| 1. |
- Abrahamsson, Per, 1985, et al.
(författare)
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An infield study of road snow properties related to snow-car adhesion and snow smoke
- 2018
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Ingår i: Cold Regions Science and Technology. - : Elsevier BV. - 0165-232X. ; 145, s. 32-39
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 Elsevier B.V. This article analyzes the properties of snow on the road related to the formation of snow smoke and contamination of the car. The increased usage of sensors for active safety in modern cars increases the importance of understanding contamination of the car body. The analysis characterizes snow in terms of shape, size, and adhesiveness. The data is related to changing weather conditions and experienced car contamination. Several different sampling positions were chosen both on the road and on the car. The temperatures during the days of measurements ranged from − 4 °C to − 12 °C, which gave cold and dry snow. Data on size and shape was obtained via microscope analysis. An infield adhesion tester for snow adhesion measurements was built. The microscope analysis showed that the shape of the snow particles in the tire tracks and on the car body generally had a rounded structure. Even soon after a fresh snow fall, the rounded shapes remained in these positions. This structure was found to change to a more edgy hexagonal shape during hoar formation on the existing snow. The particle size distributions from tire tracks, from suspended snow smoke, and from different positions on the car were analyzed. It was found that smaller particles travel higher and are more prone to enter the wake behind the car to stick to the back parts of the vehicle. The adhesion test gave little distinction between the different snow types and samples. The adhesion force was found to range from 2 to 12 dyne.
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| 2. |
- Abrahamsson, Per, 1985, et al.
(författare)
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Analysis of mesoscale effects in high-shear granulation through a computational fluid dynamics–population balance coupled compartment model
- 2018
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Ingår i: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 36, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- There is a need for mesoscale resolution and coupling between flow-field information and the evolution of particle properties in high-shear granulation. We have developed a modelling framework that compartmentalizes the high-shear granulation process based on relevant process parameters in time and space. The model comprises a coupled-flow-field and population-balance solver and is used to resolve and analyze the effects of mesoscales on the evolution of particle properties. A Diosna high-shear mixer was modelled with microcrystalline cellulose powder as the granulation material. An analysis of the flow-field solution and compartmentalization allows for a resolution of the stress and collision peak at the impeller blades. Different compartmentalizations showed the importance of resolving the impeller region, for aggregating systems and systems with breakage. An independent study investigated the time evolution of the flow field by changing the particle properties in three discrete steps that represent powder mixing, the initial granulation stage mixing and the late stage granular mixing. The results of the temporal resolution study show clear changes in collision behavior, especially from powder to granular mixing, which indicates the importance of resolving mesoscale phenomena in time and space.
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| 3. |
- Abrahamsson, Per, 1985
(författare)
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Continuum modeling of particle flows in high shear granulation
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High shear granulation is an important process in the pharmaceutical industry. The aim of the process is to produce granules with specific properties, like size and hardness, from powder mixtures. The properties of the granules are determined by the flow field in the mixer. The most common approach taken to modeling the flow includes tracking the forces on each individual particle and resolving each occurring collision. This gives detailed information but the computational cost restricts this use to small-scale equipment. Continuum modeling of particle flows means that averages are made to form a continuous flow rather than tracking individual entities. The problem that arises in this procedure is to correctly describe the transfer rates of mass and momentum in the system. The focus of the present work is on evaluating the previously used continuum model and investigating other possible techniques that have not yet been used in this application. Results show that the continuum model currently being used has a promising parameterization for describing the overall effect on the flow field due to the particle property changes that occur during granulation. The model is, however, not capable of adequately resolving the flow field in the important regions close to the walls and the impeller where the particle volume fraction is high. When solving these regions, the theory used at present suffers a strong spatial resolution dependence on the solution. The present theory is developed for low particle loadings. A critical review was made to investigate available modifications to the modeling framework for high volume fraction granular flows. Although there is no full solution to the problem the investigation shows that promising improvements to the theory are available.
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| 4. |
- Abrahamsson, Per, 1985, et al.
(författare)
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CONTINUUM MODELING OF PARTICLE FLOWS IN HIGH SHEAR GRANULATION
- 2013
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Ingår i: 6th International Granulation Workshop.
