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1.
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2.
  • Wadekar, Sandip, 1989 (författare)
  • Large-Eddy Simulation of Gasoline Fuel Spray Injection at Ultra-High Injection Pressures
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Gasoline direct injection is a state-of-the-art technique that reduces hydrocarbon and particulate emissions. However, further improvement is needed to meet current as well as future emission regulations. A prominent solution is to increase the fuel injection pressure which allows faster fuel droplet atomization, quick evaporation and improves fuel-air mixture formation under realistic engine conditions. In this work, the gasoline fuel injection process at ultra-high injection pressures ranging from 200 to 1500 bar was analyzed using numerical models. In particular, the Large-Eddy Simulation (LES) method, with the standard Smagorinsky turbulence model, was utilized using the Eulerian formulation  for the continuous phase. The discrete droplet phase was treated using a Lagrangian formulation together with spray sub-models. In the first part of study, spray was injected into an initially quiescent constant volume chamber using two different nozzle hole shape geometries: divergent and convergent. The numerical results were calibrated by reproducing experimentally observed liquid penetration length and efforts were made to understand the influence of ultra-high injection pressures on spray development. The calibrated models were then used to investigate the impact of ultra-high injection pressures on mean droplet sizes, droplet size distribution, spray-induced large-scale eddies and entrainment rate. The results showed that, at ultra-high injection pressures, the mean droplet sizes were significantly reduced and the droplets achieving very high  velocities. Integral length scales of spray-induced turbulence and air entrainment rate were better for the divergent-shaped injector, and considerably larger at higher injection pressures compared to lower ones. In the second part of the study, four consecutive full-cycle cold flow LES simulations were carried out to generate realistic turbulence inside the engine cylinder. The first three cycles were ignored, with the fourth cycle being used to model the injection of the fuel using the divergent-shaped injector only (which was found to be better in the previous part of this study) at different injection pressures. In addition to the continuous gas phase (Eulerian) and the dispersed liquid (Lagrangian), the liquid film feature (Finite-Area) was used to model the impingement of fuel spray on the engine walls and subsequent liquid film formation. The simulation results were used to evaluate spray-induced turbulence, fuel-air mixing efficiency and the amount of liquid mass deposited on the walls. The limitation of the high-pressure injection technique with respect to liquid film formation was optimized using a start of injection (SOI) sweep. Overall results showed that the mixing efficiency increased at high injection pressure and that SOI should occur between early injection and late injection to optimize the amount of mass being deposited on the engine walls.
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4.
  • Etikyala, Sreelekha, 1991 (författare)
  • Particulate Formation in GDI Engines
  • 2022
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The need to comply with stringent emission regulations while improving fuel economy and reducing criteria pollutant emissions from transportation presents a major challenge in the design of gasoline Direct Injection (DI) engines because of the adverse effects of ultrafine Particulate Number (PN) emissions on human health and other environmental concerns. With upcoming advances in vehicle electrification, it may be the case that electric vehicles completely replace all current vehicles powered by internal combustion engines ensuring zero emissions. In the meantime, Gasoline Direct Injection (GDI) engines have become the primary mode of transportation using gasoline as they offer better fuel economy while also providing low CO2 emissions. However, GDI engines tend to produce relatively high PN emissions when compared to conventional Port Fuel Injection (PFI) engines, largely because of challenges associated with in-cylinder liquid fuel injection. Cold-starts, transients, and high load operation generate a disproportionate share of PN emissions from GDI engines over a certification cycle. The mechanisms of PN formation during these stages must therefore be understood to identify solutions that reduce overall PN emissions in order to comply with increasingly strict emissions standards. This work presents experimental studies on particulate emissions from a naturally aspirated single cylinder metal gasoline engine run in a homogeneous configuration. The engine was adapted to enable operation in both DI and PFI modes. In PFI mode, injection was performed through a custom inlet manifold about 50 cm from the cylinder head to maximize the homogeneity of the fuel-air mixture. The metal head was eventually modified by incorporating an endoscope that made it possible to visualize the combustion process inside the cylinder. The experimental campaigns were structured to systematically isolate and clarify PN formation mechanisms. Tests were initially performed in steady state mode to obtain preliminary insights and to screen operating conditions before conducting transient tests. Particulate emissions were measured and correlated with the images obtained through endoscope visualization where possible. Key objectives of these studies were to find ways of reducing PN formation by increasing combustion stability. It was found that by avoiding conditions that cause wall wetting with liquid fuel, PN emissions can be substantially reduced during both steady state operation and transients. Warming the coolant and injecting fuel at later timings reduced PN emissions during warmup and cold transient conditions. Additionally, experiments using fuel blends with different oxygenate contents showed that the chemical composition of the fuel strongly influences particulate formation under steady state and transient conditions, and that this effect is load-dependent. Overall, the results obtained in this work indicate that wall wetting is the dominant cause of particulate formation inside the cylinder and that fuel-wall interactions involving the piston, cylinder walls, and valves during fuel injection account for a significant proportion of PN emissions in the engine raw exhaust.
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5.
  • Hadadpour, Ahmad (författare)
  • Spray combustion with multiple-injection in modern engine conditions
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Combustion of fuel in diesel engines emits substances harmful to the environment such as soot. These emissions can be reduced by either in-cylinder treatments or after-treatments. One of the common in-cylinder treatments is multiple-injection, which divides a single fuel injection to multiple smaller injections. There are many open questions on the physical processes of the ignition, combustion and emissions of diesel spray flame with multiple injections. The current PhD project aims at studying these processes using large-eddy simulations (LES) and strives to answer some of the open questions. To develop a fast and robust LES tool for this study, a new method is formulated for spray combustion simulation. This method is developed based on the flamelet-generated manifold (FGM) method and the Eulerian stochastic fields (ESF) method. The new ESF/FGM method relaxes some of the substantial assumptions in conventional FGM, while it still keeps the computational costs at a reasonable level for engineering applications. Additionally in this work, a new reaction progress variable for FGM models is proposed by using local oxygen consumption, and the advantages and limitations of this progress variable are explored. Spray-A from Engine Combustion Network (ECN) which is designed to mimic modern engine conditions is chosen as the baseline case for simulations. In this case, liquid n-dodecane, which is a diesel surrogate, is injected into a high-pressure constant-volume vessel. The comparison of simulation results with experimental measurements shows that the ESF/FGM method with the new progress variable can predict the spray combustion characteristics such as ignition delay time, ignition location, lift-off length, pressure rise and thermochemical structure of the spray flame, accurately. After validation of simulation results against experimental measurements, the new ESF/FGM and other available turbulence-combustion simulation tools are applied to simulate multiple-injection spray combustion. Different multiple-injection strategies are investigated by systematically changing the injection timing. The effects of applying each strategy on the ignition, combustion, mixing and emissions are investigated. The results show that in split-injection and post-injection strategies the major physical reason for reduction of soot is better air entrainment and lower local equivalence ratio. It is shown that increasing the dwell time and retarding it toward the end of injection can enhance this effect. On the contrary, for the pre-injection strategies, shortening the ignition delay time of the main injection reduces its pre-mixing and increases its soot formation. In these strategies, the high-temperature region from the pre-injection combustion can increase soot oxidation of the main injection fuel, only if this region is not cooled down as a result of air entrainment during dwell time. Therefore, in such cases shortening the dwell time decreases net soot emissions.
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6.
  • Pieringer, Astrid, 1979, et al. (författare)
  • Investigation of railway curve squeal using a combination of frequency- and time-domain models
  • 2016
  • Ingår i: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16. ; , s. 444 - 451
  • Konferensbidrag (refereegranskat)abstract
    • Railway curve squeal arises from self-excited vibrations during curving. In this paper, a frequency- and a timedomainapproach for curve squeal are compared. In particular, the capability of the frequency-domain model topredict the onset of squeal and the squeal frequencies is studied. In the frequency-domain model, linear stabilityis investigated through complex eigenvalue analysis. The time-domain model is based on a Green's functionsapproach and uses a convolution procedure to obtain the system response. To ensure comparability, the samesubmodels are implemented in both squeal models. The structural flexibility of a rotating wheel is modelled byadopting Eulerian coordinates. To account for the moving wheel‒rail contact load, the so-called moving elementmethod is used to model the track. The local friction characteristics in the contact zone is modelled inaccordance with Coulomb's law with a constant friction coefficient. The frictional instability arises due togeometrical coupling. In the time-domain model, Kalker's non-linear, non-steady state rolling contact modelincluding the algorithms NORM and TANG for normal and tangential contact, respectively, is solved in eachtime step. In the frequency-domain model, the normal wheel/rail contact is modelled by a linearization of theforce-displacement relation obtained with NORM around the quasi-static state and full-slip conditions areconsidered in tangential direction. Conditions similar to those of a curve on the Stockholm metro exposed tosevere curve squeal are studied with both squeal models. The influence of the wheel-rail friction coefficient andthe direction of the resulting creep force on the occurrence of squeal is investigated for vanishing train speed. Results from both models are similar in terms of the instability range in the parameter space and the predictedsqueal frequencies.
