Rigid Counterpart Research Articles

Influence of Molecular Conformation on Electron Transport in Giant, Conjugated Macrocycles.

We describe here the direct connection between the molecular conformation of a conjugated macrocycle and its macroscopic charge transport properties. We incorporate chiral, helical perylene diimide ribbons into the two separate macrocycles as the n-type, electron transporting material. As the macrocycles' films and electronic structures are analogous, the important finding is that the macrocycles' molecular structures and their associated dynamics determine device performance in organic field effect transistors. We show the more flexible macrocycle has a 4-fold increase in electron mobility in field effect transistor devices. Using a combination of spectroscopy and density functional theory calculations, we find that the origin of the difference in device performance is the ability of more flexible isomer to make intermolecular contacts relative to the more rigid counterpart.

Wing flexibility effects on the flight performance of an insect-like flapping-wing micro-air vehicle

This study explores the effects of wing flexibility on several characteristics of flight, in this case the trim conditions, power requirements and dynamic stability of an insect-like flapping-wing micro-air vehicle (FWMAV) based on the hawkmoth Manduca sexta. The wing structure is analyzed by the finite-element method. A potential-based aerodynamic model which encompasses the unsteady panel method and the extended unsteady vortex-lattice method is employed to compute the aerodynamic forces. The motions of the FWMAV are obtained using a flexible multibody dynamics program coupled with the potential-based aerodynamic model. The results of this study show that the trim conditions of insect-like flexible and rigid FWMAVs may differ significantly from each other. When the flight speed is less than 3.0 m/s, using flexible wings is favorable, as they help the FWMAV reduce the power requirement and stabilize the lateral dynamics. However, at 3.0 m/s, these advantages are almost unnoticeable, while at 4.0 m/s, the flexible insect-like FWMAV requires even more mechanical power than its rigid counterpart.

Aeroelastic analysis of membrane blade via panel-BEM coupling

This paper aims at introducing a methodology for aeroelastic analysis of membrane blades using panel-BEM coupling. The proposed methodology is used for evaluating the performance of a membrane blade with the baseline platform similar to the NASA-Ames Phase VI blade. The performance of the membrane blade is compared with the rigid baseline blade. The studied membrane blade has certain aerodynamic advantages over its rigid counterpart. For the studied blade and at higher wind speeds, the axial induction factor for membrane blade is nearer to the Betz optimum value of 1/3 and as a result the membrane blade is more efficient in producing power. The performance of the membrane blade is further examined via high fidelity FSI analysis. The same trend as in panel-BEM coupling is also observed in the high fidelity model, namely for higher wind speeds the studied membrane blades is more efficient than its rigid counterpart.

Crystal structure of (1S,4S)-2,5-diazo-niabi-cyclo[2.2.1]heptane dibromide.

The cage of 2,5-di-aza-bicyclo-[2.2.1]heptane is frequently employed in synthetic chemistry as a rigid bicyclic counterpart of the piperazine ring. The 2,5-di-azabicyclo-[2.2.1]heptane scaffold is incorporated into a variety of compounds having pharmacological and catalytic applications. The unsubstituted parent ring of the system, 2,5-di-aza-bicyclo-[2.2.1]heptane itself, has not been structurally characterized. We herein report on the mol-ecular structure of the parent ring in (1S,4S)-2,5-diazo-niabi-cyclo-[2.2.1]heptane dibromide, C5H12N22+·2Br-. The asymmetric unit contains two crystallographically independent cages of 2,5-di-aza-bicyclo-[2.2.1]heptane. Each cage is protonated at the two nitro-gen sites. The overall charge balance is maintained by four crystallographically independent bromide ions. In the crystal, the components of the structure are linked via a complex three-dimensional network of N-H⋯Br hydrogen bonds.

Numerical study of rigid and flexible wing shapes in hover

This study is focused on evaluating the aerodynamic performance of rigid and isotropic flexible wing shapes defined by the radius of the first moment of wing area at Reynolds number of 6000. An immersed boundary method was used to solve the 3D, viscous, incompressible Navier-Stokes equations, and coupled with an in-house non-linear finite element solver for fluid structure interaction simulations. Numerical simulations of flexible wing shapes performed with a single degree of freedom flapping shows that thrust and peak lift coefficients increase with . Higher thrust in the wing is attributed to the large induced pitch angle, and higher peak lift (compared to the rigid counterpart) results from an increase in the stroke amplitude and spanwise deformation of the wing that anchors the leading edge vortex.