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Konferensbidrag (refereegranskat)abstract
- High shear granulation (HSG) is a common process in the pharmaceutical industry. A better understanding of the flow conditions of powders and granulates in large-scale HSG equipment is crucial for constructing predictive models. The staggering amount of particles in the process makes the use of continuum flow models highly attractive. This article discusses the possibilities and problems in using continuum modelling in HSG systems and evaluates some of the available modelling approaches. We examine several dense granular flow models studying both the underlying theory and how they perform in practice. The studied models are the frictional model by Shaeffer [1], modifications to the transport coefficients that describe the solid phase stresses similar to those used in Khain and Meerson [2], and the framework developed by Jop et.al. [3] using a depth-averaged flow model for constant solid volume fraction flows.The model by Shaeffer has previously been used with the conclusion that the solid phase stresses are underestimated [4]. We show theoretically and in practice that this approach is not appropriate due to the strong resolution dependence of the model. The approach taken by Khain and Meerson, among others, to try to modify expressions from rapid granular flow to also be valid in the dense region is attractive from a theoretical point of view. Making use of the rigorous framework of kinetic theory, the applicability of a number of such models to HSG has been evaluated. The modelling framework developed by Jop et.al was used in disc impeller HSG equipment. The results show that the model can well predict the behaviour of the solid-phase viscosity of the dense granular flow. The model is nevertheless restricted to constant volume fraction flows and needs to be expanded to include a varying volume fraction. We conclude in this paper that continuum modelling of HSG has a promising outlook but there is a need to develop better models for the dense regions of the flow. We also give and evaluate some of the options available for treating these regions.
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| 5. |
- Abrahamsson, Per, 1985
(författare)
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Continuum modelling of particle flows in high shear granulation
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High shear granulation is an important process in the pharmaceutical industry. The aim of the process is to produce granules with specific properties, like size and hardness, from powder mixtures. The properties of the granules are determined by the flow field in the mixer. The most common approach taken to modelling the flow in a mixer includes tracking the forces on each individual particle and resolving each occurring collision. This gives detailed information, but the computational cost restricts this use to small-scale equipment. Continuum modelling of particle flows means that averages are made to form a continuous flow rather than tracking individual entities. The problem that arises in this procedure is correctly describing the transfer rates of mass and momentum in the system. The focus of the research in this thesis is on evaluating previously used continuum models, and finding and developing new approaches. The connection between flow field information and the evolution of particle properties is also studied through the development of a compartment model.Results show that the continuum model currently being used has a promising parameterization for describing the overall effect on a flow field caused by particle property changes that occur during granulation. The model is; however, not capable of adequately resolving the flow field in the important regions close to the walls and the impeller of the vessel where the particle volume fraction is high. A rheology-like model is used to improve the dense granular flow regions, while the theory for the more dilute parts is improved via kinetic theory models modified for inelasticity and improved for its validity in the transition region to dense flows.
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| 6. |
- Abrahamsson, Per, 1985, et al.
(författare)
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On continuum modeling using kinetic-frictional models in high shear granulation
- 2014
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Ingår i: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 13:1, s. 124-127
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Tidskriftsartikel (refereegranskat)abstract
- In this short communication we explain and demonstrate why extreme caution has to be taken when applying conventional kinetic-frictional closures to continuum modeling of high shear granulation (HSG). By conventional models, we refer to closure laws where the kinetic and frictional stresses are summed up in order to get the total stress field. In a simple dense sheared system of a Couette shear cell, we study how the lack of scale separation affects the model predictions, both quantitatively and qualitatively. We show here that the spatial resolution has a significant effect on the magnitude of the kinetic and frictional contributions to the solid phase stresses. With this new investigation and previous studies of HSG it is concluded that conventional kinetic-frictional models are inadequate for continuum modeling of HSG.
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| 7. |
- Abrahamsson, Per, 1985, et al.
(författare)
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On continuum modelling of dense inelastic granular flows of relevance for high shear granulation
- 2016
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 294, s. 323-329
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Tidskriftsartikel (refereegranskat)abstract
- This article investigates a number of possible formulations of a continuum description for modelling dense inelastic granular flows. The revised Enskog theory (RET) for expressing the granular temperature and formulation of transport coefficients has been used within the continuum framework. The framework assumes particles as inelastic spheres and can describe a granular system at a wide range of volume fractions. The transport coefficients depend on the volume fraction through a modified expression for the radial distribution function. The proposed radial distribution function is based on previous studies on the behaviour of the shear viscosity in which an earlier divergence of the latter compared to the other transport coefficients has been demonstrated for sheared dense granular systems. Our results show that the newly developed radial distribution function maintains the ability of RET to predict the occurrence of instabilities in a homogeneous cooling granular gas. The introduced function also improves predictions for the velocity and volume fraction profiles in a Couette cell dense shear flow. Thus the proposed formulation shows promising features in terms of improving predictions for volume fractions relevant in high shear granulators. We have also observed that a different formulation may be needed for the densest regions.
