Ändra sökning
Avgränsa sökresultatet
228229230231232233 11501 - 11550 av 11609
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.
  • 11501.
    Åkervik, Espen
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Haepffner, Jerome
    Ehrenstein, Uwe
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Model reduction and control of a cavity-driven separated boundary layer2008Ingår i: IUTAM Symposium On Flow Control And Mems / [ed] Morrison, JF; Birch, DM; Lavoie, P, 2008, Vol. 7, s. 147-155Konferensbidrag (Refereegranskat)
    Abstract [en]

    The control of a globally unstable boundary-layer flow along a two-dimensional cavity is considered. When perturbed by the worst-case initial condition, the flow exhibits a large transient growth associated with the development of a wave packet along the cavity shear layer followed by a global cycle related to the least stable global eigenmodes. The flow simulation procedure is coupled to a measurement feedback controller, which senses the wall shear stress at the downstream lip of the cavity and actuates at the upstream lip. A reduced model for the control optimization is obtained by a projection on the least stable global eigenmodes. The LQG controller is run in parallel to the Navier-Stokes time integration. It is shown that the controller is able to damp out the global oscillations.

  • 11502.
    Åkervik, Espen
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Hoepffner, Jérôme
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Uwe, Eherenstein
    IRPH́E, Université de Provence.
    Henningson, Dan S.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Optimal growth, model reduction and control in a separated boundary-layer flow using global eigenmodes2007Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 579, s. 305-314Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two-dimensional global eigenmodes are used as a projection basis both for analysing the dynamics and building a reduced model for control in a prototype separated boundary-layer flow. In the present configuration, a high aspect ratio smooth cavity-like geometry confines the separation bubble. Optimal growth analysis using the reduced basis shows that the sum of the highly non-normal global eigenmodes are able to describe a localized disturbance. Subject to this worst-case initial condition, a large transient growth associated with the development of a wavepacket along the shear layer followed by a global cycle related to the two unstable global eigenmodes is found. The flow simulation procedure is coupled to a measurement feedback controller, which senses the wall shear stress at the downstream lip of the cavity and actuates at the upstream lip. A reduced model for the control optimization is obtained by a projection on the least stable global eigenmodes, and the resulting linear-quadratic-gaussian controller is applied to the Navier--Stokes time integration. It is shown that the controller is able to damp out the global oscillations.

  • 11503.
    Åman, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM).
    Ekberg, Peter
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Leonardsson, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Edgren, Klas
    KTH, Skolan för industriell teknik och management (ITM).
    Sandström, Torbjörn
    Micronic Laser Systems, Stockholm, Sweden.
    Stiblert, Lars
    Micronic Laser Systems, Stockholm, Sweden.
    Recent developments in large-area photomasks for display applications2001Ingår i: Journal of the Society for Information Display, ISSN 1071-0922, Vol. 9, nr 1, s. 3-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One of the most critical areas in the manufacturing process for FPD panels or shadow masks for CRTs is lithography. Most existing lithography technologies require high-quality large-area photomasks. The requirements on these photomasks include positioning accuracy (registration) and repeatability (overlay), systematic image quality errors ("mura" or display quality), and resolution (minimum feature size). The general trend toward higher resolution and improved performance, e.g., for TFT desktop monitors, has put a strong focus on the specifications for large-area-display photomasks. This article intends to give an overview of the dominant issues for large-area-display photomasks, and illustrates differences compared with other applications. The article will also present state-of-the-art methods and trends. In particular, the aspects of positioning accuracy over large areas and systematic image-quality errors will be described. New qualitative and objective methods have been developed as means to capture systematic image-quality errors. Results indicating that errors below 25 nm can be found early in the manufacturing process is presented, thus allowing inspection for visual effects before the actual display is completed. Positioning accuracy below 400 nm (3 sigma) over 720 × 560 mm have been achieved. These results will in the future be extended up toward 1 × 1 m for generation 4 in TFT-LCD production.

  • 11504.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Two-Stroke Engine with Varaible Compression2005Patent (Övrig (populärvetenskap, debatt, mm))
  • 11505.
    Åsberg, Robbin
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Framtagande av kärldemonteringsmaskin för att kunna materialåtervinna avfallskärl2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    SÖRAB är ett kommunalt bolag som ägs av 10 kommuner (Stockholm, Danderyd, Järfälla, Lidingö, Sollentuna, Solna, Sundbyberg, Täby, Upplands Väsby och Vallentuna) i vilket omkring 90000 2-hjuliga Avfallkärl finns utplacerade (ej Stockholm inräknad). Årligen måste uppskattningsvis 1 % av dessa kärl kasseras och återvinnas. Eftersom hjulaxel, hjul och kärl måste separeras från varandra innan återvinningsprocessen kan börja så har SÖRAB efterlyst en demonteringsmaskin som kan utföra detta. Målet med projektet var att ta fram en maskin somuppfyller följande kravspecifikation:

    ● Demonteringsprocessen får ej överstiga 2 min

    ● Lösningen skall passa avfallskärl i stl. 80370 liter

    ● Kärlen skall kunna staplas efter demontering

    ● Skaderisken vid användning skall vara låg

    ● Inlärningsprocessen för användning skall vara mindre än 5 min

    ● Lösningen skall vara lämpad för inomhusbruk

    Inledningsvis så genomfördes en litterär studie där avfallskärlens tillverkningsprocess, sammansättning, utformning och användningsområde undersöktes. Därefter skapades ett Function means tree vars syfte var att reducera problemet till de enklast möjliga funktioner som måste uppfyllas. Detta gav underlag för en brainstormingfas då ett flertal koncept togs fram. Koncepten utvärderades med hjälp av empiriska tester i verkstadsmiljö samt HarrisProfilmetoden som underlättade valet av det mest lovande konceptet. Ett mer detaljerat slutkoncept togs fram och vitala delar dimensionerades i avseende på hållfastighetslära och mekanik. Resultatet blev en komplett CAD-modell skapad i Solid Edge. Ritningar togs fram på de komponenter som måste egentillverkas och en fullständig kostnadsanalys gjordes på de komponenter som måste köpas in samt material. Priset för att tillverka maskinen blev i slutändan drygt 70 000 kr. De empiriska studierna visade att maskinen uppfyller de flesta kraven med god marginal. Demonteringstiden är långt under 2 min och maskinen har även förmågan att transportera och stapla kärlen. Vissa orosmoment finns när det kommer till skaderisk eftersom maskinen består av en tung stålstruktur som rör sig i relativt höga hastigheter. Det är viktigt att detta kompenseras för genom ordentlig genomgång av användning eller att områden där stålstrukturen rör sig i spärras av tydligt. I nuläget saknas ett styrningsystem till maskinen. Det kommer bland annat krävas ett gränssnitt där operatören kan kommunicera vad för typ av kärl som är aktuellt för demonteras till maskinen. Detta kommer krävs viss programmering nåt som inte hanns med inom tidsramarna för det här projektet. Det är på författarens rekommendationer att SÖRAB går ut med exempelvis ett kandidatarbeteuppdrag där detta gränssnitt kan arbetas fram.

  • 11506. Åsbogård, M.
    et al.
    Johannesson, L.
    Angervall, D.
    Johansson, Peter
    KTH.
    Improving system design of a hybrid powertrain using stochastic drive cycles and dynamic programming2007Ingår i: SAE technical paper series, ISSN 0148-7191Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new approach for system design of hybrid powertrains was demonstrated in a case study. The method is based on the following presumptions: The performance of a Hybrid Powertrain Concept (HPC) is evaluated using computer simulation; a HPC cannot be correctly evaluated without an Energy Management Strategy (EMS) for the energy buffer; the optimal EMS is different for each HPC. Dynamic programming was used to generate EMSs that were optimal for the vehicles intended traffic environment and for each given HPC, enabling evaluation of a large number of HPCs. Over-adaptation of the EMSs was avoided by using a stochastic drive cycle model. The final delivery is a competitive powertrain component sizing and the corresponding optimal EMS.

  • 11507.
    Åslund, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Svetsteknologi. KTH, Centra, XPRES, Excellence in production research. Scania CV, Stockholm, Sweden.
    Melander, Arne
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Svetsteknologi. KTH, Centra, XPRES, Excellence in production research. Swerea KIMAB, Stockholm, Sweden.
    Johansson, Krister
    Scania CV, Stockholm, Sweden.
    Haglund, Sven
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Svetsteknologi. KTH, Centra, XPRES, Excellence in production research. Swerea KIMAB, Stockholm, Sweden.
    Hosseini, Seyed B.
    Swerea IVF, Stockholm, Sweden.
    Influence of tempering on contact fatigue2009Ingår i: New challenges in heat treatment and surface engineering, conference in honour of Prof Božidar Liščić, Dubrovnik, Cavtat, Croatia 9-12 June 2009, 2009, s. 87-94Konferensbidrag (Refereegranskat)
    Abstract [en]

    Most components are tempered after heat treatment operations such as case hardening orinduction hardening. The common opinion is that the martensitic structure after heat treatmentis too brittle and tempering is necessary to increase toughness.

