Dynamic effects in the response of offshore wind turbines supported by jackets under wave loading

Wei, Kai; Myers, Andrew C.; Arwade, Sanjay R.

doi:10.1016/j.engstruct.2017.03.074

Cited by 46 publications

(16 citation statements)

References 24 publications

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“…The dynamic performance of jacket supported OWTs incorporating Soil Structure Interaction (SSI) is an area of active research [14][15][16]. The dynamic response of jackets under the action of waves of different periods and energy is studied by [14] using Finite Element analysis where the dynamic amplification factors (DAFs) are evaluated. The study shows that depending on the wave amplitude and period, the DAF may reach values of 1.2-1.3 which is significant given the magnitude of wave loads.…”

Section: Figure 1: Schematic Of a 3-legged Jacket Supported On A Suctmentioning

confidence: 99%

Dynamic design considerations for offshore wind turbine jackets supported on multiple foundations

et al. 2019

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To support large wind turbines in deeper waters (30-60 m) jacket structures are currently being considered. As offshore wind turbines (OWT's) are effectively a slender tower carrying a heavy rotating mass subjected to cyclic/dynamic loads, dynamic performance plays an important role in the overall design of the system. Dynamic performance dictates at least two limit states: Fatigue Limit State (FLS) and overall deformation in the Serviceability Limit State (SLS). It has been observed through scaled model tests that the first eigen frequency of vibration for OWTs supported on multiple shallow foundations (such as jackets on 3 or 4 suction caissons) corresponds to low frequency rocking modes of vibration. In the absence of adequate damping, if the forcing frequency of the rotor (so called 1P) is in close proximity to the natural frequency of the system, resonance may occur affecting the fatigue design life. A similar phenomenon commonly known as "ground resonance" is widely observed in helicopters (without dampers) where the rotor frequency can be very close to the overall frequency causing the helicopter to a possible collapse. This paper suggests that designers need to optimise the configuration of the jacket and choose the vertical stiffness of the foundation such that rocking modes of vibration are prevented. It is advisable to steer the jacket solution towards sway-bending mode as the first mode of vibration. Analytical solutions are developed to predict the eigen frequencies of jacket supported offshore wind turbines and validated using the finite element method. Effectively, two parameters govern the rocking frequency of a jacket: (a) ratio of super structure stiffness (essentially lateral stiffness of the tower and the jacket) to vertical stiffness of the foundation; (b) aspect ratio (ratio of base dimension to the tower dimension) of the jacket. A practical example considering a jacket supporting a 5MW turbine is considered to demonstrate the calculation procedure which can allow a designer to choose a foundation. It is anticipated that the results will have an impact in choosing foundations for jackets.

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Section: Figure 1: Schematic Of a 3-legged Jacket Supported On A Suctmentioning

confidence: 99%

Dynamic design considerations for offshore wind turbine jackets supported on multiple foundations

et al. 2019

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“…Dynamics plays an important role in the design of such structures as it is necessary to target the natural frequency of the whole system away from the excitation frequencies of 1P (rotor frequency), 2P/3P (blade passing frequency) and wave frequencies. The dynamic response on a fixed base jacket under different types of wave loads have been studied by (Wei, et al, 2017) where the dynamic amplification factors (DAFs) for regular and irregular waves is computed. The study shows that depending on the wave amplitude and period, the DAF may reach values of 1.2-1.3 which is significant given the magnitude of wave loads.…”

Section: Jacket Supported Offshore Wind Turbinesmentioning

confidence: 99%

Closed form solution for the first natural frequency of offshore wind turbine jackets supported on multiple foundations incorporating soil-structure interaction

Jalbi

Bhattacharya

2018

Soil Dynamics and Earthquake Engineering

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“…Wang et al [12] conducted model test and numerical analysis of an offshore wind turbine under seismic, wind, wave, and current loads. Wei et al [13] studied the effect of structural dynamics on the response of an offshore wind turbine supported by a jacket and subjected to wave loads. Gho et al [14] presented an eccentric jacket substructure for offshore wind turbines to better withstand intense environmental forces and to replace conventional X-braced jackets in seismically active areas.…”

Section: Introductionmentioning

confidence: 99%

Laboratory Experimental Investigation on the Hydrodynamic Responses of an Extra-Large Electrical Platform in Wave and Storm Conditions

Zhang

et al. 2019

Water

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The application of electrical platform for converter station in offshore wind farm is highly forward-looking and strategic. The offshore electrical platform is complicated in structure, bulky in volume, and expensive in cost. In addition, the built-in electrical equipment is very sensitive to the acceleration response. Therefore, it is very important to study the hydrodynamic response of the electrical platform exposed in the open sea. Based on the elastic similarity, Froude similarity, as well as the flexural-stiffness similarity of the cross-section, the hydroelastic similarity was derived to guide the model test of a 10,000-ton offshore electrical platform in wind, wave, and current. The hydrodynamic responses including strain and acceleration at key positions of the structure were obtained for different incident angles of external environmental loads. The experimental results showed the increase of water depth can cause more than 10 times increase of strain and acceleration response of the platform. The attack angle of external environmental loads had no definite relationship with strain response of the structure. Therefore, the most dangerous attack angle cannot be determined. The strain of the structure under the combined action of wind, wave, and flow was significantly larger than that under wave load only.

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Dynamic effects in the response of offshore wind turbines supported by jackets under wave loading

Cited by 46 publications

References 24 publications

Dynamic design considerations for offshore wind turbine jackets supported on multiple foundations

Dynamic design considerations for offshore wind turbine jackets supported on multiple foundations

Closed form solution for the first natural frequency of offshore wind turbine jackets supported on multiple foundations incorporating soil-structure interaction

Laboratory Experimental Investigation on the Hydrodynamic Responses of an Extra-Large Electrical Platform in Wave and Storm Conditions

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