| 51. |
- Vesterlund, Mattias, 1980-
(författare)
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District heating system analysis and challenges within the urban transformation of Kiruna
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is currently an ongoing urban transformation in a small Swedish town named Kiruna, it is located in the very north of Sweden well above the Arctic Circle in a sub-arctic climate. Large part of the town will be relocated due to the ground deformation that is caused by the progressing iron ore mining activity and it is affecting all infrastructures of the town. This thesis aims to accomplish a holistic analysis on the district heating (DH) system for the town of Kiruna and its future challenges.Energy companies with a DH system recognize the importance in having a good understanding about the network characteristics, for obtaining an efficient and stabile heat delivery to the end-users. In this thesis, a method for modeling and simulation of meshed DH networks is described, that makes it possible to study and analyze the flow pattern in order to locate non-obvious paths, bottlenecks and overloaded pipes.For carrying out the DH simulations a fundamental input is to set the thermal losses for each pipe segment in the model, a fictitious series with all pipe diameters is created which corresponds to the annual losses in the real network. In comparison with the pipes series manufactured today the created one is best described by the series with least insulation and highest thermal losses. The studied network has its origin in the 60th and is the sum of the different piping technics that has been valid over time, this mixture is positioning the thermal performance as a close to a worst-case scenario.To the meshed DH network a number of heat production sites are connected for delivering the thermal requested by the end-users, each site consisting of several boilers and using different resources. A hybrid evolutionary-Mixed Integer Linear Programing (MILP) optimization approach is developed and applied for finding the cost-optimal heat production for three scenarios in combination of two heating demand levels. It is stated that no matter the geographically location of the site the cheapest resource should always be favorable as fuel, in the case when the same resource is viable at different sites a differentiated heat production is obtained. The supply temperature from each site is found to be the one lowest possible in order to serve all site-concerned end-users with a temperature level high enough for hot water production. The findings recommend a network temperatures reduction with the consequence in higher cost related to pumping work, but is lower than the savings due to the reduction in thermal losses.In order to provide the relocated part of the town with DH the hybrid evolutionary-MILP optimization routine is reshaped for finding different alternatives for network expansion layouts. The result is presented as a multi objective analysis between the operation cost and installation cost, showing the complete spectra of all optimal possible solutions and how the different cost correlate to each other. In this way, the outcome can be used for support in decision making, helping network owners is their planning and pipe sizing for new areas.For constructing the buildings that will populate the new city-area the Swedish government has stated a number of recommendations for achieving livable thermal indoor climate. An investigation is carried out analyzing the impact from the usage of three different heating system; air/air heat pump, air heating and floor heating in a low energy family house, where the first two system are aimed to use heat from the DH network. The analysis show that only the floor heating system satisfies the recommendations stated, but with carefully planning an air heating system could also fulfill the recommendations. Further, a techno-economical evaluation declares that the cheapest heating cost over 30 years is by using an air/air heat pump. In order to make DH competitive as heating source the needed price reduction is found for the hydronic floor and air heating system.Finally, three different building energy performance scenarios are studied in conjunction with the urban transformation in combination with the suggested energy measures from the Energy Performance certificates (EPC). In order to reach the national target entailing a reduction of 50% until 2050 all re-built buildings have to be built with passive standard and all advised measures in the EPC has to be carried out. Wort noticing is that the scenarios is analyzed as part of a 3-D City Model, which is found to be a worthwhile working tool for staff dealing with energy related issues.
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| 52. |
- Yang, Ting
(författare)
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Maturation of Clay Seals in Deep Bore Holes for Disposal of Radioactive waste : Theory and Experiments
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- KBS-3 and very deep borehole (VDH) concepts are two major types of long-term geologicaldisposal methods for high-level radioactive waste (HLW) isolating from the biosphere. TheKBS-3V concept for isolating the HLW at the depth of 400-500 m, is the officially proposedoption in Sweden and has been the subject of considerable research in the past few decades,while the VDH concept was considered as an option in the 1950s but later became discouragedbecause of insufficient experience in drilling technology. The greatest merit of the VDHconcept is that the almost stagnant groundwater in the deep boreholes prevents the transport ofthe possible release of radionuclides into the rock or up to the ground level. Since variousdisadvantages of the KBS-3V concept were found in previous research, the superiority of VDHconcept attracted the researchers to continue studying it into the late 1980s.The geological repositories of both of KBS-3V and VDH types primarily consist of a naturalbarrier (host rock) and of an engineering barrier (also known as a buffer/backfill barrier).According to the principle of IAEA and national relative research organizations, thebuffer/backfill material should have low permeability and good expandability, as well assuitable physical and sealing properties.The thesis concerns the VDH concept and is focused on the construction and performance ofthose parts of the sealed repository that are not affected by high temperature or gamma radiation.In the lower part of a VDH repository, the clay packages containing HLW will be exposed tohigh temperature (100-150 ? ) in the borehole and to highly saline groundwater. In theinstallation phase of HLW, the groundwater will be pumped out and replaced by medium-softsmectite clay mud in which the HLW packages are installed vertically. During the hydrationand maturation of the clay components, the microstructural reorganization, water transport,migration of clay particles and redistribution