Endre søk
Begrens søket
12 51 - 70 of 70
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 51.
    Raymer, Daniel
    KTH, Tidigare Institutioner                               , Flygteknik.
    Enhancing Aircraft Conceptual Design using Multidisciplinary Optimization2002Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Research into the improvement of the Aircraft ConceptualDesign process by the application of MultidisciplinaryOptimization (MDO) is presented. Aircraft conceptual designanalysis codes were incorporated into a variety of optimizationmethods including Orthogonal Steepest Descent (full-factorialstepping search), Monte Carlo, a mutation-based EvolutionaryAlgorithm, and three variants of the Genetic Algorithm withnumerous options. These were compared in the optimization offour notional aircraft concepts, namely an advanced multiroleexport fighter, a commercial airliner, a flying-wing UAV, and ageneral aviation twin of novel asymmetric configuration. Tobetter stress the methods, the commercial airliner design wasdeliberately modified for certain case runs to reflect a verypoor initial choice of design parameters including wingloading, sweep, and aspect ratio.

    MDO methods were evaluated in terms of their ability to findthe optimal aircraft, as well as total execution time,convergence history, tendencies to get caught in a localoptimum, sensitivity to the actual problem posed, and overallease of programming and operation. In all, more than a millionparametric variations of these aircraft designs were definedand analyzed in the course of this research.

    Following this assessment of the optimization methods, theywere used to study the issue of how the computer optimizationroutine modifies the aircraft geometric inputs to the analysismodules as the design is parametrically changed. Since thiswill ultimately drive the final result obtained, this subjectdeserves serious attention. To investigate this subject,procedures for automated redesign which are suitable foraircraft conceptual design MDO were postulated, programmed, andevaluated as to their impact on optimization results for thesample aircraft and on the realism of the computer-defined"optimum" aircraft. (These are sometimes called vehicle scalinglaws, but should not be confused with aircraft sizing, alsocalled scaling in some circles.)

    This study produced several key results with application toboth Aircraft Conceptual Design and MultidisciplinaryOptimization, namely:

        MDO techniques truly can improve the weight and cost ofan aircraft design concept in the conceptual design phase.This is accomplished by a relatively small "tweaking" of thekey design variables, and with no additional downstreamcosts.In effect, we get a better airplane for free.

        For a smaller number of variables (<6-8), adeterministic searching method (here represented by thefull-factorial Orthogonal Steepest Descent) provides aslightly better final result with about the same number ofcase evaluations

        For more variables, evolutionary/genetic methods getclose to the best final result with far-fewer caseevaluations. The eight variables studied herein probablyrepresent the practical upper limit on deterministicsearching methods with today’s computer speeds.

        Of the evolutionary methods studied herein, the BreederPool approach (which was devised during this research andappears to be new) seems to provide convergence in the fewestnumber ofcase evaluations, and yields results very close tothe deterministic best result. However, all of the methodsstudied produced similar results and any of them is asuitable candidate for use.

        Hybrid methods, with a stochastic initial optimizationfollowed by a deterministic final "fine tuning", proved lessdesirable than anticipated.

        Not a single case was observed, in over a hundred caseruns totaling over a million parametric design evaluations,of a method returning a local rather than global optimum.Even the modified commercial airliner, with poorly selectedinitial design variables far away from the global solution,was easily "fixed" by all the MDO methods studied.

        The postulated set of automated redesign procedures andgeometric constraints provide a more-realistic final result,preventing attainment of an unrealistic "better" finalresult. Especially useful is a new approach defined herein,Net Design Volume, which can prevent unrealisticallyhigh design densities with relatively little setup andcomputational overhead. Further work in this area issuggested, especially in the unexplored area of automatedredesign procedures for discrete variables.

