| 1. |
- Andersson, Håkan, et al.
(författare)
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Simulation of leakage flow through dynamic sealing gaps in hydraulic percussion units using a co-simulation approach
- 2021
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Ingår i: Simulation (San Diego, Calif.). - : Elsevier B.V.. - 1569-190X .- 1878-1462. ; 111
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a previously developed co-simulation method has been expanded to also simulate the dynamic behaviour of sealing gap regions in hydraulic percussion units. This approach is based on a 1D system model representing the fluid components and a 3D finite element model representing the structural parts of a hydraulic hammer. The sealing gap is a fundamental feature of a percussion unit, where the reciprocating motion of the piston is generated by the valve mechanism of the sealing gap. When the gap is closed it will prevent fluid flow between regions of different pressure levels. However, a small leakage flow through the gap will always occur which size depends on the clearance and the position of the piston. The method proposed here will take the structural motion and deformation into consideration when calculating the leakage flow. The deformed state of the structure is approximated by a cylindrical surface, in a least square manner, and communicated through the co-simulation interface to the fluid simulation module, and then used when calculating the leakage flow. This method aims at a more accurate simulation of the leakage flow that will not only yield a more realistic description of the mechanism on the local level, but also a more accurate estimation of global parameters such as overall performance and efficiency. The results indicate that the simulated leakage flow will decrease when dynamic gaps are used in comparison to static gaps, which is a consequence of the deformed structure that will generate smaller clearances. The leakage flow for the dynamic gaps will even be lower than for the static perfectly concentric case, mainly due to the reduction of clearances. The results also indicate that the dynamic eccentricity does not have a major influence on the leakage flow. The outcome from this study highlights the potentials of the described co-simulation approach for analysing the dynamics of the sealing gaps in a hydraulic percussion unit (i.e. gap heights, eccentricity ratios, etc.) including the evaluation of leakage flows and its impact on the overall performance. © 2021
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| 2. |
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| 3. |
- Cesaroni, Giulia, et al.
(författare)
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Long term exposure to ambient air pollution and incidence of acute coronary events : prospective cohort study and meta-analysis in 11 European cohorts from the ESCAPE Project
- 2014
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Ingår i: The BMJ. - : BMJ. - 1756-1833. ; 348, s. f7412-
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Tidskriftsartikel (refereegranskat)abstract
- Objectives To study the effect of long term exposure to airborne pollutants on the incidence of acute coronary events in 11 cohorts participating in the European Study of Cohorts for Air Pollution Effects (ESCAPE). Design Prospective cohort studies and meta-analysis of the results. Setting Cohorts in Finland, Sweden, Denmark, Germany, and Italy. Participants 100 166 people were enrolled from 1997 to 2007 and followed for an average of 11.5 years. Participants were free from previous coronary events at baseline. Main outcome measures Modelled concentrations of particulate matter <2.5 mu m (PM2.5), 2.5-10 mu m (PMcoarse), and <10 mu m (PM10) in aerodynamic diameter, soot (PM2.5 absorbance), nitrogen oxides, and traffic exposure at the home address based on measurements of air pollution conducted in 2008-12. Cohort specific hazard ratios for incidence of acute coronary events (myocardial infarction and unstable angina) per fixed increments of the pollutants with adjustment for sociodemographic and lifestyle risk factors, and pooled random effects meta-analytic hazard ratios. Results 5157 participants experienced incident events. A 5 mu g/m(3) increase in estimated annual mean PM2.5 was associated with a 13% increased risk of coronary events (hazard ratio 1.13, 95% confidence interval 0.98 to 1.30), and a 10 mu g/m(3) increase in estimated annual mean PM10 was associated with a 12% increased risk of coronary events (1.12, 1.01 to 1.25) with no evidence of heterogeneity between cohorts. Positive associations were detected below the current annual European limit value of 25 mu g/m(3) for PM2.5 (1.18, 1.01 to 1.39, for 5 mu g/m(3) increase in PM2.5) and below 40 mu g/m(3) for PM10 (1.12, 1.00 to 1.27, for 10 mu g/m(3) increase in PM10). Positive but non-significant associations were found with other pollutants. Conclusions Long term exposure to particulate matter is associated with incidence of coronary events, and this association persists at levels of exposure below the current European limit values.
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| 4. |
- Dovlén, Sylvia, et al.
(författare)
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Sustainable development in regional development practice : a socio-cultural view of evaluation
- 2016
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Ingår i: New Principles in Planning Evaluation. - : Taylor and Francis. ; , s. 77-102
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In 1997, the Swedish government proclaimed that sustainable development (SD) should be the lodestar for all public activities (SOU 1997, 105). The following year sustainable development was explicitly introduced as an overarching aim in Swedish regional development politics (Regeringens proposition 1998). The 21 Swedish regions were thus requested to implement and integrate a new goal and perspective, namely SD, as part of their traditional responsibilities to coordinate and promote regional economic growth and employment.
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| 5. |
- Duursma, Allard, et al.
