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Preliminary design of offshore wind turbines requires high precision simplified methods for the analysis of the system fundamental frequency. Based on the Rayleigh method and Lagrange’s Equation, this study establishes a simple formula for the analysis of system fundamental frequency in the preliminary design of an offshore wind turbine with a monopile foundation. This method takes into consideration the variation of cross-section geometry of the wind turbine tower along its length, with the inertia moment and distributed mass both changing with diameter. Also the rotational flexibility of the monopile foundation is mainly considered. The rigid pile and elastic middle long pile are calculated separately. The method is validated against both FEM analysis cases and field measurements, showing good agreement. The method is then used in a parametric study, showing that the tower length Lt, tower base diameter d0, tower wall thickness δt, pile diameter db and pile length Lb are the major factors influencing the fundamental frequency of the offshore wind turbine system. In the design of offshore wind turbine systems, these five parameters should be adjusted comprehensively. The seabed soil condition also needs to be carefully considered for soft clay and loose sand.

New types of synthetic municipal solid wastes (MSWs) were developed, exhibiting engineering characteristics similar to those of real MSWs at different states of degradation in terms of total unit weight, void ratio, water content, compressibility, permeability, stress–strain relationship, and shear strength. Using these synthetic MSWs, several centrifuge model tests on the stability of geosynthetics-lined landfills with rising water levels were performed. The test results revealed the developing processes of MSW landfill failures induced by rising water levels. In most tests, a continuous slide occurred once a critical water level was attained. The ratio of critical water level and landfill height was 0.75–0.92 for present model tests using fresh or partly degraded synthetic MSWs with landfill slope ratio of 1:1–1:3, increasing with the increases of MSW degradation states and decreases of the slope ratio. An engineered berm increased the critical water level by 1.3%–9.5%. The landfills without an engineered berm tended to slide along the bottom liner; however, for normal landfills with an engineered berm and a slope ratio of 1:3, penetrating cracks developed when the failures occurred. These results provide a good reference for water level and stability control of the landfill, and the construction of an engineered berm is suggested to improve the stability of these landfills.