This paper aims to demonstrate the application of control co-design methodology for the rotor blades of a floating offshore wind turbine. A 10 MW reference wind turbine model is utilized in the co-design framework. In this paper, the coupling effect between the system, defined by the pre-cone angle, and the controller, defined by pitch angle, is analyzed with a parametric study. The system parameters of the blade are identified by exciting the system with a step input, and by using the step response. The identified model is used to demonstrate the coupling effects of the structural parameters. The control co-design process is implemented to reduce the blade root bending moment by controlling the pitch angle as a function of the pre-cone angle. Utilizing the 10 MW reference model, the proposed control co-design method can reduce the blade root bending moment and attenuate transverse vibrations faster than the original design. Compared to a sequentially designed controller, the co-design demonstrated reduction of the blade root bending moment with similar attenuation time.

This paper presents a comparison of low- and high-fidelity structural analyses of a 10 MW offshore floating wind turbine rotor blade. For low-fidelity analysis, BeamDyn as a part of the OpenFAST toolset is used. For high-fidelity analysis, the Toolkit for the Analysis of Composite Structures (TACS) finite element method is used. First, several numerical examples with reference solutions from the literature are investigated to compare the accuracy and efficiency of the low- and high-fidelity structural models. Next, the DTU 10 MW reference wind turbine blade is analyzed using both the low- and high-fidelity methods. The bending response of the blade is analyzed. The results show that the high-fidelity model agrees with low-fidelity results and reference solutions. The high-fidelity model represents the deformations more accurately than the low-fidelity model and therefore is appropriate for structural analysis of complex wind turbine blade shapes.

This paper presents a comparison of low- and mid-fidelity aerodynamic modelling of floating offshore wind turbine rotors. The low-fidelity approach employs the conventional Blade Element Momentum theory implemented in AeroDyn of OpenFAST . This model ignores the aerodynamic interactions between different blade elements, and the forces on the blade are determined from the balance between momentum theory and blade element theory. With this method, it is possible to calculate the aerodynamic performance for different settings with low computational cost. For the mid-fidelity approach, the Actuator Line Modeling method implemented in turbinesFoam (an OpenFOAM library) is used. This method is built upon a combination of the blade element theory for modeling the blades, and a Navier-Stokes description of the wake flow field. Thus, it can capture the wake dynamics without resolving the detailed flows near the blades. The aerodynamic performance of the DTU 10 MW reference wind turbine rotor is studied using the two methods. The effects of wind speed, tip speed ratio, and blade pitch angles are assessed. Good agreement is observed between the two methods at low tip speed ratios, while the Actuator Line Modeling method predicts slightly higher power coefficients at high tip speed ratios. In addition, the ability of the Actuator Line Modeling Method to capture the wake dynamics of the rotor in an unsteady inflow is demonstrated. In the future, the multi-fidelity aerodynamic modules developed in this paper will be integrated with the hydro-kinematics and hydro-dynamics of a floating platform and a mooring system, to achieve a fully coupled framework for the analysis and design optimization of floating offshore wind turbines.

Machine learning for classification has been used widely in engineering design, for example, feasible domain recognition and hidden pattern discovery. Training an accurate machine learning model requires a large dataset; however, high computational or experimental costs are major issues in obtaining a large dataset for real-world problems. One possible solution is to generate a large pseudo dataset with surrogate models, which is established with a smaller set of real training data. However, it is not well understood whether the pseudo dataset can benefit the classification model by providing more information or deteriorates the machine learning performance due to the prediction errors and uncertainties introduced by the surrogate model. This paper presents a preliminary investigation towards this research question. A classification-and-regressiontree model is employed to recognize the design subspaces to support design decision-making. It is implemented on the geometric design of a vehicle energy-absorbing structure based on finite element simulations. Based on a small set of real-world data obtained by simulations, a surrogate model based on Gaussian process regression is employed to generate pseudo datasets for training. The results showed that the tree-based method could help recognize feasible design domains efficiently. Furthermore, the additional information provided by the surrogate model enhances the accuracy of classification. One important conclusion is that the accuracy of the surrogate model determines the quality of the pseudo dataset and hence, the improvements in the machine learning model.

