| As the energy crisis and environmental problems become more and more serious, wind energy faces an unprecedented development opportunity. Wind energy is a kind of clean and renewable energy and is available almost anywhere on our earth. In recent years, wind power technology is developing rapidly, in order to pursue more abundant and stable wind resources, the height of wind turbine tower is higher and higher. However, with increase in height, the design of wind turbine tower will be faced with huge contradiction between the cost and operating safely. On the one hand the wind turbine tower will become softer and more prone to resonance and fatigue damage under cyclic loading. On the other hand, its material and construction cost will greatly increase. Thus, the tower design optimization is very meaningful.In order to obtain an optimum design of wind turbine tower, which has the specified frequency, and meet the static strength, stability and fatigue condition, this paper presents a frequency-based design method for optimum design of tubular wind turbine tower under multiple geometric and mechanical constraints. Tower is simplified into a non-uniform cantilever beam structure, the cross section parameters of tower are considered as design variables, and the minimum volume of material as the objective function. The natural frequencies of tower are constrained to ensure the tower is stiff-stiff or stiff-soft or soft-soft design. The loads are calculated by commercial software BLADED, and the strength, stability and fatigue of the tower wall are included in constraints according design standards, these make the optimum structure more conform to the practical design. Since the load evaluation by BLADED is very costly, the whole optimization process is broken into several stages. At the beginning of each stage, optimization starts by using the previous optimum design as its initial design and the wind load of the initial tower design is recalculated. In each stage optimization problem is solved by MMA under the fixed wind load, and the sensitivities of the natural frequency, strength and fatigue constraints with respect to design variables are obtained by analytical method. A numerical example for improving the existing tower design demonstrates the optimization method.Wind turbine is a complicated system, consisting of rotor, nacelle, power train system, control system, tower and foundation etc. The structural load of wind turbine system not only is related to the complex and changeable external environment load (wind load), but also is affected by dynamic magnification which caused by the coupled vibration between tower and turbine. With the change of structure size and frequency, the structural load is also different. For wind turbine tower, there are many parameters characterizing the structure difference, such as the volume of the tower, natural frequency, cross section size (like radius and thickness). In order to verify the effect of these parameters to the load of wind turbine tower, of the parameters to the structural load by control variables method, quantitative research of load effect sizes. The results show the effects of frequency to the tower load is maximum.Wind turbine tower support the vibration load caused by the rotor rotation all the time, so avoiding the resonance under cyclic loading is very necessary. According to the relationship between the operating frequency range of rotor and natural frequencies of tower, wind turbine tower can be divided into several design types, including stiff-stiff, stiff-soft and soft-soft design. We further develop a classification of high wind turbine tower in this paper, which describes the different types of tower design more clearly. By the above optimization method, we can show that which type of the tower design is the potentially optimum candidate for specific height and turbine and provide valuable suggestions for optimum design during concept design stage for wind turbine tower. |
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