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7.
  • Li, Xiaojian, 1991, et al. (författare)
  • Installation effects on engine design
  • 2020
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Increasing the engine bypass ratio is one way to improve propulsive efficiency. However, an increase in the bypass ratio (BPR) has usually been associated with an increase in the fan diameter. Consequently, there can be a notable increase in the impact of the engine installation on the overall aircraft performance. In order to achieve a better balance between those factors, it requires novel nacelle and engine design concepts. This report mainly reviews installation effects on engine design. Firstly, the installation effects assessment methods are introduced. Then, the installation effects on engine cycle design, intake design and exhaust design are sequentially reviewed.
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8.
  • INNOTRACK: Concluding technical report
  • 2010
  • Samlingsverk (redaktörskap) (refereegranskat)abstract
    • The track structure, rails, switches and crossings account for more than 50% of maintenance and renewal costs for the rail industry. To improve the competitiveness of rail transportation, the cost-efficiency of these areas needs to be addressed.This the background to INNOTRACK, an integrated research project funded by the European Commission’s 6th research framework pro- gramme. Running from September 2006 to December 2009, INN- OTRACK has developed a multitude of innovative solutions in the areas of track substructure, rails & welds, and switches & crossings. The solutions have been assessed from technical, logistics and life cycle cost point of views.This Concluding Technical Report of INNOTRACK includes an overview of the project. It further details implementable results, and clusters them into ”highlight” areas. In addition, the book acts as a ”key” to the vast amount of information from INNOTRACK: All sections refer to project reports where more information can be found.
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9.
  • Li, Xiaojian, 1991, et al. (författare)
  • A new method for performance map prediction of automotive turbocharger compressors with both vaneless and vaned diffusers
  • 2021
  • Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 235:6, s. 1734-1747
  • Tidskriftsartikel (refereegranskat)abstract
    • A new approach to predict the performance maps of automotive turbocharger compressors is presented. Firstly, a polynomial equation is applied to fit the experimental data of flow coefficient ratios for the centrifugal compressors with both vaneless and vaned diffusers. Based on this equation, the choke and surge flow coefficients under different machine Mach numbers can be quickly predicted. Secondly, a physically based piecewise elliptic equation is used to define compressors’ characteristic curves in terms of efficiency ratio. By introducing the flow coefficient ratio into the efficiency correlation, the empirical coefficients in the piecewise elliptic equation are uniquely calibrated by the experimental data, forming a unified algebraic equation to match the efficiency maps of the compressors with both vaneless and vaned diffusers. Then, a new universal equation, which connects the work coefficient, the impeller outlet flow coefficient and the non-dimensional equivalent impeller outlet width, is derived by using classical aerothermodynamic method. The off-design pressure ratio is predicted based on the equivalent impeller outlet width with less knowledge of the compressor geometry and no empirical coefficients. Finally, three state-of-the-art turbocharger compressors (one with vaneless diffuser, two with vaned diffusers) are chosen to validate the proposed method, and the results show a satisfactory accuracy for the performance map prediction. This method can be used for the preliminary design of turbocharger compressors with both vaneless and vaned diffusers, or to assess the design feasibility and challenges of the given design specifications.
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10.
  • Caprioli, Sara, 1978 (författare)
  • Thermal impact on rolling contact fatigue of railway wheels
  • 2014
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Rolling contact fatigue (RCF) is a very common and costly damage mechanism for rails and wheels. This thesis investigates the influence of combined thermal and mechanical loading on RCF of railway wheels on the basis of numerical predictions. The established computational framework includes heat flux analyses, (two- and three-dimensional) elastoplastic finite element simulations and subsequent RCF life analyses. The computational framework is employed to quantify the influence of various operational parameters and modelling presumptions such as applied heat and tangential stress characteristics, load application schemes, mesh densities etc. Examples of results include quantifications of how partial slip conditions result in higher plastic strain magnitudes in a thin layer at the wheel tread surface, and differences in material responses between accelerating and braking wheels.The numerical model was extended to incorporate surface initiated cracks. With the extended model it is shown that 1 mm deep cracks have a substantial influence on the state of stress and strain in the bulk material between surface cracks. Further, comparisons between radial (thermal) and inclined (RCF) surface cracks show that the deformation of significantly inclined cracks (30 degrees) is more severe than that of radial cracks. Further, acceleration is found to give larger crack face displacements. However braking tends to induce tensile residual stresses that open the crack mouth, thus allowing fluid penetration that can promote crack growth. Also thermal loading is found to cause a significant crack mouth opening that is decreased by subsequent rolling contact.In a final study numerical RCF predictions are compared to full-scale experimental studies carried out at the Railway Technical Research Institute in Japan. Thermal loading tuned towards measurements by thermocameras and thermocouples are introduced in a truncated loading scheme corresponding to the test configuration. Estimated crack initiation life is found to be in good agreement with test results. The investigation also shows the significant influence of the employed material model. In addition to thermomechanical fatigue analyses, the case of purely thermal fracture has been investigated. This study quantified how the risk of fracture and resulting crack sizes depend on braking conditions and initial surface cracks. The results of this thesis are believed to be of importance in defining and enforcing sustainable operational conditions and maintenance actions. Further, this thesis provides tools to establish root causes and pertinent mitigating actions when thermomechanical wheel cracking nevertheless occurs.
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11.
  • Li, Xiaojian, 1991, et al. (författare)
  • A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles
  • 2020
  • Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19
  • Tidskriftsartikel (refereegranskat)abstract
    • Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.
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12.
  • Gantasala, Sudhakar, et al. (författare)
  • Numerical Investigation of the Aeroelastic Behavior of a Wind Turbine with Iced Blades
  • 2019
  • Ingår i: Energies. - : MDPI. - 1996-1073. ; 12:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Wind turbines installed in cold-climate regions are prone to the risks of ice accumulation which affects their aeroelastic behavior. The studies carried out on this topic so far considered icing in a few sections of the blade, mostly located in the outer part of the blade, and their influence on the loads and power production of the turbine are only analyzed. The knowledge about the influence of icing in different locations of the blade and asymmetrical icing of the blades on loads, power, and vibration behavior of the turbine is still not matured. To improve this knowledge, multiple simulation cases are needed to run with different ice accumulations on the blade considering structural and aerodynamic property changes due to ice. Such simulations can be easily run by automating the ice shape creation on aerofoil sections and two-dimensional (2-D) Computational Fluid Dynamics (CFD) analysis of those sections. The current work proposes such methodology and it is illustrated on the National Renewable Energy Laboratory (NREL) 5 MW baseline wind turbine model. The influence of symmetrical icing in different locations of the blade and asymmetrical icing of the blade assembly is analyzed on the turbine’s dynamic behavior using the aeroelastic computer-aided engineering tool FAST. The outer third of the blade produces about 50% of the turbine’s total power and severe icing in this part of the blade reduces power output and aeroelastic damping of the blade’s flapwise vibration modes. The increase in blade mass due to ice reduces its natural frequencies which can be extracted from the vibration responses of the turbine operating under turbulent wind conditions. Symmetrical icing of the blades reduces loads acting on the turbine components, whereas asymmetrical icing of the blades induces loads and vibrations in the tower, hub, and nacelle assembly at a frequency synchronous to rotational speed of the turbine.
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13.