    Fulltekst (pdf)
    FULLTEXT01
  • 52.
    Ribeiro-Ayeh, Steven
    KTH, Tidigare Institutioner                               , Flygteknik.
    On the strength of bi-material interfaces2002Licentiatavhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 53.
    Rosén, Anders
    KTH, Tidigare Institutioner                               , Flygteknik.
    Impact loads and responses for planning craft in waves2002Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 54.
    Saint Requier, Cyril
    KTH, Tidigare Institutioner                               , Flygteknik.
    Preconditioning methods and transition modeling for compressible navier-stokes code1999Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 55.
    Segerfröjd, Gabriel
    KTH, Tidigare Institutioner                               , Flygteknik.
    Fatigue of mechanically fastened joints1999Doktoravhandling, med artikler (Annet vitenskapelig)
  • 56. Sehgal, B. R.
    et al.
    Theerthan, A.
    Giri, A.
    Karbojian, Aram
    KTH, Tidigare Institutioner                               , Flygteknik.
    Willschutz, H. G.
    Kymalainen, O.
    Vandroux, S.
    Bonnet, J. M.
    Seiler, J. M.
    Ikkonen, K.
    Sairanen, R.
    Bhandari, S.
    Burger, M.
    Buck, M.
    Widmann, W.
    Dienstbier, J.
    Techy, Z.
    Kostka, P.
    Taubner, R.
    Theofanous, T.
    Dinh, Truc-Nam
    KTH, Tidigare Institutioner                               , Fysik.
    Assessment of reactor vessel integrity (ARVI)2003Inngår i: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 221, nr 03-jan, s. 23-53Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The cost-shared project ARVI (assessment of reactor vessel integrity) involves a total of nine organisations from Europe and USA. The objective of the ARVI Project is to resolve the safety issues that remain unresolved for the melt vessel interaction phase of the in-vessel progression of a severe accident. The work consists of experiments and analysis development. Four tests were performed in the EC-FOREVER Programme, in which failure was achieved in-vessels employing the French pressure vessel steel. The tests were analysed with the commercial code ANSYS-Multiphysics, and the codes SYSTUS+ and PASULA, and quite good agreement was achieved for the failure location. Natural convection experiments in stratified pools have been performed in the SIMECO and the COPO facilities, which showed that much greater heat is transferred downwards for immiscible layers or before layers mix. A model for gap cooling and a set of simplified models for the system codes have been developed. MVITA code calculations have been performed for the Czech and Hungarian VVERs, towards evaluation of the in-vessel melt retention accident management scheme. Tests have been performed at the ULPU facility with organised flow for vessel external cooling. Considerable enhancement of the critical heat flux (CHF) was obtained. The ARVI Project has reached the halfway stage. This paper presents the results obtained thus far from the project.

  • 57.
    Shipsha, Andrey
    KTH, Tidigare Institutioner                               , Flygteknik.
    Experimental characterisation of fatigue crack growth in sandwich structures1999Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 58.
    Shipsha, Andrey
    KTH, Tidigare Institutioner                               , Flygteknik.
    Failure of Sandwich Structures with Sub-Interface Damage2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 59.
    Singer, Gideon
    KTH, Tidigare Institutioner                               , Flygteknik.
    Methods for Validatng Cockpit Design The best tool for the task2002Doktoravhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 60.
    Singer, Gideon
    KTH, Tidigare Institutioner                               , Flygteknik.
    Towards a safer cockpit: improving cockpit interface through flight test2000Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 61.
    Soinne, Erkki
    KTH, Tidigare Institutioner (före 2005), Flygteknik.
    Aerodynamic and Flight Dynamic Simulations of Aileron Characteristics2000Doktoravhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 62.
    Soinne, Erkki
    KTH, Tidigare Institutioner                               , Flygteknik.
    CFD analysis and validation applied to ailerons1999Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 63.
    Starikov, Roman
    KTH, Tidigare Institutioner                               , Flygteknik.
    Experimental investigation of fatigue behaviour in composite bolted joints1999Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 64.
    Starikov, Roman
    KTH, Tidigare Institutioner                               , Flygteknik.
    Quasi-static and fatigue behaviour of composite bolted joints2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 65.
    Tjernberg, Anders
    KTH, Tidigare Institutioner                               , Flygteknik.
    Fatigue assessments of components in construction equipment2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The thesis refers to "Fatigue Assessment of Components inConstruction Equipment". The subject was chosen because ofincreasing interest in higher payloads, lower weight, highervelocities and shorter load cycles in construction equipmentvehicles.