    Tempering is an additional operation which leads to increased costs by energy, handling,and investments. Eliminating tempering from the heat treatment process leads to increasedproductivity, energy savings, and lowered environmental impact.

    Two carburised steels, Ovako 253 and 20NiCrMo2 (AISI 8620, SS2506), were tested forcontact fatigue resistance in a roller to roller rig. The tested samples were characterised withrespect to amount of fatigue damage, residual stress, amount of retained austenite andhardness. The objective was to determine if tempering is always necessary after a heattreatment operation.

    The contact fatigue tests show that tempering results in lower contact fatigue resistance.

  • 11508.
    Åstrand, Erik
    et al.
    Volvo Construction Equipment AB.
    Stenberg, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Jonsson, Bertil
    Volvo Construction Equipment AB.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Welding procedures for fatigue life improvement of the weld toe2016Ingår i: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 60, nr 3, s. 573-580Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents the results of an experimental study of gas metal arc welded, GMAW, cruciform joints made of common construction steel S355. The hypothesis is that smooth undercuts in as welded conditions can give enhanced fatigue properties similarly as post treated welds. Undercuts are generally seen as a defect or imperfection. Welders try to avoid these and repair them when they occur, which result in increased production lead time. Post weld improvement methods i.e. grinding or high-frequency-impact treatment (HFMI) as fatigue-enhancing post-treatment methods enforce amongst other effects a certain smooth undercut-shaped groove in the treated weld toe region. The obtained shallower weld toe transition reduces the geometrical notch effect and increases fatigue strength. This paper presents a study whereas welded specimens with a weld toe geometry similar to what is obtained by weld toe grinding or HFMI-treatment, has been produced, fatigue tested and analyzed. The improvement of the fatigue strength is comparable to post-weld treated specimens. It has proven to be an efficient way to achieve high-quality welds without introducing any additional operations in production, thus enabling weight reduction using cost-effective methods.

  • 11509.
    Åstrand, Max
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik. ABB Corp Res, Control Optimizat & Analyt, Automat Solut, Vasteras, Sweden..
    Johansson, Mikael
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Reglerteknik.
    Greberg, J.
    Lulea Univ Technol, Dept Civil Environm & Nat Resources Engn, Div Min & Geotech Engn, Lulea, Sweden..
    Underground mine scheduling modelled as a flow shop: a review of relevant work and future challenges2018Ingår i: The Southern African Journal of Mining and Metallurgy, ISSN 2225-6253, E-ISSN 1543-9518, Vol. 118, nr 12, s. 1265-1276Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Advanced planning and automation are increasingly important in modern mines. Sophisticated methods for long-term mine planning are often used, and the advent of autonomous machines makes the actual operation more predictable. However, the interface between these two timescales, i.e. the scheduling of the mobile production fleet, often limits the ability to operate mines at maximum profitability. We show how scheduling the production fleet in an underground mine can be modelled as a flow shop. A flow shop is a general abstract process formulation that captures the key properties of a scheduling problem without going into specific details. Thus, the flow shop enables mine scheduling to reap the benefits of scheduling research from other industries. We review recent results from the mining community and the flow shop community, and introduce scheduling methods used in these two fields. This work aims at providing value to researchers from the mining community who want to leverage their skill set, as well as to theoretical researchers by presenting the mining process as a potential application area. Lastly, we discuss the results, and outline some future challenges and opportunities facing the industry.

  • 11510. Åström, Alexander
    et al.
    Izosimov, Viacheslav
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Mekatronik.
    Örsmark, Ola
    Efficient Software Tool Qualification for Automotive Safety-Critical Systems2011Konferensbidrag (Övrigt vetenskapligt)
  • 11511.
    Åsén, Per-Olov
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    A parallel code for direct numerical simulations of pipe Poiseuille flowManuskript (Övrigt vetenskapligt)
  • 11512.
    Åsén, Per-Olov
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk Analys och Datalogi, NADA.
    Stability of plane Couette flow and pipe Poiseuille flow2007Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis concerns the stability of plane Couette flow and pipe Poiseuille flow in three space dimensions. The mathematical model for both flows is the incompressible Navier--Stokes equations. Both analytical and numerical techniques are used.

    We present new results for the resolvent corresponding to both flows. For plane Couette flow, analytical bounds on the resolvent have previously been derived in parts of the unstable half-plane. In the remaining part, only bounds based on numerical computations in an infinite parameter domain are available. Due to the need for truncation of this infinite parameter domain, these results are mathematically insufficient.

    We obtain a new analytical bound on the resolvent at s=0 in all but a compact subset of the parameter domain. This is done by deriving approximate solutions of the Orr--Sommerfeld equation and bounding the errors made by the approximations. In the remaining compact set, we use standard numerical techniques to obtain a bound. Hence, this part of the proof is not rigorous in the mathematical sense.

    In the thesis, we present a way of making also the numerical part of the proof rigorous. By using analytical techniques, we reduce the remaining compact subset of the parameter domain to a finite set of parameter values. In this set, we need to compute bounds on the solution of a boundary value problem. By using a validated numerical method, such bounds can be obtained. In the thesis, we investigate a validated numerical method for enclosing the solutions of boundary value problems.

    For pipe Poiseuille flow, only numerical bounds on the resolvent have previously been derived. We present analytical bounds in parts of the unstable half-plane. Also, we derive a bound on the resolvent for certain perturbations. Especially, the bound is valid for the perturbation which numerical computations indicate to be the perturbation which exhibits largest transient growth. The bound is valid in the entire unstable half-plane.

    We also investigate the stability of pipe Poiseuille flow by direct numerical simulations. Especially, we consider a disturbance which experiments have shown is efficient in triggering turbulence. The disturbance is in the form of blowing and suction in two small holes. Our results show the formation of hairpin vortices shortly after the disturbance. Initially, the hairpins form a localized packet of hairpins as they are advected downstream. After approximately $10$ pipe diameters from the disturbance origin, the flow becomes severely disordered. Our results show good agreement with the experimental results.

    In order to perform direct numerical simulations of disturbances which are highly localized in space, parallel computers must be used. Also, direct numerical simulations require the use of numerical methods of high order of accuracy. Many such methods have a global data dependency, making parallelization difficult. In this thesis, we also present the process of parallelizing a code for direct numerical simulations of pipe Poiseuille flow for a distributed memory computer.

  • 11513.
    Åsén, Per-Olov
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk Analys och Datalogi, NADA.
    Kreiss, Gunilla
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk Analys och Datalogi, NADA.
    On a Rigorous Resolvent Estimate for Plane Couette Flow2007Ingår i: Journal of Mathematical Fluid Mechanics, ISSN 1422-6928, E-ISSN 1422-6952, Vol. 9, nr 2, s. 153-180Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We derive a rigorous bound of the solution of the resolvent equation for plane Couette flow in three space dimensions. We combine analytical techniques with numerical computations. Compared to earlier results, our analytical techniques cover a larger part of the parameter domain consisting of wave numbers in two space directions and the Reynolds number. Numerical computations are needed only in a compact subset of the parameter domain.

  • 11514.
    Åsén, Per-Olov
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk Analys och Datalogi, NADA.
    Kreiss, Gunilla
    KTH, Skolan för datavetenskap och kommunikation (CSC), Numerisk Analys och Datalogi, NADA.
    Resolvent bounds for pipe Poiseuille flow2006Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 568, s. 451-471Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We derive an analytical bound on the resolvent of pipe Poiseuille flow in large parts of the unstable half-plane. We also consider the linearized equations, Fourier transformed in axial and azimuthal directions. For certain combinations of the wavenumbers and the Reynolds number, we derive an analytical bound on the resolvent of the Fourier transformed problem. In particular, this bound is valid for the perturbation which numerical computations indicate to be the perturbation that gives the largest transient growth. Our bound has the same dependence on the Reynolds number as given by the computations.

  • 11515.
    Åsén, Per-Olov
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Kreiss, Gunilla
    Uppsala Univ, Dept Informat Technol..
    Rempfer, Dietmar
    IIT, Chicago.
    Direct numerical simulations of localized disturbances in pipe Poiseuille flow2010Ingår i: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 39, nr 6, s. 926-935Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider pipe Poiseuille flow subjected to a disturbance which is highly localized in space. Experiments by Peixinho and Mullin have shown this disturbance to be efficient in triggering turbulence, yielding a threshold dependence on the required amplitude as R-1.5 on the Reynolds number, R. The experiments also indicate an initial formation of hairpin vortices, with each hairpin having a length of approximately one pipe radius, independent of the Reynolds number in the range of R = 2000-3000. We perform direct numerical simulations for R = 5000. The results show a packet of hairpin vortices traveling downstream, each having a length of approximately one pipe radius. The perturbation remains highly localized in space while being advected downstream for approximately 10 pipe diameters. Beyond that distance from the disturbance origin, the flow becomes severely disordered.

