| 1. |
- Andersson, Håkan, 1970-
(författare)
-
A Co-Simulation Approach for Hydraulic Percussion Units
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate of Engineering thesis concerns modelling and simulation of hydraulic percussion units. These units are often found in equipment for breaking or drilling in rock and concrete, and are also often driven by oil hydraulics, in which complex fluid-structure couplings are essential for their operation.Current methodologies used today when developing hydraulic percussion units are based on decoupled analyses, which are not correctly capturing the important coupled mechanisms. Hence, an efficient method for coupled simulations is of high importance, since these mechanisms are critical for the function of these units. Therefore, a co-simulation approach between a 1D system simulation model representing the fluid system and a structural 3D FE-model is proposed.This approach is presented in detail, implemented for two well-known simulation tools and evaluated for a simple but relevant model. The Hopsan simulation tool was used for the fluid system and the FE-simulation software LS-DYNA was used for the structural mechanics simulation. The co-simulation interface was implemented using the Functional Mock-up Interface-standard.The approach was further developed to also incorporate multiple components for coupled simulations. This was considered necessary when models for the real application are to be developed. The use of two components for co-simulation was successfully evaluated for two models, one using the simple rigid body representation, and a second where linear elastic representations of the structural material were implemented.An experimental validation of the co-simulation approach applied to an existing hydraulic hammer was performed. Experiments on the hydraulic hammer were performed using an in-house test rig, and responses were registered at four different running conditions. The co-simulation model was developed using the same approach as before. The corresponding running conditions were simulated and the responses were successfully validated against the experiments. A parameter study was also performed involving two design parameters with the objective to evaluate the effects of a parameter change.This thesis consists of two parts, where Part I gives an introduction to the application, the simulation method and the implementation, while Part II consists of three papers from this project.
|
|
| 2. |
- Andersson, Karin, 1972-
(författare)
-
Naturmöten i pedagogiska verksamheter
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The general public´s everyday encounters with nature have radically changed during the 20th century in industrial countries. Our relation towards nature in relation to environmental challenges is an important educational question, and this thesis investigates encounters with nature in educational practice. More specifically the aims are to investigate (i) how encounters with nature has been legitimated in the national curricula of Swedish school, and (ii) meaning making processes within pedagogical encounters with nature. In relation to the first aim a discourse analytical reading of the national curricula in Sweden is conducted. The results show that a scientific perspective of encounters with nature has been dominating during the last hundred years in the national curricula. In recent years, it is also more instrumental encounters that are expressed in the curricula, while students’ personal experiences and feelings are not focused in current curricula. Paper II and III examine moral meaning making in three different educational practices – Outdoor Education Centres, All-Weather Outdoor Schools and the Radical Outdoor movement. A multidisciplinary method is used in paper II, LEDmodel (Landscape, Ethical and Didactical). Paper III is based on the ethical tendency and language-game analyses. The results from these studies show that the educational purpose have an impact on moral processes in relation to nature. When the purpose is related to scientific knowledge there is often an instrumental relation towards nature in contrast to encounters that are more open. Open encounters instead seem to create relations that are built on a sense of responsibility and empathy. The results show that relations are created in different ways where some are more personal and built on emotion when other emotions are more based on stated rules or norms.
