| 1. |
- Bachmaier, Hans, et al.
(författare)
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Bereal - method for pellet stoves : Field test and round robin
- 2017
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Ingår i: European Biomass Conf. Exhib. Proc.. - : ETA-Florence Renewable Energies. ; , s. 642-647
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Konferensbidrag (refereegranskat)abstract
- Recent pellet stoves perform excellently under type test conditions. In contrast, typical real life emissions show significantly higher values under usual operational conditions. Consequently, type testing procedures may not account for real life stove operation and, thus, do not allow to distinguish between low- and high-tech appliances. The EU-project beReal aimed at the development of a testing method for pellet stoves that reflects real life operations better and to support innovative pellet stoves that perform well under typical operational conditions. Based on an online survey and field observations, an advanced real life testing procedure for pellet stoves was established reflecting real life user behavior, e.g. regarding different load levels and the ignition phase. A field test was designed at the end of the project to demonstrate the applicability and practical relevance. The field test proved that emission values for beReal at the test stand and in the field stay within the same range. A Round Robin test proved the repeatability and reproducibility of the beReal testing procedure. The beReal method can be reproduced with the same statistical variability or performed even better than the type testing method with exception of PM between different laboratories. © 2017, ETA-Florence Renewable Energies. All rights reserved.
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| 2. |
- Birk, Wolfgang, et al.
(författare)
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Interactive modeling and visualization of complex processes in pulp and paper making
- 2010
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Konferensbidrag (refereegranskat)abstract
- This paper discusses a new approach to interactive modeling, visualization and analysis of complex industrial processes. A theoretical framework based on signal flow graphs for modeling and visualization is presented. Using this framework a software tool is designed, called ProMoVis, which can be used to model a process, to visualize the models together with process construction and control system, and to perform analysis regarding e.g. feasible control strategies for the process. Moreover, a case study is conducted, where ProMoVis is used to model, visualize and analyze a stock preparation plant. The results indicate that the proposed methods and tools improve work flows, increase process understanding and simplify decision making on control strategies for complex process.
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| 3. |
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| 4. |
- Larsson, John Erik, et al.
(författare)
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Paper machine dry line position control
- 1998
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Ingår i: Reglermöte '98. - Lund : Reglerteknik, Lunds tekniska högskola. ; , s. 168-172
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Larsson, John Erik, et al.
(författare)
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Paper machine dry line positioning system
- 1998
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Ingår i: Proceedings of Control Systems 98. - : Finnish Society of Automation. ; , s. 355-362
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Konferensbidrag (refereegranskat)
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| 6. |
- Rosén, Thomas, 1967-
(författare)
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Open Source Business Model : Balancing Customers and Community
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Free and Open Source Software has not only increased researchers’ interest about community-driven software development, but lately, interest from commercial actors increased as well. In addition, some scientists have claimed that Open Source Software has entered a new phase: OSS 2.0. Even so, a coherent way of analyzing commercial Open Source ventures is still missing.Commercial Open Source firms’ strategies are often described using the term “business models”. However, these models often lack stringent structures and have been used primarily to describe the firms’ offerings and methods to earn revenue.Through the adaptation of an existing, firmly theoretically-based analytical business model framework, this thesis suggests a new analysis model for studying for-profit Open Source companies. In addition, the framework is generically constructed, ensuring its usability for other industries as well. The model consists of three elements: market positions, operational platform and offering.This particular study concerned four software product vendors, all of which base their products on Open Source Software. When analyzing their business, insights were made about how these firms operated. The result show that there are certain key elements and factors that determine if a company has a sustainable business or not. From the analysis framework, three elements were refined. The main Open Source Software project connects the market positions and the operational platform; and from the offering, the product and service and the revenue model were very important.The study identified eight key factors which influenced the elements: brand for the product, the company and the Open Source Software project; community, that is the sum of the non-paying users and developers connected to Open Source Software projects; resources, which are community-based resources such as development and testing; legitimacy, the perceived legitimacy regarding licenses and the revenue models; control, i.e. the control the firm has of the software; ability to charge, or how the company can charge for its services; customers, the paying users; and finally volume, which is the number of paying customers.The findings also indicate that companies interested in working with the open-source community have to be able to balance the demands from both their customers and the community in order to benefit and gain competitive advantage.
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| 7. |
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| 8. |
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| 9. |
- Rönnbäck, Klas, 1974, et al.
