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- Funehag, Johan, 1975, et al.
(författare)
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How the Pressure Build-Up Affects the Penetration Length of Grout-New Formulation of Radial Flow of Grout Incorporating Variable Pressure
- 2017
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Ingår i: Geotechnical Special Publication. - Reston, VA : American Society of Civil Engineers. - 0895-0563. - 9780784480793 ; 0:288, s. 143-151
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Konferensbidrag (refereegranskat)abstract
- For around two decades of research and development in the field of grouting in hard jointed rock, the design process has taken some leaps forward. Stille and Gustafson, 2005 and Funehag and Gustafson 2008, shows how a grouting design can be computed. A grouting design in hard rock can based on the penetration length of grout in rock fractures. The design comprises considerations of the fracture apertures in the rock mass, the type of grout and its rheological properties and how the grout is injected i.e pressure and grouting times. When knowing these parameters an optimized geometry fitting the design is made. Thörn, et al, 2014 describes a fundamental analysis with a comprehensive tool to retrieve the fracture distribution and aperture distribution of the fractures crossing a cored borehole. The data needed about the core is geological mapping and hydraulic section tests. In Gustafson, Claesson and Fransson, (2013) a full derivation of a radial Bingham flow in a slit is described for constant pressure. By optimizing with a specific pressure and an efficient grouting time (efficient time means the time when the pressure has reached the designed pressure) a prognosis a more realistic time consumption for grouting can be computed. However, the time it takes to reach a certain pressure is dependent on the capacity of the pump and the how large the fractures widths are. For poorly chosen pumps together with large fractures the time to reach the design pressure can be significant. The overall objective for this new formulation was to involve the grouting pressure as a variable rather than constant. A pressure build-up mimic more a realistic pumping scenario which enables better prognosis of grouting works. This paper brings up this new formulation of the radial Bingham flow with variable injection pressure in slit. The benefits of this new formulation is that it can easily be integrated in other computer programs. One program that uses this new formulation is a grouting simulator owned and developed by Edvirt AB. The simulator has been used to pedagogically demonstrate how a variable pressure and restrictions in grout flow (the pump capacity) affect the penetration length. Further, the results show that it can be used to predict suitable pump capacity to fit the coming grouting works.
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| 2. |
- Claesson, Johan, 1943, et al.
(författare)
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A load-aggregation method to calculate extraction temperatures of borehole heat exchangers
- 2012
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Ingår i: ASHRAE Transactions. - 0001-2505. ; 118:1, s. 530-539
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Konferensbidrag (refereegranskat)abstract
- Hourly simulations of extraction fluid temperatures from borehole heat exchangers tend to be very time consuming. A new load aggregation scheme to perform long-term simulations of borehole heat exchangers is presented. The starting point is the step-response function for the considered borehole heat exchanger and the corresponding long sequence of cells, each with a load and a weighting factor. On the first level, the original weighting factors are kept. On the following levels, 2, 4, 8, etc., the weighting factors are lumped together. The lumped weighting factors are obtained directly from the step-response function. The number of cells to be lumped together is chosen so that the extraction temperatures using lumped weighting factors give a sufficiently good approximation of the non-aggregated scheme. The new scheme is applied to a test case to simulate extraction fluid temperature over a 20-year time period. Comparison of the results from the new scheme with the non-aggregated setting shows that the new scheme can perform very accurate and fast simulations of borehole heat exchangers.
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| 3. |
- Claesson, Johan, 1943
(författare)
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BOLTZMANN SOLUTION OF COUPLED NONLINEAR EQUATIONS FOR MOISTURE CONTENT w(s) AND TEMPERATURE T(s), s=x/root(4t). BENCHMARK TEST I, CEN (2002).
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- There are many models for coupled moisture and heat flow in porous building materials. A question is how accurate the various models are. There is a need to compare the models with a solution with high and well documented accuracy. The model with its Mathcad files presented here tries to meet that need. It was originally presented in Dresden 2002 at a CEN meeting. The solution is now used in a provisional European standard:•European Provisional Standard prEN 15026, Hygrothermal Performance of Building Components and Building Elements – Assessment of Moisture Transfer by Numerical Simulation, 2005. The presented model may be summarized in the following way:•Highly non-linear coupled moisture and heat flow •Highly unbalanced time scales between moisture content w and temperature T•Any functional relations for flow coefficients and state functions are easily implemented•Directly verified accuracy from with errors in the equations below 0.03 %. •Implemented in Mathcad.