Fin Ray Stiffness and Fin Morphology Control Ribbon-Fin-Based Propulsion.

Ribbon-fin-based propulsion has rich locomotor capabilities that can enhance the mobility and performance of underwater vehicles navigating in complex environments. Bony fishes using this type of propulsion send one or multiple traveling waves along an elongated fin with the actuation of highly flexible rays that are interconnected by an elastic membrane. In this work, we study how the use of flexible rays and different morphology can affect the performance of ribbon-fin propulsion. We developed a physical model composed of 15 rays that are interconnected with an elastic membrane. We tested four different ray flexural stiffness and four aspect ratios. The robotic model was tested in a low-turbulence flume under two flow conditions ([Formula: see text] wavelength/s). In two experimental sets, we measured fin kinematics, net surge forces, and power consumption. Using these data, we perform a thrust and power analysis of the undulating fin. We present the thrust coefficient, power coefficient, and propulsive efficiency. We find that the thrust generation was linear with the enclosed area swept by the fin, and square of the relative velocity between the incoming flow and traveling wave. The thrust coefficient levels off around 0.5. In addition, for our parameter range, we find that the power consumption scales by the cube of the effective tangential velocity of the rays [Formula: see text] (A is the amplitude of the ray oscillating motion, and [Formula: see text] is the angular velocity). We show that a decay in stiffness decreases both thrust production and power consumption. However, for rays with high flexural stiffness, the difference in thrust compared with rigid rays is minimal. Moreover, our results show that flexible rays can improve the propulsive efficiency compared with a rigid counterpart. Finally, we find that the morphology of ribbon fin affects its propulsive efficiency. For the aspect ratio considered in our experiments, [Formula: see text] was the most efficient compared with [Formula: see text]. Our results suggest that there could be an optimal morphology for a given ribbon fin kinematics. Therefore, both natural swimmers and underwater vehicles using ribbon-fin-based propulsion can take advantage of flexible rays and optimal aspect ratio to improve propulsive performance.

Analysis of Coupled Poroviscoelasticity and Hydrodynamic Lubrication

As the state of the art pushes triboelements toward greater capabilities and longevity, the need for evolving triboelement technology exists. The following work explores a novel coupling of phenomena inspired by biomimetics. A poroviscoelastic substrate coupled to a fluid film load is modeled and compared to its rigid counterpart. It is hypothesized that poroviscoelasticity can improve triboelement properties such as damping and wear resistance and have utility in certain applications where flexibility is desired (e.g., biomechanical joint replacements, flexible rotordynamic bearings, and mechanical seals). This study provides the framework for the analysis of flexible, porous viscoelastic materials and hydrodynamic lubrication.

Fluid-Structure interaction analysis and performance evaluation of a membrane blade

Examining the potential of a membrane blade concept is the goal of the current work. In the sailwing concept the surface of the wing, or the blade in this case, is made from pre-tensioned membranes which meet at the pre-tensioned edge cable at the trailing edge. Because of the dependency between membrane deformation and applied aerodynamic load, two-way coupled fluid-structure interaction analysis is necessary for evaluation of the aerodynamic performance of such a configuration. The in-house finite element based structural solver, CARAT++, is coupled with OpenFOAM in order to tackle the multi-physics problem. The main aerodynamic characteristics of the membrane blade including lift coefficient, drag coefficient and lift to drag ratio are compared with its rigid counterpart. A single non-rotating NREL phase VI blade is studied here as a first step towards analyzing the concept for the rotating case. Compared with the rigid blade, the membrane blade has a higher slope of the lift curve. For higher angles of attack, lift and drag coefficients as well as the lift to drag ratio is higher for the membrane blade. A single non-rotating blade is studied here as a first step towards analyzing the concept for the rotating case.