This paper presents an application of a novel piezocomposite rotor system on a model-scale helicopter. The piezocomposite rotor concept can be implemented on various rotary systems, including small unmanned aerial vehicles, and tandem rotor, multi-rotor, single-rotor and other rotary systems. Based on authors’ previous research, a new design of the so-called solid-state rotor concept is implemented on a single degree of the freedom apparatus that the derived from the model-scale helicopter. An electromagnetic power generator is used to convert the mechanical energy due to the rotation of the generator into electrical energy, and this is used to actuate the piezocomposite blades. The actuation by the piezocomposite actuators on the rotor blade results in a change of the camber of the rotor blade. The change in camber generates an increase of thrust.

This paper presents the mechanical design and modeling of an active segment of a bioinspired piezocomposite aquatic pump. The design and analysis is based on an electromechanical Euler-Bernoulli beam model. The self-contained propulsion/pumping system is composed of a series of piezo-active soft cymbal-like segments that are connected by passive soft films. By applying coordinated excitations for expansion and contraction to different active segments, the design creates a traveling wave along the pump axis, which in return propels the fluid to generate a unidirectional thrust force. In the model, the insulation and mechanical properties of the waterproofing sealant layer are considered. Using the proposed electromechanical model, a parametric analysis is conducted to understand the effectiveness of the cymbal-like piezocomposite active segment. Two performance metrics are considered, including the area change of the enclosed by the cymbal-like segment, and the work done by the actuators. The optimal structural parameters of the piezocomposite pump are decided by these performance metrics.

A slotted natural-laminar-flow airfoil design is a two-element airfoil design that employs a slot between the fore and aft elements. This slot alters the pressure recovery condition on the suction surface of the fore element, minimizing skin-friction and inhibiting the laminar to turbulent transition. These benefits reduce overall aircraft drag and increase wing lift. This allows smaller planforms, in turn, reducing fuel burn. This paper investigates the proposal that by help of piezocomposite surface actuation the aft element can be moved, rotated, and morphed to be used as a high-lift effector for take-off and landing conditions. A theoretical analysis is performed using a coupled fluid-structure interaction method assuming static aero-elastic behavior. During analysis the fore-element of the multi-element airfoil is assumed rigid. Thus, shape optimization is limited exclusively to the aft element. Airfoil morphing is achieved by way of piezocomposite actuating elements applied to the pressure and suction sides of the aft element. A genetic algorithm is used to independently optimize substrate thicknesses for each piezocomposite actuator as well as voltage, chord position and piezocomposite length. The nominal and leading edge substrate thicknesses of the airfoil are also varied. The optimized geometry for the high lift configuration is presented.

Design space for morphing structures using single layer commercial piezocomposite actuators are often restricted due to limitations in actuation authority. Optimal designs are those in which the substrate-actuator composite is stiff enough to maintain shape when subjected to surface pressures but allow for the desired curvature under excitation. This trade-off limits substrate to actuator thickness ratios in applications where dynamic pressures are high. One way to improve actuation authority while maintaining stiffness is to use multiple piezocomposite actuators. This paper explores the benefits and drawbacks of using multilayer piezocomposite actuators. The actuators are modeled using the finite element method and are characterized using well-known free strain and blocked force conditions in a four-point loading condition. Material properties for substrate, piezocomposite, and glue layers are modeled based on previous experimental analysis of curvature over a range of thickness ratios for single element actuators. A parametric analysis is conducted on multilayer piezocomposites varying thickness ratio, substrate material and number of piezocomposite layers. Results for the parametric analysis are presented in the form of maximum curvature, work done, and work done normalized by number of layers. A discussion of new design space potential for multilayer actuators is provided.

