Numerical Optimization of Liner Impedance in Acoustic Duct

The SALUTE project aims at evaluating performance of metacomposites for acoustic smart lining in grazing turbulent flow. Theoretical and numerical investigations are carried out for designing innovative specimen. A specific focus is placed in the realization of prototypes for evaluating the metacomposite liner performances in 2D and 3D liners, its process complexity and robustness. The insight gain in this project is new tools for obtaining innovative samples; the acoustical experimental tests demonstrate efficiency and robustness of such technology for controlling UHBR noise emission. This paper is focused on parametric study based on the maximization of the absorption coefficient in a duct by optimizing the impedance of a treated area.

Design of Compliant Joints for Large Scale Structures

Large scale structures can benefit from the design of compliant joints that can provide flexibility and adaptability. A high level of deformation is achieved locally with the design of flexures in compliant mechanisms. Additionally, by introducing contact-aided compliant mechanisms, nonlinear bending stiffness is achieved to make the joints flexible in one direction and stiff in the opposite one. All these concepts have been explored in small scale engineering design, but they have not been applied to large scale structures. In this paper the design of a large scale compliant mechanism is proposed for novel design of a foldable shipping container. The superelasticity of nickel titanium is shown to be beneficial in designing the joints of the compliant mechanism.

Investigation and Attempt to 3D Print Piezoelectric 0-3 Composites Made of Photopolymer Resins and PZT

The present study demonstrates the manufacturing and characterization of 0-3 piezoelectric composites made of up to 10 vol% of Lead Zirconate Titanate (PZT) particles and photopolymer resins. The tape-casting method was used to investigate the curing behavior, PZT loading limitations and the overall feasibility of the suspensions for 3D printing. Piezoelectric composites were 3D printed with a commercial DLP type 3D printer. As a starting point, the maximum possible vol% loading of PZT ceramic for each photopolymer resin was investigated. Five different commercially available photopolymer resins from Formlabs (Somerville, MA, US) were used. It was found that the addition of PZT particles to the photopolymer increases the time required for the photopolymer to solidify because PZT particles scatter the UV light. The approximate solidification time of each composition was measured, followed by viscosity measurements. SEM imaging of the composites showed good particle dispersion with minimum agglomeration, low particle sedimentation, but the weak bond between PZT particles and the photopolymers. Best performed material composition with 10 vol% of PZT was used for 3D printing. An attempt to shorten exposure time during printing was done by adding photoinitiator TPO. Suspensions with and without TPO were 3D printed and compared.

Part Authentication Using Indirect Electromechanical Impedance Measurements

Motivated by its success as a structural health monitoring solution, electromechanical impedance measurements have been utilized as a means for non-destructive evaluation of conventionally and additively manufactured parts. In this process, piezoelectric transducers are either directly embedded in the part under test or bonded to its surface. While this approach has proven to be capable of detecting manufacturing anomalies, instrumentation requirements of the parts under test have hindered its wide adoption. To address this limitation, indirect electromechanical impedance measurement, through instrumented fixtures or testbeds, has recently been investigated for part authentication and non-destructive evaluation applications. In this work, electromechanical impedance signatures obtained with piezoelectric transducers indirectly attached to the part under test, via an instrumented fixture, are numerically investigated. This aims to better understand the coupling between the instrumented fixture and the part under test and its effects ON sensitivity to manufacturing defects. For this purpose, numerical models are developed for the instrumented fixture, the part under test, and the fixture/part assembly. The frequency-domain spectral element method is used to obtain numerical solutions and simulate the electromechanical impedance signatures over the frequency range of 10–50 kHz. Criteria for selecting the frequency range that is most sensitive to defects in the part under test are proposed and evaluated using standard damage metric definitions. It was found that optimal frequency ranges can be preselected based on the fixture design and its dynamic response.

