| 1. |
- Andersson, Magnus, et al.
(författare)
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Admission to master programmes : What are the indicators for successful study performance?
- 2023
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Ingår i: Bidrag från den 9:e utvecklingskonferensen för Sveriges ingenjörsutbildningar. - Västerås : Mälardalens universitet. ; , s. 9-18
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Konferensbidrag (refereegranskat)abstract
- Admission of applicants to higher education in a fair, reliable, transparent, and efficient way is a real challenge, especially if there are more eligible applicants than available places and if there are applicants from many different educational systems. Previous research on best practices for admission to master’s programmes identified the key question about an applicant’s potential for success in studies, but was not able to provide an answer about how to rate the merits of the applicants. In this study, indicators for study success are analysed by comparing the study performance of 228 students in master’s programmes with their merits at the time of admission. The null hypothesis was that the applicant’s average grade at the time of admission is the only indictor for study success. After testing for potential bias using almost 20 possible other indicators, the null hypothesis had to be rejected for four indicators (in order of importance): (i) university ranking, (ii) length of bachelor’s studies within subject, (iii) English language test and (iv) subject matching between bachelor’s and master’s education. Evaluation of quality of prior education is tricky and results from this study clearly indicate that students from higher ranked universities possess better knowledge and stronger skills for our master’s programmes. Work is ongoing to improve the merit rating model by involving more master’s programmes at KTH and analysing performance data from a larger number of students.
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| 4. |
- Griffin, Daniel, et al.
(författare)
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Cislunar Orbital Transportation Study of Space Elevator Apex Anchor Releases
- 2022
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Ingår i: 73rd International Astronautical Congress, IAC 2022. - : International Astronautical Federation, IAF.
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Konferensbidrag (refereegranskat)abstract
- As humans increasingly begin to expand beyond the threshold of Low Earth Orbit (LEO), moving supplies and astronaut safety within the vastness of space can become daunting. Limited by Tsiolkovsky's Rocket Equation, rockets are inefficient at moving material off planet as only a small percentile of the rocket's launch pad mass reaches orbital space. While commercial enterprises have greatly increased the rate of rocket launches, a human emergency occurring far from Earth raises the question of how to send aid. Space Elevators are an additional solution to overcoming the initial constraints posed by rockets. In a simplified manner, a Space Elevator is a permanent infrastructure for moving large elevators (climbers) along a tether that extends from the surface of the Earth into space. This research looks at the volume of space between Earth and the Moon, otherwise known as Cislunar Space, and the benefits that a Space Elevator would contribute. Specifically, a safety for astronauts beyond LEO by means of the Apex Anchor (space station located at the top of the Space Elevator) as well as mass distribution to the Moon by means of the Space Elevator. Mathematical and engineering details for the Space Elevator's construction or orbits for payloads are referenced but not calculated in this study.
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| 5. |
- Magnell, Marie, et al.
(författare)
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Integrating Gender Equality, Diversity, and Equal Conditions, in Engineering Education
- 2022
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Ingår i: Proceedings of the 18 th International CDIO Conference, hosted by Reykjavik University, Reykjavik Iceland, June13-15, 2022.. - : Chalmers University of Technology.
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Konferensbidrag (refereegranskat)abstract
- In engineering education, as well as in the society at large, there is an increasing focus on sustainability and sustainable development. The CDIO Standards and the CDIO Syllabus has been substantially updated to meet and drive these changes. Progressive engineering programs have by now made substantial progress in integrating environmental aspects of sustainability and sustainable development into the curriculum. However, the integration of social aspects is generally considered to be more difficult and is therefore lagging behind. This explorative research paper provides insights in efforts to integrate elements of gender equality, diversity and equal conditions (GDE) in three courses on bachelor’s, master’s, and doctoral level. The focus is on the development and implementation of reflective assignments, where a theoretical framework is used for characterizing different levels of reflection. The work has been performed by use of an action research approach that has involved close dialogue and collaboration between researchers, pedagogic developers, teachers, students, and education leaders. The paper hereby contributes with multiple perspectives on GDE integration, and significant challenges are discussed. The paper also contributes with concrete examples of reflective assignments, learning activities, and literature that can be useful also in other contexts.
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| 6. |
- Mallol, Pau, et al.
(författare)
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Experiments and simulations of the deployment of a bistable composite boom
- 2018
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Ingår i: Journal of Spacecraft and Rockets. - : American Institute of Aeronautics and Astronautics Inc.. - 0022-4650 .- 1533-6794. ; 55:2, s. 292-302
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Tidskriftsartikel (refereegranskat)abstract
- The rapidly growing use of small satellites for space missions requires deployable systems to be highly storable yet large and with adequate mechanical properties when deployed. This paper focuses on the modeling and simulation of a meter-class passively deployable boom, based on the self-contained linear meter-class deployable boom, exploiting the bistable nature of composite shells. Experimental tests were performed on a boom prototype suspended in a gravity offloading system. The strain energy level, deployment time, and spacecraft displacements calculated from the finite element method agree well with analytical analyses, confirming the theoretical accuracy of the finite element method. Because friction and strain energy relaxation were not included in the model, the finite element simulations predicted deployment times up to five times shorter than those of the gravity offloaded boom experiments. The quick deployment and violent end-of-deployment shock created boom deployment dynamics that were not seen in the experiments. The observed differences between the finite element model and the tests were mainly due to inaccurate material and friction models.
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| 7. |
- Mao, Huina, et al.
(författare)
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Experiments and analytical modeling for designing tape spring composites
- 2017
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Ingår i: ICCM International Conferences on Composite Materials. - : International Committee on Composite Materials.
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Konferensbidrag (refereegranskat)abstract
- Lightweight fiber reinforced tape spring composites are proposed for deployable space structures for nanosatellites. Neutral stable carbon fiber tape springs and bi-stable glass fiber tape springs were manufactured and their self-deployabilities after stowage were experimentally tested. The viscoelastic effects of the composites used were experimentally investigated. An analysis methodology that predicts neutral stability or bi-stability in appropriately arranging fiber directions, layups and fabric properties is presented. A design method flowchart is presented to give a reference for designing neutral or bi-stable tape springs based on the experiments and the analytical model, e.g., material type, layup, fibers direction and stability parameters. The tape spring properties before and after stowage can be predicted. The analytical model shows that fabrics of high strength fibers and low shear modulus resin with layer angle ±45° are good choices for neutrally tape springs and adding inner 0°/90° layers can increase the deployment force for bi-stable tape springs. The bi-stable glass fiber tape springs that can self-deploy after more than 6 months of stowage and high strength carbon fiber neutrally tape springs were fabricated.
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| 8. |
- Mao, Huina
(författare)
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Numerical and Experimental Studies of Deployment Dynamics of Space Webs and CubeSat Booms
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, experiments and simulations are performed to study the deployment dynamics of space webs and space booms, focusing on the deployment and stabilization phases of the space web and the behavior of the bi-stable tape spring booms after long-term stowage.The space web, Suaineadh, was launched onboard the sounding rocket REXUS-12 from the Swedish launch base Esrange in Kiruna on 19 March 2012. It served as a technology demonstrator for a space web. A reaction wheel was used to actively control the deployment and stabilization states of the 2×2 m2 space web. After ejection from the rocket, the web was deployed but entanglements occurred since the web did not start to deploy at the specified angular velocity. The deployment dynamics was reconstructed by simulations from the information recorded by inertial measurement units and cameras. Simulations show that if the web would have started to deploy at the specified angular velocity, the web would most likely have been deployed and stabilized in space by the motor, reaction wheel and controller used in the experiment. A modified control method was developed to stabilize the out-of-plane motions before or during deployment. New web arms with tape springs were proposed to avoid entanglements.A deployable booms assembly composed of four 1-m long bi-stable glass fiber tape springs was designed for the electromagnetically clean 3U CubeSat Small Explorer for Advanced Missions (SEAM). The deployment dynamics and reliability of the SEAM boom design after long-term stowage were tested by on-ground experiments. A simple analytical model was developed to predict the deployment dynamics and to assess the effects of the GOLS and the combined effects of friction, viscoelastic strain energy relaxation, and other factors that act to decrease the deployment force. In order to mitigate the viscoelastic effects and thus ensure self-deployment, different tape springs were designed, manufactured and tested. A numerical model was used to assess the long-term stowage effects on the deployment capability of bi-stable tape springs including the friction, nonlinear-elastic and viscoelastic effects. A finite element method was used to model a meter-class fully coiled bi-stable tape spring boom and verified by analytical models.
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| 9. |
- Matija, Milenovic, et al.
(författare)
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Design and Development of Damping SandwichPanels for Satellite Housing Using AdditiveManufacturing
- 2022
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Konferensbidrag (refereegranskat)abstract
- The present work investigates the performance of additively-manufactured sandwich structures with the goal of reducing the effect of vibrations on a spacecraft during launch, whilst minimizing mass. Additive manufacturing allows designers to implement custom and complex geometries, such as the sheet gyroid structures, inside sandwich panels. Accordingly, this work details the development of gyroid-based sandwich structures for damping. Several test specimens are designed, additively manufactured using ABS plastic, and their damping performances are evaluated based on both simulation and experiments. Damping values are identified using frequency response transfer functions. The results show that as theory predicts, adding more mass, through the added thickness of the gyroid reduces the amplitude of vibrations. However, on a damping-per-unit-mass basis, the experimental results are inconclusive mainly due to the measurements of vibrations in the center of the sandwich panels instead of the sides where the vibrations can be maximum. Therefore, simulations better illustrate the changes of the damping behavior at different applied frequencies. Lessons and experiences are summarized for future work, particularly in exploring the effects of varying other 3D printed composite meta-lattice sandwich structures for satellites.
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| 12. |
- Shahryarifard, Mohammadmahdi, et al.
(författare)
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Toward thermal stimulation of shape memory polymer composite bistable tape springs
- 2021
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Ingår i: Smart materials and structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 30:2
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Tidskriftsartikel (refereegranskat)abstract
- Due to their tailored thermomechanical behavior and functionality, shape memory polymer matrix composites (SMPCs) are attractive as deployable structures in aerospace applications. An analytical model based on the classical laminate theory, together with the principle of minimum potential energy is developed to capture the thermo- viscoelastic behavior of a bistable tape spring (BiTS). These tape springs are known to snap between two stable configurations by different stimulus. Here, a shape memory polymer as the matrix of a fiber-reinforced polymer BiTS is introduced to actuate the snap-back. Experimental characterization was performed to obtain the time-temperature dependent properties of a Polyurethane SMPC. The time-temperature superposition principle was employed to convert the thermal effects to a viscoelastic response. Five BiTSs were manufactured and exposed to two different thermo-viscoelastic cycles to verify the model for long-term and high-temperature behaviors. The results show that the model can estimate the coiling radius and the degree of stability of the BiTS in the coiled configuration. Analytical results, supported by experimental results, show that the temperature could initiate the snap-back in BiTS. However, time-temperature history has a significant effect on the bistability and can convert a monostable tape spring to a BiTS and vice versa.
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| 13. |
- Shahryarifard, Mohammadmahdi, et al.
(författare)
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Viscoelastic bistable tape spring behavior modeled by a two-dimensional system with rigid links, springs and dashpots
- 2021
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Ingår i: Composite structures. - : Elsevier. - 0263-8223 .- 1879-1085. ; 258
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Tidskriftsartikel (refereegranskat)abstract
- Bistable composite tape springs are often used as deployable structures in aerospace applications because of their ability to be tailored for compact size, deployed lengths and stiffness. Analytical studies of the coupling between stress-strain and moment-curvature of thin curved shells have been used to estimate the total stored strain energy in different tape spring configurations. The strain energy as function of the curvatures reveals the fundamental stability behavior of the tape springs in the different configurations. The present study investigates the minimum strain energy path between two stable equilibrium points and the passage through the unstable saddle point along this path. For a coiled fiber reinforced composite tape spring, the strain energy level for the local minimum and the saddle points will change with respect to time due to viscoelastic effects. To explain the fundamental mechanical behavior of viscoelastic bistable tape springs, a two-dimensional (2D) model composed of rigid links, elastic springs and viscous dampers was proposed. It was shown how the 2D model can be made strain energy-equivalent to a shell model with respect to the minimum strain energy paths. The 2D model was able to capture the fundamental behavior of viscoelastic tape springs during both snap-through and snap-back paths.
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