| 1. |
- Lindström, Per, 1967-, et al.
(författare)
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Non-linear fracture mechanics in LS-DYNA and LS-PrePost
- 2015
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Ingår i: European LS-DYNA Conference 2015. - Würzburg : DYNAmore GmbH.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Fracture mechanics provides an engineering framework for assessing the consequences of defects instructures. In linear elastic fracture mechanics (LEFM), stress intensity factors KI, KII and KIII are usedfor characterizing the stress singularity at the crack tip, which arises from the theory of linear elasticity.Crack growth is assumed to occur when KI exceeds the fracture toughness KC. LEFM can be usefulfor brittle materials, or when the size of the plastic zone is small compared to global dimensions. In non-linear fracture mechanics (EPFM), an energy based criterion is used for assessing the risk forcrack growth: if the energy release rate at the crack tip exceeds what is required for creating newsurfaces in the material, crack growth will occur. Under certain assumptions the energy release rate atthe crack tip can be calculated by a path independent integral, the so-called J-integral. In modernFE-based fracture mechanics applied to practical design, the structure under consideration ismodelled, including cracks at specific locations, and the J-integral values are computed and used asdesign criteria. From a numerics viewpoint, the J-integral has many appealing properties: it can beevaluated from the far-field solution, which reduces numerical errors that may arise close to the cracktip, and the expected path-independence can to some extent be used as a quick check on solutionvalidity.Evaluation of the J-integral from LS-DYNA simulation results has been implemented as a postprocessingtool in LS-PrePost, including consistent treatment of residual stresses. The implementationcovers both 2D (plane stress / plane strain) and 3D applications, using the virtual crack-tip extension(VCE) method. The tool is accessible both via the LS-PrePost GUI and via command file interface.
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| 2. |
- Tilliander, Anders, et al.
(författare)
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Effect of Ar/O-2 gas mixtures on heat-transfer and fluid-flow characteristics in AOD nozzles
- 2000
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Ingår i: Steel research. - : Wiley. - 0177-4832. ; 71:11, s. 429-434
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Tidskriftsartikel (refereegranskat)abstract
- A model of fluid flow and heat transfer in a nozzle used for injection of argon and oxygen in AOD converters was developed earlier. In this study the model was used to determine the effect of changes in the ratio of argon to oxygen in argon-oxygen gas mixtures injected through the nozzle on fluid flow and heat transfer. It was found, for the studied conditions, that the temperature and laminar kinematic viscosity at the nozzle outlet were not dependent on the gas composition. However, the velocity, density, turbulent kinetic energy and dissipation of kinetic energy varied with a change in the fraction of oxygen injected. It is therefore concluded that for use as boundary-condition input data for an AOD converter model (under development), it is important to be able to calculate reliable velocity and turbulence parameter data for gas mixtures of different argon/oxygen ratios.
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| 3. |
- Lönnberg, Hanna, et al.
(författare)
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Synthesis of Polycaprolactone-Grafted Microfibrillated Cellulose for Use in Novel Bionanocomposites-Influence of the Graft Length on the Mechanical Properties
- 2011
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Ingår i: ACS APPLIED MATERIALS & INTERFACES. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 3:5, s. 1426-1433
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, microfibrillated cellulose (MFC) made from bleached sulfite softwood dissolving pulp was utilized to reinforce a poly(epsilon-caprolactone) (PCL) biopolymer matrix. To improve the dispersibility of the hydrophilic MFC in the nonpolar matrix and the interfacial adhesion in the composite material, we covalently grafted the MFC with PCL via ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL). To be able to investigate the effect of the PCL graft length on the mechanical properties of the composite material, we performed ROP to different molecular weights of the grafts. Bionanocomposites containing 0, 3, and 10 wt % MFC were prepared via hot pressing using both unmodified and PCL grafted MFC (MFC-g-PCL) as reinforcement. PCL grafting resulted in improved dispersion of the MFC in a nonpolar solvent and in the PCL matrix. The mechanical testing of the biocomposites showed an improvement in the mechanical properties for the PCL grafted MFC in comparison to ungrafted MFC. It was also shown that there was an impact on the mechanical properties with respect to the PCL graft lengths, and the strongest biocomposites were obtained after reinforcement with MFC grafted with the longest PCL graft length.
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| 4. |
- Saffari Pour, Mohsen, 1987-, et al.
