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  • 1.
    Garmabaki, Amir Soleimani
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Thaduri, Adithya
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Hedström, Annelie
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Kumar, Uday
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Laue, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Marklund, Stefan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Bansal, Tarun
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Asplund, Matthias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Indahl, Stefan
    A Survey on Underground Pipelines and Railway Infrastructure at Cross-Sections2019Ingår i: ESREL-2019 / [ed] Michael beer, Enrico Zio, 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    Underground pipelines are an essential part of the transportation infrastructure. The structural deterioration of pipelines crossing railways and their subsequent failures are critical for society and industry resulting in direct and indirect costs for all the related stakeholders. Pipeline failures are complex processes, which are affected by many factors, both static (e.g., pipe material, size, age, and soil type) and dynamic (e.g., traffic load, pressure zone changes, and environmental impacts). These failures have serious impacts on public due to safety, disruption of traffic, inconvenience to society, environmental impacts and shortage of resources. Therefore, continuous and accurate condition assessment is critical for the effective management and maintenance of pipeline networks within transportation infrastructure. The aim of this study is to identify failure modes and consequences related to the crossing of pipelines in railway corridors. Expert opinion have been collected through two set of questionnaires which have been distributed to the 291 municipalities in the whole Sweden. The failure analysis revealed that pipe deformation has higher impact followed by pipe rupture at cross-section with railway infrastructure. For underground pipeline under railway infrastructure, aging and external load gets higher ranks among different potential failure causes to the pipeline.

  • 2.
    Chandran, Praneeth
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Lind, Håkan
    Bombardier Transportation, Stockholm, Sweden.
    Famurewa, Stephen M.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Train-based differential eddy current sensor system for rail fastener detection2019Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 30, nr 12, artikel-id 125105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One of the crucial components in rail tracks is the rail fastening system, which acts as a means of fixing rails to the sleepers to maintain the track gauge and stability. Manual inspection and 2D visual inspection of fastening systems have predominated over the past two decades. However, both methods have drawbacks when visibility is obscured and are found to be relatively expensive in terms of cost and track possession. The present article presents the concept of a train-based differential eddy current (EC) sensor system for fastener detection. The sensor uses the principle of electromagnetic induction, where an alternating-current-carrying coil is used to create an EC on the rail and other electrically conductive material in the vicinity and a pick-up coil is used to measure the returning field. This paper gives an insight into the theoretical background and application of the proposed differential EC sensor system for the condition monitoring system of rail fasteners and shows experimental results from both laboratory and field measurements. The field measurements were carried out along a heavy-haul railway line in the north of Sweden. Results obtained from both the field measurements and from the lab tests reveal that that the proposed method was able to detect an individual fastening system from a height of 65 mm above the rail. Furthermore, missing clamps within a fastening system are detected by analysing a time domain feature of the measurement signal.

  • 3.
    Saari, Juhamatti
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik. Luleå tekniska universitet, SKF-LTU University Technology Centre.
    Detecting operation regimes using unsupervised clustering with infected group labelling to improve machine diagnostics and prognostics2018Ingår i: Operations Research Perspectives, ISSN 2214-7160, Vol. 5, s. 232-244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Estimating the stress level of components while operation modes are varying is a key issue for many prognostic models in condition monitoring. The identification of operation profiles during production is therefore important. Clustering condition monitoring data with regard to operation regimes will provide more detailed information about the variation of stress levels during production. The distribution of the operation regimes can then support prognostics by revealing the cause-and-effect relationship between the operation regimes and the wear level of components.

    In this study unsupervised clustering technique was used for detecting operation regimes for an underground LHD (load-haul-dump machine) by using features extracted from vibration signals measured on the front axle and the speed of the Cardan axle. The clusters were also infected with a small portion of the data to obtain the corresponding labels for each cluster. Promising results were obtained where each sought-for operation regime was detected in a sensible manner using vibration RMS values together with speed.

  • 4.
    Jiménez-Redondo, Noemi
    et al.
    CEMOSA, Spain.
    Calle Cordón, Álvaro
    CEMOSA, Spain.
    Kandler, Ute
    Fraunhofer IVI, Dresden, Germany.
    Simroth, Axel
    Fraunhofer IVI, Dresden, Germany.
    Reyes, A.
    Universidad de Sevilla, Sevilla, Spain.
    Morales, F.J.
    Universidad de Sevilla, Sevilla, Spain.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Famurewa, Stephen Mayowa
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Morgado, João
    Infraestruturas de Portugal, Lisbon, Portugal.
    Duarte, Emanuel
    Infraestruturas de Portugal, Lisbon, Portugal.
    Iorio, Daniele
    DMA, Turin, Italy.
    Fruttero, Marco
    DMA, Turin, Italy.
    Juszt, András
    Régens Plc., Budapest, Hungary.
    INFRALERT: improving linear transport infrastructure efficiency by automated learning and optimised predictive maintenance techniques2018Ingår i: Proceedings of 7th Transport Research Arena TRA, Vienna, Austria, 2018, Vienna, Austria, 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    The on-going H2020 project INFRALERT aims to increase rail and road infrastructure capacity in the current framework of increased transportation demand by developing and deploying solutions to optimise maintenance interventions planning. INFRALERT develops an ICT platform - the expert-based Infrastructure Management System eIMS - which follows a modular approach including several expert-based toolkits. This paper presents the architecture of the eIMS as well as the functionalities, methodologies and exemplary results of the toolkits for i) nowcasting and forecasting of asset condition, ii) alert generation, iii)  RAMS & LCC analysis and iv) decision support. The applicability and effectiveness of the eIMS and its toolkits will be demonstrated in two real-world pilot scenarios, which are described in the paper: a meshed road network in Portugal under the jurisdiction of Infraestruturas de Portugal (IP) and a freight railway line in Northern Europe managed by Trafikverket

