Ändra sökning
Avgränsa sökresultatet
45678910 301 - 350 av 11613
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 301.
    Alfredsson, P. Henrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Kurian, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fransson, Jens H. M.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Segalini, A.
    Rüedi, Jean-Daniel
    Talamelli, Alessandro
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    The diagnostic plot: a new way to appraise turbulent boundary-layer data2009Ingår i: ADVANCES IN TURBULENCE XII: PROCEEDINGS OF THE 12TH EUROMECH EUROPEAN TURBULENCE CONFERENCE / [ed] Eckhardt, B., 2009, Vol. 132, s. 609-612Konferensbidrag (Refereegranskat)
  • 302.
    Alfredsson, P. Henrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    The viscous sublayer revisited-exploiting self-similarity to determine the wall position and friction velocity2011Ingår i: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 51, nr 1, s. 271-280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In experiments using hot wires near the wall, it is well known that wall interference effects between the hot wire and the wall give rise to errors, and mean velocity data from the viscous sublayer can usually not be used to determine the wall position, nor the friction velocity from the linear velocity distribution. Here, we introduce a new method that takes advantage of the similarity of the probability density distributions (PDF) or rather the cumulative distribution functions (CDF) in the near-wall region. By using the velocity data in the CDF in a novel way, it is possible to circumvent the problem associated with heat transfer to the wall and to accurately determine both the wall position and the friction velocity. Prior to its exploitation, the self-similarity of the distribution functions of the streamwise velocity fluctuations within the viscous sublayer is established, and it is shown that they can accurately be described by a lognormal distribution.

  • 303.
    Alfredsson, P. Henrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Segalini, Antonio
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    A new formulation for the streamwise turbulence intensity distribution2011Ingår i: 13th European Turbulence Conference (ETC13): Wall-Bounded Flows And Control Of Turbulence, Institute of Physics Publishing (IOPP), 2011, s. 022002-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Numerical and experimental data from zero pressure-gradient turbulent boundary layers over smooth walls have been analyzed by means of the so called diagnostic plot introduced by Alfredsson & Orlu [Eur. J. Fluid Mech. B/Fluids, 4 2, 403 (2010)]. In the diagnostic plot the local turbulence intensity is shown as a function of the local mean velocity normalized with a reference velocity scale. In the outer region of the boundary layer a universal linear decay of the turbulence intensity is observed independent of Reynolds number. The deviation from this linear region appears in the buffer region and seems to be universal when normalized with the friction velocity. Therefore, a new empirical fit for the streamwise velocity turbulence intensity distribution is proposed and the results are compared with up to date reliable high-Reynolds number experiments and extrapolated towards Reynolds numbers relevant to atmospherical boundary layers.

  • 304.
    Alfredsson, P. Henrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Segalini, Antonio
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    A new formulation for the streamwise turbulence intensity distribution in wall-bounded turbulent flows2012Ingår i: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 36, s. 167-175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The distribution of the streamwise velocity turbulence intensity has recently been discussed in several papers both from the viewpoint of new experimental results as well as attempts to model its behavior. In the present paper numerical and experimental data from zero pressure-gradient turbulent boundary layers, channel and pipe flows over smooth walls have been analyzed by means of the so called diagnostic plot introduced by Alfredsson & ÖrlÌ [P.H. Alfredsson, R. ÖrlÌ, The diagnostic plot-a litmus test for wall bounded turbulence data, Eur. J. Mech. B Fluids 29 (2010) 403-406]. In the diagnostic plot the local turbulence intensity is plotted as function of the local mean velocity normalized with a reference velocity scale. Alfredsson et al. [P.H. Alfredsson, A. Segalini, R. ÖrlÌ, A new scaling for the streamwise turbulence intensity in wall-bounded turbulent flows and what it tells us about the outer peak, Phys. Fluids 23 (2011) 041702] observed that in the outer region of the boundary layer a universal linear decay of the turbulence intensity independent of the Reynolds number exists. This approach has been generalized for channel and pipe flows as well, and it has been found that the deviation from the previously established linear region appears at a given wall distance in viscous units (around 120) for all three canonical flows. Based on these results, new empirical fits for the streamwise velocity turbulence intensity distribution of each canonical flow are proposed. Coupled with a mean streamwise velocity profile description the model provides a composite profile for the streamwise variance profile that agrees nicely with existing numerical and experimental data. Extrapolation of the proposed scaling to high Reynolds numbers predicts the emergence of a second peak of the streamwise variance profile that at even higher Reynolds numbers overtakes the inner one.

  • 305. Alfthan, J.
    et al.
    Gudmundson, Peter
    Östlund, S.
    Micro-mechanical model for mechanosorptive creep2000Konferensbidrag (Övrigt vetenskapligt)
  • 306.
    Alfthan, Johan
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Linear constitutive model for mechano-sorptive creep in paper2004Rapport (Övrigt vetenskapligt)
  • 307.
    Alfthan, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Linear constitutive model for mechano-sorptive creep in paper2005Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 42, nr 24-25, s. 6261-6276Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The creep of paper is accelerated by moisture cycling. This effect is known as mechano-sorptive creep. It is assumed that this is an effect of transient stresses produced during moisture content changes in combination with non-linear creep behaviour of the fibres. The stresses produced by the moisture content changes are often much larger than the applied mechanical loads. If this is the case, the mechanical loads are only a perturbation to the internal stress state, and it will appear as if the mechano-sorptive creep is linear in stress. It is possible to take advantage of this feature. In the present report the pure moisture problem is first solved. The mechanical load is then treated as a perturbation of the solution to the moisture problem. Using this strategy, it is possible to linearize a non-linear network model for mechano-sorptive creep and to formulate a continuum model. As a result, the number of variables in the model is reduced. This is a significant improvement as it will be possible to use the linearized model to describe the material in a finite element program and solve problems with complicated geometries.

  • 308.
    Alfthan, Johan
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Östlund, Sören
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    A micromechanical model for mechanosorptive creep in paper2002Ingår i: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, nr 3, s. 98-104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The creep of paper is accelerated by moisture cycling, a phenomenon known as mechanosorptive creep or accelerated creep. In this paper stress created at bonds due to anisotropic swelling during absorption and desorption of moisture, in combination with nonlinear creep, are proposed to be the cause for mechanosorptive creep. Two simplifled models are first discussed in order to demonstrate the suggested mechanism. A three-dimensional fibre network model composed of elastic fibres and inelastic bonds is then studied by finite element calculations. The relative sliding in the bonds is described by a nonlinear creep model which, in combination with anisotropic hygroexpansion of the fibres results in accelerated creep of the network.

  • 309. Ali, A.
    et al.
    Raza, Rizwan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Kaleem Ullah, M.
    Rafique, A.
    Wang, B.
    Zhu, Bin
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik. Hubei University, China.
    Alkaline earth metal and samarium co-doped ceria as efficient electrolytes2018Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, nr 4, artikel-id 043902Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Co-doped ceramic electrolytes M0.1Sm0.1Ce0.8O2-δ (M = Ba, Ca, Mg, and Sr) were synthesized via co-precipitation. The focus of this study was to highlight the effects of alkaline earth metals in doped ceria on the microstructure, densification, conductivity, and performance. The ionic conductivity comparisons of prepared electrolytes in the air atmosphere were studied. It has been observed that Ca0.1Sm0.1Ce0.8O2-δ shows the highest conductivity of 0.124 Scm-1 at 650 °C and a lower activation energy of 0.48 eV. The cell shows a maximum power density of 630 mW cm-2 at 650 °C using hydrogen fuel. The enhancement in conductivity and performance was due to increasing the oxygen vacancies in the ceria lattice with the increasing dopant concentration. The bandgap was calculated from UV-Vis data, which shows a red shift when compared with pure ceria. The average crystallite size is in the range of 37-49 nm. DFT was used to analyze the co-doping structure, and the calculated lattice parameter was compared with the experimental lattice parameter.