(författare)
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The behavior of impurities during producer gas implementation as alternative fuel in steel reheating furnaces : A CFD and thermochemical study
- 2016
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Ingår i: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE). - USA : American Society of Mechanical Engineers (ASME). - 9780791850589
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Konferensbidrag (refereegranskat)abstract
- The use of available and cheap industrial producer gases as alternative fuels for the steel reheating furnaces is an attractive topic for steel industry. The application of producer gases for such furnaces introduces not only the complicated combustion system of Low Calorific Value (LCV) gases, but also several impurities that could be problematic for the quality of final steel products. The quality of steel can be highly affected by the interaction of impurities with iron-oxides at hot slab surfaces. In this research, the combustion of producer gases and the behavior of impurities at the steel slab surface are studied by aid of a novel coupled computational fluid dynamics (CFD) and thermodynamics approach. The impurities are introduced as mineral ash particles with the particle size distributions of 15-100 νm. The CFD predicted data regarding the accumulation of ash particles are extracted from an interface layer at the flaring gas media around the steel slab surface. Later on, these predicted data are used for the thermo-chemical calculations regarding the formation of sticky solutions and stable phases at the steel slab surface. The results show that the particles are more likely follow the flow due to the high injection velocity of fuel (70 m/s) and the dominant inertial forces. More than 90 percent of particles have been evacuated through the exhaust pipes. The only 10 percent of remaining particles due to the high recirculation zones at the middle of furnace and the impinging effect of front walls tend to stick to the side wall of slab in the heating zone more than the soaking zone.
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| 5. |
- Capitao Patrao, Alexandre, 1988, et al.
(författare)
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Compact heat exchangers for hydrogen-fueled aero engine intercooling and recuperation
- 2024
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Ingår i: Applied Thermal Engineering. - 1359-4311. ; 243
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the application of compact heat exchangers for the purpose of intercooling and recuperation systems for short-to-medium range aircraft equipped with hydrogen-fueled turbofan engines. The primary objective is to assess the potential effects of engine-integrated compact heat exchangers on fuel consumption and emissions. The paper encompasses the conceptual design of integrated heat exchangers and associated ducts, followed by aerodynamic optimization studies to identify suitable designs that minimize air-side pressure losses and ensure flow uniformity at the inlet of the high-pressure compressor. Pressure drop correlations are then established for selected duct designs and incorporated into a system-level performance model, allowing for a comparison of their impact on specific fuel consumption, NOx emissions, and fuel burn against an uncooled baseline engine. The intercooled-recuperated engine resulted in the most significant improvement in take-off specific fuel consumption, with a reduction of up to 7.7% compared to the baseline uncooled engine, whereas the best intercooled engine resulted in an improvement of about 4%. Furthermore, the best configuration demonstrated a decrease in NOx emissions by up to 37% at take-off and a reduction in mission fuel burn by 5.5%. These enhancements were attributed to reduced compression work, pre-heating of the hydrogen fuel, and lower high-pressure compressor outlet temperatures.
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| 6. |
- Capitao Patrao, Alexandre, 1988, et al.
(författare)
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The heat transfer potential of compressor vanes on a hydrogen fueled turbofan engine
- 2024
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Ingår i: Applied Thermal Engineering. - 1359-4311. ; 236
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen is a promising fuel for future aviation due to its CO2-free combustion. In addition, its excellent cooling properties as it is heated from cryogenic conditions to the appropriate combustion temperatures provides a multitude of opportunities. This paper investigates the heat transfer potential of stator surfaces in a modern high-speed low-pressure compressor by incorporating cooling channels within the stator vane surfaces, where hydrogen is allowed to flow and cool the engine core air. Computational Fluid Dynamics simulations were carried out to assess the aerothermal performance of this cooled compressor and were compared to heat transfer correlations. A core air temperature drop of 9.5 K was observed for this cooling channel design while being relatively insensitive to the thermal conductivity of the vane and cooling channel wall thickness. The thermal resistance was dominated by the air-side convective heat transfer, and more surface area on the air-side would therefore be required in order to increase overall heat flow. While good agreement with established heat transfer correlations was found for both turbulent and transitional flow, the correlation for the transitional case yielded decent accuracy only as long as the flow remains attached, and while transition was dominated by the bypass mode. A system level analysis, indicated a limited but favorable impact at engine performance level, amounting to a specific fuel consumption improvement of up to 0.8 % in cruise and an estimated reduction of 3.6 % in cruise NOx. The results clearly show that, although it is possible to achieve high heat transfer rate per unit area in compressor vanes, the impact on cycle performance is constrained by the limited available wetted area in the low-pressure compressor.
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| 7. |
- Jonsson, Isak, 1990, et al.
(författare)
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Design and pre-test evaluation of a low-pressure compressor test facility for cryogenic hydrogen fuel integration
- 2021
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Ingår i: Proceedings of the ASME Turbo Expo. ; 2A-2021
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Konferensbidrag (refereegranskat)abstract
- The use of hydrogen as aviation fuel is again resurfacing with unprecedented vigor. It is well known that hydrogen is a formidable heat sink and the use of heat sinks in the compression system of an aero engine may enable not only preheating of the fuel but also improve the gas turbine cycle itself. One such opportunity arises from extracting heat to the fuel as part of the compression process. This work presents the design process and pre-test evaluation of a low-speed compressor test facility dedicated to aerothermal measurements. The design has been derived from a high-speed transonic compressor developed for a large sized geared turbofan engine. The proposed pre-test evaluation methodology provides a comprehensive and affordable way to estimate facility accuracy by virtually addressing all the experimental procedures, from data acquisition to a final performance map. The evaluation of gathering compressor performance parameters via a gas-path investigation process was achieved while relying on results from numerical simulations. The pre-test evaluation details uncertainties introduced throughout this process with transducers, flow and probe specific errors, traverse discretization, and data normalization. A suitable instrumentation configuration is presented which shows that the performance parameters pressure ratio (P) and isentropic efficiency (hc) can be determined with uncertainties below 1% for most operating conditions and below 0.5% at design conditions.