  • 11516.
    Åteg, Mattias
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.).
    Aktiviteter och lärande för attraktivt arbete.: Utvecklingsprocesser inom verkstadsindustrin2006Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Avhandlingsarbetet utgår från ett nätverk av mindre verkstadsföretag som under mer än fem års tid varit engagerade i utvecklingsprocesser för att skapa mer attraktiva arbeten. Arbetet har genomförts inom ramen för att…-projektet i samverkan mellan Högskolan Dalarna och Arbetslivsinstitutet. Det övergripande syftet är att utveckla kunskap om och förståelse för utvecklingsprocesser med utgångspunkt i att skapa mer attraktivt arbete. Särskilt intresse ägnas åt hur dynamiken i utvecklingsprocesserna kan analyseras utifrån ett lärandeperspektiv. Ett resonemang förs om utvecklingsprocessernas karaktär och om egenskaper i arbetets attraktivitet. Ansatsen kan beskrivas som interaktiv forskning med tät interaktion med praktiker i verkstadsföretag och i lokalt utvecklingsarbete. Metodansatsen är aktions-, och processorienterad. Attraktivt arbete ses som ett processuellt begrepp, dvs ett strävansmål utifrån individers upplevelser, vilka är stadda under förändring. En distinktion görs mellan en skalbetonad (tilldragande) och en innehållsbetonad (behållande) egenskap. Avhandlingen baseras på fyra delstudier.

    Utifrån tidigare forskning och eget material skapas en analysram över utvecklingsprocessers dynamik avseende aktivitetsnivåer och lärdimensioner. Processer kan ut¬ifrån ramen karaktäriseras som ställföreträdande förändring, skalförändrande utveckling, temporärt förändrande utveckling eller reflektiv utveckling. Faktaunderlag och diskussioner har i en spegelmetod utgjort grund för företagens reflektion om interna och externa förhållanden. Aktiviteter för att skapa attraktiva arbeten har skett på diagnos-, intentions-, och handlingsnivå. Analysramen tillämpas på dels utvecklingsprocesser inom fem verkstadsföretag, dels lokalt utvecklingsarbetet för mer attraktiv industriutbildning.

  • 11517.
    Åteg, Mattias
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.).
    Attraktiv industriutbildning på gymnasiet: Ett deltagandeperspektiv på lokalt utvecklingsarbete2005Ingår i: Arbetsliv i omvandling, ISSN 1404-8426, Vol. 2, s. 1-110Artikel i tidskrift (Refereegranskat)
    Abstract [sv]

    Studiens syfte var att skapa förståelse för hur lokalt utvecklingsarbete kan öka industriprogrammetsattraktivitet för ungdomar i valet av gymnasieutbildning, och för att programmet ska vara attraktivt förelever som studerar på programmet.Ett särskilt intresse ägnas åt samverkan mellan gymnasieskola och lokala verkstadsföretag, samt åtinsatser med betoning på utveckling av den arbetsplatsförlagda utbildningen – APU.Under ett flertal år har antalet elever på industriprogrammet i Sverige minskat kraftigt. Samtidigt sermånga industriföretag en brist på utbildad arbetskraft som ett stort hinder för framtiden.Sökandetrycket, mätt i antalet förstahandssökande, har minskat med mer än tre fjärdedelar sedan slutetav 1980-talet.År 2001 sökte två elever till industriprogrammet i Avesta. Insatser för att öka industriprogrammetsattraktivitet fick ett överväldigande resultat – totalt 63 elever sökte till industriprogrammet 2002.Tjugonio elever sökte programmet i första hand.Undersökningar har gjorts av hur ungdomar som sökt och studerar på industriprogrammet sett på sittgymnasieval, på utbildningen, på APU samt på ett framtida industriarbete. Ett särskilt fokus har varit omeleverna gett uttryck av att vara vilseledda och inlurade på utbildningen genom insatser för ett merattraktivt industriprogram.Information om industriprogrammet, om branschen och om industriarbete har visat sig vara av stortvärde för att öka utbildningens attraktivitet. Vikten av en ärlig bild poängteras: det är bättre att visa upprealistiska arbetsmiljöer och arbetsinnehåll, än att peka på en alltför ”modern” bild som branschen intekan leva upp till.Tidigare litteratur har visat att elever har känt sig utnyttjade då de ingått i den ordinarie produktionen påAPU. I denna studie har eleverna istället ansett detta vara något positivt. Det har gett en känsla av att fåarbeta ”på riktigt”, samtidigt som det gett större acceptans för det som varit tråkigare eller mindreintressant. Eleverna som fått arbeta i produktionen har förmedlat en känsla av att ha blivit behandladesom de anställdas jämlikar.

  • 11518.
    Åteg, Mattias
    et al.
    Högskolan i Dalarna.
    Andersson, Ing-Marie
    Högskolan i Dalarna.
    Rosén, Gunnar
    Högskolan i Dalarna.
    Change Processes for Attractive Work in Small Manufacturing Companies2009Ingår i: Human Factors and Ergonomics in Manufacturing, ISSN 1090-8471, E-ISSN 1520-6564, Vol. 19, nr 1, s. 35-63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The article originates from research in interaction between researchers and companies in a network,which has led to an increasing awareness among managers on issues such as reasons behind difficultiesin attracting competent labor. Particularly, attention has been directed toward the importance ofwork environment improvements that increase the attractivity of industrial work. To deal with suchchallenges, for more than 5 years a number of small engineering companies, with research support,have been engaged in change processes based on the concept of attractive work. The purpose of thearticle is to develop knowledge and understanding for how small engineering companies can createmore attractive work. One goal is to make it possible to draw conclusions about the employees’ experiencesof changes in the attractivity of industrial work. Efforts in this direction have been conductedthrough work environment assessments (before and after the changes) and through administration ofa questionnaire. The results show that it is possible to analyze how employees experience changes inthe attractivity of work. This is most interesting from the perspective that the results can be used forassisting further improvements.

  • 11519.
    Åteg, Mattias
    et al.
    KTH, Tidigare Institutioner                               , Industriell ekonomi och organisation.
    Hedlund, Ann
    KTH, Tidigare Institutioner                               , Industriell ekonomi och organisation.
    Pontén, Bengt
    Attraktiv arbete: från anställdas uttalanden till skapandet av en modell2004Ingår i: Arbetsliv i omvandling, ISSN 1404-8426, Vol. 1, s. 63-Artikel i tidskrift (Refereegranskat)
    Abstract [sv]

    Syftet med undersökningen var att skapa fördjupad kunskap och förståelse förvad som gör arbete attraktivt, samt skapa en modell vars generaliserbarhet sedanprövas. Studien hade en kvalitativ ansats, med utgångspunkt i en kartläggningsmetod.Resultaten av studien ställs mot tidigare forskning i form av organisations- ochmotivationsteorier, samt mot tidigare litteratur om attraktivt arbete och närliggandebegrepp. Ett konstaterande var att den tidigare litteraturen på områdetinte är tillräcklig för en förståelse av vad som gör arbete attraktivt, då den oftahar andra utgångspunkter.I analyserna av det empiriska materialet har tre kategorier identifierats. Attraktivtarbetsinnehåll innehåller dimensioner som handlar om vad och hur denanställde gör under utförandet av arbetet. Exempel är arbetstakt, handlingsfrihetoch variation. Arbetstillfredsställelse innehåller dimensioner som handlar om vadden anställde upplever att den får ut av att utföra arbetet. Exempel är erkänsla,status och stimulans. Attraktiva arbetsförhållanden innehåller dimensioner som ärgemensamma för alla anställda på ett företag, dvs de är inte beroende av despecifika arbetsuppgifterna eller av vad den anställda upplever att den får ut avatt utföra arbetet. Exempel är arbetstiden, den fysiska arbetsmiljön och ledarskap.Modellen av attraktivt arbete representerar en helhetssyn på vad som gör ettarbete attraktivt och kan ligga till grund för fortsatt forskning eller utvecklingsarbete.Innehållet i modellen stämmer väl överens med det som tidigareforskning har visat är viktigt. Men samtidigt finns ett behov av att lära en del avde äldre tankestrukturerna, eftersom de innehåller drag som i vissa fall står imotsats till attraktivt arbete.

