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  • 201.
    Blau, Lukas
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Towards sustainable shipping: Recommendations for the telescopic mast design of a sailing cargo vessel2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A comparative study is carried out to investigate the most promising route towardsthe lightweight construction of a retractable mast for a sailing cargo vessel.Four design families are developed and compared. The primary criteria forjudgment are the structural mass, strength, and stiffness in relation to a providedbenchmark design. Additional evaluation criteria are the capital costsfor raw materials and manufacturing.The design space includes isotropic materials as well as fiber-reinforced polymer(FRP) solutions and is navigated by employing analytical evaluation methodssupported by finite element analysis (FEA). Restrictions to the designspace are given by a general arrangement of the benchmark design. This includesthe limitation to the ULS loads and the overall mast geometry.A review of relevant Det Norske Veritas (DNV) rules for classification is performedand the guidelines for wind turbine blades and wind-powered units(WPU) are judged most suitable to the design challenge. Relevant design principlesare implemented in the structural analysis.It is concluded that pure metal constructions imply an unreasonably large weightpenalty. Local buckling is found to disqualify FRP single-skin solutions as successfulcandidates. Secondary to that, strength concerns are the major driversfor the structural mass.The report presents two designs that are judged fit for the purpose, one is ahybrid truss structure from high strength low alloy steel (HSLA steel) and carbonfiber-reinforced polymer (CFRP). The second design is a sandwich constructionwith CFRP face sheets, a PVC foam core, and additional stiffeningmembers in steel.

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  • 202.
    Blomqvist, Fredrik
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    FEM (Finite Element Method) Optimization of Load Bearing Nodular Cast Iron Component in Truck Chassis: Topology Optimization with Reaction Force Constraints on Simplified Bolt Models2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the automotive industry, there is great competition as the quality of vehicles constantly improves while at the same time fulfilling the emission and sustainability requirements. In the truck industry, Scania is a market leader who provides durability, drivability, comfort and low fuel consumption. For some trucks used in South Latin America, they failed because of fracture at one side of the truck’s frames. This was due to excessive stresses that arose within the frame because of extreme loads in the vicinity of the air spring bracket. The investigation of this thesis is whether redesign of this component would decrease the stress levels within the frame. The approach to redesign the component was solely by the use of Finite Element Analysis (FEA) and topology optimization. The optimization was formulated as minimize the compliance subject to constrained volume but also constrained reaction force at bolts that experienced higher loads. Additionally to the formulation, manufacturing constraints were applied such as casting, minimum member size and symmetry. Further, the approach was to setup a simplified Finite Element (FE)-model of the chassis including the air spring bracket to which topology optimization was employed. Based on the results of the optimization, realisation of the topologies were produced and evaluated to what extent they affected the stresses within the frame. From these results a relative change of a maximum stress-measure was obtained between -7.1 % to 2.7 % based on constraining either two, four or five bolts. Regarding the mass, a relative change in the range of -11.3 % to -5.7 % corresponding to a reduction of 3.2 kg and 1.6 kg respectively, was obtained. Conclusively, performing topology optimization such as minimize compliance with bolts’ reaction forces constrained may result in reduced stress levels in adjacent components. It would be interesting to see if a further decrease in stress levels could be obtained using other topology optimization setups or other optimization methods. Further if the interpreted designs candidates to be implemented in production, some validation of these first needs to be considered such as whether the manufacturing costs are compensated by the reduced mass and stress levels. Additionally some validation of the strength should be performed for the realised geometries.

  • 203.
    Blomström, Johan
    et al.
    Dept. of Maintenance, Analytical Services, Ringhals AB, SE-43285 Väröbacka, Sweden.
    Roudén, Jenny
    Dept. of Maintenance, Analytical Services, Ringhals AB, SE-43285 Väröbacka, Sweden.
    Efsing, Pål
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. Dept. of Maintenance, Analytical Services, Ringhals AB, SE-43285 Väröbacka, Sweden.
    Experience with Embrittlement Trend Curves in Swedish PWRs2023In: Radiation Embrittlement Trend Curves and Equations and Their Use for RPV Integrity Evaluations, ASTM International , 2023, Vol. STP 1647, p. 382-397Conference paper (Refereed)
    Abstract [en]

    There are currently two operating pressurized water reactors in Sweden, currently planning for 60 years of operation until 2041 and 2043. The acceptance of operation time is continuously evaluated at least every 10 years in a comprehensive mandatory periodic safety review that requires the utilities to continuously update and implement the developments in science and technology. The RPV welds have been shown by the applied surveillance program to be the limiting material for operation. The welds are manufactured according to the same specifications with a chemical composition with high nickel and manganese content. The welds show a large increase in transition temperature shift with an almost linear relationship to neutron fluence that is underestimated by most of the established embrittlement trend curves (ETCs). The current regulations from the Swedish Radiation Safety Authority are in general not detailed and prescriptive and hence permit plant-specific ETCs if they are sufficiently justified and based on proper material and plant conditions. This paper describes the bases for the ETCs and an ongoing work to revise the ETCs to enable the use of a material-specific master curve for crack initiation, KIC, with compliance with the reactor vessel integrity analyses.

  • 204.
    Bocquier, Antoine
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Space Technology.
    An Integrated Toolchain for Designing Commercial Lunar Rovers2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As commercial lunar rovers are being developed and planned to fly from next year, in the context of a global momentum for lunar exploration, the mindset of system design is shifting to a product-oriented approach (as opposed to traditionally single mission-designed system). This deeply affects the system engineering discipline, which is also evolving through the development of more integrated, model-centric methodologies such as Model-Based System Engineering (MBSE).

    This Master Thesis combines 2 research questions:- How to adapt systems engineering processes and tools to a commercially-driven / product-oriented approach?- How to leverage new developments (e.g MBSE) within the system engineering discipline to support the rover design transition to a product-oriented philosophy?

    These research questions are investigated through this Master Thesis, carried out as a 6-month internship at ispace Europe (Luxembourg), a global lunar exploration company developing landers, rovers and data tools. The Master Thesis is applied to ispace’s Exploration Rover currently under development within the Polar Ice Explorer (PIE) mission with support from the Luxembourg Government.The goal of this Master Thesis is to develop an integrated toolchain (set of tools) for efficiently designing rover products (Exploration Rover), including platform configuration for a given mission concept and set of payloads, system sizing and mission analysis.

    The chosen methodology can be summarized as:1. Adapting PIE models to a generic, parametric/configurable toolset that can be used for mission/platform analysis and optimization2. Defining the Exploration Rover toolchain requirements & architecture, and selecting its environment (trade-off including MBSE solutions)3. Building the Exploration Rover toolchain, integrating models inside the defined architecture

    By maturing existing models, leveraging new software functionalities (in this case Valispace) and MBSE practises along with adding new parametric models for quick feasibility studies and integrating all models together, it was successfully shown that this integrated toolchain can support rover products definition, performing frequent and insightful design iterations, analysis and trade-offs. Not only does the toolchain comply with the product-approach but also successfully supports the Polar Ice Explorer (PIE) mission, by directly contributing to the system engineering activities and models of the Phase B.

    Therefore, the Master Thesis proved to be a successful demonstrator for developing more product-driven rovers, by leveraging new practices within the system engineering discipline.

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  • 205.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Shah, Shail
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    An investigation of perforate reactance under high level and grazing flow excitation2023In: Proceedings of the 29th International Congress on Sound and Vibration, ICSV 2023, Society of Acoustics , 2023Conference paper (Refereed)
    Abstract [en]

    Perforates are frequently used as part of sound reducing treatment in for instance aircraft engine and IC engine applications. In these applications they are exposed to fluid flow and high-level acoustic excitation, and this influences the acoustic properties of the perforate, as is well known from many published papers. The acoustic properties are usually described using a transfer impedance. In a previous part of this study the effect on the real part (resistance) of the transfer impedance was studied using both a conventional impedance tube (two-port) setup and an innovative three-port setup. The three-port configuration made it possible to study both the effect of grazing flow and high-level excitation effects separately as well as jointly. The present paper is a follow-up study where the imaginary part (reactance) of the transfer impedance is the focus. Comparisons are made with results from previously published papers and empirical models.

  • 206.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Kabral, Raimo
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    The effect of high temperatures and grazing flow on the acoustic properties of liners2020In: Euronoise 2015, DC/ConfOrg , 2020, p. 2261-2266Conference paper (Refereed)
    Abstract [en]

    Acoustic liners are used to reduce fan noise in aircraft engine intakes but also in hot stream parts of the engine. To gain confidence in liner impedance models which are used for design it is important to make experimental tests under realistic conditions as possible. This paper present results of hot stream impedance eduction tests for single degree of freedom Helmholtz resonator liners with different configurations. These types of liners consist of a perforate top sheet backed by a honeycomb cavity to give a locally reacting wall treatment which can be characterized by an acoustic impedance. In the present case a number of different perforate sheet geometries were tested under varying grazing flow and temperature conditions. In some cases the liner test samples also included a thin layer of metallic foam. These types of liners are used for aircraft engine applications but are also of interest for IC-engine applications. It could be argued that the main effect of high temperatures is a change of medium properties such as: density, viscosity and speed of sound. If this is true the high temperature impedance could be predicted by scaling from the result at cold conditions. This is investigated in the paper by comparing measured results from liner impedance models available in the literature.

