This thesis has investigated the possibility of improved soil temperature modeling using an updated version of an existing soil temperature model frequently used in catchment scale biogeochemical modeling. Future (2061-2090) snow dynamics and soil temperature was projected using ensemble of bias-corrected regional climate models (RCM). Effects over a north-south gradient of Sweden were analyzed using the four Swedish Integrated Monitoring (IM) catchments as study sites. Model calibration was applied on the study sites using daily observations of soil temperature for 1996-2008. The calibrated models were able to simulate soil temperature at different depths in the soil profile in a very accurate way in all IM sites. The lowest validation NS-value (objective criterion used for measuring goodness of fit) recorded in the study was 0.93. Even though the overall model performances were good, the simulations had problem of duplicating some of the winter temperatures at the northernmost site, Gammtratten. Whether the updated soil temperature model offered an improvement of the existing model is therefore debatable. The future simulations showed increasing soil temperatures at all study sites on annual basis, more in the south than in the north. Annual soil temperatures were projected to increase by 1.31 – 2.33 °C for the different study sites. Winter soil temperatures were clearly higher than during 1996-2008 for the two southernmost sites, whilst Gammtratten in the north, had colder winter soil temperatures. At the midmost catchment, winter soil temperatures were quite similar to that of the test period. Whether the cold winter soil temperatures at Gammtratten were a result of snow loss was ambiguous. The results from the future simulations showed the complexity of predicting soil temperature and strengthened the conclusion among scientists that any general assumptions of future soil temperature based on e.g. air temperature cannot be done. / Det här examensarbetet har undersökt möjligheterna till förbättrad modellering av marktemperaturer genom införandet av en uppdaterad version av en tidigare modell, frekvent använd vid biokemisk modellering på avrinningsområdesnivå. Vidare har framtida (2061-2090) snödynamik och marktemperaturer simulerats genom att en ensemble av bias –korrigerad klimatdata används för att driva modellen. Nutida (1996-2008) klimatdata, samt marktemperatursdata för kalibrering och validering av modellen, tillhandahölls från de fyra platser som ingår i det Svenska miljöövervakningsprogrammet (IM). Dessa platser kom att utgöra en syd-nordlig gradient, längs vilken resultaten analyserades.   Det generella omdömet från kalibreringen av modellen var att den kunde erbjuda en bra representation av verkliga förhållanden i fråga om marktemperatur. Det lägsta NS-värdet (objektivt kriterium använt för att mäta modellens passningsgrad) som uppmättes under valideringen var 0,93, vilket ansågs vara mycket högt. Dock hade modellen svårigheter att efterlikna verkliga markförhållanden vid Gammtratten under vintermånaderna, vilket föranledde slutsatsen att vidare undersökningar behöver göras för att kunna fastställa om modellen utgör en förbättring av den tidigare existerande versionen.   De framtida simuleringarna visade högre årliga marktemperaturer i jämförelse med dagen värden, särskilt i söder. Baserat på simuleringarna är det troligt att framtida marktemperaturer kommer att vara mellan 1,31 och 2,33 °C högre än idag. Beträffande säsongsmässig variation var maktemperaturerna under vintern högre än dagens värden för de två sydliga platserna medans de var lägre för den nodligaste platsen (Gammtratten). Huruvida de kallare simulerade marktemperaturerna vid Gammtratten var en konsekvens av ett mindre isolerande snötäcke var tvetydigt. Resultaten från de framtida simuleringarna har visat på komplexiteten i att förutspå framtida marktemperaturer och har stärkt uppfattningen om att några generella slutsatser om vad t.ex. högre lufttemperaturer kommer få för konsekvenser för framtida marktemperaturer inte kan göras.

