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- 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. |
- Isaksson, Per
(författare)
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On crack growth under compressive stresses
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns fractures subjected to compressive stresses. In the four papers appended fracture behavior in brittle as well as ductile materials is studied. In the first paper, an expression for the mode II stress intensity factor at a straight extended kink has been calculated under the condition that crack opening is suppressed during crack growth. The expression has been found as a function of the mode II stress intensity factor K2 at the parent crack, the direction and length of the kink, and the difference between the remote compressive normal stresses perpendicular to, and parallel with, the plane of the parent crack. Crack growth directions have been suggested based on the result. At a sufficiently high non-isotropic compressive normal stress, so that the crack remains closed, the crack will propagate along a curved path maximizing the mode II stress intensity factor. Only at an isotropic compressive normal stress will the crack continue straight ahead in its original plane without directional change. By analyzing experimental crack growth patterns in paper two, the conclusion is that crack paths experimentally observed indicate that mode II crack growth under compression in some brittle materials follow a propagation path described by a function y=gx^b. In fact, the agreement between the experiments and the propagation path prescribed by the model, in which b=3/2, is astonishingly good since b was found in the interval [1.43-1.58] in all the experiments studied. Further, the investigation of the curvature parameter g has revealed that g also agree with the simplified model, even though not as good as the exponent b. However, the experimentally observed g differs in general less than 15% from the theoretical value predicted by the analytical model discussed in paper I. In paper three, a directional crack growth criterion in a compressed elastic perfectly-plastic material is considered. A slip-line solution is derived for evaluation of the stresses at the crack tip, which considers hydrostatic pressure and friction between the crack surfaces. Based upon the slip-line solution a projection stress based model is discussed for prediction of the direction of initiated crack growth. The opening displacement of an extended kink has been examined in paper four, using a finite element procedure. The conclusion is that an over-critical pressure in the plastic zone surrounding the crack tip suppresses crack opening regardless the direction of crack growth. The only possibility seems to be shear mode crack growth, which occur straight ahead in the crack plane if the crack is assumed to follow the plane of maximum shear stress. At a sub-critical hydrostatic pressure, or lower friction between the crack surfaces, the crack can extend via a kink subjected to local opening mode. An expression for the critical value determining fracture mode has been found as a function of hydrostatic pressure and friction between the crack surfaces assuming the fracture process to be predominantly controlled by local tensile stresses at the crack tip. The crack growth directions predicted by the projection stress based criterion in paper three are comparable with the directions maximizing the opening displacement of an extended kink computed in paper four.
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| 3. |
- Dahlén, Leon
(författare)
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Numerical and experimental study of performance of a hydraulic motor
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study was to develop an understanding of the fluid properties that influence the efficiency of hydraulic systems in a steady-state, especially components in hydrostatic transmission systems under different running conditions. The aim has also been to investigate and model the sources of losses in hydraulic machines, in order to estimate the losses, taking fluid properties into account. Finally, the technique of optimization has been introduced in order to improve the efficiency of a distributor valve in a radial piston hydraulic motor, Marathon M200. From an experimental field-test, which was performed on a belt conveyer using a hydrostatic transmission system, the overall efficiency of the hydrostatic transmission was compared when using a mineral oil, Shell Tellus TX 68, a synthetic fluid, Mobil SHC 526, and a vegetable fluid, Binol Hydrap II. The experimental field-test showed that vegetable and synthetic fluids improve the efficiency compared to mineral oil. The three fluids have the same viscosity but experimental tests showed that the temperature ()- and pressure() -viscosity coefficient differs between them. It was also found that the pressure-viscosity coefficient () of mineral oil was higher compared to vegetable and synthetic fluids. The proposed steady-state model gives greater accuracy regarding overall efficiency than the Wilson model, when examining fluid properties that differ in other aspects than their viscosity. The study has focused on losses in lubricated sliding contacts within a radial piston hydraulic motor, Marathon M200, and an analysis of the losses has been made using the finite element method (FEM). A FEM software package, Solvia, which takes into account fluid properties, such as temperature- and pressure- viscosity coefficient, heat conduction and specific heat, has been used to simulate the behaviour and to estimate the losses in tribological contact. This approach of simulation has been applied to two different tribological contact within the hydraulic motor: to a journal bearing contact and to a hydrostatic annular multi-recess plane thrust bearing. By using an FEM software package linked to an optimization algorithm, the losses in the tribological contact in a distributor valve were reduced significantly. The study shows that the optimized geometry of the distributor valve in the motor can successfully be improved, with regard to losses, by small changes in the geometry. Combining an FEM software package with the optimization routine offers an effective tool for designers to simulate and improve the efficiency of a hydraulic unit.