  • 207.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Sack, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Jacob, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Impedance measurements for 3-d printed liners2019In: 25th AIAA/CEAS Aeroacoustics Conference, 2019, [publishername] American Institute of Aeronautics and Astronautics Inc, AIAA , 2019Conference paper (Refereed)
    Abstract [en]

    The last twenty years have seen a great development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contributes to a continuing effort to gain confidence in the results obtained, specifically in the dependence of the results on fabrication, data acquisition and analysis. It is part of the IFAR Acoustic Liner Challenge were data from multiple test rigs with similar liner configurations fabricated using 3D printing are gathered and compared. Experimental results are reported for two liner configurations obtained in KTH’s advanced impedance eduction flow rig.

  • 208.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Sayyad Khodashenas, Niloofar
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Experimental study of nonlinear acoustic properties of perforates using band-limited random excitation information2018In: 25th International Congress on Sound and Vibration 2018, ICSV 2018: Hiroshima Calling, International Institute of Acoustics and Vibration, IIAV , 2018, Vol. 3, p. 1818-1825Conference paper (Refereed)
    Abstract [en]

    Perforates are used for noise control in automotive mufflers and aircraft engine liners as well as for other vehicles and machines. Their acoustic properties and noise reduction are known to depend on the mean flow field and other parameters such as temperature and acoustic excitation level. It is therefore of interest to understand how the properties of perforates varies with the level of acoustic excitation. This paper gives an overview of high level nonlinear effects on the acoustic properties of perforates. It includes semi-empirical models as well as experimental studies. Methods for studying nonlinear effects and harmonic interaction effects, for perforates, using single tone excitation and Poly-harmonic distortion models or nonlinear scattering matrices are discussed. These techniques typically require measurements with a number of different acoustic loads. It would be more attractive to directly be able to extract the nonlinear acoustic properties from a more limited set of experiments using either random or periodic excitation. Multi input - single output techniques for nonlinear system identification using broadband random excitation has been tried with limited success. One reason is the mixing of the sound pressure signal incident from the acoustic source with the sound pressure transferred to higher frequencies by nonlinear effects at the perforate sample. The present paper includes an attempt to combine band-limited broadband excitation with Poly-harmonic distortion models or nonlinear scattering matrices describing the nonlinear transfer of energy to higher frequencies.

  • 209.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Sayyad Khodashenas, Niloofar
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Boij, Susann
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    TRANSFER PROPERTIES OF PERFORATES UNDER HIGH LEVEL ACOUSTIC EXCITATION2022In: Proceedings of the 28th International Congress on Sound and Vibration, ICSV 2022, Society of Acoustics , 2022Conference paper (Refereed)
    Abstract [en]

    Perforates are frequently used as part of sound reducing treatment in for instance aircraft engine and IC engine applications. In these applications they are exposed to fluid flow and high level acoustic excitation. It is known since a long time that their acoustic properties become nonlinear when the acoustic excitation level is sufficiently high. To determine the no flow acoustic properties tests are sometimes made using plane wave impedance tubes where the perforate is mounted either at an open end or in the middle of the duct with microphones on both sides. The purpose is to determine the normalized transfer impedance defined as the acoustic pressure difference over the sample divided by the particle velocity through the perforate. The transfer impedance can for the case that the sample is mounted at the end of the tube be estimated as the difference between the impedance at the sample cross section with or without the perforate in place. When the sample is sitting in the middle of the impedance tube the acoustic pressure and particle velocity can be measured at both sides of the sample which can then be used to estimate the transfer impedance. It can be shown that a transfer impedance is the only quantity needed to fully describe the plane wave transmission properties of the sample only under the assumption that the particle velocity is identically the same on both sides of the sample. Otherwise, a more complete scattering matrix or transfer matrix need to be used. The assumption of identical particle velocities on both sides of the sample is very reasonable, under linear acoustic conditions, considering that the thickness and hole diameter of the perforate is very small compared to the wavelength. This paper experimentally investigates if the assumption of equal particle velocities over the sample is correct under high level acoustic excitation and discusses the potential consequences for description of acoustic transmission properties.

  • 210.
    Boestad, Albin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Investigation of the Applicability of Fracture Mechanics for Tissue Paper2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Tissue paper is a common type of paper material and is used in a variety of products. For tissue paper, several properties are of interest, such as absorbency, softness, bulk and mechanical properties. Embossing is an operation used to apply a pattern on tissue paper. It is used to improve several properties, but is known to reduce mechanical properties. Currently, no models can predict the loss of strength due to embossing. In this report base tissue paper is embossed with two different embossing patterns and tensile tests are conducted with and without edge notches. The edge notch length was varied between 0 mm to 12 mm. From the experiment, a modified Linear Elastic Fracture Mechanics model was applied on both base tissue paper and embossed tissue paper tensile test results. The experimental procedure is described. In total, four different paper qualities were tested. Two that are designed for toilet paper and two that are designed for kitchen paper. The tissue sheets were embossed using 3D-printed plates and conducted in a laboratory environment. Tensile tests with edge-notch specimens were performed. The notch lengths tested were between 0 mm and 12 mm long. It was investigated if any trends of the parameters in the model could be noticed due to embossing. The model worked well for all base tissue qualities. The embossing reduces the material's tensile strength compared to the base material. With increasing embossing load, longer notches are needed to drop the tensile strength of the specimen. Some general trends were noted. However, the impact of the embossing was different for different paper qualities and the embossing pattern used. The most significant difference between plates was noted in specimens with high embossing load. With increasing embossing load, the edge-notch must also be longer to reduce tensile strength. The model parameters changed more for machine direction (MD) specimens than crossmachine direction (CD) specimens.

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  • 211. Boettcher, M. A.
    et al.
    Gaisser, S.
    Noeldeke, C.
    Henneberg, J.
    Jacob, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Klinkner, S.
    Taubenreuther, P. R.
    In-orbit measurement of S-band radio noise during the Flying Laptop satellite mission2021In: Proceedings of the International Astronautical Congress, IAC, International Astronautical Federation, IAF , 2021Conference paper (Refereed)
    Abstract [en]

    The "Flying Laptop"small satellite was developed as a technology demonstration platform and is operated by the University of Stuttgart's Institute of Space Systems (Germany) and was launched on July 14th 2017 into a 600 km Sun synchronous Low Earth Orbit (LEO). For data exchange with ground stations, the satellite is equipped with the S-band transceivers of type SSTRX-1100. The receiver operates at a centre frequency of 2083.5 MHz and additionally provides various information about the received signals. A power indicator value is used to determine the incoming radio power on this frequency. Whereas this information normally is disregarded if the satellite is not communicating with a ground station, for this analysis, the power indication value has been used to derive the background noise temperature within 100 kHz bandwidth. For the period between February 2018 and January 2021, the incoming signal power was recorded every 20 s and later extended by the corresponding satellite position, based on on-board GPS measurements. Although the exact direction of the incoming signal cannot be determined due to the quasiomnidirectional antenna design, a statistical analysis has been performed for the large amount of measurement points for a 1° Longitude/Latitude grid. Finally, the background noise temperature is derived. Several maps show interferences and background noise, and variations over time. The presented results provide an important insight on the radio environment for a commonly used frequency for Earth-observation LEO satellites.

  • 212.
    Boivie, Tove
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Modelling of a Glued Bolt Joint in Finite Element2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report presents a master thesis project at KTH at the school of Engineering Science. The project is done in collaboration with ABB Robotics, a company who develops industrial robots.

    A robot consists of several parts and the last structural part is the wrist. During the project, a glued bolt joint, commonly named hybrid joint, in the wrist was investigated. The glued bolt joint mounts a protecting cover to the wrist and is a vital component to prevent leakage and provide structural strength to the wrist. The project's purpose was to create a time efficient and accurate methodology how to model the glue bolt joint in Finite element.

    Four different modelling methods of the adhesive layer were developed. One method includes friction contact, one method includes glue spring contact, one method includes solid element, and the last method includes cohesive elements. The developed methods were based on the pre-study and a previous master thesis project collaborated with the company. The modelling methods were verified against lab measurement where stresses in the wrist and bolt stresses were measured. Furthermore, to include the bolt preload in the models, a modelling and post-processing method was developed.

    The results showed similar simulated and measured von Mises stress in the structure of the wrist. However, the simulated bolt stress was significantly higher compared to the measured bolt stress for all methods. The main conclusion with the project is that none of the methods is accurate enough and further verification of the methods needs to be done before an accurate method can be determined.

