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  • 51.
    Aghaali, Habib
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångstrom, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Demonstration of Air-Fuel Ratio Role in One-Stage Turbocompound Diesel Engines2013Inngår i: SAE Technical Papers, 2013, Vol. 11Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the turbine efficiency and mass flow as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity.

    The main parameter influencing the turbocompound energy recovery is the exhaust gas pressure which leads to higher pumping loss of the engine and consequently lower engine crankshaft power. Each air-fuel equivalence ratio (λ) gives different engine power, exhaust gas temperature and pressure. Decreasing λ toward 1 in a Diesel engine results in higher exhaust gas temperatures of the engine.  λ can be varied by changing the intake air pressure or the amount of injected fuel which changes the available energy into the turbine. Thus, there is a compromise between gross engine power, created pumping power, recovered turbocompound power and consumed compressor power.

    In this study, the effects of different λ values and exhaust back-pressure have been investigated on the efficiency of a heavy-duty Diesel engine equipped with a single-stage electric turbocompounding. A one-dimensional gas dynamics model of a turbocharged engine was utilized that was validated against measurements at different load points. Two configurations of turbocompound engine were made. In one configuration an electric turbocharger was used and the amount of fuel was varied with constant intake air pressure. In another configuration the turbocharger turbine and compressor were disconnected to be able to control the turbine speed and the compressor speed independently; then the compressor pressure ratio was varied with constant engine fuelling and the exhaust back-pressure was optimized for each compressor pressure ratio.

    At each constant turbine efficiency there is a linear relation between the optimum exhaust back-pressure and ideally expanded cylinder pressure until bottom dead center with closed exhaust valves. There is an optimum λ for the turbocharged engine with regard to the fuel consumption. In the turbocompound engine, this will be moved to a richer λ that gives the best total specific fuel consumption; however, the results of this study indicates that turbocompound engine efficiency is relatively insensitive to the air-fuel ratio.

  • 52.
    Aghaali, Habib
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    A review of turbocompounding as a waste heat recovery system for internal combustion engines2015Inngår i: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 49, s. 813-824Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Internal combustion engines waste a large amount of fuel energy through their exhausts. Various technologies have been developed for waste heat recovery such as turbocompounds, Rankine bottoming cycles, and thermoelectric generators that reduce fuel consumption and CO2 emissions. Turbocompounding is still not widely applied to vehicular use despite the improved fuel economy, lower cost, volume, and complexity higher exhaust gas recirculation driving capability and improved transient response. This paper comprehensively reviews the latest developments and research on turbocompounding to discover important variables and provide insights into the implementation of a high-efficiency turbocompound engine. Attention should be paid to the optimization of turbocompound engines and their configurations because the major drawback of this technology is additional exhaust back-pressure, which leads to higher pumping loss in the engines. Applying different technologies and concepts on turbocompound engines makes the exhaust energy recovery more efficient and provides more freedom in the design and optimization of the engines. Turbine efficiency plays an important role in the recovery of the wasted heat so turbine design is a crucial issue in turbocompounding. In addition, variability in geometry and rotational speed of power turbines allows for more efficient turbocompound engines in different operating conditions. The conclusion drawn from this review is that turbocompounding is a promising technology for reducing fuel consumption in the coming decades in both light- and heavy-duty engines.

  • 53.
    Aghaali, Habib
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Effects of Effective Flow Areas of Exhaust Valves on a Turbocompound Diesel Engine Combined With Divided Exhaust Period2014Inngår i: Proceedings from the FISITA 2014 World Automotive Congress, 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Research and /or Engineering Questions/Objective: Exhaust gas energy recovery in internal combustion engines is one of the key challenges in the future developments. The objective of this study is to reveal the fuel-saving potential of a turbocompound Diesel engine combined with divided exhaust period (DEP). The exhaust flow is provided for two different manifolds via separate valves, blowdown and scavenging, at different timings. The main challenge in this combination is choked flow through the exhaust valves due to the restricted effective flow areas. Therefore, the effects of enlarged effective flow areas of the exhaust valves are studied.

    Methodology: A commercial 1D gas dynamics code, GT-POWER, was used to simulate a turbocharged Diesel engine which was validated against measurements. Then the turbocharged engine model was modified to a turbocompound engine with DEP. Using statistical analysis in the simulation (design of experiment), the performance of this engine was studied at different sizes, lift curves and timings of the exhaust valves and turbine swallowing capacity.

    Results: In the paper the effects of the effective flow areas of the exhaust valves are presented on the break specific fuel consumption, pumping mean effective pressure and the turbine energy recovery by increasing the valve size and modifying valve lift curve to fast opening and closing. This has been done in a low engine speed and full load. The main finding is that the flow characteristics of the exhaust valves in the turbocompound DEP engine are very important for gaining the full efficiency benefit of the DEP concept.  The turbocompound DEP engine with modified valve lift shape of the exhaust valves could improve the overall brake specific fuel consumption by 3.44% in which 0.64% of the improvement is due to the valve lift curve. Modified valve lift curves contribute mainly in decreasing the period of choked flow through the exhaust valves.

    Limitations of this study: The simulations were not validated against measurements; however, the mechanical and geometrical limitations were tried to keep realistic when manipulating the valve flow area events.

    What does the paper offer that is new in the field in comparison to other works of the author: In addition to the novelty of the engine architecture that combines turbocompound with DEP, the statistical analysis and comparison presented in this paper is new especially with demonstrating the importance of crank angle coupled flow characteristics of the valves.

    Conclusion: To achieve full fuel-saving potential of turbocompound DEP engines, the flow characteristics of the exhaust valves must be considered. The effective flow areas of the exhaust valves play important roles in the choked flow through the valves, the pumping work and the brake specific fuel consumption of the engine.

  • 54.
    Aghaali, Habib
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Externally divided exhaust period on a turbocompound engine for fuel-saving2014Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    To improve exhaust heat utilization of a turbocharged engine, divided exhaust period (DEP) and turbocompound are integrated. The DEP concept decreases pumping loss created by the turbocompound. In the DEP concept the exhaust flow is divided between two different exhaust manifolds, blowdown and scavenging. One of the two exhaust valves on each engine cylinder is opened to the blowdown manifold at the first phase of exhaust stroke and the other valve is opened to the scavenging manifold at the later phase of exhaust stroke. This leads to lower exhaust back pressure and pumping loss. The combination of turbocompound engine with DEP has been examined previously and the result showed that this combination reduces the fuel consumption in low engine speeds and deteriorates it in high engine speeds. The main restriction of this combination was the low effective flow areas of the exhaust valves at high engine speeds.

    To overcome this restriction and increase the effective flow areas of the exhaust valves, DEP is employed externally on the exhaust manifold instead of engine exhaust valves. In externally DEP (ExDEP), both exhaust valves will be opened and closed similar to the corresponding turbocharged engine and the exhaust flow is divided by flow splits on the exhaust manifold. Two valves on the outlet ports of each flow split are added. One of them is a non-return valve (check valve) and the other one is synchronized with the cam shaft.

    In this study, the fuel-saving potential of ExDEP is analysed on the turbocompound engine at different engine speeds and loads and compared with the corresponding turbocharged engine, turbocompound engine and turbocompound DEP engine equipped. The results show that ExDEP has a great fuel-saving potential in almost all load points.

    ExDEP concept, itself, is a novel concept that there is no available literature about it. Moreover, combination of this new gas exchange system with turbocompound engines is an innovative extension of combined turbocompound DEP engines.

  • 55.
    Aghaali, Habib
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Performance Sensitivity to Exhaust Valves and Turbine Parameters on a Turbocompound Engine with Divided Exhaust Period2014Inngår i: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 7, nr 4, s. 1722-1733Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Turbocompound can utilize part of the exhaust energy on internal combustion engines; however, it increases exhaust back pressure, and pumping loss.  To avoid such drawbacks, divided exhaust period (DEP) technology is combined with the turbocompound engine. In the DEP concept the exhaust flow is divided between two different exhaust manifolds, blowdown and scavenging, with different valve timings. This leads to lower exhaust back pressure and improves engine performance.