  • Wadekar, Sandip, 1989 (författare)
  • Large-eddy simulation on the effects of fuel injection pressure on gasoline spray characteristics
  • 2019
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Increasing the injection pressure in gasoline direct injection engines has a substantial potential to reduce emissions while maintaining high efficiency in spark ignition engines. Present gasoline injectors operate at pressures of 20 to 30 MPa. However, the use of higher-pressure fuel injection (40 to 60 MPa or more) could potentially reduce emissions and increase fuel efficiency. To fully exploit the capabilities of high-pressure fuel injection technology, a fundamental understanding of gasoline spray characteristics and behavior at such high injection pressures is vital. Such an understanding could also be used to further model development and facilitate the integration of advanced injection systems into future gasoline engines. This work presents numerical simulation studies on gasoline sprays formed at fuel injection pressures between 40 and 150 MPa. Three nozzle hole shapes (divergent, convergent, and straight) with different configurations (6 or 10 holes) were considered in the simulation to determine how a nozzle geometry affects spray formation. The numerical calculations were performed in a constant volume spray chamber under non-vaporizing conditions to best match the experimental setup. The gas flow was modeled using a large-eddy simulation (LES) approach, while a standard Lagrangian model was utilized to describe the liquid fuel spray. Spray atomization was modeled using the Kelvin Helmholtz –Rayleigh Taylor (KH-RT) atomization model, with the droplet size distribution being assumed to follow a Rosin-Rammler distribution function. Simulation results for the spray liquid penetration length are validated with experimental findings under different fuel injection pressures. Afterwards, an arithmetic mean droplet diameter (D10) and a Sauter mean droplet diameter (D32) as a function of pressure are compared against the measured droplet diameters. Simulated drop size distributions are presented and compared with measured droplet sizes. The results indicate that high fuel injection pressures increase the liquid penetration length and significantly reduce droplet sizes, and that nozzle shape significantly affects spray characteristics and spray formation. In addition, raising the injection pressure from 40 to 150 MPa with a divergent nozzle was predicted to reduce the SMD from 13.4 to 7.5 μm while increasing the probability of observing droplet diameters of 5-10 μm from 40% to 72%. Similar results were obtained for the other nozzle shapes.
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14.
  • Bayani, Mohsen, 1981 (författare)
  • Squeak and Rattle Prediction for Robust Product Development in the automotive industry
  • 2021
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Squeak and rattle are nonstationary, irregular, and impulsive sounds that are audible inside the car cabin. For decades, customer complaints about squeak and rattle have been, and still are, among the top quality issues in the automotive industry. These annoying sounds are perceived as quality defect indications and burden warranty costs to the car manufacturers. Today, the quality improvements regarding the persistent type of sounds in the car, as well as the increasing popularity of electric engines, as green and quiet propulsion solutions, stress the necessity for attenuating annoying sounds like squeak and rattle more than in the past. The economical and robust solutions to this problem are to be sought in the pre-design-freeze phases of the product development and by employing design-concept-related practices. To achieve this goal, prediction and evaluation tools and methods are required to deal with the squeak and rattle quality issues upfront in the product development process. The available tools and methods for the prediction of squeak and rattle sounds in the pre-design-freeze phases of a car development process are not yet sufficiently mature. The complexity of the squeak and rattle events, the existing knowledge gap about the mechanisms behind the squeak and rattle sounds, the lack of accurate simulation and post-processing methods, as well as the computational cost of complex simulations are some of the significant hurdles in this immaturity. This research addresses this problem by identifying a framework for the prediction of squeak and rattle sounds based on a cause-and-effect diagram. The main domains and the elements and the sub-contributors to the problem in each domain within this framework are determined through literature studies, field explorations and descriptive studies conducted on the subject. Further, improvement suggestions for the squeak and rattle evaluation and prediction methods are proposed through prescriptive studies. The applications of some of the proposed methods in the automotive industry are demonstrated and examined in industrial problems. The outcome of this study enhances the understanding of some of the parameters engaged in the squeak and rattle generation. Simulation methods are proposed to actively involve the contributing factors studied in this work for squeak and rattle risk evaluation. To enhance the efficiency and accuracy of the risk evaluation process, methods were investigated and proposed for the system excitation efficiency, modelling accuracy and efficiency and quantification of the response in the time and frequency domains. The demonstrated simulation methods besides the improved understanding of the mechanisms behind the phenomenon can facilitate a more accurate and robust prediction of squeak and rattle risk during the pre-design-freeze stages of the car development.
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15.
  • Cervantes, Michel, et al. (författare)
  • Porjus U9A full-scale hydropower research facility
  • 2008
  • Ingår i: Hydro technology and the evironment for the new century. - Foz do Iguassu.
  • Konferensbidrag (refereegranskat)abstract
    • Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine.
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16.
  • Korkmaz, Kadir Burak, 1989 (författare)
  • Improved Power Predictions of Ships Using Combined CFD/EFD Methods for the Form Factor
  • 2020
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Performance prediction of a ship is one of the most important tasks during the design phase. Once the design is finalized, the speed attained at a certain power consumption has to be verified with the most accurate prediction as it is specified at the contract of a new ship order and also required by the legal authorities. Considering the current commercial tendencies and the requirements enforced by legal authorities, towing tank testing and the extrapolation methods recommended by the International Towing Tank Conference (ITTC) are used and regarded as a highly accurate power prediction methodology for common cargo vessels. However, some aspects of this methodology have been questioned such as the scale effects on the form factor and its determination method. It is argued in this thesis that if a part of the Experimental Fluid Dynamics (EFD) based measure or the extrapolation procedure causes higher uncertainty than the numerical uncertainty and modelling errors of a Computational Fluid Dynamics (CFD) application, the corresponding part of the performance prediction method can be replaced or supplemented by CFD. In this study, the possibility to improve the power predictions by the introduction of a combined CFD/EFD Method was investigated by replacing the experimental determination of the form factor with double body computations based on the Reynolds-Averaged Navier-Stokes (RANS) equations, i.e. CFD based form factors. As a result of a joint, study where the double body simulations performed with seven different CFD codes, the CFD based form factors compared well with the experimentally determined form factors. Additionally, the standard deviations of the CFD based form factors were similar to the experimental uncertainty of the form factors even though the abundance of unsystematically varied methods and grids. Following the Quality Assurance Procedure proposed by the ITTC, a best practice guideline has been derived for the CFD based form factor determination method by applying systematic variations to the CFD set-ups. After the verification and validation of the CFD based form factor method in model scale, the full scale speed-power-rpm relations between large number of speed trials and full scale predictions were investigated using the CFD based form factors in combination to the ITTC-57 line and the numerical friction lines. It is observed that the usage of CFD based form factors improves the predictions in general and no deterioration in the prediction accuracy is noted within the limits of this study. Therefore, the combination of EFD and CFD is expected to provide immediate improvements to the 1978 ITTC Performance Prediction Method.
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17.
  • Lindgren, Ronny, 1976, et al. (författare)
  • Modeling gasoline spray-wall interactions and comparison to experimental data
  • 2004
  • Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of a gasoline spray impinging on a heated surface were investigated under simulated engine conditions in an earlier study. The data from the experimental investigation have now been compared to results obtained from Computational Fluid Dynamic (CFD) simulations generated using several different numerical models for spray-wall impingement found in the literature. It was found that the models based on single-drop experiments do not predict the outcome of spray impingement well in some respects. Their major drawback was that the predicted diameter distributions of the reflected drops in the secondary spray were shifted downwards from the measured drop size distributions. The tested models predicted the normal velocity component relative to the wall well. However, they were less good at capturing the tangential velocity component relative to the wall. Since the models did not capture the velocities in the tangential direction correctly, the spread of the secondary spray above the wall was under-predicted.
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18.
  • Mill, O., et al. (författare)
  • Analysis and development of hydro power research : synthesis within Swedish Hydro Power Centre
  • 2010
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The market for hydropower re-investments in Sweden is approx 2.5 billion SEK/yr the coming decade. Large investments will also be carried out in Swedish tailing dams. This will result in challenging projects and need of experts. A crucial factor for a successful management of these challenges is the supply of engineers and researchers with hydro power and dam skills and knowledge. Swedish Hydro Power Centre (Svenskt vattenkraftcentrum, SVC) is a competence centre for university education and research environments within hydro power and mining dams. SVC comprises of two knowledge areas: Hydraulic Engineering and Hydro Turbines and Generators, respectively. SVC builds high-quality and long term sustainable knowledge at selected universities...
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19.
  • Saha, Ranjan, 1984-, et al. (författare)
  • Aerodynamic Implication of Endwall and Profile Film Cooling in a Transonic Annular Cascade
  • 2013
  • Ingår i: 21st ISABE Conference. - Busan, Korea.
  • Konferensbidrag (refereegranskat)abstract
    • An experimental study is performed to observe the aerodynamic implications of endwall and profile film cooling on flow structures and aerodynamic losses. The investigated vane is a geometrically similar transonic nozzle guide vane with engine-representative cooling geometry. Furthermore, a new formulation of the cooling aerodynamic loss equation is presented and compared with the conventional methods. Results from a 5-hole pneumatic probe show that the film coolant significantly alters the secondary flow structure. The effect of different assumptions for the loss calculation is shown to significantly change the measured loss.
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20.
