| 8861. |
- Zincir, Burak, et al.
(författare)
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Investigation of environmental, operational and economic performance of methanol partially premixed combustion at slow speed operation of a marine engine
- 2019
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Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526. ; 235, s. 1006-1019
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to investigate the environmental, operational and economic performance of the methanol partially premixed combustion concept at slow speed operation of a ship to find a solution for the shipping emission effect on the coastal settlements while do not increase the risk and expense of the engine operation on the ships. The experimental study was done with partially premixed combustion, one of the advanced combustion concepts, on a Scania D13 heavy-duty diesel engine for its promising results of high engine efficiency and low engine emissions. In addition to the experimental study with methanol fuel, the performance of the methanol was compared with marine gas oil, which was mostly used at the slow speed operation of the ships. Empirical equations and coefficients in the literature were used to calculate specific fuel consumption, efficiency, and emissions of the marine gas oiled operation of the engine. The results showed that the combustion efficiency varied from 0.94 to 0.99 and the gross indicated efficiency varied from 0.42 to 0.46 from 10% to 25% engine loads, respectively, while the gross indicated efficiency of the marine gas oil-fuelled engine was 0.32 as a maximum value. The methanol showed good environmental performance with lower CO2 emissions than the marine gas oil, lower NOX emissions than the NOX Tier III levels, varied between 0.3 g/kWh and 1.4 g/kWh, zero SOX emissions and zero PM emissions. The economic investigation showed that the methanol cost at the low price scenario was 0.147 $/kWh, 0.138 $/kWh and 0.135 $/kWh at 10%, 15% and 25%, respectively, which were lower than the high price scenario and low price scenario of the marine gas oil; and the methanol high price scenario was still competitive with the marine gas oil scenarios.
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| 8862. |
- Zou, Yangfan, et al.
(författare)
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Characterizations of dissimilar refill friction stir spot welding 2219 aluminum alloy joints of unequal thickness
- 2022
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Ingår i: JOURNAL OF MANUFACTURING PROCESSES. - : ELSEVIER SCI LTD. - 1526-6125. ; 79, s. 91-101
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Tidskriftsartikel (refereegranskat)abstract
- Refill friction stir spot welding (RFSSW) is a relatively new solid-state spot welding technology. Reliability of the joint is mainly affected by the macroscopic characteristics and microstructure evolution. This method can be applied to weld plates with different thicknesses. However, the temperature distribution, microstructure and mechanical properties of joints with different thicknesses remain unclear. In the present study, 2 mm thick 2219-O aluminum alloy plates were successfully welded to 2219-C10S plates of various thicknesses (4 mm, 10 mm and 14 mm) via the RFSSW method. The effect of lower 2219-C10S plate thickness on the temperature distribution, microstructure, mechanical properties and fracture behavior of RFSSWed joints was evaluated by both experi-mental and simulation methods. The results indicated that the peak temperature decreased, and the isothermal zone became larger as the thickness of the lower plate increased. A relatively flat hook configuration could be identified in the cross-section of the joint fabricated using a 4 mm thick lower plate, while an upward hook was observed for the joints fabricated using a 10 and 14 mm thick lower plate. Lower plate thickness scarcely affected hardness of the upper plate, but HAZ width of the lower plate becomes narrower with increasing lower sheet thickness. The lap-shear load of the joints fabricated using a lower plate thicknesses of 4, 10 and 14 mm was 7.4 +/- 0.3 kN, 6.7 +/- 0.2 kN, and 6.4 +/- 0.4 kN, respectively, all of them failed as a plug fracture mode. According to the simulation results, tensile and compressive stresses were mainly distributed along the direction of the force on both sides of the weld nugget. While shear stress was primarily distributed in the direction perpendicular to the external force. Furthermore, bending stress was also identified in the joints, which increased with the in -crease of the lower plate thickness.
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| 8863. |
- Zu Ermgassen, Erasmus K.H.J., et al.