    Combining turbocompound engine with DEP has been theoretically investigated previously and shown that this reduces the fuel consumption and there is a compromise between the turbine energy recovery and the pumping work in the engine optimization. However, the sensitivity of the engine performance has not been investigated for all relevant parameters. The main aim of this study is to analyze the sensitivity of this engine architecture in terms of break specific fuel consumption to different parameters concerning the gas exchange such as blowdown valve timing, scavenging valve timing, blowdown valve size, scavenging valve size, discharge coefficients of blowdown and scavenging ports, turbine efficiency, turbine size and power transmission efficiency. This study presents the sensitivity analysis of the turbocompound DEP engine to these parameters and defines a set of important parameters that should be examined in experimental studies.

  • 56.
    Aghaali, Habib
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Temperature Estimation of Turbocharger Working Fluids and Walls under Different Engine Loads and Heat Transfer Conditions2013Inngår i: SAE Technical Papers, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Turbocharger performance maps, which are used in engine simulations, are usually measured on a gas-stand where the temperatures distributions on the turbocharger walls are entirely different from that under real engine operation. This should be taken into account in the simulation of a turbocharged engine. Dissimilar wall temperatures of turbochargers give different air temperature after the compressor and different exhaust gas temperature after the turbine at a same load point. The efficiencies are consequently affected. This can lead to deviations between the simulated and measured outlet temperatures of the turbocharger turbine and compressor. This deviation is larger during a transient load step because the temperatures of turbocharger walls change slowly due to the thermal inertia. Therefore, it is important to predict the temperatures of turbocharger walls and the outlet temperatures of the turbocharger working fluids in a turbocharged engine simulation.

    In the work described in this paper, a water-oil-cooled turbocharger was extensively instrumented with several thermocouples on reachable walls. The turbocharger was installed on a 2-liter gasoline engine that was run under different loads and different heat transfer conditions on the turbocharger by using insulators, an extra cooling fan, radiation shields and water-cooling settings. The turbine inlet temperature varied between 550 and 850 °C at different engine loads.

    The results of this study show that the temperatures of turbocharger walls are predictable from the experiment. They are dependent on the load point and the heat transfer condition of the turbocharger. The heat transfer condition of an on-engine turbocharger could be defined by the turbine inlet temperature, ambient temperature, oil heat flux, water heat flux and the velocity of the air around the turbocharger. Thus, defining the heat transfer condition and rotational speed of the turbocharger provides temperatures predictions of the turbocharger walls and the working fluids. This prediction enables increased precision in engine simulation for future work in transient operation.

  • 57.
    Aghaali, Habib
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    The Exhaust Energy Utilization of a Turbocompound Engine Combined with Divided Exhaust Period2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To decrease the influence of the increased exhaust pressure of a turbocompound engine, a new architecture is developed by combining the turbocompound engine with divided exhaust period (DEP). The aim of this study is to utilize the earlier stage (blowdown) of the exhaust stroke in the turbine(s) and let the later stage (scavenging) of the exhaust stroke bypass the turbine(s). To decouple the blowdown phase from the scavenging phase, the exhaust flow is divided between two different exhaust manifolds with different valve timing. A variable valve train system is assumed to enable optimization at different load points. The fuel-saving potential of this architecture have been theoretically investigated by examining different parameters such as turbine flow capacity, blowdown valve timing and scavenging valve timing. Many combinations of these parameters are considered in the optimization of the engine for different engine loads and speeds.

    This architecture produces less negative pumping work for the same engine load point due to lower exhaust back pressure; however, the exhaust mass flow into the turbine(s) is decreased. Therefore, there is a compromise between the turbine energy recovery and the pumping work. According to this study, this combination shows fuel-saving potential in low engine speeds and limitations at high engine speeds. This is mainly due to the choked flow in the exhaust valves because this approach is using only one of the two exhaust valves at a time. To reveal the full potential of this approach, increasing the effective flow area of the valves should be studied.

  • 58.
    Aghaali, Habib
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik.
    Turbocharged SI-Engine Simulation with Cold and Hot-Measured Turbocharger Performance Maps2012Inngår i: Proceedings of ASME Turbo Expo 2012, Vol 5, ASME Press, 2012, s. 671-679Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Heat transfer within the turbocharger is an issue in engine simulation based on zero and one-dimensional gas dynamics. Turbocharged engine simulation is often done without taking into account the heat transfer in the turbocharger. In the simulation, using multipliers is the common way of adjusting turbocharger speed and parameters downstream of the compressor and upstream of the turbine. However, they do not represent the physical reality. The multipliers change the maps and need often to be different for different load points. The aim of this paper is to simulate a turbocharged engine and also consider heat transfer in the turbocharger. To be able to consider heat transfer in the turbine and compressor, heat is transferred from the turbine volute and into the compressor scroll. Additionally, the engine simulation was done by using two different turbocharger performance maps of a turbocharger measured under cold and hot conditions. The turbine inlet temperatures were 100 and 600°C, respectively. The turbocharged engine experiment was performed on a water-oil-cooled turbocharger (closed waste-gate), which was installed on a 2-liter gasoline direct-injected engine with variable valve timing, for different load points of the engine. In the work described in this paper, the difference between cold and hot-measured turbocharger performance maps is discussed and the quantified heat transfers from the turbine and to/from the compressor are interpreted and related to the maps.

  • 59.
    Aghaali, Habib
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Förbränningsmotorteknik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Serrano, Jose R
    Universitat Politècnica de València.
    Evaluation of different heat transfer conditions on an automotive turbocharger2014Inngår i: International Journal of Engine Research, ISSN 1468-0874, E-ISSN 2041-3149, Vol. 16, nr 2, s. 137-151Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a combination of theoretical and experimental investigations for determining the main heat fluxes within a turbocharger. These investigations consider several engine speeds and loads as well as different methods of conduction, convection, and radiation heat transfer on the turbocharger. A one-dimensional heat transfer model of the turbocharger has been developed in combination with simulation of a turbocharged engine that includes the heat transfer of the turbocharger. Both the heat transfer model and the simulation were validated against experimental measurements. Various methods were compared for calculating heat transfer from the external surfaces of the turbocharger, and one new method was suggested.

    The effects of different heat transfer conditions were studied on the heat fluxes of the turbocharger using experimental techniques. The different heat transfer conditions on the turbocharger created dissimilar temperature gradients across the turbocharger. The results show that changing the convection heat transfer condition around the turbocharger affects the heat fluxes more noticeably than changing the radiation and conduction heat transfer conditions. Moreover, the internal heat transfers from the turbine to the bearing housing and from the bearing housing to the compressor are significant, but there is an order of magnitude difference between these heat transfer rates.

  • 60.
    Agmell, M.
    et al.
    Department of Mechanical Engineering, Lund University, Sweden.
    Ahadi, A.
    Department of Mechanical Engineering, Lund University, Sweden.
    Zhou, J. M.
    Department of Mechanical Engineering, Lund University, Sweden.
    Peng, Ru
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Bushlya, V.
    Department of Mechanical Engineering, Lund University, Sweden.
    Stahl, J. -E.
    Department of Mechanical Engineering, Lund University, Sweden.
    Modeling subsurface deformation induced by machining of Inconel 7182017Inngår i: Machining science and technology, ISSN 1091-0344, E-ISSN 1532-2483, Vol. 21, nr 1, s. 103-120Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Traditionally, the development and optimization of the machining process with regards to the subsurface deformation are done through experimental method which is often expensive and time consuming. This article presents the development of a finite element model based on an updated Lagrangian formulation. The numerical model is able to predict the depth of subsurface deformation induced in the high- speed machining of Inconel 718 by use of a whisker-reinforced ceramic tool. The effect that the different cutting parameters and tool microgeometries has on subsurface deformation will be investigated both numerically and experimentally. This research article also addresses the temperature distribution in the workpiece and the connection it could have on the wear of the cutting tool. The correlation of the numerical and experimental investigations for the subsurface deformation has been measured by the use of the coefficient of determination, R-2. This confirms that the finite element model developed here is able to simulate this type of machining process with sufficient accuracy.