Impact of Including Electronics Design on Design of Intelligent Structures: Applications to Multifunctional Structures for Attitude Control (MSAC)

Multifunctional Structures for Attitude Control (MSAC) is a new spacecraft attitude control system that utilizes deployable panels as multifunctional intelligent structures to provide both fine pointing and large slew attitude control. Previous studies introduced MSAC design and operation concepts, simulation-based design studies, and Hardware-in-the-Loop (HIL) validation of a simplified prototype. In this article, we expand the scope of design studies to include individual compliant piezo-electric actuators and associated power electronics. This advance is a step toward high-fidelity MSAC system operation, and reveals new design insights for further performance enhancement. Actuators are designed using pseudo rigid body dynamic models (PRBDMs), and are validated for steady-state and step responses against Finite Element Analysis. The drive electronics model consists of a few distinct topologies that will be used to evaluate system performance for given mechanical and control system designs. Subsequently, a high-fidelity multiphysics multibody MSAC system model, based on the validated compliant actuators and drive electronics, is developed to support implementation of MSAC Control Co-design optimization studies. This model will be used to demonstrate the impact of including the power electronics design in the Optimal Control Co-Design domain. The different control trajectories are compared for slew rates and the vibrational jitter introduced to the satellite. The results from this work will be used to realize closed-loop control trajectories that have minimal jitter introduction while providing high slew rates.

Additively Manufactured Continuous Fibre-Reinforced Thermoplastics for Mechanisms Subjected to Predominant Inertial Load: A Case Study

In the last decade, the adoption of additive manufacturing technologies (AMT) (3D printing) has increased significantly in many fields of engineering, initially only for rapid prototyping and more recently also for the production of finished parts. With respect to the long-established material subtractive technologies (MST), AMT is capable to overcome several limitations related to the shape realization of high-performance mechanical components such as those conceived via topology optimization and generative design approaches. In the field of structures and mechanisms, a major advantage of AMT over MST is that, for the same loading and constraining conditions (including kinematic and overall encumbrance), it enables the realization of mechanical components with similar stiffness but smaller volume (thus smaller weight, density being equal). Recently, the potentialities of AMT have also been increased by the introduction of the fuse filament deposition modeling (FDM) of continuous fibre-reinforced thermoplastics (CFRT), which combines the ease of processing of plastic AMT with the strength and specific modulus of the printed components that are comparable to those attainable via metallic AMT. In this context, the present paper investigates the potentialities of FDM-CFRT for the realization of mechanisms subjected to predominant inertial loads such as those found in automated packaging machinery. As a case study a Stephenson six-bar linkage powered in direct drive by a permanent magnet synchronous motor is considered. Starting from an existing mechanism realized in aluminum alloy with traditional MST, a newer version to be realized with FDM-CFRT has been conceived by keeping the kinematics fixed and by redesigning the links via three-dimensional topology optimization. To provide a fair comparison with the more traditional design/manufacturing approach, size optimization of the original mechanism made in aluminum alloy has also been performed. Comparison of the two versions of the mechanism highlights the superior performances of the one manufactured via FDM-CFRT in terms of weight, motor torque requirements and motion precision.

Optimization of Rapid State Estimation in Structures Subjected to High-Rate Boundary Change

Many structures are subjected to varying forces, moving boundaries, and other dynamic conditions. Whether part of a vehicle, building, or active energy mitigation device, data on such changes can represent useful knowledge, but also presents challenges in its collection and analysis. In systems where changes occur rapidly, assessment of the system’s state within a useful time span is required to enable an appropriate response before the system’s state changes further. Rapid state estimation is especially important but poses unique difficulties. In determining the state of a structural system subjected to high-rate dynamic changes, measuring the frequency response is one method that can be used to draw inferences, provided the system is adequately understood and defined. The work presented here is the result of an investigation into methods to determine the frequency response, and thus state, of a structure subjected to high-rate boundary changes in real-time. In order to facilitate development, the Air Force Research Laboratory created the DROPBEAR, a testbed with an oscillating beam subjected to a continuously variable boundary condition. One end of the beam is held by a stationary fixed support, while a pinned support is able to move along the beam’s length. The free end of the beam structure is instrumented with acceleration, velocity, and position sensors measuring the beam’s vertical axis. Direct position measurement of the pin location is also taken to provide a reference for comparison with numerical models. This work presents a numerical investigation into methods for extracting the frequency response of a structure in real-time. An FFT based method with a rolling window is used to track the frequency of a data set generated to represent the range of the DROPBEAR, and is run with multiple window lengths. The frequency precision and latency of the FFT method is analyzed in each configuration. A specialized frequency extraction technique, Delayed Comparison Error Minimization, is implemented with parameters optimized for the frequency range of interest. The performance metrics of latency and precision are analyzed and compared to the baseline rolling FFT method results, and applicability is discussed.

