Numerical simulation of 3D bubbles rising in viscous liquids using a front tracking method

The rise of bubbles in viscous liquids is not only a very common process in many industrial applications, but also an important fundamental problem in fluid physics. An improved numerical algorithm based on the front tracking method, originally proposed by Tryggvason and his co-workers, has been validated against experiments over a wide range of intermediate Reynolds and Bond numbers using an axisymmetric model [J. Hua, J. Lou, Numerical simulation of bubble rising in viscous liquid, J. Comput. Phys. 22 (2007) 769–795]. In the current paper, this numerical algorithm is further extended to simulate 3D bubbles rising in viscous liquids with high Reynolds and Bond numbers and with large density and viscosity ratios representative of the common air–water two-phase flow system. To facilitate the 3D front tracking simulation, mesh adaptation is implemented for both the front mesh on the bubble surface and the background mesh. On the latter mesh, the governing Navier–Stokes equations for incompressible, Newtonian flow are solved in a moving reference frame attached to the rising bubble. Specifically, the equations are solved using a finite volume scheme based on the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm, and it appears to be robust even for high Reynolds numbers and high density and viscosity ratios. The 3D bubble surface is tracked explicitly using an adaptive, unstructured triangular mesh. The numerical model is integrated with the software package PARAMESH, a block-based adaptive mesh refinement (AMR) tool developed for parallel computing. PARAMESH allows background mesh adaptation as well as the solution of the governing equations in parallel on a supercomputer. Further, Peskin distribution function is applied to interpolate the variable values between the front and the background meshes. Detailed sensitivity analysis about the numerical modeling algorithm has been performed. The current model has also been applied to simulate a number of cases of 3D gas bubbles rising in viscous liquids, e.g. air bubbles rising in water. Simulation results are compared with experimental observations both in aspect of terminal bubble shapes and terminal bubble velocities. In addition, we applied this model to simulate the interaction between two bubbles rising in a liquid, which illustrated the model’s capability in predicting the interaction dynamics of rising bubbles

Food distribution influences social organization and population growth in a small rodent

This is the postprint version of the article. The published article can be located at the publisher's websiteIn polygynous mammals, the spatial clumping and predictability of food should influence spacing behavior of females whose reproductive success depends to a great extent on food availability, which would in turn affect male spacing behavior. Changes in the social and mating systems can then influence individual fitness and population dynamics. To test these hypotheses, we manipulated food distribution and predictability in enclosed populations of bank voles (Myodes glareolus) and monitored spacing behavior, survival, and reproduction of adult females and males over 3 months. Food was either spread out (dispersed treatment), spatially clumped and highly predictable (clumped treatment) or spatially clumped but less predictable (variable treatment). We found that females in the clumped treatment were more aggregated and had more overlapping home ranges compared with females in the dispersed and variable treatments. Male spacing behavior followed the same patterns. Despite different social organizations between treatments, no differences in home range size and mating systems were found in females and males. In addition, we found that females in the clumped food treatment had a higher probability of successfully producing weaned offspring, likely due to lower infanticide rates. This led to higher population growth compared with the other 2 treatments. These results suggest a tight relationship between the spatiotemporal distribution of food, social organization, and population dynamics.2014-04-3