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  • 213.
    Bolin, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Conrady, K.
    Ilkka, Karasalo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Marcus Wallenberg Laboratory MWL.
    Sjöblom, A.
    An investigation of the influence of the refractive shadow zone on wind turbine noise2020In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 148, no 2, p. EL166-EL171Article in journal (Refereed)
    Abstract [en]

    This article aims to investigate if the proportion of the rotor area of a wind turbine that is in the refractive shadow zone according to a ray tracing algorithm coupled to meteorological forecast data is correlated to sound levels and amplitude modulation. The acoustic station is situated 950 m from a wind farm in Northern Sweden and the measurement period is seven months. On average, 1.9 dBA lower sound levels are measured when the part of the rotor disk of the closest turbine is in the refractive shadow zone. A higher probability of amplitude modulations are observed when around half of the turbine rotor is within the refractive shadow zone compared to conditions with no shadow zone present.

  • 214.
    Bolin, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Jacob, Stefan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Improved methods for source characterization on trains2022In: Internoise 2022: 51st International Congress and Exposition on Noise Control Engineering, The Institute of Noise Control Engineering of the USA, Inc. , 2022Conference paper (Refereed)
    Abstract [en]

    One problem for railway noise predictions is to characterize noise from various auxiliary equipment, e.g., fans, compressors, transformers. The noise from such sources can be a dominating contribution under low-speed operation or stand still. To better handle this problem the EU-project TRANSIT investigates improved methods for acoustic source characterization. As a starting point it is assumed that an acoustic source is enclosed by a control surface. The surface is sub-divided into smaller areas and each area is assumed to act as an acoustic one-port coupled to all the other areas. The properties of each area can then be described by its volume flow and internal impedance. The resulting acoustic pressure at a receiving point, can finally be expressed as a product of the source volume flows and a matrix representing the acoustic installation effects (“source+radiation impedances”). To simplify the method one can assume uncorrelated sources and use an ISO procedure for sound power to determine the volume flows. The acoustic installation effects can be obtained using a monopole point source to measure or calculate the pressure at selected receiving positions.

  • 215.
    Bonnier, Valentin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Flight Dynamics.
    Modelling of advanced components for interceptor simulation2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Since the end of the last century, numerical simulations have been widely developed in all fields because they make it possible to predict the behavior of dynamic systems. In the field of missile systems, they are used to carry out preliminary studies, performance analyzes, trajectory simulation, etc. It is then possible to determine the conditions at each point of the flight envelope without having to conduct costly tests. In this master thesis, a 6 degrees-of-freedom simulation tool is developed to model a supersonic interceptor taking into account the effects of a rotating earth. Models for propulsion, aerodynamics, guidance-control-navigation systems are described. A comparison between a control by aerodynamic surfaces and by vector thrust during a vertical launch is made.

  • 216.
    Borg, August
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Owen, Michael
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Experimental and CFD Study of Heat Pickup in Cooling System Hoses2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis investigates a process known as heat pickup which occurs in vehicle cooling system hoses. Heat pickup is an unwanted side effect of temperature differences in a car underhood compartment, whereby excess heat is tranferred into the coolant running through the cooling system hoses, affecting its operating temperature. In addition, the effectiveness of insulation in protecting against this phenomenon is investigated. This is studied experimentally by measuring the temperature change between the inlet and outlet, of coolant flowing through a hose which is subjected to a variety of air temperatures and air flow velocities. In addition to calculating the amount of heat pickup in the coolant, the overall heat transfer coefficient as a function of air temperature and air flow velocity could be quantified.

    The experiment was conducted by building a miniaturies wind tunnel and placing this in a climate chamber capable of temperatures up to 140°C and circulating the coolant at 20°C and 0.1 l/s. The wind tunnel could reach air velocities up to 6 m/s and therefore, the phenomena was nvestigated at 70, 90 and 120°C  at air velocities between 2 and 6 m/s. In addition, the effect of coolant mass flow rate was investigated in order to see if there was a change in heat pickup due to any transition between the turbulent and laminar regime, since all flow rates were in the vicinity of the critical Reynolds number of 2300 for an internal pipe flow. In addition, a CFD model was developed in Star CCM+ to model the experiment and gain more insight into the underling physics of the problem.

    The results show that the air velocity and temperature have significant effects on the heat picked up by the coolant, while only air velocity has large effects on the overall heat transfer coefficient. The insulation used in the experiments shows a 35% reduction in the heat picked up by the coolant and a 50% reduction in the overall heat transfer coefficient. The CFD model showed comparable results to the experiment but underestimated the heat pickup by approcimately 10%. These results can be used to improve the accuracy of the 1D CFD modelling of the whole cooling system and in turn, help improve the system's efficiency and reduce energy consumption.

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  • 217.
    Borne, Clément
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Space Technology.
    Analysis and comparison of trajectometry methods2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In a space launch system like Ariane 5 (and soon Ariane 6), many parts are moving relative to each other during the journey from the ground to the orbit. One can mention the boosters which separate from the main stage after burning for 130 seconds, or the rocket’s fairing which protects the payload during the ascend phase, but is the jettisoned once sufficient altitude has been reached. The trajectory of these moving parts has to be controlled: it is highly unwanted for the booster to hit the main stage after separating since it could drift the launcher off its course leading to a slight fuel overconsumption for correction in the best case, if not the rocket and its payload destruction in the worst. That is why all moving parts are tested on the ground, and their trajectories analysed. But how is it done? How can one capture the path of a part in space? This internship has been performed at one of the test departments of ArianeGroup, at Les Mureaux. Its goal was to understand methods used for trajectography and quantify the uncertainties through a reference test, as well as writing a guide, stating which method to use for a given test in order to obtain the best accuracy. Through this paper, different existing methods for trajectography will first be listed, before reducing the field of view to optical camera measurement, and especially monovision. Then a reference test will be conducted to assess each technique’s errors. Using the results, a model for the uncertainties will be developed, giving the accuracy of each method.

  • 218.
    Borrelli, Giuseppe
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Faculty of Aerospace Engineering, Alma Mater Studiorum – University of Bologna, Forlì, Italy.
    Guastoni, Luca
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Eivazi, Hamidreza
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Predicting the temporal dynamics of turbulent channels through deep learning2022In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 96, article id 109010Article in journal (Refereed)
    Abstract [en]

    The success of recurrent neural networks (RNNs) has been demonstrated in many applications related to turbulence, including flow control, optimization, turbulent features reproduction as well as turbulence prediction and modeling. With this study we aim to assess the capability of these networks to reproduce the temporal evolution of a minimal turbulent channel flow. We first obtain a data-driven model based on a modal decom-position in the Fourier domain (which we denote as FFT-POD) of the time series sampled from the flow. This particular case of turbulent flow allows us to accurately simulate the most relevant coherent structures close to the wall. Long-short-term-memory (LSTM) networks and a Koopman-based framework (KNF) are trained to predict the temporal dynamics of the minimal-channel-flow modes. Tests with different configurations highlight the limits of the KNF method compared to the LSTM, given the complexity of the flow under study. Long-term prediction for LSTM show excellent agreement from the statistical point of view, with errors below 2% for the best models with respect to the reference. Furthermore, the analysis of the chaotic behaviour through the use of the Lyapunov exponents and of the dynamic behaviour through Poincare' maps emphasizes the ability of the LSTM to reproduce the temporal dynamics of turbulence. Alternative reduced-order models (ROMs), based on the identification of different turbulent structures, are explored and they continue to show a good potential in predicting the temporal dynamics of the minimal channel.

  • 219.
    Borthakur, Manash Pratim
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Nath, Binita
    CNR, Inst Complex Syst, I-00185 Rome, Italy..
    Biswas, Gautam
    Indian Inst Technol Kanpur, Dept Mech Engn, Kanpur 208016, Uttar Pradesh, India..
    Dynamics of a compound droplet under the combined influence of electric field and shear flow2021In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 6, no 2, article id 023603Article in journal (Refereed)
    Abstract [en]

    We present a numerical investigation on the dynamics of a compound droplet under the combined influence of an applied electric field and shear flow. The paper is carried out by solving the electro-hydrodynamic equations in a two-dimensional framework, and the interface is captured using a volume-of-fluid approach. Both perfect dielectric as well as leaky dielectric fluids are considered. For the case of dielectric fluids, the deformation of both the inner and outer interfaces can be modulated by either variation of the permittivity contrast between the fluids or the applied field strength. The nature of the polarization forces acting at both the interfaces can be either compressive or tensile depending on the magnitude of the permittivity ratio. The investigations for leaky dielectric fluids reveal that the ratio of electrical permittivity and conductivity between the two phases plays a critical role in deciding the magnitude of deformation and orientation of the compound droplet. The variation of charge accumulated at the interfaces modifies the behavior of the Coulombic forces thereby fundamentally altering the droplet deformation and orientation characteristics. Furthermore, it is demonstrated that the electric field can be suitably applied to engender breakup of the compound droplets.

  • 220.
    Boubaker, Mouadh
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Numerical simulations using Lattice Boltzmann Method2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The lattice Boltzmann method (LBM) is widely studied andused in the last years to replace the conventional numerical solvers forthe Navier-Stokes equations. In this work, a general introduction tofluid dynamics equations and the changes when the flow is a reactivemulti-species one will be given first. The lattice Boltzmann method andalgorithm will then be explained in details with the kinetic theorybehind, tested and validated for canonical test cases of doubly shearlayer flow in reactive and non-reactive flows. Finally the method willbe applied to simulate a non-reacting propane jet and the results willbe validated using experimental data.

