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Ohlsson, K. A., Östin, R., Staffan, G. & Olofsson, T. (2016). Dynamic model for measurement of convective heat transfer coefficient at external building surfaces. Journal of Building Engineering, 7, 239-245
Öppna denna publikation i ny flik eller fönster >>Dynamic model for measurement of convective heat transfer coefficient at external building surfaces
2016 (Engelska)Ingår i: Journal of Building Engineering, ISSN 2352-7102, Vol. 7, s. 239-245Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Uncertainties in current empirical models for the convective heat transfer coefficient (CHTC) have large impact on the accuracy of building energy simulations (BES). These models are often based on measurements of the CHTC, using a heated gradient sensor, where steady-state convective air flow is assumed. If this requirement is not fulfilled there will be a dynamic measurement error. The objectives were to construct a validated dynamic model for the heated gradient sensor, and to use this model to improve accuracy by suggesting changes in sensor design and operating procedure. The linear thermal network model included three state-space variables, selected as the temperatures of the three layers of the heated gradient sensor. Predictions of the major time constant and temperature time evolution were in acceptable agreement with experimental results obtained from step-response experiments. Model simulations and experiments showed that the sensor time constant increases with decreasing CHTC value, which means that the sensor response time is at maximum under free convection conditions. Under free convection, the surface heat transfer resistance is at maximum, which cause enhanced heat loss through the sensor insulation layer. Guidelines are given for selection of sampling frequency, and for evaluation of dynamic measurement errors.

Ort, förlag, år, upplaga, sidor
Elsevier, 2016
Nyckelord
Convective heat transfer coefficient, Heat balance, Measurement uncertainty, Thermal network modelling, Dynamic sensor model
Nationell ämneskategori
Annan fysik
Identifikatorer
urn:nbn:se:umu:diva-121735 (URN)10.1016/j.jobe.2016.06.005 (DOI)000397386000024 ()2-s2.0-84978427729 (Scopus ID)
Forskningsfinansiär
KempestiftelsernaEnergimyndigheten, 39699-1
Tillgänglig från: 2016-06-08 Skapad: 2016-06-08 Senast uppdaterad: 2018-08-08Bibliografiskt granskad
Grundberg, S. & Girhammar, U. A. (2015). A Comparison of Exact and Approximate Analyses of Partially Interacting Composite Beam-Columns. In: J. Kruis, Y. Tsompanakis and B.H.V. Topping (Ed.), Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing: . Paper presented at The Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing. Stirlingshire, UK: Civil-Comp Press, Article ID 261.
Öppna denna publikation i ny flik eller fönster >>A Comparison of Exact and Approximate Analyses of Partially Interacting Composite Beam-Columns
2015 (Engelska)Ingår i: Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing / [ed] J. Kruis, Y. Tsompanakis and B.H.V. Topping, Stirlingshire, UK: Civil-Comp Press , 2015, artikel-id 261Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Solutions of the static Euler-Bernoulli equations of composite beam-columns with interlayer slip have been compared with an approximate theory. The inter-layer force was taken to be proportional to the inter-layer slip. The general solutions were obtained for four different sets of boundary conditions corresponding to the four Euler cases: clamped-free, pinned-pinned, clamped-pinned and clamped-clamped. A transverse static point load was considered. The beam was axially loaded. The contribution of the axial force to the bending moment, or equivalently the work done by the axial force on the beam due to its deflection, was taken into account in the second order theory and neglected in the first order theory. In the approximate theory the second order effects were described by an approximate magnification factor obtained from critical loads calculated by approximating the buckling length coefficients of the composite beam with interlayer slip by the buckling length coefficients of a solid beam. The contribution of second order effects to deflections and internal actions were calculated in terms of exact magnification factors at different stiffness of the composite action and the results were compared with the approximate theory. Two composite beams were considered. The first was a combination of concrete and timber and the second was a combination of concrete and steel. The positions of the maximum internal shear forces were shown to occur at different positions in the two layers of the beam of concrete and steel when the exact first and second order calculations were compared. The approximate theory was fairly accurate for the deflection but showed higher deviations for other quantities. The approximate theory needs further evaluation. The exact results have been obtained by analytical calculations in combination with numerical evaluation.