  • 5.
    Saari, Juhamatti
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Lundberg, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Selection of features for fault diagnosis on rotating machines using random forest and wavelet analysis2018Ingår i: Insight (Northampton), ISSN 1354-2575, E-ISSN 1754-4904, Vol. 60, nr 8, s. 434-442Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Identification of component faults using automated condition monitoring methods has a huge potential to improve the prediction of machine failures. The ongoing development of the Internet of Things (IoT) will support and benefit feature selection and improve preventative maintenance decision making. However, there may be problems with the selection of features that best describe a specific fault and remain valid even when the operation mode is changing (for example different levels of load). In this study, features were extracted from vibration signals using wavelet analysis; a feature subset was selected using the random forest ensemble technique. Three different datasets were created where the load of the system was changing while the rotational speed remained the same. The tests were repeated five times by first recording the nominal condition and then introducing four faults: angular misalignment; offset misalignment; partially broken gear tooth failure; and macro-pitting of the gear. To improve previous feature selection techniques, a method is proposed where, before training a classifier, the most promising features are compared at different degrees of torsional load. The results indicate that the proposed method of using random forests to select top variables can help to choose good features that may not have been considered in manual feature selection or in individual load zones.

  • 6.
    Jiménez-Redondo, Noemi
    et al.
    CEMOSA.
    Calle-Cordón, Álvaro
    CEMOSA.
    Kandler, Ute
    Fraunhofer Inst Verkehrs & Infrastruktursyst IV.
    Simroth, Axel
    Fraunhofer Inst Verkehrs & Infrastruktursyst IV.
    Morales, Francisco J
    Univ Seville.
    Reyes, Antonio
    Univ Seville.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Thaduri, Adithya
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Morgado, Joao
    Infraestruturas Portugal SA.
    Duarte, Emmanuele
    Infraestruturas Portugal SA.
    Improving linear transport infrastructure efficiency by automated learning and optimised predictive maintenance techniques (INFRALERT)2017Ingår i: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 236Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The on-going H2020 project INFRALERT aims to increase rail and road infrastructure capacity in the current framework of increased transportation demand by developing and deploying solutions to optimise maintenance interventions planning. It includes two real pilots for road and railways infrastructure. INFRALERT develops an ICT platform ( the expert-based Infrastructure Management System, eIMS) which follows a modular approach including several expert-based toolkits. This paper presents the methodologies and preliminary results of the toolkits for i) nowcasting and forecasting of asset condition, ii) alert generation, iii) RAMS & LCC analysis and iv) decision support. The results of these toolkits in a meshed road network in Portugal under the jurisdiction of Infraestruturas de Portugal (IP) are presented showing the capabilities of the approaches.

  • 7.
    Odelius, Johan
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Famurewa, Stephen Mayowa
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Forslöf, Lars
    Roadroid AB Ljusdal .
    Casselgren, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Konttaniemi, Heikki
    Arctic Power RDI-team, Lapland University of Applied Sciences Rovaniemi .
    Industrial internet applications for efficient road winter maintenance2017Ingår i: Journal of Quality in Maintenance Engineering, ISSN 1355-2511, E-ISSN 1758-7832, Vol. 23, nr 3, s. 355-367Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose: For the expected increase in the capacity of existing transportation systems and efficient energy utilisation, smart maintenance solutions that are supported by online and integrated condition monitoring systems are required. Industrial Internet is one of the smart maintenance solutions, which enables real-time acquisition and analysis of asset condition by linking intelligent devices with different stakeholdersᅵ applications and databases. This paper presents some aspects of Industrial Internet application as required for integrating weather information and floating road condition data from vehicle mounted sensors to enhance effective and efficient winter maintenance.

    Design/methodology/approach: The concept of real-time road condition assessment using in-vehicle sensors is demonstrated in a case study of a 3.5 km road section located in northern Sweden. The main floating data sources were acceleration and position sensors from a smartphone positioned on the dash board of a truck. Features extracted from the acceleration signal were two road roughness estimations. To extract targeted information and knowledge, the floating data were further processed to produce time series data of the road condition using Kalman filtering. The time series data were thereafter combined with weather data to assess the condition of the road.