  • 61.
    Agnelli, Filippo
    et al.
    Ecole Polytech, FRA.
    Constantinescu, Andrei
    Ecole Polytech, FRA.
    Nika, Grigor
    Weierstrass Inst Appl Anal & Stochast, DEU.
    Design and testing of 3D-printed micro-architectured polymer materials exhibiting a negative Poisson’s ratio2020Inngår i: Continuum Mechanics and Thermodynamics, ISSN 0935-1175, E-ISSN 1432-0959, Vol. 32, nr 2, s. 433-449Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work proposes the complete design cycle for several auxetic materials where the cycle consists of three steps (i) the design of the micro-architecture, (ii) the manufacturing of the material and (iii) the testing of the material. We use topology optimization via a level-set method and asymptotic homogenization to obtain periodic micro-architectured materials with a prescribed effective elasticity tensor and Poisson’s ratio. The space of admissible micro-architectural shapes that carries orthotropic material symmetry allows to attain shapes with an effective Poisson’s ratio below −1−1. Moreover, the specimens were manufactured using a commercial stereolithography Ember printer and are mechanically tested. The observed displacement and strain fields during tensile testing obtained by digital image correlation match the predictions from the finite element simulations and demonstrate the efficiency of the design cycle.

  • 62.
    Agnelli, Filippo
    et al.
    CNRS, École polytechnique, FRA.
    Nika, Grigor
    Weierstrass Institute for Applied Analysis and Stochastics, DEU.
    Constantinescu, Andrei
    CNRS, École polytechnique, FRA.
    Design of thin micro-architectured panels with extension–bending coupling effects using topology optimization2022Inngår i: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 391, artikkel-id 114496Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We design the micro-architecture of thin elastic panels to control their macroscopic behavior, accounting simultaneously for in-plane stiffness, out-of-plane stiffness and the extension–bending coupling effects. Our topology optimization method combines inverse homogenization, the Hadamard shape derivative and a level set method in the diffuse interface context to systematically capture within the unit cell the optimal micro-architecture. The efficiency of the solution method is illustrated through four numerical examples where the designed shape yields an important extension–bending coupling. The deformation responses under tensile loading are assessed numerically both on the complete periodic panel and on its homogenized twin plate. The results demonstrate that the simultaneous control of the in-plane, out-of-plane and their coupled behavior enables to shift a flat panel into a dome or a saddle shaped structure. Moreover, the obtained unit cells are elementary blocks to create directly 3D printable objects with shape-morphing capabilities.

  • 63.
    Agrawal, Vipin
    et al.
    Nordita SU; Department of Physics, Stockholm University, AlbaNova University Centre, Fysikum, 106 91 Stockholm, Sweden, Fysikum.
    Pandey, Vikash
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Mitra, Dhrubaditya
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Active buckling of pressurized spherical shells: Monte Carlo simulation2023Inngår i: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 108, nr 3, artikkel-id L032601Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the buckling of pressurized spherical shells by Monte Carlo simulations in which the detailed balance is explicitly broken - thereby driving the shell to be active, out of thermal equilibrium. Such a shell typically has either higher (active) or lower (sedate) fluctuations compared to one in thermal equilibrium depending on how the detailed balance is broken. We show that, for the same set of elastic parameters, a shell that is not buckled in thermal equilibrium can be buckled if turned active. Similarly a shell that is buckled in thermal equilibrium can unbuckle if sedated. Based on this result, we suggest that it is possible to experimentally design microscopic elastic shells whose buckling can be optically controlled.

  • 64.
    Agrawal, Vishal
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Kulachenko, Artem
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Farkostteknik och Solidmekanik, Hållfasthetslära.
    Scapin, Nicolo
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Tammisola, Outi
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
    An efficient isogeometric/finite-difference immersed boundary method for the fluid–structure interactions of slender flexible structures2024Inngår i: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 418, artikkel-id 116495Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this contribution, we present a robust and efficient computational framework capable of accurately capturing the dynamic motion and large deformation/deflection responses of highly-flexible rods interacting with an incompressible viscous flow. Within the partitioned approach, we adopt separate field solvers to compute the dynamics of the immersed structures and the evolution of the flow field over time, considering finite Reynolds numbers. We employ a geometrically exact, nonlinear Cosserat rod formulation in the context of the isogeometric analysis (IGA) technique to model the elastic responses of each rod in three dimensions (3D). The Navier–Stokes equations are resolved using a pressure projection method on a standard staggered Cartesian grid. The direct-forcing immersed boundary method is utilized for coupling the IGA-based structural solver with the finite-difference fluid solver. In order to fully exploit the accuracy of the IGA technique for FSI simulations, the proposed framework introduces a new procedure that decouples the resolution of the structural domain from the fluid grid. Uniformly distributed Lagrangian markers with density relative to the Eulerian grid are generated to communicate between Lagrangian and Eulerian grids consistently with IGA. We successfully validate the proposed computational framework against two- and three-dimensional FSI benchmarks involving flexible filaments undergoing large deflections/motions in an incompressible flow. We show that six times coarser structural mesh than the flow Eulerian grid delivers accurate results for classic benchmarks, leading to a major gain in computational efficiency. The simultaneous spatial and temporal convergence studies demonstrate the consistent performance of the proposed framework, showing that it conserves the order of the convergence, which is the same as that of the fluid solver.

  • 65.
    Ahlbert, Gabriella
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Method Evaluation of Global-Local Finite Element Analysis2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    When doing finite element analysis upon the structure of Saab’s aeroplanes a coarse global model of mainly shell elements is used to determine the load distribution for sizing the structure. At some parts of the aeroplane it is however desirable to implement a more detailed analysis. These areas are usually modelled with solid elements; the problem of connecting the fine local solid elements to the coarse global model will shell elements then arises.

     

    This master thesis is preformed to investigate possible Global-Local methods to use for the structural analysis on Gripen. First a literature study of current methods on the market is made, thereafter a few methods are implemented on a generic test structure and later on also tested on a real detail of Gripen VU. The methods tested in this thesis are Mesh refinement in HyperWorks, RBE3 in HyperWorks, Glue in MSC Patran/Nastran and DMIG in MSC Nastran. The software is however not evaluated in this thesis, and a further investigation is recommended to find the most fitting software for this purpose. All analysis are performed with linear assumptions.

     

    Mesh refinement is an integrated technique where the elements are gradually decreasing in size. Per definition, this technique cannot handle gaps, but it has almost identical results to the fine reference model.

     

    RBE3 is a type of rigid body elements with zero stiffness, and is used as an interface element. RBE3 is possible to use to connect both Shell-To-Shell and Shell-To-Solid, and can handle offsets and gaps in the boundary between the global and local model.

     

    Glue is a contact definition and is also available in other software under other names. The global respectively the local model is defined as contact bodies and a contact table is used to control the coupling. Glue works for both Shell-To-Shell and Shell-To-Solid couplings, but has problem dealing with offsets and gaps in the boundary between the global and local model.

     

    DMIG is a superelement technique where the global model is divided into smaller sub-models which are mathematically connected. DMIG is only possible to use when the nodes on the boundary on the local model have the same position as the nodes at the boundary of the global model. Thus, it is not possible to only use DMIG as a Global-Local method, but can advantageously be combined with other methods.

     

    The results indicate that the preferable method to use for Global-Local analysis is RBE3. To decrease the size of the files and demand of computational power, RBE3 can be combined with a superelement technique, for example DMIG.

     

    Finally, it is important to consider the size of the local model. There will inevitably be boundary effect when performing a Global-Local analysis of the suggested type, and it is therefore important to make the local model big enough so that the boundary effects have faded before reaching the area of interest.

