Abstract Origami-inspired structures and material systems have been used in many engineering applications because of their unique kinematic and mechanical properties induced by folding. However, accurately modeling and analyzing origami folding and the associated mechanical properties are challenging, especially when large deformation and dynamic responses need to be considered. In this paper, we formulate a high-fidelity model — based on the iso-parametric Absolute Nodal Coordinate Formulation (ANCF) — for simulating the dynamic folding behaviors of origami involving large deformation. The center piece of this new model is the characterization of crease deformation. To this end, we model the crease using rotational spring at the nodes. The corresponding folding angle is calculated based on the local surface normal vectors. Compared to the currently popular analytical methods for analyzing origami, such as the rigid-facet and equivalent bar-hinge approach, this new model is more accurate in that it can describe the large crease and facet deformation without imposing many assumptions. Meanwhile, the ANCF based origami model can be more efficient computationally compared to the traditional finite element simulations. Therefore, this new model can lay down the foundation for high-fidelity origami analysis and design that involve mechanics and dynamics.

Abstract It has been amply demonstrated that the development of SMA actuators has a great potential of application in several branches of industry. Obviously, the efficiency of the actuators depends both on the inherent features of the materials they are made of and the geometric characteristics of the devices. This work considers a particular type of actuator first conceived by [1], consisting in the association of two cantilever beams, the first presenting the shape memory effect and the second presenting the superelastic effect, coupled mechanically so as to guarantee two equilibrium positions and thus a stand-alone cyclic actuator, in which the superelastic beam provides the bias action. Numerical simulations of the behavior of the actuator are performed using the commercial finite element software COMSOL, which implements the Boyd-Lagoudas thermomechanical model. The goal of the simulations is to characterize the actuation range of the actuator, in terms of maximum displacement obtained at the tip. The effect of the dimensions of the beams on the tip displacement under some load scenarios is investigated. The results provide guidelines for the design of the actuator to fulfill specific requirements, also suggesting the use of numerical optimization for the optimal design of the actuator accounting for constraints.

Abstract 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.

Morphing winglets are innovative aircraft devices capable to adaptively enhance aircraft lift distribution throughout the flight mission while providing augmented roll and yaw control capability. Within the scope of the Clean Sky 2 REG IADP, this paper deals with nonlinear simulations of a regional aircraft wing equipped with active morphing winglets in manoeuvring conditions. The fault tolerant morphing winglet architecture is based on two independent and asynchronous control surfaces with variable camber and differential settings capability. The mechanical system is designed to face different flight static and dynamic situations by a proper action on the movable control tabs. The potential for reducing wing and winglet loads by means of the winglet control surfaces is numerically assessed by means of static aeroelastic analyses, using a feedforward manoeuvre load alleviation controller. An electro-mechanical Matlab/Simulink model of the actuation architecture is used as design tool to preliminary evaluate the complete system performance and the ability to cope with the expected morphing aeroshapes. Then, the aeroelastic model of the aircraft is combined with the nonlinear simulator of the response of the winglet actuation system to evaluate a symmetric and asymmetric manoeuvres obtained by a sudden deflection of the main control surfaces. The use of the morphing winglet tabs shows to alleviate the wing loads in such conditions. The introduction of the dynamic actuator model leads to a reduction of the performances with respect to predictions of the static analyses but a reduction of the manoeuvre loads can still be observed.

The reduction of low-frequency noise transmission through thin-walled structures is a topic of research for many years now. Due to large wavelengths and the mass law, passive solutions usually gain low performance in the frequency range below 500 Hz. Active systems promised to fill the gap and to achieve significant reductions of transmitted sound. Nevertheless, experiments showed the outstanding performance of such specialized systems, but also demonstrated the computational and hardware effort of such solutions. The upcoming additive manufacturing technology enabled new multi-material designs of complex structures. Based on this technology, acoustic metamaterials emerged in the laboratories and in literature. Arrays of miniaturized locally resonant structures are able to change the noise transmission of thin walled structures beyond the limits of the given mass law in certain frequency bands. For future aircraft contra-rotating open rotor (CROR) engines are a promising technology to reduce their CO 2 footprint. Since the contribution of CROR engines to the cabin noise is higher than for jet engines, new strategies for the reduction of noise transmissions for frequency bands below 200 Hz are necessary. For the tonal noise of the CROR engines, acoustic metamaterials seem to be an appropriate solution. In this paper a 110 × 110 × 1 mm 3 thin-walled sample plate is presented. It is covered with a 5 × 5 array of multi-material resonant structures, which are printed as mass on a beam. The rubber-like beam material combines a low Young’s modulus with a high material damping, leading to a low eigenfrequency of the resonators. The design of the resonators using simulations and experimental data is shown. To explore the potential of the design, an acoustic test box is manufactured. Starting with all resonators unblocked the emitted sound intensity of the plate is measured. Sequential blocking of selected resonators proves the concept. Additional laser scanning vibrometer measurements give insights into the vibration behavior of single resonators.

