| 1. |
- Chistiakova, Tatiana, et al.
(författare)
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Nonlinear system identification of the dissolved oxygen to effluent ammonia dynamics in an activated sludge process
- 2017
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Ingår i: IFAC-PapersOnLine. - : Elsevier B.V.. - 2405-8963. ; 50:1, s. 3917-3922
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Tidskriftsartikel (refereegranskat)abstract
- Aeration of biological reactors in wastewater treatment plants is important to obtain a high removal of soluble organic matter as well as for nitrification but requires a significant use of energy. It is hence of importance to control the aeration rate, for example, by ammonium feedback control. The goal of this paper is to model the dynamics from the set point of an existing dissolved oxygen controller to effluent ammonia using two types of system identification methods for a Hammerstein model, including a newly developed recursive variant. The models are estimated and evaluated using noise corrupted data from a complex mechanistic model (Activated Sludge Model no.1). The performance of the estimated nonlinear models are compared with an estimated linear model and it is shown that the nonlinear models give a significantly better fit to the data. The resulting models may be used for adaptive control (using the recursive Hammerstein variant), gain-scheduling control, L2 stability analysis, and model based fault detection.
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| 2. |
- Aslani, Mohammad, et al.
(författare)
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Continuous residual reinforcement learning for traffic signal control optimization
- 2018
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Ingår i: Canadian journal of civil engineering (Print). - : NRC Research Press. - 0315-1468 .- 1208-6029. ; 45:8, s. 690-702
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Tidskriftsartikel (refereegranskat)abstract
- Traffic signal control can be naturally regarded as a reinforcement learning problem. Unfortunately, it is one of the most difficult classes of reinforcement learning problems owing to its large state space. A straightforward approach to address this challenge is to control traffic signals based on continuous reinforcement learning. Although they have been successful in traffic signal control, they may become unstable and fail to converge to near-optimal solutions. We develop adaptive traffic signal controllers based on continuous residual reinforcement learning (CRL-TSC) that is more stable. The effect of three feature functions is empirically investigated in a microscopic traffic simulation. Furthermore, the effects of departing streets, more actions, and the use of the spatial distribution of the vehicles on the performance of CRL-TSCs are assessed. The results show that the best setup of the CRL-TSC leads to saving average travel time by 15% in comparison to an optimized fixed-time controller.
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| 3. |
- Aslani, Mohammad, et al.
(författare)
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Developing adaptive traffic signal control by actor-critic and direct exploration methods
- 2019
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Ingår i: Proceedings of the Institution of Civil Engineers. - : Thomas Telford. - 0965-092X .- 1751-7710. ; 172:5, s. 289-298
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Tidskriftsartikel (refereegranskat)abstract
- Designing efficient traffic signal controllers has always been an important concern in traffic engineering. This is owing to the complex and uncertain nature of traffic environments. Within such a context, reinforcement learning has been one of the most successful methods owing to its adaptability and its online learning ability. Reinforcement learning provides traffic signals with the ability automatically to determine the ideal behaviour for achieving their objective (alleviating traffic congestion). In fact, traffic signals based on reinforcement learning are able to learn and react flexibly to different traffic situations without the need of a predefined model of the environment. In this research, the actor-critic method is used for adaptive traffic signal control (ATSC-AC). Actor-critic has the advantages of both actor-only and critic-only methods. One of the most important issues in reinforcement learning is the trade-off between exploration of the traffic environment and exploitation of the knowledge already obtained. In order to tackle this challenge, two direct exploration methods are adapted to traffic signal control and compared with two indirect exploration methods. The results reveal that ATSC-ACs based on direct exploration methods have the best performance and they consistently outperform a fixed-time controller, reducing average travel time by 21%.
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| 4. |
- Lakemond, Nicolette, 1973-, et al.
