| 1. |
- Bergdahl, Lars, 1943, et al.
(författare)
-
Waves for design of wind-power plants in shallow seas
- 2009
-
Ingår i: Proceedings of the 20th International Conference on Port and Ocean Engineering under Arctic Conditions. ; 1, s. 1-11
-
Konferensbidrag (refereegranskat)abstract
- Usually there is little knowledge of long-term wave conditions at prospective sites for windpower plants, while the deep-water or open sea conditions may be more known and geographically less varying. However, most wind-energy plants are intended for water depths less than 20 m. A concept for assessing design waves at a near-shore site is to transform the offshore wave spectra to the target site by a model for spectral wave-energy transfer over the actual bottom topography. The inshore spectra can be used for linear statistics of extreme waves and design wave loads can be produced. In this context it is important to know the realism of used spectral forms.Based on 58 measured wave spectra at 6 m water depth at the near-shore wind farm Bockstigen in the Baltic the most realistic spectrum was found to be the TMA spectrum, which is a JONSWAP spectrum modified for shallow water. Some few examples are given.
|
|
| 2. |
- Fransson, Lennart, et al.
(författare)
-
Ice loads for wind-power foundations in the Gulf of Bothnia
- 2009
-
Ingår i: Proceedings of the 20th International Conference on Port and Ocean Engineering under Arctic Conditions. ; June 9-12, 2009, s. 12-19
-
Konferensbidrag (refereegranskat)abstract
- Ice loads measured on lighthouses in the Gulf of Bothnia can serve as guidance for design of foundations for wind-power generators. At some locations in the sea these structures must withstand high pressure from solid land fast ice as well as from ridges or other compacted ice masses that are drifting. Recommendations for design of offshore foundations around the Swedish coastline have recently been written by the authors. For the purpose of design, effective pressure as well as compressive strength is assumed to be independent of ice thickness. All structures should be designed for dynamic ice loads that are dependent on the natural frequency of the structure and the ice drift velocity. Increased effective pressure has earlier been indicated for high speed ice crushing both in field studies and compression tests. The presented results from ice load measurements on lighthouse Norströmsgrund support the suspicion that also design ice loads should increase with drift speed. This rate effect and other uncertainties about the worst case scenario for ice-induced vibrations suggest a more conservative design of wind-power foundations inside the dynamic ice zone.
|
|
| 3. |
- Dammann, Dyre Oliver, 1985, et al.
(författare)
-
Applications of radar interferometry for measuring ice motion
- 2021
-
Ingår i: Proceedings of the International Conference on Port and Ocean Engineering under Arctic Conditions, POAC. - 0376-6756 .- 2077-7841. - 9781713841005 ; 2021-June
-
Konferensbidrag (refereegranskat)abstract
- Ongoing sea ice decline has major implications for human activities near sea ice due to shorter seasons for on-ice operations and thinner ice with reduced load-bearing capacity and stability in many regions. This may in turn lead to increased sea ice mobility and impacts of ice movement on structures. We investigate space-borne radar interferometry (InSAR) as a technique to measure mm-scale sea ice motion of stationary ice over weeks to months. We find that InSAR enables mapping of bottomfast and stabilized landfast ice as regions with near-zero or reduced deformation. We further use this data to derive landfast ice strain and stress enabling estimation of the fracturing potential along the Northstar Island ice road in the Beaufort Sea, Alaska. We further examine ground-based radar interferometry (GRI) as a tool to collect continuous near real-time measurements on the km-scale not possible with InSAR. Based on GRI measurements conducted in Utqiaġvik, Alaska, we demonstrate the ability to evaluate ice strain in stationary ice and track vertical ice displacement due to tides. We also collected GRI measurements at 500 Hz during a drifting ice camp in the Beaufort Sea. The high sampling rate enabled tracking of continuous strain and detection of subtle variations in behavior between ice regimes. Through this work, interferometry shows promise as a tool to observe ice motion at the relevant scales needed for assessing sea ice stability, identify precursors to failure events, and better understand the relationship between different ice properties and loads on structures.
|
|
| 4. |
- Zhong, Kai, et al.
(författare)
-
Numerical study on the movement pattern of ice around the ship in the broken ice field
- 2023
-
Ingår i: Proceedings of the International Conference on Port and Ocean Engineering under Arctic Conditions, POAC. - 0376-6756 .- 2077-7841. ; 2023-June
-
Konferensbidrag (refereegranskat)abstract
- Broken ice field is among the common type of ice conditions when ships operate in Arctic navigation, where ships face a significant increase in resistance and local structural safety threats due to the interaction between the ship's hull, water, and broken ice. The hull needs to remove a large amount of broken ice from its path and disturb the surrounding broken ice, and the extent to which can reflect the intensity of the ship-water-ice interaction. In this study, a coupled CFD-DEM approach to simulate ship-water-ice interaction-related phenomena. In the calculation process, rigid particles are considered as non-rebreakable broken ice, while the effect of ship wave variations on the movement of broken ice is taken into account. The "ice boundary layer" (IBL) is found in the numerical results, and distribution of the thickness of "IBL" along the ship's bow is derived and in good agreement with the formula proposed by Aboulazm (1989). After that, the relationship between ship speed on the movement of ice is also studied.
|
|