(författare)
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UN Peacekeeping at 75: Achievements, Challenges, and Prospects
- 2023
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Ingår i: International Peacekeeping. - : Taylor & Francis. - 1353-3312 .- 1743-906X. ; 30:4, s. 415-476
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Tidskriftsartikel (refereegranskat)abstract
- This year marks the 75th anniversary of what the UN itself understands to be its first peacekeeping operation. It is therefore an appropriate time to reflect on the track record of UN peacekeeping in its efforts to try to maintain and realize peace and security. Moreover, this milestone invites us to ponder what lies ahead in the realm of peacekeeping. For this reason, this forum article brings together both academics and UN officials to assess the achievements and challenges of UN peacekeeping over the past 75 years. Through a dialogue among peacekeeping scholars and practitioners, we hope to identify current trends and developments in UN peacekeeping, as well as explore priorities for the future to improve the effectiveness of peacekeeping operations in terms of achieving their mandate objectives, such as maintaining peace, protecting civilians, promoting human rights, and facilitating reconciliation. This forum article is structured into six thematic sections, each shedding light on various aspects of UN peacekeeping: (1) foundational principles of UN peacekeeping - namely, consent, impartiality, and the (non-)use of force; (2) protection of civilians; (3) the primacy of politics; (4) early warning; (5) cooperation with regional organizations; and (6) the changing geopolitical landscape in which UN peacekeeping operates.
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| 7. |
- Hilding, T., et al.
(författare)
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Degradation behaviour of a high CSR coke in an Experimental Blast Furnace: Effect of carbon structure and alkali reactions
- 2005
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 45:7, s. 1041-1050
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Tidskriftsartikel (refereegranskat)abstract
- A high CSR coke was tested in the LKAB's Experimental Blast Furnace (EBF) at Luleå. The evolution of physical and chemical properties of the centre-line coke samples were analysed by Light Optical Microscopy (LOM), BET N2 absorption and SEM/XRF/XRD. Alkali distribution in the EBF cokes was examined by XRF/SEM and EDS. Thermo Gravimetric Analysis (TGA) was used to measure isothermal and non-isothermal CO2 reactivity of the cokes. The crystalline order of carbon and the concentration of alkalis were found to increase as the coke descended through thermal reserve zone to the cohesive zone of the EBF. The crystallite height (Lc) of EBF coke carbon displayed a linear correlation with the measured EBF temperatures demonstrating the strong effect of temperature on carbon structure of coke in the EBF. Alkali concentration of the coke was increased as it descended into the EBF, and was uniformly distributed throughout the coke matrix. The CO2 reactivity of lower zone cokes was found to increase when compared to the reactivity of the upper zones cokes, and was related to the catalytic effect of increased alkalis concentration. The deterioration of coke quality particularly coke strength and abrasion propensity were related to coke graphitisation, alkalization and reactivity, Coke graphitisation is shown to have a strong influence on the coke degradation behaviour in the EBF. © 2005 ISIJ.
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| 8. |
- Hilding, T., et al.
(författare)
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Study of gasification reaction of cokes excavated from pilot blast furnace
- 2004
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Ingår i: SCANMET II. - Luleå : MEFOS. - 9163149109 ; , s. 467-478
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Konferensbidrag (refereegranskat)abstract
- Fundamental understanding of coke reactions with gas, metal and slag phases is essential for ensuring smooth operation and optimisation of coke performance in existing and advanced blast furnace process, and is dictated by coke properties and blast furnace process conditions. In this study, coke samples excavated from LKAB's Experimental Blast Furnace (EBF) at MEFOS in Luleå, Sweden were collected. The centreline quenched coke samples from different zones of this EBF were used to observe the influence of in-furnace reactions on the evolution of coke properties and their associations with CO2 reactivity. Carbon structure of coke was found to increasingly ordered, silicon and iron concentration in the coke samples decreased, while alkali concentration particularly potassium and sodium were found to increase as the coke descended towards lower part of the EBF. Both isothermal and non-isothermal reactivity based on TGA measurements showed that coke reactivity towards CO2 is increased as coke descends towards cohesive zone despite increasing order of carbon structures. Increased reactivity of cokes at lower parts of EBF was related to alkali enrichments of cokes. The study further shows that increased alkali components in cokes have a strong impact on CO2 gasification in EBF such that influence of coke graphitisation could be compensated by catalytic influence of alkalis. To further assist with development of understanding of reactivity of coke, gasification studies were also conducted in a fixed bed reactor at 900ºC using a series of cokes made from Australian coals (varying in rank, maceral and mineral matter). The CO2 reactivity of cokes in a fixed bed reactor was also found to be strongly influenced by the coke minerals compared to carbon structure. Further studies are required to provide a critical insight into the influence of key parameters such as coke graphitisation and mineral reactions on coke gasification particularly at higher temperatures.
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| 9. |
- Sahajwalla, V., et al.
(författare)
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Structure and alkali content of coke in an experimental blast furnace and their gasification reaction
- 2004
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Ingår i: Iron & Steel Technology Conference proceedings. - Warrendale, Pa : Iron and Steel Society. - 1886362750 ; , s. 491-500
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Konferensbidrag (refereegranskat)abstract
- Coke samples excavated from LKAB's Experimental Blast Furnace (EBF) at MEFOS in Luleå, Sweden were used to observe the influence of in-furnace reactions on the changes in chemical stracture of cokes and their influence on kinetics of CO 2 reactivity. In addition to growth of carbon crystallite of coke, alkali concentration particularly potassium and sodium were found to increase as coke descended towards lower part of the EBF. The increase in carbon structure could be linearly related to measured temperature profiles of EBF. Isothermal and non-isothermal TGA measurements are shown to indicate that CO 2 reactivity of coke becomes progressively faster as it moves towards lower part of blast furnace. The study suggests that alkali enrichment of cokes in an operating blast furnace could have a strong catalytic effect on the CO 2 reactivity. Further research is expected to clarify the mechanisms of influence of coke minerals on reactivity and their implications in a blast furnace.
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