(författare)
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Match & Manage : The use of knowledge matching and project management to integrate knowledge in collaborative inbound open innovation
- 2016
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Ingår i: Industrial and Corporate Change. - : Oxford University Press (OUP). - 0960-6491 .- 1464-3650. ; 25:2, s. 333-352
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Tidskriftsartikel (refereegranskat)abstract
- Despite mounting evidence on the potential benefits of inbound open innovation, little is known about how firms purposefully manage inflows of knowledge. We investigate the use of two knowledge governance procedures—project management and knowledge matching—in collaborative inbound open innovation. Our findings suggest that, in addition to “knowledge-precursors,” which the literature on open innovation and absorptive capacity has shown to be important for the integration of external knowledge, the firm’s choice of knowledge governance matters for innovation performance.
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| 5. |
- Liu, Fei, et al.
(författare)
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Precision study on augmented reality-based visual guidance for facility management tasks
- 2018
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Ingår i: Automation in Construction. - : Elsevier BV. - 0926-5805 .- 1872-7891. ; 90, s. 79-90
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Tidskriftsartikel (refereegranskat)abstract
- One unique capability of augmented reality (AR) is to visualize hidden objects as a virtual overlay on real occluding objects. This “X-ray vision” visualization metaphor has proved to be invaluable for operation and maintenance tasks such as locating utilities behind a wall. Locating virtual occluded objects requires users to estimate the closest projected positions of the virtual objects upon their real occluders, which is generally under the influence of a parallax effect. In this paper we studied the task of locating virtual pipes behind a real wall with “X-ray vision” and the goal is to establish relationships between task performance and spatial factors causing parallax through different forms of visual augmentation. We introduced and validated a laser-based target designation method which is generally useful for AR-based interaction with augmented objects beyond arm's reach. The main findings include that people can mentally compensate for the parallax error when extrapolating positions of virtual objects on the real surface given traditional 3D depth cues for spatial understanding. This capability is, however, unreliable especially in the presence of the increasing viewing offset between the users and the virtual objects as well as the increasing distance between the virtual objects and their occluders. Experiment results also show that positioning performance is greatly increased and unaffected by those factors if the AR support provides visual guides indicating the closest projected positions of virtual objects on the surfaces of their real occluders.
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| 6. |
- Masud, Nauman, et al.
(författare)
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On stability and performance of disturbance observer-based-dynamic load torque compensator for assistive exoskeleton : A hybrid approach
- 2020
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Ingår i: Mechatronics (Oxford). - : Elsevier. - 0957-4158 .- 1873-4006. ; 69
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Tidskriftsartikel (refereegranskat)abstract
- A disturbance observer-based-dynamic load-torque compensator for current-controlled DC-drives, as joint actuator of assistive exoskeletons, has been recently proposed. It has been shown that this compensator can effectively linearize and decouple the coupled nonlinear dynamics of the human-exoskeleton system, by more effectively compensating the associated nonlinear load-torques of the exoskeleton at the joint level. In this paper, a detailed analysis of the current controlled DC drive-servo system using the said compensator, with respect to performance and stability is presented, highlighting the key factors and considerations affecting both the stability and performance of the compensated servo system. It is shown both theoretically and through simulation results that the stability of the compensated servo system is compromised as performance is increased and vice-versa. Based on the saturation state of the servo system, a new hybrid switching control strategy is then proposed to select stability or performance-based compensator and controller optimally. The strategy is then experimentally verified both at the joint and task space level by using the developed four active-degree of freedom exoskeleton test rig.
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| 7. |
- Mattsson, Per, et al.
(författare)
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Identification of cascade water tanks using a PWARX model.
- 2018
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Ingår i: Mechanical systems and signal processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 106, s. 40-48
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider the identification of a discrete-time nonlinear dynamical model for a cascade water tank process. The proposed method starts with a nominal linear dynamical model of the system, and proceeds to model its prediction errors using a model that is piecewise affine in the data. As data is observed, the nominal model is refined into a piecewise ARX model which can capture a wide range of nonlinearities, such as the saturation in the cascade tanks. The proposed method uses a likelihood-based methodology which adaptively penalizes model complexity and directly leads to a computationally efficient implementation.
