TY - BOOK

T1 - Multistable morphing structures using variable stiffness laminates

AU - Haldar, Ayan

N1 - Doctoral thesis

PY - 2020

Y1 - 2020

N2 - As the concern about climate change grows, more industries and research organizations are stepping up in search of viable solutions. Wind energy is one of the cheapest clean forms of energy, making it an attractive alternative against non-renewable sources. Upscaling of wind turbine has traditionally been considered a means to decrease the cost per kWh, and it remains a trend. However, with an increase in the size of wind turbine rotor blades, there is a need to conceptualize designs capable of reducing ultimate and fatigue loads. Active trailing edge flap is one such promising concept to alleviate loads in large wind turbine blades. Most existing flap mechanisms have the potential for quick reaction time, but it often involves intricate actuation systems, adding additional weight and complexity. Moreover, it requires a continuous supply of energy input to maintain a particular position of the flap. Multistable variable stiffness (VS) laminates have a great potential in morphing applications primarily due to the existence of multiple stable shapes. The use of VS laminates with curvilinear fiber paths allows one to improve further the performance of multistable laminates as morphing structures. The principal aim of this thesis is to exploit the properties of multistable VS laminates and apply them to a novel design of morphing trailing edge flap. This requires not only developing numerical and analytical tools, but also a suitable design to integrate VS laminates into a morphing flap. Therefore in this work, a fast semi-analytical tool is developed to predict the stable shapes of VS laminates. In addition, a systematic study is carried out to investigate the variation the curvilinear fiber paths on the stable equilibrium shapes. As a result of these investigations, VS laminates could be classified into families with similar multistable equilibrium positions. This, in turn, is applied to the envisaged design of the morphing flap. Snap-through, which is a transition from one equilibrium state to another, is a crucial process to characterize multistable laminates in morphing applications. Two different snapping mechanisms are studied, one using concentrated force and the other using piezoelectric actuators. The extension of the aforementioned semi-analytical tool provides insights that reflect the underlying mechanics and characteristics of the snap-through process. The knowledge gained from the semi-analytical calculations facilitates the design and analysis of more complex multistable rectangular plates. Optimal design of rectangular plates with actuators that leads to maximum out-of-plane displacement but with minimum snap-through voltage is determined. A novel concept of a morphing trailing edge flap with integrated rectangular bistable plates is proposed. In this new concept, the trailing edge deflection is realized by the snap-through of the multistable rectangular plates. The viability of the proposed morphing mechanism is examined using finite element tools.

AB - As the concern about climate change grows, more industries and research organizations are stepping up in search of viable solutions. Wind energy is one of the cheapest clean forms of energy, making it an attractive alternative against non-renewable sources. Upscaling of wind turbine has traditionally been considered a means to decrease the cost per kWh, and it remains a trend. However, with an increase in the size of wind turbine rotor blades, there is a need to conceptualize designs capable of reducing ultimate and fatigue loads. Active trailing edge flap is one such promising concept to alleviate loads in large wind turbine blades. Most existing flap mechanisms have the potential for quick reaction time, but it often involves intricate actuation systems, adding additional weight and complexity. Moreover, it requires a continuous supply of energy input to maintain a particular position of the flap. Multistable variable stiffness (VS) laminates have a great potential in morphing applications primarily due to the existence of multiple stable shapes. The use of VS laminates with curvilinear fiber paths allows one to improve further the performance of multistable laminates as morphing structures. The principal aim of this thesis is to exploit the properties of multistable VS laminates and apply them to a novel design of morphing trailing edge flap. This requires not only developing numerical and analytical tools, but also a suitable design to integrate VS laminates into a morphing flap. Therefore in this work, a fast semi-analytical tool is developed to predict the stable shapes of VS laminates. In addition, a systematic study is carried out to investigate the variation the curvilinear fiber paths on the stable equilibrium shapes. As a result of these investigations, VS laminates could be classified into families with similar multistable equilibrium positions. This, in turn, is applied to the envisaged design of the morphing flap. Snap-through, which is a transition from one equilibrium state to another, is a crucial process to characterize multistable laminates in morphing applications. Two different snapping mechanisms are studied, one using concentrated force and the other using piezoelectric actuators. The extension of the aforementioned semi-analytical tool provides insights that reflect the underlying mechanics and characteristics of the snap-through process. The knowledge gained from the semi-analytical calculations facilitates the design and analysis of more complex multistable rectangular plates. Optimal design of rectangular plates with actuators that leads to maximum out-of-plane displacement but with minimum snap-through voltage is determined. A novel concept of a morphing trailing edge flap with integrated rectangular bistable plates is proposed. In this new concept, the trailing edge deflection is realized by the snap-through of the multistable rectangular plates. The viability of the proposed morphing mechanism is examined using finite element tools.

U2 - 10.15488/10001

DO - 10.15488/10001

M3 - Doctoral thesis

CY - Hannover

ER -