    The objectives of this thesis are mainly: first a better understandingof the LBM, the combustion reactions, the jets and how they work, secondthe use of this method to produce a simple code that works for a basictest case, third validate this code with more developed methods, andfinally apply this method to simulate a more complex configuration whichis the non-reacting propane jet flame into co-flowing air

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  • 221.
    Boucher, Margaux
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lättkonstruktioner, marina system, flyg- och rymdteknik, rörelsemekanik.
    Estimating CO2 emissions with satellite and traffic data: a Swedish practical case study2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The large carbon footprint of industries is one of the main issues raised when talking about climate change. Active carbon monitoring methods need to be implemented to give transparency to the industry market and to spread awareness and information. This thesis investigates multiple CO2 emissions monitoring via satellite monitoring for four different industries in the EU. The pulp and paper industry was monitored in Sweden through smoke detection coming from the chimneys of factories. The CO2 aggregated emissions of 14 Swedish factories were calculated with a mean error of 12%. The metal ore roasting, and sintering industry were successfully monitored as well through smoke detection. In Sweden with an error 4.6%, and in the EU with an error 9.5 %. The production of lime and the calcination of dolomite were unsuccessfully monitored due to no suitable method found. Finally, coke industry emissions were monitored through burned gas monitoring. The CO2 emissions were correlated to the real emissions with a mean correlation coefficient of 0.64. This study took part in a public information campaign lead by a Swedish start-up, and some results were displayed in Stockholm, Sweden.

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  • 222.
    Bouchouireb, Hamza
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Advancing the life cycle energy optimisation methodology2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Life Cycle Energy Optimisation (LCEO) methodology aims at finding a design solution that uses a minimum amount of cumulative energy demand over the different phases of the vehicle's life cycle, while complying with a set of functional constraints. This effectively balances trade-offs, and therewith avoids sub-optimal shifting between the energy demand for the cradle-to-production of materials, operation of the vehicle, and end-of-life phases. This work further develops the LCEO methodology and expands its scope through three main methodological contributions which, for illustrative purposes, were applied to a vehicle sub-system design case study.

    An End-Of-Life (EOL) model, based on the substitution with a correction factor method, is included to estimate the energy credits and burdens that originate from EOL vehicle processing. Multiple recycling scenarios with different levels of assumed induced recyclate material property degradation were built, and their impact on the LCEO methodology's outcomes was compared to that of scenarios based on landfilling and incineration with energy recovery. The results show that the inclusion of EOL modelling in the LCEO methodology can alter material use patterns and significantly effect the life cycle energy of the optimal designs.

    Furthermore, the previous model is expanded to enable holistic vehicle product system design with the LCEO methodology. The constrained optimisation of a vehicle sub-system, and the design of a subset of the processes which are applied to it during its life cycle, are simultaneously optimised for a minimal product system life cycle energy. In particular, a subset of the EOL processes' parameters are considered as continuous design variables with associated barrier functions that control their feasibility. The results show that the LCEO methodology can be used to find an optimal design along with its associated ideal synthetic EOL scenario. Moreover, the ability of the method to identify the underlying mechanisms enabling the optimal solution's trade-offs is further demonstrated.

    Finally, the functional scope of the methodology is expanded through the inclusion of shape-related variables and aerodynamic drag estimations. Here, vehicle curvature is taken into account in the LCEO methodology through its impact on the aerodynamic drag and therewith its related operational energy demand. In turn, aerodynamic drag is considered through the estimation of the drag coefficient of a vehicle body shape using computational fluid dynamics simulations. The aforementioned coefficient is further used to estimate the energy required by the vehicle to overcome aerodynamic drag. The results demonstrate the ability of the LCEO methodology to capitalise on the underlying functional alignment of the structural and aerodynamic requirements, as well as the need for an allocation strategy for the aerodynamic drag energy within the context of vehicle sub-system redesign.

    Overall, these methodological developments contributed to the exploration of the ability of the LCEO methodology to handle life cycle and functional trade-offs to achieve life cycle energy optimal vehicle designs.

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  • 223.
    Bouchouireb, Hamza
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Life Cycle Energy Optimisation: A multidisciplinary engineering design optimisation framework for sustainable vehicle development2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis explores how the systemic-level environmental footprint of light-duty vehicles could be reduced through integrative design using the Life Cycle Energy Optimisation (LCEO) methodology. This methodology aims at finding a design solution that uses a minimum amount of cumulative energy demand over the different phases of the vehicle's life cycle; while complying with a set of functional constraints, thereby avoiding any sub-optimal energy demand shifts between the vehicle's different life cycle phases. This thesis further develops the LCEO methodology and expands its scope through four main methodological contributions. This work also contributes in establishing the methodology as a standalone design approach and provides guidelines for its most effective use.

    Initially, an End-of-Life (EOL) model, based on the substitution with a correction factor method, is included to estimate the energy credits and burdens that originate from EOL vehicle processing. Multiple recycling scenarios with varying levels of induced recyclate material property degradation were built, and their associated resulting optimal vehicle subsystem designs were compared to those associated with landfilling and incineration with energy recovery scenarios. The results show how the structural material use patterns, as well as the very mechanisms enabling the embodiment of the Life Cycle Energy (LCE) optimal designs, are impacted by taking into consideration the effect of a vehicle's EOL phase. In particular, the material intensity-space allocation trade-off was identified as a key factor in the realisation of the LCE optimal designs.

    This coupling existing between optimal use of material and space allocation was further explored by functionally expanding the LCEO methodology's scope to handle aerodynamic functional requirements. This involved the definition of a novel allocation strategy for the energy necessary to overcome aerodynamic drag, as well as the development of a parametrised vehicle body model that ensures that the LCE knock-on effects of aerodynamically motivated design decisions are fully accounted for at the targeted subsystem level.

    The expanded methodology was subsequently applied to perform the aero-structural life cycle-driven design optimisation of a vehicle subsystem, with the impact of the constitutive material's circularity potential being included through the previously developed EOL model and scenarios. The results demonstrate the significant extent of the coupling existing between a vehicle's fundamental aerodynamic shape, and a vehicle's structural material composition, including its EOL characteristics, within the LCEO context.

    Beyond the vehicle level implications, the LCEO methodology's position within the broader vehicle-design methodology context was further characterised by comparing its outcomes to those of the purely lightweight and purely aerodynamic approaches. It was found that the LCE optimal designs were distinctly clustered from their mono-disciplinary counterparts. They offered up to 20% energy savings over the lightweight alternatives by being, on average, larger, heavier and more aerodynamics designs; while also being shorter and lighter than the optimal aerodynamic configurations.

    Subsequently, a mixed integer nonlinear programming formulation of this expanded LCEO methodology was developed to include the effects of battery energy storage systems on the LCE optimal vehicle designs. In particular, the vehicle's battery size and number of such batteries needed over its life cycle were introduced as variables subject to a range and a cycle life constraint. The former is derived from the battery-capacity-to-structural-mass ratio of recent production vehicles, while the second ensures that the batteries' cycle lives are sufficient for the entirety of the vehicle's use phase. Additionally, three battery chemistries with varying characteristics were included: lithium nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP) and lithium cobalt oxide (LCO); along with an EOL recycling scenario. The results of the coupled aero-structural-battery energy storage LCE-driven design optimisations demonstrate that battery chemistry and recycling potential have a significant impact on the system's design in terms of overall LCE footprint, battery size and number, as well as aerodynamic shape. More specifically, a change in battery composition was found to lead to up to 12.5% variation in drag coefficient, while battery recycling can on average reduce a vehicle's associated LCE by 32%.

    Finally, elements of robust design and uncertainty quantification were included into the LCEO methodology, in order to evaluate the impact of uncertainty on the resulting LCE optimal designs. Specifically, uncertainty was introduced through the assumption that the material properties of a subset of the optimisation's candidate materials are described by statistical distributions, as opposed to a priori fixed values, thereby changing the nature of the optimisation problem from deterministic to stochastic. This change is handled through a multilevel representation hierarchy for the targeted subsystem's model, and using the Multilevel Monte Carlo (MLMC) approach in the optimisation process to evaluate the expected compliance of a given design with the transport-related functional requirements. the results demonstrate how the robust design configurations both constitute a significant departure from their deterministic counterparts and depend on the EOL scenario considered, while only incurring a marginal LCE premium. Moreover, this work also further illustrated the performance increase associated with the use of the MLMC estimator in lieu of the classical Monte Carlo one within an optimisation under uncertainty framework.

    Overall, the work presented in this doctoral thesis has contributed to the development of the state-of-the-art of the LCEO methodology to enable the early-stage conceptual design of more sustainable vehicle configurations, and demonstrated how the methodology is at its most effective when leveraging its cross-scalar and cross-disciplinary nature to enable integrative functional vehicle design.