In the framework of Clean Sky 2 Airgreen 2 (REG-IADP) European research project, a novel multifunctional morphing flap technology was investigated to improve the aerodynamic performances of the next Turboprop regional aircraft (90 passengers) along its flight mission. The proposed true-scale device (5 meters span with a mean chord of 0.6 meters) is conceived to replace and enhance conventional Fowler flap with new functionalities. Three different functions were enabled: overall airfoil camber morphing up to +30° (mode 1), +10°/−10° (upwards/downwards) deflections of the flap tip segment (mode 2), flap tip “segmented” twist of ±5° along the outer flap span (mode 3). Morphing mode 1 is supposed to be activated during take-off and landing only to enhance aircraft high-lift performances and steeper initial climb and descent. Thanks to this function, more airfoil shapes are available at each flap setting and therefore a dramatic simplification of the flap deployment system may be implemented. Morphing modes 2 and 3 are enabled in cruise and off-design flight conditions to improve wing aerodynamic efficiency. The novel structural concept of the three-modal morphing Fowler flap (3MMF) was designed according to the challenges posed by real wing installation issues. The proposed concept consists of a multi-box arrangement activated by segmented ribs with embedded inner mechanisms to realize the transition from the baseline configuration to different target aero-shapes while withstanding the aerodynamic loads. Lightweight and compact actuating leverages driven by electromechanical motors were properly synthesized to comply with stringent requirements for real aircraft implementation: minimum actuating torque, minimum number of motors, reduced weight, and available design space. The methodology for the kinematic design of the inner mechanisms is based on a building block approach where the instant center analysis tool is used to preliminary select the locations of the hinges’ leverages. The final geometry of the inner mechanisms is optimized to maximize the mechanical advantage as well as to provide the kinematic performances required by the three different morphing modes. The load-path was evaluated, and the cross-sectional size of leverages was subsequently optimized. Finally, actuating torques predicted by instant center analysis were compared to the calculated values from finite element analysis. The structural sizing process of the multi-box arrangement was carried out considering elementary methods, and results were compared with finite element simulations.

Researchers and engineers design modern aircraft wings to reach high levels of efficiency with the main outcome of weight saving and airplane lift-to-drag ratio increasing. Future commercial aircraft need to be mission-adaptive to improve their operational efficiency. Twistable trailing edge could be used to improve aircraft performances during climb and off-design cruise conditions in response to variations in speed, altitude, air temperature, and other flight parameters. Indeed, “continuous” span-wise twist of the wing trailing edge could provide significant reduction of the wing root bending moment through redistribution of the aerodynamic load leading to an increase of the payload/structural weight ratio. Within the framework of the Clean Sky 2 (CS2) European research project, the authors focused on the preliminary design of a full-scale composite multifunctional tab retrofitting the outboard morphing Fowler flap of a turboprop regional aircraft. The investigation domain of the novel device is equal to 5.15 meters in span-wise direction and 10% of the local wing chord. The structural and kinematic design process of the actuation system is completely addressed: two rotary electromechanical motors, placed in the root and tip flap sections, are required to activate the inner mechanisms enabling delta twist angles up to 10 degrees along the outboard region when the flap is stowed in the wing. The structural layout of the thin-walled closed-section composite tab represents a promising concept to balance the conflicting requirements between load-carrying capability and shape adaptivity in morphing lightweight structures. The main design parameters are optimized to minimize actuation torque required for twisting while providing proper flexural rigidity to withstand limit aerodynamic pressure distributions for large airplanes. Finally, the embedded system functionality of the actuation system coupled with the composite wing trailing edge is fully investigated by means of detailed finite element simulations. Results of actuation system performances, and aeroelastic deformations considering operative aerodynamic loads demonstrate the potential of the proposed structural concept to be energy efficient, and lightweight for real aircraft implementation.

