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  • Bergdahl, Lars, 1943-, et al. (författare)
  • Time simulation of the motion of a tension leg platform
  • 1988
  • Ingår i: BOSS'88 Proceedings of the international conference on behaviour of offshore structures. - 82-519-0855-8 ; 2, s. 875-890
  • Konferensbidrag (refereegranskat)abstract
    • The time-domain motion of a Tension Leg Platform is studied. The used method is based on a convolution technique in which the hydrodynamic reaction force from the frequency-domain solution is Fourier transformed to the time domain. Such a method allows one to consider arbitrary time varying external forces as for example non-linear reaction forces from tendons as well as transient loads.In the developed model time series of first-order wave forces and second-orde slowly varying wave forces are calculated for irregular plane and short-crested waves. Exciting forces due to wind and current are calculated using drag coefficients from model tests. The equations of motion in the time domain are solved for a tension-leg platform performing rigid body motion and results in time series of the motions as well as of the tension in the tendons.Numerical simulations have been carried out and the results are discussed. A comparison is made between calculations and model tests for a tension-leg platform in irregular long-crested waves.
  • Pieringer, Astrid, 1979-, et al. (författare)
  • Investigation of railway curve squeal using a combination of frequency- and time-domain models
  • 2016
  • Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16. ; s. 444-451
  • Konferensbidrag (refereegranskat)abstract
    • Railway curve squeal arises from self-excited vibrations during curving. In this paper, a frequency- and a timedomainapproach for curve squeal are compared. In particular, the capability of the frequency-domain model topredict the onset of squeal and the squeal frequencies is studied. In the frequency-domain model, linear stabilityis investigated through complex eigenvalue analysis. The time-domain model is based on a Green's functionsapproach and uses a convolution procedure to obtain the system response. To ensure comparability, the samesubmodels are implemented in both squeal models. The structural flexibility of a rotating wheel is modelled byadopting Eulerian coordinates. To account for the moving wheel‒rail contact load, the so-called moving elementmethod is used to model the track. The local friction characteristics in the contact zone is modelled inaccordance with Coulomb's law with a constant friction coefficient. The frictional instability arises due togeometrical coupling. In the time-domain model, Kalker's non-linear, non-steady state rolling contact modelincluding the algorithms NORM and TANG for normal and tangential contact, respectively, is solved in eachtime step. In the frequency-domain model, the normal wheel/rail contact is modelled by a linearization of theforce-displacement relation obtained with NORM around the quasi-static state and full-slip conditions areconsidered in tangential direction. Conditions similar to those of a curve on the Stockholm metro exposed tosevere curve squeal are studied with both squeal models. The influence of the wheel-rail friction coefficient andthe direction of the resulting creep force on the occurrence of squeal is investigated for vanishing train speed. Results from both models are similar in terms of the instability range in the parameter space and the predictedsqueal frequencies.
  • Thulin, Oskar, 1987-, et al. (författare)
  • First and Second Law Analysis of Radical Intercooling Concepts
  • 2018
  • Ingår i: Journal of Engineering for Gas Turbines and Power. - 1528-8919 .- 0742-4795. ; 140:8, s. 081201-081201-10
  • Tidskriftsartikel (refereegranskat)abstract
    • An exergy framework was developed taking into consideration a detailed analysis of the heat exchanger (HEX) (intercooler (IC)) component irreversibilities. Moreover, it was further extended to include an adequate formulation for closed systems, e.g., a secondary cycle (SC), moving with the aircraft. Afterward, the proposed framework was employed to study two radical intercooling concepts. The first proposed concept uses already available wetted surfaces, i.e., nacelle surfaces, to reject the core heat and contributes to an overall drag reduction. The second concept uses the rejected core heat to power a secondary organic Rankine cycle and produces useful power to the aircraft-engine system. Both radical concepts are integrated into a high bypass ratio (BPR) turbofan engine, with technology levels assumed to be available by year 2025. A reference intercooled cycle incorporating a HEX in the bypass (BP) duct is established for comparison. Results indicate that the radical intercooling concepts studied in this paper show similar performance levels to the reference cycle. This is mainly due to higher irreversibility rates created during the heat exchange process. A detailed assessment of the irreversibility contributors, including the considered HEXs and SC, is made. A striking strength of the present analysis is the assessment of the component-level irreversibility rate and its contribution to the overall aero-engine losses.