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| 8. |
- Olsson, Fredrik, et al.
(författare)
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Identification of Nonlinear Feedback Mechanisms Operating in Closed Loop using Inertial Sensors
- 2018
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Ingår i: IFAC-PapersOnLine. - : Elsevier B.V.. - 2405-8963. ; 51:15, s. 473-478
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we study the problem of identifying linear and nonlinear feedback mechanisms, or controllers, operating in closed loop. A recently developed identification method for nonlinear systems, the LAVA method, is used for this purpose. Identification data is obtained from inertial sensors, that provide information about the movement of the system, in the form of linear acceleration and angular velocity measurements. This information is different from the information that is available to the controller to be identified, which makes use of unknown internal sensors instead. We provide two examples, a simulated neuromuscular controller in standing human balance, and a lead-filter controlling a physical position servo using a DC motor. Both linear and nonlinear controllers are used in the examples. We show that the LAVA method is able to identify sparse, parsimonious models of the controllers.
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| 9. |
- Wallhagen, Marita, et al.
(författare)
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Ecological Worldview among Urban Design Professionals
- 2017
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Ingår i: Sustainability. - : MDPI AG. - 2071-1050. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- The built environment is responsible for a large proportion of the global use of energy, natural resources, and emissions. Architects and other urban design professionals are key actors in the building process whose behavior and decisions will influence these impacts. Because environmental attitudes are linked to pro-environmental behavior, this study aims to measure environmental worldview among urban design professionals involved in the architectural competition 'A New City Center for Kiruna'. The mean score registered for the New Environmental Paradigm (NEP) scale was 3.68 (standard deviation 0.51) and there were no significant differences with regard to age (mean 41.3 years) or gender (64.7% males). The ecological worldview of the participants was similar to most other samples from diverse countries, but a lower score was reported in comparison to environmentalists. The score ranged from 2.53 to 4.67 which shows heterogeneity at an individual level. Thus, future efforts to improve environmental attitudes among urban design professionals are needed.
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| 10. |
- Djuric Ilic, Danica, et al.
(författare)
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No zero burden assumption in a circular economy
- 2018
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Ingår i: Journal of Cleaner Production. - : Elsevier Ltd. - 0959-6526 .- 1879-1786. ; 182, s. 352-362
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Tidskriftsartikel (refereegranskat)abstract
- A majority of previous studies on environmental problems caused by waste generation have focused on waste disposal issues without fully highlighting the primary reasons behind the problems. As a consequence, efforts to reduce these problems are usually directed towards the stakeholders that provide waste treatment and disposal instead of the stakeholders that contribute to waste generation. In order to detect connections between different problems of sustainability and to suggest measures which may contribute to their solutions, this study provides a simplified overview of the mechanisms behind waste generation and management. The results from the study show that the only way to eliminate problems of sustainability is to apply an upstream approach by dealing with the primary problems which occur in the early stages of the system (e.g. overconsumption of products, as well as use of finite resources, toxic materials, and non-recyclable materials). By dealing with these problems, the emergence of secondary problems would be prevented. Thereby, stakeholders who have the highest possibility to contribute to the sustainable development of the waste generation and management are the stakeholders from the origin of the product's life cycles, such as product developers, manufacturing companies, product users and policy makers. Different trade-off situations such as contradictions between economics, recyclability, energy efficiency, make it even harder to deal with issues of sustainability related to the system and to detect the stakeholders who may contribute to the development. One of the main conclusions from this study is that when transforming society towards a circular economy, the traditional view of separate systems for production and waste management must be changed. In order to refer to all problems of sustainability and also cover the top steps of the waste hierarchy, life cycle assessment of waste management should include manufacture and use of products ending up as waste. Waste entering the waste management system with “zero burden” by releasing the previous actors of the waste life cycle from any responsibility related to the environment (i.e. by shifting the total environmental burden into the waste management system), does not capture the problems with waste generation.
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