Acoustic metamaterials display unusual mechanical wave manipulation behavior not seen in natural materials. In this study, nonlinear metamaterials with passive, amplitude-activated directional bandgaps are investigated. Test articles are constructed by installing periodic arrays of mass-loaded dome resonators on a square polycarbonate substrate. These resonators display nonlinear softening response with increase in excitation amplitude. Experiments conducted by mounting the test articles on low-stiffness boundaries along two adjacent sides and applying mechanical excitations at the opposite corner. A mechanically-staged laser vibrometer mounted overhead was used to make noncontact measurements at discrete plate and resonator locations. Measured displacement transmissibility verify the existence and extent of bandgap frequency ranges as well as amplitude-activated shifts in their bounds. Moreover, by tailoring the pattern of resonators within the array, preferential steering, focusing and selective beaming of waves within tunable frequency ranges depending on their amplitude are shown to be possible. Steady-state spatial maps depicting the displacement transmissibility field were generated from experiments and correlated with simulations to bring out underlying mechanisms. In addition, both lumped parameter and continuum models are considered to aid the design of scalable, passive adaptive metamaterial waveguides for applications ranging from seismic wave mitigation to MEMS transduction.

Bayesian statistics is a quintessential tool for model validation in many applications including smart materials, adaptive structures, and intelligent systems. It typically uses either experimental data or high-fidelity simulations to infer model parameter uncertainty of reduced order models due to experimental noise and homogenization of quantum or atomistic behavior. When heterogeneous data is available for Bayesian inference, open questions remain on appropriate methods to fuse data and avoid inappropriate weighting on individual data sets. To address this issue, we implement a Bayesian statistical method that begins with maximizing entropy. We show how this method can weight heterogeneous data automatically during the inference process through the error covariance. This Maximum Entropy (ME) method is demonstrated by quantifying uncertainty in 1) a ferroelectric domain structure model and 2) a finite deforming electrostrictive membrane model. The ferroelectric phase field model identifies continuum parameters from multiple density functional theory calculations. In the case of the electrostrictive membrane, parameters are estimated from both mechanical and electric displacement experimental measurements.

Engineering systems subject to high-rate extreme environments can often experience a sudden plastic deformation during a dynamic event. Examples of such systems include civil structures exposed to blast or aerial vehicles experiencing impacts. The change in configuration through deformation can rapidly lead to catastrophic failures resulting in intolerable losses in investments or human lives. A solution is to conduct fast system estimation enabling real-time decisions, in the order of microseconds, to mitigate such high-rate changes. To do so, we propose a model-driven observer coupled with a data-driven adaptive wavelet neural network to provide real-time stiffness estimations to continuously update a system’s model. This real-time system identification method offers adaptability of the system’s parameters to unforeseeable changes. The results of the simulations demonstrate accurate stiffness estimations in milliseconds for three different excitation conditions for a one degree-of-freedom spring, mass, and damper system with variable stiffness.

Vibration-based energy harvesting is a growing field for generating low-power electricity to use in wireless electronic devices, such as the sensor networks used in structural health monitoring applications. Locally resonant metastructures, which are structures that comprise locally resonant metamaterial components, enable bandgap formation at wavelengths much longer than the lattice size, for critical applications such as low-frequency vibration attenuation in flexible structures. This work aims to bridge the domains of energy harvesting and locally resonant metamaterials to form multifunctional structures that exhibit both low-power electricity generation and vibration attenuation capabilities. A fully coupled electromechanical modeling framework is developed for two characteristic systems and their modal analysis is presented. Simulations are performed to explore the vibration and electrical power frequency response maps for varying electrical load resistance, and optimal loading conditions are presented. Case studies are presented to understand the interaction of bandgap formation and energy harvesting capabilities of this new class of multifunctional energy-harvesting locally resonant metastructures. It is shown that useful energy can be harvested from the locally resonant metastructure without significantly diminishing their dramatic vibration attenuation in the locally resonant bandgap. Thus, by integrating energy harvesters into a locally resonant metastructure, there is new potential for multifunctional self-powering or self-sensing locally resonant metastructures.