  • 11520.
    Çinar, O.Y.
    et al.
    Linnæus University, International Centre of Mathematical Modelling, School of Computer Science, Physics and Mathematics, Sweden. Gebze Institute of Technology, Department of Mathematics, Turkey.
    Boij, Susann
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Çinar, G.
    Linnæus University, International Centre of Mathematical Modelling, School of Computer Science, Physics and Mathematics, Sweden. Gebze Institute of Technology, Department of Mathematics, Turkey.
    Nilsson, B.
    Linnæus University, International Centre of Mathematical Modelling, School of Computer Science, Physics and Mathematics, Sweden.
    Jet pipe reflections - Influence of geometrical and flow exit conditions2010Ingår i: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010, s. 2010-4013-Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we study the influence of the exit conditions on the acoustic reflections at a jet pipe opening. For the flow exit conditions, the model of Munt assuming a vortex sheet at the exit of a semi-infinite jet pipe is improved by considering more general coupling conditions. We focus on modelling the acoustic properties at the shear layer in general and the stability properties in particular. Experimental methods are used for studying primarily the geometric exit conditions. Both theoretical and experimental results are presented and discussed. Numerical results related to the theory show that the thickness of the shear layer causes an expected increase in the magnitude of the reflection coefficient compared to the original infinitely thin shear layer in the Munt model. The experimental results, on the other hand, show that there are additional effects due to the presence of thick walls at the exit of the straight pipes used in the experiments. These effects are observed to be more dominant than the effects due to the shape of the edges. Based on the discussions, further theoretical and experimental investigations are proposed.

  • 11521. Öberg, J.
    et al.
    Andersson, Evert
    Determining the deterioration cost for railway tracks2009Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 223, nr 2, s. 121-129Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The cost of maintaining and renewing railway tracks affected by traffic-dependent deterioration is considerable. It is important not only to have proper maintenance regimes, but also to have knowledge of the interaction between vehicles and track in order to reduce the deterioration of both. In a joint project between Banverket (Swedish Rail Administration) and KTH (Royal Institute of Technology, Stockholm), a model for track deterioration is developed, considering track settlement, component fatigue, abrasive wear, and rolling contact fatigue of rails. The basis of the model is taken from what is considered as state-of-the-art knowledge. The model is used as a basis for a proposed new track access charging regime for Banverket, able to differ between vehicle types based on their characteristics and tendency to deteriorate the tracks. The model is implemented in an Excel (R) environment and applied to Swedish mainline traffic and vehicles. Using representative vehicle characteristics in determining track deterioration, it is predicted that there are large differences between different vehicles regarding their deterioration of the tracks. The model predicts axle load, unsprung mass, and wheelset steering capability as decisive for track deterioration. The model is believed to predict realistic results also for heavy-haul rail operations.

  • 11522.
    Öhman, Henrik
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Implementation and evaluation of a low temperature waste heat recovery power cycle using NH 3 in an Organic Rankine Cycle2012Ingår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 48, nr 1, s. 227-232Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With increasing cost for power generation opportunities for small scale power generation from waste heat have increased. The awareness of untapped resources such as local waste heat streams as well as the available range of technology and products to harvest such streams is increasing steadily though field data is scarce for applications below 100 °C entry temperature. ORC applications have a large number of open parameters and therefore require field data for correlation of models.This paper presents field data and analysis of an ORC power generation plant operating with NH 3. The unit operates on waste heat from a Swedish pulp mill at an available temperature of 75 to 85 °C. Performance at varying heat source conditions and capacity is reported as well as an analysis of the particular investment case.The data was generated during a 15 day period and show a thermal efficiency of 8-9% at capacities from 50 to 100%. The results indicate a flat thermal efficiency from 20 to 100% capacity.Investment case analysis is based on a purchase model while the chosen economic model is a supplier own-and-operate arrangement supplying the mill with power at a predefined cost during an extended period of time.

  • 11523.
    Öhman, Henrik
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Implementation and evaluation of low temperature waste heat recovery power cycle using NH3 in an organic rankine cycle2011Ingår i: / [ed] Zvonimir Guzovic, Zagreb: Faculty of Mechanical Engineering and Naval Architecture , 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    With increasing cost for power generation the opportunities for small scale powergeneration from waste heat have increased. The awareness of untapped resources such aslocal waste heat streams as well as the available range of technology and products toharvest such streams is increasing steadily. For ORC power plant applications the numberof open parameters is large though the reported field data is limited, particularly for lowtemperature waste heat recovery.This paper presents field data and a performance analysis of an ORC powergeneration plant operating with NH3 as media. The ORC unit operates on waste heat froma Swedish pulp mill at an available temperature level of 75 to 85degC. Performance at lowwaste heat temperatures and during capacity variation is reported as well as an analysisof the particular investment case.The field data was generated by remote logging of control system information during a 15day period.The results show a thermal efficiency of 8 to 9% during a capacity range of 50 to 100%power generation. The results indicate a flat thermal efficiency curve from 20 to 100%power generation. The investment case is a supplier own-and-operate type of arrangement supplying thepulp mill with electric power at a predefined cost during a long period of time.

  • 11524.
    Öhman, Henrik
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Low temperature difference power systems and implications of multi-phase screw expanders in Organic Rankine Cycles2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    New and old data on screw expanders operating with 2-phase mixtures in the admission line has been combined to enable the first public correlation of adiabatic expansion efficiency as a function of entry vapour fraction. Although not yet perfected, these findings have enabled an entirely new approach to the design and optimisation of Organic Rankine Cycles, ORCs. By allowing a continuous variation of vapour fraction at expander entry optima for thermal efficiency, second law efficiency and cost efficiency can be found. Consequently one can also find maxima for power output in the same dimension.

    This research describes a means of adapting cycle characteristics to various heat sources by varying expander inlet conditions from pure liquid expansion, through mixed fluid and saturated gas expansion, to superheated gas. Thermodynamic analysis and comparison of the above optimisations were a challenge. As most terms of merit for power cycles have been developed for high temperature applications they are often simplified by assuming infinite heat sinks. In many cases they also require specific assumptions on e.g. pinch temperatures, saturation conditions, critical temperatures etc, making accurate systematic comparison between cycles difficult. As low temperature power cycles are more sensitive to the ‘finiteness’ of source and sink than those operating with high temperatures, a substantial need arises for an investigation on which term of merit to use.

    Along with an investigation on terms of merit, the definition of high level reversible reference also needed revision. Second law efficiency, in the form of exergy efficiency, turned out to be impractical and of little use. A numerical approach, based on a combination of first and second law, was developed. A theory and method for the above is described. Eventually low temperature power cycle test data was compiled systematically. Despite differences in fluid, cycle, temperature levels and power levels the data correlated well enough to allow for a generalised, rough correlation on which thermal efficiency to expect as a function of utilization of source and sink availability. The correlation on thermal efficiency was used to create a graphical method to pre-estimate key economic factors for low temperature site potential in a very simple manner. A major consequence from the findings of this thesis is the reduced dependency on unique choices of process fluid to match heat source characteristics. This development significantly simplifies industrial standardisation, and thereby potentially improves cost efficiency of commercial ORC power generators.

  • 11525.
    Öhman, Henrik
    Svenska Rotor Maskiner AB.
    Test Results of A Screw Type Expander/. Compressor and the Implication of Phase. Separators on the Refrigeration Process2004Ingår i: 2004 International Refrigeration and Air Conditioning Conference, West Lafayette, Indiana, USA: Purdue University Press, 2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    Running a refrigeration cycle at saturated liquid conditions at the evaporator inlet has a few interesting advantages in comparison to the conventional 2-phase situation. Opportunities in using novelty heat exchangers, increased cycle efficiency and significantly reduced main compressor sizes occur. Using the two rotor integrated

    compressor/expander idea developed by Olofsson (1993) in a refrigeration cycle theoretically offer the possibility of pure liquid evaporator inlet conditions, the device is called Phase Separator. This paper reports results from hardware tests as well as some theoretical results. To evaluate the efficiency of a Phase Separator three terms of efficiency are suggested. The test results prove that pure liquid conditions to the evaporator are obtainable with a practical Phase Separator.

  • 11526.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Comparison and analysis of performance using Low Temperature Power Cycles2013Ingår i: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 52, nr 1, s. 160-169Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Low Temperature Power Cycles have become increasingly interesting means of increasing energy efficiency of processes as well as for base load power generation from solar, and geothermal, heat. Theoretical understanding of the various processes, components and limitations is constantly increasing through extensive research. Practical utilisation of this knowledge is also increasing steadily though properly published field data is scarce. In this article a number of different solutions for power generation from low temperature heat sources have been gathered and analysed. Some of the studied units have not previously been described. A method for general evaluation of LTPC's is proposed and the outcome of the analysis is discussed as well as how to use it for practical purposes. By separating thermodynamic potential from irreversibilities the analysis indicates that the irreversibilities show limited dependency on temperature, size, thermodynamic cycle or working fluid. Instead performance of the studied units follows a relatively simple correlation with utilisation of the thermal potential. This correlation is defined and discussed. One conclusion is that the correlation allows for a possibility to express the maximum expected real power generation with knowledge of the characteristics of the heat source and heat sink only.