  • 310. Ali, R.
    et al.
    Noora, A.
    Fareed, M. M.
    Faraz, Z. -U.-A.A.
    Siyal, Shahid Hussain
    KTH.
    Computational analysis of PT/CT contact behavior for a heavy water reactor at high temperature and pressure2018Ingår i: Proceedings of 2018 15th International Bhurban Conference on Applied Sciences and Technology, IBCAST 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 645-650Konferensbidrag (Refereegranskat)
    Abstract [en]

    A computational model has been developed for a heavy water reactor (HWR) reactor to analyze the temperature distribution of the moderator and pressure tube and to determine the thermal stress analysis of pressure tube (PT) using the non linear elastic model for thermal expansion. For an IAEA ICSP problem, the experimental set up and model were developed by the Fuel Channel High Temperature Heat Transfer (FCHTHT) laboratory in Canada. In case of LOCA or primary heat transfer failure, PT experiences a significant heat flux that results in ballooning of PT. Following the PT deformation, PT/CT contact may occur and thus there is spike in heat flux at calandria tube (CT) resulting in the local dryout of CT. The study was divided into two parts, pre-contact phase and contact phase. The analysis is made by using the COMSOL multiphysics software. The results reveal the effect of buoyancy and support the validation of experimental set up where the graphite heater is offset below the centre to account for the buoyancy effects. The PT was deformed at higher temperature and came in contact at 74.4 seconds.

  • 311.
    Ali, Rashid
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Phase Change Phenomena During Fluid Flow in Microchannels2010Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Phase change phenomena of a fluid flowing in a micro channel may be exploited to make the heat exchangers more compact and energy efficient. Compact heat exchangers offer several advantages such as light weight, low cost, energy efficiency, capability of removing high heat fluxes and charge reduction are a few to mention. Phase change phenomena in macro or conventional channels have been investigated since long but in case of micro channels, fewer studies of phase change have been conducted and underlying phenomena during two-phase flow in micro channels are not yet fully understood. It is clear from the literature that the two-phase flow models developed for conventional channels do not perform well when extrapolated to micro scale.

    In the current thesis, the experimental flow boiling results for micro channels are reported. Experiments were conducted in circular, stainless steel and quartz tubes in both horizontal and vertical orientations. The internal diameters of steel tubes tested were 1.70 mm, 1.224 mm and the diameter of quartz tube tested was 0.781 mm. The quartz tube was coated with a thin, electrically conductive, transparent layer of Indium-Tin-Oxide (ITO) making simultaneous heating and visualization possible. Test tubes were heated electrically using DC power supply. Two refrigerants R134a and R245fa were used as working fluids during the tests. Experiments were conducted at a wide variety of operating conditions.

    Flow visualization results obtained with quartz tube clearly showed the presence of confinement effects and consequently an early transition to annular flow for micro channels. Several flow pattern images were captured during flow boiling of R134a in quartz tube. Flow patterns recorded during the experiments were presented in the form of Reynolds number versus vapour quality and superficial liquid velocity versus superficial gas velocity plots. Experimental flow pattern maps so obtained were also compared with the other flow pattern maps available in the literature showing a poor agreement. Flow boiling heat transfer results for quartz and steel tubes indicate that the heat transfer coefficient increases with heat flux and system pressure but is independent on mass flux and vapour quality. Experimental flow boiling heat transfer coefficient results were compared with those obtained using different correlations from the literature. Heat transfer experiments with steel tubes were continued up to dryout condition and it was observed that dryout conditions always started close to the exit of the tube. The dryout heat flux increased with mass flux and decreased with exit vapour quality. The dryout data were compared with some well known CHF correlations available in the literature. Two-phase frictional pressure drop for the quartz tube was also obtained under different operating conditions. As expected, two-phase frictional pressure drop increased with mass flux and exit vapour quality.

  • 312.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Dryout Characteristics During Flow Boiling of R134a in Vertical Circular Minichannels2011Ingår i: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 54, nr 11-12, s. 2434-2445Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the experimental results of dryout during flow boiling in minichannels are reported and analysed. Experiments were carried out in vertical circular minichannels with internal diameters of 1.22 mm and 1.70 mm and a fixed heated length of 220 mm. R134a was used as working fluid. Mass flux was varied from 50 kg/m(2) s to 600 kg/m(2) s and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 degrees C and 32 degrees C. Experimental results show that the dryout heat flux increases with mass flux and decreases with tube diameter while system pressure has no clear effect for the range of experimental conditions covered. Finally, the prediction capabilities of the well known critical heat flux (CHF) correlations are also tested.

  • 313.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Claudi, Martin-Callizo
    Maqbool, Mohammad H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Flow Patterns and Flow Pattern Maps for Microchannels2010Ingår i: 2010 3rd International Conference on Thermal Issues in Emerging Technologies, Theory and Applications - Proceedings, ThETA3 2010, 2010, s. 33-42Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dense packaging of electronic components generates very high heat fluxes and therefore results in challenges for proper thermal management of such components. Microchannel based evaporators with phase changing liquids are regarded as a promising solution for such high heat flux cooling applications. Due to confinement of flow and differences in the relative importance of governing phenomena, the two-phase flow and heat transfer characteristics of microchannels have been shown to be different from those of conventional sized channels. The fact that microchannel is an attractive cooling option but at the same time there is a clear lack of understanding of related hydrodynamic and thermal transport phenomena which provides an impetus for microchannel research. This paper presents the flow patterns and flow pattern maps obtained for an experimental study of R134a during flow boiling in a horizontal microchannel. The microchannel was a fused silica tube, the outer surface of which was coated with thin, transparent and electrically conductive layer of Indium-Tin-Oxide (ITO). The microchannel was 781 m in internal diameter and 191 mm in heated length. Operating parameters during the experiments were: mass flux 100-400 kg/m2 s, heat flux 5-45 kW/m2, saturation temperature 25 and 30 °C. A High speed camera was used with a close up lens to capture the flow patterns evolved along the channel. Flow pattern maps are presented in terms of superficial gas and liquid velocity and in terms of Reynolds number and vapor quality plots. The results are compared with some flow pattern maps for conventional and micro scale channels available in literature.

  • 314.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Maqbool, Mohammad H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Experimental Investigation of Two-phase Pressure Drop in a Microchannel2011Ingår i: Heat Transfer Engineering, ISSN 0145-7632, E-ISSN 1521-0537, Vol. 32, nr 13/14, s. 1126-1138Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experimental results of two-phase pressure drop in a horizontal circular microchannel are reported in this paper. A test tube was made of fused silica having an internal diameter of 781 mu m with a total length of 261 mm and a heated length of 191 mm. The outer surface of the test tube was coated with an electrically conductive thin layer of ITO (indium tin oxide) for direct heating of the test section. Refrigerants R134a and R245fa were used as the working fluids, and mass flux during the experiments was varied between 100 and 650 kg/m(2)-s. Experiments were performed at two different system pressures corresponding to saturation temperatures of 25 degrees C and 30 degrees C for R134a and at three different system pressures corresponding to saturation temperatures of 30 degrees C, 35 degrees C, and 40 degrees C for R245fa. Two-phase frictional pressure drop characteristics with variation of mass flux, vapor fraction, saturation temperature, and heat flux were explored in detail. Finally, the prediction capability of some well-known correlations available in the literature, some developed for macrochannels and others especially developed for microchannels, was assessed.