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| 8. |
- Abrahamsson, Per, 1985, et al.
(författare)
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On the continuum modeling of dense granular flow in high shear granulation
- 2014
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 268, s. 339-346
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Tidskriftsartikel (refereegranskat)abstract
- This article addresses the subject of continuum modeling of dense granular flows with an application in high shear granulation. The possible use of continuum models and their ability to reproduce correct dynamics of such flows has been a subject of debate for a long time in the literature, and no consensus has been achieved so far. In this paper, we examine and compare two ways for making it possible to study dense granular flows in a continuum framework: the one that considers the stress tensor of a particulate phase as a sum of frictional and kinetic-collisional terms and the one that is based on modification of transport coefficients of the kinetic theory of granular flow. The latter framework is based on an analogy with molecular systems and how they behave at the phase transition from a liquid to a crystalline state. We show here that the formulation proposed in this work is able to correctly capture the phase transition and coexistence of solid-like and fluid-like phases in dense granular flows. This is in contrast to the model with added friction where the stress-strain dependence is shown to give a qualitatively different behavior compared to experimental data.
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| 9. |
- Abrahamsson, Per, 1985, et al.
(författare)
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Parameter study of a kinetic-frictional continuum model of a disk impeller high-shear granulator
- 2013
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 238, s. 20-26
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Tidskriftsartikel (refereegranskat)abstract
- A disk impeller high shear granulator was modeled with a kinetic-frictional continuum model. A parameter study was made and the parameterization of the equations was assessed to investigate if the model is suited for modeling high shear granulation. A dry granule mixing was studied and the parameters investigated were the particle diameter, the angle of internal friction, the particle-particle restitution coefficient, the particle density, the particle velocity boundary condition, the packing limit and the numerical parameter frictional packing limit. All the particle related parameters can be expected to change during a granulation. The flow field prediction of the model is in agreement with the behavior described by Knight et al. (2001), showing a rigid torus. This is in contrast to a discrete element model simulation that predicts inner rotation within the torus (Gantt and Gatzke 2006). The general flow field of this system is fairly insensitive to all parameter changes, except a change to no slip boundary condition for the particle phase, even though several parameters significantly affect the solid phase viscosity. The model was used to predict the change in impeller torque when going from mixing a dry powder to a wet system. It is shown that the models have some potential for qualitative descriptions of the wet state. (
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| 10. |
- Cederblad, Lars, et al.
(författare)
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Classification of Hypoglycemic Events in Type 1 Diabetes Using Machine Learning Algorithms
- 2023
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Ingår i: Diabetes Therapy. - : Springer Nature. - 1869-6953 .- 1869-6961. ; 14:6, s. 953-965
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Tidskriftsartikel (refereegranskat)abstract
- IntroductionTo improve the utilization of continuous- and flash glucose monitoring (CGM/FGM) data we have tested the hypothesis that a machine learning (ML) model can be trained to identify the most likely root causes for hypoglycemic events.MethodsCGM/FGM data were collected from 449 patients with type 1 diabetes. Of the 42,120 identified hypoglycemic events, 5041 were randomly selected for classification by two clinicians. Three causes of hypoglycemia were deemed possible to interpret and later validate by insulin and carbohydrate recordings: (1) overestimated bolus (27%), (2) overcorrection of hyperglycemia (29%) and (3) excessive basal insulin presure (44%). The dataset was split into a training (n = 4026 events, 304 patients) and an internal validation dataset (n = 1015 events, 145 patients). A number of ML model architectures were applied and evaluated. A separate dataset was generated from 22 patients (13 ‘known’ and 9 ‘unknown’) with insulin and carbohydrate recordings. Hypoglycemic events from this dataset were also interpreted by five clinicians independently.ResultsOf the evaluated ML models, a purpose-built convolutional neural network (HypoCNN) performed best. Masking the time series, adding time features and using class weights improved the performance of this model, resulting in an average area under the curve (AUC) of 0.921 in the original train/test split. In the dataset validated by insulin and carbohydrate recordings (n = 435 events), i.e. ‘ground truth,’ our HypoCNN model achieved an AUC of 0.917.ConclusionsThe findings support the notion that ML models can be trained to interpret CGM/FGM data. Our HypoCNN model provides a robust and accurate method to identify root causes of hypoglycemic events.
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