| 1. |
- Block, J., et al.
(author)
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Optimal repair for repairable components during phaseout an aircraft fleet
- 2010
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In: IEEE Aerospace Conference Proceedings. - Piscataway, NJ. - 9781424438877
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Conference paper (peer-reviewed)abstract
- The successive removal of units from a group of systems during phasing out leads to a variable requirement for stock level of spare parts. Repairable units from phased out systems can be reused for the remaining functional systems in the group. Hence, the stock level of spare parts increases and the demand for spare parts decreases. This can lead to excessive stocking of spare parts and high maintenance costs for spare parts. This paper proposes a methodology to determine the optimum time to stop repair of repairable units to minimize the maintenance cost. It uses a Poisson Distribution based on NHPP (Non-Homogenous Poisson Process) to predict the available number of units, while fulfilling the demand for spare parts for the remaining systems. A concept, called Minimal Margin is introduced to formulate the problem and nonlinear programming is proposed to obtain the optimum solution. Finally, a numerical example is presented to demonstrate the approach
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| 2. |
- Block, Jan, et al.
(author)
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Using Monte Carlo simulation as support for decision making while negotiating a PBL contract
- 2014
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In: IEEE Aerospace Conference. Proceedings. - 1095-323X.
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Journal article (peer-reviewed)abstract
- In connection with performance-based logistics (PBL) contracts for aircraft fleets it is very important to carefully analyse both operations and maintenance before and during the contract negotiation phase. Monte Carlo Simulation is a valuable methodology in this context since it allows delimiting and exploring a complex parameter space in a transparent and relatively easily visualized manner. With timely analyses it is possible to identify both technical and economic risks and minimize the possible consequences, a process that benefits both parties in the negotiation process. This paper describes a part of this process in connection with the negotiation of a PBL contract for the Swedish Air Force SAAB 105 (SK 60) trainer fleet between Saab AB and the Swedish Defence Materiel Administration (FMV). The information used in the simulations was largely empirical data derived from previous operations of the aircraft system. The main factors that were simulated were operational requirements, fleet size, spares inventories, turn-around times, failure rates and influence of extraneous factors (e. g. weather). The simulations resulted in considerable savings due to reduction of the active fleet size, and increased reclamation of surplus spares and units from retired aircraft.
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| 3. |
- El-Jaby, S., et al.
(author)
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ISSCREM: International Space Station cosmic radiation exposure model
- 2013
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In: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781467318112
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Conference paper (peer-reviewed)abstract
- A semi-empirical model is derived from operational data collected aboard the International Space Station (ISS) with the U.S. tissue equivalent proportional counter (TEPC). The model provides daily and cumulative mission predictions of the operational dose equivalent that space-crew may receive from galactic cosmic radiation (GCR) and trapped radiation (TR) sources as a function of the ISS orbit. The parametric model for GCR exposure correlates the TEPC dose equivalent rate to the cutoff rigidity at ISS altitudes while the TR parametric model relates this quantity to the mean atmospheric density at the crossing of the South Atlantic Anomaly (SAA). The influences of solar activity, flux asymmetry inside the SAA, detector orientation, and position aboard the ISS on the dose equivalent have been examined. The model has been successfully benchmarked against measured data for GCR and TR exposures to within ±10% and ±20%, respectively, over periods of time ranging from a single day to a full mission. In addition, preliminary estimates of the protection quantity of effective dose equivalent have been simulated using the PHITS Monte Carlo transport code. These simulations indicate that the TEPC dose equivalent is a conservative estimate of the effective dose equivalent.
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| 4. |
- Orguner, Umut, 1977-, et al.
(author)
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Combined Point Mass and Particle Filter for Target Tracking
- 2010
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In: Proceedings of the 2010 IEEE Aerospace Conference. - 9781424438877
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Conference paper (peer-reviewed)abstract
- This paper presents a combined Point Mass Filter (PMF) and Particle Filter (PF), which utilizes the support of the PMF and the high particle density in the PF close to the current estimate. The result is a filter robust to unexpected process events but still with low error covariance. This filter is especially useful for target tracking applications, where target maneuvers suddenly can change unpredictably.
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| 5. |
- Orguner, Umut, 1977-, et al.
(author)
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Particle Filtering with Propagation Delayed Measurements
- 2010
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In: Proceedings of the 2010 IEEE Aerospace Conference. - 9781424438884 - 9781424438877 ; , s. 1-9
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Conference paper (peer-reviewed)abstract
- This paper investigates the problem of propagation delayed measurements in a particle filtering scenario. Based on implicit constraints specified by target dynamics and physics rules of signal propagation, authors apply the ideas that were first proposed in their previous work to the case of particle filters. Unlike the deterministic sampling based approach called propagation delayed measurement filter (PDMF) in their previous work, the new algorithm proposed here (called as PDM particle filter (PDM-PF)) has the potential to be used with general nonlinear models. This advantage and the estimation results of PDM-PF are illustrated in a challenging target tracking scenario by making comparisons to PDMF along with some other alternative particle filters.
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| 6. |
- Sihver, Lembit, 1962, et al.