    Fulltekst (pdf)
    Ahlbert_MethodEvaluationOfGlobalLocalFEM
  • 66. Ahlin, Kjell
    Comparison of Test Specifications and Measured Field Data2006Inngår i: Sound and Vibration, ISSN 0022-460X , Vol. 40, nr 9, s. 22-25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is not always obvious how to compare a given test specification with measured field data. This article presents a systematic method based on the shock response spectrum and the fatigue damage spectrum. A random-on-random test specification for tracked vehicles, AECTP 400, is used as an example.

  • 67. Ahlin, Kjell
    et al.
    Granlund, Johan
    Lindström, Fredric
    Comparing Road Profiles with Vehicle Perceived Roughness2004Inngår i: International Journal of Vehicle Design, ISSN 0143-3369, E-ISSN 1741-5314, Vol. 36, nr 2-3, s. 270-286Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Accurate road profiles are useful in vehicle design, such as for simulation of durability and ride quality. Laser/inertial profilometers typically record I mm wide profiles. The question is how well such a profile matches perceived vehicle wheel roughness. The objective here was to create a more representative wheel track longitudinal profile. Simulated and measured wheel vibration was compared on a 6km long road. Simulations were made for several definitions of the profile. Results for single laser sensor profiles showed reasonable likeness to truck perceived roughness. By far the best likeness (14.5% better) was achieved when the profile was based on triangular 25%-50%-25% weighted data from three sensors in the wheel track. Clearly, vehicle engineers can benefit from using multiple laser profile sensors, instead of a single sensor. This will improve test accuracy, thus reducing vehicle design project lead times and costs.

  • 68. Ahlin, Kjell
    et al.
    Magnevall, Martin
    Josefsson, Andreas
    Simulation of forced response in linear and nonlinear mechanical systems using digital filters2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    There exist many methods to calculate forced response in mechanical systems. Some methods are slow and the errors introduced are unknown. The paper presents a method that uses digital filters and modal superposition. It is shown how aliasing can be avoided as well as phase errors. The parameters describing the mechanical system are residues and poles, taken from FEA models, from lumped MCK systems, from analytic solutions or from experimental modal analysis. Modal damping may be used. The error in the calculation is derived and is shown to be only a function of the sampling frequency used. When the method is applied to linear mechanical systems in MATLAB it is very fast. The method is extended to incorporate nonlinear components. The nonlinear components could be simple, like hardening or stiffening springs, but may also contain memory, like dampers with hysteresis. The simulations are used to generate test data for development and evaluation of methods for identification of non-linear systems.

  • 69.
    Ahmad, Maqsood
    et al.
    Base Engine & Materials Technology, Volvo Group, Gothenburg.
    Peng, Ru
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    König, Mathias
    Materials Technology for Basic Engine, Scania CV, Södertälje.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Bending Fatigue Behavior of Blast Cleaned Grey Cast Iron2017Inngår i: Residual Stresses 2016: ICRS-10, Materials Research Proceedings 2 (2016), 2017, Vol. 2, s. 193-198Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a detailed study on the effect of an industrial blast cleaning process on the fatigue behavior of a grey cast iron with regard to the residual stresses and microstructural changes induced by the process. A comparison was also made to the effect of a machining operation which removed the casting skin layer. The blast cleaning process was found to greatly improve the fatigue resistance in both the low and high cycle regimes with a 75% increase in the fatigue limit. Xray diffraction measurements and scanning electron microscopic analyses showed that the improvement was mainly attributed to compressive residual stresses in a surface layer up to 800 μm in thickness in the blast cleaned specimens. The machining also gave better fatigue performance with a 30% increase in the fatigue limit, which was ascribed to the removal of the weaker casting skin layer.

  • 70.
    Ahn, Young Ju
    et al.
    Hongik Univ, South Korea.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Spagnoli, Andrea
    Univ Parma, Italy.
    Terzano, Michele
    Graz Univ Technol, Austria.
    Shakedown in frictional contact of discrete elastic systems: A review2022Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 241, artikkel-id 111470Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    When exposed to cyclic quasi-static loading, elastic bodies in contact may develop a favourable condition where slip ceases after a few cycles, an occurrence commonly known as frictional shakedown. If the amplitude of the cyclic load is greater than a so-called shakedown limit, shakedown cannot occur. In this review paper, the validity of shakedown theorems in the context of conforming contacts with a la Coulomb friction is first discussed. Then, an optimisation method for determining the shakedown limit of elastic discrete three-dimensional systems is reviewed. Finally, an incremental Gauss-Seidel algorithm, extended to three-dimensional systems, is here illustrated in details for the first time. The algorithm allows us to describe the transient response of normal-tangential coupled systems under a given cyclic loading scenario, and to determine their possible shakedown depending on the initial conditions. An example concerning a discrete conforming contact problem, where either coupling or uncoupling conditions can be imposed, is illustrated.

  • 71.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Analysis of multiple solutions in bifurcation diagrams to avoid unexpected dynamics2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In mechanical applications it is essential that unexpected dynamics are avoided. The industry wants to build reliable machines that are not sensitive to initial conditions. Therefore, a simple method has been developed to extract all sets of stable bifurcation diagrams. The method gives a designer a good overview of possible dynamics and thereby the possibility to select a safe operating region. The method is described and demonstrated with a rub-impact rotor. The practical usage of this method is to help the designer to determine if parameter ranges exist where coexistent solutions will appear. Thereby one can design the system to work in parameter ranges where only one acceptable solution exists.

    Fulltekst (pdf)
    FULLTEXT01
  • 72.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Dynamics of some vibro-impacting systems with amplitude constraints1995Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis concerns the dynamics of some vibro-impacting systems with fixed or moving amplitude constraints. It is based on and includes five papers, marked A to E. Simple models of three different vibro-impacting systems with applications in the fields of impact hammers, granular flow and disk brakes in vehicles are analysed. A 2-DOF (two-degree-of-freedom) model of a threshold-limited impact hammer is studied (Paper A). The stability of a class of periodic motions is analysed. For some parameter values these periodic motions are found to be qualitatively similar to the ones observed for a corresponding 1-DOF system. At other parameter combinations, however, new kinds of periodic or chaotic motions can be observed. For low damping, phenomena resembling antiresonance for linear systems can also be observed. Granular shear flows show a transitional behaviour in the rapid flow regime as the shear speed or the concentration of the grains is varied. The motion can, for example, change from smooth and orderly to erratic and turbulent. Some aspects of this transitional behaviour in granular shear flow are studied numerically, analytically and experimentally (Papers B, C and D). Simple vibro-impacting models are suggested to get some analytical insight into the dynamics of shear layers. Results from a 1-DOF model show that for high forcing frequencies, which correspond to high shear speeds, periodic as well as chaotic motions can exist, whereas, for low forcing frequencies the vibrations are completely damped out to a stationary state (Paper B). Stability of this stationary state is studied analytically (Paper C), and experimentally (Paper D), where the motions of granular particles in a transparent shear cell are followed by using video techniques. For low shear speeds a single shear layer adjacent to the bottom boundary of the shear cell is observed. As the shear speed is increased, a transition to a random like state involving many layers is found to occur. In order to understand the phenomenon of squeal in disk brakes, a 3-DOF model is suggested to simulate the dynamics of a brake pad. The region of contact between the brake pad and the disk is described by using a coefficient of friction and distributed stiffness. The brake pad is allowed to have adjustable support locations and possibilities of impacts with its surroundings. The equilibrium state of the pad is determined by using a static analysis. The assumption is that the instability of this stationary state is a possible explanation of squeal, therefore, the stability is analysed in detail. Examples of different kinds of pad motions are presented. A rich variety of motions are found to exist including periodic, seemingly chaotic, stationary behaviour in slip, vibrations with full contact with the disk, stick-slip and impacts.