  • Thulin, Oskar, 1987- (författare)
  • On the Analysis of Energy Efficient Aircraft Engines
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Aero engine performance analysis is highly multidimensional using various measures of component performance such as turbomachinery and mechanical efficiencies, and pressure loss coefficients. Using conventional performance analysis, relying on only the laws of thermodynamics, it is possible to understand how the performance parameters affect the component performance, but it is difficult to directly compare the magnitude of various loss sources. A comprehensive framework has been detailed to analyze aero engine loss sources in one common currency. As the common currency yields a measure of the lost work potential in every component, it is used to relate the component performance to the system performance. The theory includes a more detailed layout of all the terms that apply to a propulsion unit than presented before. The framework is here adopted to real gases to be used in state of the art performance codes. Additionally, the framework is further developed to enable detailed studies of two radical intercooling concepts that either rejects the core heat in the outer nacelle surfaces or uses the core heat for powering of a secondary cycle. The theory is also extended upon by presenting the installed rational efficiency, a true measure of the propulsion subsystem performance, including the installation effects of the propulsion subsystem as it adds weight and drag that needs to be compensated for in the performance assessment.
  • Ekberg, Anders, 1967-, et al. (författare)
  • INNOTRACK: Concluding technical report
  • 2010
  • Samlingsverk (redaktörskap) (övrigt vetenskapligt)abstract
    • The track structure, rails, switches and crossings account for more than 50% of maintenance and renewal costs for the rail industry. To improve the competitiveness of rail transportation, the cost-efficiency of these areas needs to be addressed.This the background to INNOTRACK, an integrated research project funded by the European Commission’s 6th research framework pro- gramme. Running from September 2006 to December 2009, INN- OTRACK has developed a multitude of innovative solutions in the areas of track substructure, rails & welds, and switches & crossings. The solutions have been assessed from technical, logistics and life cycle cost point of views.This Concluding Technical Report of INNOTRACK includes an overview of the project. It further details implementable results, and clusters them into ”highlight” areas. In addition, the book acts as a ”key” to the vast amount of information from INNOTRACK: All sections refer to project reports where more information can be found.
  • Edman, Jonas, 1973- (författare)
  • Modeling Diesel spray combustion using a Detailed Chemistry Approach
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The rapid development of computer hardware during the past decade has contributed substantially to advances in almost all branches of science. Computer modeling is being applied to increasingly small physical scales and increasingly large domains, facilitating the generation of advanced phenomenological models and models based on first principles. These developments have been especially valuable in fields where highly complex micro-scale events are observed or modeled, such as combustion studies, allowing (for instance) the incorporation of complex chemical combustion kinetics into engine spray combustion models. The crude models and global curve fits that were previously used to represent combustion phenomena have now been largely replaced by models based on "first principles". These modeling developments have coincided fortuitously with a shift in the focus of combustion concepts, from mixing-oriented combustion modes like Diesel and stratified charge Otto combustion to the kinetically controlled combustion modes usually referred to as Homogeneous Charge Compression Ignition (HCCI). The driving forces behind the development of the HCCI concept are environmental considerations, manifested in the form of emission legislation. Theoretically, HCCI combustion (characterized by fuel lean mixtures and low peak temperatures) has the potential to reduce soot and NOx emissions to current emission legislation levels even without after-treatment systems. In practical production engine applications, due to current drawbacks such as poor high load capability, the capacity to switch to conventional mode at high load operation is required. For the above reasons, computer modeling that is capable of describing both old and new combustion modes is required. In the work underlying this thesis, CFD modeling was applied to the passenger car Dl Diesel engine operated in both HCCI and conventional Diesel combustion modes. The aim was to couple chemical combustion kinetics and turbulent mixing in order to capture relevant phenomena related to ignition and emission formation for both modes. The resulting, coupled model is referred to as the Partially Stirred Reactor model (PaSR), and is the main component in the Detailed Chemistry Approach currently utilized in combustion modeling at Chalmers University of Technology (CTH). Other essential components of the Detailed Chemistry Approach are the Reference Species Technique (used to determine the relevant chemical timescales) and the Diesel fuel surrogate model (constructed to facilitate realistic treatment of the fuel in both liquid and gaseous states). The gaseous kinetic treatment of the Diesel fuel surrogate model, represented by a blend of aliphatic and aromatic components, consists of a chemical kinetic mechanism considering -75 chemical species participating in -330 elementary or global reactions describing n-heptane and toluene oxidation. Although most of the modeling was done in the CFD code KIVA-3V rel2, the development and validation of the chemical kinetic combustion mechanism was done using the SENKIN code and the CHEMKIN package. The chemical kinetic modeling has provided a kinetic mechanism for Diesel combustion that is capable of reproducing experimental ignition delay characteristics of both n-heptane and toluene oxidation in both low and high pressure regimes. In addition, it reproduces the negative temperature coefficient behavior that is an important feature of commercial Diesel fuels. It has also been able to reproduce cool flame phenomena, which play important roles in HCCI combustion. Results from the constant volume spray modeling have shown that the spray development, liquid and gas penetration and ignition characteristics observed in high pressure Diesel spray experiments are properly reproduced. Furthermore, major combustion variables such as ignition timing, heat release and pressure traces generated in engine simulations have satisfactorily reproduced experimental data acquired in tests using a single cylinder engine at Chalmers University of Technology.