(författare)
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Working in the ‘White Man’s Grave’: Wages and Migration from Europe to the Gold Coast in the Eighteenth Century
- 2019
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Ingår i: Journal of Migration History. - : Brill. - 2351-9916 .- 2351-9924. ; 5:3, s. 438-465
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Tidskriftsartikel (refereegranskat)abstract
- This article examines the economic incentives for Europeans to migrate to the socalled ‘white man’s grave’ of West Africa. Ignorance and coercion have been proposed as explanations for migration to high mortality areas. We use data on the Royal African Company and their European employees on the Gold Coast during the period 1707– 1740. We found that the employees received a premium above the wage they would have received in England. Economic reasons might therefore have swayed the decision to migrate. Nevertheless, the wage premium was low in relation to the very high risk of dying. The migrating men either placed a low value on their own lives, or did not understand the risks they were facing.
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| 10. |
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| 11. |
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| 12. |
- Rönnbäck, Stefan, et al.
(författare)
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A design algorithm for anti-windup compensators : polynomial approach
- 1993
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Ingår i: Elsevier IFAC Publications / IFAC Proceedings series. - 1474-6670. - 008042211X ; 26:2:5, s. 619-624
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Tidskriftsartikel (refereegranskat)abstract
- It is discussed how an LTI ‘polynomial controller’ for a SISO-system with actuator constraints can be designed using conventional linear pole-placement technique. This becomes possible due to the utilization of an ‘anti-windup’ technique in which the effect of control-signal saturation is interpreted as being caused by an equivalent disturbance. The results are summarized into a ‘design algorithm’ which supports a complete separation of 'servo', ‘disturbance-rejection’ and ‘anti-windup’ poles. It also supports the introduction of arbitrary 'specific factors’ into the controller polynomials, and it can be used for both continuous-time and discrete-time controllersIt is discussed how an LTI ‘polynomial controller’ for a SISO-system with actuator constraints can be designed using conventional linear pole-placement technique. This becomes possible due to the utilization of an ‘anti-windup’ technique in which the effect of control-signal saturation is interpreted as being caused by an equivalent disturbance. The results are summarized into a ‘design algorithm’ which supports a complete separation of 'servo', ‘disturbance-rejection’ and ‘anti-windup’ poles. It also supports the introduction of arbitrary 'specific factors’ into the controller polynomials, and it can be used for both continuous-time and discrete-time controllers.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Rönnbäck, Stefan
(författare)
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Linear control of systems with actuator constraints
- 1993
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the problem of how to design a linear and time invariant controller (continuous- or discrete-time) for a SISO- or SIMO-system with amplitude constraints in the actuator. One of the basic ideas is to model the constraints by means of a 'disturbance' δ acting at the input of the process. That is, whenever the actuator saturates, the difference between its output and input is interpreted as being caused by this 'disturbance'. Since the non-linearity thus becomes hidden in a non-linear relationship between the controller output and δ , the system appears to be linear. It is discussed how this makes it possible to utilize conventional linear theory to gain insight about how the closed-loop system is affected by actuator saturation. This effect is interpreted as a windup phenomenon, and its dynamic properties are characterized by the transfer operator Hδ from δ to the output of the system. By investigating some of the anti-windup methods which are most frequently encountered in the literature, it is revealed that none of them provides a sufficient parameterization with respect to the needs for manipulation of Hδ It is shown how this problem can be overcome by extending the controller with some additional 'anti-windup dynamics', in such a way that the corresponding modes are excitable only by δ This is done for both a polynomial and a state-space parameterization, where in the latter case a general form and an 'explicit-observer' form are considered. Since the additional modes appear as poles in Hδ it becomes possible to interpret the anti-windup design as a pole-placement problem. This makes the method well-suited for incorporation as a natural step in conventional text-book methods for design of linear controllers. This possibility is emphasized through the development of a design algorithm for polynomial-controllers (with antiwindup) intended for SISOsystems. It is demonstrated how suitable locations for the poles of Hδ can be found by means of either a time- or a frequency-domain approach. In the latter, describing function analysis is utilized as a tool for prediction of whether a certain location is likely to cause problems with 'repeated saturation' (non-linear oscillations).
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| 17. |
- Rönnbäck, Stefan
(författare)
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Nonlinear dynamic windup detection in anti-windup compensators
- 1996
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Ingår i: CESA'96 IMACS Multiconference. - Villeneuve d'Ascq : Gerf EC. - 2951026609 ; , s. 1014-1019
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Konferensbidrag (refereegranskat)abstract
- In order to get a fast servo performance and a fast attenuation of disturbance effects, it is often desirable to have a high loop gain in control-systems. Unfortunately, this may contradict to the requirement on having a low loop-gain in order not to violate the actuator limits, which could cause windup problems. The trade-off between these two can to some extent be handled by means of conventional anti-windup techniques, but in general not over a sufficient range of operation. In order to reduce the problem further, it is proposed that the fastness of the closed-loop should be continuously retuned with respect to the status of the windup phenomenon. For this purpose, a certain 'nonlinear dynamic windup detector' is proposed, which uses the actuator in- and outputs for detecting the presence of windup, and produces a 'fastness variable' as its output. It is outlined how to achieve anti-windup by utilizing this fastness variable for on-line tuning of the controller. Typically this could be done by pole-shifting.