  • 315.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Maqbool, Mohammad H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Flow Boiling Heat Transfer Characteristics of a Minichannel up to Dryout Condition2010Ingår i: MNHMT2009, VOL 2, New York: AMER SOC MECHANICAL ENGINEERS , 2010, s. 25-34Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.7mm and a uniformly heated length of 220mm. R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 degrees C and 32 degrees C. Mass flux was varied from 50 kg/m(2) s to 600 kg/m(2) s and heat flux ranged from 2kW/m(2) to 156 kW/m(2). The test section was heated directly using a DC power supply. The direct heating of the channel ensured uniform heating and heating was continued until dry out was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

  • 316.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Maqbool, Mohammad H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Flow Boiling Heat Transfer Characteristics of a Minichannel up to Dryout Condition2011Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 133, nr 8, s. 081501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a uniformly heated length of 220 mm. R134a was used as a working fluid, and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 degrees C and 32 degrees C. Mass flux was varied from 50 kg/m(2) s to 600 kg/m(2) s, and heat flux ranged from 2 kW/m(2) to 156 kW/m(2). The test section was heated directly using a dc power supply. The direct heating of the channel ensured uniform heating, which was continued until dryout was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux, while mass flux and vapor quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that the dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

  • 317.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Maqbool, Mohammad H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Flow Boiling Heat Transfer of Refrigerants R134a and R245fa in a Horizontal Microchannel2010Ingår i: Proceedings of 2nd European Conference on Microfluidics, 2010Konferensbidrag (Refereegranskat)
  • 318.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Maqbool, Mohammad H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Flow Boiling Heat Transfer Of Refrigerants R134a And R245fa In A Horizontal Micro-Channel2012Ingår i: Experimental heat transfer, ISSN 0891-6152, E-ISSN 1521-0480, Vol. 25, nr 3, s. 181-196Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Micro-channel-based evaporators are a promising option for high heat flux cooling applications. Micro-channels offer several advantages, including a smaller coolant inventory, superior heat transfer performance, compactness, lightness of weigh. Despite being attractive, the governing phenomena in micro-channels, especially during phase change, are less understood. This article reports the experimental flow boiling heat transfer results of refrigerants R134a and R245fa in a horizontal micro-channel. A series of experiments was conducted to measure the heat transfer coefficients in a circular micro-channel made of fused silica having an internal diameter of 781 mu m and a uniformly heated length of 191 mm. The outer surface of the test tube was coated with a thin, electrically conductive layer of indium-tin-oxide. The surface coating with the electrically conductive layer of indium-tin-oxide made it possible to visualize the flow boiling process simultaneously with uniform heating of the test section. R134a and R245fa were used as working fluids and experiments were performed at a system pressure of 7.7 bar for R134a and at 1.8 bar for R245fa, corresponding to saturation temperature of 30 degrees C. Mass flux was varied from 175 kg/m(2)s to 500 kg/m(2)s, and heat flux ranged from 5 kW/m(2) to 60 kW/m(2). A high-speed camera was used to capture the images in the case of flow boiling of R134a. The experimental results indicated that the heat transfer coefficient increased with heat flux while the mass flux proved to have a negligible effect on heat transfer coefficient.

  • 319.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Maqbool, Mohammad H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Experimental investigation of two phase pressure drop in a microchannel2009Ingår i: Proceedings of 2nd Micro & Nano flows Conference, Academic Conferences Publishing, 2009Konferensbidrag (Refereegranskat)
  • 320.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Palm, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Martin-Callizo, C.
    Maqbool, Muhammad Hamayun
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Study of flow boiling characteristics of a microchannel using high speed visualization2013Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 135, nr 8, s. 081501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents the visualization results obtained for an experimental study of R134a during flow boiling in a horizontal microchannel. The microchannel used was a fused silica tube having an internal diameter of 781 lm, a heated length of 191mm, and was coated with a thin, transparent, and electrically conductive layer of indium-tin-oxide (ITO) on the outer surface. The operating parameters during the experiments were: mass flux 100-400 kg/m2 s, heat flux 5-45 kW/m2, saturation temperatures 25 and 30 °C, corresponding to saturation pressures of 6.65 bar and 7.70 bar and reduced pressures of 0.163 and 0.189, respectively. A high speed camera with a close up lens was used to capture the flow patterns that evolved along the channel. Flow pattern maps are presented in terms of the superficial gas and liquid velocity and in terms of the Reynolds number and vapor quality plots. The results are compared with some flow pattern maps for conventional and micro scale channels available in the literature. Rigorous boiling and increased coalescence rates were observed with an increase in the heat flux.

  • 321.
    Alimadadi, Majid
    et al.
    Mid Sweden Univ, Dept Nat Sci NAT, Sundsvall, Sweden..
    Lindström, Stefan B.
    Linköping Univ, Dept Management & Engn, Div Solid Mech, Linkoping, Sweden..
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Role of microstructures in the compression response of three-dimensional foam-formed wood fiber networks2018Ingår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 14, nr 44, s. 8945-8955Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-porosity, three-dimensional wood fiber networks made by foam forming present experimentally accessible instances of hierarchically structured, athermal fiber networks. We investigate the large deformation compression behavior of these networks using fiber-resolved finite element analyses to elucidate the role of microstructures in the mechanical response to compression. Three-dimensional network structures are acquired using micro-computed tomography and subsequent skeletonization into a Euclidean graph representation. By using a fitting procedure to the geometrical graph data, we are able to identify nine independent statistical parameters needed for the regeneration of artificial networks with the observed statistics. The compression response of these artificially generated networks and the physical network is then investigated using implicit finite element analysis. A direct comparison of the simulation results from the reconstructed and artificial network reveals remarkable differences already in the elastic region. These can neither be fully explained by density scaling, the size effect nor the boundary conditions. The only factor which provides the consistent explanation of the observed difference is the density and fiber orientation nonuniformities; these contribute to strain-localization so that the network becomes more compliant than expected for statistically uniform microstructures. We also demonstrate that the experimentally manifested strain-stiffening of such networks is due to development of new inter-fiber contacts during compression.

  • 322.
    ALIN, SIMON
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Produkt- och tjänstedesign.
    RYBO, FRIDA
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Produkt- och tjänstedesign.
    Naturtoalett2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Gödsel och mänskligt urin har en liknande sammansättning av kväve, fosfor och kalium (NPK) men endast en liten del av toaletters urin tas tillvara på idag. Problemet när urin torkas är att kvävet frigörs vilket bildar ammoniak och börjar lukta. Sveriges Lantbruksuniversitet har tagit fram en lösning på detta i form av en kemisk process där kvävet binds.

    I nästan alla toaletter blandas urin och fekalier och i många toaletter transporteras avfallet medhjälp av stora mängder vatten vilket innebär ett energikrävande reningsverk. Harvest Moon harmed hjälp av Sveriges Landbruksuniversitets kemiska process utvecklat en dehydreringsenhet som gör att urin kan omvandlas till gödsel. Företaget har gett uppdraget att med hjälp av deras dehydrering utveckla en fristående offentlig toalett som inte kräver el- eller vattentillförsel samt har ett litet avtryck på miljön.