  • Saha, Ranjan, 1984-, et al. (författare)
  • Suction and Pressure Side Film Cooling Influence on Vane Aero Performance in a Transonic Annular Cascade
  • 2013
  • Ingår i: Proceedings of the ASME Turbo Expo. - 9780791855225
  • Konferensbidrag (refereegranskat)abstract
    • An experimental study on a film cooled nozzle guide vane has been conducted in a transonic annular sector to observe the influence of suction and pressure side film cooling on aerodynamic performance. The investigated vane is a typical high pressure gas turbine vane, geometrically similar to a real engine component, operated at an exit reference Mach number of 0.89. The aerodynamic results using a five hole miniature probe are quantified and compared with the baseline case which is uncooled. Results lead to a conclusion that the aerodynamic loss is influenced substantially with the change of the cooling flow rate regardless the positions of the cooling rows. The aerodynamic loss is very sensitive to the blowing ratio and a value of blowing ratio higher than one leads to a considerable higher loss penalty. The suction side film cooling has larger influence on the aerodynamic loss compared to the pressure side film cooling. Pitch-averaged exit flow angles around midspan remain unaffected at moderate blowing ratio. The secondary loss decreases (greater decrease in the tip region compared to the hub region) with inserting cooling air for all cases compared to the uncooled case.
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21.
  • Yarmohamadi, Hoda, 1980, et al. (författare)
  • Modeling of elastomeric engine mounts for commercial vehicles
  • 2007
  • Ingår i: Proceedings of the 20th Nordic Seminar on Computational Mechanics, NSCM 20, R.Larsson and K. Runesson (eds.), 23-24 November, 2007, Göteborg, Sweden. - 1652-8549.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • In this paper, a model of the conventional engine mount is developed and the nonlinear behavior of dynamic stiffness and damping of the engine mounts of commercial vehicles are investigated. The model comprises elastic, viscous and friction functional components and expresses the stiffness and damping of the mount as a function of frequency and amplitude of harmonic excitation. Optimization is done to identify model parameters using measurements for real elastomeric engine mounts.
  •  
22.
  • Asadi, Saeed, 1987, et al. (författare)
  • Global Sensitivity Analysis of High Speed Shaft Subsystem of a Wind Turbine Drive Train
  • 2018
  • Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1542-3034 .- 1023-621X. ; 2018
  • Tidskriftsartikel (refereegranskat)abstract
    • The wind turbine dynamics are complex and critical area of study for the wind industry. Quantification of the effective factors to wind turbine performance is valuable for making improvements to both power performance and turbine health. In this paper, the global sensitivity analysis of validated mathematical model for high speed shaft drive train test rig has been developed in order to evaluate the contribution of systems input parameters to the specified objective functions.Thedrive train in this study consists of a 3- phase induction motor, flexible shafts, shafts’ coupling, bearing housing, and disk with an eccentric mass.The governing equations were derived by using the Lagrangian formalism and were solved numerically by Newmark method. The variance based global sensitivity indices are introduced to evaluate the contribution of input structural parameters correlated to the objective functions. The conclusion from the current research provides informative beneficial data in terms of design and optimization of a drive train setup and also can provide better understanding of wind turbine drive train system dynamics with respect to different structural parameters, ultimately designing more efficient drive trains. Finally, the proposed global sensitivity analysis (GSA) methodology demonstrates the detectability of faults in different components.
  •  
23.
  • Berbyuk, Viktor, 1953 (författare)
  • Controlled Multibody Systems with Magnetostrictive Electric Generators
  • 2005
  • Ingår i: Proc. The ECCOMAS Thematic Conference Multibody Dynamics 2005 on Advances in Computational Multibody Dynamics, Madrid, June 21-24, 2005, Eds. J.M. Goicolea, J. Cuardrado and J.C. Garcia Orden.. - 8474933536 ; , s. 1-14
  • Konferensbidrag (refereegranskat)abstract
    • The proposed paper addresses the problem of modeling and analysis of controlled multibody systems with embedded magnetostrictive transducers. Main emphasis is put on the modeling of the considered mechatronic systems for applications in the field of power harvesting from vibrations, namely vibration-to-electric energy conversion, using novel giant magnetostrictive materials. Mathematical model of the considered mechatronic system has been developed. It comprises the constitutive equations of magnetoelastic behavior of magnetostrictive rod (active element of transducers), standard formulae of electromagnetism for induced voltage and current in the pick-up coil due to variation of magnetic field intensity, and finally the equations of motion of multibody system itself. The last one can be derived using one of the well-known multibody dynamics formalism. Assuming that massinertia parameters of magnetostrictive transducers are negligible small the inverse dynamics based algorithm has been proposed for modeling the controlled motion of multibody systems with embedded transducers. This algorithm is also suitable to evaluate electrical power output of magnetostrictive electric generators for different controlled motions of the system and to optimize the generators design. The inverse dynamics based algorithm was implemented in Matlab/Simulink with user friendly interface. Its efficiency has been confirmed by simulation of performance of different magnetostrictive electric generators under the periodic excitations exerted by the hosting multibody system.
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24.
  • Berbyuk, Viktor, 1953 (författare)
  • Inverse dynamics and Fourier-based approach to solve optimal control problems for multi-link mechanisms
  • 1997
  • Ingår i: The NATO Advanced Study Institute on Computational Methods in Mechanisms. ; 2, s. 431-440
  • Konferensbidrag (refereegranskat)abstract
    • This paper is concerned with the investigation of multi-link mechanism controlled mo­tion between fixed boundary conditions and given constraints on the phase coordinates. The mo­­duli of the controlling moments at the hinges between the links are bounded. A com­pu­ta­ti­o­nal method to the mathematical modeling of the optimal control laws which govern multi-link mechanism reaching motion is presented. This method is based on Fourier and spline appro­xi­ma­tions of the independently variable functions and inverse-dynamics approach. The me­­thod proposed makes it possible to satisfy the boundary conditions and some constraints on the phase coordinates automatically and accurately. The efficiency of the proposed method is illustrated by the solution of the energy-optimal control problem of a plane mobile three-link manipulator with a load on the grip.
  •  
25.
  • Cheung, Hon Lam, et al. (författare)
  • A multi-fidelity data-driven model for highly accurate and computationally efficient modeling of short fiber composites
  • 2024
  • Ingår i: Composites Science and Technology. - 0266-3538. ; 246
  • Tidskriftsartikel (refereegranskat)abstract
    • To develop physics-based models and establish a structure–property relationship for short fiber composites, there are a wide range of micro-structural properties to be considered. To achieve a high accuracy, high-fidelity full-field simulations are required. These simulations are computationally very expensive, and any single analysis could potentially take days to finish. A solution for this issue is to develop surrogate models using artificial neural networks. However, generating a high-fidelity data set requires a huge amount of time. To solve this problem, we used transfer learning technique, a limited amount of high-fidelity full-field simulations, together with a previously developed recurrent neural network model trained on low-fidelity mean-field data. The new RNN model has a very high accuracy (in comparison with full-field simulations) and is remarkably efficient. This model can be used not only for highly efficient modeling purposes, but also for designing new short fiber composites.
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26.
  • Okhovat, Reza, 1984 (författare)
  • Dynamic Equations foe Spherical and Cylindrical Shells Using Power Series Method
  • 2013
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Shells are commonly used in many branches of engineeringand have therefore beeninvestigated for a number of different types of shells.A shell can be considered as a curved plate having small thickness compared to the other geometrical dimensions as well as to the wavelengths of importance. The most important superiority of shells in comparison to plates is that shell structures can provide high strength and low weight because of their membrane stiffness.Spherical and cylindrical shells appear in manyapplicationsand some dynamic shell theories have thus been developed for these cases.All these theories seem to depend on more or less ad hoc kinematical assumptions and/orother approximations.In this thesis, dynamic equations for an isotropic spherical and an anisotropic cylindrical shell are derived by using a method developed during the last decade for bars, plates, and beams.The main advantage with the method is that it is very systematic and can be developed to any order. It also seems that the resulting structural equations are asymptotically correct to any order.First, dynamic equations are derived for a spherical shell made of a homogeneous, isotropic material.The starting point is a power series expansion of the displacement components in the thickness coordinate relative to the mid-surface of the shell. By using these expansions, the three-dimensional elastodynamic equations yield a set of recursion relations among the expansion functions.Applying the boundary conditions on the surfaces of the spherical shell and eliminating all but the six lowest order expansion functions give the shell equations as a power series in the shell thickness.In principle, the equations can be truncated to any order in the shell thickness, leading to very complicated expressions. Surface differential operators are introduced to decrease the length of the shell equations and tackle this complexity.the displacement field is split into a scalar (radial) part and a vector (tangential) part, and the shell equations are given in terms of the surface operators. After some manipulations, the final four shell equations are obtained in a more compact form which can be presented explicitly.Dynamic equations for an anisotropic cylindrical shell are also derived using the same technique. As a special case a 2D circular ring is considered and the eigenfrequencies are computed and are compared with the exact solution which is obtained by expressing the displacements in terms of Bessel and Neumann functions. Graphite epoxy is considered as an anisotropic material.For all cases, results are compared to exact three-dimensional theory. The computations for eigenfrequencies from the power series approximation are in good correspondence with results from the exact solution.