Capacitive Power Transfer Through a Conformal Bumper for Electric Vehicle Charging

Wireless power transfer (WPT) is emerging as a practical means for electric vehicle (EV) charging. Of the most common approaches to WPT, inductive coupling, and capacitive coupling, capacitive power transfer (CPT) is proposed to charge an EV at a kilowatt scale power level. CPT implementation replaces copper coils and permeable focusing/shielding materials of inductive approaches with foil surfaces, making CPT a cost effective and structurally simple system to implement while maintaining efficient power transfer capability. This paper addresses the primary technical hurdles to kilowatt scale CPT system development, namely, safe field confinement by achieving high coupling capacitance between the vehicle and the charging station. High capacitive coupling is achieved through a conformal (flexible and compressive) transmitter bumper that molds and contours itself to the vehicle. This minimizes the air gap and confines the field during charging. Here, a conformal surface demonstrates 3–5 times more coupling capacitance than its rigid counterpart of equal area. The associated power electronics are also discussed in detail, utilizing a Class $\text{E}^{2}$ amplifier/rectifier. An experimental docking station was built to charge the 156 V battery pack of a Corbin Sparrow EV and measured throughput power is demonstrated at $>1$ kW at $\sim 90$ % efficiency via a coupling capacitance of 10 nF operating at 530 kHz.

A finite element model for seismic response analysis of deformable rocking frames

SummaryA new finite element model to analyze the seismic response of deformable rocking bodies and rocking structures is presented. The model comprises a set of beam elements to represent the rocking body and zero‐length fiber cross‐section elements at the ends of the rocking body to represent the rocking surfaces. The energy dissipation during rocking motion is modeled using a Hilber–Hughes–Taylor numerically dissipative time step integration scheme. The model is verified through correct prediction of the horizontal and vertical displacements of a rigid rocking block and validated against the analytical Housner model solution for the rocking response of rigid bodies subjected to ground motion excitation. The proposed model is augmented by a dissipative model of the ground under the rocking surface to facilitate modeling of the rocking response of deformable bodies and structures. The augmented model is used to compute the overturning and uplift rocking response spectra for a deformable rocking frame structure to symmetric and anti‐symmetric Ricker pulse ground motion excitation. It is found that the deformability of the columns of a rocking frame does not jeopardize its stability under Ricker pulse ground motion excitation. In fact, there are cases where a deformable rocking frame is more stable than its rigid counterpart. Copyright © 2016 John Wiley & Sons, Ltd.

Drag reduction by elastic reconfiguration of non-uniform beams in non-uniform flows

Flexible systems bending in steady flows are known to experience a lesser drag compared to their rigid counterpart. Through a careful dimensional analysis, an analytical expression of the Vogel exponent quantifying this reduction of drag is derived for cantilever beams, within a framework based on spatial self-similar modelling of the flow and structural properties at the clamped edge of the structure. Numerical computations are performed on various situations, including systems involving more complex distributions of the flow or structural parameters. The scaling of drag versus flow velocity for large loadings is shown to be well predicted by fitting the system properties by simple power laws at the scale of the length on which significant bending occurs. Ultimately, the weak sensitivity of the Vogel exponent to the parameters of the system provides an explanation to the rather reduced scattering of the Vogel exponents around −1 observed on most natural systems in aquatic or aerial vegetation.

Effects of Chordwise Flexibility on the Aerodynamic Performance of a 3D Flapping Wing

Previous studies on chordwise flexibility of flexible wings generally relied on simplified two-dimensional (2D) models. In the present study, we constructed a simplified three-dimensional (3D) model and identified the role of the chordwise flexibility in full flapping motion. This paper includes two parts, the first part discusses the aerodynamic effects of the chordwise flexibility in a typical hovering-flight case; the second part introduces a parametric study of four key parameters. The primary findings are as follows. Flexibility generally degrades the lift performance of the flexible wings. However, in two special cases, i.e. when stroke amplitude is low or pitch rotation is delayed, the flexible wings outperform their rigid counterparts in lift generation. Moreover, flexibility reduces the power consumption of the flexible wings. A wing with small flexibility generally achieves a marginally higher flapping efficiency than its rigid counterpart. Furthermore, reducing stroke amplitude can effectively improve the lift performance of the very flexible wings. Aerodynamic performances of the flexible wings are not as sensitive as the rigid wing to phase difference and mid-stroke angle of attack. The effects of Re are the same for the flexible and rigid wings.