    Fulltekst (pdf)
    FULLTEXT01
  • 73.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Multiple solutions in a rub-impact Jeffcott rotor2004Inngår i: Extended abstracts, proceedings: 10th international symposium on transport phenomena and dynamics of rotating machinery / [ed] Dieter Bohn, Aachen: Inst. of steam and gas turbines, RWTH , 2004Konferansepaper (Fagfellevurdert)
  • 74.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Multiple solutions in an amplitude limited Jeffcott rotor including rubbing and stick-slip effect2005Inngår i: Proceedings ASME 2005 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference: DETC 2005, American Society of Mechanical Engineers , 2005, s. 1091-1096Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The non-linear behaviour of rub-impact rotors have been studied in several papers. In such systems rich dynamics have been found together with the coexistence of solutions within some specific parameter ranges. In this paper an attempt is made to find all stable solutions for an amplitude limited Jeffcott rotor including rubbing and stick-slip effect. The recently suggested "multi bifurcation diagram method" is used to find and extract stable sets of bifurcation diagrams. A system is chosen where the linear stationary amplitude only exceeds the clearance in a narrow region near the natural frequency. Therefore large regions in frequency are expected to have only the linear stationary response. The results show that it is only for very low frequencies that one single solution exists. Even though periodic motions are dominant, there exist large ranges in frequency with quasi-periodic or chaotic motions. For the studied cases, three coexisting stable solutions are most common. In one case as many as four stable solutions was found to coexist. For rotors with large clearances (no impacts necessary) it is still possible to find several coexisting motions. For all cases the stick motion is the most severe one with large amplitudes and high backward whirl frequencies. In real situations the consequence of this stick motion is machine failure. These high amplitude motions were found to be stable over large frequency ranges. From the stability analysis it was found that this rolling motion can be avoided by low spin speed, low contact stiffness, low coefficient of friction, small ratio of disc radius/clearance or high damping ratio. In a design situation the parameters are seldom known with high accuracy. Therefore, it is of interest to know all solutions for parameter intervals. The multi-bifurcation diagram can be used in such situations to design a robust machine or at least be prepared for unwanted dynamics.

  • 75.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Review of Mechanical Vibrations by S.S. Rao2007Inngår i: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 221, nr 1, s. 135-Artikkel i tidsskrift (Annet vitenskapelig)
  • 76.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Rotor dynamical analysis of failure due to rotor-stator contact in an overhung rotor2006Inngår i: Proceedings - 7th International Conference on Rotor Dynamics: September 25 - 28, 2006, Vienna, Austria / [ed] H. Springer; H. Ecker, Vienna: Institute of Mechanics and Mechatronics, Vienna University of Technology , 2006, artikkel-id 264Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Two new 1MW fans in a remote gas cleaning plant have failed within 12 days of operation. Due to high costs a rapid repair and modification was performed without any deeper investigation or measurements. Since the driving frequency was far below the critical speed, a theory was that contact between rotating and stationary part was the reason for failure. In this paper the rotor dynamics is studied by an amplitude limited 4DOF overhung rotor. Simulations indicate that in addition to the ordinary unbalance response there can exist a high amplitude rolling contact mode between the disc and the stationary parts. By analysis of basin of attraction it is concluded that contact is a possible cause for the failure if the damping ratio is low, coefficient of friction is high and the rotor is eccentrically positioned relative to the stator. Measurements on the system are however necessary before a satisfying explanation can be given.

  • 77.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Two vibroimpacting systems with amplitude constraints1992Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 78.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Gupta, R.B.
    Periodic and chaotic behaviour of a threshold-limited two-degree-of-freedom system1993Inngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 165, nr 2, s. 305-327Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A two-degree-of-freedom impact oscillator with proportional damping is considered. The maximum displacement of one of the masses is limited to a threshold value by a rigid wall, which gives rise to a non-linearity in the system. Impacts between the mass and the wall are described by a coefficient of restitution. The behaviour of the system is rich and includes features like period doublings, period havings, jumps, chaos, etc. Periodic motions of the system are studied by analytical methods. The influence of system parameters such as damping, coefficient of restitution, distribution of masses and clearance, etc., is studied for some extreme values of these parameters. The stability of a class of periodic motions is investigated. Parameter ranges which result in stable periodic multiple impacts are identified. Application of the results to the design of impact tools is discussed.

  • 79.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Gustavsson, Rolf K.
    Vattenfall, VRD.
    Lundström, Niklas L. P.
    Umeå university.
    Karlsson, Martin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Calleecharan, Yogeshwarsing
    Nässelqvist, Mattias
    Karlberg, Magnus
    Lundin, Urban
    Uppsala University.
    Developments in rotor dynamical modeling of hydropower units2009Inngår i: Proceedings of the IUTAM Symposium on Emerging Trends in Rotor Dynamics: held in New Delhi, India, March 23 - March 26, 2009 / [ed] Kshitij Gupta, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag, 2009Konferansepaper (Fagfellevurdert)
  • 80.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindkvist, Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Dynamics of a rubbing Jeffcott rotor with three blades2011Inngår i: Chaos Theory: Modeling, Simulation and Applications: Selected Papers from the 3rd Chaotic Modeling and Simulation International Conference (CHAOS2010) / [ed] Christos H. Skiadas; Ioannis Dimotikalis; Charilaos Skiadas, Singapore: World Scientific Publishing Co Pte Ltd , 2011, Vol. Part II. Invited and Contributed Papers, s. 97-104Konferansepaper (Fagfellevurdert)
  • 81.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lundström, Niklas L. P.
    Umeå university.
    Complex dynamic responses due to deviations of generator shape2009Inngår i: 10th Conference on Dynamical Systems - Theory and Applications: DSTA-2009, December 7-10, Łódź, Poland, 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Earlier measurements in large synchronous generators indicate the existence of complex whirling motion, and also deviations of shape in both the rotor and the stator. These non-symmetric geometries produce an attraction force between the rotor and the stator, called Unbalanced Magnetic Pull (UMP). The target of this paper is to analyse responses due to certain deviations of shape in the rotor and the stator. In particular, the perturbation on the rotor is considered to be of oval character, and the perturbations of the stator are considered triangular and eccentric. It is concluded that harmful conditions can occur due to high amplitudes especially when the whirling of the rotor changes from forward to backward. During maintenance of hydro power generators the shapes of the rotor and stator are frequently measured. The results from this paper can be used to evaluate such measurements and to explain the existence of complex whirling motion.

  • 82.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Shen, Hayley H.
    Gupta, Ram B.
    Uppsala universitet.
    Experimental and numerical studies of shear layers in granular shear cell1996Inngår i: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 122, nr 3, s. 187-196Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stability of a shear layer inside a granular material in a gravity field is studied experimentally and numerically. A shear cell is built of transparent acrylic to visualize the motion of the granular material. This shear cell consists of two concentric cylinders containing layers of uniform spheres in the annular space between the cylinders. The shearing motion of the spheres is produced by rotating the bottom boundary of the cell. Friction of the cylinder walls resists the shear motion, thus creating a single shear layer adjacent to the bottom boundary, while the rest of the layers above move with constant speed as a solid body. As the rotation speed of the bottom boundary increases, two layers adjacent to the bottom boundary begin to shear. This shearing zone quickly thickens and dilates as the rotational speed increases. The transition of this shear motion from a single layer to many layers of shearing is studied by video recording. The initiation of this transition is observed to depend on the material properties and the number of layers overlaying the shear layer. A one-dimensional numerical model is constructed to bring insight into this transitional phenomenon.