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27.
  • Bayani, Mohsen, 1981, et al. (författare)
  • Squeak and rattle prevention by geometric variation management using a two-stage evolutionary optimisation approach
  • 2020
  • Ingår i: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE). ; 2B-2020
  • Konferensbidrag (refereegranskat)abstract
    • Squeak and rattle are annoying sounds that often are regarded as the indicators for defects and quality issues by the automotive customers. Among the major causes for the generation of squeak and rattle sounds, geometric variation or tolerance stack-up is a key contributor. In the assembly process, the dimensional variation in critical interfaces for generating squeak and rattle events can be magnified due to tolerance stackup. One provision to manage the tolerance stack-up in these critical interfaces is to optimise the location of connectors between parts in an assembly. Hence, the focus of this work is to prevent squeak and rattle by introducing a geometric variation management approach to be used in the design phase in the automotive industry. The objective is to identify connection configurations that result in minimum variation and deviation in selected measure points from the critical interfaces for squeak and rattle. In this study, a two-stage evolutionary optimisation scheme, based on the genetic algorithm employing the elitism pool, is introduced to fine-tune the connectors’ configuration in an assembly. The objective function was defined as the variation and the deviation in the normal direction and the squeak plane. In the first stage, the location of one-dimensional connectors was found by minimising the objective function in the rattle direction. In the second stage, the best combination of some of the connectors from the first stage was found to define planar fasteners to optimise the objective function both in the rattle direction and the squeak plane. It was shown that by using the proposed two-stage optimisation scheme, the variation and deviation results in critical interfaces for squeak and rattle improved compared to the baseline results.
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28.
  • Heshmati, Mohsen, 1987, et al. (författare)
  • Dependency of cohesive laws of a structural adhesive in Mode-I and Mode-II loading on moisture, freeze-thaw cycling, and their synergy
  • 2017
  • Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 122, s. 433-447
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years, adhesive bonding has found its way to construction applications such as bridges. Given the harsh conditions that such structures are usually exposed to, it is necessary to account for environmental factors, particularly moisture and temperature, in the design phase. Cohesive zone modelling has attracted much attention in the last decade as a promising method to design adhesive joints. Despite this interest, the effects of moisture and thermal cycles on cohesive laws have not been investigated to the knowledge of the authors. In this paper, we present a method to directly measure the environmental-dependent cohesive laws of a structural adhesive loaded in pure Mode-I and Mode-II. Special consideration is given to overcome issues such as the time-consuming nature of moisture ingression and specimen dimensions, which could be problematic due to the size-limitations of conditioning equipment. The accuracy of this method was verified through simulation of the experiments using the finite element analysis. The effects of exposure to 95% relative humidity, immersion in saltwater and distilled water, and freeze-thaw cycles in the presence or absence of moisture were investigated. The results indicate the damaging effects of combined saltwater and freeze-thaw cycles which were clearly reflected on the shape of the cohesive laws.
  •  
29.
  • Pradas Gómez, Alejandro, 1986, et al. (författare)
  • Design automation strategies for aerospace components during conceptual design phases
  • 2023
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • This paper explores the different design automation strategies used for the design of aerospace components. A literature review of the applicable strategies, together with the strategies used in the DEFAINE project are presented and compared. An opportunity to explore the combination of two strategies is presented (Enhanced Function-Mean and Knowledge Based Engineering), which has the potential to increase the discovery of novel design solutions while being able to assess their structural performance. The preliminary results of the combined strategy are presented, using a DEFAINE use case of a Turbine Rear Structure jet engine component.
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30.
  • Aghaali, Habib, 1981-, et al. (författare)
  • Demonstration of Air-Fuel Ratio Role in One-Stage Turbocompound Diesel Engines
  • 2013
  • Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
  • Konferensbidrag (refereegranskat)abstract
    • A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the turbine efficiency and mass flow as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity.The main parameter influencing the turbocompound energy recovery is the exhaust gas pressure which leads to higher pumping loss of the engine and consequently lower engine crankshaft power. Each air-fuel equivalence ratio (λ) gives different engine power, exhaust gas temperature and pressure. Decreasing λ toward 1 in a Diesel engine results in higher exhaust gas temperatures of the engine.  λ can be varied by changing the intake air pressure or the amount of injected fuel which changes the available energy into the turbine. Thus, there is a compromise between gross engine power, created pumping power, recovered turbocompound power and consumed compressor power.In this study, the effects of different λ values and exhaust back-pressure have been investigated on the efficiency of a heavy-duty Diesel engine equipped with a single-stage electric turbocompounding. A one-dimensional gas dynamics model of a turbocharged engine was utilized that was validated against measurements at different load points. Two configurations of turbocompound engine were made. In one configuration an electric turbocharger was used and the amount of fuel was varied with constant intake air pressure. In another configuration the turbocharger turbine and compressor were disconnected to be able to control the turbine speed and the compressor speed independently; then the compressor pressure ratio was varied with constant engine fuelling and the exhaust back-pressure was optimized for each compressor pressure ratio.At each constant turbine efficiency there is a linear relation between the optimum exhaust back-pressure and ideally expanded cylinder pressure until bottom dead center with closed exhaust valves. There is an optimum λ for the turbocharged engine with regard to the fuel consumption. In the turbocompound engine, this will be moved to a richer λ that gives the best total specific fuel consumption; however, the results of this study indicates that turbocompound engine efficiency is relatively insensitive to the air-fuel ratio.
  •  
31.
  • Aghaali, Habib, 1981-, et al. (författare)
  • Temperature Estimation of Turbocharger Working Fluids and Walls under Different Engine Loads and Heat Transfer Conditions
  • 2013
  • Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
  • Konferensbidrag (refereegranskat)abstract
    • Turbocharger performance maps, which are used in engine simulations, are usually measured on a gas-stand where the temperatures distributions on the turbocharger walls are entirely different from that under real engine operation. This should be taken into account in the simulation of a turbocharged engine. Dissimilar wall temperatures of turbochargers give different air temperature after the compressor and different exhaust gas temperature after the turbine at a same load point. The efficiencies are consequently affected. This can lead to deviations between the simulated and measured outlet temperatures of the turbocharger turbine and compressor. This deviation is larger during a transient load step because the temperatures of turbocharger walls change slowly due to the thermal inertia. Therefore, it is important to predict the temperatures of turbocharger walls and the outlet temperatures of the turbocharger working fluids in a turbocharged engine simulation.In the work described in this paper, a water-oil-cooled turbocharger was extensively instrumented with several thermocouples on reachable walls. The turbocharger was installed on a 2-liter gasoline engine that was run under different loads and different heat transfer conditions on the turbocharger by using insulators, an extra cooling fan, radiation shields and water-cooling settings. The turbine inlet temperature varied between 550 and 850 °C at different engine loads.The results of this study show that the temperatures of turbocharger walls are predictable from the experiment. They are dependent on the load point and the heat transfer condition of the turbocharger. The heat transfer condition of an on-engine turbocharger could be defined by the turbine inlet temperature, ambient temperature, oil heat flux, water heat flux and the velocity of the air around the turbocharger. Thus, defining the heat transfer condition and rotational speed of the turbocharger provides temperatures predictions of the turbocharger walls and the working fluids. This prediction enables increased precision in engine simulation for future work in transient operation.
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32.
  • Aghaali, Habib, 1981-, et al. (författare)
  • Turbocharged SI-Engine Simulation with Cold and Hot-Measured Turbocharger Performance Maps
  • 2012
  • Ingår i: Proceedings of ASME Turbo Expo 2012, Vol 5. - : ASME Press. - 9780791844717 ; , s. 671-679
  • Konferensbidrag (refereegranskat)abstract
    • Heat transfer within the turbocharger is an issue in engine simulation based on zero and one-dimensional gas dynamics. Turbocharged engine simulation is often done without taking into account the heat transfer in the turbocharger. In the simulation, using multipliers is the common way of adjusting turbocharger speed and parameters downstream of the compressor and upstream of the turbine. However, they do not represent the physical reality. The multipliers change the maps and need often to be different for different load points. The aim of this paper is to simulate a turbocharged engine and also consider heat transfer in the turbocharger. To be able to consider heat transfer in the turbine and compressor, heat is transferred from the turbine volute and into the compressor scroll. Additionally, the engine simulation was done by using two different turbocharger performance maps of a turbocharger measured under cold and hot conditions. The turbine inlet temperatures were 100 and 600°C, respectively. The turbocharged engine experiment was performed on a water-oil-cooled turbocharger (closed waste-gate), which was installed on a 2-liter gasoline direct-injected engine with variable valve timing, for different load points of the engine. In the work described in this paper, the difference between cold and hot-measured turbocharger performance maps is discussed and the quantified heat transfers from the turbine and to/from the compressor are interpreted and related to the maps.
