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Piezoelectric constant and temperature vs dielectric constant measurements have been performed on the 〈001〉 and 〈011〉 oriented Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals in the rhombohedral phase with compositions near the morphotropic phase boundary under different poling fields. The investigations have revealed that the dielectric and piezoelectric properties strongly depend on composition (PbTiO3 content), and on poling field for crystals in a narrow composition region. The influence of composition on the stability of orthorhombic ferroelectric phase has been identified by x-ray diffraction on the 〈011〉 oriented crystals. And the origin of high piezoelectric response for crystals in different composition regions was proposed.

a b s t r a c tWind turbine layout optimization in wind farm is one of the most important technologies to increase the wind power utilization. This paper studies the wind turbine layout optimization with multiple hub heights wind turbines using greedy algorithm. The linear wake model and the particle wake model are used for wake flow calculation over flat terrain and complex terrain, respectively. Three-dimensional greedy algorithm is developed to optimize wind turbine layout with multiple hub heights for minimizing cost per unit power output. The numerical cases over flat terrain and complex terrain are used to validate the effectiveness of the proposed greedy algorithm for the optimization problem. The results reveal that it incurs lower computational costs to obtain better optimized results using the proposed greedy algorithm than the one using genetic algorithm. Compared to the layout with identical hub height wind turbines, the one with multiple hub height wind turbines can increase the total power output and decrease the cost per unit power output remarkably, especially for the wind farm over complex terrain. It is suggested that three-dimensional greedy algorithm is an effective method for more benefits of using wind turbines with multiple hub heights in wind farm design.