  • 83.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Shen, Hayley H.
    Department of Civil and Environmental Engineering, Clarkson university.
    Gupta, Ram B.
    Division of Solid Mechanics, School of Engineering, Uppsala University.
    Stability and bifurcations of a stationary state for an impact oscillator1994Inngår i: Chaos, ISSN 1054-1500, E-ISSN 1089-7682, Vol. 4, nr 4, s. 621-630Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The motion of a vibroimpacting one-degree-of-freedom model is analyzed. This model is motivated by the behavior of a shearing granular material, in which a transitional phenomenon is observed as the concentration of the grains decreases. This transition changes the motion of a granular assembly from an orderly shearing between two blocks sandwiching a single layer of grains to a chaotic shear flow of the whole granular mass. The model consists of a mass-spring-dashpot assembly that bounces between two rigid walls. The walls are prescribed to move harmonically in opposite phases. For low wall frequencies or small amplitudes, the motion of the mass is damped out, and it approaches a stationary state with zero velocity and displacement. In this paper, the stability of such a state and the transition into chaos are analyzed. It is shown that the state is always changed into a saddle point after a bifurcation. For some parameter combinations, horseshoe-like structures can be observed in the Poincare sections. Analyzing the stable and unstable manifolds of the saddle point, transversal homoclinic points are found to exist for some of these parameter combinations

  • 84.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Shen, H.H.
    Clarkson University, Potsdam, NY.
    Gupta, R.
    Luleå tekniska universitet.
    Babic, M.
    University of Notre Dame, Notre Dame, IN, USA.
    A model for the transitional behavior of simple shear flows of disks1992Inngår i: Studies in Applied Mechanics, ISSN 0922-5382, Vol. 31, s. 301-310Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A simple one-dimensional model is suggested to simulate some aspects of the dynamics of granular shear flows. The model consists of a viscoelastic packet bouncing between two harmonically oscillating walls. The amplitude and frequency of the wall motion are related to the concentration and shear rate respectively. The dynamics of the system is studied and it is shown that periodic as well as chaotic motions are possible for different parameters and initial conditions. Results are presented in the form of time histories, power spectral densities, phase diagrams, Poincaré maps and bifurcation diagrams. Some of the characteristics present in the two-dimensional granular shear flows are present in this simple model. It is promising that such analysis can provide better understanding of the transitional behavior of the constitutive relation between the rapid shear and the quasi-static flows.

  • 85.
    Aidanpää, Jan-Olov
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Shen, H.H.
    Gupta, R.B.
    Babic, M.
    One-dimensional model for the transition from periodic to chaotic motions in granular shear flows1993Inngår i: Mechanics of materials, ISSN 0167-6636, E-ISSN 1872-7743, Vol. 16, nr 1-2, s. 153-161Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A simple one-dimensional mechanical model to simulate some aspects of the dynamics of granular flow is suggested. The model consists of a visco-elastic packet bouncing between two oscillating walls. The motion of the walls is prescribed to be harmonic. The amplitude and frequency of the wall motion are related to the concentration and shear rate, respectively. The dynamics of the system is studied for various parameter combinations and it is shown that periodic as well as chaotic motions are possible for different parameters and initial conditions. Results are presented in the form of time histories, power spectral densities, phase diagrams, Poincare plots and bifurcation diagrams. This simple one-dimensional model presents many features that are analogous to those observed in the two-dimensional simple shear flow of disks.

  • 86.
    Aihara, Aya
    et al.
    Division of Electricity, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden.
    Bolin, Karl
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Strömningsmekanik och Teknisk Akustik, Marcus Wallenberg Laboratoriet MWL.
    Goude, Anders
    Division of Electricity, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden.
    Bernhoff, Hans
    Division of Electricity, Department of Electrical Engineering, Uppsala University, Uppsala, Sweden.
    Aeroacoustic noise prediction of a vertical axis wind turbine using large eddy simulation2021Inngår i: International Journal of Aeroacoustics, ISSN 1475-472X, E-ISSN 2048-4003, Vol. 20, nr 8, s. 959-978Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study investigates the numerical prediction for the aerodynamic noise of the vertical axis wind turbine using large eddy simulation and the acoustic analogy. Low noise designs are required especially in residential areas, and sound level generated by the wind turbine is therefore important to estimate. In this paper, the incompressible flow field around the 12 kW straight-bladed vertical axis wind turbine with the rotor diameter of 6.5 m is solved, and the sound propagation is calculated based on the Ffowcs Williams and Hawkings acoustic analogy. The sound pressure for the turbine operating at high tip speed ratio is predicted, and it is validated by comparing with measurement. The measured spectra of the sound pressure observed at several azimuth angles show the broadband characteristics, and the prediction is able to reproduce the shape of these spectra. While previous works studying small-scaled vertical axis wind turbines found that the thickness noise is the dominant sound source, the loading noise can be considered to be a main contribution to the total sound for this turbine. The simulation also indicates that the received noise level is higher when the blade moves in the downwind than in the upwind side.

  • 87.
    Ainegren, Mats
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för kvalitets- och maskinteknik. SportsTech Research Centre, Mid Sweden University.
    Michel, Frank
    Vaude Sports GmbH & Co., I-Team, Tettnang, Germany.
    Klauer, Robert
    Vaude Sports GmbH & Co., I-Team, Tettnang, Germany.
    Kopyug, Andrey
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för kvalitets- och maskinteknik. Mid Sweden University, Dept of Mechanical Engineering.
    Bäckström, Mikael
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för kvalitets- och maskinteknik. SportsTech Research Centre, Mid Sweden University.
    Samuelsson, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för kvalitets- och maskinteknik.
    Ahnesjö, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för kvalitets- och maskinteknik.
    Litzenberger, Stefan
    Competence Center Sports Engineering, Biomechanics & Ergonomics, University of Applied Sciences Technikum, Wien, Austria.
    A Study of Skin-Close Heat and Moisture with Different Types of Backpacks in Cycling2020Inngår i: The 13th Conference of the International Sports Engineering Association / [ed] Motomu Nakashima, Takeo Maruyama and Yusuke Miyazaki, MDPI, 2020, Vol. 49, artikkel-id 86Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The aim of this project was to evaluate effects of backpacks with different design intended for use during cycling on skin-close temperature and relative humidity, oxygen uptake, heart rate and aerodynamic drag. Seven subjects took part in the study cycling on a mountain bike mounted on a “smart trainer” placed on a force plate in a wind tunnel. Three series of experiments were carried out: without backpack, with conventional backpack and with a backpack having innovative rear panel design. As hypothesized, the results showed that an innovatively designed backpack with the ducts deflecting part of the airflow towards some areas of the user’s back provided lower temperature and relative humidity for the microclimate compared to a conventional backpack without airflow channels. Further, reference tests without any backpack resulted in the lowest temperature and humidity. However, no differences were found between the three tests for oxygen uptake, heart rate and aerodynamic drag.

  • 88.
    Aisvaran, Chandramohan
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Study of non-linear strain path in sheet metal forming2021Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    At present, Sheet Metal Forming (SMF) is not just limited to increasing demand from automobile industries but also to various other manufacturing industries that utilize sheet metal forming processes. The surplus demands for optimised manufacturing products warrant the need for an extended decisive study on SMF. 

    One such area of study in SMF is formability. Traditionally, formability is predicted using the conventional Forming Limit Curve (FLC). But when it comes to complex SMF processes, FLC failure model can sometimes overestimate (for low uniaxial straining) or underestimate (for bi-axial straining) failure. This thesis focuses on suitable test procedures to generate non-linear strain paths and prediction of formability using the concept of Generalized Forming Limit Curve (GFLC). Initially, through systematic literature review, two-step process is chosen as the test procedure in this thesis. The test procedure was simulated in LS-Dyna to obtain results which are then used by GFLC concept to predict formability for a bi-linear deformation history. The predicted formability using the concept of GFLC is then compared with the predicted formability using FE-simulation and using experimentation.  The found percent error for GFLC prediction compared to that of FE-simulation prediction is 11% and the percent error for GFLC prediction and experimentation prediction is 14%. However, these two predictions can not be used to validate the GFLC prediction. This is because in this thesis GFLC procedure uses data obtained from FE-simulation with GISSMO failure model. Through literature, it is identified that the GFLC concept can be applied for multi-linear deformation histories to predict formability and the method to do so is explained in detail in this thesis. Finally, it is concluded that the use of the GFLC concept in conjunction with the two-step drawing process to predict formability for bi-linear deformation history is acceptable.

