| 1. |
- Acuña, José, 1982-
(författare)
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Distributed thermal response tests : New insights on U-pipe and Coaxial heat exchangers in groundwater-filled boreholes
- 2013
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Konstnärligt arbete (övrigt vetenskapligt/konstnärligt)abstract
- U-pipe Borehole Heat Exchangers (BHE) are widely used today in ground source heating and cooling systems in spite of their less than optimal performance. This thesis provides a better understanding on the function of U-pipe BHEs and Investigates alternative methods to reduce the temperature difference between the circulating fluid and the borehole wall, including one thermosyphon and three different types of coaxial BHEs.Field tests are performed using distributed temperature measurements along U-pipe and coaxial heat exchangers installed in groundwater filled boreholes. The measurements are carried out during heat injection thermal response tests and during short heat extraction periods using heat pumps. Temperatures are measured inside the secondary fluid path, in the groundwater, and at the borehole wall. These type of temperature measurements were until now missing.A new method for testing borehole heat exchangers, Distributed Thermal Response Test (DTRT), has been proposed and demonstrated in U-pipe, pipe-in-pipe, and multi-pipe BHE designs. The method allows the quantification of the BHE performance at a local level.The operation of a U-pipe thermosyphon BHE consisting of an insulated down-comer and a larger riser pipe using CO2 as a secondary fluid has been demonstrated in a groundwater filled borehole, 70 m deep. It was found that the CO2 may be sub-cooled at the bottom and that it flows upwards through the riser in liquid state until about 30 m depth, where it starts to evaporate.Various power levels and different volumetric flow rates have been imposed to the tested BHEs and used to calculate local ground thermal conductivities and thermal resistances. The local ground thermal conductivities, preferably evaluated at thermal recovery conditions during DTRTs, were found to vary with depth. Local and effective borehole thermal resistances in most heat exchangers have been calculated, and their differences have been discussed in an effort to suggest better methods for interpretation of data from field tests.Large thermal shunt flow between down- and up-going flow channels was identified in all heat exchanger types, particularly at low volumetric flow rates, except in a multi-pipe BHE having an insulated central pipe where the thermal contact between down- and up-coming fluid was almost eliminated.At relatively high volumetric flow rates, U-pipe BHEs show a nearly even distribution of the heat transfer between the ground and the secondary fluid along the depth. The same applies to all coaxial BHEs as long as the flow travels downwards through the central pipe. In the opposite flow direction, an uneven power distribution was measured in multi-chamber and multi-pipe BHEs.Pipe-in-pipe and multi-pipe coaxial heat exchangers show significantly lower local borehole resistances than U-pipes, ranging in average between 0.015 and 0.040 Km/W. These heat exchangers can significantly decrease the temperature difference between the secondary fluid and the ground and may allow the use of plain water as secondary fluid, an alternative to typical antifreeze aqueous solutions. The latter was demonstrated in a pipe-in-pipe BHE having an effective resistance of about 0.030 Km/W.Forced convection in the groundwater achieved by injecting nitrogen bubbles was found to reduce the local thermal resistance in U-pipe BHEs by about 30% during heat injection conditions. The temperatures inside the groundwater are homogenized while injecting the N2, and no radial temperature gradients are then identified. The fluid to groundwater thermal resistance during forced convection was measured to be 0.036 Km/W. This resistance varied between this value and 0.072 Km/W during natural convection conditions in the groundwater, being highest during heat pump operation at temperatures close to the water density maximum.
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| 2. |
- Darabi, H., et al.
(författare)
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Development of a novel hybrid multi-boosting neural network model for spatial prediction of urban flood
- 2021
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Ingår i: Geocarto International. - : Taylor and Francis Ltd.. - 1010-6049 .- 1752-0762.