(författare)
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Using supply chain data to monitor zero deforestation commitments: an assessment of progress in the Brazilian soy sector
- 2020
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326 .- 1748-9318. ; 15:3
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Tidskriftsartikel (refereegranskat)abstract
- Zero deforestation commitments (ZDCs) are voluntary initiatives where companies or countries pledge to eliminate deforestation from their supply chains. These commitments offer much promise for sustainable commodity production, but are undermined by a lack of transparency about their coverage and impacts. Here, using state-of-the-art supply chain data, we introduce an approach to evaluate the impact of ZDCs, linking traders and international markets to commodity-associated deforestation in the sub-national jurisdictions from which they source. We focus on the Brazilian soy sector, where we find that ZDC coverage is increasing, but under-represents the Cerrado biome where most soy-associated deforestation currently takes place. Though soy-associated deforestation declined in the Amazon after the introduction of the Soy Moratorium, we observe no change in the exposure of companies or countries adopting ZDCs to soy-associated deforestation in the Cerrado. We further assess the formulation and implementation of these ZDCs and identify several systematic weaknesses that must be addressed to increase the likelihood that they achieve meaningful reductions in deforestation in future. As the 2020 deadline for several of these commitments approaches, our approach can provide independent monitoring of progress toward the goal of ending commodity-associated deforestation.
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| 8864. |
- Åkerblom, Cecilia
(författare)
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Ledarskap, makt och känsla : En narrativ studie av unga ledare
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to analyze how leadership is constructed as a narrative to explain what happens in organizations. Research on young co-workers in organizations has shown how young people are socialized into managerial and organizational cultures. At the same time these cultures and practices are changing. In addition, the younger generation is often expected to express new values or ideals in management. This thesis is developed from a social constructionist view on organization. The main research question is: How do young leaders construct leadership narratives in terms of their personal experience within organizations? The empirical material consists of interviews with 22 young leaders, 11 women and 11 men between 19 and 35 years old, encompassing 19 different organizations. Three of the young leaders were interviewed over a time period between one and two years. The remaining 19 were interviewed once. Leadership is constructed as the power to influence events and decisions in the organization and the responsibility for the outcome. Leadership is also constructed as an interpersonal power relationship. Leadership is analyzed as both construction and ordering of power and responsibility in interpersonal interactions. The analysis shows how the professional identity as a leader is constructed through a process of creative imitation. Emotions play an important role in the performance of the professional identity. Emotional experiences such as fear or vulnerability are often excluded or repressed in order to maintain competent professional appearances. Managers are expected to handle emotionally difficult situations. Prevailing responses– to ignore the situation or not to see at all vs. to acknowledge, act and react – are discussed. The latter category of responses is further analyzed as: to heal and to transform, to set boundaries and to react under stress. Fear or anxiety in these situations may activate survival strategies in interpersonal interactions. The underlying implication of the construction of leadership as an asymmetrical power relation may be that manipulation and codependency are plausible outcomes.
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| 8865. |
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| 8866. |
- Åkesson, B., et al.
(författare)
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Prevention of hot cracking of butt welds in steel panels by controlled additional heating of the panels
- 1976
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Ingår i: Welding Research International. - 0306-9427. ; 6:5, s. 35-52
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Tidskriftsartikel (refereegranskat)abstract
- A procedure for controlled additional heating during and after welding to prevent end cracking is devised and analyzed. The search for the optimal distribution and minimal amount of thermal energy needed for the additional heating is formulated as a mathematical programming problem. Two sided irradiation is suggested as a feasible way for transmitting the thermal energy into the panel. A case for application in a Swedish panel production line is studied. A formula for calculating the required additional heating is deduced.
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| 8867. |
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| 8868. |
- Åström, Peter, et al.
(författare)
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Friction model parameter optimization for friction welding simulation of Ti-6246
- 2006
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Ingår i: Trends in welding research. - Materials Park, Ohio : ASM International. - 9780871708427 ; , s. 849-854
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Konferensbidrag (refereegranskat)abstract
- With regard to the rotary friction welding process as used for joining of large rotationally symmetric structures in the aerospace industry, the finite element software "MSC. Marc" coupled with the optimisation code INVSYS was used to simulate the friction welding of two cylindrical titanium alloy Ti 6246 specimens while optimising parameters in the friction model. The friction model took into account the friction coefficient variation as a function of normal pressure in the contact, temperature and relative sliding velocity. The unconstrained subspace searching simplex method was employed for optimisation. An objective function was formulated to minimise the error between calculated and measured torques, and a parameter set was identified that produced better flash geometry agreement with experiment.
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| 8869. |
- Åström, Peter
(författare)
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Simulation methodologies within virtual manufacturing applied on mechanical cutting
- 2001
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Virtual manufacturing, that is, simulation of welding, heat treatment, cutting and other manufacturing processes is becoming more and more used as a tool for prediction of material- and mechanical properties in modern industry. By simulations we refer in this case to FE-simulations of the thermo-mechanical effect of the manufacturing process on the component in question. Despite the fact that simulations are becoming more widely used, there is a lack of integration of simulations of manufacturing processes in the sense that most work focuses on an individual process being simulated. It is only when a complete chain of manufacturing processes can be simulated the real benefits, of using virtual manufacturing as a tool within product- and process development, will become evident. The thesis focuses on simulation methodologies within virtual manufacturing, and specifically methodologies for cutting simulations. Simulation of mechanical cutting has been identified as a key area where computational difficulties arise when attempting to simulate a sequence of manufacturing processes involving some form of cutting operation. A distortion problem during manufacture of a shaft front to a RM12 engine has been analysed. At one time, distortions aroused during the later stages of the cutting sequences involved in the manufacture of the shaft front. The cooling from solution heat treatment temperature and the cutting sequence was to be simulated. The result from the cooling sequence however show that the cooling does not cause residual stresses that in turn cause distortions in subsequent cutting sequences, and hence only results from the cooling procedure is presented. A test case was constructed to ensure that residual stresses would be present causing distortions during subsequent cutting. The experimental set- up with both a forming operation and subsequent cutting is used as a validation tool for the simulation of cutting using an element deactivation technique. The results show that the technique developed can be a useful tool for simulation of mechanical cutting when interested in distortions on component level. Another necessity when performing analyses of a sequence of manufacturing processes is a system for exchange of Engineering Analysis Data (EAD) between each of the simulations. Further, a system for handling the increasing amount of EAD in the product- and process development process is also needed. Most engineering software is today used to solve engineering problems within a single, limited domain. Efforts have been made to develop standardised formats such as IGES and STEP for EAD exchange both within and across domains. However, by limited implementation in commercial software the user is often forced to either program translation routines that enables data sharing or even recreate meshes, boundary conditions etc. A system has been developed that supports the management of computer-based simulation information. The paper describes how information modelling and database technologies can bring new dimensions to the effective use of engineering simulations in product- and process development.
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| 8870. |
- Åström, Peter
(författare)
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Simulation of manufacturing processes in product development
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the manufacture of aero engine components, three key manufacturing processes can be identified. These are welding, heat treatment and mechanical cutting. Depending on what is required in terms of mechanical- and geometrical properties in the final product these processes are typically combined in a certain sequence. It is consistently these three processes, and the modelling and simulation of them using the finite element method, that are of concern to the work presented in this thesis. Product development phases such as the detailed design phase and the process planning phase are typically simulation intensive in aerospace industry. Normally, both more extensive component and manufacturing process data are available at these stages compared to in the previous concept development phase. It is however becoming increasingly important to enable predictions of manufacturability to be made early in the product development process. Changes made in the manufacturing process chart after a product offer is released will result in an increase in cost and a decrease in profit of that component. The aim of the work presented here is thus to develop strategies and computational technologies suitable for simulation of manufacturing processes in early stages of product development. An example of a computational technology developed in this work is the method of element deactivation used to simulate distortion effects of mechanical cutting. Within the area of simulation of manufacturing processes most research work and most publications focus on one individual process being simulated. This has been of great importance for the evolution of computational methods and analysis tools used both in industry and academia. However, when the focus of using simulations often is to determine process parameters in order to obtain desired product properties in the final product, it is essential to include the entire manufacturing process sequence in these simulations. In order to enable a sequence of manufacturing processes to be simulated, engineering information data need to be transferred between simulations of the individual processes. A system for engineering information data exchange in the context of manufacturing simulations is presented in this work. An approach commonly used for concept generation is knowledge based engineering (KBE). In KBE-systems, rules are implemented that embodies the enterprises’ product- and process knowledge. In this thesis, an integrated system where mechanical cutting simulations are performed within a knowledge based engineering software framework is presented. The thesis also deals with friction modelling in the rotary friction welding process and what is appropriate, in terms of computational matters, when attempting to simulate friction welding in a concept development context. The main theme in the thesis is thus to develop strategies, methods and computational technologies suitable for simulation of manufacturing processes such as rotary friction welding and mechanical cutting in early stages of product development.
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