  • 11527.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Experimental investigation of a Lysholm Turbine operating with superheated, saturated and 2-phase inlet conditions2013Ingår i: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 50, nr 1, s. 1211-1218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Low temperature power cycles can benefit from the use of multi-phase flow expansion devices from a thermodynamic cycle efficiency point of view. Particularly power cycles such as ORC, Kalina and Trilateral Flash Cycles can be improved by multi-phase expansion. This article presents the experimental findings in a series of laboratory tests on a semihermetic Lysholm Turbine operating with R134a with superheated, saturated and wet inlet gas conditions. The test arrangements are described as well as discussion on the relevance of such test data. Finally comparison is made with findings from other investigations and recommendations for further studies are made. A correlation between peak efficiency and sensitivity to inlet vapour fraction was discovered which allows for estimations of adiabatic efficiencies with 2-phase inlet conditions even when only test data, or simulations, from single phase inlet conditions exist. The conclusions made are that Lysholm Turbines are well suited for low temperature power generation and that further understanding of the performance during 2-phase conditions is required.

  • 11528.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    On high level evaluation and comparison of ORC power generators2015Ingår i: Proceedings of the 3rd International Seminar on ORC Power Systems, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    A review of the thermodynamic performance of ORCs from public, as well as non-public sources hasrevealed a correlation suitable to be used as a rule of thumb for  high-level performance estimation ofORC power generators. Using the correlation, the limited amount of available test data can begeneralised leading to a high level evaluation of the commercial benefits of any potential applicationfor ORCs.Power generators using ORC-technology exist in relatively low numbers. Furthermore, fieldinstallations seldom imply comparable boundary conditions. As ORCs generally  operate at lowtemperature differences between source and sink it has been shown that their relative sensitivity tovariations in temperatures i.e. the finiteness of source- and sink, is larger than the sensitivity of powergenerators operating with large temperature differences. Therefore the establishing of practical rule ofthumb performance estimation, similar to the figure of merit, Coefficient of Performance, COP, asused in refrigeration and air conditioning industry, has previously not been successful.In order to arrange field data in a manner suitable for comparison a refinement of suitable figures ofmerit was required. The suggested, refined terms are presented and explained as well as criticallyevaluated against the most common  efficiency terms traditionally used.The current lack of a performance rule of thumb leaves room for less serious vendors and laymen tomake performance claims unrealistic to practical achievements. Scrutinizing such questionablestatements requires detail process simulations and a multitude of technical assumptions. Henceargumentation becomes ineffective. If a suitable rule of thumb can be established argumentationagainst dubious claims would become significantly more forceful.This paper suggests a new term to be used as rule of thumb and explains a  method on how to use it.

  • 11529.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Screw expanders in ORC applications, review and a new perspective2015Ingår i: Proceedings of the 3rd International Seminar on ORC Power Systems, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    Performance of Organic Rankine Cycles is sensitive not only to the entry  temperature ratio betweenheat source and heat sink but also to the temperature  degradation of the heat source flow, caused bythe heat transfer to the process in pre-heater, evaporator and super heater. In order to adopt the cycleto the great variety of heat sources a multitude of fluids are required. Alternatively fluid mixtures,trans-critical or supercritical fluid conditions can be used to match the process temperatures with theheat source. Screw expanders offer an alternative, new approach to the matching problem of ORC’s asthey allow for flexible multi-phase expansion. Hereby the vapour fraction at the expander entry can beused to  partially match the temperatures of the process to a particular heat source. To provide aperspective on the use of such screw expanders in ORC-systems previous experimental andcommercial experience have been reviewed and discussed.Screw expanders are versatile machines used for the production of mechanical work in power rangesfrom 3kW to 1.5MW. As the functional characteristics differ significantly  from dynamic expandersthe explanatory models used to generalise results are different. Plenty of research has resulted in wellgeneralized explanatory models for dynamic expander analysis. For screw expanders similarexplanatory models exist mainly in commercially confidential environments. A few public sourcesdisclose test data. In the few cases data has been investigated the analyses tend to rely onthermodynamic models suitable for dry gas expansion. Typically that leads to reasonable replicationof test results but seldom to models suitable for detailed understanding of the process. In applicationswith 2-phase expansion the theories used to simulate functional characteristics is entirely insufficient.The main reason for  the scarcity of work in this field is probably the empirical difficulties in obtaininggood measuring data in multi-phase conditions.This paper describes a review of multi-phase screw expander experiences and explains why a uniquetheory is required to model its characteristics. In the absence of such a unique theory a correlationbased in empirical data is presented. This allow for estimations of screw expander efficiency in multi-phase conditions. Measured efficiency with dry expansion, or such efficiency simulated, can be usedto estimate adiabatic efficiency with expansion entry vapor fractions ranging from 0 to 1 by using thiscorrelation. Hence estimating expansion efficiency during multi-phase expansion is simplified,allowing for better optimisation of the ORC-systems. This way a new perspective of screw expanderpotential in ORC system integration can be presented.

  • 11530.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Lundqvist, Per
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Theory and method for analysis of low temperature driven power cycles2012Ingår i: Applied Thermal Engineering, ISSN 1359-4311, nr 37, s. 44-50Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new method, using a combination of traditional first law and second law analysis, is developed to facilitate characterization and comparison of power cycles using low temperature heat sources. In trying to determine the best thermodynamic cycle and working media for a given application one must take the strongly non-linear effects of matching the pinch points of a particular cycle with a particular working media into account. The new method allows unbiased comparison of arbitrarily chosen power cycles, working fluids and component characteristics. The method also allows for operating conditions with finite capacity heat source and heat sink. The usefulness of the method is illustrated by the analysis of the effects of local temperature difference distribution for three different fully reversible power cycles using three different working media.

    The driver for developing this method is to simplify comparison and communication among users and industrial professionals and thus enable a better understanding of characteristics and design criteria for low temperature heat driven power cycles.

  • 11531.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Per, Lundqvist
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Organic Rankine Cycles with variable vapour fraction expansion entry: Reduced sensitivity to choice of working fluid in modified Organic Rankine Cycles by using wet vapour expansion entry conditions2014Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The task of reducing global carbon dioxide emissions leads to a need to reduce the average CO2-emission in power generation. A more energy efficient mix of power generation on national, or regional level, will require the re-use of waste heat and use of primary, low temperature heat for power generation purposes. Low Temperature Power Cycles, such as Organic Rankine Cycles, Trilateral Flash Cycles, Kalina Cycles offer a large degree of freedom in finding technical solutions for such power generation.

    Theoretical understanding of LTPC’s advance rapidly though practical achievements in the field show very humble improvements at a first glance. Cost of applying the new knowledge in real applications seems to be an important reason for the discrepancy. One central reason for the high cost level is the diversity of process fluids required and consequently the lack of standardization and industrialization of equipment. Uses of supercritical power cycle technology tend to cause the same dilemma. Furthermore upcoming regulations prohibiting the use of several process fluids tend to lead to remedies increasing plant cost.

    By using 2-phase, variable vapour fraction, expansion inlet conditions the need to use many different process fluids is reduced, allowing simpler and more cost efficient LTPC’s by easier matching with heat source temperature characteristics. This article explores some of the associated effects on cycle output and cost efficiency. A waste heat recovery application is investigated simulating cost efficiency, thermodynamic efficiencies and power generation while using fundamentally different working fluids, lumped component efficiencies, variable utilization of the waste heat and optimisation on expansion inlet vapour fraction.

    The conclusion made is that the sensitivity to choice of working fluid is lower than intuitively anticipated, in contrast to common consensus in science. Furthermore it is shown that exceptional component efficiencies are not required in order to achieve a performance comparable to current practise and that a good business case is possible under the assumed economic conditions.

  • 11532.
    Öhman, Henrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Per, Lundqvist
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Thermodynamic pre-determination of power generation potential in geothermal low-temperature applications2014Ingår i: Geothermal Energy, ISSN 2195-9706, Vol. 2, nr 1, s. 1-10, artikel-id 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Small capacity, low temperature, geothermal heat sources providesignificant opportunities for distributed, small scale power generation. Projectdefinitions and pre-dimensioning however require advanced thermodynamicengineering at a cost independent of project size. In order to reduce this cost, anew method has been developed to allow basic level engineers to performpre-optimisation of thermodynamic potential as well as expected performance usingavailable power plant technology at such pre-optimized conditions.Results: By reducing the complexity of second-law computations, a simpletwo-dimensional diagram is shown representing the dimensioning criteria requiredfor maximum power generation using the particular heat source and sink whileconsidering expected power plant performance, using systems and componentson the market.Methods: By sensitivity analysis the combination of thermodynamic analysis and realworld data correlations was simplified and arranged for pre-dimensioning ofbusiness cases.Conclusions: Optimal pre-dimensioning of power generation system for anygeothermal heat source, with a defined heat sink, can be determined withoutadvanced thermodynamic expertise. This reduces the cost for business case proposals,pre-dimensioning and tender specifications of small-scale power generation systemsfor low temperature heat sources. The intended implication of this work is to increasethe use of low-temperature geothermal wells for distributed power generation.