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a new hybridized machine learning algorithm for urban flood susceptibility mapping, named MultiB-MLPNN, was developed using a multi-boosting technique and MLPNN. The model was tested in Amol City, Iran, a data-scarce city in an ungauged area which is prone to severe flood inundation events and currently lacks flood prevention infrastructure. Performance of the hybridized model was compared with that of a standalone MLPNN model, random forest and boosted regression trees. Area under the curve, efficiency, true skill statistic, Matthews correlation coefficient, misclassification rate, sensitivity and specificity were used to evaluate model performance. In validation, the MultiB-MLPNN model showed the best predictive performance. The hybridized MultiB-MLPNN model is thus useful for generating realistic flood susceptibility maps for data-scarce urban areas. The maps can be used to develop risk-reduction measures to protect urban areas from devastating floods, particularly where available data are insufficient to support physically based hydrological or hydraulic models.
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| 3. |
- Bin, Jiang, 1965-, et al.
(författare)
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Automatic generation of the axial lines of urban environments to capture what we perceive
- 2010
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Ingår i: International Journal of Geographical Information Science. - London : Taylor & Francis Group. - 1365-8816 .- 1365-8824 .- 1362-3087. ; 24:4, s. 545-558
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Tidskriftsartikel (refereegranskat)abstract
- Based on the concepts of isovists and medial axes, we developed a set of algorithms that can automatically generate axial lines for representing individual linearly stretched parts of open space of an urban environment. Open space is the space between buildings, where people can freely move around. The generation of the axial lines has been a key aspect of space syntax research, conventionally relying on hand-drawn axial lines of an urban environment, often called axial map, for urban morphological analysis. Although various attempts have been made towards an automatic solution, few of them can produce the axial map that consists of the least number of longest visibility lines, and none of them really works for different urban environments. Our algorithms provide a better solution than existing ones. Throughout this paper, we have also argued and demonstrated that the axial lines constitute a true skeleton, superior to medial axes, in capturing what we perceive about the urban environment.
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| 4. |
- Bin, Jiang, 1965-, et al.
(författare)
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Computing the fewest-turn map directions based on the connectivity of natural roads
- 2011
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Ingår i: International Journal of Geographical Information Science. - London : Taylor & Francis Group. - 1365-8816 .- 1365-8824 .- 1362-3087. ; 25:7, s. 1069-1082
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we introduced a novel approach to computing the fewest-turn map directions or routes based on the concept of natural roads. Natural roads are joined road segments that perceptually constitute good continuity. This approach relies on the connectivity of natural roads rather than that of road segments for computing routes or map directions. Because of this, the derived routes posses the fewest turns. However, what we intend to achieve are the routes that not only possess the fewest turns, but are also as short as possible. This kind of map direction is more effective and favorable by people, because they bear less cognitive burden. Furthermore, the computation of the routes is more efficient, since it is based on the graph encoding the connectivity of roads, which is significantly smaller than the graph of road segments. We made experiments applied to eight urban street networks from North America and Europe in order to illustrate the above stated advantages. The experimental results indicate that the fewest-turn routes posses fewer turns and shorter distances than the simplest paths and the routes provided by Google Maps. For example, the fewest-turn-and-shortest routes are on average 15% shorter than the routes suggested by Google Maps, while the number of turns is just half as much. This approach is a key technology behind FromToMap.org - a web mapping service using openstreetmap data.