    Findings: In the case study, examples of visualisation and analytics to support winter maintenance planning, execution, and resource allocation were presented. Reasonable correlation was shown between estimated road roughness and annual road survey data to validate and prove the presented results wider applicability.

    Originality/value: The paper describes a concept of floating data for an industrial internet application for efficient road maintenance. The resulting improvement in winter maintenance will promote dependable, safe and sustainable transportation of goods and people, especially in northern Nordic region with harsh and sometimes unpredictable weather conditions.

  • 8.
    Calle-Cordón, Álvaro
    et al.
    CEMOSA.
    Jiménez-Redondo, Noemi
    CEMOSA.
    Morales-Gámiz, F. J.
    CEMOSA.
    García-Villena, F.A.
    CEMOSA.
    Garmabaki, Amir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Integration of RAMS in LCC analysis for linear transportinfrastructures: A case study for railways2017Ingår i: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 236Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Life-cycle cost (LCC) analysis is an economic technique used to assess the totalcosts associated with the lifetime of a system in order to support decision making in long termstrategic planning. For complex systems, such as railway and road infrastructures, the cost ofmaintenance plays an important role in the LCC analysis. Costs associated with maintenanceinterventions can be more reliably estimated by integrating the probabilistic nature of thefailures associated to these interventions in the LCC models. Reliability, Maintainability,Availability and Safety (RAMS) parameters describe the maintenance needs of an asset in aquantitative way by using probabilistic information extracted from registered maintenanceactivities. Therefore, the integration of RAMS in the LCC analysis allows obtaining reliablepredictions of system maintenance costs and the dependencies of these costs with specific costdrivers through sensitivity analyses. This paper presents an innovative approach for acombined RAMS & LCC methodology for railway and road transport infrastructures beingdeveloped under the on-going H2020 project INFRALERT. Such RAMS & LCC analysisprovides relevant probabilistic information to be used for condition and risk-based planning ofmaintenance activities as well as for decision support in long term strategic investmentplanning.

  • 9.
    Mishra, Madhav
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Thaduri, Adithya
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Nissen, Arne
    Trafikverket, Luleå.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Particle filter-based prognostic approach for railway track geometry2017Ingår i: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 96, s. 226-238Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Track degradation of ballasted railway track systems has to be measured on a regular basis, and these tracks must be maintained by tamping. Tamping aims to restore the geometry to its original shape to ensure an efficient, comfortable and safe transportation system. To minimize the disturbance introduced by tamping, this action has to be planned in advance. Track degradation forecasts derived from regression methods are used to predict when the standard deviation of a specific track section will exceed a predefined maintenance or safety limit. This paper proposes a particle filter-based prognostic approach for railway track degradation; this approach is demonstrated by examining different railway switches. The standard deviation of the longitudinal track degradation is studied, and forecasts of the maintenance limit intersection are derived. The particle filter-based prognostic results are compared with the standard regression method results for four railway switches, and the particle filter method shows similar or better result for the four cases. For longer prediction times, the error of the proposed method is equal to or smaller than that of the regression method. The main advantage of the particle filter-based prognostic approach is its ability to generate a probabilistic result based on input parameters with uncertainties. The distributions of the input parameters propagate through the filter, and the remaining useful life is presented using a particle distribution.

  • 10.
    Mishra, Madhav
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    A Model-based Prognostic Approach to Predict Remaining Useful Life of Components2016Ingår i: Proceedings of 1st International Conference on Maintenance Engineering, IncoME-I, 2016 / [ed] Jyoti K. Sinha, Akilu Yunusa-Kaltungo, Wolfgang Hahn, 2016, artikel-id ME2016_1147Konferensbidrag (Refereegranskat)
    Abstract [en]

    One of the major problems in the industry is the extension of the useful life of high-performance systems. Proper maintenance plays an important role by extending the useful life, reducing the lifecycle costs and improving the reliability and availability. Health management using a proper condition-based maintenance (CBM) deployment is a worldwide accepted strategy and has grown very popular in many industries over the past decades. A case of CBM is when the maintenance decision is taken based on a forecast of the asset state. This strategy is called predictive maintenance or prognostic health management (PHM). PHM is an engineering discipline that aims to maintain the system behaviour and function, and assure the mission success, safety and effectiveness. This strategy is relevant in environments where the prediction of a failure and the prevention and mitigation of its consequences increase the profit and safety of the facilities concerned. Prognosis is the most critical part of this process and is nowadays recognized as a key feature in maintenance strategies since estimation of the remaining useful life (RUL) is essential.

    PHM can provide a state assessment of the future health of systems or components, e.g. when a degraded state has been found. The aim of using PHM is to estimate how long it will take before the equipment will reach a failure threshold, in future operating conditions and future environmental conditions.