  • 11533.
    Öhnander, Fred
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon.
    An Attempt Towards FE-Modelling of Fracture Propagation in Railway Wheels2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Efterfrågan på högre hastigheter och tyngre axelbelastningar för godståg leder till högre krafter på järnvägshjulen som i sin tur leder till ökade spänningar på och under ytan vid hjul-räl-kontakten. Med tiden induceras slitage på hjulen som följaktligen leder till höga underhållskostnader och i vissa fall olyckor. Förmågan att förutse utvecklingen av hjulprofiler på grund av enhetligt slitage har visats kunna ske med en noggrann precision under de flesta driftsförhållanden. Dessa slitagemodeller bygger på slitagekoefficienter, och eftersom de vanligtvis inte är giltiga under realistiska driftsförhållanden är modellerna i allmänhet kalibrerade mot verkliga händelseförlopp för att justera koefficienterna från testförhållandena till realistiska smörjförhållanden. Detta tekniska tillvägagångssätt kan vara användbart vid prognos av slitage i system där material och kontaktförhållanden inte varierar. När man addresserar materialutveckling inriktad på att reducera specifika skadelägen är emellertid tillvägagångssättet av begränsad användning eftersom de erhållna slitagekoefficienterna inte är direkt relaterade till materialegenskaper. Därför har försök gjorts till att utveckla fysikaliska sprickbildningsmodeller som relateras till kontaktförhållanden och materialegenskaper. Syftet har varit att erhålla viktig information om var en spricka initieras och hur den fortskrider. I det långa loppet är det även av stor vikt att kunna erhålla information om hur en materialpartikel avlägsnas från kontaktytan. Studier för denna typ av modeller har gjorts på 70- och 80-talet i huvudsak med stift- och skivexperiment men har inte använts inom det specifika området för hjul-räl-kontakt. Avhandligen ingår i FR8RAIL-projektet som arrangeras av det europeiska järnvägsinitiativet Shift2Rail. Literaturstudier har varit grunden för avhandlingen för att få väsentlig insikt i frakturmekanik och andra relaterade områden. De fysiska sprickbildningsmodellerna har konstrueras i FE-mjukvaran Abaqus med XFEM som implementering. För 2D-modellen initieras sprickan överst vid den implanterade imperfektionen när friktionskoefficienten är  och propagerar uppåt några få element. För  initieras sprickan på högra ytgränsen där tryckfördelning och friktionskraft appliceras. Utbredningsvinkeln för sprickan ökar relativt till ytan då friktionskoefficienten ökar. Sprickan för 3D-modellen breder ut sig mer jämfört med 2D-modellen överst vid imperfektionen då . Sprickan initieras på samma ytplats som för 2D-modellen vid . Sprickbildningen är dock obefintlig på grund av konvergensproblem. De konstruerade FE-modellerna är initiala steg mot att analysera sprickutbredningen och närbesläktade fenomen för ett godstågs järnvägshjul i detalj. I slutet av avhandlingen ger de förenklade modellerna huvudsakligen information om sprickinitiering, utbredning och dess mönster. Ytterligare justeringar och förbättringar kan ske efter denna första fas i syfte att eliminera felmarginalerna. På lång sikt kan slutligen helt integrerande modeller med ytterligare implementeringar såsom detaljerad mikrostruktur för kontaktförhållandena, oelastiskt materialbeteende och kompletta tredimensionella modeller användas.

  • 11534.
    Öhrman, Christian
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Lockhandle: Kombinerat dörrtrycke och låscylinder2016Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Såväl den skandinaviska som internationella trenden inom säkerhetslösningar går mot allt mer elektroniska och högteknologiska lösningar. Traditionella nycklar byts ut mot Near Field Communication, appar och fingeravtrycksläsare men bakom de moderna gränssnitten gömmer sig i de flesta dörrar än idag klassiska modullås som fungerat så samma sätt i flera decennier. För att gå mot strömmen och sticka ut hakan i denna trend efterfrågar säkerhetsföretaget Dorma ett helt mekanisk låssystem där ett kvalitetslås integreras i ett dörrhandtag.

    Syftet med det projekt som presenteras i denna rapport har varit att förenkla handhavandet av dörrlåsning i inomhusmiljö, såsom kontorslokaler, genom att utveckla ett koncept med en tryckesintegrerat låscylinder. På många av våra arbetsplatser har vi idag fullskaliga modullås med separata låsbeslag och handtag monterade i varenda innerdörr. Ofta är dessa säkerhets- och användarmässigt överdimensionerade för inomhusbruk varför en kompaktare lösning efterfrågas.

    I konceptframtagningen genererades, med stöd av studier och kravspecifikationer, en uppsjö av idéer vilka mynnade ut i tre vitt skilda koncept med olika lösningar för såväl låscylinderns placering i trycket som handtagets utformning och den i dörrbladet dolda låskistan. Genom att tillämpa ett antal eliminerande metoder utarbetades så ett slutkoncept som uppfyllde ställda krav på tillfredställande sätt.

    Slutkonceptet, som bland annat kom att innefatta ett innovativt sätt att överföra handtagets vridning till den storleksmässigt kraftigt reducerade låskistan, dimensionerades för att klara de laster som uppstår vid användande och modellerades i såväl CAD som fysisk form. För att överföra rotationen från vridning av handtaget förseddes trycket med ett inre ringhjul vars kuggar överför momentet till öppningsmekanismen. En kostnadskalkyl genomfördes och denna visade att material- och tillverkningskostnaderna, till skillnad från digitala lås, nästan var identiska med konventionella låssystem.

  • 11535.
    Ölundh, Gunilla
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Modernising ecodesign: ecodesign for innovative solutions2006Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The focus of environmental work in manufacturing companies has increasingly shifted from end-of-pipe solutions to the environmental performance of products and services. The product development process is central to creating value for customers. This thesis argues that companies can simultaneously create value for consumers and be profitable while taking environmental considerations into account.

    Modernising ecodesign means taking advantage of environmental benefits and the innovation potential when developing solutions rather than using ecodesign simply to ensure that legal requirements or customer demands are met. Ecodesign is a strategic issue and should be included in early product development activities, such as for project selection and when setting product targets. There is also need to perform ecodesign according to the characteristics of specific development processes as for radical product development or when developing integrated solutions, using a combination of services and products.

    This thesis reports on the findings from five different research studies, all of which adopted a qualitative approach in which the emphasis falls on exploring and creating understanding and meaning. The studies focused on three areas of ecodesign: A) rethinking approaches for manufacturing companies, B) setting environmental project targets and project selection and C) redesign of products.

    Recommendations on how to modernise ecodesign have been developed and can be summarised in six points:

    • Perform ecodesign both vertically and horizontally in a company.

    • Increase interaction between organisational units.

    • Take advantage of innovation potential in products, services, user behaviour and the delivery and take-back systems.

    • Take environmental considerations into account in the project selection process.

    • Set environmental targets for ensuring that environmental considerations are taken when developing innovative solutions.

    • Develop ecodesign procedures that fit the characteristics of the development process

  • 11536.
    Ölundh, Gunilla
    et al.
    KTH, Tidigare Institutioner, Maskinkonstruktion.
    Ritzén, Sofia
    KTH, Tidigare Institutioner, Maskinkonstruktion.
    Making an Ecodesign Choice in Project Portfolio Management2004Ingår i: 2004 IEEE EMS International EngineeringManagement Conference: Singapore, 2004Konferensbidrag (Refereegranskat)
  • 11537.
    Ölundh, Gunilla
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Ritzén, Sofia
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Setting Environmental Targets in Product Development2009Ingår i: ICED 09 - THE 17TH INTERNATIONAL CONFERENCE ON ENGINEERING DESIGN, 2009, s. 35-46Konferensbidrag (Refereegranskat)
    Abstract [en]

    An import factor for reaching environmental improvements in product development is to have relevant environmental targets that actually influence the product development process. In this paper are procedures of setting environmental targets for product development projects identified, described and analyzed based on studies in three large companies operating in different industries. The different procedures have their own advantages and disadvantages and some of them can be combined within a company. The aim is to illustrate approaches of setting environmental targets early on and show different procedures of setting the environmental targets at a strategic level and how the way of setting environmental targets early on influences the product development process. This paper has a strong empirical connection.