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| 8. |
- Malmqvist, Robert, et al.
(författare)
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E/W-Band CPW-based Amplifier MMICs Fabricated in a 60 nm GaN-on-Silicon Foundry Process
- 2021
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Ingår i: EuMIC 2020 - 2020 15th European Microwave Integrated Circuits Conference. ; , s. 137-140
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Konferensbidrag (refereegranskat)abstract
- This paper presents an experimental evaluation of two co-planar waveguide (CPW) based E/W-band amplifier MMICs realised in a 60 nm GaN-on-Si foundry process. A one-stage amplifier and a two-stage amplifier realised in this process have a measured maximum gain of 8 dB and 16 dB at 73-74 GHz, respectively. The two amplifiers have a measured gain of 3 dB and 7 dB at 93 GHz when the drain voltage (Vd) is 10 V and the drain current (Id) is 15 mA per stage. The two-stage amplifier has a measured noise figure (NF) of 2.7-3.8 dB and 2.9-4.1 dB at 90-95 GHz when the Id is 10 mA and Vd is 5 V and 10 V, respectively. The measured NF of this amplifier is equal to 4-6 dB at 92-95 GHz when an Id of 10-20 mA is used in each stage with same drain bias.
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| 9. |
- Sethi, V., et al.
(författare)
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Enabling Cryogenic Hydrogen-Based CO 2 -Free Air Transport: Meeting the demands of zero carbon aviation
- 2022
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Ingår i: IEEE Electrification Magazine. - 2325-5889 .- 2325-5897. ; 10:2, s. 69-81
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Flightpath 2050 from the European Union (EU) sets ambitious targets for reducing the emissions from civil aviation that contribute to climate change. Relative to aircraft in service in year 2000, new aircraft in 2050 are to reduce CO2 emissions by 75% and nitrogen oxide (NOx) emissions by 90% per passenger kilometer flown. While significant improvements in asset management and aircraft and propulsion-system efficiency and are foreseen, it is recognized that the Flightpath 2050 targets will not be met with conventional jet fuel. Furthermore, demands are growing for civil aviation to target zero carbon emissions in line with other transportation sectors rather than relying on offsetting to achieve 'net zero.' A more thorough and rapid greening of the industry is seen to be needed to avoid the potential economic and social damage that would follow from constraining air travel. This requires a paradigm shift in propulsion technologies. Two technologies with potential for radical decarbonization are hydrogen and electrification. Hydrogen in some form seems an inevitable solution for a fully sustainable aviation future. It may be used directly as a fuel or combined with carbon from direct air capture of CO2 or other renewable carbon sources, to synthesize drop-in replacement jet fuels for existing aircraft and engines. As a fuel, pure hydrogen can be provided as a compressed gas, but the weight of the storage bottles limits the practical aircraft ranges to just a few times that is achievable with battery power. For longer ranges, the fuel needs to be stored at lower pressures in much lighter tanks in the form of cryogenic liquid hydrogen (LH2).
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| 10. |
- Silva, Vinicius T., et al.
(författare)
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Powered Low-Speed Experimental Aerodynamic Investigation of an Over-Wing-Mounted Nacelle Configuration
- 2024
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Ingår i: Journal of Aircraft. - 0021-8669 .- 1533-3868. ; 61:2, s. 415-424
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Tidskriftsartikel (refereegranskat)abstract
- Over-wing integration of ultrahigh bypass turbofan engines can be a solution for next-generation commercial transport aircraft since it eliminates the ground clearance issue and it has the potential to reduce ground noise due to acoustic shielding. Moreover, a unique characteristic of this installation type is the powered lift benefit at low-speed flight conditions. This paper aims to experimentally investigate the effect of the engine power setting on the low-speed aerodynamic performance of an over-wing-mounted nacelle configuration comprising a conventional tube-and-wing layout. Thus, low-speed wind tunnel tests were performed for a half-span powered scale model of the aforementioned configuration. The effect of the engine power setting on the wing lift and spanwise pressure distributions was investigated. The experiments were carried out for angles of attack varying from 0 to 6 degrees and inlet mass flow ratios up to 2.4. The results were used to validate computational fluid dynamics simulations conducted for the same wind tunnel conditions. It has been shown that a significant powered lift benefit can be achieved for the studied configuration, without a penalty in the net propulsive force and that the lift increases linearly with the inlet mass flow ratio. Furthermore, it was observed that the engine power setting largely influences the pressure distributions along the wing, especially at the spanwise sections closer to the nacelle. The low-momentum zone created upstream of the engine at high power settings reduces the pressure at the wing's upper surface, which is the main factor responsible for the increased lift. By taking advantage of such behavior, drag can potentially be reduced at takeoff and climb due to a lower flap setting required for the same lift.
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