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33.
  • Capitao Patrao, Alexandre, 1988, et al. (författare)
  • Numerical modeling of laminar-turbulent transition in an interconnecting compressor duct
  • 2022
  • Ingår i: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022. ; 2022:3, s. 2033-2044
  • Konferensbidrag (refereegranskat)abstract
    • Cryogenic hydrogen is being considered as a future aviation fuel since it eliminates CO2, CO, soot, sulphur, and unburnt hydrocarbons emissions. The storage temperature and high cooling capacity of cryogenic hydrogen also makes it a suitable coolant. In this paper a integrated heat exchanger in an interconnecting compressor duct (ICD) is analyzed with respect to heat transfer and transition.
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34.
  • Munjulury, Raghu Chaitanya, et al. (författare)
  • Knowledge-based future combat aircraft optimization
  • 2016
  • Ingår i: 30th Congress of the International Council of the AeronauticalSciences (ICAS 2016). - Bonn : International Council of Aeronautical Sciences (ICAS). - 9781510834552 ; , s. 273-280
  • Konferensbidrag (refereegranskat)abstract
    • Future combat aircraft inherently conceal all the components internally essentially for stealth reasons. The geometry is optimized for subsonic and supersonic flight area distribution and the components and payload to be fitted inside the aircraft. The basic requirements to accomplish are fuel consumption, mission profile, and military performance. Analytical methods comprise of a quick aerodynamic and structural optimization. The result obtained is then compared with multi-fidelity aero-structural analysis
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35.
  • Pandian Muthuramalingam, Vignesh, 1987 (författare)
  • MULTICOMPONENT SPRAY-TURBULENCE INTERACTION
  • 2018
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Blended fuels are gaining importance in automotive industry owing to stringent legislations for emissions. It is important to understand the fuel spray formed as a consequence of injecting blended fuels into the engine (for direct injection engines) and also the influence of fuel spray on combustion properties. Fuel sprays are sought to be understood by formulating and modelling the physical processes involved in its formation and testing the predictions obtained from models using computer simulations. Complementing this procedure, experiments are performed under predefined boundary conditions either in single or multi cylinder engines or in constant volume spray chambers when deeper insight into sprays is required. The experiments are used to validate the models and also report any newly observed physical phenomenon which can be then investigated using the models. This work presents the computaional and modelling efforts for multicomponent fuel sprays whose behavior is studied in constant volume combustion vessel. Lagrangian-Eulerian framework is followed where the liquid fuel is modelled using Lagrangian approach and the gas phase is modelled using Eulerian approach. The focus of this work is on Lagrangian liquid phase modelling and it's interactions with the gas phase. The spray modelling is done using VSB2 stochastic blob and bubble (VSB2) model which is developed with the aim of minimising tuning parameters by treating spray and it's submodels as one entity. The VSB2 model also removes overshoot or undershoot in predicted quantities by using relaxation equations based on thermodynamic equilibrium. The methods for modelling secondary breakup, evaporation and momentum transfer of liquid droplets are outlined in this work. Specifically computational method for differential evaporation in multicomponent fuel sprays is discussed. The VSB2 model is validated against experiments performed in constant volume combustion vessels for multicomponent fuel sprays. Differential evaporation was predicted corrrectly by the model within acceptable limits when compared to experiments on component gasoline-diesel fuel blend. Effects of non-ideal vapor liquid equilibrium on multicomponent fuel evaporation of ethanol and iso-octane blend was also studied, and the predictions showed reasonable agreement with experiment. Ethanol was observed to have a strong influence on iso-octane and deviation from ideal behavior was strong for higher ethanol percentage and in these cases ideal vapor liquid equilibrium was seen to predict incorrect results.
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36.
  • Rao, Anirudh Narayan, 1985, et al. (författare)
  • Influence of the numerical schemes on the flow states of a simplified heavy vehicle
  • 2018
  • Ingår i: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816. ; 2018-July, s. 731-734
  • Konferensbidrag (refereegranskat)abstract
    • Recent experiments [1, 2] in the wake of a simplified heavy vehicle (also know as a ground transportation system (GTS)) have shown that the flow topology remains invariant over a large range of Reynolds numbers [3.8 × 10 4 − 2.8 × 10 6 ]. This allows numerical techniques such as large eddy simulations (LES) to accurately predict the flow topology at low Reynolds numbers. While LES requires grids of higher spatial resolution; hybrid RANS/LES turbulence models are an alternate choice, where, accurate prediction of the flow is possible on coarser grids ([3, 4]). Numerical simulations are performed using LES and a hybrid turbulence model - partially-averaged Navier–Stokes (PANS) equations at Re H = 3.8 × 10 4 for a unified tractor-trailer geometry to compare the flow topologies in the near wake. The influence of the numerical schemes on the flow topology in the symmetry plane which is susceptible to bi-stable flow is investigated using PANS, and compared with the results from LES.
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37.
  • Sarmast, Sasan, et al. (författare)
  • Validation of the actuator line and disc techniques using the New Mexico measurements
  • 2016
  • Ingår i: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596. ; 753:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Actuator line and disc techniques are employed to analyse the wake obtained in the New Mexico wind turbine experiment. The New Mexico measurement campaign done in 2014 is a follow-up to the MEXICO campaign, which was completed in 2006. Three flow configurations in axial flow condition are simulated and both computed loads and velocity fields around the rotor are compared with detailed PIV measurements. The comparisons show that the computed loadings are generally in agreement with the measurements under the rotor's design condition. Both actuator approaches under-predicted the loading in the inboard part of blade in stall condition as only 2D airfoil data were used in the simulations. The predicted wake velocities generally agree well with the PIV measurements. In the experiment, PIV measurements are also provided close to the hub and nacelle. To study the effect of hub and nacelle, numerical simulations are performed both in the presence and absence of the hub geometry. This study shows that the large hub used in the experiment has only small effects on overall wake behaviour.
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38.
  • Xu, Kewei, 1992, et al. (författare)
  • Drag reduction of ship airflow using steady Coanda effect
  • 2022
  • Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 266
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper studies the steady Coanda effect for reducing the aerodynamic drag of the Chalmers ship model (CSM) using Large Eddy Simulation (LES) with Wall-Adapting Local-Eddy Viscosity (WALE) model. The flow control mechanism is explored, and the analysis of energy efficiency is conducted to evaluate the net benefit of the flow control. Validating the numerical methods, the predicted aerodynamic drag of the ship and pressure coefficients distribution on the baseline CSM agree well with the experimental measurements and the maximum discrepancy is 4.2%. In creating the flow control models, the hanger base of the baseline CSM is modified with a Coanda surface and two different sizes of jet-blowing slots, 1%h (hanger height) and 2%h, respectively. A drag reduction of 5.34% is achieved by the 1%h slot-size case. The 2%h slot-size case further increases the drag reduction to 6.22% but has doubled power consumption. It is found that vectoring vorticity towards the low-speed area on deck is effective for enhancing the energization. Finally, the analysis of energy efficiency indicates that the net benefit is achieved in both flow control cases, and the case with the 1%h slot size is 11.9% more efficient due to a stronger Coanda effect.
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39.