    The main research goal in this thesis is to investigatetechniques to extend the fatigue life of an induction hardeneddrive shaft, with splines. Areas related to this research areresidual stress, fatigue life assessments, manufacturingprocess parameters and hardening process parameters. Themethods used to achieve the goal are process simulations,fatigue tests, finite element calculations, measurements ofresidual stress and fatigue life assessments. The aim of thepresent research is to cover several aspects of applied fatigueassessment. Most of the theoretical work has been verified withmeasurements and fatigue tests.

    The residual stresses have been calculated by simulating thehardening process with SYSWELD, a Finite Element program. Thesimulated residual stress beneath the surface was compared toX-ray and neutron diffraction measurements. The conformancewith simulations and X-ray measurements was relatively good,but the conformance with neutron diffraction measurements wasnot so good. The detrimental axial tensile residual stress atthe core was found to be in the order of 800-900 MPa, for theshafts.

    About 100 shafts have been fatigue tested in torsion, bothin constant amplitude and in variable amplitude and some of theresults have been reported in this thesis. For many of theshafts, crack initiation beneath the hardening layer wasdetected, which depends on the high tensile residual stress inthe core. Fatigue life assessments were made on the shafts,using a multiaxial strain based critical plane model, with themeasured residual stresses as input data. The generalconclusion is that the induction hardening process parametersinfluence the residual stresses to a high extent and thusinfluence fatigue life. Simulations of how different hardeningprocess parameters influence the residual stress profile havebeen done. Low hardening power and low frequency seem to reducethe detrimental tensile residual stress at the core.

    The load distribution along the axis of the spline teeth hasbeen investigated. The shear stress concentration in a splinehas been calculated by the finite element method, using anon-linear model, and was compared with results found in theliterature. An equation describing how the tooth thicknessshould vary to obtain smooth contact in the axial direction hasbeen derived. Finally, fatigue tests have been made oninduction hardened shafts in torsion with crack initiation atthe spline surface.

    The influence of pitch errors on fatigue life for splineshas also been estimated, by using a weakest link failureprobability model and combining it with a 2-parameter Weibullfailure distribution model. The conclusion is that pitch errorsin the investigated splines appear to reduce fatigue life byabout 50-70 %, compared with ideal pitch.

    Fulltekst (pdf)
    FULLTEXT01
  • 66.
    Trende, Andreas
    KTH, Tidigare Institutioner                               , Flygteknik.
    Thermal issues in thermoplastic composites manufacturing1999Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Heat transfer in thermoplastic composites duringmanufacturing is treated both numerically and experimentally inthis thesis. The related issues crystallization kinetics,residual stresses, and geometrical changes are alsoinvestigated. Three different manufacturing methods arestudied:thermoplastic pultrusion, double-belt presslamination, and compression moulding. In the experimental workglass fibre reinforced polypropylene (PP), polyamide 12 (PA12),and polyethylene terephthalate (PET) are used.

    First, an experimental parametric study on thermoplasticpultrusion is carried out. The effect of changing variousprocess variables on mechanical properties, surface finish, andfibre distribution is investigated. The results show that thedesired effect on the different evaluated composite propertiesrequires contradictory process conditions and therefore it isnecessary to decide which properties are the mostimportant.

    Heat transfer in thermoplastic composites duringmanufacturing is modelled in one dimension, numericallyimplemented using finite difference methods, and in threedimensions using finite element methods. Temperature dependentthermal conductivity and specific heat, as well as non-infinitethermal contact conductance at interfaces are included in themodels and the heat generation from crystallization is takeninto account. The temperature predictions are compared withexperimental data and the agreement is generally good.Moreover, it is found that the use of relevant thermal contactconductances at interfaces is important for accuratepredictions, especially when multi-layered items arestudied.