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| 5. |
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Proceedings of the 14th ICOLD International Benchmark Workshop on Numerical Analysis of Dams
- 2017
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Proceedings (redaktörskap) (refereegranskat)abstract
- Every second year, the Technical Committee A (Computational Aspects of Dam Analysis and Design) of ICOLD organizes an international benchmark workshop on numerical analysis of dams. The purpose is to share knowledge and experience regarding numerical modelling within the fields of dam safety, planning, design, construction as well as operation and maintenance of dams. The Terms of Reference for Committee A state; ”BenchmarkWorkshops are organised to compare numerical models between one another and/or with reference solutions, including the dissemination and publication of results”. The 14th ICOLD International Benchmark Workshop on Numerical Analysis of Dams was held from the 6th to the 8th September 2017 in Stockholm, the capital of Sweden. It was organized by the Local Organizing Committee, on behalf of the Swedish National Committee of ICOLD (SwedCold) and the ICOLD Technical Committee A. It was hosted by KTH Royal Institute of Technology, Sweden’s largest technical research and learning institution and one of Europe’s leading technical universities. With respect to hydropower and dam engineering, KTH has for many years been active within of the Swedish hydropower Center (SVC), a key centre for research and educational activities in Sweden. SwedCOLD established in 1931, and is one of the oldest members of the International Commission On Large Dams, ICOLD. The development of hydro power for electricity production was initiated in the late 19th century and made the large scale industrialisation in Sweden possible. About 2000 hydropower plants are in operation in Sweden today, producing almost half of the total electricity supply. Considering the many and relatively old dams in Sweden, organizing the benchmark workshop was important to increase the knowledge regarding managing aging hydropower structures.The 14th ICOLD International Benchmark Workshop has addressed current challenges regarding design and maintenance of existing dams and improved the understanding of these by exchange of experience on the use of numerical modelling for design, performance evaluation and safety assessment of dams. On behalf of the organizing committee, I would like to express my sincere appreciation to the formulators/moderators of each theme for their outstanding work to prepare the themes, reviewing the papers and evaluating the results. I also want to thank all participants to the benchmark workshop for their contributions and their presence to this benchmark workshop. Finally, the support from the Technical Committee A and the support from the companies and organizations that sponsored this benchmark workshop is gratefully acknowledged.
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| 6. |
- Theland, Freddie, 1989-, et al.
(författare)
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Dynamic response of driven end-bearing piles and a pile group in soft clay: an experimental validation study
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents an extensive measurement campaign of the dynamic response of driven end-bearing piles and a pile group in soft clay. Results from measurements conducted on the free-top piles and and the piles joined in a concrete cap are presented. The measured frequency responses are subsequently used to obtain the impedances, characterising the dynamic stiffness and damping of the piles and the pile foundation. The piles are instrumented with accelerometers at several points along the length of the piles which allows to validate the dynamic motion of the piles atdepth due to pile head and pile cap excitation. Numerical predictions based solely on information of the small-strain soil properties obtained from extensive site investigations are compared to the experimental results. The numerical model captures the pile-soil-pile interactions and the motion of the piles within the soil well, suggesting that reliable predictions can be made for the considered soil conditions if the small-strain soil properties are well known.
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| 7. |
- Alizadeh Khameneh, Mohammad Amin, et al.
(författare)
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Optimization of deformation monitoring networks using finite element strain analysis
- 2018
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Ingår i: Journal of Applied Geodesy. - : Walter de Gruyter GmbH. - 1862-9016 .- 1862-9024. ; 2:2, s. 187-197
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Tidskriftsartikel (refereegranskat)abstract
- An optimal design of a geodetic network can fulfill the requested precision and reliability of the network, and decrease the expenses of its execution by removing unnecessary observations. The role of an optimal design is highlighted in deformation monitoring network due to the repeatability of these networks. The core design problem is how to define precision and reliability criteria. This paper proposes a solution, where the precision criterion is defined based on the precision of deformation parameters, i. e. precision of strain and differential rotations. A strain analysis can be performed to obtain some information about the possible deformation of a deformable object. In this study, we split an area into a number of three-dimensional finite elements with the help of the Delaunay triangulation and performed the strain analysis on each element. According to the obtained precision of deformation parameters in each element, the precision criterion of displacement detection at each network point is then determined. The developed criterion is implemented to optimize the observations from the Global Positioning System (GPS) in Skåne monitoring network in Sweden. The network was established in 1989 and straddled the Tornquist zone, which is one of the most active faults in southern Sweden. The numerical results show that 17 out of all 21 possible GPS baseline observations are sufficient to detect minimum 3 mm displacement at each network point. © 2018 Walter de Gruyter GmbH, Berlin/Boston.
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| 8. |
- Bjurström, Henrik, et al.
(författare)
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Comparative Seismic Laboratory and Non-Contact Field Measurements of Asphalt Concrete
- 2016
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Ingår i: 2016 Structural Materials Technology Paper Summaries.