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  • 224.
    Bouchouireb, Hamza
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Jank, Merle-Hendrikje
    RWTH Aachen University, Laboratory for Machine Tools and Production Engineering (WZL), Campus-Boulevard 30, D-52074 Aachen, Germany..
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Schöggl, Josef-Peter
    University of Graz, Institute of Systems Sciences Innovation & Sustainability Research, Austria.
    Baumgartner, Rupert J.
    University of Graz, Institute of Systems Sciences Innovation & Sustainability Research, Austria.
    Potting, José
    KTH, School of Architecture and the Built Environment (ABE).
    The inclusion of end-of-life modelling in the life cycle energy optimisation methodology2021In: Journal of Mechanical Design, ISSN 1050-0472, Vol. 143, no 5, article id MD-20-1233Article in journal (Refereed)
    Abstract [en]

    In this work, an End-Of-Life (EOL) model is included in the Life Cycle Energy Optimisation (LCEO) methodology to account for the energy burdens and credits stemming from a vehicle's EOL processing phase and balance them against the vehicle's functional requirements and production and use phase energies. The substitution with a correction factor allocation method is used to model the contribution of recycling to the EOL phase's energy. The methodology is illustrated through the optimisation of the design of a simplified vehicle sub-system. For the latter, multiple recycling scenarios with varying levels of assumed recycling induced material property degradation were built, and their impact on the vehicle sub-system's optimal solutions was compared to that of scenarios based on landfilling and incineration with energy recovery. The results show that the vehicle sub-system's optimal designs are significantly dependent on the EOL scenario considered. In particular, the optimal designs associated with the recycling scenarios are on average substantially heavier, and less life cycle energy demanding, than their landfilling or incineration with energy recovery-related counterparts; thus, demonstrating how the inclusion of EOL modelling in the LCEO methodology can significantly alter material use patterns, thereby effecting the very mechanisms enabling the embodiment of the resulting life cycle energy optimal designs.

  • 225.
    Bouchouireb, Hamza
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    A preliminary investigation of robust design and uncertainty quantification within the life cycle energy optimisation methodology2021In: Resource Efficient Vehicles Conference, rev2021, 2021Conference paper (Other academic)
    Abstract [en]

    The Life Cycle Energy Optimisation (LCEO) methodology aims at finding a design solution that uses a minimum amount of cumulative energy demand over the different phases of the vehicle's life cycle, while complying with a set of functional constraints. This effectively balances trade-offs, and therewith avoids sub-optimal shifting between the energy demand for the cradle- to-production of materials, operation of the vehicle, and end-of-life phases. The present work describes the inclusion of robust design aspects and uncertainty quantification into the LCEO framework. In particular, uncertainty is introduced through the assumption that the material and energy properties of a subset of the optimisation’s candidate materials are described by statistical distributions as opposed to a priori fixed values. Subsequently, the nature of the LCEO-associated optimisation problem is changed from deterministic to stochastic. This change is handled by defining a multilevel representation hierarchy, and using the Multilevel Monte Carlo (MLMC) approach in the optimisation process to evaluate the expected compliance of a given design with the transport-related functional requirements. The extended framework is applied to the robust design optimisation of a subsystem of a vehicle model which is both mechanically and geometrically constrained. The ability of the LCEO methodology to include robust design aspects early during the vehicle design process, while simultaneously handling functional conflicts, to result in a robust life cycle energy optimal design is demonstrated. Furthermore, the performance increase obtained by the use of the MLMC approach instead of the classical Monte Carlo approach within an optimisation under uncertainty framework is illustrated.

  • 226.
    Bouchouireb, Hamza
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Exploring the aero-structural-battery energy storage coupling within the early-stage development of life cycle energy optimal electric vehiclesManuscript (preprint) (Other academic)
    Abstract [en]

    The Life Cycle Energy Optimisation (LCEO) methodology is used to explore the coupling existing between an electric vehicle's aerodynamic shape, structural material composition and design, and the properties of its onboard battery's chemistry in order to enable the development of more sustainable vehicle configurations. To this end, a mixed integer nonlinear programming formulation of the LCEO methodology was developed to include the effects of battery energy storage systems on the Life Cycle Energy (LCE) optimal vehicle designs. In particular, the vehicle's battery size and number of such batteries needed over its life cycle were introduced as variables subject to a range and a battery cycle life constraint. The former is derived from the battery-capacity-to-structural-mass ratio of recent production vehicles, while the latter ensures that the batteries' cycle lives are sufficient for the entirety of the vehicle's use phase. Additionally, three lithium-based battery chemistries with varying properties were included: lithium nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP) and lithium cobalt oxide (LCO); along with a closed-loop end-of-life recycling scenario for the battery materials. The results of the coupled aero-structural-battery energy storage LCE-driven design optimisations demonstrate that battery chemistry and recycling potential have a significant impact on the system's design in terms of overall LCE footprint, battery size and number, as well as aerodynamic shape. More specifically, a change in battery composition was found to lead to up to 12.5% variation in drag coefficient, while battery recycling can on average reduce a vehicle's associated LCE by 32%. Furthermore, battery material recycling was found to decrease the role played by the specific energy and cycle lives of the batteries, and increase that played by their embodied energy. Consequently, the LFP battery chemistry was found to be the best performer from an LCE perspective in the presence of battery material recycling; while the NMC chemistry was found to perform marginally better in the absence of the latter.

  • 227.
    Bouchouireb, Hamza
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    O'Reilly, Ciarán J.
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Göransson, Peter
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Schöggl, Josef-Peter
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Baumgartner, Rupert J.
    Potting, José
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Vehicle aerodynamic shape significantly impacted by vehicle material composition and material circularity potential in life cycle energy optimal vehicle designManuscript (preprint) (Other academic)
    Abstract [en]

    This paper explores how the systemic-level energy consumption of light-duty vehicles could be reduced through integrative design. To this end, the Life Cycle Energy Optimisation (LCEO) methodology is used to achieve the coupled optimal use of materials (including their circularity potential) and vehicle aerodynamic shape to reduce the overall Life Cycle Energy (LCE) footprint of light-duty vehicles, with the results being compared to the lightweight and aerodynamic alternatives. Initially, the methodology is functionally expanded to handle aerodynamic functional requirements through the definition of a novel allocation strategy for the aerodynamic energy, and a parametrised simple vehicle body model that ensures that the LCE knock-on effects of aerodynamically-motivated design decisions are fully accounted for. Subsequently, the methodology is used to perform the first, to the knowledge of the authors, aero-structural LCE-driven design optimisation of a vehicle subsystem, with the impact of the materials’ circularity potential being taken into account through various end-of-life (EOL) processing scenarios, including recycling. The results show that the environmental footprint of light-duty vehicles could significantly be reduced through integrative early-stage design. Specifically, it shows that a life cycle energy optimal vehicle's aerodynamic shape is significantly impacted by the vehicle's material composition and the latter's EOL characteristics — particularly recycling potential. Furthermore, LCE optimal vehicles have been found to be on average longer, heavier and more aerodynamic than their lightweight counterparts, as well as offering up to 20% energy savings per vehicle; while also being shorter and lighter than optimal aerodynamic configurations.

  • 228.
    Bouton, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Lightweight Structures.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Lindbergh, Göran
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Chen, Brian
    The City College of New-York, Department of Chemical Engineering.
    Structural Positive Electrodes for Multifunctional Composite Materials.2019In: Proceedings of the 2019 International Conference on Composite Materials, 2019Conference paper (Other academic)
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  • 229.
    Boutry, Oscar
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Väg- och spårfordon samt konceptuell fordonsdesign.
    Development of a shock-absorber pre-sizing tool: from vehicle to shock-absorber physical characteristics2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    During the first phase of development of a new vehicle, shock-absorber pre-sizing is a crucial issue as it will have a direct impact on the vehicle behavior, handling and comfort. The shock-absorbers force versus velocity relation has first to be defined properly, then their physical parameters are to be chosen carefully in order to get maximum performance with respect to the target force versus velocity relation. Indeed, two shock-absorbers with almost the same force versus velocity relation can give very different results in terms of comfort when it comes to subjective evaluation. This is particularly true when comparing high-end versus low-end shock-absorbers. This paper focus on the development of a global numeric shock-absorber pre-sizing tool going from vehicle physical characteristics to shock-absorbers ones. First, the target shock-absorbers force versus velocity relations are determined from the physical properties of the vehicle, from its typing, and from objective comfort criteria computed thanks to a half-vehicle simulation with non-linear shock absorbers, and compression bump stops. Then, the physical characteristics of the shock-absorbers are determined from the previously designed force versus velocity relations, and from a shock-absorber simulation together with a genetic algorithm optimization program. This tool, fully developed with Matlab, makes it possible to pre-size the shock-absorbers in an efficient and objective way, and in very few steps.

