Engineering topics
Publications and source records attributed to Zeng, Xiangwu.
A method of installing a hybrid foundation for an offshore wind turbine, the method includes providing a monopile, friction wheel, and suction bucket; installing the friction wheel and suction bucket in the sea floor; and inserting the monopile through the opening into the sea floor.
A hybrid offshore wind turbine includes a monopile, friction wheel, and suction bucket.
Not provided.
The hybrid monopile-friction wheel foundation is an innovative alternative for offshore wind turbines. The concept has wider adaptability and can be used as reinforcement method for existing monopiles. A series of centrifuge tests was performed to investigate the lateral bearing capacities of the hybrid foundation under monotonic loads. Five foundation models and two soil types were considered. According to the recorded responses, the hybrid foundation demonstrated better lateral behaviors that both lateral bearing capacity and stiffness are enhanced. Two analytical methods were proposed and compared with the centrifuge test results. The bearing capacity of the hybrid foundation is smaller than the sum of individual pile and friction wheel, and a reduction factor is suggested for both friction wheels. The friction wheel restrains rotations of monopile and provides extra restoring moments; their effects are idealized as equivalent moments acting on the pile head. The analytical results provide possible solutions in estimating the lateral bearing capacity of the innovative hybrid foundation system for offshore wind turbines by using traditional theories.
Some large capacity offshore wind turbines are constructed in seismically active areas. The occurrence of soil liquefaction during an earthquake can result in severe failures of the offshore wind turbine. The seismic response of the structure and the failure mechanism of the soil-structure interactions are necessary to investigate. In this study, the seismic response of an innovative hybrid monopile foundation is investigated through a series of centrifuge tests. The seismic performance of the combined system of the superstructure, foundation, and soil are demonstrated. Five hybrid foundation models are tested by considering the influence of the foundation thicknesses and diameters, and a monopile foundation is tested for comparison. Centrifuge test results reveal that the hybrid monopile foundation is effective in reducing the lateral displacement during the shaking. In the saturated condition, soil maintains its strength and stiffness beneath and adjacent to the foundation. The hybrid foundation system tends to settle more due to the larger shear stress caused by the soil structure interactions. Influences of the wheel specifications are illustrated. The foundations with larger thicknesses lead to smaller lateral displacements and lower tendencies of liquefaction, but the settlements are intensified. The larger diameter foundation provides a longer drainage path for the excess pore water pressure. With a similar weight, the structure settles less during the earthquake.
The monopile has been widely used to support offshore and coastal structures. A series of centrifuge tests has been performed to investigate the bearing capacity of large diameter monopiles in sandy soil. Both static tests and cyclic tests have been conducted for open-ended and close-ended model piles, and the effects of influence factors, such as loading rates, embedment depths, and loading histories are considered. The piles are then loaded by a sequence of compressive-tensile loadings to estimate the tension capacity, from which the shaft friction is derived. The cyclic load tests are performed with five varying load intensities, and the accumulated settlement is assessed. The centrifuge tests indicate that the pile bearing capacity tends to increase with the initial penetration depth, and the stress state of soil greatly influences the pile behavior. The tensile shaft friction is smaller compared to the compression test. The capacities of the piles reduce significantly under the axial cyclic load, and the maximum cyclic load intensity should be limited to 75% of the ultimate bearing capacity. The API design method is used to calibrate with the centrifuge test results. The method overestimates the bearing capacity at larger depths, and a conservative reduction factor is required.
The support structure for offshore wind turbines (OWTs) plays significant roles in maintaining the structural stability and reducing the initial cost. An innovative hybrid monopile foundation for OWTs is proposed. The concept has a wider adaptability by using established knowledge to solve for new problems. A series of centrifuge tests is performed to investigate the behavior of this hybrid foundation system in extreme and service conditions. OWTs with the original monopile foundation as well as the wheel-only foundations are tested for comparisons, and two clay profiles are considered. The test results show that the hybrid monopile foundation provides larger ultimate bearing capacities compared to the traditional foundations. Two analytical methods are proposed to estimate the ultimate bearing capacity of this innovative design, and the results are calibrated by the centrifuge tests. In service conditions, the hybrid monopile foundation shows stronger cyclic resistances. Influence factors of the cyclic responses are summarized. An analytical solution is put forward to estimate the accumulated lateral displacement of the hybrid monopile foundation. A degradation factor is suggested based on the results of the centrifuge tests. The study aims to enrich the understanding of the innovative foundation concept and to provide design references for practical applications.