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Konferensbidrag (refereegranskat)abstract
- Non-contact acoustic field measurements are performed on a newly built highway to characterize the real part of the dynamicmodulus of the asphalt concrete (AC) top layer. The in situ measurements are performed using an array of 48 micro-electromechanicalsystem (MEMS) sensors. Cores extracted from the field measurement positions are then examined in a laboratory usingseismic modal testing for comparison. The laboratory testing allows master curves to be constructed to characterize the AC over awide temperature and frequency range. It is demonstrated that the real parts of the dynamic moduli are consistent at the fieldtemperatures using the two test methods. The in situ measurements are also shown to be highly repeatable. The presentedcomparative study indicates a possible application for assuring the quality of AC based on mechanical properties using fast noncontactin situ measurements.
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| 9. |
- Ma, D., et al.
(författare)
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Numerical Simulation of Water–Silt Inrush Hazard of Fault Rock : A Three-Phase Flow Model
- 2022
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Ingår i: Rock Mechanics and Rock Engineering. - : Springer Nature. - 0723-2632 .- 1434-453X. ; 55:8, s. 5163-5182
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Tidskriftsartikel (refereegranskat)abstract
- Fault rock is a typical hazardous material of water–silt inrush during the excavation in underground mines. To investigate hydraulic characteristics of fault rock during the water–silt inrush, a one-dimensional radial three-phase flow model of water–rock–silt was established in this study. In the proposed model, the mass conservation and continuity equations of the three-phase flow were obtained; the rock particle migration and the momentum conservation of the three-phase fluid migration were described by erosion constitutive equations and non-Darcy flow equations, respectively. The laboratory tests of porosity and the evolution of volume discharge rate were compared, and the accuracy of the proposed three-phase model was verified by the comparison results. From the test and numerical results, a high standard deviation of repeated results is observed in the case with high silt concentrations, and the erosion effect is inhibited by the silt flow. Last but not least, the temporal–spatial distribution of hydraulic properties is obtained by the numerical simulation: With the progress of the three-phase flow, rock particles near the fluid outlet are first fluidized and constantly migrate outward, resulting in an increase of the porosity and permeability in fault rock. Subsequently, water-conducting pathways are gradually formed inside the fault rock, and then more fluidized rock particles flow out. Finally, the fluidized rock particles have completely migrated, and the porosity and permeability tend to be stable with the more significant non-uniform spatial distribution.
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| 10. |
- Ma, Dan, et al.
(författare)
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Water–rock two-phase flow model for water inrush and instability of fault rocks during mine tunnelling
- 2023
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Ingår i: International Journal of Coal Science and Technology. - : Springer Nature. - 2095-8293 .- 2198-7823. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Water inrush hazard is one of the major threats in mining tunnel construction. Rock particle migration in the seepage process is the main cause of water inrush pathway and rock instability. In this paper, a radial water–rock mixture flow model is established to study the evolution laws of water inrush and rock instability. The reliability of the proposed model is verified by the experimental data from a previous study. Through the mixture flow model, temporal-spatial evolution laws of different hydraulic and mechanical properties are analysed. And the proposed model’s applicability and limitations are discussed by comparing it with the existing water inrush model. The result shows that this model has high accuracy both in temporal evolution and spatial distribution. The accuracy of the model is related to the fluctuation caused by particle migration and the deviation of the set value. During the seepage, the porosity, permeability, volume discharge rate and volume concentration of the fluidized particle increase rapidly due to the particle migration, and this phenomenon is significant near the fluid outlet. As the seepage progresses, the volume concentration at the outlet decreases rapidly after reaching the peak, which leads to a decrease in the growth rate of permeability and porosity, and finally a stable seepage state can be maintained. In addition, the pore pressure is not fixed during radial particle migration and decreases with particle migration. Under the effect of particle migration, the downward radial displacement and decrease in effective radial stress are observed. In addition, both cohesion and shear stress of the rock material decreased, and the rock instability eventually occurred at the outlet.
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