    För att hitta ett marknadsbehov intervjuades både uthyrare och hyrande av portabla toaletter,vilket gav insikten att dess transport är för osäker för en såpass teknisk produkt. Däremot harnationalparker och andra naturområden permanenta toaletter utan el- eller vattentillförsel, vilketpassar bättre för projektet. Det upptäcktes ett hål på marknaden för en toalett som klarar av hög kapacitet men som inte är beroende av en välutvecklad infrastruktur och inte har en stor negativpåverkan på miljön. Nationalparkers komposteringstoaletter med högt besökstryck hinner inte med besökstakten, vilket gör att det luktar och att tömning krävs frekvent.

    För att kunna ta tillvara på näringen behöver urin och fekalier separeras, vilket på befintliga lösningar ofta görs genom att toaletten har en urinskål i sin främre del. Intervjuer med naturbevakare på nationalparker gav insikten att lösningen sällan fungerar på offentliga toaletter, eftersom papper och annat skräp slängs i urinskålen, vilket sätter stopp för flödet och urinsvämmar över. Utöver detta problem undersöktes även olika alternativ på spolning, behållare för fekalier, att förhindra urin i fekalierdelen samt ledning av urin.

    För att separera urinen används ett vertikalt galler under toalettsitsens främre del, som fungerar som ett skvättskydd och samlar upp urinen. Varken papper eller fekalier hamnar på gallret på grund av dess placering. För att förhindra att besökare står upp och kissar ner i fekalierna diskuterades en lucka som förs bort när besökare sätter sig. Istället placerades en urinoar på baksidan av huset och tydliga skyltar som förklarar den positiva miljöpåverkan om toaletten används på rätt sätt sattes upp. Hur sådana skyltar följs har dock inte testats men med tanke på att många besökare vill ta hand om sin miljö, både enligt dem själva och enligt naturbevakare, anses det vara en rimlig lösning.

    Dehydreringen drivs med hjälp av solceller och urinen torkas i skalbara filterkassetter. Produktens miljöpåverkan har inte kvantifierats men att produkten klarar sig utan tillförsel av el och vatten samt att NPK cirkuleras är bra förutsättningar för en liten påverkan på miljön.

  • 323.
    Alipanah, Ario
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Gother, Axel
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Exploring Methods for Further Development of Projects in a Cluster Initiative Context: Bridging the commercial handover gap2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Med den ökande oron om överkonsumtion och dess konsekvenser blir behovet av hållbar utveckling allt viktigare. Hållbarhet medför vissa utmaningar som helt enkelt är för stora för en organisation att ta sig an på egen hand och detta kräver att flera intressenter engagerar sig i hållbara innovationssatsningar. Ett sätt att uppnå detta är genom kluster, som är geografiska koncentrationer av företag som drar nytta av att vara belägna i samma område. Fördelarna med kluster förmedlas ofta av så kallade klusterinitiativ som är ansvariga för att utveckla aktiviteter och tjänster för klustermedlemmarna. Klusterinitiativ använder ofta ett tillvägagångssätt som kallas Triple Helix för att medla mellan privata organisationer, utbildningsinstitut och regeringen, och en viktig uppgift med detta är att assistera teknologier i övergången från statlig till privat finansiering, allmänt kallad Valley of Death.Denna uppsats är en fallstudie på en organisation i Sverige som liknar ett klusterinitiativ och har huvudsyftet att brygga den så kallade Valley of Death. Målet med studien var (1) att i ett klusterinitiativ-sammanhang undersöka förutsättningarna för vidareutveckling av (delvis) statligt finansierade projekt, efter att statliga bidrag har avslutats, och (2) att utveckla en ny projektmodell som kan implementeras hos den studerade organisationen med syftet att öka andelen av företagets projekt som kommersialiseras. Flera studier har gjort omfattande kvantitativ forskning på klusterinitiativ. Kvantitativa åtgärder måste emellertid kombineras med verksamhetsbaserade kvalitativa indikatorer. Därför fokuserade denna studie i genomförandet på kvalitativa intervjuer, analyser av projektdokumentation och workshops.Inom Valley of Death upptäcktes två gap i faserna när projekt lämnades över mellan organisationer. Med teorier om målsättning, effektevidens, Technology Readiness Levels och Commercial Readiness Index utvecklade denna studie en projektmodell och ett projektklassificeringssystem som hjälper den studerade organisationen både internt och externt med potentialen att förbättra interorganisatorisk samverkan och projektöverlämning.

  • 324.
    Alipanah, Ario
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Gother, Axel
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Kundorderstyrd tillverkning av butiksproducerat bröd: Möjligheter och hinder2016Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    En stor källa till resursineffektivitet är all mat som varje dag slängs, världen över. Produktkategorin bröd är en stor källa till detta matsvinn, där det största svinnet sker i inom handeln. Till följd av att tiden brödet måste säljas inom är kort, blir det svårt att prognosstyra tillverkningen utan att det leder till överproduktion eller brist. Alternativet till prognosbaserad tillverkning, är kundorderstyrd tillverkning. Implementering av kundorderstyrning skulle kunna resurseffektivisera tillverkningen och höja produktivitet för hela avdelningen för det butiksproducerade brödet. Syftet med arbetet var att undersöka vad som krävs för denna implementering. Genom intervjuer med butikschefer och bagare, samt besök i fyra livsmedelsbutiker, har empiri samlats in. Fyra hinder och fyra lösningar för implementering av kundorderstyrd tillverkning av butiksproducerat bröd har formulerats.Dessa hinder är:

    • de ekonomiska riskerna med implementeringen

    • att investeringskostnaderna för implementeringen är höga

    • synen på ökad arbetsbelastning

    • att produktionsprocess och existerande utrustning på marknaden inte är anpassad

    Dessa hinder löses genom att:

    • ansätta en väl avvägd kombination av bröd tillverkat mot order, med ett underproducerat basutbud av bröd tillverkat mot lager, alternativt använda en visuell presentation av butikens utbud av bröd tillgängligt för tillverkning mot kundorder

    • undersöka huruvida implementeringen ger brödet ett större kundvärde och butiken ett större varuflöde samt ta hänsyn till butiksstorleken vid bedömning av implementeringens lämplighet

    • hantera synen på ökad arbetsbelastning genom att förmedla fördelarna med implementering av kundorderstyrd tillverkning av butiksproducerat bröd

    • placera kundorderpunkten i produktionsanläggningens frys, för att förkorta brödets kundorderstyrda produktionstid samt begära ugnar som tillåter parallella produktionssatser

  • 325. Alizad Banaei, Arash
    et al.
    Shahmardi, Armin
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Nucleated capsules at finite inertiaManuskript (preprint) (Övrigt vetenskapligt)
  • 326.
    Alizadeh, Amir
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Fracture Simulation of Electrofusion Joining.2015Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta examensarbete på masternivå handlar undersökning och simulering av brott i elektromuffsvetsar. Den har typen av svets används för att sammansvetsa rör  av högdensitiets polyeten där muff och rör svetsas samman med värmen som skapas på grund av koppartråadens motstånd mot elektrisk ström. Flera tidiga brott där en spröd spricka har växt genom svetsområdet har observerats. Polyeten som material ar duktilt men sprött beteende förekommer på grund av dålig svets och svetsgränssnitt.

    I detta arbete valdes att undersöka de möjliga kritiska belastningar som kan orsaka brott och påverkan av muffens geometri på brottmotstandet hos den ihopsvetsade muff- och rörstrukturen. Den numeriska finita element-metoden användes. En dålig svets (spröd) angreps med en linjar modell och en icke linjar (CZM) modell och en bra svets (duktil) hanterades med en icke linjäar (XFEM) modell. Aktuella materialparametrar identiferades genom experiment. Resultatet visar att det inre trycket är den kritiska belastningen. I termer av respons till de geometriska parametrarna, var den linjära och icke-linjära modellen (CZM) for den dåliga svetsen konsekventa. Reducerad inre kylzon, ökning av svetslängd, och öokning av mufftjocklek ökar brottmotståndet hos den ihopsvetsade strukturen.