    The non-isothermal crystallization in thermoplasticcomposites during manufacturing is predicted using amacro-kinetic model, which is on differential form and thuswell suited for coupling together with the heat transfer model.Despite being mathematically uncomplicated, the modeladequately represents the most essential aspects of the processand agrees well with experimental data.

    Using the above described predictions as basis, residualstresses and geometrical changes in compression moulded glassmat reinforced plastics (GMT) are investigated using twodifferent material models, one transversely isotropic linearelastic and the other isotropic linear viscoelastic.Predictions are compared with some experimental data concerninggeometrical changes and the agreement is good. The limitationwith the elastic model is that only geometrical changes can bestudied. Further, as the GMT material is consideredtransversely isotropic, the results from the isotropicviscoelastic model are qualitative.

    Keywords:thermoplastic, composite, manufacturing,characterisation, pultrusion, double-belt press, compressionmoulding, modelling, heat transfer, crystallization, residualstresses.

  • 67.
    Wennhage, Per
    KTH, Tidigare Institutioner                               , Flygteknik.
    Mechanical and acoustical aspects of sandwich panels in railway applications1999Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 68.
    Wennhage, Per
    KTH, Tidigare Institutioner                               , Flygteknik.
    Structural-Acoustic Optimization of Sandwich Panels2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 69.
    Ytterström, Anders
    KTH, Tidigare Institutioner                               , Flygteknik.
    Parallel Computing for Applications in Aeronautical CFD2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 70.
    Åkermo, Malin
    KTH, Tidigare Institutioner                               , Flygteknik.
    Compression moulding of thermoplastic composite sandwich components1999Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The thesis investigates various aspects of compressionmoulding of sandwich components with thermoplastic-basedcomposite faces and thermoplastic or thermoset core.Compression moulding of glass/polypropylene (PP) faces toexpanded PP core is initially experimentally investigated usinga statistical experimental design approach. The influence ofvarious processing parameters is evaluated in terms of theshear, flexural and transverse tensile properties of mouldedcomponents. Results indicate that as long as the faces remainmelted when stacked with the core, the face-core bond strengthis always greater than the tensile strength of the core. Ingeneral properties seem to improve with reduced mouldingpressure and time.

    Bonding of thermoplastic composite faces to a thermosetclosed cell foam core is then modelled assuming that there is acorrelation between the amount of matrix penetrating into corecells at the surface and the bond strength. The model is usedin a parametric study showing that matrix penetration into corecells is initially a rapid process, but flow is interruptedbefore cells are filled owing to increasing pressure of the airtrapped in the cells. The model indicates that increasedmoulding pressure and reduced face temperature increase matrixpenetration into core cells. Initial experimental resultssupport model predictions.

    Compression moulding of thermoplastic composite faces to athermoplastic honeycomb core is also modelled focusing on theface-core bonding. A process model is developed from modelsdescribing the temperature distribution in the sandwich and theflow of the melted part of the core wall during moulding. Modelpredictions are compared to experimental data in terms of faceand core surface temperature and degree of face-coreinterfacial contact with reasonably good agreement. The modelis also used in a parametric study investigating the influenceof the major process variables on the face-core bondstrength.

    Finally, the process economy of compression moulding ofthermoplastic composite and sandwich components is modelled andcompared to predicted component costs for compression mouldingof sheet moulding compound and stamping of metals. A range ofcomponent sizes, complexities and flexural rigidities isinvestigated. The results imply that thermoplastic compositecomponents are mainly cost competitive for small to mediumsized or highly complex components and for short productionseries. Sandwich components seem to offer enhanced processeconomy for components requiring high flexural rigidity,however, still for short to intermediate production series.

    Keywords: sandwich, thermoplastic, composite,compression moulding, modelling, bonding, heat transfer, matrixflow, cost, testing

12 51 - 70 of 70
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf