| 1. |
- Bäckström, Mikael, 1963-
(författare)
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On Monitoring and Control of Machining Processes
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis presents several aspects related to the industrial and academic activities associated with monitoring and control of the machining process and machine tools A survey of the industrial situation identified some key factors for a successful implementation of monitoring and control techniques. Applicable, relatively simple, systems for cutting-process monitoring and adaptive control are available on the commercial market today but the degree of industrial utilisation of the technique is low because the systems are experienced as hard to operate and use, and are at the same time considered unreliable. In order to promote a higher degree of industrial utilisation more work has to be devoted raising the performance of the system solutions. An Integrated Supervisory Process Control (ISPC) concept is presented as an approach dealing with multi-purpose control requirements utilising the individual advantages of several sensors and modelling techniques. The ISPC system is supposed to operate as a conceptual integration of sensors, process models and different control modules. Two prototype systems, based on five-axis machining centres, for real-time control of the machining process are outlined. Different strategies for monitoring and control are developed, implemented and experimentally tried out, and the studies conducted demonstrate results that encourage further research work devoted to verification of the proposed control concept. The results obtained in the initial experiments utilising methods for process control and monitoring, such as double exponential smoothing technique (DES), multivariate monitoring applied to signal tracking and artificial neural networks applied to cutting torque control, reveal that the different techniques have potential to improve the performance of monitoring and control tasks, thus contributing to the creation of more sophisticated and reliable solutions in the ISPC concept.
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| 2. |
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| 3. |
- Tinnsten, Mats
(författare)
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Numerical and experimental study of acoustic and structural optimization
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective with this thesis has been to create a procedure (method and program code) that enables automatic optimization of acoustic response from vibrating structures. Automatic means that the proposed method, on its own, should be able to find the desired acoustic quantities for a given problem formulation by altering given variables. The main parts of such an optimization process are: availability to perform structural dynamic analysis, acoustic analysis, and optimization analysis. The structural dynamic analysis comprises eigenmode and response analyses, tools necessary to calculate surface velocities for the actual structure. These calculations are performed using a modified version of the finite element (FE) code FEMP [31]. This FE code is implemented in the acoustic optimization code and used in Papers B, C, D, E, and F. The surface velocities are used as input in the acoustic analyses. The acoustic analyses in this thesis comprises calculation of sound pressure and/or sound intensity amplitudes in specified regions outside vibrating structures surrounded by air. Calculation of the acoustic quantities (pressure and intensity) is performed using a boundary element (BE) code. The BE code is developed and used in Papers C, D, E, and F. The numerical results in Paper C is compared with experimental results A slightly modified version of the optimization routine MMA (method of moving asymptotes) [21] is used for optimization analysis together with the above-mentioned FE and BE codes. The MMA is in Paper A used for a purely structural optimization problem. The acoustic optimization process, comprising FE, BE, and optimization analysis, is performed in Papers D, E, and F. A comparison between numerical and experimental results was also performed in Paper F.
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| 4. |
- Abrahamsson, Lena
(författare)
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Att återställa ordningen : könsmönster och förändring i arbetsorganisationer
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Avhandlingen är en könsteoretisk studie av organisationsförändringar i industrin - med fokus på kvinnor som arbetar med produktionsarbete. Avhandlingen beskriver vad som händer med organisationsstrukturen och med genusordningen i organisationen när företaget försöker införa en platt integrerad arbetsorganisation. Empirin omfattar åtta svenska industriföretag: fem massa- och papper, ett tvätteri, ett charkuteri och ett elektronikföretag. Resultaten visar att återställare och dämpande krafter ute i lokala arbetsorganisationer drar organisationen tillbaka till sitt ursprungliga utseende. Många av återställarna har koppling till "kön" och genusordningen. De lokala organisationernas utgångsläge inför organisationsförändringarna bygger ofta på en struktur som ger olika villkor för kvinnor och för män. Denna könsordning är en förklaring till många återställare och det är dessutom ofta just den som återställs. Genusordningens segregerande och hierakiserande krafter gör att människor lätt återskapar gamla könsmönster i nya organisationer. Detta innebär att de nya organisationsmodellernas strävan efter integrering, tillplattning, kompetensutveckling och flexibilitet riskerar att motarbetas. En stark och omfattande könsmärkning och könsuppdelning i utgångsläget inför organisationsförändringen innebär många återställare och därmed svårare att införa den platta integrerade arbetsorganisationen.
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| 5. |
- Alerby, Eva
(författare)
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Att fånga en tanke : en fenomenologisk studie av barns och ungdomars tänkande kring miljö
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis attempts to clarify the way in which young people think about our envíronment, based on their experiences as the starting point. The aim is to make the thinking of people available and to interpret the meaning of these thoughts, whose content comprises the environment. The theoretical roots of the study are to be found within the phenomenology of the lifeworld. I also use the phenomenological method as a type of analysis method to use as inspiration when analysing the empirical material. The children and young people who are included in the study are between the ages of 7 and 16. The data collection is based on two partial studies. In one partial study, empirical material is analysed consisting of the production of drawings by 105 children and young people with attached oral comments, and in the other partial study interviews which were conducted with 16 children and young people are analysed. These two studies are partially connected and partially dependent on one another. The drawing study is aimed at developing an understanding of the thinking of the children and young people and also forms the basis for the selection of subjects for the interview study. The interview study for its part is aimed at further deepening the understanding of the thinking process and the interviews took place on two occations with each person. In the drawing analysis four themes of thoughts were crystallised which focus on: the good world, the bad world, the dialectics between the good and bad world, and symbols and actions promoting the environment. In the interview analysis eight themes emerged of thoughts which focus on: pragmatic perspectives, emotional perspectives, future and visionary perspectives, philosophical perspectives, aesthetic perspectives and romantic perspectives. It can be stated that the results which emerged in the form of the thinking of the children and young people on the environment reflect their thinking as having many nuances. If these many-faceted thoughts are to be taken seriously it is necessary in the teaching and learning situation to take into account the thinking of young citizens. Teaching and learning situations should therefore create time and room for conversation and thinking. This is to stimulate the growing power which the experiences of young people have, experiences which are in turn requirements for thinking: thinking which is constituted by beeing-in-the-world.
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| 6. |
- Andersson, Annika
(författare)
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Frazil ice at water intakes
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To provide a better understanding of how frazil ice deposits on trash racks at water intakes, the phenomenon was video recorded at two hydropower plants and in a refrigerated laboratory flume. Initial accretion of frazil ice around a single bar and the motion of particles in the vicinity of an obstacle was simulated through numerical modelling and studied using plastic particles in a laboratory flume. Ice initially accumulates on the upstream face of the bars, and it progresses then to the upstream sides of the bars. Tha frazil ice layer grows in all directions, and it finally bridges over the spaces between bars. The ice blockage starts at the upper part of the rack and progresses downward. The head losses across each intake, which are observed continuously at the plants, illustrate the degree and importance of ice growth. Observations from laboratory experiments with a single bar in a flume, showed that frazil ice particles deposited on all bar surfaces. Separate flume tests were run with plastic particles simulating ice particles. The frequency of collision of these particles with the front face of a rectangular bar varied with the particle density and the fluid velocity. In a test with particles of various sizes, the smaller particles were more likely to enter the side wake than larger ones. A mathematical model can be used to predict patterns of ice deposition that correspond to the observed results. Such a model must include a hydrodynamic part for viscous flows and a particle trajectory model. Some models neglect the term for force due to pressure gradient in their calculations of a particle trajectory because the particles had larger density than the surrounding fluid. Ice particles have almost the same density as the water and simulated results showed that this term, caused by the pressure gradient, is the dominant force that counter the momentum of the particles when they move in the region close to the obstacle. The simulated results were affected by the particle size distribution, therefore the size distribution of frazil ice particles in a river is a factor in further studies. In tests in which no particles were allowed to deposit on the front part of the bar, in a simulation of a heated bar, lesser amounts deposited on the other parts of the bar. Knowledge of the way frazil ice accumulates on water intakes and the initial ice accretion on individual trash racks should be valuable in future work for finding methods to reduce the ice blockage and in the verification of more detailed model studies.
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| 7. |
- Antti, Lena
(författare)
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Heating and drying wood using microwave power
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The potentials for moisture flux in wood during microwave heating have been investigated experimentally and theoretically. The experiments were performed in three different kinds of microwave applicators. A computer model based on the finite difference method was developed to describe and predict the heat and mass transfer. The main conclusions are that microwave energy of 2.45 GHz frequency makes it possible to heat and dry pine and spruce 20 - 30 times faster than with conventional methods without any deterioration in drying quality. Some hardwoods are dried in approximately half the time compared to the softwoods. The drying method evokes unique results either with diminishing colour changes or with possibilities to create such during drying. However, to avoid unevenness in the electromagnetic field distribution and considering the limitation in power penetration depth the drying should be performed on line where wood components continuously are fed through a microwave field.
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| 8. |
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| 9. |
- Axhag, Frank
(författare)
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Plastic design of steel bridge girders
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis assesses the feasibility of a modified plastic design method for continuous steel or composite bridges with slender I-girders. The feasibility evaluation of the design method is closely connected to the moment-rotation relationship of the I-girders at internal supports. Due to local buckling of the slender I-girders, the full plastic moment resistance cannot be sustained as the rotation develops. On the contrary, the girders will reach a moment maximum, which might be less than the full plastic moment, followed by a decline in moment resistance as the rotation increases. Assuming that the moment-rotation relationships are known for all plastic hinges developing in the bridge, a plastic design method can in principle be employed but modified for these relationships. A fundamental condition for a modified plastic design method to be employed is thus that the moment-rotation relationships can be predicted. A simple plate model is developed in this thesis, which predicts the moment-rotation relationship for girders with compact or semi-compact flanges and slender webs. Included in this thesis is also test results in fourteen slender, high- strength steel girders in three point bending tests. A study on the lateral instability of I-girders and also an evaluation of the modified plastic design method with respect to the formal risk of failure, compared to an ordinary elastic design, have also been included.
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| 10. |
- Bai, Guohua
(författare)
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A sociocybernetic approach to information systems design
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study has focused on the problems associated with the design of computer based managment Information Systems (IS) and especially on how to integrate the design, use and embedded social context into one coherent framework. The term IS is used in this study to broadly refer to areas such as Decision Support Systems (DSS), Human Computer Interaction (HCI) and Computer Supported Co-operative Work (CSCW). By viewing design activities as a social interaction process among designers and users and their social context, the study aimed to develop: 1. A socio-cybernetic and social-psychological theory of IS development and to enlighten the relationship between the IS design activities, IS use activities and embedded societal context; 2. A practicable method, called a "feedback learning strategy", for conducting IS design based on socio-cybernetic and social-psychological theory. This study has been conducted by generalisation, theoretical analysis and prototyping. A multiple disciplinary approach has been taken encompassing IS design based on activity theory, cybernetics, sociology, psychology, decision theory, and systems design theory (participatory design, prototyping).
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