| 1. |
- Amann, Peter, et al.
(författare)
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A dedicated photoelectron spectroscopy instrument for studies of catalytic reactions at pressures exceeding 1 bar
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Here, we present a new high-pressure x-ray photoelectron spectroscopy system dedicated to probing catalytic reactions under realistic conditions at pressures exceeding 1 bar. The instrument builds around the concept of a “virtual cell” in which a gasflow is directed onto the sample surface creating a local high pressure on top of the sample. This allows the instrument to maintain a low pressure of a few mbars in the main chamber, while simultaneously keeping a local pressure of around 1 bar. Synchrotron radiation based grazing incidence photoemission within ± 5° is used to enhance the surface sensitivity in the experiment. The aperture, separating the high-pressure region from the differential pumping of the electron spectrometer, consists of multiple, evenly spaced, mm sized holes matching the footprint of the x-ray beam on the sample surface. As the photo-emitted electrons are subject to strong scattering in the gas phase and the resulting signal is therefore highly dependent on the sample to aperture distance, the latter is controlled with high precision using a fully integrated manipulator that allows for sample movement with step sizes of 10 nm between 0 and –5 mm with very low vibrational amplitude. The instrumental features allows acquisition of metallic bulk spectra at He pressures up to 2.5 bar and also allows for following C1s spectra under realistic gas mixtures of CO + H2with various temperatures up to 500°C. This capability opens for studies of catalytic reactions in operandi.
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| 2. |
- Amann, Peter, et al.
(författare)
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A high-pressure x-ray photoelectron spectroscopy instrument for studies of industrially relevant catalytic reactions at pressures of several bars
- 2019
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Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 90:10
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Tidskriftsartikel (refereegranskat)abstract
- We present a new high-pressure x-ray photoelectron spectroscopy system dedicated to probing catalytic reactions under realistic conditions at pressures of multiple bars. The instrument builds around the novel concept of a "virtual cell" in which a gas flow onto the sample surface creates a localized high-pressure pillow. This allows the instrument to be operated with a low pressure of a few millibar in the main chamber, while simultaneously a local pressure exceeding 1 bar can be supplied at the sample surface. Synchrotron based hard x-ray excitation is used to increase the electron mean free path in the gas region between sample and analyzer while grazing incidence <5 degrees close to total external refection conditions enhances surface sensitivity. The aperture separating the high-pressure region from the differential pumping of the electron spectrometer consists of multiple, evenly spaced, micrometer sized holes matching the footprint of the x-ray beam on the sample. The resulting signal is highly dependent on the sample-to-aperture distance because photoemitted electrons are subject to strong scattering in the gas phase. Therefore, high precision control of the sample-to-aperture distance is crucial. A fully integrated manipulator allows for sample movement with step sizes of 10 nm between 0 and -5 mm with very low vibrational amplitude and also for sample heating up to 500 degrees C under reaction conditions. We demonstrate the performance of this novel instrument with bulk 2p spectra of a copper single crystal at He pressures of up to 2.5 bars and C1s spectra measured in gas mixtures of CO + H-2 at pressures of up to 790 mbar. The capability to detect emitted photoelectrons at several bars opens the prospect for studies of catalytic reactions under industrially relevant operando conditions.
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| 3. |
- Forsberg, Henrik, et al.
(författare)
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Maternal diabetes alters extracellular matrix protein levels in rat placentas
- 1998
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Ingår i: American Journal of Obstetrics and Gynecology. - 0002-9378 .- 1097-6868. ; 179:3 Pt1, s. 772-778
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: The aim of this study was to determine whether maternal diabetes affects placental levels of the extracellular matrix components fibronectin, laminin, and collagen-IV. STUDY DESIGN: Fibronectin, laminin, and collagen-IV deposition in term (day 20) rat placentas from normal and diabetic pregnancies was detected by use of Western blot, slot-blot, and immunohistochemical studies. RESULTS: Increased placental and decreased fetal wet weight were found in offspring of manifestly diabetic rats compared with offspring of normal pregnancies. Laminin deposition was reduced whereas fibronectin levels were increased in placentas from diabetic rats. No diabetes-induced changes of collagen-IV expression and deposition were found. CONCLUSION: The diabetes-induced alterations of laminin and fibronectin protein levels in the fetal-maternal interface may affect placental development and alter gas exchange and nutrient transfer to the offspring. This may in turn contribute to the abnormal fetal development in diabetic pregnancy.
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| 4. |
- Hyttinen, Jukka, et al.
