Currently, onshore wind turbines are economical for 2.5 mega-watt inland installation [1]. One of the alternatives to achieve the higher power capacity in onshore wind turbines is to go to higher altitude, which increases the wind speed and has more uniform wind pressure, leading to higher possible annual energy production and relatively lower maintenance costs due to wind shear induced vibrations. This paper deals with a predesign of a new type of tower that should overcome known disadvantages of steel tubular towers for heights over 150 meters. This first part of the paper addresses the viability of a hybrid support structure in respect of ultimate limit states and structural dynamics as part of the requirements in exploring the feasibility of the hybrid tower concept. The hybrid wind turbine tower concept consists of a lattice (lower) structure and a tubular tower for the higher tower segment. The study cases found in literature were designed with maximum height of 160m and the 2.5MW wind turbine. Moreover, they used commercial "L" sections which leads to high number of connections and bolts. The project that supports the present paper aims at using optimally design hollow cross sections, to reduce the number of connections, and low maintenance type bolts. The developed study case is made for 220m tower height and using 5MW wind turbine.
Biped robots path planning must suit several stability requirements of bipedal locomotion. Specifying an appropriate path with proper physical and geometrical constraints is essential due to the limited workspace for limbs. Bezier curve is a suitable solution since it is smooth, parametric and configurable for biped robots and leads to flexible trajectory generation by determination of a few control points in a plane. This paper is focused on proposing a systematic method to generate velocity profile and practical path planning with consideration of acceleration limits. Experimental results are compared with simulated ones in diverse maneuvers to verify this approach.
1 August 2019 in Proceedings of the Institution of Civil Engineers - Structures and Buildings
Offshore wind turbines (OWTs) are highly dynamically loaded by sea waves and wind forces and they operate in a narrow range of rotation frequencies close to the eigenfrequencies of the support structure. The foundation stiffness and damping are therefore very important parameters for a reliable estimation of the dynamic behaviour and cost-effective design of a wind turbine's supporting structure. However, design guidelines for offshore structures usually ignore any soil damping. This paper describes the implementation of a simple geotechnical model in the software package Ashes, which is a servo-hydro-aeroelastic code for wind turbine simulations. In order to investigate the role of the foundation damping, a 20 m monopile supporting structure with a National Renewable Energy Laboratory 5 MW OWT was considered as a case study. The OWT was subjected to standard design load cases and the results were obtained at the mudline of the wind turbine. The parametric study undertaken showed that, when soil damping is considered, ultimate limit state loads can be reduced by 8% and the number of fatigue cycles can be reduced by 1·5%.