Data-driven spatio-temporal RGBD feature encoding for action recognition in operating rooms.

Context-aware systems for the operating room (OR) provide the possibility to significantly improve surgical workflow through various applications such as efficient OR scheduling, context-sensitive user interfaces, and automatic transcription of medical procedures. Being an essential element of such a system, surgical action recognition is thus an important research area. In this paper, we tackle the problem of classifying surgical actions from video clips that capture the activities taking place in the OR. We acquire recordings using a multi-view RGBD camera system mounted on the ceiling of a hybrid OR dedicated to X-ray-based procedures and annotate clips of the recordings with the corresponding actions. To recognize the surgical actions from the video clips, we use a classification pipeline based on the bag-of-words (BoW) approach. We propose a novel feature encoding method that extends the classical BoW approach. Instead of using the typical rigid grid layout to divide the space of the feature locations, we propose to learn the layout from the actual 4D spatio-temporal locations of the visual features. This results in a data-driven and non-rigid layout which retains more spatio-temporal information compared to the rigid counterpart. We classify multi-view video clips from a new dataset generated from 11-day recordings of real operations. This dataset is composed of 1734 video clips of 15 actions. These include generic actions (e.g., moving patient to the OR bed) and actions specific to the vertebroplasty procedure (e.g., hammering). The experiments show that the proposed non-rigid feature encoding method performs better than the rigid encoding one. The classifier's accuracy is increased by over 4 %, from 81.08 to 85.53 %. The combination of both intensity and depth information from the RGBD data provides more discriminative power in carrying out the surgical action recognition task as compared to using either one of them alone. Furthermore, the proposed non-rigid spatio-temporal feature encoding scheme provides more discriminative histogram representations than the rigid counterpart. To the best of our knowledge, this is also the first work that presents action recognition results on multi-view RGBD data recorded in the OR.

Influence of structural flexibility on the wake vortex pattern of airfoils undergoing harmonic pitch oscillation

Reported herein is an investigation of the influence of the structural flexibility of sinusoidally pitching airfoils on the pattern of vorticity shed into the wake. For rigid airfoils, it is well known that, depending on the oscillation frequency and amplitude, this pattern takes the form of the classical or reverse von Karman vortex street. The pattern may be characterized by the vortex circulation (Γ o ), vortex-to-vortex streamwise and cross-stream spacing (a and b, respectively), and vortex core radius (R). In the present work, these four parameters are obtained from particle image velocimetry measurements in the wake of airfoils consisting of a rigid “head” and flexible “tail” at chord Reynolds number of 2010 for different tail flexibilities. The results show that flexible airfoils exhibit the switch from classical to reverse von Karman vortex street (i.e., change in the sign of b) at a reduced frequency of oscillation lower than their rigid counterpart. At a given oscillation frequency, the Strouhal number at which this switch occurs is smallest for a given airfoil structural flexibility; which becomes stiffer with increasing frequency. Using Strouhal number based on the actual trailing edge oscillation amplitude, reasonable scaling is found of the dependence of not only b but also Γ o , a and R on the motion and structure parameters for all airfoils investigated. These results are complemented with analyses using a vortex array model, which together with the identified scaling of the wake vortex parameters, provide basis for the computation of the net thrust acting on the airfoil.

Illustration of Wing Deformation Effects in Three-Dimensional Flapping Flight

This study numerically investigates the aerodynamic effects of deformation on three-dimensional low aspect ratio wings engaged in hover kinematics. The immersed-boundary finite-volume method is used to solve the Navier–Stokes equations. Deformations are actively prescribed and are represented as deflections about axes that transect the rectangular planform. Two distinct deformation modes associated with tip and root deflection are explored, in addition to a rigid wing counterpart. Variation of the phase between deflection and flapping enables mimicry of a range of wing behavior observed in nature. It is found the introduction of root or tip deflection can increase efficiency by as much as 19.5% or 19.0% respectively. The development of vortical structures about the wing is investigated. It is shown that while the rotational axis of the leading-edge vortex is insensitive to deformation, the shape and orientation of cores of the vortex is modified.