    The aim of the paper is to improve the estimation of bearing RUL by dynamically updating the SKF L10 bearing life length calculation. Using a physics-based prognostic approach, the behaviour of a roller in a paper machine was simulated using the finite element method (FEM). A transfer function representing the relation between bearing acceleration and bearing forces was generated and used to convert the acceleration signal into an estimation of the dynamically changing bearing force. The estimated force is then used as input to the bearing life length calculation generating an updated L10 calculation for each time step. 

  • 11.
    Jahncke, Helena
    et al.
    Department of Occupational and Public Health Sciences, Centre for Musculoskeletal Research, University of Gävle.
    Björkeholm, Patrik
    Department of Psychology, Uppsala University.
    Marsh, John E.
    School of Psychology, University of Central Lancashire, Preston.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Sörqvist, Patrik
    Department of Building, Energy, and Environmental Engineering, University of Gävle.
    Office noise: Can headphones and masking sound attenuate distraction by background speech?2016Ingår i: Work: A journal of Prevention, Assesment and rehabilitation, ISSN 1051-9815, E-ISSN 1875-9270, Vol. 55, nr 3, s. 505-513Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND:

    Background speech is one of the most disturbing noise sources at shared workplaces in terms of both annoyance and performance-related disruption. Therefore, it is important to identify techniques that can efficiently protect performance against distraction. It is also important that the techniques are perceived as satisfactory and are subjectively evaluated as effective in their capacity to reduce distraction.

    OBJECTIVE:

    The aim of the current study was to compare three methods of attenuating distraction from background speech: masking a background voice with nature sound through headphones, masking a background voice with other voices through headphones and merely wearing headphones (without masking) as a way to attenuate the background sound. Quiet was deployed as a baseline condition.

    METHODS:

    30 students participated in an experiment employing a repeated measures design.

    RESULTS:

    Performance (serial short-term memory) was impaired by background speech (1 voice), but this impairment was attenuated when the speech was masked- and in particular when it was masked by nature sound. Furthermore, perceived workload was lowest in the quiet condition and significantly higher in all other sound conditions. Notably, the headphones tested as a sound-attenuating device (i.e. without masking) did not protect against the effects of background speech on performance and subjective work load.

    CONCLUSIONS:

    Nature sound was the only masking condition that worked as a protector of performance, at least in the context of the serial recall task. However, despite the attenuation of distraction by nature sound, perceived workload was still high - suggesting that it is difficult to find a masker that is both effective and perceived as satisfactory.

  • 12.
    Mishra, Madhav
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Johnsson, Roger
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Larsson, Jan-Olof
    SKF Sweden.
    Bellander, Magnus
    SKF Sweden.
    Niemi, Ingemar
    Billerud Karlsborg AB.
    Simulations and measurements of the dynamic response of a paper machine roller2016Ingår i: Insight (Northampton), ISSN 1354-2575, E-ISSN 1754-4904, Vol. 58, nr 4, s. 210-212Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper industry is a highly automated industry that includes many different production steps, in which a variety of machine components are used. In a paper machine, where the pulp is being transformed into paper, rotating components such as bearing-mounted rollers play an important part in driving the wire with the pulp through the process. In this type of industry with a serial layout, the failure of a single roller or bearing could lead to the stoppage of several production steps, with costly consequences as a result. To ensure and optimise asset availability, a condition-based maintenance (CBM) strategy could be implemented. However, CBM is dependent on an appropriate condition monitoring (CM) technique to detect a physical phenomenon that defines the state of critical components or systems. For the development of CM techniques, it is therefore important to understand and model the physical behaviour of the system in question. In this paper, the behaviour of a roller in a paper machine is analysed using the finite element method (FEM). The physical model was compared with vibration measurements collected from an online monitoring system and an experimental modal analysis.

  • 13.
    Mishra, Madhav
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Johnsson, Roger
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Larsson, Jan-Olof
    SKF Sweden.
    Bellander, Magnus
    SKF Sweden.
    Niemi, Ingemar
    Billerud Karlsborg AB.
    Simulations and Measurements of the Dynamic Response of a Paper Machine Roller2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper industry is a highly automated industry that includes many different production steps where a variety of machine components are used. In the paper machine where the pulp is being transformed into paper, rotating components like bearing mounted rollers play an important part to drive the wire with the pulp through the process. In this type of industry with a serial layout, the failure of a single roller or bearing could lead to stoppage of several production steps with costly consequences as a result. To ensure and optimize the asset availability, a condition based maintenance (CBM) strategy could be implemented. However, CBM is dependent on an appropriate condition monitoring (CM) technique to detect physical phenomenon that defines the state of critical components or systems. For the development of CM techniques, it is therefore important to understand and model the physical behaviour of the system in question. In this paper the behaviour of a roller in a paper machine is analysed using finite element method (FEM). The physical model was compared with vibration measurements collected from an online monitoring system and an experimental modal analysis.