An Impact-Based Experimental Setup for Evaluation of Rapid Electromechanical Impedance-Based Structural Health Monitoring

This work investigates the application of structural health monitoring (SHM) in a dynamic environment with the electromechanical impedance (EMI) method. Classically, the EMI method monitors civil or mechanical structures for damage in static environments. Advances in data acquisition (DAQ) now allow the possibility of rapid damage detection in dynamic environments. An impact-based experimental setup is developed to create a repeatable dynamic event through a collision between a pneumatically actuated striker bar and a static incident bar instrumented with a piezoelectric transducer. The EMI method is employed to detect the change of state at the interface of the two colliding bars. Experimental results prove the pneumatic launching system is capable of repeatable dynamic events, but the duration of contact is only 0.03 ms and the current DAQ system is incapable of detecting the event. A 3D printed programming material interface is placed at the location of impact to increase the duration of contact to approximately 1 ms. An excitation signal is created to continuously sweep a 0.5 ms chirp signal with a frequency bandwidth from 60–70 kHz (previously identified damage sensitive frequency bandwidth from static testing) for 7.5 seconds. Results indicate that due to the sampling rate and sweep time of the excitation signal, the frequency resolution is not adequate to properly assess if the impact is detected. Improvements in the DAQ hardware must be considered for future work.

Deadbands Tell No Tails: X-56A Dynamic Actuation Requirements

Following significant effort over the past several years by AFRL and NASA, the X-56A flight vehicle has proven to be a useful platform for exploring controllers and distributed actuation on a flexible, swept flying-wing. The program sought to advance the state of the art in airworthiness for vehicles encountering flutter, leading to relaxed design constraints that could drastically decrease structural weight and improve aircraft performance. Specifically, the vehicle was designed to encounter different forms of flutter: body-freedom flutter, and wing-bending torsion flutter, making it an ideal candidate for identifying dynamic actuation challenges. Flight testing led to fundamental observations by controller designers about the actuation needs for such a vehicle. Namely, the small inherent actuator deadband led to significant constant-amplitude limit cycle oscillations of the system during post-flutter controlled flight. This work captures these observations by exploring theoretical changes in the actuators via a nonlinear simulation tuned with flight testing data and shows that a 60% reduction in actuator deadband can improve ride quality by nearly 50%. The results are combined into a set of actuation challenges for the adaptive structures community at large, including precise actuation for a large number of cycles over multiple timescales, with a relevant baseline described by original actuation system.

Prediction of the Behavior of Dynamically Actuated DE Roll-Actuators Using Equivalent Circuits

Dielectric elastomer actuators show suitable properties to be utilized for dynamic applications, e.g. speakers, shakers and pumps, with possible benefits to existing conventional systems. In this work a method to predict the performance of dynamically actuated dielectric-elastomer roll-actuators (DERA) depending on both, material and design parameters is presented. It incorporates in combination analytical computation, FEM, as well as electromechanical networks and considers a large variety of material configurations with a multitude of constructional degrees of freedom. DERA in push-configuration exhibit a distinct modal behavior in axial direction depending on the boundary conditions and loading at the actuators end terminals, which is described sufficiently by a one-dimensional longitudinal waveguide model. Several DERA were designed, manufactured and tested. The experimental studies were in good agreement with the made predictions. They allowed for further refinement regarding interface circuits and model updating, such as the estimation of inaccessible parameters (e. g. damping coefficients). The presented model allows for extensive parameter studies and the development of tailor-made actuators for given application in a very time efficient manner.