(författare)
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Development and analysis of an on-road torque measurement device for trucks
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Background: Rolling resistance and aerodynamic losses cause a significant part of a truck's energy consumption. Therefore there is an interest from both vehicle manufacturers and regulators to measure these losses to understand, quantify and reduce the energy consumption of vehicles. On-road measurements are particularly interesting because it enables testing in various ambient conditions and road surfaces with vehicles in service.Objective: Common driving loss measurement devices require unique instrumented measurement wheels, which hinders effective measurements of multiple tyre sets or measurements of vehicles in service. For this purpose, the objective is to develop a novel load-sensing device for measuring braking or driving torque.Methods: The strength of the measurement device is calculated using finite element methods, and the output signal is simulated using virtual strain gauge simulations. In addition to the signal simulation, the device is calibrated using a torsional test rig.Results: The simulation results confirm that the device fulfils the strength requirements and is able to resolve low torque levels. The output signal is simulated for the novel cascaded multi-Wheatstone bridge using the strains extracted from the finite element analysis. The simulations and measurements show that the measurement signal is linear and not sensitive to other load directions. The device is tested on a truck, and the effort of mounting the device is comparable to a regular tyre change.Conclusions: A novel driving loss measurement device design is presented with an innovative positioning of strain gauges decoupling the parasitic loads from the driving loss measurements. The design allows on-road testing using conventional wheels without requiring special measurement wheels or instrumentation of drive shafts, enabling more affordable and accurate measurements.
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| 5. |
- Lagerblad, Ulrika, 1987-, et al.
(författare)
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A fixed-lag smoother for solving input force and support motion identification problems in structural dynamics
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this work, the problem of joint input and state estimation based on measured response in a dynamic system is addressed.A fixed-lag smoother for support motion or input force estimation in linear structural dynamics is proposed. The unknown inputs are estimated in conjunction with the states in an augmented state description of the system. A fixed-lag smoother maximizes the use of information available in the measurements by allowing a small time lag in the estimation, leading to a recursive non-causal filter. This type of filter has not previously been implemented in the field of structural dynamics. The filter is capable of handling any combination of measured displacement, velocity and acceleration; furthermore are both measurement noise and model errors accounted for and simulated as stochastic processes. In this study, estimations are based on sparse noisy measurements of system displacement and model errors are simulated through the use of deliberately incorrect model descriptions. The proposed algorithm is verified by numerical simulations and the qualities of the estimations are compared to those of the augmented Kalman filter.It is shown that with this filter, significant improvements of the input estimations are achieved, especially of inputs located far away from measurement sensors. The improvement consists of noise reduction, phase correction and by a more accurate division of the individual contribution of multiple inputs.
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| 6. |
- Lagerblad, Ulrika, 1987-, et al.
(författare)
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A ROBUST ALGORITHM FOR FORCE IDENTIFICATION ON STRUCTURES BASED ON ACCELERATION MEASUREMENTS
- 2015
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Ingår i: PROCEEDINGS OF THE 22ND INTERNATIONAL CONGRESS ON SOUND AND VIBRATION. - : INT INST ACOUSTICS & VIBRATION.
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Konferensbidrag (refereegranskat)abstract
- Identifying input forces from measured structural response is an important engineering problem. This can be done by using an inverse method based on the state-space analysis. It is proposed to model dynamic systems with a set of linear state equations. The greatest challenge in applications is highly ill-conditioned state matrices appearing in large systems modelled with, for example, the finite element method. One way to overcome this problem is to describe the system on a truncated modal basis, thereby decreasing the number of degrees-of-freedom. The present work employs a smoothed Kalman filter to make an estimate of the states. The states are used by a recursive least-squares algorithm to calculate the input forces on a model system. Measurement noise and model errors are robustly managed by the algorithm. The novel method is evaluated by laboratory testing and numerical simulations of a simply supported beam.