  • 14.
    Poll, Marijke Keus van de
    et al.
    Department of Building, Energy, and Environmental Engineering, University of Gävle.
    Carlsson, Johannes
    Chalmers University of Technology, Department of Civil and Environmental Engineering.
    Marsh, John E.
    School of Psychology, University of Central Lancashire.
    Ljung, Robert
    Department of Building, Energy, and Environmental Engineering, University of Gävle, University of Gävle.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Schlittmeier, Sabine J.
    Work, Environmental and Health Psychology, Catholic University of Eichstätt-Ingolstadt.
    Sundin, Gunilla
    Akustikon Team in Norconsult AB.
    Sörqvist, Patrik
    Department of Building, Energy, and Environmental Engineering, University of Gävle, Centre for Built Environment, University of Gävle.
    Unmasking the effects of masking on performance: The potential of multiple-voice masking in the office environment2015Ingår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 138, nr 2, s. 807-816Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Broadband noise is often used as a masking sound to combat the negative consequences of background speech on performance in open-plan offices. As office workers generally dislike broadband noise, it is important to find alternatives that are more appreciated while being at least not less effective. The purpose of experiment 1 was to compare broadband noise with two alternatives - multiple voices and water waves - in the context of a serial short-term memory task. A single voice impaired memory in comparison with silence, but when the single voice was masked with multiple voices, performance was on level with silence. Experiment 2 explored the benefits of multiple-voice masking in more detail (by comparing one voice, three voices, five voices, and seven voices) in the context of word processed writing (arguably a more office-relevant task). Performance (i.e., writing fluency) increased linearly from worst performance in the one-voice condition to best performance in the seven-voice condition. Psychological mechanisms underpinning these effects are discussed

  • 15.
    Saari, Juhamatti
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Lundberg, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Using wavelet transform analysis and the support vector machine to detect angular misalignment of a rubber coupling2015Ingår i: Maintenance, Condition Monitoring and DiagnosticsMaintenance Performance Measurement and Management / [ed] Sulo Lahdelma and Kari Palokangas, 2015, s. 117-126Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Shaft misalignment is a common problem for many types of rotating systems. It can cause machine breakdowns due to the premature failure of bearings or other components. Common diagnostic approaches rely on detecting increasing vibration response spectra at multiples of the shaft speed. However, in many time-variant systems, such as wind turbines, the speed and load vary considerably, which can make spectrum analysis insufficient. In this paper, a method for detecting shaft misalignment by using wavelet analysis is proposed. The method was experimentally evaluated in a laboratory test rig for four different operating conditions by varying the rotational speed and load. An angular misalignment was introduced between a hydraulic pump (load) and a medium-sized industrial gearbox connected with a rubber coupling. Vibration data were collected by using two accelerometers mounted in an axial and a radial direction directly on the gearbox casing. The features extracted from wavelet representation were classified by using a support vector machine algorithm. The detection of misalignment and the sensitivity of the proposed method are presented using validation data and confusion matrices. The final results of the confusion matrices clearly indicate that this method can detect misalignment even when the speed and load vary. The proposed method can be used for systems which are connected with shafts and there are many similar systems (comprising an electric motor, a gearbox and a centrifugal pump) working under the same circumstances.

  • 16.
    Johnsson, Roger
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Rantatalo, Matti
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    A new test track for automotive squeak and rattle (S&R) detection2014Ingår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 80, s. 79-85Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The perceived quality of interior sounds is of increasing importance in the automotive industry since it is important for the customer perception of vehicle quality. Squeak and rattle (S&R) is a group of intermittent interior noise that reduce the sense of quality dramatically. To identify and solve S&R problems the car manufacturers do both simulations and tests in laboratory of complete vehicles as well as subsystems. As a complement, to laboratory testing and for verification, complete vehicle tests at proving grounds are done. In order to systematically test for vehicle S&R noise at proving grounds there is a need for a new type of test track that in a controlled and repetitive ways excite vehicles at different frequencies. This paper describes such a new test track, called the Frequency Sweep Test Track (FSTT). The test track is based on sweep excitation and improves the precision when detecting and solving S&R issues. Different design considerations such as sweep waveform, frequency range and sweep rate are discussed. The track design is evaluated using a quarter-car model including a tandem ellipsoid tyre model. In a case study a FSTT was built and the excitation of a car was measured. The track excited the expected frequency range and the track operated well in detecting a rattle in the dashboard of an executive production car and at which frequency the rattle occurred.