  • Eismark, Jan, 1962- (författare)
  • The role of piston bowl shape in controlling soot emissions from heavy-duty Diesel engines.
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The role of piston bowl shape in controlling soot emissions from heavy-duty Diesel engines. Diesel combustion is often subject to a trade-off between emissions of soot and nitrogen oxides (NOx). This trade-off limits the scope for restricting the CO2 footprint of diesel engines by reducing fuel consumption while simultaneously reducing emissions of soot and NOx.  This thesis examines a new piston bowl shape for diesel engines that was found to significantly reduce soot emissions, enabling the typical soot-NOx trade-off to be limited. Experimental and simulation studies showed that the improvements originated from enhancement of soot oxidation late in the combustion cycle, after the end of the fuel injection period. The late-cycle oxidation rate increased when the supply of oxygen to a radially developing turbulent mixing zone (RMZ) was improved.  The mixing features of the RMZ depended on the interaction between the high velocity, high momentum fuel jet and the piston bowl shape. A clear coupling was identified between the piston bowl shape and the transport of oxygen to the trailing edge of the RMZ. Specifically, it was shown that the presence of a wave-shaped protrusion caused a smoother flow in the flame-flame area that improved oxygen transport to the trailing edge. This improved oxygen supply increased late-cycle mixing and thus increased the soot oxidation rate, reducing net soot emissions by up to 80% and also improving fuel consumption. Experiments with different fuel types revealed that this strategy also improves late cycle mixing for renewable fuels. The findings were used to develop a qualitative model describing late-cycle heavy-duty low-swirl combustion. Together with previously introduced qualitative models of free diesel jets, this model could help clarify events that have important effects on various flame interactions. In addition, a new experimental setup was developed to enable detailed studies of RMZ behaviour in a spray-chamber. The setup consists of a two-hole fuel nozzle combined with different wall geometries. It is suggested that new insights into RMZ behaviour and late-cycle oxidation will be obtained by combining experiments using this setup with simulation studies.  The work was partly funded by the Swedish Energy Agency (project 30754-1&2).
  • Stylidis, Kostas, 1978-, et al. (författare)
  • Perceived quality framework in product generation engineering: an automotive industry example
  • 2019
  • Ingår i: Digital tvilling för geometrisäkrad produktion.
  • Tidskriftsartikel (refereegranskat)abstract
    • Perceived quality refers to customers’ cognitive and emotional responses to a particular design, often also associated with craftsmanship and customer satisfaction. Previous research defined a taxonomy of perceived quality and provided understanding about how engineering design decisions impact customer satisfaction. Furthermore, development of new products is frequently based on carrying over attributes of existing products, either from the same producer or from competitors. Previous research offered a new product development methodology combining variations of subsystems to carry over from existing products. This brief presents how these two lines of research combined to design the central console of the Porsche Panamera automobile and discusses the opportunities and challenges posed in the practical implementation of this research.
  • Stylidis, Kostas, 1978-, et al. (författare)
  • Perceived quality of products: a framework and attributes ranking method
  • 2020
  • Ingår i: Digital tvilling för geometrisäkrad produktion.
  • Tidskriftsartikel (refereegranskat)abstract
    • Perceived quality is one of the most critical aspects of product development that defines the successful design. This paper presents a new approach to perceived quality assessment by examining its elements, decomposed into a structure with the bottom-up sensory approach from the level of basic (‘ground’) attributes, covering almost every aspect of quality perception from the engineering viewpoint. The paper proposes a novel method for perceived quality attributes relative importance ranking, resulting in the balanced perceived quality of the final product within the given conditions. The proposed method helps to reach the equilibrium of the product’s quality equation from the perspective of design effort, time, and costs estimations. The authors introduce the Perceived Quality Framework (PQF), which is the taxonomy system for perceived quality attributes and the core of the attributes importance ranking (PQAIR) method. The research outcomes are based on findings of the qualitative exploratory study, including European and North American premium and luxury automotive manufacturers. An empirical structural validity test was performed to assess the usability and rigour of the proposed method. The results indicate that perceived quality evaluation can be significantly improved during all stages of product development.
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