a b s t r a c tThe contribution of foundation damping to offshore wind turbines (OWTs) is not well known, though researchers have back-calculated foundation damping from "rotor-stop" tests after estimating aerodynamic, hydrodynamic, and structural damping with numerical models. Because design guidelines do not currently recommend methods for determining foundation damping, it is typically neglected. This paper investigates the significance of foundation damping on monopile-supported OWTs subjected to extreme storm loading using a linear elastic two-dimensional finite element model. The effect of foundation damping primarily on the first natural frequency of the OWT was considered as OWT behavior is dominated by the first mode under storm loading. A simplified foundation model based on the soil-pile mudline stiffness matrix was used to represent the monopile, hydrodynamic effects were modeled via added hydrodynamic mass, and 1.00% Rayleigh structural damping was assumed. Hysteretic energy loss in the foundation was converted into a viscous, rotational dashpot at the mudline to represent foundation damping. Using the logarithmic decrement method on a finite element free vibration time history, 0.17%-0.28% of critical damping was attributed to foundation damping. Stochastic time history analysis of extreme storm conditions indicated that mudline OWT foundation damping decreases the maximum and standard deviation of mudline moment by 7e9%.
The Hattian landslide, which was triggered by the 2005 Kashmir earthquake, formed one of largest landslide dams in the world and it has posed a serious threat of flooding to people living in the lower reach of the Jhelum River. In order to understand deformation occurring in the body of the dam, physical measurements using a Differential Global Positioning System (DGPS) were conducted. Gradual deformation and slowly developing backward erosion initially were observed, leading eventually to a sudden creation of a deep hollow on the downstream slope of the landslide dam. The dimensions of this eroded gully were determined by laser scanning, and the results showed a significant loss of soil volume and a large change in the body of the dam. A breach formation model was used to predict the outflow hydrograph generated by constant downcutting of dam during a breaching event. A run-off analysis of the outflow hydrograph was conducted to evaluate inundation levels of flood waves in case the dam is breached. Hazardous downstream locations were identified near the junction of the Karli and Jhelum Rivers, suggesting a need for early warning system in order to avoid loss of lives.
A large number of landslides induced by the 2004 Mid Niigata Prefecture earthquake resulted in the closure of 233 segments of national and prefectural routes in Higashiyama mountain district, and 61 localities were completely isolated. Since railway and road facilities follow closely the motion of soils, damage to these facilities has to be discussed in terms of soil deformations that they experienced.The example of Kizawa tunnel shows that even relatively small soil deformations can be large enough to cause serious cracking of tunnel lining.
IntroductionThe strong earthquake (M6.8) that hit the inland district of Niigata prefecture on October 23, 2004 was followed by strong aftershocks in rapid succession. The district suffered four jolts with a magnitude of 6 or greater within 38 min after the main shock. A large number of landslides induced by the earthquake in the Higashiyama mountain district resulted in the closure of 233 segments of several prefecture routes and the nationalroute 249, and 61 localities were completely
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