  • 230.
    Bouysses, Valérie Aurore
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Naval Systems.
    Rig Performance Evaluation for Wind Powered Pure Car Carrier2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Carrying around 80-90% of world volume of goods, the shipping industry has a considerable environmental impact. The International Maritime Organization (IMO) fixed a 50% greenhouse gases emission reduction target by 2050 with respect to 2008 levels. Toward the objective of sustainable shipping, Wallenius Marine, together with KTH Royal Institute of Technology and SSPA Sweden, launched the project to develop a wind powered pure car carrier ship. The 200 meters long vessel is powered by four 360 degrees rotating upright wings that allow sailing in all conceivable wind conditions. The implementation of such concept strongly depends on the aerodynamic properties of the multi-wings system. However, its assessment is challenging due to flow interactions between the wings.The main goal of the study is to investigate and find a suitable wing design and configuration to propel the ship only using wind power, ie when the installed engine power is off. The first task of this study was to determine the reliability and limitations of the aero-modelling tools developed by KTH including a 2D wing trimming optimizer and a vortex lattice method code. Flapped-wing and symmetrical wing (NACA-4 digits profiles) rig designs have been investigated. The flapped wing profile enhances by 30% the thrust power of the multi-rig system compared to a symmetrical wing profile for same arrangement on deck and total sails area. The “rectangle” disposition of the rigs on deck appeared to be more performant than the in-line arrangement. Indeed, this configuration allows to sail with a larger range of incident wind angles (closer to the wind) and with higher vessel’s speed than the base design one. Further numerical testing using more accurate tools that can take turbulence effects into account, such as CFD and model testing in wind tunnel or real conditions may be done to validate the conclusions raised by this study.

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  • 231.
    Bozikis, Nikolaos
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Hydrogen-Methane combustion modeling in the burner of the SGT-800 Siemens Energy gas turbine2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Industrial gas turbines constitute an integral part of today’s electricalpower production infrastructure. Reacting gas flows in these machines arevery interesting and complex in nature since they exhibit highly turbulentbehaviour which is strongly coupled to the chemical reaction dynamics.Thus developing accurate CFD models for such flows while keeping thecomputational expense reasonable is a non-trivial task. In this studyLarge-Eddy simulations of hydrogen-methane fuel mixture combustion inthe SGT800’s (Siemens Energy Gas turbine 800) burner, in atmosphericconditions are performed using the CFD code Starccm+ (versions 16.04and 16.06).

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  • 232.
    Boåsen, Magnus
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Modeling of structural integrity of aged low alloy steels using non-local mechanics2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ageing of low alloy steels affects the structural integrity assessment as it most commonly causes embrittlement and a hardening of the material. This is due to theevolution of the microstructure during operation in the specific application. In nuclear applications, the most common causes of ageing of low alloy steels areirradiation and thermal ageing. Embrittlement in this type of materials is generally divided into hardening and non-hardening embrittlement. The formation of clusters or precipitates of solute atoms typically cause the former, and the weakening of grain boundaries generally cause the latter. This thesis is devoted to thedevelopment of models that can be used to describe the material properties of aged low alloy steels in terms of plastic properties and fracture toughness, and to thestudy of the effects of thermal ageing on the mechanical properties of a low alloy steel.

    In Paper I, a strain gradient plasticity framework is applied in order to capture length scale effects. The constitutive length scale is assumed to be related to the dislocation mean free path and the changes it undergoes during plastic deformation. Several evolution laws for the length scale were developed and implemented in a FEM-code. This was used to solve a test problem in order to probe the effects of the length scale evolution. All length scale evolution laws considered in this study results in a decreasing length scale, which causes an overall softening in cases where the strain gradient dominates the solution. The results are in tentative agreement with phenomena of strain localization that occurs in highly irradiated materials.

    In Paper II, a scalar stress measure for cleavage fracture is developed and generalized, here called the effective normal stress measure. This is used in a nonlocal weakest link model which is applied to two datasets from literature in order to study the effects of the effective normal stress measure, as well as to experiments considering four-point bending of specimens containing a semi-elliptical surface crack. The model is shown to reproduce the failure probability of all considered datasets, i.e. well capable of transferring toughness information between different geometries.

    In Paper III, a thermally aged weld from the Ringhals nuclear power plant is studied experimentally and compared to a reference material using fracture toughness testing. The main objective of the study was to investigate the effect of thermal ageing on the cleavage or brittle fracture toughness, with a specific focus on the effect of crack tip constraint. The testing showed that thermal ageing had enabled brittle fracture initiation from grain boundaries, resulting in a bimodal toughness distribution due to multiple mechanisms for brittle fracture initiation.

    In Paper IV, the non-local weakest link model in Paper II is further developed to account for multiple mechanism brittle fracture. The model is developed for brittle fracture initiation from grain boundaries and second phase particles. The grain boundary mechanism is inferred from simulations of polycrystalline aggregates using crystal plasticity. When applied to the experimental results of Paper III, the model is able to describe the fracture toughness distribution with a remarkable accuracy.

    Download full text (pdf)
    Boåsen [2020] Modeling of structrual integrity of aged low alloy steels using non-local mechanics
  • 233.
    Boåsen, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Dahlberg, Carl F. O.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Efsing, Pål
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Faleskog, Jonas
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    A weakest link model for multiple mechanism brittle fracture — Model development and application2021In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 147, article id 104224Article in journal (Refereed)
    Abstract [en]

    A multiple mechanism weakest link model for intergranular and transgranular brittle fracture is developed on the basis of experimental observations of a thermally aged low alloy steel. The model development is carried out in tandem with micro mechanical analysis of grain boundary cracking using crystal plasticity modeling of polycrystalline aggregates with the purpose to inform the weakest link model. The fracture modeling presented in this paper is carried out by using a non-local porous plastic Gurson model where the void volume fraction evolution is regularized over two separate length scales. The ductile crack growth preceding the final brittle fracture is well predicted using this type of modeling. When applied to the brittle fracture tests, the weakest link model predicts the fracture toughness distribution remarkably well, both in terms of the constraint and the size effect. Included in the study is also the analysis of a reference material.

  • 234.
    Boåsen, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Dahlberg, Carl F. O.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Efsing, Pål
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Faleskog, Jonas
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    A weakest link model for multiple mechanism brittlefracture - Model development and application2020Report (Other academic)
    Abstract [en]

    A multiple mechanism weakest link model for intergranular and transgranularbrittle fracture is developed on the basis of experimental observations in a thermallyaged low alloy steel. The model development is carried out in tandemwith micro mechanical analysis of grain boundary cracking using crystal plasticitymodeling of polycrystalline aggregates with the purpose to inform theweakest link model. The fracture modeling presented in this paper is carriedout by using a non-local porous plastic Gurson model where the void volumefraction evolution is regularized over two separate length scales. The ductilecrack growth preceding the nal brittle fracture is well predicted using this typeof modeling. When applied to the brittle fracture tests, the weakest link modelpredicts the fracture toughness distribution remarkably well, both in terms ofthe constraint and the size eect. Included in the study is also the analysis of areference material.

  • 235.
    Boåsen, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Lindgren, Kristina
    Chalmers, Microstructure Physics, Department of Physics .
    Öberg, Martin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Thuvander, Mattias
    Chalmers, Microstructure Physics, Department of Physics .
    Faleskog, Jonas
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Efsing, Pål
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Analysis of thermal embrittlement of a low alloy steel weldment using fracture toughness and microstructural investigations2020Report (Other academic)
    Abstract [en]

    A thermally aged low alloy steel is investigated in terms of its fracture toughness and microstructural evolution and compared to a reference. The main purpose of the study is to investigate the effects of thermal embrittlement on the brittle fracture toughness, and its effects on the influence of loss of crack tip constraint. Ageing appears to enable brittle fracture initiation from grain boundaries besides initiation from second phase particles, making the fracture toughness distribution bimodal as a result. The consequence is that the constraint effect is significantly reduced when grain boundary initiation dominates the toughness distribution, as compared to the reference material where the constraint effect is significant. The microstructure is investigated at the nano scale using atom probe tomography where nanometer sized Cu-rich clusters are found primarily situated on dislocation lines.

  • 236.
    Boåsen, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Lindgren, Kristina
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Öberg, Martin
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Thuvander, Mattias
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Faleskog, Jonas
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Efsing, Pål
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Analysis of thermal embrittlement of a low alloy steel weldment using fracture toughness and microstructural investigations2022In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 262, article id 108248Article in journal (Refereed)
    Abstract [en]

    A thermally aged low alloy steel weld metal is investigated in terms of its fracture toughness and microstructural evolution and compared to a reference. The main purpose of the study is to investigate the effects of embrittlement due to thermal ageing on the brittle fracture toughness, and its effects on the influence of loss of crack tip constraint. The comparison of the investigated materials has been made at temperatures that give the same median fracture toughness of the high constraint specimens, ensuring comparability of the low constraint specimens. Ageing appears to enable brittle fracture initiation from grain boundaries besides initiation from second phase particles, making the fracture toughness distribution bimodal. Consequently, this appears to reduce the facture toughness of the low constraint specimens of the aged material as compared to the reference material. The microstructure is investigated at the nano scale using atom probe tomography where nanometer sized Ni-Mn-rich clusters, precipitated during ageing, are found primarily situated on dislocation lines.

