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| 2. |
- Erikson, Li, et al.
(författare)
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A method to extract wave tank data using video imagery and its comparison to conventional data collection techniques
- 2005
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Ingår i: Computers & Geosciences. - : Elsevier BV. - 1873-7803 .- 0098-3004. ; 31:3, s. 371-384
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Tidskriftsartikel (refereegranskat)abstract
- A procedure for obtaining quantitative wave and morphodynamic data in a laboratory setting using video images has been developed. The steps include image capture, rectification, and data extraction. All the necessary steps were maintained within the MATLAB environment so the process was streamlined and large amounts of data processed. The procedure involves the use of a program to rectify images, correcting for both lens distortion and camera position. A second program automatically extracts data from images to allow for high spatial and time frequency analysis. The method is shown to produce acceptable results as compared to more conventional methods of measuring wave and profile parameters in a wave tank experiment.
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| 5. |
- Erikson, Li, et al.
(författare)
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Laboratory Investigation of Beach Scarp and Dune Recession Due to Notching and Subsequent Failure
- 2007
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Ingår i: Marine Geology. - : Elsevier BV. - 0025-3227. ; 245:1-4, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Analytical models to calculate notch development and subsequent mass failure of dunes are presented. The notch evolution model is based on a transport equation for sediment from the dune and the sediment volume conservation equation, whereas the models of mass failure are derived using elementary engineering statics and soil mechanics. An empirical transport coefficient in the model describing the notch growth rate is found to be related to the hydrodynamic forcing at the dune normalized by geotechnical parameters describing the resistive strength of the dune. Two modes of mass failure are modeled whereby the overhang generated by the removal of material from the dune foot (notching) slides downward or topples over following the development of a tensile crack some distance shoreward of the maximum notch depth. The accuracy of the notch evolution and mass failure models are assessed by comparing calculated recession distances against measurements from a small-scale laboratory experiment.
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| 7. |
- Erikson, Li, et al.
(författare)
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Prediction of swash motion and run-up including the effects of swash interaction
- 2005
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Ingår i: Coastal Engineering. - : Elsevier BV. - 0378-3839. ; 52:3, s. 285-302
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Tidskriftsartikel (refereegranskat)abstract
- Modifications to a model describing swash motion based on solutions to the non-linear shallow water equations were made to account for interaction between up-rush and back-wash at the still water shoreline and within the swash zone. Inputs to the model are wave heights and arrival times at the still water shoreline. The model was tested against wave groups representing idealized vessel-generated wave trains run in a small wave tank experiment. Accounting for swash interaction markedly improved results with respect to the maximum ran-up length for cases with rather gentle foreshore slopes (tan beta = 0.07). For the case with a steep foreshore slope (tan beta = 0.20) there was very little improvement compared to model results if swash interaction was not accounted for. In addition, an equation was developed to predict the onset and degree of swash interaction including the effects of bed friction.
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| 8. |
- Erikson, Li
(författare)
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Swash Processes and Dune Erosion: Emphasis on Vessel-Generated Waves
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In navigable waterways, owing to the relatively short fetches for wind wave generation, the free waves generated by moving vessels often produce the dominant wave action with respect to erosion of the shore. In response to the fairly recent introduction of high-speed ferries, combined with a planned expansion within the passenger- and car-carrying ship market, the need to model and predict coastline changes as a result of exposure to vessel-generated waves has become a topic of increased research. Although several studies have been and continue to be conducted, the research on the impact of these types of waves on the shore is still in its early stages. In response, this study was initiated with the objective to generate state-of-the-art technical guidance and modeling tools for quantifying cross-shore profile changes near and above the shoreline caused by vessel-generated waves. To fulfill the objective, the behavior of vessel-generated waves along the coast and their effect with regards to beach and dune erosion were investigated. Several independent, but inter-related studies were conducted for this thesis. One study presents a method to generate a set of practical tools, in the form of graphs. The graphs can be used to provide recommended maximum vessel speeds that will cause lower run-up than already naturally occurring by wind-generated waves. Based on observations of experimental vessel-generated wave trains, a characteristic wave height distribution, consisting of increasing and subsequently decreasing wave heights, was noted. On mild but reflective beaches significant interaction between subsequent waves in the swash zone was also observed. A numerical model, based on the ?ballistics theory? was modified and shown to reproduce the swash hydrodynamics well if interaction was accounted for. An analytical sediment transport model for the swash zone was also employed and calibrated to field data. Lastly, analytical models to predict dune erosion were developed, calibrated, and validated. The models describe erosion on a wave-by-wave basis, and are thought to be useful to estimate the impact from vessel-generated wave trains where the events are episodic and of relatively short duration. The total erosion is a function of the sediment properties, intensity, and frequency of the swash, where the frequency can be determined with knowledge of regularly scheduled vessel passages. In addition to erosion from the direct impact of waves, models to predict dune recession by mass failure were developed. The models are based on elementary engineering statics and soil mechanics. The models developed and/or calibrated for this study are believed to be applicable to both vessel- and wind-generated waves.
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| 9. |
- Gandolfi, D., et al.
(författare)
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The Transiting Multi-planet System HD15337: Two Nearly Equal-mass Planets Straddling the Radius Gap
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 876:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a super-Earth and a sub-Neptune transiting the star HD 15337 (TOI-402, TIC 120896927), a bright (V = 9) K1 dwarf observed by the Transiting Exoplanet Survey Satellite (TESS) in Sectors 3 and 4. We combine the TESS photometry with archival High Accuracy Radial velocity Planet Searcher spectra to confirm the planetary nature of the transit signals and derive the masses of the two transiting planets. With an orbital period of 4.8 days, a mass of {7.51}-1.01+1.09 {M}\oplus and a radius of 1.64 ± 0.06 R ⊕, HD 15337 b joins the growing group of short-period super-Earths known to have a rocky terrestrial composition. The sub-Neptune HD 15337 c has an orbital period of 17.2 days, a mass of {8.11}-1.69+1.82 {{{M}}}\oplus , and a radius of 2.39 ± 0.12 R ⊕, suggesting that the planet might be surrounded by a thick atmospheric envelope. The two planets have similar masses and lie on opposite sides of the radius gap, and are thus an excellent testbed for planet formation and evolution theories. Assuming that HD 15337 c hosts a hydrogen-dominated envelope, we employ a recently developed planet atmospheric evolution algorithm in a Bayesian framework to estimate the history of the high-energy (extreme ultraviolet and X-ray) emission of the host star. We find that at an age of 150 Myr, the star possessed on average between 3.7 and 127 times the high-energy luminosity of the current Sun.
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| 10. |
- Larson, Magnus, et al.
(författare)
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An analytical model to predict dune and cliff notching due to wave impact
- 2010
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Ingår i: Proceedings of 32nd Conference on Coastal Engineering. - : Coastal Engineering Research Council. - 0161-3782. - 9781629931210 - 9780989661102
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Konferensbidrag (refereegranskat)abstract
- A model was developed to calculate the evolution of a notch in a dune or cliff due to wave impact. Analytical solutions were derived to the model for schematized conditions regarding forcing and dune/cliff properties. Comparisons were made with laboratory experiments where the time evolution of the notch was measured. Values of the transport coefficients in the analytical solutions were determined by least-square fitting the solutions to the laboratory data. Some of these coefficients could be related to the ratio between parameters describing the forcing and the dune/cliff strength. The evolution of the dune notch displayed a linear behavior at short times, whereas the cliff notch showed a more complex response for cases where a feedback between the notch and a beach formed seaward of the cliff occurred.
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