Compliant semiconductor scaffolds: building blocks for advanced neural interfaces.

Compliant semiconductor scaffolds: building blocks for advanced neural interfaces.

Numerical Research on Segmented Flexible Airfoils Considering Fluid-structure Interaction

This paper investigated four kinds of segmented flexible airfoils with membrane material on the upper surface and rigid structure on the lower surface. Fluid-structure interaction method was adopted in the numerical simulation for the aerodynamic characteristics and response between flow field and structure of the segmented flexible airfoils. The research focuses on influence of flexible deformation on the lift and drag characteristics and the aerodynamic load distribution of four segmented flexible airfoils at Reynolds number of 1.35×105. The results show that the segmented flexible airfoils perform a higher maximum lift coefficient, and effectively delay the stall. At the higher angles of attack, the deformation of the flexible thin membrane could reduce the scale of the separation vortexes. Meanwhile the tiny vortex generated between the flexible segments with the effect called “Fluid Roller Bearing” would impel the separated boundary layer to reattach to the airfoil surface especially on the first half chord region. The three-segment flexible airfoil was proved to be the best airfoil among the four airfoils, which could increase the lift coefficient by 39% near the stall angle of attack compared with its rigid counterpart.

Flexible nanoscale high-performance FinFETs.

With the emergence of the Internet of Things (IoT), flexible high-performance nanoscale electronics are more desired. At the moment, FinFET is the most advanced transistor architecture used in the state-of-the-art microprocessors. Therefore, we show a soft-etch based substrate thinning process to transform silicon-on-insulator (SOI) based nanoscale FinFET into flexible FinFET and then conduct comprehensive electrical characterization under various bending conditions to understand its electrical performance. Our study shows that back-etch based substrate thinning process is gentler than traditional abrasive back-grinding process; it can attain ultraflexibility and the electrical characteristics of the flexible nanoscale FinFET show no performance degradation compared to its rigid bulk counterpart indicating its readiness to be used for flexible high-performance electronics.

Effect of flexibility on flapping wing characteristics under forward flight

Through two-dimensional numerical simulation and by solving the unsteady incompressible Navier–Stokes (NS) equations, coupled with the structural dynamic equation for the motion of the wing, the effect of flexibility on flapping wing characteristics during forward flight is systematically studied. The flapping wing is considered as a cantilever, which performs the translational and rotational motion at its leading edge, and the other part is passively deformed by the aerodynamic force. The frequency ratio ω* and mass ratio m* are defined and used to characterize the flexibility of the flapping wing. It has been found that an optimal range of the frequency ratio exists in which the flexible wing possesses both a larger propulsive efficiency and lifting efficiency than their rigid counterpart. Also, the flexible wing with the smaller mass ratio may be of benefit to generate thrust, while the larger mass ratio may be of benefit to generate lift. In addition, a stronger leading edge vortex and reattachment vortex are observed around the appropriate flexibility wing’s surface, which therefore leads to better aerodynamic characteristics.

Augmented robust control of a free-floating flexible space robot

The flexibility of the joints and links of space robots is considerable, arising from elasticity of the joints and links. Controlling such a robot is more complex than controlling rigid one due to the interactions of rigid and flexible motion. Only a single actuation signal could be applied at each joint, whilst it has to control the motion of the link joint, the flexure of both the joints itself, and the attached link for a flexible space robot. To investigate such an underactuated flexible-link flexible-joint space robot, a free-floating space manipulator with one flexible link and two flexible revolute joints was presented in this paper. The dynamical Lagrange equation was established, and a singularly perturbed model has been formulated. The model consisted of a rigid subsystem, a flexible-link fast subsystem, and a flexible-joint fast subsystem. Based on the two-time-scale separation of the manipulator dynamics, a reduced-order controller was designed. This controller consisted of a rigid control component and two fast control components. Based only on the possible bound of the uncertainty, an augmented robust control law was constructed for the rigid counterpart of the flexible-link flexible-joint robot. The flexible-joint fast subsystem controller would stabilize the elastic vibrations at the joints, and the flexible-link fast subsystem controller would damp out the vibration of the flexible link. Numerical simulations showed that the link and joint vibrations had been stabilized effectively with good tracking performance.