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  • 89.
    Ajpi, C.
    et al.
    UMSA Universidad Mayor de San Andres, Bolivia; KTH Royal Institute of Technology, Sweden.
    Leiva, N.
    UMSA Universidad Mayor de San Andres, Bolivia.
    Lundblad, Anders Olof
    RISE Research Institutes of Sweden, Säkerhet och transport, Elektrifiering och pålitlighet.
    Lindbergh, G.
    KTH Royal Institute of Technology, Sweden.
    Cabrera, S.
    UMSA Universidad Mayor de San Andres, Bolivia.
    Synthesis and spectroscopic characterization of Fe3+-BDC metal organic framework as material for lithium ion batteries2023Inngår i: Journal of Molecular Structure, ISSN 0022-2860, E-ISSN 1872-8014, Vol. 1272, artikkel-id 134127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work presents synthesis and spectroscopic characterization of a new metal-organic framework (MOF). The compound Fe-BDC-DMF was synthetized by the solvothermal method and prepared via a reaction between FeCl3.6H2O and benzene-1,4-dicarboxylic acid (H2BDC) or terephthalic acid using N,N-dimethylformamide (DMF) as solvent. The powder was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR) analysis. The electrochemical properties were investigated in a typical lithium-ion battery electrolyte by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charging and discharging. The synthetized Fe-BDC-DMF metal-organic framework (MOF) contains a mixture of three phases, identified by PXRD as: MOF-235, and MIL-53(Fe) monoclinic with C2/c and P21/c space groups. The structure of the Fe-BDC is built up from Fe3+ ions, terephalates (BDC) bridges and in-situ-generated DMF ligands. The electrochemical measurements conducted in the potential range of 0.5–3.5 V vs. Li+/Li0 show the voltage profiles of Fe-BDC and a plateau capacity of around 175 mAh/g. © 2022 The Author(s)

  • 90.
    Akbari, Saeed
    et al.
    RISE Research Institutes of Sweden, Digitala system, Smart hårdvara.
    Holmberg, Jonas
    RISE Research Institutes of Sweden, Material och produktion, Tillverkningsprocesser.
    Andersson, Dag
    RISE Research Institutes of Sweden, Digitala system, Smart hårdvara.
    Mishra, Madhav
    RISE Research Institutes of Sweden, Digitala system, Smart hårdvara.
    Brinkfeldt, Klas
    RISE Research Institutes of Sweden, Digitala system, Smart hårdvara.
    Packaging Induced Stresses in Embedded and Molded GaN Power Electronics Components2023Inngår i: Int. Conf. Therm., Mech. Multi-Phys. Simul. Exp. Microelectron. Microsyst., EuroSimE, Institute of Electrical and Electronics Engineers Inc. , 2023Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Residual stresses created during the packaging process can adversely affect the reliability of electronics components. We used incremental hole-drilling method, following the ASTM E 837-20 standard, to measure packaging induced residual stresses in discrete packages of power electronics components. For this purpose, we bonded a strain gauge on the surface of a Gallium Nitride (GaN) power component, drilled a hole through the thickness of the component in several incremental steps, recorded the relaxed strain data on the sample surface using the strain gauge, and finally calculated the residual stresses from the measured strain data. The recorded strains and the residual stresses are related by the compliance coefficients. For the hole drilling method in the isotropic materials, the compliance coefficients are calculated from the analytical solutions, and available in the ASTM standard. But for the orthotropic multilayered components typically found in microelectronics assemblies, numerical solutions are necessary. We developed a subroutine in ANSYS APDL to calculate the compliance coefficients of the hole drilling test in the molded and embedded power electronics components. This can extend the capability of the hole drilling method to determine residual stresses in more complex layered structures found in electronics. 

  • 91.
    Akbari, Saeed
    et al.
    RISE Research Institutes of Sweden, Digitala system, Smart hårdvara.
    Johansson, Jan
    RISE Research Institutes of Sweden, Material och produktion, Tillverkningsprocesser.
    Johansson, Emil
    Adaxis, France.
    Tönnäng, Lenny
    RISE Research Institutes of Sweden, Material och produktion, Tillverkningsprocesser.
    Hosseini, Seyed
    RISE Research Institutes of Sweden, Material och produktion, Tillverkningsprocesser.
    Large-Scale Robot-Based Polymer and Composite Additive Manufacturing: Failure Modes and Thermal Simulation2022Inngår i: Polymers, E-ISSN 2073-4360, Vol. 14, nr 9, artikkel-id 1731Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive manufacturing (AM) of large-scale polymer and composite parts using robotic arms integrated with extruders has received significant attention in recent years. Despite the contributions of great technical progress and material development towards optimizing this manufacturing method, different failure modes observed in the final printed products have hindered its application in producing large engineering structures used in aerospace and automotive industries. We report failure modes in a variety of printed polymer and composite parts, including fuel tanks and car bumpers. Delamination and warpage observed in these parts originate mostly from thermal gradients and residual stresses accumulated during material deposition and cooling. Because printing large structures requires expensive resources, process simulation to recognize the possible failure modes can significantly lower the manufacturing cost. In this regard, accurate prediction of temperature distribution using thermal simulations is the first step. Finite element analysis (FEA) was used for process simulation of large-scale robotic AM. The important steps of the simulation are presented, and the challenges related to the modeling are recognized and discussed in detail. The numerical results showed reasonable agreement with the temperature data measured by an infrared camera. While in small-scale extrusion AM, the cooling time to the glassy state is less than 1 s, in large-scale AM, the cooling time is around two orders of magnitudes longer. © 2022 by the authors

  • 92.
    Alali, Alaa
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Utveckling av kraftsensors-rigg för vindtunnel: En ny design för kraftsensors-rigg för Mittuniversitets vindtunnel2022Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    En vindtunnel används för att simulera luftflödet som verkar på till exempel en nerskalad modell av en verklig flygplansvinge eller ett fordon. Detta hjälper att förstå och ta fram de komponenter som påverkar interaktionen samt krafter och moment. 

    Mittuniversitetets laboratorium är i behov av en ny kraftsensors-rigg, detta är en rigg som mäter krafter som påverkar på en vinge profil inuti en vindtunnel. En vidareutveckling av den befintliga kraftsensors-riggen skulle innebära en alltför lång arbetsprocess, därför bestämdes det att utvecklas en ny design av sensor-riggen som löser några felkällor som den tidigare sensor- riggen har; vilka är inexakta mätvärde samt att den befintliga riggen mäter enbart lyftkraften. Genom framtagning av en ny kraftsensors-rigg som går att tillverka i Mittuniversitetets lokaler minskar tiden för att utföra vindtunnel tester samt ökar mätvärdenas noggrannhet. Syftet med detta arbete har varit att ta fram konstruktion av en ny kraftsensors-rigg som kan mäta krafter i x- och y-axeln det vill säga lyft och dragkraft. Kraftsensors-riggen kommer att installeras i vindtunneln som finns i Mittuniversitets laboratorium. 

    I detta projekt följs det designprocessens arbetsgång som är uppdelat i fyra faser. Den första fasen, förstudiefasen, definierades produktens kravspecifikation och funktionsanalys. Den andra fasen, kreativa fasen, inleddes med brainstorming för att generera konceptlösnings idéer. Sedan används Pugh-matrisen i konceptutvärdering- och framtagningsfasen för att utvärdera och välja konceptet utifrån en kvantitativ-metod. Sedan modellerades en tredimensionell modell för det färdiga konceptet med hjälp av CAD. Slutligen i konstruktion-utvecklingsfasen framställdes konstruktionen med hjälp av CAD:s modeller. därefter skrevs de komplexa delarna ut med en 3D-utskrivare samtidigt som de mindre komplexa delar framställdes av trä med en laser skärare för att spara på material samt kostnader, till slut byggdes och testades riggen i Mittuniversitets verkstad. 

    Projektet resulterade i en kraftsensors-rigg som kan mäta både luftmotstånd-och lyftkraften i en låg hastighet vindtunnel med noggrannare mätvärde än den tidigare riggen. 

