crystals

Since their discovery in the late 1800s, liquid crystals have become an important part of the technology of the modern world. As a consequence the study of anisotropic liquids in general, and liquid crystals in particular, has grown into a large interdisciplinary field involving physics, mathematics, chemistry and biology to name a few. In a series of papers we consider numerical solution of the evolution of the director, a vector valued field giving the local average orientation of the long axis of molecules in nematic liquid crystals. The flow field is assumed to be stationary throughout this work. We consider both the free elastic dynamics of the director as well as the case with applied electric fields on a finite domain. We study the dynamics of the 1D Fréedericksz transition, where an applied electric field forces reorientation in the director field. The director is assumed strongly anchored and the boundaries. Herein, we study the role of inertia and dissipation on the time evolution of the director eld during the reorientation. In particular, we show through simulations that inertia will introduce standing waves that might e ect transition time of the reorientation, but only for very small time scales or extremely high molecular inertia. The Fréedericksz transition is also numerically studied with weak boundary anchoring. For this problem it has been shown analytically that there exists a hierarchy of meta-stable equilibrium con gurations. This is in sharp contrast to the strongly anchored case, where the equilibrium is globally well defined. We derive an implicit numerical scheme for this problem and show the well-posedness of the discrete equation system. The method can be used for the fully nonlinear model with coupled electric field. Through simulations we show that the director can transition into different meta-stable states given different small perturbations to the initial data. The numerical solution of variational wave equations describing the elastic dynamics of nematic liquid crystals is considered in both 1D and 2D. Using energy respecting Runge{Kutta Discontinuous Galerkin methods we show that numerical solutions that either conserve or dissipate a discrete version of the energy can be obtained by efficient time marching. The dissipative scheme uses a dissipative up-winding at the cell interfaces combined with a shock-capturing method. Finally, we consider the application of nonintrusive sampling methods for uncertainty quantification for the elastic problem with uncertain Frank constants. The multi-level Monte Carlo (MLMC) method has been successfully applied to systems of hyperbolic conservation laws, but its applicability to other nonlinear problems is unclear. We show that MLMC is 5-10 times more efficient in approximating the mean compared to regular Monte Carlo sampling, when applied to variational wave equations in both 1D and 2D

Thematic exercises for non-IT students in Introductory Computer Science courses

Med den massive fremgangen i digital teknologi over de siste tiårene har det aldri før vært mer viktig å lære programeringsferdigheter i forbindelse med akademisk arbeid. Studenter ved Norges Teknologisk-naturvitenskapelige Universitet (NTNU) får disse grunnleggende ferdighetene igjennom sin studiegang via Inofrmasjonsteknologi Grunnkurs (TDT4110). Selv om faget dekker et bredt spekter av grunnleggende temaer innen informasjonsteknologi, er det visse usikkerheter når det kommer til studenter utenfor informasjonsteknologi-stuidene. Denne oppgaven undersøker om studenter utenfor informasjonsteknologi-stuidene er klar over hva de kan bruke disse kunnskapene til, og om det finnes måter man kan demonstrere bruk av IT-kunnskaper innenfor andre akademiske disipliner. Oppgaven ønsker også å se på muligheter for å implementere slike "tematiske" oppgaver i øvingsopplegget til Informasjonsteknologi Grunnkurs (TDT4110). Forskningen er gjort gjennom nettbaserte spørreundersøkelser og intervjuer med relevante målgrupper. Resultatene viser at studenter har en positiv holdning til implementasjon av tematiske oppgaver, men at de teoretiske løsningene er komplekse og krever merkbar tid og ressurser for å kunne implementeres. Studenter svarer også at de er mer intereserte i å få introdusert andre relevante programeringsverktøy som kan være direkte hjelpemidler for andre deler av akademiske disipliner, særlig grafiske simuleringer og plot-grafer.With the rapid increase in digital technology over the last few decades, learning programming skills for application in a broad range of scientific fields have never been more important. Students at The Norwegian University of Science and Technology (NTNU) are given fundamental knowledge of computer science through the introductory course: Introduction to computer science (TDT4110). And while the course itself covers a vast amount of basic knowledge, there is uncertainty towards students with non-IT majors on if they are fully aware of the number of applications that programming can be used in the students primary field of study. This thesis investigates the possibilities of implementing thematic exercises for non-IT students, to better demonstrate the applications programming can be applied to inside the scientific area. The research is conducted as a survey in the form of an online questionnaire and a series of interviews with students. The findings show that students show positive attitudes towards the implementation of exercises, but the theorized solutions are complex and needs substantial time and resources to implement. As of the writing of this paper, students are more interested in including other aspects of programming that they find useful, one of these aspects being graphs and plotting in Pytho