  • 327.
    Alkan, Deniz
    KTH, Tidigare Institutioner, Energiteknik. KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Investigating CVT as a Transmission System Option for Wind Turbines2013Självständigt arbete på avancerad nivå (masterexamen), 80 poäng / 120 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this study, an innovative solution is examined for transmission problems and frequency control for wind Turbines. Power electronics and the gear boxes are the parts which are responsible of a significant amount of failures and they are increasing the operation and maintenance cost of wind turbines. Continuously transmission (CVT) systems are investigated as an alternative for conventional gear box technologies for wind turbines in terms of frequency control and power production efficiency. Even though, it has being used in the car industry and is proven to be efficient, there are very limited amount of studies on the CVT implementation on wind turbines. Therefore, this study has also an assertion on being a useful mechanical analyse on that topic. After observing several different types of possibly suitable CVT systems for wind turbines; a blade element momentum code is written in order to calculate the torque, rotational speed and power production values of a wind turbine by using aerodynamic blade properties. Following to this, a dynamic model is created by using the values founded by the help of the blade element momentum theory code, for the wind turbine drive train both including and excluding the CVT system. Comparison of these two dynamic models is done, and possible advantages and disadvantages of using CVT systems for wind turbines are highlighted. The wind speed values, which are simulated according to measured wind speed data, are used in order to create the dynamic models, and Matlab is chosen as the software environment for modelling and calculation processes. Promising results are taken out of the simulations for both in terms of energy efficiency and frequency control. The wind turbine model, which is using the CVT system, is observed to have slightly higher energy production and more importantly, no need for power electronics for frequency control. As an outcome of this study, it is possible to say that the CVT system is a candidate of being a research topic for future developments of the wind turbine technology.

  • 328.
    Al-Karkhi, Saif
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Petrén, Simon
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Kritiska Framgångsfaktorer i Tjänsteinnovativa Företag2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Innovation är numera en central del av företagens aktiviteter för att upprätthålla konkurrenskraft och definieras som den praktiska tillämpningen av idé till en ny produkt eller tjänst. Tidigare forskning inom ämnet har främst fokuserat på produkt- och processinnovation inom tillverkning och industri. Parallellt har ett nytt intresse inom tjänsteinnovation uppkommit där antalet studier och undersökningar har ökat som ett resultat av en växande tjänstesektor och dess påverkan på ekonomin. Ett annat ämnesområde som hjälper företaget att upprätthålla konkurrenskraft och tillväxt, är identifikation och analys av kritiska framgångsfaktorer. Majoriteten av undersökningarna kring kritiska framgångsfaktorer är produktcentrerade och undersöker den industriella produktmarknaden. Trots att tjänsteinnovation har en alltmer betydande roll för den ekonomiska tillväxten finns dock förhållandevis lite forskning kring vilka kritiska framgångsfaktorer som existerar i tjänsteinnovativa företag. Bakgrunden till studien är ett tidigare samarbete med Innu-Science där man tillsammans tagit fram ett nytt tjänstebaserat städkoncept och syftet blir att föreslå rekommendationer för Innu-Science vid etablering. Baserat på tidigare litteratur användes en viss metodik ”Temporal/Intuitive factors” för att kunna identifiera olika kritiska framgångsfaktorer hos fyra tjänsteinnovativa svenska företag. Med hjälp av en induktiv kvalitativ studie har företagen undersökts och analyserats, för att kunna identifiera de kritiska framgångsfaktorerna. Faktorerna har därefter jämförts mot varandra för att undersöka eventuella mönster och samband. Resultat från studien visar att alla fyra företag har följande faktorområden gemensamt: Försäljning, Tjänstedynamik (kundanpassning och flexibilitet) samt Referenser. Slutligen har resultat, analys och slutsats legat till grund för vidare rekommendationer till Innu-Science, som utgör ett beslutsfattande stöd när verksamheten ska etableras.

  • 329. Alkhagen, M.
    et al.
    Toll, Staffan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    A triaxial rheometer for soft compressible solids2002Ingår i: Journal of Rheology, ISSN 01486055 (ISSN), Vol. 46, nr 1, s. 31-47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The compression and the shear of soft compressible solids were studied using the triaxial rheometer. The sample was fixed between two parallel plates and the deformation was controlled by an x, y, z displacement on one plate while the stress was measured on the other. The triaxial stress transducer eliminates the edge effects by only measuring the stress on an interior region of the plate. The edge effects and the associated measurement errors were analyzed by the simple isotropic elastic theory and were compared to the measurements done on the chloroprene rubber foam.

  • 330. Alkhagen, M.
    et al.
    Toll, Staffan
    Chalmers University of Technology, Sweden.
    Micromechanics of a compressed fiber mass2007Ingår i: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 74, nr 4, s. 723-731Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A theory is presented for the rate modeling of flexible granular solids based on affine average motion of interparticle contacts. We allow contacts to form and break continually but assume the existence of a finite friction coefficient rendering contacts force free as they form or break. The resulting constitutive equations are of the hypoelastic type. A specific model for the deformation of a fiber mass is then developed. The model improves on previous theories for fiber masses in at least two respects: First, it is more general in that it is not restricted to uniaxial compression, although it is restricted to predominantly compressive deformations histories, due to neglect of frictional dissipation. Second, by allowing torsion as well as bending of fibers, this theory covers a larger deformation range. Compression experiments are performed on carded slivers of PA6 fibers under various conditions. The measured response is found to be in close agreement with that predicted by the model.

  • 331. Alkhagen, M.
    et al.
    Toll, Staffan
    Chalmers University of Technology, Sweden.
    The effect of fiber diameter distribution on the elasticity of a fiber mass2009Ingår i: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 76, nr 4, artikel-id 041014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A random mass of loose fibers interacting by fiber-fiber contact is considered. As proposed in a previous paper, the elastic response is modeled based on the statistical mechanics of bending and torsion of fiber segments between fiber-fiber contact points. Presently we show how the statistical approach can be used to account for a distribution of fiber diameters rather than just a single diameter. The resulting expression has the same form and the same set of parameters as its single-diameter counterpart, except for two dimensionless reduction factors, which depend on the fiber diameter distribution only and reduce to unity for monodisperse fibers. Uniaxial compressibility experiments are performed on several materials with different bimodal fiber diameter distributions and are compared to model predictions. Even though no additional parameters were introduced to model the effect of mixed fiber diameters, the behavior is accurately predicted. Notably, the effect of the nonuniform fiber diameter is strong: A mixture of two fiber diameters differing by a factor of 2 can reduce the response by an order of magnitude, compared to the case of uniform diameter.

  • 332. Alkmim, M. H.
    et al.
    Cuenca, J.
    De Ryck, L.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design.
    Model-based acoustic characterisation of muffler components and extrapolation to inhomogeneous thermal conditions2018Ingår i: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics, KU Leuven - Departement Werktuigkunde , 2018, s. 3009-3020Konferensbidrag (Refereegranskat)
    Abstract [en]

    A methodology for evaluating the acoustic behaviour of two-port inhomogeneous media in experimentally unavailable thermal conditions is proposed. The method consists of an inverse estimation of the geometrical and material properties of the object at room temperature followed by a forced thermal input. The properties of interest for the inverse estimation are the spatially-varying cross-section and/or bulk properties. The underlying model relies on a transfer matrix approach, allowing for a representation of spatially inhomogeneous objects as piece-wise equivalent homogeneous fluids, while ensuring continuity conditions between successive elements. A model of non-stationary thermal conduction is used as a first approximation, where an integral formulation accounts for the cumulative effect of multiple homogeneous elements. In order to evaluate the validity of the extrapolation, a validation against a fully numerical simulation is presented in two cases, namely a simple expansion chamber and a complex muffler. 