Ort, förlag, år, upplaga, sidor
Stirlingshire, UK: Civil-Comp Press, 2015
Serie
Civil-Comp Proceedings, ISSN 1759-3433 ; 108
Nyckelord
composite beam-columns, partial interaction, interlayer slip, approximate analysis, magnification factors, timber structures
Nationell ämneskategori
Materialteknik
Forskningsämne
hållfasthetslära
Identifikatorer
urn:nbn:se:umu:diva-114536 (URN)10.4203/ccp.108.261 (DOI)978-1-905088-63-8 (ISBN)
Konferens
The Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing
Forskningsfinansiär
EU, Europeiska forskningsrådet
Tillgänglig från: 2016-01-22 Skapad: 2016-01-22 Senast uppdaterad: 2018-06-07Bibliografiskt granskad
Grundberg, S., Girhammar, U. A. & Hassan, O. A. B. (2014). Vibration of axially loaded and partially interacting composite beams. International Journal of Structural Stability and Dynamics, 14(1), 1350047
Öppna denna publikation i ny flik eller fönster >>Vibration of axially loaded and partially interacting composite beams
2014 (Engelska)Ingår i: International Journal of Structural Stability and Dynamics, ISSN 0219-4554, Vol. 14, nr 1, s. 1350047-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The vibrations of axially loaded composite beams with partial interaction are considered. The equations of motion and the pertaining boundary conditions are derived from Hamilton's principle. Mainly free — but also forced — vibrations are considered. The natural frequencies are calculated as a function of the axial force and the stiffness of the interaction between the layers. The analytical result obtained for the eigenfrequencies of the simply supported beam is taken as a starting point for an approximation of the eigenfrequencies of beams subject to other boundary conditions. The proposed approximation — which has no numerical fitting parameters — is shown to be in good agreement with the exact solutions, especially for the case of a beam clamped at both ends.

Ort, förlag, år, upplaga, sidor
Singapore: World Scientific, 2014
Nyckelord
Composite beams, partial interaction, natural frequency, axial loading
Nationell ämneskategori
Samhällsbyggnadsteknik
Identifikatorer
urn:nbn:se:umu:diva-79579 (URN)10.1142/S0219455413500478 (DOI)000328902600002 ()
Forskningsfinansiär
EU, Europeiska forskningsrådet
Tillgänglig från: 2013-08-26 Skapad: 2013-08-26 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
Grundberg, S., Hassan, O. & Girhammar, U. A. (2012). Dynamics of axially loaded and partially Interacting  composite beams. In: ECCM15: 15th European Conference on Composite Materials. Paper presented at ECCM15 - 15th European Conference on composite materials, Venice, Italy, June 24-28, 2012. ECCM15
Öppna denna publikation i ny flik eller fönster >>Dynamics of axially loaded and partially Interacting  composite beams
2012 (Engelska)Ingår i: ECCM15: 15th European Conference on Composite Materials, ECCM15 , 2012Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

The aim of this paper is to study the dynamics of partially interacting composite beams subjectedto axial loads, a situation occurring in e.g. beam-columns. The eigenfrequencies arederived for the simply supported composite beam subjected to an axial force. Measurements ofthe fundamental frequencies of a simply supported composite beam consisting of three layersare carried out considering different values of the applied axial force. The agreement betweenthe theoretical and experimental results is discussed. It is also shown that the application ofthe axial force introduces frictional moments at the boundaries, which make the experimentalboundary conditions deviate somewhat from those of an ideal simply supported beam.

Ort, förlag, år, upplaga, sidor
ECCM15, 2012
Nyckelord
Dynamics of composite materials, natural frequency, axial loading, boundary conditions of beams
Nationell ämneskategori
Samhällsbyggnadsteknik
Forskningsämne
teknisk fysik med inriktningen mikrosystemteknik
Identifikatorer
urn:nbn:se:umu:diva-54584 (URN)978-88-88785-33-2 (ISBN)
Konferens
ECCM15 - 15th European Conference on composite materials, Venice, Italy, June 24-28, 2012
Projekt
yes
Forskningsfinansiär
EU, Europeiska forskningsrådet
Tillgänglig från: 2012-05-01 Skapad: 2012-05-01 Senast uppdaterad: 2019-04-24Bibliografiskt granskad
Hassan, O., Grundberg, S. & Girhammar, U. A. (2012). Dynamics of partially interacting composite beams. In: Proceedings of the 15th European Conference on Composite Materials: . Paper presented at ECCM15 - 15th European Conference on composite materials, Venice, Italy, 24-28 June 2012.
Öppna denna publikation i ny flik eller fönster >>Dynamics of partially interacting composite beams
2012 (Engelska)Ingår i: Proceedings of the 15th European Conference on Composite Materials, 2012Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

In this work, a combined variational calculus and experimental approach are used to characterize the structural vibration behaviour of layered composite beams. Experimental dynamic tests are carried out on a composite simply supported beam with varied interaction strength between the layers. From the results, the influence of connections on the flexural natural frequencies, flexural deformation and damping is investigated. A good agreement between the derived theoretical equations and experimental results is obtained.

Nyckelord
Composite beams, structural vibrations, eigen frequency
Nationell ämneskategori
Samhällsbyggnadsteknik
Forskningsämne
teknisk fysik med inriktningen mikrosystemteknik
Identifikatorer
urn:nbn:se:umu:diva-54582 (URN)978-88-88785-33-2 (ISBN)
Konferens
ECCM15 - 15th European Conference on composite materials, Venice, Italy, 24-28 June 2012
Projekt
YES
Forskningsfinansiär
EU, Europeiska forskningsrådet
Tillgänglig från: 2012-05-01 Skapad: 2012-05-01 Senast uppdaterad: 2018-06-08Bibliografiskt granskad
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