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| 18. |
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| 19. |
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| 20. |
- Samuelsson, Jessica, et al.
(författare)
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Hur valet av förbränningsteknik påverkar utsläpp till luft vid närvärmecentraler vid eldning av spannmål
- 2006
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Rapport (refereegranskat)abstract
- The aim of this project was to take a closer look at problems connected to combustion of energy grain in a systematic way. The work was restricted to appliances of 100 - 400 kW. Eight users of energy grain were interviewed about there experiences. The majority had smaller problems, besides from relatively many running-in problems, presumably because the instructions for installation and operation were insufficient. Shutdowns were rare and caused by sintering. Burning other cereals than oat often led to sintering. Corrosion is avoided by keeping the flue gas temperature high. Measurements were performed on three boilers for energy grain. Measured carbon monoxide was 70 - 900 mg/Nm3, OGC 0 - 28 mg/Nm3, nitrogen oxides 490 - 945 mg/Nm3 and dust 160 - 440 mg/Nm3. All emissions were higher compared to pellets. Sulphur dioxide and hydrochloric acid were estimated from fuel analysis, and were higher than from combustion of wood. Energy grain does not contribute to global warming and have good properties in the form of high heating value, relatively high density and the grain has a size and form easy to combust. The Swedish Board of Housing, Building and Planning prescribes maximum allowed levels of OGC. The boilers studied in this project had emission well below these limits. For boilers < 500 kW, there are no legislations or recommendation that restrict emissions of dust, nitrogen oxides, sulphur dioxides or hydrochloric acid. The lack of legislation/recommendations makes it difficult to judge whether the emissions are acceptable or not. Today, boilers for energy grain are designed to give low emissions of unburned components and not optimised for low emissions of nitrogen oxides. By changing the design of the burner (it was equipped with three steps with air holes) the emissions were reduced by 27 % without an increase of unburned components. The objective with the steps was to divide the combustion into two zones: one with deficit of oxygen and one rich with oxygen. It is probable possible to reduce the emission even more by dividing the combustion in an even more sophisticated way. Measurements in three different boilers showed that dust emission from one of the boilers that used modulating power regulation was substantially lower than from the other two that were controlled by an on-off thermostat. This may be explained by higher degree of ash pulled by the gas flow at high power, or by lower temperature in the glow bed at low power. However, more data is required to draw general conclusions. Emissions of dust, nitrogen oxides, sulphur dioxide or hydrochloric acid constitute an obstacle for a considerable expansion of energy grain and similar fuels; because the emission will be paid attention to if they increase, especially if they increase in connection to densely populated areas. Therefore, a continuous increase of combustion of energy crops should be accompanied by continuous improvements of combustion technique to reduce the emissions.
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| 21. |
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| 22. |
- Servin, Martin, 1975-, et al.
(författare)
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Modeling and simulation of a granulation system using a nonsmooth discrete element method
- 2015
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Ingår i: ECCOMAS IV international conference on particle-based methods 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Granulation is the process of forming macroscopic granules, e.g. tablets or pellets, from microscopic particles. A common system for continuous granulation consist of a rotary drum or disc, a sieve and chrusher connected in a circuit by a number of conveyors. The granulation occur in the drum (or disc) and the main mechanisms are nucleation, layering, coalescence and breakage [1]. The process can be controlled by drum velocity and feed rate of fine material, binding agencies and moisture. The geometric design of components affect the material flow and thus the sieving capacity and ultimately the production capacity. Many granulation plants operate well below their capacity and suffer from high recycle rates and dynamic instabilities [2]. The main challenge of modelling and simulation of granulation processes is the occurrence of multiple length and time scales. The traditional approaches are typically focused either the largescale level of processing units or on the microscale level of particles. A complete model of a granulation process need to include also the intermediate scale of granule dynamics [1]. This is, however, a very challenging computational task given the vast number of granules, typically many millions or more. We present a meso-scale approach to modeling and simulating iron ore granulation systems with granules modeled as nonsmooth discrete elements (NDEM) [3-6]. This extend a previous iron ore granule model [7] used for balling drum outlet design simulation [8]. Ore fines and moisture is modeled by a quasiparticle model for slurry [9]. Interaction models for nucleation, layering, coalescence and breakage are proposed and tested in a virtual balling circuit. The computational performance is analysed and different methods for accelerating the NDEM computations are tested.