  • 333.
    Alkmim, Mansour
    et al.
    Siemens Industry Software.
    Cuenca, Jacques
    Siemens Industry Software, Leuven Belgium.
    de Ryck, Laurent
    Siemens Industry Software, Leuven Belgium.
    Göransson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Centre for ECO2 Vehicle Design.
    Model-based acoustic characterisation of muffler components and extrapolation to inhomogeneous thermal conditions2018Konferensbidrag (Refereegranskat)
  • 334. Alku, Paavo
    et al.
    Airas, Matti
    Björkner, Eva
    KTH, Skolan för datavetenskap och kommunikation (CSC), Tal, musik och hörsel, TMH.
    Sundberg, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Tal, musik och hörsel, TMH.
    An amplitude quotient based method to analyze changes in the shape of the glottal pulse in the regulation of vocal intensity2006Ingår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 120, nr 2, s. 1052-1062Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study presents an approach to visualizing intensity regulation in speech. The method expresses a voice sample in a two-dimensional space using amplitude-domain values extracted from the glottal flow estimated by inverse filtering. The two-dimensional presentation is obtained by expressing a time-domainmeasure of the glottal pulse, the amplitude quotient (AQ), as a function of the negative peak amplitude of the flow derivative (d(peak)). The regulation of vocal intensity was analyzed with the proposed method from voices varying from extremely soft to very loud with a SPL range of approximately 55 dB. When vocal intensity was increased, the speech samples first showed a rapidly decreasing trend as expressed on the proposed AQ-d(peak) graph. When intensity was further raised, the location of the samples converged toward a horizontal line, the asymptote of a hypothetical hyperbola. This behavior of the AQ-d(peak) graph indicates that the intensity regulation strategy changes from laryngeal to respiratory mechanisms and the method chosen makes it possible to quantify how control mechanisms underlying the regulation of vocal intensity change gradually between the two means. The proposed presentation constitutes an easy-to-implement method to visualize the function of voice production in intensity regulation because the only information needed is the glottal flow wave form estimated by inverse filtering the acoustic speech pressure signal.

  • 335.
    Allam, S.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Cooling fan noise control using micro-perforates2012Ingår i: Int. Congr. Expos. Noise Control Eng., INTER-NOISE, 2012, s. 10434-10445Konferensbidrag (Refereegranskat)
    Abstract [en]

    Baffle or split silencers are commonly used, e.g., in HVAC systems and as inlet/outlet silencers on gas turbines. Another application is to reduce noise from the cooling fan inlet for large IC-engines. A baffle silencer can be seen as a periodic arrangement of parallel rectangular absorbers which can be placed in a rectangular duct. The noise reduction afforded by parallel baffles depends not only on the physical properties of the lining, but also upon the angle of incidence of the sound waves impinging and the baffle length. In this paper the potential of using baffles made of Micro-Perforated Panels is investigated in particular with the cooling fan inlet application in mind. Theoretical models for the damping is derived and used to design optimum configurations. The models are based on the wave propagation in a periodic array of baffles so that only one period can be investigated in order to find the different modes. In particular the least attenuated mode is important to find in order to optimize the behavior. An important aspect is the inner structure of the MPP baffle, i.e., can it just be an empty air volume or to what extent must internal waves be prevented by putting in walls. From a stiffness point of view some inner walls might also be needed to avoid vibration problems. Due to these complexities the theoretical models are only presented for the simplest cases. In order to validate the models and to get a more complete test of different designs experiments were also carried out. During these experiments the effect of flow was also tested.

  • 336. Allam, S.
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Noise reduction for automotive radiator cooling fans2015Ingår i: FAN 2015 - International Conference on Fan Noise, Technology and Numerical Methods, Institution of Mechanical Engineers , 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    Engine cooling fans have long been recognized as one of the major noise sources in a vehicle. As the engine and other vehicle components are made quieter, the need to reduce fan noise has become more and more urgent. To reduce fan noise in a cost-effective manner, it is necessary to incorporate the component of noise reduction into an early design stage. In this paper a detailed experimental study on an automotive vehicle cooling system is presented. The aim is to investigate the flow generated noise, characterize the heat exchanger damping properties and investigate the use of near-field noise control by micro-perforated (MPP) shrouds and tuned MPP dampers. For the tested standard automotive cooling fan system the MPP shroud gave a reduction in the range 1.5 to 4.5 dB(A) depending on the fan speed. Also the absorption on the back-side is significantly increased which can reduce the noise further. The near-field tuned MPP damper concept is also promising and gives a reduction around 3 dB(A) at the operating points. 

  • 337.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. Helwan University, Egypt.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Methods for Accurate Determination of Acoustic Two-Port Data in Flow Ducts2005Ingår i: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Accurate measurement of the acoustic two port data can be used not only to determine the transmission loss but also to determine physical properties like flow resistivty as well as speed of sound and impedance. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. Techniques to improve the acoustic two-port determination have been tested in this paper. A number of possible configurations for connecting loudspeakers to the flow duct have been investigated. It was found that using a perforate pipe section with about 50% porosity between the loudspeaker side branch and the duct gave the best signal-to-noise ratio out of the studied configurations. Different signal processing techniques have been tested for reducing the adverse effects of flow noise at the microphones. The most successful techniques require a reference signal which can be either the electric signal being input to the loudspeakers or one of the microphone signals. As a reference technique stepped sine excitation with cross-spectrum based frequency domain averaging was used. This technique could give good results for most cases. Using a periodic signal (saw-tooth) and synchronised time domain averaging good results could be obtained if a sufficient number of averages was used. At flow velocities higher than M=0.2 about 10000 averages were needed. Random excitation together with cross-spectrum based frequency domain averaging also gave good result if the same number of averages was used. Ordinary frequency domain averaging is not sufficient at high flow velocities. It was also shown that using cross-spectrum based frequency domain averaging an improvement could be obtained if the microphone with the highest signal-to-noise ratio at each frequency was used as the reference microphone rather than a fixed microphone.

  • 338.
    Allam, Sabry
    et al.
    KTH, Tidigare Institutioner, Farkost- och flygteknik.
    Bodén, Hans
    KTH, Tidigare Institutioner, Farkost- och flygteknik.
    Signal to noise ratio enhancement methods in acoustic flow duct measurements2004Ingår i: ICSV12-St Petersburg, 2004Konferensbidrag (Övrigt vetenskapligt)
  • 339.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Bodén, Hans
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Over-determination in acoustic two-port data measurement2006Ingår i: ICSV13-Vienna / [ed] J. Eberhardsteiner, H.A. Mang, H. Waubke, 2006Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Measurement of plane wave acoustic transmission properties, so called two-port data, of flow duct components is important in many applications. It is an important tool for instance in the development of mufflers for IC-engines. Measurement of two-port data is difficult when the flow velocity in the measurement duct is high because of the flow noise contamination of the measured pressure signals. The plane wave acoustic two-port is a 2x2 matrix containing 4 complex quantities at each frequency. To experimentally determine these unknowns the acoustic state variables on the inlet and outlet side must be measured for two independent test cases. The two independent test cases can be created by: changing the acoustic load on the outlet side leading to the so-called two-load technique or by using one acoustic source on the inlet side and one acoustic source on the outlet side leading to the so-called two-source technique. In the latter case the independent test cases are created by first using the source on the inlet side and then the source on the outlet side. As pointed out by Åbom it is also possible to run both sources simultaneously to create more than two independent test cases. This over-determination could be used to improve the measurement results for instance if the data is contaminated by flow-noise. In this paper over-determination is tested by applying up to 5 different test cases. This procedure has been applied to a single orifice test object.