  • Berbyuk, Viktor, 1953 (författare)
  • Structural Dynamics Control, Third Edition
  • 2020
  • Bok (övrigt vetenskapligt/konstnärligt)abstract
    • Structural dynamics and especially one of its main problems, vibrations and vibration control, appear in vehicle engineering, high precision machines and mechanisms, robotics, civil engineering, wind turbines, biomechanics, and others. Over the last decades there has been much work concerned with the vibration control of different dynamical systems. The texbook “Structural Dynamics Control” aims at providing knowledge on modern methods and concepts of passive, semi-active and active vibration control, to cross the bridge between structural dynamics and control engineering, while providing an overview of the potential of smart materials, (magnetorheological fluids, magnetostrictive materials, and others), for sensing and actuating purposes in active vibration control. One of the aims of this textbook is to provide students and engineers with opportunity of becoming familiar with the standard methods of the classical calculus of variations, the linear quadratic regulator optimization methods, and modern optimal control theory with focus on their applications in structural dynamics for vibration attenuation and vibration suppression problems. The textbook consists of four main parts: Vibration dynamics, Passive and semi-active vibration control, Active and hybrid vibration control, and Applications. The textbook ends with the supplementary mathematics, list of Matlab codes and answers and hints for the exercises. The list of references consists of only those books and scientific papers which were used during preparation of the textbook or which have been recommended to stundents for additional information on a studied topic. The textbook is aimed at first towards graduate and postgraduate students following Master and PhD programmes related to structural dynamics, mechatronics, control engineering, automotive engineering, noise and vibrations. The only prerequisite for reading this book is basic knowledge in mechanics and some familiarity with vibrations, state space models and automatic control.
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40.
  • Brynskog, Erik, 1989 (författare)
  • Scoping Review on Validation Data for Submarining Prediction in Automotive Crashes
  • 2024
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Submarining, defined as “the lap belt slides over iliac crest with lap belt forces effecting the internal abdominal organs during forward displacement of the lower torso”, can lead to injuries related to belt-to-abdominal loading in frontal automotive crashes. To study this phenomena with physical, i.e. Anthropometric Test Devices (ATDs), or virtual, e.g. finite element human body models (FE-HBMs), one first needs to validate the predicted response of these models in submarining scenarios. This report presents a scoping review of the literature on existing validation data for submarining scenarios, to identify gaps in the available data and aid future research.
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41.
  • Cheemakurthy, Harsha, et al. (författare)
  • Fuzzy AHP-Based Design Performance Index for Evaluation of Ferries
  • 2022
  • Ingår i: Sustainability. - : MDPI AG. - 2071-1050. ; 14:6, s. 3680-3680
  • Tidskriftsartikel (refereegranskat)abstract
    • Within waterborne public transportation (WPT), one often observes a mismatch between the operational requirements and ferry characteristics. A method to holistically evaluate ferries with respect to local requirements could lead to tailored procurement and targeted refurbishment of existing fleet. In this study, we develop a structure for operational requirements and use it as a basis for a ferry evaluation methodology. The requirements’ structure follows a three-level hierarchy starting from broad vessel design to mandatory requirements to performance requirements. The performance requirements are based on the three pillars of sustainability, aided by commuter surveys carried out in Stockholm ferries, interviews with public transport providers (PTP) and previous literature. The evaluation of the ferry is performed using analytic hierarchic process (AHP) to convert the PTP’s subjective preferences and ferry performance into a single dimensionless index. Rules for quantification of performance metrics including social performance are proposed. The uncertainties associated with AHP are addressed by employing fuzzy AHP based on extent analysis and fuzzy AHP in combination with particle swarm optimization. Two applications including performance assessment of existing ferries and assembly of a modular ferry are discussed. The method can lead to objective decision making in ferry evaluation, potentially leading to a more efficient WPT.
  •  
42.
  • Cheemakurthy, Harsha, et al. (författare)
  • Lightweight Structural Concepts in Bearing Quasi-Static Ice Hull Interaction Loads
  • 2022
  • Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 10:3, s. 416-416
  • Tidskriftsartikel (refereegranskat)abstract
    • Lightweight ice-class vessels offer the possibility of increasing the payload capacity while making them comparable in energy consumption with non-ice-class vessels during ice-free periods. We approach the development of a lightweight hull by dividing ice–hull interactions into quasi-static loading and impact loading phases. Then, investigative outcomes of lightweight concepts for each loading phase may be combined to develop a lightweight ice-going hull. In this study, we focus on the quasi-static loading phase characteristic of thin first-year ice in inland waterways. We investigate metal grillages, sandwich structures and stiffened sandwich structures parametrically using the finite element method. The model is validated using previous experimental studies. In total over 2000 cases are investigated for strength and stiffness with respect to mass. The stiffened sandwich was found to be the most favorable concept that offered both a light weight as well as high gross tonnage. Further, significant parameters and their interactions and material differences for the three structural concepts were investigated and their trends discussed. The outcomes result in the creation of a viable pool of lightweight variants that fulfill the quasi-static loading phase. Together with outcomes from the impact loading phase, a lightweight ice-going hull may be developed.
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43.
  • Etikyala, Sreelekha, 1991 (författare)
  • Particulate Formation in Gasoline Direct Injection Engines
  • 2019
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Gasoline direct injection (GDI) engines are facing a great challenge because of the need to comply with increasingly stringent emission regulations while improving fuel economy. GDI engines are popularly known for their high fuel efficiency (by the standards of gasoline engines) and low emissions, enabling higher compression ratios and thus increased volumetric efficiency. Unfortunately, GDI engines tend to produce higher particulate number (PN) emissions than conventional port fuel injection (PFI) engines, mainly due to the challenges of in-cylinder liquid fuel injection. Cold starts, transients, and high loads account for a disproportionately high share of all PN emissions from GDI engines over a certification cycle. Understanding the mechanisms of PN formation during these stages is necessary for the further market penetration of GDI under the constraint of tighter emission standards. This knowledge becomes especially important when in future particles with sizes smaller than 10 nm are measured and legislated. This work presents experimental investigation of particulate emissions from a naturally aspirated single cylinder metal gasoline engine operated in a homogeneous configuration. The engine was modified to be capable of operating using DI, PFI, or both simultaneously. PFI was configured with a custom inlet manifold to inject about 50 cm upstream of cylinder head, forming a more homogeneous fuel-air mixture than would otherwise be possible. The experimental campaigns were structured to systematically isolate and study different PN formation mechanisms. Mixing quality was improved  ubstantially by using a small amount of upstream injection together with direct injection and could be controlled by varying the mass split between the direct and upstream injectors. It was found that using a small upstream injection when operating in GDI mode could reduce PN emissions by up to a factor of 10 while only modestly increasing fuel consumption. The chemical composition of the fuel could also strongly affect particulate emissions. Therefore, to find alternative ways of reducing PN emissions, experiments were conducted using a gasoline engine with fuel blends containing renewable oxygenates – either 10% (v/v) ethanol (EtOH) or 22% (v/v) ethyl tert-butyl ether (ETBE). It was observed that PN emissions was reduced using oxygenated fuels at low load for both PFI and DI operation, but not at higher loads where PN increased instead. Measurements of solid PN (SPN) emissions revealed that more soot was formed at high load along with an increase in emissions of volatile organic compounds (VOC). PN measurements were conducted using a DMS500 fast particle spectrometer supplied by Cambustion. In addition, solid particulate measurements were performed by passing exhaust samples through a thermodenuder and a catalyst to remove most of the volatile organic compounds (VOCs) from the raw emissions. The results indicated that wall-wetting is the dominant particulate formation mechanism inside the cylinder: fuel-wall interactions with the piston, cylinder walls, and valves during the fuel injection period account for a significant fraction of the PN content of raw exhaust.
  •  
44.
  • Jahedi, Mohammad, 1984-, et al. (författare)
  • Quenching a rotary hollow cylinder by multiple configurations of water-impinging jets
  • 2019
  • Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier. - 0017-9310 .- 1879-2189. ; 137, s. 124-137
  • Tidskriftsartikel (refereegranskat)abstract
    • Experiments have been conducted to analyze quenching of a hot rotary hollow cylinder by one and two rows of water-impinging jets. Sub-cooled water jets (ΔTsub = 45–85 K) with flow rate 8006 to 36,738 impinged on hollow cylinder with rotation speed 10 to 70 rpm at various initial wall superheat temperatures from 250 to 600ºC. Jet-to-jet and jet-to-surface spacing varied between 4 to 10d and 1.5 to 7d respectively and angular position of impinging jets were tested from 0 to 135º. Effectiveness of the defined parameters on stagnation point’s local average heat flux was found lower in the film and nucleate boiling compare to transition boiling regime where rotation speed had the highest impact. Characteristic of maximum heat flux (MHF) at stagnation point and upwash flow point were analyzed based on surface heat flux, time and temperature corresponding to MHF. Same maximum heat flux levels were captured in the both points which reveals importance of the flow behavior at the upwash flow point. The effectiveness of the parameters to improve average heat transfer was studied based on cooling area of each water impingingjet in the multiple configurations. Higher average heat transfer was obtained by increasing flow rate and subcooling temperature and lower initial wall superheat temperature corresponding to onset of transition boiling regime.
  •  
45.