|
|
| 3. |
- Andersson, Malin
(författare)
-
Aging sensitive battery control
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The battery is a component with significant impact on both the cost and environmental footprint of a full electric vehicle (EV). Consequently, there is a strong motivation to maximize its degree of utilization. Usage limits are enforced by the battery management system (BMS) to ensure safe operation and limit battery degradation. The limits tend to be conservative to account for uncertainty in battery state estimation as well as changes in the battery's characteristics due to aging. To improve the utilization degree, aging sensitive battery control is necessary. This refers to control that a) adjusts during the battery's life based on its state and b) balances the trade-off between utilization and degradation according to requirements from the specific application. In state-of-the-art battery installations, only three signals are measured; current, voltage and temperature. However, the battery's behaviour is governed by other states that must be estimated such as its state-of-charge (SOC) or local concentrations and potentials. The BMS therefore relies on models to estimate states and to perform control actions. In order to realize points a) and b), the models that are used for state estimation and control must be updated onboard. An updated model can also serve the purpose of diagnosing the battery, since it reflects the changing properties of an aging battery. This thesis investigates identification of physics-based and empirical battery models from operational EV data. The work is divided into three main studies.1) A global sensitivity analysis was performed on the parameters of a high-order physics-based model. Measured current profiles from real EV:s were used as input and the parameters' impact on both modelled cell voltage and other internal states was assessed. The study revealed that in order to excite all model parameters, an input with high current rates, large SOC span and longer charge or discharge periods was required. This was only present in the data set from an electric truck with few battery packs. Data sets from vehicles with more packs (electric bus) and limited SOC operating window (plug-in hybrid truck) excited fewer model parameters.2) Empirical linear-parameter-varying (LPV) dynamic models were identified on driving data. Model parameters were formulated as functions of the measured temperature, current magnitude and estimated open circuit voltage (OCV). To handle the time-scale differences in battery voltage response, continuous-time system identification was employed. We concluded that the proposed models had superior predictive abilities compared to discrete and time-invariant counterparts. 3) Instead of using driving data to parametrize models, we also investigated the possibility to design the charging current in order to increase its information content about model parameters. This was formulated as an optimal control problem with charging speed and information content as objectives. To also take battery degradation into account, constraints on polarization was included. The results showed that parameter information can be increased without significant increase in charge time nor aging related stress.
|
|
| 4. |
|
|
| 5. |
- Andersson, Mattias
(författare)
-
Coding for the Wiretap Channel
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We consider code design for Wyner’s wiretap channel. Optimal coding schemes for this channel require an overall code that is capacity achieving for the main channel, partitioned into smaller subcodes, all of which are capacity achieving for the wiretapper’s channel. To accomplish this we introduce two edge type low density parity check (LDPC) ensembles for the wiretap channel. For the scenario when the main channel is error free and the wiretapper’s channel is a binary erasure channel (BEC) we find secrecy capacity achieving code sequences based on standard LDPC code sequences for the BEC. However, this construction does not work when there are also erasures on the main channel. For this case we develop a method based on linear programming to optimize two edge type degree distributions. Using this method we find code ensembles that perform close to the secrecy capacity of the binary erasure wiretap channel (BEC- WT). We generalize a method of M ́easson, Montanari, and Urbanke in order to compute the conditional entropy of the message at the wire- tapper. This conditional entropy is a measure of how much information is leaked to the wiretapper. We apply this method to relatively simple ensembles and find that they show very good secrecy performance. Based on the work of Kudekar, Richardson, and Urbanke, which showed that regular spatially coupled codes are capacity achieving for the BEC, we construct a regular two edge type spatially coupled ensem- ble. We show that this ensemble achieves the whole capacity-equivocation region for the BEC-WT. We also find a coding scheme using Arıkans polar codes. These codes achieve the whole capacity-equivocation region for any symmetric binary input wiretap channel where the wiretapper’s channel is degraded with respect to the main channel.
|
|
| 6. |
|
|
| 7. |
- Andersson, Mikael
(författare)
-
Drivhusmodellen i teori och praktik : ett verksamhetsintegrerat forsknings- och utvecklingsarbete för integration av utbildning, forskning och samverkan vid Luleå tekniska universitet
- 2003
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns the development of a model for integration of education, research and cooperation intended for university use. The thesis builds on a research and development work integrated in the daily educational activity of the university. The model; the Green-house model combines experience-based learning with theory-based learning dialectically. The model and it's correspondent activities and practice is developed at the Luleå Technical University inside the four green-houses started in the Arena for Innovative Technology and Business. The purpose of the green-house is to introduce a cross-functional knowledge- building which is characterised by multidisciplinarity, the participation of different professions, the cooperation with actors from the surrounding society, that all actors are active and a cooperation that is based on equality between actors. Students and researchers participate in a green-house activity through a role/function related to a profession. In this activity situations occur that generates the need of action. If this need can be satisfied