  • 340. Allam, Sabry
    et al.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    A New Type of Muffler Based on Microperforated Tubes2011Ingår i: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 133, nr 3, s. 031005-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Microperforated plate (MPP) absorbers are perforated plates with holes typically in the submillimeter range and perforation ratios around 1%. The values are typical for applications in air at standard temperature and pressure (STP). The underlying acoustic principle is simple: It is to create a surface with a built in damping, which effectively absorbs sound waves. To achieve this, the specific acoustic impedance of a MPP absorber is normally tuned to be of the order of the characteristic wave impedance in the medium (similar to 400 Pa s/m in air at STP). The traditional application for MPP absorbers has been building acoustics often combined with a so called panel absorber to create an absorption peak at a selected frequency. However, MPP absorbers made of metal could also be used for noise control close to or at the source for noise control in ducts. In this paper, the possibility to build dissipative silencers, e. g., for use in automotive exhaust or ventilation systems, is investigated.

  • 341.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Acoustic modeling and testing of a complex car muffler2006Ingår i: International Congress on Sound and Vibration 2006, 2006, s. 1119-1126Konferensbidrag (Refereegranskat)
    Abstract [en]

    Perforated mufflers are used by exhaust system manufacturers to improve the broadband attenuation at low frequencies, with the drawback that this normally also implies an increased pressure drop. The detailed modelling of this type of muffler depends on knowledge of the perforate impedance which is influenced by hole geometry as well as the details of the flow distribution. The existing formulas for calculation of perforate impedance are semi-empirical and a number of alternatives have been published. One motivation behind this work was to review the existing formulas for perforate impedance using accurate measured data for perforated mufflers. A modified model presented by Bauer 1977 was found to be the best. A second motivation was to show that for a detailed analysis, using 3D acoustic FEM, the mean flow can be neglected except for calculating the perforate impedances.

  • 342.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Advanced experimental procedure for in-duct aero-acoustics2006Ingår i: 13th International Congress on Sound and Vibration 2006, ICSV 2006, 2006, s. 1185-1192Konferensbidrag (Refereegranskat)
    Abstract [en]

    The purpose of this paper is to present a method for characterization of in-duct aero-acoustic sources that can be described as active acoustic two-ports. The method is applied to investigate the sound produced from an orifice plate. The motivation is to obtain better data for the development of improved prediction methods for noise from flow singularities, e.g., in HVAC systems on aircrafts. Most of the earlier works fall into two categories; papers modeling the scattering of acoustic waves and papers modeling the sound generation. Concerning the scattering it is possible to obtain estimates of the low frequency behavior from linear perturbations of the steady state equations for the flow. Concerning the sound generation most of the presented work is experimental and follows a paper by Nelson&Morfey, which present a scaling law procedure for the in-duct sound power based on a dipole model of the source. One limitation with the earlier works is that the sound power only was measured on the downstream side. Also data was only obtained in 1/3-octave bands, by measuring the sound radiated from an open duct termination. Assuming plane waves and linear acoustics the flow duct singularity can be completely modeled as an active 2-port. The experimental determination of its properties is done in a two steps procedure. In the first step the passive data, i.e., the scattering matrix S, is determined using external (independent) sources. In the second step the S matrix is used and the source vector is determined by testing the system with known acoustic terminations.

  • 343.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Aeroacoustic investigation of diaphragm orifices in ducts2007Ingår i: Turkish Acoustical Society - 36th International Congress and Exhibition on Noise Control Engineering, INTER-NOISE 2007 ISTANBUL, 2007, s. 292-301Konferensbidrag (Refereegranskat)
    Abstract [en]

    Diaphragm orifices are used in duct systems to control or measure the flow rate. Such components generate complex flows and aeroacoustic phenomena, e.g., dissipation via forced vortex shedding, sound generation from eddy structures (broadband noise) and non-linear whistling. In this paper the acoustic properties (passive and active) of single and double diaphragm orifices are investigated experimentally for small Mach-numbers and low frequencies (plane waves). Using microphone arrays and wave decomposition the induct sound fields are resolved and used as input to determine the active acoustic 2-port. The work represents one of the first efforts to apply 2-port methods to characterize flow generated noise in-ducts. The motivation of this work is to obtain better understanding for noise from flow singularities in ducts, e.g., in HVAC systems on vehicles, develop and improve prediction methods and produce data for validation of CFD and other models. First the single orifice case is investigated and the 2-port data is obtained. The active (source) strength part represents a dipole type of source for which a scaling law is derived. For the passive part (the scattering matrix) a simple quasi-stationary model is tested and works well up to a few hundred Hz. Secondly the double orifice configuration is investigated and again the 2-port data is measured. To investigate the presence of orifice interaction and non-linear aeroacoustic effects, such as whistling, the double orifice data is reduced to two identical single orifices. The equivalent source data for this reduced case is then compared with the single orifice scaling law. It is found that if the separation is larger than 10 orifice diameters then orifice interaction can be neglected. Non-linear effects and tendencies for whistling were found for separations less than 3-4 duct diameters.

  • 344.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Diesel engines after treatment devices: Acoustic modeling2005Ingår i: 12th International Congress on Sound and Vibration 2005: ICSV 2005, 2005, s. 2358-2365Konferensbidrag (Refereegranskat)
    Abstract [en]

    To reduce exhaust pollutants from diesel engines a Diesel Particulate Filter (DPF) is normally fixed after a Catalytic Converter (CC) in an expansion chamber to create a complete After-Treatment Device (ATD). As part of the work in the EC-project ARTEMIS the authors have published a series of papers on the modeling of DPF units. Here the final and complete DPF model is presented. The model calculates the acoustic 2-port by solving the convective acoustic wave equations for two neighboring cells simplified in the manner of the Zwikker and Kosten theory. A segmentation approach has been employed to handle the actual flow, density, pressure, and temperature distribution inside the monoliths at each frequency. The theoretical results were compared with measured transmission loss data at different flow speeds and the agreement is excellent. The new complete model has also been compared with the 1-D model earlier suggested by the authors. It turns out that by using a wave number based on the Kirchhoff solution for plane waves in narrow pipes, the simple 1-D model works almost as well as the complete model. Another conclusion is that the effect of mean flow on the sound transmission through a filter is very small. Using the new model and existing models for standard pipe elements and the CC, the acoustic 2-port for a car ATD unit has been calculated and used to predict the transmission loss. The agreement between the predictions and the measured data for various flow speeds is good.