     

    Fulltekst (pdf)
    fulltext
  • 93.
    Alam, M. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Z.
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, SE-100 44 Stockholm, Sweden.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kaplan, Alexander F. H.
    Luleå tekniska universitet.
    Häggblad, Hans-Åke
    Luleå tekniska universitet.
    The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints2010Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 265, nr 6, s. 1936-1945Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laser hybrid welding of an eccentric fillet joint causes a complex geometry for fatigue load by four point bending. The weld surface geometry and topography were measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. It can be explained why the root and the upper weld toe are uncritical for cracking. The cracks that initiate from the weld bead show higher fatigue strength than the samples failing at the lower weld toe, as can be explained by a critical radius for the toe below which surface ripples instead determine the main stress raiser location for cracking. The location of maximum surface stress is related to a combination of throat depth, toe radius and sharp surface ripples along which the cracks preferably propagate.

  • 94.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Z
    Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering, Stockholm.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Influence of defects on fatigue crack propagation in laser hybrid welded eccentric fillet joint2011Inngår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 78, nr 10, s. 2246-2258Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fatigue cracking of laser hybrid welded eccentric fillet joints has been studied for stainless steel. Two-dimensional linear elastic fracture mechanics analysis was carried out for this joint geometry for four point bending load. The numerical simulations explain for the experimental observations why the crack propagates from the lower weld toe and why the crack gradually bends towards the root. Lack of fusion turned out to be uncritical for the initiation of cracks due to its compressive stress conditions. The linear elastic fracture mechanics analysis has demonstrated in good qualitative agreement with fatigue test results that lack of fusion slightly (<10%) reduces the fatigue life by accelerating the crack propagation. For the geometrical conditions studied here improved understanding of the crack propagation was obtained and in turn illustrated. The elaborated design curves turned out to be above the standard recommendations

  • 95.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part I2009Inngår i: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Welded joints are a major component that is often responsible for causing a structure failure or for being the point at which fatigue cracking initiates and propagates. Despite tremendous research efforts, the understanding of fatigue behaviour is still limited, particularly for new techniques like laser hybrid welding. Beside a comprehensive state-of-the-art study, the paper presents a fatigue study of laser hybrid welded eccentric fillet joint of stainless steel of 10 mm thickness, with 5 mm displacement. Motivation is to study the influence of the surface geometry shape on fatigue performance under a four point bending test. 13 samples were produced, measuring the toe radii and testing under constant amplitude loading with stress ratio R=0. Different techniques have been used to measure local weld geometry, like plastic replica, a 3D optical profiler and a 3D-digitizer. The influence of the local weld geometry, like the toe radii, on the stress concentration was studied by FE-analysis. Occasionally lack of fusion was observed, which was taken into account in the FE-analysis. Based on the nominal stress approach, SN-curves were designed for laser hybrid welded eccentric fillet joints. Macro hardness tests were carried out and the crack surfaces were observed in order to detect crack initiation and propagation. Correlations between the toe radii, the corresponding stress maxima and crack initiation locations were studied between the different samples and even along the welds.

    Fulltekst (pdf)
    FULLTEXT01
  • 96.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Zuheir
    Kungliga tekniska högskolan, KTH.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Fatigue behaviour study of laser hybrid welded eccentric fillet joints: Part II: State-of-the-art of fracture mechanics and fatigue analysis of welded joints2009Inngår i: 12th NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th - 26th August 2009 in Copenhagen / [ed] Erling Dam Mortensen, Kgs. Lyngby: ATV-SEMAPP , 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Simplified fatigue and fracture mechanics based assessment methods are widely used by the industry to determine the structural integrity significance of postulated cracks, manufacturing flaws, service-induced cracking or suspected degradation of engineering components under normal and abnormal service loads. In many cases, welded joints are the regions most likely to contain original fabrication defects or cracks initiating and growing during service operation. The welded joints are a major component that is often blamed for causing a structure failure or for being the point at which fatigue or fracture problems initiate and propagate. Various mathematical models/techniques for various classes of welded joints are developed by analytically or by simulation software's that can be used in fatigue and fracture assessments. This literature survey compiled useful information on fracture and fatigue analysis of various welded joints. The present review is divided into two major sections- fracture mechanics and fatigue analysis with widely used models. A survey table is also introduced to get the outlook of research trend on fatigue and fracture over last 3 decades. Although tremendous research effort has been implemented on fatigue and fracture analysis of conventional welding, research on relatively new welding technology (laser welding, hybrid laser welding) is still limited and unsatisfactory. In order to give guarantee or make welding standard for new welding technology, further research is required in the field of fatigue and fracture mechanics including FEM and multi-scale modeling.

    Fulltekst (pdf)
    fulltext
  • 97.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Kaplan, Alexander
    Geometrical aspects of the fatigue behaviour of laser hybrid fillet welds2009Inngår i: Proceedings of the Fatigue Design Conference, Cetim , 2009Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    FULLTEXT01
  • 98.
    Alam, Md. Minhaj
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Barsoum, Zuheir
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Kaplan, Alexander
    Häggblad, Hans-Åke
    The effects of surface topography and lack of fusion on the fatigue strength of laser hybrid welds2009Inngår i: Congress proceedings: ICALEO, 28th International Congress on Applications of Lasers & Electro-Optics : November 2 - 5, 2009 - Orlando, FL : Laser Materials Processing Conference, Laser Microprocessing Conference, Nanomanufacturing Conference, poster presentation, gallery, Orlando, Fla: Laser institute of America , 2009, s. 38-46Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The geometrical aspects of laser hybrid welding before, during and after the process differ from autonomous laser welding and from arc welding. When studying the fatigue behaviour of laser hybrid welded fillet joints we identified that the microgeometry, i.e. the surface ripples can be more critical than the macrogeometry of the weld surface and even than lack of fusion (LOF), which frequently was detected. The plastic replica method was applied to measure the toe radii at the weld edges while the topography was identified by interferometric profilometry. From metallurgical analysis of the joint interface the tendency to LOF can be explained. Stress analysis was carried out by FEA for the complex joint geometry and bending load situation, showing maximum stress on the weld toes, even when including LOF. It was shown that the position and value of the maximum stress depends on a non-trivial combination of the weld geometry, including possible LOF, and the surface topography. Thus it can be explained that at compressive stress conditions LOF does not contribute significantly to the fatigue strength of laser hybrid welds while the surface topography does. Recommendations for defining and in turn avoiding critical geometrical aspects during the welding process are discussed.

    Fulltekst (pdf)
    FULLTEXT01
  • 99. Alam, Minhaj M
    et al.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Jonsén, Pär
    Häggblad, Hans Åke
    Kaplan, Alexander
    Geometrical Aspects of The Fatigue Behaviour of Laser Hybrid Fillet Welds2009Inngår i: Proceedings of the Fatigue Design Conference, 2009Konferansepaper (Fagfellevurdert)
  • 100.
    Alaniz, Monica
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Belyayev, Serhiy
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Bergman, David
    Casselbrant, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Honeth, Mark
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Huang, Jiangwei
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Laukkanen, Mikko
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Michelsen, Jacob
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Pronenko, Vira
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Paulson, Malin
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Schlick, Georg
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Tibert, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Valle, Mario
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    The SQUID sounding rocket experiment2011Inngår i: Proceedings of the 20th ESA Symposium on European Rocket and Balloon Programmes and Related Research, European Space Agency, 2011, s. 159-166Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The objective of the SQUID project is to develop and in flight verify a miniature version of a wire boom deployment mechanism to be used for electric field measurements in the ionosphere. In February 2011 a small ejectable payload, built by a team of students from The Royal Institute of Technology (KTH), was launched from Esrange on-board the REXUS-10 sounding rocket. The payload separated from the rocket, deployed and retracted the wire booms, landed with a parachute and was subsequently recovered. Here the design of the experiment and post fight analysis are presented.

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