through re- creational actions these can be made the subject of reflection. If not the situation has generated a problem. In this case the acting unit, a person or a group must use their imagination (and creativity) to create innovative action. The starting point of the action can be found in the following areas of knowledge: the activity, the situation (needs, related problems and phenomena) and the actors function (role and/or group). The knowledge can be viewed out of the following aspects of knowledge: declarative and familiar knowledge, judgment and ability. These aspects can be discerned in connection with all these areas of knowledge. Put together this describes the learning process in the Green-house model. The long-term aim of the integration of experience-based learning with theory-based learning and the applied learning-process according to the green-house model is to enhance the possibility for development-oriented learning (which is closely related to Engeströms's Learning by expanding) in (later) working life. Development-oriented learning is defined as the individuals (or groups) own ability to interpret action, situation and his/her own function in a way that can go beyond the limits of the conditions at hand. Development- oriented learning is in its ideal form characterised by independent development of goal/task, choice of method and evaluation of outcomes. A activity-integrated frame of interpretation is developed in this thesis. It is characterised by the following critical aspects concerning model and practice: activity and practice, informal model (goal documents etc.), prescriptive model (an ideal type controlled by the researcher/developer), activity-related theory (scientific theories that can be more or less directly related to the activity) and other theories. In this work the foundation of an activity-integrated r&d program is laid. The knowledge of the model and activity/practice is developed by the participation in the following roles: operator, developer and researcher. Data has been collected inspired ethnographic method and the reflection on data has a connection to hermeneutic method. The activity-related theory, together with the activity-related frame of interpretation has been applied to the analysis of model and activity/practice. As a part of the analysis recommendations have been made to activity/practice. The recommendations and the reactions on those is an important part of the activity-integrated method. The learning process follows the characteristics of the learning process of the green-house model. The activity-integrated r&d model can be seen as an alternative to action research or other forms of research close to practice. Words in Italic represent concepts of central importance to this thesis and are defined in its text.
|
|
| 8. |
- Andersson, Mikael
(författare)
-
Performance modeling and control of web servers
- 2004
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the task of modeling a web server and designing a mechanism that can prevent the web server from being overloaded. Four papers are presented. The first paper gives an M/G/1/K processor sharing model of a single web server. The model is validated against measurements ands imulations on the commonly usedw eb server Apache. A description is given on how to calculate the necessary parameters in the model. The second paper introduces an admission control mechanism for the Apache web server basedon a combination of queuing theory andcon trol theory. The admission control mechanism is tested in the laboratory, implemented as a stand-alone application in front of the web server. The third paper continues the work from the secondp aper by discussing stability. This time, the admission control mechanism is implemented as a module within the Apache source code. Experiments show the stability and settling time of the controller. Finally, the fourth paper investigates the concept of service level agreements for a web site. The agreements allow a maximum response time anda minimal throughput to be set. The requests are sorted into classes, where each class is assigneda weight (representing the income for the web site owner). Then an optimization algorithm is appliedso that the total profit for the web site during overload is maximized.
|
|
| 9. |
|
|
| 10. |
- Andersson, Rasmus
(författare)
-
Evaluation of two hydrocyclone designs for pulp fractionation
- 2010
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The process conditions and fractionation efficiency of two hydrocyclone designs, a novel and a conventional conical design, were evaluated. The novel design comprised a modified inlet section, where the pulp suspension had to pass a narrow ring-shaped opening, and a very compact fractionation zone. The influence of feed concentration and fine fraction mass ratio was studied. The trials were performed with never-dried, unrefined bleached chemical softwood pulp. Fractionation efficiency was evaluated in terms of change of surface roughness of handsheets made out of the fractions and the feed pulp respectively.The fractionation efficiency increased considerably with decreasing fine fraction mass ratio, especially at higher feed concentrations. This finding prompted a hypothesis on the existence of a radial gradient in the composition of the suspension inside the novel hydrocyclone. Using the novel hydrocyclone in a feed-forward fractionation system would therefore prove to be more favourable as a larger total fine fraction of better properties can be obtained. A three-stage feed-forward fractionation system was evaluated in laboratory scale. Here, it was indeed possible to extract fine fractions with improved surface properties in each of the three consecutive stages. All three fine fractions had about the same surface roughness.The fractionation performance of the novel design was benchmarked against that of a conventional, best available technology (BAT) design. In terms of fractionation efficiency, the BAT design performed better. However, the fractions produced with the novel hydrocyclone had a much smaller difference in concentration, implying a much less pronounced enrichment of fines in the fine fraction. It is unclear, to what extent the lower share of latewood fibres and the increased fines content, respectively, contributed to the improved surface roughness of the fine fractions. However, it is clear that the lower enrichment of fines in the novel hydrocyclone makes it easier to install it in industrial applications without a need for auxiliary equipment to redistribute large water flows.
|
|