  • 345.
    Allam, Sabry
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Hellwan University, Egypt .
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Experimental characterization of acoustic liners with extended reaction2008Ingår i: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Suppressing of jet engine noise by inlet and exhaust duct liners and internal combustion engine (ICE) noise by intake and exhaust systems is an important part of developing environmentally acceptable vehicles. The acoustic liner is designed to provide an impedance boundary condition in the engine duct that reduces the propagation of engine noise through the duct. An accurate impedance boundary condition is necessary to optimally suppress the noise at different conditions. The goal of the research presented in this paper is to present a new technique to Educe and characterize the acoustic liner impedance for cases with extended reaction. This technique is depending on comparing both the measured and predicted 2-port transfer matrices. The measurement of the transfer matrix is performed using the two microphone technique, while the prediction of the transfer matrix is obtained assuming plane waves in the inner pipe and outer chamber coupled by a perforated wall impedance. By using a regression process the unknown wall impedance is then educed. The method is applied to investigate the effect of flow on the impedance of so called Micro-perforated panels (MPP). A MPP consists of a panel (here a plate made of Al or steel) with small perforations distributed over its surface. When these perforations are of sub-millimeter size they provide by themselves enough acoustic resistance and low acoustic mass reactance necessary for a wideband absorber.

  • 346.
    Allam, Sabry
    et al.
    Helwan University, Cairo, Egypt.
    Åbom, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Fan Noise Control Using Microperforated Splitter Silencers2014Ingår i: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 136, nr 3, s. 031017-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Splitter or baffle silencers are commonly used, for example, in heating ventilation and air conditioning (HVAC) systems and as inlet/outlet silencers on gas turbines. Another application is to reduce noise from the cooling fan inlet for large IC-engines. A splitter silencer can be seen as a periodic arrangement of parallel rectangular absorbers, which can be placed in a rectangular duct. The noise reduction afforded by parallel splitters depends not only on the physical properties of the lining but also upon the angle of incidence of the impinging sound waves, and the splitter and duct dimensions. In this paper, the potential of using splitters made of microperforated plates (MPPs) is investigated, with a particular focus on cooling fan inlet/outlet applications.

  • 347. Allegret-Bourdon, D
    et al.
    Vogt, Damian
    KTH, Skolan för industriell teknik och management (ITM).
    Fransson, Torsten
    KTH, Skolan för industriell teknik och management (ITM).
    A New test facility for investigating fluid-structure interactions using a generic model2002Konferensbidrag (Övrigt vetenskapligt)
  • 348. Allen, T.
    et al.
    Battley, M.
    Casari, P.
    Kerling, B.
    Stenius, Ivan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Westlund, Joacim
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Structural responses of high performance sailing yachts to slamming loads2011Ingår i: 11th International Conference on Fast Sea Transportation, FAST 2011 - Proceedings, 2011, s. 585-592Konferensbidrag (Refereegranskat)
    Abstract [en]

    Experimental measurements of transient strains, local accelerations and pressure were undertaken on the IMOCA Open 60' class sailing yacht Paprec-Virbac III, and on a replica hull panel section tested in a laboratory slam testing facility. The approximately 1m x 0.7m panel for laboratory testing was manufactured on a mould taken from the plug used for the vessel construction, ensuring that the panel had identical curved geometry to the vessel. The laboratory panel included two stringers as on the same region of the vessel. An instrumentation layout including arrays of resistance strain gauges, accelerometers and a transient pressure transducer was used. Linear displacement transducers were used to measure panel deformations during the laboratory tests. The laboratory testing was undertaken at a range of constant impact velocities from 0.5 to 3m/s using a Servohydraulic Slam Testing System. Sea-trials were undertaken in the Hauraki Gulf, Auckland New Zealand. There was good qualitative agreement between the field and laboratory measurements in regard to timing and relative magnitudes of strains at different positions on the structure. Results demonstrate that the hull structure undergoes very complex transient deformations during the slamming events.

  • 349.
    Allert, Anna-Lena
    KTH, Skolan för teknik och hälsa (STH), Ergonomi.
    Att mäta lean-utveckling: En sammanställning av metoder för att mäta utveckling inom lean och en fallstudie på ett företag2011Självständigt arbete på avancerad nivå (magisterexamen), 15 poäng / 22,5 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Lean produktion (LP) etablerades som begrepp i början av 1990-talet och har sedan dess spridit sig över världen och många företag vill i dag arbeta efter konceptet. Detta innebär att arbetsförhållanden för många arbetstagare påverkas och konsekvenserna för dem är inte helt klarlagda. Ett forskningsprojekt har inletts på STH/KTH för att undersöka hur arbetsförhållanden och hälsa påverkas över tid vid införande av LP. I detta projekt fanns därför ett behov av att kunna mäta eller uppskatta om någon utveckling kan relateras till införandet av LP och en önskan om en kartläggning av metoder som använts för att göra detta.Utifrån dessa behov blev syftet med föreliggande arbete att genom en litteraturstudie undersöka och sammanställa metoder som använts för att göra en bedömning eller skattning av ett företags utveckling inom lean. En intervjuguide skulle också testas gentemot resultatet av studien för att undersöka om effekter av en lean-implementering kunde synliggöras med hjälp av intervjuguiden och i vilken omfattning den täckte in de områden som kommit fram i litteraturstudien. Detta gjordes genom en fallstudie på ett företag som började arbeta med lean under 2007.För att ge en förståelse för lean produktion, historik och utveckling ges inledningsvis en beskrivning av konceptets historiska utveckling fram till och med i dag, tillsammans med dess begrepp, metoder och verktyg. Den begreppsförvirring som råder beskrivs och konsekvenserna av detta tillsammans med bristerna på en enhetlig definition av lean produktion tas upp. Av detta följer en viss problematik kring att mäta/skatta en utveckling inom lean vilken också diskuteras.Litteratursökningen resulterade i tolv olika metoder som presenteras kort tillsammans med de lean-faktorer som angetts. Med lean-faktor avses det område, faktor eller indikator som i metoden använts för att fånga upp en utveckling inom lean. Den faktor som togs upp av två eller flera metoder ansågs höra till de vanligaste. Totalt kunde 43 sådana identifieras. I dessa metoder kunde också sex olika systemkomponenter identifieras som berörda vid en lean-implementering i företaget.Som ett stöd vid mätning av lean-utveckling togs en utvecklingstrappa fram. Den användes i bedömningen av fallföretaget. Med hjälp av intervjuguiden framträdde en god bild av företagets arbete inom lean inom några områden. Med utgångspunkt i resultatet av litteraturstudien bör intervjuguiden kompletteras med frågor kring leverantörssamverkan, kunder och kvalitet för att analysen av ett företags lean-utveckling skall bli mer heltäckande.

  • 350.
    Allégret-Bourdon, Davy
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fransson, Torsten H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Study of shock movement and unsteady pressure on 2D generic model2006Ingår i: Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines / [ed] Hall, KC; Kielb, RE; Thomas, JP, 2006, s. 409-421Konferensbidrag (Refereegranskat)
    Abstract [en]

    A flexible generic model has been developed at the Chair of Heat and Power Technology in order to perform fatter experiments in a more fundamental fashion. It is made of engineered flexible material and oscillate in a controlled way at non-uniform amplitude and variable frequencies. Time-resolved measurements of the unsteady surface pressures, the instantaneous model geometry as well as unsteady Schlieren visualizations are performed in order to study the shock wave motion and the aerodynamic load acting over this flexible generic bump. The model oscillates at reduced frequencies from 0.015 to 0.294 at transonic flow condition. The mode shapes of such a flexible bump strongly depends on the excitation frequency of the generic model. Schlieren pictures are obtained for an operating point characterized by an inlet Mach number of 0.63. Moreover, the presented results demonstrate that the phase of shock wave movement towards bump local motion shows a decreasing trend for the third bending mode shapes at reduced frequency higher than k=0.074. At the pressure taps located after the shock wave formation, the phase of pressure fluctuations towards bump local motion presents the same decreasing trend.

45678910 301 - 350 av 11613
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf