| 1. |
- Yang, Jikuang, 1948
(författare)
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Injury Biomechanics and Protective Systems in Car-to-Pedestrian Collisions
- 2001
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Ingår i: Hunan Daxue Xuebao/Journal of Hunan University Natural Sciences. - 1674-2974. ; 28:3, s. 69-78
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Tidskriftsartikel (refereegranskat)abstract
- The injury biomechanics of pedestrians in vehicle impacts and research approaches are described in this paper. Of which include identification of injury patterns in car pedestrian collisions, determination of injury mechanisms and body segment tolerance levels, development of method and techniques for injury assessment and safety system evaluation. The possible protective countermeasures are summarized and further studies on pedestrian protection are proposed.
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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, 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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| 4. |
- Ahmad, Alireza, et al.
(författare)
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Scaling granular material with polygonal particles in discrete element modeling
- 2023
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Ingår i: Particuology. - : Elsevier BV. - 1674-2001 .- 2210-4291. ; 75, s. 151-164
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Tidskriftsartikel (refereegranskat)abstract
- Despite advancements in computational resources, the discrete element method (DEM) still requires considerable computational time to solve detailed problems, especially when it comes to the large-scale models. In addition to the geometry scale of the problem, the particle shape has a dramatic effect on the computational cost of DEM. Therefore, many studies have been performed with simplified spherical particles or clumps. Particle scaling is an approach to increase the particle size to reduce the number of particles in the DEM. Although several particle scaling methods have been introduced, there are still some disagreements regarding their applicability to certain aspects of problems. In this study, the effect of particle scalping on the shear behavior of granular material is explored. Real granular particles were scanned and imported as polygonal particles in the direct shear test. The effect of particle size distribution, particle angularity, and the amount of scalping were investigated. The results show that particle scalping can simulate the correct shear behavior of the model with significant improvement in computational time. Also, the accuracy of the scalping method depends on the particle angularity and particle size range.
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| 5. |
- Aronsson, Jesper, 1985, et al.
(författare)
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Modeling and scale analysis of gaseous fuel reactors in chemical looping combustion systems
- 2017
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Ingår i: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 35, s. 31-41
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates the up-scaling to commercial scale of chemical looping combustion (CLC); a next-generation technology for carbon capture and storage. Focus lies on the bottom bed, which is considered to be the critical region in up-scaling due to its large solids inventory combined with relatively inefficient gas-solids contact. Two CLC reactors of vastly different size (bench and utility scale) are studied in order to discern the difference in effects related to up-scaling. A 1-dimensional model is used in order to simulate the units studied. The model considers kinetics dependent on the degree of oxidation of the oxygen carrier and a population distribution of the oxygen carriers, whose mixing accounts for both convective and dispersive transport. The model is validated against bench scale data and applied to evaluate the performance of a 1000 MWth CLC fuel reactor using either syngas or methane as fuel.Using the model, sensitivity analyses are carried out to depict the effect on the fuel conversion of several parameters such as solids circulation, oxygen carrier reactivity, bed height and maximum bubble size allowed. It is shown that mass transfer of gas from bubbles to the emulsion phase represents a strongly limiting factor for fuel conversion in the bottom bed of utility scale fuel reactors.
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| 6. |
- Gerber, Stephan, et al.
(författare)
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A two dimensional Euler–Lagrangian model of wood gasification in a charcoal bed—Part II: Parameter influence and comparison
- 2017
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Ingår i: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 35, s. 22-30
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Tidskriftsartikel (refereegranskat)abstract
- A Euler–Lagrangian simulation was employed for a comprehensive parameter study of wood gasification in a fluidized charcoal bed. The parameters that were varied include the initial bed temperature, fuel mass flow rate, inert tar fraction, and kinetic energy losses caused by particle–particle and particle–wall collisions. The results of each parameter variation are compared with a base scenario, previously described in detail in Part I of this study (Gerber & Oevermann, 2014). The results are interpreted by comparing the reactor outlet temperature, averaged particle temperature, overall wood mass, overall charcoal mass, concentrations of several gaseous species, and axial barycenter data for particles obtained with different sets of parameters. The inert tar fraction and fuel mass flow rate are the most sensitive parameter, while the particle–particle and particle–wall contact parameters have only a small impact on the results. Increasing the reactive tar components by 19% almost doubled the amount of reactive tars at the reactor outlet, while decreasing the restitution coefficients of the particle collisions by 0.2 results in higher overall gas production but almost no change in bed height. Herein, our numerical results are discussed in detail while assessing the model restrictions.
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| 7. |
- Khalilitehrani, Mohammad, 1984, et al.
(författare)
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Characterization of force networks in a dense high-shear system
- 2018
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Ingår i: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 38, s. 215-221
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Tidskriftsartikel (refereegranskat)abstract
- We detect the strong force networks in a dense high shear system and we study their structure and stability in response to the variation of the shearing rate. The presence of strong force networks, which are usually of heterogeneous structure, restricts particle movements and can impose non-local mechanisms of momentum transfer. We identify such networks in a dense high shear system through the algorithm of community detection. Moreover, we explain the association between the mechanisms of momentum transfer and the structure, population, strength and stability of the force networks by tracking the spatial and temporal evolution of the detected networks. In addition, we show that the assumption of a monodispersed assembly of particles leads to an unrealistic enlargement of the force networks, underestimating both the rate of energy dissipation and the rate of mixing.
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| 8. |
- Liu, Hailong, et al.
(författare)
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A simulation study of airborne wear particles from laboratory wheel-rail contacts
- 2016
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Ingår i: Particuology. - : Elsevier. - 1674-2001 .- 2210-4291.
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory measurements of airborne particles from sliding contacts are often performed using a tribometer located in a ventilation chamber. Although knowledge of particle transport behavior inside the chamber is required because it can influence the analysis of measurements, this knowledge is lacking. A numerical model was built based on the same geometry as a pin-on-disc measurement system to explain particle transport behavior inside the chamber and to determine the deviation between real amounts of generated and measured particles at the outlet. The effect of controlled flow conditions on the airflow pattern and particle transport inside the chamber was studied for different experimental conditions. Calculations show that a complex airflow pattern is formed by the spinning disc, and that it differs for each rotational speed. Simulation results reveal that particle transport in the chamber is governed mainly by the airflow pattern. The deposition velocity in the chamber was estimated and the possibility that part of the generated particles would remain in the chamber was studied. This led to an approximate estimation of particle loss rate. A comparison between experimental and simulated results with respect to the particle mass flow rate close to the outlet yields a reference factor of 0.7, which provides an indication of the difference between measured and real values.
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| 9. |
- Purnomo, Victor, 1992, et al.
(författare)
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New approach for particle size and shape analysis of iron-based oxygen carriers at different oxidation degrees
- 2024
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Ingår i: Particuology. - : Elsevier. - 2210-4291 .- 1674-2001. ; 90, s. 493-503
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Tidskriftsartikel (refereegranskat)abstract
- One of the crucial issues in the chemical looping technology lies in its bed material: the oxygen carrier. Particle size analysis of an oxygen carrier is important since in a fluidized bed the material can only work well within a specific size range. While the favorable size ranges for oxygen carrier materials have already been reported, none of the published studies has analyzed the particle size and shape of oxygen carriers in detail. Furthermore, the effect of oxygen carriers’ oxidation degree on such properties has not been considered either. This study aimed to report the particle size and shape analysis of five iron-based oxygen carriers, one natural ore, one synthetic material, and three residue products, at different oxidation degrees using dynamic image analysis (DIA). The oxygen carriers were prepared at different mass conversion degrees in a fluidized bed batch reactor. The size distribution, sphericity, and aspect ratio of the oxygen carrier particles were examined experimentally using a Camsizer instrument. Our results show that the DIA method was successfully able to analyze the particle size and shape of our oxygen carriers with satisfying accuracy for comparison. The oxidation state of the investigated materials seems to only affect the particle size and shape of oxygen carriers to a minor extent. However, exposures to redox cycles in a fluidized bed reactor may alter the particle size and shape of most oxygen carriers.
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| 10. |
- Ren, Guanlong, et al.
(författare)
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CFD investigation of structural effects of internal gas intake on powder conveying performance in fuel supply systems for aerospace engines
- 2024
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Ingår i: Particuology. - 2210-4291 .- 1674-2001. ; 92, s. 140-154
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Tidskriftsartikel (refereegranskat)abstract
- Optimal design of gas intake in powder fuel supply systems is crucial for performance of aerospace engines. There is little research on the impact of intake structure on powder conveying performance. Three novel internal intakes were proposed, which are spherical, cube-shaped, and dome-shaped. After validation, CFD simulations demonstrate that fluctuation of mass flow rate of powders in the dome-shaped intake is reduced by about 73.3% compared with the annular external one. Variation trends of phase velocities are similar for the spherical and cube-shaped intakes, while those are similar for the annular external and dome-shaped internal intakes. Fluctuation of area of gas zone for the annular external and spherical internal intakes is larger than that for the cube-shaped and dome-shaped internal intakes. Pressure and relative pressure drop in the fluidization chamber have a stable stage, and fluctuation of relative pressure drop is small when dome-shaped internal intake is used.
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