  • 11538.
    Ölundh Sandström, Gunilla
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Integrerad produktutveckling.
    Ritzén, Sofia
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Integrerad produktutveckling.
    Functional sales as a further approach to Environmental Product Development – case study2001Konferensbidrag (Övrigt vetenskapligt)
  • 11539.
    Öman, Alexander
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Produkt- och tjänstedesign.
    Sandström, Gustav
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Produkt- och tjänstedesign.
    A Product-Service-System: For Electrolux to encourage people to produce their own vegetables at home2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Naturen är en begränsad tillgång och det krävs därför en effektiv matframställning ur ett hållbarhetsperspektiv. Individer har ofta inte den kunskap som krävs för hur mat kan framställas på ett hållbart sätt. 

    Denna studie syftar till att hitta användare som är intresserade av matlagning och att tillsammans med dem utforma en produkt som kan producera grönsaker i en hemmamiljö. Den skall på ett enkelt och smidigt sätt sänka den initiala tröskeln till att producera egna grönsaker, på ett miljömedvetet och enkelt sätt. 

    Referensprodukter har utforskats och ett antal studiebesök och informationsinhämtning har gjorts för att kunna ge en komplett bild av vad som erbjuds idag och hur det vidare kan implementeras för att ge en fullständig konceptuell lösning.

    Detta har gjorts i en iterativ designprocess där användaren varit i fokus. Projektet har utförts i samarbete med Electrolux, vars uppgift har varit att stå som kravställare och tillhandahålla ett ramverk för hur tekniskt avancerad denna produkt skall vara, samt till viss del hur den skall vara utformad. Målgruppen intervjuades under tre tillfällen. Vid varje tillfälle presenterades en rad triggermaterial för att provocera till reaktioner och starta diskussioner. 

    Resultaten av projektet är en produkt som ersätter ett underskåp i köket och tillgodoser de behov som växter har för att växa, vilket tillåter användaren att producera sina egna grönsaker i en inomhusmiljö. Produkten implementeras även i en service, där användaren hyr produkten och har kontinuerlig tillgång till grönsaker. Utöver produkten och tjänsten initierades en produktportfölj för att på bästa sätt låta kunden anpassa sitt ägande och användande av produkten.

  • 11540.
    Öman, Johanna
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.).
    Total Value of Ownership for Software: Focus on Value Adding Aspects Associated with Selection and Purchase of Software2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Companies are continuously striving for saving more money in order to maintain and gain market shares as well as their competitiveness. This can be gained through better understanding for how value is created and generated and which value adding aspect to consider while purchasing a product. The concept of Total Value of Ownership, TVO, incorporates Total Cost of Ownership, TCO, as well as value adding aspects. Research initiatives have been conducted within the area of TCO but little research has been focused on revealing value adding aspects. Therefore it is of interest to find which value adding aspects that are considered to be the most important ones while purchasing a product. This thesis was initiated by Ericsson with the aim at placing the concept of TVO and value adding aspects in relation to purchase of software.

    The objective of this study is to address the issue of how value is created and to reveal which value adding aspects that are considered to be the most important ones while selecting and purchasing software in relation to the concept of TVO.

    This master thesis is conducted through a literature study and a case study at Ericsson, including a combination of interviews and a survey. Two expert interviews were also conducted and the thesis is of qualitative manner.

    TVO is a philosophy which aims at understanding the total costs and value contributions of a purchase from a particular supplier. TVO recognizes that value goes beyond cost and working capital improvements to include elements that contribute to social, environmental and innovations agendas and is related to the question; “How will this create value for our customers?

    The result shows an unclear distinction between the value adding aspects to consider while selecting and purchasing software. The four aspects that were considered to be the most important ones can though be extracted and are; (1) Reducing vendor lock-in, (2) Decreased operating costs for buyer’s customer, (3) Decreased operating costs for buyer’s customer and (4) Lowering the risk associated with purchase of software. The two most salient value adding aspects are; Fit between supplier’s offering and buyer’s demand and Reducing vendor lock-in. The findings also reveal a non cohesive view on value and what should be included in the concept.

    The conclusions of the study are that TVO enables better understanding for the costs and value associated with software. By taking in consideration both TCO and value adding aspects a product’s total value of ownership can be estimated. Questions regarding value and value adding aspects have not gained a lot of attention within the organization. There is though a willingness to try to adapt this philosophy as a part of the sourcing process which is also a trend generally.

    Concluded is also to have a cohesive view on the concept on value and have a holistic view on the value chain in order to be able to understand the total value of a software. A long-term commitment and engagement from involved parties within the organization is essential while implementing TVO.

  • 11541.
    Önder, Ertugrul Deniz
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    SOLAR ENERGY & ENERGY STORAGE SYSTEM FOR A 20-HOUSE COMMUNITY IN ACCRA, GHANA2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Ett system för skörd och lagring av förnybar energi för 20 exklusiva, projekterade hus i Accra, Ghana har planerats för det svenska start-up företaget AsaDuru. Metoder för att generera och lagra förnybar energi utreds och de lämpliga typer av generationsmetoder och komponenter som skall användas i dessa bestäms. Detaljerad information om Ghana samlads genom Minor Field Studies (MFS), och en omfattande ekonomisk analys för projektets genomförande gjordes.

    Resultaten visar att ett solenergisystem, med hjälp av poly-kristallina moduler, litiumjonbatterier och en back-up generator skulle vara det lämpligaste systemdesign för detta projekt, och det enda sättet att uppfylla dets ekonomiska kriterier. En fraktion på 98% förnybar energi uppnås vid kostnadsnivån 26 740$/hus, ungefär 10% lägre än den beslutade övre gränsen på 30 000 $.

  • 11542.
    Örlu, Ramis
    et al.
    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.
    Alfredsson, P. Henrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    On near wall measurements of wall bounded flows-The necessity of an accurate determination of the wall position2010Ingår i: Progress in Aerospace Sciences, ISSN 0376-0421, E-ISSN 1873-1724, Vol. 46, nr 8, s. 353-387Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The present review paper is an account on the experimental determination of the wall position relative to the probe in wall-bounded turbulent flow studies. A thorough review on common measurement techniques as well as correction methods reveals, that there are a number of pitfalls, that-when not accounted for-can lead to wrong conclusions about the wall position and thereby also on the near-wall behaviour of mean and turbulence quantities. Employing the state-of-the-art databases from direct numerical simulations of wall-bounded turbulent flows various indirect methods have been tested and assessed in terms of their robustness and accuracy. It is also demonstrated that accurate measurements reaching the viscous sublayer are necessary in order to ensure a correctly deduced wall position, and dependent quantities as for instance the near-wall scaling of mean (e.g. Reynolds number dependence of the buffer region or the log law constants) and turbulence (e.g. the near-wall peak location of Reynolds stresses) quantities. In experiments using hot-wires near the wall it is well known that heat conduction between the hot-wire and the wall gives errors and mean velocity data from the viscous sublayer can usually not be used to determine the wall position. In this paper we introduce a new method which takes advantage of the similarity of the probability density distributions (pdf) in the near wall region. By using the high velocity data of the pdf, which is shown not to be affected by heat conduction, the heat conduction problem can be circumvented. Extensive appendices are included, describing the history and present knowledge about the scaling of the mean velocity in the near wall and overlap regions in wall bounded turbulent flows.