  • 17.
    Poll, Marijke Keus van de
    et al.
    Department of Building, Energy, and Environmental Engineering, University of Gävle.
    Ljung, Robert
    Department of Building, Energy, and Environmental Engineering, University of Gävle.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Sörqvist, Patrik
    Department of Building, Energy, and Environmental Engineering, University of Gävle.
    Disruption of writing by background speech: The role of speech transmission index2014Ingår i: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 81, s. 15-18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Speech transmission index (STI) is an objective measure of the acoustic properties of office environments and is used to specify norms for acceptable acoustic work conditions. Yet, the tasks used to evaluate the effects of varying STIs on work performance have often been focusing on memory (as memory of visually presented words) and reading tasks and may not give a complete view of the severity even of low STI values (i.e., when speech intelligibility is low). Against this background, we used a more typical office-work task in the present study. The participants were asked to write short essays (5 min per essay) in 5 different STI conditions (0.08; 0.23; 0.34; 0.50; and 0.71). Writing fluency dropped drastically and the number of pauses longer than 5 s increased at STI values above 0.23. This study shows that realistic work-related performance drops even at low STI values and has implications for how to evaluate acoustic conditions in school and office environments

  • 18.
    Nykänen, Arne
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Lindegren, David
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Wruck, Louisa
    Ljung, Robert
    University of Gävle.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Möller, Sebastian
    TU Berlin.
    Memory of AMR coded speech distorted by packet loss2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Previous studies have shown that free recall of spoken word lists is impaired if the speech is presented in background noise, even if the signal-to-noise ratio is kept at a level allowing full word identification. The objective of this study was to examine recall rates for word lists presented in noise and word lists coded by an AMR (Adaptive Multi Rate) telephone codec distorted by packet loss. Twenty subjects performed a word recall test. Word lists consisting of ten words were played to the subjects. The subjects repeated each word immediately after it had been played, to ensure that the words were heard correctly. After the complete list had been played the subjects wrote down all words remembered. In this way, both word identification and recall rates were measured. Three distorted conditions were compared with an undistorted control condition using a within-subject design: speech spectrum weighted noise at 4 dB SNR, and AMR coded speech with two levels of packet loss, one mild and one severe. The results confirmed the disruptive effect of noise on free recall of words, while no significant impairment was found for the AMR distortions. The noise and the AMR coding with mild packet loss gave approximately the same impairment of word identification. The AMR coding with severe packet loss gave a larger impairment of word identification, even though the word recall rate was unaffected. This result suggests that packet loss in AMR coded speech causes distortions which disrupt recall of words less than noise at levels resulting in the same change of word identification rates. Since impairment of word identification rates did not correlate with impairment of word recall rates models for quality prediction of speech reproductions should not be based on identification rates alone.

  • 19.
    Johnsson, Roger
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Methods for road texture estimation using vehicle measurements2012Ingår i: Proceedings ISMA 2012: International Conference on Noise and Vibration Engineering : including USD2012 : Leuven, 17 - 19 September 2010, Leuven: Katholieke Universitat , 2012, s. 1573-1582Konferensbidrag (Refereegranskat)
  • 20.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Projekt: Frekvenssvepbanan2011Övrigt (Övrig (populärvetenskap, debatt, mm))
  • 21.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Communication acoustics in classroom environments: on the use of assistive listening devices2010Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Assistive listening devices (ALDs) are used in classrooms to assist communication for students with hearing loss. An ALD, a system of external microphones, transmits sound directly to the students' hearing aids. The signal is coupled to the hearing aid using a radio frequency (FM) or an induction loop (IL) system. Using a switch on the hearing aid, the students can listen to the signal from the hearing aid microphone or the ALD signal received by a FM-receiver or a telecoil. An interest in the impact of ALD solutions on student communication and interaction prompted the work reported in this thesis. The thesis evaluates how the quality of classroom ALDs can be optimized in terms of the concept communication acoustics. Aspects of room acoustics, sound quality, and binaural hearing were explored.The methodical approach was based on self-assessment using questionnaires, interviews and listening tests. The empirical data in Paper I, II, and III consisted of responses from 25 students (10-20 years old) who were attending classes for the hard-of-hearing. In Paper I, the hearing aid microphone (M) and telecoil (T) mode were assessed using a questionnaire. When the hearing aid was in T mode, audibility increased: speech intelligibility was improved and less listening effort was required. Better awareness was achieved using M mode. The students could better hear sounds in the environment around them and participate in conversations - classified as non-teaching - when the ALD was not used. An important feature of sound quality was the distinction of sounds, which is the ability to recognize additional characteristics of a speech sample, e.g., the ability to identify students by voice and judge the mood of students from their voice. Hearing aids also offer a combined mode where the signals from the internal microphone and the telecoil/FM are mixed. In Paper II, different hearing aid mode combinations were assessed using a combined approach where the different combinations were self-rated in a questionnaire and compared in a listening test. The result supports the finding that a combination of M and T mode is a feasible compromise between audibility and awareness. The students were active in their use of different hearing aid modes and aware of the advantages and disadvantages of the alternatives. The hearing strategies varied in different classroom settings and for different degrees of hearing loss, findings that emphasize the importance of individual adjustments. In Paper III, binaural aspects of hearing and ALDs were assessed in a listening test. A binaural model was compared to an omni-directional microphone. No advantage in speech intelligibility and listening effort was found using a binaural ALD. ALD design and characteristics can be evaluated using room acoustic modelling and auralization in different room acoustic conditions. In Paper IV and V, auralization and binaural reproduction techniques used in Paper II and III were investigated. Aspects of binaural and spatial hearing were assessed in normal-hearing subjects. Auralization is a reliable method to render a binaural listening experience in a classroom environment: the performance was equal to that of using artificial head recordings. The method used for binaural reproduction - a two-loudspeaker cross-talk cancellation system - introduces distortion in reproduced interaural differences. The binaural advantages in speech intelligibility were reduced when compared to headphone reproduction. The interaural differences were sufficiently reproduced in the frequency region of ALDs (300-4k Hz); the use of cross-talk cancellation for hearing aid and ALD evaluation is to be further studied.High sound quality matches students' expectations and demands. To take an active part in the communication in the classroom, students expect to hear sounds in the classroom that they perceive as adequate. However, the students with hearing loss required speech signals with significantly reduced noise and competing speech levels. Today, students have to make a compromise between audibility and awareness. Any alternative, however, could make communication in the classroom difficult. Different classroom settings and sound environments as well as individual factors of preference and degree of hearing loss affect their decision.