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| 5. |
- Grönlund, Erik
(författare)
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Microalgae at wastewater pond treatment in cold climate : an ecological engineering approach
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Three types of wastewater ponds in subarctic climates were investigated, each of them highly dependent on microalgae. They were fellingsdams, i.e. wastewater stabilization ponds complemented with chemical precipitation, high-rate algal ponds (HRAPs), and a type of aquaculture interface ponds between a wastewater treatment plant and the natural surrounding. From a microalgae taxa perspective green algae and cryptophytes were dominant in the wastewater ponds. Green algae and cryptophytes were also, together with chryso- and haptophytes, dominating the hypereutrophic and eutrophic stages of the natural lakes. Biomasses in the different types of ponds were of very different order of magnitude. From 100-1000 mg/l in the stabilization ponds during summer and 10-100 mg/l in spring and autumn, 70- 90 mg/l in a HRAP in autumn, to 5-30 mg/l in the most hypereutrophic stage in the natural ponds, 1-10 mg/l in the eutrophic stage, and below 1 mg/l in the oligotrophic stage. The connection between wastewater pond treatment and the field of ecological engineering was recognized. Future development of pond technology may benefit from a stronger connection to the theoretical framework of systems ecology developed in collaboration with the field of ecological engineering and ecotechnology.
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| 9. |
- 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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| 10. |
- Linde, Stefan
(författare)
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Communication and Cooperation : A Study of the Relationship Between Political Communication and Large-scale Collective Action
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates the importance of communication for individual cooperation in large-scale collective action dilemmas. In small-scale collective action, where participants have the possibility to meet face-to-face, communication has been shown to drastically increase levels of cooperation. These positive effects are generally believed to be related to the possibilities of exchanging mutual commitments, sharing strategic information, creating and enforcing shared norms, developing trust, and creating a common group identity that communication offers. In large-scale dilemmas, involving thousands or even millions of participants, possibilities for communication are highly restricted beyond the immediate social vicinity of individuals. Participants are therefore unable to reap the positive benefits of communication that are available at the small-scale. Furthermore, as the public goods on which individuals cooperate in large-scale dilemmas often are both distant and abstract in nature (climate change, ozone depletion, overpopulation), the role of communication as an informational-shortcut might be even greater in large-scale dilemmas. That is, individuals need information about the characteristics of the resource in question, the relevant set of other actors participating, and the individual costs and benefits of cooperation.To compensate for the lack of communication and first-hand information, individuals in large-scale dilemmas are generally assumed to rely on different forms of judgmental and behavioral ‘heuristics’ (e.g. generalized trust and internalized norms) to make cooperative decisions. In this thesis I focus on one type of heuristic that generally has been overlooked in research on collective action; the individual reliance on information from trusted elite sources. Specifically, I study the extent to which individuals use communications from political parties when making cooperative decisions. The aim of the thesis is thus to investigate the relationship between political communication and large-scale collective action, and how this relationship varies with individual and contextual factors. This is studied in the context of climate change mitigation, which is a typical case of large-scale collective action, characterized by the large number of anonymous actors, the negligible impacts and high costs of individual cooperation, and a general lack of face-to-face communication and first-hand information.Using a country comparative approach, and cross-sectional survey data, the results show that: 1) political communications both directly and indirectly (by shaping perceptions of collective efficacy and collective benefits) influences individuals’ cooperative/non-cooperative decisions, and that this effect goes beyond other individual level factors, e.g. ideology, income, education; 2) not only specific communications, but also perceptions of the overall political climate (degree of polarization and the average party stance) affects attitudes both directly and indirectly; 3) these effects are not isolated to certain environments, but (to varying degree) can be found across political contexts and parties. The results have important implications both practically for policy makers, by creating a deeper understanding of the formation of individual climate change attitudes, and theoretically, by creating a better understanding of how individuals make decisions in large-scale collective action dilemmas. Future research should both validate the results from this study using other research designs (e.g. longitudinal or multilevel data, experimental designs), and expand on them, for example by exploring how different sources of communication and different types of information interact and influence the reception of communication content.
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