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- Almgren, Torgny, 1962, et al.
(författare)
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Optimization of opportunistic replacement activities: A case study in the aircraft industry
- 2007
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In the aircraft industry maximizing availability is essential. Maintenance schedules must therefore be opportunistic, incorporating preventive maintenance activities within the scheduled as well as the unplanned ones. At the same time, the maintenance contractor should utilize opportunistic maintenance to enable the minimization of the total expected cost to have a functional aircraft engine and thus to provide attractive service contracts. This paper provides an opportunistic maintenance optimization model which has been constructed and tested together with Volvo Aero Corporation in Trollhättan, Sweden for the maintenance of the RM12 engine. The model incorporates components with deterministic as well as with stochastic lives. The replacement model is shown to have favourable properties; in particular, when the maintenance occasions are fixed the remaining problem has the integrality property, the replacement polytope corresponding to the convex hull of feasible solutions is full-dimensional, and all the necessary constraints for its definition are facet-inducing. We present an empirical crack growth model that estimates the remaining life and also a case study that indicates that a non-stationary renewal process with Weibull distributed lives is a good model for the recurring maintenance occasions. Using one point of support for the distribution yields a deterministic replacement model; it is evaluated against classic maintenance policies from the literature through stochastic simulations. The deterministic model provides maintenance schedules over a finite time period that induce fewer maintenance occasions as well as fewer components replaced.
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| 3. |
- Lantz, Emelie
(författare)
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Sharing is Caring : Early response for community safety in rural areas with a focus on exploring part-time firefighters’ work situation and family support
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: The overall purpose of this thesis was to explore and describe early response for community safety in rural areas with a focus on parttime firefighters’ work situation and family support.Methods: The thesis used an inductive approach with an exploratory and descriptive design, including qualitative and quantitative research methods. Each study’s design was selected to align with its specific purpose. The five studies collectively contributed to fulfilling the overall purpose of the thesis. Descriptive and comparative statistics were employed to describe response times in out-of-hospital cardiac arrests in relation to population density for volunteer first responders, fire and rescue services, and emergency medical services (I). A literature review was conducted to synthesize literature regarding non-career firefighters, with a focus on recruitment, retention and resignation (II). The Delphi technique was applied to identify pivotal factors that influence the ability of main employers to have employees who are part-time firefighters in rural areas in Sweden (III). Interviews were conducted and analysed using latent qualitative content analysis to describe the experiences of part-time firefighters in rural areas in Sweden (IV). Interviews were conducted and analysed with the Critical Incident Technique to describe the experiences and actions of part-time firefighters’ family members in rural areas in Sweden (V).Findings: The fire and rescue services had a significant impact on reducing response times in non-urban settings compared to the emergency medical services (I). Culture, recognition and supportive leadership in the fire and rescue services played a crucial role in job satisfaction and retention among non-career firefighters (II). Main employers to part-time firefighters wanted to contribute to preserve a fire and rescue service in the community by encouraging employees to also work as part-time firefighters (III). Part-time firefighters shared a strong commitment and motivation but balanced the service with other responsibilities in life (IV). Family members of part-time firefighters faced challenges and dealt with uncertainties but adapted their daily lives to fit with the part-time firefighters’ work situation (V). The findings revealed that various dimensions and interrelated subsystems have an impact on part-time firefighters’ work situation and support, enabling early response for community safety in rural areas. These interrelated subsystems, driven by individual efforts, support part-time firefighters serving on-call in rural areas, demonstrating a shared commitment that involves responsibility as well as the dedication of time and resources.Conclusion: The shared commitment found among part-time firefighters, their main employers, and their family members underscores their importance in supporting part-time firefighters’ work situation. This commitment and support are essential for retaining part-time firefighters, which enhances early response efforts and ensures community safety in rural areas. Consequently, “sharing is caring” is of pivotal importance.
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| 4. |
- Putra, I Putu Alit, 1992, et al.
(författare)
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Implementation and Calibration of Active Reflexive Cervical Muscles on Female Head-Neck Model
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Problem outline ViVA OpenHBM is an open source human body model that represents the 50th percentile female population for assessing whiplash protection systems in car. ViVA OpenHBM was developed with intention to fill the gap of current available HBMs which excluded the average female size although injury statistics since 1960s have shown that females have three times higher risk to sustain whiplash injury compared to males. In this study, the current model is being enhanced by implementing active muscles as previous studies have shown that cervical muscles could alter the head and neck kinematics of the occupant during low-speed rear- crashes. Study objectives The first goal of this study was to implement a Proportional Integral Derivative (PID) feedback control mechanism adding to the Finite Element models of cervical muscles. The second goal was to calibrate the PID control gains by conducting an optimization-based parameter identification with publishedvolunteer data and to analyze the effects of three calibration objectives to the head and cervical kinematics of the model. Methodology The VIVA OpenHBM head-neck model, previously validated to PMHS data, was used. To represent the 34 cervical muscles, 129 beam elements with Hill-type material models were implemented. A closedloop control strategy was applied to activate these muscles mimicking the human body’s vestibular system. Calibration studies of head and cervical spine kinematics were conducted by comparing the model against published-volunteer responses to identify reasonable gain values for the controller. Three different calibrations were conducted with three different objectives: head kinematics in linear and angular direction, head and cervical spine kinematics in angular direction, and head and cervical spine kinematics in linear and angular direction. Results and Conclusion The simulation results show that the reflexive feedback control was numerically stable and able to control model muscle’s activation. Gain values of the implemented muscle control strategies were able to be identified from calibration simulations. Muscle activation changed the head kinematics by reducing peak linear and angular displacements, as compared to the model without muscle activation. The agreement of specific kinematic variables such as head kinematic and cervical spine angular displacement was dependent on the controller calibration objectives. Best agreement of head kinematics was observed in the model that calibrated against only volunteer head kinematics. However, in the vertical and angular direction there was a discrepancy of head response caused by anteriorposterior buckling of the cervical spine. In the model that was calibrated against head and cervical spine in angular direction, less contraction of cervical muscles was observed. As the result, good agreement was obtained in the cervical spine angular kinematics but not in the head kinematics. The best agreement was obtained by the model that calibrated against both linear and angular displacement of volunteer head and cervical spine kinematics although reduced the agreement of head kinematics compared to the model that was calibrated against only volunteer head kinematics. This was because of different calibration objectives that opposing each other.
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| 5. |
- Putra, I Putu Alit, 1992, et al.
(författare)
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Kinematics Evaluation of Female Head-Neck Model with Reflexive Neck Muscles in Low-Speed Rear Impact
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study highlights the importance of evaluating active model performance in different configurations. This study has shown that additional development of the ViVA OpenHBM must be done before being used in the development and assessement of vehicle occupant safety. This is especially relevant before using the model to conduct accident reconstructions and whiplash injury predictions.
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