of the density of the components take place. Thematuration determines the transient evolution of the clay seals and influences the rheologicaland soil mechanical behavior in the installation phase. The maturation of clay system alsodetermines their ultimate sealing potential of VDH repositories.This study presents the work carried out for investigating the maturation of the buffer-backfillclay in the HLW deep borehole. Initially in the study three types of clays, the Namontmorillonite,magnesium-rich and illite-smectite mixed layer clays, were examined for estimating their performance as the barrier candidate material. This is mainly presented in theliterature review. The experimental study was conducted on montmorillonite GMZ clays andI/S mixed-layer Holmehus clay. The expandability and permeability tests were carried out forinterpretation of the recorded swelling development and assessment of the effect of the salineconditions, with the goal of deriving a relationship between swelling pressure and hydraulicconductivity for different dry densities. The maturation tests of initially fully-saturatedHolmehus clay and partly saturated GMZ clay were performed. During the tests, the shearstrength mobilised by the relative movement of densified mud and migrated dense clay -contained in a perforated central tube - were determined. According to the results of shearstrength tests, the maximum operation time or the number of clay packages to be placed in asingle operation was evaluated, whilst the suitable saturation degree of the dense clay wasdiscussed as well.A model of the maturation of initially water-saturated clay seals based on Darcy’s law wasworked out and the evolution of the clay components in a lab-scale borehole using Holmehusclay were performed and compared with the experimental recordings. Good agreementsbetween the physical behaviors of the theoretical simulations and the measurements wasachieved by which the validity of the model was verified. Using the results, the hydration andsoil migration in the entire maturation process were presented in diagram. The model was alsoused for preliminary evaluation of the maturation products in real boreholes by assuming thesame Holmehus clay as used in the tests. Two constellation of borehole and dense clay withdifferent diameters, 80 cm borehole /60 cm clay and 80cm/50cm, were assumed. The resultsrespecting dry density and hydraulic conductivity of the ultimate maturation products, and thedegree of homogeneous of the buffer and backfill clay system in the assumed boreholes, arepresented and discussed. The options of different mineral types and initial physical propertiesof the candidate buffer clays provide a reference for engineering barrier design of HLW disposalin VDH.
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| 53. |
- Zhuang, Linqi
(författare)
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Effects of Non-uniform Fiber Distribution on Fiber/matrix Interface Crack Propagation in Polymeric Composites
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fiber/matrix interface cracking plays an important role in determining the final failureof unidirectional (UD) composites. When subjected to longitudinally tensile loading,fiber/matrix interface debonds originate from fiber breaks or initial defects propagatealong loading direction. Depending on the quality of fiber/matrix interface, debondscould keep growing longitudinally which leads to the degradation of compositestiffness or kink out of interface and connect with neighboring debonds or fiberbreaks that forms a so called critical fracture plane which leads to the final failure ofUD composite. For UD composite subjected to transversely tensile loading, theinitiation, growth and coalesce of arc-shape fiber/matrix interface debonds result inthe formation of macro-size transverse cracks, the propagation and multiplication ofthese transverse cracks, although would not directly lead to the final failure ofcomposite, could cause significant stiffness degradation of composite structures.In the presence thesis, the growth of a fiber/matrix interface debond of a UDcomposite with hexagonal fiber packing under longitudinal and transverse tensileloading was investigated numerically, with the special focus on the influence ofneighboring fibers. In the current study, energy release rate (ERR) is considered as thedriving force for the debond growth and was calculated based on J Integral andVirtual Crack Closure Technique (VCCT) using finite element software ANSSY.Papers A – C in the present thesis deal with the influence of neighboring fibers on theERR of a debond emanating from a fiber break under longitudinal loading condition.In longitudinal loading case, debond growth is mode II dominated. In paper A, anaxisymmetric model consisting 5 concentric cylinders that represent broken fiber withdebond, surrounding matrix, neighboring fibers, surrounding matrix and effectivecomposite was generated. It’s found that there are two stages of debond growth, thefirst stage is when debond length is short, the ERR decreases with increasing debondlength, and the presence of neighboring fibers significantly increase the ERR ofdebond. For relatively long debond, the debond growth is steady when ERR is almostconstant regardless of debond length. In steady state of debond growth, the presenceof neighboring fibers have little effect on the ERR. In papers B and C, a 3-D modelwas generated with broken fiber and its 6 nearest fibers in a hexagonal packed UDcomposite were modelled explicitly, surrounded by the homogenized composite.Based on the obtained results, it’s shown that ERR is varying along debond front, andhas its maximum at the circumferential location where the distance between two fibercenter is the smallest. This indicates that the debond front is not a circle. For steadystate debond, the presence of neighboring fibers have little effect on averaged ERR(averages of ERR along debond front). For short debond, the presences ofneighboring fibers increases the averaged ERR, and that increase is more significantwhen inter-fiber distance is the smallest. Paper D investigates the growth of afiber/matrix debond along fiber circumference under transverse loading. It’s foundthat debond growth in this case is mixed-mode, and both mode I and mode II ERRcomponents increase with increasing debond angle and then decreases. Debondgrowth is mode I dominated for small debond angle and then switch to mode IIdominated. The presence of neighboring fibers have an enhancement effect on debondgrowth up to certain small debond angle and then changes to a protective effect. InPaper E, the interaction between two arc-size debond under transverse loading isinvestigated. It’s found that when two debonds are close to each other, the interactionbetween two debond becomes much stronger, and that interaction leads to the increaseof ERR of each debond significantly, which facilitates further growth for bothdebond.
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