  • 11543.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Experimental studies in jet flows and zero pressure-gradient turbulent boundary layers2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis deals with the description and development of two classical turbulent shear flows, namely free jet and flat plate turbulent boundary layer flows. In both cases new experimental data has been obtained and in the latter case comparisons are also made with data obtained from data bases, both of experimental and numerical origin. The jet flow studies comprise three parts, made in three different experimental facilities, each dealing with a specific aspect of jet flows. The first part is devoted to the effect of swirl on the mixing characteristics of a passive scalar in the near-field region of a moderately swirling jet. Instantaneous streamwise and azimuthal velocity components as well as the temperature were simultaneously accessed by means of combined X-wire and cold-wire anemometry. The results indicate a modification of the turbulence structures to that effect that the swirling jet spreads, mixes and evolves faster compared to its non-swirling counterpart. The high correlation between streamwise velocity and temperature fluctuations as well as the streamwise passive scalar flux are even more enhanced due to the addition of swirl, which in turn shortens the distance and hence time needed to mix the jet with the ambient air. The second jet flow part was set out to test the hypothesis put forward by Talamelli & Gavarini (Flow, Turbul. & Combust. 76), who proposed that the wake behind a separation wall between two streams of a coaxial jet creates the condition for an absolute instability. The experiments confirm the hypothesis and show that the instability, by means of the induced vortex shedding, provides a continuous forcing mechanism for the control of the flow field. The potential of this passive mechanism as an easy, effective and practical way to control the near-field of interacting shear layers as well as its effect towards increased turbulence activity has been shown. The third part of the jet flow studies deals with the hypothesis that so called oblique transition may play a role in the breakdown to turbulence for an axisymmetric jet.For wall bounded flows oblique transition gives rise to steady streamwise streaks that break down to turbulence, as for instance documented by Elofsson & Alfredsson (J. Fluid Mech. 358). The scenario of oblique transition has so far not been considered for jet flows and the aim was to study the effect of two oblique modes on the transition scenario as well as on the flow dynamics. For certain frequencies the turbulence intensity was surprisingly found to be reduced, however it was not possible to detect the presence of streamwise streaks. This aspect must be furher investigated in the future in order to understand the connection between the turbulence reduction and the azimuthal forcing. The boundary layer part of the thesis is also threefold, and uses both new data as well as data from various data bases to investigate the effect of certain limitations of hot-wire measurements near the wall on the mean velocity but also on the fluctuating streamwise velocity component. In the first part a new set of experimental data from a zero pressure-gradient turbulent boundary layer, supplemented by direct and independent skin friction measurements, are presented. The Reynolds number range of the data is between 2300 and 18700 when based on the free stream velocity and the momentum loss thickness. Data both for the mean and fluctuating streamwise velocity component are presented. The data are validated against the composite profile by Chauhan et al. (Fluid Dyn. Res. 41) and are found to fulfil recently established equilibrium criteria. The problem of accurately locating the wall position of a hot-wire probe and the errors this can result in is thoroughly discussed in part 2 of the boundary layer study. It is shown that the expanded law of the wall to forth and fifth order with calibration constants determined from recent high Reynolds number DNS can be used to fix the wall position to an accuracy of 0.1 and 0.25 l_ * (l_* is the viscous length scale) when accurately determined measurements reaching y+=5 and 10, respectively, are available. In the absence of data below the above given limits, commonly employed analytical functions and their log law constants, have been found to affect the the determination of wall position to a high degree. It has been shown, that near-wall measurements below y+=10 or preferable 5 are essential in order to ensure a correctly measured or deduced absolute wall position. A  number of peculiarities in concurrent wall-bounded turbulent flow studies, was found to be associated with a erroneously deduced wall position. The effect of poor spatial resolution using hot-wire anemometry on the measurements of the streamwise velocity is dealt with in the last part. The viscous scaled hot-wire length, L+, has been found to exert a strong impact on the probability density distribution (pdf) of the streamwise velocity, and hence its higher order moments, over the entire buffer region and also the lower region of the log region. For varying Reynolds numbers spatial resolution effects act against the trend imposed by the Reynolds number. A systematic reduction of the mean velocity with increasing L+ over the entire classical buffer region and beyond has been found. A reduction of around 0.3 uƬ, where uƬ is the friction velocity, has been deduced for L+=60 compared to L+=15. Neglecting this effect can lead to a seemingly Reynolds number dependent  buffer or log region. This should be taken into consideration, for instance, in the debate, regarding the prevailing influence of viscosity above the buffer region at high Reynolds numbers. We also conclude that the debate concerning the universality of the pdf within the overlap region has been artificially complicated due to the ignorance of spatial resolution effects beyond the classical buffer region on the velocity fluctuations.

  • 11544.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Experimental study of passive scalar mixing in swirling jet flows2006Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Despite its importance in various industrial applications there is still a lack of experimental studies on the dynamic and thermal field of swirling jets in the near-field region. The present study is an attempt to close this lack and provide new insights on the effect of rotation on the turbulent mixing of a passive scalar, on turbulence (joint) statistics as well as the turbulence structure.

    Swirl is known to increase the spreading of free turbulent jets and hence to entrain more ambient fluid. Contrary to previous experiments, which leave traces of the swirl generating method especially in the near-field, the swirl was imparted by discharging a slightly heated air flow from an axially rotating and thermally insulated pipe (6 m long, diameter 60 mm). This gives well-defined axisymmetric streamwise and azimuthal velocity distributions as well as a well-defined temperature profile at the jet outlet. The experiments were performed at a Reynolds number of 24000 and a swirl number (ratio between the angular velocity of the pipe wall and the bulk velocity in the pipe) of 0.5.

    By means of a specially designed combined X-wire and cold-wire probe it was possible to simultaneously acquire the instantaneous axial and azimuthal velocity components as well as the temperature and compensate the former against temperature variations. The comparison of the swirling and non-swirling cases clearly indicates a modification of the turbulence structure to that effect that the swirling jet spreads and mixes faster than its non-swirling counterpart. It is also shown that the streamwise velocity and temperature fluctuations are highly correlated and that the addition of swirl drastically increases the streamwise passive scalar flux in the near field.

  • 11545.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Low Reynolds number Zero Pressure-Gradient Equilibrium Turbulent Boundary-Layer ExperimentsManuskript (preprint) (Övrigt vetenskapligt)
  • 11546.
    Örlü, Ramis
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    On the determination of the wall position in wall-bounded turbulent flowsManuskript (preprint) (Övrigt vetenskapligt)
  • 11547.
    Örlü, Ramis
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    An experimental study of the near-field mixing characteristics of a swirling jet2008Ingår i: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 80, nr 3, s. 323-350Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present experimental investigation is devoted to the mixing charac- teristics of a passive scalar in the near-field region of a moderately swirling jet issuing from a fully developed axially rotating pipe flow. Instantaneous streamwise and azimuthal velocity components as well as the temperature were simultaneously accessed by means of a combined X-wire and cold-wire probe. The results indicate a modification of the turbulence structures to that effect that the swirling jet spreads, mixes and evolves faster compared to its non-swirling counterpart. The high correlation between streamwise velocity and temperature fluctuations as well as the streamwise passive scalar flux are even more enhanced due to the addition of swirl, which in turn shortens the distance and hence time needed to mix the jet with the ambient air.

  • 11548.
    Örlü, Ramis
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    On spatial resolution issues related to time-averaged quantities using hot-wire anemometry2010Ingår i: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 49, nr 1, s. 101-110Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of spatial resolution on streamwise velocity measurements with single hot-wires is targeted in the present study, where efforts have been made to distinguish between spatial resolution and Reynolds number effects. The basis for measurements to accurately determine the mean velocity and higher order moments is that the probability density distribution is measured correctly. It is well known that the turbulence intensity is increasingly attenuated with increasing wire length. Here, it is also shown (probably for the first time) that besides the probability density distribution and hence the higher order moments, even the mean velocity is affected, albeit to subtle extent, but with important consequences in studies of concurrent wall-bounded turbulence.

  • 11549.
    Örlü, Ramis
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Passive scalar flux measurements in the near-field region of a swirling jet2008Ingår i: Heat Transfer Research, ISSN 1064-2285, E-ISSN 2162-6561, Vol. 39, nr 7, s. 597-607Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present experimental investigation is devoted to the heat flux characteristics of a passive scalar in the near-field region of a swirling jet issuing from a fully developed axially rotating pipe flow. A combined X-wire and cold-wire probe made it possible to access the instantaneous streamwise and azimuthal velocity components as well as the temperature simultaneously. Results indicate that the addition of swirl increases the integral scales and entrainment and thereby the streamwise passive scalar flux and shortens the distance and hence time needed to mix the jet with the ambient air.

  • 11550.
    Örlü, Ramis
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Fiorini, T.
    Segalini, Antonio
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Bellani, G.
    Talamelli, Alessandro
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik. Università di Bologna, Italy.
    Alfredsson, P Henrik
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik. Università di Bologna, Italy.
    Reynolds stress scaling in pipe flow turbulence-first results from CICLoPE2017Ingår i: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 375, nr 2089, artikel-id 20160187Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports the first turbulence measurements performed in the Long Pipe Facility at the Center for International Cooperation in Long Pipe Experiments (CICLoPE). In particular, the Reynolds stress components obtained from a number of straight and boundary-layer-type single-wire and X-wire probes up to a friction Reynolds number of 3.8 x 10(4) are reported. In agreement with turbulent boundary-layer experiments as well as with results from the Superpipe, the present measurements show a clear logarithmic region in the streamwise variance profile, with a Townsend-Perry constant of A(2) approximate to 1.26. The wall-normal variance profile exhibits a Reynolds-number-independent plateau, while the spanwise component was found to obey a logarithmic scaling over a much wider wall-normal distance than the other two components, with a slope that is nearly half of that of the Townsend-Perry constant, i.e. A(2,w) approximate to A(2)/2. The present results therefore provide strong support for the scaling of the Reynolds stress tensor based on the attached-eddy hypothesis. Intriguingly, the wall-normal and spanwise components exhibit higher amplitudes than in previous studies, and therefore call for follow-up studies in CICLoPE, as well as other large-scale facilities. This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.

228229230231232233 11501 - 11550 av 11609
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