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| 4. |
- Claesson, Johan, 1943, et al.
(författare)
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Explicit Multipole Formulas for Calculating Thermal Resistance of Single U-Tube Ground Heat Exchangers
- 2018
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Borehole thermal resistance is both an important design parameter and a key performance characteristic of a ground heat exchanger. Another quantity that is particularly important for ground heat exchangers is the internal thermal resistance between the heat exchanger pipes. Both these resistances can be calculated to a high degree of accuracy by means of the well-known multipole method. However, the multipole method has a fairly intricate mathematical algorithm and is thus not trivial to implement. Consequently, there is considerable interest in developing explicit formulas for calculating borehole resistances. This paper presents derivation and solutions of newly derived second-order and higher-order multipole formulas for calculating borehole thermal resistance and total internal thermal resistance of single U-tube ground heat exchangers. A new and simple form of the first-order multipole formula is also presented. The accuracy of the presented formulas is established by comparing them to the original multipole method. The superiority of the new higher-order multipole formulas over the existing formulas is also demonstrated.
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| 5. |
- Claesson, Johan, 1943
(författare)
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HOT-DISC METHOD APPLIED TO AN INSULATION COATED WITH A THIN, HIGHLY CONDUCTIVE LAYER. MATHEMATICAL REPORT
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The paper “Transient plane source techniques for thermal conductivity and thermal diffusivity measurements of solid materials” by Silas E. Gustafsson, 1991, presents the following method to measure thermal conductivity. A small, thin circular disc is placed in the center between two slabs of the studied material. The disc is heated electrically. The mean temperature over the disc area is measured as function of time. The thermal conductivity and thermal diffusivity is determined by fitting an analytical solution to the measured temperature curve. The analytical solution for a constant heat source in a circular thin plate imbedded in an infinite surrounding volume of the material is presented by Gustafsson in the paper and preceding publications in the reference list of the paper. In the first part of this study, this analytical solution is derived in a different way that gives somewhat more concise formulas, which require less computer time. The hot-disc method has been used by P. Johansson et al. to determine the thermal conductivity of vacuum insulation panels. A complication is that the panel is coved by a layer of aluminum coating. The coating is quite thin but the thermal conductivity of the coating is up to 1000 times larger than that of the vacuum insulation panel. The heat flow along the coating cannot be neglected. The second part of this study deals with this more complicated transient thermal problem. An analytical solution in the more complicated case is presented in full detail. An explicit formula for the Laplace transform is derived. The solution in the time domain is obtained from an inversion integral in the complex plane. The two solutions are studied in detail in six appended
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| 8. |
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| 9. |
- Gustafson, Gunnar, 1945, et al.
(författare)
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Steering Parameters for Rock Grouting
- 2013
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Ingår i: Journal of Applied Mathematics. - : Hindawi Limited. - 1110-757X .- 1687-0042. ; 2013, s. Art. no. 269594-
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Tidskriftsartikel (refereegranskat)abstract
- In Swedish tunnel grouting practice normally a fan of boreholes is drilled ahead of the tunnel front where cement grout is injected in order to create a low permeability zone around the tunnel. Demands on tunnel tightness have increased substantially in Sweden and this has led to a drastic increase of grouting costs. Based on the flow equations for a Bingham fluid the penetration of grout as a function of grouting time is calculated. This shows that the time-scale of grouting in a borehole is only determined by grouting over-pressure and the rheological properties of the grout, thus parameters that the grouter can choose. Pressure, grout properties and the fracture aperture determine the maximum penetration of the grout. The smallest fracture aperture that requires to be sealed thus also governs the effective borehole distance. Based on the identified parameters that define the grouting time-scale and grout penetration an effective design of grouting operations can be set up.
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| 10. |
- Hagentoft, Carl-Eric, 1958, et al.
(författare)
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Influence of rain water percolation on ground heat losses and temperature for basement foundation
- 2006
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Ingår i: 3nd International Conference on Research in Building Physics and Building Engineering, Montreal, August 2006.. - 9780415416757 ; , s. 967-971
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Konferensbidrag (refereegranskat)abstract
- This paper presents analytical formulae and numerical results for the influence of water percolation on the ground temperature and the heat loss in the case of basement foundation. The influence of flowing ground water is presented as a function depending on non-dimensional parameters, accounting for flow rate, height and thermal insulation of the wall and the thermal conductivity of the soil. The results and the example suggest that the influence from the flowing ground water is in the order of one or a few percentage only.
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