(author)
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A comparison of total reaction cross section models used in FLUKA, GEANT4 and PHITS
- 2012
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In: Aerospace Conference, 2012 IEEE. ; , s. 1-10, s. 1 - 10
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Conference paper (peer-reviewed)abstract
- Understanding the interactions and propagations of high energy protons and heavy ions are essential when trying to estimate the biological effects of Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE) on personnel on interplanetary missions, and when preparing the construction of a lunar base. To be able to calculate the secondary particles, including neutrons, and to estimate shielding properties of different materials and radiation risks inside complex geometries, particle and heavy ion transport codes are needed. The interactions of the GCR and SPE with matter include many complex properties and many factors influence the calculated results. In all particle and heavy ion transport codes, the probability function that a projectile particle will collide with a nucleus within a certain distance x in the matter depends on the total reaction cross sections, which also scale the calculated partial fragmentation cross sections. It is therefore crucial that accurate total reaction cross section models are used in the transport calculations. FLUKA, GEANT4 and PHITS are three major multi-purpose three-dimensional Monte Carlo particle and heavy ion transport codes widely used for fundamental research, radioprotection, radiotherapy, and space dosimetry. In this paper, a systematic comparison of the total reaction cross section models used as default in these three codes is performed for a variety of systems of importance for space dosimetry, and the need for future improvements and benchmarking against experimental results is discussed. The need for benchmarking and improvements of the partial nuclear reaction and evaporation models, as well as how impact parameter functions, switching time between the dynamical/pre-equilibrium and the de-excitation/evaporation stages, low energy data libraries, etc., influence the final results, is also briefly be discussed.
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| 7. |
- Sihver, Lembit, 1962, et al.
(author)
-
A comparison of total reaction cross section models used in particle and heavy ion transport codes
- 2010
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In: Aerospace Conference, 2010 IEEE. - IEEE. ; , s. 1-9:Issue Date: 6-13 March 2010, s. 1 - 9
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Conference paper (peer-reviewed)abstract
- To be able to calculate the nucleon-nucleon and nucleon-nucleus total reaction cross sections with precision is very important for studies of basic nuclear properties, e.g. nuclear structure. This is also of importance for particle and heavy ion transport calculations since in all particle and heavy ion transport codes, the probability function that a projectile particle will collide within a certain distance x in the matter depends on the total reaction cross sections. This will also scale the calculated partial fragmentation cross sections. It is therefore crucial that accurate total reaction cross section models are used in the transport calculations. In this paper, different models for calculating nucleon-nucleus and nucleus-nucleus total reaction cross sections are compared.
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| 8. |
- Sihver, Lembit, 1962, et al.
(author)
-
A study of total reaction cross section models used in particle and heavy ion transport codes
- 2011
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In: IEEE Aerospace Conference Proceedings. - : IEEE conference proceedings. - 1095-323X. - 9781424473502
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Conference paper (peer-reviewed)abstract
- Understanding the interactions and propagations of high energy protons and heavy ions are essential when trying to estimate the biological effects of Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE) on personnel in space. 12 To be able to calculate the shielding properties of different materials and radiation risks, particle and heavy ion transport codes are needed. In all particle and heavy ion transport codes, the probability function that a projectile particle will collide within a certain distance x in the matter depends on the total reaction cross sections, which also scale the calculated partial fragmentation cross sections. It is therefore crucial that accurate total reaction cross section models are used in the transport calculations. In this paper, different models for calculating nucleon-nucleus and nucleus-nucleus total reaction cross sections are compared with each other and with measurements. The uncertainties in the calculations with the different models are discussed, as well as their overall performances with respect to the available experimental data. Finally, a new compilation of experimental data is presented and new measurements to improve the current models are suggested.
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| 9. |
- Sihver, Lembit, 1962, et al.
(author)
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Monte Carlo simulations of MATROSHKA experiment outside ISS
- 2011
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In: IEEE Aerospace Conference Proceedings. Big Sky, 5-12 Mars 2011. - 1095-323X. - 9781424473502
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Conference paper (peer-reviewed)abstract
- Concerns about the biological effects of space radiation are increasing rapidly due to the perspective of long-duration manned missions, both in relation to the International Space Station (ISS) and to manned interplanetary missions to Mars in the future. As a preparation for these long duration space missions it is important to ensure an excellent capability to evaluate the impact of space radiation on human health in order to secure the safety of the astronauts/cosmonauts and minimize their risks. It is therefore necessary to measure the radiation load on the personnel both inside and outside the space vehicles and to certify that organ and tissue equivalent doses can be simulated as accurate as possible. In this paper we will present simulations using the three-dimensional Monte Carlo Particle and Heavy Ion Transport code System (PHITS) of long term dose measurements performed with the ESA supported experiment MATROSHKA (MTR), which is an anthropomorphic phantom containing over 6000 radiation detectors, mimicking a human head and torso. The MTR experiment, led by the German Aerospace Center (DLR), was launched in January 2004 and has measured the absorbed dose from space radiation both inside and outside the ISS. In this paper comparisons of measured and calculated dose and organ doses in the MTR located outside the ISS will be presented and uncertainties of the simulations will be discussed. This project was funded by the European Commission in the frame of the FP7 HAMLET project (Project # 218817).
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| 10. |
- Törnqvist, David, 1979-, et al.
(author)
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Window Based GPS Integrity Test using Tight GPS/IMU Integration Applied to a Sounding Rocket
- 2010
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In: Proceedings of the 2010 IEEE Aerospace Conference. - 9781424438884 - 9781424438877
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Conference paper (peer-reviewed)abstract
- This paper presents an integrity monitoring method for tight integration of an Inertial Measurement Unit (IMU) and a GPS receiver. The method is applied to data from a Maxus sounding rocket used for microgravity research. It is crucial to determine the rocket position during launch to ensure a safe landing location. Today, the navigation relies on IMU integration only. Involving a GPS receiver enhances the position accuracy but there is a need for protection against faulty satellite range measurements. Monitoring over a sequence of the measurements gives higher confidence to the tests.
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