Among anode materials for lithium ion batteries, silicon (Si) is known for high theoretical capacity and low cost. Si changes volume by 300% during cycling, however, often resulting in fast capacity fade. With sufficiently small Si particles in a flexible composite matrix, the cycle life of Si anodes can be extended. Si anodes also demonstrate stress-potential coupling where the open circuit voltage depends on applied stress. In this paper, we present a NMC-Si battery design, utilizing the undesired volume change of Si for actuation and the stress-potential coupling effect for sensing. The battery consists of one Li(Ni 1/3 Mn 1/3 Co 1/3 )O 2 (NMC) cathode in a separator pouch placed in an electrolyte-filled container with Si composite anode cantilevers. Models predict the shape of the cantilever as a function of battery state of charge (SOC) and the cell voltage as a function of distributed loading. Simulations of a copper current collector coated with Si active material show 11.05 mAh of energy storage, large displacement in a unimorph configuration (>60% of beam length) and over 100 mV of voltage change due to gravitational loading.

Network theory is used to formulate an atomistic material network. Spectral sparsification is applied to the network as a method for approximating the interatomic forces. Local molecular forces and the total force balance is quantified when the internal forces are approximated. In particular, we compare spectral sparsification to conventional thresholding (radial cut-off distance) of molecular forces for a Lennard-Jones potential and a Coulomb potential. The spectral sparsification for the Lennard-Jones potential yields comparable results while spectral sparsification of the Coulomb potential outperforms the thresholding approach. The results show promising opportunities which may accelerate molecular simulations containing long-range electrical interactions which are relevant to many multifunctional materials.

This paper discusses the semi-active control of helicopter ground resonance using magnetorheological (MR) damper. A dynamic model of a MR damper with bi-fold flow mode is built based on the hyperbolic tangent model and experimental data on mechanical properties; and its inverse model is derived for the control. An approximate analytical solution of a linear system is provided and a critical stability area is calculated according to the classical model of ground resonance and the method of determining the linear system stability. Then, Simulations are performed on the helicopter ground resonance model with three semi-active control strategies and the control performance is compared. Simulation results show that the comprehensive performance of the fuzzy skyhook control algorithm is superior to the on-off skyhook and continuous skyhook control algorithms.

We consider subset selection and active subspace techniques for parameters in a continuum phase-field polydomain model for ferroelectric materials. This analysis is necessary to mathematically determine the parameter subset or subspace critically affecting the response, prior to model calibration using either experimental or synthetic data constructed using density functional theory (DFT) simulations. For the 180° domain wall model, we employ identifiability analysis using a Fisher information matrix methodology, and subspace selection to determine the active subspace. We demonstrate the implementation and interpretation of techniques that accommodate the model structure and discuss results in the context of identifiable parameter subsets and active subspaces quantifying the strongest influence on the model output. Our results indicate that the governing domain wall gradient energy exchange parameter is most identifiable.

The present study concerns with the performance of a skid landing gear (SLG) system of a rotorcraft impacting the ground at a vertical sink rate of 5.0 m/s. The impact attitude is per chapter 527 of the Airworthiness Manual (AWM) of Transport Canada Civil Aviation and FAR Part 27 of the U.S. Federal Aviation Regulation. A single degree of freedom helicopter model is investigated under two rotor lift factors 0.67 and 1.0. Three Configurations are evaluated: a) A conventional SLG; b) SLG equipped with a passive viscous damper and c) SLG incorporated with a magnetorheological energy absorber. The non-dimensional solutions of the helicopter model show that the passive damper system could reduce the maximum acceleration experienced by the helicopter occupants by 21% and 19.8% in comparison to the undamped system for the above rotor lift factors, respectively. However, the passive damper fails to constrain the non-dimensional energy absorption stroke of the damper within the given 18 cm maximum stroke and a bottoming out of the damper piston was noticed. Therefore, the alternative and successful choice was to employ a magnetorheological energy absorber (MREA). To improve the MREA controllability and to resettle the payload with no oscillations, i.e. in one cycle, two different Bingham numbers for compression stroke and rebound stroke were defined in the non-dimensional solution. Several simulations were conducted for different values of Bingham numbers. Among these numerical simulation results, the solution that implemented the optimum Bingham numbers was found to be the only one feasible solution. In this case the MREA with optimum Bingham number for compression could utilize the full energy absorption stroke to attain soft landing. In the rebound stroke, the generated optimal on-state damping force successfully controls the bounce of the payload until the payload settles down to its original equilibrium position with no oscillations.