abstract: Although high performance, light-weight composites are increasingly being used in applications ranging from aircraft, rotorcraft, weapon systems and ground vehicles, the assurance of structural reliability remains a critical issue. In composites, damage is absorbed through various fracture processes, including fiber failure, matrix cracking and delamination. An important element in achieving reliable composite systems is a strong capability of assessing and inspecting physical damage of critical structural components. Installation of a robust Structural Health Monitoring (SHM) system would be very valuable in detecting the onset of composite failure. A number of major issues still require serious attention in connection with the research and development aspects of sensor-integrated reliable SHM systems for composite structures. In particular, the sensitivity of currently available sensor systems does not allow detection of micro level damage; this limits the capability of data driven SHM systems. As a fundamental layer in SHM, modeling can provide in-depth information on material and structural behavior for sensing and detection, as well as data for learning algorithms. This dissertation focusses on the development of a multiscale analysis framework, which is used to detect various forms of damage in complex composite structures. A generalized method of cells based micromechanics analysis, as implemented in NASA's MAC/GMC code, is used for the micro-level analysis. First, a baseline study of MAC/GMC is performed to determine the governing failure theories that best capture the damage progression. The deficiencies associated with various layups and loading conditions are addressed. In most micromechanics analysis, a representative unit cell (RUC) with a common fiber packing arrangement is used. The effect of variation in this arrangement within the RUC has been studied and results indicate this variation influences the macro-scale effective material properties and failure stresses. The developed model has been used to simulate impact damage in a composite beam and an airfoil structure. The model data was verified through active interrogation using piezoelectric sensors. The multiscale model was further extended to develop a coupled damage and wave attenuation model, which was used to study different damage states such as fiber-matrix debonding in composite structures with surface bonded piezoelectric sensors. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2012

Planetary science is often limited to only surface observations of planets requiring the development of modeling techniques to infer information about the planet’s interior. This work outlines three separate scientific problems that arose from planetary surface observations, the methodology utilized to explain the formation of these observation, and what we learned about the planet’s interior by solving these problems. Chapter 1 discusses why lunar mascon basins (impact basins associated with a central freeair gravity positive) form for only a limited range of basin diameters. Modeling the full formation of South-Pole Aitken (SPA) basin using a sequential two-code (hydrocode and Finite Element Model) shows that due to SPA’s great size (long wavelength) and the high geothermal gradient of the Moon at impact, the basin’s relaxation process was controlled by isostatic adjustment with minimal influence from lithospheric rigidity or membrane stresses. Additionally, the modeling shows that the Moon was hot and weak at impact. Chapter 2 addresses why there is a lack of olivine abundance on Mars around large impact basins, and the formation of the megabreccia that is associated with an orthopyroxene signature in the circum-Isidis Planitia region. Hydrocode modeling of the excavation of the Isidis forming impact shows the impact was more than capable of excavating mantle material and reproducing the observed megabreccia. This coupled with the lack of olivine signature indicates that the Martian upper mantle is orthopyroxene-rich. Chapter 3 covers the investigation into why the nitrogen ice sheet on Pluto, Sputnik Planitia, is the youngest observed terrain and why the surface is divided into irregular polygons about 20– 30 kilometers in diameter. The utilization of a new parameterized convection model enables the computation of the Rayleigh number of the nitrogen ice and shows that the nitrogen ice is vigorously convecting, making Rayleigh–Bénard convection the most likely explanation for these polygons (Trowbridge et al., 2016). Additionally, the diameter of Sputnik Planitia’s polygons and the dimensions of its ‘floating mountains’ of water ice suggest that its nitrogen ice is about five to ten kilometers thick (Trowbridge et al., 2016). The estimated convection velocity of 1.5 centimeters a year indicates a surface age of only around a million years (Trowbridge et al., 2016). The accumulation of this work is three chapters that use three separate techniques to further understand three separate planets.

No description available.

The development of improved numerical methods for computer simulation of high velocity impact dynamics is of importance in a variety of science and engineering fields. The growth of computing capabilities has created a demand for improved parallel algorithms for high velocity impact modeling. In addition, there are selected impact applications where experimentation is very costly, or even impossible (e.g. when certain bioimpact or space debris problems are of interest). This dissertation extends significantly the class of problems where particle-element based impact simulation techniques may be effectively applied in engineering design. This dissertation develops a hybrid particle-finite element method for a general hexahedral mesh. This work included the formulation of a numerical algorithm for the generation of an ellipsoidal particle set for an unstructured hex mesh, and a new interpolation kernel for the density. The discrete model is constructed using thermomechanical Lagrange equations. The formulation is validated via simulation of published impact experiments. / text