Hyperbolic Conservation Laws with Relaxation Terms: A Theoretical and Numerical Study

Hyperbolic relaxation systems is an active field of research, with a largenumber of applications in physical modeling. Examples include modelsfor traffic flow, kinetic theory and fluid mechanics. This master s thesis is a numerical and theoretical analysis of such systems, and consists of two main parts: The first is a new scheme for the stable numerical solution of hyperbolic relaxation systems using exponential integrators. First and second-order schemes of this type are derived and some desirable stability and accuracy properties are shown. The scheme is also used to solve a granular-gas model in order to demonstratethe practical use of the method. The second and largest part of this thesis is the analysis of the solutionsto 2 × 2 relaxation systems. In this work, the link between the the sub-characteristic condition and the stability of the solution of the relaxationsystem is discussed. In this context, the sub-characteristic condition andthe dissipativity of the Chapman Enskog approximation are shown to beequivalent in both 1-D and 2-D. Also, the dispersive wave dynamics of hyperbolic relaxation systems isanalyzed in detail. For 2 × 2 systems, the wave-speeds of the individualFourier-components of the solution are shown to fulfill a transitional sub-characteristic condition. Moreover, the transition is monotonic in thevariable ξ = kε, where ε is the relaxation time of the system and k is thewave-number. A basic 2 × 2 model is used both as an example-model in the analyticaldiscussions, and as a model for numerical tests in order to demonstratethe implications of the analytical results

Low-field NMR and MRI studies of fish muscle: Effects of raw material quality and processing

The present thesis aims at using non-invasive and non-destructive NMR techniques to contribute to a further understanding of fish tissue composition and its characteristics. Moreover, it aims at investigating the water dynamics and the distribution of fat and salt in fish as affected by species, raw material quality and processing from both the chemical and the physical angle at the same time. The applicability of low-field NMR as a tool for the fish processing industry was investigated. The bench top low-field NMR instrument was found suitable for fat and water determination in small Atlantic salmon (Salmo salar) samples, whereas the portable low-field NMR surface scanner (ProFiler) was appropriate for rapid fat determination in minced muscle. Thus, low-field NMR was proven to be good measuring technique, and with the introduction of the NMR surface scanner concept, online quality control may become feasible in the future. Transversal (T2) NMR relaxometry has been demonstrated to contain valuable information about water dynamics in Atlantic salmon and Atlantic cod (Gadus morhua) tissue. The thesis contributes to a further understanding of the relationship between water distribution and microstructure of fish flesh. It has been established that the method is sensitive to fish species, ante-mortem handling, rigor status, freezing/thawing, heating, and brine salting. The tissue T2 relaxation characteristics have been linked to microstructure, salt distribution and salt uptake. It is shown that T2 relaxation components correlate well with water holding capacity during salting. It has been suggested that entrapped and free water, and fat when present, give rise to the main relaxation components in fish muscle tissue. The understanding of the tissue water distribution and dynamics has been improved. However, the clarification of the relaxation characteristics in fish flesh is still an active area of research. In fatty fish, both fat and water contributes to the T2 NMR relaxation signal.  A two dimensional map of the diffusion versus T2 relaxation proved to be a good technique to increase the understanding of water and fat distribution in salmon muscle tissue, by clear separation of the NMR signals from water and fat components into different populations. MR imaging was probed for investigation of fat and salt distribution. 1H MRI was successfully applied to produce separate quantitative water and fat images. Combined 1H and 23Na imaging of brine salted Atlantic salmon revealed that the uptake and distribution of salt in the tissue was highly dependent on the spatial fat distribution. An evident relation was observed between T2 relaxation characteristics of salmon flesh and the sodium distribution in salted fillets. T2 relaxaometry and MR imaging gave further insight into the microstructure and water distribution of fish tissue of different quality and its effect on salt distribution. The combination of these NMR techniques is considered to be a useful tool to increase the understanding of the tissue water distribution and dynamics and for optimization of salting processes.                                 &nbsp