imported berry mix cake suspected to be the source of infection in Norway

Ongoing hepatitis A outbreak in Europe 2013 to 2014

The Effects of Wide-Angle Scattering on Coherent Diffraction Imaging

De potensielle negative effektene av vidvinkel-spredning på fasegjenvinningsprosessen i koherent røntgendiffraksjonsavbildning (CDI) har blitt undersøkt ved bruk av numeriske beregninger. CDI er avbildningsmetode som kan lage en digital, tredimensjonal kopi av en prøve fra et sett med småvinkel Fraunhofer-diffraksjonsmønster. Metoden er særlig ettertraktet da den kan finne de tredimensjonale detaljene av prøven, med en oppløsning på rundt et titalls nanometer, uten å kutte den opp. Teknikken har allerede vist at den kan bidra med nyttig informasjon på tvers av mange fagfelt, og med tidsoppløst CDI på trappene kan man se for seg en rekke nye bruksområder. Det finnes derimot et problem med dagens fasegjenvinningsalgoritmer, og det er at de antar at all den innkommende intensiteten vil bidra til småvinkel diffraksjonsmønstrene for hver orientering av prøven. Denne antagelsen vil sannsynligvis være riktig for ikke-krystallinske prøver, som teknikken først ble utviklet for å avbilde, men for krystallinske prøver måler man derimot et sterkt signal ved vidvinkel-detektoren. Spørsmålet blir derfor hva forholdet mellom denne spredte intensiteten og den innkommende intensiteten er, og hvordan forholdet påvirker resultatene i et CDI-eksperiment. Tidligere har jeg i en prosjektoppgave vist ved bruk av numeriske simuleringer at vidvinkel-spredning kan ha en betydelig innvirkning på rekonstruksjonskvaliteten, opp til et punkt hvor fasegjenvinningsalgoritmene ikke klarte å gjenskape prøven. I disse beregningene ble det derimot antatt en forholdsvis stor intensitetsreduksjon. Det var derfor nødvendig å undersøke om de negative effektene fortsatt ville være til stede hvis en mer realistisk fordeling av vidvinkel-spredningen ble brukt i simuleringene. For å bestemme denne fordelingen ble såkalte rocking curves av ulike simulerte aragonitt krystallitter beregnet. Dessverre klarte jeg ikke å normalisere den spredte intensiteten mhp. den innkommende strålen. Jeg fant derimot et nytt anslag på hvor stort vinkelspenn av prøveorienteringer som vil gi en målbar mengde spredning. Ved å bruke dette nye spennet på pluss-minus 0.1 grader, som var betydelig smalere enn spennet som ble antatt i prosjektoppgaven, samt de samme intensitetsreduksjonene som i prosjektoppgaven, avtok de negative effektene betraktelig. Små forverringer i rekonstruksjonskvaliteten ble observert for de største intensitetsreduksjonene, men alle rekonstruksjonene var kvalitativt lik den originale prøven, og det var kun mindre lokale variasjoner som skilte de ulike rekonstruksjonene. Jeg anser det derfor som usannsynlig at vidvinkel-spredning har en betydelig påvirkning på fasegjenvinningsprosessen. Selv om effektene av vidvinkel-spredning sannsynligvis er små, om merkbare i det hele tatt, må det gjennomføres ytterligere beregninger på det absolutte intensitetstapet før man kan trekke noen endelige konklusjoner. Hvis det viser seg at energitapet er på høyde med det som ga forverrede rekonstruksjonsresultater i denne masteroppgaven, dvs. fra og med 30%, bør det gjennomføres forsøk hvor man måler det nøyaktige forholdet mellom intensiteten til den innkommende og den spredte strålen for å se om forholdet virkelig kan bli så stort.The effects of wide-angle scattering on Coherent X-ray Diffraction Imaging (CDI) have been explored numerically to decide whether the intensity lost due to Bragg scattering might have a negative impact on the phase retrieval process. CDI is a nondestructive, three-dimensional imaging technique utilising phase retrieval algorithms to digitally reconstruct an object from a set of its small-angle diffraction patterns measured in the Fraunhofer limit. The technique is routinely able to resolve features down to tens of nanometers, and with the development of in situ CDI, several new applications can be envisaged. However, today's phase retrieval algorithms assume that all the incoming radiation will contribute to the small-angle diffraction pattern for all the orientations of the sample. This assumption is well-founded for non-crystalline samples, for which the technique initially was developed. However, for crystalline samples, there will be a measurable signal at the wide-angle detector, meaning that some of the incoming intensity has been scattered off the sample. If a sufficiently large portion of the incoming beam is scattered, the author has previously shown in a project work that these losses might have serious negative impacts on the reconstruction quality, up to a point where the applied phase retrieval algorithm could not reconstruct the examined object. It was however necessary to assume a large amount of scattered intensity, i.e. approximately 50% of the incoming beam, to see the negative effects. Therefore, it remained to see whether the negative effects still could be seen if the intensity losses were the same as in a real CDI experiment. To decide how much of the incoming intensity is lost due to the wide-angle scattering, rocking curves of simulated aragonite crystallites, with diameters ranging from approximately 75 nm to 500 nm, have been calculated using the kinematical approximation. No absolute intensity reduction could be decided, but the range of sample orientations which gave a wide-angle signal was found, and this range was significantly narrower than what had been assumed in the previous work. Building on the new range of plus-minus 0.1 degrees, the effects of Bragg scattering on CDI were examined anew. By calculating the diffraction pattern of a known object and reducing the intensity for some projections, the effects of the phase retrieval process were studied. A reduction in the reconstruction quality was observed given that the intensity reduction was large enough. However, the phase retrieval algorithm was able to reconstruct the sample for all the intensity reductions, and only minor deviations were observed. It is therefore unlikely that Bragg scattering will have a significant negative effect on the phase retrieval process. However, before drawing any final conclusions, further analysis of the absolute intensity reductions must be performed. If the reductions appear to be of the order which gave a reduced reconstruction quality in this thesis, i.e. 30% or more, it would be advisable to design an experiment which could accurately measure the relation between the incoming beam and the beam scattered to the wide-angle detector