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| 23. |
- Sternad, Mikael, et al.
(författare)
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A frequency domain approach to anti-windup compensator design
- 1993
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The effect of input saturation in linear time invariant control systems is addressed. We utilize a controller in polynomial form, with a three degrees of freedom structure. This makes it possible to add a saturation compensator (an anti-windup filter) separately, after tuning of the controller properties for unsaturated signals. Our aim is that the effect of a saturation event should decay as quickly as possible after desaturation, while the tendency for repeated re-saturations, due to nonlinear oscillations, should be suppressed. This is achieved by modifying the relevant loop gain by a safety margin. The modified loop gain is then adjusted, so that it touches the describing function of the saturation nonlinearity. The construction of the safety margin takes the magnitude of exogenous signals into account. The method requires only simple calculations. It can be automated, using a one-dimensional numerical search. Furthermore, the effect of D/A-quantization in digital feedback systems is also controlled by the same antiwindup scheme. The presence of unstructured errors in a linear plant model can be taken into account. We also provide a discussion on how the frequency domain viewpoint can improve the understanding of previously suggested anti-windup methods, such as the observer-based approach, and the conditioning technique.
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| 24. |
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| 25. |
- Walgama, Kirthi S., et al.
(författare)
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Generalisation of conditioning technique for anti-windup compensation
- 1992
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Ingår i: IEE Proceedings D (Control Theory and Applications). - : Institution of Engineering and Technology (IET). - 0143-7054 .- 2053-793X. ; 139:2, s. 109-118
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Tidskriftsartikel (refereegranskat)abstract
- For linear controllers, the anti-windup compensator based on conditioning technique is often treated as a special case of the generalised anti-windup compensator. The conditioning technique is then defined simply by a special observer in the generalised anti-windup compensator. Instead, in the paper the concept of back calculation or the modified setpoint is emphasised, which is indeed the conceptual basis for the derivation of the conditioning technique. The behaviour of the modified setpoint is investigated by use of a simple example, and an inherent weakness in the conditioning technique is demonstrated. A simple modification to the conditioning technique that reduces the effect of short-sightedness is presented, and its anti-windup compensation properties are investigated. Also, a general approach to the conditioning technique is proposed by introducing a filtered setpoint. This approach provides a parameterisation to deal not only with the short-sightedness problem but also with the other drawbacks of the conditioning technique. An important outcome of this generalisation is that it unifies and interprets through the conditioning technique a class of AWCs described in the literature.
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| 26. |
- Wang, Da, 1981-, et al.
(författare)
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Parametrization and validation of a nonsmooth discrete element method for simulating flows of iron ore green pellets
- 2015
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Ingår i: Powder Technology. - : Elsevier. - 0032-5910 .- 1873-328X. ; 283, s. 475-487
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Tidskriftsartikel (refereegranskat)abstract
- The nonsmooth discrete element method (NDEM) has the potential of high computational efficiency for rapid exploration of large design space of systems for processing and transportation of mineral ore. We present parametrization, verification and validation of a simulation model based on NDEM for iron ore green pellet flow in balling circuits. Simulations are compared with camera based measurements of individual pellet motion as well as bulk behavior of pellets on conveyors and in rotating balling drum. It is shown that the NDEM simulation model is applicable for the purpose of analysis, design and control of iron ore pelletizing systems. The sensitivity to model and simulation parameters is investigated. It is found that: the errors associated with large time-step integration do not cause statistically significant errors to the bulk behavior; rolling resistance is a necessary model component; and the outlet flow from the drum is sensitive to fine material adhering to the outlet creating a thick coating that narrows the outlet gaps.
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| 27. |
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| 28. |
- Öberg, Stefan, 1978, et al.
(författare)
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Mortality among European settlers in pre-colonial West Africa: The “White Man’s Grave” revisited
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We have created the first longitudinal dataset following European employees of the English Royal African Company during their time in West Africa, 1683–1766. The mortality was catastrophically high with limited geographical differences. Tropical diseases and epidemics thereof, contributed to the high mortality and strong variations over time. The risk was highest for the men who had just arrived from Europe but remained high also after they had spent several years on the coast. The death rate of the Europeans was increased by both the share of newcomers and by the total number of men present on the coast.
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| 29. |
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| 31. |
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