  • 22.
    Odelius, Johan
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Johansson, Örjan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Self-assessment of classroom assistive listening devices2010Ingår i: International Journal of Audiology, ISSN 1499-2027, E-ISSN 1708-8186, Vol. 49, nr 7, s. 508-517Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Self-assessment of classroom assistive listening devices (ALDs) based on induction loop systems was carried out in Swedish classes for hearing-impaired students. A questionnaire was developed and completed by 25 students (bilateral hearing aid users, 10-20 years old). Responses for hearing aid microphone mode (M) and telecoil mode (T) were collected. Two attributes, audibility and awareness, were identified and assigned to either mode. Better audibility was achieved in T-mode. Students with severe hearing loss benefited more using T-mode when compared to the better hearing students, especially in more difficult listening situations. Better awareness was achieved in M-mode; students could better hear, locate and segregate sounds in the environment around them. Depending on the situation, students make different choices between audibility and awareness. Self-assessment is a promising approach for determining what combination of ALD design and function that will best benefit the students

  • 23.
    Vasiliauskas, Gediminas
    et al.
    Lithuanian University of Agriculture.
    Nykänen, Arne
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Johnsson, Roger
    Speech intelligibility in binaural reproductions compared to real life listening2010Ingår i: Sound quality evaluation: the proceedings of the AES 38th International Conference : June 13-15, 2010, Piteå, Sweden / [ed] Jan Berg, New York: Audio Engineering Society, Inc., 2010, s. 60-67Konferensbidrag (Refereegranskat)
    Abstract [en]

    A good reproduction of speech should allow the listener to suppress noise and reverberation as if the sounds were heard in real life. An experiment was designed where room properties and reproduction techniques were varied in a way that allowed evaluation of noise and reverberation suppression based on speech intelligibility measurements. Speech intelligibility was considerably better in real life compared to artificial head recordings presented through headphones. The headphone reproductions did not provide enough information to allow the listener to suppress noise and reverberation as well as in real life. It was found that subjects were very consistent. This makes the method precise and it should be useable for making comparisons of different reproduction techniques.

  • 24. Johnsson, Roger
    et al.
    Odelius, Johan
    Nykänen, Arne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Self assessment of speech intelligibility listening to binaural recordings2009Ingår i: 38th International Congress and Exposition on Noise Control Engineering 2009: INTER-NOISE 2009 ; Ottawa, Canada, 23 - 26 August 2009 / [ed] J. Stuart Bolton, Red Hook, NY: Curran Associates, Inc., 2009, s. 43-51Konferensbidrag (Refereegranskat)
    Abstract [en]

    Our ability to focus on a talker in an environment with several talkers is improved by our binaural hearing. The ability to listen to one talker is improved if the talkers are spatially well separated. A common problem with binaural recordings is front-back confusion, which can make it more difficult to focus on the target talker among several talkers. In this study the ability to localize a talker is compared to the ability to follow a talker in situations with several talkers. In the first part the subjects were asked to localize a talker in the horizontal plane listening to binaural recordings. In the second part of the study the subjects were instructed to assess their ability to follow a target male voice in presence of a masker consisting of two voices (male and female).Target and maskers were presented through separate loudspeakers in various positions. The same listening test was also performed with binaural recordings of the test environment using different artificial heads and in-ear recordings of humans. In both parts the binaural recordings were presented to the subjects through loudspeakers using cross-talk cancellation. Correlation between localization performance and self assessed speech intelligibility was analyzed.