The so-called solid-state ornithopter concept seeks to employ piezoelectric materials to generate flapping motion instead of relying on conventional mechanisms and multi-component actuation systems. The motion can be induced on a wing-like partially-clamped composite substrate with a piezocomposite device (i.e. the Macro-Fiber Composite actuator.) In this research, a design for a flapping wing is proposed based on the analysis of critical system parameters such as geometric properties and boundary conditions. A series of finite element simulations are conducted based on the variation of those parameters. Consequently, the effects of parameters on the structural response is studied. Also, modal analysis is done to examine the effects of geometric parameters on the resonant frequencies of the system. Heaving and pitching responses are examined.

Wearable motion sensors find a great number of applications in the biomedical field by recording real-time movements and transferring data to mobile electronics. Patients with hyperkinetic movements is a group of interest for such sensors to survey their conditions for long periods. Longer and more frequent recording intervals are necessary to diagnose and treat patients’ disease. Mobile battery-operated motion sensors have a limited recording span, and they need to be charged frequently, which is inconvenient for most of the patients. In this study, vibration energy harvesters are employed to extend the battery life of motion sensors: one step closer to make autonomous sensors without chargers. A vibration energy harvester is designed for a motion sensor to harvest energy from involuntary movements of patients with hyperkinetic movements. An analytical model for charging and discharging cycles is developed to predict the battery life based on the amount of harvested power. Preliminary data from commercial devices are used as a foundation for the design and the current feasibility study.

A continuous-surface morphing airfoil is desirable for commercial aircraft in order to improve fuel efficiency, and due to the potential to morph the wing into a high-lift configuration for take-off and landing. Piezocomposite actuators have shown to be a feasible strategy for camber morphing in small unmanned fixed-wing aircraft with a Reynold’s number in the range of 50,000 to 250,000. As an extension, this paper presents a theoretical framework and results for morphing in single and multi-segment natural laminar flow airfoils with a maximum Reynold’s number of 825,000. The airfoils presented employ a continuous inextensible surface. To achieve morphing, piezocomposite actuating elements are applied on the suction and pressure surfaces of the airfoils. The geometric properties of the airfoils are determined using a genetic algorithm optimization method with a migration strategy in order to maintain population diversity. The algorithm optimizes independently the substrate thicknesses for the nominal airfoil, the leading edge, and the piezocomposite bonded surfaces. In addition, positions and voltages for each piezocomposite actuators are optimized. The genetic algorithm uses an objective function to maximize the change in coefficient of lift to morph the airfoil from its baseline (i.e. cruise) state to the high-lift state. Analysis is performed using a coupled fluid-structure interaction method assuming static aero-elastic behavior. Optimization is followed by a parametric analysis to examine lift, drag, and lift-to-drag ratio of the airfoils over their full operational range. The optimization is performed on a symmetric, asymmetric, and the aft element of a slotted multi-segment airfoil to examine the capabilities of induced-strain actuation at high dynamic pressures.

One of the means of flight is via flapping and there were many attempts to mimic the wing motion of a bird for centuries. One interesting concept for achieving flight via flapping is the so-called solid-state ornithopter concept which works by using induced strain actuators such as piezoelectric materials for flapping. In this research, we seek to gain a better understanding of the feasibility and performance of the solid-state ornithopter concept. In this paper, the purpose is to analyze a solid state ornithopter wing concept and to study the effect of different geometric parameters. A two-way fluid-structure interaction analysis method is utilized since the geometry of the wing is changing throughout the flapping cycle, and the fluid and the solid domains interact significantly. A parameterized model is utilized in both solid and fluid domains, and the two domains are coupled. Different geometric parameters are defined in the model so that the system-level performance metrics as a function of each parameter can be examined.