  • 237.
    Bragone, Federica
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Rosén, Tomas
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST). KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Sustainability, Industrial Dynamics & Entrepreneurship.
    Laneryd, Tor
    Hitachi Energy, Västerås, Sweden.
    Söderberg, Daniel
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Fiberprocesser.
    Markidis, Stefano
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Unsupervised Learning Analysis of Flow-Induced Birefringence in Nanocellulose: Differentiating Materials and ConcentrationsManuscript (preprint) (Other academic)
    Abstract [en]

    Cellulose nanofibrils (CNFs) can be used as building blocks for future sustainable materials including strong and stiff filaments. The goal of this paper is to introduce a data analysis of flow-induced birefringence experiments by means of unsupervised learning techniques. By reducing the dimensionality of the data with Principal Component Analysis (PCA) we are able to exploit information for the different cellulose materials at several concentrations and compare them to each other. Our approach aims at classifying the CNF materials at different concentrations by applying unsupervised machine learning algorithms, like k-means and Gaussian Mixture Models (GMMs). Finally, we analyze the autocorrelation function (ACF) and the partial autocorrelation function (PACF) of the first principal component, detecting seasonality in lower concentrations. The focus is given to the initial relaxation of birefringence after the flow is stopped to have a better understanding of the Brownian dynamics for the given materials and concentrations.

    Our method can be used to distinguish the different materials at specific concentrations and could help to identify possible advantages and drawbacks of one material over the other. 

  • 238.
    Brandberg, August
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Micro-mechanical characterization and modeling of paper and paperboard2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fiber networks made of cellulose fibers from trees are used as information carriers (paper) and as packaging (paperboard). This thesis investigates the mechanical performance of paper and paperboard via micro-mechanical modeling and presents new methods for the mechanical characterization of the micro scale, necessary in such models.        In Paper A the effect of the fiber-fiber bond geometry on the sheet stiffness is investigated. In thick, low density sheets, the fiber lumen remains open resulting in a more compliant bonded segment. By finite element simulations, we demonstrate the effect of the lumen configuration on the stiffness of the bonded segment. Most important for the stiffness of the segment is the average state of the fiber lumen which has a marked effect on the macroscopic response of fiber networks when the network is sparse.        Compression strength is central in many industrial applications. In Paper B we recreated the short span compression test in a simulation setting. The networks considered are three-dimensional and have a grammage of 80--400 gm^-2. By modeling compression strength at the level of individual fibers and bonds, we show that widespread fiber level buckling is unlikely to appear at the loads at which the macroscopic sheet fails.        

    In Paper C we develop a micro-mechanical model to study the creation of curl in paper sheets subjected to a moisture gradient through the thickness of a sheet. A moisture gradient is created during the printing process if the ink is water based, which may lead to  out-of-plane deformations (curl). The effect of transverse fiber shrinkage is captured using a multiscale model where the fiber-fiber bond is modeled with volume elements. We show how the swelling anisotropy of individual fibers contributes to the curl of the sheet in such settings. 

    In Paper D we present how to uniquely and compactly describe the distribution of fiber shapes (length, width, wall thickness, curl) used in network simulations. Using a canonical vine structure, fiber shapes measured using an optical image analyzer are used to construct a multivariate distribution function. New fiber geometries can then be generated by sampling from this distribution. Having access to such a complete description with both the distribution of fiber properties and the dependence between properties is shown to be superior to previously presented methods using micro-mechanical simulations of thermo-mechanical (TMP) long fiber sheets.        In Paper E we compare sheet testing, micro-mechanical tensile testing, and nanoindentation as methods to extract the elastic material properties of individual pulp fibers. Nanoindentations are performed parallel to and orthogonal to the axis of the fiber after it has gone through all steps of papermaking, and indentation moduli are extracted. By relating the indentation modulus to the components of the anisotropic stiffness tensor, the longitudinal and transverse elastic modulus can be determined via an iterative error minimization scheme. We show that nanoindentation is an alternative to traditional methods with the advantage of yielding the transverse modulus and enabling measurement of the fiber properties after papermaking.

    Download full text (pdf)
    Kappa
  • 239.
    Brandberg, August
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Compression failure in dense non-woven fiber networks2020In: Cellulose, ISSN 0969-0239, E-ISSN 1572-882X, Vol. 27, no 10, p. 6065-6082Article in journal (Refereed)
    Abstract [en]

    Investigating the compression properties of randomly ordered fiber networks experimentally is difficult which has resulted in ongoing disputes as to the mechanisms controlling the compression strength in such materials. In this work, we investigated compression properties of randomly oriented fiber networks with a special emphasis on cellulose products such as paperboard. We numerically reconstructed the conditions of the short span compression test widely used to quantify the compression strength of paperboard. We found that the phenomenological failure mode of such networks is elasto-plastic buckling. The x-shaped failure mode observed in physical experiments appears when test specimen restraints are included in the model. The most significant improvements to sheet strength can be obtained by improving the elastic properties while the strain to failure is increased most by an improvement of the plastic yield and hardening properties of individual fibers. Bond breaks were confirmed to have a smaller influence on the overall response. Fiber level microscopic buckling was investigated in depth, providing quantitative estimates of the fraction of mass likely to buckle at the microscopic level. The analysis indicated that only a low to moderate number of load carrying fibers can be expected to buckle. The inherent strength reserve in non-ordered fiber networks was investigated by introducing hinge mechanisms throughout the network, and the effect was shown to be small for a small to moderate number of hinges.

  • 240.
    Brandberg, August
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    New insights into compressive strength of paper & board2019In: Paper Conference and Trade Show, PaperCon 2019, TAPPI Press , 2019, p. 1308-1313Conference paper (Refereed)
    Abstract [en]

    Compressive properties of fiber-based materials are linked to their performance as packaging materials. This is not only due to use under compressive loads such as stacking but also since compressive strength is lower than tensile strength, causing compressive properties to be the limit in all applications involving bending. We examine the effect of changing the network structure on short span compression strength using a numerical model. In this way, we overcome one of the major challenges of working on non-woven randomly oriented composited: performing controlled parametric studies. We show that the effect of changes made to fiber in- and out-of-plane orientation as well as non-uniform through-thickness density on compressive strength is small, but that stiffness and strain-tofailure may be altered using comparatively small structural modifications.

  • 241.
    Brandberg, August
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Motamedian, Hamid Reza
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Hirn, U.
    The role of the fiber and bond in hygroexpansion and curl of paper2019In: Paper Conference and Trade Show, PaperCon 2019, TAPPI Press , 2019, p. 1256-1271Conference paper (Refereed)
    Abstract [en]

    The underlying mechanism of hygroexpansion of paper products' deformation resides on the microscale and is a product of the coupling between hydrophilic fibers and micromechanical details of the fiber network, including the geometry and alignment of fibers and bonds. We present a micromechanical framework suitable for studying hygroexpansion from the fiber- and bond-level. Using the developed model, we show that due to the threedimensionality of the bond, the transverse deformations of the fibers are not transferred effectively to the in-plane deformation of the sheet. At the same time, the longitudinal deformation of the fiber accounts for a large portion of the hygroexpansion even in highly oriented sheets. On the other hand, the out-plane deformation of paper is predominantly controlled by the strain gradient in the bonds which stems from transverse shrinkage or expansion of the fibers in the bond region. Therefore, considering the bonds as three-dimensional entities is vital for the analysis since a two-dimensional approximation overestimates the impact of the transverse deformation of the bonds to the in-plane properties and underestimates moisture-induced out-of-plane deformations of the fiber network.

  • 242.
    Brandberg, August
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. CD Laboratory for Fiber Swelling and Paper Performance, Graz University of Technology, Inffeldgasse 23, Graz, 8010, Austria.
    Motamedian, Hamid Reza
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. CD Laboratory for Fiber Swelling and Paper Performance, Graz University of Technology, Inffeldgasse 23, Graz, 8010, Austria.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. CD Laboratory for Fiber Swelling and Paper Performance, Graz University of Technology, Inffeldgasse 23, Graz, 8010, Austria.
    Hirn, U.
    The role of the fiber and the bond in the hygroexpansion and curl of thin freely dried paper sheets2020In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 193-194, p. 302-313Article in journal (Refereed)
    Abstract [en]

    A computationally efficient method to study the in-plane and out-of-plane dimensional instability of thin paper sheets under the influence of moisture changes is presented. The method explicitly resolves the bonded and the free segments of fibers in the sheet, capturing the effect of anisotropic hygroexpansion at the fiber level. The method is verified against a volumetric model. The importance of longitudinal fiber hygroexpansion is demonstrated in spite of the absolute value of longitudinal hygroexpansion being an order of magnitude lower than the transverse hygroexpansion component. Finally, the method is used to demonstrate the formation of macroscopic sheet curl due to a moisture gradient in structurally uniform sheets in the absence of viscoelastic or plastic constitutive behavior and through-thickness residual stress profiles.

  • 243.
    Brandberg, August
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Reyier Österling, Sofia
    Dalarna University.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics.
    Hirn, Ulrich
    Graz University of Technology.
    Characterization and impact of fiber size variability on the mechanical properties of fiber networks with an application to paper materials2021Report (Other academic)
    Abstract [en]

        Cellulose fibers exhibit a wide range of shapes and sizes. This variation influences the mechanical performance of paper and paperboard by affecting the stress distribution inside the network and the degree of fiber-to-fiber bonding which is possible at a given density. However, the methods used to characterize the distribution of fiber sizes in the pulp neglect that the characteristic features of a fiber are generally not independent.