  • Matrisciano, Andrea, 1986, et al. (författare)
  • Development of a Computationally Efficient Tabulated Chemistry Solver for Internal Combustion Engine Optimization Using Stochastic Reactor Models
  • 2020
  • Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 10:24, s. 1-31
  • Tidskriftsartikel (refereegranskat)abstract
    • The use of chemical kinetic mechanisms in computer aided engineering tools for internal combustion engine simulations is of high importance for studying and predicting pollutant formation of conventional and alternative fuels. However, usage of complex reaction schemes is accompanied by high computational cost in 0-D, 1-D and 3-D computational fluid dynamics frameworks. The present work aims to address this challenge and allow broader deployment of detailed chemistry-based simulations, such as in multi-objective engine optimization campaigns. A fast-running tabulated chemistry solver coupled to a 0-D probability density function-based approach for the modelling of compression and spark ignition engine combustion is proposed. A stochastic reactor engine model has been extended with a progress variable-based framework, allowing the use of pre-calculated auto-ignition tables instead of solving the chemical reactions on-the-fly. As a first validation step, the tabulated chemistry-based solver is assessed against the online chemistry solver under constant pressure reactor conditions. Secondly, performance and accuracy targets of the progress variable-based solver are verified using stochastic reactor models under compression and spark ignition engine conditions. Detailed multicomponent mechanisms comprising up to 475 species are employed in both the tabulated and online chemistry simulation campaigns. The proposed progress variable-based solver proved to be in good agreement with the detailed online chemistry one in terms of combustion performance as well as engine-out emission predictions (CO, CO2, NO and unburned hydrocarbons). Concerning computational performances, the newly proposed solver delivers remarkable speed-ups (up to four orders of magnitude) when compared to the online chemistry simulations. In turn, the new solver allows the stochastic reactor model to be computationally competitive with much lower order modeling approaches (i.e., Vibe-based models). It also makes the stochastic reactor model a feasible computer aided engineering framework of choice for multi-objective engine optimization campaigns.
  •  
46.
  • Paulsson, Björn, et al. (författare)
  • INNOTRACK -- Innovative Track System --- A unique approach from infrastructure managers and competitive track supply industry to develop the innovative products of the future
  • 2006
  • Ingår i: 7th World Congress on Railway Research. ; , s. 12 pp-
  • Konferensbidrag (refereegranskat)abstract
    • InnoTrack is a R&D project that has gathered 35 European participants to a joint project. Several leading rail infrastructure mangers (IM) and industrial suppliers are partners in the consortium. This initiative gives a unique opportunity to concentrate on research issues that will contribute to a reduction of rail infrastructure Life Cycle Cost (LCC) and doing so in close cooperation between rail IMs and industry suppliers, the two major players in the rail industry.. In addition, several of the leading European universities in the area are actively participating in the project.The EC White paper on Sustainable Transport calls for rail operators to:•Double passenger traffic & triple freight traffic by 2020•Reduce LCC by 30%The Railway Business Scenario 2020 also calls for railways to capture 15% of freight & 12% of the passenger market.To achieve these objectives, investment alone is not sufficient, but has to be complemented by significant innovation and technology transfer. This can only be achieved in a very close cooperation between IMs and industry suppliers. In this process, it is essential that the IMs, as the end users, set out their priorities and needs, at a European Level, to solve critical problems for achieving the white paper objectives.This will be done by performing research on four key topics:•Track support structure•Switches and Crossings•Rails•Logistics for track maintenance and renewalTo ensure that cost reductions can be consistently evaluated across Europe, InnoTrack will also devise an innovative generic methodology for LCC calculation, based on best LCC practices at a EU level, to be offered IMs across Europe.For each of the research topics, InnoTrack will:•Analyse root causes of the identified issues on a European scale taking into account the effect of different duty conditions whilst providing product and service solutions for cheaper and longer lasting tracks•Draw together common European specifications regarding Reliability, Availability, Maintainability and Safety (RAMS) combined with LCC•Provide innovative solutions to reduce failure rates and decrease LCC of material, equipment, machinery and systemsFinally, InnoTrack will assure a wide dissemination through UIC and UNIFE, two organisations representing IMs and industry.The current paper gives an overview of the InnoTrack project.
  •  
47.
  • Ringsberg, Jonas, 1971 (författare)
  • Foreword
  • 2018
  • Ingår i: Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment. - : SAGE Publications. - 2041-3084 .- 1475-0902. ; 232:1, s. 3-4
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
  •  
48.
  • Wang, Weizhi, et al. (författare)
  • Estimation of numerical uncertainty in computational fluid dynamics simulations of a passively controlled wave energy converter
  • 2018
  • Ingår i: Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment. - : SAGE Publications. - 2041-3084 .- 1475-0902. ; 232:1, s. 71-84
  • Tidskriftsartikel (refereegranskat)abstract
    • The wave loads and the resulting motions of floating wave energy converters are traditionally computed using linear radiation–diffraction methods. Yet for certain cases such as survival conditions, phase control and wave energy conver- ters operating in the resonance region, more complete mathematical models such as computational fluid dynamics are preferred and over the last 5 years, computational fluid dynamics has become more frequently used in the wave energy field. However, rigorous estimation of numerical errors, convergence rates and uncertainties associated with computa- tional fluid dynamics simulations have largely been overlooked in the wave energy sector. In this article, we apply formal verification and validation techniques to computational fluid dynamics simulations of a passively controlled point absor- ber. The phase control causes the motion response to be highly nonlinear even for almost linear incident waves. First, we show that the computational fluid dynamics simulations have acceptable agreement to experimental data. We then present a verification and validation study focusing on the solution verification covering spatial and temporal discretiza- tion, iterative and domain modelling errors. It is shown that the dominating source of errors is, as expected, the spatial discretization, but temporal and iterative errors cannot be neglected. Using hexahedral cells with low aspect ratio and 30 cells per wave height, we obtain results with less than 5% uncertainty in motion response (except for surge) and restraining forces for the buoy without phase control. The amplified nonlinear response due to phase control caused a large increase in numerical uncertainty, illustrating the difficulty to obtain reliable solutions for highly nonlinear responses, and that much denser meshes are required for such cases.
  •  
49.
  • Wilewska-Bien, Magda, 1977, et al. (författare)
  • Phosphorus flows on ships: Case study from the Baltic Sea
  • 2019
  • Ingår i: Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment. - : SAGE Publications. - 2041-3084 .- 1475-0902. ; 233:2, s. 528-539
  • Tidskriftsartikel (refereegranskat)abstract
    • Material flow analysis is used to identify and quantify the flow of phosphorus (P) in ship-generated food waste and wastewater. Passenger, cruise, RoPax and cargo ships in the Baltic Sea were investigated in three scenarios: (1) if all waste is discharged to sea, (2) if all waste is disposed of ashore or (3) if the food waste fraction is disposed of ashore and wastewater is treated on-board. About 107 tonnes of P is generated annually in the waste streams, with highest contribution of approximately 62 tonnes (58%) from wastewater in the ship-category RoPax. Approximately 24 tonnes of P is contained in the food waste generated by the ships in the study. Forthcoming regulations over allowed nutrient concentrations in sewage will lead to 80% reduction in P from passenger ships and can reduce about 31 tonnes of P entering the Baltic Sea environment. If both sewage and grey water instead are offloaded in port reception facilities, about 76 tonnes of P-reduction to the sea can be reached. As most phosphorus recovery practices currently only are available on land it is recommended to direct the waste streams to port reception facilities for further treatment ashore.
  •  
50.
  • Wramner, Lina, 1979 (författare)
  • Dual-mass flywheels with tuned vibration absorbers for application in heavy-duty truck powertrains
  • 2020
  • Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 234:10-11, s. 2500-2508
  • Tidskriftsartikel (refereegranskat)abstract
    • As the heavy-duty combustion engine development goes towards lower rotational speeds and higher cylinder pressures, the torsional vibrations increase. There is therefore a need to identify and study new types of vibration absorbers that can reduce the level of torsional vibrations transmitted from the engine to the gearbox. In this work, the concept of a dual-mass flywheel combined with a tuned vibration absorber is analysed. The tuned vibration absorber efficiently reduces the vibration amplitudes for engine load frequencies near the tuning frequency, but it also introduces an additional resonance into the system. By placing the tuned vibration absorber on an intermediate flange between the two dual-mass flywheels, the introduced resonance frequency will be lower than the tuning frequency and a resonance in operating engine speed range can be avoided. Numerical simulations are used to show how the torsional vibration amplitudes in a heavy-duty truck powertrain are affected by the tuned vibration absorber and how the different parameters of the tuned vibration absorber and the dual-mass flywheel affect the torsional vibrations and the resonance frequencies.
  •  
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