This paper presents a summary on the ongoing research and development of a solid-state piezoelectric composite rotor design for use in rotary systems. The paper focuses on the theoretical analysis of a two-bladed rotor with varying parameters such as flight speed, blade pitch angle, and rotational speed. XROTOR, a blade element method based software, is used for analysis. The two-dimensional aerodynamic characteristics are acquired from the previous research on a Macro-Fiber Composite actuated simply supported thin airfoil. A set of simulations are conducted to determine the best geometric configuration, so the piezoelectric increase in thrust is maximized. The proposed hub-rotor system has the potential to be implemented in unmanned-aerial-vehicles such as single-rotor, tandem-rotor, multi-copter, and ducted-fan rotorcraft, or other rotating systems such as wind turbines, turbine engines, and marine propellers. This paper presents a summary of previous findings on a solid-state rotor prototype, and a new investigation on the theoretical aerodynamic behavior.

This paper investigates the optimal geometric parameters for a bioinspired peristaltic piezocomposite pump with the use of an electromechanical Euler-Bernoulli beam model. The peristaltic pump is a self-contained propulsion system involving a series of piezo-active soft cymbal-like segments that are connected with passive soft connective segments. A series of phased excitations in expansion and contraction applied to different active segments of the channel create a traveling wave along the axis of the channel, which in return “propels” the fluid in one direction. A parametric analysis, based on the Euler-Bernoulli beam model, is conducted to improve the effectiveness of the cymbal-like piezocomposite actuators. Area change of the cymbal-like actuators, which is correlated to the propulsion power, is studied based on the analysis of the moment, curvature, and area change due to excitation. Area change is also used to evaluate the effectiveness, and to decide the optimal geometric parameters of the piezocomposite actuators.

Energy harvesting from ambient vibrations and mechanical deformations using piezoelectric materials has received significant attention over the last decade. These types of energy harvesters find applications in structural health monitoring, wireless sensor networks, etc. In this paper, vibration energy harvesting from piezocomposite beams with unconventional boundary conditions is investigated. The so-called inertial four-point boundary condition is useful in applications where the cantilevered beam setup leads to non-uniform stress-strain distribution along the beam domain. In this paper, the Euler-Bernoulli beam theory is used to model the beam. The voltage output, maximum power output, and the tip velocity are investigated. The efficiency of the four-point loaded beam is compared to a cantilever beam.

This paper investigates the feasibility of a soft-structure peristaltic pumping and propulsion concept with distributed self-contained piezocomposite actuators. The peristaltic propulsion concept is analogous to various natural and synthetic mechanisms such as: (i) pulsed jet propulsion and thrust vectoring observed in squids, and (ii) operation principle of multi-phase linear electromagnetic motors. This paper proposes a propulsion system involving a series of active soft cymbal-like segments that are connected with passive soft connective segments. The active sections of the channel have distributed piezocomposite actuators, and these embedded self-contained devices enable the active section of the channel to expand and contract much like the muscular hydrostatic mantle of squids. A series of phased excitations in expansion and contraction applied to different active segments of the channel create a traveling wave along the axis of the channel, which in return “propels” the fluid in one direction. A tubular aperture with vectoring capabilities, similar to the rotating funnel of squids, is also possible. The paper presents feasibility of the concept with theoretical and experimental analyses.