Leadership practices for sustainable success: The case of the Norwegian energy sector

Denne EMBA master oppgaven hadde som mål å finne måter å endre tankegangen til energisektoren gjennom å utforske relevant litteratur som kan gi energisektoren den ledelsepraksisen den trenger for å lykkes og samtidig være en del av løsningen på klimaendringene. Det var å vise at det å ta samfunnsansvar gir muligheter og ikke er en trussel. Forskningsspørsmålet var: Hvilken lederpraksis kreves for at energisektoren skal lykkes gjennom det grønne skiftet? Basert på datainnsamlingen ble det funnet noen ledelsepraksiser. For det første er det antydet at ledelse bør betraktes som noe som gjøres i et kollektiv mot et felles formål, det gjøres ikke av et enkelt individ. For det andre bør organisasjonene etablere et høyere formål for å sikre at organisasjonen skaper verdier til det beste for samfunnet samtidig som de produserer overskudd. For det tredje må organisasjoner innen sektoren realisere sitt samfunnsansvar for sine interessenter, og at det å ta dette ansvaret øker selskapenes overskudd og sikrer langsiktig suksess. For det fjerde kan designtenkningsparadigme gi verktøyene for å sikre god strategisk beslutningstaking og skape engasjement rundt innovasjon og endringsarbeid.This EMBA thesis set out to find ways to change the mindset of the energy sector trough exploring relevant literature that could provide the energy sector with the leadership practices it needs to be successful while also being part of the solution to the climate change. It was to show that taking social responsibility could be and opportunity and not a threat. The research question was: What leadership practices is required for the energy sector to gain success through the green shift? Based on the data collection, some leadership practices were found. First, it’s suggested that leadership should be viewed as something that is done in a collective towards a shared purpose, it’s not done by a single individual. Second, the organisations should establish a higher purpose to ensure that the organisation creates value for the greater good while also producing profits. Third, organisations within the sector needs to realise their social responsibility for its stakeholders and that taking this responsibility increase the company’s profits and ensure long term success. Fourth, design thinking paradigm can provide the tools to ensure good strategic decision making and create engagement around innovation and change efforts

Residential CO2 Heat Pump System for Combined Space Heating and Hot Water Heating

Carbon dioxide (CO2, R-744) has been identified as a promising alternative to conventional working fluids in a number of applications due to its favourable environmental and thermophysical properties. Previous work on residential CO2 heat pumps has been dealing with systems for either space heating or hot water heating, and it was therefore considered interesting to carry out a theoretical and experimental study of residential CO2 heat pump systems for combined space heating and hot water heating – so-called integrated CO2 heat pump systems. The scope of this thesis is limited to brine-to-water and water-to-water heat pumps connected to low-temperature hydronic space heating systems..dr.ing.dr.ing

Bodies speak louder than words: Norwegian Jewish parents reflecting on brit milah

This article addresses the question: how do Norwegian Jewish parents reflect on brit milah (circumcision) in a context where this practice is frequently criticised? The data are derived from twenty-five in-depth interviews. Drawing on the perspectives of Catherine Bell and Joseph Bulbulia, the text explores circumcision as part of social life. The parental narratives uncover ongoing negotiations occurring between parents and the minority/majority population. The article argues that circumcision serves as a rite of passage as much for parents as for the infant. For most parents, circumcision is utilised to strengthen a Jewish identity and as a cultural strategy to recreate a Jewish cosmos, even if it entails a costly signal, owing to ambivalence and/or majority opposition. Some individuals find the costs too high and discontinue the practice. However, they all desire to manifest Jewish identity, whether through bodily adaptation or the lack thereof. In this manner, bodies speak louder than words