        Here, we resolve this shortcoming by fitting the fiber population to a multivariate distribution without enforcing normality or independence between the properties. The high-dimensional multivariate function is recast as a set of univariate distribution functions and a series of bivariate distributions connected by a canonical vine. 

        Using a micro-mechanical model of a paper sheet the influence of this improved characterization is investigated. Reasonable margins and a description of the dependency is shown to be superior to assuming independence even for perfectly preserved marginal distributions. This result demonstrates that micro-mechanical models of paper and paperboard cannot by assumption neglect the influence of the interdependence between the characteristic features of fibers. 

  • 244.
    Brandberg, August
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. CD Laboratory for Fiber Swelling and Paper Performance, Graz University of Technology, Inffeldgasse 23, Graz, 8010, Austria.
    Österling, Sofia Reyier
    Dalarna Univ, Hogskolegatan 2, SE-79188 Falun, Sweden..
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Solid Mechanics. CD Laboratory for Fiber Swelling and Paper Performance, Graz University of Technology, Inffeldgasse 23, Graz, 8010, Austria.
    Hirn, Ulrich
    Graz Univ Technol, CD Lab Fiber Swelling & Paper Performance, Inffeldgasse 23, A-8010 Graz, Austria.;Graz Univ Technol, Inst Paper Pulp & Fibre Technol, Inffeldgasse 23, A-8010 Graz, Austria..
    Characterization and impact of fiber size variability on the mechanical of fiber networks with an to materials2022In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 239, article id 111438Article in journal (Refereed)
    Abstract [en]

    Cellulose fibers come in a wide range of shapes and sizes. The heterogeneity of the fiber length, width, wall thickness, curl and external fibrillation is detrimental to the mechanical performance of products such as paper and paperboard. Although micro-mechanical models of these materials sometimes incorporate features of this heterogeneity, so far there is no standardized method of fully incorporating this.We examine a large number of industrial mechanical fiber pulps to determine what information such a standardized method would have to have. We find that the method must allow for both non-Gaussian distributions and dependence between the variables. We present a method of characterizing mechanical pulp under these conditions that views the individual fiber as outcome of a sampling process from a multivariate distribution function. The method is generally applicable to any dataset, even a non-Gaussian one with dependencies.Using a micro-mechanical model of a paper sheet the proposed method is compared with previously presented methods to study whether incorporating both a varying fiber size and dependencies is necessary to match the response of a sheet modeled with measured characterization data. The results demonstrate that micro-mechanical models of paper and paperboard should not neglect the influence of the dependence between the characteristic shape features of the fibers if the model is meant to match physical experiments.

  • 245.
    Brandt, Luca
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Norwegian Univ Sci & Technol NTNU, Dept Energy & Proc Engn, Trondheim, Norway..
    Coletti, Filippo
    Swiss Fed Inst Technol, Dept Mech & Proc Engn, Zurich, Switzerland..
    Particle-Laden Turbulence: Progress and Perspectives2022In: Annual Review of Fluid Mechanics, ISSN 0066-4189, E-ISSN 1545-4479, Vol. 54, p. 159-189Article, review/survey (Refereed)
    Abstract [en]

    This review is motivated by the fast progress in our understanding of the physics of particle-laden turbulence in the last decade, partly due to the tremendous advances of measurement and simulation capabilities. The focus is on spherical particles in homogeneous and canonical wall-bounded flows. The analysis of recent data indicates that conclusions drawn in zero gravity should not be extrapolated outside of this condition, and that the particle response time alone cannot completely define the dynamics of finite-size particles. Several breakthroughs have been reported, mostly separately, on the dynamics and turbulence modifications of small inertial particles in dilute conditions and of large weakly buoyant spheres. Measurements at higher concentrations, simulations fully resolving smaller particles, and theoretical tools accounting for both phases are needed to bridge this gap and allow for the exploration of the fluid dynamics of suspensions, from laminar rheology and granular media to particulate turbulence.

  • 246.
    Brethouwer, Geert
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Turbulence. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Turbulent flow in curved channels2021In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 931, article id A21Article in journal (Refereed)
    Abstract [en]

    Fully developed turbulent flow in channels with mild to strong longitudinal curvature is studied by direct numerical simulations. The Reynolds based on the bulk mean velocity and channel half-width delta is fixed at 20 000, resulting in a friction Reynolds number of approximately 1000. Four cases are considered with curvature varying from gamma = 2 delta/r

  • 247.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Comment on "Turbulence Statistics of Arbitrary Moments of Wall-Bounded Shear Flows: A Symmetry Approach"2023In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 130, no 6, article id 069401Article in journal (Other academic)
  • 248.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics, Turbulence.
    Much faster heat/mass than momentum transport in rotating Couette flows2021In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 912, article id A31Article in journal (Refereed)
    Abstract [en]

    Heat and mass transport are generally closely correlated to momentum transport in shear flows. This so-called Reynolds analogy between advective heat or mass transport and momentum transport hinders efficiency improvements in engineering heat and mass transfer applications. I show through direct numerical simulations that in plane Couette and Taylor-Couette flow, rotation can strongly influence wall-to-wall passive tracer transport and make it much faster than momentum transport, clearly in violation of the Reynolds analogy. This difference between passive tracer transport, representative of heat/mass transport, and momentum transport is observed in steady flows with large counter-rotating vortices at low Reynolds numbers as well as in fully turbulent flows at higher Reynolds numbers. It is especially large near the neutral (Rayleigh's) stability limit. The rotation-induced Coriolis force strongly damps the streamwise/azimuthal velocity fluctuations when this limit is approached, while tracer fluctuations are much less affected. Accordingly, momentum transport is much more reduced than tracer transport, showing that the Coriolis force breaks the Reynolds analogy. At higher Reynolds numbers, this strong advective transport dissimilarity is accompanied by approximate limit cycle dynamics with intense low-frequency bursts of turbulence when approaching the neutral stability limit. The study demonstrates that simple body forces can cause clear dissimilarities between heat/mass and momentum transport in shear flows.

  • 249.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Passive scalar transport in rotating turbulent channel flow2018In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 844, p. 297-322Article in journal (Refereed)
    Abstract [en]

    Passive scalar transport in turbulent channel flow subject to spanwise system rotation is studied by direct numerical simulations. The Reynolds number R-e= U(b)h/nu is fixed at 20 000 and the rotation number R-o= 2 Omega h/U-b is varied from 0 to 1.2, where U-b is the bulk mean velocity, h the half channel gap width and Omega the rotation rate. The scalar is constant but different at the two walls, leading to steady scalar transport across the channel. The rotation causes an unstable channel side with relatively strong turbulence and turbulent scalar transport, and a stable channel side with relatively weak turbulence or laminar-like flow, weak turbulent scalar transport but large scalar fluctuations and steep mean scalar gradients. The distinct turbulent-laminar patterns observed at certain Ro on the stable channel side induce similar patterns in the scalar field. The main conclusions of the study are that rotation reduces the similarity between the scalar and velocity field and that the Reynolds analogy for scalar-momentum transport does not hold for rotating turbulent channel flow. This is shown by a reduced correlation between velocity and scalar fluctuations, and a strongly reduced turbulent Prandtl number of less than 0.2 on the unstable channel side away from the wall at higher Ro. On the unstable channel side, scalar scales become larger than turbulence scales according to spectra and the turbulent scalar flux vector becomes more aligned with the mean scalar gradient owing to rotation. Budgets in the governing equations of the scalar energy and scalar fluxes are presented and discussed as well as other statistics relevant for turbulence modelling.

  • 250.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Strong dissimilarity between heat and momentum transfer in rotating Couette flows2023In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 205, article id 123920Article in journal (Refereed)
    Abstract [en]

    Rotation influences flows and transport processes in many engineering applications, however, even in canonical flow cases, the effects of rotation are not fully understood. Here, we present the results of di-rect numerical simulations of heat transfer plane Couette and Taylor-Couette flows subject to rotation about the spanwise and axial axis, respectively. Temperature is a passive scalar since buoyancy is ne-glected. The Reynolds number Re and the rotation rate Rn are systematically varied to thoroughly inves-tigate the influence of rotation on heat and momentum transfer and the Reynolds analogy. We find that with increasing anti-cyclonic rotation, the Nusselt numbers for the momentum transfer Num and heat transfer Nuh both increase at first before declining and approaching unity at rapid rotation rates when the flow becomes fully laminar. The Reynolds analogy factor RA = N uh/N um is near unity for non-rotating Couette flows, but it grows significantly with increasing rotation rate. RA reaches a maximum of approx-imately 2 at low Re up to 6 and 8 near Rn = 1 at higher Re in plane Couette and Taylor-Couette flow, respectively. The simulations thus show that the Reynolds analogy between heat and momentum trans-fer breaks down and that the heat transfer can become much faster than moment transfer when plane Couette and Taylor-Couette flows are subject to anti-cyclonic rotation. This happens at low Re as well as higher Re when the flows are fully turbulent. The turbulent Prandtl becomes much smaller than unity and the mean velocity and temperature profiles differ when the Reynolds analogy breaks down. We also present empirical models for Num and RA , which agree reasonably well to very well with the data within a limited Rn range.

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