  • 25.
    Odelius, Johan
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Johansson, Örjan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    The effect of binaural processing techniques on speech quality ratings of assistive listening devices in different room acoustics conditions2008Ingår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 123, nr 5, s. 3170-Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    External microphone systems, referred to as assistive listening devices (ALD), are used in classrooms for hearing impaired students. The objective is to investigate the effect of binaural processing techniques in different room acoustic conditions. A listening experiment was conducted with 10 normal hearing adults. Response variables were judgements of clarity, pleasantness, listening effort and overall speech quality. Design variables were binaural processing, room acoustics and ALD bandwidth. Stimuli were generated using the room acoustic modelling software CATT Acoustic. Three speech sources, two male voices and one female voice, were placed at a table in the centre of a room and one Brown noise source was placed in one corner of the room. Microphones were placed 0.5 m in front of each speech source. Target source was a random choice of one of the two male voices. The binaural processing was utilized by a simple HRTF filtering. Depending on the angle to the source from a fictitious listening position at the table, corresponding interaural time difference (ITD) and the interaural level difference (ILD) was applied to the signal. Stimuli were presented by loudspeakers using cross-talk cancellation. The hypothesis is that binaural processing will give a significant improvement in speech quality.

  • 26.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Communication quality: a conceptual approach focusing on classroom assistive listening devices2007Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In a classroom an assistive listening device (ALD) is a system of external microphones that transmit sound from a sound source directly to students' hearing aids. An ALD can be a microphone close to the mouth which transmits a voice directly to listeners' hearing aids. An ALD can also be a microphone placed centrally and used by several persons at the same time. Sound quality of a listening device can be described as sound-transmission quality where maximal quality is no difference between input and output. From a wider perspective, this output can be the perceived quality of speech where a high speech quality matches given expectations, demands and necessaries. A focus on participatory learning environment in Swedish hearing impaired classes has brought out new perspectives on ALD solutions. The purpose of the studies reported in this thesis was to develop a methodical framework for the evaluation of classroom ALDs. As a basis for the evaluation of ALD communication quality is suggested. Communication quality is an extension of the sound quality concept which emphasizes student participation and peer interaction. As a pedagogical parallel, sound quality emphasizes a more cognitive view of learning whereas communication quality emphasizes participatory learning. By using room acoustic modelling and auralization in listening tests it was possible to evaluate aspects of room acoustics, signal processing techniques, speech and masking signals, and binaural advantage. A self-assessment approach was also used and a questionnaire was developed based on the Speech, Spatial and Qualities of Hearing Scale (SSQ). The studies found that students in hearing impaired classes prefer using only their hearing aids over using an ALD. Retrieving information about the acoustic environment was important aspects. Also observed was that when comparing different ALD solutions microphone distance is of importance. Listening effort correlates with hearing loss rather than with using different technologies. Today's hearing aids offer the best communication quality but it is also apparent than ALDs are preferred by students in some situations. Determining the combination of design and ALD function which can best benefit students is needed. The methodological framework described is promising for continuous studies developing and assessing classroom ALD.

  • 27.
    Odelius, Johan
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Johansson, Örjan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Ågren, Anders
    Effects on speech intelligibility using a binaural assistive listening device2006Ingår i: Proceedings of the Baltic-Nordic Acoustic Meeting: BNAM, 2006Konferensbidrag (Refereegranskat)
  • 28.
    Odelius, Johan
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Johansson, Örjan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Ågren, Anders
    Communication quality for students with hearing impairment: a study evaluating speech intelligibility and annoyance2005Ingår i: Proceedings Forum Acusticum, Scientific society for optics, acoustics, motion picture and theater technology , 2005, s. 2709-2714Konferensbidrag (Refereegranskat)
    Abstract [en]

    New pedagogical views on assistive listening devices have enlightened the technology's impact on communication patterns among students with a hearing impairment. The objective of this study was to find methods to evaluate assistive listening devices supporting a more dialogue-oriented and participatory learning environment. With this approach a three-dimensional communication quality definition was proposed. The dimensions are: 1) Speech intelligibility 2) Ambient sounds; annoyance and feeling of presence 3) Parameters concerning the students' performance given the aim and task of the pedagogical situation. In this experiment dimensions 1 and 2 were evaluated, where dimension 2 concerned annoyance. Speech intelligibility was assessed using just-follow-conversation (JFC) tasks performed by normal hearing subjects. The task consisted of adjusting the level of a masker until the listener felt he or she just could understand what was being said. In conjunction with the JFC task, the subjects were asked to estimate the annoyance of the masking signal on an eleven-point scale. The speech and masking signals were filtered by impulse responses generated in a room acoustic model. Design variables were: A) Room acoustic model; two acoustic properties B) Distance between speech source and microphone; 0.75 m or 1.5 m C) Noise masker; speech-spectrum random noise or structure-borne noise D) Microphone directivity; omni-directional or delay-and-sum beamformer E) Amplifier; linear or compression.

  • 29.
    Odelius, Johan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Utvärdering av hörseltekniska hjälpmedel i hörselklass2005Ingår i: Nordisk tidskrift för hörsel- och dövundervisning NTD, ISSN 1651-6036, Vol. 4, nr 3, s. 20-21Artikel i tidskrift (Övrigt vetenskapligt)
1 - 29 av 29
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