The dynamic behavior of a Duffing-Holmes oscillator subjected to a Hybrid Position Feedback (HPF) controller is investigated. The so-called hybrid controller is a combination of two controllers, namely, the Negative Position Feedback (NPF), and Positive Position Feedback (PPF) controllers. The controller uses the inertial properties of the structure around its stable positions to achieve large displacements by effectively destabilizing the system using an NPF controller. Once the unstable equilibrium is reached, the system is stabilized to the target stable equilibrium using the PPF controller. This dynamic switch of controllers creates the HPF control concept, which specifically enables the monotonic and controlled transition between the states of bistable systems such as the Duffing-Holmes oscillator. This concept can be implemented to morphing structures such as bistable wings, wind turbine blades, and deployable structures. In this paper, a detailed response type and stability analyses of a Duffing-Holmes oscillator controlled by the HPF controller are presented. First, the response types for the components of the HPF, NPF and PPF controllers are analyzed individually. For the NPF controller, three response types are defined. These are intra-well, single cross-well, and multiple cross-well response types describing the possible responses. For the PPF controller, only two response types are defined. These are stabilized and not-stabilized, since the role of the PPF controller is to generate an attractor to the desired stable equilibrium. Finally, the complete HPF controller is analyzed in terms of response type. In this case, three response types are defined: intra-well, single cross-well and multiple cross-well. The paper summarizes all the response types with detailed analyses, and recommends controller parameters for best control performance.

In this paper a multi-segment beam, in what is called an inertial four-point loaded configuration, is proposed and its dynamic response is analyzed. In this configuration, two symmetrical overhanging free segments extend beyond the pinned supports, and two tip masses are attached to these free segments yielding symmetrical inertial loading at the tips. By varying the configuration parameters of this multi-segment beam, such as support locations and tip loading, the dynamic response of the system can be significantly altered. The harmonically excited transverse vibration of a piezocomposite beam with four-point loaded boundary conditions is analyzed as a function of the support location and tip mass. Experimental data for several support locations is presented for validation of the analytical model and the predicted relationship between the system natural frequency, support locations, and tip masses. Comparisons are also made between the multi-point loaded cases and a reference cantilevered beam. The analytical and experimental results demonstrate that the natural frequency of a multi-point loaded beam can be continuously adjusted in a relatively wide range using the configuration changes investigated.

A common configuration for a piezoelectric vibration energy harvester is the cantilevered beam with the piezoelectric device located near the beam root to maximize energy transduction. The beam curvature in this configuration is monotonically decreasing from root to tip, so the transduction per unit length of piezoelectric material decreases with increasing patch length. As an alternative to such conventional configuration, this paper proposes a so-called inertial four-point loading for beam-like structures. The effects of support location and tip mass on the beam curvature shapes are analyzed for four-point loaded cases to demonstrate the effect of these configurations on the total strain induced on the piezoelectric patch. These configurations are tested experimentally using several different support locations and compared with results from a baseline cantilevered beam. Performance comparisons of their power ratios are made, which indicate improvement in the transduction per unit strain of the four-point loading cases over the cantilevered configuration. The paper concludes with a discussion of potential applications of the inertial four-point loaded configuration.

This paper examines the feasibility of piezocomposite morphing airfoils and trailing edge control surfaces subjected to large dynamic pressures. Piezocomposite airfoils have been shown to be feasible on small unmanned aerial vehicles, subject to relatively low dynamic pressures, operating in the Reynold’s number range of 50k to 250k. The operating range of interest in this paper has a cruising Reynold’s number range between 250k and 1M subject to relatively large wing loading. This range of Reynold’s numbers has not been explored in detail due to the large aerodynamic loads produced. Based on the authors’ previous research on small unmanned aircraft, the proposed concept is a variable-camber airfoil that employs a continuous inextensible surface and surface-bonded piezocomposite actuators. To achieve camber-morphing, multiple piezocomposite actuating elements are applied to the upper and lower surfaces. A case study is performed to determine the design parameters of the airfoil. The parameters to be varied include the substrate thickness of the baseline airfoil, leading edge, and piezocomposite bonded areas. In addition, the positions of the piezocomposites are varied. The analysis is performed using a coupled fluid-structure interaction model assuming static aeroelastic behavior. A voltage sweep is conducted on each airfoil design while being subjected to 70 m/s free stream velocity. The sweep examines the lift coefficient and lift-to-drag ratio of the airfoil over the full operational range. This research lays the groundwork for determining the feasibility of piezocomposite morphing airfoil and trailing edge concepts for use in applications subject to large dynamic pressures.