To alleviate wave and vibration transmission in automotive, aerospace, and civil engineering fields, researchers have investigated periodic metamaterials with especially architected internal topologies. Yet, these solutions employ heavy materials and narrowband, resonant phenomena that are unsuitable for the many applications where broadband frequency vibration energy is a concern, such as that injected by impact forces, and weight is a performance penalty. To overcome these limitations, a new idea for lightweight, elastomeric metamaterials constrained near critical points is recently being explored, such that improved shock and vibration damping is achieved using reduced mass than conventional periodic metamaterials. On the other hand, the internal architectures of these metamaterials have not been explored beyond classical circular designs whereas numerous engineering structures involve square or rectangular geometries that may challenge the ability to realize critical point constraints due to the lack of rotational symmetry. The objectives of this research are to undertake a first study of square cross-section elastomeric metamaterials and to assess the impact tolerance of structures into which these metamaterials are embedded and constrained. Finite element simulations guide attention to design parameters for the metamaterial architectures, while experimental efforts quantify the advantages of constraints on enhancing impact tolerance metrics for engineering structures. It is seen that although the architected metamaterial leads to slightly greater instantaneous acceleration amplitude immediately after impact, it more rapidly attenuates the injected energy when compared to the solid and heavier elastomer mass from which the metamaterial is derived.

Along with recent advancements in novel materials and manufacturing processes, the interest in morphing wings has increased in order to further improve the aerodynamic performance of flying bodies. The morphing wing can be tailored to deliver superior performance, compared to its non-morphing counterparts, for multiple operating conditions and in varying flows. In particular, the morphing wing is implemented for drag reduction and lift enhancement, and hence, the maneuverability, adaptability, and capability of the morphing wing can encompass an even wider spectrum by changing the wing shape. In this research, an existing morphing UAV wing design, Spanwise Morphing Trailing Edge (SMTE), actuated by bending Macro Fiber Composites (MFCs), is considered to generate the spanwise sinusoidal variations on the trailing edge of the morphing wing. A comparative aerodynamic study of the morphing wing by varying the spatial frequency ( i.e. , number of waves along the span) and the phase shift ( i.e. , wave shape along the span) at different angles of attack is conducted through analytical approaches and numerical Computational Fluid Dynamic (CFD) simulations, which are validated with previous experimental measurements. The analytical approach uses the three-dimensional (3D) Prandtl lifting line theory, and the CFD modeling in turbulence flow solves the 3D Reynolds-Averaged Navier-Stokes (RANS) equations with the k-ω Shear Stress Transport (SST) turbulence model. Note that the numerical simulations of a morphing wing focus on the pre-stall condition to estimate the aerodynamic performance. This work extends a prior study about a nominal flight condition testing a morphing wing at multiple flight conditions to evaluate multi-point 1 performance. The results show that there are governing aerodynamic efficiency zones of the lift-to-drag ratio, endurance, and aircraft range within a zone of angles of attack. Therefore, the morphing wing is shown to have a good aerodynamic performance as compared to the non-morphing wing.

Macro-fiber composite (MFC) piezoelectric materials are used in a variety of applications employing the converse piezo-electric effect, ranging from bioinspired actuation to vibration control. Most of the existing literature to date considered linear material behavior for geometrically linear oscillations. However, in many applications, such as bioinspired locomotion using MFCs, material and geometric nonlinearities are pronounced and linear models fail to represent and predict the governing dynamics. The predominant types of nonlinearities manifested in resonant actuation of MFC cantilevers are piezoelectric softening, geometric hardening, inertial softening, as well as internal and external dissipative effects. In the present work, we explore nonlinear actuation of MFC cantilevers and develop a mathematical framework for modeling and analysis. An in vacuo actuation scenario is considered for a broad range of voltage actuation levels to accurately identify the sources of dissipation. Several experiments are conducted for an MFC bimorph cantilever, and model simulations are compared with nonlinear experimental frequency response functions under resonant actuation. The resulting experimentally validated framework can be used for simulating the dynamics of MFCs under resonant actuation, as well as parameter identification and structural optimization for nonlinear operation regime.

Reliable operation of next generation high-speed complex structures (e.g. hypersonic air vehicles, space structures, and weapons) relies on the development of microsecond structural health monitoring (μSHM) systems. High amplitude impacts may damage or alter the structure, and therefore change the underlying system configuration and the dynamic response of these systems. While state-of-the-art structural health monitoring (SHM) systems can measure structures which change on the order of seconds to minutes, there are no real-time methods for detection and characterization of damage in the microsecond timescales. This paper presents preliminary analysis addressing the need for microsecond detection of state and parameter changes. A background of current SHM methods is presented, and the need for high rate, adaptive state estimators is illustrated. Example observers are tested on simulations of a two-degree of freedom system with a nonlinear, time-varying stiffness coupling the two masses. These results illustrate some of the challenges facing high speed damage detection.