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| 7. |
- Lagerblad, Ulrika, 1987-
(författare)
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A study of vehicle fatigue damage predictions based on state estimations
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Individual health monitoring of heavy vehicles is one of the keystones on which an optimized utility of a vehicle fleet is based. For many components mounted on the chassis of a heavy vehicle, failures due to fatigue is a major concern. The fatigue is caused by vibrations in the chassis, originating from road irregularities and the driver’s manoeuvring of the vehicle. The variation in vibration characteristics is very large, and a reliable prediction of the fatigue damage must therefore be based on vibrations measured on each specific vehicle. Even so, the prediction of fatigue damage is far from trivial. To minimize the cost of both measurement equipment and data processing, the vibrations must be measured very sparsely. Furthermore, it will in general not be possible to measure the vibrations in the locations where failures are anticipated. In Paper A, an augmented Kalman filter extended with a fixed-lag smoother is presented (hereinafter referred to as the smoothing algorithm). The smoothing algorithm is used to estimate the vibrations everywhere in a dynamic system based on sparsely measured accelerations and on a numerical model describing the system. Measurements from a vehicle component mounted in a vibration test rig are used to validate the smoothing algorithm. The numerical model is constructed from an operational modal analysis of the dynamic system. It is shown that the smoothing algorithm accurately estimates the dynamic responses.The smoothing algorithm is then investigated in more detail in Paper B. When analysing measurements from complex dynamic structures, both measurement noise and modelling errors will be present. This paper presents a study of how the magnitude of these errors affects the accuracy of the estimates. Furthermore, some of the assumptions made within the estimating process are analysed. From sensitivity analysis, it is concluded that a tuning methodology for the smoothing algorithm, presented in Paper A, results in stable estimates with a good trade-off between estimator adaptability and noise sensitivity.In Paper C, the fatigue damage in a vehicle component is predicted based on strains estimated with the smoothing algorithm. Accelerations and strains are measured on a vehicle component mounted in a vibration test rig, and together with a numerical model based on a finite element analysis, the strains in critical regions are estimated. The estimated strain is then used for computation of the accumulated fatigue damage. The predicted damage corresponds well with the failures occurring in a vibration fatigue life test of the analysed component. Finally, in Paper D the fatigue damage prediction methodology presented in Paper C is used to predict the fatigue damage in a complete vehicle. Based on a finite element model of the vehicle and on several hundred kilometres of driving, the fatigue damage in some critical regions on three different chassis-mounted components is predicted. The smoothing algorithm estimates the strains with the acceptable result, even though the model error is large and the number of acceleration measurements is low. The subsequent damage predictions correspond well with failures seen on operating trucks.
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| 8. |
- Lagerblad, Ulrika, 1987-, et al.
(författare)
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Dynamic response identification based on state estimation and operational modal analysis
- 2019
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Ingår i: Mechanical systems and signal processing. - : Academic Press. - 0888-3270 .- 1096-1216. ; 129, s. 37-53
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents and experimentally validates an augmented Kalman filter extended with a fixed-lag smoother for solving joint state and input estimation problems. Sparse acceleration measurements from a truck side skirt excited by road-induced vibrations from a vibration test track are analysed. The system model is obtained experimentally from an operational modal analysis, reducing modelling errors and avoiding the need for a finite element model and it serves itself as a numerical model. The motion of the truck component is estimated and the results are compared to those of a joint input-state estimation filtering algorithm, in addition to the actual measured motion. Both algorithms are tuned according to a novel process based on minimal a priori information concerning the system states and inputs. The focus of this work is to assess the robustness, performance, and tuning of the algorithms. Two sensor configurations are studied: one where the number of response measurement sensors is high compared to the number of estimated motions and participating modes, and another where the number of response measurements is reduced. Both algorithms perform very well within the first configuration. With a reduced number of response measurements, the fixed-lag smoother is superior to the joint input-state filter in capturing the individual motion of each position on the side skirt.
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| 9. |
- Lagerblad, Ulrika, 1987-, et al.
(författare)
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Dynamic response identification based on state estimation and operational modal analysis applied to a truck side skirt
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This work presents an experimental verification of a fixed-lag smoother for solving joint state and input estimation problems.Sparse acceleration measurements from a truck side skirt excited by road induced vibrations from the Scania vibration test track are analysed. The system model is obtained experimentally from an operational modal analysis, reducing the modelling errors and avoiding the need of a numerical model. The work is focused on estimating the motion of the side skirt in positions where no measurements are available. The estimated motions are compared to those of a joint input-state estimation algorithm and to the actual measured motion. Two sensor configurations are studied: one where the number of measurement sensors is high compared to the number of estimated motions and participating modes, and another where the number of sensors are reduced. With the first configuration, both algorithms perform very well. With the reduced numbers of sensors, the fixed-lag smoother excels the joint input-state estimator in capturing the individual motion of each position on the side skirt.
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| 10. |
- Lagerblad, Ulrika, 1987-, et al.
(författare)
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Fatigue damage prediction based on strain field estimates using a smoothed Kalman filter and sparse measurements
- 2018
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Ingår i: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics. - : KU Leuven - Departement Werktuigkunde. - 9789073802995 ; , s. 2805-2817
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Konferensbidrag (refereegranskat)abstract
- In this work, we address the problem of fatigue damage prediction in a truck component excited by road induced vibrations. The damage is computed from strains estimated from sparse measurements of the dynamic response. Two different fixed-lag smoothing algorithm are employed, an augmented Kalman filter extended with a fixed-lag smoother and a smoothed joint input-state estimation algorithm. The system is described with a finite element model, and due to the complexity of reproducing the system by the model, the resulting representation may contain a number of discrepancies. Nevertheless, both smoothing algorithms succeed in capturing the dynamic behaviour of the component, although the estimated strains are affected more by the large model error than the estimated acceleration are. Furthermore, it is shown that the proposed methodology of strain estimation and fatigue damage calculations correlate well with the observed failure of a component when tested in a full-scale fatigue test of a truck chassis- International Conference on Uncertainty in Structural Dynamics.
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